Australian Journal of Earth Sciences (2000) 47, 245–257

INTRODUCTION

The landform evolution of southeastern Australia has long been the subject of much controversy. Many of thecontroversial issues were highlighted in the recent paperby Ollier and Pain (1994) on the geomorphology andtectonics of south eastern Australia, the discussions byBishop (1996), Nott (1996a), Li et al. (1996), and the reply by Ollier and Pain (1996). One of the more importantsources of controversy is the relationship between the coast and inland plateaux around 1000 m above sea-levelnear the Great Divide—the divide between coastal andinland drainage. Remnants of old land surfaces occur bothon the inland plateaux and along the coast. They have deepweathering profiles and are in places overlain by Early to mid-Cenozoic sediments and basalt. The sediments and basalt may also be deeply weathered, and sandy andgravelly sediments are commonly converted to silcrete orferricrete.

There are at present two main schools of thought on therelationships between the old land surfaces of the coast andthe highlands. Some of the more recent authors believe thatthe differences of elevation are essentially erosional, andthat there has been no significant tectonic displacementbetween the old land surfaces of the highlands and the coastsince they were formed.

Young and McDougall (1982) concluded that there havebeen no geomorphically significant earth movements in theUlladulla area since the Permian. Nott et al. (1991) con-cluded that the coastal lowland near Merimbula is mid-Cenozoic in age and ‘therefore, uplift of the highlands musthave occurred by that time’. Nott and Purvis (1995) acceptedthe conclusions of Young and McDougall and maintainedthat there has been no significant tectonic displacement inthe Mt Dromedary area since the Early Cretaceous. Nott(1996a) and Nott and Purvis (1996) restated many of theearlier arguments of Young and McDougall against relativedownwarp of the coast. Spry et al. (1999) found evidence ofpossible neotectonics in the area between Brooman andMoruya, but also concluded that their observations ‘add fur-ther weight to claims that the coastal lowlands in southeastNew South Wales are at least mid-Oligocene in age’. Kohnand Bishop (1999) agreed with this conclusion.

The main alternative to the idea of tectonic stability asfar back as perhaps the Late Palaeozoic is that the coastalzone (and also the continental shelf) has been downwarpedrelative to the Great Divide since the rifting and separationof the Lord Howe Rise from the eastern margin of Australiain the Late Cretaceous. Ollier (1982) expressed this idea interms of relative upwarping of the Great Divide. In adiscussion of Young and McDougall’s paper (Brown 1983),I argued that they had not convincingly ruled out the

Cenozoic tectonics and landform evolution of the coast and adjacent highlands of southeast New South WalesM. C. BROWN

51 Debenham Street, Mawson, ACT 2607, Australia.

This paper has been written firstly to dispel a widely held notion that the structure and stratigraphyof Permian and Triassic sedimentary rocks of the southern Sydney Basin precludes post-Permiantectonic lowering of the coastal zone of southeast New South Wales with respect to the highlands;and secondly to present evidence of Cenozoic tectonic lowering of the coastal zone by gentle tiltingand, locally, by faulting. The apparent horizontal attitude of Triassic sandstone in an east–west sectioninland from Nowra precludes later faulting or steep monoclinal folding in this immediate area, butdoes not preclude geomorphically significant tilting or gentle warping; and it places no constraintson the tectonic and geomorphic history in areas south of the sandstone outcrop. The form of anOligocene erosion surface around Ulladulla, and the distribution of older rock units below this surfaceare also not incompatible with significant Cenozoic tectonism. Near Ulladulla, Mogo, Moruya, andMerimbula, mid-Cenozoic non-marine sediments and basalts in north–south-trending palaeovalleysdip gently seaward at angles around 1°—about the same as the eastward slope of the offshoreseismic basement and also similar to the average slope between the coastal zone and inlandplateaux; indicating that the coastal zone and continental shelf have been downwarped relativeto the inland plateaux in these areas. The area between Brooman, on the Clyde River, and the coastbetween Termeil and Bateman’s Bay, has been lowered by Cenozoic faulting. The steep slope onthe west side of the Clyde River is a dissected 200–300 m fault scarp, and there are two other east-facing fault scarps between the Clyde River and the coast. Fault blocks between the Clyde Riverand the coast are gently backtilted to the west. Further south, there may be more faults and tilt blocksbetween Bateman’s Bay and Moruya. Tectonic lowering of the coastal zone and continental shelfappears to be mostly post-mid-Cenozoic. This suggests that marine shelf sediments are likely to benot older than Miocene. There could also be older Cenozoic non-marine sediments and perhapsbasalts in palaeovalleys at the base of the section.

KEY WORDS: Cenozoic, continental shelf, landforms, Oligocene, New South Wales, tectonics

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possibility of relative coastal downwarp of 1–2°. Ollier andPain (1994) restated Ollier’s (1982) ideas in terms of coastaldownwarp rather than relative uplift of the highlands. Ina discussion (Brown 1996) of Nott and Purvis (1995) Iconcluded that evidence from the topography of the MtDromedary area and the structure of the Cretaceous Mt Dromedary intrusion was consistent with gentle east-erly downwarping of the coastal zone relative to the inlandplateau. Orr (1996) stated also that the coast near MtDromedary may have been downwarped relative to theinland plateau. Bishop and Goldrick (1999) envisaged thepossibility of relative downwarp of parts of the coastalzone but seemed to support a minimal role for tectonics inthe geomorphic evolution of the rest of eastern Australia.

There have also been suggestions that faulting mayaccount largely for the differences in elevation between oldland surfaces of the highlands and the coastal zone(Andrews 1911; Webb & O’Sullivan 1996). I agree with Youngand McDougall (1982, 1983) that the structure of thePermian sedimentary rocks rules out the possibility ofsignificant later faulting in the Ulladulla area. However,further south, there is good evidence, discussed later, thatfaulting has caused significant net lowering of an areabetween the Clyde River near Brooman and the coastbetween Termeil and Bateman’s Bay.

I believe that the inland plateaux and the presentcoastal lowlands were parts of a continuous low-relief landsurface from the Late Cretaceous to the mid-Cenozoic. Thissurface was probably exhumed from beneath a former thickcover of Early Cretaceous volcanic and volcaniclasticrocks (Brown 1996).The surface was at times differentiallyeroded to form valleys up to several hundred metres deep,which in many cases were later largely infilled withCenozoic basalt and/or sediments. Downwarping of thecoastal zone, accompanied by faulting in places, accountsessentially for the present mean differences in elevationbetween the plateaux and the coastal zone. The tectonic low-ering of the coastal zone possibly commenced in the LateCretaceous or Early Cenozoic, but much of it occurred afterthe mid-Cenozoic sedimentation and basalt flows of thecoastal zone.

