Stachyodes fasciculata Dong

Huang, Jiayuan, Liang, Kun, Wang, Yue, Kershaw, Stephen, Jeon, Juwan, Li, Yue & Qie, Wenkun, 2022, Stromatoporoids from a Middle Devonian reef in South China and their palaeoecological implication, Acta Palaeontologica Polonica 67 (3), pp. 711-736 : 728-730

Stachyodes fasciculata Dong in Dong et al., 1989

Fig. 11 .

1989 Stachyodes fasciculata sp. nov.; Dong in Dong et al. 1989: 273, pl. 17: 2a, b.

1989 Stachyodes bifurca ( Stearn, 1962) ; Dong et al. 1989: 275, pl. 16: 1a–c.

1992 Stachyodes fasciculata Dong in Dong et al., 1989; Dong and Liu 1992: 172, pl. 4: 4a, b.

2020 Stachyodes radiata Lecompte, 1952 ; Huang et al. 2020: 13.

Material.— 112 specimens from the Givetian (Middle Devonian) Jiwozhai reef, Dushan Formation , Dushan, Guizhou, South China, with three specimens ( NIGP 177060–62 ) illustrated .

Diagnosis.—Skeleton dendroid, laminar, and bulbous, formed by extremely well differentiated pachystromes and pachysteles. Pachystromes thin, in a thickness of 0.02 mm. Pachysteles thick, radiated from the central zones of the skeleton, interconnected to build the closed networks. Axial canal prominent in the dendroid forms, but branching canals common in laminar and bulbous forms.

Description.—Skeletons are dendroid, laminar, or rarely bulbous, but fragmented or overturned in most specimens ( Fig. 11A ). The dendroid branches are commonly 3–5 mm in diameter, sporadically up to 15 mm ( Fig. 11A ). The laminar forms 3–20 mm in thickness ( Fig. 11B ). The bulbous one shows a height of 40 mm and width of 30 mm ( Fig. 11C 1 ). In longitudinal section, the skeleton consists of conspicuous pachystromes and pachysteles ( Fig. 11A, B, C 1 ). Pachystromes are thin, parabolic in the dendroid forms, relatively closely spaced, spacing 10–13 per 2 mm, 0.02 mm in thickness. Pachysteles formed a closed network in the skeleton surface, 0.2 mm thick. The galleries are divided by the thin pachystromes, with a width of 0.2 mm. Axial canal is prominent in the dendroid forms, 0.4–0.5 mm in diameter, infilled with dissepiments, while branching canals are more common in the laminar and bulbous forms ( Fig. 11C 1 – C 3 ). In tangential section, axial canal is circular, pachysteles clearly radiate from the axial to peripheral zone and pachystromes distributed as concentric circles in the dendroid forms ( Fig. 11A ). Pachysteles apparently interconnect to form a closed network in the bulbous forms ( Fig. 11C 3 ). The microstructure is coarsely striated ( Fig. 11C 4 ).

Remarks.—The dendroid forms of the present species were preliminarily assigned to Stachyodes radiata Lecompte, 1952 , by Huang et al. (2020), but the latter shows more irregular and thicker pachysteles. Further study indicates the species is compatible with both Stachyodes bifurca ( Stearn, 1962) and Stachyodes fasciculata as defined by Dong in Dong et al. (1989), and thus determination is problematic. Although the two samples are different in size, the close similarity of the skeleton morphology justifies the assignment to the same species. However, the relationships between Syringostroma bifurcum Stearn, 1962 , and Stachyodes bifurca ( Stearn, 1962) are not fully clear due to the preservation quality of the samples from Canada. Here, we assign these specimens to Stachyodes fasciculata Dong in Dong et al., 1989, in relation to the high consistency of the skeleton. The laminar forms of Stachyodes are not common in the Devonian, e.g., Stachyodes australe ( Wray, 1967) and Stachyodes jonelrayi Stearn, 1975 . The difference between the three species lies in the absence of two layers in the present species. The laminar forms of this species were partly assigned to Salairella hybridina Yang and Dong, 1979 , by Huang et al. (2020) according to the closed network in the tangential section, but they are totally different in relation to microstructure and laterally extensive thin pachystromes in longitudinal section. Moreover, some of the laminar forms were assigned to Trupetostroma dushanense Yang and Dong, 1963 , T. regulamellatum Yang and Dong, 1963 , or T. sublamellatum Lecompte, 1952 , in terms of thin pachystromes and closed network formed by pachysteles, but Trupetostroma Parks, 1936 , is fundamentally featured by isolated pillars rather than interconnected pachysteles, thus these species do not belong to Trupetostroma .

