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Abstract: The Dakota Group of South-Central Colorado: Controls on Sedimentation and Stratigraphy


The Dakota Group in the Canon City Embayment-Wet Mountains region of south-central Colorado records deposition of the Kiowa-Skull Creek and Greenhorn eustatic cycles during early development of the Cretaceous Western Interior Seaway. The interplay of these eustatic cycles, fluctuations in sediment supply rate, regional variation in paleoslope gradients, and proximity to local basement-cored uplifts have created a distinctive stratigraphy.

Subdivisions of the Dakota Group (Lytle, Plainview, Glencairn and Muddy Formations) plus several interformational subdivisions are separated by sequence bounding lowstand surfaces of erosion or wave ravinement-transgressive surfaces of erosion.

The Plainview Formation exhibits tidally-influenced sedimentation in the upper reaches of incised paleovalleys and in intervening areas between depositional centers whereas fluvially-influenced sedimentation occurs adjacent to local basement-cored uplifts. The marine-influenced Glencairn Formation is composed of multiple (proximal) to single (distal) upward-coarsening parasequences. The fluvially-influenced Muddy. Formation underwent at least two periods of incisement: (1) the informally described Lower portion of the Channel Sandstone Member, characterized by trough cross-stratification, was scoured during a period of lowered sea level with the paralic Dry Creek Canyon Member filling these incised paleotopographic lows; (2) local reversal in sea level resulted in incisement into both underlying members. The informally described Upper portion of the Channel Sandstone Member, characterized by planar-tabular cross-stratification, was deposited over this second incised surface and, together with the Upper Transitional Member, records the continuation of the Greenhorn transgression.

AAPG Search and Discovery Article #90946©1997 AAPG Rocky Mountain Section Meeting, Denver, Colorado