Geological Quarterly, 2004, 48 (1): 83–88 Very large stromatoporoid indicating Early Frasnian reef core (Holy Cross Mts., Poland) Grzegorz RACKI and Ma³gorzata SOBSTEL Racki G. and Sobstel M. (2004) — Very large stromatoporoid indicating Early Frasnian reef core (Holy Cross Mts., Poland). Geol. Quart., 48 (1): 83–88. Warszawa. A large stromatoporoid Actinostroma cf. crassepilatum Lecompte, 1951, at least 8.5 m in diameter and 0.85 m in height, occurs in the Œluchowice quarry in Kielce, Holy Cross Mountains. This sponge occurs in growth position within Early Frasnian (transitans Zone) intraclast-rich reef-rubble deposits. A unique preservation of the reef-builder close to a reef core is implied for the northern flank of the developing Dyminy Reef during its maximum expansion northward into the Kostom³oty intrashelf basin. Grzegorz Racki, Ma³gorzata Sobstel, Faculty of Earth Sciences, University of Silesia, Bêdziñska 60, PL-41-200 Sosnowiec, Poland; e-mail: racki@us.edu.pl, sobstel@wnoz.us.edu.pl. (received: October 15, 2003; accepted: January 5, 2004). Key words: Stromatoporoidea, Dyminy Reef, Frasnian, Holy Cross Mountains, Poland. INTRODUCTION Devonian exposures in the Holy Cross Mountains, Central Poland (Fig. 1A and B) have provided important data on stromatoporoid-coral facies of the globally occurring Frasnian reef complexes; see for example KaŸmierczak (1971), Szulczewski (1971), Narkiewicz (1988), Wrzo³ek (1988), Nowiñski (1992) and Racki (1992). Stromatoporoids were among the dominant reef builders on extensive Middle Palaeozoic carbonate shelves (Wood, 1999). This extinct group have been interpreted recently as a class of non-spiculate sponges (Stearn et al., 1999), represented as fossils by their basal carbonate skeleton (but see stromatoporid stromatolites of KaŸmierczak, 2003). Stromatoporoids from the Holy Cross Mountains Devonian succession have been comprehensively described by KaŸmierczak (1971, 2003), while some palaeoecological aspects are discussed by £uczyñski (1998, 2003). An exceptionally large stromatoporoid specimen in growth position is described here as a record of a stromatoporoid-coral reef-core. This unique occurrence, first noted in Racki (1992, p. 128), is considered in the context of facies pattern within the Frasnian Dyminy Reef complex (Narkiewicz, 1988; Narkiewicz et al., 1990; Racki, 1992). PALAEOGEOGRAPHIC AND STRATIGRAPHIC SETTING Two distinct palaeogeographic-tectonic Devonian domains, the Kielce palaeohigh region and £ysogóry palaeolow region, coupled with the transitional Kostom³oty area, characterise the Holy Cross Mountains part of Laurussian shelf (Racki, 1992). The subsymmetrical facies plan is emphasised by the central location of the Frasnian Dyminy Reef (Fig. 1B), surrounded by deeper intrashelf basins: Chêciny–Zbrza (southern) and £ysogóry–Kostom³oty (northern), as summarised in Narkiewicz (1988), Racki (1992) and Szulczewski (1995). Developmental stages of the stromatoporoid-coral reef ecosystem, which collapsed near the Frasnian–Famennian boundary (see summary in Copper, 2002), are in an overall accordance with the Euramerican sea-level curve of Johnson et al. (1985). A succession of varied Frasnian limestones (Kostom³oty Beds in Szulczewski, 1971), developed close to the northern periphery of the Dyminy Reef, is perfectly exposed in the abandoned Œluchowice quarry, located in the NW part of Kielce (Fig. 1B and C). The locality is well-known due to well exposed folding and other tectonic phenomena seen there (Lamarche et al., 1999), but not very attractive in palaeontological terms because fossils only occur commonly in 84 Grzegorz Racki and Ma³gorzata Sobstel Fig. 1. A — location of Œluchowice quarry in Poland, B — the Holy Cross Mountains (based on Racki, 1992, fig. 2), C — general lithological column of the lower