mesozoic and cenozoic reconstructions of the south atlantic abstract the movement of antarctica with respect to south america has a number of implications for paleocirculation as well as for the reconstructions of gondwanaland recent papers on the southwest indian ridge have published new or revised poles of opening for africa and antarctica which can be combined with the poles of opening between south america and africa to give resultant motions between south america and antarctica the first indication of a complete closure between south america and the antarctic peninsula is at anomaly 28 time 64 ma as the two continents are now configured between anomaly 28 time 64 ma and anomaly m0 time 119 ma the amount of closure does not change greatly and the small computed overlap can be explained by minor uncertainties in the rotation poles used for the reconstructions or some slight extension between east and west antarctica by 135 ma some rotation or translation of the antarctic peninsula with respect to east antarctica must be postulated in addition to any presumed extension between east and west antarctica in order to avoid an overlap of south america with the antarctic peninsula having determined what we feel to be a viable reconstruction of western gondwanaland and holding south america fixed we rotated africa and antarctica with respect to south america for eight different times during the past africa moved away from south america in a more or less consistent manner throughout the time period closure to present while antarctica moved away from africa in a consistent manner only between 160 ma and 64 ma at 64 ma its motion changed abruptly it slowed its north south motion with respect to africa and began slow east west extension with respect to south america this change supports the hypothesis that a major reorganization of the triple junction between africa antarctica and south america occurred between 60 and 65 ma the triple junction changed from ridge ridge ridge to ridge fault fault at the time of the major westward jump of the mid atlantic ridge just south of the falkland agulhas fracture zone the mesozoic opening of the somali basin moved madagascar from its presumed original position with africa in gondwanaland the closure of sri lanka with india produces a unique fit for india and sri lanka with respect to africa madagascar and antarctica this fit juxtaposes geological localities in southeast india against similar localities in enderhy land east antarctica the late jurassic opening in the somali basin is tied to opening of the same age in the mozambique basin since this late jurassic movement represents the initial break up of gondwanaland it is assumed that similar movement must have occurred in what is now the western weddell sea and may also explain the opening evidenced by the rocas verdes region of southern south america

evolution of the passive continental margins of india a geophysical appraisal abstract the passive continental margins of india have evolved as india broke and drifted away from east antarctica madagascar and seychelles at various geological times in this study we have attempted to collate and re examine gravity and topographic bathymetry data over india and the adjoining oceans to understand the structure and tectonic evolution of these margins including processes such as crustal lithosphere extension subsidence due to sedimentation magmatic underplating and so on the eastern continental margin of india ecmi seems to have evolved in a complex rift and shear tectonic settings in its northern and southern segments respectively and bears similarities with its conjugate in east antarctica crustal extension rates are uniform along the stretch of the ecmi in spite of the presence or absence of crustal underplated material variability in lithospheric strength and tectonic style of evolution ranging from rifting to shearing the krishna godavari basin is underlain by a strong 30 km elastic lithosphere while the cauvery basin is underlain by a thin elastic lithosphere 3 km the coupling between the ocean and continent lithosphere along the rifted segment of the ecmi is across a stretched continental crust while it is direct beneath the cauvery basin the western continental margin of india wcmi seems to have developed in an oblique rift setting with a strike slip component unlike the ecmi the wcmi is in striking contrast with its conjugate in the eastern margin of madagascar in respect of sedimentation processes and alignment of magnetic lineations and fracture zones the break up between eastern india and east antarctica seems to have been accommodated along a proterozoic mobile belt while that between western india and madagascar is along a combination of both mobile belt and cratonic blocks

eruptive processes and caldera formation in a nested downsagcollapse caldera cerro panizos central andes mountains abstract the cerro panizos ignimbrite center in the central andes mountains produced two ignimbrite sheets and many lava flows the ignimbrite of quebrada cienago was erupted at 7 9 ma and effusive eruptions continued until the two cooling units of the crystal rich dacitic cerro panizos ignimbrite were emplaced at 6 7 ma the lower unit has no laterally continuous flow breaks and was erupted from a single vent or small cluster of vents with limited fluctuation in discharge lithic fragments reach significant concentrations 5 only in the uppermost two meters of this cooling unit where they document vent wall collapse or the opening of a new vent the upper cooling unit contains many flow units with variations in welding thicknesses and lithic fragment concentrations implying an unsteady eruption column the opening of many vents and probable caldera collapse triangulation of anisotropy of magnetic susceptibility flow direction measurements locate a single vent for the lower cooling unit whereas the upper cooling unit had many vents within the present dome cluster a 15 km diameter topographic depression marked by inward dips of 4 8 at the cooling unit contact is centered on the vent area of the lower cooling unit the depression is interpreted as a downsag caldera formed during emplacement of the lower cooling unit collapse began late in the eruption of the lower cooling unit and continued through the emplacement of the upper cooling unit resurgent magmatism occurred as lava flows that mundated the caldera area a ring of dacite domes erupted until at least 6 1 ma in the northern half of the downsag caldera traces the margin of a collapse caldera associated with the upper cooling unit maximum caldera subsidence 353 km 3 is not enough to account for the erupted volume 652 km 3 dre minimum the ash poor crystal rich nature up to 50 crystals in the pumice 75 in the matrix of the cerro panizos pyroclastic flows resulted in poor retention of gases and there is little evidence of fluidization the high crystal content however favored modified grain flow processes in which several particle support mechanisms combine with grain dispersive forces it is postulated that the flows were initially partially fluidized but rapidly lost their gases and grain flow processes grew in relative importance grain flow processes destroyed evidence of fluidization before deposition

the subsidence history of conoco well 15 30 1 central north sea abstract the depth of deposition of the sediments from north sea well conoco 15 30 1 is determined using faunal and sedimentary evidence the effects of sedimentary load corrected for compaction and variations in water depth and sea level are removed to obtain the subsidence of the basement when covered by water only a crustal stretching and lithospheric thinning of 25 35 1 35 can account for both the initial fault controlled subsidence and the later uniform subsidence

subsidence and isostasy along a sheared margin cauvery basin eastern continental margin of india we have applied a process oriented method to a seismo geological section across cauvery basin a sedimentary basin along the southern part of the eastern continental margin of india ecmi to examine the isostatic mechanism operating beneath the margin the evolution of the ecmi appears to be within a shear rift tectonic setting mainly driven by the difference in the relative motions of india and east antarctica and the subsequent direction of spreading and the cauvery basin seems to have formed in this pull apart tectonic setting shearing along the southern ecmi is modeled with gravity anomalies and the resultant crustal configuration through various models of isostasy backstripping analysis suggests a very low te of 3 km beneath the basin the shelf edge gravity anomaly reflects a strong contrast across a wrench fault parallel to the coast inferred from gravity forward modeling denoting coast parallel transform motion in the initial stages of continental separation prior to rotation and spreading

paleomagnetism magnetic fabric and 40ar 39ar dating of pliocene and quaternary ignimbrites in the arequipa area southern peru 40ar 39ar ages and paleomagnetic correlations using characteristic remanent magnetizations chrm show that two main ignimbrite sheets were deposited at 4 86 0 07 ma la joya ignimbrite lji and at 1 63 0 07 ma arequipa airport ignimbrite aai in the arequipa area southern peru the aai is a 20 100 m thick ignimbrite that fills in the arequipa depression to the west of the city of arequipa the aai is made up of two cooling units an underlying white unit and an overlying weakly consolidated pink unit radiometric data provide the same age for the two units as both units record exactly the same well defined paleomagnetic direction 16 sites in the white unit of aai dec 173 7 inc 31 2 95 0 7 k 2749 and 10 sites in the pink unit of aai dec 173 6 inc 30 3 95 1 2 k 1634 showing no evidence of secular variation the time gap between emplacement of the two units is unlikely to exceed a few years the 50 m thick well consolidated white underlying unit of the arequipa airport ignimbrite provides a very specific magnetic zonation with low magnetic susceptibilities high coercivities and unblocking temperatures of nrm above 580 c indicating a ti poor titanohematite signature the anisotropy of magnetic susceptibility ams is strongly enhanced in this layer with anisotropy values up to 1 25 the fabric delineated by ams was not recognized neither in the field nor in thin sections because most of the aai consists in a massive and isotrope deposit with no visible textural fabric pumices deformation due to welding is only observed at the base of the thickest sections ams within the aai ignimbrite show a very well defined pattern of apparent imbrications correlated to the paleotopography with planes of foliation and lineation dipping often at more than 20 toward the expected vent buried beneath the nevado chachani volcanic complex in contrast with the relatively small extent of the thick aai the la joya ignimbrite covers large areas from the altipano down the piedmont ti poor titanomagnetites are the dominant magnetic carriers and ams values are generally lower than 1 05 magnetic foliations are sub horizontal and lineations directions are scattered in the lji the ams fabrics are probably controlled by post depositional compaction and welding of the deposit rather than transport dynamics

geoid and gravity anomaly data of conjugate regions of bay of bengal and enderby basin new constraints on breakup and early spreading history between india and antarctica 1 timing of breakup of the indian continent from eastern gondwanaland and evolution of the lithosphere in the bay of bengal still remain as ambiguous issues geoid and free air gravity data of bay of bengal and enderby basin are integrated with shipborne geophysical data to investigate the early evolution of the eastern indian ocean geoid and gravity data of the bay of bengal reveal five n36 w fracture zones fzs and five isolated ne sw structural rises between the eastern continental margin of india ecmi and the 85 e ridge 86 e fz the fzs meet the 86 e fz at an angle of 39 the rises are associated with low gravity and geoid anomalies and are oriented nearly orthogonal to the fzs trend the geoid and gravity data of the western enderby basin reveal a major kerguelen fz and five n4 e fzs the fzs discretely converge to the kerguelen fz at an angle of 37 we interpret the fzs identified in bay of bengal and western enderby basin as conjugate fzs that trace the early cretaceous rifting of south ecmi from enderby land structural rises between the fzs of bay of bengal may either represent fossil ridge segments possibly have extinct during the early evolution of the bay of bengal lithosphere or may have formed later by the volcanic activity accreted the 85 e ridge two different gravity signatures short wavelength high amplitude negative gravity anomaly and relatively broader low amplitude negative gravity anomaly are observed on south and north segments of the ecmi respectively the location of continent ocean boundary cob is at relatively far distance 100 200 km from the coastline on north ecmi than that 50 100 km on the south segment on the basis of geoid gravity and seismic character and orientation of conjugate fzs in bay of bengal and western enderby basin we believe that transform motion occurred between south ecmi and enderby land at the time of breakup which might have facilitated the rifting process in the north between combined north ecmi elan bank and macrobertson land and in the south between southwest sri lanka and gunnerus ridge region of east antarctica approximately during the period between the anomalies m1 and m0 and soon after detachment of the elan bank from north ecmi the rifting process possibly had reorganized in order to establish the process along the entire eastern margins of india and sri lanka

