earth stress and reservoir quality evaluation in high and steep structure the lower cretaceous in the kuqa depression tarim basin china abstract knowledge of the state of the in situ stress field provides important insights into the petroleum engineering and geology the in situ stress orientation and magnitudes in the high and steep structure of lower cretaceous bashijiqike formation in kuqa depression were analyzed based on well log calculations and the impacts of in situ stress field on reservoir quality macroscopic reservoir properties and microscopic pore structure as well as fracture aperture were investigated the maximum horizontal stress shmax orientation was determined as nearly north south according to the image log derived drilling induced fractures and borehole breakouts the vertical stress sv shmax and minimum horizontal stress shmin magnitudes were calculated via well logs the result reveals a dominant strike slip stress regime shmax sv shmin in the bashijiqike formation in the kuqa depression the sv at the depth ranging from 5000 to 7100 m is 150 180 mpa and horizontal stresses shmax and shmin vary significantly from 130 to 210 mpa the horizontal stress difference is in the range from 40 to 70 mpa and fluid overpressures are commonly encountered the effective stress e has a positive relationship with the when the is less than 50 mpa intergranular pores can be preserved in layers with low values the microscopic pore structure will be complex and macroscopic reservoir quality will be poor with the increasing values in addition fractures are mainly corresponding with the layers where the value is low and the fracture aperture and porosity decreased significantly with the effective stress e by determining the magnitude and orientation of in situ stresses around the wellbore insights can be provided into the wellbore instability optimum drilling trajectories and reservoir quality evaluation

phase based dispersion analysis for acoustic array borehole logging data a phase based dispersion analysis method for velocity slowness extraction from guided waves recorded by an acoustic borehole logging tool in a geological formation is presented the technique consists of acquiring waveforms from an array of receivers distributed along the tool and constructing the dispersion characteristic by processing in the frequency domain and exploiting phase information to measure the travel time for each frequency component the approach is nonparametric and completely data driven and provides high resolution estimates that do not rely on velocity guesses or assumptions regarding the type of modes results are free of the aliases and spurious modes which are characteristic of some prior approaches examples of dispersion estimation curves are presented using synthesized flexural waves and field data from wireline dipole sonic tools results are compared with those from the weighted spectral semblance wss and amplitude and phase slowness estimation apes methods to demonstrate the effectiveness and utility of the proposed method

productivity controlled cold water coral growth periods during the last glacial off mauritania abstract article history received 17 june 2010received in revised form 29 october 2010accepted 11 december 2010available online 21 december 2010communicated by g j de langekeywords lopheliacold water coralscarbonate moundsbanda mound provincenw africaprimary productivity cold water corals are widely distributed along the atlantic continental margin with varying growth patternsinrelationtotheirspeci cenvironment here weinvestigatethelong termdevelopmentofcold watercoralsthat once thrived on a low latitude 17 40 n cold water coral mound in the banda mound province offmauritania duringthelastglacial interglacialcycle u thdatesobtained from20specimensofthecold watercoral lophelia pertusa revealed three distinct periods of coral growth during the last glacial at 65 to 57 kyr bp 45 to 32 kyr bp and 14 kyr bp thus comprising the cool periods of marine isotopic stages mis 2 4 thesecoral growth periods occur during periods of increased productivity in the region emphasizing thatproductivity seems to be the major steering factor for coral growth off mauritania which is one of the majorupwelling regions in the world this pattern differs from the well studied coral mounds off ireland where thecurrent regime predominantly in uences the prosperity of the cold water corals moreover coral growth offireland takes place during rather warm interglacial and interstadial periods whereas off mauritania coralgrowth is restricted to glacial and stadial periods however the on mound sedimentation patterns offmauritania largely resemble the observations reported from the irish mounds the bulk of the preservedsediments derives from periods of coral growth whereas during periods without corals hardly any netsedimentation or mound growth took place 2011 elsevier b v all rights reserved

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

n alkane and pollen reconstruction of terrestrial climate and vegetation for n w africa over the last 160 kyr abstract proxy environmental records have been obtained for the last 160 kyr from the well studied odp site 658 ca 200 km west of cap blanc n w africa 20 5 n 18 35 w 2263 m water depth this collective assessment of several terrigenous proxies lithogenic fraction n alkane content and 13 c values and pollen counts provides a better understanding of the climate and vegetation history of the n w african hinterland the results indicate that for this site beneath the main dust pathway of the saharan air layer sal the dust flux increased during dry glacial periods but the amounts of pollen and n alkanes delivered were lower in accord with the decreased density of vegetation cover of their source areas the c 4 pollen was also very low but the heavy 13 c values of the n alkanes accorded with a mainly c 4 plant origin evidently the load of sal pollen was much reduced but not the sal wind strength

paleo sea levels reconsidered from direct observation of paleoshoreline position during glacial maxima for the last 500 000 yr the drastic climatic changes which characterise the cooling trend of the last few million years of earth history led to variations in eustatic sea level that had tremendous impact on the geology and ecology of continental margins reconstructing a sea level curve back in time is not an easy task observations of shoreline positions are always a local measurement of relative sea level that needs to be corrected from the effect of tectonic and thermal subsidence sediment loading compaction and glacio hydro isostasy extensive studies have been done for the last deglaciation and for the last 100 000 yr cycle but very few studies deal with position of sea level during earlier cycles simply because conditions are very rarely favourable for the preservation of such witnesses the shelf of the golfe du lion western mediterranean reveals a unique record of shoreline paleopositions during glacial maxima of at least the last five circa 100 kyr glacial interglacial cycles in fact it is the entire glacial deltaic lobe of up to 50 m thick from delta front or shoreface to prodelta that has been preserved in place and which provides direct and independent constraints for relative sea level minima we measure a relative sea level of 112m 128 134 246 and 262 m for mis 2 6 8 10 and 12 respectively after corrections taking into account postdepositional movement of strata subsidence we find that sea level dropped to a depth of 102 6 m during the last three glaciations mis2 mis6 mis8 but reached exceptionally low values of more than 150 10 m during the preceding glaciations mis10 and mis 12 at about 340 and 434 kyr bp this general time framework and sedimentological interpretation has been confirmed by preliminary results from two deep drillings during the promess cruise july 2004 which validate our methodology however no detailed and absolute datings of such witnesses are available so far so that we cannot prove that these levels are the lowest ever reached during each glacials but they correspond undoubtedly to the last preserved shoreface before rapid sea level rise we also suggest that the abrupt change in sea level maxima might be the overprint of 400 kyr orbital periodicity cycles last but not least these results prove that the golfe du lion is indeed a unique laboratory to study paleoclimates and sea level variations on a larger time scale further work is needed for a complete glacio hydro sedimento isostatic modelling of each sequence and each glacial to further constraint local sea level versus global sea level and quantify in particular the relative effect of glacio hydro isostatic effect which differ according to ice sheet extend but also of erosion sedimentation isostatic effect erosion on land and deposition on the outer shelf and slope

