Factors controlling the chemical evolution of travertine‐depositing rivers of the Barkly karst,northern Australia

Groundwaters feeding travertine‐depositing rivers of the northeastern segment of the Barkly karst (NW Queensland, Australia) are of comparable chemical composition, allowing a detailed investigation of how the rate of downstream chemical evolution varies from river to river. The discharge, pH, temperature, conductivity and major‐ion concentrations of five rivers were determined by standard field and laboratory techniques. The results show that each river experiences similar patterns of downstream chemical evolution, with CO₂ outgassing driving the waters to high levels of calcite supersaturation, which in turn leads to widespread calcium carbonate deposition. However, the rate at which the waters evolve, measured as the loss of CaCO₃ per kilometre, varies from river to river, and depends primarily upon discharge at the time of sampling and stream gradient. For example, Louie Creek (Q = 0·11 m³ s^?1) and Carl Creek (Q = 0·50 m³ s^?1) have identical stream gradients, but the loss of CaCO₃ per kilometre for Louie Creek is twice that of Carl Creek. The Gregory River (Q = 3·07 m³ s^?1), O'Shanassy River (Q = 0·57 m³ s^?1) and Lawn Hill Creek (Q = 0·72 m³ s^?1) have very similar gradients, but the rate of hydrochemical evolution of the Gregory River is significantly less than either of the other two systems. The results have major implications for travertine deposition: the stream reach required for waters to evolve to critical levels of calcite supersaturation will, all others things being equal, increase with increasing discharge, and the length of reach over which travertine is deposited will also increase with increasing discharge. This implies that fossil travertine deposits preserved well downstream of modern deposition limits are likely to have been formed under higher discharge regimes. Copyright © 2002 John Wiley & Sons, Ltd.     

Bedload yields for sand‐bed streams in the Ngarradj Creek catchment,Northern Territory,Australia

Bedload yields were calculated by 39 methods at the East Tributary gauge, nine methods at Upper Swift Creek gauge and 11 methods at Swift Creek gauge in the Ngarradj Creek catchment in northern Australia. These methods involved combining various significant bedload rating curves determined for a measured bedload data set for a 4‐year period with either the hourly or daily hydrographs or flow duration curves for the same period, 1 September 1998 to 31 August 2002. Bedload ratings were both statistically significant (ρ ≤ 0.05) and explained at least 60% of the variance in bedload flux. Bias corrections were used with all methods based on log₁₀‐transformed ratings. Estimated mean annual bedload yields varied by three orders of magnitude at the East Tributary gauge and by two orders of magnitude at Upper Swift Creek and Swift Creek gauges. Hourly discharges usually produced higher estimated yields than daily discharges. The bedload rating‐flow duration curve technique overestimates yields and bias correction methods always produce even higher yields. Ratings using both immersed bedload weight and adjusted immersed bedload weight always under‐predicted yields because they contain an implicit threshold of motion condition that is at least four times greater than that predicted by Bagnold's threshold equation. Such a result questions the applicability of Bagnold's threshold equation to the Ngarradj Creek catchment. The best estimates of mean annual bedload yield at East Tributary, Upper Swift Creek and Swift Creek gauges are 600 ± 170 (SE), 1065 ± 150 and 1795 ± 270 t/year, respectively. © 2015 Commonwealth of Australia. Hydrological Processes © 2015 John Wiley & Sons Ltd.     

Application of multivariate analysis to suspended matter particle size distribution in a karst aquifer

Numerous quantitative and qualitative variables control suspended sediment dynamics in karst systems. The objective of this study was to identify the hydrodynamic variables controlling the transport properties of particles in a karst aquifer (western Paris basin). The particle size distribution of suspended sediment infiltrating via a swallow hole was compared to that in discharge from a spring, allowing identification of the particle transport properties of the karst system. Hill and Smith analysis, a type of multivariate analysis that allows joint examination of quantitative and qualitative variables, was used to identify the hydrodynamic parameters controlling the transport properties of the suspended matter. The results demonstrate that the particle size distribution discharging at the karst spring is controlled by spring discharge and the hydraulic gradient of the system. The hydraulic gradient is defined by the piezometric level and the stage of the Seine River, which is in turn controlled by the tide. This study illustrates the use of Hill and Smith analysis to identify those variables which control suspended sediment transport. It also illustrates the application of this analysis to identify boundary conditions and evaluate variables which control the behaviour of the hydrologic system. Copyright © 2007 John Wiley & Sons, Ltd.     