Since my 1983 attempt to refute the conclusions ofYoung and McDougall (1982) asserting a minimal role fortectonics in the Ulladulla area, none of the publicationsasserting an important role for tectonics in the geomorphicevolution of this and adjacent areas have pointed out whatI consider to be fundamental flaws in the arguments forlong-term tectonic stability—particularly those based onthe bedrock Permian and Triassic geology. This has led tothe uncritical acceptance of these arguments by some later

Figure 1 Cenozoic faulting and tilting insoutheast New South Wales. Downthrowsides of faults with well-defined scarps,and monoclines, are marked; approxi-mate vertical Cenozoic displacements(in hundreds of metres) are shown bynumbers. B.R.F., Barney’s Range Fault;B.W.F., Berridale Wrench Fault; M.F.,Murrumbidgee Fault; L.G.F., LakeGeorge Fault; S.F., Shoalhaven Fault;C.R.F., Clyde River Fault; C.F., CockwhyFault; Mg.F., Murramarang Fault; P.P.F.,Point Perpendicular Fault. Informationis from published geological maps, Sharp(1994) and the author.

Cenozoic tectonics and landforms, NSW 247

authors, the unwarranted extrapolation of Young andMcDougall’s findings into areas hundreds of kilometresaway from Ulladulla, and a lack of attention to details ofthe structure and palaeogeography of Cenozoic basalts andsediments—the key to a better understanding of the geo-morphic and tectonic history. If these arguments had beenrefuted earlier, then Nott and Purvis (1996) would have beenless justified in stating ‘To this day the avoidance of thefield evidence supporting an entirely erosional origin of thecoastal lowlands between Ulladulla and Nowra still remainsthe crux of the issue.’

While agreeing with the above statement as it stands Ialso believe that the previous interpretations of this fieldevidence, which assert a minimal role for Cenozoic tec-tonics, are based on fallacious arguments and inaccurateand incomplete observations, and that the field evidenceclearly indicates a substantial role for Cenozoic tectonics.This includes evidence from the latest careful study of mid-Cenozoic basalt and sediments in the Brooman–Moruyaarea by Spry et al. (1999), evidence downplayed by theauthors and ignored by Kohn and Bishop (1999) in theircomments on the study.

In this paper the arguments for long-term tectonicstability and their shortcomings will be discussed, concen-trating particularly on the area of the southern SydneyBasin around Bendalong and Ulladulla. Then evidence forCenozoic coastal downwarping and faulting from thecoastal zone between Bendalong and the Victorian borderwill be considered, concentrating on direct evidence of

Cenozoic tectonism from the structure, sedimentology,and pre-depositional topography of the mid-Cenozoic sedi-ments and basalts of the coastal zone (evidence which hashitherto been largely ignored). Localities mentioned in thepaper are shown on Figures 1, 2 and 5. Topographic infor-mation is taken from 1:250 000, 1:100 000, and 1:25 000 topo-graphic maps published by the Australian and New SouthWales governments. Geological information, unless other-wise noted, is taken mostly from published 1:250 000 and1:100 000 geological maps of the Australian GeologicalSurvey Organisation and the Geological Survey of NewSouth Wales.

CASE AGAINST TECTONIC LOWERING OF THECOASTAL ZONE

Structure of the Permian and Triassic rocks of thesouthern Sydney Basin

The case for long-term tectonic stability is based largely onobservations of Young (1977) on the gently dipping Triassicand Permian sedimentary rocks of the southern SydneyBasin. Young noted that the top of the Triassic HawkesburySandstone, between Tallong and Nowra, near the coastabout 45 km to the east, has a near constant elevationbetween 600 and 650 m, while the top of the NowraSandstone in the underlying Permian sequence falls from600 m to near sea-level over the same distance (an average

Figure 2 Aspects of the geology andlandforms of the Ulladulla–Bendalongarea. Palaeozoic bedrock, mostly gentlyeast-dipping Permian sedimentary rocks,is shown blank; Oligocene fluvial sedi-ments are stippled; Oligocene basaltsshown by ‘v’ symbols. Topography isshown by 100 m and 500 m topographiccontours and selected spot elevations inmetres. Structure contours (heavy lines)are drawn on the unconformity at thebase of the Oligocene sequence. Awayfrom the immediate outcrop of theOligocene basalt and sediments, struc-ture contours are speculative and aredrawn so that the contoured surface isjust above the highest bedrock outcrops.Lines A and B are the lines of section inFigures 6 and 3 respectively. Informationis from published topographic and geo-logical maps, Faul (1984), Johnson (1985)and the author.

248 M. C. Brown

dip of 0.76°). From this he concluded that there had beenno significant deformation in the area since the end of thePermian. This conclusion was repeated in the paper byYoung and McDougall (1982) on the Ulladulla area about50 km further south and well south of the outcrop limit ofthe Hawkesbury Sandstone, in which they stated that theevidence is ‘unequivocal’. In their reply to my discussionof their paper (Brown 1983), they retreated somewhat fromthis and state that they ‘cleave to the doctrine of Williamof Occam and prefer not to multiply entities unnecessarily’(Young & McDougall 1983). However, the idea of tectonicstability since the Permian has been accepted withoutreservation by Nott et al. (1991), Nott and Purvis (1995, 1996)and Nott (1996a), and extrapolated as far south as theMerimbula area, about 200 km south of the outcrop of boththe Permian and Triassic rocks.

Bishop and Goldrick (1999) noted that the TriassicHawkesbury Sandstone has been gently warped, implyingsome post-Permian tectonism, but agreed with Young thatthere could not have been any Late Mesozoic or Cenozoicdownwarp of the coastal zone in the outcrop area of thesandstone.

The structure of the rocks of the southern Sydney Basinplaces some constraints on the geological and geomorphichistory. In particular the lack of significant faults or steepmonoclinal warps rules out the possibility of such dis-placements in the Mesozoic or Cenozoic in this immediatearea.

