Showing papers on "Outcrop published in 1979"
TL;DR: In this article, geophysical surveys across ground failure zones related to ground-water withdrawal at nine sites in Picacho basin in south-central Arizona indicate that earth fissures in alluvium near exposed bedrock are spatially associated with local gravity and magnetic anomalies ranging from local highs to convex-upward changes in slope.
Abstract: Precise geophysical surveys across ground failure zones related to ground-water withdrawal at nine sites in Picacho basin in south-central Arizona indicate that earth fissures in alluvium near exposed bedrock are spatially associated with local gravity and magnetic anomalies ranging from local highs to convex-upward changes in slope. We interpret the gravity anomalies, which range from 0.1 to 1 mGal with half-widths of 50 to 300 m (160 to 980 ft), to be caused by convex-upward irregularities in the bedrock surface underlying the alluvial aquifer. Most irregularities are inferred to be at depths less than 250 m (820 ft). Bedrock irregularities were not detected beneath failures that are more than 2 km (1.2 mi) from bedrock outcrop. The association of earth fissures with zones of variable aquifer thickness suggests that differential compaction is occurring near these fissures. Theoretical estimates, based on the finite element method, of horizontal strains generated by localized differential compaction suggest that this mechanism is the dominant source of horizontal tension causing earth fissures in Picacho basin. Our analysis indicates that tensile strains at fissures at the times of their formation ranged from 0.1 to 0.4 percent.
Prediction of the location of earth fissures near exposed bedrock in Picacho basin and in adjacent basins with similar geologic settings appears feasible by delineation of convex-upward bedrock irregularities. Failures far from exposed bedrock, however, may not be as readily predicted on this basis. If the rheological properties and thicknesses of subsurface materials are known, prediction of the magnitude of water-level decline required to induce sufficient differential compaction to cause failure at potential earth fissures appears feasible.
63 citations
TL;DR: In this article, four Quaternary units occupying a shallow bedrock depression have been delineated from outcrop exposures and auger drilling on Sandon Point Beach, North Bulli, 60 km south of Sydney, N.S.W.
Abstract: Four Quaternary units occupying a shallow bedrock depression have been delineated from outcrop exposures and auger drilling on Sandon Point Beach, North Bulli, 60 km south of Sydney, N.S.W. In ascending stratigraphic order these units are: a basal muddy sand (2.2+ m) of fluvial origin; a mottled mud (3.5 m) with common iron oxides, representing alluvial deposits with a superimposed soil profile developed during a period of lower sea level; a sandy mud (3.9 m) containing estuarine shell fossils, small tree stumps (including one mangrove) and abundant wood fragments; and, at the top, a pebble layer overlain by beach and dune sands, all partly indurated with iron oxides (2.3 m). 14C dating in situ tree stumps, shell material and wood fragments from the estuarine sandy mud unit between mean sea level and +1.45 m provided ages ranging from 7520 ±. 150 to 6350 ± 100 years B.P. The age of this unit is supported by a date on in situ Myrtaceae root material (7000 ± 150 years B.P.) from a similar study san...
47 citations
DOI•
01 May 1979
TL;DR: The wave-dominated deltaic sandstone units of the Upper Cretaceous San Miguel Formation in south Texas were deposited during an overall marine transgression, and the most common San Miguel vertical sequences, produced during delta progradation, coarsen upward from silt and clay to find sand.
