关键词: 下扬子地区, 岩相古地理图, 油气潜景, 瘤石灰岩, 碳酸盐岩台地, 深水盆地, 殷坑组, 马鞍山, 岩相古地理学, 生油岩

Abstract: The Qinglong Group can be divided into four formations,i.e.Yinkeng Formation,Helongshan Formation,Biandanshan Formation and Dongmaanshan Formation.The first three formations belong to the Lower Triassic and the last one to the Middle Triassic.According to"single factor analysis and comprehensive mapping method",the petrography and lithofacies paleogeography of every formation of Qinglong Group has been studied.The paleogeographical features of Yinkeng Age and Helongshan Age in this region were characterized by shallow water elastic platform,shallow water carbonate platform,deep water slope and deep water basin,with water becoming deeper northwards.In Biandanshan Age,the deep water area gradually narrowed northwards but the shallow water sedimentary area was widened.Meanwhile,the shallow water banks were well developed.In Dongmaanshan Age,the whole Lower Yangtze Sea became a shallow water sedimentary area where gypsum lagoons,restricted sea,dolomite flats,dolo-micrite flats,banks,parabanks and embryonic banks were developed.The deep water basin and slope are beneficial to the preservation and transformation of organic materials.The isopach map of Lower Triassic dark coloured rooks has been drawn showing the distribution of possible source rocks of oil and gas.Oosparite and intrasparite which formed in shallow water banks,postpenecontemporaneous dolomites and structurally fractured limestone may be favorable for reserving oil and gas.Gypsum and anhydrite in Dongmaanshan Formation and dense micrite in all formations may serve as good cap rocks of oil and gas.From the combination of the formation,preservation and cap of oil and gas,it can be seen:(1)The formation,preservation and cap conditions are very good in Changzhuu,Liyang area in the eastern part and Tongling,Guichi,Anqing in the middle part where all the profitable conditions are concentrated;(2)In the western part,the good conditions of petroleum formation exist in the Yinkeng Formation,but the cap rocks are not good enough;(3)It can be inferred that in this region where the deep water deposits and the dark colour rocks are well developed,the primary traps such as Jurong type might be formed if there are structural fractures in rocks.