TECTONICS, VOL. 10, NO.4, PAGES 688-721, AUGUST 1991

DEVELOPMENT OF THE LATEPROTEROZOIC TO MID.PALEOZOI:C,INTRACRATOMC AMADEUS BASININ CEIYTRAL AUSIR,ALIA: A KEYTO I]NDER.STANDING TECTONIC FORCF,SIN PLATE INTERIORS

R. D. ShawBureau of Mineral Resources Geology andGeophysics, Canberra, A.C.T., Australia

M. A. Etheridge and K. LambeckResearch School of Earth Sciences, The AustralianNational University, Canberra, A.C.T., Australia

Abstract. The intraqatonic Amadeus Basin incentral Australia is a complex, composite basincovering 17,000 km2, wiûi at least nine distinctepisodes of evolution between 900 and 300 Ma.These have been identified in neighboring centralAustralian basins and are characterizedby intervals ofrenewed subsidence followed by intervals of erosionand changes in basin shape. Several unconformitiesseparating the tectonostratigraphic sequencesrepresent periods of mild regional uplifts andcorrelate wittr major episodes of compressivetectonism at the evolving margin of the earlyAustralian plate. In the absence of direct geologicalevidence for thermal events in the Amadeus Basinafter the initial period of subsidence ended, possiblyat about 800 Ma, the correlations found betweenevents in the Amadeus Basin, those in theneighboring interconnected basins, and tectonicevents at the continental orplate margins emphasizethat regional horizontal stress fields contributesignificantly to primary basin forming mechanisms.This suggess that stresses generated at continental orplate margins may propagate to the plate interior withthe lithosphere acting as a stress guide. Throughoutthe history of the Amadeus Basin both periods whencompressional stresses were dominant and whenextensional teÆtonics conrolled subsidence can beidentified. There were also ransitional periods whenneither compression nor extension dominated, so thatother processes rnasked the effects of weak horizontalstresses. The most recent compressional ttrrust beltconcentrated at the northern margin between 300 and400 Ma and has partly obscured the record of earlierbasin shape and size.

INTRODUCTION

A sound framework exists for understanding thedevelopment of sedimentary basins at plate marginsand of basins in certain tectonically well-definedintraplate settings (e.g., failed rifts, tilted fault blockbasins). However, many of the larger continental

Copyright 1991 by the American Geophysical Union.Paoer number 901C02417.\zi B-7 407 t9 1 t 90'rc-024 r7$ 10.00

masses host sedimentary basins that developedentirely within intracratonic settings, unrelated toobvious major structures or simple tectonothennaldriving processes. Some of these basins have long(>200 Ma) and complex histories, consisting ofsøcked sequences with apparently disparatesubsidence driving mechanisms. These basins havebeen termed "polyhistory" basins or "successor"basins [Klemme, 1975; Klein, 1987], but these termssimply describe their complex subsidence historieswithout addressing the causal mechanism(s). Someof these basins lie beyond the direct influence of plateboundary processes such as foreland thrust loadingwith a reach of less than 500-1000 km lQuinlan andBeaumont, 19841, or the mechanical loading effectsof passive margin development producing sag basinswith a potential reach of about 200 km fWatts et al.,1982; Cochran, 19831 Also, their accumulatedsubsidence is too great to be accounted for byrepeated rises in sea level.

These complex intracratonic basins raise a numberof important quesúons. Do they develop because ofsome fundamental structural weakness iu that part ofthe continental crusilithosphere? Do they result fromone or very few basic driving processes, with theircomplexity reflecting only minor and relativelyunimportant disruptions to otherwise simplehistories? Alternatively, do they reprcsent theessentially accidental coincidence of subsidence in thesame location driven by widely disparate drivingmechanisms? If so, do they represent sensitiverecords of more dramatic, distal events that may bepoorly preserved where the activity was moreintense?

The Amadeus Basin in central Australia and itsclosely related neighbors, the Ngalia, Georgina, andOfficer basins, are excellent examples of complexintracratonic basins. These late Proterozoic toPhanerozoic basins (Figure 1) clearly formed in anintacratonic tectonic environment as the sedimentsare characterizedby interconnected, correlatablesequences with depocenters that are several hund¡edkilometers from any present-day, Paleozoic or lateProterozoic continental margin [Shaw et al., 1984;Wells and Moss, 19831. The present outlines of thecentral Australian basin reflect principally the effectsof the Devonian to Ca¡boniferous Alice SpringsOrogeny which ultimately terminated sedimentation.

By examining ttre subsidence history of thenorthem Amadeus Basin, we establish ninemegasequences which correspond to marked andrapid changes in the shape of ttre basin. rWe alsodocument to what extent subsidence in the AmadeusBasin is linked to hinterland basin uplift and detail thecrustal structure and history of the basin=boundingfault systems. We also determine ttre degree to whichsubsidence is contemporaneous with that inneighboring basins because horizontal (inplane)compressive stresses can explain coeval subsidencein widely sepamte basins [Lambeck, 1983; Quinlan,19871. We illustrate therefore the plate-wide tectonicsetting of each episode of uplift and subsidencerecognized in the central Australia basins and explore

Shaw et al.: Development of the Intracratonic Amadeus Basin

M O N E Y S H O A L E A S I N

BONAPARTEBASIN

EXMOUTHPLATEAU

AUSTRALIAN èro"rr

L A U R A B A S I N

C A R P E N T A R I AB A S I N

Â5' e ì

. M O B E T O NB A S I N

BREM ERBASIN

Late Proterczoic -Palaeozóic basins

Phanerozoic basins

Basement

-/,1,

S O R E L LS A S I N TASMANIA

BASIN0 500 ln

the hypottresis that widespread horizontal extensionalstresses may also explain subsidence in the interior ofthe continent. From these considerations \ve suggestplausible basin-forming mechanisms for eachmegasequence in the Amadeus Basin. The principalconclusion of our study is that complex intracratonicbasins, like the Amadeus Basin, are produced by aconstantly changing interplay of mechanisms and notone single basin-forming mechanism. We list keyfeatures which provide clues to first- and second-order processes which control the progressivedevelopment of intracratonic basins.

REGIONAL SETTING OF TTIE AMADEUS ANDRELATEDBASINS

The Amadeus Basin and its close relatives, theNgalia, Georgina, and Officer basins (Figwe 1),occupy an area of nearly 1Ñ km2 in the central partof Austalia. Each of these basins contains a grossly

conformable, if variably complete, sequence ofcontinental to shallow ma¡ine sedrmentary rocksranging in age from about 900 Ma to about 300 Ma.Parts of their sequences are also related to theCanning, Wiso, and Bonaparte (GulÐ basins to thewest and north, as well as that of the AdelaideGeosyncline to the south. Throughout deposition ofits sequences the Amadeus Basin was within ab'roadiy innacratonic setting, although it had periodicmarine links, and its depositional history wasinfluenced, especially in the early Paleozoic by theevolving Pacific margin in the Tasman Fold Belt tothe east.

The basins are separated by uplifted basementmetamorphic complexes of early to middleProterozoic age and are partly onlapped by Permianand Mesozoic sediments of younger basins (Figure1). Their present boundaries therefore reflect eventslate in or postdating their depositional histories, rathetthan the spatial limits of their various depositionalepisodes.

wtlEt : : : l

Fib. 1. The distribution of the late Proterozoic to Paleozoic central Australian basins inrelation to other basins and basement regions in Australia.

Shaw et al.: Development of the Intracratonic Amadeus Basin

The Amadeus Basin is elongate east-west, incontrast to the meridional trend that dominates muchof the remainder of Australia's Precambrian andPaleozoic provinces. Along the northem andsouthern bounda¡ies, Proterozoic metamorphic rockswere thrust over the basin at various stages in its!t-rto.y..In tþ east rhe boundary is onlaþped by theMesozoic toTertiary Eromanga Basin sequencé, inthe west by the Permian to Mesozoic parts of theCanning Basin (Figure 1).

TECTONOSTRATIGRAPHIC HISTORY OF THEAMADzuS AND RELATED BASINS

Definition of Sequznces

Lindsay et al. [1987], Korsch and Lindsay[1989], and Lindsay and Korsch t19S9l ideniifiedthree major megasequences in the northern paft of theAmadeus Basin, using both well data and sèismicstratigraphy. They related the sequences to threeindependent tectonically driven subsidence events,two extensional and one compressional.

Our analysis of the well dãta (Figure 2),supplemented by reevaluation of the-stratigaphic andfacies relationships determined by the Buréaú ofMineral Resources and others duiing earlier surfacemapping programs [Wells etal.,1910; Kenna¡d et al.19861, suggests a more complex history. We haveidentified nine separate sequènces at thémggryequence level [Hubbard, 1988] (Figure 3)which can be distinguished on the subsidénce record,the stratigraphy, and in significant changes in basinshape and depocenter location. Because of thecomplexity of basin history and the significant shiftsin depocenter position with time, it is not possible to

determine the sequence/subsidence history in any onewell or section. We have built up a compositesequence from four wells in the northem part of theAmadeus Basin (Figure 4). These wells were chosento sample, as far as possible, the thicker parts of thesuccession and to avoid anticlinal and other structtlresthat grew during various stages of basindeveþment._. - Thg composite tectonic subsidence curve (Figure5) has been compured using the backstrippinemétno¿described by Sclãter and Christie tl980iándjncludesthe calculation of maximum and minimum limits forsubsidence, similar to the approach of Bond andKominz [1984]. l,ocal isostatic balance is assumed atall times and, because the basin is relativelv narrow4qting several early stages of basin rearrangement,this assumption leads to an overestimation of tireisostatic correction factor. However, the form of thesubsidence curve is not particularly sensitive to thisassumption. Sea level changes aré ignored becausethe eustatic changes for the lâte Proterozoic to earlyP4eozoic are poorly known. Also, the magnitudóso!þ poqsible sea level changes are small cbmparedwith the thicknesses of the major sedimentarysequences. Paleobathymetry corrections were notmade because the sediments are of fluvial, lacustrineand shallow marine origin. Time conrol is based onthe Harland et al. [1982] time scale for the paleozoicexcept that the Cambrian-Precambrian boundary is setq!{0! Vta (in agreement with the srratorype seótion at605-610 Ma in China lZichao et al., 19841). Thequality of the age control of the various events isvariable, but what is important in this study is thepattern of subsidence and the sequence of events, notthe absolute ages of the events oi absolutemagnitudes of tectonic subsidence.

krespective of the duration of some of theerosional breaks in the Amadeus succession,subsidence was clea¡ly episodic. The comoositesubsidence curve is cõnsîdered to provide ånadequate portrayal of the subsidence history in thenorthern part of the basin except for subsidênce{uring megasequence 4 (mainly ArumberaSandstone). In rhis case, subsidence within thelocalized Carmichael and Ooraminna subbasins(Figure 2) was 4 to 7 times greater than the moregeneral subsidence throughout the basin during thisinterval.- During the late Proterozoic and early Cambrian,

time control is inadequate to differentiaie benveenconvex and concave subsidence curves and only forthe mid-Cambrian to Ordovician interval (sequences4-6, Figure 5) is the time confrol considered ãdequateto establish that this part of the curve is broadlyconcave, but with a b¡reak in sedimentation at thesequence 4-5 boundary. The final Devonian-Ca¡boniferous segment of the subsidence curve(sequence 9) is convex.

An overall subsidence pattern of a number ofdistinct gpisodes emerges,èach corresponding to adistinct lithological sequence boundedbyunconformities and representing the evolution of thesuccessive subbasins that together make up the

Fig.2. Location of wells and Early Cambriansubbasins in the Amadeus Basin. i. Mereenie 1.Eastllereenie (oflgas); 2, Palm Valley I(gas/condensate); 3, Dingo 1 (gas); 4, Ooraminna 1(gas); 5, Alice 1 (oil); 6,East]ohnny Creek 1(oil/ga$l 7, West Walker 1 (gas); 8 Lake Amadeuslfo_Ll); 9, Gosse Bluff I (gas); 10, Orange 1 (gas);1 1, West Waterhouse l, 12,Tyler l; l3,fuouitWinter I (oil); 14 Undandita (oit); 15, Tempe Vale_l_(qit); 16,Finke 1(gas); 17 TentHill l (gãs). 18,Wallaby 1 (gas); and 19, Rodinga 1 (oil)

ARUNTA BLocK or-----Lo *t

CARMICHAEL SUB-BASIN

ryK 6_ËÌf__î,j_NEZ oo\orl*-"oMOUNT CURBTE SUB-BASIN SUB.BASIN

.lil 1 2 <\

3,4 ¿d¡

Shaw et al.: Development of the Intracratonic Amadeus Basin

A G Ef

øEVENT

(Tablo 2)

LATE TO

M ¡ D D L E

DEVONIANzts

Brewer Conglomerâre (B)

Hermênnsburg Sandstone {H)

Parke Si l tstone (P)

A l ¡ c eSpringsOrogeny

( K )

Pednjara

q

EARLYD E V O N I A N

SILUB IAN

LATE

M e r e e n i e S a n d s t o n e { M }

{r)

Rodingan

I

4

I

Carmichae l Såndstone lC l { B )

( D )

PetermannRanges

Orogeny

( H )

SouthsRange

(s)

Areyonga

Srokes S¡l ts lone (Sl

Srairuay Sandstone (R)

Horn Vâl ley Si l tstone {V)

Pacoota Sândstone {F)UpÞer Goyder Formation {G1 }

6EAR LY

O B D O V I C I A N

LATE

z

ã n r o o l eE

EABLY

ts

oots

Lower Goyder Format ¡on (G2 l

, Pe termånn Ss t

Jay Creek Lsr Shannon Fm

Decep! ¡on Fm {N}

Hugh R¡ver Sha lesands lone

r r r¿ra ssr _

(u ) G i res c reek

Dolomi reTempe Fm {K)

Chand ler Format ion

5

Nãmarjira Fm '3:1"åT:'

Upper Arumbera Sândstone {A) (T}Lower Arumbera Sandstone {Z)

4

N

Maur ice Formal ion J u l i e F o r m a t i o n(J )

S i r F reder ¡ck W¡nna l l Beds

Cong lomerare & Penata laka Format ionE l l i s S a n d s t o n e ( E )

P ioneer Sandstone/Olymp¡c Format ion (O)

5

C ã m e o i e IBoord Fo- rmat ¡on In ìnd ia Beds Ara lkâ Format ¡on {L )

Areyonga Formarion (Y)2

Pinny inna Eeds B i (e r Spr ings Format ion { l l

Dean Ouanz i te Heãv i t ree Oua(z ì te {O)

{A)

'Arunra

Orogeny "t R l

l v l t Har is Basa l tB toods nånoe b€ds Stuañ Dyke Swarm

Fig. 3. Simplified stratigaphy of the northern Amadeus Basin. (After Kennard et al., 1986).

