the mid norwegian margin a discussion of crustal lineaments mafic intrusions and remnants of the caledonian root by 3d density modelling and structural interpretation the high density lower crustal body lcb on the mid norwegian margin is almost universally interpreted to represent magmatically underplated material added to the crust during early tertiary opening of the ne atlantic the thickness of the lcb is uneven and its distribution along the margin is sharply limited by margin perpendicular lineaments three dimensional density modelling constrained by petrophysical and seismic data was performed to investigate the expression of the various lineaments bivrost jan mayen gleipne etc in the crustal architecture with and without the lcb the bivrost lineament separating the voring and lofoten margin segments is clearly expressed and so is arguably a lineament in the sw voring margin notably most of the lineaments can be interpreted as offshore prolongations of major onshore detachments stemming from late caledonian orogenic collapse an alternative interpretation of the lcb is thus that it represents high grade metamorphic rocks remnant from the caledonian root determining the nature of the lcb has profound effects for the volume estimate of magmatic rocks in the north atlantic igneous province and consequently also for the degree of crustal thinning and heat flow

extension crustal structure and magmatism at the outer voring basin norwegian margin regional analysis of new 2d and 3d multichannel seismic data has improved interpretation of the crustal configuration and structural style along the norwegian margin five domains with different structural styles and evolutions are defined along the outer voring basin 1 the nyk high naglfar dome 2 the north gjallar ridge 3 the gleipne saddle 4 the south gjallar ridge 5 the ran ridge early campanian early paleocene and early to mid cretaceous extensional events are evidenced timing of deformation and structural styles observed along each segment reflect a lateral variation of the rifted system probably affected by magma tectonic processes correlation with the deep structures of the outer voring basin shows that the shallow structure in that basin is directly controlled by a deep seated strong high amplitude reflection the t reflection marking the top of a high velocity body v p 7 km s 1 the relation between the lower crustal architecture and the subsurface basin structures has implications for the margin evolution and for the nature of the high velocity body

historical development of the gravity method in exploration the gravity method was the first geophysical technique to be used in oil and gas exploration despite being eclipsed by seismology it has continued to be an important and sometimes crucial constraint in a number of exploration areas in oil exploration the gravity method is particularly applicable in salt provinces overthrust and foothills belts underexplored basins and targets of interest that underlie high velocity zones the gravity method is used frequently in mining applications to map subsurface geology and to directly calculate ore reserves for some massive sulfide orebodies there is also a modest increase in the use of gravity techniques in specialized investigations for shallow targets gravimeters have undergone continuous improvement during the past 25 years particularly in their ability to function in a dynamic environment this and the advent of

driving mechanism of tectonic activity in the northern apennines quantitative insights from numerical modeling 1 it is shown by numerical modeling that the recent deformation pattern observed in the northern apennines mainly characterized by progressive eastward migration and bowing of the belt thrusting activity along its external front and tensional tectonics in the internal area can be reproduced at a first approximation by applying a belt parallel se nw compression to the chain which is simulated as a structural system characterized by a high mechanical strength and decoupled from the surrounding zones the above compressional regime obtained by imposing kinematic boundary conditions to the model causes the outward escape of crustal wedges from the chain in particular the northeastward displacement of the romagna marche umbria units and the counterclockwise rotation and northwestward displacement of the ligurian units this kinematics produces compressional to transcompressional strain along the external front of the chain and tensional to transtensional strain in the internal area in line with the observed features that concern both strain style and orientation of principal strains evidence and arguments supporting the kinematic boundary conditions and the model parameterization adopted in modeling are discussed numerical experiments have also been carried out to evaluate the influence of major features of the model parameterization and boundary conditions we have adopted in modeling and to provide insights into the possible influence of strong decoupling earthquakes in the central apennines on tectonic and seismic activity in the northern apennines

is there evidence for magmatic underplating beneath the oslo rift we challenge some of the long standing beliefs related to the permian oslo rift structure often referred to as a case example type locality for continental rifting the crustal structure of the oslo rift was long presumed to be thinned proterozoic crust overlying a permian high density layer interpreted as magmatic underplating new data support an alternative view of the crustal structure in the oslo rift region the bouguer gravity high in the region shows a strong asymmetry a steep westward facing gradient to the west of the rift and a much gentler eastern gradient we present a 3d density model based on petrophysical and seismic information which accounts for the bouguer gravity high using an eastward extension of old precambrian structures without invoking a prominent magmatic underplated structure reactivation of old pre rift structures appears to be an important feature affecting the evolution and location of the permo carboniferous oslo rift

early oligocene stratigraphic turnover on the west africa continental margin a signature of the tertiary greenhouse to icehouse transition the post rift stratigraphy on the west african margin is characterized by aggradation of a carbonate ramp during late cretaceous to eocene epochs and progradation of a terrigenous wedge from oligocene to the present such first order structure has been attributed in the past to geodynamic forcing however comparison of the stratigraphic record of the margin with eustasy 18o and 87sr 86sr curves shows a close temporal relationship with the tertiary climate cooling an increase of continental weathering and a long term lowering of sea level we suggest that the transition from low amplitude high frequency sea level changes during the greenhouse period to high amplitude high frequency sea level changes during the icehouse period may account for i the switch from an aggrading carbonate ramp to a prograding clastic wedge and ii the enhanced continental weathering and increased terrigenous influx to the margin

crustal structure off norway 62 to 70 north abstract extensive geophysical surveys have been undertaken on the volcanic passive continental margin offshore norway between 62 and 70 n during the last 25 years three main margin segments have been identified the lofoten vesteralen margin the voring margin and the more margin the main features of the margins are prominent marginal highs including seaward dipping reflector sequences and an up to 22 km thick volcanic and transitional crust prominent escarpments the voring plateau escarpment and the faeroe shetland escarpment and up to 12 km deep post jurassic sedimentary basins east of the escarpments velocity depth solutions from about 250 sonobuoys expanding spread profiles and refraction profiles have been compiled and contoured isovelocity horizon contour maps and velocity transects outline a crust which broadly thickens from an oceanic crust with a normal oceanic type velocity structure to a ca 35 km thick continental crust with a continental velocity structure beneath the norwegian coast anomalous features include local crustal thickening below the more and vering marginal highs and high velocity bodies in the lower crust in the extension of the precambrian lofoten vesteralen archipelago the free air seasat derived gravity anomalies show a good correlation with the high velocity bodies and show prominent ne trending highs from the rockall plateau porcupine plateau region over the more voring and lofoten vesteralen margins to the southwestern barents sea

