松辽盆地三肇地区扶余油层和杨大城子油层介形类古生态及沉积环境探讨

笔者较系统地对松辽盆地三肇地区扶余油层和杨大城子油层(以下简称扶、杨油层)介形类的组合特征、分布范围以及古生态进行了研究。研究表明,扶、杨油层沉积时期的介形类自初期少量出现,之后发展并繁盛,末期全部绝灭。这种变化不仅表现为介形类动物群的属和种数有较大幅度的增加,而且其壳饰类型、分布范围与壳体保存状况也发生了规律性变化,但总体上仍为壳饰简单、属种类型较多、大小个体混生并生活于浅水湖泊环境的介形类群体。对介形类的埋葬环境与分布范围的分析表明,仅含有少量介形类化石碎片的杨五组、杨四组的沉积环境为冲积平原环境,而含有较丰富介形类化石的杨三组—扶上组的沉积环境则以浅湖环境为主,并自杨三组沉积时期在该区中部出现大范围的浅水湖泊后,随着时间的推移,湖泊分布范围与水深在缓慢的扩大或增加,至扶下组沉积时期该湖泊向西已扩大至大庆长垣以西,从而与齐家—古龙地区的湖泊连为一体,组成统一的松辽古湖泊。湖泊水体浅、气候干燥、氧化作用强,可能是造成该时期湖相砂、泥沉积物呈现红色的主要原因。

Paleoecology and sedimentary environment of ostracods in the Fuyu and Yangdachengzi oil horizons in the Sanzhao area, Songliao basin

The assemblage characteristics, distribution and paleoecology of ostracods in the Fuyu and Yangdachengzi oil horizons in the Sanzhao area, Songliao basin, have been studied systematically. Study shows that ostracods appeared in small numbers in the early stage of the deposition of the Fuyu and Yangdachengzi oil horizons, then developed and thrived, and were all extinguished in the end of the depositional period. The above change is not only manifested by the significant increase in numbers of genera and species of ostracod assemblages, but also by their regular changes in shell ornamentations, distribution and preservation state. In general, these ostracods are characterized by simple shell ornamentations, a high diversity and mixing of individuals of varying sizes and living in a shallow-water lake environment. Further analysis of the burial environment and distribution range of ostracods shows that an alluvial plain appeared during the period of deposition of the Yang-4 and Yang-5 formations that only contain small quantities of ostracod fragments, while the depositional environment in which the Yang-3 Formation and Fu-Upper Formation containing relatively abundant ostracods were deposited was mainly a shallow lake one. After a large shallow lake appeared in the central part of the area during the deposition of the Yang-3 Formation, the lake gradually increased in area and depth with time and expanded westward to the west of Changyuan of Daqing during the deposition of the Fu-Lower Formation, and as a result, it was connected with another lake in the Qijia-Gulong area to form the unifying Songliao paleolake. During the period from the deposition of the Yang-3 Formation to the deposition of the Fu-Upper Formation, the shallow waters, dry climate and strong oxidation resulted in a red color of lacustrine sand and mud in the Sanzhao Area.