comment on formation of chenier plain of the donana marshland sw spain observations and geomorphic model by a rodriguez ramirez and c m yanez camacho marine geology 254 2008 187 196 abstract the application of the regional marine 14 c reservoir effect r to obtain an accurate calibration of conventional marine shell 14 c dates requires prior research concerning the oceanographic conditions and the r of that region rodriguez ramirez and yanez camacho a rodriguez ramirez c m yanez camacho formation of chenier plain of the donana marshland sw spain observations and geomorphic model marine geology 254 2008 187 196 and afterwards a rodriguez ramirez j a morales j borrego and e g san miguel in a reply a rodriguez ramirez j a morales j borrego e g san miguel reply to the comment on formation of chenier plain of the donana marshland sw spain observations and geomorphic model by a rodriguez ramirez and c m yanez camacho marine geology 254 2008 187 196 marine geology 263 2009 123 125 to the comment by j rodriguez vidal f ruiz and l m caceres on the paper mentioned above j rodriguez vidal f ruiz l m caceres comment on formation of chenier plain of the donana marshland sw spain observations and geomorphic model by a rodriguez ramirez c m yanez camacho marine geology 254 2008 187 196 marine geology 263 2009 120 122 use in both cases not only incorrect r values for the calibration of 14 c dates obtained from shell samples collected from the east coast of the gulf of cadiz but they also confuse the r concept with that of r t the 14 c reservoir age because the misunderstanding of these concepts by these authors and in the first case also their failure to take into account the r values obtained by us and already published from the east coast of gulf of cadiz all the calibrated dates presented either in the first paper or in the reply cannot be accepted here i present a new calibrated dataset using accurate r values and i recommend that the conclusions obtained by rodriguez ramirez and their collaborators be revised as j rodriguez vidal f ruiz and l m caceres proposed in their comment

sedimentary record of recent tsunamis in the huelva estuary southwestern spain abstract the coast of the gulf of cadiz has been repeatedly struck by tsunamis during the late holocene and the historic period historical documents record at least seven catastrophic tsunamis affecting this coast while others have been detected by oceanic instruments nevertheless very few studies have documented the sedimentary record of these tsunamis in the low energy coastal environments of the gulf of cadiz the huelva estuary is located at the central sector of the gulf of cadiz and is a mesotidal estuary fed by the tinto and odiel rivers the mean tidal range of the huelva estuary is ca 2 m and the mean significant wave height is ca 0 5 m the outer part of the estuary is characterized by extensive sand rich sedimentary bodies of marine origin whereas the central and inner parts are infilled by muddy tidally deposited sediment bodies recorded within these estuarine sediment bodies are five laterally continuous shelly units these units display many of the typical characteristics of tsunami deposits each typically comprises an erosional base followed by a fining upwards sequence that begins with the shell accumulation and ends with bioturbated muddy sand the results of 14 c ages and recent radionuclides accumulation rates in this study illustrate that these five tsunami deposits correspond with known events that occurred in ad 1755 1531 949 1033 881 and 395 381 all of which are documented in historical sources

the geochronology structure and metamorphism of early archaean rocks at fyfe hills enderby land antarctica abstract the fyfe hills of enderby land antarctica are composed of archaean cratonic rocks of the napier complex initial crustal formation possibly of plutonic volcanic and sedimentary origin was in the early archaean but probably significantly later than the 4000 ma ages previously reported at 3100 ma the rocks underwent granulite facies metamorphism and an intense regional strain d1 which rotated into parallelism pre existing discordances and produced a recumbent gneissic pile approximate sr isotopic homogenisation over at least a metre and new zircon growth and or major resetting apparently occurred at this time subsequent ductile deformation d2 also characterised by tight to isoclinal folding produced characteristic microstructure only within f2 folds but no axial plane foliation was developed peak granulite facies metamorphic conditions close to 900 c and 9 11 kbars were reached during d1 d2 considerable pb loss occurred in zircon during asymmetric open to tight folding d3 and upper amphibolite to granulite facies metamorphism 650 c 7 kbars at 2500 ma rb sr equilibration on the scale of centimetres occurred at that time after which the napier complex was essentially cratonised a subsequent semiductile deformation did not affect the whole napier complex but produced upright shear zones in the fyfe hills area which lies close to the boundary between the napier complex and the younger rayner complex to the south

major and trace element geochemistry of the archaean ntem plutonic complex south cameroon petrogenesis and crustal evolution the ntem complex crops out in south cameroon and belongs to the congo craton it corresponds to a 2 8 ga basement which in the northern part is made up of plutonic rocks 1 charnockites and 2 soo tonalites both have similar compositions and define a typical tonalite trondhjemite and granodiorite ttg suite the study of isotopes isr major elements and ree allows us to propose a petrogenetic model that may summarized as follows 1 1 partial melting of the mantle gave rise to tholeiites 2 2 tholeiites transformed into garnet bearing amphibolites underwent partial fusion thus generating the parental magma of the ttg suite 3 3 fractional crystallization mainly of hornblende and plagioclase produced the differentiated ttg suite this scheme is typical of archaean ttg suites and is supposed to have occurred in a subduction like geodynamic environment where because of the high archaean geothermal gradients the subducted oceanic crust underwent fusion before dehydration operated it is also possible to show that the ttg suite was not emplaced during the granulite facies metamorphism but that this occurred later affecting only some parts of the basement consequently the ntem complex appears to be an archaean high grade terrane where the granulitic assemblages may be early proterozoic in age characteristic that seems to be more widespread among archaean high grade terranes

