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The Great Unconformity is a widely distributed surface separating Precambrian rocks from overlying Phanerozoic sedimentary sequences. The causes and implications of this feature, and whether it represents a singular global event, are much debated. Here, we present new apatite (U-Th)/He (AHe) thermochronologic data from the central Canadian Shield that constrain when the Precambrian basement last cooled to near-surface temperatures, likely via exhumation, before deposition of overlying early Paleozoic sedimentary sequences that mark the Great Unconformity. AHe data from 11 samples (n = 57) across a broad region define a similar date-eU pattern, implying a common thermal history. Higher eU (>25 ppm) apatite form distinct flat profiles of reproducible dates at ∼510 ± 49 Ma (mean and 1σ standard deviation), while lower eU (<25 ppm) apatite define a positive date-eU trend with younger dates. The data patterns, geologic context, and thermal history modeling point toward >3 km of erosion across the entire ∼450,000 km2 study area between 650 and 440 Ma, followed by modest reheating during later burial. Plume activity associated with intracratonic basin formation or continental rifting/breakup may have caused this erosion event. The post-650 Ma timing of the last major sub-Great Unconformity exhumation phase in this region implies a late Great Unconformity that is younger than inferred elsewhere in North America. This suggests that this feature is likely the result of multiple temporally distinct erosion events with differing footprints and mechanisms. [ABSTRACT FROM AUTHOR]

Unbiased time series of diversity dynamics are vital for quantifying the grand history of life. Applications include identifying ancient mass extinctions and inferring both biotic and abiotic controls on diversification rates.We introduce divDyn, a new r package that facilitates the calculation of taxonomic richness, extinction and origination rates from time‐binned fossil data. State‐of‐the‐art counting protocols, and sampling standardization functions permit the reconstruction of biologically meaningful time series. Additional functions permit the partitioning of turnover rates by environmental affinity.Using divDyn, we display Phanerozoic‐scale diversity dynamics of marine invertebrates. With the help of the core function and standard subsampling options, we revisit the hypothesis of declining taxonomic rates over time, mass extinctions and equilibrial diversity dynamics and assess their methodological dependency. Our results suggest that rates declined only over the early Phanerozoic, only three mass extinctions stand out clearly, and evidence of equilibrial dynamics is dependent on the used methods.The modular and fast implementation of published methods ensures traceability, reproducibility and comparability of future studies. [ABSTRACT FROM AUTHOR]

Abstract The Permian-Triassic boundary (PTB) at ~252 Ma coincided with the largest mass extinction of the Phanerozoic. Previous research on diversity and abundance changes during this event has focused mainly on the terrestrial vertebrate and marine invertebrate records, with little attention to date given to the phytoplankton that form the base of the marine trophic web. Although the fossil record of Permian-Triassic phytoplankton is relatively poor owing to preservational factors, sufficient material is now available to evaluate secular changes in acritarch communities through the mass extinction interval. In this contribution, we evaluate diversity and abundance changes among 8 genera and 25 species of acritarchs, including large-spherical, small-spherical, long-spined, and short-spined forms ranging from the Upper Permian Clarkina yini to the Lower Triassic Isarcicella isarcica zones in eight sections representing different sedimentary facies of the South China Craton. Acritarchs declined sharply from the latest Permian (C. meishanensis Zone) to the earliest Triassic (I. staeschei Zone), with extinctions and abundance changes concentrated at two horizons, the first in the latest Permian C. meishanensis Zone (Bed 25 at Meishan D) and the second in the earliest Triassic I. staeschei Zone (Bed 28 at Meishan D), mirroring the pattern of mortality among marine invertebrates. Differences in the nature and intensity of these two extinction episodes (the second having a relatively larger effect on acritarch community composition) suggest that these events may have resulted from different types of environmental perturbations. Highlights • Eight genera and twenty-five species (belong to four forms) of acritarchs were record from eight sections in South China. • Two extinction events for the acritarchs across the Permian-Triassic transition. • The second event were more severe than the first one. This may result from the different causes for the two events. [ABSTRACT FROM AUTHOR]

The Phanerozoic evolution of the atmospheric CO2 level is controlled by the fluxes entering or leaving the exospheric system. In this contribution, we focus on the role played by the palaeogeographic configuration on the efficiency of the CO2 sink by continental silicate weathering, and on the impact of the magmatic degassing of CO2. We use the spatially resolved numerical model GEOCLIM to compute the response of the silicate weathering and atmospheric CO2 to continental drift for 22 time slices of the Phanerozoic. Regarding the CO2 released by the magmatic activity, we reconstruct several Phanerozoic histories of this flux, based on published indices. Again using the GEOCLIM model, we calculate the CO2 evolution for each degassing scenario. We show that the palaeogeographic setting is a main driver of the climate from 540 Ma to about the beginning of the Jurassic, with the noticeable exception of the Late Palaeozoic ice age. Regarding the role of the magmatic degassing, the various reconstructions do not converge towards a single signal, and thus introduce large uncertainties in the calculated CO2 level over time. Nevertheless, the continental dispersion, which prevails since the Jurassic, promotes CO2 consumption by weathering and forces atmospheric CO2 to stay low. Warm climates of the 'middle' Cretaceous and early Cenozoic require enhanced CO2 degassing by magmatic activity. [ABSTRACT FROM AUTHOR]

