nd and sr isotopic variations in chinese eolian deposits during the past 8 ma implications for provenance change a record of changes in nd and sr isotopic composition of the eolian deposits from the central loess plateau has been determined for the past 8 ma the isotopic records of the silicate fraction of the quaternary and tertiary eolian deposits allow interpreting the interplay between the sr isotopic variations in the eolian deposits and the late cenozoic tectonic and climatic changes the results indicate that the temporal variations of nd and sr isotopes show remarkable changes around the beginning of the quaternary the lower values of the 143 nd 144 nd and the decreasing trend of the 87 sr 86 sr ratios after 2 58 ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late cenozoic uplift induced glacial grinding in the high orogenic belts in central asia in this context the substantial changes in climate and tectonics have modified dust sources significantly and the quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the tertiary red clay d 2005 elsevier b v all rights reserved

synthesis of realistic oceanic pn wave trains the synthesis of realistic oceanic pn phases was accomplished using wave number integration wave trains with durations of the order of 100 s following the initial compressional wave arrival were generated for a laterally homogeneous vertically inhomogeneous oceanic lithosphere model the excitation of these long wave trains is primarily a result of near receiver water and sediment reverberations and does not involve scattering a late arriving wave train with a group velocity of 1 6 km s having an emergent onset and substantial duration characteristic of oceanic abyssal t phases was also generated even with phase velocities restricted to be greater than 5 5 km s the synthetic pn wave train was compared to data collected in the southwest pacific during the ngendei seismic experiment many of the spectral characteristics associated with sediment and water reverberation observed in the synthetics were also observed in the data first it was found that the amplitude falloff rate of the pn wave train is a strongly increasing function of frequency in direct contrast to results predicted for forward scattered coda this leads to a predominance of low frequencies late in the wave train which is easily interpreted in terms of the constructive interference of different modes of reverberation second the presence of spectral peaks at frequencies associated with both sediment and water reverberations was observed the predicted frequencies were computed using values of the water depth sediment thickness and sediment velocity obtained in an independent study strong alignment of the spectral peaks with the predicted frequencies illustrates the reverberating nature of the pn wave train the presence of substantial power in excess of 15 hz can be attributed to the confinement of pn to the oceanic lithosphere the oceanic pn phase is thus characterized as a refraction from the lower lithosphere with multiple reverberations in the oceanic water column and sediment layer comprising the subsequent coda complicated oceanic lithosphere models are not needed to explain the gross characteristics of pn propagation

evolution of miocene footwall derived coarse grained deltas gulf of suez egypt implications for exploration the miocene abu alaqa group exposed on the eastern side of the gulf of suez contains a series of coarse grained delta deposits located in the hanging wall of the northwest trending east margin fault zone seven major fan sequences have been identified the first three fan sequences are aggradational and cover an area of less than 2 sq km the sequences are dominated by pebble boulder conglomerates with predominantly sigmoidal high angle clinoforms between 15 and 25 degrees as much as 150 m high these fan sequences represent talus cones and fan deltas which were probably deposited during activity on the fault zone and are situated at transfer segments the other four fan sequences are predominantly progradational consisting of mixed carbonate siliciclastic braid d ltas with local reefs they are less than 30 m high have low angle clinoforms

aeolian abrasion and modes of fine particle production from natural red dune sands an experimental study a series of experiments was conducted to determine the potential for aeolian abrasion of natural dune sands to produce fine particles 125 m by 1 the release of resident fines 2 spalling chipping and breakage of particles and 3 the removal of grain surface coatings parent samples were obtained from the surfaces of four active continental dunes and abraded using a glass test tube chamber for up to 120h the fine particles produced by this abrasion process were trapped at varying time intervals and subject to detailed particle size analyses using a coulter multisizer the abrasion of untreated parent samples produced fine particles in one of two main size classes 50 m but when the parent sample was sieved to exclude particles 250 m relatively more material in the range 10 50 m was produced for unsieved parent samples the size range associated with the dominant mode varied according to the length of the abrasion time the coarsest mode 63 m was dominant during the first 16 h of abrasion then became less significant and is thought to be associated with the release of resident fines into suspension the finest mode 10 m was absent or very weak during the first 16h of abrasion then became more significant and in some instances dominated the distribution as abrasion continued removal of grain surface coatings is the main source of fine material 10 m and this may be a significant source of fine material in areas where sands are dominated by subrounded and rounded particles by comparison with previous studies of aeolian particle abrasion these natural dune sands produced very low quantities of fine material by weight but their spatial extent makes them potentially a significant source of dust sized particles at the global scale

variations of nd 143 nd 144 and sr 87 sr 86 ratios of the lingtai profile in the chinese loess plateau during the past 7 ma

characterization of late glacial continental dust in the greenland ice core project ice core twelve glacial dust samples extracted from the greenland ice core project ice core have been characterized in terms of mineralogy sr and nd isotopic composition and rare earth element concentrations the ice samples are taken from the younger dryas the bolling the last glacial maximum and both cold and mild glacial periods back to 44 kyr b p a comparison with samples from possible dust source areas determines eastern asia as being the main source area at all times hereby confirming and extending earlier results biscaye et al 1997 this finding is partly in agreement with recent atmospheric general circulation model simulations of glacial atmospheric dust transport andersen et al 1998 mahowald et al 1999 a low intersample variability in tracer characteristics is discussed in the context of a volcanogenic influence grain size dependence and variability in the conti nental dust source areas the clay mineralogy of the ice core dust shows a weak climatic de pendence while the isotopic composition of sr and nd does not correlate with climate this is interpreted as a geographical variation of source areas on a regional scale within asia two ice dust samples were size fractionated at 2 gm and the grain size dependence on tracer characteristics is in accordance with the literature

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

seasonal variability in the origin of recent atmospheric mineral dust at northgrip greenland abstract isotopic sr and nd and mineralogical analyses of dust extracted from snow deposits from the last decade at the northgrip greenland ice camp 75 1 n 042 3 w confirm the eastern asian source for greenland dust and extend it to the present day the 1998 and 1999 samples which represent a 2 4 month resolution of dust deposition show that there are at least two east asian sources for the greenland dust that vary seasonally the provenance of dust during the major spring summer deposition is the takla makan desert of northwest china

synthetic pn and sn phases and the frequency dependence of q of oceanic lithosphere the oceanic lithosphere is an extremely efficient waveguide for high frequency seismic energy in particular the propagation of the regional to teleseismic oceanic pn and sn phases is largely controlled by properties of the oceanic plates the shallow velocity gradient in the sub moho lithosphere results in a nearly linear travel time curve for these oceanic phases and an onset velocity near the material velocity of the uppermost mantle the confinement of pn sn to the lithosphere imposes a constraint on the maximum range that a normally refracted wave can be observed the rapid disappearance of sn and the discontinuous drop in pn sn group velocity beyond a critical distance dependent upon the local thickness of the lithosphere are interpreted as a shadowing effect of the low q asthenosphere wave number integration was used to compute complete synthetic seismograms for a model of oceanic lithosphere the results were compared to data collected during the 1983 ngendei seismic experiment in the southwest pacific the pn sn coda is successfully modeled as a sum of leaky organ pipe modes in the sediment layer and oceanic water column while scattering is present to some degree it is not required to explain the long duration and complicated nature of the pn sn wave trains the presence of extremely high frequencies in pn sn phases and the greater efficiency of sn than pn propagation are interpreted in terms of an absorption band rheology a shorter high frequency relaxation time for p waves than for s waves results in a rheology with the property that q q at low frequency while q q at high frequency consistent with the teleseismic pn sn observations the absorption band model is to viewed as only an approximation to the true frequency dependence of q in the oceanic lithosphere for which analytic expressions for the material dispersion have been developed

