Isovolumetric weathering and silcrete formation,southern Cape Province,South Africa

Calculations of absolute elemental gains and losses based on isovolumetric bedrock alteration are applied to deep weathering profiles and silcrete developed on Dwyka Tillite and Bokkeveld Shale. Bedrock weathering to kaolinite and illite yields sufficient SiO₂ to account for observed thicknesses of associated silcrete. Absolute accumulation of SiO₂ in silcrete is complemented by substantial absolute depletion of Al₂O₃. Absolute accumulation of TiO₂ in both silcrete and associated weathered material together with authigenic anatase concentrations in silctete recorded during micromorphological investigations indicate TiO₂ mobilization in a low pH environment (pH < 3·75) during silcrete formation. Under these low pH conditions increased Al₂O₃ solubility led to replacement of kaolinite and illite by a proportion of SiO₂ retained in the weathering profile through restricted drainage.     

Dual mechanisms for the formation of fluvial silcretes in the distal reaches of the Okavango Delta fan,Botswana

Silcretes exposed within river-marginal or valley settings have been described in a number of studies, but few models have been suggested for the development of these ‘fluvial’ silcretes. An exception is that proposed by McCarthy and Ellery (Journal of Sedimentary Research, 1995, Vol. A65, pp. 77–90) to describe mechanisms of early stage near-surface silica diagenesis in the Okavango Delta, Botswana. This paper describes the characteristics and possible origins of massive surface and sub-surface silcretes at Samedupe and Boro Junction, beyond the distal margin of the Okavango Delta and further downstream than the sites described by McCarthy and Ellery. Morphological and petrological evidence from surface exposures and three sedimentary cores suggests that other modes of formation may also be applicable. A dual model of formation is proposed: surface silcretes are suggested to have developed by silica accumulation in seasonal pools remaining after the annual Okavango flood, whilst sub-surface horizons appear to have formed under conditions of varying pH associated with fluctuating groundwater levels beneath the channel floor. This model is reviewed in the context of the fluvial silcrete debate. © 1998 John Wiley & Sons, Ltd.     

Tafoni on coastal slopes,South Devon,U.K.

Cavernous weathering (tafoni development) occurs on coastal slopes in greenschist bedrock at elevations up to 40 m above sea level. The freshly weathered surfaces of the cavern interiors are irregular in morphology, discordant to major rock structure, formed by substantially weakened rock and associated with granular weathering debris. The weathering debris contains soluble elements in proportions similar to those present in seawater, and the penetration of elements associated with sea salts into the weathering surface to estimated depths of at least 0·1–0·2 m is indicated by the presence of chlorine. Scanning electron microscopy and microprobe analyses suggest that rock breakdown occurs principally through limited chemical weathering at grain boundaries. The mechanism for the emplacement of marine salts within sheltered rock surfaces in the tafoni is postulated to be a combination of dry deposition under turbulent atmospheric conditions and wetting by coastal fog.     

Origin and palaeo‐environments of calcareous sediments in the Moshaweng dry valley,southeast Botswana

Quaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an upper surface (1095 m) containing abundant sil‐calcrete, an intermediate surface (1085 m) in which sil‐calcrete underlies nodular calcrete and lower (1075 m) surface in which sil‐calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing SiO₂ content (and increasing CaCO₃ content) with depth from the highest to the lowest surface levels. The calcretes and sil‐calcretes represent modifications of pre‐existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca⁺⁺‐rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying‐induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid‐Pleistocene age for sil‐calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late stage dissolution of CaCO₃ from pre‐existing surface calcretes or sil‐calcretes led to the formation of pedogenic case‐hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. Copyright © 2002 John Wiley & Sons, Ltd.     

The role of playas in pedogenic gypsum crust formation in the Central Namib Desert: a theoretical model

The formation of Namibia's extensive pedogenic gypsum crusts (CaSO₄·2H₂O) is interpreted in a new light. It is suggested that gypsum primarily precipitates at isolated points of evaporitic concentration, such as inland playas, and that deflation of evaporitic‐rich gypsum dust from these playas contributes to the formation of pedogenic gypsum duricrusts on the coastal gravel plains of the Namib Desert surrounding these playas. This study establishes the nature, extent and distribution of playas in the Central Namib Desert and provides evidence for playa gypsum deflation and gravel plain deposition. Remote sensing shows the distribution of playas, captures ongoing deflation and provides evidence of gypsum deflation. It is proposed that, following primary marine aerosol deposition, both inland playas and coastal sabkhas generate gypsum which through the process of playa deflation and gravel plain redeposition contributes to the extensive pedogenic crusts found in the Namib Desert region. Copyright © 2001 John Wiley & Sons, Ltd.     

