a 300 kyr high resolution aridity record of the north african continent new oxygen isotope data and a high resolution carbonate record of a core from the northwest african margin are presented in combination with geochemical zr rb ratio al ba organic carbon and biogenic opal fluxes and sedimentological median grain size parameters to show variations in african continental aridity wind strength and upwelling productivity the carbonate record is diluted by the supply of aeolian dust from the arid saharan region of north africa and is seen to vary with a characteristic sawtooth pattern indicating rapid increases in dust flux followed by gradual declines spectral analysis of the carbonate profile and comparison with specmap stacked oxygen isotope and etp solar radiation profiles shows that the precessional 23 kyr insolation induced african climate system is decoupled from global ice volume climate changes operating on a 100 kyr frequency detailed studies of glacial terminations i ii and iii confirm the presence of rapid short timescale climatic variations in aridity

quantification of foraminifer and coccolith carbonate in south atlantic surface sediments by means of carbonate grain size distributions this study presents a differentiated carbonate budget for marine surface sediments from the mid atlantic ridge of the south atlantic with results based on carbonate grain size composition upon separation into sand silt and clay sub fractions the silt grain size dis tribution was measured using a sedigraph 5100 we found regionally characteristic grain size distributions with an overall minimum at 8 mm equivalent spherical diameter esd sem observations reveal that the coarse particles 8 mm esd are attributed to planktic for aminifers and their fragments and the fine particles 8 mm esd to coccoliths on the basis of this division the regional variation of the contribution of foraminifers and coccoliths to the carbonate budget of the sediments are calculated foraminifer carbonate dominates the sed iments in mesotropic regions whereas coccoliths contribute most car bonate in oligotrophic regions the grain size of the coccolith share is constant over water depth indicating a lower susceptibility for car bonate dissolution compared to foraminifers finally the characteristic grain size distribution in fine silt 8 mm esd is set into context with the coccolith assemblage counted and biometrically measured using a sem the coccoliths present in the silt fraction are predominantly large species length 4 mm smaller species length 4 mm belong to the clay fraction 2 mm esd the average length of most frequent coccolith species is connected to prominent peaks in grain size distri butions esd with a shape factor the area below gaussian distri butions fitted to these peaks is suggested as a way to quantitatively estimate the carbonate contribution of single coccolith species more precisely compared to conventional volume estimates the quantitative division of carbonate into the fraction produced by coccoliths and that secreted by foraminifers enables a more precise estimate for source sink relations of consumed and released co 2 in the carbon cycle the allocation of coccolith length and grain size esd suggests size windows for the separation or accumulation of distinct coccolith species in investigations that depend on non to slightly mixed signals e g isotopic studies

redox reactions and carbonate preservation in deep sea sediments abstract geochemical analyses of long sediment cores in turbidite sequences from two abyssal plains in the north atlantic have provided evidence for a relationship between post depositional oxic decay of organic matter and the dissolution of carbonates palaeo oxidation zones in the upper part of individual turbidites were initially identified by distinct colour changes in the sediments these zones were found to have distinctly lower amounts of organic carbon carbonate minerals and labile metals such as fe mn ni and zn as compared with the underlying unoxidized parts of the same turbidite it appears that the initial oxidation of organic matter by oxygen results in an undersaturation of the pore water with respect to carbonates while at the same time some metals are precipitated as easily reducible and soluble oxyhydroxides after burial under suboxic conditions the palaeo oxidation zones are subjected to mildly reducing pore waters that leach the oxyhydroxides resulting in a depletion in labile metal contents in the palaeo oxidized zones it is important that these characteristics be identified in the sedimentary record as the result of diagenetic processes and not as a reflection of primary production in palaeo oceans

latest eocene early oligocene climate change and southern ocean fertility inferences from sediment accumulation and stable isotope data abstract the earliest oligocene 33 5 ma is marked by a major step in the long term transition from an ice free to glaciated world the transition characterized by both cooling and ice sheet growth triggered a transient but extreme glacial period designated oi 1 high resolution isotope records suggest that oi 1 lasted for roughly 400 000 yr the duration of magnetochron 13n before partially abating and that it was accompanied by an ocean wide carbon isotope anomaly of 0 75 one hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate induced intensification of wind stress and upwelling particularly in the southern ocean to understand how this climatic event affected export production in the southern ocean biogenic silica opal and carbonate accumulation rates were computed for the sub polar indian ocean using deep sea cores from odp site 744 kerguelen plateau our findings suggest that net productivity in this region increased by several fold in response to the oi 1 glaciation in addition calcareous primary producers dominant in the late eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the southern ocean we attribute these changes to intensification of atmospheric oceanic circulation brought about by high latitude cooling and the appearance of a full scale continental ice sheet on east antarctica higher terrigenous sediment accumulation rates support the idea that wind induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro nutrients e g iron rich dust particles we speculate that the rapid changes in biogenic sediment accumulation in the southern ocean and other upwelling dominated regions contributed to the ocean wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon the changes in burial rates in turn may have produced a positive feedback on climate by briefly drawing down atmospheric pco2

