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United Kingdom - Russia scientific workshop ""T
«What does the Devonian of the Arctic tell us
УДК 551.734.5/735.1(470.13) DOI: 10.19110/2221-1381-2019-10-16-22
DEVONIAN-CARBONIFEROUS BOUNDARY IN THE EAST OF THE PECHORA PLATE (KAMENKA RIVER AND VANGYR RIVER SECTIONS)
A. V. Zhuravlev, D. B. Sobolev
Institute of Geology FRC Komi SC UB RAS, Syktyvkar; [email protected]
The representative sections outcropping shallow-water and deep-water Devonian/Carboniferous successions in the East of Pechora Plate (Kamenka River section and Vangyr River section) are considered in respect of facies, conodont, and ostracode changes. In the Kamenka River section the D/C boundary beds are composed of bioclastic limestones interbedded with dark-gray clays (lower part of the Edzhid Fm.). The deposits contain abundant and diverse benthic ostracodes of Pseudoleperditia tuberculifera — Coryellina alba — Cribroconcha primaris ostracode Zone, and diverse conodont associations of praesulcata and sulcata zones. The negative shifts in S13Corg in conodont organic matter accompanied by weak positive shift in S13Ccarb in bulk carbonates suggest eutrophic conditions in the lagoon environment and disbalancing of the trophic web at the terminal Famennian. D/C boundary beds in the Vangyr River section are represented by calciturbidites, pelagic carbonates, and shales (Izyayu Fm.). Transgressive phase of Hangenberg Event is marked by the black shale layers. The Upper Famennian conodont associations are dominated by Palmatolepis gracilis group; the ostracodes compose diverse associations of Turingian and slope ecotypes. The D/C boundary is marked by appearance of conodonts Siphonodella sulcata in associations with ostracodes Armilla uralica.
Keywords: Devonian-Carboniferous boundary, conodonts, ostracodes, biostratigraphy, Hangenberg Event, Pechora Plate.
ГРАНИЦА ДЕВОНА И КАРБОНА НА ВОСТОКЕ ПЕЧОРСКОЙ ПЛИТЫ (РАЗРЕЗЫ НА Р. КАМЕНКЕ И Р. ВАНГЫР)
А. В. Журавлев, Д. Б. Соболев
Институт геологии ФИЦ Коми НЦ УрО РАН, Сыктывкар
Представительные разрезы, вскрывающие мелководные и глубоководные девонско-каменноугольные отложения на востоке Печорской плиты (р. Каменка и р. Вангыр), рассматриваются в отношении изменений фаций, конодонтов и остракод. В разрезе на р. Каменке пограничные отложения девона и карбона представлены биокластическими известняками, переслаивающимися с темно-серыми глинами (нижняя часть ыджидской свиты). Отложения содержат многочисленные и разнообразные бентосные остракоды зоны Pseudoleperditia tuberculifera — Coryellina alba — Cribroconcha primaris, а также разнообразные конодонтовые ассоциации зон praesulcata и sulcata. Отрицательные сдвиги в S13Corg в органическом веществе конодонтов, сопровождающиеся слабым положительным сдвигом в S13Ccarb в карбонатах, указывают на эвтрофные лагунные условия и дисбаланс трофической сети в терминальном фамене. Пограничные слои в разрезе на р. Вангыр представлены кальцитурбидитами, пелагическими карбонатами и аргиллитами (изъяюская свита). Трансгрессивная фаза события Hangenberg маркируется прослоями «черных сланцев». В верхнефаменских ассоциациях конодонтов преобладает группа Palmatolepis gracilis; остракоды представлены разнообразными ассоциациями тюрингского и склонового экотипов. Граница девона и карбона отмечена появлением конодонтов Siphonodella sulcata в ассоциации с остракодами Armilla uralica.
Ключевые слова: граница девона и карбона, конодонты, остракоды, биостратиграфия, Хангенбергское событие, Печорская плита.
Introduction
Devonian-Carboniferous boundary interval corresponds to the dramatic extinction event in the middle Palaeozoic. The latest Famennian Hangenberg Event, associated with the global transgressive-regressive couplets, corresponds to Siphonodella praesulcata conodont Zone [1]. The event led to the
well-known mass extinction among most marine organisms [10]. The traces of the Hangenberg Event, elucidating D/C boundary beds, are detected globally, but described in details mainly in the tropical realm in southern hemisphere (e. g. [1]). The Pechora Plate corresponded to low-latitude realm of the Northern Hemisphere in the terminal Famennian-earliest Tournaisian time [8].
