Multistage Landform Development in Various Settings and at ...Cadernos Lab. Xeolóxico de Laxe Coruña. 2002. Vol. 27, pp. 55-76 ISSN: 0213-4497 Multistage Landform Development in

Cadernos Lab. Xeolóxico de LaxeCoruña. 2002. Vol. 27, pp. 55-76

ISSN: 0213-4497

Multistage Landform Development inVarious Settings and at Various Scales

Desarrollo de formas multietapa en variassituaciones geomorfológicas y a diferentes escalas

TWIDALE, C. R.1; BOURNE, J. A.1 & VIDAL ROMANI, J. R.2

A B S T R A C T

That many landforms have their origins in the distant past is highlighted by the multis-tage concept, whereby the structural properties of bedrock which have been exploitedby shallow groundwaters are taken fully into account. Fractures of various types are par-ticularly vulnerable to weathering and hence to erosion. Examples are discussed fromvarious lithological and environmental settings - plutonic, volcanic and sedimentaryrocks, and different climates.

Key words: multistage; fractures; folds; magmatic, tectonic, lithological setting; under-p r i n t i n g .

(1) Department of Geology & Geophysics, University of Adelaide, Adelaide 5005, South Australia

(2) Instituto Universitario de Xeoloxía. Campus da Zapateira s/n, 15.071 A Coruña. Espagne.

INTRODUCTION

Many landforms are now widely recog-nised as being of two-stage or etch type;and this terminology acknowledges theroles of weathering and erosion in theirproduction. But because such forms aredue to the exploitation of bedrock weak-nesses by moisture at the weatheringfront, it has been suggested that accountought to be taken of the origin of theseweaknesses and that such features wouldbetter be described as multistage (TWI-DALE & VIDAL ROMANI, 1994).Multistage development is climaticallyand lithologically azonal. Most obviousexamples involve exploitation of fracturesbut, as is illustrated here, other prepara-tory events – tectonic, magmatic, sedi-mentary - ought also to be considered inthis context.

FRACTURES AS AVENUES OFWEATHERING

Most weathering takes place in theshallow subsurface and is due to water-related processes such as solution, hydra-tion and hydrolysis. Any factor which faci-litates contact with water is a significantdeterminant of the distribution of weathe-ring and hence subsequent erosion.Fractures are particularly important inthis regard, and especially in impermeableigneous rocks and such sediments ascrystalline limestone. Fractures occur atvarious scales. The importance of fracturepatterns in small scale landform develop-ment can be illustrated by reference tocorestones and boulders. These forms havethe additional advantage of signalling the

importance of other factors and the princi-ple of convergence in geomorphology.

Corestone boulders

Though some boulders are derivedfrom the disintegration of sheet structuresand subsequent rounding of the resultantblocks, most boulders are two-stageforms, having originated as a result of sub-surface weathering, of blocks defined byorthogonal fractures. Corners and edgesare rounded. This produces sphericalcorestones of fresh rock set in a matrix ofweathered bedrock. The evacuation of theweathered detritus exposes these coresto-nes as boulders. Corestones are remnantsof fracture-defined blocks located withinthe regolith and separate from the weathe-ring front, of which, however, they can beregarded as discrete parts. The operationof such a mechanism is attested not onlyin granitic terrains but also in variousother plutonic and igneous rocks inclu-ding basalt, and also in sediments such assandstone and limestone (figure 1a). Mostcommonly the tranformation of angularjoint blocks to rounded corestones is dueto the more rapid weathering of cornersand edges than of plane faces: Nature mutatquadrata rotundis (MacCULLOCH, 1814,p. 76; see also de la BECHE, 1839, p.450). Thus the spacing of fractures partlydetermines the maximum size of coresto-nes and hence boulders, though durationof subsurface weathering and of weathe-ring after exposure also play a part.

But not all corestones and boulders areformed in this way. The outlines of cores-tones of Palaeozoic granodiorite exposedin road cuttings near the Tooma Dam, in

56 TWIDALE et al. CAD. LAB. XEOL. LAXE 27 (2002)

the Snowy Mountains of New SouthWales, coincide with patterns of mineralbanding due to magmatic currents (figure1b). BARBEAU & GÈZE (1957) descri-bed from the Lake Chad region of WestAfrica corestones of granite embedded in amatrix of rhyolite and which they attribu-te not to weathering of the granite follo-wed by invasion of the rhyolite (whichwould be physically difficult, if notimpossible), but to globules of still liquidgranite being mixed with faster crystalli-sing rhyolite, i.e. to a deep-seated magma-tic process.

