THE INDEPENDENT LOWER YANGTZE BLOCK AND MESOZOIC REFORMED RESIDUAL BASINS
Ye Zhou1, Ma Li2, Liang Xing1, Wu Genyao3, Xu Keding4, Zhang Tingshan1
1. School of Resources and Environment, Southwest Petroleum Institute, Chengdu 610500; 2. Jiangsu Oilfield Branch Company, China Petroleum & Chemical Corp., Yangzhou, Jiangsu 225009; 3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029; 4. Zhejiang Oilfield Company, China National Petroleum Corp., Hangzhou 310013
There was a lot of particularities in the Lower Yangtze Block, evidenced from the paleolatitudes, occurring of volcanic rocks and granitoids, regional mineralization, sedimentary formation and tectonic deformation, which meant that the Lower Yangtze Block must be an independent tectonic unit during Late Paleozoic and Early Mesozoic, separated from the Yangtze craton. It collided the Jiao-Liao craton in the Yanshanian orogeny which created the Su-Lu orogen, and indented the Yangtze North China Block which amalgamated together in the Indosinian orogeny. So some reformed residual superimposed basins developed in the Lower Yangtze area during Mesozoic. The main characteristics of the basins were as follows. 1)The strata of foreland basins in age of Late Indosinian and Early Yanshanian periods and the strata of Middle Yanshanian continental facies were denuded strongly. 2)The strata mentioned above, together with the Paleozoic-Triassic marine facies strata, were evolved into the Yanshanian movement and experienced multi-phase deformation in Mesozoic. 3)The area reversed intensively in Late Cretaceous and Paleocene, so as to form a series of fault basins, which created a two-layer structure in the upper crust of the Lower Yangtze area. It resulted in complexity, difficulty and high risk of oil-gas exploration in the marine facies Paleozoic-Triassic and continental facies Mesozoic strata in the Lower Yangtze area, in addition, it brought up a situation that the secondly hydrocarbon generation and late pool formation could occur in the marine facies source beds.