teleseismic evidence for a break off subducting slab under eastern turkey abstract we present seismic images of the upper mantle beneath eastern turkey determined by teleseismic tomography the data are measured precisely from seismograms recoded by the eastern turkey seismic experiment network consisting of 29 portable stations and 2 permanent stations our results show that obvious high velocity high v anomalies of up to 2 are interrupted beneath eastern turkey and subcrustal earthquakes occurred along these high v anomalies pronounced low velocity low v anomalies are visible from the arabian foreland basin in the southwest to the caucasus region in the northeast which extend down to about 400 km depth these low v anomalies are consistent with the existence of late cenozoic volcanism in the region these results provide new constraints on the geodynamic processes in the east anatolian plateau suggesting that the break off of the arabian slab may play an important role in the formation of the anatolian plateau and the volcanism in the region these processes might be related to the collision of the arabian plate with the eurasian plate

kimmeridgian palaeogeography and basin evolution of northeastern iberia abstract two sedimentary basins were developed during the kimmeridgian in the northeastern part of iberia the basque cantabrian basin to the northwest and the iberian basin to the east these basins were mainly filled by carbonates deposited in a shallow epicontinental sea that was connected to the open marine realms of both the north atlantic and the western tethys respectively during the late jurassic they were temporarily linked by means of the soria seaway the uppermost oxfordian to lowermost tithonian of northeastern iberia consists of two depositional sequences sequence j3 5 spans latest oxfordian to early late kimmeridgian times sequence j3 6 spans the late kimmeridgian and early tithonian during sequence j3 5 coralgal reefs were developed in the sedimentary domains of the basque cantabrian basin and the soria seaway whereas the marginal areas of the iberian basin were dominated by oolitic shoals with variable siliciclastic influence outer ramp areas located in the central and eastern part of the iberian basin were dominated by carbonate muds and marls during the late kimmeridgian earliest tithonian shallow reefal and oolitic facies prograded over the micritic outer ramp facies the sedimentation areas were reduced and sequence j3 6 was only deposited in the iberian basin most of the western margin of the iberian basin and the southern areas of the soria seaway were covered by reefal facies during this sequence major transgressive events in the iberian basin took place in the latest oxfordian early kimmeridgian and in the middle late kimmeridgian whereas eustatic falls in sea level are recognised at the onset of the late kimmeridgian and at the kimmeridgian tithonian transition these events have also been described in other west european basins synsedimentary extensional tectonics is also evident and has been related to the onset of the late jurassic early cretaceous rifting stage synsedimentary normal faulting resulted in the presence of several troughs and highs within the basin the tectonic uplift of the western basin margin explains the progressive basinwards shift of the shorelines as observed in the iberian basin towards the end of the jurassic

seismic tomographic imaging of the eastern mediterranean mantle implications for terminal stage subduction the uplift of anatolia and the development of the north anatolian fault

a facies model for internalites internal wave deposits on a gently sloping carbonate ramp upper jurassic ricla ne spain abstract internal waves are waves that propagate along the pycnocline the interface between two density stratified fluids even though internal waves are ubiquitous in oceans and lakes their impact in the sedimentary record has remained largely unrecognized internal waves can remobilize the sediment from the depth at which the internal waves break onto the sea floor in shelf or ramp settings internal wave deposits internalites have to be distinguished from tempestites while in slope and deeper settings internalites require distinction from turbidites the upper kimmeridgian carbonate ramp succession cropping out near ricla ne spain provides some key evidence to differentiate the depositional processes induced by breaking internal waves from those related to surface storm waves sandy oolitic grainstone eventites previously interpreted as tempestites contain evidence of reworking by turbulent events related to breaking internal waves underlying rationale are 1 they occur in distal mid ramp position detached from the coeval shallow water successions 2 they do not have the characteristic coarsening and thickening upward trend of storm deposits 3 they gradually thin out to disappear both up dip and down dip interbedded with mid ramp lime mudstones and 4 they show little or no erosion towards the shallower areas a facies model for internalites produced by two sediment populations sand and mud on a gently sloping carbonate ramp is proposed the individual internalites occurring at ricla include several architectural elements sequentially organized in dip direction which can be related to the flows associated with breaking internal waves erosion in the breaker zone swash run up and tractive backwash flow individual internalites stack with down and up slope shingling configuration in dm thick packages thought to reflect the up slope and down slope migration of the breaker zone in turn related to depth variations of the palaeo pycnocline packages occur in dm to m thick clusters suggested to reflect changes in sediment supply and or variations in water stratification affecting the energy of internal waves

selective calcareous nannoplankton survivorship at the cretaceous tertiary boundary calcareous nannoplankton underwent devastating diversity loss at the cretaceous tertiary boundary 65 5 ma but recovered rapidly in the early paleocene from a small number of survivor species an understanding of this survivorship has been hampered by uncertainties introduced by reworking and mixing but new high resolution assemblage data from the northwest pacific shatsky rise ocean drilling program site 1210 allow the unequivocal identification of 10 survivors evidence of shared adaptive strategies among these species provides the first indication that the extinctions were selective with survival limited to a few neritic and or opportunistic species probably facilitated by hardiness and or life cycle escape strategies 2005 geological society of america

some comparisons between mining induced and laboratory earthquakes although laboratory stick slip friction experiments have long been regarded as analogs to natural crustal earthquakes the potential use of laboratory results for understanding the earthquake source mechanism has not been fully exploited because of essential difficulties in relating seismographic data to measurements made in the controlled laboratory environment mining induced earthquakes however provide a means of calibrating the seismic data in terms of laboratory results because in contrast to natural earthquakes the causative forces as well as the hypocentral conditions are known a comparison of stick slip friction events in a large granite sample with mining induced earthquakes in south africa and canada indicates both similarities and differences between the two phenomena the physics of unstable fault slip appears to be largely the same for both types of events for example both laboratory and mining induced earthquakes have very low seismic efficiencies eta tau a bar tau where a is the apparent stress and bar tau is the average stress acting on the fault plane to cause slip nearly all of the energy released by faulting is consumed in overcoming friction in more detail the mining induced earthquakes differ from the laboratory events in the behavior of as a function of seismic momentm0 whereas for the laboratory events 0 06 independent ofm0 depends quite strongly onm0 for each set of induced earthquakes with 0 06 serving apparently as an upper bound it seems most likely that this observed scaling difference is due to variations in slip distribution over the fault plane in the laboratory a stick slip event entails homogeneous slip over a fault of fixed area for each set of induced earthquakes the fault area appears to be approximately fixed but the slip is inhomogeneous due presumably to barriers zones of no slip distributed over the fault plane at constant bar tau larger events correspond to larger a as a consequence of fewer barriers to slip if the inequality a bar tau 0 06 has general validity then measurements of a ea m0 where is the modulus of rigidity andea is the seismically radiated energy can be used to infer the absolute level of deviatoric stress at the hypocenter

evidence for annual records of phytoplankton productivity in the kimmeridge clay formation coccolith stone bands upper jurassic dorset uk the upper jurassic kimmeridge clay formation is a c org rich sequence of mudrocks that was deposited in a dysoxic basin which served unusually to preserve primary coccolithophorid proportions strikingly contrasting within this dark coloured formation are the white coccolith stone bands which contain pristinely preserved coccolithophorid assemblages preserving potentially primary coccolithophorid abundances with minimal diagenetic alteration using methodology described herein scanning electron microscopy sem observation of mum scale laminae within selected stone bands has revealed five distinctive types of microlamina type 1 being barren clay type 2 comprising coccoliths associated with varying amounts of clay or amorphous organic matter type 3 being purely coccolithic type 4 being of putative microbial origin and type 5 containing frequent calcispheres these are all described and illustrated here illustrated sequences of these are discussed with reference to an hypothetical model sequence based on modem records representing a kimmeridgian year of coccolithophorid productivity annual signals are thus interpreted based on the observations presented here and including summaries of the palynomorph records from the stone bands we comment on watznaueriacean palaeoecology and particularly the interpretation of watznaueria fossacincta barnesiae as an opportunistic growth maximising taxon c 2004 elsevier b v all rights reserved

the carbonate signal and calcareous nannofossil distribution in an upper jurassic section balingen tieringen late oxfordian southern germany total abundance assemblage composition and the stratigraphic distribution of the six most abundant species of calcareous nannofossil were analysed in the upper oxfordian succession of balingen tieringen western swabian alb south germany this locality represents a deep shelf less than 200 m environment that is strongly influenced by its proximity to the jura shallow platform nannofossil abundance negatively correlates with carbonate content as well as with accumulation rate calcareous nannofossils thus did not produce the bulk of carbonates and their abundance was essentially controlled by the import of allochthonous carbonate mud gradual increase in carbonate content in the balingen tieringen succession can be related to an intensified carbonate mud export from the jura shallow platform to the swabian alb deep shelf during the late oxfordian changes in the nannofossil assemblage composition along the profile are interpreted as primary although a partial control by diagenesis on the assemblage can not be completely excluded the coccoliths lotharingius hauffii watznaueria britannica cyclagelosphaera margereli watznaueria barnesae watznaueria manivitae and the incertae sedis schizosphaerella spp display their highest relative abundance one after the other in a stratigraphic order this nannofossil succession parallels the gradual increase in allochthonous carbonate mud accumulation on the deep shelf as well as the gradual decrease in the intensity of siliciclastic input recorded on the jura shallow platform this suggests a climatic control by humidity on shallow platform carbonate production and export basinwards and on nutrient availability in deep shelf surface waters that itself controlled the nannofossil assemblage composition therefore the succession of highest relative abundance of l hauffii w britannica c margereli w barnesae w manivitae and schizosphaerella spp can represent a trophic preference continuum from more eutrophic to oligotrophic conditions

