燕山地区长城纪扇三角洲沉积

在燕山地区东部的滦县等地,太古代至早元古代结晶基底之上发育一套百余米厚的陆源粗碎屑沉积。长期以来,许多研究者将其与蓟县地区长城系近底部的陆相沉积地层对比,认为属于常州沟组。1980年,钱祥麟等经过系统的研究,提出这套地层为晚长城纪大红峪期的超覆沉积。此后,这套粗碎屑沉积的性质及其与盆地整体沉积环境系统的关系。一直未能确定。近年来,笔者为此进行了初步的沉积学研究,结果表明这套粗碎屑沉积与其上的碳酸盐沉积构成了较为典型的 Gilbert 型扇三角洲沉积相。该扇三角洲沉积的确立,为燕山地区中一晚元古代坳拉槽南东缘盆地界线的限定以及早期盆地拉张过程中的沉积充填方式的研究,提供了重要的依据。

CHANGCHENGIAN FAN-DELTAIC DEPOSITS IN THE YANSHAN REGION,NORTH ERN CHINA

A sequence of the coarse-grained terrigenous clastic deposits 100 m and more thick are devel- oped on the Archean to Early Proterozoic crystalline basement in Luanxian in eastern Yanshan re- gion.This sequence has long been examined by the previous workers in comparison with the conti- nental sedimentary strata near the bottom of the Changchengian strata in the Jixian region,and is as- signed to the Changzhougou Formation.Qian Xianglin et al.(1980),on the basis of the systematic study,interpreted the sequence as the Dahongyuian(Late Changchengian)onlap deposits.From that time on,the nature of these coarse-grained elastic deposits and their bearings on the whole sedimen- tary environmental systems in the basin remained uncertain.The results of research obtained by the authors in recent years show that both coarse-grained clastic deposits and overlying carbonate de- posits represent the characteristic Gilbert-type fan-deltaic deposits.The recognition of the fan-deltaic deposits provides the important basis for the limitation of the basin boundary on the southeastern margion of Middle and Late Proterozoic aulacogens in the Yanshan region and for the study of depo- sitional-filling patterns during early extension of the basin.