Reddening of dune sands—evidence from southeast India

Thin section, SEM, and TEM analyses have indicated that the red ‘teri’ sands of southeast India have formed from weathering in situ of coastal dune sands. The data does not support a detrital origin for the red sands. C¹⁴ dates indicate that dune deposition and weathering, to a maximum depth of 10 m, leading to the formation of a hematite, koalinite and illite rich matrix has taken place rapidly over the past 25,000 years. It is postulated that garnet was a major source of hematite (ferric oxide).     

Geochemical studies on the intensity of chemical weathering in Luochuan loess-paleosol sequence, China

Major and trace element analyses of the Luochuan loess-paleosol sequence in China were performed in order to understand the cheniical weathering processes occurring on the I.oess Plateau during the last 600 ka. Results reveal that most elements in the loess remain immobile durlng chemical weathering. The typical stable elements are Al, K, Ti, Rb and REE, while the main mobile elements are Ca, Sr, P, Mg and Na. 120ess and paleosol experience the incipient stage of chemical weathering characterized by acid leaching and carbonate dissolution. Alteration of silicates in the sequence seems to be limited. Features of less chemical weathering of the loess and paleosol could he indicators for the dry-cold clinlate dominated on the Loess Plateau during the Quaternary. Project supported hy thc Nzitional Natural Science Foundation of China     

A low‐dimensional model of bedrock weathering and lateral flow coevolution in hillslopes: 2. Controls on weathering and permeability profiles,drainage hydraulics,and solute export pathways

The advance of a chemical weathering front into the bedrock of a hillslope is often limited by the rate weathering products that can be carried away, maintaining chemical disequilibrium. If the weathering front is within the saturated zone, groundwater flow downslope may affect the rate of transport and weathering—however, weathering also modifies the rock permeability and the subsurface potential gradient that drives lateral groundwater flow. This feedback may help explain why there tends to be neither “runaway weathering” to great depth nor exposed bedrock covering much of the earth and may provide a mechanism for weathering front advance to keep pace with incision of adjacent streams into bedrock. This is the second of a two‐part paper exploring the coevolution of bedrock weathering and lateral flow in hillslopes using a simple low‐dimensional model based on hydraulic groundwater theory. Here, we show how a simplified kinetic model of 1‐D rock weathering can be extended to consider lateral flow in a 2‐D hillslope. Exact and approximate analytical solutions for the location and thickness of weathering within the hillslope are obtained for a number of cases. A location for the weathering front can be found such that lateral flow is able to export weathering products at the rate required to keep pace with stream incision at steady state. Three pathways of solute export are identified: “diffusing up,” where solutes diffuse up and away from the weathering front into the laterally flowing aquifer; “draining down,” where solutes are advected primarily downward into the unweathered bedrock; and “draining along,” where solutes travel laterally within the weathering zone. For each pathway, a different subsurface topography and overall relief of unweathered bedrock within the hillslope is needed to remove solutes at steady state. The relief each pathway requires depends on the rate of stream incision raised to a different power, such that at a given incision rate, one pathway requires minimal relief and, therefore, likely determines the steady‐state hillslope profile.     

Duricrust development and valley evolution: Process–landform links in the kalahari

Duricrusts are an important landscape component of the Kalahari region of central southern Africa. Their exposures within the dry valleys (mekgacha) of the Kalahari provide some of the most widespread surface outcrops of the terrestrial Jurassic to Holocene Kalahari Group sediments. Exposures have been extensively used in the construction of lithostrati-graphic sequences, on the assumption that valley systems have incised their courses through a pre-existing duricrust sequence. Recent work, however, has identified the role of groundwater erosion processes in valley development, which may have influenced duricrust formation. Studies of duricrusts from boreholes drilled within two mekgacha show that duricrust type is intrinsically related to the presence of a valley. Analyses of calcretes and silcretes in a series of profiles and thin sections from the Letlhakeng area of Botswana also indicate extensive alteration and diagenesis in association with former higher water tables. Sedimentary sequences within duricrust host materials can be identified but there is no evidence for correlation of duricrust cements between exposures. Profile studies from the Auob Valley in Namibia, however, suggest that this valley has incised through a sequence of duricrusts. Caution is advised in future attempts to correlate duricrust types on the basis of valley exposures, with the recommendation that where such exposures are used in a lithostratigraphic context, only duricrust host material characteristics and not cementing materials should be considered.     

