observatory validation of neolithic tells magoules in the thessalian plain central greece using hyperspectral spectroradiometric data abstract this paper presents the results obtained from field spectroradiometric campaigns over neolithic tells magoules located at the thessalian region in greece in each one of the four archaeological sites selected three sections were carried out using the ger 1500 handheld spectroradiometer spectral profiles of the sections and several vegetation indices such as normalized difference vegetation indices ndvi and simple ratio sr have been examined in this study this is one of the first times that ground hyperspectral data are evaluated in such context of archaeological research for the spectral characterization of archaeological features as it was found ground spectroradiometric measurements can be efficiently used in order to support and validate satellite imagery results for the detection of archaeological sites

origin and implications of early diagenetic quartz in the mississippian bowland shale formation craven basin uk abstract silica cementation exerts a key control on the compaction and geotechnical properties of mudstones and by extension the style of hydrocarbon and or mineral systems present in a given sedimentary basin integrated microscopic and bulk geochemical observations demonstrate that siliceous mudstones in the bowland shale formation a target for uk shale gas extraction exhibit abundant dispersed discrete m scale quartz cements and exhibit silica enrichment excess above a local detrital si al threshold of 2 5 dissolution of siliceous radiolarian tests during early diagenesis is identified as the main source of silica opal a required for quartz precipitation either via opal ct or directly to quartz and potentially generated as a product of anoxic marine weathering dissolution of reactive silicates during early diagenesis excess silica correlates with free hydrocarbons s1 normalised to total organic carbon oil saturation index osi we propose early diagenetic quartz precipitation suppressed pore collapse buttress effect retaining the pore space capacity to host oil quartz precipitation was likely catalysed for example via low porewater ph elevated al and or fe oxide content and or abundant labile organic matter juxtaposition of siliceous mudstones and mudstones lacking quartz cement indicates silica was immobile beyond the bed scale thus metre scale siliceous packages likely represent more prospective units within the bowland shale in terms of unconventional hydrocarbons on the basis of early diagenetic biogenic derived quartz cementation leading to improved hydrocarbon storage capacity coupled to enhanced brittleness these findings are relevant for shale oil and shale gas systems specifically where oil retained in pores subsequently cracks to generate gas these findings also suggest the bowland shale is a sub class of black shale defined by the potential to host a relatively large volume of early diagenetic fluids derived from anoxic bottom waters which were potentially s and or metal bearing this is potentially relevant for understanding the genesis of adjacent and related pb zn mineral deposits

the importance of water column processes on the dissolution properties of biogenic silica in deep sea sediments i solubility abstract flow through experiments have been performed to study the thermodynamics of biogenic silica opal dissolution in deep sea sediments they were applied for the first time on sediment from the southern ocean van cappellen and qiu 1997a van cappellen and qiu 1997b we have extended the use of these experiments to other deep sea settings thereby covering a wide range of in situ silicic acid asymptotic concentrations casympt 200 to 900 mol l and biogenic opal content bsi 0 5 to 80 performing these experiments under in situ bottom temperatures allows for the comparison between experimental apparent solubilities and casympt concentrations low values of bsi apparent solubilities have been measured in the deepest sections of the multicores collected in the northeast atlantic 229 mol l and in the equatorial pacific 505 mol l they are only 10 to 20 higher than the in situ casympt concentrations this demonstrates a clear control of pore water silicic acid concentrations by the in situ apparent solubility of the bsi i e the solubility of bsi within a complex sedimentary matrix that includes important quantities of silicate minerals in regions where the percentage detrital percentage biogenic ratio is low the apparent solubility of the biogenic silica is close to that of in situ biogenic silica in the opposite case when the percentage detrital percentage biogenic ratio is high reprecipitation reactions induce strong interference on the dissolution properties of the opal both in situ and in flow through experiments in such a sedimentary matrix it is important to determine the appropriate opal solubility to be used in early diagenetic models i e the solubility of the biogenic silica just before deposition on the seabed this has been achieved by performing flow through experiments on sediment trap material from the north atlantic site comparison of apparent biogenic silica solubility measured by flow through experiments and the silicic acid concentrations measured in the cups of the sediment traps suggested that the solubility of biogenic silica that reaches the sediment water interface is not unique and varies spatially and temporally in fact it is the degree of coupling between surface waters and the sediment water interface that will control the aging of biogenic silica in the water column and hence the dissolution properties of the biogenic silica deposited at the sediment water interface all these results call for a strong improvement of biogenic silica early diagenetic models that should include not only a reprecipitation term that takes into account interaction with silicate minerals but also the existence of several phases of biogenic silica and thus that should operate in a non steady state mode to account for seasonal variations in the quality of deposited biogenic silica

