Woodgreen, Northern Territory : explanatory notes
Northern Territory Geological Survey
E-Publications; E-Books; PublicationNT; Australia 1:100 000 Geological Map Series
2007
Australia 1:100 000 Geological Map Wood 5458; Australia 1:250 000 Geological MapAlcoota SF5310; Australia 1:250 000 Geological MapAlcoota SF5310
1:100 000
Made available via the Publications (Legal Deposit) Act 2004 (NT); Available from GEMIS - Geoscience Exploration and Mining Information System
English
Geology; Georgina Basin; Arunta Region
Northern Territory Government; Northern Territory Government
Darwin
1st ed.
Australia 1:100 000 Geological Map Series
application/pdf
9780724571321
0811-6296
Attribution International 4.0 (CC BY 4.0)
Northern Territory Government
https://creativecommons.org/licenses/by/4.0/
https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/81885 [GEMIS]
https://hdl.handle.net/10070/794795
https://hdl.handle.net/10070/794807
1 5 de pt h ). in dr i l l c or e , t he el yua h For m a t i on i s dom i na t e d by black micaceous shale with minor thin, micaceous fine s a nd s t one i nt e r be ds . a ba s a l c oa r s e pe bb l y uni t i s de ve l ope d a bov e a n unc onf or m a bl e c ont a c t w i t h ba s e m e nt gr a ni t oi ds . the el yua h For m a t i on unc onf or m a bl y ove r l i e s ar unt a re gi on ba s e m e nt a nd, l oc a l l y , t he oor a br a ar kos e a nd Boko Fo r m a t i on. it i s ove r l a i n c onf or m a bl y by t he gr a nt Bl uf f For m a t i on. it i s a bs e nt a t mount H a r pe r a nd n e a r t he nor t h e r n bounda r y of Woodgreen, w he r e a t t e nua t e d gr a nt Bl uf f For m a t i on r e s t s di r e c t l y o n ar unt a re gi on ba s e m e nt . the el yua h For m a t i on i s i nt e r pr e t e d t o be of m a r i ne or i gi n. Wi t h t he e xc e pt i on of hi gh- e ne r gy t r a ns gr e s s i ve s a n ds t one a nd c ongl om e r a t e a t t he ba s e , m os t of t he uni t w a s de pos i t e d unde r qui e t c ondi t i ons be l ow f a i r w e a t he r w a ve ba s e , punc t ua t e d by r a r e s t or m e ve nt s . the el yua h Fo r m a t i on i s ve r y r e c e s s i ve a nd r a r e l y e xpo s e d. the pr e s e nc e of a ga p w i t h no out c r op be ne a t h t he gr a n t Bl uf f For m a t i on i s t a ke n a s a n i ndi c a t or of t he p r e s e nc e of t he uni t . sm a l l ou t c r ops of r e d a nd w hi t e w e a t he r e d s ha l e ha ve be e n l oc a t e d be t w e e n t he oor a br a ar kos e a nd gr a nt Bluff Formation in the Kunoth Knob area (436500mE 7535 300m n, 434300m e 7535500m n). rounde d qua r t z pe bb l e s i n s c r e e f r om t hi s s a m e i nt e r va l hi nt a t t he e x i s t e nc e of a ba s a l c ongl om e r a t e ove r t he oor a br a ar kos e , a s i n HUCKITTA (Freeman 1986). At 444300mE 7532500mN, a da m e xc a va t i on e a s t of t he out c r oppi ng gr a nt Bl uf f For m a t i on a l s o e xpos e s r e d a nd w hi t e m i c a c e ous s i l t s t one a nd s ha l e . the s e ve r y m i nor e xpos ur e s d o not a ppe a r on t he m a pf a c e . G rant B lu f f Formation (LP ra) The Grant Bluff Formation was defined in HUCKITTA (Walter 1980, Freeman 1986). In the Woodgreen a r e a , Fi r s t edi t i on alcoota m a ppi ng r e c ogni s e d t he gr a n t Bl uf f For m a t i on onl y i n t he kunot h knob a r e a , ot he r out c r ops now a s s i gne d t o t hi s f or m a t i on be i ng i nc or r e c t l y m a ppe d as Central Mount Stuart beds (Shaw