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Evolution of drainage patterns on Cape York Peninsula, northeast


Evolution of drainage patterns on Cape York Peninsula, northeast ...

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									Australian Journal of Earth Sciences (2003) 50, 000–000

Evolution of drainage patterns on Cape York Peninsula,
northeast Queensland

School of Tropical Environment Studies and Geography, James Cook University, PO Box 6811 Cairns,
Qld 4870, Australia.

           Drainage patterns along passive continental margins are often hypothesised to be the result of
           drainage disruption following highland uplift and downwarping of the highland flank. Several studies
           of stream catchments throughout southeast Australia have demonstrated that the opposite tends to
           be the case in this region because the field evidence favours stream and continental drainage-divide
           stability. While significant advancements have been made towards understanding this phenomenon
           in the southeastern corner of the continent, little is known of the evolution of streams and highlands in
           northeast Australia. Our study examines palaeochannels and fluvial sedimentary units close to the
           continental drainage divide in six stream catchments along the length of Cape York Peninsula. The
           results show that four of the catchments (Barron–Mitchell and Stewart–Holroyd) have experienced
           continental divide and drainage stability, whereas the Pascoe–Wenlock system appears to have
           experienced westward migration of the continental drainage divide and diversion of the Pascoe River.
           River diversion here is likely to be a result of the raising of base-level and flooding of stream channels
           during the Cretaceous marine transgression and subsequent stream incision by the Pascoe River along
           structural weaknesses in the underlying strata, following cessation of marine conditions.
           KEY WORDS: Australia, Cape York Peninsula, eastern highlands, drainage evolution, passive
           continental margin.

INTRODUCTION                                                     PHYSICAL SETTING
The origin and evolution of Australia’s eastern highlands        The geology of Cape York Peninsula is dominated by pre-
remains a contentious issue. There have been considerable        Mesozoic basement rocks of the Hodgkinson Province and
advances in recent years towards resolving the likely age        the Coen, Yambo and Georgetown Inliers along with
of highland uplift, extent of denudation and subsequent          two major Mesozoic/Cenozoic sedimentary basins—the
tectonic movements, particularly through the use of              Carpentaria and Laura Basins (Figure 1). The pre-
fission track analyses, stratigraphic investigations and          Mesozoic rocks crop out to form the elevated central
isotopic analyses of weathering mantles and bedrock (Bird        section of the peninsula and substantial sections of the
& Chivas 1988; O’Sullivan et al. 1995; Bishop & Goldrick         continental drainage divide. Strata of the Carpentaria
1998). Most of these studies have been concentrated in           Basin extend along much of the western and far northern
southeast Australia with few published on the northern           sections of the peninsula, whereas the Laura Basin occu-
sector of this 3000 km-long highland chain. This imbalance       pies a relatively small area of the southeastern region with
has restricted our ability to answer important questions         the majority of the basin occurring offshore along the
concerning the evolutionary unity of the highlands and           peninsula’s eastern margin. A dome of Silurian granite
also the role that continental-margin development has            (the Kimba Arch) separates the two Mesozoic sedimentary
played in their formation.                                       basins north of Laura and in this region forms the contin-
    We attempt to partially redress this imbalance by pre-       ental divide.
senting the results of an investigation into the origin of the      The origin and age of the eastern continental margin of
drainage patterns of six major streams on Cape York              Cape York Peninsula shares a similar, but tectonically
Peninsula, northern Queensland. Drainage patterns can,           independent, origin to the southeastern Australian
to an extent, reflect the tectonic history of a highland and,     margin. The northern Australian margin was passive in
hence, provide insight into the evolution of that highland       New Guinea during the Mesozoic, whereas the eastern
following uplift. We use a sedimentological and strati-          Australian continental margin was convergent with the
graphic approach to determine whether there has been             Pacific Plate. Struckmeyer and Symonds (1997) suggested
widespread drainage disruption because of continental-
divide migration and downwarping of the eastern high-
land flank or whether drainage patterns have remained
largely stable since the late Mesozoic.                          *Corresponding author:
2       A. Forsyth and J. Nott