strontium isotopes as tracers of ecosystem processes theory and methods abstract the strontium sr isotope method can be a powerful tool in studies of chemical weathering and soil genesis cation provenance and mobility and the chronostratigraphic correlation of marine sediments it is a sensitive geochemical tracer applicable to large scale ecosystem studies as well as to centimeter scaled examination of cation mobility within a soil profile the 87sr 86sr ratios of natural materials reflect the sources of strontium available during their formation isotopically distinct inputs from precipitation dryfall soil parent material and surface or groundwater allow determination of the relative proportions of those materials entering or leaving an ecosystem the isotopic compositions of labile soil exchange complex and soil solution strontium and sr in vegetation reflect the sources of cations available to plants strontium isotopes can be used to track the biogeochemical cycling of nutrient cations such as calcium the extent of cation contributions from in situ weathering and external additions to soil from dust and rain can also be resolved with this method in this paper we review the geochemistry and isotopic systematics of strontium and discuss the use of this method as a tracer of earth surface processes

control of dust emissions by geomorphic conditions wind environments and land use in northern china an examination based on dust storm frequency from 1960 to 2003 the degree to which dust emissions are controlled by geomorphic conditions wind environments and land use was investigated using the dust storm frequency dsf and data from more than 300 meteorological stations throughout northern china our analysis showed that most dust emissions originated in gobi deserts that developed in piedmont alluvial fans of the kunlun qilian and helan mountains dust emissions are low from other gobi desert regions such as the northern gurbantunggut and eastern taklimakan where high vegetation coverage restrained dust emissions or where dust size particles are not abundant after a long period of strong wind erosion sandy deserts with relatively high vegetation coverage or an extensive cover by mobile sands are not a major dust source although the highest dust emissions did not appear in regions with the highest wind energy dsf trends in each region from 1960 to 2003 were closely related to local wind activity dsf was low in regions with high levels of human activity where the mean dsf from 1960 to 2003 did not exceed 4 days year even from the 1960s to the early 1970s the period with the greatest dsf frequency did not exceed 8 days year which indicates that extensive land use did not contribute to dsf the low dsf in these areas might result from the fact that although land use could produce abundant fine soil fractions vegetation coverage and soil moisture remained higher than in the gobi deserts of arid china thereby decreasing dust storm occurrence

compressional and shear wave anisotropy in the oceanic lithosphere the ngendei seismic refraction experiment summary synthetic seismogram modelling of seismic refraction data from the 1983 ngendei expedition to the south pacific indicate seismic anisotropy both within the top kilometre of oceanic crust and in the uppermost mantle we calculate average p and s wave velocity versus depth functions for two orthogonal azimuths n3ooe approximately aligned with the fast mantle direction and n120 e close to the fast crustal direction probable lateral heterogeneities at the ngendei site prevent perfect matching of data and synthetic waveforms crustal anisotropy is indicated by a 28 pattern of both p and s wave travel times as a function of azimuth and is consistent with an approximate 0 2 km s difference in p wave velocities and 0 1 km s difference in s wave velocities upper mantle anisotropy is characterized by pn velocity differences of 7 95 8 4 km s l and a nearly uniform s velocity of 4 65 km s we use these velocity profiles and traveltime data to calculate bounds on the properties of the elastic constants of the crust and upper mantle the crustal anisotropy can be explained by a model involving aligned cracks parallel to the original spreading ridge resulting in a fast direction perpendicular to the fossil spreading direction the upper mantle anisotropy is consistent with aligned olivine crystal models in which the fast direction is parallel to the fossil spreading direction for both of these models we use bounds from the ngendei data to place constraints on the physical properties of the lithosphere

sedimentology of rift climax deep water systems lower rudeis formation hammam faraun fault block suez rift egypt abstract in most marine rift basins subsidence outpaces sedimentation during rift climax times typically this results in sediment starved hangingwall depocentres dominated by deep marine mudstones with subordinate local development of coarser clastics in the immediate hangingwall derived from restricted catchments on the immediate footwall scarp to highlight the spatial variability of rift climax facies and the controls upon them we have investigated the detailed three dimensional geometry and facies relationships of the extremely well exposed miocene rift climax lower rudeis formation in the immediate hangingwall to the thal fault zone suez rift egypt detailed sedimentological analyses allows the lower rudeis formation to be divided into two contemporaneous depositional systems 1 a laterally continuous slope system comprising hangingwall restricted interpretation of individual facies facies relationships and their spatial variability indicate that deposition in the immediate hangingwall to the thal fault occurred via a range of submarine concentrated density flows surge like turbidity flows mass wasting and hemipelagic processes major controls on the spatial variability and stratigraphic architecture of the depositional systems identified reflect the influence of the steep footwall physiography accommodation and drainage evolution associated with the growth of the thal fault the under filled nature of the hangingwall depocentre combined with the steep footwall gradient result in a steep fault controlled basin margin characterised by either slope bypass or erosion with limited coastal plain or shelf area sediment supply to the slope apron deposits is controlled in part by the evolution and size of small footwall drainage catchments in contrast the localized submarine fan is interpreted to have been fed by a larger antecedent drainage network the structural style of the immediate footwall is also believed to exert a control on facies development and stratigraphic evolution in particular fault scarp degradation is enhanced by fault propagation folding which creates basinward dipping bedding planes in the pre rift footwall strata that large pre rift blocks slide on

petrophysical and microfacies analysis as a tool for reservoir rock typing and modeling rudeis formation off shore october oil field sinai abstract petrographically the lower miocene rudeis reservoir rock samples in october oil field can be summed up into three reservoir rock types rrts the rrt1 samples are mostly calcareous to ferruginated sandstones sometimes are fossiliferous whereas the rrt2 and rrt3 samples are carbonate rocks of grainstone and packstone microfacies respectively cementation by sparite and compaction are the most important porosity reducing diagenetic factors whereas dissolution and leaching out as well as fracturing are the most dominant porosity enhancing factors the petrophysical and reservoir quality studies include measuring density porosity permeability measurements as well as reservoir quality index rqi flow zone indicator fzi and reservoir potential index rpi calculations the permeability porosity plot is the key factor for discriminating the petrophysical behaviour into these three rock reservoir types petrophysically the studied sandstone rrt1 samples have the best storage capacity and reservoir quality the rqi fzi and the rpi indicate poor to very good reservoir quality whereas the rrt3 samples have the least prospective properties the rqi fzi and the rpi indicates impervious reservoir quality based on the fzi values the studied rudeis formation was discriminated into a number of hydraulic flow units 6 hfus hfu 5 6 are the best reservoir zones they are assigned in the central parts of the studied area whereas the least quality hfu 1 3 was assigned to the south in addition the mercury injection capillary pressure tests micp indicates that the rrt1 samples are ranked as iv fair to vi impervious ranks the rrt2 as v poor to vi whereas the rrt3 samples are impervious samples wettability of the studied rrt1 samples is mostly neutral

