Analysis of Deformation Bands in the Aztec Sandstone, Valley of Fire State Park, Nevada

UNLV Retrospective Theses & Dissertations

1-1-1989

Analysis of deformation bands in the Aztec Sandstone, Valley of Fire State Park, Nevada

Robin Eugene Hill University of Nevada, Las Vegas

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Repository Citation Hill, Robin Eugene, "Analysis of deformation bands in the Aztec Sandstone, Valley of Fire State Park, Nevada" (1989). UNLV Retrospective Theses & Dissertations. 76. http://dx.doi.org/10.25669/79kb-h1f4

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Analysis of deformaticn bands in the Aztec Sandstone, Valley of Fire State Park, Nevada

Hill, Robin Eugene, M.S. University of Nevada, Las Vegas, 1990

UMI 300 N. Zeeb Rd, Ann Aibor, MI 48106

by Robin E. Hill

A thesis submitted in partial fulfillment of the requirements for the degree of

Master of Science

Geology

Geoscience Department University of Nevada, Las Vegas December, 1989

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The thesis of Robin Eugene Hill for the degree of Master of Science in geology is approved.

/ 7 _ d L , r / - /'/. A / L ______Ch^il^erson, Ernest Duebendoifer, Ph.D

\ J(a^ ■ Examining ^Committee Member, Stephen Rowland, Ph.D.

E^^^tmining Committee Member, John Wilbanks, Ph.D.

GradiMte Faculty Representative, Boyd Earl, Ph.D.

Graduate Dean, Ronald Smith, Ph.D.

University of Nevada, Las Vegas December, 1989

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Analysis of Deformation Bands In the Aztec Sandstone Valley of Fire State Park, Nevada

Abstract

This research concerns two types of deformation structures, deformation bands and low-angle slip surfaces, that occur in the Aztec Sandstone in the Valley of Fire State Park, Nevada. Deformation bands were analyzed by mapping and describing over 500 of the structures on a bedding surface of about 560 square meters.

Deformation bands are narrow zones of reduced porosity which form resistant ribs in the sandstone. Three sets of deformation bands are present at the study site (type 1,2 and 3). Type 1 and 2 bands are interpreted as coeval and form a conjugate set with a dihedral angle of 90 degrees. These sets are usually composed of multiple bands. A third set is interpreted to be subsidiary to the older set, and intersections angles with the earlier formed sets are approximately 45 degrees. In contrast with the older sets, the third set is nearly always a single band which is sinuous or jagged along its length. Despite this sinuosity, these bands have consistent orientations and are parallel with each other from end to end. Another characteristic of these bands

111

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is that they curve sharply near the intersections with the earlier formed sets, sometimes becoming parallel with the older deformation bands.

All three sets of deformation bands are crosscut and sometimes offset by low-angle slip surfaces. These faults have reverse dip slip displacement and locally have mullions developed. Displacements indicate eastward movement of the hanging wall which is consistent with the inferred movement of major Mesozoic thrust faults in the vicinity.

The change of deformation style from deformation bands to low-angle slip surfaces may document a change in the stress regime. Paleostress interpretation of the deformation band geometry indicates the intermediate stress axis is vertical. The low-angle slip surfaces indicate the least compressive stress axis is vertical. This possible change in stress axes may be the result of increasing pore pressure associated with tectonic loading from emplacement of the Muddy Mountain thrust.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table of Contents

Section Section Title Page

1. Introduction...... 1 2. Terminology and Previous Research...... 2 3. Location...... 11

4. Stratigraphie Setting...... 14 5 Structural Setting ...... 18

6. Method of Study...... 1 9 7. Description of Structures in the Aztec Sandstone...... 24 7.1 Deformation Bands...... 2 4 7.2 Low-angle Slip Surfaces and Other Structures 3 0 8. Pétrographie Description of Deformation B ands 3 7 9. Interpretation and Discussion of Deformation Bands in the Valley of Fire...... 3 8 9.1 Comparison of Deformation Bands in the Valley of Fire with Other Areas ...... 3 8 9.2 Age Relationships Between Deformation Band Sets...... 40 9.3 Age Relationships Between Deformation Bands and Iron Oxide Staining...... 40

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9.4 Correlation of Deformation Bands with Regional Stresses...... 4 1 9.5 Poorly Understood Characteristics of Deformation Bands in the Valley of Fire...... 44 9.6 Conceptual Model for the Development of the Deformation Band Network...... 46 10. Summary ...... 51 11. References...... 5 3 12. Appendix ...... 1 5 5

List of Figures

Figure Description Page

1. Location map of the study site...... 12 2. Stratigraphie section of formations in the study area...... 1 6 3. Map of the deformation band network in the Valley of Fire State Park (in pocket) 4. Comparison of length data measured in the field with length data computer digitized...... 2 3 5. Pie chart showing the relative percentages of each type of deformation band on the pavem ent...... 27 6. Sketch of intersection characteristics _ between the three sets of deformation b an d...... s .2 8

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7. Comparison of deformation band terminations on the pavement...... 29 8. Average length, width, nearest band, and total width of deformation for each band ty p e ...... 3 1 9. Equal area projection for orientation data from the pavement...... 3 2 10. Equal area projections of orientation data for four different locations...... 3 3 11. Illustration of the proposed model for the formation of deformation bands...... 49

List of Plates

Plate Description Page

1. Location photograph of the fracture pavem ent...... 1 3 2. Wide deformation band terminating at a bedding interface...... 17 3. Aerial photograph of the fracture pavem ent...... 2 1 4. Type 3 deformation band with chevron fold appearance ...... 2 7 5. Deformation bands showing abrupt increase in density...... 3 4 6. Low-angle slip surfaces in the Valley of Fire...... 3 6

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Side view of deformation band showing primary bedding preserved...... 42

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I wish to thank the Nevada State Park Service for keeping track of me and giving me permission to work in the Valley of Fire State Park. I also appreciate the use of aerial photographs from the Bureau of Land Management. This thesis has been greatly improved by the help of Steve Laubach, Chris Barton and several co-workers at CER Corporation. I also especially thank Ernie Duebendorfer for his interest and help in completing this research.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Analysis of Deformation Bands in the Aztec Sandstone Valley of Fire State Park, Nevada

introduction

Deformation bands are narrow zones of reduced porosity that occur in high porosity sandstones. Band geometries are similar to fracture geometries, however rather than being a plane of separation they are zones of tighter grain packing, sometimes with grain cataclasis. Deformation bands have been described in several sandstones in the United States and Scotland. This study describes a network of deformation bands present in the Jurassic Aztec Sandstone and the White Sandstone Member of the Cretaceous Baseline Sandstone in the Valley of Fire State Park, Nevada that provides new insight into the geometry and overall pattern of deformation bands. Results have implication for hypotheses of band origin and for deformation processes in sandstone.

