A Paleoelevation History of the Basin and Range and Its ... and is unconformably overlain by Miocene...
Transcript of A Paleoelevation History of the Basin and Range and Its ... and is unconformably overlain by Miocene...
114°58’ W 114°57’ W 114°56’ W
38°43’ N
38°44’ N
38°45’ N
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Garrett Ranch
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Paleocene
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Members E-F
Member D
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Member A
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PzPALEOZOIC Paleozoicundifferentiated
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Garlock Fm.
Mesozoic granite
Permo-Triassicplutonics
Goler Fm.
Ricardo Fm.
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The Basin and Range Province of the western United States is one of the premier examples of diffuse continental extension in the world. Esti-mates of extension across the Basin and Range during the Cenozoic range from 200% province-wide to locally as great as 400%. However, crustal thicknesses across this region, as derived from a variety of geo-physical methods, are remarkably uniform and, at ~35 km thick, are similar to global averages. Reconciling large-magnitude crustal exten-sion with observed crustal thicknesses is difficult without calling on one of three possible alternatives: (1) an Andean-plateau crustal thickness of ~60 km at the termination of the Sevier Orogeny and prior to exten-sion; (2) substantial addition of material to the crust by syn-extensional magmatism or (3) mobilization and redistribution of fluid lower crust during extension. Quantitative paleoelevation histories can help dis-criminate between these competing mechanisms for widespread Ceno-zoic extension. New estimates of pre-extensional paleoelevations for the northern and central Basin and Range are presented using clumped isotope (Δ47) thermometry of lacustrine carbonates that suggest modest (~2-3 km) pre-extensional elevations for the northern Basin and Range and quite low (< 1 km) elevations for the southern Basin and Range. These paleoelevations are incompatible with mass balance considerations based on the observed magnitude of crustal extension and modern crustal thicknesses, and imply that crustal mass was added to the Basin and Range during extension, either from magma-tism or crustal flow.
A Paleoelevation History of the Basin and Range and Its Relation to Cenozoic Extensional TectonismNathan A. Niemi
CIRES Sabbatical Fellow and University of Michigan
Abstract
Background and Methods
Discussion
Acknowledgements
Conclusions
Much of this work formed the basis of the PhD dissertation of Alex Lechler at the University of Michigan, and he is acknowledged for providing many of the figures presernted here. Discus-sions and collaborations with Kacey Lohmann, Mike Hren, Brice Lacroix, and many others have helped to improve this work. Funding for this research was provided by the University of Michigan, a Sabbatical Fellowship from CIRES and a CAREER grant from the National Science Foundation.
Eocene Paleoelevations Miocene Paleoelevations
Goler
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SS0810 - Bena micriteAV0807 - Rocks of Pavits Spring
Carrara marble
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Elevation difference relative to m
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*22.6 Ma
*24.7 Ma (ktb 27 Ma)
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DEATH VALLEY REGION
Geologic setting of Sheep Pass and Goler Formations carbonate sample locations. (A) Geologic map of the El Paso Mountains of southeastern California, modified from Cox [1982]. The Paleo-cene Goler Formation unconformably overlies metamorphic rocks of the Paleozoic Garlock For-mation and Mesozoic plutonic rocks associated with the onset of regional Sierra Nevada arc mag-matism and is unconformably overlain by Miocene Ricardo Formation volcanics. Red star marks location of Goler Formation Member 4a micritic carbonate sample. (B) Detailed geology of Sheep Pass Canyon, southern Egan Range, Nevada where the type section of the late Cretaceous-Eo-cene Sheep Pass Formation is exposed [modified from Druschke et al., 2009b]. Yellow stars mark Sheep Pass carbonate sample locations. Both lacustrine carbonate and fossil mollusc shells were collected from the same location within Member B (K-Pspb).
