Study On Geochemical Characteristics Of The Source Rocks Of Datangpo Formation Lower Segment In Songtao Area Of Guizhou Province

As an important clean energy, shale gas has attracted more and more attention from all over the world. Domestic and foreign experts have made a deep study of shale gas exploration. The marine shale in the upper Yangtze region of Southern China is widely distributed, and it is an important area of shale gas exploration to our country. As the material base of oil and gas generation, the study of hydrocarbon source rocks is very important to the exploration of shale gas. Experts at home and abroad have made many important achievements in the study of source rocks in the upper Yangtze region of Southern China, But the organic rich black rock series at the bottom of Datangpo formation in Guizhou Songtao area, remains to be further explored the necessity.Based on the field profile measurement, indoor core logging and integrated on a large number of literature, integrated use of multi-disciplinary knowledge of petrology, geochemistry and sedimentology, this paper have made a detailed analysis on the petrological characteristics and element geochemical characteristics and the characteristics of organic matter of the black rock series at the bottom of the Datangpo Formation in Guizhou Songtao area.Lithology at the bottom of the Datangpo Formation is mainly carbonaceous shale, containing manganese carbonaceous shale, rhodochrosite, calcium Rhodochrosite and a small amount of volcanic tuff, tuffaceous clay rock.The sedimentary sequence from lithology is "lower fine upper thick".Element analysis of the black rock series at the bottom of Datangpo formation appeared that this set of strata formed in passive continental margin, deposited on the anoxic environment, sediment sources are mainly terrigenous detrital. And the sedimentary environment is different between manganese layer and carbonaceous shale. Tectonic setting of the manganese layer is deep water faulted basin, water conditions were manganese rich and rich in organic matter and strong reduction- lag deposit environment, main sediment sources is the supplement of the hot water activity. Climatic conditions of this set of strata sedimentary period was warm humid climate, tectonic activities in this period was moderate intensity.Study on the characteristics of organic matter in black rock series shows that organic carbon content all is more than 1%, have the characteristics of good hydrocarbon source rock; organic matter type was mainly I kerogen, also shows a good hydrocarbon source rock; the maturity of organic matter reached 5.58%~5.66%, which reached an over mature stage. So the black rock series of Datangpo formation has produced a lot of oil and gas in a certain period of the geological history. Under certain geological conditions, this set of strata is a set of high quality source rocks, which can provide the source of oil and gas to overlying strata.Comprehensive research on petrology, geochemistry and organic matter, considered that this set of strata is formed in the passive continental margin sedimentary environment with hypoxia. During the early stage of the deposition, the fault depression basin formed in this area because of tectonic fault activity. Ancient natural gas from the mantle leakage rise along the fault zone, forming a large number of manganese rich hot water solution, and deposited a set of manganese in this area, called manganese deposit of “Datangpo type”. It is a major production area of manganese ore resources in our country.