breakup of the newfoundland iberia rift abstract the newfoundland iberia rift is considered to be a type example of a non volcanic rift key features of the conjugate margins are transition zones tzs that lie between clearly continental crust and presumed normal penrose type oceanic crust that appears up to 150 180 km farther seaward basement ridges drilled in the iberia tz consist of exhumed serpentinized peridotite of continental affinity consistent with seismic refraction studies although the boundaries between continental crust and the tzs can be defined with relative confidence there are major questions about the position and nature of the change from rifting to normal sea floor spreading at the seaward edges of the tzs notably drilling of presumed oceanic crust in the young m series anomalies to investigate and potentially resolve these conflicts we analysed the tectonic history and deep pre cenomanian stratigraphy of the rift using seismic reflection profiles and drilling results rifting occurred in two main phases late triassic earliest jurassic and late jurassic early cretaceous the first phase formed continental rift basins without significant thinning of continental crust the second phase led to continental breakup with extension concentrated in three episodes that culminated near the end of berriasian hauterivian and aptian time the first two episodes appear to correlate with separation of continental crust in the southern and northern parts of the rift respectively suggesting that the rift opened from south to north in a two step process the third episode persisted through barremian and aptian time we suggest that during this period there was continued exhumation of subcontinental mantle lithosphere at the plate boundary and that elevated in plane tensile stress throughout the rift caused intraplate extension primarily within the exhumed mantle this rifting may have been interrupted for a time during the barremian when melt was introduced from the southern edge of the rift by plume magmatism that formed the southeast newfoundland ridge and j anomaly ridge and the conjugate madeira tore rise we propose that the rising asthenosphere breached the subcontinental mantle lithosphere in latest aptian earliest albian time initiating sea floor spreading this resulted in relaxation of in plane tensile stress i e a pulse of relative compression that caused internal plate deformation and enhanced mass wasting this aptian event produced a strong rift wide reflection that is unconformably onlapped by post rift sediments that were deposited as a stable sea floor spreading regime was established although previously considered to be a breakup unconformity associated with separation of continental crust the event instead marks the final separation of the subcontinental mantle lithosphere our analysis indicates that interpretation of tectonic events in a non volcanic rift must consider the rheology of the full thickness of the continental lithosphere in addition to spatial and temporal changes in extension that may occur from segment to segment along the rift

links between southwestern tropical indian ocean sst and precipitation over southeastern africa over the last 17 kyr abstract time series of mg ca ba ca and 18o analyzed in tests of surface dwelling planktonic foraminifer globigerinoides ruber from two marine sediment cores recovered in the mozambique channel off the zambezi river southwestern tropical indian ocean reveal climate variability over the last 17 kyr analysis of samples collected from the water column of the mozambique channel validates that mg ca in g ruber reflects calcification temperatures at 0 30 m water depth and that the surface water of the southwestern indian ocean is very sensitive to dissolved ba input from adjacent rivers foraminiferal ba ca and mg ca time series are used to reconstruct hydrological and thermal changes over southeastern african and southwestern tropical oceans the mg ca based sea surface temperature sst estimates indicate that the thermal evolution of the tropical southwestern indian ocean followed within age model uncertainties climate changes over antarctica the trend of the sst record is marked by a gradual warming from 24 7 0 6 c at 17 0 0 2 kyr bp to 26 4 0 3 c at 10 11 kyr bp interrupted by two prominent coolings of 1 5 0 2 c and 1 c centered at 15 0 1 kyr bp and 13 4 0 2 kyr bp respectively declining ssts in the early holocene reach their minimum 25 c at 8 7 0 2 kyr bp and give way to stable thermal conditions over the middle and late holocene the ba ca record indicates that the zambezi basin experienced relatively wet conditions during the early phase of the last deglaciation bolling allerod and the early holocene these wet phases coincide with an increase of sst in the mozambique channel in contrast relatively dry conditions throughout the middle and late holocene epoch are accompanied by relatively cold mozambique channel surface water these shifts likely reflect a response to meridional shifts of the austral westerlies and subtropical front these hypothesized shifts would have modulated the advection of cold southern ocean water into the mozambique channel changes in sst in the mozambique channel and possible resultant changes in the zonal gradient in the tropical indian ocean in turn had a strong impact on the precipitation over southeastern africa

influence of cone morphology on dykes stromboli italy abstract the island of stromboli represents the emerged part of a 2 6 km high composite volcano elongated in a ne direction over the period 100 13 ka bp the morphological evolution of the volcano was characterised by a series of summit caldera collapses between major building phases from 13 ka bp onward a series of large lateral collapses occurred northwestwards in one sector of the cone the results of the field study of the total 94 dyke population is discussed in this paper they show that during the last 100 ka the majority of dykes were injected with a nnegssw to ene wsw strike along a ne sw weakness zone crossing the volcano summit this is interpreted as a volcanic rift the geometry of which is controlled by regional tectonic stresses dykes injected prior to 13 ka bp at lower altitudes are generally steeper than those injected at higher elevations after 13 ka bp dykes were injected along the ne sw weakness zone and parallel and close to the margins of the earliest sector collapse at dips of 20 80 inclined towards the collapse depression i suggest that this is linked to unbuttressing of the collapse depression or to seaward gravity instability of the depression infill deposits extensive emplacement of long dykes along the ne sw weakness zone occurred only when the volcano regained a conical shape some of the dykes emplaced close to the original surface of the cone bent to assume a dip direction parallel to the local slope i propose that this local change of dyke geometry can be explained by the direct influence of the free surface of the cone leading to a rotation of the least principal stress which assumes an orientation perpendicular to the slope

late quaternary paleotemperatures derived from a speleothem from cango caves cape province south africa abstract an oxygen isotope temperature record over a large part of the past 30 000 yr has been obtained for the southern cape province of south africa by combining data on the isotopic composition of a stalagmite from a deep cave with that of a confined groundwater aquifer in the same region results show that temperatures during the last glacial maximum were on average about 6 c lower than those today with peaks up to 7 c lower a detailed analysis of the past 5000 yr suggests multiple fluctuations with generally lower temperatures 1 2 c around 4500 and 3000 yr b p the carbon isotopic composition of the stalagmite indicates significant vegetation changes between the late pleistocene and today and also during the second half of the holocene

dyke intrusion into a pre existing joint network the aiguablava lamprophyre dyke swarm catalan coastal ranges abstract a structural analysis has been performed in the upper permian lamprophyric dyke swarm of aiguablava costa brava ne iberia emplacement of sub vertical dykes is related to the presence of a widespread joint network mostly developed during the cooling and decompression of the late variscan leucogranitic host rocks the joint pattern consists on multiple sub vertical joint sets among which two orthogonal sets at n23 and n113 are predominant a sub horizontal set is also prominent the sub vertical dykes have a mean n100 n125 trend which corresponds to the trend of one of the main joint sets however dyke segmentation is noticeable at the dm to cm scale and this is inferred to be related to dyke propagation and emplacement along the variably oriented pre existing joints a mean robust sub horizontal nne ssw net dilation direction was measured from matching dyke jogs markers in the host rock and analysis of maximum dyke thicknesses and this is in line with the minimum principal stress axis 3 derived from a three dimensional paleostress analysis from dyke orientations the inferred maximum principal stress axis 1 is sub vertical indicating that dykes intruded under conditions of tectonic extension furthermore a mohr construction allowed calculation of the stress ratio 0 29 close to a prolate stress ellipsoid and a driving pressure ratio r 0 27 which corresponds to a magmatic pressure almost equal to the intermediate principal stress axis 2 it is inferred that many of the pre existing joint sets were exploited by the magma the wnw ese joint set normal to 3 being the most favorable for dyke emplacement the present study highlights the structural control of a pre existing fracture network on emplacement of the aiguablava lamprophyres in the upper crust during late permian nne ssw brittle extension

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

an abrupt change in the african monsoon at the end of the younger dryas 1 high resolution studies of variations in the elemental and stable carbon and nitrogen isotope composition of organic matter in cores from lakes malawi tanganyika and bosumtwi tropical africa indicate an abrupt change in the wind driven circulation of these lakes that within the limits of available chronologies was contemporaneous with the end of the younger dryas in the northern hemisphere the change was also coincident with shifts in surface winds recorded in cores from off the west and northeast coasts of africa a range of other proxies indicate that these changes in wind regime were accompanied by a marked increase in precipitation in the northern tropics africa south of 5 10 s on the other hand initially suffered drought conditions together the evidence suggests an abrupt northward translation of the african monsoon system at circa 11 5 0 25 ka b p the data assembled here contribute to a growing body of work showing that the younger dryas was a major climatic excursion in tropical africa furthermore they add substance to recent suggestions that climatic events in the southern hemisphere may have played a significant role in the abrupt demise of the younger dryas

