Cambrotubulus decurvatus Missarzhevsky

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 : 425

Cambrotubulus decurvatus Missarzhevsky in Rozanov et al., 1969

Fig. 79D–J, P .

Material.—Hundreds of internal moulds (SOM 1), including figured SMNH X6039–6045, X6048, from the Manykay, Nemakit-Daldyn, Medvezhya, and lower Emyaksin formations, Anabar Uplift, Siberian Platform, Russia. Correlated with the Fortunian and lower part of Cambrian Stage 2.

Description.—Variably curved to almost straight calcareous tubes with variable expansion rates, with circular transverse cross-sectionandstraightthingrowthlines.Aperturestraight, apical part tapered open (where completely preserved).

Remarks.—The type material of Cambrotubulus decurvatus came from sample M410/73 ( Fig. 4 ). It was collected by Vladimir V. Missarzhevsky from the Medvezhya Formation at section 1 of this report. Tubular straight to broader conical internal moulds with circular cross-section co-occur in the type material and topotype sample 1/46 (SOM 1). This variability is consistant with the original diagnosis of the genus and species. Rapidly expanding funnel shaped internal moulds were later referred to as Cambrotubulus conicus Missarzhevsky, 1989 , whereas coiled tubular moulds were termed C. plicativus Val’kov, 1987. Both were first described from the upper Fortunian strata of the same locality at the Olenyok River section on the Olenyok Uplift, northern Siberian Platform (see Cambrotubulus spp. in Kouchinsky et al. 2009).

In Siberia, Cambrotubulus -like fossils are reported from the uppermost Ediacaran (Khomentovsky and Karlova 2005; Zhuravlev et al. 2012; Nagovitsin et al. 2015; Rogov et al. 2015), contrary to Zhuravlev et al. (2012: 219), who tend to identify these fossils in the late Ediacaran as Chenmengella Zhuravlev,Liñán, and Gámez Vintaned,2012 . Cambrotubulus does not have a tri-radial cross-section and does have irregularly curved tubes. It, thus, is very similar to Chenmengella . Cambrotubulus decurvatus and other Cambrotubulus species reported from Siberia commonly appear in the Terreneuvian

Series, although they are reliably known only from strata correlated herein with the middle part of the Fortunian Stage though the lower Cambrian Stage 2. Cambrotubulus tubes from Siberia exhibit the same microstructure of the wall as observed in such other anabaritid species as Anabarites tristichus and Tiksitheca licis in cases of exceptional preservation (Kouchinsky and Bengtson 2002).

Cambrotubulus decurvatus also occurs in the lower and middle Bayan Gol Formation of western Mongolia ( Esakova and Zhegallo 1996), which was correlated by Demidenko and Parkhaev (2014), Landing and Kouchinsky (2016), and in this report with the pre-Tommotian beds of Siberia, and is referable to the Fortunian and, pending further study, to the lower part of Cambrian Stage 2 ( Brasier et al. 1996; Kouchinsky et al. 2012). It also occurs through Meishucunian Assemblage Zone 1 of South China (e.g., Yang et al. 2014). Cambrotubulus decurvatus was also reported from the Mongolian Khairkhan Formation ( Esakova and Zhegallo 1996, not illustrated). C. corniformis Elicki, 1994 , was first described from the Ludwigsdorf Member in the Görlitz Syncline of Germany. Additional material is, however, needed to corroborate the identification of these fossils. Thus, the upper range of Cambrotubulus tubes is uncertain and may extend into Cambrian Stage 3.

Figures

Fig. 79. Anabaritids from early Cambrian Medvezhya (A, B, D–G, I, J, L, M, P) and Emyaksin (C, H, K, N, O) formations of Anabar Uplift, Siberia, Russia; samples 3/12.2 (A, B, D, F, G), K2/21 (L), K2/26 (E, M), section 3; 5a/1.2 (C, H, K, N, O), section 96-5a; 1/22 (I, J), 1/29.5 (P), section 1. A–C, K, L. Tiksitheca licis Missarzhevsky in Rozanov et al., 1969, internal moulds, SMNH X6034, 6035 (A, B, respectively), SMNH X6037 (C), SMNH X6036 K), SMNH X6038 (L). A, B2, C, K, L, lateral views; B1, transverse view of apertural end. M. T. licis, SMNH X3410 (see also Kouchinsky and Bengtson 2002: fig. 6 and Kouchinsky et al. 2009: fig. 39E), lateral view of tube replaced by celestite and barite. D–J, P. Cambrotubulus decurvatus Missarzhevsky in Rozanov et al., 1969, internal moulds, SMNH X6039–6045 (D–J, respectively), SMNH X6048 (P). D–H, I1, J, P, lateral views; I2, transverse view of apertural end. N. Kugdatheca voluta Missarzhevsky in Rozanov et al., 1969, SMNH X6046. N1, lateral view of internal mould; N2, oblique transverse view of apical end. O. K. voluta?, lateral view of internal mould, SMNH X6047. Scale bar 500 μm (M, O), and 1 mm (A–L, N, P).

Fig. 4. The δ13Ccurve for Kotuj River section 1and sampled horizons with fossiliferous samples (arrows with numbers). Shift in stratigraphic column carb at Nemakit-Daldyn–Medvezhya formations contact indicates position of sequence boundary. Stratigraphic ranges and first appearances of fossils (see SOM 1): 2, Oelandiella korobkovi; 3, Securiconus cf. simus; 4, Bemella jacutica?; 8, Anabarella plana; 9, Watsonella crosbyi; 10, Pseudoyangtzespira selindeica; 11, Aldanella crassa; 13, Aldanella attleborensis; 15, Philoxenella spiralis; 16, Barskovia hemisymmetrica; 18, Khairkhania cf. evoluta; 19, Ceratoconus striatus; 21, Salanyella cf. costulata; 23, Purella cristata; 25, Yunnanopleura sp.; 26, Obscurania auriculata; 29, Protoconus cf. crestatus; 32, Siphogonuchites triangularis; 34, Lopochites sp.; 37, first appearance of Halkieria sp.; 39, first appearance of Chancelloria sp.; 40, Tianzhushanella sp.; 42, Khetatheca cotuiensis; 46, Turcutheca sp.; 48, Orthothecid operculum type A; 52, Fomitchella infundibuliformis; 57, Hyolithellus sp.; 62, Selindeochrea missarzhevskyi; 63, Selindeochrea ternaria; 64, Anabarites trisulcatus; 67, Anabarites kelleri; 68, Anabarites biplicatus; 71, Anabarites hexasulcatus; 74, Tiksitheca licis; 75, Cambrotubulus decurvatus; 76, Platysolenites antiquissimus; 77, Blastulospongia sp.