The origin and mechanical significance of deformation bands is controversial and poorly understood. The purpose of this study is to describe deformation bands in the Aztec Sandstone, to compare these structures with deformation bands from other areas, and to develop a mechanical model for the origin of the deformation bands in the study area.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Deformation bands are practically important because they may block or impede the migration of fluids and thus influence diagenesis and compartmentalize hydrocarbon reservoirs (Pittman, 1981). In addition, deformation bands have been used to interpret paleostress and they may be the primary style of deformation in areas where massive sandstones are flexed above faults (Jamison and Stearns, 1982; Laubach, 1988).

2, IerjniJiaLoav_ and Previous Research

Deformation bands were first recognized and named by Aydin (1978). Since then several papers have described deformation bands, and each author has used his own terminology. Aydin and Johnson (1978) use the terms "deformation band", "zone of deformation bands", and "slip surface" to describe features in the Entrada and Navajo Sandstones. Describing similar features in the Simpson Group (Ordovician), Pittman (1981) refers to the structures as "granulation seams", whereas Jamison and Stearns (1982) described them as "single microfaults" and "anastomosing microfaults" in the Wingate Sandstone of Colorado National Monument. Describing the structures present in the New Red Sandstone of Western Scotland, Underhill and Woodcock (1987) reviewed the previous work and chose the terms "faults" and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. "zone of fault, (for two or more closely spaced faults) rather than use the "confusi:ig current terminology". They also use the term "slip surface" for the throughgoing discontinuities. Clearly, there is no consensus on either the terminology or mechanisms of formation of deformation bands.

I have chosen to use the terminology of Aydin and Johnson (1978). The term fault should be reserved for a surface of discontinuity (fracture) across which there is an observable offset (Barton, 1983). The term "granulation seam" implies cataclasis as the dominant process in the formation of the structures which may or may not be true for the structures in the Aztec Sandstone. I therefore prefer the term deformation band because it is non- genetic.

As described by Aydin (1978), deformation bands are lighter in color and stand up as ribs above the surrounding sandstone because of their higher resistance to erosion. The resistant ribs are about twice as wide as the actual structures that are visible in thin sections. In the Wingate and Navajo sandstones, the formation of deformation bands was attributed to a combination of processes including shear and volume change in pore spaces, microfracturing of grains, and mixing of grain fragments with unbroken grains (Aydin, 1978).

Pétrographie analysis by Aydin (1978) revealed two zones across the deformation band, an inner zone and an outer zone. In

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 the outer zone and at terminations of bands, the deformation involves pore collapse and deformation of matrix between grains; however no undulatory extinction or deformation lamellae were observed. The inner zone is composed of crushed quartz grains (Aydin, 1978). Other workers have also generally attributed the formation of deformation bands to the process of cataclasis, however, many have described undulose extinction in the outer zone (Pittman, 1981; Jamison and Steams, 1982; Underhill and Woodcock, 1987).

Deformation band growth was described by Aydin and Johnson (1983). In the first stage of deformation, contact points and contact areas between adjacent grains increase the friction of the rock mass causing the grains to interlock so that additional strain causes the grains to fracture. The fracturing starts at grain contacts where stresses are greatest and can result from an increase in normal stress alone, however, it is usually the result of a combination of normal and shear stresses. Shear stress tends to dilate the mass, concentrating forces at fewer contact points between grains, and once fracturing starts, it continues to fracture the angular grains. During this stage the band decreases in volume as a result of pore reduction and is sheared. Both the strength and elastic modulus of the material within the band increase because the decrease in grain size results in an increase in contact points per unit area and, therefore a decrease in stress concentrated at contact points (Aydin and Johnson, 1983).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Aydin and Johnson (1983) also listed 12 key features of deformation bands in the Wingate and Navajo sandstones. They are as follows:

1) The deformation is highly localized within a narrow band.

2) Permanent deformation in a band is by fracturing and displacement of grains, by distortion of the matrix and by reduction of pore volume.

3) There is both volume decrease and shear displacement across the band. The magnitude of the volume strains is at least 0.2, and the average shear strain is of the order of 1-10.

4) The physical properties, including density and grain size, and probably elasticity and strength, change as deformation proceeds.

5) The deformation bands form side by side. This observation raises the question why further deformation is accommodated by the formation of a new band, rather than by continued displacement on a pre-existing band, and why

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the new band forms immediately adjacent to the pre-existing band.

6) Zones are at most a few decimeters wide but are tens or hundreds, of meters in extent. Thus zones of deformation bands, like individual bands, represent highly localized deformation of the sandstone.

7) The trace of an isolated deformation band tends to be straight, but the trace of a deformation band within a zone is wavy or inosculates in a plane normal to the direction of shear.

8) A slip surface represents extremely localized, large magnitude deformation. The formation of a slip surface marks a change in the style of deformation from continuous and zonal (in a band and in a zone) to discontinuous and planar (in a slip surface).

9) Slip surfaces have not been observed in the porous Entrada and Navajo sandstones except within zones of deformation bands.

10) Bands, zones and surfaces of a single set form sequentially and are parallel to one another.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The orientation of slip surfaces is controlled by the orientation of zones of deformation bands.

11) Each type of fault occurs in sets with relatively regular spacing.

12) Each type of fault occurs in networks constituted of multiple sets. In dip- and oblique-slip faulting, there are more than two and typically four sets.

Several of these points are not valid for the Aztec Sandstone in the study area as discussed below, and a new model is presented that explains the formation of deformation bands in the Aztec Sandstone. This model may have more general applicability to other areas.

Pittman (1981) describes granulation seams in the Simpson Group, Oklahoma. This research focused on the impact of cataclasis on porosity, permeability and pore aperture size. In discussing the origin of granulation seams, Pittman (1981) suggests that in addition to grain fracturing, and rigid body rotation of grains, a significant amount of the gouge material may be the result of spalling of quartz overgrowths under stress. He likens the process to gear teeth being broken off when irregularly meshed. This finding is based on the observation that the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 percentage of quartz overgrowths decrease as the percentage of granulated quartz increases (Pittman, 1981).

Jamison and Steams (1982) describe four types of deformational features in the Wingate Sandstone: 1) microfaults, 2) Riedel shears, 3) fault zones, and 4) fractures. Microfaults are defined as narrow zones in the rock which have accommodated small amounts of shear (less than 1 millimeter up to several centimeters). These are apparently the same structures described by Aydin (1978) as deformation bands. Riedel shear zones are shear structures (such as microfaults) and have a specific geometry with respect to the shear couple. Fault zones are zones which have been granulated so much that no sedimentary features are recognizable and displacements are usually at least several meters. Fractures are characterized by having lost cohesion across the fracture surface.

