strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

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

warm period growth of travertine during the last interglaciation in southern germany abstract late quaternary travertine at two sites near stuttgart formed entirely during interglacial periods the travertine contains structures from growth induced by bacteria and such structures have been dated by 230th u mass spectrometry the resulting ages from both sites imply growth episodes of short duration with growth rates up to 5 mm yr 1 at 99 800 1300 yr b p 2 n 8 and 105 900 1300 yr b p 2 n 7 these episodes were likely part of marine isotope stage mis 5 3 deposition of silt interrupted travertine growth at one of the sites 105 000 yr b p likely correlatives of this silt are the st germain i b stade recorded in the grand pile peat bog and a cold episode 1000 yr long recorded by 18o values in the grip ice core travertine also formed during stage 5 5 115 000 yr and during the early holocene we found no evidence for travertine accumulation in stages 2 3 4 and 5 1 at both sites the sr u ratio and the initial 234u 238u activity ratio resemble those of modern spring water however the sites differ in the chemical composition of spring water and in stratigraphic sequence of travertine accumulation

sedimentological evidence for a limited separation between armorica and gondwana during the early ordovician the vast extent of sedimentation deposits making up the gres armoricain and its equivalents over the north gondwanan domain is used in this study to test the hypothesis of continuity between the armorica and gondwana plates during the early ordovician the distribution of continental and marine environments the large volume of transported elastic material and the consistent current directions all indicate that the source of sediment supply on the north gondwanan margin was to the south of the sahara although there were local signs of incipient rifting between the two plates armorica was not yet detached from gondwana by arenigian time

ganderia laurentia collision in the caledonides of great britain and ireland during terrane convergence an influx of clastic sediment from an upper plate onto a lower plate is an early indication of terrane juxtaposition in the caledonides of great britain and ireland units accreted to laurentia during the early palaeozoic era include peri gondwanan terrane assemblages that earlier separated from west gondwana however the southern uplands terrane contains detrital zircon populations apparently derived entirely from laurentia characterized by a large asymmetric mesoproterozoic peak and a scarcity of zircon at 600 ma and 2 1 ga in contrast cambrian and ordovician rocks from the lake district and the leinster massif of ireland show abundant grains with these ages together with a range of mesoproterozoic zircon these characteristics are shared with the monian terrane of anglesey and with ganderia in the appalachians indicating probable derivation from amazonia in west gondwana silurian sandstones from the lake district show an influx of laurentia derived zircon and lack the peri gondwanan signal this indicates that in the caledonides ganderia was not accreted to the laurentian margin until c 430 ma in contrast to the ordovician accretion of ganderian fragments recorded in the appalachians suggesting that the configuration of the closing iapetus ocean varied significantly along the strike of the orogen supplementary material details of sample coordinates analytical procedure and u pb detrital zircon analytical data are available at www geolsoc org uk sup18739

oblique reflection of turbidity currents turbidity currents meeting obstacles for example the margins of a confined basin are subject to reflection the consequent change in flow direction is expressed in the sequence of depositional structures of the resulting bed of sediment putative examples of orthogonal reflection have been described based on 180 opposed current directions we present field evidence for the more general case of oblique reflection of turbidites and we report the results of flume experiments indicating a mechanism involving generation of internal solitary waves at an oblique ramp these propagate normal to the ramp regardless of the angle of incidence flow directions in reflected turbidites may indicate the orientation of reflecting surfaces such as basin margin slopes and thus may be of considerable help in paleogeographic and tectonic reconstructions

lithofacies of lower palaeozoic deep marine sediments in the isle of man a new map and stratigraphic model of the manx group

palaeomagnetism of palaeozoic peel sandstones and langness conglomerate formation isle of man implications for the age and regional diagenesis of manx red beds

predicting the geometry of channelized deep sea turbidites analytical relationships between the dynamic properties of a deposit forming turbidity current propagating across a sea floor with small slope and the geometry of the resulting deposit have been confirmed experimentally for a wide range of particle sizes initial concentrations and volumes of the driving suspension these simple expressions provide a basis for inferring the dynamics of natural flows from their deposits we surmise that the turbidity current responsible for depositing the black shell turbidite in the northwestern atlantic ocean had an initial sediment concentration on the order of 100 g of silt per litre and a volume on the order of 1000 km 3