tectonic control of guadalupian lopingian cherts in northwestern sichuan basin south china abstact cherts have been considered to be formed mainly through processes involving biosilicification riverine inputs and hydrothermal activities in the permian massive cherts are widely distributed in south china bearing significant implications for the reconstruction of paleogeography and paleoceanography of the eastern paleo tethys ocean the origin of the permian cherts in south china however remains inconclusive due to a lack of systematic petrographic and geochemical study in this article we analyze the petrologic and geochemical characteristics of the cherts collected from five outcrops in the northwestern sichuan basin south china these cherts are found from the upper guadalupian maokou formation ca 268 259 ma and upper lopingian dalong formation ca 254 252 ma field and microscopic observations suggest that cherts from the maokou formation occur mainly in nodular forms and consist of microcrystalline quartz silicified bioclasts and siliceous fossil debris both petrographic observation and geochemical analysis suggest that the maokou cherts are mainly of hydrothermal origin near deep faults in the southwest and of biogenetic origin with less hydrothermal influence in the northeast of the studied area the dalong cherts occur in both nodular and bedded forms with more abundant siliceous fossil debris than the maokou cherts major trace and rare earth element data support that the dalong cherts are influenced by both biosilicification and hydrothermal activities the spatial heterogeneity of the cherts origin in south china is largely controlled by tectonic activities associated with the emeishan large igneous province elip event and the closure of the paleo tethys ocean the troughs formed by the extensional tectonic activity linked to the elip could provide accommodation space and activate deep faults allowing the rise of silicon rich hydrothermal fluids from the deep and nutrient rich water from volcanogenic upwellings subsequent cooling may have facilitated the precipitation of large amounts of silica and the formation of cherts in the study region this work demonstrates that the origin of the guadalupian lopingian cherts in south china is predominantly controlled by tectonic and biological activities which sheds light on the global permian chert event

silica burp in the eocene ocean the eocene was a time of greatly increased silica accumulation in the ocean and the peak was in the early middle eocene at about 50 ma the responsible geohistorical configuration included the following elements extensive volcanism about 4 m y earlier as part of the chron 24 plate reorganization early eocene warming with deep weathering to high latitudes and accumulation of the released silica in a sluggish ocean and sharp cooling in the earliest middle eocene stimulating oceanic upwelling and biosilicification it is possible on the evidence of carbon and oxygen isotopic patterns that the trigger for the exhalation of silica was a reverse greenhouse effect

andean sponges reveal long term benthic ecosystem shifts following the end triassic mass extinction abstract thick cherts and cherty dolomites in the basal jurassic aramachay formation of peru preserve a thriving continental shelf community dominated by siliceous sponges that followed the end triassic collapse of metazoan rich carbonate accumulation similar hettangian and sineumurian deposits from nevada u s a austria and morocco suggest that an early jurassic siliceous sponge takeover was a widespread phenomenon that persisted for 2 m y until metazoan driven carbonate sedimentation recovered the post extinction dominance of siliceous sponges likely resulted from the confluence of metazoan carbonate reef collapse removal of incumbents and geochemical conditions that fostered the success of the siliceous sponge dominated ecosystem simple mass balance calculations suggest the siliceous sponge takeover was likely permitted by an increased silica flux as a consequence of weathering central atlantic magmatic province camp basalts the camp basalts alone could supply all the silica needed to sustain the sponge takeover although contributions were also likely from increased hot climate weathering of other silicates and possible reductions in dissolved silica demand by radiolarians detailed sedimentological fossil and microfacies analyses were conducted at six field sites across a shallow shelf system recorded in the central peruvian andes yauli dome focusing on the metazoan contribution to sedimentation sedimentary structures at all six sites demonstrated on shelf deposition similar to the underlying upper triassic chambara formation in contrast to the black shale rich facies of the aramachay formation in other areas of peru examination of up to 147 m of cherty dolomite from the aramachay formation revealed a siliceous sponge dominated ecosystem including sponge body fossils compressed in situ sponge materials and abundant transported spiculite sediments siliceous sponges mostly demosponges and rare hexactinellids account for the chert lithology and apparently dominated the local ecology for approximately two million years the role of metazoan biocalcifiers in sediment production and ecological structure was profoundly reduced compared to the under and overlying formations representing a clear ecological state shift from pre extinction carbonate to post extinction siliceous dominated ecosystems before the carbonate system recovered 2 m y after the extinction