dust production and deposition in asia and the north pacific ocean over the past 12 myr the silicate fractions of recent pelagic sediments in the central north pacific ocean are dominated by eolian dust derived from central asia an 11 myr sedimentary record at odp sites 885 886 at 44 7 n 168 3 w allows the evaluation of how such dust and its sources have changed in response to late cenozoic climate and tectonics the extracted eolian fraction contains variable amounts 70 of clay minerals with subordinate quartz and plagioclase uniform nd isotopic compositions nd 8 6 to 10 5 and sm nd ratios 0 170 0 192 for most of the 11 myr record demonstrate a well mixed provenance in the basins north of the tibetan plateau and the gobi desert that was a source of dust long before the oldest preserved asian loess formed nd values of up to 6 5 for samples 2 9 ma indicate 35 wt admixture of a young kamchatka like volcanic arc component the coherence of pb and nd in the erosional cycle allows us to constrain the pb isotopic composition of asian loess devoid of anthropogenic contamination to 206pb 204pb 18 97 0 06 207pb 204pb 15 67 0 02 208pb 204pb 39 19 0 11 87sr 86sr 0 711 0 721 and rb sr ratios 0 39 1 1 vary with dust mineralogy and provide an age indication of 250 ma 40ar 39ar ages of six dust samples are uniform around 200 ma and match the k ar ages of modern dust deposited on hawaii these data reflect the weighted age average of illite formation changes from illite smectite with significant kaolinite to illite and chlorite rich kaolinite free assemblages since the late pliocene document changes in the intensity of chemical weathering in the source region such weathering evidently did not disturb the k ar systematics and only induced scatter in the rb sr data we propose that when smectite forms at the expense of illite k and ar are quantitatively lost from what becomes smectite but are quantitatively retained in adjacent illite layers 40ar 39ar age data therefore are insensitive to smectite formation during chemical weathering but date the diagenetic growth of illite the major k bearing phase in the dust over the past 12 myr the dust flux to the north pacific increased by more than an order of magnitude documenting a substantial drying of central asia this climatic change however did not alter the ultimate source of the dust and neoformational products of chemical weathering always remained subordinate to assemblages reworked by mechanical erosion in dust deposited in eastern asia and the pacific ocean

asian continental nature of87sr 86sr ratios in north central pacific sediments strontium isotopic compositions were determined for silicate detritus in 152 deep sea and continental shelf surface sediment samples from the pacific ocean to trace their provenance the major characteristics of the spatial variation of the sr isotopes and the interpretation of this variation may be summarized as follows 1 sediments in the pacific have a lower average87sr 86sr ratio 0 7112 with a narrower range 0 703 0 724 than in the atlantic 0 7166 0 704 0 743 many western pacific volcanoes together with young continental crust supply material with low87sr 86sr ratios to the pacific in contrast to the large old cratonic crust that supplies material with high sr ratio to the atlantic 2 the87sr 86sr ratio is high in the north central pacific 0 711 0 719 the izu ogasawara and mariana arcs supply low87sr 86sr material to the western pacific but farther to east the abundant supply of loess carried by middle latitude westerlies from the asian continent 87sr 86sr ca 0 720 dominates the north central pacific

the blown sand flux over a sandy surface a wind tunnel investigation on the fetch effect abstract detailed wind tunnel tests were conducted to examine the fetch effect of a sandy surface on a sand cloud blowing over it the results suggest that the fetch length of a sandy surface has a significant effect on both the vertical flux profile and total horizontal flux the sand flux over a sandy surface increases with height in the very near surface layer but then decays exponentially in agreement with the widely accepted conclusion the decay function can be expressed by q aexp h b where q is the sand flux at height h coefficient a that tends to increase with wind speed implies the influence of wind while coefficient b that defines the relative decay rate shows the influence of both the fetch and wind the relative decay rate increases with fetch when the fetch length is short then becomes constant when the fetch reaches a certain length the threshold fetch length over which the relative decay rate keeps constant increases with wind speed the average saltation height generally increases with fetch both the relative decay rate and average saltation height show that the fetch effect on the flux profile becomes more significant when the wind speed increases the total sand transport equation for the total fetch can be expressed by q c 1 ut u 2u3 g where q is the total sand transport rate u and ut are the wind velocity and threshold wind velocity at the centerline height of the wind tunnel respectively g is gravitational acceleration is the density of air and c is a proportionality coefficient that increases with the fetch length implying that the total sand flux increases with the fetch length

distribution of carbonate cements within depositional facies and sequence stratigraphic framework of shoreface and deltaic arenites lower miocene the gulf of suez rift egypt abstract this study aims to unravel the spatial and temporal distribution of diagenetic alterations of the mheiherrat member the rudeis formation lower miocene of the gulf of suez rift egypt within depositional facies and sequence stratigraphy the mheiherrat member is represented by shoreface calcarenites and hybrid arenites transgressive and highstand systems tracts tst and hst respectively and deltaic rudites and coarse grained calcarenites and hybrid arenites lowstand systems tracts lst petrographic stable o and c isotopes mineral chemical and geochemical analyses have revealed that the arenites are pervasively cemented by eogenetic carbonates and to small extent by zeolite and pyrite as well as by telogenetic palygorskite the shoreface tst and hst calcarenites and hybrid arenites were dominantly cemented by microcrystalline grain rimming and inter and intragranular pore filling calcite 18 o v pdb 3 6 to 0 3 and 13 c v pdb 2 3 to 0 7 and rhombic dolomite 18 o v pdb 3 9 to 0 9 and 13 c v pdb 2 5 to 0 7 these cements are interpreted to be formed by marine to brackish waters with 18 o v smow 1 2 to 3 2 at temperature of 20 55 c the deltaic lst coarse grained calcarenites and hybrid arenites were dominantly cemented by coarse crystalline inter and intragranular pore filling calcite 18 o v pdb 4 4 to 2 3 and 13 c v pdb 2 8 to 1 3 which are interpreted to have precipitated from pore waters with 18 o v smow 3 5 to 5 5 at temperatures of greater than 55 c such pervasive cementation by carbonates is attributed to the occurrence of abundant intrabasinal carbonate grains the carbonate cement texture is suggested to be controlled by changes in pore water chemistry owing to transgression and regression events this case study revealed that better understanding of factors controlling the extent and textural habits of carbonate cements can be achieved when it is linked with depositional facies and sequence stratigraphy