tracking the last sea level cycle seafloor morphology and shallow stratigraphy of the latest quaternary new jersey middle continental shelf seafloor geomorphology and surficial stratigraphy of the new jersey middle continental shelf provide a detailed record of sea level change during the last advance and retreat of the laurentide ice sheet 120 kyr b p to present a nw se oriented corridor on the middle shelf between water depths of 40 m the mid shelf paleo shore and 100 m the franklin paleo shore encompasses 500 line km of 2d huntec boomer profiles 500 3500 hz an embedded 4 6 km2 3d volume and a 490 km2 swath bathymetry map we use these data to develop a relative stratigraphy core samples from published studies also provide some chronological and sedimentological constraints on the upper 5 m of the stratigraphic succession the following stratigraphic units and surfaces occur from bottom to top 1 r a high amplitude reflection that separates sediment 46 5 kyr old by ams 14c dating from overlying sediment wedges 2 the outer shelf wedge a marine unit up to 50 m thick that onlaps r 3 channels a reflection sub parallel to the seafloor that incises r and appears as a dendritic system of channels in map view 4 channels fill the upper portion of which is sampled and known to represent deepening upward marine sediments 12 3 kyr in age 5 the t horizon a seismically discontinuous surface that caps channels fill 6 oblique ridge deposits coarse grained shelly units comprised of km scale shallow shelf bedforms and 7 ribbon floored swales bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits we interpret this succession of features in light of a global eustatic sea level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr the morphology of the new jersey middle shelf shows a discrete sequence of stratigraphic elements and reflects the pulsed episodicity of the last sea level cycle r is a complicated marine non marine erosional surface formed during the last regression while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum wisconsin lowstand i e marine oxygen isotope stage 3 1 channels is a widespread fluvial subarial erosion surface formed at the late wisconsin glacial maximum 22 kyr b p the shoreline migrated back across the mid shelf corridor non uniformly during the period represented by channels fill oblique ridges are relict features on the new jersey middle shelf while the ribbon floored swales represent modern shelf erosion there is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession

sea level changes in the tectonically stable malay thai peninsula abstract the malay thai peninsula is part of sundaland a geological region of relative crustal stability therefore the positions of old shorelines of the past 20 000 years or so can be considered to indicate positions of actual past sea levels over 200 shoreline indicators at positions below as well as above present sea level have been radiocarbon dated these dated positions indicate that prior to 6 ka the sea rose from at least 90 m below present sea level at rates that initially amounted to 15 mm year and later became 6 mm year at ca 6 ka the rising sea surpassed its current position and at ca 5 ka it reached 5 m during this maximum marine inundation the peninsula was narrower since the low coastal plains did not yet exist in the period following this maximum transgression the available shoreline data indicate that regional sea level subsided through a series of fluctuations that were characterized by amplitudes of 2 m and periods of about 2000 years the peaks and troughs of the fluctuations became progressively lower the latest peak was at about 1 7 m or 0 7 m above present high tide a few hundred years ago the cause of these fluctuations is not yet known but the trend suggests that in the near future regional sea level may subside at annual rates between 1 5 mm and 2 mm this rate of descent is 25 to 30 of the estimated rate of sea level rise that may result from global warming in other words for the malay thai peninsula the effect of sea level rise on account of manmade greenhouse gases will be partly compensated by actual subsidence of regional sea level

late quaternary sedimentation within a submarine channel levee system offshore cap timiris mauritania aeolian and fluvial sediment transport to the atlantic ocean offshore mauritania were reconstructed based on grain size distributions of the carbonate free silt fraction of three marine sediment records of cap timiris canyon to monitor the climatic evolution of present day arid north western africa during the late pleistocene predominantly coarse grained particles which are interpreted as windborne dust characterise glacial dry climate conditions with a low sea level and extended sand seas that reach onto the exposed continental shelf off mauritania subsequent particle fining and the abrupt decrease in terrigenous supply are attributed to humid climate conditions and dune stabilisation on the adjacent african continent with the onset of the holocene humid period indications for an ancient drainage system which was discharging fluvial mud offshore via cap timiris canyon are provided by the finest end member for early to mid holocene times however in comparison to the senegal and niger river further south the river system connecting cap timiris canyon with the mauritanian hinterland was starved during the late holocene and is non discharging under present day arid climate conditions

yardang evolution from maturity to demise yardangs are enigmatic wind parallel ridges sculpted by aeolian processes that are found extensively in arid environments on earth and mars no general theory exists to explain the long term evolution of yardangs curtailing modeling of landscape evolution and dynamics of suspended sediment release we present a hypothesis of yardang evolution using relative rates of sediment flux interyardang corridor downcutting yardang denudation substrate erodibility and substrate clast content to develop and sustain yardangs corridor downcutting must exceed yardang vertical denudation and deflation however erosion of substrate yields considerable quantities of sediment that shelters corridors slowing downcutting we model the evolution of yardangs through various combinations of rates and substrate compositions demonstrating the life span suspended sediment release and resulting landscape evolution we find that yardangs have a distinct and predictable evolution with inevitable demise and unexpectedly dynamic and autogenic erosion rates driven by subtle differences in substrate clast composition

aeolian to shallow marine shelf architecture off a major desert since the late pleistocene northern mauritania abstract continental shelves off major desert regions are not expected to host substantial amounts of sediments due to long lasting and unfocused material supply and a high re mobilization potential of aeolian material this study in contrast demonstrates that significant volumes of sediments have accumulated on the northern mauritanian shelf under the arid climate conditions and prevail over consecutive climatic cycles eight late pleistocene to holocene depositional units each formed under contrasting depositional conditions are identified in high resolution seismo acoustic data and dated sediment cores these are 1 a highly differentiated pleistocene paleo landscape older than the past climatic cycle 2 a continental dune complex mis 4 3 a thick regressive shallow water clinoform late mis 3 4 a regressive to lowstand shore deposit latest mis 3 and 5 a local transgressive cover lgm to deglacial additionally 6 an open shelf highstand cover 7 an outer shelf highstand wedge and 8 mid shelf mud depocenters have formed during the holocene sea level highstand the common local offshore formation and preservation of confined stratigraphic units in particular from during mis 3 mark the interplay of a episodes of pronounced arid climatic conditions resulting in enhanced aeolian and coastal sediment input b shelf current patterns focusing sediment deposition locally and c early post depositional sediment stabilization providing protection against erosion prominent internal surfaces at 63 and 115 m modern water depths indicate widespread and intense erosional activity during late mis 3 regression and mis 2 lowstand to post lgm transgression hosting coarse shell sands and gravels from beach and shoreface paleo environments the reasons for the high preservation potential of confined stratigraphic units are a carbonaceous cementation b sediment composition massive widespread shore related gravel and shell beds with subtle minor admixtures of cohesive material and c morphological protection inside seafloor depressions and behind sheltering relief

the transition from porphyry to epithermal style gold mineralization at ladolam lihir island papua new guinea a reconnaissance study the exceptionally large gold resource at ladolam 1 300 metric tons of gold lihir island resulted from the transition of an early stage low grade porphyry gold system to a low sulfidation epithermal gold event this transition was probably triggered by rapid decompression during the partial slope failure of luise stratovolcano and accompanied by the ingress of seawater the original porphyry stage is indicated by remnant hydrothermal breccia clasts of strongly biotite magnetite altered monzodiorite with disseminated pyrite chalcopyrite and poorly developed pyrite quartz stockwork veins the breccias are overprinted by biotite magnetite alteration and their matrix is strongly mineralized with disseminated auriferous pyrite the breccias are cut by late stage epithermal quartz chalcedony illite adularia pyrite veins and associated illite adularia alteration that locally contain bonanza gold grades of up to 120 g t isotope data suggest a magmatic source of sulfur in the gold bearing fluids at ladolam electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00126 001 0230 y

