progradation of the late quaternary gediz delta turkey abstract detailed 3 5 khz seismic reflection profiling and coring have shown that the continental shelf break and slope off izmir bay turkey are formed by prograding deltaic silty mud sequences the muds contain shallow brackish water benthic and cold water planktonic foraminifera they were deposited when sea level was about 110 m below its present position during the last pleistocene glaciation slumping took place on the prodelta slope leaving rotational slump scars and imbricate slump blocks downslope delta top truncation took place in shallow water by erosive coastline retreat after distributary abandonment there has been little or no sedimentation since that time outer izmir bay is thus floored by relict sands following rapid post glacial transgression the gediz delta was reestablished in izmir bay archaeological evidence shows it has prograded during the last 3000 yrs at least six shifts in the position of the gediz mouth are distinguished during this time and abandoned delta top channels can be correlated with submarine delta lobe sequences

late quaternary evolution of the northern aegean shelf abstract a dense network of 3 5 khz and uniboom seismic profiles revealed the geological evolution of the ierissos alexandroupolis shelf area of the northern aegean during the latest sea level rise near the end of the pleistocene ca 14 000 yr b p the sea was at about 120 m and almost 5300 km2 of shelf was exposed to subaerial erosion two permanet lakes existed in the ierissos and kavalla gulfs as well as a number of ephemeral lakes scattered throughout the rest of the area kavalla gulf was drained by the nestos river which joined the strymon river at the outer strymonikos plateau on the flat samothraki plateau were dune fields marshes and a number of minor seasonal rivers while the evros river flowed east of the plateau by ca 13 000 yr b p the sea had risen to 70 m and covered 30 of the previously exposed shelf the lakes at ierissos and strymonikos gulfs were shallower and the sea approached to within about 5 km of them kavalla gulf and the adjacent eastern strymonikos plateau lay 10 m above sea level while the sea intruded along river mouths at the samothraki plateau during this transgression of the sea river bed gravels and sands were covered by silts and clays at the pleistocene holocene transition ca 10 500 yr b p the sea lay at about 50 m and in areas of steep slope the coast was close to its present position at kavalla gulf the sea advanced along the paleochannel of the nestos river and the island of samothraki was separated from the mainland by ca 7500 yr b p the sea was only 15 m below its present level and the northeastern aegean shelf assumed nearly its present morphology the nestos river changed course to the east and thassos island was separated from the mainland coarse sediment formed wedges nearshore whereas fine grained sediments were distributed widely by current action in many areas relict sediments are present

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

effectiveness of horizontal drains for slope stability horizontal drains have been commonly used in stabilising unsaturated residual soil slopes this study examines the effectiveness of horizontal drains in stabilising residual soil slopes against rainfall induced slope failures under a tropical climate the study includes field instrumentation at two residual soil slopes complemented with a parametric study relating to drain position field monitoring results indicate that rainfall infiltration is limited to a certain depth below which infiltration becomes insignificant this zone tends to be unsuitable for horizontal drains horizontal drains were found to be most effective when located at the base of a slope the parametric study indicated conditions under which horizontal drains are effective or ineffective in improving the stability of a slope it was also found that horizontal drains have little role in minimising infiltration in an unsaturated residual soil slope benefits of using horizontal drains can be obtained through the lowering of the water table

mechanisms of sediment transport and deposition sediment sequences and accumulation during the holocene on the thermaikos plateau the continental slope and basin sporadhes basin northwestern aegean sea greece abstract detailed 3 5 khz seismic reflection profiling carried out on the thermaikos plateau the slope and the basin sporadhes basin northwestern aegean has shown that during the holocene the area received fine grained sediments discharged mainly by the rivers axios aliakmon and pinios a well developed oblique sigmoid progradation pattern has been observed on the seismic profiles taken across the deltaic holocene sequences of these rivers three seismic facies have been identified within the oblique sigmoid pattern 1 dark homogeneous facies that represent fine sand deposits along the delta front topsets 2 stratified facies that represent alternating muddier or sandier horizons foresets and 3 transparent facies in which the muddy sediments predominate bottomsets the base of the holocene reflector c has been found beneath the oblique sigmoid pattern the thin homogeneous and transparent seismic facies throughout the slope and the basin has been interpreted as the holocene muddy sediment sequence in the area bottom samples from the outer thermaikos plateau have shown that it is floored by relict terrigenous sand at depths of 90 110 m the sediment and clay mineral distribution and the presence of relict sand confirm that during the holocene period the fine grained sediment dispersion and deposition was effected by the water mass circulation the majority 80 90 of the sediments dispersed from the rivers during the holocene has been captured by the extensive shelf thermaikos plateau having deposited from the near bottom nepheloid layer minor amounts 10 20 of very fine grained material have escaped and deposited from suspension hemipelagic settling in the slope and basin of the studied area

high resolution seismic reflection profiles for the reconstruction of postglacial transgressive shorelines an example from greece abstract in 1982 we carried out a shallow penetration high resolution seismic profiling study on the shelf of the southern argolid peloponnesos greece to identify and map the shores of the late pleistocene and holocene and to establish their coastal environments portable equipment and a local boat were used the lowest glacial shore occurs at 115 to 118 m within the range of global values the subsequent rise across the distinct old land surface left behind many shore features scaps beaches and beach ridges channels and lagoons now buried under a few meters of post transgressive deposits these features cluster at a small number of depths below present sea level suggesting that the rise of the sea usually too fast to leave an imprint was episodically interrupted by brief stillstands or even temporary reversals of climatic or tectonic origin the clusters can be roughly dated with reference to a global sea level rise curve after 6000 yr b p sparse archaeological data establish a local curve the seismic profiling technique convenient and not costly holds promise for the identification of postglacial shores elsewhere prior to sampling for dating it has wide application for environmental reconstructions of vanished coastal zones as a basis for prehistoric resource assessments these applications are illustrated with examples from this study

