Abstract:

Located between the west Kunlun Mountain and south Tianshan Mountain, there deposited huge thickness of coarse clastic Kezilesu Group in Lower Cretaceous southwest depression of Tarim Basin, which is one of the major reservoirs for oil/gas exploration. Based on lots of outcrops observation and well contrast, three 3rd sequences have been classified, and sedimentary system have been recognized furthermore under the sequence-stratigraphy framework, such as alluvial fan, braided river-braided delta and fluvial delta. Provenance analysis according to the heavy mineral of sandstone samples came from both outcrop and drill cores has revealed very complex source rock types, including magmatogenic, metamorphogenetic and recycled-orogenic source. Hematite, magnetite and leucoxene dominated. It’s characteristic with high grade metamorphism in the south Tianshan Mountain, low grade metamorphism and basic igneous rock in north and south of the west Kunlun Mountain, respectively. Provenance analysis provided useful information for the paleogeography restore. There mainly deposited alluvial fan and fan delta along the south Tianshan Mountain, and fluvial dominated early in the north of the west Kunlun Mountain, and evolved an alluvial fan later, while fluvial and fluvial delta dominated the south of the west Kunlun Mountain. Fan-braided delta front distributary channel, delta front distributary channel and mouth bar sandstones are favor of good reservoir. Source system and paleogeography distribution have significance to favorable reservoir prediction.

Key words: depositional paleogeography, source system, Kezilesu Group, Lower Cretaceous, southwest depression of Tarim Basin