Abstract—
The taxonomic composition of the ammonite family Cardioceratidae is studied in the Bathonian of northern Siberia in the range of distribution of the last representatives of the genus Arcticoceras and the first representatives of the genus Catacadoceras, aiming to solve the problem of the Middle-Upper Bathonian boundary. It is shown that all previous identifications of northern Siberian material as the Middle Bathonian species Arcticoceras cranocephaloide Callomon et Birkelund, 1985, were incorrect. The misidentified specimens were mainly the Late Bathonian ammonite species Catacadoceras barnstoni (Meek, 1859) or the form with a narrow umbilicus referred to herein as Cat. aff. barnstoni. An updated ammonite zonal scale of the Middle–Upper Bathonian of Siberia is proposed, which is recommended for use both in the regional stratigraphic schemes of the Jurassic deposits of Eastern (Middle) Siberia and in the Boreal (Siberian) zonal standard of the Bathonian Stage. The extreme importance of preserving an auxiliary biostratigraphic subdivision in this scale, the Cat. barnstoni Beds, is emphasized, because of the wide distribution and abundance of the index species in Siberian sections, as well as its significance for the correlation of the lower part of the Upper Bathonian of northern Canada, northern Siberia, Franz Josef Land, and East Greenland. In addition, two intervals, i.e., the interval with Cat. aff. barnstoni and interval with Cat. perrarum, are fixed as marker levels, which are useful for rapid age determination and correlation of the Upper Bathonian deposits in Arctic sections within the upper part of the Cat. barnstoni Beds.
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INTRODUCTION
The Bathonian reference sections in Siberia are located on the coast of the Laptev Sea and adjacent territory. Traditionally, rocks exposed locally are mainly dated using ammonites. Despite the long history of the study of Siberian sections and increased attention to fossil ammonites, ammonite zonal scales need at times to be revised and updated. Currently, as discussed in recent publications, such revision is needed for the Bathonian, where there are conflicting ammonite identifications in some sections, some index taxa and biostratigraphic units require revision, and data on ammonites need to be linked with the results of recent stratigraphic studies on other fossil groups of the Bathonian of Siberia, as well as with new biostratigraphic data from other Boreal areas (Mitta and Alsen, 2013; Meledina, 2014; Mitta et al., 2014, 2015; Gulyaev, 2015; de Lagausie and Dzyuba, 2017; Dzyuba et al., 2019; Alsen et al., 2020; Shamonin and Knyazev, 2020, 2021; Shamonin et al., 2020; Kiselev, 2022; Urman et al., 2022; etc.).
The zonal ammonite scale of the Bathonian Stage of Siberia uses representatives of the family Cardioceratidae. Each of the substages has various unresolved problems concerning these mollusks. However, perhaps the most pressing issues currently concern the Middle and Upper Bathonian. Examples of the level of existing problems include the issue of recognizing “beds without ammonites” in Siberia in the range of the entire Middle Bathonian (Meledina, 2014) and the problem of the age relationships and identification on the Siberian material of the species Arcticoceras cranocephaloide Callomon et Birkelund, 1985 and Catacadoceras barnstoni (Meek, 1859), used as indices of boreal ammonite zones (Shamonin and Knyazev, 2021). Therefore, the study of cardioceratids in the distribution range of the last representatives of the genus Arcticoceras and the first representatives of the genus Catacadoceras is especially important.
In this work we discuss the accuracy of identification of Arcticoceras cranocephaloide in the Bathonian of northern Siberia and, accordingly, the problem of the Middle-Upper Bathonian boundary in this region on the basis of new ammonite collections and the revision of previously known records. Accordingly, we propose updates for the regional ammonite scale. The species Catacadoceras barnstoni is described taking into account new findings and a revision of its composition, as well as a presumed new species of Catacadoceras, similar morphologically and geochronologically to C. barnstoni, but so far only known from a few specimens only.
MATERIAL, METHODS AND TERMINOLOGY
This research was mostly focused on ammonite shells collected in 2019 during the expeditionary work of the field team of the IPGG SB RAS–NSU in the lower reaches of the Lena River from the Middle Jurassic beds, exposed on the left bank of the river north of the village of Chekurovka (Fig. 1). The studied section is located on the northern wing of the Chekurovskaya Anticline and is known as the “northern section” or Outcrop 2 (Meledina et al., 1991). In this work, we consider the results of a study of material originating from members 7–9 of the Bathonian part of this section, which is represented by silty-sandy rocks of the upper Chekurovskii Formation and predominantly clayey-silty rocks of the lower part of the Stan-Yuryakh Formation with a total thickness of 28.3 m (Galabala, 1991; Shamonin and et al., 2020) (Fig. 2a). This material includes 49 ammonite specimens, all belonging to the family Cardioceratidae except for a single representative of Phylloceratidae. One ammonite specimen was found during sampling of talus at Cape Chucha below Outcrop 3 (see Meledina et al., 1991), on the southern flank of the Chekurovskaya Anticline (collected by I.N. Kosenko, 2018). In addition, the material (26 examples) collected by V.G. Knyazev in the Bathonian on the coast of Olenek Bay near the village of Ystannakh-Khocho (Fig. 1), kept in the Laboratory of Paleontology and Stratigraphy of the Mesozoic and Cenozoic at the Institute of Geology and Geology, Siberian Branch of the Russian Academy of Sciences, was studied. The specimens used for this paper were transferred to the monographic collection department of the Central Collective Use “GEOCHRON Collection” at the IPGG SB RAS (formerly a department within the Central Siberian Geological Museum, Novosibirsk), collection no. 2112. We also used published collections of ammonites housed in the same collection department as above and photographs of the East Greenland collection of ammonites made by J. Callomon and T. Birkelund (Geological Museum of Copenhagen University) provided by V.V. Mitta. The previous identifications of the Bathonian ammonites from Member 21 of Outcrop 19 D on the Yuryung-Tumus Peninsula were completely revised (Fig. 2b).
Main localities of the Middle-Upper Bathonian ammonites in the north of Eastern Siberia. (1) Yuryung-Tumus Peninsula; (2) coast of Anabar Bay; (3) the coast of Olenek Bay near the village of Ystannah-Khocho; (4) lower reaches of the Lena River in the area of the village of Chekurovka; (5) Kotelnyi Island.
Ammonites and biostratigraphic subdivision of the upper part of the Middle Jurassic section, in the lower reaches of the Lena River north of the village of Chekurovka, Outcrop 2 (a) and on the eastern coast of the Yuryung-Tumus Peninsula, Outcrop 19 “G” (b). Lithological columns are shown in a generalized form; (a): the outcrop number and member numbering are given according to Meledina et al. (1991), the name of the formations is given taking into account the work of Galabala (1991), the thickness of the members and the position of the top of the Chekurovskii Formation are given according to Shamonin et al. (2020); (b): outcrop number, unit number and thickness, formations are given according to Meledina et al. (1987). (1,2,3) Ammonite occurrences (Meledina et al., 19871, 19912; de Lagausie and Dzyuba, 20173); for the Chekurovka section, they are shown approximately, taking into account the recalculation of member thicknesses. Legend: (1) argillite; (2) clayey siltstone; (3) siltstone; (4) sandy siltstone; (5) sandstone; (6) glendonites (a) and pebbles (b); (7) ammonite occurrences; (8) calcareous nodules.
The ammonites were studied systematically and morphologically using the classical comparative morphological method, ontogenetic studies with separation (“uncoiling”) of whorls, and morphometric analysis. The terminology used in the paper for the elements of the morphology of ammonite shells followed Ruzhencev (1962) and Meledina (1973). The shell shape and ornamentation, as well as the measured parameters and their ratios play an important role in the taxonomy of ammonites. In this work, we measured the shell diameter (Dm), whorl height (WH), whorl width (WW), umbilicus width (UW) (Fig. 3), and calculated the ratios of whorl height to shell diameter (WH/Dm), whorl width to shell diameter (WW/Dm), umbilicus width to shell diameter (UW/Dm), whorl width to whorl height (WW/WH), and the branching coefficient (K) was calculated as the ratio of the number of secondary (Sr) and primary (Pr) ribs.
Basic elements of ammonite shell morphology. From left to right: lateral view, apertural view and cross section. The area of the body chamber is shaded in gray. Dm, diameter; WH, whorl height; WW, whorl width; UW, umbilical width.
Ammonite shells vary in diameter: less than 50 mm—small; 50–120 mm—medium; 120–200 mm—large. The WW/Dm parameter characterizes the relative width of the shell: less than 20% is discoid; 20–30%—flattened; 30–40%—medium width; 40–50%—inflated; 50–70%—strongly inflated. The UW/Dm parameter characterizes the relative width of the umbilicus: less than 17%—narrow; 17–25%—moderately narrow; 25–33%—moderately wide; more than 33%—wide.
SYSTEMATIC PALEONTOLOGY
Following Meledina (1977) and Alifirov et al. (2018), Catacadoceras Bodylevsky, 1960 is considered as a separate genus.
FAMILY CARDIOCERATIDAE SIEMIRADZKI, 1891
SUBFAMILY CADOCERATINAE HYATT, 1900
Genus Catacadoceras Bodylevsky, 1960
Catacadoceras barnstoni (Meek, 1859)
Plate I, figs. 1–4; Plate II, fig. 1; Fig. 4
Drawing of the cross-section of a shell of Catacadoceras barnstoni (Meek, 1859), specimen GEOCHRON, no. 2112/20 (Alifirov et al., 2018, Fig. 2A), emended. Here and in Fig. 5 numbers indicate serial numbers of half-whorls, starting from the earliest preserved whorl. In parentheses, the suggested serial number of half-whorl from the protoconch is given, no. 2112/20 (Alifirov et al., 2018, text-fig. 2A), emended.