25 000 year late quaternary records of carbonate preservation in the south china sea pelagic sediments recovered from the south china sea scs exhibit characteristic carbonate preservation fluctuations that are closely linked to major cycles of climatic change two deep sea cores scs 90 36 17 59 70 n 111 29 64 e water depth 2050 m and 31 kl 18 45 4 n 115 52 4 e 3360 m that are located respectively above and below the regional lysocline 3000 m were selected for studying the late quaternary pattern of carbonate preservation in the scs preservation indices measuring changes in the abundances of dissolution resistant planktonic foraminifers and coccoliths and in ratios of foraminiferal fragments benthonic foraminifers and radiolarians have revealed increased carbonate preservation during the last glacial period and or during the last deglaciation termination i 12 000 k y but stronger carbonate dissolution during the interglacial period of the holocene detailed comparisons of preservation and oxygen isotope records further indicate that the level of carbonate preservation increased steadily from 25 k y through termination i and that preservation reached a maximum during termination i from termination i into the holocene however the level of preservation decreased gradually to a minimum both records exhibit noticeable glacial interglacial variations 1f on the order of 104 years while the higher resolution record of 31 kl records a series of higher frequency oscillations 1f on the order of 103 years these data confirm the observation that maximal carbonate preservation tends to occur during the later half of glacial stages as shown previously in many indian and pacific deep sea core studies

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

carbonate dissolution in recent sediments of the eastern equatorial indian ocean preservation patterns and carbonate loss above the lysocline abstract multiple dissolution indices from 45 sediment samples show that the foraminiferal lysocline is near 3800 m in the eastern equatorial indian ocean close to the saturation horizon with respect to calcite in the water column below the lysocline the increase in foraminiferal fragmentation decrease in absolute abundance and progressive modification of planktic foraminiferal assemblages with depth is accompanied by an increasing rate of loss of carbonate from the sediments above the lysocline some dissolution must occur in order to produce the dramatic reduction in foraminiferal numbers up to 60 and the pattern of increased fragmentation with depth however the amount of carbonate actually lost from supralysoclinal sediments reaches at most 20 30 of the total at the depth of the lysocline the principal driving force behind supralysoclinal dissolution is most likely the oxidation of organic matter incorporated into the sediments dissolution above the lysocline has a greater apparent impact on relative preservation in the coarse 150 m fraction than it does on total carbonate loss because of redistribution of carbonate to the finer size fractions as fragments though the effects of dissolution on foraminiferal preservation are clearly visible at all depths the lysocline itself does appear to mark the local onset of large scale loss of dissolved carbonate from the sediments such an interpretation is broadly consistent with models regarding the saturation state of the overlying waters as the principal driving force behind the preservation or dissolution of recent carbonate sediments on the sea floor

equatorial aridity and climatic oscillations during the early carboniferous southern britain evidence from palaeosols palaeokarsts and styles of meteoric diagenesis shows that the early carboniferous climate of southern britain was dominantly seasonally semi arid this semi aridity occurred while the region was in an equatorial palaeolatitudinal position the cause of the seasonal aridity was possibly the deflection of easterly winds into a major low pressure zone set up over gondwana during the southern hemisphere summer

early dinantian evaporites of the easton 1 well solway basin onshore cumbria england abstract an early visean anhydrite rich carbonate clastic succession of vertical thickness 3784 feet no base was found in 1990 at the easton 1 well in the solway basin onshore cumbria the succession is stratigraphically located in the lower border group where only traces of evaporites had been found at outcrop it is proposed to name the succession the easton anhydrite facies of the lower border group abbreviated to ea beds the ea beds are divided into three units unit 1 at the top about 400 feet thick contains two sequences of upwardly thickening anhydrite beds within mixed lithologies unit 2 about 2100 feet thick consists of nine cyclic sequences of limestones shales and sandstones with numerous interbeds of anhydrite overall similarity of several of the sequences suggests similar origins unit 2 sequences are grouped into three megacycles two of approximately 750 feet and one 590 feet thick deposition is interpreted to have taken place in arid or partly arid climatic conditions within a shallow and rapidly but uniformly subsiding basin with glacio eustatically controlled rise and fall of sea level many of the unit 2 anhydrite beds are interpreted to be of subaqueous origin unit 3 about 1500 feet thick displays complex patterns of cyclicity with sedimentation apparently responding directly to solar insolation under orbitally induced control within milankovitch periodicities of 100 000 and 400 000 years seismic interpretation indicates that the regional extent of the ea beds is greater than 1000 km 2

