PROCEEDINGS
OF THE TOMSK ORDER OF THE RED BANNER OF LABOR
POLYTECHNIC INSTITUTE NAMED AFTER S. M. KIROV

Vol. 196 1969

NEW MIDDLE CAMBRIAN TRILOBITES OF THE SANDY-SHALE SEQUENCE OF THE YULIYA MINE AREA

(Batenevsky Ridge)

A. K. SEMASHKO

(Presented by Prof. A. G. Sivov)

South of the Yuliya mine, approximately one kilometer away, in the direction of Son station, deposits of a sandy-shale sequence with subordinate interbeds of dark-gray limestones extend in a narrow belt.

Until recently, this sequence, which differs markedly in material composition from the surrounding rocks and had not been characterized paleontologically, did not have a definite stratigraphic position in the Cambrian section of the Batenevsky Ridge. Having, in most cases, tectonic contacts with the enclosing rocks, the sequence was assigned by some investigators [2] to the Lower Cambrian.

In 1964, V. E. Nomokonov, a postgraduate student of the Tomsk Polytechnic Institute, discovered a fauna of trilobites, brachiopods, and hyoliths in one of the limestone interbeds southeast of the Yuliya mine. The paleontological remains submitted to the author, as well as the materials of personal collections and the results of a geological study of the area in the summer of 1965, made it possible to establish quite definitely the age of the enclosing sequence and its stratigraphic position.

As already stated above, in the area of the faunal locality the sequence is represented by brownish-yellow, commonly silicified sandstones and shales with rather rare, thin (up to 1.5–2 m) interbeds of dark-gray bedded limestones. One of these interbeds, containing remains of trilobites, has been traced for a distance of about one kilometer and has a persistent northeastern strike with a dip to the northwest at an angle of 30–40°. In general, the sequence has a uniform northwestern dip; no additional folding is established. Its relation to the underlying sequences is established in the area of Mount Skalistaya, where the sandy-shale deposits rest with angular unconformity on light-colored massive limestones that are younger in age than the deposits of Mount Dolgii Mys (Obruchevsky horizon).

The trilobite faunal locality is situated in a limestone interbed 1.5 m thick on the western spur of an elevation with a mark of 630.5 m, 100 m from the summit. From here the following genera and species have been identified: Oryctocephalops frischenfeldi Lerm., Corinexochus cf. exelsus Suv., Olenoides sp., Bathynotus fortis sp. nov., Bathynotus rotundus sp. nov., Erbia sibirica (Schm.), Erbia granulosa Lerm., Prophedinella erbiensis Sivov, Gaphuraspis cf. gaphuri Ivsh., Pachyaspis sp., Antagmopleura sp., Chondranomocare sp., Juliaspis solidus gen. et sp. nov., Guraspis punctatus

gen. et sp. nov., Binella culta gen. et sp. nov., Neopagetina nomokonovi sp. nov.

The trilobite assemblage cited, in general, has a clearly Middle Cambrian aspect; the presence of Oryctocephalops frischenfeldi Lerm., a zonal form of the Amgan Stage of the Siberian Platform [4], gives grounds for correlating the enclosing sequence with the corresponding deposits of the Siberian Platform, and also with the Sladkie Korenya Mountain horizon of the Batenevsky Ridge, for which the above-mentioned assemblage, with the possible exception of some new forms, is typical.

Thus, the age of the sandy-shale sequence is quite definitely established as Middle Cambrian. Most probably, this sequence is a facies analogue of the limestones of Sladkie Korenya Mountain, which contain a similar faunal assemblage.

Below is given a monographic description of the new trilobites. All of them were found in one locality, designated as point no. 4734 or 22, which is unambiguous. The locality is situated 625 m from the “Khakasskii” animal-breeding state farm on azimuth NW-315°.

Class Trilobita Walch, 1771.
Order Miomera Jaekel, 1909.
Superfamily Eodiscoidea Raymond, 1913.
Family Pagetiidae Kobayashi, 1935.
Genus Neopagetina Pokrovskaya, 1960.

Neopagetina nomokonovi¹ Semashko sp. nov.

(Plate 1, figs. 11—13).

Holotype: 22/9, collection of A. K. Semashko, TPI, Tomsk.

Material. Six cranidia and pygidia, well and incompletely preserved.

Description. Cranidium of small size, with a rounded anterior margin. The glabella is elongated, pointed, and bears two pairs of barely noticeable furrows. The fixed cheeks, enclosing the glabella anteriorly, end in a depression at its anterior end. The palpebral lobes are small, median; the ocular ridges are not expressed. The occipital ring is widened in the middle; possibly a spine is present. The anterior border has transverse notches. The surface of the carapace is smooth.

Dimensions (in mm):

The pygidium is rounded-triangular, with segmented pleurae surrounding the rachis. The pleural furrows are sharp, the interpleural ones weak. The rachis, consisting of six rounded-rhombic rings, narrows sharply in the depressed posterior third. The border is very thin, threadlike. The surface of the pygidium is finely tuberculate.

