松辽盆地晚白垩世青山口组—嫩江组一段介形类壳饰、壳形类型与环境关系分析

An analysis of the relationship between types of ostracoda shell ornaments and shell shapes and the environment from Late Cretaceous Qingshankou Formation to 1st Member of Nenjiang Formation in Songliao Basin

本文在对松辽盆地晚白垩世青山口组—嫩江组一段介形类壳饰、壳形类型划分的基础上,对研究层位12种壳饰类型与9种壳形类型的介形类可能生活的环境及其变化特征进行了探讨。研究表明,松辽盆地晚白垩世刺状壳饰的介形类生活的最佳环境为深湖—半深湖相环境;瘤状壳饰的介形类适宜生活于水质清、矿化度较高、pH值也较高的浅湖—半深湖相环境;深蜂孔、饰边、长瘤或隆脊壳饰的介形类生活于深湖—半深湖相环境;浅蜂孔、网状、细纹、细脊壳饰的介形类主要生活于滨浅湖相环境。三角形、长方形壳形的介形类生活于深湖—半深湖相环境;低梯形、五边形壳形的介形类部分种类生活的环境为深湖相环境,另外一些种类生活于半深湖—浅湖相环境;高梯形壳形的介形类一般适宜的环境为浅湖相环境;椭圆形壳形的介形类基本生活于滨浅湖相环境;肾形壳形的介形类一般生活于浅湖—半深湖相环境。青山口组一段的介形类群以适应深湖—半深湖相的具饰边壳饰、低五边形壳形的介形类为主;青山口组二、三段介形类的壳饰与壳形类型虽然丰富多样,但与湖泊沉积环境变化也具有很好的对应关系;姚家组介形类的壳饰均以适应浅水相环境的浅蜂孔、细脊壳饰为主,壳形以椭圆形占绝对优势为特征,后期随着湖泊水深增大,出现了少量反映较深水相环境的深蜂孔壳饰与三角形和长方形壳形类型;嫩江组一段介形类的壳饰类型较少,以深蜂孔与浅蜂孔类型为主,壳形类型相对较多,椭圆形、长肾形、长方形、三角形、低梯形类型均有一定含量。

Based on classification of shell ornaments and shapes of ostracods from the Qingshankou Formation to the 1 st Member of the Nenjiang Formation in Songliao Basin, the authors studied the possible living environment of ostracods and variation characteristics of 12 types of ostracoda shell ornaments and 9 types of ostracoda shell shapes in the above strata. Studies show that, in the Late Cretaceous in Songliao Basin, ostracods with spinalis ornament were adapted to a deep or semi-deep lake; the species with nubble ornament preferred to live in clean, high pH value and high mineralized semi-deep or deep lakes, the species with deep alveoli, ornamental edge, long nubble or hunch were concentrated in deep or semi-deep lakes, and those with shallow alveoli, reticulation, veins, narrow hunch lived in the shore or shallow lake. It has also been found that the species with a triangular or rectangular shell were abundant in a deep or semi-deep lake; those with low trapezia or pentagonal shells lived in a deep, semi-deep or shallow lake, those with high trapezia shells lived in shallow water, those with ovoid shells lived in a shallow or shore lake, and those with reniform shells lived in a semi-deep or shallow lake. The ostracods in the 1＂ Member of Qingshankou Formation are dominated by individuals with ornamental edge and pentagon shells. Although shell ornaments and shapes of ostracods are varied in the 2＂ and 3~ Members of Qingshankou Formation, they keep a corresponding relationship with the change of depositional environment in the lake. The ostracods in the Yaojia Formation are dominated by individuals with shallow alveoli and vein ornaments and ovoid shells, but a few individuals with deep alveoli ornaments and triangular and rectangular shells appear in the upper Yaojia Formation with the increasing depth of the lake. Although very few types of ostracoda ornaments are known in the 1st Member of Nenjiang Formation and dominated by deep and shallow alveoli ornaments, comparatively varied types of shell shapes are present in this member, such as ovoid, long reniform, rectangular, triangular and trapezia shells.