CC BY
19yM 561.46:551.763
https://doi.org/10.31111/palaeobotany/2018.9.18
nmeo6omanuKa, 2018, T. 9, C. 18—31 Palaeobotany, 2018, Vol. 9, P. 18—31
THE DISTRIBUTION OF SPHENOBAIERA BILOBA PRYNADA IN THE CRETACEOUS OF NORTHEASTERN ASIA
N. V. Nosova, L. B. Golovneva
Komarov Botanical Institute RAS, St. Petersburg, natanosova@gmail.com
Abstract. A revision of Sphenobaiera biloba Prynada from Northeastern Asia is based on restudy of the type material from the Zyryanka River Basin (Prynada's collection), as well as additional specimens from the type locality (Samylina's collection) and collections from the Ul'ya and Anadyr rivers. A new extended diagnosis of S. biloba based on the leaf morphology and epidermal structure is proposed. Geographic and stratigraphic distribution of this species in Northern Asia is discussed. S. biloba is known in the Aptian of Eastern Siberia (Lena River Basin) and from the early-middle Albian to Coniacian of northeastern Russia. In the Late Cretaceous this species was considered as relict and related with volcanogenic deposits of the Okhotsk-Chukotka volcanic belt.
Key words: Ginkgoales, Cretaceous, Northeastern Asia, Sphenobaiera.
INTRODUCTION
The species Sphenobaiera biloba Prynada (1938) was described from the early-middle Albian Buor-Kemyus Formation of the Zyryanka River Basin, northeastern Russia. This species was established based on the leaf morphology only. V. D. Prynada (1938) described leaves of S. biloba as large, wedge-shaped, about 11—12 cm long, divided into two wide lobes with rounded or emarginated apices. Details of epidermal characters were not indicated. Later V. A. Samylina (1967) briefly described the epidermal structure of the adaxial leaf surface based on the additional material from the type locality. We reinvestigated S. biloba leaves from the Zyryanka River Basin using light and scanning electron microscopy that allowed us to reveal the epidermal features of both adaxial and abaxial leaf surfaces for the first time. As a result, the specific diagnosis of S. biloba was emended.
Our study of morphologically similar leaves of Sphenobaiera from other Cretaceous localities of Siberia and northeastern Russia showed that their epidermal characters are identical to those of S. biloba from the Zyryanka River Basin. Based on the new data, we discuss the distribution of S. biloba in the Cretaceous of Northeastern Asia.
MATERIAL AND METHODS
The Zyryanka coal basin is located between the Indigirka and the Kolyma rivers extending as a wide strip about 500 km in length (Fig. 1). The first geological investigation of the region was made in 1933— 1935 by P. N. Ushakov and V. A. Zimin. The stratigraphy of the Zyryanka-Silyap coal field was subsequently studied by G. G. Popov (1962). He placed the Early Cretaceous deposits in the Zyryanka Group, which he subdivided into three successive formations: Ozhogina, Silyap and Buor-Kemyus. These deposits are nonmarine and contain industrial-quality coal seams and abundant fossil plants. A systematic treatment of all floral assemblages of the Zyryanka River region is contained in a series of papers by Samylina (1960, 1964, 1967). She dated the Ozhogina flora as the Neocomian, the Silyap flora as the Aptian and the Buor-Kemyus flora as early-middle Albian (Samylina, 1974, 1988).
The first collections of fossil plants from the Lower Cretaceous were described by V. D. Prynada (1938). The type material of Sphenobaiera biloba was collected by Ushakov on the left bank of the Zyryanka River, above the mouth of the Melegey Creek. It is stored at the Central Scientific-Research Geological Exploration Museum, St. Petersburg, collection CNIGRM 5350. Additional specimens were collected by Popov and Samylina in 1957 in the Zyryanka River Basin from several localities: 1) in the same exposure above the mouth of the Melegey Creek (locality 272); 2) below the mouth of the Khara-Uulakh Creek (localities 1022, 1033); 3) near the mouth of the Erosionny Creek (locality 1012). These specimens described by Samylina (1967) are stored at the Komarov Botanical Institute of the Russian Academy of Sciences (BIN RAS), St. Petersburg, collection BIN 508.
Fig. 1. Localities of Sphenobaiera biloba Prynada in Northeastern Asia: 1 — Lepiske River, Eksenyakh Formation, Aptian; 2 — Zyraynka River, Buor-Kemyus Formation, early-middle Albian; 3 — Ul'ya River Basin, Amka Formation, Coniacian; 4 — Grebenka River, Krivorechenskaya Formation, late Albian-early Turonian.