Groundwater levels,climate and anthropogenic factors affect the hydrology and water quality of an intermittent and a regulated subtropical stream

Stream hydrology and water quality are highly interconnected and impacted by climate, land use and geology. We examined this connection using monitoring data from 2000 to 2019 for two streams with contrasting hydrological regimes—intermittent and regulated perennial—in subtropical Queensland, Australia. Our main objective was to evaluate relationships between groundwater levels, climate and flow regulation on the hydrology and water quality of an intermittent and a regulated subtropical stream. In intermittently flowing Lockyer Creek, flow was highly dependent on groundwater levels and occurred when the aquifer was recharged to elevations exceeding the upper 90-percentile value. With 9.4% of the catchment area in irrigated horticulture, flow in Lockyer Creek was also likely to be reduced by drawdown of the aquifer for irrigation, with no flow for 30% to 81% of days over the observation period for stations in Lockyer Creek. In contrast, flow in the mid-Brisbane River was continuous, regulated by discharge from a large upstream dam. Nutrient and suspended sediment concentrations in Lockyer Creek were generally higher than in the mid-Brisbane River, likely associated with runoff from agricultural areas adjacent to the stream, while the upstream dam likely reduced the concentration and variability of nutrients and suspended sediment in the mid-Brisbane River. During periods of low flow in the mid-Brisbane River, longitudinal changes in nutrient and suspended sediment concentrations occurred, notably a significant decrease in total and dissolved inorganic nitrogen concentrations downstream (p < 0.05), indicating a possible effect of in-stream algal uptake and denitrification. This study highlights the impact of human modifications on stream hydrology and water quality in the face of climate change. The findings can inform decision-making on groundwater irrigation or dam release control for water security.     

Testing of the SIBERIA landscape evolution model using the Tin Camp Creek,Northern Territory,Australia, field catchment

The SIBERIA landscape evolution model was used to simulate the geomorphic development of the Tin Camp Creek natural catchment over geological time. Measured hydrology, erosion and geomorphic data were used to calibrate the SIBERIA model, which was then used to make independent predictions of the landform geomorphology of the study site. The catchment, located in the Northern Territory, Australia is relatively untouched by Europeans so the hydrological and erosion processes that shaped the area can be assumed to be the same today as they have been in the past, subject to the caveats regarding long‐term climate fluctuation. A qualitative, or visual comparison between the natural and simulated catchments indicates that SIBERIA can match hillslope length and hillslope profile of the natural catchments. A comparison of geomorphic and hydrological statistics such as the hypsometric curve, width function, cumulative area distribution and area–slope relationship indicates that SIBERIA can model the geomorphology of the selected Tin Camp Creek catchments. Copyright 2002 © Environmental Research Institute of the Supervising Scientist, Commonwealth of Australia.     

The 3.26–3.24 Ga Barberton asteroid impact cluster: Tests of tectonic and magmatic consequences,Pilbara Craton,Western Australia