bayesian geoacoustic inversion of single hydrophone light bulb data using warping dispersion analysis this paper presents geoacoustic inversion of a light bulb implosion recorded during the shallow water 2006 experiment the source is low frequency and impulsive the environment is shallow water and the acoustic signal is recorded using a single receiver in this context propagation is described by modal theory and inversion is carried out by matching modal dispersion curves in the time frequency domain experimental dispersion curves are estimated using an advanced signal processing method called warping allowing inversion to be carried out at a relatively short range 7 km moreover the inversion itself is performed using bayesian methodology this allows inference of the seabed structure from the data including the number of seabed layers resolved optimal estimates of the seabed parameters and quantitative uncertainty estimates inversion results of the experimental data are in good agreement with both ground truth and estimates from other experimental data in the same region

the senegal river mud belt a high resolution archive of paleoclimatic change and coastal evolution abstract fine grained sediment depocenters on continental shelves are of increased scientific interest since they record environmental changes sensitively a north south elongated mud depocenter extends along the senegalese coast in mid shelf position shallow acoustic profiling was carried out to determine extent geometry and internal structures of this sedimentary body in addition four sediment cores were retrieved with the main aim to identify how paleoclimatic signals and coastal changes have controlled the formation of this mud depocenter a general paleoclimatic pattern in terms of fluvial input appears to be recorded in this depositional archive intervals characterized by high terrigenous input high sedimentation rates and fine grain sizes occur roughly contemporaneously in all cores and are interpreted as corresponding to intensified river discharge related to more humid conditions in the hinterland from 2750 to 1900 and from 1000 to 700 cal a bp wetter conditions are recorded off senegal an observation which is in accordance with other records from nw africa nevertheless the three employed proxies sedimentation rate grain size and elemental distribution do not always display consistent inter core patterns major differences between the individual core records are attributed to sediment remobilization which was linked to local hydrographic variations as well as reorganizations of the coastal system the senegal mud belt is a layered inhomogeneous sedimentary body deposited on an irregular erosive surface early holocene deceleration in the rate of the sea level rise could have enabled initial mud deposition on the shelf these favorable conditions for mud deposition occur coevally with a humid period over nw africa thus high river discharge sedimentation started preferentially in the northern areas of the mud belt during mid holocene a marine incursion led to the formation of an embayment afterwards sedimentation in the north was interrupted in association with a remarkable southward shift in the location of the active depocenter as it is reflected by the sedimentary architecture and confirmed by radiocarbon dates these sub recent shifts in depocenters location are caused by migrations of the senegal river mouth during late holocene times the weakening of river discharge allowed the longshore currents to build up a chain of beach barriers which have forced the river mouth to shift southwards

rapid rise of sea level 19 000 years ago and its global implications evidence from the irish sea basin supports the existence of an abrupt rise in sea level meltwater pulse at 19 000 years before the present b p climate records indicate a large reduction in the strength of north atlantic deep water formation and attendant cooling of the north atlantic at this time indicating a source of the meltwater pulse from one or more northern hemisphere ice sheets warming of the tropical atlantic and pacific oceans and the southern hemisphere also began at 19 000 years b p these responses identify mechanisms responsible for the propagation of deglacial climate signals to the southern hemisphere and tropics while maintaining a cold climate in the northern hemisphere

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

application of the maximum likelihood method mlm for sonic velocity logging modern digital sonic tools can record full waveforms using an array of receivers the recorded waveforms are extremely complicated because wave components overlap in time conventional beamforming approaches such as semblance processing while robust sometimes do not resolve the interfering wave components propagating at similar speeds such as multiple compressional arrivals due to the formation alteration surrounding the borehole here the maximum likelihood method mlm a high resolution array processing algorithm is modified and applied to process borehole array sonic data extensive modifications of the original mlm algorithm were necessary because of the transient character of the sonic data and its effect upon the spectral covariance matrix we applied mlm to several array sonic data sets including laboratory data synthetic waveforms and field data taken by a schlumberger array sonic tool mlm s slowness resolution is demonstrated in resolving a secondary compressional arrival from the prima

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

climate and sea level induced turbidite activity in a canyon system offshore the hyperarid western sahara mauritania the timiris canyon a major outcome from studying the sedimentary archives of the timiris canyon off mauritania is that climate shifts in the saharan hinterland not only influenced offshore pelagic sedimentation processes but also controlled turbidite activity in the canyon system sediment supply to the slope predominantly by eolian dust and remobilised eolian sands was greatest during hyperarid glacial and deglacial periods and due to overall increased trade wind strengths upwelling induced pelagic productivity attained highest magnitudes turbidite activity in the timiris canyon responded rapidly to these shifts in the surrounding sedimentary regime on the continental slope during high glacial and early deglacial times the tributary gullies on the uppermost slope were rapidly and repetitively filled subsequently turbidity currents were released and large turbulent flows passed through the lower timiris canyon leading to overspill sequences on its levees in addition to this scenario partial flooding of the exposed outer shelf during successive sea level rises in mis 3 may have caused re mobilization of huge aeolian dune fields that had expanded close to the shelf edge during glacial exposure during the holocene no turbidite activity is recorded in the lower timiris canyon whereas a core from a widened area in the upper timiris canyon reveals an interesting climate controlled 900 year cyclicity of carbonate and mud turbidite events throughout the holocene

modern heterozoan carbonates from a eutrophic tropical shelf mauritania abstract heterozoan or foramol production is typical in extratropical carbonate sedimentary systems however under mesotrophic to eutrophic conditions heterozoan carbonates also form in tropical settings but such heterozoan tropical sedimentary systems are poorly understood nevertheless distinction between tropical and extratropical heterozoan carbonates in ancient successions is crucial for accurate paleoenvironmental and paleoclimate reconstructions here surficial holocene and pleistocene sediments of the northern mauritanian shelf are studied as an example of a tropical eutrophic carbonate depositional system 11 g l 1 chl a chlorophyll a upwelling nutrient rich waters push onto the wide mauritanian shelf where they can warm up to in excess of 25 c this condition favors production of heterozoan carbonates dominated by bivalves and foraminifers even in this tropical setting in addition sediments are provided by eolian input from the desertic hinterland the resulting sediments are carbonate and mixed carbonate siliciclastic facies in which the carbonates are characterized by a mixture of tropical and cosmopolitan taxa benthic photosynthetic biota are absent while suspension feeding organisms are dominant this foramol grain association on a shelf scale is reminiscent of cool water carbonates therefore recognition of warm water heterozoan carbonates relies on key taxa related to tropical waters within the biota assemblages associated with a highly productive environment

storm driven bottom sediment transport on a high energy narrow shelf nw iberia and development of mud depocenters bottom sediment transport on the nw iberian shelf was monitored during a downwelling storm in september 2014 collected data was analyzed and fed into a 3d coastal ocean model to understand storm driven sediment transport on the shelf and its impact on mid shelf mud depocenters mdcs a significantly enhanced level of bottom sediment resuspension nearly two orders of magnitude higher than that in the pre storm period was recorded at the mooring site field data analysis reveals that it was induced by a short lasting strong bottom current in combination with enhanced wave current interaction simulation results indicate that this strong current was part of a coastal jet resulted from downwelling an across shelf horizontal density gradient as high as 0 32 g m4 occurred at the interface between the downwelling and the bottom waters forming a remarkable front due to buoyancy effect the downwelling water was mostly confined to the coast with a depth limit of 80 m in the south and 120 m in the north of the region resulting in a northward directed coastal jet simulation results suggest that during the storm local near bottom sediment suspensions with concentrations on the order of 10 kg m3 would be triggered by wave current interaction and flow convergence associated with the front direct impact on the development of mdcs by transport and deposition of concentrated sediment suspensions is indicated by model results the seaward limit of the front coincided with the shoreward edge of the mdc nucleus suggesting the front as a primary control on the deposition of fine grained sediment this article is protected by copyright all rights reserved

