INSIGHT INTO THE TIMING OF CENOZOIC UPLIFT IN SOUTHWESTERN COLORADO FROM THE TELLURIDE CONGLOMERATE

Fluvial facies and stratigraphy documented in nine measured sections in the Telluride Conglomerate in southwestern Colorado reveal an extensive deposit of ancient debris flows and fluvial deposits that fine to the west. An inverted stratigraphy of rock clasts in these deposits provides evidence for rapid uplift and erosional unroofing of an adjacent highland in the late Eocene just prior to mid-Tertiary volcanism. Uplift could have been linked to a regional episode of mountain building due to magmatism or tectonic reactivation of ancient structural fabrics in the crust. This hypothesis is further supported by the lack of evidence for incision of the Needle Mountains block in Paleocene conglomerates in the area. This proposed pulse of late Eocene uplift and mountain building is inconsistent with previous hypotheses that argue for most of the uplift of the Needle Mountains at about 65 Ma, and may give new insight into the evolution of mountains in southwestern Colorado with implications for the timing of Cenozoic mountain building and development of the adjacent San Juan basin.