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Geophysical Imaging of a Buried Tertiary Valley Aquifer in an Arid Region Using Time Domain Electromagnetic Method

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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.

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