Climatic Signals and Diagenetic Overprints in Lacustrine Sediments: Reconstructing Hydrological and Environmental Changes in Lake Van During the Middle Pleistocene

Abstract

Understanding the evolution of Lake Van, the world's largest alkaline lake, is crucial for reconstructing past climate and environmental changes in the Middle East. However, the lake's early development - especially its transition from freshwater to alkaline conditions - remains poorly understood. The three interrelated objectives using Lake Van as a natural laboratory are: (1) to define a lake’s hydrological state (closed or open) and explore the potential linkage between lake’s closure and the formation of the Deformed Unit (a distinct sedimentary interval characterized by intense soft-sediment deformation structures); (2) to conduct multi-proxy reconstructions of past hydrological, climate and environmental changes during the Middle Pleistocene, before, during and after the hydrological transition from freshwater to alkaline conditions in a lacustrine system; and (3) to identify and document the dolomite records and expand the associated environmental narratives with its early diagenetic origin. We analysed Lake Van sediment cores using multiple techniques: mineralogical analyses (X-ray Powder Diffraction, Scanning Electron Microscopy—Energy Dispersive Spectroscopy), stable and clumped isotope measurements of carbonates, and fossil assemblage and ecological studies of ostracods.
Our analyses reveal three major findings: (1) the lake's transition to a closed basin occurred independently of the formation of a major deformed sediment unit; (2) the shift to alkaline conditions at ~505 ka during Marine Isotope Stage 13, driven by basin closure and enhanced evaporation; and (3) distinctive patterns of early diagenetic dolomite formation emerged after 480 ka, with a significant shift in formation processes at ~250 ka. This thesis extensively emphasises the significance of identifying different signatures recorded in lake sediments, i.e., original signals from hydrological changes and climatic impact, influenced signals by syn- or post-depositional deformation, and modified signals from diagenetic overprints.

Date of Award	29 Oct 2025
Original language	English
Awarding Institution	Northumbria University
Supervisor	Vasile Ersek (Supervisor), Ola Kwiecien (Supervisor) & Michael Rogerson (Supervisor)