Abstract:

Xuefeng thrust nappe was located on the continental slope on the southeastern margin of Yangtze fossil plate during Sinian-Silurian,and evolved progressively into Xuefeng ancient land along with the ascending and erosion of "Jiangnan uplift" during Caledonian movement.The pattern of paleofold in Xuefeng thrust nappe was near recumbent fold thrusting toward northwest during Caledonian.The frontal zone of the thrust nappe overrode large area of Paleozoic strata due to the multiple superimposition and thrusting from southeast to northwest during Indosinian-Yanshanian.Based on lithofacies zones and geophysical data,it is predicted that the thrusting distance of Xuefeng thrust nappe would not exceed dozens of kilometers,the depth of Lower Paleozoic overridden by the frontal zone is about 4000 m,and the overridden area is at least 3000 km².The lower assemblage(Sinian-Silurian) of Xuefeng thrust nappe consists of black carbonaceous mudstone,siliceous rock,phosphate rock and biogenic limestone deposited in a bathyal,stagnant and anaerobic environment with TOC value in the range of 0.01%-4.00% and good oil-generating conditions.Oil and gas pools had been formed in Caledonian,and 9 fossil oil pools and residual oil and gas pools have been discovered along the western margin of Jiangnan uplift.Reservoiring condition analysis of Huzhuang residual oil and gas pools shows that the oil and gas have come from the secondary hydrocarbon generatioin of the marine lower assemblage(Sinian-Silurian) and upper assemblage(Upper Permian-Lower Triassic).Hydrocarbons have experienced long-distance migration and have been accumulated in places having a certain preservation condition.Oil and gas pools have been formed during Late Yanshanian-Himalayan,the same as the finalization of Xuefeng thrust nappe.Therefore,it is believed that the lower assemblage of Xuefeng thrust nappe has relatively large potential of petroleum resources,and the arcuate zone along Zhenyuan-Kaili-Sandu is favorable for exploration.

Key words: recumbent fold, Huzhuang residual oil and gas reservoir, petroleum resources, Xuefeng thrust nappe