Global Extinction Event Research Articles

A temporal and causal link between ca. 1380 Ma large igneous provinces and black shales: Implications for the Mesoproterozoic time scale and paleoenvironment

Phanerozoic large igneous provinces (LIPs) have a significant influence on global climate changes and mass extinction events (MEEs). Most of the Global Boundary Stratotype Section and Points in the Phanerozoic international chronostratigraphic scale are coeval with LIPs and are marked in the sedimentary record by global-scale MEEs and/or by ocean anoxic events represented by black shales. However, due to limited knowledge on atmospheric oxygen concentrations, ocean redox conditions, and early fossils during the Meso-Neoproterozoic Eras prior to the Ediacaran period, little is known on the climate and environmental effects of LIPs during this period of a billion years, the so-called “Boring Billion” (1.8–0.8 Ga). Here we provide geochronological and geological evidence for a temporal and genetic link between the intense ca. 1380 Ma LIP activity (found on many crustal blocks) and coeval black shales in the Nuna (Columbia) supercontinent. We further propose that the ca. 1380 Ma LIPs and black shales widely distributed in the Nuna supercontinent represent a global-scale geological event and provide a robust natural marker for the Calymmian-Ectasian boundary at 1383 Ma. Further investigation of the temporal and genetic link between the LIPs and black shales at other times can contribute to understanding the variations in atmospheric oxygen concentrations and ocean redox conditions during the Boring Billion, during which virtually nothing of Earth’s climate and MEEs is known.

Salinity changes and anoxia resulting from enhanced run-off during the late Permian global warming and mass extinction event

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.

The impact of rapid heating by intrusion on the geochemistry and petrography of coals and organic-rich shales in the Illinois Basin

Igneous intrusion into organic-rich sedimentary rocks and coals has been suggested as a factor in the large-scale release of 13C–depleted thermogenic CH4, which may have led to global warming and mass extinction events in the geologic past. If a significant release of 13C–depleted thermogenic CH4 results from the intrusion of coal or organic-rich rocks, then it should produce 13C–enriched residual coal and dispersed organics in rocks adjacent to the intrusion due to the release of isotopically lighter CH4 gas. A review of the literature suggests only minor changes in the δ13Corg of coals adjacent to intrusions; however, a few studies have shown that changes in δ13Corg in intruded shales may be slightly more pronounced. The current study further evaluates the geochemical, isotopic, and petrographic changes that result from contact metamorphism and specifically compares the intrusion of coal to that of an organic-rich shale collected from the same general vicinity. Data for two different transects of intruded Pennsylvanian coal (Danville (No. 7) Coal) and an intruded organic-rich shale in the southern part of the Illinois Basin are presented.Both transects show similar increases in mean vitrinite reflectance (Rr); reflectance increases from background levels of 0.66% to 4.40% in the Danville (No. 7) Coal and 0.71% to 4.78% in the organic-rich shale. In addition, both transects show the formation of isotropic coke, and even development of fine circular mosaic anisotropic coke structure at and near the contact with the intrusion, along with the visual loss of liptinites at higher reflectances. In the Danville Coal transect, volatile matter, N, H, S, and O decrease whereas fixed carbon, C, and ash increase approaching the intrusion. The coal shows a marked decrease in remaining hydrocarbon potential (S2) and hydrogen index (HI) and an increase in Tmax (°C). Trends in most of the Rock-Eval parameters for the organic-rich shale are less clear due to variations in the amount of organic matter present, but a significant increase in thermal maturity (Tmax, 0C) is observed.No systematic changes in δ13C occur in the No. 7 Coal transect as the intrusion is approached, with δ13C varying between −25.4‰ and −24.8‰. The organic-rich shale transect shows a minor 1.2‰ enrichment in δ13C (from −25.2‰ to −24.0‰) within 2m of the intrusion. These isotopic shifts are not of a magnitude that would be expected if associated with a large-scale release of thermogenic CH4. In addition, no evidence exists in either transect for 13C–depleted condensed gas or pyrolytic carbon at the intrusion contact that could have moderated the isotopic signature. These data agree with those reported previously that indicate no clear isotopic evidence for large-scale CH4 generation due to rapid heating by igneous intrusion into coals or sedimentary rocks.

