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.