Sequence Stratigraphy, Cyclostratigraphy And The Forming Conditions Of Hydrocarbon Source Rocks In Huanghekou Depression

After 20 years' studying and application, the sequence stratigraphy have been becoming a significant theory to study basin filling and an important method for resources estimation. It is supposed that tectonic subsidence, eustatic change of sea level and sediment supply rate are the controlling factors of sequence development in marine basins. But in lacustrine basins, the sedimentary process is very sensitive to climatic changes, the climate is also a very important factor controlling the sequence development and hydrocarbon source rock formation in lacustrine basins. However, the details about these controlling mechanisms are still poorly understood temporarily. Therefore, in this paper, the paleoclimate, paleoenvironment and their control over the formation of sequences and hydrocarbon source rocks are mainly discussed.Base on the systematic studies of sequence stratigraphy, micropaleontology, paleoclimatology, cyclostratigraphy and source rock geochemistry, some conclusions are extracted;1. Through sequence stratigraphic study, the features of sequence boundary are summarized. Paleogene is divided into 4 second-order sequences and 14 third-order sequences. Afterwards, the sequence stratigraphic framework of Eogene in Huanghekou area is established. Especially, according to the saltatory evolution of the palynological assemblage in well BZ25-1-1, a significant hiatus is discovered.2. Based on the sequence stratigraphic framework, according to the analysis of spore-pollen, algae fossils and litho-face characteristics, the paleoclimatic and paleoenvironmental conditions has been reconstructed in Paleogene Huanghekou depression, Bohaiwan basin. Furthermore, the information function of the palynological assemblage in well BZ34-2-1 was computed, and the results were compared with the stratigraphic cycles.3. With wavelet analytic technique, the study of cyclostratigraphy is carried in the representative sequence, and 11 eccentricity cycles including 26 obliquity cycles are recognised. Then, the application of astronomical geochronology is discussed, and the time range of SQ32 is estimated as 1.1Ma.4. The characteristics of the three horizontal hydrocarbon source rock beds drilled by well BZ25-1-5 has been analyzed and compared with the paleoclimatic conditions. The results showed that the lake productivity affected by humid climatic conditions may have been the most important parameter controlling the formation of hydrocarbon source rocks.