Abstract: Sandstone units of the Upper Cretaceous San Miguel Formation in south Texas are wave-dominated deltaic sequences deposited during an overall marine transgression. San Miguel sediments were deposited in the Maverick basin within the Rio Grande embayment. Cross sections and sandstone maps reveal that during deposition of the San Miguel Formation, the Maverick basin consisted of two subbasins. A western subbasin received sediments from the northwest; an eastern subbasin received sediments from the north. The most common San Miguel vertical sequences, produced during delta progradation, coarsen upward from silt and clay to find sand. Burrows dominate, and the few primary structures in cores are of small scale. Large-scale cross beds are observed only in outcrop. Strandplain or barrier island facies sequences, which prevail in most wave-dominated delta deposits, are incomplete in the San Miguel Formation. In most places, only the lower shoreface is preserved. The upper parts of the sequences, which normally bear large-scale primary structures, were lost by marine reworking during subsequent transgression. Intense burrowing destroyed any primary structures at the tops of the truncated sequences. Net-sandstone patterns show that the thickest parts of the sandstone bodies are generally strike oriented. Where preserved, sand-feeder (fluvial) systems are indicated by dip-aligned net-sandstone trends on the updip sides of the sandstone units. Variability of these net-sandstone patterns indicate that a wide spectrum of wave-dominated delta types is represented. The spectrum includes wave-influenced lobate, arcuate, cuspate, and strike-elongate deltas, in order of increasing importance of wave processes.
42 citations
01 Jan 1979
TL;DR: The results of shallow seismic reflection, sonar and coring surveys carried out in the central Bristol Channel, between Morte Point and Porlock Bay, and the Lundy area are reported in this article.
Abstract: A brief report is made of the main results of shallow seismic reflection, sonar and coring surveys carried out in the central Bristol Channel, between Morte Point and Porlock Bay, and the Lundy area. Lithological and palaeontological examination of 250 bedrock cores, from over 800 coring stations, has enabled a fairly detailed Jurassic succession to be identified. Hettangian to Kimmeridgian rocks probably have a total thickness of about 2170 m. The Jurassic is underlain by about 300 m of Keuper Marl and Rhaetic Beds. Keuper Marl rests unconformably on the Devonian along the south side of the Bristol Channel syncline. Late Palaeozoic shales and sandstones outcrop between Hartland Point and Lundy, and north of the island. Soft sandstones, possibly representing the Permian, overlie the Late Devonian/Early Carboniferous north of Lundy. Late Pleistocene, glacial, pebbly clays in the northern part of the Bristol Channel contain derived Triassic and Early Jurassic rock fragments and fauna. Holocene silts and peats, occurring in the depressions on the Pleistocene sediments in mid-Channel, contain Quaternary estuarine microfaunas and freshwater microfloras. Reworked Late Cretaceous and Tertiary foraminifera also present in these Holocene silts may have been derived from submarine outcrops in the Celtic Sea.
38 citations
TL;DR: Tectonic slides are faults that have been described and discussed in the Caledonides for over fifty years but which, possibly because of misunderstanding, have failed to find acceptance in structural schemes elsewhere.
36 citations
Journal Article•
TL;DR: In this article, the chemical potentials of CO and HrO between samples during metamorphism were mapped in three dimensions in the outcrop, and they exhibit an extremely regular pattern.
Abstract: Mineral assemblages in diferent samples of metamorphosed argillaceous carbonate rock, collected from a single, large outcrop in south-central Maine, record differences in the chemical potentials of CO, and HrO between samples during metamorphism. Because all samples contain graphite and pyrrhotite of constant composition, differences in the chemical potentials of Or, H2, CH4, and HrS existed as well. Thermodynamic analysis of the mineral assemblages indicates that maximum chemical potential differences were on the order of 100 calories. Maximum differences in the chemical potentials of FeO, MgO, KrO, AlrOr, and CaO between samples are of approximately the same magnitude. The differences in chemical potentials of CO, and HrO between beds, however, correspond to a difference of only a few hundredths X.o, h the composition of a COr-HrO fluid in equilibrium with the samples. Maximum gradients in the chemical potentials of CO, and H2O during metamorphism at the outcrop were 5-6 cal/rnin magnitude. Diflerences in chemical potentials of CO, and HrO can be mapped in three dimensions in the outcrop, and they exhibit an extremely regular pattern. With the exception of one sample, there are no detectable differences in chemical potentials parallel to bedding and schistosity (which have identical orientations in the outcrop). All other differences occur between different beds. The mapped differences in chemical potentials can be used to quantitatively estimate upper bounds on mass transfer of COu and HrO during metamorphism at the outcrop. The estimated upper bounds on mass transfer are consistent with (but do not require) a model of channelized fluid transfer during metamorphism in which fluid transfer primarily occurs in directions parallel to bedding and schistosity.