Amadeus Basin (see Table 1). Similar subsidencepatterns are evident in the other basins in centralAustralia as illustrated bv the time versus thicknessbars ofFigures 6a and 6b, suggesting that themechanisms driving subsidence are regional andepisodic.

Nature, Geometry and Extent of Sequences

In addition to the subsidence history, other keyinputs into understanding the tectonic processes thatshaped these basins are (1) the nature ofthesediments in each sequence and (2) the way in whichthe basins changed shape from one sequence to thenext.

In this section a b,rief summary oteach sequenceis provided, with particular emphasis on the changes

in basin shape. The changes in geome!ry of theAmadeus Basin and its immediate northem neighborsare illustrated for the various sequences in plan view(Figures 7a-7f) and in crosssection (see Figure 13below). In addition, continental scalepaleogeographic information is summarized inFigures I to 12. Note that none ofthese figures hasbeen palinspastically reconstructed and that quite alarge amount of shortening has been superimposedon some areas (particularly the northem AmadeusBasin) during the last stage of basin development.

Activity preceding basin dcvelopment Igneousactivity was widespread in the southernmost AruntaBlock and in the Musgrave Block prior to thebeginning of sedimentation. In particular, basalts atthe western periphery of the Amadeus Basin,centered over the western Musgrave Block, appear tohave been spatially and temporally linked to and

692

TYLER 1

W. WATERHOUSE , I

Unconformity

Sequence boundary

Spilite

Sa l t

Dolostone

Limestone

Mudrock

Sandstone and siltstone

Sandstone

Con g lom erati c sa n dston e

Conglomerate

cogenetic with the 110û 1200 Ma mantle-derivedlayered mafic intrusions (Giles Complex, [Daniels,197 4; Gray et al., 198 1l). These include the TolluVolcanics of the Bentley Supergroup dated at about1064 + 23Ma (Rb-Sr age, which should beregarded as a minimum age since the data indicateisotopic disturbance [see Page et al., 1984] and theMt Harris Basalt in the southwestemmost part of theAmadeus Basin lWells et al., 1970]. Basic dykeswanns in both the Musgrave and Arunta Blocks,were intruded into the above volcanics @aniels,1974). The one age determination for the StuartDyke Swarm in the southern AruntaBlock suggests

Shaw et al.: Development of the InEacratonic Amadeus Basin

Fig. 4. Schematic, composite stratigraphic sequencefor the northern Amadeus Basin based onintersections in four key wells (located in Figure 2)and supporting field sections. The code for thestratigraphic units is given in Figure 3. (Outcropsection missing from the upper part of the wellsection of Ooraminna 1 (4 in Figure 2) is locatedfarther to the east as is the outcrop section added tothe base of the well.)

F

N

[ , . .

;luuuuï

ØØ

ffiTTT-Í

ffilË:-!+llg.:E¡l

ffiIE=TEI

[:3i"':T

ffi

O O R A M I N N A 1

ouTcRoP 3

Outcrop

that dyke emplacement lasted until at least about900 Ma (Black et al., 1980; cf. Pa¡ker et al., 1987).

Early stages of basin development The earlystages of development are best illustrated in Figures3,4 and7a.

Sequence I ûateProterozoic): Sequence 1commenced with avery widespread quartzite(Heavitree Quartzite and its conelatives) that is foundin all the major central Australian basins @igure 8a).These sediments rwere generally deposited on ametamorphic basement and unconformably on theStuart dikes in the southern Arunta Block. Thissequence of dominantly shallow marinè, quartzose

Shaw et al.: Development of the InEacratonic Amadeus Basin

1 0000

^ 4000

ooo

P€- ôooo

Tectonic basement subsidenceUn corrected sedime nt th i cknessD ecompacted sed i m ent th i ckne ss

Hiatus

Salt halite casts

Carbonate, mudrock

SandstoneSediment withb asement- derive d clastsMafic volcanics

+ Tectonic event

o

" p

Doleilte d¡ kesPegmatite dikes

sands was followed by platform carbonates, shalesand minor evaporites (see Figure 8b). Basalt, alteredby diagenetic and low-grade metamorphic processesto spilite, was extruded within the upper sequence Lcarbonates of ttre northeastern and central southemparts of the Amadeus Basin.

The secondand sequences were characterizd by distinctive,late Proterozoic, glacial deposits (Sturtian andMarinoan. resoectivelv) which have been idenMarinoan, respectively) have been identifredover large areas of Ausralia @gures 9a and 9b). Inthe Amadeus Basin a large asymmeFical east-westsubbasin developed in the south ( Figure 7a)separated by a narrow arch (Figures 7a and 13) from

TEcroNrc everur f:::þ ¡ v Vd l

v "

^

tlE:ñt . ' . . ' l

Fig. 5. Composite subsidence curve constructed for the northem Amadeus Basinassuming local isostatic conditions, based on well data (Tyler 1, sequences 7-9 plus unitF in sequence 6; West Waterhouse 1, units R and V in sequences 6; Dingo 1, unit F insequence 6 plus sequences 4 and 5; Ooraminna 1 sequences 2 and 3 plus outcrop data).The relationships of subsidence history to sediment type and to tectoñic events are alsoindicated (see text for explanation). The labeled orogenic events (recognizedin the southof the basin, in the neighboring Georgina and Ngalia basins and farther af,reld) areoutlined in Table 2 (see also Figures 6a and 6b).

a second, shallower, subbasin to the north. Basindevelopment for both sequences 2 and3 was verysimilar and deposition was characterizedby an earlyphase in which deep, relatively narow basinsformed, followed, particularly during interval 3, bywidespread, roughly synchronous, and persistenttransgressions (see FiguresTa,9a and 9b). A minorchange in basin shape, most marked in the GeorginaBasin, heralded the onset of the transgression in theupper pafi of sequence 3 (Figure 7a).

At a number of locations outside the AmadeusBasin there is a hint that ttre extensive sequence 2transgression accompanied a change in the tectonicregime to one that was locally fault controlled. For

Shaw et al.: Development of the Intracratonic Amadeus Basin

I'ABLE1. ASummaryoftheSubsidenceHistoryforEachMegæequenceintheAmadeusBasin

Major Volcanism,Code* Lithology Magmatism

MaximumSource Diiection Tectonic Subsidence

Sediment Sou¡ce (F¡om) Subsidence, m Ratel¿cuna

(Precedine)

I

6

B ,

PM

c

S t oG2

G1 toDT

L

Y

conglomerate,sandstone

sandstone

sandstone

sandstone

carbonate,mudrock,'sa¡ds in W

carbonate,sandstone

sandstone

mud¡ock

pogmatites NE ofbasin

preceded by ræepegmatiteNEof

abundant basalt insurrounding region

ra¡e ca¡bonatite NE ofbasin

¡ 1800, possibly

-300

rapid bcrease major

very slow long-lived

slow minimal

steaù decline, mino¡late inqease

rapidincrease minor

mino¡

rapid locally

rapid

moderate

moderate

steady

abundantbæement- nonhderived clasts

lægely sedimentary

largely sedimenøry

sedimentary

bæement-derivedclasts

rnarine

basement-derivedclasß

ma¡ine

south -50

east-\ryest currents -1200

-750 in SWnonn, south, west

- 800in SW

north, south, west

mainly marine west, SW -500feldspathic in west

feldspathic; basement- -400-1000,de¡ivedclastsinS south,SW localized

zJ

o

IIìANNE

minimalinnorth,mæked inSouth

minor

rnajorglacialsediments,sandstone

mud¡ock

glaciatsediments,sa¡dstone

carbonate maficvolcanisminupper unit

maJor

major

Code for Strati-

Code for Stratigraphic units, see Figures 3 and 4.Sources are \Vells et aI. [1970], Jones [1972], Black et al. Ii980], Parker et aI. [1987], Shergold et af. [1985], Shergold [1987].

example, the basic Wantapella Volcanics whichoverlie sequence 2 (Sturtian) glacials in the easternOfficer Basin are suggestive of extensional tectonismthere [Preiss, 1987,p.202], as is the Mud TankCarbonatite which intruded the southeastem AruntaBlock at 735 t 5 Ma [Black and Gulson, 1978].Similarly, narrow, deep, northwesterly trending, enechelon troughs in the western Georgina Basin datefrom about the same time.

The middle stages of basin development. Amajor change in the development of the AmadeusBasin took place at the end of the Proterozoic, duringdepositional interval4, when the main axis ofdeposition shifted from the south to the north of thebasin. Distinct changes in basin geomety marked theonset of each of the intervals, and the intervalscoincide with continent-wide events. The overallfacies changed from the grey mudrock and sandstonecharacteristic of sequence 3 to red, arkosic sandstoneof sequence 4. At the same time, the "central arch"ceased to exist and was replaced by a monoclinalhinge (HL in Figure 13). The gross features of thene'w basin were maintained until the end of sequence6 and by the beginning of sequence 7 subsidence wasvery restricted.

Sequence 4 ûatest Proterozoic to EarlyCambnian): On a continent-wide scale, deposition ofsequence 4 in the latest Proterozoic star:ted with amarked contraction in the extent of stdimentation

@gure 10a; see also Cook, [1988]), which becamelocalized in interconnected troughs near the cenualeastern margin of the continent. Tlvo periods ofarkosic sandstone deposition have been reÆognized inthe several subbasins presently surrounding theexposed Arunta Block (see inset of Figure 7b). Thetwo sandstone units overlapped older units,producing basal disconformities in the Ngalia Basinand in the western and south central parts of theAmadeus Basin @gure 13). The units weredeposited concordantly in the deeper parts of twosubbasins (Carmichael and Ooraminn4 Figure 7b) inthe northem Amadeus Basin. and seismicstratigraphic studies indicate that the two subbasinsbecame disconnected during the time of deposition ofthe second unit [Lindsay, 1987a]. The westemCarmichael subbasin thickened markedlv northwards.whereas the eastern Ooraminna subbasirí thinnednorthwards, where it may have been linked with asmall, fault-bounded subbasin in the Georgina Basin(Figue 7b) which contained only the last phase ofthis sequence. The abrrupt southward decrease inthickness that formed in ttre Carmichael andOoraminna subbasins is refe,lred to here as the EarlvCambrian hinge line (tIL in Figure 13).

The Mount Cunie subbasin in the south of theAmadeus Basin @gures 2 and 7b) which was deep,narrow, and filled with arkose and conglomerate,does not appear to have been linked to the northern

Shaw et al.: I)evelopment of the Intracratonic Amadetrs Basin 695

(a )

=E

=EË

AMADEUSBASINNoñh

Fffi-Eil--- 'lüll¡1¡1i1¡,¡l.:!:iili.irj:ti:l _

H|+

ffi

F¡Elt

0 1000m

GEORGINABASINwost Central

NGALIA

AASIN

CANNING

BASIN

(b)

0 1000m

Amadeus subbasins. Similarly, subbasins in theNgalia and Georgina basins were not obviouslylinked to each other (7b). Overall it appears that therewere several small, substantially independentsubbasins.

A more restricted Eansgression in the late EarlyCambrian was characterized by red Archaeocyathidcarbonates across a wide region of subduedtopography in the Georgina Basin but did notpenetrate far into the Amadeus Basin (Figure 10b).Two subbasins in the northwest Officer Basin formedduring this period [Jackson and van de Graaff,19811. At the end of this interval, widespread plateaubasalts erupted at the periphery of the cennal

Australian region (Figure 10b), particularly innorthern Australia (e.g., Antrim Plateau Basalt) andmay have been related to bneakup of a supercontinentwhich included Australia, North America, andpossibly eastem China [Bond et al., 1984; Bell andJefferson, 1987; Lindsay et al., 19871. The bestconstrained date on the basaltic volcanism is anapparent age of 575 + 40 Ma for the Table HillsVolcanics in the Officer Basin (apparent Rb-Sr datelcompston, 197 4]). Unconformities developedabove the basalts Uackson and van de Graaff, 1981;Cook, 1988; Shergold et al., 1985; Walley, 19871suggest that the volcanism was followed oraccompanied by regional uplift.

NOÂTHERN WESTERN EASTERN

aMADEUS GEORGINA NGALIA OFFICER

sequence l i ! i [ - -- aDELATDE GEosyNcLrNE BAstN BASIN BASIN

s -Ë"'

H '---"-- -- -

tr El= ] æ a E E - æn H ñ l j : ì r

4b El---¿t

ti ffi,'.i'i-ïffiffi H ru

æ i==

H H f f i f f ï . H1ff i f f i t f f i ; tu

F æ-:rÊ=:#:# ffi E-a:-]æffi€oor,'t" ffin--#k n H.=.=-..--.-.........-- .-===-=:-l;iËL=¡i: '1 u E¡EEEEEæ Ël

7

f.,l fü..,:FtH r oIl

¡|.¡:r'¡4 F

Lal ll ËU -E E t r

Fig. 6. Time versus raw thickness bar diagram for the central Australian basins. a) Late_Próterozoic diagram for the cenFal Australian basins and the Adelaide Geosyncline basedon tectonosrratiþaphic correlations (see Figure 1 for basin distribution). The tectonicevents, shown as dbuble-dashed lines (===) and named events S, A, and R are thoseoutlined in Figure 5 and Table 2. Volcanics are shown as V pattern. Age intervals areprobable maxima. Correlations principally follow Walter, [1980], Preiss and Forbesltggt], Preiss [987], Brewet etal. [1987]. b) Diagram for the Paleozoic centralAustralian basins (Northern Amadeus, Georgina, Ngalia and Canning basins, see Figure1). Tectonic events are labelled as above. Named events, K, T, B, and D are thoseoutlined in Figure 5 and Table 2. Correlations adopted are after Shelgold et al. [1985],Wells and Mõss t19831, Forman and Wales [1981], læhmann t19841 and B. Nicollþersonal communication, 1987).

