bluuebunny/crossref_metadata_2025 huggingface dataset:
Groundwater pollution at a pulp and paper mill at Sjasstroj near Lake Ladoga, Russia
Authors: Schoenheinz D. , Grischek T. , Worch E. , Bereznoy V. , Gutkin I. , Shebesta A. , Hiscock K. , Macheleidt W. , Nestler W.
Published: September 2007

Lake Ladoga, situated in north-west Russia, is the main source of drinking water for more than 6 million people in the region of St Petersburg. During recent years eutrophication of Lake Ladoga has increased, with pollution of the lake water and sediments by heavy metals, phenols and chloro-organic substances. This paper reports the influence of effluents from a pulp and paper mill at Sjasstroj situated on the southern shore of Lake Ladoga. At Sjasstroj, contamination of a wide area of land, and the production of large volumes of wastewater requiring treatment and disposal, threaten the sustainability of surface and domestic well supplies and lake ecosystems. A tiered approach to risk assessment was adopted in this investigation beginning with a survey of historical data and an initial field reconnaissance followed by more detailed, targeted hydrogeological and hydrochemical investigations. Concentrations of dissolved organic carbon (DOC) as high as 44 mg 1
−1
and adsorbable organic halogens as high as 130 µg 1
−1
were found in groundwater samples. The detailed field reconnaissance survey contradicted toxicity index values for the wastewater, sludge and groundwater samples calculated using a Russian method of risk characterization, which would otherwise predict a high potential environmental pollution risk. In reality, there is good evidence for natural attenuation of organic compounds in groundwater, with as much as 40–50% removal of DOC. However, the residual DOC can be problematic when chlorination of raw surface and groundwaters creates organo-chlorine by-products in treated water.
Hydrocarbon contamination of groundwater at Ploiesti, Romania
Authors: Albu M. A. , Morris L. M. , Nash H. , Rivett M.O.
Published: September 2007

The area of Ploiesti in Romania was among the first oil producing regions in the world. The refineries and oil pipelines have leaked petroleum products over many years. An area of at least 500 ha is contaminated by free product light non-aqueous-phase liquid (LNAPL), affecting one third of Ploiesti’s water supplies. To date it has been possible to compensate by extending the well fields and using surface water, but the long-term sustainability of these measures has not been investigated. The Prahova and Teleajan rivers, tributaries of the River Danube, are also at risk. A conceptual map is presented to show the evolution of LNAPL contamination between 1980 and 2000, and the quantity of oil in each plume is estimated. Potential recovery of oil using a conventional pump-and-treat system is also calculated, with costs and possible revenue. An outline programme for investigation and remediation is presented, part of which is being implemented with a European Community grant. Although the severity of contamination was at least partly realised in the 1970s, only the recent move towards privatization could mobilize sufficient financial resources to address this problem and protect groundwater resources for future use.
Heat transfer and melting in subglacial basaltic volcanic eruptions: implications for volcanic deposit morphology and meltwater volumes
Authors: Wilson Lionel , Head James W.
Published: September 2007

Subglacial volcanic eruptions can generate large volumes of meltwater that is stored and transported beneath glaciers and released catastrophically in jökulhlaups. At typical basaltic dyke propagation speeds, the high strain rate at a dyke tip causes ice to behave as a brittle solid; dykes can overshoot a rock-ice interface to intrude through 20–30% of the thickness of the overlying ice. The very large surface area of the dyke sides causes rapid melting of ice and subsequent collapse of the dyke to form a basal rubble pile. Magma can also be intruded at the substrate-ice interface as a sill, spreading sideways more efficiently than a subaerial flow, and also producing efficient and widespread heat transfer. Both intrusion mechanisms may lead to the early abundance of meltwater sometimes observed in Icelandic subglacial eruptions. If meltwater is retained above a sill, continuous melting of adjacent and overlying ice by hot convecting meltwater occurs. At typical sill pressures under more than 300 m ice thickness, magmatic CO
2
gas bubbles form
c.
25 vol% of the pressurized magma. If water drains and contact with the atmosphere is established, the pressure decreases dramatically unless the overlying ice subsides rapidly into the vacated space. If it does not, further CO
2
exsolution plus the onset of H
2
O exsolution has the potential to cause explosive fragmentation, i.e. a fire-fountain that forms at the dyke-sill connection, enhancing melting and creating another candidate pulse of meltwater. The now effectively subaerial magma body becomes thicker, narrower, and flows faster so that marginal meltwater drainage channels become available. If the ice overburden thickness is much less than
c.
300m the entire sill injection process may involve explosive magma fragmentation. Thus, there should be major differences between subglacial eruptions under local or alpine glaciers compared with those under continental-scale glaciers.
The 1969 subglacial eruption on Deception Island (Antarctica): events and processes during an eruption beneath a thin glacier and implications for volcanic hazards
Authors: Smellie J. L.
Published: September 2007

