exploration for antimony deposits in southern tuscany italy the idealized prototype of a southern tuscan antimony deposit can be described as follows the irregular mineralization is situated in the upper part of the highly porous calcare cavernoso overlain by an impermeable unit normally a flysch type rock the deposits are bound to the edge of horst positions and also to areas of elevated geothermal gradient and resulting hydrothermal activity these observations were used as variables for statistical probability calculations for antimony deposit formation within the areas determined to be of high probability 47 target areas were selected for geochemical soil sampling positive correlation of antimony with barium strontium and lead corresponding to gangue and accessory ore minerals in the deposit was found local distribution of sb of 3 representative areas are discussed in detail although no high anomalies so far unknown were identified known mineralizations were extended or neighbouring anomalies found regional correlation with horst structures and especially their fault margins e g eastern margin of the ridge of monticiano was confirmed the high density of mineralizations in the tafone area is also reflected in the geochemical results of the soil sample prospection a possible explanation for this accumulation may be seen in the large outcrops of pre carboniferous rocks which generally are expected to be the primary source of antimony from these pre variscan units antimony was remobilized and transported hydrothermally to its present position

effects of chemically active solutions on shearing behavior of a sandstone to evaluate the effect of chemical solutions on the frictional properties of a quartz rich sandstone triaxial compression tests have been performed on a sandstone saturated with distilled water solutions of nacl cacl2 and na2so4 at varying ionic strengths and ph values the sandstone although containing 90 quartz also bears about 7 clay results from these tests indicate that the presence of water alone reduces the ultimate strength by 33 the nacl solution of low ionic strength 0 2 m produces similar reductions in strength the samples saturated with nacl solutions of intermediate ionic strength 1 0 m are up to 20 stronger than those samples saturated with distilled water the samples saturated with solutions of the high ionic strength 5 0 m display the greatest weakening 41 46 from the case of the dry specimen this is a reduction of up to 20 compared to the water saturated sample reductions in ultimate strength due to changes in ph are only apparent for samples saturated with solutions of intermediate ionic strength results from the samples saturated with the divalent solutions show strength reductions of up to 52 compared to dry specimens in addition the tests demonstrate that the presence of either cations or anions appears to produce an equivalent weakening in the samples in all cases the samples saturated with the solutions of intermediate ionic strength 1 0 m display the greatest ultimate strength results from fracture tests on intact specimens indicate that the ultimate strength of nominally dry samples is approximately 15 greater than that of samples from all other environments there is no discernable difference between the strengths of specimens saturated with distilled water and those treated with more chemically active solutions scanning electron microscopic observations of the friction surfaces demonstrate that those solutions which produce the weakest mechanical behavior generate either very rough surfaces high ionic strengths or significant amounts of gouge low ionic strengths the former appear to be the result of solution of quartz which is enhanced by the clays in the sandstone these results suggest that the frictional resistance to sliding of the sandstone seems to be primarily controlled by the ionic strength of the pore fluid under most conditions with secondary control by the ph the same solution chemistry may weaken a fault zone at low concentrations but strengthen it at higher concentrations in the former case fault displacement would be facilitated and strain accumulated reduced this is believed to be more common in crustal environments

holocene climatic changes in the western mediterranean from south east france to south east spain abstract holocene climatic changes along coastal regions from south east france to south east spain were studied using pollen ratios comparing modern pollen rain vegetation and climate along selected transects from the atlantic ocean to the mediterranean we obtained threshold values of two different ratios corresponding to the different climatic conditions along the transects these pollen ratios and threshold values were employed to characterize the holocene climatic changes from nine mediterranean coastal sites the results were compared with data from marine and continental pollen sequences distributed in the western mediterranean basin and with additional regional data independent of human activity lake level fluctuations alpine glacier advance and retreat chronology 14 c anomaly and cooling phases in eastern france and central europe the role of anthropogenic activities and climate on the changes in vegetation is discussed six major changes in vegetation cover were identified they correspond to aridification phases that occurred around 9500 9000 yr bp 10 900 9700 cal bp 7500 7000 yr bp 8400 7600 cal bp 4500 4000 yr bp 5300 4200 cal bp 3700 3300 yr bp 4300 3400 cal bp 2600 1900 yr bp 2850 1730 cal bp and 1300 1000 yr bp 1300 750 cal bp these arid episodes were regional responses to more global climatic changes and determined the changes in the vegetation cover humans undoubtedly enhanced the vegetation changes but none the less had to adapt to these new climatic conditions

effects of simulated fault gouge on the sliding behavior of tennessee sandstone nonclay gouges stick slip has been considered to be a mechanism of shallow focus earthquakes along pre existing faults and thus laboratory studies relevant to stick slip may lead to a better understanding of the mechanisms of the earthquakes and eventually to an effective prediction and or control of them this paper deals with the effects of various simulated gouges on the sliding behavior of rocks with special emphasis on how fault gouge alters potentially unstable behavior of a brittle rock about 150 specimens of tennessee sandstone with various simulated gouges along a 35 precut are deformed dry in a triaxial apparatus at room temperature with shortening rate of about 2 10 4cm s and at confining pressures to 300 mpa tennessee sandstone is a brittle and strong rock quartz cemented quartzose sandstone which consistently shows stick slip without simulated gouge at confining pressures above 30 40 mpa sliding behavior with a gouge layer depends markedly on the material used to simulate the gouge experimental results from monomineralic gouges show that mohs hardness of a mineral is a useful parameter to predict the general sliding behavior the most unstable sliding is associated with gouge composed of minerals with intermediate hardness dolomite anhydrite and calcite these gouges undergo the transition from stable sliding to stick slip at pressures of 50 80 mpa gouge composed of hard mineral such as quartz or feldspar behave more stably but stick slip occurs at pressures above 250 mpa only stable sliding is observed for gouge composed of soft minerals like halite although anhydrite gouge shows violent stick slip at 100 mpa pressure whereas only stable sliding occurs for quartz at the same pressure when they are mixed the behavior changes systematically with composition the inclusion of only 10 anhydrite permits stick slip and hence even a minor constituent mineral of fault gouge may alter the sliding mode for gouge composed of two distinct layers the more stabilizing member of the two dominates the behavior and the behavior is considerably different from that of homogeneously mixed gouge with the same bulk composition this suggests the significance of internal structures of natural fault zone in understanding the effects of fault zone materials on the fault motion the gouge composed of calcite or a mineral harder than calcite all show high and approximately the same ultimate frictional strength with an exception of fluorite the frictional strength is intermediate for fluorite galena and barite gouges and it is low for halite gouge

timing of deglaciation and postglacial environmental dynamics in nw iberia the sanabria lake record abstract the multiproxy study sedimentology geochemistry and diatoms of sediment cores from sanabria lake 42 07 30 n 06 43 00 w 1000 m a s l together with a robust 14c chronology provides the first high resolution and continuous sedimentary record in the region extending back the last 26 ka the development of a proglacial lake before 26 cal ka bp demonstrates the onset of deglaciation before the global last glacial maximum similarly to other alpine glaciers in southern european mountains rapid deglaciation occurred at the beginning of the greenland interstadial gi 1e bolling 14 6 cal ka bp following a short lived episode of glacier re advance 14 4 14 2 cal ka bp gi 1d a climatic improvement at 13 9 cal ka bp suggests the glaciers retreated from the lake basin during the gi 1c another glacier reactivation phase occurred between ca 13 0 12 4 ka starting earlier than the onset of gs 1 younger dryas rapid deglaciation during the early holocene 11 7 10 1 cal ka bp was followed by a period of higher river discharge 10 1 8 2 cal ka bp after 8 2 ka the holocene is characterized by a general decreasing trend in humidity punctuated by the driest phase during the mid holocene ca 6 8 4 8 a wetter interval between 4 8 and 3 3 cal ka bp and a relatively decline of rainfall since then till present with a minor increase in humidity during some phases ca 1670 1760 of the little ice age discrete silt layers intercalated in the organic rich holocene deposits reflect large flooding events of the tera river ca 10 1 8 4 7 5 6 2 5 7 5 6 4 6 4 2 3 7 3 3 3 1 2 7 2 5 and 2 0 cal ka bp their synchronicity with a number of cold and humid events described in the atlantic demonstrates a strong control of nw iberian climate by north atlantic dynamics at centennial millennial scale comparison with western mediterranean records points to similar regional dynamics during the holocene although modulated in the nw iberian peninsula by the stronger atlantic influence

petrographic and isotopic evidence for holocene long term climate change and shorter term environmental shifts from a stalagmite from the serra do courel of northwestern spain and implications for climatic history across europe and the mediterranean abstract a small stalagmite from cova da arcoia in the serra do courel of northwestern spain provides a record both of general climate change across the holocene and of shorter term shifts between wetter and drier conditions nineteen u series dates from 9 3 ka to the present provide a chronology of the stalagmite with uncertainties of commonly only decades and at the most only 200 years these dates constrain the age of 18 petrographic surfaces that are of two types one type e inferred to result from dissolution during enhanced flow of water and the other type l inferred to result from lesser flow aragonite is more abundant in the earlier parts of the stalagmite and calcite is more abundant in the later part values of 13 c range from 5 6 to 1 3 relative to vpdb but are greatest beneath type l surfaces values of 18 o range from 5 4 to 4 4 relative to vpdb and have a weak but statistically significant correlation with 13 c greater abundance of aragonite greater values of 13 c and lesser frequency of type e surfaces early in the stalagmite suggest a drier and perhaps warmer early to middle holocene whereas greater abundance of calcite and frequent type e surfaces higher in the stalagmite suggest wetter conditions later in the holocene 18 o data are most compatible with this general conclusion however a prominent type e surface records the 8 2 ka event as an isolated wetter episode in the otherwise dry early holocene much of the stalagmite s aragonite and calcite suggests normal stalagmite growth in moderate climatic conditions however the near or complete cessation of growth at type l surfaces and greater 13 c greater 18 o and lesser fluorescence of aragonite beneath those surfaces combine to suggest at least six century scale episodes of strikingly dry conditions on the other hand evidence of dissolutional erosion at type e surfaces suggests at least ten distinct episodes of much wetter conditions these combine to suggest highly variable climate across the holocene at the scale of decades to a few centuries the record from this stalagmite is similar to records from greenland ice cores and from pollen and or stalagmite records from france northernmost spain and more broadly from northern or atlantic facing europe in contrast it suggests trends nearly opposite those in records from eastern and southern spain suggesting that the serra do courel is north of but perhaps not far from the boundary between atlantic and mediterranean regions of holocene climate trends in the iberian peninsula that general antiphasal relationship between northwestern spain and regions to the south and east extends to the specific observation that four of the most pronounced wetter events in the stalagmite s record coincide with periods of widespread drought and or cultural collapse in the mediterranean and middle east

