Paper No. 2
Presentation Time: 9:15 AM
SEA-LEVEL RISE, DEPTH-DEPENDENT CARBONATE GROWTH, AND THE PARADOX OF DROWNED PLATFORMS
KIM, Wonsuck, Department of Geological Sciences, University of Texas at Austin, 1 University Station C9000, Austin, TX 78712-025, PETTER, Andrew, St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55414, FOUKE, Bruce W., Department of Geology, Univ of Illinois at Urbana-Champaign, 1301 West Green Street, Urbana, IL 61801, QUINN, Terrence M., Jackson School of Geosciences, University of Texas at Austin, 4412 Spicewood Springs Rd, Austin, TX 78759 and KERANS, Charles, The Jackson School of Geosicences, The University of Texas at Austin, 1 University Station C1100, Austin, TX 78712-0254, delta@jsg.utexas.edu
We present a mathematical model of carbonate platform evolution in which the depth-dependent carbonate growth rate defines the deposition of a platform top responding to relative sea-level rise. The model indicates that carbonate platform evolution is controlled largely by the initial water depth and the production rate at the initial depth compared to the imposed relative sea-level rise rate. A long-standing paradox in the understanding of drowned carbonate platforms in the geologic record is based on comparing relatively slow long-term rates of relative sea-level rise with maximum growth potentials of healthy platforms. Here we present a modeling result of the carbonate platform paradoxically drowned by a constant relative sea-level rise at a rate less than the maximum carbonate production potential without other external controls of environmental changes, such as nutrient supply or siliciclastic sedimentation. If the rate of relative sea-level rise is higher than the production rate at the initial water depth, the top of the carbonate platform gradually drops below the active photic zone and becomes drowned even if the sea-level rise rate is lower than the maximum carbonate growth potential. The model thus resolves the paradox of drowned carbonate platforms.
Test modeling runs at bracketed rates of relative sea-level rise have determined how fast the system catches up and maintains the keep-up phase, which is a measure of the time necessary for the basin to respond fully to the external forcing. The duration of the catch-up phase of platform response is scaled with the initial seawater depth and the production rate, and can be significantly elongated due to increase in the rate of relative sea-level rise. The transition from the catch-up to the keep-up phases also can be delayed by a time interval associated with ecological reestablishment after platform flooding. The carbonate model here employs the logistic equation to model the colonization of carbonate-producing organisms and captures the initial time interval for a full ecological reestablishment. The relationship of the response time to self-organized processes of biological colonization and the depth-dependent growth pattern imply a greater likelihood of autogenic origin for high-frequency cyclic strata than has been previously estimated.
