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Changes in depth-transect redox conditions spanning the end-Permian mass extinction and their impact on the marine extinction: Evidence from biomarkers and sulfur isotopes
Abstract
Changes in redox conditions during the Changhsingian to Griesbachian spanning the end-Permian mass extinction were recently reported based on analyses of organic molecules. We provide more precise organic-molecular data, that detail redox conditions spanning the end-Permian mass extinction at different palaeowater depths in the neritic Palaeotethys (estimated water depths: 10, 40, 100, and 200 m; Bulla, Huangzhishan, Meishan, and Chaohu sections, respectively) during this period. Here we propose that a change from occasional euxinia to anoxia in the shallow Palaeotethys occurred at the time of the mass extinction intercalated with oxic pulses. The second extinction at 0.7 myr after the main extinction was also caused by anoxia. New and published sulfur-isotope ratios (34S/32S) measured in carbonate-associated sulfate from the neritic Palaeotethys and in sulfide from pelagic central Panthalassa sediments show high values during the Changhsingian, consistent with the development of euxinia. The mass extinction coincided with a global fall in δ34S values, as well as a shift in δ13C values, indicating a global oxidation of H2S. This organic and isotopic geochemistry implies that accumulation of hydrogen sulfide in intermediate and deep waters followed by oxidation of hydrogen sulfide led to dissolved oxygen consumption, surface-water anoxia, and acidification, resulting in the end-Permian mass extinction in the seas.
... Thallium isotopes from three widely separated Panthalassic sections ( Fig. 1) were analysed. Both the Gujo-Hachiman and Ubara sections in Japan represent abyssal settings at peri-equatorial latitudes during the Permian-Triassic transition 18,39 . These sections have been dated based on radiolarian biostratigraphy and carbon isotopic chemostratigraphy, and tentatively correlated with shallow-marine Tethyan carbonate sections, which employ conodont biostratigraphy 18,39 . ...
... Both the Gujo-Hachiman and Ubara sections in Japan represent abyssal settings at peri-equatorial latitudes during the Permian-Triassic transition 18,39 . These sections have been dated based on radiolarian biostratigraphy and carbon isotopic chemostratigraphy, and tentatively correlated with shallow-marine Tethyan carbonate sections, which employ conodont biostratigraphy 18,39 . The third study section at Opal Creek, Alberta, Canada represents a mid-latitude deep-shelf setting that has been dated using conodonts and carbon isotopic chemostratigraphy 19,40 . ...
... A similar high sensitivity of the Tl isotope proxy has been reported for other major Phanerozoic oceanic anoxic events (OAEs) [33][34][35] . The Changhsingian at Gujo-Hachiman is not characterized by a positive shift in carbonate carbon isotopes 11,39,44 , providing no indirect geochemical evidence for an increase in global organic carbon burial preceding the EPME. Although increased organic carbon burial is a recognized feature of many Phanerozoic OAEs 33-35 , such a record may have been obscured by inputs of isotopically light carbon from volcanic sources or weathering of organic carbon 5 . ...
The end-Permian mass extinction (EPME) represents the largest biocrisis in Earth’s history, a result of environmental perturbations following volatiles released during Siberian Traps magmatism. A leading hypothesis links the marine mass extinction to the expansion of oceanic anoxia, although uncertainties exist as to the timing and extent. Thallium isotopes, a novel palaeoredox proxy with a rapid global response due to its short residence time in seawater, track global rates of manganese oxide burial, one of the first redox half-reactions to occur under reduced oxygen conditions. For this study, we analysed thallium isotopes from three widely distributed sites in Panthalassa, the largest ocean basin at the time. Our results provide evidence for the onset of deoxygenation considerably before the EPME, earlier by ≥1 Myr than the onset implied by other proxy records. Notably, there is a transient negative thallium isotope excursion concurrent with the EPME, which requires substantial manganese oxide burial based on the thallium isotope mass balance. This feature suggests a brief oxygenation episode before a return to more anoxic conditions, implying a more complex redox scenario, with rapid changes in oceanic (de)oxygenation leading to spatially and temporally variable biotic stresses. This oxygenation event may have been related to a transient cooling episode, based on published oxygen isotope records. These findings show that the Earth system experienced a highly fluctuating response to forcings linked to volcanogenic volatiles during the EPME.
... data, Genming Luo and Shucheng Xie). In contrast, the DBT/P ratios of carbonates from multiple Permian-Triassic boundary sections are much lower than 1 ( Fig. 6B; Kaiho et al., 2012), consistent with low oceanic sulfate concentration (~1.5 mM) at that time, as inferred from sulfur isotope records as well as high 3-MHI values Luo et al., 2010;Song et al., 2014). The rapid transition from high DBT/P ratios in the early Late Permian to low DBT/P ratios during the Permian-Triassic transition is worthy of comment. ...
... The rapid transition from high DBT/P ratios in the early Late Permian to low DBT/P ratios during the Permian-Triassic transition is worthy of comment. First, this shift started earlier than the marine mass extinction ( Kaiho et al., 2012, Fig. S1), which suggests that declining seawater sulfate concentrations may have had a substantial impact on biogeochemical cycles and climate conditions during the pre-extinction Late Permian ( Luo et al., 2010Luo et al., , 2014). Second, the low DBT/P ratios of samples deposited in euxinic photic-zone environments at Meishan ( Kaiho et al., 2012) and Shangsi ( Fig. S2) suggest that dibenzothiophene was formed mainly in sediment porewaters, which may have been due to the slow reaction rate between organic molecules and reduced sulfur. ...
... First, this shift started earlier than the marine mass extinction ( Kaiho et al., 2012, Fig. S1), which suggests that declining seawater sulfate concentrations may have had a substantial impact on biogeochemical cycles and climate conditions during the pre-extinction Late Permian ( Luo et al., 2010Luo et al., , 2014). Second, the low DBT/P ratios of samples deposited in euxinic photic-zone environments at Meishan ( Kaiho et al., 2012) and Shangsi ( Fig. S2) suggest that dibenzothiophene was formed mainly in sediment porewaters, which may have been due to the slow reaction rate between organic molecules and reduced sulfur. In this case, the DBT/P ratio may serve as an indirect proxy for contemporaneous seawater sulfate levels. ...
Lipids can survive long geological intervals within sediments and provide a unique tool that allows the reconstruction of past organismic diversity and environmental conditions. The lipids discussed in this review include all substances produced by organisms that are insoluble in water but extractable by organic solvents. Lipid biomarkers refer to both functionalized biolipids as well as their hydrocarbon derivatives in geological materials that contain diverse information about biotic sources and environmental conditions. In spite of diagenetic and catagenetic alteration, lipid biomarkers commonly preserve the hydrocarbon structure of their biotic counterparts and have been found in rocks up to 1.6 billion years in age. These features have promoted the use of lipid biomarkers in many fields, including petroleum geology, paleoclimatology, oceanography, meteorology, geobiology and environmental science. Here, we (i) review the use of lipid biomarker records for the reconstruction of environmental conditions in deep time, including climatic conditions (temperature), sedimentary environments (redox, salinity and chemical composition) as well as catastrophic terrestrial events (soil erosion and wildfire), and (ii) generate new insights into environmental perturbations during the Permian-Triassic transition based on investigation of lipid biomarkers. We further propose that the ratio of dibenzothiophene to phenanthrene (DBT/P) in marine carbonates may be a robust proxy for seawater sulfate concentrations in deep time. Our compiled DBT/P records show substantial variations in seawater sulfate levels through Earth history that are consistent with the results of other proxies. We discuss the future outlook for application of lipid biomarker records to deep-time environmental research.
... The P-Tr succession was deposited on a carbonate ramp (Zhang et al., 1996). The limestone CHMI 109 sample originates from lower Changhsingian (Upper Permian) sedimentary rocks within the Meishan section (at a depth of 34.76 m, as described by Kaiho et al., 2012). It contains C 40 bicyclic and tricyclic biphytanes, as assigned by comparing GC retention times and mass spectra with results obtained by Oba et al. (2006) and Schouten et al. (1998). ...
... end point (Peters et al., 2005). Changhsingian sedimentary rocks in the Meishan section are defined by strongly reducing conditions, evident from the presence of isorenieratane (a biomarker for green sulfur bacteria), high C 35 homohopane index values, and low pristane/phytane values (Cao et al., 2009;Kaiho et al., 2012). Sample (CHMI 109) also contained isorenieratane (Kaiho et al., 2012), indicating the occurrence of photic zone euxinic event during deposition. ...
... Changhsingian sedimentary rocks in the Meishan section are defined by strongly reducing conditions, evident from the presence of isorenieratane (a biomarker for green sulfur bacteria), high C 35 homohopane index values, and low pristane/phytane values (Cao et al., 2009;Kaiho et al., 2012). Sample (CHMI 109) also contained isorenieratane (Kaiho et al., 2012), indicating the occurrence of photic zone euxinic event during deposition. ...
Biphytanes, which are derived from glycerol dialkyl glycerol tetraether (GDGT) lipids, are biomarkers for the presence of Archaea in geological samples. They (especially cyclic structures) are rarely reported from sediments or oils that are older than the Triassic period, where their first record may be traced back to the Late Archean. There have been only two studies that have reported diagenetic products of cyclic biphytanes using two dimensional gas chromatography. In this study, we used full scan and multiple reaction monitoring (MRM) mass spectrometry (MS) to tentatively assign a series of diagenetic products of cyclic biphytanes within uppermost Permian and Lower Triassic sedimentary rocks. We observed three distinct groups derived from mono-, bi-, or tricyclic biphytanes, echoing previous studies. Each group could be further divided into three discrete series according to structure and composition. Using MRM also revealed that numerous sedimentary rocks contained such diagenetic products, but at trace concentration below the limit of detection of full scan MS. This indicates that the presence of Archaea-containing GDGT lipids has been underestimated within paleoenvironments. Episodic occurrences of biphytanes in the Permian-Triassic transition also provide additional evidence for the distribution of Archaea in the geological past.
... Siberian volcanism was the most likely cause; however, the direct causal mechanism for the biotic crisis has long been disputed. Direct causes that have been proposed include hypercapnia (physiological effects of elevated P CO2 ; Knoll et al., 2007), the development of anoxic-suboxic or euxinic waters in the ocean including hydrogen sulfide (H 2 S) release from the intermediate to surface water (Gorjan et al., 2007;Kaiho et al., 2012) and/or atmosphere (Kump et al., 2005;Kaiho et al., 2012;Kaiho and Koga, 2013), a decrease in atmospheric oxygen (O 2 ) (small contribution; Kaiho and Koga, 2013), an increase in temperature A role of the development of anoxic-suboxic or euxinic (sulfide-bearing) deep and intermediate seawaters in the P/Tr mass extinction (Grice et al., 2005;Takahashi et al., 2014;Feng and Algeo, 2014) has been supported by the detection of small pyrite framboids and high concentrations of molybdenum (Mo), uranium (U), and vanadium (V) in deep-sea sedimentary rocks from that period in the central Panthalassic Ocean, indicating that the deep ocean was depleted of oxygen (Wignall et al., 2010;Algeo et al., 2011;Takahashi et al., 2014). estimated the redox conditions of deep water in the central Panthalassic Ocean during the latest Permian and earliest Triassic using the degree of pyritization (Raiswell et al., 1988), which indicated dysoxic conditions. ...
... Siberian volcanism was the most likely cause; however, the direct causal mechanism for the biotic crisis has long been disputed. Direct causes that have been proposed include hypercapnia (physiological effects of elevated P CO2 ; Knoll et al., 2007), the development of anoxic-suboxic or euxinic waters in the ocean including hydrogen sulfide (H 2 S) release from the intermediate to surface water (Gorjan et al., 2007;Kaiho et al., 2012) and/or atmosphere (Kump et al., 2005;Kaiho et al., 2012;Kaiho and Koga, 2013), a decrease in atmospheric oxygen (O 2 ) (small contribution; Kaiho and Koga, 2013), an increase in temperature A role of the development of anoxic-suboxic or euxinic (sulfide-bearing) deep and intermediate seawaters in the P/Tr mass extinction (Grice et al., 2005;Takahashi et al., 2014;Feng and Algeo, 2014) has been supported by the detection of small pyrite framboids and high concentrations of molybdenum (Mo), uranium (U), and vanadium (V) in deep-sea sedimentary rocks from that period in the central Panthalassic Ocean, indicating that the deep ocean was depleted of oxygen (Wignall et al., 2010;Algeo et al., 2011;Takahashi et al., 2014). estimated the redox conditions of deep water in the central Panthalassic Ocean during the latest Permian and earliest Triassic using the degree of pyritization (Raiswell et al., 1988), which indicated dysoxic conditions. ...
... Takahashi et al. (2014) provided evidence of euxinic conditions (accumulation of Mo, U, and V) in the deep waters of the central Panthalassic Ocean immediately before and during the latest Permian extinction. There is an abundance of data indicating oxic, dysoxic, and anoxic shallow waters during the latest Permian extinction in the Paleotethys (Cao et al., 2009;Kaiho et al., 2012;Brand et al., 2012). Most recently, Xiang et al. (2016) demonstrated oxic and Wang et al. (2016) reported dysoxic conditions in low-latitude shallow waters during the latest Permian extinction. ...
The largest mass extinction of biota in the Earth’s history occurred during the Permian–Triassic transition and included two extinctions, one each at the latest Permian (first phase) and earliest Triassic (second phase). High seawater temperature in the surface water accompanied by euxinic deep-intermediate water, intrusion of the euxinic water to the surface water, a decrease in pH, and hypercapnia have been proposed as direct causes of the marine crisis. For the first-phase extinction, we here add a causal mechanism beginning from massive soil and rock erosion and leading to algal blooms, release of toxic components, asphyxiation, and oxygen-depleted nearshore bottom water that created environmental stress for nearshore marine animals. For the second-phase extinction, we show that a soil and rock erosion/algal bloom event did not occur, but culmination of anoxia–euxinia in intermediate waters did occur, spanning the second-phase extinction. We investigated sedimentary organic molecules, and the results indicated a peak of a massive soil erosion proxy followed by peaks of marine productivity proxy. Anoxic proxies of surface sediments and water occurred in the shallow nearshore sea at the eastern and western margins of the Paleotethys at the first-phase extinction horizon, but not at the second-phase extinction horizon. Our reconstruction of ocean redox structure at low latitudes indicates that a gradual increase in temperature spanning the two extinctions could have induced a gradual change from a well-mixed oxic to a stratified euxinic ocean beginning immediately prior to the first-phase extinction, followed by culmination of anoxia in nearshore surface waters and of anoxia and euxinia in the shallow-intermediate waters at the second-phase extinction over a period of approximately one million years or more. Enhanced global warming, ocean acidification, and hypercapnia could have caused the second-phase extinction approximately 60 kyr after the first-phase extinction. The causes of the first-phase extinction were not only those environmental stresses but also environmental stresses caused by the soil and rock erosion/algal bloom event.
... These sections can be catalogued into three types according to sedimentary water depths: (1) shallow platform sections above fair-weather wave base (i.e., water depths b 50 m, and commonly b20 m; cf. Brett et al., 1993), including Bulla in northern Italy and Laolongdong and Cili in South China, (2) intermediate shelf/ ramp sections located between fair-weather wave base and storm wave base (i.e.,~50-200 m water depth), including Huangzhishan (Kaiho et al., 2012) and Meishan in South China (Grice et al., 2005a;Cao et al., 2009), the Perth Basin of Western Australia (Thomas et al., 2004;Grice et al., 2005a), Kap Stosch in Greenland (Hays et al., 2012), Spitsbergen (Nabbefeld et al., 2010b), and the Peace River Basin (Hays et al., 2007) and West Blind Fiord in Canada (Algeo et al., 2012), and (3) deep shelf/ramp sections (N200 m water depth), including Shangsi and Chaohu in South China (Fig. 1C). Background details for each section are given below. ...
