magmatic epidote and its petrologic significance epidote is a major magmatic mineral in tonalite and granodiorite in a belt coextensive with the mesozoic accreted terranes between northern california and southeastern alaska textural and chemical evidence indicates that epidote crystallized as a relatively late but magmatic mineral that formed through reaction with hornblende in the presence of a melt phase the observed relations concur with experimental data on crystallization of epidote from synthetic granodiorite at 8 kbar total pressure plutonic rocks bearing magmatic epidote must have formed under moderately high pressures corresponding to lower crustal depths under fairly oxidizing conditions

patterns of accretion of reefs in the sudanese red sea abstract reefs in the north towartit and shambaya groups of the sudanese red sea rest on major blocks which have been defined by large scale fault movements the dominant surface features in these areas have been formed by the sub aerial sculpting of tertiary and later limestones during late pleistocene periods of low sea level stand this has resulted in the formation of large numbers of closed depressions reaching 30 m depth these punctuate a surface lying between 20 and 30 m which is itself probably a residual of an older undulating higher level surface the margins of depressions are submarine cliffs the smooth floors are blanketted with recent sediments while the intervening ridges have become the sites for reef accretion present coral growth began about 6000 years ago and has reached a thickness of 10 to 20 m it has been limited in deeper water but in shallower areas may have been aided by establishment on existing pinnacles steep margins occur on both the windward baraja and leeward towartit harvey margins of reefs these may result from inequalities of growth but cannot be directly related to environmental energy windward and leeward shores are characterised by contrasted coral associations a windward acropora association and a leeward porites association this distribution reflects a depletion of resources downcurrent rather than major differences in water movement reef edges are the most important sediment generating zones and patterns of dispersal point to a dominant westward downwind movement 50 80 of sediments coarser than 1 o are coral and algal fragments mollusc shells are a minor component but reach 26 on the towartit fringe homotrema benthic forams bryozoa crustacean and echinoderm fragments rarely rise above a few percent each mean sizes of sediments range from 2 3167 to 1 2333 o with the coarsest close to the reef edges and the finest in deep water or down current most are poorly sorted and values for standard deviation range between 2 1714 and 0 9512 o skewness values indicate symmetrical or coarse skewed distributions 0 0132 to 0 4982 finally figures for normalised kurtosis range between 0 6023 and 0 4532 these suggest that sediments consist of at least two sub populations 1 a base stock generated in the edge zone with characteristics varying systematically down current and 2 grains formed within the transport system with characters owing more to ecological factors than hydrodynamics the irregular mixing of these two accounts for the variation shown in conclusion the character of the reefs depends both upon present day processes and an inherited morphology

derivation of isotope ratios errors and error correlations for u pb geochronology using 205pb 235u 233u spiked isotope dilution thermal ionization mass spectrometric data a comprehensive treatment of the derivation of u pb isotope ratios and their corresponding uncertainties from isotope dilution thermal ionization mass spectrometric measurements is presented standard parametric statistical methods of error propagation are utilized to convolve uncertainties associated with instrumental mass fractionation tracer subtraction blank pb and u subtraction and initial common pb correction derivations include errors and error correlations for total sample u pb and pb isotope ratios including radiogenic and initial common pb for two and three dimensional isochron calculations radiogenic u pb and pb isotope ratios for concordia and radiogenic model age calculations and the propagation of model age errors from radiogenic isotope ratios

benthic foraminiferal associations in the northern bay of safaga red sea egypt abstract in the shallow water area 0 70 m of the northern bay of safaga 73 surface samples were studied with respect to total foraminiferal fauna the samples cover a great variety of shallow water environments and yielded 239 foraminiferal taxa based on q mode cluster analysis and tested by canonical discriminant analysis the samples are grouped into 13 foraminiferal associations each characterized by several species 1 quinqueloculina mosharrafai borelis schlumbergeri brizalina simpsoni ass 2 heterostegina depressa amphlstegina lessonii bicirculata ass 3 cibicidids rosalina amphistegina lobifera pseudoschlumbergerina ovata ass 4 peneroplis planatus ass 5 peneroplis planatus varidentella neostriatula ass 6 peneroplis planatus coscinospira hemprichii varidentella neostriatula ass 7 quinqueloculina spp ass 8 hauerina diversa sorites orbiculus ass 9 verneuilina sp n articulina pacifica reussella simplex ass 10 textularia agglutinans rugulosa bolivina variabilis ass 11 textularia agglutinans challengerella bradyi elphidium jenseni simplex ass 12 operculina ammonoides adelosina laevigata brizalina striatula subspathulata ass 13 bolivina variabilis miliolinella nonion fabum elphidium simplex ass the characteristic forms of each association are linked to specific environmental parameters and modes of life as long as taxonomic uniformitarianism can be applied similar associations with comparable ecological demands may also be detected in the fossil record for comparisons with taxonomically different material the 13 associations are summarized into 4 categories each reflecting a specific type of substrate in the fossil record these categories may be recognized by general morphological characteristics of the foraminiferal tests and by sedimentological data the 4 substrate types are hardground sand with or without seagrass and or corals firmground and soft bottom

