Abstract The Koyna borehole penetrated c. 1 km through the Deccan basalt units and into the cratonic basement beneath, thus providing a unique insight into the subsurface succession of the main Deccan province. Earlier studies focused on southwestern Deccan lava packages exposed in the Western Ghat escarpment, and resolved a well-constrained stratigraphy and key reference sections, but lacked supporting subsurface data. To construct the stratigraphy and correlate it with the main Deccan formations, we report flow-wise physical and chemical data of a c. 932 m-thick core. We document 37 lava-flow units and four lava-flow groups that have similar major-oxide contents. These groups fit into two of the recognized chemostratigraphic formations, and the transitional Poladpur–Ambenali lavas. In addition, data plots on Ba v. Sr; Ba v. Zr/Nb; Ba/Y v. Zr/Nb; and Ba, Sr, Ba/Y, Zr/Nb v. height bivariate diagrams confine them to the Poladpur and Ambenali formations. Lava flows match with the Khumbarli and Mahabaleshwar Ghat sections and Killari core. The granitoid basement–basalt and the Poladpur Formation v. Ambenali Formation contacts lie at −332.5 and c. 482 m above sea-level, respectively. Further, the new data endorse the southern overstepping of chemostratigraphic units and the asymmetry of the Deccan edifice due to the northward motion of the Indian Plate over the nascent Réunion plume ( c. 67–64 Ma). For comparison, the oldest 66.4 Ma lava flow predates the Cretaceous–Paleogene boundary (KPB) (66.052 Ma) by <0.35 Ma, with much of the Wai Subgroup erupted syn-KPB or >0.55 Ma post-KPB; however, the restricted lava thickness at the contact between the Poladpur and Ambenali formations provides a reference point in the Deccan stratigraphy.

Abstract Flow-by-flow palaeomagnetic measurements of 37 lava flows in the 900 m-thick, isolated lava pile around Mandla in the eastern Deccan Volcanic Province (DVP) reveals multiple magnetic polarity events: implying C29n–C28r–C28n magnetostratigraphy. Magnetic polarity results when traced out from section to section, maintaining the order of superposition, show juxtaposition of lava packages with distinct characters near Deori (e.g. flows 1–4 abated against flows 5–14) and the Dindori areas. At Dindori and towards its south, the distinct lava packages (e.g. flows 15–27 and flows 28–37) are juxtaposed along the course of Narmada river. It is explained by the presence of four normal post-Deccan faults in the Nagapahar, Kundam–Deori, Dindori and Badargarh–Amarkantak sectors: thus, signifying structural complexity with vertical shifts or offset of 150–300 m. Magnetic chron reversals in conjunction with field and chemical data support these findings. Further, these lavas are compositionally akin to Bushe, Poladpur, Ambenali and Mahableshwar Formational lavas, and follow the same stratigraphic order as in the Western Ghats. Alternating field (AFD) and thermal demagnetizations (THD) isolate the normal mean direction of the Mandla lobe: D =344.5° and I =−30°, where D and I are the mean declination and inclination of the each lava flow (α 95 =8.2; K =72.6; N =17, where α 95 is the half-angle of the cone of 95% confidence about the mean direction, K is the precision parameter and N is the number of flows). The Virtual Geomagnetic Pole (VGP) position determined for these lavas, when compared with the Deccan Super Pole, indicates concordance with the main Deccan volcanic province, thus assigning a shorter period of eruption close to the Cretaceous–Palaeogene boundary (K/PB) for the eastern and western Deccan Traps.