Middle-Late Jurassic marine dinoflagellate cysts from the eastern Qiangtang Basin in the Qinghai-Tibet Plateau, China

摘要

Dinoflagellate cysts from two Middle-Late Jurassic sections in the Wenquan and Yanshiping regions of the Qiangtang Basin comprise 24 genera and 36 species including one new taxon of the genus Tenua . Based on their stratigraphic distribution, six assemblage zones are recognized in ascending order as follows: 1) Tubotuberella egemenii Zone, probably Callovian, in the mid-upper part of the Xiali Formation; 2) Pareodinia ceratophora Zone, probably Oxfordian, in the lower part of the Suowa Formation; 3) Batiacasphaera floralis Zone, probably Oxfordian, in the middle part of the Suowa Formation; 4) Amphorula metaelliptica Zone, probably Early Kim-meridgian, in the upper part of the Suowa Formation; 5) Alisocysta spp. Zone, probably Early Kimmeridgian, in the base of the Xueshan Formation; 6) Tenua wenquanensis sp. nov. -Dichadogonyaulax schizoblata Zone, probably Late Kimmeridgian-Tithonian, in the lower part of the Xueshan Formation. Based on our analysis the Jurassic-Cretaceous Boundary in the Wenquan section is placed higher than previously.