marine electrical resistivity tomography for shipwreck detection in very shallow water a case study from agropoli salerno southern italy abstract a marine electric resistivity survey was carried out over a submerged beach along the agropoli shore salerno italy to detect buried objects of archaeological interest below the sandy seabed we found a shipwreck a military vessel that probably sunk during the salerno landing operations of the allied forces in the second world war resistivity data provide information on the vertical and horizontal extension of the shipwreck which is characterized by very low calculated resistivity values about 2 5 ohm m such values differ significantly from the sand and the bedrock values 5 40 ohm m although the presence of the shipwreck is clearly visible from geoelectric data the joint application of electric magnetic and multibeam bathymetric techniques reduces the ambiguities inherent in each method as shown in the electrical resistivity tomography ert and confirmed by the digital elevation model obtained from the processing of bathymetric data the shipwreck extends more than 30 m in ne sw direction and it is about 13 m wide the global extension of the relic is consistent with the magnetic data that are characterized by a magnetic anomaly with an amplitude of about 1800 nt and similar dimension as inferred from the estimation of source boundaries obtained from the computation of the analytic signal the results of our survey encourage the use of marine geoelectrical methods for the detection of buried archaeological targets particularly in locations where the use of seismic prospecting is not effective e g very shallow water with sandy sea bottoms the integration of different geophysical methods allows to better define the extension depth and thickness of buried objects suggesting that such an approach is the most effective for underwater archaeological investigations

geophysical investigation of the temple of apollo hierapolis turkey abstract the ruins of hierapolis are located a few kilometres north of laodicea in the lycus valley western turkey this area is characterised by a large geothermic field that produces several hot water springs along tectonic structures fractures and faults inside hierapolis is the temple of apollo the principal deity of the city while the foundations of this temple go back to late hellenistic times the present remains of the upper structure are from the 3rd century ad next to it there is an underground chamber called the plutonion from which poisonous gases emerge this paper presents the results of a geophysical survey carried out to explore firstly the buried cavities or structures beneath the temple of apollo knowledge of which is important to understand whether the plutonion could be entered from the inside of the temple for completing the sacrifices secondly to contribute to the ongoing evaluation of ground penetrating radar gpr and electrical resistivity tomography ert as tools for research into subsurface archaeological features voids walls etc two dimensional ert imaging was used to detect the presence of an active normal fault passing under the temple of apollo as shown by geological geomorphological and archaeoseismological observations the resistivity profiles reveal the presence of conductive material clay covering the archaeological structures the presence of active normal faults is indicated by the displacement of the bedrock and the conductive material on top of it three dimensional gpr imaging was used to detect man made structures located under the temple of apollo the results of the two survey methods applied were compared assessing the relative merits and demerits of each technique their combined use is discussed in terms of providing enhanced views that are more informative than a single method

quantifying tomb geometries in resistivity images using watershed algorithms abstract quantifying the geometries defined here as width height and depth of burial of archeological structures within resistivity models produced as a result of the regularization constraints used in most inversion algorithms is difficult especially when structures are closely spaced here we apply the watershed by simulated immersion method of boundary detection to smooth 2d resistivity images generated for synthetic and field data over 3d targets the synthetic studies include a single cavity model a model for two widely spaced cavities spacing unit electrode spacing and a model for two closely spaced cavities spacing

