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Examples of sections exposing the Hauptmumienbank Member of the Vellerat Formation (see Figure 1 for geographical position of sections): (a) Voyeboeuf section from sb Ox6+ to MFs Ox6+; (b) savagnières section from sb Ox6+ to MFs Ox6+; (c) Pertuis section from sb Ox6+ to MFs Ox6+; (d) top part of the Vorbourg section around MFs Ox6+; (e) base and middle part of the Vorbourg section above sb Ox6+. the numbers refer to the elementary sequences within the small-scale sequences. compare with logs in Figures 10 and 11.
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Based on a well-established bio- and sequence-stratigraphic framework, a narrow time window in the Bimammatum ammonite zone (Late Oxfordian) is investigated in six Swiss Jura sections representing a shallow-water carbonate platform. From the detailed facies and microfacies analysis of oncoid-rich (Hauptmumienbank Member) and ooid-rich (Steinebach M...
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Context 1
... sections of 7 to 14 meters thick have been logged at a cm scale and densely sampled. then, a sequence-and cyclostratigraphic analysis was carried out for a high-resolution monitoring of the marine transgression following the Ox6+ sequence boundary (Fig. 4). For the sedimentological analysis, samples were taken at the base, in the middle, and at the top of beds. In total, 300 polished slabs and thin sections, plus 25 washing residues of marls were examined. Analyses of the texture and the semi- quantification of skeletal and non-skeletal elements were per- formed on thin sections and rock ...
Context 2
... the small road that cuts through the béridier anticline, close to the Vorbourg chapel. It is a good reference section for the Hauptmumienbank Member (cf. section rG 366 in Gygi 2000b). Along the parking area, marly deposits, which are partly covered by vegetation, constitute the röschenz Member dated of the lower Hypselum subzone (Gygi 1995; Fig. 4e). the massive limestones of the Hauptmumienbank and steinebach members, dated of the upper Hypselum subzone, are exposed in the southern extremity of the parking. the studied interval consists of 12.8 m lagoonal deposits, covering the top part of the marly röschenz Member and most of the oncoid-rich Haupt- mumienbank Member ( Fig. 10; ...
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Citations
... On the scale of Upper Jurassic carbonate platforms, such medium and small-scale sequences were identified by several authors in various formations (e.g., the Adriatic and Jura platform). These sequences were associated with sea-level fluctuations induced by orbital eccentricity cycles on periods of 100 and 400 ka (Dupraz and Strasser, 1999;Strasser and Samankassou, 2003;Husinec and Fred Read, 2007;Védrine and Strasser, 2009;Cariou et al., 2014). In our study, however, we were unable to address these first-and fourth-order sea-level fluctuations because too few case studies provided information on the record of such cyclic patterns and because chronostratigraphy is poorly constrained. ...
Carbonate systems are influenced by a great variety of physical and biological controlling factors that operate from global to local scales. The resulting intrinsic complexity of carbonate platforms makes them difficult to predict, especially when data are limited. Predicting geologic geometries and properties based on limited sampling or uncalibrated seismic data generally relies on a priori knowledge and equivocal interpretations that are marked by geologist perception and personal experience. To overcome these uncertain interpretations of such a complex natural system, which can become critical in frontier exploration, we developed an expert system that relies on a process-based method and a standardized data set using normalized information and parameters. The main innovation relies on the realization of knowledge- and process-based synthetic carbonate stratigraphic architectures that support seismo-stratigraphic interpretations. The workflow consists of four steps: (1) bibliographic compilation of a geologic database for each case study supported by quantitative parameters (e.g., sedimentation duration and thickness) and qualitative parameters (geodynamic context, seismic architecture, and facies model); (2) statistical analyses to establish consistent geologic classes and spatiotemporal trends; (3) process-based modeling to simulate stratigraphic architectures associated with carbonate sedimentation processes in a physically constrained numerical environment and testing different geologic hypotheses; and (4) realization of a predictive palaeogeographic map representing the global distribution of carbonate stratigraphic architectures, and estimation of controlling parameters for unconstrained case studies. The expert system is based on 77 case studies of Upper Jurassic carbonate platforms, which reveal the resemblance of these carbonate systems, in response to uniform global palaeoclimatic conditions and sea level. Significant local differences in stratigraphic architectures are related to specific geodynamic contexts and subsidence trends. The thickest carbonate platforms are developed in extensive/passive geodynamic settings such as the Central Atlantic Ocean margins, while thinner platforms form in intra- and peri-cratonic settings such as those of the Arabian region.
