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Variation of architecture due to changing deformation mechanisms at fault intersections and steps Nicholas C. Davatzes, Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 e-mail: [email protected] Abstract faults formed from cataclastic deformation Two different deformation mechanisms bands (Aydin and Johnson, 1978; Aydin, 1978; accommodate faulting in Jurassic sandstone units Underhill and Woodcock, 1987; Antonellini and along the Moab normal fault in Utah, USA. These Aydin, 1994) and (2) faults formed from shearing of mechanisms are (1) the formation of deformation joints and formation of splay fractures (Cruikshank et bands resulting from cataclastic shear failure of al., 1991; Myers, 1999; Dholokia et al., 1998) 1998 porous sandstone, and (2) the formation and (Figure 1). Joints form under local effective tensile subsequent shearing of joints producing splay (Pollard and Aydin, 1988) whereas fractures and breccia. We observe that formation of deformation bands form under compressive shear deformation bands consistently precedes jointing stress in porous sandstone (Mair et al., 2000; Wong along the fault and is prevalent along the entire et al., 2001; Olsson, 1999). Consequently, in a single length of the fault system. In contrast, the formation rock type, changing deformation conditions such as and shearing of joints only contribute to fault effective stress could cause a change in faulting development at geometrically complex portions of the mechanism (Bourne and Willemse, 2001). fault trace such as intersections and extensional steps In this contribution, we document the between fault segments. Contractional fault steps distribution of different types of structures produce increased deformation band density within composing the Moab normal fault, East-Central Utah, the step. The transition from deformation banding to along its trace in Jurassic sandstone. Deformation jointing implies that fault and damage zone bands are prevalent along the entire length of the development may change during the slip history of a fault trace. Joints, veins and zones of fragmentation fault. Furthermore, this change first occurs at are associated with extensional steps and structurally complex locations as result of variations intersections between fault segments. We in the stress state around slipping faults. demonstrate that structural position is a key control on fault architecture and the distribution of joints and Introduction breccia. Without recognizing the different Faults and fractures are fundamental components contributions of these two distinct deformation of the Earth’s crust. These structures focus or retard fluid flow in the subsurface (Caine et al., 1996), provide discontinuities and flaws for nucleating new deformation (Dholokia et al., 1998) and perturb the local state of stress (Zoback et al., 1987). Predicting the spatial distribution of fault properties is crucial for building a damn, a tunnel, and for effectively developing oil reservoirs and aquifer systems. The properties of a single fault may vary significantly as a result of the distribution of rock types faulted or the deformation mechanisms involved in faulting. For instance, presence of joints may enhance permeability (Taylor et al., 1999), whereas porosity loss in deformation bands inhibits fluid flow (Antonellini and Aydin, 1995; Matthai et al., 1998). Two distinct faulting mechanisms have been recognized in sandstone (Aydin, 2000; Davatzes and Aydin, in review A; Davatzes and Aydin, in review B): (1) Figure 1: Idealized faulting mechanisms and their component mstruechctuanismress (fro andm thDaveira tzes spatial an d asso Ayciatiodin, inn revwithiew fau). lt

Stanford Rock Project Vol. 13, 2002 B-1 steps and intersections, will help predict exposure: the (1) Navajo Fm, (2) Slick Rock, and (3) heterogeneity along the fault zone. Moab Tongue. Faulting in this location probably occurred Geologic Setting between 60 and 43 Ma based on K-Ar dating of shale The Moab Fault is a 45 km long normal fault gouge in the Morrison Fm. (Pevear et al., 1997; see with up to 1000 m vertical stratigraphic offset Davatzes and Aydin in review A for a summary of (Doelling, 1988; Foxford et al., 1996) (Figure 2). The evidence in the literature). This faulting event is fault is spatially associated with a salt-cored associated with a period of salt movement (Doelling, . Pennsylvian through Cretaceouse layered 1988) and takes place during maximum burial of the sandstone and shale (Figure 2) offset by the fault are Entrada Formation between 2000 and 2500 m exposed along the trace (Doelling, 1988). Late (Pevear et al., 1997; Garden et al., 2001) or during a Cretaceous and early