large scale lateral advection of seawater through oceanic crust in the central equatorial pacific the existence of large scale lateral advection of water through basaltic crust in the central equatorial pacific ocean is demonstrated by the calcium magnesium strontium sulfate and strontium isotopic compositions of pore waters from the overlying sediments the advection is believed to extend throughout the region of the equatorial high productivity sediment bulge from about 110 to 160 w and from about 5 s to 8 n the corresponding crustal ages of this region vary from east to west from about 15 to about 70 ma respectively this advection is responsible for the low conductive heat flows previously observed throughout the region the flow is recognized by the following characteristic pore water compositional variations calcium and magnesium concentrations remain nearly constant downhole from the sediment water interface to basement species such as strontium sulfate and strontium isotopes which are more affected by diagenetic reactions in the sediment column depart from seawater values with increasing depth in the sediments but then they display concentration reversals near basement at the sediment basement interface pore waters are chemically and isotopically nearly indistinguishable from present day seawater fluid flow in basement is rapid having a calculated average residence time in oceanic crust of about 20 000 years and an inferred pore fluid velocity between 1 and 10 m y 1 because of the short reaction time between basement rocks and fluids as well as the low temperature of this fluid the chemistry of basement water remains similar to seawater as a result despite the important impact of this process on oceanic heat flow the flow may have little effect on the long term major element composition of seawater

hydrothermal pits in the biogenic sediments of the equatorial pacific ocean 1 a recent expedition to the equatorial pacific surveyed over 60 000 km2 of seafloor using swath map imaging and high resolution seismic profiling this survey revealed the common occurrence of large pits in the biogenic sediments that are usually associated with basement highs the pits range in size up to a few kilometers across and are on the order of 50 m 100 m deep they were found on seafloor ranging in age from 15 ma to 55 ma with overlying sediment cover up to 500 m thick we link their origin with hydrothermal discharge through conduits created by differential compaction and fracturing over basement highs and by basement faulting that penetrates the overlying sediments although carbonate dissolution is likely to be associated with the formation of the pits their occurrence shows no consistent relationship with the present calcite compensation depth ccd

estimating 3d variation in active layer thickness beneath arctic streams using ground penetrating radar we acquired three dimensional 3d ground penetrating radar gpr data across three stream sites on the north slope ak in august 2005 to investigate the dependence of thaw depth on channel morphology data were migrated with mean velocities derived from multi offset gpr profiles collected across a stream section within each of the 3d survey areas gpr data interpretations from the alluvial lined stream site illustrate greater thaw depths beneath riffle and gravel bar features relative to neighboring pool features the peat lined stream sites indicate the opposite greater thaw depths beneath pools and shallower thaw beneath the connecting runs results provide detailed 3d geometry of active layer thaw depths that can support hydrological studies seeking to quantify transport and biogeochemical processes that occur within the hyporheic zone

biogenic silica and chert in the pacific ocean evidence for the dissolution of biogenic silica at the base of pelagic sections supports the hypothesis that much of the chert formed in the pacific derives from the dissolution and reprecipitation of this silica by hydrothermal waters as ocean bottom waters flow into and through the crust they become warmer initially they remain less saturated with respect to dissolved silica than pore water in the overlying sediments with the diffusion of heat dissolved ions and to some extent the advection of water itself biogenic silica in the basal part of the sedimentary section is dissolved upon conductively cooling these pore waters precipitate chert layers the most common thickness for the basal silica free zone 20 m lies below the most common height of the top of the chert interval above basement 50 m this mode of chert formation explains the frequent occurrence of chert layers at very shallow subbottom depths in pelagic sections of the pacific it is also consistent with the common occurrence of cherts 150 m above basement

sediment mixing in the tropical pacific and radiolarian stratigraphy 1 the reworking of older radiolarian microfossils into near surface sediments of the tropical pacific has long been the source of confusion for the development of radiolarian stratigraphy and of puzzlement over the mechanism s that could effect such pervasive reworking widespread dissolution pits in the sediments of the tropical pacific are believed to be associated with hydrothermal circulation cells in the older oceanic crust and are here linked to processes which expose older sections and inject older non carbonate material into near bottom waters discharging waters of these circulation cells tend to dissolve carbonate in near surface sediments thus only the non carbonate material including radiolarians is preserved and reworked into younger sediments results from the study of two sites in the tropical pacific indicate that reworked older stratigraphically important radiolarians are less than 2 of the total radiolarian assemblage this constitutes a minimum estimate of the amount of reworked non carbonate material in the younger sediments the oldest reworked radiolarians are no more than 10 m y younger than the underlying basement and radiolarians from the entire older section above that level can be found in the reworked material a time series of the flux of reworked material at one site is not constant but instead has varied by a factor of 3 to 4 over the past 2 5 m y during times when the flux of reworked material is particularly low the proportion of older more robust radiolarians is larger