35 citations
TL;DR: A variety of bedrock weathering features, including surface grus, polygonal cracks, siliceous glaze, tors, weathering pits, and tafoni typify upland outcrops on the Cumberland Peninsula as mentioned in this paper.
Abstract: A variety of bedrock weathering features—both modern and remnant—including surface grus, polygonal cracks, siliceous glaze, tors, weathering pits, and tafoni typify upland outcrops on the Cumberland Peninsula. Tor ridges are particularly prevalent and at lower elevations they show significant modification and streamlining by flowing ice. On summit areas at elevations above 750 m, however, remnant corestones are preserved in situ, suggesting selective preservation of upland surfaces. Bedrock structure and composition, topographic position, and intensity of process strongly influence tor development. Weathering pits are common on high level, open summit surfaces where weathering occurs in response to both climate and continued removal of derived debris. Pit enlargement through lateral undercutting has been favoured by accumulation of protective bottom residua, mechanical weathering, and the presence of exfoliation crusts. It is postulated that salt crystallization plays a role in outcrop microweathering und...
17 citations
TL;DR: In this paper, a study of Lower Permian rocks in northeastern Nevada and northwestern Utah was undertaken to provide a basis for interpretation of Early Permians history of the Cordilleran Miogeosyncline.
Abstract: This study of Lower Permian rocks in northeastern Nevada and northwestern Utah was undertaken to provide a basis for interpretation of Early Permian history of the Cordilleran Miogeosyncline. The area of study extends from the western margin of the miogeosyncline, along the eastern edge of the old Antler highlands, eastward into the Salt Lake Desert west of Salt Lake City (Fig. 1), where outcrops of Permian rocks are few. It extends along the miogeosyncline in Nevada from northern Lincoln County into northern Elko County. The base of the Permian was selected as the lower stratigraphic limit for this study. The base of the Kaibab Limestone was selected as the upper limit, although the Lower-Upper.*** Permian boundary occurs above it (Baird and Collinson, 1975), because it forms a reliable horizon for correlation and marks the commencement of a new depositional cycle in this region. Work concerning Lower Permian rocks of the central Cordilleran Miogeosyncline includes that of Steele (1959, 1960) and Bissell (1960, 1962a, 1962b, 1964, 1967, 1970, 1974), which are regional in scope, and that of Stevens (1965), Collinson (1968), Zabriskie (1970), and, Marcantel (1975), which presents more details in smaller areas. Many different facies, the distribution of which generally has been credited to various highs depocenters, troughs, basins, highlands, or shelves, often on the basis of tenuous data have been recognized.
16 citations
TL;DR: In this article, twenty-two piston cores from a small area on the north flank of the Rio Grande Rise were used to infer the depositional environment on the Rise during the late Cenozoic and place constraints on the origin of the erosional canyons.
Abstract: The Rio Grande Rise is capped by a thick sequence of pelagic carbonate and reefal sediments, ranging in age from upper Cretaceous to Recent. The north flank of the Rise is dissected by deep erosional canyons which expose the near-horizontally layered calcareous strata as outcrops on the canyon walls. Lithologic and stratigraphic studies of twenty-two piston cores from a small area ($~25 km^{2}$) on the north flank allow an interpretation of the depositional environment on the Rise during the late Cenozoic, and place constraints on the origin of the erosional canyons. A major unconformity of Pliocene age was penetrated by 12 of the cores. Sediments beneath the unconformity range in age from upper Eocene to lower Pliocene, and correspond approximately in depth with that of equivalent strata recovered at DSDP Site 357 nearby. Pliocene-Pleistocene sediments above the unconformity show systematic regional differences in rate of accumulation, extent of reworking, and the presence of stratigraphic gaps. On the f...
15 citations
TL;DR: Several different varieties of sedimentary phosphatic deposits of Neogene age occur on the southern and western continental margins of southern Africa as discussed by the authors, and their origin and distribution were influenced by major transgressions and regressions identifiable in offshore seismic reflection profiles and confirmed by onshore observations.
