basin inversion.pdf

Earth-Science Reviews 65 (2004) 277–304

www.elsevier.com/locate/earscirev

Sedimentary basin inversion and intra-plate shortening

Jonathan P. Turner * , Gareth A. Williams

Earth Sciences, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Received 22 January 2003; accepted 10 October 2003

Abstract

Sedimentary basin inversion, the shortening of formerly extensional basins, is accommodated mainly by compressional

reactivation of extant faults and fractures across a wide range of scales. As such, inversion is a large-scale manifestation of

Byerlee friction, the dynamic criterion for fault reactivation governing the effective shear strength of the shallow crust. Basin

inversion generates distinctive deformational architecture, and it is implicated strongly in sedimentary basin exhumation. As a

principal source of horizontal stress, inversion drives significant sedimentary porosity reduction and resultant fluid flow. Upper

crustal deformation is critically dependent on fluid overpressure (i.e., pore fluid pressures greater than would be calculated from

a hydrostatic gradient), and, perhaps more than in any other tectonic setting, overpressures are potentially large during

sedimentary basin inversion. This review therefore includes discussion of the role of fluid overpressure in inversion and the

evidence for it. Collectively, inversion has profound implications—good and bad—for the prospectivity of many petroliferous

sedimentary basins. Thus, recognizing the evidence for basin inversion, quantifying its magnitude and understanding the

mechanisms that accommodate inversion and other phenomena affected by it, have become essential components of the basin

analyst’s remit.

Keywords: Basin inversion; Tectonics; Fault reactivation; Reverse fault; Rift basin; Fluid overpressure; Effective stress; Exhumation; Petroleum

geology

1. Aims and scope

Furthermore, as one of the principal mechanisms

driving uplift and erosion, sedimentary basin inver-

sion is often primarily implicated in the exhumation of

basins—the exposure at the surface of formerly deep-

ly buried rocks.

To date, much of our understanding of sedimentary

basin inversion originates from seminal studies of

Mesozoic extensional basins in the NW European

Alpine foreland. They were inverted in response to

compression generated by European–African plate

collision in the Cenozoic (Ziegler, 1987) . A principal

achievement of this work has been to highlight char-

acteristic structural geometry and erosional unconform-

In this paper, sedimentary basin inversion describes

the compressional or transpressional reactivation and

shortening of formerly extensional basins. Inversion

induces significant changes in the tectonic structure

and dimensions of sedimentary basins, it has a major

influence on thermal history and rock properties, and

its impact on petroleum prospectivity is fundamental.

* Corresponding author. Fax: +44-121-414-4942.

E-mail address: j.p.turner@bham.ac.uk (J.P. Turner).

doi:10.1016/j.earscirev.2003.10.002

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J.P. Turner, G.A. Williams / Earth-Science Reviews 65 (2004) 277–304

ities resulting from intracratonic basin inversion. Fur-

thermore, without fully elucidating the mechanism(s)

responsible for the transmission of stress through the

lithosphere, these studies serve also to emphasize the

potentially far-reaching influence of basin inversion

(e.g., Cenozoic inversion affected basins some 1600

km from the Alpine front: Ziegler et al., 1995 ) . How-

ever, whilst the European Alpine foreland is an excel-

lent natural laboratory in which to investigate

sedimentary basin inversion, it is by no means the only

geodynamic setting in which inversion tectonics

occurs. Moreover, the influence of the Iceland plume

during North Atlantic opening means that it is often

difficult to isolate the effects of inversion from epeiro-

genesis in diagnosing the nature of the uplift responsi-

ble for the exhumation of NW European basins.

Sedimentary basin inversion is, literally, a global

process. For example, compressional stress originat-

ing from major changes in plate configuration during

the Santonian–Maastrichtian interval are recorded in

inversion episodes across Africa, Arabia, Australasia,

Europe and the Americas ( Guiraud and Bosworth,

1997; Davidson, 1997: fig. 31 ; P.F. Green, personal

communication). Marshak et al. (2000) show that the

inversion of North American Proterozoic extensional

basins during the Ancestral Rockies and Laramide

contractional events was largely controlled by the

trends of the basement faults. Given that these faults

formed during extensional episodes some 1.3–1.1 and

0.9–0.7 Ga that affected the entire Rodinia, we should

expect to see evidence for their inversion across

cratonic platforms worldwide.

This review integrates well-established ideas on the

geometry and kinematics of inversion structures (Coo-

per and Williams, 1989; Buchanan and Buchanan,

1995; Ziegler et al., 1995) with modern concepts of

deformational mechanics, including the role of fluid

overpressure, exhumation and geodynamics. As such,

it serves to emphasize the central role of inversion in

the long-term evolution of many, probably most,

sedimentary basins.

