SE Asia Agricultural Soils Age Analysis

Cresswell, A.J. , Sanderson, D.C.W. , Carling, P.A. and Darby, S. (2019) SE Asia Agricultural Soils Age Analysis. Technical Report. SUERC, East Kilbride, UK.

Abstract

The soils of southeast Asia include regionally extensive layers of generally sandy material, in some places 5m or more in depth, observed throughout Vietnam, Cambodia and Thailand, and upland areas of Myanmar and Malaysia, and even the Punjab. Various explanations for the origin of these layers have been proposed, with clarification of their ages and modes of emplacement remaining a significant issue. In many locations, these cover sands overlay a laterite layer containing tektites associated with a 750-800ka old meteorite impact in the region. Luminescence measurements have been used to date and characterise these sand layers, and in this report such measurements from five locations in Thailand and one site in Vietnam have been reviewed. This suggests that luminescence methods can readily distinguish between two distinct classes of material within these sand layers: 1. Sands with lower luminescence sensitivity and OSL depletion indices with ages in excess of ~50ka (the limit of SAR OSL methods); 2. Sands with high luminescence sensitivity and OSL depletion indices with ages less than 35ka. At four locations in Thailand only the younger material is present, with ages for basal samples of 9-35ka. At the other Thai site (Huai Om) both are present, with the older material in the lower 50cm of the section, and the young material immediately above this giving an age of approximately 30ka. At the site in Vietnam (Hue), there is evidence that the materials have experienced mixing, with some younger material within the older layer. The use of OSL intensities and depletion indices from the Portable OSL reader would be a method of rapidly distinguishing between these two classes of sand in the field. Dose extension methods have been used to estimate equivalent doses for the older materials. Applied to the younger materials, these give equivalent doses within 20% of the OSL method. For the older materials at Huai Om and Hue these give equivalent doses consistent with an age of 100-150ka, although the data suggest that the traps associated with these measurements have lifetimes of ~105 years at environmental temperatures of 25°C, which could significantly underestimate the age of these minerals. Further investigations into trap stability may be useful, including (if possible) collection of samples from equivalent contexts with lower environmental temperatures (eg: at higher altitude).

• Item Type: Research Reports or Papers (Technical Report)
• Status: Published
• Glasgow Author(s) Enlighten ID: Sanderson, Professor David and Cresswell, Dr Alan
• Authors: Cresswell, A.J., Sanderson, D.C.W., Carling, P.A., and Darby, S.
• Subjects: G Geography. Anthropology. Recreation > GB Physical geography; G Geography. Anthropology. Recreation > GE Environmental Sciences; Q Science > QC Physics
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Publisher: SUERC
• Copyright Holders: Copyright © 2019 Scottish Universities Environmental Research Centre
• Publisher Policy: Reproduced with the permission of the Authors