deflection versus reflection of sediment gravity flows in the late llandovery rhuddnant grits turbidite system welsh basin the rhuddnant grits turbidite system was deposited in an elongate fault bounded trough an apparently ideal locality for the reflection of sediment gravity flows as solitons however 280 palaeocurrent readings from turbidite sandstones do not show the expected high angle discrepancies between palaeocurrent directions from sole structures and those from cross lamination palaeocurrents orthogonal to the bounding lineament are not generally observed instead there is a gradual progressive anticlockwise deflection of the currents with distance from source this may be explained by banking of the currents against an intrabasinal slope by the coriolis effect or by a combination of the two processes

a 160 000 year record of dune development and atmospheric circulation in southern arabia aeolian deposits in the wahiba sands sultanate of oman reveal patterns of atmospheric circulation over the past 160 000 years luminescence dating indicates a correlation of dune activity with periods of low global sea level and decreased monsoon intensity evidence from dune orientation and sedimentary structures shows exclusively northbound transport of sand during times of high latitude glaciation these results are in contrast to the current paleocirculation model that assumes an increase of northwesterly winds because of a southward shift of the intertropical convergence zone our results indicate that the circulation pattern during glacial times was comparable to that of the present

large thin slicing a new method for the study of fabrics in lithified sediments this paper outlines a new method for the study of sedimentary fabrics in well lithified facies the technique involves the cutting of large thin slices of rock that can then be viewed in transmitted light the utility of this methodology is demonstrated in sandstone soft siltstone and even schist the technique is particularly pertinent to sedimentary geologists studying lithologically homogeneous sediments in which physical and biogenic sedimentary fabrics are difficult to discern due to a lack of contrast

the influence of lateral basinal slopes on turbidite sedimentation in the annot sandstones of se france abstract the deep water deposits of the lower oligocene annot sandstones of se france were deposited in topographically dissected basins axially derived turbidites show marked lateral onlap onto the underlying marls the original lateral slopes were at least 250 m high and up to 12 prior to compaction induced steepening they commonly show a stepped or undulatory profile lateral tracing of individual beds away from their position of onlap termination down the paleoslope reveals a characteristic succession of microfacies thin bedded nongraded fine sandstones with upper flow regime planar lamination pass downslope into medium bedded partially graded medium sandstones with ripple and planar lamination at the base of the depositional slope the turbidites become thick to very thick bed ed fully graded commonly stepwise coarse sandstones to mudstones the most likely interpretation of the lateral transition from lower flow regime to upper flow regime conditions from the axial trough to the lateral margin of the basin involves pulsatory flow conditions episodes of increased flow thickness and velocity deposited upper flow regime bed forms on the higher parts of lateral ramps while periods of waning current deposited lower flow regime bed forms in the axial trough during accumulation of the sands the underlying marls were differentially compacted with maximum compaction under the axis of the basin decreasing to zero compaction at the edges of the basin this resulted in secondary slopes on the upper surface of the sandstones overlying the marl slopes which may have been important in controlling the accumulation of successive sand packages successive onlap and overstep of sand layers onto the marls resulted in a vertical profile that shows the same succession of facies as traced downslope in individual beds the resulting vertical sections coarsen and thicken upwards over 5 10 m the characteristics of the thin bedded fine sandstones at the base of cycles may be used to distinguish between prograding and laterally onlapping turbidite packages sandstone packages in the basin axis are thick 30 60 m sharp based and sandstone rich the laterally equivalent part of a package overlying a confining slope is thinner asymmetric with a coarsening upward signature and more mudstone rich

