No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The Hirnantian (Late Ordovician) and end-Guadalupian (Middle Permian) mass-extinction events compared
Abstract
The so-called Big Five mass extinctions of the Phanerozoic include two prominent Palaeozoic episodes: the end-Ordovician and end-Permian events, both with large biodiversity loss. We consider that the end-Ordovician (Hirnantian) extinction could be best compared to the Middle Permian end-Guadalupian (=Capitanian) extinction, rather than to the end-Permian (Permo-Triassic boundary; PTB) extinction. The end-Guadalupian extinction, ca. 8 Myr before the PTB extinction, occurred as an independent episode under extremely unique global setting with the lowest sea level and lowest Sr isotopic ratios in seawater of the Phanerozoic. Multiple similarities exist between the end-Ordovician (Hirnantian) and the end-Guadalupian (Capitanian) events, such as the preferential elimination of sessile biota in the tropics, a global sea-level drop and secular changes in seawater C and Sr isotope ratios, occurring under global cooling. The limited development of land vegetation suggests that the Ordovician extinction was restricted solely to the marine realm, with no prominent damages on land, and no large igneous province (LIP) recognized in the Ordovician. The comparison indicates that the two extinctions of the Hirnantian and of the Capitanian have been essentially triggered by similar causes/processes; nonetheless, biotic responses were different, owing to the more oxygenated status of surface environments in the Permian after the mid-Palaeozoic terrestrialization.
... Chen and Xu, 2021;Gastaldo et al., 2021). Sepkoski (1996) and Alroy et al. (2008), highlighting two similar extinctions in the Paleozoic, i.e., the end-Ordovician and end-Guadalupian (Permian) episodes immediately before and after the global terrestrialization, respectively (Isozaki and Servais, 2018). Owing to the development of land forests, elevated photosynthesis changed not only landscape but also atmospheric composition, particularly the increase in O2 mirrored in decrease in CO2 (see Figure 4). ...
... abolic biochemical reactions in small-size animals with lesser heat capacity. As to the 3 major extinctions in the Paleozoic, i.e., end-Ordovician, Late Devonian, and end-Guadalupian (Permian) episodes, commonly observed geological phenomena in association with biodiversity decline were global cooling and contemporary major sealevel drop (Fielding et al., 2008;Haq and Schutte, 2008; Figure 3), as emphasized by Stanley (1988) and Isozaki and Servais (2018). It is also noteworthy that a global cooling often occurred in association with a following global warming within a short time interval, as observed in the cases of end-Ordovician, Late Devonian, end-Guadalupian (Permian), and end-Triassic (Racki, 2020). ...
... Kirschvink et al., 2000;Hoffman and Schrag, 2002) and also the end-Ordovician glaciation associated with extinction (Crampton et al., 2016), because both occurred during the pre-terrestrialization time without land plants, thus with presumably much higher atmospheric CO2 than that of the post-terrestrialization world (e.g. Royer et al., 2014;Witkowski et al., 2018;Figure 4 Figure 4. Secular change in the Phanerozoic atmospheric pCO2 and pO2 (Berner, 2006;Royer et al., 2014;Witkowski et al., 2018), and the timing of two compared extinction events, i.e., the end-Ordovician and end-Guadalupian, with respect to the mid-Paleozoic terrestrialization of continents (Isozaki and Servais, 2018). Although the two major extinctions occurred during global cooling (Fig. 3), the atmospheric compositions were significantly different between the Ordovician and Permian, before and after the major terrestrialization of continents, respectively (Fig. 1). ...
The Paleozoic Era experienced 4 major mass extinctions; i.e., end-Ordovician, Late Devonian, end-Guadalupian, and end-Permian episodes. As a cause of significant biodiversity decline, non-biological environmental change on global scale was inevitable; nonetheless, popular claims of bolide impact and/or large igneous province (LIP) with too many ad-hoc assumptions have not yet been accepted as common/universal explanations for the Paleozoic extinctions. Recent research on extinction causes evolved through two stages; i.e., the heyday of the bolide impact scenario in the 1980s, and the overtaking by a LIP-mantle plume scenario in the 19902000s. Lately, we may sense a return trend to extraterrestrial causes since the late 2000s, which is not a simple revival of the old bolide-impact model but a new proposal for a cosmoclimatological scenario relevant to extra-solar processes; i.e., supernovae explosions and relevant migration of dark clouds over the Solar System. This short article reviews the current status of extinction-related research, which emphasizes two key issues; i.e., the categorization of extinction causes and new perspectives on non-bolide extraterrestrial causes. The categorizing of extinction causes at four distinct levels is effective in separating global triggers on the Earth's surface from more essential ultimate cases within the Earth and/or on outside of the planet. Causes of extinction can be grouped into four distinct categories in a hierarchy, from small to large scale: i.e., Category 1 direct kill mechanism for each local biota, Category 2 background change in global environment, Category 3 major geological phenomenon on the planet's surface, and Category 4 ultimate cause from the interior and exterior of the planet. Recent advances in He isotope analysis for extinction-related sedimentary records suggest extraterrestrial causes, not of bolide impact but of the encounter with a dark cloud (nebula). Emerging new perspectives of cosmoclimatology leads to an alternative extinction scenario; e.g. 1) increased flux of galactic cosmic radiation (GCR) with extensive cloud cover and 2) passage of a dark cloud (nebula) enriched with micro-dusts (IDPs) enveloping the Solar System. Both meteoric cloud coverage and IDP-screen can induce lowering/shutdown of solar irradiance, which may drive global cooling and sea-level drop associated with biodiversity decline. The past star-burst events detected in the Milky Way Galaxy apparently coincide in timing with the cooling episodes associated with major extinctions of the Paleozoic, i.e., at the end-Ordovician, Late Devonian, and Late Permian. Given such astronomical processes associated with global cooling in the past, much older global freezing episodes, i.e., Proterozoic snowball Earth events developed under high atmospheric CO2 levels, can be likewise explained. The study of mass extinctions on the Earth is entering a new stage under new astrobiological perspectives.
... Recent global warming is derived from the long-term temperature increase of the Earth's climate system generated by the burning of fossil fuels by humans, especially since the Industrial Revolution and particularly since the 1950s. These changes are less than those catastrophic events that caused massive extinctions' of life recorded in previous geological periods, caused by different environmental conditions like higher temperatures (+3 to +12° C above 1960-1990 average) (Harnik, et al., 2012;Isozaki and Servais, 2018) and CO 2 concentrations (+300 to +4000 ppm levels) (Isozaki and Servais, 2018;Ward, 2007). However, they are relevant for predicting future environmental conditions generated by human actions on the planet's climate system, and their effects and consequences are occurring in our time. ...
... Recent global warming is derived from the long-term temperature increase of the Earth's climate system generated by the burning of fossil fuels by humans, especially since the Industrial Revolution and particularly since the 1950s. These changes are less than those catastrophic events that caused massive extinctions' of life recorded in previous geological periods, caused by different environmental conditions like higher temperatures (+3 to +12° C above 1960-1990 average) (Harnik, et al., 2012;Isozaki and Servais, 2018) and CO 2 concentrations (+300 to +4000 ppm levels) (Isozaki and Servais, 2018;Ward, 2007). However, they are relevant for predicting future environmental conditions generated by human actions on the planet's climate system, and their effects and consequences are occurring in our time. ...
Essays by leading researchers on the history, natural environment, society, tourism economy, and challenges this region faces for sustainable development. The threat of mass tourism is heightened by the specter of enormous mining operations that would compromise the view shed, pollute the land and water, and destroy Loreto as a destination for sustainable tourism. Freshwater is scarce and poorly managed. Climate change will increase sea levels and flooding of urban areas, raise ambient temperatures, and reduce rain while increasing drought. Adap-tive measures can offset these challenges, but require community engagement and greatly improved public administration at local, state, and federal levels.
... On the other hand, the onset of the Capitanian Sr minimum was during a cold climate with the lowest Phanerozoic sea level, and it continued until the GLB, which roughly corresponded to the termination, rather than in the middle, of the LPIA (Figure 2). As to the coeval global cooling/ sea-level decrease and Sr isotope minimum, a similar observation was confirmed also for the end-Ordovician timing (Isozaki and Servais, 2018). ...
... The seawater 87 Sr/ 86 Sr changes, the minimum or the maximum, seem to coincide with several extinction events, e.g., the end-Ordovician, the end-Guadalupian, and the end-Permian (Figure 1). Recently, various similarities were recognized between two major extinction-related episodes in the Paleozoic; i.e., the Hirnantian (end-Ordovician) and Capitanian (end-Permian) events, because both episodes commonly recorded the preferential removal of sessile biota in the tropics, global sea-level drop, negative excursion of carbon isotopes, and end of long-term geomagnetic polarity interval (Isozaki and Servais, 2018;Isozaki, 2019). This may promote further research on other cooling-relevant extinction events and coeval changes in Sr isotope signatures in global oceans. ...
The long-term trend in the Paleozoic seawater 87 Sr/ 86 Sr was punctuated by a unique episode called the "Capitanian minimum" at the end of the Guadalupian (Permian; ca. 260 Ma). This article reviews the nature and timing of this major turning point in seawater Sr isotope composition (87 Sr/ 86 Sr, δ 88 Sr) immediately before the Paleozoic-Mesozoic boundary (ca. 252 Ma). The lowest value of seawater 87 Sr/ 86 Sr (0.7068) in the Capitanian and the subsequent rapid increase at an unusually high rate likely originated from a significant change in continental flux with highly radiogenic Sr. The assembly of the supercontinent Pangea and its subsequent mantle plume-induced breakup were responsible for the overall secular change throughout the Phanerozoic; nonetheless, short-term fluctuations were superimposed by global climate changes. Regarding the unidirectional decrease in Sr isotope values during the early-middle Permian and the Capitanian minimum, the suppression of continental flux was driven by the assembly of Pangea and by climate change with glaciation. In contrast, the extremely rapid increase in Sr isotope values during the Lopingian-early Triassic was induced by global warming. The unique trend change in seawater Sr isotope signatures across the Guadalupian-Lopingian Boundary (GLB) needs to be explained in relation to the unusual climate change associated with a major extinction around the GLB.