the role of mesozoic rifting in the opening of the ne atlantic evidence from deep seismic profiling across the faroe shetland trough the fast deep seismic reflection profile traverses the whole width of the faroe shetland trough the principal target of the profile was the structure of the crust beneath the faroe basalts in this region bright reflections are seen from between 7 and 9 km depth beneath the basalts dipping westwards in the opposite direction to the dip of the basalts and reflections within the basalts these sub basalt reflections are regarded as originating from near top basement the moho has not been imaged beneath the basalts possibly because of the absence of any impedance contrast at the base of the crust the profile shows that the basement of the faroe shetland trough thins to c 10 km beneath the centre of the trough thinning of the crystalline basement is probably the result of more than one phase of extension the most recent of which occurred in the mid to late cretaceous extension appears to have been concentrated on a series of east dipping normal faults cutting through the basement these faults may have originated during a precambrian rifting event it is suggested that opening of the ne atlantic occurred to the west of the faroe islands as mesozoic rifting in the faroe shetland trough had strengthened the lithosphere in this region

crustal structure across the more margin mid norway from wide angle seismic and gravity data the more margin in the ne atlantic represents a dominantly passive margin with an unusual abrupt transition from alpine morphology onshore to a deep sedimentary basin offshore in order to study this transition in detail three ocean bottom seismometer profiles with deep seismic reflection and refraction data were acquired in 2009 two dip profiles which were extended by land stations and one tie profile parallel to the strike of the more trondelag fault complex the modeling of the wide angle seismic data was performed with a combined inversion and forward modeling approach and validated with a 3d density model modeling of the geophysical data indicates the presence of a 12 15 km thick accumulation of sedimentary rocks in the more basin the modeling of the strike profile located closer to land shows a decrease in crustal velocity from north to south near the coast we observe an intra crustal reflector under the trondelag platform but not under the slorebotn sub basin furthermore two lower crustal high velocity bodies are modeled one located near the more marginal high and one beneath the slorebotn sub basin while the outer lower crustal body is modeled with a density allowing an interpretation as magmatic underplating the inner body has a density close to mantle density which might suggest an origin as an eclogized body formed by metamorphosis of lower crustal gabbro during the caledonian orogeny the difference in velocity and extent of the lower crustal bodies seems to be controlled by the jan mayen lineament suggesting that the lineament represents a pre caledonian structural feature in the basement

the structure of the faeroe shetland trough from integrated deep seismic and potential field modelling in the faeroe shetland trough thick basaltic lava units make it difficult to image underlying structure with conventional seismic profiles we have therefore used potential field modelling to estimate crustal structure along the fast deep seismic line and other regional transects we introduce the additional constraints of crustal isostasy to gravity models and the observations of the polarity of magnetic remanence within the lava pile to magnetic models the crustal stretching factor ranges up to 3 along the fast traverse and our model also suggests that a sedimentary section with a thickness of up to 3 4 km is present beneath a c 2 km basalt layer on the faeroese shelf

on the use of different methods for estimating magnetic depth magnetic depth estimation plays an important role in magnetic interpretation a complete quantitative interpretation of potential fields data aims to estimate three types of information about sources of geologic interest the depth the dimension and the contrast in the relevant physical property such an interpretation suffers from inherent ambiguity it is impossible to obtain all three types of information simultaneously without other a priori information in many applications we are often interested in depth more than either dimension or physical property contrast thus different quick methods have been developed over half a century to estimate the magnetic depth these methods work for simplified source geometries dimensions and are independent of the susceptibility contrast the depths estimated by some method can be used as the final quantitative solution in some ideal situations i e the anomaly is well isolated and the noise is insignificant or well removed it is more often that estimated depths provide a good starting point for a genuine structural interpretation e g an interactive modeling or a constrained inversion in petroleum exploration for example the structural surface interpreted from magnetic depth estimates is often the best available approximation to the true crystalline i e metamorphic igneous basement configuration basement depth or equivalently sedimentary thickness is a primary exploration risk parameter estimates of basement depth are directly applicable to basin modeling e g source rock volume estimation and thermal maturity applications e g source rock burial depth basement structure inferred from magnetic depth estimates provides insight into the evolution of more recent sedimentary features e g sub minibasin compartmentalization salt structure distribution kinesis localization of reservoir bearing structures in areas where the inherited basement fabric architecture has affected either continuously or episodically basin evolution and development examples of the latter are the prolific passive rifted margins of the southern atlantic ocean a basin s plumbing often exploits faults and fractures within the sedimentary

orbital scale climate change and glacioeustasy during the early late ordovician pre hirnantian determined from δ18o values in marine apatite this study focuses on the 10 m y before the latest ordovician hirnantian glaciation we test whether orbital scale climatic fluctuations controlled the growth and melting of continental glaciers resulting in glacioeustatic sea level changes and the development of widespread marine sedimentary cycles 18o values of conodont apatite from 14 late ordovician katian cycles range from 17 to 21 isotopic values decrease and are lowest in the deepest water facies and increase and are highest in shallow water facies supporting the hypothesis that glacioeustasy was the dominant control on water depth changes measured intracycle 18o changes of 0 7 2 5 were controlled by changes in ice volume 60 m sea level changes sea surface temperatures 5 c and potentially local increases in seawater evaporation during drier and or windier glacial stages these interpreted orbital scale climate changes and resultant large glacial ice volume changes support recent interpretations of a dynamic and prolonged ordovician greenhouse to icehouse transition

the use of potential field data in revealing the basement structure in sub basaltic settings an example from the more margin offshore norway this study investigates the utility of the potential fields gravity and magnetics in volcanic settings as observed on the more margin synthetic models are used to investigate the effect of volcanics on the gravity and magnetic fields the focus is on detecting sub basaltic basement structures the methods applied to the models are euler deconvolution on magnetic data gravity gradients and integrated 3d gravity and magnetic forward modelling the same methods are used on the more margin and the results compared to the synthetic models the euler deconvolution on the magnetic signal does provide limited depth solutions in the volcanic environment and the use of different observation levels does not enhance the results forward gravity and magnetic models provide a valuable tool to estimate both the basalt and sub basaltic sedimentary thickness but are limited by the ambiguity inherent in potential field methods the use of gravity gradients significantly decreases the available model solutions and provides boundary detection even in sub basaltic settings

