Quantitative Stratigraphy Of Upper Cretaceous In Tethyan-Himalaya

Late-Mesozoic is an important stage in earth history. A lot of things have changed dramatically and many very interesting things happen, such as the formation of Atlantic Ocean, the Ocean Anoxic Events, the Origin of Mammals and so on. Tibet has the best Cretaceous marine facies strata in China. The late Cretaceous strata of Tethyan-Himalaya in the Southern Tibet is the place that has been studied for a long time by geologists.In 1964, Shaw published his master piece named Time in Stratigraphy, and developed the semi quantitative methods Graphic correlation. Since then, the quantitative stratigraphy has been established. With the development of computer technology, many quantitative methods emerge. Compared with the traditional methods, they are much more accurate, used broadly in the field of scientific research by oil companies.Nine sections of this area are collected, with which the database TIBETK is built. One of them is not used because of its two fault zones. Using the semi quantitative method Graphic correlation and the software Graphcor, each section is correlated with the database MIDK4's composite section, and the"bad"data are deleted. The revised data are then put into the software CONOP9. Using the quantitative stratigraphic method Constrained Optimization, eight sections are correlated by the software automatically. Consequently, the composite section is derived and all the data are revised by the software.The composite section is compared with the Foraminifer's age which is early confirmed and the equation"y = -0.1909x + 304.83"is obtained. The age of first occurrence and last occurrence of 64 species can be derived from the equation. The resolution is about 0.3Ma, which is about 10 times higher than the data got from the traditional method. From the composite section, it can be found that some fossils'range zones are too short. Maybe it is caused by the fossils not preserved properly or the samples not collected comprehensively. Most fossils'first occurrence data are later than the ages which are defined by the MIDK4 composite section. It is probably caused by the Foraminifer zones in Tethyan- Himalaya which are not isochronous with other areas. It can also be recognized that there are two major extinction and revival events at the boundary of Cenomanian/Turonian and the boundary of Coniacian/ Santonian. They are coincident with the two Ocean Anoxic Events and can be considered as the typical response by creatures.