Late Triassic brachiopods from a dredge haul on the slope below … · 2015-12-03 · Late Triassic brachiopods from a dredge haul on the slope below Rowley Terrace, northwest Australia

AGSO Journal of Austra lian Geology & Geophysics, 15/l , 135-\36 © Commonwealth of Australia 1994

Late Triassic brachiopods from a dredge haul on the slope below Rowley Terrace, northwest Australia 1.0. Campbell I

Late Triassic brachiopods (Misolia sp. , cf. Trigonirhynchella sp., and cf. Zugmayerella sp.) are described from mudstone

Introduction Two hand-specimen-sized samples from a dredging haul (BMR Cruise 95, locality DR07/13; 118°23'E, 016°18'S) were examined in this study. Each consists of fine-grained calcareous buff to grey mudstone in which brachiopods are the only macrofossils. The fossils are undistorted and shelly, occurring dispersed through the rock - they in•dicate a Late Triassic age for the sediment. The specimens have been deposited in the Commonwealth Palaeontologi•cal Collection, registered numbers crc 31599-31601.

Systematic palaeontology Order Rhynchonellida Kuhn, 1949

Superfamily Rhynchonellacea Gray, 1848

Family Wellerellidae Likharev, 1956

Genus Trigonirhynchella Dagys, 1963

Type species (original definition). TrigonirhYllchia trigona Dagys , 1961. Late Triassic (Norian Stage) , North•west Caucasus.

cf. Trigonirhynchella sp. Fig. 1 A, B, C

Material. One double-valved shelly specimen crc 31600 from sample 95/DR07/13A.

Description. Shell of modest size (L, 10.5; W, 12.5; T, 5.5mm), non-strophic, triangular with greatest width well forward. Apical angle about 96°. Beak erect, orthoc1inal. Biconvex with costation arising early in ontogeny. About 7 costae of which 3 occur on the flat plication which deflects the anterior commissure. Shell impunctate. Fo•ramen of moderate size, dethyrium covered.

Remarks. The specimen may not be fully mature as there is a single growth pause. Internal morphology cannot be observed and so the placing near to Trigonirhynchella is tentative. It should be pointed out that Moiseev's genus Salgirella (type species, Rhynchonella albertii Oppel, fide Ager, 1965) also has a triangular outline. Its plication may, however, be weaker.

Trigonirhynchella occurs in Late Triassic (Norian) sedi•ments in Northwest Caucasus (Dagys, 1961; 1963).

Order Spiriferida Waagen, 1883

Suborder Retziidina Boucot, Johnson and Stanton, 1964

Geology Department, University of Otago, P.O. Box 56, Dunedin, New Zealand.

dredged below the Rowley Terrace, northwest Australia.

Superfamily Athyrisinacea Grabau , 1931

Family Athyrisinidae Grabau, 1931

Genus Misolia von Seidlitz, 1913

Type species (original definition) . Misolia misolica von Seidlitz, 1913 Late Triassic, Misool, Indonesia.

Misolia sp. Fig. 1 D, E, F

Material. One double-valved shelly specimen crc 31599, and several shell fragments from sample 95/DR07/13A, including an incomplete ventral valve from sample 95/DR07/13B, associated with crc 31601.

Description. Modest-sized (L, 16.5; W, 13.00; T, 9.5mm) non-strophic, biconvex globular shell with prominent ventral beak. Foramen large , orthoclinal. Costae (18-20) strong, almost all persistent. Anterior commissure little deflected. Shell impunctate.

Remarks. Placing in Misolia relies on the external architecture of the shell. Internal morphology is not known in spite of an irregular longitudinal section being available (brachial skeletal parts are not preserved). External mor•phology suggests a placing near to M. misolica von Seidlitz and to M. pinajae Krumbeck. M. lenticulata Jefferies is less globular than the Canning Basin form.