The New Hypothesis of the Origin to the Emeishan LIP: Because of the “Collisions Aggregation Effect” of a Meteorite Impact

Emeishan LIP is the only accredited continental flood basalts (CFB) by domestic and international currently in China, there were a lot of explanations about its origin and based only on the petrology, chemistry, most believe its cause of formation is a mantle plume, but just stay in the geochemical basis, there is no more convincing evidence. This article combined with the experiments and data demonstrate the truth and universality of the Collisions Aggregation theory, and think that there was a violent planetary collision occurred in the other side of the earth (the point of impact), the collision caused Collisions Aggregation effect and aroused a huge impact energy aggregated in the collisions aggregation point and earthquakes, volcanic activity and massive lava overflowed, the impact point and the collisions aggregation point were at the corresponding points of the ends of the earth through the geocenter, the impact and large-scale magmatism occurred almost simultaneously. The author believe that the Emeishan basalts may not be mantle plume caused, which broke lithosphere formed overflowing may not by the dome rising or crust thinning or rift valley of the dome head effect of the mantle plume, but may be form a rising channel caused by Collisions Aggregation effect on account of a violent asteroid impact at the P/T historical periods of the earth, and the thermal fluid overflow because of external disturbances. Meanwhile, this article also explore the dynamic mechanisms of the mantle plume and make the role of better ideas to explore the relationship between the distribution of the hot spots in the surface of the earth and the asteroid impact events and the global mass extinction events.

Mixed continental-marine biotas following the Permian-Triassic mass extinction in South and North China

Correlation between marine and continental Permian-Triassic (P-Tr) strata is crucial for full understanding of the nature of this global extinction event, but it has proved difficult to achieve. Here, we show that two sections in South China and North China record similar mixed continental-marine biota in the post-extinction stratigraphic interval, including conchostracans, plants, insects, marine bivalves and lingulid brachiopods. In addition, the continental P-Tr mass extinction was represented by a sharp decrease in the diversity and abundance of the Gigantopteris flora in South China, but eliminated the Palaeozoic-type conifer flora and herbivorous pareiasaurs in North China. These mixed continental-marine biota provide the biological evidence for stratigraphic correlation between marine and continental P-Tr transitional beds in South China and North China, especially the co-occurrence of the Pteria-Towapteria-Eumorphotis bivalve assemblage and the Euestheria gutta-bearing conchostracan fauna or Euestheria gutta-Magniestheria mangaliensis-Palaeolimnadiopsis vilujensis conchostracan assemblage. We propose that these specific marine bivalve and continental conchostracan assemblages could be considered as markers of P-Tr transitional beds in marine-continental siliciclastic settings.

Conodont diversity across the late Eifelian Kačák Episode of the southern Alpine realm (central Carnic Alps, Austria/Italy)

The polyphased Kačák Episode near the Eifelian-Givetian boundary (Middle Devonian), well documented globally, resembles other global biotic extinction events driven by climate change. High-resolution conodont biodiversity patterns from shallow marine, slope and pelagic bathymetric settings within the same basin from the Carnic Alps show that while conodonts experienced diversification during the latest Eifelian ensensis Biozone, assemblages suffered extinction during the early Givetian hemiansatus Biozone. Although a similar general pattern is observed in different bathymetric settings there is a changed taxonomic composition of conodont assemblages across the stage boundary. Based on microfacies analysis this change is contemporaneous with changes in palaeoenvironmental conditions in the earliest Givetian.

The small will inherit the Earth…

Extinction Events Understanding how communities and ecosystems recovered from the previous five global extinction events sheds light on how extinctions shape broad patterns of biodiversity. Sallan et al. looked across vertebrate species during and after the Devonian extinction (see the Perspective

A palaeobotanical perspective on the great end-Permian biotic crisis

Mass extinctions are crucial to understanding changes in biodiversity through time. However, it is still disputed whether extinction dynamics in the marine and terrestrial biotas followed comparable trajectories. For instance, while marine realms have suffered five strong depletions in diversity, the so-called ‘Big Five’ mass extinctions, only the end-Permian event appears to have also resulted in a major abrupt reduction in continental diversity. However, recent evidence based on the diversity dynamics of vegetation has suggested the presence of two major episodes of extinction in the terrestrial environments, at the end-Carboniferous and the end-Permian times. This apparent contradiction is addressed in the present study. Here, we show that while the end-Carboniferous plant extinction was focused on particular environments (e.g. tropical wetlands) and affected mainly the free-sporing plant diversity (i.e. lycopsids, ferns and progymnosperms), only the end-Permian mass extinction had devastating effects on vegetation on a global scale. If we take the biosphere as a whole, the results highlight that the end-Permian biotic crisis was the only genuine global mass extinction event, affecting widely both the marine and terrestrial environments.

