Litho-structural Control Research Articles

Lithostructural Control in the Development of Potholes in the Rock Bed of the Carnaúba River, Seridó Geopark, NE Brazil

Granitic forms resulting from turbulent flow, with hydraulic vortices, characterize the rocky bed of the lower course of the Carnaúba River, in a geosite of the Seridó Geopark, in the Seridó Oriental microregion, Northeast Brazil. These forms constitute a variety of types of potholes that individually represent various stages of evolution, in addition to reflecting the variation in the erosive potential of river flow throughout the Quaternary. From a bibliographical review, fieldwork (quantification and measurements of the potholes), high-resolution photogrammetry and morphostructural analysis of the generated cartographic products, it was possible to establish a correlation between the preferential orientation of the potholes and the direction of the planes of weakness, as well as the classification of potholes by morphometric parameters. In this work it was demonstrated that the efficiency of hydraulic vortices is associated with discontinuity structures and the mineralogical composition of granite facies, with abrasive erosion being responsible for sculpting potholes, with different dimensions and geometries. In the rocky bed of the Carnaúba River, the small potholes deepen and their diameter evolves into cylindrical shapes as the turbulent vertical flow increases, eventually becoming sigmoidal. The lateral potholes, located on the walls of the river channel, are deeper than they are wide, and represent a destructive phase of evolution.

Geophysical Constraints to the Geological Evolution and Genesis of Rare Earth Element–Thorium–Uranium Mineralization in Pegmatites at Alces Lake, SK, Canada

This investigation establishes an integrated method for rare earth elements (REE) exploration through a very promising and advanced exploration prospect in the Alces Lake area (SK, Canada) by assessing the integrated analysis of several multisource geophysical datasets. The resulting outcome provides important lithostructural information to the well-exposed, mineralized middle-to-lower crust at Alces Lake, comprising deep-seated poly-phase folds, ductile shear zones, and brittle faults. Geophysical–geological models of the Alces Lake property were constructed at different scales. The area of interest is located within the Beaverlodge Domain, about 28 km north of the Athabasca Basin’s northern margin. It contains some of the highest-grade rare earth elements (REE) in the world with the REE hosted predominantly in monazites within quartzo-feldspathic granitic to biotite–garnet–monazite–zircon-rich restite-bearing/cumulate mush melt pegmatites of anatectic origin (abyssal). Geophysical magnetic, gravity, and radiometric data were used together with Shuttle Radar Topography Mission (SRTM) images to facilitate the processing, modeling, and interpretation. Consequently, major structures were identified at different scales; however, the emphasis was given to studying those at the district/camp scale. The REE zones discovered to date occur within a large district-scale refolded synformal anticline. The eastern limb of this folded structure comprises a 30–40 km long, NW-trending shear zone/fault corridor with deep-seated structural crustal roots that may have served as the major pathway for ascending fluids/melts and facilitated the emplacement of mineralization. Thus, shear zones, faults, and folds in combination with lithological contacts/rheological contrasts appear to control residual/cumulate pegmatite emplacement and monazite deposition. Anomalies obtained from the airborne equivalent thorium survey data prove to be the most useful for REE pegmatite exploration. The results herein provide new interpretation and modeling perspectives leading to a better understanding of the distribution and lithostructural controls of REE on the property, and to new guidelines for future exploration programs at Alces Lake and elsewhere in northern Saskatchewan.

Gneissic tors in the central European upland: Complex Late Pleistocene forms?