Dimensions of the pygidium (in mm):

Comparison. The cranidium of the new species is closest in structure to Pagetina primaeva Lerm. (Lermontova, 1940, p. 121, pl. 35, fig. 4,

4a–c) and differs in having a more rounded anterior margin. The pygidium of the new species is sharply distinct from the pygidia of previously described species of the genus Neopagetina Pokr.

Order Polymera Jaekel, 1909.
Superfamily Telephoidea Angelin, 1854.
Family Komaspididae Kobayashi, 1935.
Subfamily Bathynotinae Hupe, 1953.
Genus Bathynotus Hall, 1860.

Bathynotus fortis Semashko sp. nov.

Plate 1, figs. 3, 4.

Holotype: 4734/1, collection of A. K. Semashko, TPI, Tomsk.
Material. More than ten cranidia of varying degrees of preservation.
Description. Cranidium rounded-trapezoidal. Glabella rounded-conical, very broad at the base, bearing two pairs of transverse furrows. The posterior pair, directed obliquely backward, reaches its greatest depth near the middle of the glabella and is connected by a fine transverse furrow. The anterior pair is more weakly expressed and repeats the structure of the posterior one. The fixed cheeks are narrow, equal to 1/3 of the width of the glabella at the base, and slope down toward the palpebral lobes. The palpebral lobes are large, curved, directed obliquely from the anterolateral corners of the glabella; after a knee-like bend they are almost parallel to the longitudinal axis of the cranidium. The occipital ring is broad, with a small tubercle at the posterior margin. The posterolateral limbs of the cranidium are small, drawn backward. The surface is smooth.

Dimensions (in mm):

Comparison. The described species is closest to Bathynotus granulatus Lerm. (Lermontova, 1940, p. 134, pl. XI, figs. 2, 2a–c). It differs in the lesser narrowing of the glabella, its sharper furrows, the absence of sculpture, longer palpebral lobes, and posterolateral limbs of the cranidium drawn backward.

Bathynotus rotundus Semashko sp. nov.

Plate 1, figs. 1, 2.

Holotype: No. 4734, collection of A. K. Semashko, TPI.
Material. Eight cranidia of good and satisfactory preservation.
Description. Cranidium broad, rounded-trapezoidal. Its greatest width is in the middle part. Glabella conical, elongate, with two pairs of furrows. The posterior pair is connected by a fine transverse furrow; the anterior pair is very weakly expressed. Fixed cheeks relatively broad, equal to 1/2 of the width of the glabella at the base. The palpebral lobes are large, crescent-shaped. The occipital ring bears a small tubercle. The posterolateral limbs of the cranidium are very small, slightly drawn backward. The surface of the carapace is smooth.

* Fortis (Lat.) — strong.
** Rotundus (Lat.) — rounded.

Dimensions (in mm):

Comparison. It differs from Bathynotus fortis in the more elongated form of the glabella, the character of its segmentation, the semilunate form of the palpebral lobes, and the very small posterolateral lobes of the cranidium.

Superfamily Solenopleuroidea Angelin, 1854.
Family Catillicephalidae Raymond, 1938.

Subfamily Juliaspinae Semashko subfam. nov.

Cranidia small, trapezoidal in form, convex. Glabella rounded, convex. Segmentation of the glabella weak. Fixed cheeks narrow, palpebral lobes small. The brim in front of the glabella is absent; an anterior border is always present. Anterior branches of the facial sutures convergent, posterior branches divergent.

Remarks. Within the family Catillicephalidae we propose to distinguish two subfamilies: the subfamily Juliaspinae described above and the subfamily Catillicephalinae. To the subfamily Juliaspinae we assign catillicephalids whose principal distinguishing character is the presence of an anterior border. In representatives of the subfamily Catillicephalinae the anterior border is not developed.

Genus Juliaspis Semashko gen. nov.

Type species: Juliaspis solidus Semashko gen. et sp. nov.

Description. Small trilobites with a rounded-trapezoidal convex cranidium. The glabella is convex, overhangs the cranidium, and has the form of a rounded rectangle, slightly narrowing toward the blunt anterior end. The glabella is divided by two pairs of weak furrows, of which the posterior pair obliquely cuts the base of the glabella, not quite reaching the occipital furrow; the anterior pair is transverse, very weak. Palpebral lobes small, median; palpebral ridges oblique. Fixed cheeks narrow. The occipital ring is widened along the midline. A frontal brim is present only on the sides of the glabella. The anterior border is ridge-like, narrowing sharply at the anterolateral angles of the cranidium. The anterior branches of the facial sutures are convergent, the posterior branches divergent.

The surface of the carapace is smooth.

Comparison. From the closest genus Catillicephalites Rasetti [6], the genus Juliaspis differs in its rectangular-rounded glabella, which is almost not narrowed anteriorly, in the median position of the palpebral lobes, and in the broad ridge-like anterior border.

Juliaspis solidus Semashko gen. et sp. nov.

Plate 1, figs. 5a–c, 6.

Holotype: No. 22/1, collection of A. K. Semashko, TPI.