The location in the Barberton Greenstone Belt (Kaapvaal Craton) of ∼3.26–3.24 Ga asteroid impact ejecta units at, and immediately above, a sharp break between a > 12 km-thick mafic–ultramafic volcanic crust (Onverwacht Group ∼3.55–3.26 Ga, including the ∼3.298 > 3.258 Ga Mendon Formation) and a turbidite–felsic volcanic rift-facies association (Fig Tree Group ∼3.258–3.225 Ga), potentially represents the first documented example of cause–effect relations between extraterrestrial bombardment and major tectonic and igneous events [D.R. Lowe, G.R. Byerly, F. Asaro, F.T. Kyte, Geological and geochemical record of 3400 Ma old terrestrial meteorite impacts, Science 245 (1989) 959–962; D.R. Lowe, G.R. Byerly, F.T. Kyte, A. Shukolyukov, F. Asaro, A. Krull, Spherule beds 3.47–3.34 Ga-old in the Barberton greenstone belt, South Africa: a record of large meteorite impacts and their influence on early crustal and biological evolution, Astrobiology 3 (2003) 7–48; A.Y. Glikson, The astronomical connection of terrestrial evolution: crustal effects of post-3.8 Ga mega-impact clusters and evidence for major 3.2 ± 0.1 Ga bombardment of the Earth–Moon system, J. Geodyn. 32 (2001) 205–229]. Here we correlate this boundary with a contemporaneous break and peak magmatic and faulting events in the Pilbara Craton, represented by the truncation of a 3.255–3.235 Ga-old volcanic sequence (Sulphur Springs Group—SSG) by a turbidite-banded iron formation–felsic volcanic association (Pincunah Hill Formation, basal Gorge Creek Group). These events are accompanied by ∼3.252–3.235 Ga granitoids (Cleland plutonic suite). The top of the komatiite–tholeiite–rhyolite sequence of the SSG is associated with a marker chert defined at 3.238 ± 3–3.235 ± 3 Ga, abruptly overlain by an olistostrome consisting of mega-clasts of felsic volcanics, chert and siltstone up to 250 × 150 m-large, intercalated with siliciclastic sedimentary rocks and felsic volcanics (Pincunah Hill Formation-basal Gorge Creek Group-GCG [R. M. Hill, Stratigraphy, structure and alteration of hanging wall sedimentary rocks at the Sulphur Springs volcanogenic massive sulphide (VMS) prospect, east Pilbara Craton, Western Australia. B.Sc Hon. Thesis, University of Western Australia (1997) 67 pp.; M.J. Van Kranendonk, A.H. Hickman, R.H. Smithies, D.R. Nelson, Geology and tectonic evolution of the Archaean north Pilbara terrain, Pilbara Craton, Western Australia, Econ. Geol. 97 (2002) 695–732; M.J. Van Kranendonk, Geology of the North Shaw 1 : 100 000 Sheet. Geological Survey Western Australia 1 : 100 000 Geological Series (2000) 86 pp., R. Buick, C.A.W. Brauhart, P. Morant, J.R. Thornett, J.G. Maniew, J.G. Archibald, M.G. Doepel, I.R. Fletcher, A.L. Pickard, J.B. Smith, M.B. Barley, N.J. McNaughton, D.I. Groves, Geochronology and stratigraphic relations of the Sulphur Springs Group and Strelley Granite: a temporally distinct igneous province in the Archaean Pilbara Craton, Australia, Precambrian Res. 114 (2002) 87–120]). The structure and scale of the olistostrome, not seen elsewhere in the Pilbara Craton, is interpreted in terms of intense faulting and rifting, supported by topographic relief represented by deep incision of overlying arenites (Corboy Formation) into underlying units [M.J. Van Kranendonk, Geology of the North Shaw 1 : 100 000 Sheet. Geological Survey Western Australia 1 : 100 000 Geological Series (2000) 86 pp.]. The age overlaps between (1) 3.255 ± 4–3.235 ± 3 Ga peak igneous activity represented by the SSG and the Cleland plutonic suite (Pilbara Craton) and the 3.258 ± 3 Ga S2 Barberton impact unit, and (2) 3.235 ± 3 Ga top SSG break and associated faulting and the 3.243 ± 4 S3–S4 Barberton impact units may not be accidental. Should correlations between the Barberton S2–S4 impact units and magmatic and tectonic events in the Pilbara Craton be confirmed, they would imply impact-triggered reactivation of mantle convection, crustal anatexis, faulting and strong vertical movements in Archaean granite–greenstone terrains associated with large asteroid impacts, culminating in transformation from sima-dominated crust to continental rift environments.     