chemical evolution of granitic rocks in the east antarctic shield with particular reference to post orogenic granites granitic intrusives of the east antarctic shield range in age from early archaean 3930 ma to cambrian and show systematic variations in chemical and isotopic characteristics many archaean orthogneisses are of tonalitic to granodioritic composition and represent new continental crust derived from the mantle by a two stage process involving hydrous melting of mafic crustal rocks syn orogenic granitic rocks are generally of more potassic composition and were derived by intracrustal melting under lower ph2o conditions they are mostly of more typical i type derived from igneous source materials but there is an increasing proportion of s types derived by melting of sedimentary materials with time late and post orogenic intrusives are mostly granites s s with a type anorogenic affinities and were derived by melting of relatively anhydrous granulite facies lower crustal rocks they are characterised by marked enrichment of y zr nb la and ce relative to p ti and sr and commonly have high f femg znfe and gaal plagioclase apatite and ti minerals were probably residual phases during partial melting as well as being involved in fractional crystallisation whereas other minor phases such as zircon were apparently relatively soluble in the high temperature melts emplacement of a type granites at about 500 ma may have been associated with internal fracturing of gondwanaland before eventual break up

late pleistocene paleoclimatology of the central equatorial pacific a quantitative record of eolian and carbonate deposition detailed records of vso 6i3c percentage and mass accumulation rate of caco and eolian percentage mass accumulation rate and grainsize generated for core rcl l 210 from the equatorial pacific reveal the timing of paleoclimatic events over the past 950 000 yr the caco percentage record shows the standard pacific correlation of high caco content with glacial periods but displays a marked change of character about 490 000 yr ago with older stages showing much less variability the carbonate mass flux record however does not show such a noticeable change sedimentation rates vary from about 0 5 to 3 0 cm l000 yr and during the past 490 000 yr sections with enhanced sedimentation rates correspond to periods of high caco percentage eolian mass accumulation rates an indication of the aridity of the source region are usually higher during glacial times eolian grainsize an indication of the intensity of atmospheric circulation generally fluctuates at a higher frequency than the loo ooo yr glacial cycle the mid brunhes climatic event centered at 300 000 yr ago appears as a 50 000 yr interval of low intensity and reduced variability of atmospheric circulation furthermore the nature of this entire record changes then with the younger portion indicating less variation in wind intensity than the older part of the record the late matuyama increase in amplitude of paleoclimatic signals begins 875 000 yr ago in the eolian record 25 000 yr before the 6i80 and caco percentage amplitude increases about

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

holocene aeolian phases and human settlements along the atlantic coast of southern spain a combined geomorphological radiocarbon dating archaeological and historical approach permits a refining of the age of the coastal dune systems related to estuaries in the gulf of cadiz three dune systems are distinguished in this paper the oldest one d1 which accumulated under prevailing wsw winds during the first millennium bc overlays both the occupational horizons of late neolithic early copper age fourth millennium bc and the lithic workshop levels fourth to second millennia bc the middle dune system d2 containing both roman and medieval remains accumulated between the thirteenth or fourteenth centuries and the seventeenth century ad the youngest d3 system is associated with the time of building of watchtowers in the seventeenth century ad but extends to the present it is related to sw prevailing winds we explain the absence of aeolian deposits prior to 2700 cal bp as the result of trapping of a large part of the sediment supply in the estuaries which starved the neighbouring beaches and aeolian settings aeolian accumulation reached significant values when sedimentation in the coastal zone changed from being mainly aggradational in the estuaries 6500 2700 cal bp to mainly progradational in spit barriers and related dunes post 2700 cal bp the present analysis of aeolian systems suggests a non direct correlation at least in some cases between coastal progradation of spit barriers and aridity

glacial and interglacial wind regimes over the eastern subtropical atlantic and north west africa analysis of aeolo marine dust deposits in the subtropical eastern atlantic enables the strength of the major wind patterns during the late quaternary to be evaluated and gives an insight into the climate of north africa

