Photogeological Interpretation Research Articles

Geothermal Prospect Review in the Western Part of Salak Volcano, West Java, Indonesia

The Ertankian Geothermal Prospect is located in the southern area of Bogor District, West Java, Indonesia. From 1982 through the end of 1983, Unocal Geothermal of Indonesia, Ltd. (UGI) conducted extensive geological, geochemical, and geophysical surveys that outlined Ertankian as a potential geothermal field on the flanks of the Salak Volcano. This volcano forms the north-eastern part of the Salak-Perbakti-Gagak Volcanic Massif, which consists of Upper Pleistocene to Recent stratovolcanoes, parasitic vents, and phreatomagmatic craters. The exploration survey included, magnetotelluric and gravity surveys, water geochemistry, thermal manifestation gas, ion, and isotope analyses, and geological, photo-geological interpretation, and photogrammetry interpretation. Kawah Ertankian is a vigorous fumarole area with numerous superheated and boiling steam vents, boiling acid sulfate hot springs, and large areas of acid-altered ground. Elemental sulfur is common around many of the vents. Steam from the Ertankian Fumaroles contains 7 mol% H2S and the maximum reservoir temperature obtained from the NAH-CO2 gas geothermometer was 525°F. The Ertankian Hot Springs have acid sulfate character and yield little information about the underlying hydrothermal system. Bicarbonate chloride warm springs occur on the northern flanks of the Salak Volcano at northwest and northeast locations and interpreted as the outflow product of Ertankian Geothermal System. Extensive areas of low resistivity are distributed across most of the Ertankian Geothermal Prospects. Low resistivity zones are observed around the Kawah Ertankian thermal manifestation complex and broaden to the far northwestern warm spring and Gunung Perbakti in the southwest. The shallowest base of the conductor is observed in the area near Kawah Ertankian and probably extends towards the northwest in the Alpha-19 well area. Towards the south and southwest, a significant deepening of base of the clay cap is observed. The observed resistivity trend coincides with and parallels to the NW-SE South and North Ertankian Faults, which may be the outflow pathway of the hydrothermal system. The lower rock conductance values and deepening of the clay cap base toward the southwest indicate a lower possibility of connection to the main Salak geothermal system. Considering the geological, geochemical, and geophysical data, the Ertankian Geothermal Prospect is presumed to be an encouraging area for further studies.

Avaliação de imagens multipolarizadas de radar (banda L) do sensor SARR99B para mapeamento geológico no Baixo Vale do Curaçá, Bahia

In the tropical semi-arid environment of Brazil geological applications with radar are still rare. The objective of this research was the evaluation of multipolarized L-band radar images acquired by the sensor SAR-R99B (SIVAM-CENSIPAM) for geological mapping in the lower Curaca valley, an important Cu-rich district of the Bahia state. The test-site is characterized by a flat terrain, with moderate to sparse caatinga vegetation and shallow residual soils closely related to changes in the geological substratum. These characteristics favor the evaluation of SAR images for geological mapping. The test-site is part of the Sao Francisco Craton, and encompasses paleoproterozoic granulitic and gneissic rocks and an intrusive sequence of mafics and ultramafics. Subordinately, metasediments with neoproterozoic ages also occur. In this investigation it was evaluated multipolarized L-band images (L-HH, L-VV, L-HV), amplitude format with 6-meter of spatial resolution. The photogeological procedures were applied using the graphical interface of viewing and digital enhancements available in the FOCUS package (PCI Geomatics software), calibrated with bibliographic and field information. The results of the photogeological interpretation showed that L-VV presented the best performance in the discrimination of lithologies given by a higher tonal/textural contrast of more frequent units (mica- schists, quartz-feldspar gneiss) and a better detailment of more restricted ones (marbles, mafic-ultramafics). Regarding the structural characterization, the three polarizations showed a similar performance, with a slightly disadvantage of L-HH revealing the importance of the vertical component of polarization in the L-VV and L-HV images in the enhancement of structural features. The excellent radiometric quality of calibrated SAR data, high spatial resolution and good response sensitivity to variations of macro, micro-topography and moisture were responsible for the results of the analysis.