palaeoflood and floodplain records from spain evidence for long term climate variability and environmental changes abstract palaeoflood chronologies from seven spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed these fluvial records were divided in to two sub sets namely atlantic 10 ka record and mediterranean 3 ka record river basins which represent distinct modern hydroclimatic conditions in atlantic basins floods result from intense widespread rainfalls associated with atlantic frontal systems transported by westerly airflow mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems mcss during autumn months evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10 750 10 240 9550 9130 4820 4440 2865 2350 960 790 and 520 290 cal bp despite the different flood producing weather conditions in atlantic and mediterranean rivers the radiocarbon sample clusters overlap and indicate changes in large scale atmospheric circulation and climatic conditions in the iberian peninsula comparison with proxy records of mean temperature for the northern hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases e g the 2650 yr bp climatic event or ad 1590 1650 period of the little ice age radiocarbon dates from aggraded floodplain sediments were clustered at 2710 2320 2000 1830 and 910 500 cal bp the first cluster period is in phase with the timing of slackwater deposition whereas the third 910 500 cal bp occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records it is argued that the 910 500 cal bp floodplain aggradation period reflects the first post roman evidence of environmental change related to generalised land use changes at the catchment scale which produced high sediment load transported to overbank areas during high flows

the holocene and upper pleistocene pollen record from padul granada spain a new study two borings were made at the site of padul granada pollen analysis of 200 spectra from two successive sequences 14 8 and 8 m deep enables a description of the vegetational and climatic history of this region the most southern one in europe from early wurmian times the chronology is supported by twenty one 14c dates original equivalents are found for the great european prewurm interstadials a markedly arid though thermically not extreme episode exactly equivalent to stage 4 of the marine isotopic stratigraphy closes this relatively temperate period the middle part of the last glacial shows climatic fluctuations that are poorly characterized as is often the case in europe for this period a long section very probably corresponding to the complete last pleniglacial does not show any climatic amelioration towards 15 000 yr b p a change in the diagram is noted that can only be interpreted as reflecting a larger expansion of a regional steppe cover this event also reported on three occasions in southeast france marks the beginning of the oldest dryas the climatic amelioration of ca 13 000 yr b p is far more pronounced here than anywhere else in europe whereas that at 10 000 yr b p is not so clearly marked this unexpected result may be accounted for by the fact that padul is the first continental site so far south and so near pleniglacial refuges to be known on the other hand this result is consistent with what is known from oceanic isotopic stratigraphy a quite new late glacial and holocene vegetational history is revealed characterized by the early appearance and dominance of quercus ilex oak forests of a southern type and the early occurrence of quercus suber and olea it is the first account of a complete history of the postglacial reafforestation in a region with a modern semi arid mediterranean climate from the palaeoclimatic point of view it shows that the hot and humid holocene optimum was attained slightly before 8000 yr b p and that the holocene climatic fluctuations were of but small amplitude

effects of temperature and co2 on the frictional behavior of simulated anhydrite fault rock the frictional behavior of anhydrite bearing faults is of interest to a the safety and effectiveness of co2 storage in anhydrite capped reservoirs b seismicity induced by hydrocarbon production and c natural seismicity nucleated in evaporite formations we performed direct shear experiments on simulated anhydrite fault gouges at a range of temperatures 80 150 c and sliding velocities 0 2 10 ms 1 under a fixed effective normal stress of 25 mpa four types of experiments were conducted 1 dry experiments 2 experiments pressurized with water 3 dry experiments pressurized with co2 and 4 wet experiments pressurized with co2 fluid pressures of 15 mpa were used when applied over the temperature range investigated water saturated samples were found to be up to 15 frictionally weaker than dry equivalents wet samples containing co2 were also up to 15 weaker than co2 free equivalents dry sample strength without co2 was independent of temperature whereas wet samples without co2 strengthened 10 from 80 to 150 c samples containing co2 weakened by 4 dry and 10 wet from 80 to 150 c under the p t conditions investigated only dry anhydrite fault gouge showed velocity weakening behavior above 120 c required for faults to potentially generate earthquakes assuming natural fault gouges are wet in situ seismicity is unlikely to nucleate in anhydrite rich faults though the presence of dolomite or reaction produced calcite may change seismic potential co2 penetration into wet anhydrite rich faults may trigger slip on critically stressed faults due to the observed short term co2 weakening effects excluding possible formation of secondary minerals but is not expected to influence slip stability

diatom responses to holocene environmental changes in a small lake in northwest spain abstract the holocene history of lagoa grande 1360 m a s l northwest spain has been investigated through the analyses of diatom remains found in a sediment core changes in the lake have been interpreted in terms both of climatic variability and major changes in the catchment area the diatom record begins at about 9800 yr bp and exhibits three marked changes at 8200 6000 4200 and at 2600 yr bp which are interpreted as responses to climatic changes detected by marine and other terrestrial palaeoclimatic records the initial lake was shallow and aulacoseira species characteristic of acidic and oligotrophic waters were dominant the early holocene is characterised by the presence of aulacoseira ambigua which suggests an increase in water depth and nutrient levels throughout the holocene diatom assemblages underwent several changes linked to fluctuating limnological conditions these changes in lake characteristics coincide with the regional succession of vegetation suggesting that climate forcing initiated these limnological changes during the last 2000 years catchment processes appear to be the major factor controlling lake characteristics in lagoa grande site diatom responses reflected the progressive peatland development and growth of littoral vegetation in the lake and not only a change in the regional environment

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

environmental response of a fragile semiarid landscape bardenas reales natural park ne spain to early holocene climate variability a paleo and environmental magnetic approach abstract the bardenas reales natural park western ebro basin ne spain constitutes a fragile landscape where the prevailing semiarid climate and erodability of the bedrock have resulted in high sensitivity to erosion sedimentation oscillations during the holocene in this paper we present new chronologic sedimentologic paleomagnetic and environmental magnetic results from the oldest unit qah1 of a system of nested cut and fill alluvial sequences which is 18 m thick and crops out extensively in the central part of the natural park at the bardena blanca depression radiocarbon dating indicates that early holocene unit qah1 is younger than 9 38 8 89 cal kyr bp and gives ages of 8 92 8 42 and 7 59 7 37 cal kyr bp in the middle and uppermost parts of the unit respectively sedimentologic data indicate that distal alluvial sediments of unit qah1 accumulated in sandy mud flats and ephemeral playa lakes under arid conditions the coincidence of enhanced magnetite content with moderate to intense root bioturbation in the lowermost and likely also uppermost sediments of unit qah1 suggests that magnetite formed authigenically in response to relatively wetter conditions at the beginning and end of this dry period these results indicate that onset and cessation of alluvial aggradation mark the passing of a geomorphologic threshold most likely plant cover in the watershed during a progressive drying wetting event the radiocarbon based age model of unit qah1 indicates that alluvial aggradation under arid conditions began at 9 13 cal kyr bp and ended at 7 16 cal kyr bp this period is strikingly centered at around the 8 2 kyr cold event but spans a longer time period supporting the notion of a global climatic deterioration as the underlying cause for this event paleomagnetic directions do not clearly display the characteristic patterns recognized in paleosecular variation curves derived from other european lacustrine sediments and cannot be used to refine the radiocarbon based age model for unit qah1 our results demonstrate a quick and strong response of alluvial systems to early holocene climate variability in fragile mediterranean landscapes such as those at the semiarid bardenas reales natural park

the 8 2 ka event and early mid holocene forests fires and flooding in the central ebro desert ne spain abstract the impact of the 8 2 ka cooling event during the early mid holocene has not been widely observed in southern europe which in contrast to northern europe was already experiencing a cooler than present climate at this time multi proxy analysis of sediment cores from two closed basin saline lakes in the central ebro desert ne spain has allowed us to investigate the impact of climatic changes around the time of this event in more detail long term changes in climate between the early and mid holocene indicate a shift in winter to a more positive nao resulting in declining lake levels in one lake sensitive to winter groundwater recharge and cooler winter temperatures reconstructed from pollen climate analysis reconstructed summer temperatures also declined over this period while annual precipitation and forest cover increased interpreted as a result of enhanced convection driven summer precipitation association with a northward displacement of the sub tropical high pressure around 8 2 ka a marked increase in fire frequency is shown between ca 8 8 and 8 0 ka bp along with an expansion of fire tolerant evergreen oak and peak in water levels in a second storm run off fed lake a maximum in fire intensity occurred with the deposition of a charcoal layer at both lake sites dated to 8150 130 and 8285 135 cal bp respectively the increase in fire is largely attributed to a temporary return southward of the summer sub tropical high pressure over the mediterranean which not only increased summer aridity but also caused a contradictory regional warming before hemispheric cooling set in

an early holocene short climatic event in the northwest iberian peninsula inferred from pollen and diatoms abstract pollen and diatom analyses have been carried out in a 490 cm long core collected from laguna lucenza 1420 m a s l northwest iberian peninsula spanning the last 10 000 yr pollen analyses show a decrease in deciduous quercus pollen percentages and total pollen concentration after radiocarbon date 8350 80 yr bp the estimated age by linear interpolation for the peak of this event is about 9200 cal yr bp diatom analyses have been carried out using the same samples in order to obtain complementary information about past environmental conditions within the water body pollen and diatom records show a response to changes in the palaeoenvironmental conditions diatom concentrations are relatively low indicating low productivity within the lake fragilaria species are dominant and fragilaria exigua is notably more abundant than during previous periods these changes in the diatom community reflect a decrease in lake ph this would be consistent with longer periods of ice cover and cold conditions in the lake at this time we interpret this episode as a response to climatic change probably due to climatic deterioration this interval coincides at least in part with an episode of abrupt and short widespread climate change lasting from 9000 to 8000 yr bp