the holocene secche di lazzaro phreatomagmatic succession stromboli italy evidence of pyroclastic density current origin deduced by facies analysis and ams flow directions the edifice of stromboli volcano gravitationally collapsed several times during its volcanic history 100 ka present the largest holocene event occurred during the final stage of the neostromboli activity 13 5 ka and was accompanied by the emplacement of phreatomagmatic and lahar deposits known as the secche di lazzaro succession a stratigraphic and paleomagnetic study of the secche di lazzaro deposits allows the interpretation of the emplacement and the eruptive processes we identify three main units within the succession that correspond to changing eruption conditions the lower unit ua consists of accretionary lapilli rich thinly bedded parallel to cross stratified ash deposits interpreted to indicate the early stages of the eruption and emplacement of dilute pyroclastic density currents upward the second unit ub of the deposit is more massive and the beds thicker indicating an increase in the sedimentation rate from pyroclastic density currents the upper unit uc caps the succession with thick immediately post eruptive lahars which reworked ash deposited on the volcano s slope flow directions obtained by anisotropy of magnetic susceptibility ams analysis of the basal bed of ua at the type locality suggest a provenance of pyroclastic currents from the sea this is interpreted to be related to the initial base surges associated with water magma interaction that occurred immediately after the lateral collapse which wrapped around the shoulder of the sector collapse scar upward in the stratigraphy upper beds of ua and ub paleoflow directions change and show a provenance from the summit vent probably related to the multiple collapses of a vertical pulsatory eruptive column

chronology of neogene and quaternary uplift and magmatism in the caucasus constraints from k ar dating of volcanism in armenia abstract the greater caucasus is one of earth s highest actively uplifting mountain ranges the adjoining caspian sea basin contains a substantial proportion of its hydrocarbon reserves like other parts of the former soviet union the neogene and quaternary chronology of these important regions has not previously been well defined it has thus been impossible to obtain reliable estimates for rates of processes such as uplift of the caucasus and sedimentation in the caspian sea previous studies have established the relative timings of events in the region using correlation schemes between volcanism glaciations and the stratigraphy of the caspian basin however a range of absolute chronologies has previously been proposed for these sediments and igneous rocks based mainly on different interpretations of their magnetostratigraphic records by k ar dating we determine the ages of volcanism at three localities in armenia as 1 1 0 8 and 0 8 ma using these data and other evidence we propose a revision to the chronology of this region in which a distinctive brief interval of normal magnetic polarity in the local sedimentary and volcanic magnetostratigraphic records is matched to the cobb mountain event in the global record rather than the olduvai event or an earlier subchron as had previously been thought we thus interpret a 1 5 ma timing for the start of volcanism in the lesser caucasus and also suggest a 1 2 ma timing for the late akchagyl transgression of the caspian sea a key event in the regional stratigraphy when this water body reached its greatest extent we tentatively correlate this transgression with the melting event following glaciation during stage 36 of the oxygen isotope timescale which was thus the first time during the pleistocene when eastern europe was covered by a lowland ice sheet time averaged since 1 ma the flanks of the eastern greater caucasus mountains are shown to have uplifted at 0 6 mm a 1 and the lesser caucasus at 0 3 mm a 1 we show that the rate and spatial scale of this uplift are too great to be the result of plate convergence and suggest instead that this uplift is caused by crustal thickening due to inward lower crustal flow to beneath these mountain ranges at the start of magmatism in both the greater and lesser caucasus the estimated crustal thickness was 45 km we thus suggest that this magmatism has been caused by heating of the mantle lithosphere due to earlier crustal thickening the temperature rise required to initiate magmatism being the same in both cases

a laacher see eruption supplement to tephrabase investigating distal tephra fallout dynamics abstract tephrabase www tephrabase org is an online data repository and research tool for tephrochronological investigations in northern europe this paper presents and discusses an update to tephrabase that contains geographic and as far as available geochemical data on 452 data points for the widespread isochronous laacher see tephra this tephra is dated to c 12 920 calendar years bp and acts as an important chronostratigraphic marker for the lateglacial gi 1a late allerod chronozone in terrestrial and lacustrine palaeoenvironmental archives as well as in archaeological stratigraphies based on these data a revised map of the total tephra distribution is presented suggesting that the north eastern fallout lobe might contain a secondary fallout thickness maximum 230 340 km distant from the eruptive centre in addition new geochemical data from a series of distal tephra deposits spanning most of the north eastern fallout lobe are used to evaluate previous suggestions regarding the distribution of fallout from distinct eruption phases the aim of the study is that future tephrochronological investigations can use this database and the revised distribution map for effectively targeting sites for analysis

rifting process of the xihu depression east china sea basin abstract having a maximum depositional depth up to 15 km the ne trending xihu depression is evolved from a deep paleogene continental margin rifting along the present day east china sea continental shelf in this paper we use deep seismic reflection well logging and gravity data to synthesize early rifting process of the depression to study the regional tectonic subsidence history we developed a computer program that performs backstripping and simultaneous inversion for stretching factor initial lithospheric thickness and incipient age of thermal subsidence tectonic subsidence analyses of 40 industrial wells reveal nonuniform stretching preferential crustal extension along the depocenter but preferential mantle extension at the western flank uniform extension may have occurred only somewhere between the central inversion zone and the western margin in the early rifting stage subdued initial subsidence or initial uplift is observed on several wells near the western margin due possibly to flexural isostatic balance the initial mechanical lithospheric thicknesses from subsidence inversion seem to vary from about 55 km to almost 130 km suggesting significant longitudinal segmentation as well as transverse variation in the prerifting lithosphere it is likely that the southern part of the xihu depression was developed initially on a region of relatively thin lithosphere a statement conformable to geological evidences nw se trending deep seismic profiling clearly reveals the deep basement structure of the depression as well as the synrift and postrift sedimentary packages separated by a breakup unconformity crustal layer thicknesses are independently estimated from gravity modeling inversion tectonic subsidence analyses and deep seismic profiling respectively these methods all arrive at very small present day thicknesses of the crustal layer beneath the depocenter of the xihu depression

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

on archeomagnetic secular variation curves and archeomagnetic dating abstract secular variation sv of the earth s magnetic field can be used for dating purposes by comparing archeomagnetic directions of unknown ages with a well dated reference curve in this study we propose a dating technique based on the statistics of mcfadden and mcelhinny geophys j int 103 1990 725 for testing the hypothesis that two fisherian distributions of individual directions share a common mean direction the statistics are adapted to test the degree of compatibility between one individual fisherian mean direction and a reference curve constructed using the bivariate extension of the fisher distribution furthermore as the density of the data which define the archeomagnetic reference curve varies in time we suggest that one computes the mean directions with moving windows of varying duration where both the window widths and the time shifts between successive mean directions are fixed when a minimum threshold density of data is reached within each time interval in our paper we apply this new procedure to the french archeomagnetic data set

subsidence history of the tethys himalaya abstract this article reconstructs the evolution of the passive northern margin of peninsular india facing the neotethys from the earliest rifting stages in the carboniferous to final collision with the active southern margin of asia in the early eocene classical techniques of basin analysis were applied to an extensive and coherent stratigraphic data base facies analysis biostratigraphic dating and palaeoenvironmental interpretation of an over 10 km thick sedimentary succession from eight main composite sections allowed us to draw accurate sedimentation and backstripped subsidence curves and to place quantitative constraints on the palaeotectonic scenario inferred from the sedimentary record in each of the investigated composite sections three major stratigraphic gaps are consistently recognised in the rift sequence the rift unconformity mississippian the carboniferous permian hiatus largely kasimovian to asselian and the break up unconformity mid sakmarian two or even all three gaps may merge into a single hiatus spanning up to 70 ma overall gaps are associated with rift shoulder uplift which after calculation of backstripped subsidence sums up to 600 m at least in three of the investigated sections thermal subsidence and low sedimentation rates are documented by the mid permian to middle triassic drift sequence deposited while the neotethys was expanding between northern gondwana and the detached peri gondwanan blocks a marked increase in accumulation rates is recorded in the carnian norian but calculations of uniform lithospheric stretching suggest that extension was minor and associated with tectonic processes affecting distant parts of gondwana the tethys himalayan margin was uplifted around the jurassic cretaceous boundary at the onset of a major volcanic episode finally uplift exceeding in magnitude all previous events is documented by the uppermost units of the stratigraphic column deposited during the earliest stages of collision between india and asia in the latest paleocene to early eocene

some comments on two layer extensional models for the evolution of sedimentary basins simple extensional models that involve listric faulting in the brittle upper crust and plastic flow in the lower lithosphere have been shown to account for the subsidence history of various continental sedimentary basins and continental shelves in this paper we present structural evidence that extension in the continental lithosphere during rifting is not uniform we review evidence that the rifting process in major intracratonic rift basins is spasmodic rather than continuous that extension and subsidence within the rift during a tectonic phase is generally accompanied by uplift and erosion of the rift flanks that subcrustal heat input during rifting occurs over an area much broader than the rift proper and that there may be broad regional uplift before and or during rifting to explain the uplift of the flanks during rifting and their postrift subsidence we invoke two mechanisms subcrustal thinning by extension below the flanks and tilted major normal faults in the crust between graben and flanks the uplift and erosion of the flanks due to tilted faults probably do not significantly affect estimates of extension from subsidence analysis but uplift due to both sources can in certain cases be incorrectly attributed to regional uplift or doming we present a simplified analysis of the two layer extensional model for the elementary case in which extension is instantaneous and the crust is thinned by a different amount from the subcrustal lithosphere we provide a simple graphical method of data analysis to obtain the parameters that describe thinning of the crust and lithosphere during extension from the subsidence history application of this method to the central part of the pattani trough in the intracratonic gulf of thailand shows that extension and thinning of the lithosphere of a factor of 2 since late eocene can account for much of the subsidence history and the present day heat flow our analysis suggests that thinning of the crust in this area is 20 greater than thinning of the whole lithosphere assuming that none of the lithosphere is removed from the region of extension during rifting we show by simple geometric examples that a process of nonuniform extension implies that much greater thicknesses of sediment can be deposited in the center of a young basin than in the case of uniform extension of both crust and subcrustal lithosphere such an extensional process produces significant uplift of the flanks of the rift and as a result of erosion of the uplifted areas the effective cross sectional area of the basin can be increased by as much as 10 20 depending on the rate of erosion compared to the area that would have been created by a process of uniform extension finally we show that it may ultimately be possible to compute erosion rates from seismic cross sections of basins

