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Correlation of Early Cretaceous carbon isotope stratigraphy and platform drowning events: A possible link?
Abstract
The Early Cretaceous carbonate carbon isotope record is marked by three positive high-amplitude (> 1.5‰) excursions each covering time spans of more than 106 years. They are of late Valanginian-Hauterivian and early and late Aptian age. In a case study along a transect across the western Tethys Ocean we identified a coincidence between δ13C excursions, black shale formation, and widespread carbonate platform drowning events. We conclude that the δ13C excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in Cretaceous pelagic and neritic environments. Episodes of intensified greenhouse climate conditions led to an increase in weathering, erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans. The resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable. Partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea-level rise in the Valanginian and Aptian. Widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient-enhanced phytoplankton productivity. The change in marine carbon partitioning is mirrored in a shift of the δ13C record towards more positive values. The transition to the δ13C peak values lasted up to several hundred thousand years. The peaks of the excursions, also covering a time span of up to several hundred thousand years, reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks. A renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea-level rise at a high level. Decreasing δ13C values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates. These changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation.
... Stable isotopes serve as valuable tools for investigating the chemical compositions of oceans. Numerous studies have extensively utilized carbon and oxygen isotopes in both biotic and whole-rock carbonates to trace and analyze the chemical makeup of oceanic environments (Weissert et al., 1998;Veizer et al., 1999;Grossman et al., 2008;Moustafa et al., 2016;Madhavaraju et al., 2018;Saucedo-Samaniego et al., 2021). The use of δ 18 O values has been employed to signify climate changes, temperatures, and diagenetic fluids (Emiliani, 1955;Shackleton and Opdyke, 1973;Marshall, 1992;Weissert et al., 1998;Grossman et al., 2008;Zeebe, 2009;Grossman, 2012;Grossman and Joachimski, 2020). ...
... Numerous studies have extensively utilized carbon and oxygen isotopes in both biotic and whole-rock carbonates to trace and analyze the chemical makeup of oceanic environments (Weissert et al., 1998;Veizer et al., 1999;Grossman et al., 2008;Moustafa et al., 2016;Madhavaraju et al., 2018;Saucedo-Samaniego et al., 2021). The use of δ 18 O values has been employed to signify climate changes, temperatures, and diagenetic fluids (Emiliani, 1955;Shackleton and Opdyke, 1973;Marshall, 1992;Weissert et al., 1998;Grossman et al., 2008;Zeebe, 2009;Grossman, 2012;Grossman and Joachimski, 2020). Carbon isotope chemostratigraphy is considered as a powerful tool for tracing variations in seawater chemistry and facilitating global stratigraphic correlation (Halverson et al., 2005;Weissert et al., 1998;Saltzman et al., 2012;Moustafa et al., 2019;Madhavaraju et al., 2021aMadhavaraju et al., , 2021b. ...
... The use of δ 18 O values has been employed to signify climate changes, temperatures, and diagenetic fluids (Emiliani, 1955;Shackleton and Opdyke, 1973;Marshall, 1992;Weissert et al., 1998;Grossman et al., 2008;Zeebe, 2009;Grossman, 2012;Grossman and Joachimski, 2020). Carbon isotope chemostratigraphy is considered as a powerful tool for tracing variations in seawater chemistry and facilitating global stratigraphic correlation (Halverson et al., 2005;Weissert et al., 1998;Saltzman et al., 2012;Moustafa et al., 2019;Madhavaraju et al., 2021aMadhavaraju et al., , 2021b. ...
... 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.
... Lower Cretaceous Arctic sediments document two further CIEs, which are observed in both carbonate and organic carbon records from the Berriasian to Aptian worldwide, namely the Valanginian Weissert Event and the early Aptian Oceanic Anoxic Event (OAE1a) (e.g. Jenkyns, 1980;Weissert et al., 1998;Erba et al., 2004;Bodin et al., 2015;Herrle et al., 2015;Vickers et al., 2016;Galloway et al., 2020). Each of these CIEs has their own unique characteristics, and the mechanisms by which they occurred were likely different, as detailed below. ...
... The Weissert Event positive CIE is recognised in both terrestrial and marine records across the globe in the late Valanginian to early Hauterivian (e.g. Weissert et al., 1998;Erba et al., 2004;Gröcke et al., 2005), although there is much debate about the exact timing of this event (Gradstein et al., 2020). The Weissert Event is hypothesised to reflect increased burial of isotopically light ( 13 C-depleted) carbon (organic matter), and/or reduction of the isotopically heavier carbon reservoir (carbonate). ...
... The rise in CO 2 required to drive such changes in the hydrological cycle could have been sourced from volcanic carbon emissions (e.g. Weissert et al., 1998;Weissert and Erba, 2004;Duchamp-Alphonse et al., 2007; broadly coeval with the emplacement of the Paraná-Etendeka LIP ( Fig. 1; e.g. Weissert and Erba, 2004;Duchamp-Alphonse et al., 2007;Martinez et al., 2015;Gomes and Vasconcelos, 2021), a large-scale emplacement of igneous rocks on continental crust that occurred during the rifting between the South American and African plates (Peate, 1997;Hawkesworth et al., 2000). ...
... The Cretaceous marine sedimentary record is characterized by several positive carbon isotope excursions (CIEs) corresponding to perturbations in the global carbon cycle (Scholle and Arthur 1980;Weissert et al. 1998). These are mainly explained by enhanced marine and terrestrial primary productivity and/or the enhanced preservation of organic matter (Scholle and Arthur 1980;Weissert 1989;Kump and Arthur 1999). ...
... The Valanginian stage (137.7-132.6 Ma; Gale et al. 2020) records the first positive CIE of the Cretaceous and is named the Weissert OAE (Lini et al. 1992;Weissert et al. 1998;. However, its expression as an OAE is doubted due to the absence of significant and widespread organic-rich layers (Westermann et al. 2010;Kujau et al. 2012). ...
... The Weissert Event is associated with a warm and humid climate (Lini et al. 1992;Charbonnier et al. 2020), enhanced marine primary productivity (Bersezio et al. 2002;Bartolini 2003;Erba and Tremolada 2004;Duchamp-Alphonse et al. 2007;Bornemann and Mutterlose 2008;Mattioli et al. 2014) and a biocalcification crisis in platform and pelagic settings (Channell et al. 1993;Weissert et al. 1998;Wortmann and Weissert 2000;Erba and Tremolada 2004;Föllmi et al. 2006). Two main hypotheses explain the eutrophication (i.e. ...
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
... 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. ...
... Föllmi (1989),Föllmi et al. (1994), WeisseRt et al. (1998) sowie WissleR et al. (2003 verwiesen. ...
... Die Garschella-Formation dokumentiert somit eine globale Biokalzifizierungskrise aufgrund erhöhten CO 2 -Gehalts der Atmosphäre und der Ozeane sowie der damit verbundenen klimatisch-hydrologischen Veränderungen (erhöhter Eintrag von Nährstoffen und siliziklastischem Detritus). Für weitere Ausführungen zu dieser Thematik sei aufFöllmi et al. (1994), WeisseRt et al. (1998) und WissleR et al. (2003 verwiesen. Die obere Kreide, welche über der Garschella-Formation einsetzt, ist dann ausschliesslich pelagisch und hemipelagisch ausgebildet und dokumentiert tiefermarine ruhige Sedimentationsverhältnisse, die erst wieder während des frühen Paläogens durch flachmarine Bedingungen abgelöst wurden («Paleozäne Restauration», tRümpy 1973).Die Kreideabfolge der Drusberg-Decke setzt unterhalb des namensgebenden Druesbergs mit der Palfris-Formation ein. ...
... 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.
... In this time, the Iberian Plate and their margins were located in the boundary between the Tropical-Equatorial hot arid belt and the Northern High-latitude Temperate humid belt [8,9], in a latitude between 20 • N and 30 • N [1]. A major platform drowning episode is registered in the northern Tethyan margins during the Aptian-Albian transition [10][11][12]. This event has been related to a eustatic highstand recorded in several transgressive system ...
... In the Vocontian Basin (France), several authors [4,32,45,46] show values of δ 13 C between 0.65‰ and 2.32‰, while δ 18 O change between −5‰ and −1.9‰, in rocks occurring between the lower part of the Kilian level and the top of the Paquier level, with an Aptian-Albian transition age. The interval between the upper part of the R. angustus (NC7) and the lower part of the P. columnata (NC8) nannofossil zones (correlated with the upper and lower parts respectively of the ammonite zones H. jacobi and L. tardefurcata) shows values of δ 13 C between 2.5‰ and 4‰ [10]. For the Barremian-Albian of Mt. ...
... The highest and lowest values of the δ 13 C, 0.87, and −6.81‰ respectively from the samples of this study, are lower than data from Vocotian Basin, Gavrovo platform, or Ionian Basin [10,32,33,47] (Figure 9). The samples with a the most negative δ 13 C signature are recorded in the black marl levels. ...
"Abstract:
During the Aptian-Albian transition, an extensional phase of the Central Atlantic which affected the Prebetic carbonate platform (South Iberian Continental Margin, northwestern margin of the Tethys) occurred. A graben morphology was developed in the platform coeval to a relative sea level fall. As a consequence, palustrine facies characterized by rhizoliths and some ponds deposits of black lutites were established. Over these palustrine sediments, a second shallow carbonate platform was built during the early Albian. However, this process was not abrupt, as several levels with orbitolines and rudists were deposited intercalated between the continental facies, recording the transition to a new shallow marine carbonate platform developped during the Early Albian. The presence of these continental palustrine sediments between two episodes of shallow carbonate platform is described for the first time in the Prebetic. The demise of an upper Aptian isolated shallow carbonate platform drove to the deposition of these palustrine sediments in an extensional tectonic regime.
Keywords: South Iberian Continental Margin; Prebetic; Aptian-Albian transition; shallow carbonate es; charophyte; carbonate platform demise"
... Over the years, for the Cretaceous system, several multimillion-year records of temporal high-resolution have been generated from the Tethyan Realm, specifically from Italy and SE France (e.g., Weissert et al., 1998;Herrle et al., 2004;Sprovieri et al., 2006;Gyawali et al., 2017). For the Boreal Realm, the Upper Cretaceous is represented by the Chalk successions (e.g., Jenkyns et al., 1994;Mitchell et al., 1996;Jarvis et al., 2006), whereas the Early Cretaceous is almost exclusively covered by bits-and-pieces from the North Sea area, Northern Germany, and the high Arctic (e.g., Mitchell et al., 1996;Rückheim et al., 2006;Bottini and Mutterlose, 2012;Herrle et al., 2015;Möller et al., 2020;Thöle et al., 2020;Eldrett and Vieira, 2022). ...
... In the Scharrel 10 drill core, the δ 13 C values rise from −27‰ to −24‰ during the mid-Valanginian ( Figure 3A), giving way to the >2.3 My-long (Sprovieri et al., 2006;Martinez et al., 2015) positive δ 13 C excursion of the "Weissert Event" . The Weissert Event has originally been described from Tethyan successions (Lini et al., 1992;Weissert et al., 1998), as well as from Atlantic and Pacific drill cores (e.g., Erba, 1994;Wortmann and Weissert, 2000). Only recently have the first records of the event been documented from the Boreal Realm (Galloway et al., 2020;Möller et al., 2020;Thöle et al., 2020) and mid-southern latitudes (Cavalheiro et al., 2021). ...
High-amplitude changes in sedimentary δ¹³C characterize the Cretaceous system and have been proven useful for supra-regional chemostratigraphic correlation. In the Cretaceous, these δ¹³C perturbations indicate large shifts between the global carbon reservoirs that are usually caused by volcanic activity of large igneous provinces, the widespread deposition of thick organic carbon-rich sequences and/or changes in orbital parameters. Here, we present an upper Berriasian to lower Coniacian (c. 142–88 Ma) composite carbon isotope record based on 14 drill cores, 2 outcrops, and almost 5,000 samples. The total record comprises a composite thickness of more than 1,500 m. All cores and successions are located in the larger Hanover area, which represents the depocenter of the North German Lower Saxony Basin in Early to mid-Cretaceous times. In Northern Germany, Boreal Lower Cretaceous sediments are predominantly represented by CaCO3-poor mud and siltstones of up to 2,000 m thickness, which become more carbonate-rich during the Albian–Cenomanian transition and even chalkier in the upper Cenomanian to Coniacian interval. The carbon isotope record reveals a number of global key events, including the Valanginian Weissert Event, the Oceanic Anoxic Events (OAEs) 1a and d, and the Kilian Event (Aptian–Albian boundary, part of OAE 1b). For the early Late Cretaceous, the Mid-Cenomanian Event, the OAE 2 (Cenomanian–Turonian Boundary Event), and the Navigation Event, among others, have been identified. The Kilian Event represents the Aptian–Albian boundary and has been identified herein for the first time in Northern Europe. Based on the evaluation of its relative position to the Vöhrum boundary tuff, we tentatively propose a slightly older age for the Aptian–Albian boundary of c. 113.65 Ma instead of 113.2 Ma. The observed chemostratigraphic events enable a detailed stratigraphic comparison with Tethyan and other Boreal records and associated paleoenvironmental data. Thus, this new detailed chemostratigraphy provides a unique opportunity to potentially overcome many still existing Boreal–Tethyan correlation issues. The presented record can be considered almost complete, albeit a 2-Myr gap during the early Albian is likely, and condensed intervals occur specifically during the lower Aptian.
