A new species of the conodont genus Siphonodella Branson & Mehl (late Tournaisian).
Traditionally species of the genus Siphonodella are used for biostratigraphy of the lower part of the Tournaisian (Sandberg et al. 1978; Ji 1985; Ji & Ziegler 1992; Kaiser et al. 2009; Kaiser & Corradini 2011; Corradini et al. 2017). The FAD of Siphonodella sulcata marks the boundary of the Devonian and Carboniferous (Paproth et al. 1991).
A number of siphonodellids that dwelt in shallow-water facies are known in Eastern Europe, including Siphonodella bella Kononova & Migdisova, S. quasinuda Gagiev, Kononova & Pazuhin, S. semichatovae Kononova & Lipnjagov and S. ludmilae Zhuravlev & Plotitsyn. The specific morphology of these species, differing from that of the other species of the genus, consists of a poorly ornamented platform in association with a wide depressed keel and S-like bowed carina. Another group of shallow-water siphonodellids is known from China only. These endemic species, including Siphonodella simplex Ji, S. levis (Ni), S. sinensis Ji, S. homosimplex Ji & Ziegler, S. dasaibaensis Ji, Qin & Zhao and S. eurylobata Ji, were considered in detail by Ji (1985) and Ji & Ziegler (1992). Although evidently forming a separate lineage, Chinese siphonodellids share some features with the European shallow-water siphonodellids. All these species have a poor ornamentation of the platform and a wide pseudokeel or depressed keel at the aboral side of Pa elements.
The shallow-water siphonodellids of the Chinese branch appeared in the earliest Tournaisian and ranged up to the late Tournaisian (Ji & Ziegler 1992). The species of the European branch have been known from the latest Famennian through the early Tournaisian (Ji & Ziegler 1992; Zhuravlev et al. 1998, 1999). New data obtained from the shallow-water succession of the Pechora Swell (Timan-Pechora region or NE of European Russia) expand the information about the ranges and speciation of shallow-water siphonodellids.
MATERIAL AND METHODS
The Lower Carboniferous (Upper Tournaisian) conodont elements were collected from a section located in the Pechora region (North Russia, Pechora Swell, N 65[degrees]4'21", E 56[degrees]43'13"), where the host rocks represent the Idzhid Formation (Figs 1, 2). All the species of shallow-water siphonodellids of the European branch are known form this area (Zhuravlev et al. 1998, 1999). The upper part of the succession, cropping out at the right bank of the Kamenka River, was studied in detail in 1996 and 2016. This part of the section is represented by the alternation of bioclastic wacke- and packstones rich in conodonts. This study is based on 16 samples collected from the upper part of the Idzhid Formation (Fig. 2).
The morphology of the conodont elements was studied with SEM (VEGA3 TESCAN of the Institute of Geology Komi SC UrB RAS, Syktyvkar, Russia), X-ray micro CT (SkyScan 1272 of St. Petersburg Mining University, St. Petersburg, Russia) and optical microscopy. The morphological terminology of Sandberg et al. (1978) and Ji & Ziegler (1992), and the traditional conodont element notation introduced by Sweet & Schonlaub (1975) are used. All the figured specimens are stored in the A. A. Chernov Museum of the Institute of Geology Komi SC UrB RAS, Syktyvkar, collection No. 517 (Fig. 3).
The conodont association of the studied section consists of Polygnathus parapetus Druce (dominates), P. paprothae Bouckaert & Groessens, P. longiposticus Branson & Mehl, P. communis communis Branson & Mehl, Bispathodus stabilis (Branson & Mehl) Morphotype 1, Hindeodus crassidentatus (Branson & Mehl), Hindeodus cristulus (Youngquist & Miller) (Fig. 3G), Patrognathus andersoni Klapper, Patrognathus variabilis Rhodes, Austin & Druce, Pseudopolygnathus nodomarginatus (Branson), Ligonodina discreta (Austin & Husri), Siphonodella bella Kononova & Migdisova, S. quasinuda Gagiev, Kononova & Pazuhin (Fig. 3F), S. ludmilae Zhuravlev & Plotitsyn (Fig. 3L) and Siphonodella carinata n. sp. (Fig. 3A-E, H-K). The co-occurrence of Hindeodus cristulus (Youngquist & Miller), Bispathodus stabilis (Branson & Mehl) Morphotype 1, Polygnathus longiposticus Branson & Mehl and Pseudopolygnathus nodomarginatus (Branson) suggests the late Tournaisian (Lower Siphonodella crenulata Zone) age of the deposits (Fig. 2).
Thus, according to the data obtained, the shallow-water siphonodellids of the European branch, including Siphonodella bella Kononova & Migdisova, S. quasinuda Gagiev, Kononova & Pazuhin, S. ludmilae Zhuravlev & Plotitsyn and Siphonodella carinata n. sp., range into the upper Tournaisian Lower Siphonodella crenulata Zone. Earlier Siphonodella bella and S. quasinuda were considered as characteristic of the lower part of the Tournaisian (Siphonodella sulcata--S. sandbergi zones) only (Ji & Ziegler 1992).
Siphonodella carinata n. sp. Figure 3A-E, H-K
Holotype. Dextral Pa element, specimen 517/8, sample 122-5/16, Fig. 3J.