lithospheric extension and magmatism in the porcupine basin west of ireland the porcupine seabight basin is a north south trending extensional sedimentary basin situated on the continental shelf west of ireland it is filled with sedimentary rocks which range in age from devonian to present day a large amount of geological and geophysical data is now available for this basin mainly as a result of oil industry exploration in this paper information from 23 well logs and from regional seismic reflection surveys is used to determine the lithospheric stretching history of the basin subsidence analyses indicate that there was one main phase of stretching which began in late liassic times 180 ma ending in earliest cretaceous 145 ma stretching factors at the northern end of the basin are relatively small 1 1 1 7 but increase rapidly southwards along the axis of the main porcupine basin in the southern part of the region the seabight basin is greater than 6 the simplest way to accommodate this rapid variation in stretching is by clockwise rotation of the porcupine ridge through approximately 20 away from the irish shelf subsidence derived stretching values are in reasonable agreement with those determined previously from crustal thicknesses based on gravity models and deep seismic data normal incidence and wide angle the existence location and inferred age of the porcupine median volcanic ridge are also consistent with the subsidence derived stretching factors after intermittent paleocene igneous activity an anomalous increase in the rate of subsidence occurred in the eocene between 55 and 42 ma there is little evidence that this rapid increase is caused by lithospheric stretching and we conclude that it must be associated in some unknown way with melt generated by development of the iceland hotspot

high resolution magnetostratigraphy and radio isotope dating of early pleistocene lake sediments from southern armenia abstract the pleistocene geology of armenia is dominated by widespread occurrence of sediments recording recurring rapid and drastic changes of the environmental conditions during at least the last 2 million years these sediments predominantly diatomites contain a huge variety of various fossil remains allowing the reconstruction of flora fauna as well as the climatic conditions especially during dispersal of early man into eurasia 1 8 ma radio isotope dating of pumice levels as well as a detailed magnetostratigraphic study have been carried out in syunik province near the town of sisian southern armenia in order to establish a temporal correlation of all major outcrops of paleo lake sediments and to provide a timeframe for paleoenvironmental studies within this lake sediment succession a total of 455 oriented drill cores was sampled at six large and four short sections with a sampling resolution between 5 and 20 cm detailed paleomagnetic experiments reveal the presence of a characteristic remanent magnetization chrm pointing either to the north and down or south and up a positive reversal test suggests the primary character of this magnetization component combining the normal and reverse polarity directions results in an overall sample mean direction of d 354 8 i 51 5 with a fisherian precision parameter k of 14 6 and the associated 95 of 2 9 combining demagnetization data of 169 samples in addition ash layers were sampled for 40ar 39ar geochronology at five of the sections studied paleomagnetically and three additional small outcrops the resulting ages range between 1 31 ma and 1 08 ma with two samples yielding 1 65 and 1 90 ma the latter are characterized by extremely low abundances of radiogenic 40ar suggesting that the mineral system has not been closed since the time of eruption leading to substantial loss in ar integration of these radio isotope dates with the polarity data suggests that the normal polarities can be linked to the jaramillo subchron within the matuyama reversed polarity chron based on the longest interval of normal polarity identified at ashotavan 2 a lower limit for the sedimentation rate of 37 cm ky can be estimated therefore we infer the duration of lake sedimentation as 350 ky starting at 1 4 ma

total tectonic subsidence a parameter for distinguishing crust type at the u s atlantic continental margin total tectonic subsidence tts is the difference between the prerifting continental crust elevation and the present sediment unloaded basement depth in a sedimentary basin tts is calculated using observations of bathymetry and basement depth and assumptions about sediment density and the loading response of the lithosphere i use the extensional model for sedimentary basin formation to interpret the tts of a passive continental margin that model predicts that the tts on an old margin should define the major crust type boundaries and indicate the lateral distribution of extension within the extended continental crust tts analysis of the u s atlantic continental margin indicates that the boundary between extended continental and oceanic crusts lies along the east coast magnetic anomaly ecma to the north of the blake spur fracture zone bsfz and along the blake escarpment to the south there is no tts anomaly associated with the blake spur magnetic anomaly which seems to be underlain by normal oceanic crust the ecma appears to be associated with a tts minimum but i attribute that to artificially shallow estimates of depth to magnetic basement under the ecma tts estimates of extended continental crust thickness agree well with gravity models except where the problem with magnetic basement depth estimates interferes the amount of crust extension prior to seafloor spreading varies along the strike of the margin the most abrupt change is at the bsfz across the bsfz the amount of extension varies by 160 km but the volume of continental material does not vary the extension variation may be caused by lateral changes in the gross rheology of the continental lithosphere in the case of the bsfz it would be the suture of more ductile pre late paleozoic african craton with more brittle north american craton that could cause the abrupt change

cooling rates of plinian fall and pyroclastic flow deposits in the bishop tuff inferences from water speciation in quartz hosted glass inclusions cooling rates inferred from water speciation in rhyolitic glass inclusions in quartz phenocrysts from the bishop tuff california vary over more than 5 orders of magnitude from about 10 to 10 4 c s 1 many of the cooling rates are within the previously published experimentally calibrated range of this technique but the slowest rates 10 4 c s 1 are extrapolated such extrapolation suggests cooling rates as low as 10 8 c s 1 0 3 c year 1 for the interiors of thick pyroclastic flow deposits the temperatures at which oh and molecular h2o species would be in equilibrium range from 400 c for glass inclusions from plinian fall deposits to 250 c for the most slowly cooled glassy inclusions from pyroclastic flow deposits notwithstanding appreciable uncertainties cooling rates correlate with depositional process fall vs flow deposition and distance above the cold ground or below overlying hot pyroclastic flow deposits plinian inclusions within 2 5 m of the cold pre bishop ground cooled at 1 10 c s 1 consistent with thermal modeling of small pumice clasts falling through cold air very slow inferred cooling rates for pyroclastic flow deposits 10 6 to 10 8 c s 1 also agree with thermal conduction models faster cooling rates 10 1 to 10 4 c s 1 for inclusions in the lowermost 0 5 m of pyroclastic flow deposits reflect the effect of quenching against the cold ground at blind spring hill east of long valley caldera intermediate cooling rates 10 3 to 10 6 c s 1 are observed in plinian deposits overlain by and partially interbedded with pyroclastic flow deposits indicating that reheating of rapidly cooled plinian inclusions can reset water speciation melt inclusions in pyroclastic flow deposits are quenched to glass only if the deposit is relatively thin or has a relatively low emplacement temperature in relatively thick or hot deposits inclusions may be quenched to glass at the base of the deposit where it is more rapidly cooled by contact with the pre eruption ground

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

magma generation by slab steepening and breakoff beneath a subduction accretion complex an alternative model for collision related volcanism in eastern anatolia turkey 1 eastern anatolia is regarded as one of the best examples of continental collision represented by a 2 km high plateau it displays shallow and diffuse seismicity indicating that the crust is still being actively deformed perhaps the most striking aspect of eastern anatolia is the volume and compositional variability of collision related volcanic products erupted during the neogene and quaternary time a number of models have been proposed for the genesis of this volcanism in the region however recent geophysical studies have revealed that a mantle lithosphere is almost completely absent beneath a greater portion of the region which makes us question the validity of the previous models in this paper we propose a new model for magma genesis slab steepening and breakoff beneath a large subduction accretion complex this model holds that a northward subducting oceanic lithosphere beneath the eastern anatolia accretionary prism gets steepened and eventually detached from the continental lithosphere of the bitlis poturge massif following the continent accretionary complex collision this brings the asthenospheric mantle in contact with the accretionary complex at shallow depths e g around 50 km resulting in rapid regional uplift and extensive melting which leads to collisional volcanism

chironomid inferred air temperatures from lateglacial and holocene sites in north west europe progress and problems abstract non biting midges insecta diptera chironomidae are now widely recognised as powerful biological proxies for inferring past climatic change in this paper the response of chironomid assemblages to lateglacial and holocene climatic change from sites in scotland and norway is discussed analyses have shown that midge assemblages have responded to major and minor climatic fluctuations during the last 15 000 yr such as the aegelsee oscillation gerzensee oscillation and younger dryas in the lateglacial and the thermal optimum little ice age and cooling events at 8 2 and 2 0 cal ka bp in the holocene in an attempt to quantify these and other climatic fluctuations a chironomid mean july air temperature inference model based on a modern calibration set of 109 lakes in norway and svalbard has been developed the 3 component weighted averaging partial least squares inference model performs well with a root mean squared error of prediction of 0 90 c and a maximum bias of 0 59 c both based on leave one out cross validation which is lower than chironomid temperature inference models developed in canada switzerland and finland however while temperature inference models perform well in the lateglacial the more subtle climatic changes of the holocene are more difficult to reconstruct because the likely temperature changes are close to the limits of the prediction errors of the existing models to address this problem future work is required to refine and develop the calibration set by further improving taxonomic resolution by adding more lakes to the calibration set and by investigating the influence of other environmental variables on chironomid distributions and abundances

the ediacaran cambrian boundary in the tarim basin nw china geological data anomalies and reservoir implication abstract in this study unconformities t90 formed during the succession from the ediacaran to the cambrian were identified based on five types of data namely field outcrops c and o isotopes major and trace elements well logs and seismic data the outcrop data show notable lithological changes above and below the t90 interface the c and o isotope data show significant negative 13c and 18o excursions at the t90 interface the negative 13c excursion at the t90 interface occurred concurrently with the negative 13c excursions that occurred globally during the same period the average values of ca mg nd pr ce and la were higher below the t90 interface than that above the t90 interface and that the average mass fractions of zr sr zn ba mn s si ni fe al rb k cl and p were lower below that interface than that above it the well log data show that at the t90 interface the concentrations of u and th and the mass fraction of k increased suddenly from 97 66 to 104 308 ppm from 210 005 to 232 086 ppm and from 11 609 to 12 99 respectively and the gamma ray value increased significantly reflecting a brief land exposure of the interface onlap and truncation patterns were visible on the seismic sections above and below the t90 interface various types of unconformities have developed at the t90 interface in various areas of the tarim basin paraconformities are mainly distributed in the kuluketage and kalpin outcrop areas as well as the depressions in the northern tarim basin and a large area north of the tarim basin angular unconformities are distributed near the north wing of the central uplift belt the paleogeomorphology of the t90 unconformity interfaces limited the distribution of sedimentary facies in the overlying strata thereby affecting the distribution of the hydrocarbon source rocks of the yurtus formation and controlled the development of karst reservoirs in the underlying strata

tomographic evidence of slab detachment beneath eastern turkey and the caucasus summary teleseismic phase readings from the eastern turkey seismic experiment etse have been inverted using teleseismic tomography in order to create a 3 d image of the underlying mantle beneath eastern turkey the aim was to investigate the existence of an upper mantle negative velocity anomaly that is used to explain the uplift of eastern anatolian plateau and the potential pieces of detached oceanic slabs related to neo tethyan subduction suggested by previous studies using teleseismic waveforms from the 29 stations of the eastern turkey seismic experiment 2926 direct p phases from 146 events were picked by using adaptive stacking techniques in order to increase the station coverage and resolve the surrounding area the phase readings from the international seismological center isc bulletin have also been added the data set consists of 9571 p and pkp phase readings of 79 stations from 503 teleseismic events this study develops the first highresolution 3 d upper mantle p wave tomographic model for this region the tomographic results show the existence of an upper mantle negative velocity anomaly to a depth of 200 km beneath the eastern anatolian accreationary complex eaac as commonly observed in the previous studies that suggest a shallow partially molten asthenosphere the slab like high velocity anomalies beneath the eaac pontides and caucasus are interpreted as the detached southern and northern neo tethys slabs

volcanic hazards in the region of the armenian nuclear power plant abstract we address volcanic hazards in the region of the armenian nuclear power plant and discuss the assessment of these hazards conducted in the framework of the international atomic energy agency iaea programs in 1994 1995 an important problem of volcanic hazard assessment is posed by assumptions that the apparent absence of recent volcanic activity in armenia means that future eruptions in the vicinity of the site are impossible we present new historical archaeological and field data as well as records of the volcanic activity based on radiocarbon fission track k ar and plateau age determinations this new evidence attests to volcanism in armenia and adjacent areas during holocene and historical time volcanic activity is demonstrated for tskhouk karckar porak vaiyots sar smbatassar gegham ridge and ararat volcanoes volcanic eruptions occurred on ararat at distances of 27 and 52 km from the plant site in 2500 2400 bc and in 1840 ad respectively new information permits a re assessment of the volcanic hazards at a level higher than in the 1994 1995 studies