... The mechanism is high-frequence sea-level changes which are genetically related with the Milankovitch cycles (Goldhammer et al. 1987;Mei and Tucker, 2013). High-frequency sequence stratigraphy investigation was chosen for shallow carbonate platform deposits on account of their high sensitivity to sea-level changes (Védrine and Strasser, 2009). ...
Shallow-water carbonates from the Yingshan Formation are important target of hydrocarbon exploration in Tarim Basin. Detailed descriptions of outcrop, core, and thin sections, isotopic composition analysis, and trace element analysis were conducted. Seven lithofacies which consists of two facies belt groups were identified and used to interpret deposition environments of Yingshan Formation: (1) peritidal carbonate, with relatively lower δ¹³C values from −4.2% to −1.9%, mainly represented by intertidal to supratidal facies and restricted subtidal facies and (2) open-marine subtidal carbonate, with higher δ¹³C values (−1.5% to −0.3%), mainly consists of shoal facies and interbank sea facies. On the basis of the lithology sets, four types of meter-scale cycle model (types A–D) were grouped into peritidal sequences and subtidal sequences. On the basis of vertical lithofacies, cycle stacking patterns, and accommodation variations in Fischer plots, two third-order depositional sequences (SQ1–SQ2) were recognized. The sequence boundary between SQ1 and SQ2 is not only a surface of a positive shift of δ¹³C values, but also the transitional zone of cycle stacking patterns. The sequences can be further divided into four fourth-order sequence sets: Sq1–Sq4. The lower sequences (Sq1–Sq2) are dominated by peritidal facies and characterized by a progressive decreasing in accommodation space probably indicates a longer-term fall in sea level. The upper sequences (Sq3–Sq4) are mainly dominated by subtidal facies and characterized by the accommodation space with a progressive increasement, likely indicates a rising sea level with a longer term. The facies-controlled reservoirs are mainly present in the Sq3, related to the sequence boundary between SQ1 and SQ2.
... Figure 8 shows an example of correlation of elementary sequences between the sections of Fig. 7. The prominent transgressive surface at the base of the Hauptmumienbank and Steinebach members is found all over the Swiss Jura (Gygi, 1995;Védrine and Strasser, 2009). It overlies marly sediments that locally contain fully marine fauna (echinoderms, brachiopods) mixed with freshwater algae (charophytes), suggesting that the sediment deposited during the sea level lowstand terminating the previous sequence was reworked in the early phases of the transgression (Védrine, 2007). ...
Today and in the geologic past, climate changes greatly affect and have affected Earth surface processes. While the climatic parameters today can be measured with high precision, they have to be interpreted from the sedimentary record for ancient times. This review is based on the detailed analysis of stratigraphic sections of Oxfordian (Late Jurassic) age, with the aim to reconstruct and discuss the climate changes that controlled the sedimentation on the shallow marine carbonate platform that today is represented in the Swiss Jura Mountains. The sediments formed under subtropical conditions in which carbonate-producing organisms proliferated, and ooids and oncoids were common. The sections are composed of hierarchically stacked elementary, small-scale, and medium-scale depositional sequences wherein facies changes imply deepening–shallowing trends. The major sequence boundaries Ox 6, Ox 7, and Ox 8 can be correlated with those of other European basins and place the studied sections in a broader framework. The chronostratigraphic tie points imply that the medium- and small-scale sequences formed in tune with the orbital eccentricity cycles of 405 and 100 kyr, respectively, and the elementary sequences with the precession cycle of 20 kyr. Orbitally controlled insolation changes at the top of the atmosphere translated into climate changes: low insolation generally resulted in low amplitudes of sea level fluctuations at the 20 kyr frequency and in a cool and humid climate at the palaeolatitude of the Jura platform. Terrigenous material was eroded from the hinterland and distributed over the platform. High insolation led to sea level rise, as well as to warm and semiarid to arid conditions in which coral reefs could grow. However, nutrient input favoured growth of microbialites that encrusted the corals. The reconstruction of high-frequency sea level fluctuations based on facies analysis compares well with the curve of insolation changes calculated for the past 550 kyr. It is therefore assumed that the sea level fluctuations were mainly due to thermal expansion and retraction of ocean surface water. Two models are presented that explain the formation of elementary sequences: one for low and one for high insolation. Despite the important lateral facies variations typical of a shallow marine platform, and despite the uncertainties in the reconstruction of sea level changes, this study demonstrates the potential of carbonate ecosystems to record past climate changes at a time resolution of 20 000 years. Relatively short time windows can thus be opened in the deep geologic past, and processes and products there can be compared with those of the Holocene and the Anthropocene. For example, it appears that today's anthropogenically induced sea level rise is more than 10 times faster than the fastest rise reconstructed for the Oxfordian.