Ammonites barnstoni: Meek, 1859, p. 184, pl. 2, figs. 1–3.
Cadoceras elatmae: Ognev, 1933, partim, pl. 4, figs. 3, 4.
Cadoceras (Catacadoceras) laptievi: Bodylevsky, 1960, p. 64, pl. I, fig. 1; pl. II, fig. 1.
Cadoceras (Catacadoceras) ognevi: Bodylevsky, 1960, p. 65.
Cadoceras crassum: Frebold, 1961, pl. 14, fig. 2.
Cadoceras ognevi: Voronets, 1962, p. 47, pl. 23, figs. 2.
Cadoceras subcalyx: Voronets, 1962, p. 51, pl. 20, figs. 1, 2, 4.
Cadoceras subcatostoma: Voronets, 1962, p. 54, pl. 24, fig. 1; pl. 25, fig. 1.
Cadoceras variabilis: Voronets, 1962, pl. 20, fig. 3.
Cadoceras barnstoni: Frebold, 1964a, pl. 39, fig. 3; Frebold, 1964b, p. 14, pl. 8, fig. 3; pl. 12, fig. 2; Poulton, 1987, p. 54, pl. 24, figs. 1–18, pl. 25, figs. 1–8, pl. 26, figs. 1–18; Knyazev et al., 2009, p. 93, pl. 2, figs. 1–3.
Drawing of the cross-section of a shell of Catacadoceras aff. barnstoni (Meek, 1859), specimen GEOCHRON, no. 2112/3 (see Pl. III, fig. 1).
Development of views on the ammonite stratigraphy of the Middle–Upper Bathonian of Siberia and the version of the subdivision of these deposits substantiated in this work.
Correlation of the main localities of the Middle-Upper Bathonian ammonites in the north of eastern Siberia with the East Greenland ammonite sequence. Compiled taking into account published data (Bodylevsky, 1960; Stratigrafiya, 1976; Meledina, 1977, 1994, 1999; Zakharov and Shurygin, 1978; Meledina et al., 1991, 2015; Knyazev et al., 2009; Knyazev and Meledina, 2011; Nekhaev et al., 2015; Dzyuba and de Lagausie, 2018; Shamonin et al., 2020; Kiselev, 2022; Urman et al., 2022). LAD (last-appearance datum)—stratigraphically latest finds of belemnites of the genus Paramegateuthis and bivalves Retroceramus vagt.
Cadoceras (Streptocadoceras) aff. kialagvikense: Meledina, 1977, p. 86, pl. 24, fig. 2; pl. 25, fig. 1.
Catacadoceras laptievi: Meledina, 1977, p. 91, pl. 8, fig. 4; pl. 15, fig. 3; pl. 38, fig. 1; pl. 39, fig. 2.
Cadoceras (Catacadoceras) barnstoni: Meledina et al., 1991, pl. 8, figs. 3; Meledina, 1994, pl. 4, figs. 3, 4; pl. 5, figs. 4; Meledina, 1999, p. 139, pl. I, figs. 1–7, pl. 2, figs. 1–5; Kiselev, 2022, p. 177, partim, pl. 22, figs. 1, 2; pl. 23, fig. 1 (1a, 1b), figs. 2 (1c, 1d).
Arcticoceras(?) cranocephaloide: Meledina et al., 1991, pl. 6, fig. 1; pl. 8, fig. 2, non fig. 1; Meledina, 1994, pl. 5, figs. 1–3; Knyazev et al., 2009, p. 90, pl. 1, fig. 2.
Catacadoceras ognevi: Repin, 1999, pl. 3, figs. 2; pl. 4, figs. 3; Repin et al., 2007, pl. 6, figs. 6.
cf. Cadoceras (Catacadoceras) cf. barnstoni: Meledina et al., 1991, pl. 6, figs. 2, 3.
cf. Arcticoceras(?) cranocephaloide: Meledina et al., 1991, pl. 9, fig. 3.
cf. Cadoceras (Catacadoceras) barnstoni: Kiselev, 2018, pl. 3, fig. 2; Kiselev, 2022, pl. 26, fig. 1.
Holotype (by monotypy). Specimen GSC 4811, Geological Survey of Canada, Ottawa; Mackenzie River valley, northern Canada; figured (Meek, 1859, pl. 2, figs. 1–3), refigured (Frebold, 1964a, p. 39, fig. 3; Frebold, 1964b, pl. 8, fig. 3).
Plate I . Catacadoceras barnstoni (Meek, 1859) from the Upper Bathonian of northern Eastern Siberia; (1, 2) from the lower reaches of the Lena River, northern section near the village of Chekurovka, Outcrop 2, Member 8; (3, 4) from the coast of Olenek Bay near the village of Ystannah-Khocho, Outcrop 23, Bed 28, 7–8 m above the base; (1) specimen GEOCHRON, no. 2112/1, 1 m above the base of Member 8, lateral view; (2) specimen GEOCHRON, no. 2112/2, 4.5 m below the top of Member 8: (а) lateral view, (b) ventral view; (3) specimen GEOCHRON, no. 2112/5: (a) lateral view, (b) ventral view, (c) apertural view; (4) specimen GEOCHRON, no. 2112/6: (a) lateral view, (b) apertural view.
Catacadoceras barnstoni (Meek, 1859) from the Upper Bathonian of northern Eastern Siberia; (1) specimen GEOCHRON, no. 2112/4, lower reaches of the Lena River, Cape Chucha, Outcrop 3, talus: (a) lateral view, (b) ventral view. Here and in Pl. III, asterisk (*) shows the last observed suture.
Description. The shell is inflated to strongly inflated (WW/Dm from 40 to 66%). The cross section up to the 4th whorl arcuately oval in shape, the ratio of whorl width to height is 1.2–1.5. From the 7th half-whorl to the 11th, the cross-section has an isometric-rounded or rounded-square appearance, the whorl width is slightly more or slightly less than its height. From the end of the 6th whorl to the end of the shell, the cross section has the shape of an arcuately bent strip, the width of the whorl exceeds its height (WW/WH up to 1.7) (Fig. 4).
Umbilicus moderately wide or moderately narrow, deep, cup-shaped. The umbilical wall is steep. The body chamber occupies more than half of the whorl. The aperture is overhanging, at the terminal stage bounded by a pre-apertural constriction The largest shell in the collection with a fragment of the body chamber is 173 mm in diameter.
The ornamentation appears on the 4th whorl. On the 5th whorl, the primaries are simple with intercalatories and bifid. They begin on the umbilical wall; the branching point is in mid-flank. Primaries and secondaries are arcuately bent forward; on the ventral side, the ribs are bent toward the aperture. On the 6th whorl, K = 2.1. By the end of the 6th whorl, the ventral projection disappears. On the 7th whorl, the primaries become more massive than the secondaries. The primaries begin at the umbilical shoulder, with umbilical bullae, and inclined at about 45° relative to the radius. The ribs bifurcate at mid-flank or slightly higher. Three or two thinner secondary ribs extend from the primary rib, and intercalaries are sometimes present. The ribbing coefficient can reach 3.1. On the 8th whorl (Dm = 120 mm), the secondaries disappear, and the primaries are somewhat smoothed out in the distal part. At Dm > 170 mm, judging by specimen no. 2112/4 (Pl. II, fig. 1), the ornamentation is completely missing.
