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BRITISH COLUMBIA, CANADA. GEORGE D. STANLEY, JR.1 AND JOHN-PAUL ZONNEVELD2. 1The University of Montana Paleontology Center, Missoula, ...
Journal of Paleontology, 85(1), 2011, p. 29–31 Copyright ’ 2011, The Paleontological Society 0022-3360/11/0085-0029$03.00

THE OCCURRENCE OF THE HYDROZOAN GENUS CASSIANASTRAEA FROM UPPER TRIASSIC (CARNIAN) ROCKS OF WILLISTON LAKE, BRITISH COLUMBIA, CANADA GEORGE D. STANLEY, JR.1

AND

JOHN-PAUL ZONNEVELD2

1

The University of Montana Paleontology Center, Missoula, Montana 59812, USA, ,[email protected].; and 2Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3, ,[email protected].

ABSTRACT—Cassianastraea is an enigmatic colonial Triassic cnidarian first described as a coral but subsequently referred to the Hydrozoa. We report here the first occurrence in Canada of fossils we designate as Cassianastraea sp. from the Williston Lake region of British Columbia. The specimens come from older collections of the Geological Survey of Canada, collected in Upper Triassic (Carnian) strata assigned to either the Ludington or Baldonnel Formations. While well known in reef associations of the former Tethys region, Cassianiastraea is relatively rare in North America. The Carnian Baldonnel Formation contains the earliest coral reefs from the North American craton and we suspect that Cassianastraea sp. also came from this reef association.

subsequent research has revealed the presence of a series of minor thrust faults (Fig. 1.2) within the section, juxtaposing several repeated sections of Upper Triassic strata of both Carnian and Norian age (Tozer, 1984). It is clear that the Cassianastraea material originated from either the Ludington Formation or Baldonnel Formation, both of which were deposited during the Upper Carnian (Zonneveld and Orchard, 2002). The Baldonnel Formation is a shallow marine succession of bioclastic sandstone, bioclastic packstone and bioclastic grainstone deposited primarily above storm wave base in a gently dipping carbonate ramp setting with scattered scleractinian patch reefs (Zonneveld and Orchard, 2002; Zonneveld et al., 2004, 2006). Several specimens of Cassianastraea collected from talus slopes in Barren Gully (Fig. 1.2, 1.3) were attached to bioclastic, brachiopod- and echinoderm-dominated packstone and grainstone. These are identical to samples collected on the margins of the scleractinian patch reefs in the Baldonnel Formation. The Ludington Formation is the offshore equivelent to the Baldonnel Formation (Zonneveld et al., 2010). Much of this unit consists of calcareous turbidites and debrites sourced from shallower successions (Zonneveld et al., 2010). A single specimen, collected between Juvavites Gully and Lima Gully (Fig. 1.2, 1.3) was attached to a Halobia-dominated grainstone sample identical to a horizon within the upper Ludington Formation supporting the Upper Triassic interpretation of these specimens (McRoberts, 2000). At Pardonet Hill, Halobia grainstone beds are limited to Upper Carnian strata of the Ludington Formation and Norian strata of the Pardonet Formation. However the lithology of the sample strongly suggests the Ludington as its source. An upper Carnian age is based on detailed conodont biostratigraphy (Zonneveld and Orchard, 2002; Zonneveld et al., 2006). The Pardonet Hill scleractinian patch reef interval is bracketed by conodonts dominated by Metapolygnathus ex gr. nodosus and M. lindae (Zonneveld et al., 2006). The Upper Baldonnel Formation also is Upper Carnian in age with the conformable Baldonnel-Pardonet contact occurring roughly at the Carnian-Norian boundary at this locality (Zonneveld and Orchard, 2002; Zonneveld et al., 2006). Thus Cassianastraea from the northeastern locality (north side of Barren Gully; Fig 1.2, 1.3) is considered upper Carnian.

INTRODUCTION

a problematic Triassic cnidarian first illustrated as the coral Stylina reussi by Laube (1865, pl. 5, fig. 7) from the Cassian Formation, Dolomites (northern Italy). Later it was designated Cassianastraea by Volz (1896) who also regarded it as a coral. Subsequent work (Wells, 1956) recognized that the morphology of Cassianastraea was quite unusual for a coral. Cassianastraea is colonial and possesses an aragonite skeleton with some features resembling corallites but there are unusual features of the skeleton that reveal a non-scleractinian affinity. The unusual structures include tiny openings resembling corallites, but with only five incomplete and poorly developed septal-like structures. However, the simple and incomplete nature of the ‘septa’ showing no evidence of insertion in a hexameral symmetry and the tiny size of the corallite-like openings of Cassianastraea are not aspects traditionally attributed to corals. Research by Cuif (1976) provided microstructural details supporting a hydrozoan affinity for Cassianastraea and the order Lemniscaterina was proposed to contain this genus (Montanaro-Gallitelli, 1980). Two species were recognized— C. reussi Laube (1865), a nominative subspecies with small diameters of the tubes, and C. reussi major MontanaroGallitelli (1980) with tubes four times as wide. Unlike a coral, Cassianastraea is composed of thick-walled tubes connected by stolons. ‘Septa’ originate as wall foldings, protrude into the lumen of the tube and dactylopores enclose a central gastropore. We describe below new Upper Triassic (Carnian) occurrences of this genus in northeastern British Columbia, Canada at Williston Lake (Fig. 1.1, 1.2). The Cassianastraea specimens were collected in 1937 by F. H. McLearn from talus slopes in gullies (Fig. 1.2, 1.3) along the northern part of Pardonet Hill (McLearn, unpublished field notes, 1937, Geological Survey of Canada archives). Comparison of McLearn’s unpublished field notes with geological maps clearly identifies the locality of these fossils (Fig 1.3). Lithology and fossils of the samples are identical to those from Upper Carnian strata of the Baldonnel and Ludington Formations (Zonneveld et al., 2006). McLearn’s original 1937 collecting localities along the shores of the Peace River now are under the water of Williston Lake (Fig. 1.3). Although McLearn (1960) assigned the localities to the Upper Triassic (Norian) Pardonet Formation,

