Origin of Calcrete in Red Sediment from Visakhapatnam Coast, Andhra Pradesh

Abstract Red sediment with calcrete is a characteristic deposit in the coastal tracts of Visakhapatnam region on the northeastern part of Andhra Pradesh. Three structural types of calcrete. rhizoconcretionary, mottled and massive, are recognized from Ramakrishna Mission, Rishikonda and Bhimilipatnam areas. Rhizoconcretionary calcrete is recorded from three profiles, but the mottled and massive are typically absent in Bhimilipatnam. The origin of the various types of calcrete in the Visakhapatnam area is intimately linked to evapotranspiration of groundwater. The rootlet origin of the calcrete structures is beyond doubt, as the actual woody tissue of the root is occasionally found as a core to the rhizoconcretions. The massive calcrete is precipitated much above the present day water table which, in general developed in the capillary-rise zone, indicating the rise in palaeo-water table. The well-developed calcrete profiles of Ramakrishna Mission and Rishikonda suggest the possible existence of a grove of old trees in the past. On the other hand, poorly developed calcrete profile of Bhimilipatnam indicates the palaeo-heath/scrub vegetation.