BIOGEOCHEMISTRY OF THE AL AZRAQ BASIN, JORDAN: DIFFERENTIATING BETWEEN TERRESTRIAL AND AQUATIC SOURCES OF ORGANIC CARBON

The Al-Azraq basin, a closed basin and the second largest on the Jordan Plateau, contains a long and detailed sediment record of paleoenvironment change. This study identifies organic matter (OM) sources and their environments of formation. Biogeochemistry, stable isotopes and mineralogy reveal biological processes that detail a lake history significantly different from present conditions. Analysis of two hundred and fifteen samples from 23 m of playa lake sediment identifies the presence and distribution of organic matter (OM). Changes in the proportion (%) of OM, C/N ratio, carbon isotopic composition and sediment characteristics are the basis for dividing the basin into five environmental zones. The distribution of OM (as C_org), increases with depth, ranging from 0.2% to 2.8% of the total sediment. The carbon isotopic composition values range from -26.8 to -15.00. These values indicate the abundance of C₃ and CAM vegetation in the basin as a possible function of changing climates on the Jordan Plateau. C/N values differentiate terrestrial and lake OM sources. The changes in C_org %, source composition and OM origin establish a wide range of past environments that varied considerably from being both drier and wetter than the present conditions.