Anatomy of Epicontinental Flooding: Late Albian-Early Cenomanian of the Southern U.S. Western Interior Basin


The mid-Cretaceous (Late Albian-Early Cenomanian) sedimentary succession between Wyoming and Texas, which is generally attributed to transgression during the early part of the third-order Greenhorn cycle, reveals three thin sequences of unusually large, regional extent, deposited during three higher order marine cycles. These three sequences are preserved in outcrop sections and wells in central and southeastern Colorado, northeastern New Mexico and northwestern Oklahoma. We conducted an integrated study utilizing sedimentology, micropaleontology, palynology and organic geochemistry in order to understand the environmental details of the marine-terrestrial transitions during a continental flooding event and how they fit into the larger picture of the first-order Zuni Sequence. Each of the three sequences (referred to as sequences 3.1, 3.2 and 4) records biofacies shifts of over 200 km within vertical sections of less than 20 in that mark ephemeral Tethyan flooding into southeastern Colorado. In each sequence, basal fluvial-paralic sandstone with non-marine fossil assemblages and isotopic and palynofacies signals passes vertically into marine-influenced shale and sandstone. Marine fossils, mainly as moderately diverse agglutinate foraminiferal biotas, nearshore dinoflagellate cysts and acritarchs, and Skolithos ichnofauna, become progressively poorer up-dip until only brackish-tolerant ichnofauna, sparse agglutinate foraminifers and non-marine palynomorphs remain. Two of the three thin sequences record previously unrecognized transgressions that appear to have lasted no more than a million years each, accompanied by high amount of freshwater input. Therefore, the regional scale of this database covering as it does a considerable portion of the southern Western Interior Basin, provides an instructive example of the sedimentary and biotic response to transgressions across low-relief margins of epeiric seas.


Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Albian; Cenomanian; Depositional Sequence; Flooding; Inland Sea; Paleoceanography; Transgression; North America; Western Interior; Acritarcha; Dinophyceae; Foraminifera; Skolithos

Geographic Coverage

Western U.S.

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Document Type

Article - Conference proceedings

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© 2008 Geological Association of Canada, All rights reserved.

Publication Date

01 Jan 2008

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