what controls sheet intrusion in volcanoes structure and petrology of the stromboli sheet complex italy abstract a multidisciplinary study has been conducted on 109 intrusive sheets of stromboli the relation between sheet injection conditions with the magmatic and structural variations of the volcano and the parameters governing the preferential intrusion geometry inside the volcano in a time perspective have been determined during its subaerial activity the last 100 ka stromboli experienced periods of extrusive growth and sheet intrusions alternated to caldera and lateral collapses of the nw sciara del fuoco flank the sheet intrusions similar to the extrusive rocks span a large compositional range from calc alkaline to potassic through high k calc alkaline and shoshonitic series the most evolved compositions of the effusive rocks however have not been found as intrusions whereas some mafic and basic magmas of sheets were never erupted the repeated time change of location of the intrusions from strombolicchio to the ne sw trend passing trough the inferred paleostromboli summit cone and the southern flank could represent the expression of the shift of the magma chamber towards the southeast and the subsequent onset of a clear ne sw elongated magma chamber located along the main stromboli weakness zone the stromboli evolution in the last 100 ka has been characterized by the persistent n 10 55 e intrusion direction which reflects the influence of the edifice s state of stress on the magma feeding paths after 13 ka ago sheets mainly intruded along to the sector collapse scarps in a circum amphitheatre geometry which has been demonstrated to be influenced by the new cone morphostructure and not by different magma rheological characters

structural analysis of dyke emplacement directions as an aid to palaeomagnetic studies an example from northern chile summary a major problem in palaeomagnetic studies of intrusive rocks lies in determining whether or not such rocks have been subjected to post emplacement tilting structural analysis of dyke emplacement directions can be used to show the current attitude of the extension direction for the dyke swarm if the original extension direction at the time of emplacement can be deduced from geological evidence this then provides a field test for post emplacement tilting of the dyke swarm and its host rocks in the example given from northern chile we were able to make a palaeomagnetic study of and structurally analyse three successively younger dyke swarms that intrude similarly younging plutons all three dyke swarms yielded extension directions close to horizontal but with markedly diverent azimuths it is argued that the similarity in the plunge of the extension directions cannot be coincidental and that the dykes and their host plutons have not suvered significant post emplacement tilting this simple technique should be widely applicable in the assessment of post emplacement tilting of dykes in palaeomagnetic studies

holocene paleo climatic record from the south african namaqualand mudbelt a source to sink approach variations in the sediment input to the namaqualand mudbelt during the holocene are assessed using an integrative terrestrial to marine source to sink approach geochemical and sr and nd isotopic

the dilation direction of intrusive sheets abstract where a dilation dike or sill cuts two non parallel planar features the direction of dilation can be determined by 1 orthographic projection 2 equal area projection schmidt net or 3 analytical geometry

earth s precession cycle and quaternary climatic change in tropical africa high abundances of the freshwater diatom melosira spp reflecting eolian input from dry lake beds in tropical africa occur in deep sea sediments of the equatorial atlantic at discrete times during the late quaternary1 2 we report here an approximately 260 kyr record of melosira accumulation in an equatorial atlantic sediment core and demonstrate significant influence of the earth s precessional cycle on the climate of tropical africa

dike surface lineations as magma flow indicators within the sheeted dike complex of the troodos ophiolite cyprus mesoscopic flow lineations and anisotropy of magnetic susceptibility ams have been measured for dikes within the cretaceous age troodos ophiolite with the goal of comparing the direction of initial magma flow through dike conduits immediately following crack propagation with that of flow of subsequent magma emplaced during later stages of dike growth dike margin indicators of flow include cusp axes and elongate vesicles found high in the ophiolite pseudostratigraphy and ridge and groove structures termed hot slickenlines found throughout the complex a unique flow direction is determined where elongate vesicles near dike margins display imbrication with respect to the margin significant changes in vesicle elongation directions across dikes likely indicate either changes in magma flow direction after dike propagation or back flow of magma during the waning stages of intrusion surface lineations generally lie subparallel to the direction of flow inferred from ams determinations on cores within 5 cm of dike margins surface lineations also lie subparallel to the long axis e1 of the orientation ellipsoid defined by long axes of groundmass plagioclase phenocrysts measured in sections from ams cores correlation of surface lineations with interior indicators of flow ams plagioclase trachytic texture indicate that the surface features are good proxies for grain scale magma flow directions during dike propagation in troodos dikes orientations of surface flow features in the dikes of the troodos ophiolite indicate an approximately equal mix of subhorizontal to near vertical magma flow contradicting the paradigm of primarily vertical flow of magma beneath continuous axial magma chambers at oceanic spreading centers our data are consistent with a model of magma emplacement both vertically and horizontally away from isolated magma chambers beneath axial volcanoes spaced along a ridge crest

fracture propagation associated with dike emplacement at the skaergaard intrusion east greenland abstract extensive magmatic activity including several episodes of dike emplacement was associated with early tertiary continental rifting in eastern greenland exposures of the skaergaard intrusion host a large number of these dikes as well as a variety of hydrothermal veins one vein set has a characteristic outcrop expression and is filled with silica rich chlorites relative timing constraints as well as the distribution and geometric relations of these veins relative to the mafic dikes indicate that at least some of these fractures formed during the emplacement of the dikes that cut the intrusion calculations based on elastic theory permit modeling of dike geometries observed in the field and prediction of fracture geometries that could be associated with the inflation of these dikes extensional fractures may form in the area ahead of the dike termination for a variety of loading conditions the predicted width to length ratio for the dike as well as the size of the predicted fracture zone increases with increasing magma pressure within the dike and or increasing differential between the remote principal stresses for dike geometries similar to those observed in the field the predicted fracture zone is roughly elliptical in cross section and is centered in front of the dike termination the size of the zone perpendicular to the dike trend varies from less than one meter to several meters field observations indicate that dike parallel fractures are locally offset normal to the dike margin by distances of a few centimeters to a few meters our analysis implies that at least some of these fractures initiated and propagated ahead of the dikes as they were emplaced the cooling of these dikes initiated localized hydrothermal systems that formed the vein minerals currently filling the fractures

new ages for the post howiesons poort late and final middle stone age at sibudu south africa abstract optically stimulated luminescence osl measurements are reported for single grains of quartz from deposits within sibudu rock shelter such measurements enable rejection of unrepresentative grains and application of the finite mixture and central age models to obtain the most reliable age estimates three types of single grain equivalent dose de distributions were observed one sample represented a single dose population three samples indicated mixing between iron age ia and middle stone age msa deposits and 10 samples in addition to the three mixed samples showed scattered distributions the latter type resulted from differences in the beta dose received by individual grains for these samples the beta doses were modelled and adjusted accordingly ages for the 14 samples collected from msa deposits post dating the howiesons poort hp resulted in three age clusters which are stratigraphically consistent with the three informally named cultural phases at sibudu namely the post hp late msa and final msa weighted mean ages of 58 5 1 4 ka 47 7 1 4 ka and 38 6 1 9 ka were calculated for these phases respectively the three phases were separated by two occupational hiatuses with durations of 10 8 1 3 ka and 9 1 3 6 ka we hypothesise that the punctuated presence of humans at sibudu was determined by large scale fluctuations in climate during oxygen isotope stage ois 3 which resulted in alternating wet and dry periods phases of occupation correspond to wet periods when fresh water was available in the tongati river whereas intervals of site abandonment correspond to dry periods when people were forced to migrate in search of a reliable source of fresh water where people migrated to remains unresolved

siliceous microfossils as late quaternary paleo environmental indicators at braamhoek wetland south africa this thesis contributes with information on past climate and environmental changes in south africa s summer rainfall region the study is based on multi proxy analyses on wetland peat cores and analyses of stable isotope composition 13c 18o and wood anatomy in cross sections from subtropical trees breonadia salicina the peat archive covers the last 16 ka ka 1000 cal yrs bp and was analysed in terms of fossil pollen charcoal diatoms phytoliths and stable isotope composition the peat record infers relatively wet climate conditions at c 13 7 12 8 ka 10 5 9 5 ka and 2 5 0 5 ka and drier conditions at c 16 13 7 ka 12 8 10 5 ka and during mid holocene tentatively cooler late pleistocene temperatures shifted towards warmer after c 9 5 ka the study of b salicina demonstrates the paleo climatic value of subtropical trees despite absence of annual tree rings an age model was constructed from radiocarbon dating and calibration by wiggle matching 13c in b salicina shows a co variation with annual rainfall amounts suggesting that it may be considered a regional climate proxy 18o is mainly influenced by local factors but acts as a useful complement when interpreting 13c together with other regional high resolution records the 600 year long 13c record suggests dry climate conditions in northern south africa during the 1700s and mid 1500s ad inferred climate and environmental changes are suggested being a response to expansion contraction and latitudinal shifts of the tropical subtropical and mid latitude atmospheric circulation cells an observed inverse humidity pattern between southern and equatorial africa suggests that enso like teleconnections may be a possible forcing mechanism in a decadal to centennial time perspective

crustal structure of a nonvolcanic rifted margin east of newfoundland a detailed seismic refraction study was undertaken of the rifted continental margin southeast of the grand banks of newfoundland along a preexisting deep multichannel seismic reflection profile the primary objectives were to determine the topography of moho across the margin to detect any evidence for crustal underplating and to determine the position of the continent ocean boundary data were obtained from nine ocean bottom seismometers deployed along the profile with an array of six 1000 inch3 air guns as the source two additional refraction lines were shot parallel to structure over the continental slope the resultant velocity model is well constrained and consistent with the observed gravity the crust thins abruptly beneath the continental slope to a major structural transition identified as the continent ocean boundary there is no significant magmatic underplating of the thinned continental crust seaward of the transition the seismic velocity structure is characterized by a 50 km wide zone of intermediate velocity 7 2 7 6 km s beyond this is a thin 3 5 km crust with low velocity 4 5 5 km s and high gradient over mantle with a velocity of 7 7 km s increasing to 8 0 km s the zone of intermediate velocity is interpreted to be highly serpentinized mantle material beneath a very thin crust suggesting little or no magmatic activity during and immediately after rifting this interpretation is consistent with results from adjacent and conjugate margins

