Calcretes from a Late Quaternary interfluve in the Ganga Plains, India: Carbonate types and isotopic systems in a monsoonal setting

Abstract

Calcretes are abundant in Late Quaternary channel and floodplain strata of the southern Ganga plains. In a key section at Kalpi, pedogenic carbonates (nodules, rhizoconcretions, and powdery carbonate) are present within aggradational floodplain deposits, where they correspond to relatively high monsoonal precipitation and river discharge. In contrast, groundwater carbonate has cemented degradational surfaces (discontinuities), which correspond with periods of relatively low precipitation. Mixed groundwater and pedogenic calcretes are present in the deposits of small interfluve channels, and reworked nodules line degradational surfaces and locally fill channels. Most carbonates show alpha fabrics that include floating textures, shrinkage crack fills, and grain coatings. The predominance of alpha fabrics is unexpected, but is characteristic of calcretes across dryland and seasonal parts of northern India, where soil formation led to only weakly developed or poorly preserved beta fabrics.