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Abstract


The Mesozoic of Middle North America: A Selection of Papers from the Symposium on the Mesozoic of Middle North America, Calgary, Alberta, Canada — Memoir 9, 1984
Pages 173-203
Regional Synthesis and Concepts

Early Cretaceous Transgressions and Regressions in the Southern Interior Plains

W. G. E. Caldwell

Abstract

The Lower Cretaceous Series beneath the southern Interior Plains of Canada contains the record of five paired marine transgressions and regressions and part of a sixth transgression. These incursions and withdrawals are known to have controlled the palaeogeographic evolution of a major segment of the Western Interior basin, or hold the potential to have done so. The earliest four paired transgressions and regressions were confined to the Canadian portion of the basin, three of them, by their presently known extents, to the western foredeep, adjacent to the Columbian Orogen. The fifth paired transgression and regression was that of the Kiowa-Skull Creek Marine Cycle, the transgressive acme of which brought about establishment of the Western Interior seaway. The sixth recorded transgression can be identified as an early phase of the Greenhorn Marine Cycle, a cycle which, like the Kiowa-Skull Creek cycle, was first established in the United States’ portion of the basin. In the Western Interior basin, the Kiowa-Skull Creek cycle is of Late Albian age and the Greenhorn cycle of Late Albian to Middle Turonian age.

Among marine cycles previously established in the Western Interior of the United States, all except the Kiowa-Skull Creek are recorded in Upper Cretaceous rocks. They may be distinguished by great geographic extent, well-defined facies suites, durations in excess of 5 Ma, and possibly by having been strongly influenced by fluctuations in global sea level (eustasy). In contrast, three of the four paired transgressions and regressions which were restricted in varying degree to the Canadian portion of the basin may be distinguished not only by more limited geographic extent but also by less well differentiated facies suites, shorter durations, and the probability of having been controlled by local or regional tectonics. These more minor palaeogeographic events are identified as the ‘Bullhead’, Clearwater, and Hulcross transgressive-regressive couplets. They are of latest Aptian-earliest Albian (or possibly earliest Albian), Early Albian, and Middle Albian age respectively. An earlier, longer-term, transgressive-regressive event, designated Beattie Peaks, is also given tentatively the status of a couplet because of its limited geographic extent. It is of Berriasian-Valanginian age.

Forces which influenced the transgressions and regressions may be interpreted only uncertainly, if not speculatively. The Beattie Peaks Transgressive-Regressive Couplet may be an expression of Kauffman’s first global marine cycle, and the inferred ‘Bullhead transgressive-regressive couplet’ an expression of his fourth such cycle. As yet unexplained discrepancies detract from such correlations, however. The Kiowa-Skull Creek Marine Cycle correlates well with Kauffman’s fifth global marine cycle, and if given its proposed global age-span of Early to Late Albian, the Clearwater and Hulcross transgressive-regressive couplets may have been localized oscillations during Kiowa-Skull Creek transgression, controlled by local and regional tectonics. The pattern of the Early Cretaceous transgressive-regressive couplets and cycles, with transgressions extending farther south with time, is broadly in accord with Vail’s reconstruction of a pulsatory rise in global sea level to reach a highstand early in Cenomanian time. Vail’s minor drop in sea level in Late Valanginian time may correspond to the regressive maximum of the Beattie Peaks couplet. His pronounced rise in sea level from Late Aptian through Albian time may help explain the ‘Bullhead’, Clearwater, Hulcross, and Kiowa-Skull Creek transgressions, but only if the corresponding regressions are assumed to have been controlled by local and regional tectonics. It is likely that the transgressive-regressive couplets and cycles of Early Cretaceous time in the Western Interior basin were strongly influenced by both eustasy and tectonics, neither of which overall was the controlling, that is, dominant force.


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