I he l\ Ol~" IClil '\"l)(lJlllIil of Petroleum Geologi~ts Bulleon \ oK, No 7 (July 19841. P. 801-815,32 rig,.

Listric Normal Faults: An Dlustrated Summaryl

JOHN w. SHELTON"

ABSTRACT

Normal faults are commonly listric, that is, the dip flat­tens with depth. Movement along this type of fault is instrumental in formation of several types of structural traps (e.g., rollover anticlines and upthrown-fault-block closures). Some listric faults are restricted to sedimentary rocks, whereas others offset basement rocks. Tbeoretical data, rock-mechanical and simulated model experiments, and foundation-engineering tests and failures suggest tbat this type of fault may occur where brittle rocks overlie duc­tile rocks in an extensional regime. In some places the duc­tile section may be thin and bounded sharply at its top. Also, the extensional regime may be locally derived within a broader stress regime of another type, as evidenced by transtension associated with strike-slip movement and arched strata in a compressive setting.

The flattening of the fault reflects an increase in ductility of the rocks with depth and, in some cases, deformation of the fault due to compaction or tilting of the upthrown block. The dip angle may vary along the strike of the fault in response to changes in throw. In cross section, a listric fault may consist of relatively short, en echelon fault seg­ments. This geometry may be particularly cbaracteristic of growth faults. Sedimentary faults may sole in ductile strata, or they may represent the brittle part of a fault-flow system. Fault patterns commonly are characterized by bifurcation, some of which may occur near the ends of individual faults comprising a zone.

Although unequivocal recognition of listric normal faults requires unusually extensive outcrop data, close subsurface control, or high-quality seismic data, their presence is suggested indirectly by such features as increas­ing dip with depth toward tbe controlling fault ("reverse drag"), thick progradational sandstone overlying ductile strata, and in some cases arcuate fault patterns, basins, or uplifts.

©Copyright1984. The American Association of Petroleum Geologists. All rights reserved.

, Manuscript received, May 18, 1983; accepted, December 7, 1983. 2 ERICa, Inc., Tulsa, Oklahoma 74172. For documentary data which have not been published, the writer is indebted

to Shell Oil Co. for materials from the Gulf Coast and to G. W. Hart for data and interpretations in the Arkoma basin. Laura F. Serpa and R. E. Denison pro· vided information on basement·involved faults and detached sediments, respectively.

Appreciation is gratefully expressed to many colleagues and acquaintances who for more than 2 decades have stimulated thought on this subject of listric (rotational) normal faults. Kaspar Arbenz kindly reviewed the original manu· script and made numerous helpful suggestions. Appreciation is also expressed to AAPG Editors M. K. Horn and Richard Steinmetz, Science Direc· tor Edward A. Beaumont, and reviewers for their valuable comments. Yet the author must assume responsibility for errors or any aberration in accepted thought.

David E. Brooker drafted the illustrations, and Sherry Hempel, Mildred P. Lee, anet Dianne O'Malley prepared the typescript. O'Malley also assisted in compilation of the references. S. W. Carey kindly provided the reference noted herein to his work.

801

Listric normal faults form during rifting, drifting, and evolution of passive continental margins with concomi­tant basinal denlopment. Listric faults confined to the sedimentary prism are common features on passive mar­gins, especially in progradational, post-evaporite sequences. The basement is offset by listric faults as a fun­damental element in the development of other types of basins, including those whicb formed during postorogenic extension. They also occur as secondary extensional fea­tures in an overall compressive stress regime due to plate connrgence and during transform or strike-slip faulting.

INTRODUCTION

A listric fault is characterized by a decreasing angle of dip with depth. It, therefore, is a curved surface which is concave upward. Apparently the concept was introduced by Edward Suess in the early part of this century (Bally et ai, 1981) as part of his description of faults in coal mines in northern France.

Listric thrust faults have been recognized for a long time as a basic feature of thin-skinned tectonics, with decolle­ments. Now, as deep faults soling in the ductile crust, they are also considered an integral part of suturing during plate convergence (e.g., Thompson, 1976). Although lis­tric normal faults have been recognized as updip (or upslope) segments of gravitational slides (e.g., Reeves, 1925, 1946; Hubbert and Rubey, 1959; Wise, 1963), most commonly they have been regarded as a special feature of syndepositional faults in strongly subsident basins con­taining thick shale (with or without salt) below prograda­tional sandstone sections. This general opinion probably derives from the abundance of sedimentary faults in the northern Gulf Coast basin (Texas and Louisiana) and the common knowledge of "rotational slips" and associated failures in foundation engineering (Figure 1). Apparently little significance was given to the early work of Davis (1925) and Longwell (1933, 1945), who described listric normal faults offsetting crystalline and/or basement rocks in the western United States; to the theoretical treat­ment of Hafner (1951), who showed curved stress trajecto­ries including conditions for listric normal faults; or to the work of Carey (1958), who described listric normal faults as a major feature in development of rift valleys. It seems reasonable, therefore, to regard listric geometry as a com­mon feature of both thrust and normal faults displacing sedimentary and/or basement rocks.

Wernicke and Burchfiel (1982) have grouped normal faults into two categories: rotational and nonrotational. The rotational category is divided into (a) those with rota­tion of beds along listric faults, and (b) those with rotation of beds and faults along planar or listric faults. Nonrota­tional faults have no rotation of structures along planar faults.

802 Listric Normal Faults

~FlLL+b CLAY

A

Figure I-Foundation failures resembling configurations of faults in sedimentary rocks. A. Rotational slip in foundation due to localized loading of uniform clay. B. Base failure due to load­ing offoundation with thin clay. After Terzaghi and Peck (1948).

Wernicke and Burchfiel indicate that large-scale dis­placement on low-angle listric normal faults results in a series of tilted planar-fault blocks, forming "extensional allochthons."

Both normal and thrust listric faults, along with planar faults, are of major significance to the explorationist because they are an important element in the formation of traps in faulted strata. Presently a commonly held opinion is that listric normal and thrust faults may be sequentially related (or even coincident) in some areas that undergo changes in tectonic regime. For example, listric thrust faults may be reactivated as normal faults when an earlier formed orogenic belt is subjected to extension (Bally et ai, 1966), and, conversely, normal faults may be reactivated as thrusts during the evolution of a continental margin from a passive to active phase (Cohen, 1982). Further, the location of thrusts with displacement during the active phase (after basinal subsidence) may be predetermined by buried normal faults that formed during the earlier pas­sive phase (during basinal subsidence). Listric normal faults are probably important elements in the develop­ment of many basins. Downward dip-slip movement of faulted strata in the hanging wall of a listric normal fault may result in "reverse drag" in half grabens or "rollover" (dip-direction reversal), with formation of an anticlinal feature (Figure 2). Absolute movement, with rotation of an upthrown block, may result in a tilted fault block with reverse drag. Significant variations in displacement along the strike of a fault present conditions for closure against it (Figure 3). The closure may also result from differential rotation (along the strike of a fault) of an entire block which itself is downthrown with respect to a subjacent "underlying" fault (Figure 3C), or by changes in strati­graphic thicknesses along the strike of the fault. The detailed geometry of the faults provides subtle trapping potential. For example, lateral branching or overlapping ends of faults are possible elements of subsidiary traps. Also, movement along individual faults of a fault zone may result in several traps rather than one larger trap.