hydrocarbon source rock potential in the southwestern gulf of suez graben insights from organic geochemistry and palynofacies studies on well samples from the ras el bahar oilfield abstract palynological and biomarker characteristics of organic facies recovered from cretaceous miocene well samples in the ras el bahar oilfield southwest gulf of suez and their correlation with lithologies environments of deposition and thermal maturity have provided a sound basis for determining their source potential for hydrocarbons in addition to palynofacies analysis toc rock eval pyrolysis kerogen concentrates bitumen extraction carbon isotopes and saturated and aromatic biomarkers enable qualitative and quantitative assessments of sedimentary organic matter to be made the results obtained from rock eval pyrolysis and molecular biomarker data indicate that most of the samples come from horizons that have fair to good hydrocarbon generation potential in the study area the upper cretaceous paleocene lower eocene samples contain mostly type ii to type iii organic matter with the capability of generating oil and gas the sediments concerned accumulated in dysoxic anoxic marine environments by contrast the miocene rocks yielded mainly type iii and type ii iii organic matter with mainly gas generating potential these rocks reflect deposition in a marine environment into which there was significant terrigenous input three palynofacies types have been recognized the first a consists of type iii gas prone kerogen and is typical of the early middle miocene belayim kareem and upper rudeis formations the second b has mixed oil and gas features and characterizes the remainder of the rudeis formation the third association c is dominated by amorphous organic matter classified as borderline type ii oil prone kerogen and is typical of the matulla turonian santonian and wata turonian formations rock eval t max pi hopane and sterane biomarkers consistently indicate an immature to early mature stage of thermal maturity for the whole of the studied succession

mineralogical variation of sr nd isotopic and elemental compositions in loess and desert sand from the central loess plateau in china as a provenance tracer of wet and dry deposition in the northwestern pacific we determined sr and nd isotopic compositions and major trace and rare earth element ree compositions of evaporite and detrital minerals in loess and desert sand from the central loess plateau clp where 80 of the loess deposits in china are found the loess exhibited a narrow range of variation in 87sr 86sr 0 715 0 001 a sequential extraction experiment on the loess however showed that water and acetic acid hoac soluble minerals mainly halite and calcite hydrochloric acid hcl soluble minerals chlorite and phosphate and hcl insoluble minerals illite kaolinite smectite vermiculite feldspar and quartz have distinct 87sr 86sr ratios approximately 0 7111 0 0004 0 7141 0 0004 and 0 7195 0 0010 respectively the water and hoac soluble ratios were regionally uniform and were close to the 87sr 86sr value of river water from the huanghe yellow river and the maximum 87sr 86sr value of spring rainwater in japan suggesting selective solution of eolian halite and calcite into the chinese river water and into the japanese rainwater the mineralogical elemental and sr nd isotopic compositions of hcl soluble and insoluble minerals in the clp loess were different from those of the northern desert sand but were indistinguishable from those of its fine grained fraction supporting the view that the loess is composed of the fine grained fraction of desert sand that was transported to the southeast in the atmosphere the 87sr 86sr end and gd yb values of hcl insoluble minerals in the clp loess were almost identical to those of airborne dust soil minerals and deep sea sediments in the northwestern pacific considered to be of eolian origin suggesting dissolution of the loess evaporite minerals during atmospheric transportation these relationships demonstrate the usefulness of sr isotopes of water and hoac soluble minerals and sr and nd isotope ratios and ree compositions of acid insoluble minerals in loess as provenance markers for wet and dry deposition respectively

source rock potential and paleoenvironment of the miocene rudeis and kareem formations gulf of suez egypt an integrated palynofacies and organic geochemical approach abstract a study on source rock characterization and paleoenvironmental interpretation has been carried out on a relatively thick miocene sedimentary succession from three wells gh 404 2a gh 420 1 sa e6a in the southern gulf of suez egypt the compilation of detailed optical investigations including palynofacies analysis spore coloration index sci vitrinite reflectance vrr and source rock geochemical data enables a detailed evaluation of organic matter om richness kerogen type and thermal maturation level despite their high content of calcium carbonate up to 52 the studied sediments yielded sufficient palynologic residue for a detailed palynofacies and organic petrographic study the palynomorph content comprises mainly marine components essentially dinoflagellate cysts and accessorily microforaminiferal linings while terrestrial derived material is relatively rare persistent occurrence of amorphous organic matter aom indicates that dysoxic to anoxic conditions prevailed throughout the deposition of the investigated sediments the main objective of this study is to combine organic geochemical and palynological data in an attempt to assess the source rock potential of the rudeis and kareem formations in the gulf of suez these data in addition also allow for the reconstruction of the depositional environment the present investigation employs multimode microscopic methods using transmitted white light along with incident light fluorescence microscopy for the first time geochemical and petrographic analyses performed on bulk rock samples and palynological residues demonstrate that both the rudeis formation and the kareem formation are mainly of kerogen type iii or mixed type ii iii independent thermal maturation specific parameters such as rock eval tmax vrr and sci indicate an immature to early mature stage palynofacies analyses combined with organic geochemical data indicate that the rudeis formation was deposited under shallow to open marine conditions whereas the overlying kareem formation was formed mainly in an open marine setting

dust sources in arid and semiarid china and southern mongolia impacts of geomorphological setting and surface materials abstract analysis of the geomorphological settings and surface materials in arid and semiarid china and southern mongolia revealed that the dominant dust sources are gobi deserts and alluvial fans adjacent to gobi deserts in the piedmonts of the kunlun qilian helan and gobi altai mountains these areas have persistent supplies of dust sized particles deposited by intermittent floods from the mountains and fine materials are also generated by weathering and aeolian processes acting on the coarse fractions of gobi surfaces clear spatial differences in mineral types and contents and in the salt contents of surface materials also strongly affected the intensity of dust emissions inconsistencies in monitoring simulation and calculation of dust emissions in previous studies of northern china and mongolia may have been caused by insufficiently detailed considerations of variations in the geomorphological setting where the geomorphological settings in these areas are not considered in sufficient detail deviations arise in the estimation and prediction of dust using current models although the present study did not quantify the persistence and replenishment of dust sources in the study area our conclusions about the importance of geomorphology can improve future studies of dust sources and controlling factors improve assessments of the effects of climate change on dust emissions and facilitate the interpretation of paleoclimate records

