Stylostroma multiformis, Wolniewicz, 2009

Wolniewicz, Paweł, 2009, Late Famennian stromatoporoids from Dębnik Anticline ̕ southern Poland, Acta Palaeontologica Polonica 54 (2), pp. 337-350 : 340-341

Stylostroma multiformis sp. nov.

Fig. 4A–D .

Etymology: From Latin adjective multiformis , having many forms and appearances.

Type material: Holotype, UAM RAC−LAB130 (two longitudinal thin sections and a single transverse section) and paratypes UAM RAC−LAB138 , UAM RAC−LAB133 , UAM RAC−LAB155 .

Type locality: Eastern slope of the Racławka Valley, 0.9 km north of Dubie village, 150 m east from a small bridge over the Racławka stream, 25 meters above the valley floor ( Fig. 1A , locality 1).

Type horizon: Lowest part of the Racławka Formation, 13 meters above the underlying Dubie Formation. Famennian.

Material.— 29 specimens from locality 1, most of them complete.

Diagnosis.— Stylostroma with distinct mamelons, dichotomically branching pillars, dissepiments variable in size, and numerous denticles. Phases 2 and 3 with flattened cyst plates and simple pillars revealing cone−in−cone structure, and without mamelons. Stylostroma multiformis sp. nov. differs from S. sinense ( Dong, 1964) by the absence of pillars branching in dendroid form, presence of phases lacking distinct mamelons, and by the relative abundance of pillars made up of invaginating cones. It differs from S. crassum Gorsky, 1938 by lacking mamelons in extensive parts of the skeleton.

Description.—Skeleton laminar or domical. Laminar specimens up to 5 mm thick. Their basal length not exceeding 100 mm. Heights of domical forms up to 100 mm. Mamelons distinct in most specimens, intersecting the skeletons at the distance up to 50 mm, on the surface showing a relief of up to 10 mm. Axial canals absent. Cysts of variable sizes, with spans up to 5 mm, and heights of up to 1.1 mm. Smaller cysts usually more convex, while larger flat, and thickened (up to 150 µm), simulating laminae in places. Cysts spaced 5–7 in 2 mm, in areas of thickened skeletal element 2–4 in 2 mm. Pillars 0.5–3.5 mm long, simple or upwardly branching, intersecting at least 3–4 cysts. In tangential sections cut as dots, locally form short walls in central parts of mamelon columns. Pillars commonly restricted to mamelons, but in laminar specimens spaced more regularly. Denticles numerous on tops of thickened cysts, in mamelon columns absent. The basal thickness of denticles not exceeding 250 µm. Some denticles transformed into small pillars, intersecting 1–2 cyst plates.

Intraskeletal variation within Stylostroma multiformis sp. nov. wide, allowing to distinguish three separate phases sensu Stearn (1989). In many specimens two phases mixed together, passing vertically or laterally into each other.

P h a s e 1 ( Fig. 4A, D ): Strongly mammilate skeleton, usually domical. Small specimens laminar, with basal length reaching up to several, but less than 100 mm. On the surface mamelons with distinct relief, up to 10 mm. Cysts moderately convex, with heights ranging 150–3000 µm, mostly thin, less than 80 µm thick, but in areas lacking pillars strongly thickened, up to 150 µm, and more convex with heights up to 1000 µm. In the vicinity of mamelons cysts closely spaced (5–7 in 2 mm), in other parts of skeleton larger, hemispherical, thickened, and widely spaced, 2–5 per 2 mm. Pillars simple, postlike, usually restricted to mamelon columns. Their inner structure compact, with the microstructure indistinguishable, probably due to dolomitisation. Relics of primary cone−in−cone structures absent. Pillars dichotomously branching, feather−like structures absent. In tangential sections pillars rounded, but in central zone of mamelons forming short walls, up to 1 mm ( Fig. 4A 3 , lower right corner). Denticles short (not exceeding 400 µm), triangular, with basal diameter about 200 µm. On cysts between mamelon columns denticles numerous, rarely transformed into small pillars intersecting one or two cyst plates.

Phase 2 ( Fig. 4B, D ): Mamelons small with relief not exceeding 1.0 mm. Skeleton domical. Cysts convex, with heights up to 1.0 mm, and thickness up to 50 µm, strongly flattened, thickened up to 150 µm, occasionally simulating laminae. Cysts serve as a base for long pillars, intersecting 6–12 cysts, reaching lengths of up to 5 mm, commonly branching in upper parts. Long, branching pillars commonly adjacent to one another. In their vicinity cysts convex, forming indistinct mamelons. Short and unbranched pillars also common, passing 2–5 cyst plates, their length not exceeding 2.5 mm. Denticles common, usually rising from thickened cysts. In parts of the skeleton consisting of small cyst plates denticles rare.

