Bedding Orientation Research Articles

Experimental Investigation of Bedding Plane Orientation on the Rockburst Behavior of Sandstone

Rockburst is a violent rock failure process which poses a significant threat to human safety in mining and tunneling construction. Although many in situ investigations provided valuable insights on the rockburst mechanism, the failure and rock fragmentation process during a rockburst cannot be fully examined on the site. In this paper, a modified triaxial rock testing apparatus is employed to investigate the rockburst behavior of oriented sandstone. A high-speed camera is used to record the crack propagation and the ejection of rock fragments on the unloading surface. The microscopic characteristics of the fragments generated from the rockburst tests are observed using the scanning electron microscope (SEM) imaging technique. The trajectory sketches are drawn to calculate the initial velocities of the rock fragments ejected based on the photographs taken by the high-speed camera. The results show that the mass and velocity of fragments are the two main parameters for the identification of the energy-transferring process in the rockburst test. When the bedding orientation is perpendicular to the unloading surface, the rockburst is controlled by the specimen’s strength. However, when the bedding orientation is parallel to the unloading surface, the rockburst is dependent on the structural stability of the specimen.

PHYSICAL AND MECHANICAL PARAMETERS OF BOREHOLE HYDRAULIC MINING OF NONG’AN OIL SHALE

The experiments on physics and mechanics of borehole hydraulic mining were designed to determine mechanical characteristics of mined oil shale. Oil shale of Nong'an deposit belongs to slightly weathered and relatively complete rocks. Oil shale beds are characterized by a very definite discontinuity in both horizontal bedding orientation and vertical bedding direction. Compressive strength, tensile strength, Poisson's ratio and other data characterizing oil shale beds in different directions in the Nong'an min- ing site were obtained and compared. The direction of borehole hydraulic mining was determined. The vertical bedding direction to break oil shale was considered to be better, because strength in this direction is low, rock mass integrity poor, and the degree of weathering more pronounced. The diameter of borer nozzle, dynamic pressure, maximum caving capacity and other parameters needed for borehole hydraulic mining were selected.

Structural styles across the Nankai accretionary prism revealed from LWD borehole images and their correlation with seismic profile and core data: Results from NanTroSEIZE Stage 1 expeditions

[1] Four drill sites of IODP NanTroSEIZE Stage 1 Expedition transected the Nankai Trough, offshore SW Japan, from the deformation front to the Kumano fore-arc basin. Borehole resistivity images from the logging-while-drilling (LWD) data were analyzed to extract orientations of faults, fractures, and bedding planes to examine the structural styles. On the basis of these features, drilling intervals were classified into fore-arc basin deposits, surface slope sediments, and deformed accretionary wedge, and these can be compared with characteristics from seismic profiles and core structural data. Bedding orientations identified in these three data sets are generally comparable, but the difference in resolution between the data sets produces different results in interpretation where geology is highly deformed or includes finer internal structures. Faults can also be correlated between these three data sets, but the differences in their appearance require special attention for accurate correlation. Many faults imaged in seismic profiles actually consist of microfracture systems, as shown in cores, that can also be identified in borehole images. Some clear faults in seismic profiles cannot be identified in borehole images, probably because of their minimal resistivity contrast with the surrounding rocks or a more complex fault zone at the borehole scale. These results suggest that these three data sets can be used to extract not only the general structure but also different styles of deformation at different scales from core samples (mm to cm), to LWD (mm to 10 m), to seismic (10 m to tens of km). This correlation requires a deep understanding of the resolution and shortcomings of each methodology.