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JOURNAL OF PALEONTOLOGY, V. 85, NO. 1, 2011 Class HYDROZOA? Owen, 1843 Family Uncertain Order LEMNISCATERINA Montanaro-Gallitelli, 1980 Family CASSIANASTRAEIDAE Non Lemniscateridae Montanaro-Gallitelli—Stanley and Roniewicz, 1998 Genus CASSIANASTRAEA Volz, 1896, emend. MontanaroGallitelli, 1980 Hydrosclera Gaetani and Fois, 1979 Zardinophyllum (Senowbari-Daryan et al., 1993) Remarks.—Cassianastraea comes from the lower Carnian Cassian beds, northern Italy (Volz, 1896); the Anisian Upper Serla Formation, Dolomites (Senowbari-Daryan et al., 1993) as Zardinophyllum; and also as Hydrosclera plumosa (Gaetani and Fois, 1979). It was mentioned by Cuif (1976) from Lower Norian, Taurus Mountains, L’Alakir Cay, Turkey and from North America in Ladinian of central Nevada (Roniewicz and Stanley, 1998). The latter authors in error attributed their species to the family Lemniscateridae Montanaro-Gallitelli when Montanaro-Gallitelli actually had designated the family Cassianastraeidae. Pentasmilia Deng (2006) presented a new genus, Pentasmilia with type species P. guangxiensis, from both Middle and Late Triassic of China. It appears to be very close in morphology to Cassianastraea. Deng proposed family Pentasmiliidae for this taxon but it is clear that Cassianastraeidae Montanaro-Gallitelli 1980 takes priority. Cassianastraeidae thus contains two species—Cassianastraea and Pentasmilia. Cassianastraea was assigned to the order Hydrozoa by Montanaro-Gallitelli because the characteristic thin-walled tubes and underdeveloped ‘septa’ are atypical for corals. Some aspects of Cassianastraea do resemble sponges which have a cylindrical shape and similar tubes (B. Senowbari-Daryan, written communication, 2010). However previous authors (Montanaro-Gallitelli (1980) and Cuif (1976) both made strong cases for the assignment to Hydrozoa which we here accept. Although this fossil is quite common among Triassic reef faunas of the Tethys, it appears to be quite rare in the North American Triassic. Occurrence.—Cassianastraea is restricted to Middle-Upper Triassic (Anisian to Carnian stages) in the former Tethys with a lower Norian occurrence in the Taurus Mountains, Turkey and an Upper Ladinian occurrence at New Pass Range, Nevada. A very closely related taxon Pentismilia from the Anisian, South China, may also belong to this genus but further comparisons are needed. CASSIANASTRAEA SP. Figure 2.1–2.3 Description.—Colonies cylindrical or branching, 12–16 mm long, 5–6 mm wide. Coenenchyme composed of curved connecting tubes 0.16–0.30 mm diameter. In expanding part of colony, stolon tubes are average 0.2 mm diameter. Thick wall composed of radiating tubes characterized at surface of r FIGURE 1—Cassianastraea localities, British Columbia, Canada: 1, location of the study area on the Peace Reach of Williston Lake, northeastern British Columbia; 2, map of the study area showing the former path of the Peace River (now flooded) and the present position of the Williston Lake shoreline, lithostratigraphy from unpublished geological maps of E.T. Tozer; 3, map of Pardonet Hill showing distribution of the Carnian Baldonnel and Ludington Formations and the Norian Pardonet Formation. Cassianastraea was derived from both the Baldonnel and Ludington Formations.

STANLEY AND ZONNEVELD—UPPER TRIASSIC CASSIANASTRAEA FROM WILLISTON LAKE CANADA 31 Repository.—Paleontology Collections, Geological Survey of Canada, Ottawa ACKNOWLEDGMENTS

We are grateful to E. T. Tozer (Geological Survey of Canada, Vancouver) for discussions on Triassic paleontology and for access to unpublished field notes and geological maps. Thanks also to J. Doughtery for access to the Geological Survey of Canada repository in Ottawa. We acknowledge a review by B. Senowbari-Daryan. REFERENCES

FIGURE 2—Details of three specimens, scales 5.0 mm: 1, cylindrical colony showing branching tubes, GSC-9673; 2, colony encrusting skeletal debris, GSC-9690 C; 3, specimen broken open, showing tubes of wall and evidence of branching, GSC-9685.

colony by vague hint of septa. Septa difficult to count due to recrystallization but in some tubes 3–4 septa can be counted. Remarks.—Although recrystallized, the Williston Lake material is quite similar to the European holotype and the Nevada specimens. However due to the poor preservation, we refrain from assigning our material to a specific species. The Nevada material shows dimensions similar to the specimens from Williston Lake, especially in the shape of the small connected stolons (0.15–0.30 mm) and thick walls. The diameter ranges of the tubes in the Nevada material are somewhat larger (0.5 to 0.8 mm) with approximately 3–6 septa-like features in each tube. Material.—UM 9673, UM 9685 from a talus slope on the northeastern side of Barren Gully, north Pardonet Hill, Peace Reach of Williston Lake, British Columbia. UM 9690 from a talus slope between Juvavites Gully and Lima Gully, north Pardonet Hill, Peace Reach of Williston Lake, British Columbia. Both localities originally occurred on the south bank of the Peace River but they are now below the waters of Williston Lake. Occurrence.—Upper Triassic (Carnian)

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ACCEPTED 4 AUGUST 2010