Jamison and Steams (1982) list seven characteristics of microfaults which are summarized as follows:

1. The width of the low porosity and gouge zones have little dependence on the amount of offset.

2. Porosity and grain size are inversely related to offset.

3. The central half of the zone of reduced porosity consists of comminuted sand grains.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4. Microfaults develop in conjugate pairs that intersect with a small dihedral angle of 20® to 40°.

5. Displacements on the microfaults is dip slip.

6. Microfault density increases linearly with the amount of bulk strain of the rock.

7. Microfaults rarely penetrate through major bedding-unit contacts.

In addition to these seven characteristics, Jamison and Steams (1982) also describe microfaults having Riedel shear geometry. Conjugate Riedel shears form at angles of 10° to 15° (R) and 75° to 80° (R') to the principal displacement shear fractures (Blés and Feuga, 1986; Ramsay, 1987). Deformation bands with Riedel type geometries were not observed within the study area.

Underhill and Woodcock (1987) studied deformation bands in the New Red Sandstone in Scotland. This study confirmed most of the previous research regarding the microscopic description of deformation bands and attributed their origin to strain hardening after only a small increment of slip. They also described an inner and outer zone of deformation similar to those documented by Aydin (1978).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10 Thin sections from the New Red Sandstone described by Underhill and Woodcock (1987) revealed a dramatic decrease in grains larger than 0.1 mm from the undeformed sandstone to the inner zone of the band. A corresponding increase in grains less than 0.03 mm was observed over the same range, but there was little change in the percentage of grains between 0.1 and 0.03 mm in size. In addition, the percentage of angular grains rose sharply toward the center of the deformation band (Underhill and Woodcock, 1987). Their findings also revealed that the dihedral angle between deformation bands averaged 36°. They concluded that deformation bands form by rupture of grain cements, tightening of packing and reduction of grain size by fracturing. Strain hardening was attributed to denser packing, decrease in sorting and more angular fragments increasing the friction angle. They believe the transient pore pressure increases during slip, but dissipates immediately after slip. They also attributed the geometry of the fault system to regional boundary conditions (Underhill and Woodcock, 1987).

Because deformation bands strain harden, each band records a strain increment. If the stress regime changes, new deformation bands can form in an orientation to accommodate the new stress regime. Because of this, deformation bands may be used to interpret changes in the paleostress regime (Woodcock and Underhill, 1987). For example, using deformation bands and other geologic relationships. Woodcock and Underhill (1987) were

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 able to show there had been two phases of granite emplacement below the New Red Sandstone.

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The study area is located in the Valley of Fire State Park, Clark County, Nevada approximately 40 miles northeast of Las Vegas. The site is on the Valley of Fire West Quadrangle Map (7.5 minute series) at 36°28'23" north latitude and 114°31'43" west longitude. The UTM grid location is 11 SQL 2142 3904.

The site is located about 75 meters to the west of the White Dome Road which is closed to automobile traffic and requires about a 45 minute walk from the Rainbow Vista parking lot (Fig.l). When walking on the White Dome road the site is easily located by the large cottonwood tree on the west side of the road in the third wash. This is one of two trees in the Valley of Fire. The study site is located about 20 meters west of the tree on the south side of the wash (Plate 1). The size of the study area is about 560 square meters and is elongate in a north-south direction. The surface dips 18° to the northeast and because it is completely devoid of vegetation and cover it is referred to as a pavement surface or fracture pavement throughout this thesis using the terminology of Barton et al. (1987). The boundaries of the pavement were selected to limit the pavement to one “sand body” (defined below) of the Aztec Sandstone. The pavement is the principal focus of this research;

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12

NV UT

Index M a p 2 0 0 mi. 200km

Study Site

3 ml SCO it 5 km

Figure 1. Location map showing the location of the study site in the Valley of Fire State Park, Nevada.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13

Plate 1. Photogrcph showing the fracture pavement. View is to southeast.

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however, interpretation of the deformation band network utilizes observations of the excellent exposures present in the vicinity.

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The Aztec Sandstone is considered Jurassic-Triassic in age and is underlain by the Moenave and Kayenta Formations in the Valley of Fire (Stewart, 1980; Bohannon, 1983). However, paléontologie work has yielded an Early Jurassic age for the Kayenta Formation in northeastern Arizona (Padian, 1989). If this age determination applies to the Valley of Fire area, the Navajo Sandstone (and the equivalent Aztec Sandstone) must be Jurassic in age.

Four different bedding types have been described in the Navajo and Aztec Sandstones including horizontal-bedding, cross bedding, contorted-bedding, and indistinct-bedding (Sanderson, 1973). Indistinct bedding is macroscopically not bedded and has also been called structureless sandstone (Marzolf, personal communication, 1982).

In the vicinity of the field area, the Aztec Sandstone is the oldest well-exposed unit. The underlying Kayenta, Moenave, and Chinle formations outcrop in the center of the Valley of Fire but not near the study area. The overlying Cretaceous rocks are

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15 exposed just east of study site and include the Willow Tank Formation and Baseline Sandstone (Fig. 2).

The Aztec Sandstone in the study area dips consistently 15 to 25 degrees east-northeast along the north limb of the large anticline in the Valley of Fire. Due to variable bedding orientations within the Aztec, determination of the structural dip at a particular location is not always possible. The Aztec Sandstone is very thick (>2000 ft.), but it can be subdivided into bedding packages which were deposited with a continuous bedding orientation. These packages will be referred to as sand bodies. The pavement studied in this research was deliberately confined to one sand body because deformation bands are often observed to terminate or be refracted at bedding interfaces (Plate 2). In addition, this study shows that deformation bands are confined to sand bodies which have well-developed bedding. In sand bodies with indistinct or structureless-bedding, jointing is the dominant deformation mechanism and deformation bands are not present. The pavement is contained within a single sand body with bedding oriented 150°, 18° E. This orientation is consistent with the structural dip of the Aztec Sandstone in the vicinity and indicates the pavement is in a horizontal-bedded sand body.

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Baseline Sandstone White Member Kbw

K wt Willow tank Formation

Aztec Sandstone

Moenave and Kayenta Formations

Chinle Formation

m Moenkopi Formation

Kaibab and Toroweap Formations kt

Figure 2. Stratigraphie section of formations exposed in the field area showing their relative thicknesses (modified from Bohannon, 1983)

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Plate 2. Very wide deformation band (sub-vertical) which terminates at a bedding interface (moderately inclined to left).

