CONNECTING LANDSCAPE CHANGES IN EXHUMATION TO LACUSTRINE SEDIMENTATION AND SURFACE DEFORMATION IN A UNIQUE HINTERLAND BASIN, NORTHEAST NEVADA

Eocene sedimentary strata of the Elko Formation record ~11 Myr of fluvial and lacustrine deposition within an expansive paleolake system, which developed at high elevation (~2.7-3 km) in the hinterland of the Sevier orogenic belt. We couple extensive outcrop and well data of the Elko Formation, correlated with single crystal sanidine ⁴⁰Ar/³⁹Ar geochronology, to understand the genesis of widespread Eocene accommodation amidst Farallon slab removal in the hinterland. Chronostratigraphic correlations show eastward- and southward-flowing braided rivers deposited >250 m of pebble-cobble conglomerate and associated fluvial facies across the northern and central portions of the basin from ~50-39 Ma. At ~44 Ma, meandering rivers deposited fining-upward successions of cross-bedded sandstones and overbank soils within the central and southern parts of the basin before ponding into freshwater lakes at ~43 Ma. These expansive freshwater lakes deposited >50 m of mollusc-bearing microbialitic limestones, which thin towards the basin center, and >120 m of overlying carbonaceous mudstones. At ~42.8 Ma, lacustrine lithofacies show a basin-wide progression from overfilled to balanced-fill conditions that signifies enhanced lake stratification. Fluctuating profundal facies deposited after this lake-type transition include ≤200 m of finely-laminated stromatolitic kerogen-rich mudstones and calcareous siltstones, which reflect increasingly saline lacustrine waters. Syndepositional deformation accompanied deposition of these facies and reflects the periodic influx of volcaniclastic detritus as well as regional deformation that initiated ≤5 Myr prior to basin closure at 40.45 ± 0.25 Ma. Lag time analysis through detrital zircon and apatite (U-Th)/(He-Pb) double dating of the Elko Formation show an abrupt decrease in depositional lag times that occurred synchronous with the Lake Elko highstand, between 45 and 42 Ma, supporting considerable surface deformation during the onset of proximal rollback-driven magmatism. Together this record of terrestrial ponding amidst rapid source exhumation, magmatism, and ensuing regional unconformity suggests Farallon slab removal was a dominant control on hinterland basin formation and regional exhumation patterns.