Ammonites and Stratigraphy of the Upper Bajocian Garantiana Garantiana Zone in the Interfluve Between the Kuban and Urup Rivers (Northern Caucasus) V
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ISSN 0031-0301, Paleontological Journal, 2019, Vol. 53, No. 11, pp. 1188–1202. © Pleiades Publishing, Ltd., 2019. Ammonites and Stratigraphy of the Upper Bajocian Garantiana garantiana Zone in the Interfluve between the Kuban and Urup Rivers (Northern Caucasus) V. V. Mittaa, b, * aBorissiak Paleontological Institute, Russian Academy of Sciences, Moscow, 117647 Russia bCherepovets State University, Cherepovets, 162600 Russia *e-mail: [email protected] Received March 12, 2019; revised March 29, 2019; accepted April 1, 2019 Abstract—This paper presents the results of the study of the Upper Bajocian Garantiana garantiana Zone (Middle Jurassic) and characteristic ammonites in sections of the basin of the Kuban River (Karachay-Cher- kessia). The assemblage contains species of the genera Garantiana, Pseudogarantiana, Paragarantiana, Djanaliparkinsonia (all family Stephanoceratidae) and Vermisphinctes (family Perisphinctidae). A section of the Garantiana Zone on the Kyafar River contains (from bottom to top) Beds with Djanaliparkinsonia alanica (also recognized on the Kuban River), Beds with Garantiana subgaranti and Beds with Paragarantiana, approximately corresponding to the Dichotoma, Garantiana, and Tetragona subzones of the standard scale. Garantiana subgaranti Wetzel and Vermisphinctes martiusii (d’Orbigny) are described. Prorsisphinctes Buck- man, 1921 is proposed as a junior subjective synonym of Vermisphinctes Buckman, 1920. Keywords: Upper Bajocian, ammonites, Garantiana, Paragarantiana, Djanaliparkinsonia, Vermisphinctes, biostratigraphy, Northern Caucasus DOI: 10.1134/S0031030119110066 INTRODUCTION lished records of representatives of Garantianinae in the Garantiana Zone in the Northern Caucasus The Garantiana garantiana Zone is located (Ob”yasnitelnaya…, 1973; Yura…, 1992) are not sup- between the Upper Bajocian Strenoceras niortense and ported by figures or collections, and are mostly based Parkinsonia parkinsoni zones of the standard scale and on field identifications. Thus, the Garantiana Zone in is subdivided into three subzones: Pseudogarantiana the Northern Caucasus is one of the least studied dichotoma, Garantiana garantiana [=Garantiana sub- Upper Bajocian intervals, and the same applies to its garanti, by some authors] and Garantiana tetragona. In ammonites. New data on the ammonites and stratig- Western Europe, especially in Germany, France, and raphy of the Garantiana Zone of the basin of the England, the Garantiana Zone is characterized by a Kuban River are presented below. high taxonomic diversity of ammonites. Ammonites of the subfamily Garantianinae, family Stephanocer- atidae are key elements for identification and infra- MATERIAL zonal subdivision of this zone. Representatives of Peri- The paper is based on material collected by the sphinctidae, Lissoceratidae, Oppeliidae, and some author during field studies in the Zelenchuk and Ust- other families are of secondary importance. Dzheguta districts of the Karachay-Cherkessia In the Northern Caucasus, the subfamily Garan- Republic in 2014–2018. The figured specimens are tianinae appears in the Niortense Zone where it is rep- housed in the Borissiak Paleontological Institute resented by diverse species of the genera Baculatoceras (PIN), coll. no. 5546. [M], Orthogarantiana [M], Strenoceras [m], and Kep- pleritiana [M, m]). Up the section, in the Garantiana Zone, occurrences of Garantianinae are extremely DESCRIPTIONS OF SECTIONS rare in this region. Until recently, only one finding was In the Kuban–Urup interfluve, the Upper Bajo- published, from the upper subformation of the Dzhor cian is represented by terrigenous, mainly argillaceous Formation of the Khodskiy Mountain Pass (North rocks, with numerous interbeds of concretions of var- Ossetia), identified as Hlawiceras aff. subgaranti (Wet- ious shapes and compositions, and less commonly, by zel) (Besnosov and Mitta, 1993; 1998). Other pub- large lenses of siltstone and interbeds of argillaceous 1188 AMMONITES AND STRATIGRAPHY OF THE UPPER BAJOCIAN 1189 50 km N SEA OF AZOV Udobnaya Kuban Krasnodar Stavropol Novorossiisk Belaya Laba Kuban Urup Malyi Zelenchuk Kuban Bolshoi Zelenchuk BLACK SEA Ispravnaya Ust-Dzheguta Sochi (a) 44 00 II 19 1751 Pregradnaya 5(10) 1560 Krasnogorskaya Kyafar Djangura Urup Storozhevaya Zelenchukskaya Mountain Urup Kardonikskaya Malyi Zelenchuk Dausuz Urup Bizhgon Aksaut Karachayevsk 2130 Marukha Kardonik Kyafar 0 5 10 km Kuban Bolshoi Zelenchuk (b) 43 40 41 00 41 30 E42 00 Fig. 1. Schematic map showing the sections studied in the Upper Bajocian Garantiana garantiana Zone in the interfluve between the Kuban and Urup rivers: (a) general and (b) detailed. limestone. These