orbital calibration of the early kimmeridgian southeastern france implications for geochronology and sequence stratigraphy classic stratigraphic methods rarely provide high resolution correlations between intrabasinal sedimentary sequences which are important to understand the origin of sedimentation process and its environmental change in this study we investigate high resolution cyclostratigraphic correlation from magnetic susceptibility in two early kimmeridgian pelagic marl limestone successions at la meouge and chateauneuf d oze southeastern france spectral analysis reveals the complete suite of orbital frequencies precession obliquity and eccen tricity with the marl limestone couplets being primarily pre cession driven frequencies detected by the spectral analysis are similar between the sections but their relative amplitudes are somewhat different linked to the palaeoenvironmental position and the completeness of the sections high resolution correlation reveals two significant hiatuses at chateauneuf d oze early kimmeridgian platynota hypselocyclum and div isum ammonite zones were orbitally calibrated for an ultra high resolution assessment of geological time finally strong 405 kyr eccentricity cycles are recorded as third order depositional sequences

recognising the taghanic crisis in the devonian terrestrial environment and its implications for understanding land sea interactions the late mid devonian eday marl formation from the orcadian basin scotland is a terrestrial equivalent of the marine devonian taghanic crisis the eday marl from orkney contains a high resolution archive of climatic change controlled by the relative strength of the seasonal insolation this includes several distinct and discrete episodes of basin flooding as demonstrated by the deposition of lacustrine laminites bedded evaporites marginal sheet flood sands and marine influenced bioturbated sheet sands these flooding events are intercalated with intense and sustained episodes of aridity indicating that insolation was relatively weak and the monsoon climate was ineffective at drawing in seasonal rainfall recognition of these basin flooding events has enabled the definition of three new units the wha taing roeberry and berstane members the eday marl formation can be correlated offshore and also recognised within marginal facies as an aeolian intercalation an environmental hydrological and climatic interpretation is given for the different events recognised in the eday marl this sequence of events when combined with the palynological age dates enables a detailed correlation to be made with the marine tully formation of new york state this suggests that regressions forced by climatic aridity are significant for understanding the deposition of the shallow water carbonates of the tully formation in what is otherwise a clastic depositional system comparison with the pelagic marine record shows that the latter as yet gives only limited resolution of the taghanic crisis recognising the taghanic as a rapid alternation of cool arid and relatively hotter pluvial events provides a unifying explanation for the associated collapse in the terrestrial vegetation and the parallel faunal changes in the marine realm

intraplate volcanism in the danube basin of nw hungary 3d geophysical modelling of the late miocene pasztori volcano three dimensional geophysical modelling of the early late miocene pasztori volcano ca 11 10 ma and adjacent area in the little hungarian plain volcanic field of the danube basin was carried out to get an insight into the most prominent intra crustal structures here we have used gridded gravity and magnetic data interpreted seismic reflection sections and borehole data combined with re evaluated geological constraints based on petrological analysis of core samples from available six exploration boreholes the volcanic rocks consist of a series of alkaline trachytic and trachyandesitic volcanoclastic and effusive rocks the measured magnetic susceptibilities of these samples are generally very low suggesting a deeper magnetic source the age of the modelled pasztori volcano buried beneath a 2 km thick late miocene to quaternary sedimentary sequence is 10 4 0 3 ma belonging to the dominantly normal c5 chron our model includes crustal domains with different effective induced magnetizations and densities uppermost 0 3 1 8 km thick layer of volcanoclastics underlain by a trachytic trachyandesitic coherent and volcanoclastic rock units of a maximum 2 km thickness with a top situated at minimal depth of 2 3 km and a deeper magmatic pluton in a depth range of 5 15 km the 3d model of the danube basin is consistent with observed high z magnetic anomalies above the volcano while the observed bouguer gravity anomalies correlate better with the crystalline basement depth our analysis contributes to deeper understanding of the crustal architecture and the evolution of the basin accompanied by alkaline intraplate volcanism

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

potential field data in integrated frontier basin geophysics successes and challenges on australia s continental margin abstract offshore frontier sedimentary basins are characterised by a lack of constraining geological and geophysical data this lack of data is generally the result of deep water 500 m difficult geology volcanics and salt remoteness and harsh met ocean conditions these characteristics present significant challenges to marine surveying which means that frontier basins tend to be underexplored with continuing interest in exploration for energy resources in frontier regions many frontier basins around the world have been the focus of increasingly sophisticated geophysical studies that integrate a range of methodologies including those based on potential field gravity and magnetic data underexplored frontier basins around australia s continental margin have received increased attention during the last decade largely as a result of government funded programs of precompetitive data acquisition and analysis the components of this work that have relied heavily on potential field data include first pass depth to basement estimation using spectral techniques applied to magnetic data enhancement of gravity and magnetic images to aid the identification of basin depocentres and to facilitate onshore offshore geological interpretation of basement structure multi scale edge detection applied to gravity and magnetic data to aid the interpretation of basement structure 3d forward and stochastic inverse modelling of gravity data to guide seismic interpretation of sediment thickness and basement structure and using supercomputers for high resolution regional scale 3d inverse modelling of magnetic and gravity data to constrain the physical properties of the crust despite the additional insight offered by this work efforts to understand frontier basins are not without challenges one of the most fundamental of which is to ensure that non specialists are not misinterpreting data e g wrongly interpreting artefacts arising from specific processing the other main challenge in australian frontier basins arises from a lack of constraints on crustal structure this leads to significant ambiguity when using gravity data to infer sediment thickness or to understand the nature of basement this ambiguity could be vastly reduced through the acquisition of seismic refraction data that focuses on imaging crustal structure further opportunities exist in using alternative methods for automated depth to basement estimation incorporating process oriented rather than static potential field modelling and in applying 3d forward and inverse gravity and magnetic modelling to other australian frontier basins

rate and synchronicity of environmental changes on a shallow carbonate platform late oxfordian swiss jura mountains recent global change occurs within decades and leaves a significant imprint on shallow carbonate platforms to what extent can rate and synchronicity of environmental changes in the past be evaluated in order to allow comparisons with the processes and products of today sections of a carbonate dominated platform of late oxfordian age have been logged in detail in the swiss jura mountains the time frame based on ammonite biostratigraphy and the hierarchical stacking of the sedimentary sequences suggests that these formed by low amplitude high frequency sea level changes in tune with the orbital cycles the smallest unit the elementary sequence can thus be attributed to the 20 kyr precession cycle by identifying sequence stratigraphic elements such as maximum flooding surfaces within an elementary sequence an even higher time resolution can be obtained and reconstructions of changes in water depth and sea level are attempted sedimentation rates were highly irregular and discontinuity surfaces are common correlation of such surfaces from one section to the other is tentative because they could also have formed locally and are not necessarily synchronous on the scale of elementary sequences the vertical facies evolution permits interpretation of changes in water depth which were produced by eustatic sea level changes allocyclic and or by autocyclic processes the distribution of clay minerals indicates changes of sea level as well as of rainfall in the hinterland biotic changes were controlled by water depth and water quality and also by nutrient and clay input carbon and oxygen isotopes do not show significant shifts within the elementary sequences the original ecological mineralogical and geochemical signals have partly been homogenized because of time averaging through bioturbation and through reworking by storms and because of diagenetic modifications consequently there is potential to interpret environmental changes on the studied carbonate platform but the time resolution is not better than a few thousand years the rates and the synchronicity of the processes leading to the observed environmental changes can thus be estimated only within this time frame

