Title of research project: Advanced Quantitative Modeling of Sedimentary Basin Formation With Applications to Basins in FSU
Reference number of grant: MHE000
Period of performance: 1994 to 1996
Principal Investigator: Dr. B. Naimark
Total funds: US$ 34,390
Primary objectives and scope of the project. We addressed the problem of sedimentary basin evolution using quantitative models, data analysis, and rheological implications. These models were based on viscous flows induced by heavy eclogite bodies sinking in the asthenosphere. Eclogite bodies evolved through a phase change in basalt lenses formed during the rifting. In this project we planned to develop quantitative geodynamical models of basin evolution for the North American, Eastern European and Siberian platforms and to study tectonic analysis of these regions.
Technique and approach. The approach was based on the analysis of borehole and seismostratigraphic data by the backstripping technique and numerical modeling by using Galerkin-type method and bicubic spline approximations improved to allow for density discontinuities at interfacies.
The findings and implications. We constructed databases including thickness of sediments, lithological features, porosity, density, ages, and paleobathymetric data for the Tungus and Timano-Pechora basins. We examined the evolution of the Tungus Basin in the Siberian Platform using two lithological and stratigraphical sections along the deep seismic sounding profiles through the central and southern parts of the basin. Backstripping of twenty-two exploration wells provided control over vertical tectonic motions during Paleozoic geodynamic evolution of the region. Two major regional rifting episodes were identified in the calculated tectonic subsidence curves. Using the results of tectonic analysis we constructed numerical models for the geodynamic evolution of the Tungus Basin. The numerical results agree with tectonic, seismic, and gravitational data. Breaks in sedimentation can be explained by oscillatory vertical movements of the crust due to a possible instability of the boundary layer in the integral rheological model. We obtained the period of oscillations about 100 Ma. We also studied the evolution of the Timan-Pechora basin using lithologic-stratigraphic sections and data from 37 exploration wells along the deep seismic sounding profiles. The tectonic analysis indicated periods of comparatively fast subsidence alternating with slower depression phases. We associated the rapid subsidence of the basement in the Late Devonian with eclogitization of basalt rocks in the upper mantle. Tectonic subsidence curves showed that the basin actively evolved in the Ordovician, then the tectonic activity became slower in the Silurian, then a slow subsidence was found in the Early and Middle Devonian. A fast subsidence was observed in the Late Devonian followed by a comparatively slow subsidence up to the Triassic. Using the results of tectonic analysis we suggested a feasible forming mechanism and constructed numerical models for the geodynamic evolution of the Timano-Pechora basin in the post-Silurian. The numerical results agreed with tectonic, seismic, heat-flow, and gravity data. Similar approach was used for the case of three North American basins: Illinois, Michigan, and Williston.