Stelechophyllum Tolmachev, 1933

Fedorowski, Jerzy, Bamber, E. Wayne & Richards, Barry C., 2021, Mississippian colonial tabulate and rugose corals from the Flett Formation, Liard Basin, northwest Canada, Acta Palaeontologica Polonica 66 (3), pp. 679-704 : 699-701

Genus Stelechophyllum Tolmachev, 1933

Remarks.—The diagnosis of this genus emended by Sando (1983: 9) is too detailed in such characters as two orders of septa, common for the entire suborder and incomplete in such an important character as the microstructure of septa. We accepted it here on the condition of being temporary. The same is true for the geographical distribution and the species content of that genus suggested by Sando (1983). Unfortunately, the single colony available for this study cannot form the basis for a comprehensive discussion.

Stelechophyllum cf. banffense ( Warren, 1927) Fig. 16 .

Material.— Fragment of cerioid colony C-52434 = GSC 142476 , ca. 90×70× 80 mm in size from Flett Formation undivided, Viséan , Rundle Group , Liard Basin, Northwest Territories, Canada. Some corallites strongly re-crystallized (see below) .

Description. —Maximum number of septa measured—18 with n:d value 18:7.8×6.1 mm. Most common number of septa is 17 with corallite diameters 7.1×6.1 mm, 9.0×6.0 mm. Morphology of corallites varies greatly as a result of diagenetic alteration. Most altered corallites form a belt surrounding less altered part of the colony ( Fig. 16 , arrows). Boundary between those two fragments crosses several corallites as indicated by their morphology. Parts of corallites adjacent to less altered sectors of colony closely resemble corallites from that sector, whereas their opposite parts look like corallites from the diagenetically altered sector. In parts of colony showing least diagenetic alteration, major septa thin, long, approaching and some meeting thin pseudocolumella, commonly connected to both protosepta. Minor septa thin, in full number, all enter tabularium. Dissepiments mostly interseptal, regular. Lonsdaleoid dissepiments small when present. In corallites most altered diagenetically, either all, or most major septa restricted to tabularium. Minor septa very restricted in number. Few of them remain as thin, spike-like bodies attached to external walls, mostly absent. Dissepimentarium consists solely or mostly of large lonsdaleoid dissepiments, some surrounding more than 1/4 corallite diameter. Pseudocolumellae either absent from diagenetically most advanced corallites or free when surviving. Dissepiments in longitudinal sections either in one vertical row ( Fig. 16A 5) or up to three, gently dipping rows ( Fig. 16A 2 ). Tabulae complete or incomplete, deflected gently from thin pseudocolumella. Some tabellae rest upon underlying tabulae. Increase lateral ( Fig. 16A 3 , A 4 , A 6 , A 7 ). Acolumellate early growth stage of offsets continue up to their total separation from parental polyp ( Fig. 16A 6 ). Derivation of pseudocolumella from axial septum very probable, but diagenetic alterations precludes firm recognition of that process ( Fig. 16A 7 ).

Remarks.—The morphology of the colony under discussion differs from the lectotype ( Nelson 1960: pl. 23: 4, 5; Bamber 1966: pl. 3: 5) in its n:d value, in having stronger minor septa in its less altered part and in having a weaker pseudocolumella. It resembles small and simple variants of S. banffense ( Warren, 1927) , characterized by Sando (1983: 13) as “highly variable species”. Differences in the morphology illustrated by Sando (1963: pls. 8, 9) may have resulted from a differentiated intensity in diagenetic alterations. His colonies with large lonsdaleoid dissepiments and reduced minor septa may correspond to more altered parts of the colony described above, whereas those with the minor septa well developed and the lonsdaleoid dissepiments are rare and may correspond to the less altered part of that colony ( Sando 1983: pl. 8: 1, 3 and pl. 9: 1, respectively). The longitudinal section illustrated by Sando (1983: pl. 4: 2c) resembles that illustrated here ( Fig. 16A 2 , A 5). It is probable that those two corallites are conspecific. The question is whether they can be included within the limits of intraspecific variability of S. banffense or should be described as new. Having such restricted material, taking in mind the large variability of the specimens included in S. banffense so far, and considering the influence of diagenesis on the morphology of the corals documented above, the conformity of the species described here to S. banffense is the safest solution.