Movements detection of deep seated gravitational slope deformations by means of InSAR data and photogeological interpretation: northern Sicily case study

AbstractWe investigated the northern‐central portion of Sicily region (southern Italy) using aerial photographs and Synthetic Aperture Radar (SAR) data obtained by ERS1 and ERS2 satellites. This area shows a geological‐structural setting generated by the tectonic superposition of Apenninic‐Maghrebian carbonatic structures on terrigenous deposits. Such a structural setting favoured the development of large‐scale gravity‐driven phenomena (known in the geological literature as deep‐seated gravitational slope deformations) that are mostly responsible for the landscape evolution of the whole area. Morphological evidences such as landslides, sacking or rock‐flow, lateral spread and block slide can be detected from photogeological analysis. In order to understand the temporal behaviour and spatial distribution of such deformations we applied the interferometric SAR (InSAR) technique. Interferograms show fringe patterns spatially coinciding with some of the large‐scale gravitative phenomena previously identified by means of aerial‐photo analysis. The comparison between photogeological data and InSAR results allows delimiting the active sectors in the study area.

North-East Greenland 1997–1998: a new 1:500 000 mapping project in the Caledonian fold belt (72°–75°N)

The Geological Survey of Denmark and Greenland (GEUS) continued in 1997 the systematic geological mapping programme for the 1:500 000 regional map series, with initiation of field work on sheet no. 11, which covers part of North-East Greenland. Of the 14 planned map sheets at 1:500 000 which will cover all of Greenland, 11 have been published, and one additional sheet for which field work has been completed is under compilation. Only two areas of Greenland are not yet covered by map sheets of this series: part of North-West Greenland (sheet no 6) and the target for the present project in North-East Greenland (sheet no. 11). The field work for the latter sheet is planned for two seasons, with the first season completed in 1997 and the second and final season to follow in 1998. The map sheet (no. 11) covers the region between Kong Oscar Fjord and the Stauning Alper in the south (72°N) and Kuhn Ø and Grandjean Fjord in the north (75°N, Fig. 1). The western part of this region is dominated by crystalline complexes of the East Greenland Caledonian fold belt. A post-Caledonian sequence of Upper Palaeozoic and Mesozoic sediments and Tertiary plateau basalts and intrusions covers the eastern part of the region. This article focuses on the Caledonian geology, whereas results from the work in the post-Caledonian sediments are described in the article by Stemmerik et al. (1998, this volume). The new Survey work for map sheet 11 represents a reinvestigation of areas extensively studied by geologists of Lauge Koch’s expeditions to East Greenland (1926–58), the principal results of which were compiled by John Haller for the 1:250 000 map sheets covering the region 72°–76°N (Koch & Haller 1971) and incorporated into an impressive regional description of the East Greenland Caledonides (Haller 1971). The Scoresby Sund region to the south of latitude 72°N and the Dove Bugt region to the north of latitude 75°N have already been investigated by the Geological Survey of Greenland (Henriksen 1986, 1997; Higgins 1994) as part of the present ongoing 1:500 000 regional mapping programme. The 1997–1998 mapping project will fill the last remaining gap in the Survey’s 1:500 000 coverage of North-East Greenland. All of North-East Greenland is covered by a set of wide angle black and white vertical aerial photographs taken in the period 1978–87 from an altitude of c. 14 km. On the basis of these aerial photographs and ground control points established by Kort- og Matrikelstyrelsen (National Survey and Cadastre – formerly the Geodetic Institute), new topographical maps of the entire region 72°–75°N, at a scale of 1:100 000, with 100 m contours, are being drawn at the Survey and will serve as a basis for the field investigations and the subsequent geological map compilations. Drawing of the topographic maps in the Survey´s photogrammetric laboratory is combined with photogeological interpretation both prior to and following the field investigations. In addition to establishing a general overview of the regional geology, the project includes activities aimed at supplementing knowledge of the economic potential of the region, in respect to both minerals (Harpøth et al. 1986) and hydrocarbons (Christiansen et al. 1992; Stemmerik et al. 1997). The field work co-ordinated by the Survey included co-operation with a geophysicist from the Alfred Wegener Institute for Polar and Marine Research (AWI), Bremerhaven, who undertook rock magnetic investigations to facilitate interpretation of an AWI aeromagnetic survey, and four Norwegian sedimentologists from Saga Petroleum whose work was integrated with a Survey group working with Mesozoic sediments (Stemmerik et al. 1998, this volume). Logistic support was also given to three groups of geologists from the University of Oslo and three geologists from Massachussetts Institute of Technology, with whom agreements on scientific co-operation had been arranged in advance. Some aspects of the project are based on funding from the Danish National Science Foundation and Carlsberg Foundation, with support for special research topics concerning the pre-Caledonian basement terrain, Caledonian metamorphism, and studies of Upper Proterozoic carbonate sediments. The field investigations in 1997 were carried out during a seven week field season between early July and late August with participation of a total of 38 persons, including 32 geologists (Henriksen 1998). The work was supported by two helicopters and a small, fixed wing, Twin Otter aircraft, which operated from Mestersvig, a former airport which is kept open for limited special operations by the military sledge patrol Sirius. The GEUS group benefitted substantially from base facilities at Mestersvig, organised and manned by the Danish Polar Center (DPC). Transport between Mestersvig and Denmark was carried out by the Royal Danish Air Force (RDAF) using a C-130 Hercules aircraft.

