dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

correlations between fluid composition and deep seated structural style in the footwall of the simplon low angle normal fault switzerland structural and fluid inclusion analyses reveal a correlated change in structural style and fluid composition along strike in footwall mylonites of the simplon low angle normal fault of switzerland in the south early postmylonitic structures are semibrittle shears and brittle faults synkinematic fluid inclusions within the faults contain a carbonic component whereas those in the shears lack co 2 to the north early postmylonitic structures are extension veins and kinkbands and synkinematic fluid inclusions are aqueous entrapment conditions for all fluid inclusions are estimated to be 500 c and 5 kbar we speculate that different wetting characteristics of carbonic versus aqueous fluids influenced the mechanical behavior of the rocks nonwetting carbonic fluids locally increased fluid pressure and induced brittle failure resulting in development of abundant closely spaced brittle faults in areas lacking carbonic fluids ductile deformation continued to lower pressures and temperatures

a celebration of the twentieth anniversary of the fluvial archives group flag the fluvial archives group flag was founded in 1996 to bring together researchers looking at the development of fluvial systems over multiple timescales and global spatial scales fluvial archives of various types are important not just because they provide insights into past landscape dynamics e g driven by climate or crustal processes but also because they frequently contain fossil or archaeological material for which they provide stratigraphic control since 1996 flag has evolved from a research group of the british quaternary research association into an organisation with around 500 members in over 20 countries the research group held 12 biennial meetings comprising both presentations and field excursions as well as multiple themed sessions at international conferences these had resulted by 2017 in 19 journal special issues all fully detailed by cordier et al 2017 the goals of flag are provision of a community for discussion of key issues concerning fluvial archives including organising the aforementioned biennial discussion field meetings sessions at relevant international conferences and special issues of journals continued promotion of the value of fluvial archives by means of readily accessible published information and coordination of activity with other research groupings with overlapping interests e g by co convening sessions and collaborating on publications

spatial and temporal patterns in channel change on the snake river downstream from jackson lake dam wyoming abstract operations of jackson lake dam jld have altered the hydrology and sediment transport capacity of the snake river in grand teton national park prior research has provided conflicting assessments of whether the downstream river was perturbed into sediment surplus or sediment deficit in this paper we present the results of an aerial photo analysis designed to evaluate whether the history of channel change indicates either significant deficit or surplus of sediment that could be expressed as narrowing or expansion of the channel over time we analyze changes in braid index channel width channel activity and net channel change of the snake river based on four series of aerial photographs between 1945 and 1969 a period of relatively small main stem floods widespread deposition and up to 31 reduction in channel width occurred throughout the snake river between 1969 and 2002 a period of large main stem floods the style of channel change reversed with a decrease in braid index and an increase in channel width of up to 31 these substantial changes in the channel downstream from the dam primarily occurred in multithread reaches regardless of proximity to tributaries and no temporal progression of channel narrowing or widening was observed we demonstrate that channel change downstream from jld is more temporally and longitudinally complex than previously described

weak faults rotten cores earthquakes are triggered when crustal deformation produces displacements along fault zones the rock in these zones is found to be weaker than adjacent material but what are the mechanisms of this loss of strength in his perspective holdsworth 1 discusses how recent studies of exposed ancient fault zones combined with laboratory analyses are revealing that rock properties at the grain scale can determine the large scale behavior of crustal deformation 1 http www sciencemag org cgi content full 303 5655 181

the effect of fluid composition on the behavior of well cemented quartz rich sandstone during faulting abstract previous studies o kane a onasch c m farver j 2007 the role of fluids in low temperature fault related deformation of quartz arenite journal of structural geology 29 819 836 cook j dunne w m onasch c m 2006 development of a dilatant damage zone along a thrust relay in a low porosity quartz arenite journal of structural geology 28 776 792 found that quartz arenite within two fault zones in the appalachian foreland thrust belt displays very different structural styles and histories despite deforming at similar pressures and temperatures during the alleghanian orogeny a comparison of the grain scale deformation and fluid histories using transmitted and cathodoluminescence microscopy and fluid inclusion microthermometry shows that fluid composition was a controlling factor for causing these differences the cove fault zone deformed in the presence of aqueous fluids first a cacl 2 brine and then an iron rich fluid the precipitation of quartz cement from the brine kept pace with brittle deformation maintaining overall rock cohesion in the fault zone the introduction of iron rich fluids caused a switch from precipitation to dissolution of quartz along with precipitation of goethite in a damage zone along a backthrust in the cave mountain anticline early deformation occurred in the presence of an aqueous fluid from which quartz was precipitated the latest deformation however occurred in the presence of a methane rich fluid which inhibited the precipitation of quartz cement producing porous breccias and open fractures despite deformation at 6 km depth fluid composition not only affected cementation in the fault zones but also the selection of grain scale deformation mechanisms therefore it is a controlling factor in determining the behavior and strength of these fault zones

infrared microspectroscopy analysis of water distribution in deformed and metamorphosed rocks infrared microspectroscopy has been applied to thin sections of various deformed and metamorphosed rocks in order to investigate water content of quartz in these rocks the broad ir band absorbance around 3400 cm 1 probably due to fluid inclusion molecular water h2o was used to calculate water contents deformed granitic rocks from the yanazawa kamimura area near the median tectonic line mtl showed an increase of water content in quartz from about 300 ppm to 2500 ppm toward the mtl with increasing degree of deformation metacherts from sambagawa metamorphic rocks asemigawa route showed a systematic decrease of water content in quartz from about 1000 ppm to 200 ppm with increasing metamorphic degree from chlorite garnet albite biotite to oligoclase biotite zones an archaean metachert from the napier complex granulite facies has only 40 ppm water comparing this with an inuyama unmetamorphosed chert sample having water contents of 3500 to 7000 ppm a starting point of metamorphism the systematic decrease of water in quartz with increasing metamorphic grade may extend from unmetamorphosed cherts to the highest grade metacherts water contents in high pressure metamorphic rocks in japan are mostly of the order of 500 ppm 300 700 ppm except for those from kurosegawa with a water content as high as 1700 ppm these results represent an exploratory analysis of intragranular water contents in quartz in various deformed and metamorphosed rocks further micro ft ir studies of the distribution of water in crustal rocks will provide a quantitative basis for examining the geochemical cycle of water in the earth s crust

the structural geometry and evolution of foreland thrust systems northern virginia seismic reflection data reveal that the structural geometry of the central appalachians of northern virginia consists of three distinct thrust systems each thrust system is characterized by a unique internal geometry the blue ridge thrust sheet is a composite thrust sheet composed primarily of imbricated precambrian crystalline rocks it over rode cambrian ordovician carbonates and formed a sheared basement cored fault bend fold thrusts within the sheet may be taconic and earliest alleghanian whereas final thrusting and emplacement of the sheet were probably slightly younger but still early alleghanian the north mountain thrust sheet is characterized by imbricated cambrian ordovician carbonates that are deformed into large amplitude mode ii fault bend folds and fault propagation folds rocks of this sheet were transported more than 60 km across a similar section of carbonates the leading edge of the north mountain thrust sheet was deformed into a fold with a mode ii fault bend fold geometry and was juxtaposed against middle paleozoic rocks the middle paleozoic rocks occur in a ramp across which displacement along the north mountain thrust was transferred to a higher detachment more than 60 km of cover rocks displaced during the emplacement of the north mountain thrust sheet either were transported across this ramp and thrust over a similar section in the western valley and ridge province or were backthrust above the sheet the timing for imbrication and emplacement of the north mountain thrust sheet is probably main phase alleghanian the lower carbonate duplex extends from beneath the blue ridge and north mountain thrust sheets westward across the western valley and ridge province the lower carbonate duplex is characterized by imbricated cambrian ordovician carbonates that form low amplitude fault bend folds this thrust system also probably formed during main phase alleghanian deformation

