volcanic shards from santorini upper minoan ash in the nile delta egypt one of the largest volcanic outbursts recorded in early human history is the cataclysmic eruption of santorini thera which occurred about 35 centuries ago in the southern aegean sea this explosive event termed upper minoan or upper thera produced a tephra fall believed by archaeologists and volcanologists to have been widespread in the eastern mediterranean1 4 upper minoan ash has been found on land in the aegean and hellenic arc regions including crete5 6 and rhodes7 to date however there has been no confirmed observation of this ash on land across the mediterranean in north africa we now report evidence for the presence of ash ejected from this explosion in sediment cores recovered in the eastern nile delta of egypt this discovery of upper minoan glass shards extends considerably the zone of confirmed ash fall to the southeast of santorini and serves as evidence of a major natural phenomenon affecting egypt during the reign of pharaohs in the eighteenth dynasty it is quite possible that this ash fall event may have given rise to texts pertaining to darkening of the sky and veiling of the sun in early historic records

seismic frequency laboratory measurements of shear mode viscoelasticity in crustal rocks ii thermally stressed quartzite and granite forced torsional oscillation techniques have been used to explore the seismic frequency shear mode viscoelasticity of specimens of two crustal rocks cape sorell quartzite and delegate aplite cycled between room temperature and 700 c under conditions of moderate confining pressure the anisotropy and intergranular inhomogeneity of thermal expansivity in these materials give rise to large deviatoric stresses resulting in thermal cracking at temperatures above a pressure dependent threshold temperature associated with the onset of very pronounced temperature sensitivity of the shear modulus in general accord with the predictions of fracture mechanics models for delegate aplite in particular the shear modulus behaves reproducibly during multiple thermal cycles at different confining pressures consistent with the notion that the thermal cracks are of low aspect ratio minimum maximum dimension and are therefore readily closed by the prevailing confining pressure once the thermal stresses are removed marked frequency dependent dissipation of shear strain energy is observed on heating each rock to temperatures 500 c although the attenuation varies significantly with prior thermal history probably as a result of progressive dehydration and relaxation of deviatoric stresses temperature and pressure dependent crack densities for delegate aplite have been estimated by comparison of the observed shear moduli with those expected for a crack free aggregate in parallel with the forced oscillation tests measurements have been made of the rate at which argon pore pressure equilibrium is re established following a perturbation combination of these results which provide a proxy for permeability with the inferred crack densities indicates that the variation of permeability with crack density is well described by a percolation model with a threshold crack density of 0 2

seismic frequency laboratory measurements of shear mode viscoelasticity in crustal rocks i competition between cracking and plastic flow in thermally cycled carrara marble in the first phase of a seismic frequency study of the viscoelasticity of cracked and fluid saturated crustal rocks forced torsional oscillation experiments have been conducted on specimens of carrara marble subjected to multiple thermal cycles up to 560 c under confining pressure of 50 mpa the experimental results showed distinctly different behaviour of both the shear modulus and internal friction between the first and subsequent thermal cycles a pronounced reduction in shear modulus g observed during the first series of thermal cycles at temperature t 400 c presumably due to dislocation relaxation contrasts with frequency independent q 1 at lower temperatures the relatively sudden onset of markedly frequency dependence seismic wave attenuation might prove to be a useful diagnostic of temperature under crustal conditions

the effect of thermal cycling on the seismic quality factor q of some sedimentary rocks changes in q in rocks in response to thermal cycling can result from the removal of physisorbed water an increase in the crack density and therfore the internal surface area at temperatures greater than 400 sup 0 c the removal of chemisorbed oh groups which are the adsorption sites for physisorbed water and the dehydration of clays when rocks are heated to temperatures of 100 sup 0 200 sup 0 c the change is q is reversible and is due to the removal of physisorbed water sioux quartzite and berea sandstone were thermally cycled to 657 sup 0 c and 385 sup 0 c respectively the q of both rocks increased when measured over a broad range of relative humidities but decreased at low humidities 10 25 measurements of adsorption isotherms for the berea sandstone showed no loss of adsorptive capacity of the clays although the surface area of thermally cracked rocks increased the number of sites where adsorbed water molecules contribute to attenuation decreased