696 Shaw et al.: Development of the Intracratonic Amadeus Basin

COMPOSITE REFEßENCE FOR OEPOSITIONAL

INTERUALS IN CENTRAL AUSTNAUA

Ø

ffiffim:F::::-

H-+-++ÈEtrE!

mffiImNØlñlL:_1 Ì

=

A

sEouENcEs 2 & 3

121"30', 138" r27030'

tï.,.--Ttll - ;1 I- l

--.:: I^^^ |- - l>>>>-l

Ølf f i l€ o fA A I<r<<

|_ - - - - t

Soquence 2 Soquonce 3

sequence 2 DEPoCENTERS sequence 3

I ti.it" ot orr"roe

.*..- 1L Interrcd ilmtt

+J otdensition

Western lim¡t ofcatbonate deDos¡tiøn

oC L Ax¡s of msximum--t ) depos¡t¡on

>>>> l>*> rffi^ ^ 1¡¡r-|-

4 r

Minimal depos¡tionallimìts

Depocenter

Arch w¡thconglomcnte

Congtomercte

Glac¡ogen¡c sediment

lnfeïed active fault

:::lI Lim¡t oÍ onlap by

-- |

younger units

= lNB-.--- - çu.-

-' oa

-\ -l- - ls -- -N\ \ \ _ - - s \ \ . 2 - _ )

r 28.I 38.

-4 lounget lot oldol

HGrl Sttuctunl fedture

Fig. 7. Basin shapes in central Australia during late Proterozoic to mid-Paleozoicmegasequences 2-9. Smaller boxes highlight active depocenters within Amadeus Basin(AB), Georg¡na Basin (GB), and Ngalia Basin (NB). Tectonic and depositionalfeatures:are RZ, Redbank Thrust Zone; WB, Walabanba Fault Zone (Trough); SF. Sir FredericFault; PN, Petermann Ranges Nappe; WT, Woodroffe Thrust; BT, Black Hills Thrust;GT, Gardiner Thrust; and WL, V/oolanga Gravity Linearment. (a) Late Proterozoicsequences 2 and, 3. A is narrow arch separating subbasins; WX is zone ofaccommodation. (b). Latest Proterozoic to Early Cambrian sequence 4. GS isdiscordant geological structure including Goyder Pass Structure (G) and IllamurtaStructure (I); CD is western limit of initial sequence 5 transgression (ChandlerFormation). (c) Mid- to Late Cambrian sequence 5. F (Finke Line) is abrupt facieschange; DI is Davenport Inlier. (d) Latest Cambrian to mid-Ordovician sequence 6. A andB are two subbasins within the Georgina Basin outlined by the Toko Group. (e) LateOrdovician sequence 7 and Silurian? to Early Devonian sequence 8. (Ð Early Devonianto Carboniferous sequence 9. OF is Oomoomilla Fault; DS is Delny-Mount SainhillFault Zone.

f lB.f-:-- \-{o cE

- : " -1 - - ' \ v= \ r\ - - - ¡ \ \

¿ ' - l ¿ * . - ¡ '\__-/'\J"

r"dd,i,", f 17)Dotønile

L *

l f f ituñhß |ssndstonê 1 """'co,.atarês

| ___

SEOUEilCE 6

n*.u"^ | EsÐdfØé

1 o_o

uoø¡cu;e f E'j,liconstonara.e L:-.

Chdndlê. .#

DEPOCENTERS

Ø upPe¡rokoG¡ouP

F:?iÌ -]

l ï i r ¡ : l Ioo

I Low¿¡rôkoctouq

N ÐjâsênaßN Fotñør¡on

I v-nt -

c"h1;:d", 1Wsed¡moãts

L--..:

T Nl N

uia'canotml ffiS6dinenß

t - -L <<<<

sEouEl'¡cE 7 & I

Ø1ffi |

so'a'r s"a*onu

- - j

ffilllllllllì | "'-*' "-oo"'----l

I F.llSequer.e 5 |

*(Pêtøooñ' | ÍIlllfil

Gþ! i le 1 wcûÆÆþs

L êo

(t)

€o

l-l

o

5(D

(l

ñc)

C)

o

Ø

DEPOCENTERS

Fig. 7. (continued)

'rlllllilllllilr*-/-

¿¿lr'

Y|t- o._____________30*

¿ | secuoøce7 lcañ¡chaelm i sañdstonêJ

u M l

M | """"".""" ,{i;:i:",- l

ffi Seouencea?.ßeî¡dySEDdslonê

Shaw et al.: Development of the Intracratonic Amadeus Basin

F;t;¡r . ' . ' : , . 1

iT]Tnlli l l l

TAl . / A

N

) ,"u"

J

s;rrstone

1 ,",r",n"uu,o

)

sandstone

f - - t I

m I sandstonet t t! l

l - . .1 IL2)-) | Brewer--- )

Conglomerate

E I Mount Ectipse

[ïIl ] "'n'"'o'"

N B \ ^ . ' G B(-\,

-:'.?î::Ì:- -:-\\

-< : : - - - - - - l= - t - - - - - - _ /

\ = _1 3 8 " 1 2 9 '

) 26"I 38" 1 29.

) 26"r 38"

Stage 1{ Mid- Devon ian)

The felsic and minor mafic volcanics(Mooracoochie Volcanics) near the inferred cratonmargin in the Warburton Basin (see Figures 1 and10b) are ma*edly altered, highly differentiated, andlack definite andesite [Gatehouse, 1986]. The maficrocks are too altered for a definite origin to bededuced, but thet relatively high TiO2 contents areconsistent with a continental setting. The low Al andSr contents of the high silica rocks suggest an originby crustal melting. These may represent ensialicvolcanism rather than volcanism in an island arcsetting as concluded by Gatehouse [1986]. Thesevolcanics may have formed in an extensional setting,possibly on a rifted marginal plateau of ttrinnedcontinental crust.

Sequence 5 (Mid to Late Camb'rian): Thissequence, including most of the Pertaoorta Group,spanned most of the remaining par:t of the Cambrian.

Figures 7c and 13 summarize the basin shape duringthis interval, and Figures 10c and 10d summarize thecontinent-wide pattems of sedimentation andemergence. A widespread, but possibly short-lived,break in sedimentation at the start of depositionalinterval 5, at about the early Middle Cambrian, orOrdian (Figure 5), was followed by depositioncha¡acterized by peritidal plaform carbonate. Thisbreak occurred in both the Amadeus Basin and muchof the Georgina Basin (Figure 68) [Morris, 1986;Shergold et al., 1985; Walley, 19871. Thedepocenters of the Carmichael and Ooraminnasubbasins in the north of the Amadeus Basin (Figure7c) formed during the previous interval, shiftedslightly in position, and became linked while, at thesame time, the basin progressively expandedsouthwards and overall rates of subsidence increased.An abrupt facies change between carbonate and

Stage 2

{ Late- Devon ian)

Fig. 7. (continued)

stage 3(Late Devon¡an-Carbon¡ferous)

N B \- 1 ì ^ - '

G\-- GB

a A Bt s - - _

( i i ) DEPOCENTERS

N2>- [ñJ cB2-=l>s -*\- - - \ - - ' - - r -

AB

\ - - _

Fig. 9. Distribution and dominant facies of Late Proterozoic sedimentation. (a) Sturtianglacial period (megasequence 2) and (b) Marinoan glacial perid (megasequence 3).

Fig. 8. Paleogeographic sketch at megasequence 1time showing broad-scale, interpretâtive isopachs fortwo phases of sedimentation (regions of presentlyexposed early and middle Proterozoic and Archaeanbasement are shown by a cross (+) pattern). (a)Dstribution limits for the basal quartzite units(comparable to Heavitree Quartzite) outlining regionswith greater than 500 m of sediment plus maximumthickness estimates (in kilometers). (b) Distributionlimits for the inferred regions of maximum depositionfor the overlying carbonate and shale-dominaied unitsin the upper part of sequence 1 (comparable to BitterSprings Formation). Maximum thicknesses (inkilometers) are indicated. The distribution of maficvolcanics is also shown (v pattern). Assumedtectonostratigraphic correlates of Heavitree Quarøiteare: Dean Quartzite (?), Vaughan Springs QuaTownsend Quartzite, lowerLefroy beds, basalare: Dean Quartzite (?), VaTownsend Quartzite, lowerTownsend Quartzite, lowerLefroy beds, basalquartzites of Bura Group, Yackah beds, Denisonbeds, Lewis Range Sandstone, Muriel Rangebeds, Lewis Range Sandstone, MurSandstone, and Munya Sandstone (Sandstone, and Munya Sandstone (compare Figure6a). Tectonic features are T, Torrens Hinge Zone;W, Woolanga Gravity Lineament; E, EnnuganGravity Lineament; L, Lake MacKay GravityLineament; and A, Angus Gravity Lineament.

Springs Quartzite,

ngeZnne;

Fig. 9. (continued)

-jvs?-=_::17

( a) eu¡¡" . r CAMBRIAN (- TOfvIMOTTAN)

"dffi,I'*****{[Jli. ] . . .1.q.t'.(!:-* \ ' " /: , : /

+ f \ t

: . . , v

+ + ++ +

+ ¡ t + +l.l +

*trË

^ -N

^M

.l&",'a-! >

,

(C) eu¡ ¡ " " t MIDDLE CAMBRIAN ( - oRDIAN)

fl coroto-.rur", êrkose, iññaturc sediment

ffi s"ra"rorr, sandstone 6 shate

Nl oor"-,i", evaporite, chefr. shate

lM cu,bonut",

"h"t"

(b) e"¡v -caùtentAN {- n1¡ato* 'ot ,

fi sn"b. trroian. I *1 tur"^"n, r6/a,ro

Fig. 10. The evolving Australia-wide pattern of sedimentation and emergence in the EarlyCambrian (Sequence 4) and Middle Cambrian (Sequence 5). (a) earliest Cambrian (circaTommotian), (b) late Early C-ambrian (circa Atdabanian), (c) earliest Middle Cambrian(circa Ordian), and (d) mid-Cambrian (Iempletonian to ldamean). M is MooracoochieVolcanics.

+

+

4llllt; É=+-lffi

Felsic exttusive, rull

I n t e rñ e dìa t e ext¡u sive tu fl

Limit ol trcnsgrcssionldashed wherc infeffed)

Shaw et al.: Development of the Inracratonic Amacleus Basin

(a) EARLY ORDOVICIAN

Mailne deposit¡on

Teffestria I sedimentation

Deeper-water marine facies

Emergent with erosion

U nclass ified, ma i nly la nd

Present day basement

- L¡mit of mailne transgrcssion

--- Limit of teftestilal sedimentation

- l¡f¿¡¡¿¿l Ective fault

- -- Zone of decoupling

^ Felsic volcanics

u Mafic to intemediate volcanics

70'l

(b ) MrD-ORDOVTCTAN

mt7vÀ17::;:l

ffiF.]r-r-r--ÌÌÌänl::;:;ri:;:::j:l::::l

Frrl r : r : It!:1,-:i:ll : { . : r r . : r l

l : i i r : ! i i : l

Fig. 11. Evolving Australia-wide patterns of sedimentation and emergence for the periodfrom Early Ordovician to Late Silurian (megasequences 6 and 7 and lower sequence 8).(a) Early Ordovician, (b) mid-Ordovician, (c) Late Ordovician to Early Silurian, and (d)Middle to Late Silurian. (Present-day Precambrian basement areas Íre also shown toprovide a reference framework).

I .ATE ORDOVICIAN TO EARLY SILUR MIDÞIE TO I-ATE SILURIAN

Shaw et al.: Development of the Innacratonic Amadeus Basin

(a) EARLY DEVONIAN

(c) LArE DEVONIAN

_ tl::Mìtit:ì:i:::il\iir

(b l MrD-DEVONTAN

( d ) EARLY CARBoNIFEROUS

_ t

EF

_ l

W wmmffit:i::ri::l:i:r::::I

lfiil:iiril

ffitF:ll,;,:i',;,,i,,1

Marine deposition

Te üe stil a I s e d i m e nta tio n

Deepe r- wate r marine fac ies

Emergent with erosion

U ncla ss ified, ma i nly land

Present day basement

Limit of marine trcnsgress¡on

Limit of terrcstial sedimentat¡on

lnferied active fault

Zone of decoupling

Felsic volcanics

Andesitic volcanics

Fig.12. Evolving Austalia-wide patterns of sedimentation and emergence for the peridfrom Early Devonian to Early Carboniferous (upper megasequence 8 and megasequence9). (a) Early Devonian (megasequence 8), (b) mid-Devonian (circa 380-390 Ma), (c) LateDevonian, and (d) Early Carboniferous. Tectonic features are C, Calliope Volcanic Arc(Figure 12a) and A, Connors-Aubum Arc (Figure 12c).

Shaw et al.: Development of the Intracratonic Amadeus Basin

s f N

i.l'--------ljo* '/

l';./V

,B

JÃ

I ru"ffiry7

5

Fig. 13. Outline of the stages of morphologicaldeveþment in the Amadeus Basin. Basin shapesare distinctive for each megasequence. Sequence 1appears to be relatively uniform in thickness and isnot shown. Major conglomeratic units a¡ehighlighted. Section lines are located in Figures 7a to7f. "X" is at latitude 24oN, longitude 123oS.Tectonic features are: A, late Proterozoic a¡ch andHL, interval 4 hinge line. Basin shapes are based onraw sediment thicknesses. Where the basin edge isnot preserved basin shapes are inferred byextrapolation. Inferred active faults are also shown.See text for discussion of inferred active faults.

clasúc deposition ("Finke-line", F in Figure 7c)parallels a northwesterly zÐne of thinningimmediately west of a line of discontinuous structuresnoted in Figure 7c (i.e., G,I; see also Cook t19711).Red sandstone deposition continued in both theNgalia and western Amadeus basins.

The rapid subsidence and progressive onlap isalso seen in the Georgina Basin which expanded tothe west and northwest (Figures 7b and 7c). Herethe Middle Cambrian depocenters were grabenlikestructules with a norttrwesterly trend whose positionschanged little with time. Iæal and rapid faciesvariations at the basin margin [Morris, 1986] areconsistent with syndepositional transçurrent ornormal faulting.