cool episodes in the cretaceous exploring the effects of physical forcings on antarctic snow accumulation the question whether large scale glaciations on antarctica were possible in a late mesozoic greenhouse climate such as the late cretaceous is an intriguing one the most recent years have provided an increasing number of studies investigating the growth and decay of paleo continental ice sheets on antarctica possibly large enough to affect sea level since the outcome of these studies doesn t provide a basis for a conclusive decision we have performed a number of model runs using an atmospheric general circulation model agcm to test whether large volumes of snow might have accumulated even under late cretaceous greenhouse conditions by varying orbital parameters as well as topography and atmospheric co2 concentrations our models indicate the possibility of an antarctic ice shield build up large enough to drive sea level fluctuations on the order of tens of meters within 20 000 years this is supported under the assumption of pco2 levels 800 ppm low insolation and elevated topography the growth of a major antarctic ice sheet would be possible on reasonable time scales to accumulate about half the present day snow ice volume which is required to explain the documented shifts in oxygen isotopes our model results suggest a time span between 20 000 and 80 000 years for these ice volumes to accumulate

forward modelling of carbonate platforms sedimentological and diagenetic constraints from an application to a flat topped greenhouse platform triassic southern alps italy abstract quantitative analysis of depositional systems using numerical models can provide insights into the interaction of sedimentological and diagenetic processes difficult to interpret from observation of the geological products alone numerical models can highlight the interactions between controlling parameters and generate best estimate simulations of case studies from the geological record different data sources e g outcrop data uniformitarian constraints paleogeography need to be considered in the process of defining the parameters required to produce models that honour individual case studies we present a best estimate forward model of a high relief triassic carbonate platform southern alps italy generated using carb3d a 3d process based forward modelling package able to simulate sedimentary facies geometries and early diagenesis of isolated carbonate platforms the parameters used for the presented forward model have been deduced by the study of architectural sedimentological and diagenetic features of the platform and by data from modern and ancient analogues sensitivity analysis is used to tune values of the parameters within ranges defined from field laboratory and uniformitarian constraints critical evaluation of the model allowed 1 verification of the validity of the used parameters 2 evaluation of the interaction between controlling parameters 3 development of a numerical model that can be used for quantitative elaborations furthermore the process of generating the numerical model required a detailed interpretation of field and laboratory data crucial to define the required input parameters modelling the studied carbonate platform also enabled evaluation of the effects of the interaction between productivity environmental energy and creation of accommodation space promoting the understanding of their role on the architecture of carbonate systems forward modelling also allows the integration of data from conventional data sets with data from present day observations and seismic geometries promoting a transition from a qualitative to a semi quantitative quantitative sedimentological approach forward models can further be used to parameterise petrophysical properties of complex geobodies with potential application for the management of georesources

quantification of high frequency sea level fluctuations in shallow water carbonates an example from the berriasian valanginian french jura abstract when quantifying sedimentary processes on shallow carbonate platforms it is important to know the high frequency accommodation changes through time accommodation changes in cyclic successions are often analysed by simply converting cycle thickness to fischer plots this approach is not satisfactory because it does not account for differential compaction possible erosion sea level fall below the depositional surface or subtidal cycles an attempt is made here to reconstruct a realistic high frequency accommodation and sea level curve based on a detailed facies and cyclostratigraphical analysis of middle berriasian to lower valanginian sections in the french jura mountains the general depositional environment was a shallow marine carbonate platform on a passive margin our approach includes the following steps 1 facies interpretation 2 cyclostratigraphical analysis and identification of milankovitch parameters in a well constrained chronostratigraphic framework 3 differential decompaction according to facies 4 estimation of depth ranges of erosion and vadose zone 5 estimation of water depth ranges at sequence boundaries and maximum flooding intervals 6 estimation of mean subsidence rate 7 classification of depositional sequences according to types of facies evolution catch up catch down give up or keep up 8 classification of depositional sequences according to long term sea level evolution rising stable falling 9 calculation of eustatic sea level change for each depositional sequence using the parameters inferred from these scenarios assuming that sea level cycles were essentially symmetrical which is probable in early cretaceous greenhouse conditions 10 calculation of a sea level curve for each studied section 11 comparison of these curves among each other to filter out differential subsidence 12 construction of a composite eustatic sea level curve for the entire studied platform 13 spectral analysis of the calculated sea level curves limitations of the method are those common to every stratigraphic analysis however the method has the potential to improve the original cyclostratigraphical interpretations and to better constrain the high frequency sea level changes that control carbonate production and sediment fluxes

indian ocean circulation and productivity during the last glacial cycle abstract the indian ocean is an important part of the global thermohaline circulation system receiving deep waters sourced from the southern ocean and being the location of upwelling and surface ocean current flow which returns warm and salty waters to the atlantic it is also an ideal location to reconstruct the link between thermohaline circulation and deep water nutrient contents no mixing occurs between major deep water masses along flow paths within the indian ocean so changes in water mass provenance reflect changes in deep ocean circulation while nutrient contents reflect addition and dissolution of organic matter we present neodymium nd and carbon c isotope records from an equatorial indian ocean core sk129 cr2 spanning the last 150 kyr the nd isotope record shows that an increased proportion of north atlantic deep water nadw reached the indian ocean during interglacials marine isotope stages mis 1 and 5 and a reduced proportion during glacials mis 2 4 and 6 and also that changes occurred during mis 3 the magnitude and timing of deglacial and some mis 3 variability is very similar to those in the rc11 83 tno57 21 south atlantic deep cape basin nd isotope record piotrowski et al 2005 since the deep cape basin is oceanographically upstream of the indian ocean from a deep water circulation perspective the nd isotopes suggest that atlantic meridional overturning circulation changes were effectively propagated from the southeastern atlantic into the central indian ocean via the southern ocean comparison of the nd and c isotope records shows that deep ocean circulation was decoupled from nutrient content changes on glacial interglacial timescales in particular suggesting higher productivity during mis 5 increased equatorial productivity during mis 5 is supported by benthic infaunal epifaunal foraminiferal 13 c gradients as well as benthic foraminiferal 13 c gradients along deep water flow concurrent warming indicated by planktonic foraminiferal mg ca during mis 5 at the site is consistent with changing thermocline temperature and may indicate a link to surface ocean hydrographic changes