The character and age structure of valley fills in upper Wolumla Creek catchment,south coast,New South Wales,Australia

Extensive valley fills at the base of the escarpment in upper Wolumla Creek, on the south coast of New South Wales, Australia, have formed from a combination of ‘cut and fill’ processes. The valley fills comprise series of alternating, horizontally bedded sand and mud units, reflecting reworking of detritus from deeply weathered granites of the Bega Batholith. Sand units are deposited as sand sheets or splays on floodplain surfaces or in floodouts that form atop intact valley fill surfaces downstream of discontinuous gullies. Alternatively, sands are deposited from bedload and form bars or part of the valley floor within channel fills. Organic-rich mud units are deposited from suspension in swamps or in seepage zones at the distal margin of floodouts. Within 5 km of the escarpment, valley deposits grade downstream from sand sheet and splay deposition in floodouts, to mud deposition in swamp and seepage zones. Radiocarbon dates indicate that virtually the entire valley fill of upper Wolumla Creek was excavated prior to 6000 years BP . Remnant terraces are evident at valley margins. The valley subsequently filled between 6000 years BP and 1000 years BP producing valley fills around 12 m deep, but no greater than 300 m wide. Reincision into the valley fill, on a scale smaller than the present incision phase, is indicated at around 1000 years BP , following which the channel refilled. Portion plans dated from 1865 refer to the study area as ‘Wolumla Big Flat’, and show large areas of swampy terrain, suggesting that the valley fill had re-established by this time. Within a few decades of European settlement the valley fill incised once more. Upper Wolumla Creek now has a channel over 10 m deep and 100 m wide in places, draining a catchment area of less than 20 km². © 1998 John Wiley & Sons, Ltd.     

Micro-erosion meter measurements of travertine deposition rates: a case study from Louie Creek,Northwest Queensland,Australia

Although originally designed to measure surface denudation, the micro-erosion meter (MEM) can be adapted easily to measure deposition rates of chemical sediments such as travertines and speleothems. At Louie Creek, northwest Queensland, Australia, travertine deposition rates measured using the MEM average 4·15 mm a⁻¹. However, this figure masks considerable rate variability. Both purely hydraulic and hydraulically related variables appear to be the major mechanisms controlling deposition rates. The most rapid rates occur within relatively high-energy hydraulic regimes (impact and flow zones), whilst deposition rates in pools separating individual travertine barrages (standing water zones) are relatively slow. Dsposition rate variations within spray and impact zones are related directly to discharge. The highest rates in flow zones correlate with the incorporation into the travertine of in situ and allochthonous biogenic material, such as caddis fly larvae, green algal mats and phytoclasts, which proliferate or are entrapped easily under such hydraulic conditions. Considerable spatial variability in deposition rates also prevails. The highest rates for a given set of hydraulic conditions occur at two sites, the Upper Everglades and the Lower Everglades. The MEM also measures net erosion of travertines. At Louie Creek, most of the travertine erosion occurs in the wet season and is confined primarily to standing water zones. © 1997 John Wiley & Sons, Ltd.     

川西北岷山灰岩区喀斯特堰塞湖形成中的生物作用

川西北岷山灰岩区内的喀斯特堰塞湖是一种特殊的湖泊地貌类型,它是在一定的地质地貌条件及水化学条件下由生物作用参与并促进生物型灰华的快速沉积并堰塞河道而成。野外沉积构造和湖泊形态观察、水化学分析及室内对灰华体的光学显微镜和扫描电镜的观察结果表明,生物作用以多种方式存在着。多种生物(苔藓、藻类、灌草丛等)在生物型灰华堤堰的形成(也即喀斯特堰塞湖的形成)过程中的不同生物作用(包括同化作用、拦截作用、毛管作用、捕获粘结作用及构架作用)贯穿于灰华沉积的复杂循环过程之中。     

Induced seismicity at wujiangdu reservoir,China: a case induced in the karst area

To date 19 cases of reservoir-induced seismicity have been acknowledged in China and 15 of them are associated with karst. The Wujiangdu case is a typical one induced in the karst area. The dam with a height of 165 m is the highest built in a karst area in China. Seismic activity has been successively induced in five reservoir segments seven months after the impoundment in 1979. A temporary seismic network consisting of 8 stations was set up in one of the segments some 40 km upstream from the dam. The results indicate that epicenters were distributed along the immediate banks, composed of karstified carbonate, and focal depths were only several hundred meters. Most of the focal mechanisms were of thrust and normal faulting. It is suggested that karst may be an important factor in inducing seismicity. It can provide an hydraulic connection to change the saturation and pressure and also weak planes for dislocation to induce seismicity.     

