The Suborder Cheirurina is a diverse trilobite clade, ranging from the latest Cambrian to the Devonian. The Ordovician paleobiogeography of the group is explored based on the distribution of genera. ...Major tectonostratigraphic units and Ordovician ages (Tremadocian, Floian, Dapingian, Darriwilian, Sandbian and Katian) were recorded for each genus. Cluster analysis (agglomerative hierarchical clustering) and non-metric multidimensional scaling (NMDS) were performed independently for each Ordovician age. The results characterize the Ordovician distribution of Cheirurina as two main general patterns. First, there was a marked decrease in endemicity through the Ordovician. Second, latitude seems to play a significant role in the distribution of Cheirurina, at both genus and family levels. Pliomerids and encrinurids occur overwhelmingly at low latitudes. The two main exceptions are Placoparia (Pliomeridae) and Dindymene (Encrinuridae), which are distributed in high latitude terranes. Within Cheiruridae, members of Eccoptochilinae are typical of high latitude Gondwana. Conversely, acanthoparyphines, cheirurines, deiphonines, heliomerines and sphaerexochines are mainly distributed in low or intermediate latitudes.
•The distribution of the largest Ordovician trilobite clade is explored in this study.•Four major faunal provinces are recognized throughout the Ordovician.•The distribution of the group is highly influenced by the latitude.•A reduction of provincialism is observed through the Ordovician.•During the Katian the group showed a more cosmopolitan distribution than before.
During the Middle Ordovician, the Great Ordovician Biodiversification Event (GOBE) saw an accelerated diversification pulse in the marine metazoan richness, which has been linked to the oceanic and ...climatic changes. Here we have examined a deep-water slope succession, Xijinhe section, in Lower Yangtze region by integrating sedimentological and geochemical methods. This study highlights that the climatic and oceanic destabilization might have substantially impacted the marine biodiversity during the Middle Ordovician in South China. Three phases are identified based on lithological and geochemical variations. During Phase I across the Early–Middle Ordovician transition (Floian–Dapingian), the TOC and abundances of redox sensitive elements (RSE) are relatively depleted, suggesting a suboxic-oxic environment in the slope area of Yangtze Sea. The continental chemical weathering intensity transits from stable to unstable in Phase I indicated by CIA (chemical index of alteration) that gradually fluctuate to lower values, potentially caused by the secular cooling. The slowly ameliorating climate and redox conditions advanced the biodiversification across the Early–Middle Ordovician transition. During the Phase II in the Darriwilian, the continental chemical weathering intensity continues to decrease and the concentrations of RSE start to rise. The values of Mn(%)*Co(ppm) become consistently lower than 0.4, and the bio-limited elements such as P, Ba, and Ni are substantially enriched correspondingly. This phenomenon implicates that a secular cooling climate would have resulted in oceanic destabilization by improving upwelling of deeper anoxic/euxinic and eutrophic water into epicontinental sea, potentially causing a deceleration in the biodiversification during the Darriwilian in South China. The Phase III across the Middle–Late Ordovician transition, witnesses the continuous decrease of CIA values and highest abundances of TOC and RSE though some minor fluctuations, indicating a possibly even more drastic oceanic destabilization relative to Phase II. Deeper anoxic/euxinic water continuously intruded and shoaled into the shelf area during the Phase III due to the enhanced upwelling. Consequently, the habitat of marine organisms in shallow water was contracted, and becoming harsher. Additionally, bio-limited elements such as P were released from anoxic sediments and recycle into the seawater during the Middle Ordovician, boosting primary productivity level and may further deplete oxygen in seawater. This unstable oceanic state during the Middle Ordovician, particularly Darriwilian, represented by high nutrients content in epi-continental sea and expanding anoxic/euxinic water, could be attributable for the deceleration of biodiversification in South China and potentially the spatially variable paces of biodiversification in different paleo-continents during the main phase of the GOBE.
•Sedimentology and geochemistry of Ordovician shales in South China spanning GOBE were reported.•Three phases of climatic and redox evolutions during Early-Middle Ordovician in South China.•The destabilization of ocean current and redox structure caused the contraction of habitat in South China.
A promising quantitative method is the use of fluctuations of seawater silicon isotope compositions (δ30Siseawater) to estimate the silicon cycle and silicon isotopic budgets of both the marine and ...terrestrial systems in a pre-diatom ocean. However, a thorough global calibration of Phanerozoic δ30Siseawater, which is linked to continental tectonics and silicate weathering, has not been established. The silicon and oxygen isotope compositions of Darriwilian cherts (δ30Sichert and δ18Ochert, respectively) have considerable potential as proxies for δ30Siseawater and sea surface temperatures (SSTs), which can expand our understanding of the influence of continental tectonics and temperature changes on the Great Ordovician Biodiversification Event (GOBE). In this study, primary depositional and early diagenetic cherts were sampled from bedded chert, lump-shaped chert, nodular chert, and banded chert from five Darriwilian outcrops in the Kalpin and Yijianfang areas of the Tarim Basin in China. The preservation conditions of these cherts were assessed based on petrographic criteria such as the absence of calcite veins and fractures under macroscopic observation and the absence of aggregate chalcedony (CHA), microquartz (MQ), and cryptocrystalline quartz (MQC) using optical microscopy and scanning electronic microscopy (SEM). The SSTs and δ30Siseawater of Darriwilian seawater were reconstructed using the δ18Ochert and δ30Sichert of well-preserved cherts. Our results show that the SSTs were approximately 32 ± 5 °C in the early Darriwilian and approximately 30 ± 5 °C in the late Darriwilian. The δ30Siseawater was approximately +3.1‰ in the Kalpin and Yijianfang areas during the Darriwilian Stage. This is the first estimation of δ30Siseawater in the Darriwilian Stage, which provides a parameter for the global calibration of the δ30Siseawater of the pre-diatom ocean in the Phanerozoic Eon and validates the hypothesis that the pre-diatom ocean waters had higher δ30Si values than modern seawater.
•A method of calculating the initial pore water Si isotope compositions was presented.•The sea surface temperatures of Darriwilian seawater were calculated.•The Si isotope compositions of Darriwilian seawater were estimated.
The early Paleozoic sediments document two major biological events: the Great Ordovician Biodiversification Event (GOBE) and Late Ordovician mass extinction (LOME). Many investigations have focused ...on taxonomic richness patterns during these major diversification and extinction events, providing insights into their timings and potential causes. However, the coarse temporal resolutions used in previous investigations hampered their ability to document fine-scale patterns. To address these issues, we employed CONOP analysis to data collected from a large suite of southern Chinese stratigraphic successions to construct a high-resolution (temporal resolution of ~21.0 Kyr) regional chronostratigraphy and document species richness dynamics during the middle–late Cambrian to early Silurian interval. Our results showed that the GOBE began in the early Tremadocian and ended at the Dapingian–Darriwilian boundary and consisted of two major radiation phases. The main pulse of GOBE, which lasted from the late Floian to the earliest Darriwilian, exhibited a species richness increase with elevated origination and extinction rates. Major marine groups showed no significant diachroneity during the GOBE, with most presenting richness peaks in this event's main pulse of the GOBE. Plankton demonstrated a significant diversification from the late Cambrian to the GOBE climax and subsequently dominated the marine realm in South China. Marine life experienced two extinction events in the Late Ordovician, the Katian extinction and Hirnantian extinction, which resulted in a regional species loss of ~67%.
•38,122 local records of 2986 species to construct the early Paleozoic biodiversity history•The biodiversity curve achieves a resolution of ~21.0 Kyr by using CONOP and supercomputer.•GOBE showed a two-phased exponential richness increase of ~9.9 times in ~16.6 Myr.•Two extinctions in the Late Ordovician eliminated ~67% marine species.
We present new high-resolution carbonate carbon isotope data (δ13Ccarb) from four sections in the Yangtze Platform, South China, ranging in age from Tremadocian to early Katian. The data have five ...distinct characteristics: 1) A prominent δ13Ccarb increase from −2.79‰ to 0.13‰ at the base of the Ordovician within the Tremadocian Cordylodus angulatus-Rossodus manitouensis Zone. 2) A positive δ13Ccarb excursion from −2.56‰ to 0.58‰ in the Paltodus deltifer Zone during the late Tremadocian. 3) A gradual increase in δ13Ccarb from −1.16‰ at the top of the Oepikodus communis Zone to a peak of ~0.74‰ in the Baltoniodus triangularis Zone at the Floian-Dapingian boundary. 4) A moderate rise in δ13Ccarb from 0.59‰ to 1.24‰ in the middle Darriwilian Dzikodus tablepointensis Zone. 5) A distinct positive δ13Ccarb excursion from 0.86‰ to 2.32‰ at the base of the Amorphognathus superbus-Hamarodus europaeus Zone during the early Katian. These excursions can be correlated with C-isotopic trends identified in age-equivalent successions in South China, Argentine Precordillera, North America, and Central Sweden, demonstrating their potential for global correlations and providing a composite, high-resolution chemostratigraphic framework for sedimentary records of the Lower-Upper Ordovician in South China. Besides, our data demonstrate a temporal coincidence between the long-term rise in δ13Ccarb and the Great Ordovician Biodiversification Event, suggesting that enhanced organic matter burial and accompanied climatic cooling and oxygenation may have played an important role in promoting the increases in biodiversity during the Ordovician.
•High-resolution δ13C stratigraphy for nearly the entire Ordovician from South China.•Five distinct positive δ13C excursions that can be correlated globally are revealed.•Data suggest climatic cooling and oxygenation may have facilitated the GOBE.
Two major, extended diversifications punctuated the evolution of marine life during the Early Palaeozoic. The interregnum, however, between the Cambrian Explosion and the Great Ordovician ...Biodiversification Event, is exemplified by the Furongian Gap when there was a marked drop in biodiversity. It is unclear whether the gap is apparent, due to sampling failure or lack of rock, or real — associated with unique and fluctuating environments, a distinctive palaeogeography and extreme climates during the late Cambrian. Indications suggest that there has been little attention paid to this interval compared with those below and above, while some of the classical areas for Cambrian research, such as Bohemia, have poor coverage through the Furongian. Moreover, based on information available in databases and the literature, together with the ghost ranges of many higher taxa through the Furongian, data suggest that biodiversity in this stage has been significantly underestimated. Emphasis, to date, has been placed on widespread, deeper-water dark shale facies of the interval, with generally low diversity faunas, whereas shallow-water communities have often been neglected.
Organisms with external phosphatic shells diversified and became abundant at the beginning of the Early Paleozoic but gradually declined and were rare by its end. The decreasing availability of ...phosphorus in oceans is thought to be responsible for this evolutionary trend. Responses of organisms to changes in the phosphorus cycle can be traced to the late Neoproterozoic, and likely had a significant role in the Cambrian explosion, the Great Ordovician Biodiversification Event (GOBE), and the Devonian nekton revolution. Effective use of phosphorus by vertebrates during the Devonian nekton revolution caused the phosphorus pool to shift from benthic external shells to the skeletons of pelagic vertebrates, and moved the marine faunas toward the dominance patterns and ecological structure of the Modern Evolutionary Fauna.
Phosphorus had a key role in the Early Paleozoic radiation events.The decline of organisms with external phosphatic shells was caused by an increasing inaccessibility of phosphorus during the Early Paleozoic.The dominant phosphorus pool shifted from benthic groups to pelagic vertebrates during the Devonian.Recycling of phosphorus in the marine environment substantially moved phosphorous into the water column.The Devonian phosphorus pool pattern is one of the key factors controlling marine diversity and ecological patterns up to the present time.