Hydrogeology of the Gradole Spring Drainage Area in Central Istria

The delimitation of a drainage area together with the accurate estimation of it’s surface area represents an important problem in dealing with karst springs. Water gushing from the fractured karst identifies the Gradole spring as a typical karst well of the rising type. The spring never runs dry, the ratio of minimal and maximal discharge being 1:15 to 1:20 or more. The surface of the drainage area and its spatial distribution have been defined on the basis of geological data; tectonics, morphology, photo-geological interpretation, hydrogeological characteristics of the rocks, the karst morphology (sinkholes, pits) and underground water tracing data. The drainage area is predominantly composed of carbonate rocks, mainly limestone, but there is also a lesser flysch component - marls and sandstones. The karst area is without any surface waterflows, in contrast to the flysch area where a hydrographic network of intermittent surface streams is developed. There are no real barriers to underground flow within the carbonate rocks. Nevertheless, the direction of flow is influenced by structural elements, the position of layers, the appearance of rocks - thin layers, shows of some less permeable rocks - dolomites, fissured and marly limestones. The confirmation of an underground connection of Cize swallow hole with the Gradole spring shows the possibility of supplementing low waters through the swallow holes from Butoniga accumulation lake.

The role of geological structures and relict channels in the development of dryland salinity in the wheatbelt of Western Australia

Aerial photogeological interpretation techniques have been used to map the geology, delineate the geological structures and identify the relict channels of three representative dryland salinized catchments in the wheatbelt of Western Australia. Much of the variation in groundwater salinity is explained by the distribution of geological structures (dykes, veins and basement highs) in relation to the alluvial systems and relict channels and their effect in modifying groundwater flow. Salinities in the relict channels are generally higher than in other areas of the catchment. Salinity also increases in the direction of groundwater flow along the relict channel. Salinity in groundwaters upstream of geological structures is without exception higher than in other parts of the catchment. The relict channels are found to have an important role in the storage and redistribution of salt in the landscape.

