the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

foraminifera from the irish sea glacigenic deposits at aberdaron western lleyn north wales palaeoenvironmental implications in a sequence of glacigenic sediments at aberdaron foraminifera were obtained from samples located specifically in order to differentiate between opposing models of depositional environment all the diamict samples yielded remarkably uniform assemblages with similar numbers of benthic specimens and benthic species per unit weight of sediment similar planktic benthic ratios and similar ratios of clearly allochthonous to possibly autochthonous elements this is precisely as predicted by the terrestrial model of sedimentation where all of the sediments are interpreted as being derived from the melting of glacier ice rich in marine debris entrained during passage along the irish sea basin the results lend no support to a glacial marine model since no faunal responses to increasingly distal sedimentary environments are observed however the fauna is dominated by the foraminifera elphidium excavatum terquem forma clavata cushman which is commonly assumed to indicate glacial marine conditions the modern distribution of similar assemblages suggests that it is just as likely to represent the cold reduced salinity conditions that would have prevailed in the northern irish sea basin for much of the quaternary

fluid inclusion and o h c isotopic constraints on the origin and evolution of ore forming fluids of the cenozoic volcanic hosted kuh pang copper deposit central iran abstract the kuh pang copper deposit 2 8 mt 1 65 cu 0 52 g t au 34 g t ag is a volcanic hosted epithermal deposit in the central part of the late eocene oligocene urmia dokhtar magmatic arc of iran three stages of fluid evolution are identified at the kuh pang deposit i early pre ore stage with homogenization temperature of 205 372 c 298 45 c salinity of 11 3 2 9 wt nacl equiv fluid trapped at 200 bars ii main ore stage with homogenization temperature of 175 310 c 253 43 c salinity of 2 1 12 5 wt nacl equiv at 150 bars and iii late post ore stage with homogenization temperatures of 148 to 231 c 199 24 c and salinity of 1 1 9 8 wt nacl equiv these data record an evolution of mineral precipitation from deeper 2 km to shallower environments 18 o fluid values of 5 7 to 5 9 and 3 2 to 3 8 and d fluid values of 77 to 41 and 84 to 60 respectively these data indicate a major magmatic fluid source with slightly increasing mixing of meteoric waters calcite in the late post ore stage has 13 c v pdb values of 5 8 to 5 6 and 18 o v smow values of 8 2 8 6 with calculated 18 o fluid and 13 c fluid values of 1 0 to 1 4 and 5 4 to 5 2 respectively that are also consistent with a predominantly magmatic carbon source and a significant fluid mixing by meteoric waters

european contribution of ice rafted sand to heinrich layers h3 and h4 abstract this paper reports the sr nd isotopic composition of the carbonate free sand 63 m 1 mm fraction of heinrich layers 3 and 4 from about 17 cores from the northern atlantic ocean 38 n to 68 n the results indicate that the transporting icebergs were calved from many ice sheets from around the north atlantic at least the fennoscandian icelandic and laurentide our isotopic data show a more distinctly european origin for ice rafted debris ird deposited during the atypical heinrich event h3 than for background ird in contrast heinrich layer h4 a representative of typical heinrich events h1 h2 h4 and h5 presents a clear dominant laurentide signal this result confirms that these typical heinrich events are associated with a massive discharge of icebergs from the laurentide ice sheet however the theory that the laurentide ice sheet set the events into motion alley r b macayeal d r 1993 ice rafted debris associated with binge purge oscillations of the laurentide ice sheet paleoceanography 9 4 503 511 cannot explain the fact that a european signal of an early h4 sample has been observed prior to the laurentide signature of a late h4 sample in the same core along the european margin this observation indicates that the european ice sheets may have surged before the north american ones and suggests that the laurentide ice sheet was not the sole motor behind the heinrich events moreover in the norwegian sea ird has a scandinavian origin in both h3 and h4

u series and amino acid dates from jersey understanding of the raised beach and other interglacial sequences in the southern part of the british isles has been improved through use of the amino acid racemization technique this method has permitted correlation of these isolated and fragmentary marine deposits1 2 which except for the portland site are located around the shores of the bristol channel1 by applying this technique with the u series method we have obtained a geochronometric date from the 8 m raised beach of the belle hougue cave jersey channel islands our results suggest that the 8 m raised beach of the channel should be correlated with isotope stage 5 and that raised beaches above this altitude in the area may pre date this stage and thus also the ipswichian interglacial which forms part of it

evolution of magmatic vapor to gold rich epithermal liquid the porphyry to epithermal transition at nevados de famatina northwest argentina fluid inclusions in the subeconomic porphyry cu mo au system at nevados de famatina and closely associated high sulfidation epithermal cu au ag as sb te veins at la mejicana northwest argentina were studied to reconstruct the evolution of hydrothermal fluids from their deep magmatic source to the shallow epithermal environment field geology vein petrography fluid inclusion microthermometry and single inclusion microanalysis by laser ablation inductively coupled plasma mass spectrometry la icp ms were combined to determine the evolution of pressure temperature and ore metal concentrations in the fluids cathodoluminescence imaging complements transmitted light petrography to constrain the successive stages of quartz formation and the entrapment sequence of the fluid inclusion populations aqueous liquid inclusions of 5 wt percent nacl equiv salinity trapped in quartz sericite pyrite qsp veins between 360 and 325 c contain unusually high concentrations of cu 400 5 000 ppm as 200 ppm sb and te both up to 100 ppm and au several ppm along with other ore forming elements these veins are paragenetically transitional between subeconomic porphyry copper mineralization exposed in the valley floor and high sulfidation epithermal veins with high au grades which are preserved along a high ridge adjacent to the porphyry stock low density vapor and hypersaline liquid i e brine inclusions were trapped in early formed quartz of the porphyry stockwork veins between 450 and 600 c the brine contains lower cu and au concentrations than coexisting vapor inclusions and texturally even earlier inclusions of intermediate density that are trapped in phenocrysts and some stockwork veins the latter may be equivalent to a parental fluid the low and intermediate density fluids compositionally overlap in salinity with the aqueous liquids recorded by the later transitional quartz sericite pyrite veins fluid inclusions and geologic time relations indicate that the transitional quartz sericite pyrite veins were the channelways for metal rich aqueous liquids that generated the high sulfidation epithermal cu au deposit these mineralizing liquids are interpreted to have evolved by continuous density increase contraction from a low salinity s rich magmatic fluid of low to intermediate density this vaporlike fluid was produced by exsolution from a magma that existed at greater depth during the late stages of cooling of the magmatic hydrothermal complex and probably underwent minor brine separation prior to reaching the present level of exposure epithermal mineral precipitation occurred upon dilution of the low salinity magmatic fluid with meteoric water which entered the hydrothermal system as it was cooled and successively eroded during continued magmatic fluid ascent

post collisional polycyclic plutonism from the zagros hinterland the shaivar dagh plutonic complex alborz belt iran the petrological and geochronological study of the cenozoic shaivar dagh composite intrusion in the alborz mountain belt nw iran reveals important clues to decipher complex relations between magmatic and tectonic processes in the central sectors of the tethyan alpine himalayan orogenic belt this pluton is formed by intrusion at different times of two main magmatic cycles the older cycle 1 is formed by calc alkaline silicic rocks which range in composition from diorites to granodiorites and biotite granites with abundant mafic microgranular enclaves the younger cycle cycle 2 is formed by k rich monzodiorite and monzonite of marked shoshonitic affinity the latter form the larger volumes of the exposed plutonic rocks in the studied complex zircon geochronology laser ablation icp ms analyses gives a concordia age of 30 8 2 1 ma for the calc alkaline rocks cycle 1 and a range from 23 3 0 5 to 25 1 0 9 ma for the shoshonitic association cycle 2 major and trace element relations strongly support distinct origins for each magmatic cycle rocks of cycle 1 have all the characteristic features of active continental margins shoshonitic rocks cycle 2 define two continuous fractionation trends one departing from a k rich basaltic composition and the other from an intermediate k rich composition a metasomatized mantle origin for the two shoshonitic series of cycle 2 is proposed on the basis of comparisons with experimental data the origin of the calc alkaline series is more controversial but it can be attributed to processes in the suprasubduction mantle wedge related to the incorporation of subducted melanges in the form of silicic cold plumes a time sequence can be established for the processes responsible of the generation of the two magmatic cycles first a calc alkaline cycle typical of active continental margins and second a k rich cycle formed by monzonites and monzodiorites this sequence precludes the younger potassic magmas as precursors of the older calc alkaline series by contrast the older calc alkaline magmas may represent the metasomatic agents that modified the mantle wedge during the last stages of subduction and cooked a fertile mantle region for late potassic magmatism after continental collision

eliassen palm fluxes of the 2 day wave abstract high resolution doppler imager hrdi winds and temperatures are used to diagnose a 2 day wave event detected in the southern hemisphere during january 1994 a novel aspect of this study is the focus upon the wave fluxes throughout the 65 100 km range and their relationship to the background state a wave packet composed of zonal wavenumbers 2 3 and 4 propagates westward with a phase speed near 60 m s 1 the periods associated with zonal wavenumbers 2 3 and 4 are 3 5 2 1 and 1 7 days respectively the morphology of the 2 day temperature and wind fields is consistent with that of a developing baroclinic wave the divergence of the eliassen palm flux of zonal wavenumbers 2 4 is dominated by the vertical convergence of meridional heat flux the wave driving or eliassen palm flux divergence per unit mass is predominantly westward with magnitudes on the order of 5 m s 1 day 1 a steady state quasigeostrophic model of the mean meridionai circulation is used to estimate the mean wind respon

the last ice sheet in snowdonia in snowdonia there is a marked contrast between weathered summits often with well developed blockfields or tors and lower ice moulded terrain the boundary is interpreted as a trimline marking the upper surface of the last ice sheet this interpretation is supported by the presence of gibbsite an end product of prolonged weathering at the base of soils above but not below the trimline the reconstructed ice surface reaches about 850 m above present sea level along an ice divide running ne sw through the massif there is no evidence to support the popular view that ice centred further south extended over snowdonia and breaching to form the major glacial troughs can be explained by the action of local ice the field evidence presented here demonstrates that most models of the southern british and irish sea ice sheets are significantly flawed the earliest being far too thick and the most recent far too thin copyright 2000 john wiley sons ltd

