干旱区生态环境知识资源中心

Oblique shear directions along the left lateral strike-slip Dead Sea transform (DST) fault caused the formation of the Dead Sea Basin (DSB), one of the world’s largest pull-apart basins The Dead Sea, which covers the northern part of the basin, is one of the most saline lakes in world. To understand interaction of saline water from the Dead Sea with the neighbouring hydrological system is an important geoscientific problem for this arid region. Here, we report on the first continuous magnetotelluric (MT) transect crossing the entire DSB, from the eastern to the western rift shoulders and beyond. 2-D inversion of the MT data reveals an unprecedented comprehensive picture of the subsurface structures from the basin and adjacent areas. Quaternary to recent sediments of the Al-Lisan/Samara formations are expressed as highly conductive structures reaching a depth of approximately 4 km. East and west of the rift valley layered sequences of resistive and conductive structures coincide with the sedimentary formations of the Cretaceous, Jurassic and Triassic. Pre-Cambrian basement (crystalized igneous rocks) appears at depths >3 km beneath both rift shoulders as very resistive regions. The eastern boundary fault of the DST is associated with a sharp lateral conductivity contrast between the highly resistive basement structures and the conductive fill of the DSB. The transition to the western rift shoulder appears wider and smoother, in agreement with a broader fractured region, possibly caused by a combination of strong noimal faulting and strike-slip activity. The very high conductivities of less than 1 Omega m of the Al-Lisan/Samara formations can be explained with hypersaline waters of the Dead Sea reaching depths of a few kilometres and porosities of at least 37 per cent. The regional Judea and Kurnub aquifers of the Cretaceous are imaged as conductive layers with resistivities of 1-20 Omega m and we infer porosities of 15 per cent. The low resistivities observed in the Jurassic/Triassic formations can be explained with highly saline or saturated brines and a porosity of 7 per cent. From the electrical conductivity images and estimating porosities of the sedimentary rocks, we can infer salinities of the various aquifers. For the Al-Lisan/Samara foimations, salinities reach values >50 g 1(-1) in the upper 1.7 km. The Judea, Kurnub and Jurassic/Triassic aquifers have a more inhomogeneous distribution of salinity with highest values observed between normal faults at the western rift shoulder.