effect of microstructure and weathering on the strength anisotropy of porous rhyolite abstract to study the effect of microstructure and weathering on the strength anisotropy of rock unconfined compressive strength ucs tests were carried out on three porous rhyolites having the same original lithology but different weathering periods of 2600 20 000 and 40 000 years the rock is mainly composed of glassy groundmass with flow structure ucs tests were undertaken on a series of samples at 15 intervals from right angles to the flow structure 90 to parallel 0 where is the angle between the direction of the applied load and the direction of the flow structure the test results show that ucs values are maximum when 0 30 and minimum when 60 90 this differs from previous reports for layered anisotropic rocks such as sandstone sandy shale schist etc for which ucs values are maximum at 0 or 90 it is also found that ucs values for 60 90 reduce rapidly in the initial stage of weathering the first 20 000 years while for 0 30 the reduction rate increases after 20 000 years this shows that the effect of weathering on strength anisotropy is not uniform but depends on the weathering processes of the microstructures of the rock

middle terrace deposits of the tagus river in alpiarca portugal in relation to early human occupation abstract the stratigraphy and sedimentology of the q3 middle terrace alluvial sequence in the lower tagus river valley portugal were studied near the village of alpiarca approximately 40 km upstream from the estuarine area two main stratigraphic units were recognized separated by an important uncomformity the lower gravels unit lg consists of intercalations of medium to coarse gravel deposits mainly quartzitic with coarse sandy matrix organized in tabular bodies the overlying upper sands unit us consists of tabular sandy channel deposits and overbank fines the latter containing well developed paleosols and backswamp deposits showing a general aggrading trend apparently with varying rates available data indicate that deposition of the us took place under temperate climatic conditions within us deposits are several paleolithic archaeological sites the lower ones in the alluvial stratigraphy being middle acheulian whereas those embedded in overlying deposits are from bottom to top upper acheulian and micoquian some of these sites have been recently excavated the quartzite artifacts were apparently abandoned by early humans on the flood plain surface during deposition of the us unit and were subjected to limited reworking during their incorporation in the alluvium tl osl dating of sandy silty sediments though imprecise support archaeological evidence pointing to an age of 150 000 to 70 000 yr b p for the us unit

a multi proxy record of holocene climatic change in southwestern spain the laguna de medina cadiz palaeolimnological data diatoms ostracods foraminifera molluscs aquatic pollen and lithology from a radiocarbon dated sediment core from a saline lake the laguna de medina provide the first complete record of holocene lake level change for southwest spain for the last c 9000 cal years the lake has always been relatively shallow but has exhibited marked fluctuations in salinity and water depth especially in the earlier record when oscillations culminate in maximum lake levels from c 6960 6680 cal bp c 6070 5830 bp indicating enhanced early to mid holocene humidity and a mid holocene humidity maximum prolonged shallowing thereafter reflects in part increased aridity in the later holocene lake desiccation followed by a c 800 yr phase zone 2 of major limnological change commencing at c 8000 cal bp c 7200 bp and a number of other abrupt desiccation events are also noteworthy the mid holocene maximum is consistent with widespread evidence for high lake levels around 6000 bp but t

petrological and trace element geochemical features of the okete volcanics western north island new zealand the okete volcanics form small volume monogenetic volcanoes situated around the flanks of larger tholeiitic cones of the plio pleistocene alexandra volcanics in the back arc tectonic environment of western north island new zealand the lavas and tuffs of the okete volcanics have compositions which include basanites alkali olivine basalts olivine tholeiites and hawaiites most rocks have mg numbers 66 250 p p m ni 500 p p m cr and often contain ultramafic xenoliths which indicate that they are very close to being primary magmas the okete volcanics show geochemical trends from basanite to hawaiite of progressive depletion of both compatible and incompatible trace elements progressive increase in al2o3 and heavy ree and y enrichment with crossingover ree patterns in the hawaiites these geochemical trends can be accounted for by varying degrees of partial melting of a light ree enriched garnet peridotite with subsequent modification of the melts near source or during ascent by fractional crystallization of olivine and minor clinopyroxene mass balance calculations cannot quantitatively constrain the degree of partial melting or fractional crystallization but nevertheless indicate that the okete alkali olivine basalts olivine tholeiites and hawaiites have been derived by successively larger degrees of partial melting relative to basanites and have also been progressively more modified by fractional crystallization than have the basanites sources of the alkalic melts lay at depths corresponding to 20 kb and most of the ultramafic xenoliths apart from some which may be cognate cumulates are unrelated to the magmas that brought them to the surface magmas have changed in composition with time from older smaller volume volcanoes of basanite or alkali olivine basalt compositions to younger and more voluminous volcanoes which contain hawaiites the geochemical trends shown by the okete volcanics and their spatial association with voluminous tholeiitic volcanism are features which are different from those observed elsewhere in the pliocene to recent basaltic fields of northern north island and may be related to their unique tectonic setting situated in a distinct structural domain

weathering mechanisms and their effects on the landsliding of ignimbrite subject to vapor phase crystallization in the shirakawa pyroclastic flow northern japan abstract ignimbrite which is consolidated by vapor phase crystallization is weathered in humid regions to form a special type of weathering profile that consists of a hydrated zone an exfoliated zone and a disintegrated zone from the depth to the ground surface with each zone having a basal front the ignimbrite is hydrated first and loses a significant amount of phosphorous at the hydration front where rock forming tridymite is dissolved and cristobalite is precipitated the ignimbrite further loses its alkali and alkali earth components at the top of the hydrated zone by reacting with reactive water from the exfoliated zone then the leached layers are exfoliated and become part of the exfoliated zone and then they soften significantly at the top of the exfoliated zone rock is disintegrated so completely that rock texture disappears water from rainstorms infiltrates down to the exfoliation front but penetrates only slightly further downward thus saturating the weathered rock in the exfoliated and disintegrated zones and leading to a landslide with a slip surface within the exfoliated zone

quality ranking of twelve columnar basalt occurrences in the northern portion of the parana basin brazil this paper presents results obtained from a study of basal degrading conducted on samples of basaltic rocks found in the northern part of the parana basin in the state of sao paulo brazil to meet the objectives of the study natural and accelerated alteration tests were carried out followed by a comparison of the quantitative analysis of the two alteration processes the combined analysis of the information proved to be very useful tool for rock qualification and the quantification of alterability thus providing a basis for comparative analysis of massive and columnar jointed basalt relative to their use as aggregate for civil construction purposes

deep weathering of a group of thick argillaceous limestone rocks near three gorges reservoir central china rock mass characterization is one of the most basic and important tasks in rock mechanics and engineering literature review indicates that although there are many publications available on weathered rocks there are few reports in english on weathered argillaceous limestone rocks and their chemical and mechanical properties this paper presents a case study of characterizing a group of highly weathered thick argillaceous limestone rocks most importantly they can be easily and quickly decomposed into soils after they are exposed due to excavation consequently they would substantially lose their mechanical strengths geohazards such as landslides and sinkholes could occur in uncovered highly weathered argillaceous limestone rocks the problematic weathered rocks were found during the development of a new town in upper mountains above the three gorges reservoir on yangtze river in central china in the past 20 years the factual data are presented on the changes of chemical compositions and mechanical properties of the weathered argillaceous limestone rocks due to chemical weathering some empirical correlations are given to quantify the changes in their uniaxial compressive strength and deformation moduli in terms of their contents of calcium carbonate the data and findings presented in the paper can be useful to future urban development in geologically poor mountainous environments occupied by highly weathered argillaceous limestone rocks in the world

late quaternary marine mollusca as palaeoenvironmental proxies a compilation and assessment of basic numerical data for ne atlantic species found in shallow water abstract temperature salinity and depth limits are given for selected molluscs from boreal and arctic regions of the ne atlantic and adjacent shelf seas the significance of the data for palaeoenviromental analysis is briefly discussed

mesozoic petrotectonic development of the sawyers bar suprasubduction zone arc central klamath mountains northern california the sawyers bar area of the central klamath mountains california consists of three tectonically juxtaposed supracrustal units 1 on the east the stuart fork metabasalt metachert metagraywacke terrane above the low angle east dipping soap creek ridge thrust 2 the medial north fork ophiolitic terrane composed of intercalated st clair creek laminated cherts and fine grained quartzofeldspathic argillites interstratified with and overlain by two mafic igneous largely extrusive suites north fork sensu stricto mildly alkaline basalts and salmon river basaltic diabasic gabbroic arc tholeiites and 3 the cherty eastern hayfork metagraywacke melange terrane west of the minor high angle twin sisters fault mineral and bulk rock elemental and isotopic data integrated with geologic mapping document deformation and fluid rock interaction in the upper few kilometers of a suprasubduction zone basaltic arc during tectonic accretion to the western margin of north america or a nearby offshore arc the following history is advanced light rare earth element ree enriched arc tholeiites and alkaline basalts and distal turbidites of the north fork and eastern hayfork terranes were deposited in a subsea environment during permian triassic and earliest jurassic time toward land subduction resulted in production of the high pressure stuart fork blueschist complex then its exhumation ca 227 ma submarine eruption and sedimentation continued outboard during early and middle jurassic time producing the west facing north fork oceanic arc and adjacent tectonically disrupted eastern hayfork melange these two terranes underwent low temperature alteration by seawater at 100 200 c and 100 mpa alkali exchange and modest mg enrichment were accompanied by increases in greenstone bulk rock 18o values from 6 to 10 preceding and during initial stages of island arc formation at 175 200 ma by the end of this time the outboard western hayfork calc alkaline arc had accreted to the eastern hayfork terrane suturing of the north fork oceanic arc beneath the exhumed landward stuart fork terrane at 165 170 ma resulted in regional folding and subgreenschist to greenschist facies metamorphism pervasive recrystallization took place without substantial chemical or isotopic exchange under conditions of 300 425 c and 300 100 mpa metamorphic grade is higher in the north and lower in the south east descending subduction or transpression continued seaward and granitoid plutons were emplaced locally 159 164 ma heating adjacent wall rocks to a maximum of 500 600 c at pressures of 200 300 mpa the temperature increase caused devolatilization of metasediments and the exchange of high 18o fluids with intimately intercalated greenstones 18o values in metavolcanic rocks locally increased to 15 subsequent cooling yielded 150 164 ma apparent mineral ages for the metamorphic aureoles minor intrusion took place at the end of jurassic time when distinctive muscovite porphyry felsite dikes transected the stuart fork north fork thrust contact formation of hydrothermal gold bearing quartz veins dated as 147 3 ma may be associated with this event cenozoic exhumation resulted in range front faulting and erosion the documented interplay between phanerozoic convergence and or transpression and petrochemical evolution in a suprasubduction zone setting provides an illuminating model for growth of the sialic crust

