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.
Recent molecular clock data suggest with high probability a Cambrian origin of Embryophyta (also called land plants), indicating that their terrestrialization most probably started about 500 Ma. The ...fossil record of the ‘Cambrian Explosion’ was limited to marine organisms and not visible in the plant fossil record. The most significant changes in early land plant evolution occurred during the Ordovician. For instance, the earliest bryophyte-like cryptospores and the oldest fragments of the earliest land plants are from the Middle and Late Ordovician, respectively. Organic geochemistry studies on biomarker compositions hint at a transition from green algae to land plants during the ‘Great Ordovician Biodiversification Event’ (GOBE). The colonization of the terrestrial realms by land plants clearly had an impact on marine ecosystems. Interactions between the terrestrial and marine biospheres have been proposed and the radiation of land plants potentially impacted on CO2 and O2 concentrations and on global climate. In addition, the shift of strontium isotopes during the Ordovician is probably linked to changing terrestrial landscapes, affected by the first massive land invasion of eukaryotic terrestrial life. The land plants seem unaffected by the first global mass extinction at the end of the Ordovician that eliminated many marine invertebrate taxa.
•The Great Ordovician Biodiversification also includes the evolution of land plants.•Macro- and microfossil, phylogenetic and biomarker data of land plants are revised.•First Ordovician plants paved the way of the terrestrialization in the Palaeozoic.•The links between earliest terrestrial and marine ecosystems are discussed.•Land plants seem not to be affected by the end-Ordovician extinction event.
The ‘Great Ordovician Biodiversification Event’ (GOBE) saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so-called ...‘Cambrian Explosion’. The diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them. The present paper reviews the palaeoecological dimension of the GOBE. It involved major increases in α, ß and γ biodiversity largely associated with the rise of the Paleozoic Evolutionary Fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the Ecological Evolutionary Units P1 and P2. In the benthos, these include more complex food webs than those of the Cambrian, greater tiering, especially above the sediment–water interface, and the development of guild structures indicating increased competition between taxa for particular resources. The Ordovician is characterized by a profound change in reef composition, with a switch from microbial-dominated reefs in the Early and Middle Ordovician to metazoan-dominated reefs in the Late Ordovician. Increases in complexity of deep-water trace fossil assemblages began in the Early Ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities.
Within the water column, the GOBE involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton (including planktotrophic larvae from a range of invertebrate clades). This revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates, molluscs and arthropods and promoted the rise of suspension feeders in the benthos. An escalation amongst predators and thus community evolution may also have been a major driver of biodiversification.
Based on a new and exhaustive sample-based dataset of middle Cambrian to Silurian radiolarian occurrences we investigate the diversity patterns of all radiolarian species to find out trends in their ...taxonomic evolution and to evaluate possible biases influencing these patterns. We also review and discuss the long term radiolarian biotic changes in the context of the Great Ordovician Biodiversification Event (GOBE) and associated global changes that affected the Earth system at the time. The Cambrian stage 10 – Middle Ordovician interval is characterized by a protracted diversification trend peaking in the Darriwilian. The rising trend is initially produced during the Tremadocian by Archaeospicularian radiolarians and it may be partly correlated with the basal Ordovician “plankton revolution”. Subsequently, the radiolarian diversity increase is mainly due to Spumellarian and Entactinarian radiolarians; the Darriwilian peak is the highest for the entire studied interval; it reflects a profound turnover in Ordovician radiolarian plankton assemblages. The Darriwilian appears to be a “game changing” interval for radiolarians and it is likely due to the profound oceanographic changes that followed the early Darriwilian cooling trend of Earth's climate. The transition with the Silurian is separated and highlighted by a Late Ordovician large drop in diversity, which records the lowest taxonomic richness of the studied interval. Next, the Silurian is first characterized by a rapid protracted recovery culminating in the Aeronian, and, secondly, by another peak in richness recorded in the Gorstian. Our results suggest that radiolarian microzooplankton have responded during all the major diversity events recognized in the early Paleozoic evolution of the marine biosphere. However, although the long-term trends in radiolarian biodiversity are robust, the documented patterns remain partly and locally biased by uneven sampling through space and time.