environmental control on the end of the dolomia principale hauptdolomit depositional system in the central alps coupling sea level and climate changes abstract the norian in the western tethys is characterised by the deposition of early dolomitised inner platform facies dolomia principale hauptdolomit dp hd bordered on the landward side by terrigenous coastal deposits keuper and on the seaward side by calcareous backreef and reefal facies dachstein limestone passing basinward to open sea sediments hallstatt facies the inner carbonate platform is locally lombardy basin carnic alps central austroalpine dissected by normal faults leading to the development of intraplatform troughs close to the norian rhaetian boundary sedimentation records an abrupt environmental change both on platform top and basins all over the western tethys e g western carpathians transdanubian range alps central apennine the top of the dolomia principale locally emerged reflecting a major eustatic sea level fall emersion is recorded in favourable settings by the development of polycyclic paleosols up to 30 m thick in the norian intraplatform basins the succession is capped by 4 to 8 m of thin bedded fine grained limestones yielding abundant remnants of fishes and terrestrial reptiles fossil concentration as well as sedimentological features is indicative of reduced sedimentation rates due to decreased carbonate production induced by the emersion of the platform top the sea level fall was followed by deposition of mixed fine grained siliciclastic carbonate successions e g riva di solto shale kossen beds rhaetavicula contorta beds fatra formation stratigraphic evidence indicates a dry climate in the western tethys during the norian as indicated by the presence of evaporites burano apennine and arid to semi arid coastal to playa settings upper keuper germany in contrast the basal layers of the basinal shales show evidence of wet climate the end of the norian depositional system records two different phenomena 1 an important sea level fall was responsible for the emersion of the platform top and deposition of a condensed horizon in the basins and 2 transition from dry to humid climate the observed evolution is explained with a global cooling which caused the rapid sea level fall responsible for the abrupt end of the dp hd depositional system and the shift of the boundary between arid and temperate climate belts which modified the distribution and amount of rainfall triggering the deposition of shales along the western tethys margin

geometry of eclogite facies structural features implications for production and exhumation of ultrahigh pressure and high pressure rocks western gneiss region norway 1 well preserved eclogite facies structural features in metamorphosed gabbro and diorite gneiss in baltica crust formed at a minimum depth of 60 70 km during the scandian orogeny allow direct inferences to be made regarding the geometry of folds kinematics and original structural orientations related to production and exhumation of high pressure rocks folds associated with eclogite facies fabrics are isoclinal to tubular with axes parallel to the trend of a stretching lineation strain estimates and l s or l s fabrics indicate that these structures were formed in a constrictional strain field locally they are well preserved in eclogite facies mylonite zones at least 40 m thick that cut proterozoic gabbro and adjacent gneiss where steeply dipping they show a north side up shear sense across a younger northeast trending shallowly plunging amphibolite facies anticlinorium formed in a constrictional noncoaxial strain field where original structural facing direction can be inferred small circle rotation of the eclogite facies lineation about the anticline axis indicates that the relative motion vector of baltica with respect to overlying imbricated crust and laurentia was oriented 320 in a present day reference frame this result is identical to the orientation of the relative motion vector estimated from paleomagnetic plate reconstructions and consistent with late silurian to early devonian oblique sinistral convergence between baltica and laurentia results of this study indicate that coherent baltica crust at 60 70 km depth experienced subvertical and horizontal shortening while extending toward the foreland during tops southeast thrusting parallel to plate motion high pressure rocks were progressively imbricated and stacked along eclogite facies mylonite zones with the deforming zone separating coherent baltica crust from imbricated basement above the constrictional strains under eclogite facies conditions are interpreted to have resulted from stretching associated with sinking of the cool dense mantle lithosphere

neodymium isotopic variations in northwest pacific waters abstract four vertical profiles of the concentration and isotopic composition of nd in seawater were obtained in the western north pacific two profiles from the kuroshio current regime showed congruently that although the nd concentration increases gradually with depth its isotopic composition varies significantly with depth depending upon the water mass occupying the water column the high salinity kuroshio waters originating from the north pacific tropical water nptw carry the least radiogenic nd nd 7 4 to 8 7 to this region at 250 m from the western margin continental shelves most likely from the east china sea the nd isotopic compositions in the north pacific intermediate water npiw that occurs at 600 to 1000 m in the subtropical region are fairly uniform at nd 3 7 the profile data from the 38 to 40 n kuroshio oyashio mixed water region off sanriku of honshu japan also suggest that the newest npiw with nd 3 2 is formed there by the mixing of various source waters and the radiogenic component of nd is derived mainly from the oyashio waters in the pacific deep water pdw below 1000 m the nd isotopic composition is neither vertically nor horizontally homogeneous suggesting that it serves as a useful tracer for sluggish deep water circulation as well two profiles from the izu ogasawara trench showed a minimum nd value at 2000 m suggesting that there exists a horizontal advective flow in the vicinity of honshu japan there is some evidence from other chemical properties to support this observation the waters below 4000 m including those within the trench in the subtropical region have nd values of around 5 suggesting that the deep waters are fed from the south along the western boundary ultimately from the antarctic bottom water aabw in the south pacific this extends up to 40 n along the japanese islands in the subarctic region 42 n the waters have more radiogenic nd with nd 4 0 throughout the water column presumably due to the supply of nd by weathering in such igneous provinces as the kuril kamchatska aleutian island chain the lateral inhomogeneity of the nd isotopic composition in pdw suggests that there may be different circulation and mixing regimes in the north pacific basin

basin structure on the norwegian margin from analysis of digitally recorded sonobuoys during r v robert d conrad cruise 21 a large number of sonobuoys were recorded in the voring more and adjacent basins at the margin off norway the digital sonobuoy data have been transformed into the domain of intercept time tau and ray parameter p and inverted by the tau sum method to obtain better definition of the near seafloor velocities using also the precritical energy a move out correction has been applied to the tau p data conventional analyses of the x t data were also performed in general the various types of analyses complement each other and should be used interactively together with forward modeling to obtain the optimal velocity depth function the sonobuoy results have outlined in a regional sense the pre cenozoic sedimentary basin at the margin this basin attains a maximum sediment thickness of 8 10 km of which only the upper half is defined by seismic reflection profiling at the outer margin the marginal escarpments form major discontinuities in the lateral velocity distribution the survey has proven that sonobuoy profiles recorded during standard seismic reflection profiling in major marginal basins may provide important new information particularly about the deeper parts of the basins that is not directly available from the reflection profiles

