metal contents of phytoplankton and labile particulate material in the north atlantic ocean abstract phytoplankton contribute significantly to global c cycling and serve as the base of ocean food webs phytoplankton require trace metals for growth and also mediate the vertical distributions of many metals in the ocean we collected bulk particulate material and individual phytoplankton cells from the upper water column

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

palaeoproterozoic 1 9 ga extension and breakup along the eastern margin of the eastern dharwar craton se india new sm nd isochron age constraints from anorogenic mafic magmatism in the neoarchean nellore greenstone belt abstract the neoarchean nellore greenstone belt located along the eastern margin of the eastern dharwar craton was the site for younger igneous activity the timing of this magmatism and the host metabasalt critical for constraining extensional events along the deformed southeast margin of the eastern dharwar craton was conducted by the sm nd method samples from the large differentiated gabbroic kandra igneous complex a subset kandra group a define an isochron age of 1926 110 ma nd i 0 51006 12 mswd 0 98 n 5 e nd 1 7 and the kandra group b subset yielded a model 3 isochron age of 1882 120 ma nd i 0 50994 14 mswd 1 8 n 4 e nd 5 1 whereas the three samples from north pamuru gabbro anorthosite yielded an isochron age of 1882 160 nd i 0 51012 18 mswd 0 064 e nd 1 7 the kandra group a and north pamuru samples regressed together yielded a preferred isochron age of 1911 88 ma nd i 0 51008 10 mswd 0 62 n 8 e nd 1 6 for the emplacement of gabbros in contrast host greenstone belt metabasalt from chundi yielded a sm nd isochron age of 2693 94 ma nd i 0 50920 8 mswd 1 4 n 4 e nd 1 2 whereas regressing the chaganam and chundi samples yielded an isochron age of 2654 100 ma nd i 0 50923 9 mswd 1 5 n 11 e nd 0 7 basal metapelite underlying the metabasalt yields old nd model ages between 2888 and 3054 ma the results of this study show that the 2 7 ga nellore greenstone belt was intruded by enriched morb type gabbros at 1911 ma it is proposed that this palaeoproterozoic magmatism formed in response to a major extensional event along the eastern dharwar craton margin that likely initiated breakup from the southeastern margin of the north china craton this exposed craton margin later evolved as the site for collisional events during the late palaeoproterozoic to early mesoproterozoic

tertiary of the arabian gulf sedimentology and hydrocarbon potential abstract the paleogene neogene paleogeography of the arabian basin shows a change from the basic continuation of the mesozoic pattern during the paleogene to a new pattern of sedimentation established during the neogene and resulting from movements in the zagros the paleogene shallow water carbonate dominated lithologies in eastern arabia were replaced by deep water neogene carbonates near the zagros and mixed carbonate and clastics in the northern arabian gulf the hydrocarbon potential of these rocks except locally is low and the decreasing amplitude and frequency of faulted and folded structures away from the zagros front suggests that the discovery of fields in structures such as those in iraq iran is low this poverty may however suggest that the untapped potential of the mesozoic rocks may still be high

middle pleistocene to holocene coastal evolution of nw sardinia mediterranean sea italy abstract the middle pleistocene holocene sardinian stratigraphy has been revised to identify the roles played by sea and climate changes in controlling sedimentation the succession dated through optically stimulated luminescence quartz k feldspar and 14 c the most recent was grouped into eight major stratigraphic units mainly represented by coastal dunes shallow marine and alluvial systems these units range in age from mis 8 300 ka to mis1 6 ka little information is available for the period between mis 8 and 6 the available data however allow some comments on climate changes over the last 125 ka the last interglacial mis 5 is subdivided into five substages e a mis5e eemian is considered the climate optimum of this interglacial sea level was 4 6 m higher than today and climate conditions were warmer and more humid mis 5c is the second high stand peak sea level was about 1 5 m above the modern level and paleoclimatic and paleogeographic conditions were similar to the present during mis 4 at the beginning of the glacial phase a climatic deterioration occurred temperatures dropped by 6c relative to mis 5e in about 5 ka and sea level fell about 60 m this led to a progressive disruption of inland vegetation cover and to repeated valley slope denudation the sea level fall created the accommodation space for fan development in sheltered and cliffed areas where debris flows developed and filled almost completely the terminal parts of the narrow coastal valleys coves in wider areas however coastal dune fields developed contemporaneous presence of alluvial fan and dune systems is associated with the local morphology that could mitigate or amplify moist conditions within a generally arid environment during mis 3 several climate fluctuations occurred wet arid d o h events however the shallow sardinian shelf was continuously sufficiently exposed to become the source area of bioclastic sands these sands were blown inland and formed extensive dunefield systems dunes dominated the west coasts of sardinia under cold and relatively dry conditions in some areas these dunefield systems were eventually almost completely dismantled and reworked into water flow dominated alluvial fans by catastrophic rainfall events thus the local climate quickly switched from arid to humid conditions no record of the last glacial maximum deposits mis 2 was observed along the nw sardinian coast during the holocene transgression mis1 coastal dune systems developed and progressively migrated inland and temperature rose to reach the present day condition

thermo mechanical structure of the southern part of the indian shield and its relevance to precambrian basin evolution abstract the thermal and mechanical structures of the southern part of the precambrian indian shield have been estimated using available heat flow data and shear stress profiles from olivine rheology these and other geological geochronological and geophysical data including deep seismic studies dss profiles of proterozoic cuddapah basin on south indian shield are utilized to examine thermal models for the evolution of precambrian intracratonic platform basins on the archean lithosphere of indian shield evidence of mantle perturbations and cycles of thermal events are documented to be important in the cuddapah basin s evolution haxby et al s 1976 thermal model has been shown to explain the cuddapah basin s flexuring and magnitude of subsidence

1891 1883 ma southern bastar cuddapah mafic igneous events india a newly recognized large igneous province abstract a newly recognized remnant of a paleoproterozoic large igneous province has been identified in the southern bastar craton and nearby cuddapah basin from the adjacent dharwar craton india high precision u pb dates of 1891 1 0 9 ma baddeleyite and 1883 0 1 4 ma baddeleyite and zircon for two se trending mafic dykes from the bd2 dyke swarm southern bastar craton and 1885 4 3 1 ma baddeleyite for a mafic sill from the cuddapah basin indicate the existence of 1891 1883 ma mafic magmatism that spans an area of at least 90 000 km2 in the south indian shield this record of 1 9 ga mafic ultramafic magmatism associated with concomitant intracontinental rifting and basin development preserved along much of the south eastern margin of the south indian shield is a widespread geologic phenomenon on earth similar periods of intraplate mafic ultramafic magmatism occur along the margin of the superior craton in north america 1 88 ga molson large igneous province and in southern africa along the northern margin of the kaapvaal craton 1 88 1 87 ga dolerite sills intruding the waterberg group existing paleomagnetic data for the molson and waterberg 1 88 ga large igneous provinces indicate that the superior and kalahari cratons were at similar paleolatitudes at 1 88 ga but a paleocontinental reconstruction at this time involving these cratons is impeded by the lack of a robust geological pin such as a limpopo like 2 0 ga deformation zone in the superior province the widespread occurrence of 1 88 ga intraplate and plate margin mafic magmatism and basin development in numerous archean cratons worldwide likely reflects a period of global scale mantle upwelling or enhanced mantle plume activity at this time

