No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Phosphogenesis, carbon-isotope stratigraphy, and carbonate-platform evolution along the Lower Cretaceous northern Tethyan margin
Abstract
The paper distinguishes three different stages in the evolution of the Tithonian (Late Jurassic) to Aptian (Early Cretaceous) northern Tethyan carbonate platform: 1) carbonate production in the coral-oolite mode, 2) carbonate production in the crinoid-bryozoan mode, and 3) platform retrogradation and destruction, condensation, and phosphogenesis. The δ13C stratigraphies obtained from Valanginian-Hauterivian and Aptian-Albian hemipelagic successions beyond the platform correlate well with the Early Cretaceous pelagic δ13C record. -from Authors
... The onset of the Weissert event in the studied succession coincides with deeper-water facies, the spiculitic wackestone (F11), marking the transgression of S6 (Fig. 12). This is in concert with the observations of Föllmi et al. (1994), Weissert et al. (1998), Weissert and Erba (2004), and Föllmi (2012) that highlighted carbonate platforms drowning events in association with the CIE. Drowning of Tethyan platforms during the Valanginian was primarily triggered by a perturbation in the carbon cycle (Föllmi et al., 1994;Weissert et al., 1998;Föllmi, 2012). ...
... This is in concert with the observations of Föllmi et al. (1994), Weissert et al. (1998), Weissert and Erba (2004), and Föllmi (2012) that highlighted carbonate platforms drowning events in association with the CIE. Drowning of Tethyan platforms during the Valanginian was primarily triggered by a perturbation in the carbon cycle (Föllmi et al., 1994;Weissert et al., 1998;Föllmi, 2012). The effect of this is emphasized by prevailing humid conditions and accelerated hydrological cycle, leading to eutrophication of seawater, enhanced primary productivity, and changes in biotic communities. ...
... The effect of this is emphasized by prevailing humid conditions and accelerated hydrological cycle, leading to eutrophication of seawater, enhanced primary productivity, and changes in biotic communities. Through this process, the positive CIE of the Weissert event is explained by increased organic carbon burial rates in terrestrial and marine environments (Lini et al., 1992;Föllmi et al., 1994;Weissert et al., 1998;Erba et al., 2004), which is thought to have stimulated from a climatic change driven by the Paranà-Etendeka volcanism (Weissert et al., 1998;Erba et al., 2004). ...
Unlike the Tethys Realm, the carbon isotope record from the Boreal Realm exhibits a prominent negative excursion before the Jurassic-Cretaceous boundary referred to as the Volgian Isotopic Carbon Excursion (VOICE). The VOICE has been ascribed to restricted-circulation conditions in northern high latitude basins, which decoupled these basins from the global carbon pool. Similar isotopic signal has been identified in the southern hemisphere where it has been attributed to humid conditions and influx of organic matter. The restricted circulation hypothesis is tested here by examining the depositional record of the Tethyan Late Jurassic–Early Cretaceous succession from central Saudi Arabia. A multi-disciplinary approach, involving sedimentology, sequence stratigraphy, biostratigraphy, and geochemistry, was adopted for studying a composite section covering the Hith, Sulaiy, Yamama, and Buwaib formations. The succession is characterized by restricted salina and sabkha depositional settings at the base that transition upward into an open-marine depositional system. This trend records a long-term sea-level rise during the Early Cretaceous. The carbon isotope record for this succession illustrates two prominent positive excursions of 5.2‰ and 2.6‰ amplitudes at the base and top of the succession, respectively. The larger positive excursion coincides with the restricted-environment facies and shows similarities, in terms of magnitude and trend, to the recovery phase of the VOICE. The upper positive excursion is manifested after a steady drop in the carbon isotope values, and it corresponds to the globally recognized Weissert event. The results indicate that restricted circulation in the Arabian shelf interior during the Late Jurassic duplicated the VOICE signal. The recognition of the Weissert event signal, on the contrary, denotes restored circulation of the shelf interior with the Tethys. The novelty of this study is demonstrated by the findings that the VOICE might indeed be a global signal and restricted circulation driven by eustasy is the main controlling factor for the VOICE signal.
... Associated with OAE1a were nannofossil crisis (Erba et al., 2010), increased seawater temperature (Naafs and Pancost, 2016;Jenkyns, 2018), intensified continental weathering (Bottini et al., 2012;Lechler et al., 2015), and the demise of carbonate platforms Huck et al., 2011). The sedimentary evolution during OAE1a has been widely associated with eustatic rise, leading to accumulation of organic carbon-rich sediment and drowning of carbonate platforms (Föllmi et al., 1994;Weissert et al., 1998;Grötsch et al., 1998;Millán et al., 2009;Huck et al., 2011). The detailed pattern of sea-level change, however, remained poorly understood for several reasons. ...
... The detailed pattern of sea-level change, however, remained poorly understood for several reasons. Firstly, organic-carbon content cannot be used as a proxy for sea-level rise, because oxygen depletion in seawater and increased primary production also takes place during OAEs (Föllmi et al., 1994;Bodin et al., 2013;Westermann et al., 2013;Erba et al., 2015). Secondly, most drowned carbonate platforms are located along the northern margin of Neotethys (e.g., Huck et al., 2014;Núñez-Useche et al., 2020), drowning unconformities are commonly multiphase, and some preceded the OAE1a event (Huck et al., 2011;Najarro et al., 2011;Masse and Fenerci-Masse, 2013;Frau et al., 2020). ...
... Positive shifts in carbon isotopes and accumulation of sediments enriched in organic carbon during the OAE1a event have been widely associated with sea-level rise and platform drowning (Föllmi et al., 1994;Grötsch et al., 1998;Millán et al., 2009;Huck et al., 2011). However, such a correlation may be partly spurious because of two main factors: 1) condensed sedimentation in deep-water settings, where strata deposited during OAE1a are six times thinner than in shallow-water settings (Fig. 9); 2) redox state of deep seawater, which may change from oxic to anoxic conditions (Jenkyns, 2010;Westermann et al., 2013) thus favoring the accumulation of organic-carbon-rich sediments independently of sea-level change. ...
... The earliest Cretaceous was a time of significant climate shifts, eustatic sea-level variations and volcanic activity leading to major paleooceanographic and paleoenvironmental changes [ 1 ]. Demise and drowning of many carbonate platforms along the northern Tethys margin and elsewhere occurred in the mid-to Late Valanginian [2][3][4]. The crisis in marine carbonate production was concomitant with a global perturbation of the carbon cycle [ 2,3,5 ], known as the Weissert Episode or Event [ 1,6 ]. ...
... Demise and drowning of many carbonate platforms along the northern Tethys margin and elsewhere occurred in the mid-to Late Valanginian [2][3][4]. The crisis in marine carbonate production was concomitant with a global perturbation of the carbon cycle [ 2,3,5 ], known as the Weissert Episode or Event [ 1,6 ]. However, fundamental changes in the carbonate factory, such as switch from photozoan to heterozoan assemblages, have been recorded in the earliest Valanginian, i.e., predating the positive δ 13 C excursion [ 4,7,8 ]. ...
... The δ 13 C values of all analyzed samples range from 1.10 to 2.21% , and the δ 18 O values are negative ranging from −1.23 to −6.36% (Fig. 2). The limestones of Slivnitsa Formation yield relatively uniform δ 13 C compositions and a minimum value is recorded in bioclastic-peloidal The measured C-isotope values are comparable with those recorded in other Berriasian-Hauterivian marine carbonate deposits [ 2,[4][5][6][7][16][17][18], and hence they are considered to reflect a preserved primary signal. Moreover, the lack of covariance between the δ 13 C and δ 18 O compositions suggests a negligible influence of diagenesis on the isotopic signature [ 4 ]. ...
Biostratigraphic, microfacies and C–O isotope data from the lowermost
Cretaceous deposits in section Kalotina reveal the development of a shallow carbonate
platform (Slivnitsa Formation) in a photozoan mode under moderate to
high-energy conditions during the Berriasian. Around the Berriasian/Valanginian
boundary the carbonate production switched to a heterozoan-type suggesting
a biological crisis. After a subaerial exposure in the earliest Valanginian
and subsequent karst formation the platform was drowned during the latest
Valanginian. Deposition of carbonate-argillaceous sediments (Salash Formation)
occurred in a deeper, open-marine environment under mesotrophic to
eutrophic, low-energy conditions with periodical formation of crinoid-rich packstones
probably by mass gravity flows. Limestone samples from the Slivnitsa
Formation yield higher δ13C values compared to coeval open-marine deposits
which can be explained by an elevated amount of aragonite in the photozoan
carbonate production and an enrichment in δ13C of the shallow platform waters
due to high levels of photosynthesis. The most depleted δ13C value in the
uppermost part of the unit most likely reflects a change from oligotrophic to
mesotrophic conditions. The C-isotope signatures in limestones of the Salash Formation indicate correspondence to the third, smooth decrease phase in the
δ13C record of the global Weissert Event (latest Valanginian and Early Hauterivian)
where values tend to recover to pre-excursion values.
... Erdgeschichtlich dokumentiert die im Gebiet von Atlasblatt Ibergeregg erhalten gebliebene helvetische Kreideabfolge einen wesentlichen Teil der kretazischen Entwicklung des proximalen nördlichen passiven Kontinentalrands der Tethys (helvetischer Schelf, s. z. B. tRümpy 1980, Funk 1985, Föllmi 1989, Funk et al. 1993, Föllmi et al. 1994. Fazielle Ausbildung, Mächtigkeit sowie Erhaltungsgrad dieses flach-bis tiefmarinen karbonatisch dominierten Sedimentstapels wurden bestimmt durch ein Zusammenspiel globaler Faktoren (wie Meeresspiegelschwankungen, Klimaveränderungen, dem CO 2 -Gehalt der Atmosphäre oder dem pH-Wert der Ozeane) mit regionalen bis lokalen Entwicklungen (thermisch bedingte Subsidenz des helvetischen Schelfs, regionale Tektonik, Meeresströmungen, Nährstoffgehalte usw.). ...
... B. Föllmi 1989, Funk et al. 1993 In der südöstlichen Ecke des Blattgebiets, vor allem bei Chöpf, finden sich vereinzelte Aufschlüsse eines plattigen, blassgelb-grau anwitternden biomikritischen Kalks, welcher gegen den hangenden Helvetischen Kieselkalk in grauen schiefrigen Mergel übergeht. Diese früher als Teil des «Valanginienkalks» verstandene Abfolge stellt ein tiefermarines Äquivalent der neritischen Betlis-Formation und teilweise auch der glaukonitisch-phosphoritischen Gemsmättli-Bank dar (HalDimann 1977, Funk et al. 1993, Föllmi et al. 1994 ...
... seitlich sie ersetzenden Tierwis-Formation in ihrer Mächtigkeit stark reduziert (Funk et al. 1993 (BRiegel 1972, Funk et al. 1993, WissleR et al. 2003. Sie dokumentiert eine Phase tropischer und flachmariner Verhältnisse mit Ausbildung einer ausgedehnten Karbonatplattform, welche im späteren Frühen Aptien schliesslich durch eine Kombination anhaltender Subsidenz, eustatischer Meeresspiegelschwankungen und globaler klimatischer und ozeanographischer Veränderungen (erhöhter CO 2 -Gehalt der Atmosphäre, verstärkter Eintrag terrestrischer Nährstoffe und siliziklastischen Materials in die Ozeane, tiefere pH-Werte des Meereswassers usw.) «ertrank» (Föllmi et al. 1994, WeisseRt et al. 1998, WissleR et al. 2003) und durch karbonatärmere Ablagerungen der hangenden Garschella-Formation abgelöst wurde. Die Garschella-Formation ist in der Drusberg-Decke im südlichen Abschnitt von Atlasblatt Ibergeregg grossflächig aufgeschlossen und bildet die Unterlage ausgedehnter Alpweiden, namentlich östlich der Fallflue, im Gebiet der Chäseren (südwestlicher Talabschluss des Waagtals) und im Raum Wannen und Weid zwischen Waag-und oberem Sihltal. ...
... Drowning phases are regarded as a powerful tool for large-scale correlation if they are sufficiently well dated with biomarkers. Föllmi et al. (1994) and Weissert et al. (1998) postulated possible links between drowning phases, palaeoceanographic and/or paleoenvironmental change affecting carbonate factories. Furthermore, drowning phases are relatively contemporaneous to organic-rich mud deposits (black shales) in deeper marine environments, a typical feature of Oceanic Anoxic Events (OAE; Godet, 2013), which can also be used for stratigraphic correlations. ...
... The link between Early Cretaceous episodes of carbonate platform drowning and, more widespread, profound environmental changes has long been postulated in the Helvetic Realm (Föllmi et al., 1994;Godet et al., 2013;Weissert et al., 1998). Following Föllmi et al. (2006), the Helvetic platform succession documented the influence of regional environmental changes, such as relative sea ...
... Furthermore, the authors stated that each drowning phase was quickly followed by a major positive carbon-isotope excursion. Such modifications in the carbon and phosphorus cycles are associated with global oceanic anoxic events (Föllmi et al., 1994;Weissert et al., 1998;Wissler et al, 2003), which took place in neighbouring basins. The latest Hauterivian and Barremian time interval records a succession of short and repeated periods of dysaerobic to anaerobic conditions that took place in the Vocontian basin (Masse & Machhour, 1998), the central Tethys (eg., central Italy; Baudin, 2005;Baudin et al., 2002;Coccioni et al., 1998Coccioni et al., , 2006, the Boreal basins (Greenland and Norway; Mutterlose et al., 2003), and the Lower Saxony basin (northern Germany; Mutterlose & Böckel, 1998;Mutterlose & Bornemann, 2000;Mutterlose et al., 2009Mutterlose et al., , 2010, associated with the deposition of a succession of pelagic organic-rich deposits. ...
In the Alpstein massif of north-eastern Switzerland, a complete succession of uppermost Hauterivian to uppermost Barremian condensed hemipelagic sediments crops out. This succession is known as Tierwis Formation, comprising in ascending order, the Altmann and Drusberg members. The sedimentary succession bears a number of fossiliferous glauconite- or phosphate-rich beds. A large number of newly discovered ammonites from these key beds and from several poorly explored levels of the Tierwis Formation allows for a new age calibration. The new dating as well as revised sequence stratigraphic interpretations and geochemistry contribute to a better understanding of the lithostratigraphic complexity of the Tierwis Formation and its spatio-temporal relationship with the Schrattenkalk Formation. The new lithostratigraphic observations, backed by ammonites, shows that the Altmann type-section and the Tierwis paratype-section do not cover the same stratigraphic interval because of dynamic sedimentation processes as erosion and sedimentation in submarine channels. We suggest that a phosphatic conglomerate in the Dursberg Member of middle late Barremian age corresponds to the Chopf Bed, which we recognised for the first time in the Alsptein massif. The Drusberg Member strongly thickens toward the southeast and progressively covers an upward extended stratigraphic range. Furthermore, the new dating of the key-surfaces and beds highlight a dense succession of drowning phases which occurred through the latest Hauterivian to late Barremian time interval. The latest Hauterivian onset of the glauconite-rich sedimentation of the Altmann Member is associated with a first major drowning phase, followed by the Faraoni oceanic anoxic event. The change of sedimentation to a rhythmic marl-limestone alternation of the Drusberg Member takes place over a polyzonal phosphatic conglomerate. This conglomerate coincides with a second major drowning phase and the onset of the Mid-Barremian Event, which is calibrated on the Tethyan ammonite biozonation.
... The Carrack Fm. is assigned to the Late Aptian based on the occurrence of nannofossil Zone BC22; however, the poorly resolved and very low δ 13 C values prevent detailed correlation to the standard δ 13 C reference curve from the Vocontian Basin (Herrle et al., 2004;Föllmi et al., 1994). Overall, the absolute δ 13 C values from the Carrack Fm. are much Moore (1989), Fields of well-preserved foraminifera (after Veizer and Prokoph 2015;O'Brien et al., 2017) -values plotted. ...
... Lista and Maureen Fms. lower compared to the standard δ 13 C reference curve from the Vocontian Basin (Herrle et al., 2004;Föllmi et al., 1994), which may be indicative of some diagenetic overprint. The low δ 13 C values that characterize the Late Aptian from the Carrack Fm. are comparable to the Late Aptian Comanche Platform δ 13 C profile (Phelps et al., 2015, Fig. 5). ...