observations of plagioclase zoning using interference imaging abstract interference imaging techniques laser interference microscopy in transmitted light and nomarski differential interference contrast in reflected light have been used to study different types of zoning in magmatic plagioclase crystals samples studied come from a wide range of rock types and geological environments analysis of zoning profiles for individual unit zones shows that a saw tooth pattern in which an initially high an decreases as growth proceeds is the most common type of zoning configuration we recognize 2 major types of zoning type 1 small zones usually less than 10 microns thick with compositional amplitudes up to 10 an and type 2 zones up to50 microns thick with large compositional amplitudes of up to 35 an detailed analysis of zoning patterns shows that oscillatory zoning is not actually oscillatory in the sense of a sine wave it is discontinuous unit zones are characteristically bounded by discontinuities this common pattern is consistent with alternating periods of growth and periods of dissolution reaction and lack of growth or possibly very slow growth our observations firmly establish that dissolution and magmatic reaction involving both growth and dissolution are common during growth of the magmatic plagioclase which we have studied type 1 zonation appears consistent with perturbations of local conditions in a diffusion controlled boundary layer around the growing crystal type 2 zoning is probably due to large scale conditions faceted planar growth surfaces appear to be the rule in magmatic crystallization although in some instances rounded or irregular convolute zonation can occur the repetitive nature of many of the features we have observed is consistent with and suggestive of some form of self organization

variation in quartz arenite deformation mechanisms between a roof sequence and duplexes abstract microstructural abundances and histories in quartz arenite of the lower silurian tuscarora sandstone were used to determine the nature and role of microscale deformation in a cover sequence and underlying thrust system and to assess the degree to which the cover sequence accommodated emplacement of the thrust system sandstone samples are located across the transition from the central to southern appalachian foreland thrust system where the thrusts change from blind to emergent southwards and where southern deformation of early alleghanian age has been previously shown to be overprinted by central deformation of alleghanian age microstructures observed with transmitted light and cathodoluminescence microscopy indicate that grain scale deformation occurred by dislocation flow pressure solution and microfracturing with the last being generally the most important the sequence of deformation mechanisms is the same for the cover sequence and the thrust system pressure solution during sedimentary compaction dislocation flow during layer parallel shortening and localized microfracturing with limited pressure solution near major thrust ramps and in steep fold limbs a greater abundance of dislocation flow microstructures in the cover sequence from layer parallel shortening indicates grain scale accommodation in the tuscarora sandstone of some shortening associated with emplacement of the thrust system the transition zone between the central and southern appalachians contains the greatest occurrence of every microstructure which is consistent with the area having been affected by diachronous central and southern alleghanian deformations

unravelling polyphase brittle tectonics through multi software fault slip analysis the case of the voltri unit western alps italy abstract we have analyzed the brittle structures in a key area of the alps apennines transition zone nw italy here two orogens have interfered with each other since oligocene times producing a complex structural evolution and a heterogeneous fault population only relative chronologies can be reconstructed as stratigraphic constraints are lacking we have performed the inversion of fault slip data with two softwares for paleostress calculations combined with field observations at selected structural stations and photo interpretation the resulting incompatible stress tensors can be grouped in this sequence i a strike slip tensor with nnw sse trending 1 event a ii a strike slip tensor with ne sw trending 1 event b and iii an extensional transtensional tensor with nw se or ne sw trending 3 event c we correlated our results with structures of known age from adjacent areas event a is possibly rupelian early chattian linked to far field incipient rifting in the future ligurian provencal basin event b fits oligo miocene shortening the faults may belong to a sinistral strike slip zone that accommodated the oblique component of deformation during the rotation of the corsica sardinia block event c is attributed to a pliocene quaternary neotectonic event therefore combining different inversion procedures with a detailed structural analysis has successfully unravelled the polyphase brittle tectonics

the high temperature behavior of trace hydrous componentsin silicate minerals we have studied the high temperature behavior of water and hydroxide in quartz feldspar topaz zircon muscovite cordierite and beryl using high temperature infrared spectroscopy we have directly observed processes such as dehydration and changes in hydrogen speciation in some minerals trace hydroxyl and water speciation and properties at temperatures of geologic interest can be dramatically different from those at 25 c in muscovite no changes in speciation occur prior to dehydration at 750 c whereas in topaz hydroxyl sites interconvert at 500 c in metamict zircon strongly hydrogen bonded hydroxyl is preferentially lost from a continuum of sites during continuous dehydration occurring from 400 to 900 c there are only minor changes in the o h region spectrum of natural quartz at the transition point in feldspar one type of molecular water is lost at 200 c and at 600 to 800 a second water type converts irreversibly to a new hydrous species changes at high temperature common to the infrared absorption bands of all minerals studied are broadening a shift to lower wave numbers and a slight decrease in integral intensity temperature coefficients for 0 h stretching peak shifts range from 0 to 0 045 cm 1 c lattice modes also broaden and shift to lower wave numbers typically with temperature coefficients of about 0 03 cm 1 c

how natural are alpine mountain rivers evidence from the italian alps historical human induced channel adjustments in lowland gravel bed rivers have been documented in several geographical contexts worldwide in particular it is now widely accepted that the vast majority of european rivers are far from any natural reference state prior to anthropic disturbances and a complete restoration is hardly achievable however few investigations have addressed changes that have occurred in mountain rivers of the alps and these channels are commonly reckoned quite natural by society this paper intends to describe how human pressure on italian alpine basins has been quite relevant for several centuries in terms of land use variations in channel structures timber transport splash damming and riparian vegetation management such that nowadays reference conditions cannot be found even in small mountain creeks in addition recent natural climatic variations e g the little ice age are superimposed on human disturbances thus defying the definition of any equilibrium morphological conditions even under human free states a summary of published as well as unpublished works on historical channel adjustments in rivers of the italian alps is presented in order to document the impacts deriving from human pressure at different basin scales and for different river morphologies from steep confined streams to large unconfined rivers general options for river management and restoration actions aiming to combine geomorphological functionality and flood hazard mitigation are discussed in the light of the current european legislative context copyright 2011 john wiley sons ltd