spatial and temporal patterns of iceberg rafting ird along the east greenland margin ca 68 n over the last 14 cal ka twelve 1 2 m 10 cm diameter gravity cores collected in 1988 and 1991 from the continental shelf and fjords of east greenland near kangerlussuaq fjord trough ca 68 n 32 w have distinct changes in lithofacies and in the quantity of iceberg rafted ird sediments these changes are readily observed in x radiographs of the split cores we quantify the ird contribution through grain size analyses and counting the number of clasts 2 mm from the x radiographs chronological control is provided by acclerated mass spectroscopy 14c dates on foraminifera during deglaciation after 14 cal ka there was one interval of ird accumulation ca 12 13 cal ka followed by a brief return to ird conditions centred at 9 cal ka thereafter a prominent feature of most cores on the shelf is an increase in ird accumulation that started ca 5 6 cal ka and which has increased toward the present indicators of iceberg rafting such as the net sand flux and numbers of clasts 2 mm ka 1 follow a power law distribution when graphed against distance from the present east greenland coast a measure of the position of the glacier margins the form of the relationship indicates that there is a dramatic decrease in the supply of sediment from the fjords to the shelf these relationships are used to estimate changes in the location of the ice margin during the late quaternary based on a site on the east greenland slope denmark strait and to discuss factors that can negate such a simple transfer function 1997 by john wiley sons ltd

low temperature frictional characteristics of chlorite epidote amphibole assemblages implications for strength and seismic style of retrograde fault zones in retrograde faults exhuming mafic rocks shearing occurs in metamorphic and or hydrothermally altered mineral assemblages whose frictional properties are not well known here we present the results of laboratory shearing experiments on chlorite schist epidotite and hornblende dominated amphibolite and mixtures of these rocks and evaluate their frictional properties and microstructures the experiments were conducted on powdered rock samples with starting grain size of 125 m at room temperature under fluid saturated conditions and applied normal stress of 10 mpa the results show that chlorite schist is relatively weak friction coefficient of 0 36 whereas epidotite and amphibolite are strong friction coefficients of 0 63 and 0 67 respectively the friction of chlorite schist epidotite and chlorite schist amphibolite mixtures decreases nearly linearly with increasing chlorite content chlorite schist exhibits velocity strengthening behavior epidotite is velocity weakening and the amphibolite shows mostly velocity weakening friction mixtures show intermediate strength and velocity dependence of friction well developed striations formed on slip surfaces in samples with 50 chlorite schist the epidotite slip surface exhibits a mixture of very fine particles and coarser crystals amphibolite slip surfaces have less very fine grains and are composed of subhedral to euheral needles few intragranular fractures are preserved and we infer wear at contact asperities to be the likely cause of velocity weakening in our epidote gouges addition of chlorite to epidotite and amphibolite produces a striated slip surface and disrupts contacts between harder grains therefore retrograde chlorite growth is expected to facilitate frictional weakening and stable slip in higher grade mineral assemblages exhumed to low temperature conditions

textures of sheared halite and their implications for the seismogenic slip of deep faults abstract halite exhibits a wide spectrum of behavior from frctional slip in the brittle field to fully ductile shearing flow even at room temperature and the simulated halite shear zone is ideal for studying mechanical properties of large scale faults and plate boundaries with the currently available apparatus thirty nine triaxial experiments were performed on dry cylindrical specimens of tennessee sandstone with a 0 5 mm thick layer of synthetic or natural halite along a 35 precut at room temperature with a constant slip rate along the precut ranging from 3 to 300 m s and at confining pressures up to 200 mpa mechanical data are consistent with those reported previously shimamoto 1985c 1986 this paper reports observations on these and some previous specimens our new data reconfirm the earlier results by shimamoto and logan that 1 nearly homogeneous shearing deformation characterized by the formation of a well developed foliation changes into heterogeneous shearing after a critical shear strain and that 2 the potentially unstable fault motion is associated with this strain localization within the shear zones the nature of this heterogeneous deformation is examined closely in this paper and it is shown that the primary mode of internal slip within the shear zones is slip along y riedel shears interconnected with r 1 riedel shears thus some kind of brittle deformation possibly overlaps the predominantly plastic deformation after strain localization although no direct evidence of cataclastic deformation can be found owing to the nearly complete recrystallization of halite more importantly potentially unstable fault motion occurs only when internal shearing takes place along narrow nearly planar and discrete surfaces at pressures above about 100 mpa the discontinuous zones become wider and irregular and the potentially unstable fault motion disappears seismogenic slip thus extends well into the semiductile regime of deformation and mylonites should receive renewed attention with the view that at least some of them could well be associated with seismogenic fault motion

frictional properties of sedimentary rocks and natural fault gouge from the longmen shan fault zone sichuan china in this paper we report friction experiments performed on samples collected from the region hit by the 2008 wenchuan earthquake in the longmen shan fault zone lfz of sichuan southwestern china the materials tested consisted of simulated gouges prepared from intact clay rich mudstone and sandstone a calcite limestone plus a natural fault gouge from a trenched surface rupture cutting the mudstone and sandstone the clay rich samples including the natural gouge were dominated by illite and quartz in our experiments we sheared 1 mm thick gouge layers between saw cut driver blocks using a triaxial testing machine at conditions corresponding to 2 km depth in the lfz temperature was varied from 25 c to 150 c and to investigate the velocity dependence of friction we stepped the shear displacement rate between 1 22 and 0 122 m s our results show that the natural gouge was more illite rich and much weaker than the protolith mudstone and sandstone and showed a steady state friction coefficient of 0 4 compared with 0 6 for the latter the limestone gouge displayed values of 0 6 0 7 all samples except the limestone showed stable velocity strengthening slip the limestone showed velocity strengthening at 25 c 50 c but quasi static oscillations at 100 c 150 c along with velocity weakening behavior at 150 c we apply our results to discuss the role of the sedimentary rocks studied during events such as the wenchuan earthquake and argue that the clay rich sediments of the region may have a damping effect upon ruptures propagating from depth whereas the limestone may accelerate propagation producing significant stress drops

sliding behavior and deformation textures of heated illite gouge abstract the run products of a series of triaxial friction experiments on an illite rich gouge have been examined petrographically to study the relationship between textural development and sliding mode the samples show a complete range of textures from ones in which the entire gouge layer is deformed to ones in which the deformation is concentrated along narrow subsidiary shears and the rest of the gouge layer is massive the samples with a pervasively developed deformation fabric slide stably whereas the samples containing shear bands show stick slip motion if the intersection angles between boundary parallel and cross cutting riedel shears are also relatively high these textural differences suggest that localization of shear combined with higher angle riedel shears are somehow involved in stick slip motion the orientation of riedel type shears in natural fault zones may also have potential as a paleoseismological tool

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

the holocene fluvial chronology of spain evidence from a newly compiled radiocarbon database abstract a critical analysis of 74 radiocarbon dates selected from a total of 102 published and unpublished dates from holocene fluvial environments in spain has identified a number of periods of increased fluvial activity in spain namely 11 170 10 230 9630 8785 7980 6860 5800 4800 3880 3085 2895 1820 1300 0 cal bp the latter period reflecting sustained fluvial response to increased human impact the radiocarbon samples were classified according to type of depositional environment a alluvial overbank b flood basin c alluvial channel gravels d fluvio torrential deposits and e slackwater flood deposits palaeofloods dates from slackwater flood deposits indicated at least five phases of increased frequency of large magnitude floods during the holocene 10 855 10 230 9530 8780 2880 2430 975 790 and 520 265 cal yr bp flood basin type deposition occurred from 7980 to 4830 cal yr bp the main clusters of dates from alluvial floodplain deposits occurred at 2750 2150 and 930 520 cal yr bp the record is discussed in relation to other palaeoenvironmental archives including pollen records of holocene vegetation change and palaeoclimatic proxies such as the north atlantic drift ice record comparison with the latter indicates that major holocene flooding coincided with cold climate phases during 9530 9280 2880 2430 and 520 265 cal yr bp a cooling phase at 10 855 10 230 and warming phases at 9030 8780 and 975 790 cal yr bp

diatom and vegetation responses to late glacial and early holocene climate changes at lake estanya southern pyrenees ne spain abstract we investigate lake estanya s diatom and pollen records from the late glacial lg to the early holocene eh in order to compare limnological and vegetation responses to common climate forcing the biotic changes recognized in this study largely agree with the hydrological evolution of the lake described previously for the same period the diatom record shows high sensitivity to fluctuations in both lake level and salinity concentration as a consequence of climate shifts in addition vegetation results indicate that the area could have played an important role as regional vegetation refuge shallow lake conditions during the last glacial maximum lgm were punctuated by relatively deeper freshwaters between 19 3 and 18 6 cal kyr bp and at 18 0 cal kyr bp as recorded by diatom shifts a subsequent increasing aridity trend coinciding with the mystery interval mi affected the diatom accumulation rates which dropped to its minimum values between 17 2 and 14 7 cal kyr bp particularly dry and cold conditions during the lgm and mi are supported by the largest values of steppic pollen taxa of the whole sequence which account for up to 40 however relatively high values of betula during the heinrich event 1 suggest a plausible regional vegetation refuge abrupt cooling and warming episodes within the lg triggered remarkable ecological threshold crossings in the diatom communities especially during the stadial interstadial episodes at this point the vegetation reflects the onset of warm conditions during the bolling allerod with the partial substitution of betula by marcescent and evergreen quercus which probably indicates the arrival of temperate taxa to the area and the likely migration of birch to higher altitudes the younger dryas stadial shows a complex ecological response diatoms are very poorly preserved but aquatic taxa reach their highest values an increase in marcescent quercus during this cold stage lends further support to the hypothesis that this is a regional vegetation refuge low lake levels recorded during the eh affected the development and preservation of diatom communities a delay in the onset of humid conditions for the eh is also supported by the vegetation composition characterized by the maximum expansion of juniperus