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

isotopic evidence for a transition from subduction to slab tear related volcanism in western anatolia turkey abstract volcanic rocks in western turkey show age progressive magmatism migrating from northeast to southwest that reflects a southward shift of the aegean subduction zone during the miocene slab segmentation during this period of trench roll back is thought to have imposed source region heterogeneity trending northwest to southeast in this study we present new sr nd pb and o isotopic analyses from the miocene volcanic rocks of the usak gure basin and compare these to previously published data the data demonstrate a change from subduction related sources around the menderes core complex to more asthenospheric sources in the afyon region isotopic compositions sr nd pb of volcanic rocks from the demirci and selendi basins to the west and the afyon volcanic area to the east indicate minimal upper crustal contamination the most primitive lavas also reveal increasing k contents from west the ne sw trending basins to east afyon region it is suggested that the composition of the western anatolian volcanic rocks change from orogenic with lithospheric mantle sources associated to denudation of the menderes massif core complex mmcc to anorogenic with asthenospheric mantle sources in the vicinity of the kirka afyon isparta kai volcanic province with time from early miocene to quaternary there is no asthenospheric contribution during the late miocene onwards in the eastern margin of the mmcc while the asthenospheric upwelling occurred only in a small area beneath the exhuming core complex we interpret the usak gure basin to reflect a structural boundary showing a transition from a subduction influenced metasomatized mantle source to asthenospheric mantle source volcanism driven by slab tearing between the hellenic and cyprus slab segments the usak mugla transfer zone umtz most likely corresponds to slab tear related westernmost faults that were induced by initiation of slab segmentation processes following the late miocene circa 11 ma and possibly since the early miocene

depositional sequences in deep shelf environments a response to sea level changes and shallow platform carbonate productivity oxfordian germany and spain abstract oxfordian deep shelf deposits of southern germany and southern spain are characterized by marl limestone alternations that are stacked into small scale medium scale and large scale depositional sequences the german sections contain autochthonous sponge reefs and associated fragments of microbialites whereas the sections studied in spain display tempestites composed of autochthonous deeper water and allochthonous shallow water particles the facies of the german limestones and marl layers has been analyzed in detail condensed intervals implied by glauconitization of particles abundant cephalopods intense bioturbation and generally more marls are also enriched in sponge reefs and associated particles and in nannofossils limestone rich intervals however contain fewer sponges and fewer nannofossils neither bioerosion of sponge reefs nor nannofossil blooms can thus explain the abundance of carbonate mud that forms the limestones consequently it is suggested that most of the carbonate mud is exported from shallow platform areas where carbonate productivity is high the clay fraction was derived from weathering of massifs in the hinterland the observed depositional sequences can be correlated between the studied sections in germany and spain situated in different paleotectonic and paleoclimatic domains and also between deeper water sections and platform sections this suggests that they formed through allocyclical processes comparision with published time scales implies that the small scale and medium scale sequences formed in tune with the 100 kyr and 400 kyr orbital eccentricity cycles respectively however the number of marl limestone alternations is not always consistent with the expected number of 20 kyr precessional cycles 5 per 100 kyr cycle the large scale sequences reflect long term third order sea level changes the observed marl limestone alternations are interpreted to have formed through cyclically varying export of carbonate mud from the platform towards the deep shelf the variations being controlled by climatically induced high frequency sea level fluctuations enhanced marl deposition on the deep shelf can be related to sea level fall causing exposure of the shallow platform and reducing the area of carbonate production or by rapid sea level rise maximum flooding leading to partial or total drowning of the platform and or to retrogradation of facies belts enhanced carbonate deposition occurs during transgression when large production areas are created on the platform or during late highstands when progradation is forced and carbonate mud export enhanced depending on the long term trend of sea level change on which the high frequency fluctuations are superimposed one high frequency 20 kyr sea level cycle can thus create one or two marl limestone alternations or only marly deposits consequently one 100 kyr eccentricity cycle may be formed of a variable number of marl limestone alternations commonly 2 to 8 the studied deeper water depositional sequences thus are strongly linked to the history of the adjacent shallow carbonate platforms

classification and analysis of palynodebris from the palaeocene sediments of the forties field sedimentary organic matter behaves as sedimentary particles and this study attempts to interpret its occurrence in the palaeocene sands and mudstones of the forties field of the north sea new nomenclature and classification of this palynodebris are presented and are used to make quantitative counts of the palynodebris from nearly 600 samples of known sedimentary character the new categories are further refined by objective testing of the data by principal components analysis and cluster analysis it is argued that two types of sedimentary organic matter are of particular value because they are preferentially deposited in different environments palynowafers are most commonly deposited in the submarine fan lobes and channel complexes and amorphous matter occurs mostly in the lower energy basin plain sediments

facies and depositional sequence evolution controlled by high frequency sea level changes in a shallow water carbonate ramp late kimmeridgian ne spain the outcrops of the sierra de albarracin ne spain allow a precise reconstruction of the shallow sedimentary domains of a late kimmeridgian carbonate ramp developed in western marginal areas of the iberian basin the sedimentary record shows a hierarchical sequence stratigraphic organization which implies sea level changes of different frequencies the studied succession is arranged in a long term transgressive regressive sequence which is likely to reflect local variation in the subsidence rates this sequence includes four higher order sequences a to d which have variable thickness from 3 to 21 m the similar sedimentary evolution observed in distant localities suggests the existence of high frequency sea level fluctuations controlling the sequence development the average amplitude of these cycles would range from 5 to 10 m the precise estimation of their duration some few hundreds of kyr and their possible assignment to any of the long term orbital cycles the 100 or the 400 kyr eccentricity cycles is uncertain sequences a and b formed during the long term transgressive interval are relatively thin from 3 to 9 m give up sequences that were never subaerially exposed these sequences are locally formed by five shallowing upward elementary sequences sequences c and d are catch down sequences with evidence of emersion of subtidal facies sequence c formed during the stage of maximum gain of long term accommodation is the thickest sequence from 13 to 21 m and includes coral microbial reefs pinnacles up to 16 m in height the increased production rates were able to fill part of the accommodation created during the early stage of high frequency sea level rise and the shallow platform was eventually exposed to subaereal erosion and meteoric cementation

palynofacies prediction of distance from sediment source a case study from the upper cretaceous of the pyrenees quantitative variations in the size shape and preservation state of microscopic plant debris assemblages correlate with the actual distance of the sample site from the coastal siliciclastic sediment source a case study from a shelf to basin transect in the upper cretaceous of the spanish pyrenees reveals that 1 the diameter of equant black wood phytoclasts 2 the ratio of equant to lath shaped black wood phytoclasts and 3 several other parameters show predictable changes over a 55 km onshore offshore transect these parameters primarily reflect sedimentological sorting based on particle size and density rather than paleoecological gradients when only samples from the transgressive systems tract are considered multiple regression models predict the distance from the source with a standard error of 5 km r 2 0 84 0 93 these parameters also allow the maximum flooding surface to be more precisely located within mudstone dominated sections by applying the lateral regression relationship to stratigraphic data a quantitative estimate can also be made for the scale of lateral facies shifts through depositional sequences here 10 km

calcareous nannofossil assemblage turnover in response to the early bajocian middle jurassic palaeoenvironmental changes in the subbetic basin abstract the calcareous nannofossil assemblages from three lower bajocian pelagic successions from the subbetic basin well dated by ammonites have been investigated biostratigraphically they encompass the njt9 to njt10a nannofossil tethyan zones pca factor analysis performed on percentage abundances of selected taxa suggests that the main factors controlling the early bajocian nannofossil assemblages of the subbetic basin were trophic level nutrient availability and nutricline depth a gradual eutrophication is recorded in the calcareous nannofossil assemblages through an increase in the percentage abundance of watznaueria spp especially in the taxa best adapted to unstable and more eutrophic conditions w britannica gr and w manivitiae gr this eutrophication is concomitant with a trend of increasing carbonate 13 c values over the early bajocian and a rise in biogenic silica production and deposits in the study sections and other basins of the western tethys around the middle part of the laeviuscula subzone a decrease in the absolute and relative abundance of the deep dwelling taxa especially crepidolithus crassus suggests a deterioration of the environmental conditions in the lower photic zone this has been interpreted as caused by a nutricline shallowing and or greater turbidity that could be related in turn to surface water stratification two different episodes have been differentiated in relation to nutricline dynamics 1 from the latest aalenian to earliest early bajocian a weak and or deep nutricline with nutrients rather uniformly spread throughout the photic zone and concomitant with mesotrophic conditions and increasing productivity is suggested 2 a shallowing of the nutricline and or increase in surface water turbidity concomitant with more eutrophic conditions is suggested for the latest early bajocian the observed decrease in the deep dwelling taxa supports the hypothesis of a climatically driven fertilization of the surface waters instead of fertilization by upwelling for the early bajocian eutrophication episode