subaerial submarine evidence of structures feeding magma to stromboli volcano italy and relations with edifice flank failure and creep abstract structural field data including parameters of 109 sheets strike mostly n10 55 e average dip angle mostly 70 90 average thickness two peaks at 1 2 m and 4 2 m and of 14 eruptive fissures and vents as well as bathymetric and numerical data suggest that stromboli experienced the development of a volcanic rift zone across the cone summit with a tendency to widen towards the lower submarine flanks during the last 100 ka inside this rift zone intrusive sheets mostly strike ne and become more abundant more steeply dipping and thicker on approaching the rift axis this rift persistence reflects the edifice s state of stress with a nw se horizontal least principal stress on the magma intrusion paths after 13 ka ago sheets mainly intruded with a horseshoe shaped geometry in plan view along the boundaries of the northwestern unstable volcano flank where four main lateral collapses occurred during the last 13 ka they also intruded with a ne strike across the volcano summit and the northeastern volcano flank the horseshoe shaped geometry is influenced by the lateral creep of the volcano flank which provides space for intrusion along the transtensional boundaries of the unstable sector where thinner sheets were emplaced when the collapse depression was filled up by new deposits ne striking thicker dykes emplaced across the northwestern volcano flank indicating a rapid re establishment of regional tectonic forces across the cone unbuttressing due to the present sciara del fuoco depression and ongoing flank creeping can account for intrusions also inside the sciara del fuoco the latter in 2007

dissolved gas paleotemperatures and 18o variations derived from groundwater near uitenhage south africa abstract under the near ideal hydrologic conditions provided by the uitenhage artesian aquifer reliable estimates of paleotemperatures were obtained by measurement of the dissolved n2 and ar in groundwater confidently dated in the range 28 000 yr b p to the present using 14c the mean annual air temperature in this area during the last glaciation is calculated to have been on average 5 1 2 c lower than during the holocene the change in the 18 o 16 o ratio of the groundwater corrected for changes in ocean water amounted to 0 4 per c

west african paleoclimates during the last climatic cycle inferred from an atlantic deep sea pollen record abstract pollen studies of marine sediments from atlantic deep sea core v22 196 13 50 n 18 57 w 3728 m water depth are used to reconstruct paleoclimates of north tropical west africa since 140 000 yr b p high concentration of pollen mainly from saharan and arid littoral zones suggests a strengthened tradewind circulation since ca 60 000 yr b p that became even stronger after 40 000 yr b p and reached a maximum 17 000 yr b p periods of eolian transport of pollen to the atlantic occurred about 94 000 and 105 000 yr b p and during termination ii conversely high relative values of pollen from sudanian and guinean zones and from mangrove and freshwater vegetation coincident with maxima of dinocyst concentration are interpreted as reflecting both strong fluvial inputs and the expansion of humid vegetation on the adjacent continent during wet periods dated between 140 000 and 118 000 105 000 and 96 000 92 000 and 73 000 52 000 and 44 000 yr b p and 12 000 yr b p and the holocene the strong correlation of these results from the eastern tropical atlantic with those from the arabian sea corroborates fluctuations of monsoon climate

the velocity structure of the britt domain southwestern grenville province from laboratory and refraction experiments the britt domain in the southwestern grenville province of the canadian shield is believed to be an exposure of high grade upper amphibolite facies mid crustal rocks of predominantly granitic and granodioritic composition a 270 km refraction line was conducted by lithoprobe across the britt domain and the grenville front tectonic zone to the north in order to determine the deep velocity structure under the region this data set demonstrates a uniform velocity structure to a depth of 15 km in the central britt domain with near surface p and s wave velocities of 6 15 and 3 55 km s respectively and linear vertical gradients at depth of 0 02 and 0 01 s 1 respectively the data also show that the grenville front tectonic zone is strongly anisotropic at shallow depths to determine the acoustic properties of rocks from the britt domain 80 velocity samples representing different lithologies in this area were measured at confining pressure up to 600 mpa these studies show that p wave velocities at 600 m

orbital forcing of climate over south africa a 200 000 year rainfall record from the pretoria saltpan late pleistocene variations in rainfall in subtropical southern african are estimated from sediments preserved in the pretoria saltpan a 200000 year old closed basin crater lake on the interior plateau of south africa we show that south african summer rainfall covaried with changes in southern hemisphere summer insolation resulting from orbital precession as predicted by orbital precession geometry berger 1978 this south african record is out of phase with north african palaeomonsoon indices street and grove 1979 rossignol strick 1983 mcintyre et al 1989 the amplitude of the rainfall response to insolation forcing agrees with climate model estimates prell and kutzbach 1987 these results document the importance of direct orbital insolation forcing on both subtropical north and south african climate as well as the predicted antiphase sensitivity to precessional insolation forcing

water level fluctuations of lake tanganyika in phase with oceanic changes during the last glaciation and deglaciation there has been considerable controversy about the magnitude of fluctuations of the levels of lake tanganyika the earth s second deepest lake 1 470 m following the discovery of submerged valleys extending down to 550 m below present lake levels1 these fluctuations register changes in the precipitation evaporation evapotranspiration ratio in a large equatorial tropical area of catchment south of the equator here we report new palaeohydrological data back to 40 kyr bp from carbon dating of the total organic matter in two diatomaceous cores the results constrain the vertical lake level fluctuations more than has hitherto been possible2 5 and show that the fluctuations from 26 kyr bp are correlated with changes in global sea level and ice volume surpris ingly fluctuations seem to be in phase with those of the african lakes north of the equator which are clearly linked to the milankovitch mechanisms

interface inversion using broadside seismic refraction data and three dimensional travel time calculations a procedure has been developed to interpret densely sampled broadside seismic refraction data recorded from a large air gun array first arrival travel times are inverted to find the structure on an interface beneath the shot line travel times are calculated for three dimensional velocity models using a rapid finite difference algorithm adapted to allow variable sampling of the model and the determination of rays a simple inversion parameterization eliminates the need for matrix inversion the complete inversion procedure is computationally rapid yet allows the determination of detailed three dimensional structure broadside refraction data recorded in the queen charlotte basin offshore western canada during a multichannel reflection experiment are used to demonstrate the procedure the data are inverted for the basement interface beneath the shot line defining a rapidly varying thickness of sedimentary basin fill the results of the inversion stimulate a reinterpretation of the reflection data and identify a new major basement fault structure out of the plane of the reflection section is determined including the strike of the fault and other nearby features

deep crustal structure beneath a rifted basin results from seismic refraction measurements across the jeanne d arc basin offshore eastern canada a crustal seismic refraction experiment was conducted across the south jeanne d arc basin one of the rifted sedimentary basins on the grand banks offshore eastern canada that developed in mesozo

late quaternary dynamics of southern africa s winter rainfall zone abstract variations in the nature and extent of southern africa s winter rainfall zone wrz have the potential to provide important information concerning the nature of long term climate change at both regional and hemispheric scales positioned at the interface between tropical and temperate systems southern africa s climate is influenced by shifts in the intertropical convergence zone the westerlies and the development and position of continental and oceanic anticyclones over the last glacial interglacial cycle substantial changes in the amount and seasonality of precipitation across the subcontinent have been linked to the relative dominance of these systems central to this discussion has been the extent to which the region s glacial climates would have been affected by expansions of antarctic sea ice equatorward migrations of the westerlies more frequent intense winter storms and an expanded wrz this paper reviews the developing body of evidence pertaining to shifts in the wrz and the evolution of ideas that have been presented to explain the patterns observed dividing the region into three separate axes along the western and southern margins of the continent and across the interior into the karoo and the kalahari a range of evidence from both terrestrial sites and marine cores is considered and potential expansions of the wrz expansions are explored despite the limitations of many of the region s proxy records a coherent pattern has begun to develop of a significantly expanded wrz during phases of the last glacial period with the best documented being between 32 17 ka while more detailed inferences will require the recovery and analysis of longer and better dated records this synthesis provides a new baseline for further research in this key region

from rifting to passive margin the examples of the red sea central atlantic and alpine tethys abstract evolution of the red sea gulf of suez and the central atlantic rift systems shows that an initial transtensive rifting phase affecting a broad area around the future zone of crustal separation was followed by a pre oceanic rifting phase during which extensional strain was concentrated on the axial rift zone this caused lateral graben systems to become inactive and they evolved into rift rim basins the transtensive phase of diffuse crustal extension is recognized in many intra continental rifts if controlling stress systems relax these rifts abort and develop into palaeorifts if controlling stress systems persist transtensive rift systems can enter the pre oceanic rifting stage during which the rift zone narrows and becomes asymmetric as a consequence of simple shear deformation at shallow crustal levels and pure shear deformation at lower crustal and mantle lithospheric levels preceding crustal separation extensional denudation of the lithospheric mantle is possible progressive lithospheric attenuation entails updoming of the asthenosphere and thermal doming of the rift shoulders their uplift provides a major clastic source for the rift basins and the lateral rift rim basins their stratigraphic record provides a sensitive tool for dating the rift shoulder uplift asymmetric rifting leads to the formation of asymmetric continental margins corresponding in a simple shear model to an upper plate and a conjugate lower plate margin as seen in the central atlantic passive margins of the united states and morocco this rifting model can be successfully applied to the analysis of the alpine tethys palaeo margins such as rif and the western alps

