Refining the Bathonian-Callovian and Callovian-Oxfordian Stage Boundaries in Jurassic Outcrops of the Kachchh Basin, Western India

Recent revisions to the Jurassic stratigraphy of sedimentary basins along the western and northern margins of the Indian craton have improved regional understanding, yet several critical stage boundaries remain imprecisely defined. This imprecision largely stems from stratigraphic discontinuities produced by non-deposition or erosion. In contrast, the Bathonian–Callovian and Callovian–Oxfordian boundaries are exceptionally well exposed in the Kachchh Basin, where they occur within uninterrupted, conformable sedimentary successions. Targeted field investigations demonstrate that both boundaries are represented by transgressive and high stand systems tract sequences, with no evidence for major unconformities or lithological breaks. These successions therefore offer a rare opportunity for precise stratigraphic definition, provided that detailed palaeontological analyses are undertaken. This study documents two well-preserved stratigraphic intervals: 1. Bathonian–Callovian transition: a continuous succession of shallow-marine carbonates and shales. 2. Callovian–Oxfordian transition: a continuous shallow-marine sandstone succession overlain by transgressive facies. Ammonite assemblages recovered from these intervals show high diversity, although some key marker taxa are absent. To resolve the boundaries with greater precision, this work encourages collaboration with international specialists in Jurassic micropalaeontology to analyse the microfossil content of these successions. Such efforts have the potential to enable formal recognition of these stage boundaries and significantly refine the global Jurassic chronostratigraphic framework.