前陆盆地分析(中英文） .ppt

前陆盆地分析,主要内容,基本概念 构造特征 构造对沉积的控制作用 油气地质特点 中国中西部前陆盆地分析 讨论,一、基本概念,前陆，前陆盆地，前渊 前陆盆地体系 冲断带，褶皱带，前陆褶皱冲断带,1.Terminology:foreland,Foreland coast:(a)An extensive area of land,either high ground or low land,jutting out from the coast into a large body of water(usually the sea);a headland;a promontory.See also:cuspate foreland.(b)a prograded strip of low,flat land built by waves and currents at the base of a cliff;an initial stage in the development of a strand plain;(c)A part of the natural shore,located seaward of an embankment,that receives the shock of sea waves and deadens their force.,Glossary of Geology,1997,p247,Terminology,Foreland geog:The land lying in front of or adjoining other land and physiographically related to it.,Glossary of Geology,1997,p247,Terminology,Foreland glac geol:A lowland area,now or formerly covered by piedmont glaciers,or a glacio-isostatically depressed low-elevation area,which is covered with raised beach or marine deposits.,Glossary of Geology,1997,p247,Terminology,Foreland tect:The exterior area of an orogenic belt where deformation occurs without significant metamorphism.Generally the foreland is closer to the continental interior than other portions of the orogenic belt are.,Glossary of Geology,1997,p247,Terminology,Foreland 前陆:造山带边缘的稳定区。前陆通常处于克拉通边缘上，其下为大陆地壳。许多前陆区在造山运动中遭受了翘曲，也附带有表层褶皱冲断层带。造山带运动的主方向朝着前陆。造山带位于两稳定区之间，另一稳定区则称为后陆。,简明牛津地球科学辞典，1996,227,Terminology,Foreland basin:A linear sedimentary basin at a foreland tect.Syn:foredeep.,Glossary of Geology,1997,p247,Terminology,Foredeep:An elongate depression bordering an island arc or other orogenic belt.Cf:trench marine geog.A syn.of foreland basin.A syn.of exogeosyncline,so named because of its relative position,near the craton.,Glossary of Geology,1997,p247,Aubouin,1965,Terminology,pre-plate tectonic terminology:Foreland basins are one variety of the exogeosynclines of Marshal Kay(1951).,Terminology,Foredeep 前渊，陆外渊:与克拉通相邻的盆地，其中有隆起期间来自造山带的厚沉积物堆积，这些沉积物一般为非海相到浅海相的，通常在几百万年的沉积过程中发生了变形。,简明牛津地球科学辞典，1996,227,Foreland basin,Price and Mountjoy(1971)were among the first to use the word“foreland fold and thrust belt”for the Canadian Rocky Mountain belt,which falls within the foreland fold and thrust belt category as defined by Macqueen and Leckie(1992).(AAPG Memoir 55),Foreland basin,Price(1973),using the Western Canada foreland basin and fold belt as an example,qualitatively suggested that foreland basins owe their origins to their regional isostatic subsidence that results from the supracrustal load of a developing fold-thrust belts.It is this form of subsidence that creates the foredeep in which sediments accumulate.Refined quantitatively by Beaumont(1981)and others.,Foreland basin,Dickinson(1974)formally introduced the term“foreland basin”to describe the retro-arc and peripheral basins in which the basin-fill was deposited on continental crust or older rifted margin sedimentary prisms;he also discussed foreland basins and their plate tectonic settings.,Dickinson(1974)distinguished between peripheral foreland basins,which form on subducting plates in front of thrust belts that are synthetic to the subduction direction,and retroarc foreland basins,which develop on the overriding plates inboard of continental-margin magmatic arcs and associated thrust belts that are antithetic to the subduction direction.,Foreland basin,Foreland basin,Bally and Snelson(1980),St.John(1984)further categorized foreland basins and their associated fold belts as:Continental,multi-cycle basins,including cratonic margin composite basins and accreted margin basins.Foredeeps and underlying platforms,orBack-arc basins,depending on the details of the present or former tectonic setting.,Foreland basin,All foreland basins and fold belts are involved to some extent with both their plate tectonic settings and,particularly,their relationships to underlying earlier sedimentary basinscommonly platformal or continental margin basins.,Foreland basin,A foreland basin is considered to be a succession of sedimentary rocks deposited in a cratonic region adjacent to an active orogenic belt.Sediments are derived mainly from the orogenic belt and thicken toward it.Foreland basin sediments in proximity to the orogenic belt are commonly involved in post-depositional folding and overthrusting toward the craton,resulting in tectonic shortening and cannibalization of previously deposited material(Leckie and Smith,1992),Foreland Basin and Fold Belt,Macqueen and Leckie,1992AAPG Memoir 52,A foreland basin generally is defined as an elongate trough that forms between a linear contractional orogenic belt and the stable craton,mainly in response to flexural subsidence that is driven by thrust-sheet loading in the orogen(e.g.Price,1973;Dickinson,1974;Beaumont,1981;Jordan,1981,1995;Lyon-Caen&Molnar,1985).,Foreland basin,Important ancillary concepts that are equally entrenched in the literature are:(i)foreland basin sediment fill is wedge shaped in transverse cross-section,with the thickest