Graduate Thesis Or Dissertation

 

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/wm117s701

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Abstract
  • Paleozoic limestones, dolomites, quartz arenites, and other clastic rocks were mapped in the vicinity of Dobbin Summit and Clear Creek in the central Monitor Range. Sedimentary rock units present in this area represent the shallow-shelf eastern assemblage and basin and also the basin-slope facies of the traditional limestoneclastic assemblage. The four oldest, Ordovician, units were deposited in shallow shelf environments. The Lower Ordovician Goodwin Formation is composed of about 1200 feet of calcareous shales and thin-bedded limestones. The overlying Antelope Valley Limestone is about 500 feet thick and consists of wackestones, packstones, and rare algal grainstones. The Copenhagen Formation (135 feet thick) is the highest regressive deposit of sandstone, siltstone, and limestone below the transgressive Eureka Quartzite. The Eureka is a quartz arenite 181 feet thick, with an intercalated shallow marine dolomite member. The transition from shallow to deep water conditions can be seen in the change from algal boundstones to laminated lime mudstones in the Hanson Creek Formation (190 feet thick). The superjacent Roberts Mountains Formation (285 feet thick) is composed of lime mudstones and allodapic beds deposited in basinal, deep water conditions. During earliest Devonian time, the facies boundary between eastern dolomites and limestone-clastic transitional facies was situated within the map area. The Lone Mountain Dolomite (510 feet thick) is representative of the eastern facies. The limestone- clastic facies are represented by basinal lime mudstones and allodapic skeletal beds of the Windmill Limestone (170 feet thick), the Rabbit Hill Limestone (315 feet thick) and the Denay Limestone (150 feet thick). The upper plate of the Roberts Mountains thrust interrupts the stratigraphic sequence of the area, and an allochthonous unit of western assemblage cherts and fine grained clastics (Ordovician Vinini Formation) overlies Middle Devonian rocks. The Mississippian rocks of the area are part of the "overlap assemblage!! and overlie older facies boundaries in central Nevada. The Webb Equivalent is a siliceous argillite 400 feet thick and the Camp Creek Equivalent (350 feet thick) is a sequence of distal and proximal turbidites. Both were deposited in the elongate basin which paralleled the rising Antler orogenic highland to the west of the map area during early Mississippian time. The filling of the basin is indicated by the change, within the Diamond Peak- Chainman Equivalent rocks (750 feet thick), from fine-grained limestones and thin sandstones to thick chert-pebble and limestone conglomerates. Source for the detrital chert was western assemblage rocks, then eroding from the Antler Highland, and eastern shelf carbonates. The final episode of the Paleozoic evident in the area was uplift, erosion, and tectonism followed by deposition of shallow-water fossiliferous Pennsylvanian rocks (150 feet thick in incomplete section), to form an angular unconformity. The extreme thinness of uppermost Ordovician through Middle Devonian strata may be due to a shift from the eastern shelf depositional regime to a slope and basinal regime. The stratigraphic sequence of these rocks in the map area closely resembles that of Antelope Valley, 10 miles to the north. Mississippian overlap assemblage rocks more closely match those of the Carlin-Pinyon Range area 100 miles to the north.
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