early paleogene biosiliceous sedimentation in the atlantic ocean testing the inorganic origin hypothesis for paleocene and eocene chert and porcellanite abstract the widespread occurrence of lower eocene chert and porcellanite has been viewed as a major paleoceanographic issue since the advent of ocean drilling and both biotic and abiotic forcings have been proposed to explain it we present a reconstruction of indurated siliceous sediment iss and preserved biosiliceous sediment pbs occurrences in the atlantic ocean through the paleocene and eocene 66 through 34 ma iss and pbs distributions reveal dissimilar temporal trends with the peak of iss occurrences coinciding with the early eocene climatic optimum in line with previous studies pbs occurrences show a generally increasing trend culminating between 44 and 43 ma the common co occurrence of iss and pbs and their coherent geographic distribution lends strong support to the biogenic origin of the precursor to the widespread paleogene iss and argues against an inorganic mode of early cenozoic chert and porcellanite precipitation weight per cent biogenic opal records and trends in linear sedimentation rates indicate two plausible modes of silicification 1 silicification due to prolonged exposure of biogenic opal rich sediments to corrosive bottom waters and 2 silicification due to elevated pressures and temperatures caused by rapid burial of biogenic opal rich deposits the confinement of iss and pbs to proximal sites along continental margins points to the reliance of siliceous sedimentation through the paleocene and eocene on terrestrial supply of dissolved silicon consistent with this quantitative siliceous microfossil assemblage records from the blake nose in the nw atlantic indicate that the nutrient rich marginal rather than oligotrophic pelagic settings hosted the majority of siliceous plankton production through the early paleogene the inorganic sio2 precipitation model is unlikely to have been the dominant mechanism responsible for ubiquitous occurrences of early paleogene iss we favor the biogenic iss precursor scenario and reconcile it with the low productivity early cenozoic oceans by showing that large volumes of biogenic silica were supplied to the western north atlantic ocean from the north american margin through the paleocene and eocene dissolution of this surplus silica was facilitated by an early southwestward flow of young sio2 depleted waters from the north atlantic all these factors contributed to iss and pbs focusing in the western north atlantic through the early paleogene

chert in the pacific biogenic silica and hydrothermal circulation abstract data on sections drilled by dsdp and odp in the pacific have been compiled for 187 sites 105 of which contain chert the spatial pattern of siliceous deposits in the pacific generally follows the pattern of biologic productivity there is some evidence that enhanced vertical diffusivity in the ocean during the eocene warm climate gave rise to siliceous deposits on and near bathymetric highs and basin margins the most common occurrence of chert is in eocene and older sections however cherts do occur in sections as young as 7 ma in the sites investigated over half of the youngest chert occurrences in sedimentary sections are within 150 m of basement nearly all the chert occurrences on crust younger than 60 ma are within 150 m of basement the deficit in heat flow over ocean crust younger than 60 ma is explained as the result of heat advection by hydrothermal waters circulating in the upper part of the ocean crust these waters appear to dissolve biogenic silica and deposit it as chert in the lower parts of sedimentary sections diffusion of these waters into the lower sediment section is enhanced by small scale faulting this faulting may be associated with intra plate stresses that develop during ridge jumps and reorientations of plate motion the relatively warm bottom waters of the early cenozoic may have also enhanced the dissolution of biogenic silica during hydrothermal circulation in the upper oceanic crust and basal sediment section

cenozoic mass accumulation rates in the equatorial pacific based on high resolution mineralogy of ocean drilling program leg 199 1 we use continuous mineralogy logs derived from multisensor track physical properties data and reflectance spectroscopy to calculate high resolution carbonate opal and terrigenous mass accumulation rates mar for the eight sites cored during ocean drilling program leg 199 in the equatorial pacific the largest change in equatorial pacific sedimentation patterns of the last 55 myr occurs at the greenhouse icehouse transition shortly after the eocene oligocene boundary calcite compensation depth deepened dramatically the equatorial zone of opal accumulation narrowed and the intertropical convergence zone shifted to the equator during the paleogene the opal equatorial accumulation bulge extended to about 12 n whereas the neogene bulge extended only to about 7 n very low eocene carbonate mar was followed by much higher oligocene and early miocene mar with the carbonate equatorial bulge extending to 4 n terrigenous mars indicate the paleoposition of the intertropical convergence zone and a pliocene pleistocene increase in asian dust flux