quantitative assessment of weathering degree of the touzhai rock avalanche deposit in southwest china abstract weathering is one of the main preparatory causal factors for rock avalanche events and weathering assessment of involved materials can refine understanding of geomorphic processes of this class the weathering degree of the deposit of the touzhai basalt rock avalanche in china is quantitatively evaluated herein through an integrated geochemical analysis coupled with meso and micro scopic examination of fragments which can help to understand the inhomogeneity of weathering in rock slopes the clasts of 12 size classes of the debris making up the deposit ranging from meter sized boulder to fines of

crustal structure of the northwestern basin and range province and its transition to unextended volcanic plateaus 1 the northwestern margin of the basin and range province is characterized by a transition from low magnitude 20 extension in northwestern nevada to relatively unextended volcanic plateaus in northeastern california seismic velocity and potential field modeling provides new control on the mesozoic to present tectonic evolution of this poorly understood portion of the u s cordillera we document 20 crustal thinning associated with basin and range extension from a crustal thickness of 37 km under northeastern california to 31 km under northwestern nevada that is consistent with the amount of extension recorded in the upper crust in northwestern nevada suggesting the crustal response to extension was relatively homogeneous over the entire crustal column our modeling also shows a well defined 80 km wide zone of unusually low upper crustal velocities 5 9 6 1 km s that coincide with the surface location of sparse cretaceous granites locating the elusive northern extension of the sierra nevada batholith through northwestern nevada for the first time in the subsurface combining geological and geophysical data we reconstruct the late cretaceous to present crustal evolution of this region documenting an interplay between magmatic addition to the crust erosional exhumation sedimentation and extension that has reversed the direction of crustal thinning from a west facing continental margin to an east facing interior basin margin over this time interval finally we find no evidence in northwestern nevada for unusually thick crust 40 km prior to basin and range extension

weathering of the oporto granite geotechnical and physical properties abstract this paper characterizes the weathering products of the two mica oporto granite in terms of its mineralogical chemical geotechnical and physical properties this information is used to identify a physical property that can be used as an index of the degree of weathering and to estimate other properties in outcrop the oporto granite is always weathered and weathering profiles frequently exceed 20 m within these profiles granitic saprolites are composed of quartz feldspars and some mica with kaolinite and gibbsite as final weathering products the average percentage of secondary minerals determined by bulk x ray diffraction xrd is low in both weathered rock 2 4 and saprolite 8 7 geotechnically the saprolites exhibit no or low plasticity plasticity index pi 12 the skeleton character of the saprolites is reflected in the significant proportion of fines 29 5

chemical weathering of basalts southwest iceland effect of rock crystallinity and secondary minerals on chemical fluxes to the ocean river ground and peat water from a basaltic catchment area laxa in kjos southwest iceland were sampled and analyzed for major element concentrations to define the effect of glassy versus crystalline basalt the formation of secondary minerals and runoff on fluxes of dissolved elements to the ocean the proportions of the dissolved solids in the water samples derived from precipitation air and rock weathering were estimated the amounts of na mg ca k and s originating from precipitation were calculated from the respective solute cl marine ratios and the estimated aqueous cl originated from precipitation which was calculated using measured b content of the waters and b cl molal marine and rock ratios the rock contribution from weathering ranged from 22 to 46 percent of the total dissolved solids of the waters iron and al showed low mobility compared to na this was primarily due to consumption of these elements by ferrihydroxides allophane imogolite and clay minerals also si and to a lesser degree ca show apparent slightly lower mobility than na these results are in good agreement with these phases being dominant in the soils of the study area wada and others 1992 and the main secondary minerals of basaltic glass in iceland crovisier and others 1992 reaction progress calculations support these findings according to a model interaction of basaltic glass and meteoric water al fe and si are consumed by amorphous fe and al hydroxides and imogolite and allophane at low reaction progress with increasing reaction progress ca fe mg smectite became the primary secondary minerals limiting the mobility of ca fe mg si and al these findings suggest that the weathering in the laxa in the kjos catchment area has evolved into the beginning of the smectite weathering stage and that it is dominated by a relatively low reaction progress and a high water to rock ratio in the present study the effect of runoff and rock crystallinity was quantified for dissolved elemental fluxes temperature lithology other than rock crystallinity and rock age were similar in all of the catchment areas in this study silica ca f s al k mg and b had a very similar dependence on runoff on the other hand na fluxes were found to be less dependent on runoff and fe fluxes were found to be independent of runoff basaltic glass dissolves faster than fully crystallized basaltic rocks gislason and eugster 1987a therefore increased glass content of the primary rocks is thought to increase the leaching and elemental fluxes at constant runoff however because some of the solutes particularly al and fe were highly influenced or even controlled by the formation of secondary minerals this increasing dissolution with increasing glass content was hidden on the other hand basaltic glass was observed to enhance the fluxes of more mobile elements like na si ca f and s by a factor of 2 to 5 at a constant runoff of 200 cm yr constant vegetative cover and 0 to 100 percent glass content of the rocks the k and mg fluxes were found to be independent of rock crystallinity however runoff alone cannot explain the fluxes of these elements and it seems that vegetative cover and seasonal variations in biomass activities influence the k and mg fluxes

mesozoic transpression transtension subduction and metallogenesis in northern and central california middle paleozoic to middle jurassic terrane assemblies in the klamaths and sierran foothills consist of mafic ultramafic complexes fine grained terrigenous strata derived from previously accreted continental margin belts sutured oceanic terranes reflect c 230 myr of margin parallel slip involving chiefly transtension and transpression quartzofeldspathic clastic rocks and blueschists eclogites are very rare little devolatilization occurred at magmagenic depths hence coeval hydrothermal ore deposits and granitoids are uncommon in contrast nearly head on cretaceous subduction of the farallon plate generated the massive klamath sierra nevada volcanic plutonic arc reflecting dewatering of the eastward descending oceanic lithosphere in the magmagenic zone immature great valley forearc and franciscan trench deposits shed from the arc record c 70 myr of rapid crustal growth au bearing solutions rising from magmagenic depths exsolved from plutons and expelled from heated wall rocks were mobilized attending arc construction precipitation of gold bearing quartz veins occurred where h2o co2 bearing fluids encountered major geochemical discontinuities in the wall rocks

re assessment of chemical weathering indices case study on pyroclastic rocks of hong kong abstract quantitative and objective characterization of weathered states of rock by means of chemical weathering indices has significant potential in ground investigation practice this paper reviews more than thirty different chemical indices and re assesses their variations along a weathered profile developed over pyroclastic rocks under subtropical conditions chemical weathering indices are principally based on the basic assumption that distributions of chemical elements as well as loss on ignition loi content along the profile are mainly regulated by the degree of weathering however this study clearly demonstrates that the behavior of chemical elements and loi during weathering depend not only on the degree of weathering but also on microenvironmental conditions that control the type and abundance of clay minerals and sesquioxides and thus determine the level of heterogeneity of the profile it is suggested that signatures of chemical weathering should be used to establish a framework for the interpretation of the heterogeneity level and the prediction of variability in engineering properties rather than for quick classifications using chemical weathering indices

engineering geology of basaltic residual soil in leiqiong southern china the physical mechanical chemical mineralogical and microstructural properties of basaltic residual soil obtained from leiqiong area in southern china were examined emphasis was placed on the influences of minerals oxides and the soil fabric on engineering geological characteristics particularly on strength and deformation properties distinctive properties such as high strength and low compressibility relative to high void ratios high liquid limits and low natural densities were explained the soil fabric with the cement bond formed by iron oxides was considered as the main factor that caused to peculiar mechanical behavior whereas mineralogy and climate processes also played important roles under the influence of repeated cycle of alternate wetting and drying the residual soil generated a large collapsible deformation upon soaking and its strength significantly decreased because of the derogation of cement bond the formation of microcracks and the weakening of microstructure failure zones

the effects of precipitation gradients on river profile evolution on the big island of hawai i to better understand how climate affects bedrock river incision and long term landscape evolution in the absence of tectonic forcing we quantify differences in the longitudinal profiles of eroding bedrock channels across the kohala peninsula on the northern tip of the big island of hawai i an orographic rainfall gradient causes mean annual precipitation rates to vary by over an order of magnitude from greater than 4000 mm yr on the wet side to less than 250 mm yr on the dry side of the peninsula channels on the wet side are relatively deeply incised into the surrounding landscape and have developed profiles in which slope increases downstream in upstream reaches convex form and decreases downstream in downstream reaches concave form wet side river channels have relatively large 10 30 m vertical steps or knickpoints in the convex zone in contrast channels on the dry side of the peninsula are more shallowly incised have developed nearly straight longitudinal profiles in which channel slope does not significantly change from upstream to downstream and have smaller knickpoints channel profile form changes from straight to convex concave at a watershed averaged mean annual precipitation rate of between 1300 and 1750 mm yr suggesting a climatic threshold in this landscape above which bedrock incision rates are enhanced valley depth used as a proxy for the magnitude of channel incision increases with increasing mean annual precipitation and is consistent with a similar fluvial incision threshold while the lithology is entirely basalt incision patterns also appear to be affected by spatial differences in bedrock weathering due to both local climate and basalt flow age the older and more weathered polol basalts 260 450 ka are capped by the younger haw basalt series 120 260 ka and we interpret that heterogeneous weathering of these units influences channel form relief sediment production and knickpoint development

