Bedrock Character Research Articles

Compositional variation in modern estuarine sands: Predicting major controls on sandstone reservoir quality

Primary depositional mineralogy has a major impact on sandstone reservoir quality. The spatial distribution of primary depositional mineralogy in sandstones is poorly-understood and consequently empirical models typically fail to accurately predict reservoir quality. To address this challenge, we have determined the spatial distribution of detrital minerals (quartz, feldspar, carbonates and clay minerals) in surface sediment throughout the Ravenglass Estuary, UK. We have produced, for the first time, high resolution maps of detrital mineral quantities over an area that is similar to many oil and gas reservoirs. Spatial mineralogy patterns (based on x-ray diffraction data) and statistical analyses revealed that estuarine sediment composition is primarily controlled by provenance, i.e. the character of bedrock and sediment drift in the source area. The distributions of quartz, feldspar, carbonates and clay minerals are primarily controlled by the grain size of specific minerals (e.g. rigid versus brittle grains) and estuarine hydrodynamics. The abundance of quartz, feldspar, carbonates and clay minerals is predictable as a function of depositional environment and critical grain-size thresholds. This study may be used, by analogy, to better predict the spatial distribution of sandstone composition, and thus reservoir quality in ancient and deeply-buried estuarine sandstones.

Geo-hydrological response to pothole formation: a quantitative study of Kharsoti River, India

This work includes the mechanism of pothole morphology, development, growth and dynac changes in meso and micro level. The study highlights some inter linkages of certain specific parameters like geological and hydrological concerns in pothole mechanism of Kharsoti River. Reviewing our geomorphological knowledge, potholes are mainly found to be concentrated in upper most part of the river where the stream energy is maximum but here our study area is included in the middle part and lower part of the Kharsoti River which is a typical example of rejuvenated antecedent tributary river of Subarnarekha River in Chhotanagpur plateau and exist like a bedrock river. Both shearing (geological) and huge discharge (hydrological) response are the concerned mechanisms in the development of potholes as micro fluvial landforms. One the basis of the analysis it is necessary to give a new threshold of quantitative methods in landforms study under a systematic scientific geographical background. Regarding the hydrological parameters like discharge, suspended load, stream power, velocity have been considered and some normal attributes like slope, bedrock character, rocky exposed on the riverbed etc. This type of work will help to open a new window for studying the micro landform mechanism in a contemporary method.

Characteristics of a Mixed Bedrock-Alluvial Channel in a Plateau and Plateau Fringe Region: A Study on the Barakar River of the Chotanagpur Plateau, India

The rivers that bear the properties of both alluvial and bedrock character are considered as bedrock and alluvial mixed character rivers. They are characterised by stable planform, erosion resistant bank, rock outcrop, local variability in channel bed gradient and variable flow regime. The Barakar River in the Chotanagpur plateau and its fringe region of India has the distinctive features of bedrock and gravel mixed river with sinuous and braided nature in the upper and the lower sections of the river, respectively. To investigate and extract the geomorphic features of the bedrock and gravel mixed character of the Barakar River, planform view and behaviour of the sediments were considered. The sinuous bedrock and braided reaches have been analysed using the Sinuosity Index and the Braid-channel Ratio, respectively. The upper sinuous bedrock section is marked by a steep-sided, narrow valley with the presence of incised channel. In the downstream reach of the Maithon Dam, the river channel is a box-shaped bedrock channel with a low form ratio. Potholes and grooves of varying size and shape and inner channel are the main features at the mouth zone. While, in the lower section of the river, the wide and straight braided reach is characterised by higher form ratio and higher gradient than the sinuous reach. The riffle-pool sequence in the braided section is not developed significantly like in the alluvial channel. In the braided reach, the sediment grain size is continuously decreased towards the Maithon Dam and the sediment grains are well sorted. The lithology and hydraulic processes of the river determine the mixed character of the river that favours the fluvial system to maintain its lateral stability.