fluid inclusion and stable isotope study of the lubin zardeh epithermal cu au deposit in zanjan province nw iran implications for ore genesis abstract the lubin zardeh deposit is located in the western alborz magmatic belt 45 km ne of zanjan iran this deposit contains polymetallic cu au pb zn mineralization which is hosted by the cenozoic volcanic intrusive rocks of mainly intermediate and acidic composition pyrite chalcopyrite galena sphalerite bornite and tennantite tetrahedrite with native gold and silver are present in the ores quartz adularia and clay minerals illite montmorillonite with minor calcite are the most abundant gangue minerals and generally occur as fine grained assemblages some are however medium and coarse grained assemblages the ore minerals show disseminated vein veinlet replacement and brecciated textures while the gangue minerals represent replacement cockade crustiform colloform comb vein veinlet and plumose textures alteration haloes along the main vein are silicic argillic illite montmorillonite sericitic and pyritic gold contents of the quartz chalcopyrite gold veins range from 0 002 to 10 ppm with an average of 0 52 ppm the average values for total reserve of 0 5 mt of lubin zardeh deposit has been determined 1 3 0 7 and 0 4 for cu pb and zn respectively most of fluid inclusions in the quartz gold sulfide veins consist of two vapor and liquid phases at room temperature the primary fluid inclusions have a low to intermediate homogenization temperature between 127 and 327 c and salinity between 4 07 and 13 98 wt nacl equivalent stable isotope and fluid inclusion studies indicate that mineralization occurred in two stages at lubin zardeh deposit i e stage i along which base metal deposited and stage ii which is associated with copper and gold mineralization the 18oquartz values from stage i and stage ii range from 9 56 to 12 77 and from 7 23 to 9 24 respectively while their 34s values of sulfide minerals range from 0 9 to 6 2 and form 6 6 to 1 9 the isotopic and microthermometric data indicate that the hydrothermal solution evolved through mixing of magmatic fluids with meteoric waters boiling of magmatic fluid and mixing with meteoric waters were the main mechanisms of ore deposition in the lubin zardeh low sulfidation epithermal deposit

glacial interglacial variation in organic carbon burial on the slope of the n w european continental margin 48 50 n the sources and fate of organic carbon corg were examined at two sites on the goban spur and a single site within the porcupine sea bight on the n w european slope between 48 n and 50 n here we present data on the sedimentary corg concentration its 13c 12c composition 13corg and corg n of 224 total and 119 fine fraction 63 m samples as a time series running from the instantaneous marker horizon heinrich layer 2 25 5 ka bp through the last glacial isotope stage 2 and interglacial isotope stage 1 to the present the significance of the n w european slope as a depositional sink for corg has declined in the past twenty thousand years with flux values decreasing two to three fold from the late glacial 60 70 mg c cm 2 ka 1 to low late holocene values significant shifts are seen in the 13corg signature of both the total and fine fractions between the present interglacial and last glacial the open slope of the goban spur is characterised by relatively low values over the last glacial with minimum values for the total sediment of around 24 5 occurring at ca 18 ka bp and generally increasing values during the holocene with the most recent samples having values of ca 19 2 to 20 2 in the porcupine sea bight a different relationship is evident with samples from the last glacial maximum being generally higher while values from the holocene are lower with a minimum of 23 3 occurring just below the mixed layer similar trends are observed in the fine fraction albeit with a different dynamic range paired analysis of 13corg and corg n are consistent with the organic matter being a climatically forced mixture from c3 photosynthetic terrigenous and marine organic matter sources an increased influence of terrestrial corg is suggested on the glacial goban spur and holocene porcupine sea bight and vice versa we suggest that this may be explained by modern wind driven flushing of terrigenous carbon across the armorican and celtic shelves to the n w and thence into porcupine sea bight during the last glacial increased strength of westerly winds created a residual current regime driving material to the s w where it was transported in vigorous tidal off shelf flushing to the upper slope followed by slope current transfer to the goban spur much of this material was presumably delivered by the great channel river to the outer shelf thus leading to enhanced flux of terrestrial corg on the goban spur the influence of a freshwater plume from meltwater discharge of the european ice sheet in this region is supported by foramininiferal 18o data from which a palaeo salinity reconstruction shows a greatest negative anomaly of 2 55 that is s 35 at the time of maximum terrestrial corg content in the sedimentary material in addition to showing that surface waters over goban spur were relatively fresh throughout the glacial our results also reveal variability in surface salinity on shorter timescales

sedimentary evidence for deforming bed conditions associated with a grounded irish sea glacier southern ireland along the south coast of ireland a shelly diamict facies the irish sea till has been variously ascribed to subglacial deposition by a grounded irish sea glacier or to glacimarine sedimentation by suspension settling and iceberg rafting observations are presented here from five sites along the south coast to directly address this question at these sites sedimentary evidence is preserved for the onshore advance of a grounded irish sea glacier which glacitectonically disturbed and eroded pre existing sediments and redeposited them as deformation till recession of this irish sea glacier resulted in the damming of ice marginal lakes in embayments along the south coast into which glacilacustrine sedimentation then took place these lake sediments were subsequently glacitectonised and reworked by overriding glacier ice of inland origin which deposited deformation till on top of the succession there is no evidence for deposition of the irish sea diamicts by glacimarine sedimentation at these sites the widespread development of subglacial deforming bed conditions reflected the abundance of fine grained marine and lacustrine sediments available for subglacial erosion and reworking stratigraphical and chronological data suggest that the advance of a grounded irish sea glacier along the south coast occurred during the last glaciation and this is regionally consistent with marine geological data from the celtic sea these observations demonstrate extension of glacier ice far beyond its traditional limits in the celtic sea and on land in southern ireland during the last glaciation and remove the stratigraphical basis for chronological differentiation of surficial glacial drifts and thus the munsterian glaciation in southern ireland copyright 2001 john wiley sons ltd

mean motions and tidal and two day structure and variability in the mesosphere and lower thermosphere over hawaii abstract an overview of the motion field and an analysis of the tidal and 2 day wave motions observed in the mesosphere and lower thermosphere over the central pacific from 1 october 1990 through 19 august 1992 is presented characteristics and interactions of motions at lower and higher frequencies will be addressed elsewhere wind measurements were obtained with an mf radar operating on kauai hawaii 22 n 160 w using the partial reflection drift technique results presented in this paper reveal a zonal mean motion reflecting the mesopause semiannual oscillation msao observed at more equatorial latitudes from january to july coinciding with the period during which the msao and the annual cycle of the zonal mean wind at higher latitudes are in phase eastward and westward maxima are 55 m s 1 below 80 km and 45 m s 1 near 85 km during the first year with maxima of 57 and 53 m s 1 during the second year and evidence of substantial interannual variability the second msao cycle is greatly suppresse

raised beaches and sea levels in the english channel in the middle and late pleistocene problems of interpretation and implications for the isolation of the british isles

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

mineralogy hydrothermal alteration fluid inclusion and o h stable isotopes of the siah jangal sar kahno epithermal gold deposit se iran abstract siah jangal sar kahno deposit is located in the northern part of taftan volcano in the sistan and balouchestan provinces southeast of iran and is an example of a vein type epithermal gold system with related stockwork and shear zone mineralization the veins are hosted by flysch facies rocks of the makran zone and subvolcanic dioritic porphyry the ne sw fault systems played an essential role in the genesis of alteration and mineralization in the area diorite porphyry ranges from alkali na2o k2o content of 4 1 6 66 wt and plot in the calc alkaline to high k calc alkaline fields the chondrite normalized ree patterns for least altered porphyry diorite rocks altered host rocks and silica carbonate vein show a lree hree ratios of 10 40 4 03 4 00 and 2 66 respectively positive eu anomalies in the silica carbonate veins indicate the ca bearing minerals such as plagioclase decomposition causing release of eu into hydrothermal fluid and subsequent precipitation in silica carbonate veins mineralization consist of quartz adularia calcite pyrite arsenopyrite marcasite fe poor sphalerite galena chalcopyrite and native gold later supergene mineral assemblages consists of fe oxide and hydroxides covellite cerussite and scorodite hydrothermal alteration is generally well developed enveloping the ore bearing hydrothermal breccia and subdivided into prograde inner quartz chlorite pyrite muscovite and outer argillic alteration zones with a regional barren widespread near surface supergene blanket advanced argillic alteration zone chemical discrimination by means of cationic r1 r2 diagram indicates that r1 increases whereas r2 decreases with increasing argillic alteration microthermometry of fluid inclusions in quartz crystals from silica carbonate vein show the homogenization temperatures thv l of 167 332 c with salinities in the range of 0 21 4 24 wt nacl eq the o and h isotopic compositions of quartz from hydrothermal vein and argillic alteration simply show a low sulfidation epithermal environment with meteoric waters as the main fluid due to a narrow range in salinity of the fluids very low sulfide diversity sulfide volume and presence of adularia suggest dominantly meteoric water in the deposit supporting classification as a low sulfidation epithermal system

thermal regime reconstruction and fluid inclusion la icp ms analysis on intermediate sulfidation epithermal pb zn veins implications for porphyry cu deposits exploration in the xianhualing district anhui china abstract the xianhualing district at jinzhai in the northern dabie orogen china is a significant area for pb zn cu au polymetallic exploration the main rocks in the area are mica quartz schist of the neoproterozoic foziling group and magmatic rocks which are controlled by two sets of faults striking nne and nw recent drilling has revealed that the orebody occurs mainly in mica quartz schist in the form of breccia and veinlets major ore minerals include pyrite sphalerite galena chalcopyrite magnetite gold silver and silver sulfosalts with alteration assemblages of predominantly quartz sericite calcite and chlorite three types of fluid inclusions occur in quartz sulfide vein samples collected from eight drill holes two phase liquid rich inclusions type i two phase vapor rich inclusions type and halite bearing inclusions type iii microthermometric studies of type i and fluid inclusions indicate homogenization temperatures of 161 378 c and salinities of 0 5 7 8 wt nacl equivalent fluid inclusion microthermometric data and mineralization and alteration characteristics indicate an intermediate sulfidation epithermal environment current exploration is focused on the location of potential deep porphyry mineralization associated with epithermal mineralization in this study 28 drill core samples from different levels were selected for fluid inclusion microthermometry to elucidate fluid evolution pathways and hence to determine the likelihood of porphyry bodies the consistent fluid inclusion petrography distribution patterns and fluid evolution trends indicate that the deeper part of the dongchong area may have been the regional thermal center of fluid flow the estimated mineralization depths of type iii fluid inclusions are in the range 0 4 1 5 km indicating a relatively shallow formation fluid chemical compositions obtained from single inclusion laser ablation inductively coupled plasma mass spectrometry la icp ms analyses support the occurrence of a single magmatic hydrothermal fluid source which has a degree of mixing with meteoric water and a small amount of basinal brines during the migration path and the fluid evolution pattern agrees well with the fluid inclusion mapping result quartz vein hosted fluid inclusions contain significant amounts of pb zn and cu indicating good exploration prospects for porphyry cu mineralization at depth