changes in compressional and shear wave velocities and dynamic moduli during operation of a hot dry rock geothermal system compressional and shear wave velocities measured during cross well seismic surveys are found to decrease during operation of a hot dry rock geothermal system the relative p and s wave velocity decrease is very close to values predicted by o connell and budiansky 1974 who modeled velocities in rocks containing fluid saturated and dry cracks because our data fit their model quite well we attribute the velocity decrease to an increased density of fluid filled fractures in the reservoir fracture density parameters of o connell and budiansky range as high as 0 365 near the main heat transfer areas of the geothermal reservoir the dynamic shear and young s modulus are significantly lower near the principal heat transfer surfaces but the bulk modulus is largely unaffected these observations suggest that the velocity differences are caused by fully saturated fractures we demonstrate that the fractures inferred by this survey may have lengths as large as 70 cm these fractures may have been caused by shear failure microcracking associated with thermal drawdown or thermal stress cracking

the pre atlantic hf isotope evolution of the east laurentian continental margin insights from zircon in basement rocks and glacial tillites from northern new jersey and southeastern new york abstract this paper presents laser ablation u pb age and hf isotope data for zircons from basement rocks and glacial deposits in northern new jersey and southeastern new york the purpose is to understand the eastern laurentian continental margin s hf isotope record in relation to its geologic evolution prior to the opening of the atlantic ocean the basement samples encompass a meso to neoproterozoic continental margin arc an anatectic magmatic suite as well as a late ordovician alkaline igneous suite emplaced during post orogenic melting of the lithospheric mantle additional samples were collected from terminal moraines of two quaternary continental ice sheets across the entire dataset zircons with ages corresponding to the timing of continental margin arc magmatism 1 4 ga to 1 2 ga have positive e hf initial values that define the more radiogenic end of a crustal evolution array this array progresses towards more unradiogenic e hf initial values along a series of low 176 lu 177 hf 0 022 to 0 005 trajectories during subsequent anatectic magmatism 1 2 ga to 1 0 ga and later metamorphic and metasomatic re working 1 0 ga to 0 8 ga of the continental margin arc crust in contrast nearly chondritic e hf initial values from the late ordovician alkaline magmas indicate that the laurentian margin was underlain by a re fertilized mantle source such a source may have developed by subduction enrichment of the mantle wedge beneath the continental margin during the mesoproterozoic additionally preliminary data from a metasedimentary unit of unknown provenance hints at the possibility that some of the sediments occupying this portion of the laurentian margin prior to the ordovician were sourced from crust older than 1 9 ga

clay mineral distribution patterns as influenced by depositional processes in the southeastern levantine sea analysis of the clay minerals in stratigraphically defined cores 23 000 years bp to the present in the southeastern levantine nile cone sector of the eastern mediterranean indicates that depositional processes are very significant in determining the distribution of clay assemblages the interplay of long distance transport by water mass circulation downslope mass gravity transport and wind dispersal is recorded by the clay assemblages in each of the stratigraphic layers the temporal variations and spatial distribution of smectite the dominant clay mineral of the river nile can be related closely to downslope gravity related processes and to deposition from water mass flow increased kaolinite in part of wind blown origin from north africa correlates with areas receiving low terrigenous input but influenced by enhanced suspended sediment transport illite and chlorite distributions are most closely associated with a northern levantine provenance and dispersal by the circulation of eastern mediterranean water masses climatically induced changes may have altered the clay minerals in the region and minor diagenetic changes may have occurred but these factors do not fully explain observed vertical clay mineral changes in the late quaternary we conclude that palaeoclimatic interpretations based on vertical clay mineralogical changes at single core localities should be approached cautiously in small ocean basins such as the mediterranean

