Basin Evolution and Classification

Basin-Forming Tectonics

  Basin Modifying Tectonics   Basin Classification

BASIN EVOLUTION

• Key factors for basin evolution include,

• Basin configuration,

• Nature of sedimentary fill in space and time,

• Type of structural features,

• Position in the geotectonic framework

SEDIMENTARY BASINS: EVOLUTION AND

CATEGORISATION

•A basin is born from the meting of a sedimentary deposit and a more or less pronounced concavity in the basement.

•The Earth’s surface exhibits a wide variety of sedimentary basins, in different stages of evolution, at distinct ages and in varied geodynamic contexts.

•The spatio-temporal distribution of basins and their characteristics follow a two fold logic:

•Geodynamical situational logic- organised in accordance with their situation in relation to lithospheric plates- historical logic.

Basin ClassificationBeginning roughly around the mid-1960s, several

attempts were made to develop a global basin classification system that would incorporate all the data then available.

• One purpose of these attempts was simply to sort through the data and form an orderly geologic system.

• However, petroleum explorationists had a second purpose in mind: if certain types of basins were found to be consistently more productive than others, a company could gain a competitive advantage by targeting these sites in its exploration ventures.

Basin Classification

• A number of these classification schemes are published including those of Bally, Blois, Klemme and Kingston. Bally's work is based on the tectonic history of basins. Blois and Klemme's work also used plate tectonic

historical terms, and added productivity data. Kingston's system added a systematic nomenclature,

designed to allow finer detail in describing the tectonic history of individual basins.

Basin Classification I

•Interior basins - large, ovate downwarps within stable cratonic shields (Michigan Basin) •Rift basins - narrow, fault-bounded valleys of various dimensions (East African Rift System) •Aulacogens - failed rift arm at triple-point junction (Reelfoot Rift) •Passive Continental Margin - Atlantic-type margins with sedimentary prism on shelf, slope, and rise

Modern IdeasMany (if not the majority) of steeply dipping normal faults are actually curved (concave-upward) and become shallow-dipping and sub-horizontal at depth. These are now known as listric faults. As the lithosphere is stretched during continental extension, the ductile deeper crust thins by pure shear, while the upper crust is broken up and pulled apart by listric faults which 'bottom out' in the ductile layer. At the surface of course these have the appearance of graben. This is the essence of McKenzie-type and other recent models of basin formation. As the sub-continental (i.e. mantle) lithosphere is thinned by stretching it is of course partly replaced by hotter asthenosphere. This will gradually cool on a time scale of the order of 50 - 100 m.y., and as it cools it becomes denser and the shallow basin above gradually subsides and is progressively filled with shallow-water sediment. The amount of subsidence will depend on the initial amount of stretching. This can usually be estimated and is known as the stretching factor, or "beta factor". The parameter b is defined quite simpy as b/a where a was the initial width and b is the stretched width. A b factor of 1.2 will give ca. 3 km subsidence. With complete rifting (to form ocean crust and an ocean basin) then b approaches infinity.

CONTINENTAL EXTENSION AND FORMATION OF SEDIMENTARY BASINS

The important difference is in the recognition of low-angle detachments (superficially like thrusts, but with movement sense as in normal fault), first proposed for the Basin & Range province in the western USA. These may bottom out in the lower crust or the upper mantle. The main effect is to introduce asymmetry compared with the pure shear uniform-stretching McKenzie-type model, so that basins associated with the thermal subsidence phase may be offset from the thin-skinned basins associated with the initial rifting.Magmatic effects (melting resulting from the uprising asthenosphere) may be offset from the main sedimentary basins. Because of the asymmetry, the continental margins on the two sides of an opening ocean may have very different profiles.

                                                                         

         

Stages in the evolution of a rift basin. (a) Early rifting associated with several minor, relatively isolated normal faults. (b) Mature rifting with through-going boundary fault zone, widespread deposition, and footwall uplift and erosion.

                                                                     

      

Idealized rift basin showing unconformity-bounded tectonostratigraphic packages. Thin black lines represent stratal truncation beneath unconformities; red half-arrows represent onlaps.

   

Geometry of a simple half graben. (a) Map-view geometry. (b) Geometry along a cross section oriented perpendicular to the

boundary fault, showing wedge-shaped basin in which synrift strata exhibit a fanning geometry, thicken toward the boundary fault, and onlap prerift rocks.

(c) Geometry along a cross section oriented parallel to the boundary fault, showing syncline-shaped basin in which synrift strata thin away from the center of the basin and onlap prerift rocks.

