THE LINKED EVOLUTION OF SURFACE UPLIFT AND ATMOSPHERIC CIRCULATION IN THE LATE CENOZOIC SOUTHERN SIERRA NEVADA

Given the intimate links between topography, tectonics, climate and biodiversity, considerable effort has been devoted to developing robust elevation histories of orogens. In particular, quantitative geochemical reconstructions using stable oxygen and hydrogen isotopes have been applied to many of the world’s mountain belts. Yet after decades of study, determining the Cenozoic surface uplift history of the Sierra Nevada remains a challenge. While geological and geophysical evidence suggests the southern Sierra underwent 1-2 km of Late Cenozoic surface uplift, stable isotope paleoaltimetry studies to date have been restricted to the Basin and Range interior. Recent advances in atmospheric modeling have suggested that such stable isotope records from leeward sites can be affected by the complicating role that sufficiently elevated topography such as the southern (High) Sierra plays in diverting atmospheric circulation. In order to examine the potential role of these terrain blocking effects, we produced stable isotope records from three Late Cenozoic sedimentary basins in the Eastern Sierra and Basin and Range: 1) Authigenic clay minerals in the Mio-Pliocene Verdi Basin (VB), 2) Fluvial and lacustrine carbonates from the Plio-Pleistocene Coso Basin (CB), and 3) Miocene to Holocene pedogenic, fluvial and lacustrine carbonates of Fish Lake Valley (FLV). Whereas both the VB (near present-day Reno) and CB (southern Owens Valley) receive input of water directly from the Sierra crest, FLV is a region of proposed reconvergence of moisture in the Basin and Range. The oxygen isotope records in both CB and FLV increase during the Neogene by approximately 2 ‰, while the hydrogen isotope record of the VB decreases by <10 ‰. These results are consistent with a modestly-elevated Paleogene Sierra of ~2 km over which air masses traversed and underwent orographic rainout and Rayleigh distillation. A Neogene pulse of uplift in the southern Sierra could have driven modern flow around the High Sierra, increasing δ¹⁸O values in CB and FLV while simultaneously decreasing those of the VB. Future paleoaltimetry studies should evaluate the potential interactions between surface uplift and complex atmospheric circulation, as well as other confounding factors such as changes in moisture source, seasonality and vapor recycling.