The key objective of this study is to evaluate conodont and ostracode changes in the D/C boundary interval in shallow-water and slope facies in the Pechora Plate in respect to Hangenberg event.
Material
About 14 sections cropping out the Devonian-Carboniferous boundary beds are known in the North of Urals and Pechora Plate regions [7]. The representative sections demonstrating shallow-water and deep-water successions in the regions are the Kamenka River section (the eastern part of the Pechora Plate) and the Vangyr River section (Chernyshev Uplift, Subpolar Cis-Uralian) (Fig. 1). The Kamenka River section is located at the town of Pechora area, in the southern part of the Pechora-Kozhva Uplift (N 65°04'227.4", E 56°42'50.9"). The Vangyr River section is located in the southern part of the Chernyshev Uplift (N 65° 7'33.05", E 58°43'2L25"). These sections demonstrate uninterrupted D/C boundary sequences without gaps and disconformities.
Methods
Conodonts and ostracodes were studied in the Devonian-Carboniferous boundary beds in the Kamenka River and Vangyr River sections. The processing of conodont and ostracode samples followed the standard procedure: dissolution of limestone in 10 % buffered acetic acid. Some ostracode samples were processed by hot acetolysis technique to disaggregate the dehydrated limestones and release the ostracod shells [5]. The residues were washed through a sieve of 70 |im, dried, and microfossils were picked out.
The microfauna were photographed using a scanning electron microscope Tescan Vega 3 LMH. Stereo pair of ostracode picture was made with a 5° inclination.
Carbon isotope values were analyzed with the DELTA V Advantage mass spectrometer equipped with the Thermo Electron Continuous Flow Interface (ConFlo III) and Element Analyzer (Flash EA 1112). The 813C values are reported relative to the PDB standard. The analytical reproducibility (1a) for S13Ccarb value is ±0.04 %0, and for S13Corg value is ±0.15 %0.
Isotope analyzes were performed at the CKP Geonauka of the Institute of Geology Komi SC UB RAS (Syktyvkar, Russia).
Results and discussion
The Devonian-Carboniferous transition in the Kamenka River section comprises shallow-water alternation of clay and limestones. This section described in details earlier [9] demonstrates uninterrupted sequence from the upper part of praesul-cata Zone through sulcata Zone composed of bioclastic limestones interbedded with thin layers of dark-gray clays and corresponding to the lower part of the Edzhid Formation (Fig. 1). Latest Famennian regression is marked by lagoon wavy laminated clayey wacke- and packstones containing rare brachio-pods Prospira sp., abundant and diverse benthic ostracodes, and diverse conodont associations including Siphonodella praesul-cata Sandberg, Siphonodella bella Kononova et Migdisova, Siphonodella quasinuda Gagiev, Kononova et Pazuhin, Polygnathus parapetus Druce, Polygnathus communis communis Branson et Mehl, Hindeodus penescitulus Rexroad et Collinson, Pseudopolygnathus graulichi Bouckaert et Groessens, Ligonodi-na discreta (Austin et Husri) (Fig. 2). The negative shifts in 813Corg in conodont organic matter among Polygnathus communis and Polygnathus parapetus accompanied by weak positive shift in S3Ccarb in bulk carbonates suggest eutrophic conditions in
the lagoon environment and disbalancing of the trophic web (Fig. 3).
The overlaying shoal and open marine wavy laminated clayey packstones contain early Tournaisian conodonts Siphonodella bella, Siphonodella quasinuda, Siphonodella sulcata (Huddle), Siphonodella semichatovae Kononova et Lipn-jagov, Patrognathus crassus Kononova et Migdisova among others (Fig. 2). Both the latest Famennian and earliest Tour-naisian are characterized by specific ostracode association of Pseudoleperditia tuberculifera — Coryellina alba — Cribro-concha primaris ostracode Zone of the South Urals [4] or Shivaella microphtalma — Ps. venulosa Zone of the East European Platform [3] (Fig. 4). This association is known from the Middle praesulcata — Lower duplicata conodont zones of the East European Platform, Urals, and Franco-Belgian Basin [3, 4]. Most characteristic species of this interval are as follows: Bairdia felimgibba Becker, B. zaninae Posner, B. ex-tenuata Nazarova, Bairdianella cuspis Buschmina, Coryellina alba Kotschetkova, Blessites feluyensis Tschigova, and Pseudoleperditia tuberculifera Schneider. Acratia sp. A sensu Casier et Lethiers, 2001 occurring in the terminal Famennian in the section is known form the Middle — Upper praesulcata interval of the Montagnes Noire [2].