Bedrock outcrops punctuating regolith-covered surfaces in the summit/upper slope and hillside positions (tors and crags) have long been a subject of inquiry in geomorphology for their evolutionary trajectories and now also as valuable geoheritage sites. Methodological advances in research, such as DTM-based geomorphological analysis and terrestrial cosmogenic nuclide inventories, create new perspectives to decipher the spatial and temporal context of tor emergence and decay. The shape, structural controls, 10Be inventories and relation to surrounding medium-scale landforms were studied at thirteen conspicuous bedrock outcrops developed in metamorphic and sedimentary lithologies in the Bohemian-Moravian Highland, Czechia. The shapes of studied bedrock outcrops indicate significant litho-structural controls. The general outline is mainly governed by (sub)vertical joints, whereas the inclination of foliation or bedding planes dictates summit and cliff morphology. Some of the tors described in this study developed in exceptionally densely foliated and jointed gneiss, which does not comply with the generally accepted view of tors as massive rock compartments resisting weathering. A series of rock hardness measurements performed at three gneissic tors using Schmidt hammer show statistically significant within-tor variability of R-values, indicating different exposure times to subaerial weathering. The complexity of landform assemblages, within which studied tors/crags are developed, varies from isolated bedrock outcrops surrounded by smooth slopes covered with debris-rich soils to outcrops accompanied by low rock cliffs, debris-covered steps, slope benches, boulder fields and isolated large blocks. The 10Be inventories reveal ages mostly from the Late Pleistocene and rarely from the Holocene. Summit/upper slope tors and hillside crags show considerable variability in maximum denudation rates ranging from 6.4 ± 0.2 to 105.6 ± 4.8 m/Ma. Paired samples from the summits and cliffs of eight outcrops indicate three possible post-emergence evolutionary scenarios with summit downwearing while keeping the outcrop outline, balanced cliff and summit degradation rate, and backwearing as the dominant degradation process.

Litho-structural control on rock slope failures at Garmaksla, Billefjorden coastline, Svalbard

The eastern slope of Garmaksla, a flat-topped mountain at the western margin of Billefjorden, Svalbard, is affected by mass movements of different types. Rotational rock slides, rock fall and a rock avalanche affecting the coastal cliff are shallow surface expressions covering a larger rock mass instability that is bordered to the west by the Balliolbreen Fault. This structural feature is part of the Billefjorden Fault Zone and accommodated multi-phase deformation since Devonian time. Based on a comprehensive morpho-structural analysis, the mapped surface features and rock slope failures are explained by a compound rock slide model that reveals a litho-structural control on the type and mechanism of slope instability. The Balliolbreen Fault serves as an inherited zone of weakness that is reactivated as the rear rupture surface of the rock slide. In addition, favourably oriented bedding planes and pre-existing fault zones serve as prime conditioning factors for the compound rock slide. A postglacial age of at least 6 ka is derived from 14 C dated sediments of Garmaksla Lake, a perennial sag pond along the main scarp. Although the current state of activity of the compound rock slide is unclear, an increase of shallow slope instabilities is expected owing to climate warming.

Lithostructural controls in Douala-Buea Region landscape (SW Cameroon margin): Insights from morphometric analysis

The Douala-Buea Region (DBR; 4°–5°N, 9°–10°30′E), a portion of the southern Cameroon passive margin, developed on the Proterozoic granito-gneissic basement and the Cretaceous to Recent volcano-sedimentary cover, was explored in order to evaluate the lithology and tectonics controls on its landscape using the qualitative and quantitative geomorphological analyses based on 30 m resolution Digital Elevation Models (DEM) and field evidences. This area displays an uneven and complex landscape differentiated into four morphological units: Douala, Nkondjock, Kumba and Buea Units. The Douala Unit corresponds to the Coastal Plain and is extended on the Douala-Kribi/Campo sedimentary basin. The Nkondjock Unit represents a middle plateau developed on a Proterozoic granito-gneissic basement. The Kumba Unit matches with the southernmost volcanic Western Cameroon High Plateau. The Buea Unit corresponds to the Mount Cameroon stratovolcano. The relief analysis through mountain-front sinuosity (Smf, 1.19–1.43) and relative relief ratio (Rr, 0.10–2.31) vary from one unit to another. The drainage network analysis including drainage patterns, stepped longitudinal river profiles, the associated morphometric indexes, notably the concavity index (IC, 0.56–0.88), deviation (D, 267–2912 m), basin asymmetry factor (A f, 6.37–42.12), hypsometric integral (HI, 0.10–0.29), valley floor width to valley height ratio (Vf, 0.36–2.75), elongation ratio (Re, 0.30–0.50), watershed slope (S, 6.88–88.88) and stream length gradient index (SL, 0–3332) vary from one basin to another too. These results also show the heterogeneous and uneven DBR landscape controlled by its lithology and active tectonics. The drainage system reveals concave to concavo-convex longitudinal river profile shapes with knick points, asymmetric basins, and fault reactivations, and highlights the tectonics activity that used to occur through the time and their control on the morphology. Together, they document the lithostructural controls on the DBR landscape evolution, extendable in the whole SW Cameroon margin.

