The Cretaceous strata in the Vientiane region in Laos

The 1∶100 000 regional geological survey has been implemented by the authors in the Vientiane region in Laos.The Cretaceous strata in this region consist of a succession of red terrigenous clastic deposits in the fluvial-lacustrine environments,and may be grouped into the Bantala,Bannade and Pupanapataoshan Formations,where there occur the bivalve faunas Trigonioides(Trigonioides) sinensis Gu et Ma-Plicatounio(Plicatounio) naktongensis Kobayashi et Suzuki in the middle and upper parts,and the bivalve faunas Koreanaia-Eonippononaia-Plicatounio-Peregrinoconcha,the ostracod assemblage Monosulcocypris-Cyridea and charophytes as the Early Cretaceous index fossil in the lower part.The lithostratigraphy,biostratigraphy and chronostratigraphy of the above-mentioned formations may be compared with those of the Jingxing,Nanxin and Hutousi Formations in western Yunnan,China.