The Callovian and Late Jurassic ammonite-based chronostratigraphy of West Siberia: important findings, biostratigraphic review, and basin correlation West Siberia-South England

摘要

This study reviews the Callovian to Volgian biozonation in West Siberia and discusses the problems related to zonations of Jurassic sequences relying only on well core data. The West Siberian Callovian to Volgian formations are correlated with its coeval analogs in South England for the first time. The sequences within the Corallian Group and Vasyugan Suite are very similar in their age and sequence interpretation. Four event levels are proposed using revised ammonite biozonations: (1) the base of the Cornbrash Fm.--the bottom of the U_2~0 Layer; (2) the base of the Oxford Clay Fm.--the base of the Vasyugan Suite--the bottom of the Jason Zone; (3) the Berkshire/Nothe Grit boundary--the top of the U_1~3 Layer--the bottom of Densiplicatum Zone; (4) the base of the Kimmeridge Clay Fm.– the Vasyugan/Georgiev boundary--the bottom of the Baylei Zone. The authors aim to demonstrate that a detailed and reliable biozonal basis is required to correlate events.