3 d density model of the crust of southern and central finland obtained from joint interpretation of the svekalapko crustal p wave velocity models and gravity data 3 d density model of the crust of southern and central finland obtained from joint interpretation of the svekalapko crustal p wave velocity models and gravity data

shear wave anisotropy of laminated lower crust beneath urach sw germany a comparison with xenoliths and with exposed lower crustal sections in order to investigate the laminated lower crust beneath urach sw germany we analysed 1 the anisotropy and reflectivity of seismic shear waves and 2 the composition of xenoliths samples we conclude that the directional dependence of shear waves of the lower crust is effectively transversely isotropic with a maximum velocity difference of 3 to 6 both seismic signature and petrological information are compared with reference profiles deduced from the exposed lower crustal sections of ivrea and calabria italy the comparison based on synthetic seismograms shows that the observed combination of shear wave anisotropy and reflectivity pattern corresponds to alternating layers containing a high amount of metapelites such as found in the calabria profile and in the val strona subsection of ivrea the main portion of the whole rock anisotropy is caused by the lattice preferred orientation of anisotropic minerals so called intrinsic anisotropy the effect of alternating rock layering so called layering anisotropy contributes only a minor portion to the whole rock anisotropy layered mafic intrusions such as found in the val sesia subsection of ivrea are nearly isotropic both seismic anisotropy and xenoliths indicate that mafic layers do not play a major role for the laminated lower crust at urach they may be restricted to a thin layer at the crust mantle boundary

geometry spatial arrangement and origin of carbonate grain dominated scour fill and event bed deposits late jurassic jubaila formation and arab d member saudi arabia

late and deep fermentative methanogenesis as reflected in the h c o s isotopy of the methane water system in deep aquifers of the pannonian basin se hungary abstract h and o isotope ratios and h and c isotope ratios of methane as well as the abundances of some major and minor dissolved components were measured in 26 subsurface waters from se hungary produced from late neogene aquifers within the upper two kilometres in depth mixing with meteoric water of glacial age is of importance the hydrocarbon gas hc gas content of the great majority of the waters is dominated by isotopically light bacterial methane the depth of the onset of thermal gas generation varies from 0 7 to 1 2 km but the amount of thermogenic methane leaving the kerogen was not sufficient to overprint the light isotopic signature of the methane in the waters about two thirds of the waters group i samples are characterised by low sulfate content 20 and methane d values less negative than 260 they also show a direct relationship between the h isotope ratio of the methane and that of the water these waters experienced exhaustive bacterial sulfate reduction followed by a relatively shallow bacterial methanogenesis in a third of the waters group ii samples the methane d values are more negative than 278 the group ii samples which are not affected by an admixture of glacial age meteoric waters contain a relatively high amount of sulfate 35 45 mg l and do not show a direct relationship between the h isotope ratio of the methane and that of the water in group ii waters bacterial sulfate reduction was not exhaustive and the residual sulfate inhibited shallow bacterial methanogenesis as a result of continuing burial the aquifers were heated up to 40 60 c thereby allowing a relatively intensive bacterial acetogenesis followed by acetate fermentation to methane our results show that deep acetate fermentation and early thermal gas generation can occur closely in space and time even partly overlapping with each other

natural deformation fabrics of plagioclase implications for slip systems and seismic anisotropy abstract the optical and tem microstructures and fabrics of twelve naturally deformed plagioclase containing rocks of compositions from an0 an80 have been studied with a view to determining the deformation mechanisms the optical indicatrix fabrics have been recorded in all samples with respect to the foliation and lineation in general and form a girdle in the foliation plane with a high concentration of normal to the foliation in some cases the orientation of 010 and 001 cleavages or albite and pericline twins has allowed the construction of pole figures in all cases 010 has been shown to be the dominant slip plane with either 001 or 100 the dominant slip direction tem shows that the dominant slip system is 010 001 with secondary 010 100 the seismic p wave anisotropy has been calculated for the first time from the lpo data of plagioclase the anisotropy coefficient is high at around 15 the minimum p velocity is normal to the lineation in the foliation plane and the maximum is sub parallel to the foliation normal the combined information on deformation kinematics and seismic anisotropy is valuable for interpretations of deep crustal seismic sections

distinguishing tectonically and gravity driven synsedimentary deformation structures along the apulian platform margin gargano promontory southern italy abstract the assessment of deformation types within the slope of a carbonate platform can be complicated by the possible interaction of rooted tectonically induced and superficial gravity driven structures an ideal case study to document and distinguish tectonically and gravity driven structures is provided by the cretaceous slope to basin carbonates exposed in the gargano promontory southern italy these carbonates formed adjacent to the apulian platform margin which was oriented approximately ne sw to nw se along the southern and northern edges of the promontory respectively slump related folds are characterised by axial planes typically oriented either sub parallel or at small angles to the strike of the inferred paleoslope in fact the strike of folds is roughly ne sw in the southern portion of the study area whereas it is nw se in the northern part correspondingly gravity driven normal and reverse faults strike sub parallel and at acute angles to the adjacent apulian paleoslope cretaceous tectonic faults in the slope to basin carbonates form two principal sets striking nw se and wnw ese the former set is made up of normal faults and the latter one includes mainly oblique slip normal faults neither normal nor oblique slip normal faults show any relationship with the geometry of the paleoslope the results obtained from this study may help the interpretation of subsurface data in those geological contexts in which the interplay of gravitational and tectonic processes is responsible for deformation

carbonate platforms of passive extensional continental margins types characteristics and evolution abstract carbonate platforms of extensional margins may be grouped into several major categories homoclinal ramps have gentle slopes into deep water may have skeletal or ooid pellet sand shoal complexes that grade without break in slope into deep ramp nodular limestone and then into pelagic hemipelagic basin facies they generally lack significant slump and sediment gravity flow deposits in the deeper water facies distally steepened ramps differ from the above in having a marked increase in slope at the seaward edge of the deep ramp and abundant slumps slope breccias and turbidites however clasts of shallow platform margin facies are generally absent from breccias rimmed shelves have linear trends of shelf edge lime sands and reefs a marked increase in slope into deep water and foreslope and slope sands breccias with clasts of platform margin rocks and turbidites grading seaward into basin hemipelagic pelagic muds they may be divided into accretionary bypass and erosional margins isolated platforms are broad flat topped shallow platforms surrounded by deeper water few hundred meters to 4 km deep many are bypass margins but accretionary and erosional margins also occur finally incipiently to completely drowned or open platforms may develop by rapid submergence of ramps shelves or isolated platforms shallow platform margin facies are shifted landward and the earlier shallow water platform is covered with transgressive lags and deeper water blankets of hemipelagic or pelagic facies or open marine whole fossil wackestone the carbonate prisms commonly develop above a basal clastic phase ramps develop early and evolve into rimmed shelves however with drowning rimmed shelves may evolve up into ramps rimmed shelves may also develop into ramps where miogeoclinal faces prograde into filling marginal basins carbonate miogeocline deposition terminates when the shelf becomes a prograding clastic shelf or where it becomes part of a collisional orogen the various platform types may be recognized from continental margin sequences ranging from proterozoic to holocene in age

reappraisal of deep seismic reflection profile viii across the pripyat trough two deep 24 s multi channel seismic reflection profiles each 200 km in length were shot across the pripyat trough a late devonian rift basin in belarus in the 1980s by the polessian geophysical expedition of the former soviet union additional post stack processing and migration on one of these profile viii has been applied at uppsala university and allows a re evaluation of the crustal structure of the pripyat trough with particular focus on the deeper parts previous interpretations showed numerous steeply dipping faults extending from the surface to depths of 30 40 km and sometimes penetrating into the mantle which was defined to be located at the top of a reflective zone beginning at about 10 s twt this reflective zone recorded to depths of 16 s twt was interpreted as a mixture of crustal and mantle rocks based on the original stacked section and the further processing the reflective zone is reinterpreted to be reflective lower crust not upper mantle and the moho is identified to be at 45 50 km about 15 s twt the major basin bounding faults appear to be listric at depth and sole into the top of the reflective lower crust rather than be truncated by it the newly interpreted crustal structure is consistent with a model of continental rifting involving brittle failure in a thick upper crustal layer and ductile shear in the lowermost crust with some degree of detachment between crust and mantle within the lower crustal ductile layer

deep structure of the crust along the fennoscandia sarmatia junction zone central belarus results of a geophysical geological integration abstract the eurobridge 96 seismic refraction and wide angle reflection profile in belarus crosses the 2 0 1 9 ga palaeoproterozoic central belarus belt cb subdivided by ne trending minsk fault into the northwestern nwcb and southeastern secb sub terranes differing in their styles of tectonothermal evolution the first interpretation of the eurobridge 96 profile however did not indicate any difference between the nwcb and secb and revealed a high velocity zone beneath the secb with a p wave velocity of 6 6 km s at a depth of 6 km which does not correlate with any pronounced positive bouguer anomaly we present a detailed analysis of the seismic and gravity data obtained along the eurobridge 96 profile complemented with petrological and petrophysical observations on the main rock types of the cb our integrated interpretation shows that the dip orientation of the main reflectors and the p wave velocity and density are different in the nwcb and secb the minsk fault zone is distinguished as an area of relatively high velocities 6 2 km s in the upper crust increased reflectivity in the middle crust se of the minsk fault may be explained by a laminated structure composed of alternating tectonically deformed amphibolite facies and granulite facies rocks that produce a certain seismic anisotropy this seismic anisotropy is proposed as an alternative explanation for the high p wave velocity in the middle crust beneath the secb that does not result in any corresponding positive gravity anomaly the laminated structure beneath the secb might be formed during the uplift of the nwcb and juxtaposition of the nwcb and secb

multiscaling nature of sonic velocities and lithology in the upper crystalline crust evidence from the ktb main borehole the observed scaling of sonic logs is generally described using a monofractal model fractional brownian motion with hurst exponent typically between 0 1 and 0 2 or fractional levy motion even though such a description recognizes the existence of the self similarity of the logs it offers only a limited account of the actual symmetry as it misses the displayed heterogeneous fractality intermittency of the velocity increments is here observed and calls for the use of a multifractal description we quantify such a multifractality in the case of the p wave sonic log recorded at the ktb main borehole we also show that the associated lithology inferred from the gamma log has a multifractal distribution as well though characterized by a stronger intermittency it can be expected that the multifractality of the sonic log is partially induced by the lithology though the observed discrepancy in the degree of intermittency between the two logs indicates that the scaling symmetry of the seismic velocity is probably due to many different contributions such statistics for both sonic and gamma logs have important implications on our understanding of wave propagation and rock strength and permeability in the crystalline crust as they show the crust to be more heterogeneous than is usually modeled

