Chemostratigraphy Of Marine Cretaceous In Gyangze Area, Southern Tibet

Cretaceous is a special period of many climatic and tectonic changes, therfore very important in geosciences research. Marine Cretaceous strata crops out in Tethyan Himalaya zone. The latter is divided into northern subzone of Tethyan Himalayas (northern subzone) and southern subzone of Tethyan Himalayas (southern subzone) by the Dingri-Dingjie-Gangba fault. Gyangze area is located in the northern subzone. In this paper, the geochemical characteristic of the Chuangde section located in the Gyangze area is discussed.Marine Cretaceous strata at Gyangze area have been studied by several geologists, who established that the Gybure Formation was deposited in dysoxic environment. In a contrast the Chuangde Formation formed during time period when the ocean bottom water was rich in dissolved oxygen. The geochemical characteristics of Chuangde section is analyzed with higher precission than was previously available and include total organic carbon (TOC), calcium carbonate (CaCO₃), main elements, Fe oxides and features of Diffuse Reflectance Spectrocopy.TOC data divide the sequence into ten cycles, from the black unit up to the siliceous unit. The red beds have lower TOC content. TOC is highest at the top of the black unit.CaCO₃ content reaches the peak in white unit. CaCO₃ is very low at the bottom of black unit, siliceous unit and in red beds.Fe, Al, K, P, Mg and Ti have a similar behavior through the section. They increase sharply at the top of black unit, and reach highest content in red bed. This trend is opposite to the changes in the Si content. Mn has a lower content than the above elements and does not show any obvious pattern. Na and Ca content show high variability through the section. Fe²+ contents is lowest in red bed, but the Fe³+ reaches the peak.The Diffuse Reflectance Spectrocopy was used to correlate reflectancy with the content of Ca, TOC, and Fe. Reflectancy is increasing with an increase in Ca content and decreasing...