湖南慈利晚二叠世松藻类化石古生态

PALEOECOLOGY OF CODIALES FOSSILS IN LATE PERMIAN LIMESTONE FROM CILI, HUNAN PROVINCE

研究发现,湖南慈利虾米洞剖面上二叠统长兴组含有丰富的松藻类和粗枝藻类化石,并且两者各自成带。松藻类化石包括3属(Anchicodium,Gymnocodium,Permocalculus)7种;粗枝藻类化石包括3属(Epimastopora,Mizzia,Macroporella)。基于形态结构和矿物组构的相似性,本文建议将以前归入裸海松藻科的化石属全部归入松藻科。松藻类化石分布在代表低能环境的粒泥岩和泥粒岩中;而粗枝藻类化石产出在松藻类层位之上代表高能环境的亮晶颗粒岩中。由于对光线的依赖,本文把晚二叠世松藻类的古水深范围限定在20–80 m,把粗枝藻类的生活环境限定在水深约为20 m以浅的浪基面之上的较高能浅水环境。认为该剖面从下部的松藻类群落演替到上部的粗枝藻类群落的主控因素是水深的变浅。

A total of three genera and seven species are identified from the Upper Permian Changhsingian of the Xiamidong section in Cili,Hunan Province,which include Anchicodium,Gymnocodium,Permocalculus of Codiaceae.This shows an obvious upward change from a Codiales flora to a Dasycladales flora.The fossils previously assigned to the family Gymnocodiaceae are recommended to be assigned to the family Codiaceae based on morphological structure and mineral fabric.Here,for the first time,the matrix micrite content of the rocks is used to determine paleo-water depth.It is found that the Codiales occurred in deeper water environment;and Codiales fossils mainly occur in wackestones and packstones with high matrix micrite content,while Dasycladales fossils mainly in the sparite grainstones in the interval with low matrix micrite content,indicating that Codiales live in a low-energy environment and the Dasycladales in a high-energy environment.We conclude that Late Permian Codiales generally lived in deep-water,low-energy environment within the photic zone of a water depth of about 20–80 meters.The Dasycladales generally live in shallow-water,high-energy environment above the wave base and the water depth is<20 m.It is believed that the main controlling factor for the succession of the Codiales flora to the Dasycladales flora is the water depth becoming shallow.