Early Devonian Conodonts from the Southern Thomson Orogen and Northern Lachlan Orogen in North-western New South Wales Yong Yi Zhen1*, Rosemary Hegarty2, Ian G. Percival1 and John W. Pickett3 Geological Survey of New South Wales, WB Clarke Geoscience Centre, 947-953 Londonderry Road, Londonderry, NSW 2753, Australia; Geological Survey of New South Wales, 516 High Street, Maitland, NSW 2330, Australia; 3Honorary Research Associate, Geological Survey of New South Wales, WB Clarke Geoscience Centre, 947-953 Londonderry Road, Londonderry, NSW 2753, Australia. * Corresponding author: [email protected] Published on 21 November 2017 at http://escholarship.library.usyd.edu.au/joumals/index.php/LIN Zhen, Y.Y., Hegarty, R., Percival, I.G. and Pickett, J.W. (2017). Early Devonian conodonts from the southern Thomson Orogen and northern Lachlan Orogen in north-western New South Wales. Proceedings of the Linnean Society of New South Wales 139, 69-83. Early Devonian (Lochkovian) conodonts, recovered from carbonate intervals within the Amphitheatre Group of the northern Cobar Basin (Lachlan Orogen) and from unnamed correlative strata encountered in drillcore from Louth in the southern Thomson Orogen in north-western New South Wales, include the biostratigraphically important taxon Caudicriodus woschmidti. Associated species include Belodella resima, Caudicriodus spp. indet., Oulodus astriatusl, Oulodus spicula, Oulodus sp., “Ozarkodina” planilingua, Panderodus unicostatus, Wurmiella excavata, and Zieglerodina remscheidensis. These conodont faunas provide the first biostratigraphically constrained correlations between rocks of the Cobar Basin (Cobar Supergroup) in the northern Lachlan Orogen and subsurface strata in the adjacent southern Thomson Orogen. Manuscript received May 9, 2017, accepted for publication 20 September 2017. KEYWORDS: Cobar Basin, Conodonts, Early Devonian, Lachlan Orogen, Thomson Orogen. INTRODUCTION the mineral systems potential of this remote and under-explored region. One of the key objectives Considerable conjecture characterises of these projects is to investigate and improve the interpretations of the relationship between the age constraints for the Thomson Orogen rocks and southern Thomson Orogen and the Lachlan Orogen to test correlations with better-known stratigraphic in northwestern New South Wales (e.g. Burton successions to the south, including that of the Cobar 2010; Cayley 2012; Glen et al. 2013). Exposure of Basin in central NSW. rocks attributed to either orogen in the region north In the Louth area (Fig. 1), volcanic and of Cobar is very limited, and outcrops of Thomson metasedimentary rocks of uncertain age and Orogen strata are rare due to thick cover comprising association occur in sparse outcrops and mineral Cenozoic regolith units and Mesozoic sedimentary exploration drillholes. This area is located within the rocks of the Eromanga Basin. Information on east-west zone where the southern Thomson Orogen basement geology relies heavily on geophysical melds with the Lachlan Orogen. In 2010, conodonts surveys that penetrate the cover, with drillcores of latest Silurian to Early Devonian aspect were providing the only means of sampling most basement identified by Percival in residues from core obtained rocks. The southern Thomson Orogen is the focus of from drillhole L2 from south of Louth, leading to this current investigations by the Geological Survey of detailed study. Although Early Devonian conodonts New South Wales in collaboration with Geoscience were first retrieved more than three decades ago Australia, the Geological Survey of Queensland and (Pickett 1984) from