Partition of Sequence Strata and Discussion aboutSalt- rock Resource in Shahejie Formation of Eogene, Dongpu Depression

Key words: 
• sequence strata /
• systems tract /
• salt-rock resource /
• Eogene /
• Dongpu depression

Abstract: Dongpu depression is located in the southwest of Bohai Bay basin. The area is about 5300 square kilometers. The south is wide and the north is narrow. Lanliao fault controls its development and evolvement. On the basis of sequence stratigraphic theory, the author analyzed of the geologic, seimic, geochemical, paleobiological, drilling and logging data. There are two sequences (Sequence I and Sequence II) and eight systems tracts(one sequence includes LST, TST, HST and FSST) has been identified in Shahejie and Dongying formation. They are all have clear characteristics in seimic, geologic, core and logging dada. In continental basin, the influence of the three factors of tectonization, weather and sediments on sequence is different from that in marine basin, the weather is more important than that in marine sequence. After the synthetical analysis of sedimentary facies markers, the author has made the sedimentary lithofacies paleogeographic reconstruction of Shahejie formation of Eogene in Dongpu depression. In this paper the author also re-discussed the resource and the formation of salt-rock, which distributed widely and has a large thickness. The characteristics of chemical components, paleobiota, lithology and distribution of the salt-rock are different from the normal evaporite. It is not come from the evaporation of sea water. Combined the paleotectogenesis and the paleoclimate, the result of the study indicates that the salt-rock is originate from the hot bittern in deep earth and formed under a deep-water environment with a moist climate in Dongpu depression. The formed model is due to an event abruptly. Development of salt-rock is related to tectonization of Lanliao fault but not the climate. The salt-rock is located in TST or HST and developed with source rock. It is advantageous to source rock by preventing it from oxygen. It can also provide heat and pressure for source rock to change into oil or gas. The salt-rock is tighter than mudstone as seal-rock. Because of so many salt-rock formed with source rock and sand body, It is more propitious to form litho-reservoir which has a good matching relationship among source、reservoir and seal rock.