Using orthographic projection with geographic information system (GIS) data to constrain the kinematics the Central Range Fault zone, Trinidad

Fold geometry versus axis orientation can be used to constrain the kinematics of transpressional plate boundaries. This approach is typically based on bedding orientation data collected in the field, however, in some regions outcrop quality is insufficient to provide enough measurements. We extract orientation data from a georeferenced geologic map and a digital elevation model and to constrain the kinematics of a poorly exposed, active transpressional boundary: the Central Range Fault zone in Trinidad. Strike-and-dip orientations are calculated based on contact positions extracted from the digital geologic and topographic datasets. The uncertainties in the both horizontal position and elevation of the contact are propagated into the final kinematic analysis. Analysis of folds adjacent to the Central Range Fault suggests the angle of oblique convergence in transpression ( α) varies from 20° to 85°. The majority of folds, however, are consistent with a large component of contraction (i.e. α > 50°). The analysis also suggests folding in the Central Range records a minimum of 3–9 km of contraction, 3 km of strike-slip motion, and 4–9 km of total plate motion. The range of values reflects uncertainties in the position of the folded contacts. We interpret the overall kinematics of deformation, amount of shortening, and homogeneity of the finite strain field to indicate that active deformation on the Central Range Fault zone has not yet accumulated enough strain to overprint the effects of earlier (pre-strike-slip; pre-Middle Miocene) fold-and-thrust style tectonics.

A revised chronology for Tertiary sedimentation in the Sikouzi basin: Implications for the tectonic evolution of the northeastern corner of the Tibetan Plateau

The space–time pattern of development of high topography associated with the Tibetan Plateau remains incomplete, due in large part to sparse proxy data that allow estimates of the growth of individual mountain ranges. Here, we present the results of a stratigraphic investigation of a ~ 3100 m section of Tertiary fluvio-lacustrine strata in the Sikouzi basin, located at the northeastern most corner of the Tibetan Plateau. Results of magnetostratigraphic analysis, coupled with a newly discovered Miocene in-situ fossil assemblage, suggest that the section preserves a nearly complete record extending from initial basin formation at ~ 29 Myr until ~ 0.5 Myr. Sediment accumulation rates increase from relatively slow accumulation during the Oligocene–Miocene (~ 9 cm/kyr) to rapid accumulation in the Pliocene (~ 22 cm/kyr), apparently occurring in two sustained pulses at ~ 10.5 Ma and ~ 5 Ma, respectively. The increase in accumulation rates starting at ~ 10.5 Ma is interpreted as heralding the initial uplift of the Liupan Shan, consistent with cooling and exhumation of the range (Zheng et al., 2006). The Pliocene increase in accumulation rate is accompanied by a distinct change in lithofacies, the appearance of coarse detritus with provenance from the Madong Shan, and up section changes in bedding orientation that are interpreted as growth strata. Collectively, our data suggest that the generation of relief in the Madong Shan began at ~ 5.4 Ma. Moreover, analysis of paleomagnetic declinations from the Sikouzi section reveals a clockwise rotation of the Sikouzi basin during the time period 24–5.4 Ma, that was followed by a subsequent counterclockwise rotation (5.4–0.5 Ma). Our study suggests that activity along the Liupan Shan-Haiyuan fault system probably initiated at ~ 10.5 Ma, but that the present-day configuration of the fault system and associated ranges near the fault tip dates to Pliocene time.

Arkosic rocks from the San Andreas Fault Observatory at Depth (SAFOD) borehole, central California: Implications for the structure and tectonics of the San Andreas fault zone

The San Andreas Fault Observatory at Depth (SAFOD) drill hole encountered indurated, high-seismic-velocity arkosic sedimentary rocks west of the active trace of the San Andreas fault in central California. The arkosic rocks are juxtaposed against granitic rocks of the Salinian block to the southwest and against fi ne-grained Great Valley Group and Jurassic Franciscan rocks to the northeast. We identify three distinct lithologic units using cuttings, core petrography, electrical resistivity image logs, zircon fi ssion-track analyses, and borehole-based geophysical logs. The upper arkose occurs from 1920 to 2530 m measured depth (mmd) in the borehole and is composed of fistructural blocks defi ned by bedding orientations, wireline log character, physical properties, and lithologic characteristics. A clay-rich zone between 2530 and 2680 mmd is characterized by low V p and an enlarged borehole. The lower arkose lies between 2680 and 3150 mmd. Fission-track detrital zircon cooling ages are between 64 and 70 Ma, appear to belong to a single population, and indicate a latest Cretaceous to Paleogene maximum depositional age. We interpret these Paleocene‐Eocene strata to have been deposited in a proximal submarine fan setting shed from a Salinian source block, and they correlate with units to the southeast, along the western and southern edge of the San Joaquin Basin, and with arkosic conglomerates to the northwest. The arkosic section constitutes a deformed fault-bounded block between the modern strand of the San Andreas fault to the northeast and the Buzzard Canyon fault to the southwest. Signifi cant amounts of slip appear to have been accommodated on both strands of the fault at this latitude.