Multiple influences on regolith characteristics from continental-scale geophysical and mineralogical remote sensing data using Self-Organizing Maps

We investigate the characteristics of regolith through the application of statistical learning to diverse layers of terrestrial, continental-scale remote sensing data. This combination allows us to explore the multiple influences of bedrock, climate, biota, landscape and time on regolith development and properties: an interdisciplinary geoscience modeling problem. From a wide variety of available data for Australia, we select remotely sensed geophysical, geomorphological and mineralogical inputs with good spatial coverage. We use Self-Organizing Maps (SOM), a topologically constrained unsupervised statistical learning algorithm, to characterize the geophysical and mineralogical signatures of regolith and bedrock. Regolith materials cover more than 80% of the Australian continent, range in age from Precambrian to Quaternary and vary in thickness from less than a meter to more than a kilometer. The diversity of regolith cover type and character across Australia provides an opportunity to demonstrate knowledge discovery from remote sensing data. The outputs of our SOM analysis are combined with ground observations from locations showing naturally occurring anomalous concentrations of nickel, tin and uranium. We identify a minimum number of natural clusters indicating subtle but significant differences in regolith and bedrock mineralization characteristics. Our results show that SOM identifies spatially contiguous regions representing unique regolith and bedrock materials. In the Yilgarn Craton we observe key differences in landscape character, density of the crust, and relative abundance of radioactive elements and alumino-silicate and ferric oxide minerals. These properties discriminate between nickel-prospective residual deeply weathered regolith formed on mafic and/or ultramafic bedrock and uranium-prospective Cainozoic paleochannels containing felsic bedrock source materials. National-scale data are publicly available for many continental regions, as in the Australian example, and our approach has general applicability. We demonstrate that remote sensing data may be used to understand the regolith, revealing the interplay between environmental history and bedrock character at regional scales, and differences between residual and transported regolith, provenance of source materials and their relative ages.

Paleolimnological investigations of anthropogenic change in Lake Tanganyika: VIII. Hydrological evaluation of two contrasting watersheds of the Lake Tanganyika catchment

This study was conducted to delineate the impact of human activities on stream flow and water chemistry as well as other factors that influence the chemical character of both surface and groundwater in two contrasting watersheds of the Lake Tanganyika catchment. The study sites the Mwamgongo and Mitumba streams along the northern Tanzanian coastline of the lake are representative of disturbed and undisturbed watersheds, respectively, but are quite similar in other characteristics of slope, bedrock geology and size. Separation of stream flow components was undertaken using classical hydrograph analysis along with chemical methods using both Cl and 18O data. All the data show that groundwater accounts for the predominant source of total stream flow in both the Mwamgongo and Mitumba watersheds (65 and 70% respectively). The streams have an average δ18O of about -3.0% and less than 10 mg/l for Cl. The basin recession constants of 9.4×10-3-d-1 and 9.6×10-3-d-1 for Mwamgongo and Mitumba, respectively, indicate existence of both fissured and fractured aquifer systems. The chemical data exhibit low values of all determined ions. This supported the hypothesis that natural processes influence the water chemical character of the study area. An Mg–HCO3 type of water dominates in the two watersheds. Despite their similar size and bedrock character the Mwamgongo watershed has an order of magnitude in sediment transport than the Mitumba one. The data show that the disturbed watershed discharges less groundwater and more sediments, and has a poorer water quality than the forested Mitumba watershed, which lies within the Gombe National Park. The data show that soil erosion processes are more active at Mwamgongo, and that both the surface runoff component of the total stream flow and increased dissolved salt load is greater in the deforested Mwamgongo watershed than in the Mitumba watershed. The chloride and δ18O data complemented each other in delineating the amounts of groundwater in the total stream flow as the results using both data differed insignificantly. It may be concluded that the undisturbed watershed has a higher retention of good quality water and traps more sediments than the disturbed one. In addition, the groundwater component plays a dominant role in the total annual stream flow at each watershed.

