Molecular and isotopic indicators of paleoenvironmental change in low-organic-carbon soils with applications to Pleistocene archaeological sites in Greece, Algeria, and Ethiopia.

摘要

Reconstruction of terrestrial paleoenvironments in ancient soils (paleosols) is analytically challenging if the organic carbon content is less than &sim0.5% (low-organic-carbon soils). Lipid biomarkers derived from vascular plant waxes, specifically n-alkane homologues C25 through C 33, combined with stable-isotopic analyses of bulk soil organic matter (SOM) and pedogenic carbonates can enhance paleoenvironmental interpretations of paleosols. This dissertation presents three case studies of low-organic-carbon paleosols for which a combined approach is employed in paleoecosystem assessment. The first study reconstructs Plio-Pleistocene paleoenvironments at the archaeological locality of El-Kherba in Ain Hanech, Algeria. The abundance of in -alkanes and preference for odd-carbon numbered molecules combined with stable-carbon-isotopic analyses of bulk SOM and stable-carbon- and stable-oxygen-isotopic analyses of pedogenic carbonates indicate that a coastal Mediterranean ecosystem existed at El-Kherba. The second case study focuses on Pleistocene paleosols from the upper Busidima Formation at the early hominid site of Gona, Ethiopia. Using data similar to those for the Algerian study, molecular and stable-isotopic analyses indicate that vegetation varied through time in the upper Busidima as a result of lateral migrations of the paleo-Awash River through the Awash Valley. The third case study considers vegetation and rapid climate fluctuations as recorded by a stacked sequence of gravels and terra rossa paleosols at the Morphi Pleistocene site in Epirus, Greece. Vegetation changes are closely coincident with regional glacial and interglacial climate fluctuations recorded for western Epirus. Taken together, these three biogeochemical studies demonstrate the potential of biomarker analyses to form the basis of detailed paleoenvironmental reconstructions for low-organic-carbon paleosols.