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Richard J. Twitchett - One of the best experts on this subject based on the ideXlab platform.
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stratigraphic and environmental control on marine benthic community change through the early toarcian Extinction Event iberian range spain
Palaeogeography Palaeoclimatology Palaeoecology, 2019Co-Authors: Silvia Danise, Gregory D. Price, Marieemilie Clemence, Daniel P Murphy, Juan J Gomez, Richard J. TwitchettAbstract:Abstract In the Early Jurassic (~183 Ma ago) global warming and associated environmental changes coincided with an Extinction Event in the marine realm (early Toarcian Extinction Event). Anoxia was previously considered to have been the main cause of Extinction, but Extinctions also occur at localities that remained oxygenated throughout the Event, suggesting that other factors, such as temperature, may have played a major role. To test this hypothesis, we integrated quantitative analyses of benthic macro-invertebrates with high-resolution geochemical proxies on the bulk rock (TOC, δ13C, δ18O) and on belemnites and brachiopod shells (δ13C, δ18O) from two sections from the Iberian Range, Spain, with no black shale deposition. The sections are orientated SE-NW along an onshore-offshore gradient deepening to the north. The dominant benthic groups, bivalves and brachiopods, show a different response to the Extinction: brachiopods go through a complete species-level turnover, while many bivalve species range through the Event. In the shallower section, changes in richness and evenness correlate with TOC (Total Organic Carbon), suggesting that variations in nutrient input from runoff, and the possible local onset of low-redox conditions (TOC > 4 wt%), controlled faunal diversity. In contrast, at the deeper section, community change correlates with changes in δ18O, indicating that temperature variations might have influenced faunal change. Different stratigraphic patterns of Extinction occur between the two localities, with last-occurrences clustering at the maximum flooding surface in the shallower section, and at the transgressive surface in the deeper one. The observed differences between the two localities highlight the important role of local sedimentary and stratigraphic processes in controlling the shape of the geochemical and fossil record, and the need for studying multiple sections along onshore-offshore gradients in order to extrapolate regional and global patterns.
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Salinity changes and anoxia resulting from enhanced run-off during the late Permian global warming and mass Extinction Event
Climate of the Past, 2018Co-Authors: Elsbeth E. Van Soelen, Richard J. Twitchett, Wolfram M. KürschnerAbstract:Abstract. The late Permian biotic crisis had a major impact on marine and terrestrial environments. Rising CO2 levels following Siberian Trap volcanic activity were likely responsible for expanding marine anoxia and elevated water temperatures. This study focuses on one of the stratigraphically most expanded Permian–Triassic records known, from Jameson Land, East Greenland. High-resolution sampling allows for a detailed reconstruction of the changing environmental conditions during the Extinction Event and the development of anoxic water conditions. Since very little is known about how salinity was affected during the Extinction Event, we especially focus on the aquatic palynomorphs and infer changes in salinity from changes in the assemblage and morphology. The start of the Extinction Event, here defined by a peak in spore : pollen, indicating disturbance and vegetation destruction in the terrestrial environment, postdates a negative excursion in the total organic carbon, but predates the development of anoxia in the basin. Based on the newest estimations for sedimentation rates, the marine and terrestrial ecosystem collapse took between 1.6 and 8 kyr, a much shorter interval than previously estimated. The palynofacies and palynomorph records show that the environmental changes can be explained by enhanced run-off and increased primary productivity and water column stratification. A lowering in salinity is supported by changes in the acritarch morphology. The length of the processes of the acritarchs becomes shorter during the Extinction Event and we propose that these changes are evidence for a reduction in salinity in the shallow marine setting of the study site. This inference is supported by changes in acritarch distribution, which suggest a change in palaeoenvironment from open marine conditions before the start of the Extinction Event to more nearshore conditions during and after the crisis. In a period of sea-level rise, such a reduction in salinity can only be explained by increased run-off. High amounts of both terrestrial and marine organic fragments in the first anoxic layers suggest that high run-off, increased nutrient availability, possibly in combination with soil erosion, are responsible for the development of anoxia in the basin. Enhanced run-off could result from changes in the hydrological cycle during the late Permian Extinction Event, which is a likely consequence of global warming. In addition, vegetation destruction and soil erosion may also have resulted in enhanced run-off. Salinity stratification could potentially explain the development of anoxia in other shallow marine sites. The input of freshwater and related changes in coastal salinity could also have implications for the interpretation of oxygen isotope records and seawater temperature reconstructions at some sites.