that these two opposing margin settings were connected          and Townsville Troughs (Figure 1) during the Jurassic to
via a strike-slip fault system along the northeastern           Early Cretaceous. Whether the Late Mesozoic rifting
Australian margin that included possible subsidiary fault       caused uplift of the present-day highlands on Cape York
systems along the site of the present offshore Queensland       Peninsula or was possibly responsible for more localised
and Townsville Troughs (Figure 1). During the Late              uplift is yet to be determined. Nott and Horton (2000)
Jurassic to Early Cretaceous oblique extension occurred         suggested that the continental divide was already in
along this northeast strike-slip margin, resulting in the       existence during the Early to Middle Jurassic based on the
formation of the Queensland and Townsville Troughs.             sedimentology and stratigraphy of strata in the western
The transtensional tectonism in these basins is believed        Laura Basin (Figure 1). Their conclusions suggested that a
to have possibly caused volcanism and differential uplift       highland was present prior to formation of the Queensland
and erosion in adjacent regions (Struckmeyer & Symonds          and Townsville Troughs. Apatite fission track thermo-
1997). A further extensional event, although with a differ-     chronology of rocks in the Hodgkinson Province and Laura
ent orientation, during the Middle to Late Cretaceous           Basin regions of Cape York (Marshallsea et al. 2000)
culminated in breakup and opening of the Coral and              suggest, as in the case of the southeastern highlands, that
Tasman Sea basins (the former at 60–50 Ma and the latter        a major phase of denudation occurred during the Late
at ca 85 Ma). This latter extensional event was super-          Mesozoic. A similar history may also apply to the high-
imposed on the older rift system, resulting in reactivation     lands immediately south of the Cape near Townsville and
and overprinting of the primary basin-forming structures.       Charters Towers (O’Sullivan & Kohn 1998). The cooling
    The age of the northeastern Australian highlands is         history of these regions does not necessarily equate to a
much less well constrained than that of their southern          phase of regional tectonic uplift immediately prior to the
counterparts, primarily because considerably fewer              onset of denudation. Rather the apatite fission track
studies have been undertaken in this region. As in the          thermochronology data suggest that the highlands were in
case of southeastern Australia, the highlands were origin-      existence during the Late Mesozoic. It is interesting to note
ally believed to have been uplifted in response to rifting of   that the stratigraphy of the Laura Basin shows that basin
the continental margin and formation of the adjacent Coral      sedimentation was occurring at the same time as the
Sea at ca 60–50 Ma and, hence, later than in the southeast      apatite fission track thermochronology data suggests
(Veevers et al. 1991). However, Scott (1993) and Struckmeyer    rapid regional denudation was occurring. Marshallsea
and Symonds (1997) have suggested that uplift of the            et al. (2000) explained this anomaly as a product of
adjacent land mass may have occurred in response to the         increased hydrothermal activity within the basin sedi-
rifting responsible for the formation of the Queensland         ments causing anomalous fission track ages.

                                                                                             Figure 1 Location map showing
                                                                                             Queensland    and   Townsville
                                                                                             Troughs and onshore basins.
                                                                              Cape York drainage evolution                     3