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

nature of crust beneath sri lanka using teleseismic receiver function abstract sri lanka occupied a unique position in the eastern gondwana assembly surrounded by its gondwana neighbours madagascar india antarctica and africa it comprises four distinct lithologic units the highland complex the wanni complex the vijayan complex and the kadugannawa complex crustal properties crustal thickness and velocities in sri lanka have been estimated by inversion modeling of receiver functions computed using earthquake data from three stations that operated between 2011 and 2018 results reveal 38 km crustal thickness and high average shear wave velocity vs 3 7 3 8 km s beneath sri lanka low average vp vs ratio 1 72 in the highland complex and high vp vs ratio 1 79 in the wanni complex this suggests that the crust beneath sri lanka is felsic to intermediate in nature and the probable rocks are of granite to granodioritic in composition the probable rocks in wanni complex are felsic to mafic granulite in nature the crustal thickness and average vp vs ratio in the highland complex shows similarity with its gondwana neighbours denoting its unique position in gondwana the average crustal shear wave velocity in sri lanka is also found to be high 3 7 km s which is also comparable with its gondwana neighbours

effects of rifting and subsidence on thermal evolution of sediments in canada s east coast basins regional maps of lithospheric deformation and thermal history have been derived for the eastern continental margin of canada subsidence associated with the rifting and cooling stages of rifted margin formation was calculated from gridded maps of sediment thickness and bathymetry along the labrador grand banks and nova scotian margins a two layer lithospheric extension model was used to compute the deformation and thermal evolution of each region deformation results show that the crust and lower lithosphere have generally stretched by different amounts and that either crustal or subcrustal lithospheric stretching dominates beneath the various basins thermal modelling results for the older nova scotian and grand banks margins show a strong correlation between thermal gradient crustal stretching and sediment thickness and the predicted thermal gradient pattern for the younger labrador margin correlates extremely well with predicted stretching of the still cooling subcrustal lithosphere predictions

pleistocene ignimbrites of western armenia paleomagnetic and magnetic anisotropy constraints on flow direction and stratigraphy abstract voluminous early to middle pleistocene pyroclastic flow deposits were generated from mount aragats aragats volcanic province avp one of the largest volcanoes in the arabia eurasia continental collision zone here we report paleomagnetic results in combination with anisotropy of magnetic susceptibility ams analysis from 31 outcrops belonging to six ignimbrite units of the western part of the avp covering an area of more than 5000 km2 paleomagnetic directions analysis of samples from 26 outcrops of the three younger ignimbrite units yields a well defined normal polarity direction of d 339 2 i 55 7 k 278 4 and 95 1 7 the virtual coincidence of the paleomagnetic directions seems to point to an emplacement of the units within a restricted time of similar geomagnetic secular variation i e few hundred years however new isotope 40ar 39ar ages of the three units suggest two separated events at 0 65 and 0 75 ma we cannot fully exclude the possibility of similar paleomagnetic directions at 0 65 and 0 75 ma or the occurrence of a widespread remagnetization event at 0 65 ma but both scenarios are highly unlikely in contrast to that five sites from the three older units all show reversed magnetic polarity which implies an age of emplacement older than the last magnetic polarity reversal at 780 ka this agrees with recent 40ar 39ar ages of the three older units at 0 93 ma the paleomagnetic scatter of the older units is high compared to the younger ones even if paleomagnetic directions and radiometric age are similar available data cannot unequivocally indicate if the three older units were generated from the same or three different eruptions the high quality ams data result in three different types of fabric lineated foliated and undetermined that are all commonly observed in the studied pyroclastic deposits accordingly we use lineation tilt of foliation or both for the determination of paleoflow direction results reveal a radial flow pattern surrounding mt aragats which is however highly influenced by topographic features such as valleys even in proximity of the eruption center

anisotropy of magnetic susceptibility in relation to source vents of ignimbrites empirical observations the anisotropy of magnetic susceptibility ams of young undeformed ashflow deposits e g bishop tuff california bandlier tuff new mexico show alignment of the maximum axis of magnetic susceptibility kmax with inferred flow lines the sense of flow is deduced from the predominant plunge bias of kmax axes these principles are discussed in relation to four deformed settings of ashflow deposits in the great basin of the western united states the magnetic susceptibility data provide valuable but not always unambiguous insight into probable source areas various complications arise in interpreting the ams data in terms of flow directions but these can be reduced by integration with geologic observations

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

late glacial climatic oscillations as recorded in swiss lake sediments regional pollen assemblage zones for the late glacial period of the swiss plateau are introduced and defined they include four major zones artemisia juniperus hippophae betula pinus paz with several subzones pollen and oxygen isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000 9500 yr bp the first oscillation termed the aegelsee fluctuation occurs shortly before 12 000 yr bp and varve counts suggest its duration was ca 100 yr it is characterised by a short decrease in the oxygen isotopes as well as a short increase in nap associated with a depression in birch pollen values the second oscillation which occurs in the 18o record shortly before the deposition of the laacher see tephra ca 11 000 yr bp is termed the gerzensee fluctuation it occurs during a pine dominated phase and its vegetational effects cannot be determined palynologically the most prominent regressive phase is the younger dryas biozone ca 10 700 10 000 yr bp characterised by an increase in heliophilous nap and low 18o values the younger dryas biozone can often be subdivided palynologically into two parts a first part rich in grasses and juniper and a second part with higher filipendula and birch values during the preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios comparison of the swiss oxygen isotope profiles with the greenland dye 3 record suggests that not only the three major shifts in the 18o curves but also the minor ones are closely comparable suggesting some common climatic control

thermochronological dating of brittle structures in basement rocks a case study from the onshore passive margin of sw sri lanka 1 the brittle structural inventory of southern and southwestern sri lanka has been studied by kinematic mineralogical and thermochronological techniques thermochronological analyses of faults comprise apatite and zircon fission track ft data and apatite u th sm he ages from fault planes and undisturbed host rocks and range between 65 and 230 ma the ages of both settings are undistinguishable for topographic altitudes below 100 m while fault planes from higher elevations are significantly younger than the corresponding host rocks thermal history modeling and qualitative interpretation of the thermochronological data identify at least five episodes of thermal overprint associated with faulting activity occurring at 159 18 144 14 120 10 94 8 and 70 10 ma the kinematic mineralogical and thermochronological data collectively show that sri lanka was subjected to major n s oriented extension subsequent to the gondwana breakup the resulting brittle structures exert primary control on the island s geomorphology especially on the southern escarpment of the sri lankan highlands

quaternary ring plain and valley confined pyroclastic deposits of aragats stratovolcano lesser caucasus lithofacies geochronology and eruption history abstract aragats stratovolcano located on the south armenian block a micro plate in the arabian eurasian collision zone has a complex and long lasting quaternary eruption history cataclysmic eruptions formed widespread pyroclastic deposits which are interrupted by numerous basaltic to trachytic lava flows as well as lacustrine and lacustrine alluvial sediments contrary to previous concepts detailed mapping of lithofacies variation combined with stratigraphic documentation and new high precision 40ar 39ar ages revealed four eruption cycles each started with mafic lavas and generally finalized with pyroclastic deposits these data contributed to a fundamental reinterpretation of the development of the aragats volcanic province avp within an estimated activity of one million years aragats itself experienced three eruption stages two of which culminated in pyroclastic deposits of remarkable lithofacies variability with ages of 0 97 to 0 90 ma and 0 75 to 0 65 ma respectively vertical and lateral changes in proximal and distal facies distribution of pyroclastic flow deposits indicate temporal variations in eruption intensity and periods of relative volcanic quiescence aragats explosive activities were dominated by plinian eruptions with columns as high as 25 km while others are characterized by low eruption columns followed by instantaneous collapse in one case associated with vent widening possible caldera collapse and breccia formation furthermore one avp unit features juvenile lapilli and blocks including banded and armored pumice indicating magma mingling and their involvement in the erupting mixture before magma fragmentation

the north china basin an example of a cenozoic rifted intraplate basin the north china basin was a stable continental region that has undergone several distinct phases of rifting and subsidence during the mesozoic and cenozoic eras the last major phase featuring block faulting rapid subsidence and widespread calc alkaline basaltic volcanism began during early tertiary time this intraplate rifting appears to be the result of an approximately 30 extension and thinning of the lithosphere beneath the northeastern china by the late tertiary period active rifting had slowed and postrift thermal subsidence had begun this regional extension and subsidence resulted in the present day north china basin a large saucer shaped oil producing basin with thinner crust and lower upper mantle p and s wave velocities than the surrounding regions during the quaternary period however the subsidence rate increased in the north china basin the frequent occurrence of destructive earthquakes and observations of relatively high heat flow suggest that the quaternary tectonic activity differs from the late tertiary simple thermal subsidence pattern and may indicate a new phase of rifting

evolution of the cauvery basin india from subsidence modelling backstripping and sediment unloading have been carried out on stratigraphic data from wells in the various sub basins of cauvery basin to obtain tectonic subsidence curves analysis of the tectonic subsidence curves reveals that cessation of rifting extension occurred earlier on the western side and rifting persisted for a longer time on the eastern side subsidence was more or less continuous through most of cretaceous time a non uniform or two layer extension model is used to determine extension parameters from the tectonic subsidence curves the values of the crustal and subcrustal stretching parameters obtained in the various sub basins show the trends of evolution of the different sub basins the analysis suggests that the tectonic subsidence curves conform more to those in an intracratonic basin than those on a passive margin geological evidence corroborating this hypothesis are presented necessitating the classification of cauvery basin as an intracratonic failed rift basin as opposed to the earlier classification as a pericratonic basin

