DISTRIBUTION AND MAPPING OF THE CRETACEOUS TEPEE BUTTES OF THE WESTERN INTERIOR SEAWAY

The Tepee Buttes comprise the most aerially extensive seep carbonates in the world. They are found mainly in Colorado, but crop out from South Dakota south to Texas. The Tepee Buttes are Late Cretaceous, ranging in age from Late Campanian to Early Maastrichtian. Over 800 buttes were identified using aerial orthophotoquads and topographic maps at a scale of 1:24,000 and high magnification. Locations were digitized using ExpertGPS software. Large-scale patterns showed distinct linear trends in butte clusters (~1-3 km). The trends extend NE between Fountain and Boone, CO and NNW farther east. These lineations agree with previous work linking the origin of the Tepee Buttes to Laramide faulting.

A total of 106 buttes were studied in more detail at two sites ~32 km south of Colorado Springs, CO and ~5 km north east of Boone, CO. Six separate lithofacies were identified in outcrops of the Tepee Buttes and mapped at the meter scale: (I) vuggy facies, abundant vugs with thick cement rinds and coarse calcite spar and few fossils; (II) articulated clam facies, mostly articulated lucinids with some vugs; (III) muddy clam facies, lucinid clams in micrite; (IV) limestone concretion facies; (V) micrite facies; and (VI) microbialite facies, little to no fossil material with little to no early cement rinds around voids. Previous studies of the Tepee Buttes described a concentric arrangement of facies within each butte that ringed an inner, central vent pipe. Results of this study found that the facies showed distinct bedding patterns, suggesting vertical stacking of facies, rather than concentric arrangement.

The lithofacies on 106 separate buttes were mapped using differential GPS receivers. Preliminary analysis shows that a majority of the buttes (39%) are dominated by facies II, while only 16% are dominated by facies III. Facies I and VI each dominated 22% of the buttes mapped (facies VI and V had little mappable outcrop). If the buttes had a concentric arrangement of facies around a vent core, the same facies would be expected at the top and center of each butte. Our results show the presence of different facies at the center tops of different buttes. Therefore, these seep carbonates probably accumulated as vertical stacks of rapidly cemented carbonate that may or may not have had significant relief above the sea floor.