Geologic Setting
Study Area
Clumped Isotope Thermometry
Geologic Setting
Sampled Localities
Sampled Localities
Paleotemperature Results from Clumped-Isotope ThermometryPaleotemperature Results from Clumped-Isotope Thermometry
Geologic setting of sampled Miocene localities in the Sierra Nevada and Death Valley region. (A) Hillshade map of the southern Sierra Nevada-Death Valley region with extents of Cottonwood Creek (B), Marble Canyon (C), Bat Mountain (D), and Amargosa Valley (E) simplified geologic maps. Map extents are outlined and color-coded by sample localities, as shown in stratigraphic columns (below). Inset shows location and extent of hillshade map. SS = southern Sierra Nevada; DV = Death Valley; AV = Amargosa Valley. (B) Simplified geologic map of the Cottonwood Creek area of the southern Sierra Nevada where the peralic facies of the Bena Gravels were sampled (red star; modified from Bartow [1981]). (C) Simplified geologic map of the Marble Canyon area of the Cottonwood Mountains (modified from Snow and Lux [1999]) with sample location of Ubehebe Formation pisolites marked by blue star. (D) Simplified geologic map of the Bat Mountain area of the Funeral Mountains (modified from Fridrich et al. [2008]), where the Kelley‘s Well Limestone member of the Bat Mountain Formation was sampled (light blue star). (E) Simplified geologic map of the Amargosa Valley area where the Rocks of Pavits Spring were sampled (purple star; simpli-fied from Burchfiel [1966]). Thick, black lines on geologic maps mark mapped surface faults.
(A) Stratigraphic column for Bena Gravels which outcrop in the southern Sierra Nevada (Cotton-wood Creek) [Bartow and McDougall, 1984] (B) Stratigraphic columns for sampled Neogene sedi-mentary basins in the Death Valley region with marker beds and associated radiometric ages labeled (simplified from Fridrich and Thompson [2011] and references therein). 200 m strati-graphic scale bar applicable to both (A) and (B).
Age- Δ47 temperature plot for Bena Gravels and Death Valley area carbonate samples. Tempera-tures are plotted for Δ47-temperature calibrations of Ghosh et al. [2006a; circles] and Dennis et al. [2011; squares]. Samples are color-coded and labeled for clarification. Temperature differences between Bena micrite from the Sierra Nevada and samples in Death Valley indicate that the Death Valley region was not colder than the sea-level samples from the Sierra Nevada, suggesting that the Death Valley region was at low elevations prior to the onset of extension in middle-late Miocene time.
Early Cenozoic paleotopography and paleogeography of the western U.S. Cordillera with ret-rodeformed state boundaries. Locations of reference physiographic provinces (gray polygons) from McQuarrie and Wernicke [2005]. Paleotopographic contours and paleodrainages for the southern Sierra Nevada-Death Valley domain and ‗Nevadaplano‘ region are based on the re-sults of this and published studies [Gregory-Wodzicki, 1004 1997; Wolfe et al., 1998; Cassel et al., 2009a; Lechler and Niemi, 2011b]. Remaining contours and paleodrainages compiled from1006 various sources (Sierra Nevada: Mulch et al. [2006]; Cassel et al. [2009b]; Hren et al. [2010]; Cecil et al. [2010]; Henry et al. [2012]; southern Basin and Range: Abbott and Smith [1989]; Howard [2000]; Wernicke [2011]; Sevier orogen: Henry [2008]; Fan and Dettman [2009]). SN =Sierra Nevada, SP = Sheep Pass, DV = Death Valley.
Isostatic calculations of central Basin and Range (CBR) (paleo)elevations following the method of Lachenbruch and Morgan [1990] and Schulte-Pel-kum et al. [2011]. Elevationcalculations are presented for crust = 2.7, 2.75, and 2.8 g/cm3 and mantle (mantle lithosphere) = 3.3 and 3.4 g/cm3. Colorbar shows calculated elevation values relative to modern mean CBR elevations of 1 km; the – 500 to 500 m range equates to pa-leoelevations of 500 – 1500 m, which is the constrained paleoelevation range for the Middle Miocene Death Valley area based on carbonate Δ47 analysis. Dashed lines show maxi-mum crustal thicknesses permitted for ~ 1500 m paleoelevations (heavy, black lines and boxes for density combinations that produce total litho-spheric thickness comparable to modern CBR estimates [> 100 km; Schulte-Pelkum et al.,2011], gray lines and boxes for thicknesses that do not match modern observations).