source rock distribution model of the periadriatic region the periadriatic area is a mosaic of geological provinces comprised of spatially and temporally similar tectonic sedimentary cycles tectonic evolution progressed from a triassic early jurassic liassic continental rifting stage on the northern edge of the african craton through an early jurassic middle liassic late cretaceous eocene oceanic rifting stage and passive margin formation to a final continental collision and active margin deformation stage in the late cretaceous eocene to holocene this evolution occurred in a transtensional and transpressional framework resulting from the oblique separation and convergence of the african and european plates extensive shallow water carbonate platform deposits covered large parts of the periadriatic region in the late triassic platform breakup and development of a platform to basin carbonate shelf morphology began in the late triassic and extended through the cretaceous on the basis of this paleogeographic evolution the regional geology of the periadriatic region can be expressed in terms of three main upper triassic paleogene sedimentary sequences the platform sequence sequence a the platform to basin sequence sequence b and the basin sequence sequence c these sequences developed during the initial rifting and subsequent passive margin formation tectonic stages three distinct episodes of source bed deposition can be identified middle upper triassic to lower jurassic liassic organic rich oil prone and mature source beds generally are structurally controlled and are closely associated with transtensional intraplatform basins formed in the early continental rifting stage the principal triassic source basins and most of the surface hydrocarbon indications and economically important oil fields of the periadriatic region are associated with sequence b areas the second episode of organic rich rocks deposition includes both shallow and deeper water facies of jurassic cretaceous age thin immature deep water epioceanic organic rich marls and shales are generally bathymetrically controlled these units are related to basin wide anoxic events in the tethys ocean and its submerged continental margin and are associated with sequence b areas middle upper cretaceous shallow water oil prone facies occur in isolated anoxic basins within carbonate platforms these source sequences are generally thicker and are associated with sequence a areas no major hydrocarbon accumulation can be directly attributed to the jurassic cretaceous epioceanic and intraplatform source rock sequences the third episode of source bed deposition characterizes the final active margin deformation stage and is represented by upper tertiary organic rich terrigenous units mostly gas prone these are essentially associated with turbiditic and flysch sequences of foredeep basins and have generated the greater part of the commercial biogenic gases of the periadriatic region

a paleotemperature record derived from dissolved noble gases in groundwater of the aquia aquifer maryland usa low 14c activities in groundwater of the confined part of the aquia aquifer in southeastern maryland suggest that most of this water infiltrated at least 30 000 years ago however radiocarbon contents of the dissolved inorganic carbon seem to be affected by isotopic exchange possibly with secondary calcite deposits in the formation leading to overestimated 14c ages whereas the geochemistry of the aquia aquifer complicates the application of the widely used 14c dating method the accumulation of radiogenic he seems to provide a viable alternative for establishing a chronology the quasi linear increase of he concentrations with flow distance observed in the aquia aquifer can be explained entirely by accumulation of in situ produced radiogenic he u and th concentrations in aquia sand were measured in order to determine the accumulation rate of 4he with sufficient confidence to establish a he time scale concentrations of dissolved atmospheric noble gases were used to derive mean annual ground temperatures at the time of infiltration these noble gas temperatures ngts clearly show the presence of water that infiltrated under much cooler conditions than at present ngts are correlated with chloride concentrations corroborating the hypothesis that chloride variations in this aquifer constitute a climate signal in contrast the stable isotope ratios 180 and d do not provide a clear record of past climatic changes in the aquia aquifer and the correlation between ngts and stable isotope ratios is weak the ngt record suggests that mean annual temperatures in this midlatitude coastal site during the last glacial maximum lgm were 9 0 0 6 c colder than during the holocene this difference is slightly lower than estimates derived from pollen data for this region but considerably larger than the rather uniform cooling of about 5 c indicated by noble gas studies in more southern locations of north america the larger cooling is ascribed to the influence of the laurentide ice sheet which at its maximum extension came as close as 250 km to our study site

quatermalacological analyses for modeling of the upper weichselian palaeoenvironmental changes in the carpathian basin abstract the late pleistocene environmental history of the carpathian basin can be regarded as one of the missing links to our understanding of the last glacial development of europe changes in the radiocarbon dated mollusc faunas of the loess areas along with the palaeogeographic interpretations implied by them seem to underlie the latest results gained from radiocarbon dated pollen analysis of the region changes in the mollusc fauna refer to nine short lived 1000 3000 years cyclical palaeoclimatological alterations which repeatedly transformed the palaeoecological conditions and vegetation in the carpathian basin between 34 and 12 kyr on the basis of malacological data the presence of a major palaeoclimatic trend could be assumed for periods of both warming and cooling in the carpathian basin the mildest july palaeotemperatures were recorded in the sw parts and the coldest ones were recorded in the ne parts of the basin humidity and vegetation cover displayed a large scale mosaic type heterogeneity reflecting the modifying effect of local factors it seem that the upper weichselian environment was mosaic or mosaic like in the carpathian basin and the different plants and animals spread from different ecological spots during periods of climate change when the distribution of the forest grassland ecotone or tundra like habitats changed

the fennoscandia sarmatia junction in belarus new inferences from a pt study abstract in eastern belarus the ne striking junction zone between the fennoscandian and sarmatian crustal segments of the east european craton rather abruptly separates the ca 2 0 ga osnitsk mikashevichi igneous belt omb developed on the continental margin of sarmatia from a 2 0 1 9 ga old palaeoproterozoic composite terrane in the northwest the latter consists of the central belarus belt cb and the vitebsk granulite domain vg the ne trending minsk fault subdivides the cb into lithologically different northwestern and southeastern sub terranes the northwestern sub terrane of the cb is dominated by ca 2 0 ga metabasalts containing numerous tonalite trondhjemite granodiorite ttg intrusions the southeastern cb and the vg in contrast are mainly composed of metasedimentary rocks with only minor ca 1 98 ga andesitic to dacitic metavolcanics in the vg these rocks have been penetrated and contact metamorphosed by 1 96 ga cordierite bearing granites subalkaline granites and quartz syenites of ca 1 8 ga age form numerous intrusions in the southeastern part of the cb the present study of the pt conditions of metamorphism as related to the chronologies demonstrates contrasting tectonothermal evolutions in the two major parts of the overall cb vg composite terrane separated by the minsk fault in the northwestern cb the metavolcanics have been exposed to prograde metamorphism with peak temperatures varying from 640 to 725 c at depths reaching 28 30 km these peak conditions were attained approximately 1 90 ga ago during concomitant emplacement of ttg type melts a retrograde stage in the amphibolite facies lasted until ca 1 70 1 67 ga in the vg xenoliths of metapelite enclosed in 1 96 ga high temperature granites document regional pre granitic metamorphism at ca 610 c and 6 7 kbar as well as some subsequent retrogression the contact metamorphism associated with the granites resulted in heating to ca 670 c upon which followed cooling and substantial decompression in part presumably effected by the ascent of the granite melts ultimate cooling of the granites and their metapelitic xenoliths can be followed through temperatures dropping from ca 530 to 420 c at pressures decreasing from ca 3 8 to 2 kbar the metamorphic and magmatic histories of the rocks in the vg agree in many regards with those recorded from the adjacent omb the substantial differences now discovered between the tectonothermal evolutions in various parts of the overall cb vg composite terrane suggest a more complex structure and development histories than those hitherto assumed both for the fennoscandia sarmatia junction zone and the cb the role of the minsk fault is still conjectural it may either represent the upper steep part of a listric thrust fault active during the stacking of the oceanic island island arc sub terrane against the sarmatian buttress or a much later fault that uplifted the northwestern cb and juxtaposed it with the southeastern cb sub terrane and the vg after subduction and compression had ceased

structure of the saxonian granulites geological and geophysical constraints on the exhumation of high pressure high temperature rocks in the mid european variscan belt

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

sediment slump structures a review of diagnostic criteria and application to an example from newfoundland abstract in the study of the history of deformed sedimentary rocks it is important that the cause of the deformation and the timing of deformation relative to metamorphic and tectonic events be assessed there is a continuous gradation between the deformation of freshly deposited sediments by gravitational forces and the deformation of well lithified sediments by tectonic forces so determining the degree to which gravity tectonism and lithification influenced deformation can be very difficult the characteristics that may be considered in determining the origin of deformational structures in sedimentary rocks can be divided into five categories ductile deformation structures 1 can provide definitive criteria for recognizing post lithification deformation but not pre lithification deformation this also holds for 2 brittle deformation structures and decollements overprinting of sediment reworking or remobilization structures 3 are the best criteria for recognizing pre lithification structures fabrics 4 can be very useful but are as yet poorly understood and there are misconceptions in the literature about what sort of fabrics are or are not found in unlithified sediments spatial relationships 5 may also tell us a great deal but are most useful when taken in conjunction with other types of evidence complex fold patterns in sandstones on farmer head north central newfoundland provide a case study for criteria that may be used to determine the degree of lithification during deformation although these folds have been interpreted as slump folds by earlier workers fabrics and spatial relationships point to a tectonic post lithification origin for the structures a conclusion which has significant implications for the interpretation of the regional geology

a high resolution seismic reflection refraction study of the chugach peninsular terrane boundary southern alaska we present results from a high resolution seismic refraction analysis of the shallow approximately 2 km crustal structure along the 107 km long trans alaska crustal transect chugach reflection line in southern alaska and a comparison with laboratory measurements of field samples the refraction analysis includes the two dimensional interpretation of several thousand first and secondary arrival travel times digitized from 1024 channel split spread common shot gathers the velocity model derived from this analysis better defines the location and geometry of terrane boundaries than does the normal incidence reflection section and agrees well with surface mapping of lithologies furthermore the model predicts travel times within 100 ms of the reflection times recorded from the base of the quaternary on the chugach reflection section thicknesses of quaternary deposits with velocities between 1 1 and 2 0 km s correlate inversely with the quantity of observed lower crustal reflections on the chugach section suggesting that the presence or absence of these sediments in sufficient thickness exerted primary control on the quality of the deeper portion of the section there is a significant velocity contrast between crystalline rocks across the border ranges fault 5 0 versus 5 6 km s the major contact between the chugach and peninsular terranes in agreement with laboratory measurements of field specimens in the peninsular terrane the modeling indicates that an unnamed fault delimiting the southern flank of the copper river basin dips steeply northward at 50 and has about 1300 m of vertical offset laboratory measurements document a maximum velocity anisotropy of 20 for phyllitic schists of the valdez group in the chugach terrane in agreement with the observed e w strike and near vertical dip of the valdez group we determined a significant 14 velocity anisotropy for ray paths oriented n s versus ne sw

