Paleoenvironmental And Palaeoclimatic Significance Of The Silurian Red Layer In Tarim Basin And Influence To The Formation Of Oil And Gas

Silurian is the only marine clastic sediments of Eopaleozoic in Tarim Basin . Red bed of tataeltage fomation distributed well, and as the main correlation marker and cap rock it is always attractive.The stratum under the red beds is greyish-green clastic rock of Kepingtage, and above the beds is red sand shale of Tataeltage. The red beds is the instruction of the change about palaepenvironment and paleoclimate. At the same time, the distribution of this red bed have important effect.Based on the outcrop, well logging and seismic data, Silurian can be devided into three 3th order sequences as one 2th order sequence. Sequence S1kp-1, S2tt and S2ym contain highstand (HST) and transgressive system tract(TST), and S1kp-1 contains lowstand system tract (LST) besides the HST and TST.By the analysis of depositional system, Silurian have 5 types: littoral facies, shelf facies, braided river delta facies, tide dominate delta facies and tidal flat facies. With the methods of patrology and heavy mineral analysis, there were 4 source direction. Using geochemical methods the curves of paleoclimate and sea-level changes were rebuilt. The climate which were warm and humid in the whole Silurian tend to semiarid and hot. With two litres of two drop the sea level rose to the highest in the middle of Kepingtage and the Yimugantawu, but drop to the lowest level in the red beds time.The analysis about typical oil-gas reservoir prove that the stratum of Kepingtage is a good set of reservoir, and at the same time, the red bed is a stable set of regional cap rock. In geotectonic evolution, Tabei uplift which were above the water lack of the red bed, and at the same time Tazhong area were under the water, so the red bed deposited. The lack of red bed deposition is one of the reasons why there is no large gas field in Tabei area.