©Filodiritto Editore – Proceedings Interregional Correlation of the Base of the Serpukhovian Stage (Mississippian): Problems and Prospects NIKOLAEVA Svetlana1,2,3, ALEKSEEV Alexander2,4, KULAGINA Elena5, GATOVSKY Yury4, PONOMAREVA Galina6, GIBSHMAN Nilyufer2 1 Kazan Federal University, Kazan, (RUSSIA) 2 Borissiak Paleontological Institute, Russian Academy of Sciences, Moscow, (RUSSIA) 3 Natural History Museum, London, (UK) 4 Lomonosov Moscow State University, Moscow, (RUSSIA) 5 Ufa Federal Research Centre, Russian Academy of Sciences, Ufa, (RUSSIA) 6 Perm State University, Perm, (RUSSIA) Email: [email protected] DOI: 10.26352/D924F5031 Abstract A review of the proposed markers for the base of the Serpukhovian has shown that their entries are not consistent in different sections, especially when they are not controlled by other fossil groups. The diagnosis and interspecific relations in the genus Lochriea of the conodont species L. ziegleri, the primary candidate marker, needs to be reassessed and it needs to be decided which morphotype is the best marker. The first occurrence levels of the marker foraminiferal species, especially J. delicata and N. postrugosus, need to be agreed, and the taxa from the critical levels need to be illustrated before a decision can be made on the boundary choice. Keywords: Viséan-Serpukhovian boundary, GSSP, ammonoids, conodonts, foraminifers Introduction The base of the Serpukhovian Stage is one of the high priority tasks of the Subcommission on Carboniferous Stratigraphy (SCCS). In the type Serpukhovian Region in the Moscow Basin this boundary has traditionally been drawn at the base of the Tarusian Regional Substage [1] at the regional subaerial unconformity surface [2], [3]. The basal beds of the Tarusian contain ammonoids of the genus Cravenoceras and the base of the Tarusian is traditionally correlated with the base of the Pendleian (E1) of Great Britain and with the base of the Lower Namurian of Belgium and Germany [4]. However, this lithological boundary cannot be accepted as an International Standard, such as a GSSP. Therefore, for substantiation and correlation of this boundary outside the type region, it is necessary to recognize marker taxa and select a new section, in which the first appearance datum (FAD) of a proposed boundary marker would be able to be traced in a continuous phylogenetic lineage. Several markers have been proposed, including conodonts, foraminifers, and ammonoids, but there are only few sections that are known to contain all three groups [5]. The following problems currently prevent the definition of the base of the Serpukhovian. 1. Some of the proposed taxa (e.g., the conodont Lochriea ziegleri Nemirovskaya, Perret and Meischner) appear below the traditional base of the Serpukhovian. 2. The appearance of some indicative taxa does not seem to be isochronous. For example, the foraminifer Janischewskina delicata (Malakhova, 1956), Neoarchaediscus postrugosus (Reitlinger, 1949), etc. have been reported from the “Brigantian” (i.e., 183 ©Filodiritto Editore – Proceedings uppermost Viséan) of Western Europe, although they appear in the Tarusian of the type area. 3. Ammonoids that have originally been used to mark the base of the Pendleian in the UK and the Lower Namurian in Germany are not found outside Western Europe. The ammonoid species Cravenoceras leion, which was originally thought to be the boundary marker, is not found outside the type area in the British Isles, and the species Edmooroceras pseudocoronula (Bisat, 1950) is only found in Germany, northern England, and Ireland. 4. The taxonomic concept of the major candidate, the conodont species Lochriea ziegleri, is not developed, and this species is not confirmed from North America. 5. Deep-water and shallow-water successions of the boundary interval cannot currently be reliably correlated. Below we will discuss these problems in greater detail and outline possible prospects for defining the boundary in the near future. Problems in Identifying the Base of the Serpukhovian (1) In the type Serpukhovian areas, in the Novogurovsky Quarry, the FOD (First Occurrence Datum) of L. ziegleri is established in the shallow-water limestones of the upper half of the Venevian (middle part of sequence VN2, Unit 23) [3]. However, the specimens of L. ziegleri from VN2 are derived, so the FAD (First Appearance Datum) of this species should be expected lower in the section [5]. It is clear that the first occurrence of L. ziegleri is below the base of the type Serpukhovian and its equivalents [6], and a decision should be made whether lowering the base of the Serpukhovian is an appropriate measure, or whether a marker should be sought among other taxa appearing nearer to the traditional boundary. Because of the traditional correlation of the basal Tarusian with the basal Namurian, Pendleian, and Kosogorian, this decision has to take into account changes that might affect regional scales in Belgium, UK and other