geoinformatics in morphological study of river paglia tiber river basin central italy this work reports the results of a geomorphological study on the river paglia tiber basin central italy to analyse the historical evolution of the riverbed floodplain system in its lower valley reaches upstream the confluence of river tiber a morphological sedimentological approach has been used starting with an historical analysis and a survey of the forms and sediments in the riverbed alluvial plain system in order to reconstruct the current evolutionary trend and to identify the causes and processes leading to changes in natural trends this approach is not in contrast to the hydrologic hydraulic one normally applied in engineering fields but it is integrated with it in a complementary and parallel manner in order to achieve the complete knowledge of the river system result of an investigation multidisciplinary aimed to define its physical state historical data cartographic documents digital terrain models dtm topographic surveys aerial photographs etc indicate clear cut narrowing and deepening of the active channel manifested after the second world war and due to the considerable changes which affected the entire fluvial system from the recovery of land for agriculture near the river to sediments taken from its bed over the past few decades the result is a state of great disequilibrium which is shown in the passage from a braided morphology observed in the 1950s to a single channel with low sinuosity wandering type this type of morphology is certainly more unstable in fact the narrowing and deepening of fluvial sections provide a better hydraulic efficiency for the upstream so the peak discharge does not overflow such peak discharge arrives downstream next to the confluence with the tiber river not laminated causing serious flooding effects an increased vulnerability is observed in the last reach in the areas pertaining to the river where most of the industrial economic activities are concentrated and where transportation infrastructures of nationwide importance italy s most important motorway the a1 and the rome florence milan high speed rail links are located the evolution of the paglia which is not substantially different from that of many streams in italy and in general throughout europe is affected by severe anthropic constraints and intense exploitation of resources which have produced a state of disequilibrium approaching irreversibility in an already vulnerable system finally some suggestions for the correct management of the river system are pointed out with the aim of mitigating the flood risk in the lower paglia valley

microfractures and their role in deformation of a quartz arenite from the central appalachian foreland abstract microfractures are pervasive in the massanutten sandstone a quartz arenite exposed in a doubly plunging synclinorium in the central appalachian foreland they are present as fluid inclusion planes fips and microveins parallel the fips fips occur in three orthogonal sets horizontal vertical and normal to the fold axis and vertical and parallel to the fold axis the geometry distribution and age of fips relative to other microstructures shows that microfractures developed during folding microfracturing followed layer parallel shortening by dislocation flow and was coeval with the peak of pressure solution that marked the final stages of folding microfracture densities are extremely high 160 mm 1 in many samples rapid closure of microfractures suppressed brecciation and prevented microfractures from propagating unstably to form joints microfracture opening accounts for significant finite strain with extensional strains of up to 11 1 and associated volume increases of over 16 0 the general lack of shortening microstructures indicates that a net volume increase is likely and that the massanutten sandstone may have served as a sink for dissolved phases from adjacent units undergoing volume loss deformation

are fluid inclusion planes useful in structural geology abstract quantification of deformation or stresses in structural geology is often difficult due to the uncertainity of the paleodepth or fluid pressure the best records of fluid percolation are paleofluids trapped as fluid inclusions in healed microcracks of the rock forming minerals fluid inclusion planes fip are mode i cracks which form in sets with a predominant orientation perpendicular to the least principle stress 3 however the repeated microfracturing and healing of the rock forming minerals yield complex superimposed patterns of healed microcracks such patterns are often difficult to interpret due to the lack of suitable chronological criteria these problems have been recently documented and solved by coupling deformation studies detailed examination at all scales of the relationships between trapped fluids and their host structures and studies of fluid inclusions this paper summarizes recent advancements in fip analysis and suggests further ways for research

the rate of water penetration in experimentally deformed quartzite implications for hydrolytic weakening abstract in order to determine the rate at which water penetrates the grains of a quartzite we performed several types of experiments including water added deformation and hydrostatic experiments on vacuum dried samples and hydrostatic annealing experiments on previously deformed quartzites samples of heavitree quartzite with an average grain size of 200 m and intragranular water concentration of 1750 420 h 10 6 si as measured by ftir were vacuum dried at 800 c 6 pa for 12 h after vacuum drying the grains showed thermal cracks with an average spacing of 50 m and an intragranular water concentration of 240 60 h 10 6 si one constraint on the rate of water penetration into quartz was obtained by deforming vacuum dried samples with 0 3 wt 20 000 h 10 6 si water added at 800 c 1500 mpa and a strain rate of 10 6 s conditions at which as is quartzite undergoes climb accommodated dislocation creep the time between reaching experimental conditions and yielding of the sample was between 2 and 9 h the samples had yield stresses of 100 250 mpa values well below the yield stress of 1500 mpa for a vacuum dried sample deformation of the grains was homogeneous on both optical and tem scales indicating that the grains had fully equilibrated with the water related defect that is responsible for water weakening ftir measurements are consistent with this interpretation one of the deformed samples has an intragranular water concentration of 820 160 h 10 6 si and vacuum dried samples hydrostatically annealed for 3 or 10 h at the same conditions as the deformed samples have an average intragranular water concentration of 730 180 h 10 6 si to obtain a second constraint on the rate of water penetration hydrothermal annealing experiments were performed on portions of a sample of heavitree quartzite which were previously deformed without water added at 700 c 1200 mpa and 10 5 s and have a high 10 16 m 2 and homogeneous dislocation density two samples were annealed at 700 c 1500 mpa for 24 h one with 0 2 wt water and one with no water added the grains in the water added sample have a rim approximately 15 m wide with dislocation recovery microstructures indicating equilibration with the water related defect the sample with no water added has a homogeneous dislocation density throughout the grains which is similar to that of the original deformed sample the 15 m wide recovered rim suggests a penetration rate approximately an order of magnitude faster than the rate of oxygen diffusion under hydrothermal conditions the observed rate of penetration of the water related species is consistent with theoretical considerations and calculations which predict a diffusion rate for h 2 o that is an order of magnitude faster than the rate of hydrothermal oxygen diffusion we infer from our experiments that the rate of water penetration into quartz is consistent with diffusion of h 2 o

recent channel adjustments in alluvial rivers of tuscany central italy drastic channel adjustments have affected the main alluvial rivers of tuscany central italy during the 20th century bed level adjustments were identified both by comparing available topographic longitudinal profiles of different years and through field observations changes in channel width were investigated by comparing available aerial photographs 1954 and 1993 98 bed incision represents the dominant type of vertical adjustment and is generalized along all the fluvial systems investigated the arno river system is the most affected by bed level lowering up to 9 m whereas lower incision generally less than 2 m is observed along the rivers of the southern part of the region human disturbances appear to be the dominant factors of adjustments the main phase of vertical change occurred during the period 1945 80 in concomitance with the phase of maximum sediment mining activity at the regional scale the second dominant type of adjustment that involved most of the rivers in the region consists of a narrowing of the active channel based on measurements of channel width conducted on aerial photographs 38 of the reaches analysed experienced a narrowing greater than 50 of the initial channel width the largest values of channel narrowing were observed along initially braided or sinuous with alternate bars morphologies in the southern portion of the region a regional scheme of channel adjustments is derived based on initial channel morphology and on the amounts of incision and narrowing different styles of channel adjustments are described rivers that were originally sinuous with alternate bars to braided generally became adjusted by a moderate incision and a moderate to intense narrowing in contrast sinuous meandering channels mainly adjusted vertically with a minor amount of narrowing copyright 2003 john wiley sons ltd