L __________________________________ ~

Figure 2-Structural map of top of Wilcox Group (Eocene) in South Bancroft field, Beauregard Parish, Louisiana, showing rollover anticline. After Murray (1961).

A

o U

-7600'

-7650' 400011 -7700'

1000m

A A'

V= --~ I

!A'

c

(2) (4)

Z) --------- ------"------------->~---..... --~

Figure 3-A. Structural map of Lower Cretaceous marker in Pleasanton field, Atascosa County, Texas, depicting tilted-fault­block trap. After Murray (1961). B. Hypothetical fault closure due to absolute movement of upthrown block. C. Fault blocks with potential for trap in each upthrown block due to rotation of that block (e.g., dip in block 2 is due to rotational movement along fault X).

CLASTICS AND VOLCANICS

ASTHENOSPHERE

figure 4-::,chematic cross section of major rift zones rupturing a continent-before possible drifting and formation of passive con1inental margins. After Dewey and Bird (1970).

John W. Shelton 803

10mi

10km

ARE.A OF

EXTENSION

B c

--=------- 0

/

Figllre 5-"reas of extension with normal faults resulting from wrenching. A. Extension with formation of Ridge basin due to diver­gent wrenching between San Andreas and San Gabriel faults (after Wilcox et aI, 1973). B. Extension due to movement along parallel en echelon wrench or transform faults. C. Extension due to conjugate wrench faults (based on discussion in Wilcox et aI, 1973). D. En echelon normal faults of Lake Basin fault zone in south-central Montana due to left-lateral faulting (after Fanshawe and Alpha, 1954; Harding, 1974). Faults of this type may be riedel shears along which there is some dip-slip component.

This review is restricted to normal faults, with descrip­tion of (1) faults along which the apparent relative dis­placement of the hanging wall was down with respect to the footwall and (2) faults which formed in a local or regional stress regime wherein the maximum principal stress, (71' is interpreted to have been vertical or near verti­cal. In many places movement of strata along listric faults is dip-slip and rotational, with the axis of rotation being parallel with the strike of the fault. Under conditions where the primary feature is a strike-slip fault, the dip-slip component of the total displacement across the fault may also be comparatively "small," and movement along the listric fault may vary significantly from dip slip. The scale of the "small" displacement, of course, may be more than 1,000 m (3,300 ft).

In this paper, concepts are presented before examples; the topics, in order, are: causes of normal faulting and of listric normal faults, geometry, propagation, growth faults, evidence for listric faults, and occurrences. The pri­mary references are Bally et al (1981) and Bally (1983). The former is a resume of listric normal faults in various geo­logic settings, in particular, passive continental margins and orogenic systems. The latter, which is a pictorial atlas of seismic sections illustrating various structural styles, contains outstanding examples of listric normal faults from several extensional provinces.

CAUSES OF NORMAL FAULTING

Normal faults occur in response to extension, which may be crustal extension, sedimentary-section extension, or basement and/or sedimentary-section extension.

1. Crustal extension results from (a) divergent plate movement, expressed by rifts (Figure 4); (b) arching by thermal expansion (e.g., development of a plume); and (c) transtension accompanying divergent wrenching (wrench or transform faulting) and movement along parallel to subparallel en echelon faults or "plates" or along conju­gate wrench faults (Wilcox et ai, 1973; Harding anq Low­ell, 1979; Burchfiel and Royden, 1982) (Figure 5).

2. Sedimentary-section extension results from (a) flow­age of ductile substrate (shale and/or salt) (e.g., Bruce, 1973; Woodbury et aI, 1973; Humphris, 1978) (Figure 6); (b) increase in stratal dip and resultant gravitational slid­ing (e.g., Hubbert and Rubey, 1959) (Figure 7); (c) bend­ing, or arching, during uplift (e.g., associated with salt or igneous intrusion; see Figure 8), and flexural or concentric folding associated with compressional folding; (d) strike­slip faulting (possible normal separation along at least part of the length of a fault which may be a riedel shear; Figure 5D).

3. Basement and/or sedimentary-section extension results from (a) uplift during transpression accompanying

804 Listric Normal Faults

Figure 6-Schematic cross section across Texas part of northern Gulf of Mexico basin, with normal faulting due to flowage of ductile shale. After Bruce (1973).

y --L

" ..-?"

/'

ZONE OF ABNORMAL PORE PRESSURE

Figure 7-Normal faulting due to gravitational sliding in response to dip of strata with abnormal pore pressure. After Hubbert and Rubey (1959).

wrench faulting (Harding and Lowell, 1979) (Figure 9); (b) axial collapse associated with subduction (Beck et ai, 1975) (Figure 10); (c) uplift andlor arching of earlier formed foldbelt.

LISTRIC NORMAL FAULTS

The flattening of the dip of a normal fault with depth may reflect one or more environmental conditions or processes at depth. The first group is conditions that are inherent, that is, conditions that contributed to formation of listric faults.

1. Increase in ductility in sedimentary prism, generally involving thick overpressured shale andlor salt, with extension of "overburden" due to flowage or decollement of "substrate."

2. Increase in ductility in crust (with extension of ductile "substrate").

The second group includes processes that operated after formation of the fault. This includes deformation of fault by:

1. Compaction of shale in footwall (Figure 11). 2. Arching during uplift initiated in rocks below the

fault (e.g., due to salt or igneous intrusion; Figure 8). 3. Increased tilting (with rotation about an axis parallel

with strike of fault) of entire upthrown fault block reflect­ing movement along subjacent "underlying" fault (Roux, 1977) (Figure 12).

Theoretical and experimental data together with case histories from foundation engineering suggest that the lis­tric feature may be a basic element of some normal faults. Included in the theoretical and experimental data demon­strating, or allowing inference of, listricity in extensional conditions are results of the following works:

1. One set of stress trajectories derived by Hafner (1951).

UPPER

1.0

TOP NAVARRO

2.0 ;; E

~ g 4000ft

1000m

3.0 sec

Figure 8-Seismic cross section of Pescadito dome, Webb County, Texas, showing normal faults due to extension in strata overlying salt. After Halbouty (1979).

Figure 9-Seismlc cross section across wrench fault zone in Ard­more basin, Oklahoma, with flower structure which contains minor listric normal faulting due to extension of Mississippian and older strata. After Harding and Lowell (1979).

_ SEDIMENTARY FilL \ NORMAL FAULT

l11Zl ~2~J~~~~TAL ~ OCEANIC BASEMENT \ THRUST

Figure IO-Cross section of Andean orogene, showing measure of bilateral symmetry, with two outer zones of compression and axial zone(s) of block faulting, interpreted to include listric nor­mal faults. After Beck et aI (1975).

