Thrust Sequences in the Windermere Hills, Northeastern Elko County, Nevada

Abstract

Paleozoic and Mesozoic (Triassic) rocks in the Windermere Hills comprise several informally named sequences, all of which are believed to be allochthonous. The Chainman Sequence is the structurally lowest one seen and contains only the Chainman Formation of Kinderhookian (Mississippian) age. Above the Chainman Sequence is the Black Mountain Sequence which contains the Devonian Nevada and Guilmette Formations, an unnamed Kinderhookian limestone formation, and the Diamond Peak Formation whose base is Kinderhookian. The overlying Thousand Spring Sequence consists of two parts. The lower part of the sequence contains imbricate slices of eugeosynclinal and transitional belt rocks which are unconformably overlain by the upper part with Permian clastic rocks assigned to the Strathearn, Buckskin Mountain, and Carlin Canyon Formations, and the Triassic Dinwoody and Thaynes Formations. West of Highway 93, the Summer Camp Sequence, which contains Upper Ordovician eugeosynclinal belt rocks, is thrust over the Thousand Spring Sequence. East of the highway, the HD Summit Sequence, with Permian clastics, is over the Thousand Spring Sequence. The relations between the Summer Camp and HD Summit Sequences are unknown. The isolated Wilkins Siding Sequence contains Pennsylvanian rocks and may constitute a thin thrust sheet between the Chainman and Thousand Spring Sequences. Poorly defined domes and basins fold the pre-Cenozoic rocks and thrusts and were probably formed by the interaction of two sets of folds, of unknown significance. Small asymmetrical folds close to thrusts predate the domes and basins and were probably produced in response to southeasterly movement of thrust sheets during the Antler Orogeny and in post-Early Triassic time. Thrusts are accompanied by predominantly brittle deformation. High-angle faults are mostly normal; they occur throughout the area and postdate all other structures. Rocks in the thrust sequences of the Windermere Hills provide a fragmented record of Ordovician to Triassic deposition and deformation in different parts of the Cordilleran Geosyncline. Paleozoic eugeosynclinal and transitional belt rocks were first thrust southeastward during the Antler Orogeny. Permian and Triassic rocks were subsequently deposited unconformably on the thrust sheets, and post-Early Triassic thrusting moved the whole succession southeastward again to the site of the Windermere Hills. Other sequences contain rocks of various ages deposited in different tectonic environments, all juxtaposed in the Windermere Hills by post-Triassic thrusting.