mechanical strength and physical properties of oklahoma s igneous basement abstract from 2009 to 2016 a drastic increase in seismic activity occurred in the central and eastern us ceus particularly in the oklahoma kansas region the majority of hypocenters were focused in the crystalline basement rock information regarding the physical properties elastic wave velocity peak strength etc of rocks in the ceus basement to date is sparse forecasting future seismic hazard and predicting the in situ response of the crystalline basement requires their geomechanical parameters be adequately constrained this work assesses the mechanical and petrophysical properties of several sets of basement rocks from oklahoma to provide a better framework for understanding intraplate seismicity and overall basement deformation in the continental united states laboratory experiments were conducted with granite rhyolite and diabase basement rock samples collected from southern oklahoma evolution of compressional and shear wave velocity with increasing confinement was measured through a series of ultrasonic velocity tests a suite of uniaxial and triaxial tests were conducted to measure the elastic and inelastic deformation behavior of the basement rocks deformation data was evaluated using the mohr coulomb criterion and compared with additional preexisting deformation data of igneous basement rocks dynamic and static elastic properties compare favorably with available field measurements and demonstrate the role physical properties can play in varying mechanical behavior granitic samples demonstrate moderate variation of intrinsic physical properties can alter elastic properties and failure behavior significantly water weakening in the basement rocks may indicate fluid assisted processes such as stress corrosion cracking enhance deformation in the crystalline basement

global correlation of late cenozoic fluvial deposits a synthesis of data from igcp 449 abstract data on fluvial sequences from around the world collected as part of igcp 449 has allowed comparison between such records with the purpose of searching for meaningful patterns a key finding has been that fluvial incision rates as measured by the vertical separations of well dated terrace deposits one from another and from the modern valley floor which can be used as a proxy for uplift are often very similar in different parts of the world but vary significantly between systems on different types of crust the collection that this paper introduces coupled with previous igcp 449 publications cited confirms that the aim of a worldwide compilation of fluvial archives has been achieved with a number of syntheses already published

mixing processes in modern estuarine sediments from the gulf of khambhat western india abstract sandy and muddy detritus from two distinctive end member provenance terrains basaltic and granitic are transported to the estuaries of the gulf of khambhat by fluvial discharge and opposing tidal currents making this embayment ideal for investigating the effects of mineralogical and geochemical mixing on sediment composition in estuarine depositional systems rivers flowing predominantly from the north over precambrian metasediments and granites supply a felsic plutoniclastic sand to the gulf whilst a mafic volcaniclastic sand sourced by deccan basalts is transported by rivers draining the western ghats and from the local coastal erosion in the southern part of the gulf sediments from the tapti estuary are rich in basaltic rock fragments 50 and are characterised by a distinctly basaltic source composition la sc 0 25 0 86 th sc 0 12 0 40 cr th 13 121 eu eu 0 93 1 68 and lree hree 2 96 6 57 by contrast the sediments of the sabarmati inner estuary are rich in quartz grains 80 as evident from the major and trace element compositions la sc 1 38 6 63 th sc 0 58 2 98 cr th 0 58 19 39 eu eu 0 46 0 86 and lree hree 2 90 11 40 the detrital compositions of the remaining major estuaries the narmada dhadhar and mahi scatter across a broad range in a qfr diagram and contain varying amounts of quartz feldspar and rock fragments in the narmada estuary the mixed signature characterised by ree values including eu eu 0 42 2 28 and lree hree 4 37 14 80 is caused by the presence of diverse rock types that crop out in the source area in the mahi estuary which largely flows across felsic source terrains the compositional signature is controlled by mixing of felsic detritus from riverine input with mafic sediments from seaward side in the estuary the two end member detrital compositions plutoniclastic and volcaniclastic are mixed in the macro tidal estuaries mixing of sediment takes place where fluvial currents and tidal flows interact and the proportion of mixing varies systematically from outer to central to inner estuary a high degree of mixing of felsic sediments with deccan basalt derived sediments takes place in the outer estuary resulting in felsic mafic ratios of 40 60 sediments in the central estuaries 65 35 and in the fluvial dominated inner estuaries 90 10 are characterised by moderate to minor degrees of mixing the mixing in estuaries is systematic and is reflected in both the mineralogy and geochemistry of the sediments provenances of ancient estuarine successions should therefore be interpreted with great care incorporating awareness of the mixing processes which influence sediment compositions to different degrees in estuaries especially those characterised by strong tidal currents

distribution and dispersal of surface sediments on the continental margins of india abstract the vast area varying climate regimes diverse source terrain lithology of the mainland india generate complex weathering and erosional patterns and leads to diverse sediment distribution and dispersal on the surrounding continental margins of india thus to delineate the sources distribution and sediment dispersal pathways around india 254 sediment cores from the eastern and western continental margins of india were investigated for physical properties using non destructive whole core logging technique combined with grain size analyses the distribution of magnetic susceptibility gamma ray density and grain size traces the sources in the indian landmass which contribute sediments to the margins and demarcates their extent of influence the results from the magnetic susceptibility distribution indicate that the dominant influx of modern high susceptibility sediment into the margins of india originates from the weathering of deccan basalts and its subsequent transportation by narmada and tapti rivers in the west coast and krishna and godavari rivers in the east coast though the himalayan sources are the second largest supplier of magnetic minerals to the shelf their contribution when compared to the deccan sediments is not significant the lack of present day sedimentation in the outer shelf regions of margins of india is evident from the gamma ray density distribution and is confirmed by the discrete sample grain size analysis gamma ray density variations in the margins follow the same pattern as the grain size variations and demarcate the boundary between inner shelf modern clayey sediments and the outer shelf relict carbonate sands regional distribution maps of physical properties and grain size for both the margins of india are presented and geographical limits of each provenance are defined thus providing a comprehensive picture of sediment distribution and dispersal patterns in the area and highlights the use of magnetic susceptibility as a powerful tool in deciphering the source to sink pathways of sediments

analysis of borehole breakouts boreholes drilled into rock which is subjected to stresses that amount to a significant fraction of the strength of the rock may cause the rock to fail adjacent to the borehole surface often this results in the elongation of the cross section of the borehole in the direction of the minimum principal compressive stress orthogonal to the borehole axis such breakouts are valuable indicators of the direction of the minimum compressive stress orthogonal to the axis of the borehole their shapes may provide information about the magnitudes of both the maximum and minimum stresses relative to the strength of the rock borehole breakouts also may be impediments to drilling and to in situ measurement techniques such as hydraulic fracturing observations and analyses of borehole breakouts raise three important questions first how does the shape of the borehole breakout evolve second why are breakout shapes stable despite the very high compressive stress concentrations that they produce third how is the shape of the breakout related to the magnitudes of the stresses in the rock in this paper extensile splitting of rock in unconfined plane strain compression is assumed to be the process of rock failure adjacent to the circumference of the borehole by which a breakout forms to simulate the evolution of a borehole breakout this process is combined with a numerical boundary element analysis of the stresses around a borehole as its cross section evolves from the originally circular shape to that of a stable breakout the tangential stresses around a stable breakout cross section are found to be everywhere less than the unconfined plane strain tensile or compressive strength of the rock the stresses outside the stable breakout are found to be everywhere less than the limiting values of shear strength given by a mohr coulomb criterion in the regions of great stress concentrations at the ends of a breakout cross section which have a pointed shape the state of stress approaches that of equal biaxial compression in plane strain as it does ahead of a mathematical crack or notch the fact that the stresses around a breakout are less than the relevant strength establishes both the stability of the final breakout cross section and the appropriateness of an elastic analysis of the stresses according to this model the cross sectional shapes of stable breakouts are not related uniquely to the state of stress and the strength of the rock for example stable breakouts created instantly in rock already subjected to stress are much larger than stable breakouts created in the same rock with a preexisting borehole by subsequently increasing the stresses to the same values the results of drilling into an actual rock probably lie between these extremes modest changes in borehole cross section as a result of breakout do not alter significantly the minimum tangential tensile stress around a borehole with internal pressure from that given by the kirsch solution for a circular hole subjected to the same stresses therefore hydraulic fracturing interpretations based on the kirsch solution give the correct values for the far field stresses

rate of strike slip motion on the amanos fault karasu valley southern turkey constrained by k ar dating and geochemical analysis of quaternary basalts the left lateral amanos fault follows a 200 km long and up to 2 km high escarpment that bounds the eastern margin of the amanos mountain range and the western margin of the karasu valley in southern turkey just east of the northeastern corner of the mediterranean sea regional kinematic models have reached diverse conclusions as to the role of this fault in accommodating relative motion between either the african and arabian turkish and african or turkish and arabian plates local studies have tried to estimate its slip rate by k ar dating quaternary basalts that erupted within the amanos mountains flowed across it into the karasu valley and have since become offset however these studies have yielded a wide range of results ranging from 0 3 to 15 mm a 1 which do not allow the overall role and significance of this fault in accommodating crustal deformation to be determined we have used the cassignol k ar method to date nine quaternary basalt samples from the vicinity of the southern part of the amanos fault these basalts exhibit a diverse chemistry which we interpret as a consequence varying degrees of partial melting of their source combined with variable crustal contamination this dating allows us to constrain the quaternary slip rate on the amanos fault to 1 0 to 1 6 mm a 1 the dramatic discrepancies between past estimates of this slip rate are partly due to technical difficulties in k ar dating of young basalts by isotope dilution in addition previous studies at the key locality of hacilar have unwittingly dated different chemically distinct flow units of different ages that are juxtaposed this low slip rate indicates that at present the amanos fault takes up a small proportion of the relative motion between the african and arabian plates which is transferred southward to the dead sea fault zone it also provides strong evidence against the long standing view that its slip continues offshore to the southwest along a hypothetical left lateral fault zone located south of cyprus