recurrent decadal scale dust events over holocene western africa and their control on canyon turbidite activity mauritania abstract sediment records from continental shelves and slopes might provide paleoenvironmental information in the highest temporal resolution but are often hampered due to strong erosional and reworking processes here we present a holocene sedimentary record from an exceptional shelf mud belt depocenter off northern mauritania compared to a second sediment core located inside a large canyon system at the adjacent continental slope both records are of outstandingly continuous and highest temporal resolution 9 a cm and are investigated by sedimentological and geochemical methods a series of sharply defined recurrent dust peaks is preserved in the shelf archive each event has lasted for a single decade only and seems to coincide with an individual turbidite bed in the canyon a joint mechanism should thus be responsible for both of these deposits and we suggest a regional atmospheric trigger only short lasting trade wind strengthening would cause such pronounced aridity over western saharan africa the effect would be massive dust export to shelf and slope recently developed high resolution aridity and humidity records from western africa support the existence of these events over the holocene and identify them as being controlled by the atlantic system as far south as 19 n

post glacial filling of a semi enclosed basin the arguin basin mauritania semi enclosed basins are not very common features in the world and are most frequently the result of tectonic movements studies of their filling are usually based on the micropaleontological analyses of sediment cores torgersen et al 1988 reeves et al 2007 or seismic analyses lykousis et al 2007 cagatay et al 2009 van daele et al 2011 the morphology of semi enclosed basins is generally simple and bowl shaped and their edges are marked by one or more sills their depths range from a few dozen to several thousand meters semi enclosed basins are however present in some regions in the world the semi enclosed basin of the golfe d arguin northwest africa is present on a wide shallow shelf bordering the sahara desert in a stable tectonic context its sedimentary filling took place during the end of the post glacial transgression the current knowledge on sedimentary filling of semi enclosed basins is rather limited and inadequate to fully understand the processes at play three campaigns have allowed the creation of the first morpho bathymetric map of the golfe d arguin shedding new light on its large scale morphology a series of rocky shoals banc d arguin interrupted by two sills in the north and south divides the shelf into two parts the inner and outer the inner part of the golfe d arguin called the arguin basin forms a shallow semi enclosed depression the basin is situated on the stable west african margin and the lack of any vertical tectonic movement provides an ideal situation for studying the progradation regression variations and the sediment depositional conditions caused by the post glacial sea level changes based on the analysis of very high resolution seismic data seven units were identified the sedimentary sequence of deposition of the arguin basin was interpreted in relation to the bedrock morphology the sea level rise and the climatic changes their chronology was established in comparison to the regional sea level curve basin physiography and unit distribution the arguin basin is interpreted as a land locked freshwater lake during the post glacial sea level rise corresponding to wet climatic conditions the inner part was flooded ca 8 7 ka bp when the sea level reached the sills the filling then corresponded to a marine estuarine environment the climatic aridification and the sea level stabilization from 6 5 ka bp onwards allowed the deposition of the last units which are composed of aeolian sand combined with a significant marine biogenic carbonate fraction bedrock morphology plays a major role in determining the depositional sequence architecture it controls the available accommodation space and in conjunction with climate changes influences the environmental processes that shape the deposit geometry

coastal evolution in senegal and mauritania at 103 102 and 101 year scales natural and human records abstract previous works have shown that the range of marine level eustatic changes on the coast of the senegalo mauritanian basin after 5500 bp must have been relatively small on the basis of regional geological mapping this position is confirmed in two littoral regions in mauritania baie de saint jean cape timiris and in senegal saloum delta the evolution of the shoreline is linked mainly to the balance between deposition and reworking by the sea in mauritania the reworking capacity is high before 4000 bp under a more humid climate than the present one it becomes insufficient around 3000 bp as areas of aeolo marine progradation develop in the sebkhas at the inner part and the shorelines of the baie de saint jean the deposits are subjected to a constant sea level and are therefore formed by the rhythm of recurrent aridity crises on the millenary or the centenary scale in the saloum delta the evolution of the shoreline results from several processes involving more varied timescales an essential factor is the positioning of littoral sand barriers shaped like long sandy spits which divert the flow of the river towards the south and are arranged according to a basal surface also adjusted to a constant sea level the development of sand barriers such as the present sangomar spit and also the langue de barbarie occurs at a centennial rhythm higher probability events at the decade scale are likely to perturb this development by inducing gaps in the sand barrier and as the river goes beyond the sand barrier the latter becomes incorporated in the deltaic plain forcing the littoral drift to build a new sand barrier further forward these events are linked to a conjunction of factors involving different timescales aridity crises at the 10 3 or 10 2 year scales sedimentation waves at the 10 year scale seasonal exceptional swells river floods variations of the tidal range determined by modifications in the estuarian morphology

deciphering signals of late holocene fluvial and aeolian supply from a shelf sediment depocentre off senegal north west africa high resolution climatic records of the late holocene along the north west african continental margin are scarce here we combine sediment grain size elemental distribution and mineral assemblage data to trace dust and riverine sources at a shallow marine sediment depocentre in the vicinity of the senegal river mouth the aim is to understand how these terrigenous components reflect climate variability during the late holocene major element contents were measured and mineral identification was performed on three sub fractions of our sediment core i fluvial material 2 m ii aeolian material of 18 63 m and iii a sub fraction of dual origin material of 2 18 m results show that more than 80 of the total al and fe terrigenous bulk content is present in the fluviogenic fraction in contrast ti k and si cannot be considered as proxies for one specific source off senegal the al ca ratio recording the continental river runoff reveals two dry periods from 3010 to 2750 cal a bp and from 1900 to 1000 cal a bp and two main humid periods from 2750 to 1900 cal a bp and from 1000 to 700 cal a bp the match between i intervals of low river runoff inferred by low al ca values ii reduced river discharge inferred by integrated palynological data from offshore senegal and iii periods of enhanced dune reactivation in mali confirms this interpretation copyright 2011 john wiley sons ltd

numerical computation of individual far field arrivals excited by an acoustic source in a borehole in this paper i model the acoustic logging problem and numerically compute individual arrivals at far field receivers the ability to compute individual arrivals is useful for examining the sensitivities of each arrival to various factors of interest as opposed to examining the full waveform as a whole while the numerical computation of the mode arrivals peterson 1974 and the numerical computation of the first head waves tsang and rader 1979 have been previously reported the numerical computation of the entire set of head wave arrivals is new and is the major contribution of this paper following roever et al 1974 and others the full wave field is represented as a sum of contributions from both poles and branchcuts in the complex wavenumber plane the pole contributions correspond to mode arrivals while the branch cuts are associated with the body waves i e head waves both the pole and branch cut contributions are computed numerically and results are presented for the cases of a slow an