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The Aztec Sandstone at the study site is within the autochthonous block of the Muddy Mountain thrust fault. However, the Aztec Sandstone is parautochthonous in the immediate vicinity having been thrust onto the Cretaceous rocks along the Willow Tank thrust.

The Valley of Fire area has been mapped in considerable detail by Longwell (1949, 1965) and Bohannon (1983). Pertinent information describing the major structures in the area are summarized in Table 1.

The complex structural setting of the field area precludes a simple correlation of the deformation band network with regional structures. Without being able to demonstrate a direct relationship between deformation bands and large-scale structural features, any attempt to relate deformation bands with regional structures based on inferred stress pattern is tenuous. However, field relationships between deformation bands and some major structures can be used to constrain the age of deformation bands and thus limit the possibilities.

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Fault Time Distance from .Ctiaraptfiristi££ SludyJicea

Muddy Late Mesozoic 5 mi west Regional thrust fault which usually Mountain puts Bonanza King Formation over the Thrust Aztec Sandstone

Lake Mead 12.7 -11.3 my 11 mi east 65 km left lateral movement Fault System

Willow Tank Late Mesozoic less than 1 mi Minor thrust fault which puts Aztec Thrust east Sandstone over the Cretaceous Baseline Sandstone. The conglomerate at the base of the Baseline Sandstone is thought to be syntectonic.

Atlatl Fault Tertiary Immediate A series of west dipping normal faults Vicinity that flatten with depth and cause stratal tilts from block rotation.

Baseline Fault Tertiary 3 mi east Similar to the Atlatl Fault

Table 1. Summary of significant structures and their proximity to the study area (modified from Bohannon, 1983).

6. Method of Study

The principal field method employed in this research is the mapping of a deformation band network on a low-level aerial photograph. The benefits of using this method to study fracture networks is described by Barton and Hsieh (1989). This technique was used by Barton et. al (1987) to analyze fracture networks in volcanic rocks, and by Segall and Pollard (1983) to characterize fracture formation in granite. The method is ideal for the analysis of plane strain deformation, however, in cases of nonplane strain the method only provides a two-dimensional analysis of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 deformation. The method is also inadequate for characterizing planar features which intersect the pavement at a low angle, which is why low angle structures are not included on the pavement map. The deformation bands intersect the pavement at angles of between 50 to 70, and therefore afford themselves to this method of study.

The study area was selected based on the basis of good exposure and a complex network of deformation bands. One of the benefits of using the pavement method for studying deformation bands is the clear relationships which can be seen between the bands (Fig. 3, in pocket). The map of the deformation band network is one of the primary results of this research. The map was prepared on a photographic base which was obtained by photographing the outcrop from a helicopter hovering about 200 ft above the ground (Plate 3). All bands were mapped in the field. The larger bands are clearly visible on the photographic base and were mapped first. Smaller bands were then mapped by their relative position to other bands, rocks and plants which are visible on the aerial photograph.

In some areas the bands are very difficult to see clearly. Band visibility is dependent upon sufficient weathering of the surface to expose the deformation bands which are more resistant to erosion. In areas where the band traces were obscure, the bands were traced with chalk to facilitate mapping. Bands shorter

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Plate 3. Aerial photograph similar to the one used to map the deformation band network (bar at lower right is 10 m).

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than 20 cm were not mapped unless they were part of a longer band offset by faults.

Following completion of the map, the bands were numbered and the germane characteristics of each band were measured (Appendix 1). The characteristics recorded include strike, dip, length, width, nearest parallel band, and a description of the termination type at both ends.

Where possible, the attitude of each band was measured; however, because of the lack of relief of the bands, few dips were obtained. Orientation and length were obtained by digitizing the pavement map. Computer digitized orientations and lengths were compared with data collected in the field using a compass and steel measuring tape (Fig. 4). The results indicate computer digitizing is in good agreement with field data.

The width of each band was measured with a caliper. The width recorded is the width of the resistive band which stands above the undeformed sandstone. The measured width may be wider than the actual width of deformed sandstone (Aydin, 1978).

The distance to the closest parallel band was also recorded. This distance between bands was often quite variable, and an average inter-band distance was determined by visual estimate for each pair of bands.

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10.0 T

8.0 .. ■ ■ ■ 6.0 -- Digitized Length (m) 4.0 -- ■ ■

+ 4 - — I 0.0 2.0 4.0 6.0 8.0 10.0 Field Measured Length (m)

Figure 4. Comparison of length data measure in the field with length data digitized by computer.

The terminations at each end of each band were recorded using the following code:

A - Abuts, the band terminates at another band with no visible change in orientation.

E - Edge, the band extends beyond the edge of the pavement.

H - Hooks, the band curves from the recorded azimuth to the azimuth of the band which it

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 intersects. The direction that the band turns is also recorded.

M - Merge, the band merges into another band of similar orientation.

T - Termination, the band terminates within the undeformed sandstone.

CD - Change in direction, the band makes an abrupt change in direction.

When a band intersected another band the “type of band” intersected was also recorded (band types are discussed below). Clarifications and unusual observations were recorded in the remarks category.

"L Description of Structures in the Aztec Sandstone

7.1 Deformation Bands

Deformation bands in the study area appear to be restricted to well-bedded sandstone and are noticeably absent in structureless sandstone. Photographs from Aydin and Johnson (1978), Pittman (1981), and Underhill and Woodcock (1987) appear to show deformation bands in sandstones with visible bedding. The apparent restriction of deformation bands to well- bedded sandstone has not been noted by other researchers. If

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25 this affiliation holds for other areas, it is a point on which future workers may focus in attempting to explain the development of deformation bands.

In organizing data collection for fracture studies, it is common practice to group fractures into “sets”. A fracture “set” is defined as a group of fractures which are of similar character and parallel or sub-parallel with each other (Barton, 1983; Ramsay, 1987).

The map of the pavement shows three well-developed sets of deformation bands (Figure 3, in pocket). The three sets are referred to as type 1, type 2 and type 3 bands. The average orientation of type 1 bands is 155°, 60° W. The mapped traces are usually composed of multiple bands (considered one trace) which are very straight and were never observed to cross each other. Bands such as these were called zones of deformation bands by Aydin and Johnson (1978). Occasionally an individual deformation band deviates from the zone and is shown as a separate trace on the map. Type 1 bands are typically very continuous with most bands extending the entire length of the pavement. The width of the zone of deformation bands often totals several centimeters, however, the individual bands that compose the type 1 band are rarely greater than two centimeters wide.

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Type 2 bands are the same as the type 1 bands, except they are oriented 60°, 75° N. Intersections between type 1 and type 2 bands are usually cross-cutting, however examples can be found where type 2 bands terminate at type 1 bands and vice-versa. The rhombohedral blocks formed by these fractures are herein called lozenges. Ramsay (1987) applied this term to blocks of undeformed rock between intersecting shear zones.

