On Some Early Triassic Pectinacea (Bivalvia) from the Eastern Pre Caucasus and Mangyshlak

[p. 83]

ON SOME EARLY TRIASSIC PECTINACEA (BIVALVIA) FROM THE EASTERN PRE­CAUCASUS AND MANGYSHLAK

V. A. Gavrilova[*]

Information is presented on the range of bivalves of superfamily Pectinacea, discovered in Lower Triassic deposits of the Eastern Pre-Caucasus and Mangyshlak, as well as descriptions of eight species: Eumorphotis telleri, E. multiformis, Leptochondria minima, L. bittneri, L. (?) dagestana sp. nov., Ornithopecten temirbabensis, Palaeontolium microtis and Entolioides ussuricus, and also illustration of one taxon, Claraia cf. punjabiensis is given.

Ammonoids have the greatest value for the biostratigraphic partition of the Lower Triassic in the regions being studied. At that, in Mangyshlak in sections of the Tyururpinskiy Series, uncovered and revealed along the core of deep drill holes, the currently most detailed sequence of changes of complexes of late Dzhelamian [Olenekian?] ammonoids are seen, allowing the distinguishing of five biostrata [7].[1] One should emphasize that here marine Upper Dzhelamian sediments lie under and are covered by red-colored and terrigenous formations without ammonoids.

In the Eastern Pre-Caucasus, Triassic sediments have been established only as a result of deep drilling for oil and gas. In a stratigraphic chart of 1979, the Kultayskaya and Dem’yanovskaya Svitas are included in the Dzhelamian stage [8]. According to the complexes of ammonoids observed in them, the former is assigned to the Lower Dzhelamian substage, and the latter to the Upper Dzhelamian. However, poor preservation of the rock material and weak paleontological description do not allow accomplishing a more detailed partition of the Upper Dzhelamian according to ammonoids in this region.

In frequency and preservation, especially in the core of the drill hole, they are far inferior in numbers to bivalves. The presence of the latter is as well an important index of a definite facies environment which allows them to be used for reconstructing the conditions of sedimentation. Many species of bivalves had entered into stratigraphic charts of western Central Asia and the Eastern Pre-Caucasus at all only on the basis of preliminary paleontological identifications. Until now, Early Triassic bivalves of the southern regions of SNG remain very poorly studied.

Our article is devoted to the results of research of Pectinacea, most widely distributed in in Dzhelamian sediments of the Eastern Pre-Caucasus and Mangyshlak. The collections of T. V. Babicheva (Central Asian Expedition of IGiRGI) 1982, 1984 and those of the author in 1978–1980 and 1984 are used in this work.

The description of Pectinacea given below was done first and is a supplement to the paleontological description of the Parsymurunskaya, Uzen’skaya, and Tartalinskaya Svitas of Mangyshlak, and is its [p. 84] paleontological foundation for Dem’yanovskaya Svita of the Eastern Pre-Caucasus [2, 6, 7, 8].

The monographic study of Dzhelamian complexes of Pectinacea of the regions being examined allowed establishing their systematic composition and stratigraphic range. Three families are represented here: Pterinopectinidae Newell, 1938, Aviculopectinidae Meek et Hayden, 1864 and Entoliidae Korobkov, 1960. The first family is represented by six taxa: Claraia aurita (Hauer), Claraia orbicularis dagestanica Gavr. subsp. nov., Claraia stavropolica Gavr. sp. nov., Cl. australasiatica kumschokensis Gavr. subsp. nov., Cl. aff. tridentina (Bittn.), Cl. cf. punjabiensis (Witt.), examined in a separate article. Only a photo illustration of the species Cl. cf. punjabiensis (Witt.) is given for comparison in this work. The following species are assigned to Aviculopectinidae: Eumorphotis telleri (Bittn.), E. multiformis (Bittn.), Leptochondria minima (Kipar.), L. bittneri (Kipar.), L. (?) dagestanica Gavr. sp. n., and Ornithopecten temirbabensis Kipar. Only two species of Entoliidae have been studied: Palaeoentolium microtis (Witt.) and Entolioides ussuricus (Bittn.). The oldest representative of Pectinacea is endemic species Ornithopecten temirbabensis Kipar., remains of which have been discovered in the cores of many drill holes in the territory of Yuzhno-Mangyshlak depression. Finds of it coincide with variegated clay siltstones and calciferous argillites of the Upper Parsymurunskaya Svita, traced through areas in the Zheltybay-Uzen’, Zhazgurla, and Aksu­Kendyrlik zones of lithofacies. Because it lies directly under formations of the Uzen’skaya Svita with Late Dzhelamian ammonoids in all sections, its geological age is conditionally accepted as Early Dzhelamian.