... The facies succession reflects a transition from low-energy, shallow-marine settings, where matrix-supported textures and exclusively marine components prevail, to higher-energy brackish to euryhaline environments, where grain-supported textures were generated and porocharacean charophytes occurred. Similar parasequences have been associated with shallowing-upwards marginal-marine successions (e.g., Bádenas et al. 2004;Védrine and Strasser 2009), which in the case studied would include a shift towards brackish conditions. ...
... Marls with a similar fossil assemblage have been associated with deposition in low-energy, shallow-marine areas with abundant terrigenous inputs (e.g., Védrine and Strasser 2009) as it must be the case here. 4) Limestones with rare clavatoracean thalli (tL) contain small portions of charophyte thalli belonging to Favargerella sp., Clavatoraxis sp. and Charaxis sp, and rare clavatoracean utricles and porocharacean gyrogonites ( Table 2). ...
... The sedimentary features (Table 2), and the presence of marine fossils indicate that this facies corresponds to channel-fill deposits formed in a marine coastal area. Similar deposits have been associated with intertidal to shallow subtidal areas (e.g., Colombié and Strasser 2005;Védrine and Strasser 2009;Bover-Arnal and Strasser 2013) and it must be the case in this deposit as well. ...
A combined micropalaeontological, taphonomical and sedimentological study was carried out in the non-marine Barremian of the Maestrat Basin (E Iberian Chain) to elucidate the palaeoecology of Barremian charophytes. Understanding the palaeoecology of fossil charophytes is of prime importance for the accurate application of charophyte biozonations, since most species used as biostratigraphic markers and/or biozone index species are restricted to facies formed in a particular environment. Five charophyte biocoenoses were distinguished. (1) Charophyte association from freshwater alkaline lakes receiving low clastic input, mainly composed of Atopochara trivolvis var. triquetra , Clavator harrisii , Ascidiella stellata , and A. triquetra . The thalli known as Munieria grambastii , corresponding to Clavator utricles, were extremely abundant in the shallowest facies of the lake margins, and Hemiclavator -rich populations were also locally dominant. (2) An association characteristic of freshwater alkaline lakes with high clastic input was mainly composed of Echinochara lazarii , Globator maillardii var. trochiliscoides , A. trivolvis var. triquetra , C. harrisii , Hemiclavator neimongolensis var. neimongolensis , and locally also Clavator calcitrapus . (3) Monospecific populations of Porochara maestratica thrived in brackish settings with little clastic influence, whereas (4) monospecific E. lazarii populations thrived in clastic-influenced brackish settings. (5) A charophyte association grew in lakes that developed in mudflat to floodplain environments and was mainly constituted by E. lazarii , A. trivolvis var. triquetra , and C. harrisii var. harrisii and var. reyi . Accordingly, the palaeoenvironmental conditions inferred indicate that most of the charophyte species were controlled by (i) bathymetry, (ii) clastic content in the sedimentary environment and (iii) salinity. The stratigraphic succession studied shows an upwards increase in clastic content from the base to the top, which is associated with the more humid period recorded along the margins of the Tethys and the Boreal realm during the early Barremian–early late Barremian. In consequence, those species restricted to clastic-poor settings are constrained to the lower part of the section, whereas those taxa that were able to thrive in clastic-rich settings persisted throughout the entire section. This observation establishes a link between the changes observed in the charophyte floras recognized and the environmental changes that occurred during the Barremian in western Europe.