Paleomagnetic study of the Late Silurian–Early Devonian Mt Daubeny Formation from the Broken Hill area, New South Wales

The geological map of the Broken Hill area in New South Wales shows a striking feature, the Grasmere Knee Zone, which consists of a major change in structural trend. North of the Grasmere Knee Zone, the analysis of the structure of the Late Silurian–Early Devonian Mt Daubeny Basin coupled with AMS measurements suggests that the basin has undergone two phases of folding. Correction of magnetic data from bedding orientation has consisted in unfolding sequentially fold F2 to obtain a simple syncline and unfolding fold F1. Although the fold tests, conglomerate test and dyke test may be considered to be positive concerning the high-temperature component (DAU-CH), paleomagnetic results from the Mt Daubeny Formation (locality DAU) are subject to caution, in particular due to the complex unfolding procedure. If component DAU-CH, carried by hematite, is interpreted to be primary in origin, the corresponding paleopole is consistent with an X-type of apparent polar wander path for Gondwana, in particular if one relies on the proposed optimum bedding correction. South of the Grasmere Knee Zone, the Mt. Daubeny Formation is considered to be rotated clockwise relative to the north. The tentative model presented herein proposes that a block corresponding to the Southwestern Subprovince of Lachlan Orogen indented the Tasmanides between the Central Subprovince of the Lachlan Orogen and the Delamerian Orogen from the mid-Devonian (Tabberabberan event) up to the Early Carboniferous, triggering rotations in the Broken Hill area. A later magmatic event, thought to be Early Cretaceous, may have induced fluid migration and deposition of magnetite leading to the occurrence of an important magnetic overprint (DAU-CM).

Rate dependence of the flexural tensile strength of Laurentian granite

Shale gas is becoming a new energy development focus worldwide with advances in horizontal wells and hydraulic fracturing, and spontaneous water-based working fluid imbibition is one of the strongest phenomena that can impact borehole stability and the gas extraction rate. Our present experimental work was carried out on shale Brazilian discs with 5 different bedding orientations (0°, 30°, 45°, 60° and 90°) after air-drying and spontaneous water imbibition using a split Hopkinson pressure bar. The results illustrate that under the same loading rate (100–900 GPa/s), spontaneous water imbibition obviously weakens the dynamic tensile strength of shale discs, except for shale discs with a bedding orientation of 90° when the loading rate exceeds 400 GPa/s, and does not change the anisotropic dynamic tensile strength variation trend versus bedding orientations. Models that can well fit test data and reveal the coupling effects of bedding orientation and loading rate on the dynamic tensile strength of shale after air-drying and spontaneous water imbibition are proposed. The rate-dependent failure mode only appears among shale discs with bedding orientations of 30°, 45° and 60°, and this phenomenon is exacerbated and more complex after spontaneous water imbibition. Bedding planes of shale discs after air-drying and spontaneous water imbibition both play three different roles in affecting the failure crack propagation, i.e., intersecting propagation, promoting propagation and promoting turning. Finally, the dynamic tensile strength responses of shale after spontaneous water imbibition are analyzed and discussed, and potential field applications in borehole stability, perforation design and hydraulic fracturing are suggested.

