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The Effects of Fault‐Zone Cementation on Groundwater Flow at the Field Scale
Author(s) -
Sproule Tyler G.,
Spinelli Glenn A.,
Wilson John L.,
Fort Michael D.,
Mozley Peter S.,
Ciarico Jared
Publication year - 2020
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/gwat.13062
Subject(s) - geology , hydrogeology , aquifer , cementation (geology) , unconformity , groundwater , permeability (electromagnetism) , groundwater flow , fault (geology) , geotechnical engineering , petrology , geomorphology , seismology , cement , genetics , archaeology , structural basin , membrane , biology , history
Fault zones are an important control on fluid flow, affecting groundwater supply, contaminant migration, and carbon storage. However, most models of fault seal do not consider fault zone cementation, despite the recognition that it is common and can dramatically reduce permeability. In order to study the field‐scale hydrogeologic effects of fault zone cementation, we conducted a series of aquifer pumping tests in wells installed within tens of meters of the variably cemented Loma Blanca Fault, a normal fault in the Rio Grande Rift. In the southern half of the study area, the fault zone is cemented by calcite; the cemented zone is 2‐8 m wide. In the center of the study area, the cemented fault zone is truncated at a buttress unconformity that laterally separates hydrostratigraphic units with a ∼40X difference in permeability. The fault zone north of the unconformity is not cemented. Constant rate pumping tests indicate that where the fault is cemented, it is a barrier to groundwater flow. This is an important demonstration that a fault with no clay in its core and similar sediment on both sides can be a barrier to groundwater flow by virtue of its cementation; most conceptual models for the hydrogeology of faults would predict that it would not be a barrier to groundwater flow. Additionally, the lateral permeability heterogeneity across the unconformity imposes another important control on the local flow field. This permeability discontinuity acts as either a no‐flow boundary or a constant head boundary, depending on the location of pumping.