鄱阳盆地构造—沉积特征及其演化史

SEDIMENTO-TECTONIC FEATURES AND GEOLOGICAL EVOLUTION OF THE POYANG BASIN

鄱阳盆地是发育在江南—九岭和怀玉—官帽基底拆离造山带上的白垩-古近纪张扭性断陷盆地,明显受近南北走向的赣江走滑断裂系和前白垩系逆冲断裂系晚期反转的双重因素控制,呈“两坳夹一隆”的区域构造格局。受赣江、进贤—石门街走滑断裂夹持的南昌凹陷,呈近南北向凹凸相间展布格局。进贤—石门街走滑断裂以东地区,“南断北超”型断陷自南而北由北东走向渐转为北北东向展布,其源于晚印支-燕山期北东向逆冲断裂在晚期的反转作用,西缘和北部受赣江断裂系东枝走滑断裂影响明显而发生转向。鄱阳盆地经历了早白垩世晚期(冷水坞组沉积期)拉分盆地、晚白垩世早-中期(周家店组—南雄组沉积早期)走滑张扭断(坳)陷盆地、晚白垩世晚期(南雄组沉积中-晚期)走滑伸展盆地和古近纪坳陷盆地等演化阶段,东南部断陷区(江埠—二甲村凹陷)由于喜马拉雅期的隆升剥蚀而只残存周家店组早期坳陷和周家店组中期—南雄组中期断陷两个发育阶段的沉积。

The Poyang Basin, controlled by the S-N-striking Ganjiang strike-slipping fracture system and inversed pre-Cretaceous thrusting faults, was a Cretaceous-Paleogene transtensile fault-depression which occurred on the Indosinian intracontinental orogens in central-northern Jiangxi province. The basin had a tectonic framework of ＂one rise sandwiched in between two depressions＂. Based on the recent data of seismic, drilling and surface outcropping surveys, the sedimentary records, regional fractures and sub-order units of the basin were described in details. The basin＇s evolution could be divided into four stages. A pull-apart basin appeared to the east of Nanchang in late Early Cretaceous, with the sedimentary records being the Lengshuiwu Formation, which covered a limited area and indicated the Ganjiang fracture being sinistral strike slipping. A transtensile fault-depression created in early-middle Late Cretaceous, with the sedimentary records being the Zhoujiadian Formation and lower part of the Nanxiong Formation, when the basin enlarged obviously. In late Late Cretaceous, the Poyang Basin became a strike slip stretch one, with the sedimentary records being middle-upper part of the Nanxiong Formation. During this stage the Ganjiang fracture was characterized by dextral strike-slipping. In Paleogene, the Poyang Basin developed as a depression, with the strata named the Qingjiang Formation in age of Paleocene. The Late Himalayan orogeny in Neogene resulted in regional uplifting and basin closure, and some sedimentary strata were not preserved, especially in the Southeast Depression of the basin, where the Qingjiang Formation and upper part of the Nanxiong Formation were eroded. In the areas of thick deposition preserved, for example, the Xian, gtang-Erjiacun Sag, oil-gas exploration might be hopeful in the marine source rocks, with the reservoirs being both the Permian-Triassic and the basal sandstones of Cretaceous. The study on the Poyang Basin had an important inspiration to understand the Meso-Cenozoic sedimentotectonic evolution and potential of oilgas exploration in Jiangxi.