implications for the history of cenozoic opal deposition from a quantitative model in addition to being a time of enhanced crustal activity and a warmer climate the eocene also saw prolonged periods of silica accumulation on the ocean floor the peak of this accumulation occurred at approximately 50 ma creating horizon ac a layer of silica rich sediments spanning approximately 4 my horizon ac is comparatively isolated in time from known silicic acid addition processes leading mcgowran 1989 mcgowran b 1989 silica burp in the eocene ocean geology 17 pp 857 860 to suggest a novel mechanism the silica burp hypothesis that centres on the temporal decoupling of silicic acid supply and burial by climatic variation here we examine this hypothesis using a quantitative biogeochemical model of the silicon cycle our results unequivocally show that mcgowran s hypothesis is unable to account for horizon ac the model s residence time and ocean capacity for silicic acid are insufficient to permit the degree of temporal decoupling proposed by mcgowran inverting the model s results suggests that instead the sediment record may be a useful proxy for silicic acid additions to the ocean

detecting and mapping buried buildings with ground penetrating radar at an ancient village in northwestern argentina abstract we describe an archaeo geophysical investigation performed near the palo blanco archaeological site catamarca argentina a large area beyond the northern limit of the site was explored with the ground penetrating radar gpr method in order to detect new buildings the exploration showed signals of mud walls in a sector that was located relatively far from the previously known buildings a detailed survey was performed in this sector and the results showed that the walls belonged to a large dwelling with several rooms the discovery of this dwelling has considerably extended the size of the site showing that the dwellings occupied at least twice the originally assumed area high density gpr surveys were acquired at different parts of the discovered building in order to resolve complex structures interpreted maps of the building were obtained different characteristics of the walls were satisfactory determined in spite of the low contrast of the dielectric constant at their interfaces and the noticeable spatial fluctuations of the signals due to wall collapses systematic excavations confirmed the gpr maps providing further relevant information about the characteristics of the walls and the occupational floor as well as material for radiocarbon analyses these analyses indicated that the discovered building was occupied until about ad 880 this fact extends 180 years the previously known period for the village and also for the settlements in the region formerly ad 200 to ad 700 the performed investigations moreover confirmed different architectural characteristics assumed for palo blanco related to the internal and external layouts interconnection between the rooms without intermediary courtyards seems to indicate a better use of the internal spaces and a more integrated spatial conception in palo blanco than in other villages of the region

ground penetrating radar survey of a prehistoric site in southern italy abstract in this paper we present and discuss the results of a ground penetrating radar gpr study carried out in an area of southern italy where a karst cave with prehistoric remains was found the aim of the study involved the imaging of the subsurface stratigraphy both inside and outside the cave in order to assist archaeologists in an excavation programme the survey grid comprised 18 intersecting gpr profiles problems associated with the use of the gpr within a cave environment are highlighted and the data processing sequence designed to extract useful geo archaeological signatures is described interpretation of the radar sections was controlled by the excavation of two trenches inside and outside the cave allowing detailed outlining the complex stratigraphy and the reconstruction of palaeolithic and neolithic subsurface horizons

the potential role of ridge flank hydrothermal systems on oceanic germanium and silicon balances abstract sediment pore water samples and warm spring fluids from three ridge flank hydrothermal systems 40 75 c were analyzed for ge si and mg to quantify the contribution of these systems to oceanic ge and si balances these warm hydrothermal fluids have elevated concentrations of ge and si relative to bottom seawater indicating that these systems are net sources of ge and si to the oceans end member ge si molar ratios range from 12 to 34 mol mol which is similar to but elevated relative to the average ratio from high temperature 350 c midocean ridge hydrothermal systems the source for this ge and si is suggested to be a combination of seawater reaction with basalt and diffusive exchange with overlying basal pore waters which are in pseudo equilibrium with amorphous silica because the ge si molar ratio in both basalt and sediment is much less than those measured in the dissolved phase a net preferential removal of si relative to ge must occur within basaltic basement as suggested for high temperature hydrothermal systems we suggest that this removal mechanism is likely a consequence of quartz precipitation and the formation of secondary clays i e smectite we estimate that ridge flank hydrothermal systems likely provide 10 of the ge and si fluxes to the oceans