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

a 2 5 ga porphyry cu mo au deposit at malanjkhand central india implications for late archean continental assembly abstract eight re os ages from six molybdenite samples representative of the cu mo au mineralization at the giant malanjkhand deposit in madhya pradesh were obtained using id ntims these data provide a clear late archean early paleoproterozoic age for this deposit and by implication for its calc alkaline granitoid host among other diverse models the origin of malanjkhand has been debated as orogenic lode style associated with development of a quartz reef in a shear zone or as porphyry style associated with a pink granitoid intrusion that is conspicuously present in the vicinity of the brittle ductile deformed quartz reef previous models included middle proterozoic ages for the cu mo au mineralization based on poorly constrained rb sr and k ar data direct dating of molybdenite shows that stringer mineralization in the quartz reef and disseminated and vein mineralization in the granite were contemporaneous at 2490 8 ma 2489 5 1 4 ma based on regression without uncertainty in the 187re decay constant mswd 0 5 n 5 additional molybdenite from the quartz reef dated at 2475 and 2450 ma represents at least two pulses of reworking that we suggest configured the elongate and arcuate quartz reef into its present position we suggest that the quartz reef is a high silica stockwork cap embedded in its primary potassic alteration halo and subsequently tilted so that it lies convex to the east with deeper levels exposed to the north petrographic evidence coupled with high re concentrations for molybdenites 400 650 ppm support this scenario and suggest that malanjkhand is a subduction related stockwork porphyry style cu mo au deposit involving mantle malanjkhand geology shares little affinity with three surrounding and tectonically juxtaposed terranes we suggest that the malanjkhand cu mo au deposit and the surrounding batholith containing multiple cu mo au prospects may be the vestiges of a microplate captured along the north margin of the nearly amalgamated southern indian craton at 2 5 ga as the southern craton began to converge with the northern indian craton or other protocontinents now embedded or consumed within the central indian tectonic zone citz this scenario could imply an early paleoproterozoic age for the earliest development of the citz at least in the region of the central indian shear suture cis whose marked ene trend imprints the northwestern part of the malanjkhand batholith and the cu mo au deposit based on a compilation of 2 5 ga events in both the southern and northern indian cratons we suggest that some units in the citz linked an extensive and continuous late archean early paleoproterozoic orogenic belt that may extend to the moyar bavali bhavani attur palghat and cauvery shear zones in southern india and include inboard units of the eastern ghats and the aravalli delhi orogenic belts robust geochronology that can be tied to the early history within these orogenic belts is scarce and extensive reworking during grenvillian and pan african time creates a pervasive overprint at some localities this late archean early paleoproterozoic belt preserves sutures within a coalesced late archean continent that included east antarctica napier and vestfold hills complexes at 2 5 ga

geologic time series from deep sea sediments time scales and distortion by bioturbation abstract in order to evaluate the time and frequency domain characteristics of geologic time series obtained from deep sea sediments two important problems must be considered first an accurate time scale must be established for the sediment records to be studied an accurate time scale is a basic requirement for such techniques as spectral and cross spectral analysis secondly the distortion of a geologic time series by sedimentation processes such as bioturbation must be considered if inferences are to be made about the mechanisms controlling climatic and oceanographic processes reflected in the geologic record recently it has been suggested that the periodic components in paleoclimatic records which can be related to variations in the earth s orbital parameters can be used as a means for providing very detailed control for late pleistocene sediment sections a time scale is estimated by tuning an individual frequency component in a climate record to an orbital parameter the tuning procedure commonly uses the technique of bandpass filtering which removes all frequency components except the one equivalent to an orbital parameter and then adjusting the geologic time scale so that the filtered record and orbital record align since bandpass filtering will produce a periodic record from any data set a question is raised as to the circularity of this tuning approach a series of numerical experiments using synthetic time series are used to determine if the tuning of a geologic record artificially induces improved correlation and increased periodic character in a climatic record these experiments indicate that the tuning does not artificially induce these effects thus it is suggested that the careful use of orbital tuning provides a powerful means of defining a geologic time scale the degree to which bioturbation distorts a paleoclimatic record is studied by comparing the spectra of oxygen isotopic records obtained from cores with sedimentation rates ranging from 1 to 12 cm 1000 yr 1 it is shown that the systematic change in the variance spectra of these records that is predicted by models of bioturbation cannot be observed for sedimentation rates greater than 2 cm 1000 yr 1 this can be explained in part if bioturbation is a function of sedimentation rates if this is the case then bioturbation must proceed to depth of tens to hundreds of centimeters however it seems likely that the degree to which bioturbation alters the climate signal preserved in deep sea sediment cores has been overestimated

3 5 ga old amphibolites from eastern hebei province china field occurrence petrography sm nd isochron age and ree geochemistry amphibolite blocks frequently occur in association with grey gneisses within a small area near the villages of caozhuang and huangbaiyu in eastern hebei they are interpreted as remnants of an earlier bimodal suite now engulfed in late archaean k rich granitic magma and are further cut by pegmatite dykes they are considered together as giant enclaves within late archaean granite plutons u pb zircon ages 2 5 2 6 ga the amphibolites have been dated by the sm nd isochron method the results yielded t 3470 107 ma ind 0 50827 11 and nd t 2 7 0 6 this age represents the time of protolithic basalt eruption and possibly suggests a period of formation of primitive mafic crust this is the oldest reliable age so far obtained for the archaean rocks of china the sm nd results of grey gneiss samples yielded model ages tdm of about 3 24 ga it is not clear whether this younger age in comparison with that of the amphibolites indicates the intrusive nature of these rocks or is a result of contamination by later granite about 2 5 ga ago the rb sr and common pb isotopic systems have been highly disturbed and no isochron ages could be established the common pb data show retarded growth of radiogenic pb and hence imply reduction of u pb ratios in the past this is consistent with the petrographic study which suggests that the amphibolites have undergone an earlier period of granulite facies metamorphism and were subsequently retrogressed to the present amphibolite facies mineral assemblages the positive nd t value of 2 7 for the amphibolites implies that the protolithic basalt magmas were generated from mantle sources which had undergone long term depletion in light rare earth elements lree the depletion event must have taken place prior to 4 ga ago if their source had a chemical nature similar to the modern oceanic mantle it could have occurred as early as 4 5 ga ago if their source was less impoverished in lree if the mantle depletion was related to extraction of continental or sialic material the sm nd data of the caozhuang amphibolites lend support to the existence of sialic crust if not of a continental size before 4 ga ago

