Obtusoconus vostokovae (Vassiljeva, 1990)

Kouchinsky, Artem, Bengtson, Stefan, Landing, Ed, Steiner, Michael, Vendrasco, Michael & Ziegler, Karen, 2017, Terreneuvian stratigraphy and faunas from the Anabar Uplift, Siberia, Acta Palaeontologica Polonica 62 (2), pp. 311-440 : 339-340

Obtusoconus vostokovae (Vasil’eva, 1990)

Fig. 13F .

Material.—Twelve internal moulds, including figured SMNH Mo181976, from sample 5a/34.5 (section 96-5a, Fig. 2 ), Emyaksin Formation (SOM 1), Anabar Uplift, Siberian Platform, Russia. Correlated with the lower part of Cambrian Stage 2.

Description.—Bilaterally symmetrical, rapidly expanding orthoconic shells with broad oval aperture (length/width ratio of ca. 1.5) and a globular slightly displaced protoconch. The inner shell surface (as replicated on the internal moulds) has wide and low concentric folds.

Remarks.—The form is originally known as Stephaconus vostokovae Vasil’eva, 1990, from the Emyaksin Formation, Udzha River, northern Siberian Platform, from the Tommotian Stage (after Vasil’eva 1990). Obtusoconus vostokovae is distinguished from other species of the genus by a relatively broader shell and larger globular protoconch.

Stratigraphic and geographic range.— Cambrian Stage 2 of the Siberian Platform.

Figures

Fig. 13. Mollusc Obtusoconus Yu, 1979, internal moulds, from early Cambrian Emyaksin (A, C, F, I) and Kugda-Yuryakh (B, D, E, G, H, J) formations, Anabar Uplift, Siberian Platform, Russia; samples 5a/34.75 (A, C) and 5a/34.5 (F, I), section 96-5a, K2/60 (B, G) and K8 (D, E), section 3; K1a/67 (J), section 2; and M424/10 (H), section M424. A, C. Obtusoconus cf. mirabilis Vasil’eva, 1990, SMNH Mo181971 and 181973, respectively. B, G–I. Obtusoconus sp., SMNH Mo181972 (B), 181977–181979 (G–I, respectively). D, E, J. Obtusoconus cf. honorabilis (Qian, Chen et Chen, 1979), SMNH Mo181974 (D), SMNH Mo181975 (E), and SMNH Mo181980 (J), respectively. F. Obtusoconus vostokovae (Vasil’eva, 1990), SMNH Mo181976. A1–H1, I, J1, lateral; A2–H2, apical views; J2, view from right side as oriented in J1. Scale bar 1 mm.

Fig. 2. Composite δ13Ccurve for the Bol’shaya Kuonamka River sections 96-4, 5, and 5a and sampled horizons with fossiliferous samples (arrows with carb numbers). Arrow 4/4 indicates “marker bed with angustiochreids” (Val’kov 1975; Kouchinsky et al. 1999). For section 96-6 see Kouchinsky et al. (2001, 2015a). Shift in stratigraphic column at Manykay–Emyaksin formations contact indicates position of sequence boundary. Stratigraphic ranges and first appearances of fossils (see SOM 1): 1, first appearance of helcionellid molluscs; 2, Oelandiella korobkovi; 3, Securiconus cf. simus; 6, Obtusoconus vostokovae; 7, Obtusoconus cf. mirabilis; 8, Anabarella plana; 13, Aldanella attleborensis; 14, Aldanella cf. sibirica; 22, Purella antiqua; 24, Yunnanopleura accurata; 34, Lopochites sp.; 35, Tianzhushania longa; 37, first appearance of Halkieria sp.; 38, Chancelloria symmetrica; 42, Khetatheca cotuiensis; 44, Conotheca cf. mammilata; 46, Turcutheca sp.; 47, Cupitheca sp.; 50, Orthothecid operculum type C; 51, Protohertzina anabarica; 52, Fomitchella infundibuliformis; 53, Fomitchella aff. infundibuliformis; 54, Fomitchella acinaciformis; 55, Fomitchella aff. acinaciformis; 56, Hyolithellus vladimirovae; 57, Hyolithellus sp.; 60, Selindeochrea cf. tecta; 61, Selindeochrea tripartita; 62, Selindeochrea missarzhevskyi; 63, Selindeochrea ternaria; 64, Anabarites trisulcatus; 65, Anabarites latus; 66, Anabarites natellus; 67, Anabarites kelleri; 68, Anabarites biplicatus; 69, Anabarites tristichus; 70, Anabarites compositus; 71, Anabarites hexasulcatus; 72, Anabarites hariolus; 73, Aculeochrea rugosa; 74, Tiksitheca licis; 75, Cambrotubulus decurvatus; 76, Platysolenites antiquissimus.