A short-lived eruption of basaltic andesite to andesite on Deception Island in 1969 occurred from a series of fissures underneath a glacier. The glacier was thin (
c.
100 m) and the eruption created a large and sudden discharge of meltwater that overflowed the glacier, severely damaging buildings on the island. The eruption was unusually well documented and it illustrates several features of subglacial eruptions that are only poorly known and not well understood. In particular, overflowing meltwater is contrary to predictions based on existing simple hydrological models for eruptions beneath thin glaciers. The eruption is analysed in this paper and used as a model for the fluid dynamics and thermodynamics of eruptions beneath a thin glacier mainly composed of impermeable ice. It is suggested that, in eruptions of relatively fluid magmas with a low magma rise rate, volatiles and magma are able to decouple and subglacial melting is strongly influenced by the superheated magmatic and hydrothermal gases (mainly steam). Thus, melting is much faster than that due solely to coupled conductive (magma) and convective (meltwater) heat transfer. The influence of gasdriven melting also has an important effect on the shape of the meltwater cavity and may be at least partly responsible for the cylindrical ice chimneys developed above vents on Deception Island. The results of the study are important for reconstructing the shapes of englacial cavities melted above a vent. They also highlight the importance of glacier structure and densification, rather than simply glacier thickness, in determining the hydraulic evolution of an eruption. Even eruptions beneath thin glaciers can generate significant meltwater floods.
Facies analysis of proximal subglacial and proglacial volcaniclastic successions at the Eyjafjallajökull central volcano, southern Iceland
Authors: Loughlin S. C.
Published: September 2007

The long-lived (at least 0.78 Ma) Eyjafjallajökull volcano has been constructed during a period of dramatic climatic shifts, and has produced subaerial lavas and cinder cones, pillow lavas, hyaloclastite, monogenetic volcaniclastic sediments and polygenetic glacio-fluvial sediments. Subaqueous lithofacies are dominant and nine distinct cogenetic lithofacies associations are identified within the successions that are interpreted as the proximal deposits of subglacial eruptions. These associations are typically bound by unconformities and lie directly on thin diamictites or glaciated surfaces; epiclastic sedimentary rocks are absent. The lithofacies include subaqueous sheet lava flows, lobate flows, pillow lavas, breccias, hyaloclastite and hyalotuff generated by eruption of mainly basaltic lavas. Lavas associated with massive hyaloclastite breccias commonly lie on or intrude cogenetic redeposited hyalotuff, indicating rapid changes in style of activity from explosive to effusive. This suggests that the vent was initially subaqueous but became subaerial as meltwater drained away down-slope beneath temperate ice sheets. In other instances, probably under thicker ice, the eruptions were effusive throughout but lava was subjected to intense steam explosivity. There is abundant evidence that volcaniclastic material was transported downslope by mass flow, grain flow and traction currents (i.e. by running water). Lithofacies associations that ponded in ice-dammed water commonly comprise thick redeposited tephra overlain by a ‘passage zone’ of hyaloclastite and then subaerial lavas. These deposits are voluminous but conditions suitable for ponding of large volumes of water were not common in the evolution of this large volcano.

During the early stages of volcano growth, eruptive deposits were emplaced on the gentle slopes of the growing cone during both glacial and interglacial periods. Glacial erosion modified the growing edifice and, as a result, younger deposits (<600 ka) tend to be valley-confined. The unconformities produced during glacial advance represent significant time gaps within the succession. Observations support the hypothesis that there were higher volcanic production rates during periods of deglaciation, probably as a result of the rapid decrease in lithostatic pressure as ice melted.
Glacial influences on morphology and eruptive products of Hoodoo Mountain volcano, Canada
Authors: Edwards B. R. , Russell J. K.
Published: September 2007

Hoodoo Mountain volcano (HMV), a Quaternary composite volcano in northwestern British Columbia, is a well-exposed example of peralkaline, phonolitic icecontact and subglacial volcanism. Its distinctive morphology and unique volcanic deposits are indicative of subglacial, within-ice, and/or ice-contact volcanic eruptions. Distinct ice-contact deposits result from three different types of lava-ice interaction: (1) vertical cliffs of lava, featuring finely jointed flow fronts up to 200 m in height, resulted from lava flows being dammed and ponded against thick masses of ice; (2) pervasively-jointed, dense lava flows, lobate intrusions, and domes associated with mantling deposits of poorly-vesiculated breccia are derived from volcanic eruptions contained beneath relatively thick ice; and (3) an association of pervasively-jointed, highly-vesicular lava flows or dykes encased by vesicular hyaloclastite of identical composition formed by eruption under and/or through relatively thin ice. The distribution of these three deposit types largely explains the distinctive morphology of Hoodoo Mountain and can be used to reconstruct variations in ice thickness surrounding the volcano since
c
.85 ka. Our analysis suggests that at
c
.85 ka Hoodoo Mountain erupted underneath ice cover of at least several hundred metres. At
c
.80 ka eruptions were no longer subglacial, but the edifice was surrounded by ice at least 800 m high that dammed lava flows around the perimeters of the volcano. After a period of eruptions showing no apparent evidence for ice interaction, from <80 to >40 ka, subglacial eruptions began again, signalling the build-up of regional ice levels. Local ice thickness during these eruptions may well have been over 2 km thick.
Effusive intermediate glaciovolcanism in the Garibaldi Volcanic Belt, southwestern British Columbia, Canada
Authors: Kelman M. C. , Russell J. K. , Hickson C. J.
Published: September 2007