site amplification of coda waves from local earthquakes in central california the goals of this study are two fold 1 to examine the site effect of coda waves believed to be the average site effect of shear waves in order to understand its spatial and frequency dependent behavior and 2 to learn what we can about the processes that generate the coda itself we use digital data from over 90 earthquakes each recorded by a subset of some 150 stations in the coast ranges of central california between san francisco and san luis obispo results from the band 1 5 to 24 hz indicate that site amplification depends strongly on surface geology and frequency at low frequencies 1 5 to 3 0 hz changes in amplification up to a factor of 20 are observed amplification generally varies inversely with deposit age at sediment sites and is lowest at granite and franciscan basement sites at high frequencies 6 to 24 hz the pattern changes many granite sites the majority in the gabilan range exhibit increasing amplification with frequency relative to the average station this behavior differs strikingly from that observed at sediment and franciscan sites which roll off at an intermediate rate and many sediment sites adjacent to the san andreas fault zone which decay away even more rapidly with frequency these results can be explained qualitatively by appealing to variable near site impedance and attenuation however complicating phenomena such as mode excitation in valley sediments must exist at low frequencies peaked behavior at a few hard rock sites at high frequency 12 hz currently lacks explanation at a few sediment sites the low frequency excitation is so strong that the coda envelopes begin to take on different shapes this contradicts the assumption based on previous observations that the coda shape is independent of source receiver location thus some site measurements may be artificially high the working model of coda waves as body wave energy backscattered from randomly distributed inhomogeneities must be modified to include the possibility of efficient near site resonance excited by incident direct and coda wave energy

geochemical and magnetic characteristics of aeolian transported materials under different near surface wind fields an experimental study by combining field investigations field sampling wind tunnel experiments and laboratory measurements the relationships between near surface winds and the geochemical and magnetic characteristics of windtransported materials were statistically analyzed our study was conducted using bulk surface samples from a major potential dust source area in central asia the ala shan plateau under near surface wind velocities ranging from 8 to 22 m s the coefficients of variation ranged between 1 6 and 14 9 for chi if 1 4 and 11 0 for chi arm and 0 7 and 123 for sirm of the transported materials for the 26 elements and oxides investigated the coefficients of variation of ti cr as zr ce pb and cu in the samples were greater than 10 no consistent patterns were found between magnetic characteristics and elemental and iron oxide concentrations as a function of variations in near surface wind velocities in potential dust source areas under near surface wind velocities there are variations in the relationships between magnetic and geochemical characteristics in the fine fractions of transported materials with different particle sizes given the wide variation in magnetic and geochemical characteristics of aeolian transported materials under different near surface winds their use as proxies for past climate reconstruction must be carefully appraised c 2015 elsevier b v all rights reserved

low frequency noise observations in the deep ocean simultaneous measurements of ocean bottom infrasonic and ocean bottom and sub bottom seismic noise in the frequency band 0 1 20 hz are presented the data were obtained in 5 5 km deep water in the south central pacific with a triaxial borehole seismograph and six triaxial ocean bottom seismographs having externally mounted hydrophones the borehole sensors were emplaced 54 m within basement rock overlain by 70 m of pelagic clay in the band 0 1 1 hz noise propagation as seismic modes trapped in the seafloor is supported by observed spectral coherences cross phases and ratios between ocean bottom pressure and vertical ground motion and by the relatively lower noise levels in the borehole noise variations in this band are clearly correlated with changes in local wind direction and speed presumably through ocean bottom pressure fluctuations caused by nonlinear wind wave wind wave and wind wave swell interaction

natural and anthropogenic sources of east asian dust nd sr isotopic signatures of loess modern dust and their potential source materials are systematically investigated to discriminate the natural and anthropogenic sources of eastern asian dust chinese loess is an eolian deposit that has accumulated over the past few million years and is characterized by a negative nd sr isotopic correlation that implies binary sources for the natural background of eastern asian dust loess in northeastern china shows the highest end 0 value while loess in western china has the lowest end 0 considering the nd sr isotopic signatures of the potential sources we propose that the high end 0 end member is derived from the arid lands around the northern boundary of china while the low end 0 end member originates from the deserts on the northern margin of the tibetan plateau chinese loess plateau deposits are dominated by northern margin tibetan plateau dust suggesting a strong link between the thick eolian deposit in this region and the evolution of the tibetan plateau the long range transported spring dust in both nanjing south china and japan has an nd sr isotopic composition similar to that of loess however spring dust in beijing north china has a much lower end 0 value indicating an additional anthropogenic contribution of low end 0 material possibly from the sandy lands in the adjacent north and west

petroleum geology and potential hydrocarbon plays in the gulf of suez rift basin egypt the gulf of suez in egypt has a north northwest south southeast orientation and is located at the junction of the african and arabian plates where it separates the northeast african continent from the sinai peninsula it has excellent hydrocarbon potential with the prospective sedimentary basin area measuring approximately 19 000 km 2 and it is considered as the most prolific oil province rift basin in africa and the middle east this basin contains more than 80 oil fields with reserves ranging from 1350 to less than 1 million bbl in reservoirs of precambrian to quaternary age the lithostratigraphic units in the gulf of suez can be subdivided into three megasequences a prerift succession pre miocene or paleozoic eocene a synrift succession oligocene miocene and a postrift succession post miocene or pliocene holocene these units vary in lithology thickness areal distribution depositional environment and hydrocarbon importance geological and geophysical data show that the northern and central gulf of suez consist of several narrow elongated depositional troughs whereas the southern part is dominated by a tilt block terrane containing numerous offset linear highs major prerift and synrift source rocks have potential to yield oil and or gas and are mature enough in the deep kitchens to generate hydrocarbons geochemical parameters sterane distribution and biomarker correlations are consistent with oils generated from marine source rocks oils in the gulf of suez were sourced from potential source rock intervals in the prerift succession that are typically oil prone type i and in places oil and gas prone type ii or are composites of more than one type multiple types i ii or iii for oil prone oil and gas prone or gas prone respectively the reservoirs can be classified into prerift reservoirs such as the precambrian granitic rocks paleozoic cretaceous nubian sandstones upper cretaceous nezzazat sandstones and the fractured eocene thebes limestone and synrift reservoirs such the miocene sandstones and carbonates of the nukhul rudeis kareem and belayim formations and the sandstones of south gharib zeit and

dolomite as a tracer for the source regions of asian dust 1 the possibility of using dolomite as a source tracer for asian dust was assessed samples of potential dust sources were systematically collected from the arid semiarid areas in north china dolomite of detrital origin was detected only in samples taken from the regions on the north margin of tibetan plateau nmtp thus the nmtp originated dust can be detected by the presence of detrital dolomite and applications are performed for the modern dust in beijing and the ancient dust deposits of loess in north china contribution of the nmtp originated particles to the spring dust in beijing and the loess in chinese loess plateau and eastern tibetan plateau are suggested however dolomite cannot be detected in the studied dust storm dust and the loess in northeast china indicating their sources other than the nmtp regions

