Selindeochrea cf. tecta, Val'kov, 1982

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 : 413-414

Selindeochrea cf. tecta Val’kov, 1982

Fig. 70 .

Material.—About 20 phosphatic and glauconitised internal moulds, including figured SMNH X3778‒3780, 5986, from samples 3/10 (section 3, Fig. 3), 5a/34.5 and 5a/34.75 (section 96-5a, Fig. 2 ), Medvezhya and Emyaksin formations. Correlated with the upper Fortunian and lower part of the Cambrian Stage 2.

Description.—Tubes with three prominent longitudinal lobes twisted clockwise (from apex to the aperture, in the direction of growth) through several revolutions. Outer surface covered with undulating growth lines. Lumen (internal mould) with three elongated lobes with distal parts twisted up to 90°. Adapically, the lobes are lower and not twisted ( Fig. 70C 2 ). The lobes are separated by V-shaped grooves that are shallow adapically.

Remarks.— Selindeocrea tecta has straight trapezoidal lobes similar to those in Fig. 70D (see Kouchinsky et al. 2009). Unlike S. tecta , the direction of twist as described herein is clockwise in all of the available S. cf. tecta specimens, but this feature does not necessarily have to be an invariant character. Val’kov (1987: 109, pl. 13: 4‒13) described similar forms with curved distal parts of the lobes as observed in cross-sections as Anabarites cf. tricarinatus Missarzhevsky in Rozanov et al., 1969 from the lower Erkeket Formation of the Olenyok Uplift, northern Siberia. Examination of the fossils chemically extracted by Val’kov from sample 846 yielded ca. 20 poorly preserved internal moulds (AK personal observations) that are twisted clockwise in the direction of growth and similar to Selindeochrea cf. tecta .

Figures

Fig. 70. Anabaritid Selindeochrea cf. tecta Val’kov, 1982, phosphatic internal moulds, from early Cambrian Emyaksin (A–C) and Medvezhya (D) formations, Anabar Uplift, Siberia, Russia; samples 5a/34.75 (A, C), 5a/34.5 (B), section 96-5a; and 3/10 (D), section 3. A. SMNH X3779 (see also Kouchinsky et al. 2009: fig. 47G). B. SMNH X3778 (see also Kouchinsky et al. 2009: fig. 47C). C. SMNH X3780 (see also Kouchinsky et al. 2009: fig. 47H). D. SMNH X5986. A1, B2, C1, D1, D3, lateral; A2, B1, D2, transverse views; C2, transverse view of apex. Scale bar 500 μm.

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.