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Salinity changes and anoxia resulting from enhanced runoff during the late Permian global warming and mass Extinction Event
2017Co-Authors: Elsbeth E. Van Soelen, Richard J. Twitchett, Wolfram M. KürschnerAbstract:Abstract. The Late Permian biotic crisis had a major impact on marine and terrestrial environments. Rising CO2 levels following Siberian Trap volcanic activity were likely responsible for expanding marine anoxia and elevated water temperatures. This study focusses on one of the stratigraphically most expanded Permian-Triassic records known, from Jameson land, east Greenland. High resolution sampling allows for a detailed reconstruction of the changing environmental conditions during the Extinction Event and the development of anoxic water conditions. Since very little is known about how salinity was affected during the Extinction Event, we especially focus on the aquatic palynomorphs and infer changes in salinity from changes in the assemblage and morphology. The Extinction Event, here defined by a peak in spore/pollen, indicating disturbance and vegetation destruction in the terrestrial environment, postdates a negative excursion in the total organic carbon, but predates the development of anoxia in the basin. Based on the newest estimations for sedimentation rates, the marine and terrestrial ecosystem collapse took between 1.6 to 8 kyrs, a much shorter interval than previously estimated. The palynofacies and palynomorph records show that the environmental changes can be explained by enhanced runoff, increased primary productivity and water column stratification. A lowering in salinity is supported by changes in the acritarch morphology. The length of the processes of the acritarchs becomes shorter during the Extinction Event and we propose that these changes are evidence for a reduction in salinity in the shallow marine setting of the study site. This inference is supported by changes in acritarch distribution, which suggest a change in palaeoenvironment from open marine conditions before the start of the Extinction Event to more near-shore conditions during and after the crisis. In a period of sea-level rise, such a reduction in salinity can only be explained by increased runoff. High amounts of both terrestrial and marine organic fragments in the first anoxic layers suggest that high runoff, increased nutrient availability, possibly in combination with soil erosion, are responsible for the development of anoxia in the basin. Enhanced runoff could result from changes in the hydrological cycle during the late Permian Extinction Event, which is a likely consequence of global warming. In addition, vegetation destruction and soil erosion may also have resulted in enhanced runoff. Salinity stratification could potentially explain the development of anoxia in other shallow marine sites. The input of fresh water and related changes in coastal salinity could also have implications for the interpretation of oxygen isotope records and sea water temperature reconstructions in some sites.
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Subsequent biotic crises delayed marine recovery following the late Permian mass Extinction Event in northern Italy.
PloS one, 2017Co-Authors: William J. Foster, Silvia Danise, Gregory D. Price, Richard J. TwitchettAbstract:The late Permian mass Extinction Event was the largest biotic crisis of the Phanerozoic and has the longest recovery interval of any Extinction Event. It has been hypothesised that subsequent carbon isotope perturbations during the Early Triassic are associated with biotic crises that impeded benthic recovery. We test this hypothesis by undertaking the highest-resolution study yet made of the rock and fossil records of the entire Werfen Formation, Italy. Here, we show that elevated Extinction rates were recorded not only in the Dienerian, as previously recognised, but also around the Smithian/Spathian boundary. Functional richness increases across the Smithian/Spathian boundary associated with elevated origination rates in the lower Spathian. The taxonomic and functional composition of benthic faunas only recorded two significant changes: (1) reduced heterogeneity in the Dienerian, and (2) and a faunal turnover across the Smithian/Spathian boundary. The elevated Extinctions and compositional shifts in the Dienerian and across the Smithian/Spathian boundary are associated with a negative and positive isotope excursion, respectively, which supports the hypothesis that subsequent biotic crises are associated with carbon isotope shifts. The Spathian fauna represents a more advanced ecological state, not recognised in the previous members of the Werfen Formation, with increased habitat differentiation, a shift in the dominant modes of life, appearance of stenohaline taxa and the occupation of the erect and infaunal tiers. In addition to subsequent biotic crises delaying the recovery, therefore, persistent environmental stress limited the ecological complexity of benthic recovery prior to the Spathian.
