Review, development & application of stable isotope & biomarker geochemistry to Southeast Asian archaeological sites

Author: Meghan McAllister

  • Thesis download: available for open access on 5 Apr 2027.

McAllister, Meghan, 2024 Review, development & application of stable isotope & biomarker geochemistry to Southeast Asian archaeological sites, Flinders University, College of Humanities, Arts and Social Sciences

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Recent archaeological discoveries in Southeast Asia have called into question the timing of the arrival and migratory paths of Homo sapiens. A growing body of fossil, artefact and molecular evidence indicates that humans have been present in the region since at least the end of Marine Isotope Stage (MIS) 5 (~86 kilo annum (ka)). This contrasts the previously held belief that they did not reach Southeast Asia until MIS 3 (55-50 ka).

Understanding the environmental dynamics encountered by these early humans is essential to comprehending how early H. sapiens adapted to new and diverse habitats, and how environmental conditions influenced their migration routes and timings. This thesis presents new research on the application of stable isotope and lipid biomarker analysis as applied to archaeological cave sediments from tropical environments, focusing on Tam Pà Ling (TPL) Cave, northeastern Laos, the site of the oldest known H. sapiens fossils from mainland Southeast Asia. This provides a currently under-utilised but critical pathway for palaeoenvironmental reconstruction at sites characterised by highly oxic conditions that are not favourable to the preservation of pollen.

A comprehensive review of published studies demonstrates that the application of stable isotope analysis as a palaeoenvironmental proxy at Southeast Asian archaeological sites is relatively recent, particularly in comparison to European and African archaeological contexts. However, the existing research demonstrates the potential of these techniques, and indicates that environmental conditions in the region during early human occupation were more mosaic than often portrayed.

This thesis supports a history of complex and localised environmental dynamics in Southeast Asia via the first analysis of plant-derived biomarkers in the region for the period of late MIS 5-1 (~86 ka to ~3 ka). A palaeoenvironmental reconstruction based on compound-specific δ13C analysis of normal alkanes (n-alkanes) and n-alkanols demonstrates a prevalent C3 vegetation, but with variations in moisture potentially affecting vegetation density and type over time. This novel reconstruction indicates that the first H. sapiens present around TPL in the late stages of MIS 5 would have existed in and travelled through a predominantly forested ecosystem.

Lipid biomarker analysis of cave sediments is under-studied, even more so in the Southeast Asian archaeological context. Crucial issues around the taphonomy and in-cave variability of these proxies is therefore under-explored. This thesis addresses this research gap by exploring short-scale spatial biomarker variability within TPL. Analysis of sediments from two profiles 5 m apart showed significant differences in the presence of microbial biomarkers. It is hypothesised that this is predominantly due to variations in nutrient and moisture availability associated with proximity to the cave wall. These findings suggest that plant biomarker analysis in cave sediments is a robust palaeoenvironmental proxy, but that studies should include analysis of site-specific variability via bespoke sampling regimes.

Keywords: Organic Geochemistry, n-alkanes, stable isotopes, biomarkers

Subject: Archaeology thesis

Thesis type: Doctor of Philosophy
Completed: 2024
School: College of Humanities, Arts and Social Sciences
Supervisor: Mike Morley