Palaeoenvironments of the dinosaur-bearing Lameta Beds (Maastrichtian), Narmada Valley, Central India

Abstract

The Maastrichtian Lameta Beds of central India are intimately associated with the Deccan lavas and are critical to determining Upper Cretaceous palaeoenvironments and palaeogeography of the area. In the type Jabalpur sub-region, four mappable units of the Lameta Beds are recognised. The basal Green Sandstone is interpreted as a braided stream deposit. The Lower Limestone, characterised by brecciation and shrinkage cracks, is interpreted as a sub-aerially exposed palustrine flat with calcrete formation occurring on topographic highs of low relief plains. The overlying Mottled Nodular Beds exhibit a variable range of calcrete fabrics and morphologies including circum-granular and linear cracks, root casts and nodules. These are interpreted as pedogenically modified sheet wash deposits of a semiarid alluvial plain. The Upper Sandstone is a sheet flood deposit, again pedogenically modified before arrival of the basal lava flows. Overall the Lameta beds are considered to represent a regionally extensive Maastrichtian regolith. Carbon and oxygen isotope analyses of calcareous components are entirely consistent with soil-zone environments. The δ¹³C values are low, typically -8 to -9%..PDB, demonstrating a strong input of carbon from the decay of terrestrial land plants. Calcrete δ¹⁸O values are variable, -5 to -10%. PDB consistent with precipitation from meteoric water, some of which was evaporatively modified in pools on the alluvial/palustrine flat. The Lameta Beds are well known for sauropod nesting sites and sedimentological analyses of these sites suggest that the animals selected topographic highs, usually in marly or sandy, soft sediment. Multiple nests with similar egg types probably indicate colonial nesting. Isotopic analyses of eggshell carbonate agree with earlier work suggesting that the sauropods ate a "C3" plant food.