Sources of radiogenic helium in a clay till aquitard and its use to evaluate the timing of geologic events

Details Sources of radiogenic helium in a clay till aquitard and its use to evaluate the timing of geologic events Sources of radiogenic helium in a clay till aquitard and its use to evaluate the timing of geologic events

Jan 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005gecoa..69..475h&link_type=abstract

Geochimica et Cosmochimica Acta, Volume 69, Issue 2, p. 475-483.

Mathematics

Logic

4

Scientific paper

Concentrations of dissolved gases (He, Ne, Ar and N2) were measured in pore waters collected from a Pleistocene (0 80 m depth) and Cretaceous (80 156 m depth) aged, clay-rich, aquitard system using both a conventional copper-tube method and in situ diffusion samplers. Both methods yielded similar results. He data revealed a well-defined increase in concentration with depth, from 1.7 × 10-8 cm3 He STP g-1 water near the water table (at 2.3 m below ground surface) to 6.9 × 10-6 cm3 He STP g-1 water at ˜80 m below ground surface (B.G.) The concentration at depth greatly exceeded values for atmospheric solubility at in situ temperatures and could not be attributed to steady-state production from α-decay of U and Th within the aquitard system. Trends in He isotope ratios and concentrations suggest accumulation as a result of both release of residual 4He from within the Pleistocene clay-rich till (ca. 87%) and an ascending radiogenic helium flux from underlying Cretaceous-age sediments (ca. 13%). One-dimensional transport modeling of the He data suggests that between 15 ka and 25 ka were required to produce the observed profile. This time frame agrees with studies utilizing isotope tracers (i.e., D/H and 14C-DIC) to estimate the timing of deposition for the till at this site. Our results demonstrate the utility of using helium, a nonreactive tracer, for delineating hydrogeologic processes in slow permeability geologic strata, and also support the contention that thick clay-rich surficial aquitards can provide long-term containment of contaminants, including hazardous wastes.

Affiliated with

Also associated with

No associations

Rating

Sources of radiogenic helium in a clay till aquitard and its use to evaluate the timing of geologic events does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Sources of radiogenic helium in a clay till aquitard and its use to evaluate the timing of geologic events, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sources of radiogenic helium in a clay till aquitard and its use to evaluate the timing of geologic events will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-901430