Sedimentary basinFrom Wikipedia, the free encyclopediaThis article or section may be written in a style that istoo abstractto be readily understandable bygeneral audiences.Pleaseimproveit by defining technical terminology, and by adding examples. (January 2013)

Cenozoicsedimentary basins in the U.S. (from USGS)Sedimentary basinsare regions of the earth of long-termsubsidencecreating accommodation space for infilling by sediments.[1]The subsidence results from the thinning of underlying crust, sedimentary, volcanic, and tectonic loading, and changes in the thickness or density of adjacent lithosphere.[2]Sedimentary basins occur in diverse geological settings usually associated withplate tectonicactivity. Basins are classified structurally in various ways, with a primary classifications distinguishing among basins formed in various plate tectonic regime (divergent, convergent, transform, intraplate), the proximity of the basin to the active plate margins, and whetheroceanic,continentalortransitional crustunderlies the basin.[1][2][3]Basins formed in different plate tectonic regimes vary in their preservation potential. On oceanic crust, basins are likely to be subducted, while marginal continental basins may be partially preserved, and intracratonic basins have a high probability of preservation.[2]As the sediments are buried, they are subjected to increasingpressureand begin the process oflithification. A number of basins formed in extensional settings can undergoinversionwhich has accounted for a number of the economically viable oil reserves on earth which were formerly basins.Contents[hide] 1Methods of formation 1.1Lithospheric stretching 1.2Lithospheric compression/shortening and flexure 1.3Strike-slip deformation 2Ongoing development 3Study of sedimentary basins 4See also 5References 6External linksMethods of formation[edit]Sedimentary basins form primarily inconvergent,divergentandtransform settings. Convergent boundaries createforeland basinsthrough tectonic compression of oceanic and continental crust duringlithospheric flexure. Tectonic extension at divergent boundaries where continental rifting is occurring can create a nascent ocean basin leading to either an ocean or the failure of the rift zone. In tectonic strike-slip settings, accommodation spaces occur as transpressional, transtensional or transrotational basins according to the motion of the plates along the fault zone and the local topographypull-apart basins.[2]Lithospheric stretching[edit]If thelithosphereis caused to stretch horizontally, by mechanisms such asridge-pushortrench-pull, the effect is believed to be twofold. The lower, hotter part of the lithosphere will "flow" slowly away from the main area being stretched, whilst the upper, cooler and more brittlecrustwill tend to fault (crack) and fracture. The combined effect of these two mechanisms is for the Earth's surface in the area of extension to subside, creating a geographical depression which is then often infilled with water and/or sediments. (An analogy might be a piece of rubber, which thins in the middle when stretched.)An example of a basin caused by lithospheric stretching is theNorth Sea- also an important location for significanthydrocarbonreserves. Another such feature is theBasin and Rangeprovince which covers most of the USA state of Nevada, forming a series ofhorstandgrabenstructures.Another expression of lithospheric stretching results in the formation of ocean basins with central ridges; TheRed Seais in fact an incipient ocean, in a plate tectonic context. The mouth of the Red Sea is also a tectonictriple junctionwhere the Indian Ocean Ridge, Red Sea Rift andEast African Riftmeet. This is the only place on the planet where such a triple junction in oceanic crust is exposedsubaerially. The reason for this is twofold, due to a high thermal buoyancy of the junction, and a local crumpled zone of seafloor crust acting as a dam against the Red Sea.Lithospheric compression/shortening and flexure[edit]If a load is placed on the lithosphere, it will tend to flex in the manner of an elastic plate. The magnitude of the lithospheric flexure is a function of the imposed load and theflexural rigidityof the lithosphere, and the wavelength of flexure is a function of flexural rigidity alone. Flexural rigidity is in itself, a function of the lithospheric mineral composition, thermal regime, and effective elastic thickness. The nature of the load is varied. For instance, theHawaiian Islandschain of volcanic edifices hassufficient massto cause deflection in the lithosphere.Theobductionof one tectonic plate onto another also causes a load and often results in the creation of a foreland basin, such as the Po basin next to the Alps in Italy, the Molasse Basin next to the Alps in Germany, or the Ebro basin next to thePyreneesin Spain.Strike-slip deformation[edit]Deformation of the lithosphere in the plane of the earth (i.e. such that faults are vertical) occurs as a result of near horizontal maximum and minimumprincipal stresses. The resulting zones of subsidence are known as strike-slip orpull apart basins. Basins formed through strike-slip action occur where a vertical fault plane curves. When the curve in the fault plane moves apart, a region oftranstensionresults, creating a basin. Another term for a transtensional basin is arhombochasm. A classic rhombochasm is illustrated by theDead Searift, where northward movement of theArabian Platerelative to theAnatolian Platehas caused a rhombochasm.The opposite effect is that oftranspression, where converging movement of a curved fault plane causes collision of the opposing sides of the fault. An example is theSan Bernardino Mountainsnorth ofLos Angeles, which result from convergence along a curve in theSan Andreas faultsystem. TheNorthridge earthquakewas caused by vertical movement along local thrust and reverse faultsbunching upagainst the bend in the otherwise strike-slip fault environment. In Nigeria, the dominant type of basement rock intersected by wells drilled for hydrocarbons, limestone, or water is granite. The three sedimentary basins in Nigeria are underlain by continental crust except in the Niger delta, where the basement rock is interpreted to be oceanic crust. Most of the wells that penetrated the basement are in the Eastern Dahomey embayment of western Nigeria. A maximum thickness of about 12,000 m of sedimentary rocks is attained in the offshore western Niger delta, but maximum thicknesses of sedimentary rocks are about 2,000 m in theChad basinand only 500 m in the Sokoto embayment.Ongoing development[edit]As more and more sediment is deposited into the basin, the weight of all the newer sediment may cause the basin to subside further because ofisostasy. A basin can continue having sediment deposited into it, and continue to subside, for long periods of geological time; this can result in basins many kilometres in thickness.Geologic faultscan often occur around the edge of, and within, the basin, as a result of the ongoing slippage and subsidence.Study of sedimentary basins[edit]The study of sedimentary basins as a specific entity in themselves is often referred to asbasin modellingorsedimentary basin analysis. The need to understand the processes of basin formation and evolution are not restricted to the purely academic. Indeed, sedimentary basins are the location for almost all of the world's hydrocarbon reserves and as such are the focus of intense commercial interest.SynclineFrom Wikipedia, the free encyclopedia