... Recent global warming is derived from the long-term temperature increase of the Earth's climate system generated by the burning of fossil fuels by humans, especially since the Industrial Revolution and particularly since the 1950s. These changes are less than those catastrophic events that caused massive extinctions' of life recorded in previous geological periods, caused by different environmental conditions like higher temperatures (+3 to +12° C above 1960-1990 average) (Harnik, et al., 2012;Isozaki and Servais, 2018) and CO 2 concentrations (+300 to +4000 ppm levels) (Isozaki and Servais, 2018;Ward, 2007). However, they are relevant for predicting future environmental conditions generated by human actions on the planet's climate system, and their effects and consequences are occurring in our time. ...
... Recent global warming is derived from the long-term temperature increase of the Earth's climate system generated by the burning of fossil fuels by humans, especially since the Industrial Revolution and particularly since the 1950s. These changes are less than those catastrophic events that caused massive extinctions' of life recorded in previous geological periods, caused by different environmental conditions like higher temperatures (+3 to +12° C above 1960-1990 average) (Harnik, et al., 2012;Isozaki and Servais, 2018) and CO 2 concentrations (+300 to +4000 ppm levels) (Isozaki and Servais, 2018;Ward, 2007). However, they are relevant for predicting future environmental conditions generated by human actions on the planet's climate system, and their effects and consequences are occurring in our time. ...
Because of its geography, Mexico is one of the most vulnerable countries to the effects of climate change. Threats include intense and prolonged droughts, rise in the mean sea level, areas susceptible to flooding due to overflow of rivers and streams, increase in the average temperature and its heat waves, impacts on the health of the population, reduction in access to water, intensification of migratory flows, and increase in the concentration of the population in urban areas. The vulnerability of a system is the degree of ability or inability it has to face adverse effects that are generated by the action of an adverse phenomenon or event. Since human and natural systems are integrally linked, it is necessary to use a socio-economic-biological-environmental systems approach (SEBES) to assess coastal vulnerability to climate change. Human and environmental indicators for the local level are used for this analysis. For the assessment of coastal vulnerability in Loreto, González-Baheza proposed the use of 86 social, economic, biological, and environ-mental base indicators to generate composite indices. The comprehensive analysis for vulnerability in the region of Loreto adapted the index proposed by Gonzalez-Baheza and Arizpe within SEBES approach. Here, the only results of the analysis for Loreto are presented; full details of the model are to be found in Gonzalez-Baheza and Arizpe (2017) and in Gonzalez-Baheza (2017).
... The GLME extinction is considered to be a major biological event in the Phanerozoic (Rampino and Shen, 2021) where gigantic bivalves, such as Alatoconchidae, became extinct (Isozaki and Aljinović, 2009;Isozaki and Servais, 2017;Chen et al., 2018). The extinction of giant bivalves was typical of this extinction event, but overall the bivalves were less affected (Clapham and Payne, 2011). ...
... The Guadalupian-Lopingian boundary (GLB) biotic crisis has been regarded as one of the least understood crisis events in the Phanerozoic era (Raup and Sepkoski, 1982;Bambach, 2002;Jost et al., 2014). There remain debates about whether it was a sudden extinction (Stanley and Yang, 1994;Isozaki and Servais, 2018;Arefifard and Payne, 2020;Rampino and Shen, 2020) or a gradual diversity reduction Fan et al., 2020;Shen et al., 2020;Lee et al., 2022), which may be related to the varied crisis times over different areas and selective extinctions among different marine organisms. During the GLB crisis, brachiopods were severely affected, and 30% of genera and 87% of species became extinct Shi, 1996, Sun andShen, 2004), but this crisis was restricted to the genus and species level (Shen et al., 2006). ...
... The Guadalupian-Lopingian boundary (GLB) biotic crisis has been regarded as one of the least understood crisis events in the Phanerozoic era (Raup and Sepkoski, 1982;Bambach, 2002;Jost et al., 2014). There remain debates about whether it was a sudden extinction (Stanley and Yang, 1994;Isozaki and Servais, 2018;Arefifard and Payne, 2020;Rampino and Shen, 2020) or a gradual diversity reduction Fan et al., 2020;Shen et al., 2020;Lee et al., 2022), which may be related to the varied crisis times over different areas and selective extinctions among different marine organisms. During the GLB crisis, brachiopods were severely affected, and 30% of genera and 87% of species became extinct Shi, 1996, Sun andShen, 2004), but this crisis was restricted to the genus and species level (Shen et al., 2006). ...
A diverse Wuchiapingian brachiopod fauna, which contains 57 species in 28 genera, is described from the Shuizhutang Formation at the Liannan section, Guangdong province, southeastern China. Four new species Tyloplecta liannanensis n. sp., Linoproductus huananensis n. sp., Araxathyris minor n. sp., and Permophricodothyris flata n. sp. are proposed. From well-preserved Liannan specimens, characteristics of the shell microstructures in Permianella are revised, and different morphologies of muscle scars in Permophricodothyris are distinctly shown. Until now, only several Wuchiapingian brachiopod faunas have been found in South China. Compared with these faunas, the Liannan fauna shows much higher α diversity and is more like faunas from southeastern China than those from the Yangtze area in faunal composition. The Liannan fauna is dominated with Neochonetes , Transennatia , Orthothetina , Permophricodothyris , and Cathaysia , which are normally larger and more strongly ornamented than their Changhsingian counterparts. The Wuchiapingian brachiopods in South China are represented mainly by the Douling fauna and Shuizhutang fauna. The Douling fauna has relatively low diversity and presents the survival stage after the Guadalupian–Lopingian boundary crisis. The Shuizhutang fauna has a much higher diversity and more key Changhsingian taxa and shows a rapid radiation stage. Faunal compositions of the two faunas indicate that the initial recovery of brachiopods occurred mainly at the genus level followed by a more rapid radiation at both genus and species levels.
UUID: http://zoobank.org/474cd988-6ec3-4d16-b045-f84d5fe3fb66
... A lenyűgöző evolúciós vágta eredményeként a középső ordovicium kezdetétől a késő ordovicium végéig 320 új család és 1340 új nemzetség jelent meg (Trotter et al., 2008). Az impozáns fejlődésnek egy -a maga nemében -ugyancsak lenyűgöző katasztrófa vetett véget, amit a fanerozoikum öt legjelentősebb kihalási eseménye közt (Newell, 1967), a második legpusztítóbb eseményként (Sepkoski, 2001;Isozaki-Servais, 2017;Harper-Servais, 2018) tartunk számon. ...
The second most severe extinction event that hit the Earth biosphere was the end Ordovician great extinction that erased 57% of the extant marine animal genera. The cause of that extinction was considered for long time the Hirnantian glacial period, however the evidence of the glaciation were rather consequences than evidence of the great extinction. Newer data suggest that the final driver of the end Ordovician great extinction was driven by the shallow marine global anoxia. The problem is that even this is earlier than the extinction event itself. Recently the research focuses on the extra-terrestrial drivers as the possible cause of the great extinction as the gamma ray outbursts of neighbouring supernovae. The evidence of such outbursts is detected on the surface of our Moon and even in the oceanic deposits as special 60Fe isotopes not later than 6 million years. For the moment there is an open question whether our recent instruments can detect the same isotopes sent to our planet 440 million year before as it is proven from layers deposited 6 million years before.
... The GLME extinction is considered to be a major biological event in the Phanerozoic (Rampino and Shen, 2021) where gigantic bivalves, such as Alatoconchidae, became extinct (Isozaki and Aljinović, 2009;Isozaki and Servais, 2017;Chen et al., 2018). The extinction of giant bivalves was typical of this extinction event, but overall the bivalves were less affected (Clapham and Payne, 2011). ...
... The decline in biodiversity is the most important manifestation of the extinction event (Stanley, 2016;Isozaki and Servais, 2018). The warm water benthic foraminifera record from the Western Pangea tropical shelves shows that the diversity declined quickly after a mid-Capitanian boom ( Fig. 8F; Davydov, 2014). ...
The Guadalupian-Lopingian boundary (GLB) transition was regarded as a gradual warming period with the termination of the Late Paleozoic Ice Age (LPIA). However, the glacial-nonglacial cycles from Eastern Australia imply that the period was also influenced by climatic fluctuations. We here report on a GLB section of the South China Block confined by the conodont biostratigraphy to constrain weathering intensity and the associated climatic fluctuations during this critical interval. The chemical weathering indices were estimated by analyses of acid-insoluble residues extracted from carbonate rocks. Two weak weathering units (Unit 1 and 3, Early Capitanian and Early Wuchiapingian) and two strong weathering units (Unit 2 and 4, Late Capitanian and Middle Wuchiapingian) are identified. δ13Ccarb generally follow well the variation tracks of weathering indices. Two weak weathering units (Unit 1 and 3) correspond to the P3 glacial and the P4 glacial in high-latitude region of Australia. The CIA-converted land surface temperature and reported seawater temperature reflect the synchronous response of continental climate and marine conditions. The strong weathering duration (Unit 2) is closely related to the eruption of the Emeishan Large Igneous Province (ELIP) which promoted the temperature raising and induced the waning of high-latitude ice sheet accordingly. The climatic fluctuations paced with the onset, surge, and weakening of the ELIP should be responsible for the remarkable continent-ocean-biodiversity system changes and GLB extinction.
... Following the terrestrialization of the global biota that began during the Devonian (Isozaki and Servais 2017), the Carboniferous terrestrial vegetation became widespread, diverse and abundant. According to the review by Opluštil et al. (2021), the resulting fossil record has proved to be an effective biostratigraphic tool for intra-and interbasinal correlations in the palaeoequatorial Euramerican province that extended from the current locations of the North American Midcontinent basin to the Variscan basins of the Czech Republic. ...
