科研之友
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摘要
With a shallow depth, the marine strata in the central uplift of the South Yellow Sea basin is the focus target of oil and gas exploration. However, due to lacking drilling data, the geological age and strata attributes of this area are controversial for a long time. Well CSDP-02 of the "Continental Shelf Drilling Program" is the first borehole in the central uplift, also the deepest whole-coring well in the South Yellow Sea basin. Based on the cores, well logs and multichannel seismic data, this paper clarifies the geological age and rock types of Mesozoic-Paleozoic strata in the central uplift. The strata below the Neogene sedimentary filling is the lower Qinglong Formation of Lower Triassic, the Dalong-Longtan Formation and Gufeng-Qixia Formation of Permian, the Chuanshan-Huanglong-Hezhou-Gaolishan Formation of Carboniferous, Wutong group of Devonian, Gaojiabian Formation of Silurian and Ordovician. Based on the drilling results, the distribution of Mesozoic-Paleozoic marine sedimentary strata of the uplift is defined and the long debate about the properties of marine residual strata can be ended. In addition, the reflection features and corresponding geological interfaces of seismic reflectors (T2, T8, T9, T10, T11) are inferred. Of them, T2 is the bottom boundary of the Neogene sediment system as well as the marker bed of the research area with high energy, stable waveforms. T8 is the Indosinian surface, which corresponds to the top of Qinglong Formation with high amplitudes and low frequency. T9 is a reflection of wave trough with high amplitudes and low-medium frequency, which we propose is the reflection of the bottom of Dalong Formation. With obvious energy variation in line XQ09-2, T10 is the reflection of wave peak and represented by medium-high amplitude and high frequency and T11 is a discontinuous reflector of Devonian. The strata distribution of the central uplift is influenced by the tectonic movement of the South Yellow Sea basin. Specifically, the strata are almost horizontal in the early Paleozoic with little faulting. During the Caledonian, the upper Silurian and lower Devonian are lost. Strata of Carboniferous-Permian developed extensively, the maximum thickness of the Permian is 1900 meter. To Mesozoic, denuded by the Indochina movement, while the residual strata is mainly lower Triassic with great thickness variations.