On the periphery of the central Australian regionthe break in sedimentation at the start of interval 5corresponded to the end of the basic volcanism and tothe start of the most widespread transgression duringthe Cambrian, which covered much of thenorthwestern craton [Shergold et al., 1985; Cook,19881 @gure 10c), and which marked the beginningof subsidence in the Bonaparte (Gulf) Basin. Theeasterï craton margin at this ståge may havecorresponded approximately to ttre Tasman Line(Figures 9a and 9b lHill, 1951]; see also Murray etal. [1989]). Basal units of alluvial conglomerateresting on basement at the eastem and westernmargins of the Georgina Basin suggest that basementuplift and erosion preceded the widespreadtransgression in these flanking regions (e.g., DI inFigure 7c) [see Walley, 1987; Shergold et al., 1985].

Sequence 6 ûatest Cambrian to mid-Ordovician);This sequence conesponds to the Larapinta Group(Figures 3 and 4). Figure 7d summarizes the basinshape during this interval andFigures 1la and 11bsummarize the continent-wide paleogeography. Theinterval started with a widespread erosional break,known in the Ngalia Basin as the BloodwoodMovement [Wells and Moss, 1983], which maycorrespond to the Delamerian Orogeny in theAdelaide Geosyncline (Iable 2andD in Figures 5and 6b) [Shergold et al., 1985; Rutland et al., 1981;Parker, 19861. An Idamean faunal gap in theAmadeus Basin suggests the occurrence of a basin-wide hiatus, whereas in the Georgina Basin thecorresponding bneak may have occurred slightly later[Shergold et al., 1985]. A break in deposition alsooccured in the Officer Basin [ackson and van deGraaft 198 11. Very localized pegmatite wasemplaced in the southeastern Arunta Block at 520 Ma[Mortimer et al., 1987] possibly during the sameevent (Figure 5). Following this break insedimentation, the Amadeus Basin initially contracted(Pacoota Sandstone time) and a new depocenter wasformed (compare Figures 7c and 7d). Throughoutsequence 6, ttre facies were consistently uniform,being sand dominated and ma¡ine. After this initialcontraction the basin expanded sporadicallysouthward, overstepping sequence 5. There was aretun to an east-west elongation, in contrast to theprimarily northwesterly transgressions thatchuactenzed, sequence 5. The southward expansionof the basin suggests suMued topography to thesouth. A unit of probable Ordovician age in theNgalia Basin @jagamara Formation) may correspondto this period, suggesting that the main basinexpanded northwards as well as southwards. In theGeorgina Basin, two linear, asymmerical andnorthwesterly trending subbasins formed (outlined bythe Toko Group; A and B in NE of Figure 7d).

During the Early Ordovician the Amadeus Basinwas connected to an open ocean in the east (Figure1la; see also Powell t19831). By the mid-Ordovicianthe basin appears to have also been connected to anopen ocean to the west through the Canning Basin(Figure llb) [Kennard etal., 1986]. Carbonatedeposition became dominant in the neighboring

Shaw et al.: Development of the Intracratonic Amadeus Basin

Alice SpringsOrogeny

Permja:a Movement

(Ð

Rodingan Movement

(B)

hiatus at base ofsequence 6

(D)

Peærmann RangesOrogeny

GI)

Tabber¿bber¿nOrogeny (380-390Ma)

Benambrran Orogeny(43G440 Ma)

Delamerian (about505-520 Ma)Faunal gap inGeorgina Basin

l¡werCamb¡ianEarly OrodovicianMiddle CambrianDefonnation

Huckitt¿ Movernent(Georgina Basin)

folding

warping, folding,block faulting

localized faulting

foldingdiscontinuity,folding

discontinuity

east-viest folding,srike-slip faulting;widespread NEfolding; hiatusove¡ much ofAusu-alia ftommid-Ordovician

D1 folding about505-520Ma Þ

folding about 48G495 Ma

Jukesian foldingfolding, thrusting

erosion at top ofMopunga Grroup

Petermarn RangesNappe

hiatus below andwithin YuendumuSandstone

mild regionalunconformity

unconformitybetween Pinyinnaand Winnall beds

block faultingprecedes uplift andregional erosion

deformations I and 2

uplift and erosionfollowingemplacement ofStua¡tDike Swarm

high temperature,low pressure

meømorphism; openfoldine

Basins

Tæmanides: Hill EndTrough

Drummond, Darlingand Adavale Bæins

WarrabinTroughSouth l¿chlan Fold

Belt

South l¡chlan FoldBelt Àd¿vale Basin,DarlingBasin inEast (Cobar, NSW)

South I¿chlan FoldBeltThomson Fold Belt

Kanmantoo Fold Belt

WestTæmaniaWestTæmania

Georgina Basin

C¡ntral, western andsouthem AmadeusBasin

South Amadeus Basin

Ngalia Basin

Adelaide Geosyncline

Ngalia &WestGeorgina Basins

South AmadeusBasin

Ngalia, Georgina andAmadeus basins

WestTæmania

A¡unta baæment

South A¡unta Block

TABLE 2. Corælation Bemeen Unconformities and

MountEclipseOrogeny

Kanimblan Orogeny(32G350 Ma)

zJÁ

I

15J

615

18't589l4

(H)?580-605

-43ù4ø,0

-49ù525

s8G,605

680-700

800-750

865-900

1200-1100

1 1

12, t31920

J

2 , 3 , t 7

South RangeMovement

(s)

Areyonga Movement

(A)

An¡ntaMovement

(R)

Ormisontec1oth€fmâIevent

Duttonian tectonism

RinkabeenaMovement

Vaughan SpringsMovement

Sturtia¡ tectonism

Penguin Orogeny

nonconformity overmuch of continent

Kulgeran æctonism

5

J

t

2 l

10

161 7

1, \ùy'elts et al. [1970];2, Wells and Moss [1983]; 3, Frceman [1986]; 4, Powell et al. [1977] and Powell [1984];5, Fergusson et 4_, [l-9861; q,-Rary?yan¿ Van¿en¡eig t19ú7I 7, Deselins et a[ t1986]; 8, Munay [1986]; 9,]tr/rcbby et al. {19811; 1_0, Black e! f . [t_lapl_¡ t l,,195!9!11?!6] 1.2, S_!91g9_ld_e1at. tl985l; 13, S-hèrsold'tlg82ñ t¿,Ìranison tr980l; 15, Dóuich and Nichglq! tt978! 16, Wilson et al. [1960] cf. Weþþ tle!.S-li !1, Preiss [1987]; 18,Gleì et ai. t19861; 1-9, Banks ana s¡Ue ttggSl; 20, Berry and Crawfo¡d [1988]; 21, Tumer [1989]i and22, Shaw and Black [1990].

* Time scale of Ha¡land et al. [1982]; Age range estimated from references listed.f See Figures 3, 5, 6a, and 6b.

Shaw et a1.: Development of the Intracratonic Amadeus Basin

Canning and Georgina basins. In the Canning Basinthere is evidence of NE-SW extension initiating theFitzroy Trough in the Ordovician [Purcell and Poll,19841. At ttre same time subsidence rates in thenorthern Amadeus Basin appear to have markedlyincreased (Figure 5).

Sequence 7 (Late Ordovician): This sequence(Carmichael Sandstone), deposited in the LateOrdovician, is of short duration and mightalternatively be grouped with sequence 6. Wedistinguish it because it signals the onset of aprofound change in basin shape (Figure 7e). TheCarmichael Sandstone comprises a mixed fluviatileand marine unit that appears to be concordant withsequence 6 in the west of the basin [Webby et al.,19811. The infened depocenter and westem limit ofdeposition are illustrated in Figure 7e althoughconstraints on this geomeby are poor. There is asuggestion that the sediments thicken and arefluviatile and coarser grained than to the south, incontrast to sequence 6. No clearly defineddepocenter is apparent but a marked shift in the axisof maximum deposition from that of sequence 6suggests that there may be a short-duration time breakat the base of the unit and some change in the tectonicdriving forces.

The finalstages are best i 7e and7f.

A long-lived and widespread b¡eak in sedimentation is

Because of the poor age constraints, the rates ofdeposition are uncertain. The clean quartz sands areof mixed aeolian, fluviatile and arguably shallowmarine facies, characteristics that all suggestextensive winnowing and slow sedimentation. Thelack of immature sediments suggests that the nearbysource region lacked significant topography. It isapparent that in the northeast of the basin the largescale tilting occurred before or during sequence 8deposition, with the sediments to the east being

overlie the Merepnie Sandstone with only a minorerosional break (Figure 6b). Three depositionalstages are recognized, associated with distinctchanges in basin shape during this period (seeFigures Tfand 13).

1. The subbasin of the first stage, defined by ttremid-Devonian Parke Siltstone, is narrow andindicative of short wavelength (5 100 km) warping.The subbasin is obliquely inclined to the trace of theRedbank Thrust Tnne @ZinFigures 7a amd 7Ð andthe basin margin. The unit is continuous northwardsto the preserved margin without any sign of amarginal facies, and this suggests that it may haveextended considerably beyond the present margin.

2. The subbasin óf thê second init of sand-andconglomeratic sand, the Late DevonianHermannsburg Sandstone, is again oblique to thestructurally upturned basin margin, and its depocenteris to the south ofthat ofthe ea¡lierphase, close to theGardiner Thrust.

3. The depocenter for the third stage liesnorthwards of the second-stage depocenter and thebasin locally onlaps abnuptly onto the upturnednorthern margin of the basin possibly in response tosalt movements @radshaw and Evans, 1988). Thettrird stage of the subbasin cont¿ins a minimum of 2-3 km of preserved conglomeratic, molasselikesandstone and conglomerate (Late Devonian BrewerConglomerate).

In general, phenoclasts deposited during thesecond and thi¡d stages coarsen upwards, and clasttypes distinctive of each formation and basementclasts indicate erosion of 4-5 lcrn of section to exposebasement along the northem basin margin. The rateof deposition appears to have reached 250 mffa ormore [Jones, 1972; Shaw, 1987]. Evidence fromfour K-feldsp*40¡¡p9¡l age spectra from theArunta basement suggest that basin margin upliftstarted in the Late Devonian and that the site ofmaximum uplift moved southwards with time, thatsedimentation continued well into the Carboniferousand that ttre final uplift at the site of the uptumednorthern basin margin occurred in the mid-Ca¡boniferous (320-300 Ma) [Shaw et al., 1989].

In the Ngalia Basin, at least 2.2kmofsynorogenic arkosic sandstone, the Mount EclipseSandstone (Figures 6b and 7f), are recognized ashaving been deposited during thrusting of basementover the northern basin margin between the latestDevonian and the late Early Carboniferous (i.e.,

referred to as the Rodingan Movement separatessequences 7 and 8, and corresponds to the LateOrdovician to Early Silurian Benambran Orogeny inttre Tasman Orogen Clable 2 and Figure 11c).Sequence 8 comprises the Mereenie Sandstone,whose age is poorly constrained because it lacksfossils but is generally assumed to be Silurian toEarly Devonian. The main depocenter for thissequence is farther south than that of the earliersequences and appears to be unrelated to that ofsequence 7. The main depocenter is approximatelyover the Gardiner Thrust and the stratigraphicthinning there of both older and young sequencessuggests that sporadic movements occurred on thisthrust over a prolonged time interval. There is asuggestion of secondary segmentation into three enechelon subbasins [Wells et al., 1970, Figure 34].The sediments of the sequence I exhibit rapidthinning at the northern and southern basin margins[Wells et al., 1970] and this suggests differentialmovements there at the time of deposition. The basinmargins are interpreted to have been close to thepresently preserved margins of sequence 8, assequence 8 is overstepped by sequence 9 in thenortheast ofthe basin (Figure 7e) [Kennard et a1.,19861. In the central westemmost part of theAmadeus Basin, sequence 8 appears to concordantlyand gradationally overlie sequence 7 [work of MOwen, as discussed by Kennard et al. [1986]suggesting that any time break there is minimal,whereas in the northeast a considerable section(1300 m or more) appears to have been removedduring the Rodingan Movement.

of this sequence (Pertnjara Group)

Visean lWells and Moss, 1983]). As such thesesandstones are slightly younger than the youngestpreserved Late Devonian B¡ewer Conglomerate in theAmadeus Basin [see Playford et al., 1976]. Vitrinitereflection data [Jones, 1972] andpreliminarymodelling of K-feldspar404tp84¡ age spectra [Shawet al., 19891 imply that L krn or more of additionalsediment existed at the northern margin of the basinand has since been removed. The correlate of the twoearly stages of the sequence in the western GeorginaBasin is the Dulcie Sandstone which forms anasymmetrical northwesterþ trending basin containingrelatively mature sandstone. The early stages of thistectonism in the Amadeus Basin correlate withsubparallel extensional tectonism in the CanningBasin [Figure l2c, cf. Purcell and Poll, 1984].

BASEMENT STRUCTURE AND UPLIFTHISTORY

Constraints can be placed on the nature of thetectonic driving forces by determining the spatial,temporal, and geometric relationships between basinsubsidence and the uplift of basement surroundingthe basin. In this section we review the gross crustalstructure in the central Australian region andsummarize new and published data on the uplifthistory of the northern and southern margins of theAmadeus Basin.

Basement Structure

The central Australian basins coincide with aseries of Bouguer and free-air gavity peaks andtroughs of exceptional magnitude, implying that thedeep-seated structure is also of unusual magnitude(Figure 14). Gravity peaks correspondapproximately to exposed zones of uplifædgranulites, and the gravity noughs alignapproximately with underthrust granitic crust,amphibolite facies rocks and the thicker parts of thebasin sections [Forman and Shaw, 1973; Mathur,r9761.

The southern margin of the Amadeus Basinappears to have been a major reverse fault, whichwas active at various times throughout basindevelopment (Figure 13). Farther to the south theV/oodroffe Thrust (Figure 14) ovenides basemenrand, at its eastern end an offshoot of the thrustpossibly also overrides sediments [Forman andShaw, 19731 (further discussion below). Thenorthem margin of the basin is a complex thrust beltmade up of north dipping, southerly directed rhrusrs(Figures 14 and 15), and its structure is sufficientlywell constrained from both structu¡al and geophysicalstudies to enable the link between basin subsidenceand basement uplift to be examined quantiøtively.The whole northern thrust belt is, on average, onlyabout 30-50 km across. It is dominated by twoprincipal thrust complexes, the Redbank Thrust Zone

Shaw et al.: Development of the Intrac¡atonic Amadeus Basin

(RTZ in Figures 14 and 15) which is a 5-10 km widezone of a¡astomosing mylonite, and the nearbysubparallel Ormiston Thrust Zone (ON) (refened tohere as the Ormiston ThrusÐ (Figures 14 and 15). Attrird zone of faulting underlies a regional monoclinalflexure at the basin margin, referred to as theMacDonnell Homocline (orAmadeus) (MH, Figure1s).