vertical displacement trends in the aegean coastal zone ne mediterranean during the holocene assessed by geo archaeological data trends in the vertical displacement i e uplift or subsidence of the aegean sea coastal zone have been assessed by comparing observational data with those derived from the predictive glacio hydro isostatic model of lambeck and purcell 2005 for a period spanning from the mesolithic to the late roman times the data base comprises published studies that use both geomorphological with associated biological material and archaeological sea level indicators markers localities demonstrating uplift of high amplitude were detected in front of the hellenic arc antikythira crete rhodes nisyros and in the northeast aegean region thrace whilst areas experiencing tectonic subsidence were mainly observed in the central aegean region which is characterized by an extensional tectonic domain however regional scale tectonic particularities have caused uplift in parts of the west and east coast of central aegean tectonically stable sites can be found in the cyclades plateau however this is due to a bala

the early cretaceous barents sea sill complex distribution 40ar 39ar geochronology and implications for carbon gas formation abstract mafic igneous rocks of cretaceous age 80 130 ma scattered around the arctic ocean are commonly referred to as the high arctic large igneous province halip we have mapped out the distribution of halip igneous rocks in the barents sea region over the past decade based on integrated seismic gravity magnetic interpretation field work review of publications and analyses of new and vintage borehole and field samples the mapping reveals abundant igneous rocks in the northern and eastern barents sea covering an area of 900 000 km2 with a conservative volume estimate of 100 000 to 200 000 km3 of intrusions the igneous province is dominated by sheet intrusions injected into triassic and permian sedimentary rocks hydrothermal vent complexes are rare and only two potential vent complexes have been identified on seismic data in the eastern barents sea we have further done extensive radiometric dating of the igneous samples in the barents sea region new 40ar 39ar dating of thirteen samples from svalbard reveal ages of crystallization and alteration the large age span 60 140 ma for the raw ages is likely due to partial or complete overprint of the k ar system in plagioclase and the age of the magma emplacement is better represented by u pb tims ages only one of our 40ar 39ar analyses of plagioclase yielded a statistically valid age that is in line with the recently published u pb tims ages of 122 125 ma the new data clearly document that relying on published data from the k ar system can lead to erroneous conclusions on the age of crystallization in this province without a careful use of additional 40ar 39ar degassing data i e k ca we propose that the magmatism on svalbard and franz josef land represents a distinct magmatic event near the barremian aptian boundary 125 ma in the barents sea this early cretaceous barents sea magmatism resulted in the formation of the bssc barents sea sill complex bssc age rocks are also present in arctic canada sverdrup basin and on bennett island new siberia islands the massive injection of hot magma into potentially organic rich sediments in the eastern and northern barents basin caused rapid organic matter maturation and formation of thermogenic gas and oil in contact aureoles we estimate that up to 20 000 gt of carbon were potentially mobilized corresponding to 175 trillion barrels of oil equivalent the production rates and fate of the carbon gases are uncertain however we speculate that rapid release of aureole greenhouse gases methane may have triggered the oceanic anoxic event 1a oae1a and the associated negative 13c excursion in the early aptian some of the methane may also be trapped in the vast hydrocarbon gas accumulations found in the east barents basin

the etendeka igneous province magma types and their stratigraphic distribution with implications for the evolution of the parana etendeka flood basalt province detailed geochemical and field data for the volcanic sequence and intrusions of the etendeka igneous province are used to construct a stratigraphic framework for petrogenetic interpretation of the evolution of the etendeka parana continental flood volcanic event geochemical and petrographic characterization of over 1 000 analyzed samples allows 8 mafic and 17 silicic magma types to be recognized both silicic and mafic types can be grouped into high ti and low ti suites on the basis of elevated ti relative to other elements the mafic magmas are khumib high ti tafelberg kuidas horingbaai huab tafelkop albin and esmeralda all low ti amongst the silicic types the goboboseb springbok wereldsend grootberg and beacon low ti quartz latites and the nil desperandum high ti latite have been described previously in addition the hoas low ti nadas sechomib and hoarusib all high ti latites and the fria low ti sarusas ventura khoraseb naude and elliott all high ti quartz latites are described for the first time here there is a marked provinciality in the distribution of the high and low ti suites with the former concentrated in the northern etendeka region and the latter dominant in the southern etendeka stratigraphic distribution of magma types allows two new formations to be defined in the northern etendeka the khumib formation of basaltic flows and the skeleton coast formation dominated by silicic sheets the geochemical provinciality hampers precise correlations between northern and southern etendeka available evidence suggests that the lower part of the awahab formation in the southern etendeka is coeval with the lower part of the khumib formation and that the silicic units in the upper part of the tafelberg formation probably correlate with the skeleton coast formation the paucity of khumib dykes in relation to tafelberg dykes and their field relationships with regard to the volcanic sequence in the northern etendeka suggests that the main khumib eruptive centers lay further north consistent with southward thinning of the khumib basalts in the southern etendeka the doros complex is the eruptive center of the plume derived tafelkop basalts which probably built a shield volcano within the regional flood lava field this work indicates that the etendeka has a greater variety of both silicic and low ti mafic magma types than are known from the se parana detailed comparisons reveal that all the important silicic types in the parana have geochemical equivalents in the etendeka new correlations are santa maria fria ourinhos khoraseb guarapuava sarusas thus extending the previously recognized correlations between southern etendeka quartz latites and the caixas do sul and anita garibaldi rhyolites these correlations emphasize that very large volume silicic systems develop with pronounced lithospheric rifting in continental flood basalt provinces

