Topography‐driven flow versus buoyancy‐driven flow in the U.S. midcontinent: implications for the residence time of brines

Abstract

Topography-driven flow is normally considered to be the dominant groundwater flow system in uplifted sedimentary basins. In the U.S. midcontinent region east of the Rocky Mountains, the presence of brines derived from dissolution of halite suggests that significant topography-driven flushing has occurred to remove older brines that presumably formed concurrently with Permian evaporites in the basin. However, the presence of evaporites and brines in the modern basin suggests that buoyancy-driven flow could limit topography-driven flushing significantly. Here we used numerical models of variable-density fluid flow, halite dissolution, solute transport, and heat transport to quantify flow patterns and brine migration. Results indicate the coexistence of large-scale topography-and buoyancy-driven flow. Buoyancy-driven flow and low permeability evaporites act to isolate brines, and the residence time of the brines was found to be quite long, at least 50 Myr. The modern distribution of salinity appears to reflect near-steady-state conditions. Results suggest that flushing of original evaporatively-concentrated brines occurred tens of millions of years ago, possibly concurrent with maximum uplift ca. 60 Ma. Simulations also suggest that buoyancy-driven convection could drive chemical exchange with crystalline basement rocks, which could supply significant Ca 2+ , Sr 2+ , and metals to brines.

Quaternary channels within the Northeast German Basin and their relevance on double diffusive convective transport processes: Constraints from 3‐D thermohaline numerical simulations

“…[76] The described relationships among landscape topography, groundwater dynamics, and heat or salinity distributions driven by advection are obviously a general feature of geological systems occurring in nature as it has been reported by other numerical investigations as well as by conclusions based on measurements for several sedimentary basins worldwide [Lachenbruch et al, 1976;Garven et al, 2001;Lampe and Person, 2002;Nunn et al, 2005;Lazear, 2006;Bouri et al, 2007;Thornton and Wilson, 2007;Cui et al, 2010]. While acknowledging that a general correlation between these factors exists, the reliability of absolute computed temperature and salinity quantities as well as corresponding fluxes through hydrogeological windows are part of current research activities.…”

Numerically quantifying the relative importance of topography and buoyancy in driving groundwater flow

“…But in certain circumstances, buoyancy-driven flow may modify and/or limit topography-driven flow, as evidenced by the long-term presence of evaporates and brines in many sedimentary basins [6,7]. The interactions between topography-and buoyancy-driven flows are still not fully understood and hence hence need to be investigated further.…”

“…Stanislavsky and Gvirtzman [14] conducted hydrological modeling of the Dead Sea basin and found that buoyancy-driven flow might have coexisted with topography-driven flow when evaporated seawater began to sink. Thornton and Wilson [6] addressed the importance of buoyancy-driven flow in an uplifted sedimentary basin where topography-driven has long been thought to be dominant. However, all these studies assumed steady-state convection conditions, which is not always the case.…”

Underpressure in Mesozoic and Paleozoic rock units in the Midcontinent of the United States

“…Jorgensen et al (1993) and Banner et al (1989) previously recognized the approximate alignment of halite and the eastern edge of dense brine, and acknowledged the conceptual problem of downward migration through Pennsylvanian strata, which were regarded as a confining system. However, a hydrologic simulation along a cross section very similar to that of Figure 3 resulted in brine-saturated formations below the evaporite sequence, indicating that buoyancy-driven downward migration is possible (Thornton and Wilson, 2007). We maintain that downward movement of dense brine along faults and fractures is a reasonable explanation for the pervasive plume.…”