holocene palynology and palaeoenvironments in the savanna biome at tswaing crater central south africa abstract a radiocarbon dated pollen and microscopic charred particle record from the holocene section of the tswaing crater in the savanna biome of south africa give new evidence for environmental changes during the period c 9400 1800 cal years bp pollen grains are scarce or absent in layers dating from before 9400 cal years bp but deposits rich in pollen occur in overlying layers the section dated between 9400 cal years bp and c 7200 cal years bp contains grass asteraceae and dry savanna pollen types that suggest fluctuating but generally dry moisture conditions later between c 7200 and 1800 cal years bp broad leaved savanna woodland elements and local swamp pollen indicate relatively stable vegetation and wetter mildly fluctuating climatic conditions which is consistent with previously published biomarker analysis between c 6200 and 5500 cal years bp the numbers of charred particles increased slightly this indicates burning activity which can probably be attributed to dry season ignition of denser fuel under relatively moist conditions a decrease of local swamp pollen between c 3600 and 3500 cal years bp suggests that conditions became briefly drier again as pollen of woody elements declined in favour of open grassland pollen a comparison between the tswaing pollen profile and various other sequences within the central interior of south africa suggests generally similar conditions over the central interior of the sub continent during the holocene deviating from sequences further afield along the coastal areas of southern africa between 9400 cal years bp and ca 7200 cal years bp the western and southern coasts were probably controlled by different atmospheric and oceanic circulation regimes under the influence of a strong westerly winter rain system while the north eastern area where tswaing is situated experienced weaker precession and less summer rain from the intertropical convergence zone

control of insolation on stalagmite growth rainfall and migration of the tropical rain belt in northern namibia over the last 100 kyr as suggested by a rare mis 5b 5c stalagmite from dante cave abstract dating by the 230th method indicates that stalagmite danf from dante cave in northern namibia in the summer rainfall zone srz of southern africa formed about 92 ka at the boundary of marine isotope stages mis 5b and 5c in this dominantly semiarid zone stalagmite growth may be evidence of a relatively wetter period and trends in danf s mineralogy and its c o and u isotope ratios further support formation in a period wetter than those before or after its formation danf s time of formation at 92 ka like other wet periods in the srz of southern africa over the most recent 100 kyr coincides with a maximum in january insolation at 30 s that brought the srz and more generally the tropical rain belt farther south than before or after

late quaternary highstands at lake chilwa malawi frequency timing and possible forcing mechanisms in the last 44 ka the extensive shoreline deposits of lake chilwa southern malawi a shallow water body today covering 600 km2 of a basin of 7500 km2 are investigated for their record of late quaternary highstands osl dating applied to 36 samples from five sediment cores from the northern and western marginal sand ridges reveal a highstand record spanning 44 ka using two different grouping methods highstand phases are identified at 43 7 33 3 ka 26 2 21 0 ka and 17 9 12 0 ka total error method or 38 4 35 5 ka 24 3 22 3 ka 16 2 15 1 ka and 13 5 12 7 ka finite mixture model age components with two further discrete events recorded at 11 01 0 76 ka and 8 52 0 56 ka highstands are comparable to the timing of wet phases from other basins in east and southern africa demonstrating wet conditions in the region before the lgm which was dry and a wet lateglacial which commenced earlier in the southern compared to northern hemisphere in east africa we find no evidence that wet phases are insolation driven but analysis of the dataset and gcm modelling experiments suggest that heinrich events may be associated with enhanced monsoon activity in east africa in both timing and as a possible causal mechanism

dune activity as a record of late quaternary aridity in the northern kalahari new evidence from northern namibia interpreted in the context of regional arid and humid chronologies abstract sediments from presently vegetated linear dune ridges in the caprivi strip of northern namibia are optically dated to assess the timing of dune building phases and aridity in the late quaternary the dunes have been constructed from sediments likely to have been initially transported into the area by fluvial processes dune sediments do not preserve obvious evidence of hiatuses in deposition in the dated period 48 121 ka but continuous deposition and therefore continuous aridity is considered unlikely given differences in dated phases compared with chronologies from western zimbabwe to the southeast and western zambia to the north that include ages derived from the same equivalent sampling depths laboratory experiments provide evidence that dune sediments have not been bioturbated since deposition such that sample palaeodoses determined from different sampling depths are a true reflection of the duration of sediment burial independent chronologies from cave sediments provide evidence that humid episodes have occurred in the region within the dated range of dune construction it is concluded that dune construction in the late quaternary has been punctuated that the preserved record reflects the attributes of the aeolian processes that affect linear dune development and that the late quaternary record of dune building in the middle and northern kalahari was spatially complex

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

seismic imaging of broken bridges linking seismic to outcrop scale investigations of intrusive magma lobes three dimensional seismic datasets have provided unrivalled insights into magma flow within sub volcanic systems one of the key revelations is that sills appear to be constructed of a series of discrete magma lobes that form during the emplacement of magma into host rock we focus on a large sill within the faroe shetland basin north atlantic that is well imaged on seismic data and identify the presence of broken bridges within the sill developed between elongate magma lobes and reveal for the first time in three dimensions the development of broken bridges critically by relating the imaged structures to key outcrop scale examples we confirm that bridge and broken bridge structures are oriented perpendicular to the magma flow direction this work thus demonstrates a key link that can be made between seismic scale investigation of intrusions and sub seismic outcrop scale processes highlighting the seemingly scale invariant nature of the magmatic emplacement process

multi process late quaternary landscape evolution modelling reveals lags in climate response over small spatial scales landscapes evolve in complex non linear ways over quaternary timespans integrated geomorphological field studies usually yield plausible hypotheses about timing and impact of process activity landscape evolution models lems have the potential to test and falsify these landscape evolution hypotheses despite this potential lems have mainly been used with hypothetical data and rarely to simulate the evolution of an actual landscape in this paper we use a lem lapsus landscape process modelling at multi dimensions and scales to explore if it is possible to test and falsify conclusions of an earlier field study on 50 ka landscape evolution in okhombe valley kwazulu natal south africa in this lem five landscape processes interact without supervision water driven erosion and deposition creep solifluction biological weathering and frost weathering calibration matched model results to three types of qualitative fieldwork observations individual process activity over time relative process activity over time and net landscape changes over time results demonstrate that landscape evolution of the okhombe valley can be plausibly simulated a particularly interesting and persistent feature of model results are erosional and depositional phases that lag climatic drivers both by decades and by several ka within a few hundred meters the longer lag has not been reported for this spatial scale before and may be an effect of slow landscape soil vegetation feedbacks the combined modelling and fieldwork results allow a more complete understanding of these responses to climate change and can fill in hiatuses in the stratigraphical record suggestions are made for methodological adaptations for future lem studies

a simple method for the determination of the dilation direction of intrusive sheets abstract it is shown that the occurrence of offsets of various orientations along the contacts of an intrusive sheet permits the rapid establishment of the net dilation direction for the sheet the application of the method to some dykes on arran shows that oblique opening of a fissure was sometimes accompanied by a vertical component of opening the technique provides a tool for the analysis of patterns of crustal displacement associated with dyke intrusion

crustal structure beneath orphan basin and implications for nonvolcanic continental rifting a wide angle seismic profile was acquired across the northeast newfoundland margin seaward to orphan knoll the profile is complemented by existing multichannel reflection data two online deep wells and other deep seismic reflection and refraction lines modeling of data from 15 ocean bottom seismometers provides the seismic velocity structure for a significant portion of the 400 km wide stretched continental crust on this margin prerift metasedimentary rocks have a topographic relief of up to 5 km with a velocity of 5 2 km s increasing to 5 9 km s unaltered crystalline crust below the metasedimentary section has a velocity range of 6 1 6 5 km s most of the lower crust landward of orphan knoll has a typical continental lower crustal velocity 6 8 7 0 km s and the lower crust shallows significantly beneath orphan knoll our model shows no evidence for the 5 km thick 7 35 km s layer modeled from data of an earlier experiment and interpreted as magmatic underplating but instead indicates that thinned continental crust extends seaward for 360 km without underplating implying nonvolcanic rifting for the ne newfoundland margin we suggest that continental stretching persisted from 180 ma to chron 34n time 101 ma when the final breakup between canada and western europe took place leaving a 400 km wide zone of thinned continental crust underneath the shelf and deep water area of the orphan basin on the landward side of the basin gravity modeling indicates a zone of very thin 6 8 km crust possibly a failed rift center formed as a result of the northward progression of nonvolcanic rifting between canada and europe a possible sub moho reflector suggests generally uniform stretching of the crust and upper mantle and the absence of volcanics and underplating is in contrast to the observations on related rift basins of the grand banks