shear wave anisotropy of laminated lower crust at the urach geothermal anomaly abstract deep seismic reflection studies have shown that lamellae are a widespread reflectivity pattern of the lower crust of the central european variscan belt this pattern has been interpreted inter alia as alternating subhorizontal layering of mafic and felsic rocks implying a tectonic process of structural and textural ordering consequently laminated lower crust should be elastically anisotropic the specific type of anisotropy should provide some insight into the mineral composition and the preferred orientation of minerals in the lower crust we have investigated this problem in the area of the urach geothermal anomaly south germany where a classical example of lower crust lamellae is found a restricted range of subsurface points was probed in a controlled source expanding spread seismic experiment with two orthogonal azimuths of observation up to 90 km source geophone offset both p and s waves were recorded with 3 component geophones at 80 140 m geophone spacing based on polarization analysis and traveltime interpretation the following results were obtained 1 s wave splitting is observed only for sms arrivals not for shallower reflections implying that the lower crust is anisotropic 2 the type of anisotropy is quasihexagonal transversely isotropic implying that there is no preferred mineral orientation within the horizontal plane 3 the coefficient of s wave anisotropy v max v min v min is estimated at 6 13 for sv type waves the sh wave velocity shows only small variation with offset 4 the observed relation between direction and velocity of s wave propagation can be explained by mafic rocks containing a high amount of orthopyroxene minerals horizontally aligned in the pure shear stress regime

mesozoic tertiary tectonic evolution of albania in its regional eastern mediterranean context abstract research carried out since the opening of albania to the western geological community in the 1990s allows the geology and tectonics of this small balkan country to be integrated into an overall interpretation of neotethys in the eastern mediterranean region specifically greece and the former yugoslavia region albanian geology is most famous for the occurrence of contrasting ophiolites of jurassic age the country is sub divided into three main geotectonic units those in the west i e sazani ionian kruja krasta cukali and the albanian alps relate to the western margin of apulia effectively part of north africa from early mesozoic time onwards in the east is the korabi zone interpreted as a microcontinent located further northeast within neotethys between the two is the mirdita zone dominated by two contrasting jurassic ophiolites the western type ophiolite and the eastern type ophiolite taking account of evidence from greece and former yugoslavia the following tectonic evolution is proposed from early mesozoic time onwards neotethys in albania existed as a northward continuation of the pindos oceanic basin in greece pindos mirdita ocean a korabi microcontinent was rifted off apulia in the early mid triassic followed by passive margin subsidence until late middle jurassic time a rifted slow spreading mor type ophiolite formed within the western pindos mirdita oceanic basin in late triassic early late jurassic time using present co ordinates the shkoder peje scutari pec lineament in the north of albania is interpreted as an important transform fault zone that influenced the regional tectonic evolution during the entire mesozoic early tertiary rift drift emplacement history of the pindos mirdita ocean taking account of evidence from the greek and former yugoslavia ophiolites the easterly albanian ophiolites formed within the pindos mirdita ocean above a westward dipping intra oceanic subduction zone in the early late jurassic metamorphic soles were formed during initial intra oceanic displacement ca 162 174 m y and underlying melanges originated as subduction accretion complexes the mor western type ophiolite evolved into the iat boninitic eastern type ophiolite after subduction began during tithonian berriasian time trench margin collision emplaced the ophiolites eastwards over the korabi margin coupled with redeposition of ophiolitic and continental margin material as exotic blocks debris flow deposits and turbidites these were emplaced onto the upper surface of the ophiolitic thrust sheet during the latest stages of emplacement onto the korabi microcontinent following collision in the east oceanic crust remained within a small remnant pindos mirdita oceanic basin passive conditions were restored in the mid late cretaceous with shallow water carbonate deposition on microcontinental units and both pelagic and redeposited carbonates in basinal settings from the maastrichtian onwards africa eurasia convergence resulted in large scale westward thrusting deforming the apulian foreland in oligo miocene time the suture zone was re activated in oligo miocene time as the albanie thassalie piggy back type basin in central and southern albania albania as a whole was rotated 45 clockwise as part of the western aegean arc in post eocene time coastal and offshore albania experienced strong subsidence after early miocene time forming the periadriatic basin including the tirana depression interpreted as a foredeep related to continuing regional convergence southern albania experienced extensional tectonics in plio quaternary time related to southward roll back of the aegean active margin

carbonate apron models alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration sediment gravity flow deposition along the deep water flanks of carbonate platforms typically does not produce submarine fans rather wedge shaped carbonate aprons develop parallel to the adjacent shelf slope break the major difference between submarine fans and carbonate aprons is a point source with channelized sedimentation on fans versus a line source with sheet flow sedimentation on aprons two types of carbonate aprons may develop along relatively gentle 4 platform margin slopes aprons form immediately adjacent to the shallow water platform and are referred to as carbonate slope aprons along relatively steep 4 15 platform margin slopes redeposited limestones accumulate in a base of slope setting by passing an upper slope via a multitude of small submarine canyons and are referred to as carbonate base of slope aprons both apron types are further subdivided into inner and outer facies belts inner apron sediments consist of thick mud supported conglomerates and megabreccias facies f as well as thick coarse grained turbidites facies a interbedded with subordinate amounts of fine grained peri platform ooze facies g outer apron sediments consist of thinner grain supported conglomerates and turbidites facies a as well as classical turbidites facies c with recognizable bouma divisions interbedded with approximately equal proportions of peri platform ooze facies g seaward aprons grade laterally into basinal facies of thin base cut out carbonate turbidites facies d that are subordinate to peri platform oozes facies g carbonate base of slope aprons grade shelfward into an upper slope facies of fine grained peri platform ooze facies g cut by numerous small canyons that are filled with coarse debris as well as intraformational truncation surfaces which result from submarine sliding in contrast slope aprons grade shelfward immediately into shoal water platform margin facies without an intervening by pass slope the two carbonate apron models presented here offer alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration for mass transported carbonate facies

seismic properties of rocks from an exposure of extended continental crust new laboratory measurements from the ivrea zone abstract compressional wave velocities for new samples from the ivrea verbano zone ivz and strona ceneri zone scz have been measured to 600 mpa in order to better understand the petrologic controls on velocity and to provide an expanded base for seismological models of the crust as represented by these terrains these data coupled with previous measurements show that preferred orientation of mica controls both the velocity hysteresis with pressure and seismic anisotropy of scz and ivz schists and gneisses ivz paragneisses form the basis of a linear velocity density relationship for metagraywackes of various metamorphic grade this relationship falls close to that expected for mafic rocks and overlaps velocity density data for ivz mafic gneisses one dimensional near vertical reflection models based on these data and recent structural reconstructions of the terrain show that lower crustal reflectivity can be related to high reflection coefficients associated with interlayered sequences of upper amphibolite granulite facies paragneiss mafic gneiss and ultramafic rocks transparent upper crustal levels in the model result from the overall similarity of velocities for schists gneisses and granites from the structurally and lithologically complex scz a mean lower crustal velocity of 7 1 km s is calculated for the part of the ivz composed of interlayered mafic gneiss and paragneiss and for another area dominated by a mafic layered igneous complex the velocity density analysis coupled with this observation emphasize the ambiguity inherent in interpretation of crustal composition from p wave velocity data in the absence of other constraints

carbonate turbidites in a mesozoic pelagic basin scaglia formation apennines comparison with siliciclastic depositional models abstract in the central apennines during most of the mesozoic a carbonate platform shed detrital material that was discharged by turbidity currents into an adjacent basin a sedimentological study of these detrital bodies has revealed that the depositional fan models largely applied to siliciclastic turbidites are not appropriate for carbonate turbidites the downslope succession of carbonate and siliciclastic facies and deposits are similar in a general way but carbonate turbidites do not appear to be organized into fan bodies apenninic calcarenite turbidites constitute sedimentary bodies 10 20 m thick are elongated more than 40 km along strike and are less than 10 km across such a shape is not consistent either with that of a hemicircular fan or with an ellipsoidal suprafan lobe morphology it suggests instead a kind of submarine piedmont debris sheet or a debris apron the different areal distribution of carbonate turbidites versus siliciclastic ones seems to be caused by a differences in composition scaglia turbidites are very poor in mud and the turbidity currents which had low transport efficiency deposited detritus abruptly at the end of the slope and had no opportunity to disperse sediments over wide areas b differences in feeding system carbonate detritus was not supplied by one large channel but rather from many small channels along the platform margin discrete turbidity currents deposited sediment at the base of the slope producing small deposits that coalesced to form a debris apron and c tectonic control a synsedimentary fault system occasionally rejuvenated the escarpment preventing the development of a large sedimentary body the final morphology was controlled more by tectonics than by sedimentation

soft sediment deformation within seismogenic slumps of the dead sea basin abstract the late pleistocene lisan formation preserved next to the dead sea provides exceptional 3 d exposures of folds and faults generated during soft sediment slumping and deformation it is possible to generate a range of four different scenarios associated with overprinting in a single slump event the progressive evolution of slump systems may be broadly categorised into initiation translation cessation relaxation and compaction phases thrust packages typically define piggyback sequences during slump translation with back steepening of imbricate faults leading to collapse of folds back up the regional palaeoslope detailed evaluation of slumped horizons may also permit structures to be traced across apparently separate and distinct slumped units the recognition that slumps may be reworked by younger seismically triggered events suggests that in some cases the seismic recurrence interval may be shorter than previously anticipated

3 d stratigraphic architecture sedimentary processes and controlling factors of cretaceous deep water resedimented carbonates gargano peninsula se italy abstract detailed geological mapping in 3 d supported by a lidar derived dom sedimentologic and biostratigraphic analyses and 3 d numerical modelling are used to characterise the stratigraphic architecture of deep water resedimented carbonate systems in the gargano peninsula se italy the base of slope succession spanning the upper aptian to danian p p was subdivided in five lithostratigraphic units that record the complex evolution and sedimentary dynamic along a segment of the apulian platform margin that was strongly influenced by syn sedimentary tectonic activity the characteristic location in a relay zone between the nw se trending platform margin and the e w oriented mattinata fault system favoured the existence of a transtentional zone from the upper aptian up to the end of the cretaceous the spatial distribution of the gravity flow deposits the stratal geometries the lateral facies changes and the biostratigraphic data demonstrate that the base of slope systems were sourced by distinct platform blocks characterised by different slope profiles abrupt to west and distally steepened to the north in this context the nature and origin of the resedimented carbonate material were controlled by the fracturation of the margin the response of the carbonate factory to relative sea level changes but were also strongly influenced by the slope profile this study demonstrates the relevance of combining traditional field work with numerical tools to improve the understanding of ancient sedimentary systems notably by mapping the stratal architecture and lithologies in continuity and at various scales on doms and by reconstructing the paleo topographies in 3 d

