Stratigraphy of a Portion of the Lower Permian Dry Mountain Trough, Southern Sulphur Spring Range and Central Diamond Mountains, East-Central Nevada
Type of Culminating Activity
Master of Science in Geology
Dr. Walter S. Snyder
The Early Permian Dry Mountain trough (DMT), east-central Nevada, is one of many basins that developed in response to the complex Pennsylvanian and Permian tectonism along the western North American continental margin. The Dry Mountain trough was an elongate north-south trending basin which occupied a similar geographic location as the previous Mississippian Antler Basin and Pennsylvanian Ely Basin. In the southern Sulphur Spring Range (SSSR) and the central Diamond Mountains (CDM) Lower Permian carbonate and siliciclastic sediments recorded a complex depositional history. The depositional patterns were strongly influenced by relative intrabasinal tectonic uplift and the proximity to an extrabasinal siliciclastic source area. In the SSSR, a transition from basinal to shallow water subtidal/intertidal depositional environments, without a well developed slope facies, represents a shoaling upward carbonate sequence. As the shoaling upward cycle continued in the SSSR, intrabasinal erosion of shallow water carbonate beds was followed by marine deposition of poorly sorted carbonate and chert lithic conglomerate beds. Basinward migration of the shoreline continued as a siliciclastic fan-delta complex developed near, and migrated into, the study area. Clastic deposition of the fan-delta complex consists of shallow marine distal-fan and prodelta conglomerate, shallow marine distal-fan turbidite sandstone, and subaerial medial-fan and proximal- fan chert pebble-conglomerate and sandstone.
In the CDM area, Permian rocks have been divided into eight informal units by Larson and Riva (1963). Late Wolfcampian-early Leonardian deposition records an initial basinal to outer carbonate apron environment (Unit A), overlain by a progradational, coarsening upwards sequence (Unit B) reflecting outer to inner apron deposition. Unit A is mostly comprised of micrite, silty micrite, and siltstone, whereas Unit B consists of soft sediment deformed silty micrite, channelized, redeposited chert pebble and packstone mass gravity flow deposits. Units C and D record shallow carbonate shelf/platform deposition, but with increasing amounts of siliciclastic debris upsection. The transition from lower carbonates to alluvial sandstones of Unit E suggest a rapid advancement of a fan-delta facies followed the period of carbonate shelf deposition. The sandstone and conglomerate of Unit F reflect continued alluvial deposition. The conglomerate and sandstone Units Gl and Gu mark the progradation of a fan-delta complex into the area and final filling of this portion of the basin.
Many of the lithologic units in the CDM are not continuous in thickness and exhibit rapid lateral and vertical facies changes within a mixed siliciclastic and carbonate depositional setting. Many of these diverse lithologies are not found in the northern Diamond Mountains; suggesting, in addition to the differential Permian erosion (Larson and Riva, 1963), unique sediment dispersal patterns between the two areas which were controlled by changing basin morphology due to differential subsidence and close proximity to an active tectonic highland.
Dobbs, Steven W., "Stratigraphy of a Portion of the Lower Permian Dry Mountain Trough, Southern Sulphur Spring Range and Central Diamond Mountains, East-Central Nevada" (1994). Boise State University Theses and Dissertations. 481.