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

geomorphological and palaeoenvironmental investigations in the southeastern arabian gulf region and the implication for the archaeology of the region abstract during the late quaternary the climate of arabia has fluctuated between periods of higher rainfall and fluvial activity dominated by the influence of the indian ocean monsoon iom and drier arid conditions under the influence of the westerlies this has left a rich legacy of landforms from which temporal and spatial patterns of environmental change are reconstructed the coastal desert region of the southeastern arabian gulf has been a focal point for human settlement since 8000 cal yr bp the region is strategically located on an important trade route between two cradles of civilization namely mesopotamia and the indus changes in the evolution and modification of this landscape under varying climatic conditions have influenced humans living in and exploiting this landscape for food and water raw materials and trade routes in this study geomorphological and palaeoenvironmental investigations are integrated to provide a framework of environmental change for the late glacial and early mid holocene periods against which the archaeology of the area can be set the late glacial and earliest holocene was characterised by intense aridity and accumulation of mega linear dunes driven by the shamal winds in the arabian gulf region this continued into the earliest part of the holocene whilst southern arabia was under the influence of the iom the monsoon rains migrated into the gulf region between 8500 6000 cal bp during this time semi nomadic herders occupied this region and grazing their animals in a landscape covered with c3 savanna grassland the neolithic peoples also practised hunting and fishing and the collection of shellfish was an important activity pottery shows links with mesopotamia at this time from 6000 cal bp the iom retreated south and rainfall was derived from winterly westerly sources under drier conditions a switch occurred to a sparser cover of c4 grasses from 4500 cal bp the climate became much drier with the development of stronger westerly summer shamal winds and the reactivation of dunes across the region an intense arid period occurred at 4100 bp which corresponds with major drought conditions in mesopotamia and the indus region which led to major changes in society this event occurs at a major transition in the arabian gulf bronze age archaeological record with a decline in population and trade the last 4000 yr has largely been characterised by arid conditions similar to those found in the region today

stress and strain patterns kinematics and deformation mechanisms in a basement cored anticline sheep mountain anticline wyoming 1 in order to characterize and compare the stress strain record prior to during and just after folding at the macroscopic and the microscopic scales and to provide insights into stress levels sustained by folded rocks we investigate the relationship between the stress strain distribution in folded strata derived from fractures striated microfaults and calcite twins and the development of the laramide basement cored sheep mountain anticline wyoming tectonic data were mainly collected in lower carboniferous to permian carbonates and sandstones in both rock matrix and veins calcite twins recorded three different tectonic stages the first stage is a pre laramide sevier layer parallel shortening lps parallel to fold axis the second one is a laramide lps perpendicular to the fold axis and the third stage corresponds to laramide late fold tightening with compression also perpendicular to the fold axis stress and strain orientations and regimes at the microscale agree with the polyphase stress evolution revealed by populations of fractures and striated microfaults testifying for the homogeneity of stress record at different scales through time calcite twin analysis additionally reveals significant variations of differential stress magnitudes between fold limbs our results especially point to an increase of differential stress magnitudes related to laramide lps from the backlimb to the forelimb of the fold possibly in relation with motion of an underlying basement thrust fault that likely induced stress concentrations at its upper tip this result is confirmed by a simple numerical model beyond regional implications this study highlights the potential of calcite twin analyses to yield a representative quantitative picture of stress and strain patterns related to folding

analysis of variscan dynamics early bending of the cantabria asturias arc northern spain calcite twinning analysis in the cantabria asturias arc caa of northern spain provides a basis for evaluating conditions of variscan stress and constrains the arc s structural evolution twinning typically occurs during earliest layer parallel shortening offering the ability to define early conditions of regional stress results from the somiedo correcilla region are of two kinds early maximum compressive stress oriented layer parallel and at high angles to bedding strike d1c1 and later twin producing compression oriented sub parallel to strike d2c1 when all d1 compressions are rotated into a uniform east west reference orientation a quite linear north south trending fold thrust belt results showing a slight deflection of the southern zone to the south southeast north south directed d2c1 compression was recorded prior to bending of the belt calcite twinning data elucidate earliest structural conditions that could not be obtained by other means whereas the kinematics of arc tightening during d2 is constrained by paleomagnetism a large and perhaps protracted d2c1 is suggested by our results as manifested by approximately 50 arc tightening prior to acquisition of paleomagnetic remagnetizations throughout the caa early east west compression d1c1 likely resulted from the ebro aquitaine massif docking to laurussia whereas the north directed collision of africa d2c1 produced clockwise bending in the northern zone radial folding in the hinge and rotation of thrusts in the southern zone fl 2000 elsevier science b v all rights reserved

paleostress reconstructions and geodynamics of the baikal region central asia part 2 cenozoic rifting abstract investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses it appears that changes of stress field with time are an important factor that either controls or results from the rifting process the object of this paper is to study the changes of fault kinematics and paleostress field with time in the baikal rift system during the cenozoic reduced paleostress tensors were determined by inversion from fault slip data measured in the central part of the rift and its southwestern termination between 1991 and 1995 results show that the stress field varies as well in time as in space two major paleostress stages are determined corresponding broadly to the classical stages of rift evolution late oligocene early pliocene and late pliocene quaternary the first paleostress stage is related to the rift initiation and the second to the major stage of rift development similarities between the recent paleostress field and the present day stress field inverted from focal mechanisms indicate that the second paleostress stage is still active therefore we propose to use proto rift for the late oligocene early pliocene stage and active rift for the late pliocene quaternary stage of rift development during the proto rift stage the stress field was characterized by a compressional to strike slip regime a progressive change from transpression to transtension is suspected for the central part of the rift baikal and barguzin basins during this period in the western termination of the rift sayan massif tunka depression a strongly compressional stress field with oblique thrusting kinematics is well constrained in the late miocene early pliocene interval the active rift stage was initiated by a marked change in fault kinematics and stress regime in the late pliocene in the central part of the rift the stress regime changed into pure extension while in the southwestern extremity it changed into pure strike slip fault kinematics suggests that rifting was initiated by an extrusion mechanism due to the interaction of far field compressional stress on a mechanically heterogeneous crust with the southwards pointing wedge of the siberian craton acting as a passive indentor the cenozoic time space evolution of the stress field is believed to reflect the increasing influence of locally generated buoyancy extensional stresses associated with density anomalies of the lithosphere on intraplate stresses generated by the india eurasia convergence and the west pacific subduction

strain analysis from calcite e twins in the cameros basin nw iberian chain spain abstract calcite twins and c axes from sparry grains that fill micro veins were used to unravel the deformational history of the cameros massif an inverted mesozoic sedimentary basin located in the northwestern part of the iberian chain spain calcite c axis and microvein orientations indicate the existence of two extension directions nw se and ne sw during the basin formation probably related to the slip along two syn sedimentary faults calcite e twins were developed only in micro veins from the frontal ramp area i e in the northeast side of the basin where the stresses were higher during the basin inversion twin analysis yields three different orientations nw se e w and ne sw for the minimum horizontal extension direction i e s hmax under coaxial conditions which suggests that the basin inversion was developed through several thrusting episodes during which the frontal and lateral ramps of each one of these episodes are interchanged moreover the perpendicularity between c axes and the minimum extension directions suggests that the basin inversion was produced along the same faults that controlled the basin formation the minimum extension directions deduced from e twins are also consistent with the shortening directions established previously for the tertiary evolution of the iberian chain which suggest that the basin inversion involved several tectonic events during the neogene these results show the advantage of the combined c axis and e twins analysis to unravel deformational and kinematic histories

palaeoenvironmental and sea level changes during the holocene in eastern saudi arabia and their implications for neolithic populations abstract this paper presents the key findings of a multidisciplinary study investigating the nature and timing of coastal landscape evolution in eastern saudi arabia during the holocene to date most sea level reconstructions for the arabo persian gulf are based on uncalibrated 14c ages without correction for marine reservoir effects or lack precision with regard to the effects of neotectonic changes indicators of sea level used errors in elevation of sedimentary units used and the relationship with actual tides as a consequence the nature and timing of relative sea level rsl changes during the late pleistocene and holocene remain poorly understood to help address this we use sea level index points slips based on calibrated 14c ages to present a rsl curve for the central southern gulf of saudi arabia from coastal sabkha deposits near the archaeological site of dosariyah the sediments record rapid transgression during the early holocene with a mid holocene high stand immediately prior to 6880 6560 cal bp when the upper limit for the palaeo mean highest high tide water mhhw was 2 8 3 10 m above present day mean sea level transgression continued until shortly after 5575 5310 cal bp with an upper limit to the palaeo mhhw of 3 75 m above present sea levels thereafter a fall in rsl was recorded with the regression leading to the progradation of the coastal system and the development of coastal sabkhas nonetheless later transgressions are recorded in the region between 4848 4536 and 4335 3949 cal bp radiometric dating results from archaeological excavations at dosariyah one of the most important neolithic coastal sites in the gulf suggest that occupation of the site during the neolithic coincides with the mid holocene marine transgression ca 7200 6500 cal bp whilst the close proximity of the site to the sea may have facilitated maritime exchange activities occupation of the site was short lived and the phase of abandonment occurred during a period of rapid rsl rise which would have transformed the area around dosariyah into an island or certainly cut it off tidally from the mainland

