Research On The Tectonic Relation Between The South Yellow Sea Basin And Its Adjacent Area And Distribution Characteristic And Tectonic Evolution Of The Mesozoic-Paleozoic Marine Strata

The South Yellow Sea basin is located on the east of the Yangtze block. It is the extension of lower Yangtze block in the Yellow Sea. The South Yellow Sea basin is a huge superposed basin composed of Paleo-Mesozoic marine facies basin and Meso-Cenozoic terringenous sedimentary basin. In the past forty years, the petroleum geological exploration has aimed at Meso-Cenozoic terringenous sedimentary basin, but there was no breakthrough of industrial oil and gas discoverer yet. In recent years, the Pale-Mesozoic marine facies basin has been paid more and more attention as a new hydrocarbon exploration target. In resent years, geophysical survey aiming at these potential strata in the South Yellow Sea has been implemented by Qingdao Institute of Marine Geology. The marine regional geological survey of Nantong sheet in the South Yellow Sea (2002-2006) finished 1727.5 km seismic survey. The Pre-Tertiay hydrocarbon stratege survey in the South Yellow Sea project (2005-2009) carried out 3200 km seismic measurement, and more than 3000 km gravity and magnetic data had been acquired at the same time. Based on previous research result and the new seismic, gravity and magnetic data, this paper analyzed the tectonic framework of the South Yellow Sea basin and its adjacent area, divided the stratigraphic sequence, discussed the distribution and structure characteristic of Paleo-Mesozoic marine strata and the evolution process of marine Paleo-Mesozoic basin. The integrated geological and geophysical interpretation method was used in the research.A new apparent density inversion technology based on potential field separation and downward continuation in a large distance using iteration method was used in gravity data processing. The result helped to locate the position of the deep major fault, especially the extension of the block boundary fault and the other important geological boundary. The distribution of the faults and volcanic rocks were analyzed by gravity and magnetic data interpretation. New seismic data interpretation combined with the drilling data and geological correlation between land and sea were used to classify the marine Paleo-Mesozoic stratigraphic sequence. Geologic models of two profiles were rectified by 2.5D gravity, magnetic and seismic joint inversion and modeling. The depth of top surface of the marine Paleo-Mesozoic strata was got by seismic interpretation; undulation of the bottom surface was derived by 3D magnetic inversion. The residual thickness map of Triassic Qinglong limestone and Permian strata was also drawn in order to understand the distribution and structure feature of the marine Paleo-Mesozoic strata.In this paper, the junction zone in between the Yangtze massif and Sino-Korea massif was defined as Sujiao-Gyeonggi orogenic belt. Jiashan-Sihong-Lianyungang fault and the fault at north edge of Qianliyan in the sea was the boundary fault between Yangtze block and Sujiao orogenic belt. Jiangshan-Shaoxing-Kongju fault was delimitated as the boundary fault between Yangtze and South China massif. The dominant tectonic structures trend was in NE and EW direction. To the east, the Yangtze block not only includeed the South Yellow Sea, but also a small part in the central Korea Peninsula. The South Yellow Sea basin was the main part of the Lower Yangtze block, its stable Archean nucleus was beneficial to minimize the influence of tectonic movement. Thus the Yellow Sea basin was comparatively more stable than the adjacent area even though its tectonic environment was complicated and endured several tectonic movements. The volcanic and magma activities in the basin were general small scales, and which favored the preservation of the marine Paleo-Mesozoic strata.The Subei basin and the South Yellow Sea basin were an integral basin. It developed integrate Caledonian-Hercynian-Indosinian marine sequences. The basement was composed of Archean and Proterozoic metamorphic rocks. The basin developed two main tectonic stages:the prototype deposition and the late deformation. The prototype deposition stage started from Sinian and finished in the early Triassic. During the late Triassic and Quaternary, the basin had been transformed by tectonic movements. The basin could be divided into five Himalayan tectonic units, the northern depression, the central uplift, the southern depression and Wunansha uplift. The tectonic framework of marine Pale-Mesozoic strata was similar to that of the Himalayan, it also could be divided into two depressions and one uplift. But the position and trend of the units were different. The depth of the bottom surface of Paleo-Mesozoic marine strata varied from 4-13 km, the average depth was 8km. The thickness of the marine sequence was mainly controlled by the undulation of the basement, but the influence of the Indosinian movement can also be seen by the northeast-trending isopachous line. The thickness of the marine Paleo-Mesozoic strata was comparatively stable in the central uplift. The Sinian-lower Permian strata were widely spread in the basin, and the Sinian-Silurian strata had stable distribution. The distribution and thickness Devonian-lower Permian strata varied much in different area. The lower Triassic Qinglong formation and the upper Permian Dalong and Longtan formation were widely distributed in the southern depression and Wunansha Uplift of the South Yellow Sea basin, the distribution of this sequence in the northern depression was very limited, in the central uplift, few had been left due to the combined effect of uplift and denudation. At present, the residual thickness of the lower Paleozoic was still unknown due to the limited data.