Pillars at Murphy Haystacks, EyrePeninsula

Murphy Haystacks illustrate theeffects of orthogonal fracture systems inwhich individual partings are widely spa-ced and where, more importantly, theexposed bedrock forms remain in physicalcontinuity with the main mass of countryrock, suggesting that the assemblage nowexposed was once at the base of the rego-lith. The Haystacks are so called becausefrom a distance that look like haystacksand as they stand on what was Pat

CAD. LAB. XEOL. LAXE 27 (2002) Multistage landform development 57

Figure 1. Corestones in basalt, southern Drakensberg, Eastern Cape Province, South Africa.

Murphy’s property. They stand on thecrest of a low hill a short distance from thenorthwest coast of Eyre Peninsula, andconsist of two groups of granite pillarsbetween 3 and 4 m high, developed onfracture-defined blocks (figure 2). Tafoniare formed in many of the pillars. Theflanks of the pillars are flared and calcretedeveloped on a dune calcarenite is lodgedin the base of some of the joint clefts andtafoni (TWIDALE & CAMPBELL, 1984).The following compressed developmentalsequence can be reconstructed from thefield evidence:

-1. Emplacement of the granitec a. 1.58 Ga.

-2. Development of orthogonal frac-ture systems (by analogy with geometri-cally similar systems in the GawlerRanges - see below - ca. 1.4 Ga).

-3. Subsurface exploitation of steeplyinclined fractures, and development of fla-red bedrock surfaces.

-4. Lowering of surface and exposureof pillars with flared sidewalls.

-5. Covering or partial burial of thegranitic assemblage by dune calcareniteduring middle-late Pleistocene (WIL-SON, 1991).

-6. Formation of calcrete about14,000 years B.P.

-7 Erosion of much of the calca-renite cover.

Hyden Rock, Western Australia

In addition to illustrating the impactof open fractures which are some tens ofmetres apart and which give rise to majorrelief features, the multistage concept asapplied to Hyden Rock also helps explaincertain details of morphology.

Hyden Rock is a complex domicalinselberg, or bornhardt, located near thesmall town of Hyden about 120 km east ofPerth, Western Australia. It consists ofthree domes, the central and western sepa-rated by a deep valley (now occupied by areservoir), and the central and eastern lin-ked by a low platform or large radiusdome (figure 3a). Sheet structure and jointclefts are prominent, as are flared slopes,including the well-known Wave Rock(figure 3b). In addition, a wide range ofminor landforms including basins, rock


Figure 1b. Corestones and mineral bandingexposed in road cutting near the Tooma Dam,Snowy Mountains, New South Wa l e s ,Australia.

doughnuts, tafoni and pitting; small faultscarps and A-tents (or pop-ups); and lowlinear ribs and ‘tram-lines’ is developed.

Like most bornhardts, Hyden Rock isa two-stage form (cf. FALCONER 1911;TWIDALE & BOURNE, 1998). A rangeof evidence and argument can be marsha-lled in support of this conclusion (TWI-DALE, 1982, pp. 124 et seq.; VIDALROMANI & TWIDALE, 1998, pp. 153et seq.) but the most compelling evidencederives for those several occurrences inartificial exposures of incipient domicalmasses already in existence in the subsur-face. Such a two-stage interpretationexplains why, though very well represen-ted in the humid tropics, bornhardts arefound in many different climatic regions,for apart from the realities of climaticchange, weathering is ubiquitous and lowrates of weathering can be compensated bylong duration.

In the southern Yilgarn Craton, thefirst stage of differential subsurface wea-

thering took place in Cretaceous times,100-130 Ma, the second, exposure, in theCainozoic, beginning with the uncoveringof the highest crest in the Eocene, about60 Ma, for Hyden Rock was evidentlyexposed in stages (TWIDALE & BOUR-NE, 1998).

The sequence of events during whichoriginated the various major and minorfeatures displayed on the Rock can beidentified:

-1. Emplacement of the granite about2.64 Ga (CHIN et al., 1984).

-2. Development of orthogonal fractu-re systems in cooled brittle rock by shea-ring. The compressional strains were even-tually manifested in sheet fractures whichmay have originated at this time, eitherdirectly or induced by shearing (WEIS-SENBERG, 1947).

-3. Intrusion of aplite sills and alsoveins of quartz and epidote.

[Events 2 and 3 occurred soon after theemplacement of the granite.]


