فهرست مطالب somayyeh shahraki mirzaei

Of the most important characteristics of the Ranikothalia genus, as large benthic foraminifera, are the existence of ornamentation in the external part of the shell especially around the central umbilicus knob, marginal mesh channels (MMC) in the marginal chord, trabeculate system with channels, V-shape plate in the floor of chambers and accumulation of septum that differentiated this genus from Nummulites genus and placing it in the Palaeonummulitinae sub-family. The Ilerdian transgression near the P5 Zone (Pelagic P5) is a stratal key surface for the determination of the Paleocene-Eocene boundary in the neritic deposits. Ranikothalia nuttalli as an index species is used for recognition of the Paleocene–Eocene boundary in the Neo-Tethys shallow water successions. This species, in the Padagi section, resembling the Pakistan Indus Basin, accompanied with Miscellanea miscella, Discocyclina sp., Discocyclina sp., Assilina sp. that indicated SBZ5/6 and suggested lower Ilerdian (earliest Eocene) age.

Large benthic foraminiferas in Paleogene of Tethyan basin widley distributed that still remain poorly identified in the eastern Tethys specially in the southeastern of Iran. Based on systematic determination of LBFs 12 genera and 24 species in the Late Paleocene-Early Eocene interval are known that are Ranikothalia, Discocyclina, Miscellanites, Miscellanea, Kathina, Idalina, Assilina, Vania, Glomalveolina, Daviesina and Lockhartia. The base of SBZ3 biozone is defined by the first Occurence of Miscellanea juliettae, Miscellanites minutus, Miscellanites primitivus, Vania anatolica, Glomalveolina primaeva, Glomalveolina telemetensis, Glomalveolina dachelensis, Discocyclina seunesi, Ranikothalia sindensis, Ranikothalia tubleri, Kathina selveri. With respect to its high abundance and limited biostratigraphic range of above mentioned species (except Ranikothalia sindensis  and  Kathina selveri) can be taken as an index fossils of SBZ3. The base of SBZ4 biozone is defined by the first appearance of Discocyclina ranikotensis, Daviesins langhami, Miscellanea miscella which among them Ranikothalia  sindensis, Miscellanea miscella and Daviesina langhami appear in high abundance and widley distributed. It is mentioned that Miscellanites primitivus, in the studied section,is continued to SBZ5/6.SBZ5/6 biozone is defined  by Lockhartia haemei, Ranikothalia nuttalli, Ranikothalia sp., Assilina dandotica, Discocyclina dispansa and Discocyclina sella. Species of   Ranikothalia nuttalli, Assilina dandotica and Ranikothalia sindensis has high abundance and wide distributions. it is mentioned that in the some part of the eastern Tethys such as Tibet Daviesina genus has disappeared in the SBZ5/6 whilst in the studied sections has high abundance although  Alveolina vredenburgi  is not seen and Miscellanea miscella has low distribution regard to SBZ4. In the studied section, Earliest Eocene Large Benthic Foraminifera (SBZ5/6) predominantly consists of Ranikothalia and Miscellanea while the new Foraminifera assemblage that’s appear in the other locations (such as Assilina, Alveolina and Discocyclina) are less important and Nummulites are absent. In continuation of Early Eocene, gradual diversity of species of Discocyclina، Operculina and Assillina has occurred, whilst Ranikothalia is disappeared and Miscellanea  in the end of SBZ5/6 is less important. Similarity Larger Benthic Foraminifera assemblage in the other part of eastern Tethys especially India and Pakistan are recorded. Therefore this assemblage in the eastern Tethys are different from western Tethys.