nature and origin of upper crustal seismic velocity fluctuations and associated scaling properties combined stochastic analyses of ktb velocity and lithology logs the main borehole of the german continental deep drilling program ktb extends over 9000 m into a crystalline upper crust consisting primarily of interlayered gneiss and metabasite we present a joint analysis of the velocity and lithology logs in an effort to extract the lithology component of the velocity log covariance analysis of lithology log approximated as a binary series indicates that it may originate from the superposition of two brownian stochastic processes fractal dimension 1 5 with characteristic scales of 2800 m and 150 m respectively covariance analysis of the velocity fluctuations provides evidence for the superposition of four stochastic process with distinct characteristic scales the largest two scales are identical to those derived from the lithology confirming that these scales of velocity heterogeneity are caused by lithology variations the third characteristic scale 20 m also a brownian process is probably related to fracturing based on correlation with the resistivity log the superposition of these three brownian processes closely mimics the commonly observed 1 k decay fractal dimension 2 0 of the velocity power spectrum the smallest scale process characteristic scale 1 7 m requires a low fractal dimension 1 0 and accounts for 60 of the total rms velocity variation a comparison of successive logs from 6900 7140 m depth indicates that such variations are not repeatable and thus probably do not represent true velocity variations in the crust the results of this study resolve disparity between the differing published estimates of seismic heterogeneity based on the ktb sonic logs and bridge the gap between estimates of crustal heterogeneity from geologic maps and borehole logs

groundwater flow system as an archive of palaeotemperature noble gas radiocarbon stable isotope and geochemical study in the pannonian basin hungary abstract to establish the increase in temperature and the time span of the transition between the late glacial maximum lgm and the holocene the noble gas content 18 o 2 h 13 c values 3 h and 14 c activity and chemistry were studied in a groundwater flow system in quaternary sediments in hungary the study area is a sub basin of the pannonian basin where the c isotope ratios are not influenced by carbonate reactions along the flow path because the only water rock interaction is ion exchange the 18 o and 2 h values indicate a cold infiltration period followed by warming and finally warm temperature conditions the noble gas data show that the average infiltration temperature was 3 3 c in the cold 12 9 c in the warm and intermediate in the transitional stage using the noble gas temperatures geochemical batch modelling was performed to simulate the chemical processes based on the geochemical model 13 c and 14 c 0 initial radiocarbon activity in the recharging water were calculated transport modelling was used to simulate the distribution of chemical components 18 o 2 h and 14 c 0 along the flow path it was found that the main processes determining the chemical composition of the groundwater were dissolution precipitation of calcite and dolomite during infiltration near the surface and ion exchange along the flow path in the recharge area the 13 c and 14 c 0 were controlled by dissolution and precipitation of carbonate minerals c speciation and fractionation processes all these processes were influenced by the recharge temperature ngts calculated from the dissolved noble gas concentrations showed an average of 3 3 c for cold and 12 9 c for warm infiltration i e for the lgm and for the holocene the temperature difference was thus 9 1 0 8 c which is one of the largest degree of warming detected by noble gases so far the alkalinity indicates that carbonate reactions were unimportant along the flow path owing to the temperature dependence of the equilibrium constants temperature conditions during infiltration have to be taken into consideration in radiocarbon age calculation dispersive transport along the flow path modified the chemical and isotopic composition of infiltrated water the contribution of the old pore water which was free of the 14 c isotope resulted in uncertainties in radiocarbon age determination it was concluded that determination of the radiocarbon age or mean residence time requires detailed knowledge of the hydraulic conditions of groundwater

strontium isotope profiles across k t boundary sequences in denmark and antarctica strontium isotope profiles derived from minimally altered samples across marine k t boundary sequences exposed at kjolby gaard and nye klov denmark and on seymour island antarctica show neither the boundary excursions nor the boundary spikes in 87sr 86sr that have been reported for k t boundary sequences from elsewhere nor do our data conform to modelled predictions of the sr isotopic response of the oceans to a positive spike in 87sr 86sr at the terminal cretaceous boundary values for 87sr 86sr with 95 confidence intervals are 0 707828 3 in denmark and 0 707832 7 in antarctica our data suggest that 87sr 86sr stopped increasing and started decreasing at least 90 ka before the k t boundary

the nature of seismic reflections from deep crustal fault zones deep seismic reflection profiles have recorded reflections from ductile shear zones within the crystalline basement perhaps the best example is the consortium for continental reflection profiling cocorp wind river line in wyoming which shows the wind river thrust fault to be a strong reflector from the surface to depths of about 30 km to identify the physical properties responsible for the seismic reflections from fault zones we report measurements of compressional wave velocity and velocity anisotropy in mylonites recovered from exhumed ductile shear zones these rocks are characterized by extensive ductile deformation of plastic minerals brittle deformation of the more rigid minerals grain size reduction and development of a strong fabric average velocity and density were not found to change significantly and systematically between the mylonites and the adjacent undeformed rock seismic anisotropy of 7 or greater is present in several mylonites dependent upon their composition and fabric using our data on mylonite properties and models for the crustal structure near the wind river line we compute true amplitude synthetic reflection seismograms and compare them to true amplitude plots of the cocorp wind river reflection data when anisotropy and the finely laminated structure of the fault zone are considered our modeling indicates fairly strong reflections from mylonite zones in most cases we also show that elevated pore pressure in shear zones may produce strong reflections however a permeability of the order of 10 16 darcy is required to maintain sufficient pore pressure to produce a velocity anomaly in a fault zone which has long been inactive

sedimentological and marine eogenetic control on porosity distribution in upper cretaceous carbonate turbidites central albania results of a detailed petrographic and stable isotope study illustrate that sedimentological differences and eogenetic dissolution precipitation processes controlled porosity distribution within carbonate turbidites of the ionian basin central albania based on lithology characteristics and porosity distribution observed in outcrop individual turbidite beds can be subdivided into four distinct intervals i e from base to top a a non porous wackestone floatstone or packstone followed by b porous packstone grainstone that grades into c wackestone and d non porous mudstone with pelagic foraminifera wackestone interval c is characterized by an alternation of porous and non porous laminae changes in turbidity current flow regime controlled the initial presence of matrix micrite giving rise to both matrix and grain supported lithologies within turbidite sequences these are non porous and porous respectively four eogenetic diagenetic processes dissolution cementation neomorphism and compaction acted shortly after deposition and modified primary porosity characteristics and distribution alteration by meteoric water is excluded based on the continuous burial until the oligocene of the studied deep marine carbonates moreover the stable isotope data with values between 2ae1 and 0ae7 for d 18 ov pdb and between 1 and 3 for d 13 cv pdb favour alteration by marine derived pore waters compaction and aggrading neomorphism occurred dominantly in intervals characterized by higher matrix micrite content i e the floatstone base and the wackestone mudstone upper turbidite part framework stabilizing cementation occurred dominantly in the packstone grainstone middle part of the turbidite beds in the latter porous lithologies matrix micrite was not compacted because of the grain fabric and the framework stabilizing cements here neomorphism of micrite into microrhombic euhedral calcite occurred and microporosity was preserved

on the architecture of intra formational mass transport deposits insights from the carbonate slopes of great bahama bank and the apulian carbonate platform abstract large sub tropical carbonate platforms shed huge volumes of sediment onto their adjacent slopes resulting carbonate successions are comprised of gravity flow beds turbidites debrites which are occasionally reworked into mass transport deposits mtds by the failure of inconsistently lithified portions of slope strata despite their significance in the depositional record the internal architecture of mtds along relatively tectonically stable and sediment producing carbonate platforms is poorly understood in comparison with counterparts in active compressional tectonic settings this study compares carbonate slope derived mtds imaged in seismic reflection data with those observed in outcrop the internal architecture of mtds from two case studies is presented the seismically imaged mtds in miocene recent carbonate slope deposits from the bahamas and mtds off the cretaceous apulian carbonate margin exposed in outcrops of the ionian basin albania understanding the large scale kilometers to tens of kilometers internal architecture of mtds in seismic is crucial for identification of these structures in outcrop in turn only outcrop studies allow the detailed analysis of the reworking style within these massive sediment bodies at a smaller scale meters to kilometers the internal architecture of the studied carbonate mtds testifies to the existence of an along slope continuum of deformation structures characterized by vertical partitioning into distinct mass flows during single mass transport events mass wasting processes are inferred from strain partitioning structures recording along slope and slope parallel architectural heterogeneities three deformation domains are recognized extensional headwall domain translational body domain and contractional toe domain confined mtds are limited by steep and deep lateral margins and frontal ramps that mark the boundaries between failed deposits and undisturbed strata vertical strain partitioning is pronounced in the toe domain upward intensification of deformation within mtds is common and corresponds to a top down reorganization of failed strata during downslope transport intra formational mtds along carbonate slopes that are lacking exotics such as the ones studied here differ from extra formational mtds occurring in compressional tectonic settings that form sedimentary melanges ductile layer deformation structures are predominant in carbonate mtds as opposed to block in matrix fabrics in sedimentary melanges the development of shear surfaces rather than ductile shear zones in the body and toe domains presents predictive in modern environments and diagnostic criteria in fossil examples of mass wasting events along carbonate slopes

origin of reflections from the brevard fault zone the brevard fault zone is a belt of mylonitic metamorphic rocks that extends northeast over 700 km from alabama into virginia seismic reflection studies show that the fault zone produces excellent reflections which dip gently to the southeast and sole at depth the origin of these reflections has been investigated by measuring compressional wave velocities to 800 mpa confining pressure in 127 samples obtained from drill core which continuously sampled the fault zone to a depth of over 300 m densities are reported as well as chemical analyses at selected depths anisotropy at elevated pressures ranges within the fault zone from less than 5 to over 26 similarly the fault zone rocks show significant chemical variability with sio2 ranging from 58 0 to 70 4 by weight synthetic seismograms generated from the velocity and density measurements show that the reflections originate within the brevard fault zone from the complex interaction of compositional variations and seismic anisotropy resulting from ductile strain essential to this study has been the continuous coring of a major section of the brevard fault zone which has provided the necessary stratigraphic control as well as unweathered samples for laboratory studies

bahama carbonate platforms the deep and the past abstract carbonate deposition prevailed for 150 ma in the bahama florida segment of the west atlantic margin and provides an interesting test for actualism present day facies patterns on the banks are controlled by the backward decrease of waves and tides and the concomitant increase of temperature and salinity variation in the troughs influx of sand and rubble from gravity flows varies with topography and distance from shallow water sources and allows one to define facies belts a rhythmic sequence of ooze and graded beds on the basin floors subdivided into a basin margin belt of coarse thick turbidites and basin interior with fine turbidites slope facies change with increase in height and declivity from accretionary to by pass to erosional regimes stratigraphic history of the bahamas is not simply a projection of the holo scene back in time both long term natural evolution decrease in subsidence upbuilding of the banks submarine erosion and outside factors climate eustacy have caused significant changes since the jurassic the bahamas seem to have evolved from a clastics evaporite province to a single carbonate evaporite platform and finally to an array of platforms and troughs during the platform trough stage the rate of upbuilding of the platforms decreased submarine canyon erosion increased platform flanks steepened as they grew higher and changed from accretionary to by pass to erosional slopes a change imposed by extraneous factors occurred in the pliocene when the great bahama bank changed from a giant reef rimmed atoll to a flat platform covered by oolites and peloid sands the bahamas share both long term trends as well as random changes by extraneous factors with other platforms in the geologic record compared to ancient platforms however they are unusually long lived and at a more advanced stage of growth they are deeply dissected by erosion their flanks are unusually high and steep and the troughs very narrow the neogene platform sequence is strongly controlled by eustatic sea level fluctuations

