THE DISCOVERY OF EARLY CAMBRIAN FOSSILS IN THE“TAOWAN GROUP”IN SHAANXI AND THEIR GEOLOGICAL SIGNIFICANCE

Predecessors assigned the age of the“Taowan Group”to Ordovician-Silu- rian,but there is no reliable evidence of fossils.The present authors discover- ed ten occurrences of small shelly fossils and collopane mineralization in the Miaowan Formation of the “Taowan Group” defined by the predecessors at Shang’angou and other places northwest of the seat of Luonan county. According to the fossil assemblage and lithology,the Miaowan Group is divi- ded into three parts:the Dazhuang Formation of the Jixian System,the Sinian Luoquan Formation and the Lower Cambrian Hancun Formation. From an analysis of regional geological data,the Taowan Group is located to the so uth of the great Simingshan anticline（the Longjiayuan Formation- Fengiiawan Formation）,Lushi,Henan province,belonging to miogeosynclinal sediments of a mobile belt,and the Sinian Luoquan Formation and the Cambrian System with paleontological evidence are located to the north of the great Simingshan anticline,belonging to platform sediments of a stable belt.They are separated by the major Meidi Babaoshan-Machaoying fracture. Different in aspects of tectonic environments and sedimentary formation,they belong to different tectonic areas and stratigraphic subregions.On the basis of its contact relationships with the underlying strata,microflora,isotopic ages and geochemical data,it is advisable to assign the age of the Taowan Group to late Proterozoic.