The rest of the Pectinacea species were discovered together with remains of ammonoids.

Analysis of species composition of studied Pectinacea demonstrated that five species are common to those of southern Primor’ye, established earlier by A. Bittner and L. D. Kiparisova in Dzhelamian sediments but at a lower stratigraphic level (Meekoceras layers–Owenites zone): Leptochondria minima Kiparisova, L. bittneri Kiparisova, Entolioides ussuricus (Bittner), Palaeoentolium microtis (Witt.) and Eumorphotis multiformis (Bittner). Finds of the species mentioned in Upper Dzhelamian sediments of Mangyshlak and the Eastern Pre-Caucasus could be evidence of either their broader stratigraphic range as a whole, or of migration from Primor’ye to regions to the west.

With descriptions of studied Pectinacea species, terminology previously suggested byN.I. Kurushin [3] is used.

The collection is kept in the F. N. Chernyshev Central Research Geology Museum in St.Petersburg under No. 12682.

Superfamily Pectinacea Rafinesque, 1815

Family Aviculopectinidae Meek et Hayden, 1864

Subfamily Aviculopectininae Meek et Hayden, 1864

Genus Eumorphotis Bittner, 1901

Eumorphotis telleri (Bittner, 1899)

Pl. 1, Fig. 4

Pseudomonotis telleri:Bittner, 1899a, p. 710, pl. 15, figs. 11–15; 1901a, p. 568, pl. 22, figs. 1–5; Frech,1909, p. 22, pl. 2, figs. 3, 4;

Pseudomonotis (Eumorphotis) telleri:Ogilvie-Gordon, 1927, p. 20, pl. 1, figs. 6a–b; Kiparisova, 1947, pl.

14, fig. 5;

Eumorphotis telleri: Ichikawa, 1958, p. 154, pl. 22, figs. 11–13.

The lectotype is described in A. Bittner’s work [11, pl. 15, fig. 13]. Alps, Yugoslavia, Lower Triassic, Upper Werfenian strata.

Description. Shell is average size (up to 30.5 mm in height and up to 25 mm in length), oval, slightly prosocline, inequilateral, strongly elongate in height. Hinge is straight, long, somewhat less than the overall shell length. Apical angle is 82°.

Left valve is strongly convex, the maximum convexity being found in the upper half of its height. The beak is massive, turning slightly forward, hanging like a vulture over the hinge and being approximately one third of the overall valve length distant from anterior margin. Anterior slope of beak is steep, but the posterior and lower are more gently sloping. Anterior auricle is triangular, slightly convex and separated from main field of the valve by a rather deep groove. Posterior auricle is set apart by a gently sloping bend, is flat and larger than anterior.

Surface of valve is covered with weak and irregular concentric growth marks.

Dimensions(mm):

Spec. No. / H / L / H/L / Hinge Length / Hinge Length/L / Convexity / Convexity/H / 
4/12 682 / 30.5 / 24.6 / 1.23 / 23.8 / 0.96 / 10.6 / 0.30 / 82°

Comparison. The examined specimen differs from the most closely related species, Eumorphotis iwanovi (Bittner) [1, p. 8, pl. 1, figs. 1–9] from Lower Triassic beds of Yuzhno­ Ussuriyskiy Kray by having valves more elongate in height, a massive beak, turned forward, by greater difference in dimensions of auricles and by the absence of radial ribs.