Large benthic foraminifera (LBF) are important fossils with large tests and complex internal structures. In biostratigraphic studies of Paleogene large benthic foraminiferas from Alveolina, Assilina (Hottinger 1960; Drobne 1977), and Nummulites (Schaub 1981) are used for introduction of 20 shallow benthic zones in the western Tethys (Serra-Kiel et al. 1998). Large benthic foraminiferas in the eastern and western Tethys similarly described but are different with regard to taxonomy (Hottinger 1971). The Paleocene of western Neo-Tethys are dominated with coralgal reefs (e.g. Accordi et al. 1998; Turnsek and Drobne 1998; Baceta et al. 2005; Scheibner et al. 2007) although in the eastern Neo-Tethys, the large benthic foraminiferas are dominated (Wan et al. 2002; Afzal et al. 2009, 2011; Zhang et al. 2013). Based on high biodiversity of Lockhartia in the Paleocene of Ronikot Formation in India, eastern Neo-Tethys ocean is named Ranikothalia Sea (Davies 1937) or Lockhartia Sea (Hottinger 1998) that occupied southern Turkey in the west to the Tibet and Pakistan in the east and Egypt in the south (Hottinger 2007, 2014). Another important aspect of large benthic foraminifera biodiversity is that the Lockhartia genus has a distinct chronostratigraphic position in the Paleocene resemble that Alveolina, Assilina, and Nummulites in the Eocene. For example, Lockhartia retiata Sander 1962 and Lockhartia praeheimi Smout 1954 are accepted as index fossils of the shallow benthic zone 3. The objectives of this study are the determination of stratigraphic importance and migration trend of Miscellaniedae family across the Tethys ocean in the late Paleocene–early Eocene time.

For LBFs biostratigraphic investigations of the Hormak section, in field studies, 100 rock specimens are collected and 350 thin sections are prepared from them for the study of different genus and species of Miscellaniedae family. The systematic determination of this group of large benthic foraminiferas is, in the level of genus and species, are done by using a binocular microscope and then based on identified LBFs, the age of the Hormak section is suggested.

In the eastern Neo-Tethys, SBZ3 and SBZ4 are identified with increasing generic diversity and reflect the time in which LBF have experienced the new morphology (Hottinger 2001; Scheibner and Speijer 2008). In India basin (eastern Neo-Tethys) the mentioned biozones are initiated with the appearance of new taxonomic trends such as Rothalids (Kathina and Lockhartia), Miliolids (Triloculina and Quinqueloculina) Pellatispirids (Miscellanea), Alveolinids (Glomalvelina), Coskinolinids (Coskinon), Spirocyclinids (Saudia), Dictyoconids (Fallotella, Dictyoconus), Nummulitids (Ranikothalia, Assilina, and Operculina) and Lepidorbitoids (Daviesina, Orbithosiphon, and Setia) (Afzal et al. 2009) that are correlatable with a faunistic scheme in the other part of the Tethys (Hottinger 1997, 1998; Jauhri 1998; Serra-Kiel et al. 1998; Jauhri and Agarwal 2001; Jauhri et al. 2006; Green et al. 2008; Scheibner and Speijer 2008, 2009; Zamagni et al. 2008; Mathur et al. 2009; Tewari et al. 2010). Studies of different genera of Miscellaneidae in the thin sections and isolated forms led to the identification of Miscellanea miscella, Miscellanea juliettae, Miscellanites primitivus, Miscellanits minutus that accompanied with other fossils are suggested the late Paleocene–early Eocene age. In the Hormak section, SBZ3 and SBZ4 biozones are identified with Kathina, Triloculina, Idalina, Quinqueloculina, Miscellanea, glomalveolina, Ranikothalia, and Discocyclina that in respect to abundance and diversity, correlatable with eastern Neo-Tethys foraminiferal assemblage (Afzal et al. 2009).

Miscellaneidae are Paleogene larger index microfossils (Middle Paleocene–Early Eocene) that are important for biozonation of shallow marine deposits. These large benthic foraminifera have distinct architecture and ornamentation schemes which differentiated them form Nummulitidae and Rotalidae families. Miscellaneidae have different taxa that essentially are usefulness for biostratigraphic and palaeobiogeographic investigations. For biostratigraphic studies, age and systematic determinations of miscellaneidae, Middle Paleocene–lower Eocene deposits of two outcrop sections are investigated in the Padagi village in the north of Zahedan. These stratigraphic sections mainly consist of alternation of marls, marly limestones and limestones with 237.5 m thickness for PE section and 222.5 m thickness for PEP section. Study of different Misellaneidae genera led to identifications of Miscellanea miscella, Miscellanea juliettae, Miscellanites primitives and Miscellanites minutus that shows standard biozone SBZ3–-SBZ6 and therefore suggested Late Paleocene–-Early Eocene age. Moreover, global distribution patterns of older species of Miscellaneidae represents that these species belong to the eastern Tethys basin.