Airborne Geophysics: Application to a Ground-Water Study in Botswana

Summary
A ground-water study carried out in the Serowe area of eastern Botswana between 1985–1988 has provided the opportunity to evaluate the role of a multiparameter low-level airborne geophysical survey in a hydrogeological investigation. The survey included magnetic, VLF (very low frequency), and coaxial EM (electromagnetic) measurements. In total, 7,500 line kilometers were flown over an area of 3,300 km2 with a nominal ground clearance of 20 m and a line spacing of 400 m.
The main aquifer, the Ntane Sandstone Formation (Karoo age), is confined between mudstones below and basalt above, and is broken into a series of graben and horst structures by numerous E-W striking faults. All bedrock, however, is completely masked by a 20–60 m thick overburden of sands, calcretes, silcretes, and sandstones known collectively as the Kalahari beds.
Airborne magnetic and VLF geophysical surveys have been used to penetrate this masking cover. Images and stacked profiles obtained from the survey revealed structural and geological features of major hydrogeological significance. This provided the information necessary for the formulation of a conceptual model.
The results helped guide the subsequent exploration drilling program in an efficient and effective manner, cutting down the need for extensive ground surveys. The investigation confirmed the availability of a 35,000 m3/day resource, sustainable for a 25-year period. Highest yields were obtained from fracture zones associated with VLF anomalies. Potential wellfields were identified in confined sections of the aquifer, with production boreholes to be sited, where possible, on fractures associated with VLF anomalies.     

Developing a protocol for selecting and dating sandy sites in East Central Texas: Preliminary results

Vast areas of East Central Texas are overlain by deep unconsolidated sands, previously assumed to have been formed by in situ weathering and pedoturbation of the bedrock. This hypothesis would imply that palaeoenvironmental and archaeological reconstructions are of limited value. However, recent research has hinted that some elements of the landscape may have undergone repeated phases of erosion and redeposition, suggesting firstly that a reliable record of past environmental conditions may be gleaned from these deposits, and secondly that optically stimulated luminescence (OSL) may provide the key to unlocking this record. This research examines the depositional history of sites shown to provide a reliable chronology. Dates from these sites show that aeolian deposition occurred in East Central Texas at a number of times during the Holocene and Late Glacial, whilst three episodes of gullying occurred between approximately 123,000 and 44,000 years ago. The concordance of some of these results indicates that some phases of deposition may be regional.     

Sedimentological,modal analysis and geochemical studies of desert and coastal dunes,Altar Desert,NW Mexico