The earliest Tournaisian transgression is marked by decreasing clay content in the limestones (Fig. 1). The decreasing 813Ccarb value associated with positive shifts in S13Corg of conodont organic matter among Polygnathus communis and Polygnathus parapetus mark oligotrophic and trophically balanced conditions (Fig. 3). The Devonian-Carboniferous boundary interval is characterized by appearance of some species of shallow-water siphonodellids (S.quasinuda, S. sulcata, S. semichatovae) and Patrognathus crassus (Figs. 1, 2). It is notable that first appearance of Siphonodella quasinuda coincides with second transgression pulse of the Hangenberg Event (Fig. 1). Hence it can be roughly correlated with base of the Upper Siphonodella praesulcata conodont Zone [1] and with the FAD of Protogna-thodus kockeli proposing as a new level of the D/C boundary by the joint Devonian-Carboniferous Boundary GSSP Reappraisal Task Group.
Similar but poorer conodont associations of the D/C boundary interval are known in the Bolshaya Usa River section (Polar Urals), where the Late Famennian succession is composed of microbial wacke- and mudstones alternating with bio-clastic packstones, and the lowermost Tournaisian comprises wavy laminated packstones with cherty concretions. The lowermost Tournaisian packstones contain conodonts Patrognathus crassus [11].
The Devonian-Carboniferous transition in the deep-water shelf facies has been studied in a number of Cis-Uralian sections. One of the most representative successions is outcropped in the Vangyr River section (Tchernyshev Uplift). The D/C boundary beds are represented by calciturbidites, pelagic carbonates, and shales of the Izyayu Formation.
The terminal Famennian (beds with Palmatolepis gracilis roughly correlated with praesulcata Zone) comprises finegrained calciturbidites intercalating with layers of dark-gray limy shales and clayey limestones. The black shale layers mark transgression acmes probably corresponding to transgressive phases of the Hangenberg Event (Fig. 1). The abundance of calciturbidites increases upward that considered as sign of the latest Famennian regression. The conodont associations comprising subautochthonous and reworked conodont elements are mainly composed of representatives of Palmatolepis gracilis group. Presence of Hindeodus penescitulus Rexroad et Col-
Fig. 1. Reference sections of the D/C boundary interval of the north of Urals. Legend: 1 — limestone, 2 — clayey limestone, 3 — calcarenite, 4 — chert, 5 — clay and argillite
Рис. 1. Опорные разрезы пограничного интервала девона и карбона на севере Урала. Условные обозначения: 1 — известняк, 2 — глинистый известняк,
3 — калькаренит, 4 — кремень, 5 — глина и аргиллит
Fig. 2. Conodont associations ofthe Kamenka River section: a — Siphonodella bella Kononova et Migdisova, sample 121-8a/16; b — Siphonodella bella Kononova et Migdisova, sample 121-1-5/90; c — Siphonodellapraesulcata S.bella transition form, sample 121-13/16; d — Siphonodella sulcata (Huddle), sample 121a-5/10; e — Siphonodella praesulcata Sandberg, sample 121-1/96; f — Polygnathus taxophorus Cooper, sample 121-2/16; g — Pseudopolygnathus graulichi Bouckaert et Groessens, sample 121-4/16; h, i — Polygnathus communis communis Branson et Mehl., sample 121-10/16; j — Patrognathus crassus Kononova et Migdisova, sample 121-1/96; k — Siphonodella semichatovae Kononova et Lipnjagov, early form, sample 121-19b/16; l — Siphonodella semichatovae Kononova et Lipnjagov, sample 121-19/16
Рис. 2. Конодонтовые ассоциации разреза на р. Каменке: a — Siphonodella bella Kononova et Migdisova, обр. 121-8a/16; b — Siphonodella bella Kononova et Migdisova, обр. 121-1-5/90; c — переходная форма Siphonodella praesulcata — S.bella, обр. 121-13/16; d — Siphonodella sulcata (Huddle), обр. 121a-5/10; e — Siphonodella praesulcata Sandberg, обр. 121-1/96; f — Polygnathus taxophorus Cooper, обр. 121-2/16; g — Pseudopolygnathus graulichi Bouckaert et Groessens, обр. 121-4/16; h, i — Polygnathus communis communis Branson et Mehl., обр. 121-10/16; j — Patrognathus crassus Kononova et Migdisova, обр. 121-1/96; k — Siphonodella semichatovae Kononova et Lipnjagov, ранняя форма, обр. 121-19b/16; l — Siphonodella semichatovae Kononova et Lipnjagov, обр. 121-19/16
linson in association with Palmatolepis gracilis Branson et Mehl suggests correlation with Siphonodella praesulcata Zone, however numerous conodonts were probably reworked from Palmatolepis gracilis expansa Zone (Branmehla disparilis (Branson et Mehl) and Palmatolepis gracilis expansa Sandberg et Ziegler among others). The terminal Famennian ostracodes compose diverse associations of the Turingian and slope ecotypes (Fig. 5). The lowermost Tournaisian part of the suc-
cession comprises clayey fine- grained calciturbidites, which contain Siphonodella sulcata in associations with the reworked late Famennian conodonts. Mixed ostracode association occurs as well (Fig. 5). Appearance of Armilla uralica Sobolev marks the D/C boundary. The diversity of ostracodes decreased at the earliest Tournaisian.
