--> --> Revisiting the Great Basin, Part 1: Regional cross section construction and thrust sheet restoration.

AAPG Pacific Section and Rocky Mountain Section Joint Meeting

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Revisiting the Great Basin, Part 1: Regional cross section construction and thrust sheet restoration.

Abstract

In order to assist in an updated petroleum systems analysis of the Great Basin and re-examine the Basin and Range province for hydrocarbon exploration potential, a structural analysis of western Utah and Nevada has been undertaken that has involved four distinct components, including: (1) regional, balanced structural cross section construction across central and western Utah, and eastern and central Nevada; (2) identification of major thrust sheets, fault blocks, and compressional structural systems across the Great Basin; (3) sequential restoration of structural cross sections; and (4) sequential fault-block and thrust sheet restoration. Major orogenic events and structural systems that have deformed the Great Basin, that have complicated hydrocarbon exploration across western Utah and Nevada, and that have been examined for restoration of thrust sheets include: (a) the Late Devonian-Mississippian Antler orogeny and emplacement of the Roberts Mountain and associated thrust sheets; (b) the late Permian-Triassic Sonoma orogeny and emplacement of the Sonoma thrust sheet (including the Golconda thrust sheet); (c) the late Paleozoic and/or Mesozoic development of the White Pine (Eureka) deformation zone, in the footwall and east of the Roberts Mountain thrust sheet; (d) the Early to Late Cretaceous Sevier orogeny and emplacement of the Canyon Range, Pavant, Paxton, and Salina thrust sheets; and (e) Tertiary extensional deformation, including both low-angle detachment and higher-angle normal faulting. The timing and locations of Mesozoic and Tertiary igneous activity across the Great Basin are also considered during our structural and petroleum systems analysis of the region. Positions of surface and well samples used for petroleum systems analysis, including both source rock and oil samples, have been restored along extensional fault blocks and emplaced thrust sheets, in map view, to the Jurassic-Cretaceous boundary (145 Ma; pre-Sevier orogeny), mid-Permian (275 Ma; pre-Sonoma orogeny), and late Devonian (375 Ma; pre-Antler orogeny). Structural analysis, balanced cross section construction, and the sequential restoration of both cross sections and thrust sheets has allowed us to examine of the importance of depositional vs. tectonic loading to the generation of hydrocarbons, potential hydrocarbon migration pathways, and the potential for paleo-trap development during the structural evolution of the Great Basin. In addition, the positions of restored surface and well samples has allowed an updated determination of three-dimensional depositional settings for key, pre-Tertiary hydrocarbon source rocks identified within the Great Basin, including the Vinini, Valmy Woodruff, Pilot, and Chainman Formations. Depositional settings and petroleum systems analysis, based in part on sequential cross section and thrust sheet restoration, will be discussed in Part 2 of the presentation. Combining structural analysis, cross section and thrust sheet restoration, models for source rock depositional settings, and detailed 2D and 3D petroleum systems analysis is considered to be critical to future hydrocarbon exploration success in the structurally complex Basin and Range tectonic province of western Utah and Nevada.