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 H ow e ve r i t i s e xpos e d i n t he tom a ha w k ra nge j us t e a s t of t h e e a s t e r n b o u n d a r y o f Woodgreen a b o u t 5 k m s o u t h e a s t o f Bu g g y ca m p Bo r e , a n d i s h i g h l y l i k e l y t o b e p r e s e n t b e n e a t h ce n o z o i c c o v e r i n t h e e x t r e m e n o r t h e a s t e r n c o r n e r o f Woodgreen. th e to m a h a w k Fo r m a t i o n c o n s i s t s o f m e d i u m t o c o a r s e , c r o s s b e d d e d s a n d s t o n e , w i t h m i n o r i n t e r b e d s o f m u d s t o n e , l i m e s t o n e a n d d o l o s t o n e . ic h n o f o s s i l s a n d s h e l l y f o s s i l s , i n d i c a t i n g a s h a l l o w - m a r i n e e n v i r o n m e n t , a r e c o m m o n . th e f o r m a t i o n r e a c h e s a b o u t 190 m in thickness (Kruse et al 2 0 0 2 ), b u t i n m o s t a r e a s , t h e t h i c k n e s s i s u n c e r t a i n d u e t o s t r u c t u r a l c o m p l e x i t i e s . in BarroW creek, H uckitta a n d toBermorey, t h e to m a h a w k Fo r m a t i o n d i s c o n f o r m a b l y o v e r l i e s t h e up p e r ca m b r i a n ar r i n t h r u n g a Fo r m a t i o n (H a i n e s et al 1991, Freeman 1986, Kruse et al 2 0 0 2 ). al t h o u g h t h e ar r i n t h r u n g a Fo r m a t i o n m a y b e p r e s e n t i n t h e s u b s u r f a c e i n n o r t h e a s t e r n Woodgreen (s e e chabaloweFormation), a n a l t e r n a t i v e p o s s i b i l i t y i s t h a t i t d i s c o n f o r m a b l y o v e r l i e s t h e ch a b a l o w e Fo r m a t i o n i n t h i s a r e a . Fault rock and mylonite (various ages) Q u artz b re ccia (q b ) ri d g e s o f q u a r t z a n d c h e r t b r e c c i a , r e l a t e d t o h y d r o t h e r m a l a c t i v i t y a l o n g h i g h - l e v e l f a u l t s i n ar u n t a re g i o n r o c k s , a r e w i d e s p r e a d a c r o s s Woodgreen. al t h o u g h m a n y a r e a s s o c i a t e d w i t h f a u l t s a n d s h e a r z o n e s t h a t c u t ge o r g i n a Ba s i n r o c k s a n d t h u s a r e p r e s u m a b l y r e l a t e d t o t h e al i c e sp r i n g s or o g e n y , t h i s c a n n o t a l w a y s b e a s s u m e d . cl a s t s c o m p o s e d o f s i m i l a r m a t e r i a l a r e p r e s e n t i n ne o p r o t e r o z o i c g l a c i g e n e r o c k s a n d t h u s , s o m e q u a r t z b r e c c i a s a r e a s s o c i a t e d w i t h Pr o t e r o z o i c f a u l t s . in p l a c e s , quartz breccias are significantly ferruginous and locally, a r e a s s o c i a t e d w i t h b a r i t e . Q u artz mylonite (q m) th e m a j o r i t y o f m y l o n i t e i n Woodgreen i s c o m p o s e d a l m o s t e n t i r e l y o f q u a r t z , a l t h o u g h a m i n o r s e r i c i t e c o m p o n e n t o f t e n i m p a r t s a w e a k p h y l l i t i c s h e e n t o t h e r o c k . th e s e r o c k s d i s p l a y a d i s t i n c t i v e m y l o n i t i c f o l i a t i o n c o m m o n l y a s s o c i a t e d w i t h a w e l l d e v e l o p e d l i n e a t i o n . th e b e s t e x a m p l e s a r e w i t h i n t h e mo u n t id a sh e a r zo n e a n d m o s t a r e a s s u m e d t o b e r e l a t e d t o t h e al i c e sp r i n g s or o g e n y . M ylonite (m) th i s s y m b o l h a s b e e n u s e d f o r m y l o n i t i c r o c k s t h a t a r e n o t e x c l u s i v e l y q u a r t z - r i c h , s u c h a s t h e s t r o n g l y m y l o n i t i s e d granite around 429200mE 7523264mN. cenozoic S ilcre te (Cz s ) Silcrete represents relicts of an ancient silicified land s u r f a c e . ou t c r o p s o v e r l i e d e e p l y l e a c h e d a n d w e a t h e r e d b e d r o c k , m o s t c o m m o n l y t h e Wo o d g r e e n gr a n i t e co m p l e x . ex p o s u r e s a r e t y p i c a l l y t h i n (s e v e r a l m e t r e s t h i c k n e s s a t m o s t ) a n d s l o p e a w a y f r o m a r e a s o f f r e s h g r a n i t e o u t c r o p , l o c a l l y m e r g i n g w i t h t h e s u r r o u n d i n g p l a i n . Fe rricre te (Cz f ) Pi s