late quaternary alluviation and soil formation in the southern argolid its history causes and archaeological implications in the context of an archaeological survey of the southern argolid greece studies have been carried out to elucidate the evolution of the landscape since its earliest known human occupation about 50 000 years ago one of these studies was a detailed geological mapping of the late quaternary alluvium and soils in the area dated by means of thorium uranium disequilibria archaeological finds and historical information seven periods of alluviation were identified each of short duration relative to long intervening periods of stability and soil formation the three earliest alluvial phases falling before and during the last glacial interval range from about 330 000 to 32 000 years in age no alluviation accompanied the last glacial maximum around 20 000 years ago in fact a stable landscape persisted until about 4500 years ago when debris flows and widespread aggradation in the valleys resulted from major slope destabilization and soil erosion probably as a result of extensive land clearance in the early bronze age a subsequent stable period lasted through the many upheavals of the later bronze age the dark ages and the early historical period it came to an end with a brief phase of alluviation between about 300 and 50 bc stability returned through the late roman period notwithstanding considerable expansion of the settled area another period of destabilization this one marked by debris flows and hence major soil erosion is poorly fixed in time but probably coincides with expanded maquis clearance accompanying the resettlement of the area around ad 1000 subsequent events of soil erosion and aggradation vary in nature and timing from one drainage to the next and in some areas continue today nature and chronology of the soil forming and alluviation events show that simple correlations with climatic events do not suffice to explain them for the latter ones past about 2500 bc human activity seems to be the dominant cause but once again the relation between cause and effect is not straightforward land clearing or neglect of soil conservation efforts during economic downturns appear to have a more devastating effect upon the landscape than do intensive land use or total land abandonment

late quaternary depositional history of the north evvoikos gulf aegean sea greece a high resolution seismic reflection survey was carried out in the north evvoikos gulf a deep 450 m semi enclosed basin in east central greece connected to the aegean sea via a 45 m sill to the north and a 30 m wide 10 m deep straight to the south this active extensional basin is bound by major normal faults that switch polarity along strike thereby controlling the asymmetric shape of the basin the survey records show a continuous upper unit in the marine strata deposited since the post glacial transgression on an erosion surface generated during the last glacial the upper unit can be traced downslope into the basin plain where it merges into a unit of laterally continuous interbedded turbidites and hemipelagic deposits the buried erosion surface has many terraces distributed over several depth zones between 65 m and 165 m below present sea level that are evidence for a fluctuating water level when in the last glacial interval the sill depth in the north was about 55 m below today s sealevel and the gulf became isolated from the aegean sea thus during the last 70 kyr the water level of the lowstand lakes fluctuated in correspondence with the oxygen isotope stages ois and the climatic conditions in the dryer stages ois 4 2 the lake water level was lower in the wetter stages ois 1 3 the lake water level was higher these events are also correlated with sediment budgets input from the surrounding land to the basin researches carried out in many other gulfs of variable depth in the ionian and aegean seas indicated presence of sills at today s depths between 50 and 70 m the generation of these features is postulated as sedimentary as many sea level fluctuations ranged in this depth interval

quaternary transgressive regressive cycles in the gulf of argos greece abstract borings in the argive plain reveal cycles of marine incursions each ending with a mediterranean soil profile and followed by a prograded fluvial and coastal wedge the sediment prism of the gulf of argos shelf visible in high resolution seismic reflection profiles also consists of transgressive and regressive depositional sequences identified by onlap downlap and truncation of deposits at least four major reflectors recognizable by their high acoustic impedance and erosional features can be correlated across the shelf the sediments between each pair of reflectors represent the seaward part of a set of transgressive and regressive marine deposits they can be matched to the stratigraphic sequence on land where each marine unit is topped by a soil corrected for subsidence the terminations of the onlapping and downlapping units define a local sea level history its time scale can be derived from a comparison with the eustatic sea level history deduced from ocean cores thus marine seismic reflection data can be used for the correlation of quaternary oceanic and terrestrial chronologies

constraining south atlantic growth with seafloor spreading data recent models of south atlantic opening history focus on early plate divergence by incorporating intracontinental deformation which is poorly constrained aiming to avoid the uncertainties in this approach we model the entire divergence history with a joint inversion for seafloor spreading data for this history the pre campanian motion parameters are the first to feature formal uncertainty estimates we date the onset of spreading at 138 ma with movement along intracontinental accommodation zones leading to the assembly of south america by 123 ma and africa by 106 ma part of the ridge in the agulhas basin jumped westward soon afterward toward the bouvet plume initiating the motion of a short lived malvinas plate the ne georgia and maud rises and agulhas plateau formed as a large igneous province over the plume farther north part of the ridge jumped eastward toward the tristan plume around 94 93 ma but seems not to have resulted in independent plate motion our results show that the south atlantic grew by diachronous breakup of continents on just two plates cretaceous intracontinental deformation in south america and africa can be interpreted in terms of the accommodation of stress associated with northward propagation of this process the pattern of accommodation is usually envisaged as focusing all of the strain in narrow belts with our rotations a commonly used set of such belts accounts instead for just 42 67 of the implied total strain we suggest that the remainder was accommodated at all scales within the continental interiors and the extended continental margins

