INTERNAL TIDE AND INTERNAL WAVE DEPOSITES IN FLYSCH OF MIBOSHAN FORMATION

The Miboshan Formation flysch of Helan aulacogen mainly consists of rhythmically thin layers of gray fined sandstones,silt sands and dark gray mudstones in which the typical graded bedding,elegant 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.Three internal tide depositional microfacies are recognized and studied in the flysch,they are rhythmically thin layers of fine sandstones,mudstones and silt sands microfacies with elegant bedding,unidirectional cross bedding and cross lamimated sandstones,silt sands microfacies,fine sandstones,silt sands microfacies with pinnated cross bedding and bidirectional cross lamimates.Based on the study,the flysch of Helan aulacogen is inferred to be formed by deep water traction current(internal tide),gravity current and deep water in situ deposits.The classical Bouma sequence is to be brout up and analyzed various ideas,;The transformation between the traction current and and gravity current exists.