... Bown et al., 1998;in Gradstein et al., 2020); c. Vocontian Basin δ 13 C profile with named events (after Herrle et al., 2004Herrle et al., , 2015Föllmi et al., 1994); d. δ 13 C profile from the Comanche Shelf, Texas, U.S.A. (Phelps et al., 2015); e. Well 30/2a-7 δ 13 C profile (this study) with f. Boreal nannofossil zonation assignment (this study). ...
A stable carbon isotope (δ¹³C) profile of the Early Cretaceous to Paleogene (Berriasian – Danian) was generated from ditch-cuttings material recovered from well 30/2a-7, Central North Sea. The profile of δ¹³C values was integrated with calcareous nannofossil biostratigraphy and sequence stratigraphy from the Cromer Knoll Group to provide an integrated stratigraphic framework for the Early Cretaceous. Although, nannofossil data was not collected from most of the overlying Chalk Group, the associated δ¹³C profile was sufficiently resolved to correlate with other similar δ¹³C records from both the Boreal and Tethyan Realms. The δ¹³C profiles and nannofossil data from well 30/2a-7 were stacked with the nearby Shearwater A9 well data to create a composite section that provides a long-term near continuous record of the Early Cretaceous to Paleogene from the basinal deposits of the Central North Sea. Sequence stratigraphic analyses was conducted to provide an integrated bio-chemo-sequence stratigraphic framework for regional correlation. Several major globally recognized δ¹³C events that are recognized in the wells are seismically resolvable and can be correlated regionally across the Central North Sea, providing a chronostratigraphic framework for constraining hydrocarbon play elements for both exploration, production and carbon capture and storage projects.
... Several distinctive Upper Jurassic -Lower Cretaceous δ 13 C trends and excursions have been identified in numerous records from Tethyan, Atlantic and Pacific basins (Weissert and Channell, 1989;Lini et al., 1992;Föllmi et al., 1994;Weissert and Mohr, 1996;Weissert et al., 1998;Godet et al., 2006;Tremolada et al., 2006;McArthur et al., 2007;Főzy et al., 2010). Particularly well-known is the Valanginian positive carbon-isotope excursion, named the Weissert Event (e.g. ...
... The causative mechanisms for the Weissert Event have been intensely debated, but the excursion is generally inferred to record a global carbon-cycle perturbation affecting the entire exchangeable carbon reservoir based on its recognition in numerous δ 13 C carb (e.g. Lini et al., 1992;Föllmi et al., 1994;Weissert et al., 1998;Weissert and Erba, 2004;Price et al., 2016 and references therein), δ 13 C bel (Price and Mutterlose, 2004;Price et al., 2018) and δ 13 C wood (Gröcke et al., 2005; records retrieved from Tethyan, Boreal, Atlantic and Pacific basins. The event has been variously linked to: (i) bio-calcification crises related to carbonate platform drowning along the northern Tethyan margin (Föllmi et al., 1994Weissert et al., 1998;Wortmann and Weissert, 2000); (ii) global oceanic anoxia ; and (iii) emissions of the Paraña-Etendeka flood basalts causing a rise in atmospheric CO 2 and resulting greenhouse Fig. 10. ...
... Lini et al., 1992;Föllmi et al., 1994;Weissert et al., 1998;Weissert and Erba, 2004;Price et al., 2016 and references therein), δ 13 C bel (Price and Mutterlose, 2004;Price et al., 2018) and δ 13 C wood (Gröcke et al., 2005; records retrieved from Tethyan, Boreal, Atlantic and Pacific basins. The event has been variously linked to: (i) bio-calcification crises related to carbonate platform drowning along the northern Tethyan margin (Föllmi et al., 1994Weissert et al., 1998;Wortmann and Weissert, 2000); (ii) global oceanic anoxia ; and (iii) emissions of the Paraña-Etendeka flood basalts causing a rise in atmospheric CO 2 and resulting greenhouse Fig. 10. Time-calibrated correlation of stacked Kimmeridgian-Hauterivian δ 13 C org data of Svalbard with other δ 13 C org , δ 13 C bel , δ 13 C wood and δ 13 C carb records representative of the Boreal, Sub-Boreal, marginal Tethyan, Tethyan, Atlantic and Pacific realms (see Fig. 1 for palaeogeographic distributions). ...
... pre-or post-date) changes in sedimentation and benthic community assemblages (Föllmi et al., 2006); however, they are usually hard to identify using biostratigraphic methods due to the low potential of resolution of benthic biostratigraphic markers with respect to the pelagic ones. Submarine metallic crusts (hardgrounds) accompanied by pelagic condensed deposits, generally including gaps, are meaningful expressions of environmental changes (Schlager, 1991;Föllmi et al., 1994;Godet, 2013;Vörös et al., 2016). Hardgrounds, coupled with pelagites and intercalated in shallow-water carbonate successions, are associated with a long-term drowning of the carbonate platform (Godet, 2013;Christ et al., 2015;Föllmi, 2016). ...
... Demise and drowning of many carbonate platforms, associated with changes in the ecology of the carbonate-producing organisms, Fe-Mn crusts and pelagic condensed deposits, are explained as caused by palaeoceanographic changes (Föllmi et al., 1994;Peter and Simo, 1997;Pomar, 2001;Godet, 2013) and/or tectonic subsidence and sealevel rise (Santantonio, 1993;Bosence, 2005;Schlager, 2005;Basilone, 2020). ...
... The Valanginian "Weissert event" , defined as the first major perturbation in the Cretaceous carbon cycle (Lini et al., 1992;Föllmi et al., 1994;Weissert et al., 1998), was not always recorded as an oceanic anoxic event (Westermann et al., 2010;Vörös et al., 2020) but rather as a carbon cycle perturbation triggered by the activity of the Paraná-Etendeka Large Igneous Province . This hypothesis is supported by the evidence of various palaeoenvironmental changes, as indicated by the Valanginian biotic crisis of shallow-water ecosystems and pelagic environments (Duchamp-Alphonse et al., 2007;Möller et al., 2020). ...
Valanginian is a deeply investigated time interval due to the climatic, environmental and oceanographic changes that characterised it, globally recorded in sedimentary successions.
During the Valanginian, an oscillation between warm and cold climatic phases is generally accepted as causing change in sedimentation, especially along the carbonate platform successions. In this context the so-called “Weissert event” occurred.
The analysed stratigraphic interval consists of a Valanginian-Hauterivian package of two black metallic crusts (hardgrounds) and condensed pelagites, interbedded in the Lower Cretaceous carbonate shallow-water succession outcropping in the Palermo Mountains (NW Sicily). Integrating facies, structural, mineralogical and geochemical analysis, including analysis of δ¹³C and δ¹⁸O isotope records, the interaction between synsedimentary tectonics and climatic changes, as causing palaeoenvironmental and palaeoceanographic changes in the Lower Cretaceous Panormide carbonate platform, has been envisaged.
A regional extensional tectonics event in the Southern Tethyan margin was detected at the Berriasian/Valanginian boundary, as responsible for the tectonic fragmentation of the Mesozoic Panormide carbonate platform in various fault-blocks. Locally, tectonic subsidence caused drowning of some of the fault-blocks. Before the recovery of the benthic carbonate factory in the Barremian, condensed pelagites and mineralised (FeMn) crusts developed during the alternation of warm and cold climatic pulses.
The positive-negative excursions of the Valanginian-Hauterivian δ¹³C pattern of the Colombrina section provide solid evidence for the chronostratigraphic assignment of the study interval to the drowning of many carbonate platforms that preludes the onset of the “Weissert event”. In detail, the drastic negative shift of the δ¹³C in the late early Valanginian mineralised crust reveals massive release of isotopically light carbon to the atmosphere/hydrosphere reservoirs from a possible excess of volcanogenic CO2 or methane release from clathrate dissociation. Combining sedimentological data with the increase of the δ¹⁸O isotope records, two cold climate pulses are envisaged. The first one is assigned to the Berriasian/Valanginian boundary and led to the formation of the lower mineralised crust. The second and more evident positive shift of δ¹⁸O is assigned to the earliest late Valanginian, during the sedimentation of the laminated pelagites deposited immediately after the upper mineralisation event. These cold events that are comparable with the coeval cooling pulses recorded at a global scale highlight icehouse interludes during the Lower Cretaceous greenhouse mode.
... SMITH ET AL. they might provide a common factor linking geochemical records, platform drowning, and biotic turnover among calcifying organisms (Föllmi et al., 1994;Kiessling & Simpson, 2011;Krencker et al., 2020;Phelps et al., 2015;Trecalli et al., 2012). ...
... OAEs are complex events in which a single cause-commonly thought to be a rapid injection of volcanic CO 2triggers a cascade of related events that could lead to platform drowning (Jenkyns, 2010). However, anoxic conditions rarely impinge upon shallow-water environments because waves efficiently mix atmospheric oxygen into SMITH ET AL. (Phelps et al. 2014), Northern Tethyan Margin (Drzewiecki & Simo, 2000;Föllmi et al., 2006Föllmi et al., , 1994, and Oman (van Buchem et al., 2010). (b and c) Possible effects of Ocean Anoxic Events (OAEs) on depth-dependant trends in carbonate saturation state. ...
... This generality complements the nutrient-drowning hypothesis, which was calibrated to modern calcifying taxa and thus assumes that the dominant sediment producers are phototrophic organisms (Hallock & Schlager, 1986). Reduced sedimentation rates should apply to heterotrophic sediment producers (e.g., crinoids) and microbial buildups, both of which are common in drowning successions (Ettinger et al., 2020;Föllmi et al., 1994;Huck et al., 2010). One limitation of the our model is that, we grouped carbonate produced in the surface oceans as a singular pool and did not distinguish among pelagic, photozoan, heterozoan, and microbial modes of carbonate production. ...
Plain Language Summary
Carbonate minerals precipitate from ions dissolved in water. Thick packages of carbonate rocks often form in shallow, tropical waters, and their accumulation rate depends on the availability of ions as well as biological agents that catalyze carbonate deposition such as animals and microbes. Geologic patterns in carbonate rocks are sensitive to these controls on accumulation rates, tying them to Earth’s surface chemistry and ecosystems. Sometimes chemical changes in the oceans cause far‐reaching effects that influence patterns observed in carbonate rocks. During the Mesozoic Era, episodes of lowered dissolved oxygen in the world’s oceans often coincided with a phenomenon known as “platform drowning”. Platform drowning occurs when carbonate platforms—sites of carbonate deposition like the modern Bahamian Islands—experienced slower sedimentation rates and sank into deeper water. Interestingly, there are several chemical pathways that could cause platform drowning, and unraveling the underlying drivers is key for understanding the nature of past environmental changes. Here we present a concept for platform drowning that emphasizes the role of microbes and their effects on global ocean chemistry. This idea helps explain the long timescales of platform drowning and may explain similar patterns during other low‐oxygen episodes in Earth’s past.
... Varying climate conditions during the Early Cretaceous has implications for the unrolling of major paleoceanographic events such as OAE's and phases of carbonate platform demise. In the Swiss Alps, Föllmi et al. (1994) stated that the Helvetic platform underwent several crises during the Late Jurassic -Early Cretaceous; in particular, carbonate sedimentation was interrupted by major phases of condensation and phosphogenesis from the latest Hauterivian to the Barremian (Altmann Member), and in the Late Aptian (Luitere Member), straddling the deposition of Urgonian facies. ...
... In terms of facies, the Schrattenkalk Formation is interpreted as being deposited on a distallysteepened ramp; both the Lower and Upper Schrattenkalk members prograded out toward deeper environments of the ramp, while the Rawil Member is interpreted as a retrograding unit (Funk et al. 1993;Föllmi et al. 1994;Bonvallet et al. 2019). Characteristic facies indicate a hemipelagic deposition setting at the base, and a subtidal to a platform margin setting toward the top of the Lower Schrattenkalk Member, whereas they are interpreted as supratidal and transgressive environments, and hemipelagic to outer shelf setting at the base and the top of the Rawil Member, respectively. ...
Defined in the Provence region of France, the rudist-bearing Urgonian Limestone is typical of northern Tethyan shallow-marine carbonate series, and is dated based on benthic fauna and flora, calcareous nannofossils, and ammonites. This contribution reports on recent findings that refine the stratigraphy of the Urgonian Limestone in the western Swiss Jura and the Helvetic Alps of Switzerland. In the former location, the high-resolution facies and isotope analysis of samples permit the identification of major periods of subaerial exposure while a diverse assemblage of calcareous nannofossils indicates a Barremian age for the Urgonian deposits. In the latter location, biostratigraphic data indicate a Late Barremian - Early Aptian age for Urgonian deposits while the repartition of facies along a proximal-to-distal transect highlights the Late Barremian progradation of the platform. The detailed understanding of the stratigraphy of Urgonian deposits in these regions inscribes them into a broader context that acknowledge paleoclimatic and paleoenvironmental conditions. A warmer and more humid climate prone to continental weathering and transport of nutrient to epicontinental sea characterized the Early Barremian; this was detrimental to the health of carbonate-producing benthic ecosystems. In the Late Barremian, a reduced nutrient supply allowed Urgonian communities to thrive.
... Additional humid peaks and increase in trophic levels were documented from clay mineral, palynological and calcareous nannofossil assemblages in the earliest Valanginian Kujau et al., 2013;Duchamp-Alphonse et al., 2014;Charbonnier et al., 2016), and in the Valanginian-Hauterivian transition (Kujau et al., 2013;Charbonnier et al., 2016). A drowning event, the Lidernen episode, is also documented in the "middle" Hauterivian, from the Lyticoceras nodosoplicatum to the Plesiospitidiscus ligatus Tethyan ammonite zones (Föllmi et al., 1994;Godet, 2013). All these events also share the fact that they correspond to 2 nd -order transgression documented by facies changes Godet, 2013;Aguirre-Urreta et al., 2019), widespread marl formations or drownings on platforms (van de Schootbrugge et al., 2003;Godet et al., 2013;Morales et al., 2013;Pictet, 2021) and faunal migration patterns (Walter, 1996;Mutterlose and Bornemann, 2000). ...
... These correlations between lithology and climate are not only true at marl-limestone alternation scale, but are also verified at 100-kyr, 405-kyr eccentricity scales, and longer time scale (Fig. 5). In the Vocontian Basin, the trend in CaCO 3 contents of the alternations mimics the trend in neritic carbonate production at 10 7 -to-10 4 -year time scales (Ferry and Monier, 1987;Föllmi et al., 1994;Quesne and Ferry, 1995;Reboulet et al., 2003). Detailed platform-basin correlations show a progressive decrease in thickness and size of carbonate particles toward the basin, which suggest that most of carbonate mud deposited in the basin was exported from the platforms through nepheloid flows (Reboulet et al., 2003). ...
... The magnitudes of the positive carbon isotope shifts in our continental organic δ 13 C record from Utahraptor Ridge are much greater than the CIEs to which we correlate them in the marine carbonate record. Notwithstanding, it is common for terrestrial δ 13 C chemostratigraphic records to exhibit magnitudes that exceed those of correlative marine records by factors of two or more (Table 3) [4][5][6]11,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. The causes of such frequently observed differences between correlative terrestrial and marine δ 13 C records have not been fully explored. ...
... Positive CIEs with possible magnitudes of as much as +3.6 per mil at 33.75 m in stratigraphic height and of possibly as much as +2.3 per mil slightly below 40 m in our chemostratigraphic profile at Utahraptor Ridge (( Figure 5: P3, P4). Furthermore, the overall configuration of our chemostratigraphic profile between approximately 33.75 and 40 m ( Figure 5) is strongly reminiscent of the "double-peak" positive C-isotope excursion in the Valangian observed in many marine carbonate records and called the "Weissert Event" or "Weissert Episode" by some authors [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] (Figure 7). In the chemostratigraphic profile presented in Figure 5, we interpret feature P3 as the lower of the two peaks and P4 as the upper one. ...
