An Preliminary Study Of Origins Of Red-White Limestone Of Late Cretaceous' Tielongtan Group, Aksai Chin Lake Areas, Northwest Tibet

The Akesaiqin Lake area, between Karakorum and west Kunlun Mountains, northwest Tibet, is one of the areas in China where the Late Cretaceous marine strata are well developed. The Upper Cretaceous in studied area, named Tielongtan Group, is distributed in Mesozoic fault basins along E-W or SEE-NWW direction. It forms a series of shallow-marine and littoral deposits and a little terrestrial clastic rock overlying unconformably Carboniferous fine clastic rocks or Jurassic carbonate rocks.1. A detailed study in characteristics of the rock of Tielongtan group shows: Tielongtan group is composed of carbonate rocks, which predominates in the group, clastic rocks and gypsum followed, and very occasionally to see little tuff interlayer. Carbonate rocks of Tielongtan group in the area can be further divided into several types: particle - matrix limestone, bioclastic limestone / reef limestone, dolomite - limestone peperite and limestone - clastic rocks peperite.2. A study in sedimentary facies of Tielongtan group shows: According to the rock types, fossil assemblage and sedimentary structure, the types of sedimentary facies in the Tielongtan Group in study area include restricted platform facies, open platform facies. Each phase is consisting of several different rock facies and microfacies3. A study of the evolution of carbonate sedimentary environment of Tielongtan group shows: in the evolution of the overall performance have two marine transgressions. In the early-term of deposition of Tielongtan group, the sedimentary facies in study area is mainly restricted platform facies. Subsequently, the first transgression started in the study area, the sedimentary facies in study area is mainly open platform facies, and the time of the first transgression is short. In the medium-term of deposition of Tielongtan group, the second marine transgression occurred, and until the end of the Tielongtan group. In this time, the sedimentary facies in study area is mainly open platform facies.4. The elemental geochemistry characteristics indicate that the Late Cretaceous Turonian-Campanian shallow-water red-white carbonate cycles was formed in a relatively more oxidizing environment. The red colour is mainly due to presence of hematite pigment.5. Isotope geochemistry characteristic show that theδ¹³C values of the Late Cretaceous Turonian-Campanian shallow-water carbonate rocks are generally high, that the main reason for this is caused by a large number of organic carbon rapid burial, during the period of the Cretaceous OAE.