Biogeochemistry and inorganic geochemistry as indicators of the paleoenvironment and paleohydrology of the Al-Azraq Basin, Jordan
Abstract
This study investigates the biogeochemical and inorganic geochemical
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 were
collected from fifty one meters of cored playa and lacustrine sediments. Stable isotopic
composition of bulk organic matter and carbonate are the main proxies in addition to results
from supporting methodologies including: grain size analysis, X-ray diffraction (XRD), and
scanning electron microscopy (SEM). Based on the lithology of the core and geochemical
data, the core is divided into three main zones: Zone 1 with six subzones; Zone 2 with four
subzones; and Zone 3 with two subzones. Carbonate diagenesis by water enriched with
sulfate occurs in Zone 1 and Zone 3, and affects the values of carbon isotopic compositions
in some samples. Also, dolomitizition occurs in Zone 1, 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
during Zone 1. C/N ratios of bulk organic matter indicate the source of organic matter primarily from aquatic algae in Zones 1a, 1b, and 1c; whereas Zone 1d indicates mixing of
aquatic and terrestrial organic matter sources. This is considered a transition zone between
marsh deposits and lake sediments. During this time the influx of materials to the basin
increased, also indicating high precipitation and a wet climate. Zone 2 reveals changes in the
climate by the presence of a lake during this period. Zone 3a exhibited the presence of marsh
deposits as indicated by increasing abundant organic carbon concentrations. C/N ratios
identify the presence of aquatic and land plants as the source of organic matter. Zone 3b
represents a dry period from the presence of dolomite with increased sand particles and
angular chert grains. 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 record 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.
Table of Contents
Introduction -- Biogeochemistry applications -- Study area and background research -- Interpretation of lacustriene sediment and applied methods -- Results -- Statistics analysis results and discussions -- Discussion -- Conclusions -- Glossary -- Appendix A. Borehole logs -- Appendix B. Grain size data and classification -- Appendix C. XRD patterns -- Appendix D. Carbon and nitrogen isotopic composition of bulk organic matter data -- Appendix E. Carbon and oxygen isotopic composition of calcium
carbonate data -- Appendix F. Major and trace elements geochemical data -- Appendix G. Depth correlation for statistics
Degree
Ph.D.