The Early Cretaceous Yellow Cat Member of the terrestrial Cedar Mountain Formation in Utah, USA. has been interpreted as a “time-rich” unit because of its dinosaur fossils, prominent paleosols, and the results of preliminary chemostratigraphic and geochronologic studies. Herein, we refine prior interpretations with: (1) a new composite C-isotope chemostratigraphic profile from the well-known Utahraptor Ridge dinosaur site, which exhibits δ13C features tentatively interpreted as the Valanginian double-peak carbon isotope excursion (the so-called “Weissert Event”) and some unnamed Berriasian features; and (2) a new cryptotephra zircon eruption age of 135.10 ± 0.30/0.31/0.34 Ma (2σ) derived from the CA-ID-TIMS U-Pb analyses of zircons from a paleosol cryptotephra. Our interpretations of δ13C features on our chemostratigraphic profile, in the context of our new radiometric age, are compatible with at least one prior age model for the “Weissert Event” and the most recent revision of the Cretaceous time scale. Our results also support the interpretation that the Yellow Cat Member records a significant part of Early Cretaceous time.
... Also, superimposed long-and short-term eustatic sea level rises caused periodic large epicontinental seas to develop (Haq 2014). Thus, the concurrence of changing paleoceanographic and paleoclimatic conditions and considerable variations in sea level deeply affected the depositional pattern of most marine settings at that time (Föllmi et al. 1994;Burla et al. 2008;Huck et al. 2010;Föllmi 2012). For instance, most carbonate platforms in the Tethyan realm underwent a complete shutdown (Funk et al. 1993;Föllmi et al. 1994;Weissert et al. 1998;Bosellini et al. 1999;Graziano 1999;Wissler et al. 2003;Föllmi and Gainon 2008;Gaona-Narvaez et al. 2013;Godet 2013;Pictet et al. 2015), and a microencrusting-dominated community temporarily replaced once-flourishing rudist and coral reef communities, especially along the southern Tethyan margin (Immenhauser et al. 2005;Huck et al. 2010;Rameil et al. 2010). ...
... Thus, the concurrence of changing paleoceanographic and paleoclimatic conditions and considerable variations in sea level deeply affected the depositional pattern of most marine settings at that time (Föllmi et al. 1994;Burla et al. 2008;Huck et al. 2010;Föllmi 2012). For instance, most carbonate platforms in the Tethyan realm underwent a complete shutdown (Funk et al. 1993;Föllmi et al. 1994;Weissert et al. 1998;Bosellini et al. 1999;Graziano 1999;Wissler et al. 2003;Föllmi and Gainon 2008;Gaona-Narvaez et al. 2013;Godet 2013;Pictet et al. 2015), and a microencrusting-dominated community temporarily replaced once-flourishing rudist and coral reef communities, especially along the southern Tethyan margin (Immenhauser et al. 2005;Huck et al. 2010;Rameil et al. 2010). At the same time, deeper hemipelagic and pelagic settings of the Tethys and elsewhere reveal evidence of oxygen-starved conditions in deposits of black shales with high organic matter (OM) content (Schlanger and Jenkyns 1976;Jenkyns 1980Jenkyns , 2010Arthur et al. 1990;Bralower et al. 1994;Cobianchi et al. 1999;Yilmaz et al. 2004;Dumitrescu andBrassell 2005, 2006;de Gea et al. 2008;Heldt et al. 2008;Emeis and Weissert 2009;Roban and Melinte-Dobrinescu 2012;Patruno et al. 2015;Sanchez-Hernandez and Maurrasse 2016). ...
During the Cretaceous, the concurrence of changing paleoceanographic and paleoclimatic conditions, coupled with variations in eustatic sea level, contributed to episodes of globally widespread deposition of organic matter (OM)-rich marine sediments collectively termed oceanic anoxic events (OAEs). Here, we aim to investigate the response of a lower Aptian hemipelagic sequence from the northeastern Iberian margin in the context of OAE1a. Stable-carbon isotope (d 13 C org) data are consistent with the pattern reported for the end of carbon isotope segment C5 within OAE1a. Moreover, high sediment accumulation rates (bulk: ∼37.13 cm/ky, wet: ∼63.29 cm/ky) permit the establishment of refined details suitable for precise chemostratigraphic correlations. We recognized three distinct lithologic units. Within unit 1, variable pulses of fluvial fluxes explain the alternating lithology, with limestones depicting the least terrestrially influenced end member and marlstones representing episodes of highest terrigenous input. In the ensuing marlstone-dominated unit 2 interval, results show relatively higher OM, redox-sensitive trace elements (RSTEs), P, Fe, Al, Si, and Ti values than before, thus suggesting an increase in runoff with quasi-permanent eutrophic surface waters and continuous oxygen-deprived conditions, but without a fully anoxic phase, as benthic fauna, while relatively reduced, are present throughout. Unit 3 registers limestones impoverished in OM, Al, Si, Ti, P, and Fe, with a lower relative proportion of autochthonous to allochthonous OM, indicating a reduction in runoff and surface water fertility linked to drier climate conditions. Simultaneous changes in microfacies, with coarser packed biosparites, reduced planktonic foraminifera, and an increase in benthic taxa, imply shallowing of the basin, similar to that reported for sequences in the neighboring Basque-Cantabrian Basin synchronous with the negative d 13 C org shift heralding the end of segment C5.
... The Miocene phosphatisation is a departure from a long term trend where intensive phosphogenesis in the Mediterranean Tethys had, for the most part, halted as of the late Eocene (Soudry et al., 2006) due to change in circulation patterns. Phosphate accumulation later migrated primarily to the northern Central Mediterranean during the middle to late Miocene (Figure 11, Föllmi et al., 2015) while global phosphate accumulation rates declined (Föllmi, 1995;Föllmi et al., 1994). The global trend was attributed to changes in weathering patterns while the local Mediterranean was modulated by shifting circulation and climate patterns (Föllmi et al., 2019). ...
... Local tectonic trends (Papadimitriou et al., 2018;Robertson, 1977) are noted for context. (Kiessling, 2001;Kiessling and Flügel, 2002), Mediterranean phosphate accumulation (Auer et al., , 2016Föllmi et al., 2015Föllmi et al., , 2007, regional climate patterns (Böhme et al., 2008;John et al., 2003;Schneck et al., 2010), connectivity of the Mediterranean to the Indian Ocean (IO) following , initiation of sapropels (Shipboard Scientific Party, 1978;Taylforth et al., 2014), mass accumulation rate (MAR) of CaCO 3 in the Levant Basin (Torfstein and Steinberg, 2020), global phosphate accumulation patterns (Föllmi, 1995;Föllmi et al., 1994), high latitude climate patterns (AIS = Antarctic Ice Sheet; Flower and Kennett, 1994;Groeneveld et al., 2017), bulk rock carbon isotope record from the TZ section and benthic foraminifera carbon and oxygen isotopes from the North Atlantic (Cramer et al., 2009). Sea level curve from Miller et al. (2020). ...
During the early and middle Miocene, the Mediterranean had become a restricted marginal marine sea with diminishing and ultimate loss of connectivity to the Indian Ocean. This dramatically changed the heat, energy, freshwater and nutrient budgets across the Mediterranean and most notably in its eastern basin. While one of the most prominent lines of evidence of this change in the Eastern Mediterranean is the onset of sapropel formation, many other aspects of the sedimentary system changed in response to this rearrangement. Here we present a detailed analysis of a hemipelagic succession from southwestern Cyprus dated to the late Aquitanian to the early Serravallian (22.5–14.5 Ma). This sequence is carbonate-dominated and formed during the decoupling of the Mediterranean Sea and the Indian Ocean. It exhibits sedimentation with mass transport contribution from shallow water carbonates to deeper facies with phosphatization and bottom current (at intermediate depth) interactions. This succession traces both local subsidence and loss of a local carbonate factory. Additionally, it records a shift in bottom current energy and seafloor ventilation, which are an expected outcome of connectivity loss with the Indian Ocean.
... A few years later, Hallock and Schlager (1986) suggested that increased nutrient delivery to neritic areas, resulting from the overturn of deep anoxic waters, was the cause of platform drowning during OAEs. This paradigm, which highlights increased nutrient levels as the primary control on shallow-water carbonate crises, has been used to interpret episodes of drowning in the northern Tethyan carbonate platforms (Föllmi et al. 1994(Föllmi et al. , 2006Weissert et al. 1998). According to this paradigm, carbonate platforms thrived under low-nutrient conditions that favoured the development of aragonite-dominated oligotrophic photozoan communities. ...
During the Cretaceous, the Berriasian-Aptian interval witnessed a transition from a relatively cool climate with intermittent polar ice to a greenhouse state that persisted throughout the Late Cretaceous. These palaeoclimatic changes were associated with the construction of Large Igneous Provinces (LIPs), which significantly perturbed the ocean-atmosphere system by introducing large amounts of CO 2 , trace metals, and micronutrients, thereby impacting the biosphere. Our study focused on the Tethyan Ocean during the Early Cretaceous, examining the resilience of planktonic and shallow-water benthic calcifying algae to environmental changes. We observed their adaptation, recovery dynamics, and the influence of palaeo CO 2 levels on their resilience. Calcification patterns of calcareous nannoplankton served as a proxy for ecological and engineering resilience. While calcareous nannoplankton as a whole showed high resistance, individual taxa exhibited varying levels of resilience. Nannoconids, particularly narrow-canal ones, were highly sensitive and had low resistance. In contrast, Watznaueria barnesiae showed the least sensitivity and highest resistance, likely due to its adaptive strategies and long lifespan. Nannoplankton calcification recovery (engineering resilience) from the Weissert Event took approximately 3 million years. After OAE1a, instead, nannoplankton did not return to pre-perturbation conditions. In shallow-water platforms, Dasycladales, aragonitic benthic calcifiers, exhibited lower resilience compared to nannofossils. They experienced a decline in species diversity across both the Weissert Event and the OAE 1a, which could indicate higher sensitivity to reduced carbonate saturation under high p CO 2 conditions. After the Valanginian Weissert Event, Dasycladales were able to recover, albeit they show a much lower engineering resilience compared to nannoconids, as it took nearly 10 million years to revert to pre-disturbance diversity. The OAE 1a represented a more intense perturbation: their decrease of species diversity was much more drastic and permanent, and Dasycladales were unable to recover, losing their dominant role as carbonate platform biocalcifiers for the remainder of the Cretaceous. Our study provides an assessment of the resilience of Tethyan phytoplanktonic and shallow-water benthic calcifying algae to disturbances during the Early Cretaceous, with implications for tipping points associated with palaeo-CO 2 levels. The differential responses in terms of timing and magnitude and the recovery dynamics contribute to the understanding of the potential impacts of current and future global changes on the resilience of marine ecosystems and the thresholds that may lead to ecological crises.
... Enrichments of Fe, Mn, and P are common in crusts of drowning carbonates and might be related to higher nutrient content in the water column (e.g. Hallock and Schlager 1986;Föllmi et al. 1994;Drzwiecki and Simo 1997) (Table 1). A remarkable high P 2 O 5 value was found in sample HST 79-16 (grainstone). ...
A 200 m thick drill core penetrating the Givetian Hahnstätten Reef in the southwestern Lahn Syncline (Rhenish Massif) was investigated. A range of different depositional environments is described based on lithofacies and microfacies analysis. All in all, nine lithofacies types (FTs) are distinguished, which can include subfacies types. The majority of lithofacies of these ultrapure carbonates is represented by lime mudstone and fenestral microbialites, all pointing to shallow subtidal, intertidal to even supratidal low-energy palaeoenvironments. In contrast, more high-energy parts of the reef were dominated by bioclastic rubble deposits (e.g. rudstone). Autochthonous, reef-building carbonates are represented by bafflestone and framestone. Diversity of reef building organisms (stromatoporoids and corals) is low and is dominated by Stachyodes , Actinostroma , Stromatopora , and Thamnopora and alveolitids, respectively. Other bioclasts are brachiopods, gastropods, ostracods, foraminifera, echinoderms, trilobites, and conodonts in descending order. Development of the Hahnstätten Reef is interpreted as having been controlled mainly by synsedimentary tectonics and volcanism with contributions from eustasy. The occurrence of Stringocephalus burtini in the entire section and conodont findings, which provide more precise biostratigraphic data confirm an early to middle Givetian age ( Polygnathus rhenanus/varcus Zone to Polygnathus ansatus Zone) of the succession. The average quality of the ultrapure carbonates lies at 97.68% CaO (excl. loss of ignition), with 70% of the core ranging between 98% and 99% CaO. This extremely high purity makes it difficult to identify correlations between lithofacies and geochemical data.
... Change in relative sea level is one, among many, potential drivers of organic carbon burial and therefore the generation of positive carbon isotopic excursions (e.g. Föllmi et al., 1994;Jenkyns, 1996;Burdige, 2005;Jarvis et al., 2006;Anisaar et al., 2010;Eltom et al., 2018). As sea level rises, the surface area for photosynthesis increases and upwelling provides nutrients that fuel primary productivity and the burial of organic carbon. ...
... During the Cretaceous, thick carbonate successions along the northern and southern Tethyan margins usually formed in the inner and outer-shelf environments. These successions contain benthic, planktic and nektonic organisms, often used in paleontological and sedimentological studies (e.g., Föllmi et al., 1994 ;Dini et al., 1998 ;Arnaud-Vanneau, 2006 ;Masse et al., 2009 ;Schlagintweit, 2011 ;Godet et al., 2014 ;Gheiasvand et al., 2021 ;Gheiasvand and Arnaud-Vanneau, 2022 ). Large benthic foraminifera, such as Orbitolina and Balkhania , are important taxon used in biostratigraphic studies (e.g., Mehrnusch, 1973 ;Bucur et al., 2013 ;Hosseini, 2014 ;Gheiasvand et al., 2019Gheiasvand et al., , 2020. ...
... Gale et al. (2020) depicts 11 OAEs in the Cretaceous only, while pointing out that global carbon isotopic excursions are more numerous than known synchronous spreads of anoxic sediments (see also Cramer and Jarvis, 2020). Some OAEs are associated with selective extinctions of marine organisms and declines in reef building, whereas others are not (Föllmi et al., 1994;Leckie et al., 2002;Freymueller et al., 2019). ...
This paper reviews global records of anoxic events of the Middle Devonian – earliest Mississippian, as well as the possible triggers and controls of these events. These “anoxic events” are complex multistage paleoenvironmental disturbances manifested in multiple proxies, which we showcase with the Horn River Group (HRG) – a succession of basinal organic-rich shales and cherts deposited during the latest Eifelian – earliest Late Frasnian (∼386–373 My ago) on the western continental margin of Laurentia near the paleo-equator. Four major events imprinted in the HRG are the Kačák, Frasnes, basal punctata, and late punctata events, but positive δ13C excursions (measured on organic matter) are more numerous and can potentially be matched to other global events. The Kačák event in the base of the HRG manifests as a regional switch from carbonate-platform to anoxic sedimentation. Three major events of the latest Givetian – Middle Frasnian display repeating sequences characterized by: (1) an early shift to heavier δ13C values coupled with siliciclastic enrichment and mercury enrichment spikes of up to 0.48 ppm; (2) late-stage δ13C reversal to background values coincident with the onset of severe anoxia (buildup of authigenic U, Mo, V) and attenuation of siliciclastic supply. Devonian anoxic sediments, including HRG, display widespread presence of chlorobi biomarkers, which indicates episodes of photic-zone euxinia in the water column. Most of these sediments were deposited under open ocean conditions, precluding a Black Sea water-column stratification scenario. These observations indicate Devonian anoxic events are similar to classical Mesozoic oceanic anoxic events (OAEs), consistently with growing evidence for a volcanic trigger for these events (e.g. spikes in Hg and negative 187Os/188Os anomalies). Oxygen minimum zones in a greenhouse ocean, such as the one recorded in basinal HRG, were prone to expansion under volcanic CO2 reinforcement. This volcanic press-pulse also intensified the hydrological cycle, which resulted in a boost of weathering and eutrophication of shelfal seas. These factors, amplified by deoxygenation and acidification of the habitable upper ocean, drove extinctions of various magnitude. As a proxy for the input of land-plant detritus, the oxygen index from pyrolysis data shows zero response to anoxic events in the HRG, which aligns with broader evidence that counters expanding vascular vegetation to be the driver of the marine biotic crises. Finally, our review highlights how controversial the evidence of high-frequency (3rd to 5th orders) sea-level fluctuations is in the Devonian. In particular, none of the geochemical proxies usually employed to interpret sea-level changes translates unequivocally into transgressions and regressions in the greenhouse world. This sea-level puzzle clearly calls for new scrutiny and justifies scepticism in the validity of the classical “eustatic sea-level curve of the Devonian”, as well as estimates of eustatic amplitudes in excess of ∼25 m for 3rd and 4th order cycles.
