origin of fayalitic olivine rims and lath shaped matrix olivine in the cv3 chondrite allende and its dark inclusions we have studied an allende dark inclusion by optical microscopy scanning electron microscopy electron microprobe analysis and transmission electron microscopy the inclusion consists of chondrules isolated olivines and matrix which as in the allende host is mainly composed of 5 20 m long lath shaped fayalitic grains with a narrow compositional range fa42 2 and nepheline olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5 10 m wide fayalitic rims fa39 2 and 100 1000 m wide translucent zones which consist of 5 20 m long lath shaped fayalitic grains fa41 1 intergrown with nepheline these fayalitic olivines like those in the matrix of the dark inclusion contain 10 20 nm sized inclusions of chromite hercynite and fe ni sulfides the fayalitic rims around remnant olivines are texturally and compositionally identical to those in allende host suggesting that they have similar origins chondrules are surrounded by opaque rims consisting of tiny lath shaped fayalitic olivines 1 3 m long intergrown with nepheline as in the allende host fayalitic olivine veins may crosscut altered chondrules fine grained chondrule rims and extend into the matrix indicating that alteration occurred after accretion we infer that fayalitic olivine rims and lath shaped fayalites in allende and its dark inclusions formed from phyllosilicate intermediate phases this explanation accounts for 1 the similarity of the replacement textures observed in the dark inclusion and allende host to aqueous alteration textures in cm chondrites 2 the anomalously high abundances of al and cr and the presence of tiny inclusions of spinels and sulfides in fayalitic olivines in allende and allende dark inclusions 3 abundant voids and defects in lath shaped fayalites in the allende dark inclusion which may be analogous to those in partly dehydrated phyllosilicates in metamorphosed cm ci chondrites we conclude that the matrix and chondrule rims in allende were largely converted to phyllosilicates and then completely dehydrated the allende dark inclusions experienced diverse degrees of aqueous hydrothermal alteration prior to complete dehydration the absence of low ca pyroxene in the dark inclusion and its significant replacement by fayalitic olivine in allende is consistent with the lower resistance of low ca pyroxene to aqueous alteration relative to forsteritic olivine hydro thermal processing of allende probably also accounts for the low abundance of planetary noble gases and interstellar grains and the formation of nepheline sodalite salite hedenbergite pyroxenes wollastonite kirschsteinite and andradite in chondrules and ca al rich inclusions

facies and facies architecture of paleogene floodplain deposits willwood formation bighorn basin wyoming usa abstract paleogene deposits of the willwood formation were analyzed in two areas of the bighorn basin to provide a better understanding of the facies and facies arrangement of floodplain deposits and the various processes that influence floodplain construction and facies variability despite similar facies and facies organization floodplain deposits in the two areas differ in grain size hydromorphy and maturity of the paleosols and scale and organization of ribbon sandstones in the avulsion deposits these differences appear to be controlled by basin position of the study areas and differences in avulsion between the areas two kinds of cumulative floodplain paleosols red and purple paleosols formed on overbank deposits the red paleosols were better drained and formed on less clay rich parent material intense mottling and iron oxide nodules indicate that the purple paleosols which formed on more clay rich parent material were poorly drained the grain size differences reflect basin position in particular distance from a local sediment source avulsion deposits are volumetrically important comprising about half of the floodplain deposits in both areas the avulsion deposits resemble the stage iii splays described by smith et al 1989 smith n d cross ia dufficy j p clough s r 1989 anatomy of an avulsion sedimentology 36 1 24 in terms of characteristics of their ribbon sandstones and the presence of thin sheet sandstones or siltstones paleosols that formed on the fine grained facies show morphologic differences interpreted as developmental differences and attributed to differing rates of avulsion in the two study areas this study shows that avulsion belt paleosols provide a key to understanding avulsion rate in the stratigraphic record other differences between the willwood avulsion deposits in the two areas and between these ancient deposits and the modern avulsion deposits described by smith et al may reflect 1 problems in clearly recognizing ancient avulsion deposits in the field and 2 sampling bias resulting from the areally restricted view provided by the stratigraphic record of an areally extensive modern depositional feature at the same time because exposures are three dimensional the willwood strata reveal aspects of the facies and facies arrangement of avulsion belts not readily observed in the modern ones

fluvial facies model of the ganga river sediments india abstract the river ganga flows from the northwest to the southeast following the lineaments developed in response to the himalayan tectonics ganga sediments show a large number of facies developments throughout the study area from hardwar to kachhla the active channel deposits are marked by the development of large scale facies in gravel and coarse sand small scale facies comprising fine sand silt and clay are developed in inactive channel deposits and overbank deposits the depositional model shows a progressive decrease in particle size thickness of units and scale of cross bedded sets from the lower to the upper parts of sequences as well as from upstream to downstream the sedimentation of the ganga basin is seasonally and tectonically controlled

preferred orientation of phyllosilicate 001 in matrix of murchison meteorite and possible mechanisms of generating the oriented texture in chondrites abstract preferred orientation of the dominant phyllosilicate phase serpentine in the matrix of the murchison meteorite c2 was determined by x ray pole figure goniometry the basal plane 001 of the phyllosilicate shows a clear preferred orientation of an axial concentration type the preferred orientation is very weak in comparison with the orientations of known terrestrial tectonites and it resembles the weakest case observed in the loosely consolidated clayey sediments from the deep ocean bottom however gentle sedimentation of platy phyllosilicate grains on a flat surface under a weak gravity field does not generate a sufficient preferred orientation it is suggested that the preferred orientation in the matrix of murchison was generated by uniaxial compaction and the magnitude of strain to give rise to the observed degree of preferred orientation is evaluated as 9 there are two possible explanations of the deformation dynamic compression caused by impact and static compaction in a parent body though the latter case appears to be appropriate in the present case it is not straightforward however to conclude that the suggested deformation is caused by burial compaction along gravity under lithostatic stress in a small primitive parent body

active fault motion in a coastal wetland matagorda texas abstract active growth faults contribute to the subsidence of deltaic basins around the world and can significantly augment local rates of relative sea level rise which can inundate and drown wetlands little information exists on the temporal frequency and spatial magnitude of motion along these faults our objective was to quantify fault activity and displacement at multiple time scales in a salt marsh wetland on the east matagorda peninsula texas we present evidence of this activity that includes remotely sensed aerial imagery lidar data ground penetrating radar data shallow seismic data lithostratigraphic and biostratigraphic evidence from core data and sub centimeter gps and survey monitoring the results support the interpretation that the matagorda fault is currently active and has been active in the past subsurface data to depths of 150 m displays evidence of disrupted strata at the fault plane as well as thicker strata on the downthrown side of the fault in the shallow subsurface down to 3 m of depth vertical displacement in stratigraphic markers and surface deformation exhibits a sinusoidal pattern that runs perpendicular to the fault plane which we interpret to represent fault propagation folding maximum throw on this fault is estimated at 0 75 m over the last 40 50 years we also recorded a vertical drop of 0 208 m in the span of a single year at a location close to the fault on its downthrown side records of yearly elevation change also show evidence of ongoing fault propagation folding we conclude that whereas the surface at the matagorda fault moves intermittently up and down at the yearly time scale fault displacement manifests as a sinusoidal pattern of displacement and deformation which has been integrated into the stratigraphic record at decadal to millennial time scales this study presents a rare look into active motion and details its effects on the modern evolution of unconsolidated sedimentary surfaces

yield strength and critical state behavior of a tropical saturated soil the paper reports laboratory investigations carried out on a tropical soil profile to study its compressibility strength critical state and limit state conditions and their variation with depth the soil profile comprises a reddish lateritic layer horizon b underlain by a saprolitic soil horizon c from which a number of block samples were taken a series of isotropic and anisotropic compression tests and drained and undrained triaxial tests were conducted on specimens sampled at depths between 1 0 and 7 0 m and also in the exposed saprolitic soil special triaxial tests with the pore pressure increased to induce failure were performed to investigate the failure at low stress levels on this basis a tensile cutoff on the failure envelope was defined in order to assess the influence of the natural soil structure drained and undrained triaxial tests were carried out on compacted samples obtained from depths of 1 0 and 5 0 m higher strength parameters were measured for the horizon c soil which

fayalitic olivine in cv3 chondrite matrix and dark inclusions a nebular origin fayalitic olivine fa32 is the major component of the matrices and dark inclusions of cv3 and other unequilibrated chondrites it occurs most commonly as rims veins and halos in and around chondrule silicates in the allende type cv3oxa chondrites and to a much lesser extent in the reduced cv3r and bali type cv3oxb chondrites the olivines have distinctive platy tabular and lath or irregular shaped crystals with the ratio of the two types varying widely in cv3oxb chondrites matrix fayalitic olivines range up to fag99 9 whereas in the other cv3 chondrites the range is much smaller the platy and tabular anisotropic forms of the fayalitic olivines strongly suggest growth from a vapor and the nature of the occurrences suggests that cv3 matrices are unequilibrated mixtures of nebular materials we argue that the parent body hydration dehydration model has numerous inconsistencies that make this hypothesis highly unlikely these include 1 there is no direct evidence linking fayalitic olivine to precursor phyllosilicates 2 dehydration of phyllosilicates cannot explain the wide range of morphologies of the fayalitic olivines 3 fayalitic olivine clearly predates the formation of the hydrous phases in cv3 chondrites and is one of the phases that breaks down to form phyllosilicates keller et al 1994 4 the unequilibrated nature of the matrix including fine scale zoning in 10 m sized fayalitic olivine crystals would not survive the parent body metamorphism required in the dehydration model 5 a dark inclusion in the ningqiang chondrite contains fayalitic olivine rimmed by glassy and microcrystalline material zolensky et al 1997 which probably formed by radiation damage this indicates that the fayalitic olivine was exposed to solar radiation in a nebular setting 6 some allende chondrules contain unaltered primary anhydrous glassy mesostasis in contact with the host matrix e g ikeda and kimura 1995 chondrule mesostases would not have survived parent body hydration without becoming hydrated and would probably not survive the metamorphic heating required in the dehydration scenario 7 single platy and barrel shaped crystals of fayalitic olivine are present in accretionary rims in calcium aluminum rich inclusions cais macpherson and davis 1997 which developed in the nebula 8 matrix lumps completely encased in chondrules in ordinary chondrites contain mainly fayalitic olivine scott et al 1984 which indicates a nebular origin 9 oxygen isotopic compositions of allende matrix and dark inclusions strongly indicate little or no hydration for allende and its components clayton 1997 we favor a nebular vaporization recondensation model in which vaporization of chondritic dust produced a fayalite rich vapor followed by formation of the fayalitic olivine by direct recondensation from the vapor epitactic growth on surfaces of existing forsterite and enstatite in chondrules and replacement of existing forsterite and enstatite by gas solid exchange

