variations of hydraulic properties of granular sandstones during water inrush effect of small particle migration the evaluation of the hydraulic properties evolution of granular sandstones in relation with groundwater inrush within faults is an important issue for mining engineering applications this paper presents the results of an experimental investigation of small particle migration from granular sandstone samples under different original porosities particle size compositions and water flow pressures a new rock testing system has been setup to carry out the tests based on the results it is observed that the overall permeability evolution during the tests can be divided into four different phases including i re arrangement of large rock fragments ii water inrush with substantial particle migration iii continued moderate particles seepage and iv steady state water flow the crushing of edges and corners of large rock fragments and the evolution of the fracture network has mainly been observed in the first two phases of the tests the results indicate that the migration of small particles has an essential effect on permeability and porosity increase during water inrush through fractured sandstone the samples with higher original porosity higher percentage of fine particles in their formation and under higher water flow pressures achieve higher permeability and porosity values when the test is complete furthermore using the measured data the performances of a number of empirical models for permeability evolution in fractured porous media have been studied the prediction results indicate that not all of the fractures in a sample domain contribute in small particle migration there are parts of the fracture network that are not effective in particle flow a sample with less original porosity more fine particles and under lower water pressure shows less ineffective fractures therefore using the concept of the effective porosity fracture is sufficient enough for the flow calculation

a new toc rock eval and carbon isotope record of lower jurassic source rocks from the slyne basin offshore ireland abstract this paper presents an integrated assessment of total organic carbon rock eval pyrolysis carbonate 13 c and 18 o and total organic carbon 13 c record of upper sinemurian aalenian age from the slyne basin well 18 25 1 offshore ireland total organic carbon up to 5 2 wt and rock eval pyrolysis data highlights the portree shale formation equivalent lower middle toarcian as a mature t max 440 c source rock dominated by type ii kerogens this interval is more than 90 m thick in a previously unexplored paleogeographical domain regarding stable carbon isotopes the 13 c record shows positive values during the upper sinemurian a negative trend followed by a minor positive trend during the uppermost sinemurian lower pliensbachian a negative trend during the lowermost lower toarcian and then the return to more positive 13 c values despite the biostratigraphic uncertainty the coarse resolution of the dataset and the complex assessment of diagenetic effects we suggest that the 13 c record of the studied well records the raricostatum zone positive cie the sinemurian pliensbachian boundary event and the negative cie associated with the t oae the t oae positive cie is not clearly defined in the obtained dataset the slight post t oae negative cie recovery to more positive values and the continuation of a relatively high organic content is coeval with a regional organic matter preservation interval observed in several northern european locations these new datasets and their interpretation add to the understanding of the paleoenvironmental dynamics during the early middle jurassic in the northern european domain and opens new possibilities for hydrocarbon exploration in ireland s offshore

age and significance of sequence boundaries on jurassic and early cretaceous rifted continental margins the age and significance of sequence boundaries on jurassic to early cretaceous rifted continental margins in three ocean basins have been documented the margins are the santos basin in the south atlantic the grand banks in the north atlantic and the beaufort sea in the arctic ocean large industry data bases were used for the interpretation of each area megasequence boundaries separate the major phases of basin evolution for example syn rift and post rift boundaries developed with an average periodicity of 49 m y sequence boundaries define the component parts of each megasequence and developed with a modal periodicity of 10 15 m y out of 27 total boundary ages most 16 are developed on just one margin only two possible age ranges overlap on all three margins ighty percent of the megasequence boundaries and 50 of the sequence boundaries show a direct causal connection with coeval faulting and or folding the rest of the boundaries appear as unstructured surfaces separating transgressive and or regressive sedimentary wedges and are interpreted to result from changes in the rate of basin subsidence sediment input and long term eustatic sea level these data do not support theories advocating synchronous worldwide boundary development resulting from periodic short term falls in global eustatic sea level only in like basins of the same age with identical subsidence and sediment input rates are boundaries likely to develop synchronously hence the concept of global synchroneity of sequence boundary development may well be an illusion creat d by the similarity in age of the majority of basins studied as a result of this study it seems wise discard the global approach to basin analysis

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

annual textural banding in holocene estuarine silts severn estuary levels sw britain patterns cause and implications a high resolution textural study has been made of laminated and banded estuarine silts exposed intertidally at representative localities and horizons in the holocene deposits of the severn estuary levels the laminae on a submillimetre to millimetre scale are sharp based graded couplets formed of a lower silty part overlain by a finer textured clayey element the centimetre to decimetre scale banding is formed of laminae in alternating gradually intergrading sets of relatively coarse and relative fine grained examples at outcrop in the field the banding is recognizable because the coarse sets prove to be recessive to varying degrees under the influence of weathering and current action independent evidence at two localities points toward an annual origin for the banding at a third it arose during part of what appears to have been a relatively short period quantified physical arguments suggest that the textural banding is a response of suspended fine sediment to marked seasonal changes in sea tempe

a lateglacial and holocene organic carbon isotope record of lacustrine palaeoproductivity and climatic change derived from varved lake sediments of lake holzmaar germany abstract a composite varve dated 11 4 m long sediment sequence from lake holzmaar situated in the eifel region of western germany was investigated for total organic matter content total nitrogen content and stable organic carbon isotopes mean time resolution is 75 years for tn and 14 years for 13 c org on millennial time scales primary production of lacustrine algae strongly depends on the delivery of nutrients from the catchment the respective carbon isotope record is characterized by marked variations of 13 c org ranging from 36 0 to 27 0 and includes a number of pronounced shifts reactions of the lacustrine system and the catchment to changes of environmental parameters e g runoff solar radiation and temperature induce changes of algal associations and of lacustrine primary production which are reflected in the sediments as carbon isotope variations clear evidence of ecosystem reorganizations is detected by the carbon isotope record around 14 200 10 400 9600 5500 2700 1700 and 900 varve years bp in particular the holocene events of 9600 around 5500 and 2700 are interpreted as the expression of massive changes of the climate system the steady rise of 13 c org values during the mid holocene is interpreted as a continuous climatic amelioration reaching an optimum around 6500 varve years bp rapid and large changes of 13 c org values from 2700 varve years bp to the present indicate major disturbances in the catchment area these are most probably related to deforestation or reforestation and runoff changes presumably in conjunction with human impact carbon isotopes thus characterize the holzmaar ecosystem in time revealing lacustrine palaeoproductivity as well as providing palaeoenvironmental and palaeoclimatic information

