Quantitative Models of Foreland Basin Evolution and Stratigraphic Development
Clastic foreland basin stratigraphy is primarily determined by the relative rates of first-order basin controlling processes; the rate of mass accretion to an orogen by thrust tectonics, the rate of mass redistribution by surface processes, the rate of fiexural isostatic compensation, and the rate of absolute sea level change. We have developed a composite planform foreland basin model to look for model stratigraphic signatures which reflect either the dominant influence of one of these basin controlling processes or interaction among several processes.
The foreland basin model links component models of orogen tectonics, surface processes, lithospheric flexure and eustasy in an internally consistent manner. The tectonic model uses critical wedge principles to construct a doubly-vergent wedge-shaped orogen. The flexural isostasy model uses either an elastic or a thermally-activated linear visco-elastic lithospheric rheology. The surface processes model couples hillslope (mass diffusion) and climate-mediated fluvial (mass advection) transports to erode, redistribute and deposit mass across the orogen, foreland basins and peripheral bulges.
Preliminary results are presented from two models which illustrate the terminal stages of ocean closure, the ensuing continent-continent collision, and the kinematic growth of an orogen with two flanking foreland basins.
In the first model, there is no significant strike variation in model processes, therefore, cross-sections of any model are sufficient to analyze the basins and compare (hem with previously published results. The contrasting stratigraphic architecture of the basins is controlled by the inherent tectonic asymmetry and by the erosion and sediment flux which become progressively asymmetric as a consequence of the relative positions of the basins on the windward and leeward sides of the growing orogen.
The second model demonstrates the complexities that result when there is a significant strike variation in tectonic processes. This model takes the form of a diachronous continent-continent collision between two continental margins inclined at an angle of ~25°. The model collision zone evolves in time and along strike from accretionary prism to orogen. Sediment flux into the windward foreland basin is greatest adjacent to the largest part of the orogen. This region of the basin becomes subaerial first and the drainage network develops a longitudinal trunk river system, similar to those common to many foreland basins. The combination of lateral and longitudinal fluvial transport results in diachronous filling of the marine basin by an assemblage of fluvial and marine facies which prograde down the basin axis.
Figures & Tables
Stratigraphic Evolution of Foreland Basins - A strong case can be made that foreland basins are where the casual links between sedimentation and tectonic events were first recognized, as evidenced by the interpretations of geologists working in classic foreland areas. This Special Publication was derived from a Research Symposium entitled ?Stratigraphic Sequences in Foreland Basins ?held at the AAPG-SEPM joint annual meeting on June, 1992, in Calgary, Alberta, Canada. This volume provides a well-balanced perspective of current research on foreland basin stratigraphy and also serves as another element in the evolving framework that comprises our understanding of foreland basins. Given that so many of earth?s resources are found in foreland basins and that foreland basin strata often provide the only preserved record of the tectonic events that led to basin development, the impetus for continued studies of foreland basin strata should remain for many generations of geologists to come.