Photogeological and geophysical studies on the Basement rocks in Wadi El Miyah, Eastern Desert of Egypt

Wadi El Miyah area is located in the central part of the Eastern Desert of Egypt. It is covered mainly by Basement rocks of Precambrian age, overlain on its western side by Nubian sandstones. The basement rocks comprise igneous and metamorphic rocks. The different types of rocks were studied photogeologically and checked in the field radiometrically and magnetically from the air to differentiate between these rock types and to delineate the contacts between them. All the information and results obtained were used to improve and correct the geological map previously constructed for the same area. It was found that the different structural features interpreted photogeologically could be correlated with the aeroradiometric results. Besides the centers of high structural intensities in the structural contour map were found to be comparable with the centers of high radioactivity on the aeroradiometric map. Photogeological interpretation indicated that each type of rocks has its characteristics and the contacts between the main rock types are clear using the criteria of topographic expression, photographic tone, surface texture and drainage density. Radioactivity of the rock exposures was found to vary with the different rock types and each group of the same rock type has nearly the same background aeroradioactivity. The serpentinites and the geosynclinical volcanics have the lowest radioactivity level, (0.83–6.00 Ur) the geosynclinal sediments have moderate radioactivity level (3.33–5.00 Ur), the synorogenic plutonites have high radioactivity level (2.5–12.67 Ur) and the late orogenic plutonites have very high level of radioactivity (4.17–25.00 Ur). The aeroradiometric contacts were quite clear when there is marked difference in the radiometric level between the studied rock exposures and the surrounding rocks. The aeromagnetic survey showed that the NE-SW and WNW-ESE tectonic trends are the prominent structural trends in the studied area. They represent faults and dykes. There are other trends namely the NNE-SSW, N-S, NW-SE which affect nearly all types of rocks in the Basement complex.

GGU's photogeological laboratory: aerial photogrammetry – a valuable geological mapping tool in Greenland

Geological mapping in Greenland is generally greatly helped by the use of vertical aerial photographs. Bedrock surfaces are normally well exposed, vegetation is sparse in most parts of the country and glacial deposits can be scattered or completely washed away. Consequently, geological features such as bedding, stratigraphical boundaries and large-scale structures are commonly visible on aerial photographs. Since its establishment in 1946 as an independent institution, the Geological Survey of Greenland (GGU) has made extensive use of aerial photographs during mapping campaigns, and photogeological interpretation has played an important role in Copenhagen during map compilation.

Structural lineaments in the basement rocks of the central Eastern Desert, Egypt

The Egyptian basement rocks outcrop in Eastern Desert, southern Sinai and southwestern Desert. The rocks belong to Precambrian and consist of igneous and metamorphic rocks which are characterized by crystalline character. Not much work has been done on the tectonics and structure of the basement rocks in Eastern Desert. The present work is a photogeological interpretation of the structural lineaments representing dykes, faults and joints in central Eastern Desert to differentiate between igneous and metamorphic rocks. The photogeological interpretation was carried out using normal aerial photographs scale 1:40 000 and photomosaics scale 50 000. The main trends of lineaments in the studied area are: E-W, ENE-WSW and WNW-ESE, constituting 58.4% of the total length and 54.5% of the total number. Correlating the structural lineaments in igneous rocks of Gebel El Bakriya locality with those in the metamorphic rocks of Gebel Abu Mireiwa shows that there is a marked difference between the two types. Lineaments in igneous rocks are elongated and widely spaced while those in metamorphic rocks are short and closely spaced. The different trends of joints in igneous rocks can be arranged as follows: WNW>E-W>NW>NNW>ENE>NE>N-S>NNE while the different trends of lineaments in metamorphic rocks can be arranged as follows: E-W>ENE>WNW>NW>NNW>NE>N-S>NNE. Comparison between the structural contour maps constructed for the total length of all lineaments and those representing joints in igneous and metamorphic rocks indicates that igneous rocks have lower density of lineaments than metamorphic rocks. The total length of all lineaments in Gebel El Bakriya amounts to 375 km, while lineaments representing joints have a total length of 150 km. In the metamorphic rocks of Gebel Abu Mireiwa, the total length of all lineaments is 425 km and those representing joints have a total length of 175 km. It was found that there is a relationship between the structural lineaments and radioactivity of the igneous rocks in Gebel El Bakriya. The centers of high density of lineaments in the structural contour maps coincide with the center of high intensity in the radiometric map.

