SYNTECTONIC SEDIMENTATION'S PUZZELS IN THE SAN JUAN MOUNTAINS

Although much has been gleaned from the sedimentary record in the San Juan Mountains, many questions remain unanswered about of the history of the late Paleozoic Ancestral Rockies, the Mesozoic clastic wedge of the Sevier and Laramide orogenies, and the complex record of Cenozoic uplift and denudation. Recent research interests in the Late Paleozoic sedimentation associated with the Ancestral Rockies in the San Juan Mountains have focused on the timing and nature of syntectonic sedimentation at different scales. Several authors have addressed large-scale outcrop to basin correlation based on lithostratigraphy, but biostratigraphic control has remained limited. Current research in the area addresses 0.5 to 2 kilometer-scale facies geometries in the Hermosa Group, distinction of angular unconformities vs. delta progradation, sub-facies of the Molas Fm. and even discussion of possible equatorial glaciation during the Pennsylvanian. The signature of late Mesozoic subduction in western North America played a major role in controlling the fluvial and marine deposits found in and on the flanks of the Juan Mountains. Recognizing these controls at the scale of foreland basins to the reservoir scale of facies geometries in coal bed methane bearing formations remains challenging. Complex issues of provenance and paleotopography remain to be solved. Our understanding of the Cenozoic uplift and unroofing of the region to produce the peaks of San Juan Mountains today hinges, in large part, on the interpretation of much needed provenance studies and proxies for uplift such as paleofloral limitations and sediment volume estimates to contrain temporal variation in rates of erosion.