珠江口盆地早中新世碳酸盐岩生长发育、消亡的历程与受控因素

发布时间：2018-05-13 05:23

本文选题：珠江口盆地 + 珠江组　；参考：《岩石学报》2017年04期

【摘要】：碳酸盐岩(台地)的消亡是沉积学研究的前沿和热点科学问题。南海东北部珠江口盆地东沙隆起所发育的下中新统珠江组碳酸盐岩是我国海相碳酸盐岩的最高层位,东沙台地珠江组碳酸盐岩的生长、繁盛和消亡过程提供了中国南海乃至世界范围内一个典型的受构造、海平面变化和物源共同控制的研究实例。依据采自钻井岩心钙质超微化石和浮游有孔虫化石带将珠江组的上界置于钙质超微化石带NN4与NN5的界线,即中、下中新统界线,下界置于浮游有孔虫N4的底部附近,即位于中新统与渐新统界线。有孔虫属为N4-N8带,钙质超微化石为NN2-NN4带,底界年龄为23.03Ma,顶界年龄为15.97Ma,地震反射上位于T40-T60之间。而其中碳酸盐岩地层最早于21Ma左右开始生长,最晚于16.5Ma被泥岩淹没。早期的东沙隆起北低南高,21Ma以后,东沙隆起沉降而丧失了向珠一凹陷提供物源的功能,沉降较快的东沙隆起北北部地区发育碳酸盐岩;初期为一套碳酸岩缓坡沉积,20Ma以后隆起整体被淹没,开始了大规模的碳酸盐岩建造,实现了由碳酸盐岩缓坡向台地的转变,随沉降向南推移,隆起逐渐转变为北高南低,整个碳酸盐岩台地持续向东南方向退缩,台地沉积逐渐萎缩为局部礁滩复合体,北部古地貌的高部位残存零星点礁;16.5Ma以后,沉降中心向珠二凹陷迁移,北部、北西部碎屑物质持续向东沙隆起前积导致台地消亡。结合珠江组沉积时期的地质事件的分析,本文认为早期碳酸盐岩的消亡是由于这一时期的全球海平面下降到最低位,引起区域上的物源供给加快,灰岩直接被北部沉积物退覆淹没所致;20±0.5Ma~18.3±0.5Ma的碳酸盐岩的消亡时间受制于沉降造成的相对海平面的变化,基底的火山作用及沉降中心的迁移等事件,最晚一期碳酸盐岩(流花地区碳酸盐岩)的消亡应该是构造反转后,北部物源对凹陷的持续填平补齐作用引起碳酸盐岩的生长环境变化所致。由此看,陆源碎屑的注入、沉降中心的迁移、相对海平面的升降及原始古地貌形态是碳酸盐岩生长发育及消亡的主要控制因素。
[Abstract]:The extinction of carbonate rocks (platforms) is a hot scientific issue in sedimentology. The carbonate rock of the Lower Miocene Pearl River formation developed from the Dongsha uplift in the Pearl River mouth basin in the northeast South China Sea is the highest layer of marine carbonate rock in China. The process of prosperity and extinction provides a typical example for the study of tectonic, sea level change and provenance in the South China Sea and even in the world. According to the calcareous ultrafossils and planktonic foraminiferal fossils collected from drilling cores, the upper boundary of the Pearl River formation is placed in the boundary between NN4 and NN5 of the calcareous ultrafossil zone, that is, the boundary of the middle and lower Miocene, and the lower boundary is located near the bottom of the planktonic foraminifera N4. It is located at the boundary between Miocene and Oligocene. The foraminifera belongs to N4-N8 zone, the calcareous ultrafossils are NN2-NN4 zone, the lower boundary age is 23.03 Ma, the top boundary age is 15.97 Ma, and the seismic reflection is between T40-T60. The carbonate strata began to grow around 21Ma and later than 16.5Ma was submerged by mudstone. After 21 Ma of the early Dongsha uplift, the Dongsha uplift lost the function of supplying the source material to the Zhuyi sag, and carbonate rocks developed in the northern part of the Dongsha uplift. In the early stage, a set of carbonatite gentle slope deposits were inundated. After 20 Ma, the uplift was inundated, and the large-scale carbonate rock formation was started, which realized the transition from carbonate rock gentle slope to platform. The uplift gradually changed to the north high and the south low with the subsidence to the south. The whole carbonate platform continues to shrink southeast, and the platform deposits gradually shrink into a local reef and beach complex. After 16.5 Ma, the sedimentary center of the carbonate platform migrated to the Zhuer Sag, and the northern part of the paleogeomorphology remained in the high part of the paleogeomorphology after 16.5 Ma. The accumulation of clastic material in the north and west leads to the extinction of the platform. Based on the analysis of the geological events in the sedimentary period of the Pearl River formation, it is concluded that the early carbonate rock extinction was due to the global sea level falling to the lowest level during this period, which led to the acceleration of the regional provenance supply. The extinction time of carbonate rock with 20 卤0.5Ma~18.3 卤0.5Ma caused by direct submergence of the northern sediments is restricted by the relative sea level change caused by subsidence, the volcanism of the basement and the migration of the subsidence center, etc. The last stage of carbonate rocks (carbonate rocks in Liuhua area) should be due to the change of the growth environment of carbonate rocks caused by the continuous filling process of the northern provenance to the sag after the structural inversion. Therefore, the injection of continental clastic debris, the migration of subsidence center, the relative sea level rise and fall and the primitive paleogeomorphology are the main controlling factors for the growth, development and extinction of carbonate rocks.
【作者单位】：油气藏地质与开发工程国家重点实验室(成都理工大学);成都理工大学沉积地质研究院;中国地质调查局成都地质调查中心;中海石油(中国)有限公司深圳分公司研究院;
【基金】：国家自然科学基金项目(41672102)资助
【分类号】：P588.245

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