paleo sea surface temperature calculations in the equatorial east atlantic from mg ca ratios in planktic foraminifera a comparison to sea surface temperature estimates from u37k oxygen isotopes and foraminiferal transfer function we present two 270 kyr paleo sea surface temperature sst records from the equatorial divergence and the south equatorial current derived from mg ca ratios in the planktic foraminifer globigerinoides sacculifer the present study suggests that the magnesium signature of g sacculifer provides a seasonal sst estimate from the upper 50 m of the water column generated during upwelling in austral low latitude fall winter common to both down core records is a glacial interglacial amplitude of 3 3 5 c for the last climatic changes and lower holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5 5 and glacial stage 6 temperatures respectively the comparison to published sst estimates from alkenones oxygen isotopes and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods

foraminiferal assemblages and caco3 dissolution since the last deglaciation in the maxwell bay king george island antarctica abstract three sediment cores a10 01 02 and 08 from the maxwell bay king george island antarctica were quantitatively analyzed for foraminiferal fauna planktonic foraminifera of three cores are rare due to the special antarctica environment benthic foraminifera is mainly composed of globocassidulina biora globocassidulina crassa rossensis cassidulinoides parkerianus and miliammina arenacea g biora and g crassa rossensis show high percentages in the shallower core a10 08 while m arenacea displays obviously high percentage in deeper core a10 02 the lower parts of the cores have a lower abundance of foraminifera while the upper parts have a relatively higher abundance the down core variations of benthic foraminifera reflect the contrast of surface water environment between the last deglaciation and post glacial during the last deglaciation lower parts of the cores the lower abundant foraminifera was consistent with the lower toc which reflected that the extensive sea ice prevented the production of primary organisms and therefore lower flux of organic particles was delivered to the sea floor abundant foraminifera together with higher toc in the upper parts of the cores suggested a higher primary productivity after the glaciation the shallowest water depth core a10 08 45 m displayed a better carbonate preservation than the other two cores a10 01 and 02 from the depths of 85 and 105 m respectively the disparity in carbonate dissolution reflected the remarkable shallow lysocline and carbonate compensation depth ccd in the antarctic area and also reflected significant variations in water properties even within such a difference only about 60 m in water depth down core variations of benthic foraminifera dissolution index bdi and caco 3 content indicated the existence of stronger carbonate dissolution in the upper parts than those in the lower parts of the cores the down core variations of carbonate dissolution suggested changes of water properties linked to the shallow ccd in this area it was supposed that the less influence of the saline shelf water during the last deglaciation enhanced the carbonate preservation with the sea level increasing and retreat of the coastal ice after the glacial erosive water masses and the higher co 2 accumulated by the increased flux of organic material led to severe dissolution of caco 3 and foraminiferal shells in the sediment

the east irish sea basin from caterpillar to butterfly a thirty year metamorphosis in the thirty years since the award of the first licenses the east irish sea basin has emerged as a significant hydrocarbon province this paper first lists some of the occasionally almost arbitrary events that led to the first success in the basin the discovery of the morecambe field in 1974 an attempt is made to review progress over those thirty years in certain topics namely 1 stratigraphy 2 structure 3 sedimentology 4 diagenesis the platy illite problem and others 5 uplift and inversion 6 hydrocarbon sources and types 7 east irish sea basin analogues the paper concludes by summarizing the current state of knowledge 1995 represented the thirtieth anniversary of the first award of licences in the east irish sea basin eisb the twenty sixth anniversary of the drilling of the first wells and the twenty first anniversary of the discovery of the south morecambe field it is perhaps appropriate to look back on some of the crucial events of the last thirty years and on some of the earlier concepts and interpretations with a view to seeing how these last have progressed or been found wanting undoubtedly the biggest spur to exploration was the discovery in 1974 by the british gas corporation subsidiary hgb ltd of the south morecambe field how a fledgling organization came to discover this 5 tcf gas accumulation in its first venture is itself noteworthy key events that led to this discovery might be summarized as follows 1 the wish of the government in power in 1969 to foster a national presence in the exploration of british waters by allowing the then gas council to take 100 interests in eisb blocks 2 the readiness of the gas council to exploit this opportunity 3 the unwillingness of the council s main north sea partner to participate in the proposed application with its offer of a firm well 4 the unwillingness of other majors to join the application 5 the informal gift by gulf in 1973 of the logs of wells 110 8 1 and 2 on the basis of a gentleman s agreement that hgb would likewise make data available from any wells it

plio pleistocene sedimentation regimes leading to chalk marl cycles in the north atlantic dsdp site 552 hole 552a pliocene sediments from the rockall plateau northeast atlantic older than 2 4 my the onset of northern hemisphere glaciation consist of calcareous oozes and thereafter plio pleistocene sediments consist of ooze marl cycles the marls are formed through the addition of icerafted detritus to marine carbonates the two to threefold increase in glacial terrigenous matter accumulation is balanced by a concomitant reduction in carbonate accumulation carbonate dissolution is strongest in quaternary interglacial oozes and weak in glacial marls while the reverse is found in the late pliocene strong dissolution in glacial marls and weak dissolution in interglacial oozes carbonate dissolution is tied to the introduction of organic matter from surface water productivity pliocene preglacial calcareous oozes show carbonate dissolution cycles which did not however lead to the formation of marly sediments