nature origin and production characteristics of the lower silurian regional oil and gas accumulation central appalachian basin united states low permeability sandstones of the lower silurian regional oil and gas accumulation cover about 45 000 mi2 117 000 km2 of the appalachian basin and may contain as much as 30 tcf of recoverable gas resources major reservoirs consist of the clinton sandstone and medina group sandstones the stratigraphically equivalent tuscarora sandstone increases the area of the lower silurian regional accumulation lsra by another 30 000 mi2 78 000 km2 approximately 8 7 tcf of gas and 400 million bbl of oil have been produced from the clinton medina reservoirs since 1880 the eastern predominantly gas bearing part of the lsra is a basin center gas accumulation whereas the western part is a conventional oil and gas accumulation with hybrid features of a basin center accumulation the basin center accumulations have pervasive gas saturation water near irreducible saturation and generally low fluid pressures in contrast the hybrid conventional accumulations have less pervasive oil and gas saturation higher mobile water saturation and both normal and abnormally low fluid pressures high mobile water saturation in the hybrid conventional reservoirs form the updip trap for the basin center gas creating a broad transition zone tens of miles wide that has characteristics of both end member accumulation types although the tuscarora sandstone part of the basin center gas accumulation is pervasively saturated with gas most of its constituent sandstone beds have low porosity and permeability commercial gas fields in the tuscarora sandstone are trapped in naturally fractured faulted anticlines the origin of the lsra includes 1 generation of oil and gas from ordovician black shales 2 vertical migration through an overlying 1000 ft 305 m thick ordovician shale 3 abnormally high fluid pressure created by oil to gas transformation 4 updip displacement of mobile pore water by overpressured gas 5 entrapment of pervasive gas in the basin center 6 postorogenic uplift and erosion causing gas leakage and a marked reduction in fluid pressure most future natural gas production in the clinton medina sandstones is anticipated to come from the basin center accumulation the tuscarora sandstone has additional gas resources but typically low reservoir porosity and permeability and the likelihood of low energy in british thermal units gas reduce the incentive to explore for it

channel changes due to river regulation the case of the piave river italy this paper deals with the channel changes of the piave river in the eastern alps italy which have occurred during this century in response to human interventions in the fluvial system the flow regime and the sediment supply of the river have been considerably altered by hydroelectric dams flow diversions and gravel mining in addition river dynamics have been affected by the construction of streambank protection structures to document these changes a historical analysis was performed using maps and aerial photographs morphological features that were examined included planform configuration channel width braiding index and bed elevation the results indicate that as a consequence of decreases in the flows and sediment supply remarkable channel changes have occurred in the river during this century especially during recent decades the channel has undergone a general narrowing with a decrease in average width to 35 per cent of its initial value while the braiding index has decreased from about 3 to 1 5 in several reaches the planform pattern has changed from braided to wandering the observed trends of channel change suggest that the river has not yet reached a new equilibrium condition and it may therefore be predicted that reductions in width and braiding intensity are likely to continue in the immediate future copyright 1999 john wiley sons ltd

reach scale morphological adjustments and stages of channel evolution the case of the trebbia river northern italy abstract a multitemporal series of aerial photos and cross section topographic surveys have been used to analyze reach scale channel evolution along a segment length of about 22 km of the lower trebbia river northern italy with the aims to investigate the relations between channel width vs bed level adjustments and to identify spatio temporal patterns of stages of channel evolution dendrochronology was used to determine the age of tree establishment of riparian and island forests during channel evolution we identified a first phase of major adjustments 1954 1992 following a series of disturbances dominated by channel narrowing and bed incision during the final stage of narrowing woody vegetation establishment contributed to stabilize new floodplain or island surfaces a period of partial morphological recovery occurred from 1992 to 2010 dominated by an inversion of trend of channel width during the phase of partial recovery a stage of widening combined with a continuation of bed incision was identified and a last stage characterized by widening and initial aggradation was observed on the central portion of the study reaches suitability and differences of existing channel evolution models cems derived in other geographical contexts were discussed and a specific conceptual model comprising four stages of channel evolution was developed for the lower trebbia river

medium and short term channel planform changes on the rivers tay and tummel scotland abstract channel planform change was analysed using a variety of data sources for the medium term 25 years and

the role of fluids in low temperature fault related deformation of quartz arenite abstract the microstructural and fluid histories in quartz arenite deformed in a regional scale fault zone were investigated to determine the role of fluids in the selection of grain scale deformation mechanisms using cathodoluminescence fluid inclusion microthermometry and stable isotope geochemistry of quartz cements three chemically distinct aqueous fluids were identified that affected the rock at different times during deformation the earliest deformation microstructures are distributed cataclasites which were cemented by reddish brown luminescing quartz precipitated from an aqueous cacl 2 brine fluid i once cemented brittle deformation continued but localized along discrete shear surfaces in narrow zones 20 1000 m wide and on discrete microfractures microveins associated with this phase were cemented with bluish green luminescing quartz precipitated from an aqueous cacl 2 brine fluid ii water channelized along dissolution surfaces and in pervasive microfracture networks that formed at this time promoted hydrolytic weakening and crystal plastic deformation especially near fluid pathways temperatures during deformation associated with fluids i and ii were 225 235 c as determined from fluid inclusion data in the later stages of deformation an influx of iron bearing aqueous fluid fluid iii greatly accelerated the rate of quartz dissolution and filled fractures stylolites and vugs with goethite the progression of deformation mechanisms indicated by the microstructures and their relationship to the different fluids show that the selection of grain scale deformation processes is affected not only by the presence of fluids but also by their chemistry

causes of 20th century channel narrowing in mountain and piedmont rivers of southeastern france extensive channel narrowing in southeastern france provides an illustration of geomorphic response to land use changes the study region comprises a range of environments from large piedmont and intramountain gravel bed rivers to small mountain streams field measurements and analysis of historical data demonstrate two distinct periods of channel change from 1850 to 1950 channel narrowing is interpreted to be the result of a recovery process in response to widespread channel destabilization induced by major floods during the second half of the 19th century at the time the largely deforested basins were highly responsive to flooding whereas the recovery process was accelerated by floodplain and basin scale land use changes afforestation and torrential control works which in turn reduced sediment delivery and enabled vegetation development in channels from 1950 to 1970 channel narrowing accelerated in most of the studied rivers this recent phenomenon is considered as a human induced fluvial adjustment directly related to forest development on river margins and human abandonment of intensive floodplain land uses at the same time long profile degradation occurred as a result of long term bedload supply decrease in small mountain streams channel narrowing is mainly explained by channel incision which seems to progress from upstream where sediment sources are progressively stabilized by afforestation copyright 2002 john wiley sons ltd

effects of dam operation and land use on stream channel morphology and riparian vegetation dams are well known for influencing channel and vegetation dynamics downstream but little work has focused on distinguishing effects of land use and channel responses to the impoundment in this paper we examined interacting effects of a dam and land use on downstream changes in channel morphology and riparian vegetation along an agricultural stream system in northern california measurements of planform channel morphology vegetation area and land use were mapped along multiple stream segments based on a chronological sequence of historical aerial photographs over a 34 yr period prior to operation of the dam in 1983 and over a 17 yr period after dam operation and compared to a nearby undammed reference stream a two factor analysis of covariance ancova was used to examine the effect of the dam on changes in bankfull area stream length and riparian vegetation area while accounting for the effect of land use and distance downstream the dammed stream s bankfull area contracted 94 after dam operation prior to dam operation bankfull area decreased when land use area increased but not after operation of the dam stream length varied 64 less after dam operation as a consequence of less frequent episodic channel migration and entrenchment the area of riparian vegetation was decreasing during the pre dam period but then increased 72 after operation of the dam across time periods decreases in the area of riparian vegetation were also associated with increases in land use area in both the dammed and reference stream after operation of the dam reduced peak discharges and sediment reduction likely lead to channel incision and constrained channel migration which allowed vegetation to increase 50 on less accessible abandoned banks rating curve and hydraulic exponent analyses based on stream gauge measurements corroborate statistical analyses of the mapped changes in conclusion we found that operation of the dam and land use patterns together influenced spatial and temporal changes in channel morphology and riparian vegetation use of a nearby undammed reference stream in conjunction with multivariable analysis of spatially and temporally replicated observations provided an effective framework for unraveling interacting effects of dams and land use activities on stream channel and vegetation dynamics