Heterogeneities and Geometry of Sedimentary Bodies in a Fluvio-Deltaic Reservoir

Summary This paper gives the initial results of a two- and three-dimensional (2D and 3D) geological study that aimed at describing reservoir heterogeneities. This study serves as a basis for the conditional simulation of the geometry of a fluvio-deltaic reservoir presented in a companion paper. These two studies should solve the difficult problem of interpolating between wells and thereby the problem of forecasting the extension of sedimentary bodies. The research is being carried out by Inst. Français du Pétrole and Center of Geostatistics, Paris School of Mines. The study was made in the middle Jurassic in Yorkshire, which is very similar to the Brent formation in the North Sea. In the 2D phase, an outcrop consisting of a 1-km [0.6-mile] -long and approximately 30-m [100-ft] -high cliff was described with a photogeological interpretation. The sedimentological representation was carried out by means of several vertical cross sections. In the 3D phase, 36 boreholes were continuously cored and logged behind the cliff over an area of 1 km2 [0.4 sq miles]. The boreholes were about 300 m [985 ft] apart except in one grid where the distance was progressively reduced to 20 m [66 ft]. This phase was designed to follow the evolution of the sedimentary bodies and their physical properties and to compare the correlation that could have been made (1) with fewer boreholes and (2) without the existence of the cliff. These studies provide new tools for understanding and describing the shape and heterogeneities of a reservoir.

Interactive processing of satellite images for geological interpretation – a case study

AbstractInteractive digital processing of satellite images reveals significantly more information than the standard product photographic versions of the same images. Interactively processed images preserve finer details and can show information in areas which appear too dark or too bright on standard product images. This is illustrated by comparisons between both types of image as used in a photogeological interpretation of the tectonics of the Tibetan plateau.

Structural geology of central Peary Land, North Greenland

The region investigated in 1978 between Jørgen Brønlund Fjord - Øvre Midsommersø in the south and Frederick E. Hyde Fjord in the north consists of c. 1½ km thiekness of Lower Palaeozoic carbonates overlain by an up to 1 km thick series of Silurian flysch (Christie & Peel, 1977). In general the region is part of the Palaeozoic platform that ean be divided into three major E-W trending physiographic belts: a southern belt where the carbonates form plateaus incised by steep valleys, a central belt consisting of characteristic conical mountains marked by concentric terraces of resistant sandstone beds in the flyseh (Dawes, 1976, fig. 249), and in the fold belt to the north the mountains rise up to altitudes of 1000-1500 m and are covered by extensive ice caps (fig. 17). The southern border of the region, the Øvre Midsommersø - Jørgen Brønlund Fjord area, was mapped by Jepsen (1971) while the Lower Palaeozoic stratigraphy in the central part af the region has been established by Christie & Peel (1977) at Børglum Elv. Some structural aspects af the gealogy at Frederick E. Hyde Fjord are briefly described by Dawes (1971) and Dawes & Soper (1973). Prior to the field work a comprehensive photogeological interpretation was carried out on vertical aerial photographs (seale c. 1:60000) and compiled on six uneontoured l: 100000 photomosaic maps. The 1978 field work and laboratory studies using a Kern PG 2 photogrammetric instrument form the first detailed study of the fold belt margin. For descriptive purposes the region investigated in 1978 has been subdivided into seven areas (fig. 17), the main struetural features of which form the basis of this report.