Stratigraphic and geographic range.— Givetian (Middle Devonian) of Guizhou, Guangxi, and Hunan provinces, South China .

Stachyodes sp.

Fig. 12A .

Material.— Nine specimens from the Givetian (Middle Devonian) Jiwozhai reef, Dushan Formation , Dushan, Guizhou, South China, with one best preserved specimen ( NIGP 177063 ) illustrated .

Description.—Skeletons are laminar forms, with a height up to 4 mm, commonly covering the other stromatoporoids. Latilaminae are exceptionally conspicuous and laterally undulating, 1.5–2 mm in thickness. In longitudinal section, the skeleton consists of two zones ( Fig. 12A 1 ). In the basal zone, the structure is weakly differentiated, with branching astrorhizal canals irregularly distributed, 0.1–0.4 mm in diameter. In the upper zone, short pachysteles are dominant, spacing 10 per 2 mm, 0.1 mm in thickness ( Fig. 12A 1 ). Pachystromes cannot be recognized clearly. Mamelons are not apparent. In tangential section, the skeleton shows tight network formed by the interconnected pachysteles ( Fig. 12A 2 ). Astrorhizal canals conspicuous, common with two branching canals ( Fig. 12A 1 , A 2 ). The microstructure is striated ( Fig. 12A 3 –A 5 ).

Remarks.—This species apparently differs from the other dendroid species and it corresponds very well to the laminar Stachyodes species demonstrated by Wolniewicz (2021: fig. 9G) in the Frasnian of Poland. It differs from the laminar Stachyodes australe ( Wray, 1967) in terms of the two special different zones and lacking crescent growth zone in the basal layer. There is some similarity with a key species from Alberta, Stachyodes jonelrayi Stearn, 1975 , that is characterised by possessing a basal layer in the skeleton; this taxon also shows basal layers in the lower portions of successive individual latilaminae after growth interruptions. Nevertheless we are not confident that the species from Jiwozhai reef is necessarily the same as Stachyodes jonelrayi and prefer to leave it in open nomenclature in this study. Further work may be able to finalise the species-level taxon.

Figures

Fig. 11. Stromatoporoid Stachyodes fasciculata Dong in Dong et al., 1989, from the Jiwozhai reef, Jiwozhai Member, Dushan Formation, Givetian, Middle Devonian; Dushan, Guizhou, South China. A. NIGP 177060; longitudinal section and tangential section of the dendroid form. B. NIGP 177061; longitudinal section showing the thick pachysteles and thin pachystromes. C. NIGP 177062; C1, longitudinal section of the bulbous form; C2, enlargement of C1, illustrating regular skeleton; C3, tangential section showing the autotubes and astrorhizal canals; C4, enlargement of C2, showing the coarsely striated microstructure (arrow).

Fig. 1. Location and stratigraphy of the Jiwozhai reef in Dushan County, Guizhou, South China. A. Map showing southern Guizhou and northern Guangxi and the studied area in China. B. Locality of the Jiwozhai reef in Dushan County. C. Depositional successions and fossil assemblages of the supposed uppermost Eifelian to lowermost Frasnian in Dushan, Guizhou province (modified after Liao et al. 1979; Liao 2003).Abbreviations:Ei, Eifelian; Fr., Frasnian.

