Sedimentology of Upper Ordovician shoreline deposits in Tarim basin, western China

At the stage of Upper Ordovician, the north of Tarim basin was adjacent to the open sea, and a set of shoreline sediment was formed on the coast, based on the careful observation and analysis of the field outcrop in Keping area as well as the core in drilling well in Tabei area. Swash cross stratification, tabular cross stratification, wave ripples, and long-shore bars are common in these deposits, indicating that wave played a significant role in producing the sedimentary structures. On the basis of lithology, electric property, rhythmicity, sedimentary structure and fossil, two depositional facies were grouped: beach deposits and shorface deposits. What's more, the shoreface can be further divided into the upper, middle and lower shoreface. The vertical facies sequence formed by seaward progradation of beach and shoreface are common, while the Upper Ordovician sandstone units in Tarim basin are typical retrograding shoreface and beach sequences, deposited on coasts with moderate to high wave energy.