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1286 Mckellar.Vp An unusual occurrence of Pedinopariops (Trilobita: Phacopidae) within siliciclastic facies in the Devonian of Awaynat Wanin, Libya RYAN C. MCKELLAR, BRIAN D.E. CHATTERTON, GUIDO MEINHOLD & MILAD M. BEN RAHUMA A new phacopid trilobite is described from the Givetian sequence of the Awaynat Wanin Group in the southern Ghadamis Basin, Libya. The specimen displays most of the eye and sculpture features necessary for a determination and can be restricted to Pedinopariops (Hypsipariops) Struve, 1982. The new specimen does not belong to any taxon known so far and hence is considered to be a new species. The specimen remains in open nomenclature and is assigned to Pedinopariops (Hypsipariops) sp. nov. A. This is the first Devonian trilobite described from Libya, and represents an unusual occurrence of Phacopidae in a relatively coarse siliciclastic facies. • Key words: Trilobita, Phacopidae, Devo- nian, Givetian, Awaynat Wanin, Ghadamis Basin, Libya. MCKELLAR, R.C., CHATTERTON, B.D.E., MEINHOLD,G.&BEN RAHUMA, M.M. 2012. An unusual occurrence of Pedinopariops (Trilobita: Phacopidae) within siliciclastic facies in the Devonian of Awaynat Wanin, Libya. Bulletin of Geosciences 87(2), 219–225 (3 figures). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received June 14, 2011; accepted in revised form October 7, 2011; published online November 18, 2011; issued March 30, 2012. Ryan C. McKellar (corresponding author), Department of Earth and Atmospheric Sciences, University of Alberta, 1–26 Earth Sciences Building, Edmonton, Alberta, T6G 2E3 Canada; [email protected] • Brian D.E. Chatterton, Depart- ment of Earth and Atmospheric Sciences, University of Alberta, 1–26 Earth Sciences Building, Edmonton, Alberta, T6G 2E3 Canada; [email protected] • Guido Meinhold, CASP, University of Cambridge, West Building, 181a Huntingdon Road, Cambridge CB3 0DH, United Kingdom; present address: Department of Sedimentology & Environ- mental Geology, Geoscience Center, University of Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany; [email protected] • Milad M. Ben Rahuma, Libyan Petroleum Institute, Gergarish Road, P.O. Box 6431, Tripoli, Libya; [email protected] The Ghadamis Basin (Fig. 1A) covers about 350,000 km2, Evolution of ecosystems and climate”) to the Awaynat with portions in eastern Algeria, southern Tunisia and Wanin area (Königshof et al. 2008) one of the authors north-western Libya, and hosts major oil and gas fields, (GM) found a phacopid trilobite. Because of its palaeon- amongst other rocks, in Devonian sandstones (Echikh tological importance this specimen initiated a detailed in- 1998). In Libya, the Devonian rocks are subdivided from vestigation which is the focus of this paper. old to young into the Tadrart Formation, Ouan Kasa For- mation, Awaynat Wanin Group and Tahara Formation (Hecht et al. 1964, Mergl & Massa 2000, Ben Rahuma et Geological setting al. 2008). The present study focuses on the Awaynat Wa- nin Group, which has its type section in the area of Away- The Awaynat Wanin area is located at the north-western nat Wanin (also spelt “Aouinet Ouenine”) in the southern margin of the basement high of Al Gargaf (also spelt “Al Ghadamis Basin (Fig. 1A). Here, fossiliferous siliciclastic Qargaf”) in central Libya (Fig. 1A). Here, the Awaynat strata are well exposed along the scarp of the Al Hamadah Wanin Group appears to be disconformable over the Ouan al Hamra plateau, containing, amongst other marine fos- Kasa Formation and consists of an alternation of fairly sils, a well-studied brachiopod fauna (Mergl & Massa thick silty clay/claystone beds followed by relatively thin, 2000). Furthermore, a rare trilobite fauna has been mentio- ochre-coloured, fine- to coarse-grained sandstones (Ben ned in text form (Mergl & Massa 2000) but without formal Rahuma et al. 2008). Wave ripples, low angle parallel la- description or illustration. mination, and trough and hummocky cross-stratification During a field trip of the International Geoscience are common features. The sediments of the Awaynat Programme Project 499 (“Devonian land-sea interaction: Wanin Group were deposited in a shallow marine deltaic DOI 10.3140/bull.geosci.1286 219 Bulletin of Geosciences Vol. 87, 2, 2012 environment within the storm wave base, with prodelta medium-grained tidal and shoreface sandstones, recording silty clay/claystone beds passing upward into distributary a transgressive system tract (Ben Rahuma et al. 2008). channel sandstones (Vos 1981, Ben Rahuma et al. 2008). Shell fragments, probably deposited by storms, are present Fluvial intervals are minor but present. The direction of se- in siltstones and sandstones at the level where the trilobite diment transport was generally towards the northwest and specimen was