Orthophragminids with new axial thickening structures from the Bartonian of the Indian subcontinent

Authors

  • E. ÖZCAN İstanbul Technical University, Faculty of Mines
  • P. KUMAR SARASWATI Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai 400 076
  • M. HANIF National Centre of Excellence in Geology, University of Peshawar, Peshawar-25120, Khyber Pakhtunkhawa,
  • N. ALI Department of Geology, University of Peshawar, Peshawar-25120, Khyber Pakhtunkhawa,

Keywords:

Foraminiferida, Orthophragminids, Bulges, Omphaloid test, Indian subcontinent

Abstract

The ‘axial thickening’, a morphological character of certain Eocene orthophragminids refers to the thickening of the equatorial and/or lateral layers in axial directions forming radial external structures, namely the ribs. The occurrence of ribs is considered to be a diagnostic specific character of the orthophragminids in the peri-Mediterranean region and Europe (western Tethys). In the Bartonian orthophragminids of the Indian subcontinent we observe a new type of axial thickening that we name ‘bulges’. The bulges are semi-rounded to rounded, localized structures on the test surface formed solely by the greater development of lateral chamberlets. These specimens, with trybliolepidine to umbilicolepidine type embryon configuration, co-occur with ribbed discocyclinids having completely different internal features. We also record another type of axial thickening of the lateral layers in notably small omphaloid tests that are characterized by a thick umbo, deeply depressed at the center such that the periphery of it forms a thick circular structure. The reported omphaloid specimens possess a small, semiisolepidine to nephrolepidine type embryon configuration and characteristic early chambers, not comparable to any known species in the Tethys. These specimens occasionally may have incomplete and/or irregular septula, reminiscent of certain Caribbean orthophragminids. The specimens with bulges, identified in two geographically distant regions of the Indian subcontinent, possibly represent endemic foraminiferal fauna confined to the Indo-Pakistan region. We introduce two new species, Discocyclina kutchensis sp. nov. (characterized by bulges) and ‘D’. sulaimanensis sp. nov. (characterized by circular structures in omphaloid tests). The status of both taxa in the Tethys is discussed.

Author Biographies

E. ÖZCAN, İstanbul Technical University, Faculty of Mines

Department of Geology, Faculty of Mines (İTÜ), İstanbul

P. KUMAR SARASWATI, Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai 400 076

Department of Earth Sciences

M. HANIF, National Centre of Excellence in Geology, University of Peshawar, Peshawar-25120, Khyber Pakhtunkhawa,

National Centre of Excellence in Geology

N. ALI, Department of Geology, University of Peshawar, Peshawar-25120, Khyber Pakhtunkhawa,

Department of Geology

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Published

2016-07-14

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