velocity structure of reflective lower crust beneath the grand banks of newfoundland a seismic refraction experiment using air guns and ocean bottom seismometers was carried out on the southern grand banks in order to study the velocity structure of highly reflective lower crust observed on a previous deep multichannel reflection profile the data were analyzed by interactive forward modeling of travel times and amplitudes wide angle normal moveout analysis and downward continuation of slant stacks laterally varying structure was used in the final stage of modeling the results indicate an upper crust with a p velocity of 6 0 6 2 km s a zone of high velocity gradient from about 19 to 24 km depth and a lower crustal velocity of 6 6 6 8 km s moho is at 29 km the depth of the transition zone is uncertain by 2 or 3 km and its detailed velocity structure is not well resolved however the top of the zone corresponds approximately to the onset of reflectivity while the lower crustal layer is characterized by more coherent and continuous reflections a thin 1 km localized high velocity around 7 2 km s layer is tentatively correlated with one of the reflectors in the lower crust bulk anisotropy of the lower crust is less than 5 the presence of well defined high velocity layers and the lack of anisotropy tend to support mafic intrusion as the mechanism for reflectivity in the lowest part of the crust however there is no evidence of a thick high velocity underplated layer at the base of the crust

a 40 000 yr pollen and diatom record from lake tritrivakely madagascar in the southern tropics abstract links between southern and northern hemisphere climates during the late quaternary are poorly known partly due to the scarcity of continuous climatic records in the southern tropics pollen and diatom evidence from lake tritrivakely 19 47 s provides information on vegetational and hydrological changes in the central highlands of madagascar over the past 40 000 yr most of the record reflects natural environmental variability since humans arrived on the island ca 2000 yr b p during glacial times the migration of mountain plants toward lower altitudes is consistent with a temperature decrease and with reduced atmospheric co2levels in the lake a positive mean annual hydrologic balance from 38 000 to 36 000 and from 17 500 to 9800 cal yr b p coincided with periods of decreasing summer insolation and preceded by several millennia lake rises in the northern tropics a negative hydrologic budget during periods of maximum seasonal contrast in solar radiation is partly attributed to high summer evaporation rate the last glacial maximum was cool and dry the deglacial warming occurred in two steps the first step accompanied by an increase in wetness occurred abruptly at ca 17 000 cal yr b p about two millennia earlier than in the northern hemisphere it is abundantly documented in southern terrestrial data the second step at 15 000 cal yr b p was in phase with the first major temperature change in the northern hemisphere

a classification of dyke fracture geometry with examples from precambrian dyke swarms in the vestfold hills antarctica a classification of dilational fracture geometry is proposed it applies to structures that can be characterized by the combination of a fracture system and a dilation vector field the classification is illustrated with examples of igneous dykes pegmatites and pseudotachylites segmentation in the form of offsets jogs or bifurcations is common to most fracture systems four basic types of dilational fracture systems are distinguished on the basis of the geometry of segmentation these are irregular braided en echelon and zigzag zigzag fracture systems are further differentiated they consist of newly formed obliquely dilated fractures or alternatively of pre existing planes in the host rock that are reactivated by oblique dilation this paper is the first to actually report an igneous zigzag dyke involving newly formed fractures rotation of the regional stress field in the direction of propagation leads to en echelon segmentation braided fracture systems reflect high local stress intensities probably related to propagation rate two possibilities exist for the formation of zigzag dykes consisting of newly formed fractures that are obliquely dilated they may form by extreme interaction of tensile fracture segments in a regional stress field with a low differential stress alternatively they may form in a regional stress field with high differential stress through the propagation of shear fractures segmentation of dykes characterized by offsets is common such segmentation can be the result of protrusions of the fracture termination offsets also occur where a dyke cuts an older planar structure such offsets are the result of the local inhibition of fracture propagation the resulting apparent offset can lead to a misinterpretation of relative age apophyses form as a result of the dilation of a segmented fracture system

north grand banks basin offshore newfoundland a sedimentary epeiric basin west of the murre mercury detachment fault abstract the eastern newfoundland offshore area is geologically the best known region of the northwestern atlantic margin extensive geophysical coverage and about 140 exploratory and delineation wells have allowed structural and stratigraphic mapping of a mesozoic rift basin network that includes the south whale whale horseshoe south jeanne d arc carson bonnition jeanne d arc orphan and flemish pass basins a less explored basin not yet targeted by the oil industry and accordingly less explored has recently been discussed in the marine geoscience literature located on the bonavista platform west of the jeanne d arc basin bounding fault and defined here as the north grand banks basin this area has been described from refraction work correlated with deep seismic profiling lithoprobe east data as a possible mesozoic rift basin with hydrocarbon potential or as a palaeozoic basin detected first by gravity measurements but unconfirmed as a rift basin by reflection data this basin is only 2 km deep and contains palaeozoic and probably undeformed mesozoic sedimentary infill its hydrocarbon potential is low the mesozoic sedimentary rocks if present are probably platform carbonates and clastics formed during thermal subsidence episodes following the first two rifting stages that affected the grand banks of newfoundland the placement of the pre rift unconformity within the sedimentary successions of the north grand banks basin and the precise nature of the rocks situated above the avalon basement remain unresolved a geodynamic model involving simple shear extension in the upper crust is used to explain the evolution of newfoundland offshore sedimentary basins including the north grand banks according to this model the basin is located on the upthrown side of the murre mercury fault system that represents the upper crustal expression of a crustal penetrative detachment

eolian evidence for spatial variability of late quaternary climates in tropical africa abstract study of the eolian fraction of late quaternary sediments from the tropical atlantic reveals that two modes of long term climate variability have existed in tropical africa during the last 150 000 yr tropical northwest africa i e the southwestern sahara and sahel was driest during glaciations and stades but wetter than at present during interglaciations and interstades this may be a response to ice sheets at higher latitudes via equatorward displacement of the westerlies and the subtropical high in contrast central equatorial africa southeast of the sahara was most arid during interstades and times of ice growth and most humid during deglaciation wet periods in this area correspond to insolation maxima in northern hemisphere summer a 23 000 yr precessional rhythm is suggested supporting a direct link between african monsoon intensity and orbitally modulated insolation the late holocene is the only time observed when both areas are arid during an interglacial episode this may reflect in part anthropogenic disturbance of late holocene climates

stretching and subsidence rifting of conjugate margins in the north atlantic region subsidence on rifted conjugate continental margins around the north atlantic is analyzed to derive the amount and areal distribution of stretching in the crust and in the lower lithosphere during continental rifting study areas are the grand banks and orphan basin regions of the eastern canadian continental margin and the goban spur and galicia bank regions off western europe in all areas maps of synrift and postrift sediment thickness and bathymetry were used to derive maps of post and synrift subsidence a two layer lithospheric stretching model with independent amounts of stretching in the crust and in the lower lithosphere was assumed to be applicable with the rifting history approximated by several instantaneous episodes of extension this model was used to derive estimates of stretching at all points on a 0 05 geographical grid where subsidence values were available within the study regions the models are constrained with seismic measurements of crustal thickness the results imply that pure shear stretching predominates at a lithospheric scale while simple shear is more localized laterally and confined to the crust in places there is significant decoupling between crustal and mantle stretching near the continent ocean boundary final continental breakup may be localized on one side of the rift between conjugate margin pairs rather than symmetrically located total extension of the margins is compatible with that estimated from normal fault geometries and indicates that the continent ocean boundary has been extended up to 350 km seaward of its original position which should be considered in plate kinematic reconstructions

seismic velocity heterogeneity and the composition of the lower crust abstract many wide angle seismic experiments attempt to constrain lower crustal seismic velocity and thus composition deep near normal incidence seismic data recorded during the past decade suggest a widely varying and highly complex pattern of lower crustal heterogeneity synthetic seismic modelling indicates that velocities measured from wide angle experiments may depend significantly upon the geometrical arrangement and scale of the heterogeneities heterogeneities with a correlation length considerably large than the seismic wavelength will tend to produce observed velocities biased towards high values heterogeneities much smaller than the seismic wavelength can lead to a velocity bias of either sense depending upon their arrangement seismic velocities greater than 7 3 km s measured near the base of the crust in underplated and intruded passive continental margins suggest compositions that are markedly more mafic than mantle melting calculations predict our seismic modelling suggests that the mismatch between modelled and observed velocities at passive margins may be attributable to large scale correlation length greater than seismic wavelength heterogeneities

influences of high and low latitude processes on african terrestrial climate pleistocene eolian records from equatorial atlantic ocean drilling program site 663 high and low latitude forcing of terrestrial african paleoclimate variability is demonstrated using 900 ka eolian and biogenic component records from ocean drilling program site 663 in the eastern equatorial atlantic terrigenous eolian dust and phytolith savannah grass cuticle accumulation rate records vary predominantly at 100 and 41 kyr periodicities and spectral phase estimates implicate high latitude forcing the abundance of freshwater diatoms melosira transported from dry african lake beds varies coherently at 23 19 kyr orbital periodicities and at a phasing which implicates low latitude precessional monsoon forcing modeling studies demonstrate that african climate is sensitive to both high and low latitude boundary conditions african monsoon intensity is modulated by direct insolation variations due to orbital precession whereas remote high latitude forcing can be related to cool north atlantic sea surface temperatures ssts which promote african aridity and enhance dust transporting wind speeds the site 663 terrigenous and phytolith records covary with north atlantic sst variability at 41 n site 607 we suggest that pleistocene african climate has responded to both high latitude north atlantic sst variability as well as low latitude precessional monsoon forcing the high latitude influence dominates the sedimentary record prior to circa 2 4 ma terrigenous variations occurred primarily at precessional periodicities 23 19 kyr indicating that african climate was largely controlled by low latitude insolation variations prior to the onset of high amplitude glacial interglacial climate change

relationship between bowl shaped clastic injectites and parent sand depletion implications for their scale invariant morphology and composition 3d seismic reflection data provides a means to assess the impact of injection on parent sands and to quantify the character of the resulting injectite networks the morphology of a series of large injectite structures hosted in the palaeocene lower lista formation were mapped using broadband 3d seismic data from the north sea to investigate their relationship with parent sands fourteen bowl shaped structures were identified within the lista formation in the study area 60 85 m in height and 200 900 m in width sand is absent below resolution below these large scale bowls suggesting that the parent sand is the underlying maureen formation and sand welds formed rather than sand prone channelised deposits within the lista formation identification of injectite networks can be ambiguous which impacts geological model development observations from exhumed systems and core offers high resolution insights into the complexity of injectite networks to advance our understanding of this scale gap we argue for injectites being scale invariant in their shape and grain size this permits the application of outcrop scale knowledge to seismic scale interpretation the demonstrable depletion of parent sands and their scale invariance can be applied to basin fills worldwide to reduce uncertainties of the impact of sand injectites on hydrocarbon reservoirs

