Gerronostroma raclaviense, Wolniewicz, 2009

Wolniewicz, Paweł, 2009, Late Famennian stromatoporoids from Dębnik Anticline ̕ southern Poland, Acta Palaeontologica Polonica 54 (2), pp. 337-350 : 342

publication ID	https://doi.org/ 10.4202/app.2007.009
persistent identifier	https://treatment.plazi.org/id/03A887AE-FFA2-FFAE-FF89-FDFD59E9AFD6
treatment provided by	Felipe
scientific name	Gerronostroma raclaviense
status	sp. nov.

Treatment

Gerronostroma raclaviense sp. nov.

Figs. 4E View Fig , 5A–C View Fig .

Etymology: From the Racławka Valley, type locality of the species.

Type material: Holotype, UAM RAC−Z1 (a longitudinal thin section) and paratypes UAM RAC−Z51 , UAM RAC−Z74 , UAM RAC−Z142 , UAM RAC−Z145 .

Type locality: Western slope of the Racławka Valley, 0.6 km south of Paczółtowice village, 30 meters south of Żarnówczany Dół ravine ( Paszkowski 1996; Berkowski 2002), 60 m west from the Racławka stream, 20 m above the valley floor ( Fig. 1A View Fig , locality 2).

Type horizon: Upper part of the Racławka Formation, Upper Famennian .

Material.—19 fragments from localities 1 and 2. Columns usually broken, slightly abraded, attachments of stems can be traced in tangential sections. A few specimens preserved more completely, with stems rising from encrusting, laminar part of the skeleton.

Diagnosis.— Gerronostroma with laminar basal part, consisting of continuous laminae and long pillars; columns erecting as upward−extended mamelons; central parts with long, complexly branching, tripartite pillars, and reduced laminae. Gerronostroma raclaviense sp. nov. differs from other species of Gerronostroma by the presence of upwardly−extended mamelons and stems, with amalgamated axial zones. Columns of Gerronostroma raclaviense sp. nov. differs from Clavidictyon graciliramosum Dong, 1964 in the considerably smaller thickness of skeletal elements, from C. luochengense Dong, 1964 and C. regulare Dong, 1964 in having narrower peripheral parts of columns, and from C. columnare Sugiyama, 1939 by the presence of distinct boundaries between axial and peripheral zones of columns. Basal parts of all mentioned species are unknown.

Description.—Skeleton columnar, branching, with laminar basal part, commonly encrusting skeletal fragments of calcareous algae Parachaetetes or other stromatoporoids. Columns up to 50 mm long, branching dichotomously. Laminar parts of the skeleton up to 10 mm thick. Their basal parts not exceeding 50 mm in length. Inner structure of the skeleton revealing great variation of structural elements, with three phases being distinguished.

Phase 1 ( Figs. 4E View Fig , 5A View Fig ) in the basal part of the skeleton and in peripheral parts of stems, associated with phase 2. Laminae well−defined, continuous, with rare foramina. The thickness of laminae between 50 and 100 µm, not exceeding 150 µm. Laminae single−layered, rarely revealing tripartite structure, with light axial zone resulting from the amalgamation or branching. In peripheral zones of columns interlaminar spaces rectangular, in lower parts of laminar skeletons rounded. Pillars long, crossing three or more laminae. Parts of pillars lying immediately below laminae thickened, with conical axial canal. In vertical sections pillars exhibiting wide variety of shapes, mainly rounded, with upper parts oval, irregular or star−like. Vertical walls uncommon, visible only in parts of the skeleton adjacent to the mamelon columns. Astrorhizae and dissepiments absent.

Phase 2 ( Figs. 4E View Fig , 5A View Fig ) in central parts of columns, occupying 50–90% of the stem diameter, and in basal parts of the laminar form of the skeleton. Lateral transitions into phase 1 or phase 3 present. Laminae reduced, only in lateral parts more conspicuous, very thin (not exceeding 30 µm), preserved only as rods between closest pillars, with many foramina. Pillars long, branching complexly, intersecting at least three laminae. Inner structure of pillars usually tripartite, with central light zone.

Phase 3 ( Fig. 5B, C View Fig ) in basal parts of the skeleton, and in the mamelon columns. Skeletal elements strongly thickened. Laminae thick (from 100 to 350 µm), locally interrupted by foramina, single−layered, but sporadically tripartite, with darker lateral zones. In most cases that structure resulting from the amalgamation of closely spaced laminae. In the areas consisting of loosely arranged skeletal elements laminae less conspicuous, with numerous foramina. Pillars long, intersecting at least three interlaminar spaces, thinner than laminae, 150 µm thick in average. In the upper parts pillars thickened, rarely with axial canals, noticed only in loosely packed parts of the skeleton. In tangential sections pillars amalgamated, forming joined, meandering networks. Phase 3 also visible within mamelons and columns ( Fig. 5B View Fig ), if only in lateral parts, then associated with phase 2. Phase 3 in the central zone of columns visible as a mesh of branching, tripartite pillars, and reduced laminae. Within mamelons this phase differs from phase 2 by the strongly thickened pillars (up to 250 µm thick), and by the presence of a short (0.5–1.5 mm) axial canal, completely separated from surrounding interpillar spaces by long, amalgamated pillars ( Fig. 5B View Fig ).

Statistics.—Two sample Kolmogorov−Smirnov and Kruskal−Wallis tests revealed statistically significant differences between specimens assigned to Gerronostroma raclaviense sp. nov., G. cracoviensis ( Gürich, 1904) , and Gerronostroma sp. Significant differences between skeletons of G. raclaviense were detected when considering measurements of pillar and laminar thicknesses ( Table 2). This phenomenon is caused by the reduction of laminae in central parts of the columns (phase 2).

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