Cloudina, Germs, 1972

Zhuravlev, Andrey Yu., Liñán, Eladio, Vintaned, José Antonio Gámez, Debrenne, Françoise & Fedorov, Aleksandr B., 2012, New finds of skeletal fossils in the terminal Neoproterozoic of the Siberian Platform and Spain, Acta Palaeontologica Polonica 57 (1), pp. 205-224 : 217-218

Cloudina ex gr. C. riemkeae Germs, 1972

Fig. 3A, C–E .

Material.—Five etched specimens from the Kyyry−Ytyga locality, Yudoma River right bank, Yakutia−Sakha Republic, Russia (southeastern Siberian Platform); interval 10, Ust'− Yudoma Formation, Yudoma Group, upper Ediacaran.

Description.—Tubicolous, gently curving, sinuous, narrowly conical calcareous microfossil (up to 3 mm in length) consist−

http://dx.doi.org/10.4202/app.2010.0074

ing of eccentrically nested apically slightly flaring funnel−like segments (up to 10 segments per 1 mm of tube length). Segment width is relatively consistent and ranges from 0.20 mm (in its narrower lower part) to 0.25 mm in the same specimen, usually gradually increasing with increased length. The largest observed segment width is 0.50 mm. The tube inner surface is smooth. The primary composition of tubes is high−Mg calcite according to its present dolomitic composition and the presence of square holes probably formed after microdolomite crystal dissolution ( Fig. 3D ).

Remarks.—In its size range and relatively regular tube shape, Siberian Cloudina resembles Cloudina riemkeae Germs, 1972 from the Nama Group of Namibia and C. dunfeei Signor, Mount, and Onken, 1987 ( Signor et al. 1987: 4.1–4.14; = Coleolella sp. in Signor et al. 1983: fig. 3B) from the lower Deep Spring Formation in the White−Inyo Mountains of eastern California and Esmeralda County of western Nevada, USA, thus confirming Grant’s (1990) opinion on the synonymy of Nevadatubulus and Cloudina . However, differences in preservation of the material do not allow us to attribute our new specimens unequivocally to the Namibian species.

Among the last but not the least problems related to Cloudina is the question of predatory borings in its shells leading to far−reaching reconstructions of Neoproterozoic trophic webs and the basic phenomena caused the Cambrian explosive radiation. A number of such boring is discovered on Cloudina tubes from South China and Namibia ( Bengtson and Yue 1992; Brain 2001; Hua et al. 2003a). Despite the presence of some holes, the Siberian material points to another interpretation. Some tubes bear square holes rather than rounded ones ( Fig. 3C, D ) and even small fragments (0.8 × 0.3 mm) display three or more holes ( Fig. 3A, D ). Such structures are probably formed as a result of diagenetic dissolution of microdolomite crystals which formed at the tube surface due to its primary high−Mg calcite composition. Further diagenetic processes led to infilling of the holes in such a way that they finally became rounded in outline and resemble unsuccessful incomplete borings ( Fig. 3D ). Circular pits similar in both size and shape to Precambrian “borings” appeared on the calcareous cuticle of crustaceans during bacterial degradation ( Hof and Briggs 1997). No correlation between shell diameter and hole diameter was observed by Hua et al. (2003a) in Cloudina , and Sinotubulites from the same locality lacked any holes completely, probably, due to a differing primary mineralogy.

Figures

Fig. 3. SEM images of late Ediacaran Cloudina. A, C–E. Cloudina ex gr. C. riemkeae Germs, 1972; Kyyry−Ytyga (1.6 km downstream from Ulakhan−Ytyga Creek mouth), Yudoma River, right bank, Siberian Platform, Russia, Ust’−Yudoma Formation. A. SNIIGGiMS 1630/1, tube fragment with abraded shell wall. C. SNIIGGiMS 1630/2, fragment of tube with holes formed after microdolomite crystal dissolution. D. SNIIGGiMS 1630/3, detail of tube fragment with holes formed after microdolomite crystal dissolution. E. SNIIGGiMS 1630/4, tube nested funnels. B, F–H. Cloudina ex gr. C. hartmanae Germs, 1972; Tirteafuera River, Abenójar Anticline, East Lusitanian–Alcudian Zone, central Spain, lower La Grajera−Cañuelo unit, Ibor Group. B. MPZ 2007/3918, abraded tube fragment with imprints of mica crystals of the matrix. F. MPZ 2007/3919; F1, tube fragment with wall preserved; F2, detail of F1; F3, detail of F1, wall microstructure. G. MPZ 2007/3920, abraded tube fragment. H. MPZ 2007/3921; H1, tube fragment with wall preserved; H2, detail of H1 showing wall microstructure. Scale bars A, D, E, H1 100 µm; B, C, F2 300 µm; F1, G 1 mm; F3 50 µm; H2 30 µm.