<p>The Himalayan sedimentary sequences host numerous geological signatures of India-Eurasia collision held during the Paleogene Period. This study investigates the petrographic, geochemical, and clay mineralogical characteristics of a thin Paleogene carbonate rock sequence, exposed at Dalbuing Village (Type section of the Dalbuing Formation), Arunachal Pradesh, Northeast India to decipher its depositional history. Field observations reveal that Dalbuing Formation consists of alternating bands of limestone, shale, and sandstone. The limestones are light grey to dark grey in colour, well-bedded, compact, very hard, and highly effervescent with numerous calcite veins. Petrographic study has revealed that they are composed predominantly of fossils (mainly foraminifera of Eocene age) and intraclasts embedded mainly in sparite. They can be categorized as biosparite, intrasparite, and sparite, with minor micrite, as well as type-III limestone. Geochemically, they have been classified as dolomitic and magnesian limestone. Both clay and non-clay minerals are present, including illite, chlorite, kaolinite, thuringite, and corrensite, along with quartz and calcite. The integrated study of petrography, geochemistry, and clay mineralogy have pointed towards their deposition in varied marine environments such as shallow, deep, and transitional during Eocene time.</p>