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

climate variability in the botswana kalahari from the late pleistocene to the present day 1 noble gas concentrations and oxygen isotopes in groundwaters from the kalahari desert in botswana contain a 45 ka paleotemperature record indicating that mean annual temperatures during the period from 24 ka bp to 45 ka bp were 5 2 1 5 c cooler than from 16 ka to the present day in addition to enrichments in oxygen 18 groundwaters recharged after 16 ka bp also contain higher concentrations of excess air entrained air bubbles taken together the noble gas oxygen isotope and excess air based paleoclimate archives provide evidence that the high interior desert of southern africa was both cooler and dryer prior to the last glacial maximum lgm cool dry conditions also suggest a weaker hydrological cycle in southern africa this is contrary to the predicted enhancement of monsoon strength by increased summer insolation in the southern tropics induced by orbital precession during the lgm

crustal extension from exposed sheet intrusions review and method proposal abstract sheet intrusions are probably the most widespread magmatic features on earth they create a space for themselves by dilating the host rock the exposed sheet intrusions allow an estimate of a minimum value of the extension to which the crustal layers and the volcanic edifices are subject the correct evaluation of the contribution of sheet intrusions to the crustal extension is of great importance in various geologic settings the current methods used to evaluate the extension due to exposed sheet intrusions are reviewed in this paper the effect of the dip of sheet intrusions on the evaluation of horizontal crustal extension is analysed if the dip effect is neglected and the intrusions are sub vertical the error due to the dip effect in the extension evaluation is small if the intrusions are shallow dipping the error may be great and varies as a function of the dyke dip for dykes with dip range 45 65 the error due to neglecting the dip effect is 30 to 15 increasing discrepancies of more than 25 are produced on the computed dilation when the intrusions progressively dip less than 50 a simple method based on structural field measurements of exposed sheet intrusions and on trigonometric considerations is presented as an improvement of pre existing methods to estimate the horizontal component of the crustal extension using this method field data of 1154 dykes from different geodynamic contexts are analysed the horizontal component of extension is computed using dyke data from the tertiary massifs of lanzarote and tenerife and from the active stratovolcanoes of monte somma vesuvius and etna since the analysed dykes are steeply dipping the cumulative difference between the extension computed neglecting and taking into account the dip effect remains less than 10 for all the data sets the percentage difference is nearly constant and cumulatively higher for monte somma where the mean dip of the intrusions is smaller in lanzarote 237 dykes emplaced between 15 5 and 3 7 ma give a peak extension of 276 m in direction n135 and a time averaged minimum extension rate of 1 9 10 2 to 2 3 10 2 mm a 1 in tenerife an extension of 562 m is computed in the direction n65 from 563 dykes emplaced from 7 4 to 3 3 ma the time averaged minimum rate of extension for the tertiary massifs of tenerife ranges from 0 14 to 0 25 mm a 1 the peak extension computed for monte somma is 81 7 m in the direction n90 based on 96 exposed sheets very likely most of monte somma sheets intruded within 12 ka giving a time averaged minimum extension rate of 7 mm a 1 from 184 exposed dykes of etna a minimum extension rate of 6 2 mm a 1 is computed peak extension is 212 m in direction n35 the poor resolution of age constraints may affect deeply the reliability of the extension rates however from the examples presented it appears that the extension rates of pre erosional successions from intraplate volcanic islands can be smaller than those of active stratovolcanoes this may suggest a more active dynamics in the stratovolcanoes

brittle deformation and fracture patterns on oceanic rift shoulders the esja peninsula sw iceland abstract this paper provides detailed structural data on the crustal deformation of the esja peninsula at the southwestern margin of the rift zone in sw iceland forty percent of the faults are strike slip with steep dips 35 are normal dip slip with dips ranging from 50 to 90 for normal faults e w ne sw and nne ssw are the three major trends the paleostress tensors determined using the fault data indicate three main states of stress two extensional regimes 3 n180 e 10 and n110 e 10 are related to normal slip faults the third is a compressive stress regime with 1 trending n10 e n30 e associations between strike slip and dip slip faults are often observed resulting from both the geometrical requirements of interactions between faulted blocks and from local regional permutations between 1 and 2 we note a constant obliquity of 10 20 between the trend perpendicular to the regional structures and the computed direction of extension this conclusion is also supported by the major trends of dykes and tensional fractures there are two mechanisms of volcanic injection local sheets and regional dykes resulting in power law cumulative thickness distributions with exponents of 1 5 and 3 0 respectively

three and half million year history of moisture availability of south west africa evidence from odp site 1085 biomarker records ocean drilling program site 1085 provides a continuous marine sediment record off southern south west africa for at least the last three and half million years the n alkane 13 c record from this site records changes in past vegetation and provides an indication of the moisture availability of sw africa during this time period very little variation and no apparent trend is observed in the n alkane 13c record suggesting stable long term conditions despite significant changes in east african tectonics and global climate slightly higher n alkane 13c values occur between 3 5 and 2 7 ma suggesting slightly drier conditions than today between 2 5 and 2 7 ma there is a shift to more negative n alkane 13c values suggesting slightly wetter conditions during a 0 2 ma episode that coincides with the intensification of northern hemisphere glaciation inhg from 2 5 to 0 4 ma the n alkane 13c values are very consistent varying by less than 0 5 and suggesting little or no long term change in the moisture availability of south west africa over the last 2 5 million years this is in contrast to the long term drying trend observed further north offshore from the namib desert and in east africa a comparison of the climate history of these regions suggests that southern africa may have been an area of long term stability over the last 3 5 myrs

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

crustal structure of a young margin pair new results across the liguro provencal basin from wide angle seismic tomography tomographic inversion of two wide angle seismic profiles acquired during the sardinia cruise 2006 on the conjugate gulf of lions west sardinia margins pair offers insight into the deep structure of this young basin it is the first combined conjugate margins study in this area based on deep seismic data modelling of the two conjugate profiles reveals that the conjugate margins are symmetric in term of crustal velocity structure with a partitioning in three similar regions 1 a zone of low crustal vertical velocity gradients and a crustal thickness of 18 to 10 km interpreted to be thinned continental crust 2 a transitional zone characterised by high lower crustal velocities non typical of continental or normal oceanic crust and 3 a 4 to 5 km thick crust showing vertical velocity gradients and relative velocity ranges typical of oceanic crust this latter region is interpreted to be a thin oceanic crust resulting from a tectonic heritage and the possible influence of a cool slab back arc basin although the three regions are found on both sides of the margin they are asymmetric in terms of the width of these domains wide and smooth along the gulf of lions margin and narrow and abrupt along its conjugate sardinia side the width of region 2 is larger on the gulf of lions side 90 km than on the sardinia side 40 km crustal thickness in region 3 is about 1 km thinner on the sardinia side than on its conjugate in region 1 the crustal thickness is lower on the sardinia side at a given distance from the shelf break the differences in width of region 2 and in crustal thickness might be due to the origin as a back arc basin of the nw mediterranean basin with the final breakup located closer to the western sardinia margin also probably linked to the complex tectonic history of the region our results do not support a simple shear mechanism of the opening of the basin along a lithospheric detachment fault

structure and rifting evolution of the northern newfoundland basin from erable multichannel seismic reflection profiles across the southeastern margin of flemish cap we present the results from processing and interpreting five lines from the 1992 erable multichannel seismic reflection experiment extending from the southeastern margin of flemish cap into the northern newfoundland basin these profiles reveal significant along strike variations in the rifting styles experienced by flemish cap in the southwest a 100 km wide transition zone is identified between thinned continental crust and thin oceanic crust similar to the conjugate galicia bank and iberian margins this transition zone contains a section of deep basement adjacent to a series of shallower ridges and is interpreted as exhumed serpentinized mantle along strike towards the northeast this transition zone pinches out completely within 100 km and is replaced by thin oceanic crust directly adjacent to thinned continental crust by interpreting nearby seismic profiles and profiles on the conjugate margins using the same classification criteria we construct regional maps of the distribution of crustal domains on both sides of the north atlantic these maps reveal significant variations in rifting style on the conjugate margins and along strike of each margin and also highlight the role of ancient transfer zones in compartmentalizing these rifting variations into four distinct regions we propose that the limited localization of shallow topographically high serpentinized peridotite ridges on the newfoundland iberia and flemish cap galicia bank conjugate margins was directly related to an increase in the rate of extension following the separation of flemish cap and galicia bank which exhumed deeper less serpentinized mantle