Figure 2. Granite pillars at Murphy Haystacks, northwestern Eyre Peninsula, South Australia.


-4. Subsurface weathering beneath alateritised land surface in Cretaceoustimes (100-130 Ma).

-5. Dissection of surface about 60 Mafollowing separation of Australia andAntarctica and tilting of what is nowsouthern coastal area of We s t e r nAustralia. Crests of Hyden Rock expo-sed, together with some sheet fractures,basins and gutters.

-6. Concentrated moisture attackaround base of the domes: incipient flaredforms, and also large depressions, later tobecome armchair-shaped hollow, develo-ped at the weathering front.

-7. Further lowering of plains andexposure of more of the bornhardt with

flared slopes at margins. Lowering of nor-thern plain, adjacent to the palaeoriverCamm, greater (by about 20 m) than onsouthern side, so that higher flares (likeWave Rock and The Breakers) are exposedon the northern face.

-8. In recent times, (a) seismicity hascaused minor fault scarps and numerousA-tents. (b) Human activities have indu-ced changes in vegetation and hence ratesof weathering and erosion, and the valleybetween the central and western domeswas dammed (in 1951), and walls built todivert water into the reservoir. Runoff onto some flared slopes and piedmonts wasthus reduced and rate of weathering onexposed slopes and also below the soil sur-face at the margins of the Rock presu-mably decreased. (c) Meantime, weathe-ring and erosion have continued: basinsand gutters, rock doughnuts and tafonihave developed, and sheet structures havefurther broken down. Flutings with algalveneers have developed on slopes andsome have become inverted. Degradationof algal cover on some flutings has led tothe disintegration of channel floors andthe formation of "button holes". Areasprotected against water contact and scou-ring remain in local relief (TWIDALE &BOURNE, 2000a).

Bornhardt landscape of volcanicorigin

Though well and widely developed ingranitic rocks, bornhardts and bornhardtlandscapes are found in many other litho-logical environments, including volcanicand sedimentary. The only requirementsare a preferably impermeable rock with


Figure 3b. Wave Rock, a flared slope 14-15 mhigh in the northern piedmont of Hyden Rock.

compartments of contrasted fracture den-sity, and stable periods sufficient to allowquite deep differential weathering.

The chronology of evolution of a born-hardt landform assemblage (figure 4a) ofthe Gawler Ranges, developed in aMesoproterozoic ignimbrite sequence, andlocated in the arid interior of SouthAustralia, can be traced back some 1.6 Ga(CAMPBELL & TWIDALE, 1991):

-1. Extrusion of ash layers about 1.5km thick, circa 1.6 Ga (BLISSETT et al .,1993), followed by rapid cooling, weldingand development of systems of columnarjoints. The geometry of cooling surfacesdetermined the orientation of columnarjointing and hence the details of hillslopemorphology typical of a volcanic region(figure 4b).

-2. Prior to 1.4 Ga, orthogonal fractu-re systems (figure 4c) formed in brittlerocks (formed before deposition of

Pandurra Formation and intrusion of dole-rite sills dated ca 1.1 Ga).

-3. Following the late Palaeozoic(Permian) continental glaciation (whichaffected most of the continent) but priorto the Early Cretaceous, the ignimbriticmass was subjected to fracture-controlleddifferential subsurface weathering whichresulted in the subterranean formation ofordered rows of nascent bornhardts.

-4. During the Early Cretaceous(Neocomian-Aptian) and as a result ofupfaulting and tilting, the regolith waslargely stripped, the detritus deposited inmarine sequences in the Eromanga Basin,and the bornhardts exposed.

-5. Since the Early Cretaceous, thevalley floors and piedmonts of the uplandswere weathered and silcreted in Eocenetimes, and there has been some gullyingin valley floors, but the massif has remai-ned essentially unchanged.


Figure 4a. General view of part of Gawler Ranges, South Australia, showing bornhardts and beve-lled crests near Spring Hill. Note sheet structures exposed right foreground.

Sedimentary inselbergs of CentralAustralia

Bornhardt landscapes are developed insedimentary terrains as well as on plutonicand metamorphosed (welded) volcanicrocks. Examples include the cupolakarst ofmany limestone outcrops. Domical resi-duals and towers shaped in arenaceous andrudaceous rocks are exemplified by theconglomeratic towers of Meteora, conglo-meratic towers in the Pyrenees (e.g.BARRÈRE 1968) and in the Logroño areaof the Ebro Basin of northern Spain, andthe sandstone domes of West Africa(MAINGUET, 1972).