part located directly adjacent to,or even partially beneath,the associated thrust belt(Jordan,1995)(ii)foreland basin sediment is derived principally from the adjacent thrust belt,with minor contributions from the cratonward side of the basin(Dickinson Crampton&Allen,1995).,Foreland basin,2.Foreland basin system,an elongate region of potential sediment accommodation that forms on continental crust between a contractional orogenic belt and the adjacent craton,mainly in response to geodynamic processes related to subduction and the resulting peripheral or retroarc fold-thrust belt.,Peter G.DeCelles and Katherine A.Giles,1996,Foreland basin system,it consists of four discrete depozones,referred to as the wedge-top,foredeep,forebulge and back-bulge depozones which of these depozones a sediment particle occupies depends on its location at the time of deposition,rather than its ultimate geometric relationship with the thrust belt.the longitudinal dimension of the foreland basin system is roughly equal to the length of the fold-thrust belt,and does not include sediment that spills into remnant ocean basins or continental rifts(impactogens).,Foreland basin system,The wedge-top depozone is the mass of sediment that accumulates on top of the frontal part of the orogenic wedge,including piggyback and thrust top basins.Wedge-top sediment tapers toward the hinterland and is characterized by extreme coarseness,numerous tectonic unconformities and progressive deformation.The foredeep depozone consists of the sediment deposited between the structural front of the thrust belt and the proximal flank of the forebulge.This sediment typically thickens rapidly toward the front of the thrust belt,where it joins the distal end of the wedge-top depozone.,Foreland basin system,The forebulge depozone is the broad region of potential flexural uplift between the foredeep and the back-bulge depozones.The back-bulge depozone is the mass of sediment that accumulates in the shallow but broad zone of potential flexural subsidence cratonward of the forebulge.This more inclusive definition of a foreland basin system is more realistic than the popular conception of a foreland basin,which generally ignores large masses of sediment derived from the thrust belt that accumulate on top of the orogenic wedge and cratonward of the forebulge.,Fig.5.Schematic diagram showing the deposition and burial of sediment particles(solid squares)in a foreland basin system.Barbed line indicates the zone of active frontal thrust displacement.Particle F1 is deposited and buried in the foredeep depozone.The zone of thrusting steps toward the foreland,incorporating F1 into the hangingwall of the orogenic wedge;particle W1 is deposited and buried in what is now the wedge-top depozone,above F1.The zone of thrusting steps back toward the hinterland(out of sequence);particle F2 is deposited in the foredeep depozone,while particle W2 is deposited in the wedge-top depozone.Particles retain their original depozone signatures,unless they are eroded from the orogenic wedge and reincorporated into the active depositional regime.In this fashion,the boundary between the wedge-top and foredeep depozones shifts rogressively toward the foreland through time.Similarly,particles deposited in the fault forebulge and back-bulge depozones could eventually become buried by foredeep particles.,Fig.7.(A)Flexural profile for a thin,infinite,elastic plate floating on a fluid substrate,subjected to a rectangular topographic load 100 km wide and 2.5 km high located on its left side,but not shown,and a load of sediment that fills the foredeep to the level of the forebulge.The density of the load is2650 kg m-3and density of the basin fill is 2400 kg m-3.The resulting flexural parameter(a)is 97.6 km.The area outlined by the box is magnified in(B).(B)Magnified plot of the forebulge and back-bulge areas shown in(A).Note the change in vertical scale.Sloping line from forebulge crest represents a linear approximation of an exponential,aggradational profile connecting the thrust belt and the undeformed foreland.Aggradation up to this profile would produce more than 100 mof accumulation.Area outlined in box is shown in further detail in(C).,Fig.9.Isopach maps(contours in metres)showing proposed foredeep,forebulge and back-bulge depozones in Lower Cretaceous fluvial and lacustrine deposits associated with the eastward-vergent,retroarc Sevier fold-thrust belt in the western interior foreland basin of the United States.(A)The Kootenai Formation in south-western Montana,USA,which exhibits evidence for a bifurcated forebulge axis(bold Y-shaped lines)and a broad back-bulge depozone(data from DeCelles,1984).