International Journal of Paleobiology & Paleontology ISSN: 2642-1283 MEDWIN PUBLISHERS Committed to Create Value for Researchers Ichnology of the Middle Jurassic Deposits of NE Iran: Depositional Environment Interpretation Mehdi Reza Poursoltani* Research Article Department of Geology, Mashhad Branch, Islamic Azad University, Iran Volume 3 Issue 1 Received Date: October 06, 2020 *Corresponding author: Mehdi Reza Poursoltani, Department of Geology, Mashhad Published Date: November 04, 2020 Branch, Islamic Azad University, Mashhad, Iran, Email: [email protected]; [email protected] Abstract The Kopet Dagh Basin of northeast Iran formed in the Neotethys Ocean after the closure of Paleotethys in the south of Turan plate. A thick sequence of Jurassic to Miocene sediments has been deposited in this basin without any major break. The siliciclastic Kashafrud Formation (Middle Jurassic), overlying unconformably on Triassic rocks and ultrabasic rocks of in some units with different environments. The most important ichnofossils in this formation are Skolithos, Palaeophycus turbidite and fluvio-deltaic facies, consists of sandstone, shale and conglomerate. Trace-fossil assemblages are presented tubularis, Belorhaphe, Taenidium, Planoloites beverleyensis, Thalassinoides suevicus, Conichnus, Psilonichnus, Lophoctenium, Palaeophycus striatus, Rhizocorallium jenense and Scolicia.. It is interpreted, based on identified ichnofossils, the starat may have been deposited in fluvio-deltaic and deep water (turbidity conditions) environment. Keywords: Ichnofossil; Kopet-Dagh Basin; Jurassic; Turbidetic Deposition; Iran Introduction Jurassic and Cretaceous age, respectively The Kashafrud Formation (Figure 2), the focus of this study, comprises The Kopet-Dagh Basin of northeast Iran (Figure 1) formed after northeast Iran collided with the Turan Plate early in the Mesozoic [1]. This successor basin accumulated paleogeographicnearly 2 km of fluvio-deltaicsetting of the and Kashafrud deep-marine Formation siliciclastic in the 7 km of post-Triassic strata [2] after which the strata were easternstrata. The Kopet-Dagh present paperBasin baseddocuments on ichnofossils. for the first time the uplifted and deformed during Cenozoic collisional events along the southern Asian margin [3]. In the eastern part Geological Setting and Stratigraphy of the basin, the major rock units are the Kashafrud and Mozduran Formations sic) and the Shurijeh Formation The Mesozoic geotectonic setting of northeastern Iran is (Cretaceous). The Kashafrud Formation of Middle Jurassic poorly constrained, and alternative explanations are possible age crops out over a large area of the Kopet-Dagh Basin for some events. In general terms, subduction in northeastern of northeast Iran. Poursoltani and Gibling [4] suggested Iran led to Early Cimmerian deformational events during the that the Kashafrud Formation, a Middle Jurassic unit is the Late Triassic to Early Jurassic, during which the Turan Plate source rock for these hydrocarbons. Other formations in the collided with the Cimmerian continental block and Paleo- Kopet-Dagh Basin are important hydrocarbon producers. Tethys closed [2-4,6-11]. In the Mid Jurassic, sedimentation commenced in the Kopet-Dagh Basin on the southern Turan hosted in the Mozduran and Shurijeh formations of Late The Khangiran and Gonbadli gasfields near Sarakhs [5] are Plate [1,3,5,12-14], probably reflecting back-arc extension Ichnology of the Middle Jurassic Deposits of NE Iran: Depositional Environment Interpretation Int J Paleobiol Paleontol 2 International Journal of Paleobiology & Paleontology associated with northward subduction[14,15]. samples and photographs of trace fossils were obtained. The Middle Jurassic clastic deposits of the Kashafrud Ammonites were collected and identified, and outcrop Formation (Late Bajocian to Bathonian) in age, may be Result a consequence of Mid Cimmerian compressional events, evidence from the Turan Plate east of the Caspian Sea Facies Associations The strata are described in terms of 12 facies of during this period [3]. The Kashafrud Formation ranges conglomerate, sandstone, mudstone, and carbonate, which insuggests thickness that from extensional 280 m to 1753faults m,influenced rests unconformably deposition were assigned facies codes commencing with G, S, M, and on Triassic volcanogenic sedimentary rocks of the Sina C, respectively. The Basal Conglomerate Facies Association Formation or nonconformably on ultrabasic intrusive rocks, and disconformably overlain by marine carbonates of the maximum clast size in the boulder range [10]. The overlying Mozduran Formation (Oxfordian to Kimmeridgian) [5]. Sandstoneconsists largely and Mudstoneof fluvio-marine Facies Associationconglomerate consists with largely