HR: 14:25h
AN: H53E-04    [Abstracts]
TI: Unraveling Forcing Factors of Shallow Shelf Stratigraphy With Numerical Modeling
AU: * Overeem, I
EM: irina.overeem@colorado.edu
AF: INSTAAR, 1560 30th street , Boulder, CO 80309-0450 United States
AB: Shallow shelf stratigraphy is controlled by a series of geological boundary conditions; sediment supply, paleo-bathymetry, sea level, oceanic reworking processes, and tectonics. Geological boundary conditions evolve non-linearly over time; sudden changes in the rate of sea level change or abrupt climate changes dictate the stratigraphic evolution. We use numerical modeling to unravel the influence of different forcing factors on the stratigraphy. Our numerical model, SedFlux, is a two-dimensional process-based stratigraphic model. Time-varying sediment fluxes drive floodplain sedimentation and coarse bedload deposition by fluvio-deltaic processes. The suspended sediment carried by the river is dispersed in the ocean through hyper- and hypopycnal plumes. Seafloor sediment is reworked by ocean storms, failures and subsequent transport as sediment gravity flows (turbidity currents or debris flows). SedFlux records the thickness of the deposited sediment and the grain size preserved over time along a longitudinal profile. Simulations of the New Jersey shallow margin over the last 40 ka serve as an example of the unraveling of different forcing factors. Initially, the shelf is exposed and Arctic conditions prevail in the drainage areas, subsequently the high sediment supply from the rivers draining the melting Laurentide Ice Sheet is a dominant impact on the shelf stratigraphy. Over the last 10 ka the shelf becomes sediment-starved and storm-dominated. Shallow seismic data have been used to validate the large-scale deposited thicknesses of the SedFlux `base-case' prediction. It was found that the range in thickness predictions is comparable to the lateral variations reconstructed from the seismic data. In addition, we quantitatively compared SedFlux predictions with a data set of 98 seafloor grab samples taken on the New Jersey shelf between 50 and 150 m water depth. The subtle fining trend towards deeper water is evident from both observed and predicted data. However, SedFlux shows a larger component of fine sand, especially in shallower water. Twenty sensitivity tests quantify the significant impact of uncertainty in the forcing factors. Estimates of meltwater pulses (and grain-size distributions carried by the rivers at those times) and paleo-storm climate were found to have a wide range and strongly impact the predicted stratigraphy. The sensitivity experiments form a tool to quantify the relative effects of the forcing factors. We advocate an approach which couples a standard deviation based on a series of sensitivity experiments to a predicted `base-case' value. In that way the stratigraphic variability caused by ranges in the boundary conditions is evident for later users.
DE: 4219 Continental shelf processes
DE: 4255 Numerical modeling
DE: 3022 Marine sediments--processes and transport
DE: 1824 Geomorphology (1625)
DE: 1620 Climate dynamics (3309)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting