Woodgreen, Northern Territory : explanatory notes
Northern Territory Geological Survey
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Geology; Georgina Basin; Arunta Region
Northern Territory Government; Northern Territory Government
Australia 1:100 000 Geological Map Series
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Northern Territory Government
3 Figure13. Boko Formation. Well developed glacial striations on large quartzite clast. 434259mE 7535454mN, 6.5 km E of Whiterock Dam. Figure14. Boko Formation unconformably overlying Utopia Quartzite(?). Ferruginous sandstone and quartzite of Utopia Quartzite(?) exposed in foreground and to left of vehicle. Unconformity surface dips west behind vehicle, with gently dipping Boko Formation outcropping to right; best exposure is around top of small hill (see Figure12 for detail). 428550mE 755505mN, 3 km NNW of New Bore. also include granite and vein quartz. It is possible that some, or all of the clasts have been reworked from the Boko Formation, and that any facets and striations have been removed by abrasion. Faceted and striated clasts have been reported in HUCKITTA (Freeman 1986). The Oorabra Arkose unconformably overlies basement granite (432171mE 7552110mN) and quartzite (431655mE 7552292mN), and locally conformably(?), overlies the Boko Formation. A small outcrop of the unconformity surface over the Utopia Quartzite has a distinctly polished and striated appearance, and may represent a small relict of a glaciated pavement (Figure16). The striation direction (eastwest trend) is similar to that noted from beneath the Boko Formation. The Oorabra Arkose is overlain with probable unconformity by the Elyuah Formation, although the contact is poorly known. The thickness of the formation is estimated at 200 m near 433000mE 755000mN, but regional thickness variations are poorly known, due to the incomplete nature of most sections. The formation appears to be completely absent from the nearby diamond drillhole CMS3. It is also absent from holes CMS2 and CMS4, genetic similarities. For this reason, the known distribution of the unit is extended, although the formation is clearly lenticular and probably not continuous between all localities. In Woodgreen, the Oorabra Arkose is recognised in discontinuous outcrops from the Kunoth Knob area to the region east of New Bore. Near Kunoth Knob, the Oorabra Arkose consists of massive, poorly sorted, coarsegrained and pebbly arkose. Although sparse larger pebbles and cobbles may be well rounded, the matrix is comprised of angular clasts. This material has apparently been derived from the erosion of mainly granitic rocks, with relatively little transport and minimal chemical weathering. Significant facies changes occur between the Kunoth Knob area and the outcrops east of New Bore; the latter exposures comprise interbedded mudstone, sandstone, coarse arkose and cobble conglomerate (Figure15), with a pronounced high radiometric response. Spectacular exposures of cobble conglomerate are present around 433280mE 7551039mN. These stacked lenticular bodies are inferred to represent fluvial channels. Clasts are dominated by quartzite, but
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