Timing and development of sedimentation of the Cleaverville Formation and a post‐accretion pull‐apart system in the Cleaverville area,coastal Pilbara Terrane,Pilbara, Western Australia

In the Cleaverville area of Western Australia, the Regal, Dixon Island, and Cleaverville Formations preserve a Mesoarchean lower‐greenschist‐facies volcano‐sedimentary succession in the coastal Pilbara Terrane. These formations are distributed in a rhomboidal‐shaped area and are unconformably overlain by two narrowly distributed shallow‐marine sedimentary sequences: the Sixty‐Six Hill and Forty‐Four Hill Members of the Lizard Hills Formation. The former member is preserved within the core of the Cleaverville Syncline and the latter formed along the northeast‐trending Eighty‐Seven Fault. Based on the metamorphic grade and structures, two deformation events are recognized: D₁ resulted in folding caused by a collisional event, and D₂ resulted in regional sinistral strike‐slip deformation. A previous study reported that the Cleaverville Formation was deposited at 3020 Ma, after the Prinsep Orogeny (3070–3050 Ma). Our SHRIMP U–Pb zircon ages show that: (i) graded volcaniclastic–felsic tuff within the black shale sequence below the banded iron formation in the Cleaverville Formation yields an age of (3 114 ±14) Ma; (ii) the youngest zircons in sandstones of the Sixty‐Six Hill Member, which unconformably overlies pillow basalt of the Regal Formation, yield ages of 3090–3060 Ma; and (iii) zircons in sandstones of the Forty‐Four Hill Member show two age peaks at 3270 Ma and 3020 Ma. In this way, the Cleaverville Formation was deposited at 3114–3060 Ma and was deformed at 3070–3050 Ma (D₁). Depositional age of the Cleaverville Formation is at least 40–90 Myr older than that proposed in previous studies and pre‐dates the Prinsep Orogeny (3070–3050 Ma). After 3020 Ma, D₂ resulted in the formation of a regional strike‐slip pull‐apart basin in the Cleaverville area. The lower‐greenschist‐facies volcano‐sedimentary rocks are distributed only within this basin structure. This strike‐slip deformation was synchronous with crustal‐scale sinistral shear deformation (3000–2930 Ma) in the Pilbara region.     

Numerical simulation of a dam break for an actual river terrain environment

A two‐dimensional (2D) finite‐difference shallow water model based on a second‐order hybrid type of total variation diminishing (TVD) approximate solver with a MUSCL limiter function was developed to model flooding and inundation problems where the evolution of the drying and wetting interface is numerically challenging. Both a minimum positive depth (MPD) scheme and a non‐MPD scheme were employed to handle the advancement of drying and wetting fronts. We used several model problems to verify the model, including a dam break in a slope channel, a dam break flooding over a triangular obstacle, an idealized circular dam‐break, and a tide flow over a mound. Computed results agreed well with the experiment data and other numerical results available. The model was then applied to simulate the dam breaking and flooding of Hsindien Creek, Taiwan, with the detailed river basin topography. Computed flooding scenarios show reasonable flow characteristics. Though the average speed of flooding is 6–7 m s^?1, which corresponds to the subcritical flow condition (Fr < 1), the local maximum speed of flooding is 14·12 m s^?1, which corresponds to the supercritical flow condition (Fr ≈ 1·31). It is necessary to conduct some kind of comparison of the numerical results with measurements/experiments in further studies. Nevertheless, the model exhibits its capability to capture the essential features of dam‐break flows with drying and wetting fronts. It also exhibits the potential to provide the basis for computationally efficient flood routing and warning information. Copyright © 2006 John Wiley & Sons, Ltd.     

Tectonics of an early Proterozoic geosuture: The Halls Creek orogenic sub-province, northern Australia