an isotopic appraisal of the late jurassic greenhouse phase in the russian platform abstract oxygen and carbon isotope ratios have been determined from late jurassic callovian volgian belemnites from three locations on the russian platform gorodischi khanskaya gora and marievka all samples were examined by means of trace element geochemistry and petrography in order screen for diagenetic alteration oxygen and carbon isotopes from well preserved belemnites range from 2 24 to 0 09 and 0 57 to 1 77 respectively oxygen isotopes if interpreted in terms of temperature reveal a rise of temperatures during the oxfordian early kimmeridgian and indicate a prolonged episode of warmth during the kimmeridgian volgian the isotope data only equivocally reflect a number of significant changes in boreal tethyan ammonite assemblages a positive carbon isotope excursion is observed within the volgian but not seen within composite carbon isotope stratigraphies of the western tethys hence the jurassic may have been characterised by regional 13 c excursions related to non simultaneous organic matter deposition resulting from localised ponding semi restricted ocean circulation and a lack of tidal mixing

moment tensors of ten witwatersrand mine tremors ground motions recorded both underground and on the surface in two of the south african gold mining districts were inverted to determine complete moment tensors for 10 mining induced tremors in the magnitude range 1 9 to 3 3 the resulting moment tensors fall into two separate categories seven of the events involve substantial coseismic volumetric reduction v together with normal faulting entailing shear deformation ad where the summation is over fault planes of areaa and average slipd for these events the ratio v ad ranges from 0 58 to 0 92 with an average value of 0 71 for the remaining three events v is not significantly different from zero these events are largely double couple sources involving normal faulting surprisingly the two types of source mechanism appear to be very distinct in that there is not a continuous distribution of the source mix from v 0 to v ad presumably the coseismic closure indicates substantial interaction between a mine stope and adjacent shear failure in the surrounding rock under the influence of an ambient stress for which the maximum principal stress is oriented vertically

perturbation of the carbon cycle at the middle late jurassic transition geological and geochemical evidence a compilation of new and published stratigraphic paleontological and geochemical data is used to detect the reciprocal influences of carbon cycling and global environmental changes in the jurassic a major perturbation of the surface carbon cycling accompanied by pronounced climate and sea level fluctuations waxing and waning of continental ice affected earth history around the middle late jurassic transition mljt we establish the respective timing of changes of carbonate and organic matter sedimentation and global fluctuations of sea surface temperatures paleobiogeography and o isotope paleothermometry and sea level sequence stratigraphy so that causative mechanisms and feedback effects can be considered it is apparent that the global sea level rise and warming initiated in the late bathonian led to a constriction of carbonate platforms to low latitudes and enhanced marine organic deposition sea level and temperature optima were achieved several million years later during the middle callovian a detailed record of sea surface temperatures in the northern hemisphere based on migration of marine fauna and isotopic thermometry indicates that a drastic climatic decline set in during the early late callovian just post dating the increased capture of organic matter by marine sediments this decline in temperature is interpreted in terms of an inverse greenhouse effect triggered by drawdown of co 2 consequent upon excess carbon burial the magnitude of refrigeration and its coincidence in time with an abrupt global scale fall of sea level are both suggestive of continental ice formation at this time carbonate sedimentation was jeopardized at the mljt as a result of both global cooling and presumed p c o 2 lowering and resumed abruptly during the middle oxfordian by spreading again over mid latitude zones salient conclusions are that 1 the pattern of excess carbon burial coincident with elevated temperature but followed by climatic deterioration supports the general hypothesis that a major control on mesozoic climate was the abundance of atmospheric co 2 2 significant masses of continental ice may have formed during this part of the jurassic and correlatively high co 2 levels were certainly not sustained throughout this period 3 the global carbonate sedimentation budget correlated with the surface temperature and sea level but the latitudinal spreading of type tropical carbonates was not simply related to the thermal status of seawaters 4 on a global scale the c o r g and c i n o r g burial rates were coupled apparently through the correlation existing between the co 2 level and surface temperature

late triassic to early jurassic palaeogeography and eustatic history in the nw tethyan realm new insights from sedimentary and organic facies of the csővar basin hungary abstract sedimentary and organic facies of a continuous late triassic early jurassic toe of slope to basin succession of the ne transdanubian range n hungary was studied in order to reconstruct the palaeogeographical and eustatic evolution of the cs var basin an intraplatform basin of the nw neotethys margin characteristic facies successions point to sea level changes of different hierarchies cyclic patterns inferred to result from orbital eccentricity forcing are also reflected in the stratigraphical distribution of sedimentary organic matter furthermore both palaeontological and isotope data document drastic climatic changes around the triassic jurassic boundary detecting sea level changes leads to a more accurate interpretation of the late triassic palaeogeographic setting and evolution of the transdanubian range s carbonate platform our integrated sedimentological and palynological data suggest a complex topography and dynamic sea level history which contradicts a previous model of broad uniform platform setting and lack of any major drowning and emersion events during the late triassic

timing of sea level tectonics and climate events during the uppermost oxfordian planula zone on the iberian ramp northeast spain the middle oxfordian warming climate and sea level rise initiated the development of vast carbonate platforms in some western european basins at the same time however siliciclastics and siliceous sponges dominated certain marginal areas of the iberian ramp there siliciclastic input was particularly prominent during the latest oxfordian and may have been related to a global sea level fall synsedimentary tectonic activity or humid climatic conditions in the hinterland field analyses and computer modelling have been previously used to determine the factors that controlled sedimentation however it is still unclear if the specific conditions that prevailed during the latest oxfordian were due to eustasy tectonics or climate and when precisely they occurred here we document major changes in sedimentological micropalaeontological and mineralogical records on the iberian ramp during this interval detailed sedimentary facies and palynofacies analyses combined with sequence stratigraphic and cyclostratigraphic analyses of the ricla barranco section enable the establishment of a highresolution time frame based on the quartz and mica percentage fluctuations one large and seven small scale sequences are defined the large scale sequence boundaries correlate with third order sequence boundaries ox 8 and kim 1 defined by hardenbol et al 1998 the large scale maximum flooding surface corresponds to the base of the most calcareous interval and to the maximum abundance of marine phytoplankton and opaque equidimensional phytoclasts the small scale sequences correspond to the 100 kyr orbital eccentricity cycle calcareous nannofossils and clay minerals were used as palaeoclimatic proxies nannofossil abundances and fluxes are lower in the upper part than in the lower part of the interval studied suggesting a decrease in seasurface trophic conditions also shown by an increase in the relative abundance of oligotrophic taxa this upper part is also characterised by an increase in smectite which coincides with the base of the large scale highstand deposit and is interpreted as reflecting the establishment of dry conditions a first increase in smectite occurs in the lower part of the succession and coincides with high percentages of quartz and mica this latter mineralogical assemblage is interpreted as recording the onset of the late jurassic to early cretaceous rifting stage which occurred just before the planula galar ammonite subzone transition the present study points out a return toward optimum conditions for carbonate sedimentation only 300 kyr after the prominent increase in siliciclastic input due to tectonic activity the recovery of carbonate production was accompanied by a global sea level rise and by decreasing rainfall on nearby land

transgressive regressive cycles and jurassic palaeogeography of northeast iberia abstract a correlation and sequence stratigraphy study of jurassic successions has been carried out in the main sedimentary basins of northeast iberia i e asturias basque cantabrian and iberian basins based on the identification of transgressive regressive cycles the development and palaeogeographic evolution of the epicontinental carbonate platforms of northeast iberia were largely controlled by major tectonic activity at three main intervals at the beginning of the jurassic in the lower middle jurassic transition and during the uppermost jurassic respectively during early jurassic times northeast iberia was the site of a single and large carbonate ramp opened to the north this carbonate ramp suffered a progressive drowning evolving from an inner to hemipelagic ramp systems with the local development of suboxic environments in the deepest areas located to the north during the middle jurassic different open carbonate platforms were formed including the development of swells in intermediate areas during the upper jurassic the outer ramp areas were progressively moving to the east iberian basin and the ammonite faunas showing a markedly tethyan affinity thereafter three first order t r cycles bounded by major discontinuities associated with significant time gaps are identified they extend respectively from the latest rhaetian to the early aalenian from the middle aalenian to the early oxfordian and from the early oxfordian to the late berriasian major transgressive peaks occurred at the middle toarcian bifrons zone at the late bajocian upper niortense and garantiana zones and at the mid kimmeridgian divisum zone each of the first order cycles includes four second order t r cycles cycles 1 1 1 4 are identified in the northern basins cycles 2 1 2 4 display some differences in age of transgressive peaks from one basin to another cycles 3 1 3 4 are mainly identified in the iberian basin the correlation with other separated boreal and thethysian basins demonstrates that the number and age of t r cycles varies from one basin to another and are mainly controlled by the local or regional tectonic development the transgressive peaks may reflect episodes of eustatic rise during the jurassic however their different age from one basin to another is explained by different subsidence evolution

an implosive component in the seismic moment tensor of a mining induced tremor in early 1988 a special study in one of the major south african gold fields yielded seismograms that indicate seismic moment tensors having substantial implosive components the moment tensor resulting from the inversion of the ground motion data from the best recorded event was decomposed into isotropic and deviatoric components from which both the coseismic volumetric closure v and the total shear deformation ad where a is fault area and d is average slip could be estimated the finding here that v ad is consistent with earlier analyses of how the tabular mine stopes interact with the surrounding rock mass to produce seismic deformation

energy budgets of mining induced earthquakes and their interactions with nearby stopes abstract in the early 1960 s n g w cook using an underground network of geophones demonstrated that most witwatersrand tremors are closely associated with deep level gold mining operations he also showed that the energy released by the closure of the tabular stopes at depths of the order of 2 km was more than sufficient to account for the mining induced earthquakes i report here updated versions of these two results based on more modern underground data acquired in the witwatersrand gold fields firstly an extensive suite of in situ stress data indicate that the ambient state of crustal stress here is close to the failure state in the absence of mining even though the tectonic setting is thoroughly stable mining initially stabilizes the rock mass by reducing the pore fluid pressure from its initial hydrostatic state to nearly zero the extensive mine excavations as cook showed concentrate the deviatoric stresses in localized regions of the abutments back into a failure state resulting in seismicity secondly there appears to be two distinct types of mining induced earthquakes the first is strongly coupled to the mining and involves shear failure plus a coseismic volume reduction the second type is not evidently coupled to any particular mine face shows purely deviatoric failure and is presumably caused by more regional changes in the state of stress due to mining thirdly energy budgets for mining induced earthquakes of both types indicate that of the available released energy only a few per cent is radiated by the seismic waves with the majority being consumed in overcoming fault friction

carbonate production and offshore transport on a late jurassic carbonate ramp kimmeridgian iberian basin ne spain evidence from outcrops and computer modelling

