The greatest Phanerozoic mass extinction happened at the end-Permian to earliest Triassic.About 95%species,82%genera,and more than half families became extinct,constituting the sole macro-mass extinction in geological history.This event not only caused the great extinction but also destroyed the 200 Myr-long Paleozoic marine ecosystem,prompted its transition to Mesozoic ecosystem,and induced coal gap on land as well as reef gap and chert gap in ocean.The biotic crisis during the Paleozoic-Mesozoic transition was a long process of co-evolution between geospheres and biosphere.The event sequence at the Permian-Triassic boundary(PTB)reveals two-episodic pattern of rapidly deteriorating global changes and biotic mass extinction and the intimate relationship between them.The severe global changes coupling multiple geospheres may have affected the Pangea integration on the Earth’s surface spheres,which include:the Pangea integration→enhanced mountain height and basin depth,changes of wind and ocean current systems;enhanced ocean basin depth→the greatest Phanerozoic regression at PTB,disappearance of epeiric seas and subsequent rapid transgression;the Pangea integration→thermal isolation effect of continental lithosphere and decrease of mid-ocean ridges→development of continental volcanism;two-episode volcanism causing LIPs of the Emeishan Basalt and the Siberian Trap(259–251 Ma)→global warming and mass extinction;continental aridification and replacement of monsoon system by latitudinal wind system→destruction of vegetation;enhanced weathering and CH4emission→negative excursion ofδ13C;mantle plume→crust doming→regression;possible relation between the Illawarra magnetic reversal and the PTB extinction,and so on.Mantle plume produced the Late Permian LIPs and mantle convection may have caused the process of the Pangea integration.Subduction,delamination,and accumulation of the earth’s cool lithospheric material at the"D"layer of CMB started mantle plume by heat compensation and disturbed the oute
Detailed mineral magnetic measurements,integrated with grain-size distribution and X-ray diffraction(XRD) analyses,were made on the marine sediments of Core MD98-2172,retrieved from the Eastern Timor Sea.Values of magnetic susceptibility in this core drop sharply down-core from-3.85 m deep below sediment/water interface and are very low at-5.35 m.However,both XRD and grain-size distribution results show no sudden change in terrigenous input during sedimentation.Mineral magnetic results indicate that the depth of-3.85 m may be an oxic/anoxic boundary.Therefore,the sediments below-3.85 m have been subjected to intense reductive diagenesis,whereas the sediments above-3.85 m are seldom affected.The magnetic properties of the sediments shallower than 3.85 m are dominated by pseudo-single domain(PSD) magnetite,with little down-core variation in its content and grain size.Below-3.85 m,the magnetic mineral assemblages that have survived in the sediments may record different stages of the reductive diagenesis:(1) the sediments from the 3.85-5.35 m interval are at the stage of iron oxide reduction;PSD magnetite is the major magnetic contributor,but it becomes less abundant and coarser down-core;(2) the sediments below-5.35 m are at the stage of sulphate reduction;ferrimagnetic minerals almost vanish and paramagnetic minerals contribute to down-core susceptibility variations,including pyrite as evidenced by high-temperature magnetic susceptibility measurements.However,the susceptibility variations below-5.35 m of Core MD98-2172 show obvious periodicity,despite the intense effect of reductive diagenesis.Furthermore,the down-core susceptibility variations are coincident with fluctuations in the quantity of fine detrital particles(<8 μm),which may come mainly from the advection of the Indonesia Throughflow(ITF) and/or river input from Timor.Therefore,for Core MD98-2172,susceptibility variation below-5.35 m,which potentially correspond to fluctuations in the quantity of fine particles,may record the histories of the developmen
In South China, the Wuqiangxi Formation of the Banxi Group and its equivalents underlie the early Cryogenian (Sturtian) glacial deposits but their thickness varies from <200 m to >2000 m. In the Guzhang section of western Hunan, the Wuqiangxi Formation is only 152 m thick, and an ash bed 58 m below the glacial diamictite yielded a SHRIMP U-Pb age of 809.3±8.4 Ma. In contrast, 90 km south of the Guzhang section towards the basin in Zhijiang area where the Wuqiangxi Formation is ~2200 m thick, an age of 725±10 Ma has been reported from the top of this unit, 300 m below the glacial diamictite. These ages provide new evidence for the regional stratigraphic correlation across the Nanhua basin, and suggest unusually large (>2 km) stratigraphic erosion potentially associated with the Sturtian glaciation in South China. The magnitude of erosion may imply significant uplifting and tectonotopography at the onset of the Sturtian glaciation.
Stable isotope analyses in sections across a shelf to basinal transect of the Ediacaran Doushantuo basin show substantial isotope variabilities. In Songlin section where sediments were deposited in an intrashelf basin, δ 13C values are persistently negative (_3‰ to _5‰, VPDB) through the entire Doushantuo Formation, similar to those obtained from the slope section in Wuhe (_5‰ to _10‰, VPDB). Shallow water sections in Weng'an and Duoding show two broad δ 13C anomalies overprinted with significant meter-scale variations, but none of the curves has similar absolute δ 13C values compared to the Yangtze Gorges areas in South China and other sections globally. Such isotope variations, if partially recording ancient seawater signature, imply spatial and temporal chemocline instability in the Doushantuo basin. In combination with available δ 13C records from other Ediacaran successions globally, the data from the Doushantuo basin are consistent, in first order, with the existence and oxidation of a large dissolved organic carbon (DOC) reservoir in Ediacaran oceans, but imply local environmental controls on Neoproterozoic isotope values and call attentions for using δ 13C anomalies as time lines in stratigraphic correlation.
This paper systematically investigated the conodonts from the uppermost Permian to the Lower Triassic at the Dongpan Section, Southern Guangxi, South China, and obtained abundant Late Permian conodonts from the syndepositional limestone lenses of beds 3 and 5-2 at this section. One genus and eight species of conodont P1 element including one new species, Neogondolella dongpanensis sp. nov., have been identified. The feature of conodont fauna indicates that conodonts collected from beds 3 and 5 at the Dongpan Section belong to the Neogondolella yini conodont zone, and correspond to bed 24 at the Meishan Section. Based on these conodont data, we suggest that the Neoalbaillella optima radiolarian zone at the Dongpan Section at least extended to the upper part of the N. yini conodont zone.
GenMing Luo (1) (2) XuLong Lai (1) (2) QingLai Feng (1) (3) HaiShui Jiang (1) (2) Paul Wignall (4) KeXin Zhang (1) (3) YaDong Sun (2) Jun Wu (1) (2)
The Lower Triassic in Chaohu (巢湖) area, Anhui (安徽) Province, China, is well developed and its sequence is typical in South China. After a brief introduction of the Induan-Olenekian boundary of Chaohu, this article presents some new data on conodonts. More than ten times of conodont samplings and investigations have recovered thousands of conodont specimens, which are especially rich in the Induan-Olenekian boundary strata at the West Pingdingshan Section in Chaohu City, Anhui Province. The most distinctive forms are the conodonts of the Neospathodus dieneri group and N. waageni group. The first occurrence of N. waageni eowaageni, which is regarded as the indicator of the Induan-Olenekian boundary, is situated at 40.49 m above the base of Yinkeng (殷坑) Formation. Some key conodonts and seven new specimens are introduced.