morphological changes of the floodplain reach of the taro river northern italy in the last two centuries summary the quantitative analysis of the planform changes of the unconfined reach of the taro river in the italian northern apennines has allowed the channel evolution in the last 200 years to be outlined nine sets of maps and orthophotos ranging from 1828 to 2011 have been used to evaluate the medium term changes in channel morphology along the entire time interval as well as the short term changes in the most recent decade starting from the digitized channel limits and bars a number of shell scripts based on gis commands has been used for fast and automatic calculation of the main morphological parameters channel length width braiding sinuosity centerline shifting and for the drawing of graphs showing in detail their continuous variations along the entire study reach the analysis of the differences in parameters on subsequent dates has revealed that at least until the end of the 20th century continuous reduction in channel width up to a total of 75 and braiding 43 as well as continuous increase in channel length 13 and sinuosity 29 took place this is in agreement with most of the previous studies on other rivers both in italy and abroad in contrast with the results of other studies the most recent evolutionary trend of the taro river shows substantial morphological stability with possible slight narrowing the identification of the variations along the channel facilitated by the analysis of the parameter curves and supported by the historical documentation reveals that these variations can be substantially attributed to human activities in particular the continuous narrowing is largely due to the recurrent subtraction of riverbed areas to be used for agricultural and industrial purposes as well as to the construction of 10 bridges with the relevant bank protections the intense mining between 1950s and 1980s seems to have caused a sharp incision and partial narrowing only the morphological changes due to the reduction in the flow regime which seem to emerge from the sporadic and discontinuous hydrological data are expected to be negligible and in any case are immaterial when compared with the remarkable changes due to human activities

fourier transform infrared spectroscopy determinations of intragranular water content in quartz bearing rocks implications for hydrolytic weakening in the laboratory and within the earth abstract fourier transform infrared ftir spectroscopy has been used to measure intragranular water contents of quartz and feldspar within fine grained quartzites granite and naturally deformed mylonites calibrations and tests of methods developed for this application using natural and synthetic quartz standards indicate that hydrogen concentrations down to 30 ppm are detectable within apertured regions 100 200 m in diam and concentrations of 400 ppm measurable to an accuracy of 30 quartzite and novaculite starting materials used in previous studies of mechanical properties contain substantial intragranular water contents 2400 3900 ppm much larger than water concentrations commonly found in large clear natural crystals and more comparable to those of wet synthetic crystals however unlike molecular water within rapidly grown synthetic quartz most of this water is freezable resembling fluid inclusion water of natural milky quartz crystals likewise quartz and feldspar grains within granite and mylonites deformed at greenschist to upper amphibolite facies conditions contain large amounts of water from 500 to 8000 ppm as fine often submicron size fluid inclusions and ir spectra are dominated by a freezable o h absorption band comparisons between dry natural and wet synthetic quartz crystals have formed the basis for our understanding of hydrolytic weakening however mechanisms by which water related defects access dislocation cores within quartzites deformed in the laboratory and mylonites deformed within natural shear zones may differ from those within idealized natural and synthetic single crystals and their mechanical properties may not be directly comparable

effects of chemical environment on dislocation creep of quartzite the water related chemical parameter that affects dislocation creep in quartzite has been determined from variations in sample strength and microstructure with chemical environment in buffered deformation and hydrostatic annealing experiments samples were weld sealed in double capsules and were buffered using solid oxygen buffers agcl or co2 black hills quartzite was deformed at 900 c and 1 5 10 5s 1 two samples were deformed at 1700 mpa confining pressure at constant and with and varying over 8 and 15 orders of magnitude respectively both samples deformed by climb accommodated dislocation creep with flow stresses of 300 mpa two additional samples were deformed at 700 mpa at constant lower than for the 1700 mpa samples with varying over 2 orders of magnitude both samples faulted with a peak strength of 800 mpa these four experiments suggest no dependence of dislocation creep strength on or instead a strong dependence of strength on is inferred previously deformed samples of heavitree quartzite were hydrostatically annealed for 4 days at 800 c and 1200 or 500 mpa confining pressure varying and over 2 5 and 1 order of magnitude respectively the microstructures of these samples show increased rates of dislocation climb and grain boundary migration with increasing but no dependence on these buffered experiments indicate that dislocation creep is affected by alone and suggest that the exponent for the term in the power law creep flow law is 2

the nature and importance of phyllonite development in crustal scale fault cores an example from the median tectonic line japan abstract like many large crustal scale faults the median tectonic line mtl in sw japan has a long history of movement having been active predominantly as a strike slip fault since the mid cretaceous fault rock exposures in the core of the mtl preserve a history of deformation at a range of mid to shallow crustal depths ryoke mylonites 1 4 km north of the main contact record deeper level cretaceous top to the south sinistral movements the remainder of the fault zone core is surprisingly narrow exhibiting a wide variety of fault rocks that illustrate both the interaction and effects of syn tectonic fluid influx over a range of deformation conditions exposures within 50 m of the central slip zone display a progressive sequence in fault rock evolution from ultramylonite cataclasite foliated cataclasite phyllonite breccia gouge this sequence occurs because cataclasis in the vicinity of the fault core creates permeable pathways for the ingress of chemically active fluids into the fault zone this leads to the replacement of load bearing phases such as feldspar by fine grained foliated aggregates of intrinsically weaker phyllosilicates such as white mica and chlorite the grain size reduction associated with both cataclasis and mineral alteration creates conditions ideal for the operation of fluid assisted stress induced diffusive mass transfer mechanisms comparison with the findings of recent experimental studies suggest that the fault zone processes observed in the core of the mtl will lead to long term weakening provided the network of phyllosilicate rich fault rocks are able to form an interconnected thin layer of weak material on kilometre to tens of kilometre length scales

solution precipitation of k feldspar in deformed granitoids and its relationship to the distribution of water abstract we have investigated k feldspar recrystallisation in granitoid mylonites within a ductile shear zone from the ryoke metamorphic belt sw japan fine grained k feldspar 20 m on average occurs in the matrix and in pull apart areas within fractured k feldspar porphyroclasts these fine grains are elongated and oriented parallel to the main foliation in the matrix and their grain surfaces observed with the scanning electron microscope are not smooth but rough due to the development of very fine

experimental evidence for water weakening of quartzite by microcracking plus solution precipitation creep natural quartzites have been experimentally deformed at a temperature of 1073 k a confining pressure of 1 2 0 1gpa strain rates of 10 5 10 6 and 10 7 s 1 and in the presence of 0 4 wt of added water microstructures after deformation indicate that at strain rates of 10 5 10 6 s 1 crystal plastic deformation is predominant this is evident from abundant deformation lamellae in the original grains and the fact that these grains show a weak crystallographic preferred orientation new grains are absent or of relatively minor volumetric importance in contrast samples deformed at 10 7 s 1 show numerous arrays of fine new polygonal to euhedral quartz grains developed in axially aligned transgranular and grain boundary microcracks these new grain aggregates are characterized by abundant microscale voids fine intergranular channels and fluid inclusion trails syntaxial overgrowth structures on crack walls are also widespread the aggregates of new grains are thus interpreted to have formed by precipitation from solution in addition old grain boundaries oriented perpendicular to the shortening direction show evidence for dissolution the old grains show almost no deformation lamellae subgrains or c axis preferred orientation it therefore appears that at strain rates of 10 7 s 1 microcracking and solution precipitation creep are the dominant deformation mechanisms