Abstract: Several different varieties of sedimentary phosphatic deposits of Neogene age occur on the southern and western continental margins of southern Africa. Their origin and distribution were influenced by major transgressions and regressions identifiable in offshore seismic reflection profiles and confirmed by onshore observations. Offshore deposits consist of nodules eroded from outcropping Neogene strata and mixed glauconite/apatite pellets. In addition concretionary masses occur on the South West African shelf associated with siliceous muds. On the western coastal plain the oldest deposit is a Miocene phosphatic sandstone which is unconformably overlain by a Pliocene unit containing reworked Miocene material. Small volumes of phosphate-cemented surface sands are found, and a number of deposits of aluminium phosphates occur in the vicinity of Saldanha Bay.The deposits are of the platform type. No tectonic control of mineralization has been identified, but local topographic features have influenced the distribution of ores. Several modes of origin including direct precipitation, replacement, diagenesis, allochemical and lithochemical, have been identfied.
11 citations
TL;DR: The bathymetry of the Isle of Skye can be related to fundamental geological controls as mentioned in this paper, and the absence of banks in the North Minch can be explained by its location outside the limits of shallow Tertiary igneous activity, the northward growth of intrusions apparently being halted by the Rubh'Re'Kebock Head Ridge.
01 Jan 1979
01 Jan 1979
TL;DR: In this article, the first time in Catalonia from Maastrichtian "red beds" (Garumnian facies), which outcrop in vicinity of Milla (a village in the Ager Valley, Lleida), were tentatively assigned to an Ornitopod.
Abstract: Dinosaurian footprints are recorded for the first time in Catalonia from Maastrichtian "red beds" (Garumnian facies), which outcrop in vicinity of Milla (a village in the Ager Valley, Lleida). These infills are tentatively assigned to an Ornitopod.
TL;DR: In this paper, a 13,000 km2 area of Archean rocks in southeastern Manitoba has been sampled using a multi-stage statistical model and 256 outcrop composite samples were analyzed in duplicate for Si, Al, Fe, Mn, Mg, Ca, Na, K, Ti and P. The data provided an estimate of the overall composition of this portion of the Canadian Shield.
TL;DR: The Post-Diamond Hill Paleosol generally underlies Late Pleistocene sediments of the Willamette Formation as discussed by the authors, and the soils are mostly typic Pelloxererts in the fine, montmorillonitic, mesic family.
01 Jan 1979
TL;DR: A bedrock dredging program by the R/V Sea Sounder in 1977 and 1978 along the continental slope in the eastern Gulf of Alaska revealed a previously unknown Eocene sedimentary sequence that includes argillaceous rocks with favorable petroleum source rock characteristics as discussed by the authors.
Abstract: A bedrock dredging program by the R/V Sea Sounder in 1977 and 1978 along the continental slope in the eastern Gulf of Alaska revealed a previously unknown Eocene sedimentary sequence that includes argillaceous rocks with favorable petroleum source rock characteristics. Seven of 36 dredge hauls that sampled outcrop contain argillaceous rocks with more than 1 percent and as much as 1.64 percent organic carbon. Some of the rocks in samples of probable early Eocene age have undergone a thermal history that has resulted in generation of hydrocarbons. The organic matter appears to be hydrogen deficient, however, which could indicate that the rocks are more likely to be a source of gas rather than liquid hydrocarbon, unless the hydrogen loss is due to weathering. The Eocene rocks are associated with sandstone and conglomerate on the continental slope. They dip northward beneath younger Tertiary strata in the outer continental shelf where they could be an important petroleum source and exploratory target. 4 figures, 5 tables.
TL;DR: The late Oligocene San Sebastian Formation of northern Puerto Rico was deposited on an erosional surface of Eocene and Cretaceous rocks as discussed by the authors, which constitutes a transgressive sequence representing deltaic, coastal lagoon, and shallow-water marine paleoenvironments.