and Warren 1975). in o ut c r op, t he gr a nt Bl uf f For m a t i on i s dom i na t e d by thinly bedded, tabular, pale fine sandstone (Figure17). it i s c h a r a c t e r i s t i c a l l y ve r y l ow i n a l l r a d i om e t r i c c h a nne l s , e s pe c i a l l y k. ri ppl e m a r ks a nd pa r t i ng l i ne a t i ons a r e c om m on. sur f a c e w e a t he r i ng of t e n c a us e s out c r ops t o be r e dde ne d t o va r yi ng de gr e e s a nd, w he r e t hi s oc c u r s , i t c a n be difficult to distinguish the Grant Bluff Formation from t he ce nt r a l mount st ua r t For m a t i on i n i s ol a t e d out c r ops . in s om e a r e a s , pa r t i c ul a r l y ne a r kunot h knob, t he gr a nt Bl uf f For m a t i on c ont a i ns s e ve r a l uni t s of c oa r s e , bl oc ky , pe bbl y w hi t e s a nds t one . Be c a us e t he s e uni t s a r e r e s i s t a nt a nd r i dge f or m i ng, s c r e e f r om t he m of t e n c ove r s t he m or e characteristic, though recessive, finegrained tabular facies of t h e gr a nt Bl uf f For m a t i on. inc om pl e t e s e c t i ons a nd s t r uc t ur a l c om pl i c a t i ons i m pe de de t e r m i na t i ons of t hi c kne s s f r om out c r op. the f or m a t i on i s 1 50 m a nd 1 27 m t hi c k i n dr i l l hol e s cms1 a nd cms2, r e s pe c t i ve l y . it t h i ns t o t he nor t h a nd ha s a n e s t i m a t e d t hi c kne s s of onl y 203 0 m ne a r t he nor t he r n bounda r y of Woodgreen. the gr a nt Bl uf f For m a t i on i s i nt e r pr e t e d a s a s ha l l ow - m a r i ne de pos i t , f or m e d m os t l y a bove s t or m w a ve ba s e . in m os t a r e a s , t he gr a nt Bl uf f For m a t i on i s a s s um e d t o c onf or m a bl y ove r l i e t he el yua h For m a t i on, but t he l a t t e r i s ve r y r e c e s s i ve a nd i s r a r e l y e xpos e d. dr i l l c or e da t a i ndi c a t e a gr a da t i on a l c ont a c t , w i t h t he ba s e of t he gr a nt Bl uf f For m a t i on t a ke n t o be t he poi nt w he r e bl a c k s ha l e a nd minor fine sandstone of the Elyuah Formation are replaced upsection by fine sandstone and minor shale. Near the nor t he r n bounda r y of Woodgreen, t he a t t e nua t e d gr a nt Bl uf f For m a t i on unc onf or m a bl y ove r l i e s ar unt a re gi on gr a ni t e i n t he a bs e nc e of t he el yua h Fo r m a t i on . a l e nt i c u l a r , ba s a l qua r t z - pe bbl e c ongl om e r a t e i s pr e s e nt i n t hi s a r e a . a s i m i l a r r e l a t i ons hi p i s pr e s e nt a t mount H a r pe r , on t he w e s t e r n m a r gi n of Woodgreen. out c r ops ove r ba s e m e nt ne a r t he nor t he r n e dge of Woodgreen a r e c ont i nuous w i t h out c r ops m a ppe d a s t he For s t e r me m be r of t he ce nt r a l mou nt st ua r t For m a t i on i n BarroW creek (H a i ne s et al 1991). It can now be de m ons t r a t e d t ha t t he For s t e r me m be r i s e qui va l e nt t o t he gr a nt Bl uf f For m a t i on a nd t he f or m e r t e r m i s he r e a ba ndone d. Ce ntral M ou nt S tu art Formation (LP s t, L P s a) re m a ppi ng ha s de m ons t r a t e d t ha t t he uni t s how n a s ce nt r a l mount st ua r t be ds on t he Fi r s t edi t i on alcoota mapsheet (Shaw and Warren 1975) is a grouping of several Figure17. gr a nt Bl uf f For m a t i on. out c r op s how i ng t hi c ke ni ng- u pw a r d i nt e r v a l of t a bul a r w hi t e s a nds t one a nd quartzite. 421402mE 7564646mN, 14 km nW of ne w Bor e .