Simple filling model for a growing half-graben basin shown in map view (stages 1-4), longitudinal cross section (stages 1-5), and transverse cross section (stages 1-4). Dashed line represents lake level. The relationship between capacity and sediment supply determines whether sedimentation is fluvial or lacustrine.

                                            

This block model shows the subsurface configuration found at an axial margin delta system in a tropical rift valley lake. Such settings are typically major entry points for clastic material introduced into rift basins. Principal elements in the model include stacked progradational deltas, subaqueous fault controlled channels, and deep-water, organic-rich, hemipelagic sediments. Most subsidence in this part of the rift valley is accommodated by displacement on the main basin border fault.

Rift Basin Inversion

Inversion resulted from ridge push and/or continental resistance to drift during the initial stages of seafloor spreading

  Top section: model with extension and no shortening; a half graben containing very gently dipping synrift units is present.

Middle section: model with extension followed by minor shortening; a subtle anticline has formed in the half graben, and is associated with minor steepening of the dip of synrift layers.

Bottom section: model with extension followed by major shortening. The anticline in the half graben is more prominent, and is associated with significant steepening of the dip of synrift strata. New reverse faults have formed in the prerift layers. Although the inversion is obvious in this model, erosion of material down to the level of the red line would remove the most obvious evidence of inversion in the half graben. Furthermore, the prominent reverse faults cutting the prerift units could be interpreted to indicate prerift contractional deformation

Experimental models of inversion structures.  Cross sections through three clay models showing development of inversion structures (after Eisenstadt and Withjack, 1995).  In each model, a clay layer (with colored sub-layers) covered two overlapping metal plates.  Movement of the lower plate created extension or shortening.  Thin clay layers are prerift; thick clay layers are synrift; top-most layer is postrift and pre-inversion.

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Examples of positive inversion structures. a) Cross section across part of Sunda arc.  During inversion, normal faults became reverse faults, producing synclines and anticlines with harpoon geometries (after Letouzey, 1990).  b) Interpreted line drawings (with 3:1 and 1:1 vertical exaggeration) of AGSO Line 110-12 from Exmouth sub-basin, NW Shelf Australia (after Withjack & Eisenstadt, 1999).  During Miocene inversion, deep-seated normal faults became reverse faults.  In response, gentle monoclines formed in the shallow, postrift strata.

Schematic NW-SE cross sections showing development, chronologically from bottom to top, of the southwestern intraplate Palmyride fold belt, with a list of related major

Arabian plate boundary tectonic events.                                                                  

East African rift

Red sea Gulf of Aden

Thermal hypothesis of Sleep. This was the first to recognise that heating up the mantle (by a plume or whatever) could produce substantial crustal uplift (and erosion), followed by thermal subsidence. Compare the models by McKenzie and Wernicke later . .

                                                

The area looked like just before 760 m.y.

                                                

At 760 m.y. ago, rifting of the crust resulted in the creation of a rift valley.                                                

At 570 m.y., the Blue Ridge was caught up in the rifting that opened Iapetus ocean.

Passive (Atlantic-Type) Margins:

•found on continent-bearing plates •continental margin moving away from the mid-ocean spreading center •not characterized by mountain building •zone of low seismicity and no volcanism – essentially stable •characterized by thick sediment deposits and old oceanic crust •comprised of shelf, slope, and rise •examples include the eastern coasts of North and South America

Simplified relationships at a continental margin. There can be more than 10 km of shallow-water sediments at the margin – implying slow subsidence. How?

As a continent rifts apart, the nature of the sediments deposited in the divergent zone will vary over time as the rifting progresses through different stages (e.g., initial rift valley to linear sea to fully developed ocean). •Early lava flows and coarse (immature) sediments deposited during the rift valley stage•Evaporites (like halite) that precipitated in a shallow linear sea during arid conditions;•“Normal" sequence of mature sediments derived from the prolonged weathering and erosion of the continental margin at the edge of a fully developed ocean (e.g., sandstone [quartz arenite], limestone, shale...).  •Carbonate reefs (made of limestone) will only develop if the sea water is warm enough. • If the continent moves (by tectonic activity) into a colder climate, the reefs will die and be overlain by clastic sediments.