o l i t i c f e r r i c r e t e i s m o s t w i d e s p r e a d o v e r s o u t h w e s t e r n Woodgreen, w h e r e i t i s a s s o c i a t e d w i t h r e d s o i l p l a i n s (Q r ). it i s s h o w n o n t h e m a p f a c e i n a r e a s w h e r e i t f o r m s l o w , e l o n g a t e a n d a r c u a t e r i s e s t h a t c a n b e d i s t i n g u i s h e d o n a e r i a l p h o t o g r a p h s . lo c a l l y , t h e f e r r i c r e t e i s a s s o c i a t e d w i t h t r a c e s o f d e e p l y w e a t h e r e d b e d r o c k a n d , i n g e n e r a l , t h e p r e s e n c e o f f e r r i c r e t e p r o b a b l y i n d i c a t e s t h a t b e d r o c k l i e s a t s h a l l o w d e p t h . Fe r r i c r e t e i s a l s o c o m m o n l y a s s o c i a t e d w i t h o l d a l l u v i a l f a n s (cz t ) a n d w i t h o u t c r o p s t e n t a t i v e l y identified as the Cambrian Chabalowe Formation. D is s e cte d f ans (Cz t) th e s e d e p o s i t s c o m p r i s e r e l i c t s o f o l d a l l u v i a l f a n g r a v e l a n d c o b b l e d e p o s i t s t h a t a r e u n d e r g o i n g d i s s e c t i o n b y m o d e r n d r a i n a g e s . in s o m e c a s e s , t h e y a r e p h y s i c a l l y d e t a c h e d f r o m t h e r a n g e s f r o m w h i c h t h e y w e r e d e r i v e d . th e g r a v e l s a r e o f t e n f e r r u g i n i s e d a n d a s s o c i a t e d w i t h p i s o l i t i c f e r r i c r e t e . su c h d e p o s i t s a r e r e s t r i c t e d t o t h e v i c i n i t y o f s a n d s t o n e r a n g e s i n n o r t h e r n Woodgreen. th e a g e o f t h e s e d e p o s i t s i s u n c e r t a i n . W aite Formation (Cz w ) ou t c r o p s o f Wa i t e Fo r m a t i o n a r e w i d e s p r e a d t o t h e s o u t h a n d e a s t o f Woodgreen, w h e r e t h e y a r e p r e s e n t w i t h i n t h e Wa i t e Ba s i n a n d i n p a l a e o c h a n n e l s (Wo o d b u r n e 1967, Senior 1972, Shaw and Warren 1975). In the Waite Ba s i n , t h e Wa i t e Fo r m a t i o n c o m p r i s e s l a c u s t r i n e s i l t s t o n e , fluviatile siltstone, sandstone and conglomerate, overlain by chalcedonic limestone (Woodburne 1967). Only minor o u t c r o p s a r e r e c o g n i s e d i n Woodgreen a n d t h o s e e x a m i n e d a r e r e s t r i c t e d t o t h e u p p e r c h a l c e d o n i c l i m e s t o n e u n i t . th e l i m e s t o n e h a s c o m m o n l y b e e n r e m o v e d b y d i s s o l u t i o n t o l e a v e o u t c r o p s o f m a s s i v e v u g g y c h a l c e d o n y a n d m i n o r common opal, such as at 444719mE 7524877mN and 4 4 2 0 0 0 m e 7 5 2 4 5 0 0 m n. in t h e Wa i t e Ba s i n , t h e f o r m a t i o n reaches 30 m in thickness (Woodburne 1967). Its thickness i n Woodgreen i s u n k n o w n , a l t h o u g h e x p o s u r e s a r e l e s s t h a n 1 0 m t h i c k . in alcoota, t h e Wa i t e Fo r m a t i o n c o n t a i n s a g a s t r o p o d a n d v e r t e b r a t e f o s s i l f a u n a i n d i c a t i n g a la t e Miocene or Early Pliocene age (Woodburne 1967). Calcre te (Cz c) sc a t t e r e d e x p o s u r e s o f n o d u l a r c a l c r e t e a r e p r e s e n t w i t h i n p a l a e o c h a n n e l s t h a t f e e d i n t o t h e ti - tr e e Ba s i n a n d a l s o i n t h e n o r t h e a s t n e a r Bu g g y ca m p Bo r e . th e c a l c r e t e o u t c r o p s a s l o w m o u n d s a n d e l o n g a t e r i d g e s s u r r o u n d e d b y a l l u v i u m (Q a ), a e o l i a n s a n d (Q s ) o r r e d s o i l (Q r ). th e c a l c r e t e h a s a p p a r e n t l y b e e n d e p o s i t e d b y g r o u n d w a t e r m o v e m e n t a n d i s e x p o s e d i n a r e a s w h e r e t h e m o d e r n water table is close to the surface (McDonald 1990). The c a l c r e t e w a s p r e s u m a b l y f o r m e d i n t h e s u b s u r f a c e , b u t h a s b e e n e x p o s e d b y l o w e r i n g o f t h e l a n d s u r f a c e d u e t o e r o s i o n . th e a g e o f t h e c a l c r e t e i s u n c e r t a i n .


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