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Paleo-Fluid Flow and Deformation in the Aztec Sandstone at the Valley of Fire, Nevada—Evidence for the Coupling of Hydrogeolog

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Paleo-Fluid Flow and Deformation in the Aztec Sandstone at the Valley of Fire, Nevada—Evidence for the Coupling of Hydrogeolog Paleo-fl uid fl ow and deformation in the Aztec Sandstone at the Valley of Fire, Nevada—Evidence for the coupling of hydrogeologic, diagenetic, and tectonic processes Peter Eichhubl† W. Lansing Taylor‡ David D. Pollard Atilla Aydin Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, USA ABSTRACT of structural heterogeneities for focused fl uid in southeastern Nevada. The Aztec Sandstone fl ow in a porous sandstone aquifer. has undergone multiple episodes of deforma- Paleo-fl uid fl ow conditions are recon- tion and diagenetic alteration including the structed for an exhumed faulted and frac- Keywords: fl uid fl ow, sandstone, hematite, precipitation, dissolution, and remobilization tured sandstone aquifer, the Jurassic Aztec diagenesis, deformation, thrust. of iron oxides and hydroxides. These oxida- Sandstone at Valley of Fire, Nevada. This tion and reduction reactions provide a record of reconstruction is based on detailed map- INTRODUCTION paleo-fl uid fl ow that is readily identifi able in the ping of multicolored alteration patterns that fi eld, allowing the spatial reconstruction of fl ow resulted from syndepositional reddening of Understanding the spatial and temporal distri- migration pathways and fl ow direction. Based the eolian sandstone and repeated episodes of bution of fl uid fl ow in the subsurface is of funda- on crosscutting relations with structural fea- dissolution, mobilization, and reprecipitation mental importance to the successful management tures, we demonstrate that the timing and focus- of iron oxide and hydroxide. A fi rst stage of of groundwater and hydrocarbon resources. In ing of fl uid fl ow across this sandstone unit was bleaching and local redeposition of hematite addition, the interaction of formation fl uids with strongly infl uenced by deformation and tectonic is attributed to upward migration of reduc- the hydrosphere and atmosphere is of increas- processes. This paper emphasizes map-scale ing basinal fl uid during and subsequent ing environmental concern (Moore, 1999). Of processes. The relationships between alteration to Late Cretaceous Sevier thrusting and particular signifi cance to these processes are the and deformation on the outcrop scale and the in foreland deposition of clastic sediments. A effects of structural heterogeneities such as faults situ hydraulic properties of structural features second stage of bleaching and iron remobili- and fractures in controlling diagenetic precipita- were described earlier in separate publications zation, precipitating predominantly goethite tion and dissolution and the combined effects of stemming from this and related research efforts and minor iron sulfates, occurred during deformation and diagenesis in controlling the (Taylor et al., 1999; Taylor and Pollard, 2000; Miocene strike-slip faulting associated with fl uid migration pathways and their permeability. Jourde et al., 2002; Flodin et al., 2004; Sternlof Basin and Range tectonics. This second stage This study followed a paleohydrologic et al., 2004; Myers and Aydin, 2004). is explained by mixing of reducing sulfi de- approach to investigate these effects in an rich basinal fl uid with meteoric water enter- exhumed faulted and fractured sandstone res- GEOLOGIC SETTING ing the aquifer. The distribution of alteration ervoir and aquifer. This investigative approach patterns indicates that regional-scale fl uid reconstructs the spatial and temporal variation Valley of Fire State Park is situated 60 km migration pathways were controlled by of fl uid fl ow based on crosscutting relations northeast of Las Vegas, Nevada (Fig. 1), within stratigraphic contacts and by thrust faults, between structures and diagenetic features that the Basin and Range physiographic province, whereas the outcrop-scale focusing of fl ow are observable in outcrop or with analytical tech- 50 km west of the western edge of the Colorado was controlled by structural heterogeneities niques. Diagenetic features that are indicative of Plateau. The park derives its name from the mul- such as joints, joint-based faults, and defor- past fl uid fl ow include alteration boundaries that, ticolored sandstone formations that range in hue mation bands as well as the sedimentary in some cases, allow inference of the direction of from orange-red to purple, yellow, and white architecture. The complex interaction of fl uid fl ow. Outcrop analog studies of paleofl ow and that are part of the 1400-m-thick Upper structural heterogeneities with alteration systems are particularly useful in providing Triassic and Jurassic Aztec Sandstone (Bohan- is consistent with their measured hydraulic a three-dimensional view of the infl uence of non, 1977, 1983), an eolian sediment deposited properties, demonstrating the signifi cance structures on fl uid fl ow at scales ranging from in a backarc setting (Marzolf, 