Sections In South China Research Articles

Revised Chronostratigraphic Framework of the Metamorphic Strata in the Jiangnan Orogenic Belt, South China and its Tectonic Implications

Abstract:In a re‐study of regional geology by the China Geological Survey (CGS), the key problem is in the stratigraphical division and correlation. According to the new isotopic dating of the Meso‐ and Neoproterozoic in China, there have been great changes in the strata correlation and tectonic explanation. The authors obtained four zircon sensitive high resolution ion micro‐probe (SHRIMP) U‐Pb datings from the bentonite of the Lengjiaxi Group (822±10 Ma, 823±12 Ma and 834±11 Ma) and Banxi Group (802.6±7.6 Ma) in north Hunan Province, which is considered to be the middle part of the Jiangnan Orogenic Belt. On the basis of the zircon dating mentioned above, the end of the Wuling orogen is first limited in the period from 822 Ma to 802 Ma in one continued outcrop (Lucheng section) in Linxiang city, Hunan Province. Combining a series of new zircon U‐Pb datings in the Yangtze and Cathaysia blocks, several Neoproterozoic volcanic events and distribution of the metamorphic rocks in the Jiangnan Orogenic Belt have been distinguished. In the context of the global geodynamics, it is useful to set up a practical and high precision chronological framework and basic and unified late Precambrian section in South China.

Plankton and productivity during the Permian–Triassic boundary crisis: An analysis of organic carbon fluxes

Changes in marine primary productivity following the latest Permian mass extinction (LPME) have been debated at length, with little resolution to date owing to a paucity of quantitative data. Herein, we report total organic carbon (TOC) concentrations and organic carbon accumulation rates (OCAR) for 40 Permian–Triassic boundary (PTB) sections with a near-global distribution and consider their implications for changes in marine productivity during the boundary crisis. Many sections in South China exhibit abrupt declines in TOC and OCAR from the Changhsingian (latest Permian) to the Griesbachian (earliest Triassic), a pattern not observed for sections in other regions. This pattern cannot be explained through secular changes in sedimentation rates, sedimentary facies, or redox conditions, all of which would have favored higher (rather than lower) TOCs and OCARs during the Griesbachian. Further, back-calculation of OC fluxes demonstrate that this pattern cannot be attributed to diagenetic loss of OC in the sediment or, possibly, to OC remineralization in the water column. The most likely explanation is a collapse of marine primary productivity across the South China region concurrently with the LPME and continuing for an extended interval into the Early Triassic. The productivity crash as well as the coeval decimation of benthic marine fauna coincided with deposition of the “boundary clay” at Meishan D, suggesting that both events were related to a large explosive volcanic eruption of uncertain provenance. In other PTB sections having a wide geographic distribution, OCARs increased on average by a factor of ~4× across the LPME, largely owing to a concurrent increase in bulk accumulation rates (BARs). Radiometric dating uncertainties can account at most for only a fraction of the secular change in BARs, which are likely to reflect an increase in subaerial weathering rates and elevated fluxes of detrital material to Early Triassic marine systems. Intensification of chemical weathering relative to physical weathering may have increased the flux of nutrients to the Early Triassic ocean, enhancing marine productivity and contributing to the widespread development of marine dysoxia–anoxia.

Implications of Kungurian (Early Permian) conodonts from Hatahoko, Japan, for correlation between the Tethyan and international timescales

The correlation between the fusulinid-based Tethyan and the conodont-based international timescales of the Permian System has become one of themost disputed issues among the Permian community during the past two decades. In this paper, we document a conodont fauna consisting of four species including Sweetognathus guizhouensis, Pseudohindeodus augustus, Hindeodus permicus and a new genus Meiognathus pustulus from the lower part of a large exotic limestone block at Hatahoko in the Nyukawa area, Gifu Prefecture, central Japan, which all suggest aKungurian age. The Kungurian age indicated by the conodonts is consistent with the age of the associated brachiopods, but conflicts with the Murgabian age indicated by the associated fusulinids including Cancellina nipponica, Neoschwagerina simplex, Neofusulinella praecursor etc. This co-occurrence of Kungurian conodonts and Murgabian fusulinids in central Japan suggests that previously unrecognized temporal distributions of some key fusulinid or conodont elements need to be clarified and that the intensively-disputed correlation problem between the Kungurian containing theMurgabian fusulinids at the Luodian section in Guizhou, South China with the strata containing the ammonoid Waagenoceras in Oman and Sicily was caused by artificial conodont taxonomic discrepancies. The Luodian section in South China could serve as a key reference section for the correlation of the Kungurian Stage (late Early Permian) between the Tethyan and international timescales.