part of Œluchowice section (Szulczewski, 1971, fig. 7, modified), D — detailed succession of the Wietrznia Beds with the marked stromatoporoid reef at western end of the Œluchowice quarry (Racki and Bultynck, 1993, fig. 4, modified) The £ysogóry Region is shown to be limited to the £ysogóry basin sensu Racki (1993), i.e. bordered by the Holy Cross Fault, but a basin facies was also partly developed in the Frasnian intrashelf basins surrounding the Dyminy Reef B Fig. 2. A — northern part of the eastern wall, western Œluchowice quarry at Kielce; studied part of the exposure arrowed (see Fig. 2B); B — northeastern wall, with arrowed stromatoporoid (Actinostroma) reef (Ac) in the basal interval B of the Wietrzna Beds, 0.8 m thick (see Fig. 1D) Very large stromatoporoid indicating Early Frasnian reef core (Holy Cross Mts., Poland) 85 Bthe lowermost (described below) and uppermost parts, in the Frasnian–Famennian interval where corals, brachiopods, crinoid debris are found (Szulczewski, 1971; Nowiñski, 1992; Racki and Baliñski, 1998). Therefore, the coarse-grained, fossiliferous and intraclast-rich limestones under study are a distinctive variety of the generally fossil-impoverished deep-slope facies, and re-assigned therefore to the Wietrznia Beds by Racki and Bultynck (1993), characterised by intermediate facies position between fore-reef and basin settings (see also Racki, 1992). This interval, ca. 4 m thick, occurs in the northern part of the quarry (Fig. 2) and on the nearby Czarnów Hill to the west (Szulczewski, 1971), and is precisely dated by conodonts to the Early Frasnian Palmatolepis transitans Zone (Racki and Bultynck, 1993). IN-PLACE OCCURRENCE OF THE LARGE STROMATOPOROID In the western Œluchowice quarry, protected as a geological reserve, the Wietrznia Beds crop out in subordinate northeastern wall, close to the quarry floor (Fig. 2A). The horizontally arranged thick limestone layers form the lower limb of the overturned Œluchowice fold (see Lamarche et al., 1999). The oldest set A sensu Racki and Bultynck (1993), over 4 m thick, contains several fossil-poor calcarenites in a marly-shale succession with abundant rhynchonellid brachiopods assigned to Phlogoiderhynchus polonicus (Roemer) and Styliolina domanicense Lyashenko and S. ex gr. nucleata Karpinsky (see Biernat and Szulczewski, 1975; Haj³asz, 1992), as well as branched corals in some layers (Fig. 1D). This interval is questionably placed in the lower Wietrznia Beds in the Œluchowice-Czarnów succession due to its transitional nature to the underlying Szyd³ówek Beds (Racki and Bultynck, 1993), and this Givetian to Frasnian rhythmic marly unit is poorly exposed in the railway cuting to the north. The succeeding light gray biointrarudites, with dark calcarenite, 0.3 m thick, at the bottom (interval B), are marked by abundant reef-builder debris, mostly diverse dendroid and massive stromatoporoids and corals, especially alveolitid tabulates (see list of taxa in Nowiñski, 1992). The reef breccia is associated predominantly with brachiopod and echinoderm (chiefly crinoid) bioclasts, calcispheroids and other microproblematica, as well as with unsorted micritic intraclasts (with peloidal-lumpy to spongy, Fig. 3. A — close-up of the reef layer (northern part) built of in situ Actinostroma (Ac, see Fig. 2B) and reef rubble (rr), note the indistinct hemisphaerical-coalesced appearance of the stromatoporoid sheet; B — photomicrograph of the peripheral part of the Actinostroma skeleton, with visible poorly sorted intrabiosparenite enclosing sediment (see also biointrasparudite microfacies in Szulczewski, 1971, pl. 26: 1), and non-enveloping growth pattern renalcid-like fabrics in places), including large flat pebbles in conglomeratic beds (see Szulczewski, 1971, p. 60–61, pl. 24: 2, pl. 26: 1 therein; Fig. 3B). The