jurassic subsidence history in the hebrides n w scotland abstract geohistory analyses have been applied to the generally well dated triassic jurassic successions of three areas in the hebrides basin north west scotland and the importance of making corrections for decompaction palaeobathymetry and eustatic changes of sea level are assessed the thermo tectonic subsidence patterns in the skye areas north suggest a three phase history of crustal stretching though only the first phase is well developed in the mull area south episodes of relatively rapid subsidence are 1 1 late triassic c210 ma until earliest toarcian 186 ma 2 2 latest toarcian 180 ma until late bathonian c161 ma 3 3 early oxfordian 154 ma until at least early kimmeridgian incomplete these are separated by toarcian 186 180 ma and latest bathonian callovian c161 154 ma episodes of either little subsidence or of uplift but at slower rates than eustatic rise of sea level the intervals between phases at 30 ma and 26 ma are remarkably similar but the wider significance of this remains to be established

a proposal for a secondary permeability index obtained from water pressure tests in dam foundations the permeability of fissured rock masses is strongly related to joint characteristics degree of jointing opening continuity and presence of weathering in fill inspection of the drill core boxes allows for estimating to the degree of jointing and opening nevertheless continuity and weathering in fill cannot be detected in this sense the rock mass quality is defined by the secondary permeability index spi the rock mass foundation can be zoned regarding different quality classes and each zone treated separately the proposed method requires the interpretation of the results from which the water pressure test effect in the test section is confirmed and the rock mass classification criteria are applied in this sense the hydrofracturing appearance has a special importance the rock mass quality of the test section obtained from spi completed with the degree of jointing of the drill core acts as a useful reference for ground treatment design finally a theoretical approximation to the maximum water injected distance reached into rock mass from the spi is suggested

the erris ridge a major geological feature in the nw irish offshore basins the erris ridge is a narrow structural high that separates the erris and rockall troughs it has a composite internal character and its orientation is thought to be controlled by a pre caledonian structural fabric which was frequently reactivated during caledonian to cenozoic time in the north it is fault bounded and probably contains rocks of palaeozoic and older age it formed a positive topographic feature which was progressively onlapped during permo triassic to cretaceous times fault reactivation occurred along its western boundary in tertiary times and it was submerged by approximately latest miocene times further south the ridge is more complex the palaeozoic and older core is flanked to the se by interpreted permo triassic to lower jurassic strata which constitute a fault controlled uplifted remnant of a half graben basin this composite structure was probably inverted during late jurassic times and remained as a topographic feature until cretaceous times it was progressively onlapped during cretaceous and tertiary times with a minor phase of fault reactivation during the early tertiary the ridge acted as a rigid block which facilitated the focusing of several phases of crustal extension in the erris trough and in the rockall trough

a comprehensive approach to karst identification and groutability evaluation a case study of the dehou reservoir sw china abstract yunnan province in sw china has one of the most developed karst terrains in china and has been historically affected by sinkholes and other instability phenomena caused by unpredictable cavity formation and well developed underground hydraulic conduits during construction of a karst seepage control reservoir project grouting of a 4 6 km long anti seepage curtain in yunnan province some typical detection methods electromagnetic and water injection tests failed to map the complex geo structural karst zones clearly resulting in considerable grout loss and excessive leakage during the grouting phase of this project to deal with this limitation a comprehensive approach including a new drilling process monitoring system borehole electrical resistivity tomography borehole sonic logging and water injection tests is employed to identify the general characterization geometry and spatial distribution of karst zones along the anti seepage curtain additionally a deep belief network dbn model replaced the empirical relationships typically used to predict the grouting quantity for groutability evaluation in karstified areas the dbn algorithm is trained by data collected using this comprehensive approach rate of penetration rock permeability resistivity and p wave velocities and two previous grouting quantities as input data the lessons learned in this case study permit us to define an effective comprehensive approach for delineating the general characterization of karst zones between two boreholes and locations of potential conduits for grout flow through the borehole the proposed dbn model can predict the grouting quantity for karst regions and the accuracy of prediction is greatly affected by previous grouting quantity rather than the collected parameters

the structure of the rockall trough imaged by deep seismic reflection profiling westline is a 450 km long near normal incidence seismic reflection profile crossing the rockall trough from the rockall bank to the irish coast beneath rockall bank and the irish shelf unreflective upper crust overlies reflective lower crust and upper mantle crustal reflectors beneath the irish shelf are interpreted as caledonian the nw slope of the trough is dissected by a series of east dipping faults forming small sediment filled half grabens the steep se slope is formed by the erris ridge the floor of the trough is formed from rotated blocks separated by mainly east dipping faults wedges of sediment fill half grabens formed by this faulting there is no evidence for oceanic crust or a 9reflection moho9 within the trough the floor and slopes of the trough are blanketed by c 4 km of parallel bedded sediments the lower part of the parallel bedded sequence is intruded by sills and dykes that do not extend above a minor unconformity it is suggested that the bulk of the sediment preserved in the rockall trough accumulated during and following a major rifting event in the early or mid cretaceous

a quantitative comparison of microfossil extraction methods from ice cores microfossil records from ice archives allow vegetation fire and land use activity reconstructions on broad spatial scales samples typically contain low microfossil concentrations therefore large ice volumes are often needed for palynology hence it is crucial to extract maximum microfossil numbers through appropriate physical chemical treatments we compare six methods covering the main water reduction procedures evaporation filtration and centrifugation with snow samples adding a known number of lycopodium marker spores prior to sample treatment and a second marker eucalyptus after laboratory processing allows a quantitative microfossil loss assessment during pollen extraction we applied the best performing method average loss of 22 to high alpine firn cores from colle gnifetti glacier for validation with a natural archive containing extremely low microfossil concentrations we conclude that samples processed with different microfossil extraction protocols may give different results for pollen concentrations percentages and ratios between different pollen types especially if vesiculate conifer pollen is an important pollen assemblage component we recommend a new evaporation based method which delivers the smallest and least variable losses among the tested approaches since microfossil losses are inevitable during laboratory procedure adding markers prior to sample processing is mandatory to achieve reliable microfossil concentration and influx estimates

palaeoecological studies of holocene lake sediments from west greenland abstract colonisation by plants and animals and subsequent biotic development in west greenland was studied by analyses of macrofossils in four holocene lake sequences one of the lake basins located near the outer coast was deglaciated shortly after the transition from the last glacial stage to the holocene and a basal date of 12 100 11 300 cal years bp was obtained two of the lake basins located near the margin of the greenland ice sheet were deglaciated several millennia later the oldest sediments contain low diversity floras and faunas some of the first immigrants were chironomidae and daphnia pulex soon followed by other insects crustaceans and other invertebrates water mosses ranunculus confervoides hippuris vulgaris and potamogeton filiformis were among the first plants that colonised the lakes the earliest holocene terrestrial flora in west greenland was probably entirely herbaceous with salix herbacea and empetrum nigrum being some of the first woody plants to arrive a number of invertebrates are new to the fossil fauna of greenland and the ostracod ilyocypris bradyi that was found in one sequence from 7000 to 6500 cal years bp has not been recorded from greenland before