structural evolution of the li basin northern thailand exposures in the oligocene to miocene section of coal mines in the li basin of northern thailand show a complex structural evolution the basins formed under approximately east west extension nw to north south striking normal faults are dominant with some east west normal faults also being present but much less frequently episodically compressional and or strike slip events affected the basin creating new east west to ne sw striking thrusts and folds and inverting some normal faults the latest episode of compression formed nw se to north south striking thrusts and folds cross cutting structures reactivation of structures syn sedimentary deformation and unconformites help to constrain the relative timing of structural events at least five episodes of predominantly nnw sse to ne sw oriented compression interrupted the extensional development of the basin the compression was probably related to the escape tectonics of the himalayan orogeny the episodic nature of the compression and extension is inconsistent with either simple strike slip related opening of the rift basins or simple extension the data from the li basin indicate a reappraisal of current tectonic models for the region is necessary

gravity anomalies sediment loading and lithospheric flexure associated with the krishna godavari basin eastern continental margin of india abstract gravity anomalies constrained by seismic data have been used to examine the long term mechanical properties of the lithosphere beneath the krishna godavari basin a deltaic sedimentary basin on the eastern continental margin of india the gravity effect of the rift crust sedimentary loading and erosional unloading have been computed and the sum effect of these when compared with the observed gravity anomalies gives a best fitting te of 30 km at the margin the results suggest that the lithosphere which was weak during the early rifting stage has gained strength during sedimentation the onshore dipping doublet gravity anomaly at the margin reflects a weak rifted continental lithosphere abutting a strong oceanic lithosphere comparison with the results of similar investigations for the bengal basin in the north and cauvery basin in the south suggests increasing strength for the lithosphere from north to south

palaeomagnetism of the cappadocian volcanic succession central turkey major ignimbrite emplacement during two short miocene episodes and neogene tectonics of the anatolian collage abstract the central anatolian volcanic province in cappadocia includes 13 high volume calc alkaline ignimbrite sheets emplaced by plinian eruptions within a succession the urgup formation after 10 ma recording the last phase of neotethyan subduction and accompanying emplacement of the tauride orogen in southern turkey to evaluate magnetostratigraphy in the context of recent revisions of the chronostratigraphy we have extended palaeomagnetic investigation to 32 new sites yielding significant chrm directions integrated rock magnetic and palaeomagnetic investigations identify magnetic remanence residing predominantly in ti poor titanomagnetites although secondary processes within the ignimbrite sheets notably post emplacement oxidation have locally produced hematisation expressed by composite irm spectra and variable reduction in intensity of magnetisation the ignimbrite sheets possess weak anisotropies of magnetic susceptibility ams mostly 3 of pyroclastic deposits during polarity chron c4r 1n between 9 31 and 9 43 ma subsequent activity from the acigol centre further to the south west cemilkoy gelveri gordeles and kizilkaya produced in excess of 620 km 3 of pyroclastic deposits during polarity chrons between 5 3 and 7 1 ma the younger incesu ignimbrite was sourced in the sultansazligi pull apart basin to the east during the gauss chron 2 58 3 60 ma all pre incesu ignimbrites are rotated uniformly anticlockwise and the overall reversed group mean direction of magnetisation is d i 170 8 52 4 n 9 r 8 91 95 5 4 k 91 the implied tectonic rotation in this sector of central anatolia 16 4 relative to eurasia is young and postdates the 5 3 7 1 ma acigol centre whilst largely predating emplacement of the incesu ignimbrite whilst rotational deformation within anatolia is young it proves to be distributed with a temporal variation from block to block it is embraced by a complex post miocene tectonic regime of strike slip and extension during tectonic escape and suction towards the hellenic arc to the west

subsidenz und tektonik des saar nahe beckens sw deutschland the saar nahe basin in sw germany is one of the largest permo carboniferous basins in the internal zone of the variscides its evolution is closely related to movements along the hunsruck boundary fault which separates the rhenohercynian and the saxothuringian zones recent deep seismic surveys indicate that the saar nahe basin formed in the hanging wall of a major detachment which soles out at lower crustal levels at about 16 km depth oblique extension along an inverted variscan thrust resulted in the formation of a half graben within more than 8 km of entirely continental strata accumulated the structural style within the basin is characterized by normal faults parallel to the basin axis and orthogonal transfer fault zones balanced cross section construction and subsidence analysis indicate extension of the orogenically thickened lithosphere by 35 subsidence modeling shows discontinuous depth dependent extension with laterally varying extension factors for crust and mantle lithosphere thus the offset between maximum rift and thermal subsidence can be explained by a zone of mantle extension shifted laterally with respect to the zone of maximum crustal extension

effects of finite rifting times on the development of sedimentary basins abstract most thermo mechanical models for the development of sedimentary basins have assumed that the rifting responsible for the formation of the basin occurred instantaneously and have examined the post rift development of the basin this assumption greatly simplifies the mathematical treatment but is not in accord with what is found in nature where 10 to 50 m y rifting events commonly accompany the formation of sedimentary basins and continental margins the effects of a finite rifting time on the development of sedimentary basins are examined using an analytic technique which allows an arbitrary rifting history in both time and space and which considers the effects of both vertical and horizontal heat transfer this technique allows the thermal structure of the lithosphere to be calculated throughout the rifting event and thus permits the subsidence history and surface heat flow of the developing basin to be traced the effect of a finite duration extension event is that heat is lost during rifting increasing the syn rift subsidence at the expense of the post rift lateral heat flow which was not included in previous studies of the effect of finite rifting times has a significant effect on the subsidence history distribution of sediments and thermal history in particular the post rift subsidence is decreased by more than 25 for a 20 m y rifting event and by more than 10 15 for a rifting event as short as 10 m y this will significantly decrease the subsidence rates in the post rift stage and implies that inferences concerning the structure development and thermal history of the basin derived from using curves to interpret backstripped subsidence can be greatly in error variations in syn rift sediment accumulation and lithospheric thermal structure at the end of rifting resulting from different rifting histories can interact with other factors such as the flexural response of the lithosphere to sediment loading to affect the final width of the basin the total amount of sediments that accumulate and the basin stratigraphy

chronology of the last glacial cycle in the european alps chronological data for glacier advances in the european alps between the last interglacial eemian and the holocene are summarised 115 to 11 ka during this time glaciers were most extensive extending tens of kilometres out onto the forelands between 30 and 18 ka that is synchronous with the global ice volume maximum of marine isotope stage mis 2 evidence for ice expanding to just past the mountain front for an earlier major glacier advance comes from swiss sites where advances have been luminescence dated to mis 5d 100 ka and mis 4 70 ka up to now no such evidence has been found in the eastern alps by 18 ka more than 80 of the late wurmian ice volume had gone subsequently glaciers readvanced reaching into the upper reaches of the main valleys during the lateglacial gschnitz stadial which likely occurred around 17 ka with final moraine stabilisation no later than 15 4 ka the link of the egesen stadial with the younger dryas climate deterioration is supported by exposure ages from four sites as well as minimum limiting radiocarbon dates from bogs within former glacier tongue areas key questions on the spatial and temporal variability of ice extents throughout the last glacial cycle have yet to be answered copyright 2008 john wiley sons ltd

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

basin analysis predictions of known hydrocarbon occurrences the north sea viking graben as a test case abstract basin analysis can assimilate structural burial and thermal histories to predict hydrocarbon prone zones in speculative areas the validity of the modelling approach was field tested in the north sea viking graben an area for which good data are available a recent birps deep seismic reflection profile across tectonic strike of the graben was interpreted and depth converted with good well control the burial and structural histories were determined by backstripping the chronostratigraphic layers using a one dimensional fluid flow compaction model on pseudo wells after removal of each sequence the section was manually reconstructed the thermal history was examined using thermal indicator tomography extensional models and calculations of depth to detachment lack of resolution required that three different paleo heat flow trends be tested to encompass the range in variability a gradual warming trend a constant heat flow through time and a low heat flow until the cretaceous tertiary boundary where a heat pulse occurred basement subsidence extension depth to detachment calculations and thermal indicator inversions all suggest that the uk side of the graben has developed differently to the norwegian section the generation modelling predicts the position of the oil window in the cross section the areas where this window enveloped the draupne formation kimmeridge clay source rock broadly correlate with the positions of the gullfaks statfjord and thistle oilfields of the uk sector however in the norwegian sector the draupne formation was generally overmature except in the area around the troll oilfield predicted middle to late cretaceous generation in the rift axis may have caused updip oil migration towards the horda platform the correct prediction of oil prone zones validates the use of quantitative basin analysis as a tool for evaluating frontier areas where data are limited

a two layer lithospheric compressional model for the tertiary uplift of the southern united kingdom reflection seismic records show that many of the mesozoic sedimentary basins of the southern united kingdom were compressed and uplifted inverted during the late cretaceous tertiary recent quantitative studies based on apatite fission track analysis and chalk porosity data show that uplift and erosion although concentrated in the inverted basins was regional and not limited to the recognized areas of crustal shortening inversion a two layer or heterogeneous model of lithospheric compression similar to two layer models of lithospheric extension may account for this pattern of uplift upper lithospheric shortening is accommodated by reverse movement on major reactivated extensional detachments causing inversion of pre existing basins pure shear shortening of the lower lithosphere is decoupled and may be laterally displaced from that in the upper lithosphere lower lithospheric shortening and thickening displaced from that in the upper lithosphere causes initial subsidence due to the submersion of cold dense lithosphere into the surrounding asthenosphere subsequent thermal re equilibration of the lower lithosphere may have generated the uplift without attendant crustal shortening witnessed by apatite fission track and chalk porosity data

petrology and geochemistry of post collisional middle eocene volcanic units in north central turkey evidence for magma generation by slab breakoff following the closure of the northern neotethys ocean the eocene volcano sedimentary units of northern anatolia are confined into a narrow zone trending parallel to the intra pontide and izmir ankara erzincan sutures along which the northern branch of the neotethys ocean was closed during a period between late maastrichtian and paleocene the middle eocene formations overlie both the imbricated and highly deformed units of the suture zone which are paleocene or older in age as well as the formations of adjacent continental blocks with a regional disconformity therefore they can be regarded to be post collisional these units are composed of subaerial to shallow marine sedimentary beds i e the orencik formation at the base and a subaerial volcanic unit i e the hamamozu formation in the middle and at the top this sudden facies change from marine to subaerial environment in the middle eocene is a common phenomenon across northern turkey implying that a regional uplift event occurred possibly across the suture zone before the initiation of the volcanism during lutetian the middle eocene lavas span the whole compositional range from basalts to rhyolites and display a calc alkaline character except for alkaline to mildly alkaline lavas from the top of the sequence all lavas display a distinct subduction signature our geochemical data indicate that calc alkaline lavas were derived from a subduction modified source whereas alkaline to mildly alkaline lavas of the late stage were possibly sourced by an enriched mantle domain magmas evolved in magma chambers emplaced possibly at two different crustal levels magmas in deeper 13 km and possibly larger chambers fractionated hydrous mafic minerals e g amphibole and biotite two pyroxenes and plagioclase and assimilated a significant amount of crustal material intermediate to acid calc alkaline lavas and pyroclastics were derived from these chambers magmas in the shallower chambers on the other hand 12 km crystallized anhydrous mineral assemblages assimilated little or no crustal material and fed basic to intermediate lavas in the region both deep and shallow chambers were periodically replenished by mafic magmas we argue that a slab breakoff model explains better than any alternative model i why the volcanism during the middle eocene was confined into a rather narrow belt along the suture zone ii why it initiated almost contemporaneous with a regional uplift after the continental collision event iii why it postdated arc volcanism along the pontides in the north by 15 20 my iv why it assimilated significant amount of crustal material and v why alkalinity of lavas increased in time

