Internal-tide Deposits of Upper Ordovician Flysch in Linan Area of Zhejiang Province

Late Ordovician in Linan area of Zhejiang Province is located in the southeastern slope of a deep sea basin. The lower Ordovician flysch of Linan area mainly consists of rhythmically thin layers of gray fined sandstones, siltsands and dark-gray mudstones in which the typical graded bedding, flaser, wave and lenticular beddings, cross bedding, pinnated cross bedding, bimodal cross-bedding, rhythmic stratification and ripple mark are well developed. Abundance trace fossils are found in the flysch, and they are typical members of“Nerites” facies. Three internal-tide depositional microfacies are recognized and studied in the flysch of Linan area, they are rhythmically thin layers of fine sandstones, mudstones and siltsands microfacies with flaser, wave, lenticular bedding, unidirectional cross-bedding and cross lamimated sandstones, siltsands microfacies, fine sandstones, siltsands microfacies with pinnated cross-bedding and bi-directional cross lamimates. Based on the study, the lower Ordovician flysch of Liana area is inferred to be formed by deep-water traction current (internal -tide), gravity current and deep-water in-situ deposits.