华北地台中晚寒武世沉积层序中生物丘构造研究

Study on the Bioherm Structure of Middle-Late Cambrian Sedimentary Sequences in the North China Platform

华北古克拉通盆地中晚寒武世沉积层序中发育的生物丘沉积构造的生物组成有隐藻类、钙藻类和非藻类多细胞生物，它们构成了隐藻凝块石生物丘简单类型和复合的五种生物丘类型。生物丘的发生、发展、灭亡过程经历了奠基期、拓殖期、泛殖期及消亡期等四个阶段，每个阶段都受相对海平面变化的控制，它决定了丘体的大小、生物组成及内部结构及生长周期。层序地层学研究表明生物丘主要发育于崮山期和长山期，且多分布于三级旋四层序的早期高水位体系域内，并呈现规律性分布。生物丘和风暴砾屑层的空间分布特征及海绿石质凝缩层段的研究揭示华北地台晚寒武世河北秦皇岛、唐山—北京西山—山西大同这一纬度带是一开阔的中陆棚相带。该带以南为一广阔的内陆棚—滨岸带，以北则为一狭窄的外陆棚。

Bioherm sedimentary strutures were well-developed in sedimentary sequences of Middle -Late Cambrian in North China Platform. Bioherm-building organisms include cryptalgae,calcareous algae and non-algae multicelluar organisms which constutited simple type of thrombolite bioherm and composite five types of cryptalgalaminates: wave semispheroidal stromatolites bioherm (Ⅰ), wave-stacked semispheroidal stromatolites-Renalcis bioherm (Ⅱ),Epiphyton-columnar stromatolites bioherm(Ⅲ), wave-stromeatolites-EpiphytonGirvanella-columnar stromatolites bioherm (Ⅳ) and columnar stromatolites-crinoidea-sponge -wave stromatolites bioherm (Ⅴ). The complexity and diversity of bioherms indicate that bioherms can be formed in a wide area from tidal flat to deeper slope.The development process of bioherms underwent four stages: (1) basic stage; (2) pioneering stage; (3) flourishing stage and (d) decaying stage. Each stage was controlled by the relative sea-level changes which controlled the size of bioherms, organism components, inner structures and growing period.Study of sequence stratigraphy showed that most bioherm flourishing periods in the research area are the Gushan and Changshan stages, and bioherms are distributed in the early high system tract in the third-orde cyclic sequence. Bioherm types also change regularly in a sequence, for example, the composite types of Ⅴ, Ⅳ,Ⅲ, Ⅱ and simple type are successively well-developed from the bottom to the top in the sequence Ⅳ of the Dingjiatan section, Beijing west hills and in the sequence Ⅲ of the Xuankongshi section, Hunyuan County, Shanxi Province, This regularity is the products of the different stages of the third-order sea-level changes.The study on the distribution characteristics of bioherms, tempesitites and the research of glanconitic condensed section stated clearly that the latitude zone of Qinhuangdao-Tangshan (Hebei Provence)-Beijing West Hills-Datong (Shanxi Province) was a typical open middle shelf depositional environment in Late Cambrian. The depth was 40-80 meters. South of the zone was a wide inner-shelf belt, and north of the zone was a narrow outer-shelf environment. The conclusion provided the basic framework and important reference for studying the paleogeographic and sea-level changes.