New evidence from field, laboratory, and quantitative studies has
firmly established that on geologic-time scales, lateral fluid
migrations within sedimentary basins can occur over length scales
of hundreds of km and vertically through crystalline rocks to
depths greater than 6 km. These studies have also established the
important link between crustal-scale fluid flow and geologic
processes. Studies of shallow and deep groundwater flow suggest
that these systems are generally long-lived (10
to 10
years) but transient in nature. This is especially true for deep (>
10km) flow systems. The evidence of fluid flow in the deeper crust
clearly demonstrates that fluid inputs into shallow flow systems has
to be expected in areas overlying active metamorphic and tectonic
terrains. Much remains to be learned regarding the episodic nature
of these flow systems, the relative importance of different fluid
driving mechanisms within various tectonic environments, the
coupling between hydrologic, geochemical, thermal, and tectonic
processes, and the evolution of petrophysical parameters such as
permeability and porosity on geologic time scales. More detailed
studies are certainly needed that integrate quantitative models of
fluid flow, heat and mass transfer, and rock-water interactions with
laboratory and field studies at the basin or crustal scale.
During the last four years, geologically-based hydrologic studies have revealed exciting new directions to university and governmental Earth science programs. Much of the research described above has had profound implications for how geologists explore for energy and mineral deposits. For example, mathematical modeling techniques for simulating fluid flow and energy transport through sedimentary basins and some of the laboratory techniques described above are now being utilized by the petroleum industry in the exploration for hydrocarbon reservoirs [ Green et al., 1989; Ungerer et al., 1990; Harrison and Summa, 1991; Bethke et al., 1993; Lisk and Eadington, 1994]. In addition, paleohydrologic studies have also had important implications for the environmental sciences; especially in the area of nuclear waste isolation [e.g. Winograd et al., 1992].
Acknowledgments. This research was supported by the National Science Foundation under EAR 93-04873 and the Petroleum Research Fund, administered by the American Chemical Society under PRF 27964-AC8 to Mark Person and the National Science Foundation grants EAR 92-06090 and EAR 92-57160 to Lukas P. Baumgartner. E. Bekele, S. Baumgartner, M. Nicoloff, and M. Gerdes assisted in the review and preparation of the manuscript.