Figures

Fig.16. Rugose coral Stelechophyllum cf. banffense (Warren, 1927), C-52434 = GSC-142476, locality 12 (Fig. 2), from Meilleur Member, Flett Formation Mississipian), Rundle Group, Liard Basin, Northwest Territories, Canada. Thin sections.A1, transverse section of fragment of colony, note different state of preservation in middle of picture and area around it (arrows); A2, A3, longitudinal sections; A4–A7, offsets in ascending growth stages.

Fig. 2. Simplified geological map of study region showing distribution of outcrops of Carboniferous Prophet, Flett, and Mattson formations in southwest corner of Northwest Territories and southeastYukon Territory and lines of cross-sectionA–A’ and B–B’ (see Figs.4, 5 for details). Surface and subsurface sections (corallocalities are in orange):1,Twisted Mountain;2, north end Mattson anticline;3, Jackfish Gap (main coral locality); 4, Tlogotsho Plateau;5, Etanda Lakes; 6, Tika Creek; 7, Pan American Home Signal C.S.P. Celibeta Number 7; 8, Texaco N.F.A. Bovie Lake J-72; 9, Pan American A-1 Pointed Mountain P-53; 10, Canada Southern et al. North Beaver River YT 1-27; 11, Pan American Beaver YT G-01; 12, West Flett anticline; 13, Southern Liard Range; 14, Sheaf Cree.Abbreviations:Fm., Formation (formal unit); fm., formation (informal unit); fms.,formations; S., south; W., west;YT,Yukon Territory;C.S.P., Canada Southern Petroleum. Modified from Harker (1963) and an unpublished map by Andrew Okulitch from 2005 (reproduced with permission).

Fig. 3. A. Partly schematic, palinspastic stratigraphic cross-sectionA–A’ showing stratigraphic relationships of Flett Formation in eastern Cordillera of northern part of project area in southwest corner of Northwest Territories and southeast Yukon. B. Environments of deposition. See Fig. 2 for line of cross-section A–A’.Abbreviations:Fm., Formation (formal unit); fm., formation (informal unit); Mbr., Member (formal unit). Modified from Richards et al. (1989).

Fig. 4. A. Partly schematic, palinspastic stratigraphic cross-section showing stratigraphic relationships of Flett Formation in southern part of project area. B. Environments of deposition. See Fig. 2 for line of cross-section B–B’. Abbreviations: Fm., Formation (formal unit); fm., formation (informal unit); Mbr., Member (formal unit); mbr., member (informal unit); YT,Yukon Territory; C.S.P., Canada Southern Petroleum. Modified from Richards et al. (1994).

Fig. 6. Stratigraphic column of type section of Viséan Flett Formation at Jackfish Gap on Yohin Ridge, eastern Cordillera, southwest corner of Northwest Territories. Shows lithostratigraphic positions of coral collections discussed in this paper.Abbreviations: Fm., Formation. Stratigraphic column modified from Richards et al. (1989: fig. 24).

Fig. 7. Tabulate coral Michelinia expansa White, 1883. IG-91-1 = UAM-Tc.Can./2, from locality 3 (Fig. 2), Meilleur Member, Fleet Formation (middle Viséan, Mississipian), Rundle Group, Liard Basin, Northwest Territories, Canada.A1, thin section of colony, transverse in most part and longitudinal at colony edge; A2, immature corallite, note remnants of wall microstructure, arrow points to P1 pore; A3, septal spines attached to tabula; A4, pores P1 and P 2 situated close to each other (arrows).