ge distribution in the wulantuga high germanium coal deposit in the shengli coalfield inner mongolia northeastern china abstract the geological and geochemical controls of the ge distribution in the cretaceous wulantuga high germanium coal deposit in the shengli coal field inner mongolia are investigated this paper focuses mainly on the spatial distribution of the ge contents in coal the high ge coals mainly occur in three splits of the 6 coal in the southwestern part of the shengli coal field mean germanium contents in the coal range from 32 to 820 g g with a mean value of 137 g g on a bulk coal basis mean of 939 coal samples from 75 boreholes in the 6 coal seam in an area of 2 2 km 2 the highest ge content occurs sw of 6 coal seam close to the margins of the coal basin decreasing with a fan shaped trend towards nw the direction of the coal basin there is an negative correlation between the mean ge content and the thickness of the coal seam different distribution patterns of ge content were found in vertical profiles high ge concentrations may occur in the middle parts of coal seams at the bottom and or the top of thick coal seams and inconspicuous variation a major organic affinity was determined for ge with a special enriched in the banded bright and semibright coal the high ge coals and the coalified wood in the sandstone overlaying the 6 1 coal highly enriched in ge as sb w cs tl be and hg the late jurassic silicified volcanic rocks in the nw of the ge coal deposit relatively high enriched in ge ga sb as cs be ge and hg the correlation coefficients among the elements enriched showed marked variations at close sites in this deposit suggesting a possible diagenetic origin of the geochemical anomaly the main ge anomaly was attributed to early cretaceous hydrothermal fluids circulating through the fault systems and porous volcanic rocs probably from the subjacent granitoid rocks the fault systems the porous coarse clastic rocks overlying coal seam and the lithotype of coal played an important role in the transport and trapping of ge a main diagenetic origin overlapping a slight synsedimentary accumulation is deduced for the ge anomaly

germanium geochemistry and mineralogy abstract germanium is enriched in the following geologic environments 1 1 iron meteorites and terrestrial iron nickel 2 2 sulfide ore deposits particularly those hosted by sedimentary rocks 3 3 iron oxide deposits 4 4 oxidized zones of ge bearing sulfide deposits 5 5 pegmatites greisens and skarns and 6 6 coal and lignitized wood in silicate melts ge is highly siderophile in the presence of native iron nickel otherwise it is highly lithophile among silicate minerals ge is concentrated in those having less polymerized silicate tetrahedra such as olivine and topaz in deposits formed from hydrothermal solutions ge tends to be enriched mostly in either sulfides or in fluorine bearing phases it is thus concentrated both in some hydrothermal sulfide deposits and in pegmatites greisens and skarns in sulfide deposits that formed from solutions having low to moderate sulfur activity ge is concentrated in sphalerite in amounts up to 3000 ppm sulfide deposits that formed from solutions having higher sulfur activity allowed ge to either form its own sulfides particularly with cu or to substitute for as sn or other metals in sulfosalts the ge in hydrothermal fluids probably derives from enrichment during the fractional crystallization of igneous fluids or is due to the incorporation of ge from the country rocks particularly from those containing organic material germanium bonds to lignin derivative organic compounds that are found in peat and lignite accounting for its common concentration in coals and related organic material germanium is precipitated from water together with iron hydroxide accounting for its concentration in some sedimentary and supergene iron oxide deposits it also is able to substitute for fe in magnetite in a variety of geologic environments in the oxidized zone of ge bearing sulfide deposits ge is concentrated in oxides hydroxides and hydroxy sulfates sometimes forming its own minerals it is particularly enriched in some iron and manganese bearing oxides and hydroxides including goethite up to 5300 ppm and hematite up to 7000 ppm

fluvial system dynamics of sudano sahelian zone during the late holocene the yame river dogon country mali abstract in west africa most palaeoenvironmental studies have focused on the role of climatic change on the environment because of the richness of its deposits the yame river mali a tributary of the niger river offers an opportunity to reconstruct the evolution of this fluvial system in comparison with both climatic and anthropogenic changes during the late holocene to investigate more closely the spatio temporal response of the fluvial system sedimentary analyses were conducted on seven reaches distributed along the 137 km length of the yame valley this approach testifies of the possibility for each time slice and river reach 1 to reconstruct the fluvial style and processes and 2 to estimate the sediment storage volume reflecting sediment distribution patterns results reveal a wide variability of the sedimentary cascade suggesting contrasting responses to external and local controls humid 4200 2900 cal bp 450 24 cal bp or arid 2350 1700 cal bp phases have been recorded in fluvial archives while an intensification in erosion and sediment supplies even during the arid period 2900 2350 cal bp and the 20th century may be associated with an increase in human pressure two other periods are related to both climate and anthropogenic factors during 1700 1400 cal bp phase huge sediment supplies can be explained mainly by the reactivation of both hydrological processes and human occupation after an intense and long arid event dispersed sediment sinks recorded during the 450 24 cal bp period originate from the combination of intensification of colluvial processes and a wet phase context originating from global climatic change thus this study provides evidence that climate is the strongest driver for the fluvial response of these semi arid and tropical rivers while human disturbance appear as a secondary factor due to the high sensitivity of the environment to climate variability in such areas

genetic environment of germanium bearing gold silver vein ores from the wolyu mine republic of korea the wolyu mine is one of the largest vein type gold silver bearing epithermal systems in the youngdong district and is the first gold silver deposit in korea found to contain significant germanium in the form of argyrodite ag8ges6 mineralized veins 78 9 1 2 ma crosscutting late cretaceous hostrock tuff and quartz porphyry 81 5 1 8 ma consist of three stages of quartz and carbonates the first of which contains pyrite basemetal sulfides and au ag minerals stage i au ag ge mineralized veins show a systematic variation of mineral assemblage with time 1 quartz pyrite 2 quartz pyrite sphalerite electrum argentite 3 carbonate quartz sphalerite electrum argentite 4 carbonate native silver argentite ag sulfosalts argyrodite sphalerite calculated values of temperature and sulfur activity are assemblage 1 360 280 c and 10 7 10 10 2 280 210 c and 10 10 10 14 3 210 180 c and 10 14 10 16 4 180 155 c and 10 17 10 18 these data the frequent association of gold with sulfides and the abundance of pyrite in alteration zones indicate that decreasing sulfur activity and cooling were important in triggering gold deposition hydrogen and oxygen isotope compositions of ore fluids display a systematic variation with increasing time within the main ag au ge mineralization d and 18o values decrease with the transition from quartz to carbonate deposition from 78 and 2 8 to 90 and 8 7 respectively indicating increasing involvement mixing of less evolved meteoric water which resulted in progressive cooling and dilution of ore fluids in the shallow 370 600 m wolyu epithermal system

the upwelling area off northwest africa a description of phenomena related to coastal upwelling abstract this paper presents a brief review of the oceanography along the upwelling coast of northwest africa the description contains information on seasonal variations of large scale winds ocean circulation and some gross of features of the hydrography characteristic meso scale patterns of currents during the upwelling season between 16 n and 26 n air and water temperature differences during upwelling season diurnal and semi diurnal variations of temperature atmospheric pressure wind and current regional peculiarities canyons and the banc d arguin

late pleistocene and holocene dune activity and wind regimes in the western sahara desert of mauritania the western sahara desert in mauritania is dominated by extensive sand seas consisting largely of linear dunes analyses of landsat images geomorphic and stratigraphic studies and optically stimulated luminescence dating of dunes in the azefal agneitir and akchar sand seas provide evidence that three main generations of dunes were formed during the periods 25 15 ka centered around the last glacial maximum 10 13 ka spanning the younger dryas event and after 5 ka the wind regimes that occurred during each of these periods were significantly different leading to the formation of dunes on three distinct superimposed trends northeast north northeast and north and the development of the sand seas as composite geomorphic features