... (1) bioclastic limestone of the Changxing Formation, (2) alternating calcareous mudstone and muddy limestone of the Huangzhishan Formation, (3) mudstone and marlstone of the Yinkeng Formation, and (4) alternating calcareous mudstone and argillaceous limestone of the Helongshan Formation (Chen et al., 2009;Kaiho et al., 2012). The succession shows a sharp transition from high-energy, open-platform facies of the uppermost Changxing Formation to low-energy, restricted-marine facies of the lowermost Huangzhishan Formation (Chen et al., 2010). ...
... The earliest Triassic Yinkeng Formation consists of greenish mudstone interbedded with thin marlstone, representing a deepening-upward succession (Chen et al., , 2015Tian et al., 2014). With evidence of both shallow-and deep-water faunal assemblages, water depths have been interpreted as ranging from~30 to 100 m (Yin et al., 2001;He et al., 2005;Chen et al., 2010;Kaiho et al., 2012;Song et al., 2013). The EPME is located at the base of Bed 25 and the PTB in the middle of Bed 27 (Yin et al., 2001). ...
The incursion of euxinic waters into the ocean-surface layer is hypothesized to have been an important killing agent during the end-Permian mass extinction. However, both the causes and extent of oceanic euxinia during this crisis remain poorly known, making assessment of its role in the mass extinction difficult. Here, we document the distribution of aryl isoprenoids (AIs), which are biomarkers of obligate anaerobic green sulfur bacteria (Chlorobiaceae) that are indicative of photic-zone euxinia, in 12 Permian-Triassic Boundary (PTB) sections with a wide distribution globally. Profiles of AI abundance for the 12 study sections show significant spatio-temporal variation. No AIs were identified in the shallowest sections, but AIs are present both prior to and following the mass extinction in intermediate-depth sections and following the mass extinction in deep-water sections. This pattern suggests a combination of upward and oceanward expansion of photic-zone euxinia during the PTB crisis, possibly fueled by elevated riverine nutrient fluxes as a consequence of climatic warming, terrestrial ecosystem destruction, and enhanced erosion. This hypothesis is supported by the close association of AIs with elevated abundances of moretanes and dibenzofuran (DBF), which are biomarkers for terrestrial erosion. Expansion of oceanic euxinia at intermediate water depths may have established a long-term reservoir that fed episodic incursions of H2S-bearing waters into shallow-marine environments, delaying the recovery of marine ecosystems during the Early Triassic. The biomarker records of the present study thus provide significant evidence of terrestrial-marine linkage during the PTB crisis.
... The latest Permian mass extinction (LPME) was the largest biotic crisis in Earth's history, with a~90% species-level loss of diversity among marine invertebrates (Erwin et al., 2002;Alroy et al., 2008). The causes of this extinction event were complex, but an important factor is thought to have been an abrupt expansion of oceanic anoxia and photic zone euxinia (Wignall and Hallam, 1992;Wignall et al., 1995;Knoll et al., 1996Knoll et al., , 2007Wignall and Twitchett, 1996;Hotinski et al., 2001;Grice et al., 2005;Huey and Ward, 2005;Kump et al., 2005;Gorjan et al., 2007;Cao et al., 2009;Brennecka et al., 2011;Kaiho et al., 2012;Dustira et al., 2013;Takahashi et al., 2014). Some studies have claimed that the onset of widespread oceanic anoxia ('superanoxia') started during the early Wuchiapingian (Isozaki, 1997;Kato et al., 2002), whereas other studies have proposed a later onset, e.g., during the late Wuchiapingian or early Changhsingian (Nielsen and Shen, 2004;Wignall et al., 2010). ...
... The darkgray shale of the lower Feixianguan Formation (Interval IV) yields 34 Sdepleted pyrite S-isotopic compositions (b− 30‰; Fig. 7), suggesting deposition under reducing conditions. Previous studies have reported anoxia/euxinia around the LPME in the nearby Shangsi section (Riccardi et al., 2006(Riccardi et al., , 2007 as well as at other localities globally Twitchett, 1996, 2002;Isozaki, 1997;Grice et al., 2005;Kump et al., 2005;Riccardi et al., 2006Riccardi et al., , 2007Gorjan et al., 2007;Bond and Wignall, 2010;Algeo et al., 2011a;Kaiho et al., 2012;Dustira et al., 2013;Takahashi et al., 2014). However, thin limestone interbeds within the shale at Xiaojiaba contain rare or no framboids, and one of them contains large framboids (mean = 22 μm, max. ...
... = 47 μm) (Fig. 14). These features are consistent with dysoxic or oxic conditions, which appear to have episodically interrupted the reducing conditions that generally prevailed around the LPME (cf., Kaiho et al., 2012). ...
... Geochemical studies of framboidal pyrite, trace elements and biomarkers have revealed that the Permian-Triassic boundary was linked to the development of anoxic or euxinic waters (Grice et al., 2005;Fenton et al., 2007;Shen et al., 2007;Cao et al., 2009;Bond and Wignall, 2010;Wignall et al., 2010;Algeo et al., 2011b;Kaiho et al., 2012). However, few geochemical investigations have been conducted on redox conditions during the entire Early Triassic, although these conditions may have played a role in the long delay in biotic recovery after the extinction event. ...
... Organic geochemical analysis was performed on 118 carbonate, shale and marl samples from the 250 m thick sedimentary sequence at Majiashan-Pingdingshan (Fig. 1). The analysis was conducted following Oba et al. (2006) and Kaiho et al. (2012). ...
... As BSR operates under strictly anoxic conditions, the presence of OSCs is considered to be a good indicator of anoxic conditions at the time of deposition. On this basis, DBTs have been used as markers for euxinia in past depositional environments (Takahashi et al., 2009;Oba et al., 2011;Kaiho et al., 2012Kaiho et al., , 2014) and a high concentration likely indicates strongly reducing depositional conditions. ...
The greatest mass extinction on Earth occurred 252 million years ago during the latest Permian. Complete biotic recovery, characterized by a return to pre-extinction diversity levels, took an extraordinarily long time (ca. 5 x 106 yr), probably because harsh conditions developed repeatedly during the Early Triassic. Here, we show the recurrence of euxinic conditions during the Early Triassic and the development of especially severe such conditions during the late Early Triassic, just prior to full biotic recovery from the mass extinction. Dibenzothiophenes and carotenoids accumulated in upper Lower Triassic sediments from South China, located on the western margin of the Paleotethys Ocean. Among these, chlorobactane, a biomarker for green-pigmented green sulfur bacteria, and okenane, a biomarker for purple sulfur photosynthetic bacteria, were identified in upper Early Triassic samples. Both compounds were detected in limestone (micrite), and we therefore infer that planktonic green and purple sulfur bacteria were the sources of these carotenoids, and that their presence indicates photic zone euxinia at the time of deposition. Concentrations of redox sensitive elements (M, V, and U) relative to that of Al, and the U/Th ratio, progressively increased during the late Early Triassic. The euxinic conditions represented by the carotenoids and the elements were likely caused by a combination of locally shallow restricted conditions and global environmental oscillations, such as those related to global warming, during the late Early Triassic. The presence of these biomarkers, together with the increase in the abundance of redox sensitive elements relative to Al and the U/Th, suggests that euxinic conditions could be one of the causes for the delayed recovery of marine communities in the Paleotethys Ocean after the latest Permian mass extinction event.
... In this study, the δ 34 S py values vary from −41.2‰ to −19.7‰, and all are evidently lower than the δ 34 S value (~+10‰) of contemporaneous seawater sulfate (Claypool et al., 1980;Kampschulte and Strauss, 2004;Song et al., 2014). Thus, fractionation of 29.7‰ to 51.2‰ occurred, which is similar to the maximum isotopic fractionation of > 50‰ in Upper Permian sediments worldwide (e.g., Kajiwara et al., 1994;Riccardi et al., 2006;Algeo et al., 2008;Grasby and Beauchamp, 2009;Nielsen et al., 2010;Kaiho et al., 2012;Wei et al., 2015b;Shen et al., 2016;Lei et al., 2017). ...
... For instance, abundant remains of phosphatic organisms ( Fig. 3D and G) in intervals II and IV of the Niushan section imply that the surface seawater was well oxygenated or suboxic, which facilitated the flourish of plankton. Widespread surface-water oxygenation has also been inferred for contemporaneous shallow-water sections elsewhere (e.g., Kaiho et al., 2012;Proemse et al., 2013), while the report from abyssal plain settings of Panthalassa (2000-5000 m) suggests that super-anoxia was throughout the whole Changhsingian (Isozaki, 1997). By comparison, the sediments of the Niushan section were deposited under anoxic conditions in most of the Changhsingian, including recurrent euxinic conditions. ...
The late Permian oceanic anoxic event is suggested to have had a causal relationship with the Latest Permian Mass Extinction (LPME); however, the nature of spatio-temporal variations in the anoxic event prior to the LPME remains poorly known. Here we provided new constraints on this issue based on high-resolution geochemical analyses of sulfur isotopes and trace elements in the Niushan section (nearby the Meishan section) of the Lower Yangtze region, South China. Results show that the entire Upper Permian Changhsingian in the study area can be divided into five intervals according to organic carbon isotope evolutionary trend. From the bottom to top, the water was oxic (interval I) to anoxic with sporadically euxinic condition (interval II) to primarily suboxic (interval III) to anoxic with frequently euxinic condition (interval IV), to a transient euxinic event (interval VEH) under dysoxic/oxic conditions (interval V). Multiple productivity proxies (total organic carbon, Cuxs, and Znxs) suggest that the primary productivity may have experienced a stable low (interval I), then was enhanced but with strong fluctuations (interval II), followed by a transient sharp decline (interval III), and was then subsequently relatively high with small fluctuations (interval IV), and finally experienced a gradual decline with occasional peaks (interval V) through the time interval represented by the Niushan section. The relationship between redox changes and paleoproductivity supports that a redox-stratified late Permian Ocean was present in the eastern Tethys region. Combined with previous results in South China, we propose that all the deep-water sections in the northern marginal basin of the Yangtze Platform (NMBY) might display similar trends, indicating that the NMBY was part of a single paleo-ocean system during the Changhsingian, although the Niushan section records more severely euxinic benthic water. The transient euxinic event during interval extinction horizon (VEH) can be well correlated with other sections worldwide, suggesting that the end-Permian marine anoxia in the Niushan section represents a global signal. The extinction horizon accompanied by a single euxinic episode in this study provides further evidence for the LPME having been caused by widespread anoxia. The bio-environmental evolutionary history of this continuous deep-water section will help us to better evaluate the data for the nearby shallow-water Meishan section.
... Bruland, 1980) due to the photo-reduction of particulate Mn in the presence of dissolved organic substances, such as humic acid ( Sunda et al., 1983;Sunda and Huntsman, 1994). Therefore, in the P-Tr ocean, widespread oceanic anoxia, even in the photic zone, ( Wignall and Twitchett, 1996;Grice et al., 2005;Kaiho et al., 2012;Song et al., 2012b) might contribute to increased dissolved Mn in shallow water. In addition, increased dissolved Mn also suggests higher primary productivity, that would have led to elevated photo-reduction of particulate Mn. ...
... Higher productivity after the P-Tr boundary crisis is also supported by other proxies (Fig. 7). Evidence for low primary productivity, such as decreased in fossil abundance (Twitchett, 2001) and smaller fossils (Twitchett, 2007) can alternatively be explained as a response to harsh environmental conditions independent of productivity changes, e.g., ocean anoxia ( Wignall and Twitchett, 1996;Grice et al., 2005;Kaiho et al., 2012;Song et al., 2012b) and global warming Sun et al., 2012). Furthermore, species in eutrophic environments are often 'r-strategists' which are often small and show rapid growth and onset of sexual maturity (Pianka, 1970). ...
The Permian-Triassic (P-Tr)crisis was the largest mass extinction of the Phanerozoic and eliminated over 90% of marine species. However, the nature of marine productivity changes during the crisis is a matter of on-going debate. Here, thermoluminescence (TL)measurements from 144 bulk carbonate samples from Meishan (South China)show two levels of variation in TL peak intensities at ~270 °C. The first-order variation is characterized by a rapid, nearly three-fold increase. A secondary variation is interpreted to record periodic fluctuations on a Milankovitch scale (~20-kyr rhythm). The periodic variations of TL are negatively correlated with Mn concentrations, suggesting primary productivity is a key factor controlling the TL peak intensity by photo-reduction of particulate Mn in the presence of organic matter. Therefore, the periodic fluctuations of TL were likely controlled by primary productivity changes on orbital timescales. A significant rise of TL peak intensities across the P-Tr boundary represents the rapid increase of dissolved Mn associated with enhanced marine productivity and/or oceanic anoxia.
... Oceanic anoxia has been widely regarded as a major contributor to the~252-Ma latest Permian mass extinction (LPME) (Wignall andTwitchett, 1996, 2002;Isozaki, 1997;Grice et al., 2005;Algeo et al., 2007Algeo et al., , 2008Algeo et al., , 2011aBrennecka et al., 2011;Shen et al., 2011;Payne and Clapham, 2012;Kaiho et al., 2012;Chen et al., 2015;Clarkson et al., 2016). Despite extensive investigation, the extent and duration of oceanic anoxia during the Late Permian and Early Triassic remain uncertain. ...
... In anoxic marine systems characterized by low marine sulfate, low productivity, high Fe HR fluxes, or combinations thereof, ferruginous conditions can potentially develop . Because of widespread development of euxinia in Late Permian oceans (Isozaki, 1997;Kaiho et al., 2012;Takahashi et al., 2014;Chen et al., 2015), contemporaneous seawater sulfate concentrations are thought to have been much lower (~4 mM) than in the modern ocean (~28 mM) (Luo et al., 2010;Song et al., 2014;Algeo et al., 2015). This conclusion is consistent with results from Units I and III at Ganxi, which display evidence for persistent euxinia (see Section 6.1). ...
Although oceanic anoxia is regarded as a leading cause of the Permian-Triassic boundary (PTB) mass extinction, its timing, extent, and underlying causes remain unclear. Here, we conducted a high-resolution Fe-S-C-Mo geochemical study of the entire Changhsingian and lowermost Induan succession in a carbonate-ramp setting at Ganxi, western Hubei Province, South China. Six stratigraphic units representing discrete redox intervals were identified based on integrated Fe-S-C-Mo data. Units I-III are of latest Wuchiapingian to early Changhsingian age, with Units I and III characterized by euxinia and Unit II by uncertain redox conditions. Unit IV, of mid-Changhsingian age, records a gradual transition from euxinic to ferruginous conditions. Units V and VI, spanning the latest Permian mass extinction (LPME) to earliest Triassic interval, were deposited under dominantly ferruginous conditions punctuated by both euxinic and oxic episodes. Redox variations at Ganxi were controlled by contemporaneous oceanographic changes in the upper oceanic thermocline region: (i) euxinia in Units I and III may record elevated marine productivity (as suggested by mean organic carbon accumulation rates, or OCAR, of 6.5 and 5.1mg/cm²/kyr, respectively) that was possibly related to upwelling; (ii) the euxinic-to-ferruginous transition from Unit IV to Units V-VI can be attributed to a combination of reduced sulfate availability and rising terrigenous iron inputs (mean Fe of 1.7% and 3.9%, respectively, for Units V-IV and VI compared to 1.0% for Units I-III); and (iii) transient intervals of euxinia in Units V and VI were facilitated by enhanced sulfate fluxes related to episodic volcanism during this interval. An integration of the redox data from Ganxi with previously published data from the Shangsi and Xiakou sections suggests that enhanced weathering fluxes were most likely the key factor controlling the marine redox transition from euxinic to ferruginous conditions during the latest Permian across the South China region.
