浙西北前陆褶皱冲断带特征及上古生界含油气性

STRUCTURAL FEATURE AND OIL AND GAS POTENTIAL IN THE FORELAND FOLD AND THE THRUST BELT OF LATE PALEOZOIC IN NW ZHEJIANG PROVINCE

主要通过对晚古生代及中生代地层的岩石组合、岩相及构造特征的分析，认为浙西北地区直到早三叠世仍为一倾向东南的被动大陆边缘，中三叠世到白垩纪主要发育前陆磨拉石沉积；板块碰撞始于早三叠世晚期，逆冲推覆构造和冲褶席为浙西北地区的主要构造形式，推覆方向自南东向北西。浙西北地区残存的晚古生代地层中油气显示比较普遍（龙潭组显示最好），表明该区有一定油气勘探前景。该区晚古生代海相地层中的3套生储盖组合相互配套，其中油源岩在早、中侏罗世进入成熟阶段，现达成熟─高成熟或过成熟阶段；下三叠统有油源岩和储集岩，缺乏连续盖层。浙西北地区油气勘探的难题是聚集和保存条件，需要进一步研究其推覆构造及区域性滑脱面，并研究被陆相断陷沉积覆盖的海相地层潜山带的分布。

Through lithological and structural analysis for the Late Paleozoic and Mesozoic (Triassic and Jurassic) strata, this papersuggests that NW Zhejiang was a SE tilted passive continental margin till Triassic period and the foreland molasse was de-posited during the period from the Early Triassic to Cretaceous- Collision took place in the late Early Triassic period. Struc-tural analysis shows the tectonic pattern of the NW Zhejiang is of a foreland fold and thrust belt with vergence direction fromSE to NW. The structural styles of foreland fold and thrust belt are characterized by mu1ti-fold-duplexes, various folds andthrust nappes. In the resided Late Paleozoic strata of the NW Zhejiang, 0il and gas seep is relatively common, especially tothe Longtan Formation' This shows that there is certain prospect of oil and gas exploration in this area. Three sets of source-reservoir-cap rock combinations exist in the Late Paleozoic marine strata of studied area. The source rock had reached maturestage in Early and Middle Jurassic period, now it has reached mature-high mature or over-mature stage; in Lower Triassicstrata, there are source and reservoir rocks but no cap rock. The difficulty in oil and gas exploration in the NW Zhejiang is tostudy and identify the accumulation and preservation conditions of oil and gas. There fore, it is necessary to further study thecharacteristics of thrust nappes, regional decollement face, and the marine strata composed of buried hills which are coveredby the later continental fault-depression deposits.