The principal master thrusts of the RTZ dipnorthwards with surface dips ranging from 30o to 70owith an average dip of about 45o. Seismic reflectiondata down to at least 40 km show no evidence for thedip becoming shallower with depttr [Goleby et al.,19891. The Ormiston Thrust has near surface dipsranging widely benveen 30o and 60o along much of itslength, although down plunge cross sections showthat it shallows upwards and westwards. Basementreverse faults underlying both this thrust and thehomocline dip at about 70o @igure 15, see alsoMajoribanks , ï197 6l). That is, the thrusts do notappear to shallow progressively towards the forelandas is the case in a typical imb'ricate thrust belt.

Multiple detachment zones are exposed incarbonate sequences at the base of the upturnedsedimentary sequence at the homocline edge. Thesedetachment zones are thought to have formed as thesequence was progressively overturned in front of"thick-skinned" basement thrust wedges to the north[Shaw et al., 1991] (see also Majoribanks I19761).At the northeastern margin, cover nappes formedahead of and above southerlv directed basement-cored nappes (Figure 14mip, see also Stewart andOaks t19871). There, the presence ofa higher saltunit (Chandler Formation) allowed a seconddetachment zone to deveþ. Southward translationin the northeast was facilitated by ramping and thetansferring of thrust movement to a shallowerdetachment zone.

Teleseismic travel-time anomalies measuredacross the basin and Arunta Block along two north-south lines ofclosely spaced recorders, as well asgavity data, surface geology, aeromagnetic data, andpetrophysical properties of the exposed rocks, can beinterpreted in terms of a model with a singlemegashear, corresponding to the RTZ, whichpenetrates to mantle depths at an angle of about 45o.A variation in depth of the Moho of up to 20 km,over horizontal distances of less than 50 km, isrequired by these geophysical data, implying anunderthrust keel of lower crust south of the RTZ andupthrust lower crust and upper mantle north of itll-ambeck et al., 1988]. The seismic reflectionrecords support the view that the Ormiston Thrustmerges with the RTZ at depths of about 20 km[Goleby et al., 1989]. Thus it appears that the RTZis a major deep-seated fault and that the OrmistonNappe is accompanied by minimal thin-skinnedimbrrication. Much of the crustal shortening in theAruntaregion can bg..dccounted for by displacementsacross the Redbar*-and Ormiston thrusts. Balancingof c¡oss sections down to the depth of the Mohosuggests that shortening of the order 40-60 km has

MUSGRAVE BLOCK AMADEUS BASIN

ffis"ai-",,ua,o"k ffii::l::.::;;mph¡borite ffi?{TÍ,1:,"ri","",o"r ffi øaatre

1 Thrust-fault -*- Synctine j6/Nr/sro- Geological - Faultboundary

Fig. 14. Map and interpretative crosssectiou showing crustal scale structural features incentral Australia and their relation to the Bouguer gravity profile [revised after Formanand Shaw 119731, \ñ/ells and Moss [1983], Shaw et al. [1984], Webb [1985], andLambeck U9911. Faults dashed where concealed or position approximate. Tectonicfeatures are ANC, Arltunga Nappe Complex; BT, Black Hills Thrust; CB, CanningBasin; CT, Cadney Thrusq IC, Illogwa Schist Zone; LG, Iævenger Graben; MT,Munvadai Thrust.

Shaw et al.: Development of the InFacratonic Amadeus Basin

AMADEUS BASIN

occurred since inception of the RedbankThrust in themid-Proterozoic [Shaw and Black, 1991]. This is incontrast to the 50-100 km suggested by the thin-skinned style of model [Teyssier, 1985] in whichsteep imbricate thrusts were envisaged to branch froma relatively shallow dipping master sole tlrrust whichdates from the Alice Springs Orogeny.

The crustal structure of the southern basin marginis similar to ttrat of ttre northern margin (Figure 14).Modeling of teleseismic travel-time anomalies acrossthe southem margin þambeck and Burgess, 19901suggests that the shallow south dipping WoodroffeThrust steepens at depth in the region of the MannThrust (WI and MF in Figure 14 cross section). Inthe central and southern parts of the basin a region ofthin-skinned north directed thrust system is identifiedfrom surface structural and reflection seismic data[Shaw et al., 1991]. This thrust system appears tohave its root at the southern margin of the basin (seethe work of B. Simmons as discussed by Edgoose etal. [1990]) and may link up with the WoodroffeThrust at depth @gure 14). Infolded outliers ofsequence I rocks at the southwestern margin of thebasin have been interpreted to make up the PetermannRanges Nappe (Figure 14) [see Forman 1963,1966).

Uplift History of Northern Basin Margin (AruntaBlock)

The uplift history of basement in the hinterlandno¡th of the basin has been examined in detail byShaw and Black [1991] using Rb-Sr methods and byShaw et al. t1989j using x-Ài a64o¡¡pe61methods. The main results of these studies are asfollows.

1. Two ages of southerly directed overthrustingare indicated for the the Redbank Thrust Zone at1400-1500 Ma and 350-400 Ma. These twooverttrusting events arc separated by atectonothermal event at about 1100 Ma characterizúby high-temperature, low pressure metamorphism,migmatization and anatectic granite and pegmatite

EARLY STAGE

lffi carbonate,mudrock,w sandstone

2 5 k n

ç--V Gtanitoid, u.pt noì¡r"| \ | fac¡esrock

Fl^Å Granutite facies rock

emplacement. That no major shearing event isrecognized in the Redbank Thrust between about1400 and 400 Ma implies that movement on thiszone was not significant in this interval and that thisthrust did not exercise a major control onsedimentation in the Amadeus Basin until after about400 Ma.

2. a01r';p9¡ age spectra show that samplesimmediately underlying the region north of the basinwere uplifted to upper crustal levels, sufficient to coolthe micas through their closure tempemtures of 200o-300oC, by about 1100-1200 Ma. The most southerlysample sites were uplifted to upper crustal levelsbefore intrusion of the unmetamorphosed, high-levelStuart Dikes at about 900 Ma and to within 2 km ofthe surface before deposition commenced in theAmadeus Basin after 900 Ma.

3. Clasts in the sequence 2 and 3 sediments in thenorthem Amadeus Basin have been derived fromunderlying successively exhumed sequences andultimately from basement. This indicates that upliftand erosion of basement hinterland occured in twopulses at this time, to both the north and south of theAmadeus Basin [Wells et al., 1970].

4. The a06vp9 P spectra for K-feldspars over tlrcregion between the Amadeus and Ngalia basins implythat movement on the Redbank Thrust stafied slowlybetween 400-350 Ma and that movement on theOrmiston Thrust and in the adjacent homoclinecontinued until about 300 Ma.

Upltft History of the Southern Basin Mørgin(Musgrave Block)

The following events affected the basement at thesouthern margin of the basin.

l. A series of basement events, overlapping intime, occured from about 1200 Ma to 1000 Ma.These were, from oldest to youngest, granulitemetamorphism, intrusion of the mafic and ultramaficintrusions of the Giles Complex, the widespreademplacement of the Kulgera granites, and bimodal

I \4IDDLE STAGE

ffi Sandstone,mudrock.w carbonate

Fig. 15. Generalised north-south crosssection asross the northern Amadeus Basin, thesouthern Arunta Block, and the Ngalia Basin at longitude 132o40' from latitude 22"27.5'Sto 24"15'5. The final, middle, and early depositional stages are as in the text. Local onlapduring the final stage is shown schematically. Tectonic features are MH, MacDonnellHomocline, ON, Ormiston Nappe Thrust Zone and RTZ, Redbank Th¡ust Zone.

Shaw et al.: Development of the Intacratonic Amadeus Basin

vulcanism [Compston and Nesbitt, 1967; Daniels,1974; Mathur and Shaw, 1982; Page et al., 19841.Major uplift of the Musgrave Block at this timeaccords with widespread K-Ar mineral ages implyingcooling during uplift and erosion between about1120 Ma and 1000 Ma [Webb, 1985].

2. From palaeogeographic considerations itappears that the Musgrave Block was partlysubmergent at least in the west during deposition ofsequence 1 (see Figure 8, and Jackson and van deGraaff 1981).

3. Renewed minor uplift in the early stages ofsequence 2 deposition is indicated by clasts, probablyderived from sequence 1 and underlying volcanics,preserved in sequence 2 units in the western OfficerBasin [Jackson and van de Graaff, 1981], easternOfficer Basin (where rare basement clasts a¡epreserved [Preiss, 1987] and in southwest AmadeusBasin fWells et al., 1970].

4. An angular unconformity, recognized betweensequences 2 and3 in the southern Amadeus Basin[Wells et al., 1970], indicates that uplift probablyextended onto the basement to the south.

5. Some uplift and erosion of the MusgraveBlock is suggested during deposition of sequence 3by clasts derived from the basement as well as fromsequence 1 (in a conglomeratic phase of the Winnallbeds [Wells et al., 1970].

6. Uplift and erosion followed a period offolding and thrusting known as the PetermannRanges Orogeny and accounts for the unconformityseen between sequences 3 and 5 in the south ofthebasin.

Most of the uplift of the Musgrave Block, whichpreceded basin formation, is not readily related to thePetermann Ranges Orogeny at about 600 Ma asdefrned by D. J. Forman (discussed by Wells et al.t19701). The orogeny is centered in the northern partof the Musgrave Block, north of the WoodroffeThrust (see Figure 14), and produced folding in thecentral and westem parts of the basin [Cook, 1968;V/ells et al-, l970l. From a reassessment of regionalgeological relationships it is concluded tÌrat thePetermann Ranges deformation was much smaller inmagnitude and had substantially died out beforedeposition of sequence 4 (see below). Thedepositional history of the sequence 4 sediments isnot consistent with synorogenic deposition in front ofa major overthrust belt involving a giant fold nappe.In particular, the sequence 4 subbasin at the southernmargin (Mount Currie Conglomerate) is too nÍurow,of the order of 30 km, to be a foreland basin whichformed in front of a major nappe structure (sequence4 in Figure 13). To allow a basement fold nappe todevelop, upper greenschist to amphibolite faciesmetamorphic conditions are required beforepenetrative plastic flow can take place. However, theoverburden provided by sequences 2 and 3 (i.e., amaximum of 4-5 km) is insufficient to induce suchmetamorphic condiúons. Arkose and conglomerate,remarkably similarto the Mount CurrieConglomerate, occupy a small graben within theMusgrave Block [Webb, 1985; Major, 1973] and if

the latter arkose does indeed correlate with sequence4, then extensional tectonism may have affected theMusgrave Block at this time.

The Petermann Ranges Orogeny is considered tohave culminated immediately after sequence 3deposition. Clasts of sequence 3 sandstone (Winnallbeds) appear to have been litltified and redeposited inthe sequence 4 Mount Cunie Conglomerate based onthe work of D. J. Forman, as discussed by Wells etal. t19701) and substantial uplift of the MusgraveBlock may have taken place in the latest Precamb'rianduring or immediately after deposition of sequence 3,whereas sequence 4 appears to be substantiallypostorogenic. Rather than place the PetermannRanges Orogeny in the Early Cambrian, we proposettrat it was of smaller magnitude (see altemative crosssection in Forman t19631) and that it was initiatedearly in sequence 3 deposition and culminated withttre folding of sequence 3 rocks before deposition ofsequence 4 in narrow basins and its onlap bysequence 5.

TECTONIC INTERPRETATION OF AMADEUSBASIN SEQUENCES

Plau.sible Mechanisms of Basin Formationfor tluAmodeus Basin

Mechanisms of basin formation can becha¡acterized according to whether subsidence isprimarily driven by inplane, thermal, or gravitationalforces. In the first category, environments forsediment accumulation form as the lithospheredeforms in response to horizontal stresses actingwithin the lithosphere. These stresses may be eitherextensional or compressional. In ttre thermally drivenmodels the primary cause of basin formation is heatinput into the lithosphere, producing uplift followedby erosion and subsidence as the lithosphere coolsand responds isostatically to the redistribution ofmass. The gravitationally based mechanisms arethose where the lithosphere responds essentiallypassively to a redistribution of surface loads (e.g.,topography), for example, by erosion andsedimentation. Commonly, more than one of theseprocesses contributes to formation of an individualbasin. Basins such as the Amadeus Basin, whosehistory spans about 600 Ma from late Proterozoic tolate Paleozoic, are likely to exhibit a complexinterplay between the various mechanisms.

Several different single-mechanism models havebeen proposed for the Amadeus Basin. OleninÍ19671, Rutland lI976l, Veevers ll976l,Doutch andNicholas [1978], and Bozhkov t19861 proposed thatthe basin was an aulacogen formed by large-scalerifting where the other two arms formed the westemmargin of the Tasman Orogen. Veevers et al. U9841suggested that the basin was a giant pull-apart featureand that deposition was coeval with, and slightlyoblique to, several major east-northeast continentalscale transforms to the east. Lindsay et al. t19871

710

argued that all the central Ausfralian basins formed asa result of two failed rifting events, one initiated atabout 900 Ma and the second at about 600 Ma,followed by a compressional phase of inversion atabout 400 Ma. None of these models have beenquantified. Quantitative compressional modelsinvolving varying degrees of crustal warping andblock-faulting loads were proposed by Lambeckt19831 and McQueen and Beaumont [1989]. In boththese models the vertical movements in the centralAustralian basins and adiacent basement blocks areclosely linked.

Indicators of basin-forming meclønism

The nine episodes of subsidence (Figures 4, 5,6aand 6b) are each represented by lithologically andgeometrically distinct megasequencgg, andconsecutive sequences afe separated byunconformities. These episodes of subsidence can betraced over most of the central Australian region andcan be related to tectonic events occurring at itsperiphery (Iable 2). This, plus the absence of amajor thermal event within the region after about 900Ma, suggests that the primary basin-formingmechanism was the rcsponse of the lithosphere tohorizontal stress fields generated at the continental orplate margins and that the lithosphere acts as a stressguide over long distances [Richardson et a]., 197 9;Cloetingh and Vy'ortel, 1986; Lambeck et al., 1987;Ziegler, 1987).

Secondary Controls on Basin Formation

In addition to the principal driving mechanisms anumber of secondary processes amplify basinformation and may have been important at varioustimes throughout the basin's evolution.