The Olgas, Ayers Rock, and MtConner are three prominent but contras-

ted inselbergs located in the deserts ofcentral Australia southwest of AliceSprings. All are sculpted in folded EarlyPalaeozoic strata, but The Olgas is a com-plex of conglomeratic domes, Ayers Rockan arkosic monolith, and Mt Conner anisolated mesa located in the trough of aregional basin structure. The developmentof The Olgas and of Ayers Rock is not dueto lithological factors for similar strataunderlie the adjacent plains. The threeresiduals are aligned along a WNW-ESEaxis (bearing 100º) and are best explainedby cross- or interference-folding, witheffective north-south compression supe-rimposed on NNW-SSE trending foldsdeveloped during the Devonian AliceSprings Orogeny (WELLS et al., 1970;TWIDALE, 1978).

Thus the occurrence of these threeinselbergs is due to tectonic events. OnAyers Rock the Kangaroo Tail is a sheetstructure due to compressive stress relatedto continued plate migration and jogglingof constituent blocks (figure 5a), and theribbed upper summit surface and flanksreflect the steep dip of strata. The well-known Brain (figure 5b) is due to the wea-thering of bedding planes; and so on – theeffects of past tectonism continue to beexploited.

FOLDING

Faulting and folding are expressions ofcrustal stress. The end result varies accor-ding to the intensity and duration of theforces applied, and the competence of therocks affected. Conditions of sedimenta-tion in past eras as well as structure findexpression in landscape and landformdevelopment down the ages, and again atvarious scales.


Figure 4b. Columnar joints in dacite.


Figure 4c. Plan of steeply dipping fractures. Source: Landsat imagery. (After CAMPBELL & TWI-DALE, 1991).

Figure 5a. The KangarooTail, a sheet structure deve-loped in steeply dippingCambrian arkose on thenorthwestern flank of AyersRock.

Flinders Ranges, South Australia

Because of the strains imposed on sedi-mentary sequences during folding, exam-ples of structural highs becoming topo-graphic highs and of lows becoming highare commonplace in fold mountain belts.In the southern Flinders Ranges, SouthAustralia, the Willochra Basin or Plainoccupies a regional anticlinorium (figure6) and to east and west respectively, theHorseshoe and Dutchmans Stern Rangesare developed on a local basin and a pit-ching local syncline outlined by quartziticbeds (TWIDALE & BOURNE, 1996).

The Flinders Ranges, in the arid andsemiarid interior of South Australia, is afold mountain belt of Appalachian type.Though dominated by ridge and valley,

developed on Neoproterozoic andCambrian strata prior to the MiddleEocene and accentuated through pha-ses of valley floor excavation, a summitsurface, mostly of epigene or etch typeand of Cretaceous age, but exhumedand preCretaceous in the extremenorth, is also prominent (TWIDALE &BOURNE, 1996).

In large measure, the pattern of ridgeand valley reflects the relative resistance ofquartzitic and sandstone, and in lessermeasure limestone and tillite outcrops,and the relative weakness of argillaceous,and in places limestone, beds. But the dis-tribution of these strata (figure 7) of con-trasted resistance to weathering and ero-sion, reflects conditions of sedimentationin the Neoproterozoic and earliest


Figure 5b. The Brain, located high on the eas-tern slope of Ayers Rock. The crenulations aredue to the explotation by water-related wea-thering processes of steeply dipping bedding.The outline is fortuitous.

Palaeozoic as do the thickness of stratawhich in some degree – disposition andfracture density also play a part - determi-ne the topographic prominence of a givenoutcrop. In the southern and centralFlinders Ranges the Gawler Craton, to thewest of the upland, was the main source ofdetritus (PREISS, 1987; PARKER et al. ,1993; see figure 8). For this reason themajor quartzites and sandstones are thic-kest in the west and thin to the east. Forexample, the arenaceous beds of thePound Subgroup are more than threetimes as thick in the west, where theygive rise to the high ranges of Wi l p e n aPound and the Elder, Chace, Druid andHeysen ranges, as they are in TheBunkers, shaped in the easterly extensionsof the equivalent strata.