... The facies occurs only on in the Tuwaiq Mountain Limestone. The patch-reefs and the biostromal coral/stromatoporoids are developed in an open-marine and clear shallow-water environment that was free of argillaceous detrital deposits (Védrine and Strasser 2009). The circular patch-reefs are typical of a back-barrier setting (Wilson and Jordan 1983). ...
The sequence stratigraphy of the Dhruma Formation and Tuwaiq Mountain Limestone (Bajocian to middle Callovian) is based on shallow cores and outcrop measured sections along a 600-km–long N-S transect west and south of Riyadh. Correlations were extended westward in the subsurface using gamma-ray wireline logs (500 km). For the first time, the study integrates sequence stratigraphic framework with detailed semiquantitative micropaleontological analysis that allows reappraisal of stratigraphic interpretation of main biofacies associations. The outcrops provide a continuous stratigraphic record of the Middle Jurassic transgression of a large (>1000 km) epeiric tropical platform from continental braided fluvial deposits to tidal or wave-dominated mixed carbonate-siliciclastic lagoonal deposits. These formed aggraded flat-topped platform wedges and thicken northward due to evident syndepositional differential subsidence. The carbonate platforms are mud-dominated and evolved from restricted carbonate platforms that contained microbes and low-faunal diversity (early Bajocian to early Bathonian) to normal-marine carbonate platforms hosting coral/stromatoporoid-rich strata and high-faunal diversity adjacent to a deeper intrashelf basin (middle Callovian). The succession consists of two 2nd-order sequences, Dhruma and Tuwaiq sequences, separated by an unconformity (middle Bathonian hiatus). Several composite and high-frequency sequences that have a subordinate maximum flooding surface (MFS) in the lower Bathonian (zigzag Zone) and a main MFS in the middle Callovian coronatum Zone. The depositional sequences are considered to be of eustatic origin as they match well with Tethyan sea-level cycles. The carbonates developed well during late transgressive and highstand systems tract (TST and HST) of the composite sequences controlled by back stepping of the siliciclastic sources.
... In the Western Tethys, carbonate platforms were well developed during the Jurassic period (Pierre, Durlet, Razin, & Chellai, 2010;Pomar & Hallock, 2008), as observed, for example, in England (Hesselbo, 2008), France (Brigaud et al., 2014;Carpentier, Lathuilière, & Ferry, 2010;), Switzerland (Rost & Riebesell, 2004;Strasser & Védrine, 2012;Védrine & Strasser, 2009;Wetzel, Weissert, Schaub, & Voegelin, 2013), and Spain (Bádenas, Pomar, Aurell, & Morsilli, 2012;Bosence et al., 2009;Chesnel, Samankassou, Merino-Tome, Fernandez, & Villa, 2016;Ramajo & Aurell, 2010). ...
Many studies have been focused on the development of carbonate platforms, however, the controlling factors of their evolution are still unclear. The QTKT1 well, drilled in 2016 by the Chengdu Center of the China Geological Survey at the Northern Qiangtang Depression, has allowed further studies of Jurassic environments and resources in the Eastern Tethys. In this study, we investigate variations in spectral gamma‐ray logs and CaCO3 content and perform a cyclostratigraphic analysis in the Xiali mudstones and Buqu limestones and Xiali mudstone to analyse causes for the demise of the Middle Jurassic carbonate platform in the Qiangtang Basin. The concentrations of Th, K, U, and Th/U and Th/K ratios increase suddenly from the Buqu Formation to the Xiali Formation, suggesting increased terrigenous input and/or decreased carbonate production rates. Cyclostratigraphic analysis detects the existence of astronomical cycles and an abrupt change in sediment accumulation rates within the target intervals. Combined with sedimentary facies analysis, our research suggests that the demise of the Middle Jurassic carbonate platform may have been caused by terrigenous detrital inputs into the Qiangtang Basin. High‐frequency sea‐level fluctuations increased terrestrial inputs and carbonate production rates at the orbital scale. The regression happened before the facies change and controlled terrestrial inputs at a larger scale, which resulted in the demise of the carbonate platforms. Contrary to the Western Tethys, a regression took place from the Bathonian to Callovian ages in the Qiangtang Basin, Eastern Tethys, which increased the exposure levels. The large exposure led to significant erosion, accelerated detrital input from the land to the Northern Qiangtang Depression, reduced carbonate production as well as resulted in the demise of the Buqu carbonate platform. The relative sea‐level fall is mainly the result of the regional tectonism during this period.