faulting and graben formation in western and central europe rifts and rift related basins play a pre eminent role among the sedimentary basins of western and central europe through time grabens developed in a number of different megatectonic settings whereby the principal mechanisms governing their subsidence was crustal stretching and subcrustal erosion the level of volcanic activity associated with rifting is highly variable and can change significantly during the development history of a rift some rifts are totally non volcanic the development of rift domes is generally associated with volcanic activity uplifting of a rift dome can induce a reversal in the subsidence pattern of a rift intracontinental rifts with their thinned crust are prone to inversion when the respective craton is subjected to tangential stresses in the process of inversion the crust of rifts is mechanically thickened again

the sushibar an automated system for paleomagnetic investigations 1 we present a new automated system based on a three axis superconducting magnetometer and a custom made coil designed to experiment on cylindrical specimens used in typical paleomagnetic investigations the system which resembles a sushi bar facilitates stepwise alternating field demagnetization of up to 99 samples per loaded track it also enables researchers to explore magnetic properties using an anhysteretic remanent magnetization arm in any coercivity window up to peak alternating fields of 95 mt with direct current bias fields up to 0 17 mt for example partial arm parm spectra characterize magnetic grain size distributions in rocks yet rarely are parm spectra measured because the complete curve for one sample takes at least two hours to acquire manually the sushibar achieves 99 such curves in slightly less than 100 hours using the sushibar we measured the parm sprectra as well as the viscosity and anisotropy of arm in three discrete switching field windows of continental sediments from the xishuigou section western china the average grain size remains constant along the 2200 m thick section yet magnetic viscosity varies systematically from bottom to top of the section samples with high magnetic viscosities also have higher proportions of non viscous material on average principal anisotropy axis directions from the lowest switching fields correlate well with principal axis directions from anisotropy of magnetic susceptibility principal axis directions defined at higher switching fields systematically deviate from those at lower switching fields perhaps defining the fabric of the remanence carrying grains

the reliability of anisotropy of magnetic susceptibility ams data as flow direction indicators in friable base surge and ignimbrite deposits italian examples abstract the base surge deposits in linosa and procida islands italy show minimum axes k3 of the anisotropy of magnetic susceptibility ams that are mostly parallel to the flow directions inferred from field evidence but sometimes perpendicular to them samples from different heights above the base of an ignimbrite bed vulsini area italy showing a coarse tail reverse grading and a fine grained basal layer have different magnetic fabrics at 10 and 40 cm from the base the declinations of maximum axes k1 of the ams are approximately 90 from the theoretical flow direction whereas at 60 and 75 cm from the base the k1 axes are approximately parallel to the flow direction this bed also shows a decrease upward of the magnetic foliation lineation and degree of anisotropy suggesting that the ams data could be used to obtain information about flow mechanisms the airm data in the case of the ignimbrite bed show that the long shape axes of the ferromagnetic grains are probably aligned with the maximum axes of the ams for this reason the change in the magnetic fabric at different distances from the base is probably due to differences in the flow behaviour rather than the domain state of magnetite grains this study shows that the ams lineations can indicate the flow direction in base surge and ignimbrite deposits but other geological and magnetic information is necessary to assess if these lineations are flow perpendicular or flow parallel

crustal thinning and subsidence in the north sea we present here the results of a detailed study of subsidence and crystal thinning across the central graben of the north sea basin two independent lines of evidence have been used to test how well the uniform extensional model1 2 can account for the evolution of the north sea basin a long range seismic profile was shot perpendicular to the central graben from edinburgh to southern norway and data were analysed from 11 exploration wells situated close to the seismic line fig 1 the estimates of the increase in surface area due to extension from the crustal structure determined using the seismic data and from the well subsidence patterns are both compatible with a simple uniform extensional mechanism for the post palaeozoic evolution of the north sea

how preexisting weaknesses control the style of continental breakup continental breakup is a highly variable process differences occur in the relative timing and extent of volcanism uplift and graben formation as well as in the mode and amount of continental extension before breakup we propose a model which reconciles this variability with the previously recognized tendency for breakup to occur along preexisting weak trends continental lithosphere is viewed as a composite material composed of two strong layers one in the upper mantle and one in the middle crust finite element simulation indicates that extensional failure at weaknesses in the mantle causes concentrated extension in the mantle and diffuse extension in the crust this leads to early melt segregation and volcanism margin uplift during the late stages of the extension process and relatively narrow symmetrical extended margins in contrast failure at weaknesses in the crustal strong zone causes focused extension in the crust and diffuse extension in the mantle this produces initial graben formation cooling in the lower crust and upper mantle and broad asymmetrical extended margins volcanism only occurs late in the process failure at laterally offset weaknesses within both strong layers leads to a deformation pattern dominated simple shear thus differences in the prerift configuration of the continental lithosphere can control the overall style of continental breakup

the structure and stratigraphy of deepwater sarawak malaysia implications for tectonic evolution abstract the structural stratigraphic history of the north luconia province sarawak deepwater area is related to the tectonic history of the south china sea the sarawak basin initiated as a foreland basin as a result of the collision of the luconia continental block with sarawak sarawak orogeny the foreland basin was later overridden by and buried under the prograding oligocene recent shelf slope system the basin had evolved through a deep foreland basin flysch phase during late eocene oligocene times followed by post oligocene molasse phase of shallow marine shelf progradation to present day seismic interpretation reveals a regional early miocene unconformity emu separating pre oligocene to miocene rifted basement from overlying undeformed upper miocene pliocene bathyal sediments seismic well data and subsidence analysis indicate that the emu was caused by relative uplift and predominantly submarine erosion between 19 and 17 ma ago the subsidence history suggests a rift like subsidence pattern probably with a foreland basin overprint during the last 10 ma modelling results indicate that the emu represents a major hiatus in the sedimentation history with an estimated 500 2600 m of missing section equivalent to a time gap of 8 10 ma the emu is known to extend over the entire nw borneo margin and is probably related to the sabah orogeny which marks the cessation of sea floor spreading in the south china sea and collision of dangerous grounds block with sabah gravity modelling indicates a thinned continental crust underneath the sarawak shelf and slope and supports the seismic and well data interpretation there is a probable presence of an overthrust wedge beneath the sarawak shelf which could be interpreted as a sliver of the rajang group accretionary prism alternatively magmatic underplating beneath the sarawak shelf could equally explain the free air gravity anomaly the sarawak basin was part of a remnant ocean basin that was closed by oblique collision along the nw borneo margin the closure started in the late eocene in sarawak and moved progressively northeastwards into sabah until the middle miocene the present day nw sabah margin may be a useful analogue for the oligocene miocene sarawak foreland basin

magnetic petrofabric of igneous rocks lessons from pyroclastic density current deposits and obsidians abstract measurement of the anisotropy of magnetic susceptibility ams of igneous rocks can provide clues concerning their mechanism of formation and in particular are very helpful as flow direction indicators unlike other igneous rocks however pyroclastic density current deposits pdcds present a challenge in the interpretation of ams measurements due to the complexity of their mechanism of emplacement in this paper we review the most common assumptions made in the interpretation of the ams of pdcd taking advantage of key lessons obtained from obsidians despite the complexities on the mechanism of formation of pdcds it is shown that a key element for the fruitful interpretation of ams is to give proper attention to the various components likely to be involved in controlling their general petrofabric the anisotropies of ferromagnetic crystals whether as free phases or embedded within clasts or shards and those of paramagnetic minerals mainly ferrosilicates need to be taken into consideration when interpreting the ams measurements of pdcds variations of the deposition regime both as a function of position and of time also need to be considered on the interpretations nevertheless if a suitable sampling strategy is adopted the potential of the ams method as a petrofabric indicator is maximized

seismogenic strike slip faulting and the development of the north china basin the actively subsiding north china sedimentary basin is associated with an unusually high level of seismic activity this oil and gas producing basin has been the site of nine large m 7 destructive earthquakes since 1600 a d an analysis of faulting during the tangshan earthquake sequence which includes some of the largest shocks that have occurred in this basin during the past 400 years showed that the dominant pattern of deformation during this sequence was associated with displacement on right stepping right lateral strike slip faults a large amount of subsidence 1 0 1 5 m occurred in pull apart regions between steps of the north northeast nne trending strike slip faults the directivity of the p wave radiation pattern and the distribution of aftershocks of the bohai gulf earthquake of july 18 1969 also indicate strike slip faulting on planes of similar nne trend together with the four largest shocks of the hsingtai sequence in 1966 earthquakes with right lateral slip on nne trending faults account for about two thirds of the seismic moment released in this region for the past 100 years the average regional strain due to seismic slip has a dominant component of dextral simple shear on nne striking planes that is approximately twice as large as north south extension or east west shortening based on a combination of published field and borehole data the dominance of horizontal dextral simple shear over subsidence seems to have begun no later than the mid pliocene and the total amount of extension over the entire basin is only about 20 30 this pattern of deformation the spatially variable heat flow values the scattered locations of rapid deposition of quaternary sediments and the fluctuating rate of sedimentation in space and time during the neogene in this basin are difficult to explain by pure extension and thermal subsidence we propose that these observations and the shape of the whole north china basin that of a lazy z are a consequence of pulling apart associated with right lateral movement on the nne trending strike slip fault systems and that the basin as a whole has formed and evolved as a composite pull apart basin due to right lateral slip on numerous right stepping faults since the eocene

temperature gradients in northern europe during the last glacial holocene transition 14 914c kyr bp interpreted from coleopteran assemblages late glacial and early holocene climatic conditions have been reconstructed for northern europe using the mutual climatic range mcr palaeoclimate method based on fossil coleopteran assemblages altogether beetle faunas from 77 sites have been analysed ranging from ireland in the west to poland and finland in the east and mcr estimates calculated the results are plotted on 16 maps each representative of a selected time slice covering the period from 14 5 14c kyr bp to 9 0 14c kyr bp eight of the maps show the mcr estimates of tmax mean temperature of the warmest month derived from each site for which data are available while the remainder show estimated tmax isotherms interpolated from these values it can be demonstrated that at times the thermal climate was fairly uniform throughout the study area whereas at others temperature gradients were much steeper than they are in the region today there also appears to be a distinct contrast between cold periods when contours trended nw se and warmer periods when contours trend w e or even ne sw the pattern of climatic changes that emerges is shown to be very different from the traditional view that has been used up to now as a template for classifying late glacial climatic events on a wide even global scale the suddenness and intensity of changes in the thermal climate may have been partially responsible for an apparent lack of equilibrium between the flora and fauna of the time and the physical environment in which they lived 1998 john wiley sons ltd