Tertiary rock has been eroded phase of subsidence immediately preceding from both hanging wall and footwall accompanying maximum burial (Nuccio and Condon, 1999). uplift of the Colorado Plateau. Field results We used three techniques to quantify the distribution of deformation mechanisms in Jurassic sandstone units along the Moab Fault trace. First, the distribution of fault components and fault geometry was mapped in detail with a Differential Global Positioning System (DGPS) unit and aerial photographic base-maps with 0.5 m pixel resolution. The data dictionary on the DGPS allowed us to qualitatively record the occurrence of different mechanisms along the fault, the fault , the of slickenlines on the fault surface, and the strike and dip of bedding in the footwall and hanging wall at 325 stations along the fault trace. The qualitative observations helped us interpolate between stations of more detailed study. Second, detailed maps were made at key locations by mapping onto enlarged aerial photographs, mapping on graph paper from a defined grid on the outcrop, and the use of enlarged aerial photographs. Third, the frequency, orientation and crosscutting relationship of each type of structure were measured along scan-lines normal to the fault trace. Scan-line length was determined for each case Figure 2: (a) Tectonic map of the NE Paradox Basin to extend beyond the “damage zone” (Knipe, 1997; (modified from Doelling, 1985). (b) Map of the Moab Cowie and Scholz, 1992) or until the end of outcrop fault trace (modified from Foxford et al., 1996). The major fault segments referred to throughout this exposure. Twenty-nine scan-lines distributed along paper are labeled. The x on the fault trace marks the fault system were used to quantify the the location of maximum offset contribution by each to Data was collected along the segmented NW faulting. In combination with detailed maps, this also portion fault system. Jurassic sandstone units quantifies the distribution of each type of component exposed in the footwall include the units including structure as a function of position on the fault. the Wingate, Kayenta Navajo and Entrada In this paper the damage zone refers to the area Formations. The Entrada Formation is composed of around a fault in which the density of structures such three members: (1) the Dewey Bridge member, (2) as deformation bands or joints is elevated above the Slick Rock member, and (3) the Moab Tongue background density remote from faults (see Caine, et member. Starting at Courthouse Canyon, the Curtis al. 1996; Knipe, 1997). We use a value of less than Formation separates the Slick Rock and Moab one structure every five meters to define the sandstone units, thickening to the west. This study transition to background density. principally concentrates on observations in three sandstone units because of their similarity and Fault characterization The faults in Jurassic sandstone units are composed of two classes of distinct structural

Stanford Rock Fracture Project Vol. 13, 2002 B-2 elements: (1) elements associated with deformation bands and (2) elements associated with joints and shearing of joints (summarized in Figure 1). Individual deformation bands (Figure 3a) are distributed throughout the damage zone of all fault segments. Anastomosing zones of deformation bands (Figure 3b) develop along the fault in all Jurassic sandstone units. The thickest zones are adjacent to the fault slip surface. These zones are continuous along the fault trace and along dip (Figure 3c). Slip surfaces are often polished and slickensided. Crosscutting relationships indicate that deformation bands precede joints in all locations where they both occur (Figure 3a). Joints occur as veins, splay fractures, and zones of fragmented rock that are associated with the -based faulting mechanism (Figure 1). Fragmentation is associated with slip on sheared joints and fault surfaces (Figure 3d). Dense networks of massive calcite veins and breccia are developed near intersections between fault segments (Figure 3e). The northwestern portion of the Moab Fault is composed of a series of curving branches in the footwall of northwest trending normal fault segments (Figures 2 and 4). Multiple branch points may occur along a single fault. In each case, there are several branches with 1-20 m of slip, and one branch with an order of magnitude greater slip and much longer trace length. Branches all intersect at high angles. East-west trending portions of these branches consist of right stepping fault segments with long overlaps. Some of these steps are breached and the segments are linked. The western tip of a branching segment curves until it trends northwest and sub-parallel to the longest segment.