Dimensions in mm and ratios:
Specimen no. | Dm, mm | WH, mm | WW, mm | UW, mm | UW/Dm, % | WW/Dm, % | WH/Dm, % | WW/WH | Pr | Sr | K |
2112/1 | 42.5 | 24.5 | – | 10.5 | 24.7 | – | 57.6 | – | 26 | 41 | 1.6 |
2112/2 | 51 | 22 | 29 | 12.6 | 24.7 | 56.9 | 43.1 | 1.3 | 16 | 34 | 2.1 |
2112/5 | 81 | 30.5 | 48 | 23 | 28.4 | 59.3 | 37.7 | 1.6 | 22 | 52 | 2.4 |
2112/6 | 98.5 | 44.5 | 50 | 32 | 32.5 | 50.8 | 45.2 | 1.1 | 11 | 30 | 2.7 |
2112/7 | 76 | 32.5 | 43 | 24 | 31.6 | 56.6 | 42.8 | 1.3 | 17 | 43 | 2.5 |
2112/8 | – | 31 | 40 | 20 | – | – | – | 1.3 | 9 | 22 | 2.4 |
2112/9 | 68 | 30 | 36 | 19.5 | 28.7 | 52.9 | 44.1 | 1.2 | 10 | 24 | 2.4 |
2112/10 | – | 24.5 | 38 | – | – | – | – | 1.6 | 7 | 17 | 2.4 |
2112/11 | 51 | 19 | 23 | 17.5 | 34.3 | 45.1 | 37.3 | 1.2 | 6 | 13 | 2.2 |
2112/12 | – | 31.5 | 45.5 | 24.5 | – | – | – | 1.4 | – | – | – |
2112/13 | 72 | 27 | 42 | 26 | 36.1 | 58.3 | 37.5 | 1.6 | – | – | – |
2112/14 | – | 31 | 41 | – | – | – | – | 1.3 | 5 | 12 | 2.4 |
2112/15 | – | 40 | 60 | – | – | – | – | 1.5 | – | – | – |
2112/16 | 55 | 24 | 28 | 21 | 38.2 | 50.9 | 43.6 | 1.2 | 8 | 20 | 2.5 |
2112/17 | 59 | 28 | 33.5 | 19 | 32.2 | 56.8 | 47.5 | 1.2 | 19 | 43 | 2.3 |
2112/18 | 102 | 40 | 63 | 29 | 28.4 | 61.8 | 39.2 | 1.6 | – | – | – |
2112/19 | – | 38.5 | 59 | 30.5 | – | – | – | 1.5 | 5 | 12 | 2.4 |
Specimen no. 2112/20 (Alifirov et al., 2018, text-fig. 2A) | |||||||||||
No. half-whorl1 | Dm, mm | WH, mm | WW, mm | UW, mm | UW/Dm, % | WW/Dm, % | WH/Dm, % | WW/WH | |||
13 (15) | 90 | 34.7 | 59.4 | 24.8 | 27.6 | 66.0 | 38.6 | 1.7 | |||
12 (14) | 73.2 | 31.2 | 47 | 21.6 | 29.5 | 64.2 | 42.6 | 1.5 | |||
11 (13) | 55.8 | 21.7 | 30.9 | 17.9 | 32.1 | 55.4 | 38.9 | 1.4 | |||
10 (12) | 42.9 | 17.6 | 20.4 | 13.8 | 32.2 | 47.6 | 41.0 | 1.2 | |||
9 (11) | 31.2 | 12 | 12.5 | 10 | 32.1 | 40.1 | 38.5 | 1.0 | |||
8 (10) | 22.4 | 9.4 | 8.9 | 6.5 | 29.0 | 39.7 | 42.0 | 0.9 | |||
7 (9) | 15.26 | 6.43 | 6.7 | 4.5 | 29.5 | 43.9 | 42.1 | 1.0 | |||
6 (8) | 10.16 | 4.41 | 5.43 | 3.05 | 30.0 | 53.4 | 43.4 | 1.2 | |||
5 (7) | 7.37 | 3.05 | 3.58 | 2.13 | 28.9 | 48.6 | 41.4 | 1.2 | |||
4 (6) | 5.43 | 2.22 | 2.79 | 1.6 | 29.5 | 51.4 | 40.9 | 1.3 | |||
3 (5) | 3.81 | 1.6 | 1.96 | 1.1 | 28.9 | 51.4 | 42.0 | 1.2 | |||
2 (4) | 2.72 | 1.1 | 1.64 | – | – | 60.3 | 40.4 | 1.5 | |||
1 (3) | 1.96 | – | 1.31 | – | – | 66.8 | – | – | |||
Comparison. FromFootnote 1 the morphologically similar species Cat. perrarum (Voronets, 1962), the described species differs mainly in ornamentation. Secondaries of Cat. perrarum are much wider and less frequent, and are similar to the primaries in width.
Remarks. Arcticoceras cranocephaloide Callomon et Birkelund, 1985, first established in East Greenland, has a certain similarity with the described species, which has been repeatedly revised (Poulton, 1987; Meledina, 1994; Knyazev et al., 2009; Kiselev, 2022; etc.). For over 30 years, this species was also cited from the Bathonian of the north of Eastern Siberia, where it was mainly assigned conditionally to the genus Arcticoceras (Meledina et al., 1991; Knyazev et al., 2009; etc.). As was recently indicated (Shamonin and Knyazev, 2021), the main problem of Arc. cranocephaloide was its insufficiently detailed original description (Callomon and Birkelund in Callomon, 1985) and the absence of images of adult macroconchs in either the apertural or ventral views. A more detailed discussion of the occurrences of this species in Arctic sections is given in a separate section of this work. It should be noted here that the Siberian specimens attributed to “Arc.(?) cranocephaloide” included in the synonymy list differ from true representatives of that species in more strongly inflated shells and the absence of noticeable bends of the ribs on the venter, which is the basis for their assignment to Cat. barnstoni.
A specimen attributed to Cadoceras (Catacadoceras) barnstoni (Kiselev, 2018, pl. 3, fig. 1; Kiselev, 2022, pl. 1, fig. 1) was recently identified from Franz Josef Land. That specimen shows characters similar to those of Cat. perrarum (Voronets, 1962), which Kiselev (2022) synonymized under Cat. barnstoni. However, in our opinion, the species Cat. barnstoni is present in Franz Josef Land. We consider it a senior synonym of Cadoceras (Catacadoceras) ognevi (Bodylevsky, 1960, p. 65), the holotype of which had been previously incorrectly identified as Cadoceras elatmae (Ognev, 1933, pl. 4, figs. 3, 4). Later finds of Cat. barnstoni in Franz Josef Land were identified as Catacadoceras ognevi (Repin, 1999; Repin et al., 2007).
Kiselev (2022) described five morphs of Cat. barnstoni, which differ in a specific set of characters depending on the relative umbilicus width, prominence and frequency of the ribs, the obliqueness and shape of the ribs in the late whorls of the phragmocone and the adult body chamber: morph barnstoni, morph ognevi, morph perrarum, morph subcalyx, and morph subcatostoma. The morph perrarum identified by Kiselev does not correspond to our interpretation of the species under discussion.
Occurrence. Bathonian, upper substage, Cat. barnstoni Zone of northern Canada and Franz Josef Land, upper part of the Paracadoceras variabile Zone of East Greenland, Beds with Cat. barnstoni in the north of Eastern Siberia.
Material. 31 specimens of good and satisfactory preservation: lower reaches of the Lena River, northern section near the village of Chekurovka (Outcrop 2, Member 8, interval 1–6.75 m above the base, 4 specimens), Cape Chucha (Outcrop 3, talus, 1 specimen); coast of Olenek Bay near the village of Ystannakh-Khocho (26 specimens).
Catacadoceras aff. barnstoni (Meek, 1859)
Catacadoceras aff. barnstoni (Meek, 1859) from the Upper Bathonian of northern Eastern Siberia; (1) specimen GEOCHRON, no. 2112/3, lower reaches of the Lena River, northern section near the village of Chekurovka, Outcrop 2, Member 8, 0.7 m below the top: (a) lateral view of an outer whorl, (b) lateral view of an inner whorl, (c) apertural view.
Description. The shell diameter of specimen no. 2112/3 is 125 mm. After it was photographed, a cross section of the shell was made, which made it possible to draw its cross section (Fig. 5). The observed part of the shell ontogeny shows first the stage of a slight predominance of the whorl height over its width (half-whorl 2); the cross section has the form of a slightly elongated oval. As the shell grows, its width becomes greater than its height, and the cross section becomes first rounded, and then wide oval. At all observed stages of ontogeny, in terms of the relative width, the shell is characterized as inflated.
Arcticoceras cranocephaloide Callomon et Birkelund, 1985 from the Middle Bathonian of East Greenland (photographs by V.V. Mitta in the Geological Museum of Copenhagen University); (1) specimen MGUH 16569, holotype, southwest of Fossilbjerg Mountain, Outcrop 42, Bed 2: (a) lateral view, (b) ventral view; (2) topotypes, not to scale, coll. by J. Callomon and T. Birkelund.
The umbilicus is moderately narrow to narrow, deep, cup-shaped, with a moderately steep umbilical wall. Throughout the ontogeny, the relative diameter of the umbilicus gradually decreases to 22.8%. The preserved fragment of the body chamber occupies more than half of a whorl; the aperture is missing.
In the visible part of the internal whorls, the ornamentation is represented by bifid, approximately equal in width and size, primary and secondary ribs directed towards the aperture, K = 2. At the beginning of the last whorl, the primaries are bullae-shaped and split mainly into two more gently sloping and thin secondaries; secondary intercalaries are also present, K = 2.3. On the body chamber, the ornamentation gradually weakens: at first, the secondary ribs disappear and only bullae remain at the umbilical shoulder; by the end of the preserved part of the body chamber, the shell becomes completely smooth.