(B)The Cedar Mountain Formation in east-central Utah,USA(after Currie,1994);zero-thickness contour is a result of erosion,not depositional pinch-out.Note the region of irregular thickening(before erosional truncation)in the backbulge region.Solid circles represent surface sections from Currie(1994)and Craig(1955);open circles represent well datafrom Currie(1994),Craig(1955)and Sprinkel(1994).,The generally accepted definition of a foreland basin attributes sediment accommodation solely to flexural subsidence driven by the topographic load of the thrust belt and sediment loads in the foreland basin.Equally or more important in some foreland basin systems are the effects of subduction loads(in peripheral systems)and far-field subsidence in response to viscous coupling between subducted slabs and mantlewedge material beneath the outboard part of the overlying continent(in retroarc systems).,Foreland basin system,Fig.10.(A)Schematic diagram showing the principal loads in peripheral foreland basin systems.In addition to the topographic and sediment loads,a subduction load,due to a vertical shear force(V)and bending moment(M)on the end of the subducted slab,may exist at depths of 50200 km(Royden,1993).(B)Retroarc foreland basin systems involve topographic and sediment loads as well as a dynamic slab load caused by viscous coupling between the subducting slab,overlying mantle-wedge material and the base of the overriding continental plate(Mitrovica et al.,1989;Gurnis,1992).(C)Accumulation in the wedge-top depozone takes place under competing influences of regional,load-driven subsidence(downward pointing arrows),and local uplift of the orogenic wedge in response to shortening and thickening(upward pointing arrows).,Wedge-top depozones accumulate under the competing influences of uplift due to forward propagation of the orogenic wedge and regional flexural subsidence under the load of the orogenic wedge and/or subsurface loads.Whereas most of the sediment accommodation in the foredeep depozone is a result of flexural subsidence due to topographic,sediment and subduction loads,many back-bulge depozones contain an order of magnitude thicker sediment fill than is predicted from flexure of reasonably rigid continental lithosphere.Sediment accommodation in back-bulge depozones may result mainly from aggradation up to an equilibrium drainage profile(in subaerial systems)or base level(in flooded systems).Forebulge depozones are commonly sites of unconformity development,condensation and stratal thinning,local fault-controlled depocentres,and,in marine systems,carbonate platform growth.,Foreland basin system,The wedge-top comprises all sediment that accumulates above the active orogenic thrust wedge,and is characterized by Textural immaturity(especially in nonmarine systems),Progressive deformation,widespread tectonic unconformities andregional thinning toward the orogenic belt.Explicit inclusion of the wedge-top depozone in the definition ofa foreland basin system requires that basin models be geometrically parameterized(in transverse cross-sections)with a doubly tapered prismatic shape,rather than a wedge shape.The distal part of the wedge-top merges with the proximal part of the foredeep depozone.,Foreland basin system,The foredeep depozone constitutes the thickest part of the foreland basin system;it characteristically Thickens abruptly toward the thrust belt,has spatially divergent chronozones,and is deposited by a variety of distal fluvial,lacustrine,deltaic and marine depositional systems.Although foredeep depozones are relatively well understood,they should be considered in the context of adjacent wedge-top and forebulge depozones in order to provide unambiguous information about orogenic processes.,Foreland basin system,Forebulge and back-bulge depozones are typically thin relative to the distal part of the wedge-top and the foredeep depozones.Regional unconformities,well-developed palaeosols,distal fluvial,aeolian and shallow-marine deposits(including both fine-grained siliciclastic and carbonate rocks),and regionally subparallel chronozones.,Foreland basin system,3.基本概念:冲断层,Thrust fault:A fault with a dip of 45or less over much of its extent,on which the hanging wall appears to have moved upward relative to the footwall.Horizontal compression rather than vertical displacement is characteristic feature.Cf:normal falut.Partial syn:reverse fault.Syn:thrust,overthrust.Thrust:(a)An overriding movement of the crustal unit over another,as in thrusting faulting.(b)thrust sheet.,Glossary of Geology,1997,p664,基本概念:冲断层,Thrust:逆掩断层：一种低角度（通常小于45）的逆断层，有显著的倾向滑动分量，上盘外伸出下盘。当同向逆掩断层组成一个双逆掩带时，可形成叠瓦扇构造，这种构造可以成为逆掩边界。单个的逆掩断层典型地表表现为陡冲断层和缓倾断层组成的一个阶梯状轨迹。,简明牛津地球科学辞典，1996,592,基本概念:冲断席,Thrust sheet:The body of rock above a large-scale thrust fault whose surface is horizontal or very gently dipping.Syn:thrust block;thrust nappe;thrust plate.Thrust slice:A relatively thin body of rock bounded above and below by thrust faults within a zone of thrusting.Var:slice.Thrust system:An array of geometrically similar and kinematically related thrust faults.,Glossary of Geology,1997,p664,基本概念:推覆体,Nappe 推覆体 熔岩流 覆盖层:来源于法语nappe,意为“覆盖”。指一个逆掩块体或褶皱体，其褶皱翼和轴大致成水平。,简明牛津地球科学辞典，1996,392,基本概念:推覆体,Nappe hydrol:a sheet of water overflowing a dam.Nappe volc:lava flow.Nappe outlier