trace element characteristics and pb isotopic evolution of metasediments and associated proterozoic rocks from the amphibolite to granulite facies bamble sector southern norway abstract a study of trace element distribution and rb sr sm nd and pb isotopic compositions has been performed on amphibolite and granulite facies metasediments mafic granulites dioritic gneiss intrusive enderbitic veins and calc alkaline tonalitic gneisses from the proterozoic bamble sector southern norway the lile content of the granulite facies metapelites is similar to the average of the upper crust and post archaean average shales the k rb ratios of the amphibolite and granulite facies semipelites and impure quartzites are similar and the k rb ratios of the metapelites show overall similarities to the ratios of undepleted metapelites sr isotopic system and a poor correlation in the sm nd system the calculated t dm model ages for the metasediments can represent crustal residence times of 1 67 to 2 05 ga the present day lead isotopic data can be reproduced by a three stage model of pb evolution in which t 0 4 57 ga t 1 1 9 or 1 5 ga t2 1 1 ga 1 238 u 204 pb 7 9 1 232 th 238 u 2 5 2 4 15 where t 1 and t 2 are related to separation from the mantle and the sveconorwegian orogeny respectively the protolith of the metasediments the dioritic gneiss and the mafic granulites evolved in high u pb environments prior to sveconorwegian times 2 16 32 19 and18 45 respectively most of these rock units experienced conditions of 2 3 and 2 3 suggesting a large scale fractionation in the u th pb system connected to u mobility during the medium to high grade metamorphism there are no unambiguous differences in the pb isotopic composition between the amphibolite and granulite facies rocks but the mafic granulites from the classical depleted granulite area of tromoy island evolved in overall lower 2 238 u 204 pb environments than similar rocks from the neighbouring hisoy island this suggests that the similar u content of these rocks largely can be due to local pre sveconorwegian 238 u 204 pb variations sveconorwegian intrusive enderbitic dykes and veins crystallized with low lile and nb concentrations at granulite facies p t aco 2 conditions pre sveconorwegian granulite facies tonalitic gneisses show a less depleted trace element pattern and low nb concentrations and the hornblende free tonalitic gneisses have significantly lower u content than their hornblende bearing counterparts the investigated metasediments have very low contents of the less mobile elements nb sr cu and p 2 o 5 which probably represent characteristics of the pre sedimentary protolith

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

comment on formation of chenier plain of the donana marshland sw spain observations and geomorphic model by a rodriguez ramirez and c m yanez camacho marine geology 254 2008 187 196 abstract rodriguez ramirez and yanez camacho 2008 rodriguez vidal et al 2009 and rodriguez ramirez et al 2009 have kept an ongoing discussion about the validity of radiocarbon ages in reconstructing holocene palaeogeographical models in the gulf of cadiz the discussion considered the validity and correctness of the r value to be used in the area to calibrate radiocarbon ages of marine samples these papers suggest that the r value proposed by lario 1996 and dabrio et al 1999 2000 is erroneous and consequently that all the evolutionary models based on radiocarbon ages from marine samples that have been proposed in this area since 1996 must be revised however the papers commented here use erroneously the r regional r and r values after reviewing the published data it is apparent that the most reliable values of r in the gulf of cadiz for middle late holocene samples range between r 35 85 yr and r 95 15 yr this means that the values used in lario 1996 and dabrio et al 1999 2000 fall in this range and also that the calibrated ages used by several authors adopting these values are fully reliable calibrations using r values inside this range do not yield significant differences in terms of geological age owing to the magnitude of errors resulting from the methods employed

chemical and isotopic composition of the lower crust beneath the meguma lithotectonic zone nova scotia evidence from granulite facies xenoliths granulite facies xenoliths from an upper devonian lamprophyre dyke near tangier nova scotia provide new information about the lower crust in the meguma zone two mineralogically and chemically distinet groups of xenoliths occur both groups contain quartz feldspar biotite fe ti oxides sulfides in addition group a contains garnet graphite aluminosilicates spinel sapphirine hight al2o3 subgroups a1 and a2 or clinopyroxene sphene apatite high cao sub group a3 group b has highly variable proportions of orthopyroxene b1 clinopyroxene b2 and amphibole b3 trace element contents of the highly aluminous xenoliths compare closely with average to upper crustal model compositions and are similar in many aspects to other undepleted granulite facies rocks lowp t sedimentary assemblages of quartz chlorite clay minerals calcite albite or paragonite can account for the compositions of group a xenoliths within group b a high mgo mgo 13 wt subgroup with high transition metal contents and low mgo mgo 9 wt sub groups with higher lil large ion lithophile element contents exist although the rare earth and high field strength elements indicate a tholeiitic or low k calc alkaline chemistry the lil elements are as high as those from high k calc alkaline volcanic are rocks isotopically group a ranges from endt 2 56 to 0 80 and87sr 86srt 0 7046 to 0 7182 fort 370 ma for group b these values are 1 45 to 5 33 and 0 7028 to 0 7048 respectively model ages tchur are correspondingly low and are tightly constrained 544 52 ma these young ages contrast with the middle proterozoic nd model ages of the overlying meguma zone low grade flysch this time inverted stratigraphy appears to be the product of a tectonic break between a younger autochthonous tangier lower crust avalon and an older allochthonous meguma group upper crust