the larderello geothermal field a review abstract this paper reviews published geological geophysical petrological and geochemical data together with reservoir engineering parameters of the larderello geothermal reservoir of southern tuscany italy some theories are proposed on the deep origin evolution in time and natural state of this geothermal field prior to its exploitation the interaction between the vapor dominated reservoir and surrounding aquifers is discussed analysis of hydrogeochemical data suggests that meteoric waters from shallow external aquifers contribute little to the production of steam the vapor dominated system and the cold external aquifers are separated by areas of very low permeability where physical conditions change greatly over short distances the presence and significance of liquid phases in the peripheral areas of the vapor dominated reservoir are interpreted as being due to steam condensation the latter is a consequence of a low permeability conditions in the deep buried parts of the carbonate reservoir formations in the north northwestern sector of the field and b by the mixing of ascending superheated steam from depth with cold caso4 meteoric waters circulating in unconfined shallow aquifers within the outcrops of the carbonate reservoir formations in the south southeastern parts of the field the presence of steam below these liquid dominated sectors of the reservoir seems possible the limited natural recharge of the system the constant steam production rate for geothermal power generation 3000 t h 1 since 1951 the persistence of natural thermal features and the fact that reinjection has had little effect on the characteristics of the fluid discharged seem to indicate a steady state for the larderello field the main contribution to production seems to be from superheated steam ascending from depth and the in situ evaporation of water stored in the small pores of the rocks present in larderello in a system that is much larger than the one known at present

nonlinear characteristics of paleoseismicity in china detailed studies of historical seismicity and paleoseismological data for major late quaternary faults in china reveal spatial and temporal patterns in paleoseismic activity associated with these faults analysis of space time distributions of late quaternary faults and consideration of new models for deformation of the asian continent provide a basis for proposing a division of china and surrounding areas into five active tectonic provinces slip rates for active faults are highest in the himalayan collision zone between the indian and eurasian plates and gradually decrease away from the collision zone into the adjacent active tectonic provinces paleoearthquake recurrence intervals in the active tectonic provinces of china reflect seismogenic properties that are closely related to the position of these provinces relative to the converging indian and eurasian plates average recurrence intervals are 2000 years to as little as 310 900 years for active faults in the qinghai tibetan active tectonic province whereas recurrence intervals are 2000 4500 years in the xinjiang active tectonic province and longer than 2000 years to as much as 7250 years in the north china active tectonic province although average recurrence intervals are closely related to the slip rates of late quaternary faults no simple linear relationship exists between recurrence interval and slip rate further analysis of paleoseismicity on major active faults shows that there are temporal variations in recurrence intervals the case studies also indicate that for some provinces faults or fault segments there are three paleoseismic patterns linear logarithmic and stepped in the logarithmic and stepped patterns the earthquake temporal sequence is characterized by active periods earthquake clusters with relatively short recurrence intervals and quiet periods lack of clustering and relatively long recurrence intervals

implications of the mechanical and frictional behavior of serpentinite to seismogenic faulting the widespread occurrence of serpentinite along major strike slip seismogenic faults warrants systematic investigation to determine how its frictional characteristics may affect slip along the fault different locations along the motagua fault zone in guatemala were sampled to investigate the sliding mode as a function of composition and texture confining pressure and displacement rate air dried right circular cylinders 7 1 cm in length and 3 3 cm in diameter with a precut 35 to the cylinder and load axes were deformed at confining pressures up to 200 mpa room temperature and displacement rates of 10 4 and 10 7 cm s compositional analyses of specimens cored from five blocks of serpentinite that were tested show that the serpentinite can be divided into two groups one is a mesh textured serpentinite containing up to 70 serpentine mostly lizardite 11 enstatite phenocrysts 19 oxides and minor amounts of olivine and carbonate undifferentiated the other is a flare textured serpentinite containing up to 84 serpentinte mostly antigorite 10 oxides 6 magnesite and dolomite and almost no enstatite or olivine the flare serpentinite undergoes the transition from stable sliding to stick slip sliding at confining pressures as low as 10 mpa the mesh serpentinite results only in stable sliding up to confining pressures of 200 mpa and a displacement rate of 10 4 cm s at a displacement rate of 10 7 cm s only one of the three mesh blocks exhibits stick slip the shear stress required to initiate sliding for the flare textured serpentinites is given by 0 77 n for the mesh textured serpentinites at a displacement rate of 10 4 cm s it is given by 0 56 n and at a displacement rate of 10 7 cm s by 0 50 n differences in fracture strength between the five specimen blocks correlate with differences in frictional strength differences in the sliding behavior and in the deformation observed along the sliding surfaces can be related to the mineralogical components of each serpentinite type extensive deformation occurs in the mesh serpentinites as a result of hard oxide and enstatite indenters ploughing through a soft lizardite substrate lizardite lizardite contacts prevail and these deform by plastic flow the stick slip behavior in the flare textured serpentinites is explained by brittle failure of antigorite antigorite contacts the smaller grain size of the flare serpentinites relative to the mesh serpentinites may also contribute to the higher frictional strength of the flare serpentinites we discuss the implications of the antigorite rich flare textured serpentinite to seismogenic faulting in particular we consider the case of antigorite forming by shear heating induced progressive metamorphism of lizardite chrysotile serpentinites if serpentine dehydration temperatures are approached talc may form having a lower coefficient of friction than serpentine talc may act as a lubricant along the fault plane

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

slip and recrystallization of halite gouge in experimental shear zones abstract cylindrical specimens of tennessee sandstone with dry crushed halite between 35 precut surfaces are deformed at 70 mpa confining pressure at displacement rates from 10 2 to 10 6 cm s at 25 c and the shear strains of 16 0 under these conditions peak differential stress is attained at shear strains between 3 and 5 followed by quasi steady state behavior with subtle but possibly significant oscillations over the complete variation of conditions steady state stress levels range from 146 to 169 mpa at shear strains 6 0 the fabric of the halite gouge 0 2 to 1 0 mm thick changes with increasing shear strain from 1 a homogeneously elongated grains up to peak stress indicative of dislocation glide to 2 b a bimodal mosaic of recrystallized grains consisting of very fine grained neoblasts and relatively large euhedral porphyroblasts that is associated with a small stress drop to 3 c a mosaic of uniformly sized anhedral neoblasts produced from the coalescence of porphyroblasts grain size of the very fine grained neoblasts remain reasonably constant with increasing but that of the porphyroclasts and of the resulting mosaic decrease with increasing 100 of the porphyroblasts are strongly and conspicuously oriented at 45 to the shear zone boundary at 4 4 and progressively rotate with the finite strain axes so that at 9 4 100 are inclined at 70 80 and 10 20 to the shear zone it is argued that fabrics b and c are consistent with dynamic recrystallization by grain boundary migration from favorably oriented nuclei grains a ghost structure of aligned grain boundaries and impurities pervades all the shear zones and is oriented at progressively smaller angles to the shear zone boundary as shear strain increases there is a one to one correspondence between these angles and those calculated assuming simple shear this fact along with the constant thickness of the gouge with increasing shear strain indicates that the deformation is modeled by progressive homogeneous simple shear

frictional properties of simulated anhydrite dolomite fault gouge and implications for seismogenic potential the frictional properties of anhydrite dolomite fault gouges and the effects of co2 upon them are of key importance in assessing the risks associated with co2 storage in reservoir formations capped by anhydrite dolomite sequences and in understanding seismicity occurring in such formations such as the italian apennines therefore we performed velocity stepping direct shear experiments on simulated dolomite anhydrite and 50 50 anhydrite dolomite gouges at representative in situ conditions 120 c and ne 25 mpa they were conducted under vacuum or else using water or co2 saturated water as pore fluid pf 15 mpa friction coefficients varied between 0 55 and 0 7 all dry samples exhibited velocity weakening behavior whereas all wet samples exhibited velocity strengthening behavior without or with co2 this is consistent with trends previously reported for such gouges a compilation of literature data shows that the transition from velocity strengthening to velocity weakening occurs in these materials between 80 and 120 c when dry and between 100 and 150 c when wet this implies little seismogenic potential for wet dolomite anhydrite and mixed gouges under co2 storage conditions at 2 4 km depth seismic slip in the italian apennines at depths of 6 km and beyond may be explained by the velocity weakening behavior expected in anhydrite and especially dolomite at temperatures above 150 c

the origin of large or great thrust type earthquakes along subducting plate boundaries abstract seismicity deformation state of stress and abundance of fluids along subducting plate boundaries are reviewed and the origin of large or great thrust type earthquakes is discussed based on the recent experimental results on the slip behavior of halite and serpentine gouges shallow subducting plate boundaries above 20 25 km in depth are characterized by low seismicity low tectonic stress inter plate decoupling ductile deformation associated with the formation of metamorphic schistosity except at very shallow depths metamorphism suggesting solution processes on massive scale and presence of abundant h 2 o it is argued that these unique features are due to pressure solution processes to high fluid pressure to low strength and stable behavior of clayey sediments under wet environments and or to the deformation of soft unconsolidated sediments at very shallow depths the low seismicity in this zone is in marked contrast with major strike slip faults along which large earthquakes occur at depths shallower than 15 20 km it is emphasized that these unique features are expected only for restricted regions where there is constant supply of h 2 o due to progressive metamorphism or where fluids in the rocks are trapped and cannot escape to the surface large or great thrust type earthquakes in subduction zones initiate at depths of 30 50 km below the shallow decoupled zone in this focal depth range the supply of h 2 o during progressive metamorphism perhaps diminishes downwards the overriding and subducting plates are coupled and stick to each other during much of the inter seismic period and the resistance to slip or shear stress is presumably high it is suggested that these earthquakes begin to occur at a depth where the plate boundary zone becomes fairly dry deformation at these depths appears to be predominantly ductile so that the earthquakes cannot be regarded simply as a brittle phenomenon 1 creep instability i e instability associated with plastic deformation and 2 dehydration induced instability are the most likely mechanisms for initiating the earthquakes and both have some experimental support stick slip of halite gouge while undergoing ductile deformation primarily by intracrystalline gliding is described and discussed as a supporting evidence for 1 shear resistance of halite gouge increases with increasing confining pressure in stick slip regimes hence the observed stick slip may be a semi brittle phenomenon with respect to the pressure dependence of the shear resistance although the deformation texture cannot be distinguished from that formed by pressure insensitive flow serpentine gouge exhibits violent stick slip upon its decomposition under dry not wet environments supporting the mechanism 2 above exact mechanisms which lead to the unstable fault motion are poorly understood as yet but stick slip of both halite and serpentine gouges is recognized only when the slip rate dependence of friction is negative i e lower friction at faster slip rate consistent with the theoretical prediction of rice and ruina 1983 there is a possibility that the thrust type earthquakes can be explained essentially within the framework of fault constitutive laws developed by dieterich 1979 and ruina 1983