dating of sirius group tillites in the antarctic dry valleys with cosmogenic3he and21ne we measured in situ produced cosmogenic3he and21ne in boulder and bedrock surface samples in and near sirius group tillites from two localities in southern victoria land antarctica pyroxene quantitatively retains cosmogenic3he for millions of years the deposit at mt fleming has a minimum exposure age of 6 5 ma while 6 ma is a probable minimum age for the table mountain tillite these lower limits not taking into account erosion of the sampled surfaces are based on the samples with the highest concentrations of cosmogenic noble gases and currently accepted production rates since the plagioclase bearing mt fleming samples almost certainly lost part of their cosmogenic ne the minimum exposure age at this location is presumably even 50 higher than the stated value the concentrations of cosmogenic ne in our samples constrain uplift rates of the transantarctic mountains to 170 m ma these data contradict the hypothesis of a collapse of the east antarctic ice sheet in the pliocene coupled with high uplift rates and support the model of a stable ice sheet since the middle miocene

kinematics of active left lateral faulting in se turkey from offset pleistocene river gorges improved constraint on the rate and history of relative motion between the turkish and arabian plates in the arabian platform of se turkey abundant evidence exists of fluvial incision by c 110 10 m since the late early pleistocene starting in or around marine oxygen isotope stage 22 at 870 ka this incision which has accompanied regional surface uplift as the isostatic response to regional erosion has progressively locked rivers into their gorges in landscape that formerly had much lower relief we use this effect to estimate 4 44 0 06 km of left lateral slip on this time scale on the golbasi turkoglu fault a segment of the east anatolian fault zone from offset river gorges giving a slip rate of 5 10 0 07 mm a 1 piercing points indicate that this fault has slipped a total of 19 km making its age 3 73 0 05 ma a total of 33 km of relative motion between the turkish and arabian plates is documented on this time scale in the vicinity of golbasi at an overall time averaged rate of 8 85 0 12 mm a 1 the estimated euler vector for relative motion between these plates being 0 89 0 01 ma 1 about 33 4 n 42 3 e this method can be readily applied to determine slip rates time averaged since the late early pleistocene on other strike slip fault zones worldwide

the river orontes in syria and turkey downstream variation of fluvial archives in different crustal blocks the geomorphology and quaternary history of the river orontes in western syria and south central turkey have been studied using a combination of methods field survey differential gps satellite imagery analysis of sediments to determine provenance flow direction and fluvial environment incorporation of evidence from fossils for both palaeoenvironments and biostratigraphy uranium series dating of calcrete cement reconciliation of palaeolithic archaeological contents and uplift modelling based on terrace height distribution the results underline the contrasting nature of different reaches of the orontes in part reflecting different crustal blocks with different histories of landscape evolution upstream from homs the orontes has a system of calcreted terraces that form a staircase extending to 200 m above the river new u series dating provides an age constraint within the lower part of the sequence that suggests underestimation of terrace ages in previous reviews this upper valley is separated from another terraced reach in the middle orontes by a gorge cut through the late miocene early pliocene homs basalt the middle orontes terraces have long been recognized as a source of mammalian fossils and palaeolithic artefacts particularly from latamneh near the downstream end of the reach this terraced section of the valley ends at a fault scarp marking the edge of the subsiding ghab basin a segment of the dead sea fault zone which has been filled to a depth of 1 km by dominantly lacustrine sediments of pliocene quaternary age review of the fauna from latamneh suggests that its age is 1 2 0 9 ma significantly older than previously supposed and commensurate with less uplift in this reach than both the upper and lower orontes two localities near the downstream end of the ghab have provided molluscan and ostracod assemblages that record somewhat saline environments perhaps caused by desiccation within the former lacustrine basin although they include fluvial elements the ghab is separated from another subsiding and formerly lacustrine depocentre the amik basin of hatay province turkey by a second gorge implicit of uplift this time cut through palaeogene limestone the ne sw oriented lowermost reach of the orontes is again terraced with a third and most dramatic gorge through the northern edge of the ziyaret dagi mountains which are known to have experienced rapid uplift probably again enhanced by movement on an active fault indeed a conclusion of the research in which these various reaches are compared is that the crust in the hatay region is significantly more dynamic than that further upstream where uplift has been less rapid and less continuous

influence of water content and anisotropy on the strength and deformability of low porosity meta sedimentary rocks under triaxial compression abstract a reduction of uniaxial compressive strength ucs by the presence of water has been ascertained in many sedimentary rocks and even some metamorphic rocks experimentally this paper reports and discusses the influence of water content and anisotropy on the strength and deformability of two meta sedimentary rocks by triaxial compressive tests before conducting the triaxial tests the physical properties of meta siltstone and meta sandstone specimens have been carefully examined the water contents of both tested rocks are very low for instance 0 17 for meta siltstone and 0 10 for meta sandstone the porosities of the tested rocks are analyzed by the technique of mercury intrusion porosimetry mip it shows that the meta sedimentary rocks have very low porosity 0 18 for meta siltstone and 0 53 for meta sandstone on average the thin section analysis reveals that the meta siltstone contains more hydrophilic substances such as clay minerals than the meta sandstone and both two meta sedimentary rocks are characterized by distinct beddings and laminae even though the water contents of two tested rocks are very low they significantly influence the triaxial compressive strength and deformability the reduction of strength by water content is found to be related to a reduction of friction angle in the mohr coulomb failure criterion while a reduction of mi value in the hoek brown failure criterion on the other hand the influence of water on deformability of tested rocks is reflected as a reduction of young s modulus and increase of poisson s ratio which indicates that the wet meta sedimentary rocks will deform more than that of the dry ones under the same stress condition the experimental studies show that the anisotropy associated with bedding in rock specimens plays a weakening effect on the triaxial compressive strength for both tested rocks appearing more severely for meta siltstone in general the triaxial compression strength of rock specimens with transverse bedding planes is higher than the ones with longitudinal bedding planes no matter for meta siltstone or meta sandstone both dry and wet conditions under the same confining stress with regard to the stiffness both the tangent and secant young s moduli of the two tested rocks with transverse bedding are less than the ones with longitudinal bedding appearing more conspicuously for the meta siltstone the paper also discusses the axial strain calibration by two different measurement techniques one by the linear variant difference transducer lvdt technique and the other one by axial strain gages it shows that the axial strain ratio coefficient k elvdt estrain decays with the deviator stress in our present study the secant modulus estrain is usually about 1 4 1 8 times of elvdt at the peak strength point the correlation between mechanical properties and physical properties of the two tested rocks are also discussed in the paper

dating quaternary volcanism and incision by the river tigris at diyarbakir southeast turkey new high precision ar ar dating of basalt underlying the city of diyarbakir southeast turkey constrains the quaternary incision history of the river tigris strengthening the pre existing chronology based on magnetostratigraphy and k ar dates the basalt which overlies tigris terrace gravel 70 m above the river is part of the karacadag shield volcano complex centred ca 60 km to the southwest the reverse magnetised diyarbakir basalt one of relatively few flow units to reach the tigris valley axis has been dated to 1196 19 ka 2 two lower terraces have been recognised in the diyarbakir area 46 and 32 m above the present river with at least one other further downstream from this evidence the rate of middle late pleistocene incision by the tigris can be estimated it probably reached ca 0 07 mm a 1 reflecting the characteristic global increase in uplift rates observed at that time copyright 2007 john wiley sons ltd

glacial to interglacial changes in carbonate and clay sedimentation in the atlantic ocean estimated from 230th measurements abstract the cause of the climatically controlled fluctuations in the carbonate content of deep sea sediments remains the subject of uncertainty and debate three variables are involved supply of biogenic carbonate loss by dissolution and dilution by non carbonate phases it is suggested that 230 th which is produced in the ocean at a constant rate provides a reliable reference for measuring variations in rate of sedimentation on a regional scale results of a preliminary analysis based on published data indicate that for depths at and above the lysocline the carbonate fluctuations observed in cores from the north atlantic ocean are due primarily to variations in the terrigenous clay input which was 2 5 times higher during glacials than during interglacials carbonate deposition appears to have been somewhat reduced during glacials but probably not by more than a factor of 2 from published 230 th 232 th profiles it appears that the south atlantic ocean also received increased inputs of terrigenous clay during glacial periods

clay minerals and sr nd isotopes of the sediments along the western margin of india and their implication for sediment provenance mineralogy and sr nd isotopic composition of the 2 m fraction of the holocene and late pleistocene sediments from 12 gravity cores collected along the western margin of india were used to delineate the provenance and understand the response of isotopes with respect to the source rock composition holocene sediments show distinct clay mineral associations representing three major sources illite chlorite rich sediments from the indus smectite dominated sediments from the deccan traps and kaolinite and smectite enriched sediments from gneissic rocks the mixing of indus derived sediment with the deccan traps derived sediment or the deccan traps derived sediment with gneissic rock derived sediment occurs in the deeper water cores sr isotopes are very sensitive to weathering and laterization weathering does not influence nd isotopes the 87sr 86sr ratios of the holocene sediments in shallow water cores are higher and fluctuated widely than those in deeper water cores nd correlates well with the clay mineral associations indicating source rock composition or mixing of source sediments kaolinite enriched sediments coupled with high sr ratios and low nd on the sw margin of india suggest intense chemical weathering in the hinterland the influence of the sediment from the ganges brahmaputra transported by the bay of bengal waters during the ne monsoon surface current or sw monsoon underwater current on the composition of the sediments of the sw indian margin is insignificant the late pleistocene sediments reflect a decrease of hydrolytic processes resulting in decrease of smectite and sr isotopic ratio clay minerals and nd values suggest that the provenance and transport pathways of the late pleistocene sediments are the same as those of the holocene for each region