carbonate preservation and climatic changes in the central red sea during the last 380 kyr as recorded by pteropods abstract numerical abundances of pteropods and planktic foraminifera and the mode of pteropod preservation were determined in core kl 11 taken from the central part of the red sea the abundance of pteropods shells g dry sediment was compared to that of planktic foraminifera pt pf pt a technique that permits detection of changes in carbonate preservation for the last 380 kyr the numerical abundance of pteropods is influenced by the properties of the water column and preservation is influenced by the bottom water during the last 200 kyr except during isotope stage 5 5 carbonates are in general well preserved during this period the abundance pattern of the pteropods and planktic foraminifera is very similar and follows the climatic signal of the red sea with high numbers during the interglacial stages changing to very low numbers during glacial maximum conditions the similar abundance trends of the two groups and between them and the 18o curve indicates abundance is strongly linked to salinity from isotope stage 6 to the bottom of the core the pteropods occur in low numbers unlike the planktic foraminifera which continue to display the high amplitude glacial interglacial cyclicity the deviations mainly during interglacial stages between the abundance pattern of the two groups and the low pt pf pt values indicate a significant change in carbonate preservation distinctive carbonate dissolution intervals are recognized in the red sea correlating to large scale deep water dissolution events of the mid brunhes dissolution cycle in the indian ocean the anti estuarine circulation pattern of the red sea prevents a direct connection between the deep water masses of the two oceans and rules out the likelihood that changes in the deep water circulation caused these carbonate dissolution events the numerical variations between nonmigratory epipelagic and migratory mesopelagic pteropods were used to evaluate changes in the structure of the water column abundance maxima of mesopelagic pteropods as in the recent red sea indicate an aerated water column with 0 5 ml o2 l oxygen concentrations at the minimum zone mesopelagic abundance maxima coincide commonly with negative monsoonal index values indicating a more aerated water column connected to increasing aridity in the red sea region abundance maxima of epipelagic pteropods indicate a strongly stratified water column at times causing severe depletion in oxygen at intermediate water depths epipelagic peak events coincide often with positive monsoon index values implying an overall milder and more humid climate in the red sea probably associated with enhanced precessional controlled southwest monsoon activity

sequential evolution and diagenesis of pleistocene coral reefs south sinai egypt abstract the uplifted pleistocene coral reefs in south sinai represent two major depositional sequences they generally form two morphological terraces which locally are tilted and offset by still active faulting the major reef sequences are composed of several small scale sequences corals grew rapidly when accommodation space was created by eustatic sea level rise or fault block subsidence as the accommodation decreased coral rubble and siliciclastic sands prograded over reefal and lagoonal sediments thus creating a shallowing upward sequence terrigenous input was further stimulated by a more humid climate during interglacial times 230 th 234 u dating places the older reef cycle between 350 000 and 270 000 years b p which corresponds to the interglacial period of isotope stage 9 the younger reef cycle has been dated between 140 000 and 60 000 years b p isotope stage 5 an intermediate relic sequence found in only one outcrop can be attributed to isotope stage 7 correlation of the small scale sequences is difficult age dating is not precise enough and local tectonic activity in many cases overruled the smaller eustatic fluctuations the younger reef sequence commonly exhibits marine cements whereas the older sequence was exposed to freshwater dissolution and cementation an important feature is the locally pervasive dolomitization especially of the older reef oxygen and carbon isotope values suggest that the dolomite formed in a seawater dominated mixing zone multiple phases of dissolution cementation and dolomitization point to a very complex diagenetic history

three hundred eighty thousand year long stable isotope and faunal records from the red sea influence of global sea level change on hydrography stable isotope and faunal records from the central red sea show high amplitude oscillations for the past 380 000 years positive 18o anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the arabian sea was reduced due to a reduced geometry of the bab el mandeb strait salinities as high as 53 and 55 are inferred from pteropod and benthic foraminifera 18o respectively for the last glacial maximum during this period all planktonic foraminifera vanished from this part of the red sea environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level the foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka spectral analysis of the planktonic 18o record documents highest variance in the orbital eccentricity obliquity and precession bands indicating a dominant influence of climatically driven sea level change on environmental conditions in the red sea variance in the precession band is enhanced compared to the global mean marine climate record specmap suggesting an additional influence of the indian monsoon system on red sea climates

stretching lineations in transpressional shear zones an example from the sierra nevada batholith california abstract ductile shear zones and associated stretching lineations are generally considered to be the result of two dimensional simple shear deformations with stretching lineations interpreted to rotate into parallelism with the direction of tectonic transport with increasing deformation however stretching lineations perpendicular to the inferred tectonic transport direction are displayed by some shear zones field studies in the sierra nevada batholith have revealed a single shear zone the rosy finch gem lake shear zone that contains both steeply plunging stretching lineations in older metamorphosed sedimentary and granitic rocks and shallowly plunging stretching lineations in syntectonic granitoids dextral sense of shear indicators are found in all these units and deformation occurred simultaneously along the length of the shear zone theoretical strain modeling indicates that stretching lineations can be either horizontal or vertical within transpressional shear zones to investigate the kinematics of three dimensional deformation we examine the role of stretching lineations which form as a result of finite strain including the possibility of partitioning a component of the strike slip movement onto shear bands comparing the field data with the strain modeling we interpret the along strike variation in lineation behavior within the rosy finch gem lake shear zone to be a result of the differences in finite strain recorded by different units the older units showing steeply plunging lineation have recorded more finite strain across a narrower shear zone than the syntectonic granites which record shallowly plunging lineations we conclude that the orientation of the lineation within transpressional shear zones does not necessarily correlate with the transport direction but may reflect along strike variations in finite strain and or strain partitioning

seasonal rainfall in the sinai desert during the late quaternary inferred from fluorescent bands in fossil corals skeletal bands of alternating high and low density in massive coral species have been used to record their growth history1 2 in the red sea living colonies of the genus porites deposit low density skeletal bands during summer and high density bands during winter3 additionally yellow green fluorescence can sometimes be seen in these massive corals imparted to them by the incorporation of humic material carried by coastal runoff4 annual banding of fluorescent sequences in living scleractinian corals has proved to be useful in the study of terrestrial runoff in the near shore environment5 6 here we report the finding of similar yellow green fluorescent bands in fossil porites from late quaternary reef terraces in southern sinai which are absent from living porites in the nearby fringing reefs the periodic sequences of the fluorescing humics were found to be superimposed on the low density sub bands of the fossil corals we interpret our observations as evidence that during the late quaternary reef forming peaks the climate was wetter than the extreme desert conditions now prevailing with a possible summer rainfall regime