Sedimentological, compositional and geochemical determinations were carried out on 54 desert and coastal dune sand samples to study the provenance of desert and coastal dunes of the Altar Desert, Sonora, Mexico. Grain size distributions of the desert dune sands are influenced by the Colorado River Delta sediment supply and wind selectiveness. The desert dune sands are derived mainly from the quartz‐rich Colorado River Delta sediments and sedimentary lithics. The dune height does not exert a control over the grain size distributions of the desert dune sands. The quartz enrichment of the desert dune sands may be due to wind sorting, which concentrates more quartz grains, and to the aeolian activity, which has depleted the feldspar grains through subaerial collisions. The desert dune sands suffer from little chemical weathering and they are chemically homogeneous, with chemical alteration indices similar to those found in other deserts of the world. The desert sands have been more influenced by sedimentary and granitic sources. This is supported by the fact that Ba and Sr concentration values of the desert sands are within the range of the Ba and Sr concentration values of the Colorado River quartz‐rich sediments. The Sr values are also linked to the presence of Ca‐bearing minerals. The Zr values are linked to the sedimentary sources and heavy mineral content in the desert dunes. The Golfo de Santa Clara and Puerto Peñasco coastal dune sands are influenced by long shore drift, tidal and aeolian processes. Coarse grains are found on the flanks whereas fine grains are on the crest of the dunes. High tidal regimens, long shore drift and supply from Colorado Delta River sediments produce quartz‐rich sands on the beach that are subsequently transported into the coastal dunes. Outcrops of Quaternary sedimentary rocks and granitic sources increase the sedimentary and plutonic lithic content of the coastal dune sands. The chemical index of alteration (CIA) values for the desert and coastal dune sands indicate that both dune types are chemically homogeneous. The trace element values for the coastal dune sands are similar to those found for the desert dune sands. However, an increase in Sr content in the coastal dune sands may be due to more CaCO₃ of biogenic origin as compared to the desert dune sands. Correlations between the studied parameters show that the dune sands are controlled by sedimentary sources (e.g. Colorado River Delta sediments), since heavy minerals are present in low percentages in the dune sands, probably due to little heavy mineral content from the source sediment; grain sizes in the dune sands are coarser than those in which heavy minerals are found and/or the wind speed might not exert a potential entrainment effect on the heavy mineral fractions to be transported into the dune. A cluster analysis shows that the El Pinacate group is significantly different from the rest of the dune sands in terms of the grain‐size parameters due to longer transport of the sands and the long distance from the source sediment, whereas the Puerto Peñasco coastal dune sands are different from the rest of the groups in terms of their geochemistry, probably caused by their high CaCO₃ content and slight decrease in the CIA value. Copyright © 2006 John Wiley & Sons, Ltd.     

Wind as a cooling agent: substrate temperatures are responsible for variable lithobiont‐induced weathering patterns on west‐ and east‐facing limestone bedrock of the Negev

Spatial variability in lithobiont‐induced weathering patterns on desert rocks is aspect‐dependent. While differences between the northern and southern aspects have been extensively studied, little is known concerning the differences between east‐facing (EF) and west‐facing (WF) aspects in deserts, including the Negev Desert. Whereas cobbles on both slopes are inhabited by endolithic lichens, epilithic lichens, which render the bedrock a smooth appearance, and free‐living cyanobacteria, which give the bedrock a rugged microrelief, predominate on WF and EF bedrock, respectively. Following previous research that regarded dew as the principal factor that determines lithobiont distribution, measurements of radiation, temperature, wind and dew were carried out during 2008–2009 in the Negev Desert. The data indicated that albeit slightly higher midday surface temperatures that characterize WF surfaces (cobbles and bedrock), nocturnal temperatures on these surfaces were significantly lower, therefore facilitating higher dew condensation. High amounts of dew result from the relatively rapid drop in temperatures (14:00–20:00) due to the afternoon northwesterly sea‐breeze wind (with a cooling rate of the WF bedrock being 52.9% higher than on EF bedrock, 2.6 °C h^?1 in comparison to only 1.7 °C h^?1), and facilitate the growth of high‐chlorophyll dew‐fed (and rain‐fed) epilithic lichens, which may act as bio‐protectors on WF bedrock. Lack of condensation on EF bedrock results in turn in the growth of rain‐fed free‐living cyanobacteria, responsible for high rock dissolution and subsequently for a rugged microrelief. By affecting the nocturnal bedrock temperatures, wind acts as a cooling agent, impacting in turn the amount of dew, and subsequently lithobiont composition and weathering patterns in the Negev Desert. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.     

Compartmentalisation and groundwater–surface water interactions in a prospective shale gas basin: Assessment using variance analysis and multivariate statistics on water quality data

An environmental concern with hydraulic fracturing for shale gas is the risk of groundwater and surface water contamination. Assessing this risk partly involves the identification and understanding of groundwater–surface water interactions because potentially contaminating fluids could move from one water body to the other along hydraulic pathways. In this study, we use water quality data from a prospective shale gas basin to determine: if surface water sampling could identify groundwater compartmentalisation by low-permeability faults; and if surface waters interact with groundwater in underlying bedrock formations, thereby indicating hydraulic pathways. Variance analysis showed that bedrock geology was a significant factor influencing surface water quality, indicating regional-scale groundwater–surface water interactions despite the presence of an overlying region-wide layer of superficial deposits averaging 30–40 m thickness. We propose that surface waters interact with a weathered bedrock layer through the complex distribution of glaciofluvial sands and gravels. Principal component analysis showed that surface water compositions were constrained within groundwater end-member compositions. Surface water quality data showed no relationship with groundwater compartmentalisation known to be caused by a major basin fault. Therefore, there was no chemical evidence to suggest that deeper groundwater in this particular area of the prospective basin was reaching the surface in response to compartmentalisation. Consequently, in this case compartmentalisation does not appear to increase the risk of fracking-related contaminants reaching surface waters, although this may differ under different hydrogeological scenarios.     