However the structure of Sydney Basin rocks places noconstraints on the possibility of gentle regional tilting orwarping in the Cenozoic. If this has occurred then it mustof course be reflected in the dips of Sydney Basin strata.For example, if the area had been gently tilted 1° east inthe Cenozoic, then any pre-existing easterly dips must havebeen increased by 1° and any westerly dips reduced by thesame amount; and an observation that some of the Permianor Triassic rocks are now horizontal would imply that theyformerly had a westerly dip of 1°. Thus the widely heldnotion that the apparent horizontal attitude of Triassicsandstone in an east–west section rules out the possibilityof a gentle seaward Cenozoic tilt is not valid unless theMesozoic tectonic history clearly demonstrates Mesozoictectonic stability or otherwise shows that the sandstonecould not have had a gentle westerly dip component at thestart of the Cenozoic.

Brown (1983) argued along the above lines to show thatYoung and McDougall (1982) had not disproved the possi-bility of gentle Cenozoic seaward tilting in the Ulladullaarea. In reply Young and McDougall (1983) supplied no evi-dence for Mesozoic tectonic stability or any other clearstatement about Mesozoic tectonic history, and stated:‘Brown’s suggestion that a Permian sequence that oncedipped to the east and north-east could subsequently bewarped downward to the west and then returned to its orig-inal orientation is, to say the least, imaginative. Indeed onecould envisage three or four see-sawing oscillations causedby hypothetical pulsations in the hypothetical thermaldoming.’ This attempt to ridicule my suggestion that therecould well have been more than one gentle deformation inthe area since the Permian is not warranted. Multiple defor-mations on a time-scale much shorter than the Mesozoic

Era are very well documented in the geological literature,and there are well-documented cases in which a later defor-mation has brought underlying rocks closer to theiroriginal attitudes.

Events in this region during the Mesozoic, summarisedby Jones and Veevers (1983), point to the very strongpossibility of Mesozoic warping or tilting. They includewidespread Jurassic and Cretaceous igneous activity andthe Late Cretaceous rifting and separation of the LordHowe Rise from eastern Australia. Further, as pointed outby Ollier and Pain (1996), structure contours on theHawkesbury Sandstone over a larger region drawn byStandard (1969) show that it dips gently north near itssouthern outcrop limit. The horizontal dip observed byYoung (1977) in this area is an apparent dip in an east–westsection. Over most of the remainder of its outcrop, extend-ing 180 km further north, it is gently folded with dipsaround 1°. At the Lapstone Monocline 50 km west of Sydneyit is displaced downward to the east by up to 180 m. Thedeformation of the sandstone must have occurred in theMesozoic or Cenozoic.

In view of what is known about the Mesozoic tectonichistory of the region, the present gently north-dippingattitude of the Hawkesbury Sandstone near its southernoutcrop limit could well have resulted from gentle easterlyCenozoic tilting of bedding which formerly dipped gently northwest. This effectively removes the majorpremise from the argument for tectonic stability since the Permian.

Bedrock units underlying Cenozoic erosionsurfaces

Young and McDougall (1983) and Nott (1996a) noted thatOligocene sediments and basalt at the coast near Ulladullaoverlie the Snapper Point Formation near the base of thePermian sequence, while Eocene and Oligocene basalts onthe plateau about 45 km inland rest on the NowraSandstone, higher in the sequence. They conclude from thisthat the present difference in elevation, about 600 m,between the Oligocene erosion surfaces of the coast and theplateau must be erosional and cannot be due to tectonic dis-placement.

These authors do not take into account that near-flat ero-sion surfaces can cut across a wide variety of stratigraphicunits in the underlying bedrock, the distribution of theseunits being controlled by the stratigraphy of the bedrockand its structure at the time the erosion surface developed.Thus, the Oligocene erosion surfaces of the plateau and thecoast could well have originally formed at about the sameelevation as each other and with the same underlying rockunits as at present. A subsequent easterly tilt averagingonly about 0.75° (which would have increased the easterlydip of the underlying Permian rocks by the same amount)could then account entirely for their present differences inelevation. The alternative conclusion of Young andMcDougall and Nott can only be sustained if it is firstassumed that the bedrock structure has not changed sincethe erosion surfaces first formed—a circular argument thatadds nothing to the solution of the controversy aboutCenozoic tectonism.

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Form of the Oligocene erosion surface atUlladulla

Young and McDougall (1982, 1983) used evidence from theshape of the erosion surface beneath Oligocene fluvial sedi-ments and basalts at and near the coast at Ulladulla to argueagainst the possibility of significant coastal downwarp.Some of their evidence is inaccurate or incomplete, and theshape of the Oligocene erosion surface, when more cor-rectly depicted, is consistent with easterly tilting after depo-sition of the sediments and basalt.

The basalts and sediments rest unconformably onPermian sedimentary rocks which dip gently eastward atangles generally less than 10°. About 13 km inland, aplateau about 500 m above sea-level capped by near-horizontal Permian sandstone is bounded by a steep east-facing erosional scarp.

Young and McDougall (1982 figure 1) presented a mapof the area around Ulladulla with structure contoursdrawn ‘on the Oligocene surface’ according to the figurecaption. It shows only 40 m and 20 m structure contours,suggesting that the Oligocene erosion surface is all abovesea-level and mostly around 20 to 40 m above sea-level. Thisis not so. Published geological maps show that bedrock out-crop rises well above 100 m in places near the inland bound-ary of the Oligocene sediments and that much of theOligocene outcrop is at the shoreline, so that the underlyingunconformity must be below sea-level in places. In the textof the paper the authors reveal that the contours are noton any meaningful surface at all, but are ‘Contours drawnthrough scattered bodies of silcrete’. The silcretes occur atvarious stratigraphic levels in the Oligocene sequence.Thus, the contours are drawn through a coastal outcrop ofsilcrete at Red Head near Bendalong, resting on basalt nearthe top of the sequence, which is 40–60 m stratigraphicallyabove other contoured outcrops closer to the basal uncon-formity (Figure 6).

Contours on the unconformity between the Permianand Oligocene sequences (Figure 2) show a fairly uniformslope of about 1.4–2° east to east-southeast over much of theoutcrop, sloping below sea-level in places, but rising

abruptly towards coastal Permian outcrops at BannisterPoint and Warden Head. The contours suggest that thesediments and basalt were deposited in a palaeovalleytrending near-parallel to the coast and with a broad valley floor which may well have been later tilted gentlyseaward.

A small outcrop of Oligocene basalt occurs about 5 kminland from the coast on a saddle near the southwesternshore of Lake Conjola, well inland of the other outcrops ofOligocene basalt and sediments. Its contacts with sur-rounding Permian rocks are not exposed, but appear to bebetween 40 and 60 m above sea-level. This is about 60 mlower than would be predicted by extrapolating inland thestructure contours on Figure 2 of the base of the Oligocenesequence closer to the coast.