friction of ice the frictional strength of ice seems to be well below that for all other rocks triaxial testing of cylinders of pure water ice containing a 45 inclined sawcut at temperatures of 77 t 115 k and confining pressures 0 1 p 250 mpa reveals the frictional laws 0 20 n 8 3 mpa for p 10 mpa and 0 55 n 1 0 mpa for p 5 mpa where and n are the shear and normal stresses on the sawcut surface friction is independent of t and over the one order of magnitude tested of average sliding velocity the sliding behavior is invariably stick slip examination of sliding surfaces shows only minor gouge development a curious arrangement of densely packed short vertical fractures occurs primarily in samples with anomalously low strength these results apply to models of near surface tectonic activity on jupiter s three large icy moons europa callisto and ganymede they indicate for example that a global expansion on ganymede of 3 linear percent will cause extensional movement on preexisting faults at depths to 7 3 km

late pleistocene holocene palaeoenvironmental evolution of the anamaza river valley iberian range ne spain multidisciplinary approach on the study of carbonate fluvial systems abstract the uppermost pleistocene and holocene palaeoenvironmental evolution of the anamaza river valley iberian range ne spain is deduced using multidisciplinary approach including stratigraphical mineralogical palynological geochemical geophysical methods and drilling main changes were registered in distinct subenvironments of a carbonate fluvial system including the channelled zone and wetlands in the floodplain tufa barrages dominated although pools also existed geophysical survey and coring reveal tufa build ups and pool facies also in the subsoil lower water temperature and scarce evaporation are deduced for the pleistocene fluvial system that progressively changed through the holocene with more hydrologically closed areas and higher evaporation influence a general aggrading evolution during warm stages related with increasing base level and damming due to fast carbonate precipitation characterised the holocene detrital tufa indicates erosive high energy floods or colder stages when water level would decrease favouring erosion 14 c and 230 th 234 u dating reveal high sedimentation rates and three main discontinuities related with cold episodes younger dryas middle part of the holocene climate optimum and iron age epoch during the uppermost pleistocene tufa growth would be enhanced during warmer episodes as the bolling allerod in the younger dryas scarce vegetation favoured erosion of both slopes and tufa constructions subsequent warmer temperatures during the first part of the holocene favoured vegetated slopes enhanced tufa growing although interrupted in the middle part of the holocene climate optimum and development of wetlands with riparian vegetation in the floodplain where either siliciclastics or detrital tufa incoming alternated with low energy waters stages and mud settling progressive decline in tufa is deduced for the upper holocene but it is not possible to determine whether this and other palaeoenvironmental changes were related either to climate or increasing human activities during the roman and medieval warm periods more oxidizing conditions in the wetlands and increasing erosion prevailed probably conditioned by human activities the pollen record shows for the early holocene development of pinus forest with betula and expansion of deciduous quercus xerophilous and heliophilous grassland subsequent increasing moisture supported open forests with deciduous quercus ulmus corylus and evergreen quercus ilex pistacia species from ca 4000 yrbp a dominant deciduous quercus forest with groves of corylus ulmus acer fagus and taxus expanded and human activities grazing occurred from 1200 yrbp dry grassland expanded due to intensive land use agropastoral activities almost completely deforested plateaus surround the site today with slopes covered by patchy grass with junipers groves and screeds with little soil

asperity and barriers of the 2004 mid niigata prefecture earthquake revealed by highly dense seismic observations abstract a highly resolved velocity structure on the mainshock fault of the 2004 mid niigata prefecture earthquake was elucidated using arrival times from aftershocks observed by an extremely dense network of temporary seismic stations we evaluated the spatial relationship between the velocity structure and distributions of the slip stress change and aftershocks distributions of static stress drop on the fault were calculated from a kinematic slip model incorporating the 3d crustal structure a high velocity body with low aftershock activity was in proximity to the mainshock hypocenter and extended to the northeast side of the fault this high velocity body roughly coincided with an asperity where the amounts of coseismic slip and static stress drop were larger than those in the surrounding areas in contrast a zone of negative stress drop was observed on the shallow periphery of the high velocity body where the sediment thickness steeply increased southwestward and the aftershock activity was high we suggest that the structural heterogeneities of the host rocks surrounding the fault damaged zone have significant potentials to control dynamic rupture processes of the mainshock fault

paleolimnological records of climatic change in north america lacustrine fossil records provide long time series of data on limnological and climatic conditions these data are useful for establishing natural patterns of climate variability and for generating testable hypotheses about atmospheric circulation and climate ecosystem linkages shoreline features can indicate past lake level fluctuations that may reflect changes in moisture balance but often these records are discontinuous and are evidence of only extreme conditions the organisms geochemistry and sedimentology of lake sediments may provide a more continuous sequence of direct and indirect lake climate interactions in the past the most clearly interpretable paleolirnnological records of climatic change are those that use several lines of evidence to corroborate a climatic hypothesis and are from sites near an ecotone or in regions of extreme climate in all cases hydrologic setting mediates a lake s response to climate and must be considered in interpreting sedimentary sequences discussion of the impact of recent and future climatic changes necessitates a baseline against which the magnitude of observed or predicted changes can be measured commonly we look to recent history as a reference point for comparison however the landscape of recent decades or in some cases even centuries has been altered greatly by human activities thus to determine whether recent or future climatic change is unique or unusual we need long natural preanthropogenic time series against which observed or predicted climatic states and variability can be compared paleolimnological archives are a tool for looking at environmental patterns prior to anthropogenic impact and show a range of climatic states far greater than those documented by written records former strand lines of pluvial lakes bonneville and lahontan in the western u s for example testify to moisture extremes unsurpassed in recent centuries or even millennia in addition one can us the paleolimnological record as an independent climatic proxy against which patterns and rates of terrestrial response to climatic change can be compared here i present a broad overview of paleoclimatic reconstruction in north america from lacustrine records with a focus on the late quaternary the review is limited to climatic inference from paleolirnnological records a term i use in a restrictive sense to refer to records of past lake states physical biological and geochemical as opposed to records of past stream hydrology e g ely et al 1993 knox 1993 or terrestrial conditions i summarize paleolimnological tools available for reconstruction of past climate the capabilities and limitations of these tools

chemical composition of thermal springs cold springs streams and gas vents in the mt amiata geothermal region tuscany italy abstract a geochemical study of thermal and cold springs stream waters and gas emissions has been carried out in the mt amiata geothermal region the cold springs and stream waters do not seem to have received significant contribution from hot deep fluids on the contrary the thermal springs present complex and not clearly quantifiable interactions with the hot fluids of the main geothermal reservoir the liquid dominated systems in the mt amiata area like most of the high enthalpy geothermal fields in the world are characterized by saline nacl fluids the nature of the reservoir rock carbonatic and anhydritic and its widespread occurrence in central italy favor a regional circulation of ca sulfate thermal waters which discharge from its outcrop areas waters of this kind which have been considered recharge waters of the known geothermal fields dilute disperse and react with the deep geothermal fluids in the mt amiata area preventing the use of the main chemical geothermometers for prospecting purposes the temperatures obtained from the chemical geothermometers vary widely and are generally cooler than temperatures measured in producing wells other thermal anomalies in central italy apart from those already known might be masked by the above mentioned circulation a better knowledge of deep fluid chemistry could contribute to the calibration of specific geothermometers for waters from reservoirs in carbonatic rocks

constitutive behavior and stability of frictional sliding of granite an understanding of the frictional sliding on faults that can lead to earthquakes requires a knowledge of both constitutive behavior of the sliding surfaces and its mechanical interaction with the loading system we have determined the constitutive parameters for frictional sliding of initially bare surfaces of westerly granite using a recently developed high pressure rotary shear apparatus that allows long distances of sliding and therefore a greater assurance of attaining steady state behavior from experiments conducted at room temperature and normal stresses of 27 84 mpa several important results have been found 1 a gouge layer 100 to 200 m thick was developed from the initially bare rock surfaces after 18 to 70 mm of sliding 2 the steady state frictional resistance attained after about 10 mm of sliding is proportional to the negative of the logarithm of the sliding velocity 3 abrup changes in the velocity of sliding result in initial changes in the frictional resistance which have the same sign as the velocity change and are followed by a gradual decay to a new steady state value over a characteristic distance of sliding this velocity weakening behavior is essentially identical with that found by several previous workers on the same material at lower normal stress 4 our results are well described by a two state variable constitutive law the values of the constitutive parameters are quite similar to those found previously at low normal stress but the characteristic distance is about an order of magnitude smaller than that found at 10 mpa normal stress with thicker layers of coarser gouge 5 we have approximated our results with a one state variable constitutive law and compared the results with the predictions of existing nonlinear stability analysis in addition we have extended the stability analysis to systems possessing two state variables with such formulations good agreement is found between the experimentally observed and theoretically predicted transitions between stable and unstable sliding these results allow a better understanding of the instabilities that lead to earthquakes

pressure solution lithification as a mechanism for the stick slip behavior of faults many major faults including a large fraction of the san andreas appear to be virtually quiescent between great earthquakes the locked sections of the san andreas near san francisco and los angeles have little or no seismic activity on the primary fault trace although secondary faults may be active stick slip behavior on a fault can be explained in terms of a static coefficient of friction which is larger than the dynamic or sliding coefficient in this paper we propose a modification of the friction hypothesis in which chemical lithification cementation occurs on the fault between earthquakes as the stress on the fault increases it becomes large enough to break the cemented bonds between particles causing slip on the fault we treat this problem quantitatively assuming that pressure solution is responsible for the cementation an advantage of this model is that the hydrostatic pressure approaches the lithostatic pressure during cementation so that low fault strengths are predicted

