Stable isotope (δ13C and δ15N) based interpretation of organic matter source and paleoenvironmental conditions in Al-Azraq basin, Jordan

Khaldoun Ahmad, Caroline Davies

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10 Scopus citations

Abstract

This study examines the stable isotopes of carbon and nitrogen from cored lacustrine sediments of the Al-Azraq, an arid lake basin on the Jordan Plateau. Lacustrine sediments contain valuable records of paleoenvironmental conditions, recording local and regional responses to environmental change. Previous paleo-reconstructions on the Jordan Plateau are based on archaeology, pollen, mineralogy, and stratigraphy. The application of organic geochemistry analyses to these lake sediments identifies multiple sources of organic matter, biological production, and contributes to understanding the paleoenvironments of the Al-Azraq basin during the mid-Pleistocene period. Organic carbon concentration (Corg) provides an overview of the organic matter distribution. Carbon isotopic composition (δ13Corg) and nitrogen isotopic composition (δ15N) are indicators of organic matter sources and paleoproductivity. Magnetic susceptibility (MGSUS) measured the concentration of ferromagnetic minerals and indicated aeolian inputs. Organic geochemistry differentiated five paleoenvironmental zones with specific sources of organic matter, both aquatic and terrestrial. It identified a long period of climate wetter than the present, punctuated by a short intense period of aridity. Diagenesis plays an important role in the decomposition of organic matter and studies indicate this degradation can alter the isotopic signals of organic matter. Analyses of the isotopic signals and statistical analyses demonstrate diagenesis is not a factor in the Al-Azraq sediments in all but Zone 4 of the paleoenvironmental zones. This Zone is defined by less negative carbon isotopic composition and the presence of thick primary gypsum layers, in addition to the influx of high peaks of aeolian sediment as reflected in the magnetic susceptibility data. Stable isotope geochemistry provides detailed information on the paleoenvironments of lake sediments, and is applicable to typically challenging arid basin sediments.

Original languageEnglish (US)
Pages (from-to)49-60
Number of pages12
JournalApplied Geochemistry
Volume78
DOIs
StatePublished - Mar 1 2017

Bibliographical note

Funding Information:
This work was supported by a research fellowship from The American Center of Oriental Research, Amman, Jordan, a grant from the University of Missouri Research Board, with material support from the Natural Resources Authority, Amman, Jordan.

Publisher Copyright:
© 2016 Elsevier Ltd

Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.

Keywords

  • Al-Azraq
  • Arid lake
  • Jordan
  • Organic matter
  • Paleoenvironments
  • Stable isotope

Continental Scientific Drilling Facility tags

  • AZ3

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