deposits belong to the lower part of and casts of underwater desiccation cracks (Fig. 3b). the upper subformation of Djangura Formation, This interbed, subdividing the section into two almost which is in general dated Bajocian–Lower Bathonian equal parts, appears to represent a short-term discon- (Besnosov, 1967). One of the most complete Upper tinuity of deposition. Apart from riverbank outcrops, Bajocian sections, in some intervals is relatively well the Garantiana Zone was sometimes observed in the characterized by ammonites, is currently exposed on episodically drying temporary channel of the Kyafar the banks of the Kyafar River (right tributary of the (locality 36a: Fig. 4), which allowed extensive collec- Bolshoi Zelenchuk River) in the Zelenchuk District of tion owing to a large surface of natural exposure. Karachay-Cherkessia. The siltstone concretions across the entire section Outcrops of the Garantiana Zone are on the right of the Garantiana Zone have a particular shape. They bank of the Kyafar downstream of the Storozhevaya are mostly flat discoid, reaching 10–15 cm in diame- (Fig. 1). The steep river gorge shows a member of ter, and are almost devoid of fossils. The lower half of dark-gray argillite-like clay for a distance of 450 m, the section (Bed 1), unlike its upper part, large (up to with scattered gray (on the surface yellowish-brown) 0.4 m in diameter) contains infrequent nodules of dark siltstone concretions, forming numerous layers (local- gray hard limestone, often with remnants of bivalve ities 5, 10, 36) (Figs. 2, 3). The middle part of the shells and small-sized ammonites usually identifiable member contains a thin (10–20 cm) layer of argilla- only to genus. The total thickness of the Garantiana ceous limestone concretions (Fig. 3a) with a distinct Zone on the Kyafar River, taking into account the dip cone-syneresis texture (combination of cone-in-cones of the beds (5° to NNE) reaches 50 m. PALEONTOLOGICAL JOURNAL Vol. 53 No. 11 2019 1190 MITTA m Lithology Ammonites Bed Substage Chronozone Beds with fauna 45 Paragarantiana with sp. [M] 40 2 sp. [M] [m] Paragarantiana [M] 35 Garantiana [M] [M, m] Garantiana subgaranti Garantiana 30 with Pseudogarantiana minima Pseudogarantiana Garantiana subgaranti subgaranti Garantiana ? sp. 25 martiusii Vermisphinctes Djanaliparkinsonia alanica Garantiana Garantiana Upper BajocianUpper Garantiana garantiana Garantiana 20 1 15 10 Djanaliparkinsonia alanica 1 with 2 5 3 4 Fig. 2. Section of the Garantiana garantiana Zone on the Kyafar River. Explanations: (1) clay argillite-like, (2) siltstone concre- tions, (3) limestone with cone-in-cone-syneresis, (4) large limestone concretion. PALEONTOLOGICAL JOURNAL Vol. 53 No. 11 2019 AMMONITES AND STRATIGRAPHY OF THE UPPER BAJOCIAN 1191 (b) (a) Fig. 3. Exposure of the Garantiana garantiana Zone, Kyafar River, (a) middle part of outcrops with an interbed of argillaceous limestone with texture of cone-in-cone and syneresis cracks (indicated by arrows) and (b) a fragment of a surface with syneresis texture, washed by the river. Bed 1 contains frequent Djanaliparkinsonia, Vermi- In the adjacent Ust-Dzheguta District on the left sphinctes, and small incomplete shells, apparently of bank of the Kuban River downstream of the village of the genus Garantiana; Bed 2 contains fewer fossils; Krasnogorskaya, there is another outcrop of the representatives of Garantiana, Pseudogarantiana, Garantiana Zone (locality 19). Here, the towpath at Paragarantiana have been collected here. low water (from October to April) exposes argillite- like clay, similar to Kyafar clay, with layers of concre- Clays of the Garantiana Zone in the valley of the tions (Fig. 5a), and large lenses of siltstone in the basal Kyafar River are overlain (with an interruption in part. The basal 2–2.5 m of clay yielded Djanaliparkin- observation) by a member of dark-gray argillites with sonia and Vermisphinctes. These beds are basal for the rare interbeds of argillaceous limestone and numerous Garantiana Zone, overlying the sandstones with sideritic concretions, both scattered, and forming lay- numerous Zoophycos (Fig. 5b); based on the occur- ers. Besides numerous Rarecostites spp., the beds con- rence of Baculatoceras sp. these sandstones belong to tains occasional Spiroceras obliquecostatum (Quenst- the Niortense Zone. edt), Patrulia karachaica Mitta (Mitta, 2017a, 2017b; Mitta and Sherstyukov, 2018; Mitta et al., 2018). The argillite member belongs to the lower part of the Par- kinsoni Zone, Rarecostites subarietis Subzone. AMMONITES, THEIR TAXONOMIC COMPOSITION Clays of the Garantiana Zone are underlain (also AND DISTRIBUTION IN THE SECTION an interrupted observation) by a series of dark gray arenaceous clay, with interbeds of siltstone and car- As mentioned above, until recently ammonites of bonate concretions. The upper part of this series con- the Garantiana