Distribution of component structures Deformation banding is the dominant faulting mechanism along the majority of the Moab Fault trace in Jurassic sandstone (Figure 4a). On segments with throw greater than ~100 m, 90% of the fault trace is composed entirely of deformation bands and zones of deformation bands. 25% of the total fault trace, including small faults with throw less than 20 m, are characterized by significant density of joints Figure 3: (a) Individual deformation bands in Slick and fragmentation. Joints occur along portions of E- Rock Member sandstone of the Entrada Formation. W trending fault segments, but the distribution is not (b) Zone of deformation bands composing the clearly organized by either geographic position or Moab Fault trace in Navajo Formation sandstone. (c) Cross-section view of the Moab Fault zone orientation (Figure 4a). Rather, joints and the along segment 1 of the fault (see Figure 4). Offset associated structural products are developed in in (b) and (c) is ~320-350 m. Note that bedding in proximity to fault intersections and within fault steps the Navajo sandstone on the right is nearly (Figure 4b). horizontal, while bedding in the Brushy Basin We focus on the area from the intersection of member of the Morrison Formation is sub-parallel fault segment 3 with segment 2 to the intersection of to the fault near the fault plane. (d) Veins fault segment 2 with segment 3 (Figure 5). Fault associated with the Moab Fault in some locations. segments are arranged into three key fault geometries (e) Fragmentation resulting from splay fracture distinguished in Figure 4b; (1) fault intersections, (2) formation along Segment 4. Offset is about three meters. (Photograph locations in Figures 4 and 5.)

Stanford Rock Fracture Project Vol. 13, 2002 B-3 contractional fault steps and (3) extensional fault the slip vector on segment 2 approximately coincides steps. These locations are boxed in Figure 5. Each with the intersection of the two fault pattern is associated with an increase in deformation segments (Figure 7). Segment 2 is also characterized band and/or joint density. Furthermore, this increased by many well-developed deformation band faults. density is distributed over larger areas than in Each of these faults accommodates several meters of isolated portions of fault segments with simple offset and bound blocks of highly deformed rock geometry. Three locations representing each fault against the main fault segment. This geometry is pattern were mapped at 1:100 scale. At this scale reproduced at station 5, just to the west. The lines representing the mapped structures relate geometry of the fault surface undulates along strike; structural orientation and relative density rather than some of these undulations coincide with intense individual, discrete structures. Scan-lines are used to formation and brecciation. quantify the structures represented in each map. Deformation bands occur in two sets sub-parallel to each fault segment (Figure 8). In contrast, the Example of fault intersection As an example for this contribution we take the intersection between segments 1 and 2 (Figure 6). Segment 2 abuts against segment 1. A fuller treatment of this topic will be submitted to the GSA Bulletin in the near future. Average rake on fault segment 1 within 50 m of the intersection is ~78º from the SE and throw is ~250 m (Figure 7). Average rake on fault segment 2within 50 m of the intersection is ~69º from the E. Throw near the intersection on segment 2 is ~90 m and increases to the west to about 150 m by station 8. Throw on the segment decreases after the intersection with segment 3 further west. The trend and plunge of Figure 4: (a) Distribution of fault-related joints and deformation bands along the NW portion of the Moab Fault. This portion of the fault consists of several curving and stepping fault segments. Quantitative data on the density of joints and deformation bands in the damage zone were taken at scan-line locations. The relative abundance of structures at stations along each fault segment is plotted as the percentage of total structures. Qualitative designation as deformation band or jointed fault, the orientation of the fault plane and rake of slickenlines were taken with a Differential Global Position System at 325 stations fill in data between scan-lines. (b) The relative abundance of joints and deformation bands grouped by structural position, i.e., location in fault steps or proximity to branch points. Only data from footwall transects is considered for purposes of comparison. (Easting is in meters in UTM zone 12.) Detailed data from stations 5 and C are presented in Davatzes and Aydin (in review).