The Enrichment Process of Groundwater Fluorine in Sea Water Intrusion Area of Gaomi City,China

A typical area, Gaomi City in China, was chosen to discuss the enrichment process of groundwater fluorine in sea water intrusion area. The groundwater had fluorine levels of 0.09–10.99 mg/L, with an average concentration of 1.38 mg/L. The high-fluorine groundwater was mainly distributed in the unconsolidated Quaternary sediments, where concentrations in 83.6% of the samples exceeded the national limit of 1.0 mg/L. The groundwater in the Quaternary sediments also had higher levels of Cl⁻, TDS, Mg²⁺, and pH and lower levels of Ca²⁺, Co, Ni, and Cu than that in the bedrock. The groundwater fluorine levels in the Quaternary sediments are positively correlated with Cl⁻, TDS, Mg²⁺, pH, and negatively correlated with Ca²⁺, γCa²⁺/γMg²⁺, Co, Ni, Cu. Geochemical indices of Cl⁻ and TDS indicate sea water intrusion in the Quaternary high-fluorine groundwater area (F⁻ > 1.0 mg/L), while they do not indicate any intrusion in the bedrock area. The chemical weathering of minerals was intensified with the intrusion of sea water. Cation exchange was confirmed to occur in the Quaternary sediments and was promoted by sea water intrusion. Cation exchange consumes part of groundwater Ca²⁺ and permits more F⁻ dissolving. Consequently, in the Quaternary sediments, the groundwater was supersaturated with CaF₂ minerals and undersaturated with MgF₂ minerals when F⁻ > 1.0 mg/L, while CaF₂ and MgF₂ minerals both are undersaturated when F⁻ < 1.0 mg/L. Thus, the chemical weathering of minerals and cation exchange caused by sea water intrusion are the crucial processes controlling the groundwater fluorine levels, which should be considered when the groundwater fluorine enrichment mechanism is discussed along coastal zones.     

Influence of Quaternary paleoclimate change on the permeability of the loess–paleosol sequence in the Loess Plateau,northern China

Permeability differences in multi-cycle loess–paleosol aeolian sediments, which are still poorly understood, have the potential to significantly improve our understanding of climatic change during the glacial–interglacial periods of the Quaternary. In this study, the permeability of a well-preserved and continuous loess–paleosol sequence in the South Jingyang Plateau was investigated. Weathering intensity was inferred using a series of climate proxies including grain-size distribution, magnetic susceptibility and mineralogy. The results of laboratory tests showed that the average saturated hydraulic conductivity of loess layers is higher than that of paleosol layers. Also, clear differences between loess and paleosol were found in terms of depth variations of the vertical and horizontal saturated hydraulic conductivities. Differences in loess–paleosol were also found for other proxies for pedogenic weathering [i.e. clay content, sand content, Kd value (ratio of coarse silt to clay), magnetic susceptibility, dolomite content and the ratios of hornblende/illite and hornblende/chlorite]. Our results showed a high permeability of loess layers associated with weak pedogenic weathering during cold/dry paleoclimatic conditions in glacial stages. On the contrary, paleosol layers developed in a warm/humid climate during the interglacial stages experienced strong pedogenic weathering that resulted in lower permeability. Based on these results, we construct a connection between Quaternary climate change theory and the modern hydrological system. This provides a scientific basis for investigating the distribution and pollution of groundwater resources in the local region. © 2020 John Wiley & Sons, Ltd.     

