藏南Kioto碳酸盐台地对早侏罗世普林斯巴晚期碳循环扰动的沉积和生物响应OA北大核心CSTPCD

[Objective]During the Early Jurassic,multiple significant perturbations of the carbon-cycle occurred that coincided with abrupt and extreme changes in climate and environment.However,existing research has primari-ly focused on the western Tethys and northern Europe,with limited attention given to carbon cycle disturbances in the eastern Tethys and the quantitative assessment of their impact on biota.[Methods]This study examined the bio-logical(larger benthic foraminifera),sedimentological,and carbon-isotope(δ13C)stratigraphy from the southern Tibetan Kioto Platform formed in the southeastern Tethys during the Late Pliensbachian-Earliest Toarcian interval to investigate the influence of carbon-cycle perturbations and corresponding climatic and environmental variations on the evolution of carbonate-platform biota in the region.In addition,this study quantitatively analyzed the content of carbonate skeletal grains,the number and species changes of lager benthic foraminifera,and the distribution of Lithiotis Fauna to explore the impact of these events on biota.[Results]Three foraminiferal zones were recognized:Pliensbachian Bosniella oenensis-Cyclorbitosella tibetica(?)and Streptocyclammina liasica,as well as the Earliest Toarcian Siphovalvulina sp.A.According to the sedimentary structure and the quantitative analysis of grains composi-tion and content,this study identified nine carbonate microfacies(MF)from the Pupuga Formation in the Dongqiu section.These microfacies included mudstone(MF1),dolomitic peloidal wackestone(MF2),bioclastic peloidal packstone(MF3),bioclastic wackestone/packstone(MF4),intraclastic packstone-grainstone(MF5),lump grain-stone(MF6),Lithiotis rudstone(MF7),bioclastic grainstone(MF8),and oolitic grainstone(MF9).The sedimentary microfacies and microfacies assemblages reveal that the Pupuga Formation in the Dongqiu section represented the shallow-water carbonate platform deposit,characterized by minimal influence from terrigenous input.Furthermore,temporal variation in microfacies demonstrated that the Dongqiu section provided a comprehensive record of a sedimentary succession,delineating a gradual transition from the open platform and platform margin to the inner plat-form,succeeded by a swift reversion towards the open platform and platform margin.Based on biostratigraphy,two carbon isotope excursion events in the Late Pliensbachian were identified:the margaritatus zone event(ME)characterized by positive carbon isotope excursion and the margaritatus-spinatum zone boundary event(MSBE)with negative carbon isotope excursion as a feature.[Conclusions]During the ME period,there was an increase in skeletal grain content,maintenance of high species diversity and abundance of larger benthic foraminifera,and the occurrence and spread of Lithiotis Fauna.This may indicate that the persistent burial of organic matter consumed atmospheric pCO2 generated during the Late Sinemurian to Early Pliensbachian interval,creating more suitable marine environmental conditions for biotic survival.In contrast,during the MSBE period,there was a decrease in the abundance and size of Lithiotis Fauna and skeletal grain content,along with the extinction of several index larger benthic foraminifera.This evidence indicates a possible relationship between biotic crises and sea-level fall.Although there were changes in the size and frequency of occurrence of the Lithiotis Fauna,it is undeniable that they flourished throughout the Tethyan shallow carbonate platform during the Pliensbachian interval,and the conditions for skeletal production of carbonates were not completely destroyed until the Toarcian oceanic anoxic event.