a late quaternary sedimentary shelf system under hyperarid conditions unravelling climatic oceanographic and sea level controls golfe d arguin mauritania nw africa abstract the sedimentation on the mauritanian shelf off the western saharan desert is strongly influenced by dust supply and is investigated in this study by combining surface mapping shallow acoustic profiling and the analysis of sediment cores coarse grained carbonates dominate wide areas of the open shelf at places where the shelf is exposed to the atlantic ocean the sheltered golfe d arguin in contrast is characterized by muddy shoals in its inner area and locally restricted and wedge shaped muddy depocenters which extend contour parallel in mid shelf settings in both cases cross shelf currents control sediment distribution and accumulation not location or amount of primary eolian input a major discontinuity on the outer shelf is located in 85 110 m water plus sediment depth and is refilled by a sedimentary facies succession of shoreface tidal and open shelf deposits this succession has formed during temporary lower sea levels along the last overall regression mis 4 and mis 3 the last glacial maximum and during the past deglacial sea level rise significant sediment deposition and preservation is limited to very restricted areas concerning the overall shelf architecture sea level was the main factor enabling or suppressing deposition in terms of 1 creating local erosional swales which have favored subsequent trapping and preservation of sediments 2 determining the type of sedimentary facies refilling these depressions under a variety of nearshore conditions 3 interacting with the seafloor morphology and by this controlling timing of initiation and growth geometry of mud wedges these mud wedges have formed since ca 9 cal ka under a continuous sedimentation regime these bodies must have formed in hydraulic equilibrium but they are detached from a defined sediment point source which is in contrast to common mudbelt formation on shelves in general sediment storage on shelves under hyperarid conditions seems to be very limited due to comparably low sediment input strong ravinement activity during changing sea levels significant bypassing and winnowing processes and a low preservation potential of the non cohesive materials these conditions lead to the development of almost sediment starved systems with low subsidence rates over longer geological timescales

simulated climate and biomes of africa during the late quaternary comparison with pollen and lake status data new compilations of african pollen and lake data are compared with climate ccm1 ncar boulder and vegetation biome 1 2 gsg lund simulations for the last glacial maximum lgm and early to mid holocene emh the simulated lgm climate was ca 4 c colder and drier than present with maximum reduction in precipitation in semi arid regions biome simulations show lowering of montane vegetation belts and expansion of southern xerophytic associations but no change in the distribution of deserts and tropical rain forests the lakes show lgm conditions similar or drier than present throughout northern and tropical africa pollen data indicate lowering of montane vegetation belts the stability of the sahara and a reduction of rain forest the paleoenvironmental data are consistent with the simulated changes in temperature and moisture budgets although they suggest the climate model underestimates equatorial aridity emh simulations show temperatures slightly less than present and increased monsoonal precipitation in the eastern sahara and east africa biome simulations show an upward shift of montane vegetation belts fragmentation of xerophytic vegetation in southern africa and a major northward shift of the southern margin of the eastern sahara the lakes indicate conditions wetter than present across northern africa pollen data show an upward shift of the montane forests the northward shift of the southern margin of the sahara and a major extension of tropical rain forest the lake and pollen data confirm monsoon expansion in eastern africa but the climate model fails to simulate the wet conditions in western africa

estimating slowness dispersion from arrays of sonic logging waveforms acoustic wave propagation in a fluid filled borehole is affected by the type of rock which surrounds the hole more specifically the slowness dispersion of the various body wave and borehole modes depends to some extent on the properties of the rock we have developed a technique for estimating the dispersion relations from data acquired by full waveform digital sonic array well logging tools the technique is an extension of earlier work and is based on a variation of the well known prony method of exponential modeling to estimate the spatial wavenumbers at each temporal frequency this variation known as the forward backward method of linear prediction models the spatial propagation by purely real valued wavenumbers the prony exponential model is derived from the physics of borehole acoustics under the assumption that the formation does not vary in the axial or azimuthal dimensions across the aperture of the receiver array but can vary arbitrarily in the radial dimension the exponential model fits

late holocene morphodynamics in the littoral zone of the iwik peninsula area banc d arguin mauritania abstract in the littoral zone of the banc d arguin both littoral sedimentary units and man made deposits shell middens abound they were formed during the late holocene after the final onset of the post glacial transgression here a geo archaeological approach is used to study them the geomorphological and sedimentological characteristics of the coastal features define two distinct coastal sedimentary units in the iwik aouatil zone between an ancient shoreline which formed on the tafaritian substratum ca 6 7 5 7 cal ka bp and the present one i very extensive sand flats and ii linear relief features both covered by a thin veneer of anthropogenic anadara senilis shell middens they developed under a stable sea level regime the sand flats expanded at variable rates throughout the period the linear relief features represent beach barriers and coastal dunes which can be dated archaeologically thanks to the superimposed shell middens supplemented by 14 c dating two series of linear sedimentary units are identified first a complex north south system of dunes and hook ended sand barriers developed from 4 8 to 4 1 cal ka bp and secondly two regular and linear beach barriers developed between 3 7 and 3 3 cal ka bp their morphological characteristics suggest that they were generated through littoral drift processes directional changes observed between the first and the second groups demonstrate that the wave refraction pattern was dramatically modified after the closure of the strait between the former iwik island and the land a comparison with the nearby jerf el oustani coastal area in the late holocene shows that both sites shared similarities in depositional patterns but also differences in the chronology of the sedimentary units processes involved in the development of the linear units are indicative of the enhancement of both sand influx and longshore drift due to climatic change

on the geological availability of germanium based on a detailed statistical analysis of chemical data published in the scientific literature estimates were made of the minimum amounts of recoverable ge contained within sulphidic zinc ores and coals given current processing technologies it is expected that at least 119 kt 7 kt in zinc ores and 112 kt in coal of recoverable germanium exist within proven reserves at present stage of knowledge at grades in excess of 100 ppm in sphalerite and 200 ppm in coal while at least 440 kt 50 kt in zinc ores and 390 kt in coal should become recoverable in the future being associated to coal reserves at 8 200 ppm ge and zinc resources containing in excess of 100 ppm ge in sphalerite mississippi valley type mvt deposits are expected to be the most important hosts of germanium rich sphalerite while both brown and hard coals are expected to be equally important as hosts of germanium the approach taken in this publication shows that reliable minimum estimates for the availability of by product metals lacking suitable reserve resource data may be attained by using robust statistical methods and geochemical data published in the scientific literature

mid to late quaternary environments and stratigraphy of the southern sierra leone shelf west africa the middle to upper quaternary succession of the southern sierra leone shelf appears to have been deposited in response to three glacial sea level cycles the last of which has left the most complete sedimentary record the unconformable base of the succession is deeply incised off larger rivers inshore but has little relief toward the shelf break this difference results from the steep gradient of the inner shelf and the gentle gradient of the valley9s long profile incision was caused by high fluvial discharge during sea level fall decline of discharge and sediment supply during and after glacial maximum resulted in cessation of incision and in the formation of cemented beach ridges at the shelf break the lowstand wedge of the last glacial cycle is well developed beyond the shelf break and where the pre existing shelf was deep where sampled it is deposited below wave base its preservation is apparently the result of protection from wave and shelf current action during regression the subsequent transgressive wedge entirely dominates shelf deposition infilling incised valleys and contains vertically stacked fluvial estuarine littoral and sub littoral elements it is thin or absent beyond the shelf as a result of active oceanic currents hindering sedimentation active oceanic currents also result in only weak development of the highstand wedge energy regime as represented by moderate shelf currents and variable fluvial discharge has been the fundamental control on sediment architecture sediment supply has been of only secondary importance

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

borehole flexural modes in anisotropic formations a perturbation method of solution is an efficient way of analyzing elastic wave propagation along a borehole in anisotropic formations the perturbation model allows us to calculate changes in the modal dispersion curves caused by the differences in elastic constants between the anisotropic formation of interest and a reference or unperturbed isotropic formation the equivalent isotropic constants in the reference formation are obtained from the appropriate compressional and shear wave velocities for the selected propagation and polarization directions of the flexural mode this choice of the unperturbed solution means that the required perturbation is minimal resulting in enhanced accuracy of the perturbed solution computational results are presented for the dispersion curves of borehole flexural waves in a transversely isotropic ti formation as a function of borehole deviation from the ti symmetry axis in addition radial distributions of displacement and stress fields associated with the flexura

mapping formation radial shear wave velocity variation by a constrained inversion of borehole flexural wave dispersion data we have developed a novel constrained inversion method for estimating a radial shear wave velocity profile away from the wellbore using dipole acoustic logging data and have analyzed the effect of the radial velocity changes on dipole flexural wave dispersion characteristics the inversion of the dispersion data to estimate the radial changes is inherently a nonunique problem because changing the degree of variation or the radial size of the variation zone can produce similar wave dispersion characteristics nonuniqueness can be solved by developing a constrained inversion method this is done by constraining the high frequency portion of the model dispersion curve with another curve calculated using the near borehole velocity the constraint condition is based on the physical principle that a high frequency dipole wave has a shallow penetration depth and is therefore sensitive to the near borehole shear wave velocity we have validated the result of the constrained inversion with synthetic data testing combining the new inversion method with four component crossed dipole anisotropy processing obtains shear radial profiles in fast and slow shear polarization directions in a sandstone formation the fast and slow shear wave profiles show substantial differences caused by the near borehole stress field demonstrating the ability of the technique to obtain radial and azimuthal geomechanical property changes near the wellbore

delta development and channel incision during marine isotope stages 3 and 2 in the western south yellow sea abstract approximately 4100 km of high resolution seismic profiles recently obtained from the western south yellow sea were subdivided into seven seismic units by six major seismic surfaces three sediment cores between 60 and 71 m in length obtained from localities on the seismic profile lines were analyzed for sedimentary characteristics clay mineral components and benthic foraminiferal and ostracod assemblages and were also dated by ams 14 c and optically stimulated luminescence to document the environmental history of the region stratigraphic units in the cores were confidently correlated with seismic units in the profiles stratigraphic correlation among these three cores and the previous well studied core qc 2 was facilitated by the cold water deposits in marine isotope stage mis 5 the three cores document the sedimentary sequence during the period from mis 6 up to mis 1 strata formation and sedimentary environment changes since mis 5 are strongly controlled by sea level fluctuations most of the successions were formed in mis 5 mis 3 and mis 1 with major erosions in mis 4 and mis 2 particularly our data revealed the presence of a large delta active during mis 3 likely from the early stage of mis 3 to about 40 cal kyr bp that was subsequently affected by channel incision the delta succession and incised channel fills have a high concentration of smectite in their clay mineral components suggesting that the paleo yellow river was the main contributor to the delta development and channel incision the delta sequence has a coarsening upward trend and consists of two seismic facies the upper facies shows lateral alternations of chaotic and oblique or very low angle reflectors which correspond to sandy proximal delta front and delta plain facies and the lower facies is characterized by seaward dipping clinoforms which correspond to muddy distal delta front and prodelta facies the top surface of the delta inclines very gently seaward consistent with a deltaic development associated with the sea level fall in mis 3 the incised channel system consists of two main channels with multiple tributaries in a dendritic pattern the incised channel fills begin with fluvial and then estuarine sediments which are truncated by a transgressive ravinement surface and capped by transgressive deposits the main incision channels have a terraced cross sectional morphology which is interpreted to reflect multiple episodes of sea level fall during incision presumably from the late mis 3 to the last glacial maximum

fracture detection in oil based drilling mud using a combination of borehole image and sonic logs abstract the deeply buried 5 5 7 1 km lower cretaceous bashijiqike sandstones are important fractured reservoirs in the kuqa depression in these high temperature high pressure drilling environments oil based muds are used to limit drilling risks and improve efficiency making facture detection using resistivity based image logs difficult the maximum horizontal stress sh max trends close to north south 0 10 based on orientations of the drilling induced fractures and borehole breakouts core descriptions thin sections and image logs used to describe the fractures in the bashijiqike sandstone reservoirs show that opening mode natural fractures are common and the fractures range from fully open to sealed by calcite and clay minerals the open fractures are dominantly steeply dipping or vertical and primarily strike north south locally horizontal fractures or fractures with low angle dip are detected we compare fracture visibility on image logs acquired in the same ks 2 2 12 key well in oil based mud and water based mud fmi hd logs successfully detect large 0 1 mm aperture vertical fractures in oil based mud better than obmi image logs and the two imaging tools have a similar ability in detecting the high dip angle fractures since the ubi tool is not affected by oil based muds most of the fractures can be picked out on ubi images minor negative deviations of bulk density could be observed in fractured zones and the presence of fractures obviously causes an increase in sonic transit time full waveforms from dsi tools combined with electrical image logs detect fractured zones both the velocity and amplitude of the sonic waves are sensitive to fractures and the fractured zones could be identified according to the attenuation of stoneley waves the combination of cores image logs and full wave sonic logs offers comprehensive detection of fractures in oil based mud environments

estimation of formation shear and borehole fluid slownesses using sonic dispersion data in well bonded cased boreholes new inversion algorithms have been developed for estimating the formation shear and borehole fluid slownesses using either the borehole stoneley or dipole flexural dispersion in well bonded cased boreholes surrounded by a fast or slow isotropic and purely elastic formation two inversion algorithms have been developed for each type of formation the first algorithm inverts either the measured borehole stoneley or flexural dispersion at select frequencies for the formation shear slowness when all other model parameters are known the second algorithm inverts either the borehole stoneley or flexural dispersion for both the formation shear and borehole fluid compressional slownesses optimal bandwidths for the inversion of the stoneley and dipole flexural dispersions for the formation shear slowness range from about 5 to 8 khz the well bonded cased borehole dispersion sensitivity to formation shear slowness becomes larger at these higher frequencies than in an open hole moreover the stoneley dispersion s

notes on the marginal enrichment of germanium in coal beds germanium distribution in coal has long been a topic of interest the enrichment of ge near margins of coals including the margins of partings within the coal has been noted in many coals from numerous coalfields throughout the world in this paper a summary of literature on ge geochemistry on the upper and lower margins of coal seams with special emphasis on the literature of russia and the former soviet union and japan is presented

late quaternary environmental change in oujiang delta along the northeastern zhe min uplift zone southeast china abstract we present a history of late quaternary coastal evolution based on the study of a 41 9 m long sediment core from the oujiang delta multiple analytical methods are employed including sedimentary facies analysis radiocarbon dating and the investigations of grain size elemental microfossil and pollen compositions two transgression regression sequences separated by a paleosol layer are identified several lines of evidence indicate that the lower sequence was deposited during the mid early mis 3 stage under a relatively warm and wet climate an elevated mis 3 highstand sea level higher than 24 m is observed the upper sequence was created after the paleosol was flooded during a marine transgression at 9 5 cal kyr bp seven weak east asian summer monsoon easm events are identified with central years of 8 4 7 7 6 3 5 7 4 7 2 8 and 1 8 cal kyr bp these coincide with those from the ecs sediment cores and the dongge cave 18o record indicating that easm precipitation is a major controlling factor of sedimentation rates in the region the oujiang delta is also subject to typhoon impacts and east asian winter monsoon eawm induced coastal currents active typhoons and a relatively enhanced eawm occurred during the weak easm period between 4 9 and 6 4 cal kyr bp producing high sedimentation rates in the middle holocene we emphasize the high sensitivity of small asian river deltas as archives of the easm eawm and typhoons such environments merit further as a means to understand past changes as well as future responses to projected climatic and sea level change