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

sedimentology and characteristics of dispersed organic matter in tertiary niger delta origin of source rocks in a deltaic environment organic matter in tertiary strata of the niger delta is mainly a mixture of types ii and iii kerogen as defined by pyrolysis has a high pristane phytane ratio 1 and is composed of the macerals vitrinite and minor liptinite the main palynofacies are structured woody material opaque organic matter cuticles pollen and spores and minor amorphous organic matter the geochemistry petrology palynofacies and distribution data indicate a predominantly terrestrial and detrital source of the organic matter irrespective of facies formation or age the distribution and abundance of the organic matter are related to both the age of the strata and depositional environment the most significant variation is the decline in mean total organic carbon toc content from late eocene 2 2 toc to pliocene strata 90 toc and an associated general decline in pyrolysis defined hydrogen index hi and pristane phytane ratio the decrease in toc and hi in younger strata reflects increased dilution of a nearly constant supply of terrestrial organic matter with the generally higher sedimentation rates of younger strata a simple linear dilution model accounts for about 50 of the variance in measured toc the low pristane phytane ratio of younger strata may reflect less oxidizing depositional conditions the variation in organic matter with depositional environments and environmental depth zones defined by foraminiferal assemblages is significant although less important than variation due to age the highest toc and hi values occur in nonmarine swamp marsh and floodplain deposits reflecting proximity to the organic source beach barrier and offshore bar facies have lower toc and hi values due to selective winnowing of organic matter and greater oxidation from continental to transition marine depth zones a marked decline in toc and hi occurs as a result of dilution selective transport and oxidation of the organic matter from transitional to bathyal depth zones little variation is found in toc but a general increase is found in hi which reflects a relative increase in more hydrogen rich autochthonous organic matter in all facies autochthonous organic matter comprises less than 20 of the toc no interpretable variation appears in maceral or palynofacies abundance with sediment type which probably reflects the homogeneity of the organic matter paradoxically no rich source rocks occur in the tertiary succession in the niger delta and as conventionally measured the strata have little or no oil generating potential the poor quality of the source rocks has been more than compensated for by their great volume by the excellent migration routes provided by interbedded permeable sands and possibly by the relatively rapid rate of maturation niger delta type of source rock although an end member in terms of general source rock composition appears to be relatively typical of tertiary deltas

growth and demise of the jurassic carbonate platform in the intracratonic paris basin france interplay of climate change eustasy and tectonics it is usually very difficult to identify and quantify the relative influence of tectonics eustasy and climateon carbonate system evolution from sedimentary records in order to improve our understanding of these mechanisms we have traced for the first time the evolution of the eastern paris basin platform throughout the entire jurassic period this carbonate platform underwent eight successive growth and demise phases with different depositional profiles ranging from ramps to flat topped geometries the eight carbonate growth periods are compared with the standard sea level curves local tectonic regimes and recently published oxygen isotope and or clay mineralogy databases prograding heterozoan facies along ramp profiles mark periods dominated by second order eustatic sea level rise relatively cool sea surface temperatures and mesotrophic and humid conditions hettangian pliensbachian late oxfordian tithonian during these periods variable detrital contents in the sedimentary succession hampered the efficiency of shallow marine carbonate factories higher sea surface temperatures oligotrophic and humid conditions associated with either eustatic sea level rise or very high local subsidence occurred during the early bajocian and the mid oxfordian these seawater properties seem to have favoured the aggradation of scleractinian corals forming dome shaped bioherm buildups an oolitic and lime mud carbonate system deposited during the bathonian second order eustatic sea level fall is characterised by miliolid rich micritic facies on a rimmed ramp under stable cooler and drier conditions the secondorder maximum flooding associated with a sea surface temperature decline and or a seawater eutrophication caused at least five carbonate demise periods i e toarcian earliest late bajocian callovian oxfordian transition earliest late oxfordian and kimmeridgian

spatial distribution patterns of calcareous nannofossils across the callovian oxfordian transition in the french subalpine basin abstract callovian oxfordian calcareous nannofossils are documented from four sections distributed along a proximal distal slope to central basin transect in the french subalpine basin south eastern france the sections were dated and correlated using integrated ammonite dinoflagellate and nannofossil biostratigraphies the nannofossil assemblages are constantly dominated by watznaueria britannica however significant spatial changes in nannofossil assemblage composition are recorded nannofossil assemblages recovered in slope and slope to basin transition sections are characterized by high abundances lowest diversities highest percentages of smallest sized morphotypes of w britannica subordinated w britannica manivitiae a morphotype described in this study and are indicative of turbulent unstable and or eutrophic conditions towards the central part of the basin as the nutrient content and turbulence declined and paleoenvironmental stability increased the nannofossil assemblages become more diverse and characterized by lower relative abundances of w britannica but higher contribution of larger morphotypes and higher relative abundances of w barnesiae fossacincta biscutum dubium and zeugrhabdotus erectus these latter small coccoliths markers of high surface waters fertility for the cretaceous were probably not competitive with respect to smaller sized w britannica in unstable and eutrophic surface waters for the jurassic an increase in the surface water productivity is recorded both in proximal and distal sections at the callovian oxfordian transition and is demonstrated both by an increase in nannofossil total abundances and in the relative abundances of taxa adapted to high trophic levels thermal minimum in surface waters as indicated by an increase in the percentages of the cool water nannofossil taxa is associated to increased productivity further studies will be necessary to demonstrate whether surface water productivity changes already recorded in the eastern paris basin were global

coulomb stress changes from earthquakes to underground excavation failures abstract evidence from shallow tunnels and mines indicates that in certain cases deformation and failure are not confined to the vicinity of the excavation front as is widely believed this situation has recently been described as lateral strain propagation from a source to remote parts of the excavation through low strength rocks a similar situation is observed in deep excavations mainly expressed by rock bursts and micro earthquakes we suggest that slow propagation or seismic radiation of deformation away from the excavation front can be explained on the basis of the theory of coulomb failure stress changes in analogy to faulting in large earthquakes local increase of stresses due to the excavation or failure in a certain point leads to a slight increase of stresses around this point if adjacent points are already at a critical level for failure this slight increase triggers a laterally domino style propagating new failure yet in contrast to earthquakes triggered deformation in mining can in principle be predicted and counteracted

paleoclimatic control of biogeographic and sedimentary events in tethyan and peri tethyan areas during the oxfordian late jurassic abstract the paleobiogeographical distribution of oxfordian ammonites and coral reefs in northern and central europe the mediterranean area north and east africa and the middle east and central asia is compared with the distribution in time and space of the most important lithofacies interest in the oxfordian is focused on changes in facies and in biogeographical patterns that can be interpreted as the results of climatic events paleotemperature trends inferred from oxygen isotopes and paleoclimatic simulations are tested against fossil and facies data a late callovian early oxfordian crisis in carbonate production is indicated by the widespread absence of lower oxfordian reefal formations there is a gap hiatus in deposition on epicontinental platforms with middle oxfordian deposits resting paraconformably on upper callovian while shales accumulated in adjacent intracratonic basins simultaneously in mediterranean tethys radiolarites accumulated in deep troughs while rosso ammonitico facies formed on pelagic swells however deposition on swells was also discontinuous with numerous gaps hiatuses and sequences that are much reduced in thickness middle callovian deposits are generally overlain by middle oxfordian limestones the dearth of carbonates is consistent with a cooling event lasting about 1 my by the middle oxfordian a warming leading to greenhouse type conditions is suggested on the basis of both biogeographical mostly coral reef distribution and geochemical data carbonates spread onto an extensive european platform while radiolarites reached a maximum development in the mediterranean tethys two distinct latitudinal belts with seemingly different accumulation regimes are therefore inferred similar latitudinal belts were also present in the late oxfordian when carbonates were widespread the distribution of reefal facies in the late oxfordian early kimmeridgian fits relatively well with gcms simulations that imply low rainfall in the tethyan mediterranean area and slightly higher precipitation in central and northern europe local salinity variations reflecting more arid or humid conditions may bias the paleotemperature signal inferred from 18o values biogeographical and facies distributions combined with 18o values unravel the ambiguity and support a late callovian early oxfordian cooling followed by warming in the later oxfordian

