Regional analysis of bedrock stream long profiles: evaluation of Hack's SL form,and formulation and assessment of an alternative (the DS form)

The equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones, and in continental margin and other intraplate settings, as well as other base‐level changes such as due to sealevel fluctuations. The Hack SL form of the long profile, which describes a straight line on a log–normal plot of elevation (normal) versus distance (logarithmic), is the equilibrium long profile form that has been most widely used in such studies; slope–area analysis has also been used in recent years. We show that the SL form is a special case of a more general form of the equilibrium long profile (here called the DS form) that can be derived from the power relationship between stream discharge and downstream distance, and the dependence of stream incision on stream power. The DS form provides a better fit than the SL form to river long profiles in an intraplate setting in southeastern Australia experiencing low rates of denudation and mild surface uplift. We conclude that, if an a priori form of the long profile is to be used for investigations of regional landscape history, the DS form is preferable. In particular, the DS form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance (parallel shift in the DS plot) to be distinguished from disequilibrium steepening due to long profile rejuvenation (disordered outliers on the DS plot). Slope–area analysis and the slope–distance (DS) approach outlined here are complementary approaches, reflecting the close relationship between downstream distance and downstream catchment area. Copyright © 2006 John Wiley & Sons, Ltd.     

An open source,server-side framework for analytical web mapping and its application to health

In this paper, we detail the design and the implementation of an open source, server-side web mapping framework for the analysis of health data. The framework forms part of a larger project, the goal of which is to provide an analytical web geographical information system (GIS) that enables health experts to analyse spatial aspects of health data. The aim of the framework is to provide a method for the dynamic and flexible spatial visualisation of health data to facilitate data exploration and analysis. Consequently, a dynamic thematic web mapping technique, an extension to the Open Geospatial Consortium (OGC) web map service standard, was developed. The technique combines a data query, processing technique and styling methodology on the fly to generate a thematic map. The resulting thematic map represents a virtual map layer that enables a user to rapidly visually summarise properties of a data-set. A test web interface was developed to assess the efficacy of the web mapping technique. As the dynamic web mapping method builds on existing OGC web mapping standards, it can be readily integrated with the existing lightweight slippy map web clients and virtual globes.     

Automated statistical matching of multiple tephra records exemplified using five long maar sequences younger than 75 ka,Auckland, New Zealand

Detailed tephrochronologies are built to underpin probabilistic volcanic hazard forecasting, and to understand the dynamics and history of diverse geomorphic, climatic, soil-forming and environmental processes. Complicating factors include highly variable tephra distribution over time; difficulty in correlating tephras from site to site based on physical and chemical properties; and uncertain age determinations. Multiple sites permit construction of more accurate composite tephra records, but correctly merging individual site records by recognizing common events and site-specific gaps is complex. We present an automated procedure for matching tephra sequences between multiple deposition sites using stochastic local optimization techniques. If individual tephra age determinations are not significantly different between sites, they are matched and a more precise age is assigned. Known stratigraphy and mineralogical or geochemical compositions are used to constrain tephra matches. We apply this method to match tephra records from five long sediment cores (≤ 75 cal ka BP) in Auckland, New Zealand. Sediments at these sites preserve basaltic tephras from local eruptions of the Auckland Volcanic Field as well as distal rhyolitic and andesitic tephras from Okataina, Taupo, Egmont, Tongariro, and Tuhua (Mayor Island) volcanic centers. The new correlated record compiled is statistically more likely than previously published arrangements from this area.     

Geochemical correlation of Ordovician flow tuffs in North Wales

Ordovician rhyolitic tuffs in North Wales are correlated on the basis of their whole-rock trace element composition. Multivariate statistics verify that major ignimbrite sheets are chemically unique, with Zr, Y and Nb being the most useful elements to characterize individual deposits. Fractionation processes during transport and emplacement of the pyroclastic flows results in little lateral variation in the whole-rock geochemistry of deposits; different diagenetic histories in subaerial and subaqueous environments did not mask recognition of primary ignimbrite units. A partially welded vitric ash flow tuff is correlated with the Pitts Head Tuff ash flow sheet, and a tuff horizon previously assumed to be reworked Pitts Head Tuff is shown to be chemically most similar to the fourth member of the Capel Curig Volcanic Formation. Validity of these correlations is upheld by biostratigraphic and sedimentological evidence. The new correlations necessitate a revision of the stratigraphy in North Wales and indicate a significant lapse of time (perhaps one million years) between emplacement of the Pitts Head Tuff and eruption of the Lower Rhyolitic Tuff of the overlying Snowdon Volcanic Group.     

A suburban sediment budget: Coarse-grained sediment flux through hillslopes,stormwater systems and streams

Sediment in urban stormwater systems creates a significant maintenance burden, while a lack of coarse-grained bed sediment in streams limits their ecological value and geomorphic resilience. Gravel substrates, for example, provide benthic habitat yet are often scoured from the channel bed only to end up in a detention basin or treatment wetland. This dual problem of both ‘too much’ and ‘too little’ coarse-grained sediment reflects a watershed sediment budget that is profoundly altered. We developed a conceptual urban coarse-grained (>0.5 mm) sediment budget across three domains: hillslopes (urban land surfaces), the built stormwater network and stream channels. We then quantified key sources, sinks and storages for a suburban case study, using a combination of hillslope and in-channel monitoring, and interrogation of local government records. Around 36% of the sediment supplied to the stormwater network reached the catchment outlet, a level of sediment delivery much higher than observed in similar-sized natural catchments. The remainder was deposited in the sediment cascade and either stored, or extracted and removed from the catchment (e.g. material deposited in sediment ponds and gross pollutant traps). Conventional urban drainage networks are characterized by high hillslope sediment supply and low storage, resulting in efficient sediment delivery. Channel erosion, deposition in (and extraction from) pipes and channels, and floodplain deposition are small compared to sediment transport through the cascade. An understanding of the sediment budget of urban headwater catchments can provide stormwater and waterway managers with the information they need to address specific sediment problems such as sedimentation in stormwater assets and geomorphic recovery of urban streams. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