intergranular pressure solution in four quartzose sandstones abstract cathodoluminescence petrography and scanning electron microscopy reveal that several geologic variables significantly influenced intergranular pressure solution and quartz cementation in the bromide ordovician oklahoma upper minnelusa permian wyoming nugget jurassic utah and tuscarora silurian pennsylvania sandstones a linear relationship exists between mean grain size and intergranular pressure solution with finer grained samples having experienced more intergranular pressure solution than coarser grained ones samples that display pervasive illite grain coatings have also experienced more intergranular pressure solution than those with no or poorly developed grain coatings sorting and limited framework grain compositional variability have exerted little influence o intergranular pressure solution silica budgets indicate that in the bromide upper minnelusa and nugget sandstones more quartz has been dissolved by intergranular pressure solution than is present as cement these sandstones have exported silica during burial diagenesis in the tuscarora the amount of quartz dissolved by intergranular pressure solution is about equal to the amount of quartz cement present implying approximate mass balance however petrographic evidence suggests that most of the quartz cement in at least three of these sandstones predates most intergranular pressure solution implying that they acted as silica importers during shallow diagenesis and silica exporters during deeper diagenesis intergranular pressure solution has played varying roles in determining the ultimate porosity of these four sandstones in the nugget intergranular pressure solution was the single most important diagenetic process that influenced porosity evolution in the bromide intergranular pressure solution was slightly more important than mechanical compaction and considerably more important than cementation in the tuscarora intergranular pressure solution was slightly more important than mechanical compaction and of about equal importance to quartz cementation in the upper minnelusa intergranular pressure solution was less important than both mechanical compaction and gypsum anhydrite cementation

emag2 a 2 arc min resolution earth magnetic anomaly grid compiled from satellite airborne and marine magnetic measurements 1 a global earth magnetic anomaly grid emag2 has been compiled from satellite ship and airborne magnetic measurements emag2 is a significant update of our previous candidate grid for the world digital magnetic anomaly map the resolution has been improved from 3 arc min to 2 arc min and the altitude has been reduced from 5 km to 4 km above the geoid additional grid and track line data have been included both over land and the oceans wherever available the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation based on an oceanic crustal age model the longest wavelengths 330 km were replaced with the latest champ satellite magnetic field model mf6 emag2 is available at http geomag org models emag2 and for permanent archive at http earthref org cgi bin er cgi s erda cgi n 970

petrofabric test of viscous folding theory abstract compression and extension axes are deduced from quartz deformation lamellae in a quartzite and a graywacke folded into an asymetrical syncline deformation lamellae fabrics in the two sandstones are distinctly different in the graywacke regardless of bedding orientation or position on the fold compression axes are normal or nearly normal to the axial planar rough cleavage extension axes generally lie in the cleavage plane parallel to dip in most quartzite samples compression axes are parallel or subparallel to bedding at high angles to the fold axis and extension axes are normal to bedding two samples from the very base of the formation indicate compression parallel to the fold axis with extension parallel to bedding at high angles to the fold axis one of these two shows both patterns the lamellae fabric geometry in these two samples suggests the presence of a neutral surface in the quartzite the lamellae derived compression and extension axes are in good agreement with the buckling behavior of a viscous layer quartzite embedded in a less viscous medium graywacke and shale below and shale and carbonate above

channel adjustments and vegetation cover dynamics in a large gravel bed river over the last 200 years article i nfo the timing and extent of the morphological changes that occurred in the last 200 years in a large gravel bed river the piave river eastern italian alps that was heavily impacted by human activities training structures hydropower schemes and gravel mining have been analyzed by historical maps aerial photos repeated topographic measurements and geomorphological surveys results show that the channel underwent a strong narrowing during the twentieth century but with a faster pace during the 1970s 1990s and with an associated shift from a dominant braided pattern to a wandering morphology bed incision up to 2 m mostly from gravel mining has been documented for this period large areas of the former active channel were colonized by riparian forests both as islands and as marginal woodlands the ceasing of gravel extraction in the late 1990s seems to have determined a reversal in the evolutionary trend with evidence of vegetation erosion channel widening even though a significant aggradation phase is not present we conclude that alteration of sediment regime has played a major role on the long term channel evolution however only relevant flood events rin10 15 years appear to determine substantial island erosion and therefore the proportion of island vs channel area fluctuates depending on flood history

a method to detect natural fracture strike in sandstones in siliciclastic hydrocarbon reservoir rocks economic gas and oil production may depend on the attributes of natural fractures and with the advent of horizontal drilling fractures are increasingly exploration and development targets yet reliable information on such key fracture attributes as orientation strike is sparse because few fractures intersect vertical well bores this paper describes how fracture strike can be documented on a bed by bed basis even in well bores where few or no visible fractures are directly sampled quartz lined opening mode microfractures lengths of microns to millimeters in quartz cemented sandstones commonly are not visible using standard petrographic methods but systematic mapping of these microfractures is possible using photomultiplier based electron beam induced luminescence scanned cathodoluminescence imaging as shown by observations primarily from three natural gas plays and one oil play in the united states microfracture strike is a good guide to the strike of large fractures macrofractures that formed concurrently because microfractures are widespread and small specimens can be used to get accurate fracture strike data this approach can be applied to samples obtained from wireline conveyed rotary drilled sidewall coring devices as well as to samples from full diameter core

strain accumulation and fluid rock interaction in a naturally deformed diamictite willard thrust system utah usa implications for crustal rheology and strain softening abstract structural and geochemical patterns of heterogeneously deformed diamictite in northern utah usa record interrelations between strain accumulation fluid rock interaction and softening processes across a major fault willard thrust different clast types in the diamictite have varying shape fabrics related to competence contrasts with estimated effective viscosity ratios relative to micaceous matrix of 6 and 8 for large quartzite clasts respectively in the willard hanging wall and footwall 5 and 2 for less altered and more altered granitic clasts respectively in the hanging wall and footwall and 1 for micaceous clasts that approximate matrix strain within the footwall matrix x z strain ratios increase from 2 to 8 westward along a distinct deformation gradient microstructures record widespread mass transfer alteration of feldspar to mica and dislocation creep of quartz within matrix and clasts fluid influx along microcracks and mesoscopic vein networks increased westward and led to reaction softening and hydrolytic weakening in conjunction with textural softening from alignment of muscovite aggregates consistent si al and ti concentrations between matrix granitic clasts and protoliths indicate limited volume change mg gain and na loss reflect alteration of feldspar to phengitic muscovite within the hanging wall strain is overall lower with matrix x z strain ratios of 2 to 4 microstructures record mass transfer and dislocation creep concentrated in the matrix greater al and ti concentrations and lower si concentrations in matrix indicate volume loss by quartz dissolution na gain in granitic clasts reflects albitization large granitic clasts have less mica alteration and greater competence compared to smaller clasts differences in strain and alteration patterns across the willard thrust fault suggest overall downward up temperature fluid flow in the hanging wall and upward down temperature fluid flow in the footwall