Young and McDougall (1983) interpreted this basalt asa small remnant of a lava flow, and suggest that the smallangle of slope between it and a coastal basalt outlier nearPattimore’s Lagoon is an initial slope, thus ruling out anysignificant eastward tectonic tilt. Nott (1996a) agreed withthis interpretation. However, this inland basalt outcropdoes not negate the possibility of significant Late Cenozoiceastward tilting if it was originally at a lower elevationthan the coastal outlier. Thus it may be the remnant of alava flow in a separate palaeovalley, originally at a lowerelevation; or it could possibly be an intrusive volcanic plug,in which case its present contacts with the Permian rockscould be well below the Oligocene land surface. These twopossible interpretations are shown on Figure 3.

Summary

In summary, the case against Cenozoic tectonic loweringof the coastal zone is not soundly based and is certainly not ‘unequivocal’ as has previously been asserted. It hingeson the following: (i) a belief that Triassic sandstone in the southern Sydney Basin could not possibly have had a gentle west component of dip in the Late Mesozoic or Early Cenozoic; (ii) a mistaken belief that the original topography of an ancient erosion surface can

Figure 3 Geological and topo-graphic cross–section per-pendicular to the coast fromthe highland valley of theShoalhaven River throughBannister Point and offshore,along line B on Figure 2 andits continuation furtherinland. Upper broken line isan inferred (?)Cretaceouspalaeosurface. Lower brokenlines are Cenozoic palaeo-valleys. Folded Ordovicianand Devonian sedimentaryand volcanic rocks (shown bydiagrammatic fold traces) areoverlain unconformably by gently dipping Permian sedimentary rocks (stippled); the coarser stipple is the Nowra Sandstone, a promi-nent resistant marker unit. Permian intrusive monzonite is shown by cross symbols. Early to mid-Cenozoic basalt and fluvial sedi-ments are shown black. Offshore sediments are shown by short dash symbols. The small basalt outcrop 4.5 km north-northeast of thesection line and two prominent hills near the section line are projected onto the section. Information is from published geological andtopographic maps and Davies (1975).

250 M. C. Brown

be determined from the distribution of rock units which immediately underlie it; and (iii) erroneousstructure contouring of an Oligocene erosion surface nearUlladulla.

DIRECT EVIDENCE FOR CENOZOIC DOWN-WARP AND FAULTING IN THE COASTAL ZONE

Landforms and drainage patterns indicatingcoastal downwarp

Most of the evidence to date supporting tectonic loweringof the coastal zone in southeast New South Wales has beenpresented in papers by Ollier (1978, 1982), Ollier and Taylor(1988), and Ollier and Pain (1994). In general it is based onregional variations in the general level of the landscape andthe levels of ancient erosion surfaces, analysis of drainagepatterns, and seismic evidence for the geometry of the off-shore sediment basement and thicknesses of offshore sedi-ments (Davies 1975).

In general the higher peaks and ridges of the landscapeand remnants of ancient erosion surfaces show a decreasein elevation from the Great Divide to the coast, consistentwith an average east tilt of about 1°, and the offshore sediments rest on a surface with a similar average angle ofslope. Figures 3 and 4 illustrate these relationships.

Hubble et al. (1992) found a conical hill 800 m high ofCretaceous monzonite on the continental slope 50 km east-northeast of Mt Dromedary, and interpreted the contin-ental slope here as a former subaerially eroded landscape,now downwarped at least 1200 m.

Modern drainage between the Great Divide and thecoast has anomalous patterns, including boat-hook bendsand anomalous directions of tributaries, suggestive ofreversal of drainage which formerly flowed west to north-northwest (Ollier & Pain 1994).

Fault-controlled landforms

While the landform evidence is generally consistent witha simple coastal downwarp model, this is not the case inthe area between the coast and the Clyde River betweenBrooman and Runnyford, where landforms indicate sig-nificant Cenozoic fault displacements (Figure 5). The ClydeRiver in this area is in a near-straight valley trending near-parallel to the coast. The valley is markedly asymmetrical,rising steeply to altitudes of 250–350 m above river levelwithin 1.5–3.5 km of the river in a highly dissected slope onthe western side, and with much gentler slopes with sub-parallel drainage on the eastern side. Between the ClydeRiver and the coast, slopes are mainly gently to the west,but are interrupted by two steep southeast-facing scarpsaround 100 m high; one between Cockwhy Ridge andCockwhy Creek, and the other on the northwest side ofCullendulla Creek. There is another steep scarp facing thecoast, with maximum height of 283 m on the Cenozoicbasalt outlier of Mt Durras on the Murramarang Range.Further south, in the area between Bateman’s Bay and theTomaga River, there are two seaward-facing scarps around100 m high with gentle west-northwest slopes behind them.

The bedrock in the area comprises a highly deformedEarly Palaeozoic sequence of thinly interbedded marinesandstone, mudrock and chert, overlain unconformably inthe east by Permian marine conglomerate, sandstone, andmudrock which dip gently east. The Palaeozoic rocks areoverlain in places by Oligocene fluvial gravels and basalt(Spry et al. 1999) preserved mainly in a palaeovalleyimmediately east of the Clyde River near Brooman and ina southern extension of this palaeovalley between Mogoand Moruya (Figure 5).

The landforms described above do not reflect thebedrock structure, and can only reasonably be interpretedas the direct expression of Cenozoic faulting and tilting of a low relief land surface with steep east- to southeast-facing fault scarps separating gently back-tilted fault

Figure 4 Geological and topographiccross-section east–west through MtDromedary from the margin of theinland plateau to the continental shelf.Projected on to the profile are prominentpeaks up to 30 km north and south of thesection line (plotted according to theirdistance from the coast); also an outcroparea of late Early Cretaceous volcanicrocks 4 km south of the section line. Thearea is underlain by highly deformedOrdovician sedimentary rocks, intrudedby Silurian–Devonian granitoids andoverlain by Late Devonian sedimentaryrocks with open folds. The ‘palaeoplainsurface’ shown on the profile is aninferred Early Cretaceous palaeoplain,formerly covered at least in part by vol-canic and volcaniclastic rocks eruptedfrom Early Cretaceous volcanic centresincluding the Mt Dromedary intrusionand others nearby and offshore.Information is mainly from the 1996 Bega1:250 000 geological map; also from Davies(1975) and Nott and Purvis (1995).

Cenozoic tectonics and landforms, NSW 251

blocks between the Clyde River and the coast. The faults arenamed on Figure 5. Those north of Bateman’s Bay are themost clearly expressed in the landforms.