... It was followed by an interval of disturbed marine environmental conditions characterized by widespread anoxia, large carbon (C) isotope excursions, low-diversity ecosystems, and rapid evolutionary turnover that lasted for at least 2 million years into the Early Triassic (Wignall and Twitchett, 2002; Payne et al., 2004; Bottjer et al., 2008; Brayard et al., 2009). The marine sulfur (S) cycle was also severely perturbed as indicated by large S-isotopic (d 34 S) fluctuations (Newton et al., 2004; Marenco et al., 2008a; Kaiho et al., 2012 ) and possible substantial drawdown of the seawater sulfate reservoir (Luo et al., 2010). All of these perturbations have been hypothesized to have resulted from massive eruptions of the Siberian Traps magmatic province (Wignall, 2007; Korte et al., 2010; Algeo et al., 2011). ...
... These studies have reported a wide range of isotopic values ($+10& to +25&) without yielding a coherent pattern of secular d 34 S CAS variation (Fig. 1A). Variation in d 34 S CAS during the Early Triassic has been the examined in several studies (Riccardi et al., 2006; Marenco, 2007; Marenco et al., 2008a; Kaiho et al., 2012), but small sample numbers and/or lack of detailed biostratigraphic information limited the stratigraphic resolution achieved in these studies (Fig. 1B ). In addition, none of these studies has documented any relationship between d 34 S CAS and other geochemical proxies (e.g., d 13 C carb ) that might yield insights regarding operation of the marine S cycle during the crisis interval. ...
... This, in turn, should have caused H 2 S release into the atmosphere, resulting in extensive extinctions on land. 67 High levels of Ni from the end of the Permian period found in sediments of the Southern Sydney Basin, Australia, have also been directly implicated in terrestrial plant extinction and replacement. 68 A similar conclusion has been reached by Rampiro et al ., who have proposed that the worldwide Ni anomaly of the Permian end was provoked by Ni-rich volatiles and magma intrusions. ...
Although nickel (Ni) is a minor element of the Earth's crust, it has played a major role in the evolution of life. This metal is a component of the active sites of several archaeal and bacterial anaerobic enzymes essential for bioenergy processes such as H2 and CO oxidation and CO2 fixation. Furthermore, Ni of meteoritic origin was probably involved in primordial organic phosphorylations. However, depending on its concentration, Ni can also be extremely toxic to most species. Through Earth's history this paradoxical situation has provoked complex interactions between microorganisms, such as sulfate-reducing bacteria and the highly Ni-dependent methanogens. Ni-rich volcanic emissions have resulted in alterations of the biological carbon cycle caused by high archaeal production of greenhouse CH4 gas and the ensuing global temperature elevation. These emissions are also thought to have directly helped producing the most serious of the five major extinctions at the end of the Permian period.
... Major and trace elements were measured by inductively coupled Burgess et al. (2014). Data for Arrow Rocks, Akkamori and Ubara sections are modified from Hori et al. (2007), Takahashi et al. (2010) and Kaiho et al. (2012), respectively. The horizontal bars indicate correlative stratigraphic zones around the Permian-Triassic boundary. ...
The end-Permian mass extinction (EPME) has been linked with the widespread development of oxygen-poor oceanic conditions. However, information on the spatial extent of anoxia in the Panthalassa super-ocean has been limited. This study reports oceanic redox records from a deep-sea chert succession (the Waiheke 1 section, WHK 1, New Zealand) that was located in southern mid-latitudes of Panthalassa. High-resolution carbon isotope (δ13C) correlation between Waiheke and the Permian-Triassic boundary (PTB) type section indicates that the EPME is recorded in a thin black claystone interbedded between siliceous mudstone beds at WHK 1. Pyrite-dominated enrichment in highly reactive iron, coupled with elevated U/Al and Mo/Al ratios, are prevalent through this black claystone bed and the overlying Permo-Triassic transition strata, suggesting the development of euxinic water column conditions. Similar redox variations across the EPME horizon have been reported from other Panthalassic deep-sea PTB sections. Comparison with these PTB sections indicates that euxinic conditions were widespread in low-latitude regions of the Panthalassan ocean, and such conditions developed earlier than in mid-latitude settings, up to 100,000 years before the EPME. This suggests there was a gradual expansion of ocean anoxia from low to middle-high latitude regions during the Permo-Triassic transition. The extent of ocean anoxia resulted in a decrease in the seawater inventory of redox sensitive trace metals (e.g., Mo), which is evident in the earliest Triassic strata of the studied section and other PTB sections. Panthalassic anoxia during the EPME coincides with extreme climate warming and the associated effects (e.g., changes in ocean circulation, marine eutrophication intensified by terrestrial weathering) were likely critical triggers for ocean deoxygenation.
... The unit II is overlain by the black siliceous claystones. The accumulation of black siliceous claystone around the P-TB is commonly observed in mid-Panthalassan deep-sea sequences in Japan, and has been thought to be a result of the demise of radiolarians and the decline in biogenic silica production during the global extinction [5,112,113]. Based on regional correlations, the extinction horizon at Gujo-Hachiman could be placed at the base of the black siliceous claystones (unit III) (Figure 9a). ...
The end-Permian mass extinction was the largest biodiversity crisis in the Phanerozoic. Based on characteristic negative ∆³³S signals of sedimentary pyrite, previous multiple sulfur isotope studies suggested shoaling of anoxic/sulfidic deep-waters onto a shelf, leading to the shallow-marine extinction. However, the validity of this shoaling model has been controversial. I compiled previously-reported multiple sulfur isotope records during the Permian-Triassic transition interval, and examined a stratigraphic relationship between the extinction horizon, redox oscillation in the depositional settings, and the multiple sulfur isotope record in each studied section. The compilation shows that the negative ∆³³S signals do not correspond clearly to the extinction horizon or to the benthic anoxia/euxinia in the studied sections. The compilation also documents that the multiple sulfur isotope records during the Permian-Triassic transition are substantially variable, and that the negative ∆³³S signals were observed in various types of sediments including shallow-marine carbonates, carbonates/siltstones of relatively deep-water facies, and abyssal deep-sea cherts. Those observations allow me to infer that the negative ∆³³S signal is not a robust indicator of shoaling. Rather, this isotopic signal may reflect substantial sulfur isotope heterogeneity in the sediments controlled by local factors.
... Although both terrestrial and marine biotic and environmental investigations have progressed in recent decades, one of the remaining issues, as noted by Bottjer (2012), is that the correlations between land Kaiho et al., 2012;original map from Ziegler et al., 1998) and South China (b, modified from Xie et al., 2017), showing the locations of the Xiaohebian, Shangsi, and Meishan sections and their correlation with respect to estimates of the time intervals between bioenvironmental events (c). Numerical ages are from the Meishan section (Burgess et al., 2014). ...
A terrestrial ecosystem collapse event accompanied by extensive soil erosion has been widely recorded in marine sedimentary rocks at the vicinity of the end-Permian mass extinction. However, the precise timing of this event and its impact on the marine extinction have not yet been ascertained. Here we present an organic geochemical study of non-marine and marine sections from the South China Craton, which shows that terrestrial ecosystem collapse was accompanied by a soil erosion event, and was followed by the end-Permian marine extinction. Two separate events devastated the terrestrial ecosystem prior to the marine extinction event, over a timespan of dozens of kyr. Bacteria flourished in the non-marine section coeval with a decline in terrestrial plants and in the marine section during the end-Permian marine extinction. A proto-recovery of herbaceous plants (not woody plants) occurred dozens of kyr after the end-Permian marine extinction and coincided with a global warming maximum and oceanic anoxia/euxinia.
... The methods used to analyze sedimentary organic molecules were based on Kaiho et al. (2012). First, to eliminate any contamination, the surface of each sample was removed, and in each case, the sample was washed thrice with an organic solvent using a 3:2 volumetric mix of dichloromethane with methanol. ...
The Hangenberg Crisis at the Devonian–Carboniferous boundary is known as a polyphase extinction event that affected more than 45 % of marine and terrestrial genera. As the cause of this event is still debated, analyses were carried out on sedimentary samples from the Devonian–Carboniferous Pho Han Formation in northeastern Vietnam to reconstruct the paleoenvironment around the time of this event using stable carbon isotopes; total sulfur; manganese; vanadium; molybdenum; and sedimentary organic matter, such as dibenzothiophenes, cadalene, and regular steranes. These geochemical signatures provide a high‐resolution redox history for this section and show that transgression‐driven high primary productivity, possibly enhanced by terrestrial input, caused severe oxygen depletion along the continental margin of the South China block during the Hangenberg Crisis. Multi‐proxy analyses were carried out on Devonian¬–Carboniferous sediments from the Pho Han Formation, northeastern Vietnam to reconstruct the paleoenvironment around the time of the Hangenberg Crisis. The geochemical signatures provide a high‐resolution redox history for this section and show that transgression‐driven high primary productivity possibly enhanced by terrestrial input caused severe oxygen depletion along the continental margin of South China block during the event.
... The main sources of proxy data employed to reconstruct the redox histories of paleo-oceans/paleo-lakes include paleontology (benthos) (Bromley and Hanken, 2003;Miller, 2003;Kaiho et al., 2012), T mineralogy (pyrite and hematite) (Wilkin et al., 1996;Bond and Wignall, 2010;Chang and Chu, 2011;Sato et al., 2011), geochemistry (elemental and isotopic compositions) (Morford and Emerson, 1999;Arnold et al., 2004;Tribovillard et al., 2006;Algeo et al., 2008;Lin et al., 2016). However, each proxy has its own limitations (Wilkin et al., 1996;Tribovillard et al., 2006;Brumsack, 2006;Zhou et al., 2012;Zhang et al., 2017). ...
The mineral assemblages of lacustrine mixed sediments have vital significance for reconstructing paleo-lake environments, and typical lacustrine mixed sediments deposited during the Eocene are distributed throughout the Yingxi area in the western Qaidam Basin. Accordingly, the framboid size distributions and sulfur isotope (δ³⁴Spy) characteristics of pyrite in addition to the carbon isotope (δ¹³Ccarb) characteristics and redox-sensitive element ratios (Th/U, V/(V + Ni) and V/Cr) of authigenic carbonates were investigated to reconstruct the high-frequency redox variations in cyclic lacustrine sediments. Corresponding to different redox conditions, three types of mixed sediments developed during transgression and regression stages within the saline basin in the Yingxi area during the Eocene: mixed terrigenous clasts formed in oxic-dysoxic water column conditions during lake transgression, mixed carbonates formed in anoxic water column conditions during early-stages lake regression, and mixed evaporites formed in anoxic-sulfidic water column conditions during middle-late-stage lake regression. The redox proxies correlate well with the water salinity, exhibit little or no correlation with the water temperature, and show an incongruity with the water depth, suggesting that the redox conditions were predominantly controlled by the water salinity rather than the water depth or temperature. Therefore, based on the water redox condition variations and the salinity, three dynamic formation models of the high-frequency sedimentary cycles in a saline basin are established: a deep-water, low-salinity, oxic-dysoxic model (Model I), a medium-water, medium-salinity, anoxic model (Model II) and a shallow-water, high-salinity, anoxic-sulfidic model (Model III). Because the climate gradually turned dry and hot from lake transgression to regression, the continued closure of the basin enhanced evaporation and salinization. In addition, mixed terrigenous clasts, mixed carbonates and mixed evaporites deposited successively. Correspondingly, salinity stratification gradually developed within the lake water, increasing the extent of bacterial sulfate reduction in the bottom water.
... In recent years, substantial progress has been made in characterizing marine redox conditions during the Permian-Triassic crisis based on the study on geochemical data and pyrite framboids, which show that pulses of shallow-marine anoxia and periodic euxinic conditions proliferated during the end-Permian Period to the Smithian Substage (Huang Y G et al., 2017;Chen et al., 2015;Tian et al., 2014;Grasby et al., 2013;Kaiho et al., 2012;Song et al., 2012;Shen et al., 2011;Bond and Wignall, 2010;Liao et al., 2010;Cao et al., 2009;Riccardi et al., 2006;Grice et al., 2005). Although the extent and duration of anoxia events differ in different areas, (Wignall, 1994nized: Dunbar 1994. ...
After the end-Permian mass extinction, genus Claraia (Bivalvia) was the most abundant and most noticeable fossil during the survival and recovery stage. However, the reasons for the proliferation of Claraia are still debated. This paper describes a new Griesbachian (Early Triassic) mollusc fauna from deep-water settings in South China in the aftermath of end-Permian mass extinction. This fauna yielded five bivalve species in two genera (Claraia griesbachi, C. wangi, C. stachei, C. radialis, and Promyalina putiatinensis) and two ammonoid species (Ophiceras sp. and Ussuridiscus sp.) and could be assigned to the Claraia wangi-C. griesbachi assemblage zone, indicating a Middle-Late Griesbachian Age. The bivalves were dominated by Claraia griesbachi and were featured by articulated Claraia fossils. As Claraia was epibyssate, it was an excellent autochthonous fauna. While the shallow and deep marine water became dysoxic to anoxic globally, as indicated by recent studies of the early Early Triassic, we suggest the genus Claraia could tolerate dysoxic and/or anoxic conditions and its proliferation could be attributed to its physiological features which were adapted to the stressed environment. The wide distribution of Claraia was probably related to its planktonic larval stage. Where the larva of Claraia could have been transported by ocean flow and increased its potential for long-distance dispersal. In addition, Claraia was a significant disaster and opportunistic taxon during the Early Triassic based on observations in South China.
... Paleogeographic factors argue against input of significant amounts of terrigenous debris to sections on the South China Craton: Zuodeng and Nhi Tao were located on isolat- ed carbonate platforms, and even the deep-ramp and basinal sections (Chaohu, Daxiakou, Dongpan, Shangsi, and Xinmin) are unlikely to have accumulated much terrigenous material owing to the small size of subaerially exposed landmasses on the periphery of the craton (Fig. 1B). These inferences are supported by petrographic, isotopic, and biomarker studies of these and correlative sections on the South China Craton ( Kaiho et al., 2012;Sawada et al., 2012;Meyer et al., 2013;Luo et al., 2014;Saitoh et al., 2014). ...
The latest Permian mass extinction (LPME) coincidedwithmajor changes in the composition ofmarine plankton
communities, yet little is known about concurrent changes in primary productivity. Earlier studies have inferred
both decreased and increased productivity inmarine ecosystems immediately following the end-Permian crisis.
... Various geochemical and paleoecologic proxies have been employed to reconstruct the marine redox history, such as authigenic uranium concentrations, iron concentrations, cerium anomalies, molybdenum isotopes, uranium isotopes, sulfur isotopes, carbon isotopes, framboidal pyrite petrography, and biomarkers (e.g., Wignall andTwitchett, 1996, 2002;Isozaki, 1997;Wignall and Newton, 2003;Newton et al., 2004;Grice et al., 2005;Kaiho et al., 2006Kaiho et al., , 2012Riccardi et al., 2006Riccardi et al., , 2007Algeo et al., 2007Algeo et al., , 2008Gorjan et al., 2007;Xie et al., 2007;Brennecka et al., 2011;Shen et al., 2007Shen et al., , 2011Shen et al., , 2015Takahashi et al., 2009Takahashi et al., , 2013Takahashi et al., , 2014Takahashi et al., , 2015Zhou et al., 2012;Proemse et al., 2013;Dustira et al., 2013;H.Y. Song et al., 2013H.Y. ...