petrogenesis of the gross spitzkoppe topaz granite central western namibia a geochemical and nd sr pb isotope study abstract the early cretaceous gross spitzkoppe granite is one of several igneous complexes that formed in the damaraland of namibia during an episode of continental rifting and magmatism associated with opening of the south atlantic this is a classic setting of rift related anorogenic magmatism showing the typical association of mantle derived mafic and alkaline rocks along with silicic units the gross spitzkoppe granite is an important example of the latter because its peraluminous composition and crustal isotopic signature makes it well suited to characterize the crustal contribution to magmatism the gross spitzkoppe stock gss is composed of three texturally distinct topaz bearing biotite monzogranites average 76 wt sio 2 30 wt rb sr and 0 5 wt f iron rich biotite is the only mafic silicate in proximity to the stock are numerous felsic dikes rhyodacites to rhyolites the elevated high field strength elements hfse contents and high ga al ratios of the granites and felsic dikes are typical of a type granites the granites and dikes show similar geochemical differentiation trends and the compositions of the more evolved dikes overlaps with the granites this and similar initial isotope ratios suggest that the dikes and granites have a common origin major and trace element modeling confirms that the composition of the gross spitzkoppe granite can be produced by fractional crystallization from magma with the average felsic dike composition rb sr isotope data for nine whole rock samples of the gss yield an age for emplacement of the complex at 125 1 ma initial 87 sr 86 sr ratios vary from 0 710 to 0 716 neodymium isotope compositions of the granites and dikes yield initial e nd 125 values from 5 6 to 6 4 the pb isotopic ratios k feldspar or age corrected whole rock fall in the range 206 pb 204 pb 18 70 18 82 207 pb 204 pb 15 66 15 71 and 208 pb 204 pb 38 57 39 07 these geochemical and isotopic characteristics are consistent with derivation of the gross spitzkoppe granitic magma from a granulite facies metasedimentary source batch melting calculations suggest that low 10 20 degree partial melting of a felsic granulitic source is capable of producing melt compositions similar to those of the felsic dikes with further fractional crystallization being required to produce the granites the source rocks are thought to be damara belt metasediments that were melt depleted in the early paleozoic by extraction of the s type damara granites the most likely scenario for crustal melting is by basaltic underplating of the source region in the lower crust the range in initial nd and sr values is attributed to minor mixing of basaltic magma with the crustal melts although sr was also affected by minor contamination from the radiogenic damara granites near the level of emplacement

community infrastructure and repository for marine magnetic identifications magnetic anomaly identifications underpin plate tectonic reconstructions and form the primary data set from which the age of the oceanic lithosphere and seafloor spreading regimes in the ocean basins can be determined although these identifications are an invaluable resource their usefulness to the wider scientific community has been limited due to the lack of a central community infrastructure to organize host and update these interpretations we have developed an open source community driven online infrastructure as a repository for quality checked magnetic anomaly identifications from all ocean basins we provide a global sample data set that comprises 96 733 individually picked magnetic anomaly identifications organized by ocean basin and publication reference and provide accompanying hellingerformat files where available our infrastructure is designed to facilitate research in plate tectonic reconstructions or research that relies on an assessment of plate reconstructions for both experts and nonexperts alike to further enhance the existing repository and strengthen its value we encourage others in the community to contribute to this effort

quaternary sedimentary history and neotectonic evolution of the eastern part of central aegean sea greece abstract four distinct unconformities can be traced below the e cyclades margins s ikarian basin that separate four oblique progradational delta sequences these have been deposited during sea level lowstands within middle late quaternary glacial stages oxygen isotopic stages 2 6 and possibly 12 8 22 16 the topset foreset transition of these sequences located at 110 152 and 212 m below present sea level reflect continuous subsidence of the s ikarian margins with a calculated rate of 0 33 0 57 m kyr 1 the mean sedimentation rates were estimated as 20 90 cm kyr 1 for the late pleistocene turbiditic deposits 250 kyr b p today for the post isotopic 6 128 kyr b p today sediments the accumulation rates were 10 30 cm kyr 1 on the slopes and 45 60 cm kyr 1 within the basins while for the post late glacial sediments 18 kyr b p today the calculated maximum accumulation rates were 30 cm kyr 1 within the basins and 6 14 cm kyr 1 within the basin margins of north and south ikarian basins a pronounced compressional phase during the middle early quaternary within the north and south ikarian basin can be recognised within the n ikarian basin indications of quaternary strike slip deformations appeared to be related with en echelon of transpressional reverse faults from the middle quaternary onward continuous subsidence and the reduction in size of subaerial regions are attributed to extension tectonics

age of mesozoic igneous rocks in northwesternnamibia and their relationship to continental breakup mesozoic igneous rocks of northwestern namibia comprise continental flood basalts and quartz latites of the parana etendeka province and a suite of central sub volcanic intrusions the damaraland complexes conventional k ar ages published for these rocks range from 377 88 ma with the majority of samples yielding ages of 150 110 ma this large spread of ages is interpreted as being due to disturbance of the k ar system by low temperature alteration which is ubiquitous among the volcanic rocks rb sr and 40 ar 39 ar dating methods which are less susceptible to such disturbance yield a narrower range of ages 132 124 ma with one outlier at 149 ma new rb sr internal isochron ages of 129 8 3 8 ma 126 8 1 3 ma and 126 1 7 3 ma have been determined for an etendeka quartz latite and nepheline syenite intrusions in the messum and okorusu complexes respectively in addition 40 ar 39 ar release spectrum ages of 137 0 0 7 ma 135 0 0 7 ma and 126 9 0 6 ma have been determined for samples from the paresis comendite cape cross nepheline syenite and okorusu nepheline syenite complexes respectively a 13 ma period between 137 and 124 ma is considered to be the best estimate of the timing of mesozoic igneous activity in northwestern namibia the continental flood basalt volcanism was probably limited to the early part of this period and is inferred to have been relatively short lived 1 2 ma magmatic activity among the damaraland complexes was contemporaneous with the onset of flood basalt volcanism but continued for approximately 15 ma and terminated after the onset of sea floor spreading in this area 130 125 ma both the flood basalt volcanism and the magmatic activity of the damaraland complexes are thought to have occurred in response to rifting across the upwelling tristan mantle plume the linear distribution of intrusions in damaraland is interpreted as being due to magmatism focused along a structural discontinuity between the pan african damara terrain to the south and proterozoic cratonic basement to the north

