Depositional Environments of the Pictured Cliffs Sandstone, Late Cretaceous, near Durango, Colorado

Abstract

The Pictured Cliffs Sandstone was deposited in the northwestern part of the San Juan Basin (Colorado-New Mexico) during the last regression of the Cretaceous Interior Seaway. The unit is generally interpreted as deltaic or marginal marine; however, outcrops near Durango, CO, consist of repetitive sequences of hummocky stratified (HS) sandstone. Each HS sequence consists of a scoured surface overlain by hummocky-stratified, fine-grained sandstone 20-50 cm thick, overlain by ripple- to planarlaminated, bioturbated, very fine-grained sandstone to mudstone. Amalgamated HS sequences are as much as 7 m thick.