anisotropy in multi offset deep crustal seismic experiments modelling of deep seismic wide angle data commonly assumes that the earth is heterogeneous and isotropic it is important to know the magnitudes of errors that may be introduced by isotropic based wide angle models when the earth is anisotropic it is equally important to find ways of detecting anisotropy and determining its properties this paper explores the errors introduced by interpreting anisotropic seismic data with isotropic models errors in p wave reflector depths are dependent on the magnitude of the velocity anisotropy and the direction of the fast axis the interpreted isotropic model velocity function is found to correspond closely to the horizontal velocity of the anisotropic medium an additional observed parameter is the time mismatch which we define to be the difference between the vertical two way traveltime to a reflector and the time converted wide angle position of the reflector the magnitude of the time mismatch is typically 1 0 s when the whole crust is anisotropic and is found to be closely related to the magnitude and sign of the anisotropic anellipticity the relationships are extendible to more complicated models including those with vertical velocity gradients crustal zonation and lower symmetry orders a time mismatch may be symptomatic of the presence of anisotropy we illustrate the observation of a time mismatch for a real multi offset seismic data set collected north of scotland and discuss the implications for crustal anisotropy in that region

seismically induced slumps in lower maastrichtian peritidal carbonates of the apulian platform southern italy abstract in the southeastern murge apulian foreland southern italy a lower maastrichtian carbonate section showing soft sediment deformation structures is composed of peritidal lithofacies associations developed in a wide low energy inner platform system shear induced soft sediment deformation structures correspond to multilayer deformed horizons 1 5 to 2 m in thickness sandwiched between undeformed layers overturned and recumbent folds lying on decollement surfaces and asymmetrical fault inception folds allow us to interpret the observed deformed horizons as slump sheets the detailed description of the main morphological features of the deformed beds and the recognition of unconformable surfaces and undeformed beds between slumped beds allow us to distinguish three different events of deformation preferential orientation of slump folds has been measured and every slumped bed shows a different direction of shortening randomly oriented direction of shortening suggests that each deformation event was driven by the presence of local very gentle gradients developed in peritidal settings by excluding other potential trigger mechanisms of deformation the observed slumps are interpreted as seismically induced slides even if no data about the distance of the seismic source may be obtained near field earthquake tectonics affected the apulian platform during late cretaceous times

the cretaceous megabreccias of the gargano promontory apulia southern italy their stratigraphic and genetic meaning in the evolutionary framework of the apulia carbonate platform huge megabreccias occur at the eastern margin of the cretaceous apulia carbonate platform gargano promontory southern italy their stratigraphic and genetic meaning are controversial in the debated geological evolution of the apulia platform new stratigraphic analyses have revealed that three distinct megabreccia levels occur within the coarse debrites that were previously interpreted to be the result of repeated collapses of a scalloped platform margin during the late albian cenomanian each level has peculiar chronostratigraphic distribution geometry composition and genetic features they are the posta manganaro megabreccias late early aptian to late albian pp monte s angelo megabreccias early middle cenomanian and belvedere di ruggiano megabreccias middle turonian these deposits overlie regional tectonically enhanced unconformities of late early aptian late albian and late cenomanian age these megabreccias which were formed respectively during drowning prograding and exposure events of the apulia platform reflect important turning points in its cretaceous geodynamic evolution

climate related variations in the composition of the late glacial and early holocene sediments of lake perespilno eastern poland abstract this paper presents an array of analyses of the laminated sediments of lake perespilno eastern poland covering the period between older dryas and preboreal using the varve chronologies pollen and 14 c data the laminated sequence of lake perespilno has been synchronised with that of lake go ciaz the length of the allerod and younger dryas periods derived from lake perespilno sediments agrees well with the previous estimates according to our data the climate in the allerod was relatively mild with some increase of precipitation and humidity after ca 13 2 kyr cal bp the beginning of the younger dryas is marked by drastic changes in temperature as well as humidity thinning of forests facilitated input of allochtonous material to the lake it seems that the groundwater level as well as lake level dropped significantly and the period of lowest water table was prolonged for ca 300 years surprisingly the abrupt warming at the beginning of the holocene is only slightly reflected in the sediments changes in sediment composition at that time seem to be controlled more by the development of surrounding vegetation than by the climate itself

crustal structure of the whipple mountains southeastern california a refraction study across a region of large continental extension summary closely spaced refraction profiling across the whipple mountains metamorphic core complex in southeastern california yields a complex picture of crustal structure in this region of large continental extension a ne directed profile parallel to the extension direction reveals a high velocity mid crustal layer 6 6 6 8 km s at 16 18 km depth bounded above and below by laterally discontinuous low velocity zones 6 0 km s in marked contrast a nw dnected profile shows a more uniform 6 0 km s crust down to the crust mantle boundary the apparent contrast between these two perpendicular profiles may be related not only to a more complex geologic structure in the nw se direction but also to velocity anisotropy associated with mid crustal mylonites despite the differences between the two refraction profiles both define a flat moho at 26 27 km depth with an associated upper mantle velocity of 7 8 km s this observation is significant as it suggests that although the amount of extension has been highly variable regionally the crust is no thinner beneath the whipple mountains where extension has been extreme than the surrounding mountain ranges such an observation requires either that the crust was considerably thicker prior to extension or that lateral flow in the lower crust and or inflation of the crust via magmatism occurred contemporaneous with extension

upper lithospheric seismic velocity structure across the pripyat trough and the ukrainian shield along the eurobridge 97 profile abstract we present new results on the structure resulting from palaeoproterozoic terrane accretion and later formation of one of the aulacogens in the east european platform seismic data has been acquired along the 530 km long n s striking eurobridge 97 traverse across sarmatia a major crustal segment of the east european craton the profile extends across the ukrainian shield from the devonian pripyat trough across the palaeoproterozoic volyn block and the korosten pluton into the archaean podolian block seismic waves from chemical explosions at 18 shot points at approximately 30 km intervals were recorded in two deployments by 120 mobile three component seismographs at 3 4 km nominal station spacing the data has been interpreted by use of two dimensional tomographic travel time inversion and ray trace modelling the high data quality allows modelling of the p and s wave velocity structure along the profile there are pronounced differences in seismic velocity structure of the crust and uppermost mantle between the three main tectonic provinces traversed by the profile i the pripyat trough is a ca 4 km deep sedimentary basin fully located in the osnitsk mikashevichi igneous belt in the northern part of the profile the velocity structure is typical for a precambrian craton but is underlain by a ca 5 km thick lowest crustal layer of high velocity the development of the pripyat trough appears to have only affected the upper crust without noticeable thinning of the whole crust this may be explained by a rheologically strong lithosphere at the time of formation of the trough ii very high seismic velocity and vp vs ratio characterise the volyn block and korosten pluton to a depth of 15 km and probably also the lowest crust the values are consistent with an intrusive body of mafic composition in the upper crust that formed from bimodal melts derived from the mantle and the lower crust iii the podolian block is close to a typical cratonic velocity structure although it is characterised by relatively low seismic velocity and vp vs ratio a pronounced sw dipping mantle reflector from moho to at least 70 km depth may represent the proterozoic suture between sarmatia and volgo uralia the structure from terrane accretion or a later shear zone in the upper mantle the sub moho p wave seismic velocity is high everywhere along the profile with the exception of the area above the dipping reflector this velocity change further supports a plate tectonic origin of the dipping mantle reflector the profile demonstrates that structure from palaeoproterozoic plate tectonic processes are still identifiable in the lithosphere even where younger metamorphic equilibration of the crust has taken place

sedimentary patterns and geometries of the bahamian outer carbonate ramp miocene lower pliocene great bahama bank core logging and high resolution seismic data from odp leg 166 were used to analyse deposits of the neogene miocene lower pliocene bahamian outer carbonate ramp ramp sediments are cyclic alternations of light and dark grey wackestones packstones with interbedded calciturbidite packages and minor slumps cyclicity was driven by high frequency sea level changes light grey layers containing shallow water bioclasts were formed when the ramp exported material whereas the dark grey layers are dominantly pelagic calciturbidites are arranged into mounded lobes with feeder channels internal bedding of the lobes shows a north directed shingling as a result of the asymmetrical growth of these bodies calciturbidite packages occur below and above sequence boundaries indicating that turbidite shedding occurred during third order sea level highstands and lowstands highstand turbidites contain shallow water components such as green algal debris and epiphytic foraminifera whereas lowstand turbidites are dominated by abraded bioclastic detritus gravity flow depocentres shifted from an outer ramp position during the early miocene to a basin floor setting during the late miocene to early pliocene this change was triggered by an intensification of the strength of bottom currents during the tortonian which was also responsible for shaping the convex morphology of the outer ramp the miocene and lower pliocene of the leeward flank of great bahama bank provides an example of the poorly known depositional setting of the outer part of distally steepened carbonate ramps the contrast between its sedimentary patterns and the well known upper pliocene quaternary slope facies associations of the flat topped great bahama bank shows the strong control that the morphology of a carbonate platform exerts on the depositional architecture of the adjacent slope and base of slope successions

gravity driven structures and deposits resulting from slope collapse in the margin of a carbonate platform pennsylvanian cantabrian zone nw iberia abstract lower slope to basin floor deposits associated to isolated microbial carbonate platforms of the valdeteja formation carboniferous foreland basin cantabrian zone nw spain containing large slid blocks and debrites exhibit a combination of contractional and extensional structures which include thrusts backthrusts folds extensional faults and joints and boudinaged beds several lines of evidence indicate that deformation took place in poorly lithified conditions such as thickened hinges hydroplastic fractures fold axes scatter or folding of microbial limestones once restored all structures indicate a transport direction towards the nne ene this azimuth coincides with the direction towards which the thrust nappes of the southern branch of the cantabrian zone were emplaced during the variscan orogeny however the interpretation of the deposits and structures as gravity related associated to the collapse of the carbonate platform slope is supported by features such as the rootless character of thrusts the parallelism between transport direction and paleocurrent orientation the concomitant development of contractional and extensional structures the development of normal listric faults affecting the valdeteja platform the sedimentary environment lower slope to basin floor and the geological context of the valdeteja carbonate platforms which predate the variscan deformation in the study area