Calcite twinning strains in Alpine orogen flysch: Implications for thrust-nappe mechanics and the geodynamics of Crete

Recent uplift in Crete, along the Hellenic trench, has exposed the internal portions of Alpine nappes that were transported south along north-dipping thrusts from the middle Cretaceous to the Oligocene (100–20 Ma). Flysch deposited along the leading, southern edge of the Alpine foreland basin dates the timing of nappe transport and contains twinned calcite in synorogenic limestones and calcite veins that record the stress-strain fields associated with nappe transport and stacking for a 17 Ma period between 35 and 18 Ma. The flysch ages young away from the craton thereby documenting thin-skin thrusting and nappe motion, for the first time, toward the trench. Fossiliferous marine limestones and calcareous shales were deposited in marginal basins on the leading edges of four thrust-nappes in Crete: the higher and older flysch deposits (Asteroussia, Pindos) are underlain by younger flysch deposits of the Tripolitza and Plattenkalk nappes. The ages of these flysch deposits are well constrained and the flysch sequences are now found deformed between nappes without visible signs of Alpine metamorphism, except the lowest Plattenkalk flysch. Field observations in the flysch deposits include variable bedding, vein, fold axis, and kinematic orientations. Twinned calcite in the flysch limestones (16 samples, n = 425) and veins (23 samples, n = 612) generally preserve subhorizontal, in-transport shortening and vertical extension; where there is a strain overprint (high negative expected values [NEV]), a vertical shortening strain with transport-parallel extension (~N-S) is preserved. Strain magnitudes are greater in the vein sample suite, and differential stress magnitudes responsible for twinning are −230 bars for the entire sample suite. The tectonic evolution of the region involved thin-skinned shortening with south-vergent nappe formation, from north to south, followed by thrust motion on the Cretan detachment. Today, metamorphosed rocks (i.e., Phyllite-Quartzite unit [PQU]) overlie the basal Plattenkalk nappe placing earlier exhumed rocks of the Asteroussia, Tripolitza, and Pindos nappes on top of high-pressure (HP)-metamorphic rocks of the PQU without the deposition of any flysch.

Local to regional scale structural controls on mineralisation and the importance of a major lineament in the eastern Mount Isa Inlier, Australia: Review and analysis with autocorrelation and weights of evidence

Although major crustal lineaments may play an important role in mineralisation, the relationship between lineaments and mineral deposits can be quite cryptic, and structural controls may vary as a function of scale along lineaments. Major lineaments alone may be of limited use for detailed target generation. The Cloncurry Lineament in the Eastern part of the Mount Isa Inlier is a crustal scale structure defined by potential field-derived ‘worms’. Weights-of-evidence quantifies the association between mineral occurrences and this lineament. Autocorrelation is used to recognise structural controls on mineralisation at different scales, by progressively limiting the lengths of the vectors between mineral occurrence points in the autocorrelation plot. The weights-of-evidence analysis shows that Au, Au–Cu, Cu–Au and Cu deposits have a positive spatial correlation to the Cloncurry Lineament, which suggests it that acted as a primary crustal scale control on the localisation of Cu and Au through focussing mineralisation systems on a broad scale. However, autocorrelation defines a variety of local structural controls, which can be interpreted as shear zones, variably oriented fault sets, en echelon fault arrays, and potentially the orientation of bedding and/or iron formations which localise fluid flow and mineral deposition at finer scales. The results suggest that major lineaments defined by geophysical contrasts can be used in conjunction with techniques of spatial analysis for targeting structurally controlled mineralisation in areas under thin cover adjacent to mineralised terrains such as the Mt Isa Inlier.

The lower cretaceous paraflysch of the Vardar zone: Composition and fabric

The Lower Cretaceous paraflysch forms an outstanding, 250 km-long belt in the Vardar Zone. It is composed of a basal unit, uncomformable over Jurassic limestones and older rocks, and of two megasequences with the a clastic lower and clastic-carbonate upper member. In this study, We analyzed the orientation of the sedimentary bedding, cleavage and schistosity, fold hinges and axial surfaces and cleavage - bedding intersection lineation, were analysed. The area experienced two phases of folding, first with fold hinges oriented NNW and the second with hinges oriented WSW. The regularities of these structures and their relationships are, as shown by these investigations, only statistically to be used in practical study of fabric.