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The Late Triassic Mass Extinction Event
Topics in Geobiology, 2016Co-Authors: Colin G. Barras, Richard J. TwitchettAbstract:The Late Triassic Extinction Event is recognized as one of the five largest such Events of the Phanerozoic and is now generally believed to have been caused by global warming and concomitant environmental changes triggered by emplacement of the Central Atlantic Magmatic Province. The trace-fossil record, both terrestrial and marine, shows signs of change and perturbation through the Extinction interval and across the Triassic–Jurassic boundary. On land, there is a decline in nondinosaurian ichnotaxa coincident with a rise in large dinosaur ichnotaxa. In the marine realm, there is a temporary reduction in ichnodiversity and the size and depth of individual ichnotaxa, coincident with peak global warming, followed by an increase in size during Hettangian and Sinemurian. Although data are relatively sparse, the Triassic–Jurassic trace-fossil record suggests that major changes to the tracemaker communities on land and in the sea may have been driven by coeval climatic and environmental change.
Vivi Vajda - One of the best experts on this subject based on the ideXlab platform.
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early jurassic microbial mats a potential response to reduced biotic activity in the aftermath of the end triassic mass Extinction Event
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Olof Peterffy, Vivi Vajda, Michael CalnerAbstract:Wrinkle structures are microbially induced sedimentary structures (MISS) formed by cyanobacteria and are common in pre-Cambrian and Cambrian siltstones and sandstones but are otherwise rare in the Phanerozoic geological record. This paper reports the first discovery of Mesozoic wrinkle structures from Sweden. These are preserved in fine-grained and organic-rich heterolithic strata of the Lower Jurassic (Hettangian) Hoganas Formation in Skane, southern Sweden. The strata formed in a low-energy, shallow subtidal setting in the marginal parts of the Danish rift-basin. Palynological analyses of fine-grained sandstones hosting the wrinkle structures show that the local terrestrial environment probably consisted of a wetland hosting ferns, cypress and the extinct conifer family Cheirolepidaceae. Palynostratigraphy indicates a Hettangian age, still within the floral recovery phase following the end-Triassic mass Extinction Event. The finding of wrinkle structures is significant as the presence of microbial mats in the shallow subtidal zone, (in a deeper setting compared to where modern epibenthic microbial mats grow) suggests decreased benthic biodiversity and suppressed grazing in shallow marine environments in the early aftermath of the end-Triassic mass Extinction Event.
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Early Jurassic microbial mats—A potential response to reduced biotic activity in the aftermath of the end-Triassic mass Extinction Event
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Olof Peterffy, Michael Calner, Vivi VajdaAbstract:Wrinkle structures are microbially induced sedimentary structures (MISS) formed by cyanobacteria and are common in pre-Cambrian and Cambrian siltstones and sandstones but are otherwise rare in the Phanerozoic geological record. This paper reports the first discovery of Mesozoic wrinkle structures from Sweden. These are preserved in fine-grained and organic-rich heterolithic strata of the Lower Jurassic (Hettangian) Hoganas Formation in Skane, southern Sweden. The strata formed in a low-energy, shallow subtidal setting in the marginal parts of the Danish rift-basin. Palynological analyses of fine-grained sandstones hosting the wrinkle structures show that the local terrestrial environment probably consisted of a wetland hosting ferns, cypress and the extinct conifer family Cheirolepidaceae. Palynostratigraphy indicates a Hettangian age, still within the floral recovery phase following the end-Triassic mass Extinction Event. The finding of wrinkle structures is significant as the presence of microbial mats in the shallow subtidal zone, (in a deeper setting compared to where modern epibenthic microbial mats grow) suggests decreased benthic biodiversity and suppressed grazing in shallow marine environments in the early aftermath of the end-Triassic mass Extinction Event.
Paul B. Wignall - One of the best experts on this subject based on the ideXlab platform.
