一个大型的古河流-三角洲沉积体系——论苏皖中—上三叠统黄马青组沉积环境

Sedimentary Environments and Facies Architecture of Middle_Upper Triassic Huangmaqing Formation: A Palaeofluvio_deltaic Depositional System

通过对苏皖地区黄马青组的沉积学研究，确认其为发育于前陆盆地内的大型海退河流－ 三角洲沉积体系。根据岩石成因类型划分了８ 个微相，并对其所反映的沉积环境进行了分析。整个层序自下而上可分为前三角洲、三角洲前缘及三角洲平原３ 个亚环境，并对亚环境内的微环境进行了讨论。

This paper has studied the sedimentary environments facies and depositional system of the Middle_Upper Triassic Huangmaqing Formation in Anhui and Jiangsu Provinces,China.On the basis of sedimentary structures and their genetic types,we have recognized eight lithophases in the profiles of Huangmaqing Formation.\;Lithophase 1 Grey,greyish green and brownish grey claystone intercalated with dolomitic silty claystone,with marine fossils\;Lithophase 2 Greyish purple sandy coarse siltite,siltite and clay siltite,with marine brackish water fossils\;Lithophase 3 Grey,greyish green very fine to fine quartz sandstone and coarse siltite,with marine fossils\;Lithophase 4 Greyish purple and purplish red silty claystone and clay siltite with fresh water fossils and plant fragments\;Lithophase 5 Greyish purple coarse siltite,siltite intercalated with clay siltite,with scours,small_scale cross bedding and climbing ripple bedding\;Lithophase 6 Greyish purple to greyish brown fine feldspathic quartz sandstone of lithic quartz sandstone,with medium_large scale cross bedding\;Lithophase 7 Greyish purple siltite,clay siltite and silty claystone bearing calcite nodules,with paleosol characteristics\;Lithophase 8 Greyish purple,brown lenticular fine conglomerate with scour surfaces\;According to the sedimentary sequence and lithophase association of the succession,we consider that Huangmaqing formation formed a large fluvio_deltaic depositonal system,and its depositonal tectonic setting is a foreland basin.Depositional environments shown in the succession include prodelta,delta front consisting of delta front sand,mouth of distal bars and interdistributary bays,and delta plain consisting of fluvial distributary channels,natural levees,crevassing splays as well as floodplain and lake settings.