a link between paleoceanography early diagenetic cementation and shear strength maxima in late quaternary deep sea sediments near surface sediments from the equatorial east atlantic and the norwegian sea exhibit pronounced shear strength maxima in profiles from the peak holocene and pleistocene these semi indurated layers start to occur at 8 102 cm below the sediment surface and can be explained neither by the modal composition nor by the effective overburden pressure of the sediments however scanning electron microscope and microprobe data exhibit micritic crusts and crystal carpets which are clearly restricted to undisturbed samples from indurated layers and form a manifest explanation for their origin the minerals precipitated comprise calcite aragonite and in samples more proximal to the african continent sio2 needles and needles of as yet unidentified k mg fe al silicates crusts of which dominate the indurated layers in the norwegian sea by their stratigraphic position in deep sea sediments the carbonate based shear strength maxima are tentatively ascribed to dissolved adjacent pteropod layers from the early holocene and hence to short lived no analogue events of early diagenesis possibly they have been controlled by a reduced organic carbon flux leading to increased aragonite preservation in the deep sea

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

light dark cycles in opal rich sediments near the plio pleistocene boundary dsdp site 532 walvis ridge continental terrace diester haass l meyers p a and rothe p 1986 light dark cycles in opal rich sediments near the plio pleistocene boundary dsdp site 532 walvis ridge continental terrace mar geol 73 1 23 samples taken at 10 cm intervals from dsdp core 532b 17 contain variations in carbonate opal organic carbon and terrigenous components that correlate with light dark cycles in sediment color the core site at 1300 m water depth is well above the ccd yet the color variations appear to result largely from cyclical fluctuations in carbonate dissolution which was greater during glacial periods higher concentrations of organic carbon and of terrigenons sediment components correlate with enhanced carbonate dissolution but opal concentrations inversely correlate and suggest that biological productivity at this site diminished during glacial periods a complicated glacial interglacial picture emerges from the data in interglacial times upwelling associated with the benguela current produced abundant opaline material organic matter was fairly well preserved and carbonate was only moderately dissolved in glacial times the upwelling core shifted as sea level fell and winds intensified productivity in the waters over site 532 decreased but lateral supply of oxidizable organic matter enhanced carbonate dissolution giving rise to light dark cycles in these sediments

abyssal erosion and scarp retreat deep tow observations of the blake escarpment and blake spur abstract deep tow surveys conducted at two sites at the base of the blake spur and blake escarpment serve to delineate the contact between mesozoic platform carbonates of the blake plateau and adjacent abyssal strata the continental margin in the surveyed areas consists of steep limestone cliffs and headlands with over 2 km of relief this extreme topography distorts the hydrographic structure of the water column and intensifies abyssal current flow in the surveyed areas significant lateral scarp retreat is indicated by the presence of broad nearly horizontal benches of mesozoic limestone presently exposed at the base of the blake spur and escarpment in 4 5 5 km water depth and by angular apparently truncated limestone ledges that crop out on the cliff face at the blake spur the contact between mesozoic platformal limestones and basinal tertiary strata does not occur directly at the foot of the cliff but is exposed on the abyssal plain within a 50 m deep erosional moat here strong 2 knots south flowing bottom currents occur within 100 m of the sea floor the coincidence of this vigorous current flowing within the moat near the base of the escarpment and the eroded character of the sea floor suggests that currents are an important mechanism in sculpting this abyssal headland and contributing to lateral scarp retreat similar erosional processes are indicated along the blake escarpment near 29 03 n where the relatively straight cliff face is interrupted by occasional steep walled box canyons on the headland between the canyons the mesozoic outcrop projects into the blake bahama basin for several kilometers as a broad arcuate gently sloping bench these outcropping benches of mesozoic strata at the base of the escarpment are analogous to larger scale buried benches observed in the subsurface that were formed by pre miocene erosion neogene and quaternary scarp retreat is suggested by the location of the contact between mesozoic rocks and younger strata seaward of the steeper cliff face and is probably the result of current induced erosion focused erosion may be facilitated by the presence of a thin 50 m filament of corrosive antarctic bottom water aabw that flows vigorously along the base of the cliff at both sites the recessed position of the canyons shelters them from the main flow of this abyssal current but the steepness and morphology of the canyon walls suggest that additional unidentified erosional processes are focused at the canyon heads