Severe selenium depletion in the Phanerozoic oceans as a factor in three global mass extinction events

Selenium (Se) is one of the key trace elements required by all animal and most plant life, and Se deficiencies in the food chain cause pathologies or death. Here we show from new geochemical analyses of trace elements in Phanerozoic marine pyrite that sustained periods of severe Se depletion in the past oceans correlate closely with three major mass extinction events, at the end of the Ordovician, Devonian and Triassic periods. These represent periods of Se depletion >1.5–2 orders of magnitude lower than current ocean abundances, being within the range to cause severe pathological damage in extant Se-reliant organisms. Se depletion may have been one of several factors in these complex extinction scenarios. Recovery from the depletion/extinction events is likely part of a natural marine cycle, although rapid rises in global oxygen from sudden major increases in marine productivity and plant biomass after each extinction event may also have played a crucial role.

Upper Kellwasser carbon isotope excursion pre-dates the F–F boundary in the Upper Devonian Lennard Shelf carbonate system, Canning Basin, Western Australia

Abstract Here we report four high-resolution carbon isotope records in addition to trace element data for the Frasnian–Famennian (F–F) boundary interval in the Lennard Shelf carbonate system of the Canning Basin, Western Australia. This region lacks the characteristic black shale horizons associated with the global Late Devonian Kellwasser extinction events, yet still exhibits a trend in carbon isotope character similar to what has been reported from elsewhere in the world (two positive δ13C excursions with ~ 3–4‰ amplitudes). Enrichments in select trace element ratios suggest that both excursions are related to periods of oxygen deprivation and perhaps increased biological productivity. Given the continuous and stratigraphically expanded nature of Lennard Shelf sections, together with high-density sampling constrained by both conodont biostratigraphy and magnetostratigraphy, we observe that the Upper Kellwasser isotope excursion (maximum δ13C values) and associated trace element enrichments occur distinctly lower than the F–F boundary level. These results have implications for the paleoenvironmental conditions leading up to the Late Devonian Mass Extinction in terms of ocean chemistry and circulation patterns. This data set allows for a rare, detailed look at the temporal relationship between the Kellwasser events and the F–F boundary and constrains the pattern of carbon isotope perturbations at the intra-zonal scale.

Changes of palaeoenvironmental conditions recorded in Late Devonian reef systems from the Canning Basin, Western Australia: A biomarker and stable isotope approach

Although the Late Devonian extinctions were amongst the largest mass extinction events in the Phanerozoic, the causes, nature and timing of these events remain poorly restrained. In addition to the most pronounced biodiversity loss at the Frasnian–Famennian (F–F) boundary and the end Famennian, there were also less extensively studied extinction pulses in the Middle to Late Givetian and the Frasnian. Here we used a combination of palynological, elemental, molecular and stable isotope analyses to investigate a sedimentary record of reef-systems from this time period in the Canning Basin, Western Australia.The acquired data generally showed distinct variations between sediments from (i) the time around the Givetian–Frasnian (G–F) boundary and (ii) later in the Frasnian and indicated a distinct interval of biotic stress, particularly for reef-builders, in the older sediments. Alterations of pristane/phytane ratios, gammacerane indices, Chlorobi biomarkers, δDkerogen and chroman ratios describe the change from a restricted marine palaeoenvironment with an anoxic/euxinic hypolimnion towards a presumably open marine setting with a vertically mixed oxic to suboxic water column. Simultaneous excursions in δ13C profiles of carbonates, organic matter (OM) and hydrocarbons in the older sediments reflect the stratification-induced enhancement of OM-recycling by sulfate reducing bacteria. Alterations in sterane distributions and elevated abundances of methyltrimethyltridecylchromans (MTTCs) and perylene indicate an increased terrigenous nutrient input via riverine influx, which would have promoted stratification, phytoplankton blooms and the development of lower water column anoxia.The detected palaeoenvironmental conditions around the G–F boundary may reflect a local or global extinction event. Our data furthermore suggest a contribution of the higher plant-expansion and photic zone euxinia to the Late Devonian extinctions, consistent with previous hypotheses. Furthermore, this work might contribute to the understanding of variations in Devonian reef margin and platform-top architecture, relevant for petroleum exploration and development in the global Devonian hydrocarbon resources.