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the impact of the cretaceous paleogene k pg mass Extinction Event on the global sulfur cycle evidence from seymour island antarctica
Geochimica et Cosmochimica Acta, 2018Co-Authors: James D Witts, Paul B. Wignall, Robert J Newton, Benjamin J W Mills, Simon H Bottrell, Joanna L O Hall, Jane E Francis, Alistair J CrameAbstract:Abstract The Cretaceous–Paleogene (K–Pg) mass Extinction Event 66 million years ago led to large changes to the global carbon cycle, primarily via a decrease in primary or export productivity of the oceans. However, the effects of this Event and longer-term environmental changes during the Late Cretaceous on the global sulfur cycle are not well understood. We report new carbonate associated sulfate (CAS) sulfur isotope data derived from marine macrofossil shell material from a highly expanded high latitude Maastrichtian to Danian (69–65.5 Ma) succession located on Seymour Island, Antarctica. These data represent the highest resolution seawater sulfate record ever generated for this time interval, and are broadly in agreement with previous low-resolution estimates for the latest Cretaceous and Paleocene. A vigorous assessment of CAS preservation using sulfate oxygen, carbonate carbon and oxygen isotopes and trace element data, suggests factors affecting preservation of primary seawater CAS isotopes in ancient biogenic samples are complex, and not necessarily linked to the preservation of original carbonate mineralogy or chemistry. Primary data indicate a generally stable sulfur cycle in the early-mid Maastrichtian (69 Ma), with some fluctuations that could be related to increased pyrite burial during the ‘mid-Maastrichtian Event’. This is followed by an enigmatic +4‰ increase in δ34SCAS during the late Maastrichtian (68–66 Ma), culminating in a peak in values in the immediate aftermath of the K–Pg Extinction which may be related to temporary development of oceanic anoxia in the aftermath of the Chicxulub bolide impact. There is no evidence of the direct influence of Deccan volcanism on the seawater sulfate isotopic record during the late Maastrichtian, nor of a direct influence by the Chicxulub impact itself. During the early Paleocene (magnetochron C29R) a prominent negative excursion in seawater δ34S of 3–4‰ suggests that a global decline in organic carbon burial related to collapse in export productivity, also impacted the sulfur cycle via a significant drop in pyrite burial. Box modelling suggests that to achieve an excursion of this magnitude, pyrite burial must be reduced by >15%, with a possible role for a short term increase in global weathering rates. Recovery of the sulfur cycle to pre-Extinction values occurs at the same time (∼320 kyrs) as initial carbon cycle recovery globally. These recoveries are also contemporaneous with an initial increase in local alpha diversity of marine macrofossil faunas, suggesting biosphere-geosphere links during recovery from the mass Extinction. Modelling further indicates that concentrations of sulfate in the oceans must have been 2 mM, lower than previous estimates for the Late Cretaceous and Paleocene and an order of magnitude lower than today.
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Sub-marine palaeoenvironments during Emeishan flood basalt volcanism, SW China: implications for plume-lithosphere interaction during the Capitanian (‘end Guadalupian’) Extinction Event.
'Elsevier BV', 2016Co-Authors: Da Jerram, Paul B. Wignall, Widdowson M, Yd Sun, Lai X-l, Bond Dpg, Th TorsvikAbstract:Plume-induced lithospheric uplift and erosion are widely regarded as key features of large igneous province (LIP) emplacement, as is the coincidence of LIP eruption with major Extinction and oceanic anoxic Events (OAE). The Emeishan LIP, which erupted during the Capitanian (formally ‘end Guadalupian’) Extinction Event, has provided the most celebrated example where advocates argue that in excess of 500 m of axisymmetric uplift occurred over >30 000 km2 causing extensive radially-distributed erosion and alluvial fan formation. However, the recognition of submarine and phreatomagmatic-style volcanism, as well as syn-volcanic marine sediments interbedded in the eruptive succession, now requires further examination to this simple plume – uplift model. Here we present data from newly-discovered sections from the center of the putative uplifted area (around Lake Er Hai, SW Yunnan Province,) that provide a more complete history of the Emeishan volcanism. These reveal that platform carbonate deposition was terminated by rapid subsidence, followed quickly by the onset of volcanism. For at least the lower two thirds of the 4-5 km thick lava pile, eruptions continued at or below sea level, as testified by the presence of voluminous mafic volcaniclastic deposits, pillow lavas and development of syn-volcanic reefal limestones