Gravity flow deposits of Paleogene Liushagang Formation in Fushan Sag, Hainan Province

Paleogene Liushagang Formation in Fushan Sag is a set of clastic rock sedimentary formation. Ac-cording to the comprehensive analysis of the lithology, well logs and seismic data, the sedimentary facies of the Liushagang Formation have been systematically studied. The braided delta lies in the south of the studying area, the semi-deep to deep lacustrine sub-facies lies in the north. And the gravity flow deposits develop in the semi-deep to deep lacustrine. The types of the gravity flow deposits in the studying area are the turbidity current deposit and the debris deposit. In addition, there is slump deposit, a kind of associated deposit with the gravity flow deposits. These sedimentary types and mudstone combine three different vertical assemble as follows: the mudstone-turbidity current deposit assemble, the debris flow deposit-slump sediment-turbidity current deposit assemble and the mudstone-debris flow deposit assemble. In general, the gravity flow deposits take the form of intercalated bed in the semi-deep to deep lacustrine, and they can also form large-scale sedimentary body, which is sub-lacustrine fan. Generally, the shape of SP curve of turbidity current deposit in sub-lacustrine fan assumes bell-shaped, and debris flow deposit assumes box-like and funnel-shaped. On the seismic profile, the reflection characteristic of sub-lacustrine fan appears moundshaped. In the studying area, the good forming conditions of the gravity flow deposits are well-developed semi-deep to deep lacustrine sub-facies, abundant source and tectonics activity in the east and west of Fushan sag. There is a bright prospect for exploration of sub-lacustrine fan for its favorable condition of source-reservoir-cap rock.