The Garibaldi Volcanic Belt (GVB) in southwestern British Columbia is dominated by intermediate composition volcanoes in a setting that has been intermittently subjected to widespread glaciation. The glaciovolcanic features produced are distinctive, and include flow-dominated tuyas, subglacial domes, and ice-marginal flows. Flow-dominated tuyas, which are intermediate in composition, are unlike conventional basaltic tuyas; they consist of stacks of flat-lying lava flows, and lack pillows and hyaloclastite. They are inferred to represent subglacial eruptions that ultimately breached the ice surface. Subglacial domes occur as steep-sided masses of heavily-jointed, glassy lava, and represent eruptions that were entirely subglacial. Ice-marginal flows derive from subaerial flows that were impounded against ice.

Two unique aspects of GVB glaciovolcanic products are the presence of flow-dominated tuyas and the apparent scarcity of primary fragmental deposits. These unique features result from lava composition, the minimization of direct lava-water contact during eruptions, and topography. Composition influences morphology because eruption temperature decreases, and viscosity and glass transition temperature both increase with silica content. The result of this is that silicic subglacial volcanoes melt less water and are less likely to trap it near the vent, leading to the formation of structures whose shapes are strongly influenced by the surrounding ice. Topography also enhances meltwater drainage, favours lava flow impoundment in ice-filled valleys, and may, through erosion, influence the observed distribution of fragmental glaciovolcanic deposits.
Volatiles in basaltic glasses from a subglacial volcano in northern British Columbia (Canada): implications for ice sheet thickness and mantle volatiles
Authors: Dixon J. E. , Filiberto J. R. , Moore J. G. , Hickson C. J.
Published: September 2007

Dissolved H
2
O, CO
2
, S and Cl concentrations were measured in glasses from Tanzilla Mountain, a 500 m-high, exposed subglacial volcano from the Tuya-Teslin region, north central British Columbia, Canada. The absence of a flat-topped subaerial lava cap and the dominance of pillows and pillow breccias imply that the Tanzilla Mountain volcanic edifice did not reach a subaerial eruptive phase. Lavas are dominantly tholeiitic basalt with minor amounts of alkalic basalt erupted at the summit and near the base. Tholeiites have roughly constant H
2
O (
c.
0.56 ± 0.07 wt%), CO
2
(<30 ppm), S (980 ± 30 ppm) and Cl (200 ± 20 ppm) concentrations. Alkalic basalts have higher and more variable volatile concentrations that decrease with increasing elevation (0.62–0.92 wt% H
2
O, <30 ppm CO
2
, 870–1110 ppm S and 280–410 ppm Cl) consistent with eruptive degassing. Calculated vapour saturation pressures for the alkalic basalts are 36 to 81 bars corresponding to ice thicknesses of 400 to 900 m. Maximum calculated ice thickness (
c.
1 km) is at the lower end of the range of predicted maximum Fraser glaciation (
c.
1–2 km), and may indicate initiation of volcanism during the waning stages of glaciation. Temporal evolution from tholeiitic to alkalic compositions may reflect compositional gradients within a melting column, instead of convective processes within a stratified magma chamber. The mantle source region for the subglacial volcanoes is enriched in incompatible elements similar to that for enriched mid-oceanic ridge basalt (e.g. Endeavour Ridge) and does not contain residual amphibole. Thus, metasomatic enrichment most likely reflects small degree partial melts rather than hydrous fluids.
The hyaloclastite ridge formed in the subglacial 1996 eruption in Gjálp, Vatnajökull, Iceland: present day shape and future preservation
Authors: Gudmundsson M. T. , Pálsson F. , Björnsson H. , Högnadóttir ℋ
Published: September 2007

In the Gjálp eruption in 1996, a subglacial hyaloclastite ridge was formed over a volcanic fissure beneath the Vatnajökull ice cap in Iceland. The initial ice thickness along the 6 km-long fissure varied from 550 m to 750 m greatest in the northern part but least in the central part where a subaerial crater was active during the eruption. The shape of the subglacial ridge has been mapped, using direct observations of the top of the edifice in 1997, radio echo soundings and gravity surveying. The subglacial edifice is remarkably varied in shape and height. The southern part is low and narrow whereas the central part is the highest, rising 450 m above the pre-eruption bedrock. In the northern part the ridge is only 150–200 m high but up to 2 km wide, suggesting that lateral spreading of the erupted material occurred during the latter stages of the eruption. The total volume of erupted material in Gjálp was about 0.8 km
3
, mainly volcanic glass. The edifice has a volume of about 0.7 km
3
and a volume of 0.07 km
3
was transported with the meltwater from Gjálp and accumulated in the Grímsvötn caldera, where the subglacial lake acted as a trap for the sediments. This meltwater-transported material was removed from the southern part of the edifice during the eruption. Variations in basal water pressure may explain differences in edifice form along the fissure. Partial floating of the overlying ice in the northern part is likely to have occurred due to high water pressures, reducing confinement by the ice and allowing lateral spreading of the edifice. The overall shape of the Gjálp ridge is similar to that of many Pleistocene hyaloclastite ridges in Iceland. Future preservation of the Gjálp ridge will depend on the rate of glacial erosion it will suffer. Besides being related to future ice flow velocities, the erosion rate will depend on the rate of consolidation due to palagonitization and shielding from glacial erosion while depressions in the ice are gradually filled by ice flow directed towards the Gjálp hyaloclastite ridge.
Subglacial volcanic features beneath the West Antarctic Ice Sheet interpreted from aeromagnetic and radar ice sounding
Authors: Behrendt John C. , Blankenship D. D. , Morse D. L. , Finn C. A. , Bell R. E.
Published: September 2007

