--> --> ABSTRACT: Sequence Stratigraphy and Facies Analysis of the Greenhorn Eustatic Cycle (Late Albian-Middle Turonian), Western Interior Basin: Arizona to Minnesota, by Erle G. Kauffman, P. J. Harries, J. I. Kirkland, B. B. Sageman, D. G. Wolfe; #91002 (1990).

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ABSTRACT: Sequence Stratigraphy and Facies Analysis of the Greenhorn Eustatic Cycle (Late Albian-Middle Turonian), Western Interior Basin: Arizona to Minnesota

Erle G. Kauffman, P. J. Harries, J. I. Kirkland, B. B. Sageman, D. G. Wolfe

The Greenhorn cyclothem (late Albian-middle Turonian) is the most extensive transgressive-regressive sequence in the Western Interior basin, and marks the greatest Cretaceous eustatic highstand. It is ideally suited for testing models of sequence stratigraphy in a large, tectonically complex epicontinental basin. Over 35 stratigraphic sections and cores along a WSW to ENE transect from Arizona to Minnesota yield high-resolution stratigraphic and chronostratigraphic data which, integrated with molluscan assemblage biozonation, allow correlation of lithofacies across the basin within 100 kyr or less time intervals. In particular, geometrically/chemically fingerprinted bentonite beds, geochemical (isotope, carbon, trace element) spikes, Milankovitch climate cycle

bedding, concretion zones, and ammonite-inceramid bivalve biozones form the basis for this system of stratigraphy; graphic correlation provides a means for relating sections on a fine scale. The Greenhorn cyclothem represents a second-order, disconformity-bounded stratigraphic sequence of 11-12 myr duration, including basal aggradational fluvial facies of the Dakota Group. High-resolution chronostratigraphy demonstrates the correlation of at least nine third and fourth-order sequences, 1-3 myr and 0.1-0.4 myr average duration, respectively. Smaller parasequences are abundant and may be related to Milankovitch-climate forcing at levels of 20-100 kyr-duration and, in some cases, can be individually correlated between strand plainshoreface and basinal pelagic facies. The geometries and t ming of facies tracts within the Greenhorn cycle and its internal sequences have been constructed from high-resolution chronostratigraphic correlations, and only partially fit the passive margin sequence models. Lowstand deposits are especially poorly defined.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990