The Unconformity Type and Distribution in Eastern Qaidam Basin

Qaidam Basin has undergone many tectonic movements and formed several unconformities.According to the hydrocarbon accumulation of unconformities and their origins and seismic reflection characteristics,the unconformities of East Qaidam Basin can be divided into five kinds:fold unconformity,fault-fold unconformity,truncation unconformity,onlap unconformity and parallel unconformity.The zonal distribution law of unconformity type is decided by the tectonic movements,sea level elevation and denudation.Laminar textures due to uneven weathering and denudation processes are typical of unconformities,and the unconformity surfaces in vertices are divided into three parts including basal conglomerate,weathering clay stone and semi-weathering leached zone.The different types of unconformity show different hydrocarbon accumulation mechanism and hydrocarbon patterns.The fold unconformity and fault-fold unconformity are of most favorable types for hydrocarbon accumulation.