Taxonomy And Evolution Of Brachiopods From Deep-water Facies In The End Permian In South China

The Permian-Triassic mass extinction is the most significant mass extinction event in the Phanerozoic transitional stages,and it's focus which geologists concern for a long-time. Brachiopod is an important category in the extinction event.Contrasting other regions of the world during the stage,brachiopods have high abundance and diversity in South China.However, brachiopod research focused on shallow-water limestone facies,fewer papers of brachiopod in deep-water were published.Based on the study of deep-water brachiopod taxonomic in Permian-Triassic,we statistic with the deep-water brachiopod diversity changes,to support the brachiopod extinction pattern in the Permian-Triassic mass extinction.Majiashan Section and Rencunping Section have sequential strata from Late Permian to Early Triassic,where ammonite assemblages were established.Based on the precise stratigraphic deivision,the two faunas can correlate with each other and contrast to the Meishan D Section.Through collecting brachiopod fossils from Majiashan Section and Rencunping Section,we obtained more than 2000 brachiopod fossils,including 17 genera,17 species and 13 undetermined species.And we statistic with brachiopod diversity changes from Changhsingian to Induan layer by layer,the statistical results as following:Phase 1:From Layer 19(5 genera and 12 species) to Layer 16(7 genera and 13 species) in Majiashan Section,from Layer 17(3 genera and 3 species) to Layer 20(5 genera and 8 species) in Rencunping Section,brachiopod diversity showed a distinct rise.Phase 2:From Layer 16(7 genera and 13 species) to Layer 12(5 genera and 11 species) in Majiashan Section,from Layer 20(5 genera and 8 species) to Layer 21(4 genera and 4 species) in Rencunping Section,brachiopod diversity showed a distinct decline.There has a fluctuated diversity from Layer 12(5 genera and 11 species) to Layer 8(7 genera and 12 species) in Majiashan Section,but it slightly raise in the trend.Brachiopod diversity shows a apparent rising from Layer 21(4 genera and 4 species) to Layer 23b(7 genera and 8 species) of Rencunping Section.Phase 3:From Layer 8(7 genera and 12 species) to Layer 7(3 genera and 4 species) in Majiashan Section,from Layer 23b(7 genera and 8 species) to Layer 23d(1 genera and 1 species) in Rencunping Section,brachiopod diversity shows the most suddenly decline.From Layer 7(3 genera and 4 species) to Layer 1(1 genera and 1 species),brachiopod diversity show a slight rise in Layer 6,and then show a distinct decline.Brachiopod diversity remains a low level from Layer 23d(1 genera and 1 species) to Layer 25(1 genera and 1 species) of Rencunping Section. Through the stratigraphic correlation by ammonite assemblages and clay layers,the most distinctly decline(or extinction event) of brachiopod diversity occurred just below the clay layer (equivalent to the Layer 25 of Meishan Section),about the Layer equivalent to Layer 24 of Meishan Section,nevertheless,it occurred from Layer 27 to Layer 28 in Meishan Section.The contrastive result supports that the most distinctly decline of brachiopod diversity in deep-water occurred earlier than that in shallow-water.Furthermore,we reconstruction water oxygen content and marine productivity by using the methods of geochemistry and quantitative fossil plants,and then contrast them with brachiopod fauna diversity curves.It point out that the most distinctly decline of Permian-Triassic brachiopod diversity may be mainly affected by the decline of marine productivity.