The sedimentology and paleoclimatology of Early Triassic regional marine oxic event (Beduh Formation), Kurdistan region – Northern Iraq

Abstract

Sedimentological study of Beduh Formation (Lower Triassic) is carried out through three outcrop sections at the Northern Thrust Zone – northern Iraq. Lithologically, the formation consists of alternation of dominantly purple and reddish brown shale with subordinate greenish grey shale and wisps of sandstone and/or siltstone.Beduh Formation comprises two lithofacies, dominantly shale lithofacies and wisps of sandstone lithofacies. These facies are divided into five subfacies on the basis of colour, composition, texture and sedimentary structures. Deposition took place in oxic offshore and deep shelf environment and lapping on the shoreface zone (shale-dominated ramp.X-ray diffractometry reveals that the shales are composed mainly of clay minerals such as illite, in a major proportion, kaolinite, chlorite and interstratified clays in minor proportions. In addition to clay minerals, the non-clay minerals are quartz and calcite with minor proportions of feldspar and hematite. Glass shards, foraminifera and conodonts are extracted by washing 26 samples. Petrographically the sandstone and siltstone beds are composed essentially of quartz with little proportions of rock fragments, feldspars and mica, in addition to some fossil remains (posidonia and microconchids).The clays originated from terrigenous influx from land and explosive volcanoes. The predominance of reddish colour and marine fossil content infer deposition in oxic condition during halmyrolysis with minor alternations with anoxic conditions.