A detailed, 10 m.y. redox history of Changhsingian to Anisian (latest Permian to Middle Triassic) oceans in ramp settings is reconstructed based on framboidal pyrite analysis from South China. The result shows that the well-established phenomenon of intense ocean euxinia-anoxia is faithfully recorded in pyrite framboid data. Three major euxinia-anoxia episodes, namely, the end-Changhsingian to end-Smithian, middle to late Spathian, and early to middle Anisian, have been recognized from the ramp successions. The first reducing episode is subdivided into four subepisodes: Permian-Triassic boundary, Griesbachian-Dienerian boundary, earliest Smithian, and end-Smithian. Redox variations broadly track other oceano-graphic proxies. Euxinia-anoxia episodes coin-cide with positive excursions of conodont Omega Ce anomalies, negative excursions of delta S-34(cas) (carbonate-associated sulfate), increases in sea-surface temperature, and negative excursions of delta C-13 in most cases. However, euxinia-anoxia near the Dienerian-Smithian boundary coincided with positive excursions of d13C and a general cooling - period. This exception may be the result of locally developed water-column anoxia. The Permian-Triassic boundary subepisode witnessed two ephemeral euxinia-anoxia events separated by a dysoxic to oxic period. The former, together with a rapid increase in sea-surface temperature (up to 8 degrees C), may have been responsible for the biodiversity crisis, while the latter anoxic event destroyed ecosystem trophic structures. In addition to the Permian-Triassic boundary euxiniaanoxia event, which spread over habitats in all oceans, the Spathian and Anisian euxinia-anoxia episodes also prevailed in global oceans. Variation of the oxygen minimum zone are suggested as the driving mechanism that facilitated the movement of oxygen-poor water columns in various paleogeographic settings over this critical period.
... Paleogeographic factors argue against input of significant amounts of terrigenous debris to sections on the South China Craton: Zuodeng and Nhi Tao were located on isolat- ed carbonate platforms, and even the deep-ramp and basinal sections (Chaohu, Daxiakou, Dongpan, Shangsi, and Xinmin) are unlikely to have accumulated much terrigenous material owing to the small size of subaerially exposed landmasses on the periphery of the craton (Fig. 1B). These inferences are supported by petrographic, isotopic, and biomarker studies of these and correlative sections on the South China Craton ( Kaiho et al., 2012;Sawada et al., 2012;Meyer et al., 2013;Luo et al., 2014;Saitoh et al., 2014). ...
Although marine productivity is a key parameter in the global carbon cycle, reliable estimation of productivity in
ancient marine systems has proven difficult. In this study, we evaluate the accumulation rates of three commonly
used proxies for productivity froma set of primarily Quaternary sediment cores at 94 marine sites, compiled from
37 published sources. For each core, mass accumulation rateswere calculated for total organic carbon (TOC), organic
phosphorus (Porg), and biogenic barium (Babio). Calculated mass accumulation rates were compared to two
independent estimates ofmodern regional primary productivity and export productivity, aswell as to twopotential
controlling variables, bulk accumulation rate (BAR) and redox environment. BAR was found to exercise a
strong control on the preservation of organic carbon. The linear regression equations relating preservation factor
to BAR can be transformed to yield equations for primary and export production as a function of TOC and BAR,
two variables that can be readily measured or estimated in paleomarine systems. Paleoproductivity can also be
estimated fromempirical relationships between elemental proxy fluxes andmodern productivity rates. Although
these equations do not attempt to correct for preservation, organic carbon and phosphorus (but not barium) accumulations
rates were found to exhibit a systematic relationship to primary and export production. All of the
paleoproductivity equations developed here have a large associated uncertainty and, so, must be regarded as
yielding order-of-magnitude estimates.
... Paleogeographic factors argue against input of significant amounts of terrigenous debris to sections on the South China Craton: Zuodeng and Nhi Tao were located on isolat- ed carbonate platforms, and even the deep-ramp and basinal sections (Chaohu, Daxiakou, Dongpan, Shangsi, and Xinmin) are unlikely to have accumulated much terrigenous material owing to the small size of subaerially exposed landmasses on the periphery of the craton (Fig. 1B). These inferences are supported by petrographic, isotopic, and biomarker studies of these and correlative sections on the South China Craton ( Kaiho et al., 2012;Sawada et al., 2012;Meyer et al., 2013;Luo et al., 2014;Saitoh et al., 2014). ...
... cano. In addition, at the part of the Permian-Triassic ocean, from the fact that sulfur sulfate isotope ratio (δ34Ssulfate) and sulfide sulfur isotope ratio (δ34Ssulfide) the both are decreasing, that the sea is rich in hydrogen sulfide, and that had reached a reductive environment, have been reported (by Newton et al, 2004;. by Gorjan et al, 2007;. by Kaiho et al, 2012). For example, when attention is paid to the silicate clay in the clay deposit, ejecta shows similarities with the clay layer. The silicate clay tends to perform ion exchange. Although generation temperature of nickel ferrite is 700℃ or more, the jetting temperature of from the crater of the magma of rhyolitic containing rich silicic ac ...
The cause of mass extinction in the Cretaceous-Paleogene (K-P) boundary (about 65.5 million years ago) is known to due to the collision of the asteroid. Furthermore the evidence of huge meteorite impact was found from the formation of Late Triassic (about 215 million years ago), and it was reported that the Manicouagan crater of Canada had been formed by it. However, a temporary cause theory such as the collision of giant meteorite or asteroid is not appropriate about the mass extinction of Mesozoic from the involvement of the continental variation, and the two craters might have been formed by the eruptions of volcano. The formation of the both craters, are inferred from the environmental factors along with the division of the supercontinent Pangaea. From the involvement of the magma and the limestone layer, the announced ejecta has been left inclusive the unreviewed issues. Such as ocean acidification and anoxic conditions, as the factor of mass extinctions at the Triassic and the K-P boundary, disturbance of the carbon cycle is pointed out. Evolution of Proteromorphosis of conodonts had connected to the reproduction of the ancestors of the marine ecosystem of oxygen deficiency caused by the division of the supercontinent Pangaea. The Manicouagan crater of Late Triassic, and the Chicxulub Crater of Cretaceous-Paleogene boundary, the both origins might be due to the eruption of the volcano. Evolution had to follow the earth.
... One of the more controversial proposals is that an extraterrestrial impact (Becker et al. 2001;Kaiho et al. 2001;Basu et al. 2003) could have triggered the rapid volcanism that produced the extensive Siberian flood basalt known as the Siberian Traps (Renne and Basu 1991;Renne et al. 1995;Kamo et al. 2003;Korte et al. 2010). This event could, in turn, have led to an enhanced production of carbon dioxide (Hallam and Wignall 1997;Brand et al. 2012), a climatic warming (Hallam and Wignall 1997;Kidder and Worsley 2004;Joachimski et al. 2012), a change in ocean chemistry to more anoxic conditions (Wignall and Twitchett 1996;Isozaki 1997), a significant disturbance of the carbon cycle (Berner 2002), a change in ocean salinity (Kidder and Worsley 2004), a large shift in the composition of sulphur and strontium isotopes (Newton et al. 2004;Riccardi et al. 2006;Algeo et al. 2008;Kaiho et al. 2012), and a denitrification of the water mass (Knies et al. 2013). Drops in atmospheric oxygen (Weidlich et al. 2003) and sea level have also been suggested (Hallam and Wignall 1999;Wu et al. 2010). ...
The Permian-Triassic mass extinction is postulated to be related to the rapid volcanism that produced the Siberian flood basalt (Traps). Unrelated volcanic eruptions producing several episodes of ash falls synchronous with the Siberian Traps are found in South China and Australia. Such regional eruptions could have caused wildfires, burning of coal deposits, and the dispersion of coal fly ash. These eruptions introduced a major influx of carbon into the atmosphere and oceans that can be recognized in the wall structure of foraminiferal tests present in survival populations in the boundary interval strata. Analysis of free specimens of foraminifers recovered from residues of conodont samples taken at a Permian-Triassic boundary section at Lung Cam in northern Vietnam has revealed the presence of a significant amount of elemental carbon, along with oxygen and silica, in their test wall structure, but an absence of calcium carbonate. These foraminifers, identified as Rectocornuspira kalhori, Cornuspira mahajeri, and Earlandia spp. and whose tests previously were considered to be calcareous, are confirmed to be agglutinated, and are now referred to as Ammodiscus kalhori and Hyperammina deformis. Measurement of the 207Pb/204Pb ratios in pyrite clusters attached to the foraminiferal tests confirmed that these tests inherited the Pb in their outer layer from carbon-contaminated seawater. We conclude that the source of the carbon could have been either global coal fly ash or forest fire-dispersed carbon, or a combination of both, that was dispersed into the Palaeo-Tethys Ocean immediately after the end-Permian extinction event.
... Generally, Pr/Ph ratio <1 indicates anoxic conditions while Pr/ Ph ratio >1 indicates oxic conditions (Didyk et al., 1978), though some researchers have proposed a higher threshold Pr/Ph ratio of 2 for the anoxic/oxic transition (Hays et al., 2007Kaiho et al., 2012). High gammacerane index indicates a stratified, anoxic water column (Schoell et al., 1994;Sinninghe Damsté et al., 1995). ...
... , Gradstein et al. (2012), Jin et al. (2000), Cao et al. (2002), Kaiho et al. (2009), Kaiho et al. (2012), and Xie et al. (2005). The chemo-stratigraphic Permian-Triassic boundary (mass extinction horizon) and biostratigraphic Permian-Triassic boundary place at the top of Bed 24e and within Bed 27, respectively. ...
The most severe mass extinction in Earth's history occurred at the end of Permian Period, and recovery from this mass extinction extended until the subsequent Early Triassic. Organic geochemical works from many studies of shallow water platform sedimentary strata have indicated that increases in green sulphur bacterial and cyanobac-terial biomasses as well as terrigenous organic material occurred in end-Permian to earliest Triassic shallow-marine environments. Additionally, recent studies on pelagic deep sea sedimentary rocks in accretionary complexes of Japan have increased understanding of the low latitudinal Panthalassic record through the Late Permian and into the Early Triassic. Correlations of conodont fossil occurrences and stable carbon isotope compositions of organic matter in the continuous deep-sea Permian-Triassic boundary section indicate that the mass extinction horizon is located at the onset of black claystone above microfossil-rich siliceous claystone beds. Although this black claystone bed suggests oxygen-poor conditions, bacterial blooms and terrigenous inputs in the pelagic region were not especially significant based on the detected smooth organic carbon isotope curve, which does not include any isotopically heavier signals. Subsequent recovery of radiolarian chert deposition occurred at the late Early Triassic–early Middle Triassic transition. Organic molecules have been detected from these strata. Considering their producing processes in the pelagic deep sea, highly concentrated dibenzothiophene in the latest Early Triassic black chert indicate sulfur-rich depositional conditions. Also, high concentrations of polycyclic aromatic hydrocarbons (PAHs) suggests a high flux of marine organic matter during the latest Early Triassic. As these occurrences coexist with changes in perhaps bacterial community and decreases in radiolarian fossil diversity, this event may be related to the delay in the recovery of life and environments after the end-Permian mass extinction.
... A number of studies have attempted to reconstruct changes in marine redox conditions during the crisis interval, mostly focusing on the PTB transition, based on biomarkers, carbon isotopes, sulfur isotopes, U isotopes and Mo isotopes (Wignall and Newton, 2003;Newton et al., 2004;Grice et al., 2005;Kaiho et al., 2006Kaiho et al., , 2012Riccardi et al., 2006;Algeo et al., 2007Algeo et al., , 2008; Gorjan et al., 2007;Gorjan et al., 2007;Riccardi et al., 2007;Xie et al., 2007;Liao et al., 2010;Nielson et al., 2010;Brennecka et al., 2011;Y.A. Shen et al., 2011;Dustira et al., 2013;He et al., 2013;Zhou et al., 2013). In contrast, relatively few studies have attempted to reconstruct longer-term changes in marine redox conditions or other environmental parameters during the Early Triassic (Isozaki, 1997;Marenco et al., 2008Marenco et al., , 2012Takahashi et al., 2009;Grasby et al., 2013;H.Y. ...
Widespread oceanic anoxia has been implicated as an important factor in the PTB (Permian Triassic boundary) mass extinction and the delayed recovery of Early Triassic marine ecosystems. An investigation of framboidal pyrite in the Bianyang section (Nanpanjiang Basin, South China) suggests that euxinia/dysoxia peaked during the Induan, late Smithian to earliest Spathian and late Spathian. These anoxic episodes show a relationship, albeit imperfect, to major episodes of climatic warming during the Early Triassic that were associated with intensified oceanic stratification, reduced marine productivity and organic carbon sinking fluxes, as well as diminished burial fluxes of organic carbon and reduced sulfur. In contrast, intervals of better-oxygenated marine conditions were associated with episodes of relative climatic cooling during the early to middle Smithian and mid-Spathian. The degree of ventilation of the thermocline region, in particular, had a profound effect on marine biotas, with intervals of improved ventilation resulting in increased global diversity among ammonoids and conodonts and increased local abundance of foraminifera in the Nanpanjiang Basin. These observations suggest that oceanic redox fluctuations played an important role in the delayed recovery of Early Triassic marine ecosystems, and, specifically, that episodic expansion of oceanic oxygen-minimum zones (OMZs) resulted in repeated setbacks to the recovery process, a pattern that persisted until the late Spathian.
... The ensuing biogeochemical disruption would likely have been widespread. For example, anaerobic methane oxidation may have increased sulfide levels (47), possibly resulting in a toxic release of hydrogen sulfide to the atmosphere, causing extinctions on land (48). Although such implications remain speculative, our work makes clear the exquisite sensitivity of the Earth system to the evolution of microbial life. ...
Significance
The end-Permian extinction is the most severe biotic crisis in the fossil record. Its occurrence has been attributed to increased CO 2 levels deriving from massive Siberian volcanism. However, such arguments have been difficult to justify quantitatively. We propose that the disruption of the carbon cycle resulted from the emergence of a new microbial metabolic pathway that enabled efficient conversion of marine organic carbon to methane. The methanogenic expansion was catalyzed by nickel associated with the volcanic event. We support this hypothesis with an analysis of carbon isotopic changes leading up to the extinction, phylogenetic analysis of methanogenic archaea, and measurements of nickel concentrations in South China sediments. Our results highlight the sensitivity of the Earth system to microbial evolution.
... DBTs are aromatic sulfur compounds (ASCs) found in sediments and soils of various geological ages (Chakhmakhcehv and Suzuki, 1995;Hughes et al., 1995;Ramanampisoa and Radke, 1995;Takahashi et al., 2009;Oba et al., 2011;Kaiho et al., 2012). ASCs such as DBTs are predominantly formed by the reaction of reduced inorganic sulfur species with functionalized organic molecules during deposition and early diagenesis (Hughes, 1984;Sinninghe Damsté and de Leeuw, 1990). ...
Oceanic Anoxic Event 2 (OAE 2) during the Cenomanian-Turonian (C/T) transition caused stepwise marine extinctions. Using organic compounds, stable carbon and oxygen isotopes, and foraminifera from three depth-transect sections in northern Spain, this study revealed repeated anoxic/euxinic events coinciding with warming and stepwise extinctions of planktonic and/or benthic foraminifera within intermediate to surface waters in the proto-North Atlantic during the C/T transition. Those short-duration euxinic events occurred four times: at 93.95 Ma, marked by the extinction of Rotalipora greenhornensis; at 93.90 Ma, marked by the extinction of Rotalipora cushmani; at the mid-time maximum of the plateau of the δ13C of carbonates (93.70 Ma); and at the time of the C/T boundary (93.55 Ma). Furthermore, the main benthic foraminiferal extinctions occurred during the first and second euxinic events in the upper slope, during the second and third euxinic events in the outer to middle shelf, and during the third and fourth events in the middle shelf. The main euxinic events in each section also showed a progression to the shallow shelf. The main anoxia-extinction events occurred in the upper slope and outer shelf then moved to the middle shelf. The shallowest section had relatively weak anoxia and a proportionally low extinction rate. These new findings indicate that foraminiferal extinctions started from the intermediate water and the continental slope and then moved to the continental shelf. This was the result of the repeated progression of euxinic-anoxic water from the upper slope to the middle shelf on the eastern continental margin of the proto-North Atlantic four times during a 400 kyr period, to the end of the Cenomanian.