hrdi observations of mean meridional winds at solstice abstract high resolution doppler imager hrdi measurements of daytime and nighttime winds at 95 km are used to deduce seasonally averaged eulerian mean meridional winds during six solstice periods these estimates are compared with seasonally averaged radar meridional winds and with results from dynamical and empirical wind models hrdi mean meridional winds are directed from the summer pole toward the winter pole over much of the globe peak equatorward winds of about 15 m s 1 are usually observed in the summer hemisphere near 30 a local minimum in the equatorward winds is often observed poleward of this latitude with winds approaching zero or reversing direction a similar structure is seen in contemporaneous radar winds this behavior differs from residual meridional wind patterns predicted by models the discrepancies may be related to gravity wave paramaterizations or a consequence of planetary wave influences

new geological geochronological and geochemical investigations on the khoy ophiolites and related formations nw iran abstract this paper gives a detailed geological description of the region of khoy nw iran and its ophiolites and presents a new geological map the main conclusion is that there are not one but two ophiolitic complexes in the khoy area 1 an old poly metamorphic ophiolite tectonically included within a metamorphic subduction complex whose oldest metamorphic amphiboles yield a lower jurassic apparent 40kn 40ar age and whose primary magmatic age should logically be pre jurassic 2 a younger non metamorphic ophiolite of upper cretaceous age overlain by a turbiditic flysch like volcanogenic series of upper cretaceous lower paleocene age this latter ophiolite was created at a slow spreading oceanic center according to the lherzolitic mantle sequence the small volume of gabbroic rocks the absence of a diabasic sheeted dike complex and the abundant phyric basalts in the extrusive sequence a scenario for the geodynamic evolution of the khoy oceanic basin is proposed in conclusion

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

biostratigraphic zonation and 40ar 39ar ages for the neotethyan khoy ophiolite of nw iran abstract the khoy ophiolite in northwestern iran represents a piece of oceanic lithosphere formed in the mesozoic neotethys this ophiolite consists from bottom to top of well defined basal metamorphic rocks peridotites gabbros and a variety of upper to lower cretaceous deep marine rocks these include pelagic fossiliferous carbonates and basalts as interlayers or exotic blocks four hornblende separates from gabbros and amphibolites give values from 108 to 111 ma the results from microfossil studies show the presence of late cretaceous e g marginotruncana globotruncana and middle to late eocene e g globorotalia orbulonoides planktonic foraminifera the data suggest that although the initial rifting and crystallization of the oceanic crust of the khoy ophiolite began in the late albian the volcanic activities continued through to the late eocene time another possibility for such variation of lithofacies and biofacies and disturbances in the fossil record may be the result of bioturbation and transportation and rapid changes of depositional conditions during eruption of the basaltic lava flows pelagic sediments alone have been listed and of the foraminiferas the first three are planktonic as would be expected only orbulonoides is a benthic form and aberrant the third possibility is that the khoy ophiolite may represent a classic supra subduction type ophiolite where volcanic members of the different parts of oceanic environment e g morb volcanic arc ocean island are now juxtaposed

the global residual mean circulation in the middle atmosphere for the northern winter period abstract the residual mean circulation rmc has been calculated from the transformed thermodynamic equation using lims limb infrared monitor of the stratosphere data for the 100 0 1 mb region for discussion it has been divided into two components the diabatic circulation associated with the diabatic heating and the transient circulation more directly connected to eddy activity the slowly varying diabatic circulation reveals an equator to pole circulation at lower levels in the stratosphere usually overlain by a summer to winter pole circulation however there are strong seasonal variations so that the pole to pole circulation fills the entire region at the december solstice while the equator to pole circulation extends to above 0 1 mb at the equinoxes the transient circulation is characterized by rapid variations and small vertical and horizontal scales though generally smaller than the diabatic circulation it can dominate in the lower stratosphere during disturbed conditions this circul

glaciomarine sediments of the isle of man as a key to late pleistocene stratigraphic investigations in the irish sea basin the northern part of the isle of man in the central irish sea basin is identified as a raised marine foreland containing the largest subaerial exposure of last glaciation marine and glaciomarine sediments yet recognized on the british continental shelf a large push ridge that crosses the foreland identifies a major ice limit the ridge divides the foreland stratigraphy into a coarsening upward marine sequence of pelagic muds with dropstones sand and gravel to the south from offlapping stratified and massive sandy diamict assemblages overlying glaciotectonized marine sediments to the north coarse grained diamicts are argued to form part of a push ridge subaqueous outwash depositional system deposited when processes of suspension deposition density underflow ice rafting highly variable traction current activity and sediment gravity flow were operative adjacent to a grounded marine ice margin the identification of large offshore submarine banks aligned parallel to the bride moraine suggests that construction of the push ridge subaqueous outwash depositional system may have been repeated during ice recession this and published descriptions of other irish sea tills indicate that analogous structures and sediments are present offshore and around the irish sea basin

amino acid geochronology of raised beaches in south west britain abstract based on 1 the epimerization of l isoleucine to d alloisoleucine d l ratios in patella vulgata littorina littorea l littoralis l saxatilis littorina species and nucella lapillus from raised beaches in south west britain 2 statistical analysis of the d l ratios and 3 lithostratigraphic and geomorphic evaluation three d l stages are proposed the d l ratios for all the species measured are converted to a patella vulgata standard the three d l stages are 1 1 the minchin hole d l stage d l ratios 0 175 0 014 defined at a stratotype in minchin hole cave gower wales 2 2 a provisionally defined but as yet unamed d l stage because of the current unavailability of a suitable stratotype with d l ratios of 0 135 0 014 3 3 the pennard d l stage d l ratios 0 105 0 016 defined at a stratotype in minchin hole cave gower wales two geochronological models of the three high sea level events representing the d l stages are constrained by uranium series age determinations on stalagmite interbedded with marine beds in minchin hole and bacon hole caves gower wales a potential fixed point in model evaluation is an age determination which is equivalent to oxygen isotope sub stage 5e 122 ka the two models are oxygen isotope stage and age ka bp d l stage d l ratio model 1a model 1b model 2 pennard 0 105 0 016 5a ca 80 5e 122 5e 122 5c ca 100 unnamed 0 135 0 014 5e 122 7 194 minchin hole 0 175 0 014 7 186 245 7 186 245 7 216 the ages of the raised beaches are used to constrain the timing and extent of glaciation in the area the extent of the late devensian glaciation is fixed by reference to localities where raised beaches of the pennard d l stage outcrop as well as by using unpublished data on molluscs incorporated into glacial deposits two pre devensian glaciations antedate the minchin hole d l stage the irish sea glaciation of the bristol channel irish sea older drift of south wales fremington till of north devon is ascribed to oxygen isotope 10 or earlier while the paviland welsh glaciation is ascribed to oxygen isotope stage 8 or earlier an earlier glaciation berwyn glaciation is inferred from erratics of known welsh provenance in essex

age of pleistocene faunas from bacon hole wales at present it is difficult to match british early upper pleistocene vertebrate faunas with the growing evidence for complex climatic change at this time derived from the oceanic oxygen isotope record and from long pollen cores however we report here new analyses of dated faunal assemblages from bacon hole wales which indicate that the ipswichian interglacial fauna dated at 125 kyr bp was followed by a devensian interstadial fauna dated at 81 kyr bp which still supported some supposedly typical inter glacial mammals combined with evidence of an intervening cold fauna from stump cross cave dated at more than 83 kyr bp these indications of complexity in faunal change at the ipswichian devensian transition are more consistent with the oxygen isotope and pollen core data than traditional views

satellite observations of mean winds and tides in the lower thermosphere 2 wind imaging interferometer monthly winds for 1992 and 1993 1 satellite observations of monthly i e 60 d averages centered on the 15th of each month zonal mean and migrating tide winds in the region of 90 120 km and 40 s 40 n from the wind imaging interferometer are presented the zonal mean zonal winds are characterized by annually varying eastward winds at midlatitudes with a maximum in summer and semiannually varying westward winds in the tropics with maxima at equinox below 105 km the zonal mean meridional winds are characterized by a summer to winter flow below 100 km at solstice and by a cell like structure at equinox the latter is the first such global observation of this tidally driven structure two distinct types of diurnal tide are observed an upward propagating one and an evanescent one of comparable magnitude the propagating tide which is dominant in the subtropics below about 105 km exhibits a semiannual variation with a primary maximum in march april and a secondary maximum in september october the evanescent tide which is dominant poleward of 20 n s and above 100 km has an annual variation with a maximum in the summer months the coupling of the two produces a double peaked structure in the vertical profile of the diurnal amplitude the semidiurnal tide is generally weaker than the diurnal tide the maximum semidiurnal winds are at 30 40 n s and at 105 110 km both zonal and meridional components are stronger in april september than in october march in both hemispheres but in the equatorial region in april september the meridional component has a maximum whereas the zonal component has a minimum

quaternary deposits and glacial stratigraphy in ireland quaternary stratigraphic studies in ireland have been based largely on lithostratigraphy the division of complex sedimentary sequences into the traditional framework of munsterian and midlandian events has created a series of stratigraphic scenarios which cannot be fully substantiated either by biostratigraphy or by facies basin analysis many of the current problems of glacial stratigraphy in ireland therefore arise directly from the field procedures used and the frameworks used to subdivide sedimentary sequences these problems are centred on the selection of type sites the subdivision of sedimentary sequences into unnatural divisions the concepts of direct and indirect stratigraphy classical models of climatically determined ice advance retreat cycles and the genetic inferences of the term till the conceptual basis of various stratigraphic schemes has changed little since the work of farrington 1934 1966 it is argued that a more realistic approach to description and assessment of glacigenic sediments should be based on basinal facies analysis and must include a documentation of the composition and geometry of three dimensional facies variations palaeoenvironmental interpretations of complex glacigenic sequences especially in coastal locations should take account of the influences of marine ice sheets on the sedimentary record in the past most sequences were interpreted in terms of glacioterrestrial models a large body of sedimentary evidence now indicates that shallow glaciomarine environments occurred along the margins of the last ice sheet during its maximum and subsequent retreat phases the locations and patterns of associated icemarginal systems indicate that the magnitude of and patterns of crustal deformation were greater and more complex than formerly realised thus the primary control on sea level variation at successive ice sheet margins was largely a function of glacioisostatic disequilibrium although complex glacial and glacially related sequences are known it is argued here that most of the multiple glacigenic sequences in ireland can be accommodated within the midlandian cold stage the basal units from certain sequences and erratic fans have been attributed to events earlier than the midlandian however it is difficult to compare these traces of earlier events from different sectors of the island due to poor dating correlation and the fact that direct and indirect stratigraphy is not adequately defined or separated the age of the gortian style interglacial sequences the implications of their floristic composition and their relationships to drift stratigraphy remains a major problem in stratigraphic constructions of the irish quaternary the stratigraphic significance of many till units must remain largely unknown until these matters are resolved at present it is not clear if the gortian sequences represent more than one interglacial a series of exposures in ulster provide evidence for major environmental changes during the midlandian cold stage these include an early stadial an early forest biozone 48 1 ka bp an early herb biozone 41 5 ka bp a middle interstadial phase of cold but non glacial aspect 30 5 ka bp a late stadial max 24 22 ka bp and a late glacial climatic oscillation the late midlandian stadial comprises a major glaciation that almost covered the island and a later more restricted phase when drumlins formed in the northern and western parts of the island max 17 ka bp