Surface Geomorphological Features of Deep-Seated Gravitational Slope Deformations: A Look to the Role of Lithostructure (N Apennines, Italy)

The attention to deep-seated gravitational slope deformations (DSGSDs) has steadily increased in the last few decades, because such features are ubiquitous in mountain areas. Their geomorphological surface expression, especially when related to the effects of lithostructural control in sedimentary stratified bedrocks, is well characterized in theory, but sometimes not as well documented in field cases. In this contribution the investigation of several DSGSDs in the area of the Northern Apennines of Italy is reported. A survey of the area was conducted using fast and low-cost satellite imaging techniques, in order to describe the surface features of selected DSGSDs and verify how their occurrence is linked to the effect of lithostructural constrains such as bedding and folding. Surface features developed in parallel to the strike of the slope are mostly related to the main gravitative strain acting on the deformation. Features along slope dip are instead formed by the release of tension caused by compressive forces at the landslide foot or by the presence of pre-existing weak lines. One example of a DSGSD, formed on the hinge of a vertical fold, shows a corrugated appearance due to the release of vertical fractures that mask most other features usually associated with DSGSDs. This potentially impairs the detection of these landforms during field and remote surveys.

ROCK-LANDFORM-SOIL RELATIONSHIP FOR GEOMORPHOPEDOLOGICAL CHARACTERIZATION IN THE REGION OF LAVRA VELHA, OCCIDENTAL CHAPADA DIAMANTINA, BAHIA

The Lavra Velha region is situated on the western edge of the Chapada Diamantina and comprised of a crystalline basement and a metasedimentary cover that corresponds to the Ibitiara Granitoid and the Espinhaço Supergroup, respectively. The Chapada Diamantina is internationally recognized for mineral production and tourism, and because of that it has become a constant target for novel research that aims at characterizing its main geological and physiographic aspects. The present work aims at pointing out geomorphopedological associations of the Lavra Velha region by analyzing the interdependence between rock, landform and soil. To this end, geology, geomorphology and pedology data were obtained from literature, remote sensing data and field expeditions. In the studied area, we recognized metasedimentary and crystalline rocks, on which flat to gently undulating landforms beside crests and cliffs developed. Oxisols occur on flat to gently undulating landforms while Entisols, Inceptisols and rock outcrops appear in the aligned crests, cliffs and undulating hills. Alfisols predominate in undulating hills associated with mafic rocks. Features of the landscape show landforms resembling the Appalachian geomorphological model as first described by William Morris Davis, and they suggest landform evolution by geochemical and mechanical erosion under a strong litho-structural control. The geomorphopedological associations allowed the understanding of the relationship between the major elements of the physical environment from Lavra Velha region and, consequently, a predictive model of the rock-landform-soil distribution that can be useful for geomorphopedological mapping of the western edge of the Chapada Diamantina.

Litho-structural controls on mineralisation at the Pillara carbonatehosted Zn-Pb Deposit, Lennard Shelf District, Western Australia

The Pillara Zn-Pb deposit is located on the northeast margin of the Canning Basin, Western Australia where it is hosted by a series north-northeast-trending, en echelon, conjugate normal faults tha...

Litho-structural controls on orogenic gold deposits within the Sandstone greenstone belt, Yilgarn Craton, Western Australia: implications for exploration targeting

ABSTRACTThe 920 km2 Archean Sandstone greenstone belt lies in the central-northern part of the Southern Cross Domain of the Youanmi Terrane, Western Australia. The belt, forming an arrow-head geometry, is bounded by the Youanmi and Edale shear zones on its eastern and western margins, respectively. The belt has a total gold endowment, including historic production, resources and reserves, of approximately 62 t (2.0 Moz). Most known deposits are situated within a central-southern ultramafic domain, although this is likely a function of exploration focus. The distribution of historical exploration efforts and domaining of deposit types, based on litho-structural controls on ore formation, highlight the potential for significant undiscovered deposits, hosted within arrays of shear zones parallel and adjacent to the lithosphere-scale Youanmi and Edale shear zones.