hydrologic framework of a sabkha along arabian gulf during the last 4 000 to 5 000 years sedimentary offlap and a relative fall in sea level have resulted in the development of broad gently seaward sloping about 1 3 000 planar areas or sabkhas along much of the south shore of the arabian persian gulf the depth of the water table below the sabkha surface increases with distance from the sea until it reaches 1 0 to 1 5 m after which it remains constant when the water table depth is in the range of 1 0 to 1 5 m the sabkha surface has reached a state of deflational equilibrium the water table beneath the sabkha always slopes seaward indicating that the direction of ground water flow is toward the sea the subsurface flow system beneath the sabkha is part of a regional seaward flowing groundwater regime in the seaward part of the sabkha a downward flow component is superimposed on the general seaward ground water flow pattern as a result of the infiltration and percolation of water from shallow bodies of seawater that are propelled inland over the sabkha surface by strong onshore winds farther inland where marine flooding does not occur the vertical flow component is directed upward in response to evaporative losses at the sabkha surface the net rate of evaporation from the central parts of the sabkha is on the order of 6 cm factor of 2 of ground water per year a regional ground water flow system which causes the water table level to rise as the sabkha progrades appears to be a requirement for the development and the preservation of broad sabkhas fluctuations in sea level during sabkha development influence the rate of progradation and the thickness of sedimentary facies the refluxing of sabkha brines beneath the lagoons in the abu dhabi area indicates a mechanism for preserving anhydrite during marine transgressions thus permitting the development of stacked sabkha successions which are common in the rock record

gas venting and late quaternary sedimentation in the persian arabian gulf abstract high resolution 3 5 khz echo sounding profiles and piston cores were used to reconstruct the microtopography and late quaternary depositional history of the persian gulf perversive throughout the seafloor of the gulf is an extensive network of pockmarks formed by seepages of thermogenic gas these gas seeps and bottom water exiting the gulf via the strait of hormuz are the most significant processes controlling present day sedimentation in the region erosion by these seeps has been so intense in the baiban shelf in the strait of hormuz as to create a hoodoo like terrain on the outer shelf the surfical geology of the gulf documents a short lived transgression 29 400 to 22 800 years ago during the wisconsin regression which began 125 000 years ago the wisconsin regressive maxima when sea level dropped to 120 130 m about 21 000 20 000 years ago and the climate was dry and eolian and paralic sedimentation characterized the gulf the holocene transgression 18 000 to 12 000 years ago when the climate was more humid than during the climax of the wisconsin regression a dry phase 12 000 to 9000 years ago when the persian gulf was a site of eolian and carbonate deposition and the present sediment cycle during the last 9000 years under a more humid regime it was during the present cycle that southeast trending marl lobes were deposited off iran arabia acquired its hyper arid climate about 3000 years ago and the gulf attained its present configuration about 1000 years ago as a result of the construction of the tigris euphrates delta at its head and tectonism and aggradation along its arabian and iranian flanks

coastal staircase sequences reflecting sea level oscillations and tectonic uplift during the quaternary and neogene many coasts feature sequences of quaternary and neogene shorelines that are shaped by a combination of sea level oscillations and tectonics we compiled a global synthesis of sea level changes for the following highstands mis 1 mis 3 mis 5e and mis 11 also we date the apparent onset of sequences of paleoshorelines either from published data or tentatively extrapolating an age for the uppermost purported oldest shoreline in each sequence including the most documented mis 5e benchmark we identify 926 sequences out of which 185 also feature holocene shorelines six areas are identified where elevations of the mis 3 shorelines are known and 31 feature elevation data for mis 11 shorelines genetic relationships to regional geodynamics are further explored based on the elevations of the mis 5e benchmark mean apparent uplift rates range from 0 01 0 01 mm yr hotspots to 1 47 0 08 mm yr continental collision passive margins appear as ubiquitously uplifting while tectonic segmentation is more important on active margins from the literature and our extrapolations we infer ages for the onset of formation for 180 coastal sequences sea level fingerprinting on coastal sequences started at least during mid miocene and locally as early as eocene whether due to the changes in the bulk volume of seawater or to the temporal variations in the shape of ocean basins estimates of eustasy fail to explain the magnitude of the apparent sea level drop thus vertical ground motion is invoked and we interpret the long lasting development of those paleoshore sequences as the imprint of glacial cycles on globally uplifted margins in response to continental compression the geomorphological expression of the sequences matches the amplitude and frequency of glacial cyclicity from middle pleistocene to present day moderately fast 100 000 yrs oscillating sea levels favor the development of well identified strandlines that are distinct from one another pliocene and lower pleistocene strandlines associated with faster cyclicity 40 000 yrs are more compact and easily merge into rasas whereas older cenozoic low frequency eustatic changes generally led to widespread flat lying coastal plains

rapid late pleistocene holocene uplift and coastal evolution of the southern arabian persian gulf the coastline along the southern arabian gulf between al jubail kingdom of saudi arabia and dubai uae appears to have risen at least 125 m in the last 18 000 years dating and topographic surveying of paleo dunes 43 53 ka paleo marine terraces 17 30 ka and paleo marine shorelines 3 3 5 5 ka document a rapid 1 mm a subsidence followed by a 6 mm a uplift that is decreasing with time the mechanism causing this movement remains elusive but may be related to the translation of the coastal area through the backbasin to forebulge hinge line movement of the arabian plate or alternatively by movement of the underlying infracambrian age hormuz salt in response to sea level changes associated with continental glaciation independent of the mechanism rapid and episodic uplift may impact the design of engineering projects such as nuclear power plants airports and artificial islands as well as the interpretation of sedimentation and archeology of the area

ams dated mollusks in beach ridges and berms document holocene sea level and coastal changes in northeastern kuwait bay abstract in northeastern kuwait ancient beach ridges and associated berms are separated from the present shoreline by a 4 6 km wide sabkha a diverse mollusk fauna in the beach ridges attests to a former open marine environment a total of 21 ams dates were obtained in this study thirteen mollusk samples from beach ridges yielded ams dates ranging from 6990 cal yr bp in the southeast to 3370 cal yr bp in the northwest suggesting a southeast to northwest age progression during the holocene transgression in contrast four samples from berms throughout the study area yielded ams dates of 5195 3350 cal yr bp showing no age progression these berms consist largely of conomurex persicus gastropods that aggregated by storms during a highstand at 5000 3500 cal yr bp the berms are presently at 6 m above sea level 2 3 m above the beach ridges human settlements were common on the ridge crests before and after the highstand regression to present day sea level commenced after the highstand which is when the sabkha began forming a landward marine built terrace which yielded ams dates 43 500 14 c yr bp probably formed during marine oxygen isotope stage 5e and hence is not genetically related to the beach ridges

determining deviatoric stress tensors from calcite twins applications to monophased synthetic and natural polycrystals theoretically calcite twins analysis makes possible the full determination of the deviatoric stress tensor responsible for the formation of the twin lamellae that is the orientations of the principal stress axes and the three differential stress values i j may be calculated assuming conditions of constant resolved shear stress for twinning inverse method using nonlinear regression and robust estimation is proposed applications to monophased synthetic polycrystals that are generated numerically by solving the direct problem and to a natural sample from the quercy southwest of france have given good results comparison with the first method proposed by turner 1953 modified by nissen 1964 for principal stress orientations and by jamison and spang 1976 for differential stress values clearly emphasizes the considerable interest of this new method

