early and late holocene paleoenvironmental reconstruction of the pearl river estuary south china sea using foraminiferal assemblages and stable carbon isotopes abstract proxy reconstructions of estuarine evolution provide perspectives on regional to global environmental changes including relative sea level changes climatic changes and agricultural developments here we present a new benthic foraminiferal record along with 13c and c n and lithological data from a sediment core in the pearl river estuary lingding bay adjacent to the south china sea the core has relatively thick holocene sediments 40 m due to its location in the paleo valley of the pearl river the lithologic and foraminiferal record reveal an evolution in paleoenvironment from fluvial inner estuary to middle estuary between 11300 and 8100 cal a bp in response to rapid sea level rise 13c and c n data indicate high freshwater discharge from 10500 to 8100 cal a bp driven by a strong asian monsoon the middle holocene 8100 3300 cal a bp sediment is absent in the core due to subaqueous erosion resulting from the unique geomorphology of the pearl river delta in the late holocene from 3300 cal a bp to the present the lithology and foraminiferal assemblages suggest a further evolution from outer estuary middle estuary channel to middle estuary shoal resulting from deltaic progradation under stable relative sea levels in the last 2000 years 13c and c n values reveal the intensive development of agriculture coupled with the reduction of freshwater input derived from a weakening asian monsoon

microstructures and c axis fabrics indicative of quartz dissolution in sheared quartzites and phyllonites abstract quartzites sheared in low metamorphic grade shear zones that extend along the contact with migmatitic gneissic complexes in the quadrilatere ferifero region southeastern brazil show quartz microstructures indicating deformation by dissolution dissolution occurred adjacent to the foliation planes preferentially in quartz porphyroclasts oriented with their 0001 planes parallel to the foliation dissolution worked as an efficient mechanism to remove porphyroclast edges smoothing foliations and enabling strain accommodation both dissolution and crystal plasticity were competitive crystallographically controlled processes operating in different domains of the evolving microstructure dissolution occurred along the foliation planes while isovolume crystal plasticity and accompanying recrystallization operated essentially in the quartzose domains between folia phyllonites formed in the most strained domains of the shear zones fine grained quartz grains in phyllonites show uncommon c axis fabrics c axis oriented at low angles to the stretching lineation which were interpreted to form either by direct reprecipitation or by residual concentration of grains unfavourably orientated to undergo dissolution domainal c axis fabrics reflect a deformation partitioning path with increasing participation of solution transfer strengthening c axis maxima at low angles with the stretching lineation at the expense of crystal plastic processes during progressive phyllonitization

late quaternary environmental changes in the pearl river mouth region china abstract this study presents findings concerning late quaternary environmental changes in the pearl river mouth region china based on the study of over 300 boreholes out of these 35 boreholes are selected for the reconstruction of transects across the deltaic plain and estuary 39 radiocarbon dates obtained from these boreholes are used to help define the chronology of stratigraphic units present including two terrestrial units t1 and t2 and two marine units m1 and m2 diatom assemblages are studied in 6 boreholes revealing similarities and differences between the two marine units before the area was inundated by the last interglacial sea mis 5 an older terrestrial unit of sand and gravel t2 was laid down in a number of palaeo valleys during the last interglacial period an older marine unit of silt and clay m2 was laid down which was subsequently subaerially exposed when sea level regressed during the last glacial period mis 4 2 causing the uppermost section to be weathered during the same period a younger terrestrial unit of sand and gravel t1 was deposited along palaeo river channels around the early holocene before 8 2 cal ka bp the postglacial rise in sea level initiated a new phase of sedimentation in the outer part of the estuary characterised by the high percentages of marine diatoms in the sediments in the early holocene strong monsoon freshwater discharge resulted in sedimentation of a fine sand layer in the inner part of the estuary after 8 2 cal ka bp rapid rises in sea level caused widespread marine inundation and sedimentation the diatom data suggest that the relative sea level associated with the m2 and m1 units were both at similar levels because the m2 unit is typically recorded at altitudes of 15 m and 20 m below the present sea level this is likely to be a result of long term subsidence although numerical dating of the pre m1 units has not been made in the present study the chronology of these units can be inferred from uranium series ages and optically stimulated luminescence dating obtained from the adjacent coastal waters of hong kong the t1 unit has yielded ages of about 30 0 cal ka bp while the m2 unit has yielded ages about 130 0 cal ka bp confirming their mis 4 2 and mis 5 ages respectively

a new approach to backstripping and sequential restoration in subsalt sediments in this paper a new approach to calculating and restoring the effects of physical compaction in subsalt units is presented the loading of subsalt units and associated physical compaction is controlled by a combination of suprasalt sedimentation and salt movements here it is proposed that the change in load affecting the subsalt units is equivalent to the thickness between paleosurfaces of the basin regional levels reconstructed for successive stratigraphic horizons this is in contrast to suprasalt units where the changes in load are equivalent to the thickness of the stratigraphic unit the new approach is integrated into a complete workflow for sequential restoration in a salt basin which involves 1 removing the effects of physical compaction in suprasalt units 2 reconstructing the paleosurfaces of the basin regional level 3 restoring faults 4 unfolding to the reconstructed regional level to restore the effects of salt movement in the suprasalt units 5 reconstructing the change in load affecting subsalt units and restoring the associated physical compaction and 6 restoring any isostasy and postrift thermal subsidence results obtained using this workflow are compared with other methodologies to assess the differences in subsalt sediment thickness and structural configurations these results suggest that the workflow proposed in this paper will improve the accuracy of sequential restoration of subsalt hydrocarbon plays allowing their structural configurations through time to be more accurately quantified and will ultimately reduce the risks in developing subsalt resources

worldwide review of seals for major accumulations of natural gas abstract about 62 of the caprock seals for the world s 176 giant gas fields are shales and about 38 are evaporites these two lithologies make up essentially all of the caprock for the 2 650 tcf of gas expected to be recovered from these fields caprock thickness data is lacking from many fields but 20 to several hundred meters are typical optimal conditions for seal preservation occur in areas which had a comparatively simple geologic evolution complex fold belts and overthrust belts are commonly subject to seal destruction of the world s 25 largest gas fields 21 are in cratonic settings and four in fold belts those in fold belts have evaporite seals lateral continuity of caprock has a favorable impact on the retention of gas over large areas such as the arabian platform gas hydrate accumulations illustrate both seal and reservoir seal destruction is caused by changes in the phase equilibrium considerable multidisciplinary research still needs to be done to quantify knowledge of seal prediction for giant gas fields end of article last page 933

experimental pressure solution in halite the effect of grain interphase boundary structure to investigate the mechanisms and kinetics of pressure solution we measured deformation at contacts between polished convex lenses of halite and polished flat lenses of either halite or fused silica in saturated brine at 50 2 0 2 c and fluid pressures of 0 1 mpa loads applied using small springs ranged from 0 1 4 2 n mean effective normal stresses within the contact zone ranged from 1 14 mpa the geometry and diametric growth rate of the contact spot neck growth and the rate at which the lenses approached one another convergence were monitored during deformation using transmitted and reflected light photomicrography time dependent convergence did not occur at measurable rates when two halite lenses were pressed together in saturated brine but did occur when halite and fused silica lenses were pressed together in brine convergence rates in the halite silica experiments were 0 01 0 05 m day although the initial deformation during loading involved elastic and plastic processes control experiments without brine showed no time dependent convergence indicating that dislocation creep did not contribute to the observed rates no undercutting or cataclasis was observed in any experiments residual fluid inclusions were formed along grain boundaries between two halite lenses loaded in brine indicating non zero wetting angles

diatom records and sedimentary responses to sea level change during the last 8000 years in roudsea wood northwest england diatom biostratigraphies are recorded in close stratigraphical intervals from two sites in roudsea wood northwest england these diatom sequences are used to reconstruct sediment surface elevation which is then compared with the mid and late holocene sea level history of the region four new sea level index points are added to the sea level data base for the region and the sea level history is subjectively divided into three time periods for discussions the established model of sediment surface elevation for roudsea wood suggests that the sedimentary responses to the changing sea level have varied through time and appeared as site dependent in roudsea wood valley a site sheltered from the estuary the sedimentary equilibrium was not reached until the end of the first period around 6200 yr bp coincided with the development of a sand barrier across the mouth of the valley in roudsea marsh a site opened to the estuary the sedimentary equilibrium was reached as late as the end of the second period aro

subsalt play gulf of mexico a review exploration for deep water sandstone reservoirs beneath allochthonous salt in the gulf of mexico represents a major new frontier play in north america more than 30 wells thus far have been drilled with subsalt targets resulting in 8 discoveries at least 3 of which are commercial and 3 that have reserves of 100 million bbl oil equivalent or more reservoirs consist of miocene pleistocene sandstones deposited in submarine fan channel system environments on the paleoslope where salt deformation has a complex late cenozoic history salt sheets exist at various stratigraphic levels and have overridden sandstone fairways on the present day outer continental shelf and upper slope where water depths are moderate and where pipeline and other infrastructure facilities already exist potential reserves for the subsalt play have been estimated at 1 2 billion bbl of oil and 15 tcf gas from 25 or more significant fields recent success in the subsalt play has depended upon 1 advances in 3 d three dimensional seismic acquisition and processing in particular 3 d prestack depth imaging and 2 improved geologic modeling of salt deformation and depositional systems in addition better understanding of the drilling risks frequently encountered in penetrating salt sheets has been important progress in all these areas ismore certain to continue and will result in significant new tools and techniques for exploration as a whole less

a flexible approach to assessing synchroneity of past events using bayesian reconstructions of sedimentation history the dating of depths in two or more cores is frequently followed by a study of the synchroneity or otherwise of events reflected in the cores the difficulties most frequently encountered are a determining precisely the depths associated with the events and b determining the ages associated with the depths there has been much progress in recent years in developing tools for the study of uncertainties in establishing chronologies this has not yet been matched by similar progress in modelling event depth relationships this paper proposes a simple and flexible approach showing how uncertain events can be married to uncertain chronologies difficulties in studying event depth age relationships typically involve a confounding of two different problems first what exactly do we mean by an event a point in history a single depth in the core corresponding to a single time or a depth time range sometimes event is in fact a shorthand for a space time process do the data reflect more than one type of event process this can reflect vagueness in definition second what are the sources and implications of the uncertainties here we illustrate the issues involved by examination of several features seen in north european holocene pollen records the alnus rise is regarded as a diachronous early holocene event in contrast the ulmus decline is widely seen as a near synchronous event in the mid holocene the third feature we examine is the interval between the ulmus decline and the first occurrence of cerealia type pollen the evidence for these events lies in cores of lake sediment from which are determined a the proportions of pollen at many depths and b radiocarbon age estimates from usually fewer depths for this illustration we focus on six sites we draw attention to a new and flexible method implemented in the free r software package bchron haslett j parnell a 2008 a simple monotone process with application to radiocarbon dated depth chronologies journal of the royal statistical society series c 57 4 399 418 for the establishment of the uncertainties surrounding the dating of samples in such cores we illustrate its flexibility by assessing the synchroneity of past events