Mineral resources inventory in the northern part of haiti: A basic rationale for selecting areas of potential mining interest

Agriculture has always been the major source of income of the Republic of Haiti. Only in the late sixties did the Haitian Government decide to move toward industrialization and explotation of natural resources, but no reliable inventory of mineral potential was available. In June 1970 the Resources and Transport Division of the U.N. (now CNRET) undertook a structural analysis of the Caribbean with reference to defining favorable loci for ore disposition. One of the conclusions of this survey was that from the metallogenetic point of view, the Northern part of Haiti was a favorable area for prospecting for habe metal deposits, especially for copper. Those conclusions were acknowleadged with great enthusiams by the Haitian authorities, and they welcomed in July 1971 a UN technical adviser who outlined a first phase of exploration. Following this mission, a “Mineral exploration Project” was created by the Haitian Government with the cooperation of UNDP, and an area of 9000 km2 was selected, based on structural, lithological, and metallogenetic reasons, as an exploration target. The most important aspects of this project were:Mineral Exploration—First Phase (1973–1974). The following operations were carried out by a small team: (a) photo interpretation at 1:50,000 and 1:200,000 scale, (b) geological reconnaissance at 1:50,000 scale, (c) geochemical reconnaissance (stream sediment) at 1:50,000 scale. The photo interpretation helped outline zones of particular structural interest and was followed up by ground control studies. Stream sediment geochemical reconnaissance was carried out over half of the project area, following the indications given by the photo geological interpretation. finally, combining all the data, five areas were selected for detailed follow up survey: (1) Terrier Rouge—Perche, (2) Vallieres, (3) Mont-Organise, (4) Limonade, (5) Gros Morne—Le Borgne.Mineral Exploration—Second Phase (1975–1976). The main zones of interest were reduced to a few hundred km2 and porphyry copper type deposits appeared to be the most promising target. Detailed geological mapping (1:25,000 to 1:2,000) and soil geochemistry were carried out on the above mentioned five areas, the most promising appearing quickly to be Terrier Rouge-Perges, with porphyry-type copper mineralization. A geophysical survey (IP and Mag) confirmed the geochemical results. At the end of the second phase of exploration (December 1976) two of the five prospects of the Terrier Rouge area have been diamond drilled and appeared to be of potential economic interest. Because of the number and importance of the prospects discovered a third phase of exploration was deemed necessary with the purpose of continuing the detailed prospection work and drilling the other prospects. This third phase started in January 1977 and was expected to last until December 1979.

Rayed craters on the moon and Mercury

Many fresh craters on the moon and Mercury exhibit systems of bright rays. Statistical comparison of the diameter/density distributions of fresh craters and rayed craters on these two bodies indicate that the rayed-crater populations are representative samples of the larger populations of fresh craters. The rayed-crater population on Mercury, however, is not similar either to the rayed- or to the fresh-crater population on the moon. Photogeological interpretation of the best available lunar imagery indicates that “ray material” is indeed ejected from the primary craters, and should be present in the lunar soil. Although the distribution of the ray material may be patchy, it probably occurs in deposits of thickness greater than the characteristic depth to which subsequent impact processes overturn the regolith. The time needed to darken a ray system thus may be more dependent on the thickness of the ray material than on the rates of the various darkening processes, and darkening rate may be a function of crater size. Ray darkening on the lunar surface is an inefficient process at present. The rays of craters more than 1 b.y. old are still bright, whereas the rays of craters older than Class 1 have generally faded to imperceptibility.

Significance of fold and lineament patterns in sulphide mineralization in the northeastern part of the Jabalpur (India) mineralized belt — A photogeological interpretation