Rim uplift and crater shape in Meteor Crater: Effects of target heterogeneities and trajectory obliquity

We have analyzed the rim structure of Meteor Crater, Arizona, in order to understand the mechanism of rim uplift in simple craters and the causes of the shape of polygonal impact craters. For this purpose, we systematically determined bedding orientation of the autochthonous crater wall and overturned flap and analyzed the kinematics of major radial faults. We found that rim uplift correlates with the crater shape and increases in the corners of the crater. The two main mechanisms of differential uplift are the formation of horizontal interthrust wedges, leading to the doubling of strata in the rim, and radial corner faults, or tear faults, that vertically displace bedrock. The development of Meteor Crater's quadrangular shape is caused by more effective crater excavation flow parallel to major joint sets. Additionally, we infer the impact direction with a newly developed technique, the two corners model, and review the arguments in favor of an oblique trajectory. While the data set is ambiguous, several indicators suggest an impact direction from the NNW. We conclude that oblique impacts should have an effect on early cratering and excavation flow, whereas target heterogeneities like joints start to play a prominent role in later stages when the stresses induced by the excavation flow are in the same order of strength as the material involved.

Structure and stratigraphy of Home Plate from the Spirit Mars Exploration Rover

Home Plate is a layered plateau observed by the Mars Exploration Rover Spirit in the Columbia Hills of Gusev Crater. The structure is roughly 80 m in diameter, and the raised margin exposes a stratigraphic section roughly 1.5 m in thickness. Previous work has proposed a pyroclastic surge, possibly followed by aeolian reworking of the ash, for the depositional origin for these beds. We have performed a quantitative analysis of the structure, stratigraphy, and sedimentology at this location. Our results are consistent with an explosive volcaniclastic origin for the layered sediments. Analysis of bedding orientations over half of the circumference of Home Plate reveals a radially inward dipping structure, consistent with deposition in the volcanic vent, or topographic draping of a preexisting depression. Detailed observations of the sedimentology show that grain sorting varies significantly between outcrops on the east and west sides. Observations on the western side show a well‐sorted population of sand sized grains which comprise the bedrock, while the eastern margin shows a wider range of grain sizes, including some coarse granules. These observations are consistent with primary deposition by a pyroclastic surge. However, aeolian reworking of the upper stratigraphic unit is not ruled out. Identification of explosive volcanic products on Mars may implicate magma interaction with subsurface hydrologic reservoirs in the past.

Channelized and hillslope sediment transport and the geomorphology of mountain belts

This paper uses the results of landscape evolution models and morphometric data from the Andes of northern Peru and the eastern Swiss Alps to illustrate how the ratio between sediment transport on hillslopes and in channels influences landscape and channel network morphologies and dynamics. The headwaters of fluvial- and debris-flow-dominated systems (channelized processes) are characterized by rough, high-relief, highly incised surfaces which contain a dense and hence a closely spaced channel network. Also, these systems tend to respond rapidly to modifications in external forcing (e.g., rock uplift and/or precipitation). This is the case because the high channel density results in a high bulk diffusivity. In contrast, headwaters where landsliding is an important sediment source are characterized by a low channel density and by rather straight and unstable channels. In addition, the topographies are generally smooth. The low channel density then results in a relatively low bulk diffusivity. As a consequence, response times are greater in headwaters of landslide-dominated systems than in highly dissected drainages. The Peruvian and Swiss case studies show how regional differences in climate and the litho-tectonic architecture potentially exert contrasting controls on the relative importance of channelized versus hillslope processes and thus on the overall geomorphometry. Specifically, the Peruvian example illustrates to what extent the storminess of climate has influenced production and transport of sediment on hillslopes and in channels, and how these differences are seen in the morphometry of the landscape. The Swiss example shows how the bedding orientation of the bedrock drives channelized and hillslope processes to contrasting extents, and how these differences are mirrored in the landscape.