Dimensions and ratios:
Half-whorl no. | Dm, mm | WH, mm | WW, mm | UW, mm | UW/Dm, % | WW/Dm, % | WH/Dm, % | WW/WH | Pr | Sr | K |
Specimen no. 2112/3 | |||||||||||
8 (16) | 125 | 55.4 | (51.5) | 28.5 | 22.8 | ? | 44.3 | ? | 6 | 14 | 2.3 |
7 (15) | 95.5 | 39 | 46.8 | 23.7 | 24.8 | 49.0 | 40.8 | 1.2 | – | – | – |
6 (14) | 74.4 | 31 | 38.6 | 20.7 | 27.8 | 51.9 | 41.7 | 1.2 | – | – | – |
5 (13) | 54.6 | 22.8 | 26.8 | 15.4 | 28.2 | 49.1 | 41.8 | 1.2 | 8 | 16 | 2 |
4 (12) | 40.5 | 17.4 | 18.7 | 12.3 | 30.4 | 46.2 | 43.0 | 1.1 | – | – | – |
3 (11) | 29.5 | 12 | 14.7 | 8.7 | 29.5 | 49.8 | 40.7 | 1.2 | – | – | – |
2 (10) | 20.7 | 10.3 | 9.6 | – | – | 46.4 | 49.7 | 0.9 | – | – | – |
1 (9) | 13.8 | – | 6.4 | – | – | 46.4 | – | – | – | – | – |
Specimen no. 856-21 (Knyazev et al., 2009, pl. 1, fig. 1) | |||||||||||
14 | 83.5 | 35.6 | 49.6 | 18.7 | 22.4 | 59.4 | 42.6 | 1.4 | – | – | – |
13 | 67 | 29 | 40.5 | 14.8 | 22.1 | 60.4 | 43.3 | 1.4 | – | – | – |
12 | 51 | 23 | 30.1 | 11 | 21.6 | 59 | 45.1 | 1.3 | – | – | – |
11 | 38.5 | 16.6 | 21.6 | 9.4 | 24.4 | 56.1 | 43.1 | 1.3 | – | – | – |
10 | 28.9 | 12.5 | 14.4 | 7.2 | 24.9 | 49.8 | 43.3 | 1.2 | – | – | – |
9 | 21.3 | 9.4 | 9.4 | 5 | 23.5 | 44.1 | 44.1 | 1.0 | – | – | – |
8 | 15.3 | 7.2 | 6.7 | 3 | 19.6 | 43.8 | 47.1 | 0.9 | – | – | – |
7 | 10.5 | 5.1 | 5.3 | 1.7 | 16.2 | 50.5 | 48.6 | 1.0 | – | – | – |
6 | 6.9 | 3.7 | 3.9 | 0.9 | 13 | 56.5 | 53.6 | 1.1 | – | – | – |
5 | 4.5 | 2.5 | 2.8 | 0.6 | 13.3 | 62.2 | 55.6 | 1.1 | – | – | – |
4 | 3 | 1.5 | 2.1 | – | – | 70 | 50 | 1.4 | – | – | – |
3 | 2 | 1 | 1.25 | – | – | 62.5 | 50 | 1.3 | – | – | – |
2 | 1.3 | 0.79 | 0.92 | – | – | 70.8 | 60.8 | 1.2 | – | – | – |
1 | 0.6 | – | 0.73 | – | – | – | – | – | – | – | – |
Remarks. The specimen found in the northern section near the village of Chekurovka is very close to Cat. barnstoni, in the shell ontogeny, the shape of the shell cross-section and ornamentation. However, it is distinguished by a noticeably narrower umbilicus (Cat. barnstoni is characterized by an interval of variation in the relative diameter of the umbilicus, starting from 25–27%). Specimen no. 856-21, identified from a close level in the same section as Arcticoceras(?) cranocephaloide (Meledina et al., 1991, pl. 8, fig. 1) has a similar feature. Knyazev et al. (2009, pl. 1, fig. 1c) illustrated the cross-section of this ammonite, which makes it possible to study the ontogeny of its shell shape (see Dimensions and ratios). The explanation of the plate (Knyazev et al., 2009, p. 88) incorrectly indicates the provenance of the specimen as from Member 9, while the ammonite was found in Member 8 of Outcrop 2 “in a narrow interval, 20 cm under the Bed with pebbles” (Meledina et al., 1991, p. 16) and, as is clear from the explanation of the plate in the same work, in Bed 13 of Outcrop 2 (Meledina et al., 1991, p. 194), which also corresponds to Member 8, according to B.N. Shurygin field notes.
Another record of an ammonite close to the one described, illustrated as Arc. cranocephaloide (Kiselev, 2022, pl. 18, fig. 1), is represented by a relatively large and semi-crushed mold, with a narrow umbilicus, which makes it more similar to Cat. aff. barnstoni than to Arc. cranocephaloide. This specimen, the undeformed diameter of which was presumably 120–130 mm, is distinguished from Cat. aff. barnstoni, by well-pronounced ribbing up to the end of the body chamber. There is not sufficient material of Cat. aff. barnstoni to accurately estimate the limits of variability of this character. The discussed find of “Arc. cranocephaloide” comes from the southern section near the village of Chekurovka, from the top of Member 7, which corresponds to the top of Member 8 in Outcrop no. 2 in Meledina et al. (1991).
Material. 1 well-preserved specimen from the Beds with Cat. barnstoni in the lower reaches of the Lena River, northern section near the village of Chekurovka (Outcrop 2, Member 8, 0.7 m below the top).
ARCTICOCERAS CRANOCEPHALOIDE CALLOMON ET BIRKELUND, 1985 VS. CATACADOCERAS BARNSTONI (MEEK, 1859)
Both species named in the title are indices of the ammonite scales of the Bathonian stage of the Arctic regions (Callomon, 1985, 1993, 2003; Poulton, 1987; Meledina, 1991, 2014; Poulton et al., 1992; Shurygin et al., 2000, 2011; Knyazev et al., 2009; Nikitenko et al., 2013; Callomon et al., 2015; Kelly et al., 2015; etc.). However, the insufficiently informative original description of Arcticoceras cranocephaloide Callomon et Birkelund, 1985 (Callomon, 1985) and the significant similarity of the shell of this species with Catacadoceras barnstoni (Meek, 1859) in morphology of the flanks and in the ornamentation of the outer whorls often made it difficult to distinguish them in practice. The problem was exacerbated by the geographic isolation of the finds of most representatives of Arc. cranocephaloide and Cat. barnstoni illustrated in publications vs. close stratigraphic position of these species, and for a long time not fully clarified (documented) chronological relationships with each other and with a number of other cardioceratid species. All this led to different opinions on the biostratigraphy and Pan-Arctic correlation of the boundary Middle-Upper Bathonian interval using ammonites. Below we consider the results of a detailed analysis of the morphological features of Arc. cranocephaloide compared to Cat. barnstoni, made possible in many ways by photographs of the East Greenland Arc. cranocephaloide collection, kindly provided by V.V. Mitta (pl. IV).
Arc. cranocephaloide was originally described from the Jameson Land Peninsula in East Greenland (Callomon and Birkelund in Callomon, 1985). The description of this species says that the inner whorls have the appearance of early representatives of Cadoceras, i.e., relatively evolute (W/L about 30%) with a rounded cross section, while the outer whorls are more involute and compressed at the adult body chamber; the relative width of the shell (WW/Dm) varies on average from 40 to 50%, but in one case it reaches 80%. According to the description and cited images (Callomon, 1985, pl. 1, figs. 1–3; text-figs. 8i, 9A, 9B), the ribbing on the inner whorls is prominent, regularly bifurcating, and slightly slanting forward. The ornamentation continues on the body chamber, the primary ribs become coarser than the secondaries, sometimes with intercalaries. However, the description of inner whorls of Arc. cranocephaloide is relatively brief with no indication of specific diameters. Specimens of the type series of Arc. cranocephaloide, except for the paratype MGUH 16573 (Callomon, 1985, pl. 1, fig. 3), separately illustrated topotypes (Callomon, 1993, fig. 3), including the photographs provided by V.V. Mitta (pl. IV), and also two specimens from Callomon’s collection from Outcrop 43 (near the type locality—Outcrop 42) by Kiselev (2022, pl. 13, figs. 1, 2), represented by adult forms, most of which are deformed and/or do not have inner whorls. Thus, it can be assumed that the inner whorls could only be described from specimen MGUH 16573, later whorls of which are not known; the identification of this specimen as Arc. cranocephaloide was most likely made on the basis of its occurrence at the same stratigraphic level with adult specimens of this species. This specimen, along with the allotype MGUH 16570, was reported to have been discovered southwest of Mount Olympen, in Outcrop 70, while the holotype, the other two illustrated paratypes, and other topotypes come from sections near Mount Fossilbjerg (Callomon, 1985, 1993), which is 25–30 km southeast of Outcrop 70. Because typical adult forms of Arc. cranocephaloide are not listed in Outcrop 70 together with specimens MGUH 16573 and MGUH 16570, this does not allow us to confidently attribute the latter to this species. It is possible that the first illustrated adult forms, – “Arc. cranocephaloide sp. nov. MS” (Callomon, 1975, fig. 4D) and “Arc. cf. cranocephaloide sp. nov. MS” (Callomon, 1975, fig. 4E), come from a locality near Outcrop 70; of these occurrences it is only known that they come from a locality south of Mount Olympen, but these specimens are not mentioned in the formal first description of the species in question. If, however, we accept the point of view of J. Callomon and interpret the juvenile specimen as internal whorls of Arc. cranocephaloide, perhaps its generic name should be reconsidered according to the ontogenetic principle of taxonomy since the shape of the shell of MGUH 16573 has more in common with cadoceratins than with early Arcticoceras.
Also, the original description did not pay enough attention to the shape of the outer whorls of the Arc. cranocephaloide shell, while no images of the shell in the apertural or ventral view were provided. In addition to the characteristic of the relative width of the shell mentioned above, the description mentioned a flattened venter of the adult body chamber of this species. The umbilicus was described as open, shallow, with a rounded umbilical edge. The variability of the relative width of the umbilicus and the relative height of the adult shells of Arc. cranocephaloide can only be obtained from images, e.g., of holotype MGUH 16569 and paratypes MGUH 16571 and 16572. Thus, the UW/Dm ratio varies from 26 to 29%, while the WH/Dm of adult shells is 38 and 40% (paratypes) and 41% (holotype). Consequently, the WW/WH ratio varies approximately in the range from 1 to 1.25. Considering the indication of the presence of a specimen with a WW/Dm ratio of 80%, then the range of WW/WH ratio will expand to approximately 2; accordingly, the whorl height will be noticeably less than its width. Judging by the photographs of paratypes MGUH 16571 and 16572 at our disposal, the WW/WH of these specimens is 1.1 and 1; the whorl height is equal to or slightly less than the width, while in the holotype (Pl. IV, fig. 1) the height exceeds its width: WW/WH is 0.88. The general view of adult shells in the photographs gives the impression that the species under discussion is characterized by a flattened shell, while the cross-section of the outer whorls should be isometric-rounded or slightly extended in height. No shell image with a relative width of reliably 80% was found.