... An increase in marine primary productivity requires enhanced nutrification and there are two main hypotheses: higher continental weathering rates and/or intensified oceanic upwelling (Lini et al. 1992;Föllmi et al. 1994;). These two processes would have different impacts in proximal and distal marine settings. ...
The Cretaceous marine sedimentary record is characterized by time intervals rich in organic matter correlating with positive carbon-isotope excursions, often called oceanic anoxic events. The Weissert Event corresponds to the first such event in the Cretaceous during the Valanginian stage. The associated palaeoenvironmental perturbations which include increasing marine surface-water primary productivity are hypothesized to be triggered by volcanic activity from large igneous provinces, and the source of nutrients is not well-constrained (continental runoff vs. oceanic upwelling). We present isotope ratios of Pb, Sr and Nd together with concentrations of major and trace elements for sediments coming from the central Moroccan margin to test these hypotheses. We demonstrate that the nutrient input was dominated by continental weathering. Also, the source of sedimentary material remained stable during the Valanginian interval and it originated in an old source, probably the African Sahara region. The radiogenic isotope signatures do not show a significant contribution of volcanic products from any known Valanginian large igneous province to the geochemical budget of sediments deposited on the central Moroccan margin. While this does not preclude an impact of volcanic activity on the composition of seawater, it demonstrates that erupted volumes were not sufficient to affect the deposited sediments.
Supplementary material: Supplementary table contains three sheets: (1) “Central Moroccan Margin”, the analytical data generated and analysed during this study; (2) “Fig. 8 Data - LIPs”, the data of known Valanginian large igneous provinces used for comparison; and (3) “Figs 9 and S5 Data - source areas”, the data of potential surrounding source areas used for comparison, available at https://doi.org/10.6084/m9.figshare.c.6333040
... Gale et al. (2020) depicts 11 OAEs in the Cretaceous only, while pointing out that global carbon isotopic excursions are more numerous than known synchronous spreads of anoxic sediments (see also Cramer and Jarvis, 2020). Some OAEs are associated with selective extinctions of marine organisms and declines in reef building, whereas others are not (Föllmi et al., 1994;Leckie et al., 2002;Freymueller et al., 2019). ...
... For the Tithonian to Valanginian interval, the Tethyan profile shows a slightly decreasing trend with values between ~ + 2.5 and + 1‰ (Fig. 6). Minor events in the middle and late Berriasian (MBeE and LBeE, respectively), and a major increase up to +3 and + 4‰ in the upper Valaginian (Weissert event) would be the result of global perturbations in the carbon cycle (Lini et al., 1992;Föllmi et al., 1994;Erba et al., 2004;Bodin et al., 2009;Cramer and Jarvis, 2020). In contrast, the profile from the PC section in the Neuquén Basin displays much more negative δ 13 C carb values with 3 large-scale increasing-decreasing cycles (0-420 m), and an overall increasing trend (Fig. 6). ...
The stable carbon isotopic compositions of carbonate sediments (δ¹³Ccarb) have been widely used to reconstruct the global carbon cycle and as a stratigraphic correlation tool. This work investigates a δ¹³Ccarb record of marine organic-rich, mixed siliciclastic‑carbonate mudstones accumulated from the Tithonian (late Jurassic) to the early Valanginian (early Cretaceous) in a retro-arc basin connected to the Proto-Pacific Ocean (Neuquén Basin, Argentina). The high-resolution record of δ¹³Ccarb values of these strata from outcrops at various locations in the basin differ from those in the coeval pelagic strata of the Tethys. The δ¹³Ccarb profile in the Puerta Curaco area shows an overall increasing trend from average values of −7‰ (early Tithonian) to approximately 0‰ (early Valanginian). The negative δ¹³Ccarb values occur in a ~ 400 m thick TOC-rich succession (TOC > 2%) and are arranged in 3 large-scale increasing-decreasing cycles. Although absolute values are offset, main trends are similar in other outcrops and in subsurface wells. The co-occurrence of the highest U/Th (>1.4) and the most negative δ¹³Ccarb values suggests that the major trends in the δ¹³Ccarb profile might be modulated by oscillations in oxygen content within the basin probably driven by sea-level changes. Clastic-dominated transgressive hemicycles have higher TOC and more negative δ¹³Ccarb values while the opposite occurs in carbonate-rich regressive hemicycles. A trend from “normal” Tithonian surface-water values (avg. +2‰) in the southern shelf to increasingly negative δ¹³Ccarb values towards the basin center indicates a mixing between platform-derived carbonate material unaffected by diagenesis and carbonate precipitated or altered in a dysoxic/anoxic basin. The δ¹³Ccarb profile in the Tethyan realm does not record this episode of high burial of organic carbon occurred in the Neuquén basin during the Tithonian and Berriasian but display a slightly decreasing trend between +2.5 and + 1.5‰.
... Phosphogenesis commonly coincides with carbonate shut-down because sediment starvation allows time for this process to occur (e.g. Föllmi et al., 1994;Föllmi, 1996Föllmi, , 2016. ...
The shutdown of carbonate productivity and its replacement by black shale deposition is often observed in the geological record and yet the factors driving such a change are debated. The latest Famennian of western Laurentia (present day North America) provides a good example of a limestone – black shale transition that is roughly contemporaneous with the global Hangenberg Crisis – a series of environmental and biotic changes associated with the widespread development of black shale deposition. However, in western Laurentia limestone deposition ceased and black shale deposition began prior to this crisis. Examining the type section of the Exshaw Formation at Jura Creek (Alberta) reveals that declining seafloor oxygen levels were likely responsible for the loss of carbonate productivity, followed by phosphogenesis of the youngest carbonates. The top surface of the limestone is a hard ground that was reworked, possibly by internal wave action, producing a lag of phosphatic clasts and pyrite grains including giant framboids (reaching 100 μm diameter) and polyframboids. The subsequent redox history of the lower Exshaw Formation shows substantial variations. Initially, the occurrence of small framboids, and elevated FeHR/FeT and Fepy/FeHR combined with enhanced U, Mo and Re concentrations indicates intense euxinia in the water column. These conditions were replaced by ferruginous anoxic conditions recorded in radiolarian-rich black shales that have moderate concentrations of trace metals, and low pyrite content, as confirmed both by low Fepy/FeHR ratios and scanning electron microscope observation. MoU covariation trends suggest that Mo enrichment under ferruginous conditions was promoted by drawdown in association with Fe minerals precipitated in the water column. The return of better ventilated conditions around the Devonian/Carboniferous boundary is marked by a decrease in trace metal content and the loss of syngenetic pyrite. The Hangenberg Crisis is thus marked by an improvement in ventilation, from euxinic to ferruginous conditions in our study, and evidence from other basins in western North America suggests an even greater increase in oxygenation at this time.
... Greenhouse gas emissions lead to a cascade of environmental feedbacks, including global warming, changes in ocean and atmospheric circulation, enhanced chemical weathering, continental runoff and increased primary productivity, which collectively lead to marine anoxia/euxinia and enhanced organic-matter burial (Jenkyns, 1999;Föllmi, 2012;Erba et al., 2015;Naafs et al., 2016). These mechanisms play a central role in the ending of OAEs due to their negative feedback effects (Föllmi et al., 1994;Weissert and Erba, 2004). ...
The understanding of the climatic evolution during the Early Cretaceous in general, and across Oceanic Anoxic Event 1a (OAE-1a) in particular, has generally been derived from Tethyan localities, implying large uncertainties about their significance at a global scale. In this study, high-resolution clay-mineral assemblage analyses have been performed on the Hauterivian to lower Aptian cored section of the North Jens-1 well, located in the Danish Central Graben, North Sea, in the Boreal Realm. Large amounts of detrital kaolinite are observed throughout the core, indicating the presence of a local, kaolinite-rich source. A long-term decline in kaolinite content is recorded from the upper Hauterivian to the lowermost pre-OAE-1a Aptian, followed by a sharp rise within the OAE-1a interval. This trend is similar to that observed in the Tethyan Realm, where a supra-regional climatic evolution is observed, including: (i) relatively humid conditions in the late Hauterivian; (ii) a shift towards overall drier conditions in the latest Barremian – earliest Aptian; and (iii) renewed humid conditions during the unfolding of OAE-1a. However, the precise timing of climate change across OAE-1a differs between the Tethyan and Boreal Realms. The shift towards humid conditions coincides with the onset of OAE-1a (segment C3) in the Tethyan Realm, followed by a return to drier conditions in the second half of the event. In the Boreal Realm, however, the onset of OAE-1a was characterised by a relatively dry climate, followed by an increase in humidity within its middle part (segments C4–C5) that persisted through the remainder of the early Aptian. Consequently, there was a non-linear change in precipitation patterns across latitudinal belts during the unfolding of OAE-1a. Similar conclusions have been drawn for other OAEs, suggesting a more complex weathering feedback mechanism during hyperthermal events than generally assumed.
... Following the P-ToBE, at the transition to the earliest Toarcian (Tenuicostatum Zone), carbonate productivity at the platform margin was unable to keep pace with the ongoing transgression, allowing the deposition of open-sea thin-bedded micritic limestones, which contain few bivalves and sponge spicules. The presence of siliceous sponges at the platform margin is indicative of sustained, high organic particulate flux on the platform (Föllmi et al., 1994), which is unfavorable for platform growth (e.g., Hallock & Schlager, 1986;Hottinger, 1987). Eutrophication, combined with the ongoing transgression, dampened carbonate productivity. ...
We explore the effects of the Pliensbachian–Toarcian Boundary Event (P–ToBE) on tropical carbonate productivity in the interior to margin and slope of the Venetian Platform (Northern Italy). We document the P–ToBE for the first time in the shallow‐water platform margin, and we bio‐ and chemostratigraphically tie it to transgressive/regressive cycles. Following the latest Pliensbachian sea‐level drop and emersion, transgressive grainstones at the platform edge record the P–ToBE negative carbon isotope excursion (CIE) of 1–1.5‰, also found in marl/limestone couplets on the slope. Recovery of platform productivity was ephemeral, as the platform drowned right after the peak negative CIE and was covered by deep‐sea thin‐bedded micritic limestones. The end of the P–ToBE correlates with a regression and renewed recovery of carbonate productivity. The negative CIE of the subsequent Toarcian Oceanic Anoxic Event is recorded in open‐sea cherty limestones both at the marginal and interior platform. These limestones document an even wider transgression and the renewed partial drowning of the platform in the Serpentinus Zone. We investigate the causes of the carbon perturbation at the P–ToBE, using a simple carbon cycle model. The duration and magnitude of the CIE suggest a rapid release of methane in driving the CIE, perhaps related to the preceding sea‐level drop and associated cryosphere perturbation, or to thermogenic alteration of coals near the Karoo‐Ferrar Large Igneous Province (LIP). The extent of the warming and the magnitude of the P–ToBE CIE implies a contribution of volcanogenic carbon dioxide from the Karoo‐Ferrar LIP.
... None of the geometries (erosional and constructional) found in the Bositra limestone exists in this formation. While the disappearance of posidoniids was a palaeobiological event (see above), the switch to an echinoderm (echinoids, crinoids) calcarenite facies could indicate a local environmental/circulation change on the Plateau, possibly linked with raised trophic levels (Föllmi et al., 1994). ...
The stratigraphic succession in the San Vincenzo Gorge (Saccense Domain, western Sicily) documents deposition on a vast pelagic carbonate platform, the Sciacca Plateau, during the Middle and Late Jurassic. This succession caps a peritidal limestone (Inici Formation), which underwent extension during the Western Tethyan Early Jurassic rift phase, and displays a set of unique features, which have never been previously reported on a Tethyan drowned platform. The upper part of the Bositra limestone (late Bajocian‐early Oxfordian p.p.) comprises elongate convex‐up, mound‐shaped bodies, made of thin‐shelled bivalve wacke‐ to grainstone, a few tens of metres across and producing a topographic relief of up to 10 m. Planar beds within the mound cores are seen to thin out laterally with tangential downlaps along sections perpendicular to the mounds’ longer axes, and the mounds are in lateral association with concave‐up bedsets. Following halt of the Bositra‐dominated deposition and demise of mound accretion, the draping units inherited an antiformal geometry. The mounds are interpreted as being part of a sediment drift, produced by bottom currents sweeping the Plateau top, the source areas being sediment‐depleted sectors now documented by extremely condensed and hiatus‐ridden sections, with parallel‐sided beds. Following draping and partial levelling of the submarine relief by the Knobbly limestone (?middle Oxfordian/early Kimmeridgian‐late Kimmeridgian), the Coquina limestone is locally a thick (>20 m) ammonite/brachiopod rudstone (Tithonian p.p.). This unit displays evidence for lateral accretion, with large scale clinoforms dipping up to 12°, and is interpreted as a mud‐poor, bioclastic‐gravel drift, with the action of bottom currents being apparently linked with a bloom of cephalopods. This is an early‐cemented deposit, where clotted, micropeloidal fabrics document the calcification of microbial communities and are followed by growth of early diagenetic fibrous calcite. The description and interpretation of the mounded Bositra limestone and of the clinostratified Tithonian limestone are the main focus of this paper. The San Vincenzo Gorge outcrop displays similarities with pelagic shelves, like the Upper Chalk basin of northern Europe.
... An attempt to quantify the stratigraphy of the Shu'aiba Formation by Vahrenkamp (1996) and Follmi et al. (1994) by means of carbon isotope dating has not proved useful at Shaybah so far . Strontium isotope analysis of selected cores produced results of limited value because of the apparent inaccuracy of the standard Sr seawater curve. ...
The Aptian Shu’aiba Formation forms a major carbonate reservoir in the Shaybah field of eastern Saudi Arabia. Lack of exposures and poor seismic data have forced the cored intervals to be fully exploited to provide evidence of the depositional environment and layering of the reservoir rocks and associated lithofacies. Rudist, foraminiferal and coccolith evidence indicates an Aptian age for the entire Formation, most of it being early Aptian. A major unconformity at the top of the Shu’aiba separates it from the overlying Nahr Umr Formation. Rapid biofacies variations suggest possible sequence boundaries within the Shu’aiba Formation. Semi-quantitative macropaleontological and micropaleontological analyses indicate significant paleoenvironmentally influenced lateral and vertical bioassemblage variations. Lagoon, rudist-associated back-bank, bank-crest and fore-bank, and upper-ramp depositional environments have been interpreted, of which the bank represents the gradual amalgamation of earlier isolated rudist shoals. Integrating the micropaleontological analyses with rudist assemblages has facilitated the prediction of rudist-associated reservoir facies. Variations in the micro- and macrofacies permit the Formation to be divided into three layers. (1) The “lower Shu’aiba” (without rudists) is dominated by a regionally extensive, moderately deep marine planktonic foraminiferal/algal association of Palorbitolina lenticularis-Hedbergella delrioensis-Lithocodium aggregatum and the benthonic foraminifera Debarina hahounerensis, Praechrysalidina infracretacea, Vercorsella arenata and rotalids. (2) The “middle Shu’aiba” shows the significant lateral and vertical differentiation of a rudist-rimmed shallow carbonate platform typically associated with a marine highstand. A predominance of rudist species Glossomyophorus costatus and Offneria murgensis occurs together with Lithocodium aggregatum, Palorbitolina lenticularis, Trocholina spp. and miliolid foraminifera. (3) The “upper Shu’aiba” represents an expansion of the lagoon (associated with a marine transgression), and a predominance of Agriopleura cf. blumenbachi and A. cf. marticensis rudists, together with Debarina hahounerensis, Praechrysalidina infracretacea and Vercorsella arenata. The localized distribution of the rudist Horiopleura cf. distefanoi in association with corals, is a feature of the eastern flank of the field. A coarse assemblage-based biozonation for the Shu’aiba has been proposed, but a detailed scheme is precluded by rapid diachronous biofacies variations across the Shaybah field. In addition to the major biocomponent assemblages, minor variations reveal high-frequency depositional cycles that may assist in the interpretation of the distribution and correlation of reservoir facies. The identification of bioassemblages, and the paleoenvironmental interpretation of formation micro-imager logs from vertical cores in exploration wells, has assisted the calibration of images from uncored horizontal development wells.
... Positive excursions in the pelagic δ 13 C record, well documented in the Umbria-Marche Basin for this interval of geologic time, can correlate to episodes of platform drowning (Bartolini et al., 1996;Morettini et al., 2002), as the drowning, in the early Pliensbachian, of the fault-bounded small platforms created by the Sinemurian rift tectonics, and their conversion into PCPs (Marino and Santantonio, 2010;Santantonio, 1993). This suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning (Föllmi et al., 1994). ...
