Subsurface Characterization of the Depositional System for the Paleocene Raton Formation, Colorado and New Mexico, USA
The Raton Formation lies within the Raton Basin, which spans the Colorado-New Mexico border within the foreland of the Sangre De Cristo Range. The formation consists of sandstone, shale, coal, and conglomerates that were deposited within a closed intermountain basin and is now an important target for coal bed methane within the region. Foreland subsidence in the Raton Basin accommodates the deposition of four key formations; the Cretaceous Trinidad Sandstone, the Upper Cretaceous Vermejo Formation; the Paleocene Raton and Poison Canyon Formations. The Raton Formation is notable for the discovery by C. Pillmore who found that the formation contains the global K-T boundary iridium layer. The development of coal bed methane within the Raton Formation has provided a great deal of new subsurface data, which is the basis of this research. The goal is complete high-resolution correlations between available data to evaluate the influence of orogenic uplift to the west on sedimentation patterns as well as the extent and importance of a regional unconformity that persists within the western part of the basin. To the east, the section is conformable, which could be interpreted as a shifting and east directed broadening of the Raton Basin as a function of the growing orogenic wedge to the west. Alternatively, uplift of the western margin of the basin may have been driven by eastward migration of the deformation front. In the case of the latter one would expect to see evidence of sedimentary bypass and erosion that varies at a local scale. For the former, the western basin may have been abandoned entirely over regional scales producing a more uniform progression of depositional facies. To evaluate these models we are conducting a high-resolution correlation study of electrofacies throughout the available data. The results of which can identify key stratigraphic events to test these models. A primary issue concerning the data is that many of the sand bodies within the system are arkosic and have a strong gamma response similar to shale. This will require that we consider a range of petrophysical characteristics to accurately differentiate sand from shale.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California