燕山西段前寒武系雾迷山组叠层石的环境意义

叠层石广泛见于燕山西段前寒武系雾迷山组,文中将其分为六种类型:核形石、凝块石、层状叠层石、波状叠层石、锥状叠层石和柱状叠层石。叠层石形态的变化由前向后代表由低能向高能的环境转变,其中以层状叠层石在雾迷山组最为丰富。研究表明,在当时无捕食动物与钻孔动物存在的情况下,大多数叠层石发育于潮下带环境。层状和波状叠层石主要出现在潮下高能带的下部,少量见于受保护的潮间环境。潮下层状和波状叠层石以其色深、纹层密集、缺乏干裂收缩缝和窗格状组构区别于潮间带。锥柱状叠层石出现于潮间带和潮下高能带的上部;潮间带的锥柱状叠层石可能因暴露干裂而继承性地有壁,但潮下带的却可能没有。核形石和凝块石占据着泻湖和水下凹地(生物丘之间的低洼地或废弃潮汐沟道)等低能环境。燕山西段的叠层石罕见于潮上带和波基面之下的潮下低能带。

THE ENVIRONMENT SIGNIFICANCE OF STROMATOLITES IN WDMISHAN FORMATION OF PRECAMBRIAN IN WESTERN YANSHAN MOUNTAINS OF NORTH CHINA

Stromatolitees are abundant in Wumishan formation of prec-ambian, Western Yanshan Mountains (Beijing and North Hebei province, China). They can divided into six types; oncolit.es, thrombolitcs, stratifcra, dornal stromatolites,conophyton and columnar stromatolites. The morphology variation from a former one to a latter one shows the environment varying from low energy to high energy. And stratifera is the most abundent stromatolites in Wumishan formation.Most of stratifera and domal stromatolites occurred in the lower parts of high-energy sublidal (above normal wave base) , while a litlie of them occurred in protected intertidal environments. The subtidal stratifera and domal stromatolites are dis tinguished from ituer-tidal ones by their darkfabrics. Conophyton (conical stromatolites) and columnar stromatolites occurred in intertidal and the upper parts of the high-energy subtidal environments.The intertidal ones may have wall structures as a result of exposure and desiccation cracks, and subtidal ones may have not. Oncolites and thrombolites occurred in low energy environments, sucb as Ia-goon and pond-underwater (depression between biostromea or abandonl channels). Stromatolites are rarely ween in supra tidal and low energy subtidal environments (under normal wave base).