Channelized and hillslope sediment transport and the geomorphology of mountain belts

This paper uses the results of landscape evolution models and morphometric data from the Andes of northern Peru and the eastern Swiss Alps to illustrate how the ratio between sediment transport on hillslopes and in channels influences landscape and channel network morphologies and dynamics. The headwaters of fluvial- and debris-flow-dominated systems (channelized processes) are characterized by rough, high-relief, highly incised surfaces which contain a dense and hence a closely spaced channel network. Also, these systems tend to respond rapidly to modifications in external forcing (e.g., rock uplift and/or precipitation). This is the case because the high channel density results in a high bulk diffusivity. In contrast, headwaters where landsliding is an important sediment source are characterized by a low channel density and by rather straight and unstable channels. In addition, the topographies are generally smooth. The low channel density then results in a relatively low bulk diffusivity. As a consequence, response times are greater in headwaters of landslide-dominated systems than in highly dissected drainages. The Peruvian and Swiss case studies show how regional differences in climate and the litho-tectonic architecture potentially exert contrasting controls on the relative importance of channelized versus hillslope processes and thus on the overall geomorphometry. Specifically, the Peruvian example illustrates to what extent the storminess of climate has influenced production and transport of sediment on hillslopes and in channels, and how these differences are seen in the morphometry of the landscape. The Swiss example shows how the bedding orientation of the bedrock drives channelized and hillslope processes to contrasting extents, and how these differences are mirrored in the landscape.

Dam Fun: A Scale-model Classroom Experiment for Teaching Basic Concepts in Hydrology and Sedimentary Geology

This paper describes a scale-model classroom experiment that illustrates several fundamental concepts in sedimentary geology and hydrology, speaks to relevant societal issues, and provides an inexpensive and straightforward demonstration for single to multiple classroom period(s). The model simulates the cross-section of an earthen dam and reservoir system using a flat acrylic tank (ant farm dimensions). The dam is constructed by pouring sand into the middle of the tank. During this process, visible grain-size sorting occurs, and the concepts of gravitational settling, superposition, and angle of repose are illustrated. Water is poured into the reservoir side of the dam, and the concepts of porosity and permeability are illustrated as water seeps into the dam. The initial water movement is dominated by capillary flow in the fine-grained layers, whereas flow in the saturated state is dictated by differences in permeability and hydraulic head. Water is observed to move uphill, and then downhill, following bedding orientation. The possibility of toxic waste storage in dams is evaluated by injecting water with brightly colored dye into the dam. The dye illustrates the movement and ultimate fate of the ‘toxic waste’, and forms a coherent pool on the downstream side of the dam. The grand finale occurs when the dam is overtopped by water and catastrophically fails. The experiment is suited for teaching K-12 and college undergraduate audiences, has been universally well received by students and teachers, and leaves lasting visual impressions of processes in sedimentology, hydrology, and environmentally relevant water issues.

Gully systems under undisturbed indigenous forest, East Coast Region, New Zealand

Gully erosion is commonly associated with agricultural landscapes where vegetation clearance and farming practices increase runoff, leading to fluvial incision. However, gully erosion can also occur in forests that have undergone some form of disturbance, either natural or resulting from human impacts. This paper reports on recent gully development within areas of undisturbed indigenous forest as a result of a high magnitude rainfall event on the East Coast of New Zealand's North Island. This region, through a combination of crushed and sheared rock types, steep topography, and tectonic and climatic setting, has high natural rates of erosion, exacerbated by European deforestation in the late 19th and early 20th centuries. Sequential air photographs, spanning a 58 year period between 1939 and 1997 were used to classify and document the growth and recovery of gully systems in the 14.1 km 2 headwaters of the Mangaoporo catchment. Following a severe cyclone in 1988, with a rainfall of 535 mm, there were 21 active gully systems within the indigenous forest. On photography prior to 1988 only four gully systems were present. During this period there were 8 major rainfall events (150–250 mm). Despite further 5 rainfall events of 150–250 mm between 1988 and 1997 all gully systems showed signs of recovery, with a combined reduction in active area of 37%. The nature and location of these features is strongly influenced by lithology (orientation of jointing and bedding), and to a topographic threshold defined by catchment slope and catchment area.