Type 3 bands are by far the most common bands on the pavement (Fig. 5), and they differ from type 1 and 2 bands in several respects. They are generally single, only rarely multiple, bands that average about 0.5 centimeters wide. Type 3 bands have a consistent orientation over their entire length, but they are often sinuous in detail. The sinuosity is commonly sharply angular resulting in an apparent chevron fold geometry of the band (Plate 4). The individual “limbs” sometimes parallel type 1 and 2 band orientations. The average orientation of the bands is 13°, 65° W. These bands never cross type 1 or type 2 bands, and hence, they are shorter than those band types. Near intersections with type 1 and 2 bands, type 3 bands commonly curve into parallelism with the band being intersected (Fig. 6). Other type 3 bands terminate within the lozenge before reaching any other bands, and a few were observed to merge into other type 3 bands. It is extremely rare for there to be any visible offset across type 1, 2 or 3 bands. The lack of significant shear displacement

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Type 2

Type 1

Type 3

Figure 5. Pie chart showing the relative percentages of each type of deformation band present.

Plate 4. Type 3 deformation band with chevron fold appearance.

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Type 2

Type 1 Type 3

Figure 6. Sketch showing the key relationships between the three sets of deformation bands on the pavement.

on bands was also documented from outcrops in the vicinity of the field area (e.g. Plate 2).

Relative percentiles of each type of termination were plotted for each type of band (Fig. 7). These charts show that type 1 and 2 bands usually terminate at the edge of the pavement, whereas type 3 bands usually terminate within the pavement. Type 3 bands also merge with each other much more often than types 1 and 2 bands.

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Type 1 Bands Type 1 Bands North Terminations Soirth Terminations

Type 2 Bands Type 2 Bands West Terminations East Terminations

Type 3 Bands Type 3 Bands North Terminations South Terminations

L egend

■ Abut m Hook □ Terminate B Edge □ Merge

Figure 7. Fie charts showing the relative percentage of each type of intersection for each d^ormation band termination.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 The average length, width, closest parallel band, and the total width were calculated for each band type. The results show that type 1 bands are longer, wider, and more widely spaced than the other two sets of deformation bands (Fig. 8). Type 2 bands have nearly the same average length as type 1 bands, however, these results are biased by the size of the pavement since more type 1 bands extend to the edge of the pavement. The total width for each type indicates that type 3 bands have by far the greatest total width. The significance of total width is discussed in section 9.4.

In addition to the pavement study, four other localities were examined which had three sets of deformation bands present. Based on three to five measurements of each band type, these sites show good agreement with the orientations from the pavement (Figs. 9 and 10).

The intensity of band development is variable. The density of bands increases abruptly at the tops of numerous hills in the vicinity of the study area (Plate 5). These abrupt changes do not appear to be controlled by bedding or any other inhomogeneity in the rock.

7.2 Low-angle Slip Surfaces and Other Structures

In addition to the three sets of deformation bands, there are also numerous low-angle slip surfaces present on the pavement.

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^ 2 0 0 I s m «g I 100 & S o> I f I 2 3 Band Type Band Type

300

u 200-

« 100-

1 2 3 1 2 3 Band Type Frac. Type

Figure 8. Bar graphs which compare the average length, width, closest parallel band and strike for each type of deformation band..

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T3 T1 T2

Figure 9. Equal area projections showing the orientation of deformation bands and bedding from the pavement (B-bedding orientation, Tl- type 1 bands, 72- type 2 bands, 73- type 3 bands).

Because these slip surfaces intersect the pavement at such a low angle, their map trace curves across the pavement erratically due to subtle variations in relief. For this reason, the structures were omitted from the map, however, they are important in interpreting the chronology of deformation band development. Type 1, 2 and 3 bands are offset by these low-angle structures.

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T1 Tl T2 T2

iT3

Figure 10. Equal area projections showing the orientation of deformation bands and bedding from four localities in the vicinity of the pavement(A^,CJD) (B- bedding orientation, Tl- type 1 bands, T2- type 2 bands, T3- type 3 bands).

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Plate 5. Deformation bands showing an abrupt increase in density with no apparent change in bedding.

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however, some type 3 bands may terminate at the low-angle structures.

The low-angle slip surfaces have two basic styles. One forms slip surfaces with a consistent orientation over their entire extent. These faults have measurable offset (usually 2 to 20 cm apparent offset) and are either parallel to bedding or form an acute angle with bedding. The hanging wall of these slip surfaces has moved up relative to the footwall. There is only one slip surface of this type present on the pavement, and that surface has slickenside striae oriented S 60® E. Slip surfaces were observed at many outcrops in the Valley of Fire area and nearly all indicate an eastward thrust-type offset (Plate 6). The second type of slip surfaces are irregular surfaces of very small displacement. They are abundant on the west side of the pavement, where they both parallel and cross bedding. These structures are termed low- angle slip surfaces; however, they often intersect the pavement at angles up to 50® and often dip in different directions. Some of these structures appear to have a festoon shape that is not controlled by bedding.

One other type of fracture was observed in the Aztec Sandstone. These are not deformation bands or low-angle slip surfaces, but instead are a localized type of fracture with random orientation. They are apparently a localized type of fracturing

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Plate 6. Low-angle slip surfaces oriented at an acute angle with bedding (inclined to right) and offsetting deformation bands (LA - low-angle slip surface, DB - dfformation band). View is to the northeast of a nearly vertical exposure.

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with random orientation. One example of this fracture type is spatially associated with a well-developed, low-angle slip surface but elsewhere the fractures are not associated with low-angle slip surfaces. This fracture set was not studied in detail.

Joints are also well-developed in the Aztec Sandstone throughout the Valley of Fire. In most areas, joints are by far the most common structural feature in the Aztec Sandstone. Although joints were not the subject of this study, it was observed that joints are comparatively rare in outcrops that have deformation bands. 8. Pétrographie Description of Deformation Bands

Thin sections of deformation bands from the pavement show only reduced porosity and long grain contacts indicating minor pressure solution. There is no discrete plane of separation present nor any broken grains. Therefore, the recognition of deformation bands in thin-sections is quite difficult. The structures do not exhibit a visible fabric which would allow cross-cutting relationships between band types to be determined.

The thin sections examined in this study suggest that grain cataclasis may not be required for the formation of deformation bands. Thin sections of a deformation band in the Cretaceous White Member of the Baseline Sandstone, a sample containing a

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38 high density of deformation bands, and a sample of a small displacement (21 cm visible offset) fault were the only samples that showed significant grain cataclasis.