The West Antarctic Ice Sheet (WAIS) flows through the volcanically active, late Cenozoic West Antarctic rift system. Active subglacial volcanism and a vast (> 10
6
km
3
) extent of subglacial volcanic structures have been interpreted from aerogeophysical surveys over central West Antarctica in the past decade, combined with results from 1960s and 1970s aeromagnetic profiles over the WAIS. Modelling of magnetic anomalies constrained by radar ice sounding shows volcanic sources at the base of the ice throughout large areas, whose subglacially erupted hyaloclastite edifices have been eroded by moving ice, as in Iceland. The 1800 m-high divide of the WAIS is underlain by the 400 km-long volcanic Sinuous Ridge, which rises above sea level; most hyaloclastite edifices there have also been glacially removed, indicating migration of the ice divide through time. Northeast of the divide of the WAIS there is a 400-nT positive magnetic anomaly over the shallowest, most rugged bedrock topography (elevation +380m above sea level), probably comprising subaerially erupted flows erupted when the Sinuous Ridge area was deglaciated. Uplift of the Sinuous Ridge may have forced the advance of the WAIS. Other aspects of the subglacial volcanism in Antarctica can be observed in Iceland and have a direct bearing on our understanding of the subglacial conditions of the WAIS and its dynamics.
Spectroscopic and geochemical analyses of ferrihydrite from springs in Iceland and applications to Mars
Authors: Bishop J. L. , Murad E.
Published: September 2007

Ferrihydrite samples were collected from a thermal spring and a cold stream in the Landmannalaugar region of Iceland. Chemical and spectroscopic analyses have been performed on the air-dried and fine-grained fractions of these samples. The ferrihydrite from the cold stream is a pure sample, containing small amounts of Ca, P and Si. The ferrihydrite from the thermal spring is a less pure sample, containing larger amounts of amorphous Si and P with some of the Si incorporated in the ferrihydrite structure. The spectral character of these Icelandic ferrihydrites is compared with those of synthetic ferrihydrites and other iron oxide/oxyhydroxide minerals. Ferrihydrite is characterized by a broad Fe
3+
excitation band near 10 900 cm
−1
(
c.
0.92 μm), a strong Fe-O vibrational feature near 475 cm
−1
(
c.
21 μm), and multiple bands due to H
2
O and OH. Highly pure ferrihydrite has a pair of spectral bands near 1400 and 1500 cm
−1
(
c.
7 μm). Natural ferrihydrites frequently exhibit an extra band near 950–1050 cm
−1
(
c.
10 μm) that is attributed to Si-O bonds. Hydrothermal springs may have been present at one time on Mars in association with volcanic activity. Ferrihydrite formation in such an environment may have contributed to the ferric oxide-rich surface material on Mars.
Distinguishing palagonitized from pedogenically-altered basaltic Hawaiian tephra: mineralogical and geochemical criteria
Authors: Schiffman P. , Southard R. J. , Eberl D. D. , Bishop J. L.
Published: September 2007

Palagonitization is a common, but imperfectly defined process that greatly modifies the physical and chemical properties of glassy basaltic tephra deposited in subaquatic/subglacial environments on Earth and perhaps Mars. It also results in textures and mineralogies that are distinct from other forms of (mainly pedogenic) low temperature alteration. Specifically, the process of palagonitization (1) initially results in the formation of ‘palagonitized glass’, a quasi- or nano-crystalline, rind-like material that contains smectite, as well as lesser amounts of other clays (e.g. serpentine), and (2) eventually results in consolidation of tephra, mediated through the accretion of palagonitized glass and later-formed authigenic cements. Conversely, pedogenic weathering of glassy basaltic tephra is characterized by disaggregation of tephra, and formation of a wide range of pedogenic products, including layer silicates (although not primarily smectite), short-range-order aluminosilicates and oxyhydroxides, whose composition reflects the intensity of the weathering environment. These mineralogical and textural properties can be readily recognized through a variety of techniques including electron microscopy/microprobe analysis, reflectance spectroscopy, X-ray diffraction and soil chemistry. Analyses of samples collected from the summit regions of Kilauea and Mauna Kea volcanoes on the island of Hawaii are presented here in order to illustrate differences between palagonitization and pedogenic weathering of glassy basaltic tephra. In the young Hawaiian tephras studied, palagonitization has occurred in response to hydrothermal activity shortly after deposition. Although some, non-hydrothermally affected tephras may eventually become palagonitized, those that have been strongly desilicated by intense pedogenic weathering will probably never become palagonitized.
Identifying bio-interaction with basaltic glass in oceanic crust and implications for estimating the depth of the oceanic biosphere: A review
Authors: Furnes H. , Thorseth I. H. , Torsvik T. , Muehlenbachs K. , Staudigel H. , Tumyr O.
Published: September 2007