central virginia volcanic plutonic belt as a host for massive sulfide deposits strata bound massive sulfide deposits of the central virginia piedmont occur in a volcanic plutonic belt composed of lower cambrian metamorphosed volcanic rocks and locally of pre upper ordovician low potassium granitoid rocks the belt interpreted as an ancient island arc begins about 50 km south of washington d c and extends some 175 km south westward the volcanic rocks within the belt are located along the flanks of the quantico columbia synclinorium and the arvonia syncline the chopawamsic formation a western facies of the belt consists of volcanic rocks that have the geochemical features rare earth and immobile elements of a tholeiitic island arc suite it also contains calc alkaline components tholeiitic amphibolites of the ta river metamorphic suite on the eastern side of the belt form an oceanward facies of the island arc coeval with the chopawamsic this distribution suggests an underlying westward dipping cambrian subduction zone contrasts in stratigraphy geochemistry and magnetic and gravity features indicate that the central virginia volcanic plutonic belt is not related to the carolina slate belt as has been proposed in the past known sulfide bodies in the chopawamsic and its coeval units total about 13 5 million tons the mineral district on the northwest flank of the quantico columbia synclinorium has the largest deposits and contains about 10 million tons sulfide bodies in the belt consist largely of pyrite with minor sphalerite and chalcopyrite zn and pb are important in a few of the smaller deposits there are local concentrations of sphalerite and other base metal minerals within the major pyritic deposits zn 1 12 5 cu 1 2 pb as much as 5 the dominantly sphaleritic deposits are found in and northward for about 15 km from the mineral district sulfide mineralization is found in all types of volcanic rock but the large sulfide bodies on the northwest flank of the quantico columbia synclinorium are in felsite amphibolite containing local beds of iron formation is abundant on the southeast flank of the arvonia syncline however most sulfide mineralization there took place in felsitic to intermediate layers mineralization attributed to submarine volcanic exhalation took place during formation of the island arc

impact of late quaternary environmental changes on deep sea benthic foraminiferal faunas of the red sea abstract fluctuations in abundance diversity and species composition of benthic foraminifera from two sites of the northern and southern red sea indicate strong variability of deep sea ecosystems during the last four glacial to interglacial cycles in total five and four different benthic foraminiferal assemblages have been identified in the northern core and southern core respectively comparison with recent faunas from the red sea and adjacent oceans allowed the reconstruction of temporal changes in deep water ventilation salinity and food availability at the seafloor generally the abundance of infaunal and miliolid taxa increase during glacial intervals indicating increased organic matter fluxes oxygen decrease and salinity increase in deep waters during these times these fluctuations are attributed to enhanced oxygen consumption rates and temporarily reduced deep water formation in the northern red sea during glacial intervals the recorded environmental changes are a reflection of both high and low latitude climate changes the northern red sea is mainly influenced by glacio eustatic sea level fluctuations that control deep water formation rates and by mid latitude climate changes of the mediterranean region that control surface productivity in contrast deep sea ecosystem variability of the southern red sea is additionally influenced by low latitude climate changes attributed to the ne monsoon intensity that drives the inflow of nutrient rich surface waters from the gulf of aden these results demonstrate the high sensitivity of deep sea ecosystems of the red sea to both global and regional climate changes

stratigraphic and paleoceanographic significance of late quaternary pteropods from deep sea cores in the gulf of aqaba elat and northernmost red sea abstract the quantitative distribution of 16 thecosomatous pteropod species from four deep sea cores recovered from the gulf of aqaba elat and northernmost red sea is summarized the distribution facilitates a relatively high resolution stratigraphic subdivision of the 6 8 m long core sequences and their correlation the sequences of pteropod assemblages can be related to oxygen isotope curves and thus dated beyond the radiocarbon range the oldest strata penetrated are dated at about 150 000 yr b p considering the present day distribution of the species recognized the core assemblages are of a tropical subtropical character throughout the late quaternary on the basis of the composition of the living pteropod populations in the hypersaline 41 moderately oligotrophic and desert enclosed gulf of aqaba the pteropod core assemblages associated foraminiferal assemblages and the oxygen isotope values determined on both groups a sequence of paleoceanographic changes during the late quaternary is derived these changes are primarily influenced by productivity of the waters and pertain less to temperature and salinity the glacial periods isotope stages 2 3 4 and upper 6 were characterized by lower temperature than at present higher salinity and greater fertility of the waters during the glacial maxima monospecific creseis acicula assemblages characterize periods of metahaline more than 50 salinity conditions in highly productive waters although not identical in detail the last interglacial stage 5 assemblages are similar to the holocene warm water oligotrophic ones between 8000 and 3000 yr b p a short period of slightly higher productivity is indicated