Fig. 3. Schematic vertical section of stromatoporoids in the Jiwozhai reef (Huang et al. 2020) showing the spatial distribution of different stromatoporoids, note the predominance of the Gerronostromaria grossum Dong, 1974, in the laminar form stromatoporoids.1, Gerronostromaria grossum Dong, 1974; 2, Clathrocoilona spissa (Lecompte, 1951); 3,?Habrostroma laminosum (Lecompte, 1952); 4, Parallelopora sp.; 5, Pseudotrupetostroma porosum (Yang and Dong, 1979); 6, Salairella buecheliensis (Bargatzky, 1881); 7, Stachyodes costulata Lecompte, 1952; 8, Stachyodes fasciculata Dong in Dong et al., 1989; 9, Stachyodes sp.; 10, Stictostroma saginatum (Lecompte, 1951); 11, Synthetostroma actinostromoides Lecompte, 1951. Black, stromatoporoids; gray, other organisms between stromatoporoids.

Fig. 4. Pie charts illustrating palaeoecological parameters of the stromatoporiod fauna. A. External morphology. B. Thickness. C. Substrate types. D. Thickness of growth interruption. Abbreviations: Ger, Gerronostromaria grossum Dong, 1974; Cla, Clathrocoilona spissa (Lecompte, 1951);?Hab, Habrostroma laminosum (Lecompte, 1952); Par, Parallelopora sp.; Pse, Pseudotrupetostroma porosum (Yang and Dong, 1979); Sal, Salairella buecheliensis (Bargatzky, 1881); Sta, Stachyodes sp.; Stac, Stachyodes costulata Lecompte, 1952; Staf, Stachyodes fasciculata Dong in Dong et al., 1989; Sti, Stictostroma saginatum (Lecompte, 1951); Syn, Synthetostroma actinostromoides Lecompte, 1951.

Fig. 12. Stromatoporoid Stachyodes sp. NIGP 177063, from the Jiwozhai reef, Jiwozhai Member, Dushan Formation, Givetian, Middle Devonian; Dushan, Guizhou, South China.A1, longitudinal section; A2, tangential section, note the autotubes and conspicuous astrorhizal canals; A3, enlargement of A1, note the coarsely striated microstructure (arrow); A4, enlargement of the upper middle part of A2, note the probably striated microstructure (arrow); A5, enlargement of the lower left part of A2, note the black dots in the tangential section.

Fig. 2. Field photographs of the Jiwozhai reef. A. A panoramic view of the whole reef unit, with a white rectangle indicating the studied area. Note the reverse fault in the east. B. A general view shows the studied area of the reef unit. C. Enlarged field photo of the reef fragment marked in B, showing the thick or thin laminar stromatoporoids (undulating dashed line) covered on branching tabulate corals (triangles), solitary rugose corals (crosses), dendroid stromatoporoids (squares), bulbous stromatoporoid (circled line), and clay-rich micrites (fine grained sediments between the metazoan skeletons). D. An example of polished block of the Jiwozhai reef limestone showing toppled dendroid or laminar Stachyodes fasciculata Dong in Dong et al., 1989, and encrusting Stictostroma saginatum (Lecompte, 1951) in the upper area. Note the conspicuous digitation of mamelons of Stictostroma saginatum (Lecompte, 1951) in the lower right corner. Sti, Stictostroma saginatum (Lecompte, 1951); Sta, Stachyodes fasciculata Dong in Dong et al., 1989; Tha, Thamnopora cf. pansiensis Tchi, 1966.

Fig. 5. Stromatoporoid Gerronostromaria grossum Dong, 1974, NIGP 177047, from the Jiwozhai reef, Jiwozhai Member, Dushan Formation, Givetian, Middle Devonian; Dushan, Guizhou, South China.A1, longitudinal section, note the well differentiated network constructed by thin laminae and pillars; A2, tangential section showing the distinct mamelons;A3, enlargement of A1, illustrating the common occurrence of the diagenetic “clinoreticular” microstructure inside the continuous pillars; A4, enlargement of A2, showing the isolated pillars.