structure degradation and changes in the mechanical behaviour of a stiff clay due to weathering the paper discusses the results of research into the causes of weathering of stiff pleistocene clays located in the montemesola basin ta italy and on the effects of weathering on the clay s mechanical behaviour the weathered clays are yellow brown and overlie the original grey clays in the whole basin the liquidity indexes of both the yellow and the grey clays their fabric as observed by means of scanning electron microscopy as well as the yellow clay oxidation features suggest that drying has been the main weathering process in the basin this is confirmed by the results of drying wetting cycle tests carried out in the laboratory on undisturbed clay samples which show the drying wetting cycles to produce changes in the grey clay similar to those present in situ due to weathering results of oedometer stress path and triaxial tests show that weathering has caused a degradation of the clay bonding and an associated reduction in the size of the clay state boundary surface both one dimensional an

hidden secrets of deformation impact induced compaction within a cv chondrite the cv3 allende is one of the most extensively studied meteorites in worldwide collections it is currently classified as s1 essentially unshocked using the classification scheme of stoffler et al 1991 however recent modelling suggests the low porosity observed in allende indicates the body should have undergone compaction related deformation in this study we detail previously undetected evidence of impact through use of electron backscatter diffraction mapping to identify deformation microstructures in chondrules aoas and matrix grains our results demonstrate that forsterite rich chondrules commonly preserve crystal plastic microstructures particularly at their margins that low angle boundaries in deformed matrix grains of olivine have a preferred orientation and that disparities in deformation occur between chondrules surrounding and non adjacent matrix grains we find heterogeneous compaction effects present throughout the matrix consistent with a highly porous initial material given the spatial distribution of these crystal plastic deformation microstructures we suggest that this is evidence that allende has undergone impact induced compaction from an initially heterogeneous and porous parent body we suggest that current shock classifications stoffler et al 1991 relying upon data from chondrule interiors do not constrain the complete shock history of a sample

understanding the emplacement of martian volcanic rocks using petrofabrics of the nakhlite meteorites in order to validate calculated ages of the martian crust we require precise radiometric dates from igneous rocks where their provenance on the martian surface is known martian meteorites have been dated precisely and quantitatively but the launch sites are currently unknown inferring the formation environment of a correlated suite of martian meteorites can constrain the nature and complexity of the volcanic system they formed from the nakhlite meteorites are such a suite of augite rich rocks that sample the basaltic crust of mars and as such can provide unique insights into its volcanic processes using electron backscatter diffraction we have determined the shape preferred and crystallographic preferred orientation petrofabrics of four nakhlites governador valadares lafayette miller range 03346 and nakhla in order to understand the conditions under which their parent rocks formed in all samples there is a clear link between the shape preferred orientation spo and crystallographic preferred orientation cpo of augite phenocrysts this relationship reveals the three dimensional shape of the augite crystals using cpo as a proxy for 3d spo and also enables a quantitative 3 dimensional petrofabric analysis all four nakhlites exhibit a foliation defined by the cpo of the augite axis in a plane although individual meteorites show subtle textural variations nakhla and governador valadares display a weak cpo lineation within their axis foliation that is interpreted to have developed in a combined pure shear simple shear flow regime indicative of emplacement of their parent rock as a subaerial hyperbolic lava flow by contrast the foliation dominated cpo petrofabrics of lafayette and miller range 03346 suggest formation in a pure shear dominated regime with little influence of hyperbolic flow these cpo petrofabrics are indicative of crystal settling in the stagnant portion of cooling magma bodies or the flattening area of spreading lava flows the cpo foliation of lafayette s is substantially weaker than miller range 03346 probably due to its higher phenocryst density causing grain grain interactions that hindered fabric development the cpo petrofabrics identified can also be used to determine the approximate plane of the martian surface and the line of magma flow to within 20 our results suggest that the nakhlite launch crater sampled a complex volcanic edifice that was supplied by at least three distinct magmatic systems limiting the possible locations these rocks could have originated from on mars

deciphering holocene sea level history on the u s gulf coast a high resolution record from the mississippi delta published holocene relative sea level rsl curves for the u s gulf coast are in mutual conflict with some characterized by a smooth rsl rise akin to widely accepted eustatic sea level curves versus others including several recent ones that are characterized by a conspicuous stair step pattern with prolonged millennium scale rsl stillstands alternating with rapid meter scale rises in addition recent work in texas and alabama has revitalized the notion of a middle holocene rsl highstand estimated at 2 m above present mean sea level an extensive sampling program in the mississippi delta louisiana focused on the collection of basal peats that accumulated during the initial transgression of the pre existing consolidated pleistocene basement we used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the 30 cm zone between mean spring high water and mean sea level and we selected plant macrofossils that were subjected to ams 14c dating nearly 30 sea level index points from a 20 km2 study area on the eastern margin of the delta suggest that rsl rise followed a relatively smooth trend for the time interval 8000 3000 cal yr b p thus questioning the occurrence of major rsl stillstands alternating with abrupt rises given the narrow error envelope defined by our data set any sea level fluctuations if present would have amplitudes of 1 m although a true middle holocene highstand never occurred in the mississippi delta the high level of detail of our time series enables a rigorous test of this hypothesis correction of our data set for a hypothetical tectonic subsidence rate of 1 1 mm yr 1 assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of texas leads to sea levels near 2 m above present during the time interval 6000 4000 cal yr b p however this model also implies a rsl position near 2 m around 8000 cal yr b p which is inconsistent both with data of this age from texas as well as with widely accepted sea level data from elsewhere we therefore conclude that a middle holocene highstand for the u s gulf coast is highly unlikely and that the entire area is still responding glacio isostatically by means of forebulge collapse to the melting of the laurentide ice sheet

the mineral chemistry and origin of inclusion matrix and meteorite matrix in the allende cv3 chondrite the two textural varieties of olivine rich allende inclusions rimmed and unrimmed olivine aggregates consist primarily of a porous fine grained mafic constituent inclusion matrix that differs from the opaque meteorite matrix of cv3 chondrites by being relatively depleted in sulfides metal grains and perhaps carbonaceous material olivine is the most abundant mineral in allende inclusion matrix clinopyroxene nepheline sodalite and ti al pyroxene occur in lesser amounts olivine in unrimmed olivine aggregates type 1a inclusions is ferrous and has a narrow compositional range fo50 65 olivine in rimmed olivine aggregates type 1b inclusions is on average more magnesian with a wider compositional range fo53 96 olivine grains in the granular rims of type 1b inclusions are zoned with magnesian cores fo 80 and ferrous rinds fo 70 ferrous olivines fo 65 in both varieties of inclusions commonly contain significant amounts of al2o3 as much as 0 7 wt cao as much as 0 4 wt and tio2 as much as 0 2 wt refractory elements that probably occur in submicroscopic inclusions of ca al ti rich glass rather than in the olivine crystal structure defocussed beam analyses of allende matrix materials demonstrate that 1 inclusion matrix in type 1a inclusions is more enriched in olivine and feo than inclusion matrix in the cores of type 1b inclusions 2 opaque matrix materials are depleted in feldspathoids and enriched in sulfides and metal grains relative to inclusion matrix 3 the bulk compositions of type 1a and type 1b inclusions overlap and 4 excluding sulfides and metal the bulk compositions of allende matrix materials cluster in a complementary pattern around the bulk composition of c1 chondrites inclusion matrix and meteorite matrix in allende and other cv3 chondrites are probably relatively primitive nebular material but a careful evaluation of the equilibrium condensation model suggests that these matrix materials do not consist of crystalline phases that formed under equilibrium conditions in a relatively cool gas of solar composition allende inclusion matrix is interpreted as an aggregate of condensates that formed under relatively oxidizing non equilibrium conditions from supercooled supersaturated vapors produced during the vaporization of interstellar dust by aerodynamic drag heating in the solar nebula cv3 meteorite matrix contains in addition a proportion of interstellar material that was heated but not vaporized in the nebula granular olivine in rimmed olivine aggregates may have formed during the recrystallization and incipient melting of aggregates of inclusion matrix in the nebula the mineral chemistry of matrix olivine in allende seems to have been established by three different processes non equilibrium vapor solid condensation recrystallization and partial melting in the nebula and femg equilibration without textural homogenization in the meteorite parent body

accretionary rims on inclusions in the allende meteorite abstract many inclusions in allende particularly those with irregular shapes are surrounded by a sequence of thin layers which differ from one another in texture mineralogy and mineral chemistry the layer underlying all others contains either ia pyroxene needles olivine clumps of hedenbergite and andradite ib olivine doughnuts or ic rectangular olivine crystals the next layer outward ii contains tiny

mapping coastal environments with lidar and em on mustang island texas u s we explore whether lidar light detection and ranging and em electromagnetic induction can improve the accuracy and resolution of wetland mapping that has historically been based chiefly on analysis of aerial photographs using mustang island on the central texas coast as an example we exploit 1 the known strong relationship between elevation and coastal habitat by comparing a lidar derived digital elevation model dem with existing wetland maps and detailed vegetation transects and 2 another known strong relationship between soil and water salinity and coastal habitat by collecting and comparing em derived conductivity data with elevation and vegetation type across the island