Stanford Rock Fracture Project Vol. 13, 2002 B-4 Figure 5: Map of the focus area of this study distinguishing the different faulting mechanisms along the fault trace. Locations of Figures 6, 7 and 8 are indicated.

Stanford Rock Fracture Project Vol. 13, 2002 B-5 Figure 6: Schematic map detailing the geometry and distribution of component structures at the intersection between fault segments 1 and 2 (location in figure 5). Both fault segments have a small right-lateral component.

Figure 7: Fault orientation and slickenline data near the intersection of segments 1 and 2. The intersection line between the faults and average trend and plunge of the slip vectors are computed.

Figure 8: (a) Distribution of joints and deformation bands along scan-line 3 in the footwall of segment 1 (scan-line indicated in Figure 6). (b) Orientation of joints and deformation bands along scan-line. Average orientations were measured for groups of parallel structures in a one-meter bin. n represents the number of these measurements. Stereograms are weighted by the number of structures each measurement represents. (c) Scan-line 4 in hangingwall of segment 2 quantifying the distribution of joints and deformation bands. (d) Orientation of joints and deformation bands along the scan-line.

Stanford Rock Fracture Project Vol. 13, 2002 B-6 majority of joints are sub-parallel to fault segment 1. reduction haloes, indicating they acted as conduits Joint density and deformation band density are for reducing fluids associated with oil migration. similar. Most joints are filled with calcite cement that Davatzes and Aydin (in review A) recognized the may be several centimeters thick. Vein filling in a occurrence of both deformation bands and joints joint is often discontinuous along the length of the resulting from each faulting mechanism during joint implying partial closure during calcite development of the Moab Fault. In some locations, precipitation. Veins adjacent to the fault slip surface each mechanism may accommodate 50% of the total and minor secondary faults are organized into dense, offset. anastomosing networks. Similar vein networks surround breccia bodies adjacent to the fault. Veins Discussion of different orientation adjacent the fault are mutually Distribution of faulting mechanisms crosscutting and abutting indicating roughly coeval Deformation bands are the dominant fault formation. component throughout most of the fault trace exposed in the Jurassic sandstone units. This includes Comparison between faults intersections multiple units with slightly different rock properties with different offset such as porosity, cementation and composition. In Several faults with offset between 3 m and 20 m fault steps and intersections where joints are such as segments 4 and 5, and the small fault in Mill prevalent, deformation bands also occur, but are Canyon (Figure 5) branch from faults with larger older than joints. Thus, the gross fault geometry offset. Each of these examples is associated with a set developed during deformation band formation. of fault parallel joints, veins, sheared joints, Subsequently, joints formed at restricted locations fragmentation and breccia. The intersection between along the fault. We contend that two separate faulting segments 1 and 5 shows a second set of joints and mechanisms contribute to Moab Fault formation veins sub-parallel to segment 1. This second set is far (Figure 1) because joints and breccia overprint only less developed than in the intersection between small portions of the Moab Fault. Davatzes and segments 1 and 2. Furthermore, joints at this Aydin (in review A) document that fault architecture intersection display mutually cross cutting and reflects the relative proportion of slip each faulting abutting relationships indication coeval or mechanism accommodates. Continued fault slip alternating, episodic formation. At station 5, segment produced joints and eventually breccia as suggested 2 only displays fault parallel joint development, in Figure 1, changing the fault architecture. The similar to the joints associated with the segments 4 transition from deformation banding to jointing and 5. implies that fault and damage zone development may change during the slip history of a fault. Summary of results from fault steps Large increases in damage zone width are Steps between fault segments provide the associated with steps and intersections between fault simplest insight into the distribution of faulting segments. The increase in damage is principally mechanisms. Steps with