the bouma sequence and the turbidite mind set abstract conventionally the bouma sequence bouma a h 1962 sedimentology of some flysch deposits a graphic approach to facies interpretation elsevier amsterdam 168 pp composed of ta tb tc td and te divisions is interpreted to be the product of a turbidity current however recent core and outcrop studies show that the complete and partial bouma sequences can also be interpreted to be deposits formed by processes other than turbidity currents such as sandy debris flows and bottom current reworking many published examples of turbidites most of them hydrocarbon bearing sands in the north sea the norwegian sea offshore nigeria offshore gabon gulf of mexico and the ouachita mountains are being reinterpreted by the present author as dominantly deposits of sandy debris flows and bottom current reworking with only a minor percentage of true turbidites i e deposits of turbidity currents with fluidal or newtonian rheology in which sediment is suspended by fluid turbulence this reinterpretation is based on detailed description of 21 000 ft 6402 m of conventional cores and 1200 ft 365 m of outcrop sections the predominance of interpreted turbidites in these areas by other workers can be attributed to the following 1 loose applications of turbidity current concepts without regard for fluid rheology flow state and sediment support mechanism that result in a category of turbidity currents that includes debris flows and bottom currents 2 field description of deep water sands using the bouma sequence an interpretive model that invariably leads to a model driven turbidite interpretation 3 the prevailing turbidite mind set that subconsciously forces one to routinely interpret most deep water sands as some kind of turbidites 4 the use of our inability to interpret transport mechanism from the depositional record as an excuse for assuming deep water sands as deposits of turbidity currents 5 the flawed concept of high density turbidity currents that allows room for interpreting debris flow deposits as turbidites 6 the flawed comparison of subaerial river currents fluid gravity flows dominated by bed load transport with subaqueous turbidity currents sediment gravity flows dominated by suspended load transport that results in misinterpreting ungraded or parallel stratified deep sea deposits as turbidites and 7 the attraction to use obsolete submarine fan models with channels and lobes that require a turbidite interpretation although the turbidite paradigm is alive and well for now the turbidites themselves are becoming an endangered facies

d h ratios of fluid inclusions of soreq cave israel speleothems as a guide to the eastern mediterranean meteoric line relationships in the last 120 ky abstract d h studies of fluid inclusions of speleothems of the soreq cave israel are made using the method of vacuum thermal extraction d h measurements of present day carbonate pool margins and waters show that the value of the vacuum thermal extraction fractionation ex d extracted water d cave water is 30 0 1 4 for the soreq cave deposits d h analyses of fluid inclusions of two fossil speleothems formed during periods equivalent to glacial times suggest that their isotopic compositions follow the global meteoric water line mwl d 18 o relationship compared to present day waters which follow the mediterranean meteoric water line mmwl trend two samples from interglacial periods show isotopic trends between these lines these differences are presumed to reflect cooler less evaporative conditions in the eastern mediterranean sea during glacial times

quantitative allochem compositional analysis of lochkovian pragian boundary sections in the prague basin czech republic abstract quantitative allochem compositional trends across the lochkovian pragian boundary event were examined at three sections recording the proximal to more distal carbonate ramp environment of the prague basin multivariate statistical methods principal component analysis correspondence analysis cluster analysis of point counted thin section data were used to reconstruct facies stacking patterns and sea level history both the closed nature allochem percentages and their centred log ratio clr coordinates were used both these approaches allow for distinguishing of lowstand transgressive and highstand system tracts within the praha formation which show gradual transition from crinoid dominated facies deposited above the storm wave base to dacryoconarid dominated facies of deep water environment below the storm wave base quantitative compositional data also indicate progradative retrogradative trends in the macrolithologically monotonous shallow water succession and enable its stratigraphic correlation with successions from deeper water environments generally the stratigraphic trends of the clr data are more sensitive to subtle changes in allochem composition in comparison to the results based on raw data a heterozoan dominated allochem association in shallow water environments of the praha formation supports the carbonate ramp environment assumed by previous authors

terrane assemblage of the leinster massif se ireland during the lower palaeozoic compilation of irish geological survey mapping is used to construct a synthesis of the tectonic evolution of the leinster massif during the lower palaeozoic the massif is interpreted as a series of ne sw trending tectonostratigraphic terranes of diverse origin and provenance brought together along major sinistral transcurrent faults with minor discrepancies the age of these terranes decreases from se to nw the precambrian basement rosslare terrane is succeeded by the early cambrian continental margin cullenstown cahore terrane in the waterford wicklow terrane late cambrian early ordovician accreted ocean floor materials are overlain by a late ordovician volcanic arc the early to mid ordovician accreted ocean floor dublin terrane to the nw is overthrust by the early cambrian continental margin bray terrane and is followed to the nw by the mainly silurian midlands terrane these terranes were juxtaposed after substantial sinistral movement along transcurrent faults during the silurian consolidation of the massif also took place from se to nw stages in the consolidation are marked by the intrusion of the saltees 437 ma carrigmore 415 ma and leinster 404 ma stitching plutons fault movement ceased before the deposition of late devonian and carboniferous sediments on a linking unconformity across the massif

