Kara Timm | DRP Petrographic and Materials Investigations
Geochemical and micropaleontological evidence of paleoenvironmental change in the Late Cretaceous Western Interior Seaway from the Niobrara to the Pierre Shale Formation
Deposition of the Upper Cretaceous Niobrara Formation and overlying Sharon Springs Member of the Pierre Shale occurred during transgressive phases within the Western Interior Cretaceous (WIC) Seaway, however their respective geochemical and biological differences are significant. The Niobrara Formation is an alternating calcareous chalk/marl system, biologically defined by fecal pellets and robust foraminifers including Heterohelix globulosa, Globigerinelloides ultramicrus, Hedbergella, Gümbelina and two Archaeoglobigerina species. However, the Sharon Springs is primarily argillaceous in composition with lesser amounts of biogenic calcite and silica. Larger foraminifers within the Sharon Springs are primarily arenaceous whereas foraminifers of the same species found in the Niobrara are dwarfed in the Sharon Springs. Dwarfism of foraminifers species and the presence of dispersed diatoms, which flourish in cold waters, indicate a shift in paleocurrents. Deposition of the Niobrara occurred during times where warm Gulfian currents allowed for carbonate production through the Early Campanian. Paleogeographic maps of the Middle Campanian indicate a southerly restriction of the WIC during the time of the southerly Claggett Transgression. The influx of cold, southerly waters resulted in an environment conducive to diatoms and environmentally stressful to foraminifers.
Lithological and geochemical evidence from the Sharon Springs indicates that the cold-water Claggett Transgression resulted in a stratified water column in the middle of the WIC, as well as, increased organic matter production. Petrographic analysis of preserved organic matter show clumped floccules or flattened amalgamations of floccules in laminated facies. While dispersed amorphous organic matter is also present, flocculation had a major influence on organic matter preservation. Two possible depositional mechanisms, each dependent on water density, probably produced these water conditions. If density contrasts existed between the cold water influx and the warm waters present during the deposition of the Niobrara, the cold waters would have progressed along the bottom of the basin leading to upwelling along the basin margin and basin stratification. If no significant density contrast existed, caballing would occur at the mixing front, leading to downwelling, rapid transport of organic matter to the sea floor, better organic matter preservation and basin stratification.
Originally from Kansas City MO, she graduated with her B.Sc. from the University College Cork, in Ireland. She went on to work for the Institute of Geological and Nuclear Sciences in New Zealand while studying at the University of Otago. Her first foray in the petroleum industry was a position as a quantitative interpreter geophysicist with DownUnder GeoSolutions in Perth, Western Australia. After returning to America, she worked with Pason Systems Corp. as lead night geologist providing geosteering support for operations geologists prior to returning to college. Kira Timm recently completed her PhD at the Colorado School of Mines, researching the petroleum geology of the Pierre Shale and Niobrara Formations in the historic Cañon City Embayment. Her research focuses on subsurface, seismic, core, geochemistry and petrographic investigations associated with the petroleum systems.