The Henson Gletscher Formation, North Greenland, and its bearing on the global Cambrian Series 2–Series 3 boundary

The Henson Gletscher Formation of North Greenland yields moderately diverse trilobite faunas which bracket the Cambrian Series 2-Series 3 boundary interval. A number of the trilobite taxa permit correlation into other parts of Laurentia and to other Cambrian continents, thus enhancing correlation within this stratigraphical interval of the traditional Lower-Middle Cambrian boundary. In particular, the occurrence of Ovatoryctocara granulata and O. yaxiensis substantially improves the intercontinental recognition of the O. granulata level, a prime GSSP candidate. In contrast, the level with Oryctocephalus indicus cannot be located in a number of Cambrian continents with sufficient precision, making this level unsuitable for the definition of a GSSP for the base of the Cambrian Series 3 and Stage 5. Further support for the correlation potential of the base of the range of Ovatoryctocara granulata comes from recent carbon isotope studies that indicate a striking negative excursion in sections of South China (ROECE event) that probably coincides with similar excursions in Laurentia. Four new trilobite species are described: Zacanthopsis blakeri sp. nov., Protoryctocephalus arcticus sp. nov., Eoptychoparia pearylandica sp. nov. and Onchocephalus? freucheni sp. nov.

Recovery tempo and pattern of marine ecosystems after the end-Permian mass extinction

Research Article| August 01, 2011 Recovery tempo and pattern of marine ecosystems after the end-Permian mass extinction Haijun Song; Haijun Song 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China2School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Paul B. Wignall; Paul B. Wignall * 2School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK *E-mails: p.wignall@see.leeds.ac.uk; jntong@cug.edu.cn. Search for other works by this author on: GSW Google Scholar Zhong-Qiang Chen; Zhong-Qiang Chen 3School of Earth and Geographical Sciences, University of Western Australia, Perth, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Jinnan Tong; Jinnan Tong * 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China *E-mails: p.wignall@see.leeds.ac.uk; jntong@cug.edu.cn. Search for other works by this author on: GSW Google Scholar David P.G. Bond; David P.G. Bond 2School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Xulong Lai; Xulong Lai 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Xiaoming Zhao; Xiaoming Zhao 4Wuhan Institute of Geology and Mineral Resources, Wuhan 430205, China Search for other works by this author on: GSW Google Scholar Haishui Jiang; Haishui Jiang 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Chunbo Yan; Chunbo Yan 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Zhijun Niu; Zhijun Niu 4Wuhan Institute of Geology and Mineral Resources, Wuhan 430205, China Search for other works by this author on: GSW Google Scholar Jing Chen; Jing Chen 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Hao Yang; Hao Yang 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Yongbiao Wang Yongbiao Wang 1State Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China Search for other works by this author on: GSW Google Scholar Geology (2011) 39 (8): 739–742. https://doi.org/10.1130/G32191.1 Article history received: 18 Feb 2011 accepted: 14 Mar 2011 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Haijun Song, Paul B. Wignall, Zhong-Qiang Chen, Jinnan Tong, David P.G. Bond, Xulong Lai, Xiaoming Zhao, Haishui Jiang, Chunbo Yan, Zhijun Niu, Jing Chen, Hao Yang, Yongbiao Wang; Recovery tempo and pattern of marine ecosystems after the end-Permian mass extinction. Geology 2011;; 39 (8): 739–742. doi: https://doi.org/10.1130/G32191.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract High-resolution sampling of more than 10,000 microfossils from seven Late Permian−Middle Triassic paleoequatorial sections in south China refutes claims for a 5 m.y. recovery delay after the end-Permian mass extinction. We show that level-bottom seafloor diversity began to recover in the early Smithian, little more than 1 m.y. after the mass extinction, while recovery of reef-building metazoans began 4 m.y. later, in the Anisian. A further mass extinction in the late Smithian, identified in the pelagic fossil record, is weakly manifest as a temporary pause in diversification among benthic communities. In the Early Triassic of south China, the offshore diversity increase began before then, in shallower settings. The recovery from the end-Permian mass extinction in south China was therefore significantly more rapid and environmentally more complex than hitherto known. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Stable carbon isotope stratigraphy in the Ordovician of South China