Mineral deposits of northeastern Algeria (southern Medjerda mounts and diapiric zone): regional-scale structural controls, spatial distribution, and importance of geophysical lineaments

The Southern of Medjerda mounts and the diapiric zone in the northeast of Algeria host a significant hydrothermal Pb-Zn-Fe-Ba (±Cu, ±F, ±Sr, ±Au, ±Ag) ore deposits and showings. The integration of geophysical data (ground gravity and aeromagnetic datasets) was undertaken in order to clarify and define the litho-structural control of the mineralization. These geophysical surveys allowed the identification of several prominent geophysical features. Some of these features correspond to lithological contacts; others reflect tectonic trough zones, Triassic salt diapirs, sedimentary basins, anticlines, and faults. The preferential (primary) trend of structural features within the study area is NE–SW and NW–SE. Integrated interpretation of geological and regional geophysical data helped the identification of the main factors controlling the distribution of mineral deposits within the study area. Most of the mineral deposits are likely to be found along or near major NE–SW/NW–SE deep lineaments. These major deeper lineaments have probably controlled the kinematic evolution of geological structures, sedimentary basins, and the ascension of the Triassic rocks during the lower Cretaceous. They seem to play a significant role providing favorable pathways for the migration and ascent of mineralized fluids to depositional sites along smaller faults into the sedimentary cover or at contact between Triassic salt outcrops and lower Cretaceous carbonate rocks.

Litho-structural controls on Quaternary landslide distribution in the Rangitikei hill country, North Island, New Zealand

ABSTRACTThe aim of this research is to investigate the influence of stratigraphy and structure on the development of present-day topography in the Rangitikei hill country. This is achieved by (1) comparing a new inventory of deep-seated Late Quaternary relict landslide zones to the hydraulic, physical and structural properties of the Whanganui Basin fill, (2) analysing the proximity of landslides to structures and rivers, and (3) exploring the relationships between geology and slope morphology. Analysis suggests postglacial incision and daylighting of the Whanganui Basin fill is a primary control on landslide distribution, providing the necessary conditions upon which a range of triggering mechanisms operate. Faults display a clear relationship to landslide frequency, suggesting earthquakes are possibly an important triggering mechanism. Landscape evolution involves inversion and denudation of alternating coarse and fine-grained sedimentary units. Frequent, shallow landslides dominate on steep, northern scarp slopes, and deep-seated rock planar slides dominate on gentle, southern dip slopes.

Boulder coastal deposits at Favignana Island rocky coast (Sicily, Italy): Litho-structural and hydrodynamic control

Boulders are frequently dislodged from rock platforms, transported and deposited along coastal zones by high-magnitude storm waves or tsunamis. Their size and shape are often controlled by the thickness of bedding planes as well as by high-angle to bedding fracture network. We investigate these processes along two coastal areas of Favignana Island by integrating geological data for 81 boulders, 49 rupture surfaces (called sockets) and fracture orientation and spacing with four radiocarbon dates, numerical hydrodynamic analysis, and hindcast numerical simulation data. Boulders are scattered along the carbonate platform as isolated blocks or in small groups, which form, as a whole, a discontinuous berm. Underwater surveys also highlight free boulders with sharp edges and sockets carved out in the rock platform. Boulders are composed of ruditic- to arenitic-size clastic carbonates. Their size ranges from 0.6 to 3.7m, 0.55 to 2.4m, and 0.2 to 1m on the major (A), medium (B), and minor (C) axes, respectively. The highest value of mass estimation is 12.5t. Almost all of boulders and sockets are characterized by a tabular or bladed shape. The comparisons between a) the fractures spacing and the length of A- and B-axes, and b) the frequency peaks of C-axis with the recurrent thickness of beds measured along the coastal zone demonstrate the litho-structural control in the size and shape of joint-bounded boulders. These comparisons, together with the similarity between the shapes of the boulders and those of the sockets as well as between the lithology of boulders and the areas surrounding the sockets, suggest that blocks originate by detachment from the platform edge. Thus, the most common pre-transport setting is the joint-bounded scenario. Hydrodynamic equations estimate that the storm wave heights necessary to initiate the transport of blocks diverge from ~2m to ~8m for joint-bounded boulders and from few tens of centimeters up to ~11m for submerged boulders. The comparison between the wave heights at the breaking point of the coastal zones with the results of hydrodynamic equations shows that waves approaching the coastline are able to transport all surveyed boulders. Our data suggest that boulders have been transported by several storm events, even in very recent times.