SHALE AFTEIICOMI"ACTION

Figure II-Flattening of fault due to compaction of shale.

John W. Shelton 805

B --

-E

-f---

"" o E 8 8 N

2000ft 500m

----A -- __

-0.- _

--

Figure 12-Seismic cross section of local structure in offshore Texas part of northern Gulf Coast basin, showing deformed fault due to rotation of upthrown block reflected by attitude of strata 1-4. After Roux (1977).

Figure 13-A. Profile of slope before failure. B. Cross section of clayey deposits after slide flow. After Longwell and Flint (1962, p. 142·143). This type of failure, occurring where clays are very sensitive, is thought to be analogous to fracture (fault) and flow (incipient diapir) relationship of numerous sedimentary listric faults.

E .:: 08 f5 ~ 2000ft

500m

TERTIARY -UPPER CRETACEOUS

SHALE

LOWER CRETACEOUS CARBONATE

Figure 14-Cross section through Fashing field, south-central Texas, showing listric normal fault in Tertiary and Upper Creta­ceous shale. Dip of fault steepens with further depth in Lower Cretaceous carbonates. After Murray (1961).

2. Theoretical model for shale tectonics by Ode (Crans et aI, 1980).

3. Geomechanical model by Crans et al (1980). 4. Theoretical considerations by Muehlberger (1961)

predicting decreasing dip angle of fracture surface with increase in confining pressure.

5. Rock -mechanical experiments by Handin and Hager (1957) showing decreasing angle of internal friction with increase in confining pressure, and by von Karman (Han­din and Hager, 1957) showing decrease in angle between fracture surface and least principal stress axis with increase in pressure.

6. Rock-mechanical experiment by Heard (1966) show­ing listric normal fault with distributed flow under high confining pressure and high temperature.

7. Model experiment by H. Cloos (1930) simulating gra­bens and rifts.

8. Model experiment by Rettger (1935) simulating fault­ing due to gravitational gliding.

9. Model experiment by P. Diebold (Crans et ai, 1980) simulating faulting due to loading.

10. Model experiments by E. Cloos (1968) simulating growth faults.

GEOMETRY

Dip

The dip of a listric fault flattens with depth, but it either "dies out" in ductile rocks that deform by flowage or it becomes a decollement zone. There is a strong tendency to consider the latter as the dominant disposition of a listric fault. Where gentle regional dip exists, creep may contrib­ute to development of decollement zones or sole ductile faults. Yet, the relationship of listric faults to shale and salt diapirs suggests that a fault-flow system (Figure 13), which is analogous to the slide flow in soil mechanics, may be very common. In terms used in foundation engineer­ing, base failures, where the ductile substrate flows in response to asymmetric loading, are probably more analo­gous to listric sedimentary faults than slope failures, which are not necessarily bounded by listric surfaces. Flowage associated with base failure may be regarded as a form of

806 Listric Nmmal Faults

lateral "extrusion" that results in extension and subsi­dence in the area of loading. Ductility of the substrate gen­erally reflects overpressure in shale and/or plasticity of salt.

Some faults flatten at depth through a shale and steepen below it (e.g., Murray, 1961)(Figure 14). That relationship is generally attributable to shale compaction, but in places it may reflect a lower original angle of dip through the

"-

~ ~-,,~ A

B H. Cloos (1930)

1965; Holmes, 1965; Anderson, 1971; Robson, 1971; Ste­wart, 1971), and from subsurface data in basins such as the Gulf of Mexico, North Sea, and coastal Nigeria (e.g., Weber and Daukoru, 1976; Evamy et aI, 1978; Gallowayet aI, 1982) (Figure 16). Several miscellaneous features are noted below.

Arcuate sedimentary faults are probably common in del­taic strata, whereas essentially straight fault traces may be

~ ........... --~ ~!

c Figure I5-Configuration of listric normal faults in cross section. A. Triassic growth faults which are discontinuous (en echelon in part). After Edwards (1976). B. Faults produced experimentally in small-scale clay models. After H. Cloos (1930) and E.Cloos (1968). C. Proposed pattern of discontinuous en echelon faults comprising listric normal fault zone.

more ductile shale. Roux (1977) presents a very persuasive case that shale compaction does significantly reduce the dip and throw. However, the listric nature of faults in rela­tively brittle rocks and the listric nature of rotational slips in foundation failures indicate that flattening of dip is an inherent feature of many normal faults.

Dip of the steeper part of a listric normal fault com­monly has been recorded as approximately 60 0

, following the theoretical/experimental work of Anderson (1942) and Hubbert (1951) and from subsurface data. However, some faults are near vertical at the surface or in the near surface.

According to de Sitter (1964), the dip of a fault is gener­ally steeper near its ends (along strike) and flatter along the middle section, where throw is commonly greater.

Small-scale faults in Svalbard are zones which show en echelon patterns in cross sectional view (Edwards, 1976) (Figure 15A). This configuration is shown also in some of the experiments by H. Cloos (e.g., 1930) and E. Cloos (1968) (Figure 15B). It seems reasonable that some listric faults may in fact be zones composed of shorter faults, some of which are listric (Figure 15C),

Plan View

Local and regional normal fault pCltterns are well known from outcrops in the Middle Ea,l, east Africa, and the western United States (e.g., de Sitter, 1964; Hamblin,

./" ~ ~~------------~~--

A

--?>~------------~~ B

Figure 16-Map-view patterns of normal faults. A, Hypothetical subsidiary faults (after de Sitter, 1964); B, branches (or splays) developed near ends of major faults. C. Oligocene fault pattern in part of Texas Gulf Coast.

common in nondeltaic deposits. This difference may reflect "point" loading in the former and "line" loading in the latter. In map view, tilted upthrown fault blocks are generally convex in the direction of tilt (Moore, 1960). It is common for faults to branch or splay toward their ends or to show subsidiary faults there (de Sitter, 1964) (Figure

John W. Shelton 807

Figure 17--Contour map and cross section of listric normal fault at Lone Star field, northeast Texas. Fault is near vertical at surface, which is strongly erosional. After Bunn (1951). Nacatoch Sand dips away from fault in both blocks, suggesting that it was part of anticlinal feature at time faulting was initiated.

16). Although a fault zone may be very extensive, individ­ual faults within it may be very limited in length, and con­tiguous (or successive) faults along strike may show some overlap of their lengths. Also, in the Gulf of Mexico basin where the age of major fault zones decreases gulfward (generally basinward), a particular zone may contain older

faults immediately gulfward of younger faults.

Propagation

Many faults are initiated in a local area and extend, propagate, or grow laterally (de Sitter, 1964). With propa-

808 Listric Normal Faults

gation of a fault, one or both blocks may move in such a way that the greatest displacement (shift) of the block(s) is at or near the fault-a circumstance that results in reverse drag in the active block(s), including possible rollover in the downthrown block where the direction of dip of the fault is the same as regional dip. In an active upthrown block, the most favorable area for trap development would correspond to the section of fault with most dis­placement (Figure 3B).