... These timescale estimations are not consistent but do at least argue that this reducing water preceded the end-Permian mass extinction by about a hundred thousand years. At a similar time (less than a million years before the main mass extinction event), euxinic shallow water was reported to have been present on the east Tethyan platform from biomarker evidence (Grice et al., 2005;Cao et al., 2009;Kaiho et al., 2012). These developments of both oxygen-poor shallow water and deep water may be linked. ...
... The evolution of the mid-water refuge zone during the Early Triassic. Carbon isotope data3,7,29 , sulfur isotope data30,31 , temperaturedata 3,5 , and conodont VCe data showing redox conditions 22 are all from South China. Environmental data in the Changhsingian and PTB strata are from Meishan section whereas those in the Lower and Middle Triassic are from Nanpanjiang Basin. ...
The Permian-Triassic mass extinction was the most severe biotic crisis in the past 500 million years. Many hypotheses have been proposed to explain the crisis, but few account for the spectrum of extinction selectivity and subsequent recovery. Here we show that selective losses are best accounted for by a combination of lethally warm, shallow waters and anoxic deep waters that acted to severely restrict the habitable area to a narrow mid-water refuge zone. The relative tolerance of groups to this double whammy provides the first clear explanation for the selective extinction losses during this double-pulsed crisis and also the fitful recovery. Thus, high temperature intolerant shallow-water dwellers, such as corals, large foraminifers and radiolarians were eliminated first whilst high temperature tolerant ostracods thrived except in anoxic deeper-waters. In contrast, hypoxia tolerant but temperature intolerant small foraminifers were driven from shallow-waters but thrived on dysoxic slopes margins. Only those mollusc groups, which are tolerant of both hypoxia and high temperatures, were able to thrive in the immediate aftermath of the extinction. Limited Early Triassic benthic recovery was restricted to mid-water depths and coincided with intervals of cooling and deepening of water column anoxia that expanded the habitable mid-water refuge zone.
While it is widely accepted that early animals originated and primarily evolved during the Neoproterozoic to
Cambrian period, there remains ongoing debate over how fluctuations in marine-atmospheric oxygen levels
influenced their evolution and diversification. To investigate this, we analyzed pristane/phytane ratios—a redoxproxy
based on organic geochemistry—in surface sediments from the Cryogenian to Cambrian successions in
South China, Oman, and Australia. The temporal changes in this proxy exhibited consistent patterns across all
sites, revealing five cycles of anoxic to oxic conditions in the ocean between 660 and 510 Ma. By examining the
average pristane/phytane ratios, we identified three events when oxygen levels increased. This represents a
transition from anoxic conditions to anoxic-dysoxic boundary at 630–600 Ma, followed by a shift to dysoxic
conditions at 570 Ma (Shuram event), and finally reaching oxic conditions at 520 Ma (Cambrian explosion).
Significantly, these oxygenation events align with eumetazoan evolution. An inverse relationship was observed
between oceanic redox events and positive/negative shifts of δ13Ccarb, occurring between the first and second
oxygenation events, suggesting an increase in atmospheric oxygen levels. Based on these findings, we propose
that there were global increases in oceanic and atmospheric oxygen levels, at least during the early Ediacaran
period. These shifts in oxygen levels likely played a role in influencing the rate of evolution among early animals.
The composition of past photosynthetic organisms provides information about the paleo-environment based on the habitat characteristics of photosynthetic organisms. Therefore, analysis of chlorophyll-derived materials from photosynthetic organisms in sedimentary rocks is important for understanding paleo-environmental changes. Fossilized chlorophylls present in sedimentary rocks can be detected by their conversion into maleimides and phthalimides. This can be achieved through the chromic acid oxidation of sedimentary rocks. Since the maleimides and phthalimides are derived from the pyrrole skeleton of fossil chlorophylls, their composition reflects the composition of paleo-photosynthetic organisms. We herein propose an indicator for detecting anoxic-sulfidic conditions in the paleo oceanic photic zone, which is based on the composition ratio of the maleimides produced during the oxidation process. The maleimide index in this study would be a useful analytical method to indicate that anoxic-sulfidic conditions in the paleo oceanic photic zone, which is associated with mass extinction events, have occurred.
Despite the extensive use of sulphur isotope ratios (δ³⁴S) for understanding ancient biogeochemical cycles, many studies focus on specific time-points of interest, such as the end-Permian mass extinction (EPME). We have generated an 80 million-year Permian–Triassic δ³⁴Sevap curve from the Staithes S-20 borehole, Yorkshire, England. The Staithes δ³⁴Sevap record replicates the major features of the global curve, while confirming a new excursion at the Olenekian/Anisian boundary at ~ 247 million years ago. We incorporate the resultant δ³⁴Sevap curve into a sulphur isotope box model. Our modelling approach reveals three significant pyrite burial events (i.e. PBEs) in the Triassic. In particular, it predicts a significant biogeochemical response across the EPME, resulting in a substantial increase in pyrite burial, possibly driven by Siberian Traps volcanism. Our model suggests that after ~ 10 million years pyrite burial achieves relative long-term stability until the latest Triassic.
Redox variations across the Permian‐Triassic boundary (PTB) have long been debated, especially during the proliferation of PTB microbialites. Here, we report redox fluctuations across the PTB to evaluate links between the two based on pyrite framboid analysis from basin to platform settings in South China. During the end‐Permian extinction, abundant framboids indicate a widespread anoxia that was likely a direct cause of extinction. In the earliest Triassic (Hindeodus parvus conodont zone), pyrite framboids were absent in ramp to basin and shallow, nonmicrobialite platform sections. In contrast, the coeval microbialites yield abundant framboids indicative of dysoxia. The fact that framboids were only confined to PTB microbialites and absent in other habitats indicates that microbe bloom may have stimulated dysoxic watermass and triggered the framboid growth within microbe aggregates. Thus, microbialites were not built in reducing settings, but instead, microbial proliferation caused local, dysoxia within shallow oxygenated platforms after the extinction.
The Permian−Triassic mass extinction was the most severe biotic crisis of the past 540 million years, eliminating 80–90% of species in the ocean and ~ 70% of land-based vertebrate families. Researchers have debated whether terrestrial vegetation collapse occurred before or after the marine extinction, or if they were synchronous. We analyzed the ratios of normal alkanes of terrestrial plant origin to total normal alkanes (terrestrial plant index) as well as those of pristane to phytane, which are affected by terrestrial plant inflow and ocean redox, in shallow marine, terrestrial lagoon, and central deep-ocean sedimentary rocks from China, Italy, India, and Japan to elucidate the terrestrial vegetation history. Interpretation of pristane/phytane ratios was conducted through comparison with other seawater redox indices. Both proxies indicate that two terrestrial vegetation collapses occurred, before and at the end-Permian marine extinction in the coastal sea environment, followed by the complete plant devastation, and a subsequent terrestrial vegetation proto-recovery in the earliest Triassic. The two proxies showed opposite patterns in a terrestrial lagoon setting section, and those from a central deep-ocean setting indicate that little terrestrial plant material reached the central ocean. These differing responses of the pristane/phytane ratios among geographical settings are consistent with natural phenomena, indicating that the method proposed in this study results in valid reconstruction of vegetation changes. Cyanobacterial blooms occurred from the end-Permian vegetation collapse until after the massive plant-soil erosion, suggesting that terrestrial ecosystem disturbance caused deterioration of the environment for eukaryotic algae in the coastal sea and terrestrial lagoon.
The late Neoproterozoic (645–535 Ma) represents a key geological period, when a climate shift and revolutionary biological innovations occurred during the Precambrian–Cambrian transition. The Marinoan glaciation impacted the climate and chemical composition of the oceans, restraining the evolution of early life. To elucidate evolutionary processes during the Marinoan–Ediacaran transition, this study presents biomarker evidence (molecular fossils) from the Nantuo Formation and the lower part of the Doushantuo Formation at the Jiulongwan section, China. Our results reveal possible photosynthetic activity (n-C17 + n-C19 [algae] and pristane + phytane [photosynthesis]) during the Marinoan glaciation, followed by low productivity during the early period of cap dolostone precipitation, and recovery of photosynthetic organisms (n-C17 + n-C19: from 0.00 to 0.96 μg/g TOC; pristane + phytane: from 0.00 to 3.6 μg/g TOC) or other bacteria (hopanes: from 0.00 to 0.07 ng/g TOC) during late cap carbonate deposition, with the expansion of eukaryotes (steranes/[hopanes + steranes]: from 0.0 to 0.6) after cap carbonate deposition in the early Ediacaran.
Combustion-derived polycyclic aromatic hydrocarbons (PAHs) are frequently used as molecular proxies for wildfire in recent and ancient sediments. Here, we document the abundances of four hydrocarbon compounds, i.e., phenanthrene (Phe), benzo[e]pyrene (BeP), benzo[ghi]perylene (Bpery), and coronene (Cor), across the Permian–Triassic boundary (PTB) in five marine sections of South China. High values of PAHs are present below the end-Permian mass extinction (EPME) horizon, from the Clarkina changxingensis Zone to the Clarkina yini Zone, suggesting strong perturbations to terrestrial ecosystems predating the marine crisis. PAHs peaked in the uppermost C. yini Zone, correlative with the EPME, reflecting simultaneity of the most severe phases of the terrestrial and marine crises. The proxy records document suitable climatic conditions for wildfires (high pO2) throughout the P-Tr transition. The results of the present study are also significant in validating the utility of BeP, Bpery, Cor, and BeP/Phe as proxies for terrestrial wildfires in deep-time marine successions.
The study of accretionary tectonics in Japan is intrinsically linked to Paleozoic and Mesozoic microfossil research, with advances in one area determining progress in the other. This paper provides a review of biostratigraphic and biological research of radiolarians and conodonts conducted in Japan over the past 25 years. Following ‘the Radiolarian Revolution’ that was a breakthrough of interpretation of accretionary complexes by establishment of radiolarian biostratigraphy in the late 1970s and early 1980s, our understanding of radiolarian biostratigraphy has advanced significantly. Notably, since the 1990s the resolution of radiolarian biozones has greatly increased, leading to an improved understanding of middle Paleozoic to Mesozoic biostratigraphy. In contrast, the study of conodont biostratigraphy in Japan has been limited over the last 25 years. However, conodonts are increasingly acknowledged internationally as an important index fossil group for the study of Permian and Triassic stratigraphy. Further advances in radiolarian and conodont biostratigraphy will be gained from more accurately calibrating microfossil biozones to one other and to a chronostratigraphic scale. The study of radiolarian biology in Japan has focused on phylogenic analysis and reproduction. Well-preserved Triassic conodont specimens have been identified within pelagic sedimentary rocks in accretionary complexes, facilitating studies of conodont paleontology. The future of radiolarian and conodont research depends on the next generation of researchers. For the further progress of the microfossil study, more effort should be placed on student training and popularizing microfossils.
Quasi-periodic changes in Earth's orbital parameters (i.e., Milankovitch cycles) are widely recorded in rhythmic sediments. Astrochronology, which uses such sedimentary cycles, has been used to improve the geologic timescale and advance our understanding of Earth system dynamics, principally during the Cenozoic Era. Paleozoic to Mesozoic radiolarian bedded chert deposits consist of rhythmic alternations of chert and shale that are potentially related to Milankovitch-scale changes in the flux of biogenic silica . Here we review recent progress in astrochronology and its applications to Permian to Cretaceous bedded chert deposits. The sedimentary rhythms of bedded chert display a full range of climatic precession- and eccentricity-related cycles: a 20 kyr cycle is preserved as a chert-shale couplet and ~100, 405, 2000-4000, and 10,000 kyr cycles are recorded as variations in the thicknesses of individual beds. Using an anchor at the end-Triassic extinction level at 201.5 ± 0.2 Ma, an astronomical timescale for the Triassic-Jurassic Inuyama bedded chert (Inuyama-ATS) is established. Estimates of the burial flux of biogenic silica show fluctuations of 20%-50% over 100 kyr to 30 Myr cycles, suggesting that orbital-scale chemical weathering on Pangea would have controlled the sedimentary rhythms of bedded chert through the biogeochemical Si cycle.
Biogenic carbonates are important archives for reconstructing the marine sulfur cycle. However, uncertainties exist about the exact location of carbonate associated sulfate (CAS) and a possible biological control on sulfate incorporation. The behavior of CAS in biogenic carbonates during diagenetic alteration is even more poorly constrained. To investigate the mechanisms of sulfur incorporation and the effects of alteration on sulfur in biogenic carbonates, modern marine bivalve shells of Arctica islandica species were hydrothermally altered at 100 °C and 175 °C. Fluorescence microscopy, element mapping via NanoSIMS and μ-XRF, sulfur XANES analyses, and δ³⁴S measurements were performed on the experimentally altered shell segments. Changes in elemental compositions and δ³⁴S of sulfate in the post-alteration solutions were also determined. Results indicate clear differences between the δ³⁴S values of the CAS (+21‰, V-CDT) that reflects ambient seawater sulfate and the organically bound sulfur that is isotopically lighter (+14.8‰, V-CDT or less). Carbonate associated sulfate is primarily incorporated in the mineral phase of the shell, whereas reduced sulfur phases are mainly found within the intrashell organic matter. Hydrothermal alteration experiments at 100 °C resulted in minimal changes of sulfur within the bivalve shells. In contrast, the 175 °C experiments triggered decomposition of intrashell organic matrices which then led to extensive diagenetic alteration in both the shell microstructure and chemistry. Changes in total concentration, speciation, and spatial distribution of sulfur reflect the diagenetic processes that occurred within the shells. Preferential incorporation of CAS in a neomorphic calcite phase with Mg/Ca ratios of 0.13-0.21 was observed. Due to its presence in both organic and inorganic phases and its multiple oxidation states with different isotopic compositions we conclude that sulfur is a useful and sensitive proxy for diagenetic alteration in biogenic aragonite.
Paleoceanic environmental stresses (e.g., expanded anoxia, elevated siliciclastic fluxes) are thought to have been important factors in the latest Permian mass extinction (LPME). Here, we investigate changes in redox conditions and siliciclastic fluxes during the Permian-Triassic transition in South China through in-situ analysis of the rare earth element (REE) composition of albid crowns of single conodont elements measured using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). For comparison, we also analyzed REEs in the sediment matrix enclosing the conodonts (i.e., whole-rock samples). The study locale (Yangou) was located on a shallow carbonate platform on the eastern margin of the Yangtze Platform to minimize the influence of detrital siliciclastics and, thus, enhance the chances of recovering a hydrogenous (seawater-sourced) REE signal.
The Late Ordovician glaciation (Hirnantian) is one of the most critical glaciation events in Earth history. The end-Ordovician mass extinction and associated environmental changes are well recorded at the GSSP section (Wangjiawan) in Yichang, South China. In this study, we investigated and sampled across Ordovician-Silurian boundary from Wangjiawan riverside section (~180 m south to the GSSP section), attempted to reconstruct the carbon and oxygen isotope variation in high-resolution. Guanyinqiao Formation is underlain by Upper Ordovician Wufeng graptolite shale and overlain by Lower Silurian Longmaxi graptolite shale. It is characterized by a set of argillaceous limestone with less than 30cm in thickness and preserves abundant Hirnantia fauna fossils. High-resolution measurement of stable carbon and oxygen isotope composition of 25cm-thick Guanyinqiao interval suggests that δ13Ccarb variation appears an obvious negative excursion with the nadir of -12.8 ‰ as the most depleted δ13Ccarb value reported at this interval so far globally. We interpret that the distinct negative excursion indicates abrupt changes in environment during Guanyinqiao period, which reveals the injection of massive extra light carbon (12C) component into the dissolved inorganic carbon reservoir (DIC) with sea-level drop during glaciations. It is inferred to be associated with the aerobic and anaerobic oxidation of methane (AOM) and organic matter.