photic zone palaeoenvironments of the kimmeridge clay formation upper jurassic uk suggested by calcareous nannoplankton palaeoecology nannoplankton abundance data has revealed significant and systematic population fluxes through all representative lithologies and cycle types of the kimmeridge clay formation kcf and also through intervals in which lithology is visually homogeneous the majority of kcf samples yielded nannofossil assemblages of low species richness 1 to 10 and marked unevenness independent of preservational state all samples were dominated by coccoliths of one family the watznaueriaceae while assemblage unevenness is characteristic of nannofossil populations such low species richness is atypical particularly when compared with coeval assemblages of similar latitude such anomalously low nannofossil diversity may be explained as a response to nutrient rich euphotic environments we postulate that consistently high trophic conditions supported the eurytopic watznaueriaceans but excluded most normal open ocean taxa the switching of dominance within this group most likely reflects different adaptations within an r selected ecological strategy related to nutrient concentration lowest diversities were recorded in mudstone oil shale lithologies where watznaueria britannica is the dominant species suggesting adaptation to the highest nutrient concentrations watznaueria barnesiae fossacincta is particularly dominant in coccolith stone bands where diversity is slightly higher suggesting adaptation to lower high nutrient levels cyclagelosphaera margerelii appears to be the most extremely r selected species exploiting unusual very high trophic lowered sea level conditions that excluded even w britannica d 2005 elsevier b v all rights reserved

distribution of sedimentary organic matter in a mixed carbonate siliciclastic platform environment oxfordian of the swiss jura mountains outcrop sections from the swiss jura consisting of carbonate siliciclastic deposits spanning the middle late oxfordian boundary provide a palaeogeographical cross section ranging from coastal to shallow platform and intra platform basin environments using a sedimentological and a 3rd order sequence stratigraphic framework based on those sections the distribution of sedimentary organic matter palynofacies has been spatially studied in relation to sequence stratigraphy the main factors influencing the spatial variations of sedimentary organic matter are the proximity of land organic productivity level of biodegradation and hydrodynamic conditions of the palaeoenvironment these factors determine the distribution of the land derived relatively allochthonous organic constituents phytoclasts pollen and spores and marine relatively autochthonous constituents phytoplankton and foraminifera linings five main palynofacies parameters appear as good indicators of proximal distal trends the relative proportion of total phytoclasts the proportion of fresh translucent fragments among these phytoclasts the ratio of marine to continental palynomorphs and the relative amount and species diversity of dinoflagellate cysts in lowstand deposits high energy hydrodynamic conditions may affect these trends on the shallow platform where storms tend to increase the proportion of the marine organic fraction landwards these five palynofacies parameters are largely related to water depth therefore when compared with the established 3rd order sequence stratigraphic framework their stratigraphic variations indicate relative sea level changes or alternatively proximality changes parameters indicative of more distal conditions increase in the transgressive and early highstand and decrease in the late highstand the opposite occurs for parameters indicative of more proximal conditions foraminifera linings seem to be particularly concentrated near the shelf edge and on the slope finally bisaccate pollen may display cyclicity associated with alternating humid and dry periods this palaeoclimatic signature may be related to orbital cyclicity

climatic fluctuations and seasonality during the late jurassic oxfordian early kimmeridgian inferred from δ18o of paris basin oyster shells abstract oxygen isotope data from biostratigraphically well dated oyster shells from the late jurassic of the eastern paris basin are used to reconstruct the thermal evolution of western tethyan surface waters during the early oxfordian early kimmeridgian interval seventy eight oyster shells were carefully screened for potential diagenetic alteration using cathodoluminescence microscopy isotope analyses were performed on non luminescent parts of shells n 264 intra shell 18 o variability was estimated by microsampling along a transect perpendicular to the growth lines of the largest oyster shell the sinusoidal distribution of the 18 o values along this transect and the dependence of the amplitude of variations with bathymetry suggest that intra shell variability reflects seasonal variations of temperature and or salinity average amplitudes of about 5 c in shallow water environments and of about 2 3 c in deeper offshore environments are calculated these amplitudes reflect minimum seasonal temperature variation our new data allow to constrain existing paleotemperature trends established from fish tooth and belemnite 18 o data and are in better agreement with paleontological data more specifically a warming trend of about 3 c is reconstructed for oceanic surface waters during the early to middle oxfordian transition with maximum temperatures reaching 24 c in the transversarium zone late middle oxfordian from the transversarium zone to the bimmamatum zone a cooling of about 7 c is indicated whereas from the bimmamatum zone temperatures increased again by about 7 c to reach 24 c in average during the cymodoce zone early kimmeridgian

warm palaeotemperatures from high late jurassic palaeolatitudes falkland plateau ecological environmental or diagenetic controls abstract oxygen and carbon isotopes have been determined from late jurassic oxfordian tithonian belemnites and inoceramid bivalves from two deep sea drilling project dsdp sites located on the falkland plateau mean belemnite 18o values derived from well preserved skeletal material were 1 29 from dsdp site 330 and 1 45 from dsdp site 511 assuming a seawater smow value of 1 0 mean palaeotemperatures calculated from the oxygen isotopic composition are 17 2 c and 17 9 c respectively the inoceramid bivalves yielded much lighter 18o values mean 3 58 petrographic and geochemical evidence points to the inoceramid bivalves being altered by diagenesis which accordingly accounts for the observed differences in isotopic values vital effects or the importation of belemnites or inoceramids from another area are considered not to account for the observed isotopic trends the palaeotemperatures interpreted from the belemnites are significantly warmer than other recent estimates of late jurassic temperature from oxygen isotope studies and climate model predictions from similar southern palaeolatitudes we suspect our apparent warmer temperatures are because of a combination of increased freshwater runoff depleting surface waters with respect to 18o and related to the semi enclosed nature of the depositional basin retaining warmth relative to the open ocean of similar latitudes

violations of gutenberg richter relation in anthropogenic seismicity anthropogenic seismicity as is the undesired dynamic rockmass response to technological processes as environments are shallow hence their heterogeneities have important impact on as moreover as is controlled by complex and changeable technological factors this complicated origin of as explains why models used in tectonic seismicity may be not suitable for as we study here four cases of as testing statistically whether the magnitudes follow the gutenberg richter relation or not the considered cases include the data from mponeng gold mine in south africa the data observed during stimulation of geothermal well basel 1 in switzerland the data from acu water reservoir region in brazil and the data from song tranh 2 hydropower plant region in vietnam the cases differ in inducing technologies in the duration of periods in which they were recorded and in the ranges of magnitudes in all four cases the observed frequency magnitude distributions statistically significantly differ from the gutenberg richter relation although in all cases the gutenberg richter b value changed in time this factor turns out to be not responsible for the discovered deviations from the gutenberg richter born exponential distribution model though the deviations from gutenberg richter law are not big they substantially diminish the accuracy of assessment of seismic hazard parameters it is demonstrated that the use of non parametric kernel estimators of magnitude distribution functions improves significantly the accuracy of hazard estimates and therefore these estimators are recommended to be used in probabilistic analyses of seismic hazard caused by as

spatial and temporal distribution of calcareous nannofossils along a proximal distal transect in the lower jurassic of the umbria marche basin central italy abstract three upper pliensbachian lower toarcian successions of the umbria marche basin were analysed for sedimentology and calcareous nannofossil content across a 120 km long transect from proximal to distal areas with respect to the shallow latium abruzzi platform the uppermost part of the corniola unit uppermost pliensbachian and the marne di monte serrone formation p p lower toarcian polymorphum to levisoni ammonite zones that contains organic matter rich levels were studied in the three localities the analysis of the sedimentary structures in the studied successions indicates that the basin was a shallow water system above storm wave base during the late pliensbachian early toarcian the stratigraphic evolution of the sedimentary structures recorded in the studied localities shows that the upper pliensbachian corresponded to a regressive sedimentary interval whereas a complete transgressive regressive relative sea level cycle occurred during the lower toarcian polymorphum zone a further transgression occurred in the lowermost levisoni zone lower toarcian changes from carbonate dominated to marl dominated sediments form decimetre to metre scale lithological units that can be correlated from succession to succession and may have resulted from short term sea level and or palaeoenvironmental variations the mean duration of these lithological units suggests that they formed in tune with the first orbital eccentricity cycle 100 ka the analysis of calcareous nannofossil quantities abundance per mm2 of the smear slide percentage mean abundance shows both spatial and temporal changes in the community structure schizosphaerella spp and crepidolithus crassus were more abundant in proximity to the shallow latium abruzzi platform these two taxa were likely affiliated to oligotrophic conditions in marine surface waters explaining why they were generally more abundant in carbonate rich intervals than in marls mitrolithus jansae is interpreted as being a deep dwelling species which was more abundant during rising sea level in the earliest toarcian species of the genera lotharingius biscutum and calyculus were more abundant when higher trophic conditions occurred and were thus more common during periods of marl deposition the stratigraphic distribution of calcareous nannoplankton and its interpretation in terms of palaeoecological affinities allow three main phases in the environmental evolution during the early toarcian anoxic event to be recognised the first phase corresponds to a long term transgression and high nannoplankton abundance in distal areas mainly lotharingius biscutum and calyculus species suggests high productivity that may have resulted from upwelling the beginning of accumulation and preservation of organic matter in the sediments occurred during this phase the scarcity of nannoplankton during the second phase may indicate oligotrophic conditions in surface waters possibly due to water stratification during the highest sea level stand a high abundance of schizosphaerella spp and c crassus is recorded in proximal areas probably resulting from sporadic nutrient input from continental or shallow platform areas the maximum of organic matter preservation is recorded during this phase during the third phase relative sea level fall and efficient water mixing by frequent storm events led to enhanced nannoplankton productivity in proximal and distal areas and to a decrease in organic matter accumulation in the umbria marche basin