The paleoecology, habitats, and stratigraphic range of the enigmatic cretaceous brachiopod peregrinella.

Modern and Cenozoic deep-sea hydrothermal-vent and methane-seep communities are dominated by large tubeworms, bivalves and gastropods. In contrast, many Early Cretaceous seep communities were dominated by the largest Mesozoic rhynchonellid brachiopod, the dimerelloid Peregrinella, the paleoecologic and evolutionary traits of which are still poorly understood. We investigated the nature of Peregrinella based on 11 occurrences world wide and a literature survey. All in situ occurrences of Peregrinella were confirmed as methane-seep deposits, supporting the view that Peregrinella lived exclusively at methane seeps. Strontium isotope stratigraphy indicates that Peregrinella originated in the late Berriasian and disappeared after the early Hauterivian, giving it a geologic range of ca. 9.0 (+1.45/–0.85) million years. This range is similar to that of rhynchonellid brachiopod genera in general, and in this respect Peregrinella differs from seep-inhabiting mollusks, which have, on average, longer geologic ranges than marine mollusks in general. Furthermore, we found that (1) Peregrinella grew to larger sizes at passive continental margins than at active margins; (2) it grew to larger sizes at sites with diffusive seepage than at sites with advective fluid flow; (3) despite its commonly huge numerical abundance, its presence had no discernible impact on the diversity of other taxa at seep sites, including infaunal chemosymbiotic bivalves; and (4) neither its appearance nor its extinction coincides with those of other seep-restricted taxa or with global extinction events during the late Mesozoic. A preference of Peregrinella for diffusive seepage is inferred from the larger average sizes of Peregrinella at sites with more microcrystalline carbonate (micrite) and less seep cements. Because other seep-inhabiting brachiopods occur at sites where such cements are very abundant, we speculate that the various vent- and seep-inhabiting dimerelloid brachiopods since Devonian time may have adapted to these environments in more than one way.

Geochemical evidence for euxinia during the Late Devonian extinction events in the Michigan Basin (U.S.A.)

Several mass extinction events occurred in the Late Devonian, but the trigger for these events remains elusive. In this study, geochemical evidence in the Late Devonian Antrim Shale, Michigan Basin, U.S.A., records episodic euxinia contemporaneous with these extinction events. Diagnostic changes in iron proxy data and elevated trace metal enrichments correspond to the Kellwasser Crisis. In this study, carbon, sulfur, iron and trace metal geochemistry preserved in the Antrim Formation validates the establishment and expansion of euxinic conditions associated with the Kellwasser Crisis and the Frasnian–Famennian boundary. The strength of the sequential extraction iron mineral data presented here, in concert with trace metal and sulfur isotope proxies, provides definitive signatures of euxinia when other data may be more ambiguous in regard to paleoredox conditions. During the time of the Frasnian–Famennian boundary extensive sulfide oxidation at the chemocline, the result of Fe-limiting conditions within the basin, provides an alternative explanation for the oceanic decline in δ34SSO4 during, and following, the Frasnian–Famennian event. Our geochemical evidence, indicating the presence of anoxia in the Michigan Basin, is consistent with data from other globally distributed locations. Euxinia should be considered a key driver for these global extinction events, and possibly others such as the Hangenberg Event in the Late Devonian.