The Carboniferous chronostratigraphic scale consists of two subsystems, six series and seven stages. Precise numerical age control within the Carboniferous is uneven, and a global magnetic polarity timescale for the Carboniferous is far from established. Isotope stratigraphy based on Sr, C and O isotopes is in an early stage but has already identified a few Sr and C isotope events of use to global correlation. Cyclostratigraphy has created a workable astrochronology for part of Pennsylvanian time that needs better calibration. Chronostratigraphic definitions of most of the seven Carboniferous stages remain unfinished. Future research on the Carboniferous timescale should focus on GSSP selection for the remaining, undefined stage bases, definition and characterization of substages, and further development and integration of the Carboniferous chronostratigraphic scale with radioisotopic, magnetostratigraphic, chemostratigraphic and cyclostratigraphic tools for calibration and correlation and the cross correlation of nonmarine and marine chronologies.
... The Late Ordovician precedes the "terrestrialization" of the global biota that took place during the Devonian-Carboniferous (Isozaki and Servais, 2017). It could thus be argued that the nonmarine fossil record of the Late Ordovician is too sparse to support definitive conclusions. ...
A critical review of putative nonmarine mass extinctions associated with the so-called “Big 5 mass extinctions” of marine invertebrates (Late Ordovician, Late Devonian, end Permian, end Triassic and end Cretaceous) as well as a likely sixth mass extinction in the marine realm, the end-Guadalupian extinction, reveals little evidence of coeval marine and nonmarine mass extinctions. Little lived on land during the Ordovician other than a bryophyte-like flora that appears to have been diversifying, not going extinct, during the Late Ordovician. No case can be made for mass extinctions on land coeval with the marine extinctions of the Late Devonian-land plant diversity increased into the Carboniferous, and the tetrapod fossil record is inadequate to identify any mass extinctions. A case can be made for coeval plant/tetrapod extinctions and the end-Guadalupian marine extinctions, so this may be the first coeval marine-nonmarine mass extinction. However, problems of timing and questions about the extent of the nonmarine late/end-Guadalupian extinctions indicate that further research is needed. There were no mass extinctions of land plants, insects or tetrapods across the Permo–Triassic boundary. The Late Triassic was a time of low origination and high extinction rates on land and in the seas; there was no single end-Triassic mass extinction in either realm. The end-Cretaceous provides the strongest case for coeval
land–sea mass extinctions, but there is no mass extinction of land plants, evidence of insect extinction is based on assumption-laden analyses of proxies for insect diversity and the tetrapod extinction was very selective. So, whether the nonmarine extinction at the end of the Cretaceous was a mass extinction is worth questioning. Part of the inability to identify nonmarine mass extinctions stems from taphonomic megabiases due to the relatively
poor quality and uneven sampling of the nonmarine fossil record. Extinction resistance and resilience of terrestrial organisms is also a likely factor in the dearth of nonmarine mass extinctions, and this merits further investigation.
... At the end of Guadalupian, a mass extinction event happened, although the ages of the marine extinction remain unclear but mostly occured at ~260 Ma (Jin et al., 1995;Day et al., 2015), thus it coincided with the activities of ELIP, the low global sea-level and the low Sr isotope record in the marine deposits (Korte and Ullmann, 2018). Reasons of the extinction event could be complicated: the severe environmental crisis in marine (e.g., anoxic and acidification) played an important role for the losses of ~70% species in marine invertebrates (Isozaki and Servais, 2018) and at least 56% of plant species (Day et al., 2015). Rapid sealevel fallen happened during the Capitanian and it reached its minimum to the Phanerozoic around the Guadalupian (Middle Permian)-Lopingian (Late Permian) boundary, causing the widespread disconformity in sedimentary sequences (Isozaki et al., 2008;Kofukuda et al., 2014). ...
Economically important manganese deposits are hosted in the Middle Permian Maokou Formation of Zunyi, northern Guizhou, South China. During the Middle Permian, the intense rifting related to the initial stage of the Emeishan Large Igneous Province (ELIP) led to the development of carbonate platforms and inter-platform troughs. The manganese deposits occur in the transitional zone between carbonate platforms and troughs. Previous studies emphasized that the hydrothermal activities at the bottom of the trough basin controlled the formation of manganese deposits. In this study, new sedimentary, mineralogical, and stable isotope evidence are acquired from this manganese deposit, indicating that the microbially-mediated metallogenic mechanism also made an important contribution for the Middle Permian manganese deposition. The metallogenesis of this manganese deposit is highly like the combination of hydrothermal and microbial processes. Manganese ores in Zunyi are manganese carbonate, showing massive and clastic structures, no macroscopic nor microscopic lamination are found, samples are coarse-grained, diagenetically recrystallized with abundant mineralized microbial and microfossil biosignatures. FTIR, EPMA, and Raman analyses recognize micrometer-scale cyclic mineralogical assembly and help reconstruct the proposed new model of microbial manganese metallogenesis. Hydrothermal activity in the basin provided dissolved Mn²⁺ ions into the anoxic basal watermass. In the syngenetic stage, microbial systems could be subdivided into three categories: (1) cyanobacterial system, (2) Mn-biomat system and (3) Fe-biomat system. Cyanobacterial activity led to the precipitation of calcite, and it could be partially affected by Mn-metasomatism and transformed to Mn-bearing calcite. Mn-oxidizing microbes led to the precipitation of manganese bio-oxide (δ-MnO2) near the redoxcline of the basin. Fe-biomat system was responsible for the precipitation of Fe-oxides (hematite) and Fe-hydroxides (ferrihydrite and lepidocrocite). After burial, manganese oxides reacted with the organic matter in the sediments through the microbially-mediated processes during the early diagenesis and the Mn-metasomatism of the cyanobacterial carbonate jointly contributed to formation of early diagenetic manganese carbonate ore. The redox fluctuations between oxic/suboxic and anoxic zones led to the re-oxidation process and resulted in cyclic marcasite. Anatase cycles observed in samples were interpreted as the diagenetic product of Fe-biomat system.
... The marine "end-Guadalupian mass extinction" or "pre-Lopingian crisis" has been discussed by numerous previous studies (Jin, 1993;Jin et al., 1994;Stanley and Yang, 1994;Shen andShi, 1996, 2002;Bond and Wignall, 2009;Huang et al., 2019). It was once ranked as the third largest mass extinction, behind only the end-Permian and end-Ordovician mass extinctions (Bambach et al., 2004), or as a major mass extinction (Rampino and Shen, 2020) comparable to the end-Ordovician mass extinction (Isozaki and Servais, 2018). Originally, the end-Guadalupian mass extinction was lumped together with the end-Changhsingian mass extinction, which eliminated about 95% of marine faunas (Raup and Sepkoski, 1982;Sepkoski, 1984). ...
The Guadalupian Epoch is marked by the formation of the Pangean supercontinent, global sea-level change, rifting and drifting of the Cimmerian continents, formation of large igneous provinces and dramatic biotic changes. A high-resolution biostratigraphic, chemostratigraphic and high-precision geochronologic framework of this critical transition is fundamental to understanding these events. Extensive studies of the latest Cisuralian and Guadalupian Series in both South China and North America reveal the same conodont lineages, but the conodont interval zones based on Jinogondolella within the Guadalupian Series are slightly diachronous. High-precision U-Pb geochronological studies (CA-ID-TIMS method) calibrate the base of the Guadalupian Series (base Roadian) at 273.01 ± 0.14 Ma. A previously reported age from an ash bed overlying the Emeishan flood basalts, 259.51 ± 0.21 Ma, is adopted for the Guadalupian/Lopingian boundary (GLB). Based on recently published geochronology and Bayesian age modeling from the Guadalupian Series, the base of the Capitanian is constrained at 264.28 ± 0.16 Ma and the base of the Wordian is interpolated to be 266.9 ± 0.4 Ma. The Illawarra Reversal is of early-middle Wordian age. Both North America and South China possess a distinct negative δ13Ccarb excursion of 3-5‰ at the latest Kungurian and early Roadian (LK-ER CIE), which coincides with the early stages of a significant 3rd order sea-level rise. The large end-Guadalupian δ13Ccarb negative excursion may have been affected by post-depositional diagenesis or a warming event associated with the Emeishan volcanism. The 87Sr/86Sr ratios in both regions declined from the latest Kungurian to the late Capitanian, but have different ratios and reveal several fluctuations in the middle Guadalupian. Measured δ18Oapatite values suggest that the Delaware Basin was 3-4°C cooler than the eastern Yangtze Block. Analysis of a new high-resolution database of marine taxa indicates only a minor pre-Lopingian diversity drop from 261.04 Ma to 259.98 Ma, which coincides with the peak Emeishan volcanism. The widely-perceived “end-Guadalupian mass extinction” in North America is evidently masked by, and possibly an artefact of, a stratigraphic truncation effect due to rapid lithofacies changes from limestone to laminated evaporites with the closure of the west Texas basins.
... A cold period and first high extinction zone follow the end of the superchrons. The two extinctions in this zone (end-Capitanian and end-Ordovician) have been identified as having 'multiple similarities' (Isozaki and Servais, 2018). The cooling events in this region encompass examples varying in intensity and duration, with interpretation affected by the resolution of available data, e.g., from Maastrichtian fluctuations of a few degrees on 100 kyr timescales (Thibault et al., 2016) to the Marinoan glaciation, identified as one of the two most severe in Earth's history, occurring over at least four million years (Prave et al., 2016). ...