shock fabrics in fine grained micrometeorites the orientations of dehydration cracks and fracture networks in fine grained unmelted micrometeorites were analyzed using rose diagrams and entropy calculations as cracks exploit pre existing anisotropies analysis of their orientation provides a mechanism with which to study the subtle petrofabrics preserved within fine grained and amorphous materials both uniaxial and biaxial fabrics are discovered often with a relatively wide spread in orientations 40 60 brittle deformation cataclasis and rotated olivine grains are reported from a single micrometeorite this paper provides the first evidence for impact induced shock deformation in fine grained micrometeorites the presence of pervasive low grade shock features in cm chondrites and cm like dust anomalously low density measurements for c type asteroids and impact experiments which suggest cm chondrites are highly prone to disruption all imply that cm parent bodies are unlikely to have remained intact and instead exist as a collection of loosely aggregated rubble pile asteroids composed of primitive shocked clasts

significance of active growth faulting on marsh accretion processes in the lower pearl river louisiana abstract neotectonic processes influence marsh accretion in the lower pearl river valley active growth faults are suggested by groupings of ponded river channel sections transverse and linear river channel sections and down and across valley contrasts in channel sinuosity seismic profiles identified several likely fault induced structural anomalies two of which parallel the axes of surface distributary networks lithostratigraphy and biostratigraphy of six cores from across a suspected fault in the west middle river combined with 14 c based age control yielded evidence of vertical offsets indicating that this river section is on the plane of a growth fault these data were used to estimate fault slip rates over two time intervals 1 2 mm y over the last 1300 yr and 0 2 mm yr 1 over the last 3700 yr and delineated a sinusoidal pattern of deformation moving distally from the fault which we interpret as resulting from fault propagation folding higher rates of sediment accumulation of the order of cm yr 1 from 210 pb xs and 137 cs activity data on the down thrown side are consistent with sedimentary response to increased accommodation space and mass based sediment accumulation rates g cm 2 yr 1 exhibit a pattern inverse of that shown by fault driven sinusoidal deformation we contend that near surface growth faults are critically important to driving accretion rates and marsh response to sea level rise

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

cenozoic evolution of sediment accumulation in deltaic and shore zone depositional systems northern gulf of mexico basin abstract paleogeographic and volumetric lithofacies mapping of 18 cenozoic genetic sequences within the northern gulf of mexico basin quantifies the proportional sequestering of sediment within wave dominated shore zone vs deltaic systems through time three long term depositional phases are revealed by plots based on paleogeographic and sediment isochore maps of total shore zone system area and volume to total delta system area and volume sz d 1 sz d area and volume ratios are highly variable in paleocene through eocene sequences however typical volume ratios for major genetic sequences upper middle and lower wilcox queen city qc and yegua range between 0 2 and 0 6 minor sequences sparta sp jackson js which record very low rates and volumes of sediment accumulation have the greatest variability in their ratios 2 oligocene and miocene sequences display consistently high proportions of shore zone sediment sz d area ratios range from 0 6 to 1 0 and volume ratios cluster between 0 4 and 0 8 3 a substantial late neogene decrease in sz d ratios is presaged in the late miocene sequence pliocene and pleistocene sequences are uniformly characterized by very low ratios of

the post yield behaviour of four eocene to jurassic uk stiff clays a detailed study is described of the post yield behaviour of four medium plasticity heavily overconsolidated uk stiff clays sub layers of the stiff to hard gault kimmeridge and oxford clays were identified sampled and tested these along with facies investigated in an earlier london clay study had broadly similar depositional histories the intention in considering a spread of similar sediments from the jurassic to the eocene was to allow any strong effects of geological age or burial depth to be identified a strongly fissured meso structure was present in three of the four clays which had a controlling influence on their effective shear strengths considering that the representative element volume is of paramount importance in measuring the strengths of such soils all four soils were brittle in shear and when sheared to sufficient displacements developed low residual shear strengths the stiff clays were investigated further through comparisons between natural and reconstituted behaviour usi

coastal geomorphology and restoration abstract increases in human development of the coastal zone sea level rise and intensity of coastal storms will test the resilience of coastal systems an integrated approach is needed to describe geomorphic biologic dependencies feedbacks between processes and responses and determine how coastal systems can be maintained or restored the 2013 binghamton geomorphology symposium focused on three themes in these research areas 1 the geomorphic response of coastal landforms to changes in sea level and episodic storms 2 the way these stressors alter geomorphic biotic interactions and reduce the resilience of coastal environments and 3 the way natural and human processes are being integrated to restore or maintain dynamic geomorphic and biologic linkages this issue contains eighteen papers presented at the symposium six papers are devoted to each of these themes the papers point to the importance of ecological systems in modulating the responses to natural physical processes and in turn responding to geomorphic change and the role of humans in assisting natural processes

meltwater pulse 1a from antarctica as a trigger of the bolling allerod warm interval meltwater pulse 1a mwp 1a was a prominent feature of the last deglaciation which led to a sea level rise of 20 meters in less than 500 years concurrent with mwp 1a was the onset of the bolling allerod interstadial event 14 600 years before the present which marked the termination of the last glacial period previous studies have been unable to reconcile a warm northern hemisphere with mwp 1a originating from the laurentide or fennoscandian ice sheets with the use of a climate model of intermediate complexity we demonstrate that with mwp 1a originating from the antarctic ice sheet consistent with recent sea level fingerprinting inferences the strength of north atlantic deep water nadw formation increases thereby warming the north atlantic region and providing an explanation for the onset of the bolling allerod warm interval the established mode of active nadw formation is then able to respond to subsequent freshwater forcing from the laurentide and fennoscandian ice sheets setting the stage for the younger dryas cold period the melting of continental ice sheets during the last deglaciation provided a freshwater source to the ocean that affected global sea level and the strength of the thermohaline circulation an exceptionally large melting event inferred from far field relative sea level records occurred

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

ca carbonate in the orgueil ci carbonaceous chondrite mineralogy microstructure and implications for parent body history the orgueil ci carbonaceous chondrite is a breccia and some of its constituent clasts contain ca carbonate grains whose mineralogy is undetermined but may yield new information on the history of its asteroidal or cometary parent body characterisation of one such clast shows that in addition to ca carbonate it contains magnetite olivine and orthopyroxene grains that are supported within a finely crystalline saponite serpentine ferrihydrite groundmass the ca carbonate grains are typically rounded less than 10 m in diameter and backscatter kikuchi patterns identify all those analysed as calcite electron backscatter diffraction orientation contrast maps show that most calcites have sub m sized e twins some of which are cut by corroded grain margins these microstructures demonstrate that the clast experienced very mild shock during aqueous alteration and probably accompanying impact gardening of the parent body regolith the sample studied hosts several other millimeter sized clasts and a fine grained clastic matrix that are free of ca carbonate olivine and orthopyroxene although can contain apatite dolomite and pyrrhotite within one of these clasts is a network of phyllosilicate magnetite veins that are inferred to have acted as fluid flow conduits during parent body aqueous alteration sulphur rich reaction rims within the same clast are likely to have formed during post fall remobilization and crystallization of pre terrestrial sulphates this study provides good evidence for alteration of the ci carbonaceous chondrites in a dynamic parent body regolith

earliest rock fabric formed in the solar system preserved in a chondrule rim rock fabrics record the formation compaction and deformation history of that rock high resolution mapping of tiny grains in the allende cv meteorite reveals preservation of a spherical fabric that may have formed in the solar nebula and could be the oldest rock fabric to have formed in the solar system

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

avulsion deposits in lower eocene alluvial rocks bighorn basin wyoming abstract eocene alluvial rocks in the northern bighorn basin can be subdivided into three major kinds fine grained deposits on which cumulative paleosols developed lithologically heterogeneous packages associated with immature paleosols and major sheet sandstone bodies the heterogeneous packages which alternate vertically with the cumulative paleosols are dominated by fine grained deposits and also contain ribbon sandstone bodies and thin 1 m sheet sandstone bodies most ribbon sandstones are less than 3 m thick and are more common in the middle and upper parts of the packages cut and fill deposits with fine grained fills are locally important because the lithologic packages are readily apparent in the field because of the immature or simple paleosols developed on the fine grain d facies they are referred to as simple paleosol packages the major sheet sandstones were deposited by meandering trunk rivers and locally overlie and truncate the other deposits contrary to classical models of meandering streams only a portion of the fine grained rocks in the study area were deposited by overbank flooding of a trunk channel on the basis of their stratigraphic position and few ribbon sandstones the upper parts of some simple paleosol packages are interpreted as ancient levee deposits associated with a trunk channel farther from the trunk channel overbank floods deposited alluvium on which the cumulative paleosols formed the greater parts of the simple paleosol packages including their fine grained deposits were deposited rapidly during channel avulsion ribbon sandstone bodies represent ancient splay channels on the avulsion belt simple paleosol packages in the willwood formation support the contention of smith et al 1989 that n many meandering river systems a significant portion of the fine grained deposits were deposited as the trunk channel avulsed deposits that resemble the simple paleosol packages may provide a means of recognizing avulsion episodes in other alluvial sequences

active near surface growth faulting and late holocene history of motion matagorda peninsula texas abstract the structural framework of the northern gulf of mexico coastal zone includes numerous growth fault systems neotectonic processes in coastal environments here have been shown to be important contributors to subsidence and relative sea level rise as well as having significant influences on sedimentary accretion processes one active growth fault at east matagorda peninsula texas was subjected to detailed study to address the hypotheses that 1 this fault was present and active before the peak of regional hydrocarbon recovery in the mid 20th century and that 2 slip along this fault has been episodic over the resolved period of record to characterize the late holocene behavior of this fault three core transects were established normal to the surface fault trace and stratigraphic analysis was conducted with the use of radiocarbon 14c for chronological control correlation of time equivalent stratigraphic boundaries reveals a maximum total late holocene offset of 0 7 m the matagorda fault was in place long before the peak of regional oil and gas extraction but experienced a late holocene rejuvenation initiated between 2500 and 1500 years bp the kinematic behavior of the fault expressed as temporally and spatially variable measures of expanded stratigraphic thicknesses on the downthrown extent suggest that sediment loading from the transgressive matagorda barrier complex may have contributed to this rejuvenation and that slip along the fault persists to the present radiocarbon chronology also revealed clear differences in the magnitude of fault throw during the late holocene with maximum displacement 0 7 m occurring at the southwestern most transect and minimum throw at the northeastern most transect 0 2 m

high precision measurements of wetland sediment elevation ii the rod surface elevation table abstract a new high precision device for measuring sediment elevation in emergent and shallow water wetland systems is described the rod surface elevation table rset is a balanced lightweight mechanical leveling device that attaches to both shallow 1 m in order to be stable the pipe is driven to refusal but typically to a depth shallower than the rod bench mark because of greater surface resistance of the pipe thus the rset makes it possible to partition change in sediment elevation over shallower e g the root zone and deeper depths of the sediment profile than is possible with the set the confidence intervals for the height of an individual pin measured by two different operators with the rset under laboratory conditions were 1 0 and 1 5 mm under field conditions confidence intervals for the measured height of an individual pin ranged from 1 3 mm in a mangrove forest up to 4 3 mm in a salt marsh

experimental investigation of both the disturbed and undisturbed granitic saprolite soil granitic saprolites are abundant in many regions around the world and they are widely employed in various engineering projects behavior of such kinds of soils is not sufficiently understood and our knowledge about the fundamental behavior of saprolites is to a far less extent than the sedimentary soils owing to the limited knowledge many problems occurred in the engineering applications that used saprolites as a construction material this study presents results of a set of conventional drained and undrained triaxial compression shearing tests on the granitic saprolites in both the disturbed and undisturbed conditions this study showed that the soil fabric was the paramount factor governing on the soil stress strain response rather than the soil bonds under the drained shearing condition the undisturbed soil revealed a strain softening behavior with a dilative response at the low consolidation stress level while a contractive response was present at the high consolidation stress levels however the disturbed soil showed a strain hardening behavior with a contractive response regardless of the consolidation stress levels during the drained shearing the undrained response was complicated as the soil showed both the contractive and dilative responses with phase transformation points regardless of the soil condition i e disturbed or undisturbed and the consolidation stress levels the bond effect of the intact soil persisted during the consolidation stage however its effect did not extend to the large strain controlled shearing stage where the tangential stiffness suddenly decreased at the axial strain of 1 5

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

current subsidence rates due to compaction of holocene sediments in southern louisiana 1 relative contributions of geologic and anthropogenic processes to subsidence of southern louisiana are vigorously debated of these shallow sediment compaction is often considered dominant although this has never been directly observed or effectively demonstrated quantitative understanding of subsidence is important for predicting relative sea level rise storm surge flooding due to hurricanes and for successful wetland restoration despite many shallow borings few appropriate stratigraphic and geotechnical data are available for site specific calculations we overcome this by determining present compaction rates from monte carlo simulations of the incremental sedimentation and compaction of stratigraphies typical of the holocene of southern louisiana this approach generates distributions of present compaction rates that are not expected to exceed 5 mm yr but may locally locations with present subsidence rates greater than the predicted maximum probable shallow compaction rates are likely influenced by additional processes

geometric models of listric normal faults and rollover folds existing geometric models allow master fault shapes to be constructed given the shape and heave or displacement of a deformed marker horizon in the hanging wall these models assist in projecting normal faults to depth where the fault geometry is poorly constrained by available seismic data currently it is unclear which model best predicts the actual relation between rollover and fault geometries to address this deficiency the relative accuracies of the constant heave constant displacement constant bed length slip line and inclined shear constructions are evaluated using clay model analogs and seismic examples each of the geometric models predicts a different fault shape and depth to detachment for the same rollover shape because different hanging wall deformat on mechanisms are assumed a construction is developed for determining the hanging wall geometry from a known fault geometry this construction is based on the inclined shear model and geometric constraints imposed by material displacement paths viewed from different reference frames fixed to the hanging wall and footwall blocks in clay models the inclined shear antithetic shear greek alpha 20 degrees and slip line constructions produce the best agreement between actual and modeled fault and marker bed shapes in rollovers for subsurface examples the inclined shear model antithetic shear greek alpha 20 40 degrees and the constant displacement model predict fault trajectories that are the most similar to the positions and shapes of the master fault segments interpreted fr m offshore norway and gulf of mexico seismic lines the shear angle required in the inclined shear model can often be estimated from the orientation of minor faults in the hanging wall the shear angle may also be determined through iterative modeling in which the shear angle is systematically varied and the resultant model fault shape is compared to the shape of the shallow segment of the master fault interpreted from the seismic record

geometric and experimental models of extensional fault bend folds the geometric models ranged from simple models of listric normal faults with continuous hanging wall deposition to complex models of normal faults with ramps and flats and footwall deposition and or erosion the inclined shear angle i e the angle between the horizontal and the shear direction was 70 in all models withjack and peterson 1993 describe the modeling technique in the experimental models a 4 cm thick layer of either wet clay or dry sand covered a flat metal base consisting of overlapping plates or precut blocks movement of the plates or blocks produced a listric normal fault in the overlying clay or sand layer we added growth layers after every centimeter of displacement withjack and callaway 2000 describe the properties of the wet clay and dry sand

intragranular dynamic recrystallization in naturally deformed calcite marble diffusion accommodated grain boundary sliding as a result of subgrain rotation recrystallization abstract intragranular microshear zones within a greenschist facies calcite marble were studied to try to constrain better the processes of dynamic recrystallization as well as the deformation processes that occur within newly recrystallized grains intragranular recrystallized grains within large twinned calcite porphyroclasts can be related to the host from which they have recrystallized and are the focus of an electron backscatter diffraction study lattice distortions low angle boundaries and some high angle boundaries 15 in the microshears within a porphyroclast have the same misorientation axes suggesting that deformation occurred by climb accommodated dislocation creep involving subgrain rotation recrystallization changes in the ratio of host and twin domain as the deformation zone is entered show that twin boundary migration also occurred recrystallized grains have similar sizes 10 60 m to subgrains suggesting that they formed by subgrain rotation however within the intragranular microshear zones the misorientations between recrystallized grains and porphyroclasts are considerably larger than 15 and misorientation axes are randomly oriented moreover recrystallized grain orientations average around the porphyroclast orientation we suggest that the recrystallized grains once formed are able to deform partly by diffusion accommodated grain boundary sliding which is consistent with predictions made from lab flow laws

the porosity and permeability of chondritic meteorites and interplanetary dust particles abstract we have investigated the porosity of a large number of chondritic interplanetary dust particles idps and meteorites by three techniques standard liquid gas flow techniques a new noninvasive ultrasonic technique and image processing of backscattered images the latter technique is obviously best suited to sub kilogram sized samples we have also measured the gas and liquid permeabilities of some chondrites by two techniques standard liquid gas flow techniques and a new nondestructive pressure release technique we find that chondritic idps have a somewhat bimodal porosity distribution peaks are present at 0 and 4 porosity a tail then extends to 53 type 1 3 chondrite matrix porosities range up to 30 with a peak at 2 the bulk porosities for type 1 3 chondrites have the same approximate range as exhibited by the matrix which indicates that other components of the bulk meteorites including chondrules and aggregates have the same average porosity as the matrix these results reveal that the porosities of primitive materials at scales ranging from nanogram to kilogram are similar which implies that similar accretion dynamics operated through 12 orders of size magnitude permeabilities of the investigated chondrites vary by several orders of magnitude and there appears to be no simple dependence of permeability with degree of aqueous alteration chondrite type or porosity

growth fault rollover systems birth growth and decay growth fault rollover systems are extremely common structures of thin skinned extensional systems resulting from gravity gliding above salt their development is studied using laboratory experiments based on brittle ductile models where the sedimentary cover and synkinematic sediments are simulated using brittle sand and the underlying decollement layer by viscous silicone putty the experiments are compared to natural examples from seismic lines the experimental results are used to present the evolution of growth fault rollover systems these being the result of a finite amplitude instability with three distinct stages birth growth and decay each of these stages is identified with typical structures which can be recognized on seismic sections a discussion is presented on the interactions in time and space between synthetic and antithetic listric faults parallel and transverse to the direction of displacement

petrography mineralogy and geochemistry of lunar meteorite sayh al uhaymir 300 we report here the petrography mineralogy and geochemistry of lunar meteorite sayh al uhaymir 300 sau 300 sau 300 is dominated by it fine grained crystalline matrix surrounding mineral fragments plagioclase pyroxene olivine and ilmenite and lithic clasts mainly feldspathic to noritic mare basalt and kreepy rocks are absent glass melt veins and impact melts are present indicating that the rock has been subjected to a second impact event feni metal and troilite grains were observed in the matrix major element concentrations of sau 300 al 2 o 3 21 6 wt and feo s 16 wt are very similar to those of two basalt bearing feldspathic rei regolith breccias calcalong creek and yamato y 983885 however the rare earth element ree abundances and pattern of sau 300 resemble the patterns of feldspathic highlands meteorites e g queen alexandra range que 93069 and dar al gani dag 400 and the average lunar highlands crust it has a relatively lree enriched 7 to 10 x ci pattern with a positive eu anomaly similar to 11 x ci values of fe mn ratios of olivine pyroxene and the bulk sample are essentially consistent with l lunar origin sau 300 also contains high siderophile abundances with a chondritic ni ir ratio sau 300 has experienced moderate terrestrial weathering as its bulk sr concentration is elevated compared to other lunar meteorites and apollo and luna samples mineral chemistry and trace clement abundances of sau 300 fall within the ranges of lunar feldspathic meteorites and fan rocks sau 300 is a feldspathic impact melt breccia predominantly composed of feldspathic highlands rocks with a small amount of mafic component with a bulk mg of 0 67 it is the most mafic of the feldspathic meteorites and represents a lunar surface composition distinct from any other known lunar meteorites oil the basis of its low th concentration 0 46 ppm and its lack of kreepy and mare basaltic components the source region of sau 300 could have been within a highland terrain a great distance from the imbrium impact basin probably on the far side of the moon

fabric analysis of allende matrix using ebsd fabric analysis of the interstitial matrix material in primitive meteorites offers a novel window on asteroid formation and evolution electron backscatter diffraction ebsd has allowed fabrics in these fine grained materials to be visualized in detail for the first time our data reveal that allende a cv3 chondrite possesses a uniform planar short axis alignment fabric that is pervasive on a broad scale and is probably the result of deformational shortening related to impact or gravitational compaction interference between this matrix fabric and the larger more rigid components such as dark inclusions dis and calcium aluminium rich inclusions cais has lead to the development of locally oriented and intensified matrix fabrics in addition dis possess fabrics that are conformable with the broader matrix fabric these results suggest that dis were in situ prior to the deformational shortening event responsible for these fabrics thus providing an argument against dark inclusions being fragments from another lithified part of the asteroid kojima and tomeoka 1996 fruland et al 1978 moreover both dis and allende matrix are highly porous 25 corrigan et al 1997 mobilizing a highly porous di during impact induced brecciation without imposing a fabric and incorporating it into a highly porous matrix without significantly compacting these materials is improbable we favor a model that involves allende dis cais and matrix accreting together and experiencing the same deformation events

magnetization of extraterrestrial allende material may relate to terrestrial descend abstract the origin of magnetization in allende may have significant implications for our understanding of core formation differentiation dynamo processes in chondrite parent bodies the magnetic allende data may contain information that could constrain the magnetic history of allende the measurements on allende chondrules reveal an existence of magnetization component that was likely acquired during the meteorite transit to terrestrial conditions both the pyrrhotite carrying magnetic remanence intensity and direction of the chondrules change erratically when subjecting the allende meteorite s chondrules to temperatures near 77 k and back to room temperature chondrules with more intense original magnetization are denser and contain larger inverse thermoremanent magnetization itrm temperature dependent monitoring of itrm revealed that magnetization was acquired at temperature near 270 k such temperature is consistent with the condition when in addition to temperature increase the atmospheric uniaxial pressure applied during the meteorite entry on the porous material was responsible for meteorite break up in the atmosphere during this process collapse of the pore space in the matrix and some chondrules would generate crystalline anisotropy energy accumulation within pyrrhotite grains in form of parasitic magnetic transition

integrated geophysical studies over an active growth fault in houston active growth faults cutting the land surface in the gulf coast area represent a serious geohazard considering the average movement of these faults is a few inches per decade the potential is high for structural damage to highways industrial buildings residential houses and railroads that cross these features

the mechanics of cemented carbonate sands the behaviour of artificially cemented carbonate sand was investigated in triaxial tests at confining pressures of up to 9 mpa the results show that an important effect of cementing is a reduction in specific volume resulting from the increase in fines content this influences both the stress strain behaviour and the peak strength at strains beyond those required to fracture the cement bonding comparisons between the behaviour of cemented and uncemented soils should therefore be carried out on samples with the same gradings for cemented samples it is possible to identify a yield curve outside the state boundary surface of the uncemented soil a framework for the behaviour has been defined which depends on the relative magnitudes of the confining pressure and cement bond strength the behaviour of a natural cal carenite agreed well with this framework which is also likely to be applicable to other cemented soils le comportement d un sable carbonate artificiellement cimente a ete etudie a l aide d essa

a test of models of fluvial architecture and palaeosol development camp rice formation upper pliocene lower pleistocene southern rio grande rift new mexico usa numerical experimental and theoretical models of fluvial architecture and palaeosol development are tested with outcrops of upper pliocene lower pleistocene sediment in the southern rio grande rift new mexico the sediment was deposited and subsequently exhumed in the jornada del muerto basin a westward tilted half graben whose footwall corresponds to the rincon hills and san diego mountain fault blocks the axial river the ancestral rio grande shared time between the jornada del muerto basin and the adjacent corralitos basin the ancestral rio grande entered the jornada del muerto basin via a gap between the footwall blocks periodically flowing southward towards san diego mountain or making a broad northward sweep into the northern fluvial salient towards the rincon hills fault block and unfaulted northern edge of the basin ten logged sections up to 35 m thick are correlated using the top of the formation la mesa surface a 1 59 ma pumice conglomerate and a ground water carbonate opal bed additionally one of the sections is dated by reversal magnetostratigraphy consistent with the model of bridge leeder 1979 and bridge mackey 1993a differential tilting of the jornada del muerto half graben resulted in sections directly adjacent to the faults that consist almost exclusively of multistorey channel sands sandstones whereas more distal sections contain a greater proportion of crevasse splay fine sand and overbank mudstone and calcic palaeosols along the axis of the northern fluvial salient a northward decrease in channel floodplain ratio a decrease in channel recurrence interval from 171 kyr to 685 kyr and an increase in the maturity of calcic palaeosols are consistent with southward tilt of the unfaulted northern edge of the basin an upsection decrease in sediment accumulation rate in the northern fluvial salient from 0 036 mm yr to 0 017 mm yr corresponds to an increase in the ratio of channel floodplain facies and in the number of multistorey channel sands sandstones and is consistent with the model of bridge leeder 1979 in which avulsion frequency is independent of sediment accumulation rate stage ii and iii calcic palaeosols indicate 103 105 year of landscape stability and soil formation between periods of floodplain deposition in response not only to basin tilting but also because the ancestral rio grande had multiple paths within the jornada del muerto basin and shared time between the corralitos and jornada del muerto basins

evidence of regional subsidence and associated interior wetland loss induced by hydrocarbon production gulf coast region usa analysis of remote images elevation surveys stratigraphic cross sections and hydrocarbon production data demonstrates that extensive areas of wetland loss in the northern gulf coast region of the united states were associated with large volume fluid production from mature petroleum fields interior wetland losses at many sites in coastal louisiana and texas are attributed largely to accelerated land subsidence and fault reactivation induced by decreased reservoir pressures as a result of rapid or prolonged extraction of gas oil and associated brines evidence that moderately deep hydrocarbon production has induced land surface subsidence and reactivated faults that intersect the surface include 1 close temporal and spatial correlation of fluid production with surficial changes including rapid subsidence of wetland sediments near producing fields 2 measurable offsets of shallow strata across the zones of wetland loss 3 large reductions in subsurface pressures where subsidence rates are high 4 coincidence of orientation and direction of displacement between surface fault traces and faults that bound the reservoirs and 5 accelerated subsidence rates near producing fields compared to subsidence rates in surrounding areas or compared to geological rates of subsidence based on historical trends subsidence rates in the gulf coast region near producing fields most likely will decrease in the future because most petroleum fields are nearly depleted alternatively continued extraction of conventional energy resources as well as potential production of alternative energy resources geopressured geothermal fluids in the gulf coast region could increase subsidence and land losses and also contribute to inundation of areas of higher elevation

on the mechanics of structured sands to date the effect of structure on the behaviour of natural sands has focused almost exclusively on the component of bonding and the effect of fabric has been largely overlooked the paper describes a detailed investigation of the behaviour of two natural sands by means of triaxial testing over a wide range of pressures one material had bonding as the principal element of its structure and the other fabric following on from a paper of cuccovillo and coop which examined the influence of the two structural elements on the small strain stiffness the current paper develops a new framework for the yielding and large strain behaviour it is suggested that structure should be considered as an element of the nature of a sand in addition to properties such as mineralogy particle shape and grading the resulting framework is then capable of encompassing the patterns of behaviour seen for both bonding and fabric dominated sands while bonding results in a cohesive mode of shearing it is demonstrated that when

new insights into the formation of fayalitic olivine from allende dark inclusions abstract although considerable progress has been made in unraveling the origin s of fayalitic olivines in dark inclusions dis many questions remain still unresolved and or controversial we combine a chemical and petrographic study of the allende dark inclusion 4884 2b amnh new york and atem studies of a fragment of the dark inclusion allende af nhm vienna and discuss an alternative way in which fayalitic olivines could have formed allende dark inclusion 4884 2b contains a few aggregates with variable proportions of transparent and feathery olivine two such objects aggregates a and b are the focus of this study as they preserve glasses that can help in deciphering the nature of the processes involved during olivine growth and subsequent olivine transformation the petrographic and chemical characteristics of aggregates a and b indicate that the forsteritic stack olivines may be pseudomorphs of clear olivine crystals the atem studies in all af suggest that fayalitic olivines may be the result of secondary processes e g metasomatic exchange reactions operating in the solar nebula transformation may have occurred through the mediation of a dry gas phase involving nonvolatile major elements such as mg and fe e g dohmen et al 1998 this mechanism could reveal olivine growth patterns e g stacked platelets due to a rapid growth regime and may have contributed to the development of their fibrous aspect while preserving the shape i e volume of the crystals this highly selective process did completely or partially transform ferromagnesian minerals but affected the fine grained mesostasis only slightly

