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Reworked Latest Cambrian (Furongian) and Early Ordovician Conodonts from the Late Devonian of the Amadeus Basin, Central Australia

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Reworked Latest Cambrian (Furongian) and Early Ordovician Conodonts from the Late Devonian of the Amadeus Basin, Central Australia Reworked latest Cambrian (Furongian) and Early Ordovician conodonts from the Late Devonian of the Amadeus Basin, central Australia ROBERT S. NICOLL, JOHN R. LAURIE, ANDREW KELMAN & JOHN D. GORTER NICOLL, R.S., LAURIE, J.R., KELMAN, A. & GORTER, J.D., 2007:12:21. Reworked latest Cambrian (Furongian) and Early Ordovician conodonts from the Late Devonian of the Amadeus Basin, central Australia. Memoirs of the Association of Australasian Palaeontologists 34, 545-554. ISSN 0810-8889. A fauna of reworked conodonts from a lithic sandstone in the Ellery Creek Fan of the Late Devonian Brewer Conglomerate comprises mostly unidentifiable, elongate, rounded fragments indicating erosion to discrete grain particles prior to redeposition. The fauna is of mixed age, consisting of Early Ordovician (Aloxoconus iowaensis) and Furongian, latest Cambrian, (Hirsutodontus simplex) elements implying sourcing from multiple stratigraphic units. The latter species has not been recovered previously from the Amadeus Basin despite extensive sampling of Cambro-Ordovician units. Another small conodont fauna obtained from a large limestone clast from a conglomerate in the Late Devonian Hermannsburg Sandstone includes Oepikodus cleftus, previously recorded from the lower part of the Early Ordovician Horn Valley Siltstone. These conodonts suggest that the northern depositional edge of the Amadeus Basin lay far to the north of the present structural and erosional northern margin of the basin. The elements have a conodont color alteration index (CAI) of 1 indicating that they have never been deeply buried, either originally or after reworking. Robert S. Nicoll, Department of Earth and Marine Science, Australian National University, Canberra ACT 0200; John R. Laurie, Andrew Kelman, Geoscience Australia, GPO Box 378 Canberra, ACT 2601, Australia; John D. Gorter, Eni Australia Limited, PO Box 1265, West Perth, WA 6005, Australia. Received 19 November 2007. Keywords: Devonian, Late Cambrian, Early Ordovician, conodont, reworking, Amadeus Basin. THE DEVONIAN Parke Siltstone, Hermannsburg Conglomerate represents the culmination of Sandstone and Brewer Conglomerate of the the Alice Springs Orogeny (Jones 1991). Dated Pertnjara Group represent the foredeep molasse as Late Devonian (Frasnian) by Playford et deposits of the Alice Springs Orogeny in the al. (1976), the 3100 m thick unit thins rapidly Amadeus Basin. These units include reworked southward into the Missionary Trough (Jones sediments that had been initially deposited 1991). The Ellery Creek Fan, one of several north of the present basin margin before being distinct fanglomerates on the northern margin rapidly stripped and transported south to the has been noted as containing abundant Cambrian basin foredeep. Clasts from within the molasse and Ordovician clasts in its lower part (Jones were derived from rocks of the Arunta basement 1972, 1991). complex up to at least the Early Ordovician The deposition of the Pertnjara Group in the Horn Valley Siltstone and probably the Middle Amadeus Basin (Jones 1991) was initiated by a Ordovician Stairway Sandstone, Stokes Siltstone sequence of tectonic uplifts to the north of the and the Silurian? Mereenie Sandstone. present basin margin in which progressively The present northern edge configuration of older sediments were stripped from the now the Amadeus Basin is not depositional, but the removed, uplifted northern part of the basin and result of uplift during the Alice Springs Orogeny redeposited over the central part of the basin. (Lindsay & Korsch 1991). On the eroded edge of This destruction effectively now masks the the steeply southward dipping northern margin depositional configuration of the Amadeus Basin of the present Amadeus Basin, the Brewer in Cambrian and Ordovician time. 546 AAP Memoir 34 (2007) Fig. 1. Locality map of the Ellery Creek sample locality showing geology. Filled ellipses are probable source levels in the Pacoota Sandstone (i.e. seq 2 from sequence 2; seq 3 from sequence 3). Open elipse (HV) is probable source level within the lower part of the Horn Valley Siltstone. Open square (Herm) is the locality of the sample in the Hermannsburg Sandstone (JG 2005-1) from which conodonts from the Horn Valley Siltstone were obtained. Filled squares are samples obtained by Tingate (1990; 44 = 8351-44; 45 = 8351-45; 46a = 8351-46a) containing conodonts from the Pacoota Sandstone. Rock unit symbols are listed in Figure 2. This work documents the conodont SAMPLING faunas obtained from samples taken from The reworked conodonts used in this study were the Hermannsburg Sandstone and Brewer obtained from four samples from the Brewer Conglomerate and discusses the implications of Conglomerate and Hermannsburg Sandstone the reworking of these conodonts for the tectonic in the Ellery Creek section in the Amadeus history and depositional extent of the Amadeus Basin. Comparative material was obtained from Basin. Sequence 3 of the Pacoota Sandstone in the same section and from the Jiggamore Member AAP Memoir 34 (2007) 547 Brewer Conglomerate Db Sample Taxon N Hermannsburg Sandstone De 8351-44 gen. et sp. indet. 