Study On The Sedimentary System Of The Beach And Bar In The Upper Sha4 Member In Boxing Sag

Based on the research about the core data, the log data, the well log information, the analytical data, the testing data and so on, this paper studies the genesis, the types, the controlling factors and the sedimentatary features of beach and bar in the Sha4 upper Member in Boxing sag, according to the theory of high resolution sequence stratigraphy, sedimentology, well log geology, tectonic geology and so on. The main achievements are as follows:(1) According to the features of the clastic beach-bars in Boxing sag, they can be divided into sandy beach-bar and pebbly beach-bar.(2) Sedimentary features of sandy beach and bar: A single sand layer of bar is relative thick and it is much thinner of beach. The main bedding types of bar are parallel bedding, wave bedding and wave-built cross bedding. There are a lot of fossil fragments, which prove that the hydrodynamic force is strong. Its burrows are main angled and vertical. The main bedding types of beach are swash bedding, wave bedding and linsen bedding. Its burrows are main angled and horizontal.(3) Well log features of sandy beach and bar: The shape of bar is wide forward dactylic or jagged hopper. And the beach is the association of the highly abnormal amplitude dactylitic curve. In FMI, the features of bar is that between the bright belts there are several thin dark belts and the features of beach is that the bright and dark belts are interbedded.(4) The features of pebbly beach-bar: The roundness of the gravels in beach-bar is good. Its well log shapes are mainly jagged hopper or jagged box.(5) The controlling factors: There are four important controlling factors of the development of beach and bar, which are the palaeogeomorphology, the sources, the palaeohydrodynamic condition and the change of the base level.(6) There are five main conditions that the beach and bar are more development in lowstand systems tract. They are: the Jinjia-Fanjia nosing structure, the enough sources supplied by LuXi uplift, the strong palaeohydrodynamic condition, the sustained base level and the good preservation condition.