High-resolution stratigraphic forward modeling of a Quaternary carbonate margin: Controls and dynamic of the progradation

Abstract : The relationships between the margin sedimentary regime and the platform progradation are studied using forward stratigraphic numerical simulations on the Leeward (Western) prograding margin of the Great Bahama Bank (GBB) during the Quaternary (1.7–0 Ma). The corresponding sedimentary regime in the slope and the platform is well known from the ODP leg 166 and Bahamas Drilling Project wells located along the “Western line” seismic transect. However the sedimentary regime on the margin is not well established: the coral reefal margin observed before between 1.7 and 0.8 Ma in the well Clino is not active anymore at present-day, and the Holocene sedimentary regime is geometrically unable to account alone for the progradation. This study is based on three 2D high-resolution forward stratigraphic numerical modeling experiments with the software DionisosFlow that include the platform, margin and slope domains on the “Western Line Section” in the same sedimentary models. The results are compared to the six sedimentary cores and to the present day bathymetry in order to identify the more realistic scenario. The three experiments test different models of carbonate sediment production and transport. Experiment 1 shows that the highstand shedding of the fine-grained uncemented platform production is unable to reproduce the progradation and the present-day profile. Experiments 2 and 3 incorporate cemented facies in the margin, with the best results obtained with the cemented marginal wedges produced in Experiment 2 during platform emersion. From these results a high-resolution interpretation of the margin seismic section is proposed. This study shows that the platform progradation can be decoupled from the highstand shedding of the fine-grained platform production. It is dependent on the accumulation in front of the steep margin of coarse or cemented material. Before 0.8 Ma this corresponds to the coral reef identified in Clino. The transition after 0.45 Ma to 100-kyr large eustatic cycles with total platform flooding created two distinct marginal regimes: (1) during platform flooding aggrading accumulation of non-skeletal sands, and (2) during platform emersion prograding cemented marginal wedges produced in-situ.