The Ordovician Lagerstätten record substantial amounts of excellent preservation and soft-bodied fossils during the Great Ordovician Biodiversification Event (GOBE). However, few Lagerstätten are ...known from the Lower Ordovician, most of which are preserved in restricted environments and high-latitude regions. Here, we report on a new tropical Lagerstätte, Liexi fauna, which has been recently discovered from a carbonate succession within the Lower Ordovician Madaoyu Formation in western Hunan, South China. It contains a variety of soft tissues, as well as rich shelly fossils, including palaeoscolecidan worms, possible
, trilobites, echinoderms, sponges, graptolites, polychaetes, bryozoans, conodonts and other fossils. The fauna includes taxa that are not only Cambrian relics, but also taxa originated during the Ordovician, constituting a complex and complete marine ecosystem. The coexistence of the Cambrian relics and Ordovician taxa reveals the critical transition between the Cambrian and Palaeozoic Evolutionary faunas. The unusual Liexi fauna provides new evidence for understanding Ordovician macroevolution and the onset of the GOBE.
•Mid-Upper Ordovician black shales yield new insights into ocean-redox dynamics.•Cooling induced upwelling led to high productivity on the Yangtze Platform margin.•Nitrogen depletion resulted in ...enhanced microbial N fixation and low 15Nbulk.•Increases in reactive Fe and trace metals (Mo, U) record expanded deep-water anoxia.•Climatic cooling and marine anoxia caused biodiversity losses following the GOBE.
The Great Ordovician Biodiversification Event (GOBE) achieved its peak during the Middle Ordovician, likely in association with climatic cooling and a rise of atmospheric O2. However, unstable redox states developed widely in contemporaneous epeiric seas, challenging previous assumptions about sustained oceanic oxygenation driven by deep-ocean ventilation in the aftermath of Ordovician cooling. Here, we investigate two Middle-Upper Ordovician shale-dominated successions from intra-shelf basin and slope settings of the Yangtze Sea, South China. Negative shifts in bulk δ15N and productivity proxies reveal temporal changes in the pattern of nutrient cycling under moderate-to-high productivity conditions, which were likely sustained by increased upwelling of cold and nutrient-rich deep waters in sync with contemporaneous climatic cooling. As a result, marine anoxia likely expanded in deep waters of the Yangtze Sea, as reflected in enrichments of highly reactive iron and redox-sensitive metals (Mo, U). Although moderate Mo abundances (25-50 ppm) and δ98/95Mo values (+0.4 to +0.8‰) within the euxinic interval suggest that bottom waters had low sulfide concentrations, the δ98/95Mo values are comparable with those of coeval euxinic facies (∼+0.6‰). Furthermore, our modeling results show that low δ98/95Mo can be produced when sulfidic sinks dominate Mo removal, suggesting that Middle-Late Ordovician oceans may have been less oxygenated than previously assumed, at least for the continental seas of South China, Baltica and Laurentia. These environmental changes may provide a new explanation for the ∼50% decline of invertebrate species following the peak of GOBE. Our findings thus link the progressive expansion of marine anoxia and climatic cooling to a profound biotic change during the Mid-Late Ordovician Period.
In order to improve our understanding of the biodiversification of marine life that took place during the early Palaeozoic, we present this special issue focused on the Ordovician radiations. The ...Great Ordovician Biodiversification Event (GOBE) is a conceptual term that is today largely used to refer to the most significant increase of marine biodiversity of the Phanerozoic that occurred during the Ordovician Period between 485 and 444 Ma. Some authors, focusing on taxonomic diversity counts of selected groups, understand the GOBE to be related to a single dramatic biodiversification event of short duration in the Darriwilian Stage of the Middle Ordovician Series between 470 and 455 Ma, whereas others follow the more traditional view and consider the Ordovician biodiversification as an aggregation of radiation events capturing a large and complex increase of taxonomic diversity but also ecological complexity of marine organisms covering the entire Ordovician. This special issue features 16 selected papers that provide different perspectives on these Ordovician biodiversification events, illustrating a variety of radiations occurring during the Ordovician Period. Several papers focus on the available biodiversity datasets and their biases, and the difficulty to distinguish and interpret the various regional and global scales. It becomes clear that the Cambrian and Ordovician radiations are artificially separated by a late Cambrian ‘Furongian Biodiversity Gap’ and that a single long-term early Palaeozoic radiation is more and more visible. A few papers provide additional data on this crucial interval across the Cambrian-Ordovician boundary displaying a much higher ecological complexity than previously assumed. Both the diversification of the plankton and the evolution of nektonic groups during the Ordovician are investigated, in papers including Computational Fluid Dynamic simulations. The virtual special issue closes with papers documenting the development of reefs during the Late Ordovician.
•This is the editorial preface for the VSI on Ordovician radiations.•16 papers are included and shortly introduced.•One review paper is included.•The 16 papers provide new views on the Ordovician radiations.•They cover intervals from the late Cambrian to early Silurian.
