Sedimentary laminations in the lacustrine Jianshangou Bed of the Yixian Formation at Sihetun, western Liaoning, China

Extremely fine sedimentary laminations of the lacustrine Early Cretaceous Yixian Formation were studied in the excavated Sihetun Fossil Museum section in western Liaoning, China. The section consists mainly of mudstones, shales and layers of volcanic ash. The mudstones and shales are composed of siliciclastic and organic-rich laminae. Most of the laminations are varves that record seasonal climatic changes. Varve thickness measurements show that the sedimentation rate for the majority of the mudstones and shales was 0.2–0.7 mm/year. Quiet, anoxic lacustrine bottom waters were critical for the preservation of the laminations.