The passage of our Solar System through the spiral arms has been implicated as a contributor to global environmental perturbations. The suggestion of a consistent structure within the arms, informed by density wave theory, raises the possibility of repeating patterns of events at each arm crossing. Here we test the hypothesis that the structure of the arms of our galaxy influences the stratigraphic record on Earth. We construct independent structural and temporal models and combine these to compare the timings of arm tracers, materials from the earliest Solar System and events on Earth, including the largest extinctions. We find that a recurring sequence of events across the four arms emerges with an average arm-passing time of 188 million years. We suggest that the multiple temporal overlaps of events across arms, and their alignment with arm tracers and the earliest Solar System, presents an opportunity for a greater understanding of both Earth-based phenomena and galactic structure.
... The initial major decline of Permian, during which nearly 60 % of marine invertebrate species became extinct, occurred immediately before the G-LB (Stanley, 2016). Although the G-LB extinction has been overlooked for years in the great shadow of the P-TB mass extinction, its significance has recently drawn more serious attention (Bond et al., 2010;Isozaki, 2009;Isozaki & Servais, 2018;Jin et al., 2006). ...
Immediately before the extinction of the end‐Guadalupian (Middle Permian; ca. 260 Ma), a significant change to the global carbon cycle occurred in the superocean Panthalassa, as indicated by a prominent positive δ13C excursion called the Kamura event. However, the causes of this event and its connection to the major extinction of marine invertebrates remain unclear. To understand the mutual relationships between these changes, we analyzed the sulfur isotope ratio of the carbonate‐associated sulfate (CAS) and HCl‐insoluble residue, as well as the carbon isotope ratio of bulk organic matter, for the Middle‐Upper Permian carbonates of an accreted mid‐oceanic paleo‐atoll complex from Japan, where the Kamura event was first documented. We detected the following unique aspects of the stable carbon and sulfur isotope records. First, the extremely high δ13C values of carbonate (δ13Ccarb) over +5‰ during the Capitanian (late Guadalupian) were associated with large isotopic differences between carbonate and organic matter (Δ13C = δ13Ccarb ‐ δ13Corg). We infer that the Capitanian Kamura event reflected an unusually large amount of dissolved organic matter (DOC) in the expanded oxygen minimum zone (OMZ) at mid‐depth. Second, the δ34S values of CAS (δ34SCAS) were inversely correlated with the δ13Ccarb values during the Capitanian to early Wuchiapingian (early Late Permian) interval. The Capitanian trend may have appeared under increased oceanic sulfate conditions, which were accelerated by intense volcanic outgassing. Bacterial sulfate reduction with increased sulfate concentrations in seawater may have stimulated the production of pyrite that may have incorporated iron in pre‐existing iron hydroxide/oxide. This stimulated phosphorus release, which enhanced organic matter production and resulted in high δ13Ccarb. Low δ34SCAS values under high sulfate concentrations were maintained and the continuous supply of sulfate cannot by explained only by the volcanic eruption of the Emeishan Trap, which has been proposed as a cause of the extinction. The Wuchiapingian δ34SCAS–δ13Ccarb correlation, likely related to low sulfate concentration, may have been caused by the removal of oceanic sulfate through the massive evaporite deposition. This article is protected by copyright. All rights reserved.
... However, as more and more evidence emerged in recent years, current views on this biotic crisis to some extent have changed. The extinction rate at the end-Guadalupian was ranked very high in the early studies, only lower than the end-Permian and end-Ordovician mass extinctions (Sepkoski, 1996;Bambach et al., 2004;Isozaki and Servais, 2018). Re-evaluation of the Phanerozoic taxonomic-severity (McGhee et al., 2013) suggested that the end-Guadalupian mass extinction is not severe as previously thought, and only happened at the community level and taxonomically selective (Shen and Shi, 2002;Clapham et al., 2009;McGhee et al., 2013;Clapham, 2015). ...
Current understanding of biodiversity changes in the Permian is presented, especially the consensus and disagreement on the tempo, duration, and pattern of end-Guadalupian and end-Permian mass extinctions. The end-Guadalupian mass extinction (EGME; i.e., pre-Lopingian crisis) is not as severe as previously thought. Moreover, the turnovers of major fossil groups occurred at different temporal levels, therefore the total duration of the end-Guadalupian mass extinction is relatively extended. By comparison, fossil records constrained with high-precision geochronology indicate that the end-Permian mass extinction (EPME) was a single-pulse event and happened geologically instantaneous. Variation of geochemical proxies preserved in the sedimentary records is important evidence in examining potential links between volcanisms and biodiversity changes. Some conventional and non-traditional geochemical proxy records in the Permian show abrupt changes across the Permian-Triassic boundary, reflecting climate change, ocean acidification and anoxia, carbon cycle perturbation, gaseous metal loading, and enhanced continental weathering. These, together with the stratigraphic coincidence between volcanic ashes and the end-Permian mass extinction horizon, point to large-scale volcanism as a potential trigger mechanism.
To further define the nature of volcanism which was responsible for global change in biodiversity, main characteristics of four Permian large igneous provinces (LIPs; i.e., Tarim, Panjal, Emeishan, and Siberian) are compared, in terms of timing and tempo, spatial distribution and volume, and magma-wall rock interactions. The comparison indicates that volcanic fluxes (i.e., eruption rates) and gas productions are the key features distinguishing the Siberian Traps from other LIPs, which also are the primary factors in determining the LIP’s potential of affecting Earth’s surface system. We find that the Siberian Traps volcanism, especially the switch from dominantly extrusive eruptions to widespread sill intrusions, has the strongest potential for destructive impacts, and most likely is the ultimate trigger for profound environmental and biological changes in the latest Permian-earliest Triassic. The role of Palaeotethys subduction-related arc magmatism cannot be fully ruled out, given its temporal coincidence with the end-Permian mass extinction. As for the Emeishan LIP, medium volcanic flux and gas emission probably limited its killing potential, as evident from weak changes in geochemical proxies and biodiversity. Because of its long-lasting but episodic nature, the Early Permian magmatism (e.g., Tarim, and Panjal) may have played a positive role in affecting the contemporaneous environment, as implicated by coeval progressive climate warming, termination of the Late Palaeozoic Ice Age (LPIA), and flourishing of ecosystems.
... It is considered to mark the start of the Paleozoic-Mesozoic transition in the marine realm (Isozaki 2009b;Bond et al. 2015). The age of the crisis is currently debated with estimates ranging from the Wordian-Capitanian transition (Gand & Durand 2006;Lucas 2009;Shen & Shi 2009;Groves & Wang 2013) to the early Lopingian (Nielsen & Shen 2004;Kaiho et al. 2005), with most favouring either an end-Guadalupian (end-Capitanian, Wang & Sugiyama 2000;Leven 2003;Yang et al. 2004;Retallack et al. 2006; Isozaki 2009a, b) or mid-Capitanian ( Wignall et al. 2009aWignall et al. , 2012Bond et al. 2010a, b;De la Horra et al. 2012;Isozaki & Servais 2018) age. In order to be consistent and clear in the following text, from herein we refer to this event as the 'Capitanian mass extinction'. ...
The Capitanian (Guadalupian) witnessed one of the major crises of the Phanerozoic and, like many other extinctions, it coincided with the eruption of a large igneous province, in this case the Emeishan Traps of SW China. However, the timing and causal relationships of this event are in dispute. This study concentrates on the deep-water chert-mudstone strata of the Gufeng Formation and its transition to the Yinping Formation at Chaohu. Zircons from tuffs in the uppermost Gufeng Formation yield a U-Pb age of 261.6 ± 1.6 Ma, and comparison with sections around Emeishan suggests that the tuffs appeared in the Jinogondolella altudaensis conodont zone and persisted to the Jinogondolella xuanhanensis zone. This coincides with the Emeishan eruptions, and suggests that the tuffs probably derived from this province. Mineralogical and geochemical characteristics also show the tuffs are of acid volcanogenic origin and have a geochemical fingerprint of the Emeishan large igneous province. Our dating shows that a crisis amongst radiolarian and a subsequent productivity decline occurred during the middle Capitanian, prior to the Guadalupian-Lopingian boundary. The Emeishan eruptions began immediately before this, indicating a likely causal relationship between these events. Major regression and marine anoxia/euxinia are two other important extinction-relevant environmental changes that occurred during this critical interval.
Six species of silicified gastropods, Retispira sp., Discotropis girtyi? Yochelson, 1956a, Shwedagonia elegans Batten, 1956, Lamellospira aff. L. conica Batten, 1958, Apachella aff. A. translirata Winters, 1956, and Soleniscus variabilis Erwin, 1988a are recognized from a carbonate debris flow in the Reef Trail Member of the Bell Canyon Formation in the Delaware Basin, west Texas. The mollusk assemblage contains the youngest middle Permian (Guadalupian) gastropod fauna known from the Permian Basin. The small shell size of the abundant gastropod fauna suggests they were foliage grazers in a community dominated by mollusks.
Latest version that removes previous errors and adds new data
In recent years, significant progress in shale gas exploration has been achieved in the Upper Ordovician (Wufeng Formation)-Lower Silurian (Longmaxi Formation) shales in the Upper Yangtze area, South China. Although many studies have been carried out on the Upper Ordovician-Lower Silurian shales, the controlling factors causing organic matter accumulation of these shales remain controversial. This study uses trace-element geochemistry and sedimentological methods to evaluate terrigenous input, redox conditions and primary productivity to explore the mechanisms of organic matter accumulation. The variation of terrigenous fraction elements (Al, Th and Sc) concentrations reflect a mixed influence of sea-level change and weathering. The sea-level of the Upper Yangtze Sea went through two cycles of transgression to regression during the Ordovician-Silurian transition. The Linxiang Formation, Kuanyinchiao Bed and the upper part of Longmaxi Formation developed during the periods of regression, whereas the Wufeng Formation and the lower part of the Longmaxi Formation developed during the periods of transgression. The paleo-productivity indexes of TOC content, ratios of Ba/Al and P/Al, and redox conditions proxies of Mo concentration, ratios of U/Th and V/Cr generally display similar variation patterns with respect to the sea-level changes. High TOC contents and Ba/Al and P/Al ratios indicate the paleo-productivity was high on the sea surface, as shown by relatively good positive correlations between Th vs. TOC, and Sc vs. TOC. This indicates that the paleo-productivity was controlled by the nutrients input through weathering. The good positive correlations between redox conditions indexes (U/Th and V/Cr ratios) with TOC content reflects reductive preservation conditions (anoxic to euxinic), thus implying they were an important controlling factor for organic matter accumulation. Nevertheless, redox conditions were closely associated with sea level change and organic matter decomposition. Therefore, the sea-level change and weathering were the primary controlling factors for organic matter enrichment across the Ordovician to Silurian transition.