Roux (1977) suggests that the throw of a fault not only decreases laterally toward the ends but also both upward and downward. This type of fault configuration is an indi­cation that the horizontal (plan view) fault pattern in some cases may assist in estimating the general vertical geome­try. This relation is inferred also from the work of Moore (1960), who correlated the direction of convexity of uplifted (upthrown) fault blocks with the direction of fault-block tilt, although Stewart (1978) has noted that other situations are common.

Propagation of a fault upward and/or downward is gen­erally inferred to be along a continuous surface. However, Roux (1977) and Crans et al (1980) suggest that fault prop­agation is not that simple and that many individual faults may compose a major fault as generally mapped. The en echelon pattern has appeal because the propagation of an existing listric fault upward or downward may require an unrealistic geometry if that fault is one continuous sur­face. For example, the Lone Star fault (Bunn, 1951) (Fig­ure 17) and the Mount Enterprise fault zone (Jackson, 1982) in east Texas show very steep dips at the present sur­face, and their upward extensions to the original surface before erosion would require an unusually large compo­nent with near vertical dip. The same problem exists where faults are characterized by many episodes of movement during deposition. Therefore. it is suggested that en eche­lon faults in cross section may comprise a zont; which is generally shown as one continuous listric fault.!

Roux (1977) has documented relatively steep branch (horsetail) faults which formed after compaction and flat­tening of master faults (Figure 18A). This type of branch may reflect reactivation of a fault which was initiated at or near the surface. Where faulting is initiated at depth, a branch fault may form in the downthrown block (Figure 18B).

Growth Faults

If growth faults are defined as those which were active during deposition, almost all normal faults are growth faults because the downthrown block is a likely deposi­tional site. Listric growth faults seemingly are regarded by most workers as a basic feature of regions where the faults are considered to be sedimentary, but it is now reasonable to conclude that listric growth faults are common even where the faults offset the basement (Figures 19-23), It seems possible that a listric growth fault may represent a zone of smaller listric faults or a zone of en echelon faults (Figure 24). A reason for that suggestion is that an original listric fault surface. if extended during significant growth (deposition) as a single continuous surface, would proba­bly not retain a realistic shape for a normal fault.

A B

_A

_____ 6--~~---A---

8--

Figure i8-Brancbing (horsetailing) of normal faults in cross section. A. Late, downward borsetail fault in uptbrown block of listric growth fault in Upper Tertiary of offsbore Texas. After Roux (1977). B. Hypotbetical upward horsetail in downthrown block of major fault.

10pcriALK LlEGEN

Figure 19-5eismic cross section of Argyll field, North Sea, with listric fault bounding riftlike Central graben on west. After Pen­nington (1975).

v';';';] TERTIARY ...... Ly*~ CRETACEOUS ANO PRE-CRETACEOUS

S PRE-CRETACEOUS

10mi I 1D1<m '

Hgure 2O-Schematic cross section of southern part of Bay of Biscay showing listric faults which formed during rifting. After Boillot et aI (1971).

Evidence for Listric Faults

The best types of evidence include abundant data on the position of fault surfaces in the subsurface, generally in an oil or gas field, unusual outcrop data where local relief allows delineation of the fault surface with depth, and seis­mic definition of the fault (Bally, 1983). Indirect, but not conclusive, evidence suggesting listric faults includes:

1. Sharply arcuate fault patterns. ' 2. Sharply arcuate uplifts or basins. I

3. Increase in stratal dip in hanging walls with depth together with increase in dip toward controlling growth

John W. Shelton 809

---y--------1-----------... '-'. -1' "-. .. _--

---- IIftR TERTIARY

- LOWER TERTIARY -CRETAClOUII

Figure 11-Selsmic cross section in central Mediterranean region Illustrating listric normal faults which formed during rifting.

TRIASSIC - __ -----:---------]

~_1L------_r--'ER~~-t------

~ WRENCH FAULT ZONE •

Figure ll-Seismic cross section across Tornquist· Teisseyre wrench fault zone separating Danish·Polish basin Oeft) from Fennoscan· dian shield (right). Fault zone in cross section contains lower Paleozoic listric normal growth faults.

l:nl:1 Jurassic - Triassic I + + + I Basement

++++ ~ +++++51 ++++++1

&Om;

Figure 13 ..... Palinspastic paleostructural cross section of eastern Italian Alps showing development of basin due to movement along listric normal faults. After BernouUi et aI (1979).

fault (reverse drag). 4. Reverse drag in hanging wall where footwall strata

show no evidence of rotation about an axis parallel to the strike of the fault. If strata in the subsurface were inclined before faulting, the attitude of these beds with respect to the fault may not be a criterion for a listric fault. For example, the Nacatoch in Figure 17 dips away from the lis­tric fault. Also, it should be noted that absolute movement of the downthrown block from geometric considerations could result in reverse drag along a planar fault with signif­icant lateral changes in throw (Figure 2S).

S. Differential tilt between imbricate fault blocks (suc-

-------

Fipre 24-Hypothetical configuration of growtb fault in cross section showing propagation of individual listric faults within zone.

cessively steeper dips in the dip direction of the faults) (Wernicke and Burchfiel, 1982).

6. Progradational stratigraphic succession, with thick ductile shale below brittle sandstone.

Planar faults rather than listric faults may form where the affected strata are entirely brittle (i.e., fault dies out above any ductile rocks) or, in some cases, where the fault has not been deformed. -

OCCURRENCES

In terms of global tectonics,listric normal faults occur: 1. In rifts within various geologic settings. Some may

810 Listric Normal Faults

precede formation of passive con:inental margi!t~ ,t.g., Bally et al, 1981; Harding, 1983)

2. On passive continental margins during drifting as they form and subside.

3. As sedimentary faults related to subsidence of passive continental margins (e.g., Bruce, 1973; Bally et aI, 1981), with "base failure" (involving overpressured shale and a salt) or gravity sliding.

4. In deformed basins, including those which formed along passive margins (miogeosynclines) (Ballyet al, 1981)

OLIGOCENE

---------EOCENE----___ _

E~ 00 0" ~ 4000ft

1000m

Hgure 25-Hypothetical structure map and cross section show­ing reverse drag along a planar normal fault due to movement of down thrown block of areally restricted fault.

A

OLIGOCENE

______ .!.OCENE

B

-------_______ OLIGOCENE

~======================::.:::;l--EOCENE--

E§ S§ o 4000ft

1000 m

c

Figure 26-Cross sections A and B across Vicksburg flexure. Significant subregional displacement across this fault lone, with inter­pretive listric faults, apparently reflects basinal development. C. Schematic cross section showing possible relationship between major fault in basinal development Oike that reflected by Vicksburg flexure) and sedimentary faults. After unpublished Shell Oil Co. report.