hydrothermal recharge and discharge across 50 km guided by seamounts on a young ridge flank hydrothermal circulation within the sea floor through lithosphere older than one million years myr is responsible for 30 of the energy released from plate cooling and for 70 of the global heat flow anomaly the difference between observed thermal output and that predicted by conductive cooling models 1 2 hydrothermal fluids remove significant amounts of heat from the oceanic lithosphere for plates typically up to about 65 myr old3 4 but in view of the relatively impermeable sediments that cover most ridge flanks5 it has been difficult to explain how these fluids transport heat from the crust to the ocean here we present results of swath mapping heat flow geochemistry and seismic surveys from the young eastern flank of the juan de fuca ridge which show that isolated basement outcrops penetrating through thick sediments guide hydrothermal discharge and recharge between sites separated by more than 50 km our analyses reveal distinct thermal patterns at the sea floor adjacent to recharging and discharging outcrops we find that such a circulation through basement outcrops can be sustained in a setting of pressure differences and crustal properties as reported in independent observations and modelling studies

phase relationships of s type granite with h2o to 35 kbar muscovite granite from harney peak south dakota muscovite granite 13 8 muscovite 4 8 normative corundum was reacted with varying percentages of h 2o in cold seal vessels at 2 kbar and in piston cylinder apparatus between 10 and 35 kbar the diagrams illustrating melting crystallization relationships are p t sections with both excess h 2o and with no h 2o added 0 66 h 2o in rock t x h 2o sections at 15 kbar and 25 kbar showing h 2o undersaturated conditions the h 2o undersaturated surface for the crystallization of quartz coesite small amounts of aluminosilicate minerals persist to higher temperatures glass compositions measured by electron microprobe from samples with 5 h 2o at 15 kbar confirm that liquids are syenitic through at least 100 c above the solidus as predicted from the effect of pressure on the residua system results are explained successfully by phase relationships involving muscovite quartz and orthoclase in k 2o al 2o 3 sio 2 h 2o with reactions depicted in a p total p e h 2o t model with special reference to the divariant surfaces in the region p e h 2o p total with reduced p e h 2o or a h 2o produced either by small amounts of h 2o and h 2o undersaturation or by co 2 h 2o mixtures subsolidus dehydration reaction temperatures decrease vapor present solidus temperatures increase and muscovite stability in presence of liquid increases in general muscovite biotite and amphibole can be precipitated from magmas containing only a few tenths per cent h 2o although the h 2o undersaturated liquids coexisting with crystals may contain 3 or more dissolved h 2o this particular granite cannot be a primary magma from mantle or subducted oceanic crust it is a possible product of partial fusion of pelitic rocks between about 20 km and 40 km depth given sufficient h2o and xenocrystal muscovite or sillimanite from the source rocks the phase relationships are consistent with the idea of s type granites but not sufficient to prove the origin of this rock additional tests require phase relationships of other associated granitic rocks and details of geochemistry geophysics and field relationships

integrated near surface geophysical survey of the cathedral of mallorca abstract this paper describes an integrated near surface geophysical study carried out in order to obtain high resolution images of the shallow subsurface under and around the cathedral of mallorca the study was a part of a global project focused on determining the state of the building structure and on evaluating the cathedral s dynamical behaviour natural frequencies and vibration modes ground penetrating radar gpr and the capacitively coupled resistivity method were used to obtain 2d images of the shallow subsurface refraction microtremor array measurements remi were also used to characterize the rock and soil properties and several invasive boreholes provided detailed and exact information on the stratigraphy the information from the geophysical data was used to determine a final model of the ground with indications of the most likely vulnerable zones as a part of this final model gpr profiles enabled us to delineate the superficial ground structure and to detect some archaeological features electrical resistivity imaging data were in good agreement with the gpr results and showed shallow major changes in the soil and rock under the filling materials the refraction microtremor array remi results indicate the existence of compacted soils in different areas probably corresponding to old filled zones in good correlation with gpr and resistivity profiles in the most superficial part of the ground