The exposed elements of the Lower Proterozoic orogenic belts of the Halls Creek sub-province, Northern Australia, lie in fault zones which have suffered repeated tectonic activity at various times through the Proterozoic and Phanerozoic. The Halls Creek and King Leopold orogenic domains subtend an angle of 80° and are characterized by linear late tectonic batholithic complexes several hundred kilometres long but only a few tens of kilometres wide, reminiscent of those in Phanerozoic Cordilleran orogenies. The associated superposed folding and high temperature metamorphism are more akin to those in Phanerozoic collision orogenies.The sub-province is analyzed in the wider context of the North Australian orogenic province which was deformed, metamorphosed and intruded by granitic plutons approximately 1900-1800 Ma ago. In this province the Archaen basement was extended and broken into a mosaic of blocks, some of which (now largely concealed by younger Kimberley and McArthur basin sediments) retained a more positive character and fed sediment to intervening regions (such as the Pine Creek Geosyncline) which suffered greater extension and subsidence, but which retained a thinned Archaean basement.The Halls Creek Group was deposited in a trough to the south-east of the Kimberley island continent, and deposition was probably broadly contemporaneous with, and continuous with, that in the Pine Creek geosyncline. A volcanic—fine grained clastic—carbonate phase of marine deposition, following basin formation, is represented by the Biscay Formation. During the later phase of basin evolution widespread flysch facies (Olympio Formation), partly derived from the island continent, was deposited and is now preserved in low grade zones on both sides of the main belt of high strain and upper amphibolite to lower granulite facies metamorphism which displays recumbent folding and nappe tectonics with fold axes oblique to the major faults.No island arc compex or paired metamorphic belts are present in the orogenic belts, and it is concluded that the lithospheric extension and subsequent convergence did not involve the generation of oceanic crust or B-subduction.In the Halls Creek domain vergence is south-easterly across all zones and is related to oblique convergence leading to limited A-subduction of the basinal area in the south-east beneath the island continent to the north-west, accompanied by left-lateral strike-slip or transform fault movements on the north-trending major faults. The convergence generated the associated high temperature metamorphism and plutonism on the leading edge of the lower plate.A phase of upright folding (with trends varying continuously form E-W in the King Leopold belt to NNE-SSW in the Halls Creek belt) intervenes between the main recumbent deformation and metamorphism (ca 1920 Ma ago) and the emplacement of the late tectonic granite batholiths (ca 1840 Ma ago) which are fault controlled.The province represents a distinctive type of linear Proterozoic ensialic orogeny, not explicitly identified previously, and it needs to be distinguished both from true collision orogenies of the Phanerozoic, involving a Wilson Cycle, and from the areally extensive Proterozoic orogenies with which it is associated. Its essential characteristics are due to convergence between a small continent and an ‘oceanic’ area underlain by thin continental crust, resulting in limited A-subduction of the latter prior to crustal shortening.     

Thin surface soil layers attributable to rain-flow transportation on low-angle slopes: An example from semi-arid tropical Queensland,Australia

Particle-size analyses have been made on surface soils and a thin, overlying sandy pavement at 16 sites along a gently sloping transect at Torrens Creek in North Queensland. The transect is 1590 m long and has a maximum gradient of 0.018 (less than 1°). The sandy pavement is enriched in coarse components due to the sorting and differential downslope transport of the finer soil fractions. Particle movement is ascribed to the action of raindrops impacting very shallow, flowing water. The process, referred to as ‘rain-flow transportation’, is active wherever overland flow is too weak to generate rills and channels and occurs in areas of very low slope with permeable surface soils that allow rapid infiltration during storms. Rain-flow transportation is discussed with particular reference to the development of soil profiles in an old, subdued landscape of semi-arid tropical Australia.     

Structural controls on groundwater flow and groundwater salinity in the Spicers Creek catchment,Central West region,New South Wales

Saline seepage zone development, and hence the onset of dryland salinity, is a major environmental problem occurring within the Spicers Creek catchment. The primary objective of this paper was to identify previously unmapped faults and show the correlation between these faults and groundwater salinization. As identified from this study, there is a close association between geological structural features and the formation of saline seepage zones. The most saline groundwaters in the catchment were encountered where two geological structures join and form a fault intersection. These saline groundwaters are found at various depths within the fractured aquifers, and changes in groundwater chemistry in the aquifers are associated with the presence of fault zones. ¹⁸O and δ²H stable isotopes, together with ⁸⁷Sr/⁸⁶Sr isotopic ratios, indicate that groundwaters within the fault zones are enriched in ¹⁸O and have a strontium signature similar to seawater. This study identifies several geological structures in the Spicers Creek catchment and demonstrates that groundwaters with the highest salinity arise where fault intersections occur. The results of this study may be used to interpret further the mechanisms leading to seepage zone formation in dryland salinity‐affected catchments located throughout the Central West region of New South Wales, Australia. Copyright © 2006 John Wiley & Sons, Ltd.     