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

reservoir monitoring and characterization using satellite geodetic data interferometric synthetic aperture radar observations from the krechba field algeria deformation in the material overlying an active reservoir is used to monitor pressure change at depth a sequence of 11 field estimates allows us to construct a measure of diffusive traveltime throughout a reservoir the dense distribution of traveltime values means that we can construct an exactly linear inverse problem for reservoir flow properties application to interferometric synthetic aperture radar insar data gathered over a carbon dioxide c o2 injection site in algeria reveals pressure propagation along two northwest trending corridors an inversion of the traveltimes indicates the existence of two northwest trending high permeability zones the high permeability features trend in the same direction as the regional fault and fracture zones model parameter resolution estimates indicate the features are well resolved

ground movements due to shallow tunnels in soft ground i analytical solutions this paper presents simplified closed form analytical solutions that can be used to interpret and predict ground movements caused by shallow tunneling in soft ground conditions these solutions offer a more comprehensive framework for understanding the distribution of ground movements than widely used empirical functions analytical solutions for the displacement field within the ground mass are obtained for two basic modes of deformation corresponding to uniform convergence and ovalization at the wall of a circular tunnel cavity based on the assumption of linear elastic soil behavior deformation fields based on the superposition of fundamental singularity solutions are shown to differ only slightly from analyses that consider the physical dimensions of the tunnel cavity except in the case of very shallow tunnels this work demonstrates a simplified method to account for soil plasticity in the analyses and illustrate closed form solutions for a three dimensional 3d tunnel heading a companion paper describes applications of these analyses to interpret field measurements of ground response to tunneling

modeling and mechanistic interpretation of creep of rock salt below 200 c abstract upper and lower bound estimates of the steady state strain rates of rock salt from five locations are analyzed the measurements were obtained in triaxial creep tests including systematic changes in stress and temperature the various data sets are correlated in activation analyses and fitted by models and combinations of models for power law creep cross slip and dislocation glide to show that a cross slip model yields the best mechanistically most credible fit good fits for cross slip and high power law stress exponents rule out the possibility that pressure solution affected the data in a major way to the lowest recorded strain rates of order 10 10s 1

late holocene 2 ka east asian monsoon variations inferred from river discharge and climate interrelationships in the pearl river estuary a sediment core from the pearl river estuary pre was analyzed for grain size and organic geochemistry parameters toc and delta c 13 org the results showed that high mean grain size value and increased sand content were correlated with the high toc and negative delta c 13 org these results indicated high river runoff in the pre area peak river discharge occurred during the periods 1900 1750 1500 1600 1400 1200 1000 900 and 750 600 cal yr bp the main changes recorded in grain size distributions toc contents and delta c 13 org variations appear to be directly related to monsoon precipitation in the sediment source area an increased east asian summer monsoon rainfall easm and or an enhanced east asian winter monsoon rainfall could result in the increasing of monsoon rainfall typhoon related rainfalls could act as positive influence on precipitation levels the study of the correlations between the rainfall records and enso activities revealed a close relationship between the monsoon rainfall in the pre and the tropical pacific variations the frequent occurrence of enso might result in the southern migration of the easm rain belt and lead to more typhoon derived rainfall in the prd during the late holocene c 2013 university of washington published by elsevier inc all rights reserved

weakening of rock salt by water during long term creep the rheological properties of rock salt are of fundamental importance in predicting the long term evolution of salt based radioactive waste repositories and strategic storage caverns and in modelling the formation of salt diapirs and associated oil traps1 2 the short term high stress rheology of rock salt is well known from laboratory experiments however extrapolation to appropriately low stresses fails to predict the rapid flow seen in certain natural structures furthermore experiments have failed to reproduce the recrystallized microstructure of naturally deformed salt here we report experiments indicating that the above discrepancies can be explained by taking into account the influence of trace amounts of brine trace brine is always present in natural salt but sometimes escapes during experiments our tests on dry dilated salt show more or less conventional dislocation creep behaviour but brine bearing samples show marked weakening at low strain rates this is associated with dynamic recrystallization and a change of deformation mechanism to solution transfer creep because natural rock salt always contains some brine these results cast substantial doubt on the validity of presently accepted dislocation creep laws for predicting the long term rheological behaviour of salt in nature

offshore quaternary sediments and their engineering significance in hong kong yim w w s 1994 offshore quaternary sediments and their engineering significance in hong kong in e f j de mulder editor engineering geology of quaternary deposits eng geol 37 31 50 investigation works undertaken for coastal engineering projects in hong kong has provided abundant information on the quaternary sedimentary sequence beneath the sea floor although the significance of such information may not have been realized at the time of these projects valuable lessons have often been learnt afterwards some examples of the important engineering applications concerning offshore quaternary sediments include 1 the provision of information on water movement sediment transport and sedimentation rates during the holocene period 2 the identification of exploitable offshore sand and gravel resources 3 the interpretation of marine geophysical data through the availability of reliable borehole descriptions 4 the enhancement of engineering soil testing results and their interpretation 5 the prediction of rates of long term ground settlement in coastal land reclaimations 6 the selection of offshore sites for waste disposal 7 the reduction in cost of coastal engineering projects through choosing the most cost effective site 8 the provision of baseline data to assist environmental impact assessment a new geological model is proposed for the offshore quaternary sedimentary sequence of hong kong the engineering properties of the sediments are found to be closely related to the palaco environmental changes

reservoir creep and induced seismicity inferences from geomechanical modeling of gas depletion in the groningen field the groningen gas field in the netherlands experienced an immediate reduction in seismic events in the year following a massive cut in production this reduction is inconsistent with existingmodels of seismicity predictions adopting compaction strains as proxy since reservoir creep would then result in a more gradual reduction of seismic events after a production stop we argue that the discontinuity in seismic response relates to a physical discontinuity in stress loading rate on faults upon the arrest of pressure change the stresses originate from a combination of the direct poroelastic effect through the pressure changes and the delayed effect of ongoing compaction after cessation of reservoir production both mechanisms need to be taken into account to this end we employed finite element models in a workflow that couples kelvin chain reservoir creep with a semi analytical approach for the solution of slip and seismic moment from the predicted stress change for ratios of final creep and elastic compaction up to 5 the model predicts that the cumulative seismic moment evolution after a production stop is subject to a very moderate increase 2 10 times less than the values predicted by the alternative approaches using reservoir compaction strain as proxy this is in agreement with the low seismicity in the central area of the groningen field immediately after reduction in production the geomechanical model findings support scope for mitigating induced seismicity through adjusting rates of pressure change by cutting down production the author s 2017 published by oxford university press on behalf of the royal astronomical society

influence of pore fluid salinity on pressure solution creep in gypsum abstract the uniaxial compaction creep behaviour of wet granular gypsum is investigated under chemically closed drained conditions known to favour pressure solution the experiments were performed using applied stresses of 1 to 4 mpa and grain sizes in the range 50 to 280 m at room temperature the tests were carried out using saline pore fluids with a nacl concentration of 0 01 to 6 m saturated with respect to the unstressed gypsum starting material since gypsum is almost always associated with other evaporite minerals such as halite pore fluid compositions in gypsum will generally be highly saline data on the effect of pore fluid salinity on pressure solution in gypsum are thus directly relevant to the behaviour of gypsum in geological situations the results obtained in terms of mechanical behaviour and microstructures developed are in good agreement with the results obtained in previous experiments performed using nacl free pore fluids however the absolute creep rates obtained here are up to 50 times faster than in the nacl free tests comparison with theoretical models for pressure solution creep and crystal growth data reveals that diffusion is unlikely to be the rate controlling mechanism of pressure solution in the present experiments since the growth rate of gypsum increases with nutrient salinity the observed effect of nacl on pressure solution is consistent with the possibility of rate control by the precipitation reaction however the absolute creep rates observed are one to two orders of magnitude slower than creep rates predicted by a precipitation rate limited model so that the detailed mechanism remains unclear

microfossil analysis of sediments representing the 1964 earthquake exposed at girdwood flats alaska usa abstract diatom pollen foraminifera and thecamoebian assemblages from an outcrop of peat and silt at girdwood flats in the upper turnagain arm of the cook inlet alaska record four phases of relative land and sea level changes the first phase is the development of freshwater swamp above high marsh sediments during relative land uplift caused by strain accumulation along the locked portion of the alaska aleutian subduction zone in second phase the top 2 cm of the peat all microfossil groups record pre seismic relative sea level rise relative land subsidence the third phase is rapid land subsidence 1 7 m during the earthquake of march 1964 that initiated intertidal silt accumulation above the peat the final phase is the colonisation of mudflat by salt marsh communities during post seismic land uplift the microfossil data compare favourably with sequences from washington oregon and british columbia that record late holocene submergence events caused by earthquakes the comparable changes in microfossil assemblages record the different phases of relative land and sea level changes and the magnitude of land subsidence caused by each earthquake expressed relative to the tidal range at the site these results raise the question whether preseismic sea level rise represents any kind of warning of large earthquakes

some remarks on the relation between vertical motions of the lithosphere during extension and the necking depth parameter inferred from kinematic modeling studies a well established fact of continental stretching is that during the extension phase the lithosphere retains a finite flexural strength vertical loads caused by the redistribution of material with crustal and mantle densities during lithospheric thinning can therefore be supported by the lithosphere whether these loads cause flexural uplift or subsidence depends on the strength distribution within the continental lithosphere in kinematic model studies stratigraphic and other data acquired in the vicinity of sedimentary basins and passive margins are inverted for these loads in these models vertical rebound loads are parameterized in terms of a necking depth parameter we use thermal mechanical finite element simulations to investigate whether rheological information about the continental lithosphere can be extracted from the necking depth parameter derived from kinematic models we conclude that spatial and temporal variations in necking depths near basin edges and passive margins as derived from our dynamic simulations are not consistent with the uniform and stationary necking depth that is usually assumed in kinematic models this is very important since typically the stratigraphic data used in kinematic model studies are acquired in these regions we therefore conclude that there is no one to one relation between the necking depth parameter and the strength distribution in the lithosphere

