In 1998 the Denver Museum of Nature and Science assembled a multi-disciplinary team to examine the Laramide synorogenic sediments in the Denver Basin. Major funding was obtained from the National Science Foundation and the Colorado Water Conservation Board. One of the principal goals of the Denver Basin Project is to build a rigorous time-framework for the fossiliferous strata in the basin providing a context to better understand the uplift and denudation of the Front Range. A continuous 2256 foot core was obtained in 1999 at Kiowa in Elbert County. The 2.5 inch diameter core recovered 93% of the drilled strata and serves as a primary calibration point for our stratigraphic studies of the Basin. The core is archived at the U.S. Geological Survey's core research facility in Lakewood, CO. Two synorogenic sequences were completely sampled as were the Laramie and Fox Hills Formations. The core hole reached TD in the upper Pierre Shale.
A chronological framework for fluvial strata preserved during the latest Cretaceous and early Paleogene in the Denver Basin has been established using radiometric dating, paleontology and magnetostratigraphy. In the Denver Basin, Laramide style synorogenic sedimentation spans the K/T boundary and extends into the Eocene. The synorogenic strata occur in two unconformity-bounded sequences which are interpreted to reflect two episodes of uplift and deformation in the adjacent Front Range. The first, termed the D1 sequence, accumulated during the first phase of uplift of the Front Range. This sequence started to accumulate about 68 MY, spans the end of the Cretaceous and extends up to about 64 MY. Rates of accumulation in the central part of the Basin are on the order of 100 m/million years with rates of up to 150 m/million years on the active western margin. The synorogenic strata are comprised of alternating fluvial channel sandstone and overbank mudstone beds. Coal and lignite beds occur in the central and eastern portion of the Basin suggesting low gradients and under-filled basin conditions. Sandstone compositions vary as a function of the unroofing of the Front Range and the eruption and subsequent erosion of an andesitic volcanic terrain. Compositions range from andesite-rich litharenites to arkoses, these changes reflect the evolution of the catchments feeding the rivers draining the uplifting Front Range. Fossil plants are common, and vertebrates are locally abundant. Moist, warm and generally well-drained to swampy conditions are indicated. Near the end of this period of accumulation, sedimentation became fine-grained, then ceased for a period of approximately 9 MY during which time little sedimentary record is preserved other than a thin aggradational paleosol.
Sedimentation resumed approximately 54 MY ago and spanned a poorly-defined interval during the early Eocene, comprising the unconformity-bounded D2 sequence. During this interval, arkosic fluvial strata record the erosion of a granite-rich source terrain much like we see today in the modern Front Range. Fossil plants are less common and vertebrate remains are rare in this sequence. Paleocurrent indicators together with isopach and composition patterns suggest derivation from the Pike's Peak area during a second pulse of Laramide deformation. Long after these strata accumulated, the region underwent asymmetric epeirogenic uplift and headward incision of the Arkansas and South Platte river systems sculpted the landscapes we see today in the Denver Basin area.
Colleagues working on the Denver Basin Project have examined the faunal and floral records and efforts are underway to tie the Denver Basin paleontological record to data sets developed elsewhere in the Rocky Mountain West. Significant megafloral heterogeneity may result from orographic effects. Pollen and vertebrate remains are being correlated to more extensive records in Wyoming to extend and refine previously established biozonation patterns. Groundwater resources, sandstone mineralogy, fission track analysis, and present-day temperature profiling have also been conducted under the aegis of this project.
As one of the synthesis products of the research, a series of detailed paleo-landscapes have been reconstructed and painted. These will be used to illustrate the results of the research to the general public.