Gerronostroma cracoviensis ( Gürich, 1904 )

Wolniewicz, Paweł, 2009, Late Famennian stromatoporoids from Dębnik Anticline ̕ southern Poland, Acta Palaeontologica Polonica 54 (2), pp. 337-350 : 344-346

Gerronostroma cracoviensis ( Gürich, 1904)

Figs. 5D–G , 6D, E .

1904 Stromatoporella cracoviensis sp. nov.; Gürich 1904: 2, pl. 1: 1–3.

Neotype: Specimen UAM RAC29 (two longitudinal and two transverse thin sections) ( Fig. 5D, F ).

Type locality: Gürich's “Stromatoporoid Rock” ( Gürich 1904): western slope of the Racławka Valley, 0.9 km south of Paczółtowice village, 70 m north of Rokiczany Dół ravine ( Paszkowski 1996; Berkowski 2002), 100 m west from the Racławka stream ( Fig. 1A , locality 3). Góra Żarska Member of the Dubie Formation.

Type horizon: Quasiendothyra communis – Quasiendothyra regularis Zone ( Palmatolepis marginifera –middle Palmatolepis expansa conodont zones), Famennian.

Material.— 16 specimens from localities 1 and 3, all broken and abraded, often penetrated by the tabulates.

Emended diagnosis.— Gerronostroma with mostly thin laminae (30–100 µm), occassionally thickened up to 200 µm. Pillars with conical axial canals, intersecting 2–9 interlaminar spaces, thickened when lying directly below laminae. Mamelons low, commonly composed of long, branching pillars and reduced laminae ( Fig. 6A 2 ).

Description.—Skeleton laminar or domical, with mamelons showing relief up to 7 mm. Laminar specimens between 4 and 15 mm milimeters thick. Heights of domal skeletons up to 150 mm, and with basal length often exceeding 150 mm. Great variation within skeletons visible, allowing to distinguish three different phases. Each of them could be described as separate species, but with transitions between phases within single specimens.

Ph a se 1 ( Figs. 5D–G , 6E ): Skeleton domical, of height up to 150 mm, mammilate. Laminae thin (30–100 µm) and distinct, with rare foramina, one−layered, sometimes dichotomously branching. Spacings between laminae between 200 and 600 µm, but locally interlaminar spaces extremely narrow, allowing adjacent laminae to amalgamate, and forming single thick skeletal elements, usually with a middle lighter zone ( Fig. 5D 1 ). Foramina more conspicuous in areas adjacent to mamelons. Pillars 80 to 175 µm thick, superposed, intersecting at least two interlaminar spaces, with conical axial canals at tops. In tangential sections pillars cut as dots, rarely as ovals. Next to laminae the axial canals visible in centres of pillars, simulating ring pillars ( Fig. 5E ). Dissepiments common in most but may nearly absent in others ( Fig. 5D 2 ), always convex, intersecting laminae and pillars. Mamelons up to 7 mm high, approximately one−third of them associated with indistinct astrorhizae. Axial canals poorly visible ( Fig. 5F ). Astrorhizae marked rather by long and branching pillars than by the presence of an axial canal. In tangential sections pillars forming short vertical walls radiating from the centre of astrorhizae. In central parts of low mamelons pillars long, branching, in tangential sections forming meandering walls ( Fig. 6E ), and laminae commonly reduced, closely resembling phase 2 of Gerronostroma raclaviense sp. nov.

Phase 2 ( Fig. 5G ): Skeleton laminar, rarely domical, usually less than 10 mm thick. Mamelons indistinct, associated with astrorhizae, but less common than in phase 1. Laminae up to 300 µm thick, with lighter central zone commonly revealing tripartite structure resulting from amalgamation of adjacent laminae. Foramina very rare, less common than in phase 1. Galleries subrectangular or rounded, joining together through wide foramina in parts of specimens showing strongly thickened skeletal elements, and forming short vertical canals, visible as indistinct astrorhizae in tangential sections. These structures sometimes associated with mamelons. Pillars superposed, intersecting at least 2–3 interlaminar spaces, 80 up to 200 µm thick, thickened in their upper parts. In tangential sections pillars rounded, oval, rarely spool−shaped, in many cases revealing conical axial canal in their upper parts, simulating ring pillars. Dissepiments uncommon, rarely covering foramina. Phase 2 in several specimens overlying phase 1 ( Fig. 5G ).

UAM Gerronostroma cracoviensis Gerronostroma sp. Gerronostroma raclaviense RAC−Z51 RAC−Z RAC4 RAC7 RAC9 RAC13 RAC22 RAC29 RAC122 RAC68 RAC70 RAC−Z1 142 Gerrono− stroma craco− viensis RAC4 3 1, 2 3, 4 3 1 RAC7 2, 4 4 2, 4 3 2 2 RAC9 RAC13 RAC22 2, 4 4 3, 4 3 3 1, 4 4 4 2 1 4 4 4 RAC29 2, 4 3 4 3, 4 3, 4 1 RAC122 3 4 1, 2, 4 4 1 Gerrono− stroma sp RAC68 RAC70 3 1, 2 3 2 3, 4 1, 4 3 3 3 4 3 4 3 2, 3 3 Gerrono− stroma racla− viense RAC−Z1 3, 4 4 4 3, 4 1, 2, 4 3 4 RAC−Z51 RAZ−Z74 3 4 2 3, 4 4 3 2, 3 2 2 2 RAC−Z142 1 1 1 1 3 4