variations in pleistocene coral assemblages in space and time in southern and northern central ryukyu islands japan we studied the taxonomic and morphological compositions of pleistocene coral assemblages in 24 quadrats in okinawa jima southern central ryukyus and in 14 quadrats in kikai jima northern central ryukyus a total of 72 species belonging to 35 genera were identified in okinawa jima whereas 65 species coming under 33 genera were recorded in kikai jima cluster analysis of the bray curtis bc similarity coefficient produced 8 coral associations and 3 ungrouped taxa they correspond to a wide range of reef environments from shallow lagoon to lower reef slope settings the analysis of taxonomic similarities among quadrats leads to the identification of 7 clusters and 5 isolated quadrats the segregation of quadrats indicating a same reef zone into distinctive groups or single branches in the cluster diagram reflects the within reef slope variability in community structure specifically encrusting acropora palifera indicative of the upper reef slope zone shows a great variability of associated coral species and morphologies we also report differences in the geographic distribution of acropora palifera and platygyra contorta between present day and pleistocene reefs which may be linked to changes in sea surface temperature the decrease in the total species and generic richness recorded in modern reefs is not clearly detected in the fossil record in addition mds ordination of the bc similarities highlights patterns of reef zonation and geographic differences in taxonomic composition one way tests of similarity anosim show that differences in the composition of upper reef slope coral assemblages between okinawa jima and kikai jima are not larger than those observed between southern and central okinawa jima finally we report various types of coral successions sea level changes resulted in transitions from one reef zone to another whereas local disturbances are likely to have been responsible for the successions of distinctive coral assemblages with overlapping depth ranges which reflect the within reef zone variability

relationship between the ellisville pluton and chopawamsic fault establishment of significant late ordovician faulting in the appalachian piedmont of virginia

docking carolina mid paleozoic accretion in the southern appalachians accretion of the extensive carolina zone to laurentia is one of the most critical unresolved problems in southern appalachian tectonics synthesis of southern appalachian tectonism reveals three lines of evidence from across the orogen that indicate a late ordovician to silurian time of accretion a tectonic unconformity in native laurentian rocks an extensive magmatic pulse in the piedmont zone of the orogen and active uplift in the carolina zone are all related to this accretionary event structural geometries in the carolina zone suggest that accretion involved sinistral transpression this new model for carolina accretion is consistent with models for the accretion of northern appalachian peri gondwanan terranes collectively their timing and mode of accretion to laurentia place tectonic constraints on paleozoic global reconstructions

salinity changes during late oligocene to early miocene asmari formation deposition zagros mountains iran abstract the distributions of sediment grain types and microfacies in two outcrop sections in the central part of the zagros fold and thrust belt iran are used to interpret changes in salinity during late oligocene chattian to early miocene burdigalian deposition of the asmari formation conditions of hypersalinity are interpreted from analogy with the modern salinity gradient in shark bay western australia and the time scale is derived from foraminiferal biozonation and sr isotope stratigraphy the study demonstrates that frequent changes in sedimentary facies and salinity conditions took place in the central zagros basin during the late chattian aquitanian and burdigalian five main findings of the study are as follows 1 a significant shallowing from the outer neritic zone 100 m to 200 m deep to the innermost neritic zone 50 psu occurred during aquitanian deposition of the asmari formation at both localities 5 deposition of the upper asmari formation and lowest gachsaran formation burdigalian was mainly under slightly hypersaline conditions 40 psu to 50 psu with some normal marine intervals at tang e sapou and some normal marine intervals as well as severe hypersaline episodes 50 psu at tang e ban to the west the patterns of salinity change seem to have been widespread in the central zagros foreland basin and transitions from normal marine to hypersaline conditions may represent falls in relative sea level or be due to build up of sand banks forming sills that restricted water circulation changes from hypersaline to normal marine conditions may represent relative sea level rise however there is insufficient chronological resolution at present to allow confident correlation of the major salinity changes to sequence boundaries and surfaces previously recognized in the basin

dated coral reefs of southern sinai red sea and their implication to late quaternary sea levels abstract coral reefs of sinai constitute four morphological terraces three emergent fossil reefs and one submergent modern fringing reef labeled i 28 35 m above sea level ii 13 18 m iii 5 8 m and iv 1 to 1 m four genetic reef complexes which do not necessarily correspond to the morphological terraces were identified and dated the reef terrace age relationships are as follows 1 ophira terrace i 330 290 ka 2 mureikha terraces ii and or iii 215 170 ka 3 na ama terraces ii and or iii 141 81 ka 4 umm sid terrace iv 6 5 2 5 ka the age groups correspond to the oceanic oxygen isotope stages 9 7 5e and 1 the vertical uplift of the southern sinai coast which is situated along the western margin of the dead sea transform did not exceed 28 35 m during the last 300 000 years

biodiversity of foraminifera from late pleistocene to holocene coral reefs south sinai egypt tropical coral reefs are among the most diverse marine ecosystems in order to better understand temporal and spatial variation in late quaternary biodiversity foraminiferal faunas of two fossil raised reef terraces at the southern sinai peninsula were studied and compared to modern coral reef faunas eleven u series dates of shell fragments of the giant clam tridacna sp indicates deposition largely during marine isotope stage 5 mis 5 77 129 kyr bp for the two raised terraces in these terraces amphistegina a lessonii and a lobifera dominates the five fossil foraminiferal associations the fossil reef flat association 1 has common gypsina plana homotrema rubra and acervulina spp and fossil reef flat association 2 consists of amphistegina spp of the three fossil fore reef associations one has abundant porcelaneous taxa including sorites amphisorus peneroplis and borelis one has a mix of porcelaneous taxa and attached arborescent taxa homotrema and placopsilina and one has abundant attached and arborescent taxa miniacina gypsina acervulina and planogypsina the modern fringing reef is dominated by porcelaneous foraminifera and three modern associations are identified these include a lagoonal association with abundant peneroplis pertusus a reef flat association dominated by sorites orbiculus and a fore reef association with porcelaneous taxa plus common h rubra amphistegina lessonii and a lobifera based on our data and including additional published information on regional biodiversity it appears that during mis 5 foraminiferal biodiversity was higher and community structure was different than within the modern reefs these data and regional paleo climate patterns indicate that oceanographic conditions in the red sea were probably closer to normal marine conditions during the last interglacial than they are today