Abstract Glass ramps are coastal marine sedimentation regimes of siliceous biomineralization, and present alternatives to carbonate or siliciclastic deposition. Prominent chert deposits around the world record glass ramps from the Eocene, Jurassic, Permian, and Mississippian. These events ranged from regional to continental scale, and lasted from a couple million years to over ten million years. This review compares established cases of glass ramp deposition to clarify the bio-depositional features that distinguish glass ramps from other bedded or mounded biosiliceous deposits, and from carbonate ramp regimes. It also compares environmental contexts of glass ramp initiation and persistence. The primary sediment on these glass ramps is disaggregated spicules of siliceous sponges. The sponges formed meadows on level-bottom inner- and mid-ramp settings, and loose spicules were redistributed along the shelf. Carbonate bioclasts were generally present but diluted by the great abundance of spicules. Carbonate factories were either limited to small, dense patches; moved offshore; or re-established at a later time. Glass ramps initiated in a wide variety of climates and oceanographic settings but appeared to initially require partial protection from storm energy. The importance of marine silicic acid for such widespread biosiliceous factories is also estimated, showing that glass ramps required long-term adjustments in silica supply. Glass ramps lack modern analogues, but their ecology can be interpreted in light of stable state dynamics in other modern invertebrate communities. It is suggested that siliceous sponge meadows were an alternate stable state locally on carbonate ramps, occurring with greater frequency and carrying greater ecological significance than have been previously expected. This model warrants additional scrutiny on sponge meadows' possible stabilizing feedbacks and on the thresholds of state switching. Highlights • Glass ramps are shallow coastal depositional regimes dominated by siliceous sponges. • Sponge meadows were alternate stable states in contrast to carbonate factories. • Glass ramps were limited by silica flux and lack modern analogues. • Review of Phanerozoic cases reveals sponges' environmental flexibility and ecological dominance. [ABSTRACT FROM AUTHOR]

Competitive interactions have been invoked as major drivers of ecological and evolutionary trends through time, but the strength and frequency of such interactions is notoriously difficult to evaluate. Here we use inferences from species co-occurrence patterns to determine the frequency of the extreme endmember of competition--competitive exclusion--in modern and fossil benthic marine invertebrate assemblages. Within environmentally and temporally well-constrained species pools, we examine the percentage of all species pairs that co-occur less often than expected by chance (segregated pairs) as a maximum measure of competitive exclusion. Segregated pairs are very rare, with most assemblages containing none, and the frequency of segregated pairs shows no trend throughout the Phanerozoic. Contrary to the competition-relatedness hypothesis, we find little evidence that segregated pairs are more common among closely related species except potentially for congeneric pairs in deeper water settings where physical disturbance is relatively low. Although taphonomy, post-mortem transport, and time-averaging could obscure original co-occurrence patterns, analyses suggest that these factors are unlikely to fully explain the low frequency of segregated pairs. Our findings support the hypothesis that predation and disturbance keep marine benthic communities below carrying capacity and thus reduce the potential for competitive interactions to dictate community composition in shallow waters. [ABSTRACT FROM AUTHOR]

The ichnotaxonomy of the Phanerozoic trace fossil Teichichnus Seilacher, 1955 is revised and its ethology, producers and environmental affiliation are re-evaluated. Newly studied material reveals that Teichichnus is a sub-vertical spreite burrow with an arcuate shape, containing stacked laminae and a passively filled terminal causative burrow. Funnel-like extension of the terminal causative burrow and wall ornamentation may occur. High variation of burrow morphology is common and has resulted in the erection of 18 ichnospecies, of which only four are herein regarded as valid: Teichichnus rectus , T. zigzag , T. patens and T. duplex . These ichnospecies are characterised by their overall burrow shape, spreite morphology and, more subordinate, occurrence of branching and sculpture as recommended ichnotaxobases. Combined modes of feeding become evident, including deposit- and suspension-feeding, suggesting that Teichichnus is a dwelling trace rather than a feeding trace. Aside from the classical interpretation of polychaetes as producers, many features accord with an interpretation of dwelling echiurans and holothurians. This interpretation may apply for many post-Palaeozoic T. rectus and T. zigzag , whereas T. duplex and partly T. patens are likely produced by arthropods (i.e. trilobites and crustaceans). Bivalves are also considered for producing Teichichnus -like traces. Teichichnus is a marine trace fossil with predominance in shallow-marine environments. Low-diversity and high-density occurrences of Teichichnus characterise marginal-marine (paralic) environments with reduced salinity (i.e. brackish water) and oxygen (i.e. dysoxia), whereas in shoreface and offshore settings Teichichnus occurs in association with many other ichnotaxa and in low density. Deep-marine occurrences of Teichichnus are comparably sparse, and isolated records may indicate dysoxic bottom conditions. [ABSTRACT FROM AUTHOR]