The description of the ornamentation of adult shells of Arc. cranocephaloide is not very detailed. It reflects only the information that is visible in the images presented in Callomon’s (1985) paper. Almost nothing was known for a long time about the nature of the ribbing on the venter. In a photograph of a general view of a part of the collection (Birkelund and Perch-Nielsen, 1976, text-fig. 269), reflected in synonymy (Callomon and Birkelund in Callomon, 1985) and later re-illustrated (Callomon, 1993, text-fig. 3), in a small number of specimens it can be seen that the ribs on the venter have a well-defined bend directed towards the aperture. After examining all available photographs, including those chosen for illustration (pl. IV) and those given in (Kiselev, 2022, pl. 13, figs. 1, 2), it became clear that such a pattern of ribbing on the venter is typical of the species Arc. cranocephaloide.
In the north of Siberia, the species “Arc.(?) cranocephaloide” was first identified from finds in the lower reaches of the Lena River, in the sections of the northern and southern wings of the Chekurovskaya Anticline (Meledina et al., 1991), and then on the coast of Olenek Bay near the village of Ystannah-Khocho as a result of reidentifying a specimen from Outcrop 16, Bed 28, originally described by Meledina (1977) as Cadoceras (Streptocadoceras) aff. kialagvikense Imlay, 1953 (Meledina, 1994Footnote 2). The first detailed description of the North Siberian “Arc.(?) cranocephaloide” was published by Knyazev et al. (2009). In it, shells of this species are characterized as strongly inflated (WW/Dm about 60%) with a moderately narrow umbilicus (UW/Dm 20–25%), reaching more than 100 mm in diameter. In the available images, the ornamentation of the initial whorls of the shells is represented by relief bifurcating ribs with intercalaries, forming a bend towards the aperture on the venter. On the outer whorls, the primary and secondary ribs are differentiated: the primaries begin from the umbilical shoulder, acquire the appearance of a strongly elongated tubercle, and on the lateral side they bend noticeably forward; the secondary ribs, which are considerably less coarse than the primary ribs, cross the venter almost straight. For each primary rib, there are two or three secondary ones.
Thus, “Arc.(?) cranocephaloide” identified in the north of Eastern Siberia are similar to Arc.(?) cranocephaloide in morphological characters visible on the flanks of the East Greenland specimens since the UW / Dm ratio of the images cited in publications is 28–30% (the UW/Dm value of 20–25% indicated in the description of this species (Knyazev et al., 2009) is typical only of specimen no. 856-21, identified as Catacadoceras aff. barnstoni in the present paper; WH/Dm is 38–40%, the ornamentation consists of primary and secondary ribs, varying in width and prominence and slanting forward. There are two or three secondary ribs for one primary. However, in shell shape and ornamentation on the venter, they differ significantly from the East Greenland specimens of Arc. cranocephaloide: in the North Siberian specimens, the shell is more strongly inflated, and ribs on the venter do not bend towards the aperture, while in the East Greenland specimens, the WW/Dm ratio does not exceed 50% and ribs definitely bend on the venter.
The original description of Arc. cranocephaloide says (Callomon and Birkelund in Callomon, 1985, p. 78): “Nothing comparable appears yet to have been described from anywhere else”. However, in the ornamentation on the flanks, ribbing retained in the later whorls, relative whorl height variability range and relative umbilicus diameter, i.e., in characters visible on the flanks, this species is quite similar to geochronologically younger cadoceratins, i.e., Catacadoceras barnstoni. These two species differ in the shell shape. In Cat. barnstoni, the shell is strongly inflated (WW/Dm 50–60%), whereas in Arc. cranocephaloide it is more flattened (WW/Dm 40–50%) and have a pronounced rib bending on the venter, which is not observed in Cat. barnstoni. Deformed and especially compressed shells, with characters similar to both of these species, cannot be attributed with complete certainty to either of them. Thus Arc. cranocephaloide differs from Cat. barnstoni mainly in the shell shape and ornamentation on the venter, which allow positive assignments of most Siberian ammonites previously identified as Arc. cranocephaloide, to Cat. barnstoni. The two specimens discussed in the “Remarks” section of the systematic description of Cat. aff. barnstoni are an exception.
A specimen of (?)Arcticoceras sp. juv. (cf. Arc. cranocephaloide), found on the Yuryung-Tumus Peninsula 10.5 m above the base of Member 21 (de Lagausie and Dzyuba, 2017, pl. 1, figs. 6–8), is represented by a fragment of an inner whorl, which has isometrically rounded cross-section with a wide venter (WW = 10 mm, WH = 10 mm), slight forward bending of the ribs on the venter. Arc. ishmae (Keyserling, 1846), the type species of the genus Arcticoceras, is characterized by an oval and sometimes subacute cross-section of the inner whorls. The isometric section is more characteristic of the genus Arctocephalites, however, ribs in the latter are not bent forward. Judging by ornamentation, the specimen under consideration may correspond to the genus Catacadoceras, in which, the cross section is isometric with similar height and width. Therefore, in this work, this specimen is identified as Catacadoceras sp. juv. (Fig. 2b). A species-level identification of this specimen is not possible due to its small size.
It is possible that a juvenile ammonite shell found approximately 2 m below the base of the Paracadoceras variabile Zone on the eastern coast of Anabar Bay and identified as Arcticoceras sp. (Knyazev et al., 2009, pl. 1, figs. 3) in fact belongs to Arc. cranocephaloide. This specimen differs from Arc. ishmae (Keyserling, 1846) and Arc. crassiplicatum Callomon, 1993 [MS] in Kiselev, 2022, in the isometrically rounded cross-section. However, as stated above, there are no reliable data on the internal whorls of Arc. cranocephaloide of East Greenland. Arc. aff. cranocephaloide sensu Callomon, 1993 (= Arcticoceras/Cadoceras sp. nov. ? aff. variabile Spath: Callomon and Birkelund, 1980, pl. 1, fig. 1 (macroconch), fig. 2 (microconch)) was published from the Kepplerites tychonis Biohorizon of East Greenland, i.e. from the topmost beds of the Arc. cranocephaloide Zone. The illustrated microconch is clearly deformed and in lateral view differs little from microconchs from adjacent levels. The macroconch Arc. aff. cranocephaloide is interesting as in contrast to Arc. cranocephaloide, it has only well-defined elongated umbilical nodes at a late growth stage, which makes quite similar to early members of the subfamily Cadoceratinae. The relative umbilicus width and external morphology of the flanks of this specimen are similar to those of Cat. aff. barnstoni (pl. III, fig. 1). However, in the relative shell width, it still more closely resembles Arc. cranocephaloide. Apparently, compared to Arc. cranocephaloide, Arc. aff. cranocephaloide shows even more morphological characters that are similar in the later Arcticoceras with the earliest members of Cadoceratinae. The latest Arcticoceras in East Greenland were reported from the P. variabile Zone (Callomon, 1993). We could not find their illustrated description. In Siberia, representatives of Arcticoceras were not found in co-occurrence with P. variabile.
Thus, no reliable finds of Arc. cranocephaloide are yet known from Siberian sections.
POSITION OF THE CATACADOCERAS BARNSTONI BIOSTRATON IN THE AMMONITE ZONAL SCALE OF THE BATHONIAN OF SIBERIA
The zonal ammonite scale of the Bathonian Stage in northern Siberia is based on the phylogenetic sequence of taxa of the family Cardioceratidae. The subfamily Arctocephalitinae, which appeared in the Bajocian, was relatively quickly replaced by genera and species of the subfamily Cadoceratinae in the second half of the Bathonian. Below we substantiate the need to revise the modern ammonite zonation for the upper part of the Bathonian of Siberia and discuss stratigraphic position of the Catacadoceras barnstoni biostraton in the Arctic sections, and in particular in the north of Siberia.
The state of knowledge of the problem
For the first time, a biostratigraphic unit with Catacadoceras barnstoniFootnote 3 as an index species was recognized in northern Canada, in the Northern Yukon, where the Cat. barnstoni Zone was established above the Arcticoceras ishmae Zone and below the Cadoceras bodylevskyi Zone (Poulton, 1987). At the same time, the intervals between all three zones are characterized as poorly exposed. In fact, the used criteria for separating this zone correspond to those for identifying beds with fauna, if the author had to follow the recommendations of the stratigraphic code adopted for the territory of Russia (Stratigraficheskii…, 1977, 2019). Apart from the index species, the zonal assemblage included Phylloceras billingsi, Iniskinites sp., Kepplerites sp. aff. K. rosenkrantzi, and Kepplerites sp. B.
In Siberia, the Cat. barnstoni Zone was first established by Meledina (1991) between the Arcticoceras cranocephaloide and Paracadoceras falsum zones, also recognized here for the first time. The upper part of the Cat. barnstoni Zone was distinguished as the Beds with Paracadoceras variabile (Fig. 6). The entire ammonite sequence recognized by Meledina was included in the first version of the boreal zonal standard (Zakharov et al., 1997). Later, the Cat. barnstoni Zone was recognized as Beds with fauna and was moved to the top of the Arc. cranocephaloide Zone, above which the P. variabile zone was indicated (Knyazev et al., 2009). Gulyaev (2011) considered the Siberian biostraton as the Cat. barnstoni ammonite level corresponding to the Kepplerites rosenkrantzi faunal horizon of the P. variabile Zone of East Greenland. The biostraton Cat. barnstoni is absent in the boreal zonal standard version, for which Siberia is proposed as the stratotype region (Shurygin et al., 2011; Nikitenko et al., 2013). Kiselev (2022) synonymized the Cat. barnstoni Zone under the P. variabile Zone as its stratigraphic equivalent.