Range. Lower Triassic of Darvaz, Hungary, Yugoslavia; Upper Dzhelamian of Mangyshlak.

Material. Single steinkern of left valve of satisfactory preservation.

Eumorphotis multiformis (Bittner, 1899)

Pl. 1, figs. 2, 3

Pseudomonotis multiformis: Bittner, 1899, p. 10, pl. 2, figs. 15–22;

Pseudomonotis(Eumorphotis) multiformis:Spath, 1935, p. 74, pl. 22, fig. 8; Kiparisova, 1947, p. 97, pl. 15, figs. 1–9; 1954, p. 10, pl. 1, figs 11–13;

Eumorphotis multiformis: Kiparisova, 1938, p. 224, pl. 2, figs. 4, 9, 12; pl. 3, figs. 2–4; Ciriacks, 1963, p. 77, pl. 15, figs. 13–15; Nakazawa, 1971, p. 117, pl. 23, figs. 7–12; Chen, 1976, p. 184, pl. 30, figs. 34–35; Yin Hongfu et Ho Yuanliang, 1979, pl. 14, fig. 3;

Eumorphotis multiformis var. regularaecosta:Kiparisova, 1938, p. 227, pl. 2, figs 10–11;

Eumorphotis multiformis var. rara:Kiparisova, 1938, p. 227, pl. 3, fig. 1;

Eumorphotis multiformis var. rudaecosta: Kiparisova, 1938, p. 226, pl. 2, figs. 5 14;

Eumorphotis multiformis regularaecosta: Ciriacks, 1963, p. 77, pl. 15, fig. 14; Chen, 1976, p. 185, pl. 30, fig. 29

Eumorphotis multiformis rudaecosta: Okuneva, 1976, p. 28, pl. 1, figs. 1,3; Chen, 1976, p. 185, pl. 30, fig. 33.

The lectotype is illustrated in Bittner’s work [1, pl. 2, fig. 21]. No. 45/221, TsNIG Museum. Yuzhno, Ussuriyskiy Kray, Shamara River, Lower Triassic.

Description. Shell is of average size (up to 39.5 mm in height and 31.5 in length), slightly prosocline, oval, elongate in height,

[p. 86]

[p. 87] not equilateral. Beak strongly protrudes beyond the long straight hinge, visibly close to anterior margin. Apical angle is equal to 88 - 90°.

Left valve is strongly convex with maximum convexity in upper half of its height. Anterior auricle is close to right-angled, convex and set well apart from main field of valve by a narrow groove. Larger, slightly separated auricle, flat, elongate in length, pointed. { sic }

Entire surface of the valve, including auricles, is covered with radial ribs of three-four orders, varying in nature of arrangement, length and prominence. Thus, in the Dagestan specimen (Ill. 1, fig. 2), the coarsest ribbing, situated in a three-order system, is visible. Ribs of the first and second orders differ slightly in length and prominence, and ribs of the third order are substantially finer and have an irregular arrangement: on the anterior half of valve surface, interspaces of ribs of first and second orders are developed in twos, but in the posterior margin, they {are developed} either singly or are absent altogether.

In the largest outer steinkern of the left valve, without an anterior auricle with ragged surface in the part around the beak (Ill. 1, fig. 3), the radial sculpture is regularly situated and is slightly distinguishable in prominence of ribs of four orders.

Distinct concentric, but irregular growth lines are developed as well on valves, as a result of the intersection with which, ribs acquire unevenness or serration. On the auricles, growth lines bend, turned toward the beak with convexity.