holocene marine terraces on two salt diapirs in the persian gulf iran age depositional history and uplift rates slightly inclined holocene marine terraces cover parts of two circular salt diapirs hormoz and namakdan in the persian gulf their relative altitude above present sea level results from a combination of general marine transgression regression affecting the whole area and of local uplift related to salt diapirism differential uplift rate of the studied diapirs in centre to rim profiles was calculated from results based on i radiocarbon ages of skeletal remains of benthic faunas 19 samples which originally grew close to sea level ii original altitude of samples estimated from general sea level oscillation curves for the last 10 kyr and iii present sample altitude measured in the field calculated uplift rates increase from rim to centre on both diapirs in the range from 2 mm yr 1 at the rim to 5 6 mm yr 1 at the interior of hormoz and 1 3 mm yr 1 at the rim to 3 5 mm yr 1 at the interior of namakdan such uplift rate distributions fit into the parabolic profile of newtonian fluid rather than to profiles typical for pseudoplastic fluids the increase in uplift rate with distance from rim to centre of diapirs is gradual as demonstrated also by generally smooth surface of marine terraces no tectonic dissections were found the depositional history on both salt diapirs is similar although they are situated more than 100 km apart marine sedimentation started at about 9 6k cal yr bp on hormoz and at 8 6k cal yr bp on namakdan owing to rapid transgression the sea partially truncated both salt diapirs and rapidly deepened and carbonate mud was deposited on the peripheries of both salt diapirs between 7 and 5k cal yr bp beach deposition replaced carbonate mud soon after 5k cal yr bp the sea retreated from most of the marine terraces on both salt diapirs copyright 2006 john wiley sons ltd

emplacement and deformation of the vinukonda meta granite eastern ghats india implications for the geological evolution of peninsular india and for rodinia reconstructions abstract the u pb and rb sr systematics of zircon populations from two samples and biotite white mica pairs from four samples constrain the time of emplacement and deformation of the vinukonda meta granite eastern ghats india sm nd and lu hf systematics of whole rock samples provide information on the magma source and its evolution the granitic magma intruded into granitic gneisses of the vinjamuru domain krishna province andhra pradesh india which were already deformed and metamorphosed at epidote amphibolite facies peak conditions consistent sm nd and lu hf whole rock model ages suggest an isotopically homogeneous crustal source and a multi stage evolution of the granitic magma u pb analyses of prismatic zircon multi grain fractions define two discordias with identical upper intercepts at 1588 4 7 1 and 1589 7 5 7 ma interpreted to date magma emplacement rb sr ages of strongly annitic biotite xmg 0 07 0 20 and phengitic white mica 3 13 3 23 si pfu show a complex age pattern due to low temperatures during deformation the rb sr system only partly re equilibrated in biotite synkinematically grown phengitic white mica evidence a low grade metamorphic overprint at 501 474 ma the deformation was associated with w nw directed nappe stacking which caused the actual geological configuration of southern andhra pradesh with the arcuate nallamalai fold belt as most prominent feature regional considerations lead to the proposition that thrusting in the krishna province is the expression of intracratonic deformation in response to the amalgamation of the eastern ghats rayner province terrane with subcontinental india in early palaeozoic time

palaeostress estimation using calcite twinning experimental calibration and application to nature abstract by means of high temperature deformation experiments on calcite rocks of different grain sizes we have established the relationships between differential stress and twinning incidence twin density and volume fraction and the way that these relationships depend on grain size both twinning incidence and volume fraction increase with grain size at a constant level of differential stress log twin density is proportional to stress but is independent of grain size at a given grain size volume fraction of twinning increases non linearly with differential stress twinning activity measured by twinning incidence increases linearly with stress the behaviour of each of these parameters is independent of temperature strain and strain rate these relationships can be used as a basis for the estimation of palaeostress values in naturally deformed calcite rocks this is illustrated by a study of twinning activity in limestones close to thrust faults in the cantabrian zone of the variscan orogenic belt in northwestern spain high peak differential stresses were measured ranging from 150 to 250 mpa using the turner dynamic analysis technique however it is clear that shear stresses resolved parallel to the fault planes were very low the attainment of high stress differences when the resistance to faulting was low is attributed either to bending forces induced during the motion of the non planar surfaces relative to each other or to the stress peak being attained prior to the localization of deformation onto the fault surfaces

detrital mineral age radiogenic isotopic stratigraphy and tectonic significance of the cuddapah basin india abstract the cuddapah basin is one of a series of proterozoic basins that overlie the cratons of india that due to limited geochronological and provenance constraints have remained subject to speculation as to their time of deposition sediment source locations and tectonic geodynamic significance here we present 21 new stratigraphically constrained u pb detrital zircon samples from all the main depositional units within the cuddapah basin these data are supported by hf isotopic data from 12 of these samples that also encompass the stratigraphic range and detrital muscovite 40ar 39ar data from a sample of the srisailam formation taken together the data demonstrate that the papaghni and lower chitravati groups were sourced from the dharwar craton in what is interpreted to be a rift basin that evolved into a passive margin the nallamalai group is here constrained to be deposited between 1659 22 ma and 1590 ma it was sourced from the coeval krishna orogen to the east and was deposited in its foreland basin nallamalai group detrital zircon u pb and hf isotope values directly overlap with similar data from the ongole domain metasedimentary rocks depositional age constraints on the srisailam formation are permissive with it being coeval with the nallamalai group and it was possibly deposited within the same basin the kurnool group saw a return to dharwar craton derived provenance and is constrained to being neoproterozoic it may represent deposition in a long wavelength basin forelandward of the tonian eastern ghats orogeny detrital zircons from the gandikota formation which is traditionally considered a part of the chitravati group constrain it to being deposited after 1181 29 ma more than 700 ma after the lower chitravati group it is possible that the gandikota formation is correlative with the kurnool group the new data suggest that the nallamalai group correlates temporally and tectonically with the somanpalli group of the pranhita godavari valley basin which is tightly constrained to being deposited at 1620 ma these syn orogenic foreland basin deposits firmly link the se india proterozoic basins to their orogenic hinterland with their discovery filling a missing link in the tectonic development of the region

use of a new 10be and 26al inventory method to date marine terraces santa cruz california usa marine terraces along active continental margins reflect the interplay between sea level oscillations and rock uplift well dated marine terraces record the timing of sea level highstands and delimit both uplift and geomorphic rates cosmogenic radionuclides provide a new tool for dating previously undatable terraces because the five marine terraces north of santa cruz california are capped by well developed soils formed in regressive marine sands both predepositional cosmogenic radionuclide inheritance and bioturbation of the profile must be accounted for we present a new cosmogenic radionuclide inventory method that uses the depth integrated cosmogenic radionuclide concentration to determine the terrace age this method yields terrace ages that correlate well with sea level highstands of marine oxygen isotope stages 3 5a 5c 5e and 7 the implied uplift rate is steady at 1 1 mm yr and is two to three times higher than rates suggested by earlier studies

the cuddapah salient a tectonic model for the cuddapah basin india based on landsat image interpretation abstract analysis of geologic geophysical data and lineaments derived from landsat image interpretation has revealed a pattern of tectonic inheritance of archean structural elements by the folded and thrusted eastern margin of the middle late proterozoic cuddapah basin in india a structural pattern set by deep crustal faults in the archean and intracratonic basin fabric is apparent in both sedimentary and tectonic trends in the basin the lineaments represent broad zones of en echelon and parallel alignments that appear to have nucleated on deep crustal faults which were reactivated as structural uplifts lateral and frontal ramps and transverse tear faults the major zones recognized are the northeast trending veldruti guntur lateral ramp to the north and the northwest trending cuddapah nellore transverse tear fault to the south east west directed compression during the eastern ghats latest proterozoic orogeny was apparently confined within these converging lineament zones that effectively buttressed the west verging thrust fronts block uplift along the ne trending veldruti guntur lateral ramp acted as a boundary to east to west thrust translation the northeastern ends of folds and thrusts were pinned down with relative displacement being clockwise and greater increasing to the southwest the lack of a lateral ramp or basement buttress to the south resulted in the development of the left lateral cuddapah nellore transverse tear fault steep imbricate thrust ramps in the foreland resisted further movement westward the resulting convex to the west arcuate nallamalai and vellikonda thrust fronts broadly paralleled by the east coast gravity high anomaly kaila and bhatia 1981 is herein named the cuddapah salient