Maximum Cenozoic displacements on the faults, inter-preted from heights of fault scarps, are about 200–300 m onthe Clyde River and Murramarang Faults and 100–120 m onthe others.

The Clyde River Fault appears to die out about 6 kmnorth of Brooman, where no fault scarp can be recognised.Further north the Permian sedimentary rocks are notfaulted. The fault cannot be traced with certainty south ofRunnyford but could continue a further 5 km south along

the Buckenboura River. Spry et al. (1999) recorded over-steepening of the long profile of the Oligocene palaeovalleyat Brooman. This is consistent with some fault movementafter deposition of the Oligocene sediments, with thedownthrow of the eastern block near Brooman increasingtowards the south.

The Cockwhy Fault appears to die out in the southwestwhere Cockwhy Creek turns west around the southernlimit of the fault scarp. Northeast of Termeil no fault scarpcan be recognised in the easily erodable Permian sedi-mentary rocks. The fault could continue to the northeastand offshore to join the Point Perpendicular Fault at the

Figure 5 Tectonic interpreta-tion of landforms betweenBrooman and Moruya. Thebedrock of the area compriseshighly deformed Ordoviciansedimentary rocks and Devoniangranitoids, overlain uncon-formably by gently east-dippingPermian sedimentary rocks, theunconformity trending north–south through Durras. Landabove 75 m is finely stippled; spotelevations in metres are shown.Cenozoic faults with well definedscarps are shown by unbrokenheavy lines; other possible faults by broken heavy lines.C.R.F., Clyde River Fault;Ca.F., Cullendulla Fault; Mg.F.,Murramarang Fault. Longarrows show directions of gentletilting. Thin broken lines show Oligocene palaeodrainage.Geological boundaries and topo-graphic information are frompublished geological and topo-graphic maps and Spry et al.(1999).

coast near Jervis Bay, continuing offshore to the northeastto form a prominent step in the offshore seismic basementmapped by Davies (1975). The Cullendulla Fault appears toterminate relatively abruptly in the southwest near thehead of the Bateman’s Bay estuary at Chinaman’s Point,and more gradually to the northeast near Benandarah. Thelateral extents of the other faults are not well-defined.

The east-flowing tract of the Clyde River, now drownedto form Bateman’s Bay, is a diversion from a formerOligocene valley which continued further south (Galloway1978; Spry et al. 1999). This diversion initially follows a fault-angle depression at the foot of the scarp of the CullendullaFault, strongly suggesting that the diversion was caused bythe faulting, and also implying that the faulting post-datesthe Oligocene sediments and basalt. Spry et al. (1999) sug-gested that this diversion could have been due either touplift in the Mogo area to the south or to ‘valley aggradationand subsequent sea-level change’.

The landform evidence for the Cockwhy Fault is rein-forced by the bedrock geology, as shown on the Ulladulla1:250 000 geological map. Where the fault intersects the baseof the Permian sequence 2 km south southwest of Termeil,the unconformity is about 140 m above sea-level at the topof the scarp and about 40 m above sea-level at the foot ofthe scarp, suggesting that the unconformity is displacedabout 100 m by faulting—about the same as the height of thefault scarp at that place.

The fault along the Clyde River near Brooman and those along Cockwhy Creek and the east side of theMurramarang Range were first noted by Spry (1996). Theywere also mentioned by Brown (1998). Spry et al. (1999) didnot mention these faults, apart from a somewhat inaccuratereference to Brown (1998) which they quote as suggestingminor Cenozoic reactivation of older structures.

Orr (1994) had previously concluded that the Clyde Riverwas incised into an area of tectonic subsidence. This nowappears to be confirmed, although Orr did not specificallymention faulting as part of the mechanism of tectonicsubsidence.

Structure of mid-Cenozoic basalts and sediments

Many outcrops of Cenozoic basalts and sediments at andnear the coast of southeast New South Wales are shown onpublished geological maps. Basalts associated with sedi-ments near Ulladulla, Brooman and Moruya have early LateOligocene K/Ar ages between about 30 Ma and 27 Ma(Wellman & McDougall 1974; Young & McDougall 1982; Spryet al. 1996, 1999). Sediments near Merimbula (Long BeachFormation) have been dated as Oligocene to Early Mioceneby palynology and palaeomagnetic pole directions (Nott etal. 1991).

In view of the controversy about the possibility ofCenozoic tectonic lowering of the coastal zone, surprisinglylittle has been written about the structure of the Cenozoicsediments and basalts.

Young and McDougall (1982), referring to beds of silcretenear Ulladulla, stated: ‘Most beds dip only very gently,whereas some dip at angles of 5° or more.’ They gave noinformation on dip directions. In the area around Moruya,Bembrick (1972) has noted that the base of the OligoceneCoila Basalt has an average ‘gentle seaward dip of about

0.5°’ and that ‘the sediments above and below the basaltappear to conform to this general easterly dip’. Nott et al.(1991), describing a near-north–south coastal section ofCenozoic Quondolo Formation near Merimbula, stated that‘Bedding within the unit is mainly horizontal, except for asudden dip southward under the Long Beach Formation.’They also noted a local easterly dip in the boundarybetween weathering horizons in the sediments, whichthey attributed to slumping.

In well-exposed east–west sections at Bendalong andBannister Point and the quarries south of Pattimore’sLagoon, all in the Ulladulla area, the Tertiary sedimentsand basalt dip gently east. The contact between basalt andsediments near Pattimore’s Lagoon slopes at about 2.2° tothe east-southeast.

In the area around Moruya (Figure 5), Bembrick’s esti-mate for the seaward dip of the Coila basalt is a little low.Using Bembrick’s data and information from Spry et al.(1999) and published geological maps, I estimate seawarddips to be between 0.7 and 1°. For example, south ofMoruya the contact between sediments of the MeringoCreek Formation and the underlying Coila Basalt risesfrom sea-level at the coast to about 50 m a.s.l. about 3 kminland near Bergalia, an east dip of about 1°. North ofMoruya the contact between the Coila Basalt and under-lying sediments is at 76 m above sea-level at Burrawong Hill,about 3 km west of Mogo and more than 9 m below sea-levelat Broulee Island 11 km to the southeast (Bembrick 1972),an average slope of nearly 0.5°. This could be interpretedas the southeast component of an easterly dip of about 0.7°,the same as the easterly slope of the base of the BergaliaFormation between Burrawong Hill and Mogo.

