内蒙古二连盆地白音查干凹陷早白垩世介形类及其古生态

EARLY CRETACEOUS OSTRACODS FROM THE BAIYINCHAGAN DEPRESSION OF WEST INNER MONGOLIA AND THEIR PALEOECOLOGICAL FEATURES

本文报道了近年来采自二连盆地白音查干凹陷下白垩统钻井剖面中的介形类属种 ,其中新种 7个 ,未定种 4个 ,并进行了描述。

This paper deals with the early Cretaceous Ostracods including 11 genera and 54 species (including 7 new species and 4 unamed species) collected from the drilling holes in the Baiyinchagan Depression of the Eren Basin, Inner Mongolia. These fossils can be divided into three fossil assemblages in ascending order: 1. Cypridea (Cypridea) unicostata Cypridea (Cypridea) delnovi Rinocypris nomugenensis assemblage; 2. Limnocypridea trapezoidea Clinocypris ventriconcava sp. nov. Cypridea (Yumenia) subremota assemblage; 3. Limnocypridea minuta dominated assemblage. Their geological ages are Early Cretaceous Hauterivian, Barremian and Aptian respectively (The present authors have described their assemblage features in brief in 1996).\;In view of the paleoecology, the Early Cretaceous fauna in the area is of the following features: ① The individals and taxa are both abundant, and mainly distributed in the second member and the third member of the Duhongmu Formation; ② The non Cypridea (Cypridea) elements abounded; ③ The native elements occury an important position; ④ The elements which are of smooth shells or simply ornamented shells are much more abundant than those of complicated shells.\; These features suggest that the Baiyinchagan Depression was a some confined depression and the water body in it was rather salted; the sedimentary period of the second member and the third member of the Duhongmu Formation was the flourishing phase of the ostracod fauna and was also the most well developed stage of the ancient lake in the area, but, the scale and the water depth of the lake were confined, may be much less than those of the ancient lakes in the Songliao Basin during Cretaceous and in the Bohai Gulf Basin during the Early Tertiary.