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|Title:||Compaction-Driven Groundwater Flow and Heat Transfer in Intracratonic Sedimentary Basins and Genesis of the Upper Mississippi Valley Mineral District (Hydrology, Migration, Petroleum, Ore Deposits, Numerical Models)|
|Author(s):||Bethke, Craig Martin|
|Department / Program:||Geology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||A new numerical method allows calculation of compaction-driven groundwater flow and associated heat transfer in evolving sedimentary basins. A calculation of compaction-driven flow during evolution of an idealized intracratonic sedimentary basin including a basal aquifer predicts slow groundwater movement over long time periods. Fluids in shallow sediments tend to move upward toward the sedimentation surface, and deeper fluids move laterally. The hydraulic potential gradient with depth reverses itself near the basal aquifer, and fluids in this area have a tendency to migrate obliquely into stratigraphically lower sediments. Only small excess pressures develop, suggesting that intracratonic basins are not subject to overpressuring during their evolutions. Due to the small fluid velocities, heat transfer remains conduction-dominated and the geothermal gradient is not disturbed. Variational studies show that excess hydraulic potentials, but not fluid velocities, depend on assumptions of permeability, and that both excess potentials and velocities scale with sedimentation rate. These results cast doubt on roles of compaction-driven flow within intracratonic basins in processes of secondary petroleum migration, osmotic concentration of sedimentary brines and formation of Mississippi Valley-type ore deposits.
Application of this method to study of the paleohydrology of the Illinois Basin shows that gravity-driven groundwater flow is the preferred process of forming the Upper Mississippi Valley Mineral District. Fluids displaced from the deep Basin by compaction-driven flow would have cooled by conduction to the surface before reaching the District. Episodic dewatering events are unlikely to have occurred, because the Basin did not develop overpressures during subsidence. Gravity-driven flow due to uplift of the Pascola Arch in post-early Permian and pre-late Cretaceous time, however, could have carried warm fluids to the District. Temperatures attained by this process depend on flow rates through the Basin, heat flow along flow paths, and presence of structures to cause convergence and upwelling of fluids. Predicted flow rates and timing of mineralization agree with previous estimates. These results suggest that exploration strategies for Mississippi Valley-type deposits should account for tectonic histories of basin margins distal from targets.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.
|Date Available in IDEALS:||2014-12-16|