... The circular patch-reefs and the coral/stromatoporoid biostromes are interpreted to have developed in a clear shallow and open-marine environment that was free of argillaceous matter (Védrine and Strasser, 2009). The paleogeographic and stratigraphic location of the reef biostromes and buildups suggest that these formed in a back-barrier depositional environment (Wilson and Jordan, 1983). ...
... For example, the Jura Platform in the northern margin of the Tethys Ocean had discontinuous subsidence history and wobbling blocks movement during the Oxfordian (Strasser et al., 2015). Syndepositional tectonic activities have been documented in Tunisia (Walley, 1985) and in NW Tethys in central Europe (Dardeau et al., 1988;Lhamyani, 1985;Pittet and Strasser, 1998;Allenbach, 2001;Chevalier et al., 2001;Védrine and Strasser, 2009;Strasser et al., 2015). In particular, Late Oxfordian (late bifurcatus Zone) inversion in the Swiss Jura Mountains (Allenbach, 2001(Allenbach, , 2002 could be synchronous with the tectonic event noticed herein (between HCS1 and HCS2). ...
... As argued here, a major sequence boundary and disconformity between HCS1 and HCS2 is most likely to be Late Oxfordian in age. This sequence boundary could correlate with the Western Europe 2nd-order regression and sequence boundary between OX6 and OX7 ( Fig. 16; Hardenbol et al., 1998;Strasser et al., 2000;Védrine and Strasser, 2009) and corresponds to JOx6 sequence boundary of Haq (2018). ...
The sequence stratigraphy of the Late Jurassic (Oxfordian to Kimmeridgian) of the central Arabia is based on outcrop measured sections. The sequence stratigraphic framework is extended eastward across the Arabian Basin through surface-to-subsurface gamma-ray correlations (550 km long to the east). It provides an insight into the development of an intrashelf basin in a large epeiric tropical platform. The outcrop depositional environments range from semi-arid shoreline to carbonate inner-lagoon and back-barrier lagoon. These formed an aggraded flat-topped platform with evident syndepositional differential subsidence. The Upper Jurassic successions are composed of several transgressive third-order sequences interrupted by short emersion sequence boundaries. The Hanifa Platform evolved from proximal argillaceous-limestone with low-faunal diversity to open-marine carbonate platforms with reef bearing and high-faunal diversity adjacent to a deep intrashelf basin in the subsurface. The Hanifa maximum flooding surfaces (MFS's) are placed in terrigenous-free open-marine carbonate sediments. The Jubaila-Arab-D is a conformable succession marked at the base by storm-influenced inner-platform grainstones with quartz sandstone, and proximal barren lime-mudstone. The Jubaila-Arab-D MFS is placed higher in the Arab-D reservoir in a backstepping of back-barrier high-energy reef facies. During sea-level highstand, the reef facies are gently prograding toward the Rimthan Arch leaving behind a restricted lagoon deposits consists of sabkhah/salina anhydride. These composite sequences are probably controlled by climatic driven eustasy, coupled with local tectonic disruption, as they have some similarity with other Tethyan sequence stratigraphy. For the first time, this outcrop study reveals a detailed and complete stratigraphic framework that subdivided the Upper Jurassic prolific petroleum systems into genetically related sequences that are not always obvious from subsurface data. The study allows the assessment of the Upper Jurassic tectono-stratigraphic events of the central Arabian Platform.