second bed of interval B, 0.7–0.9 m in thickness, shows a stromatoporoid skeleton in growth position along most of the exposure, i.e., over a distance of ca. 12 m (Fig. 2B). The almost non-weathered rock surface, partly covered with ferric oxide and an organic coating, is inconvenient for detailed observations, but the stromatoporoid apparently continued laterally over at least 8.5 m. Sorted fine-grained, as well as unsorted talus-like deposits are found as the enclosing lithology, and the Fig. 4. Actinostroma cf. crassepilatum Lecompte, 1951 from the Early Frasnian Wietrznia Beds at Œluchowice quarry (see Fig. 1D); A — longitudinal section, B — obliquely-tangential section 86 Grzegorz Racki and Ma³gorzata Sobstel Table 1 Dimensions of reticular tissue elements for Actinostroma cf. crassepilatum Lecompte, 1951 from Œluchowice (Fig. 4) Laminae Pillars max/2 mm min/2 mm thickness max/2 mm min/2 mm 10 7 0.06–0.14 7 5 thickness 0.18–0.29 moderately irregularly undulose upper contact between the pale stromatoporoid skeleton and the coral-rich biosparudite is clearly visible in the higher portion of the bed in some places (see Figs. 2B and 3). The largest stromatoporoid thickness (0.85 m) is noted in the middle part of the wall, but the partly erosional vs. burial nature of its top is unrecognised due to its poorly visible, probably non-enveloping growth pattern (sensu Kershaw, 1998). The low-relief profile and non-enveloping growth are typical of large examples of “massive” stromatoporoids (£uczyñski, 2003). Thin sections from two outer parts of the stromatoporoid indicate assignment to the genus Actinostroma (Fig. 4). Despite differential recrystallization in both skeletal fragments, highly thickened pillars (up to 0.3 mm; Table 1) are seen in the reticular tissue. Therefore, a large tabular actinostromatid specimen is implied to be the rock-former of the layer under study, even if coalescence of several laminar individuals into one large mass is likely (cf. Kershaw 1998, p. 523). When compared with species described by KaŸmierczak (1971, 2003) from coeval strata of the Holy Cross Mts., this specimen is assignable only to A. crassepilatum Lecompte, 1951 (see KaŸmierczak, 1971, p. 137, pl. 40: 3, pl. 41: 6; 2003, p. 696, pl. 393: 3), widely distributed in European Givetian–Frasnian carbonate complexes. Notably, this single Actinostroma species has been determined by KaŸmierczak (1971, 2003) in the Wietrznia Beds (at the type locality), as the largest of the stromatoporoids there (up to 1.3 m in diameter and 0.75 cm high). FINAL REMARKS AND IMPLICATIONS FOR THE DYMINY REEF Meter-sized autochthonous Actinostroma sponge skeletons are not rare, because this genus is the commonest frame builder of the Givetian to Frasnian stromatoporoid-coral reefs worldwide (Stearn et al., 1999, p. 33). However, its dimension is noteworthy: the speciemen described here is the largest stromatoporid reported so far from the Upper Devonian deposits from Poland. However, a giant tabular example of Actinostroma expansum (Hall and Whitfield, 1873), ca. 1.5 m high and 30 m wide, has been reported from the middle Frasnian Shell Rock Formation (Nora Member) of Iowa (Stock, pers. comm., 2003). Wood (2000) also described remarkably large actinostromatids from the Western Australian Frasnian reef that can reach sizes of up to 5 m in diameter and 1.5 m in height. The Australian species A. windjanicum Cockbain, 1984 is marked by highly complex platy-multicolumnar growth, which may be presumed also for the incompletely exposed specimen from Œluchowice (see Fig. 3A) that stabilised skeletal debris and fine-grained substrate. A widespread Actinostroma assemblage was discerned by Racki (1992, p, 128) as a principal ecological component of the wave-resistant accretion rim of the Dyminy Reef in fairly