accuracy assessment of georectified aerial photographs implications for measuring lateral channel movement in a gis aerial photographs are commonly used to measure planform river channel change we investigated the sources and implications of georectification error in the measurement of lateral channel movement by testing how the number 6 30 and type human versus natural landscape features of ground control points gcps and the order of the transformation polynomial first second and third order affected the spatial accuracy of a typical georectified aerial photograph error was assessed using the root mean square error rmse of the gcps as well as error in 31 independent test points the rmse and the mean and median values of test point errors were relatively insensitive to the number of gcps above eight but the upper range of test point errors showed marked improvement i e the number of extreme errors was reduced as more gcps were used for georectification using more gcps thus improved overall georectification accuracy but this improvement was not indicated by the rmse suggesting that independent test points located in key areas of interest should be used in addition to rsme to evaluate georectification error the order of the transformation polynomial also influenced test point accuracy the second order polynomial function yielded the best result for the terrain of the study area gcp type exerted a less consistent influence on test point accuracy suggesting that although hard edged points e g roof corners are favored as gcps some soft edged points e g trees may be used without adding significant error based upon these results we believe that aerial photos of a floodplain landscape similar to that of our study can be consistently georectified to an accuracy of approximately f5 m with 10 chance of greater error the implications of georectification error for measuring lateral channel movement are demonstrated with a multiple buffer analysis which documents the inverse relationship between the size of the buffers applied to two channel centerlines and the magnitude of change detected between them this study demonstrates the importance of using an independent test point analysis in addition to the rsme to evaluate and treat locational error in channel change studies d 2005 published by elsevier b v

river channel planform change software for historical analysis abstract er mapper an image processing system was used to manipulate scanned maps plans and aerial photographs to enable detailed analysis of historical river channel planform change the er mapper package offers the opportunity to spatially reference each item of planform data into the same scale and co ordinate space as a base map using a warping algorithm and operator selected ground control points once all the data are in the same co ordinate space and at the same scale a given point can be returned to over time and a number of indices can be easily calculated to examine past channel behaviour here lateral shift channel width sinuosity and area of sedimentation within the reach were used as the maps and aerial photographs themselves are used the errors associated with digitising vectors are avoided and a more flexible approach towards analysis and the identification of important indices can be adopted at the outset results obtained for the cleekhimin burn a site in southern scotland are briefly presented and discussed and the advantages of the package and the limitations of the historical database are also outlined

palaeoseismic events recorded in archaean gold quartz vein networks val d or abitibi quebec canada archaean gold quartz vein deposits are commonly hosted in high angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment this paper presents the results of a combined structural and fluid inclusion study on three gold quartz vein deposits of the val d or area abitibi quebec consisting of subhorizontal extensional veins and e w steeply dipping shear veins crack seal structures tourmaline fibres stretched quartz crystals and open space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure co2 rich and h2o nacl fluid inclusions interpreted as two coexisting immiscible fluids occur typically in microcracks of different orientations interpreted to have formed in the 1 2 plane horizontal co2 rich fluid inclusion planes are contemporaneous with the opening of these veins 3 vertical vertical h2o nacl fluid inclusion planes as well as some microstructures such as deformed minerals indicate that the same extensional veins have experienced episodic vertical shortening 3 horizontal alternating with the opening events deformation and slip opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear except that the h2o nacl fluid inclusion planes tend to be oriented at high angles to the slip direction the successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip opening events in shear veins respectively and are attributed to cyclic fluid pressure fluctuations in the system they are thus consistent with the fault valve model sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post failure following seismic rupturing along the shear zone sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form the intermittent change in orientation of 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture the complex internal structures of the gold quartz veins provide an excellent record of archaean seismic activity along high angle reverse faults

hydrographic evolution in relation to neotectonics aided by data processing and assessment some examples from the northern apennines italy abstract geomorphological morphotectonic stratigraphical structural and geological data were collected in the area between the rivers scrivia and nure the po plain and the headwaters of the rivers trebbia aveto and borbera northern italy the data were used to implement databases and to computerise geo related thematic maps which are easily comparable and readily updated reaches of the borbera and lambro meridionale rivers that show anomalous diversions were investigated in detail several thematic maps geolithological geomorphological etc were constructed and overlain on the digital terrain model the results of the processing hillshade slope aspect drainage etc are important elements for identifying and reconstructing the main tectonic phases that have constrained the hydrography of the area

shelf paralic and fluvial environments and eustatic sea level fluctuations in the origin of the tuscarora formation lower silurian of central pennsylvania abstract the tuscarora formation lower silurian of central pennsylvania owes its origin to a combination of tectonic eustatic and depositional events tuscarora deposition began at the beginning of the silurian period at the time of both glacioeustatic sea level rise and renewed tectonic elevation of the taconic source terrain braided alluvial systems transported coarse sediment northwestward to a wave dominated coast yet sea level rise was so rapid that the shoreline retrograded from western to eastern pennsylvania at the time of transgression shoreline characteristics varied from high energy beaches in central pennsylvania to estuaries along the south central border region of pennsylvania seaward of the shoreline sand was fashioned into shelf sand wave complexes analogous to moder shoreface connected sand ridges much of the tuscarora formation west of the susquehanna river accumulated in this shallow marine shelf environment later in the early silurian eustatic sea level fall resulted in progradation of lower energy coastal sand mud flats northwestward over the former shelf shortly before a subsequent sea level rise terminated tuscarora development with the return of the sea in which the rose hill formation was deposited the basis for these interpretations is the analysis of five major lithofacies in the exposed tuscarora formation of central pennsylvania the basal part of the tuscarora consists of two lithofacies of coastal origin the horizontally laminated lithofacies high energy beach and the pink transitional lithofacies estuary the main body of the tuscarora comprises the eastern cross laminated lithofacies braided fluvial and the western cross laminated lithofacies shelf sand wave complexes capping the tuscarora is the red skolithos burrowed lithofacies coastal sand mud flats

evidence for silica gel and its role in faulting in the tuscarora sandstone abstract silica gel has been proposed as a fault weakening mechanism that may offer a solution to the stress paradox of faulting and be important in promoting seismic slip evidence that a gel was present in a fault zone during displacement has proven elusive owing to the unstable nature of a gel and its descendants examination of faults in the middle silurian tuscarora sandstone and other quartz rich rocks in the region has shown that the microcrystalline quartz in bands and cement in cataclasites was derived from a silica gel the presence of comminuted grains silica nanospheres flow features amorphous silica and polygonal crystal domains of low dislocation density within microcrystalline quartz on and adjacent to the fault surfaces is interpreted as evidence of a mobile silica gel precursor brecciated microbreccias and mutually crosscutting relationships between microfractures microcrystalline quartz bands and microveins along and adjacent to fault surfaces suggest that formation of these features was cyclic mutually overprinting textures between brittle and fault creep microstructures stylolites indicate alternating episodic brittle deformation and pressure solution as silica rich rocks are common understanding the process of silica gel formation on fault surfaces and its behavior may provide new insights into the mechanics of faulting in the brittle crust