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

isotope geochemistry of quaternary deposits from the arid lands in northern china abstract quaternary deposits of various types lacustrine desert sand river loess and loess like deposits from the southwestern tarim basin north tianshan northeast china and the central loess plateau exhibit an nd 0 range from 5 to 12 8 and a 147 sm 144 nd range from 0 110 to 0 140 their nd depleted mantle model ages are between 1 50 and 1 92 ga with a mean value of 1 7 ga th sc ratios vary over a wide range from 0 1 to 2 comparison of these geochemical signatures with those of the old australian shales and modern pacific ocean dust suggests a continuous input of mantle derived material into the crust over geological time the deposits from the north tianshan show clearly different chemical and isotopic features with significantly higher sm nd high 143 nd 144 nd low 87 sr 86 sr and low la lu and th sc ratios relative to those in the deposits from the other areas this indicates a geological control on the local source which has an overall young age and an enrichment of basic components the ce 0 values of two loess samples from the central loess plateau are 1 8 and 3 9 corresponding to depleted mantle model ages of 2 2 and 3 4 ga like the rb sr system the evolution of the la ce isotopic system in the crust may be to some extent decoupled from the sm nd system due to la ce fractionation by sedimentary processes the loess deposits and the desert sand are not distinguishable in isotopic composition but show somewhat different chemical compositions we conclude that the loess can have originated from desert processes since the difference in the chemistry of the desert sand and loess may result from mineral sorting during desert processes and aeolian transportation the loess deposits on the central loess plateau chemically and isotopically resemble the desert loess deposits in the southwestern tarim basin but do not resemble those of the north tianshan accordingly the loess on the plateau may have a source region in the tarim basin but clearly not in the north tianshan

a wind tunnel simulation of the effects of stoss slope on the lee airflow pattern over a two dimensional transverse dune 1 secondary airflow plays an important role in dune formation and development the lee airflow pattern over transverse dunes is important in determining the shape alignment and spacing of dunes and is influenced significantly by the lee slope angle in this paper we present the results of scaled wind tunnel simulations of the effects of stoss slope on the mean lee airflow patterns of transverse dunes the leeward velocity field was measured nonintrusively using particle image velocimetry to assess the airflow pattern we found that the flow separated over the dunes with a leeward angle close to the slip face angle of natural transverse dunes and was insensitive to stoss angle separation cells were characterized by a back eddy reattachment distance height area and aspect ratio were used to characterize the separation cell the first three parameters increased with increasing stoss angle for angles less than 15 but remained constant or decreased slightly with angles greater than 15 on the basis of the leeward velocity profiles six flow regions corresponding to those in previous models were recognized these regions are initially bounded by kinks but gradually transition downwind and merge to recover a uniform velocity profile after a significant distance we suggest that the separation cell is most developed when the angle of stoss slope reaches 15 but the significance of this angle in the evolution of transverse dunes needs further exploration

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

sedimentological evidence for early miocene fault reactivation in the gulf of suez the sedimentary response to early miocene fault reactivation and marginal uplift in the gulf of suez is strikingly evident within the gemsa half graben this mid rudeis event occurred in the late burdigalian 16 5 ma approximately 8 m y after the onset of rifting in outcrop complicated lateral facies transitions reflect the change from a ramped margin to a structurally controlled depositional environment angular unconformities and truncation mark this event atop marginal tilt block crests distal downlapping sequences are present in adjacent topographic lows that acted as sand depocenters channels draining the rift margins acted as point sources for basinward alluvial fan development sand ratio isopach maps reveal the presence of four active upper rudeis formation fan systems within the gemsa half graben

synthetic seismogram modelling of the oceanic pn phase the seismic oceanic pn phase is characterized by low spatial attenuation a high frequency wavetrain of extremely long duration and an onset velocity near 8 0 km s 1 in an effort to explain these properties models have been proposed for the mode of propagation of this phase which include energy entrapment within a low velocity channel1 2 propagation within an extremely low attenuation lithosphere waveguide3 4 and forward scattering from local heterogeneity within the oceanic crust5 6 through synthetic seismogram modelling we have generated realistic oceanic pn phases for an oceanic lithosph re model that did not contain any of these intrinsic properties the synthetic pn phase can be explained rather simply as a set of refractions from the lower lithosphre with subsequent reverberations within the oceanic water column and sediment layer many of the spectral properties associated with layer reverberation observed in the synthetic pn phase are revealed in data collected in the south west pacific complicated oceanic lithosphere models are not required to explain the gross characteristics of pn propagation

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

anisotropy in the oceanic lithosphere theory and observations from the ngendei seismic refraction experiment in the south west pacific summary p wave travel time data from a seismic refraction experiment on the 1983 ngendei expedition to the south pacific indicate anisotropy at two levels in the oceanic lithosphere in the upper mantle p wave velocities vary between 8 0 and 8 5 km s 1 with the fast direction at n30 e crustal anisotropy within layer 2 is characterized by azimuthal p wave velocity differences of about 0 2 0 4 km s 1 with the fast direction at n120 e orthogonal to the upper mantle anisotropy the observed anisotropy is consistent with a model in which aligned olivine crystals cause anisotropy in the upper mantle and aligned cracks within layer 2 cause anisotropy in the crust we examine a model of p wave propagation from a point source in an isotropic layer above an anisotropic half space and show that under these conditions anisotropy can cause seismic ray paths to deviate from the vertical plane connecting source and receiver this deviation has a negligible effect on seismic travel times but must be taken into account in modelling p wave polarization anomalies p wave polarization anomalies within the anisotropic half space are the sum of the particle motion deviation from the ray path and ray path deviation from the source receiver azimuth and are typically range dependent p wave polarization anomalies will also occur in the overlying isotropic layer purely as a result of the ray path deviation with greater deviations at long ranges a simple model of upper mantle anisotropy 6kms 1 crust above 8 0 8 6 km s 1 anisotropic mantle produces surface polarization anomalies of 1 5 3 5 in practice p wave polarization anomalies are difficult to observe because they are small compared to observed scatter in polarization data and are sensitive to differences in horizontal seismometer gain levels we examine the implications of anisotropic ray path deviations on travel times and p wave polarizations for the ngendei data as well as some previous marine seismic refraction experiments

nd and sr isotopic characteristics of chinese deserts implications for the provenances of asian dust silicate nd sr isotopes of the fine grained fractions of the 10 major deserts and sandy lands in north china and the loess in chinese loess plateau were systematically investigated wide ranges in nd sr isotopic compositions have been observed the results of the 7 0 b the deserts on the northern margin of tibetan plateau with end 0 ranging from 11 9 to 7 4 and c the deserts on the ordos plateau with the lowest end 0 11 5 the distribution of the threes isotopic regions is controlled by the tectonic setting in north china which implies that the materials of the deserts are derived from the locally eroded rocks from the surrounding mountains and the nd sr isotopic signatures of these deserts could be quit stable over the past million years on the sub tectonic time scales if there is any desert at those times the nd sr isotopic compositions of the loess are mostly close to those of the deserts in isotopic region b suggesting that the main source regions of the last glacial loess in the chinese loess plateau are badain jaran desert tengger desert and qaidam desert also the comparison between the nd sr isotopes of the 5 lm silicate fractions of the deserts and the ancient dust falls in the north pacific and greenland show that the asian end members of these dust falls are derived most from the deserts in the isotopic region b and less from those in the isotopic region c

