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Late Cenozoic paleogeographic evolution of northeastern Nevada: Evidence from the sedimentary basins

¹ U.S. Geological Survey, MS 176, Mackay School of Earth Sciences and Engineering, University of Nevada, Reno, Nevada 89557, USA
² Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA
³ U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA

View larger version (49K): [in this window] [in a new window]   Figure 1. Locations of the Miocene Elko, Carlin, Ivanhoe, Chimney, and adjacent sedimentary basins, shown with the light blue color, and major geographic features in northeastern Nevada. Areas with the "v" pattern are underlain by middle Miocene rhyolitic and basaltic volcanic rocks; JR—Jarbidge Rhyolite; NNR—northern Nevada rift; SR-C—Santa Rosa–Calico volcanic field. The dotted yellow lines indicate the major late Eocene gold-deposit trends; BM-E—Battle Mountain–Eureka; C—Carlin; G—Getchell; J—Jerritt Canyon. The solid red circles are the locations of middle Miocene epithermal systems that were active at the same time as the sedimentary basins; other epithermal systems beyond the limits of this study area are not shown. Abbreviated geographic locations: B—Beowawe; EH—Elko Hills; LT—Lone Tree mine; MC—Mule Canyon; MM—Marys Mountain; P—Preble mine; PH—Peko Hills; PV—Paradise Valley; R—Rain mine; TC—Twin Creeks mine. R-EH—Ruby Mountains–East Humboldt Range detachment and high-angle faults. Inset map shows the location of the study area (gray); W—Winnemucca; PF—Pine Forest Range.

View larger version (26K): [in this window] [in a new window]   Figure 2. Duration and primary lithologies (air-fall and epiclastic) of Miocene sedimentary basins in north-central Nevada, shown from west to east. Also portrayed are significant volcanic eruptions ("v") that took place in the basins. The broad green line represents the duration and general location of the northern Nevada rift. The two, best-exposed parts of the Elko basin (Huntington Creek, Wells area) are presented and represent the age and lithologic variability of the basin as a whole. Parallel ash-rich and epiclastic bars indicate that both lithologies were being deposited at the same time in different parts of the basin. Basin abbreviations: CaB—Carlin basin; ChB—Chimney basin; EB—Elko basin; IB—Ivanhoe basin; IV—Independence Valley. Age data are provided in Table 1.

View larger version (79K): [in this window] [in a new window]   Figure 3. Map of the Chimney basin and Snowstorm Mountains areas, showing the original known and inferred extents of the sedimentary basin, middle Miocene volcanic fields, dates of various sedimentary and volcanic units, and post-sedimentation normal faults and synforms. Areas that do not have an overlay color are underlain by pre-Miocene basement rocks (especially in the Santa Rosa and Hot Springs Ranges and Osgood Mountains), post-middle Miocene sedimentary cover (Paradise, Eden, and Kelly Creek Valleys), and post-sedimentation volcanic cover (Owhyee Plateau region). Some volcanic units along the northern Nevada rift and in the Santa Rosa–Calico volcanic fields were erupted after sedimentation ended, but they are included within the volcanic fields regardless of relative age. See Table 1 for geochronologic information. The modern digital elevation map is used as the base.

View larger version (125K): [in this window] [in a new window]   Figure 4. Photographs of middle Miocene sedimentary and volcanic units in the Chimney basin. A: Fine-grained, thin-bedded, ash-rich lacustrine sedimentary strata overlying a thick ash bed at the base of the exposure. Photo was taken in the western part of the basin. B: Phreatic, vitric megabreccia in base of basal flow of the 15.5 Ma Little Humboldt rhyolite above lacustrine sedimentary units (blocky hill), possibly indicating eruption onto wet sediments or water. The overlying, younger flow unit (left background) overlies both the breccia and the sedimentary units but does not have a basal breccia. Photo was taken at the Little Humboldt ranch along the Little Humboldt River (Fig. 3). C: Conformable contact (dashed white line) between the lacustrine and fluvial facies; a tephra sample from 2 m below the contact produced a 14.7 Ma correlation age. Photo taken between Chimney Reservoir and the Snowstorm Mountains (right far background). D: Closer view of contact between lacustrine (below, light colored) and conformably overlying fluvial sediments (tan). The cobbles concentrated along the contact zone were derived from volcanic units exposed in the Snowstorm Mountains to the east (right).