Phase 3 ( Fig. 4C, D ): Skeleton laminar, up to 40 mm in diameter. Inclusions of sediment incorporated into the skeleton common. Upper surface smooth and flattened. Mamelons rare, rounded in tangential section, composed of limited number, up to 4, cyst plates. Cysts of variable size, with spans ranging 0.7–2.4 mm. Large cysts more common. Convex cyst plates rare, their top surfaces serving as bases for denticles, usually transformed into small pillars. Some cysts strongly flattened and thickened up 1to 150 µm, in places resembling laminae, with numerous denticles on their upper surfaces. Other cysts thinner, not exceeding 80 µm in thickness. Pillars common, usually resting on flattened cysts, not branching. Two types of pillars present: up to 3 mm long, more than 200 µm thick, intersecting at least 6 cysts; and short rods, usually superposed denticles attached to flattened cysts. The latter common in parts of the skeleton with the predominance of thin and strongly convex cysts. The short rods up to 120 µm thick, intersecting less than 5 cysts. Their length not exceeding 0.8 mm. Pillars irregularly spaced, with areas with numerous, long pillars accompanied by parts of the skeleton composed only of thin, slightly convex cysts. In several specimens transitions between areas of phase 3 with sparse pillars and the phase 1 are present. Long pillars showing internal structure composed of convex cysts, invaginating into central parts of pillars. In other parts of specimens pillars with compact inner structure. In extensive areas of skeleton cone−in−cone structures visible only as thickenings on pillars at junctions with cysts. In tangential sections pillars rounded, long and thickened with concentric structure ( Fig. 4C 1 ), probably an effect of invagination of cyst plates. Other pillars compact, rarely oval or spool−like. Denticles less common than in skeletons assigned to phases 1 and 2, rising only from flattened cysts. In parts of the skeleton lacking long pillars, with short rods, intersecting less than 3 cyst plates only.

Statistics.—Two sample Kolmogorov−Smirnov and Kruskal−Wallis tests, taken on five skeletal features (height and span of cysts, number of cyst plates intersected by pillars, pillar length, spacing of dissepiments), revealed no statistically significant differences between decribed phases. Therefore all three forms of the skeleton are described as a single species. The null hypothesis was rejected in the case of pillar spacing. Specimens assigned to phase 1 show pillars restricted to mamelon columns and therefore larger values of pillar spacing.

Discussion.— Stylostroma multiformis sp. nov. could perhaps be divided into two species, on the basis of different structures of pillars and the absence of mamelons, with phase 3 assigned to genus Labechia . However, cone−in−cone structure is not clearly visible in all specimens of this phase. On the other hand, thickenings noticed on pillars at junctions with cysts may be interpreted as recrystallized parts of convex cyst plates. Transitions between the phase 3 and other phases were observed. Thus all phases are considered as belonging to a single species.

Stratigraphic and geographic range.—Southern Poland, Dębnik Anticline, both slopes of the Racławka Valley between Dubie and Paczółtowice villages. Lower part of the Racławka Formation. Upper Famennian.

Figures

Fig. 4. Famennian labechiid Stylostroma multiformis sp. nov. and clathrodictyid Gerronostroma raclaviense sp. nov., Dębnik Anticline. A. Stylostroma multiformis sp. nov., A1–A3 Phase 1, holotype UAM RAC−LAB130. Longitudinal (A1, A2) and transverse (A3) sections. Note pillars and short walls adjacent to mamelons (A3). B. Phase 2, paratype UAM RAC−LAB138, longitudinal section. C. Phase 3, paratype UAM RAC−LAB133. Longitudinal (C1) and transverse (C2) sections. Note significant signs of dolomitisation, cone−in−cone structures (C1), and pillars revealing concentric structure (C2, arrows). D. Paratype RAC−LAB155. Longitudinal section showing phase 1 (at the bottom) overlaid by phase 2 and phase 3 (near the upper margin of the photograph). E. Gerronostroma raclaviense sp. nov. Holotype UAM RAC−Z1. Longitudinal section of phase 1 (peripheral parts of column, dolomitised) and phase 2 (axial zone). Scale bars 1 mm.

Fig. 1. Upper Famennian in the Racławka Valley, Dębnik Anticline, southern Poland. A. Simplified geological map of the Dębnik area. B. Simplied map of Kraków region, southern Poland.

Fig. 3. Measurements taken for the purpose of statistical analysis. A. Measurements taken from longitudinal sections of Labechiida. 1, pillar length; 2, span of cysts; 3, height of cysts; 4, spacing of dissepiments; 5, number of cyst plates intersected by pillars.B. Measurements on Gerronostroma specimens (longitudinal sections). 1, pillar length; 2, pillar spacings; 3, laminae spacings; 4, thickness of laminae; 5, thickness of pillars. C. Measurements taken from transverse sections of Gerronostroma. 1, pillar diameter.