About 500 samples from 11 Ordovician sections in South China have been analysed for their δ 13C carb composition. Four sections are located in the Yangtze platform region, the remaining seven sections in the Jiangnan slope region. The sections span more or less the entire Ordovician, but the sample resolution in its lower part (Tremadocian to Dapingian) is lower than in its upper part (Darriwilian to Hirnantian). Overall, the data show a good correlation with the published global isotope curve. At the Cambrian–Ordovician boundary positive values are observed. In the succeeding Tremadocian the values decrease and remain negative into the early Floian. In the late Floian, the values increase to slightly positive. The correlation of Dapingian rocks between the Yangtze and the Jiangnan regions is somewhat problematic which might be due to high siliciclastic input in the Yangtze section. In the Darriwilian a small positive excursion is observed in the Yangtze platform area, however, it is missing in the Jiangnan slope area. This excursion probably correlates with the mid-Darriwilian excursion (MDICE) reported from Baltoscandia. Both chemostratigraphy and conodont biostratigraphy indicate a possible gap between the Shihtzupu Formation and the Pagoda Formation, i.e. most of the Sandbian is probably not represented in the Upper Yangtze region. The earliest Katian is characterised by a pronounced positive excursion correlating with the well-known global Guttenberg excursion (GICE). In the late Katian at least one additional positive excursion was determined. The precise biostratigraphy, however, is not clear, and therefore it is not known which of the known four to five remaining Katian δ 13C excursions identified in Baltica correlate(s) with the one(s) observed in the present study, and further biostratigraphic study is required. The lower part of the Hirnantian excursion (HICE) is probably not preserved, with only small remnants of the HICE observed near the base of the Kuanyinchiao Bed.

Geochemical Stratigraphy and Microvertebrate Assemblage Sequences across the Silurian/Devonian Transition in South China

Abstract:Carbon isotope (δ13Corg) analyses of non‐marine clastic rocks and neritic carbonates and black shales spanning the Silurian/Devonian transition are compared from two richly fossiliferous sequences in Qujing of East Yunnan and Zoige of Sichuan, South China. The two sections, Xishancun and Putonggou sections in South China, reveal positive δ13Corg shifts happening in the Upper Pridoli and Lower Devonian and reaching peak values as heavy as –25.2%‰ (Xishancun) and –19.9%‰ (Putonggou) in the lowermost Lochkovian following the first occurrence of the thelodont Parathelodus and the conodont Icriodus woschmidti woschmidti (only in Putonggou Section and together with Protathyris‐Lanceomyonia brachiopod fauna). These results replicate a globally known positive shift in δ13Corg from the uppermost Silurian to the lowermost Devonian. The δ13Corg variations across the Silurian/Devonian Boundary (SDB) at the two sections in South China exhibit a shift in carbon isotopic composition similar to the detailed SDB curves from the borehole Klonk‐1 drilled at top of the Klonk Global Standard Stratotype‐Section and Point (GSSP) in the Prague Basin, Czech Republic. In addition, four microvertebrate assemblages, including the Liaojiaoshan, Xishancun, Yanglugou and Xiaputonggou assemblages, are recognized from the Silurian/Devonian transition exposed in the Xishancun and Putonggou sections, respectively. The results from both carbon isotope stratigraphy and microvertebrate assemblage sequences suggest that the SDB in South China is located at the base of the Xishancun Formation (between sample QX‐20 and sample QX‐21) in the Xishancun Section and the lower part of the Xiaputonggou Formation (between sample ZP‐09 and sample ZP‐10) in the Putonggou Section. The isotopic trend for organic carbon together with the changes of microvertebrate remains across the SDB can offer an approach to a potential correlation of the SDB from different sedimentary facies, which help to correlate the marine with non‐marine deposits.