granulometric characterization and evaluation of annually banded mid holocene estuarine silts welsh severn estuary uk coastal change sea level and climate abstract holocene silts salt marshes and highest intertidal supratidal peats are superbly exposed on a 15 km coastal transect which reveals two laterally extensive units of annually banded silts beds 3 7 associated with three transgressive regressive silt peat cycles early sixth early fourth millennium bc bed 3 in places is concordantly and gradationally related to peats above and below but in others transgresses older strata bed 7 also grades up into peat but everywhere overlies a discordance the banding in bed 3 at three main and two minor sites was resolved and characterized texturally at high resolution 2 5 5 mm contiguous slices using laser granulometry ls230 with pids and a comprehensive scheme of data assessment most of bed 3 formed very rapidly at peak values of several tens of millimetres annually in accordance with modelled effects of sea level fluctuations on mature marshes bed concordant and gradational and on marshes growing up after coastal erosion and retreat bed with discordant base using data from the modern severn estuary the textural contrast within bands and its variation between bands points to a variable but overall milder mid holocene climate than today the inter annual variability affected marsh dynamics as shown by the behaviour of the finely divided plant tissues present given local calibration the methodology is applicable to other tidal systems with banded silts in britain and mainland northwest europe

influence of structure and water pressure on the hydraulic conductivity of the rock mass around underground excavations abstract in this study in situ water injection tests and numerical modeling in conjunction with core logs and television image measurements were applied for an investigation of the hydraulic properties of the rock mass around underground excavations the aim of our work was to investigate the influence of rock structure and water pressure on the hydraulic conductivity of the rock mass around underground excavations thus water injection tests were conducted in four boreholes that were drilled in the rock mass in underground tunnels in china seepage connection initiation and steady state seepage were proposed to identify the seepage evolution course within the rock mass by combining the results of pressure and hydraulic conductivity generally hydraulic conductivity is strongly related to rock structure and water pressure the results also revealed that a rearrangement of rock structure would occur in the damage zone resulting in an increase in hydraulic conductivity of nearly one to several orders of magnitude the results from the modified numerical model showed that the pore water distribution and the groundwater inflow rate are affected by both the hydraulic conductivity and the thickness of the damage zone and they are influenced more by the thickness of this zone

middle holocene dry period in the northern midwestern united states lake levels and pollen stratigraphy abstract four cores from lake mendota in the yahara river valley of south central wisconsin provide pollen charcoal and sediment stratigraphic evidence of a middle holocene dry period in the northern midwest the lake level was lower between about 6500 and 3500 yr b p indicating that runoff from the upper yahara river basin may have ceased during the drier seasons of the year derived estimates of precipitation between 6500 and 3500 yr b p indicate a decrease of about 10 down to about 700 mm from the present precipitation value of 800 mm a warming between 6500 and 3500 yr b p is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr b p to quercus savanna with increased charcoal abundances after that time after 3500 yr b p a closed quercus forest and decreased charcoal suggest a cooler and wetter climate the qualitative paleoecological interpretations quantitative precipitation reconstructions based on pollen from the region including the lake mendota data and estimates of hydrologic budget based on lake level changes all show indications of a dry and warm middle holocene evidence from a large regional array of sites also supports these interpretations

particle motion and the theory of charcoal analysis source area transport deposition and sampling principles from particle motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data 1 fires within catchments of lakes often produce no record in fossil charcoal curves and 2 periods characterized by no local fire e g 20th century fire suppression often display as much charcoal as times when local fire was frequent quantitative theory on source area transport deposition and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis pollen slides for particles 5 80 m in diameter petrographic thin sections for particles 50 10 000 m diameter and charcoal diagrams the relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods charcoal recorded on pollen slides is of a size that is difficult to lift but once entrained it remains in suspension thin section charcoal is lifted at relatively low wind velocities but it is not suspended at normal surface wind speeds thermal buoyancy during fire lofts charcoal above the forest canopy depending on particle size and wind speed pollen slide charcoal sizes are underrepresented near the fire because they remain in suspension and are preferentially exported from the burn area thin section charcoal is convected to lower heights on average and is deposited nearby following fire thin section charcoal is redistributed locally by wind and thus may enter lakes because of cohesive forces and aerodynamics more pollen slide charcoal remains on the ground and less enters lakes source areas for pollen slide charcoal are subcontinental to global and diagrams of pollen slide charcoal are biased toward nonlocal charcoal they can be used to interpret importance of fire for broad spatial and temporal scales thin section charcoal represents the catchment fire regime simulation models that generate charcoal during fire mix sediments and then sample at specified intervals indicate that 1 in the absence of sediment mixing the pollen slide method should consistently resolve individual fires that occur with an expectation of 30 50 yr 2 unless samples are continuous neither method will produce useful estimates of fire frequency and 3 even a modest amount of sediment mixing will obscure the signal

a geological assessment method of floor water inrush risk and its application abstract the risk assessment of floor water inrush is essential to assure the safe production in a coal pit floor aquifuge is the key factor controlling water inrush both the impermeability and the resistance to water pressure of an aquifuge vary with its lithology and structure features with the increase of mudstone content the permeability and resistance to water pressure of the floor drops the dense tectonic fissures in floor will transform intact blocky structure into very blocky or blocky disturbed structure lower the resistance to water pressure increase the permeability of floor aquifuge and thereby will raise the risk of water inrush considering the lithology and structure features and based on a conventional water inrush coefficient a coal floor water inrush risk assessment method is put forward with fangezhuang coal mine of china as a case study the implementation of this method is elaborated