in the Emeishan inner zone. Only in the later stages of eruption did terrestrial lava flows become widely developed. This onset of volcanism in a submarine setting and the consequent violent, phreatomagmatic-style eruptions may have exacerbated the cooling effects of volcanism during the Capitanian. The late Permian of SW China at the time of the Emeishan was an extended area of thinned lithosphere with epeiric seas, which appear to have been sustained through the onset of LIP emplacement. Therefore, whilst there remains substantial geochemical support of a plume origin for Emeishan volcanism, LIP emplacement cannot be ubiquitously associated with regional pre-eruption uplift particularly where complex lithospheric structure exists above a plume
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submarine palaeoenvironments during emeishan flood basalt volcanism sw china implications for plume lithosphere interaction during the capitanian middle permian end guadalupian Extinction Event
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Paul B. Wignall, Da Jerram, Th Torsvik, Mike Widdowson, Yadong Sun, Xulong Lai, David P G BondAbstract:Abstract Plume-induced lithospheric uplift and erosion are widely regarded as key features of large igneous province (LIP) emplacement, as is the coincidence of LIP eruption with major Extinction and oceanic anoxic Events (OAE). The Emeishan LIP, which erupted during the Capitanian (previously termed ‘end Guadalupian’) Extinction Event, has provided the most widely discussed example of axisymmetric doming above a rising mantle ‘plume’; advocates have argued that in excess of 500 m of uplift occurred over > 30 000 km 2 causing extensive radially distributed erosion and alluvial fan formation. However, the recognition of submarine hydromagmatic and phreatomagmatic-style volcanism, as well as syn-volcanic marine sediments interbedded in the eruptive succession, now requires further examination to this simple plume–uplift model. Here we present data from newly discovered sections from the center of the putative uplifted area (around Lake Er Hai, SW Yunnan Province,) that provide a more complete history of the Emeishan volcanism. These reveal that platform carbonate deposition was terminated by rapid subsidence, followed quickly by the onset of volcanism. Importantly, these eruptions also coincide with widespread losses amongst fusulinacean foraminifera and calcareous algae. For at least the lower two thirds of the 4–5 km thick lava pile, eruptions continued at or below sea level, as testified by the presence of voluminous mafic volcaniclastic deposits, pillow lavas, and development of syn-volcanic reefal limestones in the Emeishan inner zone. Only in the later stages of eruption did terrestrial lava flows become widely developed. This onset of volcanism in a submarine setting and the consequent violent, phreatomagmatic-style eruptions would have had a profound effect on marine fauna and exacerbated any volcanically induced climate effects during the Capitanian. The late Permian of SW China at the time of the Emeishan was an extended area of thinned lithosphere with epeiric seas, which appear to have been sustained through the onset of LIP emplacement. Therefore, while there remains substantial geochemical support of a plume origin for Emeishan volcanism, LIP emplacement cannot be ubiquitously associated with regional pre-eruption uplift, particularly where complex lithospheric structure exists above a plume.
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An eastern Tethyan (Tibetan) record of the Early Jurassic (Toarcian) mass Extinction Event
Geobiology, 2006Co-Authors: Paul B. Wignall, Anthony Hallam, Emanuela Mattioli, Robert J Newton, Eoghan P. Reeves, Stephen F CrowleyAbstract:A record of the Early Jurassic mass Extinction Event is reported from eastern Tethyan (Tibetan) locations for the first time. In the Mount Everest region a thick Lower Jurassic carbonate formation, here named the Yungjia Formation, is developed within the predominantly clastic Triassic–Jurassic succession. Within the formation a sharp transition from peloidal packstones/grainstones to thin-bedded, pyritic micrite-shales interbeds records a sharp pulse of deepening and development of dysoxic bottom waters. Both the lithiotid bivalves and the lituolid foraminifera are important constituents of the lower Yungjia Formation but they disappear at this flooding surface or a short distance below it. This Extinction Event is comparable to that seen at the base of the Pliensbachian/Toarcian boundary in western Tethyan platform carbonates but the Tibetan Events occurred late in the Toarcian Stage as indicated by nannofossil biostratigraphy and C isotope chemostratigraphy. The Early Jurassic Extinction Event (and the associated spread of oxygen-poor waters) was therefore not synchronous throughout the Tethyan region.