17O-depleted barite from two Marinoan cap dolostone sections, South China

Distinct, non-mass-dependent 17O depletion was reported in barite from Marinoan cap dolostones (~ 635 Ma) in South China, and has been interpreted as an indication of an extremely high- pCO 2 atmosphere (Bao et al., 2008). There is a significant variation in the magnitude of the 17O anomaly even among samples from the same outcrops. Understanding the origins of this barite and particularly the source of sulfate is critical to interpreting the anomalous 17O signature and its implication on sulfur and oxygen cycles at the aftermath of Marinoan glacial meltdown. In this study, we analyzed 160 micro-sampled barite samples from 20 hand specimens collected from two cap dolostone sections in South China. Together with field, petrographic, and Sr isotope data, the expanded dataset 1) confirms the large variability in ∆ 17O (from − 0.09‰ to − 0.87‰, VSMOW), δ 18O (+ 13.3‰ to + 23.5‰, VSMOW), and δ 34S (+ 20.0‰ to + 45.5‰, VCDT) of barite; 2) demonstrates a hyperbolic relationship between the ∆ 17O and δ 34S of various barite samples with more negative Δ 17O values generally corresponding to lower δ 34S values; 3) reveals that individual barite crystal fans and fans of the same layer possess a well-clustered set of δ 18O, Δ 17O, and δ 34S values; and 4) shows, correspondingly, that barite crystal fans of different layers bear different sets of Δ 17O, δ 18O, and δ 34S values. The study suggests that 17O-depleted barite crystals were formed under supersaturation when Ba 2+ from sulfate-free deepwater came to mix with sulfate-bearing shallow water. There were multiple upwelling episodes which resulted in multiple barite layers. The large variability in sulfur and triple-oxygen isotope composition and the high 87Sr/ 86Sr ratios indicate that the two sites from South China were sufficiently close to the continent so that the isotopic composition of sulfate was easily influenced by changes in riverine flux when seawater sulfate concentration at that time was exceedingly low. Our depositional model for the barite is consistent with the proposed sequence of events after the meltdown of Marinoan glaciation in South China by Zhou et al. (2010), and is also consistent with the proposed atmospheric origin of sulfate 17O depletion by Bao et al. (2008).

Multiple S-isotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction

Global fossil data show that profound biodiversity loss preceded the final catastrophe that killed nearly 90% marine species on a global scale at the end of the Permian. Many hypotheses have been proposed to explain this extinction and yet still remain greatly debated. Here, we report analyses of all four sulphur isotopes (32S, 33S, 34S and 36S) for pyrites in sedimentary rocks from the Meishan section in South China. We observe a sulphur isotope signal (negative δ34S with negative Δ33S) that may have resulted from limitation of sulphate supply, which may be linked to a near shutdown of bioturbation during shoaling of anoxic water. These results indicate that episodic shoaling of anoxic water may have contributed to the profound biodiversity crisis before the final catastrophe. Our data suggest a prolonged deterioration of oceanic environments during the Late Permian mass extinction.

δ 13C evidence that high primary productivity delayed recovery from end-Permian mass extinction

Euxinia was widespread during and after the end-Permian mass extinction and is commonly cited as an explanation for delayed biotic recovery during Early Triassic time. This anoxic, sulfidic episode has been ascribed to both low- and high-productivity states in the marine water column, leaving the causes of euxinia and the mechanisms underlying delayed recovery poorly understood. Here we use isotopic analysis to examine the changing chemical structure of the water column through the recovery interval and thereby better constrain paleoproductivity. The δ 13C of limestones from 5 stratigraphic sections in south China displays a negative gradient of approximately 4‰ from shallow-to-deep water facies within the Lower Triassic. This intense gradient declines within Spathian and lowermost Middle Triassic strata, coincident with accelerated biotic recovery and carbon cycle stabilization. Model simulations show that high nutrient levels and a vigorous biological pump are required to sustain such a large gradient in δ 13C, indicating that Early Triassic ocean anoxia and delayed recovery of benthic animal ecosystems resulted from too much productivity rather than too little.