found. west (Vos 1981). In its type area, the Awaynat Wanin Group is subdi- vided into four formations, Awaynat Wanin I to IV, and is Materials and methods unconformably overlain by sandstones of the late Famennian Tahara Formation (Mergl & Massa 2000, Ben Morphological terminology generally follows that of Chlu- Rahuma et al. 2008). Lateral thickness variations within páč (1977), and Crônier et al. (2011): most terms are also the Awaynat Wanin Group are very frequent within a few illustrated in these works. kilometres (Mergl & Massa 2000). Macrofossils known from the type area of the Awaynat Abbreviations. – Anatomical directions: d.v. – dorsoven- Wanin Group are mainly brachiopods, gastropods, bi- tral, exsag. – exsaggital, sag. – saggital, and tr. – trans- valves, pteropods, trace fossils (e.g., Tigillites sp., verse; L1–L3 – cephalic lobes, S0–S3 – cephalic sulci; in- Spirophyton sp., Diplocraterion sp.), casts of plant fossils, stitutions: SMF – Senckenberg Museum, Frankfurt am and rarely trilobites (Hecht et al. 1964, Mergl & Massa Main, Germany. 2000, Ben Rahuma et al. 2008). Analysis of the brachiopod fauna suggests a Middle to Late Devonian (Eifelian to Famennian) age for the Awaynat Wanin Group in its type Systematic palaeontology area (Mergl & Massa 2000). Genus Pedinopariops Struve, 1972 Subgenus Pedinopariops (Hypsipariops) Struve, 1982 Previous trilobite findings Type species. – Pedinopariops (Hypsipariops) lyncops Two species of trilobites, Phacops granulatus (Münster, Struve, 1982. 1840) and Greenops sp., have so far been reported from the Awaynat Wanin Group (Mergl & Massa 2000, Ben Rahuma Remarks. – The subgenus Pedinopariops (Hypsipariops) et al. 2008), however, in text form only without illustration was recently elevated to the genus rank by Basse (2006), or formal description and no clear stratigraphic assignment but we prefer to treat the taxon as a subgenus until there is (i.e., no indication of the fossil locality in the logged sec- cladistic support for such an elevation. Overarching simila- tion). This fauna together with the large bivalve Myalinella, rities make distinctions difficult within the tribe Geesopini, bryozoans and rugose corals indicates a deeper, calmer sub- and Pedinopariops (Hypsipariops) has been variably re- tidal environment and a latest Givetian age (Mergl & Massa cognized at the subgeneric rank (e.g., Struve 1995), sunken 2000). Note that Myalinella is predominantly found in the within Pedinopariops (e.g., Basse 1998, Basse & Weddige Carboniferous to Middle Triassic, but the family Myalinidae 2004), or treated as its own distinct genus. is present in the Devonian if Myalina squamosa Sowerby, 1827 is considered to be a true myalinid (McRoberts & Ne- well 2005). Unfortunately, no formal description of Myali- Pedinopariops (Hypsipariops) sp. nov. A nella reported from the Awaynat Wanin Group can be found Figures 3A–F in the literature, which makes it difficult to accurately evalu- ate its stratigraphic significance. Material examined. – The trilobite cephalon (an external mould, SMF 92899a) and its latex peel (a cast, SMF 92899b). Sample locality Diagnosis. – Glabella with reduced convexity on dorsal The trilobite specimen was found about 3 km south-west of surface, and without significant overhang of anterior bor- the Awaynat Wanin water well in a small gorge cutting the der; glabellar sculpture of low, mid-sized pustules with re- scarp of the Al Hamadah al Hamra plateau (geographic co- latively wide spacing and nearly hemispherical shapes on ordinates: N 28°25´20˝ E 12°46´17˝) (Fig. 1B). The stra- dorsal surface, with pustules becoming crowded and fine tigraphic position of the sample is indicated in Fig. 2. The with slight transverse expansion on anterior surface of gla- trilobite specimen was found about 20 m above the base of bella, and with transverse sculpture predominantly in small the Awaynat Wanin II Formation, which comprises fine- to patch adjacent to anterior border; eyes long (exsag.) and 220 Ryan C. McKellar et al. Pedinopariops (Trilobita: Phacopidae) within siliciclastic facies in the Devonian of Libya A B Figure 1. A – map of Libya showing surface outcrops with Palaeozoic rocks (dark grey colour) and the location of Awaynat Wanin in the southern Ghadamis Basin.•B–simplified geological map of the Awaynat Wanin area (after Gundobin 1985) showing the locality where the phacopid trilobite specimen was found. low (close to lateral border) with 18 vertical rows of lenses width approximately 0.53 of total cephalic width, with dor- and apparent maximum of 7 lenses per row; interlensar sal projection above eye approximately 0.28 times height sclera thick with six tubercles surrounding each lens in he- of visual surface; fine pits sparse between glabellar
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