Parallelopora, Bargatzky, 1881

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 : 233-235

Parallelopora sp.

Fig. 7D,E

Material. Two specimens, UQF.47983 and UQF.47979, both from UQL. 2974 in reworked pebbles of the Chinaman Creek Limestone (Broken River Group), South Chinaman Creek, north of abandoned Pandanus Creek Station (material collected by C.W. Mallett in the late 1960s).

Description. Skeleton dominantly of long, continuous, thickened, pachysteles composed of coarsely microreticulated material, and successive, moderately close-spaced and laterally extended, thin microlaminae; pachysteles usually from 0.25 to 0.35 mm thick in areas where allotubes or other gallery spaces are well developed, and typically spaced from 3 to 4 in 2 mm; adjacent pachysteles sometimes merge locally or branch, where no gallery spaces intervene as pachystromal intervals; up to 2.5 mm long and 0.025 mm thick but such relationships do not normally maintain marked longitudinal continuity. Flattened to gently undulant microlaminae are apparently diagenetic derivatives of regularly aligned microcolliculi, and have lateral continuity over distances of 6 mm or more (shorter where allotubes intersect them or a microlamina acutely divides); they appear mainly as thin, dark lines from 0.02 to 0.04 mm across, in a few places showing a line of dark melanospheric dots and in places showing small-scale disruptions in continuity that may represent pores; spacing of microlaminae from 10 to 13 in 2 mm.Allotubes are common in places, showing slightly elongated outlines (circular to subcircular in tangential section), 0.2 to 0.3 mm wide; only a few small, oblique to concave cyst-like dissepiments seen; astrorhizal canals common, usually elongated, vermiform or branching and, typically 0.25 mm in diameter; in addition a few larger, irregularly-shaped, near millimetre-size, gallery spaces occur.

Microstructure of pachysteles is coarsely microreticulate (seemingly orthoreticular), composed of microgalleries, 0.075 to 0.125 mm in diameter; they are typically an association of micropillars that seem to have coalesced into superposed, walled, radially-aligned, tubules, and crossed by microlaminae that seemingly bound tops and bottoms of microgalleries (not possible to determine whether they are micro-beams or floors); nevertheless they are thinner and noticeably less markedly regularly spaced, and imprinted than the microlaminae at tops and bottoms of “interlaminar” spaces.

Remarks. The Broken River species is referred to the genus Parallelopora but owing to its indifferent preservation cannot be assigned to a named species. The material was studied previously by C.W. Mallett (1968, p. 225) as part of an unpublished Masters thesis at University of Queensland. Mallett revised Lecompte’s species of Stromatopora laminosa Lecompte, 1952 (p. 276) from the Givetian of Olloy, Belgium, as a representative of Parallelopora based on the differentiation of its fine compact microlaminae and pillars (=pachysteles) with an amalgamated and microreticulated skeletal framework and presence of “pseudozooidal tubes” (=allotubes). Furthermore, Mallett accommodated the Queensland material in Lecompte’s species. However, the assignment of S. laminosa to Parallelopora remains in some doubt; for example, Stearn (1993, p. 222; and see species list in 24-page Supplementary Publication No. SUP 14042 deposited by Stearn in British Library, Boston Spa, Yorkshire, UK) regarded S. laminosa as a representative of the genus Habrostroma . For instance, the poorly preserved Broken River material does not show the characteristic short pachysteles of Habrostroma . In contrast, it does have coarsely microreticulated and extended pachysteles that are diagnostic features of Parallelopora .

Little close similarity exists between the Broken River species and other known Australian species of Parallelopora . P. ampla Webby, Stearn & Zhen, 1993 from the Emsian of the Murrundal Limestone of Victoria has much thinner pachysteles and only one or two longitudinally aligned rows of microgalleries in each pachystele. Another species from the Middle Devonian lower Burdekin Formation of the Burdekin Basin (northern Queensland) was reported by Cook (1999, p. 542, fig. 57) as? Parallelopora sp. (though Cook named it also as “ Parallelostroma sp.” in his caption to figure 57). It shows a closer relationship to the Broken River species with similarly spaced microlaminae, but the pachysteles are comparatively thinner, and astrorhizae do not appear to be present.

ACKNOWLEDGEMENTS. We thank Colin W. Stearn (McGill University, Canada) for his comments on the manuscript, especially in relation to the well-preserved microreticulation, and for permission to quote from parts of his “in press” Treatise contributions, especially the syringostromatid section, and also, A.E. (Tony) Cockbain (South Perth, Western Australia) for his constructively helpful review of the manuscript. Additionally, we acknowledge John A. Talent and Ruth Mawson (Macquarie University) for initially inviting us to undertake the study of the Broken River stromatoporoids, and for their efforts in establishing age relationships through the succession, and John S. Jell (University of Queensland) for loan of Clive W. Mallett’s University of Queensland stromatoporoid collection.

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.