四川江油含增一带下石炭统顶部生物灰岩层特征及其沉积环境

CHARACTERISTICS OF BIOLOGICAL LIMESTONE AT THE TOP OF LOWER CARBONIFEROUS AND ITS SEDIMENTARY ENVIRONMENT IN THE HANZENG AREA OF JIANGYOU,SICHUAN

川西地区下石炭统顶部生物灰岩层在江油含增一带较为发育,岩石类型包括灰白、灰色厚层至块状灰岩、介壳灰岩、鲕粒灰岩、瘤状灰岩或砾状灰岩和泥质灰岩,夹4层厚约0.22m^0.81m的紫红色钙质泥页岩,灰岩中普遍含珊瑚、腕足类、类等化石。在野外地质调查的基础上,测制下石炭统大塘组生物灰岩层剖面(1条,359.56m长),发现珊瑚礁(Lonsdaleiasp.)灰岩层,生物礁可见长10余m,宽为1m^3m。系统分析研究区的构造发展史、岩相古地理及沉积环境特征,认为这套生物灰岩层属于典型潮间高能环境下浅滩相沉积的产物,与区域上的风暴沉积有关。该研究为地层对比、古气候的变化、海平面的升降和沉积盆地的演化提供了新的证据。

Biological limestone at the top of Lower Carboniferous is well developed in the Hanzeng area of Jiangyou County,western Sichuan Province. The lithology includes gray-white, gray colored, thick to massive bedded, limestone, shell limestone, oolitic limestone, nodular or con- glomeratic limestone and argillaceous limestone, with 4 layers of purple colored calcareous shale （thickness of single layer： 0.22 m-0.81 m） intercalated with these limestone. There are many fossils in the limestone,such as coral,brachiopoda and Aeshnidae. 359.56 m long cross section is measured on biological limestone of Datang Formation,from which 10 m long and 3 m wide coral reef （Lonsdaleia sp. ） is found. The analysis of tectonic development,lithofacies,paleogeography and sedimentary environment in the study area indicates that the biological limestone layers are product of shoal facies sedimentation in a typical intertidal high energy environment, and has a connection with regional tempestite deposit. This research provides new evidence for the under- standing of stratigraphic correlation, paleoclimate change, rise and fall of sea level and evolution of sedimentary basin.