genesis of acid sulfate alteration and au cu ag mineralization at summitville colorado the summitville au cu ag deposit occurs within a porphyritic quartz latite primarily in a zone of vuggy silica alteration characterized by leaching of all major elements except silica and iron vuggy silica is best developed between an elevation of 3 700 and 3 500 m where it occurs in irregular pipes and lenticular pods up to 70 m wide and is enclosed by up to 30 m of intense quartz alunite alteration the vuggy silica zones diminish in size with decreasing elevation and rarely exceed a width of 2 m below an elevation of 3 400 m these deep vuggy silica zones are enclosed by quartz kaolinite alteration with little or no alunite sulfide mineralization occurs primarily within the vuggy silica the sulfide assemblage changes with decreasing elevation from covellite luzonite or native gold to chalcopyrite tennantite sulfides occur lining voids or in microveinlets and are accompanied by minor kaolinitc but not by alunite gold also occurs in a near surface barite goethite jarosite assemblage that crosscuts the vuggy silica consideration of alunite kaolinitc and pyrite stability relations and of aluminum speciation at 250 degrees c indicates that a ph of 2 or below and a log f sub o 2 of 31 or 1 at 250 degrees c were necessary to produce vuggy silica alteration the chalcopyrite tennantite mineralization occurring at depth in the vuggy silica zone is indicative of less oxidizing and less acidic conditions the covellite luzonite or gold assemblage requires conditions intermediate between those necessary for vuggy silica alteration and for deep sulfide mineralization barite gold mineralization is interpreted as a near surface assemblage produced under highly acidic oxidizing conditions these textural and geochemical relationships indicate that sulfide and gold mineralization postdate the formation of vuggy silica alteration in the deposit and are not directly related to the highly acidic solutions necessary for this early acid leaching event the change from extreme acid leaching to copper sulfide and precious metal deposition may represent a transition from a magmatic vapor dominated to a liquid dominated system leading to more reducing and less acidic conditions during sulfide deposition

glaciation and sea level change for ireland and the irish sea since late devensian midlandian time the sea level change around the coast of ireland and the irish sea for the past 20 000 years is primarily the combined result of the glacio isostatic adjustment of the crust to the removal of ice over the british isles and the total eustatic change from the global ice sheets however the isostatic effects due to the removal of ice from northern europe and north america and the addition of meltwater into the oceans also make a significant contribution predictions of sea level change based on glacio hydro isostatic models are compared with observations to constrain the ice volume over ireland at the time of the last glacial maximum and the maximum ice height appears to have been of the order of 600 m the models predict well the spatial variability in sea level change observed across the region for holocene and lateglacial time with levels above present being predicted only for northeastern ireland and north of about morecambe bay the models do not support suggestions that lateglacial levels along the east coast of ireland or the coast of wales were 50 150 m above their present levels consistent models that would produce such large lateglacial highstands are incompatible with all other sea level and glacial evidence for the british isles palaeobathymetry and palaeoshoreline reconstructions for the irish sea indicates that a tenuous landbridge between britain and ireland developed only across the celtic sea between about 18000 and 14000 years bp

till and moraine emplacement in a deforming bed surge an example from a marine environment the glacier sefstrombreen in spitsbergen surged across an arm of the sea between qsr 1882 and 1886 and rode up onto the island coraholmen marine and terrestrial geological observations and archive records show that the glacier advanced on a deforming carpet of marine mud which was eroded from its original location transported and smeared over the sea bed and coraholmen as a deformation till the glacier emplaced about 210sm 0 2 km 3 of drift in the terminal 2 km of its advance in a maximum of 14 years leaving a thickness of up to 20 m on coraholmen which was doubled in size as a result during the surge subglacial muds were characterised by high water pressures low effective pressures and low frictional resistance to glacier movement original sedimentary inhomogenities permit fold structures to be identified but repeated refolding and progressive remoulding produce mixing and homogenisation of deformation tills the surge was probably shortlived and as the heavily crevassed glacier stagnated underlying water saturated muds were intruded into crevasses and then extruded on the glacier surface reticulate crevasse intrusion ridges on coraholmen and the sea floor reflect the orientation of surge generated crevasses water and sediment was also extruded beyond the glacier at its maximum extent to form extensive flows producing till tongues both on coraholmen and the sea floor extending over 1 3 km from the glacier it is argued that subglacial deformation of pre existing sediment will almost invariably be associated with glaciation of marine areas and that this process will not only produce deformation tills through remoulding of pre existing sediments but will also play a fundamental role in glacier dynamics criteria which perrait glacial tills produced by such events from marine and glaciomarine muds are discussed copyright 1996 elsevier science ltd

trace fossils of talitrid sandhoppers in interglacial littoral calcareous sandstones cornwall u k small 6cm isolated cylindrical shafts observed in carbonate cemented current bedded interglacial littoral sands sandrock in cornwall have previously been interpreted as intrasedimentary stalactites an alternative explanation as trace fossils of the ichnogenus skolithos is proposed probable attribution to talitrid amphipoda sandhoppers in particular talitrus saltator montagu is supported by the similarity of the features to the modern burrows of this organism the facies dependence of the features and by independent evidence on the backshore frontal dune environment of deposition the ecological requirements of t saltator support the interpretation of the raised beaches as interglacial in status based on thermoluminescence tl dating and aminostratigraphy and conflict with a recent suggestion that they may be of cold stage origin

the gabbro shoshonitic monzonite granodiorite association of khankandi pluton alborz mountains nw iran abstract the khankandi pluton forms part of a group of gabbro granodiorite intrusions in the alborz mountains of nw iran a petrographical and geochemical study of this plutonic association reveals the existence of several magmatic cycles with different origins and slight differences in age the oldest cycle c1 is represented by granodiorites a second cycle c2 is formed by a gabbro monzonite association with a clear shoshonitic affinity that dominates most of the intrusive volume gabbros and monzonites form a co magmatic association zircons from the monzonites were analyzed by la icp ms for u pb dating an average age of 28 9 ma ranging from 23 7 to 33 6 ma was obtained gabbros monzonites and granodiorites share a nearly common isotopic ratio for sr and nd both initial sr and nd ratios are clustered within a narrow range from 0 7045 to 0 7047 for the 87sr 86sr ratio and end from 1 46 to 1 89 comparison with experimental studies together with mantle like isotopic ratios and comparisons of ree patterns points to an origin by variable melting rates from a common metasomatised mantle source for gabbros and monzonites melting of a subducted melange is suggested for the granodiorite magmas predating the gabbro monzonite intrusion the two sources a metasomatised mantle and ascending silicic plumes are direct consequence of subduction

fluid rock interactions and the role of late hercynian aplite intrusion in the genesis of the castromil gold deposit northern portugal abstract castromil northern portugal is one of several important orogenic gold deposits located within the central iberian geotectonic zone of northwest iberia the deposit occurs at the margin of a variscan syn to late d3 biotite granite and is spatially associated with a small tourmaline aplite body that intrudes the granite at its contact with a secondary anticline of palaeozoic arenaceous and argillaceous metasediments of the valongo belt identification of the ore fluids and their pathways and the reconstruction of the p t x conditions during mineralisation were obtained by combining the geometric characteristics of veins and microstructures together with a detailed study of the inclusion fluids several stages of fluid percolation following contact metamorphism can be recognised at each stage the contact zone characterised by intrusive aplites related faults and fractures appears to have focused the hydrothermal flow and acted as a structural conduit for deeper sourced hydrothermal fluids the earliest fluid stage stage i is characterised by aqueous carbonic fluids dominated by co2 and ch4 that were probably generated by high temperature fluid rock interaction 400 500 c with graphitic schists interbedded with the metasediments these fluids were responsible for significant alteration greisenisation of the aplite and its host granite and the formation of silicified flat lying structures that can be traced along the strike length of the deposit at temperatures between 400 and 500 c fluid pressure ranges from 230 to 300 mpa which is equivalent to a depth of 10 1 5 km the second stage of mineralisation stage ii as ore stage is also characterised by aqueous carbonic fluids and represents the main phase of quartz arsenopyrite pyrite deposition the third stage of mineralisation stage iii au ore stage was accompanied by intense microfracturing of the preexisting quartz veins and the preferential deposition of gold along microfractures in the sulphides the introduction of gold corresponds to the percolation and mixing of two distinctive aqueous fluids of contrasting salinity at relatively low temperatures 150 275 c based on compositional and temperature data it is suggested that during the main phase of uplift shallow waters penetrated deep into the basement allowing gold to be leached from potential source rocks most probably the palaeozoic metasediments and deposited in structural and geochemical traps formed during earlier stages of the hydrothermal system the decrease in pressure during the as ore stage corresponds to a significant tectonic uplift around 5 6 km and probably marks the transition from lithostatic to hydrostatic pressure conditions furthermore if uplift had already been initiated during aplite emplacement the prevailing sub isothermal high temperature conditions provide an explanation for the presence of decrepitated aqueous carbonic inclusions in metamorphic quartz lenses and veins in the surrounding metasediments to conclude localised heat flows linked to late hercynian magmatism at deeper structural levels appears to be the main cause of fluid circulation at castromil evidence suggests that contact zones related to faulting along a secondary anticline of the valongo belt controlled both aplite intrusion and subsequent long lived hydrothermal fluid circulation the proposed genetic model differs from orogenic gold deposit models in emphasising the role of late stage aqueous fluids in the development of economic grade 10 15 g t gold ores