improved modelling of the quaternary evolution of the gulf of corinth incorporating erosion and sedimentation coupled by lower crustal flow abstract numerical modelling incorporating coupling between surface processes and induced flow in the lower continental crust is used to address the quaternary evolution of the gulf of corinth region in central greece the post early pleistocene marine depocentre beneath this gulf overlies the northern margin of an older early pleistocene and earlier lacustrine basin the proto gulf of corinth basin or pgcb in the late early pleistocene relief in this region was minimal but subsequently dramatic relief has developed involving the creation of 900 m of bathymetry within the gulf and the uplift by many hundreds of metres of the part of the pgcb south of the modern gulf which forms the gulf s main sediment supply it is assumed that as a result of climate change around 0 9 ma erosion of this sediment source region and re deposition of this material within the gulf began both processes occurring at spatial average rates of 0 2 mm a 1 modelling of the resulting isostatic response indicates that the local effective viscosity of the lower crust is 4 10 19 pa s indicating a moho temperature of 560 c it predicts that the 10 mm a 1 of extension across this 70 km wide model region at an extensional strain rate of 0 15 ma 1 is partitioned with 3 mm a 1 across the sediment source 2 mm a 1 across the depocentre and 5 mm a 1 across the hinge zone in between the latter value being an estimate of the extension rate on normal faults forming the major topographic escarpment at the southern margin of the gulf this modelling confirms the view suggested previously that coupling between this depocentre and sediment source by lower crustal flow can explain the dramatic development in local relief since the late early pleistocene the effective viscosity of the lower crust in this region is not particularly low the strong coupling interpreted between the sediment source and depocentre results instead from their close proximity in detail the effective viscosity of the lower crust is expected to decrease northward across this model region due to the northward increase in exposure of the base of the continental lithosphere to the asthenosphere in the south the two are separated by the subducting hellenic slab the isostatic consequences of such a lateral variation in viscosity provide a natural explanation for why since 0 9 ma the modern gulf has developed asymmetrically over the northern part of the pgcb leaving the rest of the pgcb to act as its sediment source

active crustal shortening in ne syria revealed by deformed terraces of the river euphrates the africa arabia plate boundary comprises the red sea oceanic spreading centre and the left lateral dead sea fault zone dsfz however previous work has indicated kinematic inconsistency between its continental and oceanic parts the palmyra fold belt pfb splays ene from the dsfz in sw syria and persists for 400 km to the river euphrates but its significance within the regional pattern of active crustal deformation has hitherto been unclear we report deformation of euphrates terraces consistent with quaternary right lateral transpression within the pfb indicating anticlockwise rotation estimated as 0 3 ma 1 about 36 0 n 39 8 e of the block between the pfb and the northern dsfz relative to the arabian plate interior the northern dsfz is shown to be kinematically consistent with the combination of euler vectors for the pfb and the red sea spreading resolving the inconsistency previously evident the sw pfb causes a significant earthquake hazard previously unrecognized to the city of damascus

late cenozoic surface uplift revealed by incision by the river euphrates at birecik southeast turkey incision by the river euphrates has created a dramatic erosional landscape in the northern arabian platform in se turkey we obtain accurate heights of its terrace deposits in the birecik area using differential gps and summarise evidence regarding heights of late miocene basalt flows and low altitude wetland sediments we thus estimate 600 m of uplift since the early late miocene 9 ma represented by 270 m of fluvial incision the difference reflecting downstream channel lengthening as the coastline has retreated to the persian gulf 1400 km away the oldest recognised sediments inset below this level form a thick aggradation between 100 and 130 m above the present level of the euphrates we estimate that this accumulated during 5 3 ma when uplift rates were low such that aggradation was necessary to maintain a downstream channel gradient in response to the coastal retreat palaeolithic artefacts have been reported locally in euphrates deposits up to 80 m above present river level which we tentatively date to 1 8 ma the euphrates subsequently incised to within 10 m of its present level before aggrading 45 m higher in the late early pleistocene the final 55 m of incision reflects the increase in uplift rates observed worldwide in the early middle pleistocene following the mid pleistocene revolution

ar ar dating of late cenozoic basaltic volcanism in northern syria implications for the history of incision by the river euphrates and uplift of the northern arabian platform 1 ar ar dating of basalt flows capping terrace deposits of the river euphrates in northern syria has provided a new quantitative chronology for the late cenozoic evolution of this important river system and for the associated history of surface uplift of the northern arabian platform through which it flows a region of relatively strong crust that has experienced only slow deformation notably fluvial deposits 65 m above the euphrates are overlain by basalt dated to 2717 20 ka those 45 m above the river are overlain by basalt dated to 2116 39 ka and those 8 9 m above the river are overlain by basalt dated to 402 11 ka these new dates require the previous dating scheme based on paleolithic archaeology to be revised the euphrates terrace deposits and the associated incised valley are much older than was previously thought rates of incision by the euphrates providing a proxy for regional surface uplift that is inferred to be the isostatic response to regional erosion have varied significantly over the past 3 ma with indications that between 1 2 and 0 9 ma there was regional subsidence which gave rise to fluvial aggradation this unusual pattern involving reversals in the sense of vertical crustal motions is interpreted to be a consequence of a relatively cold and thin mobile lower crustal layer no more than 5 km thick evidently due to the presence of a much thicker underlying layer of mafic underplating at the base of the crust this study thus indicates previously unsuspected complexity in the isostatic response to regional erosion in an area of high crustal stability

effect of fluid pressure on rock compressive failure in a nearly impermeable crystalline rock implication on mechanism of borehole breakouts abstract we conducted laboratory true triaxial experiments in the nearly impermeable pohang rhyolite to investigate failure mechanisms under dry and wet rock conditions under dry conditions prismatic specimens were jacketed all around to prevent confining fluid penetration under wet conditions one pair of the specimen faces was left unjacketed and in direct contact with the confining fluid kerosene applying the least principal stress in an attempt to simulate the case of an unlined borehole wall in both testing setups the true triaxial compressive strength for a given least principal stress increases significantly as the intermediate principal stress rises the unjacketed rhyolite strength is however only 60 to 85 of the strength under dry conditions depending on the magnitude of the intermediate principal stress in dry rhyolite the failure process begins upon dilatancy onset followed by microcrack localization and ending in a steeply dipping shear fracture on the other hand brittle fracture in wet specimens occurs almost immediately after the onset of dilatancy by the development of one or more through going extensile fractures subparallel and adjacent to one of the unjacketed faces resembling the extensile cracks leading to borehole breakouts in crystalline rocks we infer that upon dilatancy the confining fluid intrudes and quickly propagates newly opened stress induced microcracks subparallel to the unjacketed faces leading to early failure

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

geochemistry of sediments from the mangalore cochin shelf and upper slope off southwest india geological and environmental factors controlling dispersal of elements abstract the geochemical investigations on 136 surficial sediment samples of the mangalore cochin shelf and upper slope were undertaken to understand the distribution sources and processes by which various major and trace elements are incorporated into the sediments texturally the inner shelf 120 m water depth are dominantly composed of clayey sediments whereas the outer shelf 50 120 m water depth is carpeted by relict 10 000 yr in age sands the results show that sediment texture largely controls the distribution of elements the sandy relict sediments of the outer shelf 59 samples and of the upper slope restricted coverage have high contents of sio 2 caco 3 and sr amongst which sio 2 is present as terrigenous quartz sand while caco 3 and sr being well correlated with skeletal components are biogenous extremely good positive correlation between sr and caco 3 r 0 77 suggests presence of sr in the lattices of aragonite which is the main carbonate mineral the clay rich sediments of the inner shelf 52 samples and upper slope 25 samples are both very rich in organic carbon content and low in sio 2 content and very high in al 2 o 3 tio 2 fe 2 o 3 mgo na 2 o k 2 o p 2 o 5 mn cu ni zn and li contents as compared to the sandy sediments of the outer shelf except for organic carbon p 2 o 5 and tio 2 strong positive correlations of these components with al 2 o 3 r 0 41 0 90 suggest their association mainly with clay minerals within the clay minerals these are present in the crystal lattice either as essential constituent or incorporated by cation exchange or adsorbed onto clay platelets organic carbon p 2 o 5 and tio 2 also show positive correlation with al 2 o 3 mainly due to their physical association with fine grained clayey sediments phosphate in these sediments is mainly present in association with organic matter and to some extent it also occurs either as ferric phosphate or as authigenic apatite in general the geochemistry of these sediments clearly reflects their mineralogy formation of fe and mn hydroxides in the nearshore regions is responsible for scavenging of ni cu and zn and effectively incorporating them into the inner shelf sediments these trace elements also show significant correlation with organic carbon r 0 51 0 56 suggesting that a part of their content is biogenous

estimation of maximum horizontal principal stress magnitude from stress induced well bore breakouts in the cajon pass scientific research borehole in this paper we utilize the mechanical properties of core samples detailed observations of stress induced well bore breakouts and estimates of the magnitude of shmin from hydraulic fracturing experiments to construct a vertical profile of the maximum horizontal principal stress shmax to 3 5 km depth in the cajon pass borehole as in essentially all other boreholes the hydraulic fracturing stress measurements in the cajon pass borehole yielded appreciably more and more reliable data on the magnitude of the least principal horizontal stress shmin than the maximum principal horizontal stress shmax to utilize the breakout observations to constrain the magnitude of shmax a brittle failure criterion was used that is based on the effective strain energy concept this failure criterion also allows us to account for the polyaxial stress around the borehole and to incorporate the role of pore fluid pressure on rock strength in various ways a comparison of the shmax profile estimated from the breakouts with estimates of shmax obtained from the hydraulic fracturing tests indicates that they compare fairly well for the case when the effect of pore pressure on hydraulic fracture initiation is negligible the overall stress state to a depth of 3 5 km in the well corresponds to a normal strike slip faulting regime the shmax profile indicates several marked decreases in stress magnitude associated with major fault zones an observation consistent with the shmin profile obtained from hydraulic fracturing tests