2 Hirsutodontus simplex 1 Parke Siltstone Dj Pertnjara Gp Pertnjara Aloxoconus iowaensis 1 Devonian Drepanodus sp. 3 Mereenie Sandstone Pzm 8351-45 Drepanodus ? sp. 3 Sil. Scolopodus sp. 5 Ulrichodina sp. 1 indet. coniform elements 47 Drepanodus ? sp. 1 Os Stairway Sandstone 8351-46a Scolopodus ? sp. 1 Horn Valley Siltstone Oh indet. coniform elements 14 Ordovician Sequence 4 P 17 Sequence 3 Oepikodus cleftus Pacoota S 36 ЄOp P 157 Sandstone Sequence 2 Oepikodus communis S 131 Sequence 1 M 52 Pa 3 Jumudontus gananda Upper Goyder Formation Єg JG 2005-1 Pb 1 Bergstroemognathus kirki 6 Lower Goyder Formation Єg S,M 32 Cooperignathus nyinti Pa 3 Jay Creek Limestone Єj Pb 2 Cornuodus longibasis 39 Cambrian indet. coniform elements 357 Table 1. Reworked Ordovician and Cambrian Hugh River Shale Єh conodonts from the Devonian Brewer Conglomerate and Hermannsburg Sandstone, Ellery Creek, Amadeus Basin. N refers to number of elements. preserved conodonts. These samples, 8351-44, Arumbera Sandstone LP-Єa 8351-45 and 8351-46a (see below), are from lithic sandstone units interbedded with conglomerates in the lower part of the Brewer Conglomerate Julie Formation LPuj in Ellery Creek (Fig. 1). In addition to the Ediacaran Tingate samples, one of us (JDG) collected a Fig. 2. Stratigraphic column with ages, indicating the conodont reworking. Conodonts from samples in the large limestone clast of cobble size (sample JG Brewer Conglomerate are reworked from Pacoota 2005-1) from a conglomerate bed within the Sandstone Sequence 2 and Sequence 3, while the Hermannsburg Sandstone also in Ellery Creek sample from the Hermannsburg Sandstone contains (Fig. 1). The samples collected and their location conodonts reworked from the lower part of the Horn are listed below. Valley Siltstone. Rock unit symbols are as used in Figure 1. Note that in the Ellery Creek section, from Brewer Conglomerate which this column is taken, the Stokes Siltstone is Tingate sample 8351-44; Grid Ref LP025622 absent, having been eroded prior to deposition of the Hermannsburg 1:250, 000 (1979). Mereenie Sandstone. Tingate sample 8351-45; Grid Ref LP023625 Hermannsburg 1:250, 000 (1979). of the Ninmaroo Formation in the Georgina Tingate sample 8351-46a; Grid Ref LP025629 Basin (Fig. 3). The latter sample was used to Hermannsburg 1:250, 000 (1979). obtain comparative material of Hirsutodontus simplex, which was previously unknown from Hermannsburg Sandstone the Amadeus Basin. Gorter sample JG 2005-1; 23°49’31.30”S, Some of the samples formed part of a Ph.D. 133°04’14.30”E Hermannsburg 1:250, 000. study of fission track ages in the Amadeus Basin and adjacent provinces by Tingate (1990), who Ninmaroo Formation, Jiggamore Member collected a number of samples from the Brewer BMA section of Ripperdan et al. (1992) (see Conglomerate which yielded reworked, poorly Shergold et al. 1991a). Black Mountain, 548 AAP Memoir 34 (2007) North Amadeus Georgina Period, Epoch, Australian N. American Atlantic Basin Basin Stage graprolites Midcontinent conodonts conodonts stratigraphy stratigraphy 471.8 ± 1.6 Ch2 l.primulus Ch1 D.protobifidus O.evae R.andinus Be4 Be3 P.fruticosus Horn Valley Floian Be2 Siltstone Be1 P.elegans O.communis T. La3 approximatus O.elongatus 478.6 ± 1.7 A.deltatus Coolibah Pacoota Formation Early P.gracilis sequence 4 Ordovician Tripodus D.deltatus- La2b A.pulchellus P.proteus Kelly Creek Fm O.costatus D. aff.amoenus Tremadocian P.deltifer M.dianae La2a A.victoriae R.manitouensis Datson Pacoota Member P.jacksoni C.angulatus C.angulatus La1b sequence 3 La1a Anisograptus Corrie Member Pre-La1 l.fluctivagus l.fluctivagus 488.3 ± 1.7 Mort Mbr Cordylodus Cordylodus Pacoota intermedius spp. Jiggamore sequence 2 Member Stage 10 Cordylodus proavus Ninmaroo Formation Furongian Cambrian Unbunmaroo Pacoota Eoconodontus Member sequence 1 Fig. 3. Correlation of Furongian and Early Ordovician stratigraphic units from the Amadeus and Georgina basins. These are calibrated against the global standard scale of stages, the Australia graptolite succession and the North Atlantic and Midcontinent conodont biostratigraphic schemes. Georgina Basin, western Queensland. Sample All illustrated specimens have been lodged in BMA 102 is approximately at the 662 m level the Commonwealth Palaeontological Collection in the section. 22° 31.65’S, 140° 16.80’E. (CPC) at Geoscience Australia, Canberra. All of the faunal elements discussed here have Pacoota Sandstone, Sequence 3 a conodont colour alteration index (CAI) of 1, the 87-2047/S-T, 24 m above the base of sequence 3; same as in situ conodonts from the Horn Valley approximately at ‘seq 3’ locality in Fig. 1; 23° Siltstone and Pacoota Sandstone. This suggests 48.83’S, E 133° 03.88’E. that the source sediments, either first or second 88-2052/55, 82.5 m above base of sequence 3; cycle, were never buried to depths of greater than approximately at ‘seq 3’ locality in Fig. 1; 23° about 1200 to 1500 m (Epstein et al. 1977). 48.92’S, 133° 03.84’E.
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