| Title: | A Possible Record of Glacioeustatic Sea Level Changes from the Cenomanian-Turonian Western Interior Basin |
| Author: | R. Mark Leckie |
| Date Submitted: | 05/15/2002 |
| Address: | Department of Geosciences
611 N. Pleasant St.
Amherst
MA
USA
01003
|
| Phone: | 413-545-1948 |
| Email: | mleckie@geo.umass.edu |
| Co-Authors: | Leithold, Elana L., North Carolina State University, leithold@ncsu.edu; Tibert, Neil E., University of Massachusetts and Smith College, ntibert@science.smith.edu; McCormick, Michael; Polyak, Desiree, University of Massachusetts, depolyak@geo.umass.edu |
| Affiliation: | University of Massachusetts |
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| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725658 |
| Keywords: | Cenomanian-Turonian, Western Interior Sea, foraminifera, glacioeustasy |
| Abstract: | Cenomanian-Turonian (Upper Cretaceous) marine strata of the Western Interior Basin typically contain rich assemblages of foraminifera. Variations in the proportions of agglutinated, calcareous, and planktic taxa are used to characterize fluctuating water depths and/or to distinguish water mass influences, including cooler, less saline Boreal waters and warmer, more saline Tethyan affinities (e.g., Eicher and Worstell, 1970; Eicher and Diner, 1985; Fisher et al., 1994; Leckie et al., 1998; West et al., 1998). Agglutinated foraminifera and ostracods can be used to distinguish estuarine, lagoonal, and marsh facies (Tibert et al., in press). By analogy with modern foraminiferal distribution patterns, estuarine and lagoonal environments represent water depths <10 m, whereas marsh facies develop to within 1 m of sea level. A mix of agglutinated and calcareous benthic foraminifera characterize modern continental shelf depths ranging from 10-100 m. In contrast, planktic taxa typically dominate foraminiferal populations (>50%) in water depths deeper than 100 m on the continental shelf and slope. Wide ranging planktic to benthic (P:B) ratios and alternations of agglutinated to calcareous benthic populations can therefore be used to recognize and constrain ancient sea level amplitude.
The Cenomanian-Turonian Greenhorn marine cyclothem comprises a third-order eustatic sequence in the Cretaceous Western Interior Basin. Calcareous mudrock and marl accumulated across the western basin during much of the transgressive-regressive sequence. Within the Greenhorn Cyclothem, Leithold (1994) recognized six fourth-order carbonate cycles in prodeltaic deposits of Utah. Based on radiometric age dates of bentonites (Obradovich, 1993) and ammonite biostratigraphy, these six carbonate cycles are of variable duration (~150-950 kyr). We have subsequently traced these cycles across the U.S. Western Interior Basin including Black Mesa (northeastern Arizona), Mesa Verde (southwestern Colorado), Kaiparowits Plateau (south-central Utah), and Billings (south-central Montana). In addition, the fourth-order marine cycles deposited during the transgressive phase of the Greenhorn Cycle (Cycles 1-3) have been correlated into marginal marine facies of southwestern Utah where they are preserved as coal-bearing strata (Tibert et al., in press). Planktic foraminiferal maxima coincide with bulk carbonate maxima that record sea level high stands. We interpret the planktic:benthic fluctuations as sea level amplitude changes on the order of tens of meters.
The forcing mechanisms for these sea level changes are difficult to decipher. Correlation of the planktic and carbonate peaks across a large geographic area, coupled with the recognition of a forced regression in the lower middle Turonian (Cycle 5), suggest that allogenic processes controlled the observed stratal cyclicity. The amplitude and possible long eccentricity periodicity (400 kyr) of these cycles in the Milankovitch band (e.g., Meyers et al., 2001) suggest that glacioeustasy would seem a possible driving mechanism. |
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