â:____Interpretation and Discussion of Deformation Bands in the Valley of Fire

9.1 Comparison of Deformation Bands In the Valley of Fire with Other Areas

The description of deformation bands in the Aztec Sandstone and White Member of the Baseline Sandstone suggest that these bands are similar to the structures described in other areas. However, it is also clear that there are many differences.

Twelve features of deformation bands were described by Aydin and Johnson (1983) and listed previously in this thesis (Section 2). Many of these features are different in the Valley of Fire. For instance, the bands in the Valley of Fire generally have no detectable slip in contrast to those reported by Aydin and Johnson (1983) (point 3). Where shear offset is observed, the offset is less than two millimeters.

The seventh point, regarding deformation band geometry, is not valid in the study area, either. The zones of deformation bands consist of type 1 and 2 bands which are typically very straight, whereas the type 3 bands, which are typically isolated.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39 are usually quite sinuous. This is exactly the opposite of the deformation bands described by Aydin and Johnson (1983,).

Points 8, 9 and 10 all refer to the formation of slip surfaces. Aydin and Johnson described a progression of deformation from a single deformation band to a zone of deformation bands, and then the development of a slip surface within the zone of deformation bands. In the Valley of Fire, slip surfaces appear to form after deformation bands, but their orientation is not controlled by the existence of deformation bands. The slip surfaces are usually at a low angle to the pavement surface, a high angle to the deformation bands, and both cut across and merge into bedding.

The geometry of the type 1 and 2 deformation bands in the Valley of Fire is different from that described in. previous studies. Type 1 and 2 bands form a conjugate set which have a dihedral angle of 90 degrees. This is about 30 to 40 degrees higher than has been reported by other researchers. In the Wingate Sandstone, Jamison and Stearns (1982) reported conjugate pairs of microfaults with a dihedral angle of 20 to 40 degrees, and in the New Red Sandstone of Arran, Scotland the dihedral angle between bands is 36° (Underhill and Woodcock, 1987). Both of these angles are in close agreement with the 22° to 50° experimental results of Aydin and Reches (1982).

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9.2 Age Relationships Between Deformation Band Sets

The chronology of the three sets of deformation bands is unambiguous. Type 1 and 2 bands are the oldest and formed contemporaneously. This is evidenced by their mutually cross cutting geometry and the fact that bands of each type locally terminate at intersections with the other set.

Type 3 bands are interpreted to have formed after type 1 and 2 bands based on the fact that type 3 bands never cross type 1 or 2 bands and commonly curve into parallelism with the older bands. This same chronology was also observed at the four other localities studied.

The low-angle faults that cross the pavement formed after deformation bands since they offset them, however some faults may have formed either synchronously or prior to type 3 bands because type 3 bands locally seem to terminate at the low-angle faults. However, the field evidence for this synchronous relationship is equivocal.

9.3 Age Relationships Between Deformation Bands and iron Oxide Staining

The chronology and relationships of deformation bands with iron oxide staining is variable. There are many examples where deformation bands have clearly controlled fluid migration. Iron

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 oxide staining of the Aztec is often confined to areas between deformation bands. This implies that deformation bands were present before staining and occluded fluid migration. However, there are also numerous examples where staining crosses deformation bands.

Another interesting feature of staining involves the distinctly banded sandstones consisting of red and buff striped sandstone. This staining highlights the primary bedding of the sandstone that crosses deformation bands with no detectable offset of bedding. The same lack of bedding disruption caused by deformation bands can also be seen in rocks which are not stained (Plate 7). This preserved bedding within the deformation band is strong evidence that very little shear displacement has occurred across deformation bands.

9.4 Correlation of Deformation Bands with Regional Stresses

Previous researchers have stated that there is no visible deformation in the Aztec Sandstone associated with emplacement of the Muddy Mountain thrust. Longwell et al. (1965) state, “the direction in which the thrust plate moved is not suggested by deformation of the overridden Aztec Sandstone, in which the weakly cemented sand grains yielded without the formation of drag folds or minor thrusts.”

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Plate 7. Side view of deformation band which shows primary bedding is undisturbed.

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Despite the lack of physical or spatial correlation among deformation bands and major structures in the region, there is evidence that relates the formation of deformation bands with Sevier age thrust faulting.

The deformation band network mapped in this research may be used to infer a possible stress field that could have created the deformation bands. This inference is based on the premise that the decrease in porosity that occurs in deformation bands results in a net shortening perpendicular to the bands, and that the most common band type has therefore experienced the greatest shortening (see Fig. 8). If this premise is true, the greatest shortening occurred in the direction perpendicular to type 3 bands, or S 77° E. This value is in close agreement with the orientation of the bisector of the dihedral angle between type 1 and 2 bands of S 74° E (see Fig. 3 and Fig. 9). Both of these values are in close agreement with an inferred movement direction along the Muddy Mountain thrust of S 70° E (Longwell et al., 1965).

Low-angle slip surfaces in the Aztec Sandstone that are not confined to bedding planes have approximately east-northeast- trending mullions. Furthermore, the hanging wall of these low- angle slip surfaces has moved up and toward the east, consistent with inferred movement along the Muddy Mountain and Willow tank thrusts (Longwell et al., 1965). Although not studied in detail for this research, these structures may be good kinematic

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44 indicators of thrust fault displacement provided structural tilt is resolved.

The age of the Aztec Sandstone is Jurassic and thrusting began in late Mesozoic time (Bohannon, 1983). The low-angle structures crosscut the deformation bands and therefore are interpreted to postdate them. It follows that if the low-angle slip surfaces are correlative with thrusting, then deformation bands developed between Jurassic and Late Cretaceous. Since there are no other tectonic events known to have occurred then, it is possible that the deformation bands in the Valley of Fire formed in response to the compressional stresses associated with Sevier age thrusting.

9.5 Poorly Understood Characteristics of Deformation Bands In the Valley of Fire

This study has documented some characteristics of deformation bands that are not accounted for in current models. First, the type 3 bands are sinuous, commonly having the appearance of chevron folds with “limbs” roughly parallel with type 1 and 2 bands (Plate 4). A fold origin is unlikely, however, since there is no detectable offset on type 1 and 2 deformation bands that could induce shortening within the lozenges. In addition, the alignment of “limbs” with type 1 and 2 bands would be highly fortuitous if it was the result of folding. The folded

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45 appearance is therefore most likely the original growth pattern of the band. The alignment of limbs with the type 1 and 2 bands may indicate that the same stress field created all three sets of deformation bands, and perhaps the type 3 bands are a hybrid of type 1 and 2 bands.