To the north, however, the CurnamonaBlock, located to the east of the upland(figure 8) was the main source area forsediment and here formations are thickestin the east and thin to the west. Easternranges such as the Gammons are topogra-

phically prominent. This distribution alsoinfluences drainage patterns (figure 8).Though trellis and annular patterns dueto a combination of structural control andstream piracy are characteristic of the ran-ges, the notable asymmetry of theWilpena-Siccus drainage, for example,reflects the regional structure and henceProterozoic environments. The headwa-ters of the Wilpena Creek rise within akilometre of the western escarpment ofthe upland, but they flow east across therange before joining the Siccus and run-ning to Lake Frome: headward erosion wasmore rapid through the thinner steeplydipping quartzites of the east thanthrough the massive quartzites that formthe western ramparts of the Flinders.Similarly but conversely, to the north,westerly- and northerly-flowing riverssuch as the Ta y l o r, Frome, Burr andWindy systems are areally dominant oversuch eastern stream systems as theDonkey Wa t e r, Mount McKinlay andWeetoota creeks.


Figure 6. East–west section across the Willochra Basin and Plain.


Lochiel Landslip, South Australia

The Lochiel Landslip (figure 9a), loca-ted about 115 km north of Adelaide,represents a slippage of about 250,000 m3

of quartzite downslope and along a bed-ding plane. It formed overnight on 9-10August 1974. The Landslip occurs on theeast-facing side of a valley incised into theeastern slope of the Bumbunga Range.The Range trends north-south, and isbounded on the east by an Eocene fault;there is geophysical evidence suggestive ofa fault to the west also, so that the rangemay be a horst block. It is developed on an

east-dipping sequence of cross-bedded(the detailed sedimentary structures areoutlined by thin bands of magnetite)Proterozoic quartzite overlying shale.Numerous earthflows and landslides wereinitiated in 1916 and 1923 and have beenrecurrently active since, and especially inthe '70s. They score the the west-facingscarp where they originate at the junctionbetween the quartzite above and the silts-tone below, and in the heads of valleys.Apart from a small slide formed at thelithological junction and low on the scarp,the Landslip is the only mass movementon the eastern slope.


Figure 8. Tectonic setting of the Flinders Ranges (northern Adelaide Geosyncline) between theGawler Craton and Curnamona Block.

The Landslip is unusual in that it isdeveloped in quartzite. It is not due tounbuttressing by river erosion of the toe ofthe hillslope for the river was not runningat the time of its formation and the Slipdoes not extend quite to the base of theslope. The winter of 1974 was wet and theLandslip originated as a crack formed highon the hillslope in the previous May. InAugust, strata to a depth of at least 12 mslid in three connected lobes, along bed-

ding planes, which were lubricated byattenuated lenses of smectite. A promi-nent tension crack was created at the headof the movement (figure 9b). Since 1974,cracks have extended northwards alongthe slope. A large area will eventuallymove downslope (TWIDALE, 1976,1986).

Thus in order to understand theLandslip it is necessary to go back to theProterozoic:


Figure 9a. The LochielLandslip, South Australia,from the southeast.

Figure 9b. Tension crackat head of Landslip, 1974.

-1. Deposition of Tregolana Shale(c a. 1 Ga).

-2. Deposition of Simmens Quartziteas beach or shallow water sand plain andwith intercalated lenses of clay laid downin shallow intertidal pools (1 Ga).

-3. Folding and faulting of sedimen-tary sequence in Delamerian Orogeny(Early Palaeozoic, ca. 520-420 Ma).

-4. Renewed(?) upfaulting ofBumbunga Range (Eocene, ca. 60 Ma).

-5. Clearing of woodland (second halfof 19t h Century) and development ofearthflows and landslides (mainly in 1916and also 1923 with reactivation in 1956and the 1970s) on the western scarp.

-6. Wet winter of 1974, and lubri-cation of easterly dipping bedding pla-nes, resulting in mass movement,August 9-10.

-7. Extension of cracks from Slipnorthwards along adjacent slope 1974 andcontinuing.

RESURGENCE AND UNDERPRIN-TING

The effects of past events is perpetua-ted, first, because existing weaknessestend to be re-exploited by later tectonicevents and second, because their effects arepassively transmitted through overlyingstrata. Once formed, a fracture zone tendsto be a zone of weakness on which laterstresses are concentrated. This tendencyfinds obvious expression in recurrentlyactive faults such as those of the DeathValley and adjacent areas, with compositefault scarps formed during more than onephase of dislocation and with such featuresas wineglass valleys associated with them.

