Permian Ergs, Colorado Plateau


Introduction

Permian rocks on the Colorado Plateau comprise four unconformity-bounded sequences, each of which contains rocks of eolian origin. The external geometry of the sequences as well as the distribution of eolian facies varies significantly. However, the patterns of eolian sedimentation display numerous similarities, especially at the outcrop scale. Variation was in response to basin geometry, influx of sand, and local and regional subsidence patterns. Each of the sequences displays episodic deposition, some cyclic at several scales. The largest scale, reflected in each of the sequences, documents broad transgresive-regressive events that formed the sequences and resulted from interactions of eustatic cycles and patterns of basin subsidence. Intermediate-scale cycles punctuate the largest patterns and reflect glacio-eustatic fluctuations. Smaller-scale cycles are observed within unconformity-bound sets or cosets of dominantly drying-upwards or regressive accumulations of eolian and related deposits. Sequence 1 was deposited along the Wasatch (Cordilleran hingeline) line and in remnants of the Paradox Basin. Eolian deposits expanded through time to nearly blanket the region and then were buried beneath fluvial deposits. Sequence 2 was deposited in the Holbrook basin. Eolian deposition began as a narrow band around the margins of the horseshoe basin and then expanded to blanket all of northern Arizona and vicinity. Sequence 3 also paralleled the Wasatch line. Eolian deposits intertongue with marine-sabkha deposits vertically throughout much of the interval but are areally restricted to the eastern margin of the sequence. Sequence 4 contains only a narrow band of eolian deposits along the eastern margin and only in the northern portion of the study area. Geometry and facies patterns strongly parallel those of sequence 3. By comparing and contrasting Permian eolian deposits and their relations to adjacent deposits, a coherent framework of eolian deposition is established. This framework can be used to evaluate tectonic, eustatic, and climatic controls on Permian deposition on the Colorado Plateau. (Abstract from: Blakey, R. C., 1996, Permian eolian deposits, sequences, and sequence boundaries, Colorado Plateau, in Longman M, W. and Sonnenfeld, M. D. (eds), Paleozoic systems of the Rocky Mountain Region: Rocky Mountain Section SEPM, p. 405-426.)



Permian Erg graphics


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