Studies on Peat in the Coastal Plains of Sumatra and Borneo : Part II : The Clay Mineralogical Composition of Sediments in Coastal Plains of Jambi and South Kalimantan

Abstract

The clay mineralogical composition of sediments in the coastal plain of Jambi and South Kalimantan was studied in order to find support for field observations. The Pleistocene terrace underneath the deep peat in the coastal plain of Jambi shows a predominance of the 1 : 1 type clay minerals (7.2Å). More recent sediments form uplifted tidal flats and mangrove deposits contain relatively higher amounts of the 14Å minerals than the Pleistocene terrace, although kaolin minerals still dominate these sediments. In South Kalimantan, the samples come only from recent sediments of tidal flats and mangrove deposits. Although all samples show a predominance of the 1 : 1 type clay minerals, they also contain appreciable amounts of 14Å minerals. The amount of 14Å minerals in recent sediments in South Kalimantan is higher than in Jambi. The recent levee materials are characterized by illite (10Å) and 14Å minerals. These clay minerals were transported by the river from the hinterland as weathering products. The transformation of clay mineral in the sediments was controlled by : (1) the sediment source, (2) the acid environment resulting from organic matter decomposition and pyrite oxidation, and (3) the marine environment.