再论假裸枝叠层石科

概要地介绍了假裸枝科叠层石的特征、分布时限、分类系统、研究方法和形成环境.提出该科叠层石有可能作为我国中元古代乃至蓟县系叠层石标志的意见.

A RESTUDY OF PSEUDOGYMNOSOLENACEAE

This paper gives a brief account on the stromatolitic characteristics, time ranges, distribution and taxonomic position of the Pseudogymnosolenaceae, with the suggestion that these small stromatolites should be used as guide fossils for the division and correlation of the Middle Proterozoic strata or even the Jixian (Chihs n) Sy?em. The stromatolitic characteristics of the Pseudogymnosolenaceae are recognized as follows; 1. Individual of stromatolite small and short, generally 0.02-2 cm in diameter; 2. Radial-fibrous fabric and microcrenate lamellae usually present; and 3. Synchronic growth also observable. These small stromatolites are widespread along the north, west, south and northeast margins of the North China platform, with their time range approximately from 1 800 to 1 200 Ma. As proposed by geologists Sun Da-zhong and Lu Sun-lian, the lower boundary of the Jixian System in China should be put at the bottom of the Gaoyuzhuang Formation, which s 1652 Ma in age. If their argument is correct, then the Pseudogymnosolenaceae should be regarded as the guide fossils for the division and correlation of the Middle Proterozoic strata or even the Jixian System. The above statement agrees to the adoption of the "Longitudinal Section through Axis" method for studying the stromatolites. This paper proposes a classification scheme with five grades (Supertype, Type, Family, Genus and Species), based on which all the stromatolites from East China may be subdivided into 15 families, with Pseudogymnosolenaceae as one of them. It is inferred that the Pseudogymnosolenaceae were formed in a peritidal sea, according to the newly-procured abundant practical materials, such as the radial-fibrous fabric, microcrenate lamellae and synchronic growth, all the three groups of the small stromatolites together with their original sedimentary structures, Numerous practical materials indicate the existence of some epeiric seas in the Gaoyuzhuang and Wumishan Stages in Yanshan, Taihangshan, Helanshan, Liupanshan, and Xiaoqinling.