    Pain et al. (1998, 1999) have proposed that following       Barron Falls, flows through the Barron Gorge and crosses
highland uplift, and at some time since the Cretaceous,         the coastal plain to enter the Coral Sea near Cairns.
the highlands experienced continental-divide migration              The Barron River’s eastward bend occurs ~1 km to the
because of downwarping of the highland’s eastern flank.          east of the continental drainage divide and here at the bend
They suggested that fluvial sediments near the divide            a southeast–northwest-aligned fault diagonally intersects
along with topographic depressions through the divide are       the river. At this point the divide itself is virtually indistin-
evidence for stream reversals and rearrangements that           guishable from the broad, low-relief floodplain composed of
occurred in response to the post-uplift tectonic movements.     sediments up to 34 m deep (Jensen 1998) and underlain by
The apatite fission track thermochronology data, however,        Upper Silurian – Upper Devonian Hodgkinson Formation
suggest a different story—that downwarping is unlikely to       (Bultitude et al. 1996). Streams draining to the west of the
have occurred (O’Sullivan & Kohn 1998; O’Sullivan et al.        continental divide flow into the Mitchell River, which
1998) because, as is the case with the southeast Australian     debouches into the Gulf of Carpentaria approximately
highlands, the fission track ages of rocks increase west-        400 km to the northwest. Jensen (1963) claimed that a
wards or inland across the coastal plain. The issue of divide   continuous bed of river gravel traverses the divide in this
migration or stability clearly needs to be resolved and this    area and Ollier (1991) subsequently interpreted this sup-
requires the collection of substantially more data from         posed gravel bed to indicate that the Mitchell River or one
many more field studies. Our contribution to this end has        of its tributaries had been captured by the Barron River.
been to undertake detailed examinations of those sites          Willmott and Stephenson (1989) also suggested that the
where fluvial sediments and the regional stratigraphy may        Barron River’s sharp eastward bend was evidence for
record the long-term history of streams close to the contin-    capture of the Mitchell River drainage network by the
ental drainage divide. Our field sites include the Pascoe        Barron River. However, such claims are difficult to substan-
and Wenlock Rivers towards the northern end of Cape             tiate because in order for the Barron River to have been a
York, the Stewart and Holroyd Rivers in the central Cape        pirate stream the Barron Falls (the major knickpoint)
region, and the Barron and Mitchell Rivers west of Cairns       would need to be at or upstream of the sharp eastward bend
at the Cape’s southern extremity  .                             (point of supposed capture), but as stated the falls are 24 km
                                                                downstream of the bend.

SITE DESCRIPTIONS                                               Stewart and Holroyd Rivers
                                                                From its source near Coen, approximately 400 km north-
Barron and Mitchell Rivers
                                                                east of Cairns, the Stewart River flows southward before
The Barron River flows northward from its source on the          taking a sharp turn towards the east (Figure 3). The
Atherton Tableland and turns sharply eastward ~36 km            Stewart River then flows over the eastern escarpment
west-northwest of Cairns (Figure 2). Approximately 24 km        approximately 2 km downstream after which it traverses
further downstream from the eastward bend, the Barron           the coastal plain to enter the Coral Sea. The continental
River descends the eastern escarpment via the 90 m-high         drainage divide separates the Stewart from the nearby

                                                                Figure 3 Coen Inlier and nearby rivers. Note the coincidence of
Figure 2 Location map showing the rivers of northeast Queen-    the northern tract of the Pascoe River with the boundary of the
sland.                                                          Coen Inlier and Carpentaria Basin.
4   A. Forsyth and J. Nott
                                                                                 Cape York drainage evolution                5