... The nuclei are micritized; they exhibit round to elongate structures and are rarely asymmetrical. Facies F5c is characterized by large oncoids (up to several centimetres), encrusted by thin biofilms that top some oncoidic layers (Type 2 oncoids of Vedrine et al.,, 2009). This facies is interrupted by large, sheet-like fractures several metres in lateral extension. ...
The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian reefs and bioaccumulations that contain fenestral-microbialites and various benthic and pelagic organisms. Ecological and environmental changes during the Early Triassic commonly are assumed to be associated with numerous perturbations (productivity changes, acidification, redox changes, hypercapnia, eustatism and temperature changes) post-dating the Permian–Triassic mass extinction. New data acquired in the Mineral Mountains sediments provide evidence to decipher the relations between depositional environments and the growth and distribution of microbial structures. These data also help to understand better the controlling factors acting upon sedimentation and community turnovers through the Smithian–early Spathian. The studied section records a large-scale depositional sequence during the Dienerian(?)–Spathian interval. During the transgression, depositional environments evolved from a coastal bay with continental deposits to intertidal fenestral–microbial limestones, shallow subtidal marine sponge–microbial reefs to deep subtidal mud-dominated limestones. Storm-induced deposits, microbialite–sponge reefs and shallow subtidal deposits indicate the regression. Three microbialite associations occur in ascending order: (i) a red beds microbialite association deposited in low-energy hypersaline supratidal conditions where microbialites consist of microbial mats and poorly preserved microbially induced sedimentary structure; (ii) a Smithian microbialite association formed in moderate to high-energy, tidal conditions where microbialites include stromatolites and associated carbonate grains (oncoids, ooids and peloids); and (iii) a Spathian microbialite association developed in low-energy offshore conditions that is preserved as multiple decimetre thick isolated domes and coalescent domes. Data indicate that the morphologies of the three microbialites associations are primarily controlled by accommodation, hydrodynamics, bathymetry and grain supply. This study suggests that microbial constructions are controlled by changes between trapping and binding versus precipitation processes in variable hydrodynamic conditions. Due to the presence of numerous metazoans associated with microbialites throughout the Smithian increase in accommodation and Spathian decrease in accommodation, the commonly assumed anachronistic character of the Early Triassic microbialites and the traditional view of prolonged deleterious conditions during the Early Triassic time interval is questioned.
... The Jurassic is thought of as a period of well-developed carbonate platforms with widespread oolitic/skeletal facies deposited in vast epicontinental seas and rift domains in the Western Tethys (Pomar and Hallock, 2008;Pierre et al., 2010). Numerous examples of intracratonic Jurassic carbonate platforms are known in (1) England (Sellwood et al., 1985;Hesselbo, 2008), (2) France (the Paris Basin: Rioult et al., 1991;Dromart et al., 1996;Garcia et al., 1996;Pittet et al., 2000;Gaumet et al., 2001;Quiquerez and Dromart, 2006; the South-East Basin: Hamon and Merzeraud, 2008;Brigaud et al., 2009a;Carpentier et al., 2010), (3) Switzerland (Gonzalez and Wetzel, 1996;Strasser and Vedrine, 2009;Vedrine and Strasser, 2009;Wetzel et al., 2013), (4) Germany (Ruf et al., 2005), (5) Spain (the Iberian Basin: Aurell et al., 1995;Bádenas and Aurell, 2001a, b;Aurell et al., 2003;Bádenas et al., 2003;Ramajo and Aurell, 2008;Bosence et al., 2009;Bádenas et al., , 2012 and (6) Iran (Wilmsen et al., 2010). Despite this extensive set of studies, major uncertainties remain about the factors controlling the development of carbonate platforms in stable, intracratonic basins and about the evolution of their geometries, depositional profiles from homoclinal ramps to rimmed-shelves, and facies distributions (Burchette and Wright, 1992;Aurell et al., 1998;Pomar, 2001;Mutti and Hallock, 2003;Schlager, 2005). ...