Tectonics, lithology and climate controls of morphometric parameters of the Edea - Eseka region (SW Cameroon, Central Africa): Implications on equatorial rivers and landforms

Shuttle Radar Topography Mission (SRTM) - 3 data for Digital Elevation Model through morphometric analyses of the Sanaga, Nyong and Kelle watersheds and landform were correlated with field survey in a Geographical Information System (GIS) model in the Edea-Eseka Region in SW Cameroon; erected on Paleo-to Neoproterozoic crystallophyllian rock types, Cretaceous to Recent sedimentary formations later affected by reactivated and neotectonic faults. This study that aimed to evaluate the lithology, tectonic and climate interactions on operating processes and landform characteristics based on the morphometric parameters of watersheds. Parameters vary from one watershed to another establishing one to three controls. The density drainage (0.05–0.29), the constant of channel maintenance (3.5–19.47) and the drainage pattern; outlines the lithological, the tectonic and the climate controls of the morphology. The Bifurcation ratio (2–5.25), the mean bifurcation ratio (3.67–4.09), the relative relief ratio (0.21–0.27), the watershed slope (5.75–9.35) and the watershed deviation (105–507); highlights the lithostructural controls of the morphology; whilst the wandering ratio (1.54–2.12) individualises both, the structural and climate controls. The stream number (370–2473) and the stream length ratio (0.57–1.91), the elongation ratio (0.47–0.55), the circularity ratio (0.25–0.29), fitness ratio (0.56–0.63), dissection index (0.91–0.99), the concavity index (−0.1-0.56), the hypsometric integral (0.45–0.49) and the stepped longitudinal length profiles, establishes the dominant tectonic controls of the morphology; while the rho coefficient (0.34–0.43) and drainage texture (1.91–4.75) displays the lithological control of the morphology and; the drainage intensity (1.76–7.62) and the length overland flow (1.75–9.74) typified the climate control of the morphology. The Edea-Eseka Region uplift rejuvenates old watershed each time they evolve to equilibrium because of lithological variations, neotectonics, differential erosion and climate variations; overriding its morphology. This geodynamic and climatic control of morphometric processes in the SW Cameroon can be extended to the whole of Central Africa and in Equatorial Regions that display similar evolutions.

Structural and Lithological Study of Gold Mineralization in the Areas of Bena and Bakolobi, Mali, West Africa

The areas of Bena-Bakolobi are located in the eastern part of the Kedougou-Kenieba in layer. This sector contains several deposits of gold, including the mines of Sadiola, complex Gara-Yalea and Gounkoto, gold mines of Tabakoto and the gold deposit of Fekola, all located around the (SMS) Senegalo Malian shear zone. The work carried out is summarized in two parts: The first part is based on the detailed mapping of the Bena and Bakolobi target. It was necessary to make a detailed mapping in order to understand and assess the target. The second part is to determine the term and the litho-structural control of gold mineralization. This study is based on lithology, alteration, structures and mineralization of the two areas. The ultimate purpose is to draw a regolith map for a future research program. Two types of alteration affect the rock formations of the two zones: weathering (supergene) that consists in hematization, limonitisation and the kaolinitization. The hydrothermal alteration consists in albitization, chloritisation, the sericitization, the tourmalinisation, the sulphidation, silicification and carbonation. This paper improves structural and lithological study of gold mineralization in the areas of Bena and Bakolobi. The analysis of the results of the work carried out in the two zones allowed us to have an overview on the geology of these two zones, which are located in the Kedougou-Kenieba window in the volcano-sedimentary rocks of Proterozoic Formation of Kofi. The lithological and structural studies carried out in the area have demonstrated the relationship between structures and mineralization and/or lithology.