Element geochemistry of weathering profile of dolomitite and its implications for the average chemical composition of the upper-continental crust--Case studies from the Xinpu profile,northern Guizhou Province,China

Geochemical behavior of chemical elements is studied in a dolomitite weathering profile in upland of karst terrain in northern Guizhou.Two stages can be recognized during the process of in situ weathering of dolomitite:the stage of sedentary accumulation of leaching residue of dolomitite and the stage of chemical weathering evolution of sedentary soil.Ni,Cr,Mo,W and Ti are the least mobile elements with reference to Al.The geochemical behavior of REE is similar to that observed in weathering of other types of rocks.Fractionation of REE is noticed during weathering,and the two layers of REE enrichments are thought to result from downward movement of the weathering front in response to changes in the environment.It is considered that the chemistry of the upper part of the profile,which was more intensively weathered,is representative of the mobile components of the upper curst at the time the dolomitite was formed,while the less weathered lower profile is chemically representative of the immobile constitution.Like glacial till and loess,the "insoluble" materials in carbonate rocks originating from chemical sedimentation may also provide valuable information about the average chemical composition of the upper continental crust.     

Element geochemistry of weathering profile of dolomitite and its implications for the average chemical composition of the upper-continental crust

Geochemical behavior of chemical elements is studied in a dolomitite weathering profile in upland of karst terrain in northern Guizhou. Two stages can be recognized during the process ofin situ weathering of dolomitite: the stage of sedentary accumulation of leaching residue of dolomitite and the stage of chemical weathering evolution of sedentary soil. Ni, Cr, Mo, W and Ti are the least mobile elements with reference to Al. The geochemical behavior of REE is similar to that observed in weathering of other types of rocks. Fractionation of REE is noticed during weathering, and the two layers of REE enrichments are thought to result from downward movement of the weathering front in response to changes in the environment. It is considered that the chemistry of the upper part of the profile, which was more intensively weathered, is representative of the mobile components of the upper curst at the time the dolomitite was formed, while the less weathered lower profile is chemically representative of the immobile constitution. Like glacial till and loess, the “insoluble” materials in carbonate rocks originating from chemical sedimentation may also provide valuable information about the average chemical composition of the upper continental crust.     

Comment on Hearty,P.J. and O'Leary,M.J., 2008. Carbonate eolianites,quartz sands,and Quaternary sea-level cycles,Western Australia: A chronostratigraphic approach. Quaternary Geochronology 3: 26–55

A proposal that the yellow sands which commonly overlie Pleistocene eolianites along the west coast of Western Australia may have their origin from major extensions of inland deserts during times of severe aridity, is refuted on several grounds. The eolianites typically are deeply degraded remnants of the original coastal dunes, which contained a high content of non-calcareous detritus. Hence plentiful residual sand will accumulate during weathering of a dune. Studies on heavy mineral content of the yellow sands have shown that there is an inland ageing trend consistent with local derivation from successive dune belts, and have also pointed to local sources for yellow color in the sand, without need to postulate a distant source. Localized denudations have however occurred, during which sand is blown inland to leave tracts of bared limestone. No remnants of the alleged desert extensions exist in the hinterland of the coastal belt.     

Contributions of bedrock groundwater to the upscaling of storm‐runoff generation processes in weathered granitic headwater catchments

We examined the contributions of bedrock groundwater to the upscaling of storm‐runoff generation processes in weathered granitic headwater catchments by conducting detailed hydrochemical observations in five catchments that ranged from zero to second order. End‐member mixing analysis (EMMA) was performed to identify the geographical sources of stream water. Throughfall, hillslope groundwater, shallow bedrock groundwater, and deep bedrock groundwater were identified as end members. The contribution of each end member to storm runoff differed among the catchments because of the differing quantities of riparian groundwater, which was recharged by the bedrock groundwater prior to rainfall events. Among the five catchments, the contribution of throughfall was highest during both baseflow and storm flow in a zero‐order catchment with little contribution from the bedrock groundwater to the riparian reservoir. In zero‐order catchments with some contribution from bedrock groundwater, stream water was dominated by shallow bedrock groundwater during baseflow, but it was significantly influenced by hillslope groundwater during storms. In the first‐order catchment, stream water was dominated by shallow bedrock groundwater during storms as well as baseflow periods. In the second‐order catchment, deeper bedrock groundwater than that found in the zero‐order and first‐order catchments contributed to stream water in all periods, except during large storm events. These results suggest that bedrock groundwater influences the upscaling of storm‐runoff generation processes by affecting the linkages of geomorphic units such as hillslopes, riparian zones, and stream channels. Our results highlight the need for a three‐dimensional approach that considers bedrock groundwater flow when studying the upscaling of storm‐runoff generation processes. Copyright © 2014 John Wiley & Sons, Ltd.