Investigating laminated sediments of the Al-Azraq basin, Jordan and the implications for paleoenvironmental variability
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Abstract
This research examines cored sediments recovered from the Al-Azraq basin, Jordan for laminated sediments. Laminated sediments have long been recognized from the Dead Sea basin, and determined to be varved deposits, or seasonal couplets forming annual deposits. A current debate in the literature refutes the varve designation of Dead Sea sediments (Lopez et al. 2016; Ben Dor et al., 2019; Bookman, 2020; Ben Dor et al., 2020). This study focuses on the Al-Azraq sediments in a micro-scale analysis within the context of this current debate, shedding light on the potential for laminated sediments beyond the Dead Sea basin, and the implications for climate variability. The sediments analyzed from the Al-Azraq basin are in close proximity to the Dead Sea, but separated by the Jordan Plateau into an eastern drainage. It is a low lying, endorheic basin draining an area of approximately 12,700 km2 of the interior desert extending from Syria to Saudi Arabia. The basin formed by the Hamza Graben is a rare deep sediment archive. Multiple environmental proxies including: lithology, smear slides, x-ray fluorescence (XRF), scanning electron microscopy (SEM) ,and energy dispersive X-ray spectroscopy (EDS) investigate the potential for laminated sediments and characterize the paleolake environments. Lithology and smear slides identified the presence of fine laminated sediments and diatoms. Detailed examination of ten sediment sections totaling 5.76 meters identified three sediment sections 2.02 m in length for further analyses. From these sections subsamples with high probability of laminated sediments were sent for XRF examination. XRF results of micro-scale analysis demonstrate changes in depositional processes, alternating fine laminae of terrestrial material and Ca evaporite, possibly aragonite, and accompanying changes in moisture flux. The data demonstrate visible laminated rhythmites. XRF results identify alternating laminae of Ca and Si, SEM scans identify seasonal diatoms and EDS demonstrates an encrusting evaporite matrix. Results reveal variability in paleoenvironment with differing sedimentation above and below rhythmite sediments.
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Introduction -- Project background -- Study area -- Results -- Discussion -- Conclusions -- Appendix A. Grain Size Data -- Appendix B. X-Ray Florescence Data -- Appendix C. XRF Section Graphs of Major and Minor Elements -- Appendix D. Scanning Electron Microscopy Diatom Images
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M.S. (Master of Science)