experimental evidence linking slip instability with seafloor lithology and topography at the costa rica convergent margin seismicity patterns offshore costa rica central america at the middle america trench have led to speculation that large moment magnitude m w 7 0 earthquakes are associated with subducting topographic highs in areas of high basement topography a regionally extensive nannofossil chalk unit is exposed at the seafloor on the incoming plate whereas in regions of low basement topography hemipelagic clay rich sediment is exposed because the entire sediment section is subducted at this margin lithologic variation in the uppermost subducting sediments may control plate boundary fault behavior our laboratory experiments reveal that the chalk is frictionally strong 0 71 0 88 and characterized by velocity weakening and stick slip behavior notably at elevated temperature in contrast the hemipelagic sediment is weak 0 22 0 35 and in many cases velocity strengthening we suggest that the presence of frictionally unstable carbonates at bathymetric highs may play a key previously unrecognized role in governing earthquake nucleation

the role of fault zone fabric and lithification state on frictional strength constitutive behavior and deformation microstructure 1 we examine the frictional behavior of a range of lithified rocks used as analogs for fault rocks cataclasites and ultracataclasites at seismogenic depths and compare them with gouge powders commonly used in experimental studies of faults at normal stresses of 50 mpa the frictional strength of lithified isotropic hard rocks is generally higher than their powdered equivalents whereas foliated phyllosilicate rich fault rocks are generally weaker than powdered fault gouge depending on foliation intensity most samples exhibit velocity strengthening frictional behavior in which sliding friction increases with slip velocity with velocity weakening limited to phyllosilicate poor samples this suggests that lithification of phyllosilicate rich fault gouge alone is insufficient to allow earthquake nucleation microstructural observations show prominent throughgoing shear planes and grain comminution in the r1 riedel orientation and some evidence of boundary shear in phyllosilicate poor samples while more complicated anastomosing features at lower angles are common for phyllosilicate rich samples comparison between powdered gouges of differing thicknesses shows that higher riedel shear angles correlate with lower apparent coefficients of friction in thick fault zones this suggests that the difference between the measured apparent friction and the true internal friction depends on the orientation of internal deformation structures consistent with theoretical considerations of stress rotation

laboratory study of fault healing and lithification in simulated fault gouge under hydrothermal conditions abstract seismic data geologic observations and laboratory friction studies suggest that faults lithify and strengthen heal during the interseismic period of the earthquake cycle we report on experiments to investigate the influence of healing duration and temperature on the strength and healing rate of simulated faults layers of m sized quartz powder were used to simulate granular fault gouge gouge layers were sheared within sioux quartzite in a triaxial pressure vessel at elevated pressures p c 250 mpa elevated temperatures 230 636 c and in the presence of water p h 2 o 75 mpa we performed hold slide experiments in which samples were subjected to a period of healing under hydrostatic load followed by shear deformation healing times ranged from a few hundred s to 10 5 s to isolate the effects of lithification and temperature on friction we ran two types of hold slide experiments 1 samples were subjected to healing and shear deformation at elevated temperature and 2 following healing at elevated temperature temperature was reduced prior to shear we also ran slide hold slide experiments in which samples were healed under shear load at elevated temperature 636 c experiments in which deformation was carried out at a lower temperature than healing show that both the static and sliding coefficient of friction increase with heal time samples healed and deformed at higher temperature showed lower peak strengths and within the scatter of our data did not exhibit time dependent strengthening these data are interpreted to result from enhanced lithification rates at elevated temperature samples healed under shear load exhibited a log linear decrease in friction with hold time modeling using rate and state dependent friction laws indicates velocity strengthening behavior with friction a b values of 0 05 to 0 08 our data indicate that at high temperature the effective state evolution term b is negative moreover the data indicate the rate of frictional strengthening varies significantly for hydrostatic and non hydrostatic load conditions our measurements of healing are consistent with seismic estimates of fault healing rates if stress drop is a fraction of the total shear stress and effective fault normal stress is 60 to 100 mpa

effects of simulated clay gouges on the sliding behavior of tennessee sandston abstract the effects of simulated fault gouge on the sliding behavior of tennessee sandstone are studied experimentally with special reference to the stabilizing effect of clay minerals mixed into the gouge about 30 specimens with gouge composed of pure clays of homogeneously mixed clay and anhydrite or of layered clay and anhydrite along a 35 precut are deformed dry in a triaxial apparatus at a confining pressure of 100 mpa with a shortening rate of about 5 10 4 sec and at room temperature pure clay gouges exhibit only stable sliding and the ultimate frictional strength is very low for bentonite mont morillonite intermediate for chlorite and illite and considerably higher for kaolinite anhydrite gouge shows violent stick slip at 100 mpa confining pressure when this mineral is mixed homogeneously with clays the frictional coefficient of the mixed gouge determined at its ultimate frictional strength decreases monotonically with an increase in the clay content the sliding mode changes from stick slip to stable sliding when the frictional coefficient of the mixed clay anhydrite gouge is lowered down below 90 95 of the coefficient of anhydrite gouge the stabilizing effect of clay in mixed gouge is closely related to the ultimate frictional strength of pure clays that is the effect is conspicuous only for a mineral with low frictional strength only 15 20 of bentonite suppresses the violent stick slip of anhydrite gouge in contrast violent stick slip occurs even if the gouge contains as much as 75 of kaolinite the behavior of illite and chlorite is intermediate between that of kaolinite and bentonite bentonite anhydrite two layer gouge exhibits stable sliding even when the bentonite content is only 5 thus the presence of a thin clay rich layer in a fault zone stabilizes the behavior much more effectively than do the clay minerals mixed homogeneously with the gouge this result brings out the mechanical significance of internal structures of a fault zone in understanding the effects of intrafault materials on the fault motion based on the present experimental results incorporated with some other experimental data it is argued that although the stabilizing effect of montmorillonite and vermiculite is indeed remarkable at room temperature the effect should be much less pronounced at elevated temperatures due perhaps to the dewatering of the clays in most geological environments where shallow earthquakes occur the stabilizing effect of clays is probably not so conspicuous as to completely suppress the unstable motion of a fault

the nature of transitions from dry to wet condition during sapropel events in the eastern mediterranean sea abstract benthic foraminifera were analyzed at high resolution millennial scale along core md84 641 33 02 n 33 38 e recovered in the eastern mediterranean sea and covering the last four climatic cycles the succession of benthic foraminiferal assemblages shows that the decrease in oxygen content of eastern mediterranean deep water was progressive for sapropels s8 s7 s6 s5 s4 and s3 and rapid for sapropels s10 s9 and s1 this suggests that climatic conditions conducing to the wet epochs associated with sapropels s8 s7 s6 s5 s4 and s3 were progressive whereas they were rapid for sapropels s10 s9 and s1 however hydrological conditions responsible for organic matter preservation events seem to be different from one sapropel to another benthic foraminifera did not disappear completely during sapropels s10 s8 s6 and s4 suggesting an episodic activation of deep water convection and an instability of humid period

sb hg ore deposit distribution controlled by brittle structures the case of the selvena mining district monte amiata tuscany italy abstract this paper deals with the tectonic control on the hydrothermal system that gave rise to sb hg ore deposits in the monte amiata area that was one of the most relevant mining district for the exploitation of mercury in italy the study area selvena mining district is located in southern tuscany inner northern apennines one of the most important mineralized area in the western mediterranean region southern tuscany was severely affected by middle late miocene low angle normal faults later dissected by pliocene pleistocene faults coeval magmatism late miocene pleistocene and hydrothermal activity pliocene present the selvena mining district is located south of middle pleistocene monte amiata volcanic complex our structural and kinematic study is based on the integration among fieldwork borehole and mine data the results highlight two pleistocene holocene left lateral transtensional shear zones linked by normal faults defining a coeval pull apart structure here the sb hg mineralization transported by meteoric hydrothermal fluids mainly is particularly diffuse and concentrated in the cataclasites and in damage zones of the normal faults furthermore a widespread mineralization also occurs in the cataclasites of miocene low angle normal faults mine evidence suggests that ore bearing fluids percolated through structural conduits located along the fault planes and resulting parallel to the intermediate stress axis geological structures and ore deposit distribution are related to a single hydrothermal circuit with meteoric water channelled to depth through conduits parallel to the intermediate stress axis of the transcurrent shear zones then hydrothermal fluids mainly ascended through the almost vertical deformation zones located at the intersection between normal and strike slip faults thus hydrothermal fluids permeated also the middle late miocene cataclasites this study shed light on the relationships between geological structures and mineralization in southern tuscany and underlines the importance to investigate mine areas to understand hydrothermal fluids path

abrupt changes in north american climate during early holocene times recent studies of the greenland ice cores have offered many insights into holocene climatic dynamics at decadal to century timescales1 2 3 despite the abundance of continental records of holocene climate few have sufficient chronological control and sampling resolution to compare with the greenland findings4 butannually laminated sediments varves from lakes can provide high resolution continental palaeoclimate data with secure chronologies here we present analyses of varved sediments from deep lake in minnesota usa trends in the stable oxygen isotope composition of the sedimentary carbonate indicate a pronounced climate cooling from 8 9 to 8 3 kyr before present probably characterized by increased outbreaks of polar air decreased precipitation temperatures and a higher fraction of the annual precipitation falling as snow the abrupt onset of this climate reversal over several decades was probably caused by a reorganization of atmospheric circulation and cooling of the arctic airmass in summer that resulted from the final collapse of the laurentide ice near hudson bay and the discharge of icebergs from the quebec and keewatin centres into the tyrell sea the timing and duration of this climate reversal suggest that it is distinct from the prominent widespread cold snap that occurred 8 200 years ago in greenland and other regions1 5 6 no shifts in the oxygen isotope composition of sediment carbonate occurred at 8 2 kyr before present at deep lake but varve thickness increased dramatically probably as a result of increased deposition of aeolian dust taken together our data suggest that two separate regional scale climate reversals occurred between 9 000 and 8 000 years ago and that they were driven by different mechanisms