The fossil record is a unique resource on the history of life, but it is well known to be incomplete. In a series of high-profile papers, a residual modelling technique has been applied to correct the raw palaeodiversity signal for this bias and incompleteness, and the claim is made that the processed time series are more accurate than the raw data. We apply empirical and simulation approaches to test for correlation and directionality of any relationships between rock and fossil data. The empirical data comprise samples of the global fossil record through the Phanerozoic, and we use simulations to assess whether randomly sampled subsets of modelled data can be improved by application of the residual modelling technique. Our results show that using formation counts as a sampling proxy to correct the fossil record via residual modelling is ill founded. The supposedly independent model of sampling is information-redundant with respect to the raw palaeodiversity data it seeks to correct, and so the outputs are generally likely to be further from the truth than the raw data. We recommend that students of palaeodiversity cease to use residual modelling estimates based on formation counts, and suggest that results from a substantial number of papers published in the past ten years require re-evaluation. [ABSTRACT FROM AUTHOR]

The 87Sr/86Sr isotope ratio has been widely used as a physical tool to date and correlate carbonate successions due to the long Sr residence time in comparison with the ocean mixing time. If this method works on oceanic successions, marginal basins may show different Sr isotope records in comparison with the coeval ocean one due to sea-level variations, continental run-off and restricted water exchanges. In this work, we present the 87Sr/86Sr isotope record of the upper Miocene carbonate ramp of the Lithothamnion Limestone (Majella Mountain, central Apennines), as an example of the onset of restricted water exchanges between a marginal basin and the ocean water masses. The overall latemost Tortonian-early Messinian Sr isotope record of the Lithothamnion Limestone fits below the global reference line. This deviation has been interpreted as due to the strong control that freshwater input and enhanced continental run-off, linked to the migration of the Apennine accretionary wedge and foredeep system, have had on the central Adriatic water chemistry. These results imply that an accurate oceanographic and geodynamic framework along with diagenetic overprint investigation has to be taken into consideration prior to apply SIS on carbonate successions on marginal basins, even when facies analyses indicate fully marine conditions. This seems to be the case for the upper Miocene Central Mediterranean carbonate successions, but may have more general validity and be extended to other recent or past marginal basins. [ABSTRACT FROM AUTHOR]

A global rise in oxygen levels has been proposed to coincide with the Ediacaran to Cambrian radiation of animals, yet the precise timing and nature of this change remains unresolved. One hypothesis is that the ocean/atmosphere system became temporarily well-oxygenated in the earliest Ediacaran, directly following the Marinoan Snowball Earth glaciation (~ 635 Ma). The evidence for oxygenation is based on large enrichments of redox-sensitive trace elements in black shale from South China presumably deposited under a euxinic water column. These enrichments meet or exceed the bulk concentrations of redox-sensitive trace elements found in Phanerozoic shale deposited under euxinic water columns. Here we test the early Ediacaran post-Snowball oxygenation hypothesis with new data from a high-resolution, multi-proxy geochemical and sedimentological study of three stratigraphic sections in the earliest Ediacaran Sheepbed Formation of the Mackenzie and Wernecke Mountains, NW Canada. Iron speciation data from all sections suggest that the local water column was dominantly ferruginous, with a notable exception of probable euxinic conditions recorded in part of one section. Redox-sensitive elements show no appreciable enrichments in the basal Sheepbed Formation, with maximum concentrations of molybdenum, vanadium, uranium and chromium only slightly above world average shale values. The lack of substantial elemental enrichments within the Sheepbed Formation is consistent with results from coeval ferruginous strata in Svalbard. The dominance of local ferruginous conditions in NW Canada cannot alone account for the muted redox-sensitive element enrichments as V, U, and Cr are thought to be enriched under these conditions, and samples deposited under euxinic conditions also lack Phanerozoic-style enrichments. These contrasting results from different localities highlight a need to further investigate the veracity of trace metal enrichments in all localities as representing global redox conditions as the results have important implications for the timing of oxygenation with respect to early animal evolution. [ABSTRACT FROM AUTHOR]

