Integrated biostratigraphy of the middle to upper Eocene Kırkgeçit Formation (Baskil section, Elazığ, eastern Turkey): larger benthic foraminiferal perspective

Abstract

The Baskil section, located to the west of Elazığ in eastern Turkey, represents deep-marine facies of the Eocene Kırkgeçit Formation, deposited in a wide spectrum of environmental conditions ranging from shelf to basin. The 390-m-thick sequence was deposited at bathyal depths in the Tethys, at the edge of the subsiding Anatolide-Tauride plate and is highly promising for an integrated study of Bartonian to earliest Priabonian mid-latitude neritic and deep-marine biota. The section contains numerous allochthonous limestone beds, characterized either by turbidites or debris flows with resedimented larger benthic foraminifera (LBF). The section spans the planktonic foraminiferal Zones E10/11 to E14, the calcareous nannofossil zones NP15-NP18, shallow benthic zones (SBZ) SBZ16/17 to SBZ18A, including orthophragminid (OZ) zones OZ12-OZ14. The Bartonian-Priabonian boundary is placed at NP17/18 boundary by the lowest occurrence of Chiasmolithus oamaruensis, which lies within Subchron C17n.1n and Zone SBZ18A. The LBF, obtained as loose specimens from 17 turbiditic and debris flow beds, are characterized predominantly by 21 orthophragminid lineages and 13 nummulitid species as well as some other stratigraphically diagnostic genera. Most of the orthophragminid lineages straddle the Bartonian-Priabonian boundary, whereas Orbitoclypeus douvillei and Discocyclina pulcra appear to be the only orthophragminids confined to SBZ17 at its upper range. The Nummulites fabianii-lineage first appearing in zones E12 and NP16 in the Bartonian shows a well-documented evolution of the embryon, and is referred to Nummulites garganicus in the Bartonian, whereas its successor Nummulites hormoensis straddles the Bartonian/Priabonian boundary. The first appearances of N. hormoensis and Heterostegina armenica as well as the last occurrences of Nummulites ptukhiani and Assilina exponens in the section are almost coeval and are utilized to mark SBZ17-18 boundary. The first appearance of the H. armenica-lineage is recorded in zones E14 and upper part of NP17. Two important species, Chapmanina gassinensis and Silvestriella tetraedra, have been first recorded in SBZ18A just above the Bartonian-Priabonian boundary. Thus, the transition of N. garganicus to N. hormoensis, the first appearances of H. armenica, C. gassinensis and S. tetraedra as well as the last occurrences of N. ptukhiani, Assilina exponens, Discocyclina pulcra and Orbitoclypeus douvillei, all across the SBZ17-18 boundary or within the SBZ18A, appear to be the most useful bioevents in the transition from the Bartonian to the Priabonian in shallow-marine realms.

MECO and Alpine orogenesis: Constraints for facies evolution of the Bartonian nummulitic and Solenomeris limestone in the Argentina Valley (Ligurian Alps)

“…and Medocia blayensis , exclude a late Bartonian age (SBZ18b/SBZ18c). In particular the first appearance of Heterostegina that usually marks the Bartonian/Priabonian boundary (Özcan et al ., 2019), together with N. biedai and Spiroclypeus specimens usually mark the base of the late Bartonian (Serra‐Kiel et al ., 1998; Less et al ., 2008; Less & Özcan, 2012; Tomassetti et al ., 2016; Tomassetti & Benedetti, 2020).…”

A new, complex hyaline larger benthic foraminifer, Bigaella orbitoidiformis n. gen. n. sp., from the upper Bartonian-Priabonian of NW Turkey

“…Samples ŞEV10 and 11, ~10 m above the samples yielding Bigaella n. gen., contain Heterostegina armenica (Fig. 3.16), which is a key species that first appears close to the Bartonian-Priabonian boundary (SBZ 18A) (Less et al, 2008; Özcan et al, 2019). Therefore, the studied samples can be attributed to either the late Bartonian or the late Bartonian–early Priabonian transition.…”

Integrated biostratigraphy and benthic foraminifera of the middle-upper Eocene deposits of Urtsadzor section (Southern Armenia)

“…Genus Spiroclypeus Douvillé, 1905 Eocene Spiroclypeus in the western Tethys is exclusive to the SBZ19-20 zones . According to the recent interpretation of the Bartonian/Priabonian boundary (Agnini et al, 2011;Özcan et al, 2019a), Spiroclypeus occurrence corresponds to the middle and late part of the Priabonian stage. Eocene Spiroclypeus are unrelated to the Oligo−Miocene representatives of the genus and differ from them in having a much tighter spire.…”

“…11J-L, N-R, 12-14, 15A-K. ( This species first appears in the SBZ18B zone, which was formerly (Serra-Kiel et al, 1998; attributed to the late Bartonian. However, based on more recent studies (Agnini et al, 2011;Özcan et al, 2019a) it belongs to the earliest Priabonian. According to , the species forms a rapidly developing single evolutionary lineage through the whole Priabonian, which, based on the reduction of undivided postembryonic chambers (parameter X), is arbitrarily subdivided into seven chronosubspecies.…”

“…In the last decade, the extensive study of the stratigraphic ranges of the Bartonian and Priabonian stages activated the search for new criteria for the definition of the boundary between these stages in terms of nannofossil and foraminiferal zonations, aside from lithological (Tizian ash layer) and paleomagnetic criteria (Agnini et al, 2011;Costa et al, 2013;Less and Özcan, 2012;Cotton et al, 2017;Özcan et al, 2019a). The nannofossil markers include the lowest occurrence (LO) of Chiasmolithus oamaruensis, defining the base of the NP18 zone, and the base of Cribrocentrum erbae acme (Agnini et al, 2011).…”