View larger version (67K): [in this window] [in a new window]   Figure 5. Map of the Ivanhoe basin area, showing the original known and inferred extents of the sedimentary basin, middle Miocene volcanic units, dates of various sedimentary and volcanic units, major post-sedimentation normal faults, and the late Eocene Carlin gold trend. Uncolored areas include areas of pre-Miocene basement rocks in the Tuscarora Mountains and post-middle Miocene sedimentary cover in Boulder and Kelly Creek Valleys; the extent of volcanic units beneath sediments in Boulder Valley is based upon exposures of identical volcanic units in the cliffs on either side of the valley. See Table 1 for geochronologic information. The modern digital elevation map is used as the base.

View larger version (143K): [in this window] [in a new window]   Figure 6. Photographs of middle Miocene sedimentary and volcanic units in the Ivanhoe basin. A: Area between Willow Creek Reservoir and the Ivanhoe district, looking east. RR—Rimrock mercury mine; a—andesite flow unit; vt—15.4 Ma vitric tuff unit, both of which were erupted subaerially. Light-colored, ash-rich strata below the andesite were deposited subaqueously, as were strata between the andesite and the vitric tuff. Dark capping units in distance are 15 Ma rhyolite porphyry flow units and domes, which dip 10° less than the underlying units, indicating tilting between ca. 15.4 and 15 Ma. The Rimrock mercury deposit formed in silica replacement bodies in lacustrine sedimentary units that overlie the vitric tuff unit. B: Thin-bedded, ash-rich lacustrine sedimentary units exposed in the north wall of the open pit of the Hollister gold mine, Ivanhoe district. These beds are stratigraphically between the andesite and the vitric tuff unit (see Fig. 6A). Draping near the base of the exposure is above the irregular top of an andesite flow unit that is exposed just below the photo. Note the progressive upward change to planar bedding. The variegated colors are due to hydrothermal and supergene alteration. C: Sinter and silicified lacustrine sedimentary units (light, massive unit in lower part of photo), overlain by unsilicified lacustrine sediments (middle of photo) and a capping 15.4 Ma rhyolite flow unit. The silicified horizon is widespread throughout the Ivanhoe district and formed prior to the deposition of the 15.4 Ma vitric tuff. Photo was taken 2 km east of the Hollister gold mine. D: Tan, pebble-rich sandstone bodies along Antelope Creek south of the Ivanhoe district. The pebbles are subangular to angular and were derived from the ca 15 Ma rhyolite exposures in the left background, although the main transport direction for the sand component was from right to left. Arrows point to soil horizons between sand bodies. E: Tan—epiclastic sedimentary units overlain by a 15 Ma basalt flow in the southwestern part of the Ivanhoe basin just southwest of the confluence of Rock and Antelope Creeks (Fig. 5). The basalt flow was emplaced subaerially. F: Midas district, looking to the north-northwest. Unwelded tuffs and lacustrine sedimentary units (light tan in foreground) are overlain by 15.7 Ma red rhyolite flows at the skyline. A wide, north-northwest–striking dike fed the flows and intruded the tuffs and sedimentary units in that area. The mine workings are along veins that filled north-northwest–striking faults in the tuffs and sediments; the veins formed at ca. 15.4 Ma (Leavitt et al., 2004).

View larger version (58K): [in this window] [in a new window]   Figure 7. Map of the Carlin basin area, showing the original known and inferred extents of the sedimentary basin, the middle Miocene andesite and Palisade Canyon rhyolite flow units, and dates of various sedimentary and volcanic units. Uncolored areas include areas of pre-Miocene basement rocks in the surrounding ranges. See Table 1 for geochronologic information. The modern digital elevation map is used as the base.