thermal stress cracking in granite we have developed a comprehensive experimental capability to study thermally induced microfractures in rock we count acoustic emissions and measure compressional wave velocities while a sample is heated to a maximum temperature of 300 c under confining pressures up to 55 mpa after a heating cycle we measure crack porosity and crack compressibility we count the cracks under an sem sorting them by grain boundary and intragranular types and by mineral pair occurrence our observations reveal that 1 significant thermal cracking occurs in granites heated above 200 or 250 c under 28 and 55 mpa and above 100 c in granites heated under 7 mpa 2 most newly created thermal cracks close at pressures below 40 mpa 1 5 km depth 3 grain boundaries between quartz grains or between quartz and another mineral are preferentially cracked 4 the threshold temperature for acoustic emissions is a positive linear function of pressure 5 total acoustic emission counts in westerly granite heated to 300 c are slightly lower under 55 than 28 mpa confining pressure and are substantially lower under 28 than 7 mpa 6 the compressional velocity decreases 22 as westerly granite is heated to 300 c at 7 mpa 15 at 28 mpa and 10 at 55 mpa and 7 greater hysteresis in compressional velocities occurs in samples heated at lower pressures the acoustic emission counts in westerly granite during heating show one or more peaks of activity as a function of temperature with more peaks at lower pressures we interpret this result to mean that additional crack populations are able to open at lower confining pressures the curves of acoustic emission count rates can be fit by summing one to three gaussian density functions

origin of late glacial holocene hemipelagic sediments in the aegean sea clay mineralogy and carbonate cementation abstract four hemipelagic lithological units are identified in the late glacial to holocene sediments in the aegean sea these lithologies are silty clay and clay in texture and include a varying mixture of loose terrigenous sediments supplied from the adjacent landmass gravel to sand sized cemented carbonate clasts and nodules sand to silt sized air born volcanic debris and biogenic remains sediment dispersal during the past 14 000 years was controlled mainly by the fluvial discharge rate by sea level variations which determined the proximity of basins to river mouths and by oceanographic conditions in the aegean sea cemented carbonate clasts and nodules occur in all sediments except unit c sapropel s1 they are well to friably cemented mottled to peloidal micrite or microcrystalline inter granular cement between terrigenous and bioclastic debris and the carbonate is 10 11 mole magnesium calcite during the deposition of sapropel s1 unit c the aegean sea was strongly stratified with colder more saline water masses occupying the deep basins which prevented the development of cemented carbonate nodules and clasts aragonite as pteropods and microcrystalline aragonite is present throughout the cores and together with the cemented carbonate clasts and nodules show that shallow pore waters in the aegean sea have been saturated to supersaturated with respect to both aragonite and magnesium calcite for at least the past 14 000 years results of xrd studies show that unit c sapropel s1 is characterized by lower smectite and kaolinite and higher illite and chlorite than the other units lower smectite illite and kaolinite chlorite ratios in unit c may reflect increased supply of illite and chlorite from european lowland rivers flowing into the black sea from rivers discharging directly into the northern and eastern aegean sea and decreased supply of kaolinite which is mainly of north african origin

on the late pleistocene holocene sapropel record of climatic and oceanographic variability in the eastern mediterranean sapropels and intercalated marls in a piston core from the eastern mediterranean are chemically and mineralogical distinct kaolinite smectite and total s contents fe a1 ba a1 co a1 mo a1 and v a1 are higher whereas quartz mg calcite illite contents si a1 ti a1 k a1 rb a1 and zr a1 are lower in the sapropels missing and ghost sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis primary production was higher ba a1 and bottom water and or interstitial oxygenation was lower co a1 mo a1 ni a1 and v a1 during sapropel formation wind speeds quartz clay si a1 and zr a1 and bottom water salinities mg calcite calcite were higher during periods of marl formation sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes which altered circulation production and sediment source areas

quartz grain surface textures and depositional interpretations nile delta region egypt abstract this study using the scanning electron microscope sem identifies the assemblages of quartz grain surface textures in sands from six modern environments in the northeastern nile delta and adjoining regions of egypt differences in the proportions of mechanical and chemical features serve to distinguish aeolian dominated settings desert coastal dunes from subaqueous ones the assemblage of surface features also serves to identify open marine nearshore offshore shelf beach and river sands the sem results show a considerable overlap in the types of surface features from environment to environment as might be expected in this deltaic system where sediment has been recycled between markedly different dune fluvial coastal marine settings in some cases this overlap phenomenon complicates the correlation of subsurface sand layers of late pleistocene and holocene age between cores nevertheless the present investigation shows that identification of surface textures in the nile delta is most helpful in interpreting subsurface layers in cores such as those of river and dune origin i e those quartz rich sands that otherwise are usually devoid of depositionally diagnostic mineralogical faunal and floral components