ALLUVIAL CHARACTERISTICS,GROUNDWATER–SURFACE WATER EXCHANGE AND HYDROLOGICAL RETENTION IN HEADWATER STREAMS

Conservative solute injections were conducted in three first-order montane streams of different geological composition to assess the influence of parent lithology and alluvial characteristics on the hydrological retention of nutrients. Three study sites were established: (1) Aspen Creek, in a sandstone–siltstone catchment with a fine-grained alluvium of low hydraulic conductivity (1·3×10⁻⁴ cm/s), (2) Rio Calaveras, which flows through volcanic tuff with alluvium of intermediate grain size and hydraulic conductivity (1·2×10⁻³ cm/s), and (3) Gallina Creek, located in a granite/gneiss catchment of coarse, poorly sorted alluvium with high hydraulic conductivity (4·1×10⁻³ cm/s). All sites were instrumented with networks of shallow groundwater wells to monitor interstitial solute transport. The rate and extent of groundwater–surface water exchange, determined by the solute response in wells, increased with increasing hydraulic conductivity. The direction of surface water–groundwater interaction within a stream was related to local variation in vertical and horizontal hydraulic gradients. Experimental tracer responses in the surface stream were simulated with a one-dimensional solute transport model with inflow and storage components (OTIS). Model-derived measures of hydrological retention showed a corresponding increase with increasing hydraulic conductivity. To assess the temporal variability of hydrological retention, solute injection experiments were conducted in Gallina Creek under four seasonal flow regimes during which surface discharge ranged from baseflow (0·75 l/s in October) to high (75 l/s during spring snowmelt). Model-derived hydrological retention decreased with increasing discharge. The results of our intersite comparison suggest that hydrological retention is strongly influenced by the geologic setting and alluvial characteristics of the stream catchment. Temporal variation in hydrological retention at Gallina Creek is related to seasonal changes in discharge, highlighting the need for temporal resolution in studies of the dynamics of surface water–groundwater interactions in stream ecosystems. © 1997 by John Wiley & Sons, Ltd.     

Paleomagnetic study of Cambrian Potsdam Group sandstones,St. Lawrence Lowlands,Quebec

We report paleomagnetic results from oriented drill core samples collected at 10 sites (80 samples) from the Covey Hill and 19 sites (96 samples) from the overlying, fossiliferous Cha?teauguay Formations of the gently dipping Late Cambrian Potsdam Group sandstones exposed in the St. Lawrence Lowlands of Quebec. Stepwise thermal demagnetization analyses ave revealed the presence of two predominant groups of coherent magnetizations C-1 and C-2, after simple correction for bedding tilt. The C-1 group magnetization is a stable direction (D=332°, I=+18°) with unblocking temperatures (T_UB) between 550 and 650°C, present in the older Covey Hill Formation; this direction is probably a chemical remanence acquired during the Covey Hill diagenesis and carried predominantly by hematite. The C-2 group magnetization (D=322°, I=+9°) is present at 13 sites of the younger Cha?teauguay Formation; this is probably carried by magnetite and represents a penecontemporaneous, depositional DRM, characterized by T_UB spectra 400–550°C. We believe that C-2 is relatively younger than C-1 based on a combination of arguments such as the presence of opposite polarities, internal consistency, similarity and common occurrence of C-1 and C-2 respectively in the Covey Hill and Cha?teauguay members. The corresponding paleomagnetic poles C-1 (46°N, 149°E; dp, dm=3°, 5°) and C-2 (37°N, 156°E; dp, dm=2°, 5°) are not significantly different from most of the other Late Cambrian (Dresbachian-Franconian) poles derived from sediments exposed in the southern region (Texas) of the North American craton which are also believed to have been deposited during Croixian Sauk sea transgression similar to the Potsdam sandstones. Although adequate faunal control is lacking (in particular for the Covey Hill Formation), this comparison with the Cratonic poles suggests a Late Cambrian age to the Potsdam poles. The agreement between the results also gives the evidence for internal consistency of cratonic poles at least for Late Cambrian.The incoherent C-3 group remanence (D=250°, I=?15°) is commonly present at 7 sites in both the formations; this may not correspond to a reliable paleomagnetic signal. The other remanence C-4 (D=180°, I=+10°) is found only at 3 sites located in the uppermost stratigraphic levels of the Cha?teauguay Formation; the corresponding paleomagnetic pole (40°N, 107°E) does not differ significantly from the Ordovician and some Late Cambrian poles. The present data are insufficient to resolve a problem in apparent polar wander for Middle and Late Cambrian time posed by the existence of high-latitude poles for some strata of Middle Cambrian age and low-latitude poles for some strata of Late Cambrian age.     

