Lakota Formation, southern Black Hills, South Dakota: an Early Cretaceous evolving fluvial system

Conference · Fri Aug 01 04:00:00 EDT 1986 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:6963132

Dahlstrom, D J; Fox, J E

The fluvial, Early Cretaceous Lakota Formation consists of four spatially and temporally distinct sandstone units in the southern Black Hills and southeastern Powder River basin. Three of these units crop out in proximity to an area of uranium roll-front development (Edgemont mining district) where approximately 2300 wells were drilled and logged. Comparison of the resistivity logs of several of these wells with continuous cores of the Lakota Formation confirms their lithologic sensitivity. These logs (utilized to assist in subsurface facies interpretations where cores were not available), cores, and outcrops are the basis for the following facies interpretations. The discharge, sediment load, and resulting sinuosity of this fluvial system varied substantially throughout the time of Lakota deposition. The oldest unit consists of tabular deposits with complex internal architecture comprised of cross-cutting lateral accretion deposits. Upward-fining grain size, upward-decreasing scale of sedimentary structures, and the angular relationship between lateral accretion surfaces and overlying crevasse-splay deposits support this conclusion. The intermediate unit of ephemeral stream sediments is characterized by abundant pebble- and cobble-strewn erosional surfaces with up to 1.5 m relief, very poor clast sorting, and trough and planar cross-bedding with concave-upward foresets. The youngest unit has a predominance of tabular cross-bedding with back flow climbing ripples and low dispersion of paleocurrent directions, suggesting a relatively straight, bed-load-type channel dominated by trains of sand waves.

• Research Organization: South Dakota School of Mines and Technology, Rapid City
• OSTI ID: 6963132
• Report Number(s): CONF-8609129-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 70:8
• Country of Publication: United States
• Language: English

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02 PETROLEUM
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11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
CRETACEOUS PERIOD
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
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SOUTH DAKOTA
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USA