late quaternary stratigraphy and paleogeography of the eastern nile delta egypt abstract a petrological study of numerous sediment borings identifies the late pleistocene and holocene lithofacies in the northeastern nile delta of egypt a coarsening upward sequence characterizes the major holocene depocenters located along the northern margin of the present delta stratigraphic correlation of radiocarbon dated sections and mapping of key facies such as delta front mud reveal the locations of four major holocene delta lobes related to former distributary branches of the nile river mendesian pelusiac tanitic and pre modern damietta these lobes formed primarily of marine prodelta and delta front deposits interfinger geographically but radiocarbon dating indicates that their bases are not synchronous lobes developed for the most part since 8000 years b p i e as the rate of eustatic sea level rise began to decrease climatic and sediment discharge fluctuations lateral migrations of distributaries and isostatic subsidence of land are additional factors that affected the temporal and spatial distributions of the lobes paleogeographic maps reveal the changes with time in the distributions of different lobes and deltaic plain environments marsh lagoons and concomitant displacement of the coastline holocene sediment accumulation rates to 500 cm per 1000 years are calculated this is 10 times greater than that on the nile cone and 50 times greater than on the egyptian continental shelf the delta coastal margin in the study area migrated northward by as much as 50 km during the past 5000 years an average progradational rate of up to 10 m per year the general configuration of the present delta developed during the past millennium the major changes recently induced by man in this region coupled with a series of continuing natural phenomena slow rise in sea level coastal erosion subsidence have markedly affected the evolution of the delta petrological study of the nile delta sediments provides baseline reference information to help recognize changes in the recent geological past to help identify those taking place at present and possibly to help predict those likely to occur in this region in the future

accelerated currents and sediment transport off the damietta nile promontory severe erosion of valuable agricultural and recreational lands along the apex of the damietta nile promontory fig 1 following the closure of the aswan high dam remains a problem despite extensive shoreline studies the fate of eroded material and the main mechanism of sediment transport along this coast are unclear1 an 11 day bathymetric survey provided exploratory measurements in the coastal waters surrounding the promontory we report here current meter and side scan sonar observations which indicate that a high speed jet forming off the promontory is driving a field of actively migrating sand ridges easterly over a smooth mud plain these ridges seem to be the dominant along shore pathway for sediment transport between damietta and the suez canal

prediction of elastic moduli via crack density in pressurized and thermally stressed rock the elastic moduli of crystalline rocks show marked reductions when heated to high temperatures t even when subjected to confining pressure p this degradation of moduli has been attributed to the creation of new microcracks or opening of preexisting microcracks from thermal stresses due to differential thermal expansion between mineral grains a similar lowering of moduli is observed on depressurization of crystalline rock and is also thought to be due to microcrack opening a spherical inclusion model has been used to predict whether a given change in t or p will introduce a tensile crack between a mineral constituent and the rock matrix by using the principal thermal expansions and compressibilities of individual minerals and simplifying assumptions we are able to predict crack densities as a model rock is subjected to changes of p and t experimental crack densities for three granitic rocks a gabbro and two basalts are calculated from high temperature high pressure young s modulus data the predicted and inferred crack densities are then compared for these six rocks the results are dependent upon the p t path to which the rock is subjected and comparisons are for the case in which the rocks are heated only at maximum p and then decompressed isothermally considering the simplicity of the model we believe the comparisons are quite close for the three granitic rocks the model underestimates the crack densities of the quartz free gabbro and basalts

geochemistry of pelitic and psammopelitic precambrian metasediments from southwestern sri lanka implications for two contrasting source terrains and tectonic settings most of the pelitic and psammopelitic metasediments of southwestern sri lanka are compositionally transitional between shales and greywackes and are of two isotopically distinct types metasediments of the northern part have nd model ages of 1 5 ga and belong to the relatively younger nd model age province of wanni complex wc model ages of two southerly located samples are 2 8 ga being compatible with those of the highland complex hc in accordance with mostly mesoproterozoic to late archaean crustal residence ages cr ni la th and ree data also suggest that the sources of these metasediments are plagioclase fractionated post archaean upper crustal material crustal differentiation of source terrains corresponding to the hc and the wc probably occurred at distinctly different time intervals significant differences exist between the major and trace element chemistry of the metapelites from the wc north and the hc south suggesting derivation from two different source terrains metasediments of the south are slightlymmore siliceous low in sc and v and highly enriched in lree 220 ppm their sources have been chemically evolved felsic igneous rocks and or recycled sediments relatively high v sc feo mgo tio2 and slightly low sio2 in the rocks of the wc indicate contribution of more basic sources cia chemical index of alteration estimates and comparative alkali alkaline earth element patterns suggest relatively fresh source material the o isotope data indicate that the pre metamorphic isotope signatures are preserved and the clay component of the original sediments mainly consisted of illite typifying continental weathering conditions sediments of the south hc were probably deposited in a passive continental margin continental rift environment while those of the northern part wc were probably formed at an andean type active continental margin the two units were tectonically juxtaposed prior to pan african granulite metamorphism