A new interpretation of the Middle Jurassic-Early Cretaceous paleogeographic evolution of the NW sector of the Latium-Abruzzi carbonate platform facing the Umbria-Marche Basin is proposed, based on Monte Giano area (central Apennines, Italy). During Late Triassic-early Bajocian time, the area was characterized by shallow water sedimentation. Inner and marginal carbonate platform deposits are overlain by pelagic deposits (Posidonia level), early Bajocian p.p. in age. This unconformity testifying the sudden drowning of the Monte Giano area, while shallow water sedimentation persisted in the remaining sectors of the carbonate platform. The Posidonia level is paraconformably overlain by distal slope deposits of the Velino Gorge limestones Formation, Kimmeridgian p.p.-Tithonian p.p. in age. Therefore, a 12Ma gap is recorded as in the Umbria-Marche Basin pelagic carbonate platforms. An extensional Bajocian tectonic phase, possibly related to the Piemont-Ligurian Ocean opening coupled with rheologic differences at the basin/platform boundary, drastically changed the regional paleogeography causing the breakup and the drowning of the NW sector of the Latium-Abruzzi carbonate platform and the creation of a large flat-topped pelagic carbonate platform. The estimate offset of the early Bajocian fault is around 300-350m. The Velino Gorge limestones fm. pass laterally and vertically to the Upper Tithonian platform-margin reef complex of the Ellipsactinia limestones fm.; these units constitute a shallowing and coarsening upward sequence and levelled the paleobathymetric gradient created by the Bajocian extension. The progradation of the Latium-Abruzzi carbonate platform continued during Early Cretaceous time. These results have strong implications on the tectonic and paleogeographic evolution of the major domains of the central Apennines.
... The main triggers of this process are associated with oceanic anoxic events (e.g. Föllmi et al., 1994;Drzewiecki and Simo, 1997;Weissert et al., 1998;Wortmann and Weissert, 2001), oceanographic changes (e.g., van Tuyl et al., 2018van Tuyl et al., , 2019, tectonics (e.g. Ruiz-Ortiz et al., 2004;Sulli and Interbartolo, 2016), and changes in the photic zone and in the carbon dioxide content of the oceans or of the atmosphere (e.g. ...
Drowning unconformities are surfaces characterized on seismic data by high amplitude contrast between deepwater and shallow water facies. Such surfaces are created by the covering of the platform by onlapping siliciclastic sediments or other non-platform material. The key aspect of this paper is the application of the drowning unconformity concept, commonly used in marine settings, to a more restrictive one: the coquinas of the Itapema Formation, in the pre-salt succession of the Santos Basin (Brazil). In the studied area the sequence boundaries of the deposits related to the Itapema Formation are often associated with high reflectivity seismic horizons, which are tied to radioactive peaks of low-energy sedimentary facies in the gamma ray logs and also to the siliciclastic supply rate increase. However, the stratigraphic significance of these reflectors still lacks further investigation and an adequate description. In this way, it is proposed that the space-time filling of the Itapema Formation occurred by the successive migration of proximal facies towards the structural highs, under continuous accommodation space generation conditions and high carbonate production rate, with the depocenters limited by rapid expansions of the basin. The results presented here, therefore, suggest that the sedimentary record of this section was punctuated by instantaneous transgressive surfaces that altered the ecological accommodation, forcing the backstepping of the coquina deposits and the development of a drowning unconformity in the final stage of the Itapema Formation deposition. This configuration produced at the top of this unit a specific facies association characterized by packstones and mudstones composed of micritized grains, which increase in volume and thickness towards the structural lows and tend to be thinner on the way up to the structural highs, where they may be eroded by the Pre-Alagoas Unconformity. The correct identification of such surfaces is essential for understanding the sedimentary filling of the studied area. Depending on which surface is mapped, they may be related to different processes and occur in opposite positions in the base-level cycles. Thus, we propose the existence of two surfaces at the end of the deposition of the Itapema Formation. The first limits the top of the coquinas and is represented by the contrast of low-energy sediments (packstones and micritized mudstones) and the coquinas deposits, configuring the platform drowning itself. The second one, in turn, is understood here as the Pre-Alagoas Unconformity, a subaerial unconformity associated with the regional platform exposure, developed after the drowning events recognized here.
... Increasing marine nutrient levels as a consequence of global climatic change is often mentioned as a prime factor leading to carbonate factory demise (e.g. Hallock and Schlager, 1986;Zempolich, 1993;Föllmi et al., 1994;Bodin et al., 2006;Godet, 2013). Other factors such as drastic change in sea-surface temperature, shallow-water oxygen levels, siliciclastic poisoning, or ocean acidification have also been evoked (e.g. ...
The early Bajocian environmental crisis is marked by floral and faunal turnovers, and a positive carbon excursion recognized in both marine and continental archives. In the basinal setting of the Central High Atlas Basin, it is concomitant to a drastic drop of carbonate content, interpreted as a result of a severe carbonate demise event in neritic settings. In order to provide a carbonate platform perspective of this demise event, we have investigated a proximal–distal transect consisting of five sections of the Errachidia Platform, which represents upper neritic settings on the southern margin of the basin. New nannofossils and brachiopod findings, supported by organic matter carbon isotope chemostratigraphy, allow for the establishment of a high-resolution chronostratigraphic framework of the Errachidia Platform and a detailed reconstruction of carbonate factory evolution during the late Aalenian to middle Bajocian interval. The early Bajocian (Propinquans Zone) environmental crisis triggered a severe demise event which restricted carbonate production to supra- to intertidal settings, where microbial and peloidal limestones are the only trace of carbonate production. As a consequence, most of the platform is dominated by extended marl deposits that are usually interpreted as hemipelagic deposits. This observation demonstrates that caution must be exerted when interpreting the depositional environments of marl-dominated successions during time of neritic carbonate factory demise.
... Lower Cretaceous successions are distributed worldwide along the northern and southern margins of the Tethys (e.g., Kilian, 1907;Jankičević, 1978;Afshar-Harb, 1979;Föllmi et al., 1994;Dini et al., 1998;Arnaud-Vanneau, 2006;Husinec and Sokač, 2006;Velić, 2007;Sudar et al., 2008;Masse et al., 2009a;Vasković et al., 2010;Godet et al., 2010Godet et al., , 2014Morsilli et al., 2017;Schlagintweit, 2011;Stein et al., 2012;Picotti et al., 2019;Bonvallet et al., 2019;Gheiasvand et al., 2019Gheiasvand et al., , 2020 among others), the Pacific Ocean (e.g., Winterer et al., 1993;Arnaud-Vanneau and Sliter, 1995;Ogg, 1995;Martin et al., 2004), and the Gulf of Mexico (e.g., González-León, 1994;Monreal and Longoria, 2000;González-León et al., 2008). These successions are usually located on the shallow-water platform and outer shelf, beyond the platform margin, and record changes of nektonic (ammonites), planktonic, and benthic organisms (e.g., foraminifera, colomiellids, rudists, calcareous algae), which are useful as biostratigraphic indicators and for environmental reconstructions. ...
Lower Cretaceous carbonate successions outcrop extensively along the northern Tethyan margin in the Kopet-Dagh (NE Iran) and Yazd Block (Central Iran). These carbonate units are not well constraint in terms of stratigraphic, sedimentological, geochemical, and paleobiogeographic view point. To improve our knowledge, a detailed multidisciplinary study has been presented on two roughly coeval stratigraphic units in the two different areas, and correlated with other tethyan carbonates. The two stratigraphic units (Taft and Tirgan formations) have been deposited along a carbonate shelf with microfacies associations ranging from the outer-shelf to the inner-shelf settings. Diachrony in ages at the base and top of the stratigraphic units suggests the long-term subsidence effects during the Early Cretaceous, followed by a Cimmerian phase of epi-orogenesis, and also the remnant paleoreliefs. New biostratigraphic data coupled with stable isotope δ¹³C records shows that the onset of carbonate production started much earlier than previously thought (Valanginian rather than Barremian). Our results also permit us to correlate the lower Aptian stratigraphic units with the OAE1a. The worldwide distribution of index microfossils including benthic foraminifera and colomiellids reported on paleobiogeographic reconstructions. They have been used to define paleobiogeographic provinces for the Valanginian, Hauterivian and Aptian intervals and show predominant basin connections. Significantly, the allochem content of the lithostratigraphic units and their phosphorus accumulation show phases of important heterozoan to photozoan carbonate production, which are recorded in other localities of the Tethyan realm as the consequence of global paleoceanographic changes.
... It is notable that outer-shelf sedimentation along this part of the northern Tethys margin was not affected by increased erosive current activity during the Aptian, as has been observed in numerous northern Tethyan successions of the alpine Tethys (Föllmi et al., 2006). Strong erosive currents related to the Aptian perturbation of the global carbon cycle resulted in the formation of widespread phosphoritic condensation levels (e.g., Föllmi et al., 1994), ...
A high‐resolution δ13Ccarb record from Cau (Spain) is proposed as a new global reference for stratigraphic correlation of the Aptian
The ultrahigh‐resolution record of the onset of OAE 1a documents a long‐term negative excursion in C‐isotope values, punctuated by several marked negative spikes
Evidence for the importance of OM burial as a feedback mechanism in response to increased carbon inputs into the ocean‐atmosphere system
... It is notable that outer-shelf sedimentation along this part of the northern Tethys margin was not affected by increased erosive current activity during the Aptian, as has been observed in numerous northern Tethyan successions of the alpine Tethys (Föllmi et al., 2006). Strong erosive currents related to the Aptian perturbation of the global carbon cycle resulted in the formation of widespread phosphoritic condensation levels (e.g., Föllmi et al., 1994), ...
A high‐resolution carbonate C‐isotope stratigraphy for the Aptian is presented for the Cau core (Spain). The biostratigraphically calibrated C‐isotope stratigraphy of the core is used to refine the previously defined C‐isotope segments of the Aptian. Thirteen C‐isotope segments have been identified and correlated, and further subdivisions are presented. Correlation with other sections worldwide demonstrates the robustness of the C‐isotope stratigraphy of the Cau core. The studied succession includes a continuous record of the early Aptian Oceanic Anoxic Event (OAE 1a). Its onset has been studied at an ultrahigh‐resolution scale (0.2–0.5 kyr spacing), revealing a succession of sharp δ¹³Ccarb negative spikes, interpreted as a record of pulses of volcanism and methane emissions. The largest spike was rapid (<10 kyr) and marks the base of OAE 1a, which occurs within a longer‐term falling δ¹³Ccarb trend. The C‐isotope profile across OAE 1a perfectly records the negative (C3/Ap3), positive (C4/Ap4), steady (C5/Ap5), and positive (C6/Ap6) segments that were defined from Cismon (Italy) and subsequently identified worldwide. The Ap7 to Ap14 segments record a C‐isotope negative excursion, coupled with high TOC contents, probably related to regional paleogeography. The links with global environmental changes, episodes of widespread deposition of organic matter, and ultimately to major volcanic episodes are discussed. We propose the Cau core as a new reference section for the Aptian, and specifically for OAE 1a, based on its expanded and well‐preserved sedimentary, geochemical and biotic archives, which provide further insights into the environmental and biotic changes that occurred during this time interval.
... The onset of the Weissert Event is linked with the drowning of the carbonate platforms in both the Tethyan and North Atlantic realms. This perturbation is also associated to an increment on the humidity, probably triggered by an increase of the pCO 2 in the atmosphere caused by the Paraná-Etendeka volcanic activity (e.g., Föllmi et al., 1994;Wortmann and Weissert, 2000;Erba et al., 2004;Charbonnier et al., 2017). The change towards more humid conditions in the hinterlands is well documented by a kaolinite-bearing interval and a significant increase in feldspar, clay minerals and quartz contents in the CVMb of the Chacay Melehue section and thus suggesting that the PCIE B is linked to the onset of the Weissert Event (Fig. 11). ...
The Vaca Muerta-Quintuco (VM-Q) system of Tithonian-early Valanginian age was studied in the Chacay Melehue section of the Neuqu´en Basin (western Argentina) by means of sedimentological, mineralogical and geochemical analyses in order to determine the main driving factors that triggered the paleoenvironmental change from a carbonate ramp (Vaca Muerta Formation, VMFm) to a mixed siliciclastic/carbonatic marine environment (Quintuco Formation, QFm). The VMFm was divided into two stratigraphic intervals: Lower VMFm (LVMFm) and Upper VMFm (UVMFm), whereas the QFm is subdivided into the Puesto Barros Member (PBMb) and the Cerro La Visera Member (CVMb), which can be correlated to other sections in the basin (e.g., Puerta Curaco). Isolated, turbiditic sandstone beds, correlated to the Huncal Member, are included in the QFm. The LVMFm (Tithonian) and the UVMFm (Berriasian) are constituted by dark, well-laminated marls, mudstones, calcite concretions and tuffs. The PBMb (earlier early Valanginian) is constituted by marls and sandstones,
whereas the CVMb (later early Valanginian) is constituted by marls, mudstones, siltstones, sandstones and coquinas. The LVMFm (Total organic carbon, TOC ~ 1–4 wt%) is characterized by the enrichment of redox sensitive trace elements (RSTE), where the enrichment of Ni and Cu suggest high productivity in the water column, and the enrichment of Mo, U, V points to sea bottom anoxia, with periods of increased oxygenation as deduced from higher P concentrations in marls and mudstones. The clay mineral association is constituted by mixed-layer illite/smectite formed by the transformation of smectitic layers. The predominance of smectite in coeval sucessions, less overprinted by burial diagenesis, suggests a temperate and semi-arid climate in the
adjacent continent. The UVMFm (TOC ~ >1 wt%) is characterized by a gradual decrease of the RSTE pointing to a decrease in productivity and a slight increase in the oxygenation of the sea bottom. In addition, a change towards more humid conditions in the continent is inferred by both the increase in the Chemical Index of Alteration and the Al2O3/TiO2 ratio. The PBMb (TOC ~1 wt%) has even lower content of RSTE indicating diminished sea water productivity and a gradual rise of the oxygenation of the sea bottom. In this interval, increased illite contents suggest periods of enhanced physical weathering, probably related to the tectonic uplift of the Huincul Ridge. The RSTE in the CVMb (TOC <1 wt%) documents a fully oxygenated sea bottom, where the productivity of the water column was negligible. The presence of kaolinite and the increment of the detrital sedimentation in the CVMb indicate a change towards more humid conditions in the hinterlands. The enhanced runoff caused by this paleoclimatic change towards more humid conditions that started in the early Berriasian and increased during the later early Valanginian triggered the change from carbonate ramp to mixed siliciclastic/carbonatic to siliciclastic marine paleoenvironments. The organic carbon isotope composition (δ13Corg vs. VPDB) of the VMFm ranges between - 30.0 and - 23.4‰, whereas in the QFm values range between - 29.0 and - 23.9‰. Two positive carbon isotope excursions (PCIE) are recorded in the system: PCIE-A in the lower part of the VMFm (early Tithonian) with δ13Corg values ~ - 25‰, and PCIE-B in the upper part of the QFm (later early Valanginian) with δ13Corg values ~ - 24.5‰. The shift in δ13Corg at PCIE-B is up to +4.2‰ and marks the onset of the Weissert Event. This is the first time that the onset of this event is recorded in the Neuqu´en Basin, within the Lissonia riveroi ammonite zone. The results of our study confirm that clay mineralogy, trace elements and stable isotopes are valuable proxies of past ocean-climate variability even in sediment deposits that underwent nearsurface and deep burial diagenesis.
... Jenkyns 1980;Skelton et al. 2003). The high temperature recorded during this period and the acceleration of the hydrological cycle (Menegatti et al. 1998) have increased the primary productivity and led to euxinic conditions (Föllmi et al. 1994;Föllmi 2012) with the occurrence of distinctive episodes of organic-rich deposit accumulations called oceanic anoxic events (OAEs; Jenkyns 1980). The Cretaceous oceanic anoxic events are well identified and studied in the northern Tethys Margin (Jenkyns 1980;Cecca and Pallini 1994;Leckie et al. 2002;Jenkyns 2010). ...