Material. About two dozen cranidia of varying degrees of preservation.

Description. The description of the species is identical to that of the genus.

* Solidus (Lat.) — solid.

Measurements (in mm):

Superfamily Corynexochoidea Angelin, 1854.
Family Dorypygidae Kobayashi, 1964.
Subfamily Milaspinae Suvorova, 1964.

Genus Guraspis Semashko gen. nov.

Type species: Guraspis punctatus Semashko gen. et sp. nov.

Description. Anterior-cheeked trilobites with small cranidia (up to 2–2.5 mm). The glabella is narrow, cylindrical, sharply widening at the anterior margin, and has pointed anterolateral angles. Segmentation of the glabella is well expressed in adult specimens as three pairs of depressions on the glabella at the dorsal furrows, the anterior pair being the most distinct. The dorsal furrows are sharp. The fixed cheeks are convex, equal to or slightly greater than the width of the glabella in its middle part. The palpebral lobes are small, median; the palpebral ridges are not expressed. The occipital ring is smooth, equal in width to the anterior part of the glabella. The border is absent; a sharp marginal furrow separates the glabella from the threadlike anterior marginal rim. The posterolateral lobes of the cranidium are drawn out into sharp spines, equal to 1/3 the length of the glabella.

Comparison. The genus Guraspis is closest to the genus Milaspis Sivov and differs from it in the cylindrical form of the glabella, with its sharp expansion at the anterior end; in Milaspis the glabella widens smoothly from the base. In addition, the new genus differs from Milaspis in the median position of the palpebral lobes and in the indistinct palpebral ridges.

Guraspis punctatus¹ Semashko gen. et sp. nov.

Plate 1, figs. 8–10.

Holotype: No. 4734/3, collection of A. K. Semashko, TPI.

Material. More than 10 cranidia of good and satisfactory preservation.

Description. The description of the species is identical to the description of the genus.

Measurements (in mm):

Superfamily Ptychoparioidea Matthew, 1888.
Family Alokistocaridae Resser, 1939.

Genus Binella Semashko gen. nov.

Type species: Binella culta² Semashko gen. et sp. nov.

Description. The cranidium is small, rounded-trapezoidal, with a width at the base slightly exceeding the length (3 by 2.5 mm). The glabella is fairly broad at the base, keeled, sharply

¹ Punctatus (Lat.) — punctate.
² Culta (Lat.) — elegant.

narrowing toward the middle, it widens again at the blunted anterior end. The segmentation of the glabella is not expressed, except for a constriction in the anterior part before the widening. The palpebral lobes are small, almost median. The palpebral ridges are slightly curved forward, almost horizontal. The fixed cheeks, equal to 3/4 of the width of the glabella at the base, rise gently from the dorsal furrows toward the palpebral lobes. The occipital ring widens in the middle and bears a median tubercle displaced toward the occipital furrow. The anterior border is ridge-like, upturned, reaching its greatest height and width in front of the glabella; it narrows and descends toward the facial sutures. The sculpture present on the border, in the form of tubercles, may be regarded as notching. A broad and shallow marginal furrow passes into a limbus that rises toward the anterior end of the glabella.

The anterior branches of the facial sutures are subparallel; the posterior ones diverge.

The surface of the cranidium is covered with smoothed, closely spaced tubercles.

Comparison. The new genus has some resemblance to the genus Amecephalina Poulsen in the general form of the cranidium; however, the structure of the glabella, the character of the sculpture, and the great width of the fixed cheeks preclude assigning the form described to that genus.

Binella culta Semashko gen. et sp. nov.

Plate 1, fig. 7.

Holotype: No. 22/8, collection of A. K. Semashko, TPI.
Material. Two cranidia of satisfactory preservation.
Description. The description of the species corresponds to the description of the genus.

Dimensions (in mm):

REFERENCES

1. Biostratigraphy of the Paleozoic of the Sayano-Altai Mountain Region. Trudy SNIIGGiMS, vol. 1, issue 19, 1960.

2. R. T. Bognibova. Stratigraphic position and age of the archaeocyathid-trilobite limestone unit in the area of Mount Arkheotsiatovaya and Sladkie Koreni (Batenevsky Ridge). Trudy SNIIGGiMS, issue 34, 1965.

3. E. V. Lermontova. Class Trilobita. Atlas of the Guide Forms of Fossil Faunas of the USSR, vol. 1. Cambrian. Gostgeolizdat, 1940.

4. Resolutions of the Interdepartmental Conference on the Development of Unified Stratigraphic Schemes for Siberia. Gosgeolizdat, 1959.

5. N. E. Chernysheva. Cambrian stratigraphy of the Aldan anteclise and paleontological substantiation for the recognition of the Amginian stage. Gostoptekhizdat, 1961.

6. Rasetti F. Middle Cambrian ptychoparioid trilobites from the conglomerates of Quebec. Journ. Paleontol., vol. 37, no. 3, 1963.

1. The name is given in honor of the geologist V. E. Nomokonov, who first found the trilobite fauna described here. ↩