Paper No. 269-8
Presentation Time: 10:00 AM
BIOGEOCHEMISTRY REVEALS PALEOENVIRONMENTS AND PALEOHYDROLOGY OF THE AL-AZRAQ BASIN, JORDAN
This study investigates the biogeochemical indicators for past environments and paleohydrology of a high-resolution sediment record from the Al-Azraq Basin, Jordan. The second largest basin in Jordan, it is an important aquifer for a majority of the population in this arid region. Thirteen hundred samples, collected from 51 m of cored playa and lacustrine sediments, for stable isotopic composition of bulk organic matter and carbonate analyses are the main proxies. Additionally, results from supporting methodologies include: grain size analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Based on the lithology and geochemical data, the core divides into three main zones. Carbonate diagenesis by water enriched with sulfate occurs and affects the values of carbon isotopic compositions in some samples. Also, dolomitizition occurs, but does not affect the values of oxygen isotopic composition. Bulk organic matter revealed no effect of diagenesis except in Zone 3b, which impacts the carbon isotopic composition values. Mineralogy and oxygen isotopic composition revealed the presence of low lake levels punctuated by dry periods. C/N ratios of bulk organic matter indicate a transition zone between marsh deposits and lake sediments by mixed aquatic and terrestrial organic matter sources. Concurrent influx of materials to the basin increased, also indicating higher precipitation. Zone 2 reveals changes in the climate by the presence of a lake during this period. The presence of marsh deposits is indicated by increasing abundant organic carbon concentrations. C/N ratios identify the presence of aquatic and land plants as the source of organic matter. The presence of dolomite with increased sand particles and angular chert grains indicate a dry period. This research identifies detailed environmental patterns of marsh to lake to playa environments with multiple cycles of seasonal deposition, indicative of significant climate shifts throughout the Middle to Late Pleistocene. Holocene age sediments are missing. The oxygen isotope records for the upper sediments correlate well with regional records from the eastern Mediterranean through Marine Isotope Stage (MIS 5). The base of the core dates between MIS 15 and 9 (570 to 300 ka) reflecting climates generally similar to a deglaciation.