These secondary controls include the following.1. Preexisting topography is likely to persist

between one episode of basin formation and the next[cf. England and Richardson, 1980; Stephenson,19841.

2. Simultaneous erosion from highs anddeposition in troughs on flexed and stressedlithosphere can cause resurgence of subsidence andamplification of the deformation. It is, for example, amajor factor enhancing lithospheric flexu¡e incompressional models [Lambeck, 1983; McQueenand Beaumont, 19891.

3. Stress-relaxation due to flow in relativelyductile layers of ttre lower crust or upper mantle, orbnittle failure in the upper crust, modifies the shapeand depth of preexisting basins. During phases ofcompressional basin formation the effect of theflexural sEess relaxation is to reduce the basin'swidth and increase its depth, by amounts that are afunction of lithospheric rheology, the magnitude ofthe stress-differences generuted, the ttrermal evolutionof the lithosphere, and time [Lambeck, 1983; Quinlanand Beaumont, 19841. During intervàls when

Shaw et al.: Development of the Intracratonic Amadeus Basin

compressional st¡esses a¡e reduced, stress relaxationwill produce a rebound of the earlier generateddeformation and a widening of the basin, assumingno permanent or plastic deformation, as ttre region asa whole attempts to reestablish a hydrostatic stressstate.

4. Differential compaction increases rapidly withthe depth of overburden and is greatest in the deepestpart of the basin. The resulting increase in sedimentload may be further accentuated by time-dependentdiagenetic processes such as dolomitization andsilicification related to fluid flow in preexisting andthicker parts of the basin [Gallagher and Lambeck,19891 and this may be one reason why youngersuccessor basins invariably preserve aspects of theshape of ttre precursor basin.

5. Changes in sea level generated by globaltectonic processes outside the region may account forsmaller-scale retrogradational and progradationalcycles superimposed on the mega cyclescorresponding to major changes in basin shape.These processes, including changes in the rate ofseafloor spreading or the breakup of continents, inthe latest Proterozoic and Early Cambrian, may havecontributed further to sea level changes in theintervals 4, 5, and 6. The melting of the lateProterozoic ice sheets would also have producedsignificant changes in sea level and may havecontributed to ttre widespread transgressions thathave been identified during the depositional intervals2 and 3. The maximum sea level change from eitherglacial or tectonic causes does not exceed a fewhundred meters and, on its own, cannot account forany of the Amadeus fluvial and shallow marinesequences, all of which have compacted thicknessesin excess of 900 m. Neither can sea level changesaccount for the varying amounts of subsidence withinany one basin.

6. Tectonic processes which operate within theupper crust, particularly within the basin sediments,may be only partly dependent on processes on thescale of the lithosphere. One example of this is theeffect of salt flowage, which may have had a majorcontrol on the development of the Amadeus Basin(Lindsay, 1987b).

Tectonic Development of tlte Amndew Basin

Sequence 9 (Early Devonian to Carboniferous):An examination of the tectonic development of theAmadeus Basin in terms of the evolving basin-forming mechanism is best treated by starting withthe most recent sequences for which the evidence isbetter preserved than older sequences, thepreservation of which was reduced by denudationduring the Devonian-Carboniferous Alice SpringsOrogeny (see Table 2).

An appropriate model for the Amadeus Basinduring the compressive phases may be the tilted faultblock model of McQueen and Beaumont U9891.Foreland basin models based on gravitational loadingof the lithosphere by subhorizontal, "thin-skinned"

Shaw et al.: Development of the Intracratonic Amadeus Basin

ttrust belts such as those of Beaumont [1981] neglectthe effect of the horizontal compressive force whichwill tend to magnify the lithospheric flexure andreduce the basin width and/or will make the plateappear to be flexurally weaker than it actually is.Figure 16 summarizes conceptually ttre results ofcalculating the loading effects of movement on alithospheric'thick-skinned" thrust fault using elasticplate theory in which the lithosphere is assumed tobehave as a broken semi-infinite plate. It is importantto realize that as a result of the interplay betweeninplane stresses, flexural stress, and surface loading,the overall driving force may be compressional andthe local response may be extensional depending onfactors such as depth, location, and changes inoverall stress magnitudes. The model succeeds inexplaining basin shapes deveþed during depositionof sequence 9.

In the preliminary models deveþed so fm,translation on a preexisting fault through thelithosphere is produced initially by the vertical

AMADEUS BASIN

Per¡pherclarch

Thick- skinnedfault

Main basin

[, *'L r 5 0 k m l

lal Th ick- skin n ed fau lti ng ( b roken plate)

lbl Positive feedback due to s¡multaneouserosion and deposition

component of the compressive force acting directlyacross the fault and not by the thrust sheets movingahead of their root zone as in the foreland basinmodel. The compressional forces cause thelithosphere to nìove upwards on the hanging wall anddownwards on the footwall as the plates flex inresponse to the redistribution of the stress @igure16a) in the manner demonstrated in the models ofGunn [1947]. The model incorporates the load of theoverthrust block and the load due to seawater orsediments filling the uough. E¡osion of the hangingwall of the fault and sediment deposition on thefoonryall increase the effectiveness of tltis mechanismand, by building up stress differences on the faultsurface, reactivate the faults (Figure 16b). Thusperiods of fault activity might be expected to altematewith periods of inactivity or even rebound. When thefault is locked, the load is disnibuted over acontinuous lithospheric plate and subsidence andflexural uplift takes place over a wider region. Thebasin depocenter and the peripheral arch migrateaway from the fault (Figure 16c). Uplift and erosionof basement continued after the deposition ofsequence 9, suggesting that the compressional stress,albeit at a reduced magnitude, may have persistedover an extended period after the main orogenic eventand led to the development of more complex structwein the upper crust (Figure 16d). That is, the stain inthe upper crust is distributed widely over a number ofthrusts at the northem margin of the basin, as shownin the deep seismic reflection image where severalmajor thrusts splay upwards and southwards fromthe Redbank Th¡ust Znne (RTZ) [Goleby et al.,19391. +oAtp9Ar apparent age spectra for K-feldsparsuggest that the thrusts young progressively towatdsthe basin margin and that displacements on the masterfault (the RTZ proper) need not have been more than2-3 km before movement was transfenedsouthwards onto the Ormiston Thrust. Analysis ofús a04r/694¡ age spectra also suggests that thecombined thrust wedge, including the RTZ, wasuplifted a further 8-10 km or more. A break insimple basinward translation of thrusts may resultfrom resistance to further uplift, due to the increasingload of the rising basement. Th¡ust stacking andback thrusting may occur, producing the uptum thatis cha¡acteristic of ttre northem margin of this basin.Unhindered southward movement of the thrustcomplex may also have been constrained by northerlydirected thrusting for which the Gardiner Thrustformed the leading edge (GT in Figure 14; see alsoShaw et al. [1991]). We consider that theconvergence of these thrust systems in the later stagesof the Alice Springs Orogeny resulted in the rapidnarowing of the forelandlike footwall basin.

In summary, sequence 9 is characterizedbysiltstone, sandstone, and finally, thick polymictic fanconglomerates deposited during thg Lge Devonian inresponse to major movements on the Redbank andassociated thrusts. Basin development at this stage isb'roadly comparable to that of the mature Wind RiverBasin [Berg, 1963; Brown, 1984] and also shows

NGALIA BASIN

Back basin

+

.>

T

* Back hasin

M¡grated dlpocentef(clStatrc loading of a continuous plate

(dlBasinwards migration of thrusts and progressivehomoclinal upturn of basin margin (sequence 9)

16/Nr/4a4

Fig. 16. Models for basin formation as a result of thetilting and flexing of fault blocks induced byhorizontal compression. S is the subsidence due towater loading in @gure 16a) and sediment loading in@igure 16b). E represents the eroding mountain; Uis the uplift due to buoyant effect of a load beingremoved due to erosion. T represents the mass of themountain topography acting oir a continuous platewith no inplane compression. X represents thepredicted migration of the peripheral arch. GT isGardiner Thrust; RTZ is Redbank Thrust Zone.

Perioheral :árch Main basin V

'IABLE 3. Comoarable Basins and Plausible Basin-Formine Me.ha¡ism for Each Mega-Sequence in the Amadeus Basin

Sequence ReferenceFormations TerminatingEvent ComparableBasins Mecha¡ism References

Pertnjara Group

MereenieSandstone

CarmichaelSandstone

upper Goyder-StokesFormaúon

Cha¡dler to lowerGoyder Formation

Arumbera SandstoneTodd RiverDolomite

Winnall beds

lnindia beds

Heavigee Quartzite,Bitter SpringsFomration

Alice SpringsOrogenylKanimblan

Pertnjara MovemeníTabberabbe¡an

Rodingan MovemenVBenambran Orogeny

hiatus (major change inbasin shape)

hiatus conelated withDelamerian Orogeny

disconformity

Petermann RangesOrogeny/tluckittaMovement

South Ralge Movement/Rinkabeena Movement

Aæyonga Movement/Vaughan SpringsMovement

WindRiver, Ta¡im

early Wind RiverEifel

Sverdnp

Sverdrup

Canadian RocþMountai¡s

Argentinecontinental margir

Pa¡is Basin

Denver-Julesburg

Denver-Julesburg

rWillistonAmundsen

tilted-block

successor,compressional orextensional warp

successor

successor

thermal (post-extension)

ramp (mid-crustaldetachmenQ

tilted fault block?

tilted fault block?

thermal

123

¿ 56

78

78

9

12I J

3

A

14l )

I i

1, Berg [1963]; 2, Hefu [1986]; 3, McQueen and Beaumont [1989]; 4, Brown [1984]; 5, Lambeck [1983]; 6, Made¡ t19831; T, Balkwill {19871;8, Stephenson et al., [1987]; 9, Bond and Kominz [1984]; i0, Urien and Zambrano [1973]; i I, A. D. Gibbs þersonal communication, 1990);12, Chaplin and Cather [1981]; 13, Baars et al. [1988]; 14, C'rowley et al. [1985]; 15, Young [1984].

features similar to that seen in the Pliocene andQuatemary stages of the Tarim Basin in northwestChina [Hefu, 1986] (see Table 3). Reactivation ofthe RTZ was initiated bv north-south horizontalcompression beginning at about 350-400 Ma,possibly at the time of the Tabberabberan Orogeny inthe Tasmanides. A resurgence of fault movementsstarted at abut 370 Ma and reached a peak at aboutthe time of the Kanimblan Orogeny in the Tasmanidesat about 320-350 Ma. The preserved synorogenicdeposits of sequence 9 account for about 257o of thetotal basin fill, but a significant part of the finaldepositional phase has been removed by subsequenterosion. It is this final thrusting phase that producedthe present-day basin shape and which makesreconstruction of earlier sub-basin shapes difñcult.

Sequences 6 to 8: Secondary conEols on basinformation, particularly those characteristics inheritedfrom the previous stage discussed in the previoussection, are important to basin development duringdeposition of sequences 6, 7, and 8 (upper GoyderFormation to Mereenie Sandstone).

Secrtrence 8 (Silurian to Earlv Devonian). TheLate Ordovician to Early Silurian emergence of awide subaerial region northeast of the Amadeus Basin(Rodingan and precursor movements), extending intothe Georgina Basin, corresponds to a period ofwidespread folding in the Tasman Orogen to the east(culminating in the Benambran Orogeny at about 440-430 Ma). Emergence in the northwest of the Basincorresponds to the region where a thin-skinned thrustsystem developed during the Devonian-Carboniferous Alice Springs Orogeny lStewart and

Oaks, 1987]. Early movements on this thrust systemmay have taken place during the Silurian RodinganMovement. The thinning of sediments over theGardiner Thrust in the central part of the basinsuggests activity on this structure during this periodof compressional tectonism. In the Late Silurian andEarly Devonian the basin conracted considerably inwidth; although the subsidence does not appear to berelated to structures, such as the Gardiner Thrust, thatagain became active during ttre main compressionaltectonism in the Late Devonian. The sequence Idepression shows features similar to those suggestedby Lambeck t19831 and may represent initiallittrospheric warping driven by compression (Table3). The warping appea$ to have preceded a phase ofnorthward directed overthrusting in which theGardiner Thrust formed the leading edge. Similarbasin warping preceding crustal faulting has beeninfened in the early Tertiary ståge of the Wind RiverBasin in the American Rocky Mountains [Brown,1984, p. 311. A contrary view is that the sequence 8depression represents a "successor" basin resultingfrom the effects of a sEess drop, corresponding tomildly extensional or Eanscurrent tectonism.Transcurrent tectonism would be consistent with theapparent en-echelon secondary depositional axes.Comparable basin development, with srongtopogxaphic conEol and evidence oflocal rifting, isshown by the extensional warping of the TriassicEiffel region in western Europe [Mader, 1983] (seeTable 3). In both tectonic scenarios, the subsidencemay have been accentuated by stress relaxation,combined with simultaneous erosion and depositiongiven the long time span involved.

Shaw et al.: Development of ttre Intracratonic Amadeus Basin

Sequence 7 (Late Ordovician): The depositionalintewal in the Middle to Late Ordovician is of shortduration, but the major change in basin shape thatoccurred between sequence 6 and 7 suggests that it isa significant event. There are, however, insufficientdata to deduce much about the mechanism. It ispossible that movements that \ilere precursors to theRodingan Movement, which affected the northeast ofthe basin, caused the basin to contract westwards [seeShaw et al., 1990; Stewart and Oaks, 19871.

Sequence 6 ûatest Cambrian to mid-Ordovician):The continuation of subsidence and ttre widening ofthe basin from the l¿te Camb'rian into the Ordovicianmay þ a consequence of continued thermal relaxationand thickening of the lithosphere which started in thelatest Proterozoic (sequence 4). The basin again tookon an elongated east-west shape and deepenedtowards its northern margin, possibly in response torenewed faulting there. The change in basin shape isindicative of a change in driving mechanism andcorrelates with the contractional Delamerian Orogeny.That is, thermal subsidence may have occurredduring depositional intervals 6ãnd possibly 7, butcompression may have perturbed the simple trend.Renewed rapid subsidence appears to have occuredin the late Early Ordovician. The cause of this isuncertain but it may be related to the riftingrecognized in the Canning Basin in the Ordovician[see Purcell and Poll, 1984, figure 5] to which theAmadeus Basin became linked atthis time.

