北京西山下苇甸中寒武统张夏组生物丘发育特征及其地质意义

The Bioherm and Geological Significance of Middle Cambrian Zhangxia Formation at Xiaweidian Profile in West Hill,Beijing,China

北京西山下苇甸剖面寒武系地层出露完整,中寒武统张夏组底部和顶部发育两期生物丘地层。通过野外观察及薄片鉴定发现,张夏组底部发育的生物丘为凝块石生物丘,顶部发育的为叠层石生物丘,两期生物丘的造丘生物主要为藻类。凝块石生物丘生长在低能的潮下带环境,而叠层石生物丘则形成于海水能量较高的潮间带或潮下带上部。不同的沉积环境造成了两期生物丘内部结构的差异,主要体现在造丘生物的排列方式上。根据该剖面两期生物丘的特征,总结了生物丘的发育模式,并对其地质意义进行了探讨。

The Xiaweidian profile, exposed well, is one of the best profiles for study of Cambrian sedimen- tation in Western Hill, Beijing. Two phases of bioherms developed in the bottom and upper Middle Cam- brian Zhangxia Formation respectively. By the outcrop and thin section , the bottom bioherm is a clot bio- herm and the upper bioherm is a stromatolite bioherm. The bioherm-building organisms are dominated by algae. The clot bioherm developed in subtidal environment and the stromatolite bioherm in intertidal or up- per subtidal environment. The sedimentary environment controls the inner structure of both bioherms dif- ferently. The main differences are arrangement of bioherm-building organisms. This paper discusses the hioherm-forming model and geological significance on the detail characteristics of two phases of bioherms.