Micropaleontology and systematic determination of Miscellaneidae family in the Middle Paleocene–lower Eocene deposits in the north of Zahedan, Padagi stratigraphic sections

Abstract

Abstratct 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. Keywords: Late Paaleocene–Early Eocene, Large Benthic Foraminifera, Sistan Suture Zone Introduction: Large benthic foraminifera (LBF) are important fossil and extant forms that in respect to systematic and biostratigraphy, extensively are studied and some biozonation schemes based on them are suggested. This group of foraminifera shows rapid diversification events and sudden extinctions in the geological history (Hallock 1985). Development and occurrence of them related to the warming period, relative dryness, sea level rising, development of tropical and sub-tropical habitats and decreasing of oceanic cycles in the global scale (Hallock and Glenn 1986). In the Early Cenozoic, Nummulitids (Nummulites, Assilina and Operculina), Orthophragminids (Discocyclina) and Alveolinids (Alveolina) are LBFs that distributed in the shallow water oligotrophic environments in the Tethys ocean and are one of the most important carbonate producers in the inner and middle ramp environments (Bouxton and Pedley 1989). Therefore in the eastern Tethys, LBFs such as Miscellanea and Ranikothalia are found in the Early Eocene of carbonate platforms, whilst Alveolina are less important and Nummulites is not found (Scheibner and Speijer 2008a). In addition, in the other part of Tethys ocean genera such as Miscellanea and Ranikothalia, after Paleocene–Eocene boundary accompanied with Nummulites and Alveolina assemblages are found. In Paleocene and Eocene of the Tethys basin LBF biozonation are represented by Sarra-Kiel et al. (1998) which based on these group of foraminifera Paleocene and Eocene series are divided into 20 shallow benthic zones (SBZ1–-SBZ20). The boundary between Paleocene and Eocene is considered between SBZ4–-SBZ5 (Scheibner and Speijer 2009). Miscellaneidae are an index microfossils that are very important group for zonation of Middle Paleocene and earliest Eocene shallow marine deposits. Miscellaneidae family have different genera and species that are used for biostratigraphic and paleobiogeographic studies. Material & Methods: For LBFs biostratigraphic investigations of Padagi section, 125 rock specimens are collected and 580 thin section are prepared. The systematic determination of foraminifera, in level of genus and species, are done by using of binocular microscope and then based on identified LBFs, the age of the succession is suggested. Discussion of Results & Conclusions: Studies of different genera of Miscellaneidae in the thin sections and isolated forms led to identification of Miscellanea miscella، Miscellanea juliettae،Miscellanites primitivusMiscellanits minutus that accompanied with other fossils are suggested the Late Paleocene–Early Eocene age. Miscellanea miscella in Salt Range, Egypt and Aquitaine (south western of France) appearance in the SBZ4 (Late Thanetian) and continued up to SBZ6. Zhang et al. (2013, 2018) has reported Miscellanea miscella from SBZ5/6 in the Tibet area (eastern Tethys). In Padagi section, this species is found accompanied with Ranikothalia nuttali, Assilina dandotica, Discocyclina sella and D. Ranikotensis, which shows SBZ4 and in thSBZ5/6 and suggested Late Paleocene–Early Eocene age. Existence of Miscellanea juliettae, Vania anatolica, Miscellanites primitivus and Glomalveolina primaeva in the lower part of the Padagi section shows SBZ3 biozone and Late Paleocene (Early Thanetian) age. This fossils assemblge belong to the SBZ3–SBZ6 standard biozones that with respect to Miscellanea miscella distribution pattern and accompanied with Miscellanites and Ranikothalia and absence of earliest Eocene benthic foraminiferas such as Nummulites, Alveolina and Ranikothalia in the Padagi section shows that the mentioned species belong to the eastern Tethys which has migrated to the younger time horizons to the western Tethys. In Iran, different species of Miscellanea and Miscellanites in the Taleh-Zang Formation, Zagros Mountain, Shiraz and Sistan basin (Rahaghi 1983) are reported. In the Tibet area differentiation and diversity of genera and species, primary dimorphism and adult size of shell of LBFs such as Keramosphaerinopsis haydeni (SBZ3), Daviesina langhami (SBZ4–5), Miscellanea miscella (SBZ5) refer to, probably, Paleocene LBFs more faster and quickly has evolved relative to the western part of the Tethys and shows that LBF turnover (LFT), in the eastern part has happened earlier in time (Zhang et al. 2013, 2018). With respect to the abundance and development of the Ranikothalids and Miscellanids and absence of Alveolinid genera and species in the SBZ5/6 biozones and similarities of foraminiferal assemblage indicated that the Padagi section and Late Paleocene–Early Eocene sediments are deposited in eastern part of the Tethys in the north of Zehedan. Abscene of Nummulites and Alveolina genera in Early Eocene time fascinate the survival of these genera in the eastern Tethys. In the other part of the Tethys, especially western Tethys, the Paleocene LBFs, totally replaced with Nummulites, Alveolina and Assilina genera (Orue-Etxebarria et al. 2001). With regards to affinity and similarity of LBF assemblages (widespread of Ranikothalia and Miscellanea and absence of Nummulites and Alveolina genera in the SBZ5 and SBZ6) of Sistan basin (Padagi section) with Indus basin (in Pakistan and India) concluded that, palaeobiogeographically, the mentioned basin are related to the eastern part of the Tethys.

Keywords

• late paaleocene–early eocene
• large benthic foraminifera
• sistan suture zone