depositional history of estuarine infill during the last postglacial transgression gulf of cadiz southern spain abstract the late pleistocene and holocene evolution of the estuaries in the gulf of cadiz is interpreted for the first time using drill cores logs trenches and 38 new radiocarbon data and the results compared with the shelf the odiel tinto and guadalete rivers deposited conglomerates during a highstand that did not reach the present sea level dated at ca 25 30 ka isotopic stage is 3 corresponding to a relatively humid period in the area rivers incised these coarse grained deposits during the last main lowstand at ca 18 ka when sea level dropped to 120 m and the coastline lay 14 km seawards from the present the erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise overlain by the valley fill deposits of the transgressive and highstand phases of the last fourth and fifth order depositional sequences recognised in the shelf the first marine influence in the estuaries during the transgression occurs at 25 30 m at ca 10 000 years bp according to fossil assemblages the transgressed basins changed from brackish to more open marine as the sea rose until ca 6500 years bp when it reached the maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy central basins then the rate of eustatic rise decreased drastically and the estuarine filling followed a two fold pattern governed by the progressive change from vertical accretion to lateral centripetal progradation at ca 4000 years bp the fluvial input surpassed the already negligible rate of rise causing partial emergence of tidal flats and spit barriers in the largely filled estuarine basins prevalence of coastal progradation upon vertical accretion at ca 2400 years bp caused accelerated expansion of tidal flats and rapid growth of the sandy barriers further changes since the 16th century reflect widespread anthropic impacts

distribution of biogenic silica and quartz in recent deep sea sediments all available quartz and biogenic silica concentrations from deep sea surface sediments were intercalibrated plotted and contoured on a calcium carbonate free basis the maps show highest concentrations of biogenic silica opal along the west african coast along equatorial divergences in all oceans and at the polar front in the southern indian ocean these are all areas where upwelling is strong and there is high biological productivity quartz in pelagic sediments deposited far from land is generally eolian in origin its distribution reflects dominant wind systems in the pacific but in much of the atlantic and indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

formation of chenier plain of the donana marshland sw spain observations and geomorphic model abstract the guadalquivir estuary is one of the most important in europe it is isolated from the sea by two important littoral spits donana and la algaida its sedimentary filling occurred as a result of deltaic contributions of the guadalquivir river giving rise to marshes primarily composed of mud deposits among which a succession of sandy and shelly ridges can be found the aim of this paper is to explain the genesis and evolution of these sandy and shelly ridges clarifying what types of ridges are found and their spatial distribution identifying the processes responsible for their formation these ridges extend in the form of long strands along the estuary influencing its evolution during the late holocene the geomorphologic and lithostratigraphic features of these ridges allow them to be defined as transgressive cheniers regressive cheniers and laterally accreted ridges spits as components of the guadalquivir estuary chenier plain complex this chenier plain has the peculiarity of developing on a semi enclosed shoreline contrary to other chenier plains in the world which develop on open coasts in the guadalquivir estuary the chenier plain formation is related to two relatively higher sea level 4200 2800 yr bp and 1400 1000 yr bp during which high energy events occur storms and tsunamis that transgressed the large littoral spits the carrizosa 4000 yr bp and vetalengua 1400 1300 yr bp spits have been formed across the inlet and prograded landwards of the estuary from here several sequences of cheniers mainly transgressive cheniers associated with these events were formed these cheniers form two groups las nuevas 1100 1000 yr bp and marilopez 3000 yr bp composed mainly of shells and shell fragments these cheniers were constructed by waves which reworked the shells above estuarine levees and led to their intense landward migration thus explaining the peculiar high inland position of the cheniers

sr and nd isotope systematics of polymetamorphic archean gneisses from southern west greenland and northern labrador sr and nd isotopic data for middle to late archean polymetamorphic felsic gneisses from localities in the nuuk area west greenland are compared and contrasted with new isotopic results for early archean amitsoq gneisses and with data for isotopically reworked kiyuktok gneisses from the saglek area labrador sr isotopic data for individual suites of felsic gneisses record the time integrated effect of variable rb sr fractionation during prograde and retrograde events as well as the effect of source inhomogeneity contrasting petrologic and sr nd isotopic characteristics are the result of differences in level of exposure caused partially by juxtaposition of terranes of different metamorphic character by movement on ductile shear zones and post shearing folding deformation sm nd systematics of felsic gneisses from nordafar ikerasakitsup akornga tinissaq and kangimut sammisoq qasigianguit define a geologically meaningless ca 3280 ma nd isochron which is the result of mixing of samples from unrela