vertical saltmarsh accretion and its relationship to sea level in the severn estuary u k an investigation using foraminifera as tidal indicators saltmarsh vertical accretion has been used as a proxy for sea level rise in previous studies on the assumption that accretion is in quasi equilibrium with sea level rise this assumption requires verification in each case as accretion may lag or exceed sea level rise leading to under or over estimates of sea level rise respectively verification may be provided by biostratigraphic analysis where biological remains in saltmarsh sediments may be related to former tide levels foraminifera are well suited as studies of modern saltmarshes have demonstrated distinct tidal relationships which may be used to calibrate downcore temporal foraminifera sequences it is hypothesized that depending on the relationship between sea level rise and accretion quasi equilibrium submergence and emergence foraminifera sequences may be recognized these are explored here in a severn estuary u k saltmarsh where an emergence foraminifera sequence is identified suggesting that previous sea level rise rates for the severn estuary based on saltmarsh accretion rates may be over estimates wider consequences of this may include over estimation of regional crustal subsidence rates required to accommodate artificially high sea level rise rates saltmarsh accretion rates are clearly not a suitable proxy for sea level rise in all cases and as such each saltmarsh requires biostratigraphic evaluation to establish sea level rise accretion relationships preferably independent sea level index points slips should be used over saltmarsh accretion rates in constructing sea level histories

lateglacial and holocene environmental changes in portuguese coastal lagoons 2 microfossil multiproxy reconstruction of the santo andre coastal area benthic foraminiferal ostracod calcareous nannoplankton and diatom assemblages have been analysed from the 25 45 sedimentary succession of a borehole drilled in the santo andre lagoon southwestern portugal the zones and subzones recognized according to their microfossil content have been used to define six palaeoenvironmental stages extending from the lateglacial to the present stage a and the lower part of stage b 14 2 to 10 0 ka represent a postglacial terrestrial environment when sea level was below present following eustatic sea level rise a normal marine open bay environment established during the upper part of stage b 10 0 to 5 4 ka before 5 4 ka a coastal lagoon developed as a consequence of a sandy barrier formation since then natural variation in the permeability of the detrital barrier through time has been the primary control of the physical chemical and biological features of the lagoonal environment during stage c 5 4 to 3 6 ka as a freshwater dominated lagoon stage d 3

relationships between chemical weathering indices and physical and mechanical properties of decomposed granite abstract chemical weathering is one of the dominant mechanisms for weathering of granite in subtropical and tropical regions resulting in modifications of its chemical physical and mechanical properties thus the changes in chemical properties may provide insight about the changes in physical and mechanical properties of weathered granite in this paper three quantitative chemical weathering indices are correlated to the dry density of decomposed granite a linear relationship is found between each chemical weathering index and dry density for granitic saprolites mobiles index i mob gives the highest coefficient of correlation among the three chemical weathering indices further investigations were conducted to establish the relationships between i mob and other physical and mechanical properties of granitic saprolites the test results showed that fines content increases with increasing i mob but peak strength increases with decreasing i mob the peak states of granitic saprolites are consistent with rowe s stress dilatancy relationship dilatancy increases with decreasing i mob that contributes to a higher peak strength based on some test results presented in this study it seems that i mob could be a good indicator to quantify the effects of chemical weathering on physical and mechanical properties of granitic saprolites

lateglacial and holocene environmental changes in portuguese coastal lagoons 1 the sedimentological and geochemical records of the santo andre coastal area the sedimentological and geochemical study of a core corresponding to sedimentation in the santo andre lowland since 14 000 bp allowed the reconstruction of environmental changes of this area and discussion of the relative importance of local versus global forcing factors responsible for its evolution the pre holocene section of the core represents terrestrial sedimentation in a fluviatile environment contemporaneous of a low sea level and a distal shoreline sediment inputs were terrestrial and resulting from intensive weathering and high erosion rate in the adjacent watershed during the early holocene c 10 020 to 5380 bp the sea invaded this lowland and defined an open marine shallow environment corresponding to a wide gulf which has been disturbed by multiple terrestrial inputs that might have been induced by massive episodes of fluvial discharge the first symptoms of confinement were noticed close to 5400 bp and c 5380 bp a major environmental threshold occurred possibly reflecting the marke

palynological evidence for climatic change and human activity during the holocene on minorca balearic islands four pollen diagrams from minorca balearic islands have been correlated with other previously studied sequences from majorca and minorca to define a holocene landscape sequence for the region from 8000 yr b p to the present the lower part of the pollen diagrams reflects a climatic phase with more rain and less marked seasonality than today significant quantities ofcorylus buxus and mesophilous taxa are found in the middle part between 5000 and 4000 yr b p a strong change is recorded in composition and structure of the vegetational landscape with vegetation appearing that was adapted to mediterranean conditions this episode coincided with the first human colonization of the island and also with a widespread climatic change in the western mediterranean region the change in taxa was complex and some sclerophyllous taxa sucholeaplayed an important role in the transformation of the landscape physiognomy from the mid holocene until the present although human activities have removed much of the mediterranean vegetation on the balearic islands it seems clear that the changes have been brought about in part by increasing dryness

holocene aeolian phases and human settlements along the atlantic coast of southern spain a combined geomorphological radiocarbon dating archaeological and historical approach permits a refining of the age of the coastal dune systems related to estuaries in the gulf of cadiz three dune systems are distinguished in this paper the oldest one d1 which accumulated under prevailing wsw winds during the first millennium bc overlays both the occupational horizons of late neolithic early copper age fourth millennium bc and the lithic workshop levels fourth to second millennia bc the middle dune system d2 containing both roman and medieval remains accumulated between the thirteenth or fourteenth centuries and the seventeenth century ad the youngest d3 system is associated with the time of building of watchtowers in the seventeenth century ad but extends to the present it is related to sw prevailing winds we explain the absence of aeolian deposits prior to 2700 cal bp as the result of trapping of a large part of the sediment supply in the estuaries which starved the neighbouring beaches and aeolian settings aeolian accumulation reached significant values when sedimentation in the coastal zone changed from being mainly aggradational in the estuaries 6500 2700 cal bp to mainly progradational in spit barriers and related dunes post 2700 cal bp the present analysis of aeolian systems suggests a non direct correlation at least in some cases between coastal progradation of spit barriers and aridity

above the weathering front contrasting approaches to the study and classification of weathered mantle abstract weathered mantle comprises the materials above bedrock and below the soil it can vary in thickness from millimeters to hundreds of meters depending primarily on climate and parent material study of the weathered mantle comes within the realms of four disciplines geology geomorphology soil science and civil engineering each of which uses a different approach to describe and classify the material the approaches of engineers geomorphologists and geologists are contrasted and compared using example papers from the published literature soil scientists rarely study the weathering profile as such and instead concentrate upon soil forming processes and spatial distribution primarily in the solum engineers including engineering geologists study the stability and durability of the weathered mantle and the strength of the materials using sophisticated procedures to classify weathered materials but their approach tends to be one dimensional furthermore they believe that the study of mineralogy and chemistry is not useful geomorphologists deal with weathering in terms of process how the weathered mantle is formed and with respect to landform evolution using a spatial approach geologists tend to ignore the weathered mantle because it is not bedrock or to study its mineralogy and or chemistry in the laboratory i recommend that the approaches of the various disciplines be integrated geomorphologists and geologists should consider using engineering weathering classifications and geologists should adopt a spatial perspective to weathering as should engineers and engineering geologists

coast line evolution in portugal since the last glacial maximum until present a synthesis abstract an effort has been made to assemble a data set on the evolution of coastal morphology of the west iberian continental margin in portugal which has occurred since the last glacial maximum in this integrated review a particular attention was given to the analyses of coastline shaping phenomena on different time scales several overlapping processes such as shore erosion local sediment supply rate climatic changes anthropic impacts and mean sea level rise mslr were identified and their combined effects assessed the eustatic see level rise appears as a principal factor in shaping the shore line contour until mid holocene since then the non eustatic factors namely the terrigenous sediment supply rate and the dynamics of barriers and spits systems became dominant in the evolution of the near shore morphology since the 15th century ad the anthropogenic activities namely deforestation and land cultivation contributed decisively to the positive sedimentary balance in the portuguese coastal zone finally the multiple damming of the major rivers in 20th century and exploitation of sand and gravel from the river beds led to the sediment starving of the coastal zone and generalized shore line retreat

from andic non allophanic to non andic allophanic inceptisols on alkaline basalt in mediterranean climate a toposequence study in the marghine district sardinia italy abstract the properties of a non andic allophanic inceptisol pom1 and two andic non allophanic inceptisols flm5 and spm8 representative of a toposequence on basanite rocks of mt st antonio central western sardinia marghine sub region were analyzed to better elucidate factors and processes that lead to a different expression of andic properties and allophane formation in xeric mediterranean environment a series of laboratory techniques including physical chemical micromorphological x ray diffraction xrd scanning electron microscopy sem analyses were used all soils are usually rich in organic carbon dystric at the great group level with saturation base from 72 to 10 and with ph from subalcaline to acidic allophanic inceptisol appears more intensely weathered than non allophanic inceptisols volcanic glass content is in any case negligible pom1 formed on the plateau shows a shallow solum 45 cm with a 2 horizon that meets all the criteria for andic soil properties the amounts acid oxalate extractable al o and si o together with pyrophosphate extractable al p typifies such a pedon as allophanic inceptisol 0 19 p al o 2 the allophanic inceptisol pom1 is located at the plateau of the toposequence where lower surface runoff greater water infiltration rate the absence of significant erosion and colluvial movement may have increased the degree of weathering processes in these conditions the prolonged soil moistness prevents the transformation of short order components on the whole the results emphasize the role of topography and the importance of al fe amorphous compounds in expressing soil andic properties and allophane content versus the volcanic origin of parent material and the insufficiency of volcanic glass the results also suggest that the occurrence of soil with andic properties and significant allophane content in hot and dry environments like the mediterranean climate in sardinia may be more widespread than expected