dynamic recrystallization in semi brittle faults abstract experiments designed to investigate the microstructure and mechanical behavior of shear zones across the cataclastic faulting to dislocation creep transition indicate that some mylonites may be the products of frictional faulting under semi brittle conditions the experiments involve simple shear of thin layers of polycrystalline halite to strains of 5 8 at temperatures to 250 c normal stresses to 90 mpa and at shear strain rates of 7 10 3 s 1 microstructural and mechanical data define a transitional field of semi brittle flow steady state stress in the semi brittle field is a function of the normal stress and the temperature and is significantly less than that predicted by the power law equation used to describe dislocation creep and by the friction law used to describe cataclastic faulting fracture and localized slip are characteristic processes in the fields of cataclastic faulting and semi brittle flow whereas intracrystalline plasticity recovery and dynamic recrystallization are characteristic of semi brittle flow and dislocation creep for both semi brittle flow and dislocation creep migration recrystallization is activated only after a critical strain and temperature stress condition are achieved the recrystallized grain size is consistent with previously established piezometric relations for dislocation creep these experiments indicate that the field of semi brittle flow for halite is characterized by frictional behavior even though the corresponding microstructure primarily reflects microscopic plastic deformation and softening processes

the origin of s c mylonites and a new fault zone model abstract this paper presents a synthesis of experimental data on mechanical behaviour and deformation textures of simulated halite shear zones with special regard to the internal structures of s c mylonites and their mechanical implications halite is the only mineral so far for which a complete transition between brittle shearing deformation to fully ductile shearing flow in the dislocation glide regime has been studied experimentally under large shear strains that may be encountered along faults or plate boundaries moreover deformation textures in the shear zones are similar to those of mylonites and cataclasites thus the experimental results provide an insight into the petrogenesis of fault rocks mylonites in particular and the establishment of a realistic fault model between the brittle regime and the fully ductile regime i e pressure insensitive inelastic regime there exists a wide and distinct regime called semiductile in which deformation textures are nearly identical to those developed in the ductile regime yet the shear resistance is pressure dependent and potentially unstable fault motion can occur in the low pressure part in cooking salt shear zone experiments the characteristic texture in the semiductile and ductile regimes is foliation resembling mylonitic foliation which formed in the direction of maximum elongation in the semiductile regime nearly homogeneous shearing deformation characterized by the formation of uniform and pervasive foliation changes into heterogeneous deformation after a critical shear strain and this strain localization induces potentially unstable fault motion the primary mode of internal slip after the strain localization is slip along y riedel shears parallel to the shear zone boundary interconnected with r 1 and some p riedel shears these shear surfaces of concentrated deformation are very similar to the internal structures of so called s c mylonites hence the semiductile regime is the primary candidate for the formation of s c mylonites and at least some s c mylonites must have formed at seismogenic depths this interpretation is consistent with recently reported interlaced pseudotachylytes and mylonites it is also shown that the size of recrystallized halite grains presumably mostly postdeformational decreases with increasing shear strains but not with the shear stress and this is consistent with the grain size reduction with strain concentration which has been confirmed for many mylonites in the world thus estimation of flow stress from recrystallized grains needs to be done with great care and might often be erroneous existing fault models are critically examined from the viewpoint of the halite experiments and a new fault model is proposed whereby fault zones are divided into brittle semibrittle semiductile and ductile regimes with increasing depth the shear resistance of faults is highest in the semiductile regime and the seismogenic depth is likely to extend down to the upper part of this regime the semiductile regime thus emerges as an area of primary interest with regard to the petrogenesis of many s c mylonites modelling of large and great shallow earthquakes along pre existing faults and plate boundaries and quantitative evaluation of the mechanical interactions of plates across their boundaries

early holocene environments in the wadi faynan jordan hunt c elrishi h gilbertson d grattan j mclaren s pyatt b rushworth g barker g early holocene environments in the wadi faynan jordan the holocene 2004 14 6 pp 921 930

coulomb constitutive laws for friction contrasts in frictional behavior for distributed and localized shear we describe slip rate dependent friction laws based on the coulomb failure criteria frictional rate dependence is attributed to a rate dependence of cohesionc and friction angle we show that differences in the stress states developed during sliding result in different coulomb friction laws for distributed shear within a thick gouge layer versus localized shear within a narrow shear band or between bare rock surfaces for shear within gouge shear strength is given by c cos n sin whereas for shear between bare rock surfaces the shear strength is c cos n tan where and n are shear and normal stress respectively in the context of rate dependent coulomb friction laws these differences mean that for a given material and rate dependence of the coulomb parameters pervasive shear may exhibit velocity strengthening frictional behavior while localized shear exhibits velocity weakening behavior we derive from experimental data the slip rate dependence and evolution ofc and for distributed and localized shear the data show a positive rate dependence for distributed shear and a negative rate dependence for localized shear indicating that the rate dependence ofc and are not the same for distributed and localized shear even after accounting for differences in stress state our analysis is consistent with the well known association of instability with shear localization in simulated fault gouge and the observation that bare rock surfaces exhibit predominantly velocity weakening frictional behavior whereas simulated fault gouge exhibits velocity strengthening followed by a transition to velocity weakening with increasing displacement natural faults also exhibit displacement dependent frictional behavior and thus the results may prove useful in understanding the seismic evolution of faulting

the brittle ductile transition in a deformation mechanism map for halite abstract the brittle ductile transition in rock deformation has been studied extensively but is still poorly quantified progress in our understanding of this and other transitions in mechanical behavior and deformation mechanisms is facilitated by use of deformation mechanism maps a preliminary deformation mechanism map for halite is presented based on shear experiments at room temperature 22 c over the range of normal stress up to 350 mpa and average shear strain rates between 10 to 10 6 s 1 the map illustrates that transitions in mode of failure mechanical behavior and dominant deformation mechanism which often are referred to collectively as the brittle ductile transition do not necessarily coincide the analysis also suggests that the transition from dominantly cataclastic to crystal plastic deformation mechanism fields is adequately described by the distinct and independent mechanism field of semi brittle flow

holocene sea level fluctuations and coastal evolution in the central algarve southern portugal in armacao de pera bay southern portugal environmental changes during the holocene can be interpreted based on the morphological and sedimentological similarities between older geomorphic features cemented beach and dune rocks and present coastal features using knowledge of the present beach and dune processes we propose a two step model for the evolution of armacao de pera bay first during the rapid sea level rise between about 8 800 and 6 600 yr cal bp the bay changed from a positive to a negative budget littoral cell and transgressive dunes formed favoured by drought conditions at about 5 000 yr cal bp during a sea level maximum beach width was less than the critical fetch and dunes stabilized and underwent cementation during the wetter atlantic climatic event the second phase of dune accumulation started at about 3 200 yr cal bp due to a regression of sea level during which the bay changed back to a positive budget littoral cell in which beach width was greater than the critical fetch currently the beach width is less than the critical fetch dunes are inactive and the sedimentary budget is negative due to sediment storage in local river systems

strain localization in direct shear experiments on solnhofen limestone at high temperature effects of transpression some features of natural shear zones formed under non coaxial strain geometries including some effects of transpression can be simulated in the laboratory by using the direct shear experimental configuration slices of similar to 1 mm thick solnhofen limestone were deformed in direct shear between two stronger forcing blocks of cores of tennessee sandstone pre cut at 45 degrees to the cylinder axis experiments were run dry at 600 degrees c 200 mpa confining pressure and bulk shear strain rates of similar to 5 x 10 3 s 1 at which conditions solnhofen limestone deformed by dislocation creep with a stress exponent of 4 7 when loaded strain concentrates in the limestone band producing non coaxial deformation as one pre cut block slides past the other the orientation and intensity of the shape fabric developed in calcite grains indicate that strain is heterogeneous across the specimen with the formation of two high strain shear bands close to the limestone sandstone interface separated by a central zone of low strain crystallographic preferred orientation patterns in the calcite grains measured by electron backscatter diffraction are consistent with a switch in deformation geometry from flattening dominated in the middle of the specimen towards shear dominated in the high strain bands from tests on thin slices of the same material compressed axisymmetrically without shearing normal to the layer heterogeneous thinning of the slice develops from a maximum in the centre of the slice to zero at the edges the formation of the paired shear zones observed in the sheared experiments is interpreted in terms of superposed strain fields with shearing in the centre of the slice being inhibited by the strain hardening that accompanies the higher flattening strain in the centre of the specimen c 2008 elsevier ltd all rights reserved

frictional strength of fault gouge in taiwan chelungpu fault obtained from tcdp hole b abstract three fault zones fzb1136 fzb1194 and fzb1243 are found in core samples in hole b borehole penetrating through the chelungpu fault central taiwan that activated at the 1999 taiwan chi chi earthquake each fault zone is composed of a black gouge zone bgz and a gray gouge zone ggz surrounded by a fault breccia zone bz and or fracture damaged zone fz we conducted tri axial friction experiments on samples collected from subzones of the above three fault zones under the 1 km depth ambient condition with axial shortening rates of 0 1 to 10 m s to investigate frictional strength and its velocity dependence we found that the coefficient of friction is 0 3 for the bgz at fzb1136 1136bgz which is lower than those at other fault zones this result indicates that fault slip at the chi chi earthquake occurred at the 1136bgz the estimated frictional strength profile across fzb1136 was that the frictional strength was the lowest the coefficient of friction was 0 3 for the bgz and increased up to 0 5 for undeformed host rock with increasing distance from the bgz presence of the intermediate frictional strength zone consisting of the ggz and the bz suggests a development of off fault damage zone where deformation occurred not only in the bgz but also in the intermediate zone this feature should be important to estimate total fracture energy released during earthquakes we also suggest that coefficients of friction and the velocity dependences of the samples are closely related to localization of shear deformation and clay content respectively