Second, the type 3 deformation bands commonly curve abruptly into parallelism with the type 1 and 2 bands. This curvature is not the result of drag because the length of parallelism is far greater than any possible shear along type 1 and 2 bands. This type of intersection has been termed “intersecting parallel” (Dyer, 1988). Dyer (1988) describes this type of intersection as occurring when the stress perpendicular to a crack is tensile and the stress parallel to the crack is compressive. A fracture propagating toward the existing crack will curve into parallelism as it approaches the crack in order to open against the tensile stress perpendicular to the existing crack (Dyer, 1988). If the type 3 bands formed in this way, it requires that the stresses perpendicular to the type I.and 2 bands be tensile. Alternatively, deformation bands may curve to align themselves perpendicular with a compressive stress acting perpendicular to preexisting bands, since deformation bands are compressive structures rather than tensile structures.

The curvature of type 3 bands into parallelism with type 1 and 2 bands is further evidence that suggests the type 3 bands

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46 formed in the same stress regime as the type 1 and 2 structures. I therefore propose that type 3 bands may be a result of deformation of the lozenges that occurs after development of type 1 and 2 bands.

The third enigma regards the abrupt increase in deformation bands that occurs at certain horizons in the Aztec Sandstone (Plate 4). These high density zones usually occur at the tops of hills, probably because the more densely banded sandstone has a greater resistance to erosion. At present, this phenomenon cannot be explained.

9.6 Conceptual Model for the Development of the Deformation Band Network

The fundamental processes of deformation band initiation, growth, and termination are still poorly understood. However, the macroscopic pattern of deformation bands in the Aztec Sandstone places restrictions on their possible origins that can be tested with further pétrographie and theoretical study. The proposed model attempts to relate the formation of the deformation band network with the inferred stress field described in section 9.4.

The dihedral angle between the type 1 and 2 bands is in the range of conjugate shear fractures according to the classification of Hancock (1985). However, this classification is based on a 30 degree angle of internal friction. The angle of internal friction

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 47 varies with lithology, decreasing in less competent rocks (Hancock, 1985). A decrease in the angle of internal friction would cause higher dihedral angles for a given failure mode, however the interpretation of stress directions based on maximum shortening direction (section 9.4) indicates a dihedral angle of 92 degrees for type 1 and 2 bands. This would require a significant reduction of the assumed 30 degree angle of internal friction to change the interpretation that type 1 and 2 bands formed in response to compressional shear failure. Unfortunately this interpretation contradicts the field evidence which indicates no slip has occurred across the structures. To resolve this paradox, I tentatively propose a model similar to the dilatancy-fluid diffusion mechanism for periodic fault motion as described by Ramsay (1987). This mechanism is summarized as follows:

Shear stress along a fault surface creates dilation of the pore space. Increasing the pore space reduces the fluid pressure near the fault zone which increases the effective normal stress across the fault. Gradually fluid pressure will rise in the dilated pore space, and fault motion occurs when the normal stress across the fault is reduced (which lowers the frictional resistance to slip). During and after fault displacement the porosity is likely to be reduced and excess fluid will be expelled rapidly in

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48 the direction of least confining pressure, usually upwards (Ramsay, 1987).

The conceptual model for the formation of deformation bands that I propose is based on a similar process, modified to prevent the formation of a discrete fault surface that does not appear to form in deformation bands. This model is based on processes similar to those described by Aydin (1978), Aydin and Johnson (1978), and Underhill and Woodcock (1987). The model deviates from previous models in that deformation bands could form without shear displacement or significant rupture of grains.

Shear stresses in the Aztec Sandstone create dilation as described above with the accompanying increase in stress normal to the dilation. However, instead of fluid pressure being restored in the dilated zone and producing shear failure, either the increased normal stress causes a repacking and interlocking of grains that prevents shear slip; or the increased permeability induced by dilation itself allows fluid to escape, and the dilation is closed by a repacking of grains caused by the increased normal stress (Fig. 11). However, the reduction of pore space would have the effect of increasing pore pressure near the newly formed deformation band (Underhill and Woodcock, 1987). This could impede additional pore reduction and offset the normal stress prior to grain failure. In the dilatancy-fluid diffusion mechanism, pore pressure rises until slip occurs, however in this model the

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D illo n of maximum shortening

Shear stress creates dilation that increases porosity and decreases pore pressure. A decrease in pore pressure results In increased stress normal to the plane

Type 1 and 2 deformation bands

The increased normal stress causes a repacking of grains and decreased porosity

Figure 11, Illustration showing the key steps in the formation of a deformation kdnd.

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pore pressure is not allowed to rise high enough to allow shear failure, just high enough to prevent grain rupture from the increased normal stress. This model describes a process whereby the creation of deformation bands could occur with the orientation of conjugate shear fractures without shear displacement. This mechanism could be repeated many times to produce the multiple bands, since each strain increment results in strain hardening caused by the tighter packing of grains. The model is consistent with previous interpretations for the development of deformation bands.

In order to account for the formation of type 3 bands with this mechanism, it is necessary that the initial shear dilation occur parallel to the interpreted maximum compression direction. That is an unlikely possibility, and other evidence suggests that the stress field did not change. Therefore, I interpret that type 3 bands formed in a local stress field within each lozenge, or they are a hybrid structure of the type 1 and 2 bands (see also section 9.5).

The change from deformation band formation to faulting on low-angle slip surfaces documents a change in the style of deformation. Assuming the origin of deformation bands is similar to shear fractures, or at least the geometry of deformation bands is similarly related with the principal stress axes, it is possible that the change in deformation style may record a rotation of the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51 least compressive stress axis from horizontal to vertical (assuming that Anderson (1951) failure criteria applies to deformation bands). This change in stress axes could occur as a result of increased pore pressure reducing the effective vertical stress (Gretner, 1969).

10. Summary

This research has described deformation structures including deformation bands and minor faults in the Aztec Sandstone that may document paleostress directions in the area. Results indicate that maximum horizontal stress was oriented S 74° E to S 76° E during formation of the deformation band network. This value is kinematically compatible with regional compression associated with the Sevier orogeny.

Deformation bands had not previously been recognized in the Aztec Sandstone. This example of deformation bands is significant because they exhibit many features that contrast with those described elsewhere by other researchers. Some of these contrasts are significant because the are incompatible with the generally accepted models of deformation band formation. The characteristics of deformation bands in the Valley of Fire are as follows:

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1. Type 1 and 2 are straight and usually composed of multiple bands which have a total width of several centimeters.

2. The dihedral angle between type 1 and 2 bands is 90 degrees.

3. A third set of deformation bands (type 3) are confined by type 1 and 2 bands and often curve into parallelism near intersections with the type 1 and 2 bands. Maximum widths are rarely greater than 1 centimeter.

