湖北利川二叠纪生物礁的埋藏学特征及其环境意义*

二叠纪钙质海绵礁的研究已逾百年,但缺乏埋藏学方面的研究。本文选取鄂西利川典型钙质海绵礁剖面,对造架生物的属种组成、保存状态(直立还是倒伏)、个体大小、古石孔藻包壳和泥晶含量进行统计研究。共鉴定出17个属种的钙质海绵和一个属种的水螅;通过统计研究发现,含钙质海绵的灰岩厚98m,其下部4/5厚度所含钙质海绵以倒伏的为主,上部1/5厚度以直立的为主;含倒伏钙质海绵的灰岩中藻包壳(古石孔藻)不发育,钙质海绵以直立为主的灰岩中,藻包壳发育;钙质海绵的个体大小由海绵灰岩下部而上增大不明显;泥晶基质的含量自海绵灰岩的下部而上明显减少。由此推断:下部的钙质海绵灰岩形成时由于没有藻包壳,大多被风浪打倒。上部具有藻包壳的钙质海绵灰岩,尽管形成时的水动力能量更强,但由于有藻包壳,其抗风浪能力得到加强,所以大多直立保存。

TAPHONOMIC CHARACTERISTICS OF A PERMIAN CALCISPONGE REEF IN LICHUAN,HUBEI PROVINCE AND ITS PALEOENVIRONMENTAL SIGNIFICANCE

The calcisponge reefs in Lichuan, western Hubei Province is analyzed for reef-building organism composition, preservation status of calcisponges,size of calcisponges,contents of Archaeolithoporellaencrustations and micrites.A total of 17 genera of calcisponges and one genus of hydrozoan are found in the reef-core facies(Layers8-10).The 8 th to 9 th layers are mainly composed of toppled sponges and have little content of Archaeolithoporellaencrustations,while the 10 th layer has more contents of erect calcisponges and Archaeolithoporella encrustations. The average diameters of the calcisponges in the 8 th to 10 th layers increase a little,but the content of micrites gradually declines.Thus we infer that the reefbuilding organisms in the 8 th to 9 th layers formed under less strong hydrodynamic conditions,and were mostly toppled.For the 10 th layer,the hydrodynamic conditions are stronger,but,the Archaeolithoporella encrustations enhanced the anti-wave capability of the reef-building organisms,and they were preserved in erect positions.