贵州桐梓红花园剖面下奥陶统桐梓组灰岩微相和区域沉积分异

早奥陶世桐梓红花园剖面位于扬子区的内陆架沉积带,碳酸盐岩相的桐梓组浅滩序列中频繁出现强水动力环境下三叶虫、棘皮类、腕足类、砾屑和鲕粒单独或混合构建的沉积单元,有些滩相单元是在高能带风暴浪中快速堆积的,间或出现有云坪带沉积的白云岩。盐度异常和强水动力条件皆不利于后生动物造礁,仅见薄层钙质微生物席。通过与红花园之南的贵阳乌当以及之北的桐梓水坝塘剖面桐梓组的岩相学比较,厘定它们分别由蒸发云坪为主—高能滩为主—潮下带为主的相变序列构成,藉此划定桐梓组沉积期由南到北古地理背景差异性,认为朝北方向海水有逐渐变深的趋势,水深控制了白云岩化强度和海水能量指标。

MICROFACIES OF THE LOWER ORDOVICIAN TUNGTZU FORMATION AT THE HONGHUAYUAN SECTION,TONGZI,GUIZHOU PROVINCE WITH SPECIAL REFERENCES ON REGIONAL FACIES DIFFERENTIATIONS

The Honghuayuan section of the Tongzi County was situated in the inner shelf belt of the Upper Yangtze Platform during the Early Ordovician.Bioclastics of the trilobite,crinoid,brachiopod etc.together with conglomerate and ooid are rich grains of the bank units frequently occurred from the carbonates of the Tungtzu Formation.They are proxies of high-energy depositions in shallow shore.Some of them were punctured frequently by tempestite beds.Dolostones as indicators of dolomitic flat are occasionally intercalated with bank facies.Such a disturbed and anomalous salinity environment was not favorable for the thriving of metazoanal reef contributors.Nevertheless,calcimicrobial community was occasionally survived for the forming of thin-bedded algal mats.Comparing to the coeval lithofcaies of the southward Wudang section in Guiyang and northward Shuibatang section,a lithogeographic pattern is outlined as dolomitic flat-dominated,high-energy bank-dominated and subtidal zone,which are arranged along northward with increasing sea water depth.Depth variety did play key role for the facies differentiation especially in regard to dolomitization and parameters of energy of the sea water from place to place.