4. Type 3 bands have a consistent orientation from end to end but are often sinuous or jagged along their length. The sinuosity creates a chevron fold appearance with the limbs sub-parallel with the type 1 and 2 bands.

5. Deformation band networks similar to the pavement (i.e. 3 sets present) have similar orientations.

6. Deformation band formation doe^ not destroy primary bedding.

7. Deformation bands occur only in sandstones that have well-developed bedding.

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8. The deformation bands are locally offset by low- angle slip surfaces that are therefore interpreted to have formed after the deformation bands.

12. References Anderson, E.M., 1951, The dynamics of faulting and dyke formation: Oliver and Boyd, Edinburgh, 206 p. Aydin, A., 1978, Small faults formed as deformation bands in sandstone: Pageoph, V.116, p.913-930. Aydin, A. and Johnson, A.M., 1978, Development of faults as zones of deformation bands and as slip surfaces in sandstones: Pageoph, v.ll6, p.931-942. Aydin, A. and Johnson, A.M., 1983, Analysis of faulting in porous sandstones: Journal of Structural Geology, v.5, p. 19-31. Aydin, A. and Reches, Z., 1982, Number and orientation of fault sets in the field and in experiments: Geology, v.lO, p. 107-112. Barton, C.C., 1983, Systematic jointing in the Cardium Sandstone along the Bow River, Alberta, Canada [Ph.D. thesis]: Yale University, 302 p. Barton, C.C. and Hsieh, Paul A., 1989, Physical and hydrogeologic-flow properties of fractures: Field Trip Guidebook T385, 28th International Geological Congress, 36 p. Barton, C.C., Larson, Eric, Page, W.R., and Howard, T.M., 1987, Characterizing fractured rock for fluid flow, geomechanical, and paleostress modeling: methods and preliminary results from Yucca Mountain, Nevada: USGS— OPR—87—XXX(draft), 36 p. Blés, Jean-Louis and Feuga, Bernard, 1986, The fracture of rocks: Elsevier Science Publishing Co. Inc., Oxford, 131 p. Bohannon, Robert G., 1983, Geologic map, tectonic map and structure sections of the Muddy and northern Black Mountains, Clark County, Nevada: USGS, Miscellaneous Investgations Series, Map 1-1406,2 sheets.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 Dyer, R., 1988, Using joint interactions to estimate paleostress ratios: Journal of Structural Geology, v.lO, p. 685-699. Gretner, P.E., 1969, Fluid pressure in porous media-its importance in geology: a review: Bulletin of Canadian Petroleum Geology, v.l7, p. 255-295. Hancock, P.L., 1985, Brittle microtectonics: principles and practice: Journal of Structural Geology, v.7, p. 437-457. Horowitz, D.H., 1979, Description and origin of soft-sediment deformational features in the Aztec Sandstone, Red Rock Canyon area, Nevada: 1979 RMAG-UGA Field Conference and Symposium of Geology of the Great Basin, Eastern Nevada. Jamison, W.R. and Steams, D.W., 1982, Tectonic deformation of Wingate Sandstone, Colorado National Monument: American Association of Petroleum Geologists Bulletin, v.66, p.2584-2608. Laubach, Stephen E., 1988, Fractures generated during folding of the Palmerton Sandstone, eastern Pennsylvania: Journal of Geology, v.96, p. 495-503. Longwell, C.R., 1949, Structure of the northern Muddy Mountain area, Nevada: Geological Society of America Bulletin, v.60, p. 923-967. Longwell, C.R, E.H.Pampeyan, Ben Bowyer, and R.J. Roberts, 1965, Geology and mineral deposits of Clark County, Nevada: Nevada Bureau of Mnes, Bulletin 62, 218 p. Marzolf, J.E., 1982, Paleogeographic implications of the Early Jurassic (?) Navajo and Aztec sandstones, unpublished manuscript, 16 p. Padian, Kevin, 1989, Presence of the dinosaur Scelidosaurus indicates Jurassic age for the Kayenta Formation (Glen Canyon Group, northern Arizona): Geology, v. 17, p. 438-441. Pittman, E.D., 1981, Effect of fault-related granulation on porosity and permeability of quartz sandstones, Simpson Group (Ordovician), Oklahoma: American Association of Petroleum Geologists Bulletin, v. 65, p.2381-2387. Ramsay, J.G. and Huber, M.L, 1987, The Techniques of Modem Structural Geology, Volume 2: Folds and Fractures, Academic Rress, London, 700 p. Sanderson, Ivan D.,1973, Sedimentary stmctures and their environmental significance in the Navajo Sandstone, San Rafael Swell, Utah: Brigham Young University Studies, V.21, p.215-246. Segall, Paul and Pollard, David D., 1983, Joint formation in granitic rock of the Sierra Nevada: Geological Society of America Bulletin, v.94, p.563-575.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55 Stewart, John H., 1980, Geology of Nevada: Nevada Bureau of Mines and Geology Special Publication 4,136 p. Underhill, John R. and Woodcock, Nigel H., 1987, Faulting mechanisms in high porosity sandstones; New Red Sandstone, Arran Scotland: from Jones, M^E. and Preston, R.M. (eds). Deformation of Sediments and Sedimentary Rocks: Geological Society Special Publication No. 29, p.91-105. Woodcock, Nigel H. and Underhill, John R., 1987, Emplacement-related fault patterns around the Northern Granite, Arran, Scotland: Geological Society of America Bulletin, v.98, p. 515-527.

11. Appendix 1

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reproductionI y ' prohibited without permission.

Reproduced with permission of the ci Valley of Fire Pavement

Leaend

— Type I 8iT yp e2 Band / / — Type 3 Bond

— Intensely Fractured Zone

/ — Boundary / / / — Boundary Truncated Band / /

— Rotated Block

Scale I r 1------1------1 I 2 3 4 6 meters

Prepared by RE. Kill

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Valley of Fire Pavement

Legend / — Type I 8 Type 2 Band — Type 3 Band

— Intensely Fractured Zone / / — Boundary

y — Boundary Truncated Band /

^ j — Rotated Block

Scale

I 1------1------1------1------1 I 2 3 4 5 meters

Prepared by RE. Hill

VOF

Index Map 20Qm, —I—' 200 km

White Domes

Study Site

Roinbow Vista

Stole

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T -| r T I 2 3 4 meters

Prepared by RE. Hill

NV UT

Index Map 2 0 0 mi. ! ' 200km

White Domes

Study Site

Rainbow Vista

Visitor Center

------1 scale I------1------!------? '------1 I ' : ' I ' " i Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. White Domes

Rainbow Vlsto

Scale

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I II u c A mufj S O Q m i . — 1— ' 200km

White Domes

Study Site

Rainbow Vlsto

3 mi Scale 5 km

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