Critical Mutation Rate Has an Exponential Dependence on Population Size in Haploid and Diploid Populations

Understanding the effect of population size on the key parameters of evolution is particularly important for populations nearing extinction. There are evolutionary pressures to evolve sequences that are both fit and robust. At high mutation rates, individuals with greater mutational robustness can outcompete those with higher fitness. This is survival-of-the-flattest, and has been observed in digital organisms, theoretically, in simulated RNA evolution, and in RNA viruses. We introduce an algorithmic method capable of determining the relationship between population size, the critical mutation rate at which individuals with greater robustness to mutation are favoured over individuals with greater fitness, and the error threshold. Verification for this method is provided against analytical models for the error threshold. We show that the critical mutation rate for increasing haploid population sizes can be approximated by an exponential function, with much lower mutation rates tolerated by small populations. This is in contrast to previous studies which identified that critical mutation rate was independent of population size. The algorithm is extended to diploid populations in a system modelled on the biological process of meiosis. The results confirm that the relationship remains exponential, but show that both the critical mutation rate and error threshold are lower for diploids, rather than higher as might have been expected. Analyzing the transition from critical mutation rate to error threshold provides an improved definition of critical mutation rate. Natural populations with their numbers in decline can be expected to lose genetic material in line with the exponential model, accelerating and potentially irreversibly advancing their decline, and this could potentially affect extinction, recovery and population management strategy. The effect of population size is particularly strong in small populations with 100 individuals or less; the exponential model has significant potential in aiding population management to prevent local (and global) extinction events.

40Ar/39Ar ages of flood basalt provinces in Russia and China and their possible link to global faunal extinction events: A cautionary tale regarding alteration and loss of 40Ar∗

The hypothesis that the Permo–Triassic boundary (PTB) mass extinctions were caused by flood basalt volcanism in Russia (Siberian Traps) and/or China (the Emeishan Traps) is investigated from the point of view of time of occurrence (40Ar/39Ar ages). Numerous published ages in the literature are rejected as good estimates of the time of crystallization. The filters applied in this respect are (a) statistical reliability of plateau/isochron sections of stepheating data and (b) the alteration state of the material that was dated. Alteration appears to be ubiquitous, unsurprising since most of the material dated was used without acid leaching – a procedure that is effective in yielding fresh(er) samples. Of ∼70 ages in the literature for the main pulse of Siberian Trap volcanism, less than ten prove to be reliable ages. Similar techniques applied to 40Ar/39Ar for the Emeishan Traps, leaves only a single reliable age for the magmatic episode. These ages are compared to both published and new 40Ar/39Ar ages for the PTB as based on analysis of minerals from critical ash beds in China. There is good overlap in the ages (PTB – 250.0±0.1Ma, Siberian Trap lavas – 250.1±0.4Ma), lending credence to a genetic link between the formation of the Siberian Traps and the faunal extinction event at the PTB. A similar link for the formation of the Viluy Traps (Russia) and the Late Devonian extinction event is investigated; only a single reliable 40Ar/39Ar age is available for the Viluy Traps, and falls close to the interpolated age for the Frasnian–Fammenian boundary. The use of the unspiked K–Ar technique to yield accurate ages for such (altered) samples is questioned.A review of U–Pb data pertinent to these problems suggests a close temporal link between the formation of the Siberian Traps and the PTB. Comparison of U–Pb and 40Ar/39Ar ages for the PTB, raises questions about the accuracy of high precision sanidine ages, possibly resulting from very slow leakage of 40Ar∗ from this mineral.

Global versus local extinction in a network model of plant–pollinator communities

The loss of a species from an ecological community can trigger a cascade of additional extinctions; the complex interactions that comprise ecological communities make the dynamics and impacts of such a cascade challenging to predict. Previous studies have typically considered global extinctions, where a species cannot re-enter a community once it is lost. However, in some cases a species only becomes locally extinct, and may be able to reinvade from surrounding communities. Here, we use a dynamic, Boolean network model of plant–pollinator community assembly to analyze the differences between global and local extinction events in mutualistic communities. As expected, we find that compared to global extinctions, communities respond to local extinctions with lower biodiversity loss, and less variation in topological network properties. We demonstrate that in the face of global extinctions, larger communities suffer greater biodiversity loss than smaller communities when similar proportions of species are lost. Conversely, smaller communities suffer greater loss in the face of local extinctions. We show that targeting species with the most interacting partners causes more biodiversity loss than random extinctions in the case of global, but not local, extinctions. These results extend our understanding of how mutualistic communities respond to species loss, with implications for community management and conservation efforts.

