ABSTRACT: High-Resolution Cretaceous Stratigraphy and Sealevel History of the Canon City Embayment, Central Colorado
Erle G. Kauffman
The Canon City structural embayment separates the Northern Colorado Front Range from the southern Wet Mountains. Cretaceous marine marginal-marine sections are well exposed along northern/ western margins, allowing an east-west stratigraphic transect from Pueblo to Canon City. Integrated high-resolution event chronostratigraphy and molluscan biostratigraphy facilitate detailed correlation of five Cretaceous 2nd order marine cyclothem/disconformity-bounded sequences: (1) Kiowa-Skull Creek Cyclothem (middle late Albian) comprising (ascending) the shoreface Plainview and Glencairn formations lying unconformably (sequence boundary; SB) on the fluvial Lytle formation. The Plainview-Glencairn contact is a 3rd-order SB. The Glencairn Formation comprises four upward-coarsening, 3 d-4th order shoreface sequences. The uppermost Glencairn is marked by a major SB produced during lowstand channeling. (2) The latest Albian-middle Turonian Greenhorn Cyclothem, a subsymmetrical 2nd-order sequence, represents maximum Cretaceous sea-level highstand. It comprises (ascending) the Muddy Sandstone (channel fill shoreface), proximal to medial offshore Mowry and Graneros shale facies, and medial-distal offshore Greenhorn Formation (carbonate facies maximum transgression/eustatic highstand). On regression the cyclothem contains the Fairport, Blue Hill, and Codell members; numerous sequence/parasequence boundaries lie within the cyclothem. A major marine SB cuts the upper Codell Sandstone. (3) The asymmetrical Niobrara Cyclothem (late Turonian-early Campanian) has a condensed tran gressive sequence cut by multiple anastomosing disconformities that expand westward. The Niobrara Formation (highstand) is punctuated by four 3rd-order sequences represented by basinal highstand carbonate facies. Final Niobrara regression is marked by the Apache Creek Sandstone Member, Pierre Shale (early Campanian) and a poorly defined SB. (4) The Clagget Cyclothem (early-late Campanian) is poorly defined by the Sharon Springs Member (highstand) overlain by regressive offshore facies (Rusty Zone). (5) A late Campanian-early Maastrichtian Bearpaw cyclothem is poorly preserved in the embayment; peak transgression is represented by the Tepee zone, Pierre Shale, containing submarine spring deposits emplaced along Laramide faults.
AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990