Holroyd River, which flows west into the Gulf of Carpen-             part of a groundwater hydrology investigation, allowed the
taria. In a similar fashion to the Barron and Mitchell              reconstruction of the bedrock topography below the flood-
Rivers, the catchments of the Stewart and Holroyd Rivers            plains of the Barron and Mitchell Rivers in the region near
are separated by a low-relief plain. This area forms part of        the Barron’s sharp eastward bend. The results from 27
the central Coen Inlier near the boundary between Siluro-           boreholes to bedrock in this area highlight the existence
Devonian granites and the Coen Metamorphic Group                    of two significant, buried palaeochannels. These palaeo-
rocks of the Savannah Province (Blewett & Trail 1995).              channels parallel each other and are separated by the
Largely unconsolidated fluvial sand and gravel occur as a            present continental drainage divide. They diverge where
high terrace above the surrounding incised stream net-              the eastern palaeochannel turns eastward following a
work near the headwaters of the Stewart River and Pain              near-identical course to the present-day Barron River. The
et al. (1998) regarded these sediments as evidence that             western palaeochannel continues northwestwards like the
the Stewart River once formed part of the Holroyd                   present-day Mitchell River. Figure 4 depicts the inter-
catchment.                                                          polated bedrock contour levels from the drillhole data.
                                                                        The eastern palaeochannel is at least 33.8 m deep and
                                                                    occurs close to the present position of the Barron River
Pascoe and Wenlock Rivers
                                                                    (Figure 4). The sediments filling this palaeochannel are
The Pascoe River rises in the Tozer Range 146 km east of            predominantly composed of brown and grey sandy clay and
Weipa and 544 km northeast of Cairns (Figure 3). The                occasional sand lenses. The western palaeochannel has
course of the river essentially forms a large loop for it flows      filled with ~25 m of sediment similar to that in the eastern
south from its headwaters for approximately 19 km before            palaeochannel. However, the western palaeochannel also
turning sharply towards the west-northwest. It then takes           contains layers of volcanic strata at depth and gravel
another sharp turn to the north 33 km further downstream                                         .
                                                                    higher in the stratigraphy The western palaeochannel
and after a similar distance makes another abrupt change            runs subparallel to its eastern counterpart until it veers
of direction to flow eastwards towards the Coral Sea. The            toward the west ~3.5 km northwest of Biboohra (Figure 4).
northward flowing reach of the Pascoe River follows the              The borehole data also show a tributary palaeochannel
boundary between the Coen Inlier and the Mesozoic                   entering the main western palaeochannel from the south-
Carpentaria Basin sediments to the west (Figure 3). The             west.
river’s final eastward bend coincides with an east-trending              Previous interpretations of the drainage evolution of
fault at its junction with Hamilton Creek. The valley of            the Barron and Mitchell catchments suggested that a
Hamilton Creek follows this fault and while not clearly                                                               ,
                                                                    palaeochannel may have once joined the Clohesy a tribu-
expressed at the surface beyond this valley it is likely that       tary of the Barron, or the upper Barron River to the
the eastward flowing reach of the Pascoe River also follows          Mitchell River (Ollier 1991). No evidence, based on the
this structural control. Hence, in a somewhat unusual               borehole data, could be found that any palaeochannel
fashion, the Pascoe River rises in country east of the              crossed the divide in this region. The most likely location
continental drainage divide, flows towards it, turns and             for a former channel to have crossed the divide is near the
essentially follows the divide to later turn away and head          eastward bend in the present-day Barron River and it could
seawards. The Wenlock River rises in the Sir William                be expected that such a feature may be depicted by simil-
Thompson Range that forms part of the continental                   arities in stratigraphy between boreholes on either side of
drainage divide near the beginning of the northward                 the present-day divide. However, this is not the case. The
flowing reach of the Pascoe River. The two rivers flow                western group of boreholes contain sediments similar to
close to each other before the Pascoe turns east and the            that found in the eastern boreholes but, as stated, unlike
Wenlock continues northwest to enter the Gulf of Carpen-            the latter, basic volcanic flows and gravels were found in
taria. Pain et al. (1998) suggested that river capture or           the western examples. This provides some evidence,
reversal is indicated in the Pascoe–Wenlock interfluve               although not conclusive, that at least in this region the
area by a ‘very clear’ palaeochannel ‘above which the               western and eastern palaeochannels have different
Pascoe River turns north’.                                          stratigraphies and appear unlikely to have been joined
                                                                    by a channel crossing the present continental drainage
STABILITY?                                                          Stewart–Holroyd interfluve

Barron–Mitchell interfluve                                           Pain et al. (1998) claimed that the Stewart River is an
                                                                    obvious example of drainage disruption. In support of
The results of a detailed drilling program by the Queens-           their claim they suggested that a nearby elevated unit of
land Department of Natural Resources (Jensen 1998), as              gravels marks the ancient course of the Stewart across the
                                                                    present continental drainage divide and the presence of a
                                                                    ‘boathook’ or sharp eastward bend in the Stewart River
Figure 4 Borehole locations, subsurface (bedrock) topography
and palaeochannels and cross-sections of the palaeo-Barron and
                                                                    marks the location of drainage capture or reversal. Sharp
Mitchell Rivers west of Cairns. Note that palaeochannels existing   bends are common in coastal streams, and indeed in
parallel to the Barron and Mitchell Rivers and the palaeo-Barron    some west-flowing streams, along the length of eastern
River take a sharp eastward bend. Note also that there is no sub-   Australia. We suggest that the presence of such bends
surface channel joining the Barron and Mitchell catchments.         alone cannot be taken as evidence for drainage
6        A. Forsyth and J. Nott

