Estimating the hydraulic properties of an aquitard from in situ pore pressure measurements

A workflow is described to estimate specific storage (S _s) and hydraulic conductivity (K) from a profile of vibrating wire piezometers embedded into a regional aquitard in Australia. The loading efficiency, compressibility and S _s were estimated from pore pressure response to atmospheric pressure changes, and K was estimated from the earliest part of the measurement record following grouting. Results indicate that S _s and K were, respectively, 8.8?×?10^?6 to 1.2?×?10^?5 m^?1 and 2?×?10^?12 m s^?1 for a claystone/siltstone, and 4.3?×?10^?6 to 9.6?×?10^?6 m^?1 and 1?×?10^?12 to 5?×?10^?12 m s^?1 for a thick mudstone. K estimates from the pore pressure response are within one order of magnitude when compared to direct measurement in a laboratory and inverse modelled flux rates determined from natural tracer profiles. Further analysis of the evolution and longevity of the properties of borehole grout (e.g. thermal and chemical effects) may help refine the estimation of formation hydraulic properties using this workflow. However, the convergence of K values illustrates the benefit of multiple lines of evidence to support aquitard characterization. An additional benefit of in situ pore pressure measurement is the generation of long-term data to constrain groundwater flow models, which provides a link between laboratory scale data and the formation scale.     

A New LA‐ICP‐MS Method for Ti in Quartz: Implications and Application to High Pressure Rutile‐Quartz Veins from the Czech Erzgebirge

Experimental determination of the pressure and temperature controls on Ti solubility in quartz provides a calibration of the Ti‐in‐quartz (TitaniQ) geothermometer applicable to geological conditions up to ~ 20 kbar. We present a new method for determining ⁴⁸Ti mass fractions in quartz by LA‐ICP‐MS at the 1 μg g^?1 level, relevant to quartz in HP‐LT terranes. We suggest that natural quartz such as the low‐CL rims of the Bishop Tuff quartz (determined by EPMA; 41 ± 2 μg g^?1 Ti, 2s) is more suitable than NIST reference glasses as a reference material for low Ti mass fractions because matrix effects are limited, Ca isobaric interferences are avoided, and polyatomic interferences at mass 48 are insignificant, thus allowing for the use of ⁴⁸Ti as a normalising mass. Average titanium mass fraction from thirty‐three analyses of low temperature quartz from the Czech Erzgebirge is 0.9 ± 0.2 μg g^?1 (2s) using ⁴⁸Ti as a normalising mass and Bishop Tuff quartz rims as a reference material. The 2s average analytical uncertainty for individual analyses of ⁴⁸Ti is 8% for 50 μm spots and 7% for 100 μm spots, which offers much greater accuracy than the 21–41% uncertainty (2s) incurred from using ⁴⁹Ti as an analyte.     

Assessment of integrity and geochronology of archaeological sites using amino acid racemization in land snail shells: Examples from central Texas

Detailed racemization analyses were carried out on samples of the land snail Rabdotus mooreanus from archaeological sites at Fort Hood, in central Texas. D -alloisoleucine/L -isoleucine (A/I) values were determined for 260 individual shells from 29 proveniences, including sites in alluvium, colluvium, and rockshelters, as well as burned rock middens. A/I values show a good correlation with radiocarbon age, and so provide reasonably precise estimates of ages. Analyses indicate the presence of redeposited material in a large number of proveniences. These result from sedimentary processes involved in burial of the sites as well as from later disturbance (aboriginal or recent) of site stratigraphy. Because amino acid racemization analyses are relatively easy to carry out, this method lends itself to very detailed chronostratigraphic analyses of archaeological sites, thus permitting assessment of site integrity and assisting in the interpretation of site formation processes. © 1996 John Wiley & Sons, Inc.