东濮凹陷古近系沙三段、沙四段介形类生物地层及界线

根据十余口探井微体古生物分析结果和对多年来积累的大量微体古生物分析资料的复查 ,将东濮凹陷古近系沙河街三段 (ES3)和四段 (ES4 )的介形类化石群自下而上分为 3个组合和 3个亚组合 :Cyprinotus igneus组合 ,分布于沙四段下亚段 ;Cyprinotus altilis- Cyprinotus jiyangensis组合 ,分布于沙四段上亚段 ;H uabeinia sinensis组合 ,分布于沙三段 ,其中 H uabeinia obscura- H uabeinia costatispinata亚组合分布于沙三段下亚段 ,H uabeiniasinensis- Candona binxianensis亚组合分布于沙三段中亚段 ,H uabeinia huidongensis- Cyprinotus dongmingensis亚组合分布于沙三段上亚段。各化石组合特征比较清楚 ,为东濮凹陷沙三段、沙四段的划分以及与渤海沿岸盆地的对比提供了依据。虽然东濮凹陷缺少渤海沿岸盆地沙四段顶界的标志性化石 Austrocypris,但该区沙三段、沙四段介形类化石组合整体面貌与整个渤海沿岸盆地相比仍然具有可对比性 ,从介形类化石组合方面来确定本区沙三段、沙四段的界线仍然是可行的

OSTRACODA ASSEMBLAGES FROM THE THIRD AND FOURTH MEMBERS OF THE PALAEOGENE SHAHEJIE FORMATON AND THEIR BOUNDARY IN THE DONGPU DEPRESSION

Based on the detailed studies of the fossil ostracodes from more than 10 boreholes and the review of a great amount of ostracode data, this paper summarizes the ostracode biostratigraphic sequence from the E s 3 and E s 4 of the Palaeogene Shahejie Formation in the Dongpu Depression.Three ostracode assemblages and three subassemblages are grouped in ascending order as follows: Cyprinotus igneus Assemblage from the lower submember of the E s 4; Cyprinotus altilis Cyprinotus jiyangensis Assemblage from the upper submember of the E s 4; Huabeinia chinensis Assemblage from the the E s 3 Member,including Huabeinia obscura Huabeinia costatispinata , Huabeinia chinensis Candona binxianensis and Huabeinia huidongensis Cyprinotus dongmingensis Subassemblages. These three subassemblages were found in the lower, middle and upper submembers of the E s 3 respectively.These assemblages and subassemblages are of remarkable feature and are helpful in the correlation and classification of the E s 3 and the E s 4 in the Dongpu Depression. In the Bahai Gulf Basin,the boundary of the E s 3/E s 4 is defined mainly based on the biostrtigraphic characteristics and the extinction of Austrocypris has been regarded as the indication of the upper limit of the E s 4 Member. For the Austrocypris is always rare in the Dongpu Depression. The determination the E s 3/E s 4 boundary has been a question for a long time in this depression.The present study reveals that the main features of the ostracode assemblages near the E s 3/E s 4 boundary in the Dongpu Depression are similar to those in the Bahai Gulf Basin. So,the division of the E s 3/E s 4 boundary should emphasized on the chief assemblage features of the whole ostracode fauna,rather than a few so called “indicating fossils”.