7 - TEM analysis of smectite-illite mixed-layer minerals of core BDP 96 hole 1: Preliminary results

Abstract

X-ray diffraction (XRD) analysis of sediments from B DP-cores 93-1 and 93-2 has shown that clay minerals are a useful proxy for paleoclimate reconstruction in Lake Baikal. However, the XRD analyses of clay minerals are semiquantitative and do not give such detailed information about the structure of the different clay mineral types. Thus, to use the clay mineral distribution in Baikal sediments over time as an indicator for climate, a more precise description of the clay minerals themselves is needed. This information, supplementing the semiquantitative XRD-analysis, can be obtained with a transmission electron microscope (TEM) combined with a scanning electron microscope (STEM) and energy-dispersive X-ray analysis (EDX). TEM, STEM, and EDX analyses were carried out on four clay samples from Lake Baikal core BDP-96-1, which according to paleomagnetic data were formed ca. 3.29, 2.85, 2.78, and 2.42 Ma ago. The results showed that these methods are a useful and indispensable supplement to XRD measurements that provide additional information on the formation and transformation of clay minerals before deposition, and thereby assist in paleoclimatic interpretation. The illite-rich mixed-layer minerals in all of the samples generally have a higher Fe content, which is probably displaced by AI during transformation into smectite. The smectite phase of all the samples can be identified as montmorillonite.