1983, 1990). The microscopic to regional. In addition, outcrop Aztec Sandstone is part of a Mesozoic clastic analog studies can assess temporal variations in sequence that overlies upper Paleozoic carbon- †E-mail: [email protected]. ‡Present address: Anadarko Petroleum Corpora- fl ow regimes over geologic time scales. ates and shale (Bohannon, 1983). Triassic red tion, 1201 Lake Robbins Drive, The Woodlands, We investigated paleo-fl uid fl ow in the Juras- beds of the Moenkopi, Chinle, and Moenave Texas 77380, USA. sic Aztec Sandstone at Valley of Fire State Park Formations, with a combined thickness of up GSA Bulletin; September/October 2004; v. 116; no. 9/10; p. 1120–1136; doi: 10.1130/B25446.1; 11 fi gures; 1 table; Data Repository item 2004123. For permission to copy, contact [email protected] 1120 © 2004 Geological Society of America PALEO-FLUID FLOW AND DEFORMATION IN THE AZTEC SANDSTONE, VALLEY OF FIRE 114°33' 114°32' 114°31' Tertiary & Quaternary Cretaceous Willow Jurassic Aztec Sandstone Tank upper red and banded red and white units Thrust 600 middle alteration units lower red unit 662 Tearfault + Mesa NEVADA 20 Triassic (undiff.) BH White Dome + fault (dotted where inferred) 600 thrust fault Las Vegas 600 39 roadway 22 34 20 655 36°28' + 600 L Figure 1. Geologic map of 32 the northern part of Valley C 34 of Fire State Park, modifi ed WP BH B from Flodin and Aydin (2004). 700 600 W WP—Waterpocket fault; BH— 36 Bighorn fault; W—Wall fault; 700 L—Lonewolf fault; C—Classic 900 600 fault; M—Mouse’s Tank fault; 33 36°27' B—Baseline fault. M Silica Dome 28 + 800 WP 20 600 700 Figure 2 700 25 700 700 20 Mouse's Tank 600 900 700 700 36°26' 30 N 800 36°26' 36°27' 36°28'700 36°29' 36°30' 700 1 km B M 600 UTM zone 11 NAD 1983 contour interval 25 m 4034000 4036000 4038000 4040000 4042000 114°33' 114°32' 114°31' 114°30' 114°29' 720000 722000 724000 726000 to 2100 m (Bohannon, 1977), are composed Tank Formation includes locally derived red eastern margin of this klippe (Longwell, 1949), of sand-, silt-, and mudstone with evaporite Aztec Sandstone components (Longwell, 1949) indicating that the eastern edge of the klippe layers (Marzolf, 1990). The Aztec Sandstone is among far-traveled quartzite components, indic- represents the leading edge of the thrust sheet. unconformably overlain, with a discordance of ative of partial exhumation and erosion of the Upper portions of the Baseline Sandstone are locally up to 10°, by a distinctive conglomerate Aztec Sandstone subsequent to its deposition deposited on top of the Willow Tank thrust that forms the basal member of the Cretaceous (Bohannon, 1983). sheet, constraining the age of thrusting to Late Willow Tank Formation. The Willow Tank For- The Willow Tank Formation and lower por- Cretaceous (Maastrichtian) (Longwell, 1949; mation, composed of predominantly mudstone, tions of the Cretaceous Baseline Sandstone are Bohannon, 1983). and the overlying sandstone and conglomerate overthrust by Aztec Sandstone of the Willow With a hiatus during Paleogene times, depo- layers of the Baseline Sandstone have a com- Tank thrust sheet (Figs. 1 and 2), the lowest of sition of clastic units continued conformably bined thickness of about 1300 m (Bohannon, the Sevier thrust sheets in the study area (Long- during Oligocene to Pliocene times (Bohan- 1977). These units are interpreted as synoro- well, 1949; Bohannon, 1983). Tearfault Mesa in non, 1983). An ~25° angular unconformity genic foreland deposits of the eastward-directed the northern part of Figure 1 forms a klippe of at the base of the Upper Miocene (10–4 Ma) Cretaceous Sevier thrust sheets (Bohannon, the Willow Tank thrust sheet. Cretaceous strata Muddy Creek Formation (Bohannon et al., 1983). The basal conglomerate of the Willow are steepened and locally overturned along the 1993) constrains the time of tilting of the Aztec Geological Society of America Bulletin, September/October 2004 1121 EICHHUBL et al. 722000 114°31' ** 600 * 36°29' BH Fig. 7 600 Holocene Cretaceous (undiff.) 600 4040000 Jurassic Aztec Sandstone red white 4040000 B yellow orange 600 purple A banded red and white banded purple and white banded orange and white banded purple and yellow 36°28' BH kaolinite cemented layer L * quartz cementation A B paleoflow direction measurement (Fig. 11) C fault (dashed where inferred) 600 M fault name (see Fig. 1) W 4038000 thrust fault road 4038000 N 700 M 1 km 36°27' UTM zone 11 NAD 1983 contour interval 25 m 36°27' 36°28' 36°29' 700 114°32' 722000 114°31' Figure 2. Map of diagenetic alteration units for area shown in Figure 1. 1122 Geological Society of America Bulletin, September/October 2004 PALEO-FLUID FLOW AND DEFORMATION IN THE AZTEC SANDSTONE, VALLEY OF FIRE Sandstone, presently dipping 20°–30° north- Two sets of oblique-slip faults with pre- 4°–65° 2θ at 1°/min on a Rigaku powder diffrac- east. The Muddy Creek Formation, in turn, dominant strike-slip and lesser normal-slip tometer. Samples for elemental analysis were dips 5°–8° northeast, indicating continued components occur as two sets, a left-lateral fault prepared by lithium-tetraborate fusion and ana- tilting throughout the Late Miocene.
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