The largest mass extinction in the Phanerozoic occurred at the boundary between the Paleozoic and Mesozoic eras (about 252 million years ago). The end-Paleozoic extinction that determined the fate of modern animals including human beings occurred in two steps: first around the Middle-Late Permian boundary (G-LB) and then at the Permian-Triassic boundary (P-TB). Biological and non-biological aspects unique to these two distinct events include changes in biodiversity, isotope ratios (C, Sr, etc.) of seawater, sea level, ocean redox state, episodic volcanism, and geomagnetism. This article reviews possible causes proposed for the double-stepped extinction in regard to the current status of mass extinction studies. Causes of extinction can be grouped into four categories in hierarchy, from small to large scale, i.e., Category 1, direct kill mechanism; Category 2, global environmental change; Category 3, trigger on the planet’s surface; and Category 4, ultimate cause. As the G-LB and end-Ordovician extinctions share multiple similar episodes including the appearance of global cooling (Category 2), the same cause and processes were likely responsible for the biodiversity drop. In addition to the most prevalent scenario of mantle plume-generated large igneous provinces (LIPs) (Category 3) for the end-Permian extinction, an emerging perspective of cosmoclimatology is introduced with respect to astrobiology. Galactic cosmic radiation (GCR) and solar/terrestrial responses in magnetism (Category 4) could have had a profound impact on the Earth’s climate, in particular on extensive cloud coverage (irradiance shutdown). The starburst events detected in the Milky Way Galaxy apparently coincide in timing with the cooling-associated major extinctions of the Phanerozoic and also with the Proterozoic snowball Earth episodes. As an ultimate cause (Category 4) for major extinction, the episodic increase in GCR-dust flux from the source (dark clouds derived from starburst) against the geomagnetic shield likely determined the major climate changes, particularly global cooling in the past. The study of mass extinctions on Earth is entering a new stage with a new astrobiological perspective.
We introduce and briefly summarize a collection of papers contextualizing the onset of the Great Ordovician Biodiversification Event, initiated during the first meeting of IGCP project 653 at Van Mildert College, Durham University, UK, in September 2016.
The Late Ordovician mass extinction (LOME), one of the five largest Phanerozoic biodiversity depletions, occurred in two pulses associated with the expansion and contraction of ice sheets on Gondwana during the Hirnantian Age. It is widely recognized that environmental disruptions associated with changing glacial conditions contributed to the extinctions, but neither the kill mechanisms nor the causes of glacial expansion are well understood. Here we report anomalously high Hg concentrations in marine strata from south China and Lau-rentia deposited immediately before, during, and after the Hirnantian glacial maximum that we interpret to reflect the emplacement of a large igneous province (LIP). An initial Hg enrichment occurs in the late Katian Age, while a second enrichment occurs immediately below the Katian-Hirnantian boundary, which marks the first pulse of extinction. Further Hg enrichment occurs in strata deposited during glacioeustatic sea-level fall and the glacial maximum. We propose that these Hg enrichments are products of multiple phases of LIP volcanism. While elevated Hg concentrations have been linked to LIP emplacement coincident with other Phanerozoic mass extinctions, the climate response during the LOME may have been unique owing to different climatic boundary conditions, including preexisting ice sheets. Our observations support a volcanic trigger for the LOME and further point to LIP volcanism as a primary driver of environmental changes that caused mass extinctions.
Gigantism-very large body size-is an ecologically important trait associated with competitive superiority. Although it has been studied in particular cases, the general conditions for the evolution and maintenance of gigantism remain obscure. I compiled sizes and dates for the largest species in 3 terrestrial and 7 marine trophic and habitat categories of animals from throughout the Phanerozoic. The largest species (global giants) in all categories are of post-Paleozoic age. Gigantism at this level appeared tens to hundreds of millions of years after mass extinctions and long after the origins of clades in which it evolved. Marine gigantism correlates with high planktic or seafloor productivity, but on land the correspondence between productivity and gigantism is weak at best. All global giants are aerobically active animals, not gentle giants with low metabolic demands. Oxygen concentration in the atmosphere correlates with gigantism in the Paleozoic but not thereafter, likely because of the elaboration of efficient gas-exchange systems in clades containing giants. Although temperature and habitat size are important in the evolution of very large size in some cases, the most important (and rare) enabling circumstance is a highly developed ecological infrastructure in which essential resources are abundant and effectively recycled and reused, permitting activity levels to increase and setting the stage for gigantic animals to evolve. Gigantism as a hallmark of competitive superiority appears to have lost its luster on land after the Mesozoic in favor of alternative means of achieving dominance, especially including social organization and coordinated food-gathering.
The Great Ordovician Biodiversification Event (GOBE) was the most rapid and sustained increase in marine Phanerozoic biodiversity. What generated this biotic response across Palaeozoic seascapes is a matter of debate; several intrinsic and extrinsic drivers have been suggested. One is Ordovician climate, which in recent years has undergone a paradigm shift from a text-book example of an extended greenhouse to an interval with transient cooling intervals – at least during the Late Ordovician. Here, we show the first unambiguous evidence for a sudden Mid Ordovician icehouse, comparable in magnitude to the Quaternary glaciations. We further demonstrate the initiation of this icehouse to coincide with the onset of the GOBE. This finding is based on both abiotic and biotic proxies obtained from the most comprehensive geochemical and palaeobiological dataset yet collected through this interval. We argue that the icehouse conditions increased latitudinal and bathymetrical temperature and oxygen gradients initiating an Early Palaeozoic Great Ocean Conveyor Belt. This fuelled the GOBE, as upwelling zones created new ecospace for the primary producers. A subsequent rise in δ13C ratios known as the Middle Darriwilian Isotopic Carbon Excursion (MDICE) may reflect a global response to increased bioproductivity encouraged by the onset of the GOBE.
Mass extinctions are crucial to understanding changes in biodiversity through time. However, it is still disputed whether extinction dynamics in the marine and terrestrial biotas followed comparable trajectories. For instance, while marine realms have suffered five strong depletions in diversity, the so-called ‘Big Five’ mass extinctions, only the end-Permian event appears to have also resulted in a major abrupt reduction in continental diversity. However, recent evidence based on the diversity dynamics of vegetation has suggested the presence of two major episodes of extinction in the terrestrial environments, at the end-Carboniferous and the end-Permian times. This apparent contradiction is addressed in the present study. Here, we show that while the end-Carboniferous plant extinction was focused on particular environments (e.g. tropical wetlands) and affected mainly the free-sporing plant diversity (i.e. lycopsids, ferns and progymnosperms), only the end-Permian mass extinction had devastating effects on vegetation on a global scale. If we take the biosphere as a whole, the results highlight that the end-Permian biotic crisis was the only genuine global mass extinction event, affecting widely both the marine and terrestrial environments.
: Variations in the 13 C/ 12 C value of total dissolved inorganic carbon (DIC) in the world’s oceans through time have been documented through stratigraphic study of marine carbonate rocks (δ 13 C carb ). This variation has been used to date and correlate sediments. The stratigraphic record of carbon isotopes is complex because the main process fractionating 12 C from 13 C is photosynthesis, with organic matter depleted in the heavy isotope ( 13 C). The carbon isotope record (on the geological time scales considered here) is to a large extent defined by changes in the partitioning of carbon between organic carbon and carbonate, and therefore linked directly to the biosphere and the global carbon cycle. This chapter summarizes δ 13 C carb variations through geologic time compiled from multiple literature sources. Materials analyzed for curve-construction differ between authors and between geological time periods, and one should carefully consider whether skeletal carbonate secreted by specific organisms or bulk carbonate has been used in evaluating or comparing carbon isotope stratigraphic records. Mid-Jurassic through Cenozoic curves have been mainly derived from pelagic carbonates, and exhibit low amplitude δ 13 C carb variability (from −1 to +4‰) relative to curves for the earlier part of the record (from −3 to +8 ‰ for the Phanerozoic, from −15 to +15‰ for the Proterozoic and Archean). The Mid-Jurassic and older curves are dominantly based on data from platform carbonates, which show greater variability and more spatial heterogeneity. The different character of carbon isotope curves derived from older platform carbonates as compared to younger pelagic records may reflect primary and/or diagenetic processes, difference in paleoenvironments, difference in calcifying organisms, or inherent changes in the global carbon cycle with geologic time and biotic evolution (e.g., changes in reservoir size).
ABsTRAcT-Polydiexodina oregonensis, n. sp., of late Guadalupe (late Permian) age is described from a float boulder in central Oregon. The boulder apparently came from nearby beds of boulder conglomerate of late Triassic age, of which most of the boulders contain the fusulinid fauna of the Coyote Butte Formation of Leonard (late early Permian) age. Uplift in the area during late Triassic time and removal of rocks of late Guadalupe age and a considerable thickness of beds of Leonard age are suggested.
Despite their utility for bio- and chemostratigraphy, many carbonate platform sequences have been difficult to analyze using paleomagnetic techniques due to their extraordinarily weak natural remanent magnetizations (NRMs). However, the physical processes of magnetization imply that stable NRMs can be preserved that are many orders of magnitude below our present measurement abilities. Recent advances in reducing the noise level of superconducting magnetometer systems, particularly the introduction of DC-SQUID sensors and development of a low-noise sample handling system using thin-walled quartz-glass vacuum tubes, have solved many of these instrumentation problems, increasing the effective sensitivity by a factor of nearly 50 over the previous techniques of SQUID moment magnetometry.
