Patterned Sedimentation of Pennsylvanian and Permian Marine Strata in Part of the Cordilleran Area: ABSTRACT

Repetitive to cyclic sedimentary patterns characterize many sequences of marine rocks of Pennsylvanian and Permian age in parts of eastern Nevada and western Utah. The assemblages accumulated in different (at End_Page 350------------------------------ times connected) depocenters of the miogeosyncline. Ely Limestone (Pennsylvanian) exhibits rhythmic arrangement of skeletal to bioclastic, calcarenitic, matrix, and micritic limestones with some interbedded calcareous sandstones. The sedimentary cyclic pattern occurs in stratigraphic sections totaling 1,000 to 1,500 feet, particularly in the Burbank Hills, Confusion Range, and Leppy Range of western Utah, and in the Cherry Creek Mountains, Butte Mountains, Pequop Mountains, Diamond Range, and Pancake Range of Nevada. Ferguson Mountain Formation (Wolfcampian) of northeastern Nevada and part of adjacent Utah is approximately 2,000 feet of alternating reefoid, bioclastic matrix, and micritic limestones arranged in a remarkable pattern in which this tetrad is repeated numerous times by patterned sedimentation. Farther south in east-central Nevada and west-central Utah the Riepe Spring Limestone and restricted Arcturus Formation (both Wolfcampian) aggregate 1,000 to 2,000 feet of cyclically arranged reefoid, bioclastic-lithoclastic, matrix, and micritic limestones with which occur interbedded calcareous quartzose sandstones. The Leonardian-age Pequop Formation crops out in a large area of eastern Nevada and western Utah; essentially all sections studied display patterned or rhythmic sedimentation of bioclastic, skeletal, matrix, and micritic limestones. Butte Mountains and Pequop Mountains of Nevada contain finest stratigraphic sections; the one at Moorman Ranch near U.S. Highway 50 about 35 miles northwest of Ely is a remarkable arrangement of about 2,500 feet of criquinites, fusulinid coquinites, sandy matrix limestones, and micrites. A normal triad of criquinites with fusulinids, sandy matrix limestones, and micritic limestones typifies the section in rhythmic succession. Marine strata of Guadalupian age in western Utah and eastern Nevada include, in ascending order, the Loray Formation, Kaibab Limestone, Plympton Formation, Indian Canyon Formation, and Gerster Formation. The Loray contains shale, siltstone, dolosiltites, evaporitic dolomites, and petroliferous limestones arranged in cyclic manner; this succession evidently formed in marine to non-marine environments under transgressive-regressive conditions. The overlying Kaibab, Plympton, and Indian Canyon do not display marked pattern sedimentation. Gerster Formation normally is less than 1,000 feet thick, but where more than 4,000 feet thick in south-central Elko County, Nevada, it consists of cyclically arranged tetrads of skeletal, matrix, and micritic limestones, and arenaceous criquinites. Evidence suggests that periodicity of diastrophism of marginal and intra-basin landmasses substantially controlled the pattern of sedimentation in depocenters of the Late Paleozoic miogeosyncline. Marine oscillations and concomitant transgressive-regressive sedimentation across the broad shelves, banks, basin, troughs, and evaporite pans established a pattern of carbonate deposition. Rhythmic activity of the Antler-Sonoma orogenic belt, Northeast Nevada Highland, West-Central Utah Highland, Ely Uplift, and others provided detritus and otherwise initiated and controlled patterned sedimentation. End_of_Article - Last_Page 351------------