Rock-Eval pyrolysis, total organic carbon (TOC) determination and gas chromatography-mass spectrometry (GC-MS) analysis were performed on samples from outcrop sections of the upper Barremian (M’Cherga Formation), Albian (Fahdene Formation), and Cenomanian–Turonian (Bahloul Formation) in the Oued Bazina area located in the NE of the diapiric structure of Thibar, northern Tunisia. The upper Barremian and Cenomanian–Turonian organic-rich strata display high TOC values with a mean of 3.39% and 2.82%, respectively, while the Albian succession deposits exhibit TOC values lesser than 2%. The half-graben structures developed at these epochs have acted as restricted mini-basins favouring the water stagnation, the accumulation and the preservation of the organic matter and consequently the development of locally euxinic conditions in the bottom waters. The generative petroleum potential (S1 + S2) of the upper Barremian and Cenomanian–Turonian studied organic-rich strata is good to very good and appears to be moderate for the Albian organic-rich deposits. The n-alkane distributions of the Cretaceous source rocks are typical for a marine planktonic origin. The Pristane/Phytane ratio indicates a sub-oxic depositional environment for the upper Barremian and Albian successions and a sub-oxic to anoxic environment for the Cenomanian–Turonian organic-rich strata. Regarding the maturity degree of the three studied organic-rich strata, only the upper Barremian source rock presents a high maturity level with Tmax values ranging from 441 °C to 448 °C, which indicates that the deposits have been deeply buried and consequently have generated hydrocarbons that have been recognized in the studied oil seep. The integration of our results with available data of Tmax values on other outcrops in the salt dome zone allowed drafting a maturity trend of the studied source rocks. A general northeast-southwest trend of maturity increase is observed with Tmax values varying from 436 to 446 °C.
The study of Aptian-Albian sequence in many parts of the Zagros Basin and the Arabian plate has always
been limited due to the discontinuity of sediments during this period. The Tang-e Maghar, located in the
Dezful Embayment, is one of the few continuous sequences of the Aptian-Albian marine sediments on
the Arabian plate, the study of which provides valuable information about the paleogeological status of
this period. In this study, in addition to examining the trend of changes in% TOC and% CaCO3 values
through the Aptian-Albian transition sequence in order to analyze the state of the oceans, sedimentary
micro-losses have also been investigated using a thin section study. In the Tang-e Maghr section, the
TOC level at the base of the albino turbulence has reached 5.8%, which indicates the presence of black
shale in this section. This important finding, along with the biostratigraphic data of previous studies, in
addition to determining the chronostratigraphic position of this shale, has made it possible to accurately
match it with other black shale horizons in other sedimentary basins. Changes in CaCO3 levels have also
been recorded in different layers with different values. The most important of these fluctuations in terms
of paleoecological interpretations have been at the end of Aptian and the beginning layers of Albian,
which is known for a significant decrease in CaCO3 levels. This combined with fossil data from previous
studies can confirm the acidic conditions of seawater at the time of Aptian-Albian sediment deposition.
The Cretaceous Period was marked by the formation of numerous Large Igneous Provinces (LIPs), several of which were associated with geologically rapid climate, environmental, and biosphere perturbations, including the early Aptian and latest Cenomanian Oceanic Anoxic Events (OAEs 1a and 2, respectively). In most cases, magmatic CO 2 emissions are thought to have been the major driver of climate and biosphere degradation. This work summarises the relationships between Cretaceous LIPs and environmental perturbations, focussing on how volcanism caused climate warming during OAE 1a using osmium-isotope and mercury concentration data. The new results support magmatic CO 2 output from submarine LIP activity as the primary trigger of climate warming and biosphere stress before/during OAE 1a. This submarine volcanic trigger of OAE 1a (and OAE 2), two of the most climatically/biotically severe Cretaceous events, highlights the capacity of oceanic LIPs to impact Earth's environment as profoundly as many continental provinces. Cretaceous magmatism (and likely output of CO 2 and trace-metal micronutrients) was apparently most intense during those OAEs; further studies are needed to better constrain eruption histories of those oceanic plateaus. Another open question is why the Cretaceous Period overall featured a higher rate of magmatic activity and LIP formation compared to before and afterwards.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.7026011
Microfacies, diagenesis, and stable isotope analysis of Kuldhar Member Limestone (KML) has been carried out to reconstruct
the depositional environment and palaeogeography as well as to evaluate the infuence of diagenesis on its reservoir quality.
The KML is characterized by thin bedding, a high abundance of fossils, and fne to medium grain size. The grains range
from angular to well rounded and vary in their sphericity. The KML is composed of diverse array of skeletal grains such
as brachiopods, echinoderms, bivalves, gastropods, corals, foraminifera, and bryozoans, as well as non-skeletal grains such
as intraclasts, ooids, and peloids, with poor to well-sorted nature. Twelve microfacies were identifed in the KML based on
detailed petrographic studies, which are echinoderm grainstone (MF1), coated bioclastic grainstone (MF2), oncoid grainstone
(MF3), oolitic wackestone (MF4), peloidal wackestone (MF5), ooidal grainstone (MF6), algal packstone (MF7), aggregategrain grainstone (MF8), bioclastic packstone (MF9), bioclastic lithoclastic packstone (MF10), whole fossil wackestone
(MF11), and bioclastic rudstone (MF12). The KML was deposited in shoal, lagoon, and open marine environments and
inferred to be a product of fuctuating sea level and varying energy conditions which include shallowing as well as deepening
of the sea throughout the deposition. Micritization, cementation, physical and chemical compaction, dissolution, fracturing,
neomorphism, and precipitation of calcite veins in some fractures are the main diagenetic processes afecting the KML. The
investigations of diagenetic aspects and stable isotopes (δ13C and δ 18O) show that the KML was infuenced by early marine,
meteoric, and burial diagenesis. Micritization, cementation, neomorphism, physical compaction, and precipitated calcite
veins had a detrimental efect on the reservoir quality. On the other hand, dissolution, fracturing, and chemical compaction
had a positive impact and enhanced the reservoir quality, making the rocks conducive to hydrocarbon accumulation. This
study could point to a potential carbonate resource and aid in future exploitation of the under-explored Jurassic carbonates
in the Jaisalmer Basin.
The Rio Muni Basin is a hotspot for deep-water oil exploration in West Africa. The discovery of thirteen oil and gas fields, including Ceiba, Akom 1, and Oveng, proves the basin’s excellent exploration prospects, but only limited research has thus far been carried out there. The recent new drilling indicates that there are organic matter-rich fine-grained sedimentary rocks in the Albian and Cenomanian–Turonian stages of the Cretaceous strata. However, the depositional models of organic-rich, fine-grained sedimentary rocks are not clear. The main objectives of this study are as follows: (1) to identify the lithofacies characteristics of fine-grained sedimentary rocks in the Albian–Turonian stages of the Rio Muni Basin; and (2) to establish a depositional model for organic-rich fine-grained sediments. In this study, the mineralogical characteristics of Albian–Turonian fine-grained were determined by means of X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and thin section analysis. In addition, the integration of mineralogical features with the total organic carbon (TOC) content allows for the recognition of three distinct lithofacies: (1) siliceous-clayey rock, (2) terrigenous clastic mixed fine-grained rock, and (3) lime-mixed fine-grained rock. Based on the evolutionary history of the passive continental margin basins in West Africa and the lithofacies characteristics, the deposition mode of organic-rich fine-grained sedimentary rocks in the Albian–Turonian stages was reconstructed by combining geochemical features with the characteristics of framboidal pyrite. The depositional models for the Albian stage are “continental margin–restricted sea–marine algae–source rocks” with the development of organic-rich fine-grained sedimentary rocks. The depositional models for the Cenomanian–Turonian stage are “continental margin–semiopen sea–mixed-source rocks”. The Albian and Cenomanian–Turonian organic-rich fine-grained sedimentary rocks represent two different deposition modes with restricted sea and semiopen sea conditions. The sedimentary characteristics in the study area during the two periods were both inherited and notably different.
Designing carbonate facies models requires the integration, correlation and conceptual interpretation of multiple geological data sets. Potential significant errors are sourced from uncertain stratigraphic correlations, speculative palaeoecological interpretations and poorly recorded palaeotopographic profiles. The present study explores a methodological workflow to define a well-supported facies model. An exhaustive literature review is presented on sedimentary facies and depositional profiles of Urgonian carbonate platform from SE France and Switzerland (Barremian–Aptian interval). The historical evolution of Urgonian facies models and related sedimentological concepts is investigated to contextualise published models. The presented conceptual model and table of depositional facies shows a consistent, process-based organization of specific elementary facies, facies associations and carbonate system. Within the chronostratigraphic framework, the study of synchronous strata correlations provides quantitative analyses of facies-belt extents and palaeobathymetric estimations. The resulting depositional profile is based on general palaeoecological and sedimentological concepts, facies distribution on palaeogeographic maps and stacking trends. In rare locations in the field, direct lateral facies belt transitions are recorded. Proximal ( i.e. emersive and peloidal-foraminiferal) depositional facies are rarely observed; most outcrops record the (i) rudist facies association, which corresponds to distal parts of the inner platform, (ii) coral, ooidal and bioclastic facies associations, which are interpreted to occur on the outer platform, and (iii) calcisiltite, slope and basinal deposits. Key data and concepts allow for the building up of a robust, harmonised facies model that can be used to properly interpret palaeoenvironmental changes, stacking trends and stratigraphic sequence evolution, the resolution of which depends on the available chronostratigraphic framework.
The Lower Cretaceous (Barremian) Camarillas Formation in the Galve Sub‐basin of eastern Spain is an exceptionally muddy, synrift, aggradational then retrogradational paralic succession. Deposition within these arid, equatorial paralic systems was strongly controlled by crustal rifting of the Iberia plate linked to the geodynamic evolution of the Atlantic Ocean, the Bay of Biscay and the Tethys Ocean. Although synsedimentary extensional tectonics controlled thickness and facies distributions, the parasequence stacking patterns point to a superimposed high‐order allogenic control on the paralic succession. Field data and drone imagery are combined to document changes in sedimentology and three‐dimensional stratigraphic architecture of these deposits to interpret changes in depositional environments as this basin filled. Three evolutionary stages are identified: (i) tide‐dominated estuary; (ii) mixed‐energy estuary, with a well‐developed wave‐dominated barrier island system; and (iii) barrier island–tidal inlet suite. An exceptional record of back‐barrier‐island depositional interactions is preserved in this high‐subsidence, extensional‐basin setting, including deposition of washover fans, flood‐tidal deltas and ebb‐tidal deltas. Drone‐derived imagery facilitates three‐dimensional architectural characterization of these complex paralic deposits, including multi‐episodic tidal inlets, and correlation of basin scale stratigraphic markers. Spatio‐temporal interactions between climate change, sea‐level variations and rift‐related subsidence generated complex estuarine and barrier island geobodies. The general transgressive trend recorded in the Camarillas Formation correlates well with global eustatic sea‐level rise during the Barremian.
A detailed stratigraphic analysis was carried out on Valanginian deposits of six Moroccan sections of the Essaouira-Agadir Basin (EAB, South Tethyan margin) in order to characterize the Weissert Event and propose correlations with the North Tethyan margin (south–east France Basin). The studied successions consist of alternating marlstone and limestone beds with sandy intercalations, and are well exposed and relatively rich in ammonites. Ammonite biostratigraphy and sequence stratigraphy were established for all successions, whereas calcareous nannofossil and carbon stable isotope analyses were performed for two and five sections, respectively. For each succession, an accurate ammonite zonal scheme allows to recognize the standard zonation established for the Mediterranean Province. A calcareous nannofossil zonation is provided for Zalidou and Aït Hamouch, considered as reference sections. The detailed biozonations allowed to ascribe an accurate age for most of the sedimentary discontinuities and depositional sequences identified in the EAB. East–west and north–south transects are established for the Valanginian depositional system. Despite some stratigraphic gaps, the Valanginian carbon isotope excursion (CIE) was recognized in most of the studied sections. The Moroccan successions are correlated with those of reference sections of south–east France i.e., the Vocontian Basin (Vergol-La Charce) and Provence Platform (Carajuan), using bio-sequence-chemo-stratigraphy. These inter-basin correlations allowed to evidence major “mid-Valanginian” and upper Valanginian eustatic regressions; the possible role of tectonics and glacio-eustacy is also discussed.
The second half of the Devonian featured widespread deposition of organic matter on continental shelves. Distinct pulses of anoxic sediments, associated with positive δ13C excursions, are recognized as Devonian anoxic or carbon-cycle perturbation events. Many of these events are coupled with turnovers in marine faunas, including those ranked as major mass extinctions. Causes and controls on these events are debated. In the absence of ocean-floor stratigraphic archives, much-needed elucidations can be provided by high-resolution multiproxy records in oceanographically open, offshore sedimentary successions. The Canol Formation of NW Canada, one of such stratigraphic archives, is composed of siliceous pyritiferous shales and bedded cherts. These strata are overall lean in siliciclastics and enriched in authigenic U, Mo, V, and planktogenic organic matter. We focus on three horizons of highest U and Mo enrichment within this formation, indicative of severe anoxia, labelled AH-II, AH-III, and AH-IV (AHs = anoxic horizons). These AHs are robust and traceable within the same sedimentary basin in the Northwest Territories (our study area) and adjacent NE Yukon. The δ13Corg data from three sections reveal multiple positive isotope excursions, also traceable in NE Yukon (~400 km from the study area). A broad positive shift of ~2.5‰ amplitude is traced at the base of AH-II. New conodont data are consistent with identification of the AH-II and associate isotopic excursion as the Frasnes anoxic event at the Givetian-Frasnian boundary. Further up the section, an abrupt swing of up to 2.3‰ occurs just underneath AH-III, and a similar deflection to heavier isotope values occurs at the base of AH-IV. The carbon isotopic signature of AH-III is characteristic of the “basal punctata” event (latest Early Frasnian), which is confirmed with conodonts. The AH-IV and the associated δ13Corg excursion are placed within the punctata Zone and identified as the late pulse of the global punctata event. Distinct positive δ13Corg offsets of up to 3.0‰ occur in grey-shale units below and above the black-shale succession of our study. We interpret these excursions as a response to high coaly detritus contents and not as related to anoxic events. Elemental Hg data reveal distinct spikes just below AH-III and AH-IV and possibly in the base of the δ13C shift preceding AH-II. The repetitive sequence of signals at main event horizons (Hg spike – δ13C excursion and highest Corg – AH) corroborates the growing evidence that Devonian anoxic events reflect oceanic perturbations triggered by pulses of volcanic activity within the “super-greenhouse” epoch of the Middle-Upper Devonian. Geochemical signatures of Late Givetian – Frasnian events imprinted in the Canol Formation fall within the variability of Jurassic-Cretaceous oceanic anoxic events (OAEs). This OAE identity for the Middle-Late Devonian events challenges the hypothesis holding evolutionary spread of vascular plants accountable for Devonian anoxic pulses and decimation of faunas in shelfal seas.
During the early and middle Miocene, the Mediterranean had become a restricted marginal marine sea with diminishing and ultimate loss of connectivity to the Indian Ocean. This dramatically changed the heat, energy, freshwater and nutrient budgets across the Mediterranean and most notably in its eastern basin. While one of the most prominent lines of evidence of this change in the Eastern Mediterranean is the onset of sapropel formation, many other aspects of the sedimentary system changed in response to this rearrangement. Here we present a detailed analysis of a hemipelagic succession from southeastern Cyprus dated to the late Aquitanian to the early Serravallian (22.5 – 14.5 Ma). This sequence is carbonate-dominated and formed during the decoupling of the Mediterranean Sea and the Indian Ocean. It exhibits sedimentation with mass transport contribution from shallow water carbonates to deeper facies with phosphatization and bottom current (at intermediate depth) interactions. This succession traces both local subsidence and loss of a local carbonate factory. Additionally, it records a shift in bottom current energy and seafloor ventilation, which are an expected outcome of connectivity loss with the Indian Ocean.