Map of sample locations. Upper map shows carbonate sample locations (stars) in modern geographic coordinates with major physiographic provinces of the western US shown in gray. Inset map of the continental US indicates map extent. Lower map shows sample site locations in their Paleocene paleogeographic positions prior to Tertiary Basin and Range extension. Pa-leocene sample locations and paleogeography of retrodeformed state boundaries and physio-graphic provinces are based on palinspastic reconstructions of McQuarrie and Wernicke (2005). SP = Sheep Pass Formation; Goler = Goler Formation.
Simplified stratigraphic columns (Goler Fm. - Cox, 1982; Sheep Pass - Fouch, 1979; Drus-chke et al., 2009b) are included to provide stratigraphic correlation of the Goler (red lines) and Sheep Pass (blue lines) Forma-tions. Dashed lines indicate approximate cor-relations. Stars mark approximate stratigraph-ic position of analyzed carbonate samples. Sampled molluscs from Sheep Pass Member B also shown. North American Land Mammal Age (NALMA) assignments and age uncer-tainties are based on Sheep Pass molluscan biostratigraphy (Good, 1987) and radiometric dating (Druschke et al., 2009b) and Goler For-mation biostratigraphy (e.g. Lofgren et al., 2008) and magnetostratigraphy (Albright et al., 2009). NALMA abbreviations: Puer. = Puercan, Torr. = Torrejonian, Tiff. = Tiffanian, Clark. = Clarkforkian, Was. = Wasatchian, Brdg. = Bridgerian, Uint. = Uintan.
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*Zachos et al., 2001
shells
Carbonate clumped isotope temperature record. Age-temperature plot for Goler and Sheep Pass carbonate samples. Dashed gray line marks average carbonate clumped isotope temperature for Sheep Pass Formation Members B and E (~ 23.5ºC). Zachos et al. (2001) marine δ18O record is shown for reference. Temperature difference between Sheep Pass Formation and presumed Pa-leocene sea-level temperatures at that time suggest that the paleoelevation of the Sheep Pass Formation was not significantly different from its modern elevation. This implies that there was not significant topographic change in concert with large-magnitude extension of the northern Basin and Range.
Heated gas line and isotopo-logue data. δ47 versus Δ47 for Goler and Sheep Pass carbon-ate samples, the Carrara marble interlab carbonate stan-dard, and heated CO2 gases.See text for discussion of heated gas line. Linear regres-sion of heated gas isotopo-logue values includes analyses of heated CO2 gases with δ47 values ranging from -54 to +10‰.Temperature values for carbonate samples are deter-mined by normalizing mea-sured Δ47 values using stochas-tic heated gas compositions at equal δ47 values.analytical results and calculat-ed temperatures.
Clumped isotope thermometry is based on the temperature dependence of the “clumping” of rare heavy isotopes in isotopologues. For paleoelevation studies, the isotopologue of mass 47 of CO3 in calcium carbonate is frequently used to measure the formation temperature of carbonate, a ubiquitous geo-logic material in lakes, soils, and other archives. The occurrence of this par-ticular isotopologue can be used to infer paleo-surface temperatures.
This preliminary study of Basin and Range paleoelevations from the Paleocene, just at the end of the compressional Sevier Orogeny, and from the Miocene, just prior to the onset of Basin and Range extension, suggests that paleoelevations of the Basin and Range are similar to observed modern elevations, despite >200% extension. These results suggest that crustal extension and thinning must be countered by another process that adds material to the crust to compen-sate for extensional strain. Lower crustal flow and magmatic addition are both possible mechanisms to accomplish this. Further work is required to discrimi-nate between these two possibilities.
Paleocene Shoreline
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enilerohS enecoelaP
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