1920; Stille, 1924; Pruvost, 1930; Voigt, 1963 ). The

Geological Society Special Publication on Inversion

Tectonics (Cooper and Williams, 1989) included ex-

tensive discussion on the uses and abuses of basin

inversion (Cooper et al., 1989) . This suggested it

should be confined to (1) basins whose extensional

phase was actively controlled by faults and (2) sce-

narios in which changes in the regional stress field

resulted in the extensive re-use, or reactivation, of pre-

existing faults. Such a definition includes inversion in

orogenic belts, but it implicitly excludes flexural,

thermal and isostatic mechanisms of sedimentary

basin uplift, such as the synkinematic uplift of normal

fault footwalls (footwall uplift). The use of ‘‘negative

inversion’’ to describe changes in the sense of fault

displacement from reverse to normal is generally

discouraged, though it remains a useful and relevant

concept for understanding the processes of syn- and

postorogenic extension.

3. Tectonic settings

Sedimentary basin inversion has been widely docu-

mented from most of the main types of basins, namely

continental rifts (e.g., Daly et al., 1989 ) , aulacogens

(e.g., Hamilton, 1988; Bartholomew et al., 1993;

Varga, 1993; Molzer and Eerslev, 1995; Knott et al.,

1995 ), rifted continental margins (e.g., Boldreel and

Andersen, 1993; Guiraud and Bosworth, 1997; Gas-

perini et al., 2001; Benkhelil et al., 2002; Turner et al.,

2003 ), backarcs (e.g., Letouzey et al., 1990 ) , orogenic

foredeeps (e.g., Camara and Klimowitz, 1985; Gillcrist

et al., 1987; Turner and Hancock, 1990 ) , intracratonic

basins (e.g., Tucker and Arter, 1987; Butler, 1998;

Underhill and Paterson, 1998 ) and ‘peri-orogenic’

regions of continental escape tectonics (e.g., Morley

et al., 2001 ). Furthermore, rapid switches between

transtensional and transpressional strain experienced

by pull-apart basins as they are translated between

releasing and restraining bends along strike-slip fault

systems means that they often exhibit classic inversion

features (e.g., intra-continental strike-slip fault zones:

Storti et al., 2001a,b; Crowell, 1976; Harding, 1985;

transform margins: Basile et al., 1993; Mascle et al.,

1996 ).

Whilst the ‘inversion’ of pull-apart basins will not

feature significantly in this review, it is worth noting

2. Definition

Although the term ‘‘inversion’’ was first coined by

Glennie and Boegner (1981) , inverted basins have

been recognized for a long time (e.g., Lamplugh,

J.P. Turner, G.A. Williams / Earth-Science Reviews 65 (2004) 277–304

279

that most inversion episodes are non-coaxial, and

hence, oblique-slip or strike-slip kinematics are im-

portant modes of fault reactivation during inversion.

In this context, non-coaxiality describes scenarios in

which the bearing of the axis of maximum horizontal

stress during inversion does not coincide with that of

the earlier axis of minimum horizontal stress. In such

a setting, shortening strains will often be partitioned

between faults displaying dip-slip, oblique-slip and

strike-slip kinematics (e.g., Williams, 2002 ) . A

classification of inverted settings in terms of the

relative magnitudes of compression and strike-slip

components (Lowell, 1995) highlights several ba-

sins in South America whose inversion was highly

non-coaxial.

Reversals in the sense of dip-slip fault displacement

result in the formation of reverse faults. Terms

‘‘reverse’’ and ‘‘thrust’’ fault should be applied rig-

orously. Thrusts are dip-slip faults that originate in a

horizontally compressive stress field, typically at

angles of 30j to maximum principal stress. Whilst

reverse faults also are a product of horizontal com-

pression, they attain steeper angles (c. 60j) to the

horizontal. Reverse faults owe their steep inclination

either to: (1) back-rotation and steepening of a thrust

fault after its formation; (2) transpressional settings in

which shallow thrust faults steepen with depth as

they converge on a strike-slip basement lineament

from which they splay; or (3) initiation as normal

faults, subsequently reactivated as reverse structures

during sedimentary basin inversion. Thus, in non-

orogenic settings and away from the comparatively

unusual transpressional tectonics described above, the

presence of reverse faults is a strong indication that

inversion has occurred.

The diagnostic criterion for recognizing sedimen-

tary basin inversion is identification of the null point

(Williams et al., 1989) , or, in three dimensions, the

null line. Fig. 1 shows a reactivated fault in an

inverted basin along which net displacement changes

4. Structural criteria for recognition

To varying degrees, inverted basins are character-

ized by reversals in the sense of dip-slip fault

displacement, from normal to reverse (Fig. 1) , a

change in the polarity of structural relief (i.e., low-

lying basin areas become structural culminations) and

expulsion of the synrift fill of a basin (Fig. 2) .