disruption because in many instances these bends can be                Field inspection of the elevated unit of gravels believed
structurally controlled (see Young 1977 for an example              to mark the course of the stream connecting the present-
from Shoalhaven River, and the Pascoe River in this                 day Stewart and Holroyd catchments shows that they are a
study).                                                             thin sheet of fluvial sediments whose location and extent

Figure 5 Location of high-level fluvial sediments near the headwaters of the Stewart River catchment. Continental drainage divide fol-
lows Peninsula Development Road.
                                                                                  Cape York drainage evolution                    7

are shown in Figure 5. These sediments abut the eastern             ental drainage divide. Westwards of this point to the divide
side of the continental drainage divide at approximately            itself the sediments are predominantly composed of sub-
200 m a.s.l. (above sea-level). The unit stands 20–35 m above       angular clasts up to 10 mm diameter, set within a ferru-
surrounding streams, is 2 km long and varies in thickness           ginous sandy soil. The clasts have been derived from a local
from a few metres to less than a metre. The sediments are           hill composed of metamorphic rocks. There is no evidence
characterised by well-rounded clasts of quartzite within a          of a similar unit of fluvial sediments on the western side of
matrix of rounded to subangular grains of siliceous sand.           the divide in the headwaters of streams draining into the
In general, the quartzite clasts increase in size eastwards         Holroyd catchment. A similar outcrop of fluvial sediments
(Figure 6) and in places where the clasts are imbricated            occurs on top of a hill, again at approximately 200 m a.s.l.,
they indicate a stream flow direction towards the north to           to the east of the sharp eastward bend in the Stewart River
northeast. The sedimentary unit pinches out at its western          (Figure 5). At this point the sediments are composed of
end approximately 200–300 m east of the present contin-             clasts of subrounded quartzite within a sand matrix. No

Figure 6 Stratigraphy of high-level fluvial sedimentary unit near the headwaters of the Stewart River catchment. Note that the fluvial
unit pinches out east of the continental drainage divide.

Figure 7 Stratigraphy of Mesozoic strata across and near the continental drainage divide near the Pascoe and Wenlock Rivers. See
Table 1 for details on the age and depositional environment of the strata.
8        A. Forsyth and J. Nott

suitable sections were found from which to derive a palaeo-       Pascoe River, but no fluvial sediments were evident in this
current direction here, but the near-identical elevation of       valley or was there any sign that a stream may have
this sedimentary unit suggests that it was probably depo-         crossed the divide here at any time in the past. Farther
sited contemporaneously with the fluvial sediments                 north, the valley of Hamilton Creek, which joins the
described closer to the divide.                                   Pascoe at its sharp eastward bend, extends towards the
                                                                  northwest as a shallow depression across the continental
                                                                  drainage divide. However, this valley is fault controlled
Pascoe–Wenlock interfluve
                                                                  and is marked by a series of springs that were likely to be
There are no easily identifiable sequences of sediments            responsible for the gradual weathering and denudation
close to the continental drainage divide separating the           that formed this feature. The Miocene Yam Creek beds are
Pascoe and Wenlock river catchments. There is a shallow           confined to the valley of Hamilton Creek. These beds are
depression in the divide close to the north bend in the           composed of fluvial sediments that display increasing clast

Table 1 Stratigraphy of the Mesozoic sedimentary sequences in the Pascoe–Wenlock interfluve region (after Senapati 1988).

Unit                             Depositional environment

Garraway Sandstone
Wenlock Member                   Fluvial deposition derived from a highland to the east.
Bromley Member                   Shallow marine. Highland to the east remained exposed during deposition.
Wreath Member                    Prograding fluvial flowing west.
Gilbert River Formation
Batavia Member                   Transitional between braided fluvial and near-shore marine. Bimodal palaeocurrent direction.
Glennie Member                   Wave-dominated deltaic – shallow marine. Bimodal palaeocurrent direction.
Briscoe Member                   Shallow marine. Bimodal palaeocurrent direction.
Rolling Downs Group              Shallow marine (<50 m).