Fig. 3. Variations of the carbon isotope composition of bulk carbonates and organic matter of conodont elements in the Devonian/ Carboniferous
boundary beds, Kamenka River section
Рис. 3. Вариации в изотопном составе углерода карбонатов и органического вещества конодонтовых элементов в пограничных
слоях девона и карбона, разрез на р. Каменке
Conclusions
The Hangenberg black-shale event corresponding to the transgression pulses at the Siphonodella praesulcata Zone are known just in the deep-water shelf facies. The traces of transgression-regression couplets in the carbonate platform and ep-icratonic facies mark the event interval. The regressions at the latest Famennian and earliest Tournaisian caused erosion and forming of discontinuity in some shallow-water sequences. These regressions led to developing of calciturbidites in the deep-water shelf and bathyal environments as well. Siphonodella sulcata and Armilla uralica in the deep-water facies are documented just from the calciturbidites, so the D/C boundary cant be precisely biostratigraphically determined. Pelagic deposits in the boundary interval are barren as a rule [6, 7]. Exceptional preservation of the D/C boundary interval in the Kamenka River section (eastern Pechora Plate) demonstrates very gradual changes in conodonts and ostracodes in the shallow-water environment.
Acknowledgements. The authors are appreciated to S. Shuyskiy and I. Smoleva for assistance in SEM and isotope studies. Also the authors would like to thank the referees for their constructive reviews.
References
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2. Casier J.-G., Lethiers F. & Preat A. Ostracods and rock facies associated with the Devonian-Carboniferous boundary series in the Puech de la Suque section, Montagne Noire, France. Bulletin de lInstitut royal des Sciences naturelles de Belgique. Sciences de la Terre, 2001, 71, pp. 31—52.
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5. Lethiers F., Crasquin-Soleau S. Commeat extaire les microfossiles a tests calcitiques des roches calcaires dures. Rev. micropaleontol., 1988, V. 31, No. 1, pp. 56—61.
6. Ovnatanova N. S., Kononova L. I., Kolesnik L. S., Gatovsky Yu. A. Upper Devonian conodonts of Northeastern European Russia. Paleontological Journal, 2017, 51(10), pp. 973—1165.