changes in silicate utilisation and upwelling intensity off peru since the last glacial maximum insights from silicon and neodymium isotopes we combine the stable silicon isotope composition 30si of diatoms and the radiogenic neodymium isotope compositions end of past seawater extracted from the authigenic fraction of the sediments mn fe coatings of particles and benthic foraminifers as well as the radiogenic isotope compositions nd sr of the detrital material itself to reconstruct silicic acid utilisation water mass mixing and upwelling intensity from the same marine sediments in the peruvian upwelling region during the past 20 000 years additionally the sedimentary signals were compared to the water column isotope compositions along the peruvian shelf the dissolved end in the water column ranges from 5 7 to 0 6 the corresponding end signatures of the coatings and the benthic foraminifers of the surface sediments range from 4 5 to 1 8 and from 2 5 to 2 2 respectively the detrital end 87sr 86sr signatures range from 6 3 to 0 0 70508 0 71049 all phases show a trend from more radiogenic end values in the north towards less radiogenic values in the south broadly reflecting local weathering inputs and hinterland geology the end signatures of the coatings extracted from sediment core so147 106kl located in the present day centre of coastal upwelling near 12 s have been essentially constant 1 5 throughout the past 20 000 years while the detrital end 87sr 86sr varied between values of 0 7 0 70620 during the last glacial and 4 5 0 70849 during the late holocene reflecting changes in the origin of the sediment and current transport from a more northerly towards a more southerly source and from overall stronger to weaker upwelling the 30si signature of both total biogenic opal 30siopal and of hand picked diatoms 30sidiatom ranged from 0 3 last glacial to 1 4 late holocene confirming large variations in upwelling intensity driving silicic acid utilisation by diatoms our combined bsio2 mar 30siopal and detrital radiogenic isotope results demonstrate that the strongest el nino southern oscillation conditions off peru of the past 20 ka have prevailed during the past 5 ka

widespread formation of cherts during the early eocene climate optimum radiolarian cherts in the tethyan realm of jurassic age were recently interpreted as resulting from high biosiliceous productivity along upwelling zones in subequatorial paleolatitudes the locations of which were confirmed by revised paleomagnetic estimates however the widespread occurrence of cherts in the eocene suggests that cherts may not always be reliable proxies of latitude and upwelling zones in a new survey of the global spatio temporal distribution of cenozoic cherts in deep sea drilling project dsdp and ocean drilling program odp sediment cores we found that cherts occur most frequently in the paleocene and early eocene with a peak in occurrences at 50 ma that is coincident with the time of highest bottom water temperatures of the early eocene climatic optimum eeco when the global ocean was presumably characterized by reduced upwelling efficiency and biosiliceous productivity cherts occur less commonly during the subsequent eocene global cooling trend primary paleoclimatic factors rather than secondary diagenetic processes seem therefore to control chert formation this timing of peak eocene chert occurrence which is supported by detailed stratigraphic correlations contradicts currently accepted models that involve an initial loading of large amounts of dissolved silica from enhanced weathering and or volcanism in a supposedly sluggish ocean of the eeco followed during the subsequent middle eocene global cooling by more vigorous oceanic circulation and consequent upwelling that made this silica reservoir available for enhanced biosilicification with the formation of chert as a result of biosilica transformation during diagenesis instead we suggest that basin basin fractionation by deep sea circulation could have raised the concentration of eeco dissolved silica especially in the north atlantic where an alternative mode of silica burial involving widespread direct precipitation and or absorption of silica by clay minerals could have been operative in order to maintain balance between silica input and output during the upwelling deficient conditions of the eeco cherts may therefore not always be proxies of biosiliceous productivity associated with latitudinally focused upwelling zones 2007 elsevier b v all rights reserved

contribution of the resistivity method to characterize mud walls in a very dry region and comparison with gpr abstract mud walls are frequent in many archaeological sites including sites located in semi desert regions in cases with buried walls the geophysical methods can be useful tools for their investigation since they provide maps of the subsoil in a non invasive way and in relatively short times this article deals with the characterization of mud walls in very dry soils through the resistivity method discussing a methodology to satisfactorily apply the method in this kind of adverse environment and how to interpret the results the case of the palo blanco archaeological site a pre incaic village located in the nw region of argentina is analyzed in very dry soils it is frequent that the electrical current cannot be injected due to the high values of electrical resistivity at the shallowest portions of soil which makes the resistivity method useless here we show how this problem can be systematically overcome by wetting a shallow thread between each pair of injection electrodes and the manner in which the resulting profiles can be analyzed we perform numerical simulations of the resistivity profiles considering 3d models of mud walls and wetted threads that reproduce experimental situations and compare them to 2d field data the resistivity profiles are analyzed for different orientations and distances between the wall and profile and fluctuations of the soil parameters the experimental profiles are interpreted from these simulations and compared to ground penetrating radar gpr profiles the resistivity methodology shows effective for characterizing the size and depth of the mud walls even in cases with collapsed or much eroded walls for which gpr often fails