geochemistry and origin of elements in some uk coals abstract twenty four uk coals ranging in rank with 4 6 37 6 volatile matter were analysed for 46 major and trace elements the samples were obtained from the uk coal bank and are representative of the major uk coal fields the major element distributions are interpreted in terms of the mineralogical variations quartz and kaolinite are largely responsible for the si and al carbonates for ca and mg and pyrite for fe also exerting an influence in some samples are siderite al phosphate minerals and illite based on statistical relationships with the major elements rb cr th ce zr y ga la ta nb and v are thought to be mainly present in the clay minerals and as mo sb tl se and bi and pb are probably present in pyrite strontium and ba are concentrated in a restricted number of samples related to the phosphate minerals germanium is the only element for which a major organic association can be demonstrated elements with an indirect association with the organic matter are na cl and br in porefluids and possibly te the ash content is controlled mainly by the detrital input and the trace elements related to the ash content are therefore those elements associated with the clay minerals variations with rank would appear to be mainly related to the moisture content porefluids the trace elements associated with the quartz and clay minerals are thought to be dominantly detrital in origin the non detrital elements essentially those contained in pyrite are thought to have been incorporated in the depositional environment from waters with enhanced salinities through seawater ingress hence there are positive relationships between s and trace element concentrations

holocene evolution of mud depocentres on a high energy low accumulation shelf nw iberia the high energy low accumulation nw iberian shelf features three confined holocene mud depocentres here we show that the evolution of such depocentres follows successive steps the flooding of inner shelf zones and river catchment areas by the late deglacial sea level rise provided the precondition for shelf mud deposition following this the holocene deceleration of the sea level rise caused a rapid refill of the accommodation space within river valleys subsequently the export of major amounts of fines was initiated the initial onset and loci of shelf mud deposition were related to deposition favouring conditions in mid shelf position or to the presence of morphological highs which act as sediment traps by providing protection against stronger hydrodynamic energy the detailed reconstruction of the holocene depocentre evolution shows for the first time that the expansion of such shelf mud deposits cannot only occur by linear growth off the associated sediment source rather they might develop around centres that are fully disconnected from the source of original sediment supply and expand later into specific directions based on these differences and on the connection of the individual mud depocentres to the material source we propose a conceptual subdivision of the group mid shelf mud depocentres

provenance of present day eolian dust collected off nw africa 1 atmospheric dust samples collected along a transect off the west african coast have been investigated for their physical grain size distribution mineralogical and chemical major elements composition on the basis of these data the samples were grouped into sets of samples that most likely originated from the same source area in addition shipboard collected atmospheric meteorological data modeled 4 day back trajectories for each sampling day and location and total ozone mapping spectrometer aerosol index data for the time period of dust collection february march 1998 were combined and used to reconstruct the sources of the groups of dust samples on the basis of these data we were able to determine the provenance of the various dust samples it appears that the bulk of the wind blown sediments that are deposited in the proximal equatorial atlantic ocean are transported in the lower level 900 hpa ne trade wind layer which is a very dominant feature north of the intertropical convergence zone itcz however south of the surface expression of the itcz down to 5 s where surface winds are southwesterly we still collected sediments that originated from the north and east carried there by the ne trade wind layer as well as by easterly winds from higher altitudes the fact that the size of the wind blown dust depends not only on the wind strength of the transporting agent but also on the distance to the source hampers a direct comparison of the dust s size distributions and measured wind strengths however a comparison between eolian dust and terrigenous sediments collected in three submarine sediment traps off the west coast of nw africa shows that knowledge of the composition of eolian dust is a prerequisite for the interpretation of paleorecords obtained from sediment cores in the equatorial atlantic

geometry lateral variation and preservation of downlapping regressive shelf deposits eastern tyrrhenian sea margin italy abstract the shelf of the eastern tyrrhenian sea margin changes substantially in width shelf break depth and sea floor steepness over relatively short distances largely owing to pronounced lateral changes in subsurface geologic structure remnants of late pleistocene prograded coastal deposits are locally preserved on the middle and outer parts of the shelf we recognize two major controls on the distribution lateral extent thickness and preservation potential of these prograded deposits first prograded downlapping deposits formed only where the physiographic shelf break was deeper than the lowstand shoreline thus providing accommodation space for the lowstand deposits second the proximity and relative size of sediment sources and the local coastal dispersal system apparently infl enced the geometry of the deposit midshelf and shelf margin bodies composed of seaward steepening downlapping reflectors were deposited as thin to thick continuous prograding sheets over an irregular eroded shelf surface and onto the shelf edge during the latest fall and lowstand of sea level decreased sedimentation at the end of this lowstand resulted in net erosion during sea level rise shoreface erosion created a major marine erosional ravinement surface landward of the 120 m isobath and much of the downlapping deposits were removed preservation of these downlapping deposits is largely a function of their thickness thick continuous deposits are common on the shelf edge whereas on the midshelf only thin remnants are preserved locally where depressions or morphologic steps were present in the shelf surface

homomorphic processing of the tube wave generated during acoustic logging we have developed a new method to process the tube wave which is generated during acoustic logging to obtain estimates for its wavenumber attenuation coefficient amplitude and phase at every frequency to improve the accuracy of the estimates the method can use data from multiple sources and data collected at successive depths in the borehole this new method has several advantages over other methods that are currently used to process acoustic logging data the new method can obtain accurate estimates of the wavenumber and amplitude from only a few receivers the receivers can be irregularly spaced and no spurious estimates are generated nonetheless this new method has one disadvantage compared to others it can only estimate the parameters for one high amplitude wave like the tube wave also like all other existing methods the new method obtains only reasonable estimates for the attenuation coefficient when data from many receivers are processed

the giant mauritanian cold water coral mound province oxygen control on coral mound formation abstract the largest coherent cold water coral cwc mound province in the atlantic ocean exists along the mauritanian margin where up to 100 m high mounds extend over a distance of 400 km arranged in two slope parallel chains in 400 550 m water depth additionally cwcs are present in the numerous submarine canyons with isolated coral mounds being developed on some canyon flanks seventy seven uranium series coral ages were assessed to elucidate the timing of cwc colonisation and coral mound development along the mauritanian margin for the last 120 000 years our results show that cwcs were present on the mounds during the last interglacial though in low numbers corresponding to coral mound aggradation rates of 16 cm kyr 1 most prolific periods for cwc growth are identified for the last glacial and deglaciation resulting in enhanced mound aggradation 1000 cm kyr 1 before mound formation stagnated along the entire margin with the onset of the holocene until today the mauritanian mounds are in a dormant state with only scarce cwc growth in the canyons live cwcs are abundant since the late holocene at least thus the canyons may serve as a refuge to cwcs potentially enabling the observed modest re colonisation pulse on the mounds along the open slope the timing and rate of the pre holocene coral mound aggradation and the cessation of mound formation varied between the individual mounds which was likely the consequence of vertical lateral changes in water mass structure that placed the mounds near or out of oxygen depleted waters respectively

geoacoustic inversion in a dispersive waveguide using warping operators this paper presents a single receiver geoacoustic inversion method adapted for low frequency impulsive sources it is applied to light bulb data collected during the shallow water 2006 experiment the inversion is carried out by extracting dispersion curves from the received signal and comparing them to simulated replicas to achieve dispersion curve estimation in the time frequency domain modal separability is improved using a signal processing method called warping the inversion scheme allows for a reliable estimation of the new jersey shelf sediment properties compressional sound speed and density it also provides an accurate estimation of the source receiver range