Identifying large‐scale erosion and deposition processes from airborne gamma radiometrics and digital elevation models in a weathered landscape

Patterns of erosion and deposition are difficult to identify and measure at catchment and regional scale but it may be possible to infer their distribution from remote sensing using easily measured surrogate variables. Airborne geophysical surveys provide data on gamma ray emissions from surface and near‐surface material and allow estimation of K, Th and U content. Gamma ray signatures are largely determined by lithology but also change with weathering and with erosion and deposition, and may be used as a partial surrogate for those processes. Comparison of gamma ray signatures with topographic characteristics closely related to sediment transport capacity, downstream sorting of sediments, and the extent of erosion and deposition shows strong linkages. Studies in four small catchments in southeastern Australia indicate that K consistently increases as slopes become steeper while Th and U may either increase or decrease. This suggests the presence of fresh rock rather than weathered material and implies removal of material by erosion, although some patterns may result from systematic changes in lithology across catchments. Analysis by lithology confirms the increase in K with slope in granites, metamorphosed sediments and basalt, and also shows a tendency for U to decrease with slope in the granites and basalt. Gamma ray emissions vary only slightly with catchment area (a surrogate measure of water discharge) suggesting that water erosion is limited or that discharge is not closely related to area. Gamma radiometric profiles down hillslopes, averaged across the full range of gradients, show that, in most cases, radioelements initially decrease, probably reflecting increased weathering, but then increase close to valley floors because of accumulation of fine sediments. Analysis by lithology confirms the increase in radioelements close to valley floors in granites and metamorphosed sediments but the trend is less clear in basalt. Gamma ray profiles down floodplains are variable and indicate the amount of deposition and accumulation of weathered material in valley openings and exposure of bedrock in valley constrictions. Simple erosion and deposition models, based on the conservation of mass equation, and applied to the four catchments, show that all radioelements increase as the potential for deposition increases. They reach a low point in zones of no net erosion or deposition and subsequently increase as erosion becomes more intense and weathered material is lost from slopes. Analysis by lithology largely confirms this pattern. The usefulness of airborne geophysical survey data is limited by flight line spacing with most data being flown at a 200–400 m spacing in Australia. However, general trends in erosion and deposition can still be distinguished and there is capacity for calibrating long‐term erosion and deposition models once better approaches to interpretation of gamma ray data have been developed. Copyright © 2000 John Wiley & Sons, Ltd.     

Late Pleistocene and Holocene coastal palaeoeconomies: A reconsideration of the molluscan evidence from northern Spain

The worldwide increase in shell midden deposits on coastlines during the Holocene has been variously explained as the result of human population growth, economic intensification, changes in the visibility of midden deposits with changes in sea level, or climatic and environmental changes. Since coastlines are relatively unstable in geological and ecological terms, and since many archaeological sequences span periods of major climatic change, a critical issue is the ability to disentangle palaeoenvironmental from cultural and anthropogenic effects. We draw on a case study from the cave sequences of northern Spain to illustrate the problems and possibilities of palaeoeconomic and palaeoenvironmental interpretation, using studies of palaeogeographical context and analysis of abundance, taxonomic representation, ecological tolerances, size, growth structures, and other physical and chemical characteristics of the molluscs themselves. We demonstrate that the dominant, but by no means exclusive, factor in archaeologically visible long‐term changes in shell‐gathering behavior is environmental change rather than cultural change. © 2003 Wiley Periodicals, Inc.     

The West Spitsbergen Fold Belt: The result of Late Cretaceous-Palaeocene Greenland-Svalbard convergence?

The West Spitsbergen Fold Belt, together with the Eurekan structures of northern Greenland and Ellesmere Island, are suggested to be the result of Late Cretaceous-Palaeocene intracontinental compressional tectonics. The Late Palaeozoic –Mesozoic rocks of western Spitsbergen are characterized by near-foreland deformation with ramp-flat, top-to-the east thrust trajectories, whereas structurally higher nappes involving Caledonian complexes are typified by more listric thrusts and mylonite zones. A minimum of 40 km of shortening is estimated for the northern part of the West Spitsbergen Fold Belt. The axial trends in the West Spitsbergen and the North Greenland Eurekan fold belts parallel the principal fault zones which accommodated the separation of Greenland and Svalbard after Chron 25/24. In northern Greenland, north directed Eurekan thrusts associated with mylonites and cleavage formation represent at least 10 km of shortening. Between 50 and 100 km of shortening is estimated for the markedly arcuate Eurekan Fold Belt of Ellesmere Island, but the principal tectonic transport is eastwards. Kinematic reconstructions suggest that Svalbard was linked to North America before the opening of the Eurasian Basin and Norwegian — Greenland Sea. In the Late Cretaceous — Palaeocene interval, the relative motion between Greenland and North America was convergent across the Greenland — Svalbard margin, giving rise to the West Spitsbergen Fold Belt and the Eurekan structures of North Greenland.