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

arrested charnockite formation in southern india and sri lanka arrested prograde charnockite formation in quartzofeldspathic gneisses is widespread in the high grade terrains of southern india and sri lanka two major kinds of orthopyroxene producing reactions are recognized breakdown of calcic amphibole by reaction with biotite and quartz in tonalitic granitic gray gneiss produced the regional orthopyroxene isograd manifest in charnockitic mottling and veining of mixed facies exposures as at kabbal karnataka and in the kurunegala district of the sri lanka central highlands chemical and modal analyses of carefully chosen immediately adjacent amphibole gneiss and charnockite pairs show that the orthopyroxene is produced by an open system reaction involving slight losses of cao mgo and feo and gains of sio2 and na2o rb and y are depleted in the charnockite another kind of charnockitization is found in paragneisses throughout the southern high grade area and involves the reaction of biotite and quartz garnet to produce orthopyroxene and k feldspar although charnockite formation along shears and other deformation zones at such localities as ponmudi kerala is highly reminiscent of kabbal close pair analyses are not as suggestive of open system behavior this type of charnockite formation is found in granulite facies areas where no prograde amphibole bearing gneisses exist and connotes a higher grade reaction than that of the orthopyroxene isograd metamorphic conditions of both kabbaltype and ponmudi type localities were 700 800 c and 5 6 kbar lower p h2o in the ponmudi type metamorphism was probably the definitive factor

late pleistocene paleoclimatology of the central equatorial pacific sea surface response to the southeast trade winds proxy indicators of sea surface temperature and equatorial divergence based on radiolarian assemblage data and of trade wind intensity based on eolian grain size data show similar aspects of variability during the late pleistocene all indicators fluctuate at higher frequencies than the 100 000 year glacial interglacial cycle display reduced amplitude variations since 300 000 years ago exhibit a change in the record character at about 300 000 years ago the mid brunhes climatic event and have higher amplitude variations in sediments 300 000 850 000 years old time series analyses were conducted to determine the spectral character of each record 18o of planktonic foraminifer sea surface temperature values equatorial divergence indicators and wind intensity indicators and to quantify interrecord coherence and phase relationships the record was divided at the 300 000 year clear change in climatic variability nonstationarity the 18o based time scale is better lower in the core so our spectral analyses concentrated on the interval from 402 000 774 000 years the 18o spectra show 100 000 and 41 000 year power in the younger portion 0 300 000 years and 100 000 41 000 and 23 000 year power in the older interval all highly coherent and in phase with the specmap average stacked isotope record unlike the isotope record the dominant period in both the eolian grain size and equatorial divergence indicators is 31 000 years this period is also important in the sea surface temperature signal where the dominant spectral peak is 100 000 years the 31 000 year spectral component is coherent and in phase between the eolian and divergence records confirming the link between atmospheric and ocean surface circulation for the first time in the paleoclimate record since the 31 000 year power appears in independent data sets within this core and also appears in other equatorial records j imbrie personal communication 1987 we assume it to be real and representative of both a nonlinear response to orbital forcing possibly a combination of orbital tilt and eccentricity and some resonance phenomenon required to amplify the response at this period so that it appears as a dominant frequency component the mid brunhes climatic event is an important aspect of these records but its cause remains unknown

geochemistry and geochronology of proterozoic tholeiite dykes of east antarctica evidence for mantle metasomatism two episodes of tholeiite dyke emplacement have been identified in archaean high grade metamorphics of the napier complex in enderby land middle proterozoic amundsen dykes are typical continental tholeiites and most of the chemical variation in individual suites can be explained in terms of different degrees of partial melting and low pressure crystal fractionation group i amundsen tholeiites were derived from a relatively homogeneous source region 1 190 200 m y ago whereas that of the group ii amundsen tholeiites was chemically and isotopically heterogeneous group ii dykes have various degrees of enrichment in incompatible elements and commonly show normalised trace element abundance patterns with negative nb anomalies these features imply variable metasomatism of the source region by a volatile rich fluid phase rather than a melt of any observed igneous composition enriched in k rb ba th and possibly la and ce early proterozoic 2 350 48 m y tholeiites were emplaced at considerable depths in the crust during the waning stages of granulite facies metamorphism and include a high mg suite of possible komatiitic affinity ranging in composition from hypersthene rich tholeiite norite to quartz rich tholeiite they tend to have higher ratios of highly to moderately incompatible elements e g k zr k ce and larger nb anomalies i e higher k nb compared with middle proterozoic tholeiites suggesting derivation from more enriched source regions isotopic data are not compatible with significant crustal contamination but constrain source metasomatism to a time immediately before emplacement metasomatism of the source region of the much younger group i tholeiites may have been contemporaneous with that of the high mg suite

