FACIES CHARACTERIZATION OF THE CRETACEOUS-PALEOGENE RATON FORMATION FROM CORE ANALYSIS, COLORADO

The Raton Basin has been a significant resource for the production of coal and coal bed methane (CBM) in northeastern New Mexico, and southeastern Colorado. Coal and CBM production in the basin is located within the Upper Cretaceous Vermejo Formation and Upper Cretaceous-Lower Paleogene Raton Formation. Previous studies of the Raton Formation have relied on the use of data from outcrop and geophysical logs, however, there are no significant studies that have been published utilizing core data. In this study we analyze 5 cored CBM wells from the Raton Formation in Colorado to identify and characterize the lithofacies assemblages, and depositional environments of the Raton Formation through the use of facies analysis.

Deposition of the Raton Formation occurred within a fluvial environment during the regression of the Western Interior Seaway in the Upper Cretaceous-Paleogene. The Raton is ~2,100 ft thick and can be divided into three informal members: the lower coal zone, barren series, and upper coal zone. Deposition of the lower coal zone occurred during a period of high accommodation, and is comprised of a basal pebble conglomerate that fines upwards into very fine grained sandstone, siltstone, mudstone, and carbonaceous shale with thin discontinuous coal beds interspersed. The barren series represents deposition during a period of low accommodation, and consists of medium to very fine grained sandstones with minor amounts of mudstone, siltstone, carbonaceous shale, and thin coals. The upper coal zone represents a return to high accommodation to deposition and is comprised of very fine grained sandstone, siltstones, mudstones, carbonaceous shale, and thick coal beds. High accommodation fluvial strata of the Raton Formation are predominantly fine grained, and floodplain dominated.

Preliminary results of this facies analysis has identified a range of fluvial deposits that are consistent with channel sandstones, floodplain soils, floodplain lakes, splay/splay complexes and splay deltas. This study provides insight into the depositional environments and subsurface characteristics of the Raton Formation, and has implications for future surface to subsurface correlations.