inversion of calcite twin data paleostress reconstruction and multiphase weak deformation in cratonic interior evidence from the proterozoic cuddapah basin india abstract paleostress orientations from mechanically twinned calcite in carbonate rocks and veins in the neighborhood of large faults were investigated to comment on the nature of weak upper crustal stresses affecting sedimentary successions within the proterozoic cuddapah basin india application of turner s p b t method and spang s numerical dynamic analysis on cuddapah samples provided paleostress orientations comparable to those derived from fault slip inversion results from the neighborhood of e w faults cutting through the paleoproterozoic papaghni and chitravati groups and the neoproterozoic kurnool group in the western cuddapah basin reveal existence of multiple deformation events 1 ne sw 3 in strike slip to extensional regime along with an additional event having nw se 3 for lower cuddapah samples 2 compressional transpressional event with ese wnw or nne ssw 1 mainly from younger kurnool samples integrating results from calcite twin data inversion fault slip analysis and regional geology we propose that late mesoproterozoic crustal extension led to initial opening of the kurnool sub basin subsequently influenced by weak compressional deformation the dynamic analysis of calcite twins thus constrains the stress regimes influencing basin initiation in the southern indian cratonic interior and subsequent basin inversion in relation to craton margin mobile belts and plausible global tectonic events in the proterozoic

geologically constraining india in columbia the age isotopic provenance and geochemistry of the protoliths of the ongole domain southern eastern ghats india abstract the ongole domain in the southern eastern ghats belt of india formed during the final stages of columbia amalgamation at ca 1600 ma yet very little is known about the protolith ages tectonic evolution or geographic affinity of the region we present new detrital and igneous u pb hf zircon data and in situ monazite data to further understand the tectonic evolution of this columbia forming orogen detrital zircon patterns from the metasedimentary rocks are dominated by major populations of palaeoproterozoic grains ca 2460 2320 2260 2200 2100 2080 2010 1980 1920 1850 and 1750 ma and minor archaean grains ca 2850 2740 2600 and 2550 ma combined u pb ages and lu hf zircon isotopic data suggest that the sedimentary protoliths were not sourced from the adjacent dharwar craton instead they were likely derived from east antarctica possibly the same source as parts of proterozoic australia magmatism occurred episodically between 1 64 and 1 57 ga in the ongole domain forming felsic orthopyroxene bearing granitoids isotopically the granitoids are evolved producing ehf values between 2 and 12 the magmatism is interpreted to have been derived from the reworking of archaean crust with only a minor juvenile input metamorphism between 1 68 and 1 60 ga resulted in the partial to complete resetting of detrital zircon grains as well as the growth of new metamorphic zircon at 1 67 and 1 63 ga in situ monazite geochronology indicates metamorphism occurred between 1 68 and 1 59 ga the ongole domain is interpreted to represent part of an exotic terrane which was transferred to proto india in the late palaeoproterozoic as part of a linear accretionary orogenic belt that may also have included south west baltica and south eastern laurentia given the isotopic geological and geochemical similarities the proposed exotic terrane is interpreted to be an extension of the napier complex antarctica and may also have been connected to proterozoic australia north australian craton and gawler craton

sevier laramide deformation of the continental interior from calcite twinning analysis west central north america abstract paleozoic mesozoic carbonates that cover cratonic western north america contain a regional layer parallel shortening lps fabric that is preserved by mechanically twinned calcite shortening directions are generally parallel to the sevier thrust transport direction e w in carbonates of the idaho wyoming portion of the thrust belt and within carbonates as far as 2000 km into the plate interior the inferred calcite twinning differential stress magnitudes generally decrease across the thrust belt and decrease exponentially away from the orogenic front into the craton synorogenic calcite cements and veins preserve a distinct twinning deformation history in the thrust belt twinning strains commonly record local out of transport piggyback strain events with high differential stresses

precision and accuracy of the calcite strain gage technique the twinned calcite strain gage technique allows the determination of strain magnitude and direction in mildly deformed sedimentary rocks in that the measurements required for the calculation are rather time consuming it is important to know the minimum number required to obtain a precision that is comparable with the accuracy of the result this paper documents a series of tests on three different limestones having different textures and porosities in order to determine the precision and accuracy of the technique as a function of the number of measurements and the number of perpendicular thin sections the tests show that for most purposes the best measurement strategy will be to make 25 measurements on each of two perpendicular thin sections the best determined principal strain axis is the one having a magnitude that is opposite in sign from the other two over the range of zero to 11 shortening the magnitude of the odd signed strain axis will than have a precision and accuracy of about 11 in magnitude and a precision and accuracy of about 6 to 8 in orientation differences in texture and porosity do not appear to have significant effects upon precision and accuracy

calcite twins from microveins as indicators of deformation history abstract in order to investigate whether the evidence of the deformation history is preserved in the microvein calcite twinning microstructures several families of calcite veins have been studied from weakly deformed mesozoic limestones of the western iberian chain eastern iberian peninsula the maximum shortening directions established with this method correspond to the previously established paleostress evolution of this chain the reconstructed stress regimes evolve from predominantly compressional four compressional episodes with the maximum shortening direction oriented successively nw se n s ne sw and e w to extensional the established orientations of maximum shortening axes are consistent with the directions of paleostrains that have been independently deduced from stylolites and fault striations in the same region moreover the results clearly show that the e twins record some paleostress orientations that are not registered in the studied area by fault population analysis in this sense the e twins record older paleostress orientations than the small faults probably because the faults were reactivated several times and the twins were not modified since their formation the calculated values of twin strains 1 differential stress magnitudes 62 mpa and the existence of type i twins formed below 200 c confirm that this region was slightly deformed under low p t conditions

characterization of stress perturbations near major fault zones insights from 2 d distinct element numerical modelling and field studies jura mountains abstract we consider and discuss the presence of discontinuities in the crust as a major source of stress perturbations based on 2 d distinct element modelling we reconstruct the local stress field around a vertical discontinuity in various geological contexts the resulting stress distribution reveals that major directional stress changes occur near the tips of the discontinuity so that stress deviations can reach values as large as 50 we establish simple relationships controlling stress changes around a pre existing fault zone as a function of 1 the remote differential stress magnitude 1 3 2 the friction coefficient on the discontinuity and 3 the strike of the discontinuity relative to the far field stress as a geological example we present the morez fault zone in the internal jura paleostress reconstruction in forty two sites indicates that the trends of the mio pliocene compression are n110 on average near the fault whereas they are n130 in the surrounding areas a comparison between the results of the tectonic study and those of theoretical modelling suggests that the 20 counterclockwise deviation is directly related to the reactivation of this large weak zone we thus evaluate the role of mechanical decoupling along pre existing zones of weakness especially with consideration to the accommodation of the alpine deformation in the jura belt

multi stage deformation in the nallamalai fold belt cuddapah basin south india implications for mesoproterozoic tectonism along southeastern margin of india abstract the common occurrence of small scale refolded folds deformed lineations and overprinting of foliation in the northern nallamalai fold belt nfb within the intracratonic cuddapah basin south india suggest three phases of deformation d 1 d 2 and d 3 during the late paleoproterozoic to neoproterozoic d 1 structures are represented by tight to isoclinal folds a slaty cleavage and local development of mylonites d 2 structures include ne trending tight to open folds f 2 with variable plunge indicating control of large domal structures and a steep crenulation cleavage developed in phyllites and other schistose rocks the above structures are overprinted by e w trending d 3 folds and cleavage which affect mesoproterozoic rocks of the srisailam formation uppermost nallamalai group in the e w trending vami konda range and metasediments of the palnad area thought to be equivalent of the neoproterozoic kurnool group taking into account the ages of intrusive vellaturu granite 1575 ma which is post d 2 deformation in the nfb and the chelima lamproite 1400 ma which intrudes the folded nallamalai rocks we suggest that the earlier episodes of multiple deformation in the nfb represent either late paleoproterozoic or early mesoproterozoic nw se compression in this part of the east gondwana the e w fold thrust structures affecting the srisailam quartzite and adjacent metasediments in the palnad area represent late mesoproterozoic and or neoproterozoic event the granite gneisses and schists of the nellore schist belt bordering the nfb are affected by both early and later events and thrust over rocks of the nallamalai group we propose that early deformation in the nfb lying southwest of the eastern ghats and roughly parallel to the present southeastern coast of india was unrelated to and occurred prior to the main deformation in the eastern ghats which is generally correlated with the 1000 ma old grenville event alternatively in view of the complex protracted evolution of the eastern ghats and published geochronological data supporting pre grenvillian tectonism particularly in the western charnockite zone of the eastern ghats d 1 and d 2 deformation in the nfb may be linked to this older 1600 1400 ma tectonic disturbance in the eastern ghats