Sedimentation during rifting and on a passive margin

Basin Classification II

•Ocean basins - created by rifting, resulting in deep ocean floor •Subduction-related settings - seismically active continental margins with deep-sea trenches, active volcanic arc, and arc-trench separating (Aleutian Arc-Trench System)

•Strike-Slip basins - small pull-apart basins in response to lateral fault movement (Los Angeles Basin; transform marginal setting) •Collision-related basins - foreland basin development in response to thrust-loading of continent (Appalachian Basin)

Active (Pacific-Type) Margins

• continental margin moving toward a subduction zone • characterized by volcanism, many earthquakes, and active mountain building

• friction of subducting plate causes earthquake activity and heat generation • ocean crust is heated to melting point • molten rock (magma) rises to the surface to create island arcs and volcanoes

• dense oceanic crust is subducted beneath thicker, less dense continental crust • Chilean (e.g., Peru, Chile) - shallow trench, accretionary prism, volcanic mountains • Marianas (e.g., Japan, Marianas) - deep trench, volcanic island arc, back-arc basin • considered 'destructive'

Active (Pacific-Type) Margins: •continental margin moving toward a subduction zone •characterized by volcanism, many earthquakes, and active mountain building

•friction of subducting plate causes earthquake activity and heat generation •ocean crust is heated to melting point •molten rock (magma) rises to the surface to create island arcs and volcanoes

•dense oceanic crust is subducted beneath thicker, less dense continental crust •Chilean (e.g., Peru, Chile) - shallow trench, accretionary prism, volcanic mountains •Marianas (e.g., Japan, Marianas) - deep trench, volcanic island arc, back-arc basin •considered 'destructive'

   

SUBDUCTION ZONES and ISLAND ARCS

Subduction Zones are where cool lithospheric plates sink back into the mantle.

FRAMEWORK OF AN ISLAND ARC SYSTEMThe commonly held model of an arc - back-arc system has the following components:(1) Subduction Zone(2) Fore-arc region with accretionary sedimentary prism(3) Frontal Arc(4) Active Arc(5) Marginal Basin with spreading centre(6) Remnant Arc(7) Inactive Marginal BasinAlthough the extensive fore-arc region of many island arcs was thought to be composed of off-scraped sediments, drilling has not substantiated this. It appears that - at least at intraoceanic arcs - abyssal sediments on the downgoing plate are largely subducted.That the back-arc region is a zone of asthenospheric upwelling is supported by seismic evidence which suggests a low-Q (seismic attenuation) zone behind the arc, compatible with a small amount of melt in the back-arc region:

MARGINAL BASINS & BACK ARC SPREADINGMarginal basins are small oceanic basins, usually adjacent or "marginal" to a continent, which are separated from larger oceans by an island arc. Some marginal basins at continental margins may be imperfectly developed and represented by thinned crust, often associated with basic volcanism. Karig (1971, 1974) divided marginal basins into:

(1) Active marginal basins with high heat flow.(2) Inactive marginal basins with high heat flow.(3) Inactive marginal basins with normal heat flow.

The first two are thought to have formed by back-arc spreading, either still active (1), or recently active (2). The third may represent basins formed by even older back-arc spreading, or normal ocean crust that has been "trapped" behind a recently developed oceanic island arc. Marginal basins are a common feature of the Western Pacific. Examples (north to south) are the Sea of Japan, the West Philippine Basin, the Parace Vela & Shikoku Basins, the Mariana Trough, the Woodlark Basin, the Fiji and Lau Basins. By contrast marginal basins are rarer in the Eastern Pacific. The two examples in the Atlantic are the Caribbean and the Scotia Sea.

Uprising Harzburgite Diapir:

This model (Oxburgh & Parmentier 1978) depends on the fact that refractory lithosphere (which has lost its basalt component at mid-ocean ridges) is less dense and inherently more buoyant than normal fertile mantle. Thus it would rise if heated to same temperature as surrounding mantle. Such diapirs could in theory be derived from subducting lithosphere, although it is doubtful that subducting lithosphere could be heated within 10 my; more likely it takes 1000 - 2000 my according to megalith concepts of Ringwood (1982):

Convection-driven:

This model proposed by Toksoz & Bird (1978), and requires that subsidiary convection cells are driven by the downward drag of the downgoing slab. Calculations suggest that spreading would occur about 10 my after the start of subduction. This might explain why back-arc spreading is more common in oceanic regions, the lithosphere is thinner and thus more easily disrupted than under continents:

Passive Diapirism:

This results from regional extensional stresses in the the lithosphere across the arc system. In effect the downgoing slab, although acting like a conveyor belt, also has a vertical component that causes "roll-back". The arc and forearc then stays with the subduction zone, as a result of a supposed trench suction force.