The lastest Permian mass extinction (LPME) coincided with major changes in the composition of marine plankton communities, yet little is known about concurrent changes in primary productivity. Earlier studies have inferred both decreased and increased productivity in marine ecosystems immediately following the end-Permian crisis. Here, we assess secular and regional patterns of productivity variation during the crisis through an analysis of the burial fluxes of three elemental proxies: total organic carbon (TOC), phosphorus (P), and biogenic barium (Babio). Primary productivity rates appear to have increased from the pre-crisis Late Permian through the Early Triassic in many parts of the world, although the South China Craton is unusual in exhibiting a pronounced decline at that time. Most of the 14 Permian-Triassic study sections show concurrent increases in sediment bulk accumulation rates, suggesting two possible influences linked to subaerial weathering rate changes: (1) intensified chemical weathering, resulting in an increased riverine flux of nutrients that stimulated marine productivity, and (2) intensified physical weathering, leading to higher fluxes of particulate detrital sediment to continental shelves,thus enhancing the preservation of organic matter in marine sediments. An additional factor, especially in the South China region, may have been intensified recycling of bacterioplankton-derived organic matter in the ocean-surface layer, reducing the export flux rather than primary productivity per se. The ecosystem stresses imposed by elevated fluxes of nutrients and particulate sediment, as well as by locally reduced export fluxes of organic matter, may have been important factors in the ~ 2- to 5-million-year-long delay in the recovery of Early Triassic marine ecosystems.
Kaiho et al. (2013) showed that high values of organic molecule indices of combustion, soil erosion, and euxinia occurred at the Frasnian-Famennian transition at Sinsin, Belgium. Marynowski and Racki (2014) commented on the paper. Their issues mainly address (1) the low resolution of the data, (2) the reliability of the proxies, (3) weathering as a cause of the peaks of the proxies, (4) the discrepancy between rare charcoal occurrence and the high combustion proxy, and (5) the stepwise collapse of the huge global reef ecosystem ending well before the F-F boundary. In response to comment (1), the positive excursion of δ13Ccarb marking the F-F transition in the Sinsin section indicates that the Sinsin section has enough strata to detect environmental changes during the culmination of the Late Devonian stepwise mass extinction. On comment (2): soil erosion was indicated not only by dibenzofuran but also by a spike of cadalene. Dibenzothiophene should have increased when euxinic water developed on the surface of sediments, which is supported by the coincidence of isorenieratane and dibenzothiophene on the middle shelf in the late Permian. We show the combustion index at the Cretaceous-Paleogene transition, indicating that this ratio is useful as a proxy of combustion. On comment (3): we cannot explain the high and low combustion, soil erosion, and euxinia index values by weathering because of the consistently well-preserved state of the rock samples. On comment (4): we need to detect charcoal during the F-F transition and early Famennian, corresponding to maxima of high sea levels, to clarify the discrepancy. On comment (5): our model is only for the F-F transition event marked by the extinction acme; it may not explain the collapse of the reef ecosystem that ended before the F-F boundary, but it can explain the extinction acme at the F-F transition.
The widespread development of anoxic and dysoxic deposition in marine settings occurred during the Permian-Triassic (P-Tr) transition interval. Facies varied according to paleobathymetry and paleolatitude. Thus, dark gray, uranium-enriched shales characterize deeper shelf locations over wide areas of northern Boreal seas, whereas the oceanic record consists of condensed, organic-rich, black shales. Finely laminated, pyrite-rich, micritic mudstones occur in equatorial Tethyan sections. Contemporaneous dolomitization in many shallow-marine settings provides further indirect evidence for widespread P-Tr anoxia. Similarly, common reports of unusual stromatolites in the earliest Triassic Griesbachian Stage could reflect the widespread occurrence of direct calcite precipitation from carbonate-saturated anoxic bottom waters. Oxygen-poor conditions are first recorded from the Late Permian, deep-water, accreted oceanic terranes of Japan. Such conditions vastly increased in extent in the interval between the latest Permian and the late Griesbachian, when dysaerobic facies developed in all but the shallowest of marine settings. The Panthalassa ocean was probably truly euxinic in this interval. Anoxia was never so extensive or so intense after this interval, and the superanoxic event ceased abruptly in equatorial Tethyan latitudes in the latest Griesbachian. Elsewhere, anoxia persisted at least into the Dienerian Stage in the Perigondwanan shelf sections of the Neo-Tethys, and deep-water anoxia may have persisted in Panthalassa until the middle Triassic.
The cause of the great Permian-Triassic (P-T) boundary mass extinctions remains unknown. A crucial step in identifying the cause involves a precise timing of the mass extinction interval (MEI) in order to reconstruct the pattern of biotic evolution and the chronologic record of potential triggers. Here we present an estimate of the P-T boundary MEI duration based on astronomical tuning of multiple cyclic sedimentary records. Magnetic susceptibility data from Shangsi, southern China, provide evidence for strong 405 k.y. orbital eccentricity forcing throughout the P-T boundary interval. Radioisotope dating combined with 405 k.y. tuning provides an absolute time scale through the P-T boundary interval at unprecedented high resolution. An estimated similar to 700 k.y. duration for the MEI at Shangsi is supported by eccentricity tuned estimates of four other sections in China and Austria. In addition, at Shangsi, the onset of mass extinction occurred shortly following a coincidence of minima in the observed similar to 1.5 m.y., 405 k.y., and similar to 100 k.y. cycles. A change in the magnetic susceptibility response to astronomical forcing occurred just prior to the onset of extinction, with reduced 100-k.y.-scale cyclicity continuing into the Early Triassic for more than 2 m.y.
We found earliest Triassic (Griesbachian) conodont, Hindeodus parvus, from the basal part of the black carbonaceous claystone of the Ubara Permian/Triassic boundary section in the Tamba Belt. We also obtained Late Permian (Changxingian) conodonts from the underlying gray siliceous claystone as already reported from other P/T boundary sections. The lithologic boundary between the gray siliceous claystone and the black carbonaceous claystone is confirmed to be the Permian/Triassic boundary in deep-sea sedimentary rocks.
We have detected a family of benzohopanes cyclised at C-20 and two families of diaromatic 8(14)-secohopanoids, in carbonates from the Late Permian Meishan (China) and Bulla (Italy) sections. Furthermore, we have identified a C 33 8(14)-secohopanoid possessing a fluorene moiety. The relative distribution of 8(14)-secohopanoids with a fluorene moiety was similar to that of benzohopanes cyclised at C-20, suggesting that the secohopanoids might be diagenetic products of benzohopanes, or that the benzohopanes and secohopanoids share the same precursor. Furthermore, the series of benzohopanes cyclised at C-16 was not detected from the carbonates of the two sections, which might suggest that the benzohopanes cyclised at C-16 are thermodynamically less stable than those with the aromatic ring attached at C-20.
Our studies in southern China have revealed a remarkable sulfur and
strontium isotope excursion at the end of the Permian, along with a
coincident concentration of impact- metamorphosed grains and kaolinite
and a significant decrease in manganese, phosphorous, calcium, and
microfossils (foraminifera). These data suggest that an asteroid or a
comet hit the ocean at the end of Permian time and caused a rapid and
massive release of sulfur from the mantle to the ocean-atmosphere
system, leading to significant oxygen consumption, acid rain, and the
most severe biotic crisis in the history of life on Earth.
Patterns of taxonomic and ecologic selectivity are the most direct record of processes influencing survival during background and mass extinctions. The Guadalupian (Capitanian) and end-Permian (Changhsingian) extinctions have both been linked to environmental degradation from eruption of large flood basalts; however, the extent to which taxonomic selectivity conforms to the expected stresses remains incompletely understood because many of the relevant bio-logical traits are mutually correlated. Here we use a large occurrence-based database to quantify extinction selectivity during background and mass extinction intervals from the Kungurian (latest Early Permian) to Changhsingian. Our multiple logistic regression analysis confirms that the end-Permian extinction was a physiological crisis, selecting against genera with poorly buffered respiratory physiology and calcareous shells. Genera with unbuffered physiology also fared poorly in the Guadalupian extinction, consistent with recognition of a pronounced crisis only among protists and reef-builders and implying similar respiratory physiological stresses. Despite sharing a similar trigger, the end-Permian extinction was considerably more severe than the Guadalupian or other Phanerozoic physiological crises. Its magnitude may have resulted from a larger environmental perturbation, although the combination of warming, hypercapnia, ocean acidification, and hypoxia during the end-Permian extinction likely exacerbated the crisis because of the multiplicative effects of those stresses. Although ocean carbon cycle and evolutionary changes have reduced the sensitivity of modern ecosystems to physiological stresses, extant marine invertebrates face the same synergistic effects of multiple stressors that were so severe during the end-Permian extinction.
Simple calculations show that if deep-water H2S concentrations increased beyond a critical threshold during oceanic anoxic intervals of Earth history, the chemocline separating sulfidic deep waters from oxygenated surface waters could have risen abruptly to the ocean surface (a chemocline upward excursion). Atmospheric photochemical modeling indicates that resulting fluxes of H2S to the atmosphere (>2000 times the small modern flux from volcanoes) would likely have led to toxic levels of H2S in the atmosphere. Moreover, the ozone shield would have been destroyed, and methane levels would have risen to >100 ppm. We thus propose (1) chemocline upward excursion as a kill mechanism during the end-Permian, Late Devonian, and Cenomanian Turonian extinctions, and (2) persistently high atmospheric H2S levels as a factor that impeded evolution of eukaryotic life on land during the Proterozoic.
The Meishan section across the Permian-Triassic boundary in South China is the most thoroughly investigated in the world. A statistical analysis of the occurrences of 162 genera and 333 species conÞrms a sudden extinction event at 251.4 million years ago, coincident with a dramatic depletion of d13C carbonate and an increase in microspherules.
There is growing evidence of the Lilliput effect in the end-Permian mass extinction and its aftermath. However, very little has been published on assessing the Lilliput effect on protozoans in the Early Triassic based on quantitative analysis of a great quantity of samples from outcrop sections. This study investigates foraminiferal test size variations through the Changhsingian to the Olenekian based on fossil records from three outcrop sections in South China. The sharp reduction in foraminifer sizes coincides with the first or main episode of the end-Permian mass extinction. Foraminifers remained small in sizes in the early Induan. Their body sizes increased slowly in the late Induan to Olenekian, but never recovered to the pre-extinction test size levels. The Lilliput effect on foraminifera in the aftermath of the end-Permian crisis is indicated by the extinction of large taxa, decrease in size for surviving taxa and rise of small-sized new forms. Physiological reactions of various foraminifer groups reveal that several defaunation events such as anoxia, ocean acidification, and global warming that prevailed through the Permian–Triassic interval may be responsible for both the end-Permian crisis and the Lilliput effect.
Coeval records of ocean, atmosphere, and terrestrial change are crucial to understanding the pattern and causes of global mass extinction across the Permian-Triassic boundary (PTB). However, relationships among changes in different settings remain largely unclear, primarily due to the challenges associated with the correlation among disparate records. Here we compare marine carbon isotopic records with marine and terrestrial environmental and biotic events recorded in sediments from the Meishan PTB section of south China. Time-scaled carbonate carbon isotopes exhibit two gradual major shifts across the PTB at Meishan, and these are duplicable elsewhere around the Tethys Ocean. The two shifts are associated with two episodes of enhanced terrestrial weathering indicated by an increased abundance of 13C-enriched moretanes relative to hopanes and an elevated abundance of black carbon fragments. Key marine events previously reported for the PTB, including photic zone euxinia, faunal mass extinction, and cyanobacterial expansion, also occur as two episodes, coinciding with both of the progressive shifts to negative δ13C values and enhanced weathering. The temporal sequence of the duplicable events suggests that the biotic crisis was a consequence of prolonged and episodic changes in the marine and continental systems, and argues against an extraterrestrial impact as the main cause.
Eight brachiopod species in seven genera are described from the Permian–Triassic boundary beds of South China and northern Italy. The brachiopods from northern Italy are described for the first time and include two new species: Orbicoeliadolomitensis Chen and Spirigerella? teseroi Chen. The Permian affinity of these brachiopods and their stratigraphical position above the extinction horizon demonstrate that they are survivors from the end-Permian mass extinction. The surviving brachiopods from South China, which was located at the eastern margin of the Palaeo-Tethys Ocean, are considerably abundant and diverse and are dominated by geographically widespread generalist elements adapted to a wide variety of environments. They were mostly limited to the Upper Permian to lowest Griesbachian. In contrast, the survivors in northern Italy, which was situated at the western margin of the Palaeo-Tethys, comprise elements ranging from the Carboniferous to Permian or widespread Tethyan genera. These survivors did not occur in the pre-extinction western Tethyan oceans but migrated into this region after the end-Permian extinction event. Disaster taxon Lingula proliferated slightly earlier in western Tethyan oceans than in eastern Tethyan regions following the event. Survival brachiopods from both regions appear to have a generic affinity, although they do not share any species. Both South Chinese and Italian survival faunas support the view that the survival interval is the duration when survivors are dominated by geographically widespread generalist organisms adapted to a wide variety of ecological conditions.
The Huangzhishan section, 40 km from the well-known Meishan section, Zhejiang Province, South China, records a carbonate–siliciclastic Permian/Triassic (P/Tr) boundary succession. The P/Tr boundary sequences in both sections correlate well with one another, although the succession is much thicker at Huangzhishan than its equivalent at Meishan. The P/Tr transition is constrained by the Neogondolella yini, N. meishanensis and Hindeodus parvus conodont zones. Of these, the boundary between the first two zones marks the end-Permian mass extinction horizon. The base of H. parvus Zone defines the P/Tr boundary. The P/Tr mass extinction event is also indicated by a dramatic negative shift of the δCcarb profile. This ecological crisis was facilitated by an abrupt environmental devastation indicated by an anoxic event. At Huangzhishan benthic habitats varied from open, oxygenated, to anoxic, to dysoxic-oxygenated and to dysoxic-anoxic conditions throughout the latest Changhsingian to early Griesbachian. Biotic turnover across the P/Tr boundary suggests the P/Tr mass extinction may have included two episodes in Huangzhishan. The first, perhaps major, episode occurs at the base of N. meishanensis Zone, corresponding to the event recorded at the base of Bed 25 in Meishan. The second coincides with the boundary between the H. parvus Zone and overlying Claraia–Ophiceras Assemblage zone, equivalent to the event recorded at the base of Bed 28 in Meishan. The first event did not see a significant decline in biodiversity, but is marked by an apparent loss of high-classification groups such as corals, sponges, macroalgae and most foraminifers. The Huangzhishan section records the most abundant and diverse surviving faunas among the P/Tr boundary sections around the world, with 54 species in 36 genera. However, they are severely affected by the Lilliput effect over the P/Tr extinction. Several fossil groups (bryozoans, blastoids and crinoids) temporarily survived the first episode of the P/Tr extinction and persisted into the earliest Triassic in Huangzhishan. Most survivors became extinct in the second episode of the P/Tr crisis. The Eumorphotis–Towapteria–Pteria bivalve fauna, widespread in shallow-water facies conodont-free P/Tr boundary sections in South China, occurs within the H. parvus Zone in Huangzhishan. This bivalve fauna therefore marks the P/Tr boundary in the conodont-barren P/Tr boundary sections. The top of this bivalve assemblage zone marks the second episode of the P/Tr crisis. Another slightly older bivalve fauna dominated by primitive forms of Claraia (e.g. C. bioni) marks the first/or main episode of the P/Tr extinction in the conodont-barren P/Tr boundary sections.
