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Volume 37, issue 1 | Copyright
J. Micropalaeontol., 37, 357-381, 2018
https://doi.org/10.5194/jm-37-357-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 18 Apr 2018

Research article | 18 Apr 2018

Paleocene orthophragminids from the Lakadong Limestone, Mawmluh Quarry section, Meghalaya (Shillong, NE India): implications for the regional geology and paleobiogeography

Ercan Özcan1, Johannes Pignatti2, Christer Pereira3, Ali Osman Yücel1, Katica Drobne4, Filippo Barattolo5, and Pratul Kumar Saraswati3 Ercan Özcan et al.
  • 1Department of Geological Engineering, Faculty of Mines, İstanbul Technical University (İTU), Maslak, 34469 Istanbul, Turkey
  • 2Dipartimento di Scienze della Terra, Università degli Studi di Roma “La Sapienza”, Rome, Italy
  • 3Department of Earth Sciences, Indian Institute of Technology, Bombay, Powai, Mumbai 400 076, India
  • 4Palaeontological Institute I. Rakovec ZRC SAZU, Novi trg 2, 1000 Ljubljana, Slovenia
  • 5Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse Largo San Marcellino, 10, 80138 Naples, Italy

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 199µm). The embryon diameters of O. multiplicatus, recorded only in SBZ 4, range between 300 and 319µm 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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We carried out a morphometric study of late Paleocene orthophragminids from the Mawmluh Quarry section in the Shillong Plateau, India. We recorded the occurrence of two species of Orbitoclypeus, whereas the other typical Tethyan genera Discocyclina is absent. We also identified the associated benthic foraminifera and algae. Shallow benthic zones (SBZ) 3 and 4 have been recognized in the section. The timing of transition from shallow marine to continental deposition is commented on.
We carried out a morphometric study of late Paleocene orthophragminids from the Mawmluh Quarry...
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