In the east–west section at ‘The Pinnacles’, betweenMerimbula and Eden, well-defined bedding near the top ofthe Long Beach Formation slopes eastward at about 0.75°.

At Bendalong, about 20 m of Tertiary sediments areoverlain by two basalt flows. Bedding in the sediments, thecontact between sediments and basalt, and the contactbetween the two basalt flows all dip gently eastward (Figure6). The basalt–sediment contact slopes at 1.5° east in theeast–west section behind Washerwoman’s Beach. Structurecontours on this boundary, as mapped over a wider area byJohnson (1985), indicate an average dip of 1° to the east-southeast. The boundary between the two basalt flows hasan average slope eastward of about 1° in the cliff sectioneast of Boat Harbour Beach. These dips are close to the 1.4°east-southeast dip of the unconformity between the

252 M. C. Brown

Figure 6 Geological and topographic cross-section of theBendalong area. The line of section is approximately normal tothe coast and is line A on Figure 2. Information is from publishedtopographic and geological maps, Johnson (1985) and the author.

sediments and underlying Permian rocks in the Bendalongarea.

In both the Bendalong and Moruya areas, successivelayers of non-marine sediment and basalt with total thick-ness of 50 m or more have a similar dip to that of the basalunconformity over distances of several kilometres in thedirection of dip. This is strong evidence that the seawarddips in both areas are tectonic, due to east-tilting of thearea, and not initial dips. I would expect initial dips, dueto deposition on a sloping surface, to decrease markedlyupward in the sequence.

Mid-Cenozoic palaeodrainage and palaeoflowdirections

The mid-Cenozoic sediments of the coastal zone have beeninterpreted as of fluvial origin, but little is available frompublished sources on palaeodrainage trends or palaeoflowdirections of the sediments or the basalts.

In the Moruya area (Figure 5), Oligocene sediments andbasalt occur in an outcrop trending generally north–southabout 35 km long and about 5–10 km wide with higherbedrock outcrop on either side. They clearly occupy anorth–south palaeovalley. The palaeovalley continuedfurther north, being continuous with the palaeovalley ofthe Clyde near Brooman (Galloway 1978; Spry et al. 1999).Spry et al. found that elevations of the bed of the Broomanpalaeovalley fall to the south, and that imbrication in grav-els indicates a southerly palaeoflow direction. They alsofound sandstone pebbles, derived from Sydney Basin sedi-ments to the north, in Oligocene sediment outliers on theTomago–Clyde divide near Mogo, confirming the formercontinuity of the two palaeovalleys.

In the Tathra area, sediments of probable Oligocene ageoccur in a south-southeast-trending palaeovalley about4 km wide and 16 km long, incised 200–300 m into Palaeozoicbedrock (Nott et al. 1991). Nott et al. interpreted this as aformer south-southeast course of the Bega River, but didnot record palaeocurrent data. In the Merimbula area themain outcrop of Cenozoic sediments exposed along LongBeach described by Nott et al. (1991) appears to occupy anorth–south palaeovalley. Nott et al. also noted that thedominant sedimentary structures in the sediments aretrough cross-beds, but did not give an interpretation ofpalaeoflow directions. My observations of directions of trough axes and dips of cross-beds at ‘The Pinnacles’indicate a northerly palaeocurrent flow for the Long BeachFormation.

It was suggested above that the shape of the unconfor-mity surface at the base of the Oligocene sequence atUlladulla (Figure 2) indicated that the basalts and sedi-ments occur in a palaeovalley trending parallel to the coast.This interpretation is supported by measurements byJohnson (1985) of feldspar lath orientations from severalhorizontal sections of both basalts in the Bendalong area.They show a consistent preferred orientation parallel to thecoast, indicating a north-northeast or south-southwestflow direction for the lavas. A section from the basalt nearPattimore’s Lagoon, west of the inferred palaeochannelaxis, shows an east-southeast preferred orientation, sug-gesting that it may be in a tributary palaeovalley enteringfrom the west.

The alluvial sands, muds, and gravels and the basaltspreserved in these north–south palaeovalleys are veryunlikely to have had appreciable easterly initial dips;hence the east dips near Bendalong, Bannister Point,Mogo, Moruya and Merimbula are tectonic, resulting fromsubsequent easterly downwarp of the coastal zone.

Spry et al. (1999) noted that the alluvial sediments of thepresent Clyde River contain pebbles derived from outcropsof Devonian sedimentary and volcanic rocks near the pres-ent plateau margin 25 km to the west and that these areabsent in alluvial gravels of the Oligocene palaeovalley,implying significant drainage reorganisation in the area tothe west of the Clyde River. These drainage reorganisationsare consistent with Late Cenozoic tectonic lowering of theClyde River valley.

Structure of the Cretaceous Mt Dromedaryintrusion

The attitudes of steep-dipping flow structures in the lateEarly Cretaceous main intrusion at Mt Dromedary (Figures1, 2) are consistent with a later gentle east-tilting of the area (Brown 1996). On a map by Boesen and Joplin (1972),flow structures striking near north–south are dominantlyeither vertical or steeply west-dipping. Nott and Purvis(1996) disputed my interpretation, suggesting that theintrusion was originally dome-shaped, with flow structuresdipping radially outward from its centre. However, the flowstructures are near-vertical over the entire outcrop of theintrusion, showing that it is a near-vertical stock. A dome-shaped intrusion should have flow structures shallowingto near-horizontal at the centre of its outcrop. In any case,the dome structure interpretation still does not explain thedominance of west over east dips. Furthermore, steep-dipping flow structures in the smaller satellite intrusionsin the area are also mainly west-dipping.

Environments of deposition of mid-Cenozoicsediments

The mid-Cenozoic sediments of the coastal zone of south-east New South Wales have been interpreted as sedimentsof non-marine, dominantly fluvial, environments. (Young& McDougall 1982; Nott et al. 1991; Spry et al. 1999). The onlyfossils recorded are terrestrial plants and their spores andpollen. In this they are very similar to Early to mid-Cenozoic sediments of the inland plateaux (Taylor et al.1991; Nott 1992). Nott et al. (1991) suggested that the rela-tively large thickness of mid-Cenozoic sediments in theMerimbula area is the result of aggradation in a low-lyingcoastal zone due to rising sea-levels. However, there is noother evidence for marine influence. Similarly thick accu-mulations of Cenozoic sediments on the inland plateauxhave been explained, with good supporting evidence, as theresult of partial or complete damming of drainage byCenozoic tectonism (Gill & Sharp 1957; Singh et al. 1981;Taylor & Walker 1986; Sharp 1994) or by basaltic lava flows(Nott 1992; Brown et al. 1993; Brown 1994). Such mechanismscould well explain the thick Cenozoic sediments of thepresent coastal zone.