Integrating indicators, endpoints and value systems in strategic management of the rivers of the Kruger National Park

Summary1. In trying to operationalize the notion of sustainable ecosystem health, ecologists have focused on identifying sets of indicators which can be used to assess river condition relative to some normative, undegraded condition. Recognition and description of this normative state has proved elusive, particularly in highly variable semiarid ecosystems. Without an operational definition of the desired system condition that reflects both scientific rigour and broader societal value systems, rivers are unlikely to be managed effectively.2. Managing river health should not be confused with measuring it. Many monitoring or assessment programs become ends in themselves instead of being the means to achieving specific management goals. The absence of a test of the results of monitoring further introduces the risk of management by observation and ‘pseudo‐fact’. Health ‘endpoints’ provide a scientific description of management goals, while ‘values’ provide a societal perspective. Together they complement the use of indicators and provide the basis for a strategic rather than reactive approach to management.3. The integration of value systems, endpoints and indicators of ecosystem health or ecosystem integrity forms the cornerstone of a consultative management process for the rivers of the Kruger National Park.4. An objectives hierarchy has been developed to service management’s institutional hierarchy. ‘Vision’ and objectives serve upper levels of management with value based statements of strategic intent which have been tested against public opinion. Goals provide managers on the ground with specific ecological endpoints termed ‘thresholds of probable concern’ (TPCs). TPCs are described by a range of spatially and temporally bounded indicators of the system’s response to the main potential agents of change.5. TPCs represent statements or hypotheses of the limits of acceptable change in ecosystem structure, function and composition. They thereby provide an inductive and strategic approach to adaptive management in a data poor situation. Integrated monitoring, research and modelling track criteria relative to TPCs and question whether management action, or recalibration of the TPC, is needed. TPCs thus provide direction for management but their validity and appropriateness are frequently challenged and adaptively modified.6. The objectives hierarchy gives Kruger Park management a mandate to ‘maintain biodiversity in all its natural facets and fluxes’. Alluviation, as a consequence of increased sediment supply and decreased sediment transport capacity, is a major threat to the biodiversity of the bedrock‐controlled rivers which flow through the park. Thus, for example, TPCs for geomorphic diversity reflect permissible ranges of change in bedrock character of the physical template. They are measured as change in the proportion of different geomorphic units in identified representative reaches. TPCs for riparian vegetation are measured as change in population structure of selected species within the representative reaches. They reflect a likely range of biotic responses to change in the physical template. A specific set of indicators, reflecting response to the major agents of change, therefore provides a parsimonious program for assessing ecosystem condition relative to explicit goals and a clearly defined management process.

Early stages of till genesis: an example from Fanore, County Clare, Ireland

Traditional views of glacigenic processes focus on erosion of hard bedrock and deposition of unconsolidated till. In the 1960s and 1970s attention was directed towards the glacier debris cascade, which linked these two end members. A limited understanding of the relationship between bedrock character, the supposed processes of erosion, debris comminution and texture emerged. In the 1980s researchers began to appreciate the important role which glaciotectonism plays in the spectrum of glacigenic processes, although little attention has been paid to the interface between glacial erosion, glaciotectonism and the early stages of the debris cascade system. A coastal section at Fanore, County Clare, Ireland affords a unique opportunity to examine a range of glacial deposits which represent a series in the erosion, tectonism and comminution stages of till genesis. Major elements of the site are bedrock rafts, glaciotectonic breecias, immature till and mature till. In all cases > 98% of the elements comprise Carboniferous limestone. Research at Fanore has focused on textural properties. Analysis of bulk samples of the sediments demonstrates a continuum of textural development from the glaciotectonism of the bedrock (breecia production and bedrock raft comminution) to a homogenized but immature till and to a more mature matrix‐dominated deposit.

Repeating patterns in the relief and in the structure of land

Relief Patterns in Landscapes CHARACTER PROFILES To the physiographer who has critically surveyed the relief forms of many districts with their manifold diversities in character of bedrock, in structure, and in physiographic history, there is much which may be read at the first glance. Perhaps first of all are noted those features of the landscape which disclose the stage in the geographic cycle through which the district is passing. There may be, further, distinguishing lines which reveal in one case the work of waves, in another of mountain glaciers or of a continental ice-sheet; again, it is a partial submergence of the land which is disclosed, or a moulding of the surface under arid conditions rather than the more familiar, if not more prevalent, denudational processes of a humid climate. In the more striking instances—with purer types—fault topography may be distinguished from fold topography (see figures 1 and 2 ), though . . .