Neotectonism at Minnipa Hill, EyrePeninsula

Minnipa Hill is a low granitic domelocated near the small township ofMinnipa, on northwestern Eyre Peninsula.It was affected by a minor earthquake (2.3on the Richter scale and with its epicentre80 km to the east) in the late morning of19 January 1999. This caused rock bursts,and the formation of fault scarps, disloca-ted blocks, and A-tents (TWIDALE &BOURNE, 2000b; figure 10). Mappingof these features disclosed the presence ofan earlier generation of similar forms, andsubsequent monitoring allowed the smallsuite of later forms, including an A-tent(probably formed sometime in early 2001)to be identified.

The major dislocations involved eitherthe reactivation of dominant fracture pat-terns or rupture resulting from shearingalong these lines. The dominant fracturepatterns are related to lineaments datingfrom the later Proterozoic.

Straight rivers of Great ArtesianBasin

The western part of the Murray Basinis underlain by a thick sequence of flat-lying Cainozoic strata, yet fracturesystems concordant with Precambrianpatterns, and in particular lineamenttrends, are clearly discernible (e.g. HILLS,1956; FIRMAN, 1974). One strong pos-sibility is that resurgent (or recurrent)movements along ancient fractures has ledto their trends being imposed from below,or underprinted, on the cover beds.

Several major, as well as innumerableminor, sectors of rivers drain parts of theGreat Artesian Basin (figure 11). The best


known example is the Darling-Culgoariver which runs straight for almost 800km between St George and Menindee, yetwhich flows through Quaternary alluviafor most of this distance. Other examplesare the stretches of the Bulloa, Paroo andWarrego (NNE-SSW), the Cooper,Warburton, Thompson and Diamantina(NE-SW), and the Leichhardt, Flinders,G e o rgina, Hay and Eyre (NNW- S S E ) ,though the courses of the two last-namedmay be influenced by dune trend.

The trends indicated are well-knownlineament trends (e.g. HILLS, 1956,1961) and the suggestion is (HILLS,1961) that the rocks beneath the variousand varied Late Cainozoic covers in whichthe rivers have carved their channels carrythe imprint of lineaments, that these frac-ture zones are zones of weathering andthese are underprinted on the alluvia,facilitating and favouring river develop-ment. above.

The fracture patterns of the Euclaand western Murray basins, and in thelatter region, associated major drainagepatterns, provide further examples ofl a rge scale underprinting (HILLS, e.g.1946, 1961, 1963; LOWRY, 1970;FIRMAN, 1974).

Dolines in dune calcarenite, EyrePeninsula

A similar mechanism can plausiblybe invoked in explanation of anomalousdolines developed in calcarenite on wes-tern Eyre Peninsula (TWIDALE &BOURNE, 2000c).

Late Pleistocene dune calcareniteunderlies a broad zone inland from thewest coast of Eyre Peninsula. It originatedas a field of coastal dunes formed at timesof lower sea level, and the rolling topo-graphy reflects the original dune morpho-logy. The lack of surface drainage is typi-


Figure 10. Fault developed in the late morning of 19 January, 1999, on Minnipa Hill, northwesternEyre Peninsula, South Australia.

cal of karst terrains but the calcarenite is abioclastic rock and despite buttressing byvarious calcrete horizons is too weak tosupport extensive cave development.Dolines, however, are abundantly develo-ped. They vary in size from a few centi-metres to a few tens of metres diameter.As might be anticipated, many are develo-ped in lows in the topography, in the flo-ors of swales or depressions. But several ofthe larger dolines are found high in thelocal relief, some on or very close to thecrests of broad rises. Moreover, severallarge and small dolines, occur in groups

and are aligned along NNW-SSE axes(WILSON, 1946-7; figure 12a). They aremost plausibly explained in terms ofstructural conditions, not primarily in thedunerock, but inherited or underprintedfrom the underlying Precambrian igne-ous, metamorphic and sedimentary rocks,of which representatives are exposed onthe coast. Fractures in the basement rockbeneath the calcarenite attracted flows ofgroundwater, and as these in some instan-ces are located below high points in thepalaeodune topography - the pattern andtopography of the dunefield is indepen-


Figure 11. Map of eastern Australia showing relationship between major rivers and lineaments.

dent of local basement structure – aligneddolines form on the hills (figure 12b).

Thus the aligned large dolines can beexplained:

-1. Emplacement, formation anddeposition of Precambrian rocks, morethan 1 Ga.

-2. Development of fractures withNNW-SSE sets prominent.

-3. Deposition of fields of coastal fore-dunes in later Pleistocene times (630,000-180,000 years B.P.: WILSON, 1991).