rakes indication contraction confined within the fault step, but occurs on both across the step show increased deformation band sides of the abutting fault. This may indicate that the concentration. The increase in density is bounded damage zone for isolated, straight portions of the within the fault step. In contrast, fault steps with faults is a lower limit on damage zone dimension. rakes indicating extension contain large Similarly, breccia bodies and deformation band zones concentrations of joints and breccia. Again, this are largest in fault steps indicating a similar control deformation is contained within the step. on fault zone and fault rock distribution. Hence, the development of a fault by propagation or by linkage Timing of joints and deformation bands of fault segments plays a key role in determining the Several lines of evidence suggest that the high variation of fault and damage zone width along density of joints, sheared joints, and fragmentation strike. overprint deformation bands during the phase of fault Cementation and veining is localized in areas of activity between 60 and 43 Ma. First, joints cut high joint density at steps and intersections (Eichhubl deformation bands indicating they are younger than et al., in preparation). This results in porosity loss the deformation band they cut (Figure 3a). Second, and may increase rock stiffness (Dvorkin et al., 1994; some joints and sheared joints contain bitumen stains Zang and Wong, 1993). Since deformation band and tar (Figure 5). Third, calcite veins and associated formation is sensitive to porosity and grain contact nodules include remnant oil droplets (Eichhubl et al., strength (Steen and Andresen, 1999; Zang and in preparation). The last two observations indicate Wong, 1993, Dunn et al., 1973), this may inhibit the presence of joints during oil migration. In deformation band formation. Open joints provide addition, many joints are surrounded by white avenues for increased fluid flux providing the

Stanford Rock Fracture Project Vol. 13, 2002 B-7 potential for increased cementation. Ultimately, this similar in the Navajo, Slick Rock and Moab Tongue sort of feedback could incrementally change the rock sandstones where it can be observed. A second properties to favor joint-based failure rather than system of joints is developed throughout the NE deformation banding. Paradox Basin in the Moab Tongue, and to a lesser A similar feedback results if the principal extent in Slick Rock and Wingate sandstone units. stresses rotate after joint formation and shear stress is This system has much greater spacing, ~1/15-20 m resolved on joints. Shearing of joints or other and a regular, systematic geometry near the Moab discontinuities requires shear stress to overcome the Fault. Close to the Moab Fault, the strike of these frictional strength of the joint surfaces (Silliphant et joints change to become parallel to the fault trend. al., 2002; Davatzes and Aydin, in preparation). The Rawnsley et al. (1998) concludes that existing faults resulting slip concentrates stress at the joint tip can strongly influence the pattern of younger joint helping to produce effective tensile stress and sets. This effect is enhanced by faults that juxtapose formation of new joints as splay fractures (Segall and materials of distinct stiffness such as the Pollard, 1983). Once fracture bounded volumes of juxtaposition of Entrada Sandstone against Morrison rock develop, rotation and impingement of these shale in the study area (Peacock, 2001). Foxford et blocks on other blocks lead to stress concentrations at al. (1996) suggests that the regional joint set may the limited contact areas, further promoting fracture form in response to regional uplift and exhumation development. post-dating fault activity. In general, structure distribution corresponds with the trace geometry. The lack of examples of Faulting mechanisms and fluid flow joint concentrations away from fault segment steps or The Moab Fault experienced a complex intersections suggest that the effect of down-dip diagenetic history associated with its role as an geometry is minor in the study site. Vertical intermittent hydrocarbon barrier and pathway constraints on fault geometry may be most important (Garden et al., 2001, Foxford et al. 1996, 1998; Chan at the contact between distinct formation such as the et al., 2000). Locations where jointing and breccia Wingate sandstone and underlying shale rich Chinle are prevalent develop a host of diagenetic products Formation (Rawnsley et al., 1998). At