the structure and evolution of the northumberland trough from new seismic reflection data and its bearing on modes of continental extension an 18 km long n s seismic reflection profile has been acquired across the faulted boundary between the alston block and the northumberland trough a nw se geological cross section has been constructed across the trough by integrating this line with other data and a tricentrol seismic profile confirms the suitability of this model the trough has a markedly asymmetric form with a thickness of more than 4 2 km of dinantian strata adjacent to its faulted southern margin the present day surface faults stublick ninety fathom are related to variscan and later inversion and transpression and do not everywhere correspond precisely to the earlier syn depositional normal faults the basin is believed to have formed in response to reactivation of the iapetus suture in a dominantly n s extensional stress field basin evolution has been analysed by fault restorations and subsidence modelling the fault restorations indicate an upper crustal extension factor of 1 15 to 1 19 subsidence modelling indicates a whole crustal extension factor of 1 30 with similar sub crustal lithospheric extension it is possible that the difference between the inferred extension factors is due to non uniform increasing downwards lithospheric extension but the uncertainties inherent in both methods are such that this cannot yet be confirmed

present water mass calcium carbonate corrosiveness in the eastern south atlantic inferred from ultrastructural breakdown of globigerina bulloides in surface sediments abstract the atlantic is regarded as a huge carbonate depocenter due to an on average deep calcite lysocline however calculations and models that attribute the calcite lysocline to the critical undersaturation depth hydrographic or chemical lysocline and not to the depth at which significant calcium carbonate dissolution is observed sedimentary calcite lysocline strongly overestimate the preservation potential of calcareous deep sea sediments significant calcium carbonate dissolution is expected to begin firstly below 5000 m in the deep guinea and angola basin and below 4400 m in the cape basin our study that is based on different calcium carbonate dissolution stages of the planktic foraminifera globigerina bulloides clearly shows that it starts between 400 and 1600 m shallower depending on the different hydrographic settings of the south atlantic ocean in particular coastal areas are severely affected by increased supply of organic matter and the resultant production of metabolic co2 which seems to create microenvironments favorable for dissolution of calcite well above the hydrographic lysocline

late quaternary sedimentation on the eastern walvis ridge se atlantic hpc 532 and four piston cores five sediment cores from the eastern walvis ridge have been investigated by means of a quantitative coarse fraction analysis 40 m numerous biogenous terrigenous and authigenic particles have been distinguished the variations in composition suggest the following conclusions core walda ks 12 from the northern flank of the walvis ridge consists entirely of a slump which contains mainly glacconite sands and biogenous opal foraminiferal skeletons and terrigenous matter the sediments in the other four cores comprise the late quaternary oxygen isotope stages 1 6 there are several levels at the transition from warm to cold intervals where benthos plankton foraminiferal ratios increase from 10 up to 50 90 here imperforate benthonic foraminifera decrease strongly dissolution of planktonic foraminifera can only partly explain this finding lateral supply of benthos or the influence of reduced oxygen content in the bottom water might have played an additional role calcium carbonate dissolution as revealed by the fragmentation of planktonic foraminifera shows intermediate values in coldest and warmest periods dissolution maxima occur at warm cold stage boundaries dissolution minima have been found at the transition from cold to warm periods upwellinginfluence is reflected in varying amounts of biogenous opal in interglacial periods the influence of upwelling is strong in all cores with an increase in intensity to the east core v19 259 it is explained by eddies of upwelled water which drifted westward under the influence of the westward turning benguela current in glacial periods the influence of upwelling at the core sites was very reduced the benguela current problably was close to the continent and turned westward only at 17 s thus it did not affect the core sites climate in the near coastal area has been arid in the latitude of 20 s throughout the investigated time slice accumulation rates reflect the position of the cores hpc 532 and circe gb 211 are in the area of the sediment filled trough which forms the walvis ridge terrace here accumulation rates are 2 to 3 times higher in stages 2 4 and 5 than in v19 259 and walda ks 09 which are from the steeper flank of the terrace outside the trough mean values of calcium carbonate dissolution are similar in all cores lower caco3 content in v19 259 and lower sand fraction percentages are explained by lateral supply of fine grained terrigenous matter in the area of core v19 259 which probably received insoluble material from the kuene shelf area by the n s flowing countercurrent