Here we report the successful isolation of a two-polarity characteristic remanent magnetization from Middle–Late Permian limestone formed in the atoll of a mid-oceanic paleo-seamount, now preserved in the Jurassic accretionary complex in Japan, which had proved difficult to analyze in past studies. Paleothermometric indicators including Conodont Alteration Indices, carbonate petrology, and clumped isotope paleothermometry are consistent with peak burial temperatures close to 130 °C, consistent with rock magnetic indicators suggesting fine-grained magnetite and hematite holds the NRM. The magnetic polarity pattern is in broad agreement with previous global magnetostratigraphic summaries from the interval of the Early–Middle Permian Kiaman Reversed Superchron and the Permian–Triassic mixed interval, and ties the Tethyan–Panthalassan fusuline zones to it. Elevated levels of hematite associated with the positive δ^(13)C_(carb) of the Kamura event argue for a brief spike in environmental oxygen. The results also place the paleo-seamount at a paleolatitude of ~ 12° S, in the middle of the Panthalassan Ocean, and imply a N/NW transport toward the Asian margin of Pangea during Triassic and Jurassic times, in accordance with the predicted trajectory from its tectono-sedimentary background. These developments should expand the applicability of magnetostratigraphic techniques to many additional portions of the Geological time scale.
The 87Sr/86Sr value of Sr dissolved in the world's oceans has varied though time, which allows one to date and correlate sediments. This variation and its stratigraphic resolution is discussed and graphically displayed. INTRODUCTION The ability to date and correlate sediments using Sr isotopes relies on the fact that the 87Sr/86Sr value of Sr dissolved in the world's oceans has varied though time. In Fig. 7.1, we show this variation, plotted according to the time scale presented in this volume. More detail is given in Fig. 7.2, on which we plot both the curve of 87Sr/86Sr through time and the data used to derive it. Comparison of the measured 87Sr/86Sr of Sr in a marine mineral with a detailed curve of 87Sr/86Sr through time can yield a numerical age for the mineral. Alternatively, 87Sr/86Sr can be used to correlate between stratigraphic sections and sequences by comparison of the 87Sr/86Sr values in minerals from each (Fig. 7.3). Such correlation does not require a detailed knowledge of the trend through time of 87Sr/86Sr, but it is useful to know the general trend in order to avoid possible confusion in correlation near turning points on the Sr curve. Strontium isotope stratigraphy (SIS) can be used to estimate the duration of stratigraphic gaps (Miller et al., 1988), estimate the duration of biozones (McArthur et al., 1993, 2000, 2004) and stages (Weedon and Jenkyns, 1999), and to distinguish marine from non-marine environments (Schmitz et al., 1991; Poyato-Ariza et al., 1998).
The Ordovician 87 Sr/ 86 Sr isotope sea-water curve is well established and shows a decreasing trend until the mid-Katian. However, uncertainties in calibration of this curve to biostratigraphy and geochronology have made it diffi cult to determine how the rates of 87 Sr/ 86 Sr decrease may have varied, which has implications for both the strati-graphic resolution possible using Sr isotope stratigraphy and efforts to model the effects of Ordovician geologic events. We measured 87 Sr/ 86 Sr in conodont apatite in North Ameri-can Ordovician sections that are well studied for conodont biostratigraphy, primarily in Nevada, Oklahoma, the Appalachian re-gion, and Ohio Valley. Our results indicate that conodont apatite may provide an accu-rate medium for Sr isotope stratigraphy and strengthen previous reports that point toward a signifi cant increase in the rate of fall in seawater 87 Sr/ 86 Sr during the Middle Ordovician Darriwilian Stage. Our 87 Sr/ 86 Sr results suggest that Sr isotope stratigraphy will be most useful as a high-resolution tool for global correlation in the mid-Darriwilian to mid-Sandbian, when the maximum rate of fall in 87 Sr/ 86 Sr is estimated at ~5.0–10.0 × 10 –5 per m.y. Variable preservation of conodont elements limits the precision for individual stratigraphic horizons. Replicate conodont analyses from the same sample differ by an average of ~4.0 × 10 –5 (the 2σ standard de-viation is 6.2 × 10 –5), which in the best case scenario allows for subdivision of Ordovician time intervals characterized by the highest rates of fall in 87 Sr/ 86 Sr at a maximum reso-lution of ~0.5–1.0 m.y. Links between the increased rate of fall in 87 Sr/ 86 Sr beginning in the mid-late Darriwilian (Phragmodus po-lonicus to Pygodus serra conodont zones) and geologic events continue to be investigated, but the coincidence with a long-term rise in sea level (Sauk-Tippecanoe megasequence boundary) and tectonic events (Taconic orog-eny) in North America provides a plausible explanation for the changing magnitude and 87 Sr/ 86 Sr of the riverine Sr fl ux to the oceans.
A total of 2128 calcitic and phosphatic shells, mainly brachiopods with some conodonts and belemnites, were measured for their , and values. The dataset covers the Cambrian to Cretaceous time interval. Where possible, these samples were collected at high temporal resolution, up to 0.7 Ma (one biozone), from the stratotype sections of all continents but Antarctica and from many sedimentary basins. Paleogeographically, the samples are mostly from paleotropical domains. The scanning electron microscopy (SEM), petrography, cathodoluminescence and trace element results of the studied calcitic shells and the conodont alteration index (CAI) data of the phosphatic shells are consistent with an excellent preservation of the ultrastructure of the analyzed material. These datasets are complemented by extensive literature compilations of Phanerozoic low-Mg calcitic, aragonitic and phosphatic isotope data for analogous skeletons. The oxygen isotope signal exhibits a long-term increase of from a mean value of about −8‰ (PDB) in the Cambrian to a present mean value of about 0‰ (PDB). Superimposed on the general trend are shorter-term oscillations with their apexes coincident with cold episodes and glaciations. The carbon isotope signal shows a similar climb during the Paleozoic, an inflexion in the Permian, followed by an abrupt drop and subsequent fluctuations around the modern value. The ratios differ from the earlier published curves in their greater detail and in less dispersion of the data. The means of the observed isotope signals for , , and the less complete (sulfate) are strongly interrelated at any geologically reasonable (1 to 40 Ma) time resolution. All correlations are valid at the 95% level of confidence, with the most valid at the 99% level. Factor analysis indicates that the , , and isotope systems are driven by three factors. The first factor links oxygen and strontium isotopic evolution, the second and , and the third one the and . These three factors explain up to 79% of the total variance. We tentatively identify the first two factors as tectonic, and the third one as a (biologically mediated) redox linkage of the sulfur and carbon cycles. On geological timescales (≥1 Ma), we are therefore dealing with a unified exogenic (litho-, hydro-, atmo-, biosphere) system driven by tectonics via its control of (bio)geochemical cycles.
The concept of the Ordovician gastropod genus Maclurites LeSueur,1818, at present includes much variation. Maclurina Ulrich in Ulrich and Scofield, 1897, is removed as a subjective synonym of Maclurites and reestablished as a separate genus. Species of Maclurites with spiral grooves on the outer whorl surface and a relatively small umbilicus are transferred to Maclurina. Maclurina manitobensis (Whiteaves, 1890) forms a distinctive part of the Late Ordovician-age "Arctic Ordovician fauna." An ususually large specimen (25 cm in diameter) from the Bighorn Dolomite (Upper Ordovician), Wyoming, is illustrated; this Wyoming specimen is the volumetrically largest Paleozoic gastropod ever reported.
Oscillatory-zoned euhedral single zircons from the upper Sandbian (Upper Ordovician) Kinnekulle K-bentonite exposed in a hillock at Pääsküla in Estonia and at the type locality on Mt Kinnekulle in Sweden were dated in a grain-by-grain manner by laser ablation-inductively coupled plasma mass spectrometer. The U–Pb (weighed mean) ages of the 25 grains from Mt Kinnekulle and 24 grains from Pääsküla are 453.4 ± 6.6 and 454.9 ± 4.9 Ma, respectively. This study provides the first ca. 454 Ma (late Sandbian) age for the Ordovician K-bentonite in northern Estonia and confirmed its correlation with the type Kinnekulle bed across the Baltic Sea.
The end Ordovician glaciation is distinct among Phanerozoic glaciations
in that CO2, levels were generally high, yet major
continental ice sheets accumulated on the Gondwana supercontinent. New
oxygen isotopic data indicate substantial changes in sea-water
temperatures and ice volume coinciding with glacio-eustatic changes in
sea level reflecting the growth and decay of the Gondwana ice cap. Major
glaciation was apparently confined to the Hirnantian and was 0.5-1 m.y.
long, rather than the 35 m.y. of earlier estimates. Carbon isotope
values indicate significant changes in carbon cycling as the oceans
changed from a state with warm saline bottom waters to a state with cold
deep-water circulation and then back again. We believe that the changes
in the carbon cycle effected a reduction in PCO2
levels in the oceans and atmosphere and thus promoted glaciation but
were unable to sustain icehouse conditions in a greenhouse world.
We present new magnetostratigraphic results obtained from a well-dated Ordovician key section located along the Angara River, near the terminus of the Rozhkova River (southern Siberian platform). More than 220 samples were thermally demagnetized up to 670°C in order to isolate their characteristic ancient magnetization. Samples from the Arenig, the Llanvirn and the Llandeilo stages are all (but two) of reversed magnetic polarity. In contrast, samples dated of the Caradoc yield a sequence of several magnetic polarity intervals. These new data therefore confirm the occurrence of a long reversed magnetic polarity interval during the Ordovician, the so-called Moyero superchron, which ended during the middle or late Llandeilo.