the locations such as bitumen staining, calcite and ankerite veins, discussed the contact Moab Tongue sandstone and calcite cement, bleaching, malachite and liesegang Tidwell shale is the best example. banding (Foxford et al., 1996; Echhubl et al., in Fault intersections at small offsets indicate that preparation). In locations characterized solely by linkage may form quite early in the development of a deformation band zones these products are absent branching fault. From these examples it seems likely even in sandstone-sandstone juxtaposition. This that branching segments may propagate from the suggests that the change in fault architecture to fault segment they abut. However, the issue is not include joints fundamentally changed the hydraulic entirely clear because the small fault just south of the properties of the fault system including the fault zone intersection between segments 1 and 2, and north of and damage zone. Faults with small offset such as segment 4, does not intersect segment 1 in the current segments 4 and 5 (Figure 5) also act as fluid conduits stratigraphic exposure. even in sandstone-sandstone juxtapositions. At larger Fault parallel joints dominate these smaller offsets when the Jurassic sandstone units are faults, rather than two sets of joints associated with juxtaposed against thick late Jurassic Morrison the intersection in Figure 6. As we noted earlier, two Formation shale and Cretaceous shale units, the fault sets of joints are only observed very close to the may still act as a preferred fault parallel fluid conduit. intersections, and they have mutually abutting In these cases the distribution of joints and relationships. This suggests that each fault segment deformation bands becomes key to determining may contribute to the formation of the two sets of transmissibility across or parallel to the fault and joints. damage zones. We suggest that a change in fault properties, Regional joint sets such as permeability, will first develop and Joint density is greatest close to the fault and geometrically complex structural positions. These are fragmentation only occurs along faults, in the the locations where the stress state may depart most proximity to fault intersections and in extending fault dramatically the far field stress state. Straight isolated steps. Joints associated with fault development occur fault segments develop by a faulting mechanism in densities greater than 5/1 m along the fault. This consistent with the deformation conditions at the density rapidly decreases away from the fault. burial depth of faulting and the rock type faulted. In Similarly veins and joints with alteration haloes only this case, the over-all compressive conditions and occur in proximity to faults. At fault steps and normal fault formation in porous sandstone intersections, the joint-based fault architecture is correspond to deformation band formation. Thus an

Stanford Rock Fracture Project Vol. 13, 2002 B-8 important limiting factor in predicting fault different contributions of these two distinct architecture and analyzing its role in fault deformation mechanisms and their spatial association conduit/barrier behavior is the resolution of the fault with fault steps and intersections, heterogeneity along geometry. the fault zone would be seemingly random. Instead, because the distribution of mechanisms corresponds Future work with the spatial changes in fault geometry we Above, we document that the distribution of demonstrate that the heterogeneity within Jurassic deformation mechanisms correlates with fault sandstone units along the Moab fault follows a segment intersections and overlaps. Joints, splay predictable pattern. fractures, fragmentation and veins are spatially The primary control on the distribution of associated with fault intersections and steps mechanisms is the geometry of the fault system. In demonstrating minor extension. The remaining fault steps and at intersections the local is straight, isolated portions of the fault system develop most strongly perturbed and these are the locations solely by deformation band formation. Contractional where fault architecture will change first. In this fault steps enhance deformation band density and study, this manifested in outcrop by a wider deformation band formation parallel to the bounding distribution of structures such as deformation bands fault segments. The slip vector on fault segment 2 is and joints, and the occurrence of joints that only parallel to the intersection lineation between the two occur near these