Litho-structural control on interbasin groundwater transfer in central Ethiopia

In central Ethiopia, litho-structural setup of the three sub-basins of the southern flank of the Middle Blue Nile basin (Guder, Muger and Jema) and the adjacent Upper Awash River basin have been investigated to develop conceptual groundwater flow model and to characterize the groundwater hydrodynamic relationship between the aquifer systems of the two basins. The development of conceptual groundwater flow model is based on interpretation of Digital Elevation Model (DEM) from SRTM and Landsat images together with field geological observation, integrated with existing boreholes lithologic logs and pumping test data. The litho-structural framework, reconstructed from regional stratigraphy and analysis of major regional fault systems, controls the size of recharge area for aquifer systems and aquifer distributions in the groundwater sub-basins. The study has indicated the distinctive geometric setting of the litho-strata of aquifers and aquicludes. The NW–SE trending horsts beneath the volcanic successions and the overlying volcanic ridges control aquifer distribution in the Guder, Muger and Jema groundwater sub-basins, while the E–W trending horsts control aquifer distribution between the Middle Blue Nile and the Upper Awash Rivers basins. Impermeable mudstone constitutes the upper part of the E–W oriented horst at the center of the Muger River sub-basin. This mudstone capped horst underlying the volcanic aquifers is a groundwater divide channeling recharged water in the Blue Nile basin partly towards the Upper Awash basin. Significant proportion of groundwater recharged in the Middle Blue Nile basin (Muger and Jema River sub-basins) contributes to the storage of the aquifer systems of the Upper Awash basin.

Morphometric analysis of fluvial network and age constraints of terraced surfaces of the Ofanto basin, Southern Italy

The Ofanto basin is an intermontane depression located in an intermediate position between the axial zone and the thrust front of the southern Apennines, Italy, filled by Pliocene to Quaternary sediments of both marine and continental origin. This basin presents some peculiarities such as the orientation of the elongation axis with regard to the strike of the chain, marked anomalies of the drainage network, and the asymmetric distribution of the terraced surfaces. Our paper focuses on the morphotectonic evolution of such a complex intermontane basin and tries to explain all those characteristics. The results obtained from both quantitative and morphostructural analyses allowed us to reconstruct the Quaternary evolution of the basin, particularly referred to the ancient land surfaces and the younger fluvial terraces. The hypothesis of a long-term process driven by the differential tectonic behaviour of the two basin flanks instead of a pure litho-structural control responsible for the fluvial network asymmetry of the Ofanto River catchment is here presented and discussed.

The role of airborne geophysics in facilitating long-term outback water solutions to support mining in South Australia

Mining and energy development in South Australia's far north is set to have significant consequences for the water resources of the region. These sectors generate significant economic value to the State and their support remains a priority for the government. The scale of the planned developments and the potential from current exploration programs facilitated by the South Australian Government through PACE Program will result in a substantial increase in infrastructure requirements, including access to water resources and Aboriginal lands for potential mine developments. Increased demand for water and in particular groundwater is compromised by the limited knowledge we have about these resources. This includes information about their character, variability, sustainability and their relationship to environmental and cultural assets, which is most notable in the priority areas for development. There is a recognised need to develop this knowledge so that water is not a limiting factor to development. In this paper results from the Goyder Institute's Long-Term Outback Water Solutions (G-FLOWS) Project are presented. Particular reference is made to work completed in the Musgrave Province. It illustrates the role of local scale AEM, acquired for exploration, and regional scale airborne magnetics in helping develop a hydrogeological conceptual model for the Province. The AEM data reveal a complex, extensive inset palaeovalley system which contains groundwater of variable quality (2000 - 4500 mg/L TDS). Examination of their location against the regional magnetics indicates a strong lithostructural control on their orientation and distribution. If mineral resources were to be developed in the area, these groundwater systems would represent the best option for water supply. A regional scale water resource map, based on information gleaned from the geophysics, existing hydrogeological and digital elevation data, is presented that provides a framework for groundwater resource determination when/if mineral deposits were to be mined in the region.