fauna and habitat types driven by turbidity currents in the lobe complex of the congo deep sea fan abstract this study characterizes the habitats and megafaunal community of the congo distal lobe complex driven by turbidity currents through the use of remotely operated vehicle rov still imagery transects covering distances in the order of kilometers in this sedimentary abyssal area about 5000 m deep and 750 km offshore from western africa large quantities of deposited organic material supplied by the congo river canyon and channel support aggregations of large sized foraminifers bathysiphon sp and vesicomyid clams christineconcha regab abyssogena southwardae often associated with methane cold seeps as well as opportunistic deep sea scavengers additionally bacterial mats assumed to be formed by large sulfur oxidizing filamentous bacteria beggiatoa type and black patches of presumably reduced sediment were seen which are together with sulfur oxidizing symbiont bearing vesicomyids indicators of sulfide rich sediments habitat and faunal distribution were analyzed in relation to the microtopography obtained with the rov multibeam echosounder at three sites from the entrance of the lobe complex where the channel is still deep to the main flatter area of turbidite deposition specific characteristics of the system influence animal distributions both the forams and the vesicomyid clams tended to avoid the channels characterized by high speed currents and are therefore preferentially located along channel flanks affected by sliding and on levees formed by channel overspill foram fields are found in flat areas and form large fields whereas the vesicomyids have a patchy distribution and appear to show a preference for regions of local topographical relief such as slide scars or collapsed blocks of sediments which likely facilitate sulfide exhumation the colonization of sulfide rich sediments by vesicomyids is limited but nonetheless was seen to occur in the main deposition area where they have to cope with very high sedimentation rates up to 20 cm yr and frequent turbidity currents other biological adaptations to the local conditions likely determine the presence and survival of animals in the system large agglutinated forams are known to be adept at quickly colonizing disturbed sediment and capitalizing on abundant but irregular food sources and vesicomyid clams have a mobile lifestyle that enables them to maintain their population in the ever changing landscape of sulfide rich sediment outcrops turbiditic systems appear to be intermediate between other energy rich habitats sustaining chemosynthesis in the deep sea being locally less stable in terms of energy supply than cold seeps limiting the number of cold seep specialists able to colonize but constituting a longer lived habitat than food falls turbidite fans therefore represent distinct deep sea habitats that contribute to sustaining populations of both chemosynthesis based and opportunistic taxa in the deep sea

millennial scale precipitation changes over central africa during the late quaternary and holocene evidence in sediments from the gulf of guinea we combine environmental magnetism geochemical measurements and colour reflectance to study two late quaternary sediment cores geob 4905 4 at 2 30 n off cameroon and geob 4906 3 at 0 44 n off gabon this area is suitable for investigating precipitation changes over central and west africa because of its potential to record input of aeolian and fluvial sediments three magnetozones representing low and high degree of alteration of the primary rock magnetic signals were identified the magnetic signature is dominated by fine grained magnetite while residual haematite prevails in the reduced intervals showing increase in concentration and fine grain size at wet intervals our records also show millennial scale changes in climate during the last glacial and interglacial cycles at the northern location the past 5 5 ka are marked by high frequency oscillations of ti and colour reflectance which suggests aeolian input and hence aridity the southern location remains under the influence of the intertropical convergence zone and thus did not register aeolian signals the millennial scale climatic signals indicate that drier and or colder conditions persisted during the late holocene and are synchronous with the 900 a climatic cycles observed in northern hemisphere ice core records copyright 2009 john wiley sons ltd

plio pleistocene sedimentation on the walvis ridge southeast atlantic dsdp leg 75 site 532 influence of surface currents carbonate dissolution and climate an investigation of the quantitative composition of the coarse 40 m and clay 2 m fraction of hpc 532 dsdp leg 75 in 1300 m water depth on the eastern walvis ridge off southwest africa yielded the following results 1 1 the sediments reflect a complete latest miocene to recent depositional history sedimentation rates vary between 2 3 and 7 8 cm 10 3 years 2 2 preservation of calcium carbonate is subject to strong variations short term 100 000 years and long term about 1 m y cycles in carbonate dissolution have been observed with strongest dissolution occurring during periods of lowered sea level 3 3 upwelling influence from the near coastal upwelling centre has been detected by means of the opal content interglacial periods show high opal contents because the benguela current turned westward at about 20 s and carried opal laden upwelled water to the west sediments from glacial periods however show opal minima besides these short term cyclic variations in opal content long term cycles have been found with maximum upwelling influence in the latest pliocene early quaternary 4 4 each caco3 dissolution minimum maximum is correlated with an opal maximum minimum throughout the sediment sequence 5 5 the oceanographic system off southwest africa remained essentially unchanged since the latest miocene sea level rose and fell periodically on a small and on a large scale and the benguela current flowed southeast northwest and turned to the west at the latitude of site 532 during interglacial periods when sea level was high 6 6 the climate in the near coastal area of southwest africa in the latitude of site 532 has probably been arid throughout the investigated period

upper palaeozoic basins of the british isles caledonide inheritance versus hercynian plate margin processes hypotheses to explain the origin and location of upper palaeozoic sedimentary basins are presented group a basins were those old red sandstone basins whose location and subsidence were controlled by caledonide features including active and remnant fore arc basins midland valley and major transcurrent movements orcadian basin newer granite plutonic magmas in the southern uplands subduction complex post dated subduction and resulted from post collision cratonization processes as yet little understood group b basins were those whose initial positions in space were controlled by palaeo plate factors in particular the location of granitoid plutons but whose subsidence was controlled by active hercynian neoplate processes some group a basins were regenerated by this process midland valley a new hypothesis is presented to account for the origin of a carboniferous rift to sag trend similar to that proven in modern continental margin basins such as the north sea the hypothesis is an adaptation of mckenzie9s lithospheric stretching model some of whose major features are well shown in the carboniferous history of the north and central british isles group b processes were controlled by ligurian bretonic plate consumption in the s brittany massif central vosges areas group c basins in the rheno hercynian zone also owe their location and origin to back arc rifting and continental crustal oceanization processes caused by liguro bretonic subduction