driving mechanisms of coastal change peat compaction and the destruction of late holocene coastal wetlands abstract this paper examines the role of peat compaction as a driving mechanism behind the widespread inundation of a late holocene coastal wetland in southeast england uk detailed stratigraphic and dating evidence lithology grain size foraminifera pollen and radiocarbon dates from a sample site in romney marsh documents the gradual inundation of a coastal wetland after 1263 1085 cal yr bp c 700 850 ad and the establishment of a saltmarsh shortly thereafter there was a rapid increase in water depth that was associated with the deposition of nearly 4 m of laminated intertidal mudflat and tidal channel sediments prior to site reclamation from the sea by ad 1460 grain size data and statistical analysis of sand and mud laminae thicknesses suggest the laminated sediments accumulated rapidly c 0 2 m per year as heterolithic tidal rhythmites rapid compaction of the thick peat bed that underlies the study site provided the accommodation space for their deposition this process began with the gradual tidal inundation of the site but accelerated following the widening of a breach in a coastal barrier in the 13th century compaction lowered the peat surface by at least 3 m and was associated with widespread landscape change the study demonstrates the powerful influence that compaction had on the evolution of the late holocene landscape at this site and we believe at many other coastal lowlands in northwest europe this process is likely to have been a key driving mechanism behind rapid late holocene coastal change far exceeding the longer term effects of either eustatic change or crustal uplift subsidence

jurassic sequence stratigraphy in the hebrides basin nw scotland abstract stratigraphical analysis of the triassic jurassic succession outcropping in the hebrides in terms of genetic sequences has identified seven major sequences and seven minor sequences the major sequence boundaries are defined at abrupt facies changes which usually represent deepening events often associated with a hiatus they are dated as 1 late triassic 2 mid sinemurian birchi subzone turneri zone diachronous to oxynotum zone 3 early toarcian exaratum subzone falciferum zone 4 latest toarcian aalensis subzone levesquei zone 5 late bajocian dichotoma subzone garantiana zone 6 late bathonian discus zone 7 early callovian medea subzone jason zone integrating stratigraphical with subsidence history analyses enables identification of basin tectonics as the causal mechanism for sequence boundaries 1 2 4 and 5 eustatic rises of sea level during toarcian and callovian phases of relative tectonic quiessence were the causes of sequence boundaries 3 6 and 7 late jurassic tectonic events are not reflected in the sequence stratigraphy on the basis of available data

the effect of the alteration degree of ophiolitic melange on permeability and grouting knowledge of rock alteration can be used to give a reliable zonation of a dam foundation for grouting purposes rock alteration does affect both water loss and the uptake of grout by the rock and the existence of a close connection between water loss and grout consumption has been accepted for years however the strength of this relationship is still debated and at the same time rock alteration is not considered to be possible indicator of grout consumption in this study the effect of rock alteration upon permeability and grout consumption has been investigated using the results of grouting at the yenihayat dam in turkey using a geological field study the alteration categories at the investigation area are identified and zonation of the dam site according to these categories is made the need for grouting was determined with the help of these alteration categories and these conjectures are tested using the results of injection work furthermore the relationship between water loss and grout take is investigated and a linear formula with a moderate explanatory power is established by statistical analysis the formula also has a physical interpretation this study shows that zonation according to the alteration degree can be a useful approach for grouting decisions similar studies at different sites and on different rock types are needed to verify the validity of this approach

late flandrian coastal change and tidal palaeochannel development at hills flats severn estuary sw britain an eclectic range of stratigraphical sedimentological geochemical archaeological and historical evidence relating to a tidal palaeochannel exposed at a deep erosional level in the modern intertidal zone on the avon gloucestershire border demonstrates that tidal wetlands reclaimed during the roman period ranged much further seaward than the modern coastline vigorous late medieval early modern erosion linked to the cool disturbed conditions of the little ice age forced the coastline by the mid seventeenth century to a location inland of its present line a possible medieval landing place was destroyed and it was necessary to set back the flood defences as the result of renewed mudflat marsh growth the coast at hills flats has built outward during modern times but in three distinct stages and by no means as far seaward as its likely roman position

hoek brown parameters for predicting the depth of brittle failure around tunnels a review of underground openings excavated in varying rock masstypes and conditions indicates that the initiation of brittlefailure occurs when the damage index di expressed as theratio of the maximum tangential boundary stress to the laboratoryunconfined compressive strength exceeds approx0 4 when thedamage index exceeds this value the depth of brittle failure around a tunnel can be estimated by using a strengthenvelope based solely on cohesion which in terms of thehoek brown parameters implies that m 0 it is proposed that inthe brittle failure process peak cohesion and friction are notmobilized together and that around underground openings thebrittle failure process is dominated by a loss of the intrinsiccohesion of the rock mass such that the frictional strengthcomponent can be ignored for estimating the depth of brittlefailure an essential component in designing support for theopening case histories were analyzed using the hoek brownfailure criterion with traditional frictional parameter

seasonality of modern pollen and sediment deposition in an estuarine context the severn estuary levels southwest england recent sedimentological and palynological research on subfossil holocene banded sediments from the severn estuary levels suggested seasonality of deposition registered by variations in mineral grain size and pollen assemblages between different parts of the bands here we provide data that strengthen this interpretation from sampling of modern sediments and pollen deposition on an active mudflat and saltmarsh on the margin of the severn estuary and comparison with a vegetation survey and contemporary records of climate river and tidal regimes the results of grain size analysis indicate deposition of comparatively coarse grained silts during the relatively cool and windy conditions of winter and comparatively fine grained sediments during relatively warm and calm summer months pollen analysis demonstrates the significance of long term storage of pollen grains and fern spores in the estuarine waterbody superimposed on which seasonal variations in pollen inputs from local and regional vegetation remain detectable copyright c 2007 john wiley sons ltd

the elasto plastic response of underground excavations in rock masses that satisfy the hoek brown failure criterion abstract this paper is intended to illustrate the relationship between the hoek brown parameters describing the strength of rock masses and the mechanical response of underground openings a formulation of the elasto plastic behavior of rock in terms of the hoek brown criterion is presented the analysis assumes that the joint system present in the rock mass has no preferred orientation so that the medium can be considered to behave as an isotropic continuum it is shown that appropriate scaling of the hoek brown parameters leads to considerable simplification in defining the elasto plastic response of the rock mass the classical case in which the excavation process is treated as a uniform reduction of internal pressure in symmetrically loaded cylindrical and spherical cavities is considered closed form expressions are given for the extent of plastic behavior and the related stress and displacement fields a dimensionless graphical representation of these solutions is provided that allows accurate estimates of the response of excavations in hoek brown materials to be made quickly and easily examples are given to illustrate the use of the graphs illustrative applications of the derived closed form solutions are also described the construction of ground reaction curves for the design of cylindrical tunnels according to the convergence confinement method and a case study of stability analysis of spherical cavities produced by underground nuclear explosions in french polynesian atolls are discussed

seasonality of δ13c and c n ratios in modern and mid holocene sediments in the severn estuary levels sw britain bulk organic d 13 c and c n ratios from mid holocene salt marsh deposits with sedimentary banding reveal subtle but significant differences between coarse and fine grained deposits these are consistent with findings from seasonally sampled modern silts and with the interpretation on physical and palynological grounds of the fine grained and coarse grained components as warm season and cold season deposits respectively the control is considered to be seasonal variations in the character of the organic matter supplied

