Early Cenozoic topography, morphology, and tectonics of the northern Sierra Nevada and western Basin and Range

Abstract

Debate surrounds the origin, uplift, and evolution of the northern Sierra Nevada and western Basin and Range. The studies presented here integrate different scales of observation, from local paleovalley morphology, estimation of local slopes, and braided stream alluvial architecture, to regional assessments of sediment and volcanic provenance and paleoelevations across the proposed ancestral Sierra Nevada-Nevadaplano to gain a better understanding of early Cenozoic topography, morphology, and landscape evolution of the region, and to assess the possible tectonic and climatic drivers for that evolution. Results from sedimentologic analysis of Eocene fl uvial deposits show diachronous, localized paleovalley incision and braided stream aggradation in a system infl uenced by Eocene climate, eustasy, and Laramide tectonism, and suggest that previous estimates of the timing and amount of range uplift based on paleochannel gradients may be invalid. Overlying Oligocene ignimbrites deposited in the Sierra Nevada were geochemically and geochronologically correlated to sources in central Nevada, and results from this work show that ignimbrites traveled over 200 km from their source calderas across what is now the crest of the Sierra Nevada, and that in the Oligocene, no drainage divide existed between Nevada source calderas and sample locations 200 km west. Hydrated volcanic glass from these units was used as a proxy for the isotopic composition (δD) of Oligocene meteoric water, which refl ects the effect of ancient topography on precipitation. δD decreases from west to east across the Sierra Nevada by ~48‰, which is similar to the isotopic gradient of precipitation over the area today. δD across Nevada decreases at a signifi cantly lower gradient, refl ecting a signifi cant reduction in the rate of increase of paleoelevation with distance, and may refl ect a gradual increase in mean elevation from west to east or partially closed system hydrology. This multidisciplinary approach provides both a detailed reconstruction of the evolution of the ancestral Sierra Nevada drainage system from Eocene to Oligocene time and multiple lines of evidence to support the conclusion that the northern Sierra Nevada likely acted as the steep western fl ank of a gradually sloping high-elevation plateau ("Nevadaplano") in the Oligocene. Miocene to Holocene extension lowered elevations across what is now the Basin and Range, possibly associated with gravitational spreading of overthickened, magmatically and radiogenically heated crust.

Mechanics of relative and absolute displacements across normal faults, and implications for uplift and subsidence along the eastern escarpment of the Sierra Nevada, California

“…Apparently, the eastern escarpment developed in a region that was already relatively high. This conclusion is consistent with fi eld-based studies suggesting that the Sierra Nevada and the areas immediately east of it retained high crestal elevations throughout the Cenozoic (e.g., Mulch et al, 2006;Cassel et al, 2009Cassel et al, , 2012Hren et al, 2010). It is also consistent with previous modeling work by Chase and Wallace (1986) and Thompson and Parsons (2009).…”

“…This view is based on a variety of stratigraphic and geomorphic data, including inclinations of bedding, analyses of rigid-body rotations (tilts), stream channel gradients, and incision rates, and exhumation rates derived from thermochronometric data. In contrast, others contend that the range has been high for perhaps as long as 40 m.y., and might have undergone little to no late Cenozoic uplift (e.g., Wernicke et al, 1996;DeCelles, 2004;Mulch et al, 2006;Cassel et al, 2009Cassel et al, , 2012Hren et al, 2010). That view is based on differing interpretations of the stratigraphic and geomorphic data, as well as paleobotanical data and isotopic analyses of meteoric water preserved in weathered volcanic ash and fl uvial sediments.…”

Epeirogenic transients related to mantle lithosphere removal in the southern Sierra Nevada region, California: Part II. Implications of rock uplift and basin subsidence relations

“…House et al, 1998House et al, , 2001Poage and Chamberlain, 2002;Wakabayashi and Sawyer, 2001;Jones et al, 2004;Mulch et al, 2006;Busby and Putirka, 2009;Cassel et al, 2009Cassel et al, , 2012Molnar , 2010;Wakabayashi, 2013). Rarely is the question of transient vertical displacements considered in this debate.…”

“…Estimates for late Cenozoic rock uplift along the eastern Sierra crest are 2 ± 0.5 km (Huber, 1981;Unruh, 1991;Wakabayashi and Sawyer, 2001;Wakabayashi, 2013) to little or zero (Poage and Chamberlain, 2002;Mulch et al, 2006;Cassel et al, 2009Cassel et al, , 2012. The former interpretation is based mainly on the updip projection of upper Cenozoic strata lying along the Foothills ramp, and basement incision beneath Neogene surfaces, both determined north of 37°N.…”

Eocene-Early Miocene paleotopography of the Sierra Nevada-Great Basin-Nevadaplano based on widespread ash-flow tuffs and paleovalleys

“…(1) Based on stable isotope studies, Cassel et al (2010Cassel et al ( , 2012a interpreted that the Oligocene Sierra Nevada had an elevation and steep gradient simi lar to its present-day elevation and gradient, and that the Nevadaplano east about to the Campbell Creek caldera had a much shallower gradient. A shallow gradient in the central Nevadaplano would have allowed the tuff of Campbell Creek, as well as any other tuff, to fl ow more easily upstream.…”