Ever since their discovery nearly 50 years ago, geomagnetic superchrons have been a puzzle for the geophysical community. Although there have only been a few during Phanerozoic time, Driscoll and Evans (2016) recently proposed multiple superchrons during the Proterozoic. Biggin et al. (2012) suggested that superchrons are the result of low heat flow at the Core Mantle Boundary (CMB), which causes low dynamo activity, and that they are generally separated by 180–190 Myr. According to Courtillot and Olson (2007), one potential process for ending a superchron is via the generation of a superplume at the bottom of the mantle, followed by the eruption of a large igneous province (LIP) 10–20 Myr later. However, this theory is unable to explain the Middle Cretaceous LIP activity and recent modelling favors a longer plume rise-time of 20–50 Myr (Biggin et al., 2012).
A Fourier analysis of the magnitudes and timing of the Phanerozoic mass extinctions (MEs) demonstrates that many of the periodicities claimed in other analyses are not statistically significant. Moreover we show that the periodicities associated with oscillations of the Solar System about the galactic plane are too irregular to give narrow peaks in the Fourier periodograms. This leads us to conclude that, apart from possibly a small number of major events, astronomical causes for MEs can largely be ruled out.
Significance
This paper shows that background extinction definitely preceded mass extinctions; introduces a mathematical method for estimating the amount of this background extinction and, by subtracting it from total extinction, correcting estimates of losses in mass extinctions; presents a method for estimating the amount of erroneous backward smearing of extinctions from mass extinction intervals; and introduces a method for calculating species losses in a mass extinction that takes into account clustering of losses. It concludes that the great terminal Permian crisis eliminated only about 81% of marine species, not the frequently quoted 90–96%. Life did not almost disappear at the end of the Permian, as has often been asserted.
A new full description of the bivalve Shikamaia akasakaensis Ozaki (genotype species of Shikamaia ) is presented, providing the first documentation of its hinge and ligament, and resolving many uncertainties about Shikamaia , the first described genus of the Permian bivalve family Alatoconchidae. The genus Shikamaia has a unique ligament, modified from typical duplivincular ligaments in occupying only half of the cardinal area, and having ligament sheets that extend themselves towards the beak with continued growth. This ligament is strikingly different from the ligaments of other alatoconchid genera. All alatoconchids are believed to have a common ancestry, but the magnitude of difference in their hinges warrants dividing the family into two subfamilies. The subfamily Saikraconchinae is erected new.
The largest known trilobite fossil, a virtually complete articulated dorsal shield of the asaphid Isotelus rex new species, has been recovered from Upper Ordovician (Cincinnatian, Richmondian) nearshore carbonates of the Churchill River Group in northern Manitoba. At over 700 mm in length, it is almost 70 percent longer than the largest previously documented complete trilobite, and provides the first unequivocal evidence of maximum trilobite length in excess of one-half metre. Comparisons with other fossil and extant members of the phylum suggest that in terms of maximum linear dimensions it was among the biggest arthropods ever to have lived. Sediments of the Churchill River Group were deposited in an equatorial epeiric setting and the extremely large size of I. rex n. sp. thus marks a striking example of low-latitude gigantism, in sharp contrast to the widespread phenomenon of “polar gigantism” in many modern marine benthic arthropods. Lack of extensive epibiontic colonization of the exoskeletal surface and the presence of large distinctive trace fossils in the same unit suggest that I. rex n. sp. may have been a semi-infaunal predator and scavenger that employed a shallow furrowing and probing mode of benthic feeding. The extinction of the isotelines (and virtually the entire asaphide lineage) at the end of the Ordovician cannot be related to the near contemporaneous achievement of exceptionally large adult size in some representatives. Failure to survive the terminal Ordovician extinction event was most likely a consequence of a pelagic larval life-style that proved ill-adapted to the rapid onset of global climatic cooling and loss of tropical shelf habitats.
High-resolution (930 samples) magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) analyses were conducted on the ~ 49 m thick Middle Permian Maokou Formation at Dukou, South China. Spectral analysis of covariant MS and ARM series reveal Milankovitch cycles with eccentricity, obliquity, and precession. A 5.7 myr floating 405 kyr eccentricity cycle-calibrated astronomical time scale was constructed and used as a geochronometer for estimating the durations of the conodont zones. The results indicate that the durations of the Jinogondolella postserrata, J. altudaensis, J. prexuanhanensis, and J. xuanhanensis conodont zones were 490 kyr, 560 kyr, 820 kyr, and 750 kyr, respectively. The 405 kyr-calibrated MS and ARM series also show prominent ~ 1 myr cyclicity, which may correspond to the secular frequencies of Earth and Mars, s4–s3, in the Middle Permian. The early Capitanian time interval was synchronous with the Kamura cooling event, and the accentuated obliquity cycling may signal ice-sheet expansion. The modulations of the obliquity have a close relationship with third-order eustatic sequences of the Wordian and Capitanian stages, suggesting a glacioeustatic origin during the Middle Permian.
Terrestrialization probably began more than one billion years ago and irreversibly altered biogeochemical processes at planetary scale. In this paper, we focus on the terrestrialization process of the Streptophyta, the division that includes charophytes and land plants (embryophytes) and whose members are today ecologically dominant in all terrestrial environments. The timing and the phylogenetic context of the early evolution of land plants are reviewed. The available information on the relationships within embryophytes and related organisms is compiled in two informal consensus trees based either on morphological/anatomical or on molecular data. We also consider the algal/embryophyte transition through the analysis of the evidence provided by microfossils (cryptospores and spores). The ongoing debate about the definition of the term cryptospores, but more importantly about the biological affinities of these microfossils that are possibly derived from early land plants, is discussed. All important clades of embryophytes, with a focus on their Palaeozoic representatives, are described; the significance of several embryophyte key characters is evaluated. The terrestrialization of land plants evolved in different steps. The new term “proembryophytic phase” is introduced to define the very long period of time during which the green algae ancestor of land plants acquired all the evolutionary characters that ultimately allowed their terrestrialization since the late Precambrian. Since the Middle Ordovician, an “eoembryophytic phase” characterized the earliest evidence of liverwort-like plants, before the first fossil record of trilete miospores in the Late Ordovician and of first macrofossils of vascular land plants in the Silurian, marking the “eo −/eutracheophytic phase.”
Ordovician black shales have been investigated extensively for at least three basic reasons: (1) they bear one of the system's most useful biostratigraphic tools, graptolites; (2) many of them are richly petroliferous; and (3) they are relatively widespread. Review and analysis of environments in which modern analogues of black shales may form indicate that they accumulate under hypoxic to anoxic conditions. Investigations of these environments in modern oceans indicate that they form in settings where an abundance of organic matter is present, and oxygen supply and possible resupply is shut off, or those in which oxygen resupply is at a slower rate than oxygen consumption. Ordovician black shales likely accumulated in environments relatively similar to modern hypoxic-anoxic environments under oceanic oxygen minimum zones as well as in shelf sea basins of varying depths and shallow shelf seas in which density stratification shuts off oxygen supplies.
Long-term carbon and sulfur cycle models have helped shape our understanding of the Phanerozoic history of atmospheric CO2 and O2, but error analyses have been largely limited to testing only a subset of input parameters singly. As a result, the full ranges of probable CO2 and O2 are not quantitatively known. Here we investigate how variation in all 68 input parameters of the GEOCARBSULF model, both singly and in combination, affect estimated CO2 and O2. We improve formulations for land area, runoff, and continental temperature, the latter of which now excludes land area not experiencing chemical weathering. We find our resampled model CO2 and O2 estimates are well bounded and provide high confidence for a "double-hump" in CO2 during the Phanerozoic, with high values during the early Paleozoic and Mesozoic, and low values during the late Paleozoic and late Mesozoic-to-Cenozoic. Our analyses also support a distinct atmospheric O2 peak during the late Paleozoic (>30%) followed by low values near the Triassic-Jurassic boundary (∼10%). Most of the spread in CO2 is contributed by three factors: climate sensitivity to CO2-doubling and the plant-assisted chemical weathering factors LIFE and GYM. CO2 estimates during the Paleozoic to early Mesozoic are highly concordant with independent records from proxies, but are offset to lower values during the globally warm late Mesozoic to early Cenozoic. The model-proxy mismatch for the late Mesozoic can be eliminated with a change in GYM within its plausible range, but no change within plausible ranges can resolve the early Cenozoic mismatch. Either the true value for one or more input parameters during this interval is outside our sampled range, or the model is missing one or more key processes.
The thermal structure of the solid Earth was estimated from the phase diagrams of MORB and pyrolite combined with seismic discontinuity planes at 410-660 km, thickness of the D″ layers, and distribution of the ultra-low velocity zone (ULVZ). The result clearly shows the presence of two major superplumes and one cold super-downwelling. A temperature difference at the core-mantle boundary layer reaches an average of 1500 K, strongly indicating that the driving force of mantle convection is core heat that generates superplumes as a main engine to drive the mantle dynamics. Superplumes cause the breakup of supercontinents and control plate tectonics, until subduction zones develop at the ocean margins. The major driving force of whole Earth dynamics is derived from a superplume that transports core heat to planetary space. Plume tectonics dominates in the mantle, except for the uppermost part where plate tectonics operates, but only independently if a slab-pull force is generated. Comparison of the thermal structure combined with seismic tomography under the western Pacific, Asia, Africa, and the Pacific leads us to speculate on the mechanism of the formation of a superplume. A mantle made extremely cold by extensive subduction during the formation of a supercontinent is transformed into the hottest mantle triggered by the exothermic reaction of perovskite to post-perovskite (pPV) underneath the supercontinent over several 100 million years. The fuel to develop a superplume is recycled MORB at the CMB that partially melts to sink down to form an anti-crust and a buoyant andesitic restite to promote a rising plume. When all recycled MORB slabs are spent, it is the time of the demise of a superplume. We propose here that mantle dynamics evolved from double-layer convection in the Archean to episodic whole mantle convection thereafter. This change was due to the widespread occurrence of majorite (Mj) instead of ringwoodite in the MBL in the Archean and vice versa thereafter. During the transition period mantle overturn occurred at 2.8-2.7 Ga, and probably at 2.3 Ga, when pPV was born at the CMB to initiate a new superplume-supercontinent cycle that lasted until now. The return-flow by the subduction of seawater into the mantle began at 0.75 Ga causing the sea-level to drop. Through the extensive surface erosion of the continental landmass, the surface environment of the Earth drastically changed making it possible that the large multi-cellular animals appeared to evolve in the Phanerozoic.