The Cenomanian Mata Amarilla Formation (MAF) in southern Patagonia (⁓55° S paleolatitude, Austral-Magallanes Basin, Argentina) is composed mainly of stacked fluvial deposits with intercalated paleosols, which document Cenomanian environments at high-paleolatitudes in the Southern Hemisphere. We performed a multiproxy study of the paleosols and sediments of the MAF in order to (1) understand the composition of the soil-and sediment-derived organic matter (OM), (2) apply carbon isotope stratigraphy as a tool to correlate patterns obtained from the MAF with existing marine and non-marine δ 13 Corg records worldwide, and (3) investigate the relationship between variations in spore-pollen assemblages of the MAF and the climatic conditions prevailing in the Cenomanian Southern Hemisphere. An integrated dataset was generated, including total organic carbon content, Rock-Eval pyrolysis data,stable isotope (δ 13 Corg) composition, and palynological data, combined with published paleosol-derived mean annual temperatures and mean annual precipitations. The results indicated that the OM preserved in the MAF paleosols allowed its use as a chemostratigraphic tool. The MAF δ 13 Corg curve showed the rather stable pattern characteristic for the Early to Late Cenomanian interval. The absence of the major positive carbon isotope excursion associated with oceanic anoxic event 2 provided an upper limit for the stratigraphic range of the MAF. The palynological data suggested the development of fern prairies during warmer and moister periods at the expense of the background gymnosperm-dominated forests. Overall, the multiproxy record provided new insights into the long-term environmental conditions during the Cenomanian in the high latitudes of the Southern Hemisphere.
Even being the more studied of the interior basins of Northeast Brazil, the Araripe Basin still lacks research in organic geochemistry designed to support interpretations of depositional systems and conditions of formation. This work aims to investigate the organic behavior of evaporites and shales from the Santana Group (Lower Cretaceous), as well as discuss their role in the evolution of its depositional systems. A total of 23 samples, 17 shales and six evaporites, were collected in outcrops and quarries. Analyses of Total Organic Carbon (TOC), Total Sulfur (TS), Rock Eval pyrolysis, and the δ34S isotope ratio were performed. The TOC results revealed high organic content for seven intervals, of which only five had high TS content. From the Rock Eval pyrolysis, dominance of the Type I kerogen was verified, thus corresponding to the best type of organic matter (mainly algal) for the generation of liquid and gaseous hydrocarbons. The Lower Cretaceous (probably Aptian) response to the progressive evolution in redox conditions is linked to a remarked Oceanic Anoxic Event (OAE-1a). The TOC/TS ratio suggests variable palaeosalinity, indicating most of the shales were formed under brackish waters with saline influence, yet tending to increase the salinity upwards where hypersaline conditions dominate in the Ipubi Formation. The isotope data also suggest the occurrence of marine ingressions in the depositional systems even prior to the well-documented event of the Romualdo Formation.
Compiles evidence for biotic interactions of both living and fossil crinoids to elucidate the role of biotic interactions in crinoid evolution. Direct interactions between crinoids and with other organisms are considered in the contexts of predation, competition, and associations (with polychaetes, molluscs, crustaceans and fish, and in terms of commensalism, stereomic malformations, epizoans and parasitism). Crinoids also modify their habitat to affect other organisms. Predation and competition are considered to have played significant roles in crinoid evolution.-P.J.Jarvis
The Nicaraguan Rise is an active tectonic structure in the western Caribbean. Carbonate accumulation on its platforms has not kept pace with relative Holocene sea-level rise, despite a tropical location remote from terrigenous sedimentation. Trophic resources apparently exceed levels favoring coral-reef development because sponge-algal communities dominate the drowning western platforms, in contrast to mixed coral-algal benthos on Pedro Bank and well- developed coral reefs along the north coast of Jamaica. Concentrations of biotic pigments in sea-surface waters show a corresponding west-east gradient; oceanic waters flowing over the western banks carry nearly twice as much biotic pigment as oceanic waters north of Jamaica. Sources enriching the western Caribbean are terrestrial runoff, upwelling off northern South America, and topographic upwelling over the Nicaraguan Rise. That relatively modest levels of trophic resources can suppress coral-reef development holds important implications for understanding carbonate platform drownings in the geologic record.
Upper Cretaceous neritic to hemipelagic successions from the eastern Colombian Cordillera display frequent and rhythmic intercalations of phosphate-rich sediment. Their accumulation is attributed to a back-arc setting between the Andean arctrench system and the Guayana cratonic shield. In three examined sections near Tausa, Tunja, and Iza (all north of Bogotá), respectively, the phosphate-rich sediments occur in 1-15 m thick coarsening-upward series ideally consisting - from the base to the top - of porcelanite, organic-rich claystone, siltstone, sandstone, and a condensed and thoroughly burrowed top bed. Phosphatic particles appear either in thin gravity-flow deposits or in pristine, in-situ occurrences near the base of these successions, intercalated in fine-grained biosiliceous or clay-rich sediment, or in the condensed top bed. The major portion of this coarsening-upward series (porcelanite to sandstone) is considered a shallowing-upward succession and the thin condensed phosphatic top bed a deepening-upward succession. These rhythmic successions are interpreted as parasequences resulting from fourth-order relative sea-level changes. Based upon biostratigraphic age estimates, the time span of formation of these parasequences range between approximately 100,000 and 200,00 yr. The allochthonous phosphate intercalations near the base of the parasequences are derived from condensed phosphatic top beds, which may have been exposed at the sediment-water interface in proximal directions. This suggests that the parasequence boundaries, i.e., marine flooding surfaces, are diachronous and become younger in onshore directions. using the vertical stacking patterns of these parasequences, we distinguish between transgressive and highstand-systems tracts (TST and HST). TST's are characterized by the dominance of phosphatic sediment, laminated and organic-rich claystone, and laminated porcelanite. This suite of sediments documents high nutrient fluxes and the presence of an oxygen-minimum zone, both probably induced by coastal upwelling. HST's include laminated to well-bioturbated siliciclastic successions, which may reflect a weakening or basinward shift of upwelling cells and higher levles of bottom-water oxygenation. The dominance of siliciclastics in HST's is indicative of high detrital fluxes, which outpaced sediment-accomodation rates on the shelf. Upper Campanian ammonoids have been found in three levels of the Lower Plaeners Member of the Guadalupe Formation in the section near Tausa - Nostoceras (Nostoceras) liratum sp.n., Exiteloceras jenneyi (Whitfield, 1887), and Libycoceras sp. E. jenneyi is an important zonal marker in the U.S. Western Interior that is also known from the basal Mount Laurel Sand of Delaware, USA. Its occurrence at Tausa is the first record outside the USA and provides an important datum for intercontinental correlation. The type of Libycoceras sp. encountered in Tausa is also known from the upper Campanian of Peru and Angola. Together with the presence of Andalusiella polymorphia (Malloy, 1972), a dinoflagellate cyst, an age range is given for the formation of the Lower Plaeners Member at Tausa (late Campanian to early Maastrichtian).
The Adriatic/Dinaric carbonate platform of Yugoslavia was influenced by rapid sea level rise and an oceanic anoxic event during the Cenomanian-Turonian. Open-marine biota such as planktonic foraminifera, radiolarians, and locally even ammonites, associated with and bracketed by successions of typical shallow-water carbonates, indicate partial drowning of substantial areas of the platform during this time, suggestive furthermore that the rate of increase of water depth was locally great enough to outpace carbonate production. The presence of carbon-rich and fish-bearing platy limestones, commonly cherty, as an associated coeval facies indicates the development of anoxic or euxinic environments, and the stromatolitic laminations in such rocks are attributed to the action of bacterial mats. It is suggested that an extensive column of deoxygenated water developed in the neighboring Marche-Umbrian-Adriatic deep-water basin and was carried on to the carbonate platform during the Cenomanian-Turonian transgression.
The prevailing explanation for the origin of organic-rich sediments and rocks invokes deposition under conditions of anoxia. However, recent research suggests that high primary production and not water-column anoxia provides the first-order control on the accumulation of organic-rich facies in the modern oceans. Oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments. Sediments accumulating in the modern Black Sea, the type euxinic basin, are not particularly enriched in organic matter despite the presence of an anoxic water column, although a sapropel containing extremely high carbon concentrations was deposited during the Holocene at a time when the basin was oxic. Results of a recently published co pled ocean-atmosphere model indicate that during the Cretaceous, thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions, despite the overall equable climate. Such conditions confound the idea that circulation in the Cretaceous Atlantic, for example, was punctuated by oceanic anoxic events brought about by more sluggish circulation. Sporadic temporal and spatial increases in primary production, reflecting changes in the behavior and/or state of the ocean-atmosphere system, constitute a more tenable explanation for the occurrence of modern and Quaternary carbon-rich sediments and Cretaceous black shales. Consequently, the fundamental control on the accumulation of carbon-rich facies in the oceans and marginal seas is not the presence or absence of anoxia.
The Cretaceous is characterized by unusually widespread distribution of "black shales', and the Cretaceous record offers a unique opportunity to develop a better understanding of the factors that led to such episodes of enhanced organic matter preservation in marine strata in the past, particularly during periods characterized by warm, more equable climate, maximum extent of shelf seas and pronounced volcanism. The effort to elucidate this record will require collaboration of a broad spectrum of earth scientists. A global perspective on Cretaceous black shale deposition should be developed. -after Authors
The authors have modeled the slow, long-term cycle in which geochemical processes transfer carbon among land, sea, and atmosphere. The model suggests that the earth may have been warmed in the past when buildups of atmospheric carbon dioxide enhanced the greenhouse effect. The model predicts that the slow natural fluctuations of atmospheric carbon dioxide may rival or even exceed the much faster changes that arise from human activities or from the biological carbon cycle. The main purpose in modeling the geochemical carbon cycle is to expose how little is known about the rates of important global processes and how seemingly unrelated processes (such as tectonism and climate) are linked.
The tectonic subsidence is reconstructed for 57 sections covering the Mesozoic record of the Jura, Swiss Plateau and Helvetic realm. The tectonic subsidence obtained is polyphase and cannot be described by a single event. Several short term phases with a mean duration of 50 to 60 M.y., are superimposed on the long term Mesozoic subsidence. Each paleogeographic realm is composed of several tectonic subsidence patterns: the number, timing, duration and shape of the different phases vary significantly from one profile to another. However, subsidence is relatively uniform within each Helvetic paleogeographic sub-domain. The 1st order Mesozoic subsidence is often difficult to model, and adequate correlations are not realistic (too long rifting periods). It is proposed that Mesozoic subsidence resulted from several successive rifting events. The 2nd order tectonic subsidence phases are more easily modelled. Relatively low stretching factors are obtained: 3 to 15% for the crust and 0 to 25% for the lithospheric mantle. Two or three models are necessary to reproduce the tectonic subsidence in each paleogeographic realm. -from Author
Based on a palinspastic restoration of the Helvetic realm, the Swiss Plateau and the Jura, the Mesozoic subsidence history of this area is reconstructed for about 50 stratigraphic sections and by taking into account the following parameters: age of the sediments, compaction corrected sediment thickness, depositional depth estimations and eustatic sealevel corrections for each lithological unit. The following major subsidence phases may be deduced from the geohistory diagrams: Triassic (mainly in the Jura); Early Jurassic (in the southernmost and western Helvetic realm only); early Middle Jurassic (in the Jura and the western part of the Helvetic realm); Early Cretaceous (in the southernmost and western part of the Helvetic and the Subalpine realms). In the Jura, the Triassic and Middle Jurassic phases are probably due to intracontinental rifting following Late Variscan structures. The Early Jurassic phase due to extensional tectonics is locally well established in the Helvetic realm. For the Late Jurassic and Early Cretaceous phases, the subsidence is mainly due to extensional tectonics on the northern margin of the Tethys. -Authors
The exponential increase in mining of igneous and sedimentary phosphates, and their utilization in agriculture, industry, and the household in the last few decades have lead to a progressive mobilization of phosphorus, which affects the global phosphorus cycle to an increasing degree (Sheldon, 1969, 1982; Stumm, 1973; Lerman et al., 1975). The present-day anthropogenic share in the transfer of reactive phosphorus from sedimentary and igneous reservoirs into the marine and terrestrial biosphere amounts to an estimated 0.4x1012 g P/yr. This number approximates 35% of total phosphorus influx rates into the oceans and, according to Mackenzie et al. (this volume), may balance 10% of the yearly increase in atmospheric CO2 from manmade sources, assuming an average atomic C/P ratio of 250:1, and a complete and permanent storage of the biologically produced carbon (Figure 1; cf. Mackenzie et al.; Meybeck, both this volume).
Distinguishes between (1) phases of "healthy' progradation and aggradation, characterized by the presence of hermatypic organisms and development of oolitic shoals, and (2) phases of "unhealthy' platform growth, typified by the absence of hermatypic organisms and the evolution of widespread crinoid, oyster, and bryozoan biostromes, as well as by increased influx of siliciclastic detritus. These environmental conditions appear to have been regulated by weathering rates on the adjacent European continent and by the increased input of detritus and nutrients. -from Authors
The carbonate carbon isotope record established in sediments from the Vocontian Trough is more noisy than carbon isotope curves derived from pelagic sections. A correlation of the diagenetically altered Vocontian carbon isotope stratigraphy with a carbon isotope curve from a Tethyan pelagic section shows that an original, marine pattern was not completely destroyed. -from Authors
Delayed maturation and growth to large sizes are only advantageous under stable environmental conditions where food resources are limited. Specialization to algal symbiosis is also highly advantageous under those conditions if sunlight is available. The coevolution of these two characteristics has occurred many times in many foraminiferal lineages. These traits are sometimes associated with increased embryon size and suppression of sexual reproduction, which are also characteristics most advantageous under stable environmental conditions. Specialization for these traits, ensuring success in warm, shallow, stable, oligo-trophic environments, often dooms the species or lineage to extinction when conditions change. -Author
Because rates of carbonate production and bioerosion are similar, even modest increases in nutrient avalability can shift a reef community from net production to net erosion. In the geologic record, drowned reefs and carbonate platforms typically exhibit evidence of nondeposition, bioerosion, and reduced redox potential, which indicate excess nutrient availability during drowning. -from Authors
The Aptian to Lower Cenomanian condensed phosphatic beds, deposited in the Helvetic Shelf along the northern Tethyan margin, consist of thin strata of densely packed phosphatized particles and crudely laminated crusts embedded in glauconitic sands, marls, and pelagic micrites. The beds record very low net sediment-accumulation rates (typically 2-20 cm Ma-1). The condensed phosphatic beds formed along the axis of a stable westward-flowing current system contouring the northern Tethyan margin. Respective cycles of deposition, phosphogenesis, re-exposure and reworking, and deposition (Baturin Cycles), caused by current-induced lateral migration of sand bodies, shaped the internal stratification and composition of the condensed phosphatic beds. Catastrophic burial of entire benthic communities was crucial to phosphogenesis. -from Author
Detailed study of Miocene carbonates in the Mediterranean region and their analogues on modern carbonate shelves (in the Mediterranean Sea, Brazil and other areas) reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef (chlorozoan) lithofacies: (a) chloralgal lithofacies, similar to the chlorozoan, but without hermatypic corals; (b) rhodalgal lithofacies, characterized by abundant encrusting coralline algae; and (c) molechfor lithofacies, consisting of benthic foraminifers, molluscs, echinoids, bryozoans and barnacles. These carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature, although other factors (e.g., water circulation, river discharge, suspended sediment) controlling water salinity and temperature, nutrient content, light penetration, etc., also play important roles. Chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end-members: the chlorozoan lithofacies, which characterizes shallow tropical shelves; and the molechfor lithofacies, which characterizes colder and/or deeper areas. Detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks.
A calculation of Earth's ocean crustal budget for the past 150 m.y. reveals a 50% to 75% increase in ocean crust formation rate between 120 and 80 Ma. This "pulse" in ocean crust production is seen both in spreading-rate increases from ocean ridges and in the age distribution of oceanic plateaus. It is primarily a Pacific Ocean phenomenon with an abrupt onset, and peak production rates occurred between 120 and 100 Ma. The pulse decreased in intensity from 100 to 80 Ma, and at 80 Ma rates dropped significantly. There was a continued decrease from 80 to 30 Ma with a secondary peak near the Cretaceous/Tertiary boundary at 65 Ma. For the past 30 m.y., ocean crust has formed at a nearly steady rate. Because the pulse is seen primarily in Pacific oceanic plateau and ridge production, and coincides with the long Cretaceous interval of normal magnetic polarity, I interpret it as a "superplume" that originated at about 125 Ma near the core/mantle boundary, rose by convection through the entire mantle, and erupted beneath the mid-Cretaceous Pacific basin. The present-day South Pacific "superswell" under Tahiti is probably the nearly exhausted remnant of the original upwelling. How this superplume stopped magnetic field reversals for 41 m.y. is a matter of speculation, but it probably involved significant alteration of the temperature structure at the core/mantle boundary and the convective behavior of the outer core.