petrogenesis of plutonic rocks in a proterozoic granulite facies terrane the bunger hills east antarctica abstract several compositionally varied suites of plutonic rocks gabbro quartz monzogabbro granite quartz monzodiorite in the bunger hills were emplaced at depths of 20 km over a relatively short time interval 1170 1150 ma during the waning stages of granulite facies metamorphism the peak of which occurred 1190 ma ago alkaline syenite to granite rocks were emplaced west of the denman glacier at david island 515 ma ago most of these rocks crystallised from magmas derived by melting of heterogeneous mantle comprising at least two components nb poor long term enriched lithosphere and a nb rich oib ocean island basalt type within plate component metasomatic enrichment of the source of the plutonic rocks as well as that of 500 ma alkaline dykes may have been contemporaneous with continental crust formation in the area during the late archaean or early proterozoic much of the chemical variation of the different suites can be explained by fractional crystallisation but other processes particularly variations in the extent and or p t conditions of melting were also important crustal contamination does not appear to have been a major factor in the petrogenesis of the bunger hills magmas but cannot be entirely discounted particularly for some of the granitic rocks the more evolved david island syenitic intrusives may have been derived by melting of lower crustal rocks

geochemistry of precambrian gneisses relevance for the evolution of the east antarctic shield archaean granulite facies orthogneisses of the napier complex in enderby land metamorphosed 3070 maago comprise two chemically distinct suites the more abundant mainly of tonalitic to granodioritic composition shows strong y depletion explicable by hydrous partial melting of a garnet bearing source garnet amphibolite or possibly eclogite it apparently represents new continental crust other gneisses predominantly of trondhjemitic to granitic s s composition do not show y depletion and have higher tio2 zr nb la ce and ga al and lower cao sr and mg mg total fe they probably originated by relatively dry melting of predominantly felsic crystal rocks both suites show evidence for loss of rb relative to k th and u during metamorphism late archaean 2800 ma amphibolite facies gneisses of macrobertson land are of undepleted type and may be representative of a higher crustal level than those of enderby land late proterozoic 1000 ma granulite facies gneisses of enderby land rayner complex are to a large extent remetamorphosed napier complex rocks of igneous derivation in contrast gneisses of similar age in macrobertson land include a much higher proportion derived either directly or by partial melting from sedimentary protoliths

a record of past ocean atmosphere radiocarbon differences from the northeast pacific a record of the 14c age differences between atmosphere and the mixed layer of the northeast pacific ocean was obtained from 58 radiocarbon measurements on shells and associated wood from coastal sediments in british columbia this series of mixed layer reservoir ages spans the holocene and extends into the period of the younger dryas cold event in the north atlantic and surrounding regions the data reflect the extent of upwelling in the northeast pacific and thus constrain models of carbon cycling and ocean circulation most of the reservoir ages are only slightly less than than the present preindustrial value of about 800 years and may be identical when probable sampling errors are taken into account either the north pacific reached a state close to its present mode of circulation at or before the end of the younger dryas or a different circulation fortuitously produced a similar reservoir age our results support the hypothesis that slow changes in atmospheric radiocarbon concentrations over the holocene arose from 14c production rate changes data corresponding to a radiocarbon age of around 6400 years b p give a reservoir age of 1200 years if this result is confirmed it indicates a much greater variability for the holocene ocean circulation than was previously believed possible

adakites the key to understanding lile depletion in granulites abstract for more than 20 years it has been argued that granulites of the lower continental crust are depleted in fluid mobile elements such as cs rb u and th either because they were removed by melting of the lower crust or through dehydration we argue that there is little evidence for a simple relationship between granulite facies metamorphism and element depletion and propose that for felsic orthogneisses the depletion may be a primary feature of crust generation processes modern adakites show a range of fluid mobile element ratios and adakites from the austral volcanic zone avz chile show fluid mobile element ratios very similar to those found in lower crustal felsic granulites this suite of adakites has a strong slab derived component we propose that modern adakites of the type found in the austral volcanic zone are analogous in their genesis to lower crustal felsic granulites and that their mafic precursors were already depleted in fluid mobile trace elements prior to melting an incremental melting model in which fluid mobile elements are released from an eclogitic slab prior to partial melting can explain the fluid mobile element behaviour of both modern adakites and lower crustal felsic granulites

changes in sedimentation trends in sw iberia holocene estuaries spain abstract an analysis of sedimentation rates during the holocene in estuaries in the southwestern coast of the iberian peninsula using depth age diagrams reveals the existence of two distinct phases the first between ca 10 000 and 6500 cal bp still in the transgressive phase yields values of sedimentation rates of 5 mm yr the second phase extends after the maximum transgressive ca 6500 cal bp until the present with sedimentation rates of 1 5 2 mm yr these results support the idea that marine sedimentation began during the transgressive phase and continued during the highstand phase far beyond the time of the transgressive maximum as postulated in some previous papers