Sequences 4 and 5 (Latest Proterozoic toLateCambrian): Lindsay et al. [1987] interpretedsequences 4 and 5 to represeÌt most of the secondmajor rift and sag phase of their three-phase basinevolution scheme. They appealed to the rapidsubsidence, especially in the northern pat of thebasin, during se4uence 4 and to the generally concaveshape of the backsripped subsidence curve for theperid to support their interpretation. ln particular,they compared the subsidence history of sequences 4and 5 with that of the late Proterozoic and Cambriansequences of the eastern part of the North AmericanCordillera. The laner is generally accepted to havebeen deposited in a passive margin environment andto contain an early extensional orrift phase followedby a more widespread, thermal subsidence phase[Bond and Kominz, 1984;Young, 1984].

We agree that during sequences 4 and 5 theoverall subsidence history of the cenüal Ausralianregion, and the northern Amadeus Basin in particular,reflects a broad extensional tectonic regime, but anumber of points argue against simple McKenzie-type, uniform horizontal extension of the wholelithosphere, followed by thermal relaxation.

1. There is virnrally no evidence of extensionalfaulting in central Australia at this time, even wherethe supposed synrift sediments (sequence 4) arethickest in the northern Amadeus Basin.

2. There is no sign of extensional faultingbeneath the thickest accumulations of the interpretedpostrift (thermal sag) sediments of sequence 5.

3. The central Australian basins extend a longdistance inboard from the nearest posSible

contemporaneous passive margin (to the east) [seeMunay et al., 19891. Although it has been variouslyinterpreted as an aulacogen or strongly oblique riftassociated with that margin [Rutland, 1976; Veeverset al., 19841, the lack ofevidence for the requiredfaulting, especially in the areas of thickest sediment,is difficult to reconcile with such models.

What then was the geomebry and kinematics oflithospheric extension beneath and around cenEalAusralia during sequence 4, and how did that relateto thermal subsidence during sequence 5? Details ofthe geomeury of the developing eastem Australianpassive margin at this time are poorly understood, butthe gloss geomebry is interpreted in Figure 17, whichshows a NNE trending rift system segmented bymajor transfer faults. The region underlying theEromanga Basin (Figure 1, i.e., southeast of theTasman Line (see also Figures 9a and 9b))corresponds approximately to Geophysical DomainsVI and D( of Munay et al. [1989], which wereinterpreted by them to be parts of a rifted lateProterozoic or early Paleozoic passive continentalmargin. A similar tectonic setting has been suggestedfor western Tasmania [Turner, 1989, p. 48] and mayalso apply to the basement underlying the MurrayBasin @igure 1) [see Brown et al., 1988]. Thecentral Australian region is interpreted to have beeninboard of an upper plate margin according to themodel of Lister et al. [1986], with the WarburtonBasin interpreted to have developed on a marginalplateau or ttrinned continental crust. With thedetachment extensional models of Lister et al. [ 1986],it may be possible to have deep-seated extension,without significant upper crustal stretching andfaulting, beneath central Australia. Such extensionmay be partitioned into the lower crust and uppermantle along one or more shallowly dippingdetachment faults, as shown in Figure 18, to producesome stretching of the lower cn¡st and/or mantlelithosphere, beneath largely unextended upper crust.

In such models [see also Royden and Keent19801 and Keen and Beaumont [1989] there are twoways in which to produce synrift subsidence withoutupper crustal extension. First, extension of themiddle to lower crust beneath a subhorizontaldetachment may lead to synrift subsidence, providedttrat the geometric subsidence due to lower crustalttrinning is greater than the thermal uplift due to thecorresponding thinning of littrospheric mantle. Thiscondition will only hold if a signifrcant originalcrustal thickness is subject to extension and thinning,that is, if the detachment is originally at fairly shallowdepths and/or the original crust is unusually thick.Second, if the detachment has aramp to flatgeometry, the pulling of an unfaulted upper platedown a ramp will produce a syncline or basin[Gibbs, 1987]. The depth of the basin is equal to theheight of the ramp or step in the detachment, and thewidth of the basin is approximately equal to thedisplacement at the foot of the ramp (Figure 19).Ramp basins may be terminated or offset along strikeby transfer faults, which act as the equivalent oflateral or tear-fault ramps in thrust fault geometries.

Straw et al.: Development of the Intracratonic Amadeus Basin

-"'Sþ--t"Y¡

þ$ fa;1"\-\

s

ìa

{

\ ,' : tflr

J

1I

\ì,/

1 , 9ruZ Transtensíonal zone with sedimentation

::=:::== D¡scordant geological zone

$*ì

i

sJMarginal plateau or th¡nned crust

Zone of intra-plate spreading

Sub-plate boundary

Discordant gravity I¡neament

Zone of ramping

Basaltic volcanism

Bimodal volcanism

Section lines for Fig.2O

Presently exposed Precambrian orogenic provinces

Tasman line

Amadeus Bas¡n

Georg¡na Bas¡n

Warburton Basin

Off icer Bas¡n

Ngal¡a Bas¡n

Bonaparte Bas¡n

Fig. 17. Map showing structures inferred to havebeen active during widespread continental extensionin the Early Cambrian (see Figure 20 and text forfurther discussion). Discordant geological, graviryand aeromagnetic features are also shown. EarlyCambrian accommodation and transtensional basins,including half-grabens, are occupied by the followingunits: 1, Mount Baldwin Formation; 2, CenûalMount Stuart beds; 3, Yuendumu Sandstone; 4,possibly the Mount Cunie Conglomerate; 5, beds inClunerbuck Graben (northwesternmost OfficefBasin); 6, beds in Levenger Trough (centralMusgrave Block); 7, sediments west of the Peake andDenison Ranges; 8, Sylvester Sandstone(southwestern Georgina Basin); and 9, Mount Burniebeds (Burke River Belt, eastern Georgina Basin).Basins of preservation are AB, Amadeus Basin; BB,Bonaparte Gulf Basin; GB, Georgina Basin; NB,Ngalia Basin; WB. Warburton Basin; and OB,Officer Basin.

C D

AB

G B

WB

OB

NB

BB

/.í- r.--í"

BOUNDARY.FAULTBASIN

DUCTILE LOWER CRUST

Fig. 18. Models for extension by the development of detachment shear zones combinedwith variable subdet¿chment pure shear [after Gibbs, 1987; Lister et al., 1986] (a) islithospheric wedge and (b) is flat-ramp detachment.

RamD Bas¡n

A thtd mechanism, transtensional thinning,especially of the upper crust, adjacent to majortransfer faults, may also lead to local syndftsubsidence in small fault-bounded basins.

All three of these processes are incorporated into aschematic model for an extensional tectonic settingfor this time period along sections (located in Figure17) across the Amadeus and Georgina basins (Figure20). In this model the cenral Australian region isinterpreted as an upper plate passive margin andhinterland, in which the master detachment faultsurfacing beneath eastern Ausralia extendssubhorizontally, but with localized ramps, for800 km or more beneath central Australia. Whiledocumented cases exist where thinned crust wittrextensive normal faulting extends up to 1100 kminboard of a continental margin (e.g., NW NorthAmerica, see seismic images documented by Keen etal. [1987]), examples of subhorizontal detachmentzones separating linle-deformed, upper crust fromextended lower crust have not vet been documented.Such a geometry cannot be exiluded in regions ofthickened continental crust.

Basin development in central Australia duringsequence 4 is interpreted as being due directly to theextension of the lithosphere and operation of adetachment fault (synrift). Three types of syn-riftbasins developed:

1. Broad, shallow basins above regions wherethe lower crust was extended beneath a relativelyshallow detachment. Thin sequence 4 sediments inthe Georgina and Warburton basins are interpreted tobe of this type, and a regional component of theAmadeus Basin subsidence at this time may also bedue to this effect.

2. Smaller basins in which significant localsubsidence took place, but beneattr which there is noevidence for upper crustal normal faulting (e.g.,Carmichael and Ooraminna subbasins). These basins

Fig. 19. Kinematic model of the development of aramp basin above a step or ramp in an extensionaldetachment. The geometry of the progressive fill inthe ramp basin is shown. The relationship of basinshape to ramp shape and fault displacement isoutlined in the text.

.....XRamp:.i.i.

"""" ' . ">L)))))) '' , . , . , ' , . , . , ' , . ,>1..)¡) i

. ì . ì .F lat .

Shaw et al.: Development of ttle Intacratonic Amadeus Basin

A EARLY CAMBRIAN

Deposi t ional Interual 4^ AMADEUSY BASIN

Local ramping and sub-crustal extension

M I D C A M B R I A N

Deoositional lnterual 5

Fig. 20. Model, vertically exaggerated crosssectionsacross central Australia, illustrating basin formationby extension concentrated in the lower crust andlithospheric mantle. The location of sections A-B andC-D a¡e illustrated in Figure 17. (a) Interpretativesection C-D for extension in the eastern Amadeus andWa¡burton basins in the Early Cambrian (sequence 4)due to local rarnping on a midcrustal detachment zonecombined with more rviclesp:ead subdetachment pureshear. RTZ is Redbank Thrust Zone. (b)Interpretative section C-D for extension in the eastemAmadeus and Warburton basins for the mid-Cambrian. Subsidence leading to a deepening andwidening of the basins is driven by thermal relaxationof the lithosphere. The thermal response is inferedto be substantially a consequence of attenuation of thelower plate þrincipally the subcrustal mantle) duringextension in the previous period (megasequence 4).(c) Interpretative section A-B for continentalsubsidence across the Georgina Basin in the mid-Cambnian caused by thermal relaxation followingsubcrustal extension in the Early Cambrian(megasequence 4). A midcrustal detachmentseparates a substantially unstructured upper plaæfrom a lower plate (lower crust and lithosphericmantle) which underwent subcrustal pure shearduring interval4.

[Christie-Blick and Biddle, 1985; McCutcheon andRobinson, 19871.

As pointed out by Lindsay et al. [1987], thebackstripped subsidence curve for sequence 5 isconcave upwards and resembles that predicted by theexponential decay of such a thermal anomaly. Thewidespread subsidence during this interval, affectingall the central Australian basins wittr the exception ofthe Officer Basin, is therefore interpreted to havebeen driven by the decay of the thermal anomalyinduced by extension of the lithospheric mantlebeneath the northwest dipping detachment duringsequence 4 time. The amount of subsidence directlyreflects the magnitude of the extension of the mantlelithosphere beneath the various parts of ttre cenEalAustralian region.

The proposition that deep-seated extension can betransferred into continental interiors on subhorizontaldetachment sEuctures for over 1000 km from theactively rifting passive margin is certainlycontroversial, and there is little direct geophysicalevidence of such structures in central Australia.However, it is supported in this case by (1) thecoincident timing of subsidence and the remoterifting, (2) the approximate spatial coincidencebetween the proposed ramp basin subsidence andimmediately subsequent subsidence (sequence 5)which has the signature of thermal relaxation, (3) theabnupt onlap of sequence 4 sediments onto thesouthern margins of their subbasins, as predicted inramp basins @gure 19), and (4) the evidence fromBouguer gravity and surface faulting data for theextension of the contemporaneous transfer faults intothe continental interior for the same distances.

cThermal relaxation and lithospheric thickening

M I D C A M B R I A N

Depositional Interual 5

GEORGINABASIN

Th¡nnedupp.er plate

Thermal relaxation following attenuafion of sub-crust

showed detailed east-west segmentation fl-indsay,1987al which suggests that some syndepositionalnortherly trending strike-slip faulting occurred.These basins are interpreted to be ramp basins(Figures 19 and 20), and theiren-echelonarrangement is interpreted to be due to offset of theramp on a major northwest Fending tansfer fault(Figure 17). The location of the ramp(s) may alsohave been influenced by the abrupt crustal thickeningbeneath the Souttrern Arunta province inherited fromits early to middle Proterozoic tectonic evolution, asproposed by Shaw t19871.

3. Along the southem margin of the GeorginaBasin a number of localized basins (e.g., in zones 1,2, and 8 in Figure 17) characterized by grcwthfaulting and half-graben morphology are alignedalong a prominent gravity/fault trend. These basinsare too localized to represent regional extension of theupper crust during sequence 4 and are interpreted tobe transtensional features aligned along a majortransfer fault, presumably at what were dilational jogs

0 800 km

AMADEUS WARBURTON

Shaw et a1.: Development of the Intracratonic Amadeus Basin

The spatial relationship between sequence 4 and 5depocenters (Figure 13) suggests that a simple rampbasin model, without pure shear lithosphericextension, is oversimplified. Figure 21 provides aqualitative model of subsidence during sequences 4and 5 in the northern Amadeus Basin, based upon aramped detachment and localized subdetachmentextension. It illustrates how two.laver extensionaccommodated by a detachment sbúctu¡e with a rampmay produce subbasins of the dimensions andrelative positions as those occupied by sequences 4and 5 in the northem Amadeus Basin.

MODEL2 RAMP BASIN

necessarily precisely synchronous throughout thecentral Australian region.

2. A ransitional phase between sequences 4 and5, approximately corresponding to the late EarlyCambrian, represents the time when the uplift drivenby the thermal effects of the hot, rising asthenospherepeaked. The ouçouring of extensive flood basalts(e.9., Annim Plateau Basalt) at the periphery of thecental Australian region took place during thisinfened thermal peak.

3. In sequence 5, postextension thermalsubsidence is recorded by the extensive Eansgressionover much of central and northern Australia in ttreearly Middle Cambrian (Figure 10c). Thermalsubsidence was intemrpted by a tectonic event in thelatest Cambrian, which may correspond with theDelamerian compressional orogeny in southernAustralia.

Sequences 2 and 3 (Late Proterozoic): Basinmorphology for sequences 2 and 3 shows somesimilarity to that of sequence 9. For example,uptums similar to that developed at the northernmargin of the basin during sequence 9 a¡e alsoidentified as having developed during intervals 2 and3 at the southwestern margin of the Amadeus Basinin the Black Hills area [Moss, 1962] and at thenorthwest margin of the Officer Basin [Jackson andvan de Graaff, 19811. The basin morphology forsequences 2 and3 is similar in dimension to that forthe second phase unit of sequence 9 (HermannsburgSandstone). The basins appear to have widened anddeepened in the last stages ofintervals 2 and 3 at thesame time as major transgressions were taking placeover a wider region.

