宁夏石嘴山石炭系中的半咸水遗迹群落及其古生态环境分析

宁夏石嘴山石炭系纳缪尔期的砂 泥岩互层中赋存有低分异度的遗迹化石群落，但这套岩系中的砂岩层和泥岩层各具有不同的遗迹种。ＰｌａｎｏｌｉｔｅｓｍｏｎｔａｎｕｓＲｉｃｈｔｅｒ仅限于保存在砂岩的下层面，形成表生迹；它们的造迹生物是泥质沉积物中潜穴生存的、营沉积摄食方式的蠕虫类。仅限于砂岩上层面的遗迹化石是Ｍｏｎｏｃｒａｔｅｒｉｏｎｎｉｎｇｘｉａｅｎｓｉｓ（ｎ．ｉｃｈｏｓｐ．），系本文新建立的一个遗迹种，均为底生迹。其造迹生物是营悬浮滤食方式的蠕虫类。导致这两种遗迹化石交替出现的因素是半咸水条件和沉积物粒度的变化。这两类造迹生物都属于在高环境压力下所形成的爆发性繁衍的机会种群，并由此指示着具有最低生物分异度的、其含盐度在０５％～０９％的中盐度域的沉积环境，同时也表明这一时期古气候潮湿温暖并伴之以周期性的大量降水

A BRACKISH WATER TRACE FOSSIL ASSEMBLAGE IN UPPER CARBONIFEROUS OF SHIZUISHAN, NINGXIA PROVINCE AND ITS ENVIRONMENTAL SIGNIFICANCE

A trace fossil assemblage characterized with low diversity has been found from the Namuriam(Carboniferous)deposits which consist of alternating beds of sandstone and mudstone in Shizuishan, Ningxia Province. The lower surfaces of sandstone beds were very often characterized with planolites montanus Richter, 1937, whereas the upper surfaces of the sandstones beds are frequently occupied by Monocraterion ningxiaensis which is a new ichnospecies established in the present note. Producer of planolites montanus is proposed to have survived in soft muddy bottom as a deposit feeder; while producer of Monocraterion ningxiaensis is assumed to be of suspension feeder which was well adapted to sandy bottom. These two ichnospecies can be regarded as opportunity species fairly adapted in a brackish and shallow water environment. The high environmental stress for the trace fossil assemblage can be explained by both salinity fluctuating within mesohaline realm(5%～9%)and periodic alternation of bottom distinction from muddy to sandy deposits. Approach of ethologic and taphonomic work on these trace fossils indicates that a warm and damp paleoclimate accompanied with periodic and strong precipitation took place in the area during Namurian times.