View larger version (118K): [in this window] [in a new window]   Figure 8. Photographs of middle Miocene sedimentary units in the Carlin basin. A: Thin andesite flow units underlain by ca. 15.1 Ma, ash-rich strata (white); sediments of the upper epiclastic unit (not shown) overlie the andesite. Faulting and tilting occurred after basin sedimentation. Photo taken looking north along the west side of the Adobe Range. B: Sand, pebbles, and cobbles in braided stream and channel deposits of the basal epiclastic member; hammer for scale. Photo taken east of the Cottonwood Gulch area in the northwestern part of the basin. C: Soft-sediment deformation in the ash-rich unit along the west side of the Adobe Range. The deformed bed is 1 m thick. D: Alternating fluvial, epiclastic sand beds and lacustrine ash-rich beds of the mixed epiclastic and ash-rich unit. The thick ash bed being sampled was deposited at 16.3 Ma. The underlying sand bed fills a 2-m–deep channel just to the right of the photo. Photo taken along upper Susie Creek in the northeastern part of the basin. E: Contact between the ash-rich unit (white) and the upper epiclastic unit (tan) along Interstate 80 west of Carlin. A tephra in the ash-rich unit near where the photo was taken produced a 14.7 Ma correlation age. The contact is conformable and, where exposed, sharp. F: The upper epiclastic unit (f) and a local zone of the underlying ash-rich unit (a, arrow), both of which overlie weathered and oxidized Paleozoic sedimentary rocks and the Gold Quarry gold deposit in the left side of the photo. The dashed white line delineates the sediment-bedrock contact. Photo taken looking north in the Gold Quarry mine on the west side of the Carlin basin.

View larger version (67K): [in this window] [in a new window]   Figure 9. Paleogeographic map of the Carlin basin area during its early stages of formation. Shown are late Eocene highlands (estimated from page-size figure in Haynes, 2003), possible early-basin normal faults, and the distribution of the basal fluvial unit of the Humboldt Formation, which was the first Miocene unit to be deposited in the basin. Shown also is the approximately outline of the Carlin gold trend (yellow lines), from which numerous Oligocene to early Miocene supergene alunite dates were obtained.

View larger version (34K): [in this window] [in a new window]   Figure 10. Map of the Elko basin area and the Independence Valley. The map shows the original known and inferred extents of the middle Miocene and Pliocene sedimentary units, dates of various sedimentary and volcanic units, and the Ruby–East Humboldt detachment fault system. Uncolored areas include areas of pre-Miocene rocks and, in some areas to the north, the Jarbidge Rhyolite (see Fig. 1). Areas east and south of the Ruby Mountains and East Humboldt Range are outside of the study area and include both pre-Miocene basement units and Quaternary sediments but only trivial amounts of Miocene units. The gravity, depth-to-basement contours were created from gravity data and maps in Ponce (2004). See Table 1 for geochronologic information. The modern digital elevation map is used as the base.

View larger version (152K): [in this window] [in a new window]   Figure 11. Photographs of middle Miocene sedimentary units in the Elko basin. A: Basal Miocene, epiclastic sand and conglomerate beds on the west side of the Adobe Range. Photo taken looking north along the western outskirts of Elko. The beds overlie more steeply dipping volcanic units of the late Eocene Indian Wells Formation (light-colored, below). The gentle eastward dip of the Miocene units may be nearly primary. B: Peko Hills (behind the green floodplain of the North Fork Humboldt River) and fluvial Miocene sediments (tan, foreground) on the eastern dip slope of the Adobe Range. The fluvial sediments continue across the river valley, underlie the low bench to the left (north) of the Peko Hills, and depositionally overlie Paleozoic rocks in the Peko Hills, indicating that the hills were paleohighs during sedimentation. The snowcapped peaks in the background are the Ruby Mountains. Late Cenozoic erosion of the Miocene strata during downcutting of the river has progressively exposed the Peko Hills. C: Conglomerate in an east-trending paleovalley north of Cedar Ridge (Fig. 10). The clasts were derived from Paleozoic units exposed in the Piñon Range to the west. When the channel filled, finer grained epiclastic sand and pebbles formed a continuous cover over the channel fill and adjacent bedrock areas. D: Pebble-rich fluvial sediments in the Huntington Creek area in the southern part of the Elko basin. All of the clasts are crystalline metamorphic and igneous rocks derived from the Ruby Mountains to the east. These fluvial beds overlie ash-rich lacustrine units along Huntington Creek. Arrow points to 6-cm pocket knife for scale. E: Ash-rich, thin-bedded lacustrine sediments in a railroad cut near Wells. Green beds to the right have been altered to chert and zeolites. An unaltered tephra from this sequence was dated at 10.5 Ma. Hammer in right-center of photo (arrow) provides scale. F: Horizontal Pliocene (ca. 2.1 Ma) lacustrine units (light, P) cover lowlands cut into gently west-dipping fluvial strata of the middle Miocene Humboldt Formation (M, tan in middle distance). Photo taken looking east-northeast at the Secret Pass area between the East Humboldt Range (left horizon) and the Ruby Mountains (to right of photo).

