Analysis and Correlation of Growth Strata of the Lower Dawson Formation: Insight into the Tectono-stratigraphic Evolution of the Colorado Front Range

Harvey, Korey; Aschoff, Jennifer

Despite numerous studies of Laramide-style (i.e. basement-cored) structures, their 4-dimensional structural evolution and relationship to adjacent sedimentary basins are not well understood. Analysis and correlation of growth strata along the eastern Colorado Front Range (CFR) help decipher the along-strike linkage of thrust structures and their affect on sediment dispersal. Growth strata, and the syntectonic unconformities within them, record the relative roles of uplift and deposition through time; when mapped along-strike, they provide insight into the location and geometry of structures through time. We present an integrated structural- stratigraphic analysis and correlation of three growth strata assemblages within the fluvial and fluvial megafan deposits of the uppermost Cretaceous to Paleocene Dawson formation on the eastern CFR between Colorado Springs, CO and Sadalia, CO. Structural attitudes from 12 stratigraphic profiles at the three locales record dip discordances that highlight syntectonic unconformities within the growth strata packages. Ten high-resolution syntectonic unconformities were identified at the Air Force Academy north of Colorado Springs, CO. These syntectonic unconformities provide a window of detail into the kinematics but only two of these could be correlated to the other northward stratigraphic profiles at the Air Force Academy. Three syntectonic unconformities were identified at Wildcat Mountain that correlate to the south with three syntectonic unconformities at Wildcat Tail west of Sedalia, CO. Correlation of the syntectonic unconformities show diachronous development of emerging structures first in the South, then propagating in a northward direction along the eastern side of the CFR. Lithofacies and paleocurrent analysis within the growth strata record the transition from axial fluvial deposition to fluvial megafan deposition. Sediment entry points for megafans were likely controlled by lateral linking of along strike thrust faults (i.e. traverse or transfer zones) that bound the CFR. Provenance analysis supports the linkage of thrust structures controlling the provenance and sediment entry points to the Denver Basin. The study has implication for predicting clastic sediment distribution in punctuated foreland basins, which ultimately controls reservoir presence for conventional plays and clay content for unconventional shale plays.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013