Paleogeography and sedimentary environments of Middle Cambrian period in Tarim area

Abstract：The Middle Cambrian (corresponding to Stage 5，Drumian，Early Guzhanqian of Series 3) is an important sedimentary period of gypsum-halite rocks in Tarim area. Researches on paleogeography and sedimentary environments of Tarim area will help recognize the reservoir and distribution regularity. Based on previous studies, the authors investigated and analyzed 13 outcrops and 17 borehole sections, and consulted some seismic sections. By means of an analysis of stratigraphic and petrologic characteristics, the paleogeographic framework was rebuilt and a tectonic-sedimentary environment map of Tarim area was compiled. Some conclusions have been reached：（1）The paleogeographic pattern in Middle Cambrian period inherited the characteristics of Early Cambrian, but the South Tianshan Ocean, North Kunlun Ocean and Kuluketage-Manjiaer bathyal-deep sea basin were enlarged, and the areas of Tarim epeiric sea basin was reduced in Middle Cambrian. （2）Because the climate of Tarim area was xerothermic in that period, the evaporative platform of 23×104 km2 was formed. Gypsum-halite rocks hundreds of meters in thickness were deposited in an evaporative environment, which provided high quality caprocks.