the development of irish offshore sedimentary basins a variety of ensialic mesozoic and cenozoic sedimentary basins surround ireland three main periods of basin development occurred the first in the permo triassic produced a series of small rift basins which nucleated along reactivated generally caledonian structures the second in the mid and late jurassic represents a period of crustal extension and rifting the third phase reflects thermal subsidence of cretaceous and tertiary age and coincides with seafloor spreading in the north atlantic the basins developed in response to general east west extension simple extensional structures accompanied by crustal thinning dominated in the north south trending porcupine basin the ne sw oriented basins in the celtic sea slyne erris donegal and rockall areas developed in a transtensional setting until early cretaceous times the goban spur basins at the confluence of regional structural trends and adjacent to the continent ocean boundary are dominated by transtensional structures the effects of early tertiary alpine compression are seen especially in the celtic sea basins the basins whilst having some broad geological similarities which reflect eustatic sea level variations differ in their detailed evolution each basin experienced unique facets of local structural control tectonic history and facies distribution

identifying hydraulically conductive fractures with a slow velocity borehole flowmeter the u s geological survey used a recently developed heat pulse flowmeter to measure very slow borehole axial water velocities in granitic rock at a site near lac du bonnet manitoba canada the flowmeter was used with other geophysical measurements to locate and identify hydraulically conducting fractures contributing to the very slow vertical water flow in the two boreholes selected for study the heat pulse flowmeter has no moving parts and operates on the tag trace principle it is an improved version of the flowmeter developed by the water research centre in england in 1975 the u s geological survey s heat pulse flowmeter has a flow measuring range in water of 0 06 6 m min and can resolve velocity differences as slow as 0 01 m min this is an order of magnitude slower than the stall speed of spinner flowmeters the flowmeter is 1 16 m long and 44 mm in diameter it was calibrated in columns of 76 and 152 mm diameter to correspond to the boreholes studied the heat pulse flowmeter system is evalu

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

late holocene paleoecology and sedimentary history of a small lowland catchment in central england a variety of paleoecological and sedimentary techniques were used to investigate the storage of sediment within a small lowland catchment during the holocene radiocarbon dating of vertically accreted floodplain deposits allowed the calculation of inorganic accumulation rates these rates show a dramatic increase in sediment deposition during the late bronze age and early iron age 2900 2300 yr b p due to deforestation and cultivation of the catchment slopes and resultant soil erosion the soils within the catchment were susceptible to structural damage surface waterlogging and slope wash erosion from the calculated increases in sediment storage estimates of catchment erosion were made which vary from around 20 to 140 tons km 2 yr 1 the study of alluvial chronology at this scale can provide unique information on the source areas of holocene floodplain sediments and provide long term erosion rates

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

mesozoic rocks from the hebrides shelf and implications for hydrocarbon prospectivity in the northern rockall trough abstract shallow boreholes drilled in the west lewis and west flannan basins outer hebrides shelf have proved rocks of probable latest bajocian bathonian to barremian age where previously a mainly permo triassic infill has been assumed the full geological succession of the basins remains unproved although the permo triassic history of the basins may be similar the rocks encountered suggest that the basins may have dissimilar geological histories during the jurassic and early cretaceous lithologies are mainly fine grained poorly sorted sandstones or organic rich mudstones some correlation can be made with the isle of skye and the west shetland area the sandstones are poor hydrocarbon reservoirs but the middle jurassic and ryazanian mudstones although immature where drilled have excellent oil source rock potential and may have generated large amounts of hydrocarbons if they are present at depth in the adjacent northern rockall trough

the climatic significance of clastic varves in the angermanalven estuary northern sweden ad 1860 to 1950 multiple regression analyses were applied to decipher the correlation between monthly discharge precipitation and temperature records and annual varve thickness data from river angermanalven north central sweden between 1860 and 1950 over the whole 90 year period we found generally a strong correlation between spring summer precipitation and annual varve thickness however there are clear indications that precipitation during the months of january and march may was more important for the formation of varves in the early part of the twentieth century while january march april and june seem to have been more significant during the later part of the nineteenth century monthly temperatures and annual varve thickness on the other hand did not show any significant correlations over the whole 90 year period but when split into 30 year periods a dependence of varve thickness on october 1862 90 and march 1919 50 temperatures could be observed our results show that it is important to test each specific varve record against instrumental data sets before any conclusions can be drawn in terms of precipitation and or temperature dependence they also emphasize the necessity to correlate varve thickness records against long instrumental series in order to detect any changing forcing mechanisms

comparative sequence stratigraphy and structural styles of the slyne trough and hebrides basin the slyne trough to the west of ireland is divided into three sections north central and south the south and central sub basins are separated by a seismic dead zone along the line of the clew bay disturbance the central and north sub basins are separated by a zone transferring the fault bounding the main basin from the western margin in the central sub basin to the eastern margin in the north sub basin five stratigraphic sequences from the slyne trough which span the rhaetian to middle jurassic are recognized in the 27 13 1 well and they are compared to the equivalent sequences in the hebrides basin the late jurassic hebridean sequences are expected in the deeper parts of the central slyne trough the slyne trough and hebrides basin sediments are mainly tectonically controlled although major eustatic events in the early toarcian and late bathonian are recognized

the impeller meter for measuring aquifer permeability variations evaluation and comparison with other tests a knowledge of the variation of horizontal hydraulic conductivity with vertical position k z is important in understanding the transport and dispersive properties of aquifers using an impeller meter to measure the discharge distribution in a screened well while pumping at a constant rate is a promising technique for obtaining the k z function such an application is described herein and the resulting k z functions are compared with those obtained previously using tracer tests and multilevel slug tests impeller meter data were the most convenient to obtain and tracer data the most difficult the k z functions obtained by the three methods were not identical but quite similar overall this similarity between both borehole tests and the larger scale tracer test showed that nonstationary hydraulic conductivity trends in a stochastic hydrologic sense exist in the test aquifer the impeller meter method was better able to detect the higher k layers than was the multilevel slug approach overall the results suggest that a practical strategy for fitting impeller meter tracer or multilevel slug test data to a given aquifer is to use the selected testing procedure to obtain a dimensionless distribution and then a standard pumping test to measure combining both types of information enables dimensional values for k z to be calculated in low permeability aquifers or near the bottom of a test well the fluid velocity due to pumping may be below the stall velocity of an impeller thus there is a definite need for the commercial development of more sensitive flow measuring devices such as heat pulse flowmeters hess 1986 which will extend the resolution of this field method

