Active, moribund and buried tidal sand ridges in the East China Sea and the Southern Yellow Sea

摘要: Shallow seismic profiles and borehole data revealed active, moribund buried tidal sand ridges in the East China Sea Southern Yellow Sea. The consist of relatively clean, well-sorted sands with fairly uniform sequences. microfossil assemblage exhibits a high diversity including both euryhaline stenohaline species. are huge elongated bodies (several kilometres wide, 10–60 km long up to 20 m thick) occur groups spacing several >10 km. Normally, they parallel each other, extending direction currents. field on shelf covers an area 57,000 km2. Tidal were formed estuarine shallow environments, where strong currents reworked, transported redeposited large amounts relict from older deltaic fluvial sediments. development estuary-mouth areas is accompanied by net transport into estuary. The evolution closely related transgressions. Active during sea-level rises. They show distinct morphology active migrations lateral as well landward direction. generally equilibrium present-day processes their distribution patterns flow As sea level rises further, these become less morphologies. Their upper surfaces covered thin calcareous-rich layer very contents foraminifera tests, reflecting submarine hiatus condition highstand period. During subsequent steady fall level, often fine-grained prodelta have, therefore, good chance being preserved stratigraphic records. The sequential buildup rise (TR-tract) (HS- LS-tract) would channel flat facies, ridge mud delta facies ascending order. Tidally dominated estuary conditions may also when major distributary abandoned, such at Northern Branch modern Changjiang River mouth, accumulation abandoned lobe have been observed. The observed features important implications for subsurface recognition fossil ridges, reconstruction regional palaeogeography transgressional history prediction potential reservoir sandstones.