geotechnical and landslide aspects in weathered granitoid rock masses serre massif southern calabria italy abstract the weathering processes produce important chemical and physical transformations in rock masses producing a decay of their strength and then stability in this study different methodologies were employed to define the physical mechanical properties and the minero petrographical changes at each grade of weathering useful to determine a geological model of the weathered granitoids involved in mass movements the paper focuses on a multidisciplinary research on the weathering profiles of the paleozoic granitoid rocks surrounding the village of fabrizia located in the serre massif southern calabria italy fabrizia lies on an old erosion surface composed of basement rocks made up of weathered granitoids belonging to the serre massif granitoid complex and overlain by thin eluvial colluvial deposits the tectonic uplift of the area combined with mediterranean climatic conditions both active at least since the quaternary are the main causes of the deep weathering of the plutonic rocks the weathered profiles of the granitoid complex have been studied through field observations borehole explorations with geotechnical tests and seismic surveys coupled to minero petrographical analysis and laboratory tests weathered profiles are mainly composed by rock masses varying from completely weathered and residual soil classes v vi to moderately weathered rocks class iii characterized by a progressive increase of geotechnical properties e g seismic wave velocity rock quality designation internal friction angle uniaxial compressive strength with a decrease of weathering the weathered rocks display a wide variety of mass movement landslide types are rockfalls for the fresher rocks class iii translational slides occur between different weathering degrees classes iv and v and rotational slides dominate at the top of the slopes and generally involve the weathering grades from class iv to classes v vi the shallow horizons are composed of thin eluvial colluvial deposits and more weathered granitoids classes v vi that may generate dangerous debris flows or debris avalanches during intense and prolonged rainfall the landslide surface is usually at a depth lower than 2 m in the debris flow type while deeper landslides depth 2 m are rotational and translational types with sliding surfaces occurring mainly in the transition between the classes iv and v the field survey coupled to geotechnical geophysical and minero petrographical data allowed the recognition of the different weathered horizons and relative geotechnical properties useful to the reconstruction of the reliable geological model the model represents an important support for the study of the landslide processes and for a sustainable management of the territory the used approach provided results to set a general reference framework for establishing more precise correlations between mass movement phenomena and weathering processes

mobility and fluxes of major minor and trace metals during basalt weathering and groundwater transport at mt etna volcano sicily abstract the concentrations and fluxes of major minor and trace metals were determined in 53 samples of groundwaters from around mt etna in order to evaluate the conditions and extent of alkali basalt weathering by waters enriched in magma derived co 2 and the contribution of aqueous transport to the overall metal discharge of the volcano we show that gaseous input of magmatic volatile metals into the etnean aquifer is small or negligible being limited by cooling of the rising fluids basalt leaching by weakly acidic co 2 charged water is the overwhelming source of metals and appears to be more extensive in two sectors of the s sw paterno and e zafferana volcano flanks where out flowing groundwaters are the richest in metals and bicarbonate of magmatic origin thermodynamic modeling of the results allows to evaluate the relative mobility and chemical speciation of various elements during their partitioning between solid and liquid phases through the weathering process the facts that rock forming minerals and groundmass dissolve at different rates and secondary minerals are formed are taken into account at mt etna poorly mobile elements al th fe are preferentially retained in the solid residue of weathering while alkalis alkaline earth and oxo anion forming elements as se sb mo are more mobile and released to the aqueous system transition metals display an intermediate behavior and are strongly dependent on either the redox conditions mn cr v or solid surface related processes v zn cu the fluxes of metals discharged by the volcanic aquifer of etna range from 7 0 10 3 t a th to 7 3 10 4 t a na they are comparable in magnitude to the summit crater plume emissions for a series of elements na k ca mg u v li with lithophile affinity but are minor for volatile elements basalt weathering at mt etna also consumes about 2 1 10 5 t a of magma derived carbon dioxide equivalent to ca 7 of contemporaneous crater plume emissions the considerable transport of some metals in etna s aquifer reflects a particularly high chemical erosion rate evaluated at 2 3 10 5 t a enhanced by the initial acidity of magmatic co 2 rich groundwater

holocene palaeoecology and floodplain evolution of the muge tributary lower tagus basin portugal abstract the lower muge valley a tributary of the lower tagus river portugal features an important archaeological record of mesolithic shell midden sites archaeological research has long assumed that tidally influenced valley floor environments in the immediate locality of the sites provided a rich food resource attracting mesolithic settlement to date there has been little attempt to use palaeoenvironmental records to reconstruct holocene floodplain evolution in the lower tagus valley the cultivated freshwater lower muge floodplain is locally underlain by 11 m of homogeneous fine grained sediments and peat comprising buried floodplain environments contemporary with mesolithic occupation 6200 4800 cal bc pollen and foraminifera analyses demonstrate that fine grained deposition forced by sea level rise commenced 6200 cal bc in an estuarine setting the lower muge floodplain experienced maximum tidal influence 5800 5500 cal bc subsequently sediment supply rates overtook the decreasing rate of sea level rise and fluvial environments expanded the pollen record may suggest regional desiccation from 5000 cal bc estuarine environments disappeared suddenly 3800 cal bc when freshwater wetlands were established although the initiation of mesolithic settlement is shown to coincide with the beginning of tidal influence site abandonment does not match with any major environmental change sea level still stand 2600 cal bc has been linked to valley floor stabilisation and soil formation alder floodplain woodland developed prior to 230 cal bc and was cleared probably during roman times for agriculture renewed deposition after 230 cal bc may relate to internal mechanisms or to human impact upon the catchment vegetation

weathering indices for rhyolitic tuff and granite in hong kong a series of chemical analyses and dry density tests of rhyolitic tuff and granitic samples have been carried out the test results have been interpreted using a newly developed theoretical weathering model for calculating a mobility index of major elements in rock and soil it is found that this index is useful for describing changes of rock and soil during weathering and classifying the degrees of weathering based on the theoretical model a new parameter called the volume index which combines chemical and physical data is suggested this index appears to be a good indicator for classifying the degree of weathering in hong kong a quantitative classification scheme is suggested

the sedimentology and dynamics of crater affiliated wind streaks in western arabia terra mars and patagonia argentina abstract wind streaks comprise recent aeolian deposits that have been extensively documented on venus earth and mars martian wind streaks are among the most abundant surface features on the planet and commonly extend from the downwind margins of impact craters previous studies of wind streaks emerging from crater interior deposits suggested that the mode of emplacement was primarily related to the deposition of silt sized particles as these settled from plumes we have performed geologic investigations of two wind streaks clusters one situated in western arabia terra a region in the northern hemisphere of mars and another in an analogous terrestrial site located in southern patagonia argentina where occurrences of wind streaks emanate from playas within maar craters in both these regions we have identified bedforms in sedimentary deposits on crater floors along wind facing interior crater margins and along wind streaks these observations indicate that these deposits contain sand sized particles and that sediment migration has occurred via saltation from crater interior deposits to wind streaks in arabia terra and in patagonia wind streaks initiate from crater floors that contain lithic and evaporitic sedimentary deposits suggesting that the composition of wind streak source materials has played an important role in development spatial and topographic analyses suggest that regional clustering of wind streaks in the studied regions directly correlates to the areal density of craters with interior deposits the degree of proximity of these deposits and the craters rim to floor depths in addition some but not all wind streaks within the studied clusters have propagated at comparable yearly earth years rates extensive saltation is inferred to have been involved in its propagation based on the studied terrestrial wind streak that shows ripples and dunes on its surface and the martian counterpart changes orientation toward the downslope direction where it extends into an impact crater

evolution and facies architecture of the mesotidal guadiana river delta s w spain portugal abstract the guadiana river estuary and delta is one of the most important mesotidal fluvio marine systems of the southwestern iberian peninsula the river mouth was formed as a narrow channel excavated by fluvial incision during the pleistocene lowstand and then flooded 6500 yr ago during the flandrian transgression holocene the estuary is in an advanced state of sediment infilling in its proximal part due to its narrow morphology which prevents passage of sediment through to the open coast consequently sediment is accumulating in the river mouth causing progradation as response of the interaction between coastal and fluvial processes sedimentation is controlled by the interaction of sediment load delivered by the guadiana river and the active longshore current which also supplies sand eroded from barrier islands and friable cliffs in the portuguese algarve to the west tidal range is mesotidal 2 0 m and mean significant wave height is 0 6 m with an average period of 3 6 s morphological differences exist between the two sides of the river mouth the western side has a large spit separated from the mainland by a marsh and the eastern side shows an array of old barrier islands separated by salt marsh areas a vibracore study allows us to distinguish 12 different depositional facies in the system fluvial delta tidal inlet flood tidal delta washover beach dune estuarine channel lagoon tidal creek channel margin tidal flat and salt marsh furthermore a different architectural scheme of these facies is present on each side to the east there is a longitudinal repetition of the sandy facies corresponding to the barrier islands on the west side there is a transverse growth of a single spit containing eolian dunes these differences result from asymmetric interaction between the tidal and fluvial currents at the river s mouth and the waves and tidal currents of the open coastal zone

the effects of weathering on rare earth element y and ba abundances in tertiary basalts from southeastern australia tholeiitic basalts showing anomalously high ba y and rare earth element ree concentrations occur within the tertiary newer volcanic province of victoria and these geochemical characteristics are related to incipient alteration accompanying weathering ree and y released during weathering of basalts are retained either in secondary phosphate or clay minerals and in rocks showing very high ba concentrations the ba is present as baso4 leaching experiments suggest that glassy or fine grained rocks are more likely to release ree y and ba while more extensively altered rocks are likely to hold these elements probably because they substitute in or are adsorbed on clay minerals or because secondary baso4 and ree phosphates are resistant to acid leaching samples taken sequentially across a weathering profile in a tholeiitic basalt flow from fresh to intensively altered rock illustrate that in the very earliest stages of alteration extreme variations in the abundances of ba y and ree can occur this is reflected in the broad patterns of trace element behaviour manifested by an extensive analysed sample suite from the victorian newer volcanic province where there is no correlation between anomalous enrichments in ba y or ree and the level of incipient alteration ba anomalies are not necessarily accompanied by abnormal y and ree behaviour and this is probably because the mobility of each trace element is a function of a the ionic radius and charge of the ionic species it forms in solution b local groundwater parameters such as eh ph groundwater flux and concentrations in the groundwater of species such as so42 and c the secondary mineral assemblages developed in a particular situation sr isotopic compositions are not strongly affected by incipient weathering and do not show significant changes until alteration has progressed to the point where plagioclase begins to break down the study illustrates that relatively slight alteration at the earliest stages of weathering can produce drastic changes in the concentrations of ree y and ba and petrographic assessment of the freshness of samples is not precise enough to eliminate prior to analysis cases where these effects may be manifested where weathering has caused changes in abundance patterns these may be recognised by careful comparisons of appropriate elemental ratios e g ba rb throughout a particular analysed sample suite