limestone intersected by several universities - these studies aim to uncover drillholes in the Cobar Basin adjacent to the southern EARLY DEVONIAN CONODONTS FROM NORTH-WESTERN NEW SOUTH WALES Fig. 1. Map showing the four sites (three subsurface and one surface) from where Early Devonian cono- donts were collected for this study in the southern Thomson Orogen and northern Lachlan Orogen of northwestern New South Wales (background: NSW Surface Geology Map, third edition); 1, (Louth L2 drillhole); 2, (Kiri DDH K1 and DDH K6 drillholes); 3, (limestone outcrop near Stoney Tank, in the Mount Gunderbooka area). margin of the Thomson Orogen, these have not been deep weathering and covering of the Palaeozoic (and described or illustrated. Additional sampling has possibly older) rocks comprising the Thomson Orogen provided more diverse faunas which are documented by a thick succession of Mesozoic Eromanga Basin herein, supporting greater precision in regional and Cenozoic sediments, there are few surface data to correlations for subsurface strata in the Louth area. constrain the exact geometry and kinematics of these When integrated with geophysical and geochemical major structures. Based on seismic interpretation and data being gathered in the Southern Thomson gravity modelling (Glen et al. 2013; Folkes 2017), Project, these age constraints will be crucial for better the Olepoloko Fault is interpreted as a north-dipping, understanding the geological and tectonic history of crustal-scale fault system. The Louth-Eumarra Shear the southern Thomson Orogen, and its relationship Zone, including the Mount Oxley and Little Mountain with the Lachlan Orogen during the Early Devonian. Faults, is steep to south-dipping based on potential field gradients and modelling (Van der Wielen and Korsch 2007). GEOLOGICAL SETTING Basement rock types identified by drilling and outcrop in the Louth area include black shale, The Thomson Orogen (Fig. 1), one of the turbiditic sandstone/siltstone sequences, low-grade major geological provinces of the Tasmanides in east¬ slate and minor limestone, with basaltic andesite and ern Australia, extends from north-western NSW into tuff, volcaniclastic rocks and gabbro/dolerite. Ages of southwestern, central and north-eastern Queensland, these rocks are not well understood and are reliant on with minor extensions into the northeastern corner of very few data as follows: South Australia and the far southwest of the Northern 1. Poorly preserved graptolites in core from drillhole Territory. In NSW its southern boundary against the L5, sited 9 km south of Louth, were identified by Pickett Delamerian Orogen in the southwest and the Lachlan (1965) as Climacograptus sp. and Dicellograptus sp. Orogen in the south is defined by the curved W-NW of probable Late Ordovician age. trending Olepoloko Fault in the west and the broad 2. Bryozoa and Tentaculites sp. found in limestone E-NE trending Louth-Eumarra Shear Zone in the from drillhole L2, located 32 km south-southeast of east (Glen et al. 2013; Dunstan et al. 2016). Due to Louth, suggested a late Silurian age (Pickett pers. 70 Proc. Linn. Soc. N.S.W., 139, 2017 Y.Y ZHEN, R. HEGARTY, I.G. PERCIVAL AND J.W. PICKETT comm., cited in Brunker 1968 and Glen et al. 2010). (including some indeterminate forms), of which 389 3. Calcareous fossil fragments within quartz-rich specimens were recovered from unnamed limestones sandstone from drillhole LI (collar location same as in core from Louth L2 in the southern Thomson L2, but drilled towards the east) were identified as a Orogen near Louth, and a further 190 from limestone heliolitid tabulate coral of uncertain