Paleoelevation estimates for the northern and central proto-Basin and Range from carbonate clumped isotope thermometry

Quantitative paleoelevation histories can help explain both why and how widespread Cenozoic extension occurred in the Basin and Range Province of western North America. We present new estimates of preextensional paleoelevations for the northern and central Basin and Range using clumped isotope ((47)) thermometry of lacustrine carbonates collected from each region. Comparison of carbonate (47)-derived mean annual air temperature (MAAT) estimates (similar to 16 degrees C-20 degrees C) for the Late Cretaceous-Eocene Sheep Pass basin of east central Nevada with published MAAT estimates for the Eocene, coastal northern Sierra Nevada (similar to 20 degrees C-25 degrees C), suggests that the early Paleogene Sheep Pass basin had a paleoelevation of 2km. Such a modest paleoelevation suggests that either (1) the proto-northern Basin and Range did not attain maximum paleoelevations of 3-4km until the late Eocene-early Oligocene; or (2) the Sheep Pass basin was a local, high-relief (>1km) setting contained within a >3km orogenic highland (Nevadaplano). Similarity of (47)-derived MAAT estimates (similar to 17 degrees C-24 degrees C) for carbonates from the central Basin and Range and the near-sea level southern Sierra Nevada Bena basin indicate that middle Miocene paleoelevations in the Death Valley region were 1.5km. These fairly low paleoelevations are incompatible with preextensional crustal thicknesses >52km and indicate that mean elevation change was minor (500m) and lithospheric mass was not conserved during >100% Neogene extension of the central Basin and Range, but was instead likely compensated by synextensional magmatic additions to the crust.