Quantitative study of delta front deposits.

摘要

This project represents a combination of modern, ancient and numerical modeling studies to understand some of the processes that are associated with delta front sedimentation and discuss the delta front heterogeneities of the resulting deposits. This study is the first that describes delta terminal distributary channels in ancient deposits and quantifies them in terms of dimensions and occurrence within the delta system. Sedimentary facies associations and facies architecture of terminal distributary channels of fluvial-dominated deltas indicate that delta front deposits are more complex than were previously described, with channelized deposits and upstream accretion surfaces. Delta fronts of fluvial-dominated deltas formed in shallow-water basins have multiple-scale, coeval terminal distributary channels with mouth bars that coalesce into a relative thin sandy apron. This is the first study that describes a natural system that has a continuous, river-derived hyperpycnal flow. The Red River/Lake Texoma system is a peculiar modern environment where the river water is saltier than the lake water. This study demonstrates that the combination between the saltier river water during low discharge and high suspended sediment concentration during high discharge creates permanent hyperpyncal (negatively buoyant or sinking) plumes. To demonstrate the type of the river plumes, a new remote sensing methodology is described in addition to historical and field data collection. Because the river effluent forms a hyperpycnal plume, delta progradation into Lake Texoma is controlled by basin (lake) topography. A multi-temporal aerial and satellite geomorphological observation of Red River Delta progradation indicate that (1) delta plain morphology changes with discharge and (2) some parts of the lake are bypassed by the delta, as it follows the steepest gradient, in this case the old river talweg. The magnitude of plume deflection, which is a function of river discharge and lateral lake slopes, was tested using a simple numerical exercise.; To evaluate the variability and the uniqueness of delta deposits formed as a function of initial parameters that control sedimentation, a stratigraphic inversion model has been built. Because the sedimentary processes are non-linear, an inversion method using genetic algorithms has been used. Genetic algorithms represent a novel tool for stratigraphic studies and in this project have been applied for the first time to a 3-D stratigraphic numerical model. The inversion procedure can estimate a most probable model (not necessarily the correct model) as well as assess the parameter accuracy and the range of non-uniqueness (which should cover the correct model).