... The Early Cretaceous was marked by several pronounced disturbances to the global carbon cycle (e.g., Weissert et al., 1998), many of which were associated with global climate change, oceanic anoxia, and large igneous province (LIP) volcanism (e.g., Weissert and Erba, 2004;Jenkyns, 2010). The Valanginian Weissert Event (ca. ...
... 134 Ma;Cavalheiro et al., 2021;Martinez et al., 2023) was the first such Cretaceous environmental perturbation. This time interval is marked globally by a positive carbon isotope (δ 13 C) excursion of ∼2‰ in carbonate and up to 4‰ in organic material across Valanginian-Hauterivian strata (e.g., Weissert et al., 1998;Erba et al., 2004;Bornemann and Mutterlose, 2008;Littler et al., 2011;Price et al., 2018). ...
The Valanginian Weissert Event (ca. 134.5 Ma) has long been linked to emplacement of the Paraná-Etendeka large igneous province (LIP). Although several Mesozoic crises were triggered by volcanic CO2 emissions and global warming, causing oceanic oxygen depletion, the Weissert Event featured climate cooling and limited marine anoxia. Here, the impact of silicate weathering on environmental change during the Weissert Event is investigated by presenting the first osmium isotope (187Os/188Os) data sets for the late Berriasian–Valanginian interval. These records document a possible rise in weathering and nutrient runoff during the latest Berriasian, followed by a switch to Paraná-Etendeka basalt erosion during the Valanginian. The high weatherability of LIP basalts enhanced global silicate weathering despite limited coeval climate warming. This weathering triggered the documented cooling, with consequent micronutrient runoff potentially aiding ocean fertilization, highlighting a mechanism linking LIP formation with environmental change that was uniquely different than that of other Mesozoic crises.
... Dramatic Episodes of Environmental Changes (EECs) punctuated the Early Cretaceous period (Föllmi, 2012). According to Föllmi et al. (2012), these EECs occurred at time of reinforced greenhouse climatic conditions, when an accelerated hydrological cycle led to higher levels of continental weathering, increase of primary productivity, and high amounts of organic carbon storage (Weissert et al., 1998;Bodin et al., 2009;Föllmi, 2012;Stein et al., 2012;Aguado et al., 2014;Duchamp-Alphonse et al., 2014;Mattioli et al., 2014). From the Valanginian to the Barremian stages (~137 to ~121 Ma; Gale et al., 2020), the documented EECs are the Weissert Event during the mid-Valanginian, the Faraoni Event at the end of the Hauterivian, the Mid-Barremian Event and the Taxy Event at the end of the Barremian (Föllmi, 2012;Fig. ...
... The Weissert Event is defined as a positive carbon-isotope excursion of +1.5 to +2‰ PDB amplitude in bulk carbonate, fossil shells and organic carbon, starting at the end of the Early Valanginian (Karakaschiceras inostranzewi Tethyan Ammonite Zone; Fig. 1) and culminating in the lower part of the Late Valanginian (Saynoceras verrucosum Tethyan Ammonite Zone), with worldwide expression (Cotillon and Rio, 1984;Lini et al., 1992;Weissert et al., 1998;Hennig et al., 1999;Erba et al., 2004;Gröcke et al., 2005;McArthur et al., 2007;Aguirre-Urreta et al., 2008;Gréselle et al., 2011;Kujau et al., 2012;Aguado et al., 2018;Cavalheiro et al., 2021). Carbon-isotope values remained high in the Late Valanginian and decreased slowly until the Early-Late Hauterivian transition (Hennig et al., 1999;Sprovieri et al., 2006;Aguirre-Urreta et al., 2019;Fig. ...
... 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.
... Drowned carbonate platforms and reefs have been common in the geological record since the Cambrian (Schlager, 1981). They represent valuable archives of palaeo-environment and climate (Weissert et al., 1998) with significant economic importance as hydrocarbon reservoirs on passive margins (Hendry et al., 2021) and in tectonically active regions, such as in Southeast Asia (Vahrenkamp et al., 2004). However, their demise by drowning is still a geological paradox because the production of carbonate factories in the euphotic zone and the related growth and accumulation rates normally exceed rates of eustatic sea-level rise (Schlager, 2005). ...
... Several mechanisms for drowning have been proposed. These mechanisms can include insufficient autotrophic carbonate factories that cannot keep up with the relative sea-level rise ensuing from the eustatic sea-level increase and/or subsidence (DiCaprio et al., 2010), and environmental drivers, such as (volcano-) clastic and nutrient input, changes in salinity and biota, platform-margin collapse, climate variability (Weissert et al., 1998;Van Tuyl et al., 2019), and strong currents (Betzler et al., 2021). Mathematical models also indicate a combination of initial water depths and the response time of carbonate to an increase in eustatic sea-level rise as a cause of drowning (Kim et al., 2012). ...
High-resolution bathymetric and shallow seismic data along the northeast Red Sea margin reveal a previously disregarded mechanism for carbonate platform drowning at a steep-flanked rift basin. At the seafloor, salt extrusions highlight the influence of extensional salt tectonics, with a salt flow from the southern flank of the Al Wajh carbonate platform that likely originates from below. Salt-flow direction, morphology, and kilometer-sized slumps and rotated blocks indicate platform-margin disintegration and rafting of platform blocks toward the southwest. The outlines of several smaller detached or semi-detached carbonate platforms to the south of the main platform can be refitted to the larger platform margin by counter-moving the direction of mass wasting. Several platforms, reaching heights above the seafloor of up to 650 m, are partially or fully submerged in the mesophotic zone and appear to be in danger of drowning. We conclude that the southern outer rim of the Al Wajh platform is breaking apart owing to salt withdrawal, which indicates that carbonate platforms on top of salt sequences grow on mobile ground, leading to platform disintegration, basinward rafts, and the demise of broken-off, smaller pieces of platform. Salt displacement also controls the growth geometries of individual platform rafts, with keep-up reef growth (growth rate equal to sea-level rise) and drowning occurring in close spatial proximity. Therefore, the interplay between salt diapirism and platform growth is not limited to platforms growing on the apexes of diapirs and is more complex than previously thought.
... 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 ]. ...
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.
... Climate reconstructions demonstrated intensified hydrolyzing conditions culminating around the early-late Valanginian transition observed from clay mineral distributions (Duchamp-Alphonse et al., 2011;Charbonnier et al., 2020) and spore-pollen ratios (Kujau et al., 2013). Eutrophication in pelagic settings could be explained by the introduction of limiting bio-metals from hydrothermal vents during the break-up of Gondwana (Lini et al., 1992;Weissert et al., 1998;. Sea-level changes might have also influenced the fertilization of the ocean. ...
... The different hypotheses that could cause the fertilization of the ocean need to be tested for the Weissert positive CIE. A biocalcification crisis in both platform and pelagic settings has been inferred from carbonate platform drowning around the early-late Valanginian (Weissert et al., 1998;Wortmann and Weissert, 2000;Föllmi et al., 2006), and a nannoconid decline predating the positive CIE has been identified (Channell et al., 1993;Bersezio et al., 2002;Erba and Tremolada, 2004;Gréselle et al., 2011;Barbarin et al., 2012). ...
Paleoceanographic conditions across the Valanginian Weissert oceanic anoxic event were reconstructed for the first time on the central Moroccan margin from a quantitative-based calcareous nannofossil study. Two onshore successions in the Essaouira-Agadir Basin and one offshore from DSDP Hole 416A were studied, providing a proximal-distal transect on the central Moroccan margin. The paleoceanographic conditions were reconstructed in an accurate chronostratigraphic framework. The sedimentary evolution of the Essaouira-Agadir Basin shows that sea-level variations controlled the paleogeographic context, clastic input, and nutrient availability. A thick photic zone and mesotrophic conditions favored the development of a diverse nannofossil community before the Weissert Event in the early Valanginian. In all studied successions, a collapse of the nannofossil community was recorded during the onset of the Weissert Event at the early-late Valanginian transition, and was caused by a major sea-level fall. The nannofossil community gradually recovered and reached its highest nannofossil production associated with high surface-water fertility during the Weissert Event in the late Valanginian. This eutrophication is coeval with the high and stable δ¹³Ccarb values of the carbon-isotope positive shift. After the Weissert Event, surface-water fertility and nannofossil production decreased but remained higher than during the early Valanginian. Additionally, the nannoconid decline started in the early Valanginian and was linked to a low sea-level. Their recovery in the early late Valanginian occurred during conditions of high sea-level and of high surface-water fertility. The central Moroccan margin is integrated into a global paleoceanographic reconstruction.
... In contrast to most other carbonate-platform depositional systems (Skelton and Gili, 2012), the Arabian Plate has recorded a nearcontinuous record of shallow-water limestones throughout the episodes of prominent negative and subsequent positive CIEs that bracket OAE 1a (Fig. 2). The evolution of global and regional carbonate depositional environments during this time-episode has been extensively studied and discussed in the context of environmental change related to perturbations of the carbon cycle (e.g., Weissert et al., 1998;Huck et al., 2010;Rameil et al., 2010;Strohmenger et al., 2010;Skelton and Gili, 2012;Yamamoto et al., 2013;Granier, 2014;Amodio and Weissert, 2017;Núñez-Useche et al., 2020). ...
... This was followed by increased continental weathering and increased fluxes of nutrients and alkalinity to seawater, resulting in increased organic carbon burial that may have additionally been facilitated by high seawater temperature due to the CO 2 greenhouse effect of LIP volcanism (e.g. Schlanger and Jenkyns, 1976;Jenkyns, 1980;Erba, 1994;Weissert et al., 1998;Zeebe, 2001;Erba et al., 2010;Hönisch et al., 2012;Föllmi, 2012;Bauer et al., 2017;Jenkyns, 2018;Adloff et al., 2020;Matsumoto et al., 2022). These environmental perturbations caused the demise of northern Tethyan carbonate platforms, while microbial carbonates apparently became more abundant in central and southern Tethys, as postulated for Bacinella-rich carbonates that are abundant before and after OAE 1a (e.g. ...
We report the first high-resolution sedimentological and geochemical record of the negative carbon-isotope excursion (CIE) at the onset of the early Aptian oceanic anoxic event (OAE) 1a from a carbonate-ramp depositional environment, analysed from a well core from c. 2500 m depth, 100 km offshore Abu Dhabi, United Arab Emirates. Time-series analysis of stable oxygen isotope values and concentrations of Si, Al, and Ti resulted in durations of the C3 and C4 segments of the CIE that support relative completeness of the C3 segment and high sediment preservation rates of c. 13 cm/kyr of the studied sedimentary sequence. Stable oxygen-isotope ratios of bulk carbonates are interpreted to indicate two episodes of cooling, separated by rapid warming during the peak of the negative CIE. The contributions of diagenesis and seawater pH on the bulk oxygen-isotope record will have affected the palaeoclimatic signal and are critically discussed. A major shift in oxygen isotope values at the peak of the negative CIE in the C3 segment coincides with relatively carbonate-poor, marly deposits, time-equivalent with other, global evidence for a reduction of carbonate saturation of sea-surface water. According to our chemo- and cyclostratigraphic calibration, this episode of low carbonate saturation of seawater reflects a pulse of major volcanic CO2 release from the Ontong-Java large igneous province that was sufficiently short to have escaped internal buffering by the dynamics of the ocean lysocline.
... Those phenomena are considered as resulting from different factors controlling the marine ecosystem, amongst which the most important are: (i) bioproductivity, which is predominantly conditioned by the availability of nutrients within the photic zone; (ii) seafloor oxygenation, which has an impact on the benthic fauna on one hand and inform about the intensity of marine circulation (mixing of the water column) on the other; and (iii) water pH, which affects the amount of available CO 2À 3 ions for biocenosis (i.e. Weissert & Mohr, 1996;Weissert et al., 1998;Weissert & Erba, 2004). The abovementioned parameters were additionally modified and/or controlled by other, higher-rank (and often overlapping) environmental processes, such as climate changes, eustasy and tectonic activity. ...
The Jurassic/Cretaceous transition was characterized by several distinct palaeoenvironmental processes and events, amongst which some of the best known are the late Tithonian-early Berriasian aridization and the late Berriasian tectonic reactivation in the Neotethyan Collision Belt. This study aims to reconstruct the latest Jurassic-earliest Cretaceous palaeoenvironment and its evolution in the area of the Transdanubian Range (Hárskút and Lókút successions, Hungary), and provide new data on the relation between climate changes, palaeoceanography and marine ecosystems. Herein, calcareous nannofossil and geochemical data are presented and put into a geochronological framework in order to evaluate and compare palaeoenvironmental signals recorded in the two studied successions; the resultant scenario is compared with published literature data from both the western Tethyan region and northern Europe. Accordingly , in the Transdanubian Range, the relatively humid climate of the early Tithonian was followed by the late Tithonian-early Berriasian arid phase and the late Berriasian humidification. Besides, two intervals of palaeoceanographic perturbations were documented in the upper Tithonian-lowermost Berriasian (OD I), and the lower/upper Berriasian transition beds (OD II); these are manifested by the record of seafloor hypoxia and elevated accumulations of micronu-trients, as well as changes in calcareous nannofossil assemblages. In the view of this study, the most probable trigger of the late Tithonian-early Berriasian aridi-zation was a restriction in the atmospheric circulation (including monsoons), which was forced by climate cooling and lowering thermal gradient between landmasses and the ocean. Under such conditions, the mechanism of a wind-induced water mixing might become less efficient, driving seawater strati-fication, seafloor hypoxia and increased burial of nutrients. Although the humid climate of the late Berriasian likely resumed the monsoon-type circulation, the tectonic reactivation and uplift in the NeoTethyan Collision Belt might have effectively separated the Bakony Basin from the 'open' NeoTethys, which hampered the marine circulation and efficient water mixing in the former.
... When compared to the T/R cycles of the eustatic chart (Haq et al., 1987;Haq, 2014), the maximum flooding possibly extends over most of the L. cabri zone of the U3, followed by a highstand in the U4 covering the P. luterbacheri zone (Fig. 15A). This interpretation is consistent with several authors observations of a major transgression and sea-level highstand associated with the G. blowi to P. luterbacheri Zones (Schlanger and Jenkyns, 1976;Erbacher et al., 1996;Weissert et al., 1998;Jones and Jenkyns, 2001;Föllmi et al., 2006;Heldt et al., 2008;Lehmann et al., 2009;Ben Chaabane et al., 2019, 2021. ...
The Early Aptian organic-rich deep marine deposits of the Lower Cretaceous M’Cherga Formation of northern Tunisia were studied based on multidisciplinary approach including biostratigraphy, sedimentology and organic geochemistry. In this study based
on the analysis of 128 samples collected from three sections (Oued Bazina, Djebba and Tel Ghozlene) selected in the salt dome zone (SDZ), and one section (Jebel Oust) situated westward of the Tunisian range, supplemented by previous research works undertaken on Oued Zarga and Jebel Amar sections. The taxonomic analysis of the available data (ammonites and planktonic foraminifera) indicate that three informal litholigical units rich in organic matter (U1, U2 and U3) are of Early Aptian in age (Upper Bedoulian), covering both Blowiella blowi and Leupoldina Cabri planktonic foraminiferal zones and Deshayesites deshayesi ammonite zone, correspond to the Oceanic Anoxic Event (OAE1a).
The Rock-Eval analysis suggested that the studied Early Aptian strata are relatively rich in total organic carbon (TOC) content with values reaching 4.6 % especially within the U3 (Leupoldina cabri biozone). The latter recorded in the different studied sections an important deepening phase related to a global sea-level rise testified by the development of well laminated platy limestones containing abundant ammonites and radiolarians fauna. The palynofacies assemblages show that the organic matter is mainly represented by amorphous particles. The Tmax values ranging from 437°C to 456°C (Mean Tmax: 446°C) and the measured vitrinite reflectance ranging from 0.79 to 1.03 %, indicate that most samples are early mature except for those of the TG section which are within the peak oil-generation-window. Lateral facies and thickness variation, in addition to the organic matter distribution throughout the studied domains, strongly
suggest the imprint of salt tectonics both on the sedimentological pattern and associated anoxic conditions during the Aptian and the maturity of the organic-rich facies, at local scale, during the late Cretaceous-Paleogene compressional phase and associated salt dome remobilization. The source rock deposited during the OAE1a included within the M’Cherga Formation should be also considered when evaluating the petroleum systems and unconventional resources (Oil and shale gas) in northern
Tunisia.
... The changes in δ 13 C carbonate marked variations in paleoproductivity, and depletion of δ 13 C carb. occurs due to changes in the carbon cycle, directly impacting calcifying organisms, while enrichment indicates a stable environment with the re-establishment of those organisms (Weissert et al., 1998). δ 13 C carbonate showed impoverishment in the basal samples of the Romualdo Formation, while towards the upper samples there is an enrichment of δ 13 C carbonate . ...
The geochemical record of the early Aptian and the transition to the Albian exposes the presence of Hg/TOC
anomalies, revealing the interference of LIPs in paleoenvironmental changes in the Araripe basin. Redox-
sensitive (VEF, FeEF, CrEF, MnEF, PbEF, V/Cr, V/V + Ni and V/Ni) and paleoproductivity (CuEF, ZnEF, NiEF and
BaEF) proxies in the Santana Group (Barbalha, Crato and Romualdo formations) indicate conditions ranging from
oxic to anoxic, and increased paleoproductivity and of trace elements concentrations during LIPs activation.
Statistical analyses demonstrated that volcanism was associated with oscillations in paleosalinity (Sr/Ba) and
detrital supply (Al). LIPs activity was responsible for the emission of CO2 into the atmosphere, generating pa
leoclimatic changes in temperature (δ18O), a crisis in the productivity of calcifying organisms (δ13Ccarbonate), and
an increase in the load of organic matter (TOC). We suggest that trace elements anomalies found in the early
Aptian (Barbalha Formation) are associated with Ontong Java Plateua (OJP), responsible for OAE 1a, while the
volcanism’s proxies found in the Romualdo Formation occurred due to the Kerguelen South Plateau (SKP)
volcanism, triggering the OAE 1 b.
... While the environmental, climatic, and biotic impacts of the OAE 1aassociated perturbations on deep-and shallow-water marine carbonate succession have been extensively studied worldwide (e.g., Weissert et al., 1998;Huck et al., 2010;Husinec et al., 2012;Amodio and Weissert, 2017;Hueter et al., 2019;Steuber et al., 2022), the relationship between organic carbon burial, redox conditions, terrigenous input, and productivity remains poorly constrained. Carbonates precipitated in equilibrium with seawater incorporate trace elements and stable isotopes whose values reflect the composition of the ambient seawater (Brand and Veizer, 1980). ...
The biotic, environmental, climatic, oceanic, and sea-level perturbations during the Early Aptian oceanic anoxic event (OAE) 1a have been extensively documented from both deep- and shallow-marine deposits worldwide. However, there has been relatively little comparative assessment of the simultaneous interplay among organic carbon burial, redox conditions, terrigenous output, and productivity, leading to a lack of precise constraints on these relationships. Here, we use analyses of stable carbon isotopes (δ13Corg, δ13Ccarb, and Δ13C), total organic carbon (TOC), detrital proxies (Al, Si, Ti, K), redox-sensitive (RSTE: U, V, Mo) and productive-sensitive (PSTE: P, Cu, Ni) trace elements from a continuous, predominantly carbonate succession of the Kazhdumi Intrashelf Basin to evaluate the culprits for the OAE1a-associated changes in bottom-water oxygenation, organic-rich layer formation, and biotic shifts along the Arabian margin of the Neo-Tethys. Concentrations of Al-normalized RSTE and TOC values indicate that the bottom-water conditions ranged from oxic prior to and at the onset of the OAE 1a (carbon-isotope segments C2 to basalmost C4 sensu Menegatti et al., 1998), to anoxic-suboxic but not euxinic (Mo < 25 ppm) during the lower C4 through C5 + C6 segments, and then returned to oxic-suboxic in the remaining C5 + C6 segment. The increase in Al-normalized PSTE coupled with TOC concentrations in the basal C4 is coeval with a change from predominantly orbitolinid-ostreid to planktic foraminifera-radiolarian biota. The periodically high productivity, driven both by the surface-water productivity as well as by phosphorus recycling from the sediments, continued through the C5 + C6 segments as evidenced by matching Si/Al and PSTE peaks (Cu/Al and Ni/Al). The study sheds new light on the causes of variations in bottom-water deoxygenation, organic content, nutrient availability, and biotic shifts in semi-restricted, relatively deep (>100 m), continental-margin basins during major oceanic perturbations.
... Climatic conditions changed from a semi-arid and arid climate to a semi-humid climate (Carvalho et al., 2002;Scotese et al., 1999;Carvalho, 2014Carvalho, , 2017. The climatic seasonality also became more frequent, throughout the Atlantic-Tethys Ocean opening in the early Cretaceous, with alternating hot and dry periods with hot and humid ones (Weissert et al., 1998;Carvalho et al., 2010;Souza-Lima and Silva, 2018). The high dispersion of paleoweathering and chemical-textural maturity indices (Table 3), which suggest weak to moderate chemical weathering under a semi-arid to semi-humid climate (Fig. 15), may reflect climate changes that occurred during the Early Cretaceous. ...
... The latest Jurassic-earliest Cretaceous interval constitutes a period with considerable paleoenviron-mental perturbations, which manifest in both facies development (for instance, in the switch from radiolarite-to carbonate-dominated deposition or subsequent drastic limitation of the facies; e.g., Cecca et al. 1992;Jach and Reháková 2019) and paleoecologic processes (for instance, several nannofossil calcification events, radiolarian to calpionellid-dominated depositional turnover, and the waning of -dominated carbonates; Casellato 2009; Grabowski et al. 2019;Jach and Rehákova 2019;Casellato and Erba 2021;Lodowski 2022a). These disturbances likely resulted from the interplay of numerous factors, such as biotic productivity, water column pH and redox state (e.g., Weissert and Mohr 1996, Weissert and Erba 2004, Weissert et al. 1998) climatic changes (Abbink et al. 2001, Hesselbo et al. 2009, Föllmi 2012, Bover-Arnal and Strasser 2013, eustasy (Hardenbol 1998;Haq 2014Haq , 2018, oceanographic phenomena (e.g., De Wever et al. 2014) and/or tectonics (e.g., Stampfli and Hochard 2009;Missoni and Gawlick 2011;Plašienka 2018). When attempting to prepare consistent paleoenvironment interpretations and models it is crucial to determine whether, and to what extent, these mechanisms manifest in different tectonic units. ...
This paper presents an interpretation of sedimentologic, paleomagnetic, and geochemical data collected in the upper Kimmeridgian–Valanginian carbonates of the Giewont series (Giewont and Mały Giewont sections, High-Tatric succession, Western Tatra Mountains, Poland). The studied succession provides insight into the sedimentary conditions prevailing in the South Tatric Ridge (Tatricum), a submarine elevation located between the Zliechov Basin (Fatricum) and the Vahic (=South Penninic) Ocean. The sedimentary sequence includes micrites, pseudonodular limestones, cyanoid packstones, lithoclastic packstone, and encrinites. The results are discussed with regards to their significance for detrital input, paleoclimate, and paleoproductivity, which in turn are considered in the context of both local and regional paleoenvironmental trends and events. The greatest depositional depths during the latest Kimmeridgian–earliest Tithonian are documented by the occurrence of pseudonodular limestones. A Tithonian shallowing trend is demonstrated via the increasing size and roundness of cyanoids, while the final (?)emergence and erosion in the South Tatric Ridge is documented by earliest Cretaceous disconformities. This process might have been related to both falling sea-level during the major eustatic regressive cycle and tectonic uplift caused by the mutually related (re)activation in the Neotethyan Collision Belt and rifting in the Ligurian-Penninic-Vahic Oceans. The highest lithogenic influx (although still low; max 0.5% of Al content) during the late Kimmeridgian is considered as associated with relatively humid climate conditions, whereas a subsequent decreasing trend is thought to result from aridification during the latest Kimmeridgian–earliest Tithonian. Ultimately, deposition in the High-Tatric zone was affected by both large-scale environmental perturbations characteristic of the latest Jurassic (climate changes, variations in seawater pH, monsoonal upwelling, lithogenic input, etc.), as well as local sedimentary controls, predominantly the oxygenation state of bottom waters and tectonic movements.
... Peperite rocks are typically formed by the interaction of a lava flow into an unconsolidated sediment, normally under wet conditions 26 . The peperite-forming processes are diverse and result in two categories-dry and wet-both of which are found in Paraná Basin [1][2][3][4]9 . These primary volcaniclastic rocks are classified as basaltic breccias set in a non-volcanic matrix with a heterolithic lamination 3,8,25 . ...
Large igneous provinces (LIPs) are major magmatic events that have a significant impact on the global environment and the biosphere, for example as triggers of mass extinctions. LIPs provide an excellent sedimentological and geochemical record of short but intense periods of geological activity in the past, but their contribution towards understanding ancient life is much more restricted due to the destructive nature of their igneous origin. Here, we provide the first paleontological evidence for organic walled microfossils extracted from wet peperites from the Early Cretaceous Paraná-Etendeka intertrappean deposits of the Paraná basin in Brazil. Wet peperites are a volcaniclastic rock formed by the interaction of lava and subaqueous sediments.The Paraná-Etendeka was formed during the Valanginian (ca. 132 Ma) as a continental flood basalt in present day South America and Namibia, and released enormous amounts of carbon dioxide, sulfur dioxide, methane and hydrogen fluoride into the atmosphere. The organic walled microfossils recovered from the Paraná-Etendeka peperites include pollen grains, spores, acritarchs, and other remains of unidentifiable organic matter. In addition to the peperites, organic walled microfossils were also found in heterolithic sandstones and interpillow sandstones. Our findings represent the first insight into the biodiversity of the Paraná Basin during the Early Cretaceous during a period of intense magmatism, and the microfossil assemblages corroborate a regional paleoclimatic transition from arid to more humid conditions that were likely induced by the volcanic activity. We corroborate the potential of wet peperite rocks as a valuable source of paleobiological data and emphasize the importance of sampling volcaniclastic units that have been traditionally considered with lower fossiliferous potential due to their igneous origin.
... 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. ...
... Factors that led to the formation or extension of the intrashelf basins in Abu Dhabi in the Late Jurassic-Cretaceous period can be attributed to a combination of differential sedimentation, climatic, and eustacy processes that were strengthened by differential intraplate subsidence (e.g., Vahrenkamp et al., 2015b;Ziegler, 2001). The Early Jurassic-Cretaceous periods are associated with global oceanic anoxic events, which led to the deposition of organic-rich pelagic deposits within these intrashelf basins (Jenkyns, 1980;Schlanger and Jenkyns, 1976;Vahrenkamp et al., 2015b;Weissert et al., 1998). However, the dataset used in this study did not reveal evidence of structural control suggested by Davies et al. (2002) and van Buchem et al. (2002). ...
... The Saergan-nCIE, by its duration, magnitude and shape, requires a rapid onset and steady release of isotopically light carbon (likely CO 2 ; less likely CH 4 ) to overcompensate for the effects of increased burial of C org . In the second step, the initial effect should be successively counterbalanced (net-input of 13 C) via carbonate compensation (shifting lysoclines) and weathering feedback (Broecker and Peng, 1987;Weissert et al., 1998;Berner, 2003;Ridgwell and Zeebe, 2005;Tyrrell et al., 2007;Jenkyns, 2010;Vervoort et al., 2019). By now, there is some independent evidence (notably Hg/TOC) for intense outgassing (CO 2 , SO 2, H 2 S) during the deposition of the lower part of the Saergan Formation (Liu et al., 2019b;Yao et al., 2021). ...
... The earliest Aptian episode of carbonate platform growth terminated with the onset of OAE1a, which in many cases resulted in the demise of the carbonate platforms (e.g. Weissert et al. 1998;Föllmi 2012;Skelton and Gili 2012;Clavel et al. 2013;Hay et al. 2019;Skelton et al. 2019). ...
The Middle Member of the Llopis Fm in the Sierra de Bedmar-Jódar Unit of the Prebetic Zone of Jaén (southern Spain) was deposited on a shallow-marine platform of the Southern Iberian Continental Margin during the earliest Aptian. Detailed field logging of nine stratigraphic sections and facies mapping have allowed seven lithofacies associations (L1–L6) to be distinguished, one siliciclastic (L1) and five carbonate facies (L2–6). The succession is composed of eight consecutive elemental sequences of lithofacies associations L1–L6. Each elemental sequence is interpreted as representing one episode of shallowing-upwards carbonate deposition in a very shallow platform-lagoon that was bounded shoreward by clastic/ooid bars and passed seaward either to stromatoporoid bioconstructions (bioherms and biostromes) or rudist biostromes. The successive elemental sequences show north-eastward progradational geometries. Three phases of platform development are identified: (1) installation of the shallow platform; (2) development of a lagoon bounded by a stromatoporoid barrier and (3) development of an Urgonian-type platform dominated by rudists. During the early Aptian, the Bedmar-Jódar platform was partially isolated from the rest of the Prebetic platform and showed overall progradation towards the NE, in contrast to the general south-eastward progradational trend of the Prebetic platform. Sedimentation was controlled by rift-generated extensional tectonics that resulted in tilting of the platform block, causing the deviation of progradation from the general trends of the Prebetic Platform. In addition, climatic influence is inferred from the presence of siliciclastic sediments derived from weathering of the hinterland, which restricted the carbonate factory.
... The earliest Aptian episode of carbonate platform growth terminated with the onset of OAE1a, which in many cases resulted in the demise of the carbonate platforms (e.g. Weissert et al. 1998;Föllmi 2012;Skelton and Gili 2012;Clavel et al. 2013;Hay et al. 2019;Skelton et al. 2019). ...
The Middle Member of the Llopis Fm in the Sierra de Bedmar-Jódar Unit of the Prebetic Zone of Jaén (southern Spain) was deposited on a shallow-marine platform of the Southern Iberian Continental Margin during the earliest Aptian. Detailed field logging of nine stratigraphic sections and facies mapping have allowed seven lithofacies associations (L1–L6) to be distinguished, one siliciclastic (L1) and five carbonate facies (L2–6). The succession is composed of eight consecutive elemental sequences of lithofacies associations L1–L6. Each elemental sequence is interpreted as representing one episode of shallowing-upwards carbonate deposition in a very shallow platform-lagoon that was bounded shoreward by clastic/ooid bars and passed seaward either to stromatoporoid bioconstructions (bioherms and biostromes) or rudist biostromes. The successive elemental sequences show north-eastward progradational geometries. Three phases of platform development are identified: (1) installation of the shallow platform; (2) development of a lagoon bounded by a stromatoporoid barrier and (3) development of an Urgonian-type platform dominated by rudists. During the early Aptian, the Bedmar-Jódar platform was partially isolated from the rest of the Prebetic platform and showed overall progradation towards the NE, in contrast to the general south-eastward progradational trend of the Prebetic platform. Sedimentation was controlled by rift-generated extensional tectonics that resulted in tilting of the platform block, causing the deviation of progradation from the general trends of the Prebetic Platform. In addition, climatic influence is inferred from the presence of siliciclastic sediments derived from weathering of the hinterland, which restricted the carbonate factory.
... The Cretaceous record of these benthic communities is punctuated by several episodes of demise and extinction (Skelton, 2003;Skelton and Gili, 2012), which appear to have coincided with recurrent episodes of oceanic anoxic events (OAEs). These were related to the activity of large igneous provinces, short-term pulses of increased atmospheric CO 2 concentrations, hyperthermals, and changes in the carbonate saturation of seawater (e.g., Schlanger and Jenkyns, 1976;Erba, 1994;Weissert et al., 1998;Zeebe, 2001;Jarvis et al., 2002;Leckie et al., 2002;Weissert and Erba, 2004;Erba et al., 2010;Jenkyns, 2010;Föllmi, 2012;Mutterlose and Bottini, 2013;Bauer et al., 2017;Foster et al., 2018;Matsumoto et al., 2022;Steuber et al., 2022). Most of the geochemical proxies that have helped to decipher the sequence of events during Cretaceous OAEs have, however, been derived from the more continuous pelagic and hemipelagic sedimentary sequences (e.g., Erba et al., 2010;Jenkyns, 2018;Sullivan et al., 2020;Castro et al., 2021). ...
... Factors that led to the formation or extension of the intrashelf basins in Abu Dhabi in the Late Jurassic-Cretaceous period can be attributed to a combination of differential sedimentation, climatic, and eustacy processes that were strengthened by differential intraplate subsidence (e.g., Vahrenkamp et al., 2015b;Ziegler, 2001). The Early Jurassic-Cretaceous periods are associated with global oceanic anoxic events, which led to the deposition of organic-rich pelagic deposits within these intrashelf basins (Jenkyns, 1980;Schlanger and Jenkyns, 1976;Vahrenkamp et al., 2015b;Weissert et al., 1998). However, the dataset used in this study did not reveal evidence of structural control suggested by Davies et al. (2002) and van Buchem et al. (2002). ...
... One of the most significant of the Cretaceous OAE's occurred during the Early Aptian (OAE-1a; ~120 Ma) associated with magmatic degassing from the Greater Ontong-Java Plateau LIP (Percival et al., 2021) and marked by a rapid negative carbon isotope (δ 13 C) excursion followed by a long-lasting positive shift (Menegatti et al., 1998), as well as osmium isotope ( 187 Os/ 188 Os) anomalies supporting nearly a million year period of continual hydrothermal weathering of very large quantities of mafic and ultramafic rocks during a major phase of submarine LIP emplacement (Dickson et al., 2021). Additional OAE's are recorded in the Valanginian (Weissert event;Weissert et al., 1998;Gröcke et al., 2005) and Late Aptian -Early Albian (OAE-1b set), both expressed by δ 13 C excursions and deposition of organic-rich sediments (Bralower et al., 1993). The record of these Early Cretaceous OAE's is mainly documented in marine paleo-shelf sequences around the globe where the sedimentary successions contain marine microfossils that have been robustly calibrated to the international Geologic Time Scale (GTS 2020; Gradstein et al., 2020). ...
Early Cretaceous rift basins of the incipient South Atlantic have been the focus of intense hydrocarbon exploration and production activities and host some large oil accumulations in sections predating an interval of major salt deposition, particularly in the central segment of the South Atlantic. Understanding the timing (and associated uncertainties) of source rock and reservoir deposition and their relationship with rift evolution is critical for successful exploration. However, there are still many unresolved issues and data gaps regarding the precise age and duration of salt deposition. Better chronological constraints are particularly needed to determine the timing of deposition of Pre-Salt reservoirs and the primary evaporites, as well as the secondary phase of halokinensis that resulted in variable reservoir sealing potential. To help address this gap, stable carbon isotope (δ¹³C) records from bulk organic matter and insoluble kerogen were generated for the Early Cretaceous salt and Pre-Salt intervals from two exploration wells offshore of Gabon. The bulk organic δ¹³C stratigraphies for the two wells were then integrated with palynological and ostracod biostratigraphy and placed within a sequence stratigraphic and regional tectonic framework, providing new constraints on the timing of rift lake evolution and salt deposition. The good correlation between the offshore Gabon δ¹³C record with other published sections calibrated to the current Geologic Time Scale as well as other regional sections from NE Brazil, supports the reliability of our new Gabon δ¹³C record. Several δ¹³C excursions are identified in the Pre-Salt sequence and are correlated with the Valanginian Weissert event and Early Aptian δ¹³C event(s). Salt deposition on the Gabon margin is interpreted to have occurred during an interval straddling the Early-Late Aptian boundary (∼118.4–116.8 Ma). These findings are comparable with other published estimates for salt deposition from northeast Brazil but differ from published estimates from the Campos-Santos basins; the latter are critically discussed. This study provides an important stratigraphic dataset for offshore Gabon and contributes to the ongoing debate regarding the timing of rifting and salt deposition in the Early Cretaceous of the South Atlantic passive margin system.
... In this geodynamic and paleogeographic framework, the Neotethyan ecosystems were fueled by a high nutrient flux, leading to formed of massive radiolarites during the Middle and Late Jurassic, while they were substituted by deep-sea phytoplankton carbonates from the Tithonian to Berriasian period. This is mainly due to the fact that calcareous nannoplankton underwent a significant global radiation from the Latest Jurassic to the Earliest Cretaceous (Weissert et al. 1998, Bornemann et al. 2003, Falkowski et al. 2004, Weissert & Erba 2004. This global revolution in calcareous phytoplankton could have had a significant impact on marine carbonate sedimentation from the Early Cretaceous (Bornemann et al. 2003, Tremolada et al. 2006, and these significant changes in the sedimentary processes can also be clearly observed in the Transdanubian Range. ...