Figure 8 Schematic diagram illustrating the infilling of the lower reaches of pre-Cretaceous Pascoe–Wenlock River with sediment
during Cretaceous marine transgression. Note the change in position (westward migration) of the continental drainage divide
following regression of Cretaceous seas and subsequent diversion of the Pascoe River along structural controls.
                                                                               Cape York drainage evolution                  9

size and bed thickness in the downstream direction. The           sion as it eroded into a new land surface and followed
Yam Creek beds do not extend across the continental               structural weaknesses. This may explain why in this
drainage divide, but rather pinch out to the east of the          region the Tozer and Hamilton Ranges from which the
divide. These facts suggest that this valley was not the site     Pascoe River rises lie to the east of, and are considerably
of a former west-flowing channel across the continental            higher than, the present continental drainage divide.
    There is evidence for westward migration of the contin-
ental drainage divide in this region, but this evidence alone     DISCUSSION AND CONCLUSION
does not suggest that divide migration resulted from
downwarping of the eastern flank of the highlands. The             Except for the Pascoe–Wenlock Rivers the available field
Pascoe–Wenlock interfluve and the headwaters of the                evidence suggests that there has been minimal, if any,
Pascoe River (Tozer and Hamilton Ranges) are capped by a          disruption to major drainage patterns on Cape York
thick sequence of Mesozoic strata (Figure 7). These strata        Peninsula. Palaeochannels infilled with sediment in the
are composed of both fluvial and marine facies (Senapati           Barron–Mitchell Rivers region west of Cairns show con-
1988). The stratigraphy, age and depositional environment         sistency in stream patterns with no evidence for a river
of these strata are presented in Table 1. The sequence now        system from the Barron catchment previously traversing
forms part of the western edge of the Mesozoic Carpentaria        the present continental drainage divide. The unit of high-
Basin and is believed to have once overlain a large part of       level fluvial sediments near the headwaters of the Stewart
the Coen Inlier to the east (Senapati 1988; Pain et al. 1998).    River were deposited by a stream, possibly the Stewart
    The present elevation of the Mesozoic strata in this          River itself, that flowed towards the east coast from the
region increases towards the east rising to 220 m a.s.l. in       present divide. These two locations, separated by approxi-
the Hamilton Range east of the present continental drain-         mately 700 km, together with the findings of Nott and
age divide (160 m a.s.l.). From here the strata dip to the west   Horton (2000) for the Laura region mid-way between these
at approximately 1 (Figure 7). Individual units in the            two locations, suggest that the continental divide has
Mesozoic sequence increase in thickness to the west and           remained stable along the length of much of Cape York
palaeocurrents show a westerly flow direction in the               Peninsula. Unfortunately the lack of a reliable chronology
fluvial units and bimodal direction in the littoral facies         for the stream sediments in the Barron–Mitchell and
(Senapati 1988).                                                  Stewart–Holroyd systems limits our ability to determine
    Considered together, the palaeocurrents, regional dip         the antiquity of this divide stability, although the divide
and increasing unit thicknesses to the west suggest that the      has been stable since at least the Early Jurassic (180 Ma) in