palaeoenvironmental information gained from calcareous dinoflagellates the late quaternary eastern and western tropical atlantic ocean in comparison abstract the environmental preferences of calcareous dinoflagellates have been investigated over the last 140 ka by comparing material from two sediment cores one from the highly productive equatorial divergence of the eastern atlantic ocean and the other from the low productivity western tropical atlantic ocean pronounced differences in palaeoproductivity between the two sediment cores are indicated by high and variable organic carbon accumulation rates in the east in contrast to relatively constant and low values in the west calcareous dinoflagellates show just the opposite pattern high accumulation rates in the west and lower in the east at the equatorial divergence temporal variations of calcareous dinoflagellate and organic carbon accumulation rates show for the most part an inverse relationship high calcareous dinoflagellate content coincides with low organic carbon accumulation rates and vice versa in the investigated region and time interval enhanced production of calcareous dinoflagellates can be correlated to periods of reduced palaeoproductivity probably related to relatively stratified conditions of the upper water column

revised stratigraphic framework of pre westphalian carboniferous petroleum system elements from the outer moray firth to the silverpit basin north sea uk

coal deposition in carbonate rich shallow lacustrine systems the calaf and mequinenza sequences oligocene eastern ebro basin ne spain two main coal bearing sequences developed during the oligocene in the tertiary ebro basin the calaf early oligocene and mequinenza late oligocene coal basins coal deposition took place in shallow marsh swamp lake complexes which sometimes became closed and evolved under warm climatic conditions with fluctuating humidity these shallow lacustrine systems are closely interrelated with the terminal parts of the distributive fluvial systems which spread from the tectonically active ebro basin margins laterally extensive lignite bearing sequences including rather thin lenticular autochthonous and or hypautochthonous coal seams with high ash and sulphur contents characterized coal deposition in the shallow lacustrine systems coal seam geometry which makes them nearly subeconomic resulted from the tectonic instability during basin margin evolution and the sometimes closed arid conditions under which the lacustrine systems evolved high ash and sulphur contents resulted from the inadequate isolation of peat forming environments from clastic influx and from the very low acidity and sometimes high sulphate contents of the lacustrine waters coal exploration in shallow lacustrine sequences similar to those described here must take into account that the spread of coal forming environments and maxima of coal deposition are usually coincident with lake expansions and retraction or shifting of the terminal fluvial zones interrelated with the lacustrine areas

rotational motions of seismic surface waves in a laterally heterogeneous earth a number of recent studies have analyzed seismic rotational data using a relationship between transverse acceleration and rotation rate derived for a homogeneous full space in this study we explore this relationship further theoretically by presenting a full ray theory frt method to simulate rotational motions of fundamental mode seismic surface waves in smooth laterally heterogeneous earth models in the ray picture of wave propagation the vertical component of the rotational rate motion of fundamental mode love waves is obtained by dividing the transverse component of ground acceleration by the love wave local phase velocity beneath the seismic recording station we illustrate the method with examples of theoretical calculations of t 40 sec rotational rate ground motions of fundamental love waves using the crust model crust2 0 combined with the mantle model s20rts for the 25 september 2003 m 8 1 tokachi oki earthquake japan frt rotation synthetics match complete calculations using the spectral element method very well and fit real data reasonably well furthermore we show that the effect of realistic local structure beneath receivers on rotational motions is strong enough to be observable frt calculations could potentially help to determine love wave local dispersion curves and thus to estimate the 1d local shear velocity structure beneath seismic stations from point measurements of rotational rate and acceleration ground motions

controls on modern carbonate preservation in the southern florida straits abstract the water masses in the florida straits and bahamas region are important sources for the northern atlantic surface ocean circulation in this study we analyse carbonate preservation in surface sediments located above the chemical lysocline in the florida straits and bahamas region and discuss possible reasons for supralysoclinal dissolution calcite dissolution proxies such as the variation of the foraminiferal assemblage fragmentation index benthic foraminifera index and resistance index displayed a good preservation in both areas the pteropod species limacina inflata showed very good preservation in sediments of inter platform channels from the great bahama bank providence channel exuma sound above the aragonite lysocline supralysoclinal aragonite dissolution however was observed at two water depth levels 800 1000 m and below 1500 m in the florida straits our observations suggest that the supralysoclinal dissolution in the florida straits is due to the degradation of organic material the presence of antarctic intermediate water aaiw may be a contributing factor for the significant aragonite dissolution in 800 1000 m the comparison of modern preservation patterns of the surface sediments with hydrographical measurements shows that the l inflata dissolution index ldx might be an adequate proxy to reconstruct paleo water mass conditions in an area which is highly saturated with respect to calcium carbonate