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

aqueous alteration of the martian meteorite northwest africa 817 probing fluid rock interaction at the nakhlite launch site the nakhlite meteorites characteristically contain iddingsite a hydrous iron magnesium silicate that formed by aqueous alteration on mars iddingsite is most abundant in northwest africa nwa 817 and alteration products in this meteorite also have the lowest deuterium hydrogen ratio of any nakhlite taken together these distinctive properties could be interpreted to show that nwa 817 was altered under different physico chemical conditions than the other nakhlites and by liquid water from a separate reservoir here this interpretation is tested through a petrographic mineralogical chemical and isotopic study of nwa 817 we find that its iddingsite occurs as olivine hosted veins of nanocrystalline smectite and fe oxyhydroxide strong similarities in the mineralogy of iddingsite between nwa 817 and other nakhlites suggest that these meteorites were altered under comparable physico chemical conditions with the fe rich composition of nwa 817 olivine grains rendering them especially susceptible to aqueous alteration analyses of nwa 817 bulk samples by stepwise pyrolysis confirm that its iddingsite has unusually low deuterium hydrogen ratios but owing to terrestrial weathering of this meteorite the hydrogen isotopic data cannot be used with confidence to infer the origin of martian aqueous solutions nwa 817 was most probably altered along with the other nakhlites over a short time period and in a common aqueous system one interpretation of a correlation between the eruption ages of three of the nakhlites and the chemical composition of their iddingsite is that water originated from close to the surface of mars and flowed through the nakhlite lava pile under the influence of gravity

tectonic control of subsidence and southward displacement of southeast louisiana with respect to stable north america 1 gps data collected between 1995 and 2006 suggest that southeast louisiana including new orleans and the larger mississippi delta are both subsiding vertically and moving southward with respect to stable north america both motions are likely related due to their common tectonic setting subsidence in the new orleans area occurs in part because it is located in the hanging wall of a large listric normal fault system that forms the northern boundary of a 7 10 km thick allochthon that is detached from stable north america southward motion of this allochthon relative to stable north america occurs at 2 2 0 6 mm yr the average subsidence rate for gps sites located on the allochthon is 5 2 0 9 mm yr relative to earth s center of mass or 7 mm yr relative to mean sea level motion of the allochthon is likely due to the gravity instability created by rapid holocene sediment deposition in the delta following continental glacial retreat and is facilitated at depth by weak salt horizons because new orleans and other communities of southeastern louisiana lie atop this active allochthon future motion of this body should be considered during rebuilding of the region following hurricanes katrina and rita

mississippi delta subsidence primarily caused by compaction of holocene strata coastal subsidence causes sea level rise shoreline erosion and wetland loss which poses a threat to coastal populations this is especially evident in the mississippi delta in the southern united states which was devastated by hurricane katrina in 2005 the loss of protective wetlands is considered a critical factor in the extensive flood damage the causes of subsidence in coastal louisiana attributed to factors as diverse as shallow compaction and deep crustal processes remain controversial current estimates of subsidence rates vary by several orders of magnitude here we use a series of radiocarbon dated sediment cores from the mississippi delta to analyse late holocene deposits and assess compaction rates we find that millennial scale compaction rates primarily associated with peat can reach 5mm per year values that exceed recent model predictions locally and on timescales of decades to centuries rates are likely to be 10 mm or more per year we conclude that compaction of holocene strata contributes significantly to the exceptionally high rates of relative sea level rise and coastal wetland loss in the mississippi delta and is likely to cause subsidence in other organic rich and often densely populated coastal plains

structural deformation of the leoville chondrite foliations defined by alignment of elongated chondrules have been noted previously in chondrites but none displays this effect so well as leoville cv3 the shapes of leoville chondrules were produced by deformation in situ as indicated by inclusions and clasts with similar shapes and preferred orientations to those of chondrules similarities in the aspect ratios of apparent strain ellipses measured for chondrules alone 1 9 and 2 0 by several methods and for the whole meteorite 2 0 indicate either that leoville deformed homogeneously or that it deformed as a framework of touching chondrules this amount of strain corresponds to approximately 33 uniaxial shortening assuming constant volume because the strain ellipse was measured in only one orientation this strain value is a minimum estimate for the meteorite lack of correlation between foliation and either shock or thermal effects argues that impact or metamorphism are unlikely to have produced this deformation compaction due to overburden from progressive accretion on the chondrite parent body is suggested to have been its cause estimates of maximum deviatoric stresses in the interiors of asteroid sized bodies and constraints on maximum temperatures for cv3 chondrites are consistent with diffusional flow as the deformation mechanism for olivine in these chondrules diffusional flow is also suggested by the scarcity of observed lattice dislocations deformation of leoville olivines by this mechanism at geologically reasonable strain rates appears to require higher temperatures than those believed to have been experienced by this meteorite 600 c however differences in olivine grain size the presence of water or a more complex deformation history might explain this discrepancy

abundance major element composition and size of components and matrix in cv co and acfer 094 chondrites abstract the relative abundances and chemical compositions of the macroscopic components or inclusions chondrules and refractory inclusions and fine grained mineral matrix in chondritic meteorites provide constraints on astrophysical theories of inclusion formation and chondrite accretion we present new techniques for analysis of low count pixel si mg ca al ti and fe x ray intensity maps of rock sections and apply them to large areas of co and cv chondrites and the ungrouped acfer 094 chondrite for many thousands of manually segmented and type identified inclusions we are able to assess pixel by pixel the major element content of each inclusion we quantify the total fraction of refractory elements accounted for by various types of inclusion and matrix among co chondrites both matrix and inclusion mg si ratios approach the solar and bulk co ratio with increasing petrologic grade but si remains enriched in inclusions relative to matrix the oxidized cv chondrites with higher matrix inclusion ratios exhibit more severe aqueous alteration oxidation and their excess matrix accounts for their higher porosity relative to reduced cv chondrites porosity could accommodate an original ice component of matrix as the direct cause of local alteration of oxidized cv chondrites we confirm that major element abundances among inclusions differ greatly across a wide range of co and cv chondrites these abundances in all cases add up to near chondritic solar bulk abundance ratios in these chondrites despite wide variations in matrix inclusion ratios and inclusion sizes chondrite components are complementary this complementarity provides a robust meteoritic constraint for astrophysical disk models

response of alluvial rivers to slow active tectonic movement alluvial rivers respond to valley slope deformation caused by active tectonics in various ways depending on the rate and amount of surficial deformation and on the type of river on the basis of experimental results and field examples hypothetical models of river response to anticlinal uplift and synclinal subsidence were developed for different types of alluvial rivers an experimental braided channel responded to anticlinal uplift across the channel with degradation and terrace formation in the central part of the uplift with subsidence aggradation in the central reach was the main response transverse bars developed downstream of the subsidence axis an experimental meandering channel responded to slope steepening with a sinuosity increase bank erosion and point bar growth occurred downstream of the anticlinal axis and upstream of the synclinal axis upstream of the uplift axis and downstream of the subsidence axis where the slope was flattened water flooded over bars local convexity in longitudinal profiles of the middle rio grande new mexico is considered to be formed by a domal uplift local aggradation and degradation could be explained by the effect of uplift the san joaquin river california which is now highly controlled does not show clear adjustment to the rapid subsidence due to ground water withdrawal it shows however a channel pattern adjustment to active tectonic subsidence that has been occurring for a long time the san antonio and guadalupe rivers in texas both increase their sinuosity significantly where monoclinal movements steepen valley slopes

evidence for impact induced pressure gradients on the allende cv3 parent body consequences for fluid and volatile transport carbonaceous chondrites such as those associated with the vigarano cv parent body exhibit a diverse range of oxidative reduced alteration mineralogy mcsween 1977 although fluids are often cited as the medium by which this occurs rubin 2012 a mechanism to explain how this fluid migrates and why some meteorite subtypes from the same planetary body are more oxidized than others remains elusive in our study we examined a slab of the well known allende cv3oxa meteorite using several petrological techniques e g fry s and flinn and computerized tomography ct we discover it exhibits a strong penetrative planar fabric resulting from strain partitioning among its major components calcium aluminum rich inclusions cais 64 5 ct matrix 21 5 fry chondrules 17 6 ct in addition to the planar fabric we found a strong lineation defined by the alignment of the maximum elongation of flattened particles interpreted to have developed by an impact event the existence of a lineation could either be non coaxial deformation or the result of a mechanically heterogeneous target material in the later case it could have formed due to discontinuous patches of sub surface ice and or fabrics developed through prior impact compaction macpherson and krot 2014 which would have encouraged preferential flow within the target material immediately following the impact compacting pore spaces we suggest that structurally controlled movement of alteration fluids in the asteroid parent body along pressure gradients contributed to the formation of secondary minerals which may have ultimately lead to the different oxidized subtypes

the effects of weathering on the physical and mechanical properties of a granitic saprolite less research has been carried out on the changes induced by weathering to the mechanical properties of reconstituted and intact soils that originate from chemical decomposition of rocks saprolite

cm chondrites exhibit the complete petrologic range from type 2 to 1 we have characterized the most phyllosilicate rich members of the cm chondrite group based upon petrographic and compositional factors we conclude that these particular meteorites have experienced pervasive aqueous alteration far beyond that witnessed by typical cms the lack of anhydrous silicates cai and except as relicts chondrules merits the classification of type cmi for three meteorites eet 83334 alh 88045 and one kaidun lithology still other cms notably alh 83100 eet 90047 and yamato 82042 are clearly intermediate between types 1 and 2 brecciated cm chondrites like cold bokkeveld contain all of these varied lithologies the cm chondrites thus exhibit the complete petrologic range from 2 through 1 our results show that progressive aqueous alteration on the parent cm asteroid s was locally accompanied by significant increases in temperature to a peak of 450 c for the kaidun lithology fo2 and locally degree of chemical leaching all well beyond the conditions recorded by typical cm2s the most altered cms also are commonly deformed displaying a distinct lineation probably due to static rather than dynamic forces