Active Diapirism:

One of the earliest models, based on the Mariana Arc System, is that of an uprising diapir splitting the arc. The diapir is initiated either as a result of frictional heating at the subduction zone, or more likely through fluids released from the dehydrating subducting slab. The rising diapir then splits the arc in two and the two halves

are progressively separated by seafloor spreading:                                                             

 

Stepwise Migration:

Here it is assumed that the subducting slab is snapped off near the hinge, presumably because something on the downgoing slab is too light to go down, and so a new subduction zone is initiated oceanwards. The arc stays near the hinge and the asthenosphere wells up behind it:

Sedimentation in active tectonic marginsActive tectonic margins are characterized by rapid erosion from volcanic island arcs (like Japan), volcanic mountain chains (like the Andes), or continental collision zones (like the Himalayas). 

Rapidly eroded volcanic material will result in a muddy sand with chunks of dark volcanic rock which later gets turned into "greywacke". 

Rapidly eroded non-volcanic mountains generate an abundance of pink K-feldspar and quartz grains from the erosion of granites, which later gets transformed into "arkose". 

                

    

Mountains form when two masses of continental crust collide. A. Subducting oceanic lithosphere compresses and deforms sediments at the edge of continental crust on overriding plate (left). Sediments at the edge of continental crust on subducting plate (right) are undeformed. B. Collision. Sediment at the edge of continental crust on subducting plate is deformed and welded onto already deformed continental crust on overriding plate. C. After collision. The leading edge of the subducting plate breaks off and continues to sink. The two continental masses are welded together, and a mountain range stands where once there was ocean.

Foreland Basin

Foreland basins subside as a result of the load. The crust beneath the Foreland basins subside as a result of the load. The crust beneath the thrust load is depressed as a result of isostacy and the adjacent crust is thrust load is depressed as a result of isostacy and the adjacent crust is

depressed via flexure since it is attached.depressed via flexure since it is attached.

Schematic diagrams comparing patterns of uplift and subsidence in foreland and extensional basins during times of active deformation (A) and quiescence (B).

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•Cratonic Basins (e.g. Illinois basin; Michigan basin) •Rift Basins and Passive Margins (e.g. Viking Graben & North Sea; Atlantic Margin) •Flexure Basins (e.g. Baltimore Canyon Trough •Fore-Arc Basins (e.g. Great Valley Basin) •Intra-Arc and Backarc Basins (e.g. Nigata basin, Hokkaido basin) •Pull-Apart Basins (e.g. Los Angeles basin; Ridge basin; Ventura basin, St. Georges basin •Foreland Basins (e.g. Arkoma basin, Wyoming-Idaho basin; Appalachian basin)

EXAMPLES OF BASIN TYPES

Tranaspression and transtension

Restraining bends result in compression. Releasing bends result in extension and deep basins (pull-apart basins) form.                                                                      

The bend lead to push against each other, preventing easy sliding, so this particular bend is known as a "restraining" or "convergent" bend resulting uplift of the Transverse Ranges by the action of reverse and thrust faults

If the plate motion were the opposite, and the slip along the San Andreas fault became left-lateral in nature, the existing bend would cause extension in the area near the bend and this bend would be called a "releasing" or "divergent" bend (bottom left). This action would likely cause a basin to form around the bend

Basin Classification

Basin Classification

Basin Classification

• One of the most recent studies of basin-forming processes (Mohriak, Hobbs and Dewey, 1990) was done in Brazil.

• Deep wells, gravity and deep seismic data provided a basis for this analysis.

A. basins formed along active master faults.

B. basins formed along inactive faults.

C. basins with no fault control.

D. basins formed by low-angle detachment faults.

E. basins containing crustal thinning and Moho uplift.

F. basins formed by pervasive pure shear, or an approximately pure shear, where the lower crust has been locally extended by a different amount than the upper crust.

Basin Classification

Basin Classification

• Basin classification scheme comparison: plate tectonics scheme vs. Mohriak, Hobbs and Dewey (1990).

• Plate Tectonic Basins 1990 Descriptive Basin Class

• Intracratonic sag basin C No major fault control

• Rift basin A Basins associated with active, deep penetrating master faults

• B Basins associated with major faults that do not control subsidence

• D Basins associated with low-angle detachment

• E Basins associated with crustal thinning and Moho uplift

• F Basins of almost unstretched crust carrying a thin veneer of sediments

• Divergent margin basins A, D or E

• Oceanic basins flanking oceanic ridges Not foreseen or C

• Convergent margin basins A and D