زیست چینه نگاری نهشته‌های دونین پسین کربنیفر پیشین (فامنین پسین تورنزین) در برش زو (شمال شرق ایران) بر اساس فونای کنودونتی

بررسی فونای کنودونتی نهشته‌ های دونین پسین کربنیفر سازندهای خوش‌ییلاق و مبارک در برش زو (شمال شرقی شهر جاجرم) به شناسایی 10 جنس، 23 گونه و 8 زیرگونه‌ منجر شده است. زیای کنودونتی به دست آمده در این مطالعه، موید زیست‌زون bispathodus ultimus (فامنین پسین) و گستره‌های زیستی معادل base of siphonodella duplicata to within siphonodella crenulata (تورنزین) و pseudopolygnathus multistriatus  (ویزین) می‌باشد. این امر نشان می‌ دهد که گذر فامنین تورنزین در انتهای سازند خوش‌ییلاق و 6 متر بالاتر از لایه دیاباز قرار دارد. زیای کنودونتی مزبور، نشانگر غلبه زیست‌رخساره polygnathid می ‌باشد. زیست‌رخساره ‌های کنودونتی پیش‌روی سطح آب در کربنیفر را تایید می‌کنند. برش مذکور هم از دیدگاه رخسارۀ سنگی و هم از دیدگاه رخسارۀ زیستی، با دیگر برش‌ های البرز شرقی مشابه است. شاخص تغییر رنگ کنودونت ‌ها در عناصر کنودونتی کربنیفر نسبت به دونین پسین افزایش نشان می ‌دهد.

Biostratigraphy of Late Devonian-Early Carboniferous deposits in the Zoo section (northeast of Iran) based on conodont fauna