recent geomorphological changes of the middle and lower calore river campania southern italy the geomorphological changes experienced by the middle and lower calore river southern italy between 1957 and 1998 were investigated data derived from field surveys and interpretation of topographic maps and aerial photos were introduced into a geographic information system gis and processed the results showed that the calore river underwent a mean narrowing of 66 with a peak of 86 the channel length increased by approximately 75 m and the sinuosity from 1 311 to 1 314 the extension of fluvial bars reduced by more than 83 while their number increased from 151 to 381 field evidence of riverbed lowering such as river terraces formed in the considered time span and exhumation of foundations of bridges and flood walls were also constantly detected due to these channel adjustments the calore river morphology changed from transitional to single thread these results were coherent with those reported in the pre existing literature about channel adjustments experienced by many rivers during the twentieth century they all were explainable with a reduction of the bedload transport this latter in turn is completely in accordance with the environmental changes that affected the calore river system in the considered period i e damming and or channelization of the main tributaries reduction of liquid discharge due to water withdrawals and sediment mining from the riverbed

fluid controlled quartz recovery in granulite as revealed by cathodoluminescence and trace element analysis bamble sector norway dispersed quartz veinlets in proterozoic enderbitic charnockite from tromoy bamble sector southern norway with ti concentrations of mostly 80 180 ppm produce bright blue cathodoluminescence cl against contrasting micro textures of secondary pure quartz with low cl intensity the textures comprise grain boundary alteration healed micro fractures patches of secondary quartz and euhedral quartz nuclei the secondary quartz locally makes up 50 of the total quartz trace element analysis has been done by electron probe micro analysis epma laser induced coupled plasma mass spectrometry la icpms and additional electron paramagnetic resonance epr spectroscopy these studies testify systematic trace element reduction and extensive quartz recovery during retrograde metamorphism we assume healing of a part of the aqueous fluid inclusions during a late thermal event possible correlated with paleozoic magmatic activity in the oslo rift during final cooling aqueous fluids were largely retrapped in patches of secondary quartz associated with healed fractures whereas carbonic inclusions without secondary quartz may have survived retrograde metamorphism the variable but generally high salinity of fluid inclusions is assumed to be in part the result of quartz recovery by which ion concentrations were increased in the percentage range

evolutionary trajectory of channel morphology and controlling factors in a large gravel bed river abstract interpretation of channel changes is not always straightforward since it requires a detailed reconstruction of the evolutionary trajectory of channel morphology a quantitative analysis of controlling factors and finally identification of links between evolutionary trajectories and controlling factors the aim of this paper is to explain channel adjustments and controlling factors in the tagliamento river a large gravel bed river in northeastern italy traditional methods for studying historical channel changes i e use of aerial photos topographic data were employed but numerical modelling turned out to be very useful for the quantification of bedload transport and for supporting interpretation of past changes and likely future channel evolution river channel underwent three main phases of adjustment over the last 200 years the first two phases from the end of the nineteenth century to the early 1990s were characterized by narrowing channel width decreased from 1250 to 540 m and incision about 1 m and the third phase from the 1990s to present day by widening from 540 to 600 m and slight aggradation about 0 2 m combining evolutionary trajectories of channel morphology and analysis of controlling factors we argue that the long term channel evolution of the tagliamento river was driven mainly by human intervention at the reach scale i e sediment mining and channelization changes in sediment supply in the catchment area had no or minor effects in the study reach the most recent changes i e widening and slight aggradation are explained as a response to past disturbances that have produced a remarkable change of channel geometry and an increase of unit stream power in the reach magnitude and frequency of formative discharges are a key driving factor of the intensity of recent changes while this was not the case during the previous phases of adjustment

a reappraisal of the sibson scholz fault zone model the nature of the frictional to viscous brittle ductile transition along a long lived crustal scale fault outer hebrides scotland the widely cited sibson scholz conceptual fault zone model suggests that seismically active upper crustal brittle faults pass downward across a predominantly thermally controlled transition at 10 15 km depth into ductile shear zones in which deformation occurs by aseimic viscous creep the crustal scale outer hebrides fault zone ohfz in nw scotland has been described as the type example of such a continental fault zone it cuts precambrian basement gneisses and is deeply exhumed allowing direct study of the deformation products and processes that occur across a wide range of crustal depths a number of fault rock assemblages are recognized to have formed during a long lived displacement history lasting in excess of 1000 myr during caledonian movements that are recognized along much of the 190 km onshore fault trace brittle cataclasite bearing faults in the west of the ohfz are unequivocally overprinted to the east by a younger fabric related to a network of ductile shear zones field observations and regional geochronological data demonstrate that there is no evidence for reheating of the fault zone due to thrust related crustal thickening or shear heating microstructural observations show that the onset of viscous deformation was related to a major influx of hydrous fluids this led to retrogression with the widespread development of new finegrained phyllosilicate bearing fault rocks phyllonites and the onset of fluid assisted grain size sensitive diffusional creep in the most highly deformed and altered parts of the fault zone phyllonitic fault rocks also occur in older more deeply exhumed parts of the fault zone implying that phyllonitization had previously occurred at an earlier stage and that this process is possible over a wide temperature depth range within crustal scale faults our data provide an observational basis for recent theoretical and experimental studies which suggest that crustal scale faults containing interconnected networks of phyllosilicate bearing fault rocks will be characterized by long term relative weakness and shallow 5 km frictional viscous transition zones similar processes acting at depth may provide an explanation for the apparent weakness of presently active structures such as the san andreas fault

deformation processes and weakening mechanisms within the frictional viscous transition zone of major crustal scale faults insights from the great glen fault zone scotland abstract the great glen fault zone ggfz scotland is a typical example of a crustal scale reactivated strike slip fault within the continental crust analysis of intensely strained fault rocks from the core of the ggfz near fort william provides a unique insight into the nature of deformation associated with the main phase of sinistral movements along the fault zone in this region an exhumed sequence of complex mid crustal deformation textures that developed in the region of the frictional viscous transition ca 8 15 km depth is preserved fault rock fabrics vary from mylonitic in quartzites to cataclastic in micaceous shear zones and feldspathic psammites protolith mineralogy exerted a strong control on the initial textural development and distribution of the fault rocks at lower strains crystal plastic deformation occurred in quartz dominated lithologies to produce mylonites simultaneously with widespread fracturing and cataclasis in feldspar and mica dominated rocks at higher strains shearing appears to increasingly localise into interconnected networks of cataclastic shear zones many of which are strongly foliated textures indicative of fluid assisted diffusive mass transfer mechanisms are widespread in such regions and suggest that a hydrous fluid assisted grainsize controlled switch in deformation behaviour followed the brittle comminution of grains the fault zone textural evolution implies that a strain induced fluid assisted shallowing and narrowing of the frictional viscous transition occurred with increasing strain it is proposed that this led to an overall weakening of the fault zone and that equivalent processes may occur along many other long lived crustal scale dislocations

strain fields in and around boudins in a clay experiment abstract boudins were deformed by stretching of a three layer wet clay cake on a deformation table the middle layer was more competent than the others one edge of the boudin was sampled for strain measurements and a total of twenty three sample points were studied the preferred orientation of the basal plane of kaolinite crystals was measured for each sample point with an x ray goniometer from these preferred orientations strain was determined according to the theory of march strain due to the compaction of the clay under its own weight was removed from the total strain observed in order to isolate the strain due to boudinage local changes in volume related to water migration within the clay cake took place during deformation appropriate corrections were made in the procedure of strain removal the strain field due to boudinage was compared with previous results of stress obtained in theoretical and experimental studies and found to be in general agreement