Biodiversity patterns of Early–Middle Ordovician marine microphytoplankton in South China

Based on new materials from six sections and all available literature data, new diversity curves are presented for the phytoplankton (acritarchs) from South China, covering the Early–Middle Ordovician interval, when the Great Ordovician Biodiversification Event took place. The total diversity curve and the origination data imply that a major radiation of the phytoplankton occurred during the analysed interval. A peak of the total acritarch diversity curve appears in the A. suecicus graptolite biozone. The diversity changes vary in the different parts of the investigated area, most probably depending on the position of the analysed sections on the carbonate shelf or the slope, reflecting diversity differences due to the position on an inshore–offshore transect.The Early–Middle Ordovician diversity pattern of the phytoplankton is compared with those of several marine invertebrate groups. Compared with the diversity curve peak of the acritarchs, the conodonts and brachiopods reached their highest diversities before the acritarchs, while the highest diversity of the chitinozoans appears slightly later. The graptolites show two peaks during the Early–Middle Ordovician, while the trilobites diversity curve shows a peak only in the Sandbian. The different fossil groups, such as chitinozoans, conodonts, graptolites, brachiopods and trilobites show therefore different evolutionary patterns to that of the acritarchs, that are not yet fully understood, and correlations are so far difficult.The acritarch diversity changes can partly be compared to the local sea-level changes from four sections in South China. At a larger scale, the acritarch radiation coincides with a general transgression. At a regional or local scale, correlations are not straightforward, pointing out that more detailed data, based on both acritarch studies and more precise sea-level investigations, are necessary.

Evolutionary dynamics of the Permian–Triassic foraminifer size: Evidence for Lilliput effect in the end-Permian mass extinction and its aftermath

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.

Isotopic evidence for an anomalously low oceanic sulfate concentration following end-Permian mass extinction

The cataclysmic end-Permian mass extinction was immediately followed by a global expansion of microbial ecosystems, as demonstrated by widespread microbialite sequences (disaster facies) in shallow water settings. Here we present high-resolution carbonate carbon ( δ 13C carb) and carbonate-associated sulfate–sulfur isotope ( δ 34S CAS) records from the microbialite in the Cili Permian–Triassic (P–Tr) section in South China. A stepwise decline in δ 13C carb begins in the underlying skeletal limestone, predating the main oceanic mass extinction and the first appearance of microbialite, and reaches its nadir in the upper part of the microbialite layer. The corresponding δ 34S CAS, in the range of 17.4‰ to 27.4‰, is relatively stable in the underlying skeletal limestone, and increases gradually from 2 m below the microbialite rising to a peak at the base of the microbialite. Two episodes of positive and negative shifts occurred within the microbialite layer, and exhibit a remarkable co-variance of sulfur and carbon isotope composition. The large amplitude of the variation in δ 34S CAS, as high as 7‰ per 100 kiloyears, suggests a small oceanic sulfate reservoir size at this time. Furthermore, the δ 13C carb and δ 34S CAS records co-vary without phase lag throughout the microbialite interval, implying a marine-driven C cycle in an anoxic ocean with anomalously low oceanic sulfate concentrations. On the basis of a non-steady-state box model, we argue that the oceanic sulfate concentration may have fallen to less than 15%, perhaps as low as 3%, of that in the modern oceans. Low oceanic sulfate concentration likely was the consequence of evaporite deposition and widespread anoxic/sulfidic conditions prior to the main mass extinction. By promoting methanogenesis and a build-up of atmospheric CH 4 and CO 2, low oceanic sulfate may have intensified global warming, exacerbating the inimical environmental conditions of the latest Permian.