locations. fault segments, consistent with predictions from mechanical models of faulting (Maerten et al., 1999). Acknowledgments We postulate that the geometry of the faults and the Stephan Bergbauer, Peter Eichhubl, and Phil loading conditions are the key parameters controlling Resor provided invaluable help and insight during the distribution, geometry and type of component several field sessions at the Moab Fault. I would like structures. to thank Frantz Maerten and Jordan Muller for We plan to use Poly3D to evaluate this helping me learn to use Poly3D and create useful hypothesis and the mechanical control of mechanism fault geometries to study. David Pollard provided distribution. Poly3D will also provide the useful suggestions and answers to questions opportunity to examine the orientations of secondary concerning Poly3D and a scientific approach to structures, the impact of different aspects of fault numerical modeling of geologic faults. I would also geometry, and potentially the role of fault like to acknowledge the students at the Rock Fracture propagation. This is the subject of the remaining Project at Stanford University for a wonderful, work on this problem. supportive research environment and useful The roles of down-dip fault geometry and fault suggestions. Funding from the Rock Fracture Project propagation have not been directly addressed in this supported this work. paper. A study of fault propagation could use the consistent stepping and branching geometry of the References: Moab Fault and abundant rake data to solve for the Antonellini, M. A., Aydin, A., Pollard, D. D. 1994. remote principal stress magnitudes and orientations. Microstructure of deformation bands in porous Joints and deformation bands also occur in the fluvial sandstones at Arches National Park, Utah. Journal of sandstone units within the Salt Wash member of the 16, 941-959. Morrison formation and in the Cedar Mountain Antonellini, M., Aydin, A. 1995. Effect of faulting on fluid formation in the study area. These structures are flow in porous sandstones; geometry and spatial developed in folded portions of the sandstone close distribution. AAPG Bulletin 79, 642-671. to the Moab Fault such as in Figure 3c. In addition, Aydin, A. & Johnson, A. M. 1978. Development of faults we plan to address the role of underlying shale units as zones of deformation bands and as slip surfaces in sandstone. Pure and Applied Geophysics 116, 931- in fault geometry and the potential effect of shale 942. incorporation into the fault zone on subsequent fault Bourne, S. J., Willemse, E. J. M. 2001. Elastic stress and damage zone development in a new paper. control on the pattern of tensile fracturing around a small fault network at Nash Point, UK. Journal of Conclusions Structural Geology, 23, 1753-1770. Each faulting mechanism produces distinct, Caine, J. S., Evans, J. P., Forster, C. B. 1996. Fault zone different fault architecture, resulting in heterogeneity architecture and permeability structure. Geology 24, 1025-1028. in the types of structures composing the fault and Chan, M. A., Parry, W. T., Bowman, J. R. 2000. damage zones. Fault rock and damage zone Diagenetic hematite and manganese oxides and fault- dimension is strongly influenced by the initial fault related fluid flow in Jurassic sandstones, southeastern geometry including the formation of a larger fault by Utah. American Association of Petroleum Geologists linking multiple segments. Without recognizing the Bulletin 84, 1281-1310.

Stanford Rock Fracture Project Vol. 13, 2002 B-9 Cruikshank, K. M., Zhao, G., Johnson, A. M. 1991. Faulting, fault sealing and fluid flow in hydrocarbon Analysis of minor fractures associated with joints and reservoirs 147, 157-191. faulted joints. Journal of Structural Geology 13, 865- Myers, R. D. 1999. Structure and hydraulics of brittle 886. faults in sandstone [Ph.D.thesis]:Leland Stanford Jr. Davatzes, N. C., Aydin, A. in review A. Overprinting University, 176 p. faulting mechanisms in sandstone. Journal of Nuccio, V. F. a. C., S. M. 1999. Burial and thermal history Structural Geology. of the Paradox Basin, Utah and Colorado, and Davatzes, N. C., Eichhubl, P., Aydin, A. in review B. petroleum potential of the middle Pennsylvanian Overprinting faulting mechanisms during the Paradox Formation. In: Huffman, A. C. J., Lund, W. development of multiple fault sets in sandstone, R. and Godwin, L. H. (eds) Geology and Resources of Chimney Rock fault array, Utah, USA. the Paradox Basin. 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