Stratigraphic distributions of foraminifer species from the Permian-Triassic (P/Tr) transition of the Meishan section, South China demonstrate two episodes of biotic mass extinction near the P/Tr boundary. The first episode is calibrated to the top of Bed 24 and is indicated by a loss of 49 out of 64 Changhsingian species (77%). The second phase is expressed by the disappearance of 32 out of 34 species (94%) recorded in Beds 25-27 and corresponds to the base of Bed 28. Only Nodosinelloides aequiampla survived into the early Griesbachian and another species, Glomospira regularis, rebounded in the late Griesbachian. The Lagenida and Textulariida lost 71% and 50% of species, respectively, in the first episode of the P/Tr extinction. In the Lagenida, only one taxon temporarily survived over the second crisis but became extinct soon after in Bed 29, while one newcomer occurred in the late Griesbachian. In the Textulariida, one Lazarus species rebounded in the late Griesbachian when two new forms rose. Both the Fusulinida and Miliolida suffered a great loss in the first extinction event, losing about 85% and 89% of the species, respectively. Their temporary survivors were wiped out in the second episode of the P/Tr crisis. The large, architecturally complex taxa suffered the first crisis much more severely than the small, simple tests. Selective extinction and rebound among the forms bearing various test walls probably indicate the different physiological reactions of various foraminifer groups to the defaunation events such as biocalcification crisis, hypercapnia, elevated CO2 content and global warming that prevailed in the aftermath of the P/Tr mass extinction.
The greatest mass extinction occurred at the end of the Permian. Most records of the mass extinction are not from pelagic sediments, but from shallow-marine and terrestrial sediments. Although several pelagic sections that span the end-Permian mass extinction have been found, these sections contain few index fossils and are often discontinuous because of small faults. We found the index fossils Albaillella cf. triangularis (Radiolaria) in siliceous claystone beds, Hindeodus parvus (Conodont) in the overlying black claystone beds, and Neospathodus cf. cristagalli and Ns. waageni (Conodont) in the subsequent siliceous claystone beds in Akkamori section-2 in northern Japan. These fossils suggest that this section ranges from the late Permian to the Early Triassic, including the early Induan and Olenekian stages. Furthermore, the lithological changes in the section, i.e., starting from bedded chert through siliceous claystone and black claystone to siliceous claystone, are concordant with those of well-known Permian–Triassic pelagic sequences in Japan. There is no gap between each lithofacie of the Akkamori section-2. Critical lithological continuity between Upper Permian siliceous claystone beds and uppermost Permian to lowermost Triassic black claystone beds of the Akkamori section-2 was recognized by observing hand-polished specimens and thin sections. Such paleontological and sedimentological evidence implies that the Akkamori section-2 is a continuous pelagic section that records the end-Permian mass extinction event. The carbonaceous black claystone beds have high total organic carbon (TOC) concentrations (1.06–3.31 wt.%), suggesting oceanic anoxia at least deep and probably stable primary productivity. A decrease in radiolarian abundance from 26–563 to 0.27–20 specimens/cm2 coincided with an increase in TOC content from 0.01–0.16 to 1.06–3.31 wt.% at the boundary of the siliceous claystone and the overlying black claystone beds near the top of the Permian, implying that radiolarian extinction occurred at the end of the Permian coinciding with oceanic anoxia. Although TOC contents decreased in the early Olenekian (Smithian), radiolarian abundance did not increase at that time, indicating that radiolarian recovery was delayed by >1.5 m.y.
The Permian-Triassic (P-T) boundary is marked by the most severe mass extinction in the geologic record. High-resolution cyclostratigraphy on a 104 yr scale across the P-T boundary in a core from the Carnic Alps (Austria) revealed significant cycles in the ratio ˜40:10:4.7:2.3 m, identified with Milankovitch cycles of ˜412:100:40:20 k.y. (eccentricity 1 and 2, obliquity, and precession). Wavelet analysis indicates continuity of deposition across the boundary, with an average accumulation rate of ˜10 cm/k.y. The dramatic faunal changes at the P-T boundary can be constrained within an interval of
The greatest loss of biodiversity in the history of animal life occurred at the end of the Permian Period (∼252 million years ago). This biotic catastrophe coincided with an interval of widespread ocean anoxia and the eruption of one of Earth's largest continental flood basalt provinces, the Siberian Traps. Volatile release from basaltic magma and sedimentary strata during emplacement of the Siberian Traps can account for most end-Permian paleontological and geochemical observations. Climate change and, perhaps, destruction of the ozone layer can explain extinctions on land, whereas changes in ocean oxygen levels, CO2, pH, and temperature can account for extinction selectivity across marine animals. These emerging insights from geology, geochemistry, and paleobiology suggest that the end-Permian extinction may serve as an important ancient analog for twenty-first century oceans.
Our increasing knowledge of the geochemical processes of present-day sedimentation conditions provides a basis for evaluating the role of oxic and anoxic sedimentary environments. In particular, there are organic geochemical parameters, such as lipid composition, sulphur and organic pigments, which link Recent sediments with their geologically older counterparts, and these may therefore be used to assign the depositional palaeoenvironments of ancient sediments and petroleums.
New δ13Corg analyses of two
boundary sections between the late Permian Kapp Starostin
Formation and the early Triassic Vardebukta Formation of
western Spitsbergen confirm field evidence that
their contact is a conformable one. Thus, contrary to previous
reports, some Spitsbergen sections contain a
complete record of the environmental and faunal changes during
the crisis interval of the end Permian mass
extinction. No environmental deterioration is recorded in the
late Permian until near the end of the terminal
Changxingian Stage, whereupon the abundant siliceous sponge
fauna of the Kapp Starostin Formation disappears
along with the deep-burrowing fauna responsible for the
Zoophycus trace fossil. A low diversity
dysaerobic trace fossil assemblage is briefly developed before
a transition to finely laminated, pyritic facies
immediately beneath the Permo-Triassic boundary. Analysis of the
S/C ratios from the laminated strata suggests
that free H2S was present in the water column
(euxinic conditions) even in relatively nearshore settings
subject to storm sandstone deposition. The mass extinction
crisis in Spitsbergen is therefore coincident with
the extensive development of oxygen-poor conditions in the
water column and compares closely, both in
timing and nature, with the crisis seen in lower latitude
Tethyan settings. However, the subsequent aftermath
and recovery in the Boreal sections of Spitsbergen was more
rapid than in Tethys. Thus, a shoreface sandstone
body within the Dienerian Stage contains an appreciable
diversity of fauna (by the standards of the
early Triassic), including bryozoans, calcareous algae and
deep infaunal bivalves, that suggests the marine
ecosystem recovery began earliest in higher palaeolatitudes.
Changes in oxygen concentrations at the sediment-water interface play a major role in controlling benthic foraminiferal assemblages and morphologic characteristics; such changes are reflected in size, wall thickness, porosity, and also taxa (genera and species) of foraminifera present. These morphologic and taxonomic differences have been quantified as a dissolved-oxygen index. This paper demonstrates that the foraminiferal oxygen index derived from bathyal and abyssal Holocene faunas correlates well with the dissolved-oxygen levels in overlying waters. This index is then used for paleoenvironmental interpretations.
Permian and Triassic rocks in the eastern Tethyan region form continuous marine sequences that record the waning phases of the Paleozoic and the early stages of the Mesozoic eras. This book describes and interprets these rocks, summarizing the distribution of major fossil groups in a way that will allow detailed comparison with strata of comparable age in the western Tethys and other parts of the world. The sixteen contributions by forty authors are the culmination of the five-year long International Geological Correlation Programme Project 203. The detailed information presented here is gathered from many areas in the eastern Tethyan region - from France to Australia - and will be of use in the evaluation of the major changes in the global marine biosphere known to have taken place at the end of the Paleozoic era. The stratigraphic record for this fascinating segment of Earth history is not widespread elsewhere in the world and is most continuous in the region covered by this book.
Briefly summarizes some of the modes in which organic matter, by virtue of its composition, may store historical information. There is a short discussion of the pathways and budgets for the principal chemical elements which cycle between living and nonliving organic pools and inorganic reservoirs in the Earth's crust. Then follows a synopsis of how biological, chemical, and geological factors interact to effect environmental change and evolution on a global scale. Books, review articles and some of the key, primary research papers in biogeochemistry are cited, and one intended purpose is to introduce the reader to the more detailed primary literature about this extensive, important, and fascinating field of science. -from Author
In today's oceans, surface water masses exert a controlling effect on biogeographic provinces, climate-sensitive sediments and organic productivity, so it is important to understand the factors that generate and differentiate these water masses. A generalised temperature and salinity map of the Recent, with related effects like upwelling, sea ice, and surface runoff, has been compiled in a new attempt to define marine climates. Present-day climate-sensitive sediments are included to test their reliability as water mass indicators in the geological past. Then, reversing the approach, water mass maps for the nine Permian stages have been reconstructed from the sediment types as well as from biogeographic considerations. It is clear from the Present-day water mass map that geographically or bathymetrically restricted seaways are more likely to reflect local climate and be distinct from open ocean water masses in salinity or temperature. Our Permian maps have been prepared with this duality in mind: epeiric seaways are portrayed with the most differentiated water masses, while narrow continental shelves are generally similar to adjacent oceanic areas.
The primarily marine deposits between the Adige Valley and Carnia, are compared with deposits in adjacent Yugoslavia. Permian continental sequences of the South-Alpine region, mainly west of the sector are then discussed and their contact with overlying units is considered. The biostratigraphy of the marine uppermost Permian and lowermost Triassic of the Southern Alps is documented in detail. Vertical ranges of foraminifers, brachiopods, mollusks, and palynomorphs are known bed by bed near the boundary between the Bellerophon and Werfen formations in the Butterloch-Bletterbach, Sass de Putia, and Tesero sections of the western Dolomites. Investigations in the eastern Dolomites (Cadore) and in Carnia support the events recognized at localities in the western Dolomites. -from Authors
Permian waning of the low-latitude Alleghenian/Variscan/Hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high-CO2 atmosphere and global warming. The correspondingly reduced delivery of nutrients to the biosphere caused further increases in CO2 and warming. Melting of polar ice curtailed sinking of O2- and nutrient-rich cold brines while pole-to-equator thermal gradients weakened. Wind shear and associated wind-driven upwelling lessened, further diminishing productivity and carbon burial. As the Earth warmed, dry climates expanded to mid-latitudes, causing latitudinal expansion of the Ferrel circulation cell at the expense of the polar cell. Increased coastal evaporation generated O2- and nutrient-deficient warm saline bottom water (WSBW) and delivered it to a weakly circulating deep ocean. Warm, deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling WSBW. With the loss of polar sinking, the ocean was rapidly filled with WSBW that became increasingly anoxic and finally euxinic by the end of the Permian. Rapid incursion of WSBW could have produced ∼20 m of thermal expansion of the oceans, generating the well-documented marine transgression that flooded embayments in dry, hot Pangaean mid-latitudes. The flooding further increased WSBW production and anoxia, and brought that anoxic water onto the shelves. Release of CO2 from the Siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse. Increasingly frequent and powerful cyclonic storms mined upwelling high-latitude heat and released it to the atmosphere. That heat, trapped by overlying clouds of its own making, suggests complete breakdown of the dry polar cell. Resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest Permian coal forests that could not migrate any farther poleward because of light limitations. Loss of water stored by the forests led to aquifer drainage, adding another ∼5 m to the transgression. Non-peat-forming vegetation survived at the newly moist poles. Climate feedback from the coal-forest extinction further intensified warmth, contributing to delayed biotic recovery that generally did not begin until mid-Triassic, but appears to have resumed first at high latitudes late in the Early Triassic. Current quantitative models fail to generate high-latitude warmth and so do not produce the chain of events we outline in this paper. Future quantitative modeling addressing factors such as polar cloudiness, increased poleward heat transport by deep water and its upwelling by cyclonic storms, and sustainable mid-latitude sinking of warm brines to promote anoxia, warming, and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data.
For the first time we report δD of kerogen (δDkerogen) for three Permian–Triassic (P–Tr) sequences (Hovea#3, Perth Basin, Western Australia; Jameson Land, East Greenland and Lusitaniadalen, Spitsbergen). We have compared δDkerogen with δ13C of kerogen (δ13Ckerogen) and δ34S of total reduced inorganic sulfur (TRIS, essentially pyrite; δ34Spyrite) of all the sections and for one sample set with δ13C of carbonate (δ13Ccarbonate) to establish (i) similarities between the sections and (ii) evaluate whether these signals are local and/or global. Stable isotope shifts occur for all three sample sets either at the P–Tr transition (Western Australia) or coinciding with the marine ecosystem collapse (Spitsbergen and East Greenland). δDkerogen reflects organic matter (OM)/ kerogen type and is not sensitive to the low level of thermal maturation. Reliable palaeoenvironmental information in terms of the use of δD can therefore only be obtained for the P–Tr transition from hydrogen compound-specific isotope analyses (CSIA) of biomarkers (Nabbefeld et al., 2010b). The negative shifts in δ13Ccarbonate (primary) and δ13Ckerogen are attributed to the release of 13C-depleted carbon into the atmosphere, whereas the isotopic excursions in δ34Spyrite relate to palaeoredox changes. However, the global coincidence in timing of the shifts in δDkerogen, δ34Spyrite and δ13Ckerogen suggests a relation between the sulfur, carbon and hydrogen cycles. The negative shifts in δ13Ccarbonate (primary) are in general attributed to the release of 13C-depleted source of carbon into the oceans and atmosphere, whereas δ13Ckerogen can reflect the latter in certain cases, but can also be superimposed by varying sources of OM/kerogen type. Isotopic excursions in δ34Spyrite relate to global changes in the palaeoredox conditions that affect sulfur cycling in the ancient seas.
The ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane, when coupled together, provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies. Such knowledge can significantly assist in identifying the source formation(s) in a basin thereby providing valuable guidance for further exploration. The ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and/or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation(s). A cross-plot of dibenzothiophene/phenanthrene versus the pristane/phytane ratios measured on seventy-five crude oils from forty-one known source rocks ranging in age from Ordovician to Miocene consistently classified the oils into the following environment/lithology groups: marine carbonate; marine carbonate/mixed and lacustrine sulfate-rich; lacustrine sulfate-poor; marine and lacustrine shale; and fluvial/deltaic carbonaceous shale and coal. The dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments. The classification scheme is based on the premise that these ratios reflect the different Eh-pH regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments. The dibenzothiophene/phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane/phytane ratio assesses the redox conditions within the depositional environment. Interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography-isotope ratio mass spectrometry.
Benthic macrofauna and sediment column features were sampled at five stations along a bathymetric transect (depths 140, 300, 940, 1200, 1850 m) through the Pakistan margin Oxygen Minimum Zone (OMZ) during the 2003 intermonsoon (March–May) and late-post-monsoon (August–October) periods. Objectives were to compare patterns with those described from other OMZs, particularly the Oman margin of the Arabian Sea, in order to assess the relative influence of bottom-water oxygenation and sediment organic content on macrofaunal standing stock and community structure. Macrofaunal density was highest at the 140-m station subject to monsoon-driven shoaling of the OMZ, but there was no elevation of density at the lower OMZ boundary (1200 m). Numbers was extremely low in the OMZ core (300 m) and were not readily explicable from the environmental data. There was no consistent depth-related trend in macrofaunal biomass. Macrofaunal densities were consistently lower than found off Oman but there was less contrast in biomass. A significant post-monsoon decline in macrofaunal density at 140 m was driven by selective loss of polychaete taxa. Polychaeta was the most abundant major taxon at all stations but did not dominate the macrofaunal community to the extent reported from Oman. Cirratulidae and Spionidae were major components of the polychaete fauna at most stations but Acrocirridae, Ampharetidae, Amphinomidae and Cossuridae were more important at 940 m. Polychaete assemblages at each station were almost completely distinct at the species level. Polychaete species richness was positively correlated with bottom-water dissolved oxygen and negatively correlated with sediment TOC, C:N ratio and total phytopigments. Community dominance showed the opposite pattern. The strongly inverse correlation between oxygen and measures of sediment organic content made it difficult to distinguish their relative effects. The strongly laminated sediments in the OMZ core contrasted with the homogeneous, heavily bioturbated sediments above and below this zone but were associated with minimal macrofaunal biomass rather than distinctive functional group composition. In general, data from the Oman margin were weak predictors of patterns seen off Pakistan, and results suggest the importance of local factors superimposed on the broader trends of macrofaunal community composition in OMZs.