reasons for the low sedimentation and slow progradation in the pearl river delta southern china during the middle holocene abstract holocene sea level rise monsoonal discharge and human activity have been the main drivers for the evolutionary history of asian deltas in theory when sea level ceased to rise in around 7000 cal a bp deltas should have started to prograde seawards however previous studies revealed that the progradation of modern deltas was initially very slow and more importantly sediment accumulation within central deltaic basins was exceptionally low between 7000 and 4000 cal a bp in order to investigate the main reasons for such slow progradation and low sedimentation during the middle holocene this study reconstructed the sedimentary history of the head area of the pearl river delta the results show marine transgression from 9500 to 7500 cal a bp followed by marine regression starting from 7500 to 4000 cal a bp in response to sea level change during the latter period sedimentation was concentrated in the head area the amount of sediment entering the central basin was significantly reduced this limited amount of sediment was spread thinly across the wide deltaic basin a portion of it could have been transported out into the south china sea by the strong tidal currents resulting in an exceptionally low sedimentation in the central basin however in locations adjacent to former present islands locally supplied sediment helped sedimentation to continue from 7500 to 4000 cal a bp by about 4000 cal a bp the deltaic shoreline advanced into the central basin this period saw an increase of human activity that caused soil erosion and sediment supply leading to a marked increase in sedimentation rate active land reclamations also helped the acceleration of shoreline advance this sedimentary evolution model in the pearl river delta mirrors those of other deltas in the monsoonal asia

rheology of rocksalt abstract we review progress in experimental determinations of transient and steady state flow properties and processes of natural rocksalt aggregates focusing primarily on results from avery island louisiana domal salt the steady state flow field established from constant stress and constant strain rate tests at temperatures from 50 to 200 c strain rates from 10 5 to 10 9 s 1 and differential stresses from 20 7 to 2 5 mpa has been separated into two flow regimes each fit by a power law relation at the higher stresses and strain rates this relation is e 1 6 10 4 exp 68 1 rt 10 3 5 3 for which the pre exponential constant is expressed in mpa 5 3 s 1 and the apparent activation energy is in j mol 1 creep rates predicted by equation a do not differ appreciably from those predicted previously the relatively low stress low strain rate data are very well fit by e 8 1 10 5 exp 51 6 rt 10 3 2 4 which is comparable conditions predicts creep rates higher and equivalent viscosities lower than does equation a by two orders of magnitude the change in behavior from a to b is ascribed to a change in rate limiting mechanism from cross slip of screw dislocations to the climb of edge dislocations in this dry material subgrain formation dominates microstructural development during steady state flow of salt and from determinations of average subgrain diameters in crystals from 20 different rocksalt bodies flow stress levels between 0 6 and 1 4 mpa have been estimated these values do not bear directly on arguments concerning the nature of forces initiating salt pillow growth because apparently evidence relating to the early deformational history has been overprinted at that stage fluid assisted grain boundary diffusional processes might dominate dislocation creep leading to a linear stress strain rate mechanical response considering buoyancy forces alone behavior described by equation b rather than a reduces the relief necessary to initiate pillow growth but a 1000 fold amplification is required to produce stress differences near 1 mpa that forces other than buoyancy are important is indicated by the occurrence of these same paleostress levels in bedded salts and in shallow offshore concordant intrusions differential loading generally provides the most plausible initial driving force for the growth of diapiric salt structures

sea floor morphology and plio quaternary sedimentary cover of the mallorca channel balearic islands western mediterranean a complete multibeam coverage of the sea floor of mallorca channel in the western mediterranean was recorded during the spanish exclusive economic zone surveys in 1995 1996 and 1997 these data combined with previous high resolution seismic reflection profiles allow an assessment of the geomorphology of the area the channel seafloor is disrupted by a fault complex and pockmarks motion along the faults split the sea floor into a series of undulations separated by narrow v shaped notches faulting may be a consequence of recent seaward gravitational sliding that occurred along a soft surface at the top of a late messinian early pliocene unit and a late messinian evaporite these units have been tilted during recent subsidence of the mallorca channel at the same time that the insular shelf was uplifted along a fault at the shelf s edge the set of pockmarks in the channel sequence were probably formed by the expulsion of gas of hydrothermal origin and expulsion may have been enhanced by the faulting this gas seepage could be an additional factor leading to sediment instability

initiation and growth of gypsum piercement structures in the zechstein basin abstract the importance of tectonic processes in initiating halite diapirs has become much better understood in recent years less well understood is the development of diapiric structures involving rocks composed predominantly of gypsum below about 1000 m gypsum dehydrates to anhydrite which often obscures primary sedimentary textures if the strain associated with diapiric rise in the rock induces the transition to anhydrite obliteration of primary features in the gypsum can be expected in our study we infer that the diapiric movement in the werra anhydrite member of cycle 1 of the zechstein formation of europe occurred before the initial transition of gypsum to anhydrite based on the presence of pseudomorphs of bedded primary gypsum crystals the overburden lithologies and depositional environment and the mechanical properties of gypsum anhydrite and carbonate rocks faulting and differential loading of a shallow overburden were the key components in initiating the gypsum diapirism the transition to anhydrite occurred after burial and after cessation of diapirism in comparison the diapirism of calcium sulfate of the leine anhydrite into the leine halite members of cycle 3 of the zechstein formation probably occurred much later after burial and appears to have been triggered by halite diapirism which in turn triggered the dehydration reaction causing the calcium sulfate to become the incompetent phase relative to the halite

the role of sea level rise monsoonal discharge and the palaeo landscape in the early holocene evolution of the pearl river delta southern china abstract the early holocene history of the pearl river delta is reconstructed based on a series of sediment cores obtained from one of the main palaeo valleys in the basin sedimentary and microfossil diatom analyses combined with radiocarbon dating provide new evidence for the interactions between sea level rise antecedent topography and sedimentary discharge changes within the deltaic basin since the last glacial these new records show that river channels of last glacial age incised down to c 40 m into an older possibly mis5 age marine sequence which forms the floor of the deltaic basin and exists primarily at c 10 m 15 m below present mean sea level rapid postglacial sea level rise flooded the incised valleys by the beginning of the holocene and prior to c 9000 cal years bp marine inundation was largely confined within these incised valleys the confined available accommodation space of the incised valleys combined with strong monsoon driven freshwater high sediment discharge and a period of rapid rising sea level meant that sedimentation rates were exceptionally high towards c 8000 cal years bp as sea level rose to about 5 m marine inundation spilled out of the incised valleys and the sea flooded the whole deltaic basin as a result the mouth of the pearl river was forced to retreat to the apex of the deltaic basin water salinity within the basin increased markedly as the previously confined system dispersed across the basin and the sedimentation changed from fluvial dominated to tidal dominated sea level continued to rise albeit at a much reduced rate between 8000 and 7000 cal years bp and deltaic sedimentation was concentrated around the apex area of the basin during the last 7000 cal years bp the delta shoreline moved seawards and the sedimentary processes changed gradually from tidal dominated to fluvial dominated

salt tectonics along the atlantic margin of morocco abstract the moroccan salt basin appears to be very unique in the sense that it is not sedimentary loading but tectonic inversion which appears to drive the latest stages of salt related deformation in the central part of the basin the gravity potential to maintain salt tectonics is provided by the differential uplift of the atlas mountains located adjacent and striking almost perpendicular to the margin along the offshore part of the moroccan salt basin there are many play types most of them related to the triassic syn rift salt toe thrust anticlines at the basinwards edge of the salt basin form very large structures traps associated with salt tongues and diapirs define a more classical salt flank play numerous salt tongues sheets and canopy complexes provide for a gulf of mexico style subsalt play despite the numerous untested play types there have been only four deep water exploration wells drilled in the entire moroccan salt basin none of them having subsalt penetrations

ground motions induced by a producing hydrocarbon reservoir that is overlain by a viscoelastic rocksalt layer a numerical model hydrocarbon reservoir pressure depletion leads to stress changes inside the reservoir and ground deformation which is registered at the surface as subsidence as reservoirs are often overlain by layers of rocksalt or other evaporites which are materials that flow so as to relax stresses inside them there is the potential for time varying surface subsidence this work focuses on understanding the macroscopic mechanisms that lead to rocksalt flow induced ground displacements a finite element model is used for this purpose in which the rocksalt layer is represented by a viscoelastic maxwell material two distinct mechanisms that lead to displacement are observed these are active during different stages of the deformation and have different timescales associated with them an important observation is that the timescale for deformation that is measured at the ground surface is not equal to the timescale for deformation of a viscoelastic material element but can be many times larger than that the sensitivity of the response to the thickness and location of the rocksalt layer is also presented conclusions are drawn which allow for the relative importance of the presence of the rocksalt layer to be assessed and for a framework for understanding time dependent subsidence above producing hydrocarbon reservoirs to be developed finally the changes in stress distribution around a producing reservoir are also briefly discussed

the development of late holocene coastal cooling in the northern south china sea abstract paired high resolution sea surface temperature sst records based on the long chain alkenone unsaturation index u 37 k were reconstructed to decipher the sst evolution over the past 8000 years and its possible driving mechanisms at the hong kong coastal region the two sst records derived from a sediment core in the pearl river estuary and an offshore core in the northern south china sea scs show different patterns of sst changes the coastal record shows relatively stable warm temperatures during the mid holocene 7 4 2 6 ka and substantial cooling 2 c thereafter the cooling was most pronounced in the past 0 6 ka likely associated with the little ice age lia the offshore record generally reveals a warming trend from 8 ka to 3 5 ka and relatively warm temperatures since then as a result the sst difference sst between the two sites increased over time suggesting that the sst gradient gradually developed in the northern scs the declining coastal sst with the increasing sst likely indicates and results from the intensified east asian winter monsoon since 7 ka especially during the late holocene consistent with previous terrestrial records revealing winter monsoon variability and modern observations sst between coastal and offshore sites could thus be used as an indicator of winter monsoon variability

sedimentary facies diatom and foraminifer assemblages in a late pleistocene holocene incised valley sequence from the mekong river delta bentre province southern vietnam the bt2 core abstract a detailed description of sediment facies diatom mollusca and foraminifer assemblages and 14 c ages of the mekong river delta southern vietnam is presented in this paper a 71 m long core recovered in 1997 at the bentre province in the eastern part of the mekong river delta is divided into eight units and nine sediment facies on the basis of sedimentary properties diatom and foraminifer assemblages and 14 c ages these units show facies changes from transgression to regression in relation to the late pleistocene holocene sea level changes the postglacial transgression caused by a sea level rise led to infilling of the incised valley and formation of estuarine sediments and open bay muddy sediments in ascending order estuarine sediments consist of slightly oxidized yellowish grey silty sand and intercalated greenish grey and stiffly brownish grey sandy silt and silty clay the muddy facies 13 5 m thick is characterized by abundant marine planktonic diatoms and open sea foraminifers this facies indicates the maximum holocene marine influence was around 5300 cal yr bp at the bt2 site the regressive succession is composed of deltaic sediments from prodelta delta front sub to inter tidal flat and beach ridge in ascending order 14 c ages indicate that the delta front passed the core site at approximately 4000 3000 cal yr bp the coastal progradation rate was 17 18 m yr 1 during the 5300 3500 cal yr and decreased to 13 14 m yr 1 during the last 3500 cal yr

mid holocene sea level highstand along the southeast coast of china various sea level curves have been proposed for the coast of china in the past two decades these sea level curves indicate a complex history of holocene sea level and so the debate on whether or not a higher mid holocene sea level highstand exists in the coast of china has continued this paper aims to re examine the holocene sea level history for the low latitude part of the china coast between 18 n and 32 n by re assessing all the sea level data available from the east to south coasts and separating them according to geological settings in order to examine the influences of global and local factors the reconstructed sea level histories from different coastal sectors of the china coast reveal a certain degree of variability in the timing and height of mid holocene sea level highstand within large river deltas the mid holocene sea level highstand occurred earlier by almost 1000 years than that from other coastal sites the highstand from large river deltas appears also lower in altitude a few metres below the present day sea level due probably to the local factors of subsidence and sediment consolidation in geologically stable coastal sites the highstand is recorded at the same altitude as the present day sea level a 1 2 m higher highstand is found from sites where tectonic uplift is observed

lead isotope systematics of epigenetic lead zinc mineralization in the western part of the rheinisches schiefergebirge germany in the western part of the rheinisches schiefergebirge three different types of epigenetic lead zinc vein mineralization in paleozoic rocks can be distinguished 1 syntectonic variscan veins 2 post variscan saxonian veins mainly in paleozoic siliceous clastic rocks 3 post variscan carbonate hosted mineralization in the aachen stolberg area ore impregnations occur in the triassic buntsandstein bunter sandstone and muschelkalk of the maubach mechernich triangular depression covering the paleozoic rocks data points define two distinct populations in both lead isotope diagrams and thus indicate two major variscan and post variscan mineralization events the lead isotope pattern of the paleozoic sedimentary rocks bears good evidence that this thick rock sequence may be the main source of metals for the mineralization the metals were mobilized at deeper levels by saline fluids at different times there are no direct indications for remobilization of the older variscan vein ore deposits the sandstone and carbonate hosted ore impregnations of maubach mechernich have a similar lead isotope pattern to the post variscan mineralization in the paleozoic sedimentary basement

diatom based tidal level transfer functions as an aid in reconstructing quaternary history of sea level movements in the uk this research analyses the diatom asssemblages recorded from six uk coastal sites and relates these diatom assemblages to tidal levels the relationship between diatom assemblages and tidal levels is examined statistically in order to develop a diatom based tidal level transfer function the results suggest that there is highly significant correlation between the diatom assemblages and water levels from mean high water of neap tides to highest astronomical tide p 0 01 99 random permutations a weighted average wa transfer function is thus established and the predictive ability of this transfer function is highly satisfactory finally this transfer function is applied successfully to estimate palaeotidal levels from fossil diatom data recorded in late holocene coastal sequences copyright 1999 john wiley sons ltd

holocene sea level change and coastal evolution in the humber estuary eastern england an assessment of rapid coastal change new stratigraphic data collected from six sites in the humber estuary establish a record of holocene relative sea level rsl change and enable testing of four possible causes of rapid coastal change sea level rise changes in sedimentation storm surge history and human impact mean high water of spring tides mhwst in the humber rose from c 9 m od at 7500 cal yrs bp to 0 m od by 4000 cal yrs bp at an average long term rate of c 3 9 mm yr 1 after this the rate of rise gradually decreased to c 1 mm yr discrete episodes of rapid rsl rise are not identified although their absence may reflect limited data availability however we do observe two episodes of rapid coastal change in the humber estuary the first occurs between c 3200 and 1900 cal yrs bp as marine conditions expand to their holocene maximum and then contract this pattern of coastal development differs from that in the east anglian fenlands suggesting local processes control sedimentation at one or both of these sites the sec

experimental investigation into the microstructural and mechanical evolution of phyllosilicate bearing fault rock under conditions favouring pressure solution abstract mature crustal fault zones are known to be zones of persistent weakness this weakness is believed to result from microstructural modifications during deformation such as grain size reduction and foliation development around the brittle ductile transition phyllosilicates are expected to have a significant effect on fault strength in particular under conditions favouring pressure solution to study such effects we performed rotary shear experiments on brine saturated halite kaolinite mixtures aimed at investigating the relation between microstructural and mechanical evolution in a system where pressure solution and cataclasis dominate the results show significant strain weakening and a transition with progressive strain towards more rate sensitive and less normal stress sensitive behaviour this was accompanied by a microstructural evolution from a purely cataclastic microstructure to a mylonitic microstructure consisting of elongate asymmetric clasts in a fine grained foliated matrix the results demonstrate that strain weakening and the development of a typical mylonitic microstructure can occur as a consequence of grain size reduction by cataclasis and a transition to pressure solution accommodated deformation even in the absence of dislocation creep the data raise questions regarding the reliability of microstructures as rheology indicators as well as on the use of low strain monomineralic flow laws for modelling crustal dynamics

the influence of an embedded viscoelastic plastic layer on kinematics and mass transport pattern within accretionary wedges abstract the major aim of this study was to examine the influence of an embedded viscoelastic plastic layer at different viscosity values on accretionary wedges at subduction zones to quantify the effects of the layer viscosity we analysed the wedge geometry accretion mode thrust systems and mass transport pattern therefore we developed a numerical 2d sandbox model utilising the discrete element method starting with a simple pure mohr coulomb sequence we added an embedded viscoelastic plastic layer within the brittle undeformed sediment package this layer followed burger s rheology which simulates the creep behaviour of natural rocks such as evaporites this layer got thrusted and folded during the subduction process the testing of different bulk viscosity values from 1 1013 to 1 1014 pa s revealed a certain range where an active detachment evolved within the viscoelastic plastic layer that decoupled the over and the underlying brittle strata this mid level detachment caused the evolution of a frontally accreted wedge above it and a long underthrusted and subsequently basally accreted sequence beneath it both sequences were characterised by specific mass transport patterns depending on the used viscosity value with decreasing bulk viscosities thrust systems above this weak mid level detachment became increasingly symmetrical and the particle uplift was reduced as would be expected for a salt controlled forearc in nature simultaneously antiformal stacking was favoured over hinterland dipping in the lower brittle layer and overturning of the uplifted material increased hence we validated that the viscosity of an embedded detachment strongly influences the whole wedge mechanics both the respective lower slope and the upper slope duplex shown by e g the mass transport pattern

isotope composition of medieval lead glasses reflecting early silver production in central europe the lead isotope composition of 32 lead glasses excavated from strata of the twelfth to early fifteenth century in six countries of nw europe made the predominance of the harz mountains in this period of the medieval european lead and silver production highly probable post variscan vein type galena devonian syngenetic hydrothermal ore rammelsberg and blended ore from both deposits in the harz were used our evaluation of 200 mining sites in germany britain and ireland also demonstrated that minor lead sources for lead glass were located in bavaria bohemia and england lead ores from the rhenohercynian orogenic belt in germany are derived from rock sources close to the upper continental crust composition in 238u 204pb of about 10 and th u of about 4 the ores in central england originated from rocks with 238u 204pb of about 11

buckling of a pervasively faulted lithosphere we investigated the buckling response of a faulted elastic plate under horizontal compression using the finite element technique to better understand the effect of faults on the elastic behavior of a plate we studied the effect of changes in fault spacing depth and dip on the effective young s modulus buckling stress and wavelength our model consists of a thick elastic plate whose entire upper surface is cut by evenly spaced faults we impose either an initial sinusoidal deformation with a fixed wavelength or a random deformation to the grid a fault is represented as a free surface with no resolved shear stress and is allowed to slip in a specified direction using the method of slippery nodes with the assumption of free slip on the faults our model results represent an end member case in which the buckling wavelength and buckling stress are minimized by the presence of the faults

evidence for two great earthquakes at anchorage alaska and implications for multiple great earthquakes through the holocene abstract multiple peat silt couplets in tidal marsh sediment sequences at anchorage suggest up to five possible great earthquakes during the last 2500 years litho stratigraphic diatom and radiocarbon data of the youngest two couplets record the last two great earthquakes ad 1964 and 950 850 cal yr bp similar multiple peat silt couplets around cook inlet suggest recurring great earthquakes associated with marsh subsidence over large areas comparable in extent to that recorded in ad 1964 potential difficulties in interpreting evidence include lack of modern analogues for applying quantitative diatom transfer functions to parts of the fossil record and the observation that under certain sedimentary conditions co seismic subsidence in the case of ad 1964 of known magnitude is recorded by a transitional peat silt boundary this differs in diatom stratigraphy from a phase of pre seismic relative sea level rise recorded for other great earthquakes a field experiment to simulate co seismic subsidence identifies limited mixing at the top of submerged marsh sediment and indicates how mixing must be shown to differ from evidence for pre seismic relative sea level rise analysis of diatom assemblages from ice frozen intertidal sediment and melt out sediment demonstrates the importance of winter processes in transporting diatoms and their interpretation in fossil sequences winter processes may also be important in transporting organic material that leads to significant differences 120 2800 yr between radiocarbon ages from plant macrofossils and bulk peat samples this necessitates a new approach for establishing between site correlations recurrence intervals and spatial extent of great holocene earthquakes in southern alaska

geophysical imaging of subsalt geology about four years ago the prevailing perception regarding offshore exploration in the gulf of mexico was that the shelf was all but played out and in steady decline and because of limited technology and experience the deepwater was deemed far too risky for most and therefore reserved for only a handful of deep pocketed majors in fact most companies were in an exit strategy from the gulf of mexico then in october 1993 the mahogany subsalt discovery changed this direction seemingly overnight and ignited the hopes of many who yearned for new discoveries and better times ahead

origin of an anhydrite sheath encircling a salt diapir and implications for the seismic imaging of steep sided salt structures egersund basin northern north sea the ingress of meteoric fluids into the crests of salt structures typically results in the formation of anhydrite dominated caprock the migration of connate fluids up the margins of salt structures has also been documented although the products related to this are rarely sampled in the deep subsurface we use 3d seismic reflection and borehole data to document the geometry and lithology of a salt diapir seismic data suggest that a weld is developed along the diapir stem although borehole data indicate that the stem consists of an inner c 1500 m thick halite dominated zone and an outer c 250 m thick anhydrite dominated sheath the anhydrite may have formed early in the basin history as a depositional anhydrite or crestal caprock an alternative interpretation is that the anhydrite represents lateral caprock which formed late in the basin history in response to the migration of nacl poor fluid up the margins of the diapir and dissolution of halite the possibility that lateral caprock may form adjacent to salt structures has implications for understanding the patterns and vigour of groundwater flow in sedimentary basins furthermore our study shows the margins of steep sided salt structures may be misidentified by several hundred metres if time migrated seismic reflection data are used

impact of rock salt creep law choice on subsidence calculations for hydrocarbon reservoirs overlain by evaporite caprocks accurate forward modeling of surface subsidence above producing hydrocarbons reservoirs requires an understanding of the mechanisms determining how ground deformation and subsidence evolve here we focus entirely on rock salt which overlies a large number of reservoirs worldwide and specifically on the role of creep of rock salt caprocks in response to production induced differential stresses we start by discussing available rock salt creep flow laws we then present the subsidence evolution above an axisymmetric finite element representation of a generic reservoir that extends over a few kilometers and explore the effects of rock salt flow law choice on the subsidence response we find that if rock salt creep is linear as appropriate for steady state flow by pressure solution the subsidence response to any pressure reduction history contains two distinct components one that leads to the subsidence bowl becoming narrower and deeper and one that leads to subsidence rebound and becomes dominant at later stages this subsidence rebound becomes inhibited if rock salt deforms purely through steady state power law creep at low stresses we also show that an approximate representation of transient creep leads to relatively small differences in subsidence predictions most importantly the results confirm that rock salt flow must be modeled accurately if good subsidence predictions are required however in practice large uncertainties exist in the creep behavior of rock salt especially at low stresses these are a consequence of the spatial variability of rock salt physical properties which is practically impossible to constrain a conclusion therefore is that modelers can only resort to calculating bounds for the subsidence evolution above producing rock salt capped reservoirs

paleoclimate of southwestern china for the past 50 000 yr inferred from lake sediment records abstract long sediment cores 12 5 and 13 5 m from two lakes in yunnan province were used to infer the paleoclimate of southwest china over the past 50 000 yr during the holocene and marine isotope stage mis 3 bio induced carbonate precipitation and organic matter om production was high suggesting warm temperatures and high primary productivity in contrast sediment inorganic carbon ic and organic carbon oc concentrations were low in last glacial deposits from 38 000 to 12 000 cal yr b p indicating cool temperatures and low productivity the 50 000 yr record has alternating peaks of carbonate and coarse grain 38 m quartz that reflect warm moist interglacial or interstadial conditions alternating with cold dry glacial or stadial conditions respectively spectral analysis of the carbonate and quartz signals reveals power concentrated at periods of 7200 and 8900 cal yr respectively that may reflect a nonlinear climate response to precessional forcing at a time of reduced eccentricity modulation mcintyre and molfino 1996 oxygen isotope values of calcite from yunnan lake cores indicate the summer monsoon was weak during the last glaciation from 50 000 to 12 000 cal yr b p the summer monsoon intensified between 12 000 and 8000 cal yr b p but weakened gradually in response to insolation forcing during the mid to late holocene our results support the overpeck et al 1996 model that posits a weak summer monsoon during the last glaciation that responded nonlinearly to insolation forcing when its intensity was affected by eurasian snow cover and ice sheet extent the summer monsoon intensified and responded linearly to seasonal insolation forcing in the holocene when ice volume diminished

influence of grain boundary structural evolution on pressure solution creep rates intergranular pressure solution is a well known rock deformation mechanism in wet regions of the upper crust and has been widely studied especially in the framework of compaction of granular materials such as reservoir sandstones and fault rocks several analytical models exist that describe compaction creep by stress induced mass transport and the parameters involved are relatively well constrained by laboratory experiments while these models are capable of predicting compaction behavior observed at relatively high porosities they often overestimate compaction rates at porosities below 20 by up to several orders of magnitude this suggests that the microphysical processes operating at low porosities are different and are not captured well by existing models the implication is that available models cannot be extrapolated to describe compaction of sediments and fault rocks to the low porosities often reached under natural conditions to address this problem we propose a new thermodynamic model that describes the decline of pressure solution rates within individual grain contacts as a result of time averaged growth of asperities or islands and associated constriction of the grain boundary diffusion path here termed grain boundary evolution the resulting constitutive equations for single grain grain contacts are then combined and solved semianalytically the compaction rates predicted by the model are compared with those measured in high strain compaction experiments on wet granular halite a significant reduction in compaction rate is predicted when grain boundary evolution is considered which compares favorably with the experimental compaction data

salt structures and hydrocarbon accumulations in the tarim basin northwest china the tarim basin is one of the most important hydrocabon bearing evaporite basins in china four salt bearing sequences the middle and lower cambrian the mississippian the paleogene and the neogene have various thickness and areal distribution they are important detachment layers and intensely affect the structural deformation in the basin the kuqa depression is a subordinate structural unit with abundant salt structures in the tarim basin salt overthrusts salt pillows salt anticlines salt diapirs and salt withdrawal basins are predominant in the depression contraction that resulted from orogeny played a key function on the formation of salt structures growth strata reveal that intense salt structural deformation in the kuqa depression occurred during the himalayan movement from oligocene to holocene with early structural deformation in the north and late deformation in the south growth sequences also record at least two phases of salt tectonism in the yingmaili tahe and tazhong areas low amplitude salt pillows are the most common salt structures and these structures are commonly accompanied by thrust faults the faulting and uplifting of basement blocks controlled the location of salt structures the differences in the geometries of salt structures in different regions show that the thickness of the salt sequences has an important influence on the development of salt cored detachment folds and related thrust faults in the tarim basin salt sequences and salt structures in the tarim basin are closely linked to hydrocarbon accumulations oil and gas fields have been discovered in the subsalt intrasalt and suprasalt strata salt deformation has created numerous potential traps and salt sequences have provided a good seal for the preservation of hydrocarbon accumulations large and small scale faults related with salt structures have also given favorable migration pathways for oil and gas when interpreting seismic profiles special attention needs to be paid to the clastic and carbonate interbeds within the salt sequences because they may lead to incorrect structural interpretation in the tarim basin the subsalt anticlinal traps are good targets for hydrocarbon exploration

modern fine grained sedimentation spatial variability and environmental controls on an inner pericontinental shelf hong kong abstract fine grained sediments in hong kong form part of an extensive cover that extends from nearshore locations to the mid continental shelf this featureless mud blanket is associated with sediment inputs from the pearl river and has generally been considered to be homogeneous in its characteristics however detailed sedimentological and geochemical analyses have revealed that the superficial deposits show systematic spatial variations that reflect contrasts in deposition between the pearl river estuary to the west and fully marine conditions to the east results indicate significant differences in particle size accumulation rates biogenic silica organic carbon content c n ratios and stable carbon and nitrogen isotopes that reflect location with respect to the pearl river delta calcium carbonate content varies widely tending to be higher close to land major controls over spatial variability include rainfall patterns and the supply of estuarine suspended particulate matter the effects of palaeotopography and modern water depth resuspension induced by monsoon winds and typhoons and human impacts on the sea floor

postglacial sea level changes in the northern south china sea continental shelf evidence for a post 8200 calendar yr bp meltwater pulse abstract a postglacial sea level record reconstructed through the study of 25 cores and 10 grab samples obtained from the siliciclastic dominated northern south china sea continental shelf between hong kong and dongsha is presented the seven sedimentary facies recognized are 1 pleistocene overconsolidated mud facies affected by palaeosol development due to sub aerial exposure during the last glacial maximum lgm 2 bioclastic sandy gravel facies occurring at a present day seabed depth exceeding 120 m 3 lgm bioclastic beach dune sand facies at a present day seabed depth between 110 and 120 m 4 postglacial siliciclastic beach dune sand facies formed during at least two episodes of sea level stillstands at present day seabed depths between 80 and 90 m and 30 and 50 m respectively 5 postglacial transgressive sand facies of late pleistocene to early holocene age radiocarbon dating shows that this facies was deposited in two stages before and after the 8200 calendar yr bp cold event 6 postglacial sand and gravel dominated facies with acoustic turbidity at a present day seabed depth of about 50 m 7 postglacial mud facies based on the radiocarbon ages obtained from samples located above and below the holocene pleistocene hiatus in the two innermost shelf cores and large variations of atmospheric radiocarbon concentration found during the last glacial period in a submerged stalagmite from the bahamas beck et al 2001 science 292 2453 2458 ages exceeding 8200 calendar yr bp are likely to represent minimum values ages postdating this limit which are less affected by variations of atmospheric radiocarbon concentration indicate the presence of a post 8200 calendar yr bp cold event meltwater pulse caused by eustatic sea level rise from approximately 40 m below present to the present level by about 6000 calendar yr bp inaccuracies of the pre 8200 calendar yr bp radiocarbon ages may be attributed to large variations of atmospheric 14 c during the postglacial period with greenhouse gases released from the sub aerially exposed continental shelf probably accounting for a significant proportion

sedimentary evidence of late holocene human activity in the pearl river delta china this study examines the sedimentary evidence of human activities during the last 4000 years in the pearl river deltaic area the analyses are focused on indentifying agricultural signatures present in the sedimentary record and establishing the timing of a change from a simple rice based agriculture to a more advanced diverse agriculture the examination is based on modern sediment and plant samples and a sediment core collected from the deltaic area the analyses include particle size and diatom analysis to determine the environmental conditions that were associated with the period of human activities organic carbon isotope ratios and major metal elements reveal an expansion in commercial crop production and metal smelting in the pearl river delta area about 2000 years ago the input of organic matter from introduced sugarcane a c4 plant elevates the bulk organic carbon isotope values in the estuarine sediments above that represented by other common agricultural crops in the study area including rice banana and lotus which are all c3 plants the increase in bulk organic isotopic value coincides with the rise in the concentration of copper iron and lead in the sedimentary sequence suggesting a wider use of metal tools these results indicate that advanced agriculture started about 2000 years ago as an expansion in human population took place in the area this record also provides sedimentary evidence that help ascertain the timing and type of human activities that are linked to subsequent land reclamation on the deltaic plain resulting in rapid shoreline advancement in the last 2000 years copyright 2010 john wiley sons ltd

creep of rocksalt abstract a review is presented of the fundamental flow properties and processes in experimentally deformed natural and synthetic halite single crystals and polycrystalline aggregates included in the summary are discussions of a microstructures induced during steady state creep b creep rupture of rocksalt c experiments associated with project salt vault and more recent field studies and d brine migration a representative steady state flow law determined for natural aggregates and maximum natural deviatoric stresses deduced from subgrain sizes are applied briefly to considerations of creep in waste repositories and of salt dome dynamics while the mechanical behavior of rocksalt is probably better understood than for all other rock types further investigations especially on load path stress history and creep rupture are clearly mandated furthermore additional investigations of brine migration and of bench and field scale deformations are needed the latter incorporating realistic rocksalt flow properties into numerical simulations of natural rock mass response

initiation of asymmetric extension in continental lithosphere govers r and wortel m r 1993 initiation of asymmetric extension in continental lithosphere in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 x 96 the physical conditions are investigated under which the lithospheric scale style of extension is pure shear or simple shear we focus on the initial stages of continental extension to monitor how symmetric or asymmetric modes of extension evolve from specific tectonic conditions continental collision magma intrusions and interaction between the lithosphere and the underlying mantle are investigated as sources for extension we use a finite element method to model the thermo mechanical evolution of continental lithosphere experimental flow laws are used to model the elastic hutle power law creep or diffusion creep rheology of lithospheric rocks our results indicate that if in plane forces change from compressive to tensile immediately after a rapid mountain building phase initiation of a lithosphere scale detachment fault is possible we find a strong dependence of the extensional style on the distribution with depth of residual stresses from the collision phase this result is consistent with observations of gravitational collapse in regions like the aegean and the basin and range province where detachment faults have exhumed lower crustal rocks the predicted dip direction of the fault also agrees with observations in these areas intrusion of magma into continental lithosphere which is subject io in plane tensile forces will cause localization of pure shear deformation the style of deformation resulting from mantle plumes impinging to the base of the lithosphere is symmetric delamination of lithospheric mantle may initiate detachment faults if delamination occurs at the end of a collision phase when in plane forces change sign from compressive to tenstle this result also strongly depends on the assumed residual stress distribution if delamination occurs during the mountam huilding phase the style of deformation will be pure shear another interesting outcome from our modeling is that dramatic strain weakening as a result of a deformation mechanism change from dislocation creep to diffusion creep reduces the tendency to strain localization a large volume of the published work on continental extension has been concentrated on quantifying the stretching factor p of the pure shear model of mckenzie 1978a in some basins it was found that the kinematics of deformation could be more accurately described by depth dependent stretching factors royden and keen 19801 which introduced asymmetry near basin edges in the simple shear model of wemicke

creep of garnet in eclogite mechanisms and implications abstract the rheological properties of subducting rocks represent a fundamental parameter in the dynamics of subduction zones making robust predictions about these properties and the general strength evolution of subducting plates is hampered by a relatively restricted understanding of the mechanisms by which rocks deform at high and ultrahigh pressure this uncertainty is relates to the discrepancy between experimental and field based observations of eclogite deformation and in particular the role of garnet to further investigate this important aspect we performed a textural and micro structural investigation applying optical microscopy element mapping and electron backscatter diffraction on deformed garnet polycrystals from an eclogite mylonite the results were compared to those from a study of undeformed polycrystals that formed from a supercooled frictional melt at hp conditions the mylonites polycrystals are flattened parallel to the main high pressure foliation in the rock and individual grains were shortened by an average 15 although dislocation creep is commonly presumed to dominate garnet straining in eclogites no record of this mechanism was found instead the garnet grains have dissolution surfaces indicative of deformation by intergranular pressure solution the observations provide compelling evidence for the role of fluids and syn tectonic porosity in the weakening of garnet a supposedly rigid eclogite component such weakening represents a crucial step in the fundamental feedback loop between fluid ingress metamorphism and near instantaneous competence loss in rocks undergoing deep subduction

reconstruction of holocene monsoon history from the pearl river estuary southern china using diatoms and carbon isotope ratios this study employs a multiproxy approach in the reconstruction of holocene monsoon history from sedimentary sequences obtained from the pearl river estuary southern china a set of modern surface sediment samples were collected within and outside the estuary and a sediment core was obtained from the mouth of the estuary a range of modern environmental variables were recorded including water salinity summer winter and annual average and water depth the diatom results show a good relationship with water salinity with marine diatoms dominating the more distal samples from outside the main estuary and freshwater diatoms dominating the proximal samples influenced by higher freshwater flux this pattern is matched by the bulk organic carbon isotopes the isotope values vary between 21 1 0 3 0 for samples from the fully marine environment between 23 2 0 8 and 23 7 0 8 for samples from the mid to outer estuary brackish water environment and less than 24 7 1 3 for samples from the inner estuary close to the freshwater sources similarly the c n ratios vary from below 7 0 6 in the marine end members to over 14 8 3 0 in the freshwater end members both the diatom and carbon data from the sediment core reveal a significant increase in freshwater flux from 8500 cal yr bp resulting from the enhanced summer monsoon regime in early holocene the strength of freshwater flux reached its highest between 7500 and 6000 cal yr bp in the last 6000 years freshwater flux decreased towards present reflecting a gradual weakening of the summer monsoon

lithosphere tearing at step faults response to edges of subduction zones abstract slab edges are a relatively common feature in plate tectonics two prominent examples are the northern end of the tonga subduction zone and the southern end of the new hebrides subduction zone near such horizontal terminations of subduction trenches ongoing tearing of oceanic lithosphere is a geometric consequence we refer to such kinks in the plate boundary as a subduction transform edge propagator or step other steps are the north and south ends of the lesser antilles trench the north end of the south sandwich trench the south end of the vrancea trench and both ends of the calabria trench volcanism near steps is distinct from typical arc volcanism in some cases slab edges appear to coincide with mantle plumes using 3d mechanical models we establish that step faults are stable plate tectonic features in most circumstances in the probably rare cases that the resistance to fault propagation is high slab break off will occur relative motion along the transform segment of the plate boundary often is non uniform and the step is not a transform plate boundary in the rigid plate tectonics sense of the phrase step propagation may result in substantial deformation rotation topography and sedimentary basins with a very specific time space evolution surface velocities are substantially affected by nearby steps

simple approach to predicting ground displacements caused by tunnelling in undrained anisotropic elastic soil an attempt to develop a kinematically based approach to predicting ground settlements due to tunnelling is represented by using the more reliable data of the commonly observed settlement troughs rather than imposing the boundary conditions on the tunnel surface which have a high level of uncertainty the anisotropic elastic model used in this work is highly simplified and the resulting analytical solution is of an approximate nature nevertheless it seems to provide good agreement with both the shape and the magnitude of the observed settlement trough based on this solution a modification is proposed for the widely used empirical gaussian curve by correlating the trough width parameter k with the ratio between the two anisotropic shear moduli ghh gvh

balancing sub and supra salt strain in salt influenced rifts implications for extension estimates the structural style of salt influenced rifts may differ from those formed in predominantly brittle crust salt can decouple sub and supra salt strain causing sub salt faults to be geometrically decoupled from but kinematically coupled to and responsible for supra salt forced folding salt influenced rifts thus contain more folds than their brittle counterparts an observation often ignored in extension estimates fundamental to determining whether sub and supra salt structures are kinematically coherent and the relative contributions of thin i e gravity driven and thick skinned i e whole plate stretching deformation to accommodating rift related strain is our ability to measure extension at both structural levels we here use published physical models of salt influenced extension to show that line length estimates yield more accurate values of sub and supra salt extension compared to fault heave before applying these methods to seismic data from the halten terrace offshore norway we show that given the abundance of ductile deformation in salt influenced rifts significant amounts of extension may be ignored leading to the erroneous interpretations of thin skinned gravity gliding if a system is kinematically coherent supra salt structures can help predict the occurrence and kinematics of sub salt faults that may be poorly imaged and otherwise poorly constrained

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico part ii structure abstract the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope autochthonous salt allochthonous salt and detached allochthonous salt are typical stages of evolution major down to the basin growth faults separate allochthonous salt sheets from their original feeder stocks extension along down to the basin master growth faults is compensated mainly by salt withdrawal and partly by basinward shortening

the migration of fluid filled grain boundaries in recrystallizing synthetic bischofite first results of in situ high pressure high temperature deformation experiments in transmitted light the effect of fluids on recrystallization behaviour is well known however the detailed microscale distribution of fluid in grain boundaries and the influence of fluid on grain boundary migration are still unresolved in this study in situ deformation experiments in transmitted light microscopy were undertaken as this allows continuous and direct observation of the whole range of processes involved in fluid assisted grain boundary migration a new see through deformation apparatus was developed to enable the control of fluid pressure bischofite containing small amounts of aqueous fluid was deformed at temperatures between 50 and 90 c over a range of fluid pressure from 0 5 to 1 mpa and strain rates of 5 10 6 to 1 10 4 s 1 the rates of grain boundary migration were measured at different temperatures and strain rates detailed observations during and after the deformation illustrate the evolution of migrating fluid filled grain boundaries and show that the incorporation of fluids from inclusions as well as their pinch off is dependent on the grain boundary velocity the thickness of the grain boundary and the size and shape of the inclusions direct evidence is presented for the contraction of the grain boundary fluids into isolated inclusions after equilibrium conditions are attained

subaerial salt extrusions in iran as analogues of ice sheets streams and glaciers abstract ice h20 and salt halite nacl share many physical properties and resemble each other in hand specimens and subaerial gravity driven flows however while most significant bodies of ice accumulate in cold highlands and gravity spread where and soon after they form most significant bodies of salt accumulate in tropical marine basins and have to be buried by 1 km of other rocks before they flow buried salt is driven by differential loading into various categories of piercing structures known as diapirs many diapirs extrude onto the surface as sheets of allochthonous out of place salt thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years mainly in the toes of passive continental margins and in orogenic belts where some are 103 km2 in area most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in iran these were compared to ice glaciers soon after they were introduced to western science a comparison that has been neglected since here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists the profiles internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss however whereas snow merely compacts where it accumulates salt sheets are fed from below by already deformed salt when salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier like flows known as namakiers after locally exhausting their deep source layers salt fountains spread to the profiles of viscous droplets normal for ice caps ice typically deforms at 80 usually 90 of its absolute melting temperature while most salt deforms at

towards an improved understanding of the mechanical properties and rheology of the lithosphere an introductory article to rock deformation from field experiments and theory a volume in honour of ernie rutter ernie rutter s influential contribution to our understanding of rock deformation spans the whole continental crust from deformation just under the grass e g rutter green 2011 to melt migration in the lower crust e g rutter neumann 1995 ernie has also worked on many aspects of the deformation of oceanic crust rutter brodie 1988 however here we reflect on the wide range of deformation conditions ernie has studied by presenting key aspects of the strength and rheology of the continental lithosphere as we understand it today with the aim of providing the context for the contributions included within this volume the continental crust forms just over a third of the earth s surface and it is different from the crust of any other planet in our solar system it is rich in those elements that partition in a silicate melt and its formation and evolution determined the composition of the mantle and that of the atmosphere hawkesworth 2006 thanks to its physical and chemical fingerprint the earth s crust has sustained life uninterrupted for 3 8 ga and it is the source of major natural resources such as hydrocarbons and mineral deposits and others such as geothermal energy the continental crust is less dense than its oceanic counterpart and is therefore more buoyant it forms a substantial part of the cold thermal layer of the earth and its rheology from greek r1v rhe flow and logia logia study the study of the flow of matter is a key factor controlling plate tectonic processes at the earth s surface and in its interior davies 2011 beneath the continental crust lies the lithospheric mantle and together they form the continental lithosphere considerable variations in structure thickness and composition of the continental lithosphere mean that despite its importance we currently have limited understanding of the rheology of this complex system thatcher pollitz 2008 significant advances in our knowledge of continental rheology have been possible through

integrating laboratory creep compaction data with numerical fault models a bayesian framework 1 we developed a robust bayesian inversion scheme to plan and analyze laboratory creep compaction experiments we chose a simple creep law that features the main parameters of interest when trying to identify rate controlling mechanisms from experimental data by integrating the chosen creep law or an approximation thereof one can use all the data either simultaneously or in overlapping subsets thus making more complete use of the experiment data and propagating statistical variations in the data through to the final rate constants despite the nonlinearity of the problem with this technique one can retrieve accurate estimates of both the stress exponent and the activation energy even when the porosity time series data are noisy whereas adding observation points and or experiments reduces the uncertainty on all parameters enlarging the range of temperature or effective stress significantly reduces the covariance between stress exponent and activation energy we apply this methodology to hydrothermal creep compaction data on quartz to obtain a quantitative semiempirical law for fault zone compaction in the interseismic period incorporating this law into a simple direct rupture model we find marginal distributions of the time to failure that are robust with respect to errors in the initial fault zone porosity

a constitutive law for low temperature creep of water saturated sandstones an accurate predictive model for the long term strength of the continental lithosphere is important in a range of geophysical and geodynamic problems while laboratory experiments are consistent with mohr coulomb brittle faulting in the cold upper continental crust there is increasing evidence that time dependent processes may also be important in these rocks even at low temperature however there is some ambiguity as to the exact form of the constitutive law for describing time dependent behavior of upper crustal rocks here we present results of room temperature creep experiments on a suite of water saturated sandstones spanning a range of petrophysical and rheological properties and underlying deformation mechanisms on physical and microstructural grounds our analysis suggests that a modified power law creep of the form a d f where d is the differential stress and f is the long term failure fundamental strength provides a more complete description of the experimental data in particular the parameters can be used to differentiate between sandstone types with a f and varying systematically with cementation state rock rheology and confining pressure the fundamental strength f for time dependent deformation varies much more than the other parameters of the distribution making it a potentially sensitive indicator of underlying creep mechanisms further tests would be needed to prove the constitutive law on a wider range of rock types and to prove that the three parameter model is statistically better in the general case

frontal accretion along the western mediterranean ridge the effect of messinian evaporites on wedge mechanics and structural style in the context of the imerse project several crossings of the deformation front of the western mediterranean ridge were made in the region of the sirte abyssal plain the messina abyssal plain and the intervening region in this paper we present seismic images and interpretations across the deformation front with particular emphasis on the role the messinian evaporites have played in controlling the accretionary tectonics of the thin frontal portion of the wedge the seismic images show that the basal detachment generally is located at the base of the evaporites from a consideration of the mechanics of the wedge for both coulomb and plastic rheologies we show that the low wedge taper c 2 requires that the detachment is characterised by extreme fluid overpressuring within 2 of lithostatic in places and that the basal yield stress less than 1 mpa is lower than that of a wet salt decollement zone this supports the seismic interpretation that the detachment occurs in overpressured sediments beneath the impermeable evaporites lateral variations in the accretionary style can be related to lateral variations in evaporite thickness the effectiveness of the evaporite as an impermeable seal and to local relief on the subducting plate these factors control the escape of fluids from beneath the evaporites and hence fluid pressure and basal yield stresses

rapid deformation rates along the wasatch fault zone utah from first gps measurements with implications for earthquake hazard anomalously high rates of crustal deformation have been measured at the basin range transition to the rocky mountains along the wasatch fault zone utah by repeated global positioning system gps measurements four gps field campaigns 1992 1995 and comparisons with older 1962 1991 geodetic data have revealed east west extensional strain at a rate of 0 05 0 02 strain yr corresponding to a 2 7 1 3 mm yr rate of horizontal displacement across a 55 km wide area this rate is more than 20 of the total 12 mm yr extension rate across of the 800 km wide basin and range province it is also two to three times larger than the average late quaternary fault slip rate on the wasatch fault and tens of times larger than the displacement rates inferred from the cumulative seismic moments of historic earthquakes while we do not yet know the source of this unexpected contemporary deformation possible mechanisms include homogeneous crustal extension loading of the wasatch and adjacent faults and pressure solution creep if the wasatch fault is being loaded by this high strain rate it increases the expected peak ground acceleration significantly from standard values these new findings demonstrate the importance of gps in earthquake hazard assessment

the history of water salinity in the pearl river estuary china during the late quaternary this research reconstructed the late quaternary salinity history of the pearl river estuary china from diatom records of four sedimentary cores the reconstruction was produced through the application of a diatom salinity transfer function developed based on 77 modern surface sediment samples collected across the estuary from shallow marine environment to deltaic distributaries the statistical analysis indicates that the majority of sediment samples from the cores has good modern analogues thus the reconstructions are reliable the reconstructed salinity history shows the older estuarine sequence formed during the last interglacial was deposited under similar salinity conditions to the younger estuarine sequence which was formed during the present interglacial further analysis into the younger estuarine sequence reveals the interplays between sea level monsoon driven freshwater discharge and deltaic shoreline movement key factors that have influenced water salinity in the estuary in particular a core from the delta plain shows the effects of sea level change and deltaic progradation while cores from the mouth region of the estuary reveal changes of monsoon driven freshwater discharge this study demonstrates the advantages of quantitative salinity reconstructions to improve the quality of reconstruction and allow direct comparison with other quantitative records and the instrumentally observed values of salinity copyright 2010 john wiley sons ltd

an evolutionary model for the holocene formation of the pearl river delta china this paper reconstructs the evolutionary history of the pearl river delta over the last 9000 years and investigates land sea interaction in a large deltaic complex which formed under the influence

numerical study of tectonic structure evolution in a multi layer evaporite sequence abstract field studies carried out in the klodawa salt structure kss poland reveal that within a carnallite halite kieserite sequence finger like structures developed during an early pre diapiric stage of the kss evolution we used 99 numerical simulations to model finger development and investigate mechanical properties of carnallite halite and kieserite during deformation models used inverse density stratification of a three layer set with varying 1 layer viscosities 2 thicknesses and 3 density difference ratios finger shapes in the models were categorized into single and multiwavelength structures among the single wavelength shapes bulb mushroom thumb and bloated i e without a regular shape structures were distinguished we show two transitions between the single and multiwavelength structures which correspond to the cases of either the lower or upper layer having viscosity more than an order of magnitude larger than the two other layers through comparison of finger shapes developed in the models and in the natural structures we estimate viscosities of 1017 pa s for halite

early medieval origins of iron mining and settlement in central sweden multiproxy analysis of sediment and peat records from the norberg mining district the historical norberg mining district in central sweden with its shallow easily accessible iron ores figures prominently in the earliest documents from the 14th century concerning mining or metallurgy this 1000 km2 district is considered to be one of the first areas in sweden exploited for iron ores and in fact europe s oldest known blast furnace lapphyttan is located in the norberg district about 10 km from the mines in the village of norberg norbergsby earlier archaeological excavations suggest the furnace was in operation as early as the 11th or 12th century 870 and 930 14c yr bp and a number of other sites in the district have been dated to the 13th 15th centuries here we have analyzed two lake sediment records kalven and noren from the village of norberg and a peat record from lapphyttan the lapphyttan peat record was radiocarbon dated whereas the sediment from kalven is annually laminated which provides a fairly precise chronology our pollen data indicate that land use in the area began gradually as forest grazing by at least c ad 1050 with indications of more widespread forest disturbance and cultivation from c 1180 at lapphyttan and 1250 at kalven based on 206pb 207pb isotope ratios in kalven s varved sediment record there is an indication of mining or metallurgy in the area c 960 but likely not in immediate connection to our sites evidence of mining and metallurgy increases gradually from c 1180 when there is a decline in 206pb 207pb ratios and an increase in charcoal particles at lapphyttan followed by increasing inputs of lithogenic elements in noren s sediment record indicating soil disturbance which we attribute to the onset of mining the iron ore bodies surrounding noren from ad 1295 onwards evidence of mining and metallurgy are ubiquitous and activities accelerate especially during the late 15th century the maximum influence of bergslagen ore lead i e the minimum in 206pb 207pb isotope ratios in both kalven and noren occurs c 1490 1500 when also varve properties change in kalven and in noren sharp increases occur in the concentrations of a range of other ore related metals e g arsenic cadmium copper iron lead mercury and zinc from the 15th century onwards mining and metallurgy are the dominant feature of the sediment records

tsunami generation and associated waves in the water column and seabed due to an asymmetric earthquake motion within an anisotropic substratum in this paper closed form integral expressions are derived to describe how surface gravity waves tsunamis are generated when general asymmetric ground displacement due to earthquake rupturing involving both horizontal and vertical components of motion occurs at arbitrary depth within the interior of an anisotropic sub sea solid beneath the ocean in addition we compute the resultant hydrodynamic pressure within the seawater and the elastic wavefield within the seabed at any position the method of potential functions and an integral transform approach accompanied by a special contour integration scheme are adopted to handle the equations of motion and produce the numerical results the formulation accounts for any number of possible acoustic gravity modes and is valid for both shallow and deep water situations as well as for any focal depth of the earthquake source phase and group velocity dispersion curves are developed for surface gravity tsunami mode acoustic gravity rayleigh and scholte waves several asymptotic cases which arise from the general analysis are discussed and compared to existing solutions the role of effective parameters such as hypocenter location and frequency of excitation are examined and illustrated through several figures which show the propagation pattern in the vertical and horizontal directions attention is directed to the unexpected contribution from the horizontal ground motion the results have important application in several fields such as tsunami hazard prediction marine seismology and offshore and coastal engineering in a companion paper we examine the effect of ocean stratification on the appearance and character of internal and surface gravity waves this article is protected by copyright all rights reserved