the late rifting phase and continental break up of the southern south atlantic the mode and timing of volcanic rifting and formation of earliest oceanic crust

late quaternary sea level change sedimentation and neotectonics of the gulf of gokova southeastern aegean sea abstract the sedimentary and tectonic late quaternary evolution of the gulf of gokova located at the southwest anatolia southeastern aegean sea region has been interpreted from 800 line km of 3 5 khz and single channel airgun seismic reflection profiles the older part of the gokova basin is formed by mainly e w trending faults and filled by the latest miocene pliocene quaternary hemipelagic sediments with thickness up to 2 5 km the lycian nappes which primarily cover extreme southwestern anatolia represent the basement rocks for the gokova region younger active faulting so called gokova transfer fault gtf which has not been previously discussed in the literature trends ne in the central part of the gulf of gokova basin and records sinistral strike slip motion broadly parallel to the convergence direction of the aegean anatolian and african plates the continental shelf of the northeastern gulf of gokova is mostly formed by numerous superimposed deltaic successions depositional sequences separated by major erosional unconformities during times of lowered sea level associated with late quaternary glaciations deltas prograded more than 40 km seaward from their present positions foreset progradation terminated with the rise of sea level in interglacial and post glacial times and deltas were relocated far inland these major transgressions resulted in unconformities that are correlated with the beginning of oxygen isotope stages 9 7 5 and 1 and provide chronostratigraphic markers for a detailed analysis of sedimentation patterns in the late quaternary all seismic lines show that the topset to foreset transition of the youngest pleistocene delta system developed around 145 150 ms below present sea level thus the maximum pleistocene sea level lowering 18 000 years bp was about 110 m the positions of maximum regression for isotopic stages 6 8 and 10 were found as 160 190 and 215 m below present sea level respectively paleo shoreline positions during isotopic stages 2 6 and 8 suggest an overall gradual subsidence of gokova basin during the last 0 5 ma in the southeastern aegean sea the seismic sedimentary chronology suggests that the gokova basin is subsiding at 0 3 0 4 mm year three bathymetric low and e w wnw ese directed two main ridges in the gulf area are noticeable from the bathymetric data and are well correlated to the seismic data while the main orientation of the gulf is e w more recent ene wsw and wnw ese structures are remarkable in the western and the mid eastern part of the gulf respectively subsidence rates are greatest in the southern center of the basin and decrease northward so that the northern area is being tilted southward

quartz latite rheoignimbrite flows of the etendeka formation north western namibia the etendeka formation of north western namibia consists of a sequence of interbedded quartz latites and tholeiitic basalts and forms part of the karoo igneous province in southern africa the age of the etendeka formation is approximately 130 135 ma the quartz latites make up a significant proportion of the stratigraphic succession 25 of the total stratigraphic thickness and form as much as 60 of the outcrop area in the southern etendeka apart from some systematic differences between pitchstones and devitrified quartz latite largely explained by alteration processes individual quartz latite units exhibit remarkably uniform compositions with no significant vertical or lateral variation geochemistry can be used as a primary criterion for the correlation of major quartz latite units over much of the southern etendeka area enabling the reconstruction of the etendeka formation stratigraphy in this region individual quartz latite units occur as voluminous 400 2600 km3 widespread up to 8800 km2 sheet like deposits typically between 40 and 300 m thick each unit consists of basal main and upper zones the main zone generally constitutes over 70 of the thickness of the unit and typically consists of texturally featureless devitrified quartz latite in contrast the basal and upper zones of the flow are characterised by flow banding pitchstone lenses and breccia with rare occurrences of pyroclastic textures the quartz latites are sparsely porphyritic 10 phenocrysts with glassy or devitrified groundmass textures the phenocrysts consist of plagioclase pyroxene titanomagnetite and rare ilmenite pyroxene geothermometry indicates high 1000 1100 c temperatures of crystallisation which coupled with the absence or primary hydrous phases indicates that the quartz latites were relatively hot h2o undersaturated magmas the quartz latites display features common to both rhyolite lavas and ignimbrites and are clearly the products of an unusual eruption style the local preservation of pyroclastic textures and the broad areal extent of these units lead to the conclusion that the quartz latites are high temperature rheomorphic ignimbrites i e rheoignimbrites a combination of high eruption temperature and relatively low viscosity helps to explain the often completely welded and homogeneous textures observed in most quartz latite outcrops in the etendeka area

quaternary tectonics of the argolikos gulf and adjacent basins greece a single channel seismic reflection survey of the argolikos gulf and idhra channel casts light on the tectonic history of this extensional basin of which the current subsidence phase is less than 0 5 ma old although the gulf has very low seismicity holocene subsidence on the western boundary faults increases southward from 50 to 100 cm ka 1 the eastern margin of the gulf is offset eastward twice for these offsets we postulate two left lateral strike slip faults accommodating a southward increase in the extension rate these features can be traced on land where at least one of them shows evidence of left lateral movement the idhra channel has a different tectonic pattern of e w trending extensional troughs separated by basement ridges the latter diverge westward and continue into the southern argolid as mesozoic limestone ridges separated by ophiolite floored tectonic valleys the causes of this discordant pattern remain obscure

