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Macrofossils And Biostratigraphy Of The Bakken Formation (Devonian And Mississippian) In Western North Dakota, Lawrence C. Thrasher

Theses and Dissertations

The Bakken Formation, up to 145 feet thick in North Dakota, is a subsurface formation in the Williston Basin that typically consists of two black shale members separated by a middle member of predominantly gray siltstone or silty limestone up to 85 feet thick.

Well over 500 macrofossils representing more than 50 taxa were collected from cores of 40 wells. Brachiopods, the most common fossil, represent 17 genera, 1 of which have not been previously reported from the Bakken. Nonbrachiopod fossils of this study, mostly not previously reported from the Bakken, are a hylothyrid, a conulariid, a syringoporid coral, several …

Lexicon Of Bedrock Stratigraphic Names Of North Dakota, Joanne Van Ornum Groenewold

Theses and Dissertations

This lexicon of bedrock stratigraphic names of North Dakota consists of a general definition of each unit as well as the history of stratigraphic nomenclature, An attempt was made to include all units for North Dakota whether formally or informally named, or cur rently being used in the state. The general definition includes name(s) of the unit, age, area of extent, lithology, relationships to other units, characteristic fossils, economic significance, depo sitional environment, type section (1£ one has been proposed), and other remarks that might be significant. The history of strati graphic nomenclature includes a chronological listing of the first …

Glacial Stratigraphy Of Southeastern North Dakota, Michael Camara

Theses and Dissertations

Seven lithostratigraphic units are recognized in the glacial sediment {till) of southeastern North Dakota. Five of these units are not formally named; eventually most of these units will be correlated with formations in surrounding regions. Two of these units, Gardar and Dahlen, are formations recognized in northeastern North Dakota {Hobbs, 1975). The seven lithostratigraphic units are differentiated and correlated using the percentage of the sand, silt, and clay fractions of the till and using the proportion of igneous and metamorphic rock fragments, limestone and dolomite fragments, and shale fragments in the very-coarse-sand fraction (1 to 2 mm) of the till. …

Petrography Of Xenolith Zones In The Black Face-Ames Plutons, Western San Juan Mountains, Colorado, Richard B. Moore

Theses and Dissertations

The middle to late Tertiary Black Face-Ames plutons are irregularly-shaped, intrusive bodies located in the San Miguel Mountains of southwestern Colorado. The Ames pluton is generally a composite sill; the Black Face pluton is an asymmetric laccol1th. The two plutons are probably joined at depth, and together they form a crudely annular outcrop pattern, open toward the west. The principal rock type within the plutons is granodiorite porphyry, although part of the Ames pluton consists of porphyritic rhyodacite.

Two major zones of xenoliths of Precambrian rock occur within the Black Face-Ames plutons; scattered xenoliths are found at widely separated locations. …

The Geology Of The Elliston Area, Western Montana, Thomas R. Walker

Theses and Dissertations

The Elliston area includes four townships located along the continental divide west of Helena, Montana on the northwest margin of the Boulder Batholith and within the Laramide disturbed belt. Strata ranging in age from Precambrian through recent are present, with all but the Ordovician, Silurian, and Triassic System& represented. The sedimentary rocks are mainly marine and continental carbonates, shales, and sandstones typical of a relatively stable shelf. The Precambrian Belt "Series" comprise the oldest rocks. The lower Cretaceous Blackleaf Formation is the youngest pre-Laramide unit. Post-Laramide sediments include fine-grained mid-Tertiary basin fills, terrace gravels, a moraine, and a mantle of …