zircon fission track age for middle pleistocene rangitawa tephra new zealand stratigraphic and paleoclimatic significance rangitawa tephra is an important stratigraphic marker in mid pleistocene marine and terrestrial sequences in new zealand and adjacent ocean basins zircon fission track ages zfta on rangitawa tephra from five sites in the southern north island yield mean site ages in the range 0 34 to 0 40 ma with a weighted mean of 0 35 0 04 ma 1 on the basis of glass shard major element chemistry ferromagnesian mineralogy zfta and similarity of paleomagnetic dates of proposed tephra correlatives in deep sea cores it is concluded that rangitawa tephra represents a major eruptive event in the taupo volcanic zone most probably associated with eruption of the whakamaru group ignimbrites 0 35 0 39 ma or less likely the paeroa range group ignimbrites 0 36 0 38 ma pollen analyses from two onshore sites together with regional loess stratigraphy show that rangitawa tephra was erupted during a glacial period the zfta and previously reported oxygen isotope data from dsdp site 594 indicate that rangitawa tephra was erupted near the end of oxygen isotope stage 10

a non destructive tool for detecting changes in the hardness of engineering materials application of the equotip durometer in the coastal zone non destructive tools capable of measuring the condition and geomechanical properties of construction materials through time are of considerable value in engineering here the ability of the equotip durometer proceq type d to detect changes in the hardness of concrete and rock exposed to marine conditions was tested results indicated a progressive loss of hardness for limestone while concrete hardness increased granite showed no significant change our results relate to alteration of the materials primarily via chemical and biological weathering the equotip is sensitive enough to detect subtle changes in the condition of construction materials over relatively short periods of time

ams 14c dating of holocene estuarine deposits consequences of high energy and reworked foraminifera benthic foraminiferal species were used to ams date holocene sediments adjacent to trangressive overlap boundaries tob in two high energy estuaries in northern spain it had previously been recognized that the foraminifera could be divided into indigenous and exotic components whereas it was known that the exotic forms had been transported into the estuaries from the adjacent inner shelf it was assumed that the indigenous forms were in situ the ams dates based on indigenous forms obtained from pairs of samples adjacent to the tob showed an inverse relationship in three out of four boreholes i e the age of the higher sample was older than that of the lower the most probable explanation of this unexpected result is that there had been significant reworking of indigenous foraminifera especially associated with the transgressive episode it is concluded that in high energy estuaries ams dating on foraminiferal shells is influenced by transport and reworking even of the indigenous component therefore if only foraminifera are available for dating we recommend that closely spaced pairs of samples should be dated in order to assess the reliability of the results

in situ gamma ray spectrometric study of weathered volcanic rocks in hong kong in situ gamma ray spectrometry grs measurements were conducted at 35 sites in hong kong where volcanic rocks with varying extent of weathering were exposed elemental analyses using x ray fluorescence spectrometry and inductively coupled plasma mass spectrometry were carried out on samples collected from these 35 plus 22 other locations to assess the feasibility of using the grs method to quantify the extent of weathering the parker weathering index varying within a range of 0 0 0 8 for the samples studied was used as a geochemically based reference scheme for correlating the gamma ray spectrometric results with the extent of weathering for the former 35 sites the concentrations of the three major radioelements k u and th determined by in situ grs were compared to laboratory determined values from the samples the study reveals that no significant change occurs to the contents of the three radioelements during the initial state of weathering but once the rocks become highly weathered further progression of weathering is accompanied by a systematic removal of k and an increased dispersion of u and th the results show that k content which is indicative of the extent of weathering can be retrieved reliably with the gamma ray spectrometry technique the study has given support to the potential use of the downhole spectral gamma method for evaluation of weathering grade and the detection of subsurface clay rich levels copyright 2002 john wiley sons ltd

the sedimentary record of the post glacial transgression on the gulf of cadiz continental shelf southwest spain abstract four seismic units ta to td have been identified from the analysis and interpretation of high resolution seismic profiles in a sector of the gulf of cadiz shelf they constitute a composite seismic unit attributed to the transgressive systems tract tst of the last depositional sequence the earliest transgressive unit was deposited on the outer shelf and represents the distal facies of a coastal deposit a process of shelf partitioning seems to have occurred during the formation of the three later transgressive parasequences the shelf sector offshore from the guadiana river mouth was a high energy environment dominated by storm events by contrast the shelf sector offshore from the donana national park was a low gradient shelf where large barrier island and lagoon systems were formed the sparse occurrence of marine deposits within the tst is a consequence of the episodic nature of the sea level rise the generation and preservation of these transgressive deposits results from the interaction of the following controlling processes 1 relative sea level rise the formation of coastal transgressive deposits is related to intervals of reduced sea level rise or stillstands within a period of continuous sea level rise those sea level changes were probably driven by short term periods of colder climate during the late pleistocene holocene deglaciation the younger dryas interval is the most widely recognised climatic event of this type but probably other events of similar characteristics had the same effect on the glacio eustatic sea level rise 2 sediment supply changes short lived climatic events probably also involved changes in the sediment supply to the continental shelf due to changes in erosion rates and river regimes of the river basin hinterlands 3 effect of the paleophysiography paleogeography the sedimentary environments differentiation processes are associated to the formation of an exposed coastal promontory offshore from the guadiana river mouth and a semi protected embayment offshore from donana national park this coastal configuration was controlled by previous tectonic evolution and influenced the non uniform landward migration of the coastline

kinematic significance of l tectonites in the footwall of a major terrane bounding thrust fault klamath mountains california usa abstract detailed geologic mapping cross section reconstructions strain analyses and kinematic analyses enable the reconstruction of a one kilometer wide domain of l tectonites in the east west striking subhorizontal to gently south dipping pigeon point high strain zone pphsz associated with a major thrust fault separating oceanic and arc affinity terranes in the klamath mountains california l tectonites are associated with 1 a convex upward warp of the upper high strain zone boundary 2 a transition from mafic metavolcaniclastic rocks to micaceous quartzites 3 folds subparallel with mineral lineations 4 emplacement of synkinematic ultramafic mafic intrusive bodies and 5 a local temperature increase from greenschist to amphibolite facies conditions pure shear dominated deformation accommodated zone normal shortening and transport parallel elongation coupled with subordinate top to the west directed thrust style simple shear l tectonite formation was controlled by the shape of the high strain zone boundary driving lateral flow into the apex of the lens shaped zone in response to a favorable kinematic geometry and bulk strain in the constrictional field localized magmatic heating best explains the shape of the high strain zone boundary but l tectonites are not partitioned into a single rheological domain during terrane amalgamation strain path partitioning occurred with localized top to the west directed simple shear partitioned into a structurally overlying thrust zone and pure shear dominated subvertical shortening and transport parallel elongation partitioned into the pphsz

the effects of weathering on the physical and mechanical properties of igneous and metamorphic saprolites abstract the present paper presents three extensive datasets of laboratory testing on weathered geomaterials which are emblematic of soil types widely found worldwide the overall dataset includes soils originating from igneous and metamorphic rocks either coarse or fine grained and having either felsic or mafic minerals in particular the data are interpreted to highlight the effects that weathering has on the physical and mechanical properties of these natural geomaterials comparing them with published data with the aim to provide a general framework of interpretation that takes into account this geological process and links soil mechanics to engineering geology generally weathering induces a reduction in the grain size both due to physical actions e g opening of grain contacts and to the chemical decomposition of minerals resulting in the formation of clay minerals as weathering proceeds and the soil becomes finer the in situ specific volume and the location of the normal compression and critical state lines move upwards in the volumetric plane on the other hand the clay minerals cause its angle of shearing resistance to reduce when analysing the behaviour of the intact soil in all cases positive effects of structure albeit small compared to some sedimentary soils were observed and these reduced as a consequence of weathering

the holocene transgression into the estuarine central basin of the odiel river mouth cadig gulf sw spain lithology and faunal assemblages abstract six estuarine facies were distinguished recording the holocene history of sea level rise relating according to the start and development of the holocene transgression which flooded the coast of huelva facies 2 gravels facies 3 grey clayey silts facies 5 well sorted sands facies 4 silty sands facies 5 black clayey silts and facies 6 red muds this group overlies neogene sediments facies 1 three faunal assemblages open bay ob central estuary ce and wave domination wd including remains of macrofauna foraminifers and ostracods plus depositional features are identified in a sedimentological log constructed from a borehole with a continuous core sunk in the central basin of the odiel river estuary huela coast sw spain the ob assemblage requires shallow and protected zones controlled by low energy tidal currents the ce assemblage is located within an intertidal zone where reworked marine forms of foraminifers ostracods and scattered macrofauna co exist with small estuarine foraminifers and ostracods the wd assemblage comprises tests of marine macrofauna with fractured shells plus large marine foraminifers and estuarine ostracods during the first stage of continuous sea level rise 8720 260 bp to 5390 155 bp estuarine accretion high energy tidal currents and wave action took place successively allowing the development of the ob ce and wd assemblages the second stage 5390 155 bp to present with a stabilized sea level comprised a vertical decrease of energy with tidal currents favouring deposition in shallow tidal channels and marsh zones leading to less energetic ce assemblages within the estuarine central basin high sediment supply resulted in deposition during this stage which shows a regressive nature

weathering and damage 1 weathering of rock surfaces is often associated with a surface dissolution process chemical interactions occur on grain boundaries and diffusion is the controlling process a dissolution boundary layer rind develops adjacent to the weathering surface we quantify the extent of dissolution by introducing a damage variable f f 0 for pristine rock and when f f0 the rock disintegrates we assume that the variations of the damage variable are given by the diffusion equation we solve two problems the first is for the structure of the transient dissolution boundary layer prior to surface disintegration we find an incubation time ti before active weathering disintegration begins the second is the solution for steady state weathering with a constant weathering velocity vw our results are entirely consistent with weathering studies on carrera marble gravestones in the united kingdom