late cenozoic surface uplift basaltic volcanism and incision by the river tigris around diyarbakir se turkey we document the staircase of terraces of the river tigris in the diyarbakir area of se turkey in the northern arabian platform and improve control on the ages of these terrace deposits by dating of overlying basalt flows using the unspiked k ar technique these fluvial terraces are formed of polymict gravel including clasts derived from the anatolian metamorphic terrane farther north as well as of local basalt at least 9 tigris terraces have been recognised so far the highest of which 200 m above present river level marks the local transition from stacked deposition to fluvial incision the timing of which is bounded between the mid late miocene and the middle pliocene our k ar dating indicates a hiatus in fluvial incision in the late early pleistocene as basalts dated to 1 22 0 02 and 1 07 0 03 ma overlie tigris gravels at very similar levels 60 70 m above the present river the lower terraces record the subsequent entrenchment of the modern tigris valley following an increase in incision rates in the early middle pleistocene evident from the disposition of younger basalt dated to 0 43 0 02 ma capping fluvial gravel only 21 22 m above the present river level numerical modelling can account for the observed uplift history as the response to coupling between surface processes and induced flow in the lower crust with the mobile lower crust thin 5 7 km thick consistent with the known presence of a thick layer of mafic underplating at the base of the crust beneath the arabian platform

post gondwana geomorphic evolution of southwestern africa implications for the controls on landscape development from observations and numerical experiments the relationship between morphology and surficial geology is used to quantify the denudation that has occurred across southwestern africa since the fragmentation of gondwana during the early mesozoic two main points emerge significant denudation of the order of kilometers is widespread except in the kalahari region of the continental interior the denudation is systematically distributed so that the continental exterior catchment draining directly to the cape basin is denuded to a greater depth than the interior catchment inland of the great escarpment the analysis also implies that the majority of the denudation occurred before the beginning of the cenozoic for both the exterior and interior catchments existing models of landscape development are reviewed and implications of the denudation chronology are incorporated into a revised conceptual model this revision implies that the primary effect of rifting on the subsequent landscape evolution is that it generates two distinct drainage regimes a marginal upwarp or rift flank uplift separates rejuvenated rivers that drain into the subsiding rift from rivers in the continental interior that are deflected but not rejuvenated the two catchments evolve independently unless they are integrated by breaching of the marginal upwarp if this occurs the exterior baselevel is communicated to the interior catchment that is denuded accordingly denudation rates generally decrease as the margin evolves and this decrease is reinforced by the exposure of substrate that is resistant to denudation and or a change to a more arid climate the observations do not reveal a particular style of smaller scale landscape evolution such as escarpment retreat that is responsible for the differential denudation across the region it is proposed that numerical model experiments which reflect the observational insights at the large scale may identify the smaller scale controls on escarpment development if the model and natural systems are analogous four numerical experiments are presented in which the roles of antecedent topography resistant substrate climate change and lowering the baselevel of the interior catchment are investigated for an initially high elevation margin bordered by an escarpment the model results suggest several styles of landscape evolution that are compatible with the observations escarpments may retreat in a regular manner but they also degrade and are destroyed only to reform at the drainage divide between exterior and interior catchments

late quaternary faunal change in coastal arabian sea sediments carbonate content and faunal composition of two gravity cores from the coastal arabian sea provide evidence of a major environmental change in surface ocean waters about 13 000 yr b p radiocarbon dating indicates that deposition rates ranged from 1 8 to 9 8 cm 103 yr with a major change in rate occurring in one core at about 7500 yr b p

influences of holocene sea level regional tectonics and fluvial gravity and slope currents induced sedimentation on the regional geomorphology of the continental slope off northwestern india abstract regional geomorphology derived from echosounding and bathymetric data lines of a total of 12 000 km depth to basement regional deep seated tectonic features surficial sediment distribution and holocene sedimentation rates of the continental margin off northwestern india are presented results indicate that the shelf edge over most of the region shelf break between 80 and 154 m water depth is covered with relict carbonate facies and partially buried bioherms of holocene age particularly off bombay and saurashtra regions significant changes in the depth and orientation of the shelf edge adjacent to saurashtra and the bombay high areas in relict carbonate facies are recorded at locations shelf edge depth is much more up to 150 m than the early holocene eustatic sea level still stand in this region about 100 m the upper boundary of the slope also varies considerably in depth about 1450 m in the vicinity of the indus fan having high sedimentation and 2900 m further southwards the gradient of the slope off the kachchh is steepest and some regional notches are observed at the upper slope the gentler slope off saurashtra and the bombay high area has large benches at depths of 180 230 m width 2 10 km and 650 780 m well below the holocene sea level the bombay high area has slope breaks between 400 and 600 m whereas off saurashtra steep breaks in the slope occur between 560 and 960 m depth further southwards at the foot of the slope elevations and depressions are present variations in the geomorphology of the slope off the northwestern continental margin of india are attributed to 1 late pleistocene holocene sea levels 2 regional tectonics 3 fluvial sedimentation and 4 gravity and slope currents induced sediment dynamics the locations under influences of slumping turbidity and tectonic movements with altered in situ sequence of sedimentations are delineated

accumulation rates of th 230 pa 231 and some transition metals on the bermuda rise abstract measurements of 238u 234u 230th 232th 231pa mn fe co ni cu and zn were made on 23 samples from core gpc 5 a 29 m giant piston core from a water depth of 4583 m on the northeastern bermuda rise 33 41 2 n 57 36 9 w this area is characterized by rapid deposition of sediment transported by abyssal currents unsupported 230th and 231pa are present throughout the core but because of large variations in the sedimentation rate show marked departures from exponential decay with depth the trend with depth of the 231 pa ex 230 th ex ratio is consistent with the average accumulation rate of 36 cm 1000 y reported earlier on the basis of radiocarbon dating and caco3 stratigraphy when expressed on a carbonate free basis concentrations of mn co ni cu zn 230thex and 231paex all show cyclic variations positively correlated with those of caco3 the correlations can be explained by a model in which all of these constituents including caco3 are supplied to the sediments from the water column at a constant rate concentration variations are controlled mainly by varying inputs of terrigenous detritus with low inputs occurring during interglacials and high inputs during glacials relationships between the metal and 230thex concentrations permit estimates of the rates at which the metals are removed to the sediment by scavenging from the water column the results in g cm2 1000 y are 4300 1100 for mn 46 16 for ni and 76 26 for cu these rates are somewhat larger than ocean wide averages estimated by other methods and the absolute rate of 230th accumulation in gpc 5 averages about nine times higher than production in the overlying water column this part of the bermuda rise and similar bottom current deposits may act as important accumulators of elements scavenged from seawater

late cenozoic uplift of the amanos mountains and incision of the middle ceyhan river gorge southern turkey ar ar dating of the duzici basalt using the ar ar technique we have obtained the first numerical dates for the pleistocene volcanism along the valley of the river ceyhan in the duzici area of southern turkey in the western foothills of the amanos mountains our six dates indicate a single abrupt episode of volcanism at 270 ka we have identified a staircase of 7 fluvial terraces at altitudes of up to 230 m above the present level of the ceyhan using the disposition of the basalt as an age constraint we assign these terraces to cold climate stages between marine oxygen isotope stages 16 and 2 indicating rates of fluvial incision equated to surface uplift that increase upstream through the western foothills of this mountain range at between 0 25 and 0 4 mm a 1 extrapolation of these uplift rates into the axis of the range suggests that the entire 2300 m of present day relief has developed since the mid pliocene a view that we confirm using numerical modelling since 3 7 ma the amanos mountains have formed a transpressive stepover along the northern part of the dead sea fault zone where crustal shortening is required by the geometry using a physics based technique we have modelled the overall isostatic response to the combination of processes occurring including crustal thickening caused by the shortening erosion caused by orographic precipitation and the resulting outward flow of mobile lower crustal material in order to predict the resulting history of surface uplift this modelling suggests that the effective viscosity of the lower crust in this region is in the range 1 2 1019 pa s consistent with a moho temperature of 590 10 c the latter value being in agreement with heat flow data this modelling shows that the nature of the active crustal deformation is now understood to first order at least in this key locality within the boundary zone between the african and arabian plates the structure and geomorphology of which have been fundamentally misunderstood in the past

distribution and dispersal of clay minerals on the western continental shelf of india abstract sediment samples distributed over a distance of 1700 km from the inner continental shelf of western india were analysed for their clay mineral content by x ray diffraction the clay minerals present in the sediments in order of abundance are montmorillonite kaolinite illite chlorite and gibbsite based on the abundance of montmorillonite and kaolinite four clay mineral provinces on the continental shelf have been demarcated these are 1 the montmorillonite kaolinite illite chlorite province off the gulf of kutch 2 the montmorillonite rich zone off the gulf of cambay 3 a transition zone on the central parts of the shelf and 4 a relatively montmorillonite poor gibbsite province on the southwestern part of the shelf source rock influence on clay mineral composition appears to be more important than physical transport the southwest monsoon drift in the present case in the northwestern part of the study area the high velocity tidal streams of the macrotidal gulf of kutch act as dynamic barriers to longshore sediment dispersal leading to distinct clay mineral assemblages on the shelf north and south of the gulf mouth