a model for the development of the irish variscides a clear correlation exists in the southern irish variscides between extensional structures which controlled late palaeozoic sedimentation in the munster basin and contractional thrusts and folds of end carboniferous age this correlation is interpreted to indicate that the extensional structural framework of the basin including a basal low angle detachment and an array of superjacent normal faults was reused during transpressive inversion of the basin to produce the fold thrust belt the extensional framework which in turn was to some extent derived by reactivation of caledonian structures therefore exerted a fundamental control on the geometry and style of contractional deformation it is not evident that the detachment had a discrete link to the fold belt in south wales or the main variscan orogen in europe

a regional tephrostratigraphic framework for central and southern european climate archives during the last glacial to interglacial transition comparisons north and south of the alps abstract this paper summarises the results of tephrochronological investigations into a suite of central and southern european records which include rotmeer southern germany soppensee and rotsee central swiss plateau lago di lavarone and lago piccolo di avigliana italian southern alpine foreland these sites provide records of palaeoenvironmental changes for the last glacial to interglacial transition lgit at the boundary between north atlantic and mediterranean climatic influences chemical characterisation of glass shards in volcanic ash layers indicates that multiple volcanic sources have contributed to the central european tephra record amongst other volcanic markers the laacher see tephra originating from the eifel region of germany c 12 9 0 1 ka and the vedde ash from iceland c 12 1 0 1 ka are found co located within the sediments of rotmeer soppensee rotsee and lago piccolo di avigliana these key horizons which bracket the onset of the younger dryas stadial provide precise calendrically dated tie points around which a detailed picture of the timing of local and regional environmental transitions can be constructed using the co located tephra layers the re colonisation of northern italian catchment areas by quercus is shown to occur just prior to the deposition of the laacher see tephra layer whereas to the north of the alps quercus and other thermophilous trees do not reappear until several centuries after the deposition of the vedde ash furthermore the discovery of the vedde ash in lago piccolo di avigliana and lago di lavarone is indicative of atmospheric transport of polar air into southern europe during the younger dryas stadial matching evidence proposed for such transport of polar air during the last glacial maximum lgm

geological geophysical and inherited tectonic imprints on the climate and contrasting coastal geomorphology of the indian peninsula abstract the indian subcontinent comprises accreted cratonic fragments that underwent subsequent rifting subduction collision processes along major mobile belts it is also a storehouse of a prolonged history of crustal evolution involving repeated episodes of magmatism volcanism sedimentation and metamorphism and the formation of intracratonic and foreland basins the geologic geomorphic evolution of the peninsula is recorded in relic faults suture zones that confine paleozoic mesozoic and cenozoic sedimentary basins and landforms in addition escarpments plateaus waterfalls deltas planation surfaces and strandlines are either aligned parallel and or formed over them asymmetric relief across the western eastern parts of the peninsula orographic effect on the precipitation pattern and climatic zones provide important constrains on the geologic and geomorphic evolution of the region though extensive continental and coastal deposition occurred during permo triassic and early cretaceous only the downwarped grabens of gondwana basins preserved the sedimentary records occurrences of extensive cenozoic deposits offshore and neogene holocene deltaic deposits along the entire east coast as opposed to the absence of comparable deltaic sequences in the west coast are linked to intense and recurrent episodes of denudation indicating first order control of basement structures over landscape evolution inheritance and continuum of basement structures over climate and landscape evolution of peninsular india can also be witnessed by the unique and diverse drainage patterns of major rivers while most of the major rivers follow a general easterly direction the landscape morphology of their catchments indicates youthful character and tectonically active nature the east flowing rivers show an asymmetry between the areal extents of drainage basin size and delta whereas the west flowing rivers are short and straight and their catchments are miniscule in comparison with the rivers flowing toward east the western ghats escarpment forms an orographic barrier and acts as the main divide between these two drainage systems there is a disparity between the quanta of sediment discharge as well in addition the eastern and western parts of india across the western ghats escarpment show significant differences in terms of climatic zones humid to per humid on the west while it is arid to subhumid on the east the west coast is characterized by 3000 mm year annual rainfall that often reaches 5000 mm year dominance of sw monsoon winds occurrence of narrow here we propose a conceptual tectono geomorphic model demonstrating the inheritance and continuum of gondwanan structural trends on the transient landscape of peninsular india

oxygen isotope wiggle matching as a tool for synchronising ice core and terrestrial records over termination 1 abstract in nw europe the large number of terrestrial records that are now available from termination 1 15 10 kcal yr bp form the basis for a highly detailed picture of lateglacial environmental change nevertheless the greenland oxygen isotope records grip gisp2 are still regarded as the best high resolution climate proxy for the north atlantic region in order to evaluate spatial contrasts and leads and lags in the climate system integration of ice core marine and terrestrial records is becoming increasingly important intimate objectives however comparisons between different environments require a common time scale for the proxy climate records stable isotope analyses performed on lateglacial lacustrine calcareous deposits in the netherlands provide a terrestrial oxygen isotope record comparable to that from the greenland ice core these atmospherically controlled lacustrine oxygen isotope signals not only constitute an independent palaeoclimatic proxy but provide the basis for synchronising records from these environments as well more over this synchronisation reveals some remarkable aspects concerning the timing of the oxygen isotope and palynological events as recorded in the netherlands above all oxygen isotope wiggle matching offers a means of correlating terrestrial and ice core records

a historical declination curve for munich from different data sources abstract long series of geomagnetic field changes are important for studying processes in the earth s core we have compiled 635 historical declination values for southern germany and surrounding areas indirect estimations including the oldest ones from back in the 15th century come from 185 sundials and compasses with declination information and 15 historical maps measurements carried out by monks in the time interval 1668 1854 amount to 122 annual mean values and data related to the orientation of mine shafts contributes by 313 annual values for several locations all these data can be useful to improve historical geomagnetic field models previously compiled german church orientations however are shown to be no reliable sources of the past declination the compiled new declination curve for munich shows general agreement with previously published curves for london and paris and allows to detect geomagnetic jerks with a temporal uncertainty of 10 years more or less regular impulses on a decadal time scale ranging from 30 to 60 years are identified for most of the time interval 1400 2000 but the century from about 1760 to 1860 seems to be devoid of sudden secular variation changes

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

gravity anomalies and flexure of the lithosphere at the middle amazon basin brazil the middle amazon basin is a large paleozoic sedimentary basin on the amazonian craton in south america it contains up to 7 km of mainly shallow water sediments a chain of bouguer gravity highs of approximately 40 to 90 mgals transects the basin roughly coincident with the axis of maximum thickness of sediment the gravity highs are flanked on either side by gravity lows of approximately 40 mgals the observed gravity anomalies can be explained by a steeply sided zone of high density in the lower crust varying in width from 100 to 200 km wide within this region the continental crust has been intruded replaced by more dense material to more than half its original thickness of 45 50 km the much wider sedimentary basin results from regional compensation of the subsurface load and the subsequent load of accumulated sediments by flexure of the lithosphere the observed geometry of the basin is consistent with an elastic lithosphere model with a mechanical thickness of 15 20 kin although this value is lower than expected for a stable cratonic region of early proterozoic age it is within the accepted range of effective elastic thicknesses for the earth rapid subsidence during the late paleozoic may be evidence of a second tectonic event or lithospheric relaxation which could lower the effective mechanical thickness of the lithosphere the high density zone in the lower crust as delineated by gravity and flexural modeling has a complex sinuous geometry which is narrow and south of the axis of maximum sediment thickness on the east and west margins and wide and offset to the north in the center of the basin the linear trough geometry of the basin itself is a result of smoothing by regional compensation of the load in the lower crust

magnetic fabric of ignimbrites a case study from the central anatolian volcanic province the magnetic fabric of the pliocene kizilkaya ignimbrite in the central anatolian volcanic province has been investigated by anisotropy of magnetic susceptibility ams and isothermal remanent magnetization airm seven sections were sampled at various stratigraphic heights within the devitrified portion of the ignimbrite the magnetic mineralogy is complex titanomagnetite occurs as magmatic grains and as inclusions in other phenocryst and glass shards an oxidized phase and hematite occur in deposit levels affected by alteration processes the disturbance produced by lithic and pumice clasts has been reduced by discarding the specimens that deviate more than 1 from the site mean value of the density the ams fabric varies along each individual section neither the ams magnetic lineation nor the magnetic foliation plunge clearly define a common area as the vent location the airm fabric of low coercivity minerals mainly represented by free titanomagnetite grains of magmatic origin is consistent between sites and the inferred flow directions converge on a region near derinkuyu in the nevsehir plateau previously reported as the kizilkaya ignimbrite source area this study shows that systematic use of the remanent fabric improves the results given by ams and aids the identification of the primary magnetic fabric related to the ignimbrite emplacement dynamics

a stretching model for the oslo rift abstract data on the tectonic and magmatic activity crustal thickness seismic velocity and gravity have been integrated to constrain a stretching model for the late carboniferous early permian oslo rift the crustal structure and numerical modelling of temperature and melt generation during rifting suggest that the oslo rift in skagerrak developed in response to crustal stretching with a factor between 1 4 and 1 6 however upper crustal extension by faulting accounts for a stretching factor of only 1 1 1 2 thermal expansion of the lithosphere due to an increased asthenospheric potential temperature the intrusion of melted mantle material into the lower crust and probably a lowering of the erosional base by a fall in sea level all contributed to the erosion of 2 4 km of lower palaeozoic pre rift sediments over large areas the lateral extent of the thermal anomaly reached far beyond the oslo and skagerrak grabens

paleomagnetic correlation of columbia river basalt flows using secular variation a statistical method is developed to evaluate stratigraphic correlations that are based on the similarity of paleomagnetic directions it involves comparison of the probabilities that such directions could have arisen by either simultaneous or random samplings of the ancient magnetic field to calculate these probabilities one must estimate the effects of paleomagnetic errors and paleosecular variation respectively the method is tested successfully on sections of 8 10 grande ronde basalt columbia river basalt group flows at sentinel gap and umtanum ridge which are separated by only 25 km and contain two flows thought to be the same on geological grounds more significantly for widely separated sections at sentinel gap and butler canyon the analysis again shows that simultaneous magnetization is a much more likely explanation of the general similarity of paleomagnetic directions than chance agreement of ancient field directions the simplest interpretation of this result is that many of the flows at the two sites are the same implying that series of grande ronde flows extended over distances of several hundred kilometers