Misolia is known from Indonesia (Misool, Seram, Sulawesi and Timor) where it may be an abundant member of Late Triassic invertebrate assemblages, and from India (Spiti) and Arabia (Oman) (Hudson & Jefferies, 1961). Within the Misool sequence it occurs with Cochloceras and Rhabdoceras variously cited as Rhaetian and Norian•Rhaetian indicators (.l.A. Grant-Mackie & F. Hasibuan, pers. comm. 1993). It is a common fossil in the Bogal Formation, a calcareous deposit of the continental shelf (Hasibuan, 1990).

Superfamily Spiriferinacea Davidson, 1884

Family Laballidae Dagys, 1962

Genus Zugmayerella Dagys, 1963

Type species (original definition). Spiriferina koessenen•sis Zugmayer 1880. Rhaetian Stage, Austria.

ct. Zugmayerella sp. Fig. 1, G.H.

Material. One dorsal valve, shelly. crc 31601 from sample 95/DR07/13B.

Description. Small shell (L, 6.05; W, 9.0 mm), strophic with greatest width slightly forward of the hinge-line.

136 J.D. CAMPBELL

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Figure 1. A, B, C: cf. Trigonirhynchella sp. (CPC 31600), dredge station 95/DR07/13A; Late Triassic; A: ventral view, B: dorsal view, C: anterior view, scale bar: 1.0 cm. D,E,F: Misolia sp. (CPC 31599), dredge station 95/DR07/13A; Late Triassic; D: partially excorticated specimen viewed from the dorsal side, E: drawing of the same view, F: profile of both valves drawn from a photograph. Scale bar: 1.0 cm. G,H: cf. Zugmayerella sp. (CPC 31601), dredge station 95/DR07/13B; Late Triassic; G: shelly specimen, dorsal exterior. H: drawing of the same view. Scale bar: 1.0 cm.

Valve convex, costate with about 9 strong costae . Shell finely punctate.

Remarks . Dorsal valves of the Family Laballidae and some other spiriferinaceans have generalised form, and associat ion with Zugmayerella is only one of several possibilities. The family is especially characteristic of Triassic faunas (Campbell, 1991).

References Ager, D.V. , 1965. Mesozoic and Cenozoic Rhynchonel•

lacea. In R.C. Moore (Editor). Treatise on Invertebrate Paleontology, H. Universi ty of Kansas Press, Geologi•cal Society of America, 597-632.

Campbell, J.D ., 1991. A Late Triassic spiriferinacean brachiopod (Family Laballidae) from the Taringatura Hills, Southland, New Zealand. New Zealand Journal of Geology and Geophysics, 34, 359-363.

Dagys, A.S ., 1961. Ova novykh roda Triasovykh rink•honellid. Paleontologicheskiy Zhurnal 4, 93-99 (in Russian).

Dagys, A.S., 1963. Upper Triassic brachiopods of the Southern USSR. Akademiya Nauk USSR Sibirskoe Otdelenie, 248 p. (in Russian).

Hasibuan, F., 1990. Paleoenvironment and sea-level changes in the Mesozoic of Misool Archipelago, Indonesia . Geological Society of New Zea land Miscel•laneous Publication 50A, 62 (Abstract).

Hudson, R.G.S. & Jefferies, R.P.S., 1961. Upper Triassic brachiopods from the Oman Peninsula, Arabia. Palae•ontology, 4, 1-41.

Krumbeck, L., 1923. Brachiopoden, Lamellibranchiaten und Gastropoden aus der oberen Trias der Insel Seran. Palaeontographica Supp\. 4, Pt. 3.

Moiseev, A.S., 1936. On new Triassic and Liassic genera of the Rhychonellidae. Travaux de la, Societii des Naturalistes de Leningrad, 65, 40-51 (in Russian).

von Seidlitz, W., 1913. Mis6lia, eine neue Brachiopoden - Gattung aus den Athyridenkalken von Buru und Mis6\. Palaeontographica. Supp\. 4 Pt 2, 163-193.

Zugmayer, H., 1880. Untersuchungen tiber rhatische Brachiopoden. Beitriige zur Paliiontologie und Geolo•gie Osterreichs-Ungarns und des Orients, 1, 1-42.