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

cenozoic cooling histories in the menderes massif western turkey may be caused by erosion and flat subduction not low angle normal faulting abstract since the early 1990s a prolific literature has developed on the interpretation within western turkey of apparent mid to late cenozoic low angle normal faults extension on these structures has been thought responsible for the exhumation of this region s principal metamorphic massif the menderes massif which has thus been interpreted as a metamorphic core complex nonetheless no convincing supporting structural evidence has emerged some reported instances of low angle normal faulting affecting the menderes massif can be shown from field relationships to have formed as steep normal faults and to have since become back tilted others seem to be misinterpretations of structures with no demonstrable relationship to extension at all the main evidence for low angle normal faulting in this region has instead emerged through thermochronology which indicates highly non uniform cooling histories that have seemed to lack any other explanation however this evidence can alternatively be explained by a combination of the cooling effects caused by flat subduction and by erosion there is thus no evidence for cenozoic low angle normal faulting affecting the menderes massif extension started at 11 ma in parts of western turkey but most of this region s late cenozoic extension on normal faults with steep initial dips has occurred since 7 ma synchronous with slip on the north anatolian fault zone

pliocene and quaternary regional uplift in western turkey the gediz river terrace staircase and the volcanism at kula abstract along the upper reaches of the gediz river in western turkey in the eastern part of the aegean extensional province the land surface has uplifted by 400 m since the middle pliocene this uplift is revealed by progressive gorge incision and its rate can be established because river terraces are capped by basalt flows that have been k ar and ar ar dated at present the local uplift rate is 0 2 mm a 1 uplift at this rate began around the start of the middle pleistocene following a span of time when the uplift was much slower this was itself preceded by an earlier uplift phase apparently in the late late pliocene and early early pleistocene when the uplift rate was comparable to the present the resulting regional uplift history resembles what is observed in other regions and is analogously interpreted as the isostatic response to changing rates of surface processes linked to global environmental change we suggest that this present phase of surface uplift amounting so far to 150 m is being caused by the nonsteady state thermal and isostatic response of the crust to erosion following an increase in erosion rates in the late early pleistocene most likely as a result of the first large northern hemisphere glaciation during oxygen isotope stage 22 at 870 ka we suggest that the earlier uplift phase responsible for the initial 250 m of uplift resulted from a similar increase in erosion rates caused by the deterioration in local climate at 3 1 ma this uplift thus has no direct relationship to the crustal extension occurring in western turkey the rate and sense of which are thought not to have changed significantly on this time scale our results thus suggest that the present often deeply incised landscape of western turkey has largely developed from the middle pleistocene onwards for reasons not directly related to the active normal faulting that is also occurring the local isostatic consequences of this active faulting are instead superimposed onto this background of regional surface uplift modelling of this surface uplift indicates that the effective viscosity of the lower continental crust beneath this part of turkey is of the order of 1019 pa s similar to a recent estimate for beneath central greece the lower uplift rates observed in western turkey compared with central greece result from the longer typical distances of fluvial sediment transport which cause weaker coupling by lower crustal flow between offshore depocentres and eroding onshore regions that provide the sediment source

the effect of the intermediate principal stress on fault formation and fault angle in siltstone abstract we conducted true triaxial compression tests on specimens prepared from two siltstone core sections one above and one below the chelungpu fault taiwan for different constant 2 and 3 magnitudes the maximum principal stress 1 was raised until a post failure stage was reached and a through going fault had developed despite differences between the properties of the two cores in all tests peak 1 increased as 2 was set at higher levels than 3 in contrast to mohr coulomb condition predictions the fault normal vector was aligned with the 3 direction and made an angle with 1 direction the angle which corresponds to fault dip in case of normal faulting increased monotonically with 2 for fixed 3 a variation that is also inconsistent with mohr coulomb theory the results of shear band localization theory are used with fault angles observed for axisymmetric compression and deviatoric pure shear to infer properties of the inelastic constitutive behavior these properties are significantly different for the two cores using them to predict for other deviatoric stress states yields good agreement with the observations for core ii and acceptable agreement for core i the results are used to predict the angle variation for constant mean normal stress decreases as the deviatoric stress state varies from axisymmetric extension to axisymmetric compression and at fixed deviatoric stress state decreases monotonically with increasing mean normal stress

polyaxial strength criteria and their use in estimating in situ stress magnitudes from borehole breakout dimensions abstract we conducted laboratory simulation tests of borehole breakouts and investigated their potential use as an indicator of in situ stress magnitudes in westerly granite and berea sandstone we also carried out simple triaxial tests and used the results to derive several strength criteria for these rocks using the assumption that the state of stress at the breakout boundary on the borehole wall is in a state of limit equilibrium with the rock strength we attempted to determine the appropriate strength criterion for each of the two rocks we concluded that the well known mohr coulomb criterion is not compatible with the condition of stress at breakout failure on the other hand truly triaxial polyaxial strength criteria which incorporate the effect of the intermediate principal stress on failure are much more in agreement with the stress at the breakout boundary one such criterion due to nadai and another due to mogi appear suitable for determining breakout failure in the sandstone and the granite respectively thin section analysis suggests that breakout failure mechanism may play an important role in determining the appropriate strength criterion for a given rock type utilizing the appropriate strength criterion for the corresponding rock type and having knowledge of the breakout span at the borehole wall and the minimum horizontal and vertical principal stresses we were able to estimate the maximum far field principal stress within an average of 14 error

palaeomagnetic study of tertiary volcanic domains in southern turkey and neogene anticlockwise rotation of the arabian plate abstract following collision with eurasia the arabian shield indenter has continued to deform into the weak anatolian collisional collage that resulted from subduction of the neotethyan ocean differential movements have involved rotation and continuing northwards translation and have been accommodated mainly by slip along major transforms including the northward extension of the dead sea fault zone dsfz and the east anatolian fault zone eafz to aid in evaluating post collisional motions the palaeomagnetism of extensive volcanic domains at the northern margin of the stable shield in southern turkey is reported here together with the timing of emplacement as constrained by k ar study the age dating results indicate that volcanic activity occurred mainly during mid late miocene times corresponding to the final stages of suturing volcanic fields in the east of the investigated region are younger and correspond to neotectonic volcanism in brunhes and matuyama chrons thermal and alternating field demagnetization of 399 cores from 83 sites in basaltic lavas identifies 29 units of normal and 43 of reversed polarity with 11 sites having transitional or random directions volcanic fields west of the euphrates kilis gaziantep region with ages in the range 7 0 20 3 ma average 14 9 ma sd 4 3 ma have mean remanence d i 353 52 38 sites 5 3 lava fields east of the euphrates urfa region are dated 10 4 12 1 ma and yield a comparable mean remanence d i 350 50 17 sites 6 0 these collections are shown to have properly recorded palaeosecular variation with only minimal inclination shallowing and inferred anticlockwise rotations with respect to eurasia since mid miocene times are 10 9 4 3 and 14 0 5 0 respectively these contrast with clockwise rotation of 6 3 4 3 derived from late matuyama brunhes epoch volcanic rocks immediately to the north west of the arabian margin where rotational impingement of the shield indenter into fault blocks within the karasu rift at the northern extension of the dsfz interacts with left lateral motion at a rate of 0 5 cm year along this zone to produce small scale vertical axis rotations results from the volcanic suites sited on the stable shield are compared with other results from the arabian plate to conclude that it did not rotate significantly following closure of the bitlis suture until late miocene early pliocene times since when it has rotated anticlockwise at a rate of 1 0 myr this is comparable to the present day rate of rotation deduced from gps and correlates with crustal separation and sea floor spreading in the red sea it also temporally links the rotation of the arabian plate to the initiation of the intracontinental transforms north and east anatolian fault zones within anatolia and to the subsequent extrusion of blocks within this accretionary domain by tectonic escape to the west

late palaeogene neogene evolution of the triple junction region near maras south central turkey the marao region of turkey includes the anatolian arabian african triple junction the african arabian margin is marked by left lateral transtension along the dead sea kara su rift motion on the anatolian arabian boundary is partitioned between the left lateral east anatolian fault and a fold thrust belt termed the engizek zone equivalent to the bitlis suture further east the african anatolian boundary lies along the cyprus misis andirin trend and is expressed near the triple junction as the aslantao iskenderun zone now undergoing slow left lateral transtension the neogene evolution of these boundaries is largely recorded in the stratigraphy and structure of the basins that lie along the anatolian arabian lice basin and anatolian african aslantao iskenderun basin boundaries these basins appear to have developed in the early miocene along major strike slip zones large half graben in the pre neogene 9basement9 of the western misis andirin block developed contemporaneously with motion on the anatolian african boundary these extensional features evolved subsequent to the intense shattering of the mesozoic carbonate sequence in the misis andirin block and its mixing with panels of deep water palaeogene strata to form an extensionally disrupted assemblage transpression and conversion of both anatolian african and anatolian arabian boundaries to fold thrust belts occurred in the late miocene transpression continues along the anatolian arabian boundary but transtension has recurred along the anatolian african boundary since the pliocene

flow in the lower continental crust as a mechanism for the quaternary uplift of south east england constraints from the thames terrace record abstract the sequence of terraces of the river thames in south east england has been shown to date from the early pleistocene onwards and to provide an indication of the quaternary uplift history of the region using this evidence supplemented by altitudes of pliocene and early pleistocene marine sediments we have determined the pliocene and quaternary uplift histories of five representative localities clacton colchester and dartford for the lower thames and cookham and reading for the middle thames these uplift histories have been modelled using a physics based technique which calculates the isostatic response involving flow in the lower continental crust induced by cyclic loading at the earth s surface our results suggest that the late pliocene and early pleistocene part of the uplift history of our study region was initiated following the deterioration in climate starting at 3 1 ma which marked the start of upland glaciation elsewhere in europe the later increase in uplift rates in the middle pleistocene followed the start of intensified cyclic loading by very large continental ice sheets during and after oxygen isotope stage ois 22 at 0 87 ma dartford cookham and reading in the interior of south east england are all shown to have begun to uplift quite rapidly at rates of up to 0 1 mm a 1 following the start of forcing at 3 1 ma they have since uplifted by distances which increase gradually westward from 200 to 250 m of which a uniform 70 m has occurred since ois 22 at 0 87 ma in contrast clacton and colchester near the present north sea coastline experienced slow subsidence until the late early pleistocene but have nonetheless uplifted since ois 22 by similar distances to the other sites

forested arctic evidence from north greenland shallow water marine sediments of the kap kabenhavn formation at lat 82 30 n perry land north greenland contain an abundance of well preserved remains of terrestrial vegetation and invertebrate fauna indicative of a mosaic of forest tundra environments having similarities to present conditions in labrador the presence of foraminifera faunas marine molluscs and one mammal species supported by studies of paleomagnetism and amino acid diagenesis suggests an age of 2 ma at the pliocene pleistocene transition at this time the arctic tree line was located 2500 km to the north of its present position in the northwest atlantic region and forest tundra vegetation existed in lowland areas bordering on an arctic ocean without perennial sea ice cover

