广西贺州地区寒武系沉积环境及其演化分析

Evolution of sedimentary environments of Cambrian deposits in Hezhou area,Guangxi Province

贺州地区临近扬子陆块和华南新元古代—早古生代造山带的边界,对该区寒武系沉积环境及其演化进行分析,有助于进一步阐明寒武纪华南海盆西南缘的特征,进而为扬子板块和华南新元古代—早古生代造山带的界限划分提供依据。综合分析岩石类型及其组合、生物化石、沉积构造等特征,对研究区沉积环境及演化进行了研究。结果表明:研究区寒武系岩性主要为砂岩和泥(页)岩,多形成类复理石韵律。生物化石以原始海绵化石Protospongiasp.和舌形贝Obolus sp.、Lingulellasp.等为主。沉积环境以陆棚、斜坡及盆地边缘为主。区内在早寒武世初期至早寒武世中期、早寒武世中期至早寒武世末期、中寒武世初期至晚寒武世末期寒武纪发生了3次较大规模的海侵、海退旋回过程,海平面总体上呈下降趋势。研究区早寒武世可能处于华南海盆裂解拉张最大规模阶段。

Hezhou area is close to the boundary between the Yangtze Plate and the Neoproterozoic-early Paleozoic Orogenic Belt of South China.By analysing sedimentary environments of Cambrian sequence,we further clarify characteristics of southwestern part of the South China basin in Cambrian,which provides evidence for defining the southwestern boundary between Yangtze Plate and Neoproterozoic-early Paleozoic South China Orogenic Belt.Through the comprehensive analysis of rock types and their association,sedimentary structures,fossils and other characteristics,we studied sedimentary environment and its evolutionary during Cambrian.The Cambrian is mainly composed of sandstones and mudstones （shales）,which often occurs as flysch rhythm. Fossils include Protospongia sp.,Obolus sp.,Lingulella sp.etc.Sedimentary environments are mainly varying among shelf, slope and marginal basin.Three large-scale transgressive-,regressive cycles have been recognized during Cambrian in the study area.They are early stage of early Cambrian to middle stage of early Cambrian,middle stage of early Cambrian to late stage of early Cambrian,and early stage of middle Cambrian to late stage of late Cambrian,respectively.In the vertical direction,the sea level gradually droped in general trend.In early Cambrian of the studied area,the Southern China basin may be at a stage of max-imum tensile and breakup.