continental drainage divide was farther east of its present       the Laura region (Nott & Horton 2000). Volcanics inter-
position during the Cretaceous, possibly in the area of the       bedded with the sediments in the palaeo-Mitchell channel
Hamilton Range (Figure 7). It is possible that the Pascoe         suggest that the sediments here may be several millions of
River flowed across the region now occupied by the present         years in age, based on the general age of volcanics on the
continental divide into the present Wenlock River catch-          Atherton Tableland (Coventry et al. 1985). The age of
ment prior to the Cretaceous. This may explain the west-          the fluvial sedimentary unit near the headwaters of the
erly course of the Pascoe in its upper reaches and the fact       Stewart River is even less well constrained, although it
that it rises east of the present continental divide. But its     clearly pre-dates incision of streams in the region to ~30 m
path has been subsequently diverted to the north and then         below this level and, therefore, appears to be many tens of
east to become an east-coast draining stream. We cannot be        millions of years in age and potentially older. Despite these
certain why the Pascoe River was diverted, but it is clear        difficulties in providing a reliable chronology for these
that there is no conclusive evidence that it is due to            deposits, the evidence at hand clearly demonstrates that
tectonic processes. It appears that diversion has occurred        stream patterns have maintained their general form and
since the Cretaceous. Figure 8 shows the sequence of infill-       do not display evidence of disruption.
ing of the pre-Cretaceous landscape with Cretaceous strata            The field evidence from the Pascoe–Wenlock Rivers
in concert with the marine transgressions. The lower              region is probably the first reliable evidence yet recognised
Pascoe–Wenlock valley was filled with these sediments as           for divide migration and drainage disruption anywhere
sea-levels rose, resulting in a shallowing of stream gradi-       along the east coast of Australia. Such claims have been
ents and the eventual cessation of stream flow into the area       made for several other stream systems such as the
now occupied by the present Wenlock catchment during              Clarence–Morton Rivers in northern New South Wales
full marine conditions. We suggest that following the final        (Haworth & Ollier 1992) and the Shoalhaven–Wollondilly
marine regression the Pascoe River incised into the Creta-        Rivers on the New South Wales south coast (Taylor 1911;
ceous strata along the boundary between the Coen Inlier           Ollier & Pain 1994), but the actual evidence presented has
and the Carpentaria Basin and followed this structural            always been ambiguous and in the latter case has been
weakness along its present north-flowing reach. Much of            repeatedly refuted since 1931 (Craft 1931; Young 1977; Young
the modern course of the Pascoe River appears to be               & McDougall 1982). In the case of the Pascoe–Wenlock
structurally controlled both in its north-flowing reach and        Rivers, the west dip and west-flowing palaeocurrents of the
likewise where it meets the fault at the junction with            Mesozoic fluvial strata (Table 1) across the present contin-
Hamilton Creek and turns east. It is likely that diversion of     ental divide suggest that the divide was located farther east
the Pascoe River following the Cretaceous marine trans-           than its present position prior to the Cretaceous. The
gression was not a function of divide migration, but rather       Pascoe River now in its north-flowing reach, and where it
divide migration was a function of the Pascoe River’s diver-      turns sharply to the east, is structurally controlled and
  10        A. Forsyth and J. Nott