Early Palaeozoic intervals of the Amphitheatre Group encountered in age in a petrographic study of Louth core by Vickery drillholes Kiri DDH K6 and DDH K1 (Fig. 2). The (2008). remaining 234 specimens were obtained from a 4. Two maximum depositional ages based on U/Pb small limestone outcrop near Stoney Tank (on Belah zircon provenance studies reported by Glen et al. Station) in the northern Cobar Basin (Fig. 1; Table (2010) indicate that turbidites in the L5 drillhole 1). The CAI of the conodonts from these localities is cannot be older than 470 Ma and volcanogenic consistently similar, about 4 to 4.5. sandstone from drillhole L2 at a depth of 139 m was Louth L2, located about 32 km south of Louth most probably 422 Ma (i.e. Pridoli, latest Silurian or township (grid ref. 30.802657°S, 145.194924°E; Fig. younger. 1), was drilled by the Electrolytic Zinc Company of 5. A few non-diagnostic specimens of conodonts Australasia Ltd. in 1965, and reached a depth of 570.9 Ozarkodina sp. and Walliserodus sp. were extracted m (Fig. 2). The drillcore is stored at the Londonderry from Burracurry Hill, 25 km northeast of Louth, by Core Library of the Geological Survey of New South Iwata et al. (1995) as part of a study of cherts from Wales in outer western Sydney. A total of 11 conodont outcrops of the Ballast Formation. They suggested samples (half core samples, about 1 kg each) were an uncertain Late Ordovician age for these samples. collected from calcareous intervals over the past Radiolarians were also visible but have not yet been decade and of these ten were productive, yielding a successfully extracted using HF. total of 389 conodont specimens (Table 1). At Mount Gunderbooka, located in the Getty Oil drilled Kiri DDH K6 (grid ref. Gundabooka Syncline 58 km east of Louth, (Fig. 1), 30.901510°S, 145.450495°E) and DDH K1 (grid ref. Devonian sequences of the Cobar Basin (Lachlan 30.903339°S, 145.452558°E) in 1984, 50 km south¬ Orogen) unconformably overlie the Early to Middle east of Louth (Figs. 1, 2). Conodont samples C0986, Ordovician Girilambone Group. Mount Gunderbooka C0987 (both DDH K6) and C0816, C0817 (both is a prominent outlier of gently-dipping sandstones from DDH Kl) collected from limestones intersected overlying fossiliferous siltstones and limestone in these drillholes were initially reported by Pickett (exposed at Stony Tank along the western side of (1984, 1988), and are included in this study (Table the outlier). Mapping and sedimentological studies 1). Glen et al. (2013:fig. 3) depict the location of Kiri by Sharp (1992) identified a coarsening-upwards in the northern extremity of the Cobar Basin, south sequence from Early to Late Devonian age deposited of the boundary fault separating the Thomson and in a prograding shelf environment. Lachlan orogens. Glenetal. (2013) suggested that the Thomson A spot sample (C0964) from a limestone and Lachlan orogens were amalgamated or interacted lens exposed about 400 m east of Stoney Tank (Belah around the Middle/Late Ordovician boundary interval Station) in the Mount Gunderbooka district (grid (about 460 Ma). Current geological mapping in the ref. 30.641012°S, 145.655903°E) of the northern region indicates that Cobar Basin stratigraphy has Cobar Basin yielded abundant conodonts. These been confidently extrapolated approximately 80 km were initially reported by Pickett (1987) and are also north of Cobar to the Kerrigundi mine area, but does incorporated in this contribution. Mathieson (2006) not extend further north towards Louth. Improved age and Mathieson et al. (2016) described other Early control for the complex rocks around Louth would