Sm;

Skm

Figure 27-Seismic cross section of listric sedimentary growth faults due to salt and shale flowage. Area is outer continental shelf in offshore southeast Texas and Louisiana where diapiric uplifts are semicontinuous. After Woodbury et al (1973).

1 mi 1 km i

Figure 28-Cross section of Valentine salt dome, La Fourche Parish, Louisiana, with listric normal fault associated with dia­piric shale and salt. After Halbouty (1979).

John W. Shelton 811

.-..... _-_ ... ./

/ ,

/ I

/

DUCTILE

SHALE

5mi 5km

2.0 sec

4.0 sec

Figure 29-Seismic cross section of offshore Texas showing lis­tric normal faults above ductile shale, which probably is incipient diapir. After Bruce (1973).

OLIGOCENE SAND WITH SHALE

EOCENE SHALE

tral Mediterranean (Figure 21); Gulf of Suez (Lowell and Genik, 1972; Lowell et ai, 1975; interpretation of Robson, 1971, by Harding and Lowell, 1979; Harding, 1983); Lake Superior Precambrian rift (Weiblen and Morey, 1980); and Rio Grande rift (Brown et aI, 1983).

Passive Continental Margins

Falvey (l974)*uggested that rifted stratigraphic sections and basement on passive margins commonly underlie less deformed sequences which formed during "drifting." Although the subsidence of passive margins undoubtedly reflects to some extent isostatic adjustment to the load of the sedimentary prism (Dietz, 1963; Hsu, 1965; Bott, 1978), subsidence to significant depths is thought to be by movement along basement faults (e.g., Shelton, 1968). It is suggested that these faults may be listric (Figure 26), that they are similar to and possible outgrowths of faults bounding rifts at earlier stages, and that they may be ulti-

/ /

/

/"

Figure 30-Cross section of North Maude Traylor field, Jackson and Calhoun Counties, Texas. listric normal fault is related to flowage of ductile Eocene shale. After unpublished Shell Oil Co. report.

or as foredeeps. 5. As late-orogenic and postorogenic faults after earlier

formation of foldbelts-very similar tCJ rifts (Bally et ai, 1981).

6. In axial zones of oro genes on active continental mar­gins (Beck et ai, 1975).

7. Along transform fault boundaries as a result of tran­stension or in extended upper part of transpressional (flower) structures.

Rifts

Examples of rifts, excluding postorogenic faults, where listric normal faults are fairly well documented or where interpretation of them from available data is reasonable, include North Sea (e.g., Bowen, 1975; Pennington, 1975; Evans and Parkinson, 1983; Harding, 1983) (Figure 19); Bay of Biscay (Boillot et aI, 1971; de Charpal et ai, 1978; Montadert et ai, 1979) (Figure 20); offshore eastern United States (Sheridan, 1974; 1977; Crutcher, 1983); cen-

mately responsible for sedimentary faults where ductile strata are thick owing to movement along this type of fault during deposition (Figure 26C). Basement-involved faults in this type of setting are illustrated by Morgan and Dow­dall (1983) from Baltimore Canyon Trough, and by Petro­bras (1983) from Potiguar basin, offshore Brazil.

Sedimentary Faults on Passive Margins

Deformation of progradational sedimentary sequences on passive margins may be dominated by half grabens, reverse drag, and rollover related to listric normal faults, which commonly are associated with overpressured or dia­piric shale or salt diapirs, and which were active during deposition. The best known areas for this type of defor­mation with listric growth faults are the northern Gulf of Mexico (Figures 6, 27-30) and the Niger Delta (e.g., Har­din and Hardin, 1961; Ocamb, 1961; Bruce, 1973; Busch, 1975; Lehner and de Ruiter, 1977; Curtis and Picou, 1978; Evamy et ai, 1978; Raux, 1979). Other areas are Sarawak

812 Listric Normal Faults

PURCELL RANGE

GALTON RANGE

PCmsed

."-.. PCmsed ."",.~

::: E 88 00 ... C')

5mi 5km

------ ~N SHIELD PCmsed Pf\EC~t-/lSf\\

'-,~".

-PCmsed

"- ..... "

PRECAMBRIAN METASEDIMENTS PURCELL LAVA

Figure 31-Seismic cross section across Rocky Mountain trench in southwestern Canada showing listric normal fault which devel­oped by opposite movement (backslippage) along earlier listric thrust fault. After Bally et al (1966).

NNW SSE UPPER MIDDLE ATOKA DATUM

='=-=-~~~C~-:--=-~-===~-~=-=-~-~-~~-~-~~~=='-=-\ MIDDLE ATOKA SANDSTONE SECTION

§LE " WAPANUCKA

~ 100m ~ 500ft '"

Figure 32-Paleostructural cross section of part of Arkoma basin, Oklahoma, with Atokan (Pennsylvanian) listric normal growth rault. After G. W. Hart (1978; personal communication, 1983).

and Sabah, east Malaysia (Schuab and Jackson, 1958; Scherer, 1980), offshore Brazil (Brown and Fisher, 1977), offshore eastern North America (Jansa and Wade, 1975; Sheridan, 1977), and North Sea (Gibbs, 1983).

Late-Orogenic to Postorogenic Faults

Bailey et al (1981) described examples of listric normal faults from western North America which may be interre­lated. These include (1) faults that may represent opposite movement ("backslippage") along preexisting listric thrust faults (Bally et aI, 1966; Royse et aI, 1975; Allmen­dinger et al, 1983) (Figure 31); (2) rifts, horsts1i.nd grabens, and half grabens; and (3) two types of faults in a mountain and valley system, with (a) an older decollement zone exposed in the mountain and (b) younger listric faults of the valley which may offset the decollement and contrib­ute further to basinal development in the valley.

This region is where some of the early studies demon­strated tilted fault blocks and low-angle listric normal faults (Davis, 1925; Longwell, 1933, 1945). Additional

studies documenting listric normal faults in this region include those of Mackin (1960), Moore (1960), Osmond (1960), Hamblin (1965), Hamilton and Myers (1966), Anderson (1971), Armstrong (1972), MacDonald (1976), Proffett (1977), Bally et al (1981), and Robison (1983). It is suggested that listric normal faults in this tectonic setting may be common in many orogenic belts. Listric faults may bound some grabens and half grabens in which the Trias­sic of the Appalachian system is present (Barrell, 1915; King, 1959, p. 50). As noted previously, faults in this type of setting may be parts of rift systems; correspondingly, the Triassic would be related to rifting which preceded opening of the Atlantic.

Axial Zones of Orogenes

In regard to subduction zones of island arcs, Beck et al (1975) have proposed that Pacific island arcs show a cen­tral collapse zone. The Andean orogene also contains an axial zone of block faulting and collapse (Figure 10). This zone apparently has a causal relationship to a young vol­canic belt.