the influence of valley aggradation and listric normal faulting on styles of river avulsion a case study of the brazos river texas usa abstract the holocene avulsion history of the lower brazos alluvial valley of east texas usa was studied using 10 drill cores 26 radiocarbon dates aerial photos and a digital elevation model this study shows that two long term processes aggradation and localized valley tilting along a normal listric fault are responsible for generating two styles of avulsion the first process precedes avulsion by progradation while the second process precedes avulsion by annexation as valley aggradation migrated updip over the last 7 5 ka three regional backstepping avulsions occurred along the lower 140 km of the valley and each generated sizable deposits a pattern emerges of landward stepping progradational avulsions tracking the locus of valley aggradation and of valley aggradation migrating inland even after the rate of sea level rise diminishes at the same time several local nodal avulsions occurred between 50 and 55 km updip of the current highstand shoreline but generated no observable deposits geomorphic evidence indicates that since the late pleistocene active movement along a previously undocumented normal listric fault has occurred at the location of the nodal avulsion these two long term processes do not operate mutually exclusive of each other to promote avulsions rather they operate concurrently only aggradation promotes avulsions that affect floodplain alluviation although the total volume of these deposits comprises a small portion of the valley fill

land subsidence in houston texas measured by radar interferometry and constrained by extensometers 1 we present results from a radar interferometry study over the houston galveston texas gulf coast region from the nearly 60 potential interferograms considered an atmospheric artifact assessment is performed and a tractable set of interferograms selected for detailed processing and error analysis the subsequent interferogram time series spanning 1996 1998 is constrained by coincident extensometer data with root mean square error less than 2 5 mm the interferogram time series confirms that historic subsidence in east houston has stopped consistent with current groundwater use patterns broad scale subsidence bowls are observed in west and northwest houston where maximum subsidence rates are in excess of 2 and 4 cm yr 1 respectively linear interferogram phase signatures associated with approximately 1 cm of differential subsidence across faults including the long point fault in northwest houston are observed near the seabrook extensometer a hereto unidentified subsidence bowl with a maximum subsidence rate in excess of 3 cm yr 1 is revealed this study demonstrates that when used in conjunction with a set of traditional geodetic measurements radar interferometry can measure the spatial and temporal evolution of urban land subsidence within even the most challenging of environments

on the persistence of weathering abstract the term weathering has been in use for a very long time but it has come to mean different things to different people and hence as scientific short hand it no longer functions here we question the tenets underpinning the most common usage of the term and note that the climate process linkage implicit to the term is often missing and amounts to misdirection rather than climate as the primary driver behind specific weathering processes it is argued that rock properties constitute the dominant control further a case is made for reconsideration of our present bipartite mechanical chemical division of weathering processes and of the weathering processes currently deemed to be those that occur as process studies become evermore reductionist in nature so the functionality of the term comes more and more into question the linkage between process and landform the scaling up attribute is seen as a current weakness and one that will become more confusing as reductionist approaches continue as a way forward it is suggested that weathering stripped of specific preconceived notions of specific processes be envisaged as a function of energy transfer and be investigated in that light identification of new processes as well as restructuring of known processes particularly when considering weathering on other planets is a potential outcome of such an approach with a process foundation rooted in energy transfer rock decay provides a better umbrella term and liberates researchers from the inescapable conceptual baggage implicit to the term weathering

the role of neo tectonics in the sedimentary infilling and geomorphological evolution of the guadalquivir estuary gulf of cadiz sw spain during the holocene abstract a multidisciplinary analysis of cores and geomorphic patterns in the marshes of donana national park sw spain has yielded new evidence regarding the sedimentary infilling and geomorphological evolution of the guadalquivir estuary during the holocene the sedimentation and geomorphological disposition have been strongly conditioned by neotectonic activity along a set of sw ne alignments interrupted by other alignments that follow e w and nw se directions the most conspicuous of the sw ne alignments is the torre carbonero marilopez fault tcmf south of this fault the estuary experienced a marked subsidence from about 4000 to 2000 cal yr bp through a series of sedimentary sequences of retrogradation and aggradation within the context of relative sea level rise from c 2000 cal yr bp to the present the subsidence has remained relatively dormant with progradation of the littoral systems and infilling of the marshland progressing within a context of sea level stability our results reveal that neotectonic activity is a critical factor that must also be reckoned with in any attempt to understand the holocene geomorphological evolution in the guadalquivir estuary

indicators of aqueous alteration and thermal metamorphism on the cv parent body microtextures of a dark inclusion from allende abstract an unusual dark clast in the allende cv3 chondrite termed allende af which was previously interpreted as a primary aggregate formed in the solar nebula kurat et al 1989 palme et al 1989 was re examined our study reveals abundant evidence suggesting that it probably experienced extensive aqueous alteration and subsequent thermal metamorphism on the meteorite parent body allende af contains numerous rounded to oval shaped inclusions embedded in a dark matrix the inclusions consisting predominantly of fine grains of fe rich olivine have internal textures suggesting that they are pseudomorphs after chondrules several inclusions appear to be replaced cais veins filled with fibrous olivine grains occur abundantly in both inclusions and matrix some veins up to 4 mm in length penetrate several inclusions providing strong evidence that aqueous alteration occurred after accretion the fibrous morphology of olivine in veins and inclusions suggests that the olivine was produced by dehydration and thermal transformation of phyllosilicate that had been formed by aqueous alteration olivine grains in the matrix contain numerous micro inclusions of fe ni sulfide which were probably incorporated during transformation from phyllosilicate allende af is probably related to the fine grained variety of dark inclusions reported from cv3 chondrites that has been described as the type containing abundant porous aggregates of fe rich olivine by johnson et al 1990 many dark inclusions previously described appear to be similar in texture and mineralogy to allende af and probably experienced similar secondary process on the meteorite parent body the wide variation in texture of dark inclusions can be explained by different degrees of aqueous alteration that preceded thermal metamorphism the size distribution of chondrule pseudomorphs and the abundance of cai pseudomorphs suggest that the precursor of allende af is a cv type chondrite probably allende itself oxygen isotopic and chemical compositions are consistent with this interpretation the cv parent body has been commonly thought to have escaped major secondary processing however allende af provides evidence that extensive aqueous alteration and thermal metamorphism have occurred locally on the cv parent body

the general and congruent effects of structure in natural soils and weak rocks the engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as soils are reviewed and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock while this structure can arise from many causes its effects follow a simple general pattern that involves stiff behaviour followed by yield this yield can be described in a similar way to that occurring due to overconsolidation although it is a separate phenomenon the effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress history which are the basic concepts of soil mechanics as it can be described in a general way it is concluded that structure and its effects should be treated as a further basic concept of equal importance l article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor malement traites comm

experimental shock metamorphism of the murchison cm carbonaceous chondrite abstract a series of shock recovery experiments were carried out on the murchison cm carbonaceous chondrite by using a single stage propellant gun the murchison samples were shocked in nine experiments at peak pressures from 4 to 49 gpa the recovered samples were studied in detail by using an optical microscope a scanning electron microscope and an electron probe microanalyzer chondrules are flattened in the plane of the shock front at 4 to 30 gpa the mean aspect ratio of chondrules increases from 1 17 to 1 57 roughly in proportion to the intensity of shock pressure up to 25 gpa at 25 to 30 gpa the mean aspect ratio does not increase further and chondrules show increasingly more random orientations and degrade their preferred orientations and at 35 gpa they are extensively disrupted most coarse grains of olivine and pyroxene are irregularly fractured fracture density increases with increasing shock pressure and at 30 gpa almost all are thoroughly fractured with subgrains of local shock melting occurs as melt veins and pockets at 20 to 30 gpa fracture filling veins of fine grains of matrix are also produced at 25 to 30 gpa the melts and the fine grains seem to result mainly from frictional heating due to displacement along fractures at 35 gpa melting occurs pervasively throughout the matrix the melts are mainly produced from the matrix however they are consistently more enriched in fe s and ca which indicates that these elements are selectively incorporated into the melts the melts contain tiny spherules of fe ni metal fe sulfide and numerous vesicles at 49 gpa the matrix is totally melted and coarse grains of olivine are partially melted the melts contain much larger vesicles 50 300 m in diameter than those in the samples shocked at lower pressures which indicates that much more intense devolatilization and gas expansion took place for the purpose of comparing shock thermal effects between the experimentally shocked samples and naturally shocked targets surface materials in the murchison parent body we calculated internal energy increase for compression by multiple shock wave reflections experimental case and for compression by a single shock wave natural case the results suggest that postshock thermal effects observed at each experiment may be attained by impact on the natural targets at a considerably lower shock pressure than the peak shock pressure from the results of our experiments and calculations we conclude that if the murchison parent body were shocked on the surface at pressures higher than 25 gpa shocked material would probably undergo drastic increase in the degree of comminution and simultaneous generation of strong expansive forces on pressure release thus the results support the hypothesis of scott et al 1992 that volatile rich carbonaceous chondrites shocked above 20 to 30 gpa escaped from the parent body and formed particles that are too small to survive as meteorites

fluvial response to active extension evidence from 3d seismic data from the frio formation oligo miocene of the texas gulf of mexico coast usa tectonic deformation of the land surface is known to influence the gradient water and sediment discharge and the grain size of modern fluvial systems any change in these variables alters the equilibrium of a fluvial system potentially causing a change in channel morphology 3d seismic data from the tertiary miocene age upper frio formation kelsey field south texas in the us are used to examine changing fluvial channel morphology through time during a period of active growth of a rollover anticline in the hangingwall of a normal fault the vicksburg fault the studied interval varies between 22 and 47 m thick and spans several hundred thousand years it consists of an alternation of fluvial sandstones overbank mudstones and coal seismic extractions show the evolution of sinuous fluvial channels during a phase of growth fault activity prior to growth a single sinuous channel is imaged during growth the fluvial system became decapitated by a developing rollover anticline and a highly sinuous drainage network formed with frequent avulsion events headward propagation of streams and related stream capture increased channel sinuosity was spatially associated with increased avulsion frequency in the area down dip to the east of the rollover anticline more than 10 km from the active fault more than 25 m of relative accommodation developed on the flank of the growing rollover anticline compared with on the crest the increased channel sinuosity is interpreted as reflecting an increase in longitudinal valley slope analogous to observations made in flume experiments and modern river systems the increase in avulsion frequency is attributed to increased aggradation as the rivers adjusted back to equilibrium grade following the increase in slope