geochronology of betula extensions in pollen diagrams of alpine late glacial lake deposits a case study of the late glacial deposits of the gasserplatz soil archives vorarlberg austria pollen diagrams of alpine late glacial calcareous lake deposits show several extensions of betula the geochronology of these extensions cannot be based on radiocarbon dating due to reservoir effects of such lakes on the radiocarbon ages a robust geochronology can be based on the oxygen isotope stratigraphy additionally recognition of 12 920 calbp lst in the sediment cores provides a secure time marker the combined results of pollen macro remains and stable isotope analyses of the gasserplatz cores point to a correlation of the betula extensions with the oscillations in the oxygen isotope curve and are related to global climatic oscillations this is sustained by the correlation of the gasserplatz isotope oscillations with the oscillations as registered in the greenland ice cores comparison of the results of the gasserplatz cores with the results of similar alpine lake deposits makes clear that the fluctuations in the betula curve are not a local but a regional phenomenon

high resolution sediment and vegetation responses to younger dryas climate change in varved lake sediments from meerfelder maar germany abstract this work focuses on a 1900 year section of varved sediments from lake meerfelder maar mfm extending from the late allerod to the preboreal varve counting provides the chronological framework and determines the length of younger dryas to 1025 1090 years a strong relation between climate change environment response and depositional processes has been found in consequence varve microfacies variations are a sensitive proxy for environment changes these are reflected for example in erosion processes within the lake s catchment minerogenic input and lake productivity diatom blooms the observed varve changes have been quantified by multiproxy analyses of physical and chemical sediment parameters with a resolution of between 8 and 40 years depending on sedimentation rate in addition high resolution palynological investigations provide the biostratigraphical subdivision based on changes in the vegetation occurring during the same time interval varve observations reveal that environment changes at the beginning and the end of the younger dryas occurred within 20 50 years furthermore sediment and vegetation changes were synchronous within the actual precision of the mfm and grip chronologies divergence of only a few decades terrestrial responses in western europe occurred quasi synchronous to temperature changes in greenland

oxygen isotopes of lake marl at gerzensee and leysin switzerland covering the younger dryas and two minor oscillations and their correlation to the grip ice core the ratio of oxygen isotopes is a temperature proxy both in precipitation and in the calcite of lacustrine sediments the very similar oxygen isotope records from greenland ice cores and european lake sediments during the last glacial termination suggest that the drastic climatic changes occurred quasi simultaneously on an extra regional probably hemispheric scale in order to study temporal relations of the different parameters recorded in lake sediments for example biotic response times to rapid climatic changes a precise chronology is required in unlaminated lake sediments there is not yet available a method to provide a high resolution chronology especially for periods with radiocarbon plateaux alternatively an indirect time scale can be constructed by linking the lake stratigraphy with other well dated climate records new oxygen isotope records from gerzensee and leysin with an estimated sampling resolution of between 15 and 40 years match the greenlandic isotope record in many details under the assumption that the main variations in temperature and thus in oxygen isotopes occurred about simultaneously in greenland and switzerland we have assigned a time scale to the lake sediments of gerzensee and leysin by wiggle matching their stable isotope records with those of greenland ice cores which are among the best dated climatic archives we estimate a precision of 20 to 100 years during the last glacial termination

did rifting on australia s southern margin result from tectonic uplift subsidence analyses from australia s southern margin are used to investigate the idea that rifting on the margin was caused by an extensional lithospheric stress field induced by a hot thermal plume impinging on the base of the lithosphere from beneath the continental lithosphere is modelled as a thin sheet with depth dependent rheology the model does not explicitly include elastic flexural or thermal stresses the excess buoyancy of a thermal plume pushes the lithosphere upward by as much as 1 km thereby increasing its potential energy if the horizontal components of lithospheric stress are fixed at some distant plate boundary the lithosphere is a stress guide the lithospheric stress field above the plume will produce horizontal extension that may ultimately be followed by continental separation and seafloor spreading the uplift is modelled by a time dependent function which increases smoothly from zero to its peak value and then decreases back to zero using a plausible mantle rheology the amount of extension inferred at well sites on the margin typically 20 to 30 extension is explained by uplift of the lithosphere to approximately 900 m with a subsequent decay of the uplift over a period of approximately 60 m y the rise time of the uplift function is poorly constrained in the uplift model extension occurs in the subaerial environment during the late jurassic early cretaceous the initial stage of rapid subsidence observed at most well sites on the margin is due in large part to decrease of the vertical stress anomaly caused by the decay of the thermal plume or by the lithosphere moving away from above it the rapid subsidence is followed by very gradual continued subsidence attributed to cooling of the extended lithosphere as in previous studies

detailed jaramillo field reversals recorded in lake sediments from armenia lower mantle influence on the magnetic field revisited abstract while it is well established that the earth s magnetic field is generated by a self sustaining dynamo that reversed its polarity at irregular intervals in the geological past the very mechanisms causing field reversals remain obscure paleomagnetic reconstructions of polarity transitions have been essential for physically constraining the underlying mechanisms in terms of time scale but thus far remain ambiguous with regard to the transitional field geometry here we present new paleomagnetic records from a rapidly deposited lacustrine sediment sequence with extraordinarily stable paleomagnetic signals which has captured in unprecedented detail the bottom reverse to normal r n and top normal to reverse n r transitions of the jaramillo subchron at 1 072 ma and at 0 988 ma the obtained virtual geomagnetic pole vgp path indicates an oscillatory transitional field behavior with four abrupt transequatorial precursory jumps across the pacific the distribution of vgp positions indicates regions of preferred occurrence our results are in agreement with previously proposed bands of transitional vgp occurrence over the americas and australia northwest pacific additionally our vgp positions seem to avoid large low shear velocity provinces llsvps above the core mantle boundary cmb thus our data supports the idea that the transitional field geometry is controlled by heat flux heterogeneities at the cmb linked to llsvps

tephrochronology of last termination sequences in europe a protocol for improved analytical precision and robust correlation procedures a joint scotav intimate proposal the precise sequence of events during the last termination 18 000 9000 ka 14 cy r bp and the extent to which major environmental changes were synchronous are difficult to estab lish using the radiocarbon method alone because of serious distortions of the radiocarbon time scale as well as the influences of site specific errors that can affect the materials dated attention has there fore turned to other methods that can provide independent tests of the chronology and correlation of events during the last termination with emphasis on european sequences we summarise here the potential of tephrostratigraphy and tephrochronology to fulfil this role recent advances in the detection and analysis of hidden tephra layers cryptotephra indicate that some tephras of last termination age are much more widespread in europe than appreciated hitherto and a number of new tephra deposits have also been identified there is much potential for developing an integrated tephrochronological framework for europe which can help to underpin the overall chronology of events during the last termination for that potential to be realised however there needs to be a more systematic and robust analysis of tephra layers than has been the practice in the past we pro pose a protocol for improving analytical and reporting procedures as well as the establishment of a centralised data base of the results which will provide an important geochronological tool to support a diverse range of stratigraphical studies including opportunities to reassess volcanic hazards although aimed primarily at europe the protocol proposed here is of equal relevance to other regions and periods of interest copyright 2004 john wiley sons ltd

complex remanent magnetization in the kizilkaya ignimbrite central anatolia implication for paleomagnetic directions abstract pyroclastic flow deposits known as ash flow tuffs or ignimbrites are invaluable materials for paleomagnetic studies with many applications for geological and tectonic purposes however little attention has been paid to evaluating the consistency and reliability of the paleomagnetic data when results are obtained on a single volcanic unit with uneven magnetic mineralogy in this work we investigate this issue by concentrating on the kizilkaya ignimbrite the youngest large volume unit of the neogene ignimbrite sequence of the central anatolian volcanic province in turkey bringing evidence of significant magnetic heterogeneities in ignimbrite deposits magnetic mineralogy susceptibility magnetic remanence coercivity etc and emphasizing the importance of a stratigraphic sampling strategy for this type of volcanic rocks in order to obtain reliable paleomagnetic data six sections were sampled at different stratigraphic heights within the devitrified portion of the ignimbrite isothermal remanence measurements point to low ti titanomagnetite as the main magnetic carrier at all sites at some sites the occurrence of oxidized ti magnetite and hematite is disclosed the bulk susceptibility k m decreases vertically at two out of six sections its value for the topmost samples is commonly one order of magnitude lower than that of the samples at the base in most cases low k m values relate to high coercivity of remanence b cr values which range from 25 to 400 mt and to low s ratios measured at 0 3 t between 0 28 and 0 99 these data point to the occurrence of oxidized magnetic phases we therefore consider the k m parameter as a reliable proxy to check the ignimbrite oxidation stage and to detect the presence of oxidized ti magnetite and hematite within the deposit the characteristic remanent magnetization is determined after stepwise thermal and af demagnetization and clearly isolated by principal component analysis at most sites for these sites the site mean paleomagnetic direction is consistent with data from the literature at a few other sites the remanence is more complex the direction moves along a great circle during demagnetization and no stable end point is reached the occurrence of oxidized ti magnetite or hematite as well as two remanence components with overlapping coercivity and blocking temperature spectra suggest that the kizilkaya ignimbrite acquired first a thermal remanent magnetization and then during the final cooling or a short time later a secondary remanent magnetization component which is interpreted as a crm acquired during post emplacement devitrification processes notwithstanding the kizilkaya ignimbrite is a single cooling unit its magnetic properties suffered substantial variations laterally and vertically within the deposit the kizilkaya case shows that thick pyroclastic deposits should be sampled using a stratigraphic approach at different sites and different stratigraphic heights at each individual sampling location otherwise under sampling may significantly affect the paleomagnetic results when sampling is performed on a short duration or on very poorly preserved deposits we recommend drilling the lower central portion in the most strongly welded and devitrified facies such sampling strategy avoids complications arising from the potential presence of a pervasive secondary crm masking the original chrm

thermal history of the eastern margin of the gulf of suez i reconstruction from borehole temperature and organic maturity measurements abstract the gulf of suez is a tertiary continental rift associated with prominent flank uplift despite numerous studies which focused mainly on the western and central parts of the graben the thermo mechanics controlling the tectonic evolution of the gulf of suez is still enigmatic we have integrated borehole temperatures and organic maturity measurements in the eastern margin of the gulf of suez in order to study rift related paleothermometry and the present day thermal regime the data obtained suggest that the present thermal regime represents the maximum heat flow and temperatures for the sedimentary section in the basin furthermore lateral distributions of geothermal gradient and heat flow in the gulf of suez do not correlate mainly because of extensive variability in lithology and thermal conductivity rift related heat flow increases systematically and subparallel to the rift axis from about 60 mw m2 in the darag subbasin in the north to about 80 mw m2 in the ras garra area in the south both values are higher than 45 mw m2 the average heat flow assumed for the pre rift stage and the characteristic level for the present day heat flow away from the rift the north to south increase in heat flow probably reflects the southward increase of extension as well as lateral transfer of heat flow from the red sea this latter conclusion is supported by the fact that heat flow in the southern gulf of suez recorded by the paleothermometric reconstructions and borehole temperature data is somewhat higher than that estimated by model calculations for the extension derived from structural and subsidence reconstruction