Hydrography of the eastern Arabian Sea during summer monsoon 2002

Abstract

Many physico-chemical variables like rock-type,climate,topography and exposure age a ffect weathering environments.In the present study,an attempt is made to understand how the nature of clay minerals formed due to weathering differs in tropical regions receiving high and low rainfall. Clay mineralogy of weathering pro files in west coast of India,which receives about 3 m rainfall through two monsoons and those from the inland rain-shadow zones (<200 cm rainfall)are studied using X-ray di ffraction technique.In the west coast,1:1 clays (kaolinite)and Fe –Al oxides (gibb-site/goethite)are dominant clay minerals in the weathering pro files while 2:1 clay minerals are absent or found only in trace amounts.Weathering pro files in the rain shadow region have more complex clay mineralogy and are dominated by 2:1 clays and kaolinite.Fe –Al oxides are either less or absent in clay fraction.The kaolinite –smectite interstrati fied mineral in Banasandra pro files are formed due to transformation of smectites to kaolinite,which is indicative of a humid paleo-climate.In tropical regions receiving high rainfall the clay mineral assemblage remains the same irrespective of the parent rock type.Rainfall and availability of water apart from temperature, are the most important factors that determine kinetics of chemical weathering.Mineral alteration reactions proceed through di fferent pathways in water rich and water poor environments