<p>The present investigation seeks to explore the geochemical features of Late Miocene Upper Bhuban shales from Mamit District, Mizoram, India for the first time. The clastic sediments forming these shales originated from intermediate (andesite) to felsic (granodiorite) igneous rocks as evident from SiO₂ (55.64–63.84 wt %) and Al₂O₃/TiO₂ ranges (17.06–22.86). The clay mineral composition obtained from the index of compositional variation suggests dominance of montmorillonite over kaolinite. The palaeoweathering indices, i.e., chemical index of alteration (68.58–79.73), weathering index of Parker (30.41–39.95), and plagioclase index of alteration (75.43–92.41) indicate moderate provenance weathering. The A-CN-K diagram complements this observation and depicts favorable production and deposition of smectite over kaolinite in these shales. The Fourier transform infrared (FTIR) spectra additionally reveal lower kaolinite abundance compared to the quartz and feldspar substantiating moderate weathering of provenance. Such weathering intensity is generally associated with cold, semi-arid to sub-humid climatic regimes featuring moderate precipitation. These palaeoclimatic characteristics are consistent with global-scale cooling, aridification, and weakened rainfall in northeast India during the Late Miocene. Besides, the clastic sediment input (ash yield: 90.60–96.02 wt%) possibly hindered organic matter preservation in the depositional environment through dilution and/or promoting oxic redox conditions that favored microbial decay of organic matter. Oxidation (relative hydrocarbon potential (RHP) = 0.32– 0.82) and consequent poor organic matter preservation likely led to low total organic carbon (TOC) content (0.20–0.45 wt%) and abundance of type IV kerogen in these shale samples.</p>