... It has been postulated that ocean acidification episodes resulted in a marine calcification crisis during the OAEs of the Early Cretaceous (e.g., Erba et al., 2010;Zeebe, 2012;Bottini et al., 2015;Matsumoto et al., 2020). In addition, there was an increase in long-term global sea level, with fluctuations in the short-term curve marked by rising sea-level episodes that eventually allowed for the creation of epicontinental seas and the development of large carbonate shelves, in which sea-level drop events may have altered nutrient inputs (e.g., Weissert et al., 1998;Leckie et al., 2002;Haq, 2014). ...
Calcareous nannofossil distribution, environmental magnetism, and geochemical data provide stratigraphic evidence concerning the paleoceanographic changes across the lower/middle Albian and the Oceanic Anoxic Event 1b (OAE1b, Kilian Level) at South Atlantic Ocean. In this study, we analyzed samples from the sedimentary records at Deep Sea Drilling Project (DSDP) Site 364, Kwanza Basin, Angola. This section is associated with the initial phases of evolution of the South Atlantic Ocean, characterized by the deposition of extensive evaporite layers under restricted marine conditions, which were preserved in many sedimentary basins of the Brazilian and African continental margins. The open marine conditions that followed this period are recorded in the sequences of limestones interbedded with organic matter-rich black shales. In the Kwanza Basin, Site 364 contains a well-preserved sedimentary record of these post-salt sequences. In this study, we address the Lower Cretaceous sedimentary records at Site 364 from a paleoceanographic perspective, investigating the influence of OAE1b and local paleoenvironmental conditions. Our data analysis indicates a progressive reduction in hypersaline conditions during the lower/middle Albian. In these conditions, five paleoceanographic intervals (PIs) were described, which show different evidence of dysoxia/anoxia and salinity fluctuations, euxinic intervals, surface-water temperature changes, and hydrothermal activity signals, as well as possible ocean acidification episodes. These paleoceanographic conditions at Site 364 are associated with a stratified thermocline composed of warm surface-water from the North Atlantic (Western Tethys) and cool deep-water incursions from the Austral Atlantic, which strongly affected the composition of the calcareous nannofossil assemblages. We propose that the lower/middle Albian paleogeographic and paleoceanographic conditions observed in the Kwanza Basin were likely related not only to local events linked to the early development of the South Atlantic, but also to the OAE1b - Kilian Level recognized in several basins from around the world.
... 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.
... late Tithonian into the Valanginian (Fig. 14C) which also greatly reduces the shallow marine areas of the Tethyan carbonate platforms (e.g., Flügel and Kiessling, 2002;Kiessling et al., 2003;Kocsis and Scotese, 2021). The Valanginian-Hauterivian interval also represents general platform drowning phase both in the northern (e.g., Weissert et al., 1998;Föllmi et al., 2006;Morales et al., 2013;Grȃdinaru et al., 2016) and the southern (e.g., Amodio et al., 2008;Bodin et al., 2010;Basilone, 2021) margins of the Tethys Ocean that is also the case for the PCP (e.g., Yilmaz et al., 2012). In this interval, disappearances dominate the shallow marine bioevents and this is why the lower and upper Valanginian in the shallow marine carbonates are mostly zoned by criteria based on last appearances and absence of certain taxa present in the underlying biozones (e.g., Pseudocyclammina lituus Zone of Granier, 2019a) instead of cosmopolitan first appearance datums. ...
The Late Jurassic–Early Cretaceous is an interval of unstandardized stages and includes the only Mesozoic system boundary without a Global Boundary Stratotype Section and Point – the Jurassic/Cretaceous (J/K) boundary. Recent researches have been mainly focused on deep marine continuous successions from the Tethyan region and provided important progress in calibration of pelagic bioevents. Correlation of these pelagic zonations with the schemes from shallow marine deposits is still obscure. Biostratigraphical data from marginal carbonates containing fossils both from the platform and basinal facies can provide the required links between these two distinct depositional environments. This kind of Upper Jurassic–Lower Cretaceous carbonates widely crop out in the Pontides (northern Turkey) in close association with related shallow and deep marine successions. A biostratigraphical dataset including 17 stratigraphical sections from this Pontides Carbonate Platform is synthesized. The fossil data include organisms from various depositional environments (i.e., benthic and planktonic foraminifers, calpionellids, algae, microencrusters and crinoids) and provides 139 bioevent datums (stratigraphic levels). This fossil dataset is analyzed through the methods of Graphic Correlation (GC) and Unitary Associations (UA) in order to overcome facies (past depositional conditions) controlled local biohorizons and calibrate fossil datums from unrelated phylogenies. Calibration of the Pontides Composite Reference Section (CSRS) with the Geological Time Scale (2020) reveals relative positions of both shallow and deep marine bioevents with respect to the Oxfordian–Hauterivian stage boundaries. The Tithonian/Berriasian and the Berriasian/Valanginian boundaries can be easily delineated by calpionellid bioevents in pelagic successions. However, no synchronous shallow marine first/last occurrence bioevents are available for both of these levels. Increased rates of originations toward Berriasian provide clustering of bioevents around the Tithonian/Berriasian boundary and brackets for both pelagic and shallow marine deposits. Several last occurrences provide unreliable approximations for the Berriasian/Valanginian boundary in neritic deposits. The species richness declines mid-Berriasian onward in accordance with the general trend toward lower sea levels through the late Tithonian into the Valanginian that diminished shallow marine factories and paved the way for a general Valanginian–Hauterivian drowning phase for the Tethyan carbonate platforms. This also adds difficulties in finding reliable origination events in the shallow marine environments for this extinction dominated interval.
... Paleogeographic and paleoclimatic changes were potential drivers of eustatic sealevel changes (Leckie et al., 2002;Hay, 2008). Rising sea-level episodes eventually allowed the flooding of epicontinental seas and the development of large carbonate shelves, whereas sea-level drop events may have led to altered nutrient input (e.g., Weissert et al., 1998;Leckie et al., 2002;Hay, 2008). The deepening and widening of Atlantic oceanic gateways shifted the prevailing west-east circulation to the newly formed north-south circulation, especially across the South Atlantic sedimentary basins, which invigorated oceanic heat transportation from low to high latitudes (Pucéat et al., 2005;Dummann et al., 2020). ...
Early Cretaceous sedimentary basins on the South Atlantic continental margins of South America and Africa are closely related with the Gondwana break-up, and record coeval paleoceanographic, paleoclimatic, and biotic changes during the late Barremian–Albian. The Sergipe-Alagoas Basin of northeastern Brazil contains one of the most complete Lower Cretaceous stratigraphic successions of the South Atlantic Ocean, including sedimentary and paleontological records nearly absent in nearby basins on the African/Brazilian continental margins. Fossil-rich sedimentary successions from the Sergipe-Alagoas Basin have allowed to assess: (i) evolutionary stages of the early South Atlantic Ocean; (ii) paleobiogeography of marine incursions (Austral and/or North Atlantic/Tethyan influences); and (iii) local signatures of global-scale paleoceanographic, paleoclimatic, and biotic events. Here we provide an overview on fossil-based biostratigraphic and paleoenvironmental studies of the Sergipe-Alagoas Basin, from the first marine incursions in a continental setting, to fully open-marine conditions. Based on eight fossil groups (ammonites, calcareous nannofossils, echinoids, planktonic and benthonic foraminifera, ostracods, palynomorphs, and radiolarians) from 107 sites, we observed that the marine biota shows strong affinity with Tethyan Realm in the Aptian–Albian interval, and provincialism/endemism is likely tied to the early-stage development of the South Atlantic Ocean. Based on late Barremian–late Albian lithological, paleontological, and geochemical data, we suggest three Sergipe-Alagoas Paleoenvironmental Stages (SAPSs): (i) continental conditions with possible episodic marine incursions (SAPS-1); (ii) transitional system, from continental to restricted-marine conditions (SAPS-2); (iii) transition from restricted- to open-marine conditions (SAPS-3). These local-scale evolutionary stages are correlated with early phases of the South Atlantic Ocean and major late Early Cretaceous paleoceanographic and paleoclimatic events. Moreover, we provide new approaches on the response of low-latitude biota to changing ocean circulation patterns in a hot, ice-free “greenhouse” world.
... The Saergan-nCIE, by its duration, magnitude and shape, requires a rapid onset and steady release of isotopically light carbon (likely CO 2 ; less likely CH 4 ) to overcompensate for the effects of increased burial of C org . In the second step, the initial effect should be successively counterbalanced (net-input of 13 C) via carbonate compensation (shifting lysoclines) and weathering feedback (Broecker and Peng, 1987;Weissert et al., 1998;Berner, 2003;Ridgwell and Zeebe, 2005;Tyrrell et al., 2007;Jenkyns, 2010;Vervoort et al., 2019). By now, there is some independent evidence (notably Hg/TOC) for intense outgassing (CO 2 , SO 2, H 2 S) during the deposition of the lower part of the Saergan Formation (Liu et al., 2019b;Yao et al., 2021). ...
Bulk-rock based carbon-oxygen chemostratigraphy should be combined with a detailed understanding of depositional facies (mineralogy, porosity), its 2D-chronostratigraphic architecture, and diagenesis. The Ordovician of the western Tarim Basin recorded a peculiar litho-biostratigraphic succession. The Darriwilian Yijianfang Formation formed part of a carbonate ramp dominated by filter feeders. Toward its top, there is condensation succeeded by a multi-Myr hiatus. The hiatus correlative succession is a black-shale (Darriwilian to early Sandbian Saergan Formation) preserved in slope-to-basin settings. A marine red-bed interval (Sandbian Tumuxiuke Formation) diachronously succeeded toward a more basin-wide record. Finally, the late Sandbian to Katian Lianglitag Formation re-established a shallow-water carbonate factory (ramp-to-platform), but this time being highly productive and hosting a diversifying assemblage of benthic primary producers. By exploring diagenesis associated with a first component-specific data-set of δ13C - δ18O values and by integrating and filtering respective literature bulk-rock data, a synoptic chemo-chronostratigraphic sequence is presented. It displays segments lasting from tens of Myrs to several 100 kyrs. There is a long-term trend of increasing δ13C values culminating in the early Katian at 3.2 ‰ followed by a steady decrease. This tipping point is associated with a precursory baseline shift that interferes with the short-term Guttenberg carbon-isotope excursion presumably associated with a positive shift of δ18O values. The baseline shift was driven by regional effects of photosynthesis and a boosting (dasycladacean-related) production of aragonite along the Sandbian-Katian boundary interval. There is a medium-term (Darriwilian to earliest Sandbian) negative δ13C excursion coinciding with both a basal positive δ18O excursion and the demise of the Darriwilian carbonate ramp (Suecicus-Event, new term). It might represent the effects of volcanism/SO2-outgassing during the switch from a passive to an active continental arc. This event masquerades the elsewhere recorded middle Darriwilian carbon-isotope excursion. Caution is needed to consider the Tarim realm for global Ordovician chemostratigraphy.
... The Lower Cretaceous sedimentary record indicates that greenhouse conditions with sea surface temperatures warmer than at present prevailed on Earth during that time (Barron et al., 1981;Huber et al., 1995;Weissert et al., 1998;Bernaus et al., 2003;Föllmi, 2012;Navarro-Ramirez et al., 2017;O'Brien et al., 2017). By comparison, present sea surface temperatures in the tropical Atlantic Ocean are ca 27.4 to 29.4 °C (https://www.seatemperature.org ...
