辽河断陷盆地西部晚寒武世至早奥陶世牙形石生物地层

CONODONT BIOSTRATIGRAPHY OF LATE CAMBRIAN AND EARLY ORDOVICIAN IN THE WEST DEPRESSION OF LIAOHE FAULT BASIN

辽河断陷盆地西部凹陷古潜山顶部地层的时代 ,自 70年代末期以来 ,一直被认为属于中、上元古代。本文通过在总面积为 60 0 km2 的西部凹陷中段系统、详尽的牙形石生物地层研究 ,并结合疑源类、小壳化石以及岩石地层学资料 ,确认研究区内古潜山顶部地层的时代主要为晚寒武世至早奥陶世。中、上元古代地层在研究区内虽然存在 ,但分布极其局限。从而 ,彻底改变了2 0年以来对该地区古潜山地层划分和对比上的传统认识。

Since the late 1970's, all the strata of the buried hills in the West Depression of Liaohe Fault Basin had been considered as Meso and Neo Proterozoic, only based on the lithology and acritarch assemblages. A total of 108 core samples from three information wells were processed for conodonts in 1978 and 1979, but no conodonts were recovered at all. It was not until December, 1996, when the first author of the present paper recovered three conodont specimens respectively from the core samples of three different wells, that the strata of the buried hills in the certain part of West Depression of Liaohe Basin were considered as Cambrian and Ordovician. In order to identify the correct age and re establish the succession of the strata of the buried hills in the West Depression of Liaohe Basin, the present authors carried out the research on conodont biostratigraphy in the middle district, with an area of 600 km 2 , of the West Depression of Liaohe Basin. We processed 601 core samples from 63 wells all over this district for conodonts. More than 4,000 conodont specimens have been recovered from the core samples of 16 wells in different parts of the district. The Early Ordovician conodonts are abundant, while the Late Cambrian conodonts are relatively rare and scattered. Based on the conodont elements as well as the new data of lithology, acritarch and small shelly fossils, it is concluded that the overwhelming majority of the upper strata of the buried hills in the West Depression of Liaohe Basin are of Late Cambrian and Early Ordovician in age rather than Meso and Neo Proterozoic.