Instructural geology, asynclineis afoldwith younger layers closer to the center of the structure. Asynclinorium(pluralsynclinoriumsorsynclinoria) is a large syncline with superimposed smaller folds.[1]Synclines are typically a downward fold, termed a synformal syncline (i.e. a trough); but synclines that point upwards, or perched, can be found when strata have been overturned and folded (an antiformal syncline).Contents[hide] 1Characteristics 2Notable examples 3Gallery 4See also 5ReferencesCharacteristics[edit]On a geologic map, synclines are recognized by a sequence ofrocklayersthat grow progressively younger, followed by the youngest layer at the fold's center orhinge, and by a reverse sequence of the same rock layers on the opposite side of the hinge. If the fold pattern is circular or elongate circular the structure is abasin. Folds typically form during crustal deformation as the result of compression that accompaniesorogenicmountain building.Notable examples[edit] Powder River Basin,Wyoming, U.S.A. Sideling Hillroadcut alongInterstate 68in westernMaryland, USA, where theRockwell Formationand overlyingPurslane Sandstoneare exposed. WesternLake Superior, which occupies a basin created by theMidcontinent Rift System Saou, acommunein theDrmedepartment in southeastern France The Catlins, an area in the southeastern corner of theSouth Islandof New ZealandGallery[edit] Syncline exposed inSideling Hillroadcut Snow-dusted syncline inProvo Canyon,Utah. Road cut nearFort Davis, Texasshowing a syncline. Rainbow BasinSyncline in theBarstow FormationnearBarstow, California. Syncline in the lower parking lot ofCalico Ghost Town; note ductile folding at base, brittle above. Synclinal fold inSilurianWills Creek FormationorBloomsburg FormationatRoundtop Hill (Maryland) East wall ofBear Valley Strip Mine, nearShamokin, Pennsylvania Syncline inNavajo Sandstone,Upheaval Dome,Canyonlands National Park, Utah.AnticlineFrom Wikipedia, the free encyclopedia

Diagram of an anticline.

Anticline with syncline visible at far right- USGS. Note the man standing before the formation, for scale.

