Stratigraphy, correlation, depositional environments, and cyclicity of the Early Cretaceous Yixian and ?Jurassic-Cretaceous Tuchengzi formations in the Sihetun area (NE China) based on three continuous cores

摘要: Abstract Three continuous cores acquired in the Sihetun area of Liaoning Province, famous for feathered non-avian dinosaurs Jehol Biota, reveal stratigraphic and facies relationships divisions Early Cretaceous Yixian underlying ?Jurassic-Early Tuchengzi formations. Based on these cores, we propose a modified lithostratigraphic nomenclature Sub-basin which Formation is divided into three members: Lujiatun Member, fluvial alluvial volcaniclastic sandstone conglomerate, unconformably overlying Formation, with articulated tetrapods plausibly preserved burrows; Xiatulaigou an extrusive basaltic flow breccia comprising only true lavas area; Jianshangou cyclical lacustrine mudstone containing taphocoenosis compression fossils soft tissue preservation including dinosaurs, birds, pterosaurs, mammals, fish, crustaceans, insects, mollusks, plants. The latter, 4 units: basal Dajianshanzi Bed, shallow-water unit abundant mollusks rooted zones; Anjiagou main tetrapod-bearing unit, consisting microlaminated dark gray mudstones many interbedded airfall ashes deposited meromictic lake; Hengdaozi Bed comprised thin rhythmically to medium bedded light tan sandstones few discrete ashes, its diverse insects plants, early angiosperms alternating dysoxic oxygenated bottom water; Huangbanjigou most obviously units, intervals vertebrates more massive lighter colored lakes that oscillated depth. Cyclicity Member dominated by meter-scale cycles may be paced orbital variations. Unambiguous, relatively rapid, lateral changes within are suggestive local relief, not giant flat-bottomed basin.