IntroductionDevonianCarboniferous boundary is an exciting issue for researchers all over the world. In this boundary, significant events have occurred on marine organisms (specially conodonts elements) and terrestrial organisms, consisting of weather and sealevel changes, and relative coincidence with the Hangenberg bioevent (Mc. Ghee, 1998; Sandberg et al., 2002; Caplan Bustin, 1999; Kaiser et al., 2006, 2011, Bahrami et al., 2011, 2019; Konigshof et al., 2021; Sattari et al., 2021). According to ICS, the DevonianCarboniferous boundary, as defined by the first Appearance Datum (FAD) of the conodont species Siphonodella sulcata within the Siphonodella praesulcata Siphonodella sulcata lineage and the GSSP is located in the La Serre Trench E’ section in France (Paproth et al. 1991). Khoshyeilagh Formation in Zoo section consists of shallow marine deposits attributed to the Late Devonian (FrasnianFamennin) (Najjarzadeh, 1997). This study focuses on identifying and reviewing the DevonianCarboniferous boundary in a part of the Eastern Alborz area and study the biostratigraphy of deposits near this boundary based on conodont fauna.Materials and Methods58 carbonate and 11 noncarbonate samples (34 kg/each) were collected and processed for conodonts. The samples were processed with the conventional acetic acid technique, but formic acid 10% with 10 hours was also used for some silty samples and compacted limestones. Then picked remaining deposits with the handpicking method. The following steps include pasting the conodont specimens on stab, photographing them under an SEM microscope, and naming conodonts elements based on available references (e.g., Branson Mehl, 1934; …). Accordingly, the biozonation of the studied sequence using the global standard zonings of Ziegler Sandberg (1990), Sommervile (2008), Poty et al. (2006), Spalletta et al. (2017).Discussion and ConclusionKhoushyeilagh and Mobarak formations Late DevonianCarboniferous conodonts fauna of Zoo section, (NE Jajarm), led to identifying 10 conodont genera, 23 species, and 8 subspecies. The conodont faunas which be obtained in this research indicate the presence of these biozones: Bispathodus ultimus Zone (Latest Famennian), From the base of Siphonodella duplicata to within Siphonodella crenulata interval (Tournaisian), and Pseudopolygnathos multistriatus Zone (Visean). According to this study, the Fm/T boundary is located at the end of Khoushyeilagh formation, 6m above the diabase layer. The conodonts, as mentioned above, are indicators for Polygnathid biofacies. These sequences are similar to other FamennianTournaisian deposits in the east Alborz, both in the lithofacies and biofacies peculiarities. The conodont Color Alteration Index in the Carboniferous conodonts element increased compared to the Late Devonian elements.ReferencesBahrami A., Corradini C., Jeffrey Over, D., Yazdi, M., 2011. Conodont Biostratigraphy of the Upper FrasnianLower Famennian transitional deposits in the Shotori Range, Tabas area, CentralEast Iran Microplate. Bollettino della Società Paleontologica Italiana, 50: 3553.Bahrami, A., Königshof, P., VaziriMoghaddam, H., Shakeri, B., Boncheva, I., 2019. Conodont stratigraphy and conodont biofacies of the shallowwater KuheBandeAbdolHossein section (SE Anarak, Central Iran), Palaeobiodiversity and Palaeoenvironments, 99: 477–494.Branson, E.R., 1934. Conodonts from the Hannibal Formation of Missouri. Missouri University Studies, 8: 301343.Caplan M.L., Bustin, R.M., 1999. Devonian–Carboniferous Hangenberg mass extinction event, widespread organicrich mudrock, and anoxia: causes and consequences. Palaeogeography, Paleoclimatology, Paleoecology, 148: 187–207.Kaiser, S.I., Steuber, T., Becker, R.T., Joachimski, M.M., 2006. Geochemical evidence for major environmental change at the DevonianCarboniferous boundary in the Carnic Alps and the Rhenish Massif. Palaeogeography, Paleoclimatology, Paleoecology, 240 (1–2): 146–160.Konigshof, P., Bahrami, A., Kaiser, S.I., 2021. DevonianCarboniferous boundary sections in Iran. Palaeobiodiversity and Paleoenvironments, 101: 613632.Mc.Ghee, G.r.J.r., 1996. The Late Devonian Mass Extinction: The FrasnianFamennian Crisis. Columbia University Press, New York, 303 p.Najjarzadeh, M.T., 1998. Biostratigraphy of the Devonian strata on based of Conodonts elements in Zoo section (Eastern Alborz), Iran. Unpublished M.Sc. Thesis, Ferdowsi University of Mashhad, (in Persian).Paproth, E., Feist, R., Flajs, G., 1991. Decision on the DevonianCarboniferous boundary stratotype. Episodes, 14 (4): 331336.Poty, E., Devuyst, F.X., Hance, L., 2006. Upper Devonian and Mississippian foraminiferal and rugose coral zonations of Belgium and northern France: a tool for Eurasian correlations. Geological Magazine, 143 (6): 829857.Sandberg, C.A., Morrow, J.R., Ziegler, W., 2002. Late Devonian sealevel changes, catastrophic events, and mass extinctions. Geological Society of America Special Paper, 356: 473487.Sattari, E., Bahrami, A., Königshof, P., VaziriMoghaddam, H., 2021. Late Devonian (Famennian) to Carboniferous (MississippianPennsylvanian) conodonts from the Anarak section, Central Iran. Palaeobiodiversity and Paleoenvironments, 101: 781802.Sommervile, I.D., 2008. Biostratigraphic zonation and correlation of Mississippian rocks in Western Europe: some case studies in the late Visean/Serpukhovian. Geological Journal, 43: 20940.Spalletta, C., Perri, M.C., Over, D.J., Corradini, C., 2017. Famennian (Upper Devonian) conodont zonation: revised global standard. Bulletin of Geosciences, 92: 3157.Ziegler, W., Sandberg, C.A., 1990. The Late Devonian Standard Conodont Zonation. Courier Forschungs Institut Senckenberg, 121: 1115.