reply to the comment on formation of chenier plain of the donana marshland sw spain observations and geomorphic model by a rodriguez ramirez and c m yanez camacho marine geology 254 2008 187 196 abstract the application of the regional reservoir effect r on the south atlantic coast of iberia requires adjustments as a result of the variations it has undergone throughout the holocene since 1996 a constant value of 440 84 14c yr has been used dabrio c j zazo c lario j goy j l sierro f j borja f gonzalez j a flores j a 1999 sequence stratigraphy of holocene incised valley fills and coastal evolution in the gulf of cadiz southern spain geologie en mijnbouw 77 23 281 dabrio c j zazo c lario j goy j l sierro f j borja f gonzalez j a flores j a 2000 depositional history of estuarine infill during the last postglacial transgression gulf of cadiz southern spain marine geology 162 381 404 however a constant value for the whole of the holocene cannot be expected which has led to time intervals with different r being established morales j a borrego j san miguel e g lopez gonzalez n carro b 2008 sedimentary record of recent tsunamis in the huelva estuary southwestern spain quaternary science reviews 27 734 746 deduced from the marine reservoir correction database from calib radiocarbon calibration version 5 0 2html by m stuiver p j reimer and r reimer later soares soares a m m 2008 radiocarbon dating of marine samples from gulf of cadiz abstracts annual conference igcp 495 faro portugal 6 7 established a constant r value of 135 20 14c yr which can be applied to samples younger than 4000 14c yr bp rodriguez vidal et al comment on formation of chenier plain of the donana marshland sw spain observations and geomorphic model by a rodriguez ramirez and c m yanez camacho marine geology 254 2008 187 196 marine geology 2009 in press use these disquisitions about the correct r value to question the geodynamic model proposed by rodriguez ramirez and yanez camacho rodriguez ramirez a yanez camacho c m 2008 formation of chenier plain of the donana marshland sw spain observations and geomorphic model marine geology 254 187 196 without providing any data of their own these authors base their particular critique on the chronological difference caused by using a different r value from the one they use which in this case is the soares soares a m m 2008 radiocarbon dating of marine samples from gulf of cadiz abstracts annual conference igcp 495 faro portugal 6 7 value however if we take into account new progress in the r value all studies since 1996 have some kind of chronological error of this kind and therefore this critique should extend to all these works including their own a critique on geodynamic models based solely on chronological differences of this kind is not justifiable at the same time the ages determined by these authors by re calibrating the samples in rodriguez ramirez and yanez camacho rodriguez ramirez a yanez camacho c m 2008 formation of chenier plain of the donana marshland sw spain observations and geomorphic model marine geology 254 187 196 do contain serious errors due to the incorrect use of the calib 5 0 2 programme

geochemical evolution of archaean granulite facies gneisses in the vestfold block and comparisons with other archaean gneiss complexes in the east antarctic shield the vestfold block like other archaean cratons in east antarctica and elsewhere consists predominantly of felsic orthogneiss mossel and crooked lake gneisses with subordinate mafic granulite tryne metavolcanics and paragneiss chelnok supracrustals two major periods of continental crust formation are represented the mossel gneiss metamorphosed about 3 000 ma ago is mainly of tonalitic composition and is similar to much of the roughly coeval napier complex in enderby land the crooked lake gneiss was emplaced under high grade conditions about 2 450 ma ago and comprises a high proportion of more potassic rocks monzodioritic and monzonitic suites as well as tonalite and minor gabbro and diorite both mossel and crooked lake gneisses are depleted in y and have moderate to high sr ce y and ti y consistent with melting of a mafic source subducted hydrated oceanic crust leaving major residual hornblende garnet most crooked lake gneisses are more enriched in incompatible elements p sr la ce and particularly rb ba and k than mossel gneisses suggesting derivation from a more enriched mafic source the vestfold block contains few orthogneisses derived by melting of older felsic crustal rocks in marked contrast to the archaean napier complex and in particular southern prince charles mountains both mossel and crooked lake tonalites are strongly depleted in rb k th and u and have very low rb sr and high k rb more potassic orthogneisses are depleted in th u and to lesser extents rb tryne metavolcanics are depleted in th and rb but appear to have been enriched in k and probably na possibly during early low grade alteration

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

role of a thin komatiite rich oceanic crust in the archean plate tectonic process in the archean tectonic regime the time available for oceanic lithosphere to cool on its journey from ridge to convergent plate boundary was far less than at present under these conditions only an inherently dense lithosphere could have acquired the negative buoyancy necessary for it to subduct at this time plate tectonics could have operated only if 1 the oceanic crust was rich in komatiite lava and 2 the thickness of this crust was not much greater than the thickness of modern oceanic crust

lewisian gneiss geochemistry and archaean crustal development models abstract the geochemistry of lewisian amphibolite facies gneisses from northwest scotland is described with particular reference to the rare earth elements ree and compared with the geochemistry of lewisian granulite facies gneisses the results show that there are no significant differences between laxfordian amphibolite facies and scourian granulite facies gneisses in terms of ree and other immobile trace elements at equivalent silica levels although the mobile radioactive heat producing elements k rb th u are significantly lower in the granulites in both types the basic gneisses have moderately fractionated ree patterns while the intermediate and acid gneisses have strongly fractionated ree patterns with low heavy ree abundances and decreasing levels of total ree with increasing sio 2 the most silicic gneisses develop large positive europium anomalies these gross chemical similarities between gneisses from intermediate amphibolite facies and lower granulite facies crustal levels constrain models for the evolution of the archaean crust the depletion of k rb cs th and u in granulites but not other incompatible trace elements cannot be explained by magmatic processes the positive eu anomaly in the more siliceous gneisses of both facies is a function of the primary processes of crustal generation and not secondary processes such as intracrustal melting or fractional crystallisation fractionation of radioactive heat producing elements from other trace elements is a result of granulite facies metamorphism with these elements being removed by an active fluid phase the apparent lack of partial melting in lower crustal granulites suggests a model for archaean crustal growth largely through underplating by primary tonalitic magmas