CLASSIFICATION OF FORELAND BASINS AND ASPECTS OF HYDROCARBON RESOURCES

Foreland basins can be classified into 5 types in accordance with their tectonic settings: periland foreland basin, retroarc foreland basin, broken foreland basin, hinterland foreland basin and strike slip foreland basin. Foreland basins are formed in compressional tectonic environment and show some similar characteristics of formation. Such as discordance of depocentre and subsidence centre; 3 segment of subsidence curve showing steep, gentle and steep; and 3 to 5 deformation zones as a result of compression in sediments of foreland basins, are the common characters. The filling patterns and basinal structures are different in foreland basins formed in different tectonic settings and showed different hydrocarbon potential. Periland foreland basin is flextural basin formed in subducting plate resulted from continental-continental collision. It is generally transformed from rifting basin of passive continental margin. The basin showed dual-layer structure of filling. The flysch foreland basin with great thickness was developed in the early stage and thick source rocks were deposited; and molasse foreland basin with coarsing-upward sequence was developed in the late stage and thick reserviors was formed. This kind of foreland basin is the most favorable petroliferous basins. Retroarc foreland basin was related to A-type subduction and could be transformed from retroarc rif-ting basin. Basin filling can be in dual-layer or single layer patterns. Volcanic-flysch forelang basin with thick sediments was developed in the early and source rocks were relatively thick; and volcanic-molasse foreland basin was developed in the late. This kind of foreland basin showed favorable hydrocarbon potential. The formation of broken foreland basin is due to basement involved foreland deformation, which resulted in isolated basins separated by block uplift and basement fold. The sediments is thin and hydrocarbon potential is poor in the basin. Hinterland foreland basin was formed in the interior of a plate and was far away from collisional orogenic belt. It may be related to long distance effect of collisional orogenic zone. The basin was filled in dual-or single-layer patterns and dominated by molasse foreland basin with little development of early flysch. This kind of foreland basin showed certain hydrocarbon potential.Strike-slip foreland basin was developed on both sides of main continental strike-slip system, accompanying with pull-apart basin. The basin filling pattern was single layer structured and molasse foreland basin was developed.The depocentre were obviously arranged in en echelon. Hydrocarbon potential in the basin was limited.The structures of foreland basin was asymmetric.Piedmont thrust, foreland depression, front slope and fron uplift were successively developed from orogenic ane to basin, in which distribution of hydrocarbon accu-mulation was different: a) hydrocarbon was rnainly distributed in fods of hanging wall of piedmont thrust; b)hydrocarbon was entrapped in stratigraphic and diagenetic traps in foreland depression; c) sedimentary wedge thenned or pinch out towards the front slope, so accurnulation in sand driies sealed by upper-dip pinch out orstraopaphic onlap can be formed; and d) large scale of anticline can be developed in front uplift, such as triangeare, drape anticline, and faulted fold structures and so on are habitat of hydrocarbon.