John W. Shelton 813

Transform Boundaries and Strike-Slip Faults

Normal faults may form as a result of transtension asso­ciated with lateral movement-transform and/or strike­slip fault zones (Wilcox et al, 1973) (Figure 5). These normal faults may be listric (e.g., Southwest Lone Grove field, southern Oklahoma; Westheimer and Schweers, 1956). Those superimposed on a more fundamental crustal wrench or transform fault zone may be large-scale features (Figure 22).

In areas of transpression, normal faults in the extended part of the uplifted flower structure may possibly be listric (Figure 9), similar to those associated with compressional folding or extension over salt or igneous intrusives.

Deformed Basins

Faults in these settings are essentially of the same types as those which formed during rifting and drifting. Bernoulli et al (1979) have mapped Mesozoic listric normal growth faults in the eastern Italian Alps (Figure 23). These faults affect a dominantly carbonate section. Woodward (1961) and Wagner (1976) have described growth faults affecting the lower Paleozoic section in the Appalachian basin; they may well be listric.

The Arkoma basin of Oklahoma and Arkansas was a foredeep during the Atokan (Pennsylvanian), when both basement faults and listric sedimentary faults were active (G. W. Hart, personal communication, 1983) (Figure 32). The latter type is very similar to those of the Gulf of Mex­ico basin.

CONCLUSIONS

Listric normal faults may be an integral part of basinal development, and formation of several types of struc­tures, with potential for entrapment of hydrocarbons, results from movement along them. Listric normal faults occur in the various geologic settings reflecting exten­sional stress reaimes that are crustal and/or relatively superficial (restricted to the sedimentary prism). Their for­mation is enhanced by, or perhaps requires, a ductile "sub­strate."

The detailed three-dimensional geometry of listric faults may be expressive of subsidiary structures with some exploration or development potential. For example, short en echelon faults in cross section may constitute a zone, and define tilted fault blocks which are areallyand strati­graphically restricted. Further, splays or subsidiary faults, commonly developed near the ends of major faults, present conditions for potential traps.

REFERENCES CITED

A1lmendinaer, R. W., J. W. Sharp, D. Von Tish, L. Serpa, 1. Brown, S. Kaufman, J. Oliver, and R. B. Smith, 1983, Cenozoic and Mesozoic stnK:t\lre of the eastern Basin and Range province, Utah, from COCORP seismic-reflection data: Geology, v. II, p. 532-536.

Anderson, E. M., 1942, The dynamics of faulting and dyke formation with applications to Great Britain: Edinburgh, Oliver and Boyd, 191 p.

Anderson, R. E., 1971, Thin-skinned distension in Tertiary rocks of southeastern Nevada: GSA Bulletin, v. 82, p. 43-58.

Armstrong, R. 1., 1972, Low-angle (denudation) faults, hinterland of

the Sevier orogenic belt, eastern Nevada and western Utah: GSA Bul­letin, v. 83, p. 1729-1754.

Bally, A. W., ed., 1983, Seismic expression of structural styles: AAPG Studies in Geology 15, vs. 1-2.

-- D. Bernoulli, G. A. Davis, and 1. Montadert, 1981, Listric nor­mal faults: Oceanologica Acta, 26th International Geological Con­gress. Paris, 1980, p. 87-101.

-- P. L. Gordy, and G. A. Stewart, 1966, Structure, seismic data and orogenic evolution of southern Canadian Rocky Mountains: Bulletin of Canadian Petroleum Geology, v. 14, p. 337-381.

Beck, R. H., P. Lehner, P. Diebold, G. Bakker, and H. Doust, 1975, New geophysical data on key problems on global tectonics: 9th World Petroleum Congress Proceedings, Tokyo, v. 2, p. 3-17. London, Applied Science Publishers Ltd.

Bernoulli, D., C. Caron, P. Homewood, O. Kiiglin, and J. Van Stuijven­berg, 1979. Evolution of continental margins in the Alps: Schweizeris­che Mineralogische und Petrographische Mitteilungen, v. 59, p. 165-170,

Boillot, G,. p. A. Dupeuble, M. Lamboy, et ai, 1971, Structure et histoire geologique de la marge continentale au nord d l'Espagne (entre 4° et 9°W). in Histoire structurale du Golfe de Gascogne: Institut Fran~ois duPetwle, Collected Colloquial Seminars, no. 22, v. 22, p. V6-1-V6-52.

Bott, M. H. p', 1978, Subsidence mechanisms at passive continental mar­gins, in Geological and geophysical investigations of continental mar­gins: AAPG Memoir 29, p. 3-9.

Bowen, J. M., 1975, The Brent field, in A.W. Woodland, ed., Petroleum and the continental shelf of north-west Europe: New York, John Wiley and Sons, p. 353-362.

Brown, L. D.,S.Kaufman, and J. t:, Oliver, 1983, COCORP seismictra­verse across the Rio Grande rift, in Seismic expression of structural styles: AAPG Studies in Geology 15, v. 2, p. 2.2.1-1-2.2.1-6.

Brown, 1. F., Jr., and W. L. Fisher, 1977, Seismic-stratigraphic interpre­tation of depositional systems-examples from Brazilian rift and pull-apart basins, in Seismic stratigraphy-applications to hydrocar­bon exploration: AAPG Memoir 26. p. 213-248.

Bruce, C. H., 1973, Pressured shale and related sediment deformation­mechanisms for development of regional contemporaneous faults: AAPG Bulletin, v. 57, p. 878-886.

Bunn, J. R., 1951, Lone Star field, in F. A. Herold, ed., Occurrence of oil and gas in northeast Texas: University of Texas Publication 5116, p. 195·200.

Burchfiel, B. C., and L. Royden, 1982, Carpathian foreland fold and thrust belt and its relation to Pannonian and other basins: AAPG Bul­letin, v. 66, p. 1179-1195.

Busch, D. A., 1975, Influence of growth faulting on sedimentation and prospect evaluation: AAPG Bulletin, v. 59, p. 217-230.

Carey, S. W., 1958, The tectonic approach to continental drift, in S. W. Carey, ed., Continental drift-a symposium: Hobart, Australia, Uni­versity of Tasmania, p. 173-363.

Cloos, E., 1968, Experimental analysis of Gulf Coast fracture patterns: AAPG Bulletin, v. 52, p. 420-444.

Cloos, H., 1930, Zur experiment ellen Tektonik: Naturwissenschaften, v. 18, p. 741-747.

Cohen, C. R., 1982, Model for a passive to active continental margin transition: implications for hydrocarbons exploration: AAPG Bulle­tin, v. 66, p. 708-718.

Crans, W., G. Mandl, and J. Haremboure, 1980, On the theory of growth faulting-a geomechanical delta model based on gravity sliding: Journal of Petroleum Geology, v. 2, p. 265-307.

Crutcher, T. D., 1983, Southeast Georgia embayment, in Seismic expres­sion of structural styles: AAPG Studies in Geology 15, v. 2, p. 2.2.3-27-2.2.3-29.