The alteration of basaltic glass in the volcanic part of the oceanic crust is, to a substantial extent, biologically mediated. Evidence of microbial interaction with basaltic glass can be provided by a number of independent observations, such as: (1) Textures at the alteration front, generated by dissolution of the glass and subsequent precipitation. These bio-generated textures can be defined as a granular type (dominant) and a tubular type, and show size and form which are compatible with microbial etching. (2) Filament-like structures, representing organic remains, appear in connection with bio-generated textures. (3) Within areas of the bio-generated textures, particularly at the alteration front, DNA and ribosomal RNA have been demonstrated to be present in relatively young samples. (4) X-ray mapping shows that carbon and nitrogen invariably appear within the bio-generated textures, in young samples most strongly enriched at the alteration front. (5) Carbon isotopes (δ
13
C) in carbonates extracted from the glassy margin of pillows show highly variable values which can be explained in terms of bio-fractionation of the
12
C and
13
C isotopes. Estimates of the proportion of bio-genetic alteration products of basaltic glass, on the basis of textural relationships, suggest that bio-alteration is dominant compared to abiotic alteration in the upper 300 m of the oceanic crust, and declines to become insignificant at a depth of about 500 m.
Thermal expansion and its control on the durability of marbles
Authors: Zeisig Annette , Siegesmund Siegfried , Weiss Thomas
Published: September 2007

Marbles as ornamental stones as well as in their natural environments show complex weathering phenomena. The physical weathering of marbles due to thermal treatment is often discussed as the initial stage of deterioration. Eighteen different well-known marble types were selected to quantify experimentally the effect of heating and cooling within the temperature range of 20°C to 85°C while three different ramps at 40°C, 60°C and 85°C were performed. The marbles differ in composition from calcitic to dolomitic as well as in their fabrics. The average grain size varies from 50 μm up to 3 mm, while the grain boundary geometry differs from a granoblastic foam structure to those with weakly inequigranular-amoeboid structure. The lattice preferred orientations are also highly different in c-axis and a-axis distributions. With respect to the heating and cooling cycles three distinct groups of marbles can be distinguished: Type I is characterized by an isotropic thermal expansion (α) and large isotropic residual strain (permanent length changes); Type II exhibits an anisotopic α and no or small isotropic residual strains; while Type III shows an anisotropic α and anisotropic residual strain. Most samples show deteriorations due to thermal treatment, which cannot be uniformly explained without taking into account the rock fabrics. The magnitude and directional dependence of the thermal expansion is mainly controlled by the lattice and shape preferred orientation. The composition, grain size, grain boundary geometry and pre-existing microcracks modify in a more complex way the progressive loss of cohesion due to dilatancy caused by the anisotropic thermal expansion.
Experimental study on the variation in porosity of marble as a function of temperature
Authors: Malaga-Starzec Katarina , Lindqvist Jan E. , Schouenborg Björn
Published: September 2007

The current condition of many building claddings and historical monuments clearly reveals that they are not immune to weathering action due to daily or seasonal temperature changes. In this study, porosity changes by variation in temperature have been investigated for two marble types: one calcitic and one pure dolomitic. The samples were exposed to ascending temperatures from 40 to 200°C. The results indicate that intergranular decohesion starts between 40 and 50°C. Some significant differences in temperature response for these two marble types could be distinguished. The temperature range 40–60°C is easily reached on building surfaces in most European countries during the summer months. A better understanding of the effect that temperature has on the porosity of marble could be used to develop a methodology for assessing suitable conditioning of marble before testing as well as to suggest appropriate impregnation and/or surface treatments of buildings and outdoor sculptures.
Anisotropic technical properties of building stones and their development due to fabric changes
Authors: Strohmeyer Daniel , Siegesmund Siegfried
Published: September 2007

Technical properties of building stones are of critical importance in applied geosciences such as engineering geology, and also with respect to construction or building physics. Among the many factors which control the technical properties, special importance is given to the rock fabrics influencing the anisotropy of these technical properties. To demonstrate this relationship a sequence of mylonitic rocks, i.e. metagranitoid progressively deformed to mylonite and ultramylonite, was selected. The mineralogical and chemical composition of the protolith and mylonite is nearly identical. All investigated parameters (tensile strength, compressive strength, abrasive strength, magnetic susceptibility and ultrasound wave velocities) are anisotropic and finally controlled by the mineralogical composition and the different fabric elements like microstructural features, the crystallographic and shape preferred orientations and the state of microcracking. The development of the rock fabric with mylonitization, in particular the preferred orientation of mica, seems to be most important for the directional dependence of rock physical properties, at least in mica-rich rocks. However, various sets of microcracks, the degree of grain size reduction, the intensity of the foliation and the compositional layering can significantly modify the results. The interaction of superimposing parameters for different technical properties does not allow any simple cross-correlation.
Impact of endolithic biofilms on carbonate rock surfaces
Authors: Pohl Wolfhart , Schneider Jürgen
Published: September 2007