In the result of our investigation, the remains of S. biloba were also revealed from the Amka and Krivorechenskaya formations in northeastern Russia and from the Eksenyakh Formation in Eastern Siberia.
The Amka Formation is distributed in the Ul'ya River Basin, southern part of the Okhotsk-Chukotka volcanic belt, northeastern Russia (Fig. 1). It is composed of felsic and medium-felsic volcanic and volcano-sedimentary rocks yielding abundant plant fossils which are known as the Ul'ya flora (Golovneva, 2013). This flora is correlated in systematic composition with the Coniacian Chaun flora of the Central Chukotka, with the Coniacian Aliki flora from the Viliga-Tumany interfluve area, and with the Coniacian Kholchan flora of the Magadan Region (Golovneva, 2018). The U-Pb age of zircon (ID-TIMS method) from tuffites of the Amka Formation at the Uenma River is 86.1 ± 0.3 Ma (Akinin et al., in press). Thus, the Coniacian age of the Ul'ya flora and plant-bearing pyroclastic deposits of the Amka Formation are defined according to both palaeobotanical and isotopic data. Two specimens from the Ul'ya River Basin were assigned to S. biloba. The specimen, found at the Dukchanda River by E. L. Lebedev, is housed at the Geological Institute of the Russian Academy of Sciences in Moscow (collection GIN 3389). One more specimen, collected at the Gyrbykan River by L. B. Golovneva in 2013, is stored at the BIN RAS, collection BIN 1578.
The Krivorechenskaya Formation is widespread in the middle reaches of the Anadyr River (Fig. 1). This formation was deposited in a fore-arc basin and reflects depositional environments of alluvial plains and adjacent shallow marine basin (Spicer et al., 2002). The lower subformation (400—600 m thick) is largely composed of conglomerates containing no paleontological remains (Shczepetov et al., 1992). The upper plant-bearing subformation is composed of conglomerates, gravelites, sandstones, and tuffaceous siltstones, which contain diverse fossil plants, jointed in the Grebenka flora, and marine molluscs. Based on these fossils and the results of the 40Ar/39Ar dating of two samples of tuff from the Yelisseev outcrop, the age of the Grebenka flora is determined as the late Albian—early Turonian (Shczepetov et al., 1992; Spicer et al., 2002).
Leaves of S. biloba come from the Yelisseev outcrop, one of the richest localities of fossil plants on the right bank of the Grebenka River, a right tributary of the Anadyr River. Initially, these leaves were described
as S. vera Samylina et Shczepetov (1991) based on both the morphological and epidermal features. Our reexamination of the Samylina's cuticle slides of S. vera shows that the epidermal characters of S. vera are identical to those of S. biloba. Therefore we consider the name S. vera as young synonym of S. biloba, although some specimens from the Krivorechenskaya Formation differ from the type material in the leaf morphology. They are characterized by both entire lanceolate and bilobed leaf shapes. The specimens from the Yelisseev outcrop are stored at the North-East Interdisciplinary Scientific Research Institute RAS in Magadan (collection NEISRI PF-I, collected by S. V. Shczepetov and A. B. Herman in 1988); the cuticle slides of the holotype are kept at the BIN RAS.
The specimens of Sphenobaiera biloba, described by A. I. Kiritchkova (1985) under the name S. subtilis Kiritchkova, come from the Lepiske River, a right tributary of the Lena River, Eastern Siberia (Fig. 1). The plant-bearing deposits belong to the Eksenyakh Formation, consisting of varied sandstones, siltstones and industrial-quality coal layers. This formation is dated as the Aptian based on composition of floristic assemblage (Kiritchkova, 1985). Fossil plants are stored at the BIN RAS (collection BIN 744).
Cuticles of Shenobaiera leaves were prepared according to the standard procedures outlined by Kerp (1990). The preparations were examined and photographed using a Carl Zeiss Axio Scope.A1 and a Jeol JSM—6390LA scanning electron (SEM) microscopes.