A regional scale Fixed-Wing TDEM survey of the Palaeo-Proterozoic Bryah Basin, Western Australia: Providing insights into a setting highly prospective for VMS Cu-Au and mesothermal Au Systems

The Bryah Basin is part of the Capricorn Orogen, a collision zone between the Archaean Pilbara and Yilgarn Cratons in western Australia . It was formed during back-arc sea-floor spreading and rifting on the northern margin of the Yilgarn Craton, and contains a succession of mafic and ultramafic rocks of mid-oceanic ridge basalt to oceanic plateau affinity, overlain by clastic and chemical sedimentary rocks. The Basin is host to significant mineralisation, including mesothermal orogenic gold, coppergold volcanogenic massive sulphides (e. g. DeGrussa). The regolith of the region is complex and varied, and although well mapped, a more complete understanding of this variability has remained undetermined except at very local scales. In June 2012, CSIRO in collaboration with GSWA, flew a reconnaissance, regional scale, airborne SPECTREM AEM survey over the Bryah Basin at a line spacing of 5500 m. The data were inverted using a smooth model layered earth inversion, with the GA-LEI algorithm. The data show that the Basin is characterised by a regolith that exceeds 150m in depth in places. The most dominant regolith features are associated with sediment filled palaeovalleys, valleys that underlie the current track of the Murchison and Gascoyne Rivers and their tributaries. The orientation of the palaeovalleys are show indicates a strong lithostructural control. The regional regolith framework defined from the AEM data provides a basis for better understanding and interpreting the regolith geochemistry that has been acquired across the Basin. The AEM data also indicate the presence of several strong basement conductors that lithologically related. The survey further demonstrates the value of regional AEM surveys in the pre-competative data suite.

Bedding control on landslides: a methodological approach for computer-aided mapping analysis

Abstract. Litho-structural control on the spatial and temporal evolution of landslides is one of the major typical aspects on slopes constituted of structurally complex sequences. Mainly focused on instabilities of the earth flow type, a semi-quantitative analysis has been developed with the purpose of identifying and characterizing litho-structural control exerted by bedding on slopes and its effects on landsliding. In quantitative terms, a technique for azimuth data interpolation, Non-continuous Azimuth Distribution Methodological Approach (NADIA), is presented by means of a GIS software application. In addition, processed by NADIA, two indexes have been determined: (i) Δ, aimed at defining the relationship between the orientation of geological bedding planes and slope aspect, and (ii) C, which recognizes localized slope sectors in which the stony component of structurally complex formations is abundant and therefore operates an evolutive control of landslide masses. Furthermore, some Litho-Structural Models (LSMs) of slopes are proposed aiming at characterizing recurrent forms of structural control in the source, channel and deposition areas of gravitational movements. In order to elaborate evolutive models controlling landslide scenarios, LSMs were qualitatively related and compared with Δ and C quantitative indexes. The methodological procedure has been applied to a lithostructurally complex area of Southern Italy where data about azimuth measurements and landslide mapping were known. It was found that the proposed methodology enables the recognition of typical control conditions on landslides in relation to the LSMs. Different control patterns on landslide shape and on style and distribution of the activity resulted for each LSM. This provides the possibility for first-order identification to be made of the spatial evolution of landslide bodies.

MAPEAMENTO DE UNIDADES DE RELEVO NA MÉDIA SERRA DO ESPINHAÇO MERIDIONAL - MG

This paper proposes a mapping of landforms units for the southern portion of the middle third of the Serra do Espinhaço Meridional. The landforms units were delineated from the integrated analysis of thematic maps and satellite images that allowed the observation of changes in morphology, altimetry, slope, lithostructure and organization of the drainage network. The step of digital mapping, processed in the software ArcGIS 9.2, was based in the use of SRTM products (Shuttle Radar Topography Mission). The methodological procedures also included field work and literature research. The taxonomy of geomorphological mapping proposed by IBGE (2009) was applied , through which fourteen Geomorphologycal Units were individualized. The units are distributed amongst five different compartments as follows: two plateaux, two escarpments, six depressions, three sets of ridges and one set of intermediate levels. It was observed that the general layout of the units reflects the strong lithostructural control forced to regional relief. The differentiated resistance of the various lithologies in relation to denudational processes and the influence of neotectonic on landscape evolution are noteworthy.