THERMAL AND HYDROGEOLOGICAL EVOLUTION OF 
TAYLORSVILLE BASIN IN VIRGINIA: IMPLICATIONS FOR 
SUBSURFACE GEOMICROBIOLOGY EXPERIMENTS

TSENG, Hsin-Yi, ONSTOTT, T. C., Department of 
	Geosciences,  Princeton University, Princeton, NJ 
	08544
BURRUSS, R. C., U. S. Geological Survey, Denver, CO 
	80225
PERSON, M., Department of Geology and Geophysics, 
	University of Minnesota, Minneapolis, MN 55455

Micro-organisms were extracted from sidewall cores at 2800 m below 
land surface in fine-grained sandstone and shale of the Triassic age 
Doswell Formation of the Taylorsville Basin in Virginia (Stevens and 
Boone, 1993). These micro-organisms containing saline tolerant, 
thermophilic, anaerobic metal-reducers and fermenters appear to be 
indigenous to the rock strata (McKinley et al., 1993). The observed 
physiological traits of these bacteria, including thermophilicity, 
salinity tolerance and pH preference, appear to be compatible with 
geophysical estimates of current environmental conditions (Boone et 
al., 1995). However, the thermal models from analyses of fluid 
inclusions (Tseng et al., in press), of vitrinite reflectance, and of 
apatite fission tracks, suggest that the strata have been exposed to 
temperatures of 160-200°C at ~210 Ma followed by fast cooling and 
that the current temperature was not attained until sometime in the 
Tertiary. This implies that the bacteria migrated to their current 
location. A two-dimensional steady-state fluid flow model indicates 
that the present day groundwater flow rates are insufficient to transport 
this microbial community from the surface. Instead, it is likely that the 
migration of these bacteria is closely linked to the paleo-
hydrogeological evolution of the basin. A two-dimensional transient 
fluid flow model suggests that the topographic relief generated at the 
beginning of uplifting stage (e.g., 210-190 Ma) could drive 
groundwater flow deep into the subsurface and yield the greatest flow 
rate of 0.1 m/yr. This groundwater circulation caused fast cooling of 
the strata after the thermal maximum, reduced the salinity of water as 
recorded in secondary aqueous inclusions, changed hydrocarbon 
compositions, and probably introduced bacteria into the microbial 
sampling zone.

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T.O., and Aldrich, H.C., 1995, Bacillus infernus-sp. nov.: an 
Fe(III)- and Mn(IV)-reducing anaerobe from the deep terrestrial 
subsurface: International Journal of Systematic Bacteriology, v. 
45, p. 441-448.
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C., 1993, The application of perfluorocarbon tracers to 
subsurface microbial sampling: Abstract of Second International 
Symposium of Subsurface Microbiology, Bath, UK..
Stevens, T.O. and Boone, D.R., 1993, Thermophilic anaerobic bacteria 
in 2800-m-deep samples from the terrestrial subsurface: 
Abstract of Second International Symposium of Subsurface 
Microbiology, Bath, U.K..
Tseng, Hsin-Yi, Onstott, T. C., Burruss, R. C., and Miller, D. S., 1996, 
Constraints on the thermal history of Taylorsville Basin, Virginia, 
from fluid inclusion and fission track analyses: Implications for 
subsurface geomicrobiology experiments: Chemical Geology (in 
press).