The escalation hypothesis posits that predation by increasingly powerful and metabolically active carnivores has been a major driver of metazoan evolution. We test a key tenet of this hypothesis by analyzing predatory drill holes in fossil marine shells, which provide a ~500-million-year record of individual predator-prey interactions. We show that drill-hole size is a robust predictor of body size among modern drilling predators and that drill-hole size (and thus inferred predator size and power) rose substantially from the Ordovician to the Quaternary period, whereas the size of drilled prey remained stable. Together, these trends indicate a directional increase in predator-prey size ratios. We hypothesize that increasing predator-prey size ratios reflect increases in prey abundance, prey nutrient content, and predation among predators. [ABSTRACT FROM AUTHOR]

Abstract: Fishes represent more than half of all living vertebrate species, but patterns of fish diversity remain little explored in the fossil record. A compendium of fossil occurrences from Great Britain was assembled in order to address a series of questions concerning the palaeontological record of fishes. There are broad similarities between British richness trajectories and those compiled from global data, including an initial peak in the mid-Palaeozoic (Devonian or Carboniferous, depending on the compilation), with a late Palaeozoic trough followed by a sharp rise in diversity in the Late Cretaceous and Paleogene. The British dataset is too small to reveal any significant differences in richness between time bins using subsampling, but a modelling approach based on sampling and geological proxies consistently shows lower-than-predicted richness in the Silurian–Devonian and higher-than-predicted richness in the Late Cretaceous and Eocene. This positive excursion is robust to the exclusion of data from the early Eocene London Clay Lagerstätte. Chondrichthyans (sharks, rays, and ratfishes) and osteichthyans (ray-finned and lobe-finned fishes) show contrasting relationships with geological and sampling proxies, possibly reflecting different taphonomic profiles or idiosyncratic variation in the relative proportion of freshwater and marine deposits over the British Phanerozoic. [Copyright &y& Elsevier]

Nautiloids were cosmopolitan species during the Mesozoic, being well-known from the worldwide realms. They could often be found togheter with the ammonites in the same beds, but the nautiloid fauna is much scarcer in the taxonomic diversification and frequency of records than the ammonites have been documented. Given this general background, on the one hand, and its diversity and particular records, on the other, the Timon Klippe could be regarded as important instance of Late Triassic nautiloids in the Eastern Carpathians. The present paper adds new coiled nautiloid records (Grypoceras sp. ?G. mesodicum HYATT, 1883), Syriongonautilus sp. (one of the latest occurrences of this genus), Syringoceras sp., Paranautilus simonyi (HAUER, 1849), and Proclydonautilus sp. (specimen with intermediate features between several Proclydonautilus species) to the previously-known fauna [ABSTRACT FROM AUTHOR]

The sediments atop the sequence of ophiolite usually contain Fe(-Mn-Si) exhalites, chemical sediments that are mainly composed of amorphous Fe-Mn oxy-hydroxides and chert/jasper. They were precipitated from hydrothermal fluids produced by deep leaching of basalt particularly during volcano activity or seafloor spreading. These hydrothermal Fe exhalites provide a good record for the depositional environment and the ocean environment as well. A well-preserved Phanerozoic Fe deposit, Motuosala Fe-Mn deposit, resulted from hydrothermal exhalation, was investigated for its trace element and Fe isotope geochemistry. The deposit is located in Xinjiang province, China and is hosted in a suit of Carboniferous volcano-sedimentary clastic rocks. The Fe deposit is mainly composed of massive hematite Fe oreand banded hematite-jasper ore. The hematite ore/band and jasper band were subjected to be analyzed. They are both composed mainly of Fe2O3 and SiO2, with very low contents of Al2O3 and TiO2 (>1%), indicating they were chemical precipitates with little detrital contamination. They both show slightly LREE depleted or near flat PAAS-normalised REE patterns, with positive Eu anomalies and Y anomolies, indicating that they were sourced from a mixture of high-temperature fluids and seawater. Compared to the hematite Fe ore/band, the jasper band shows higher EuSN/EuSN* but lower Y/Ho values. δ56Fe values for the hematite Fe ores are clustered around −0.3‰, similar to those for high-temperature fluids. The jasper samples show heavier Fe isotope compositions varying from −0.1‰ to 0.5‰, indicating that they were resulted from partial Fe precipitation. For all samples, δ56Fe values are related to Y/Ho and EuSN/EuSN* values. The results indicate that the hematite Fe ore and jasper were deposited in different environments. The jasper was deposited in a more anoxic condition with higher hydrothermal fluids/seawater ratio, probably when the hydrothermal activity was more intense; while the hematite Fe ore was deposited in a more oxic condition with lower hydrothermal fluids/seawater ratio, probably when the hydrothermal activity was weaker. [ABSTRACT FROM AUTHOR]