Orthophragminids (Foraminifera) Across the Paleocene-Eocene Transition From North Africa: Taxonomy, Biostratigraphy, and Paleobiogeographic Implications

Abstract

The platform margin and slope deposits in Galala, Egypt, record a larger benthic foraminiferal turnover (LFT), previously proposed to coincide with the Paleocene-Eocene (P/E) boundary based on the negative carbon isotope excursion (CIE) consistent with the Paleocene-Eocene Thermal Maximum (PETM). The LFT in these deposits was established on the basis of supposed synchronous first appearances of such taxa as Alveolina, Nummulites, and Orbitolites at or around the P/E boundary, although the response of orthophragminids, assigned only to the genus Discocyclina, was not studied. The orthophragminids in the late Paleocene-early Eocene interval in some of these deposits (sections B3, D5, D6, and D8) are represented by species of Discocyclina Gümbel, Orbitoclypeus Silvestri, and Nemkovella Less, reported for the first time from the southern margin of the Tethys. The Thanetian orthophragminids consist of Orbitoclypeus multiplicatus, O. schopeni, Discocyclina seunesi, and D. tenuis, while assemblages in the early Eocene are characterized by Discocyclina archiaci, D. dispansa, Orbitoclypeus schopeni, and Nemkovella stockari, suggesting a significant change in composition through the sections. The assemblages below and above the P/E boundary, only recorded in sections B3 and D8, mark the orthophragminid zones OZ 1B and 3, respectively. The OZ 2, correlated to shallow benthic zones SBZ 5 and 6 in the basal part of the Eocene and recognized by the first appearance of asterocyclinids, nemkovellids, and some ribbed orbitoclypeid species in northern Tethyan platforms, was not found. This may suggest either a hiatus, recorded previously in section D8 based on calcareous plankton, across the P/E transition in section B3 or an artifact of sampling. Consequently, our data raise some doubts about the aforementioned compositional changes related to the LFT and P/E boundary. We discovered an advanced developmental stage of N. stockari (N. stockari bejaensis n. subsp.) from a new section in Tunisia. This subspecies seems to be a key taxon for the early Eocene of the southern Tethyan platforms and extends the geographic and stratigraphic range of the species. We conclude that orthophragminids at Galala bear a close resemblance to those in the northern Tethyan platforms, especially assemblages from Turkey.

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

“…The late Paleocene phylogeny of Tethyan orthophragminids was reconstructed from localities in Europe and the peri-Mediterranean region, a part of the western Tethyan bioprovince (Schlumberger, 1903;Douvillé, 1922;Neumann, 1958;Samuel et al, 1972;Less, 1987;Zakrevskaya, 2007;Less et al, 2007;Özcan et al, 2014), whereas a systematic study from the eastern Tethys is lacking. In the western Tethys, Paleocene orthophragminids are represented by several species (lineages) of Discocyclina Gümbel and Orbitoclypeus Silvestri, enabling us to characterize the Thanetian by two orthophragminid zones (OZ), 1a, b and a part of OZ 2 crossing the Paleocene-Eocene boundary (Less et al, 2007).…”

“…Despite their widespread distribution and a reasonably high number of evolutionary lineages established from the peri-Mediterranean region (western Tethys), a Tethyan-scale biostratigraphic model and a paleobiogeographical scheme have not yet been established because of lack of data from the eastern Tethys (Wan, 1991;Wan et al, 2010;Zhang et al, 2013;Özcan et al, 2014;BouDagher-Fadel and Price, 2017). In the peri-Mediterranean region and Europe, both Discocyclina Gümbel and Orbitoclypeus Silvestri appear simultaneously in the Thanetian and orthophragminids become more diverse with the first appearance of Nemkovella Less and Asterocyclina Gümbel after the Paleocene-Eocene boundary (Less et al, 2007;Özcan et al, 2014). The main records of Paleocene orthophragminids from the eastern Tethys come from the Lakadong Limestone in Meghalaya, where a detailed taxonomic study of the group has until now not been available.…”

Early Eocene orthophragminids (Foraminifera) from the type-locality ofDiscocyclina ranikotensisDavies, 1927, Thal, NW Himalayas, Pakistan: insights into the orthophragminid palaeobiogeography

“…The correlation of western Tethyan orthophragminids to those in the coeval deposits in Indo-Pakistan region (NW Himalayas) and Himalayas is hampered by a lack of taxomic studies in these regions, posing a handicap for the creation of a thorough synthesis of orthophragminid palaeogeography for Tethys and worldwide (Ben İsmail-Lattrache et al, 2014;Less, 1987;Özcan et al, 2014). Nevertheless, our present study provides the first concrete data to overview the early Eocene orthophragminid distribution in Tethys.…”

“…D. a. bakhchisaraiensis is a key subspecies for OZ 3 in western Tethys, first appearing in the lower part of early Eocene but not immediately at or around the P/E boundary ( Figure 9) Özcan, Scheibner, & Boukhalfa, 2014 (Figure 13; Table 1). …”

Towards a Calibrated Larger Foraminifera Biostratigraphic Zonation: Celebrating 18 Years of the Application of Shallow Benthic Zones

“…During the eighteen years since the appearance of the SB zonation, a wealth of data on the morphology, biostratigraphy, and paleogeography of Paleogene LBF became available, leading to significant updates ( Fig. 1): (1) Increasing the precision in determining boundaries and achieving further subdivision of the previous standard zones as results of biometric studies on different nummulitid genera such as Heterostegina and Spiroclypeus (Less and Ozcan 2008) or through a multidisciplinary study of a section (Less et al 2011;Zakrevskaya et al 2011;Ozcan et al 2009Ozcan et al , 2014Ozcan et al , 2015; (2) Increasing knowledge of the characteristic foraminiferal assemblages in standard biozones, due to new studies on composition, ecology, and age attribution of regional faunas spanning from the Pyrenean Basin, to the Adriatic-Apulian area, Greece, Eastern Africa, Turkey, Oman, Pakistan, and Tibet (Benedetti et al 2010(Benedetti et al , 2011Pearson 2011, 2012;Zhang et al 2013;Accordi et al 2014;Cotton et al 2014Cotton et al , 2015Drobne et al 2014;Kahsnitz et al 2016); (3) New attempts at correlating the SB zones with isotope and magnetic stratigraphy and with the standard plankton zones (Rodriguez-Pintó 2012Gebhardt et al 2013;Egger et al 2013;Molina et al 2016); (4) New studies of foraminiferal assemblages from the Peritethys (Crimea, Northern Caucasus to Mangyschlak, Northern Peri-Aralian areas) and from the Caribbean region (Zakrevskaya 2011;Molina et al 2016); and (5) New detailed studies of the systematics and inner structures of particular LBF groups, such as rotaliids, larger miliolids, and ophtalmidids (Hottinger 2009(Hottinger , 2014Benedetti and Briguglio 2012;Benedetti 2015;Briguglio et al 2011Briguglio et al , 2013Briguglio et al , 2016.…”