high rates of sea level rise during the last interglacial period sea level during the last interglacial stood at least 4 m higher than at present with evidence of short term fluctuations of up to 10 m a new continuous sea level record from the red sea and coral ages suggest that during these fluctuations sea level changes were on the order of 1 6 m per century

modern foraminiferal distribution and diversity in two atolls from the maldives indian ocean abstract foraminifera from the coral reef lagoons of two atolls are used to investigate the distribution and diversity of assemblages in the central indian ocean eight assemblages and 270 species of foraminifera are identified three assemblages are reefal and dominated by amphistegina and calcarina only one lagoon assemblage is present in both atolls which is characterized by abundant ammonia sp 1 and smaller miliolid foraminifera in ari atoll abundant amphistegina sp 1 operculina ammonoides amphistegina radiata and nummulites venosa characterize one lagoon assemblage and abundant neoeponides bradyi and textularia cf t cushmani characterize the other in rasdhoo atoll abundant textularia gr foliacea and spiroloculina nummiformis characterize one lagoon assemblage and abundant textularia cf t cushmani and textularia sp 5 characterize the other the assemblages compare well with sedimentological characteristics which is also reflected in their distributions species diversity in the maldives appears to be higher than the western indian ocean region due to the stronger influence of central indo pacific faunas it is not however as high as the central indo pacific region which may be due to lower habitat diversity

dating quaternary raised coral terraces along the saudi arabian red sea coast abstract late pleistocene raised coral reef terraces form extensive outcrops up to 5 km wide along the saudi coast porites coral were dated using u th while clastic sediment from jeddah was dated using thermoluminescence the pooled mean age for the coral samples is 121 5 0 2 ka suggesting mis 5e even for the uplifted 16 20 m high terrace in the north at haql in jeddah the mis 5e back reef succession is overlain by fluvial sediment that gave a tl age of 66 13 ka the structure and faunal composition of the coral terraces suggests that they accumulated in broad shallow embayments following the last interglacial transgression the consistent elevation of these terraces suggests that the central and southern saudi coast has been tectonically stable for at least the past 125 000 years and the coral reef terraces at 3 5 5 5 m elevation are consistent with the mis 5e sea level high stand that peaked at 6 9 m above present sea level the saudi coastal coral terrace north of duba shows progressive uplift to 16 20 m near haql since 108 120 ka as a result of ongoing transform faulting in the gulf of aqaba

seismicity seismic reflection gravity and geology of the central virginia seismic zone part 3 gravity bouguer gravity anomalies at 1 870 locations on the central piedmont of virginia from 37 37 n to 37 52 n and 77 44 w to 78 23 w display patterns of variation produced by upper crustal density contrasts and thickening of the crust in a west northwest direction no other deep sources are evident upper crustal density contrasts are associated with rock units known from geologic mapping the subsurface distribution of these rock units interpreted from seismic reflection data was confirmed by measured variations in gravity a two dimensional model analysis indicates the following average in situ density values for the principal formations arvonia formation 2 77 gm cc columbia granite 2 75 gm cc tonalite and 2 73 gm cc pegmatite chopawamsic volcanics 2 77 gm cc felsic units and 2 79 gm cc malic units catoctin lynchburg evington 2 82 gm cc maidens gneiss 2 78 gm cc and grenville basement 2 71 gm cc gravity anomalies are consistent with the existence of a major thrust fault at depths between 9 km and 16 km that probably separates grenville basement rocks from younger catoctin lynchburg rocks these anomalies confirm that the slight eastward dip of this thrust fault beneath the western part of the area increases significantly east of 78 05 w

changes in diversity and assemblages of foraminifera through the holocene in an atoll from the maldives indian ocean abstract this study presents the first high resolution holocene records of diversity and assemblages of benthic foraminifera from tropical reef environments in the indian ocean two 3 2 m and 4 4 m long cores from the lagoon of rasdhoo atoll 4 n 73 w in the central maldives were sampled at 250 yr intervals core 16 covers most of the holocene 10 32 0 kyr bp and was taken in the deep lagoon of the atoll 35 m water depth core 19 covers the time span 7 375 0 kyr bp and is from a sublagoon 14 m water depth on the northern margin of the atoll in core 16 an early colonization phase during holocene sea level rise is characterized by an ammonia sp 1 dominated assemblage until 7 kyr bp the slowdown of sea level rise in the mid holocene 4 kyr bp marks the onset of a phase of stable environmental conditions in the deep lagoon with high diversity a shift toward lower diversity and the dominance of textularia foliacea has occurred from 4 1 kyr bp which may be explained with the intermediate disturbance hypothesis an environmental change at 1 4 kyr has caused a distinct faunal change the decrease of t foliacea and an increased recovery in diversity in core 19 a significant faunal change at 4 0 kyr bp from an ammonia sp 2 dominated fauna to a fauna with ammonia sp 1 miliolid taxa and a higher diversity might be related to the formation of a sand spit that separates the sublagoon from the main lagoonal basin the westward extension of the sand spit during the late holocene could have changed the restricted bottom water circulation in the main lagoon and caused longer residence times of water and the build up of lower oxygen and higher nutrient concentrations this study underlines the importance of the factor time on diversity and the significance of lagoon circulation and bottom water residence times on assemblages and diversity of benthic foraminifera