the terraces of corinth gerrce a detailed record of eustatic sea level variations during the last 500 000 years abstract between corinth and xylokastro 20 marine terraces reflect the interaction of the northern peloponnese uplift and the global eustatic sea level fluctuations during the last 500 000 years correlation of the terraces with oxygen isotope records in deep sea cores allowed accurate dating of these fossilized transgressive shorelines curves of altitude versus age have been plotted they show a regular decrease of the uplift rate and a frequent return of the sea level very close to the present day one not only during the interglacial periods 5 7 9 11 13 but also during glacial periods 3 1 3 3 6 8 the alternative would be to suppose very complicated and highly improbable vertical movements of the substratum to explain the regularity of the curves the rhythm of these high sea levels is around 20 30 ka since at least 330 000 years ago

palaeomagnetism and k ar ages of the south west african basalts and their bearing on the time of initial rifting of the south atlantic ocean summary palaeomagnetic and isotopic results from the kaoko lavas hoachanas basalts and dolerite sills of south west africa indicate that the upper triassic lower jurassic stormberg flows of south africa may have extended into sw africa and that younger igneous events of lower cretaceous age were simultaneous with the serra geral volcanism in brazil five analyses on three samples of the keetmanshoop sills gave k ar ages between 178 4 and 199 4 ma four analyses of two samples of the hoachanas basalts gave ages between 161 3 and 173 2 ma and eight analyses of five samples of kaoko basalt gave ages between 110 4 and 128 2 ma the components of remanent magnetization rm used to compute palaeomagnetic pole positions for the kaoko lavas 48 n 93 w a95 3 and for the hoachanas basalts 61 n 106 w a95 7 are stable to alternating field af and thermal demagnetization correlation on a pre drift map and on a map reconstructed for 112 ma bp before present between the palaeomagnetic poles from the kaoko and serra geral lavas suggests that the south atlantic had not opened appreciably by 112 ma bp cretaceous pole positions for s america and africa on a map reconstructed for 80 ma bp are also discussed

the african plate a history of oceanic crust accretion and subduction since the jurassic we present a model for the jurassic to present evolution of plate boundaries and oceanic crust of the african plate based on updated interpretation of magnetic gravity and other geological and geophysical data sets location of continent ocean boundaries and age and geometry of old oceanic crust jurassic and cretaceous are updated in the light of new data and models of passive margin formation a new set of oceanic palaeo age grid models constitutes the basis for estimating the dynamics of oceanic crust through time and can be used as input for quantifying the plate boundary forces that contributed to the african plate palaeo stresses and may have influenced the evolution of intracontinental sedimentary basins as a case study we compute a simple model of palaeo stress for the late cretaceous time in order to assess how ridge push slab pull and horizontal mantle drag might have influenced the continental african plate we note that the changes in length of various plate boundaries especially trenches do not correlate well with absolute plate motion but variations in the mean oceanic crust age seem to be reflected in acceleration or deceleration of the mean absolute plate velocity

sea level changes and tectonics in the quaternary extensional basin of the south evvoikos gulf greece the tectonically active south evvoikos gulf forms the submerged part of a young basin produced by neogene fragmentation of the hellenides so furnishing an opportunity to study the earliest stages of an extensional rift reflection profiles show three seismo stratigraphic units a thin holocene unit a a thick late and middle pleistocene unit b and a deformed mesozoic cenozoic basal unit c in the eastern gulf at least seven alternatingly stratified and acoustically transparent subunits are related to pleistocene sea level changes that episodically isolated the gulf correlation with the global eustatic sea level curve indicates that deposition in the gulf formed by southeastward divergence of its northern and southern boundary faults began during the last million years subsequent glacio eustatic sea level changes superimposed major variations in depositional conditions on long term subsidence lack of pleistocene marine beds on the adjacent land implies that a high rate of subsidence confined lacustrine and marine deposition to the basin itself

testing early cretaceous africa south america fits with new palaeomagnetic data from the etendeka magmatic province namibia abstract we provide an independent test for the proposed pre breakup fits between the south american and african continental margins based on new palaeomagnetic data in the course of modelling the opening of the south atlantic ocean several reconstructions have been proposed which correspond to different estimates of the amount of pre drift extension in the south american and african continental margins and amounts of displacement along intracontinental accommodation zones the parana etendeka large igneous province erupted during a brief time interval between 136 and 131 ma just prior to opening of the south atlantic and has magmatic products on both the african etendeka lavas and south american parana lavas plates here we provide new palaeomagnetic constraints on the etendeka volcanic rocks these yield a declination of d dx 314 4 7 0 and inclination of i ix 42 7 8 3 plat 47 5 plon 88 9 k 26 1 a95 6 3 n 21 when our results are combined with another recently published dataset we obtain an etendeka palaeopole at 49 1 s 87 6 e d dx 315 9 3 8 i ix 43 9 4 4 k 23 4 a95 3 5 n 75 we compare three recent models for south atlantic ocean opening discuss which of the models best fits the palaeomagnetic data and present a revised reconstruction for west gondwana during the early cretaceous

late pleistocene unconformity in the gulf of kavalla northern aegean greece abstract a 147 cm core from the gulf of kavalla on the northern aegean shelf displays two different lithologies separated by an erosional contact the upper part 0 128 cm consists of clayey silt to silty clay grading into silty sand and represents a neritic to nearshore marine environment the lower section 128 147 cm is a stiff calcareous mudstone with scattered microcrystalline calcite nodules and probably represents part of a subaerial soil horizon b ca seismic data indicate that at this location the unconformity between the late glacial subaerial surface and the overlying post glacial transgressive deposits occurs at a depth of 150 cm and has apparently been sampled by the core