Photogeological reconnaissance studies in the investigated area of known base-metal occurrences aided in revealing the structural significance of fold and associated shear or lineament patterns in relation to sulphide mineralization. The structural analysis from aerial photographs of complexly folded and faulted, metamorphosed calcareous and argillaceous sediments indicated that the principal fold axis strikes ENE-WSW, which is normal to the theoretical NNW principal stress direction. Syntectonic with this fold deformation, first-order complementary shear or wrench faults (strike-slip faults) developed in N10°E and N50°W directions. The idea of a possible second-order fold system striking nearly parallel to the principal stress direction can be conceived from the development of thrust or longitudinal shears striking parallel or sub-parallel to the principal fold axis. The mineralized quartz veins in the area, the fluorite-bearing quartz porphyry in Imalia (lying outside and WSW of the present area in the mineralized belt) and the chalcopyrite-pyrite bearing, diorite-porphyry dyke exposed in the Mahanadi (a tributary of the Son) river section at Karua Kap (falling outside and ENE of the present area of investigation) mainly follow the N-S shears or wrench faults. Less frequently, the mineralized quartz veins follow the ENE-trending thrust shears which appear to displace the earlier N-S shears.

Possible applications of photogeology to the study of rock mechanics

Summary Photogeology may provide useful general information in some spheres of rock mechanics, particularly in the very earliest stages of an investigation before ground is broken. Possible aspects for study are hydrogeology, major fracture systems, broad changes in rock character, structure and regional stress, soil mapping and natural slope failures. Much research is still needed in some of these fields, and suggestions for this are given. Some types of detailed ground based rock mechanics research would be helped by using the methods of ground photogrammetry, and by photogeological interpretation of ground stereoscopic photographs.

A comparison of black-and-white, color and infrared photographs for geological interpretation at Witvlei, South West Africa

A study was made of photographs from an area north of Witvlei, South West Africa. Four sets of photographs were taken, namely black-and-white, infrared, and two sets of color. The infrared and one set of color were taken soon after rain had fallen. The four sets of photographs were compared for their effectiveness for photogeological interpretation, and the following conclusions were reached. (1) Color photographs are only marginally better than black-and-white, and then only if taken soon after rain. (2) Infrared offers little advantage over black-and-white. (3) Color and infrared offer slight advantages for study of superficial deposits. (4) Even under relatively unfavorable conditions, normal black-and-white photography can be of great value, particularly in the early stages of mapping an unknown area.