strain dependent attenuation observations and a proposed mechanism the measured attenuation q 1 of a rock is a function of a number of parameters one of those being the applied strain amplitude it is important to understand the effect that strain amplitude has on q 1 for several reasons different measurement techniques use differing strain amplitudes and may measure a dissimilar q 1 near source large strain wave propagation may behave highly non linearly and the strain amplitude dependence can provide insight into the attenuation mechanism a physical model based on the contact friction between crack surfaces in the rock has been developed to describe rock deformation and dissipation under large applied strain the three dimensional crack surfaces are characterized by a statistical distribution of asperity heights the sliding contact of these spherically tipped asperities dissipates frictional energy hertzian theory is applied to the average asperity contact and predicts that the large strain attenuation is given by q 1 k e p4 3 where k is a constant consisting of the matrix elastic parameters is the crack density e is the strain amplitude and p is the confining pressure the total attenuation measured appears to be the sum of this strain dependent term and a strain independent term the results of ultrasonic pulse transmission experiments are compared with the model s prediction both p and s waves with strain amplitudes from 10 8 to 10 5 were employed frequencies from 0 4 to 1 5 mhz were used in conjunction with rock confining pressures of 2 to 580 bars on dry berea sandstone and lucite samples the spectral ratio method and rise time technique were applied to deduce the q 1 values the observed data and other observations from the literature compare well with the model s prediction for the dependence of q 1 on large strain amplitude crack density and pressure

how much gabbro is in ocean seismic layer 3 ocean seismic layer 3 is distinguished from layer 2 by higher velocities lower variability and lower gradients in velocity with depth based on studies of rocks recovered from ophiolites and walls of fracture zones most models of lower ocean crust correlate seismic layer 3 with sequences of gabbroic lithologies the average velocity 6 5 km s for a vertical seismic profile in a gabbro sequence at ocean drilling program odp hole 735b is consistent with refraction values for layer 3 however the q inverse attenuation obtained from these data after correction to temperature and pressure conditions in lower crust are too low to be consistent with amplitudes of signals observed in refraction experiments laboratory measurements of q on gabbros from hole 735b and ophiolites are also one to two orders of magnitude lower than seismic refraction q these results indicate that the gabbro sequence at hole 735b cannot be typical of seismic layer 3 based on q upper layer 3 may be metadolerite and lower layer 3 may include interbedded gabbros and ultramafics serpentine is highly attenuating and is unlikely to be a major component

crack propagation by differential insolation on desert surface clasts abstract in the southwest u s cracks in alluvial fan surface clasts have a preferred orientation independent of rock fabric and shape in this paper we show that differential insolation of incipient cracks of random orientations predicts a distribution of crack orientations consistent with field observations in this model crack growth by hydration and or thermal weathering is primarily a function of local water content at the crack tip crack tips that experience minimal solar insolation maintain a greater average moisture and hence weather more rapidly than cracks that experience greater solar insolation to show this we used a numerical radiative transfer code to quantify the solar insolation of rectangular cracks at 35 n latitude with a range of depths and orientations the amount of solar energy reaching the bottom of each crack was calculated at 5 min intervals over the day for several days of the year to determine hourly daily seasonal and annual energy deposition as a function of crack depth and orientation by assuming that only crack orientations that effectively shield their interiors and minimize their water loss are able to grow the pattern of cracks produced by the model is consistent with field observations the annual average insolation which controls water retention is associated with the two primary modes of crack orientation the effect of daily recharge by summer rains of the north american monsoon system is consistent with the observed deviations from these primary modes model results suggest that both the annual average insolation and the daily pattern of rainfall is recorded in the preferred crack orientations of surface clasts in the southwest u s