satellite observations of mean winds and tides in the lower thermosphere 1 aliasing and sampling issues 1 the canadian middle atmosphere model a general circulation model extending up to 200 km is used to analyze the impact of aliasing and data gaps on satellite observations of zonal mean winds and migrating tides in the lower thermosphere focus is placed on measurements from the wind imaging interferometer windii mock data sets are constructed by sampling daily zonal mean and migrating tides from the model like the satellite previously unverified assumptions that satellite observations of the zonal mean zonal winds and the meridional component of the diurnal tide winds are largely unaffected by aliasing are confirmed of the two the meridional component of the diurnal tide is more robust the amplitude of the zonal component of the diurnal tide is not strongly affected by aliasing tidal phase is nearly unaffected gaps in the windii data do not adversely affect the results provided sufficient local time coverage is available the analysis suggests that more subtle features in the windii observations such as the tidally driven cell like structures in the zonal mean meridional wind at low latitudes may be observable issues pertaining to the sampling interval and the use of daytime only data are also addressed sampling every second or third day provides nearly as good results as sampling every day and that using daytime only data results in substantial biases in the zonal mean zonal winds in the lower thermosphere the latter underscores the importance of the accurate removal of the migrating diurnal tide from climatologies generated from daytime only satellite data

upper pleistocene facies sequences and relative sea level trends along the south coast of ireland upper pleistocene sequences deposited around 20 ka provide a record of sedimentation during the last glacial deglacial cycle along the south coast of ireland a stratigraphy based on eight lithofacies associations is recognized typically the facies sequences overlie a glaciated shore platform furrowed by subglacial meltwaters elements within the stratigraphy comprise 1 ice advance southwards onto the continental shelf 2 stagnation zone retreat triggered by rising sea level related to isostatic depression coupled with subglacial meltwater events that furrowed the platform 3 progressive rise in relative sea level recorded by a submergent facies sequence on an isostatically depressed slope beach gravels 2 subaqueous jet afflux sediments 2 wave influenced sands 2 glaciomarine mud drape ice marginal oscillation is recorded by glaciotectonically deformed gravels sands and foliated diamict 4 terrestrial emergence is marked by angular breccias derived from local slopes by periglacial weathering there is a clear facies transition between the breccias and underlying wave influenced sands facies sequences suggest that the local deglacial cycle was out of phase with the global eustatic cycle along the south coast of ireland stagnation zone retreat was largely dependent on magnitudes of isostatic depression high relative sea level and meltwater events and not on climatic forcing

late pleistocene tidewater glaciers and glaciomarine sequences from north county mayo republic of ireland late pleistocene deposits in north county mayo were deposited in three main glacigenic environments 1 drumlins and basal tills were formed when ice moved from the irish lowlands and local mountain catchments into donegal bay 2 gilbert type deltas accumulated up to 80m i o d on the lowlands and subaqueous moraines formed across minor valleys when marine based ice grounded inland 3 a thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice rafting immediately outside of these ice limits the muds contain an elphidium clavatum dominated low diversity microfauna which is characteristic of cold water conditions adjacent to glacier termini valves of macoma calcarea from the mud have been 14c dated at 16940 120 and 17300 100 bp the high level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north county mayo although the field evidence cannot be used to determine former sea level history with any accuracy it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of ireland raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in ireland and represent marine transgressions prior to glacial unloading it is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in ireland than hitherto realised

geochemistry and geochronology of the banxi sb deposit implications for fluid origin and the evolution of sb mineralization in central western hunan south china abstract central western hunan in south china hosts the largest antimony belt in the world with two types of sb deposits identified sb au woxi type and sb only xikuangshan type banxi is the most representative deposit in the region with vein type sb mineralization hosted in neoproterozoic clastic rocks stibnite developing in ores and arsenopyrite mainly occurring in altered country rocks trace element contents including rare earth elements ree and isotopic ratios s pb sr nd he and ar in stibnite and or arsenopyrite were analyzed to determine the timing of ore formation and to elucidate fluid origin and evolution processes most sulfides have high ree contents 45 103 ppm moderate fractionation between lree and hree lree hree 6 38 11 56 and slightly negative eu anomalies eu eu 0 53 0 72 the 34 s values are 3 88 5 81 for stibnite and 9 25 11 82 for arsenopyrite the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios range from 18 617 to 18 635 15 695 to 15 739 and 38 965 to 38 981 for stibnite and from 18 594 to 18 609 from 15 587 to 15 698 and from 38 893 to 38 926 for arsenopyrite the 87 rb 86 sr and 87 sr 86 sr ratios are 0 3016 3 538 and 0 711463 0 717591 respectively for stibnite and 0 2251 2 214 and 0 711244 0 711565 respectively for arsenopyrite the 147 sm 144 nd and 143 nd 144 nd ratios are 0 1174 0 9816 and 0 511942 0 512768 for stibnite with end t values t 130 ma ranging from 12 4 to 6 6 and two stage model ages t 2dm ranging from 1457 to 1932 ma the 40 ar 36 ar and r ra ratios where ra is the atmospheric 3 he 4 he ratio of 1 4 10 6 are 409 545 and 0 0088 0 0348 respectively for stibnite the rb sr and sm nd isotopic analyses of the sulfides yield isochron ages of 129 4 2 4 ma 2 mswd 1 3 and 130 4 1 9 ma 2 mswd 1 6 respectively the combined trace element and isotopic data set indicates that the ore forming fluids were a mixture of dominantly deep basement derived solute rich parent water and a small amount of dilute heated meteoric water the decreases in ree 34 s 206 pb 204 pb 207 pb 204 pb 208 pb 204 pb 87 rb 86 sr 87 sr 86 sr 147 sm 144 nd and 143 nd 144 nd and increases in 40 ar 36 ar and 4 he contents in the stibnite from the earlier quartz stibnite mineralization stage stage ii through to the later stibnite mineralization stage stage iii indicate that the influx of meteoric water increased during sb mineralization the deep sourced relatively high temperature rock reacted fluid mixed with increasing amounts of more oxidized low temperature meteoric fluids causing the precipitation of arsenopyrite and stibnite sequentially at the banxi deposit a two period genetic model has been proposed for the world class sb mineralization in the central western hunan region the woxi type sb au deposits were derived from orogenic fluids generated from folding and shearing during the caledonian and indosinian orogeny whereas the xikuangshan type sb deposits were formed by mixing heated basement derived hydrothermal fluid circulating during the flare up of magmatism in south china with lower temperature meteoric water

a critical review of the glaciomarine model for irish sea deglaciation evidence from southern britain the celtic shelf and adjacent continental slope in support of their glaciomarine model for the deglaciation of the irish sea basin eyles and mccabe cited the occurrence of distal glaciomarine mud drapes onshore in the isles of scilly and north devon and of arctic beach face gravels and sands around the shores of the celtic sea glacial and sea level data from the southern part of the irish sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model the suggestion that the glacial sequences of both the isles of scilly and fremington in north devon are glaciomarine mud drapes is rejected an actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south central celtic sea relative sea levels were lower and therefore glacio isostatic depression less than envisaged in the glaciomarine model geochronological sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the celtic sea and english channel were deposited at or during regression soon after interglacial eustatic highstands evidence for ice rafting at a time of high relative sea levels is restricted to a phase s earlier than the late devensian these data indicate that the raised beach sequences have no bearing on the style of irish sea deglaciation copyright 2001 john wiley sons ltd

sea floor morphology outside a grounded surging glacier brasvellbreen svalbard abstract acoustical profiling and bottom photography reveal several different sea floor morphological features adjacent to the grounded brasvellbreen glacier on svalbard northwestern barents sea some of the features and their distribution may be closely related to a major glacial surge in 1936 1938 and as such are valuable in identifying former surges in other locations a continuous wide ridge with a characteristic asymmetrical cross section running subparallel to the glacier is the end moraine defining the maximum extent of the surge a large part of the material forming this ridge is most likely rapidly deposited from meltwater during the surge a rhombohedral pattern of smaller mounds inside the ridge is probably an expression of relief in the glacier sole during the surge discontinuous arcuate ridges define local minor oscillations during retreat of the ice at a later stage iceberg plough marks are most frequent seaward of the end moraine their orientation is controlled by the combination of a coastal current offshore katabatic winds and topography superimposed on plough marks are secondary features such as a washboard pattern and striae most likely caused by push up of overconsolidated material during gouging and multi keel icebergs respectively bottom sediments observed in photographs and cores are loose pebbly muds with high variability in clast content resting on overconsolidated material probably basal till mud deposition presently prevails close to the glacier

the granite hosted gold deposit of moulin de cheni saint yrieix district massif central france petrographic structural fluid inclusion and oxygen isotope constraints the moulin de cheni orogenic gold deposit is the only granite hosted deposit of the saint yrieix district french massif central it occurs in 338 1 5 ma old peraluminous leucogranites and is characterized by intense microfracturing and bleaching of the granite in relation to pervasive sulfide crystallization formation of quartz veins and gold deposition occurred in two successive stages an early mesozonal stage of quartz sulfide fe as s deposition usually devoid of gold and a late epizonal stage of base metal and gold deposition both stages postdate peak metamorphism and granite intrusion the genesis of the deposit is the result of four successive fluid events 1 percolation of aqueous carbonic metamorphic fluids under an assumed lithostatic regime of 400 450 c at a maximum depth of 13 km 2 formation of the main quartz lodes with coeval k alteration and introduction of as and s from aqueous carbonic fluids percolating along regional faults arsenopyrite and pyrite deposition was linked to the alteration of fe silicates into k feldspar and phengite at near constant iron content in the bulk granite temperature was similar to that of the preceding stage but pressure decreased to 100 50 mpa suggesting rapid uplift of the basement up to 7 5 km depth 3 the resulting extensional tectonic leads to the deposition of gold boulangerite galena and sphalerite in brecciated arsenopyrite and pyrite from aqueous fluids during a mixing process temperature and salinity decrease from 280 to 140 c and 8 1 wt eq nacl to 1 6 wt eq nacl respectively 4 sealing of the late fault system by barren comb quartz which precipitated from dilute meteoric aqueous fluids 1 6 wt eq nacl to 0 9 wt eq nacl under hydrostatic conditions at 200 150 c