Type horizon. The upper part of the Idzhid Formation, Lower crenulata conodont Zone, Upper Tournaisian, Lower Carboniferous.
Type locality. The Kamenka River section, Pechora Swell, North Russia.
Derivation of name. From Latin carina--ridge.
Diagnosis. Pa-elements with spoon-like strongly asymmetrical platform, ornamented by wide fan-like transverse coarse costae in outer side and by wide short costae or nodes in inner side. Rostrum composed of up to three short ridges converging slightly or being parallel to carina. Depressed keel (sensu Sandberg et al. 1978) is present.
Material. 5 dextral and 7 sinistral Pa elements.
Description. Pa-elements have a spoon-like strongly asymmetrical platform, which is ornamented by wide fan-like transverse coarse costae in the outer side and by wide short costae or nodes in the inner side. The outer part of the platform is much wider than the inner one. The rostrum is composed of three (at the late stages of ontogeny) short ridges that converge slightly or are parallel to the carina. The third rostral ridge appears in ontogeny on the outer side in the sinistral element (Fig. 3E), but on the inner side in the dextral element (Fig. 3J). Thus the species is characterized by the asymmetrical rostral structure corresponding to Class III symmetry of Lane (1968).
A low pseudokeel is located in the anterior part of the platform on its aboral side, however, the keel is depressed in the middle and posterior parts (Fig. 3D). In some cases the keel does not reach the posterior end of the platform. A small basal pit with lens-like flanks is situated in the anterior third of the platform (Fig. 3D).
Remarks. Siphonodella carinata differs from S. semichatovae and S. ludmilae in the asymmetry between the dextral and sinistral elements, Class III symmetry of Lane (1968). Each element has three rostral ridges at the late stages of ontogeny. The new species differs from S. dasaibaensis Ji, Qin & Zhao and S. levis (Ni) in having a prominent platform ornamentation represented by coarse transverse costae.
Stratigraphic distribution. Lower Siphonodella crenulata Zone, upper Tournaisian, Lower Carboniferous.
Siphonodella carinata n. sp. is the first late Tournaisian shallow-water European siphonodellid species possessing three rostral ridges. This species probably evolved from Siphonodella ludmilae by the development of an additional rostral ridge on the left side of both the sinistral and dextral Pa elements, and by the change of the symmetry class from II to III. A similar morphological sequence is observed in the deep-water siphonodellids in the S. duplicata--S. quadruplicata lineage (Zhuravlev & Plotitsyn in press).
According to the data obtained, the stratigraphical ranges of S. bella, S. quasinuda and S. ludmilae comprise the lower part of the Lower Siphonodella crenulata Zone (upper Tournaisian) as well, but the FAD of S. carinata corresponds approximately to the base of the zone in the shallow-water facies. The FAD of S. carinata is close to the FAD of Hindeodus cristulus and can be used as a marker of the base of the upper Tournaisian in the shallow-water facies.
Acknowledgements. The referees P. Mannik and C. Corradini are thanked for constructive reviews of the manuscript. The publication costs of this article were covered by the Estonian Academy of Sciences.
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Andrey V. Zhuravlev
Institute of Geology Komi SC, UrB RAS, Pervomayskaya 54, 167000 Syktyvkar, Russia; email@example.com
Received 3 April 2017, accepted 6 June 2017, available online 16 October 2017
[c] 2017 Author. This is an Open Access article distributed under the terms and conditions of the Creative Commons Attribution 4.0 International Licence (http://creativecommons.org/licenses/by/4.0).
Uus liik konodondiperekonnas Siphonodella Branson & Mehl (Hilis-Tournai)
Andrey V. Zhuravlev
On kirjeldatud siphonodelliid Siphonodella carinata n. sp., uus Ulem-Tournai (Alam-Karbon) konodont. Uuritud kollektsioon parineb madalveelist tuupi lubjakividest Petsoora kerkealalt Timaani-Petsoora regioonist Euroopa Venemaa kirdeosast. Koos kirjeldatud uue liigiga leitud konodondid Hindeodus cristulus (Youngquist & Miller), Bispathodus stabilis (Branson & Mehl), Polygnathus longiposticus Branson & Mehl ja Pseudopolygnathus nodomarginatus (Branson) naitavad, et tegemist on Hilis-Tournai vanusega kihtidega (vastavad Alumisele Siphonodella crenulata Tsoonile). Morfoloogiliselt on uue liigi Pa-element lahedane konodontide Siphonodella semichatovae Kononova & Lipnjagov ja S.ludmilae Zhuravlev & Plotitsyn Pa-elementidele, kuid erineb viimastest skulptuurilt: ontogeneesi hilises staadiumis kujuneb elemendi rostrumile kolmest ribist koosnev ornament. Ka iseloomustab S. carinata n. sp. Pa-elementi kolmandat tuupi (Class III) summeetria. Esmakordselt tehti Tournai ulemises osas kindlaks madalveeliste siphonodelliidide Siphonodella bella Kononova & Migdisova ja S. quasinuda Gagiev, Kononova & Pazuhin esinemine.
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|Author:||Zhuravlev, Andrey V.|
|Publication:||Estonian Journal of Earth Sciences|
|Date:||Dec 1, 2017|
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