Palaeosols and palaeoclimate reconstruction of the Maastrichtian Lameta Formation, Central India

Various geological studies have been done worldwide of Upper Cretaceous palaeosols, however similar extensive palaeosol studies are lacking in India. It is well established that palaeosols of any age are one of the best proxies for palaeoclimate reconstructions and for local to regional stratigraphic correlations of continental deposits. The Cretaceous deposits in Central India occur as isolated outcrops along the Narmada valley, known as the Lameta Formation. The Upper Cretaceous Lameta (~infratrappean) Formation of the Jabalpur area (Madhya Pradesh, Central India) preserves one of the most diverse Late Cretaceous reptilian assemblages (largely dominated by dinosaurs) and other significant biotic elements of the Indian subcontinent. The Lameta Formation in the Jabalpur region comprises excellent exposures, wherein the Mottled Nodular Bed (MNB) consists of sandy marl lithofacies together with palaeosol facies. Therefore, detailed pedofacies investigations on the basis of morphological, micromorphological and geochemical studies have been carried out in the MNB exposed at the Chui Hill (CH) and the Chhota Simla Hill (CSH) locations in Jabalpur city of Madhya Pradesh (Central India). These studies reveal the presence of various in-situ pedofeatures. For example, abundant bioturbation features, moderately developed blocky and granular microstructure, crystallitic and undifferentiated b-fabrics, Fe-Mn oxide/clay, silica to carbonate coatings, hypocoatings as well as quasicoatings, nodules/concretions and other textural as well as depletion pedofeatures. These palaeosols are interpreted as moderately to well-developed palaeosols that formed under tropical warm, humid climatic conditions rather than semi-arid conditions as deduced on the basis of diagnostic pedogenic characters. Tropical humid conditions are further supported by indices of base loss, salinization and hydrolysis in these palaeosols. The calculated mean annual precipitation (MAP) values range 779.44 ± 182 to1150.02 ± 235 mm/yr and CIA-K (Chemical Index of Alteration without potassium) values document significant chemical weathering. The present study will be important for future studies such as Upper Cretaceous palaeosol investigations along the east-west and central Narmada valley of peninsular India in order to utilize them as stratigraphic tools, taking into account worldwide reports of contemporaneous dinosaur-bearing Upper Cretaceous palaeosols in different parts of the world.