Significant short-term carbon isotope fluctuations are present in Cretaceous pelagic limestones from widely distributed onshore sections in the Circum-Atlantic-western Tethyan region. More than 1000 closely spaced samples were analyzed during this study. At least seven major delta/sup 13/C excursions can be correlated from section to section. The most important heavy events occur near the Aptian-Albian and Cemonanian-Turonian boundaries, whereas light events are near the Jurassic-Cretaceous, Albian-Cemonanian, Turonian-Coniacian, and Cretaceous-Tertiary boundaries. The association of events with stage boundaries and the consistent correlation of events between stratigraphic sections provides a significant new tool for time-rock correlation independent of standard biostratigraphic techniques. The temporal association of these carbon isotope events with stage boundaries (faunal and floral events), global eustatic sea-level variations, and oceanic anoxic events demonstrates the potential usefulness of carbon isotope studies in interpreting variations in paleo-oceanic circulation. Furthermore, the association of carbon isotope variations with anoxic events is potentially useful for evaluation of the precise timing and the magnitude of preservation of organic matter in deep-sea and continental-margin sediments. Thus, isotopic studies may aid in estimating potential hydrocarbon resources in largely unexplored oceanic basins or along continental margins. 12 figures, 1 table.
Zooxanthellate organisms, which are among the major carbonate producers on coral reefs, are highly adapted to nutrient-deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant. Reef-dwelling bioeroding organisms, on the other hand, seem to increase in abundance with increasing availability of nutrient and food resources. Maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion. The dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability.
The temperature variation of the fractionation of oxygen in exchange reactions between dissolved carbonate and water and between calcite and water and calculated on theoretical grounds, and checked experimentally. In the course of the experiments it was necessary to investigate several methods of decomposing calcium carbonate to carbon dioxide for mass spectrometer analysis. A method was developed for growing calcium carbonate from solution with the same isotopic composition as the carbonate shells of organisms produced at the same temperature from water of the same isotopic composition, and the results of these experiments at various temperatures are expressed in an equation relating the temperature of formation with the isotopic composition of the calcium carbonate and of the water.
The carbon isotope record in four pelagic carbonate sections from the
Southern Alps (northern Italy) across the Jurassic-Cretaceous boundary
has been correlated to biostratigraphy and magnetostratigraphy. The
carbon isotope curve from bulk carbonates shows a decrease from
Kimmeridgian to Early Tithonian (CM24-CM22) values of
δ13C=+2.07 (± 0.14)‰ to Late Tithonian
and Berriasian (CM18-CM14) values of δ13C=+1.26
(± 0.16)‰. The change in the carbon isotope record
coincides with changes in Tethyan calcite and silica accumulation rates,
with a drop in the calcite compensation depth in the Atlantic and Tethys
oceans and with changes in organic carbon burial along the Eurasian
margin of the Tethys. Reduced surface water productivity due to
diminished transfer rates of biolimiting elements into the Atlantic and
Tethys oceans can explain these observations. The decreased transfer
rates of elements such as silica or phosphorus from continents into the
oceans resulted from drier climatic conditions and decreased water
runoff on continents bordering the Tethys and Atlantic oceans. The
proposed changes in Tithonian - Berriasian ocean chemistry and
paleoclimate suggest that variations in the global carbon cycle were
coupled with changes in the global hydrological cycle and in associated
material cycles.
Proposes the following topics as a focus for research:- 1) Determine rates of sediment production, rates of aggradation and large-scale facies patterns of Cretaceous platforms. 2) Construct at least parts of a sea level curve solely from the record of carbonate platforms. 3) Examine the repeated global crises of platforms in the Cretaceous. 4) Compare early diagenesis and compaction of Cretaceous platforms and their recent counterparts. -from Authors
Shallow-water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation, and benthonic carbonate production ceases. Drowned platforms are common in the geologic record, but they present a paradox if one considers rates of processes involved. The growth potential of reefs exceeds any relative rise of sea level caused by long-term processes in the geologic record. Rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning. The geologic record shows examples of both of these processes. - from Author
Lower Cretaceous pelagic carbonates outcropping along the Southern Alps of northern Italy provide a record of Tethyan palaeoceanography as well as of low frequency fluctuations in the global carbon cycle. The carbonate C-isotope stratigraphy established at five selected localities in the Southern Alps allows an accurate picture to be drawn of the duration and amplitude of the Valanginian C-isotope event. δ13C values near 1.25–1.50% determined in Berriasian and lower Valanginian sediments are replaced by more pdsitive δ13C values near 3% in the late Valanginian. The carbonate C-isotope excursion ends in the early Hauterivian with values fluctuating between 1.5% and 2%. The carbonate C-isotope excursion is accompanied by a positive excursion in the total organic carbon C-isotope curve. The Valanginian C-isotope excursion identified in Tethyan sediments correlates with a C-isotope excursion recorded in the western North Atlantic, in the Gulf of Mexico, and in the Central Pacific (DSDP Sites 534,391,535 and 167). By analogy with the Aptian stage, also marked by a significant positive C-isotope excursion, the time of positive δ13C values is regarded as a time of accelerated carbon cycling coupled with increased burial rates of organic carbon and detrital material in oceanic sediments. A warm and humid climate, possiblycoupled with a high atmospheric CO2 content and a high global sea-level, may have triggered the acceleration of the global carbon cycling. In this case the Valanginian C-isotope event would reflect a first episode of Greenhouse Earth conditions during the Cretaceous.
Today's disturbance of the global carbon cycle induced by anthropogenic processes has raised new interest in the history of the global carbon cycle and its relationship to climate and other geochemical cycles. Carbon-isotope stratigraphy proves to be most useful as a monitor of the history of the carbon-cycle during the last 200 million years. In the introductory paragraphs of this review the mode of functioning of the global carbon-cycle is summarized and the connection between carbon-cycle and carbon isotope geochemistry is documented. A case study on the disturbance of the global carbon cycle during the Aptian-Albian is presented. The disturbance of the carbon cycle lasting up to millions of years is recorded in the carbon-isotope stratigraphy of pelagic sediments. It is superimposed on high frequency sedimentological cycles, related to climate and oceanographic cycles of 20, 40 or 100 ky duration. The data reviewed suggest that the change in the global carbon system was linked to a global acceleration of geochemical cycles triggered by a long-term change in atmospheric CO2 controlled by the rate of sea-floor formation and by volcanic activity. Increased accumulation rates of terrestrial material and terrestrial organic matter in marine sediments may be used as an indicator of an intensified hydrological cycling resulting in higher water-discharge rates. An intensification of the Aptian-Albian water cycle is further reflected in continental sediments monitoring a period of elevated humidity. An increase in water discharge rates should have affected the transfer rate of dissolved nutrients from continents to oceans. Elevated concentrations of phosphorus may have led to an increase in Aptian-Albian oceanic productivity enhancing the transfer of marine organic matter from the oceanic into the sedimentary reservoir. Increased productivity, increased bulk sedimentation rates and poorly oxygenated deep-water led to increased preservation of marine and terrestrial organic matter in marine sediments. The accelerated output of marine organic carbon from the oceanic reservoir is ultimately registered in the positive carbon-isotope excursion of the marine carbonate carbon-isotope stratigraphy.
The dominance of volcanic processes and the importance of vertical tectonics in the geological evolution of the Pacific Basin has been recognised since the time of Charles Darwin. Data gathered on several legs of the Deep Sea Drilling Project (DSDP) and numerous marine expeditions in the past decade have confirmed Menard's postulate that the Pacific Basin was the scene of volcanism on an enormous scale in Mesozoic time. Widespread mid-plate volcanism between ∼110 and 70 m.y. B.P. characterised the area bounded by the Line Islands, the Mid-Pacific Mountains and the Nauru Basin-Marshall Islands. Heating of the Pacific lithospheric plate during this period of volcanism resulted in regional uplift and the bathymetric evolution of the area diverged significantly from a “normal” Parsons-Sclater subsidence curve. The Farallon plate, now almost entirely subducted, was also the scene of mid-plate volcanism that produced such features as the Nicoya Plateau now found as an allochthonous ophiolitic terrain landward of the middle America trench. Large, benthonic, reef-associated foraminifera comprising a pseudorbitoid fauna, hitherto considered to be largely restricted to Central America, have now been additionally recorded from DSDP Sites 165, 315 and 316 in the Line Islands, Site 462 in the Nauru Basin, and in New Guinea. The distribution of this fauna, of Campanian/Maastrichtian age, is interpreted as indicating “stepping stone” connections (aseismic ridges, plateaus and seamounts) between the Caribbean, Farallon, and Pacific plates 70–80 m.y. B.P. Similarities between the geology of the Nauru Basin and the Caribbean Ocean crust reinforce the interpretation of the latter as a former part of the Farallon plate. Estimates of the sea-level and continental freeboard change caused by the thermally induced uplift of the Pacific and Farallon plates, as well as substantial areas in the Atlantic and Indian Ocean Basins, indicate that such shallowing of the sea floor could have been the major factor in causing global Cretaceous transgressions.
Francolite (carbonate fluorapatite) from predominantly peloidal phosphorite grains in the Miocene Hawthorn Group from the Babcock Deep core (southwestern Florida) is highly substituted with an average composition of (Ca4.61Na0.22Mg0.14K0.05Sr0.02) (PO4)2.23(CO3)0.62(SO4)0.12(F)1.04. δ13C values of −1.0–−7.8 %. PDB of the francolite CO3 indicate a substantial contribution of C from an organic source. The sulfur isotopic composition of francolite SO4 is depleted to slightly enriched relative to Miocene seawater and suggests that phosphogenesis occurred during early burial diagenesis in organicrich sediments above or in the zone of sulfate reduction. The uniformly high Sr, Na, Mg, SO4, and CO3 contents of the francolite, the δ18O values of the francolite CO3 (−0.2–−4.2%. PDB), and the inclusion of pyrite and organic matter in phosphorite grains suggest that the francolite has had minimal chemical alteration since its formation.
On rimmed shelves of Bahamian-type, characterized by chlorozoan associations and typical of tropical seas, carbonate production keeps pace with normal sea-level rise except when rapid rise or drastic environmental changes occurs. On the other hand, open temperate carbonate shelves are characterized by low carbonate production of the foramol association (molluscs, benthic foraminifera, bryozoans, coralline algae, etc.) and generally show seaward relict sediments, because carbonate production cannot keep pace with normal rate of sea-level change.Several examples of recent drowning foramol carbonate platforms (e.g., large areas of the Mediterranean Sea, eastern-northeastern Yucatan Shelf) as well as analogous ancient drowned foramol-type carbonate platforms (e.g., early to middle Miocene of the Southern Apennines; Miami Terrace) may support the idea that the drowning of many ancient carbonate platforms has been favoured by their biogenic (foramol sensu lato) constitution. Because of their typically low rate of growth, foramol carbonate platforms are fated to be drowned even if the sea-level rise is one with which the normal growth of chlorozoan platforms can keep pace. Similar conditions may also occur in tropical areas where variations in environmental conditions, such as the presence of cold waters, changes in salinity and increased nutrients, preclude the development of chlorozoan associations.
Information on grain types present in modern, marine, carbonate sands has been collected from published descriptions of 78 shelf areas between the equator and latitudes 60°S and 60°N. Two major associations of skeletal grains are recognised: one (chlorozoan) is almost entirely restricted to warm, tropical waters, the other (foramol) is characteristic of temperate waters but also extends well into the tropics. Non-skeletal grains are largely restricted to warm-water shelf environments with the chlorozoan association, but pellets can also occur with the foramol association in areas near to the chlorozoan/foramol boundary. Annual minimum and mean water temperatures appear to be major factors limiting the development of the chlorozoan association, but the distributions of the skeletal associations cannot be explained in terms of temperature alone.
Magnetic reversal frequency correlates inversely with mantle plume activity for the past 150 Ma, as measured by the volume production rate of oceanic plateaus, seamount chains, and continental flood basalts. This inverse correlation is especially striking during the long Cretaceous magnetic normal “superchron”, when mantle plume activity was at a maximum. We suggest that mantle plumes control magnetic reversal frequency by the following sequence of events. Mantle plumes rise from theD″ seismic layer just above the core/mantle boundary, thinningD″ to fuel the plumes. This increases core cooling by allowing heat to be conducted more rapidly across the core/mantle boundary. Outer core convective activity then increases to restore the abnormal heat loss, causing a decrease in magnetic reversal frequency in accord with model predictions for bothα2 andαω dynamos. When core convective activity increases above a critical level, a magnetic superchron results. The pulse of plume activity that caused the Cretaceous superchron resulted in a minimum increase in core heat loss of about 1200 GW over the present-day level, which corresponds to an increase in Joule heat production of about 120 GW within the core.
A hierarchy of interpreted eustatic cyclicity in siliciclastic sedimentary rocks has a pattern of superposed cycles with frequencies in the ranges of 9–10 m.y., 1–2 m.y., 0.1–0.2 m.y., and 0.01–0.02 m.y. (second- through fifth-order cyclicity, respectively). Stratigraphic units displaying this cyclicity include composite sequences, sequences, and parasequences. On the Exxon global cycle chart, fundamental third-order cycles (1–2 m.y. average duration) stack into related groups (second-order cycles: 9–10 m.y. duration). A much larger pattern (about 200 m.y.) is interpreted as tectonically controlled eustasy probably related to sea-floor spreading rates.One and probably two higher orders of cyclicity (fourth-order: 0.1–0.2 m.y.; and fifth-order: 0.01–0.02 m.y.) are now observed in work with well logs, cores, and outcrops in areas of very rapid deposition. These frequencies are in the range of Milankovitch cycles, and may represent part of the Milankovitch hierarchy which has been widely interpreted for cyclical units in carbonate rocks.High-frequency (fourth-order) sequences, which form at a 0.1–0.2 m.y. cyclicity, have all the stratal attributes of conventional sequences, including constituent parasequences and systems tracts, and play a dominant role controling reservoir, source, and sealing rock distribution. A consistent hierarchy of stratigraphy is observed. Parasequences (probable fifth-order cyclicity) stack into sets to form systems tracts in fourth-order sequences. Groups (sets) of fourth-order sequences are deposited between major third-order boundaries within third-order composite sequences. Sequences in these sets stack in prograding and backstepping patterns to form third-order lowstand, transgressive, and highstand sequence sets.Third-order sequence boundaries are marked by greater basinward shifts in facies, by larger more widespread incised valleys, and by more extensive onlap than are fourth-order sequence boundaries. Third-order condensed sections commonly are widespread, faunally rich, and widely correlated biozone and mapping markers. Fourth-order sequence analysis helps to understand reservoir, source, and seal distribution at the play and prospect scale. An example from the Gulf of Mexico is discussed.
Differences among depositional systems, here called depositional bias, strongly influence sequence patterns. Siliciclastics and shallow-water carbonates, for instance, shed most of their sediment during opposite phases of a sea-level cycle (lowstand shedding and highstand shedding, respectively). Furthermore, the two systems generate their own, system-specific relief on the sea floor, disperse their sediment load along different avenues and differ in the way they are deactivated: reefs and carbonate platforms can be drowned, whereas siliciclastic deposition can be shut off and renewed at any depth. As a consequence of these differences, pronounced unconformities (drowning unconformities) develop where carbonate platforms are terminated and buried by siliciclastics (the siliciclastic-to-carbonate transition tends to be more gradual). Drowned platforms and drowning unconformities appeared world-wide in great abundance in the Miocene, Cretaceous (Valanginian-Turonian), Jurassic (Toarcian) and Devonian (Frasnian/Famennian). Examples of drowning unconformities interpreted as sequence boundaries, include those of the Early Cretaceous platforms off New Jersey and off Morocco, the mid-Cretaceous unconformity in the Gulf of Mexico and Miocene unconformities on top of reefs in the Far East.
Diss. Nr. 9805 Naturwiss. ETH Zürich.
Auch im Buchh. Zürich, Eidg. Techn. H., Diss.
Diss. Naturwiss. Bern (kein Austausch).
Explores the possibility that the middle Cretaceous demise of mid-Pacific and other carbonate-bank communities, and related extinctions elsewhere, reflects sporadic, possibly volcanogenic, upwelling of anoxic water. -from Author