buried salt marsh edges and tide level cycles in the mid holocene of the caldicot level gwent south wales uk combining stratigraphical sedimentological and biofacial foraminifera approaches a high resolution time constrained study has been made of a mid holocene c 5800 4900 14c yrs bp estuarine su

a review of existing methods used to evaluate the hydraulic conductivity of a fractured rock mass we review the existing methods for evaluating the hydraulic conductivity of a rock mass rock mass permeability may be assessed using empirical analytical and numerical approaches empirical methods use data from in situ field tests to derive the relationship between depth and permeability by applying a curve fitting method and establishing the relationship between hydraulic conductivity and a geological index analytical methods rely on darcy and cubic laws to estimate the permeability of a rock mass by taking into account the geometrical characteristics of the joint sets analytical equations of the flow rate into underground excavations are also developed by solving the laplace equation for homogeneous and isotropic aquifers under various boundary conditions numerical modeling can evaluate the outcomes of both empirical and analytical approaches and vice versa and can provide a sensitivity analysis of the parameters that affect rock mass permeability the importance of stress and joint set characteristics is often investigated via numerical modeling as are the scale effect and directional permeability in this review paper we provide a comprehensive review of these approaches for studying rock mass permeability we summarize the advantages and disadvantages of existing methods and highlight potential future research directions

a sediment record of barrier estuary behaviour at the mesoscale interpreting high resolution particle size analysis abstract at present limited understanding of mesoscale years decades centuries back barrier lagoon barrier estuary behaviour is a critical shortcoming for resource managers and decision makers in this paper high resolution particle size analysis of a sediment core from an intermittently open and closed barrier estuary is utilised to reconstruct a history of back barrier environmental change at mesoscale temporal resolution sediments from pescadero marsh california were analysed for their particle size distribution at consecutive 2 mm intervals down core site selection informed by a time series of maps and aerial photographs coupled with a robust core chronology ensured that the particle size data primarily reflect changing hydrodynamics of the back barrier area over the european american era 1850 to the present following more traditional plotting of particle size data and summary statistics and statistical analysis of particle size end members visual analysis and categorisation of particle size distribution curves psdcs provide an effective basis for the identification of recurring modal sizes and subpopulations these particle size windows psws are interpreted as reflecting different modes of sediment transport and deposition i e suspension and saltation loads the varying prominence of which is interpreted as being modified by barrier integrity when considered together the down core mean particle size mps trend and individual psdcs offer considerable insight into mesoscale system behaviour at subannual resolution over multiple years this behaviour is expressed in the recurrence of characteristic barrier estuarine environments closed lagoon tidal lagoon tidal marsh and open estuary and the overall barrier regime and their persistence over the last c 150 years subannual and multiannual fluctuations in back barrier environmental configuration are seen to be superimposed on a longer term quasi stable barrier regime demonstrating the value of the applied methodology with regard to bridging the estuarine evolution long term stratigraphic and process short term geomorphic knowledge bases the documented behaviour suggests a level of innate morphological resilience in the system over the long term despite episodic disturbance by high energy storms such empirical demonstrations of resilient behaviour in coastal environments are rare at the mesoscale

annually laminated lake sediments and the study of quaternary environmental changes a review abstract annually laminated lake sediments non glacial varves have in recent years been discovered in increasing abundance especially since the development of in situ freezer samplers so far the majority of examples have been found in three main areas eastern north america northern and central europe and east and central africa a much more widespread distribution seems highly probable however the formation of annual laminations in freshwater lakes is governed by a number of factors the most important of which appears to be morphometry seasonality of sediment supply which may be controlled by physical biological or even cultural processes in the lake or in its catchment is also clearly significant four main types of laminations here termed ferrogenic calcareous biogenic and clastic have so far been recorded although it is quite clear that others exist special field and laboratory techniques are needed in order that the particular properties of varved sediments may be fully exploited annually laminated sediments have so far been applied to the investigation of a number of aspects of the quaternary these include the study of a geochronology b climatic change c vegetation history especially the role of fire in forest ecosystems d the calculation of rates of sediment influx to lakes and of rates of erosion from their catchments and e the monitoring of processes in the modern environment such as heavy metal pollution eutrophication and acid rain annually laminated lake sediments combine an internal independent chronology with the preservation of discrete visible increments of seasonal and annual sedimentation given this unique property and the likelihood that many more examples will be discovered the prospects for further applications of studies of these sediments to the investigation of the quaternary seem very good indeed

characterization of damage evolution in granite under compressive stress condition and its effect on permeability abstract with the aid of 3d acoustic emission ae monitoring system the cracking process of granite under compressive stress condition and its effect on the hydro mechanical properties is experimentally studied the granite is taken from beishan area a preferable region for high level radioactive waste hlw disposal in china the experiment results suggest that the rock failure and degradation of mechanical properties are essentially related to the propagation and coalescence of induced cracks using an anisotropic damage tensor proposed by shao et al the damage evolution during the whole loading process is studied according to the experimental data it is revealed that the damage evolution is mainly initiated with the appearance of nonlinear mechanical behaviour and accelerated close to the failure point and in post peak region the estimated damage variable in lateral direction is found be globally higher than the value in vertical direction the recorded ae events indicate that cracking process of granite could be accelerated due to the existence of hydraulic pressure as a result much lower compressive strength is obtained under same effective confining pressure in hydro mechanical coupling tests a similar tendency of damage and permeability is noticed and the permeability variation in granite is found to be negligible before the coalescence of microcracks finally an empirical relation is proposed to describe the influence of damage evolution and confining pressure on permeability variation

holocene land and sea level changes in great britain analysis of more than 1200 radiocarbon dated samples that constrain relative sea levels in great britain over the past 16 000 yr provides estimates of current land level changes negative of relative sea level change maximum relative land uplift occurs in central and western scotland ca 1 6 mm yr 1 and maximum subsidence is in southwest england ca 1 2 mm yr 1 sediment consolidation arising from autocompaction as the sediment accumulates and from land drainage increases the subsidence in areas with thick sequences of holocene sediments with an average effect equivalent to at least an extra ca 0 2 mm yr 1 land subsidence but more in parts of southeast england 0 5 1 1 mm yr 1 modelled changes in tidal range during the mid to late holocene in eastern england suggest that the calculated rate of land subsidence is overestimated unless such changes are quantified the effect is most significant for large coastal lowlands the fenland and humber ca 0 5 and 0 6 mm yr 1 that were tidal embayments during the mid to late holocene