paleostress stratigraphy a new technique for analyzing tectonic control on sedimentary basin subsidence the authors propose a new technique paleostress stratigraphic analysis based on the orientation of minor structures particularly striated fault surfaces in the strata of sedimentary basins these structures are interpreted to be the response to local or regional stress field controlling subsidence of tectonically active basins a method is used that allows multiple stress tensors to be extracted from a fault population by extracting the stress tensor from the youngest part of a stratigraphic sequence and by imposing that same tensor on the underlying rocks one can in principle isolate the faults associated with the youngest tectonic event by reiterating this procedure on progressively older units until the fault data are exhausted a chronologic succession of paleostress tensors during basin subsidence emerges the authors paleostress stratigraphy to the relatively undeformed paleogene central basin of spitsbergen and its underlying cretaceous strata and define five major paleostress tensors coeval with the earliest stages of the opening of the norwegian greenland sea a late cretaceous dextral transpressive regime was probably responsible for the major pre tertiary unconformity and possibly initiated development of the central basin during subsequent sedimentation movement reversed yielding well constrained sinistral shearing during early danian time a composite compressional event followed that themore authors interpret as being coeval with the culmination of folding and thrusting west of the central basin the youngest strata studied record a final extensional event that they correlate with rifting of spitsbergen from greenland less

quaternary calcareous hard rocks and the associated sediments in the intertidal and offshore zones of kuwait abstract the geomorphological and petrographical characteristics of the quaternary calcareous hard rocks in the offshore and intertidal zone of kuwait northern arabian gulf were investigated these rocks can be divided into three types 1 submerged calcareous hard layers 2 beachrocks and 3 lithified intertidal terraces submerged calcareous hard layers usually cover a submarine terrace about 15 m below present sea level this hard rock is generally underlain by an uncemented oolitic sand and overlain by holocene mud which reaches up to 13 m in thickness submerged calcareous hard layers are generally lithified allochemical limestone four types were recognized biosparite biomicrite oosparite and oomicrite beachrocks outcrop over distances of several hundred metres along the coast of kuwait they are partially eroded by mechanical and biological processes the field occurrences and petrography of the beachrocks vary from place to place however two main types were recognized quartzitic and calcarenitic the occurrence of each type is related to the nature of the coastal bedrock from which the framework grains of the beachrocks were derived lithified intertidal terraces are almost flat benches of hard calcareous layers which are petrographically similar to beachrock but genetically different they are developed as a result of intertidal lithification of the surficial part of the quaternary semiconsolidated coastal terraced deposits textural and mineralogical investigations of the intertidal sands indicate that these sands are derived from the coastal deposits high energy waves are responsible for the good sorting of these sands along the southern coast

holocene shoreline variations in the persian gulf example of the umm al qowayn lagoon uae abstract the united arab emirate lagoons display several generations of successively settled coastal spits the study of which allows reconstruction of the holocene shoreline changes from the end of the last marine transgression the very variable volume of sediment migrating along the coast attests climatic changes on the other hand vertical shoreline variations are documented by high sea level evidence around 6000 4500 3500 and 2500 bp when compared with other areas on the persian gulf southern coast kuwait and bahrain such holocene oscillations might be interpreted as tectonic in origin

stratigraphic and structural development of the precambrian cuddapah basin s e india abstract the present work recognizes a subdivision of the cuddapah basin into 3 separate main units of deposition some of the earlier correlations proved to be untenable for practical reasons king s widely used stratigraphy is retained where possible in a revised form we recognise the cuddapah group 2000 1490 1450 ma nallamalai group 1490 1450 1090 870 ma and the kurnool group 1090 870 500 ma on the basis of surface geology mapping and photo interpretation we discern 5 tectonic zones the boundaries of these zones coincide with deep crustal faults encountered in a deep seismic sounding survey three phases of tectonic activity are 1 1 crustal movements resulting in broad folds affecting the cuddaph rocks exposed in the western area followed by 2 2 folding of the nallamalai rocks east of the rudravaram line and 3 3 later folding and metamorphism in the eastern tectonic zones structural sections allow an interpretation of an eastward continuation of the cuddapah basin rocks into the highly metamorphosed series underlying the eastern ghats complex a colour geological map and sections are included

calcite fabrics in a natural shear environment the helvetic nappes of western switzerland the aim of this contribution is to describe and interpret the crystallographic orientations and microstructures of calcite in the upper jurassic limestones of the helvetic nappes between the mont blanc and aar massifs over a distance along strike of about 180 km the c axis preferred orientation pattern which could be inferred is regionally very constant the c axis point maxima are everywhere subperpendicular to the regional strike of the chain there is an obliquity between the orientation of the macroscopically dominant cleavage and the microscopically visible long axes of individual grains the c axis maxima in most specimens are parallel to the axis of shortening of the microscopic grain shape fabric this fabric geometry indicates either continuous shear deformation or alternatively a two stage deformation history the obliquity of the grain shape fabric may be due to the fact that the flattening plane of the individual grains reflects only the last increment of a continuous shear process or it may represent a later finite deformation which has led to the formation of a regionally developed second cleavage there is a systematic relationship between the direction of these late shear movements and the main overthrust direction as given by the finite strain pattern this suggests that the microfabric of the rocks was acquired during a progressive rotation with time of the main overthrust direction the observed pattern of preferred orientation has been correlated by several authors with intracrystalline deformation mechanisms a combination of slip on r and twinning on e however the e twinning observed in the specimens investigated is younger than the development of the crystallographic fabric a new method for stress determination from e twinning is proposed

holocene coastal carbonates and evaporites of the southern arabian gulf and their ancient analogues abstract the holocene sediments of the coast of the united arab emirates in the southeastern arabian gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates evaporites and siliciclastics throughout the geologic record this paper is intended as a convenient single source for the description of sediments of this region providing information on how to reach the classic localities and some of the analogs the holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide the sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud with these latter fine sediments increasing as the water deepens the pelecypod rich sediments also collect east of abu dhabi island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons west of abu dhabi island the shallow water margin is the site of coral reefs and coralgal sands whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common they are particularly common on the less protected shallow water margins of the lagoons west of abu dhabi island pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern abu dhabi lining the inner shores of the protected lagoons of abu dhabi and on other islands to the west are cyano bacterial mats and mangrove swamps landward of these a prograding north facing shoreline is formed by supratidal salt flats sabkhas in which evaporite minerals are accumulating this paper describes the localities associated with 1 the mangrove swamps of the west side of the al dhabaiya peninsula 2 the indurated cemented carbonate crusts cyanobacterial flats and sabkha evaporites on the shore of the khor al bazam south of qanatir island 3 the reef and oolitic sand flats on the coast just east of jebel dhana and 4 the marine travertine and aragonite coats associated with the beach sediments in a small bay south of jebel dhana and 5 the sabkha mutti between jebel barakah and al sila similar sedimentological associations of carbonate and evaporites to those of the holocene of the united arab emirates are to be found in the tertiary and mesozoic sedimentary rocks of the immediate subsurface in the arabian gulf other analogs to this setting include the paleozoic carbonates of the western usa europe and asia mesozoic carbonates of the gulf of mexico europe and middle east and tertiary sedimentary rocks in the middle east

shoreline reconstructions for the persian gulf since the last glacial maximum abstract sea level change in the persian gulf since the time of the last maximum glaciation at about 18 000 yr bp is predicted to exhibit considerable spatial variability because of the response of the earth to glacial unloading of the distant ice sheets and to the meltwater loading of the gulf itself and the adjacent ocean models for these glacio hydro isostatic effects have been compared with observations of sea level change and palaeoshoreline reconstructions of the gulf have been made from the peak of the glaciation until about 14 000 yr bp the gulf is free of marine influence out to the edge of the biaban shelf by 14 000 yr bp the strait of hormuz had opened up as a narrow waterway and by about 12 500 years ago the marine incursion into the central basin had started the western basin flooded about 1000 years later momentary stillstands may have occurred during the gulf flooding phase at about 11 300 and 10 500 yr bp the present shorelines was reached shortly before 6000 yr ago and exceeded as relative sea level rose 1 2 m above its present level inundating the low lying areas of lower mesopotamia these reconstructions have implications for models of the evolution of the euphrates tigris karun delta as well as for the movements of people and the timing of the earliest settlements in lower mesopotamia for example the early gulf floor would have provided a natural route for people moving westwards from regions to the east of iran from the late palaeolithic to early neolithic