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Carbon and nitrogen isotope disturbances and an end-Norian (Late Triassic) Extinction Event
Geology, 2002Co-Authors: Mark A. Sephton, Paul B. Wignall, Robert J Newton, Ken Amor, Ian A. Franchi, John-paul ZonneveldAbstract:Major perturbations of organic carbon and nitrogen isotope ratios from a Norian-Rhaetian (Late Triassic) boundary section in British Columbia coincide with an Extinction of the dominant, deep-water invertebrate fauna of the Late Triassic (monotids and most ammonoids). The carbon isotope excursion is attributed to the development of widespread oceanic stagnation that favored organic-rich shale deposition. The coincident nitrogen isotope excursion suggests that progressively more nitrate-limited productivity forced a change to nitrogen-fixing cyanobacteria populations as ocean stagnation created nutrient-starved conditions. The biotic crisis and geochemical Events of the Norian-Rhaetian boundary predate the latest Rhaetian (end-Triassic) mass Extinction. Thus, the Late Triassic interval was marked by more than one Extinction Event.
Attila Voros - One of the best experts on this subject based on the ideXlab platform.
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demise of the last two spire bearing brachiopod orders spiriferinida and athyridida at the toarcian early jurassic Extinction Event
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Attila Voros, Adam T Kocsis, Jozsef PalfyAbstract:Brachiopods were severely hit by several mass Extinctions which fundamentally shaped their long evolutionary history. After the devastating end-Permian Extinction, the fate of the four surviving orders differed significantly during the Triassic and Jurassic. Two orders, the rhynchonellids and terebratulids are extant today, whereas spiriferinids and athyridids, which possess spiral brachidia, suffered heavy losses at the end of the Triassic and became extinct in the Early Jurassic Toarcian Event. Although the doom of the spire-bearing orders has been thought to be related to physiological traits, Extinction selectivity across the end-Triassic and Toarcian Event has not been rigorously assessed previously, and the reasons for their demise at the later and lesser Toarcian Event, rather than at the earlier and greater end-Triassic crisis remained unexplored. Using primarily the Paleobiology Database, we constructed diversity curves, estimated taxonomic rates, and assessed the temporal changes in geographic distribution of the two spire-bearing and two other orders in the Triassic-Jurassic interval. After shared trends and similar origination rates in the post-Permian recovery leading to a Late Triassic diversity maximum, the end-Triassic Extinction was selective and preferentially eliminated the spire-bearers. In contrast to the rebound of rhynchonellids and terebratulids, spire-bearers failed to recover in the Early Jurassic, and their repeated selective Extinction at the Toarcian Event led to their final demise. The end-Triassic Event also terminated the worldwide geographic distribution of spire-bearers, confining them to the Western Tethys, whereas the other groups were able to re-establish their cosmopolitan distribution. The morphologically diverse spire-bearers represent specialized adaptation, which further increased their Extinction vulnerability compared to the other groups with conservative biconvex shell morphology. Another key difference is the physiological disadvantage of the fixed lophophore and passive feeding of spire-bearers, which became critical at times of increased environmental stress. The spire-bearing spiriferinids and athyridids were “dead clades walking” in the Early Jurassic and their disappearance in the Early Toarcian represents the last major, order-level Extinction Event for the brachiopods.
Stephen F Crowley - One of the best experts on this subject based on the ideXlab platform.
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An eastern Tethyan (Tibetan) record of the Early Jurassic (Toarcian) mass Extinction Event
Geobiology, 2006Co-Authors: Paul B. Wignall, Anthony Hallam, Emanuela Mattioli, Robert J Newton, Eoghan P. Reeves, Stephen F CrowleyAbstract:A record of the Early Jurassic mass Extinction Event is reported from eastern Tethyan (Tibetan) locations for the first time. In the Mount Everest region a thick Lower Jurassic carbonate formation, here named the Yungjia Formation, is developed within the predominantly clastic Triassic–Jurassic succession. Within the formation a sharp transition from peloidal packstones/grainstones to thin-bedded, pyritic micrite-shales interbeds records a sharp pulse of deepening and development of dysoxic bottom waters. Both the lithiotid bivalves and the lituolid foraminifera are important constituents of the lower Yungjia Formation but they disappear at this flooding surface or a short distance below it. This Extinction Event is comparable to that seen at the base of the Pliensbachian/Toarcian boundary in western Tethyan platform carbonates but the Tibetan Events occurred late in the Toarcian Stage as indicated by nannofossil biostratigraphy and C isotope chemostratigraphy. The Early Jurassic Extinction Event (and the associated spread of oxygen-poor waters) was therefore not synchronous throughout the Tethyan region.