geomechanical and geochemical changes during early stages of weathering of karamu basalt new zealand abstract variations in geochemical and geomechanical characteristics were measured through a basalt weathering sequence exposed at an abandoned quarry at karamu near hamilton new zealand geochemical measurements show that at the early stages of weathering fresh to slightly weathered reductions in the concentrations cao and mgo are rapid although they are not accompanied by major mineralogical change during later stages of weathering secondary clay minerals form following well described mineralogical changes fresh basalt is strong uniaxial compressive strength 262 mn m 2 point load index 5 59 with well developed closely spaced columnar jointing slightly weathered material is distinguished in the field only by slight discolouration along joint planes but laboratory tests show a dramatic loss of strength in slightly weathered rock point load index 0 41 cbr 43 a causal relationship between the loss of cations and loss of strength in the early stages of weathering is suggested this stage of weathering is diffusion controlled whereby cations are lost from the constituent primary minerals and replaced by h this process disrupts the lattice structure and causes a marked loss of strength implications are that slightly weathered rock which appears competent in the field is likely to have much lower strength and durability than assumed from field evidence

depositional history of estuarine infill during the last postglacial transgression gulf of cadiz southern spain abstract the late pleistocene and holocene evolution of the estuaries in the gulf of cadiz is interpreted for the first time using drill cores logs trenches and 38 new radiocarbon data and the results compared with the shelf the odiel tinto and guadalete rivers deposited conglomerates during a highstand that did not reach the present sea level dated at ca 25 30 ka isotopic stage is 3 corresponding to a relatively humid period in the area rivers incised these coarse grained deposits during the last main lowstand at ca 18 ka when sea level dropped to 120 m and the coastline lay 14 km seawards from the present the erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise overlain by the valley fill deposits of the transgressive and highstand phases of the last fourth and fifth order depositional sequences recognised in the shelf the first marine influence in the estuaries during the transgression occurs at 25 30 m at ca 10 000 years bp according to fossil assemblages the transgressed basins changed from brackish to more open marine as the sea rose until ca 6500 years bp when it reached the maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy central basins then the rate of eustatic rise decreased drastically and the estuarine filling followed a two fold pattern governed by the progressive change from vertical accretion to lateral centripetal progradation at ca 4000 years bp the fluvial input surpassed the already negligible rate of rise causing partial emergence of tidal flats and spit barriers in the largely filled estuarine basins prevalence of coastal progradation upon vertical accretion at ca 2400 years bp caused accelerated expansion of tidal flats and rapid growth of the sandy barriers further changes since the 16th century reflect widespread anthropic impacts

postglacial sea level rise and sedimentary response in the guadiana estuary portugal spain border abstract the study of sedimentological features foraminifera and molluscan fauna in samples recovered from four rotary boreholes permitted after 14 c dating the first assessment of the post glacial transgression in guadiana river estuary the holocene sequence is underlain by coarse sediments from delta fan enclosing continental swamp deposits dated 16 980 year bp the holocene sedimentary sequence was deposited either directly on this delta fan gravels or on top of fluvial sands deposited probably between 11 000 and 10 000 yr bp an accelerated phase of the estuary infilling by clayey sediments containing the salt marsh foraminifer trochammina began ca 9800 year bp when sea level was about 39 m below present between 7500 and 7000 year bp the central part of the estuary started to accommodate coarser sediments partially introduced from the continental shelf the first phase of holocene sea level rise at a rate of 0 85 m century terminated ca 6500 year bp since then lagoonal sediments in the vicinity of the estuary have been enclosed behind sand spits and predominantly sandy sedimentation was initiated within the estuary after a second phase of slower rise at the rate of 0 3 m century which lasted until ca 5000 year bp the sea approached the present level

pollen and mollusc records for environmental change in central spain during the mid and late holocene the central part of the iberian peninsula has few radiocarbon dated records of vegetation and climatic history for the holocene extinct and active tufa forming sites occur along the northwestern margin of the sierra de alcaraz tufas are often closely associated with the remains of plants and animals and two extinct systems near the settlements of el jardin and alcaraz have yielded a record of environmental history that spans much of the last 6000 years the record indicates that the present day sedimentological regime and vegetation are human induced and probably extend back to about 2700 yr bp before this date oak dominated scrub mattoral was widespread prior to around 5000 yr bp the climate appears to have been relatively humid and possibly cooler and the catchments for the two sites were more wooded than today

guadalupe pluton mariposa formation age relationships in the southern sierran foothills onset of mesozoic subduction in northern california we report a new 153 2 ma sims u pb date for zircons from the hypabyssal guadalupe pluton which crosscuts and contact metamorphoses upper crustal mariposa slates in the southern sierra a 950 m thick section of dark metashales lies below sandstones from which clastic zircons were analyzed at 152 2 ma assuming a compacted depositional rate of 120 m myr accumulation of mariposa volcanogenic sediments which overlie previously stranded middle jurassic and older ophiolite chert argillite belts in the sierran foothills began no later than 160 ma correlative oxfordian kimmeridgian strata of the galice formation occupy a similar position in the klamath mountains we speculate that the late jurassic was a time of transition from 1 a mid paleozoic middle jurassic interval of mainly but not exclusively strike slip and episodic docking of oceanic terranes 2 to transpressive plate underflow producing calcalkaline igneous arc rocks outboard blueschists at 170 150 ma whose erosion promoted accumulation of the mariposa galice overlap strata 3 continued transpressive underflow attending 200 km left lateral displacement of the klamath salient relative to the sierran arc at 150 140 ma and development of the apparent polar wander path cusps for north and south america and 4 then nearly orthogonal mid and late cretaceous convergence commencing at 125 120 ma during reversal in tangential motion of the pacific plate after 120 ma nearly head on subduction involving minor dextral transpression gave rise to voluminous continent building juvenile and recycled magmas of the sierran arc providing the erosional debris to the great valley fore arc and franciscan trench

late jurassic magmatism metamorphism and deformation in the blue mountains province northeast oregon an early to mid mesozoic record of sedimentation magmatism and metamorphism is well developed in the blue mountains province of northeast oregon detailed studies both north and south of the blue mountains province e g terranes of the intermontane belt klamath mountains and western sierra nevada have documented a complex middle to late jurassic orogenic evolution however the timing of magmatic metamorphic and deformational events in the blue mountains and the significance of these events in relationship to other terranes in the western north american cordillera remain poorly understood in this study we investigate the structural magmatic and metamorphic histories of brittle to semibrittle deformation zones that indicate widespread late jurassic orogenesis in the blue mountains province folding and faulting associated with contractional deformation are primarily localized along terrane boundaries e g baker wallowa and baker izee olds ferry boundaries and within the composite baker oceanic melange terrane e g bourne greenhorn subterrane boundary these brittle to semibrittle deformation zones are broadly characterized by the development of e w oriented slaty to spaced cleavage in fine grained metasedimentary rocks of the baker terrane e g elkhorn ridge argillite approximately n s bivergent folding and n and s dipping reverse and thrust faulting on opposite flanks of the baker terrane similarly oriented contractional features are also present in late middle triassic to early late jurassic i e oxfordian stage ca 159 ma sedimentary rocks of the john day and huntington areas of northeast oregon radiometric age constraints from youngest detrital zircons in deformed sedimentary rocks and crystallization ages of postkinematic plutons which intrude the deformation zones limit deformation to between ca 159 and ca 154 ma we suggest that the widespread approximately n s directed contractional features in the blue mountains province record a short lived intense early late jurassic deformational event and preserve an example of upper crustal strain localization associated with terminal arc arc collision between the olds ferry and wallowa island arc terranes the age interval of deformation in the blue mountains province is younger than middle jurassic deformation in the canadian cordillera and klamath mountains siskiyou orogeny and predates classic nevadan orogenesis

major element ree and other trace element behavior in amphibolite weathering under semiarid conditions in southern india abstract a body of komatiitic amphibolite an enclave within the archean high grade orthogneisses in southern india shows mild chemical weathering under semiarid conditions along fractures chemical weathering has advanced chemical index of alteration documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm cia 53 end document cia of fresh documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

the effect of rock moisture on schmidt hammer rebound tests on rock samples from marion island and south africa in an assessment of the influence of internal rock moisture content on schmidt hammer readings rebound r values are found to decrease with increasing moisture content for samples of basalt sandstone and dolerite the maximum decrease in r values is found between oven dry values and saturated rock rebound values the magnitude of which varies from 2 to 10 points on the r scale a quartzite block has the greatest decline of 6 points at 60 per cent saturation for certain rock types under differing site to site field moisture conditions the moisture effect can be a significant factor in the interpretation of the relative state of weathering from rebound values copyright 2002 john wiley sons ltd

deformation related alteration of basaltic clasts during deep burial in sedimentary basins abstract the once deeply buried conglomerates of the solund basin contain up to 30 basaltic clasts together with up to 20 altered peridotite clasts both derived from the adjacent solund stavfjord ophiolite complex ssoc the basaltic clasts range in size from 2 to 30 cm across and display centimeter thick hematite reddened zones four types which form an alteration related evolutionary sequence can be distinguished type 1 consists of a green core with a 1 2 cm thick red zone along its rim type 2 shows in addition a perturbation of the red zone into the center of the clasts in type 3 numerous compartments with green cores surrounded by red zones build up the clast type 4 displays diffuse red zones and patches typically with a circular form that resembles liesegang s structures this evolutionary sequence relates to a progressive deformation evident from fractures faults and shear zones hematite reddened zones form along clast boundaries and along fractures that are oriented at high angle to the boundaries of the clasts the boundary parallel zones migrate towards the center of the clasts and the fracture parallel zones migrate away from the fractures these fracturing and deformation are coupled with chemical and mineralogical changes responsible of the changes in color of the alteration zones compared to the basaltic rocks of the ssoc the basaltic clasts of the solund basin contain higher contents of k 2 o volatiles loi and mgo lower contents of cao and are more oxidized with an average fe 3 fe 3 fe 2 ratio of 0 43 0 10 as compared to 0 30 0 07 in the ssoc basalts the replacement of magmatic clinopyroxene by chlorite induces the decrease in cao the replacement of ilmenite by titanite provides iron to form hematite in the red zones the red zones progressively replace the green core and are at their external boundary in turn replaced by mg riched green alteration zones characterized by a high content of zoned amphibole a decrease in cao and an increase in mgo towards the rim of the basaltic clasts is contrary to the chemical evolution of the peridotite clasts where the mgo is depleted and the cao increases with increasing degree of alteration this suggests that clasts of different lithologies exchanged components during the alteration process to explain these observations we use a model including internal stresses through a diffusion reaction process and external stresses through sediment loading and tectonic forces the mineralogy of the altered basaltic clasts chlorite epidote albite actinolite corresponds to low grade metamorphic conditions in accordance with or slightly higher than the peak temperature of 230 320 c previously calculated for this basin the study shows that the final compaction of multicomponent clast systems takes place through an interaction between mineral reactions metasomatism and deformation which differs from the compaction of monocomponent systems that occurs dominantly through pressure solution