It should be noted that the co-occurrence of Catacadoceras barnstoni and “Arcticoceras(?) cranocephaloide” was reported only in relation to the northern section near the village of Chekurovka in the lower reaches of the Lena River (Shamonin and Knyazev, 2020; Shamonin et al., 2020). The above results of a repeated study of ammonites from this section and analysis of materials from other localities in Siberia showed that: (1) specimens previously identified here as Arc.(?) cranocephaloide should be assigned to Cat. barnstoni or to the form described in this work as Cat. aff. barnstoni, (2) recent find of Arc. cranocephaloide (Kiselev, 2022, pl. 18, fig. 1) is also not evidence for the presence of this species in Siberian sections. Thus, the stratigraphic interval, which previously corresponded in the Siberian sections to the Arc. cranocephaloide Zone should be entirely assigned to the range of distribution of Cat. barnstoni. This raises the question of whether it would be appropriate to replace the name of the Arc. cranocephaloide Zone to Cat. barnstoni Zone in the zonal ammonite scale of the Bathonian of Siberia and, accordingly, in the Boreal (Siberian) zonal standard of this stage. To answer this question, it is necessary to consider the problem of the geochronological age of the species Cat. barnstoni and Arc. cranocephaloide and Paracadoceras variabile, which has been the subject of much discussion (Poulton, 1987; Meledina, 1991, 1994; Hillebrandt et al., 1992; Callomon, 1993; Repin, 1999, 2005; Knyazev et al., 2009; Gulyaev, 2011, 2012, 2015; Knyazev and Meledina, 2011; Kiselev, 2022; etc.), apparently, with a no-consensus result. It should be noted that in this work, Arc. cranocephaloide is considered to be Middle Bathonian in age (Callomon, 2003; Mitta et al., 2014; Callomon et al., 2015; Kelly et al., 2015; Dzyuba et al., 2019; Alsen et al., 2020; Shamonin and Knyazev, 2020; Kiselev, 2022; etc.). The main localities of Cat. barnstoni are considered below.
Northern Canada. The bulk of finds of Cat. barnstoni in Northern Canada comes from a rather condensed section, according to the description of T. Poulton, of the Salmon Cache Canyon on the Porcupine River of the northern Yukon and is confined here only to Bed 62, 30 cm thick, composed of large concretions (Poulton, 1987). It is assumed that the holotype of the species could have originated from the same bed, the geographic reference of which is limited to the valley of the Mackenzie River (Meek, 1859). The concretions contained relatively diverse macrofaunal remains including Paracadoceras variabile, Kepplerites sp. aff. K. rosenkrantzi, Phylloceras billingsi, and the bivalves Retroceramus sp., i.e., taxa known in Siberia. The condensed nature of the Salmon Cache Canyon section does not exclude the possibility that the cited assemblage of the Cat. barnstoni Zone recognized there could be mixed from faunas of different ages.
East Greenland. The problem of this region for a long time was the lack of any images or descriptions of Cat. barnstoni. The only available evidence was the list of Latin names published by Callomon (1993), which accompanied the faunal horizons he identified in the Boreal (East Greenland) ammonite zonal scale, containing, among others, “C. cf. or aff. barnstoni” and its synonym “C. subcatostoma”. According to this list, finds of Cat. barnstoni in East Greenland are confined to the Kepplerites rosenkrantzi faunal horizon, recognized in the upper half of the Paracadoceras variabile Zone, which overlies the Arcticoceras cranocephaloide Zone. The find of Arcticoceras sp. nov. 1, marking the upper limit of distribution of arctocephalitins in Greenland (this species has not been formally described) was also assigned to this horizon. The possibility of mixing in the K. rosenkrantzi horizon of two faunal assemblages of slightly different ages, not always recognizable in the field, was suggested (Callomon, 1993). Thus, documentary evidence of the distribution of the species Cat. barnstoni together with K. rosenkrantzi and later P. variabile was not provided. The problem was solved by the work of D.B. Gulyaev (2011, Fig. 2), which shows an image of two specimens of Cat. barnstoni from the collection of J. Callomon, which can be used to confirm the presence of this species in the K. rosenkrantzi faunal horizon of in East Greenland. Considering the presence of Cat. barnstoni in northern Yukon (Poulton, 1987; etc.) and Kepplerites aff. rosenkrantzi on the Kanin Peninsula in the European part of Russia (Meledina, 1987, pl. IV, fig. 1), Callomon (1993) suggested the presence of equivalents of the K. rosenkrantzi faunal horizon outside East Greenland.
Franz Joseph Land. All the illustrated finds, now attributed to Cat. barnstoni (see the “Remarks” section), come from Hooker Island and are confined to the Cat. barnstoni Zone (Repin, 1999; Repin et al., 2007), as in Northern Canada, established here in the absence of a continuous zonal sequence. Also, the Bathonian of Hooker Island contains Cat. perrarum (= “Cadoceras (Catacadoceras) barnstoni” (Kiselev, 2018, pl. 3, fig. 1; 2022, pl. 1, fig. 1)).
Northern Siberia. In northern Siberia, together with Cat. barnstoni, assemblages predominantly contain cardioceratids of the genus Catacadoceras – Cat. aff. barnstoni and Cat. perrarum. At the same time, occurrences of Cat. aff. barnstoni are confined to the upper part of the Cat. barnstoni range, while finds of Cat. perrarum come from the uppermost part of this range, thus marking different levels in the sections (Figs. 2a, 7). Beds with Cat. barnstoni are widely traced in northern Siberia. They are best represented in the lower reaches of the Lena River, where finds of this species (taking into account the revision reflected in the synonymy) are recorded in sections near the village of Chekurovka, on Cape Chucha and the Chubukulah River. As a result of the study, a relatively large vertical range of distribution of Cat. barnstoni was established in the northern section near the village of Chekurovka (Outcrop 2), almost throughout the entire Member 8 (Fig. 2a). Previously, its possible presence in this section was indicated only by a single find of Cat. cf. barnstoni in Member 9 (Meledina et al., 1991). It is noteworthy that in Member 9, we did not find Cat. barnstoni, which, however, could have resulted from about 1.7 m of the section of this member being completely covered by dense scree in 2019. Evidently, the “covered” interval is also associated with the erosion boundary observed in geochronologically similar portion of Outcrop 3 (Chucha) of the southern limb of the Chekurovskaya Anticline (Meledina et al., 1991). The lower part of the distribution interval of Cat. barnstoni contained Phylloceras sp. and Arcticoceras(?) sp. juv., and the upper part contained Cat. aff. barnstoni (Fig. 2a). Previously, Cat. perrarum (Meledina et al., 1991, pl. 9, fig. 1) and Phylloceras billingsi (Meledina et al., 1991, pl. 8, fig. 5) were found 3 m above the base of Member 9. Considering that, according to the occurrence of Paracadoceras ex gr. elatmae during fieldwork of 2019, the base of the Callovian in this section was established 3.3 m above the base of Member 9 (Shamonin and Knyazev, 2020), we analyzed the ammonite originally identified as Cadoceras (Bryocadoceras) falsum (Meledina, 1977, pl. 10, fig. 1; pl. 11, fig. 1; pl. 12, fig. 1; Meledina, 1994, pl. 4, fig. 1), later reidentified as Catacadoceras calyx (Knyazev et al., 2009). This ammonite was found 6 m above the base of Member 9 together with Cadoceratinae gen. et sp. ind. (= Kepplerites(?) sp. (Meledina et al., 1991, pl. 10, figs. 6–8)) and Phylloceras sp. In this paper, we accept the initial identification of this specimen by Meledina and other occurrences of Paracadoceras falsum in the Chekurovka sections. Outcrop 3 (Chucha) contained Cat. cf. perrarum (Meledina et al., 1991, pl. 9, fig. 2; pl. 10, fig. 4), established, according to Meledina et al. (1991, figs. 2, 4), above the distribution range of Cat. barnstoni. On Cape Chucha, Paracadoceras variabile (Kiselev, 2022, pl. 26, fig. 2), was discovered in the same locality with Cat. barnstoni, which is consistent with data from northern Canada and East Greenland.
On the eastern coast of the Yuryung-Tumus Peninsula, the interval under consideration probably corresponds to the middle part of Member 21, which contains an ammonite identified in this work as Catacadoceras sp. juv. (Fig. 2b). The level of the find is comparable to the lower part of the interval with Cat. barnstoni in the lower reaches of the Lena River, since bivalves of the genus Retroceramus (R. cf. vagt) are still found in the middle part of Member 21 on the Yuryung-Tumus Peninsula (Urman et al., 2022). Outside the Yuryung-Tumus Peninsula, the last representatives of Retroceramus (R. vagt) are associated with early Cat. barnstoni. This is best documented in the northern section near the village of Chekurovka, where the uppermost finds of this bivalve genus were found 1 m below the top of Member 8, near the unconformity, above which, in contrast to Cat. barnstoni, they were not found (Shamonin et al., 2020). At Cape Chucha (Outcrop 3), according to Meledina et al. (1991) and taking into account the revision of the taxonomic composition of ammonites in this work, a similar pattern is observed. As noted above, in the Salmon Cache Canyon section of northern Canada, Retroceramus finds are known from the nodule bed, which also contains Cat. barnstoni, and above that level, no Retroceramus are found here (Poulton, 1987). In East Greenland, records of Retroceramus are rare and have not been mentioned above the Arcticoceras cranocephaloide Zone (Callomon and Birkelund, 1980; Kelly et al., 2015).
