THE ULTRA DEEP-WATER LAKE OF MIDDLE SHA 3 FORMATION DURING PALEOGENE IN DONGYING SAG, EASTERN CHINA

It is an important content of petroliferous basin research to investigate paleo-water depth, and nevertheless, is also a very difficult problem, and so far, there are no perfect methods to carry on quantitative research on the lake paleo-water depth. People can only conduct qualitative research, through paleontology and geochemistry methods. This paper, based on 6 seismic profiles, combining with connected wells’ profiles, attempts to discusses the (maximum) paleo-water depth during the middle Sha 3 Formation of Donying Sag, which is a delta deposition period. Surprisingly, the 6 seismic profiles tell us that the average height of the delta foresets is statistically more likely to be approximately 485 meters and by the compaction correlation we obtain the original height of foresets is theoretically 681 meters. This suggests that the maximum paleo-water depth during the middle Sha 3 Formation would even be among unambiguous 485-681 meters, undoubtedly. The delta foreset bed is mainly a set of fine grain sediments such as grey siltstone and dark mudstone and the siltstone contains drifting mud boulders. The feature reveals that it is a kind of debris flow deposition along the delta front slope. Turbidity current deposits also develop rather common. Convincingly, it is exactly under the condition of ultra-deep water that forms high-quality source rocks, mainly in middle Sha 3 Formation, and further establishes solid material foundation for Jiyang Depression to become China’s large petroliferous basin.