impact of chemical weathering on micro macro mechanical properties of oolithic iron ore this article concerns the problem of collapses of abandoned underground room and pillar iron mines in lorraine north eastern france a study on the ageing of iron ore was carried out using different analytical techniques sem eds empa x ray diffraction mossbauer and icp spectroscopy as iron ore is a reactive environment in an oxidizing atmosphere created by anthropic activity this kind of weathering is triggered or activated by chemical processes and differs from diagenetic evolution under reducing conditions the weathering is characterized by the chemical alteration oxidation of reduced minerals siderite and berthierine in the inter oolithic cement mechanical disaggregation of oolithes recrystallization of berthierine and neo crystallization of a honeycombed hematite crust i e rust on all mineral surfaces this corrosion of iron ore was found to occur at a large scale in pillars especially in very old pillars which have been exposed to the mine atmosphere for 70 100 years the alteration of the inter oolithic cement which ensures material cohesion was not found to have been compensated by the crystallization of new minerals thus inducing the decrease in the micro macro mechanical properties of iron ore microindentation tests at millimetric scale micro compression triaxial tests at centimetric scale and macrocompression triaxial tests at decimetric scale this chemical weathering of anthropic origin plays a large scale and major role in the long term behavior of pillars and is probably one of the main causes of mine collapses that occured in lorraine therefore the decision to stop pumping of mine drainage thus inducing flooding of iron mines by groundwater was the correct decision since oxidation reactions in iron ore are necessarily less important under anaerobic condition than under aerobic condition in addition the knowledge of iron ore ageing allows for improved assessment of the long term stability of iron mines which have yet to collapse i e flooded iron mines and also iron mines which are still above the ground water table

tropical chemical weathering of hillslope deposits and bedrock source in the aburra valley northern colombian andes abstract tropical chemical weathering produces extensive lateritization and formation of deep weathering profiles both processes are fundamental to landscape evolution and slope instability the aburra valley of the northern colombian andes is characterized by tropical conditions the valley slopes are mostly covered by hillslope deposits originating from four basement rock suites which comprise contrasting granitoid volcanic sedimentary ophiolitic and metamorphic sources respectively tropical chemical weathering of the aburra hillslope deposits and their respective bedrock were examined using x ray fluorescence and x ray diffraction analysis to document and quantify their chemical weathering profiles compositions and mineralogical properties the chemical index of alteration cia loss on ignition loi and the mobiles index imob were used to quantify the degree of weathering of hillslope deposits and bedrock source weathering trends were analyzed using a cn k and a cnk fm diagrams the material mantling the slopes in the aburra valley records an intense weathering history chemical weathering is characterized by increased development of clay minerals kaolinite halloysite and iron and aluminum sesquioxides lateritization characterizes the final stage of the weathering profiles concentrations of cao na2o k2o decrease markedly in the weathering products compared to the fresh bedrock source whereas concentrations of al2o3 fe2o3 and mgo increase significantly cia ratios of matrix slope deposits derived from all four sources near 100 whereas those of boulder slope deposits and saprolites are lower but exceed source rock values different a cn k weathering paths are evident for each lithotype validating the correlation established between the hillslope deposits and their various parents chemical weathering indices in some samples are strongly influenced by the presence of sesquioxides as reflected by high loi anomalously low cia and varying enrichment trends on the a cnk fm diagrams consequently different chemical indices based on different criteria need to be combined to obtain best results as illustrated here by the combination of loi cia and imob the overall results suggest that tropical conditions have dominated for a long time in the northern colombian andes leading to uniformly high weathering indices in matrix slope deposits irrespective of parent lithotype prolonged warm and humid conditions could thus be responsible for the weathering and remobilization of extensive old hillslope deposits during the quaternary however in addition to the influence of climatic factors tectonism has also undoubtedly influenced slope evolution in the aburra valley

a 3 5 ga record of water limited acidic weathering conditions on mars abstract the secondary mineral budget on earth is dominated by clay minerals al hydroxides and fe oxides which are formed under the moderate ph high water to rock ratio conditions typical of earth s near surface environment in contrast geochemical analyses of rocks and soils from landed missions to mars indicate that secondary mineralogy is dominated by mg fe ca sulfates and fe oxides this discrepancy can be explained as resulting from differences in the chemical weathering environment of earth and mars we suggest that chemical weathering processes on mars are dominated by 1 a low ph sulfuric acid rich environment in which the stoichiometric dissolution of labile mineral phases such as olivine and apatite fe ti oxides is promoted and 2 relatively low water to rock ratio such that other silicate phases with slower dissolution rates e g plagioclase pyroxene do not contribute substantially to the secondary mineral budget at the martian surface under these conditions al mobilization is limited and the formation of significant al bearing secondary phases e g clays al hydroxides al sulfates is inhibited the antiquity of rock samples analyzed in situ on mars suggest that water limited acidic weathering conditions have more than likely been the defining characteristic of the martian aqueous environment for billions of years

modeling the influence of rainfall gradients on discharge bedrock erodibility and river profile evolution with application to the big island hawai i motivated by convex concave bedrock river profiles developed across a climate gradient on the wetside of the kohala peninsula of the big island of hawai i we numerically model how rainfall gradients may influence longitudinal fluvial incision patterns first we model transient profile adjustment with two tectonic boundary conditions subsidence and uplift in this generalized analysis we assume that rainfall gradients only influence incision by modifying the relation between upstream drainage area and local discharge using a detachment limited model downstream increases in rainfall lead to profile convexities during transient adjustment in both tectonic settings and this is the opposite of the predicted increase in profile concavity that would develop in a steady state uplifting profile a transport limited erosion model develops only concave channel profiles without clear signatures of the rainfall pattern second we model the development of convex concave transient profiles and incision patterns on kohala using a detachment limited model if rainfall gradients only influence incision through the local discharge reasonable rainfall gradients can only develop channel convexities that are much smaller than those observed instead we hypothesize that local bedrock erodibility increases with the degree of rainfall dependent chemical weathering when local erodibility is assumed to scale with local rainfall rate the model can produce convex concave profiles similar to those observed in kohala our results suggest that changes in local bedrock erodibility due to local climate dependent weathering may be an important mechanism by which climate influences landscape form and rates of evolution this hypothesis requires further testing in this study area and beyond

global and regional factors controlling changes of coastlines in southern iberia spain during the holocene the interaction between global glacio eustatic sea level rise and regional factors oceanographic and tectonic has controlled the evolution of coastline during the holocene in southem iberia at ca 10 000 14c years bp a deceleration of relative sea level rise took place both in the atlantic and mediterranean littorals with a maximum transgression at 6450 14c years bp in subsiding areas present tidal flats estuaries illustrate a clear marine influence recorded both in sediments and the fauna while in uplifting areas prograding spit bar systems developed two phases of major progradation are distinguished in these systems the first one between 6450 and 3000 14c years bp with a sedimentary gap at ca 4000 14c years bp and the second one from 2750 14c years bp up to present with an intervening gap between 1200 and 1050 14c years bp these progradation phases develop during stillstands followed by relative sea level fall while the sedimentary gaps represent relative high sea level in the mediterranean areas with a higher uplift rate marine terraces almost coeval to those gaps occur the most pronounced modifications in littoral dynamics occurred at between 3000 and 2750 14c years bp represented by changes in the direction of longshore drift and prevailing winds and in the predominance of progradation over aggradation processes at ca 1000 14c years bp the estuaries record a greater fluvial than marine influence and at 500 years ago an extraordinary increase in coastal progradation took place in all littoral zones the european medieval warm period is characterized at least during its initial phase by low pressure climate conditions while during the little ice age anticyclonic conditions gave rise to a strong coastal progradation

chemical weathering in the volcanic soils of isla santa cruz galapagos islands ecuador abstract forty three soils 130 horizons sampled by the geo pedological mission organized by the state university of gent belgium in 1962 on isla santa cruz galapagos islands were analysed in order to determine their degree of chemical evolution several weathering indices weathering index of parker wip chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and silica titania index sti and multivariate statistical analysis principal components analysis based on chemical composition were used with the only exception of the sti the indices were highly correlated r 0 85 the highest wip and sti values 20 9 8 2 and 70 2 2 2 respectively were found for soils developed on basalt flows near the coast slightly lower values wip 16 8 5 1 and sti 61 3 4 were shown by brown soils developed from basaltic flows at elevations between 140 and 225 m a s l while the lowest values wip 9 5 and sti 47 6 8 representing the more weathered materials were found for soils located at the highest elevations 400 m a s l and mostly developed on pyroclastic materials tuff and tephra as the chemical composition of the geological material basalt and tephra is highly homogeneous the degree of weathering is likely to depend on climatic conditions controlled by altitude and orientation on the windward slopes of the island a gradient of increasing weathering is observed from the arid conditions predominant at the coast to elevations of 400 500 m a s l where much more humid conditions prevail principal component analysis on elemental composition also supported the interpretation that the degree of weathering first component and soil horizonation second component are both related to climatic conditions both the variation of the chemical indices and the principal components of the geochemical composition are related to the bioclimatic zones soils with the lowest degree of weathering are located in the arid coastal zone slightly higher intensity was found for soils located in the transition and scalesia zones while the most weathered soils appear in the brown zone compared to other volcanic soils studied in the literature soils from isla santa cruz are in the upper range of chemical weathering intensity only comparable to soils from azores islands and canary islands tenerife and la gomera developed on basalts under oceanic conditions

