AGES 2021 Proceedings, NT Geological Survey Update on geological mapping in the central and western Amadeus Basin Charles Verdel 1,2, Anett Weisheit 1, Nigel Donnellan 1 and Christine Edgoose 1 Over the last several years, the Northern Territory geology interpretation based on previous geology maps, and Geological Survey (NTGS) has been conducting mapping airborne magnetic, gravity and drillhole data. This project projects focused on the central and western parts of the identified, for the first time, the prevalence of faulting and Northern Territory’s portion of the Amadeus Basin. Specific fault-related folding across a large part of the central and goals of these projects include refined understanding of western Amadeus Basin. Faulting in this region is largely the structural geology of the region, as well as reconciling attributable to shortening during the late Neoproterozoic to Neoproterozoic stratigraphic nomenclature between Cambrian Petermann Orogeny (eg Raimondo et al 2010) and the eastern and western Amadeus Basin. The projects the mid-Palaeozoic Alice Springs Orogeny (eg Haines et al are now reaching their conclusion and will culminate 2001). The Petermann Orogeny resulted in a north-vergent, with five new maps: a 1:500 000-scale solid geology thick- and thin-skinned fold-and-thrust belt in the southern map covering the western part of the Northern Territory and central parts of the Amadeus Basin. Deformation during portion of the Amadeus Basin (Weisheit 2021), second the Petermann Orogeny was responsible for a series of edition 1:250 000-scale geological maps of HENBURY 3 unconformities referred to as the Petermann unconformity (Donnellan et al in prep), LAKE AMADEUS (Verdel et al (an example of the Petermann unconformity is illustrated in prep) and BLOODS RANGE (Verdel et al in prep), and in Figure 2a), which forms an important seismic horizon a first edition 1:100 000-scale Henbury Special geological across much of the Amadeus Basin (eg Menpes et al 2018). map (Donnellan and Normington in prep; Figure 1). The The younger Alice Springs Orogeny was south-directed 1:500 000 map covers ~150 000 km2 (including more than and pervasive in the southern Aileron Province, Warumpi half of the total extent of the Amadeus Basin), and the new Province and northern part of the Amadeus Basin. Some 1:250 000 maps cumulatively cover ~50 000 km2. Some of Petermann Orogeny structures were reactivated during the the major outcomes from the geological mapping projects Alice Springs Orogeny. Both Petermann Orogeny and Alice are summarised below. Springs Orogeny structures generally trend northwest– southeast, and they are cut by a series of northeast–southwest- West Amadeus Basin 1:500 000 solid geology striking reverse faults that formed late in the Alice Springs interpretation Orogeny (Isles and Rankin 2013, Weisheit 2021). Throughout the west Amadeus Basin map area, the clearest surface The west Amadeus Basin solid geology interpretation evidence for deformation attributable to the Petermann and (Weisheit 2021) covers the central and western parts of the Alice Springs orogenies are northwest–southeast-elongate NT portion of the Amadeus Basin, parts of the Aileron doubly-plunging folds (eg Forman 1963). and Warumpi provinces (eg Scrimgeour 2013a and b) to the north of the basin, and part of the Musgrave province Central Amadeus Basin 1:250 000 and 1:100 000 (eg Close 2013) to the south (Figure 1). The map is a solid geological mapping (HENBURY and Henbury Special) 1 Northern Territory Geological Survey, GPO Box 4550, Darwin HENBURY lies in the central part of the Amadeus Basin NT 0801, Australia (Figure 1), a key region for linking the stratigraphic 2 Email: [email protected] 3 Names of 1:250 000 and 1:100 000 mapsheets are shown in nomenclature of the Neoproterozoic succession used for large and small capital letters respectively, eg BLOODS the northeastern part of the Amadeus Basin (eg Areyonga, RANGE, Henbury. Aralka, Olympic, and Pertatataka formations; eg Edgoose 22°S Murraba Basin Murraba Basin Yuendumu Georgina Basin Amadeus Aileron Province Basin Ngalia Basin Aileron Province Kiwirrkurra WESTERN AUSTRALIA Plenty Highway 23°S TERRITORY NORTHERN Wes Aadeus asin Tanami Road Irindina 100 000 Canning Basin Kintore Province Warumpi Province Namatjira Drive Alice Springs Larapinta Drive Hermannsburg Ross Highway 24°S Amadeus Amadeus Basin Basin Stuart Highway Ernest Giles Road Amadeus Basin Canning Basin HENBURY S ANGE AE AAES ENY SPECIAL N 25°S 120 000 120 000 120 000 1100 000 Docker River Pedirka (Kaltukatjara) Lasseter Highway Basin Yulara E ° Officer Eromanga Basin Eromanga Basin 126 Basin E Musgrave Province E E E E E E Great Central °30’ Road ° °30’ ° °30’ ° °30’ 26°S 127 129 130 132 133 135 136 Figure 1. Extents of new NTGS mapping projects in the western part of the NT portion of the Amadeus Basin. Background image shows shaded relief (Morgan-Wall 2020) of the Amadeus Basin and surrounding area. © Northern Territory of Australia 2021. With the exception of government and corporate logos, and where otherwise noted, all material in this publication is provided under a Creative Commons Attribution 4.0 International licence (https://creativecommons.org/licenses/by/4.0/legalcode). 