diatom inferred salinity and carbonate oxygen isotopes in holocene waterbodies of the western sahara and sahel africa abstract thirteen holocene palaeolakes in the western sahara and sahel have provided diatom records with carbonate oxygen isotope profiles available from eight of them most of these palaeolakes were groundwater fed lake water chemistry is reconstructed using diatom transfer functions lake water salinity and 18 o records are assembled with some isotopic and chemical groundwater data to better understand the response of the hydrological systems to climate changes over the past 15 000 yr data are in general agreement with climate simulations using coupled atmosphere ocean vegetation models which show a mid holocene wetting over the whole of northwest africa and a rapid drying by 6 4 ka the lake record also shows that at many sites the major lake infilling lags the end of the younger dryas by 1 2 ka regional differences also appear in the timing of the lake hydrological optimum ca 10 5 8 5 and 7 5 4 5 ka in the northern sahara 10 8 5 ka in the air tenere 10 5 7 or 4 5 in the sahel and 7 5 ka in lake chad the whole of the holocene is punctuated by short term drying events changes in water isotopic composition through time are partly explained by changes in rainfall amount and air humidity during the wet holocene period however the very low values in the southern sahara also imply changes in the moisture transport pattern or rainfall mechanisms data suggest an apparent decrease in 18 o content of precipitation along the monsoon flow in contrast with modern patterns changes in water availability and quality have driven population migrations in and out of the sahara sahel but relationships between climate and cultures are complex short term dry events might have driven inventive adaptations in the sahara drying at 5 4 5 ka coincides with both the collapse of the classical neolithic civilization and the settlement of new cultures

the stratigraphy correlation provenance and palaeogeography of the skiddaw group ordovician in the english lake district a new lithostratigraphy is presented for the skiddaw group lower ordovician of the english lake district two stratigraphical belts are described five formations are defined in the northern fells belt ranging in age from tremadoc to early llanvirn they are all mudstone or sandstone dominated of turbidite origin in ascending order they are named the bitter beck watch hill hope beck loweswater and kirk stile formations two formations are defined in the central fells belt ranging in age from late arenig to llanvirn these are the buttermere formation a major olistostrome deposit overlain by the tarn moor formation consisting of turbidite mudstones with volcaniclastic turbidite sandstone beds a revised graptolite and new acritarch biostratigraphy for the skiddaw group is presented with eight graptolite biozones and thirteen acritarch assemblages and sub assemblages the provenance of the group is assessed from detailed petrographical and geochemical work this suggests derivation in the early ordovician largely from an old inactive continental arc terrane lying to the south east with the appearance of juvenile volcanic material in the llanvirn comparisons and correlations of the skiddaw group are made with the isle of man and eastern ireland

changing moisture sources over the last 330 000 years in northern oman from fluid inclusion evidence in speleothems speleothems from hoti cave in northern oman provide a record of continental pluvial periods over the last 330 000 yr periods of rapid speleothem deposition occurred from 6000 to 10 500 78 000 to 82 000 120 000 to 135 000 180 000 to 200 000 and 300 000 to 330 000 yr ago with little or no growth during the intervening periods during each of these five pluvial periods d values of water extracted from speleothem fluid inclusions dfi are between 60 and 20 vsmow and 18o values of speleothem calcite 18oc are between 12 and 4 to vpdb these values are much more negative than modern rainfall for d or modern stalagmites for 18o previous work on the isotopic composition of rainfall in oman has shown that northern and southern moisture sources are isotopically distinct combined measurements of the d values of fluid inclusion water with calculated 18o values from peak interglacial speleothems indicate that groundwater was predominantly recharged by the southern indian ocean moisture source when the monsoon rainfall belt moved northward and reached northern oman during each of these periods