onlap offlap and the origin of unconformity bounded depositional sequences christie blick n 1991 onlap ofttap and the origin of unconformity bounded depositional sequences mar geol 97 35 56 unconformity bounded depositional sequences represent the fundamental building blocks of sedimentary successions they are typically characterized by onlap at the base and by offlap at the top and they tend to be markedly asymmetrical with onlap accounting for a larger part of any cycle of sedimentation than offlap offlap cannot be attributed solely to erosional truncation but instead implies that sequence boundaries develop over a finite interval of time depositional sequences are commonly associated with a cyclic arrangement of facies but transgressive regressive cycles are out of phase with respect to sequence boundaries which in down dip locations are both overlain and underlain by progradational deposits and hence form during times of regression of the shoreline these observations are used to develop some ideas about the origin of unconformity bounded sequences with reference to the inter related roles of changes in depositional base level and sediment supply in particular it is shown than onlap and offlap are due to lateral migration of a line of critical bypassing defined so as to incorporate the effects of sediment loading and compaction as well as the rate of change of elevation with respect to sea level downward shifts in onlap may be achieved by either an increase in the rate of eustatic fall or a decrease in the rate of tectonic subsidence and it is premature to assume that eustatic and tectonic controls on sea level may be distinguished solely on the basis of the frequency of depositional cyclicity small shifts in the position of onlap can also be produced by changes in sediment supply and more attention needs to be paid to the influence of sediment supply in the development of minor boundaries unconformities related to eustatic fluctuations are thought to correspond approximately to times of relatively rapid sea level fall inflection points but questions remain about the existence of possible leads and lags of up to cycle and hence about the degree to which sequence boundaries of eustatic origin may vary in age both within a given basin and from one basin to another

depositional sequences in shallow carbonate dominated sedimentary systems concepts for a high resolution analysis abstract oxfordian and berriasian sections representing shallow water carbonate dominated sedimentary systems have been studied in the swiss and french jura in spain and in normandy they all display a hierarchical stacking of depositional sequences facies evolution and stacking pattern allow to define elementary small scale medium scale and large scale sequences some depositional sequences display well marked sequence boundaries others are limited by transgressive or maximum flooding surfaces the hierarchical organisation of such sequence stratigraphic elements implies that sea level fluctuations were an important factor in their formation and that these fluctuations had different frequencies the superposition of high frequency sea level changes on a long term sea level trend leads to repetition of diagnostic surfaces defining sequence boundary and maximum flooding zones wherein the corresponding high frequency surfaces are well developed chronostratigraphic tie points permit us to estimate the duration of large scale sequences this time control and the observed hierarchical stacking suggest that the high frequency sea level changes were controlled by climatic cycles in the milankovitch frequency band the variability of stacking pattern and facies evolution between sections illustrates the complexity of the studied environments furthermore because of the minimal accommodation space available in these shallow water settings much of the geologic time is not recorded nevertheless detailed analysis of the depositional sequences allows the interpretation of the evolution of the sedimentary system with a high time resolution thus there is a potential to monitor sedimentological ecological and diagenetic processes on a time scale of 20 to 100 ka

shallow platform palaeoenvironmental conditions recorded in deep shelf sediments c and o stable isotopes in upper jurassic sections of southern germany oxfordian kimmeridgian a high resolution carbon and oxygen isotope analysis of late oxfordian early kimmeridgian deep shelf sediments of southern germany is combined with investigation of nannofossil assemblage composition and sedimentological interpretations in order to evaluate the impact of regional palaeoenvironmental conditions on isotopic composition of carbonates this study suggests that carbonate mud was essentially derived from the jura shallow platform environments and also that the isotopic signature of carbonates deposited in the swabian alb deep shelf indirectly expresses the palaeoenvironmental evolution of the platform short term fluctuations in d 13 c and d 18 o are probably controlled by changes in salinity fresh water input versus evaporation in platform environments long term fluctuations in carbon and oxygen isotope record throughout the late oxfordian early kimmeridgian result from the interplay of increasing temperature and decreasing humidity which both control the trophic level changes from mesotrophic to oligotrophic conditions in platform environments and in the deep shelf surface waters are inferred during the late oxfordian bimammatum subzone to planula zone the d 13 c curve displays a positive shift of about 1x which is comparable in intensity to global perturbations of the carbon cycle this evident isotopic shift has not been documented yet in other basinal settings it can be reasonably explained by local palaeoenvironmental changes on the jura platform salinity temperature and nutrient availability that controlled platform carbonate production and the geochemistry of overlying waters however increasing carbonate production on the jura platform and related positive d 13 c shifts recorded in the

temporal and spatial variations in tectonic subsidence in the iberian basin eastern spain inferences from automated forward modelling of high resolution stratigraphy permian mesozoic by subsidence analysis on eighteen surface sections and 6 wells which cover large part of the iberian basin e spain and which are marked by high resolution stratigraphy of the permian triassic jurassic and cretaceous we quantify the complex permian and mesozoic tectonic subsidence history of the basin backstripping analysis of the available high resolution and high surface density of the database allows to quantify spatial and temporal patterns of tectonically driven subsidence to a much higher degree than previous studies the sections and wells have also been forward modelled with a new automated modelling technique with unlimited number of stretching phases in order to quantify variations in timing and magnitude of rifting it is demonstrated that the tectonic subsidence history in the iberian basin is characterized by pulsating periods of stretching intermitted by periods of relative tectonic quiescence and thermal subsidence the number of stretching phases appears to be much larger than found by earlier studies showing a close match with stretching phases found in other parts of the iberian peninsula and allowing a clear correlation with discrete phases in the opening of the tethys and atlantic

nannofossil assemblages fine fraction stable isotopes and the paleoceanography of the valanginian barremian early cretaceous north sea basin calcareous nannofossil assemblages have been investigated in three sections from around the margins of the early cretaceous north sea basin both absolute number of nannofossils per gram and relative percent of the assemblage of different taxa abundance data have been collected absolute abundances up to 10 billion nannofossils per gram are somewhat higher than those reported previously from other stratigraphic intervals stratigraphic correlation of trends in assemblage data in different sections points toward the existence of large uniform water masses stable over long 0 5 to 1 m y time periods these water masses contained a characteristic nannoplankton which appears to have been driven largely by variations in fertility possibly tied to changes in sources of surface waters which in turn may have been controlled by relative sea level fine fraction isotopic data show fluctuations on shorter time periods 0 1 to 0 5 m y we postulate that some of these isotopic fluctuations were controlled by relative changes in sea level which affected the balance of surface waters derived from runoff and those imported from the boreal sea these oceanographic changes appear to have affected nannofossil assemblages only in discrete intervals data are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p95 001 2 50 payment must accompany order

identification of systems tracts in low angle carbonate ramps examples from the upper jurassic of the iberian chain spain abstract the upper jurassic of the iberian chain in northeast spain was selected for the study and identification of sequence boundaries and systems tracts in low relief carbonate ramp systems the study area provides a special opportunity for sequence stratigraphic analysis because the outcropping upper jurassic carbonate ramps are relatively undeformed well exposed from proximal to distal areas and have an established ammonite zonation two sequences are recognized sequence a uppermost callovian to uppermost oxfordian in age up to 60 m thick in the proximal areas and between 15 and 5 m thick in the middle and distal areas and sequence b kimmeridgian to lowermost tithonian from 80 to 160 m in thickness across the basin the evolution of the first sequence is related to regional relative sea level changes i e tectono eustatic changes superimposed on the sedimentary basin on the other hand the larger accommodation created during the second sequence is regarded as controlled mainly by steady subsidence sequence boundaries indicative of subaerial exposure show as unconformities with stratigraphic hiatuses in the proximal areas of the basin the lowstand systems tract in sequence a is represented by a decimetre thick reworked level consisting of several ammonite biozones in sequence b this systems tract consists of a thick wedge shaped marly unit in both sequences the transgressive surface overlaying these lowstand deposits is generally planar and marks a sharp boundary between the restricted and open marine fossils however in sequence b in the middle part of the basin the transgressive surface can be absent instead a transitional change to open marine facies exists the transgressive systems tracts show sedimentary condensation at least in the distal areas of the basin with mostly ammonites and benthic fossil wackestones the transgressive unit is generally overlain by a hard ground surface that corresponds to a maximum flooding surface finally in the upper part of both sequences highstand systems tracts are represented by progradational siliciclastic and shallow carbonate complexes in the proximal areas of the basin in sequence a sedimentation is condensed in the distal areas with glauconite marl levels present the descriptions of sedimentary features of the systems tracts of these two sequences developed in a low angle carbonate ramp are suggested to be used as tools for the recognition of systems tracts patterns within sequences in comparable depositional settings

coseismic and other short term strain changes recorded with sacks evertson strainmeters in a deep mine south africa summary during 1977 march and april three sacks evertson borehole dilatometers were installed at the ends of boreholes drilled into the sidewall of an experimental tunnel at a depth of 3 1 km in the erpm gold mine near johannesburg in the following year coseismic strain changes ranging from 5 10 10 to values exceeding 5 10 6 were recorded for hundreds of mine tremors in the magnitude range 1 to 3 7 and at hypocentral distances of 50 m to about 2 km hypocentral coordinates and magnitudes were determined from seismograms recorded from an underground array of geophones amplitudes and polarities of the coseismic strain steps are generally in excellent agreement with theoretical expectations based on point source dislocation theory specifically the strain steps are proportional to the seismic moment divided by the cube of hypocentral distance at a strain level of 5 10 9 or greater the tremors do not appear to be preceded by any short term indications of instability even for tremors producing coseismic steps greater than 5 10 6 and for which the strainmeters were within a source radius of the hypocentre continuous strain changes observed at the times when the mine excavation at a distance of about 100 m is extended are in good agreement with calculated changes based on the theory of elasticity a similar calculation is consistent with post seismic strain changes observed to follow some of the closer tremors these post seismic strains show a logarithmic dependence on time following the tremor and appear to be due to the interaction of a tremor with the adjacent mine excavation rather than to deformation within the actual seismic source region

