Abstract: The Dakota Group of South-Central Colorado: Controls on Sedimentation and Stratigraphy
ODIEN, ROBERT J.
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