Oligocene–Miocene formation of the Haifa basin: Qishon–Sirhan rifting coeval with the Red Sea–Suez rift system

During mid-Oligocene to early-Miocene times the northeastern Afro-Arabian plate underwent changes, from continental breakup along the Red Sea in the south, to continental collision with Eurasia in the north and formation of the N–S trending Dead Sea fault plate boundary. Concurrent uplift and erosion of the entire Levant area led to an incomplete sedimentary record, obscuring reconstructions of the transition between the two tectonic regimes. New well data, obtained on the continental shelf of the central Levant margin (Qishon Yam 1), revealed a uniquely undisturbed sedimentary sequence which covers this time period. Evaporitic facies found in this well have only one comparable location in the entire eastern Mediterranean area (onland and offshore) over the same time frame — the Red Sea–Suez rift system. Analysis of 4150 km of multi and single-channel seismic profiles, offshore central Levant, shows that the sequence was deposited in a narrow basin, restricted to the continental shelf. This basin (the Haifa Basin) evolved as a half graben along the NW trending Carmel fault, which at present is one of the main branches of the Dead Sea fault. Re-evaluation of geological data onland, in view of the new findings offshore, indicates that the Haifa basin is the northwestern-most of a larger series of basins, comprising a failed rift along the Qishon–Sirhan NW–SE trend. This failed rift evolved spatially parallel to the Red Sea–Suez rift system, and at the same time frame. The Carmel fault would therefore seem to be related to processes occurring several million years earlier than previously thought, before the formation of the Dead Sea fault. The development of a series of basins in conjunction with a young spreading center is a known phenomenon in other regions worldwide; however this is the only known example from across the Arabian plate.     

Biased monitoring of fresh water-salt water mixing zone in coastal aquifers

In coastal aquifers, significant vertical hydraulic gradients are formed where fresh water and underlying salt water discharge together upward to the seafloor. Monitoring boreholes may act as "short circuits" along these vertical gradients, connecting between the higher and the lower hydraulic head zones. When a sea tide is introduced, the fluctuations of both the water table and the depth of the mixing zone are also biased due to this effect. This problem is intensified in places of long-screen monitoring boreholes, which are common in many places in the world. For example, all approximately 500 boreholes of the fresh water-salt water mixing zone in the coastal aquifer of Israel are installed with 10 to 50 m long screens. We present field measurements of these fluctuations, along with a three-dimensional numerical model. We find that the in-well fluctuation magnitude of the mixing zone is an order of magnitude larger than that in the porous media of the actual aquifer. The primary parameters that affect the magnitude of this bias are the anisotropy of the aquifer conductivity and the borehole hydraulic parameters. With no sea tide, borehole interference is higher for the anisotropic case because the vertical hydraulic gradients are high. When tides are introduced, the amplitude of the mixing zone fluctuation is higher for the isotropic case because the overall effective hydraulic conductivity is greater than the conductivity in the anisotropic case. In the aquifer, the fresh water-salt water mixing zone fluctuations are dampened, and tens of meters inland from the shoreline, the fluctuations are on the order of few centimeters.