Study Of Permian-Triassic Boundary Brachiopod Fauna In Western Guizhou Province, And Its Regional Correlation In South China

Zhongzhai section, as its unique location in the shallow-water clastic-shelf facies, which provides a well-preserved brachiopod fauna differing from the other faunas in the shallow-water carbonate platform and deep-water siliciclastic facies of South China and serves as a correlation between marine and non-marine Permian-Triassic boundary (PTB) sections in western Guizhou and eastern Yunnan provinces by its conodont biostratigraphy work. Therefore, the two main topics of this thesis include the studies of conodont biostratigraphy and brachiopod fauna in the PTB transitional period.The new Zhongzhai conodont fauna, which comprises five identified species and two undetermined species in Hindeodus and Clarkina, have been restudied in this thesis. Significantly, the first local occurrence of Hindeodus parvus at the Zhongzhai section is 18 cm lower than the accepted PTB which have been confirmed by multiple evidences (e.g., conodont index fossil, carbon isotope, U-Pb age and PTB interval claystone layers).Fifty-six brachiopod species [including ten new species:Tethyochonetes sheni, T. cheni, T. minor, Neochonetes (Huangichonetes) archboldi, N. (Sommeriella) waterhousei, N. (S.) rectangularis, N. (Zhongyingia) transversa, N. semicircularis, Paryphella acutula, Orbiculoidea liaoi; ten undetermined species and three comparative species] have been systematically descripted for the exceptionally well-preserved and diverse Zhongzhai brachiopod fauna of late Changhsingian age.This is the first systematic palaeontological study of a diverse Changhsingian brachiopod fauna representing the shallow-water clastic-shelf facies anywhere in South China. In addition, several morphologic terms (e.g., hinge spines, tubes) have been renewed and some endemic South China Orbiculoidea species have been first descripted in English.With the layer occurrences of each brachiopod species, the extinction horizon has been statistically confirmed between Beds 27 and 28 (or at the base of Bed 28) by using the likelihood ratio test. And the diachronous brachiopod extinction horizons have been proved by comparing brachiopod extinction patterns among the six key PTB sections in South China, which occurred earlier in the deep-water sections (Rencunping, Majiashan and Dongpan sections) and Zhongzhai section than that in the shallow-water carbonate sections (Huangzhishan and Meishan sections).By using the quantitative data (e.g., measurements of shell size, numbers of each species in key layers) of this brachiopod fauna, several results have been found that:1) Tethyochonetes (at Bed 27) have replaced the Neochonetes (at Beds 4,6,12 and 14) as the dominant genus of Zhongzhai brachiopod fauna in the uppermost Permian; 2) pre-extinction dwarfing was proved in the Neochonetes and Tethyochonetes; 3) body-size reduction of Tethyochonetes species occurred earlier than Neochonetes species.4) three new species of Neochonetes and Tethyochonetes did not show any significant change in body size.With the proxy indexes (e.g., acritarch, spore and pollen), the food supply have been reconstructed over the latest Permian at the Zhongzhai section. And the food shortage (in the upper part of the uppermost Permian of this section) could be the possible key factor which causes the earlier occurrence of brachiopod extinction, the dominance shift of Zhongzhai brachiopod fauna from Neochonetes to Tethyochonetes and the significant pre-extinction brachiopods body-size reduction.In addition, with the quantitative palaeoecology analysis of the Zhongzhai brachiopod fauna and the review of previous literatures, three Changhsingian brachiopod assemblages (Neochonetes-Tethyochonetes Assemblage, Spinomarginifera-Peltichia-Oldhamina Assemblage and Tethyochonetes-Paracrurithyris-Paryphella Assemblage) have been respectively proposed for the shallow-water clastic-shelf facies, shallow-water carbon platform facies and deep-water siliciclastic facies in South China.