中国西北地区第四纪盐湖沉积中钙质超微化石的发现及其古环境意义

DISCOVERY OF THE QUATERNARY CALCAREOUS NANNOFOSSILS IN THE DEPOSITS OF INTERIOR SALINE LAKES FROM NORTHWESTERN CHINA AND ITS PALEOENVIRONMENTAL SIGNIFICANCE

报导了中国西北地区的甘肃、青海、新疆等地陆相第四纪盐湖沉积中发现的钙质超微化石，它们主要是：Ｇｅｐｈｙｒｏｃａｐｓａｏｃｅａｎｉｃａ，Ｃｏｃｏｌｉｔｈｕｓｐｅｌａｇｉｃｕｓ，Ｃａｌｃｉｄｉｓｃｕｓｌｅｐｔｏｐｏｒｕｓ，Ｃ．ｍａｃｉｎｔｙｒｅｉ，Ｒｅｔｉｃｕｌｏｆｅｎｅｓｔｒａｍｉｎｕｔｕｌａ等。上述钙质超微化石群具有以下特征：（１）化石丰度中等，属、种分异度低，化石保存差；（２）赋存化石的层位均为富含石膏盐层的微咸水咸水的沉积物，或为盐湖沉积；（３）产出化石地点远距该地质时期时的古海岸线。它们与古海域既无通道相连，亦非残留海。中国西北地区盐湖沉积中钙质超微化石的发现说明了中国东部地区第三纪沙河街组某些层位中的钙质超微化石不能作为“海相生物”的标志，否定了这些化石层位与“海侵”或“海泛”的关联。

A certain number of calcareous nannofossils were recovered in samples from the Quaternary deposits of interior saline lakes of more than ten localities in provinces of Qinghai, Gansu and Xinjiang. They are mainly the Quaternary taxa, such as Gephyrocapsa oceanica, Coccolithus pelagicus, Calcidiscus leptoporus, C.macintyrei, Reticulofenestra minutula etc. These calcareous nannofossils all bear the following features: (1) The fossil assemblages are characterized by medium fossil abundance, low species diversity and poor preservation. (2) The deposits which yielded calcareous nannofossils are slight brackich brackich, containing abundant gypsum saline beds, or even consisting of salt lake deposits. (3) They were as far as up to more than one thousand kilometers away from the paleo seashore. They neither had conclusive passage linking with paleoseas nor were relic seas during the Quaternary. In summary, these calcareous nannofossils recovered from the Quaternary deposits of salt lakes in northwestern China arid region can not be simply taken as marine indicators. The present discovery will provide the so called ‘marine organisms’ found in the Shahejie Formation of the Bohai region with new decipherment.