75 AGES 2021 Proceedings, NT Geological Survey 2013, Normington and Donnellan 2020) with that used in Sandstone of the northeastern Amadeus Basin. The central, southern and western portions (Inindia and Winnall overlying Winnall beds have been subdivided into six beds; eg Wells et al 1963, Jackson et al 1984). Outcrops of the formations (Quandong Conglomerate, Breaden, Gloaming, former Inindia beds on HENBURY have now been identified Froud, Liddle and Puna Kura Kura formations), which as belonging to the Tonian Wallara Formation (Figure 2b), comprise the new Winnall Group (Figure 2d–f; Donnellan Cryogenian Areyonga and Aralka formations (Figure 2c), and Normington 2017). These strata seem to correlate with and Cryogenian to Ediacaran Olympic Formation/Pioneer Ediacaran rocks (eg Pertatataka Formation, Julie Formation a b c d e f Figure 2. Field photographs from the Amadeus Basin. (a) Angular unconformity (‘Petermann unconformity’) between underlying Ediacaran Liddle Formation and overlying Ordovician Stairway Sandstone in the southeastern part of LAKE AMADEUS. (b) Domical stromatolite of Wallara Formation (formerly mapped as Inindia beds) in HENBURY. (c) Characteristic festoon cross-stratification in sandstone of the Cryogenian Limbla Member of Aralka Formation, HENBURY. (d) Quandong Conglomerate, a lower part of Winnall Group, HENBURY. (e) Microbially-induced sedimentary structures (Kinneyia) from the Ediacaran Gloaming Formation, HENBURY. (f) Clay galls within Gloaming Formation, HENBURY. Hammer is 30 cm long. (Continued on next page). 76 AGES 2021 Proceedings, NT Geological Survey and lower Arumbera Sandstone) of the northeastern northwest–southeast-trending folds described above. The Amadeus Basin (Donnellan and Normington 2017, Verdel Henbury Special 1:100 000 map is thus being prepared to et al 2020). HENBURY also includes Palaeozoic strata illustrate the complexity of this area at a suitable level of (Figure 2g) that range in age from Cambrian to Devonian. detail. The southeastern part of HENBURY is a particularly structurally-complex area, which departs considerably from Western Amadeus Basin 1:250 000 geological mapping the overall central and western Amadeus Basin pattern of (LAKE AMADEUS and BLOODS RANGE) g LAKE AMADEUS and BLOODS RANGE are located to the west of HENBURY (Figure 1). Like HENBURY, Amadeus Basin strata exposed in LAKE AMADEUS and BLOODS RANGE are predominantly Neoproterozoic to Devonian sandstones, which are largely covered by sand dunes, as well as by the extensive Cenozoic playa lake deposits of Lake Amadeus and Lake Neale (Figure 2h; eg Chen et al 1993). The first-order structural pattern of LAKE AMADEUS and BLOODS RANGE is that of doubly-plunging, generally broad to open folds with northwest-striking axial planes. The recently defined Liddle and Puna Kura Kura formations of the Winnall Group (Donnellan and Normington 2017) extend along strike from HENBURY onto LAKE AMADEUS; sandstone of Liddle Formation (formerly mapped as Winnall beds in the western Amadeus Basin) extends across HENBURY, LAKE h AMADEUS and BLOODS RANGE. Unlike HENBURY, strata previously mapped as Inindia beds on LAKE AMADEUS and BLOODS RANGE are not recognisable as a distinct part of the northeastern Amadeus Basin Neoproterozoic succession, due primarily to extensively weathered, small, isolated exposures. In the northeast corner of LAKE AMADEUS, the Mereenie oil and gas field produces from Palaeozoic sandstone of the doubly-plunging Mereenie anticline (eg Jackson 1984, Ambrose 2006). LAKE AMADEUS also includes the excellent exposures of Carmichael Sandstone and overlying Mereenie Sandstone at Watarrka National Park (Bagas 1988). In addition to the Amadeus Basin stratigraphy described above, BLOODS RANGE also covers a northern part of the Musgrave Province that consists of late Mesoproterozoic i (Stenian) felsic rocks of the Pottoyu Granite Suite (Close et al 2003). These rocks are nonconformably overlain by volcanic and metasedimentary rocks of the Tjauwata Group, which comprise a latest Mesoproterozoic rift succession (Ngaanyatjarra Rift) that is poorly exposed in the southern part of BLOODS RANGE (Close et al 2003, Aitken et al 2013). Major periods of deformation in the Musgrave Province include Stenian rifting (resulting in deposition of