Higher horizons of the Bathonian of the Yuryung-Tumus section are exposed on the northwestern coast of the peninsula, from where, according to Bodylevsky (1960), Cat. cf. calyx has been recorded (Fig. 7). On approximately the same stretch of coast, Cat. ex gr. barnstoni, Paracadoceras variabile (Meledina et al., 2015, pl. 1, fig. 5), and Callovian taxa were found in talus, while Early Oxfordian ammonites were found in situ (Meledina et al., 2015; Nekhaev et al., 2015).
On the eastern coast of Anabar Bay, the upper part of Member 41 of Outcrop 109, that contained Arcticoceras sp. (Knyazev et al., 2009, pl. 1, fig. 3), also contained Cat. barnstoni (Meledina, 1994, 2014), but not confirmed, on the basis of a single find of loosely collected “Cadoceras (Catacadoceras) cf. ognevi” (= Cat. barnstoni sensu Meledina, 1991), previously mention without an illustration (Saks et al., 1963). It was originally suggested that “C. (Cat.) cf. ognevi” was found in Member 42 (Stratigrafiya…, 1976), currently assigned to the Paracadoceras variabile Zone (Knyazev et al., 2009). We consider any interpretation of this find to be too speculative. Cat. perrarum was recorded from the talus on the western coast of Anabar Bay (Knyazev and Meledina, 2011, p. 122, pl., fig. 1), and 2 km to the south, a poorly preserved shell identified as Kepplerites ex gr. rosenkrantzi (Knyazev and Meledina, 2011, p. 122, pl., fig. 2) was also found in the talus. Taking into account all the existing re-identification, Cat. barnstoni was found in Bed 28 of Outcrop 16 on the coast of Olenek Bay near the village of Ystannah-Khocho, according to Meledina (1977, 1994) and Knyazev et al. (2009). The new collections of Bathonian ammonites from this locality also contain specimens of Cat. barnstoni (pl. 1, figs. 3, 4). The presence of Cat. barnstoni and Cat. perrarum was also confirmed on Kotelnyi Island room to a large number of finds collected in alluvial deposits of the Dragotsennaya River (Meledina, 1999).
Thus, in northern Siberia, localities of Cat. barnstoni also contain Cat. aff. barnstoni, Cat. perrarum, and also single finds of Paracadoceras variabile, Arcticoceras(?) sp. juv., and Phylloceras billingsi. Presumably, this assemblage should also include “Kepplerites ex gr. rosenkrantzi”. The available data, judging by the stratigraphic position of Cat. barnstoni in East Greenland, suggest that the range of distribution of Cat. barnstoni corresponds to the K. rosenkrantzi faunal horizon isolated in the upper part of the Upper Bathonian P. variabile Zone of East Greenland.
Biostratigraphic conclusions
It needs to be mentioned that compared to the Paracadoceras variabile Zone, a biostraton based on Cat. barnstoni, no matter what rank it is assigned, in practical terms will be more in demand in the Siberian sections due to the greater geographic distribution and abundance of the index species. However, given the confinement of the age range of Cat. barnstoni to the upper part of the P. variabile Zone, replacing the latter with the Cat. barnstoni Zone in the ammonite scale of the Upper Bathonian of Siberia is hardly justified. Also note that in none of the Siberian sections it is possible to establish biostratigraphic units adjacent to Cat. barnstoni distribution interval (Fig. 7). Therefore, in this case, the separation of the Beds with Cat. barnstoni in the upper part of the P. variabile Zone (Fig. 6) seems to be the best decision. Beds with Cat. barnstoni are recognized in Franz Josef Land and northern Canada, and their equivalents are present in the Kepplerites rosenkrantzi faunal horizon of East Greenland.
The relationship of the Beds with Cat. barnstoni with underlying deposits is well observed in the northern section near the village of Chekurovka in the lower reaches of the Lena River, where there is an interval, without ammonites and containing an unconformity, between the level of the first finds of Cat. barnstoni and the underlying Arcticoceras ishmae Zone (Fig. 2a). Summarizing the published data, we conclude that this is a typical situation for the northern Siberian sections (Fig. 7). In general, from bottom to top in these sections, the following sequence of event levels is observed: first the ammonite species Arc. ishmae disappears, slightly higher, one or two unconformities are observed near which the last appearance of belemnites of the family Megateuthididae (genus Paramegateuthis) is recorded, followed by the appearance of the earliest representatives of Cat. barnstoni up the section. The same pattern is typical of the Bathonian section on the eastern coast of Anabar Bay, with one exception: Cat. barnstoni is not found here, however, the first appearance of Paracadoceras variabile is recorded 25 m above the unconformityFootnote 4. Obviously, stratigraphically, this is the most complete section in the region in the interval under consideration. In the same section, immediately below the occurrences of P. variabile finds, a small shell of Arcticoceras sp. was found, which could possibly be identified as Arc. cranocephaloide, as noted above. Therefore, it seems appropriate not to remove the Arc. cranocephaloide biostraton from the zonal ammonite scale of the Bathonian of Siberia, but to use it tentatively (Fig. 6), given the absence of reliable finds of the index species in Siberian sections. As possible options for designating this interval of the scale, the following units can be proposed: “? Arcticoceras cranocephaloide Zone” or “Beds with Arcticoceras ex gr. cranocephaloide”.
We should also discuss the proposal of Meledina (2014) concerning the separation of “Beds without ammonites” between Arc. ishmae and Arc. cranocephaloide zones in the Siberian ammonite scale. Meledina proposed this informal subdivision for the entire middle Bathonian since the Arc. cranocephaloide Zone was dated Late Bathonian (Fig. 6). Nevertheless, even taking into account its Middle Bathonian age, the presence above the Arc. ishmae Zone of the interval with no ammonites, can be considered quite characteristic of boreal sections. For instance, in addition to Siberia, such an interval is also present in the basin of the Izhma River in the north of European Russia (Mitta et al., 2015). At the same time, it is evident (Fig. 7) that in Siberia, geochronological intervals without ammonites often correspond to unconformities, which may be associated with the loss of a significant part of the Middle Bathonian succession from the section. With increasing efforts in the search for ammonites in the preserved beds, the intervals not characterized by ammonites become not so large (Fig. 2). Accordingly, in our opinion, even though beds without ammonites should be recorded in specific sections, however, there is no need to distinguish such a special interval in the regional ammonite scale.
We also note in this context that we consider the proposals of Mitta and Alsen (2013) on updating the standard East Greenland ammonite scale of the Bathonian, especially the proposed transfer of the Arc. crassiplicatum faunal horizon from the upper part of the Arc. ishmae Zone to the lower part of the Arc cranocephaloide Zone. Despite the fact that this horizon was originally formally recognized as part of the Arc. ishmae Zone, in fact, throughout several decades, only the remaining part of this zone was recognized as the Arc. ishmae Zone. The reason for this was the lack of a formal description of its index species Arc. crassiplicatum until 2022 (Kiselev, 2022). Accordingly, it was not known what exactly should be recognized as the tops of the Arc. ishmae zone, which, unlike the Arc. cranocephaloide Zone is extremely widespread in Boreal regions. Unfortunately, one of the authors revised the previously put forward proposal (Alsen et al., 2020). However, in this work, following a number of authors (Kelly et al., 2015; Morton et al., 2020), we support Mitta and Alsen’s (2013) proposal (Fig. 7).
The relationship of the Siberian Beds with Catacadoceras barnstoni with the overlying rock stratum is also most evident in the Chekurovka sections in the lower reaches of the Lena River (Fig. 2a), especially in the southern Chucha section—Outcrop 3 (Meledina et al., 1991, text-fig. 4). Apparently, Callovian deposits directly overlie these beds over an unconformity. The confinement of the occurrences of Cat. aff. barnstoni and Cat. perrarum to relatively narrow stratigraphic intervals within the upper part of the Beds with Cat. barnstoni (Figs. 2a, 7) makes it possible to recognize biostratigraphic marker levels, which can be used for dating and correlating of Upper Bathonian deposits. In essence, they correspond to the concept of biohorizons, however, due to the single occurrence of Cat. aff. barnstoni and Cat. perrarum in situ, a formal description of these biostratons appears to be premature. It is possible that it would be more correct to recognize the Cadoceras lenaense Biohorizon (Kiselev, 2022), previously placed in the upper part of the Paracadoceras variabile Zone, in the lower Callovian, rather than in the lower part of the Catacadoceras calyx Zone, as the author of the biostraton suggested. Expressing doubts about the dating of the biohorizon, Kiselev took into account that the holotype of the index species was found at the base of the “Cat. calyx” Zone on the southern flank of the Chekurovskaya Anticline (Meledina, 1977; Meledina et al., 1991), formerly known as the Paracadoceras falsum Zone (Meledina et al., 1991), but later renamed due to the reidentification of ammonites (Knyazev et al., 2009). However, as stated above, their original identification as P. falsum seems correct. Judging by the comments of D.N. Kiselev, given in the description of the C. lenaense Biohorizon, the decisive factor in determining its age was the co-occurrence of C. lenaense with Paracadoceras variabile in the Upper Bathonian on the eastern coast of Anabar Bay. Probably, the possible erroneous locality details of the Chekurovka specimens were implied. This is supported by the inclusion of information on ammonites obtained during the study of the southern section near the village of Chekurovka (Meledina, 1977), into the characterization of the upper 10 meters of Member 8 Outcrop 3 at Cape Chucha (Meledina et al., 1991, p. 21). Only from other parts of the latest work (Meledina et al., 1991, p. 23, fig. 2), where, when mentioning a number of finds, including C. lenaense, references are made to their images in the monograph by Meledina (1977), it becomes clear that they actually come from a different section. We did not find C. lenaense in the northern section near the village of Chekurovka, nor was it previously recorded from this section. Nevertheless, in our opinion, it is still premature to draw conclusions about the factual material from the typical locality for C. lenaense, the southern section near the village of Chekurovka (Outcrop 7, Bed 36, 4–5 m below the top, along with P. falsum; after Meledina, 1977). It is highly desirable to once again carefully study the Anabar material for its correspondence to the species C. lenaense.
