Depositional features and forming mechanism of the limestone member of Funing Formation in Jinhu Sag

The Paleogene limestone member in the Jinhu Sag is an important petroleum producing formation. However, the depositional features and forming mechanism of the limestone member are not clear, which brings difficulty for the forecast of reservoir. Different from peperites in other Paleogene basins in East China, the limestone member in the Jinhu Sag is the mixture of siliciclastic-carbonate sediments, based on the comprehensive analysis of core, seismic and logging data. The limestone member is mainly of lake, delta and lacustrine fan facies, among which the lake facies is dominant. The delta and lacustrine fan facies, controlled by faults and provenance, mainly distribute close to sediment sources. Clastic rock content decreases upwards in the limestone member, indicating the expansion of transgression, during which the limestone member was deposited. During the deposition of the limestone member, widespread syn-sedimentary faults served as the channels for sediment migration, and adjusted clastic rock distribution. Additionally, clastic rock deposition and provenance rechanneling made the terrain flat and water clear. As a result, biolithite limestones cover clastic rocks and there are no clastic rocks in the limestone. Provenance and faults are the main controlling factors for the limestone member in the study area.