late quaternary carbonate sedimentation at the sierra leone rise eastern equatorial atlantic ocean abstract in the eastern equatorial atlantic ocean changes in the concentration of carbonate in late quaternary sediments resulted from reduced production of carbonate in surface waters and increased dilution with non carbonate sediments during glacial maxima during glacial stages production of carbonate in surface water measured as its accumulation rate in shallow undissolved cores decreased by one half the glacial accumulation rate of non carbonate components increased 1 5 to 4 times over holocene values the greatest increases occurred in the deepest cores carbonate dissolution during stages 2 3 and 4 increased the proportion of foraminiferal fragments and decreased the accumulation rate of susceptible species in the deep sites in shallow sites slightly increased dissolution can be detected during stage 3 while greatly increased dissolution occurred during stage 4 bathymetric profiles of foraminiferal fragmentation and accumulation document a shoaling of the foraminiferal lysocline by 1000 m during glacial isotopic stages we present a mass balance model of sediment accumulation for carbonate and insoluble components and from this model we estimate the rate of downslope transport and dissolution of carbonate at the sierra leone rise our results show that during stage 4 the rate of carbonate loss to dissolution was greater than the rate observed today or during other interglacial stages the calculated rates of dissolution for stages 2 and 3 are not significantly different from those calculated for stage 1

δ34s of lower carboniferous anhydrite cumbria and its implications for barite mineralization in the northern pennines recent hydrocarbon exploration in the solway basin has revealed the existence of lower carboniferous paralic sediments which contain numerous discrete anhydrite beds anhydrite s isotope ratios from the easton 1 well are compared with new isotopic data from barite mineralization that occurs along the faulted southern margin of the northumberland solway basin and published data from the northern pennine orefield similarities betw een the 34 s of anhydrite and barites from major mines at haydon bridge and the alston district of the northern pennine orefield supports a lower carboniferous marine sulphate source for mineralization at these sites identification of extensive evaporite deposits hi the solway basin resolves several longstanding problems associated with mineralization hi the northern pennines including the source of barite sulphate and the origin of hypersaline mineralizing fluids in an earlier investigation of the s isotope geochemistry of carboniferous hosted barite mineralization in and around the alston district of thenothern pennine orefield npo fig 1a solomon et al 1971 drew attention to the similarity between the 34 s of lower carboniferous marine sulphate and the sulphur isotopic composition of barite deposits a model for barite mineralization was proposed in which deep circulating bacl 2 brines mixed with shallow et al 1971 is consistent with aspects of barite mineralization more recent studies of the evolution of pore fluid geochemistry in sedimentary basins land 1987 hanor 1994a b argue against a marine connate origin for the sulphate component

late pleistocene glacial interglacial changes in planktonic foraminiferal biofacies and carbonate dissolution patterns in the vema channel abstract a suite of closely spaced giant gravity cores between 1500 and 4500 m on the east flank of the vema channel was examined to determine variations in carbonate preservation for the last two interglacials present day and isotopic stage 5e and glacials isotopic stages 2 and 6 as had been previously observed present day sediment dissolution facies i e foraminiferal and sedimentary lysoclines are closely related to hydrographic changes in the major water masses which occupy the vema channel nadw and aawb carbonate preservation is systematically better during interglacials than during glacials throughout the entire depth range of the transect the positions of the foraminiferal and sedimentary lysoclines however appear to have remained relatively constant through the glacial interglacial cycles of the last 140 000 years the lack of any substantial vertical movement of these dissolution facies during the late pleistocene suggests that there has not been any significant change in the position of the water masses flowing through the vema channel during this time interval however the overall poorer preservation of glacial sediments indicates that the glacial equivalents of both nadw and aabw were more corrosive to carbonate than at present this overall increase in dissolution can most simply be attributed to a general stagnation of deep and bottom flow through this region during glacial episodes

carbonate dissolution and abyssal hydrography in the atlantic ocean abstract surface sediment samples from two regions in the eastern atlantic angola basin and cape verde basin and two regions in the western atlantic brazil basin and vema channel were examined to evaluate the relationship among carbonate dissolution abyssal hydrography and carbonate chemistry of the water column at each of these locations the position of the lysocline was determined carbonate saturation 1 was calculated and major deep water mass boundaries were identified as previously observed the correlation among these variables is strikingly different between the eastern and western atlantic in the vema channel and the brazil basin there is a first order correlation among the position of the lysocline the benthic thermocline aabw nadw boundary and the transition from saturation to undersaturation with respect to carbonate this relationship breaks down in the eastern atlantic where there is no noticeable benthic thermocline and the lysocline occurs significantly deeper than the saturation undersaturation transition