intraplate paleostresses reconstructed with calcite twinning and faulting improved method and application to the eastern paris basin lorraine france this study deals with the reconstruction of intraplate paleostresses calcite twinning inversion provides paleostress directions and differential values even in poorly outcropping areas however existing methods are not well adapted to multiphase deformation cases and the calculation of stress values provides unreliable estimates modifications were brought to a calcite twinning inverse method and to the processing of results in a new twin data separation process the whole set of data is used to calculate each tensor the variability of yield stress value for twinning with strain hardening is taken into consideration a first order yield stress calcite grain size dependence function has been established with a sample showing various grain sizes this modified method of calcite twinning inversion was applied in the eastern paris basin lorraine france in this platform area measured fractures are preferentially trending ne sw and nw se at all scales the meso cenozoic paleostress succession reconstructed with fault slips is complex jurassic sedimentation occurred during the tethys rifting a mainly strike slip phase with r1 successively striking nnw and nne is attributed to the tertiary pyrenean orogenesis and is followed by wnw extension in the oligocene after local ene compression wnw compression was probably due to the alpine late miocene collision the calcite twinning inversion has confirmed these tectonic events and their succession order and the directions of stress axes were specified using grain size and strain rate sensitive yield stress values the differential stresses can be estimated with an uncertainty of few mpa they range between 20 and 30 mpa depending on the tectonic event the oligocene paleodepths of the sampled calcite estimated using differential stress values are structurally sensible thus the original calcite twinning inverse method has been improved complex paleostress successions such as in platform areas may be deciphered by combination with fault slip inversion even if additional improvement is possible this calcite twinning inverse method opens new ways to determine stress distributions in tectonic plates d 2004 published by elsevier b v

plate margin paleostress variations and intracontinental deformations in the evolution of the cuddapah basin through proterozoic abstract the sedimentary basins are often influenced by adjoining mobile belts as is the case of the proterozoic cuddapah basin in southern india lying in proximity of the eastern ghats granulite belt egb and the southern granulite terrain sgt two major faults gani kalva and kona faults in the western part of the cuddapah basin have been examined in this work to comment on the changes in paleostress conditions affecting the basin evolution punctuated by several stages of extensional and compressional regimes in the time interval 1 9 0 5 ga the tensor solutions were obtained for the mesoscale faults and fault striae using the improved right dihedron method followed by the rotational optimization method tensor delvaux and sperner 2003 combining the paleostress field reconstruction and other structural stratigraphic attributes we propose a possible scenario of punctuated evolution of the cuddapah basin and its inversion the stress regimes are tentatively correlated with multiple stages of basin opening and deformation of basin in fill representing the pre grenvillian through the pan african orogeny the paleostress conditions derived from various stratigraphic horizons provide an opportunity to comment on the changes in tectonic stresses including several stages of extensional and compressive regimes in the cuddapah basin the tensor solutions were obtained for the mesoscale faults and fault striae in the neighborhood of above two fault lines using the improved right dihedron method followed by the rotational optimization method tensor delvaux and sperner 2003 the most prominent stress states recorded around the two fault lines can be classified into those affecting 1 the paleoproterozoic lower cuddapah successions 2 the younger kurnool group and 3 both the groups integrating the stress states of the fault slip analysis obtained from different unconformity bounded rock groups of lower cuddapah and other geologic data we suggest extensional to transtensive pure strike slip regime to be active during the first phase of basin opening and c 1 89 ga mafic igneous activity late compressional to transpressive pure strike slip regimes are well recorded from the younger kurnool group representing late neoproterozoic deformations the tensor solutions from different unconformity bound stratigraphic horizons constrain different states of deformation we relate the extensional to transtensive pure strike slip regimes from lower cuddapah successions to the ongoing basin opening events and the associated palaeoproterozoic igneous activities the late neoproterozoic to early paleozoic compressional to transpressive strike slip regime present the possible effects of compressional activities happening around the cratonic margin the present analysis lends further support to the idea that estimation of paleostress states from fault slip data even in regions of relatively weak deformation in continental interior are important while assessing influence of plate margin stresses on the continental interior

an overview of the tertiary geology and hydrogeology of the northern part of the arabian gulf region with special reference to kuwait abstract tertiary sediments constitute the main source of usable groundwater in kuwait tectonics depositional environment lithology and the hydrogeology of these sediments have been reviewed on a regional scale with special reference to kuwait the review showed that kuwait was situated at the boundary of the stable shelf towards southwest and the unstable shelf towards northeast throughout the tertiary period the tertiary sedimentation started in this area with a marine transgression in the palaeocene shallow marine to sabkha conditions prevailed in the area until the end of the eocene a carbonate evaporite sequence umm er radhuma rus and dammam formation was deposited during this period the sea regressed at the end of eocene and a widespread unconformity causing the absence of oligocene deposits over most of the area marked the event the karstification of the dammam limestone formation that provides localized easier pathways for ground water took place during this period the deposition of the clastic sediments of the kuwait group and its equivalents on the stable shelf under mostly continental conditions started in the early miocene the tertiary aquifers of the area are recharged by occasional rainstorms in the outcrops of saudi arabia and iraq the water flows towards the north and east in the direction of the regional dip and discharges along the present day coast of the gulf the water quality deteriorates in the same direction being more mineralized as it flows through the aquifers the aquifers are presently being exploited at a comparatively high rate since the aquifers extend beyond the political boundaries cooperation among the countries of the region is recommended to ensure the optimum utilization of the scarce water resources of this desert environment

beach ridges definitions and significance abstract beach ridges frequent components of quaternary coastal plains and other coastal landforms have been cited as indicators of the positions of ancient seashores and associated sea levels numerous authors utilized the term beach ridge for active and relict usually wave built supratidal and or intertidal forms wind built ridges have been only occasionally included in the definition the term was applied also to submerged landward shifting eventually stranded bars a consistent redefinition of the term is highly desirable beach ridges should include all relict strandplain ridges whether dominated by wave swash built or by eolian lithosomes all active ridge like shore features regardless of dimensions morphology and origin are excluded because of the resistance of coarse clastic ridges to wave and wind erosion swash built gravel or coarse shell storm ridges may build several meters above the level of high tide swash built high berms even on pure sandy beaches exceed the highest tides during episodes of wind induced record water levels frequently but not always burying underlying low relief berm ridges of berm lithosomes sequences of relatively steep multiple foredunes are commonly named beach ridge plains the narrow subparallel relict foredunes that form these strandplains presently are designated as eolian beach ridges beach ridges thus are defined as relict semiparallel multiple wave and wind built landforms that originated in the inter and supratidal zones until separated from the shoreline by progradation sandy pebbly or shell enriched backshore berm ridges behind an active foreshore should not be considered beach ridges strandplain progradation is either continuous or with the inclusion of subtidal cat s eye ponds discontinuous contrary to claims transgressive cheniers do not represent true cheniers alone within their overall progradational context cheniers a special category of beach ridges bracketed by subtidal intertidal mudflats may be transgressive or regressive in character landward driven transgressive ridges should be designated beach ridges only after they are stabilized on intertidal flats when recognizable between clearly identifiable intertidal and overlying eolian intervals the horizontal interface between these lithosomes in beach ridges may help the reconstruction of ancient tide lake levels diagnostic sedimentary textures structures and fossils however often may be unavailable in the deposits along with various types of elevated terraces composed of raised marine deposits and certain coastal landforms of erosional origin that occur worldwide beach ridges of clearly proven wave built origin may also serve as indicators of ancient higher than present sea levels

