江西玉山祝宅上奥陶统下镇组蓝细菌化石及其古环境意义

CALCIFIED CYANOBACTERIA FROM THE CORAL BIOSTROME OF THE UPPER ORDOVICIAN XIAZHEN FORMATION OF ZHUZHAI,YUSHAN,JIANGXI PROVINCE,AND THEIR PALEOENVIRONMENTAL IMPLICATIONS

江西玉山祝宅上奥陶统下镇组发育一层珊瑚生物层,是扬子板块奥陶纪以珊瑚为主的生物碳酸盐岩建造的典型代表,其形成的水深一直缺乏有效的限定。本文研究首次在该珊瑚层中发现蓝细菌,包括Girvanella和Rothpletzella。蓝细菌生活的水体深度不超过50m,从而将该珊瑚生物层形成时的水体深度限定在50m以内。珊瑚生物层的下伏灰岩地层产出大型腕足动物,但属种单调,不产任何珊瑚。本文研究在该层灰岩中发现的蓝细菌Hedstroemia和Garwoodia,是两个典型的潟湖相蓝细菌,因此推测该层灰岩中珊瑚的缺失不是因为水太深,而是因为环境的局限。该剖面下部有一套与页岩互层的灰岩,以前被认为是深水相的,但这次在其中发现了蓝细菌Acuasiphonoria,因此也应该是浅水相的。

The coral biostrome of the Upper Ordovician Xiazhen Formationin of Zhuzhai,Yushan,Jiangxi Province,is a typical representative of the biological constructions on the Yangtze Plate.However,there is no effective method to constrain the paleo water depth of the biostrome for a long time.Cyanobacteria were found in the coral biostrome for the first time in this study,which indicates that the water depth of the coral biostrome is<50m.The cyanobacteria in the coral biostrome include Girvanella and Rothpletzella.The limestone bed underlying the coral biostrome contain only large monotonous brachiopods,without any coral.Hedstroemiaand Garwoodia,two typical lagoon-facies cyanobacteria were found in the bed with brachiopods.It is inferred that the restricted environment has inhibited corals rather than the depth of the water.Acuasiphonoria was found in the limestone interbeds of the lower part of this section,and implies this part is not of deep-water facies unless that the Acuasiphonoriais floating.