carbonate production by rudist bivalves the record of late barremian requieniid communities from provence se france abstract rudist bearing sediments from platform carbonates of late barremian age early cretaceous cropping out in the marseille region provence se france were investigated on a 46 km wide transect after seven stratigraphic sections to quantify the role of rudists in the corresponding stratigraphic system by using various proxies the regional stratigraphic contribution of total thickness of rudist beds is relatively high 43 1 each rudist community type possesses a specific skeletal contribution of skeletal content in the range of 19 2 to 31 5 at a stratigraphic scale including rudist rich and rudist free beds the skeletal contribution drops to 13 8 this value is derived from the standard skeletal contribution obtained for each community type combined with the stratigraphic contribution of rudist beds in vertical successions and horizontal stratigraphic units a closely related value 12 8 is obtained from calculations using specific lateral dimensions of rudist bodies and their spacing i e modules depending on community types each community has a particular potential quantitative contribution to the overall regional stratigraphic system rudist production is deduced from the cyclostratigraphic approach of accumulation rates for each community type estimates of caco 3 net production are in the range of 19 to 50 kg m 2 ka 1 these values are very low when compared with those obtained at a biological scale for modern bivalves late cretaceous rudists and recent coral reefs the geological scale used for our estimates may partly account for this difference whereas low accommodation rates linked to cretaceous greenhouse conditions appear a potential important factor in this respect the low net production of requieniid dominated communities sediment dwellers not framework builders also reflects their limited sedimentogenetic power

geophysical response of flood basalts from analysis of wire line logs ocean drilling program site 642 voring volcanic margin analysis of wire line logs at ocean drilling program site 642 the deepest scientific hole yet drilled in an offshore large igneous province lip reveals the main features of the extrusive complex constructed during formation of a volcanic margin a characteristic cyclic log response images tholeiitic lavas and thin tuffs corresponding to the seaward dipping reflectors in the seismic record flows are 0 6 18 5 m thick while most sediments are 2000 m focused resistivity kicks the large flow scale variations in physical properties show that representative core measurements must be densely sampled both on flow and sequence scales site 642 log responses appears typical for the north atlantic volcanic province and other lips but differs from logs in deep ocean crustal holes principal differences in log responses reflect mode of crustal emplacement and alteration hence site 642 forms a reference hole for extrusive constructions on oceanic lips

facies architecture of an early jurassic carbonate platform slope jbel bou dahar high atlas morocco the plateau of jbel bou dahar high atlas morocco represents an outstanding example of a well preserved early mesozoic carbonate platform field observations of the large scale sedimentary structures and the arrangement of lithofacies associations within the mid and lower slope were combined with detailed microfacies analyses and gamma ray measurements the investigations were carried out in order to 1 resolve the sequence stratigraphic architecture of the slope and 2 reconstruct the sediment export patterns and depositional processes related to high frequency sea level variations the slope strata are arranged into two different types of lithofacies associations that are bounded by characteristic discontinuities and show a specific occurrence along the investigated slope section the steep 8 18 mid slope is dominated by thick to medium bedded limestone successions that were able to maintain a high angle of repose due to their detrital composition the sediment packages are bounded by basal low angle unconformities and wedge out within the lower slope or thin into the adjacent basin as single carbonate layers the sediments are characterized by coarse grained and poorly sorted floatstones to rudstones which show low gamma ray values and contain components derived mainly from the platform edge the facies associations were interpreted as debris flow deposits that were exported during sea level lowstands when the flattened platform top and extended parts of the margin were exposed and sediment production was restricted mainly to the outer margin and upper slope section in contrast the gently dipping lower slope 4 18 is characterized by rhythmic limestone marl alternations that show increasing thicknesses with increasing distance from the platform from the lower part of the mid slope down the successions onlap the debris flow deposits forming a characteristic interfingering pattern of different lithofacies associations the medium to thin bedded carbonates of the limestone marl alternations comprise two different microfacies types 1 mudstones to wackestones with high gamma ray values and a mixed shallow marine to deep marine microfacies overlain by 2 well sorted arenitic packstones to grainstones with low gamma ray values and a shallow marine component composition the latter points to the platform interior and margin as primary source areas the shallow marine material was exported during sea level highstands when the carbonate factory included the entire platform margin and the flooded lagoons of the platform top during these periods the exported fine grained sediments could maintain only low angles of repose thus they bypassed the steep upper and mid slope sections developed into turbidites during downslope transport and were finally redeposited on the gently dipping lower slope and in the adjacent basin the architecture of the investigated slope area shows a characteristic interfingering of different facies associations that can be interpreted as genetic highstand and lowstand stratigraphic sequences the arrangement of these sequences along the slope as well as their composition were controlled by high frequency sea level fluctuations affecting the primary sediment production source area export patterns and sedimentary processes resulting in a shift of the depositional centers during different sea level stands

stratigraphic and oxygen isotope evidence for my scale glaciation driving eustasy in the early middle devonian greenhouse world article i nfo million year scale 3rd order depositional sequences few 10s to 100 m thick are common in the devonian marine record and are correlated between sedimentary basins and across widely separated continents implying a eustatic origin tectonically driven changes in mid ocean ridge spreading rates lengths are too slow to account for the calculated 3rd order rise fall rates and typical orbital frequencies 20 400 ky are too fast we analyzed oxygen isotopes from conodont apatite to evaluate if early middle devonian 3rd order sea level changes were controlled by paleoclimatically driven ice volume glacio eustasy and seawater temperature change thermo eustasy two successive depositional sequences in the western u s nevada and czech republic prague basin were sampled the 18 o values range from 17 8

seismic characteristics of basaltic extrusive and intrusive rocks transient voluminous basaltic volcanism is frequently associated with continental breakup forming so called volcanic rifted continental margins until recently most rifted margins were considered nonvolcanic however the improvement in seismic imaging techniques has shown that breakup volcanism is a common phenomenon at the november 1997 volcanic margin workshop in potsdam it was shown that at least 70 of the atlantic margins are volcanic a number which may apply to the indian ocean margins as well