New stable carbon isotope data (δ13Ccarb) from Lower–Middle Ordovician (Tremadocian to Darriwilian) carbonate mudstone and wackestone rocks of the Pogonip Group are presented from two sections in the ...Great Basin region (USA) — Shingle Pass (east-central Nevada) and the Ibex area (western Utah). The Pogonip Group is a succession of mixed carbonate and siliciclastic rocks that accumulated on a carbonate ramp under normal marine conditions during the Late Cambrian (Furongian) to Middle Ordovician (Darriwilian). The Shingle Pass and Ibex area sections have been previously studied for their conodont biostratigraphy and contain a North American Midcontinent conodont fauna that range from the Cordylodus intermedius Zone (uppermost Cambrian) to the Phragmodus polonicus Zone (Darriwilian). The δ13C trend has four distinct characteristics recognized in both Great Basin sections: 1) a drop in δ13C from +1‰ at the base of the Ordovician (Tremadocian) to −0.7‰, 2) a 1 to 2‰ positive δ13C shift in the uppermost Rossodus manitouensis Zone during the late Tremadocian, 3) a gradual δ13C increase from −2‰ to ca. 0‰ during the end of the Early Ordovician (Floian), and 4) a steady δ13C decrease from 0‰ to −4 to −5‰ during Middle Ordovician (Dapingian–Darriwilian).
In the Lower Ordovician, δ13C trends reported here from the Great Basin are not consistent with a causal mechanism involving sea level change and the migration of isotopically distinct water bodies. Instead, these Lower Ordovician isotope data most likely reflect primary seawater chemistry and changes in δ13C on a global scale. This interpretation is supported by the excellent correlation of δ13C in the Lower Ordovician to other δ13C trends reported from the sections in the Argentine Precordillera (La Silla and San Juan formations) and in western Newfoundland (St. George and Table Head groups). These correlations using δ13C are consistent with published biostratigraphic data and provide an integrated and high-resolution chemo-biostratigraphic framework for the Lower Ordovician sedimentary record of the Laurentian margin. The Middle Ordovician portion of the δ13C curves in the Great Basin represented by the Kanosh and Lehman formations shows significant isotopic depletion relative to the section in Argentina. Thus, although there is some indication that minima and maxima in the Middle Ordovician curves can be correlated, the Great Basin sections show clear evidence of overprinting by local variables related to both diagenesis (dolomitization) and platform restriction.
•New high-resolution δ13C data from Nevada and Utah are globally correlative.•Thin section analysis and isotope cross plots indicate that isotope data are primary.•Sea level changes are not the dominant driver of δ13C variability.•Other isotope proxy data may elucidate drivers of Ordovician biodiversification.
Since the early 20th Century, when the first cephalopods from late Cambrian strata were discovered in North China, more than 160 species belonging to 39 genera in nine families and five orders, have ...been described from both North and South China, together with North America, Siberia and Kazakhstan. We compiled and analysed all published Cambrian cephalopod occurrences in these regions: the results show that the oldest undisputed cephalopods are from the Jiangshanian Stage of North China. After their origination, cephalopods reached their first diversity peak in the late Cambrian Acaroceras–Sinoeremoceras Biozone (early Stage 10). This initial diversity peak was followed by the “late Trempealeauan Eclipse”, which eradicated nearly 95% of late Cambrian genera. The extinction event coincides with similar extinctions of trilobites and some other groups of marine life. The rapid subsequent diversification of cephalopods during the Tremadocian (Early Ordovician) was paralleled by a diversification of graptoloids and radiolarians.
During the EarlyöMiddle Ordovician characteristic red carbonate beds, i.e., the Zitai Formation and its coeval units, developed in the deeper-water marine setting of the Yangtze Platform, South ...China. The temporal and spatial distribution of these reddish limestones is discussed based on published data and our own observations and analyses. The red limestones formed along the margin of the Yangtze Platform on a carbonate ramp during six stages. The different stages, (0) early Fl3 and before, (1) middle to late Fl3, (2) early Dp1, (3) middle to late Dp1, (4) Dp2, and (5) Dp3 to early Dw1, are associated with regional sea-level changes and tectonic movements. Several positive shifts in the δ13Ccarb record occur in the succession beneath the red beds. Their formation presumably was induced by a global transgression in association with the drowning of the Yangtze Platform. Better ventilation and oxygenation of sediments on the platform are also indicated by the marine red beds and together intensified the Great Ordovician Biodiversification Event. Other factors such as iron presumably play a significant role in controlling occurrences and distribution of the red limestone beds.
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