origin of a vertical lineation in conjugate transcurrent shear zones at broken hill australia abstract shear zones at little broken hill are interpreted as conjugate transcurrent structures they developed before dolerite dyke emplacement in response to n s horizontal shortening they were reactivated as conjugate transcurrent structures after dyke emplacement in response to horizontal e w shortening shear zone deformation was accompanied by retrograde metamorphic conditions for at least the later part of the history displacement on the shear zones was accommodated by coeval deformation within the shear zone bound blocks this deformation involved shear on the pre shear zone s1 foliation and resulted in incomplete retrogression of earlier peak metamorphic mineral assemblages it also resulted in a vertical extension and a component of dip slip on the shear zones a near vertical stretching lineation occurs parallel to the intersection of the shear zones and is interpreted as a localised response to an overall vertical extension localisation of the lineation is explained in terms of grain scale partitioning of deformation mechanisms in the country rock vertical extension was achieved by shear on s1 with very little intragranular deformation consequently this deformation failed to produce a lineation in the shear zones where all fabric elements were tending to vertical the only deformation mechanism available for vertical extension was intragranular deformation which resulted in a shape fabric viz the stretching lineation shear within the zones had both horizontal and vertical components parallel to the shear zone foliation because the shear was achievable by slip on the foliation and did not involve intragranular mechanisms it did not modify the lineation late shear zone movement resulted in local crenulation of the shear zone foliation about the early formed stretching lineation the result was vertical plunging folds and a more pronounced stretching lineation it is concluded that stretching lineations in shear zones should not be considered indicators of movement direction or of instantaneous or finite strain axes

a two stage emplacement for the cabonga allochthon central part of the grenville province evidence for orthogonal and oblique collision during the grenville orogeny the article by j martignole and p pouget november 1994 issue received in january 1995 presents a large body of data on the geothermobarometry of an area that had hitherto received little attention these data will allow the formulation of a more precise geotectonic model for the evolution of a part of the central grenville province however it is regrettable that the authors were remiss in not citing the sources of the information pertaining to the major structural features presented in their figs 2 4 more specifically we are referring to the two major structures previously identified by us the cayamant lineament and the baskatongdcsert lineament which the authors are trying to rebaptize the baskatong shear zone etc since 1990 our studies on the cayamant lineament and the baskatong desert lineament have been well documented published and widely publicized at all available geoscientific events such as ministbre des ressources naturelles du quebec publications and information seminars uvesque et al 1990 sharma et al 1990 1993a uvesque and sharma 1990 sharma 1991 1992a 1992b 1992c sharma and gigubre 1993 madore et al 1993a 1993b 1994 abitibi grenville project lithoprobe workshops sharma and uvesque 1991 sharma et al 1992b the 1992 grenville workshop friends of grenville sharma and uvesque 1992 the 1992 grenville field excursion friends of grenville led by k n m sharma sharma et al 1992a 1993 geological survey of canada current activities forum sharma 1993 toronto 94 annual general meeting and trade exhibition of the cana

sediment transport trends from a tropical pacific lagoon as indicated by homotrema rubra taphonomy wallis island polynesia the assessment of sediment transport pathways in carbonate settings is complicated by ecologically sourced sediment tracers such as foraminifera have previously been used in these settings to describe the movement of coastal sediments on spatial and temporal scales where traditional grain size methods have limited use the present study builds on the foraminifera based tracer method by using homotrema rubra a foraminifer with an attached life habit i e defined provenance in the reef to document modern sediment transport trends at wallis island a tropical pacific lagoon at wallis island homotrema taphonomic results discriminated amongst modern reef lagoon and island beach samples reef samples contained high concentrations of fragments that were large 250 m and exceptionally to well preserved e g intact chambers red color angularity in general concentrations and degree of taphonomic alteration decreased with distance landward from the reef lagoon samples were characterized by lower concentrations of homotrema that were smaller in size and less preserved e g pink in color no chamber structure rounding of edges at the greatest distance from the reef island beach samples contained the lowest concentrations of homotrema fragments that were small well rounded and bleached in this regard homotrema taphonomy is a useful indicator of the direction and forcing of sediment transport and will therefore be useful in detecting overwash deposits in tropical settings where distinguishing event deposits from surrounding sediment is problematic

seismicity seismic reflection studies gravity and geology of the central virginia seismic zone part i seismicity the central virginia seismic zone is an area of persistent low level seismicity in the piedmont province of that state its north south dimension is 120 km and it extends some 150 km in an east west direction from richmond to lynchburg the results of instrumental monitoring there by a seismic network during the past 5 yr are reported herein to provide a useful constraint on geologic structural models considerable care must be exercised in the location of earthquakes and in the specification of the accuracy of those locations our procedures for accomplishing those tasks were as follows first a velocity model specific to the network locale was developed from seismic refraction and reflection data second evaluation of the detection capability of the network indicated that the detection of seismic events should be virtually complete down to a magnitude of 1 5 third the locational capability of the network was assessed by locating blasts originating from three different quarries operating within the network area as if they were earthquakes of unknown location the average calculated locations when compared to the known blast sites indicated average differences of 2 km horizontally and 4 km vertically except for the northeastern portion there the location capability degrades to fair for epicenters 4 km and to poor for estimation of focal depths 8 km the resultant decrease in locational capability is probably due to the presence of low velocity coastal plain sediments fourth the location of all of the earthquakes relative to each other was tested by use of special joint hypocenter calculations the recalculated locations differed from the original locations in a random manner on the average that difference was 3 km and it indicates the absence of serious bias introduced by combining earthquake locations derived from different subnetworks of seismographs ninety six pre network pre 1978 earthquakes for the most part felt events with noninstrumental locations and 34 network determined hypocenters 1978 1982 for mostly smaller not felt shocks form the basic data set of this study the spatial distribution exhibited by the 130 hypocenters is diffuse both vertically and horizontally such a pattern favors multiple rather than singular seismogenic structures seventy five percent of the focal depths are in the upper one third of the crust at depths of 11 km or less these multiple shallow sources will be shown in part 4 of this sequence of papers to be along and above a master detachment fault