investigations of water inrushes from aquifers under coal seams in many coal mines limestone confined aquifers underlie coal seams during coal extraction from these mines water inrushes occur frequently with disastrous consequences this paper introduces the hydrogeological conditions of the coal mines and the potential water inrush disasters from aquifers under coal seams it then presents the water inrush mechanism the main factors which control water inrushes include strata pressure mining size geologic structures and the water pressure in the underlying aquifer analysis shows that reduction of confinement due to mining is the major cause of the water conducting failure in the floor strata the depth of the failure zone is strongly dependent on the mining width this paper also presents field observation results of the water conducting failure in the floor strata and applies the finite element method coupled with stress dependent permeability to analyze hydraulic conductivity enhancement due to coal extraction finally theoretical and empirical methods to predict water inrushes are given and technical measures for improving mine design and safety for coal extraction over aquifers are presented these measures include fault and fracture grouting and mining method modification such as changing long wall to short wall mining

damage induced permeability changes in granite a case example at the url in canada abstract this paper concerns both in situ measurements of permeability and numerical modelling of changes in permeability induced by microcrack growth hydraulic experiments including pulse tests with the seppi probe are in progress these tests are a part of the tunnel sealing experiment tsx at the 420 m level of canada s underground research laboratory whose aim is to estimate the in situ hydraulic properties of lac du bonnet granite based on laboratory investigations the anisotropic damage model developed by homand et al comput geotech 22 1998 135 and recently reviewed by shao et al int j rock mech min sci 36 1999 1001 has been extended in order to account for changes in permeability induced by microcrack growth we have implemented this extension in the three dimensional code flac 3 d triaxial compression tests with permeability measurements carried out on two different granites provide a verification of the numerical implementation with a good agreement between experiments and predictions comparison between in situ measurements of permeability and predictions indicates that both the results of numerical modelling and observations are globally in agreement finally numerical modelling as well as the in situ measurements indicate that a depth of 50 70 cm is a good estimation of the extent of excavation disturbed zone in the tsx tunnel

late flandrian holocene tidal palaeochannels gwent levels severn estuary sw britain character evolution and relation to shore abstract the exceptionally well exposed flandrian sediments on the welsh shores of the severn estuary reveal tidal palaeochannel networks uniquely tied to vertically stacked peat silt couplets field relationships show that channels multiplied and were enlarged as each peat organogenic marsh was rapidly transgressed replaced by and buried beneath silt mineralogenic marsh the networks infilled and shrank as the silt marsh later gave way regressively to the next peat marsh simulation and hydraulic models show that this cycle depended on an increase followed by a decrease in the tidal prism imposed on the marsh during a sea level fluctuation coupled patterns of channel width downstream orientation and coarseness of fill suggest that the many networks tied to the final flandrian peat silt couplet cycle iii ranged inland from a marsh edge lying of the order of 2 km seaward from the modern coast

varve formation and the climatic record in an alpine proglacial lake calibrating annually laminated sediments against hydrological and meteorological data processes leading to the formation of varves in proglacial oeschinensee switzerland are investigated the aim is to calibrate annually laminated sediments of the last three decades against hydrological and meteorological instrumental data results from water samples and sediment traps show that the suspended sediment in the lake is mainly distributed by underflows during the time of the largest sediment input from may to mid august this leads to the deposition of the basal silt layers of the varves settling of fine grained suspension from interflows dominates sedimentation between august and october forming the final layer of fine grained material at the end of the annual deposition cycle the median grain size at the top of the varves is always below 5 m and thus defines the varve boundaries varve thickness is a function of the annual discharge of suspended load from the catchment this is supported by evidence from hydrological and meteorological data compiled for a glaciated catchment loetschen

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

pollen studies in the junin area central peruvian andes laguna junin is a large lake 675 km long but only 4 m deep located in the grass covered altiplano at an altitude of 4 100 m northeast of lima pollen analysis of a 30 m core indicates that from about 12 000 yr ago until some time after 3 000 yr ago about 30 of the pollen was carried in by easterly winds from the east andean forests which today are at least 600 m lower in elevation contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the junin plain was dominated by local grassland types and had little contribution from this easterly source at some time after 3 000 yr ago perhaps about 1 200 yr ago the pollen influx to laguna junin from this distant forest source greatly diminished perhaps because of deforestation by increased human populations between about 12 000 and 24 000 yr ago in the junin core the sparse pollen concentration was dominated by grassland types supplemented by polylepis acaena alnus and compositae blown in from the sub puna shrublands that may have occupied much of the east andean slopes in place of the humid forest that occurs there today the silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain especially from the cordillera to the west these glaciers left a distinctive pattern of moraines and outwash fans which served to dam tine lake basin an unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago when the lake was probably dry before this time the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation recorded on the landscape by an older set of moraines and outwash fans which initially dammed the lake basin

paleoclimatic estimates from water and energy budgets of east african lakes abstract the turkana nakuru elmenteita and naivasha basins in the rift valley of east africa experienced high water levels during the period of 10 000 7000 yr b p analyses of the modern hydrologic and energy budgets for these basins along with that of lake victoria were used to infer the amount of precipitation that would have been required to maintain the enlarged paleolakes of the early holocene precipitation must have been at least 150 300 mm yr 15 to 35 above the modern average the precipitation estimates were fairly consistent among the various basins but no quantitative estimate was made for the additional precipitation required to account for overflow from the rift valley lake basins discharge from the lake victoria basin around 1880 a d was considerably above the more recent average and the increased discharge into the white nile for that period might have been similar to that of the early holocene a sensitivity analysis showed that temperature changes were probably not too important for changing the hydrologic energy budget changes of albedo bowen ratio and cloudiness were likely to have been of greater importance