SYSTEMATICS Class GINKGOOPSIDA Order GINKGOALES Genus SPHENOBAIERA Florin, 1936 Sphenobaiera biloba Prynada Plate I—IV; Fig. 2
Sphenobaiera biloba Prynada, 1938, p. 47, pl. V, fig. 1a. — Kiritchkova, Slastenov, 1966, pl. III, fig. 4, 5. — Samylina, 1967, p. 143, pl. VIII, figs. 5, 6, 7a, pl. IX, figs. 8, 9. — Philippova, 1979, p. 113, pl. XXII, figs. 6, 7.
S. ex gr. biloba Prynada: Golovneva, 2016, p. 83, pl. II, fig. 2, pl. III, fig. 6.
S. aff. biloba Prynada: Philippova, Abramova, 1993, p. 81, pl. XX, figs. 1—4, pl. XXI, fig. 8, pl. XXIII, fig. 4. S. vera Samylina et Shczepetov, 1991, p. 953, pl. I, figs. 2—9, pl. II, fig. 1—6. —Shczepetov et al., 1992, pl. 23,
fig. 6a, pl. 27, figs. 1—5, pl. 26, figs. 4, 8. — Spicer et al., 2002, fig. 10 i. S. subtilis Kiritchkova, 1985, p. 113, pl. LIX, figs. 1—5, pl. LX, fig. 1—4. S. longifolia auct. non (Pomel) Florin: Kiritchkova, Slastenov, 1966, pl. III, fig. 6. Desmiophyllum sp., Philippova, 1979, p. 112, pl. XXII, fig. 12, pl. XXIII, fig. 9.
Holotype. spec. CNIGRM 5350/51, northeastern Russia, Kolyma River Basin, Zyryanka River, Buor-Kemyus Formation, early-middle Albian; Prynada, 1938, pl. V, fig. 1a. — Pl. I, fig. 1.
Diagnosis emended. Leaves large and medium in size; usually wedge-shaped, bilobed, sometimes entire linear-lanceolate; lobes linear to lanceolate with rounded, truncate or emarginated apices; leaves hyposto-matic, with solitary stomata on the adaxial side near the leaf base, cells of the adaxial side short, rarely elongate, periclinal walls with small flattened to hollow papillae; cells of the abaxial side with one to three hollow papillae or a cuticular ridge in costal zones and with hollow papillae in the stomatal bands; most of subsidiary cells with proximal papillae, but sometimes they luck papillae and their thick aperture walls forming a cuticular rim around the aperture.
Description. Most part of the leaves from the Buor-Kemyus, Amka and Eksenyakh formations are wedge-shaped and bilobed with deep incision (Fig. 2, pl. I, fig. 1, pl. II, fig. 1, 2, pl. III, fig. 1—5, pl. IV, fig. 1), but some leaves from the type locality have very short incision (Fig. 2, pl. II, fig. 3, 4). The leaves from the Krivorech-enskaya Formation vary from bilobed to entire linear-lanceolate. The leaves dichotomize once at an angle of 20—40°. Lobes are linear to lanceolate. The apices of the lobes are rounded, truncate or emarginated.
The leaves from the type locality are more than 135 mm long and 45 mm wide in the widest part (pl. II, fig. 1—4). One almost entirely preserved bifurcated leaf (spec. BIN 508/653) is 115 mm long with an incision to 70 mm, lobes are 13—22 mm wide. The leaves from the Lepiske River are more than 150 mm long, lobes are 8—15 mm wide (pl. III, fig. 2—5).
One leaf from the Ul'ya River (spec. BIN 1578/93) is about 90 mm long, 25 mm wide in the widest part, with an incision up to 70 mm, lobes are up to 20 mm wide (pl. III, fig. 1). The second leaf (spec. GIN
Fig. 2. Shape variability in Sphenobaiera biloba Prynada leaves.
3389/82) is 4 mm wide near the base and up to 60 mm in the widest part, >165 mm long, with an incision to 125 mm, lobes are up to 20 mm wide (pl. IV, fig. 1). Vein density for all studied leaves is approximately 15—20 veins per 1 cm.
All studied leaves have similar epidermal features. They are hypostomatic, but solitary stomata occur on the adaxial side near the leaf base (pl. IV, fig. 2).
The cells of the adaxial side are short, rarely elongate, rectangular to rhombic, forming rows (pl. II, fig. 6, 10, 12, pl. III, fig. 9, pl. IV, fig. 2, 3). Cell sizes are ca. 25—80 x 15—40 |im. The anticlinal cell walls are straight; the periclinal walls are with small flattened to hollow papillae.