areas, which will lead to objections by some authors [7]. In the Dombar Section in the Mugodzhary Region of the South Urals, the entry of L. ziegleri was recorded within the Hypergoniatites- Ferganoceras Genozone, the topmost in the Upper Viséan succession of the South Urals [8]. Similar results were obtained in the Verkhnyaya Kardailovka Section on the eastern slope of the South Urals where L. ziegleri first appears in the interval 19.53-19.63 m (L. cruciformis appears in the interval 19.63-19.72) from the base of the section, which is below the entry of Ferganoceras constrictum Nikolaeva and Konovalova, 2017 at 20.8 m from the base of the section [9], [10]. In the Wenne Section (Rhenish Massif, Germany) the FOD of L. ziegleri was reported from the Upper Viséan Lyrogoniatites suerlandense Zone [11], but this morphotype does not belong to this species [12]. It is more difficult to correlate the entry of L. ziegleri with foraminiferal markers because both are facies dependent, and in basinal sections indicative foraminifers are scarce or absent. (2) Among foraminifers, several species have been proposed as possible markers, the main candidates were Janischewskina delicata, Endothyranopsis plana Brazhnikova in Brazhnikova et al., 1967, Planoendothyra ex gr. aljutovica (Reitlinger, 1950), Eostaffellina decurta (Rauser- Chernousova, 1948), Neoarchaediscus postrugosus, Eolasiodiscus donbassicus Reitlinger, 1956, Monotaxinoides gracilis (Dain in Reitlinger, 1956) [13], [14], [15]. The FADs of these taxa do not seem to be consistent. For instance, Janischewskina delicata, Plectomillerella tortula (Zeller, 1953), Planoendothyra sp., and Endothyra phrissa (Zeller, 1953), were reported ca. 6 m above the base of the Venevian (middle of sequence VN2, Unit 23) [3], but this still needs to be confirmed, because in Zaborie (Moscow Basin) it is recorded from the Tarusian and in the Khudolaz Section from the Sunturian (see references in [5]). Vdovenko in [1] cited 184 ©Filodiritto Editore – Proceedings Janischewskina sp., Janischewskina ex gr. typica, Janischewskina ex gr. rovnensis (Ganelina, 1956) from the Moscow Basin. However, their distribution was not clearly shown. J. typica was illustrated ([1], pl. XVII, Fig. 3) from Sample G-15-16, which according to [1], p. 78, text- fig. 35, is approximately in the middle of the Tarusian in the Gurievsky Quarry, Tula Region, Moscow Basin. No J. delicata was illustrated. Gibshman et al., [2] illustrated J. delicata in pl. 5, Figs. 17 and 18 (Sample 14/40, Bed 25, Lower Tarusian); and J. typica in pl. 5, Fig. 13 (Sample 14/40, Bed 25). In the same publication J. delicata is shown in text-fig. 4 to occur in the middle of Bed 23, Sample 13/40, in the upper part of Bed 23, Sample 13/42, in the middle of Bed 24, Sample 13/43 (all Venevian), then near the base of Bed 25, Sample 14/40, middle of Bed 25, Sample 14/41, upper part of Bed 25, Sample 14/42, all Tarusian, and then in the Protvian. However, the description of the succession in the Novogurovsky Quarry mentions ([2], p. 22) the presence of J. cf. delicata in Beds 23 and 24, and J. cf. typica and J. delicata are reported from Bed 25. These discrepancies need to be clarified. Neoarchaediscus postrugosus in the Moscow Basin and Izyayu River (Subpolar Urals) enters in the basal Serpukhovian (i.e., in the Tarusian) [5], [16]. However, it has been reported from the Brigantian and its equivalents in British Isles and Morocco [17], [18] and Spain [19], [20]. In the Ladeinaya Gora Section in the Middle Urals, where Lochriea ziegleri is recorded in Bed 17, Neoarchaediscus postrugosus appears 1.5 m below it, at the base of Bed 17, Sample 17.3; and in the Mariinsky Log Section Neoarchaediscus postrugosus enters at the level of Sample 3c.3 in Unit 3b, 3 m above the FOD of L. ziegleri [21], [22]. Monotaxinoides gracilis is recorded in many regions and it is more or less associated with the Serpukhovian, appearing somewhat above the entry of L. ziegleri (Canalón Member of the Alba Formation, basal unit in the Vegas de Sotres Section, Cantabrian Mountains, Spain) above the level of the first appearance of L. ziegleri [19]. In the South Urals, in the Suleimanovo Section, it is also found ca. 4 m above the base of the Serpukhovian, probably in the equivalents of the Steshevian (the base of the stage is drawn by the appearance of Eostaffellina decurta [23]). In the Muradymovo Section, also South Urals, M. gracilis is found in the Yuldybaevian Regional Substage [24]. Summaries of the proposed foraminiferal markers published by [5], [25] and [41] showed considerable discrepancies in their FODs. It has been proposed to use two zonal foraminiferal schemes for the inner and outer shelf [25]. The summaries have suggested that the taxonomy of the key taxa and their detailed records need to be re-examined and published in greater detail. (3) The base of the Serpukhovian in the British Isles was traditionally considered to be close to the base of the Pendleian Stage.