facies cycles and controls on the evolution of a keep up carbonate platform kimmeridgian swiss jura during the late jurassic accelerated ocean floor spreading and associated sealevel rise were responsible for a worldwide transgression which reached its maximum in the late kimmeridgian in many western european basins this major sea level rise led to the formation of marly and condensed sections in the swiss jura however a shallow carbonate platform kept growing and only subtle changes in the stratigraphic record suggest an increasingly open marine influence field observations and thin section analyses reveal that the central swiss jura was at that time occupied by tidal flats and by more or less open marine lagoons where shoals and bioherms developed the evolution through time of sedimentary facies and bed thicknesses permits the definition of small medium and large scale depositional sequences the diagnostic features of these sequences are independent of scale and seem largely controlled by the kimmeridgian second order transgression a high resolution sequencestratigraphic correlation with biostratigraphically well dated hemipelagic and pelagic sections in the vocontian basin in france reveals that i the most important increase in accommodation recorded in the kimmeridgian of the central swiss jura occurs in the eudoxus ammonite zone late kimmeridgian and corresponds to the second order maximum flooding recognized in many sedimentary basins ii the small and medium scale sequences have time durations corresponding to the first and second orbital eccentricity cycle i e 100 and 400 ka respectively suggesting that sedimentation on the platform and in the basin was at least partly controlled by cyclic environmental changes induced by insolation variations in the milankovitch frequency band the comparison of the high resolution temporal framework defined in the swiss jura and vocontian basin with the sequencestratigraphic interpretation realized in other western european basins shows that the large scale sequence boundaries defined in the kimmeridgian of the swiss jura appear in comparable biostratigraphic positions in most western european basins discrepancies that occur are probably because of local or regional tectonics

carbon cycle and sea water palaeotemperature evolution at the middle late jurassic transition eastern paris basin france abstract a very high resolution carbon and oxygen stable isotope analysis bulk carbonate of a biostratigraphically well constrained callovian oxfordian series is provided here for the first time the homogeneity of the clayey series and the weak diagenetic alteration allow the isotopic signal variations to be considered as primary in origin a prominent and brief negative excursion in the 13c curve 2 occurring at the start of the middle callovian jason zone obductum subzone and correlated regionally suggests a possible methane release the increasing 13c values thereafter up to the early oxfordian concomitant with a warming episode highlight the burial of carbon in organic rich layers which in return may have triggered a decrease in atmospheric pco2 at higher frequencies observed fluctuations of the 13c and 18o values are orbitally driven 405 kyr and 100 kyr eccentricity cycles and may correspond to the salinity and temperature variability recorded in sea water the 18o isotopic measurements from well preserved diagenetically screened belemnites and bivalves along the series compared to available data from tethyan domains agree with the scenario of a global cooling at the middle late jurassic transition the well dated 18o isotopic curve suggests that the onset of this cooling event occurred at the end of the coronatum zone middle callovian

the shifting biogeography of reef corals during the oxfordian late jurassic a climatic control until recently the jurassic was thought to have been a period characterised by a predominantly warm and equable climate during the oxfordian a time span of six million years in the late jurassic the distribution of tropical coral reefs was limited to about 35 n and near to 25 s however in middle oxfordian time coral reefs were abundant only at higher latitudes and almost entirely missing near the equator during that time the area of maximum reef development had shifted poleward to a belt lying between 20 n and 35 n leaving hardly any coral formations at the lower inner tropical latitudes after demise towards the end of middle oxfordian time the low latitude reefs recovered during the late oxfordian accompanied by a southward migration of reef corals in the northern hemisphere as suggested by stable isotope and palynological data the faunal migration can be correlated with a significant rise in seawater temperature during the middle oxfordian

sedimentary organic matter in condensed sections from distal oxic environments examples from the mesozoic of se france a detailed analysis of sedimentary organic matter or palynofacies was carried out on thermally immature to early mature upper jurassic and hauterivian condensed intervals in deep sea carbonate marl alternations outcropping in the vocontian basin se france all the condensed sections studied are characterized by intense bioturbation and very low organic carbon content 0 25 wt indicative of oxic depositional conditions oxic condensed sections display variable palynofacies signatures which are best illustrated by 1 the ratio of continental to marine constituents 2 the ratio of opaque to translucent phytoclasts i e woody debris and 3 the preservation of palynomorphs based on fluorescence intensity and morphological preservation state in transmitted light microscopy both of the ratios increase with the degree of palynomorph degradation which shows that phytoclasts especially the opaque ones become relatively concentrated in the most degraded facies these observations lead to the classification of oxic condensed sections into three organic facies types showing different degrees of preservation and palynofacies signatures type 1 organic facies display intense degradation and are characterized by high values of the ratio of continental to marine fraction they record unfavourable depositional environments for preservation of organic matter type 2 organic facies are most common and are characterized by a decreasing value of the ratio of continental to marine fraction type 3 organic facies display the same trend of the ratio of continental to marine fraction as type 2 but the palynomorph assemblage is better preserved type 1 and type 3 organic facies are relatively rare recognizing these organic facies types is important when analysing the relationship between sedimentary organic matter and sequence stratigraphy because it allows the use of the appropriate palynofacies parameters in particular the use of the ratio of continental to marine constituents usually a very good indicator of regressive transgressive trends becomes questionable in highly degraded intervals moreover distinguishing between well preserved or highly degraded palynofacies in condensed intervals provides valuable information on the oxicity of the depositional environment

the hydraulic equivalence of mica abstract settling experiments performed on silt to fine sand sized mica flakes with a holographic micro velocimeter revealed that mica is the hydraulic equivalent of quartz spheres having diameters a factor of 4 to 12 times smaller mica in the very fine to fine sand sizes has been traditionally used by sedimentologists to delineate areas of deposition or nondeposition and potential winnowing of fines and is here found to be the hydraulic equivalent of silt sized particles but not of clay experiments also showed that mica flakes tend to settle at orientations which are neither perpendicular nor parallel to the gravitational vector and tend to generally maintain their orientation throughout equations for the settling of a disc in lerman and others 1974 and that developed by komar and reimers 1978 are shown to be mathematically similar for the coarse silt to fine sand ranges of discs and are adequate predictors of settling rates of mica flakes a comparison of the hydraulic equivalency of quartz spheres to coarse silt through fine sand sized mica flakes is presented

seismic heterogeneity and small scale convection in the southern california upper mantle we invert traveltime residuals of teleseismic p and s phases for 3 d perturbations in vp vs and vp vs structures in the southern california upper mantle the tomographic inversion uses frequency dependent 3 d sensitivity kernels to interpret traveltime residuals measured in multiple frequency bands and recent advances in regional crustal thickness and velocity models to better isolate the mantle component of traveltime residuals in addition to separate vp and vs tomography we jointly invert the p and s data sets for vp vs perturbations by imposing a smoothness constraint on the lnvs lnvp field the regional upper mantle is very heterogeneous with the greatest amplitude of velocity and vp vs perturbations in the upper 200 km and mantle structures that correlate spatially with the major physiographic provinces of southern california our imaging improves the resolution of the geometry and amplitude of these features in addition to the major structures imaged and discussed in previous papers we find a large high velocity anomaly at depths between 340 and 500 km beneath the borderland transverse ranges and northern peninsular ranges this anomaly is separate from the well known uppermost mantle transverse ranges anomaly which extends no deeper than 175 200 km the strongest low velocity high vp vs anomaly is found beneath and west of the salton trough and is attributed to relatively high partial melt in the asthenosphere as a result of lithospheric thinning the magnitudes of vp vs and vp vs perturbations and knowledge of regional 1 d velocity and attenuation lead us to conclude that the asthenosphere contains up to 1 partial melt extending to depths as great as 150 200 km

paleoenvironmental controls on the morphology and abundance of the coccolith watznaueria britannica late jurassic southern germany the coccolithophore species watznaueria britannica is dominant in middle upper jurassic calcareous nannofossil assemblages and presents morphological variation including different coccolith size shape and length of the central area and of the bridge six morphotypes can be recognized in the polarizing light microscope the aim of this work is to better understand the morphological variability of w britannica and determine if this variability is controlled by paleoecological factors in order to investigate the potential paleoecological controls on w britannica morphology and abundance we carried out a biometric study on a restricted temporal interval the late oxfordian in the swabian alb southern germany characterized by increasing carbonate production linked to climatic changes the balingen tieringen section where previous works on sedimentology nannofossil assemblage composition and 18o and 13c analyses were performed was selected for this study the variations in morphology and abundances ofw britannicawere studied on 40 samples of the balingen tieringen section presenting variable lithologies and calcium carbonate contents for each level seven biometric parameters coccolith length width and ellipticity central area length width and ellipticity and central area proportion with respect to the coccolith were measured or calculated on digitally captured images of the first 100 w britannica coccoliths observed in the light microscope the relationships between the different biometric variables were described using bivariate and principal component analyses biometric parameters and principal component factors extracted from nannofossil assemblages as well as other paleoenvironmental proxies were investigated using regression and their stratigraphic trends were compared principal component analysis of the six biometric variables 3938 measurements on w britannica coccoliths shows a reduced morphological variability compared to a significant size gradient an allometric trend recognized on the total placolith and on the central area within thew britannica assemblages suggests that the different morphotypesmay represent intra specific variability rather than different species the general trend through late oxfordian shows an increase in size ofw britannica coccoliths mainly driven by an increase in the contribution of the largemorphotypes increasing placolith size is associated with drier and warmer climatic conditions during the latest oxfordian