geochemical and isotopic studies of aeolian sediments in china the sr and nd isotopic rare earth element ree and major element compositions together with mineral and grain size proportions are reported for aeolian loess deposits and desert sands from several chinese localities the study was carried out in order to examine regional variations in the isotopic and geochemical features of these aeolian sediments and to constrain the provenance of chinese loess samples include loesses from the tarim and junggar basins and desert sands from the taklimakan desert in north west china loess from the ordos area and desert sands from the tengger and mu us deserts in north central china as well as loess and desert sands from the naiman area north east china ree distributions show minimal variation among the chinese loess deposits whereas those for the desert sands show regional variations new isotopic data document a latitudinal variation in sr and nd isotopic features for the loesses and desert sands the naiman and junggar loesses have distinctly lower 87sr 86sr ratios and higher end 0 values than the loesses from the tarim basin the ordos area and the loess plateau among the desert sands the naiman samples have higher end 0 values than the taklimakan tengger and mu us samples isotopic data suggest that loesses of the loess plateau were supplied from the tarim basin loesses and taklimakan desert sand and that the naiman loesses were supplied from the junggar basin loesses the latitudinal variation in the loesses and desert sands may be partly explained by isotopic variations reported previously for moraines from the tianshan and west kunlun mountains which are possible sources for the loesses and desert sands these inferences on the provenance of the loesses and desert sands are consistent with the dust transport pattern over east asia

sr and nd isotopic composition of dust in dunde ice core northern china implications for source tracing and use as an analogue of long range transported asian dust abstract this study presents the sr and nd isotopic composition of dust from a shallow dunde ice core 38 06 n 96 24 e 5325 m a s l northern china in order to trace its source regions and the provenance of long range transported lrt asian dust dunde dust samples show similar sr 87 sr 86 sr averages 0 719982 and varies between 0 715220 and 0 721874 and nd e nd 0 averages 10 6 and ranges from 11 1 to 9 9 isotopic composition to desert sand from taklimakan and qaidam revealing that the tarim and qaidam basins are the most possible source areas for dunde dust while the contribution from badain jaran and tengger seems very small or unlikely our results indicate that materials from taklimakan can be entrained from the tarim basin and transported to qilian shan by westerlies under the present climate the sr nd isotopic composition of dunde dust which is a good analogue for the long range transported asian dust resembles that of north pacific and greenland dust indicating that the important provenance of end members of the asian dust seems to be taklimakan on a regional scale

the influence of near surface winds on the sr isotope composition of aeolian sediments a wind tunnel experiment article we used wind tunnel experiments to simulate the effect of near surface wind velocity on the silicate stron tium sr isotopic compositions of the fractions b10 m in windblown dust using intact surface samples obtained from a potential dust source area in arid northern china our results showed that the 87 sr 86 sr ratios of the silicate fractions in the windblown dust varied with near surface wind speed and with the total amount of the fraction b10 m for the five samples that we analyzed the variances of the 87 sr 86 sr ratio under a range of wind velocities were 0 00014 0 00004 0 00052 0 00151 and 0 00012 in addition although most samples were collected at the same site and were treated in the same way there were still differences in the 87 sr 86 sr ratios with an intersample variance of up to 0 00409 these observations suggest that although

size dependent geochemical signatures of holocene loess deposits from the hexi corridor china well dated holocene loess sequences from uplifted river terraces at the northern margin of the tibetan plateau are characterised by their chemical grain size sr isotope and their oxygen and carbon isotope composition of the carbonate fractions prevailing wind directions suggest the source areas of the loess to be largely restricted to dry lands in northwest china and the deserts north to the hexi corridor e g badain jaran and tengger desert which receive fluvial input by rivers draining the qilian shan the dry lands of northwest china are one of the most important dust source areas globally local and conditions make the investigated loess sequences insensitive to element leaching the loess is characterised by a relatively narrow variation of sr 87 sr 86 0 7139 0 7164 the sr 87 sr 86 ratios of surface and carbonate bound sr are similar 0 7114 and 0 7111 and lower than those of silicate bound sr 63 2 mu m fractions similar to 0 7196 2 mu m fractions similar to 0 7247 since the clay fractions have higher caco3 contents than the silt fractions the isotopic contrast between the silicate debris of clay and silt size is camouflaged in the bulk compositions of these grain size fractions oxygen isotope and chemical compositions of clay and silt sized carbonate particles differ significantly silt sized loess carbonates formed authigenically and they are largely present as coatings of silicate grains whereas clay sized carbonate particles are of remote provenance and precipitated under evaporative conditions in line with further implications from the multi proxy study upward trends in the composition of the pedogenic carbonate document climate change to drier conditions after the mid holocene c 2009 elsevier ltd all rights reserved

surface and near surface effects on seismic waves theory and borehole seismometer results a simple plane wave model is adequate to explain many surface versus borehole seismometer data sets using such a model we present a series of examples which demonstrate the effects of the free surface near surface velocity gradients and low impedance surface layers on the amplitudes of upcoming body waves in some cases these amplitudes are predictable from simple free surface and impedance contrast expressions however in other cases these expressions are an unreliable guide to the complete response and the full plane wave calculation must be performed large surface amplifications are possible even without focusing due to lateral heterogeneities or nonlinear effects both surface and borehole seismometer site responses are almost always frequency dependent ocean bottom versus borehole seismic data from the 1983 ngendei seismic experiment in the southwest pacific are consistent with both a simple plane wave model and a more complete synthetic seismogram calculation the borehole seismic response to upcoming p waves is reduced at high frequencies because of interference between the upgoing p wave and downgoing p and sv waves reflected from the sediment basement interface however because of much lower borehole noise levels the borehole seismometer enjoys a p wave signal to noise advantage of 3 to 7 db over nearby ocean bottom instruments

the effect of quaternary alluvium on strong ground motion in the coyote lake california earthquake of 1979 abstract the effect of alluvium on strong ground motion can be seen by comparing two strong motion records of the coyote lake california earthquake of 6 august 1979 m l 5 9 one record at a site on franciscan bedrock had a peak horizontal acceleration of 0 13 g and a peak horizontal velocity of 10 cm sec the other at a site 2 km distant on 180 meters of quaternary alluvium overlying franciscan had values of 0 26 g and 32 cm sec amplifications by factors of 2 and 3 horizontal motions computed at the alluvial site for a linear plane layered model based on measured p and s velocities show reasonably good agreement in shape with the observed motions but the observed peak amplitudes are greater by a factor of about 1 25 in acceleration and 1 8 in velocity about 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance the remainder may represent focusing by refraction at a bedrock surface concave upward there is no clear evidence of nonlinear soil response fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model in particular the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value indicating that no significant nonlinearity occurs in the secant shear modulus computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0 5 to 1 0 or greater the data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections and more the simple effect of the low near surface velocity application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear wave velocity