3 d 40ar39ar geochronology in the parana continental flood basalt province new 40ar39ar analyses of borehole samples from the parana etendeka continental flood basalt province provide critical evidence of eruption rates in unexposed regions when combined with surface samples the new data clarify the duration of this major volcanic province new ages from both surface and borehole samples confirm a 10 12 million year duration of magmatism which post dates the tithonian mass extinction and provide a unique 3 dimensional picture of the spatial and temporal eruption of the lava pile chemically defined magma types are diachronous and the onset of magmatism occurred 500 1000 km inland migrating southeast towards the incipient south atlantic ocean calculated eruption rates increased from 0 03 km3 yr 1 between 138 and 135 ma through 0 13 km3 yr 1 between 135 and 133 ma to 0 21 km3 yr 1 between 133 and 131 ma supporting the notion that the rate of magmatism increased with time and proximity to the developing south atlantic after 131 ma the continental eruption rates dropped dramatically to 0 01 km3 yr 1 presumably because rifting had occurred and eruption centred in the oceanic rio grande rise with eruption rates of around 0 3 0 5 km3 yr 1 given the available constraints on the potential temperature of the plume thickness of the continental lithosphere and degrees of extension through time predicted melt production rates within the plume seriously underestimate the calculated eruption rates on the continent however the eruption rates can be reconciled if melting occurred by conductive heating of volatile enriched mantle the diachronous nature of the magma types supports the idea that melting occurred over a wide area and that the different magma types reflect different source regions rather than the temporal evolution of magmas from a single source given that 10 million years is appropriate to the timescales for conductive heating above the mantle plume it is suggested that these distinct source regions were located within the lithospheric mantle consistent with geochemical studies

development of drain hole design optimisation a conceptual model for open pit mine slope drainage system with fractured media using a multi stage genetic algorithm high rainfall in equatorial regions leads to high groundwater levels or pore pressures and a high risk of landslides on the slopes of open pit mines hindering mining operations to lower the groundwater level surrounding a slope a drainage system is needed a drain hole is a part of a drainage system which utilises gravity to drain groundwater drain hole installation in fractured media requires the determination of the number location length and other parameters of the drain holes drain holes are frequently installed in uniform configurations or in layouts with uniform spacing which are often ineffective and uneconomical as some holes are not in the right positions or directions within the fractured media this paper attempts to develop a conceptual model of an optimised configuration of drain holes by setting the drain hole parameters or decision variables such as number location and length in such a way that it produces the most effective and efficient outcome by maximising groundwater lowering and minimising cost the optimisation is supported by the multi stage genetic algorithm method in combination with a groundwater simulator hereafter called the multi stage gwsim ga so method the procedure of the conceptual model will be further developed and used as a framework in the groundwater management of fractured media of an open pit mine slope

permeability tensor for discontinuous rock masses rock masses which commonly contain a large number of discontinuities are treated as homogeneous anisotropic porous media to formulate the corresponding permeability tensor this has been successfully achieved by introducing a symmetric tensor crack tensor which depends only on the geometry of the related cracks aperture size and orientation the principal directions associated with the symmetric crack tensor are coaxial with those of the permeability tensor the first invariant of the crack tensor is proportional to the mean permeability while the deviatoric part is related to the anisotropic permeability these results are well supported by numerical experiments on the permeability of cracked media by long remer wilson and witherspoon an actual rock mass moderately jointed granite was studied to see whether the crack tensor can be determined in situ stereology based on geometrical statistics provides a sound basis for determining the crack tensor in situ the crack tensor is obtained by

an early cretaceous paleomagnetic pole from ponta grossa dikes brazil implications for the south american mesozoic apparent polar wander path paleomagnetic results from the early cretaceous ponta grossa dike swarm are reported these dikes crosscut sediments and basement rocks associated with the ponta grossa arch a tectonic feature in the eastern border of the paleozoic mesozoic parana basin these dikes are vertical or subvertical and trend mainly nw and ne samples from 127 dikes were submitted to both alternating field and thermal demagnetizations 121 of them yielded characteristic directions interpreted as original thermal remanent magnetizations both normal and reversed polarities as well as intermediate directions 6 dikes are recorded the paleomagnetic pole is located at 30 3 e 82 4 s n 115 95 2 0 k 43 8 this pole along with the available paleomagnetic poles for the parana basin volcanics serra geral formation recalculated in this paper in the light of reported 40 ar 39 ar ages describe an apparent polar wander path segment corresponding to a clockwise rotation 6 9 of the south american plate this movement is compatible with the initial phase of the south atlantic opening with rifting progressing from south to north however the calculated plate velocity is higher than the predicted velocities reported so far based on oceanic floor magnetic anomalies the new data reported in this paper allowed the calculation of a mean early cretaceous pole 60 3 e 83 8 s n 7 95 2 9 which can be discriminated from the middle late jurassic 191 3 e 86 2 s n 3 95 7 8 and late cretaceous 346 5 e 84 1 s n 5 95 4 9 mean poles for south america indicating a more complex movement of the continent than the simple east west drift generally proposed

late quaternary tectonic and sedimentary history of outer izmir and candarli bays western turkey abstract air gun and 3 5 khz seismic profiles from the eastern aegean sea off turkey show that the continental shelf of outer izmir and candarli bays is formed by several superimposed deltaic sequences during times of lowered sea level associated with late quaternary glaciations deltas prograded seaward more than 60 km from their present positions foreset progradation ceased with the rise of sea level in interglacial and post glacial times and deltas were reestablished far inland in drowned river valleys these major transgressions resulted in unconformities within the superimposed prograded delta sequences the most recent three unconformities are correlated with the beginning of oxygen isotope stages 5 3 and 1 and provide chronostratigraphic markers for a detailed analysis of sedimentation patterns in the late quaternary the coastal shelf and basins are subsiding at an average rate of about 1 m per 1000 years this tectonic subsidence manifests itself as widespread normal block faulting which can be related to the pre miocene structural framework of the region

