西藏羌塘盆地半岛湖中生代索瓦组的层状礁： 群落结构和时代

西藏北羌塘盆地索瓦组底界可对比为上侏罗统,关于该组上界能否达到下白垩统还需证实.半岛湖地区3个地点见隆起平缓且以珊瑚和层孔虫格架岩为主的层状礁,底栖群落结构显示以Pachythecopora pachytheca Deng,Actinostromaria motianlingensis Dong et Wang和Spongiomorpha robusta Yang et Wang为主体,其次还含有Latusastraea xigazeensis Liao et Xia,Preverastraea sp.,Ptychochaetes cf.globosus Koechlin和Spongiomorpha asiatica xainzaensis Deng.索瓦组上部孢粉组合中的Dicheiropollis etruscus为特提斯海周边地区早白垩世早期的特征分子；Senegalosporites和Steevesipollenites两属多见于早白垩世晚期乃至更晚的孢粉组合中,尚未见产于白垩纪以前地层的记录.珊瑚及孢粉组合指示索瓦组的主体部分为上侏罗统,而上部可对比为下白垩统.

The biostromal community structure and biostratigraphic correlation of the Mesozoic Suowa Formation in Bandaohu area, Qiangtang depression, Tibet

The Lower part of Suowa Formation in the north Qiangtang depression of Tibet has been correlated to the Late Jurassic. However, dating evidence of the upper part of the formation remains insufficient. Three reefal units from Suowa Formation in Bandaohu area are gentle morphologically and composed of corals and stromatoporoids frameworks. The community structures show that benthic metazoanl taxa are mainly of Pachythecopora pachytheca Deng, Actinostromaria motianlingensis Dong et Wang and Spongiomorpha robusta Yang et Wang, and subordinately of Latusastraea xigazeensis Liao et Xia, Preverastraea sp., Ptychochaetes cf. globosus Koechlin and Spongiomorpha asiatica xainzaensis Deng. The pollen assemblages marked by Dicheiropollis etruscus from the upper part of the Suowa Formation are initial elements of the Early Cretaceous in the surrounding areas of the Tethys. Moreover, Senegalosporites and Steevesipollenites have never been recorded from horizons in advance of the Cretaceous, and they are common in the pollen assemblages of the late Early Cretaceous and even later. Therefore, coral and pollen assemblages indicate that the main part of the Suowa Formation is correlated to the Upper Jurassic, and the upper part of the formation is reasonably assigned to the Lower Cretaceous.