A Deccan Large Igneous Province related Maastrichtian regolith of Lameta Formation, Central India: Insights into the genesis and development of calcrete profiles and implications for palaeoclimate variability

ABSTRACT Emplacement of volcanics of the Deccan Large Igneous Province in the late‐Maastrichtian to early‐Danian has been linked to global climatic perturbations and the related biotic crisis. Sedimentary sequences associated with these lavas, known as infra‐trappean and inter‐trappean successions, preserve records of this Large Igneous Province induced climatic and biotic changes. The Lameta Formation of Jabalpur is the type section for the infra‐trappean succession; it preserves a unique stack of 13 calcrete profiles and one calcic‐vertisol, which together constitute the Mottled Nodular Beds. This stratigraphic unit evolved over a significant time period, most likely a few hundred thousand years in Chron C29R, making it a unique section suitable for obtaining insights on terminal Cretaceous palaeoclimatic variability. Micromorphological, clay‐mineralogical, geochemical and stable carbon‐isotopic (organic matter) data of calcretes of the Mottled Nodular Beds have been used to understand their genesis and obtain insights on climatic variability during their formation. These calcretes/calcareous palaeosol profiles are largely characterized by alpha‐fabric with the development of some biogenic features indicating predominantly evaporation/evapotranspiration driven carbonate precipitation with minor biochemically induced precipitation, respectively. Strontium isotopic compositions of the carbonate fraction of these calcretes indicate derivation of calcium from the Precambrian Mahakoshal Group marbles. On the basis of multiple datasets, these calcretes are interpreted to be pedogenic having formed in the soil‐vadose zone following the per descensum model. Based on a multiproxy approach that includes micromorphology, clay‐mineralogy, geochemistry (Mean Annual Precipitation and salinization) and stable carbon isotope ratio (organic matter), the conditions of formation of the Mottled Nodular Beds in C29R are interpreted to have varied mostly from semi‐arid to sub‐humid, with two intervening shorter arid episodes in the middle and upper parts of this succession. This climatic variability broadly aligns with the recently suggested changes in eruptive dynamics in the neighbouring Malwa Plateau of the Deccan volcanic province.