Regional Geology of Northern Yukon1

ABSTRACT Structurally the northernmost Yukon is part of the Eastern Cordilleran System, and in many respects it is an eastward extension of Brooks Range and the adjacent structural provinces of northern Alaska. Comparisons may also be made between the geological history of the northern Alaska - northern Yukon region and that of the Canadian Arctic Islands, a fact that has led to some speculation concerning the possible contiguity of these two areas throughout much of Phanerozoic time. This report will deal with British and Barn Mountains, Old Crow Plain and Dave Lord Ridge. Richardson Mountains will not be discussed in detail. The Ordovician, Silurian and possibly much of the Cambrian are represented east of Dave Lord Ridge by approximately 10,000 ft of fine-grained clastic sediments, the Road River Formation. Rocks of similar age in British and Barn Mountains and Brooks Range are strongly deformed metasediments (Neruokpuk Formation). Deposition of the Road River Formation took place in a basin named the Richardson Trough, which may have been a southward extension of the Franklinian Geosyncline of the Canadian Arctic Islands. A major tectonic episode, the Ellesmerian Orogeny, affected northern Yukon, northern Alaska and the Arctic Islands in several separate phases during the Devonian. The Neruokpuk underwent low-grade regional metamorphism at this time and several granite stocks were emplaced, including that at Mount Sedgwick in British Mountains. Thick syntectonic and post-tectonic clastic wedges were formed nearly everywhere near the present Alaskan and Canadian Arctic coasts, except within the Yukon, as a result of a mid-Devonian pulse of the Ellesmerian Orogeny. Between the Early Mississippian and the Late Triassic the Lisburne Group and the Sadlerochit and Shublik formations were deposited. The Lisburne and Sadlerochit are two of the most important reservoir rocks at Prudhoe Bay. Lisburne sediments, mainly carbonates, are confined (within the report area) to British and Barn Mountains. The Sadlerochit Formation (coarse-grained, porous clastic deposits) is well developed in the Dave Lord Ridge area but is thin or absent in northeastern British Mountains. The Shublik is typically developed in British Mountains. The principal sediment source area for northern Alaska and northern Yukon during the Cambrian to Jurassic period appears to have been located off the 1 Manuscript received February 9, 1972. 2 Shell Canada, P.O. Box 880, Calgary, Alberta. Present address: Institute of Sedimentary and Petroleum Geology, Calgary. This paper has developed from a field and photogeological study carried out between July 1970 and March 1971 while the author was in the employ of J. C. Sproule and Associates Ltd. The project was carried out for Charter Oil Company Ltd. Both these companies are to be thanked for granting me permission to publish the material. C. W. Drew provided an invaluable preliminary photogeological interpretation of the project area. R. Cech was my very energetic field assistant. The ideas presented herein have benefited considerably from discussions with D. K. Norris, I. Tailleur and W. O. Kupsch, all of whom have read the manuscript. Finally, grateful thanks are due to Shell Canada Limited for providing me with drafting and typing services. L. H. Taylor drew the illustrations and Mrs. J. Barnes typed the final manuscript. End_Page 81------------------------- present Arctic Coast and may have been part of the same source area that contributed detritus to the Canadian Arctic Islands region. Jurassic, Cretaceous and Tertiary sediments are almost exclusively clastic in northern Yukon. They were derived from several sources including an ancestral Brooks Range and Campbell Uplift of the Inuvik area. The Cretaceous marks a major shift in sediment dispersal patterns, particularly in northern Alaska, as a result of large-scale changes in the distribution of land and water masses at this time. These may have been caused by major continental-drift movements in the area of the Arctic Ocean Basin. A major tectonic episode, the Eurekan Orogeny, took place between Middle Cretaceous and Early Tertiary times in northern Yukon (and in Alaska and the Arctic Islands), involving all but the most recent sediments. No igneous activity has been recorded in connection with the Eurekan Orogeny in northern Yukon but most of the structural deformation of the post-Devonian rocks dates from this time.

The Mozambique orogenic belt and its foreland in northeast Tanzania: a photogeologically-based study

The tectonic relationships within a rather large part (130,000 sq. km) of the Mozambique orogenic belt in N.E. Tanzania were investigated by photogeological interpretation and ground control Within the granitoid foreland (part of the Tanganyika Shield) the Dodoman and Nyanzian Greenstone belts, and charnockitie granulites are recognized. These were intruded and replaced by the chelogenie Katarchaean granite. Within the orogenic belt pre-Mozambiquian gneisses (termed Parangan) are exposed at the western margin, and in the floor of the orogen. These were tectonically reworked and transformed into L-tectonites and flaggy gneisses in the main Mozambiquian tectonism (termed Kondoan): this took place by strong folding about south-easterly-plunging axes, the folds being characteristically reclined. It is observed that structures transverse to the regional trend are a feature of other orogenic fronts such as the Grenville and Caledonian. In Tanzania they are succeeded by flexure folds on nne axes (termed Bongan), which locally become the predominant structures, parallel to the regional trend. In the north they are overturned towards the foreland and over-ride it. The Mozambiquian tectonism deforms the margin of the Shield and may penetrate it for considerable distances, perhaps contributing to the deformation in the Greenstone belts.

Linear geological features as an aid to photogeological research

As most photogeological interpretation tends to be of linear features (e.g., faults, rock and soil contacts) it is suggested that these should be exploited for research studies. It is possible to use them to assess the relative performance of various means of sensing, the factors affecting the usefulness of sensors, and to develop interpretation criteria for various instruments and environments. To do this it is necessary to record the characteristics of the appearance of these linear features on the air photographs or imagery, the relevant field data, and situations where features do not show. If the details are recorded for each feature on punched cards, a computer can be used to test large numbers of correlations and permit a useful interchange of data files between researchers working on different problems in different places. It could also form a useful prelude to attempts to create an automatic pattern recognition system.