-4. Consolidation (self cementation) ofdunes, and attack by meteoric waters,resulting in solution dolines. In additionsurface waters were funnelled into zones

above prominent NNW-SSE trendingfractures in the basment rocks, and resul-ted in formation, by solution and collapse,of rows of large sinkholes in the calcareni-te above.

CONCLUSION

Thus the origin of landscapes andlandforms in various settings can be tracedinto the distant past:

- In some areas of igneous outcrop thesize and shape of the corestones, and even-tually of the associated boulders, datesfrom Palaeozoic magmatic events.

- At Murphy Haystacks landform evo-lution goes back to the formation of frac-ture patterns probably and by comparisonwith adjacent regions, to theMesoproterozoic.

- The morphology of Hyden Rock isthe result of events which can be tracedback 2.64 Ga. and in the Gawler Rangesto 1.6 Ga (Mesoproterozoic) when theoutlines of the present bornhardts wereinitiated. This landscape is one of oldestknown and determined (120-130 Ma).

- In the Flinders Ranges, the topo-graphy and some aspects of drainage weredetermined by source areas and relatedsedimentation in the later Proterozoic andearly Palaeozoic.

- The Lochiel Landslip is also multista-ge, albeit in a rather different and complexsense from the other bedrock etch formscited here. Its origins can be traced backabout 1 Ga.

- The straight rivers of the GreatArtesian Basin and location and the align-ment of some dolines is related to patternsof lineaments dating from the Proterozoic.


Figure 12a. Aligned Weepra dolines east ofLake Newland, Eyre Peninsula, SouthAustralia.

- Patterns of faulting and tectonic dis-trurbance are related to the exploitation ofcrustal weaknesses determined inPrecambrian times.

W. M. DAVIS (1909, p. 268) stated"To look upon a landscape ... without anyrecognition of the labour expanded in pro-ducing it ... is like visiting Rome in theignorant belief that the Romans of todayhad no ancestors"; thus emphasising thevital temporal aspect of geomorphologicalinvestigations. Many familiar landformtypes have complex chronologies of deve-

lopment. Many owe their development tothe exploitation by subsurface moisture offractures in the country rock. In orderfully to attempt to understand such formsit is necessary to extend consideration farback in geological time to environmentsof sedimentation, early and recurrent tec-tonism and even to events and in magma-tic chambers.

Recibido: 17-X-01Aceptado: 12-II-02


Figure 12b. Suggested development of aligned dolines through underprinting.

REFERENCES

BARBEAU, J. & GÈZE, B. (1957). Les coupolesgranitiques et rhyolitiques de la région de Fort-Lamy (Tchad). Comptes Rendus Sommaire etBulletin Societé Géologique de France (Serie 6), 7:341-351.

BARRÈRE, P. (1968). Le relief des Pyrénées cen-trales occidentales. Journal d’Etudes Pau-Biarritz, 194: 31-52.

BECHE, H. T. de la (1839). Report on the Geology ofCornwall, Devon and West Somerset (GeologicalSurvey of England and Wales). Longman,Orme, Brown, Green and Longmans, London,648 pp.

BLISSETT, A. H., CREASER, R. H., DALY, S. J.,F L I N T, R. B. & PARKER, A. J. (1993).Gawler Range Volcanics. In: Drexel, J. F.,Preiss, W. V. & Parker, A. J. (eds): The geology ofSouth Australia. Vol. 1. The Precambrian.Geological Survey of South Australia Bulletin,54: 107-124.

CAMPBELL, E. M. & TWIDALE, C. R. (1991).The evolution of bornhardts in silicic volcanicrocks in the Gawler Ranges. Australian Journalof Earth Sciences, 38: 79-93.

CHIN, R. J.; HICKMAN, A. H. & THOM, R.(1984). Hyden, Western Australia. Sheet SI 50-3 International Index, 1:250 000 GeologicalSeries. Geological Survey of Western AustraliaExplanatory Notes.

DAVIS, W. M. (1909). Geographical Essays . Dover,Boston, 777 pp.

FALCONER, J. D. (1911). The Geology andGeography of Northern Nigeria. Macmillan,London, 295 pp.

FIRMAN, J. B. (1974). Structural lineaments inSouth Australia. Transactions of the Royal Societyof South Australia, 98: 153-171.

HILLS, E. S., (1946). Some aspects of the tectonicsof Australia. Journal and Proceedings of the RoyalSociety of New South Wales, 79: 67-91.

HILLS, E. S. (1956). A contribution to the mor-photectonics of Australia. J o u r n a l of theGeological Society of Australia, 3: 1-15.