Curtis, D. M., and E. B. Picou, Jr., 1978, Gulf Coast Cenozoic-a model for the application of stratigraphic concepts to exploration on passive margins: Gulf Coast Association of Geological Societies Transac­tions, v. 28, p. 103-120.

Davis, G. A., J. L. Anderson, and E. G. Frost, 1979, Regional Miocene detachment faulting and early Tertiary(?) mylonitic terranes in the Colorado River trough, southeastern California and western Ari­zona, in P. L. Abbott, ed., Geological excursions in the southern Cali­fornia area: San Diego State University, Department of Geological Sciences, p. 73-108.

Davis, W. M., 1925, The Basin Range problem: Proceedings of the NationaJAcademy of Sciences, v. 11, p. 387-392.

814 Listric Normal Faults

de Charpal, 0., P. Guennoc, L. Montadert, and D. G. Roberts, 1978, Riftina, crustal attenuation and subsidence in the Bay of Biscay: Nat­ure, v. 275, p. 706-711.

de Sitter, L. U., 1964, Structural geology, second edition: New York, McGraw-Hill Book Co., p. 119-137.

Dewey, J. R, and J. M. Bird, 1970, Mountain belts and the new global tee­tonics: Journal of Geophysical Research, v. 75, p. 2625-2647.

Dietz, R. S., 1963, Collapsina continental rises-an actualistic concept of geosynclines and mountain buildina: Journal of Geology, v. 71, p. 314-333.

Edwards, M. B., 1976, Growth faults in Upper Triassic deltaic sediments, Sva1bard: AAPG Bulletin, v. 60, p. 341-355.

Evamy, B. D., J. Haremboure, P. Kammerling, W. A. Knaap, R A. Mol­loy, and P. H. Rowlands, 1978, Hydrocarbon habitat of Tertiary Niaer Delta: AAPG Bulletin, v. 62, p. 1-39.

Evans, A. C., and D. N. Parkinson, 1983, A half-graben and tilted fault block structure in the northern North Sea. in Seismic expression of structural styles: AAPGStudies in Geology IS, v. 2. p.2.2.2-72.2.2-11.

Falvey, D. A., 1974, The development of continental margins in plate tee­tonic theory: APEA Journal, v. 14, p. 59-106.

Fanshawe, J. R., and A. G. Alpha, 1954, Tectonic map of portions of southern Montana and northern Wyoming: Billings Geological Soci­ety 5th Annual Field Conference Guidebook.

OaIIoway, W. E., D. K. Hobday, and K. Magara. 1982, Frio Formation of Texas Gulf coastal plain-depositional systems, structural frame­work, and hydrocarbon distribution: AAPG Bulletin. v. 66, p. 649-688.

Gibbs, A. D., 1983, Secondary detachment above basement faults in North Sea-Clyde field growth fault (abs.): AAPG Bulletin, v. 67, p. 469.

Hafner. W., 1951, Stress distributions and faulting: GSA Bulletin, v. 62, p.373-398.

Halbouty, M. T., 1979, Salt domes, Gulf region, United States and Mex­ico, second edition: Houston, Gulf Publishing Co., p. 47-87.

Hamblin, W. K., 1965, Origin of "reverse drag" on the downthrown side of normal faults: GSA Bulletin, v. 76, p. 1145-1164.

Hamilton, W., andW. B. Myers, 1966, CenozoicteC1onics of the western United States: Review of Geophysics, v. 4, p. 509-549.

Handin, J., and R. V. Hqer, 1957, Experimental deformation of sedi­mentary rodts under confining pressure: tests at room temperature on dry samples: AAPG BuBetin, v. 41, p. I-50.

Hardin, R R., and G. C. Hardin, 1961, Contemporaneous normal faults of Gulf Coast and their relation to flexures: AAPG Bulletin, v. 45, p. 238-248.

Harding, T. P., 1974, Petroleum traps associated with wrench faults: AAPO BuUetin, v. 58, p. 1290-1304.

-- 1983, Graben hydrocarbon plays and structural styles: Geologie enMijnbouw, v. 62, p. 3-23.

--and J. D. Lowell, 1979, Structural styles, their plate-tectonic hab­itats, and hydrocarbon traps in petroleum provinces: AAPG Bulletin, v. 63, p. 1016-1058.

Hart, O. w., 1978, Structural influence of growth faults on middle Ato­kan sandstone distribution in the Oklahoma portion of the Arkoma basin (abs.): GSA Abstracts with Programs, v. 10, p. 7.

Heard, H. C., 1966, IDustration on cover: Journal of Geological educa­tion, v. 14, no. 5.

Holmes, A., 1965, Principles of physical geololY, second edition: New York, Nelson and Sons/Ronald Press Co., p. 1044-1108 p.

Hm, K. J., 1965, lsostosy, crustal thinning, mantle changes, and the dis­appearance of ancient land masses: American Journal of Science, v. 263, p. 97-109.

Hubbert, M. K .• 1951, Mechanical basis for certain familiar geologic structures: GSA Bulletin, v. 62, p. 355-372. .

-- and W. W. Rubey, 1959, Role of fluid pressure in mechanics of overthrust faultiq: I. mechanics of fluid-filled porous solids and its application to overthrust faulting: GSA Bulletin, v. 70, p. 115-166. .

Humphris, C. C., 1978, Salt movement on continental slo~, northern Gulf of Mexico: AAPG Studies in Geology 7, p. 69-86.

Jackson, M. P. A., 1982, Fault tectonics of the East Texas basin: Univer­sityofTexas Bureau of Economic Geology Geological Circular 82.4, 31p.

Jansa, L. F., and J. A. Wade, 1975, Geology of the continental margin off Nova Scotia and Newfoundland, in W. J. M. van der Linden and J. A. wade, cds., Offshore aeology of eastern Canada, v. 2-regional geol-

ogy: Geological Survey of Canada Paper 74-30, p. 51-106. King, P. B., 1959, The evolution of North America: Princeton. New Jer­

sey, Princeton University Press, 190 p. Lehner, P., and P. A. C. de Ruiter, 1977, Structural history ofthe Atlantic

margin of Africa: AAPG Bulletin, v. 61, p. 961-981. Longwell, C. R., 1933, Rotated faults in the Desert Range, southern

Nevada (abs.): GSA Bulletin, v. 44, p. 93. -- 1945, Low-angle normal faults in the Basin and Range province:

Transactions of the American Geophysical Union, v. 26, p. 107-118. -- and R. E. Flint, 1962, Introduction to physical geology, second

edition: New York, John Wiley and Sons, 504 p. Lowell, J. D., and G. J. Genik, 1972. Sea-floor spreading and structural

evolution of southern Red Sea: AAPG Bulletin, v. 56, p. 247-259. ---- T. H. Nelson, and P. M. Thcker, 1975, Petroleum and

plate tectonics of the southern Red Sea, in A. G. Fischer and S. Jud­son, eds .• Petroleum and global tectonics: Princeton, New Jersey, Princeton University Press. p. 129-153.