tectonic rotation within the british paratectonic caledonides and early palaeozoic location of the orogen magnetizations of late ordovician caradoc early ashgill age in the paratectonic caledonides of wales and the lake district are directed westerly and northerly respectively they identify c 55 of relative rotation of probable acadian age southward subduction of iapetus ocean crust occurred in ordovician times beneath a latitudinally oriented orogen sited in mid southerly latitudes with the borrowdale and snowdonia volcanic provinces forming parallel fore arc and back arc lineaments respectively mid ordovician to mid devonian palaeomagnetic poles from the orogen correlate with contemporaneous gondwana data to identify a former location sited west of the south american perimeter and not near to north africa as assumed in previous reconstructions

speleothem based paleoclimate record from northern oman u th age dating and stable isotope measurements of speleothems from hoti cave in northern oman yield paleoclimate information from the region extending to 125 ka the results 1 provide further confirmation of an early holocene wet period in southern arabia extending from some time prior to 9 7 ka and ending at 6 2 ka 2 demonstrate a second period of wetness closely coinciding with the last interglacial period marine isotope stage mis 5e 3 indicate that during mis 5e southern arabia was considerably wetter than during the early holocene and 4 demonstrate that periods of increased monsoon wind strength based on data from marine sediments do not always coincide with evidence of greatly increased precipitation even from nearby continental areas

the recovery and isotopic measurement of water from fluid inclusions in speleothems the isotopic composition of speleothems is a useful palaeoclimatic indicator but its value would be enhanced if information on the composition of the parent dripwaters could be recovered from fluid inclusions in the speleothem calcite to develop a robust method for extracting and measuring oxygen and hydrogen isotopic composition of fluid inclusions we have used anhydrous iceland spar and microlitre glass capillaries of water as an analogue system crushing the capillary and calcite together in a high vacuum cell we have investigated the adsorbtive and isotopic behaviour of water when exposed to clean fracture surfaces significant water adsorption occurs at room temperature accompanied by large negative isotopic shifts of both oxygen and hydrogen in the recovered foe water at h2o caco3 mass ratios c for 60 min totally desorbs the water and allows retrieval of the correct isotopic composition application of these methods to a british late holocene speleothem yields delta o 18 and delta h 2 compositions for the inclusion water which are closely comparable with the modern cave dripwaters and local precipitation the results show that isotopic compositions can be recovered from inclusion samples of l equivalent to approximately ig of calcite with precisions that are useful for palaeoclimatic research 0 4 for delta o 18 and 3 for delta h 2 greater precision than this will require replicate analysis for each speleothem growth increment copyright c 2001 elsevier science ltd

isotope study of moisture sources recharge areas and groundwater flow paths within the eastern batinah coastal plain sultanate of oman oxygen and hydrogen isotope analyses of rainfall samples collected on the eastern batinah coastal plain of northern oman between 1995 and 1998 indicate two different principal water vapor sources for precipitation in the area a northern mediterranean source and a southern indian ocean source as a result two new local meteoric water lines were defined for the study area isotopic analyses of groundwater samples from over 200 springs and wells indicate that the main source of water to the batinah coastal alluvial aquifer is high altitude rainfall from the adjacent jabal akhdar mountains originating from a combination of northern and southern moisture sources the groundwater recharged at high altitude forms two plumes of water which is depleted in the heavy isotopes 18o and 2h and stretches from the mountains across the coastal plain to the sea thereby retaining a chemical homogeneity horizontally and vertically down to a depth exceeding 300 m in contrast in areas adjacent to these two plumes the alluvial aquifer is geochemically stratified near the coast saline intrusion results in abrupt changes in chloride concentrations and isotope values

rifting during separation of eastern avalonia from gondwana evidence from subsidence analysis subsidence curves for cambrian ordovician sequences from the anglo welsh segment of the paleocontinent of avalonia reveal two periods of regionally enhanced basement subsidence early cambrian 545 518 ma and late cambrian to early tremadocian 505 490 ma the earlier event may record transtension following the avalonian cadomian orogeny the second event may be a transtensional precursor to the late tremadocian volcanic arc on eastern avalonia however paleomagnetic faunal volcanic and sedimentary evidence suggests that the main separation of eastern avalonia from gondwana occurred after middle arenigian time rifting during separation is probably recorded by localized middle arenigian to llanvirnian 480 462 ma subsidence along the welsh basin margin but rifting must have occurred mainly on the now obscured southern margin of the avalonian continent pronounced caradocian 462 449 ma subsidence is associated with back arc rifting after separation from gondwana