Almost all natural carbonate rock surfaces as well as carbonate building stones are ubiquitously colonized by micro-organisms such as cyanobacteria, chlorophyceae, fungi and lichens. This colonization occurs endolithically, mostly euendolithically, through active penetration into the rock. Freshly exposed surfaces, such as in glacial forelands of the Dachstein Mountains (Austria) show mature, fully differentiated endolithic colonization after only 15 years of atmospheric exposure. After a time period of 100 to 150 years, coverage of carbonate rock surfaces by endolithic biofilms is almost complete.

Most endolithic biofilms (lichens) show similar internal architecture. Under a residual, protective carbonate rock layer are photobiontic micro-organisms. They occupay a well defined zone between 150 to 300 μm beneath the rock surface. In this zone up to 60% of the rock substrate is replaced by microbial biomass. Within the photobiontic layer a constant recycling of cells takes place, where bacteria act as decomposers. Deeper beneath the substrate develops an initially dense, then progressively thinning hyphal network of the mycobiont (i.e. a fungus).

Significant differences in amounts and distribution of biomass were observed and quantified which are regional and climatic, but also local and surface age-controlled. Temperature, irradiation and water availability are presumed to be the primary factors. Evidence for a biogenic mechanical surface destabilization (grain loss, desquamation, exfoliation) as observed on siliciclastic rocks, was not found on natural carbonate rock surfaces.

The ‘life strategy’ of endolithic biofilms is adapted to conserve their substrates. It commences with quick emplacement within the rock, initially causing some material loss. However, as soon as the endolithic biofilm is established, approaching an equilibrium with the climatic and ecological conditions, it behaves essentially conservatively: it does not continue with growth increments or habitat enlargement.

This adaptation of euendolithic biofilms has a generally
more protective
than destructive impact on their carbonate rock substrates. These observations are important for a better understanding of weathering and deterioration processes, applicable to protection policies and maintenance of cultural monuments.
Biodeterioration of calcareous and granitic building stones in urban environments
Authors: Schiavon Nick
Published: September 2007

Scanning electron microscopy in secondary (SEM) and back-scattered (BSEM) mode associated with energy-dispersive X-ray spectroscopy has been used to investigate decay features associated with biological colonization of calcareous and granitic building stones in monuments and rock outcrops in the UK, Portugal and Spain. In combination with physical decay caused by lichen hyphae penetrating the stone substrate, this study reveals how chemical attack by organic acid exudates derived from metabolic activity of lichens and leading to the crystallization and growth of inorganic salt compounds within the stone microfabric is contributing to the destruction and weakening of the building stone surface. BSEM analysis is particularly useful in showing extensive dissolution and corrosion of mineral surfaces underneath biological patinas. Both Ca-sulphate (gypsum) and Ca-oxalate (weddellite) precipitates are clearly associated with the presence of fungal hyphae and bacterial activity particularly in the case of calcareous building stones; the Ca-oxalates present in the example examined are then the result of biomineralization processes and do not derive from past restoration treatments or from air pollution as suggested by many authors. In urban locations, lichenous cover may facilitate the deposition of particulate airborne pollutants on the stone surface. Biological patinas are by no means forming a protective layer on the biocolonized substrate; as is the case with sulphate or non-sulphate soiling patinas from urban air pollution, they act as localized sites of intense desegregation of the stone underneath. Their promot (but careful) removal and a biocidal treatment of the infested sites in the building is then suggested to avoid permanent loss of detail, particularly harmful in the case of carved surfaces.
Biofilms and their extracellular environment on geomaterials: methods for investigation down to nanometre scale
Authors: Hoppert M. , Berker R. , Flies C. , Kämper M. , Pohl W. , Schneider J. , Ströbel S.
Published: September 2007

On solid surfaces of building material, micro-organisms form a tightly attached layer that may affect the underlying substratum. The biofilm is mainly composed of cells and extracellular polymeric substances (EPS; mostly various polysaccharides). Attachment of the mature biofilm on the substratum is mediated by the EPS. For analysis by transmission electron microscopy, the biofilm structure must be maintained by appropriate methods that stabilize the organisms and especially the EPS. Specially adapted preparation techniques allow detachment of a surface biofilm or dissolution of the substratum without affecting the biofilm structure. The cellular and extracellular structures are retained in such a way that they are detectable by various specific marker systems.
Limestone weathering of historical monuments in Cairo, Egypt
Authors: Fitzner Bernd , Heinrichs Kurt , La Bouchardiere Dennis
Published: September 2007