Computational Fluid Dynamic simulations (CFD) show that the Ordovician trilobite Microparia speciosa had a high stability in the horizontal plane (parallel to the flow currents), suggesting that it ...could be very stable in the water column when it was enrolled, for hovering or to get stabilization when the current disturbed the swimming. This indicates a new way to use enrolment in trilobites during the Ordovician radiation, not only for protection against predators or the environment but also as a hydrodynamic tool to maintain stability within the water column. Metachronal propulsion was likely used by Microparia speciosa for swimming and, in a high-viscosity scenario, also for feeding. This is suggesting given that the vortex below Microparia speciosa takes particles directly to the mouth, and taken more particles when the trilobite is orientated in the way of the current (and no countercurrent). This suggests a passive feeding strategy for better energy saving when the trilobite is hovering in water column.
•Trilobites occupied the pelagic habitats during the Ordovician.•Metachronal system is a suitable mechanics for swimming in Microparia.•CFD suggests that enrolment could be used for hovering and/or stabilization.•Feeding currents could be used for feeding in the water column by Microparia.•Gradual adoption of nektonization in the the Palaeozoic seas.
We employ modified tip-dating methods to date divergence times within the Strophomenoidea, one of the most abundant and species-rich brachiopod clades to radiate during the Great Ordovician ...Biodiversification Event (GOBE), to determine if significant environmental changes at this time correlate with the diversification of the clade. Models using origination, extinction and sampling rates to estimate prior probabilities of divergence times strongly support both high rates of anatomical change per million years and rapid divergences shortly before the clade first appears in the fossil record. These divergence times indicate much higher rates of cladogenesis than are typical of brachiopods during this interval. The correspondence of high speciation rates and high anatomical disparity suggests punctuated (speciational) change drove the high frequencies of early anatomical change, which in turn suggests increased ecological opportunities rather than shifting developmental constraints account for high rates of anatomical change. The pulse of rapid evolution began coincident with cooling temperatures, the start of major oscillations in sea level and increased levels of atmospheric oxygen. Our results suggest that these factors permitted major geographical and ecological expansion of strophomenoids with intervals of geographical isolation, resulting in elevated speciation rates and corresponding elevated frequencies of punctuated change.
Paired measurements of bulk carbonate (δ13Ccarb), organic matter (δ13Corg), and their difference (Δ13C) can be used to estimate changes in isotopic fractionation through time as a function of O2/CO2 ...in the atmosphere. However, because local scale processes can also affect Δ13C, it is essential to compare sections from widely separated water masses. Here we present new δ13Corg data from Ordovician carbonate rocks from the Great Basin, Oklahoma, and Appalachian Basin and compare with published δ13Ccarb records from these sections and paired δ13C values from other carbonate successions around North America. These new data complement previous studies that focused on Upper Ordovician δ13Ccarb excursions and now provide a composite Ordovician δ13Corg record. New Lower Ordovician (Tremadocian Stage) δ13Corg data range from ca. −26 to −28‰, decreasing throughout the Lower–Middle Ordovician (Floian–Dapingian Stages) to ca. −29 to −31‰. δ13Corg values remain at their lowest throughout the Sandbian and are similar to other published Upper Ordovician (Sandbian–Katian) δ13Corg data from North America. Δ13C values from well-preserved intervals generally vary between +26 to +28‰ throughout the Lower to Middle Ordovician (Tremadocian to early Darriwilian), but increase to +31‰ during the mid–late Darriwilian and mid Sandbian, similar to published data from younger Late Ordovician positive δ13C excursions known as the Guttenberg (GICE) and Hirnantian (HICE) events. The overall Δ13C trend shows a ~3‰ increase throughout the Early–Middle Ordovician and coincides with a previously interpreted period of ocean cooling and some of the earliest pulses of global biodiversity of marine invertebrates and planktonic organisms. Modeling studies predict that pCO2 decreased during this time, suggesting that the effect of pCO2 on Δ13C may have been overwhelmed by other controls, such as an in increase in pO2 or a higher O2/CO2 ratio during this biodiversification event.
•New Early–Middle Ordovician paired carbon isotopic analyses are reported here.•New organic isotope data combined with published data make an Ordovician composite.•A 3‰ increase in Δ13C coincides with the onset of the GOBE and possible ocean cooling.•Cooling or pCO2 changes cannot explain the entire Δ13C increase.•Increased pO2 or atmospheric O2/CO2 ratios may explain the long-term Δ13C increase.
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