emplacement related fault patterns around the northern granite arran scotland conspicuous faults in the new red sandstone nrs mainly permian triassic of arran are shown to be kinematically related to the intrusion of the northern granite in paleocene time early inflation of the granite pluton in the upper crust induced radial stretching in the overlying sedimentary cover recorded in predominantly normal offsets on the faults in the nrs continued ballooning of the pluton superimposed strong concentric dip slip displacement over its flanks both stretching and uplift were heterogeneous strongly controlled by a nonuniform stratigraphy and by reactivation of older faults striking predominantly north northwest and northeast and dating back at least to permian time the paleocene displacements on these discrete weak sub nrs faults diffused upward through nrs sandstones on numerous minor faults each with only small offset this behavior resulted from slip hardening on each fault in the poorly cemented nrs rocks late in the intrusion history the major faults on the southeast side of the granite formed a conjugate strike slip system that accommodated radial expansion of the pluton mainly during intrusion of a discrete magma batch that now forms the inner fine grained granite other structures around and within the northern granite are shown to be more compatible with this two stage ballooning model than with a vertical plug emplacement model previous assessments of the ballooning process in general have been made on deep level lateral margins of plutons where radial shortening dominates in the envelope north arran is an important example of the complexities of ballooning at shallow levels in a heterogeneous crust

evidence for global teleconnections in a late pleistocene speleothem record of water balance and vegetation change at sudwala cave south africa abstract understanding the global response to millennial scale climatic events is essential to our comprehension of climatic teleconnections and projection of future change however the extent and nature of their expression in areas of the southern hemisphere is often viewed as equivocal here we report uranium thorium dating of speleothem formations sampled at sudwala cave in the north eastern lowveld region of south africa s summer rainfall zone srz the growth intervals of multiple formations alongside a detailed chronology and multi proxy analysis of two periods of growth 40 35 ka and 13 8 12 8 ka in a stalagmite sc1 provide information regarding key fluctuations in the palaeoclimatic and palaeoenvironmental conditions during the late pleistocene high resolution stable isotope trace element and micro raman analysis are used alongside petrographic investigation to provide a detailed assessment of the climatic conditions associated with the onset and termination of growth in sc1 the combined raman and petrographic analysis represents a rare approach enabling the identification of aragonite calcite shifts both within and across growth intervals and diagenetic events potentially significantly influencing the recorded signal and often resulting in the major loss of chemical information consequently the identification of this post depositional chemical alteration could become a crucial prerequisite in speleothem palaeoclimatology particularly in areas prone to aragonite speleothem deposition susceptible to calcite conversion such as cave sites hosted by dolomitic karst systems the multiple proxies used in this study highlight the complex forcing relationships between climatically related environmental change and local cave conditions on speleothem precipitation contesting a common paradigm by associating drier conditions at sudwala with the initiation of speleothem growth the growth interval identified in stalagmite sc1 during the late deglaciation 13 85 12 79 ka coincides convincingly with both the southern hemispherically forced antarctic cold reversal 14 1 12 8 ka and the younger dryas 12 9 11 5 ka of northern hemispheric origin identifying southern africa as a vital location for the investigation of the hemispheric to global expression of the millennial scale fluctuations of the last deglaciation

late quaternary palaeoenvironments of the winter rainfall zone of southern africa palynological and sedimentological evidence from the agulhas plain abstract south africa s winter rainfall zone is a climatically sensitive region lying at the interface of the earth s temperate and sub tropical climatic systems its seasonally arid climate has generally prevented the preservation of long and organic rich sedimentary deposits producing a spatially limited and temporally biased quaternary record this paper seeks to address this issue further and develop a fuller understanding of the wider climatic changes in this region during the late quaternary modern climatic data does not support the definitions of the winter rainfall zone presented in previous syntheses and this factor amongst others may explain difficulties in resolving the palaeoenvironmental record in this region we present palaeoenvironmental evidence from the agulhas plain an area marginal to the modern winter rainfall zone cored sedimentological and palynological records from two pans are integrated with previously reported records of aeolian activity providing evidence for phases of enhanced aridity and humidity during the late quaternary the record is fragmentary which may reflect the cycling of sediment between the pans and their accompanying lunette dunes lacustrine sedimentary sequences dating to c 33 ka 47 ka provide evidence for enhanced humidity consistent with evidence in the winter and year round rainfall zones increased humidity is also recorded from c 2 ka following drier conditions than the present c 2 7 2 5 ka palynological evidence supports the sedimentological interpretations of pan water status and offers rare insights into the nature of the region s unique fynbos vegetation during the late pleistocene

structure of archean crust and passive margin of southwest greenland from seismic wide angle data to investigate the structure and composition of the archean crust beneath the shelf of southwest greenland parallel to the passive margin we conducted an onshore offshore seismic wide angle experiment in 1989 one of our goals was to obtain a velocity depth profile along the thinned continental or transitional crust to place constraints on the magmatic rifting history in the northern labrador sea seismic recording instruments at four locations along the coast recorded energy from an air gun array up to 400 km distance due to the dense shot spacing of 100 to 150 m we were able to identify continuous reflected and refracted phases from the upper to lower crust results from a one dimensional extremal inversion indicated a high velocity zone hvz with p wave velocities of more than 7 2 km s at the bottom of the transitional crust combined two dimensional travel time forward modeling and inversion produced a velocity depth model that contains midcrustal and lower crustal discontinuities between 12 and 25 km depth and a moho dipping northward at 30 to 42 km depth an average crustal velocity of about 6 6 km s indicates a high portion of mafic components in the crust the lowermost crust consists of a hvz with a maximum thickness of 8 km and temperature corrected velocities of 7 5 to 7 85 km s the hvz may be explained by an underplated igneous complex often observed under passive margins worldwide metamorphism to garnet pyroxene granulite during postrift isobaric cooling of the 30 to 40 km deep thinned continental crust could explain the velocities that are higher than on other margins a large volume of magmatic material must have been added to the crust but did not produce extrusions magmatic underplating of the thinned continental or transitional crust of sw greenland is likely associated with a possible hot spot magmatism in the davis strait and baffin bay region magmatism associated with continental rifting was found to reach farther south along the northern and central part of the archean block than previously thought

pleistocene sea level fluctuations and human evolution on the southern coastal plain of south africa abstract humans evolved in africa but where and how remain unclear here it is proposed that the southern coastal plain scp of south africa may have served as a geographical point of origin through periodic expansion and contraction isolation in response to glacial interglacial changes in sea level and climate during pleistocene interglacial highstands when sea level was above 75 m human populations were isolated for periods of 360 3400 25 yr generations on the scp by the rugged mountains of the cape fold belt climate and vegetation barriers the scp expands five fold as sea level falls from 75 to 120 m during glacial maxima to form a continuous unobstructed coastal plain accessible to the interior an expanded and wet glacial scp may have served as a refuge to humans and large migratory herds and resulted in the mixing of previously isolated groups the expansive glacial scp habitat abruptly contracts by as much as one third in 300 yr during the rapid rise in sea level associated with glacial terminations rapid flooding may have increased population density and competition on the scp to select for humans who expanded their diet to include marine resources or hunted large animals successful adaptations developed on an isolated scp are predicted to widely disperse during glacial terminations when the scp rapidly contracts or during the initial opening of the scp in the transition to glacial maxima the hypothesis that periodic expansion and contraction of the scp as well as the coastal plain of north africa contributed to the stepwise origin of our species over the last 800 thousand years kyr is evaluated by comparing the archeological dna and sea level records these records generally support the hypothesis but more complete and well dated records are required to resolve the extent to which sea level fluctuations influenced the complex history of human evolution

dike intrusion under shear stress effects on magnetic and vesicle fabrics in dikes from rift zones of tenerife canary islands a theoretical model predicting how anisotropy of magnetic susceptibility ams and vesicle fabrics are modified by shear stress resolved on the dike walls prior to the final cooling of magma is developed for vertical dikes the resulting fabrics are asymmetric with respect to initial fabrics assumed to be symmetric application of this model together with collected data on magma flow direction dike propagation direction and mechanism and shear sense allow us to interpret dike fabrics in terms of shear resolved on the dike walls during intrusion en echelon arrangement offsetting and dike curvature the interpretation of ams and vesicle fabrics of the margins of four dikes shows a reasonable agreement with the proposed theoretical models suggesting that asymmetric fabrics can be used to infer magma flow and may provide valuable information on the shear resolved on the dike walls during intrusion

near synchroneity of new zealand alpine glaciations and northern hemisphere continental glaciations during the past 750 kyr the brunhes magnetochron 0 730 kyr at deep sea drilling project site 594 off eastern south island new zealand comprises up to 100 m of alternating units of pelagic and hemipelagic ooze formed during interglacial and glacial periods respectively the youngest hemipelagic interval corresponds to glacial isotope stage 2 and can be correlated with extensive glacial and glacio fluvial deposits of the late last glaciation 27 13 kyr bp on south island inferring the same genetic link for the other hemipelagic sediment units down core we show here that as many as 12 major episodes of expanded alpine glaciation have occurred on south island in the past 730 kyr each of these glacial episodes coincided with a period of significant 18o enrichment 2 in the core resulting from changes in ocean isotope composition associated with major growth phases of the northern hemisphere ice sheets the inferred history of alpine glaciations on this remote south pacific island appears to be closely phase locked 3 kyr to world wide climate changes