fabric related velocity anisotropy and shear wave splitting in rocks from the santa rosa mylonite zone california the directional dependence of p and s wave velocities have been measured at pressures up to 600 mpa and temperatures up to 700 c in rocks from the santa rosa mylonite zone southern california during tectonism these were progressively deformed from granodiorite protolith to mylonite and ultimately phyllonite the mineralogical and chemical composition of protolith and mylonite is nearly identical thus these rocks provide excellent material for documenting the effect of microstructural and textural changes on rock anisotropy velocity anisotropy increases significantly with the degree of deformation whereas average velocities and densities do not change at low pressure 50 mpa the velocity anisotropy ranges from 1 7 in granodiorite up to 19 in phyllonite and is due to both oriented microfractures and crystallographic preferred orientation at high pressure 600 mpa the residual anisotropy up to 12 is mainly due to preferred mineral orientation in particular of biotite significant shear wave splitting is measured parallel to the foliation plane and shows a good correlation with the biotite texture these observations confirm that oriented microcracks and preferred orientation of minerals should be taken into account in the interpretation of seismic reflection and refraction data in terranes with deformed rocks

contribution to the understanding of the ionian basin sedimentary evolution along the eastern edge of apulia during the late cretaceous in albania abstract integrated in the peri adriatic domain the ionian basin extended along a nw se direction during the late cretaceous limited on its sides by the apulian and the kruja platforms the basinal slope succession was studied in seven outcrops exposed in the albanian fold and thrust belt sedimentological investigations supported by bio and chronostratigraphy were performed on calcareous upper cretaceous hemipelagites gravity flow deposits and slumps the western part of the basin was studied revealing a strong influence of the apulian margin alternatively shedding sediment basinward by means of a tectonically controlled edge the late albian to cenomanian period is characterized by the settling of muddy debrites along the margin a deep basinal environment characterizes this period which prolongs until the santonian with no significant influx of the platform basinward this sedimentary setting abruptly changed at the end of the santonian with an important influx derived from both platforms coarsening and thickening upward sequences show a progressive increase in sediment shedding during the campanian the late campanian early maastrichtian period points out a major change on the resedimentation processes with the settling of several slumped units reworking thick sediment packages the latter can be traced along the apulian margin testifying of instabilities along the edge of apulia

riphean rifting and major palaeoproterozoic crustal boundaries in the basement of the east european craton geology and geophysics abstract the east european craton which occupies the northeastern half of the european continent is characterized by the presence of giant even transcratonic systems of riphean meso to neoproterozoic rifts aulacogens the largest of these riphean rift systems tend to follow the course of palaeoproterozoic sutures and junction zones that subdivide the craton into three crustal segments with autonomous development histories these segments named fennoscandia volgo uralia and sarmatia are marked by distinct t magsat anomalies genetically the intersegment junction zones represent different types of collisional and accretional interaction between the component crustal segments of the craton in accordance with this the riphean rift systems vary in width the presence or absence of moho uplifts and other properties like for instance heat flow values however all of them follow belts of weakly magnetized crust studded with local magnetic maxima due to the presence of mafic rocks associated with the rifting the rift system intersegment junction zone relationships in consequence similarly represent a range of variation and cannot be referred to one single model

seismic velocity structure across the fennoscandia sarmatia suture of the east european craton beneath the eurobridge profile through lithuania and belarus

palaeoproterozoic upb zircon ages from belorussia new geodynamic implications for the east european craton abstract the crust in the northwest of the east european craton has traditionally been regarded as part of an archaean nucleus in eastern europe recent correlation with the baltic shield in scandinavia however suggests the need of reappraisal to study this problem zircons from three boreholes in the basement of the russian platform in belorussia belarus have been dated by the u pb and pb pb methods the ages indicated by two u pb discordias are 1982 26 ma for a metadacite from the central belorussian belt of volcanic arc igneous rocks and 1800 7 ma for mafic granulite from the baltic belorussian granulite belt largely built up of mafic igneous rocks for another central belorussian metadacite a pb pb age of 1975 10 ma was obtained in previous stratigraphies of belorussia all three dated rocks have been considered to be important components of an archaean even early archaean crust analyses of abraded crystal cores of complex zircons in one sample and separated core and rim zircons in another do not suggest substantially older ages of the core materials together with previous ages of granitoids and charnockites which had however been explained as a result of late magmatism and metamorphism and therefore not characterizing the age of the crust our data indicate the dominance of palaeoproterozoic rocks in the basement of the northwestern part of the east european craton that adjoins the tornquist line boundary between central and northeastern europe in conjunction with the results of a finnish estonian study of similarly allegedly archaean but in actual fact proterozoic rocks in southern estonia our results suggest the existence of large palaeoproterozoic crustal belts extending all the way from the finnish gulf to eastern poland this implies a substantial revision of established concepts on the precambrian geology in the northeastern half of the european continent

absolute dating of brittle fault movements late permian and late jurassic extensional fault breccias in western norway 40ar 39ar geochronological and palaeomagnetic dating methods applied to fault breccias in western norway have isolated two brittle reactivation episodes of the syn post caledonian extensional nordfjord sogn detachment these events of latest permian and latest jurassic early cretaceous ages demonstrate temporal relationships between development of chemical remanent magnetism and partial resetting of ar isotopic systems during distinct breccia forming episodes a third event of carboniferous age was also identified in the breccias with the 40ar 39ar technique and is a relict unroofing signature inherited from the fault wall rocks these brittle faults are significant time markers and become relevant to interpretations of offshore seismic data which attempt to place ages on faults that have undergone multiple reactivation episodes

a record of temperature and monsoon intensity over the past 40 kyr from groundwater in the north china plain abstract the well known temperature dependence of noble gas solubilities in water enables the determination of absolute paleotemperature records from radiocarbon dated groundwater an advantage of the noble gas paleothermometer is that noble gas temperatures ngts can directly be related to stable isotope ratios from the same groundwater archive in order to calibrate the stable isotope thermometer over long time scales our record from heavily used aquifers of the north china plain constitutes a unique combined ngt and stable isotope data set from the region affected by the east asian monsoon in addition to providing a reliable estimate for the glacial interglacial temperature change the data enable the separation of the effects of temperature and precipitation monsoon strength on the stable isotopes although the record extends from modern waters to near the limit of the radiocarbon dating range at about 40 kyr bp the last glacial maximum is not represented probably because arid conditions limited groundwater recharge during that period the coldest observed period at about 30 kyr bp was 4 6 1 2 c cooler than the holocene whereas ngts show no systematic variation during the holocene the 18 o values increased by about 1 between the early and late holocene a similar increase of 18 o has been observed before in speleothems and ascribed to decreasing monsoon strength in response to decreasing insolation during the holocene our results confirm that the holocene trend in stable isotopes is not related to temperature in contrast 18 o and ngt are correlated within the pleistocene group of samples indicating a 18 o ngt slope of 0 18 0 05 c 1 similar to the temperature effect in modern precipitation of the region thus of the overall increase of 18 o by about 2 between 30 kyr bp and the late holocene about half is due to a temperature increase whereas the other half is due to a decrease of monsoon strength

seismic anisotrdpy in granuulte facies rocks of the arunta block central australia using travel times from explosive sources recorded at distances less than 36 km evidence for p wave anisotropy was obtained in an area of central australia where granulite facies rocks from the lower crust are exposed at the surface these rocks form the hanging wall of one of the most prominent ancient thrust structures seen anywhere in a continental interior the azimuthal variation in seismic velocity for rocks at depths less than about 1 km is about 5 and is comparable in magnitude to values reported for both continental and oceanic upper mantle the maximum velocity east west is parallel to the predominant strike direction of gneissic foliation observed in outcrop in the survey region which was produced during granulite facies metamorphism at about 1 800 ma

the upper cretaceous carbonates of the gargano murge region southern italy a model of platform to basin transition the outcrops in gargano murge region are good examples of the upper cretaceous carbonate systems of the peri adriatic area they enable the architecture and the processes of the platform to basin transition to be studied in detail the platform carbonates are juxtaposed to the deeper marine carbonates by the intermediary of a faulted scarp the base of slope is characterized by bioclastic and conglomeratic aprons interbedded with pelagic mudstones the outer shelf domain which was the prolific source of rudistid bioclastic aprons is not preserved the platform is mainly built of mud dominated transgressive systems tracts whereas highstand systems tracts are developed as bioclastic base of slope aprons the volume of the resedimented bioclasts largely exceeds the volume of missing outer shelf indicating that carbonate production and sediment bypass are more critical for this stratigraphic response than carbonate erosion the lowstands which were controlled by tectonic deformations are characterized by base of slope breccia and blocks eroded from the shelf edge this erosion resulted in the progressive retreat of the shelf edge the best potentials for hydrocarbon reservoir are found in the bioclastic base of slope aprons formed during the cenomanian and maastrichtian highstands this model is considered as an analog for the hydrocarbon reservoirs formed by the deep marine deposits of cretaceous tamabra limestone in the gulf of mexico

coincident normal incidence and wide angle reflections from the moho evidence for crustal seismic anisotropy abstract we explore the consequences of interpreting wide angle crustal seismic data assuming isotropic models when the real crust may be anisotropic we have used a simple anisotropic model to generate synthetic travel times and have inverted these assuming an isotropic layered model for the crust we show that neglecting the effects of anisotropy can produce estimates of crustal thickness and crustal velocity structure that are significantly in error for realistic levels of anisotropy 10 the error in crustal thickness can be several kilometres and the error in average velocity can be 0 5 km s we show that isotropic inversion of anisotropic data can lead to an apparent mismatch between the position of the moho inferred from normal incidence and wide angle data as an example of such a mismatch we show data acquired over the continental crust offshore the north of scotland the dataset we have modelled includes a wide angle expanding spread profile a conventional ocean bottom seismometer profile a high resolution wide angle onshore offshore experiment a synthetic aperture 16 km offset cdp profile and a conventional deep reflection profile these data show unusually sharp bright and continuous reflections from the moho at all offsets the normal incidence reflection moho and the moho modelled from the wide angle data both show the same lateral structure however they are offset one from the other in normal incidence two way travel time this mismatch is considerably larger than the maximum error expected in the wide angle model and is much greater than the accuracy with which the moho can be picked on the reflection data if we assume that this mismatch is caused by crustal scale seismic anisotropy then the synthetic results indicate that anisotropy in the crust north of scotland is about 7