A major extinction of intermediate-water (500–1000 m) benthic foraminiferal species coincided with a major decrease in δ13C (2.8‰) of terrestrial organic matter (n-C29 alkane) and δ34S (20‰) of whole rock sulfide in a continuous siltstone sequence in the Tawanui Section (46°S paleolatitude) along the Akitio River, southeastern North Island, New Zealand, in the middle part of the uppermost Paleocene nannofossil zone (CP8). The benthic extinction (25% of species) occurred over ∼3 kyr at ∼55.5 Ma. Increases in kaolinite/illite and kaolinite/smectite ratios and in terrestrial organic carbon percentages started ∼3 kyr before the major benthic extinctions, lasted over ∼40 kyr, and probably reflect warmer climate and increased rainfall. The productivity of planktonic foraminifera and calcareous nannoplankton decreased ∼3 kyr prior to the major extinctions and recovered at the time of benthic extinctions. These events that started ∼3 kyr before the extinction can be best explained by warming, increased rainfall, reduced salinity of surface waters, and increased influence of warm saline deep water (WSDW). Benthic foraminiferal oxygen indices indicate a strong decrease in dissolved oxygen levels within the intermediate water from low oxic (1.5–3.0 mL/L O2) to suboxic (0.3–1.5 mL/L O2) conditions coinciding with the benthic extinctions. Increases in total organic carbon (TOC) and in the hydrocarbon-generating potential of kerogen (measured as the hydrogen index (HI)) agree with the interpretation of decreased dissolved oxygen levels of the intermediate water. The lowest oxygen conditions lasted ∼40 kyr and coincided with a decrease in calcareous benthic foraminiferal productivity, highest TOC levels, and lowest δ13C of terrestrial organic carbon. Dominant formation of WSDW or sluggish intermediate-water circulation caused by warming and high rainfall in high-latitude areas most likely led to the ∼3-kyr time lag between events on land and in surface waters preceeding the extinction and the development of dysaerobia in the sea, coinciding with the major benthic extinction and decrease in δ13C and δ34S in New Zealand. Global warming of deep and intermediate waters may have caused decomposition of methane hydrate in sediments, resulting in a strongly decreased δ13C of marine carbonates, promoting dysaerobia in the ocean, and warming global climate by increased methane concentrations in the atmosphere. Upwelling of WSDW, occurring soon after it became dominant in high-latitude areas, is likely responsible for the recovery of normal salinity and the concomitant recovery of planktonic foraminifera and calcareous nannoplankton productivity in high-latitude surface waters. Minor benthic foraminiferal extinctions (9% of species) occurred ∼40 kyr after the major extinctions, lasted ≤ ∼6 kyr, and coincided with the initiation of environmental recovery.
The Gujo-Hachiman section in central Japan provides a rare window into environmental conditions within the Panthalassic Ocean, which encompassed more than half the Earth's surface at 251 Ma. The section is characterized by a sharp transition from green-gray organic-poor cherts to black siliceous shales in the uppermost Permian. Normalization to the clay fraction demonstrates that apparent increases in the concentrations of organic matter and trace metals above this transition were due primarily to the loss of a diluent biogenic (radiolarian) silica flux and only secondarily to a small shift toward more reducing bottom waters. In the black shale, pyrite abundance increases by a factor of ~30× and is dominated by framboidal grains of probable syngenetic origin. These observations suggest that the expansion of low-oxygen conditions within the Panthalassic Ocean was focused within the oxygen-minimum zone rather than at the seafloor. Such a pattern implies that (1) changes in nutrient fluxes and primary productivity rates, rather than stagnation of oceanic circulation, were a key factor influencing oceanic redox conditions around the Permian-Triassic boundary, and (2) large regions of the Panthalassic Ocean underwent only limited redox changes, providing potential refugia for marine taxa that survived into the Triassic.
A combination of sequence stratigraphic and conodont biostratigraphic analyses of sediment cores from five petroleum exploration wells, together with reference to nearby outcrops, has allowed us to construct a composite geological section through the Permian–Triassic transition in the Peace River Basin of Western Canada. The cores contain significant contents of organic matter comprising kerogen and bitumen of low to moderate thermal maturity. Extraction and analysis of the bitumens has revealed patterns of biomarker hydrocarbons consistent with marine deposition and photic zone euxinia. In particular isorenieratane and aryl isoprenoids, derived from the carotenoid pigments of green sulfur bacteria (Chlorobiaceae), are abundant and pervasive throughout the section and indicate that hydrogen sulfide must have been present in the photic zone for significant periods of time. These findings mirror the geochemical results obtained for other Permian–Triassic boundary sections of the Tethys realm (e.g. Western Australia, East Greenland and South China) and suggest that euxinic conditions prevailed widely, though perhaps periodically, and that hydrogen sulfide toxicity could have been an important factor in the extinction of marine invertebrates.
Carbonate-associated sulphate (CAS) extracted from a Permo–Triassic succession at Siusi in northern Italy is shown to preserve a true seawater-sulphate isotope record. Two periods of increasing δ34S and δ18O in CAS provide evidence for increased oceanic anoxia in the Late Permian and the Early Triassic. These two anoxic episodes are separated by an event characterised by the addition of isotopically light sulphur and oxygen to the oceanic sulphate pool. Simple mass balance calculations suggest that this sulphate originates from the reoxidation of bacterially derived H2S during oceanic mixing, rather than a volcanogenic source. A dramatic fall in CAS-δ18O directly above the P–T boundary, not accompanied by a large change in CAS-δ34S, records an oceanic deoxygenation event probably caused by the release of methane from gas hydrates, subsequently recorded in the carbonate-carbon isotope record. The decline of Early Triassic oceanic anoxia is not recorded by a fall in CAS-δ34S, but is preserved by declining CAS-δ18O. This is because of an increase in the flux of reactive iron to the oceans during the Early Triassic anoxic episode, triggered by the demise of land plants. This permanently removes a greater proportion of light sulphur from the oceanic sulphate reservoir as pyrite, and means that the heavy residual sulphate-sulphur isotope signature of Griesbachian anoxic seawater is preserved as a geochemical ‘fossil’ until the beginning of the Middle Triassic.
The Arabian Sea’s unusual features have drawn attention from oceanographers and other scientists since the late 1800s. Water-column processes, including the seasonally reversing monsoon-driven circulation and the associated upwelling and productivity, as well as a basin-wide, mid-water layer of intense oxygen depletion have been the foci of many studies. However, the importance of benthic processes in the Arabian Sea has also been recognized. Both the abyssal region and the continental margins have been sites of major studies focused on the biology and geochemistry of surficial sediments and key biogeochemical processes that occur across the benthic boundary layer, especially in the last decade. A summary of benthic studies carried out up to the 1990s is followed by descriptions and syntheses of biological and geochemical studies conducted since that time. The results highlight that the benthic system of the Arabian Sea is highly dynamic, with evidence of strong benthic–pelagic coupling displayed as a cross-basin trophic gradient and in benthic response to seasonal variability in productivity and C flux. Benthic biogeochemical processes, especially on the upper slope and within the oxygen minimum zone, including denitrification, phosphogenesis, and fluxes of trace metals, nutrients and dissolved organic matter, may be of global significance but remain poorly quantified. Sedimentary organic matter distributions across the Arabian Sea have served to fuel an ongoing debate over the controlling environmental factors. Recent studies have illustrated that factors including the supply of reactive organic matter, oxygen exposure, digestion and mixing by the benthos, sorptive preservation, and sediment dilution, winnowing and down-slope transport, all interact in a complex fashion and with varied impact to determine distributions of sedimentary organic matter across the different margins of this basin. Notable features include the facts that it is only at the core of the oxygen minimum zone on the Indian and Pakistan margins where laminated sediments occur and oxygen concentrations appear to fall below the threshold required for macrobenthos, and that sulfate reduction is surprisingly suppressed when compared to rates observed on other upwelling margins with oxygen minimum zones. The review is completed by suggestions for future benthic research in the Arabian Sea.
The Global Stratotype Section and Point (GSSP) of the Permian-Triassic boundary has been ratified by IUGS. The boundary is defined at the base of Hindeodus parvus horizon, i.e. the base of Bed 27c of Meishan section D, Changxing County, Zhejiang Province, South China.
The Permian/Triassic (P/Tr) transition is ecologically assessed based on examining 23 shelly communities from five shallow platform, ramp and shelf basin facies Permian–Triassic boundary (PTB) sections in South China. The shelly communities have undergone two major collapses coinciding with the two episodes of the end-Permian mass extinction. The first P/Tr extinction event devastated shelly communities in all types of settings to some extent. The basin communities have been more severely impacted than both platform and ramp communities. The survival faunas have rebounded more rapidly in shallow niches than in relatively deep habitats. The second P/Tr crisis destroyed the survival communities in shallow setting and had little impact on the basin communities in terms of community structures. The early Griesbachian communities are overall low-diversity and high-dominance. The governorship switch from brachiopods to bivalves in marine communities has been facilitated by two pulses of the end-Permian mass extinction and the whole takeover process took about 200ka across the P/Tr boundary. Bivalve ecologic takeover initially occurred immediately after the first P/Tr extinction in shallow water habitats and was eventually completed in all niches after the second P/Tr event. Some post-extinction communities have the irregular rarefaction curves due to the unusual community structures rather than sampling intensities.
Unlike the high-abundance, low-diversity macrofaunas that characterize many Early Triassic benthic palaeocommunities, ichnofossils were relatively common in the aftermath of the end-Permian mass extinction worldwide. Ichnofossils therefore are a good proxy for ecosystem recovery after the end-Permian biotic crisis. This paper documents 14 ichnogenera and one problematic form from Lower Triassic successions exposed in the Lower Yangtze region, South China. Post-extinction ichnodiversity remained rather low throughout the Griesbachian–early Smithian period and abruptly increased in the late Smithian. However, several lines of evidence, including extent of bioturbation, burrow size, trace-fossil complexity, and tiering levels, indicate that diversification of ichnotaxa in the late Smithian did not signal full marine ecosystem recovery from the Permian/Triassic (P/Tr) mass extinction. Marine ichnocoenoses did not recover until the late Spathian in South China. The marginal sea provided hospitable habitats for tracemakers to proliferate in the aftermath of the end-Permian mass extinction.
Evaporitic sulfates of Permian and Triassic ages from Italian occurrences were analyzed
for sulfur and oxygen isotopes in order to supplement the corresponding isotope-age
curves and to use isotopic data to trace the origin of the sulfate in hydrologic systems.
The sulfur-isotopic composition-age relationships obtained in this study generally
agree with those found throughout the world. In two cases, i.e. in samples from the
Carniola di Bovegno Formation (Bergamo and Brescia Alps) and from the lower part of
the Gracilis Formation (Recoaro, Vicenza), sulfur isotopes suggest different ages for
the rocks than the formerly ascribed ones.
Oxygen-isotopic compositions show the same range from ~ +10.5 to + 18.5°0, without
any consistent relationship with sulfur. These ranges of values are almost identical to
those published previously for sulfates of Permian and Triassic ages from other locations.
The stable isotope ratio of sulfur (34S/32S) in dissolved sulfate and hydrogen sulfide was measured for 20 water samples from two deep hydrocasts from the south-central Black Sea. The isotope ratio of total reduced sulfur was also measured for surface sediment collected below each hydrocast. The range in the δ34S measurements for sulfate was +18.20 to +20.17‰ and for hydrogen sulfide −38.71 to −4.85‰. The distribution pattern for δ 34S in both sulfate and sulfide appears to be the result of in situ sulfate reduction.
This study demonstrated that phase state and compositional variations of hydrocarbons in the Buzuluk depression, Russia, are related to maturity levels of Devonian source rocks. Maturity levels of organic matter of source rocks estimated by Rock-Eval Tmax and vitrinite reflectance (Ro%) are in the range from ‘oil window’ to ‘overmature’ and increase from east to west in the depression. The volume of the gas-condensate deposits increases in the same direction. Geochemical analyses using GC with dual FID/FPD and GC-MS show the variation in distributions of aromatic sulfur compounds in oils and condensates with different maturity levels. Very mature petroleums are characterized by very low concentrations of benzothiophenes (BTs) and abundant methyldibenzothiphenes (MDBTs). Maturity parameters such as the 4-MDBT/1-MDBT and newly proposed dimethyldibenzothiophenes (DMDBT) ratios of sulfur aromatics correlate well with other maturity indicators based on hydrocarbon distributions in gasoline-range and saturate fractions of petroleum. Sulfur aromatic parameters work well over a wide range of catagenesis, showing no reversal at the advanced levels of thermal evolution and can efficiently discriminate very mature petroleums.
Systematic sulfur isotope data for whole-rock sulfides have been obtained from the chert-dominated, continuous, pelagic sedimentary sequences spanning the Permian/Triassic (P/Tr) boundary at Tenjinmaru in the Chichibu Terrane and at Sasayama in the Tanba Terrane in Japan. The P/Tr boundary is characterized by the occurrence of siliceous shales in association with a carbonaceous black mudstone which is similar in appearance to the worldwide distributed Cretaceous/Tertiary (K/T) boundary claystone. The observed data clearly demonstrate a significant bimodalism. The 34S/32S ratios with respect to CDT are generally low throughout the Middle Permian (ca.−39 to −25%0) and show a remarkable increase beginning in the lower Upper Permian and persisting into the Lower Triassic (ca.−20 to −2%0), with a temporary and drastic negative shift, down to roughly the same isotopic level as in the Middle Permian, just at the suspected P/Tr boundary (ca.−41 to −23%0). Interestingly, the mode of isotopic excursion across the P/Tr boundary is in striking contrast to that across the K/T boundary which was recently described at Kawaruppu in Hokkado, Japan. The apparent extent of fractionation, with respect to contemporaneous seawater sulfate, in the high 34S/32S group lies within the range of −25 ± 10%0, which is quantitatively equivalent to the currently confirmed range of kinetic isotope effect during bacterial dissimilatory sulfate reduction, and that in the low 34S/32S group mostly exceeds this range, giving the values typically in the range of −45 ± 10%0, which is similar to what is generally observed in the present-day oceanic sediments. The present data would provide strong evidence for the development of a largely stagnant, anoxic, stratified ocean, which presumably began to form in the lower Upper Permian and persisted into the Lower Triassic, and for a brief episode of its temporary massive mixing just at the suspected P/Tr boundary. Such an oceanic oxic-anoxic history may account to some extent for the relatively high enrichments of chalcophile elements in basal Triassic sediments in the world and add a significant constraint to the current arguments on the cause and consequence of the terminal Permian mass extinction.
A new genus, Meishanorhynchia, is proposed based on new material from the Lower Triassic of the Meishan section, South China. It is of a late Griesbachian age based on both associated biozones (ammonoids and bivalves) and radiometric dates of the intercalated volcanic ash beds. Comparison with both Palaeozoic and Mesozoic–Cenozoic-related genera suggests that it may represent the first radiation of progenitor brachiopods in the aftermath of the end-Permian extinction. The lowest brachiopod horizon that contains the genus is estimated to be about 250.1 ± 0.3 Ma. This implies that the initial stage of recovery of Brachiopoda in the Early Triassic was probably about 1.3 ± 0.3 myr after the major pulse of the end-Permian mass extinction (dated as 251.4 ± 0.3 Ma). This is in agreement with Hallam’s expectancy that biotic recovery typically begins within one million years or so of major mass extinctions, in contrast to current views on the end-Permian extinction event which propose that the recovery of most if not all biotic groups in the Early Triassic was severely delayed and only began about five million years after the end-Permian extinction.