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8. Scotese C. R. PALEOMAP PaleoAtlas for GPlates and the PaleoData Plotter Program. PALEOMAP Project, 2016. http://www.earthbyte.org/paleomappaleoatlas-for-gplates/
9. Vevel Y. A., Zhuravlev A. V. & Popov V. V. Pogranich-nye otlozheniya devonskoi i kamennougolnoi sistem v razreze na r. Kamenka (Pechoro-Kozhvinskii megaval, Timano-Pechorskaya provintsiya) (Deposits of the Devonian and Carboniferous boundary in the Kamenka River section (Pechora-Kozhvinsky megaswell, Timan-Pechora province)). Oil and gas geology. Theory and practice, 2012, 7(1), available at: http:// www.ngtp.ru/rub/2/6_2012.pdf
Fig. 4. Ostracode associations of the Kamenka River section: a, b — Pseudoleperditia tuberculífera Schneider, 1956, sample 121-1/16: a — №333/37-51, lateral view of right valve; b — №333/34-28, stereo-pair of carapace in dorsal view; c, d — Coryellina alba Kotschetkova, 1987, sample 121-18A/16: c — №333/39-19, carapace in left lateral view; d — №333/39-18, carapace in posterior view; e—g — Blessites feluyensis Tschigova, 1977: e — №333/37-44, carapace in left lateral view, sample 121-1/16; f — №333/37-45, carapace in dorsal view, sample 121-1/16; g — №337/6-21, carapace in ventral view, sample 121-1-10; h — Bairdiacypris ex gr. cylindrica (Samoylova et Smirnova, 1960), №333/39-26, carapace in right lateral view, sample 121-19A/16; i, j — Bairdianella cuspis Buschmina, 1970: i — №333/39-16, carapace in right lateral view, sample 121-17/16; j — №333/38-39, carapace in dorsal view, sample 121-6/16; k—m — Glyptopleura ex gr. plicata (J. et K., 1867), sample 121-1-10: k — №333/35-18, juvenile left valve in lateral view; l — №333/35-21, carapace in left lateral view; m — №333/35-20, juvenile in dorsal view; n, o — Bairdia extenuata Nazarova, l951: n — №333/36-13, carapace in right lateral view, sample 121-5/16; o — №333/ 39-4, carapace in dorsal view, sample 121-16/16; p — Bairdia felimgibba Becker, 1982, №333/36-12, carapace in left lateral view, sample 1212/16; q, r — Bairdia zaninae Posner, 1979: q — №333/38-31, carapace in right lateral view, sample 121-6/16; r — №333/38-32, carapace in dorsal view, sample 121-6/16; s, t — Pustulobairdia ex gr. confragosa (Samoilova & Smirnova 1960), sample 121-1-10: s — №335/7-11, carapace in right lateral view; t — №335/7-12, carapace in dorsal view; u, v — Acratia sp. A sensu Casier & Lethiers, 2001: u — №333/36-14, carapace in right lateral view, sample 121-5/16; v — №333/39-12, carapace in anterior view, sample 121-17/16
Рис. 4. Остракодовые ассоциации разреза на р. Каменке: a, b — Pseudoleperditia tuberculifera Schneider, 1956, обр. 121-1/16: a — №333/37-51, вид сбоку правой створки; b — №333/34-28, стереопара раковины, вид сверху; c, d — Coryellina alba Kotschetkova, 1987, обр. 121-18A/16: c — №333/39-19, вид раковины слева сбоку; d — №333/39-18, вид раковины сзади; e—g — Blessites feluyensis Tschigova, 1977: e — №333/37-44, вид раковины слева сбоку, обр. 121-1/16; f — №333/37-45, раковина, вид сверху, обр. 121-1/16; g — №337/6-21, раковина, вид снизу, обр. 121-1-10; h — Bairdiacypris ex gr. cylindrica (Samoylova et Smirnova, 1960), №333/39-26, вид раковины справа сбоку, обр. 121-19A/16; i, j — Bairdianella cuspis Buschmina, 1970: i — №333/39-16, вид раковины справа сбоку, обр. 121-17/16; j — №333/38-39, вид раковины сверху, обр. 121-6/16; k—m — Glyptopleura ex gr. plicata (J. et K., 1867), обр. 121-1-10: k — №333/35-18, ювенильная левая створка, вид сбоку; l — №333/35-21, вид раковины слева сбоку; m — №333/35-20, ювенильная форма, вид сверху; n, o — Bairdia extenuata Nazarova, l951: n — №333/36-13, вид раковины справа сбоку, обр. 121-5/16; o — №333/394, вид раковины сверху, обр. 121-16/16; p — Bairdia felimgibba Becker, 1982, №333/36-12, вид раковины слева сбоку, обр. 121-2/16; q, r — Bairdia zaninae Posner, 1979: q — №333/38-31, вид раковины справа сбоку, обр. 121-6/16; r — №333/38-32, вид раковины сверху, обр. 121-6/16; s, t — Pustulobairdia ex gr. confragosa (Samoilova & Smirnova 1960), обр. 121-1-10: s — №335/7-11, вид раковины справа сбоку; t — №335/7-12, вид раковины сверху; u,v — Acratia sp. A sensu Casier & Lethiers, 2001: u — №333/36-14, вид раковины справа сбоку, обр. 121-5/16; v — №333/39-12, вид раковины спереди, обр. 121-17/16
