Abstract
A time domain electromagnetic survey was conducted in the eastern part of the Jordanian desert to image a buried Tertiary valley aquifer in the context of the characterization of groundwater resources and groundwater resources management. The Tertiary chert-limestone rocks (B4) of the investigated valley constitute the major part of the shallow-depth aquifer (less than 100 m) which is the main source of water in the area. Thus, delineation of the geometry of the valley deems necessary for a better understanding of its structural setting and hydrogeological potential. For this purpose, 141 central-loop sounding stations were conducted in the area; they were positioned along six NE-SW directed profiles and one profile (TDEM profile 1) that extends for about 9 km in the NW-SE direction. Resistivity pseudo-sections and resistivity depth maps reveal that the subsurface is composed of two main geoelectric layers: a resistive layer of 25 - 40 ohm.m that indicates the water-bearing rocks which is composed of an alteration of massive chert and limestone. The second layer is conductive one that has a resistivity values in the range from 10 to 15 ohm.m; it consists mainly of gravel and bituminous marl. A lateral variation in resistivity that is associated with the presence of block-like structures is also noted. The good contrast in resistivity between the B4 chert-limestone water-bearing rocks and marl layer enhanced the obtained results and proved that the TDEM is efficient in imaging the boundaries of the Tertiary valley. The lateral extensions of the valley were well-imaged at three fixed-elevation slices (550, 500 and 450 m amsl). The subsurface elongation direction of the valley is confirmed by the NW-SE surface elongation of the valley. The vertical boundary of the valley is extended to an elevation of at least 450 m amsl; this corresponds to a depth of about 100 m.
Highlights
Electromagnetic methods such as Time-domain Electromagnetic Method (TDEM) can map subsurface layers and distinguish their lithology due to the contrast in the electrical properties of earth materials
141 central-loop sounding stations were conducted in the area; they were positioned along six NE-SW directed profiles and one profile (TDEM profile 1) that extends for about 9 km in the NW-SE direction
Buried-valley aquifers are widely known as vital sources of water in arid areas that suffer from scarcity of water resources and heavily depend on groundwater resources for drinking, domestic, agricultural and industrial uses
Summary
Electromagnetic methods such as Time-domain Electromagnetic Method (TDEM) can map subsurface layers and distinguish their lithology due to the contrast in the electrical properties (conductivity) of earth materials. The non-invasive nature and the rapid field procedure make the TDEM a valid geophysical method in investigating and imaging subsurface stratification and structures such as faults and buried valleys. This is significant in characterizing subsurface structural features which has critical role in controlling the characteristics of groundwater resources. Numerous case studies have been reported in the literature that demonstrated the successful use of geophysical methods for structural and hydrogeological investigations, and for mapping of buried valleys (Danielsen et al, 2003; Jørgensen et al, 2003; Sandersen & Jørgensen, 2003; Christiansen et al, 2006; Bedrosian et al, 2013; Sharma & Baranwal, 2005; Gonçalves et al, 2017)
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