Fig. 1. Cross-section showing typical inversion geometry in an inverted half-graben from the East Java Sea basin, Indonesia. After Goudswaard

and Jenyon (1988) . White polka dot signifies the position of the null point, marking the divide between reverse displacement above and normal

displacement below. Thus, progressively more severe inversion leads to migration of the null point (or, in three dimensions, the null line) from

the tips of a fault toward its centre, where pre-inversion normal displacement was greatest.

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J.P. Turner, G.A. Williams / Earth-Science Reviews 65 (2004) 277–304

where displacement is by definition zero, to its

centre where the fault (system) will have under-

gone the greatest number of increments of

displacement. Subsequent reversal of the sense

of fault displacement, from normal to reverse,

means that the fault tip regions will display net

reverse offset before the centre. Consequently,

segments of net reverse and net normal displace-

ment will be separated by the so called null point

at which fault displacement is zero.

2. Scissor-like fault kinematics in which each side of

the fault essentially pivots about a ‘false’ null

point positioned more or less halfway between the

fault tips. This pivoting motion may take place

about horizontal, vertical or obliquely inclined

axes. Such faults have been mapped from 3D

seismic surveys and may be interpreted as large-

scale Riedel shears that develop within torsional

strain fields.

Fig. 2. Geological map of an inverted half-graben near Chambery,

external French Alps, SE France. The cuspate outcrop pattern of the

Lower Barremian synrift limestone, exhibiting marked along-strike

variation in thickness, records its synkinematic deposition in the

hanging wall of an east-dipping listric normal fault during regional

Cretaceous extension. Subsequent reactivation of the fault during

Alpine shortening led to expulsion of the synrift succession in the

hanging wall of a major thrust (shown with barbs in hanging wall)

such that it now forms a major topographic culmination. Map from

Carte Geologique Detaille de la France (1960) .

As the magnitude of inversion increases, that is,

the ratio of shortening strain to initial extensional

strain, the null point(s) will migrate progressively

along a fault, toward its centre. Consequently, sedi-

mentary basin inversion will often generate shorten-

ing in the cover sequence before the net extension at

basement level has been cancelled. As an elegant

explanation for apparently bizarre structural geome-

tries, such as faults that change from normal to

reverse along strike (Fig. 3) , seamless vertical tran-

sitions from hanging wall rollover monocline to

compressional anticline (Fig. 1) , upthrown hanging

wall depositional ‘thicks’ (Figs. 2 and 4) and com-

pressional folds in the hanging walls of normal faults

(Fig. 5) , the null point concept is an essential tool for

seismic interpreters and field geologists working in

inverted basins.

An inevitable consequence of null points is that

reactivated faults in inverted basins are likely to

confound the wealth of empirical data on displace-

ment – length relations (cf. Walsh et al., 2002 ) . This

mainly reflects the fact that, except along the neo-

formed segments of reactivated faults (i.e., the near-tip

segments that propagated during a fault’s reactiva-

tion), the measured total displacement between foot-

wall and hanging wall markers is apparent. Following

an inversion episode, therefore, the thickest area of

synrift sediment accumulation will not necessarily be

from normal in the lower reaches of the fault, to

reverse in its upper reaches. Such fault displacement

patterns are best explained by invoking either:

1. Reverse reactivation of a normal fault. Fault

systems evolve during many increments of

coseismic displacement. Consequently, fault dis-

placement will increase progressively from its tip,

J.P. Turner, G.A. Williams / Earth-Science Reviews 65 (2004) 277–304

281

Fig. 3. Geological map of an onshore segment of the Abbotsbury–Purbeck fault system (in bold), Wessex basin, southern England. According

to the concept of the null point, the switch from normal to reverse displacement (shown respectively by lines with a polka dot and barbs in the

hanging wall) is interpreted as the result of compressional reactivation of a normal fault, with the magnitude of bulk reverse displacement lying

within the range of the variation in pre-inversion normal displacement. Grid line labels from the UK National Grid, map from Geological Survey

of England and Wales (1974) .

sited adjacent to that part of a fault where normal

offset was greatest.

Breakdown of displacement – length relations in

inverted settings also reflects greater partitioning of

strain between major faults and their wall rocks. We

consider this to be a consequence of: (1) more rapid

strain rates (Ziegler et al., 1995: Table 1) ; (2) non-

coaxial fault kinematics; and (3) greater brittleness of

Fig. 4. Cross-section through the St. George’s Channel basin, offshore North Wales, UK. It exemplifies the inversion of relief that often

accompanies basin inversion, with pronounced thickening of the syntectonic Lower Jurassic succession toward what is now an uplifted

structural culmination (the St. Tudwal’s Arch). From authors’ own data.

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