Fig. 5. Ostracode associations of the Vangyr River section; Upper Famennian (a—e), Famennian-Toumaisian (f—j), Toumaisian (k—n): a — Ceratacratia cerata Blumenstengel, 1965, № 333/20-5, internal view of right valve, sample w22-z8; b — Absina (Absina) ventrorostrata Grundel, 1962, № 333/20-6, internal view of right valve, sample w22-z8; c — Rectoplacera neoelongatata Blumenstengel, 1979, № 333/20-3, lateral view of right valve, sample w22-z8; d — Cornigella ? verrucosus Sobolev, 2014, № 333/20-40, lateral view of left valve, sample w22-z3; e — Mennerites famenica Sobolev, 2014, № 333/50-5, lateral view of righ valve, sample w22-4; f — Timorhealdia nitidula praenitidula (Blumenstengel, 1979), № 333/20-2, lateral view of left valve, sample w22-z8; g — Armilla decorata Sobolev, 1997, № 333/21-10, lateral view of left valve, sample w22-z1; h — Corrugobythere longa Sobolev, 1998, № 333/21-65, lateral view of right valve, sample w22-5; i — Bairdia felimgibba Becker, 1982, № 333/20-46, lateral view of left valve, sample w22-z3; j — Bairdiacypris ex gr. cylindrica (Samoylova et Smirnova, 1960), № 333/21-39, carapace in right lateral view, sample w22-4; k — Calcarofera calcarata Schornikov, 1993, № 333/21-112, lateral view of right valve, sample w22-10; l — Armilla uralica Sobolev, 1994, № 333/21-67, lateral view of right valve, sample w22-6; m — Strumibythere simplex Sobolev, 2017, № 333/21-117, lateral view of right valve, sample w22-10; n — Compositocostata cumina Sobolev, 2017, № 333/21-113,
lateral view of left valve, sample w22-10
Рис. 5. Остракодовые ассоциации разреза на р. Вангыр; верхний фамен (a—e), фамен-турне (f—j), турне (k—n): a — Ceratacratia cerata Blumenstengel, 1965, № 333/20-5, внутренний вид правой створки, обр. w22-z8; b — Absina (Absina) ventrorostrata Grundel, 1962, № 333/20-6, внутренний вид правой створки, обр. w22-z8; c — Rectoplacera neoelongatata Blumenstengel, 1979, № 333/20-3, вид сбоку правой створки, обр. w22-z8; d — Cornigella ? verrucosus Sobolev, 2014, № 333/20-40, вид сбоку левой створки, обр. w22-z3; e — Mennerites famenica Sobolev, 2014, № 333/50-5, вид сбоку правой створки, обр. w22-4; f — Timorhealdia nitidula praenitidula (Blumenstengel, 1979), № 333/20-2, вид сбоку левой створки, обр. w22-z8; g — Armilla decorata Sobolev, 1997, № 333/21-10, вид сбоку левой створки, обр. w22-z1; h — Corrugobythere longa Sobolev, 1998, № 333/21-65, вид сбоку правой створки, обр. w22-5; i — Bairdia felimgibba Becker, 1982, № 333/20-46, вид сбоку левой створки, обр. w22-z3; j — Bairdiacypris ex gr. cylindrica (Samoylova et Smirnova, 1960), № 333/21-39, вид раковины справа сбоку, обр. w22-4; k — Calcarofera calcarata Schornikov, 1993, № 333/21-112, вид сбоку правой створки, обр. w22-10; l — Armilla uralica Sobolev, 1994, № 333/21-67, вид сбоку правой створки, обр. w22-6; m — Strumibythere simplex Sobolev, 2017, № 333/21-117, вид сбоку правой створки, обр. w22-10; n — Compositocostata cumina Sobolev, 2017, № 333/21-113,
вид сбоку левой створки, обр. w22-10
10. Walliser O. H. Global events in the Devonian and Carboniferous. O.H. Walliser (Ed.). Global Events and Event Stratigraphy in the Phanerozoic. Berlin: Springer, 1996, pp. 225-250.
11. Zhuravlev A. V., Plotitsyn A. N., Vevel Y. A., Ero-feevskiy A. V. Pogranichnye otlozheniya devona i karbona na
Vorkutinskom poperechnom podnyatii (r. Bol'shaya Usa) (Devonian-Carboniferous boundary beds in the Vorkuta transverse uplift (Bolshaya Usa River)). UchenyeZapiskiKazanskogo Uni-versiteta. Seriya Estestvennye Nauki (Proceedings of Kazan University. Natural Sciences, 2018, V. 160, No. 3, pp. 467— 483.