palaeomagnetism of the mesozoic serra geral formation southern brazil abstract palaeomagnetic results from 20 volcanic sequences and 11 intrusive bodies sills and dykes of the serra geral formation parana basin are reported in this paper the sequences are widespread all over the basin while sills and dykes ponta grossa arch come from the northeastern portion three mean palaeomagnetic poles were computed for the serra geral formation which account for a time interval of 15 ma pole sg1 is located at 85 s 108 e 95 1 1 n 18 and represents the main phase of the magmatic activity in the basin with a mean age of 135 ma pole sg2 is located at 82 s 38 e 95 7 8 n 2 and represents a younger magmatic phase with an associated age of 130 ma pole sg3 72 s 37 e 95 6 8 n 10 is the youngest pole it is computed from the intrusive rocks and its age is assumed to be not younger than 118 ma the lower limit of the cretaceous normal magnetic interval these three poles describe a shifting path which suggest that the south american platform moved 5 southwards and rotated 10 clockwise during the lower cretaceous preceding the south atlantic opening

greek tectonics and seismicity abstract the validity of existing tectonic models for the area of greece is examined in the light of the new recalculated parameters for earthquakes of the region makropoulos and burton 1981 relocated hypocentral positions are extracted from the catalogue to form radial and vertical distance depth cross sections centred on a reference point near the mid point of the aegean volcanic arc and these are used to form a three dimensional topography of the base of earthquake occurrence below 60 km isodepth maps are extracted from this topography as both three and two dimensional map presentations these maps reveal several significant features of deep seated tectonic processes in the region isodepths exceeding 150 km are seen in the northwest aegean and these are more closely linked to the sporadhes and gulf of thermaicos rather than the north aegean trough the 150 km isodepths are also seen in the northeast aegean straddling the dardanelles in the northeastern part of the peloponnesus gulf of saronikos and eastern gulf of corinth in the southern peloponnesus towards crete and extending from north of kos to south of rodos the largest extent of deepest activity is seen south of rodos and this continues towards southwest of turkey the subduction zone of the hellenic arc is clear but smooth benioff zones are not the norm and these data show that structural complexity is more readily observed it is concluded that none of the proposed tectonic models completely explain the observed activity over the whole area and rather than propose yet another model places where further work is still particularly necessary are identified

the impacts of sea level changes during latest pleistocene and holocene times on the morphology of the ionian and aegean seas se alpine europe abstract the tentative coastline configuration in the ionian and aegean seas in three late pleistocene holocene time slices is given based on the global eustatic sea level curve in combination with local geological and geoarcheological data at lowstand stage 2 21 500 cal yr bp years before present sea level 120 m extensive shelves existed in the northern aegean sea and to a second degree in the eastern aegean sea and in the northern and central parts of the ionian sea many islands were connected with each other and with the mainland a great part of the periphery of gulfs that have an entrance less than 120 m deep was subaerially exposed while in their central parts lakes were formed at 11 500 cal yr bp sea level 60 m the exposed shelf was much restricted most of the gulfs were overflowed by the advancing sea and only a few islands were still connected with the mainland finally at 8000 cal yr bp and onward the sea initially intruded the lowlands and the gulfs but the subsequent sediment input by the rivers regressed the sea to its present position thus many human settlements and old cities that were maritime during hellenistic or older times are now a few to tens of kilometers inland

groundwater dewatering optimization in the shengli no 1 open pit coalmine inner mongolia china impacted by groundwater faults lithology and other factors the slope of the shengli no 1 open pit coalmine has been in a state of instability among these factors groundwater in the quaternary aquifer is considered primary thus an optimum design for dewatering well pumping rates is presented in this paper a two dimensional groundwater simulation model is built to characterize the groundwater flow of the study area a steady state model was applied to the observed data head and discharge to verify and calibrate the groundwater model the pilot point method with a regularization option provided by parameter estimation was used to identify the hydraulic conductivity field afterward a groundwater optimization model is integrated with the calibrated simulation model to realize groundwater dewatering optimization in the studied open pit coalmine and an optimization method called modified pareto dominance based real coded genetic algorithm is adopted taking into account the safety of the mine slope and dewatering wells seepage discharge is added to objective function and the maximum aquifer saturated thickness is set as the constraint condition in the optimization model the results indicate that the dewatering optimization procedure developed in this paper can serve as a useful template and framework for solving mining related water problems

quaternary neotectonics of the south aegean arc abstract the sedimentary and tectonic quaternary evolution of the south aegean arc has been interpreted from 8000 line km of sparker seismic reflection profiles the older parts of basins formed by e w trending faults and accumulated hemipelagic sediment younger active faulting trends nnw in the western part of the arc and ene in the eastern arc the ene trending faults record sinistral strike slip motion broadly parallel to the convergence direction of the aegean anatolian and african plates the north south faults in the western arc are similar to those on land in the south peloponnese chronology is estimated from sedimentation rates in cores and from stacked progradational units on basin margins controlled by eustatic changes in sea level the younger fault pattern developed at 0 6 0 8 ma in the western and central arc but progressively younger in the southeastern part of the arc the older basin fill with e w faults is of early quaternary and pliocene age an older regional unconformity corresponds to an early pleistocene unconformity in the cretan basin particularly in the area east of santorini faulting has resulted in startling changes in palaeogeography such that some areas were late pliocene basins positive features during the pleistocene and then subsided 600 m in the last 0 2 ma such rapid basin inversion resulted in uplift of stratified hemipelagic muds which were deformed by creep or failure so that debris flow deposits accumulated in valleys and ponded basins these fundamental tectonic changes in the past two million years indicate that much of the deformation resulting from the interaction of the eurasian african and anatolian aegean plates is taken up at the southern margin of the aegean microplate probably because subduction of the african plate has slowed as a result of collision of continental crust regional fault patterns are a consequence of spatially varying effects of subduction roll back