LECKIE, R. MARK¹, OONA SNOEYENBOS-WEST¹, and ELANA L. LEITHOLD^2
1Univ. of Massachusetts, Amherst, MA
²North Carolina State Univ., Raleigh, NC

Abstract: Response of Cenomanian-Turonian (Late Cretaceous) Foraminifera to High Frequency Changes in Relative Sea Level in the U.S. Western Interior Sea

During episodes of transgression and highstands of sea level, subtropical water masses invaded the U.S. Western Interior Sea (WIS) from Tethys. One such episode occurred during the late Cenomanian-middle Turonian third-order "Greenhorn Cycle".

Assemblage analysis shows that benthic taxon dominance correlates to the third-order transgression and regression of the WIS and fourth-order sea level fluctuations. Six fourth-order cycles are recognized from AZ to MT. Subtropical water masses rapidly moved into the seaway with transgression. Benthic conditions abruptly improved and normal marine, warm water molluscs, foraminifera, and calcareous nannoplankton invaded the seaway. This event also coincides with the onset of a global perturbation in the carbon system (Oceanic Anoxic Event 2).

Neobulimina, an infaunal taxon, dominated during the late third-order transgression and highstand when warm, oxygen-poor Tethyan waters advanced into the seaway. In contrast, the epifaunal/shallow infaunal taxon Gavelinella proliferated briefly during times of water mass mixing (coupled with increased influx of terrigenous and/or marine organic matter?) at/near fourth-order low stands. Neobulimina returned during fourth-order transgressive pulses with renewed expansion of oxygen-poor Tethyan water masses. Neobulimina and the biserial planktic foram Heterohefix show a significant correlation with carbonate content suggestive of fifthorder parasequences.

During third-order regression, Tethyan waters were replaced by cooler, lower salinity water masses of Boreal affinity as marked by an abrupt change to agglutinated benthic foraminifera and loss of nearly all planktic foraminifera. The WIS foraminifera responded to fluctuating sea level and its influence on water mass distribution, organic matter flux, and benthic oxygenation.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas