Tectonic controls on the development of sedimentary sequences in foreland basins
Columbia University, NYC
258 p., Illus., Maps
Alaska Resources Library & Information Services: QE501.3 C63 1991
This thesis is composed of three studies, linked by an introduction, which consider the development of sequence bounding unconformities in terms the tension between tectonic events which build topography and sedimentary processes which destroy and redistribute that topography. Tectonic and sedimentary processes are complementary, each works toward an independantly defined equilibrium, each prevents the other from achieving that stable state. Each study presents an example of progressive, tectonic loading on an elastic lithosphere. Through the constraint offered by known physical processes and the information gained from stratigraphic analysis, the discontinuous sedimentary record is interpreted in terms of continuous tectonic forcing. The stratigraphy of two foreland basins, the Swiss Molasse Basin and the Colville Trough of northern Alaska, is analyzed and interpreted in terms of large scale sequences. Deposition within these sequences is relatively continuous. The regional unconformities that bound them can be related to deformational events within the adjacent thrust wedge. Basin modelling is used to establish this relationship by demonstrating that the timing of the event is appropriate to explain the unconformity. These computer models are quantatively validated by reproducing both the geometry and time relationships observed in the sedimentary package. The unconformity that divides the Lower from the Upper Molasse, the two major sequences in the Molasse basin, can be related to internal deformation of the Alpine thrust wedge, the underplating of the external massifs. The unconformity that divides the Torok/Nanushuk Group sediments from the overlying Colville Group is explained by the changing geometry of the thrust front of the Brooks Range, controlled by its interaction with the Beaufort passive margin to the north. The stratigraphy of the Hawaiian flexural moat is composed of a series of stacked debris flow deposits that, by identifying angular discordance and stratal terminations, can be mapped as sequences. The moat stratigraphy can be understood in terms of the independant evolution of each island, first as a load flexing the lithosphere and subsequently as a sediment source. Mass wasting dominates the island flanks and is shown to be the primary mechanism driving the development of the rift zones which characterize Hawaiian volcanism.
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