Since pharaonic times local limestones have been used in Cairo for monument construction. Weathering damage on many historical stone monuments in Cairo is alarming. Studies on properties and weathering behaviour of the limestones were carried out by means of laboratory tests and in situ investigation of many historical monuments. The laboratory studies reveal considerable petrographical variations for the Middle Eocene limestones. The limestone weathering was assessed with respect to weathering forms, weathering products and weathering profiles. A classification scheme of weathering forms and their intensities was tailored to optimal applicability for all Cairo historical monuments constructed from limestones. Monument mapping has been applied for the detailed registration of weathering forms and as a basis for the quantitative rating of stone damage by means of damage categories and damage indices. For the historical monuments in the centre of Cairo the combined evaluation of weathering forms, weathering products and weathering profiles shows clear correlations between the development of weathering damage and salt loading of the limestones as a consequence of air pollution and rising humidity. They demonstrate the need and urgency for monument preservation measures.
Characterizing the construction materials of a historic building and evaluating possible preservation treatments for restoration purposes
Authors: Alvarez de Buergo Ballester M. , Fort González R.
Published: September 2007

The palace of Nuevo Baztán is a state-designated historic monument in central Spain built in the early eighteenth century. The main building material used in its facades is limestone. The aim of this investigation was to characterize the limestone, defining deterioration mechanisms contributing to the decay of the stone facades and testing a series of potential preservation treatments. The limestone is a biosparite; two microfacies were identified according to microscopic differences (limestones A and B) with distinct petrophysical characteristics mainly due to their different pore systems. Primary deterioration mechanisms were identified as those related to cycles of thermal and hygric stress, biodeterioration and those associated with structural movements. Main decay forms in the surface of the stone are erosion with material loss, spalling and flaking, chromatic alteration, fissures and biodeterioration. Conservation products prossessing water-repellent properties were therefore considered. From an initial selection of ten products, two siloxane-based products were ultimately determined to be the most effective on the basis of chromatic variables, water vapour permeability, water-stone contact angle, scanning electron microscope observations and durability (artificial ageing tests). Both products reduce water absorption rates and are expected to slow the rate of limestone decay. This study also demonstrates the value of advance testing of potential treatment methods before application in the field.
Investigations into provenance and properties of ancient building sandstones of the Zittau/Görlitz region (Upper Lusatia, Eastern Saxony, Germany)
Authors: Michalski Steffen , Götze Jens , Siedel Heiner , Magnus Michael , Heimann Robert B.
Published: September 2007

Mineralogical and technical properties were investigated of building sandstones from ancient monuments of the Zittau/Görlitz region (Germany) as well as material from potential source quarries. The complex study included macroscopic rock description and detailed investigations by polarizing microscopy (phase composition, texture, grain size distribution), cathodoluminescence (quartz types, feldspar and kaolinite content), scanning electron microscopy (accessories, pore cement, diagenetic grain surface features) as well as the analysis of open macroporosity (total water uptake) and the pore size distribution function (Hg porosimetry). For the first time, mineralogical and technical data were obtained for building sandstones of the Zittau region. The results not only confirmed earlier conjectures concerning different source areas for the ancient building sandstones of the Zittau and Görlitz area but also allowed the unequivocal assignment of historically used material to specific sandstone occurrences. The data obtained provide a comprehensive basis for the interpretation of weathering damage suffered by the historical monuments and give useful hints for their successful conservation and reconstruction.
Constraints on the structural development of Afar imposed by the kinematics of the major surrounding plates
Authors: Garfunkel Z. , Beyth M.
Published: September 2007

The development of the Afar rift-rift-rift triple junction is analysed from the view-point of the Nubia, Arabia and Somali plate kinematics. A variety of constraints allow definition of a range of kinematic models that approximate well to the plate motions with a resolution of a couple to tens of kilometres. Rigid plate kinematics probably cannot resolve smaller motions. The size and location of the new area that opened between the major plates is inferred from plate kinematics and this provides a framework in which to assess the structural development that accommodates plate separation.

The development of the Afar region was complicated by the presence of microplates — the Danakil and Aisha blocks — which results in a complex plate boundary geometry. This led to local deformation that does not directly reflect the divergence of the major plates, e.g. rotations of microplates and of minor blocks about vertical axes and strike-slip faulting. The opening of new area was accommodated by various crustal growth and accretion mechanisms, e.g. building of thick new igneous crust, normal seafloor spreading, and/or crustal stretching. Thus, plate motions by themselves do not determine the development of the plate boundaries, as this is strongly influenced by other factors such as lateral variations of the rates of magma supply (e.g. away from, and over, the Afar plume).

