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Regional analysis of rhythmic bedding in the Fort Hays limestone member, Niobrara Formation (Upper Cretaceous), US western interior

Thesis/Dissertation ·
OSTI ID:6935706
Results of a regional stratigraphic investigation of the rhythmically bedded Fort Hays limestone member of Kansas, Colorado, and New Mexico indicate at least two levels of cyclicity. Regional development of these cycles strongly supports the hypothesis that they are climatic in origin. Departures from simple cyclical patterns resulted from sedimentary effects of Late Cretaceous orogenic activity, erosional events associated with eustatic sea level changes, diagenetic modification, and possibly from interference between orbital parameters having different periodicities. The vulnerability of Milankovitch-type cyclicity to overprinting by tectono-sedimentologic effects makes units such as the Fort Hays useful as indicators of subtle tectonic activity. Regional thickness changes in groups of shale-limestone couplets were identified, correlated, and mapped in the subsurface using geophysical well log information in order to locate subtle structural elements that influenced Fort Hays sedimentation. In the Denver-Julesburg Basin of Colorado and western Kansas, thinning of the section between Fort Hays marker horizons occurs dominantly along northeastwardly trending belts that resulted apparently from Late Cretaceous reactivation of the Transcontinental Arch. Isotopic and petrographic analyses were conducted on pelagic (carbonate matrix) and benthic (inoceramid bivalve) constituents of selected shale/limestone couplets. These data suggest that there was little difference in temperature or salinity between times of terrigenous detrital input and times of nearly pure carbonate deposition. Isotopic information from matrix samples suggests a westward decrease in salinity of surface water in the Western Interior Sea. Isotopic data from largely unaltered inoceramid bivalves indicate bottom-water conditions of near-normal marine salinity.
Research Organization:
Indiana Univ., Bloomington (USA)
OSTI ID:
6935706
Country of Publication:
United States
Language:
English

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Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
CARBONATE ROCKS
COLORADO
CRETACEOUS PERIOD
DIMENSIONS
EROSION
FEDERAL REGION VI
FEDERAL REGION VII
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
GEOPHYSICAL SURVEYS
ISOTOPE RATIO
KANSAS
LIMESTONE
MESOZOIC ERA
NEW MEXICO
NORTH AMERICA
OROGENESIS
PALEOCLIMATOLOGY
PALEONTOLOGY
PALEOTEMPERATURE
PETROGRAPHY
REGIONAL ANALYSIS
ROCKS
SALINITY
SEDIMENTARY ROCKS
SHALES
STRATIGRAPHY
SURVEYS
TECTONICS
THICKNESS
USA
WELL LOGGING