lithosphere structure along the northern part of eurobridge in lithuania results from integrated interpretation of dss and gravity data abstract in the summer of 1995 the first on shore phase of the eurobridge dss experiment took place in lithuania the quality of recordings was good and contained clear p wave reflections from inter crustal interfaces and the moho boundary very clear reflections were also registered from the interface below the moho boundary the arrivals of both reflected and refracted p waves from 10 shotpoints were processed using the seis 83 ray tracing program as a result a 2 d seismic model along the lithuanian part of eurobridge has been obtained the comparison of synthetic and experimental seismograms showed good agreement of the model with registered travel times to visualise better the existing tectonic discontinuities an integrated 2 d seismic and density model along the northern part of eurobridge was compiled for this purpose the technique of gravity data inversion based on a non linear relationship between density and seismic p wave velocity was used this integrated velocity density model helped to reveal differences in deep lithosphere structure beneath the northern part of eurobridge where the tectonic contact of two proterozoic terrains is located

chemical evolution of groundwater in the river danube deposits in the southern part of the pannonian basin hungary processes controlling the groundwater chemical composition were studied in the river danube deposits in the southeastern part of hungary phreeqm a combined geochemical and one dimensional transport model and phreeqe netpath and wateqf geochemical computer codes were used to simulate these processes the main processes controlling water chemistry are equilibrium with calcite undersaturation in dolomite and albite weathering in the recharge area ion exchange along the flow path and ion exchange and mixing with old water at the end of the flow path ion exchange seems to be the most important process controlling groundwater chemistry along the flowpath in the fluvial sediments studied isotopic data support the geochemical model the groundwater ages adjusted for the modeled c mass transfer range from 3300 to 20 200 a b p cation exchange suggests that displacement of a former aqueous solution by the present groundwater occurred this displacement is attributed to tectonic and paleoclimatic events at the end of the pleistocene

platform margin collapses and sequence stratigraphic organization of carbonate slopes cretaceous eocene gargano promontory southern italy we describe the sequence stratigraphic organization and the associated sedimentological characteristics of cretaceous to eocene slope and base of slope carbonate successions the study area is located in the gargano promontory which belongs to the stable foreland of southern italy the succession consists of three superimposed depositional sequences separated by major unconformities the upper two sequences are clear examples of sequence stratigraphic organization in fact they both start with huge megabreccia wedges lst followed upward by thin pelagic units tst and a thick package of calciturbidites and debrites that alternate with pelagic mudstone hst the cretaceous highstand systems tract is clearly arranged in a number of coarsening upward cycles while the eocene one which also comprises a toplap shallow water unit is not the gargano stratigraphic palimpsest and the entire margin of the apulia platform show remarkable similarities with present day carbonate platform margins and slopes where irregular convex bankward embayments suggest large scale failures it is clear that classic sequence stratigraphic organization can result from simple platform dismantling having no or little time relation with global sea level fluctuations in fact as the margin failure lst interrupts the carbonate production a period of starvation tst along the entire slope and base of slope follows necessarily finally when the margin once again becomes active and productive sediment exportation starts again and the system begins to prograde hst

heterozoan carbonate deposition on a steep basement escarpment late miocene almeria south east spain heterozoan temperate water carbonates mixed with varying amounts of terrigenous grains and muddy matrix azagador limestone accumulated on and at the toe of an inherited escarpment during the late tortonian early messinian late miocene at the western margin of the almeria nijar basin in south east spain the escarpment was the eastern end of an uplifting antiform created by compressive folding of triassic rocks of the betic basement channelized coralline algal bryozoan rudstone to coarse grained packstone together with matrix supported conglomerate are the dominant lithofacies in the higher outcrops comprising the deposits on the slope these sediments mainly fill small canyon shaped half graben depressions formed by normal faults active before during and after carbonate sedimentation roughly bedded and roughly laminated coralline algal bryozoan rudstone to coarse grained packstone are the main lithofacies forming an apron of four small kilometre scale lobes at the toe of the south eastern side of the escarpment almeria area channelized and roughly bedded coralline algal bryozoan rudstone to coarse grained packstone conglomerates packstone and sandy silt accumulated in a small channel lobe system at the toe of the north eastern side of the escarpment las balsas area carbonate particles and terrigenous grains were sourced from shallow water settings and displaced downslope by sediment density flows that preferentially followed the canyon shaped depressions roughly laminated rudstone to packstone formed by grain flows on the initially very steep slope whereas the rest of the carbonate lithofacies were deposited by high density turbidite currents the steep escarpment and related break in slope at the toe favoured hydraulic jumps and the subsequent deposition of coarse grained low transport efficiency skeletal dominated sediment in the apron lobes accelerated uplift of the basement caused a relative sea level fall resulting in the formation of outer ramp carbonates on the apron lobes which were in turn overlain by lower messinian coral reefs this is the first known example of a base of slope apron within temperate water carbonate systems this article is protected by copyright all rights reserved

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

western greece and ionian sea petroleum systems in western greece the ionian and pre apulian zones represent respectively the basin and the transitional zone slope to the apulian platform the apulian platform constitutes the weakly deformed foreland of the external hellenides the pre apulian zone appears in the ionian islands and the eastern ionian sea whereas the apulian platform is exclusively found in the ionian sea the ionian zone consists of triassic evaporites jurassic upper eocene mostly pelagic carbonates minor cherts and shales overlainbytheoligoceneflysch organic richsourcerocks occur within triassic evaporites and jurassic cretaceous pelagic argillaceous siliceous rocks the pre apulian zone consists of triassic to miocene deposits mainly mixed neritic pelagic carbonates hydrocarbon source rocks include pelagic and hemipelagic deposits rich in marine organic material although terrigenous organic matter is also found in siliciclastic layers apulian platformsourcerocksaremainlytheorganic richshaleswithinthe triassic burano evaporites western greece contains major petroleum systems which extend into the ionian sea ionian pre apulian and apulian petroleum systems contribute to the probable hydrocarbon accumulations within the big offshore ionian sea anticlines western greece contains important oil and gas shale reservoirs with a potential of unconventional exploration promising areas for hydrocarbons need systematic and detailed threedimensional seismic data exploration for conventional petroleum reservoirs through the interpretation of seismic profiles and the abundant surface geologic data will provide the subsurface geometric characteristics of the unconventional reservoirs their exploitation should follow that of conventional hydrocarbons to benefit from the anticipated technological advances eliminating environmental repercussions

climate and groundwater recharge during the last glaciation in an ice covered region a multitracer study of a small aquifer in northern switzerland indicates that the atmosphere in central europe cooled by at least 5 c during the last glacial period the relation between oxygen isotope ratios 18o and recharge temperatures reconstructed for this period is similar to the present day one if a shift in the 18o value of the oceans during the ice age is taken into account this similarity suggests that the present day 18o temperature relation can be used to reconstruct paleoclimate conditions in northern switzerland a gap in calculated groundwater age between about 17 000 and 25 000 years before the present indicates that during the last glacial maximum local groundwater recharge was prevented by overlying glaciers

seismic anisotropy of the crystalline crust what does it tell us the study of the directional dependence of seismic velocities seismic anisotropy promises more refined insight into mineral composition and physical properties of the crystalline crust than conventional deep seismic refraction or reflection profiles providing average values of p and s wave velocities the alignment of specific minerals by ductile rock deformation for instance causes specific types of seismic anisotropy which can be identified by appropriate field measurements vice versa the determination of anisotropy can help to discriminate between different rock candidates in the deep crust seismic field measurements at the continental deep drilling site ktb s germany are shown as an example that anisotropy has to be considered in crustal studies at the ktb the dependence of seismic velocity on the direction of wave propagation in situ was found to be compatible with the texture composition and fracture density of drilled crustal rocks

nature of crustal reflectivity along the dekorp profiles in germany in comparison with reflection patterns from different tectonic units worldwide a review reflectivity of the continental crust displays many different patterns the dekorp lines are used as a basis for comparing and reviewing reflectivity in different tectonic units the brittle upper crust generally exhibits only two types of reflectivity it is either rather transparent preferably in some extensional provinces or and it shows traces of thrust and shear zones of former or present ruptures as these zones have a low impedance interior with few exceptions their first reflection onsets have a negative polarity and evince strong but short signals which sometimes can be correlated over several kilometers the generally ductile lower crust displays a completely different reflectivity in warm extensional and thin crusts the lower part is full of reflecting lamellae it is suggested that this type of reflectivity has a thermo rheological origin the creation of lamellae must take place in a ductile material with contrasting impedance under extensional stresses it can be associated with mineral alignment and corresponding seismic anisotropy destruction of lamellae may take place by a cooling process transforming parts of the lower crust into a brittle regime small stresses might deform or break the lamellae and leave a certain dispersed reflectivity like that in some old and cold shields there are no observations of reflecting lamellae in the upper crust or in the upper mantle in all areas the moho is the last reflecting band reflection moho which most often is identical with the classical refraction moho there are isolated mostly dipping reflections in the uppermost mantle in zones where the last tectonic event a delamination or subduction was not succeeded by a heating process the uppermost mantle is brittle again in most areas and may keep the memory of a cold collision over billions of years

genesis of limestone megabreccias and their significance in carbonate sequence stratigraphic models a review a re appraisal of the factors controlling the deposition of carbonate megabreccias and their sequence stratigraphic significance is presented based on an examination of the mechanisms for instigating carbonate seafloor slope instability and a review of the depositional settings of these distinctive rock deposits limestone megabreccias have classically been interpreted as formed by the catastrophic collapse of high angle metastable oversteepened carbonate platform margins however a review of megabreccia occurrence shows that these deposits formed on a broad range of carbonate slope angles and that metastable oversteepened slopes are not necessary for their genesis a re evaluation constructed from first principles of mechanisms promoting submarine gravitational instability indicates that pore water overpressure of confined aquifer horizons beneath the seafloor rather than slope oversteepening is the critical control on megabreccia deposition catastrophic release of overpressure may initiate gravitational instability of previously kinematically stable slopes the relative importance of endogenic processes intrinsically linked to the depositional system and exogenic processes operating independently in generating megabreccias is assessed two particularly important mechanisms in generating megabreccias are endogenic processes causing overpressure at discrete hydrologically confined horizons beneath the seafloor during relative sea level falls and increases in stress as pore fluid drains from the sediment when the platform top becomes subaerially exposed during relative lowstands of sea level the increased likelihood of megabreccia genesis during relative sea level falls is supported by an empirical trend identified from a review of the stratigraphic distribution of documented megabreccias exogenic causes of gravitational instability with inherently random periodicity especially seismicity may account for the small number of documented megabreccias that do not conform to this underlying trend the proposed endogenic pattern favouring megabreccia deposition during relative sea level falls is important in a sequence stratigraphic context megabreccia deposits may build volumetrically significant toe of slope wedges and aprons during relative lowstands of sea level partially compensating for the decrease loss in the supply of fresh granular sediment as the platform top carbonate factory contracts lowstand wedges and aprons in carbonate systems therefore generally differ in composition from equivalent highstand deposits in being composed not of calciturbidite deposits but of megabreccias cannibalized from the upper slope