statistical empirical index of chemical weathering in igneous rocks a new tool for evaluating the degree of weathering abstract chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering however the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock to overcome this limitation the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis pca of a large dataset derived from unweathered igneous rocks and their weathering profiles the pca analysis yields two principal components pc1 and pc2 which capture 39 23 and 35 17 of total variability respectively the extent of weathering is reflected by variation along pc1 primarily due to the loss of na 2 o and cao during weathering in contrast pc2 is the direction along which the projections of unweathered felsic intermediate and mafic igneous rocks appear to be best discriminated therefore pc1 and pc2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock subsequently pc1 and pc2 were then mapped onto a ternary diagram mfw diagram the m and f vertices characterize mafic and felsic rock source respectively while the w vertex identifies the degree of weathering of these sources independent of the chemistry of the unweathered parent rock the w index has a number of significant properties that are not found in conventional weathering indices first the w index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides whereas most conventional indices are defined by between two and four oxides second the w index provides robust results even for highly weathered sesquioxide rich samples third the w index is applicable to a wide range of felsic intermediate and mafic igneous rock types finally the mfw diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock

spheroidal weathering of granite porphyry with well developed columnar joints by oxidation iron precipitation and rindlet exfoliation spheroidal weathering one of the important rock weathering styles has been attributed to chemical weathering by the water from joint surfaces and mechanical aspects of the weathering have not been well addressed we made an investigation on spheroidal weathering of miocene granite porphyry with well developed columnar joints and found that this spheroidal weathering proceeds through chemical processes and accompanying mechanical processes the investigation of the textures physical properties mineralogy and chemistry of the porphyry revealed the presence of a brown band on the surface margins of corestones representing the oxidation of pyrite and chlorite and the precipitation of iron hydroxides and the consequent generation of micro cracks within the band during weathering oxidation progresses inwards from joints that surround the rindlets including both high angle columnar and low angle planar joints and causes rounding of the unweathered interior portion of the rock microscopic observations of the brown band embedded with fluorescent resin show that pores are first filled with iron hydroxides and that micro cracks then form parallel to the oxidation front in the outer portion of the brown band iron hydroxide precipitation increases the p wave velocity in the brown band while micro crack formation decreases the tensile strength of the rock where the brown band has thickened to 6 cm the micro cracks are connected to one another to create continuous cracks which separate the rindlets from the corestone micro crack formation parallel to the corestone surface may be attributed to compressive stresses generated by small amounts of volumetric expansion due to the precipitation of iron hydroxides in the brown band earth surface is under oxidizing environments so that precipitation of iron hydroxides commonly occurs the spheroidal weathering in this paper is a typical example of the combination of chemical and mechanical processes under such environments copyright 2016 john wiley sons ltd

crossing forest thresholds inertia and collapse in a holocene sequence from south central spain a holocene palaeoecological sequence from villaverde south central spain is presented the pollen stratigraphy is used to infer past vegetation changes within a catchment area that represents the boundary between semi arid plateau and mountain vegetation from c 9700 7530 cal yr bp pinus is dominant probably as a result of a combination of a relatively dry climate and natural fire disturbance from c 7530 5900 cal yr bp moderate invasion by quercus appears to be a migrational response following increased moisture and temperature but in part shaped by competitive adjustments from c 5900 5000 cal yr bp the pine forests are replaced by deciduous quercus forests with an important contribution from corylus betula fraxinus and alnus mediterranean type forests spread from c 5000 to 1920 cal yr bp coincident with expansions of artemisia juniperus and other xerophytes from c 1920 1160 cal yr bp pinus becomes dominant after a disturbance mediated invasion of the oak forests human impact u

the palaeogeography of mesolithic settlement subsistence and shell midden formation in the muge valley lower tagus basin portugal this paper reports the first detailed palaeogeographical analysis of the environmental context of late mesolithic shell midden sites in the lower tagus area and focuses on the lower muge valley which contains an internationally significant mesolithic record the lower muge valley fill comprises buried estuarine and fluvial environments contemporary with mesolithic settlement holocene environmental and palaeogeographic changes influenced mesolithic settlement subsistence and midden accumulation the sudden appearance of large late mesolithic shell middens throughout portugal represents a process of increased visibility and preferential preservation of the archaeological record prior to 6100 cal bc aggrading valley floor environments did not occupy the entire width of the present lower tagus floodplain and any sites located in the early holocene valley are currently deeply buried shell midden occupation on terrace levels followed the establishment of aggrading estuarine environments containing produ

radiocarbon dating chronologic framework and changes in accumulation rates of holocene estuarine sediments from chesapeake bay abstract rapidly accumulating holocene sediments in estuaries commonly are difficult to sample and date in chesapeake bay we obtained sediment cores as much as 20 m in length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of holocene sediment accumulation in the bay carbon in these sediments is a complex mixture of materials from a variety of sources analyses of different components of the sediments show that total organic carbon ages are largely unreliable because much of the carbon including coal has been transported to the bay from upstream sources and is older than sediments in which it was deposited mollusk shells clams oysters and foraminifera appear to give reliable results although reworking and burrowing are potential problems analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower chesapeake bay the biogenic carbonate radiocarbon ages are compatible with 210pb and 137cs data and pollen stratigraphy from the same sites post settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries including the chesapeake our data show that large variations in sediment mass accumulation rates occur among sites at shallow water sites local factors seem to control changes in accumulation rates with time our two relatively deep water sites in the axial channel of the bay have different long term average accumulation rates but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay mass accumulation rates at the two deep water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the chesapeake watershed

european lakes as palaeohydrological and palaeoclimatic indicators abstract lakes in temperate regions have fluctuated in size on annual to millenial time scales changes in water level or depth can be reconstructed by applying geomorphic sedimentological and biostratigraphic methods to transects of sediment cores this systematic field based approach has been used at a number of sites in europe it is illustrated by reconstructions of water level changes in lakes from southern sweden these lakes have shown broadly synchronous changes during the holocene such synchronous changes in water levels at several sites in a region reflect climatic changes inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction magnitude and timing of lake level changes between regions continental compilations of lake level data are therefore necessary detailed studies are not available from enough sites but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake level changes has greatly increased the number of sites available for a continental scale synthesis in europe this eclectic literature based approach is illustrated with examples from southern europe lakes in the mediterranean region were high around the glacial maximum and again somtime during the first half of the holocene in the western mediterranean the peak of late glacial aridity occurred at 15 000 16 000 bp and the lakes were already high again by 12 000 bp in the east maximum late glacial aridity occurred between 13 000 and 11 000 bp and there was a gradual return to wetter climates during the early holocene such that 9000 bp was more arid than 6000 bp most lakes in the mediterranean region were high at 6000 bp the transition to arid conditions after 5000 bp occurred abruptly in the west and more gradually in the east the lakes of southern sweden indicate drier climates in the early holocene ca 9000 bp more effective moisture between 8000 and 6000 bp increased aridity between 5500 and 3500 bp and increased effective moisture again during the last 3000 years the history of lake level changes in southern sweden and the mediterranean region can be partially explained in terms of changes in the direct effects of insolation and in the strength and position of the westerlies and of the subtropical high pressure cell during the late quaternary

recent coastal evolution of the donana national park sw spain abstract since the last holocene sea level rise about 6900 bp a series of depositional littoral landforms has been generated at the outlet of the guadalquivir river with progradation along the predominant longshore drift towards the east the first coastal progradation occurred between 6900 and 4500 bp the donana and perhaps la algaida spits both associated with the oldest and highest marshland in the donana national park are assumed to have been developed at an early stage originally the guadalquivir estuary was wider and deeper than now and its environment was mainly marine the oldest littoral formations have been dated as ca 4735 bp they show erosional events and indicate the breaking up of earlier spit barriers to form inlets the marine environment became increasingly dominant with heavy erosion of cliffs and a retreating coastline this period was followed by another sedimentary cycle 4200 2600 bp that surrounded the earlier eroded barriers the size of the estuary decreased due to the increasing marsh deposits and a fluvial environment was born about 2600 years ago progradation gave way to a new period of intense erosion the resulting morphology of littoral strands and erosional surfaces permitted the return to a marine environment the shoreline again retreated from 2300 bp coastal progradation has prevailed with an erosional interruption at 1000 bp the present day outlet of the guadalquivir is an estuarine delta of inactive marshland the donana national park the dominant environment is fluvial

the effects of weathering on the strength and chemistry of columbia river basalts and their implications for mars exploration rover rock abrasion tool rat results abstract basalt physical properties such as compressive strength and density are directly linked to their chemistry and constitution as weathering progresses basalts gradually become weaker and transition from intact rock to saprolite and ultimately to soil here we quantify the degree of weathering experienced by the adirondack class basalts at the mars exploration rover spirit site by performing comparative analyses on the strength and chemistry of a series of progressively weathered columbia river basalt crb from western idaho and eastern washington crb samples were subjected to compressive strength tests rock abrasion tool grinds neutron activation analysis and inductively coupled plasma optical emission spectroscopy analyses of terrestrial basalts indicate linked strength chemical changes as expected weathering sufficient to induce the loss of more than 50 of some cations including 50 of mgo and mno as well as 38 of fe 2 o 3 and 34 of cao was observed to weaken these samples by as much as 50 of their original strength in comparison with the terrestrial samples adirondack class basalts are most similar to the weakest basalt samples measured in terms of compressive strength yet they do not exhibit a commensurate amount of chemical alteration since fluvial and lacustrine activity in gusev crater appears to have been limited after the emplacement of flood basalt lavas the observed weakness is likely attributable to thin film weathering on exposed displaced rocks in the gusev plains in addition to some likely shock effects the results indicate that adirondack class basalts may possess a several mm thick weak outer rind encasing an interior that is more pristine than otherwise indicated and also suggest that long rock residence times may be the norm