understanding the red sea response to sea level here we outline a new pragmatic methodology to derive relative sea level estimates from central red sea oxygen isotope records based on a previously published model in this paper the methodology is described in detail and it is shown that sea level change is the dominant factor responsible for the recorded variability in red sea 18o pdb for sea level changes greater than 12 m variables such as temperature or net evaporation are shown to have relatively small effects on the oxygen isotope record the modelled 18o pdb to sea level relationship is given in terms of a fifth order polynomial which may be used to describe relative sea level from central red sea oxygen isotope records we show how established sea level records from fossil reef terraces for the last 20 kyr are successfully simulated from central red sea oxygen isotope records we also examine the spatial variability of 18o pdb in the basin over the last 13 kyr

u pb geochronologic nd isotopic and geochemical evidence for the correlation of the chopawamsic and milton terranes piedmont zone southern appalachian orogen abstract we report u pb crystallization ages from four metavolcanic rocks and two granitic gneiss samples as well as whole rock chemical analyses and sm nd isotopic ratios from 25 metaigneous and metasedimentary rocks from the chopawamsic and milton terranes southern appalachian orogen a metarhyolite sample from the chopawamsic formation and a metabasalt sample from the ta river formation in the chopawamsic terrane have indistinguishable u pb crystallization ages of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 471 4 pm 1 3

increased seasonality in middle east temperatures during the last interglacial period the last interglacial period about 125 000 years ago is thought to have been at least as warm as the present climate owing to changes in the earth s orbit around the sun it is thought that insolation in the northern hemisphere varied more strongly than today on seasonal timescales which would have led to corresponding changes in the seasonal temperature cycle here we present seasonally resolved proxy records using corals from the northernmost red sea which record climate during the last interglacial period the late holocene epoch and the present we find an increased seasonality in the temperature recorded in the last interglacial coral today climate in the northern red sea is sensitive to the north atlantic oscillation a climate oscillation that strongly influences winter temperatures and precipitation in the north atlantic region from our coral records and simulations with a coupled atmosphere ocean circulation model we conclude that a tendency towards the high index state of the north atlantic oscillation during the last interglacial period which is consistent with european proxy records contributed to the larger amplitude of the seasonal cycle in the middle east

late quaternary reorientation of stress field and extension direction in the southern gulf of suez egypt evidence from uplifted coral terraces mesoscopic fault arrays and borehole breakouts uplifted pleistocene coral terraces and modern earthquakes show that several large normal faults are presently active in the southern gulf of suez rift basin the footwall of one of these faults is exposed at gebel el zeit where terraces at elevations of 10 18 and 42 m have been radiometrically dated as 125 ka and 426 ka respectively after correcting for eustatic sea level changes this results in net tectonic uplift rates of about 0 1 m kyr published interpretations and our own observations indicate that the average extension direction during the miocene to pliocene synrift history was 055 analysis of borehole breakouts and published earthquake fault plane solutions however suggests that the present day stress field in the southern gulf has a 010 020 shmin orientation detailed structural observations show that a change in extension direction occurred in the late pleistocene with rotation of the stress field beginning prior to formation of the 125 ka terraces but after formation of older pleistocene terraces whose ages are less tightly constrained using a horizontal slip direction of 015 and our observed net footwall uplift rate we calculate a separation velocity between sinai and africa of 0 8 1 2 m kyr the proposed pleistocene change in extension direction in the gulf of suez corresponds closely with the post 500 ka change in extension direction documented in the kenyan rift system and a similar change in extension direction recorded in the central red sea these regional similarities in tectonic history suggest that the underlying causes of these events may be a plate scale phenomenon affecting the entire afro arabian rift system rather than local changes in the quaternary stress field

antarctic temperature and global sea level closely coupled over the past five glacial cycles sea level has varied by over one hundred metres across glacial interglacial cycles over the past 520 000 years an extended sea level reconstruction shows a strong coupling between these sea level changes and antarctic surface temperatures over the past five glacial cycles

suspect terranes and accretionary history of the appalachian orogen the north american connection or the grenvillian continental crust that separated from eastern north america during the initiation of the appalachian orogenic cycle is poorly defined within the present orogen a variety of terranes occur outboard of the north american miogeocline all structurally uncoupled and therefore suspect stratigraphic analysis indicates that appalachian accretion progressed from the miogeocline outward the boundaries of the earliest accreted western terranes are marked by melange and ophiolite complexes later boundaries between eastern terranes are steep mylonitic zones and brittle faults accretionary events defined by stratigraphic analysis correspond to times of major deformation plutonism and metamorphism in the history of the orogen

