Assessment of sandstone deterioration at Ta Keo temple (Angkor): first results and future prospects

A first application of geomorphological methods to the assessment of sandstone deterioration at Angkor is presented. Damage diagnosis was carried out on the first eastern tier of the central pyramid of the 1,000 year-old Ta Keo temple. Methods combine field observations and measurements at 230 sampling points, high-resolution lasergrammetry and stereophotogrammetry on a 2-m² test zone, and SEM observations. The first results indicate that decay operates through a synergistic combination of weathering phenomena dominated by scaling and solution, and exhibits a high spatial variability. Percentages of deteriorated surfaces vary from 17.6 to 93.8%, and average stone recession values from 0.00 to 2.71 cm (minimum) and 0.34 to 5.49 cm (maximum). On the test-zone, stereophotogrammetry and 3D-mapping of the present and reconstructed initial states using lasergrammetry indicate that erosion scars up to 6 cm deep have formed since 1963. On the whole, the amount of deteriorated surfaces more than tripled between 1963 and 2008. The degree of implication of salts in stone decay remains unclear for most efflorescences are composed of calcite (CaCO3), with secondary importance of barite (BaSO4) and gypsum (CaSO₄·2H₂O). Future prospects aim to evaluate the impact on stone decay of the clearing out of the temple from the forest in the 1920s.     

A 3.5 ka record of paleoenvironments and human occupation at Angkor Borei,Mekong Delta,southern Cambodia

Microfossil and sedimentological data from a 3.1 m core extracted from a reservoir (baray) at the ancient Cambodian settlement of Angkor Borei in the Mekong Delta have provided a continuous record of sedimentation and paleoenvironments dating from about 2000 cal yr B.C. Palynological data indicate that for much of the cal. 1st and 2nd millennia B.C. mangroves dominated the regional vegetation, while extensively and regularly burnt grasslands dominated the local vegetation. Turbid, nutrient‐rich standing water characterized the core locality, perhaps suggesting a connection with rivers in the area. An abrupt change during the cal. 5th to 6th centuries A.D. involved a dramatic reduction in grasslands and the expansion of secondary forest or re‐growth taxa. These changes are synchronous with an abrupt decline in the concentration of microscopic charcoal particles in the sediments, and the colonization of the core locality by swamp forest plants. These changes are taken to indicate a shift in land‐use strategies or, possibly, a period of land abandonment. The age for the construction of the baray is interpreted to be in the 17th–19th centuries, but this dating remains speculative. Construction of the Angkor Borei baray exploited a preexisting body of standing water, so its construction was fundamentally different from the methods used at the Angkorian capital in northern Cambodia. © 2003 Wiley Periodicals, Inc.     

Petrographical and petrophysical properties of sandstones: statistical analysis as an approach to predict material behaviour and construction suitability

Most studies dealing with material properties of sandstones are based on a small data set. The present study utilizes petrographical and petrophysical data from 22 selected sandstones and ~300 sandstones from the literature to estimate/predict the material and weathering behaviour of characteristic sandstones. Composition and fabric properties were determined from detailed thin section analyses. Statistical methods applied consist of data distributions with whisker plots and linear regression with confidence regions for the petrophysical and weathering properties. To identify similarities between individual sandstones and to define groups of specific sandstone types, principal component and cluster analyses were applied. The results confirm an interaction between the composition, depositional environment, stratigraphic association and diagenesis, which leads to a particular material behaviour of sandstones. Three different types of pore radii distributions are observed, whereby each is derived from different pore space modifications during diagenesis and is associated with specific sandstone types: (1) bimodal with a maximum in capillary and micropores, (2) unimodal unequal with a maximum in smaller capillary pores and (3) unimodal equable with a maximum in larger capillary pores. Each distribution shows specific dependencies to water absorption, salt loading and hygric dilatation. The strength–porosity relationship shows dependence on the content of unstable lithic fragments, grain contact and type of pore radii distribution, cementation and degree of alteration. Sandstones showing a maximum of capillary pores and micropores (bimodal) exhibit a distinct hygric dilatation and low salt resistance. These sandstones are highly immature sublitharenites–litharenites, characterized by altered unstable rock fragments, which show pointed-elongated grain contacts, and some pseudomatrix. Quartz arenites and sublitharenites–litharenites which are strongly compacted and cemented, show unimodal unequal pore radii distributions, low porosity, high strength and a high salt resistance. The presence of swellable clay minerals in sublitharenites–litharenites leads to a medium to high hygric dilatation, whereas quartz arenites show little hygric dilatation. Sandstones with unimodal equal pore radii distribution mostly belong to weakly compacted and cemented mature quartz arenites. These are characterized by high water absorption and high porosity, low to medium strength and a low salt resistance. The data compiled in this study are used to create a sandstone quality catalogue. Since material properties are dependent on many different parameters of influence, the transition between different lithotypes is fluent.     

Formation of phyllosilicates in a fault zone affecting deeply buried arkosic sandstones: their influence on petrophysic properties (Annot sandstones, French external Alps)

The Restefond fault, located in the Late Eocene-Early Oligocene Alpine foreland basin, affects the well lithified and low porosity Grès d??Annot. The fault core zone is characterized by the occurrence of highly deformed sandstone lenses. Deformation inside the lenses corresponds to mm to sub-mm-spaced cleavage planes rich in phyllosilicates and up to cm-thick and dm-long quartz-calcite pure extensional veins. The cleavages are mostly composed of newly-formed synkinematic white mica and chlorite. By using thermodynamic thermometers based on the chemical composition of chlorite, a temperature of 200?±?20?°C of fault activity was computed. This temperature shows that the Restefond fault was active at burial conditions comprised between 6.5 and 8?km, assuming a mean geothermal gradient between 25 and 30?°Ckm^?1. The petrophysic properties of sandstones from the core zone and in the hanging and foot wall of the fault were determined on drilled plugs following three spacial directions. The permeability of the highly deformed sandstone from the core zone is about one order of magnitude higher than in the host rock. This increase in permeability occurs in the direction parallel to the S?CC structures and is explained by the occurrence of well-connected micropores localized between platy phyllosilicates. This study shows that the fault petrophysic properties are mostly controlled by the precipitation of synkinematic phyllosilicates under deep burial conditions.     

华庆地区延长组长6油层组储集砂岩特征及对储层物性的影响

长6油层组储集砂岩主要为岩屑长石砂岩,粒度较细,分选中等偏差,填隙物主要为碳酸盐矿物和粘土矿物。砂岩的物质组成影响着其储层性能,储层物性随着石英含量的增加而变好,而随着岩屑含量的增加而变差。砂岩中长石的溶蚀作用是改善储层物性的关键因素。填隙物的含量越大,则孔隙喉道堵塞和充填的程度增加,导致储层物性变差。     

Slope stability assessment and design of remedial measures for Tungnath Temple at Uttarakhand,India: a case study

Natural Hazards - The present paper assesses the slope stability of the Tungnath Temple at Rudraprayag District, in the Indian state of Uttarakhand, and suggests the remedial measures. The...     

Archaeological exploration using magnetic and GPR methods at the first court of Hatshepsut Temple in Luxor, Egypt

The Hatshepsut Temple at Luxor, southern Egypt was built as a garden for Amun, and the first court indeed had exotic trees and vegetations. The pathway to the temple was along a sphinx-lined causeway linking the valley to pylons, which are missing now. As an effort to outline remains of the vanished garden and missing pylons and any other possible archaeological structures at this first court site, an extensive integrated magnetic/ground-penetrating radar (GPR) geophysical survey was conducted. The magnetic survey covered the entire area of the first court (100?×?60 m), while the GPR survey covered only an area of 50?×?50 m. The acquired GPR data were processed and presented as 2-D depth sections providing a reasonable vertical/horizontal resolution for the upper 6 m of the investigated site. The acquired magnetic data was processed and presented as 2-D image. The integrated interpretation of the acquired GPR and magnetic data revealed some archaeological features including a rectangular depression which is presumably an ancient man-made pond in the garden of the temple, a rectangular feature that may be a foundation of the missing pylon of the temple, and a suite of aligned anomalies that could be the remnants of sphinx. Such findings reflect the archaeological potentiality of the surveyed site and outline the extension of the temple. Meanwhile, these results necessitate further geophysical investigation or archaeological excavation to be confirmed.     

Geophysical and hydrological investigations at the west bank of Nile River (Luxor, Egypt)

Luxor, the modern Egyptian city that occupies the site of ancient Thebes, is famed for its magnificent ancient monuments. Since 1967, the Aswan high dam has prevented the annual flooding of the Nile River, resulting in excessive salt accumulation on the Nile floodplains and on exposed monument surfaces. In addition, the expansion of agricultural land within the Luxor study area has resulted in increased salinity and groundwater level. These conditions accelerate the degradation of buried and exposed monuments that were fairly well preserved in the past. To mitigate this problem, it is necessary to first understand the near-surface setting and the groundwater conditions of the Luxor area. A geophysical investigation was carried out using resistivity and electromagnetic surveys. In addition, a chemical analysis was conducted of some surface water samples collected from canals and the sacred lake of Memnon Temple. Based on the results of the geophysical surveys and the chemical analysis of the water samples, the shallow subsurface was characterized into four geoelecterical units. Groundwater flow directions were determined to be from the central area to the west, causing a rise in the groundwater levels and groundwater salinity in the area of monuments.     

Seismic properties of the upper crust in the central Friuli area (northeastern Italy) based on petrophysical data

The compressional and shear wave velocities have been measured at room temperature and pressure up to 450 MPa on 5 sedimentary rock samples, representative of the most common lithologies of the upper crust in the central Friuli area (northeastern Italy). At 400 MPa confining pressure the Triassic dolomitic rock shows the highest velocities (Vp  7 km/s, Vs  3.6 km/s), the Jurassic and Triassic limestones samples intermediate velocities (Vp  6.3 /s, Vs  3.5 km/s) and the Cenozoic and Paleozoic sandstones the lowest velocities (Vp  6.15 km/s, Vs  3.35 km/s). The Paleozoic sandstone sample is characterized by the strongest anisotropy (10%) and significant birefringence (0.2 km/s) is found only on the Cenozoic sandstone sample. We elaborated the synthetic profiles of seismic velocities, density, elastic parameters and reflection coefficient, related to 4 one-dimensional geological models extended up to 22 km depth. The synthetic profiles evidence high rheological contrasts between Triassic dolomitic rocks and the soft sandstones and the Jurassic limestones. The Vp profiles obtained from laboratory measurements match very well the in-situ Vp profile measured by sonic log for the limestones and dolomitic rocks, supporting our one-dimensional modelling of the calcareous-carbonatic stratigraphic series. The Vp and Vs values of the synthetic profiles are compared with the corresponding ones obtained from the 3-D tomographic inversion of local earthquakes. The laboratory Vp are generally higher than the tomographic ones with major discrepancies for the dolomitic lithology. The comparison with the depth location of seismicity reveals that the seismic energy is mainly released in correspondence of high-contrast rheological boundaries.     

丹阳天王寺边坡稳定性评价及防治措施

针对苏南地区典型露采边坡的地层岩性及地质构造特点,以极限平衡理论为基础,运用GeoStudio软件中的SLOPE/W模块和VADOSE/W模块计算分析江苏丹阳天王寺边坡在天然工况、暴雨工况及地震工况下的稳定性。结果表明:天然工况下,潜在滑动面分布范围最小,稳定性最高,存在滑动的危险性;暴雨工况下,潜在滑动面分布范围有所增大,稳定性降低,边坡滑动的可能性较大;地震工况下,潜在滑动面分布范围最广,稳定性最低,边坡滑动的可能性很大。基于上述结果,提出防治措施。     

The identification and use of petrophysical anomalies to forecast the mineralization at the Antey uranium deposit (Southwestern Trans-Baikal Region)

The determination of petrophysical parameters in conjunction with the geological, structural, mineralogical, and petrographic study of rocks is necessary to assess the localization conditions of uranium–molybdenum ore, the processing prospects, and the extent of mineralization at the Antey vein–stockwork deposit, which is the Russia’s largest, confined to the granitoid basement of the Streltsovo Caldera in the Southeastern Trans-Baikal Region.     

Diagenesis of Cretaceous sandstones of the Kootenay Formation at Elk Valley (southeastern British Columbia) and Mt Allan (southwestern Alberta)

Vitrinite reflectance data for two sections of the Kootenay Formation are different, but increase with depth. Illite crystallinities (XRD) are irregular with depth but detailed S.E.M. examination shows that crystal size and morphology increase with depth.At Elk Valley (low reflectance) S.E.M. examination shows kaolinite + dolomite as the authigenic assemblage. At Mt Allan (45 km north, higher reflectance) kaolinite disappears at 265 m and chlorite + calcite appears implying the equilibrium 5 CaMg(CO₃)₂ + Al₂Si₂O₅(OH)₄ + SiO₂ + H₂OagMg₅Al₂Si₃O₁₀(OH)₈ + 5CaCO₃ + 5CO₂. (1)Equilibrium (1) involves CO₂ and H₂O which form an immiscible fluid at diagenetic conditions. Thermochemical data, activity coefficients for the fluid mixture (Margules solution model), and fugacity coefficients allow the position of intersection of the miscibility surface and equilibria similar to (1) to be calculated. Maximum temperatures (180–250°C) in water-rich fluids are in accord with geothermal gradients of 33°C/km and temperatures from vitrinite reflectance (220°C). It is suggested that produced CO₂ may be responsible for the development of secondary porosity during deep burial.     

Natural deterioration and conservation treatment of the granite standing Buddha of Daejosa Temple, Republic of Korea

The Daejosa Buddha is formed of highly weathered coarse grained biotite granite. The main body is dark green due to a covering of lichens. The main body of the Buddha has developed nearly vertical, horizontal and oblique joint systems. Results of physical properties for the rock samples from the Daejosa Buddha are lower than for normal fresh granite as the primary minerals of the host rocks have been altered to clay and iron hydroxide minerals. Spore and mycelium of green algaes and some plants cover the surface of the standing Buddha and fill the pore space of the surrounding rocks. Considering the weathering and state of deterioration, the Buddha statue requires conservation treatment. Restoration may be largely divided into the head part, upper and lower parts, and the back side of the Buddha. The head and the cap rock were joined and restored with unslaked lime filling. The head and stone crown of the Buddha were fitted and restored using an epoxy type resin with high viscosity that was mixed with granite powder and talc as petro-fillers. For the back side, resin was applied for reinforcement. Araldite and hardener of low viscosity that were used with the addition of glass fibers. Finally, texture and color matching treatments were carried out.     

Provenance of Palaeozoic sandstones from the Carnic Alps (Austria): petrographic and geochemical indicators

An integrated approach of petrographic analysis, whole rock geochemistry and microprobe analysis has been applied to obtain information on the geodynamic development and the provenance for Ordovician to Permian siliciclastic successions exposed within the Carnic Alps (Austria). Sandstone detrital mode and geochemical results refine previous geodynamic interpretations. Late Ordovician samples indicate a stable craton and recycled orogenic and, possible, extensional setting. The Early Carboniferous is interpreted to represent a compressional environment, followed by a Late Carboniferous molasse-type foreland basin, and a Permian extensional geodynamic setting. Contrasting geochemical patterns of post-Variscan and Permian sequences suggest a rift setting. Electron microprobe data of detrital white mica also indicate changes in the provenance. Compositional data reflect a shift from low- to medium-grade metamorphic (Ordovician) to high-grade metamorphic (Carboniferous) to low- to medium-grade metamorphic and plutonic source rocks (Permian). Additionally, our data show that various chemical discrimination diagrams do not include all possible ranges of sandstones, and that high contents of detrital mica and ultra-stable heavy minerals may cause misclassification. Consequently, we propose the use of multi-method approach for provenance studies, including the control of geochemical data by modal analysis and heavy mineral investigations.     

Causes, mechanism and environmental impacts of instabilities at Himmetoğlu coal mine and possible remedial measures

 Since the commencement of mining at the Himmetoğlu coal mine, northwest Turkey, serious stability problems have led to interruptions in mining and some environmental effects. A geotechnical investigation was initiated in 1997 and the significant factors that influence the stability have been defined. This paper outlines the results of the field and laboratory studies associated with the causes and mechanism of the slope instabilities and their environmental impacts. The possible remedial measures to improve the stability and to minimize the environmental problems are also described. Back-analyses and data from long-term monitoring indicate that the failures occur along two or three planar surfaces by combination of faults and localized strata steepening adjacent to the faults. The stability is sensitive to changes in length of the lower part of the basal sliding surface and shear strength of the bedding surfaces in the overburden. Suitable remedial measures include slope flattening (i.e. staged bench stripping), proper drainage and spreading of a rock blanket on the pit floor to increase spoil pile stability. Received: 18 April 2000 · Accepted: 15 August 2000     

Holocene landscape reconstruction in the surroundings of the Temple of Pepi I at ancient Bubastis,southeastern Nile Delta (Egypt)

In ancient Egypt, lakes, canals, and other water bodies were an essential part of the sacred landscape in which temples were embedded. In recent years, geoarchaeological research at the site of the Temple of Bastet at Bubastis in the southeastern Nile Delta has proven the existence of two water canals surrounding the temple. It has now been investigated whether these canals were connected to the Temple of Pepi I (2300–2250 B.C.E.), located approximately 100 m to the west of the Temple of Bastet. To explore the Holocene landscape genesis of the Temple of Pepi I, 15 drillings and six geoelectrical profile lines were performed in the surroundings of the temple in spring 2022. The results show loamy to clayey sediments in deeper sections of all drillings with a maximum thickness of 1.70 m, indicating a marshy or swampy depositional environment. Based on the recovered sediment sequences and archaeological remains in the vicinity of the Temple of Pepi I, the marshy or swampy area existed before the Fourth Dynasty. During the Old Kingdom (ca. 2850–2180 B.C.E.), the former marshland either dried up through natural processes or was intentionally drained and filled with sediments for subsequent use for occupation. Regarding the original research question, there is as yet no evidence for a direct connection to the canals of the Temple of Bastet.     

Some medium properties at friuli (Italy) from amplitude spectrum analysis: A possible change in time or in space

We have studied the relation log M₀+ versus M_L in Friuli (Italy) by considering the amplitude spectra of local earthquakes. We show a possible time variation of the apparent average stress in the focal region between the two periods of May and November, 1976. Furthermore, the quality factor Q_p obtained from the same spectra indicates a spatial variation which could be correlated to the difference in the seismicity level.     

The Blagodatnoe gold-sulfide deposit (Yenisei Ridge,Russia): the nature of geophysical anomalies and the succession and causes of formation of petrophysical zoning

Data on geophysical fields and petrophysical heterogeneity, parageneses and the thermodynamic conditions and age of their formation, and fluid inclusions were used for the genetic reconstruction of petrophysical zoning at the Blagodatnoe gold-sulfide deposit. Petrophysical associations of the preore and ore stages of the deposit formation are clearly reflected in anomalies of the magnetic and natural electric fields and the aureoles of radioactive elements. At the early preore stage (752 Ma), reduced solutions with high activity of K, enriched in U, Th, and, probably, Au, were supplied to intensely foliated tectonic zones. Their interaction with initial metasedimentary rocks gave rise to contiguous zones of quartz–muscovite and chlorite metasomatic rocks. Accompanying graphitization led to a high electrochemical activity of the metasomatic rocks, which generated anomalies of up to –300 mV in the natural electric field; the most intensely carbonized zones became enriched with U (up to 6.5 × 10^–4%) and, probably, Au. The quartz–muscovite metasomatic rocks accumulated Th and K (up to 29 × 10^–4% and 4%, respectively), whereas the chlorite metasomatic rocks accumulated rock-forming elements (particularly Fe), which led to the compaction of these rocks and the acceleration due to gravity in local positive anomalies. The nonmagnetic character of the fresh pre-ore metasomatic rocks suggests the predominantly pyritic composition of early sulfides. At the ore stage (698 Ma), the minerals were deposited from H₂O–CO₂–As–S solutions at 560 to 315 °C. The activity of these solutions caused a redistribution of radioactive elements and a high petrophysical differentiation of the ore-bearing structure. The amplitudes of the anomalies above this structure vary from 500 to 80 nT in the magnetic field and from –130 to + 10 mV in the natural electric field. It has been found that the hydrothermal fluid hardly affected the polarization properties of graphitized rocks at the maximum temperatures but caused an intense removal of U and the development of magnetic pyrrhotite after pyrite. The temperature decrease in the mineral-forming system was favorable for the formation of siderite. Carbonaceous schists which experienced carbonatization lost their electrochemical activity. The binding of carbon dioxide in the solid phase influenced the migration capability of trace elements and their zonal distribution. With this evolution of the solution, Th accumulated at the lower levels of the mineralized zone, whereas the upper levels of the deposit became enriched with U. Productive gold–arsenopyrite–pyrite–pyrrhotite paragenesis with anomalous magnetic susceptibility evolved at the ore stage. The late galena–sphalerite–chalcopyrite paragenesis (365 Ma) was of strictly local occurrence and reduced the magnetic susceptibility of ores.     

Alterations of cretaceous siltstones and sandstones near basalt contacts (Nûgssuaq,Greenland)

The influence of the intrusion of basaltic dykes and sills was investigated on sandstones and siltstones of the Atane Formation (Turonian-Coniacian) from the Sarqaq area (Nûgssuaq peninsula, central West Greenland).In the unaltered rock sequence, the siltstones are dominated by kaolinite, quartz and feldspar. No cementation was observed. The sandstones which are prevalent in this formation are arkoses and lithic arkoses with quartz/feldspar ratios of about 1, with variable contents of rock fragments and with minor amounts of matrix. The matrix consists mainly of kaolinite, less frequently of illite-muscovite and smectite or interstratified illite-smectite. Cement minerals include calcite, Fe-calcite, both mainly in concretions, and subordinate Fe-oxide hydrates.The porosity of the sandstones and siltstones indicates a former maximum depth of burial of 1000 m in the Sarqaq region.Adjacent to thin dykes and sills (1–2 m) the above-described rocks are altered as follows. In sandstones albite (fibrous), quartzine, smectite, goethite were all formed at the expense of kaolinitic matrix, and aragonite cement. In siltstones, interstratified illite-smectite, illite, smectite and low-cristobalite replaced kaolinite. These minerals, especially smectite, exclude temperatures above 200°C; they were probably formed during a cooling period.Adjacent to thicker basalt intrusions—only sills, over 5 m thick, and no dykes are known from this area—the following alterations are observed. In sandstones two textural types of albite were formed in addition to: (1) fibrous albite mentioned above; (2) undulose lath-shaped albite; (3) coarse-twinned non-undulose replacement albite. Moreover, brownish luminescing undulose quartz, muscovite, chlorite, epidote, nontronite and anatase occur. In siltstones the mineral association muscovite-chlorite-pyrophyllite-albite occurs, suggesting temperatures in the range of 250–500°C. Additionally a 22–26 Å mixed-layer mineral (chlorite-muscovite?) formed. At the contacts of thick as well as thin basalt intrusions the detrital grains directly adjoining the basalt are partly fractured; potassium feldspar grains show also a chemical disintegration.The temperatures calculated by application of a cooling model are higher than those indicated by the mineral alterations observed. Convective heat transfer by pore water is suggested as an explanation.