three dimensional gravity inversion using simulated annealing constraints on the diapiric roots of allochthonous salt structures in the northern continental slope of the gulf of mexico large oil and gas reservoirs are often found beneath sheetlike allochthonous salt structures that are laterally extensive some of these salt structures retain their diapiric feeders or roots beneath them these hidden roots are difficult to image seismically in this study we develop a method to locate and constrain the geometry of such roots through 3 d inverse modeling of the gravity anomalies observed over the salt structures this inversion method utilizes a priori information such as the upper surface topography of the salt which can be delineated by a limited coverage of 2 d seismic data the sediment compaction curve in the region and the continuity of the salt body the inversion computation is based on the simulated annealing sa global optimization algorithm the sa based gravity inversion has some advantages over the approach based on damped least squares inversion it is computationally efficient can solve underdetermined inverse problems can more easily implement complex a priori information and does not introduce smoothing effects in the final density structure model we test this inversion method using synthetic gravity data for a type of salt geometry that is common among the allochthonous salt structures in the gulf of mexico and show that it is highly effective in constraining the diapiric root we also show that carrying out multiple inversion runs helps reduce the uncertainty in the final density model

holocene evolution in weathering and erosion patterns in the pearl river delta sediments in the pearl river delta have the potential to record the weathering response of this river basin to climate change since 9 5 ka most notably weakening of the asian monsoon since the early holocene approximate to 8 ka cores from the pearl river delta show a clear temporal evolution of weathering intensity as measured by k al k rb and clay mineralogy that shows deposition of less weathered sediment at a time of weakening monsoon rainfall in the early mid holocene 6 0 2 5 ka this may reflect an immediate response to a less humid climate or more likely reduced reworking of older deposits from river terraces as the monsoon weakened human settlement of the pearl river basin may have had a major impact on landscape and erosion as a result of the establishment of widespread agriculture after around 2 5 ka weathering intensity sharply increased despite limited change in the monsoon but at a time when anthropogenic pollutants e g cu zn and pb increased and when the flora of the basin changed sr 87 sr 86 covaries with these other proxies but is also partly influenced by the presence of carbonate the sediments in the modern pearl river are even more weathered than the youngest material from the delta cores we infer that the spread of farming into the pearl river basin around 2 7 ka was followed by a widespread reworking of old weathered soils after 2 5 ka and large scale disruption of the river system that was advanced by 2 0 ka

submarine salt flows in the central red sea the central red sea an oceanic basin floored by miocene evaporites reaching kilome ters in thickness in places is at an early stage of development where seafl oor spreading has geologically only recently replaced continental rifting surveys using a high resolution multibeam echo sounder around thetis deep a new spreading center have revealed a remarkable series of structures resembling viscous gravity fl ows which are here interpreted as originating from fl owage of the evaporites laterally unloaded by axial rifting and other processes developing the relief of the deep the fl ow margins are marked by stream wise lineaments and some apparently rotated markers their fronts in the fl oor of the deep are rounded in plan view and profi le their surfaces contain small closely spaced features resembling extensional faults in one area below declining gradients the surface contains along slope ridges and valleys typical of compression folds ogives flowparallel lineaments and extensional faults lie respectively parallel and orthogonal to the direction of maximum seabed gradient movement is apparently heterogeneous at least in part because of varied blocking by relief in underlying basement observed protruding between fl ows flowage is currently transporting materials into the fl oor of the deep where they have the potential to become incorporated into the young oceanic crust by repeated eruption of axial lavas over them in the light of these new data we reexamine the possibility and implications of fl owage in the south atlantic marginal evaporites in particular whether fl owage contaminated early oceanic crust in such areas

the influence of shortening and sedimentation on rejuvenation of salt diapirs a new discrete element modelling approach abstract this study employs a novel discrete element modelling approach to investigate the interplay of sedimentation with rejuvenation of diapirs by shortening the inherent complexity of salt tectonics the complications encountered when imaging structures beneath salt and the lack of outcrop analogues coupled with its importance to petroleum systems make salt tectonics one of the most interesting and debated topics in basin studies model results successfully reproduce the geometric and dynamic behaviour of active diapirism and show the effects of sedimentation thickness rate and timing on the generation of distinct diapir geometries including i salt tongues and ii squeezed upright diapirs models with late sedimentation or a lower sedimentation rate relative to salt mobility show development of asymmetric diapirs with allochthonous salt tongues whereas models with earlier sedimentation or a faster sedimentation rate generate upright squeezed diapirs early sedimentation at a moderate rate results in a symmetrical hour glass shaped structure resembling a tear drop diapir results are fully reproducible and comparable with many natural examples and include overburden deformation which is difficult to simulate using other numerical techniques extending this approach to different problems and basinal contexts could improve our understanding of deformation mechanisms and sediment distribution around salt structures

three dimensional inverse modeling of the refractive heat flow anomaly associated with salt diapirism this article introduces a technique for three dimensional inverse modeling of geothermal heat conduction through heterogeneous media the technique is used to determine the basal geometry of a diapiric salt structure found on the continental slope offshore texas salt is two to four times more thermally conductive than other sedimentary rocks the geothermal field is perturbed by the presence of salt and results in an anomaly in the heat flow through the seafloor the spatial variation pattern of the anomalous heat flow reflects the geometry of the salt body the inverse modeling obtains a model for the thermal conductivity structure that causes the heat flow anomaly observed on the seafloor the inversion algorithm systematically searches for an optimal thermal conductivity model by iteratively minimizing the misfit between the model predicted and the observed heat flow to reduce the problem of nonuniqueness the inversion incorporates a priori information constrained independently such as the upper surface geometry of the salt and the lateral extent of the salt body which can be delineated by a limited coverage of two dimensional seismic data in addition it is assumed that the thermal conductivity of the sedimentary strata surrounding the salt body is well constrained this inversion method is applied to a heat flow data set obtained over a salt structure on the texas continental slope the salt structure was first surveyed with the single channel seismic reflection which yielded the a priori information necessary the base of the salt was not imaged seismically then three dozen heat flow measurements were obtained on the seafloor over and off the salt feature the inverse heat flow modeling performed here shows that this structure is a salt tongue which has a diapiric root on one side according to the most optimal thermal conductivity model obtained the root seems to extend to 6 km below the seafloor refinement in the model geometry and additional constraints on thermal conductivities of the surrounding strata should yield a model that is more detailed and would allow more thorough geological interpretation of the salt structure

monitoring land motion due to natural gas extraction validation of the intermittent sbas isbas dinsar algorithm over gas fields of north holland the netherlands the differential interferometric synthetic aperture radar dinsar remote sensing technique has proven to be invaluable in the remote monitoring of earth surface movements associated with the extraction and geostorage subsurface injection of natural resources water oil gas however a significant limitation of this technique is the low density and uneven coverage that may be achieved over vegetated rural environments the intermittent small baseline subset isbas method an amended version of the established sbas algorithm has been designed to improve coverage over rural vegetated land cover classes by allowing for the intermittent coherence that is predominant in such areas in this paper we perform a validation of the isbas method over an area of gas production and geostorage in north holland the netherlands forty two ers 2 sar c band images 1995 2000 and 63 envisat asar c band images 2003 2010 were processed using the isbas technique and the derived measurements enabled the identification of subsidence patterns in rural and urban areas alike the dominant feature was an area of subsidence to the west of alkmaar attributed to natural gas production from the bergermeer reservoir where subsidence rates in the region of 3 mm year were measured displacements derived using linear and non linear surface deformation models were validated with respect to the first order system of levelling benchmarks which form the amsterdam ordnance datum nap it was established that isbas products were accurate to within 1 52 mm year and 1 12 mm year for the ers and envisat data sets respectively errors achieved were comparable to results using persistent scatterers interferometry psi during a validation activity carried out in the european space agency terrafirma project these results confirm the capability of the isbas method to provide a more regular sampling of land motion measurements over gas fields that may be critically used in future to infer the properties of buried fluid filled porous rock

microstructural evolution and grain boundary structure during static recrystallization in synthetic polycrystals of sodium chloride containing saturated brine the effects of brine on recrystallization in halite are well known however properties of brine such as morphology connectivity diffusivity and the resulting influences on deformation mechanisms are still a matter of debate this paper presents a microstructural study of dense statically recrystallizing synthetic polycrystalline halite containing small amounts of brine we used powders of two different grain size classes 10 m and 200 355 m the aggregates were compacted to brine filled porosities less than about 2 and annealed at room temperature without an external stress field

microfossil evidence for land movements associated with the ad 1964 alaska earthquake microfossil diatom and pollen data from a number of cores at coastal marshes at girdwood flats and kenai flats in cook inlet alaska suggest that there was a phase of gradual land subsidence prior to the main shock of the ad 1964 earthquake this phase followed a long period of gradual land uplift since the last large earthquake which occurred about 730 900 years ago caesium 137cs records indicate that subsidence started approximately 15 years before the 1964 earthquake this pre seismic subsidence is evident in the coastal marsh sediment sequences in changes in diatom and pollen assemblages that indicate changes in tidal marsh environments or a change from raised bog to marsh conditions the microfossil evidence indicates 0 15 m pre seismic land subsidence at both girdwood flats and kenai flats and co seismic subsidence of 1 8 m and 0 2 m respectively

salt geology and tectonics of selected brazilian basins in their global context this work addresses the geological and geophysical interpretation of salt structures in selected brazilian sedimentary basins from intracratonic palaeozoic evaporites in the amazon and solimoes basins to divergent margin evaporite basins formed during the mesozoic break up of gondwana there is an intriguing correlation between evaporite basins and hydrocarbon accumu lations in all the selected basins discussed the solimoes and amazonas basins developed eva porite depositing environments as the middle carboniferous sea was closing during a plate convergence phase the salt basin along the eastern brazilian and western african margins devel oped along the mesozoic rifts of the south atlantic regional seismic interpretation and potential field gravity and magnetic data over the eastern brazilian and west african margins suggest a very thick autochthonous salt layer deposited over rifted continental crust and particularly above the thick sag basin sediments over the hyperextended crust that marks the transition from continen tal to oceanic crust most of the hydrocarbon discoveries in the eastern brazilian and western african margins are in post salt turbidite and carbonate reservoirs but recent discoveries in the deepwater salt basins along the southeastern brazilian margin indicate that pre salt plays will rep resent an important contribution to hydrocarbon production in the near future