critical re evaluation of differential stress estimates from calcite twins in coarse grained limestone abstract comparison of two techniques to estimate differential stress magnitude based on calcite twinning reveals significantly different calculated values of differential stress for limestone experimentally and naturally deformed at low temperature this inequality may be due to fundamental differences between the rock type marble versus limestone and deformation temperatures above and below 200 c for samples used in technique calibration versus samples used in testing and application a technique that was empirically derived from marble experimentally deformed at 200 800 c yields values of differential stress that are factors of 2 to 9 times larger than maximum differential stress measured during experimental deformation of limestone at low temperature

rbsr ages of proterozoic kimberlites of india evidence for contemporaneous emplacement abstract rb sr analyses of leached phlogopite macrocrysts from kimberlite pipes 1 2 5 and 7 in south india give concordant ages of 1091 20 1092 15 1093 20 and 1091 10 ma respectively indicating contemporaneous emplacement of these pipes the present results are in contradiction with earlier measurements groundmass mineral assemblages with low rb sr ratios give a tight set of initial sr ratios at 0 7029 2 0 7019 2 0 7029 2 and 0 7030 4 suggesting derivation of the primary kimberlite magma from a relatively uniform and depleted mantle source a similar age and initial sr isotopic ratio of one sample of the majhgawan lamproite from central india imply that the proterozoic kimberlite lamproite activities in india though widely separated in space were nearly contemporaneous

calcareous dunes of the united arab emirates and noah s flood the postglacial reflooding of the persian arabian gulf abstract aeolian dunes cover most of the united arab emirates and a large part of the eastern arabian peninsula although these sands as well as older aeolianites are largely composed of quartz there is a high percentage of detrital carbonate in them south of the persian arabian gulf for more than 40 km this percentage decreases inland these carbonate grains consist mainly of marine bioclastic fragments and calcareous ooids and were derived from the floor of the persian gulf which was exposed during low sea level of the last glacial period the postglacial rise in sea level rapidly reflooded the floor of the persian gulf cutting off the source for these aeolian sediments between 12 and 6 ka the sea transgressed more than 1000 km inundating the extended route of the tigris euphrates river and forcing people living on the exposed floor of the gulf to abandon their settlements because of the varying rate of eustatic sea level rise these waters at times flooded across the flat floor of the persian gulf at more than a kilometer per year we proposed that the stories of a great flood recorded in the bible as noah s flood and in babylonian history on clay tablets excavated in the tigris euphrates delta as the epic of gilgamesh are a record of this rapid postglacial flooding of the floor of the persian gulf

holocene land and sea level changes in great britain analysis of more than 1200 radiocarbon dated samples that constrain relative sea levels in great britain over the past 16 000 yr provides estimates of current land level changes negative of relative sea level change maximum relative land uplift occurs in central and western scotland ca 1 6 mm yr 1 and maximum subsidence is in southwest england ca 1 2 mm yr 1 sediment consolidation arising from autocompaction as the sediment accumulates and from land drainage increases the subsidence in areas with thick sequences of holocene sediments with an average effect equivalent to at least an extra ca 0 2 mm yr 1 land subsidence but more in parts of southeast england 0 5 1 1 mm yr 1 modelled changes in tidal range during the mid to late holocene in eastern england suggest that the calculated rate of land subsidence is overestimated unless such changes are quantified the effect is most significant for large coastal lowlands the fenland and humber ca 0 5 and 0 6 mm yr 1 that were tidal embayments during the mid to late holocene

relative sea level fall since the last interglacial stage are coasts uplifting worldwide the growing interest in quantification of vertical ground motion stems from the need to understand in detail how the earth s crust behaves for both scientific and social reasons however only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies although there are many local studies of quaternary vertical motions of coastlines we know of no comprehensive worldwide synthesis here we provide a compilation of 890 records of paleoshoreline sequences with particular emphasis on the last interglacial stage marine isotopic stage mis 5e 122 ka the quality of dating mis 5e makes it a reliable marker to evaluate vertical ground motion rates during the late quaternary on a global scale the results show that most coastal segments have risen relative to sea level with a mean uplift rate higher than 0 2 mm yr i e more than four times faster than the estimated eustatic drop in sea level the results also reveal that the uplift rate is faster on average for active margins than for passive margins neither dynamic topography nor glacio hydro isostasy may explain sustained uplift of all continental margins as revealed by the wide distribution of uplifted sequences of paleoshorelines instead we suggest that only plate tectonic processes reconcile all observations of quaternary coastal uplift we propose that long term continental accretion has led to compression of continental plates and uplift of their margins therefore this study concludes that plate tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic these results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record

calcite twin morphology a low temperature deformation geothermometer abstract twinning of the e plane is the dominant crystal plastic deformation mechanism in calcite deformed below about 400 c calcite in a twin domain has a different crystallographic orientation from the host calcite grain so called thin twins appear as thin black lines when viewed parallel to the twin plane at 200 320 magnification under a petrographic microscope thick twins viewed in the same way have a microscopically visible width of twinned material between black lines calcite e twin width and morphology has been correlated with temperature of deformation in naturally deformed coarse grained calcite in this paper we present a compilation and analysis of data from limestones of the frontal alps france and switzerland and the appalachian valley and ridge and plateau provinces eastern united states to document this temperature dependence mean calcite twin width correlates directly with temperature of deformation such that thin twins dominate below 170 c and thick twins dominate above 200 c above 250 c dynamic recrystallization is an important deformation mechanism in calcite mean twin intensity twin planes mm correlates negatively with temperature and a cross plot of twin intensity with twin width can yield information about both strain and temperature of deformation these relationships provide a deformation geothermometer for rocks that might otherwise yield little or no paleotemperature data

determination of deviatoric stress tensors based on inversion of calcite twin data from experimentally deformed monophase samples part ii axial and triaxial stress experiments three samples of a bioclastic bajocian limestone from burgundy france were experimentally deformed under axial and triaxial conditions at 200 and 300 c in each sample a series of three mutually orthogonal thin sections were studied using a u stage the intracrystalline deformation of the calcite grains involved mainly twinning on the e planes precise measurement of the e twin lamellae combined with the etchecopar inverse method 1984 allowed the calculation of the four parameters of the reduced stress tensor responsible for the twinning as the principal differential stress values of the experimental deviatoric stress tensors were known the critical resolved shear stress crss values tau s for twinning on the e planes were then determined in each case at 200 c and 4 8 strain tau s is close to 15 mpa at 300 c and at 8 7 and 9 4 strain the calculated tau s values are close to 10 1 and 13 4 mpa respectively when compared with the data published by turner et al 1954 turner and heard 1965 and lacombe and laurent 1996 our results confirm that the crss values are more or less dependent on both the temperature and the bulk amount of strain consequences for the estimation of the actual principal differential stress values sigma 1 sigma 3 are described particularly for very weakly deformed cover rocks in the forelands of mountain chains

taphonomy of ghost shrimps decapoda axiidea callianassidae associated with their burrows within a middle miocene mud volcano complex of persian arabian gulf kuwait abstract shallow marine strata of the ghar formation exposed along the kuwait arch in the north of kuwait contains fields of mud volcanoes associated with an assemblage dominated by pectinid bivalves and callianassid ghost shrimps the depositional palaeoenvironment is interpreted to be intertidal to subtidal with the water depth not exceeding 50 m and with normal to hypersaline conditions based on the microfossil assemblage a middle miocene age early langhian is inferred suggesting a longer stratigraphic span of the formation despite the previous studies treating the ghar formation as strictly early miocene callianassid body fossils and numerous trace fossils assignable to ophiomorpha have been identified ghost shrimp remains consisting of isolated cheliped elements are assigned to neocallichirus s l which is the likely producer of ophiomorpha burrows as documented by cheliped elements present within burrows and in the substrate around them stable isotopes discrimination modelling confirmed that fluids in the substrate were derived from at least two sources implying the presence of active mud volcanoes in the environment inhabited by ghost shrimps effusive activity of mud volcanoes further enhanced disarticulation and fragmentation of callianassid remains the micritic matrix of ghost shrimp exoskeletons is indicated to have resulted from a mixture of local seawater with fluid of continental origin this ghost shrimp occurrence is the first formal report of fossil decapod crustaceans from kuwait