Calibrating Mid-Permian to Early Triassic Khuff sequences with orbital clocks

ABSTRACTThe Middle East Geologic Time Scale (ME GTS) seeks to document and age-calibrate Arabian Plate transgressive-regressive (T-R) depositional sequences using: (1) Geological Time Scale of the International Commission on Stratigraphy (GTS), and (2) Arabian Orbital Stratigraphy time scale (AROS). AROS is based on an orbital-forcing glacio-eustatic model that offers three orbital clocks to date T-R sequences: (1) Stratons @ ca. 405 Ky; (2) Dozons @ ca. 4.86 My (12 stratons); and Orbitons @ ca. 14.58 My (36 stratons, three dozons). The Earth today is in Orbiton 0, which started ca. 1.5 Ma (SB 0); the ages of lower boundaries of orbitons can be estimated with the formula SB n = n × 14.58 + 1.5 Ma. This scheme was used to calibrate the Arabian Plate’s Mid-Permian to Early Triassic Khuff sequences, which contain one of the largest gas-bearing carbonate reservoirs in the World.The Khuff and equivalent formations have been interpreted by several authors in terms of six long-period sequences in outcrop belts and subsurface sections (Khuff sequences KS6 to KS1 in ascending order). Their type sections are briefly reviewed with emphasis on their boundaries, higher-order architecture and stage assignments. The age calibration starts at the basal Khuff Sequence Boundary (Khuff SB, Sub-Khuff Unconformity) defined in a type section in Al Huqf outcrop in Oman. Above the Khuff SB (ca. 268.9 Ma) the type sections of the oldest Khuff sequences KS6 (ca. 268.9–264.0 Ma) and KS5 (ca. 264.0–259.1 Ma) are defined in Oman and interpreted to each consist of twelve subsequences (stratons) with the predicted architecture of two consecutive dozons. By biostratigraphy they span the Mid-Permian (Guadalupian Epoch), Wordian and Capitanian stages.Type-Sequence KS4 (ca. 259.1–254.2 Ma) is defined in Iran and corresponds to the Wuchiapingian Stage. The Iranian type-Khuff Sequence KS3 (ca. 254.2–249.4 Ma) contains nine subsequences (stratons) grouped between two major exposure surfaces. By correlation to the Changhsingian Stage and Permian/Triassic Boundary (PTrB) type section in South China, it is interpreted as a dozon with three missing stratons. Khuff Sequence KS2 (ca. 249.4–247.8 Ma) contains the PTrB with an orbital age of ca. 249.0 Ma, compared to 251.0 ± 0.4 in GTS and 249.0–253.0 Ma by radiometric dating in its type section. Khuff sequences KS2 and KS1 contain 13 subsequences (stratons) between ca. 249.4–244.1 Ma spanning latest Permian and Early Triassic. The boundary of the Khuff with the overlying Sudair Formation, Sudair Sequence Boundary, is defined in Borehole SHD-1 (Central Saudi Arabia) and calibrated at ca. 244.1 Ma falling near the age of the Early/Mid-Triassic Boundary in GTS. The enclosed Chart shows a work-in-progress correlation of the six Khuff sequences across the Arabian Plate.

Conodonts and radiolarians through the Cisuralian–Guadalupian boundary from the Pingxiang and Dachongling sections, Guangxi region, South China

Serrated gondolellid conodonts (Jinogondolella) are used to define the Cisuralian–Guadalupian (C–G) or Kungurian–Roadian (K–R) boundary in the stratotype sections of West Texas and in some sections of South China, but in other sections Jinogondolella is absent. This absence has been interpreted to be the result of strong provincialism during this interval and geographic clines have been demonstrated between an Equatorial Warm Water Province (EWWP) and a North Cool Water Province (NCWP). Results from a succession of deep-water limestones in the Pingxiang section, southwestern Guangxi, China, suggest that the distribution of warm-water and cool-water lineages may not in all cases be separated over large geographic scales, but may be segregated in some areas by local changes of water-mass temperature or depth and, in some cases, fossil assemblages from these lineages may be mixed. Two contemporaneous gondolellid evolutionary lineages are represented within warm-water and cool-water conodont assemblages from limestones spanning the Cisuralian–Guadalupian (C–G) boundary in the Pingxiang section, southwestern Guangxi, China. The warm-water conodont lineage begins with the first occurrence (FO) of Mesogondolella saraciniensis, followed by Mesogondolella siciliensis, then M. idahoensis lamberti and finally Mesogondolella pingxiangensis sp. nov. The latter new species lacks serration, but has a platform outline and lateral profile similar to J. nankingensis nankingensis found elsewhere in South China and they may be closely related. Although less common in the samples, a coeval cool-water lineage begins with M. idahoensis idahoensis and develops successively with the evolution of J. nankingensis gracilis; serration is also lacking in the latter species. The lack of serration on these forms is ascribed to some form of environmental control. The contemporaneous appearance of Mesogondolella pingxiangensis and Jinogondolella nankingensis gracilis is correlated with the C–G boundary. This correlation is supported by the co-occurrence of the zonal indices of the cool-water lineage with important zonal radiolarians in a C–G boundary section at Dachongling, southeastern Guangxi. Here the radiolarian assemblages are assigned to the Albaillella foremanae Zone, Pseudoalbaillella globosa Zone and P. fusiformis Zone in ascending order. The first appearance of J. nankingensis gracilis within this succession defines the base of the Guadalupian to be at the base of the P. globosa Zone. Conodont correlation between carbonate ramps of platform margins and radiolarian-bearing pelagic environments has determined that the first appearance of J. nankingensis gracilis precisely defines the base-Guadalupian boundary in the cool-water settings.