aplanktonic zones in the red sea abstract we use micropalaeontological and stable isotope results for a series of cores from north to south through the red sea to assess temporal and spatial patterns of change in planktonic foraminiferal faunas leading up to the remarkable full glacial red sea aplanktonic zones aplanktonic zones reflect salinities in the red sea in excess of the lethal 49 p s u limit caused by reduced exchange transport through the strait of bab el mandab due to glacial sea level lowering concerning the last glacial cycle aplanktonic conditions began at 39 ka bp in the north where salinities eventually reached 55 57 p s u paradoxically planktonic faunas are reported to have survived the last glacial maximum in the northern gulf of aqaba suggesting a poorly understood freshwater dilution at that time aplanktonic conditions s 49 p s u reached the south central red sea by 22 ka bp while planktonic foraminiferal faunas continued albeit in very low abundances and limited diversity s 45 p s u in the southernmost red sea during marine isotope stage mis 6 the 49 p s u isohaline appears to have resided in the central red sea between cores kl11 and md921017 we observe a systematic sequence of species disappearances before all glacial maxima of the last 500 kyr absence of a logical relationship with sea levels suggests that the disappearance sequences are not related to a general salinity increase instead we argue that the sequences were driven by complex reorganisations in hydrography stratification productivity food availability and subsurface oxygenation reproduction habitats the onset is marked by dramatic basin wide expansion of conditions that today are restricted to only the southern red sea suggesting an expansion of the dominance of ne monsoonal circulation over the entire red sea this expansion occurred 15 or more kyr before the aplanktonic zones of mis 12 6 and 2 and also before mis 10 and 8 which never reach the aplanktonic stage regarding the last glacial cycle this event occurred as early as 75 ka bp mis 4 5 boundary after this major climatic reorganisation we reconstruct progressive intensification of the new conditions especially marked by northward expansion and intensification of the subsurface oxygen minimum zone omz during the last glacial cycle a shallow and very distinct omz affected the central red sea as early as 68 ka bp and the north as late as 55 ka bp the omz expansion intensification appears to have been interrupted by episodes of increased ventilation

influence of northern hemisphere climate and global sea level rise on the restricted red sea marine environment during termination i 1 we present high resolution paleoceanographic records of surface and deep water conditions within the northern red sea covering the last glacial maximum and termination i using alkenone paleothermometry stable oxygen isotopes and sediment compositional data paleoceanographic records in the restricted desert surrounded northern red sea are strongly affected by the stepwise sea level rise and appear to record and amplify well known millennial scale climate events from the north atlantic realm during the last glacial maximum lgm sea surface temperatures were about 4 c cooler than the late holocene pronounced coolings associated with heinrich event 1 2 c below the lgm level and the younger dryas imply strong atmospheric teleconnections to the north atlantic owing to the restricted exchange with the indian ocean red sea salinity is particularly sensitive to changes in global sea level paleosalinities exceeded 50 psu during the lgm a pronounced freshening of the surface waters is associated with the meltwater peaks mwp1a and mwp1b owing to an increased surface near inflow of normal saline water from the indian ocean vertical 18o gradients are also increased during these phases indicating stronger surface water stratification the combined effect of deglacial changes in sea surface temperature and salinity on water column stratification initiated the formation of two sapropel layers which were deposited under almost anoxic condition in a stagnant water body

early diagenesis in pleistocene coral reefs southern sinai egypt response to tectonics sea level and climate the uplifted pleistocene terraces along the coast of southern sinai exhibit a well developed reef system formed during isotope stage 9 and a younger one formed during isotope stage 5 an intermediate reef corresponding to isotope stage 7 occurs only as an erosional relic in the study area the sediments comprise reefal framestones peri reefal facies coral rubble and siliciclastic dominated beach and aeolian facies the compositional and textural complexity of the sediments leads to a highly variable spatial distribution of diagenetic features however the geometric relationships and elemental analyses allow a reconstruction of the general diagenetic evolution during the major eustatic sea level highstand of isotope stage 9 the older reef was constructed and cemented with aragonite and high mg calcite climate was probably semiarid with some rainy periods which permitted the installation of ephemeral freshwater lenses especially during the minor sea level lowstand within isotope stage 9 in these lenses and during the subsequent major sea level lowstand some freshwater dissolution occurred the highstand during isotope stage 7 led to the construction of the intermediate reef in the older reef some high mg calcite precipitated at that time dolomite cement formed either in marine interstitial waters modified by some freshwater input or in a hypersaline context phreatic meteoric low mg calcite cement covers and partly replaces previous marine cements and dolomite but is still attributed to the major highstand of isotope stage 7 when freshwater lenses could develop during minor sea level lowstands the subsequent major sea level lowstand was dominated by an arid climate and only a little freshwater corrosion occurred the younger reef formed during the major highstand of isotope stage 5 aragonite and high mg calcite cements as well as some dolomite are common within the reef whereas freshwater cements are limited to beach and aeolian facies due to tectonic uplift only the lower part of the older reef was reflooded during isotope stage 5 and only some aragonite crystals precipitated on top of dolomite or low mg calcite the interrelationships between tectonics sea level variations of different orders and climatic changes thus had a profound impact on the diagenetic history of these reef systems

late quaternary biostratigraphy and paleotemperatures of the red sea and the gulf of aden based on planktonic foraminifera and pteropods abstract the quantitative distributions of planktonic foraminifera and pteropods were analyzed in seven red sea cores and two deep sea cores from the gulf of aden and off sokotra island biostratigraphic intervals were distin guished corresponding to oxygen isotope stages 1 5 in the red sea and stages 1 3 in the gulf of aden the faunal assemblages demonstrate that in the red sea hydrological conditions changed significantly during the late quaternary especially at the last glacial maximum when water exchange at the bab el mandeb straits was at a minimum and at the pleistocene holocene boundary at the end of deglaciation water exchange renewal and pluvial conditions resulted in surface salinity decrease and stable stratification which was followed by a rise in planktonic fauna abundance and stagnation of bottom waters the more constant composition of rather cold water subtropical faunal assemblages in the gulf of aden during the last 40 000 50 000 yrs points to more stable hydrological parameters and to local upwelling or influx of arabian upwelling waters during the last stadial mean annual sea surface temperatures fell by at least 5 c compared to the present in the central part of the red sea and by 3 5 c in the western gulf of aden