Shifting palaeoceanographic and palaeoclimatic conditions together with fluctuating eustatic sea levels during the Early Cretaceous Aptian stage led to a globally widespread deposition of organic‐rich marine sediments designated Oceanic Anoxic Event 1a. Here a detailed lithostratigraphic and geochemical study is presented for 35.6 m of the Cabó Formation, part of the Organyà Basin, North‐East Spain, to assess intermittent periods of enhanced organic carbon preservation in Lower Aptian sediments preceding Oceanic Anoxic Event 1a. The Organyà area contains well‐exposed outcrops of Mesozoic black to dark grey marlstones and limestones with variable amount of organic matter indicative of oxygen‐deficient conditions. Previous work in a section near the town of Organyà focussed on lithostratigraphy and biostratigraphy and assigned a Barremian‐Aptian age. This study aims to provide an updated age based on carbon isotope correlation established elsewhere, and assess the chemostratigraphic characteristics of the Barremian – Aptian to clarify environmental changes regarding oxygen deficient conditions in the basin at that time. The δ13Corg values fluctuate from ‐22.1 to ‐24.4‰ showing concurrence with results at the El Pui section west of the studied section. Chemostratigraphic correlation of the δ13Corg reveals that the section is within segment C2, in the Lower Aptian. Redox sensitive trace elements (V, Ni, Co, Cr, Cu, Mo) indicate heightened dysoxic conditions at five organic‐rich layers, here designated carbonaceous layers (TOC > 2%), associated with enhanced terrigenous fluxes coincident with increased major elements (Al, Si and Ti) during these intervals. Biomarkers from six levels showed n‐alkane distributions with chain lengths from nC14 to nC34, mostly below nC21 indicating a predominance of marine‐derived organic matter. Climate conditions inferred from variable smectite, and kaolinite content suggests fluctuating humid‐warm conditions. The results thus reveal that the Organyà Basin experienced intervals of distinct oxygen‐poor conditions prior to the onset of Oceanic Anoxic Event 1a.
... Collectively, these events resulted in a biotic crisis, the so-called mid-Aptian event. This event mostly affected the organisms living in neritic environments (Skelton and Gili 2012), and involved widespread episodes of shallow carbonate platform drowning (Weissert et al. 1998;Föllmi et al. 2006;Najarro et al. 2011;Castro et al. 2012Castro et al. , 2014Masse and Ferneci-Masse 2013), leading to a maximum reduction in the extent of Aptian carbonate platforms (Skelton and Gili 2012). The upper Aptian recorded a progressive recovery of the neritic faunas and shallow carbonate platforms along with the successive development of progradational carbonate platforms, very well expressed in different basins such as the Prebetic in the Southern Iberian Palaeomargin (Vilas et al. 2004;Castro et al. 2008). ...
Abstract
Four lithofacies and 12 microfacies types recognized in an upper Aptian section in the Sierra de Bedmar-J dar (Prebetic
of Ja n) represent shallow lagoonal environments (marl and marly limestone) and sand bars that delimited the lagoon. The
lagoonal facies reflect subtidal restricted water circulation with low energy. The sand bar facies (intertidal environment)
have upper surfaces that show the effects of supratidal and subaerial conditions. The presence of early fractures in particular
lithofacies shows the importance of local synsedimentary tectonics during sedimentation. Thalassinoides, ?Arenicolites,
Diplocraterion, Circolites, Gastrochaenolites and Trypanites are recorded in different beds of this section, reflecting various
states of substrate consistency, in the form of firmground, hardground, and rockground. Whereas firmground conditions were
dominant in the lower part of the section, hardgrounds and rockgrounds are mainly present in the upper part of the section.
Four types of shallowing-upward elementary sequence are recognized. All the sequences show at the base mudstone or
wackestone microfacies representing a lagoonal environment, overlain by sand-bar grain-pack-stone facies corresponding to
a bar bounding the lagoon. The factors that controlled their development were carbonate production and tectonic movements.
Keywords: Prebetic Aptian Facies Microfossils Paleoenvironments Substrate consistency Sedimentary sequences
Lower Cretaceous stratigraphy of the high palaeo-latitude Arctic-Boreal Realm is generally more poorly understood than its lower-latitude Tethyan counterpart, prohibiting regional correlations and evaluation of global climate dynamics during this important high- p CO 2 period. In this paper, a holostratigraphic scheme and lithostratigraphic revision are presented for the Valanginian-lower Barremian, siliciclastic ramp succession of the Rurikfjellet Formation in Svalbard, drawn from synthesis of the latest published sedimentological, biostratigraphic, petrophysical, sequence stratigraphic, chemostratigraphic and chronostratigraphic results, supplemented by new measured sections from five localities. The offshore mudstone-dominated Wimanfjellet Member (Valanginian-lower Barremian) is retained, whereas three new members are defined according to their distinct geographic, sedimentological and stratigraphic characteristics: The Adventpynten Member (upper(?) Valanginian-lowermost upper Hauterivian) constitutes a thick, relatively localized succession of mass-transport deposits. The Kikutodden Member (Hauterivian-lower Barremian) is discarded and replaced by the northern Bohemanneset Member and southern Fotografryggen Member, representing respectively: heterogeneous prodelta to delta front deposits; and sandy offshore transition to shoreface deposits. The Rurikfjellet Formation records Valanginian-earliest late Hauterivian shoreline progradation followed by late Hauterivian-early Barremian shoreline retreat and flooding across a low-gradient ramp, which never experienced full regression into continental deposits within the extent of the present-day outcrop belt.
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.
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
Mesozoic strata record numerous negative and positive carbon isotope excursions (CIEs). The Middle Jurassic records a negative ~0.5 ‰ CIE at the Aalenian-Bajocian boundary followed by a positive ~1.5 ‰ CIE covering the entire early Bajocian. Although these CIEs are recorded in northern and southwestern Tethys and may reflect perturbations of the global carbon cycle, they remain poorly investigated. In this study, we present new geochemical and sedimentological data from the Chaudon-Norante section in France and Murtinheira section in Portugal to better constrain the origin of the lower Bajocian CIEs. Associated with the previously published carbon isotopic composition of bulk carbonate (δ13Cbulk carbonate) we provide new δ13Corg records, as well as total phosphorus content, phosphorus accumulation rates (AR), and CaCO3 and organic matter data. In contrast with previous interpretations, our results show no evidence of a carbonate production crisis during the early Bajocian. A slight increase in siliciclastic and phosphorus AR would argue for oceanic fertilization but without a parallel increase in organic matter AR. The obtained stratigraphic δ13Cbulk carbonate vs. of the carbon isotopic composition of bulk organic matter (δ13Corg) patterns are distinctive and mimic previous box modeling results simulating an increase in productivity forced by higher phosphorus rates from riverine and weathered-carbon input burial. The subsequent organic carbon burial produced counter-greenhouse conditions, which in turn produced a cooling by CO2 uptake. Our results indicate that the lower Bajocian event shows several similarities with the late Valanginian positive CIE (also known as the Weissert event). An accurate comparison of both events may help for a better understanding of the origin and consequence of such carbon cycle perturbations.
The Aptian sedimentary deposits of the Castro Urdiales area in north Spain record an episode of disoxia/anoxia which postdates Oceanic Anoxic Event 1a (OAE 1a). Carbonate platform and overlying facies are analysed for stratigraphy, sedimentology, total organic carbon and carbon isotopes. Lower Aptian shallow-water limestones are covered by deeper-water marlstones and organic-carbon-rich black lutites of early to late Aptian, ranging from Dufrenoyia furcata Zone to Cheloniceras (Epicheloniceras) martinioides Zone. Biostratigraphy and chemostratigraphic calibration are based on ammonites, carbon isotopes and total organic carbon analyses, revealing consistency with the global Aptian reference framework. The Castro Urdiales black-shale levels of the early to late Aptian transition together with their encasing series are correlated with other Aptian sections of the Basque-Cantabrian Basin (northern Spain) and southeastern France. The Castro Urdiales black shales are correlated with the Aparein Level of the eastern Basque-Cantabrian Basin. Prior to this oxygen deficient episode, glauconite-and-ostreid facies were also deposited under oxic conditions during the Gutiolo volcanic event of the Basque-Cantabrian Basin. This volcanism correlates in part with the Cretaceous superplume eruptions of Ontong Java, Manihiki Plateaus and the North Atlantic opening as a result of increasing seafloor spreading rates.
Weathering of organic carbon contained in sedimentary rocks (petrogenic OC, OCpetro) is an important control on the concentrations of carbon dioxide (CO2) and oxygen in the atmosphere. Of particular significance are steep mountainous catchments, where high rates of physical erosion introduce OCpetro to the surface, where oxygen in air and water can help drive oxidative weathering reactions, yet measurements of CO2 emissions from OCpetro oxidation are still scarce. Here, we use in situ gas accumulation chambers and show that CO2 fluxes, and their environmental controls, can be determined during a stand-alone, short-term (8 days) field campaign, applied to a remote setting. In the rapidly eroding Waiapu River catchment, New Zealand, dominated by mudstones, we measured high rates of CO2 release (222–1590 mgC m⁻² d⁻¹) in five accumulation chambers in the near-surface of naturally fractured and bedded rock outcrops. The corresponding CO2 concentrations are very high (pCO2 ~ 4700–27,100 ppmv), and such values could influence acid-hydrolysis reactions during chemical weathering of co-occurring silicate minerals. The CO2 is radiocarbon depleted (fraction modern, F¹⁴C = 0.0122–0.0547), confirming it is petrogenic in origin. Stable carbon isotopes suggest a source from OCpetro, but δ¹³C values of the CO2 are lower by ~3.5–3.7 ± 0.1 ‰ from those of OCpetro (−25.9 ± 0.1 ‰), consistent with isotope fractionation associated with microbial respiration of OCpetro. Over 6 days of measurement, we find that CO2 fluxes respond quickly to changes in temperature and humidity, indicating an environmental regulation that is captured by our short-term installation. The approaches applied here mean that future research can now seek to constrain the climatic, lithological and biological controls on OCpetro oxidation across regional to global scales.
Predictions of how marine calcifying organisms will respond to climate change rely heavily on the fossil record of nannoplankton. Declines in calcium carbonate (CaCO3) and nannofossil abundance through several past global warming events have been interpreted as biocalcification crises caused by ocean acidification and related factors. We present a global record of imprint-or "ghost"-nannofossils that contradicts this view, revealing exquisitely preserved nannoplankton throughout an inferred Jurassic biocalcification crisis. Imprints from two further Cretaceous warming events confirm that the fossil records of these intervals have been strongly distorted by CaCO3 dissolution. Although the rapidity of present-day climate change exceeds the temporal resolution of most fossil records, complicating direct comparison with past warming events, our findings demonstrate that nannoplankton were more resilient to past events than traditional fossil evidence suggests.
Global correlation of negative excursions in the δ¹³C values of shallow water carbonates have been used to interpret and identify major environmental changes through geologic time, such as the glaciations of the Neoproterozoic. As a result of their global reproducibility and similar geometry, these signals have predominantly been interpreted as being representative of the original δ¹³C values of dissolved inorganic carbon in the oceans, which in turn reflect major changes in the global carbon cycle. In this paper δ¹³C values from cores drilled in Enewetak Atoll (Pacific) and the Great Bahama Bank (Atlantic), are shown as examples of how similarly correlating variations in global δ¹³C values, can arise from diagenetic processes. It is further shown that while the profiles of the changes in δ¹³C values may appear synchronous, as a result of varying rates of deposition and subsidence, that the actual timing of the two changes can be quite different. By comparison of the geometry and global correlation of δ¹³C values measured in this study, it is proposed that the δ¹³C values of ancient sequences, may have resulted from non-synchronous diagenetic processes, rather than true changes in the global carbon system. This emphasizes the need for precise chronological control when interpreting sediment records, which is not present during many older geological time periods, in order to constrain the origin and correlation of carbon isotope variations.
The main Alpine-Mediterranean Mesozoic lithofacies, excluding flysch, are outlined and placed in their paleogeographic setting within the broader context of an evolving ocean basin. In the external (ophiolite-free) zones of the Alpine-Mediterranean orogeny, Mesozoic pelagic facies almost invariably overlie kilometers-thick successions of Bahamian-type platform carhonates. Wherever the basement of these platform carbonates is exposed, it is continental, comprising low- to high-grade metamorphic rocks and granites. We suggest that the pelagic sediments of these zones were deposited on a deeply submerged continental margin of the Atlantic type. Palinspastic reconstructions of the central Alpine- Mediterranean area place the depositional setting of most of these pelagic facies on the southern continental margin of the Tethys. In this area supply of clastics and organic matter was minimal, thus encouraging pelagic conditions.
The earliest pelagic sediments of the Alpine-Mediterranean region are of Triassic age and comprise gray and red limestones or cherts that commonly are associated with volcanics. These sediments were deposited in embayments and basins between extensive carbonate platforms and reefs. During the Liassic Epoch, a phase of block faulting, probably related to rifting in the oceanic Tethys, destroyed many of these shallow-water sites, and pelagic conditions became more widespread. During the Jurassic Period a basin-swell morphology was produced by irrcgular suhsidence of the different blocks. On submarine highs, or seamounts, the following stratigraphically condensed facies were developed: pisolitic ironstones, red biomicrites containing ferromanganese nodules and crusts, crinoid-pelagic bivalve- gastropod-ammonite biosparites, pelagic pelmicrites and micro-oncolitic sparites and certain red, fine-grained nodular limestones. In the neighboring basins more expanded successions containing slumped blocks and turbidites accumulated; the basinal facies were developed as red, more clay-rich, nodular limestones, gray limestone-marl interbeds, radiolarian cherts, and white nannofossil limestones. The Cretaceous Period saw a smoothing of submarine topography and a general deepening of the water as the continental margin continued to founder. Deposition of varicolored marls and red and white coccolith limestones was widespread.
