冀西北长城纪宣龙式铁矿层中微体植物化石的发现及其意义

DISCOVERY AND SIGNIFICANCE OF MICROFOSSILS FROM THE CHANGCHENGIAN XUANLONG-TYPE IRON FORMATIONS IN NORTHWESTERN HEBEI

本文研究的是笔者等在冀西北长城系串岭沟组宣龙式铁矿层中发现的微体植物化石,这些化石都保存在铁质叠层石(肾状赤铁矿)和铁质核形石(鲕状赤铁矿)的基本层中。微化石以丝状体为主,部分为球状体。归属于原核生物蓝藻门颤藻科的两个属和色球藻科的一个属。化石层同位素年龄约在1800—1757Ma。这些化石与北美冈弗林特组微化石比较,既有些相似,又有些区别。该化石的发现为研究铁矿的成因,指示沉积环境及层位对比都很有意义。

Microfossils discovered first in the Xuanlong--type iron formation in north-western Hebei are described in the paper. They are well preserved in the basiclaminae of iron stromatolites ('kedney hematite') and the concentric laminae ofiron oncolites ('oolitic hematite') in the lower part of the Chuanlinggou Forma-tion of the Changcheng System. The microfossils include filamentous and partlyspheroidal forms and form stromatolite--building mats. There are three genera ofmicrofossils, which may be classified as Oscillatoriaceae and Chroococcaceae ofprocaryote Cyanophyta. The isotopic age of the fossil--bearing horizon is about1800--1757 Ma. They show obvious differences from and some similarities to themicroflora from the Gunflint Formation of North America. The discovery of the microfossils is of important significance in enriching bio-logical categories in iron formations. studying the origin of iron and indicatingsedimentary environments and stratigraphical correlation.