evidence for an impact induced magnetic fabric in allende and exogenous alternatives to the core dynamo theory for allende magnetization we conducted a paleomagnetic study of the matrix of allende cv3 chondritic meteorite isolating the matrix s primary remanent magnetization measuring its magnetic fabric and estimating the ancient magnetic field intensity a strong planar magnetic fabric was identified the remanent magnetization of the matrix was aligned within this plane suggesting a mechanism relating the magnetic fabric and remanence the intensity of the matrix s remanent magnetization was found to be consistent and low 6 t the primary magnetic mineral was found to be pyrrhotite given the thermal history of allende we conclude that the remanent magnetization was formed during or after an impact event recent mesoscale impact modeling where chondrules and matrix are resolved has shown that low velocity collisions can generate significant matrix temperatures as pore space compaction attenuates shock energy and dramatically increases the amount of heating nonporous chondrules are unaffected and act as heat sinks so matrix temperature excursions are brief we extend this work to model allende and show that a 1 km s planar impact generates bulk porosity matrix porosity and fabric in our target that match the observed values bimodal mixtures of a highly porous matrix and nominally zero porosity chondrules make chondrites uniquely capable of recording transient or unstable fields targets that have uniform porosity e g terrestrial impact craters will not record transient or unstable fields rather than a core dynamo it is therefore possible that the origin of the magnetic field in allende was the impact itself or a nebula field recorded during transient impact heating

spatial variation of overbank aggradation rate and its influence on avulsion frequency river avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges and the associated increase in cross valley slope relative to either the down channel slope or the down valley slope the latter is termed the slope ratio in the present paper therefore spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion dominated models of alluvial architecture detailed evidence on centennial to millennial scale floodplain deposition has to date been largely unavailable new data on such long term overbank aggradation rates from the rhine meuse and mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto and can be similar to observations for single overbank floods this leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios potentially resulting in increased avulsion frequencies a revised input parameter for overbank aggradation rate was used in a three dimensional model of alluvial architecture to study its effect on avulsion frequency realistic patterns of avulsion and interavulsion periods 1000 years were simulated with input data from the holocene rhine river with avulsions occurring when the slope ratio is in the range 3 5 however caution should be practised with respect to uncritical use of these numbers in different settings evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value irrespective of whether critical slope ratios are used as in the present study or superelevation as has been proposed by other investigators

aragonite in the murray cm2 carbonaceous chondrite implications for parent body compaction and aqueous alteration the matrix of the cm2 carbonaceous chondrite murray contains rare micrometer sized prismatic crystals of aragonite that formed during late stage parent body aqueous alteration the aragonite was identified by x ray microanalysis coupled with electron backscatter diffraction ebsd tem selected area electron diffraction and cathodoluminescence spectroscopy the sixteen crystals found all occur within loose and elongate submillimeter sized clusters and one cluster is present in each of the two thin sections studied orientation determinations using ebsd show that the c axes of aragonite crystals within each cluster lie roughly in a plane itself aligned approximately parallel to the long axis of the host cluster aragonite is inferred to have crystallized after calcite but before completion of static impact related compaction the clusters developed by growth of aragonite within films of aqueous fluids that had a relatively high mg ca ratio these fluids were focused within zones of high porosity and permeability along a weak compactional fabric in the matrix and this fabric is also likely to have influenced the orientations of aragonite crystals as they grew these results suggest that aragonite probably occurs in most of those carbonaceous chondrites that have undergone moderate degrees of parent body aqueous alteration and may provide further insights into the evolution of pore fluid compositions and volumes and the chronology of asteroidal evolution

surface deformation in houston texas using gps abstract surface deformation in the houston area has been quantified by using a variety of methods including lidar insar extensometers drilling to approximately 100 m and ground penetrating radar in this paper we report on gps data acquired during the period between 1995 and 2005 that found evidence of ongoing subsidence up to 56 mm year in northwestern houston and of possible horizontal surface movement towards the gulf of mexico up to 6 mm year we describe the methods of data processing used in the study and speculate on the possibility that the active elevation of salt domes mainly at the south and east of the city may indirectly influence other surface movements including fault movements and subsidence over areas 1 km 2 making use of our observations and analysis could help in natural hazard mitigation in the houston area and possibly also indicate approaches to surface subsidence study that might be used in other urban areas

the implications of the magnetism of ordinary chondrite meteorites abstract the magnetic properties of eleven ordinary chondrites eight ll chondrites and three l chondrites have been analysed the samples were repeatedly fragmented and oriented to a common reference direction natural remanent magnetisation nrm susceptibility and anisotropy of susceptibility measured at each stage the response of some fragments to alternating field a f demagnetisation thermal demagnetisation isothermal remanent magnetisation irm and magnetic hysteresis has been measured it was found that the orientation of the stable nrm was random down to a scale of 1 mm 3 the dominant magnetic carrier in types 4 6 was the ordered iron nickel mineral tetrataenite the type 3 s measured contained no tetrataenite and the nrm was carried by fine grained taenite a magnetic fabric analogous to a physical fabric was found in all samples in all but two the fabric was foliated tuxtuac and wold cottage showed lineation thermal demagnetisations of nrm showed a trend towards higher blocking temperatures for type 6 chondrites over types 3 5 because the fabric was continuous in the majority of samples and the nrm randomly orientated it was concluded that the magnetic carriers were magnetised before emplacement in the meteorite and that the meteorites are not finescale breccias the preservation of the random nrm leads to the preference of hot accretion as the mechanism for producing chondritic textures as opposed to metamorphic reheating as this would tend to erase the random magnetisation

defining the mechanism for compaction of the cv chondrite parent body the allende meteorite a relatively unaltered member of the cv carbonaceous chondrite group contains primitive crystallographic textures that can inform our understanding of early solar system planetary compaction to test between models of porosity reduction on the cv parent body complex microstructures within 0 5 mm diameter chondrules and 10 m long matrix olivine grains were analyzed by electron backscatter diffraction ebsd techniques the large area map presented is one of the most extensive ebsd maps to have been collected in application to extraterrestrial materials chondrule margins preferentially exhibit limited intragrain crystallographic misorientation due to localized crystal plastic deformation crystallographic preferred orientations cpos preserved by matrix olivine grains are strongly coupled to grain shape most pronounced in shortest dimension yet are locally variable in orientation and strength lithostatic pressure within plausible chondritic model asteroids is not sufficient to drive compaction or create the observed microstructures if the aggregate was cold significant local variability in the orientation and intensity of compaction is also inconsistent with a global process detailed microstructures indicative of crystal plastic deformation are consistent with brief heating events that were small in magnitude when combined with a lack of sintered grains and the spatially heterogeneous cpo ubiquitous hot isostatic pressing is unlikely to be responsible furthermore allende is the most metamorphosed cv chondrite so if sintering occurred at all on the cv parent body it would be evident here we conclude that the crystallographic textures observed reflect impact compaction and indicate shock wave directionality we therefore present some of the first significant evidence for shock compaction of the cv parent body

characteristics of weathering zones of granitic rocks in malaysia for geotechnical engineering design tropical climatic conditions cause severe weathering to rock masses resulting in thick weathering profiles consisting of different weathering zones with complex characteristics feasible geotechnical engineering design requires a detailed understanding of the characteristics of each weathering zone a typical weathering profile is usually characterized by field scale observation and geological study this paper presents the characteristics of weathering zones of various granitic rocks in the south of malaysia this region has a tropical climatic condition the study was carried out in four active quarries located in johor province malaysia and forty sections were investigated in the study areas a typical granitic weathering profile was characterized based on the geological and structural parameters i e joint characteristics corestone occurrence rock soil ratio mass homogeneity color of rock and discoloration at joints surfaces the profile includes common zones ranging from fresh to residual soil however two subzones are introduced based on corestone boulder occurrence in the highly weathered and completely weathered zones this study based on detailed field observations at the mentioned quarries followed by analysis presents an amalgamated picture of weathering zones in granitic profiles of a tropical region like malaysia moreover it is believed that the characterization of the typical weathering profile allows further classification of generally complex weathered rock masses for a specific geotechnical engineering design

a rock fabric in chondrite matrix introduction the description and interpretation of petrofabrics is a fundamental aspect of geology chondritic meteorites are the most primitive rocks available to us recording a range of nebula and asteroidal processes but due to the abundance of fine grained matrix these samples have largely resisted traditional fabric analysis magnetic susceptibility natural remanent magnetisation and x ray pole figure goniometry studies of bulk meteorites 1 3 have revealed that many chondrites contain petrofabrics but the fabrics themselves are only observed in situ in the preferred orientation of large 100s m components e g non spherical chondrules 1 4 7 lithic fragments 8 and large isolated grains 9 here we present a preliminary study of allende matrix using orientation contrast imaging oci and electron backscatter diffraction ebsd to provide crystallographic orientation data oci combined with electron backscatter diffraction patterns ebsp separates grains based on crystallographic orientation 1 for misorientations we previously used oci to study textures in chondritic metal grains 10 applied to chondrite matrix the technique allows the orientation of all grains down to 50nm to be determined enabling matrix fabrics in primitive meteorites to be analysed and imaged in addition to providing a size frequency distribution of matrix grains results areas of allende matrix were mapped using a fegsem equipped with forescatter detectors and a phosphor screen to collect ebsps the figure shows an ebsd map of grain orientation in matrix adjacent to a chondrule right together with a pole figure inset the data suggest that allende matrix possesses a fabric defined by preferred orientations in grains 50nm to a few m s in size which is coherent over large regions of the sample