Shallow, old, and hydrologically insignificant fault zones in the Appalachian orogen

Abstract

The permeability of fault zones impacts diverse geological processes such as hydrocarbon migration, hydrothermal fluid circulation, and regional groundwater flow, yet how fault zones affect groundwater flow at a regional scale (1-10 km) is highly uncertain. The objective of this work is to determine whether faults affect regional patterns of groundwater flow, by using radioactive radon and chloride to quantify groundwater discharge to lakes underlain by faults and not underlain by faults. We sampled lakes overlying the Paleozoic Appalachian fold and thrust belt in the Eastern Townships in Québec, and compared our results to a previous study in a crystalline watershed in the Canadian Shield. The field data was analyzed with an analytical geochemical mixing model. The uncertainties of model parameters were assessed in a sensitivity analysis using Monte Carlo simulation, and the difference between lakes tested with statistical analysis. While the model results indicate non-negligible groundwater discharge for most of the lakes in the Paleozoic orogen, the difference between the groundwater discharge rate into the lakes located on faults and the other lakes is not statistically significant. However, the groundwater discharge rate to lakes in the Paleozoic orogeny is significantly higher than lakes that overlay crystalline bedrock, which is consistent with independent estimates of permeability. The rate of groundwater discharge is not significantly enhanced or diminished around the thrust fault zones, suggesting that in a regional scale, permeability of fault zones is not significantly different from the bedrock permeability at shallow depth in this old, tectonically-inactive orogen.

Interactions between groundwater and seasonally ice‐covered lakes: Using water stable isotopes and radon‐222 multilayer mass balance models

“…, ; Kluge et al . , ; Malgrange & Gleeson, ). For simplicity, most studies assumed constant 222 Rn activity for the whole water column and disregarded vertical gradients related to lake stratification, although these are widely known to potentially be informative (Cook et al .…”

“…However, the use of 222 Rn in lakes has only gained attention in recent years, probably due to generally low 222 Rn activity in lakes (in the range of a few Bq/m 3 ), in contrast to the high activity in groundwater (typically between 1,000 and 100,000 Bq/m 3 ). The first lake water budget based on 222 Rn was demonstrated by Corbett et al (1997) and led to many subsequent applications (Cook et al, 2008;Gilfedder, Frei, Hofmann, & Cartwright, 2015;Gleeson, Novakowski, Cook, & Kyser, 2009;Kluge et al, 2007;Kluge et al, 2012;Malgrange & Gleeson, 2014). For simplicity, most studies assumed constant 222 Rn activity for the whole water column and disregarded vertical gradients related to lake stratification, although these are widely known to potentially be informative (Cook et al, 2008;Schmidt & Schubert, 2007).…”

Regional-Scale Distribution of Helium Isotopes in Aquifers: How Informative Are They as Groundwater Tracers and Chronometers?

“…It can be questioned if other parameters, such as faulting (see also the isolated anomalies along the downmost branch of the Foulon Fault, in the eastern sector of the Bécancour watershed; Figure 3a), could locally influence the spatial distribution of helium in the basin. The previous work on the hydrogeology of the region did not find any evidence of tectonic control on the hydrodynamics of the basin [24,25,35]. However, a study of helium and methane in the groundwater from the same region, completed by Moritz et al [55], showed a rough possible relation between the concentration of 4 He and the distance to the main tectonic accidents.…”

“…Larocque et al [24,25] did not identify any hydrogeological influence of the faults. Malgrange and Gleeson [35] also showed the limited influence of the Appalachian fault system on the local hydrogeology.…”