The basalts associated with the Cenozoic sediments ofthe coastal zone appear to have been extruded subaerially,

Cenozoic tectonics and landforms, NSW 253

supporting the non-marine interpretation for the sedi-ments. Bembrick (1972) noted that the Coila Basalt of theMoruya area ‘crops out at and below sea level, but nofeatures have been observed which would suggest that it was extruded into a standing body of water’. The same can be said for the basalts of the Ulladulla–Bendalongarea.

If the present coastal plains between Bendalong and theVictorian border have been at their present elevations nearsea-level since the Oligocene or earlier, as suggested byauthors arguing for long-term tectonic stability, they shouldhave been flooded by the later sea-level rises of the EarlyMiocene and perhaps the Pliocene. The absence of anyrecords of marine sediments of these ages is consistentwith the present coastal zone having been well above sealevel during these sea-level rises; its present elevation theresult of Late Cenozoic tectonic lowering, continuing per-haps as late as the Pliocene. The alternative explanation,that Miocene and perhaps Pliocene marine sedimentswere deposited but have since been eroded off, faces thedifficulty that large thicknesses of Cenozoic sediments arestill there, in places with intact Miocene to Pliocene deep-weathering profiles close to present sea-level (Nott et al.1991).

Further north, at Little Bay near Sydney, Miocene estu-arine sediments occur in a palaeovalley close to the coastat about 30 m above sea-level (Pickett et al. 1997). Thus thispart of the Sydney area can not have been significantly low-ered since the Miocene, and appears to have had a tectonicand geomorphic history different from that of the coastalzone further south.

DISCUSSION

Long-term tectonic stability versus Cenozoictectonism

The arguments for tectonic stability in southeast NewSouth Wales since the Permian are baseless. The two mostfrequently used arguments, based on the structure ofPermian and Triassic rocks of the southern Sydney Basinand on rock units which underlie Cenozoic sediments andbasalt, are certainly not ‘unequivocal evidence for long-term tectonic stability’ as stated by Young and McDougall(1982).

On the other hand there is clear and direct evidencefrom the structure and palaeogeography of many of theoccurrences of mid-Cenozoic basalts and sediments ofthe coastal zone that they have been tilted seaward at anglesbetween 0.7 and 2°, and some less convincing evidence thatthe Cretaceous Mt Dromedary intrusion has been tilted sea-ward. The continental slope has also been interpreted as adownwarped former land surface. There is also geomorphicand stratigraphic evidence, and evidence from offshoreseismic profiling, that faulting with some accompanyingback-tilting of fault blocks contributed to tectonic lower-ing of the coastal zone around Brooman and Bateman’s Bayand part of the continental shelf further north.

Nott (1996b), discussing landscapes of southeast NewSouth Wales, stated ‘Since the 1930’s detailed field studiesconsistently show that Late Mesozoic to Cainozoic tectonics

have played a minimal role in shaping the modern land-scape’, a statement which encapsulates the views of thoseadvocating long-term tectonic stability.

There are two main problems with Nott’s statement. Thefirst is a scale problem. Detailed studies of relatively smallareas may indeed demonstrate a minimal role for tectonicsin some of these individual areas, but may be largelyirrelevant to the kilometre-scale changes in elevation on aregional scale between different parts of the highlands, andbetween the highlands and the coast and inland plains.Determining origins of these regional-scale landformsrequires integration of evidence from the geology and geo-morphology of the highlands and the stratigraphy andsedimentology of the sediments in adjacent sedimentarybasins.

The second problem with Nott’s statement is that itincorrectly summarises the conclusions of the authors ofmany detailed studies, particularly in the highlands.Studies in the highlands have generally revealed Cenozoicfaulting, tilting and warping, with relative vertical tectonicdisplacements of tens to hundreds of metres directlyreflected in the topography (Taylor 1910; Gill & Sharp 1957;White et al. 1977; Singh et al. 1981; Taylor & Walker 1986;Brown et al. 1993; Sharp 1994). In places, damming ofstreams by tectonism has resulted in accumulations of Cenozoic lacustrine and fluvial sediments (mostlyMiocene and younger) up to 200 m thick. Many of thesestudies have also revealed considerable erosional relief,both in the present landscape and in ancient landscapespresently being exhumed from beneath a cover of basaltand/or sediments. In general this erosional relief differslittle from the tectonic relief.

The broad north–south-trending highland valley of theupper Shoalhaven River (Ruxton & Taylor 1982; Nott 1992),is one area of the highlands where Nott’s statement isapplicable; but the southern part of this valley is itselfbounded by the east-facing dissected fault scarp of theShoalhaven Fault, over 400 m high in places. (Figure 1.)

Nott is not alone among recent authors in minimisingthe contribution of tectonics to the geomorphology of thehighlands. In their recent review of tectonics and geo-morphology of eastern Australia, Bishop and Goldrick(1999) discussed none of the many detailed studies whichconclude that there has been significant Cenozoic tecton-ism in the highlands.

The conclusions of most of the more recent detailedstudies in the coastal zone suggest a minimal role for tec-tonics in landform evolution. I believe, however, that theseconclusions are incorrect, and that the style of Cenozoictectonism near the coast of southeast New South Wales issimilar to that in the highlands. Figure 1 shows some of theCenozoic structures of the coastal zone and adjacent high-lands.

Tectonic lowering of the coast and continentalshelf and its timing

The coastal downwarp model outlined in various publi-cations of Ollier, and Ollier and Pain, but with somemodifications, accounts for the geomorphic and tectonicrelationships between the highlands and coastal zone ofsoutheast New South Wales. The simple coastal downwarp

254 M. C. Brown

model is complicated locally by the faulting in theBrooman–Bateman’s Bay area.

Ollier and Pain are somewhat vague about the timingof downwarp. As presented in their 1994 paper they appearto associate downwarp with the Late Cretaceous rifting andbreakup, but as pointed out by Li et al. (1996) and Nott(1996a), some of the statements in the paper imply a muchlater mid- to Late Cenozoic downwarp. Most recently(Ollier & Pain 1997), they proposed that the coastal down-warp model is generally applicable to passive continentalmargins world-wide. They proposed that the unconformitybelow continental shelf sediments on such margins is anerosional palaeoplain, the former land surface, which wasdownwarped during or soon after the rifting.

