Study On The Sequence Stratigraphy And Its Forming Mechanism Of Paleogene In Jiyang Depression

Based on the identification of the sequence boundry with the comprehensive analyses of the seismic, well logging and well drilling data, the palaeogene in Jiyang depression can be divided into one lst-order and three 2nd-order sequences, of which six 3rd-order sequences can be subdivided from the third stage of Shahejie formation to Dongying formation. Combined with the analysis of the archaeomagnetic age and the ESR age, this paper has built the relationship between the sequence stratigraphic framework and the age. A 3rd-order sequence usually lasts from IMa to 4Ma, while a para-sequence is from 1.3 ten thousand years to 20 ten thousand years.The lake-margin canyon formed around the lake margin and in the special period of a sequence is a special sedimentary system. Its bottom surface usually corresponds to the sequence boundary.Based on the analysis of the lake basic equation on the sedimentation, this paper has listed climate changing, tectonic uplift, differential settling movement etc. as its dynamic factors that leads to the forced lake regression. Meanwhile, it has explicated the forming meachnism of the sequence boundary in rift basin and stressed the sequence boundary is located on the top surface of the forced lake regressional sedimentary body.The sequence structure is controlled by the relative lake level change. According to the characteristics of the lake level change in a sequence, a 3rd-order sequence can be divided into binary sequence, threefold sequence and quartering sequence. The relative lake level change cycle of the quartering sequence, which includes four systems tracts, is a sine cruve. The threefold sequence absent the quickly falling stage is composed of three systems tracts. The binary sequence composed of twosystems tracts only develops the quickly rising stage and the quickly falling stage.The genetic types of top and bottom boundary can control the sequence structure. The forming of sequence boundaries, which can be divided into two types according to the genetic mechanism: tectonic controlling boundary (type T) and tectonic-climate synthetical controlling boundary (type TC) in Jiyang depression, is controlled by climate and tectonic movement. The type T boundary generally corresponds to the 3rd-order SB and the type TC boundary to the lst-order or 2nd-order SB. The genetic types of SB can also control the distribution rule of the sandbody and hydrocarbonate. The sandbody nearby the type TC boundary develops well, while it has less probability of forming reservoirs in them. On the contrary, the sandbody nearby the type T boundary doesn't develop, but it has great probability of forming reservoirs.