Tectonic Evolution And Its Control On Coal-measure Source Rocks In Zhu-3Depression Of Pearl River Mouth Basin

Based on the plate tectonics theory, analyse tectonic structure and evolution inZhu-3depression of Pearl River Mouth Basin via the balanced-section techniqueThen according to seismic sections, divide the depression into several kitchens anddiscuss their characteristics. At last but not the least, obeying the principle co-controlof source and heat, and judging by the distribution of prolific gas depressions in thenorthern SCS (South China Sea), discuss the tectonic control on coal-measure sourcerocks. Major research results as follows:Firstly, surrounded by the paleo-Asian, circum-Pacific and Tethyan tectonicdomains, Zhu-3depression is one of the non-volcanic passive continental margin inCenozoic era. In response to Shenhu, Zhuqiong, Nanhai and Dongsha movement,Zhu-3depression has experienced fault sag stage (K12-E3), depression stage (E213-N1)and neotectonism stage (N21-Q), where are intersected, superposed or compoundedby New Neocathaysian, Nanhai System, and Reversed S-shaped Structural Belt.Fault sag stage was outstanding with multistage episodic rifting, and the third onewas convenient for coal accumulation. At depression stage, thermal subsidence wasin priority, and fold structure inversion occurred somewhere. The very strongmovement at neotectonism stage and inversion structure made Zhu-3depressiondifferent from the typical passive continental margin basin and become a new type innorthern SCS.Secondly, the faults controlling sags usually active weakly, then strongly, andlater weakly again in Zhu-3depression, characterized with division and linkage.Sedimentary center migrate like seesaw, along with fracture systems sometimesbreaking up, or combining a total one. Zhu-3south fault is the most representativeone.Thirdly, there are14sub-sags in Zhu-3depression, which are face to face, backto back, in serial or in parallel to form sequence styles of gentle slope, steep slopecontrolled faults and fault terrace. According to the characteristics of the structureand sedimentary facies, the gentle slope belts with relative simple tectonic activitiesin Wenchang Aand Wenchang B sag are better for peat accumulation.Fourthly, the tectonics has controlled formation and thermal evolution history ofcoal-bearing stratum. At early Oligocene, with stable subsidence and overcompensation filling, the gentle slope belts such as the northern Wenchang A sag should become coal-rich zones as a result of the very wide and superior coalaccumulation for a long time. What’s more, with the high geothermal gradient andhuge thick post-rift sequence, the northern Wenchang A sag was advantageous fortectonic-thermal evolution. So the northern Wenchang A sag has become the mostpotential area for coal-bearing source rocks due to the remarkable coupling relationsbetween source rocks and heat.