Paleopedology of ferricrete horizons around Chennai, Tamil Nadu, India

Some soils around Chennai, Tamil Nadu, are represented by ferricrete horizons, and these can be related to the underlying bedrock In the present study, Red Soils and ferricretes have been studied from four different sites: Red Hills, Vaiyapur Uttukkadu, and Pallavaram, which were formed from different parent rocks. Red Soils and ferricretes around Vaiyapur and Red Hills are formed from the Upper Gondwana sandstone and shale, while around Pallavaram they are formed from Precambrian charnockites. In this paper morphology, micromorphology, and geochemistry of ferricretes and Red Soils are presented. Microfabric elements in polished thin sections provide a basis for the interpretation of processes involved in Red Soil and ferricrete formation. Micromorphology of Red Soils and ferricretes reveals high content of the clay minerals gibbsite, smectite, halloysite, and kaolinite. Fe-oxide mineralogy is represented by hematite, limonite, goethite, and magnetite. Pedogenesis has produced iron segregation that has formed, both in external and internal forms, in a great variability of colors. Cracks and fractures are filled by either kaolinite or hematite. Some of the fractures are lined with black manganese oxide representing the final depositional phase. Based on geomorphology, the soils date to the late Neogene to early Quaternary period Climatic conditions are interpreted to have been wetter than today.