a long term comparison of middle atmosphere winds measured at saskatoon 52 n 107 w by a medium frequency radar and a fabry perot interferometer since late 1988 a medium frequency radar mfr and an imaging fabry perot interferometer fpi have been operating continuously at saskatoon measuring winds and waves in the upper mesosphere and lower thermosphere when weather and auroral conditions permit the fpi measures doppler winds from the atomic oxygen oi 557 7 nm airglow layer centered at an altitude of about 97 km this study is similar to earlier comparisons between the mfr fpi systems except that it draws on 4 years of simultaneous observations because the mfr and fpi are somewhat mutually exclusive in their data acquisition rate real time comparisons of winds are often poor however with the much larger fpi data set now available rather better long term comparisons between the two systems can be made once again strong similarities in the mf radar and fpi doppler wind fields are observed although there are some differences these differences and the causes are discussed

intermediate sulfidation type base metal mineralization at aliabad khanchy tarom hashtjin metallogenic belt nw iran abstract the aliabad khanchy epithermal base metal deposit is located in the tarom hashtjin metallogenic belt thmb of northwest iran the mineralization occurs as cu bearing brecciated quartz veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation ore formation can be divided into five stages with most ore minerals such as pyrite and chalcopyrite being formed in the early stages the main wall rock alteration is silicification and chlorite argillic and propylitic alteration microthermometric measurements of fluid inclusion assemblages show that the ore forming fluids have eutectic temperatures between 30 and 52 c trapping temperatures of 150 290 c and salinities of 6 6 12 4 wt nacl equiv these data demonstrate that the ore forming fluids were medium to high temperature medium to low salinity and low density h2o nacl cacl2 fluids calculated 18o values indicate that ore forming hydrothermal fluids had 18owater ranging from 3 6 to 0 8 confirming that the ore fluid system evolved from dominantly magmatic to dominantly meteoric the calculated 34sh2s values range from 8 1 to 5 0 consistent with derivation of the sulfur from either magma or possibly from local volcanic wall rock combined the fluid inclusion and stable isotope data indicate that the aliabad khanchy deposit formed from magmatic hydrothermal fluids after rising to a depth of between 790 and 500 m the fluid boiled and subsequent hydraulic fracturing may have led to inflow and or mixing of early magmatic fluids with circulating groundwater causing deposition of base metals due to dilution and or cooling the aliabad khanchy deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the mineralization at aliabad khanchy and other epithermal deposits of the thmb formed by hydrothermal activity related to shallow late eocene magmatism the altered eocene volcanic and volcaniclastic rocks especially at the intersection of subvolcanic stocks with faults were the most favorable sites for epithermal ore bodies in the thmb

thermoluminescence dating of late devensian loesses in southern england scattered across southern england are many isolated deposits of loess like material1 a few such as that at pegwell bay in kent are highly calcareous and unweathered but most have been reworked by fluvial or colluvial processes there is good stratigraphical evidence for a few pre devensian loesses also in kent but dating of more recent loess has so far been based on indirect evidence much work has been done on the pegwell bay loess as it is the most extensive truly aeolian loessic deposit in britain kerney2 compared the late devensian deposits in the isle of thanet and at pegwell bay with similar deposits in holland and belgium where radiocarbon dates have been obtained for interstadial deposits correlation of the east kent deposits with these in northern europe indicates that the loesses in kent were formed between 30 000 and 14 000 yr ago i report here dates for six of the more recent deposits in southern britain from the scilly isles to kent the dates have been obtained on the loess itself using a recently developed thermoluminescence tl dating technique3 4 and confirm the ages as being late devensian

late devensian and holocene shorelines of the british isles and north sea from models of glacio hydro isostatic rebound sea level change around the british isles since the time of the last glacial maximum is largely due to of the crustal rebound from the glacial unloading of northern britain and the concomitant melt water loading of the adjacent seas and atlantic ocean minor but not insignificant contributions also result from the rebound caused by the unloading of the distant ice sheets including fennoscandia and north america observations of sea level change for this period constrain the glacio hydro isostatic rebound model parameters describing the effective lithospheric thickness or rigidity and the effective mantle viscosity as well as certain ice sheet characteristics such as the ice thickness at the time of the last glacial maximum the models permit palaeobathymetry and palaeoshorelines to be predicted for the british isles region including the north sea the resulting evolution of the coastlines exhibits a complex behaviour through time one that is quite different from the usual models in which sea level change is assumed to be a function of time only in part this is because of the delayed response of the mantle to the spatially variable and time dependent ice and water loads and in part because the unloading history of the british ice sheet is different from those of the major global ice sheets thus maximum emergence of the north sea occurred after deglaciation had started and lasted for an extended period from about 15 000 to 12 000 radiocarbon years bp during this relative sea level still stand shoreline features could have formed for example along the western edge of the norwegian trough when access to the firths of eastern scotland would have been via a long and shallow marine inlet shoreline retreat across the north sea became relatively rapid after about 10000 years the model predictions for the irish and celtic seas also suggest a complex behaviour with the formation of a wide land bridge between about 20000 and 13 000 years ago the model also suggests that as long as the scottish ice extended across the northern irish sea until about 14 000 years ago there would have been a large freshwater periglacial lake located further south both the predicted sea level height age relations and the shoreline positions are consistent with a large body of observational evidence but some discrepancies occur particularly in northern scotland and ireland where the ice heights may have been somewhat greater than assumed in the model

evidence of sea level change from coastal caves with raised beach deposits terrestrial faunas and dated stalagmites abstract investigation of interfingering marine and terrestrial quaternary deposits preserved in minchin hole and bacon hole on the coast of south wales uk provides evidence of two phases of high sea level equal to or greater than that of today the younger of these is assigned to the 125 000y by high sea level event of oxygen isotope sub stage 5e overlying the deposits which represent this event a series of terrestrial vertebrate faunas indicate a further significant cool warm oscillation before the onset of major frost shattering attributed to the devensian cold stage

origin and evolution of hydrothermal fluids in the marshoun epithermal pb zn cu ag deposit tarom hashtjin metallogenic belt nw iran abstract the marshoun epithermal pb zn cu ag deposit is located in the tarom hashtjin metallogenic belt thmb northwest iran the epithermal base metal veins are mainly hosted in eocene volcanic and volcaniclastic rocks of the karaj formation and late eocene pyroxene quartz monzodiorite the mineralization process can be divided into five stages 1 quartz chalcopyrite pyrite veins and breccias 2 quartz calcite sphalerite galena chalcopyrite pyrite veins and breccias 3 barren post ore quartz veinlets 4 barren post ore calcite veinlets and 5 supergene mineral assemblages the primary metallic minerals are pyrite chalcopyrite sphalerite and galena gangue minerals are mainly quartz calcite sericite and chlorite the main wall rock alteration is silicification intermediate argillic carbonate and propylitic alteration microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were mainly formed at temperatures between 173 and 285 c from fluids with salinities between 3 4 and 6 3 wt nacl equiv coexisting lv vl and v inclusions in quartz and sphalerite provide evidence for boiling in ore stage breccia and veins additionally the occurrence of bladed calcite as well as plumose and colloform crustiform banded quartz in the ore zones and the presence of hydrothermal breccias are consistent with boiling obtained oxygen and sulfur isotope compositions 18owater 9 2 to 1 5 34sh2s 10 0 to 5 7 indicate there was a major contribution from a magmatic component to metallogenesis the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at marshoun the marshoun deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the epithermal mineralization in the thmb are related to late eocene ca 36 37 ma shallow magmatic hydrothermal activity the altered eocene volcanic subvolcanic rocks particularly at the intersection of subvolcanic rocks with faults were the most favorable locus for exploration targeting of epithermal ores at thmb

sedimentology and micropalaeontology of glacimarine sediments from the central and southwestern celtic sea thin discontinuous glacigenic sediments occur at or close to the sea bed as far south as 49 n in the celtic sea the northern samples facies a are clast rich overconsolidated lodgement tills or proximal glacimarine sediments containing sparse reworked microfaunas the southern samples facies b are distal glacimarine plastic silty clays containing abundant cold water microfaunas both these facies are correlated with the late devensian scilly till enabling a quantitative reconstruction of ice thicknesses grounding line sea level and shoreline elevations in the celtic sea at 19 000 years bp the ice advance terminated in marine waters towards the shelf edge break and is likely to have constituted a thin lobate surge over deformable marine sediments 1990 the geological society

albian cenomanian a type granite related ag pb zn veins in the central yidun terrane sw china constraints from the xiasai deposit the xiasai lianlong metallogenic belt in the central yidun terrane china hosts several sn ag and sn ag pb zn deposits which are spatially associated with cretaceous granites the xiasai ag pb zn deposit about 0 27 mt pb zn 1028 t ag and 20 000 t sn is the largest deposit in the belt and is related to a monzogranite intrusion the deposit consists of sulfides in hydrothermal veins resulting from three successive mineralization stages i iii a rb sr isochron of sphalerite samples yielded an age of 99 3 ma and zircon u pb laser ablation inductively coupled plasma mass spectrometry la icp ms dating of the xiasai monzogranite gave ages between 102 1 and 101 1 ma the xiasai monzogranite has a weakly peraluminous a type granite composition with high sio2 alkali and feot contents and low cao mgo and tio2 contents it is marked by enrichments in rb th and u with depletions in ba nb sr p and ti relative to the primitive mantle the ree patterns show a negative slope due to lree enrichment with negative eu anomalies eu eu 0 1 0 3 the xiasai monzogranite with variable ehf t values 2 7 to 0 6 and meso to neoproterozoic two stages hf model ages tdm2 925 1095 ma was probably derived from mixing of melts derived from partial melting of the paleoproterozoic crustal basement and the early cretaceous mantle in an extensional tectonic setting hydrothermal fluids are characterized by high temperatures 423 481 c and salinities 14 9 19 0 wt nacl for sn mineralization stage i moderate temperatures 285 386 c and salinities 3 5 8 0 wt nacl for the cu zn mineralization substage ii 2 and low temperatures 158 242 c and salinities 3 4 5 7 wt nacl for the ag pb mineralization substage ii 3 the h o isotopes indicate that the hydrothermal fluid likely has a magmatic component that mixed over time with infiltrating meteoric water and organic matter during fluid rock interactions the 34s values of sphalerite range from 9 7 to 3 1 and those from galena from 10 5 to 4 9 the estimated 34s value of the hydrothermal fluid is 8 5 using the sulfur isotopic fractionation of sphalerite galena pairs that are interpreted to be in equilibrium sulfides from substages ii 2 and ii 3 have relatively homogeneous pb isotopic compositions which are similar with those of k feldspars from the xiasai monzogranite geochronological and isotope data support a magmatic hydrothermal origin for the xiasai ag pb zn deposit