milankovitch fluctuations on supercontinents observational and modeling studies support the concept of significant milankovitch fluctuations in the pre pleistocene many of these studies have focused on the mid cretaceous a time of high sea level and moderately dispersed land sea distribution in this paper we utilize a two dimensional energy balance climate model to examine the potential effects of milankovitch fluctuations for a supercontinent configuration early jurassic 195 ma we calculate that milankovitch variations can modulate the magnitude of summer warming by as much as 14 16 c on pangaea with large changes occurring in both the northern and southern hemispheres these values are comparable to or slightly larger than the calculated range for the present eurasian landmass for the pleistocene in addition mean monthly summer temperatures of 25 c reach 65 paleolatitude for hot orbit configurations this latter result suggests that some organisms may have been able to migrate into higher latitudes during precession half cycles of 10 000 years duration and a potential bias should be considered when evaluating evidence for past high latitude warmth our results indicate that general circulation model gcm runs for past time periods which use only one orbital configuration may be missing a substantial amount of the potential variance on large land masses

translating milankovitch climate forcing into eustatic fluctuations via thermal deep water expansion a conceptual link sedimentological evidence indicates metre scale cyclic changes in global sea level during mesozoic greenhouse climates the cyclicity is thought to be due to milankovitch forcing the absence of continental ice caps requires other mechanisms than glacier build up to explain these variations we propose that thermal expansion of the entire oceanic water column may partly explain the observed sea level variations on milankovitch timescales using existing climate model results we show that an increase in deep water temperature of 2 c and a corresponding sea level rise of 1 7 m by thermal expansion can be induced by milankovitch forcing via increased formation of warm deep waters in low latitudes

on the origin of cenozoic and mesozoic third order eustatic sequences abstract the origin of third order eustatic sequences is reviewed by comparing recent sequence stratigraphic data to the latest best constrained astronomical model middle eocene to holocene icehouse sequences correspond to 1 2 myr obliquity cycles constraints from oxygen isotope records highlight the link between icehouse sea level lowerings sequence boundaries and 1 2 myr obliquity nodes mesozoic greenhouse sequences show some relation with the 2 4 myr eccentricity cycles suggesting that orbital forcing contribute to sea level change we suggest that during the icehouse large ice sheets associated with significant glacioeustatic changes 25 m up to 120 m changes were mainly governed by obliquity forcing during icehouse worlds obliquity forcing was the stongest control on global sea level and depositional sequences additionally during the middle eocene third order sequences were glacioeustatically driven in tune with 1 2 myr obliquity cycle suggesting that the presence of significant ice sheets is earlier than previously supposed i e early eocene in contrast during greenhouse worlds e g ephemeral small to medium sized or no ice sheets 0 25 m glacioeustatic changes the expression of obliquity in the sedimentary record is weak and intermittent instead the eccentricity signature which is the modulator of climatic precession is documented moreover we presume that greenhouse sequences on the myr scale are global and hence cannot be caused by regional tectonism e g intraplate stress or mantle hot blobs instead the eccentricity link implies a weaker glacioeustatic control because thermoeustasy is too small to explain the sea level changes stratigraphically well documented fourth order sequences may be linked to the astronomically stable strongest amplitude 405 kyr eccentricity cycle and possibly to 160 200 kyr obliquity modulation cycles fifth order sequences to the short 100 kyr eccentricity cycles and finally sixth order sequences to the fundamental obliquity 40 kyr and climatic precession 20 kyr cycles these astronomical cycles could be preserved in the sedimentary record and have been demonstrated to control sea level changes accordingly by placing depositional sequence orders into a high resolution temporal framework i e orbital periodicities standardization of eustatic sequence hierarchy may be possible

north atlantic volcanic margins dimensions and production rates early tertiary lithospheric breakup between eurasia and greenland was accompanied by a transient 3 m y igneous event emplacing both the onshore flood basalts of the north atlantic volcanic province navp and huge extrusive complexes along the continent ocean transition on the rifted continental margins seismic data show that volcanic margins extend 2600 km along the early eocene plate boundary in places underlain by high velocity 7 2 7 7 km s lower crustal bodies quantitative calculations of navp dimensions considered minimum estimates reveal an areal extent of 1 3 106 km2 and a volume of flood basalts of 1 8 106 km3 yielding a mean eruption rate of 0 6 km3 yr or 2 4 km3 yr if two thirds of the basalts were emplaced within 0 5 m y the total crustal volume is 6 6 106 km3 resulting in a mean crustal accretion rate of 2 2 km3 yr thus navp ranks among the world s larger igneous provinces if the volcanic margins are considered the velocity structure of the expanded crust seaward of the continent ocean boundary differs from standard oceanic and continental crustal models based on seismic velocities this volcanic margin crust can be divided into three units of which the upper unit corresponds to basaltic extrusives the regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust including the high velocity lower crust which extends some distance landward of the continent ocean boundary was emplaced during and subsequent to breakup the volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling probably reflecting the interaction of a mantle plume and a lithosphere already extending

simulated circulation of an idealized ocean for pangaean time an eight level dynamical ocean model driven by prescribed surface forcing wind stress temperature precipitation minus evaporation from a previously published pangaean time climate simulation is used to study possible features of ocean circulation temperature and salinity for the early mesozoic the simulations are sensitivity experiments rather than estimates of the actual circulation because many simplifying assumptions are made concerning the prescribed surface forcing and the ocean basin s shape and depth simulated features include relatively warm water in high latitudes warm deep water a westward flowing equatorial current across panthalassa and into the tethys sea poleward and eastward flowing currents along the tethys coasts and relatively vigorous meridional and longitudinal vertical overturning cells cool relatively fresh polar water combines with warm saline tethys water to produce the relatively warm deep water there are few geological estimates of early mesozoic pangaean time ocean circulation available for comparison with the simulated circulation

cyclostratigraphy of the global stratotype section and point gssp of the basal guzhangian stage of the cambrian period abstract the cambrian is the first period of the phanerozoic during which numerous major geological and biological events occurred understanding these events requires a high resolution time scale the luoyixi section in guzhang hunan province china is the global stratotype section and point gssp for the guzhangian stage here magnetic susceptibility and 13c data were used to conduct cyclostratigraphic analyses covering the upper drumian through lower guzhangian stages the results of the power spectral analyses and average spectral misfit analyses indicate that the 25 25 53 m 6 25 6 91 m 1 90 2 03 m and 1 08 1 19 m sedimentary cycles may represent long eccentricity short eccentricity obliquity and precession cycles respectively a 1400 kyr floating astronomical time scale was constructed using the stable 405 kyr eccentricity cycles to calibrate the agnostoid trilobite zones the obtained fundamental obliquity period 30 7 0 7 kyr implies 370 180 1220 km vs 384 000 km for present day for the earth moon distance and 21 58 0 18 h vs 23 93 h for present day for the length of day during the middle cambrian 500 ma

