A review of research on Late Cretaceous volcanic-sedimentary sequences of the Mandla Lobe: implications for Deccan volcanism and the Cretaceous/Palaeogene boundary

Abstract

Regional mapping and detailed petrographic studies of the volcanic-sedimentary sequences of the Mandla Lobe, coupled with lateral tracing has enabled the recognition of 37 physically distinct lava flows, and major oxide chemistry grouped them into eight chemical types. The lava pile becomes structurally complex to the east of Jabalpur where the juxtaposition of distinct groups of lava flows is observed near the Deori (flows 1–4 abutting flows 5–14) and Dindori areas. At Dindori, distinct lava packages (flows 15–27 and 28–37) are juxtaposed along the course of Narmada River, indicating the presence of four post-Deccan faults in the Nagapahar, Kundam, Deori and Dindori areas, and arguing against the idea of a small regional dip. Major geochemical breaks, when traced from section to section, exhibit shifts in height of approximately 150 m near Nagapahar and 300 m near Deori and Dindori. These findings, when considered in conjunction with magnetic chron reversal heights, support the presence of four NE–SW-trending faults. Major and trace element abundances in 15 lava flows in the Jabalpur area are similar to those of the south-western Deccan flows. The Ambenali Formation and a few flows of the Khandala and Bushe formations are present in north-eastern Deccan. Improved stratigraphic correlation is needed to define the lateral continuity and spatial distribution of the western-defined formations in regions to the east. The dominance of smectites in the detrital assemblage of the Lameta Formation suggests their derivation from a volcanogenic source rock. IR spectra support the commonality of the mineralogical attributes of the Lameta Formation and the Deccan basalt in their mutual resemblance of absorption bands. Structural formulae indicate that smectites of the Lameta deposits are rich in octahedral Mg and Fe. The abundance of Fe together with Mg further favours derivation from the Deccan basalt as do similarities in the concentrations of immobile trace elements, REE patterns, and the negative Ce anomalies observed. These findings correlate the smectite-dominant detrital clays with the Deccan basalt, implying the availability of the latter during deposition of the Lameta Formation in the Maastrichtian. These findings do not match models suggesting an extremely short period of Deccan volcanism (<0.5 myr) at the Cretaceous/Palaeogene transition; it is congruent with the models advocating a more prolonged volcanism.