Anticline nearEhden,Lebanon.Instructural geology, ananticlineis afoldthat isconvexup and has its oldestbedsat its core. The term is not to be confused withantiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships between variousstrataare unknown, the term antiform should be used.On a geologic map, anticlines are usually recognized by a sequence ofrocklayersthat are progressively older toward the center of the fold because the uplifted core of the fold is preferentially eroded to a deeperstratigraphiclevel relative to thetopographicallylower flanks. The stratadipaway from the center, orcrest, of the fold.If an anticline plunges (i.e., is inclined to the Earth's surface), the surface strata will formVs that point in the direction of plunge. Anticlines are often flanked bysynclinesalthoughfaultingcan complicate and obscure the relationship between the two. Folds often form duringcrustaldeformation as the result of shortening that accompaniesorogenicmountain building. In many cases anticlines are formed by movement on non-planar faults during bothshorteningandextension, such asramp anticlinesandrollover anticlines.Contents[hide] 1Anticline terminology 2Economic significance 3Gallery of anticlines 4See also 5References 6BibliographyAnticline terminology[edit]Any fold whose form isconvexupward is an antiform. Antiforms containing progressively younger rocks from their core outwards are anticlines.An anticline or antiform has acrest, which is the highest point on a given stratum along the top of the fold. Ahingein an anticline is the locus of maximum curvature or bending in a given stratum in the fold. Anaxisis an imaginary line connecting the hinges in the different strata in a two-dimensional cross-section through the anticline. Connecting the hinges or points of maximum curvature in the different layers in three dimensions produces anaxial planeoraxial surface.In a symmetrical anticline, a surface trace of the axial plane coincides with the crest. With an asymmetrical anticline, the surface trace of the axial plane or axis will be offset from the crest toward the steeper flank of the fold. Anoverturned anticlineis an asymmetrical anticline with a flank or limb that has been tilted beyond perpendicular so that the beds in that limb are upside-down.A structure that plunges in all directions to form a circular or elongate structure is adome. Domes are generally formed from one main deformation event, or viadiapirismfrom underlying magmatic intrusions or movement of upwardly mobile, mechanically ductile material such as rock salt (salt dome) and shale (shale diapir). TheRichat Structureof the Sahara is considered a dome that has been laid bare by erosion.An anticline which plunges at both ends is termed adoubly plunging anticline, and may be formed from multiple deformations, or superposition of two sets of folds, or be related to the geometry of the underlying detachment fault and the varying amount of displacement along the surface of that detachment fault. The highest point on a doubly plunging anticline (or any geologic structure for that matter) is called the "culmination."An elongate dome which developed as the sediments were being deposited is referred to as apericline.Ananticlinoriumis a series of anticlinal folds on a regional-scale anticline. Examples include the LateJurassicto EarlyCretaceousPurcell Anticlinorium inBritish Columbia[1]and the Blue Ridge anticlinorium of northernVirginiaandMarylandin theAppalachians,[2]or theNittany Valleyin centralPennsylvania.Economic significance[edit]

Structural trap: anticlinal foldDoubly plunging or faulted anticlines, culminations, and structural domes are favored locations foroilandnatural gasdrilling; the low density of petroleum causes it to buoyantly migrate upward to the highest parts of the fold, until stopped by a low-permeability barrier such as an impermeable stratum or fault zone. Examples of low-permeability seals that contain the hydrocarbons, oil and gas, in the ground include shale, limestone, sandstone, and even salt domes. The actual type of stratum does not matter as long as it has low permeability.Periclines are important focal points for pooling of hot, metal-laden formationalbrines, which can formmanto ore deposits, Irish-type lead-zinc deposits and uranium deposits, amongst others.Culminations in folded strata which are cut byshearsand faults are favoured loci for deposition of saddle-reef style lode gold deposits.Gallery of anticlines[edit] Tight folds inlimestoneandchert,Crete, Greece Tight anticline in theWills Creek Formation, Pennsylvania Weathered marble anticline atGeneral Carrera Lake,Chile Nittany Valleyin centralPennsylvaniais an anticlinorium Elk Basinis a breached anticline TheTuscarora Formationforms a clear anticline inWills MountainatCumberland Narrows, Maryland Anticline inWills CreekorBloomsburgFormation atRoundtop Hill, Maryland Anticline with well-developed axial planarcleavage.Carboniferoussand-shale sequence above Tudes, SE of Potes, Cantabria, Spain Anticline and quartz "saddle reef" vein in theHalifax Formation(Cambrian),The Ovens,Nova Scotia Anticline in DevonianCatskill Formation,I-70,Fulton County, Pennsylvania Anticline in the CambrianConococheague Formation, in the wall of Holcim Quarry, Hagerstown, Maryland The Cave Mountain Anticline, exposed on Cave Mountain, West Virginia (seeSmoke Hole Canyon).