Exceptional preservation of microbial lipids in Paleozoic to Mesoproterozoic sediments

Exceptional preservation of microbial lipids in Paleozoic to Mesoproterozoic sediments

Molecular carbon isotope variations in core samples taken at the Permian–Triassic boundary layers in southern China

Stable carbon isotope composition (δ13C) of carbonate sediments and the molecular (biomarker) characteristics of a continuous Permian–Triassic (PT) layer in southern China were studied to obtain geochemical signals of global change at the Permian–Triassic boundary (PTB). Carbonate carbon isotope values shifted toward positive before the end of the Permian period and then shifted negative above the PTB into the Triassic period. Molecular carbon isotope values of biomarkers followed the same trend at and below the PTB and remained negative in the Triassic layer. These biomarkers were acyclic isoprenoids, ranging from C15 to C40, steranes (C27 dominates) and terpenoids that were all significantly more abundant in samples from the Permian layer than those from the Triassic layer. The Triassic layer was distinguished by the dominance of higher molecular weight (waxy) n-alkanes. Stable carbon isotope values of individual components, including n-alkanes and acyclic isoprenoids such as phytane, isop-C25, and squalane, are depleted in δ13C by up to 8–10‰ in the Triassic samples as compared to the Permian. Measured molecular and isotopic variations of organic matter in the PT layers support the generally accepted view of Permian oceanic stagnation followed by a massive upwelling of toxic deep waters at the PTB. A series of large-scale (global) outgassing events may be associated with the carbon isotope shift we measured. This is also consistent with the lithological evidence we observed of white thin-clay layers in this region. Our findings, in context with a generally accepted stagnant Permian ocean, followed by massive upwelling of toxic deep waters might be the major causes of the largest global mass extinction event that occurred at the Permian–Triassic boundary.

Influence of global, regional, and local factors on the genesis of the Jurassic manganese ore formation in the Transdanubian Range, Hungary

Economically important black shale-hosted manganese carbonate deposits occur in certain parts of the Transdanubian Range in Hungary. These ore deposits were formed in a short interval coinciding with the Early Toarcian global anoxic and mass extinction event that was associated with drastic perturbations of the oceanographic conditions. During the Early Jurassic the Transdanubian Range Unit was located between two ocean basins. Simultaneous opening of these two basins created an extensional regime resulting in a complex topography with tectonically-controlled small scale basins above an attenuated continental lithosphere. Sluggish circulation led to the development of layered water masses in certain parts of these basins, with oxygenated upper and oxygen-depleted lower reservoirs. This paleogeographic and paleoenvironmental setting favoured the microbially-mediated accumulation of manganese and iron.

Early Jurassic gastropods from England

Abstract: Twenty-five gastropod taxa are reported from the Early Jurassic (Hettangian to Toarcian) of England. Of these, 14 are identified to species level, and the remaining 11 are treated in open nomenclature. One genus (Lensataphrus) and six species are introduced as new. The new species are Lensataphrus tatei, Lensataphrus tenuis, Tricarilda toddi, Cylindrobullina dorsetensis, Cylindrobullina ventricosa and Consobrinella greeni. The following new combinations are introduced: Cassianopsis hebertana (d’Orbigny, 1852) for Neritopsis hebertana; Cryptaulax abscisum (Terquem and Piette, 1868) for Cerithium abscisum; and Cylindrobullina avena (Terquem, 1855) for Striactaeonina avena. Most of the genera and some of the species are also known from Central Europe (Germany and France). Typical vetigastropod genera that are present in England and Central Europe are Colpomphalus, Costataphrus, Ooliticia, Eucycloscala and Eucycloidea. The caenogastropod genera Levipleura and Cryptaulax are present in both regions, as are the heterobranchs Tricarilda and Cylindrobullina. The heterobranch genus Consobrinella is reported from England for the first time. Gastropods seem to follow the diversity trends of other marine invertebrates during the Early Jurassic. They diversify until the Late Pliensbachian but decrease sharply in number around the Pliensbachian–Toarcian boundary. This may reflect both regional anoxia and a global mass extinction event in the Early Toarcian.