of interbedded packages of deep-water sandstone Although most fossils are too fragmented for formal and mudstone. The facies are described below with the association in which they predominate. Sandstone and the brachiopod Capillirhynchia, and the ammonites mudstone together form more than 90% of the formation, Parkinsonia,identification, Partschiceras, the presence ofCalliphylloceras, the gastropod Lepidorrochus,and Lytoceras with sand proportions of 24% to 68.5% in individual sections. formation. Indeterminate shell fragments may have been contemporaryconfirm a Late orBajocian reworked to Bathonian from older age bedrock. for the bulk of the Trace Fossils and Paleogeographic Setting some stratigraphic intervals that may have formed under differentTrace-fossil environmental assemblages conditions. have Thebeen most identified important in Palaeophycus tubularis, Belorhaphe, Taenidium, Planoloites beverleyensis,ichofossils identified and Thalassinoides in this formation suevicus. are Thickbedded Skolithos, sandstones yielded Conichnus, Psilonichnus, Lophoctenium, Palaeophycus striatus, and Rhizocorallium jenense and Scolicia (Figure 2). Figure 1: Present location of the Kopet-Dagh Basin relative to plates and major structural lines. CI=Central Iran. HB=Helmand Block. PTS=Paleo-Tethys Suture. NTS=Neo- Tethys Suture. M=Mashhad. Capitalized names indicate major mountain belts. The arrows indicate present-day study area. relative motions. Modified from [10]. Black circle showing Methods The Kashafrud Formation was studied in four stratigraphic sections (Agh-Darband, Kole-Malekabad, top are observed. The sections were measured bed-by-bed, Sefid-Sang, Ghale-Sangi), where the formation’s base and outcrops provide good exposure of conglomerate, sandstone, Figure 2: Kashafrud Formation trace fossils: A) and limestonefacies types but were only identified.limited exposure Vegetation of mudstone. is sparse, Field and Planololites beverlyensis; B) Scolicia; C) Lophoctenium; observations were used to assess the lateral extent and D) Thalassinoides suevicus; E) Palaeophycus striatus; F) thickness variation of sandstone and mudstone packages. Skolithos. Mehdi Reza Poursoltani. Ichnology of the Middle Jurassic Deposits of NE Iran: Copyright© Mehdi Reza Poursoltani. Depositional Environment Interpretation. Int J Paleobiol Paleontol 2020, 3(1): 000115. 3 International Journal of Paleobiology & Paleontology turbidity currents [10]. A broadly similar trace fossil suite evidences, the depositional environment of Kashafrud Based on identified ichnofossils as well as sedimentological turbidite.Although evidence for bioturbation was observed suspensionhas been identified feeders (includingin many other Skolithos) deep-water in minor basins channels [7-9, Formation has been interpreted as fluvio-deltaic and and15]. sandyBuatois plains and Lopezdistant Angriman from deep-water [12] identified channels, a suite with of a the upper part of the formation. suite of deposit feeders in muddy substrates. Within slope at many levels, more identifiable occurrences were noted in Discussion and Conclusion ichnofacies in thick-bedded sandstones, attributed to lobes orminibasins, channel-termination Shultz and Hubbard sheet complexes. [16] identified Consistent the Skolithos with the The Kashafrud ichnotaxa are largely traces made by observations of Crimes [13] and Shultz and Hubbard [16], deposit feeders, with a few formed by suspension feeders. many of the Kashafrud ichnofossil assemblages are probably turbidity currents, that traversed submarine channels and food to deep-water settings. The apparent upward increase laidThe sandstonesdown sand wereon levees, deposited lobes from and density distal overbank flows, including areas. inrelated trace tofossil sediment occurrences gravity may flows record that a broughtgreater frequency oxygen and of Separating the sandstone sheets are mudstone units tens to to shallowing of the basin. According to Kashafrud Formation hundredsRare boulder of metres beds are thick. attributed They are to submarinemainly grey-green debris flows. with ichnofossils,energetic sediment it was gravitydeposited flows in witha large, time, rapidly possibly subsiding linked some darker beds, and contain plant fragments, ammonites, intracontinental basin, intertidal to shoreface, offshore and belemnites, brachiopods and gastropods. They are interpreted deeper water (Figure 3) [17]. as the deposits of hemipelagic settling and low-concentration Figure 3: Identified ichnofossil assemblages of Kashafrud Formation, based on depth formation. Acknowledgment Cretaceous (Neocomian) sandstones, eastern Kopet Dagh Basin, northeastern Iran. American Association of The author thanks the Islamic Azad University, Mashad Petroleum Geologists