reconstructing precipitation changes in northeastern africa during the quaternary by clay mineralogical and geochemical investigations of nile deep sea fan sediments abstract clay mineralogy combined with high resolution element geochemistry of core md90 9064 located in the distal part of the nile deep sea fan levantine basin have been investigated to reconstruct rainfall changes in northeastern africa during the quaternary and to determine possible climatic controls clay minerals of core md90 964 are derived mainly from three sedimentary sources the sahara nile river and egyptian wadis and are characterized by contrasted mineralogical composition variations in illite content and logarithm ratios of si al and k al permit the tracking of eolian input from sahara to the mediterranean sea it is suggested that precipitation changes in the sahara are mainly dominated by glacial interglacial cycles such variations are owing to a shift of climatic conditions in the north atlantic from a nao positive like condition in glacial times to a nao negative like condition in interglacial times fe content in the levantine sediments is mostly derived from fe bearing heavy minerals brought by the nile river therefore variations of fe al ratios can be used to establish precipitation changes in the nile river basin long term variation in precipitation in the nile river basin is governed by precessional and eccentricity signals implying that the african monsoon is the most significant controlling factor for precipitation changes in this region precipitation changes in the northeastern coasts of africa are reconstructed using kaolinite contents provided by the egyptian wadis it is reported that precipitation in coastal northeastern africa is mainly of the mediterranean climate type long term variations in rainfall in this region are also affected by the nao like climatic variability and thus dominated by the glacial interglacial cycles

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

composition of clays along the continental shelf off israel contribution of the nile versus local sources the eastern mediterranean sedimentary regime is dominated by sediment transport from the nile river and its delta but recent studies have also suggested a certain contribution of clay fraction from streams to the continental shelf and slope off israel in the present study we focused on clay fraction deposition along the inner 40 1000 m water depth shelf of israel in order to substantiate and quantify its different sources for this purpose detailed xrd mineralogical determinations as well as chemical compositions of the clay 2 m fraction of marine and continental sediments were used the clay mineral composition of israeli stream sediments is variable with no distinct spatial or temporal trend but within a limited assemblage this clay assemblage is made up of illite smectite is phases 70 90 kaolinite 5 25 and illite 10 and is similar to that of the nile however it is clearly distinguished by the type of the is phases which are derived mainly from mesozoic outcrops and recent sediments soils and are less expandable than those of the nile which are derived mainly from weathered basalt the nile derived component is depleted in the marine clay fraction along the israel coast evidenced by a decrease of is expandability and the fe2o3 al2o3 ratio and an increase in the k2o al2o3 mgo al2o3 and cao al2o3 ratios the depletion is well pronounced north of tel aviv where the largest coastal plain stream flows to the sea a northward increase of carbonates in the clay fraction and particularly of the bioskeletal component is indicated by the ratios of mgo and sr to cao the contribution of the local streams to the shallow shelf marine clay fraction is estimated to be about 50 a minor contribution of desert dust is identified by the relative increase in kaolinite in the marine sediments south of tel aviv

cortlandt beemerville magmatic belt a probable late taconian alkalic cross trend in the central appalachians a belt of alkalic to alkalic calcic pipes lamprophyres and intrusive complexes of probable late ordovician age extends from the peach lake croton falls area of westchester county new york about 100 km s80 w to beemerville new jersey the rocks are intruded across a taconic dynamothermal belt ranging from sillimanite grade on the east to chlorite grade on the west foliated middle ordovician and older rocks containing slaty cleavage or coarser grained metamorphic fabrics are crosscut by dikes that are posttectonic to late syntectonic relative to the taconian dynamothermal events analysis of thrust faults and fold structures within this belt suggests that this cross grain belt of alkalic to weakly alkalic rocks intruded steeply dipping brittle fractures trending n40 to 50 w n35 to 60 e and n70 to 80 e and along more ductile zones trending n20 to n70 e this plutonic activity was restricted to a discrete east west belt the clear posttectonic to syntectonic nature of the dikes and the spatial and temporal association with ordovician tectonism suggest that magmatic activity may be related to fracturing of mantle rock at the junction of two salients of taconic age that intersect in the new york recess the tectonic setting of the intrusive belt is unusual because it is associated in space and time with compressional tectonics of the taconic orogeny rather than with extensional rifting