Pl. 1. Fig. 1. Claraia cf. punjabiensis (Wittenburg, 1909). Spec. No. 11/2682, a – left valve, x1.5; b –view from beak side, x2. Mangyshlak, southwestern slope of Kumshoky Mountain, outcrop 2, layer 7, sample 2–7–78f/80. Upper Dzhelamian, Tartalinskaya Svita. Collections of V. A. Gavrilova, 1980. Figs. 2–3. Eumorphotis multiformis (Bittner, 1899). 2 – Specimen No. 2/12682, left valve, xl. Dagestan, Darginskaya area, drill hole 2, 4126–4116 m depth. Upper Dzhelamian, Dem’yanovskaya Svita. Collections of V. A. Gavrilova, 1984; 3 – Specimen No. 3/12682, left valve, x1. Mangyshlak, southwestern slope of Kumshoky Mountain, outcrop 2, layer 8, specimen 2–8–79f/80. Upper Dzhelamian, Tartalinskaya Svita, Collections of V .A. Gavrilova, 1980. Fig. 4. Eumorphotis telleri (Bittner, 1899) Specimen No. 4/12682, left valve, x1. Mangyshlak, north slope of Karatauchik Range, region of Dollapa Well, outcrop 3, sample 3–11f/79. Upper Dzhelamian, Tartalinskaya Svita. Collections of V. A. Gavrilova, 1979. Figs. 5, 6. Leptochondria minima (Kiparisova, 1938), 5 – Specimen No. 5/12682, 5a – left valve, x4; 5b – the same, x5; 6 – Specimen No. 6/12682, 6a – left valve, x4; 6b – the same, x5. Mangyshlak, northern slope of Karatauchik Range, Dollapa Well region, outcrop 3, sample 3–24f/79. Upper Dzhelamian, Tartalinskaya Svita. Collections of V. A. Gavrilova, 1979. Figs. 7, 8. Leptochondria bittneri (Kiparisova, 1938). 7 – Specimen No. 7112682, left valve, x3. Mangyshlak, southwestern slope of Kumshoky Mountain, outcrop 2, layer 8, sample 2–8–79f/80. Collections of V. A. Gavrilova, 1980. 8 – Specimen No. 8/12682, right valve, x2. Northern slope of Karatauchik Range, Dollapa Well region, outcrop 3, sample 3–16f/79. Upper Dzhelamian, Tartalinskaya Svita. Collections of V. A. Gavrilova, 1979. Figs. 9, 10. Leptochondria (?) dagestanica Gavrilova, sp. nov. 9 – Specimen no. 9/12682, left valve, x1. Mangyshlak, northern slope of Karatauchik Range, region of Dollapa Well, outcrop 3, sample 3–16f/79. Upper Dzhelamian, Tartalinskaya Svita. Collections of V. A. Gavrilova, 1979. 10 – holotype No. 10/12682, 10a – left valve, x1; 10b – the same; x2.5. Dagestan, Solonchakovaya area, drill hole 47, 4470–4465 m depth. Upper Dzhelamian, Dem’yanskaya Svita. Collections of V . A. Gavrilova, 1984. Figs. 11, 12. Ornithopecten temirbabensis Kiparisova, 1980. 11 – Specimen No. 11/12682, left valve, x5. Southern Mangyshlak, Zhilandy area, drill hole 4, 3944–3937 m depth. 12 – Specimen No. 12/12682, impression of right valve, x5. Tasbulat area, drill hole 26, 3642–3633 m depth. Lower Dzhelamian, Parsymurunskaya Svita. Collections of T. V. Babicheva, 1982, 1984.

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Dimensions(mm):

Spec. No. / H / L / H/L / Hinge Length / Hinge Length/L / Convexity / Convexity/H / 
23/12 682 / 19.2 / 18.l / 1.06 / 17.3 / 0.95 / 7.8 / 0.40 / 88°
2/12 682 / 35.4 / 27.2 / 1.30 / – / – / 6.4 / 0.18 / –
3/12 682 / 39.5 / 31.5 / 1.25 / – / – / 12.l / 0.31 / 90°

Comparison and remarks.The collection of syntypes of species Eumorphotis multiformis (Bittner), which was the basis of study for its designation and the first description carried out by A. Bittner [1], contains 6 left valves. I suggest the largest left valve of these, with slightly damaged auricles, be the lectotype; it has an exceptionally a well-preserved sculptured surface, the most typical for the species being examined.