Devonian (Pragian) conodonts from the vicinity of help determine whether deposition was continuous this locality. from the Cobar Basin into the southern part of the Conodonts attributed to Caudicriodus Thomson Orogen during the late Silurian to Early woschmidti (Ziegler, 1960) from the Derriwong Group Devonian. in the Trundle area (samples C0227, C0228, and C0230) and Caudicriodus sp. from the Yarrabandai Formation of the Bogan Gate area (sample C0001), MATERIAL AND SAMPLE LOCALITIES both units of the Lachlan Orogen in central western NSW (Pickett 1975, 1992), were examined and The conodont faunas documented herein illustrated for comparative purposes. comprise 813 specimens assignable to 16 species Proc. Linn. Soc. N.S.W., 139, 2017 71 EARLY DEVONIAN CONODONTS FROM NORTH-WESTERN NEW SOUTH WALES METHODS AND REPOSITORY residue volume for picking. Specimens illustrated were gold coated and photographed by using a Limestone samples were dissolved in 10% mix of secondary and backscattered electrons. All acetic acid, and insoluble residues were separated by photographic illustrations shown in Figures 3-7 using sodium polytungstate solution to reduce the are SEM photomicrographs of conodonts captured Fig. 2. Stratigraphic logs of the Lower Devonian and sampled horizons yielding conodonts in the Louth L2 drillcore, about 32 km south of Louth township in northwestern New South Wales, and the Kiri DDH K1 and DDH K6 drillholes, 50 km south-east of Louth (based on data from Lewington 1984). 72 Proc. Linn. Soc. N.S.W., 139, 2017 Y.Y ZHEN, R. HEGARTY, I.G. PERCIVAL AND J.W. PICKETT o|- tn t'' Of <N m co 'o Louth gin of cunsodxo es (mar *is wa V9198600D3 soLB‘ 1jj6n s e drillholouthern ££9188866000333 9£•‘66£8lL1-68- 5‘8X€l81 ntered in subsurfacn) adjacent to the s uo 8£££3 £-0I£-££‘60£ coati enSt 65ZI89£Z33 --Z98IU8089T''''£0t\XZ£f£r££5££ elative units Tank (Belah L12ZD -PV0Z9 orrey cn 908£3 ~V£S9'Z'\VPS9 nd Sto p aar 9L'6P9 ue 508£3 on -ZL'SPS Grd e £08£3 -8Wr685555 atre xpos ee 1708^3 "89517XX9955 CO CO Xh hithure ps mo 6£'5 95 p 108Z3 Ax -69X95 he e e 0£5£3 6‘0£5-5£‘695 - CO £ - - - samples from turface limeston uth Wales. jd o _s_r *c2o Jt-il nt species in the ), and a small s western New So doKl h- onoDH nort "S "j• 5Qs .<a .^CaQ OPh M stribution of cDH K6 and D on Orogen in ng_0_ O U O O -Q ^O3 O^3 P"S3 Table 1. DiL2, Kiri D the Thoms Proc. Linn. Soc. N.S.W., 139, 2017 73 EARLY DEVONIAN CONODONTS FROM NORTH-WESTERN NEW SOUTH WALES digitally (numbers with the prefix IY are the file uppermost Pridoli to middle Lochkovian in North names of the digital images). Figured specimens (69 America and the Spanish Pyrenees (Murphy and in total) bearing the prefix MMMC (5173 to 5241) Valenzuela-Rios 1999:text-fig. 1). In central New are deposited in the microfossil collection of the South Wales, “O. ” planilingua has a very similar Geological Survey of New South Wales, housed at range, extending through the uppermost Pridoli the WB Clarke Geoscience Centre at Londonderry in (uppermost eosteinhornensis Biozone) to lower outer western Sydney. Lochkovian {woschmidti Biozone) in the Camelford Limestone at the Gap, about 10 km NE of Cumnock (Farrell 2004). CONODONTS FROM THE SOUTHERN THOMSON OROGEN EARLY DEVONIAN CONODONTS FROM THE Conodonts from the unnamed carbonate LACHLAN OROGEN intervals within the Amphitheatre Group encountered in Louth L2 drillhole (Table 1; Figs 3-6) include a Pa In the Lachlan Orogen of central NSW, element (Fig. 3b-d) and doubtfully assigned M and conodont faunas of Early Devonian age characterized S (Fig. 3j-o) elements of Caudicriodus woschmidti, by the occurrence of C. woschmidti were reported