age and origin of the cortlandt complex new york implications from sm nd data sm nd systematics for nine whole rock samples of hornblende norites pyroxenites and a lamprophyre from various parts of the cortlandt complex were analyzed six of these samples from the central and eastern parts of the complex give an isochron age of 430 34 2 ma with an nd value of 2 9 0 5 and the other three samples from the western part including the lamprophyre define a similar age of 394 33 2 ma but with a distinctly different nd value of 1 4 0 4 the two different initial 143nd 144nd ratios corresponding to these values are interpreted to reflect continental crustal contamination of the lamprophyric parental liquid prior to final emplacement and crystal fractionation to produce the different rock types of the complex the intrusion age of 430 ma for the complex clearly post dates the major metamorphic event of the taconic orogeny the nd isotopic data also suggest a relationship between the cortlandt complex and a belt of lamprophyric dike rocks to the west known as the beemerville trend which cuts across the metamorphic trends of the taconic ratcliffe 1981

nile sediment dispersal altered by the aswan high dam the kaolinite trace abstract proportions of kaolinite have increased substantially in lower river nile clay mineral assemblages since emplacement in 1964 of the high dam at aswan egypt monitoring this recent increase can be used to help gauge sediment load changes induced by the high dam in the lower river nile between the dam and nile delta and eventually offshore in the mediterranean s levantine basin high kaolinite values to 50 are recorded north of the new nile delta presently forming in lake nasser and are even higher below the high dam to 70 kaolinite is introduced to lake nasser from adjacent desert terrains largely from wind transported material and wave erosion of lake margins as the major clay component of the suspended sediment load in lake waters this mineral is released through the dam additional kaolinite enters the nile system just below the high dam from late pleistocene and older sections scoured by swift turbulent nile waters flowing northward of the dam during the past 31 years sediment containing higher concentrations of kaolinite 30 has migrated northward at a rate of 10 km year and presently extends to qena 350 km north of the dam this stretch defines the river nile sector most altered since closure of the high dam it is predicted that enhanced proportions of kaolinite will be recorded at cairo and the southern nile delta within 50 years and at the mediterranean coast by the end of the next century

clay mineral variations in the northeastern nile delta as influenced by depositional processes abstract a study of five holocene sections cored in the northeastern nile delta egypt indicates that smectite and kaolinite dominate the clay mineral assemblages that illite is of lesser importance and that proportions of chlorite are usually very low of note is the poor or lack of correlation among the clay mineral assemblages and time related stratigraphic position in the cores and the moderate to good relationships among mineral assemblages grain size and geographic location of the three major minerals illite appears most closely related with grain size we suggest that changes in deposition particularly those related to transport processes and flocculation effective in former nile delta front environments best explain upcore fluctuations in the proportions of clay minerals observed in the five cores the percentages of kaolinite in the delta clay mineral assemblages are generally higher than those recorded in the nile river and in distal offshore nile cone and levantine basin regions this probably resulted from selective entrapment of kaolinite relative to smectite near former coastlines and by passing of the latter mineral to sectors beyond the delta front moreover smectite values are highest in one core located south of lake manzala a site near what may have been the mouth of a former branch tanitic of the nile which flowed east of the present damietta branch climate and related paleoceanographic conditions fluctuated markedly in the eastern mediterranean during the holocene it is concluded however that depositional processes rather than climate have been largely responsible for observed vertical and lateral changes in clay mineral proportions in deposits accumulating in these sedimentologically active nile fluviomarine environments

fault properties from seismic q summary a previously published investigation of seismic q from a north sea vertical seismic profiling data set has revealed an abrupt increase in attenuation to a q value of 45 which is associated with a region between 1000 and 2000 m depth where the borehole intersects a major fault zone dipping at approximately 50 this q anomaly is modelled using a linear slip theory fractures are considered to be imperfectly bonded interfaces where displacement is not required to be continuous the resulting apparent attenuation of the vertically propagating incident p wave is shown to be very dependent on the dip angle of the fault due to the relatively high predicted values of shear compliance compared to the normal compliance of fluid filled fractures at 30 60 mpa confining pressure the observed frequency independence of q is satisfactorily reproduced in addition to the low pass filtering of the downgoing p wave a difference in the frequency content of the first arriving p wave on the vertical compared to the horizontal components has been observed this difference is interpreted as resulting from rayleigh scattering from 3 d inhomogeneities within the fault zone no assumptions are required concerning the existence of intrinsic q although our results do not preclude this possibility