between scylla and charybdis part 2 the sedimentary dynamics of the ancient early pleistocene messina strait central mediterranean based on its modern analogue abstract the 3 km wide messina strait divides sicily from the italian peninsula representing one of the most impressive examples of tide dominated marine passageway of the central mediterranean sea the tidal hydrodynamics governing the strait results from a semi diurnal phase inversion between two interlinked wider basins i e the tyrrhenian sea to the north and the ionian sea to the south due to the presence of a nodal tidal point in the centre of the strait this condition associated with coastal narrowing causes continuous water exchanges and a local phenomenon of tidal amplification producing collinear tidal currents up to 3 m s 1 in velocity in the point of tidal maxima of the strait centre currents follow bi directional patterns across the strait decelerating towards either opposite peripheries because of the progressive enlargement of the cross sectional areas tides exert a relevant influence on the strait bottom shaping characteristic erosional features governing the main sediment transport routes and promoting the migration of distinctive bedforms the textural and dimensional attributes of these bottom features vary according to the current velocity trends and main directions indicating a specific partition of the strait in individual sedimentary zones in the early pleistocene analogous conditions established across the same area and huge quantities of siliciclastic and bioclastic deposits accumulated in the ancient messina strait under a similar tidal hydrodynamics the 250 m thick strait fill succession which is magnificently exposed across the two opposite margins i e scylla and charybdis of the modern passageway represents a crucial correlative element in supporting the reconstruction of the sedimentary dynamics of the past strait based on the observation of the modern system in this work which represents the second part of a first article focused on the modern messina strait previous stratigraphic data are reviewed and integrated with new sedimentological observations carried out in both onshore and offshore key areas in particular outcrop analysis allows distinguishing a number of facies associations which are described and interpreted by taking into account the correspondent modern depositional strait setting the results of this study highlight a mutual correlation between the depositional zones detected in the modern messina strait and the individual facies associations recognised in the onshore margins the strait centre zone represented a bedload parting sector in the ancient system this zone which is one of the most difficult environment to detect in ancient straits due to a condensed sedimentary record is suggested to coincide with a structural palaeo high exposed in the southern sector of the investigated onshore area and continuing offshore in the modern strait this tectonic horst symmetrically separated two opposite highly depositional zones to the north and to the south hosting gravel and sand size siliciclastic and bioclastic deposits exhibiting diffuse motifs of large scale tidal cross stratification and a specific vertical facies stacking these characteristic tidal deposits which are believed to record the migration of several generations of tidal dunes forming extensive bedform fields in the strait reflect a tidal asymmetry between flood and ebb currents tidal asymmetry is referable to the oceanographic setting observable nowadays in the messina strait and deriving from a marked density driven water mass stratification between the two opposite flows in the ancient system tidal dunes transited down current to highly bioturbated fines including sporadic small scale tidal cross strata representing the distal periphery of the early pleistocene strait here bedforms followed migration pathways not always reflecting mutually evasive net gross sediment transport routes due to local conditions of current rotation occurring during each tidal phase inversion during these stages similar to slack water periods currents were weak enough to allow fine sediments to be settled from suspension reproducing a signature typical of other tide dominated coastal systems e g estuaries tidal flats etc these sedimentary zones of the ancient messina strait were laterally bounded by tectonically active margins where fan deltas clastic aprons and carbonate wedges developed under the constant interplay between mass transport processes and tidal currents the resulting architectural and sedimentary features observable in outcrop reveal impressive similarities with the morpho bathymetric features nowadays documented in the correspondent strait margin modern environments these considerations allow deciphering a general palaeo environmental reconstruction of the ancient strait which although suffering of limitations due to a partial preservation of the whole rock record discloses sedimentary processes and depositional environments of the ancient messina strait the process based analysis of this field based case study is crucial in predicting long term environmental changes and facies migration pathways and improves the state of knowledge on tidal straits which are the less understood among the most common tidal depositional systems

very fast environmental changes at the pleistocene holocene boundary recorded in laminated sediments of lake gościz poland abstract this paper presents a reconstruction of the climatic changes at the pleistocene holocene transition recorded in the annually laminated sediments of lake go ci a z poland this reconstruction is based on pollen stable isotope mineralogical and chemical analyses of sediments made with a time resolution of 1 4 yr it reveals a sequence of abrupt climatic changes which preceded and followed the major warming around 11 500 cal bp our data show that the warming period was preceded by a 30 yr long phase of increased winter and decreased summer precipitation 11 550 11 520 cal bp about 11 520 cal bp a very brief period of wetter conditions occurred simultaneously with the beginning of the major warming however most of the first phase of the major warming 11 520 11 500 cal bp was characterised by a generally dry climate presumably due to lowered winter precipitation our records suggest that in this phase the warming concerned winter seasons mostly in the second phase 11 500 11 460 cal bp the warming also concerned summer seasons also a distinct increase of humidity is noted in this period which caused moistening of soils and despite enhanced evaporation and evapotranspiration inhibited the process of lake level drop the following 70 years 11 460 11 390 cal bp were rather dry which caused a distinct lowering of the lake and probably also of groundwater level in this period maximum biological productivity per unit area in the lake is noted the whole sequence of phases of rather different climates was completed within a time interval 160 years spanning two human lifes only one should stress that the transitions between the consecutive phases were rather abrupt lasting no longer than 10 years

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

seasonal deposition of holocene banded sediments in the severn estuary levels southwest britain palynological and sedimentological evidence abstract banded sediments outcrop widely in the intertidal zone of the severn estuary and have been suggested on the basis of textural analysis to have formed in response to seasonal variations in sea temperature and windiness holocene 14 2004 536 here palynological and sedimentological analyses of banded sediments of mid holocene date from gold cliff on the welsh side of the severn estuary are combined to test and further develop the hypothesis of seasonal deposition pollen percentage and concentration data are presented from a short sequence of bands to establish whether textural variations in the bands coincide with variations in pollen content reflecting seasonal flowering patterns it is shown that fine grained band parts contain higher total pollen concentrations and a higher proportion of pollen from late spring to summer flowering plants than coarse grained band parts pollen in the coarser deposits appears primarily to reflect deposition from the buffering reservoir of suspended pollen in the estuarine water body and from rivers when there is little pollen in the air in winter while the finer sediments contain pollen deposited from the atmosphere during the flowering season superimposed on these background sources the potential of such deposits for refining chronologies and identifying seasonality of coastal processes is noted and the results of charcoal particle analysis of the bands presented as an example of how they have the potential to shed light on seasonal and annual patterns of human activity

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

late permian to early mesozoic rifting and sedimentation offshore nw ireland abstract a late permian triassic and early lias rift succession up to 1 km thick is revealed from offshore nw ireland sediments are preserved in deep narrow grabens from the donegal basin in the north southwestwards through the erris and slyne troughs to a series of newly defined basins collectively forming the north porcupine basin with a further structure the galway graben on the porcupine bank this line of basins superimposed on a caledonoid fractured basement underwent a complex structural evolution but since the late permian they developed primarily as a wrench modified rift system during the latest lias crustal doming west of britain may have produced a regional angular unconformity and created a source for thick middle jurassic alluvial clastics deposited in the main porcupine basin to the south early tertiary transpression of the north porcupine area caused late stage fragmentation of the basin the rift succession consists of continental red beds bounded by two dateable transgressive intervals these intervals provide valuable stratigraphic control for constraining the timing and scale of seaways propagating across the fracturing pangean supercontinent from the late permian to the early jurassic evidence is also presented for an episode of syn rift volcanism temporally unique to western britain and ireland