Caudicriodus sp. indet. (Pa element; Fig. 3e-f), from the Amphitheatre Group of the northern Cobar Caudicriodus sp. indet. (coniform elements; Fig. 4a- Basin (Pickett 1987,1988), the White Tank Limestone p), Gen. et sp. indet. A (Fig. 3p), Gen. et sp. indet. Fig. 3 (next page), a, Icriodontidae gen. et sp. in¬ B (Fig. 4q), Icriodontidae gen. et sp. indet. (Pa det., Pa element, MMMC5173, from sample element; Fig. 3a), Oulodus sp. (Fig. 5n-q), Oulodus C2530 (Louth L2), upper view (IY310-020), b-d, astriatus? Mathieson, Mawson, Simpson and Caudicriodus woschmidti (Ziegler, 1960). Pa ele¬ Talent, 2016 (Fig. 6a), “Ozarkodina” planilingua ment, MMMC5174, from sample C2817 (Louth Murphy and Valenzuela-Rios, 1999 (Fig. 5a-b), L2), b, outer-lateral view (IY308-012), c, up¬ Panderodus unicostatus (Branson and Mehl, 1933), per view (IY310-022), d, close up of upper view and Zieglerodina remscheidensis (Ziegler, 1960) (IY310-023). e-g, Caudicriodus sp. indet., Pa ele¬ (see Fig. 5c-m). A well preserved specimen (Fig. ment, e, MMMC5175, from sample C2804 (Louth 3b-d) assignable to the Pa element of C. woschmidti L2), upper view (IY309-009); f, MMMC5176, from was recovered from sample C2817 from 520.14- sample C2530 (Louth L2), upper view (IY279- 521.06 m depth in the L2 drillhole, and supports 022). g, MMMC5177, from sample C0986 (DDH the correlation of this fauna with the typical basal K6), upper view (IY310-010). h, Caudicriodus wo¬ Lochkovian Caudicriodus woschmidti Biozone schmidti (Ziegler, 1960). Pa element, MMMC5178, recognized worldwide. Several broken specimens from sample C964 (Belah Station), upper view (Fig. 3e-f) recovered from samples C2530 and C2804 (IY303-001). i, Caudicriodus woschmidti? (Zie¬ were assigned to Caudicriodus sp. indet. These likely gler, 1960). Pa element, MMMC5179, from sam¬ represent the Pa element of C. woschmidti, but lack ple C964 (Belah Station), upper view (IY303-002). the diagnostic posterior part. Ramiform and coniform j-o, ?Caudicriodus woschmidti (Ziegler, 1960). j, elements tentatively assigned to the species apparatus Sb element, MMMC5180, from sample C2804 of C. woschmidti were also recovered from three (Louth L2), outer-lateral view (IY309-001); k- samples in the Louth L2 drillhole (Table 1), and are l, Sc element, MMMC5181, from sample C2817 identical with those documented by Serpagli (1983 :pl. (Louth L2), k, inner-lateral view (IY308-015), 1, 7, A-D, H, I) from Europe. The Sc element (Fig. 3k-l, close up showing surface striation (IY308-016); n-o) has a single denticle on the posterior edge, and m, M element, MMMC5182, from sample C2817 the Sb element (Fig. 3j) typically has two denticles and (Louth L2), outer-lateral view (IY308-023); n- a sharp blade-like protoprocess on the outer-lateral o, Sc element, n, MMMC5183, from sample side. The M element is scandodiform, with the cusp C2530 (Louth L2), anterior view (IY279-024); o, proclined and also curved posteriorly (Fig. 3m). The MMMC5184, from sample C2804 (Louth L2), other biostratigraphically important species recovered outer-lateral view (IY309-002). p, Gen. et sp. in¬ from the L2 drillcore samples is “Ozarkodina” det. A, coniform (asymmetrical, short-based) ele¬ planilingua, which is characterized by having larger ment, MMMC5185, from sample C2530 (Louth basal platform lobes with a small terrace compared L2), outer-lateral view (IY308-023). Scale bar 100 with the associated Z. remscheidensis. “Ozarkodina” pm unless otherwise indicated. planilingua has a stratigraphic range from the 74 Proc. Linn. Soc. N.S.W., 139, 2017 Y.Y ZHEN, R. HEGARTY, I.G. PERCIVAL AND J.W. PICKETT Proc. Linn. Soc. N.S.W., 139, 2017 