Bulletin of the Geological Society of Malaysia, Volume 61, December 2015, pp. 23 – 28
1Institute of Oceanography, University Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia
2School of Marine Science and Environment, University Malaysia Terengganu, 21030 Kuala Terengganu, Malaysia
3State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
*Corresponding author: firstname.lastname@example.org
Abstract: Clay mineral assemblages and major-element geochemistry of surface sediments of the tropical river-estuary system of Kelantan, Terengganu and Pahang Rivers were investigated. Clay minerals in these three major rivers mainly consist of kaolinite (72%-75%), illite (13%-20%), chlorite (7%-10%) and minor smectite (<1%). A change in clay mineral contents (chlorite+illit) from upstream to the downstram (kaolinite) pointed to the alteration sequence of more stable mineral under the hot and humid conditions. The geochemical study indicated that the concentrations of major elements decrease from the middle course to estuary. Elemental ratios suggest that CaO and Na2O are the most chemically mobile elements while Fe2O3 is the least for the three investigated rivers. Formation of clay minerals (Al-rich) occur with enrichment of quartz (Si-rich) and feldspar (Na-rich). The illite chemistry index in these river basins averages 0.49 and is supported by the high chemical index of alteration (CIA) (>80) which shows that intensive chemical weathering had occurred in the Kelantan River, Terengganu River and Pahang River basins. The CIA values increase both north and southward directions from the Terengganu River pointing to the localized variations. The CIA values in clay fraction (<2μm) generally increased from the middle to the lower watershed.
Keywords: clay minerals, geochemistry, chemical weathering, tropical rivers, Peninsular Malaysia