摘要
一、前言云南中东部是我国震旦紀地层发育良好地区之一。1938年,熊秉信最先报导昆明附近的震旦系。随后地貭工作者陆續发表有关文章,对本区震旦紀地层的划分提出了意見,并为以后的地貭工作所引用。解放以后,通过一系列地貭矿产普查工作,在地层方面获得不少新知識。1960年,笔者前去云南中东部的一些震旦系出露較好的地区,进行了剖面实测工作(图1)。
The occurrence of Sinian sediments in central eastern Yunnan has been known for a long time,but their systematic study and classification still leaves much for amendment.With reference of the accomplishments of earlier workers,the writers,in 1960,made some regional statigraphical investigation of the Sinian system in Yunnan.The following is a brief summary of such study.The base is defined by a profound unconformity(Tsinning disturbance),which is represented by a conspicuous erosion-surface trunkating the metamorphosed Kunyang group.The upper or Sinian-Cambrian boundary is limited by the supra Hyolithes-bearing phosphatic formation,where is noted a disconformity.The succession is separated naturally into two parts by a weak but distinct uncon-formity(Chenkiang disturbance);thus,a twofold division for the system into series is determined.By variations of rock types and lithologic characters,the series are classified into separate formations:the Chenkiang and Niutoushan formations of the Lower,the Nanto,Toushanto and Tengying formations of the Upper.For the existence of stratigraphic break under the highly fossiliferous Cambrian strata,and the lack of reliable fossil of the Tengying formation,the system is included in the upper Proterozic.Type sections,lithologic characteristics and compositions and sedimentary facies of formations are described and correlated.Total thickness of the Lower Sinian reaches 2500 m.,the Upper approaches 1500 m.The paleogeographic evolutions as interpreted from rock patterns and specific features are as follows:(1)The beginning of Early Sinian was just in a post-orogenic period and under an arid climate,as menifested by the Chenkiang formation,which consists of 1800 m.red mollasse-like clastics,accumulated in a strongly subsiding basin at the foreside of the Kantien highland.It began to disperse as a piedmont alluvaial fan with local fluvial isolated depositions.(2)During Niutoushan age,a lacustrine environment predominated,though river deposition re-played an important rǒle in the basin.An appreciable amount of the Niutoushan mudstone-siltstone-sandstone formation represents lake-alluvial deposits which merge westward into sediments of a flood-plain.(3)Early Sinian ended with a weak ologeny——Chenkiang disturbance,which was accompanied with a distinct differentiation of relief,and followed by a phase of erosion.Prior to the deposition of Upper Sinian,the Niutoushan-Chenkiang sequence was deformed and eroded.(4)A prevailance of cold climate in the beginning of Late Sinian subjected central eastern Yunnan(as extensively known in lower Yangtze)to a course of glaciation.Consequently,a reduction of the upland areas to a surface of low relief and the aggregation of the glaciogenous Nanto formation came into effect.(5)With a recommenced epeirogenic subsidence,a shallow sea invaded the basin.Much of the Toushanto sediments accumulated in nearshore oscillatory sites,but an off-shore neritic environment predominated in a certain area of the transgressive sea.(6)During the Tengying age,there was a widespread transgression of the sea.The laminated massive calcitic dolomites of Tengying formation were deposited in quiet water of normal marine conditions.(7)With a regenerated epeirogenic emergence,the sea retreated from central eastern Yunnan,and thus made the region to undergo a time of subaerial erosion until the subsequent invasion of the Early Cambrian sea.
作者
刘鴻允
刘钰
LIU HUN-YUN;LIU YÜ
出处
《地质学报》
1963年第1期53-78,102-103,共28页
Acta Geologica Sinica
