The Research Of Ecostratigraphy On Middle Late Jurassic In Easten Qiangtang Basin

Ecostratigraphy is using the way of reconstructing palaeocommunite to analyse stratum,to recover the real feature in geology history.It has important value in stratum partition,stratum correlation and palaeoenvioment recovering etc.Others.it has very important function in researching living being's evolution,extinction,evolvement,development stage and it's controlling factors.Qiangtang basin .locating at northern Tibert and southern Qinghai,is growing the most completest Jurassic marine facies. So, deep studying the Qiangtang basin has the most important value. This article, based on the four sections of Wulanwula Lake aera and Anduo aera at Qiangtang basin, using the way of ecostratigraphy, finds way to ecostratigraphy study.From the lithofacies analysis, these four sections can be separated Quemocuo formation Buqu formation, Xiali formation and Suowa formation at the upper middle Jurassic. Using the fossils, we can seperate into nine communities at these four sections. The nine communities are Corbula community, Corbula-Protocardia community, Donacosmilia coralline community, Chlamys-Protocardia community, Entolium community, Gervillella-Protocardia community, Chlamys-Astarte community, Ceratomya concentrica community and Blanfordiceras-Buchia community. The time of these nine communities is Bathonian age of middle Jurassic and Oxford-Kimmeridgian age of upper Jurassic.Contrasting and analysing these nine communities, we can find that the desalting seawater environment frequently appears at Xuelianhu aera of Wulanwula Lake. And the most possible reason is this aera near the estuary. Others, the Chlamys-Astarte community at Lanlihe section is most likely with the Chlamys-Protocardia community at Maliaoshan section,.So, they must be the same ecostratigraphy cell. Two communities of Anduo aera reflect the progress of detrital beach transiting more deeper water continental shelf of neritic sea.Combining the conception of dermarsal combination,we put the nine communites into BA2,BA3 and BA4 dermarsal combination, then comfirm these nine communites' ecological niche.And using the Blanfordiceras- Buchiacommunite as the example, discussing the progress of communite from birth to death.From contrasting with chronostratigraphy, lithostratigraphy, biostratum and ecostratigraphy, ecostratigraphy can improve stratum partition precision. Especially for paleoenvironment and paleogeography, it has original function.