Columnostroma, Bogoyavlenskaya, 1972

Webby, Barry D. & Zhen, Yong Yi, 2008, Devonian Syringostromatid Stromatoporoids from the Broken River Region, North Queensland, Records of the Australian Museum 60 (3), pp. 215-236 : 232-233

Columnostroma sp.

Fig. 7 A–C

Material. Available material is fragmentary and recrystallized, comprising two specimens, SD260-11-3 ( AM F.134919, AM FT.15150, AM FT.15151) and SD260-11-4 ( AM F.134920, AM FT.15152, AM FT.15153, AM FT.15154), from 11 m above the base of the Dosey Limestone in SD260 section of Sloan et al. (1995), 2 km NNW of Storm Hill; the latter specimen is somewhat better preserved.

Description. Skeleton laminar to weakly mamelonate and latilaminate; dominated by long, thickened and radially aligned pachysteles, 0.2 to 0.35 mm across, with spacing from 3 to 5 in 2 mm; commonly they are close spaced, and often in contact, but rarely seen to merge or branch; because of alteration, pachysteles are preserved mainly as compact, dense, rod-like elements, but a few aligned dark melanospheric dots are preserved confirming an incomplete microreticulation of micropillars and microlaminae, from 0.02 to 0.03 mm thick, defining subrounded microgalleries about 0.04 to 0.05 mm in diameter. Pachystromes are irregularly developed between pachysteles; they may be represented as thicker pachystromal extensions about 5 mm in length and up to 0.2 mm in thickness, but in other areas represented by short lengths of a poorly differentiated network that may include one or more microlaminae; they may be inconsistently aligned laterally, and much interrupted by intervening allotubes. Typically allotubes are elongated to rather irregular, and divided by slightly domal to obliquely aligned dissepiments, at intervals of 10 to 15 in 2 mm longitudinally; in tangential section allotubes are small and circular in outline, about 0.2 mm in diameter. Astrorhizal canals may be centred in broad mamelons, their branches extend tangentially through other parts of skeleton; some exhibit tabulae from 0.2 to 0.4 mm apart.

Remarks. The Broken River species should probably be assigned to the genus Columnostroma on the basis of its long, stout, rounded, close-spaced pachysteles, less important pachystromes and traces of a fine reticular microstructure, though the particular type of microreticulation, sensu Stock (1989), cannot be ascertained. However, owing to the incompletenss of available material and poor preservation overall, the species must be left in open nomenclature. The type species of Columnostroma , C. ristigouchense ( Spencer, 1884) from the Early Devonian of New Brunswick, Canada, shows some resemblances, having rather similar overall dimensions, but the pachysteles of the Broken River species are slightly thicker and more closely spaced, and the laminae within pachystromal segments are not demonstrably colliculate. Only one Australian species of Columnostroma , C. clathratum Webby, Stearn & Zhen, 1993 has been described previously from the Pragian Lilydale Limestone of Victoria, and this bears little resemblance to the Broken River species, being much finer in overall skeletal structure, and the pachystromes more regular, continuous, and finetextured, with microlaminae mainly in conformity with the horizontal dissepiments crossing the allotubes.

Figures

Fig. 7. Columnostroma sp., A–C, specimen AM F.134920, from the Dosey Limestone, 11 m above the base of the SD260 section, NNW of Storm Hill; (A) longitudinal section (AM FT.15152), ×10; (B) longitudinal section (AM FT.15152), showing within much thickened pachysteles small areas where incompletely aligned longitudinal rows of microgalleries and dark melanospheric rows of dots occur, confirming the poorly preserved microreticulation, ×20; (C) tangential section (AM FT.15154), ×10. Parallelopora sp., D, E, both specimens come from the same locality at UQL.2974 of Mallett 1968, as reworked pebbles from Chinaman Creek Limestone along South Chinaman Creek; (D) tangential section of specimen UQF.47979, ×10; (E), longitudinal section of specimen UQF.47983, ×10. Scale bars = 1 mm.