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Geology Newsletter- 1981, Department Of Geology

Geological and Environmental Sciences News

Vol. 1 No. 6

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• Faculty News
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An Analysis Of Nitrate Concentrations In The Ground-Water Of Antwerp Township, Van Buren County, Michigan, John Emil Klanke

Masters Theses

Private wells were tested for nitrate during the spring of 1979 throughout sections of Antwerp Township, Van Buren County, southwestern Michigan (sections 1-5, 7-22, 24-26, 28-31, 33-36). Water samples were collected from 159 private wells and analyzed for nitrate. Nitrate concentrations ranged from less than 1 mg/1 NO₃-N to 14.6 mg/1 NO₃-N. Seven wells were found to have nitrate concentrations equaling or exceeding the National Interim Primary Drinking Water Standard of 10 mg/1 NO₃-N. Nitrate concentrations were related to age of septic system, well depth below static water level, land use, and soil type. …

Petrology Of Fluvial And Shoreline Sands In A Modern Arc-Trench Gap, Guatemala, James Robert Bartel

Masters Theses

Petrographic studies of modern sands, derived from areas with known source rocks, climate, relief, environments of deposition, and tectonic setting, are essential for compiling compositional models for ancient sandstones. The Pacific coastal plain of Guatemala is terminated 25-60 km inland by the steep slopes of a row of active Quaternary volcanic and granitic rocks.

Sands being deposited on the coastal plain by the Rio Nahulate, which drains the older volcanic and granitic terrane, show significant compositional differences with those supplied by the Rio Samala, which drains an area dominated by active volcanism: Q₉F₃₅L₅₆ vs. Q …

Structural Analysis Of Precambrian Metasedimentary Rocks Of The Swede Gulch Formation, Nahant, South Dakota, Richard G. Cookman

Masters Theses

Precambrian X tectonites deformed between thermal domes in the northern Black Hills 1.7 B.Y.B.P. display variably trending isoclinal folds cross-cut by southeast trending slip-folds developed in discrete shear zones. Eugeosynclinal sedimentary rocks consisting of shale, quartzarenite , sublitharenite, and graywacke were metamorphosed to phyllite, quartzite, and metagraywacke during two syntectonic phases and one post-tectonic phase. The earliest syntectonic metamorphism was associated with development of isoclinal folds and may have produced amphibolite or greenschist facies. It was succeeded by retrograde metamorphism of greenschist facies syntectonic with and post-tectonic to development of southeast trending folds.

Mica, chlorite, iron oxides, and graphite are …

Dolomitization Of The Brassfield Formation (Lower Silurian) In Adams County, Ohio, Lisa L. Varga

Masters Theses

The Lower Silurian Brassfield Formation which outcrops in the Tri-state area of Ohio, Indiana and Kentucky is a transgressive sequence consisting of a series of interbedded shales, limestones and dolostones. Evidence from depositional environments, petrography and spatial relationships of dolomitized and undolomitized rock suggests dolomitization in southwestern Ohio was a two-stage process. Initial dolomitization was restricted to the basal Belfast Member and probably occurred penecontemporaneously on small supratidal islands in a manner analagous to that which occurs in the modern sabkha environment of the Persian Gulf. Regional dolomitization was a later diagenetic event related to the formation of a fresh-seawater …

The Petrology And Geochemistry Of Keweenawan Diabase Dikes In Ontonagon, Gogebic, Iron And Dickinson Counties, Michigan, James J. Hahnenberg

Masters Theses

Petrographic and chemical studies of Keeweenawan-age diabase dikes in Michigan's Upper Peninsula show two major groupings, Porcupine Mountain dikes and Lower Keweenawan dikes consist of two major rock types, fine-grained smaller dikes and the coarse-grained central portions of larger dikes. Major minerals are subophitic plagioclase and pyroxene. The rocks, as compared to the "average" basalts, are low in Al₂0₃, high in Ti0₂, K₂0, P₂0₅ and contain moderate amounts of Fe0_t. They are classified as quartz tholeiites. Several parental magma sources that would account for these and other …

U-Pb Systematics And Ages Of Rocks From The Zone Of Cataclasis, Bitterroot Dome, Southwestern Montana, Edward Charles Arruda

Masters Theses

The eastern flank of the Bitterroot range, western Montana, consists of a 100 km-long zone of cataclasis which dips to the east. Zircons in sheared granitic plutons from three localities within this zone were dated using U-Pb methods. These zircons, which consist of anhedral cores and euhedral overgrowths, yield concordia lower-intercept ages of 48-52 million years before the present, dates which likely represent crystallization ages of the plutons. Shearing which affected these plutons, therefore, is significantly younger than the 72-76 million year age assigned for eastward movement of the Sapphire tectonic block whose detachment zone has been interpreted as the …