The Late Paleocene-Early Eocene sections from Lakadong Limestone (Mawmluh Quarry) and Umlatdoh Limestone (Komorrah Quarry) in Meghalaya, Northeast India were examined for larger benthic foraminiferal microfacies and carbon isotopes. We generated high-resolution age models using larger benthic foraminifera biostratigraphy and recorded the change in microfacies. The LBF microfacies in SBZ 3 (∼58–60.7 Ma) and SBZ 4 (56–58Ma) is dominated by Miscellanea, Glomalveolina, Ranikothalia, orthophragminids, dasycladalean green algae and coralline red algae, indicating that deposition occurred within inner to mid-ramp environments. An abrupt shift in the depositional setting from open marine Lakadong Limestone to restricted marine Lakadong Sandstone across the PETM possibly indicates major changes in hydrological cycle during the extreme warmth that followed the PETM. The marine sedimentation continued during the Early Eocene (SBZ 7–9 corresponding to 55.1–52.8 Ma) within Meghalaya that led to the formation of Umlatdoh Limestone dominated by Halimeda, Alveolina, and miliolids. The larger foraminiferal extinction and origination in the Meghalaya basin is marked by the extinction of late Palaeocene Ranikothalids, Glomalveolinids, dominating the Lakadong Limestone and the dominance of Alveolinids and Discocylinids in the early Eocene Umlatdoh Limestone.

Abstract. The late Paleocene orthophragminids, hitherto poorly known from the Himalayan foreland basins, are studied from the Lakadong Limestone in Meghalaya, northeastern India, in order to establish a systematic, biostratigraphic, and paleobiogeographical framework for them in the eastern Tethys. In the Mawmluh Quarry section (MQS) on the Shillong Plateau, to the southeast of Tibet, orthophragminids are associated with typical Paleocene orbitoidiform taxa endemic to the Indian subcontinent, i.e., Lakadongia Matsumaru & Jauhri (= Setia Ferràndez-Cañadell) and Orbitosiphon Rao, and various species of alveolinids, miscellaneids, and rotaliids, characterizing the Shallow Benthic Zones (SBZ) 3 and 4. The orthophragminids belong to two lineages of the genus Orbitoclypeus Silvestri: O. schopeni (Checchia-Rispoli) and O. multiplicatus (Gümbel), both well known from the peri-Mediterranean region and Europe (western Tethys). The latter species is identified here for the first time from the eastern Tethys. Previous records of the genus Discocyclina Gümbel from the Lakadong Limestone actually correspond to misidentified Orbitoclypeus; this implies that the late Paleocene orthophragminid assemblages from Meghalaya and eastern Tethys were less diverse than in the western Tethys. The lineage of Orbitoclypeus schopeni in the lower part of the Lakadong Limestone (SBZ 3) is identified as O. schopeni cf. ramaraoi based on the morphometry of a few specimens, whereas in the upper part (SBZ 4) it corresponds to a transitional development stage between O. schopeni ramaraoi and O. schopeni neumannae (with average Dmean values ranging between 192 and 199 µm). The embryon diameters of O. multiplicatus, recorded only in SBZ 4, range between 300 and 319 µm on average, corresponding to transitional development stages of O. multiplicatus haymanaensis and O. multiplicatus multiplicatus. Our data, along with a review of previous Paleocene and Eocene records from India and Pakistan, suggest that Orbitoclypeus is the only orthophragminid in the Paleocene of the eastern Tethys, whereas Discocyclina first appears in early Eocene times, being mainly represented by endemic taxa confined to the Indian subcontinent. Facies change in the MQS from a marine to continental setting within SBZ 4 corresponds to the oldest record from the Indian plate in the Paleogene, which may be linked to the flexural uplift of the passive margin of the Indian plate, marking the onset of the collision of the Indian and Eurasian plates.

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