True ocean-floor lithofacies are represented by those rocks associated with or lying upon ophiolites. In the central Mediterranean area they comprise ophicalcites, umbers, radiolarites, white nannofossil limestones and black shales. Their age is Jurassic and Cretaceous.
In the western central Atlantic pelagic facies of Late Jurassic and Cretaceous ages occur. These facies resemble both the continental margin and ocean-crust lithologies of the Alpine Mediterranean Tethys. A section through the Mesozoic portion of this undeformed continental margin and ocean-basin complex comprising the Bahamas, the inter-platform straits, and oceanic realm illustrates a paleogeographic arrangement that strongly resembles the reconstructed section for the Alpine-Mediterranean Tethys. This resemblance illustrates the parallel evolution of these two now widely separated areas, so that they both can be considered as representatives of an east-west Mesozoic seaway or Tethyan realm that stretched from the Caribbean to Indonesia.
The Aptian-Albian Scisti a Fucoidi, widespread in the Umbrian-Marchean Basin consist of a pelagic cyclic varicolored sequence of marls, marly limestones and black shales. A core was drilled through this formation at Piobbico (Marche) and a detailed biostratigraphic investigation based on calcareous nannofossils was undertaken. The total abundance of the nannofloras shows relatively high fluctuations depending on the lithology. The preservation is moderate to poor. In the Piobbico core calcareous nannofossils yielded an improved biostratigraphic resolution. Ten biohorizons were recognized. The nannobiostratigraphy was integrated with the planktonic foraminiferal scheme. An improved calibration of bio- and chronostratigraphic horizons was achieved. The proposed nannobiostratigraphic framework was also verified in other sections, within the Umbrian-Marchean Basin. More precise correlations and better estimates of hiatuses were obtained. -from Author
A detailed isotopic profile is presented for a stratigraphically expanded Cenomanian-Turonian boundary section in Chalk facies exposed at Eastbourne, Sussex and compared with data from Pueblo, Colorado. In both sections macro- and micropalaeontological markers (first appearances and disappearances) are well-constrained, and their relative positions and relationship to the structure of the carbon-isotope curve are identical. This consistent relationship between two independent phenomena, one geochemical, the other biostratigraphical, is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon-isotope excursion in these two areas. This interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon-isotope excursion in Europe and North America.
Matching of Lower Cretaceous carbon-isotope curves derived from pelagic sediments of the Tethyan-Atlantic sector with that obtained from peritidal carbonates of Resolution Guyot (Site 866, Mid-Pacific Mountains) provides constraints in positioning the Hauterivian/Barremian, Barremian/Aptian, and Aptian/Albian stage boundaries. A negative excursion in the earliest Barremian of the reference sections suggests that the Hauterivian/Barremian boundary on Resolution Guyot should lie in the interval 1425 to 1500 mbsf. A major positive isotopic excursion, whose onset is positioned just below the base of a major oolitic sand package, is ascribed to the blowi Zone (late early Aptian), a time of regional deep-marine organic-carbon burial (Selli Level) in the Pacific, Atlantic, and European regions. A finely laminated organic-carbon-rich level (14.2% total organic carbon) in the shallow-water packstone-wackestones is exactly coincident with the beginning of the isotopic excursion and can be considered an equivalent to the Selli Level deposited in water of very modest depth. The Barremian/Aptian stage boundary must be located below strata attributed to the blowi Zone, and should lie close to 900 mbsf. Decay of the excursion is complete by about 500 mbsf, a level which should be near to the Aptian/Albian boundary.
Large igneous provinces (LIPs) are a continuum of voluminous iron and magnesium rich rock emplacements which include continental flood basalts and associated intrusive rocks, volcanic passive margins, oceanic plateaus, submarine ridges, seamount groups, and ocean basin flood basalts. Such provinces do not originate at “normal” seafloor spreading centers. We compile all known in situ LIPs younger than 250 Ma and analyze dimensions, crustal structures, ages, and emplacement rates of representatives of the three major LIP categories: Ontong Java and Kerguelen-Broken Ridge oceanic plateaus, North Atlantic volcanic passive margins, and Deccan and Columbia River continental flood basalts. Crustal thicknesses range from 20 to 40 km, and the lower crust is characterized by high (7.0–7.6 km s−1) compressional wave velocities. Volumes and emplacement rates derived for the two giant oceanic plateaus, Ontong Java and Kerguelen, reveal short-lived pulses of increased global production; Ontong Java's rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid-ocean ridge system. The major part of the North Atlantic volcanic province lies offshore and demonstrates that volcanic passive margins belong in the global LIP inventory. Deep crustal intrusive companions to continental flood volcanism represent volumetrically significant contributions to the crust. We envision a complex mantle circulation which must account for a variety of LIP sizes, the largest originating in the lower mantle and smaller ones developing in the upper mantle. This circulation coexists with convection associated with plate tectonics, a complicated thermal structure, and at least four distinct geochemical/isotopic reservoirs. LIPs episodically alter ocean basin, continental margin, and continental geometries and affect the chemistry and physics of the oceans and atmosphere with enormous potential environmental impact. Despite the importance of LIPs in studies of mantle dynamics and global environment, scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features.
Marine strata deposited during late Cenomanian and early Turonian time display lithological, faunal, and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient. At, or very close to, the Cenomanian-Turonian boundary, between 90.5 and 91.5Ma ago, oxygen deficiencies were particularly marked over a period of <1Ma. This short-lived episode of oceanic oxygen deficiency has been termed the Cenomanian-Turonian 'Oceanic Anoxic Event' (OAE). The widespread distribution of anoxic sediments deposited synchronously during such a short-lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the Cenomanian-Turonian oxygen-minimum zone related to feedback between sea level rise and regional palaeoceanography. The palaeoceanography of the Cenomanian Turonian OAE is discussed in detail in a companion paper by Arthur et al, 1987.-from Authors
Large negative excursions in marine carbonate δ¹³C are commonly associated with period boundaries and mass extinctions. Explanations for these events must be consistent with limitations imposed by carbon-isotope mass balance. At steady state (i.e., for excursions lasting more than 10ⵠyr), the surface ocean δ¹³C is set by the organic fraction of the total carbon burial rate and the magnitude of the photosynthetic isotope effect. The δ¹³C of the deep ocean and the surface-to-deep isotope gradient are set by both the organic fraction of the ocean's remineralized particulate flux and the magnitude of the isotope effect. Thus it is the carbon-isotope composition of the deep ocean that is most reflective of internal oceanic processes; the surface ocean records changes in the longer term throughput of carbon in the system. The cessation of organic export from the surface ocean, such as is presumed to have caused the Strangelove ocean condition of the Cretaceous/Tertiary (K/T) boundary, leads to an isotopically homogeneous ocean in decades to centuries. If this condition persists, the ocean's isotopic composition approaches that of the riverine weathering input (in 10ⵠyr). Failure to approach this value during the K/T event suggests continued production and burial of organic carbon, dominantly in either terrestrial or shallow-marine environments.
A group of calcareous nannoplankton named nannoconids experienced a crisis in the early Aptian and recovered only later in the late Aptian after a period of virtual absence. Although no extinctions occurred, the widespread nature of the "nannoconid crisis' suggests a global causal factor. At least 1 m.y. prior to the "nannoconid crisis', the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level. The "nannoconid crisis' seems to be synchronous with the early Aptian volcanic eruptions in the Pacific Ocean. Hence calcareous nannoplankton were severely affected by the "superplume' volcanic episode. The coccolithophorid bloom/nannoconid crisis was possibly induced by the excessive CO2 levels in the atmosphere and/or caused by changes in nutrient content of oceanic surface waters. Concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion. -from Author
THE Cretaceous period was a time of global warmth1-4. Mid-Cretaceous equatorial temperatures were similar to today's5, but the equator-to-pole temperature gradient is the subject of some controversy5-7. Although it is unlikely that the poles were ice-free8-10, fossil evidence3-5,11,12 indicates that near-polar temperatures were much higher than they are today. Little is known, moreover, about oceanic poleward heat transport, and this makes it hard to model the Cretaceous climate or to evaluate the extent to which it provides an analogue for a 'greenhouse' world warmed by increased atmospheric CO2 alone. Here we use relationships between leaf physiognomy (such as shape and size) and modern climate to determine Cretaceous climate conditions in the Arctic region from fossil leaves. We find that the Arctic Ocean was relatively warm, remaining above 0 °C even during the winter months. This implies that there was significant poleward heat transport during all seasons.
Evolutionary developments among vascular land plants may have been the ultimate cause for oceanic anoxic events, biotic crises, global climate change, and geochemical and sedimentologic anomalies of Late Devonian age. The influence of vascular land plants on weathering processes and global geochemical cycles is likely to have increased substantially during the Late Devonian owing to large increases in root biomass associated with development of: 1) arborescence (tree-sized stature), which increased root penetration depths, and 2) the seed habit, which allowed colonization of drier upland areas. It is hypothesized that rapidly increasing root mass led to transient intensification of the rate of soil formation and to permanent gains in the thickness and areal extent of deeply weathered soil profiles. -from Authors
Numerous climate models predict that the geography of the supercontinent Pangea was conducive to the establishment of a "megamonsoonal" circulation. In general, geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the Triassic. Pangea in the Late Carboniferous had widespread peat formation in what is now central and eastern North America and Europe and relatively dry conditions on the Colorado Plateau. The equatorial region of the continent became drier through the end of the Carboniferous. By the Permian, the equatorial region of Pangea was dry, and indicators of aridity and rainfall seasonality became more widespread. Wind directions from Colorado Plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time. In the Triassic, climate in the Colorado Plateau region became relatively wet, though still seasonal, and the few eolian sandstones indicate a major shift in wind direction at that time. In addition, sedimentation in Australia, which was in relatively high latitudes, took on a much drier and more seasonal character. These two events support the hypothesis that the Pangean monsoon was at maximum strength during the Triassic. In the Early Jurassic, the Colorado Plateau region became arid again, but climate apparently became wetter in eastern Laurussia and Gondwana. Finally, drying occurred in Gondwana and southern Laurasia, indicative of the breakdown of the Pangean monsoon.
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 presence of fault blocks appears to control occurrence of Cretaceous carbonate buildups regardless of basement lithology. Increased subsidence and/or sea level rise during the Albian created accomodation space for fringing rudist reefs that partially circumscribed the basin and permitted deposition of offshore pelagic carbonate sediment in the basin center. -from Authors
Early Cretaceous carbonate platforms extend along the eastern North American margin as far north as offshore Nova Scotia. They form a narrow belt preferentially located at the Late Jurassic paleoshelf edge. The shallow carbonate platform strata are Berriasian-Aptian in age and in most cases represent the continuation of Jurassic carbonate megaplatform deposition into the Cretaceous. The segmentation of the Early Cretaceous carbonate buildup into a chain of isolated platforms was caused by intensified progradation of delta-borne clastics across the shelf. -from Author
The Lower Cretaceous "Urgonian' limestones from Provence represent a carbonate platform system of Valanginian-early Aptian age. Pre-Cretaceous rocks also show carbonate platform development, especially in the Middle and uppermost Jurassic sequence, thus early Cretaceous Urgonian systems continued preexisting ones. This epicontinental platform system lacked true coastal environments. The platform facies grade into basinal facies that yield diverse ammonites. Consequently, important early Cretaceous stadial stratotypes in these facies permit precise chronostratigraphic correlations. The paper describes the regional setting, stratigraphy, sedimentology and platform evolution of these deposits. -from Author
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
Coral-rudist buildups are known from 3 outcrop areas of Cretaceous age in France. These are: 1) Paris Basin; 2) Sud-Est Basin; and 3) Aquitaine-Pyrenees Basin. The development of these buildups is traced from Beriasian time to Maestrichtian. 2 groups of coral-rudist formations have been distinguished: 1) those associated with off-shore 'highs', and 2) those associated with carbonate platforms. 3 types of off-shore 'highs' are: 1) coral 'highs', from the Lower Cretaceous, 2) oobioclastic/coral 'highs' from the lower Barremian and 3) rudist banks in the Upper Cretaceous. A platform may be subdivided into 2 zones: 1) an outer zone with high energy deposits and organic buildups, and 2) an inner zone of quiet energy deposits with abundant rudists. Development of coral-rudist formations appears to be governed by 6 important factors. These are; 1) shallow water conditions, 2) relative basement stability; 3) eustatic stability of transgression; 4) low terrigenous influx; 5) absence of organism restricting oceanographic conditions, and 6) a warm climate.-from Authors.