Abstract: The late Oligocene San Sebastian Formation of northern Puerto Rico was deposited on an erosional surface of Eocene and Cretaceous rocks. It constitutes a transgressive sequence representing deltaic, coastal lagoon, and shallow-water marine paleoenvironments. The northward extension of the formation has been traced as far as the Kewanee Interamerican Oil Co. 4CPR well, 8 km east of Arecibo and about 12 km north of the closest outcrop. In the well, the formation occurs at depths between 1,352 and 1,652 m. In previous descriptions of the well cuttings, "silicified tests of planktonic foraminifers" were reported; review of the assemblages has revealed that the "siliceous tests" are actually light-brown spherulites of siderite, some of which have shapes similar to Orbulina, Biorbulina, Globigerinoides, and Globigerina. They probably formed in a freshwater or brackish-water paleoenvironment.
01 Jan 1979
TL;DR: In this article, it was shown that the peridotite in the area of this study is anomalously rich in copper and sulfur compared to worldwide averages for peridotsite.
Abstract: Partly serpentinized peridotite of early Keweenawan age crops out in two places along a 20-kilometer-long zone of positive aeromagnetic anomalies in northern Marquette County, Michigan. Most of the area is mantled by Pleistocene drift with few bedrock exposures. Petrographic and electron microprobe studies show that the peridotite was originally a plagioclase lherzolite containing 40 to 50 percent olivine (Fo80) and approximately 10 to 15 percent each of enstatite (En78Wo04Fs18) and diopsidic augite (En47Wo42Fs11). The plagioclase varies from 5 to 10 percent, and according to Morris (1977) is labradorite, with a composition of An57-65. Major oxide minerals (4 to 6 percent) are ilmenite and magnetite. Sulfides comprise 1 to 2 percent of the peridotite and are chiefly pyrrhotite, pentlandite, and chalcopyrite. Figure 1. Yellow Dog Plains general regional geology and location. Ground magnetic, gravity, and very low frequency electromagnetic (VLF-EM) surveys have refined the location and magnitude of anomalies previously known only from aeromagnetic studies. These surveys together with soil geochemical studies suggest that peridotite, and possibly other mafic rocks forming a differentiated igneous complex, may occur throughout a belt 20 kilometers long (east-west) and 1 to 2 kilometers wide (north-south). Differentiated igneous complexes in many parts of the world are hosts for copper, nickel, chromium, or preciousmetal deposits. The peridotite in the area of this study is anomalously rich in copper and sulfur compared to worldwide averages for peridotite. Positive electro-magnetic anomalies found near the peridotite outcrops may be caused by sulfide-rich zones in the igneous rocks and should be explored further for copper-nickel mineralization. INTRODUCTION The Yellow Dog Plains in northern Marquette County, Michigan, is a nearly featureless area covered by Pleistocene sand and gravel and is nearly devoid of bedrock exposures. The bedrock beneath the plains is mostly slate and other metasedimentary rock of the Michigamme Formation and has been shown as such on virtually all geologic compilations of the region. However, in Sections 11 and 12, T50N, R29W, there are two outcrops of massive, partly serpentinized peridotite. The outcrops lie on and form the highest magnetic peaks of a west-trending linear aeromagnetic anomaly which is about 20 kilometers long (see Figure 1). The anomaly lies parallel to another anomaly of comparable magnitude about 0.5 to 1 kilometer to the south. Both anomalies appear to cut the regional structural trends at low angles. The two anomalies were first evaluated by Case and Gair (1965) and were inferred by them to be caused by magnetic sedimentary units in the Michigamme Formation. At that time, the existence of the peridotite outcrops was not generally known. Because of the close association of the peridotite outcrops with the observed aeromagnetic anomalies and because the anomalies appear to cut across structural trends in the Michigamme Formation, we believe that both anomalies are associated with peridotite. The relatively fresh, undeformed nature of the peridotite suggests that it is younger than the Penokean orogeny which deformed and metamorphosed other rocks in the area about 1.9 billion years ago. Because komatiitic magmas are not common in rocks younger than about 2.5 billion years and because the texture and chemical composition of the peridotite suggest that it is a crystal cumulate, we estimate it is more likely that the peridotite is a differentiate from a less mafic magma rather than a product of a parental ultramafic magma. 1/ U. S. Geological Survey, Reston, Virginia 2/ Geological Survey Division, Michigan Department of Natural Resources, Lansing, Michigan The present study was undertaken to determine if a relatively large differentiated igneous complex is beneath the Yellow Dog Plains and, if so, to determine its configuration and potential economic mineralization. An integrated program including ground magnetic, very low frequency electromagnetic (VLF-EM), gravity, paleomagnetic, rock chemistry and mineralogy, and soil chemistry studies was carried out in 1976 as a cooperative project between the U. S. Geological Survey, Eastern Mineral Resources Branch and the Geology and Minerals Research Unit of the Geological Survey Division, Michigan Department of Natural Resources. This report presents the results of that study and our inferences of the geology and mineral resource potential of the area of the Yellow Dog Peridotite and associated anomalies.