holocene alluvial morphopedosedimentary record and environmental changes in the bardenas reales natural park ne spain abstract a holocene alluvial morphostratigraphy based on geomorphological mapping sedimentological analysis soil development and radiocarbon chronology is presented for the semiarid blanca basin in the bardenas reales natural park ne spain four morphopedosedimentary alluvial units mu1 mu2 mu3 and mu4 were differentiated which may correspond to two palaeogeographical stages the first one includes the morphopedosedimentary unit mu1 and is the most extensive in the area it is made up of a complex aggradation fill up sequence comprising a braided channel system a sand mud flat 9200 7900 cal bp and a playa lake environment related to a nearly closed depression an intensive fluvial entrenchment period is recognized leading the opening of the blanca basin before the second stage that includes the units mu2 mu3 and mu4 this set of units forms a sequence of cut and fill and nested fill terraces recording the alluvial activity in the blanca basin during the last 6 ka the mu2 unit 5900 3300 cal bp in age represents a period of high geomorphic instability with rapid alluvial sedimentation channel incision oscillating changes on the other hand the mu3 unit has an age of 1050 500 cal bp and appears as a thin extensive alluvial cover overlying previous units finally the mu4 unit comprises superposition of numerous flood depositional sequences centimetric in scale dated from 450 10 cal bp the established soil chronosequence supports the numerical chronology of the four units these accumulation periods mu1 mu2 mu3 mu4 are associated with dry phases and or high hydrological variability floods and droughts at a regional scale changes on the north atlantic atmospheric circulation mode over southern europe may provide the key to explain the nature of alluvial activity during holocene in bardenas reales

a heinrich like event h 0 dc 0 source s for detrital carbonate in the north atlantic during the younger dryas chronozone in the north atlantic we define h 0 as a heinrich like event which occurred during the younger dryas chron on the se baffin shelf prior to 11 ka surface water productivity was reasonably high as measured by the numbers of diatom and planktic foraminifera per gram but an abrupt increase in detrital carbonate dc 0 event from approximately 15 up to 50 carbonate by weight occurred at 11 14c ka and continued to circa 10 ka these deposits 2 6 m thick are dominated by detrital calcite and silt and clay sized sediments during this event dc 0 h 0 ice extended onto the inner shelf but did not reach the shelf break and probably originated from a center over labrador ungava as a consequence the pattern of ice rafted debris and sediment provenance shown by h o in the north atlantic is different from that during h 1 14 5 ka or h 2 20 ka when the ice sheet extended along the axis of hudson strait and may have reached the shelf break for example there is no concrete evidence for dc o is cores on the floor of the labrador sea due east of hudson strait hu75 55 56 but h o has been noted in cores off newfoundland and west of ireland a coeval carbonate event to dc 0 but this one dominated by dolomite occurs in hu82 su5 on the west side of davis strait with a source either from northern baffin bay or cumberland sound although other sources for north atlantic detrital carbonate cannot be totally excluded our evidence suggests that h 0 represents the expression of glaciological instability of the laurentide ice sheet within the general region of hudson strait and probably to the north cumberland sound and northernmost baffin bay there is one younger dc event dated circa 8 4 ka present in sediments along the labrador margin and in hudson strait which represents the final collapse of the ice sheet within hudson strait and hudson bay

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

a new simple shear deformation apparatus for rocks and soils abstract we present a new design for a simple shear type deformation apparatus which has the capacity to deform medium strength anisotropic rocks as well as soils and similar strength materials the special feature of the design is that the deformation is achieved by the application of a particular set of boundary displacements so that a specimen is constrained to deform by a progressive simple shearing history these boundary displacements are applied through three pairs of steel platens each of which are in contact with opposite sides of the specimen which is initially a right rectangular prism one pair of platens is fixed so that deformations are plane strain a second pair of platens remains horizontal but they are free to slide against the reaction frame in the shear direction while at the same time they can apply a vertical normal force through hydraulic actuators the third pair of platens are vertical faces cut longitudinally through two steel shafts so that the shaft axes lie horizontally through the centre of the faces shear is applied by rotation of the two shafts so that the two vertical end faces of the specimen are rotated about the shaft axes this rotation means that horizontal planes in the specimen remain horizontal and suffer no shape change while vertical planes normal to the shaft axes remain vertical but suffer a shearing type change in shape the combination of these boundary displacements is a progressive simple shearing of the specimen we show typical stress strain responses for a number of different material types and discuss the degree of strain homogeneity throughout the specimen examples are presented of the microstructural changes which occur in specimens deformed in the apparatus

synchronous holocene climatic oscillations recorded on the swiss plateau and at timberline in the alps eight synchronous pre roman cold phases were found at 9600 9200 8600 8150 7550 6900 6600 6200 5350 4900 4600 4400 3500 3200 and 2600 2350 radiocarbon years bp by reconstructing past climate at two sites on the swiss plateau and at timberline in the alps the cooling events during the early and mid holocene represent temperature values similar to today and apparently the onset of cooling events represents a deviation from today s mean annual temperature of about 1 c and is triggered at a 1000 year periodicity at wallisellen langachermoos 440 m a former oligotrophic lake near zurich the correlation between sum mertime lake levels and the seed production of the amphi atlantic aquatic plantnajas flexilis was used to reconstruct lake levels over a 3000 year period during the first part of the holocene at lake seedorf on the western swiss plateau 609 m the sedimentological palynological and macrofossil record revealed fluctuations of lake levels for the complete holocene from lago basso in the

pollen record of the centennial climate changes during 9 7 cal ka bp in the changjiang yangtze river delta plain china we reconstructed the centennial climate changes for the period of 9 7 cal ka bp in the upper region of the changjiang yangtze river delta plain a general warming and wetting trend from 8560 to 7220 cal yr bp was indicated by the decrease in quercus deciduous and increases in quercus evergreen pinus and polypodiaceae spores however there were several brief climate fluctuations a notable palynological change from regional assemblages dominated by arboreal pollen to local assemblages mainly consisting of nonarboreal pollen reflects climate fluctuations the key indices of quercus deciduous pinus herbs fern spores and palynological concentrations showed similar signs of centennial climate fluctuations we suggest that the climate changes of the dongge cave and yangtze river delta regions were mainly affected by the east asian summer monsoon easm during the period of 9 7 cal ka bp the general warming trend may be associated with an intensified easm and solar activity may be one of the important factors driving the centennial climate changes the 8 2 ka event was also recorded in the yangtze river delta region which suggests that there was a close relationship between the easm and greenland climate during the early holocene

reconstruction of holocene environmental changes in the kiso ibi nagara compound river delta nobi plain central japan by diatom analyses of drilling cores abstract holocene environmental changes were reconstructed by analyzing diatom assemblages from sediment cores ym kzn nk and mc from the nobi plain central japan five diatom assemblage zones were identified 1 at the beginning of the holocene freshwater species were dominant 2 then marine and brackish marine species increased indicating transgression 3 in the middle holocene proportions of marine and brackish marine species became almost constant with marine species dominant 4 marine species began to be replaced by freshwater species indicating marine regression as a result of delta progradation and 5 freshwater species again became dominant these diatom assemblages correlate with previously defined lithological units zones 1 and 2 with unit b fluvial to coastal plain zone 3 with unit c inner bay or prodelta zone 4 mainly with unit d1 delta front slope and zone 5 with units d2 delta front platform and e delta plain and flood plain although the shoreline migrated landward transgression faster than it migrated seaward regression transgressive diatom assemblage changes decrease in marine brackish water species took up to 1000 years whereas regressive changes required only a few hundred years diatom analysis is useful for reconstructing not only holocene sea level changes and sedimentary environments but also local geographic effects

holocene climate variability vegetation dynamics and fire regime in the central pyrenees the basa de la mora sequence ne spain abstract high resolution multiproxy data pollen sedimentology geochemistry chironomids and charcoal from the basa de la mora bsm lake sequence 42 32 n 0 19 e 1914 m a s l show marked climate variability in the central southern pyrenees throughout the holocene a robust age model based on 15 ams radiocarbon dates underpins the first precise reconstruction of rapid climate changes during the holocene from this area during the early holocene increased winter snowpack and high snowmelt during summer as a consequence of high seasonality led to higher lake levels a chironomid community dominated by non lacustrine taxa orthocladiinae related to higher inlet streams and a forested landscape with intense run off processes in the watershed from 9 8 to 8 1 cal ka bp climate instability is inferred from rapid and intense forest shifts and high fluctuation in surface run off shifts among conifers and mesophytes reveal at least four short lived dry events at 9 7 9 3 8 8 and 8 3 cal ka bp between 8 1 and 5 7 cal ka bp a stable climate with higher precipitation favoured highest lake levels and forest expansion with spread of mesophytes withdrawal of conifers and intensification of fires coinciding with the holocene climate optimum at 5 7 cal ka bp a major change leading to drier conditions contributed to a regional decline in mesophytes expansion of pines and junipers and a significant lake level drop despite drier conditions fire activity dropped as consequence of biomass reduction two arid intervals occurred between 2 9 and 2 4 cal ka bp and at 1 2 0 7 cal ka bp 800 1300 ad the latter coincides with the medieval climate anomaly and is one of the most arid phases of the holocene in bsm sequence anthropogenic disturbances were small until 700 ad when human pressure over landscape intensified with olea cultivation in the lowlands and significant deforestation in highlands colder and unfavourable weather conditions during the second part of the little ice age caused a temporary cease of high land management the most intense anthropogenic disturbances occurred during the second half of 19th century last decades are characterized by recovery of the vegetation cover as a result of land abandonment and lowered lake levels probably due to higher temperatures

sliding mechanical properties of fault gouge studied from ring shear test based microscopic morphology characterization abstract fault activity is a factor causing geological disasters and controlling their spatial distribution the information on fault activity can be recorded by the microstructure of the fault gouge sliding surface which provides an approach to study the macroscopic mechanical behavior of faults in this study the ring shear test was used to simulate the shear sliding behavior of a fault gouge under different stress states and water contents and the microstructure of the shear sliding surface was quantitatively analyzed using scanning electron microscopy sem the results revealed an evident relationship between the microstructure and macroscopic mechanical properties of the fault gouge the microstructure represented by sliding scratches was primarily created by the movement of coarse particles such as sand and quartz an index of the sliding scratch ratio was proposed to characterize the microstructure the sliding scratch ratio is negatively correlated with water content and normal stress and a multivariate model of sliding scratch ratio was established with water content normal stress and coarse particle contents allying the model to natural scratches of the fault gouge reveals that the observed sliding scratches were formed during slope sliding which proves the influence of fault on the occurrence of the studied landslide influenced by the gully land consolidation projects in the loess plateau of china the groundwater level may increase and then weaken the shear strength of fault gouge reducing the stability of slopes crossed by fault zone therefore more attention should be paid to potential geological disasters induced by faults in gully filled areas

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