The specimens studied differ from the species Eumorphotis telleri (Bittner) described above in having large dimensions, smaller apical angle and by the presence of radial ribbing.

It is distinguished from Eumorphotis iwanovi [1, p. 8, pl. 1, figs. 1-9], described by A. Bittner from Lower Triassic of Yuzhno-Ussuriyskiy Kray, by smaller size of valves elongate in height and multi-order system of radial ribbing, which covers the entire surface of the shell.

Range.Lower Dzhelamian of Yuzhnoye Primor’ye, Khabarovskiy Kray; upper Dzhelamian of Dagestan and Mangyshlak; Lower Triassic of Greenland, U.S., China, and Japan.

Material.One impression and three steinkerns of left valves in various states of preservation from three localities.

Genus Leptochondria Bittner, 1891

Leptochondria minima (Kiparisova, 1938)

Pl. 1, Figs. 5, 6

Pecten (Leptochondria?)ex. aff. albertii: Bittner, 1899, p. 6, pl. 2, figs 1,2, 4–10;

Pecten (Velopecten) minimus:Kiparisova, 1938, p. 246, pl. 4, figs. 10, 12; pl. 5, figs. 4–6; 1947, p. 113, pl. 21, figs. 3, 6. 9, 10; 1954, p. 12, pl. 3, figs. 3–7;

Pecten (Velopecten) minimus var. reticulatus:Kiparisova , I 938, p. 247, pl. 5, figs. 1–2;

Pecten (Velopecten) minimus var. laevis:Kiparisova, 1938, p. 247, pl. 5, fig. 3;

Leptochondria minima:Nakazawa, 1971, p. 119, pl. 23, figs. 13 &14 ; Chen, 1976, p. 159, pl. 29, figs. 1–3; Yin Hongfu et Ho Yuanliang, 1979, pl. 14, fig. 6.

Holotype is illustrated in L. D. Kiparisova’s work [4, pl. 5, fig. 5]. No 42/10909, TsNIG Museum. Ussuriyskiy Kray, Russkiy Island, Karpinskaya Bay; Lower Triassic.

Description.Left valves are small (up to 10 mm in height and length), close to round in outline, almost equilateral. Beaks are small, central, slightly protruding beyond the straight hinge. Apical angle is equal to 100-109°. Valve is convex with auricles slightly delimited. Anterior auricle is substantially larger than posterior and is set apart from overall surface of valve by a weak depression. It is slightly convex, and when joining the anterior margin, has an almost right-angled outline. The posterior auricle, in no way separated from the valve surface, gradually is joined to the posterior margin at an obtuse angle.

Valve surface is covered with numerous radial thread-like, straight anddensely situated riblets of one order, strongly pronounced with the aid of a magnifying glass. In some specimen [p. 89] they are more bold, and in others, they are flatter. Five mm from the beak, the number of riblets reaches 60–70. On the valve, concentric, regularly situated, more feebly marked, fine growth lines and irregular, coarse folds are developed as well; in some specimens, 11–14 such folds are observed. At the intersection with them, the riblets bend and the surface of the valve acquires a concentrically undulating nature. Auricles are covered with radial striae and thread-like growth lines.

Dimensions(mm):

Spec. No. / H / L / H/L / Hinge Length / Hinge Length/L / 
5/12 682 / 8.5 / 8.7 / 0.98 / 4.9 / 0.56 / 100°
6/12 682 / 9.6 / 10.0 / 0.96 / 6.8 / 0.68 / 109°

Comparison.The Mangyshlak specimens are very closely related to shells of Leptochondria bittneri [4, p. 243, figs. 5–9, 11, 13] from the Lower Triassic of Ussuriyskiy Kray, being distinguished from the latter by smaller size and more feeble and simple radial sculpture on the left valve.

From Leptochondria albertii [3, p. 90, pl. 17, figs. 3–8] from Anisian deposits of northern Central Siberia, it differs not only by substantially smaller dimensions, but also by more convex left valve, as well as by thread-like radial sculpture.

