Territory Stories

Woodgreen, Northern Territory : explanatory notes

Details:

Title

Woodgreen, Northern Territory : explanatory notes

Issued by

Northern Territory Geological Survey

Collection

E-Publications; E-Books; PublicationNT; Australia 1:100 000 Geological Map Series

Date

2007

Location

Australia 1:100 000 Geological Map Wood 5458; Australia 1:250 000 Geological MapAlcoota SF5310; Australia 1:250 000 Geological MapAlcoota SF5310

Map scale

1:100 000

Notes

Made available via the Publications (Legal Deposit) Act 2004 (NT); Available from GEMIS - Geoscience Exploration and Mining Information System

Language

English

Subject

Geology; Georgina Basin; Arunta Region

Publisher name

Northern Territory Government; Northern Territory Government

Place of publication

Darwin

Edition

1st ed.

Series

Australia 1:100 000 Geological Map Series

File type

application/pdf

ISBN

9780724571321

ISSN

0811-6296

Use

Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government

License

https://creativecommons.org/licenses/by/4.0/

Related links

https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/81885 [GEMIS]

Parent handle

https://hdl.handle.net/10070/794795

Citation address

https://hdl.handle.net/10070/794807

Page content

19 However it is exposed in the Tomahawk Range just east of the eastern boundary of Woodgreen about 5 km southeast of Buggy Camp Bore, and is highly likely to be present beneath Cenozoic cover in the extreme northeastern corner of Woodgreen. The Tomahawk Formation consists of medium to coarse, crossbedded sandstone, with minor interbeds of mudstone, limestone and dolostone. Ichnofossils and shelly fossils, indicating a shallowmarine environment, are common. The formation reaches about 190 m in thickness (Kruse etal 2002), but in most areas, the thickness is uncertain due to structural complexities. In BARROW CREEK, HUCKITTA and TOBERMOREY, the Tomahawk Formation disconformably overlies the Upper Cambrian Arrinthrunga Formation (Haines etal 1991, Freeman 1986, Kruse etal 2002). Although the Arrinthrunga Formation may be present in the subsurface in northeastern Woodgreen (see chabaloweFormation), an alternative possibility is that it disconformably overlies the Chabalowe Formation in this area. Fault rock and mylonite (various ages) Quartz breccia (qb) Ridges of quartz and chert breccia, related to hydrothermal activity along highlevel faults in Arunta Region rocks, are widespread across Woodgreen. Although many are associated with faults and shear zones that cut Georgina Basin rocks and thus are presumably related to the Alice Springs Orogeny, this cannot always be assumed. Clasts composed of similar material are present in Neoproterozoic glacigene rocks and thus, some quartz breccias are associated with Proterozoic faults. In places, quartz breccias are significantly ferruginous and locally, are associated with barite. Quartz mylonite (qm) The majority of mylonite in Woodgreen is composed almost entirely of quartz, although a minor sericite component often imparts a weak phyllitic sheen to the rock. These rocks display a distinctive mylonitic foliation commonly associated with a well developed lineation. The best examples are within the Mount Ida Shear Zone and most are assumed to be related to the Alice Springs Orogeny. Mylonite (m) This symbol has been used for mylonitic rocks that are not exclusively quartzrich, such as the strongly mylonitised granite around 429200mE 7523264mN. cenozoic Silcrete (Czs) Silcrete represents relicts of an ancient silicified land surface. Outcrops overlie deeply leached and weathered bedrock, most commonly the Woodgreen Granite Complex. Exposures are typically thin (several metres thickness at most) and slope away from areas of fresh granite outcrop, locally merging with the surrounding plain. Ferricrete (Czf) Pisolitic ferricrete is most widespread over southwestern Woodgreen, where it is associated with red soil plains (Qr). It is shown on the mapface in areas where it forms low, elongate and arcuate rises that can be distinguished on aerial photographs. Locally, the ferricrete is associated with traces of deeply weathered bedrock and, in general, the presence of ferricrete probably indicates that bedrock lies at shallow depth. Ferricrete is also commonly associated with old alluvial fans (Czt) and with outcrops tentatively identified as the Cambrian Chabalowe Formation. Dissected fans (Czt) These deposits comprise relicts of old alluvial fan gravel and cobble deposits that are undergoing dissection by modern drainages. In some cases, they are physically detached from the ranges from which they were derived. The gravels are often ferruginised and associated with pisolitic ferricrete. Such deposits are restricted to the vicinity of sandstone ranges in northern Woodgreen. The age of these deposits is uncertain. Waite Formation (Czw) Outcrops of Waite Formation are widespread to the south and east of Woodgreen, where they are present within the Waite Basin and in palaeochannels (Woodburne 1967, Senior 1972, Shaw and Warren 1975). In the Waite Basin, the Waite Formation comprises lacustrine siltstone, fluviatile siltstone, sandstone and conglomerate, overlain by chalcedonic limestone (Woodburne 1967). Only minor outcrops are recognised in Woodgreen and those examined are restricted to the upper chalcedonic limestone unit. The limestone has commonly been removed by dissolution to leave outcrops of massive vuggy chalcedony and minor common opal, such as at 444719mE 7524877mN and 442000mE 7524500mN. In the Waite Basin, the formation reaches 30 m in thickness (Woodburne 1967). Its thickness in Woodgreen is unknown, although exposures are less than 0 m thick. In alcoota, the Waite Formation contains a gastropod and vertebrate fossil fauna indicating a Late Miocene or Early Pliocene age (Woodburne 1967). Calcrete (Czc) Scattered exposures of nodular calcrete are present within palaeochannels that feed into the TiTree Basin and also in the northeast near Buggy Camp Bore. The calcrete outcrops as low mounds and elongate ridges surrounded by alluvium (Qa), aeolian sand (Qs) or red soil (Qr). The calcrete has apparently been deposited by groundwater movement and is exposed in areas where the modern water table is close to the surface (McDonald 1990). The calcrete was presumably formed in the subsurface, but has been exposed by lowering of the land surface due to erosion. The age of the calcrete is uncertain.


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