geochemical characteristics of igneous host rocks of lubin zardeh au cu deposit nw iran abstract the lubin zardeh au cu pb zn deposit is located in the azerbaijan western alborz zone 45 km ne of zanjan iran it is situated within the eocene oligocene volcanic plutonic belt of the tarom subzone of the alborz mountains range quartz monzonite and tuffs are the main host rock of the lubin zardeh au cu pb zn deposit granitoid rocks are predominantly high k calc alkaline with shoshonitic affinities they are i type metaluminous magnesian and are characterized by lile lree and th enrichment relative to hfse depletion in nb ta ti and weak depletion in hree and y these granitoids show some affinities with adakites e g high sr y and la yb ratios coupled with low yb and y and enrichment in lree and lile with weak eu anomalies their relatively low to moderate initial 87sr 86sr values 0 7047 0 7051 positive nd t 36 ma values 0 39 2 1 and tdm ages of 0 69 to 1 06 ga with pb isotopic ratios of initial 206pb 204pb 18 49 18 68 initial 207pb 204pb 15 58 15 61 and initial 208pb 204pb 38 33 38 77 are consistent with a phlogopite bearing amphibole rich and enriched lithospheric mantle source metasomatized by earlier subducted sediments the geochemical and isotopic compositions of the granitoids are similar to the host rocks of porphyry and epithermal deposits in the urumieh dokhtar zone

geochemistry of igneous rocks associated with mineral deposits in the tarom hashtjin metallogenic province nw iran an analysis of the controls on epithermal and related porphyry style mineralization abstract cenozoic magmatism in iran is associated with many epithermal porphyry cu au ore systems which mainly occur within the alborz magmatic arc and urumieh dokhtar magmatic arc systems the tarom hashtjin metallogenic province in the nw part of iran is located in the western alborz magmatic arc and is host to numerous ls is and hs type epithermal deposits within eocene volcano plutonic rocks whole rock geochemical data indicate that volcanic rocks vary extensively and continuously from subalkaline basaltic to rhyolitic compositions granitoid rocks are characterized by subalkaline metaluminous to peraluminous i to a type magmatism geochemical and geochronological studies of the igneous rocks associated with epithermal deposits particularly the enrichment of large ion lithophile elements depletion of high field strength elements including nb ta depletion and their eocene ages are consistent with extensional back arc tectonic settings suggesting that primary source magmas were generated by partial melting of the mantle wedge garnet bearing depleted lithospheric upper mantle and were subsequently affected by both fractional crystallization and crustal assimilation during their magmatic evolution the regional magmatism likely contributed to the heat advection and composition of metal bearing hydrothermal fluids in the formation of the epithermal deposits considering strong plagioclase fractionation relative to hornblende fractionation an extensional back arc tectonic setting the lack of any skarn mineralization and a considerably shallower depth of magma generation the tarom hashtjin metallogenic province is proposed to be prospective for precious metal epithermal mineralization by contrast the urumieh dokhtar magmatic arc and ahar arasbaran zone systems are probably more eroded and thus more prospective for porphyry cu au exploration

only four major 100 ka glaciations during the brunhes chron early attempts at land sea correlations between continental glaciations and the marine 18o record were premature without a high resolution continental stratigraphy existing schemes of continental subdivision and correlation based facies floras and facies faunas do not provide the necessary resolution this paper reports on a new high resolution subdivision and correlation of the pleistocene of the british isles subdivision and correlation is accomplished primarily by aminostratigraphy based on aminozones which is calibrated by other geochronological means u series tl osl esr 14c palaeomagnetic and 36cl rock exposure dating for correlation with oxygen isotope stratigraphy these data are then used to test the hypotheses of shackleton 1987 and raymo 1997 that only four major glaciations occurred in the brunhes chron during oxygen isotope stages 16 12 6 and 2 their hypotheses are confirmed except for stage 2 when at least part of the british ice sheet was at its maximum somewhat earlier during stages 4 and 3

palynology aminostratigraphy and u series dating of marine gortian interglacial sediments in cork harbour southern ireland abstract palynological analysis amino acid epimerization analysis and uranium thorium disequilibrium age determination of three irish interglacial cores support the suggestion that there may have been more than one holsteinian style temperate interval in europe the cores were taken from estuarine deposits beneath glacial diamicton in cork harbour southwest ireland the pollen records an incomplete temperate stage the biotic signature is similar to those from several interglacial sites in ireland and is considered part of the gortian group the pollen signature is holsteinian hoxnian in character amino acid epimerization analysis suggests the deposits to be oxygen isotope stage 7 in age whereas uranium thorium disequilibrium suggests a minimum stage 5 age possible correlatives of the gortian group in europe are suggested

amino acid evidence for devensian ice west gower south wales complete inundation of south wales by ice during the penultimate wolstonian glaciation has been widely suggested1 3 although it is generally agreed that the last glaciation was less extensive than the preceding one4 6 there has been controversy concerning its limits stemming mainly from the lack of clear geomorphological evidence and the dearth of datable material7 9 14c dates from the shelly till in pembrokeshire were first thought to indicate an extension of last glaciation ice into the area10 but serious doubts were subsequently raised about the reliability of finite dates on shells of this age range11 12 we present here results of amino acid analysis of shells from recently exposed till and from underlying raised beach remnants at broughton bay west gower total d allo l iso ratios from the raised beach are consistent with analyses on shells from comparative beach remnants elsewhere in south west britain7 13 15 shells of 21 identifiable littoral species extracted from the till suggest inshore marine conditions similar to those at present amino acid ratios from littorina spp provide firm evidence for the encroachment of devensian ice on to gower approximately to the limit suggested by bowen7 fig 1a

mineral assemblages fluid evolution and genesis of polymetallic epithermal veins glojeh district nw iran abstract the glojeh district contains silver and base metal rich epithermal veins and is one of the most highly mineralized locations in the tarom hashtjin metallogenic province northwestern iran it consists of four major epithermal veins which are located in the south glojeh and north glojeh areas alteration in the glojeh district consists of propylitic sericitic and argillic assemblages as well as extensive silicification the ore bearing veins comprise three paragenetic stages 1 early cu au as sb fe bearing minerals 2 middle stage pb zn cu cd ag bearing minerals and 3 late hematite ag bi au pb mineralogy the veins are best classified as the product of an early high sulfidation hydrothermal system which was overprinted by an intermediate sulfidation system that was rich in ag and base metals hematite is locally altered to goethite in zones of as much as 40 m in width during supergene alteration and the goethite is an important exploration tool fluid inclusions from the early middle and late stages respectively have salinities and homogenizations temperatures ranging from 5 to 11 wt nacl eq and 220 c to 340 c to 1 to 8 wt nacl eq and 200 c to 290 c and finally to 0 1 to 2 wt nacl eq and 150 c to 200 c the oxygen isotope values in quartz range from 8 8 to 13 3 and most calculated fluid 18 o values are between 4 and 8 suggesting a magmatic fluid with some meteoric water contamination sulfur isotope values for chalcopyrite pyrite sphalerite and galena are mainly 7 3 to 1 3 and 0 3 to 8 4 for north glojeh and south glojeh respectively sulfur isotope data suggest a magmatic origin boiling isothermal mixing and dilution are the main mechanisms for ore deposition in the glojeh veins recent 40 ar 39 ar age measurements of 42 20 0 34 ma and 42 56 1 47 ma for the north glojeh and south glojeh veins respectively overlap with the 41 87 1 58 ma age of the goljin intrusion in the northern part of the district which we interpret as the main heat source controlling the hydrothermal systems

evolution of the zonal mean state in the equatorial middle atmosphere during october 1978 may 1979 abstract the evolution of the zonal mean state in the equatorial middle atmosphere is investigated with the use of daily mapped temperatures derived from the limb infrared monitor of the stratosphere lims experiment these quasi global high vertical resolution data cover the pressure range 100 05 mb and the period 25 october 1978 28 may 1979 the equatorial semiannual oscillation sao in zonal mean temperature derived zonal wind and meridional shear of the zonal wind is described in detail rocket profiles are used to validate features seen in lims data these include ranges in temperature and zonal wind of 20 k and 100 m s 1 and cross equatorial shears of at 3 day 1 consistent with the theory that the wave mean flow interaction is essential to the sao flow acclerations over the equator exhibit strong week to week variations while easterly accelerations are moderate and occur in deep cool layers westerly accelerations are generally stronger and occur in shallow warm layers which descend with time

sedimentation at the margins of a late pleistocene ice lobe terminating in shallow marine environments dundalk bay eastern ireland late pleistocene morainic sequences around dundalk bay eastern ireland were deposited in a variety of shallow glaciomarine environments at the margins of a grounded ice lobe the deposits are essentially ice proximal delta fan and apron sequences and are divided into two lithofacies associations lithofacies association 1 occurs as a series of morainal banks formed at the southern margin of the ice lobe in a body of water open to influences from the irish sea the morainal banks consist mainly of diamictic muds deposited from turbid plumes and by ice rafting with minor occurrences of turbidites cross bedded gravels subaqueous outwash and massive boulder gravels high density debris flows lithofacies association 2 was deposited in a narrow arm of the sea at the north eastern margin of the ice lobe the deposits consist mainly of a series of coalescing ice proximal gilbert type fan deltas which are interbedded distally with tabular and lens shaped subaqueous deposits the latter are mainly ice rafted diamictons debris flow deposits and subaqueous sands and gravels both lithofacies associations are draped by diamictons formed by a combination of rain out debris flow and traction current activity at a few localities the upper parts of the sequence have been sheared by minor oscillations of the ice sheet margin these sequences form part of an extensive belt of glaciomarine deposits which border the drumlin swarms of east central ireland lithostratigraphic variability is partially related to the arrival of large volumes of debris at the ice lobe margin when the main lowland ice sheet surged during drumlin formation complex depositional continua of this type lack any major erosional breaks and should not be used either as climatic proxies or for stratigraphic correlations

a dated cave sediment record of pleistocene transgressions on berry head southwest england berry head a limestone headland in torbay southwest england exhibits a series of subaerial marine erosion platforms and raised beaches spanning an altitude range of 97 m solution caves on the headland show preferred horizontal development at elevations that are correlated with the marine erosion platforms and developed in a marine freshwater mixing zone whose position was controlled by high sea level still stands corbridge cave in berry head quarry lies below the raised beaches in torbay and contains evidence of three marine transgressions in the form of fine grained marine ponding deposits with a marine microfauna uranium series dating of intercalated speleothems indicates that a transgression during oxygen isotope stage 5e reached an elevation of 5 8 m od while an earlier transgression probably during stage 7 reached at least 7 2 m od these findings are used to constrain possible interpretations of the aminostratigraphy of raised beaches in southwest britain and a correlation of the unnamed stage of bowen sykes reeves miller andrews brew and hare with oxygen isotope stage 5e is proposed