The costal zones on the abaxial surface are 130—470 |im wide. Ordinary epidermal cells in the costal zones are predominantly elongate, tetragonal. Most of the cells have one to three hollow papillae or a cuticular ridge. The intercostal zones correspond to the stomatal bands (210—480 |im wide). There are 2—4 stomata per width of the stomatal band (pl. II, fig. 7, pl. III, fig. 6, 11, pl. IV, fig. 5, 6). The stomata are orientated longitudinally or rarely obliquely. Ordinary epidermal cells in the stomatal bands are variably elongate to short, with hollow papillae. The anticlinal cell walls are straight.
The cuticular thickenings and papillae of the periclinal cell walls occur more often in the area where the leaf lobes diverge and in the lobes, but towards the leaf base the periclinal cell walls are often smooth (pl. III, fig. 7, pl. IV, fig. 4, 8, 9).
The stomatal complexes are with 5—7 subsidiary cells. Most of the subsidiary cells bear proximal papillae (pl. II, fig. 7, 9, pl. III, fig. 6, 8, 10, 12, 14, pl. IV, fig. 10—12), but in some cases subsidiary cells luck papillae and their aperture walls are thickened to form a cuticular rim around the aperture (pl. II, fig. 5, pl. IV, fig. 8, 9).
Material studied. Coll. GIN 3389, spec. 82; coll. BIN 508, spec. 540, 541, 545, 653, coll. BIN 744, spec. 6 — 9, 22-1, 32; coll. BIN 1578, spec. 93; coll. NEISRI PF-1, spec. 22-460, 22-514-2, 22-540a-1, 35-635, 35616-1.
Stratigraphic horizon and occurrence. East Siberia, Lena River Basin, Lepiske River, Eksenyakh Formation, Aptian; northeastern Russia, Kolyma River Basin, Zyryanka River, Buor-Kemyus Formation, early-middle Albian; Anadyr River Basin, Grebenka River, Krivorechenskaya Formation, late Albian-early Turonian; Khabarovsk Region, Ul'ya River Basin, Amka Formation, Coniacian.
DISCUSSION
The present study has shown that Sphenobaiera biloba was widespread from the Aptian to the Coniacian on vast territory from Eastern Siberia to northeastern Russia.
The earliest occurrence of S. biloba is known from the Aptian of Eastern Siberia (Lena River Basin, Lepiske River). In northeastern Russia (Zyryanka River Basin) this species occurs only in the early-middle Albian. Here S. biloba is a common element of the Buor-Kemyus flora as well as other numerous and diverse ginkgoaleans including other species of Sphenobaiera.
Most part of the Early Cretaceous ginkgoaleans did not persist into the Late Cretaceous. In the late Albian-early Turonian Grebenka flora the species S. biloba is already considered as relict. Here S. biloba leaves vary from bilobed to entire linear-lanceolate. The last shape is unusual for Sphenobaiera.
Younger (Coniacian) occurrences of S. biloba are known only from the deposits of the Okhotsk-Chukotka volcanic belt (Belyi, 1977; Lebedev, 1987). Ash-fall tuff deposits of the Okhotsk-Chukotka volcanic belt (OCVB) contain numerous plant fossil remains, which reflect mountain vegetation. The Late Cretaceous floras of the OCVB were distinct from the contemporaneous floras of adjacent coastal lowlands (Samylina, 1988; Philippova, Abramova, 1993; Herman, 2013). These upland floras are marked by a predominance of ferns and conifers, a rarity of angiosperms, and by a considerable amount of the Early Cretaceous elements in all plant groups (ferns, cycadophytes, Leptostrobales and Ginkgoales).
Cuticle was preserved only at S. biloba specimens from the Amka Formation, but morphologically similar bilobed leaves were recorded also from other Coniacian localities of the OCVB: the Chaun Group of the Central Chukotka (Golovneva, 2018), the Leurvaam and Tumaninskaya formations of the Eastern Chukotka (Golovneva, Shczepetov, 2015), and the Kholchan Formation of the Magadan Region (Golovneva, Shczepetov, 2014). These leaves were identified as Sphenobaiera sp. or Sphenobaiera ex gr. biloba. It is likely that these fossils had the same structure of the epidermis, as leaves from the Amka Formation. In this case, the distribution area of S. biloba covered the whole territory of the OCVB, which had a length of about 3000 km.