Continuous wavelet analysis on Ce/La and magnetic susceptibility records in Permian-Triassic Dongpan Section in South China

INTRODUCTION The Permian–Triassic (P–T) mass extinction event (251.4±0.3 Ma) was the largest one in the Phanerozoic (Erwin, 1994). Establishing a high-precision chronostratigraphic framework is fundamental for a better understanding of the global climate change across the Permian–Triassic. Owing to the general limitations of chronostratigraphy inferred from radiometric ages and paleontological records, the astronomical time scale (ATS), established by tuning astronomical forcing signals recorded in sedimentary strata, plays critical roles on defining and correlating the P–T mass extinction event (Rampino and Adler, 1998). In the last two decades, refinement of Quaternary to Paleogene chronostratigraphy by astronomical tuning to calculated orbital variations has allowed a more detailed understanding of the relationship between the sedimentary record and orbital cycles

Structural changes of marine communities over the Permian–Triassic transition: Ecologically assessing the end-Permian mass extinction and its aftermath

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 200 ka 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.

Environmental and biotic turnover across the Permian–Triassic boundary on a shallow carbonate platform in western Zhejiang, South China

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 δ13Ccarb 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.

Size variation of conodont elements of the Hindeodus–Isarcicella clade during the Permian–Triassic transition in South China and its implication for mass extinction

Based on the analysis of thousands of conodont specimens from the Permian –Triassic (P–T) transition at Meishan (the GSSP of P–T Boundary) and Shangsi sections in South China, this study investigates the size variation of Hindeodus and Isarcicella P1 elements during the mass extinction interval. The results demonstrate that Hindeodus– Isarcicella underwent 4 episodes of distinct size reduction during the P–T transition at the Meishan Section and 2 episodes of size reduction in the earliest Triassic at Shangsi. The size reductions at Meishan took place at the junctions of beds 24d/24e, 25/26, 27b/27c and 28/29, and at the junctions of beds 28/29c and 30d/31a at Shangsi. The two earliest Triassic size reduction episodes were correlative between the two sections. These changes coincide with some important geological events such as eustatic sea-level changes, anoxic events, carbon isotope oscillations, miniaturization of brachiopods and microbial changes. Through detailed investigation of the palaeoenvironment and the palaeoecology of Hindeodus– Isarcicella, the authors propose that the main causes of the size reduction was a sharp decline of food availability because of the mass extinction and the anoxic event during the P/T transition. The pattern of size reduction supports suggestions that the end-Permian mass extinction was multi-episodal, consisting of 3 extinction events rather than a single catastrophic event.

Further SHRIMP geochronology on the early Cambrian of South China

Zircon 206Pb/238U ages are reported for bentonites from two Cambrian sections in South China, the Meishucun and the Fandian. The analyzed zircons vary widely in age because of the presence of detrital and altered grains. Spot ages were corrected for calibration drift during analysis, and the age of reference zircon SL13 was calibrated as 580 Ma against other standards using SIMS. Use of mixture modeling was essential to resolve the different age components and to identify the volcanic ages. Two age groups occur within the Meishucun Bed 5 bentonite, of which the larger at 518.7 ± 2.5 Ma (σ) is interpreted as a post depositional zircon growth event and the other at 539.4 ± 2.9 Ma as the volcanic age. Bentonites from the Meishucun Bed 9 and its Fandian equivalent have two age groups, 526.5 ± 1.1 Ma and 540.2 ± 1.0 Ma. We interpret the younger of these as the tuff magmatic age and the older as detrital. Small shelly fossils indicate Meischucunian Bed 5 is an equivalent of the late Nemakit Daldynian, and its 539.4 ± 2.9 Ma age both closely times the base of the Cambrian and is a maximum for the basal Tommotian. The 526.5 ± 1.1 Ma for Bed 9 and its equivalents approximates the close of the Tommotian.