It is usually very difficult to identify and quantify the relative influence of tectonics, eustasy and climate on carbonate system evolution from sedimentary records. In order to improve our understanding of these mechanisms, we have traced for the first time, the evolution of the eastern Paris Basin platform throughout the entire Jurassic period. This carbonate platform underwent eight successive growth and demise phases, with different depositional profiles ranging from ramps to flat-topped geometries. The eight carbonate growth periods are compared with the standard sea-level curves, local tectonic regimes and recently published oxygen-isotope and/or clay mineralogy databases. Prograding heterozoan facies along ramp profiles mark periods dominated by second-order eustatic sea-level rise, relatively cool sea surface temperatures, and mesotrophic and humid conditions (Hettangian, Pliensbachian, late Oxfordian, Tithonian). During these periods, variable detrital contents in the sedimentary succession hampered the efficiency of shallow-marine carbonate factories. Higher sea surface temperatures, oligotrophic and humid conditions associated with either eustatic sea-level rise or very high local subsidence occurred during the early Bajocian and the mid-Oxfordian. These seawater properties seem to have favoured the aggradation of scleractinian corals forming dome-shaped bioherm buildups. An oolitic and lime-mud carbonate system, deposited during the Bathonian second-order eustatic sea-level fall, is characterised by miliolid-rich micritic facies on a rimmed-ramp under stable, cooler and drier conditions. The second-order maximum flooding associated with a sea surface temperature decline and/or a seawater eutrophication caused at least five carbonate demise periods (i.e. Toarcian, earliest late Bajocian, Callovian/Oxfordian transition, earliest late Oxfordian and Kimmeridgian).
... The thickness of Mesozoic strata in the study area is approximately 800 m (Thury et al. 1994). Sedimentation pattern during the Mesozoic were influenced by the multiple reactivation of Paleozoic basement structures, as is indicated indirectly by unconformities, erosional surfaces, lateral variations in lithofacies, and abrupt thickness changes (Pittet 1996;Quesne et al. 2000;allia 2000, 2003;allenbach 2002;Jank 2004;Ziegler et al. 2004;allenbach and Wetzel 2006;Jank et al. 2006;Védrine and Strasser 2009). Direct evidence of tectonic activity in the Swiss Jura Mountains during the Mesozoic period is, however, missing, because of the lack of obvious synsedimentary tectonic features on the scale of seismic resolution (allenbach 2002). ...
A combination of petrographic and geochemical techniques was applied to better constrain the origin and evolution of the fluid systems responsible for the formation of disseminated, Cd-rich (up to 0.6 wt%), sphalerite (ZnS) mineralization in the northeastern part of the Jura Mountains, Switzerland. The Rb-Sr ages of sphalerite samples indicate that a main phase of sphalerite formation occurred near the boundary between the late Middle and early Late Jurassic, at around 162 Ma. The negative δ34S values (-22.3 to -5.3 ‰) suggest that biogenic sulfide sulfur was involved in ZnS precipitation. The strontium isotope composition is more radiogenic than that of contemporaneous seawater, reflecting the interaction of mineralizing fluids with silicate rocks. Lead isotope signatures are very uniform (206Pb/204Pb = 18.63-18.67, 207Pb/204Pb = 15.63-15.64, 208Pb/204Pb = 38.51-38.63), indicating an isotopically well-homogenized fluid system. The basement rocks underlying the Jurassic strata are considered to be the main source of metals for the sphalerite mineralization. The migration of deep-sourced hydrothermal saline metal-bearing fluids into the Bajocian host carbonates containing sedimentary reduced sulfur resulted in the precipitation of sulfides. The period of sphalerite formation near the Middle-Late Jurassic boundary is characterized by enhanced tectonic and hydrothermal activity in Europe, related to the opening of the Central Atlantic and tectonic/thermal subsidence during spreading of the Alpine Tethys. Our study provides evidence that the Bajocian carbonate rocks in the Jura Mountains area were affected by the circulation of deep-sourced metal-bearing hydrothermal fluids in response to these continent-wide tectonothermal events. The presence of sphalerite mineralization and associated geochemical anomalies in Zn and Cd contents in carbonate rocks may also be used to trace basement features.
