北京昌平青白口系痕迹化石

北京昌平青白口系长龙山组和景儿峪组发育有丰富的痕迹化石，其中长龙山组产有Ｈｅｌｍｉｎｔｈｏｐｓｉｓ ｓｐ．，Ｃｏｃｈｌｉｃｈｎｕｓ ｓｐ．，代表潮下低能环境；景儿峪组产有Ｓｋｏｌｉｔｈｏｓ ｓｐ．和Ｍｏｎｏｃｒａｔｅｒｉｏｎ ｓｐ．，代表高能潮间环境。

TRACE FOSSILS FROM QINGBAIKOU SYSTEM OF CHANGPING COUNTY, BEIJING

Trace fossils studied in this paper are discovered from the Late Proterozoic Qingbaikou System in Changping County,Beijing, comprising 4 ichnogenera,namely: Helminthopsis, Cochlichnus,Skolithos and Monocraterion. Based on the trace fossils combined with sedimentary features of the strata,the sedimentary environments of the Qingbaikou System may be inferred as follows: (1) The Changlongshan Formation consists of sandstones and mudstones interbedded with siltstones.The trace fossils Helminthopsis and Cochlichnus are preserved in the middle part of the Changlongshan Formation with glauconite,iron pyrites and tubular cross bedding,and were formed in low energy environments of subtidal siltstones,belonging to the Cruziana ichnofacies. (2) The Jingeryu Formation composed of marlites interbedded with limestones yields microphytolites and trace fossils Skolithos and Monocraterion. The trace fossils occur in the uppermost part of the Jingeryu Formation,accompanying with small carbonate flaser lenticular bedding, and were formed in high energy environments of intertidal muddy carbonates,belonging to the Skolithos ichnofacies. Based on the potassium argon age determination,the age of the strata bearing trace fossils is about 884-855 Ma. Skolithos and Monocraterion from the Jingeryu Formation may be the oldest vertical burrows in the world.The occurrence of these vertical burrows may provide a new way for metazoa to suit better to the life environments.