75 EARLY DEVONIAN CONODONTS FROM NORTH-WESTERN NEW SOUTH WALES Legend on next page 76 Proc. Linn. Soc. N.S.W., 139, 2017 Y.Y ZHEN, R. HEGARTY, I.G. PERCIVAL AND J.W. PICKETT Fig. 4 (preceding page), a-p, Caudicriodus sp. indet. (coniform elements); a-d, Sa element; a, MMMC5194, from sample C2804 (Louth L2), posterior view (IY309-003); b, MMMC5195, from sample C2530 (Louth L2), posterior view (IY279-029); c, MMMC5196, from sample C2530 (Louth L2), posterior view (IY279- 026); d, MMMC5197, from sample C2530 (Louth L2), upper view (IY280-002);e-i, Sb element; e, MMMC5198, from sample C2530 (Louth L2), outer-lateral view (IY280-003); f, MMMC5199, from sam¬ ple C2817 (Louth L2), posterior view (IY308-021); g, MMMC5200, from sample C2804 (Louth L2), out¬ er-lateral view (IY309-005); h, MMMC5201, from sample C2804 (Louth L2), inner-lateral view (IY309- 004); i, MMMC5202, from sample C2804 (Louth L2), inner-lateral view (IY309-007); j-m, Sc element; j, MMMC5203, from sample C2804 (Louth L2), outer-lateral view (IY309-006); k, MMMC5204, from sample C2817 (Louth L2), upper view (IY308-020); 1-m, MMMC5205, from sample C2530 (Louth L2), 1, inner-lateral view (IY279-031), m, close up showing surface striation (IY279-032); n-o, Sd element; n, MMMC5206, from sample C2817 (Louth L2), basal-posterior view (IY308-017); o, MMMC5207, from sample C2817 (Louth L2), posterior view (IY308-018); p, Sc element, element, MMMC5208, from sam¬ ple C2817 (Louth L2), outer-lateral view (IY308-022). q, Gen. et sp. indet. B, S? element, MMMC5209, from sample C2530 (Louth L2), inner-lateral view (IY279-028). r-v, Panderodus unicostatus (Branson and Mehl, 1933), all from sample C964 (Belah Station), r, qg element, MMMC5210, outer-lateral view (IY303-017); s, qa element, MMMC5211, outer-lateral view (IY303-010); t, qa element, MMMC5212, outer-lateral view (IY303-008); u, qg element, MMMC5213, outer-lateral view (IY303-011); v, qg ele¬ ment, MMMC5214, outer-lateral view (IY303-016). Scale bar 100 pm unless otherwise indicated. Fig. 5 (next page), a-b, “Ozarkodina” planilingua Murphy and Valenzuela-Rios, 1999; Pa element; a, MMMC5215, from sample C2804 (Louth L2), upper view (IY309-018); b, MMMC5216, from sample C2530 (Louth L2), outer-lateral view (IY279-010). c-m, Zieglerodina remscheidensis (Ziegler, 1960). c-d, Pa element; c, MMMC5217, from sample C2817 (Louth L2), inner-lateral view (IY308-003); d, MMMC5218, from sample C2817 (Louth L2), outer-lateral view (IY308-008); e-g, Pb element; e, MMMC5219, from sample C2817 (Louth L2), inner-lateral view (IY308-002); f, MMMC5220, from sample C2817 (Louth L2), inner-lateral view (IY308-009); g, MMMC5221, from sample C2817 (Louth L2), outer-lateral view (IY308-001); h-i, Sa element; h, MMMC5222, from sample C2817 (Louth L2), posterior view (IY308-013); i, MMMC5223, from sample C2801 (Louth L2), posterior view (IY309- 010); j-k, Sc element; j, MMMC5224, from sample C2817 (Louth L2), inner-lateral view (IY308-011); k, MMMC5225, from sample C2817 (Louth L2), outer-lateral view (IY309-011); 1-m, M element; 1, MMMC5226, from sample C2817 (Louth L2), posterior view (IY308-006); m, MMMC5227, from sam¬ ple C2804 (Louth L2), anterior view (IY309-013). n-q, Oulodus sp.; Sb element, n-o, MMMC5228, from sample C2817 (Louth L2), n, upper view (IY309-014), o, close up showing cross section of cusp (IY309- 015); p, MMMC5229, from sample C2817 (Louth L2), anterior view (IY308-010); q, MMMC5230, from sample C2817 (Louth L2), posterior view (IY308-004); Scale bar 100 pm. Proc. Linn. Soc. N.S.W., 139, 2017 77 EARLY DEVONIAN CONODONTS FROM NORTH-WESTERN NEW SOUTH WALES 78 Proc. Linn. Soc. N.S.W., 139, 2017