In the proposed conceptual model @gures 16aand l6b) movement on a conrolling master fault atthe southem margin produces a tilted fault blockbasin in response to horizontal compression of thelithosphere. Flexure results in a peripheral a¡ch in thecenter of the basin which becomes accentuated bvlocal structuring (Figure 13, intervals 2 and 3). ihe

' model incorporates a controlling fault that is predictedto be at the southern margin of the basin, possibly onor north of the site of the Woodroffe Thrust. Slowupthrusting of about 2 km by the fault during eachsequence could account for the preserved geomely.The widening and deepening of the basins (Figure16c) that led to the major transgressions are explainedby a drop in compressive stress and cessation offaulting.

At the easte¡n margin of the region there areindications of a change from simple compression to atectonic regime involving strike-slip motion on a fewfaults and related to transtensional basindevelopment. An analogous situation may apply tothe upper part of interval 3. For example, the basicWantapella Volcanics which overlie interval 2(Sturtian) glacials in the eastern Officer Basin, aresuggestive of an extensional environment there[Brewer et al., 1987; Preiss, 1987,p.202], as is theMud Tank Carbonatite intruded at 735 + 5 Ma[Black and Gulson, 1978] in the southeastem AruntaBlock alongside the Woolanga gravity lineament (WL

Eêily stagês

Late stoges

B

6 > þ - t l P > ô > t lô ) É = r ' ô > P > t '

þ > 8 > ,6 > p > l

MC0Z

.^u", ,j.,'

//// MANTLE

BTZ Redbank Thrust Zone v

HL H inge l ine { in te rva l 4 ) î=zs

Fig. 21. Model of basin formation in the nortirernpart of the Amadeus Basin during deposition ofmegasequences 4 and 5 based on simple shear.modeling by Issler et al. [1989], as adopted by Shaw[1991]: (a) Model for the formation of ramp basinsin the northern Amadeus Basin during slow,heterogeneous stretching of the whole lithospherefollowed by progressively more rapid stretchingwhich became channelled into an increasingly moreductile lower crust and lithospheric mantle. Fl, F2and F3 represent linked ramps. Tectonic features aremid-crustal detachment zoneMCDZ and ramps Fl,F2 and F3. (b) The interpreted final stage ofsubsidence controlled predominantly by thermalrelaxation and snengthening of the mantle lithospherewhich had been thinned substantially during the finalstages of accelerated extension. MCDZ is thepostulated mid-crustal detachment zone.

The tectonic setting of the central Australianregion during sequences 4 and 5 can be summarizedas follows.

1. In sequence 4, northwest-southeast extensionbegan throughout much ofeastem and centralAusralia in the latest Precamb,rian and becameprogressively more rapid into the earliest Cambrian.Extension was heterogeneously distributed and not

I P = ¡ * r| ô > þ = t

in Figures Taand 7b). An en echelon continuation ofthe Woolanga lineament (WL in Figure 7b) separatesdistinct interval 2 subbasins to the southeast.Natrow, north-northwest trending half-grabens in thesouthwest Georgina Basin are also suggestive of aperiod of transtension [Walter, 1980]. Transtensionaccompanying formation of these half-grabens wasapproximately orthogonal to the proposedcompressional regime initiating subsidence in theAmadeus Basin, and this is consistent with wrenchreactivation of preexisting oblique on what may be anoverall contractional tectonic regime.

The widespread subsidence in the later stages ofintervals 2 and 3 may signify a drop in the level of thecompressional stress, consistent with the tilted faultblock models (see Figure 16c). Marginal basementinvolvement to the north and to the south duringsequences 2 and3 is indicated by syndepositionalbasement-derived clasts and is consistent withcompressional tectonics, possibly controlled by deep-seated fault zones at the southem margin of the basinand resulting in the folding of sequences and in mildregional uplift. We equate this early faulting aidsubsequent folding with the traditionally recognizedPetermann Ranges Orogeny, but regard sequence 4deposition as posttectonic. The basin geometry canbe explained qualitatively by the compressional tiltedfault block model outlined by McQueen andBeaumont tl989l and applied above to sequence 9.

The style of basin development for early stages ofsequences 2 and3 is broadly comparable with that ofthe Denver-Julesburg Basin in the American RockyMountains for the Late Cretaceous and Tertiary, asreviewed by Chaplin and Cather [1981], Brown[1984], and Baars et al. [1988] (Table 3).

Sequence 1: Widespread mafic dikes precedingthe earliest sedimentation in the basin indicate tensilestress, but not substantial extension. Upper crustalextension appea$ to have been minimal as normalfaulting is absent. Because the basic volcanics lie inthe upper part of sequence 1, they are not necessarilyrelated to rifting which more generally precedes awidespread sag phase. The smooth nonconformity,covering much of the continent, at the base of thesequence is consistent with the simple thermal modelsproposed for the Williston Basin [Crowley et a1.,19851 (see Table 3).

DISCUSSION AND CONCLUSIONS

The Amadeus Basin is a complex, long-lived,composite basin, built up of a series of 'successor'

basins, as defined by Klemme tl975l and Klein17987, p.1041 as "a succession ofchanging basintypes along zones of tectonic weakness." In thisrespect it is b'roadly comparable to the Cambrian toPermian Appalachian Basin analyzed by Cottont19701. Nine distinct episodes of evolution arerecognized in the Amadeus Basin in the period fromabout 900 Ma to 300 Ma. These episodes are notconfined to the Amadeus Basin, and similar andsynchronous sequences have been identified in theother basins of central Australia. The distinctiveepisodes are characterized both by intervals of

renewed subsidence, following upon erosionalbreaks, and/or by changes in basin shape. A numberof unconformities separating the tectonosnatigraphicsequences represent periods ofmild regional upliftand correlate with tectonism at the evolving eastemmargin of the early Palæmic Australian plate (Iable2).

The synchronous developments over a number ofbasins within the plate interior and the correlation ofthese developments with tectonism at ttre periphery ofthe region or at the plate's bounda¡ies indicate that thebasin forming mechanisms were primarily driven byhorizontal forces, with the lithosphere acting as asress guide over large distances (1000-2000 km).The subsidence and uplift histories ofthe centralAustralian basins and exposed basement blocksprovide arecord of complex tectonic history affectingthe outboard parts of the Australian plate.

The present study shows that the simplisticapplication of single models to the development ofbasins like the Amadeus Basin is unrealistic. Severalkey features need to be taken into account as astafiing point for the formulation of realistic,quantified, mechanical models of basin formation,and these need to be applied to each successor phase.In particular, the following factors need to beanalysed:

The timing and synchroneity of events.Megasequences, separated by unconformities orsequence boundaries, need to be delineated and thenassessed in terms of their relationship to majorchanges in basin shape and subsidence rate, as wellas the degre€ to which they can be conelated withinterregional events. These megasequences aredistinct from depositional stages (e.g., wedges oftransgressive marine and regressive nonmarinesediment [see Kingston et al., 1983] which relate tochanges in relative sea level on a smaller time scale,and which may be more global in origin [Watts et al.,1982; Klein, 19871. The megasequencesdistinguished in this study are commonly made up ofone to three, or more, depositional stages [Kingstonet al., 19831.

Subsidcnce history. Patterns of episodicsubsidence can commonly be related to other featuresof basin development such as changes in basin shapeand synchronous tectonic events outside the region.

Basin shape. Basin width may be related to theeffective elastic thickness of the lithosphere (see, forexample, Steckler and Watts, t19821). Details ofbasin asymmetry and internal basin featwes such asarrches and hinges may be related to specific basin-forming mechanisms. Changes in basin shape signaleither a change in tectonic mechanism or in themagnitude of the tectonic driving forces.

Structural geometry. Deep crustal faults mayexercise a major control on basin formation atparticular søges of basin development if the in-planeforces acting on the lithosphere are suitably orientedand/or of sufficient magnitude [Etheridge, 1986].Reactivation of these faults mav lead to basinamplification or inversion as iishown to be the casefor the Redbank Thrust Znne incentral Australia.

Thermal history. The thermal history of a basinmay also be diagnosic of basin-forming mechanism.

Shaw et al.: Development of the Intracratonic Amadeus Basin

For example, in the deeper pmts of the basin thethermal peak occurs early in an extensional basin butdevelops late in a compressional basin where it relatesto the time of maximum burial.

Basement upffi history. Marginal, hinterlandbasement uplift is more markedly linked tosubsidence in the adjoining basin duringcompressional tectonism than during extensionaltectonism. Determination of the basement uplifthistory at the margin of the Amadeus Basin hasallowed major constraints to be placed on the natureand timing of basin-forming tectonism.

Controls on basin formation can be grouped intothree categories:

1. The first order controls are inplane, thermal,and graviøtional forces. In central AusFalia, basindevelopment by compressional or transpressionalmechanisms is more in evidence than in the morefamiliar continental margin settings away fromCordilleran fold/thrust belts. Compressionaltectonism had a major effect on basin deveþment inthe inversion phase in the Late Devonian andCarboniferous when 20-30 per cent of the total basinfill accumulated. Extensional tectonism related to fa¡-field passive margin development appears to havecontrolled major phases of subsidence from the latestProterozoic to the Middle Cambrian, but in asomewhat unusual fashion.

2. Important secondary controls are (1) changesin sea level generated by global processes, (2) thepersistence ofpreexisting topography, (3) the stressrelaxaúon of the lithosphere, (4) enhanced differentialcompaction in deeper parts of the basin, and (5)perturbations in upper crustal structure due to localtectonic conditions and processes. Secondarycontrols may begin to dominate basin formation whenfar-field inplane forces are not strongly extensional orcompressional. These secondary controls areparticularly in evidence in the Amadeus Basin fromttre Late C-ambrian to the Early Devonian duringdeposition ofmegasequences 6, 7, and 8.

REFERENCESBaa¡s, D. L., et al., Basins of the Rocky Mountain

rcgloî, Sedimentnry Cover - North AmericanC/aron,' U.S., The Geolog,v of North America,vol. D-2, edited by L. L. Sloss, pp. 109-195,Gælogical Society of America, Bouldcr, Cnlo.,1988.

Balkwitl, H. R., Evolution ofSverdrup Basin, ArcticCanada, Am. Assoc. Pet, Gcol. Bull.,62,1004-1028. 1987.

Banks, M. R., and P. \V. Bailie, Late Cambrim toDevoniaa in Geology and Mímal Resources ofTosmonia, diteÅby C. F. Bmen md E. L.Ma¡tin, Spec. Publn. Geol. Soc. Aßt., 15, L82-237,1989.

Beaumont, C., Fo¡elmd basins, Geophys. J. R.Astron. Soc., ó5, 291-329, 1987.

Bell, B. T., and C. W. Jeffermn, A hypothesis form Australim Cmadian conne¡tion the lateP¡oterozoic and the bi¡th of the Pacific Oceu. inProceedings ofthc Pacific Rim Congress,pp.39-50, Ausu'alian Instituæ of Mining md Meullurgy,Pukville, Vic., 1987.

Berg, R. R.,Iøamide sediments along the rilindRiverThrust, in.Bacilone of the Americas, ditedby O. E. Childs md W, BeeÀe, Am. Assoc. Pet.Geol. Mem. 2, 220-230, 1963.

Berry, R. F., æd A. J. Cnwford, The tectonicsienificmce of Cmbdil allochthonous ma-fic-

ulrmafic complexesn"fasrwia, Arct. J. EøthSci., 35, 523-533, 1988.

Black, L. P. and B. C. Gulmn, The age of the MudTmk Cubonatite, Strmgways Rmge, NorthemTeritory, B.MR. J. Aust. Geol. Geophys., 3,2n-232,1978.

Black, L. P,, R. D. Shaw a¡¡d L, A. Offe, The ageof the Stuart Dyke Swm md is bering on theonæt of I¡te P¡ecmbrim sedimnøtion in cenu-¿lAustralia, "¡. Geol. Soc. Arct.,27, 151-155,1980.

Bond, G. C., and M. A. Kominz, Construction ofþctonic subsidence cwes for the earlv Paleozoicmiogeocline, southem Canadian Rocky Mountains:Implications for subsidence mcchanisms, age ofbreak-up md cnrstal thinning, Geol. Soc. Am.B ull., 95, 155-173, 1984.

Bond, G. C., P. A. Nickeson, and M. A. Kominz,Break-up of a super-æntinent between 625 Ma æd555 Ma: New evidence and implications forcontinental histo¡ies, Earth Planet. Sci. l¿tt.,70,325-345, t984.

Bozhkov, N. ,A.., The evolution of the rnobile zonesof Gondwma md l¿uruia in l¿te P¡mbrim,Tectonop hysics, 126, 125-135, 1986.

Bradshaw, J.D., md P.R. Evms, Paleozoictectonics, Aûadeus Basin, cenual Ausralia, ÁPEáJowmL 28, 267 -282, 1988.

Brewer, A. M., J. N. Dunster, C. G. Gatehouse, R.L. Henry, and G. Weste, A ¡evision of the

3. Basement inheritance is due to theheterogeneous rheological behavior of thelithospheric basement when subject to extension orcompression. Maximum basin subsidence andhinterland basement uplift were centered atvarioustimes at either the northem or southern margins of theAmadeus Basin, reflecting the weakness of the moredeformed parts of preexisting Proterozoic mobilebelts (see also Plumb fi9791, Mathur and Shawt19821 and Shawet al. [1984]). Inparticular, themain architectural framework for development of thebasin was provided by the reactivation of theProterozoic Redbank Thrust Tnne at the northernbasin margin of the Amadeus Basin and possibleearlier¡eactivation of the V/oodroofe Thrust andnearby subparallel structures at the southern basinmargm.

Table 3 summarizes the plausible basin-formingmechanisms for each subsidence episode and listspossible analogies with basins elsewhere. Thedominant basin-forming mechanisms have not beenestablished unequivocally for each of the majorsubsidence episodes. While the exact combination ofmechanisms controlling the subbasin developmentduring each depositional phase is debatable it is clearthat changes in mechanisms have occured throughtrme.

Acknowledgments. We wish to thank K.Gallagher, H. W. S. McQueen, C. Wright, and B.Goleby for comments on the manuscript. I. Chertok,A. R. Convine, S. R. Ross, V. R. Ashby, C.Krayshek, and J. K. Sti¡zaker assisted with thedrafting of the figures. The study was calried out atthe Research School of Earth Sciences, AustralianNational University in collaboration with the Bureauof Mineral Resources, Australia. Russell D. Shawpublishes with the permission of the ExecutiveDirector, Bureau of Mineral Resources.

stratigraphy of the eastem Officer Basin, Q. Geol.Notes, 102,2-15, 1987.

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