MacDonald, R. E .• 1976, Tertiary tectonics and sedimentary rocks along the transition: Basin and Range province to Plateau and Thrust Belt province, Utah, in G. J. Hill, ed., Symposium on the geology of the Cordilleran hingeline: Rocky Mountains Association of Geologists, p.281-317.

Mackin, J. H., 1960, Structural significance of Tertiary volcanic rocks in southwestern Utah: American Journal of Science, v. 258, p. 81-131.

Montadert, L., D. G. Roberts, O. de Charpal, and P. Guennoc, 1979, Rifting and subsidence of the northern continental margin of the Bay of Biscay: Initial Reports of the Deep Sea Drilling Project, v. 48, p. 1025-1060.

Moore. J. G., 1960, Curvature of normal faults in the Basin and Range province of the western United States: U. S. Geological Survey Pro­fessional Paper 400-B, p. 409-411.

Morgan, L., and W. Dowdall, 1983, The Atlantic continental margin, in Seismic expression of structural styles: AAPG Studies in Geology 15, v. 2, p. 2.2.3-30-2.2.3-35.

Muehlberget, W. R., 1961, Conjugate joint sets of small dihedral angle: Journal of Geology, v. 69, p. 211-219.

Murray, O. E., 1961, Geology of the Atlantic and Gulf Coastal province of North America: New York, Harper and Brothers, p. 167-201.

Ocamb, R. D., 1961, Growth faults of south Louisiana: Gulf Coast Asso­ciation of Geological Societies Transactions, v. 11, p. 139-173.

Osmond, J. C .• 1960, Tectonic history of the Basin and Range province in Utah and Nevada: Mining Engineering, v. 12, p. 251-265.

Pennington, J. J., 1975, Geology of Argyll field, in A. W. Woodland, ed., Petroleum and the continental shelf of north-west Europe: New York, John Wiley and Sons, p. 285-297.

Petrobras, 1983. Potiguar basin, Brazil • .in Seismic expression of struc­tural styles: MPG Studies in Geology 15, v. 2, p. 2.2.3-59-2.2.3-65.

Proffett, J. M., Jr., 1977, Cenozoic geology of the Yerington district, Nevada, and implications for the nature and origin of Basin and Range faulting: GSA Bulletin, v. 88, p. 247-266.

Reeves, F., 1925, Shallow folding and faulting around the Bearpaw Mountains: American Journal of Science, 5th series, v. 10, p. 187-200.

-- 1946, Oriain and mechanics of thrust faults adjacent to the Bear­paw Mountains, Montana: GSA Bulletin, v. 57, p. 1033-1047.

Rettger. R. E., 1935, Experiments on soft rock deformation: AAPG Bul­letin, v. 19, p. 271-292.

Robison, B. A .• 1983. Low-anaIe normal faulting, Marys River valley, Nevada, in Seismic expression of structural styles: AAPG Studies in Geology 15, v. 2, p. 2.2.2-12-2.2.2-16.

Robson, D.A., 1971, The structure ofthe Gulf of Suez (Clysmic) rift with special reference to the eastern side: Quarterly Journal of the Geologi­cal Society of London, v. 127, p. 247-276.

Roux, W. F., Jr., 1979, The development of growth fault structures: MPG Structural Geology School Course Notes, 33 p.

Royse, F., M. A. Warner, and D. C. Reese, 1975, Thrust belt structural geometry and related stratigraphic problems, Wyoming-ldaho­northern Utah, in Symposium on deep dri1ling frontiers of the central Rocky Mountains: Rocky Mountains Association of Geologists, p. 41-54.

Schaub, H. P., and A. Jackson, 1958, The northwestern oil basin of BOi . neo, in L. G. Weeks, ed., Habitat of oil: AAPG, p. 1330-1336.

Scherer, F.C., 1980, Exploration in east Malaysia over past decade, itl Giant oil and gas fields of the decade 1968-1978: AAPG Memoir 30. p.423-440.

John W. Shelton 815

Shelton, J. W., 1968, Role of contemporaneous faults during basinal sub­sidence: AAPG Bulletin, v. 52, p. 399-413.

Sheridan, R. E., 1974, Atlantic continental margin of North America, In

C. A. Burk and C. L. Drake, eds., The geology of continental mar­gins: New York, Springer-Verlag, p. 391-408.

--- 1977, Passive margin structural ~tvles: AAPG Structural Geol­ogy School Course Notes, 11 p.

Stewart, J. H., 1971, Basin and Range structure-a system of horsts and grabens produced by deep-seated extension: GSA Bulletin, v. 82, p. 1019-1044.

-- 1978, Basin-range structure in western North America, itl R. B. Smith et al, eds., Cenozoic tectonics and regional geophysk, of the western Cordillera: GSA Memoir 152, p. 1-31.

Terzaghi, K., and R. B. Peck, 1948, Soil mechanics, in engiflcering prac­tice: New York, John Wiley and Sons, p. 394-406.

Thompson, T. L., 1976, Plate tectonics in oil and gas exploration of conti­nental margins: AAPG Bulletin, v. 60, p. 1463-1501.

Wagner, W. R., 1976, Growth faults in Cambrian and Lower Ordovician rocks of western Pennsylvania: AAPG Bulletin, v. 60, p. 414-427.

Weber, K. J., and E. Daukoru, 1975, Petroleum geology of the Niger Delta: 9th World Petroleum Congress Proceedings, Tokyo, v. 2, p.

209-221. London, Applied Science Publishers Ltd. Weiblen, P. W., and G. B. Morey, 1980, A summary of the stratigraphy,

petrology and structure of the Duluth complex: American Journal of Science, v. 280-A. p. 88-133.

Wernicke, B., and B. C. Burchfiel, 1982, Modesofcxtensional tectonics: Journal of Structural Geology, v. 4, p. lOS-liS.

Westheimer, J. M., and F. P. Schweers. 1956, Southwest Lone Grove field, Carter County, Oklahoma, in Petroleum geology of southern Oklahoma, vol. I: AAPG, p. 144-153.

Wilcox, R. E., T. P. Harding, and D. R. Seely, 1973, Basic wrench tecton­ics: AAPG Bulletin, v. 57, p. 74-96.

Wise, D. U., 1963, Keystone faulting and gravity sliding driven by base­ment uplift of Owl Creek Mountains, Wyoming: AAPG Bulletin, v. 47, p. 586-598.

Woodbury, H. 0., I. B. Murray, P. J. Pickford, and W. H. Akers, 1973, Pliocene and Pleistocene depocenters, outer continental shelf, Louisi­ana and Texas: AAPG Bulletin, v. 57, p. 2428-2439.

Woodward, H. P., 1961, Reappraisal of Appalachian geology: AAPG Bulletin, v. 45, p. 1625-1633.

Ziegler, P. A., 1982, Geological atlas of western and central Europe: Amsterdam, Elsevier, 130 p.