The results of the research indicate a significant stratigraphic incompleteness of the Middle-Upper Bathonian deposits in the lower reaches of the Lena River, which is obviously a characteristic feature of most sections in northern Siberia (Fig. 7). A significant part of the middle and upper Bathonian has not been preserved here due to erosion. This problem is exacerbated by complete absence of a stratigraphic equivalent of the Cadoceras apertum ammonite zone of the East Greenlandic reference sequence, including in the most complete section of the Upper Bathonian on the eastern coast of Anabar Bay. Even though no traces of a surface of erosion at the Bathonian–Callovian boundary were mentioned here (Knyazev et al., 2009, 2010), the possibility of hidden unconformity should not be ruled out. According to the latest data, the C. apertum Zone overlying the Catacadoceras calyx Zone is compared with the international standard Discus chronozone (Mitta and Alsen, 2013; Callomon et al., 2015; Kelly et al., 2015; Mönnig and Dietl, 2017; Alsen et al., 2020; Morton et al., 2020; etc.). It seems necessary to reflect the described situation in the zonal ammonite scale of Siberia, at least by a question mark at this level (Fig. 6).
CONCLUSIONS
The main result of the study is the updated ammonite zonal scale of the Middle–Upper Bathonian Siberia, which is recommended for use both in the regional stratigraphic schemes of the Jurassic deposits of eastern (Middle) Siberia and in the Boreal (Siberian) zonal standard of the Bathonian Stage. The proposed version is in the best way adapted to the present knowledge of ammonite biostratigraphy in the region and takes into account the following results and conclusions.
(1) It has been established that all northern Siberian specimens previously assigned to Arcticoceras cranocephaloide Callomon et Birkelund, 1985 are misidentified and do not provide evidence of the presence of this species in Siberian sections. Most of these ammonites belong to Catacadoceras barnstoni (Meek, 1859) or the narrow umbilical taxon referred to in this paper as Cat. aff. barnstoni. Accordingly, the stratigraphic interval, which previously corresponded in the Siberian sections to the Arc. cranocephaloide Zone should be entirely assigned to Beds with Cat. barnstoni.
(2) Arc. cranocephaloide affinity is not excluded only for the juvenile ammonite Arcticoceras sp., the find of which is known 2 m below the base of the Paracadoceras variabile Zone on the eastern coast of Anabar Bay. Hence, as possible options for designating the interval located between the Arc. ishmae and P. variabile zones in the zonal ammonite scale of Siberia, the following options are proposed: “? Arcticoceras cranocephaloide Zone” or “Beds with Arcticoceras ex gr. cranocephaloide”.
(3) At present it has been established that Cat. barnstoni co-occurs in northern Siberia with Cat. aff. barnstoni, Cat. perrarum, as well as with the ammonites Paracadoceras variabile, Arcticoceras (?) sp., Phylloceras billingsi and the last known members of the bivalve genus Retroceramus, similar to the fossil assemblages of northern North America. Judging from the macrofaunal composition and stratigraphic position of Cat. barnstoni in East Greenland, the Siberian Beds with Cat. barnstoni correspond to the Kepplerites rosenkrantzi faunal horizon marking the upper part of the P. variabile Zone in East Greenland. So far, only a single find of “K. ex gr. rosenkrantzi”, represented by a strongly distorted loosely collected shell, is known in northern Siberia.
(4) It seems extremely important to preserve Beds with Cat. barnstoni in the Bathonian zonal ammonite scale of Siberia, since this biostraton is more in demand here compared to the Paracadoceras variabile Zone due to the greater areal distribution and abundance of the index species. Its auxiliary status results from the impossibility to establish biostratons adjacent to it in any of the known Siberian sections. The interregional correlation function of Beds with Cat. barnstoni is also of significant importance as it allows correlation of this interval in the Siberian sections with the eponymous biostratigraphic unit in northern Canada and Franz Josef Land, as well as with the Kepplerites rosenkrantzi faunal horizon of East Greenland.
(5) In view of the absence of any signs of a stratigraphic equivalent of the Cadoceras apertum ammonite Zone of the East Greenland reference scale in northern Siberia, an taking into account the presence of Bathonian-Callovian transitional beds in the Anabar region, it was concluded that it would be reasonable to designate with a question mark a gap in the zonal ammonite succession of Siberia. This gap is confined to the upper part of the Upper Bathonian of the regional scale.
In addition to the updating of the zonal ammonite scale of the Bathonian of Siberia, two reference intervals (with Cat. aff. barnstoni and Cat. perrarum) are recognized, successively located within the upper part of the Upper Bathonian Beds with Cat. barnstoni useful for intra-regional (and possibly, in the future, inter-regional) correlations.
Notes
Here and further, the number (#) of a half-whorl means its ordinal number in ontogeny, starting from the protoconch or (if the protoconch has not been preserved for some reason) from the earliest preserved half-whorl. In the latter case, the presumed ordinal number of a half-whorl from the protoconch is indicated in parentheses.
In this work, in Fig. 17, it is erroneously indicated coming from Beds 26–27.
Here and below, the generic affiliation of index species of biostratigraphic units is cited in accordance with the taxonomy accepted in this work.
A level with numerous rounded belemnite rostra and fragments of rostra in the middle part of Member 40 (the base of Member 23a in a different stratification system) was taken as the unconformity level (Zakharov and Shurygin, 1978).
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ACKNOWLEDGMENTS
The authors are grateful to the reviewers D.B. Gulyaev (Commission for the Jurassic system of the Interdepartmental Stratigraphic Committee, Yaroslavl), D.N. Kiselev (K.D. Ushinsky Yaroslavl Pedagogical University, Yaroslavl) and M.A. Rogov (Geological Institute, Russian Academy of Sciences, Moscow) for critical analysis of the manuscript and suggestions for its improvement. We are grateful to V.V. Mitta (Paleontological Institute, Russian Academy of Sciences, Moscow) for providing photographs of the East Greenland ammonite collection (collected by J. Callomon and T. Birkelund), A.E. Igolnikov and A.G. Konstantinov (Trofimuk Institute of Petroleum Geology and Geophysics of the Siberian Branch of the Russian Academy of Sciences (IPGG SB RAS), Novosibirsk) for discussing a number of issues related to the morphogenesis of ammonites, B.N. Shurygin (IPGG SB RAS, Novosibirsk) for providing the 1987 field notes for Chekurovka sections and consultations on the location and geology of these sections, O.S. Urman (IPGG SB RAS, Novosibirsk) for the organization of field work on the northern Chekurovka section in 2019, in the study of which O.S. Dzyuba, E.K. Metelkin, E.S. Shamonin and P.A. Yan (IPGG SB RAS, Novosibirsk) also participated.
Funding
The study was supported by the Russian Science Foundation (grant no. 22-17-00228, https://rscf.ru/project/22-17-00228/, at Trofimuk Institute of Petroleum Geology and Geophysics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk. The geological structure of the northern Chekurovka section was studied in the course of the fieldwork supported by the Russian Ministry of Education and Science (projects FUUM-2019-0004, FWZZ-2022-0004, IPGG SB RAS, Novosibirsk; budget project, Diamond and Precious Metal Geology Institute of the Siberian Branch of the Russian Academy of Sciences (DPMGI SB RAS), Yakutsk).
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AUTHORS’ CONTRIBUTIONS
Ammonite identifications and the section “Arcticoceras cranocephaloide Callomon et Birkelund, 1985 vs. Catacadoceras barnstoni (Meek, 1859)” were prepared by E.S. Shamonin with consultations by V.G. Knyazev. The sections “Material, methods and terminology” and “Systematic paleontology” were written by E.S. Shamonin, who also prepared the ammonite specimens and prepared them for publication including photography. The sections “Introduction”, “Position of the Catacadoceras barnstoni biostraton in the zonal ammonite scale of the Bathonian Stage of Siberia” and “Conclusions” were written by E.S. Shamonin together with O.S. Dzyuba (emphasis on comprehensive data analysis, taking into account information on associated groups of macrofauna).
The same authors, as part of the field team of the IPGG SB RAS–NSU, studied the northern section near the village of Chekurovka in the lower reaches of the Lena River, where new fossils were collected. Ammonites from the Bathonian of Olenek Bay coast were collected by V.G. Knyazev.
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Translated by S. Nikolaeva
Reviewers D.B. Gulyaev, D.N. Kiselev, and M.A. Rogov
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Shamonin, E.S., Knyazev, V.G. & Dzyuba, O.S. The Ammonite Catacadoceras barnstoni Beds and the Problem of the Separation of the Middle and Upper Substages of the Bathonian Stage in Northern Siberia. Stratigr. Geol. Correl. 31, 275–298 (2023). https://doi.org/10.1134/S0869593823040032
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DOI: https://doi.org/10.1134/S0869593823040032