sedimentology and mineralogy of surficial bottom deposits from the aegean canakkale marmara transition eastern mediterranean effects of marine and terrestrial factors abstract grain size carbonate and xrd mineral data of surficial shelf sediments from 113 stations in the aegean marmara transition revealed the presence of three distinctive sectors which were controlled by the changing morphologic hydrodynamic benthic and terrigenous conditions that lasted during the late quaternary the northeastern aegean sea forms the western sector of the study area this region shows several bank and ridge like bottom features at 60 70 m water depths which are widely capped with sand and gravel up to 93 of both biogenic 30 caco 3 and terrigenous 3 origin the low abundances of fine grained materials 1 24 mud in this biogenic belt are probably in response to higher current velocities in the sea and to low fluvial discharges from the adjacent land masses biogenic materials consist of a large variety of calcareous remains of benthic organisms which are partly cemented by carbonate it is hypothesized that this biogenic belt at least in part is a relict feature canakkale strait is the central sector of the study area and its bottom is covered largely by terrigenous sand and gravel 3 the coarse grained nature of the sea floor of canakkale strait can be explained by the prevailing high current velocities western marmara sea is the eastern sector of the study area where the local major rivers supply a great part of the terrigenous materials and the prevailing low current velocities favour fine grained materials deposition here 3 up to 99 mud calcite mainly mg calcite 5 92 quartz 3 72 feldspars mainly plagioclase 7 56 and micas are the major bulk minerals in the sediments except for mg calcite which is mainly derived from calcareous biogenic components bulk minerals reflect a terrigenous source from the adjacent land masses in particular the overall lower qtz fsp ratios in the study area 0 4 1 2 showed significant increases i e enrichment of quartz relative to feldspars qtz fsp 1 2 2 4 in the inner biogenic belt of the northern aegean sea where older or relic early holocene sediments are suspected to occur if so these values can be used as an indicator for long duration of lowstands of sea level and associated intense current and wave activities 17 a expandable smectite 23 84 illite 12 43 and kaolinite 6 38 determined in the less than 2 m of the sediment are the major clay minerals higher abundances of smectite relative to illite and kaolinite found in sediments particularly off the mouths of rivers karamenderes gonen and biga and off the gokceada and bozcaada islands reflect mainly local sources for the clay minerals studied the higher smectite illite ratios of abundances are largely attributed to the weathered volcanic rocks which are widely distributed on the surrounding land masses however the prevailing current and wind patterns seem to be important factors controlling clay mineral distribution in marine sediments of this study

the role of aqueous fluids in the internal friction of rock the effects of water on elastic energy dissipation in rock under upper crustal conditions are considered briefly in this paper experimental evidence indicates that in dry rock the energy dissipation process involves water adsorbed on the surfaces of very thin cracks in one mechanism the adsorbed water is regarded as a viscoelastic film portions of this layer are forced to relax as crack thickness changes with the passing elastic wave a second possible mechanism involves the relaxation of electrostatic repulsion stresses between oriented polar water molecules on opposing crack faces when water is present as a bulk fluid attenuation can be explained by the flow of a viscous fluid into and out of very thin cracks in response to dynamic stresses associated with a passing elastic wave

subsidence in the northeastern nile delta rapid rates possible causes and consequences holocene fluvial and marine deposits have accumulated in a graben like structure on the northeastern margin of the nile delta this part of the delta which includes lake manzala port said and the northern suez canal has subsided rapidly at rates of up to 0 5 centimeter per year since about 7500 years ago this subsidence has diverted at last four major distributaries of the nile river into this region the combined effects of continued subsidence and sea level rise may flood a large part of the northern delta plain by as much as 1 meter by the year 2100 the impact of continued subsidence now occurring when sediment input along the coast has been sharply reduced because of the aswan high dam is likely to be substantial particularly in the port said area and as far inland as south of lake manzala