The seaward dips of around 1° in mid-Cenozoic sedi-ments and basalts along the coast of southeast New SouthWales, which I regard as tectonic, are about the same as theeastward slope of the offshore seismic basement and aresimilar to the average slope angles between inland plateauxand the coast. (Figures 3, 4) This strongly suggests that thecoastal zone and offshore seismic basement have beendownwarped relative to the inland plateaux, with thedownwarp accounting largely or completely for the differ-ences in elevation between the plateaux and the coast. Thisdownwarp must be mid-Cenozoic or younger since it hastilted the mid-Cenozoic basalts and sediments. It most likelycontinued into the Miocene and perhaps the Early Plioceneas indicated by the absence of onshore marine sedimentsof these ages and the presence of intact Early Miocene deepweathering profiles near present sea-level.

The mid- to Late Cenozoic age which I propose for most,if not all of the tectonic lowering of the coastal zone andcontinental shelf is much younger than the Late Cretaceousrifting and separation of the Lord Howe Rise from south-eastern Australia. There are, however, some indicationsthat downwarp may have commenced earlier. The seaward-flowing Towamba River, near the Victorian border,presently has its head at the edge of the inland plateau. Itappears to have drained seaward and to have extendedmuch further inland in the Late Paleocene, before its deeplyincised palaeovalley, up to 500 m deep, was covered bybasalts of the Monaro Volcanic Province (Veitch 1986;Brown et al. 1993; Brown 1994). This may imply some LateMesozoic to Early Cenozoic seaward tilting to provide theenergy for its rapid headward erosion after continentalbreakup. Nott (1992) has argued that the east-flowing lowerShoalhaven River was flowing eastward in the EarlyCenozoic. This is a drainage line which Ollier and Pain(1994) believed has been reversed by easterly downwarp ofthe coastal zone. Thus downwarp in this area may also havecommenced by the Early Cenozoic.

Orr (1994) suggested that the Clyde River formerlyflowed towards the north-northwest, and that it had beenreversed by tectonic lowering of its present drainagebasin. It flowed southward in its Oligocene palaeovalley(Spry et al. 1996, 1999) indicating that the reversal and henceat least some of the tectonic lowering must have occurredbefore then. Orr suggested a pre-Eocene reversal.Furthermore, the Oligocene valley at Brooman is in thefault-angle depression of the Clyde River Fault, suggestingagain that at least some of the fault movement had occurredby the Oligocene.

Implications for the offshore geology

The tectonic and geomorphic history of the area betweenthe highlands and coast should be reflected in the historyof sedimentation on the continental shelf. Unfortunatelythe continental shelf sediments of southeast New SouthWales have not been drilled, and there is no direct infor-mation on their ages and sedimentology. However, predic-tions of the likely offshore geology can be made for variousonshore scenarios.

If the preferred ‘late downwarp’ model is correct, thefollowing offshore geology would be expected. The offshorebasal unconformity would be a former Oligocene land sur-face with hundreds of metres of erosional relief, probablywith Early to mid-Cenozoic basalts and/or non-marinesediments in palaeovalleys, and perhaps remnants ofCretaceous erosion surfaces on topographic highs. Therewould be no Eocene marine sediments, and the sedimentswould be dominantly Miocene and younger, with initialvery rapid clastic sedimentation rates as the less resistantmaterials were rapidly stripped from the slopes onshore. Ifsome palaeovalleys in the former land surface have a fill ofbasalt, the upper surface of the basalt would very likelyshow on the seismic profiles as seismic basement. Relief onthe basal unconformity could thus be greater than the reliefof the seismic basement.

The model proposed by Ollier and Pain (1997) impliesdownwarping of the area between the shelf edge and theinland plateaux in the Late Cretaceous, the basal uncon-formity being a Cretaceous palaeoplain. If this is correct,then sedimentation on the shelf would have commenced,with initial high rates of clastic input, in the LateCretaceous. Marine sediments deposited during the majortransgressions of both the Eocene and Miocene would alsobe expected. Because of the overall lower sedimentationrates, non-clastics such as carbonates would be more abun-dant than in the previous scenario.

CONCLUSIONS

(1) The structure and stratigraphy of Permian andTriassic rocks around Nowra and Ulladulla shows thatthere could not have been any Mesozoic or Cenozoic fault-ing or steep monoclinal folding in that area but places noconstraints on the possibility of gentle regional tilting orwarping.

(2) Evidence from the structure, palaeogeography anddepositional environments of mid-Cenozoic sediments andbasalts strongly supports tectonic lowering of the coastalzone relative to inland plateaux, an idea based previouslyon landform evidence.

(3) The tectonic lowering was mostly by gentle regional seaward tilting at angles around 1°, butcomplicated by faulting and back tilting in the area around Brooman.

(4) Most of the tectonic lowering occurred in the LateCenozoic.

(5) The tectonically lowered surface was a mid-Cenozoic erosion surface with relief of a few hundredmetres, with some palaeovalleys partly filled with Early tomid-Cenozoic non-marine sediments and basalt.

Cenozoic tectonics and landforms, NSW 255

(6) The sediment wedge on the continental shelf islikely to be mostly Miocene and younger. There are unlikelyto be any pre-Miocene marine sediments, but there maywell be Early to mid-Cenozoic non-marine sediments andbasalts in palaeovalleys at the base of the section.

(7) Further progress in the understanding of theCenozoic tectonic and geomorphic history of southeastNew South Wales will depend largely on the drilling of off-shore sediments, and on further careful studies, like thatof Spry et al. (1999) of the onshore Cenozoic sediments andbasalts.

ACKNOWLEDGEMENTS

My field observations in southeast New South Wales weremade mostly as a staff member of the University ofCanberra (formerly Canberra CAE) and supported in partby University research grants. I thank Graham Taylor andother members of the Cooperative Research Centre forLandscape Evolution and Mineral Exploration (CRCLEME)based at the University of Canberra and the AustralianGeological Survey Organisation for encouragement andassistance in preparation of the manuscript, in particularColin Pain who drafted the text figures. Cliff Ollier has pro-vided constructive comments on two earlier versions of themanuscript. Some of the ideas in this paper were presentedat a CRCLEME seminar in Canberra in May 1997 and at theTownsville convention of the Geological Society ofAustralia in July 1998, and I thank participants for theirquestions and comments. I also thank Bernie Joyce andDavid Gibson, who reviewed the manuscript for thejournal, for their helpful comments.

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Received 24 September 1999; accepted 11 December 1999

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