a numerical modelling technique that can account for alternations of uplift and subsidence revealed by late cenozoic fluvial sequences abstract alternations between fluvial incision and aggradation in response to switches between uplift and subsidence and occurring over timescales of many hundreds of thousands of years have been documented in many regions worldwide contrasting markedly with the monotonic histories of uplift or subsidence evident elsewhere it has been noted that this pattern of reversals in vertical crustal motion is only observed in regions where the mobile lower crustal layer is thin 6 km thick suggesting a cause and effect connection with the physical properties of the underlying continental lithosphere it is proposed that these reversals result from the interplay between the isostatic responses to erosional unloading by lower crustal flow and by mantle lithosphere relaxation estimates of the characteristic timescale for relaxation of the continental mantle lithosphere range from several hundred thousand years in regions of cold crust with a thin mobile lower crustal layer to a few tens of thousands of years in regions of hot crust where the mobile lower crustal layer is thicker in regions of hot crust relaxation of the mantle lithosphere requires a shorter characteristic timescale than flow within the lower crust the complex interaction between these processes means that isostatic compensation of crustal thickening in regions of hot crust will typically involve surface uplift the development of a lower crustal root and thinning of the mantle lithosphere the observation of alternations between uplift and subsidence in long timescale fluvial sequences and the proposed physical interpretation demonstrate the importance of fluvial records for providing unique high resolution control on deformation of the continental lithosphere and for constraining its layered rheology

palaeomagnetic study of the karacadag volcanic complex se turkey monitoring neogene anticlockwise rotation of the arabian plate abstract the karacadag volcanic centre in south east turkey is a major basaltic complex sited at the northern margin of the arabian plate and emplaced in several pulses between 11 ma and late quaternary times we have sampled 71 sites in lavas of this complex to constrain the palaeomagnetic record and hence the chronology of magmatic activity and regional rotation palaeomagnetic study at sixty two sites yields significant component definition with mixed normal and reversed polarities from age dating and morphologic criteria we identify three major episodes of lava emplacement and site mean directions of magnetisation for these divisions resolve migration of the palaeofield direction for the northern sector of the arabian plate since mid miocene times successive reversed polarity group mean directions are d i 175 50 5 n 37 r 33 13 95 4 1 for the oldest siverek division mean age estimate 11 1 6 7 ma d i 173 4 46 0 n 16 r 15 67 95 5 5 for the middle karacadag division mean age 3 3 ma and d i 167 7 47 6 n 6 r 5 93 95 7 9 for the youngest ovabag division 1 9 ma present the first two results merit a tectonic interpretation and consistent anticlockwise rotation of 9 is recognised in the karacadag volcanic centre between 11 and 3 3 ma the mean directions conform to palaeomagnetic results from other undeformed neogene igneous complexes of comparable age range further to the west along the northern perimeter of the arabian plate the amount of tectonic rotation observed in late pliocene and older volcanic units from this plate is found to be statistically constant tectonism responsible for rotation therefore appears to have been temporally confined to the last 2 myr which is long after collision with the anatolides and closure of the bitlis suture this conclusion conforms to the young distributed block rotations recognised in the anatolides and aegean and correlates with the regime of tectonic escape of terranes to the west

regional stress alignments in the kutai basin east kalimantan indonesia a contribution from a borehole breakout study abstract borehole breakout data from 134 wells located within the kutai basin region east kalimantan were analyzed to determine the present day regional horizontal stress alignments the data were extracted from various types of dipmeter logs the study reveals that the majority of the data give a coherent picture of breakout orientation the mean azimuths for the entire unweighted ellipticity weighted and magnitude weighted data sets are preferentially aligned in the regional mean direction of 48 9 n or 128 9 n most of the data have a low dispersion value s o and the ranking of reliability in zoback s classification is a there is no significant azimuth variation with depth these relatively consistent alignments of breakout azimuths indicate that the maximum regional stress direction in the study area is nw se this regional mean of breakout azimuths deviates from the axis of the anticlinorium trends and from the strike of the thrust fault patterns in the region it is believed that these structural patterns are influenced by reactivation of weak zones related to sediment loading structural inversion

river terrace development in the ne mediterranean region syria and turkey patterns in relation to crustal type it is widely recognized that the optimal development of river terraces globally has been in the temperate latitudes with nw and central europe being areas of particular importance for the preservation of such archives of quaternary environmental change there is also a growing consensus that the principal drivers of terrace formation have been climatic fluctuation against a background of progressive but variable uplift nonetheless river terraces are widely preserved in the mediterranean region where they have often been attributed to the effects of neotectonic activity with a continuing debate about the relative significance of fluctuating temperature glacials interglacials and precipitation pluvials interpluvials research in syria and southern central turkey specifically in the valleys of the tigris and ceyhan in turkey the kebir in syria and the trans border rivers orontes and euphrates has underlined the importance of uplift rates in dictating the preservation pattern of fluvial archives and has revealed different patterns that can be related to crustal type the ne mediterranean coastal region has experienced unusually rapid uplift in the late quaternary the relation between the kebir terraces and the staircase of interglacial raised beaches preserved along the mediterranean coastline of nw syria reinforces previous conclusions that the emplacement of the fluvial terrace deposits in the mediterranean has occurred during colder climatic episodes

response of infaunal macrobenthos to the sediment granulometry in a tropical continental margin southwest coast of india abstract surficial sediment samples collected from the continental margin of the southwest coast of india in july 2004 were examined for the grain size and soft bottom macrobenthic fauna to understand the sediment granulometry and its effect on the faunal distribution samples were collected using smith mcintyre grab from 20 to 200 m depth range consisting of mid shelf outer shelf and slope fine grained sediment located in the mid shelf and supported low faunal abundance polychaetes constituted the bulk of the fauna feeding guild changed with depth and sediment granulometry coexistence of deposit feeders and carnivores in outer shelf and deposit feeders and filter feeders in the slope region indicated the effective utilization of different food resources in general richness and diversity were high in the southern region depth wise the diversity and abundance were relatively high in the 50 75 m depth range correlation and bio env analysis showed that combination of different factors such as sediment texture sediment sorting and depth were found to influence the distribution of macrobenthos hence spatial variations observed in benthic community were presumably linked to the variations in sediment granulometry and the energy level conditions prevailing in the area

uranium isotopes in rivers estuaries and adjacent coastal sediments of western india their weathering transport and oceanic budget the two major river systems on the west coast of india narbada and tapti their estuaries and the coastal arabian sea sediments have been extensively studied for their uranium concentrations and 238u238u activity ratios the 238u concentrations in the aqueous phase of these river systems exhibit a strong positive correlation with the sum of the major cations na k mg ca and with the hco3 ion contents the abundance ratio of dissolved u to the sum of the major cations in these waters is similar to their ratio in typical crustal rocks these findings lead us to conclude that 238u is brought into the aqueous phase along with major cations and bicarbonate the strong positive correlation between 238u and total dissolved salts for selected rivers of the world yield an annual dissolved 238u flux of 0 88 1010g yr to the oceans a value very similar to its removal rate from the oceans 1 05 1010g yr estimated based on its correlation with hco3 contents of rivers in the estuaries both 238u and its great grand daughter 234u behave conservatively beyond chlorosities 0 14 g l these data confirm our earlier findings in other indian estuaries the behavior of uranium isotopes in the chlorosity zone 0 02 0 14 g l was studied in the narbada estuary in some detail the results though not conclusive seem to indicate a minor removal of these isotopes in this region reexamination of the results for the gironde and zaire estuaries martin et al 1978a and b also appear to confirm the conservative behavior of u isotopes in unpolluted estuaries it is borne out from all the available data that estuaries beyond 0 14 g l chlorosities act neither as a sink nor as a source for uranium isotopes the behavior in the low chlorosity zones warrants further detailed investigation a review of the uranium isotope measurements in river waters yield a discharge weighted average 238u concentration of 0 22 g l with a 234u238u activity ratio of 1 20 0 06ismissing the residence time of uranium isotopes in the oceans estimated from the 238u concentration and the 234u238u a r of the rivers yield conflicting results the material balance of uranium isotopes in the marine environment still remains a paradox if the disparity between the results is real then an additional 234u flux of about 0 25 dpm cm2 103 yr into the oceans about 20 of its river supply is necessitated

stress magnitudes in the basel enhanced geothermal system abstract this paper presents the results of an evaluation of stress magnitudes in the granitic egs reservoir in basel switzerland the profile of minimum principal horizontal stress shmin is constrained by hydraulic tests but the magnitude of the maximum horizontal principal stress shmax is uncertain here we derive estimates for shmax by analysing breakout width data from an acoustic televiewer logs run in the granitic basement section of the bs 1 borehole some 81 of the borehole in the granite is affected by breakouts the approach employed to derive shmax magnitude from the estimated breakout widths is taking into account all stress components at the borehole wall including the remnant thermal stress arising from the cooling of the borehole wall by the drilling in bs 1 breakouts width tends to decrease with depth assuming there is no significant systematic change in the strength characteristics of the rock along the length of the hole for which there is no evidence the large scale trend has the consequence of implying a small gradient of the shmax profile a low shmin gradient was also implied by a stress analysis that additionally considered the occasionally coincident presence of drilling induced tension fractures the absolute values of shmax depend upon the failure criterion used criteria that consider the strengthening effect of the intermediate stress mogi coulomb and hoek brown 3d yield profiles that violate frictional limits on the strength of the crust above 4 km whereas the profiles of the mohr coulomb and rankine criteria do not the mohr coulomb criteria profiles indicate a trend in shmax from favoring strike slip faulting above 4200 m to strike slip normal faulting below this is consistent with focal mechanisms recorded during the reservoir stimulation which show a mix of strike slip and normal faulting throughout the depth range considered

non dilatant deformation and failure mechanism in two long valley caldera rocks under true triaxial compression abstract we conducted laboratory rock strength experiments in two ultra fine grained brittle rocks hornfels and metapelite which together are the major constituent of the long valley caldera california usa basement in the 2025 2996 m depth range both rocks are banded and have very low porosity uniaxial compression tests at different orientations with respect to banding planes reveal that while the hornfels compressive strength is nearly isotropic the metapelite possesses distinct anisotropy conventional triaxial tests in these rocks reveal that their respective strengths in a specific orientation increase approximately linearly with confining pressure true triaxial compression experiments in specimens oriented at a consistent angle to banding in which the magnitudes of the least 3 and the intermediate 2 principal stresses are different but kept constant during testing while the maximum principal stress is increased until failure exhibit a behavior unlike that previously observed in other rocks under similar testing conditions for a given magnitude of 3 compressive strength 1 does not vary significantly in both long valley rock types regardless of the applied 2 suggesting little or no intermediate principal stress effect strains measured in all three principal directions during loading were used to obtain plots of 1 versus volumetric strain these are consistently linear almost to the point of rock failure suggesting no dilatancy the phenomenon was corroborated by sem inspection of failed specimens that showed no microcrack development prior to the emergence of one through going shear failure plane steeply dipping in the 3 direction the strong dependency of compressive strength on the intermediate principal stress in other crystalline rocks was found to be related to microcrack initiation upon dilatancy onset which rises with increased 2 and retards the failure process we infer that strength independence of 2 in the long valley rocks derives directly from their non dilatant deformation

well bore breakouts and in situ stress the detailed cross sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data we show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression this work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ

210pb activities in and fluxes to sediments of the washington continental slope and shelf abstract surface sediments of the washington coast have 210 pb activites which average 104 48dpm g for submarine canyon and slope regimes and 18 12dpm g for the continental shelf regime 210 pb sedimentary fluxes are also higher in canyons averaging 18 13dpm cm 2 per yr compared to 5 2 3 1 dpm cm 2 per yr for slope and 4 8 1 8dpm cm 2 per year for shelf regions these 210 pb activities and fluxes are 2 7 times greater than those reported for other coastal regions inputs from the atmosphere and the columbia river are not sufficient to supply the 210 pb but advection of seawater containing dissolved 210 pb produced in situ from 226 ra provides an input several times larger than the sedimentary fluxes the sedimentary 210 pb flux is limited by scavenging reactions rather than by supply of dissolved 210 pb calculations of maximum biological uptake and fluxes of 210 pb and selective chemical leaching experiments all show that the primary scavenging processes are due to hydrous mn and fe oxides rather than biological phases the pattern of higher 210 pb depositional fluxes in canyons than in nearby open slope areas of comparable water depth is most reasonably explained by enhanced scavenging of dissolved 210 pb near the sea floor rather than by processes operating throughout the water column relatively rapid removal of dissolved 210 pb from the near bottom nepheloid layer to slope and canyon sediments is shown by its mean residence time of less than two years in this layer

the somme valley terrace system northern france a model of river response to quaternary climatic variations since 800 000 bp recent research on the somme valley terrace deposits that began in 1987 has resulted in an integrated sequence of geological and geomorphological evidence for this area that is of particular significance for prehistoric investigations this has been achieved using previous evidence and new results from archaeological and geological excavations these include longitudinal profiles cartography and detailed synthesis of sections of alluvial deposits stratigraphy of river deposits and overlying loess sequences the work based on a study of the geometry of the terrace system has resulted in the identification of ninestepped alluvial formations that occur along 70 km of the valley detailed study permits the integration of the various alluvial sequences this suggests that each alluvial sequence results from sedimentation through a single glacial interglacial climatic cycle this hypothesis is confirmed by investigation of soil and loess sequences of the deposits overlying the fluvial sediments the synthesis presented provides a basis for understanding the deposition of the terrace system and an initial chronostratigraphic interpretation for the deposits

durability assessment of the basalts used in the diyarbakir city walls turkey the diyarbakir city walls dcw which were recently added to unesco s world heritage list are among the largest and one of the most impressive monuments from ancient times the history of the dcw stretches back more than 4000 years therefore making the extant city walls a combination and reflection of influences of the various civilizations that settled in the region basalts having such different textural properties as massive and vesicular were employed as the principal material in the construction of the dcw like many other historical structures the dcw are suffering from stone deterioration a large variety of weathering forms can be observed on the basalts used in different sections of the dcw the behavior of the basalt under different cyclic environmental conditions is not known in this study deterioration mechanisms of the basalts were investigated with field and laboratory studies it is found that iddingsite is a common weathering product developed through the crystal boundaries of olivine accelerated weathering tests show that salt crystallization is the most effective deterioration mechanism the field and laboratory studies indicate that both massive and vesicular basalts are durable however the massive basalts are more durable than the vesicular ones it is also observed that although chemical processes slightly trigger the deterioration mechanisms of the rocks most of the weathering forms on the dcw are controlled by the physical factors affecting the parameters of the basalts such as porosity water absorption and uniaxial compressive strength

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

late cenozoic regional uplift and localised crustal deformation within the northern arabian platform in southeast turkey investigation of the euphrates terrace staircase using multidisciplinary techniques we present the results of detailed field investigations of the fluvial succession exposed along the euphrates valley adjoining the ataturk dam in the northern part of the arabian platform within se turkey this work which has used differential gps surveying to obtain accurate heights of deposits and shuttle radar topographic mission imagery for location purposes has included documentation of many fresh sections exposed by quarrying the work has been supplemented by unspiked kar dating of late middle miocene to late miocene basalt flows which are widespread in the region providing a chronology for the early stages of development of this river system following regional emergence above sea level in the early middle miocene for example beside the ataturk dam lake at siverek iskelesi basalt dated to 10 24 0 22 ma 2 caps a polymict euphrates gravel some 80 m above the modern river this is the oldest euphrates terrace currently recognised however amounts and rates of fluvial incision are shown to vary across the northern arabian platform in a complex manner due to the interaction between regional uplift and localised vertical crustal motions caused by slip on active reverse faults beneath anticlines the study reach downstream of the ataturk dam includes the footwall of one such fault beneath the bozova anticline we estimate that the resulting rate of localised subsidence superimposed onto the regional uplift that has also been occurring has been 0 01 mm a 1 during the present phase of crustal deformation which began at 3 7 3 6 ma but was higher maybe 0 03 mm a 1 during the previous phase which began at 6 ma when the pattern of plate motions in the surrounding region was different a large palaeo lake centred north of the present study region around the city of adiyaman is inferred to have existed during this 6 ma to 3 7 3 6 ma phase of plate motion apparently because the relatively rapid localised hanging wall uplift on the northern flank of the bozova anticline dammed the euphrates valley near the site of the modern ataturk dam the uppermost part of a thick fluvial aggradation west of the euphrates near karababa bridge inferred to date from around the mid pliocene reaches 100 m above the modern river and after correction for an estimated 30 m of localised subsidence and by 50 m for subsequent downstream lengthening of the euphrates channel indicates 180 m of subsequent regional uplift the euphrates then incised to within 20 m of its present level by the mid early pleistocene then a switch to regional subsidence accompanied the deposition of a second thick fluvial aggradation the top of which is 70 m above the modern river subsequent renewed regional uplift following the mid pleistocene revolution has resulted in the development of a succession of fluvial terraces typically inset into these older aggradations which are correlated with the cold stages of milankovitch climate cycles the early part of the euphrates chronology constrained mainly by the disposition of basalt flows indicates 800 m of regional uplift since the early middle miocene of which an estimated 330 m is masked by the subsequent downstream lengthening of the river components of localised uplift and subsidence caused by slip on reverse faults beneath anticlines are superimposed onto this regional pattern the hanging wall uplift being much larger in one case roughly five times larger than the footwall subsidence our results provide for the first time detailed documentation of the complex development of the euphrates valley in se turkey during the late cenozoic due to the interaction between regional uplift and localised crustal deformation this work also demonstrates the benefits of applying multidisciplinary techniques to investigate an important but hitherto poorly documented river system

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

regional heat flow in western anatolia using silica temperature estimates from thermal springs regional trends of variation of heat flow in western anatolia have been outlined using the silica temperature estimator on thermal springs silica heat flow values from 187 springs have been calculated the data are corrected for local long term mean annual surface temperature a mean value of heat flow for the western part of anatolia of 107 45 mw m 2 has been obtained which is about 60 above the world average the silica heat flow data are compared with available conventional heat flow values for this region a general agreement is observed and new patterns are recognized a close association exists between areas of high silica heat flow values above 100 mw m 2 and areas of tertiary and younger volcanism high heat flow is also observed in palaeozoic units of the menderes massif which is under tensional stress the highest heat flow estimate of 247 mw m 2 is obtained near gediz 38 57 n 29 13 2 e this area is part of a seismically active region and is located near a middle eocene subduction zone which is an area of later collision tectonics the new heat flow data from western anatolia improve our knowledge of the thermal conditions within the crust this information is important for the analysis of various geophysical and geological phenomena including seismicity

a note on the factors controlling the sedimentation rate along the western continental shelf of india abstract to study variations in sediment accumulation along the western continental shelf of india sedimentation rates have been measured in two cores from the shelf off mangalore the rates obtained are 0 72 and 0 56 mm yr for water depths of 35 and 45 m respectively these are significantly lower than those of the northern continental shelf north of 18 n where sedimentation rates range between 1 8 and 19 mm yr the low rates in the southern area are due to the low concentrations of suspended particulate matter spm coming from rivers such as the netravati and gurpur that drain into the study area these rivers contribute only about 8 of the total discharge of all the west flowing rivers of the indian peninsula whereas rivers flowing onto the northern continental shelf have high spm concentrations and contribute about 45 of the total discharge of the west flowing rivers the occurrence of outer shelf sands ranging in age from 9000 to 11 000 yrs b p at various depths below mean sea level in the northern and southern parts of the western continental shelf may be indicative of neotectonic activity and the presence of such activity is supported by the occurrence of recent earthquakes and hot springs in western india the northward compression of the western indian continental margin coastal geomorphic features and epeirogenic movement of the west indian landmass however it could also be the result of differing influxes of terrigenous sediment and of riverine particulates travelling over different distances into the arabian sea