Channel change following European settlement: Gilmore Creek,southeastern Australia

European settlement in southeastern Australia led to rapid changes in the morphology of many upland streams. However, our knowledge of the nature of these changes is limited as historical records and preserved palaeochannels are rare. In this study we compare a well‐preserved section of the late Holocene palaeochannel of Gilmore Creek to its present channel. We used a combination of map and aerial photograph interpretation, field survey, OSL dating and discharge analysis to describe and compare the modern and palaeochannels and establish a firm date for the timing of channel change. In common with many other streams in southeastern Australia Gilmore Creek's late Holocene channel meandered across a stable well‐vegetated and frequently inundated floodplain. After about 1830 European settlers quickly modified the catchment by clearing riparian and hillslope vegetation, introducing grazing animals and other exotic species and mining for alluvial gold in the headwaters. The OSL dates show that between about 1850 and 1880 the small meandering channel aggraded with coarse sands and then up to about 1 m of silty sand was deposited over the floodplain. Declining sediment input from upstream channel avulsion before 1890 resulted in the establishment of a straighter, larger capacity channel that incised to the level of basal cobbles and, in places, to bedrock. The dramatic change in channel pattern resembles that described on the Cann River in eastern Victoria following the removal of riparian vegetation and within‐channel coarse woody debris. At Gilmore Creek increased channel capacity has greatly reduced the average frequency of floodplain inundation. High values of specific stream power suggest that channel morphology is now well adjusted to the present flow regime. Copyright © 2007 John Wiley & Sons, Ltd.     

Shoreline erosion: a cautionary note in using small farm dams to determine catchment erosion rates

Data from 10 small farm dams in SE Australia show that shoreline erosion due to farm livestock access to the dams can account for a significant proportion (up to 85%) of sediment contained in the dam. The volumes of sediment resulting from such shoreline erosion may be of the same order as the volumes produced by gully erosion in the dams' catchments, prompting caution in using farm dams to which livestock have access to determine small catchment erosion rates. Other issues, related to the trap efficiency, also mean that erosion estimates based on farm dam sedimentation should be treated with caution. © 1998 John Wiley & Sons, Ltd.     

Relating aerial erosion,soil erosion and sub‐soil erosion to the evolution of Lunan Stone Forest,China

Stone forest (‘Shilin’ in Chinese) is a unique karst landform with a complex evolution process. Based mainly on the characteristics and interrelationships of sub‐soil, soil and sub‐aerial erosion in Lunan karst area, the authors develop a triplex erosion model to describe the evolution of stone forest, and apply it to examine the current development stage and the prospect of the Lunan Stone Forest. The study shows that sub‐soil corrosion, a basic driving force for the vertical scope of a stone forest, usually occurs within 10 m below ground surface but is observed to be most active within the top 2 m, which constitutes the best development zone for stone forest. Under modern climatic conditions, the tip of the stone pillars in Lunan karst area is lowering at a rate of 10·4 mm ka^?1, whereas the base of the stone pillars is deepening at 26·17 mm ka^?1. Therefore, the height of stone pillars is increasing at a rate of 15·77 mm ka^?1. Considering that soil erosion in the study area is as high as 650 mm ka^?1, the visible height of the stone forest is actually increasing at a rate of 639·6 mm ka^?1. However, the best evolution time for Lunan Stone Forest has already passed despite the fact that it is still growing taller at the present time. This is because the soil layer, which plays an extremely significant role in the heightening of stone pillars, is rapidly thinning at a rate of 623·83 mm ka^?1. Copyright © 2006 John Wiley & Sons, Ltd.