new evidence for a reduced water balance in east africa during the last glacial maximum implication for model data comparison some syntheses of lake level data for the last glacial maximum lgm in east africa 10 n and 30 s east of 25 e show apparently wetter conditions than present for some basins whereas palaeovegetation reconstruction indicates a generally dry climate pmip gcm simulations for the lgm support both scenarios for this region when run under different boundary conditions here we compare three new records from lakes in the data poor southern part of east africa lake malawi lake massoko and lake rukwa we also re assess previously published lake level data and apply a salinity transfer function to the diatom record from lake manyara our results show that in contrast to previous interpretations these lakes were at least as low as today at the lgm and are thus in agreement with the palaeovegetation data relative drought across east africa is best simulated by gcms that use computed ssts rather than the higher climap values lower ssts and the presence of the northern hemisphere ice sheets must have been dominant over any monsoon precipitation rise caused by astronomically induced summer insolation enhancement in the southern african tropics

major crustal rotations in the andean margin paleomagnetic results from the coastal cordillera of northern chile paleomagnetic analyses of mesozoic lavas and dike swarms from the northern chilean coastal cordillera between 25 4 s and 26 4 s reveal a clockwise rotation of about 42 magnetizations from lava flows of andesitic basaltic composition of the middle jurassic la negra formation pass both fold and reversal tests and are interpreted as prefolding remanences five dike swarms of middle jurassic to early cretaceous age yield similar directions to that obtained from the la negra formation four of the five swarms have mixed polarity suggesting that they too carry a primary or very early remanence the structural setting of the dikes suggests that they have not suffered any substantial tilting about nonvertical axes since acquisition of the remanence the clockwise rotation of the area is believed to have been the consequence of transpressional deformation of mid late cretaceous age post 100 ma associated with abandonment of the jurassic early cretaceous magmatic arc in this region and its eastward migration to form a new mid late cretaceous magmatic arc in the former back arc region this younger arc is located east of the coastal cordillera and lies in the central valley region the clockwise sense of rotation is consistent with other paleomagnetic data from northern chile and southern bolivia south of the arica deflection in the andean margin although it is the largest yet reported to the north of the arica deflection paleomagnetic studies report counterclockwise rotations and several large scale models have been proposed to explain the overall pattern of rotations models include oroclinal bending of an originally straight margin differential shortening across the margin at a preexisting bend which is subsequently tightened by the passive rotation of the limbs of the bend and distributed shear throughout the margin as a consequence of oblique convergence at a preexisting bend in contrast to these models several workers have argued that rotation is better explained in terms of localized in situ rotations we review these models in light of our results and present a domino type model with blocks bounded by left lateral faults and rotating clockwise in response to mid late cretaceous transpression within a crustal scale shear zone this is consistent with the observed strike slip fault systems identified in the coastal cordillera

the pretoria saltpan a 200 000 year southern african lacustrine sequence abstract the pretoria saltpan is a circular crater 1130 m in diameter and is situated some 40 km n of pretoria lat 25 34 30 long 28 04 59 e a recent tube sampling and core drilling programme has revealed an infilling consisting of some 90 m of fine lacustrine sediments chiefly organic muds underlain below 30 m depth by micrites which rest upon a further 61 m of coarse clastic debris granite bedrock was encountered at 151 m broad sedimentary zones correspond with major phases in the evolution of the crater lake superimposed cyclical patterns of accumulation reflect environmental changes on millenial to seasonal timescales 14c age determinations on algal debris from the upper 20 m of the core indicate a mean rate of sedimentation of about 1 m 2000 yr suggesting that the lacustrine sequence may span almost 200 000 yr over this period major environmental changes are apparent from sedimentological chemical mineralogical and isotopic analyses of the core and studies of the pollen spectra and diatom assemblages present within it this long continental sequence is therefore providing a high resolution palaeoenvironmental record for southern mid latitudes over much the same period as is covered by the vostok ice core in antarctica

palustrine wetland formation during the mis 3 interstadial implications for preserved alluvial records in the south african karoo abstract dryland alluvial successions across interior south africa are a focus of pedosedimentary research because they provide insights into past hydrogeomorphic changes and improve our understanding of allogenic and autogenic controls on fluvial system behaviour this paper focuses on an alluvial succession preserved within the wilgerbosch river on the great escarpment south africa the pedosedimentary architecture of a calcretized palaeosol formed within an abandoned mis 3 51 39 ka floodplain was investigated using grain size micromorphological xrd and mineral magnetic analyses the primary controls on pedogenesis are inferred and the impacts of their products on subsequent landscape development outlined the biologically dominated calcrete micromorphology is consistent with the rhizogenic calcrete variety which together with xrd grain size and soil magnetic data provides evidence for a palustrine palaeowetland system palustrine wetland systems have been documented across interior south africa but the formation of rhizogenic calcretes in association with these systems has to our knowledge not been reported previously we interpret these palaeowetlands to have resulted from basin wide hydrogeomorphic adjustments rather than localised discontinuous channel and floodout processes magnetic enhancement of the soil column overlying the calcrete compared to the overlying floodplain deposits is indicative of moister climate conditions at 51 ka relative to 39 ka we hypothesise that the longevity of geomorphic quiescence coupled with relatively moist climate conditions in early mis 3 resulted in enhanced soil caco3 accumulation the resultant cementation of this abandoned floodplain deposit accounts for an alluvial record that is dominated by older rather than younger e g holocene deposits despite the narrow valley context

astronomically forced variations in western african rainfall 21 n 20 s during the last interglacial period this study documents the long term evolution of western african precipitation during the last interglacial lig we compare geochemical records obtained on nine sediment cores from the western african margin to a transient simulation 130 115 ka performed with an ocean atmosphere general circulation model and insolation as sole forcing good agreement between proxy records and model outputs indicates that long term changes in western african precipitation largely responded to insolation variations during most of the lig after an early lig dry phase related to high latitude iceberg melting or dating uncertainties boreal summer insolation controlled the intensification of the north african monsoon between 127 and 122 ka perhaps facilitating human migrations out of africa equatorial african rainfall slightly increased throughout the lig in response to increasing annual insolation east west contrasting rainfall evolutions at 10 20 s illustrate the complex southern african response in contrast to more direct responses of north and equatorial western africa to insolation forcing

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

sedimentary evidence from the south mediterranean region sicily crete peloponnese evia used to test alternative models for the regional tectonic setting of tethys during late palaeozoic early mesozoic time

nutricline variation in the equatorial atlantic coincident with the younger dryas variations in nutricline depth during the last deglaciation are recorded by the phytoplankton species florisphaera profunda a stacked record of six deep sea cores shows that across the entire equatorial atlantic there was a brief shallowing of the nutricline centered on 11 ka coincident with the younger dryas this shallowing is linked with high latitude north atlantic deglacial events we invoke high albedo and cool sea surface temperatures in the northern latitudes during 11 ka which steepened an already higher than expected winter insolation and hence temperature gradient for a time of june perihelion we postulate that the resultant increased pressure gradient caused an intensification of the northern hemisphere winter tropical easterlies which in turn caused equatorial divergence to occur in boreal winter

blunt ended dyke segments two examples of blunt ended dykes from the rooi rand dyke swarm in south africa are examined in order to determine the mechanism by which such features form although other interpretations of blunt ended dykes have been proposed evidence in the rooi rand examples suggests that dilation was transferred along a zone of shear at the dyke tip oriented at a high angle to the dyke plane microscopic analysis of samples from blunt ended tip regions reveals cataclasis and mineral straining in the dyke walls in the zone of dyke linkage the indication is that adjacent blunt ended en cchelon dyke segments dilate along a shear zone producing cataclasis of the host rock both segments dilate in this manner and are blunt ended prior to linkage horns may develop at the outer corners of the blunt tips so that subsequent to linkage the overall geometry resembles that predicted by the conventional model of bridge failure between overlapped en tchelon dykes however permanently strained bridges predicted by that model are not necessary for the model described here in addition blunt ended dykes that dilate along a cross linking shear zone do not need to overlap in order to link together in contrast to existing model predictions dilation adjacent to a blunt ended dyke may also be accommodated by intrusion of magma into shear zone fractures that vary in orientation with respect to the main dyke near the dyke the near tip stress field overrides the remote stress field and generates magma filled shear related fractures at high angles to the dyke plane with increasing distance from the dyke the remote stress field becomes dominant and resultant shear related fractures are oriented at successively lesser angles to the dyke plane

crustal structure of the newfoundland rifted continental margin from constrained 3 d gravity inversion the rifting history of the atlantic continental margin of newfoundland is very complex and so far has been investigated at the crustal scale primarily with the use of 2 d seismic surveys while informative the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling of the margin a 3 d gravity inversion of the free air data over the newfoundland margin allows us to generate a 3 d density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage results of the gravity inversion show good correspondence with moho depths from seismic results a shallowing of the moho to 12 km depth is resolved on the shelf at the northern edge of the grand banks in a region poorly sampled by other methods comparisons between sediment thickness and crustal thickness show deviations from local isostatic compensation in locations which correlate with faults and rifting trends such insights must act as constraints for future palaeoreconstructions of north atlantic rifting