  any suggestions as to why the divide has migrated here                       HAWORTH R. J. & OLLIER C. D. 1992. Continental rifting and drainage
  needs to take these structural controls of the drainage                          reversal: the Clarence River of eastern Australia. Earth Surface
                                                                                   Processes and Landforms 17, 387–397.
  into account. We suggest that the subsequent stream
                                                                               JENSEN H. I. 1963. Sketch of the geology and physiography of Cape
  incision by the Pascoe River following the last Mesozoic                         York. Queensland Geographical Journal 62, 12–60.
  marine regression (post-deposition of Cretaceous Rolling                     JENSEN G. 1998. Biboohra Groundwater Investigation. State Water
  Downs Group) effectively resulted in divide migration                            Projects and Department of Natural Resources, Brisbane.
                                                                               MARSHALLSEA S. J., GREEN P. F. & WEBB J. 2000. Thermal history of the
  not the reverse. Hence, this was a localised event and
                                                                                   Hodgkinson Province and Laura Basin, Queensland: multiple
  does not appear to have occurred elsewhere on Cape York                          cooling episodes identified from apatite fission track analysis and
  Peninsula.                                                                       vitrinite reflectance data. Australian Journal of Earth Sciences
      The development of geomorphic features along passive                         47, 779–797.
  continental margins is frequently attributed to highland                     NOTT J. F. 1992. Long-term drainage evolution in the Shoalhaven
                                                                                   catchment, southeast highlands, Australia. Earth Surface
  downwarping and consequent widespread drainage
                                                                                   Processes and Landforms 17, 361–374.
  disruption following uplift of the margin highland                           NOTT J. F. 1998. Unravelling the evolution of drainage patterns in the
1 (Gilchrist & Summerfield 1991). While this may be the                             Shoalhaven catchment; a brief case history. Geological Society of
2 case on other continents (Gilchrist & Summerfield 1991), a                        Australia Special Publication 20, 50–54.
                                                                               NOTT J. F. & HORTON S. 2000. 180 Ma continental drainage divide in
  growing body of evidence suggests that this hypothesis
                                                                                   northeast Australia: implications for passive margin tectonics.
  may not be the most applicable for Australia’s eastern                           Geology 28, 763–766.
  highlands. Where the hypothesis has been tested against                      O’SULLIVAN P. B., FOSTER D. A., KOHN B. P., GLEADOW A. J. W.
  field evidence in individual stream catchments in eastern                         & RAZA A. 1995. Constraints on the dynamics of rifting and
  Australia the results have either been very ambiguous, for                       denudation on the eastern margin of Australia: fission track
                                                                                   evidence for two discrete causes of rock cooling. In: Mauk J. L. &
  example, the Clarence–Morton region (Haworth & Ollier
                                                                                   St George J. D. eds. Proceedings of the 1995 PACRIM Congress,
  1992), or they have clearly demonstrated that down-                              pp. 441–446. Australasian Institute of Mining and Metallurgy
  warping, divide migration and stream diversions have                             Publication 9/95.
  not occurred (Young 1977; Bishop et al. 1985; Taylor et al.                  O’SULLIVAN P. B. & KOHN B. P. 1998. Episodic late Palaeozoic
                                                                                   to Cainozoic cooling/denudation along the northeastern
  1985, 1990; Nott 1992, 1998). A growing body of field evidence
                                                                                   Queensland margin. Geological Society of Australia Abstracts
  is providing the same conclusions for the northern sector                        49, 345.
  of Australia’s eastern highlands. Together with the apatite                  O’SULLIVAN P. B., KOHN B. P., GLEADOW A. J. W. & BROWN R. W. 1998.
  fission track thermochronology data and the antiquity of                          The palaeoplain model does not work for the southeast Australian
  the continental divide near Laura on Cape York, the                              passive margin: evidence from AFT thermochronology. Geo-
                                                                                   logical Society of Australia Abstracts 49, 346.
  results of this study suggest that divide and drainage
                                                                               OLLIER C. D. 1991. Ancient Landforms. Belhaven Press, London.
  stability may be the norm for substantial sections of                        OLLIER C. D. & PAIN C. F. 1994. Landscape evolution and tectonics in
  eastern Australia.                                                               southeastern Australia. AGSO Journal of Australian Geology &
                                                                                   Geophysics 15, 335–345.
                                                                               PAIN C. F., WILFORD J. R. & DOHRENWEND J. C. 1998. Regolith of Cape
                                                                                   York Peninsula. In: Bain J. H. C. & Draper J. J. eds. North
  ACKNOWLEDGEMENTS                                                                 Queensland Geology. Australian Geological Survey Organisation
                                                                                   Bulletin 240.
  We thank journal reviewers D. Dunkerley and G. Taylor for                    PAIN C. F., WILFORD J. R. & DOHRENWEND J. C. 1999. Regolith of Cape
  their comments.                                                                  York Peninsula: implications for mineral exploration. In:
                                                                                   Taylor G. & Pain C. eds. New Approaches to an Old Continent,
                                                                                   3rd Australian Regolith Conference Proceedings, Regolith ‘’98,
                                                                                   pp. 55–66. Cooperative Research Centre for Landscape Evolution
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                                                                                      Cape York drainage evolution                   11

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   Cairns District. Queensland Department of Mines, Brisbane.            near Ulladulla, southern new South Wales. Journal of the Geo-
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   Geomorphologie 21, 262–283.                                        Received 19 April 2002; accepted 24 October 2002

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