arabia eurasia collision and the forcing of mid cenozoic global cooling the end of the eocene greenhouse world was the most dramatic phase in the long term cooling trend of the cenozoic era here we show that the arabia eurasia collision and the closure of the tethys ocean gateway began in the late eocene at 35 ma up to 25 million years earlier than in many reconstructions we suggest that global cooling was forced by processes associated with the initial collision that reduced atmospheric co2 these are 1 waning volcanism across southwest asia 2 increased organic carbon storage in paratethyan basins e g black sea and south caspian 3 increased silicate weathering in the collision zone and 4 a shift towards modern patterns of ocean currents associated with increased vigour in circulation and organic productivity

from platform to basin to swell orbital control on sedimentary sequences in the oxfordian spain climatic oceanographic and ecological changes that control the formation and deposition of sediment in shallow and deep depositional environments commonly occur with periodicities of a few 10 000 years consequently in order to interpret sedimentary sequences in the geological past high time resolution is required this is best obtained by cyclostratigraphy three sections have been studied in the oxfordian of north eastern spain one represents a shallow siliciclastic carbonate platform with repetitive subaerial exposures one an intraplatform basin with sponge bioherms and one a swell where iron ooids and glauconite formed the platform section displays a well defined stacking pattern of depositional sequences the deeper water sections are well dated by ammonites the correlation between the three sections is a best fit solution integrating biostratigraphy sequence stratigraphy and cyclostratigraphy it is concluded that the small scale depositional sequences formed in tune with the 100 ka orbital eccentricity cycle an additional factor was differential subsidence that ruled basin morphology

strontium isotope stratigraphy and oxygen and carbon isotope variation during the middle jurassic early cretaceous of the falkland plateau south atlantic abstract 87sr 86sr data of belemnites are presented from a middle jurassic early cretaceous succession from the falkland plateau deep sea drilling project sites 511 and 330 that was deposited in a periodically anoxic semi enclosed shallow water basin diagenetically screened strontium isotope values of 0 706789 rise to 0 707044 before increasing sharply to 0 707428 in the uppermost part of the sampled succession comparison with published strontium calibration curves suggests that the oldest samples were callovian to oxfordian in age whilst the remainder of the jurassic part of the succession consisted of kimmeridgian and early tithonian age sediments the nannofossil dinoflagellate and molluscan assemblages provide comparable age determinations the strontium isotope analysis of the youngest belemnites points to a hauterivian barremian age whilst age interpretations based upon the fauna provide a wide age range from the barremian to early albian strontium isotope stratigraphy of this succession hence offers increased age resolution providing data regarding the timing of episodes of bottom water anoxia which have been recorded throughout the south atlantic basin well preserved belemnite specimens display an oxygen isotope range between 0 08 and 2 22 pdb peedee belemnite international standard and a carbon isotope range from 2 35 to 1 33 pdb 13c values become increasingly negative through the late jurassic early cretaceous and in concert with the 87sr 86sr data reveal a trend that could be accounted for by increasing levels of weathering and erosion the oxygen isotope data if interpreted in terms of palaeotemperature are consistent with warm palaeotemperatures in the kimmeridgian and slightly cooler temperatures for the tithonian and early cretaceous parts of the succession the proposed relative kimmeridgian warmth based upon strontium isotope age assignments is thus in good agreement with other published palaeotemperature records

a typical evolution of seismicity patterns resulting from the coupled natural human induced and coseismic stresses in a longwall coal mining environment abstract a very unusual time space distribution of seismicity accompanying coal exploitation has been observed in a polish mine the earthquakes did not follow the depth of mining but exhibited changing depths from far below to close to the mined seam one of the deep events which occurred at close epicentral distance to the active mining front was m l 3 7 event this paper presents the study of possible coupling of natural human induced and coseismic stresses in a longwall coal mining environment the full moment tensor solution showed that the strong earthquake occurred on an almost vertical plane consistent with approximate strike of local tectonic structure the signal correlation analysis revealed some highly correlated pairs within both deep and shallow event groups to evaluate inducing factor of ongoing and past exploitation geomechanical modelling of its influence on strain and stress at the target depth has been performed the results exhibited a changing vertical stress regime which might have promoted failure on preexisting almost vertical planes of weakness the earthquakes rate variation in time showed no increase in activity right after the occurrence of m l 3 7 event the p s wave spectra corner frequency ratio had an average of 1 0 suggesting slow rupture however the coulomb stress change analysis showed that the magnitude of stress changes due to coseismic slip of m l 3 7 event at the hypocentral depth is of the same order as the stress changes caused by mining thus the distribution of seismicity at this level could have been driven by both exploitation and coseismic stresses moreover the seismicity which occurred within first few weeks after m l 3 7 event followed positive stress changes all the obtained results let us prove that the m l 3 7 event was a tectonic earthquake triggered by ongoing exploitation and that the distribution of following seismicity was affected by coupled natural exploitation induced and coseismic stresses

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

carbonate ramp depositional systems from a late jurassic epeiric platform iberian basin spain a combined computer modelling and outcrop analysis no counterparts to epeiric sea carbonate ramps are known in present day environments this hinders the interpretation of the factors controlling the growth and evolution of these depositional settings in this study we analyse the facies and geometries of two jurassic examples both from outcrop study and through computer modelling this analysis is constrained by two important features of these oxfordian and kimmeridgian ramps firstly they are very well exposed allowing accurate reconstruction of a 200 km section from proximal to distal ramp environments and secondly a time framework for correlation section reconstruction and modelling is provided by a well defined ammonite biostratigraphy the modelling results in a synthetic stratigraphy which closely matches the reconstructed cross sections and when integrated with the field study constrains and provides additional quantitative data on the following aspects of carbonate ramp systems resedimentation by storms is an important process in maintaining the ramp profile through time down ramp transport distances of between 25 and 40 km are indicated from the distribution of storm beds and shallow water allochems and from model matching known stratigraphic thicknesses and geometries modelling sediment production within the time constraints from the ammonite biozones indicates that shallow water carbonate production was 1 2 orders of magnitude less than that predicted for present day open marine carbonate platforms deeper water production rates were reduced by lesser amounts these proportionally higher outer ramp production rates also help to maintain ramp geometries through time the enigmatic slope crest of ramps is shown to result from a combination of higher shallow water production and erosion rates together with loss of accommodation during highstands and high stillstands in the modelled sea level curves the most parsimonious modelling of the two ramp sequences comes from a relative sea level curve composed of a linear subsidence component superposed by 20 and 100 kyr cycles on a third order cycle the third order cycles and their timing do not correspond to those of the exxon curve

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km

tectonic and eustatic control on a mixed siliciclastic carbonate platform during the late oxfordian kimmeridgian la rochelle platform western france boreal and tethyan realms of western europe present significant sedimentological paleontological and stratigraphic differences the purpose of this study is to constrain regional versus global controls on the dynamics of a sedimentary system located at the interface of these two realms in order to better understand the origin of their differences detailed sedimentological palynofacies and calcareous nannofossil analyses were performed on two sections from the la rochelle platform western france the pas section includes part of the late oxfordian and early kimmeridgian and the rocher d yves section is assigned to the late kimmeridgian they correspond to monotonous marl argillaceous limestone alternations limestones are essentially mudstones with echinoderms bivalves and foraminifera that suggest low energy open marine conditions highly bioclastic and or peloidal deposits occur commonly and show wackestones to wacke pack grainstones textures these deposits indicate frequent high energy events and are interpreted as storm deposits marls dominate in the most proximal depositional environments while calcareous deposits are more important in more distal environments the rocher d yves section is globally more marly than the pas section suggesting a more proximal setting palynofacies are dominated by woody particles suggesting shallow water proximal depositional environments calcareous nannofossils are ascidian spicules coccoliths and schizospheres watznaueria britannica dominate calcareous nannofossil assemblages in the pas section the rocher d yves assemblages are quasi exclusively composed of cyclagelosphaera margerelii and indicate more proximal paleoenvironments than those of the pas section different orders of depositional sequences are defined with sequence boundaries corresponding to the most rapid relative sea level falls they are hierarchically stacked and correlate on the basis of ammonite zones with the sequences of contemporaneous sections from tethyan and boreal realms the stacking pattern of these sequences suggests an orbital control on sedimentation small medium and large scale sequences correspond to precession 20 ky cycles and to 100 ky and 400 ky eccentricity cycles respectively the elementary sequences have durations shorter than 20 ky the kimmeridgian was a period of global sea level rise that ended in the late kimmeridgian more proximal depositional environments in the rocher d yves section late kimmeridgian than in the pas section early kimmeridgian imply a progradation of the la rochelle platform during the kimmeridgian this progradation resulted from a slowdown of the subsidence in the aquitaine basin during the kimmeridgian corresponding to the first steps of atlantic ocean opening high frequency cycles on the la rochelle platform formed in sync with milankovitch orbital cycles while tectonics controlled the formation of the low frequency cycles