Comparison of oceanic anomaly block models in the M0-M29 interval from the Japanese, Phoenix, Hawaiian and Keathley lineations indicates that the Hawaiian block model represents the closest approximation to a constant spreading rate record. The new Hawaiian block model differs slightly from that of Larson and Hilde (1975). Currently popular numerical age estimates for polarity chrons, base CM0 (121 Ma), CM16-CM15 (137 Ma) and top CM25 (154 Ma), are consistent with constant spreading rate in the new Hawaiian block model but inconsistent with constant spreading in the Larson and Hilde (1975) block model. A new time scale (CENT94) is based on the above ages and constant spreading in the new Hawaiian block model. Land section magnetostratigraphy, mainly from Italy and Spain, has provided direct correlations of polarity chrons to stage boundaries through ammonite biozones, and indirect correlation through nannofossil and calpionellid biozonations. -from Authors
A continuous carbon isotope curve from Middle-Upper Jurassic pelagic carbonate rocks was acquired from two sections in the southern part of the Umbria-Marche Apennines in central Italy. At the Colle Bertone section (Terni) and the Terminilletto section (Rieti), the Upper Toarcian to Bajocian Calcari e Marne a Posidonia Formation and the Aalenian to Kimmeridgian Calcari e Marne a Posidonia and Calcari Diasprigni formations were sampled, respectively. Biostratigraphy in both sections is based on rich assemblages of calcareous nannofossils and radiolarians, as well as some ammonites found in the upper Toarcian-Bajocian interval. Both sections revealed a relative minimum of δ13CpoB close to + 2‰ in the Aalenian and a maximum around 3.5 ‰ in early Bajocian, associated with an increase in visible chert. In basinal sections in Umbria-Marche. this interval includes the very cherty base of the Calcari Diasprigni Formation (e.g. at Valdorbia) or the chert-rich uppermost portion of the Calcari a Posidonia (e.g at Bosso). In the Terminilletto section, the Bajocian-early Bathonian interval shows a gradual decrease in δ13CPDB values and a low around 2.3‰. This part of the section is characterised by more than 40 m of almost chert-free limestones and correlates with a recurrence of limestone-rich fades in basinal sections at Valdorbia. A double peak with values of δ13CPDB around + 3‰ was observed in the Callovian and Oxfordian, constrained by well preserved radiolarian faunas. The maxima lie in the Callovian and the middle Oxfordian, and the minimum between the two peaks should be near the Callovian/Oxfordian boundary. In the Terminilletto section, visible chert increases together with δ13CPDB values from the middle Bathonian and reaches peak values in the Callovian-Oxfordian. In basinal sections in Umbria-Marche, a sharp increase in visible chert is observed at this level within the Calcari Diasprigni. A drop of δ13C values towards + 2‰ occurs in the Kimmeridgian and coincides with a decrease of visible chert in outcrop. The observed δ13C positive anomalies during the early Bajocian and the Callovian-Oxfordian may record changes in global climate towards warmer, more humid periods characterised by increased nutrient mobilisation and increased carbon burial. High biosiliceous (radiolarians, siliceous sponges) productivity and preservation appear to coincide with the δ13C positive anomalies, when the production of platform carbonates was subdued and ceased in many areas, with a drastic reduction of periplatform ooze input in many Tethyan basins. The carbon and silica cycles appear to be linked through global warming and increased continental weathering. Hydrothermal events related to extensive rifting and/or accelerated oceanic spreading may be the endogenic driving force that created a perturbation of the exogenic system (excess CO2 into the atmosphere and greenhouse conditions) reflected by the positive δ13C shifts and biosiliceous episodes.
Large amounts of organic C. were deposited and preserved in marine sediments of late Barremian through M. Albian and late Cenomanian-early Turonian age owing to the development of poorly oxygenated oceanic water masses and expanded oxygen minimum zones during 'oceanic anoxic events'. Sediments rich in organic C. which were deposited during such events are thick sequences of basinal black shale or mudstone, thin black beds in shelf chalks, and thin beds and lenses in rudist reef and associated limestones. We propose that the relative abundance of Mesozoic oil in the world oil picture is in part the result of maturation of organic carbon deposited during Cretaceous oceanic anoxic events. -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
Data in the tropical Indian Ocean show an excursion of d13C signals toward heavier values, lasting for about 4 million years. The excursion terminates at approximately 13.5 Ma. The Chron 16 Carbon shift coincides with the cessation of an early Miocene warming trend. Hypothesizes that a feedback loop was established. An initial increase in the planetary temperature gradient started thermocline development which led to organic carbon extraction at the ocean margins which resulted in a drop in atmospheric carbon dioxide concentration. Concomitant cooling (reverse greenhouse effect) strengthened thermocline development, leading to further cooling. The loop was broken when available nutrients were used up. -from Authors
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
A review is presented from the Jurassic terrestrial and marine fossil record, and the record of sediments and clay minerals, insofar as it bears on the two principal climatic parameters, temperature and precipitation. It is shown that there is a generally good agreement between palaeoclimatic data derived from fossils and rocks and the results of modelling experiments, provided a substantially higher atmospheric content of carbon dioxide is assumed for Jurassic times. The Jurassic world was relatively equable compared with the present day, but there were probably strong seasonal contrasts of temperature within the large continental areas, as well as some polar ice. Monsoonal effects were dominant on the continents and rainfall in low and mid latitudes was probably strongly seasonal, with arid conditions prevailing at low latitudes. Significant changes of temperature through the course of the period cannot be discerned, but some evidence tentatively favours a slight increase. A notable spread of aridity in southern Eurasia in the late Jurassic can be related to orographic effects. Some minor cyclicity in the sedimentary sequence may relate to orbital forcing.
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
Investigation of four sections of Tithonian to Valanginian pelagic limestone have led to refinement of the correlation of calpionellid zones to the magnetic polarity time scale. The correlations are self-consistent but differ slightly from those previously published. The discrepancy with the published correlation from the Bosso section [1] has been resolved by re-evaluation of the biostratigraphy of this sequence. The revised correlation places the base of the Chitinoidella Zone in the lower part of polarity chron CM21n, the base of Zone A near the top of CM20n, the A/B boundary at the base of CM18, the B/C boundary in the upper part of CM17, the C/D boundary at the top of CM16 and the D/E boundary at the top of CM14.
It is shown that the present geoid has a simple, low-order configuration with an axis of symmetry in the equatorial plane. It is shown further that it is a 'tennis-ball' pattern, with an equatorial high belt and a polar low one, which is clearly controlled by the rotation of the earth. Finally, it is shown that the outline of Pangea between at least 200 Ma and 125 Ma ago lay along a great circle passing through the paleopoles of rotation. Thus, it also had an axis of symmetry in the equatorial plane. This hemispheric supercontinent configuration ended in Middle Cretaceous time during a major geologic catastrophe which was accompanied by high rates of spreading, hotspot outbreaks and high sea-level stands. This evidence is interpreted in terms of separate steady state lower mantle convection, responsible for the present geoid, weakly coupled to the upper mantle one. This weak coupling leads to the hemispheric continent configuration which ends when excessive heating of the upper mantle due to the insulating continental cap leads to continent dispersal. The complete cycle, from one supercontinent to the next, might be of the order of 400 Ma.
Evidence for eustatic fluctuations in mean sea level during the Cretaceous is provided, with the dating of thirteen transgressive episodes between late Valanginian and early Maastrichtian time, separated by intervals of eustatic regression. The assumption of a direct genetic link between mean sea level and volumetric changes in the mid-oceanic ridge systems would, in turn, imply that plate motion was strongly episodic, with individual movements probably having a time span of the order of one to two million years, and being separated by several million years of subdued plate motion. The concept of marine cycles of strongly diachronous transgression is rejected and episodes of eustatic transgression are considered to be short-lived, rarely extending beyond two million years duration and, in general, probably much less. The relationship between the major Cretaceous transgressions and regressions and contemporary magnetic polarity reversals, orogeny and continental volcanism are discussed. An interpretation is also presented of the effects of eustatic fluctuations on Cretaceous oceanic sedimentation and the input of nutrients into the marine environment, as well as on palaeoclimate and such biological phenomena as species diversification, population “explosions”, mass faunal extinctions and evolutionary theory.
A review is presented from the Jurassic terrestrial and marine fossil record, and the record of sediments and clay minerals, insofar as it bears on the two principal climatic parameters, temperature and precipitation. It is shown that there is a generally good agreement between palaeoclimatic data derived from fossils and rocks and the results of modelling experiments, provided a substantially higher atmospheric content of carbon dioxide is assumed for Jurassic times. The Jurassic world was relatively equable compared with the present day, but there were probably strong seasonal contrasts of temperature within the large continental areas, as well as some polar ice. Monsoonal effects were dominant on the continents and rainfall in low and mid latitudes was probably strongly seasonal, with arid conditions prevailing at low latitudes. Significant changes of temperature through the course of the period cannot be discerned, but some evidence tentatively favours a slight increase. A notable spread of aridity in southern Eurasia in the late Jurassic can be related to orographic effects. Some minor cyclicity in the sedimentary sequence may relate to orbital forcing.
Recent ammonite finds in Italian Maiolica limestones allow direct correlation of Hauterivian and Barremian ammonite zones (stage boundaries) to polarity chrons. At Laghetto and Alpetto (Lombardy, Italy), Lower Aptian ammonites occur just above polarity zone M0 and below the Selli Level, and Upper Barremian ammonites occur in polarity zone M1n. These correlations are consistent with the Barremian/Aptian boundary being close to older boundary of (polarity chron) CM0. The uppermost Hauterivian ammonite (Faraoni) guide level has been correlated to CM4 at Bosso (Umbria-Marche), confirming the recent correlation of the Hauterivian/Barremian boundary to CM4. At Monte Acuto (Umbria-Marche), ammonites spanning the Valanginian/Hauterivian boundary interval, and the last appearance of the nannofossil T. verenae, occur close to the CM11/CM11n boundary. The Valanginian/Hauterivian boundary has previously been placed between the first appearance of L. bollii and the last appearance of T. verenae, or between CM10 and CM11. The published Polaveno (Lombardy) magnetostratigraphy for the CM3–CM11 interval has now extended to CM16. This 260 m section, recording the CM3–CM16 interval, is the most complete single-section record of Cretaceous M-sequence polarity chrons. No diagnostic ammonites have been found in this section; however, the correlations of nannofossil and calpionellid events to polarity chrons are consistent with previous studies.
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 history of Phanerozoic reef-building is reassessed according to an analysis of trophic structure. Broad global patterns may be largely explained by changes in nutrient availability. Differing rates of oceanic circulation linked to climatic fluctuations and sea-level changes determined the range of trophic regimes available in shallow marine tropical habitats. Most Phanerozoic reefal buildups are revealed as soft-substrate dwelling heterotrophic communities and as such were not well-adapted to oligotrophic conditions: they were trophically quite unlike modern coral reefs and had markedly different environmental requirements. -from Author
Carbon isotope measurements in deep-sea sediments may be used to obtain the history of the mean ¹³ C content of CO 2 dissolved in the ocean, of ¹³ C gradients within the ocean, and of the globally averaged ¹³ C content of the carbonate accumulated on the sea floor. The last has some interest in relation to energy reserves, because it provides a means of monitoring the changing rate of accumulation of organic matter on the globe.
Data are shown for the ¹³ C composition of Cenozoic marine carbonates, based on a suite of sites from DSDP (Deep Sea Drilling Project) Leg 74 in the South Atlantic. If the published estimates of global accumulation rates for marine carbonate are recalculated on the basis of recent timescales for the Cenozoic it is found that changes were rather subtle, contrary to the conclusion of Davies and Worsley (1981), so that a model of constant carbon input may be used to estimate changes in organic carbon accumulation from the ¹³ C data. A cumulation of changes in the global organic carbon reservoir is also obtained and is used to infer changes in the amount of oxygen in the atmosphere, which was 20% higher than today during most of the Cenozoic. However, the solubility of oxygen in the warm early Cenozoic oceans was about 20% lower than today’s value, so that the early Cenozoic ocean had a similar dissolved oxygen content to today’s ocean.
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.
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