Range.Lower Dzhelamian: Ussuriyskiy Kray; Upper Dzhelamian; Mangyshlak; Lower Triassic: China, Japan.

Material.Three steinkerns and five impressions of left valves in varying states of preservation from two localities.

Leptochondria bittneri (Kiparisova, 1938)

Pl. 1, Figs. 7, 8

Pseudomonotis cf. multiformis:Bittner, 1899, p. 10, pl. 2, figs. 11–14;

Pecten (Velopecten) bittneri:Kiparisova, 1938, p. 243, pl. 4, figs. 5–9, 11, 13; 1947, p. 113, pl. 21, figs. 4, 5, 7, 8;

Leptochondria cf. bittneri:Chen, 1976, pl. 29, fig. 4.

Holotype is illustrated in L. D. Kiparisova’s work [4, pl. 4, fig. 11]. No. 38/10909, TsNIG Museum. Ussuriyskiy Kray, Russkiy Island, Lower Triassic.

Description.Shells are small (up to 14 mm in height and 13 mm long), from rounded to slightly elongate in height, almost equilateral. Beaks are small, central, protruding slightly over the straight hinge. Apical angle is equal to 105-116°.

Left valve is uniformly convex with slightly delimited auricles. Anterior auricle is slightly larger than the posterior one and separated from the overall field of the valve by an outlining groove. Auricles are slightly convex and joined to the anterior and posterior margins at almost identical obtuse angles. Valve surface is covered with fine radial riblets of several orders, concentric growth lines and nicks. At that, several variations in the manner of arrangement of radial riblets on the valves are visible. Between two ribs of the first order, a single rib of the second order proceeds from the beak to the lower margin. Riblets of the third order appear at a distance equal to approximately 1/3 of height from the beak. One more riblet of the fourth order is wedged in from the middle of the valve height, but they are not visible in every rib interspace. Ribs of the first two orders are coarser and more bold, which, in their prominence are visibly distinguished [p. 90] from each other, and the ribs of the third and fourth orders are more smoothed out {softened} and fine, almost identical in prominence. At 5 mm from the beak, the number of ribs reaches 50–55. The concentric sculpture is represented by thread-like growth lines and disorderly nicks. Sometimes, where intersecting with the latter, the radial ribs break down and acquire a somewhat displaced new direction. Auricles are covered with more strongly pronounced concentric growth lines and scarcely visible radial striae.

The right valve is slightly convex, not equilateral in outline, with attenuated anterior margin. Anterior auricle is set apart from the main valve field by a groove, which replaces a deep byssal notch. Radial sculpture is more feeble and simpler than in the left valve.

Dimensions(mm):

Spec. No. / H / L / H/L / Hinge length / Hinge length/L / 
7/12 682 / l.v. / 11.6 / 11.8 / 0.98 / 7.1 / 0.60 / 116°
8/12 682 / r.v. / 13.l / 12.5 / 1.04 / 7.6 / 0.60 / 110°
24/12 682 / l.v. / 13.7 / 12.1 / 1.13 / 6.9 / 0.57 / 105°

Comparison.From Leptochondria albertii [3, p. 90, pl. 17, figs. 3–8], from the Anisian of northern Central Siberia, the species being described differs by having smaller dimensions, more complicated differentiated radial ribbing and larger apical angle.

Range.Lower Triassic: China; Lower Dzhelamian of Ussuriyskyi Kray; Upper Dzhelamian: Mangyshlak.

Material.Two steinkerns of left valves and one inner steinkern of a right valve of satisfactory preservation from two localities.

Leptochondria (?) dagestanica[2] Gavrilova, sp. nov.

Pl. l , Figs. 9, 10

Holotype No. 10/12682, TsNIG Museum. Eastern Pre-Caucasus, Dagestan, Solonchakovaya area, drill hole 47, 4465–4470 m depth. Lower Triassic, upper Dzhelamian substage, Dem’yanovskaya Svita.

Description.Shell is of average dimensions (up to 25 mm in height), of oval outlines, elongate in height, acline or slightly prosocline. Apical angle is equal to 82–90°.