HILLS, E. S. (1961). Morphotectonics and the geo-morphological sciences with special reference toAustralia. Quarterly Journal of the GeologicalSociety of London, 117: 77-89.

HILLS, E. S. (1963). Elements of Structural Geology.Methuen, London, 483 pp.

LOWRY, D. C. (1970). The geology of the WesternAustraliapart of the Eucla Basin. GeologicalSurvey of Western Australia Bulletin, 122: 201 pp.

MacCULLOCH, J. (1814). On the granite tors ofCornwall. Transactions of the Geological Society, 2:66-78.

MAINGUET, M. (1972). Le Modelé de Grès. InstitutGéographique National, Paris, 2 volumes.

PARKER, A. J., PREISS, W. V. & RANKIN, L. R.(1993). Geological framework. In: Drexel, J. F.,Preiss, W. V. & Parker, A. J. (eds): The geology ofSouth Australia. Vol. 1. The Precambrian.Geological Survey of South Australia Bulletin,54: 9-31.

PREISS, W. V. (1987). The Adelaide Geosyncline.Geological Survey of South Australia Bulletin, 53:438 pp.

TWIDALE, C. R. (1976). The origin of recentlyinitiated exogenetic landforms, SouthAustralia. Environmental Geology, 1 (4): 231-240.

TWIDALE, C. R. (1978). On the origin of AyersRock, central Australia. Zeitschrift fürG e omo r p h o l o g i eS u p p l e m e n t B a n d, 31: 177-206.

TWIDALE, C. R. (1982). Granite Landforms.Elsevier, Amsterdam, 372 pp.

TWIDALE, C. R. (1986). The Lochiel Landslip,South Australia. Australian Geographer , 17 (1):35-39.

TWIDALE, C. R. & BOURNE, J. A. (1996).Development of the land surface. In: M. Davies,M., Twidale, C. R. & Tyler, M. J. (Editors)Natural History of the Flinders Ranges. RoyalSociety of South Australia, Adelaide, pp.: 46-62.

TWIDALE, C. R. & BOURNE, J. A. (1998).Origin and age of bornhardts, southwest ofWestern Australia. Australian Journal of EarthSciences, 45 (6): 903-914.

TWIDALE, C. R. & BOURNE, J. A. (2000a). Anote on the role of protection in landform deve-lopment: examples from granitic terrains.Zeitschrift für Geomorphologie, 44 (2): 195-210.

TWIDALE, C. R. & BOURNE, J. A. (2000b).Rock bursts and associated neotectonic forms atMinnipa Hill, northwestern Eyre Peninsula,South Australia. Environmental and EngineeringGeoscience, 6 (2): 129-140.

TWIDALE, C. R. & BOURNE, J. A. (2000c).Dolines of the Pleistocene dune calcareniteterrain of western Eyre Peninsula, South


Australia: a reflection of underprinting?Geomorphology, 33 (1-2): 89-105

TWIDALE, C. R. & CAMPBELL, E. M. (1984).Murphy Haystacks, Eyre Peninsula, SouthAustralia. Transactions of the Royal Society of SouthAustralia, 108: 175-183.

TWIDALE, C. R. & VIDAL ROMANI J. R.(1994). The multistage origin of etch forms.Geomorphology, 11: 107-124.

VIDAL ROMANI, J. R. & TWIDALE, C. R.(1998). Formas y Paisajes Graniticos. SerieMonografias 55, Servicio de Publications daUniversidade da Coruña, A Coruña, 411 pp.

WEISSENBERG, K. (1947). Continuum theory ofrheological phenomena. Nature, 159: 310-311.

WELLS, A. T., FORMAN, D. J., RANFORD, L.C. & COOK, P. (1970). Geology of theAmadeus Basin, central Australia. Bureau ofMineral Resources, Geology and GeophysicsBulletin, 100: 222 pp.

WILSON, A. F. (1946-7). Observations on depres-sions resembling meteorite craters on EyrePeninsula, South Australia. Proceedings of theRoyal Geographical Society of Australasia (SouthAustralian Branch), 48: 25-36.

WILSON, C. C. (1991). Geology of the QuaternaryBridgewater Formation of southwest and centralSouth Australia . Ph. D. thesis, School of EarthSciences, The Flinders University of SouthAustralia, Adelaide.


Documents

Multistage Landform Development in Various Settings and at ...Cadernos Lab. Xeolóxico de Laxe Coruña. 2002. Vol. 27, pp. 55-76 ISSN: 0213-4497 Multistage Landform Development in