اهمیت چینه‌نگاری و روند مهاجرت خانواده miscellaneidae در پالئوژن نئوتتیس نمونه پژوهش: حوضه سیستان، جنوب شرق ایران

خانواده miscellaneidae از روزن‌داران کف‌زی بزرگ پالئوژن هستند که به‌منظور بررسی پخش و انتشار چینه‌نگاری و جغرافیای زیستی گذشته آنها در حوضه نئوتتیس مطالعه شده‌اند. برش چینه‌نگاری حرمک شامل 470 متر تناوبی از مارن، سنگ‌آهک مارنی و سنگ‌آهک است. با بررسی مقاطع نازک، گونه‌های miscellanea miscella،miscellanea juliettae، miscellanites primitivus و miscellanites minutus شناسایی شدند که سن پالئوسن پسین ائوسن پیشین برای نهشته‌های مدنظر پیشنهاد می‌شود. مرز پالئوسن ائوسن با ظهور اولیه جنس‌های alveolina و nummulites مشخص می‌شود که ویژگی نئوتتیس غربی در اوایل ائوسن پیشین است؛ در حالی که این نمونه‌ها در حوضه نئوتتیس شرقی در این زمان دیده نمی‌شوند و فقط گونه‌هایی از alveolina به‌صورت کمیاب در پالئوسن پسین و اوایل ائوسن و گونه‌هایی از جنس glomalveolina حضور دارند که به همراه جنس‌های ranikothalia و miscellanea بیان‌کننده شباهت نهشته‌های برش حرمک با حوضه ایندوس و تبت در نئوتتیس شرقی است. براساس پژوهش‌های انجام‌شده در نئوتتیس شرقی و غربی، میسلانیدآ برای نخستین‌بار در بیوزون‌های sbz1sbz2 در نئوتتیس غربی (اروپا آفریقا) ظاهر شده است؛ در حالی که در نئوتتیس شرقی (هند تبت و پاکستان) دیده نمی‌شود و در sbz3sbz4 در دو حوضه نئوتتیس شرقی و غربی وجود دارد. در بیوزون‌های sbz5/6 –sbz7 و sbz8، این گروه در حوضه نئوتتیس غربی ناپدید شده‌اند، اما در نئوتتیس شرقی در بیوزون‌های sbz5/6 فقط در ناحیه هند و پاکستان دیده و پس از آن ناپدید شده‌اند. با توجه به نتایج به‌دست‌آمده از شناسایی جنس‌ها و گونه‌های این خانواده در برش چینه‌نگاری حرمک و شباهت فونی توالی‌های بخش جنوبی حوضه سیستان با حوضه ایندوس در هند تبت و پاکستان (نئوتتیس شرقی)، به نظر می‌رسد با از بین رفتن سد اقیانوس‌نگاشتی در پالئوسن پسین ائوسن پیشین از حوضه نئوتتیس غربی به این ناحیه مهاجرت کرده‌اند.

Stratigraphic importance and migration trend of Miscellaneidae family in the Paleogene of Tethys basin, Sistan suture zone

Abstract Miscellaneidae is Paleogene larger index microfossils (middle Paleocene–early Eocene) that for determination of stratigraphic and palaeobiogeographic distributions are investigated in the NeoTethys Ocean. For biostratigraphic studies, depositional ages and systematic determinations of family Miscellaneidae, middle Paleocene–lower Eocene deposits in the Hormak section, in the north of Zahedan, are investigated. This stratigraphic section (470 meters) mainly consists of an alternation of marls, marly limestones, and limestones. Study of different miscellaneidae taxa led to identifications of Miscellanea miscella, Miscellanea juliettae, Miscellanites primitivus, and Miscellanites minutes that indicated standard biozone SBZ3–SBZ6 and therefore suggested late Paleocene–early Eocene age. Paleocene–Eocene boundary is identified with the appearance of Nummulitids and Alveolinids (SBZ5/6) in the western NeoTethys, whilst in the eastern NeoTethys these group of large benthic foraminiferas are absent. Some of Alveolina species accompanied by Glomalveolina, Miscellanea, and Ranikothalia species are seen which shows similarities between the Hormak section and other sections in the Indus basin and Tibet in the eastern NeoTethys. Based on biostratigraphic investigations, family Miscellaniedae, firstly appeared in SBZ1/2 in the western Neo–Tethys (Europe and Africa) whereas in the eastern NeoTethys (India, Tibet, and Pakistan) are not seen although the mentioned family in SBZ3/4 are recognized in the both western and eastern NeoTethys. In biozones SBZ5/6, SBZ7 and SBZ8, in the western NeoTethys family, Miscellaniedae disappeared whereas in the eastern NeoTethys are seen in the SBZ5/6 biozones. With respect to identified Miscellaniedae genus and species in the Hormak section and similarities with eastern NeoTethys, it seems that, with the omission of palaeoceanogrphic barrier in the Paleocene–Eocene boundary, the Miscellaniedae genus and species are migrated to the eastern NeoTethys. Keywords: Late Paleocene–early Eocene, Large Benthic Foraminifera, Sistan Suture Zone   Introduction 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 (SerraKiel 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 NeoTethys 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 NeoTethys, 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 NeoTethys 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.   Material & Method 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.   Discussion of Results & Conclusions In the eastern NeoTethys, 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 NeoTethys) 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; SerraKiel 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 NeoTethys foraminiferal assemblage (Afzal et al. 2009).