increasing nd isotopic ratio of asian dust indicates progressive uplift of the north tibetan plateau since the middle miocene the time and rate of tibetan uplift is critical in understanding both the geodynamics of plateau growth and the influence of mountain building on climate change models predict that the uplift of the north tibetan plateau ntp occurred later than uplift of the south and central tibetan plateau uplift of the ntp is believed to have initiated the aridity in the interior of asia and to have critically affected the evolution of asian monsoon and ultimately global climate the history of ntp uplift has remained uncertain however scenarios range from early miocene to the past million years this work provides new evidence by relating the nd isotopic evolution of asian dust to ntp uplift the sources of the asian dust are located in the arid lands between the ntp and the central asia orogen mass balance calculations indicate that the decreasing e nd values from 8 2 to 10 4 for pacific dust since 15 ma reflects increasing relative contribution of ntp materials 40 to 70 to the dust source as paleoelevation in the central asia orogen has largely remained constant the increasing relative ntp detritus contribution is interpreted to reflect the progressive surface uplift of the ntp at a rate of at least 0 12 mm yr 1 since 15 ma

sedimentology and sequence stratigraphy of a transfer zone coarse grained delta miocene suez rift egypt this study focuses on miocene sedimentation and stratigraphic evolution in a major transfer zone at the northern tip of the thal fault segment gulf of suez the succession generally shoals upwards from offshore mudstone containing pro delta turbidites into conglomeratic delta foresets and topsets with sandstone dominated shoreface facies coexisting laterally despite this upward shoaling key stratal surfaces marking abrupt changes in relative sea level allow the succession to be divided into four stratal units the stacking pattern of the stratal units suggests an initial relative sea level rise that generated a major marine flooding surface a relative sea level fall followed resulting in widespread exposure and incision during the ensuing relative sea level rise a lowstand coarse grained delta and coeval shoreface succession prograded several kilometres basinward the stratigraphic development of the transfer zone delta is in marked contrast to that of aggradationally stacked deltas that occur near the centre of the baba sidri fault segment further south at the transfer zone low rates of subsidence and accommodation development coupled with a high sediment supply derived from a large fault tip drainage catchment have produced a strongly progradational delta subject to marked changes in relative sea level in the fault centre location however higher rates of accommodation development coupled with lower rates of sediment supply from footwall catchments have produced aggradationally stacked deltas the results from this study have implications for sequence stratigraphic models and hydrocarbon exploration within extensional basins

variations in 87sr 86sr ratios of calcites in chinese loess a proxy for chemical weathering associated with the east asian summer monsoon abstract 87sr 86sr ratios of loess paleosol calcites of luochuan in china over the past 130 ka display a regular change with increasing trend of 87sr 86sr ratios in the following order loess calcite weakly pedogenetic paleosol calcite paleosol calcite pure secondary calcite the observed variations in the 87sr 86sr record of loess paleosol calcites correlate closely with the records of the magnetic susceptibility coarse grain fraction content in the same profile an et al chin sci bull 39 1994 182 184 and the specmap stacked 18o record of global ice volume imbrie et al in berger et al eds milankovitch and climate part i reidel boston 1984 pp 269 305 strata from the last glacial consist mostly of loesses and weakly developed paleosols and have lower 87sr 86sr ratios averaging 0 71079 paleosols which developed during the last interglacial have higher 87sr 86sr ratios averaging 0 71131 the four periods ca 125 110 98 90 80 75 and 9 5 ka b p of increased summer monsoonal rainfall coincide with the four peaks in 87sr 86sr values a series of 87sr 86sr high frequency high amplitude fluctuations is superimposed on the last glacial interglacial cycle over the past 130 ka occurring on millennium timescales with an average time span of about 3 ka during the last glacial the fluctuations of the 87sr 86sr ratios of the luochuan loess paleosol calcites lie in the range 0 71036 0 71176 for the past 130 ka the study shows that the sr isotopic system in loess paleosol calcites may therefore be an excellent proxy of chemical weathering on continents associated with the east asian summer monsoon

a comparison between a downhole seismometer and a seismometer on the ocean floor abstract we have compared the signal and noise characteristics recorded by a downhole seismometer and a nearby within 200 m ocean bottom seismometer in the deep ocean 5 5 km absolute noise levels and signal to noise ratios from the two instruments are remarkably similar we attribute this unexpected similarity to the shallow emplacement depth of the downhole instrument 194 m subbottom and the soft sediment into which it was clamped

the gulf of suez northern red sea neogene rift a quantitive basin analysis abstract subsidence analysis backstripping was carried out on a series of wells from the gulf of suez and northern red sea region of egypt in order to examine the interplay between tectonic events basin subsidence sedimentation and sea level changes in a young developing ocean basin and continental margin using constraints on chronostratigraphy and paleodepth from various sources combined with stratigraphic and structural information from industry wells and other geophysical sources it has been possible to compile the data necessary to perform geohistory analyses throughout the region major subsidence due to crustal thinning began 25 ma with sedimentation initially occurring in isolated sub basins these earliest sediments record the transition from continental to marine depositional environments subsequently during early and middle miocene times subsidence was rapid and uniform along and across the entire rift basin open marine sedimentation occurred across all structural regimes the mid clysmic tectonic event 16 5 ma resulted in structural rearrangement of the rift basin and uplift of the rift shoulders rapid subsidence continued as global sea level fell producing a series of prograding siliciclastic fan deltas at the rift margins at 15 5 ma opening of the suez rift was terminated tectonic subsidence decreased dramatically in the southern rift and ceased entirely in the northern rift tensional plate motion probably was transferred from the gulf of suez to sinistral strike slip movement on the dead sea transform at this time the quiescence in subsidence combined with a lowered global sea level resulted in the deposition of a thick up to 4 km series of evaporites within the central trough of the rift from the middle to latest miocene the accumulation of such a thick sequence of sediments during a phase of decreased tectonic subsidence is interpreted as a filling in of the rift topography which developed during the earlier period of rapid subsidence and rift shoulder uplift and continued compaction a rapid global sea level rise concomitant with a subsequent pulse of increased tectonic activity in the latest miocene earliest pliocene returned the rift to dominantly marine conditions

modeling the seismic response of sedimentary basins we compare displacements due to incident sh waves on the surface of a polyurethane foam model of a two dimensional semi cylindrical basin with theoretical results based upon an analytic solution by trifunac 1971 and obtain excellent agreement observations indicate that the sv response is similar to the sh response except that the sv induced resonances are of somewhat shorter period further measurements are made on a foam model of an idealized alluvial fan sh responses observed in cross profiles across the mouth and head of the fan indicate that the resonance observed on the deeper foam at the mouth of the fan is of longer period than the resonance observed at the head on shallower foam finally the amplitudes on the fan are observed to be somewhat larger for sh and sv waves traveling downdip than for such waves traveling updip given the same source receiver distance and source amplitude the agreement between theory and experiment for the two dimensional semicylindrical basin geometry indicates that polyurethane foam with different densities and rigidities can successfully model the seismic responses of piecewise homogeneous linear elastic media in configurations with arbitrarily complicated three dimensional geometries once constructed such models provide inexpensively the response to various kinds of input motion incident at arbitrary angles the applicability of foam models to real earth structures depends upon the validity of assuming linear elastic behavior and piecewise homogeneity