中下扬子区海相三叠纪叠层石及其环境演变

EXPLANATION ON EVOLUTION OF STROMATOLITES AND THEIR COUNTRY ROCKS OF MARINE TRIASSIC SYSTEM ON LOWER AND MIDDLE REACHES OF YANGTZE RIVER

中、下扬子区三叠纪叠层石大多产自中三叠统嘉陵江组白云岩中，仅少数产自下三叠统青龙组灰岩中。这些叠层石可根据各自所处环境分为下列２种类型：１）浅滩相叠层石生物丘；２）潮坪相叠层石生物层。这些叠层石及其围岩常含丰富的石膏晶痕或盐溶角砾，显示了一种干燥炎热气候中一低能水动力环境产物的特征。根据中、下扬子区三叠纪叠层石的形态及发育特点研究，结合有关沉积特征分析，发现该区由早三叠世的陆表海演变为中三叠世早期的潮坪复合体，其较深的部位转变为青盐湖，而较浅的部位则变为藻坪或萨布哈盐坪。这种转变暗示着此期间扬子地块已由主要受热带低气压控制下的赤道附近地区移至常年受副热带高气压或干燥信风控制的回归线附近地区。

Triassic stromatolites on the lower and middle reaches of the Yangtze River (east sideof the Yangtze Block)scattered over Naming, Wuxi and Liyang of Jiangsu Province andAnqing, Guangde, Tongling and Fanchang of Anhui Province, mostly yielded from thedolomite of the Jialingjiang Formation (approximately lower Anisian) in the middle Triassic series,with a small amount of them yielded from the limestone of the Qinglong Formation (approximately indian-Olenikian) in the Lower Triassic series. The bioherms andbiostromes formed by carbonate mud silted up and cemented within the stromatoliticframes are classified into the following types based on their respective environments of location.