agitated waters at most 10 m below sea level, but most “massive” stromatoporoid occurrences are post-mortem hydrodynamically reworked (KaŸmierczak, 1971; Narkiewicz et al., 1990; £uczyñski, 1998, 2003). Findings of large in situ stromatoporoid skeletons are quoted by Szulczewski (1971, p. 86) and Racki (1992, p. 128), also from talus-like Stromatoporoid-Detrital Beds. Szulczewski (1971, p. 107–112) broadly discussed some basic limitations of reef recognition in this region, and he concluded that “part of detrital limestones with large-sized stromatoporoids make up an actual reef core” (Szulczewski, 1971, p. 112). In fact, a common feature of fossil reefs which represent diverse and complex biogenic structures, is a low preservation probability of the wave- and storm-agitated accreted rim formed by essentially in situ skeletons (e.g. Hoffman and Narkiewicz, 1977; Longman, 1981; Wood, 1999; Riding, 2002), even if an alternative (ramp model) explanation was highlighted by Stanton and Flügel (1995; see also Machel and Hunter, 1994). In the case of the Wietrznia Beds under study, reef-rubble intraclastic deposits have continued both to the east (eastern Œluchowice quarry) and west (Czarnów Hill; Szulczewski, 1971; Racki and Bultynck, 1993), but the autochthonous frame-builders are limited to the western Œluchowice locality only. The spectacular in situ growth of Actinostroma cf. crassepilatum indicates that this species seems to live preferably in turbulent habitats that appeared to be optimal to support huge reef-building organisms. This unique framestone layer determines a portion of the Early Frasnian Dyminy Reef, representing a true reef-core (cf. Szulczewski, 1971) or at least very proximal fore-reef facies, during its extreme progradation northward into the £ysogóry–Kostom³oty basin. Notably, this initial developmental phase of the reef-complex (= foundation stage of Racki, 1992) was associated also with the ephemeral appearance of the distinctive Kadzielnia-type mud mounds on gentle irregular reef flanks, marked by sheet-like stromatoporoid mud binders (KaŸmierczak, 1971; Szulczewski, 1971; Racki, 1992; £uczyñski, 1998). This suggests strongly hydrodynamically changing conditions over the differentiated bioherm-fringed margin of the early “table”-type Dyminy Reef (Szulczewski, 1971; Racki, 1992). Northward progradation on a similar scale has been recorded only for the final reef-cap developmental stage of the latest Frasnian (see Narkiewicz, 1988; Racki, 1992; Racki and Baliñski, 1998). Acknowledgements. Carl W. Stock is kindly acknowledged for constructive comments on the manuscript, and Jan Malec for useful editorial remarks. M. Racka provided the photo for Figure 2A. We thank M. Lewandowski for digital preparation of figures. This work has been partly supported by the State Committee for Scientific Research (KBN grant 3 P04D 040 22 for G. Racki) and the Silesian University. Very large stromatoporoid indicating Early Frasnian reef core (Holy Cross Mts., Poland) 87 REFERENCES BIERNAT G. and SZULCZEWSKI M. (1975) — The Devonian brachiopod Phlogoiderhynchus polonicus (Roemer, 1866) from the Holy Cross Mountains, Poland. Acta Palaeont. Pol., 20 (2): 199–221. COPPER P. (2002) — Reef development at the Frasnian/Famennian mass extinction boundary. Palaeogeogr., Palaeoclimatol., Palaeoecol., 181 (1–3): 27–65. HAJ£ASZ B. (1992) — Tentaculites from the Givetian and Frasnian of the Holy Cross Mountains. Acta Palaeontol. Pol., 37 (2–4): 385–394. HOFFMAN A. and NARKIEWICZ M. (1977) — Developmental stages of Lower to Middle Palaeozoic banks and reefs. N. Jb. Geol. Palaont. Mh., 2: 272–283. JOHNSON J. G., KLAPPER G. and SANDBERG C. A. (1985) — Devonian eustatic fluctuations in Euramerica. Bull. Geol. Soc. Am., 96 (5): 567–587. KAZMIERCZAK J. (1971) — Morphogenesis and systematics