proterozoic sutures and terranes in the southeastern baltic shield interpreted from babel deep seismic data abstract a hitherto unknown terrane and its bounding sutures have been revealed by a combined study of normal incidence and wide angle seismic data along the babel profile in the baltic sea this intermediate terrane is situated between a northern terrane of svecofennian age and a southwestern terrane of gothian age it is delimited upwards by two low angle and oppositely dipping sutures and occupies mainly middle and lower crustal levels with a width of 300 km at moho level the 1 86 ga suture against the northern terrane is imaged by a prominent almost continuous ne dipping crustal reflection from 3 5 to 14 s twt over 175 km where it downlaps on the moho sub moho velocities change from 8 2 to 7 8 km s 0 2 over less than 25 km a relatively strong ne dipping normal incidence and wide angle reflection at 19 23 s twt indicates that the suture extends into the upper mantle the pervasive ne dipping reflection fabric of the intermediate terrane is interpreted as shear zones that developed during collision and possibly were reactivated by later events high poisson s ratios suggest a mafic composition or high fluid content the 1 86 ga collision was probably succeeded by continental break up and removal of an unknown continent except for the intermediate terrane subsequent formation of an east dipping subduction zone further to the west led to the emplacement of 1 81 1 77 ga old granitoids in the southern part of the transscandinavian igneous belt the 1 65 1 60 ga suture against the southwestern terrane is defined by a semi continuous band of strong sw dipping reflections between 3 and 8 s twt over 65 km which are interpreted as a low angle thrust zone along which gothian crust overrode the intermediate terrane the identification of three individual seismic terranes in the southeastern part of the baltic shield provides new evidence for palaeoproterozoic plate tectonic processes

late glacial and early holocene palaeoenvironmental changes in geneva bay lake geneva switzerland abstract detailed interdisciplinary investigations demonstrate that geneva bay lake geneva sediments clearly record important palaeoenvironmental and palaeoclimatic changes occurred during the late glacial and early holocene sediments are in fact differentiated by changes in texture mineralogical and geochemical composition distal turbidite and glacial rhythmite deposition associated with wind transported sediment supply dominate during the oldest dryas these were replaced during the allerod by detrital settling of sediment from turbid water and by endogenic calcite precipitation the younger dryas climate reversal for the first time in lake geneva well documented by a pollen record was characterized by an increase in detrital supply owing to increased run off from the bay slopes surrounding and within the catchment area caused by thinning of vegetation cover a brief pause in endogenic precipitation related to decreased productivity also occurs at this time endogenic carbonate sedimentation abruptly resumed at the start of the preboreal biozone in response to the rapid global climatic warming in the middle preboreal renewed detrital sedimentation is interpreted as the sedimentological response to increased erosion in high altitude regions of the catchment area caused by a minor early holocene cooling phase preboreal oscillation and interrupts the trend towards increasing endogenic calcite precipitation favourable limnic conditions are reached during the late preboreal when diatom calcite rhythmites begin to form stable isotope analysis 18 o 13 c in bulk carbonate highlight the transition from clastic dominated to endogenic dominated sedimentation endogenic calcite deposition continues during the boreal biozone occasionally interrupted by local high energy sedimentary processes wave induced erosion and reworking of littoral deposits enhanced by progressive lake level lowering during the older atlantic biozone sedimentation was mainly dominated by low energy deposition creating enhanced conditions for the development of benthic fauna we will discuss the factors that make geneva bay an important site for recording the late glacial holocene climate and environmental changes the comparison with other swiss plateau lacustrine systems allowed us to emphasize the role played by the particular geographical and morphological setting of the site investigated and links with climate sensitive regions in the catchment area

very fast environmental changes at the pleistocene holocene boundary recorded in laminated sediments of lake gościz poland abstract this paper presents a reconstruction of the climatic changes at the pleistocene holocene transition recorded in the annually laminated sediments of lake go ci a z poland this reconstruction is based on pollen stable isotope mineralogical and chemical analyses of sediments made with a time resolution of 1 4 yr it reveals a sequence of abrupt climatic changes which preceded and followed the major warming around 11 500 cal bp our data show that the warming period was preceded by a 30 yr long phase of increased winter and decreased summer precipitation 11 550 11 520 cal bp about 11 520 cal bp a very brief period of wetter conditions occurred simultaneously with the beginning of the major warming however most of the first phase of the major warming 11 520 11 500 cal bp was characterised by a generally dry climate presumably due to lowered winter precipitation our records suggest that in this phase the warming concerned winter seasons mostly in the second phase 11 500 11 460 cal bp the warming also concerned summer seasons also a distinct increase of humidity is noted in this period which caused moistening of soils and despite enhanced evaporation and evapotranspiration inhibited the process of lake level drop the following 70 years 11 460 11 390 cal bp were rather dry which caused a distinct lowering of the lake and probably also of groundwater level in this period maximum biological productivity per unit area in the lake is noted the whole sequence of phases of rather different climates was completed within a time interval 160 years spanning two human lifes only one should stress that the transitions between the consecutive phases were rather abrupt lasting no longer than 10 years

development of rudist lithosomes in the coniacian lower campanian carbonate shelves of central southern italy high energy vs low energy settings abstract the late cretaceous shallow water depositional areas of southern tethys were complexes of unprotected shelves occupied by foramol assemblages that produced loose diagenetically stable bioclastic debris not involved in significant in situ cementation processes both storm and wind induced currents and waves exercised a strong control on the distribution of the shifting biogenic sediments which covered the open sea floor constituting large coalescing sheets of winnowed fine to coarse skeletal sands rudists spread over all shelf sectors from more open and external areas to more internal ones occupying different substrata and furnishing the bulk of the skeletal component by means of bioerosion processes they colonised mobile sediments giving rise to complex bodies with peculiar characteristics related to environmental parameters of the different sectors of the shelf on the basis of detailed sedimentological taphonomic and palaeontological data we recognised two main rudist rich depositional settings end members in the southern italy senonian rudist bearing successions in successions pertaining to hypothesised marginal shelf sectors characterised by high energy regime deposits rudist lithosomes are metric in thickness and lateral extent and lens like in morphology rich in bioerosion derived skeletal sand and silt rudists are highly diversified large elongated cylindro conical hippuritids mostly pertaining to the genera hippurites and vaccinites thick shelled radiolitids and plagioptychids largely dominate rudists clustered in life position are subordinate they often form small bouquets more commonly these organisms appear fallen but only barely reworked the rudist rich bodies laterally pass into clean bioclastic grainstone in which sedimentary structures related to current and or storm erosional action are common no evidence of significant original relief of the rudist bodies in respect of the neighbouring sediment can be recognised the submarine erosion and or the high energy processes operating presumably inhibited the aggradation of the tidal sediments above the marginal ones as a consequence the vertical facies organisation shows widespread subtidal cycles as commonly recognised in open shelves with ramp like morphologies in successions pertaining to more internal and or low energy sectors rudist rich beds rhythmically alternate with finer grained foraminiferal limestones small elevator radiolitids with oligospecific diversity are dominant mostly concentrated in clumps rudists in growth position are abundant although a large quantity of shells appear toppled with little reworking they may form laterally continuous biostromal shell beds sedimentary structures such as cross lamination and gradation are only occasionally present the resulting facies are commonly arranged in peritidal shallow subtidal cycles in which evidence of subaerial up to pedogenic modifications on a large and small scale and less frequently submarine exposure is common intermediate successions have been recognised characterised by deposits of silty sand plains which present intercalations of graded bioclastic storm related beds sedimentological characteristics seem to document more open conditions in which submarine erosion was intermittently prevalent in these successions rudist species that are commonly found both in high energy and low energy assemblages coexist

three dimensional interpretation of the ktb gravity and magnetic anomalies a combination of a closely spaced surface gravity survey with a high resolution helicopter aeromagnetic survey as well as borehole gravity and magnetometer measurements allowed a detailed three dimensional 3 d modeling of the anomalies at the ktb drill site the models could be constrained by new evidence from a 3 d seismic survey and by structural geology and petrophysical data from drill cores and cuttings the source body for the positive gravity anomaly consist of high density metabasite the vertical derivative of the bouguer anomaly does not resemble the aeromagnetic anomaly in all areas indicating that parts of the metabasites are more or less nonmagnetic surprisingly and confirming the observation in other deep drill holes into continental crystalline basement rocks pyrrhotite is the dominant magnetic mineral below a depth of about 300 m magnetite mainly occurs in the depth intervals 360 520 m and 7300 7900 m the lower interval causes the anomalous vertical gradient of 60 nt km for the geomagnetic field the occurrence of strongly magnetic minerals in the borehole down to about 3000 m correlates with the lithology while in the deeper parts it is more related to fissures and fault zones where chemical processes reduction oxidation are active

long term event stratigraphy of the apulia platform margin upper jurassic to eocene gargano southern italy abstract the upper jurassic to eocene apulia platform margin and the eastward transition to the adjacent basinal deposits are well exposed in the gargano promontory southern italy a carbonate block that is part of the slightly deformed foreland of the southern apennine thrust belt the long term stratigraphy of this margin and slope transect is punctuated by five major dynamic phenomena that subdivide the succession into six second order sequences these events include 1 a valanginian drowning unconformity 2 an early aptian albian drowning and demise of the platform 3 late albian cenomanian platform margin failures 4 a santonian campanian retreat of the platform margin and 5 eocene uplift and platform margin collapse the first event is documented worldwide and is probably eustatic in origin the second is concomitant with some oceanic anoxic events oae the last three processes are probably related to foreland reaction to subduction and collision in the dinarides and hellenides thrust belts the ultimate cause of the albian cenomanian failures is more problematic a worldwide eustatic regression is documented at this time but regional geology seems to favor tectonic uplift

fluid flow evolution in the albanide fold thrust belt insights from hydrogen and oxygen isotope ratios of fluid inclusions tectonic forces generated during thrust emplacement along active margins may drive complex fluid flow patterns in fold thrust belts and foreland basins isotope data 2h and 18o of fluid inclusions hosted in calcite vein cements are used to reconstruct regional fluid migration pathways in the albanide fold thrust system the calcite veins used in this study developed in a sequence of naturally fractured cretaceous eocene carbonate rocks as a result of episodic throughput of fluids from the early stages of burial onward the acquired fluid inclusion isotope data demonstrate that fluids circulating in the carbonates were derived from an underlying reservoir that consisted of a mixture of meteoric water and evolved marine fluids probably derived from deep seated evaporites the meteoric fluids infiltrated in the hinterland before being driven outward into the foreland basin and ascended as soon as fracturing induced a sufficient increase in permeability structural and petrographic observations provide time constraints for the various phases of fracture infilling and reveal an increasing dominance of meteoric water in the system through time as migration pathways shortened and marine formation fluids were progressively flushed out similar fluid flow evolutions have previously been recorded in various fold thrust belt settings elsewhere in the world