鄂尔多斯盆地北部奥陶系碳酸盐岩层序地层研究

CARBONATE SEQUENCE STRATIGRAPYH OF ORDOVICIAN IN THE NORTHERN ORDOS BASIN

碳酸盐岩的物源性质、形成背景、沉积机理和扩散方式都与碎屑岩有很大的差异．对于碳酸盐岩层序地层，需要从成因上、从台地的性质与演化、海不的进退、台地的淹没与暴露等方面进行研究．在总结露头层序地层工作方法的基础上，阐述了密集段、首次洪泛面和层序边界的识别标志，建立了高分辨率层序地层格架．鄂尔多斯盆地早奥陶世三道坎组沉积时，为碳酸盐岩－碎屑岩混合缓坡背景；桌子山组及克里摩里组沉积时为镶边陆架与末端陡倾缓坡的背景；乌拉力克组及中奥陶世时，转化为拗拉槽背景．

The formation of carbonates is different from that of siliciclastic sediments.The controlling factors,such as the combination of in situ production of carbonates,the transport,local variation in depositioal processes and the way of dispersal,are unique to carbonates systems,resulting in the formation of a wide variety of stratigraphic patterns.It is believed that the factors influencing the formation of carbonates,including the evolueion of carbonate platform,transgressive and retrogressive,drowning and exposing of the platform shoud be taken into account in the study of carbonates sequence stratigraphy.The studying procedure for outcrops is summarized first,and then the integrated identifications of condensed section,first flooding surface,and maximum flooding surface are describde.Consequently,the framework of high resolution sequence stratigraphy is constructed.During the deposition of Sandokan Formation of Early Ordovician,there was a carbonate siliciclastic ramp and a carbonate rimmed shelf and distally steepened ramp during Zuozishan and Kelimoli periods.A break appeared in Wulalike and Middle Ordovician,when the sedimentary setting changed into aulocogen.According to the evolution of the basin mentioned above,some different idealized depositional sequence and systems tract models have been established.