ACKNOWLEDGEMENTS The present study was carried out within the framework of the research project of the Komarov Botanical Institute of the Russian Academy of Sciences and supported by the Russian Foundation for Basic Research (project No. 16-04-00946).We would like to thank anonymous reviewers for their helpful comments during the preparation of the manuscript.
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PLATE I
Sphenobaiera biloba Prynada 1 — spec. CNIGRM 5350/51, holotype, North-East of Russia, Kolyma River Basin, Zyryanka River, Buor-
Kemyus Formation, early-middle Albian; 2—6 — specimens from coll. NEISRI PF-1, North-East of Russia, Anadyr River Basin, Grebenka River, Krivorechenskaya Formation, late Albian-early Turonian:
2 — spec. NEISRI PF-1/22-460, bilobed leaf;
3 — spec. NEISRI PF-1/35-635, entire narrowly lanceolate leaf;
4 — spec. NEISRI PF-1/35-616-1, incomplete wedge-shaped leaf, holotype of Sphenobaiera vera
Samylina et Shczepetov;
5 — spec. NEISRI PF-1/22-540a-1, entire linear-lanceolate leaf;
6 — spec. NEISRI PF-1/22-514-2, entire linear-lanceolate leaf. Scale bar 1 ot.
PLATE II
Sphenobaiera biloba Prynada 1—4, 6, 8—10, 12 — North-East of Russia, Kolyma River Basin, Zyryanka River, Buor-Kemyus Formation, early-middle Albian (1—4 — leaf morphology, 6, 8—10, 12 — epidermal structure):
1 — spec. BIN 508/540, bilobed leaf with deep incision;
2 — spec. BIN 508/653, bilobed leaf with deep incision;
3 — spec. BIN 508/545, bilobed leaf with short incision;
4 — spec. BIN 508/541, bilobed leaf with short incision; 6 — adaxial side, spec. BIN 508/541;
8 — adaxial side, spec. BIN 508/540;
9 — stomata, spec. BIN 508/653;
10 — adaxial side, spec. BIN 508/545; 12 — adaxial side, spec. BIN 508/653.
5, 7, 11 — spec. NEISRI PF-1/35-616-1, holotype of Sphenobaiera vera Samylina et Shczepetov, NorthEast of Russia, Anadyr River Basin, Grebenka River, Krivorechenskaya Formation, late Albian-early Turonian, epidermal structure: 5, 7 — abaxial side; 11 — adaxial side. Scale bars: 1—4 — 10 mm; 5—12 — 50 |im.
PLATE III
Sphenobaiera biloba Prynada 1 — spec. BIN 1578/93, Khabarovsk Region, Ul'ya River Basin, Gyrbykan River, Amka Formation, Coniacian, bilobed leaf.
2—15 — Eastern Siberia, Lena River Basin, Lepiske River, Eksenyakh Formation, Aptian (2—5 — fragments of bilobed leaves, 6—15 — epidermal structure):
2 — spec. BIN 744/6;
3 — spec. BIN 744/8;
4 — spec. BIN 744/7;
5 — spec. BIN 744/22-1;
6 — abaxial side in the middle part of the leaf, spec. BIN 744/7;
7 — abaxial side near the leaf base, spec. BIN 744/7;
8, 12 — stomata on the abaxial side, spec. BIN 744/22-1;
9 — adaxial side, spec. BIN 744/7;
10 — stoma on the abaxial side, spec. BIN 744/7;
11 — resin body, spec. BIN 744/7;
13 — stoma, SEM, internal view, spec. BIN 744/8;
14 — stoma, SEM, internal view, spec. BIN 744/22-1;
15 — stomata, SEM, external view, spec. BIN 744/7.
Scale bars: 1—5 — 10 mm; 6, 7 — 100 ^m; 8—10, 11, 12, 15 — 50 ^m; 13, 14 — 20 ^m.
PLATE IV
Sphenobaiera biloba Prynada 1 — 12 — spec. GIN 3389/82, Khabarovsk Region, Ulya River Basin, Dukchanda River, Amka Formation, Coniacian: 1 — bilobed leaf; 2, 3 — adaxial leaf surface;
4, 8, 9 — abaxial leaf surface with solitary stomata near the base;
5, 6 — abaxial leaf surface with the stomatal bands; 7, 10, 11 — stomata;
12 — stoma, SEM, external view. Scale bars: 1 — 10 mm; 2—11 — 50 |im; 12 — 20 |im.