of the Devonian Stromatoporoidea from the Holy Cross Mountains, Poland. Palaeontol. Pol., 26. KAZMIERCZAK J. (2003) — Grupa Stromatolity stromatoporoidowe. In: Budowa Geologiczna Polski. III. Atlas skamienia³oœci przewodnich i charakterystycznych, part 1b, Dewon (ed. L. Malinowska): 690–707. Pañstw. Inst. Geol. Warszawa. KERSHAW S. (1998) — Stromatoporoid palaeobiology and its applications in palaeoenvironment analysis. Palaeontology, 41 (3): 509–544. LAMARCHE J., MANSY J. L., BERGERAT F., AVERBUCH O., HAKENBERG M., LEWANDOWSKI M., STUPNICKA E., ŒWIDROWSKA J., WAJSPRYCH B. and WIECZOREK J. (1999) — Variscan tectonics in the Holy Cross Mountains (Poland) and the role of structural inheritance during Alpine tectonics. Tectonophysics, 313 (1–2): 171–186. LONGMAN M. W. (1981) — A process approach to recognizing facies of reef complexes. In: European Fossil Reef Models (ed. D. F. Toomey). Econ. Paleont. Mineral., Spec. Publ., 30: 9–40. £UCZYÑSKI P. (1998) — Stromatoporoid morphology in the Devonian of the Holy Cross Mountains, Poland. Acta Palaeontol. Pol., 43 (4): 653–663. £UCZYÑSKI P. (2003) — Stromatoporoid morphology in the Devonian of the Holy Cross Mountains, Poland, and its palaeoenvironmental significance. Acta Geol. Pol., 53 (1): 19–27. MACHEL H. G. and HUNTER I. G. (1994) — Facies model for Middle to Late Devonian shallow-marine carbonates, with comparisons to modern reefs: a guide for facies analysis. Facies, 30: 155–176. NARKIEWICZ M. (1988) — Turning points in sedimentary development in the Late Devonian in southern Poland. In: Devonian of the World (eds. N. J. McMillan, A. F. Embry and D. J. Glass). Can. Soc. Petrol. Geol., Mem., 14 (2): 619–636. NARKIEWICZ M., RACKI G. and WRZO£EK T. (1990) — Lithostratigraphy of the Devonian stromatoporoid-coral carbonate sequence in the Holy Cross Mountains (in Polish with English summary). Kwart. Geol., 34 (3): 433–456. NOWIÑSKI A. (1992) — Tabulate corals from the Givetian and Frasnian of the Holy Cross Mountains and Silesian Upland. Acta Palaeontol. Pol., 37 (2–4): 183–216. RACKI G. (1992) — Evolution of the bank to reef complex in the Devonian of the Holy Cross Mountains. Acta Palaeontol. Pol., 37 (2–4): 87–182. RACKI G. and BALIÑSKI A. (1998) — Late Frasnian Atrypida (Brachiopoda) from Poland and the Frasnian-Famennian biotic crisis. Acta Palaeont. Pol., 43 (2): 273–304. RACKI G. and BULTYNCK P. (1993) — Conodont biostratigraphy of the Middle to Upper Devonian boundary beds in the Kielce area of the Holy Cross Mts. Acta Geol. Pol., 43 (1–2): 1–25. RIDING R. (2002) — Structure and composition of organic reefs and carbonate mud mounds: concepts and categories. Earth-Sci. Rev.: 163–231. STANTON R. J. and FLÜGEL E. (1995) — An accretionary distally steepened ramp at an intrashelf basin margin: an alternative explanation for the Upper Triassic Steinplatte “reef” (Northern Calcareous Alps, Austria). Sediment. Geol., 95 (3–4): 269–286. STEARN C. W., WEBBY B. D., NESTOR H. and STOCK C. W. (1999) — Revised classification and terminology of Palaeozoic stromatoporoids. Acta Palaeontol. Pol., 44 (1): 1–70. SZULCZEWSKI M. (1971) — Upper Devonian conodonts, stratigraphy and facies development in the Holy Cross Mts. Acta Geol. Pol., 21 (1). SZULCZEWSKI M. (1995) — Depositional evolution of the Holy Cross Mountains in the Devonian and Carboniferous — a review. Geol. Quart., 39 (4): 471–488. WOOD R. (1999) — Reef Evolution. Oxford University Press. Oxford. WOOD R. (2000) — Palaeoecology of a Late Devonian back reef, Canning Basin, Western Australia. Palaeontology, 43 (4): 671–703. WRZO£EK T. (1988) — Tetracoral zonation of the Devonian stromatoporoid-coral limestones in the SW Holy Cross Mountains, Poland. In: Devonian of the World (eds. N. J. McMillan, A. F. Embry and D. J. Glass). Can. Soc. Petrol. Geol., Mem., 14 (3): 413–424.