View larger version (40K): [in this window] [in a new window]   Figure 12. Diagrammatic geologic and paleogeography history of northeastern Nevada, including uplands (medium brown), areas of basin sedimentation (blue), Miocene volcanic fields ("v" pattern), major normal faults (bar and ball), and stream flow directions (blue arrows); lighter brown areas are uplands that may or may not have been present or were very subdued. Shown also are late Eocene gold trends (gold dotted lines) and middle Miocene epithermal deposits (red dots) from Figure 1. The area shown is the same as in Figure 1, where other geographic locations are presented; county boundaries (dashed lines) can be used as references. Time intervals include: (A) pre-middle Miocene, prior to the inception of middle Miocene basin sedimentation; (B) ca. 16 Ma, when the four basins described in this paper (Chimney (ChB), Ivanhoe (IB), Carlin (CB), and Elko (EB) basins and Independence Valley (IV)) began to form and fill with sediments; (C) ca. 14–9 Ma, the period when the western basins drained externally to form the early Humboldt River system, with continued sedimentation in the Elko basin (EB); and (D) ca. 9 Ma to the present, by which time the Elko basin had integrated into the Humboldt River system, with temporary Pliocene sedimentation in the Elko basin and late Pliocene and Pleistocene sedimentation in Pine Valley (PV) and downstream parts of the Humboldt River (latter two from Reheis, 1999a). The pre-middle Miocene uplands are simplified from Haynes (2003) and include only those related to this study. Uplands had subdued topography, on the basis of only minor amounts of coarse fluvial material except near fault-controlled range fronts. Note the contraction in the exposed extents of some uplands after partial burial by middle Miocene sediments (B to C) and their somewhat increased extent during late Cenozoic erosion of Miocene strata (C to D).

View larger version (18K): [in this window] [in a new window]   Figure 13. Supergene alunite dates and geomorphic events in northeastern Nevada. The vertical blue bars indicate the sedimentary lifespans of the basins, simplified from Figure 2. Basin abbreviations: CaB—Carlin basin; ChB—Chimney basin; EB—Elko basin; IB—Ivanhoe basin; IV—Independence Valley. Supergene alunite dates for the Carlin and Getchell gold trends are shown as squares (open, Rain deposit in the northern Piñon Range; solid, all other deposits); data are provided in Table 2. The major geomorphic periods and processes are shown along the right margin.

View larger version (28K): [in this window] [in a new window]   Figure 14. Map showing middle Miocene (blue arrows) and late Miocene and younger (red arrows) streamflow directions in northeastern Nevada. Miocene streamflow directions are based on data presented in this paper. Pliocene and younger directions are based on data in this paper and in Reheis et al. (2002). Note the streamflow reversals in Pine Valley (PV) and the southern Elko basin (EB). Also shown are the general locations of the Chimney (ChB), Ivanhoe (IB), and Carlin (CB) basins. The semicircular tan areas are the major eruptive centers that formed along the east-northeast–migrating track of the Yellowstone mantle plume (from Perkins and Nash, 2002). The thick dashed green line is the middle Miocene axis of a proposed thermal bulge related to the mantle plume, with wetter conditions to the west and drier conditions to the east (from Pierce et al., 2002).