The plate boundaries changed — e.g. the Gulf of Aden spreading centre propagated westward
c.
2 Ma ago and normal seafloor spreading began along portions of the Red Sea axis since
c.
5 Ma ago — while there were no resolvable changes in the plate motions. Such changes therefore signify a reorganization of the way in which plate divergence and addition of new area is accommodated: diffuse extension may give way to separation along a narrow spreading centre, or new plate boundaries may form at the expense of other boundaries that became inactive.
Mantle upwellings, melt migration and the rifting of Africa: insights from seismic anisotropy
Authors: Kendall J.-M. , Pilidou S. , Keir D. , Bastow I.D. , Stuart G.W. , Ayele A.
Published: September 2007

The rifting of continents and eventual formation of ocean basins is a fundamental component of plate tectonics, yet the mechanism for break-up is poorly understood. The East African Rift System (EARS) is an ideal place to study this process as it captures the initiation of a rift in the south through to incipient oceanic spreading in north-eastern Ethiopia. Measurements of seismic anisotropy can be used to test models of rifting. Here we summarize observations of anisotropy beneath the EARS from local and teleseismic body-waves and azimuthal variations in surface-wave velocities. Special attention is given to the Ethiopian part of the rift where the recent EAGLE project has provided a detailed image of anisotropy in the portion of the Ethiopian Rift that spans the transition from continental rifting to incipient oceanic spreading. Analyses of regional surface-waves show sub-lithospheric fast shear-waves coherently oriented in a north-eastward direction from southern Kenya to the Red Sea. This parallels the trend of the deeper African superplume, which originates at the core-mantle boundary beneath southern Africa and rises towards the base of the lithosphere beneath Afar. The pattern of shear-wave anisotropy is more variable above depths of 150 km. Analyses of splitting in teleseismic phases (SKS) and local shear-waves within the rift valley consistently show rift-parallel orientations. The magnitude of the splitting correlates with the degree of magmatism and the polarizations of the shear-waves align with magmatic segmentation along the rift valley. Analysis of surface-wave propagation across the rift valley confirms that anisotropy in the uppermost 75 km is primarily due to melt alignment. Away from the rift valley, the anisotropy agrees reasonably well within the pre-existing Pan-African lithospheric fabric. An exception is the region beneath the Ethiopian plateau, where the anisotropy is variable and may correspond to pre-existing fabric and ongoing melt-migration processes. These observations support models of magma-assisted rifting, rather than those of simple mechanical stretching. Upwellings, which most probably originate from the larger superplume, thermally erode the lithosphere along sites of pre-existing weaknesses or topographic highs. Decompression leads to magmatism and dyke injection that weakens the lithosphere enough for rifting and the strain appears to be localized to plate boundaries, rather than wider zones of deformation.
Palaeomagnetic constraints on continental break-up processes: observations from the Main Ethiopian Rift
Authors: Kidane Tesfaye , Platzman E. , Ebinger C. , Abebe B. , Rochette P.
Published: September 2007

We report the first palaeomagnetic results from the Main Ethiopian Rift (MER), the northernmost sector of the East African rift system. This part of the MER shows an along-axis tectono-magmatic segmentation pattern similar to that of slow-spreading mid-ocean ridges, which developed during the past 1.9 Ma. The aims of our palaeomagnetic, structural and geochronological studies are to test plate kinematic models for the right-stepping, en echelon 60–80 km-long magmatic segments. Twenty palaeomagnetic sites were sampled on either basalt or ignimbrite outcropping in the region adjacent to, and within, the <1.9 Ma-old tectono-magmatic segments of Gademsa-Koka, Boset and Fentale-Dofan. Five K-Ar age determinations were made to bracket the age of units studied in the palaeomagnetic analyses. The natural remanent magnetization intensity possibly exhibited a unimodal distribution with a value of 6.6 A/m (σ = 5.6 A/m) for the basalts and a bimodal distribution with magnetization intensity of 0.69 A/m (σ = 0.55 A/m) and 0.03 A/m (σ = 0.02 A/m), statistically similar to values from previous studies in the Afar triple junction zone (e.g. Kidane
et al.
1999, 2002). Progressive heating, alternating field analysis, and susceptibility vs. temperature measurements indicated unblocking temperature ranging between 300 °C−600 °C for basalts and between 500 °C−660 °C for ignimbrites, suggesting the magnetic mineralogy to be titanomagnetite and magnetite for the former and magnetite and titanohematite for the latter. Palaeomagnetic measurements using both TH and AF technique revealed quasi-single component of magnetization with viscous remanent magnetization (VRM) on a few samples. Principal component analysis and statistical averaging resulted in an overall mean palaeomagnetic direction of (D
s
= 2.3°, I
s
= 7.8°, α
95
= 7, K = 26.9, N = 17) which is statistically identical to the expected direction (D = 1.9°, I = 13.5°, α
95
= 2.5, K = 105.6, N = 32) from the Apparent Polar Wander Path reference curve for Africa at 1.5 Ma (Besse & Courtillot 2003). The angular difference between the observed and expected directions above with their uncertainty is calculated to be 0.4° ± 7.5°. These results indicate that the Late Pliocene-Pleistocene rocks of the MER in the studied region do not suffer vertical axis rotation, arguing against transtensional and seafloor-spreading-transform kinematic models. We suggest that magma intrusion, rather than large offset faults, produce the right-stepping, en echelon magmatic segments of the MER, which is at the transition from continental to oceanic extension.