Variations in Eolian Architecture and the Relation of Ergs to Sequences and Sequence Boundaries, Colorado Plateau

Ronald C. Blakey

Permian through Jurassic rocks on the Colorado Plateau contain abundant, diverse erg deposits. These ergs are distributed within 14 of 16 sequences and their sequence-bounding unconformities. Based on volume and areal distribution, ergs range from dominant (6) to subordinate (4) to minor (4). Five are marine coastal ergs, four are continental (fluvial-related) ergs, and five are mixed continental-coastal ergs. Five of the ergs have a tabular geometry, three are wedge shaped, and six are variable or irregular. All of the eolian deposits consist of (at least in part) multiple stacked ergs arranged in parasequence sets bounded by eolian super surfaces. Erg position and geometry within the sequences varied greatly. Nine of the ergs contain significant areas where they rest di ectly on the lower sequence boundary; eight have significant areas where they are truncated by the upper sequence boundary. None of the sequences are entirely eolian and only six of the sequences locally contain eolian deposits from top to bottom. Only two of the sequences are everywhere eolian at the top beneath the overlying sequence-bounding unconformity.

The above patterns when placed in overall stratigraphic context provide powerful information concerning erg generation, migration, decay, and erosion Super surfaces and their lateral relations identify smaller-scale controls and processes. Overall, eolian architecture and its orchestration with adjacent non eolian deposits and sequence-bounding unconformities provides critical information regarding the significance and origin of Permian, Triassic, and Jurassic rocks or the Colorado Plateau.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California