Sedimentary Characteristics of the Lower Ordovician in the North Margin of Qaidam Basin

The Lower Ordovician Shihuigou Formation in the north margin of Qaidam Basin consists mainly of dark-gray to black shales with minor intercalated beds of calcirudite, calcarenite, sandstone and siltstone, and the Duoquanshan Formation consists mainly of grayish to dark-gray thin calcilutite with calcirudite on the top. The study shows that dark shales are deep-water fine-grained deposits from slope to margin of slope, calcirudites are debris flow deposits, and calcarnites, sandstones and siltstones are typical turbidity current deposits. The sedimentary environments of Lower Ordovician in the study area may be deep-water shelf, slope to margin of basin where water is gradually deepened.