Depositional History Of Middle Paleozoic Carbonate Rocks Deposited At An Ancient Continental Margin Central Nevada

Author : Robert Allen Schalla
Publisher :
ISBN 13 :
Total Pages : 236 pages
Book Rating : 4.:/5 (269 download)

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Download or read book Paleozoic Stratigraphy of the Southern Mahogany Hills, Eureka County, Nevada written by Robert Allen Schalla and published by . This book was released on 1978 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt: Paleozoic dolomites, limestones, and detrital clastic rocks were mapped in the Bellevue Peak 15 minute quadrangle in the southern Mahogany Hills, Nevada. Sedimentary rock units in this area represent shallow-shelf eastern assemblage deposits. Shallow-shelf carbonates characterized deposition from at least Ordovician through Late Devonian time, when clastics derived from the Antler orogenic belt overwhelmed the previous environments. The Ordovician Eureka Quartzite, a quartz arenite of unknown thickness in the map area, probably represents a beach-bar-dune environment. The superjacent Hanson Creek Formation comprises limestones and dolomites of probable Late Ordovician-Early Silurian age and represents a semi-restricted lagoonal environment. Total thickness of this unit in the map area is unknown. Above the interval black dolomites which was chosen as the top of the Hanson Creek, are light-colored dolomites which are assigned to the Lone Mountain Dolomite. These deposits are generally coarse-grained, recrystallized, and lack primary structures. An abrupt contact, interpreted as an unconformity, marks the top of this formation. Extremely fine-grained, largely unfossiliferous, light grey dolomites of the Beacon Peak Dolomite (107 m thick) overlie the Lone Mountain Dolomite in the eastern part of the map area. To the west, bioclastic limestones and dolomites of the Mc Colley Canyon Formation (155 m thick) overlie the Lone Mountain Dolomite. The Beacon Peak Dolomite and the Mc Colley Canyon Formation are thought to be lateral equivalents in this area, with the Beacon Peak having been deposited in a supratidal environment and the Mc Colley Canyon in a subtidal, normal-marine environment. Progressive deepening resulted in an eastward shift of these facies during the late Early Devonian. Evidence of shoaling is present in the crinoidal dolomites of the Sadler Ranch Formation (137 m thick). This shoaling continued and resulted in the westward incursion of a tongue of the upper Oxyoke Canyon Sandstone (21 m thick) during the early Middle Devonian. Deepening of the carbonate shelf is again evident in the eastward retreat of the high-energy Oxyoke Canyon Sandstone environment and the initiation of shallow-water, Middle Devonian Simonson Dolomite (396 m thick) deposition in the map area. The superjacent Devils Gate Limestone represents increased water depth and enhanced circulation over the depositional platform. This shallow water carbonate environment persisted until detrital clastics from the Antler orogenic belt, to the west, terminated carbonate deposition in the map area. The presence of basinal deposits of the Roberts Mountains Formation and the Denay Limestone, 10 kilometers northwest of the map area at Lone Mountain, indicates that the shelf-slope break probably persisted west of the map area from at least the Late Silurian through the Middle Devonian. The stratigraphic sequence in the map area is typical for the area near Eureka, Nevada.