74 RAC−Z.

P h a s e 3 ( Fig. 6D ): Skeleton domical, with a low relief, up to 30 mm. Mamelons numerous, up to 6 mm high. Laminae non−enveloping, one−layered, thin (30–75 µm), with numerous foramina. Spacings between laminae showing great variation, between 200 and 550 µm. In places laminae reduced, visible as short processes of pillars. Pillars long, intersecting at least two, but up to 9 laminae, postlike, simple, immediately below the laminae thickened, rarely dichotomously branching in their upper fragments. Thickness of pillars between 75 and 200 µm, usually larger than laminae. In tangential sections pillars rounded, rarely oval, joining in areas surrounding laminae and forming dense network. Dissepiments common in dense skeleton, absent from areas of light skeleton, with reduced laminae, and numerous foramina. All specimens assigned to phase 3 reveal transitions into and from phase 1 ( Fig. 6D , lower part of the photograph).

Statistics.—Data analysis using Kruskal−Wallis test performed on pillar length, pillar spacing, pillar diameter and laminar spacing reveal no significant differences between specimens assigned to Gerronostroma cracoviensis ( Gürich, 1904) . Identical results were also attained when considering measurements collected from the parts of skeletons representing different phases ( Table 2).

Discussion.— Gürich (1904) assigned Gerronostroma cracoviensis to Stromatoporella . However, photographs of specimen described in his paper and the material studied in the present paper do not display features considered diagnostic for that genus. Ring pillars appear on the bottom boundaries of laminae, at the cross sections of pillars with conical axial canals. In the order Stromatoporellida these structures are present above the laminae, and resulted from inflections of the laminae in areas surrounding foramina. Gürich (1904) noticed also tripartite laminae, but they appear to be a result of merging of two adjacent, separate laminae. Thus this species does not exhibit the diagnostic characteristics of Stromatoporella .

Gürich's collections deposited at Wrocław (formerly Breslau) and Hamburg Universities were destroyed during World War II (Wolfgang Weitschat and Joanna Haydukiewicz, personal communications 2007). Thus, the type material of Gerronostroma cracoviensis is apparently lost. Therefore I decided to designate a neotype selected from material collected at the so−called Stromatoporoid Rock, the original type locality of Gürich (1904). Specimen UAM RAC 29 closely matches illustrations in Gürich (1904: pl. 1), and therefore I selected it as the neotype.

Stratigraphic and geographic range.—Southern Poland, Dębnik Anticline, both slopes of the Racławka Valley between Dubie and Paczółtowice villages. Góra Żarska Member of the Dubie Formation. Quasiendothyra communis – Quasiendothyra regularis Zone ( Palmatolepis marginifera –

middle Palmatolepis expansa conodont zones), Famennian. Stromatoporoid assemblage 1.

Figures

Fig. 5. Famennian clathrodictyids Gerronostroma raclaviense sp. nov. and Gerronostroma cracoviensis (Gürich, 1904), Dębnik Anticline. A, B. G. raclaviense. A. Paratype UAM RAC−Z142. Transverse section through basal part of the skeleton (phase 1), showing upward−extended mamelon (central part, phase 2). B. Phase 3, paratype UAM RAC−Z74. Longitudinal section showing low mamelon erecting from laminar part of the skeleton. Note short axial canal in central part of mamelon (arrow). C. Phase 3, transverse section of paratype UAM RAC−Z 51. D. G. cracoviensis. Phase 1, longitudinal sections of neotype UAM RAC29. Note tabulate coral penetrating the stromatoporoid skeleton and amalgamation of surrounding laminae (D1, arrow). E. Phase 1, transverse section of specimen UAM RAC4. Note cross sections of pillars with conical axial canals simulating ring pillars (arrows). F. Phase 1, longitudinal section of neotype UAM RAC29. Note astrorhiza with short axial canal and numerous dissepiments, accompanied by foramina (upper left corner). G. Phase 2, longitudinal section of specimen UAM RAC7. Note transition between phases 1 and 2 located in the bottom part of the photograph. Scale bars 1 mm.

Fig. 6. Famennian clathrodictyids Gerronostroma cracoviensis (Gürich, 1904) and Gerronostroma sp., Dębnik Anticline. A. Gerronostroma sp. A1, phase 2 overlaid by phase 1, longitudinal section of specimen UAM RAC14; A2, transverse section of the same specimen, phase 2 located in the upper right corner. B. Phase 1, longitudinal section of specimen UAM RAC68. Note planar, tripartite laminae. C. Longitudinal section of specimen UAM RAC70. Phase 2 (in the middle of the photograph) bounded by denser skeleton (phase 1). D, E. Gerronostroma cracoviensis. D. Phase 3, longitudinal section of specimen UAM RAC9. A transition from phase 1 into phase 3 indicated by the arrow. E. Phase 1, longitudinal section of specimen UAM RAC62. Low mamelon formed by long, complexly branching pillars resembling phase 2 of G. raclaviense sp. nov. 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. 2. Detailed profiles of the studied localities. A. Detailed profile of exposure 1, displaying succession of three stromatoporoid assemblages. B. Geological logs of locality 2 (uppermost part of the profile, Racławka Formation, all samples collected from the scree, no bedrock available) and exposure 3 (the so−called “Gürich's Stromatoporoid Rock”).