Geology Comparison Study Of Southwest Depression In Tarim Basin With Northwest Depression In Qiadam Basin

With 'West Development' policy carrying out and the exploration of oil & gas developing in Western China, the tectonic outline of West China continent was paid more and more attention by both native and foreign scholars. How to understand the relationship of Tarim & Qiadam basin , as well as the character of strike-slip Altyn fault which separates those two basins is one of the controversial points. Tarim basin and Qiadam basin are two main petroliferous basins in Western China which burn plenty of oil & gas resources. With the methods of geophysics exploration getting more perfect and well data continual accumulating, researches of basins' have gone deeply. One of important results is cognizant that Qiadam basin and southwest depression of Tarim basin belong to one tectonic cell in all probability, as displaced by the Altyn strike-slip fault later. But when the Altyn fault got to work and when separated those two basins have been the problems. Aims at those question above, we study with emphases Ht96-260 seismic profile in Hotan zone of southwest of Tarim basin and YD118 seismic profile in Mangya depression of northeast of Qiadam basin, and use the ways of seismic stratigraphic, tectonic geology, paleobiology, as well as data of wells., comparing the character of seismic reflector , tectonic and stratum development along each side of Altyn fault. It reveals there is many same things between southwest depression of Tarim basin and Qiadam basin,such as Presinian crystallline basement, typical drift sheet of Sinian system, biotic community of later Paleozoic era, tectonic movement; However, after Mesozoic era they experienced differenttectonic and sea level movement, especially in Paleogene system marine and land facies differ obviously. All above suggest that from Sinian period to early Mesozoic era Tarim and Qiadam basin are one basin or in the same sediment cell, as displaced by Altyn strike-slip fault in Mesozoic era, which has proofed by dating the fault activities of others. Form the well data now available, Paleocene and Eocene sedimentary facies and typical marine biologic groups in bay of the west Tarim basin provided in thish paper differ completely form those of Qaidam basin. The source controlling theory(the distribution of oil and gas fields are controlled by sourcesage) is still the principle efficient for directing petroleum exploration in continental sedimentation in the west Qaidam basin. It is misunderstanding to regard source rocks of oil fields founded in the southwest Tarim basin as Paleogene marine sediments. It's also misleading to put the exploratin method of Paleogene marine sediments into exploration of Paleogene continental sediment in the west Qaidam basin. This study has directly relationship with strategic evaluation of Tarim and Qiadam basin's future oil & gas exploration, as well as has very important significance for re-understanding the tectonic framework and deposit belt distributions in western China.