01 Jan 1979
TL;DR: In this article, the authors provide a data base for decisions about lignite mining and reclamation in the Wilcox Group of East Texas, and present a set of environmental geologic maps which depict the character of the land that will be affected by mining.
Abstract: This report provides a data base for decisions about lignite mining and reclamation in the Wilcox Group of East Texas. A set of environmental geologic maps, which accompanies this report, depicts the character of the land that will be affected by mining. The environmental geologic maps of the East Texas lignite belt provide an accurate inventory of land resources. The maps identify areas where mining is most likely to occur, areas of critical natural resources that could be affected by mining, such as aquifer recharge areas, and areas of natural hazards, such as floodplains. Principal areas of both active and planned surface mining are also located. The seven environmental geologic maps cover the outcrop area of the Wilcox Group, the major lignite host, and adjacent geologic units from Bastrop County to Texarkana. This report begins with a discussion of various physical aspects of the lignite belt, including geology, hydrology, soils, climate, and land use, to aid in understanding the maps. The criteria and methodology used to delineate the environmental geologic units are discussed. Varied applications of the environmental geologic maps are considered. 23 references, 9 figures, 3 tables.
TL;DR: In-situ measurements of rock stress in Iceland have been made by Hast in 1967-1968 at five sites and two sites by Haimson and Voight in 1976 as mentioned in this paper.
01 Jan 1979
01 Jan 1979
TL;DR: In this article, a depositional model has been developed to account for this sandstone by using modern continental shelf areas as partial analogs and then placing the Sussex sandstone interval within its proper stratigraphic setting.
Abstract: The Sussex Sandstone was deposited as part of a series of extensive sediment sheets which prograded southward and eastward into the central part of the Late Cretaceous epicontinental seaway of western North America. Although surface exposures of these sandstone units are few, lithologic characteristics and lateral and vertical sequences studied in outcrop have been used with core data to interpret well-log signatures in terms of lithologic facies distributions. A depositional model has been developed to account for this sandstone by using modern continental shelf areas as partial analogs and then placing the Sussex sandstone interval within its proper stratigraphic setting. This model calls upon storm-generated and tidal currents to form and shape sand ridge complexes upon prograding sediment sheets. The eastern and southern termini of these sheets were probably marked by abrupt depositional slopes as indicated by lithostratigraphic, biostratigraphic and seismic studies. Petroleum accumulations appear to be localized along the updip edges of high porosity sandstones within the upper portions of the ridge complexes.
TL;DR: The magnetic maps of the Willyama Complex contain a considerable amount of significant geological information, and if carefully integrated with other available geological data, are a cost-effective means of resolving structural and stratigraphic problems in many areas.
