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Evolution of drainage patterns on Cape York Peninsula, northeast ...
Australian Journal of Earth Sciences (2003) 50, 000–000 Evolution of drainage patterns on Cape York Peninsula, northeast Queensland A. FORSYTH AND J. NOTT* 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: Jonathan.Nott@jcu.edu.au 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 divide. STREAM CAPTURE/REVERSAL OR DIVIDE 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. 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. 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"Evolution of drainage patterns on Cape York Peninsula, northeast "