CLAY MINERALS OF THE JORDAN PLATEAU INDICATE PALEO-ENVIRONMENTS SINCE THE UPPER MIOCENE

Investigating the clay minerals from cored sediments of the Al-Jafr basin, Jordan provides insight to the paleoenvironmental conditions of formation and approximate basal age of the basin. The Al-Jafr basin is approximately 25 km east of Ma'an, Jordan. It is the largest closed-basin drainage system in the region and covers an area of approximately 15,000 km². In this study, 17 sediment samples analyzed by X-Ray Diffraction (XRD) and scanning electron microscope (SEM) with elemental analysis through Energy-dispersive X-Ray Spectroscopy (EDS) identify key clay minerals. The first three samples collected from meters 1-10 are from sediment uniformly reddish brown in color. The remaining samples collected from the upper centimeters of every meter to the base of the sediment core at meter 31. X-Ray Diffraction identified Kaolinite and quartz as the predominate minerals from the upper centimeters to approximately 11 meters. The presence of these minerals suggests derivation from crystalline rocks, pre-existing soils, and aeolian processes. Kaolinite is no longer present at meter 12 in XRD. Palygorskite in trace amounts in the upper layers, likely to be detrital in origin, dominates mineral assemblage with concentrations of gypsum in meters 12-14, and with dolomite in XRD at meters 15 - 20. The presence of palygorskite with sulfate minerals (gypsum) and carbonate minerals (dolomite) suggest an evaporative phase for the basin. Palygorskite reduces in concentrations beginning at meter 20, and disappears from XRD from meters 25-29. Dolomite also reduces in concentration through meters 25-29. Calcite is the only mineral present in XRD at those depths. Both palygorskite and dolomite are present with calcite at meter 30. SEM images of samples from the lower half of the core reveal crystals of calcite coated with palygorskite, but no other clay minerals. Preliminary analysis of the cosmogenic nuclide Beryllium 10, indicates the bottom of the core (meter 31) was exposed in the upper Miocene.