Abstract: Geological and aeromagnetic trends in the Willyama Complex are generally parallel, but there is an almost complete lack of correlation in detail between magnetic rock units and mapped rock units. In particular, anomalies do not consistently correlate with amphibolites or with linear zones of retrograde metamorphism. Ground follow-up in four selected areas has shown that major anomalies in these areas delineate outcropping stratigraphic magnetite bearing horizons within pelitic and psammitic metasediments, gneisses and leucocratic rocks, except to the northeast of the Mount Vulcan antiform. Here, a roughly circular anomaly which is grossly discordant with outcrop geology delineates a magnetic body at a depth of about 250 m and with a diameter of about 4 km. The continuous stratigraphic magnetite bearing horizons generally include minor discontinuous lenses of chemically precipitated magnetite rich rocks such as quartz-magnetite, banded iron formation and sillimanite-magnetite. The magnetic horizons occur close to Broken Hill type lode horizon in two of the areas investigated, and close to stratiform copper mineralization in the other two areas. Because of their continuity they are of great assistance in delineating complex structures within these prospective stratigraphic intervals. It is concluded that detailed magnetic maps of the Willyama Complex contain a considerable amount of significant geological information, and if carefully integrated with other available geological data, are a cost-effective means of resolving structural and stratigraphic problems in many areas.
01 Jan 1979
01 Jan 1979
TL;DR: The Urgonian facies (s.s.) in the Soviet Carpathians are represented by massive zoogenic (bioherms) and well stratified biomicritic limestones as discussed by the authors.
01 Jan 1979
TL;DR: Fractures from Outcrop and Fractures from outcrop were investigated in this article. But the results were limited to a single set of locations and geologic setting, and they did not cover the entire outcrop.
Abstract: List of Figures Purpose Location and Geologic Setting Method of Investigation Results Fractures from Outcrop KLl Fractures from Outcrop KL2 F‘rdctures from Outcrop KL3 Fractures from Outcrop KL4 Fractures from Outcrop KL5 Fractures from Outcrop KL6 Conclusions References Cited
01 Jan 1979
TL;DR: In this paper, the first steps taken in following up a geochemical soil anomaly are to try to locate the bedrock source of the anomalous values, but in areas where the soil cover is thin, it is often possible to do this by examination and sampling of outcrops.
Abstract: One of the first steps taken in following up a geochemical soil anomaly is to try to locate the bedrock source of the anomalous values. In areas where the soil cover is thin, it is often possible to do this by examination and sampling of outcrops, but in areas with a thick soil profile, the location of the anomalous source may involve a long and detailed deep sampling programme. In addition to following up surface anomalies, deep sampling methods may be employed in evaluating alluvial or eluvial deposits, or in reconnaissance geochemical surveys of areas covered by superficial deposits such as peat, alluvium and glacial till, or of areas with heavy surface leaching which may have removed elements of interest from the near-surface soil horizons.
TL;DR: The area of interest lies 145 km south-west of Palembang where Mio-Pliocene coals of the Muara Enim formation outcrop in country around Tanjung Enim as discussed by the authors.
Abstract: Introduction Recent exploration of Indonesian government coal concessions in South Sumatra by Shell Mijnbouw N.V. has revealed small-scale surface instability of recent origin, which could be important with respect to the construction of large spoil dumps. The area of interest lies 145 km south-west of Palembang where Mio-Pliocene coals of the Muara Enim formation outcrop in country around Tanjung Enim. These coal seams and the related coal-bearing strata of claystones, siltstones, and sandstones are gently folded and faulted having dips in the range of 5°-30°. In places, the sediments are intruded by andesites which have locally upgraded the coal to anthracite or semi-anthracite, although away from the intrusions the coals have a semi-lignitic or sub-bituminous aspect. Irrespective of the degree of alteration, the coals are frequently more competent than the associated strata and outcrop as the cap rocks to escarpments and waterfalls. Preliminary sampling of three coal seams in one such setting took place along the valley of the Air Muara Tiga. A series of trenches up to 90 m long were dug down the valley slopes to depths of 3–6 m. The location of the coal seams, a generalized geological sequence, and the positions of the trenches referred to in this note (A and B) are shown in Fig. 1. The side slopes to this strike valley are convex with gradients increasing downwards from 3° to 45°, although much of the slope is inclined at 12° –16°. The local vegetation consists of secondary jungle, giving way to tropical grasses (alang