Explosive eruptions from volcanoes are recorded in the stratigraphic record throughout the Phanerozoic, but evidence of these eruptions in the form of preserved tephra layers appears to be concentrated at times of active plate collision and concomitant high stands of sea level. The products of volcanic eruptions are lavas, tephra, and gases. Basaltic magmas (low-silica content) are usually erupted in the form of lava flows, whereas rhyolitic magmas (high-silica content) are commonly explosively erupted as plinian and ultraplinian plumes, and associated pyroclastic flows. Fallout tephras are preserved in ancient sedimentary sequences as tonsteins, bentonites, and K-bentonites. Middle Ordovician K-bentonites represent some of the largest known fallout ash deposits in the Phanerozoic Era. They cover minimally 2.2 × 106 km2 in eastern North America and 6.9 × 10 5 km2 in central and northwestern Europe as a result of explosive volcanism, which affected both Laurentia and Baltica during the closure of the Iapetus Ocean. The three most widespread beds are the Deicke and Millbrig K-bentonites in North America and the Kinnekulle K-bentonite in northwestern Europe. Similar successions are well known in South America and China. Sedimentation rates of volcanic ejecta range from meters per year locally to ∼1 mm/1000 yr in the deep sea. Volcanogenic sediments react with seawater to produce secondary phases such as zeolites and clay minerals. Studies of recent ashfall behavior suggest that the preservation potential in the stratigraphic record can be viewed as somewhat remarkable in that such sudden events are preserved at all, much less produce such a wealth of valuable geologic information.
Time series of global diversity and extinction intensity measured from data on stratigraphic ranges of marine animal genera show the impact of bio-events on the fauna of the world ocean. Measured extinction intensities vary greatly, from major mass extinctions that eradicated 39 to 82% of generic diversity to smaller events that had substantially less impact on the global fauna. Many of the smaller extinction events are clearly visible only after a series of filters are applied to the data. Still, most of these extinction events are also visible in a smaller set of data on marine families. Although many of the episodes of extinction seen in the global data are well known from detailed biostratigraphic investigations, some are unstudied and require focused attention for confirmation or refutation.
ABSTRACT—A large and abundant columnar stromatoporoid, Quasiaulacera n. gen., from the Ellis Bay Formation, up to 3 m long and 40 cm in diameter, marks the Hirnantian (latest Ordovician) of Anticosti Island. Two species are present: Quasiaulacera stellata n. sp. from the basal Ellis Bay Formation (basal Prinsta Member, lower Hirnantian) along the northeastern coast of the island, and the type species Q. occidua n. sp. from the upper Ellis Bay Formation (Lousy Cove Member, upper Hirnantian) in the western carbonate facies of the island. Quasiaulacera is rare or absent in the reefal Laframboise Member (uppermost Hirnantian) of the formation. The new genus differs from Aulacera in the underlying Vaureal Formation (upper Katian) in having a large central axial zone marked by a single stack of large, convex-up cystplates, that is surrounded by a middle layer of small, concentric microcyst-plates, in places denticulate, and an outer layer composed of concentric laminae with dense pillars, in which microcyst-plates are either absent or rare. The outer two layers are defined by longitudinal fluting; there are no branching forms. Both species demonstrate a ball-like holdfast system, some with diameters of 30 to 70 cm, microbially cemented into the substrate. Quasiaulacera ‘‘gigantism’’ in the paleotropical Anticosti Basin evolved at a time of global cooling associated with the Hirnantian glaciation in south polar Gondwana, but terminated in mass extinction of the aulaceratids at the O/S boundary in Laurentia. This supports other evidence that the Hirnantian featured not only generic loss, but also innovation and migration in tropical latitudes.
The age of the Emeishan lavas in SW China remains poorly constrained because the extrusive rocks are (1) thermally overprinted and so represent an open system unsuitable for 40Ar/39Ar geochronology, and (2) in most cases devoid of zircon so that it is impossible for the application of U-Pb geochronology. Existing radiometric age constraints of Emeishan large igneous province are mainly from the application of SIMS and LA-ICP-MS U-Pb techniques to zircons from mafic and felsic intrusions, which represent indirect constraints for the lavas. In an attempt to directly determine the age of the Emeishan lava succession, high-resolution chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) zircon U-Pb techniques have been used on the felsic ignimbrite at the uppermost part of the Emeishan lava succession. These techniques have yielded a weighted mean 206Pb/238U age of 259.1 ± 0.5 Ma (n = 6; MSWD = 0.7). We interpret this age as the termination age of the Emeishan flood basalts. The age of the Guadalupian-Lopingian boundary is still unconstrained by high-resolution geochronology but is likely to be close to our new age for this felsic ignimbrite.
The only published δ13C data from the Ordovician of China are from the Lower and Upper Ordovician, and only the latter records include a significant excursion, namely the Hirnantian excursion (HICE). Our recent chemostratigraphic work on the Upper Ordovician (Sandbian–Katian) Pagoda and Yanwashan formations at several localities on the Yangtze Platform and Chiangnan (Jiangnan) slope belt has resulted in the recognition of a positive δ13C excursion that has values of ~+1.5‰ above baseline values. This excursion starts a few metres above a stratigraphic interval with B. alobatus Subzone conodonts as well as graptolites of the N. gracilis Zone. The distinctive conodonts Amorphognathus aff. Am. ventilatus and Hamarodus europaeus first occur at, or very near, the excursion interval. Because these conodonts appear in the stratigraphic interval of the Guttenberg δ13C excursion (GICE) in Estonia, we identify the Chinese excursion as the GICE. This is the first record of the GICE in the entire Asian continent. It confirms that GICE is a global excursion and provides an illustration of how δ13C chemostratigraphy, combined with new biostratigraphic data, solves the problem of the previously controversial age of the Pagoda Formation and how this classical stratigraphic unit correlates with the Baltoscandian and North American successions.
Near the end of the Late Ordovician, in the first of five mass
extinctions in the Phanerozoic, about 85% of marine species died. The
cause was a brief glacial interval that produced two pulses of
extinction. The first pulse was at the beginning of the glaciation, when
sea-level decline drained epicontinental seaways, produced a harsh
climate in low and mid-latitudes, and initiated active, deep-oceanic
currents that aerated the deep oceans and brought nutrients and possibly
toxic material up from oceanic depths. Following that initial pulse of
extinction, surviving faunas adapted to the new ecologic setting. The
glaciation ended suddenly, and as sea level rose, the climate moderated,
and oceanic circulation stagnated, another pulse of extinction occurred.
The second extinction marked the end of a long interval of ecologic
stasis (an Ecologic-Evolutionary Unit). Recovery from the event took
several million years, but the resulting fauna had ecologic patterns
similar to the fauna that had become extinct. Other extinction events
that eliminated similar or even smaller percentages of species had
greater long-term ecologic effects.
The Capitanian minimum in the Permian represents one of the most significant features in the Phanerozoic seawater 87Sr/86Sr history. In order to establish the detailed Sr chemostratigraphy around the Guadalupian minimum, 87Sr/86Sr ratios were measured for the Capitanian (upper Middle Permian) paleo-atoll limestones at Akasaka in Japan. The limestone was primarily deposited on a paleo-seamount in the low-latitude mid-Panthalassa, and was secondarily accreted to Japan (South China block) margin in the Jurassic. As being free from local continental influences, the Akasaka limestone recorded well-mixed seawater isotope composition of the Permian low-latitude mid-superocean. We detected extremely low 87Sr/86Sr ratios (ca. 0.7068–0.7069) in the 70 m-thick Capitanian interval, immediately below the Guadalupian–Lopingian (Middle-Late Permian) boundary (G–LB), of the Akasaka limestone. This Sr isotopic profile at Akasaka suggests that the global seawater was least affected by radiogenic continental flux throughout the Capitanian. As these values correspond to the lowest in the Paleozoic, this interval with low 87Sr/86Sr ratios, lasted for at least some milllion years, represents the Capitanian minimum, which marks the significant turning point from the Late Paleozoic decrease to Early Mesozoic increase in seawater 87Sr/86Sr ratio. The geological lines of evidence indicate that the Capitanian minimum was caused likely by the mid-Permian cooling that may have driven extensive ice-cover over continental crusts to suppress continental flux enriched in radiogenic Sr into the superocean. The rapid increase in 87Sr/86Sr values after the minimum can be explained either by the deglaciation or by the Pangean rifting.
The end Ordovician (Hirnantian) extinction was the first of the five big Phanerozoic extinction events, and the first that involved metazoan-based communities. It comprised two discrete pulses, both linked in different ways to an intense but short-lived glaciation at the South Pole. The first, occurring at, or just below, the Normalograptus extraordinarius graptolite Biozone, mainly affected nektonic and planktonic species together with those living on the shallow shelf and in deeper water whereas the second, within the N. persculptus graptolite Biozone, was less focused, eradicating faunas across a range of water depths. In all about 85% of marine species were removed. Proposed kill mechanisms for the first phase have included glacially-induced cooling, falling sea level and chemical recycling in the oceans, but a general consensus is lacking. The second phase is more clearly linked to near-global anoxia associated with a marked transgression during the Late Hirnantian. Most recently, however, new drivers for the extinctions have been proposed, including widespread euxinia together with habitat destruction caused by plate tectonic movements, suggesting that the end Ordovician mass extinctions were a product of the coincidence of a number of contributing factors. Moreover, when the deteriorating climate intensified, causing widespread glaciation, a tipping point was reached resulting in catastrophe.