The influence of geological fabric and scale on drainage pattern analysis in a catchment of metamorphic terrain: Laceys Creek, southeast Queensland, Australia

The relationship between geological fabric and drainage patterns in the 81.8 km 2 Laceys Creek sub-catchment of the North Pine River catchment, southeast Queensland, Australia, is analysed using a new channel–ordination system. The Laceys Creek catchment is situated on the South D'Aguilar Block, which underwent metamorphism, faulting and uplift from the Late Carboniferous to Late Triassic. The catchment drains exposures of two main rock units, the Neranleigh–Fernvale Beds and the Bunya Phyllite. Both units are composed of metamorphosed deep-sea sediments that accumulated as an accretionary wedge during late Palaeozoic subduction of the palaeo-Pacific plate under the eastern margin of the Australian craton. The new channel ordination system used in this study allows improved classification of stream segments of equal prominence or rank in comparison to previous schemes. A 10 m contour digital elevation model (DEM) was produced within which drainage channels were digitised. Planar geological features, including bedding, faults, joints and cleavage, were mapped in the field and collated with data from previous geological mapping programs. Regional and local trends of geological fabric are reflected in the variable orientation of channels of different rank in the catchment. Cleavage and fractures are the dominant planar features of the Bunya Phyllite and these correlate most closely with the orientation of middle-order incised stream segments. In contrast, middle-order channels on the Neranleigh–Fernvale Beds most closely correlate with bedding, which dominates the fabric of this unit. Although anthropogenic factors exert local influence and climatic processes exert broad influence on the catchment, this study focuses on structural and lithological fabrics, which are the apparent dominant controls on middle-order channel orientations. Identification of congruent patterns between bedrock fabric and channel ranks is variable, depending on the scale and number of channels included in the analysis. Many low-rank channels correspond closely to the orientation of fine-scale bedding and foliation and these influences may not be detected by coarse-scale mapping. Understanding the extent of geological controls on the morphology of a catchment may assist geo-hazard identification, land-use planning and civil-engineering projects.

No Stone Unturned—a Re-assessment of Anglo-Saxon Long-and-Short Quoins and Associated Structures

An investigation of almost all recognized Anglo-Saxon churches has been undertaken to scrutinize carefully their quoins, pilaster strips and arch jambs, where these are readily visible for detailed study from ground level. The geological orientations within the stones in these structures have been recorded where they are clearly discernible. The stones, irrespective of their size and shape, display in all visible instances distinct patterns and styles of Anglo-Saxon construction. A simple nomenclature is proposed to identify the bedding orientations of the stones. These patterns of stone orientation, particularly when applied together with an understanding of the different rock lithologies, can be used to enable the structural portions of Anglo-Saxon church buildings to be identified with greater precision.

Remote surface mapping using orthophotos and geologic maps draped over digital elevation models: Application to the Sheep Mountain anticline, Wyoming

Remote mapping of surface structures can be conducted by draping digital orthophotos and geologic maps over digital elevation models in geographic information systems. Formational contacts can be mapped by viewing the intersections of these contacts with the topography on a true-to-scale, three-dimensional image. Bedding orientations can be determined from (1) the trends and slopes of dip slopes or (2) best fit planes to multiple points of intersection of a bedding surface with the topography. The methods are tested against mapped formation contacts and bedding attitudes for the Sheep Mountain anticline in the Bighorn basin, Wyoming. Detailed mapping of formation contacts is improved by careful observations of the contacts on three-dimensional images. Interpreted bedding attitudes from slope and multiple-point solutions show strong positive correlations with field measurements. This mapping method provides an efficient and accurate alternative to stereoscopic mapping using aerial photographs and satellite images, particularly for remote and inaccessible areas.