a critical evaluation of depositional parameters controlling the variability of organic carbon in arabian sea sediments abstract organic carbon distribution in the surficial sediments of the arabian sea to some extent mirrors the surface productivity being both high in the peripheral portions and low in the central region suggesting that the productivity is a primary source of organic matter however a critical examination reveals that the organic enrichment on the slope of the indian margin is two to four higher max 16 71 than on the slope of the arabian peninsula max 7 54 while the productivity in the former region is three to four times lower than the latter this observation suggests that the influence of productivity on organic enrichment is of secondary importance high concentrations 4 of organic carbon exactly coincide with the oxygen minimum zone 150 1500 m water depth evidently reflecting the crucial role played by the anoxic bottom waters in the preservation of organic carbon incidently the organic rich band along the western indian slope is wide long and highly concentrated as compared to that of the slope of the arabian peninsula and no organic enrichment is found on other continental slopes of the arabian sea although an equally intense oxygen minima impinge on the floor of the slope such a variability of organic carbon on the slopes is attributed to various geological parameters such as texture of sediments rates of fine terrigenous sediment deposition shelf width slope gradient bottom currents and adsorption capacity of individual clay minerals all these observations suggest that the productivity is not an ultimate control for the organic enrichment of bottom sediments but it is the bottom water anoxia in conjunction with various depositional parameters which determine the degree of preservation

climate controlled river terrace formation in the kizilirmak valley cappadocia section turkey inferred from ar ar dating of quaternary basalts and terraces stratigraphy abstract this study was carried out on the cappadocia section of the kizilirmak river valley the longest river completely within the borders of turkey 1355 km a staircase of fifteen terraces found in the valley is maintained against erosion at elevations up to 160 m above the current river level the gulsehir karaburna quatenary basalts four basalt flows which cap four terraces were numerically dated for the first time using the ar ar technique the evren ridge basalt 1 160 m above the river level and capping terrace 1 was dated to 1989 4 38 9 ka the karaburna basalt plateau 2 is 128 m above the river level and caps terrace 4 and was dated to 1228 2 46 4 ka the tuzkoy basalt plateau 3 29 m above the river level and capping terrace 12 was dated to 403 8 9 8 ka and the karniyarik hill basalts 4 at 4 5 m above the river level and capping terrace 15 were dated to 96 0 13 0 ka these basalt ages provide minimum ages for the underlying fluvial deposits on the one hand these data show that kizilirmak river incised its valley by 160 m during the last 2 ma of its evolution on the other hand by using terrace sequences and basalt ages the time averaged incision rate of the river during the last 2 ma was determined as approximately 0 08 mm a 1 but important variations within that time span are also apparent the highest incision rate during this period was determined to be 0 12 mm a 1 between the late early and mid middle pleistocene from the numerical chronology terrace stratigraphy and paleosol records it is suggested that the main incision phases of the kizilirmak river led to terrace formation during the cold periods and the deposition phases occurred during the warm periods including cold warm transitions as a result of assigning terraces to marine oxygen isotope stages it was inferred that nearly all terrace levels had formed during the eccentricity driven climate cycles in association with high uplift rates which were interpreted as being complete in the valley

stress orientations from borehole wall fractures with examples from colorado east texas and northern canada azimuthally aligned breakouts in oil wells are explained as shear fractures in the zone of amplified stress difference near the borehole in a stress field having unequal horizontal principal stres

three dimensional s wave structure of the upper mantle beneath turkey from surface wave tomography summary a 3 d upper mantle structure beneath turkey is investigated using phase speeds of fundamental mode rayleigh waves employing a conventional two station method with high density seismic networks in turkey we analyse 289 seismic events with moment magnitude 5 5 and greater and with focal depth shallower than 100 km between 2006 and 2008 waveform data are derived from 164 three component broad band seismic stations operated by two national seismic networks at first rayleigh wave phase speed maps are obtained from the inversion of two station phase speeds using about 1000 3000 paths depending on the period of rayleigh waves the three dimensional s wave model is then obtained in the depth range from 40 to 180 km using the phase speed maps in the period range from 25 to 120 s our model reveals the fast anomalies in the north of cyprus associated with the subducted portion of the african oceanic lithosphere from the cyprus trench we identify a vertical discontinuity of the fast anomaly associated with the cyprus slab starting at 60 80 km depth which may represent a minor tear of the cyprus slab we observed that the western part of the cyprus slab is getting closer to the edge of the hellenic slab beneath the isparta angle ia and antalya basin our model also indicates a slow wave speed anomaly beneath the ia and antalya basin probably due to hot materials of asthenosphere rising from a tear of the subducted african oceanic lithosphere that is a slab tear between the cyprus and the hellenic subductions in the eastern part of turkey a widespread slow anomaly appears in the model that corresponds to the eastern anatolian accretionary complex eaac our model shows a fast anomaly beneath the eaac that can be interpreted as the detached portion of the subducted arabian lithosphere

modern sediment accumulation and strata formation on the amazon continental shelf abstract formation of fine scale cm strata on the amazon continental shelf was investigated using radiographic and radiochemical e g 210pb techniques three distinct sedimentary environments are found within the inner shelf m water depth mud deposit 1 interbedded mud and sand in a corridor extending from the river mouth across the inner shelf 2 faintly laminated muds on both flanks of the corridor and 3 bioturbated muds comprising the remainder of the deposit high rates of sediment accumulation 2 cm yr are found in the region of interbedded mud and sand and in the regions of faintly laminated muds accumulation rates in the region of bioturbated muds are relatively low 0 1 2 cm yr and an inverse relationship is observed between accumulation rate and extent of sedimentary structure alteration by benthic fauna a first order sediment budget indicates that sediment accumulation on the amazon shelf between the brazil french guiana border and the para river is nearly equal to estimates of sediment discharged by the amazon river 9 10 8 tons yr the model of amazon shelf sedimentation most consistent with the radiographic and radiochemical data suggests that the inner shelf mud deposit is a subaqueous delta prograding seaward over relict basal sands and that a turbulent jet emanates from the river mouth with competence during some flood periods to carry sand as bedload across the inner shelf the presence of cross bedded sands in the corridor of interbedded mud and sand supports the hypothesis of a turbulent jet the faintly laminated muds probably represent suspended sediment rapidly deposited on both sides of the jet

clay sediment accumulation rates on the monsoon dominated western continental shelf and slope region of india abstract clay accumulation rates shown in sediment cores from the nearshore to outer continental shelf and slope regions in water depths of 10 1246 m on the western continental margins of india were determined by the 210 pb dating technique the 210 pb excess concentration encountered in these regions is about 3 5 dpm g and is independent of water depth the range of clay accumulation rates is from 1 8 to 19 mm yr for the shelf region and decreases southward from the tapti and narbada river confluence in the gulf of cambay this pattern indicates sediment dispersal in the coastal region regulated by southwest monsoon dominated littoral currents the same trend is encountered all along the southwestern traverse this suggests that suspended matter transport across the shelf is minimal since clay accumulation rates on the outer shelf are only 1 8 2 5 mm yr the clay accumulation rate in the slope region is 3 8 mm yr the high accumulation rates encountered on the upper continental slope may be attributed to the terrigenous influx of indus river sediment

an obliquity controlled early pleistocene river terrace record from western turkey investigation of the pleistocene sequence of the gediz river western turkey has revealed a record of early pleistocene river terraces eleven terraces spanning the interval from 1 67 to 1 245 million years ago mis 59 37 are preserved beneath basaltic lava flows the high number of terraces over this short time period reflects high frequency sedimentation incision cycles preserved due to the fortuitous combination of relatively high uplift rates 0 16 mm yr 1 and progressive southwards valley migration comparison of this record with odp967 from the eastern mediterranean basin suggests a link between the production of terraces and obliquity driven 41 000 year climate cycles in the early pleistocene

changing environmental conditions in recent past reading through the study of geochemical characteristics magnetic parameters and sedimentation rate of mudflats central west coast of india abstract geochemical sediment components major and trace metals magnetic related parameters concentration mineralogy and grain size and radionuclide 210 pb analyses were carried out on sediment cores collected from mudflat regions of central west coast of india viz kolamb creek malvan mandovi estuary panaji and tadri creek gokarn in order to study the variations in sediment characteristics with time the changes in spatial and temporal depth distributions of sediment composition were observed to be mainly controlled by the catchment area geology geomorphology and anthropogenic activities the sedimentation rate in the study area varied from 0 13 to 2 cm yr the rate was extremely low at the lower half of the cores 0 13 0 31 cm yr before 1980 as compared to the near surface 1 21 2 cm yr after 1980 with two clear phases of sedimentation rates the higher sedimentation rate in the upper portions of the cores was found to correspond to increased deposition of finer sediment components metals and magnetic minerals which in turn were found to be mainly controlled by geology and or human activities the results of the present study reveal variations in sediment properties with time and support the use of geochemical in addition to magnetic susceptibility parameters on mudflats to understand changing environmental conditions of recent past

glaciers and rivers pleistocene uncoupling in a mediterranean mountain karst abstract large scale coupling between headwater catchments and downstream depocentres is a critical influence on long term fluvial system behaviour and on the creation of the fluvial sedimentary record however it is often difficult to examine this control over multiple quaternary glacial cycles and it has not been fully explored in karst basins by investigating the pleistocene glacial and fluvial records on and around mount orjen 1894 m in montenegro we show how the changing connectivity between glaciated mountain headwater source zones and downstream alluvial basins is a key feature of long term karst system behaviour especially in relation to the creation and preservation of the surface sedimentary record middle and late pleistocene glacial deposits are well preserved on mount orjen uranium series dating of 27 carbonate cements in fluvial sediments shows that many alluvial depocentres were completely filled with coarse glacial outwash before 350 ka during the largest recorded glaciation this major glaciation is correlated with the skamnellian stage in greece and marine isotope stage 12 mis 12 c 480 420 ka this was a period of profound landscape change in many glaciated catchments on the balkan peninsula later glaciations were much less extensive and sediment supply to fluvial systems was much diminished the extreme base level falls of the late miocene produced the world s deepest karst networks around the mediterranean after mis 12 the subterranean karst of mount orjen formed the dominant pathway for meltwater and sediment transfer so that the depositional basins below 1000 m became disconnected uncoupled from the glaciated headwaters there is little evidence of post mis 12 aggradation or incision in these basins this absence of later pleistocene and holocene fluvial activity means these basins contain some of the thickest and best preserved outwash deposits in the mediterranean