mineral chemistry of the xiasai ag pb zn deposit in the central yidun terrane sw china insight into ni ag bi mineralization and formation conditions abstract sulfides and sulfosalts are major ore minerals for most of ag pb zn deposits and can be used to study enrichment and distribution of ore forming elements and formation conditions the xiasai ag pb zn deposit zn 0 141 mt 4 30 pb 0 132 mt 4 03 ag 1028 t 337 8 g t cu 10058 t 0 56 and sn 20000 t 0 75 is a hydrothermal vein type deposit in the central yindun terrane sw china it consists of proximal quartz cassiterite veins and distal ag pb zn sulfide veins to a cretaceous monzogranite three successive mineralization sub stages are recognized for ag pb zn veins i e arsenopyrite coarse grained pyrite py1 pyrrhotite sphalerite chalcopyrite fine grained pyrite py2 and silver minerals native bismuth galena nickel minerals such as breithauptite and ullmannite were identified as inclusions hosted within pyrrhotite using energy dispersive x ray spectroscopy eds and electron probe microscopy epm analysis and mapping trace amounts of invisible silver have been detected in chalcopyrite and galena whereas a significant amount of silver is incorporated in pyrargyrite freibergite miargyrite and electrum as intimate intergrowths with galena or inclusions within galena a high content of invisible bismuth is detected within galena 0 21 16 95 wt as well as numerous grains of native bismuth occur as inclusions in galena based on the bi concentrations determined and the modal composition a large sized bismuth deposit would be estimated with about 23 800 t of bi resource the presence of nickel minerals and native bismuth together with zn cd ratios 58 151 of sphalerite indicate that the ore forming materials are derived from the xiasai monzogranite based on mineral assemblages and chemical features for sulfides and sulfosalts the formation of ag pb zn ores was triggered by a decrease in temperature fs2 fo2 and sulfidation the early episode of arsenopyrite py1 pyrrhotite and nickel minerals formed at temperature of 320 470 c lower fs2 and decreasing sulfidation conditions from low alkaline fluids in contrast the late episode of silver minerals native bismuth and galena deposited at 160 270 c with a lower fs2 state and neutral or acidic ph however a slight increase of fs2 fo2 and sulfidation intermediate sulfidation occurred during precipitation of zn cu

advanced argillic lithocaps in the bolivian tin silver belt zones of advanced argillic alteration constituting lithocaps are commonplace in the shallow parts of porphyry copper systems similar lithocaps are also recognized in the shallowly eroded southern part of the bolivian tin silver belt where mineralization typically is centred on felsic volcanic domes a well preserved lithocap at potosi is dominated by vuggy residual quartz and contained the world s largest silver resource whereas the basal remnant of a lithocap at pulacayo is composed of barren quartz alunite minor gold occurs in the structurally controlled roots of a lithocap at tasna the mineralization in these lithocaps is of high sulphidation type and was generated in the epithermal environment in contrast the tin and base metal bearing massive sulphide veins and associated sericitic and quartz tourmaline alteration that underlie the bolivian lithocaps are typified by sulphides of low sulphidation state but are dominantly mesothermal rather than epithermal in character magma chemistry is believed to account for the characterization of bolivian lithocaps by silver tin antimony and porphyry copper lithocaps by gold copper arsenic low grade bulk tonnage silver mineralization within bolivian lithocaps and high grade tin bearing veins concealed beneath them both constitute attractive exploration objectives

the origin of heinrich layers evidence from h2 for european precursor events recent well dated isotopic sr nd fingerprinting of heinrich layer ice rafted detritus ird on the european margin indicates supply from european ice sheets as precursors to laurentide ice sheet lis supply f e grousset et al geology 28 2000 123 126 h snoeckx et al mar geol 158 1999 197 208 these precursorevents lead lis input by up to 1 5 ka f e grousset et al geology 28 2000 123 126 and have been interpreted to indicate lis collapse during heinrichevents stimulated by events originating on the european side of the atlantic f e grousset et al geology 28 2000 123 126 such phasing of ird supply from different sources within heinrich layers therefore has implications for the origin and mechanics of heinrichevents we present evidence here that the ird comprising heinrich layer 2 h2 20 21 14c ka bp on the european continental margin contains detrital campanian upper chalk deriving from bedrock sources eroded on the celtic shelf by the british ice sheet bis in addition to lithic material sourced from the lis high resolution radiocarbon chronology indicates chalk grain deposition as discrete pulses both before and coincident with supply of lis sourced detritus the specificity of the chalk fingerprint to the bis enables a 700 1000 yr lag between the bis and lis events to be identified this phasing indicates a more rapid response of the outlet lobes draining the smaller bis than those draining the lis and implicates external climatic forcing of heinrichevents it is unlikely that this precursorevent represents ird event 18 the recently identified 1 2 ka ird cycle event which immediately precedes h2 because the lag between precursor and main event is here less than 1 5 ka and because such pervasive periodicity is not apparent in european continental margin ird records the later synchroneity between the bis and lis input in h2 identifies glacio eustatic sea level rise associated with lis discharges as a possible feedback mechanism causing destabilisation of ice streams elsewhere during heinrichevents

the late devensian glaciation of the eastern lleyn peninsula north wales evidence for terrestrial depositional environments the glacial deposits of the eastern lleyn peninsula record the advance coalescence and subsequent retreat and uncoupling of welsh and irish sea ice sheets during the late devensian cold stage during advance a thick sheet of basal diamict was deposited over much of the area and during retreat and uncoupling which occurred after 14 5 ka the eastern part of the area was dominated by the formation of a large sandur system draining from the retreating margin of the irish sea ice sheet subsequent stages of retreat are marked by a series of arcuate cross valley moraines formed either by ice contact deposition during stillstand or by structural deformation during minor snout oscillation in the western part of the area sedimentation was controlled by a series of dead ice ridges running parallel to the retreating ice margin and this led to the development of a complex assemblage of localised depositional environments including ice front alluvial fans marginal sandur troughs and pro glacial lake basins all formed under supraglacial ice marginal conditions no evidence of glaciomarine deposition is recorded 1998 john wiley sons ltd

the chronology palaeogeography and archaeological significance of the marine quaternary record of the west sussex coastal plain southern england u k abstract the quaternary sediments of the west sussex coastal plain have produced a wide range of floral faunal and archaeological remains these sediments consist of marine sands and gravels exhibiting transgressive and regressive trends which occur from present day sea level to c 43 0 m o d and are overlain by terrestrial silts and cold climate periglacial sediments at the present day coastline channel fill deposits occur below modern beach levels new field observations coupled with a re investigation of old sites and literature suggest that five discrete high stands of sea level may be preserved in the area of the west sussex coastal plain age estimates for these deposits suggest that they span large parts of the middle and upper pleistocene oxygen isotope stages 13 to 5 conformable relationships between many of the marine and terrestrial sediments suggest that the potential exists within the area to correlate the marine and terrestrial quaternary stratigraphic records in addition sediments associated with two of these high sea level stands are associated with extensive buried landsurfaces covering large areas of the coastal plain at some locations these intact landsurfaces are associated with evidence for human activity and represent stratigraphic and cultural resources of international importance

sea level change in the irish sea since the last glacial maximum constraints from isostatic modelling models of glacio hydroisostatic sea level change have been published for the british isles that are broadly consistent with the observational evidence as well as with glaciological constraints it has been argued however that the models fail to represent sea level change along the irish sea margins and in southern ireland for the post deglaciation period the argument rests on the interpretation of the depositional environment of the elevated irish sea drift on both sides of the irish sea whether this is terrestrial or glaciomarine the isostatic models for the british isles are consistent with the former interpretation in that sea levels on either side of the irish sea south of about the isle of man are not predicted to have risen above present sea level at any time since the deglaciation of the irish sea this implies that ice over both the irish sea and ireland was relatively thin ca 600 700 m over ireland if the glaciomarine interpretation of the elevated irish sea drift is correct then the maximum ice thickness over central and southern ireland would have to reach 2000 m exceeding that over scotland furthermore for the resulting sea level change to be consistent with the holocene evidence this thick ice sheet could not have extended to the eastern side of the irish sea nor could it have been very thick at its northern and western limits if such an ice model is extreme and incompatible with glaciological observations then the alternative is to accept the interpretation of the irish sea drift as terrestrial in origin copyright 2001 john wiley sons ltd

the quaternary history of the central and southwestern celtic sea abstract the british sector of the celtic sea south of the isles of scilly has recently been investigated by the institute of geological sciences igs using several types of bottom sampler and several types of acoustic device by this means the bathymetry has been improved a surface sediment chart constructed and the stratigraphy established by comparison of boreholes with seismic sections a great deal of new information has emerged regarding the late pliocene quaternary history of the area the celtic sea shelf is very wide with a low general gradient and a relatively deep shelf edge the inner shelf is topographically almost featureless whereas the middle and outer shelf are diversified by a series of large tidal sand ridges tsr running approximately normal to the shelf edge the late pliocene quaternary sediments in the area consist of two main formations the late pliocene early pleistocene upper part of the little sole formation and the late devensian early flandrian melville formation both formations appear to be composed predominantly of sand with subordinate gravel and a minor proportion of mud the upper little sole probably consists mainly of fluvial deposits accompanied by subordinate shallow marine deposits in its upper part whereas the melville consists essentially of tidal deposits which have been fashioned probably by the huthnance mechanism into the tidal sand ridges later erosion has developed a gravelly lag pavement layer b across the top of the melville formation and across exposures of upper little sole or older formations between the ridges above this comes a layer of mobile sandy sediment layer a never more than a few metres thick but fashioned in most places into bedforms appropriate to the local current regime these include ripples megaripples sand waves and sand ribbons ice rafting has evidently been responsible for depositing 1 occasional small mounds of material revealed by side scan sonar which are found on the sea bed between the tsr 2 scattered boulders which occur in the normally pebbly lag pavement and 3 scattered outcrops of till revealed by sampling some of which may represent mounds massive marine planation has occurred in the celtic sea shelf area prior to the upper little sole following the deposition of that formation and probably many times during the pleistocene depths of deposition of samples from the upper little sole together with similar data from the almost coeval st erth beds on the cornish mainland indicate that the area has been tilted oceanwards subsidence of the outer shelf area is confirmed by the relatively deep shell edge the most likely mechanism for these displacements appears to be the resolution of large scale gravity anomalies in the asthenosphere