Shrinkage and sediment supply control on multiple calcrete profile development: a case study from the Maastrichtian of Central India

Multiple calcrete profiles of the Mottled Nodular Beds, form part of an extensive dinosaur-bearing infratrappean regolith in Central India. The profiles have clear variations in the distribution of carbonate morphologies (powdery, nodular, and sheet (platy) calcretes). Sheet calcrete is, however, distinctive and resembles, to some extent, a K horizon. These calcretes are interpreted as having formed in the soil-vadose zone. Profile development was governed mainly by the pattern and depth of shrinkage. It is possible that the mature (stage 3 to incipient stage 4) calcrete sheets of these shrinkage-related profiles formed quite rapidly and certainly in no more than about 400,000 years. Prominent shrinkage cracking appears to have favoured quite rapid calcrete formation and associated rhizocretion formation was also likely to have been rapid. A combination of climatic conditions, carbonate availability, and volcanism-induced sediment-starved conditions resulted in the development of a stack of fourteen calcrete profiles. Sediment starvation allowed most of the stratigraphic interval to be affected, to some degree, by calcareous pedogenesis. This contrasts with other Phanerozoic calcrete stacks where nodular carbonate typically occurs in discrete horizons, caused by relatively higher sediment supply.