RECONSTRUCTING MIOCENE PALEOGEOGRAPHY OF THE MIDDLEGATE AND EASTGATE BASINS, NV THROUGH GEOLOGIC MAPPING AND SEDIMENTARY PROVENANCE ANALYSIS

Continental lithospheric extension and magmatism produce topographic relief that alters sediment dispersal patterns and regional basin organization. Although these processes are broadly understood, little work has been done to provide a temporal model that sequences the onset of extension through basin reorganization in areas with differences in pre-extensional crustal magmatic addition and subsequent crustal thinning.

Middlegate and Eastgate Basins are two structurally bound, adjacent, non-marine basins in the northern Basin and Range Province (NV, USA) that exhibit similarities in sedimentology, paleoflow, geochronology, and geochemistry. Miocene stratigraphy of the two basins have been previously described and mapped, with the interpretation that Basin and Range segmentation occurred prior to deposition of the Middlegate and Eastgate stratigraphy. This study incorporates geologic mapping and new detailed sedimentology and stratigraphy, U-Pb zircon ages, U-Pb detrital zircon ages, and detrital zircon trace and rare earth element (TREE) geochemistry to determine if the Miocene basin fill is laterally continuous chronostratigraphically and lithostratigraphically between present-day Middlegate and Eastgate Basins and if so, when segmentation occurred.

Our data suggest that ca. 16-9 Ma, Middlegate and Eastgate stratigraphy belonged to a larger, connected depocenter with sedimentation patterns that were largely unaltered by Oligocene volcanic topography. After ca. 9 Ma, the uplift of the Eastgate Hills through high-angle normal faulting partitioned the two areas forming Middlegate and Eastgate Basins (sensu stricto) and the local basin and range topography observed today. Results from this work may guide future studies tracking changes in basin connectivity and sediment transportation routes through various stages of rifting, especially in settings that exhibit complexities such as previously thickened lithosphere by silicic magmatic addition, inherited crustal shortening, are more ancient, or may not exhibit well-preserved sediment sources and basin fill.