oscillations of global sea level elevation during the paleogene correspond to 1 2 myr amplitude modulation of orbital obliquity cycles abstract the mechanisms involved in the formation of 1 to 2 myr long third order stratigraphic sequences through the phanerozoic have been extensively debated but the main underlying forcings remain uncertain in this study we investigated third order sequences of paleocene eocene age in the east china sea shelf basin identifying a prominent 1 2 myr periodicity in the 405 kyr tuned gamma ray profile of the wp 1 borehole we infer that this 1 2 myr cycle which corresponds to long period amplitude modulation of obliquity was the main driver of third order sea level changes and sequence development this modulation entails variation in the range of obliquity amplitude between a maximum of 2 4 i e 24 5 22 1 and a minimum of 0 3 i e 23 3 23 0 as a result of interactions among the three primary parameters of earth s orbit i e eccentricity obliquity and precession we anchored our floating astronomical time scale ats to the t42 seismic horizon a major sequence boundary between the lin feng and mingyuefeng formations that corresponds to the top of nannofossil zone np8 reported age of 57 7 ma this yields a fixed ats for the late paleocene to middle eocene interval spanning 60 84 to 48 71 ma finally we evaluated our findings relative to the third order sequence stratigraphy of the east china sea shelf basin and to records of early cenozoic eustasy and global events

crustal structure of the northern part of the voring basin mid norway margin from wide angle seismic and gravity data abstract three regional ocean bottom seismograph obs profiles with a total of fifteen recovered obss were acquired in the northern part of the voring basin mid norway margin in 1996 the data have been modelled by inversion and forward modelling of the obs vertical components p waves the velocity is found to increase downwards within the sedimentary layers due to increasing depth of burial confining pressure within the two deepest sedimentary layers there seems to be an increase of 0 5 1 km s in velocity northwestwards this increase is most likely caused by high velocity sill intrusions in the sedimentary rocks emplaced during the rift episode leading to early eocene opening of the ne atlantic the presence of significant amounts of sills seems to terminate close to the nyk high along profile 5 dip profile and close to a dome northwest of the shelf edge along profile 6 dip profile the velocity in the top of this dome is anomalously high 3 4 km s at only 1 km depth beneath the seafloor suggesting that the high consists of volcanic rocks or heavily intruded sedimentary rocks the relatively low velocities derived from within the upper crystalline crust 5 9 6 2 km s confirms that the crust is of continental origin within the lower crust there seems to be a clear increase in velocity northwestwards from about 7 0 km s to about 7 4 km s suggesting that the amount of high velocity intrusions underplating in the lower crust decreases landwards the modelling of the strike profile profile 7 suggests that the transition from a lower crust dominated by magmatic intrusions to a more undisturbed continental lower crust is located approximately beneath this profile the model for profile 7 ties closely southwestwards to the models derived from obs data acquired in 1992 and northeastwards to lofoten obs data acquired in 1988 the models indicate that the thick magmatic intrusions in the sedimentary rocks and lower crust extend further landwards in the area of the 1992 survey and that the transition zone is related to the surt lineament the distribution of magmatic rocks thus seems to correlate strongly with pre breakup structures in addition to the p wave modelling gravity modelling has been performed along all profiles the gravity modelling confirmed all main aspects of the obs models and provided constraints on the crustal structures towards the ends of the profiles

impact of dynamic sedimentation on facies heterogeneities in lower cretaceous peritidal deposits of central east oman this study based in the haushi huqf area of central east oman aims to characterize the controls on facies distribution and geometries of some of the best preserved examples of lower cretaceous tidal flat facies within the tethyan epeiric platform field petrographic and geochemical data were acquired from the barremian aptian jurf and qishn formations that crop out in a 500 1000 m2 butte thus allowing for pseudo three dimensional quantitative data acquisition of the dimensions and spatial distributions of discontinuity surfaces and sedimentary bodies the interpretation presented here suggests that the main processes impacting sedimentation in the lower cretaceous peritidal environment of the haushi huqf were transport and erosion processes related to storm waves and currents the vertical evolution of the carbonate system is organized into six types of metre scale depositional sequences from subtidal dominated sequences to supratidal capped sequences which are bounded by regional discontinuity surfaces at subaerial exposure and submarine erosion surfaces associated with a base level shift sedimentary horizons along the entire depositional profile are cut by scours possibly created by storm events chemostratigraphy allows correlation between the haushi huqf and the age equivalent sections logged in the interior of the platform in oman the correlation suggests that the change from subtidal to intertidal depositional sequences during the late highstand is coeval with the development of rudist dominated shoals on the shelf this study is the first to discuss the controls on lower cretaceous peritidal carbonate cyclicity of the arabian epeiric platform the results presented here also offer a unique quantitative dataset of the distribution and dimensions of peritidal carbonate shoals and storm scours in a regional sequence stratigraphic context

climate forcing of fine grained deep marine systems in an active tectonic setting middle eocene ainsa basin spanish pyrenees abstract a multi proxy approach to understand environmental change in deep time was undertaken on about 150 m of core from a 230 m long middle eocene core from the ainsa basin spanish pyrenees representing deep marine siliciclastic sediments using detailed sedimentary logging high resolution multi element xrf geochemistry total organic carbon and stable carbon isotopes the well a6 was drilled as part of an industry university consortium through siltstones fine very fine grained sandstone turbidites and hemipelagic structureless mudstones that were deposited as overbank and off axis deposits from a sandy submarine fan and interfan deposits for comparative mineralogy between the sandstone turbidites and siltstones scanning electron microscopy sem and x ray diffraction xrd were undertaken on selected samples the sandstone turbidites show enrichment of detrital elements such as si zr and ti that can be linked to greater quartz and heavy mineral content compared with adjacent siltstones structureless hemipelagic mudstones comprise mainly clay minerals and carbonate we interpret the sandstone turbidites as from hyperpycnal flows during high river sediment discharge whilst hemipelagic mudstones resulted from the suspension fall out of hypopycnal flows cyclostratigraphic analysis of the core reveals milankovitch cyclicity at frequencies of 0 03 cycles m short eccentricity 0 09 cycles m obliquity 0 15 cycles m precession couplet and 0 19 cycles m precession couplet orbital parameters appear to have controlled the cyclic delivery of coarser grained sediment by turbidity currents two equally plausible depositional models both as milankovitch driven can explain the cyclical changes in the deep marine sediments 1 climatic cycles with humid periods of enhanced chemical weathering increased storminess and greater riverine run off leading to high sediment flux to the deep basin as sandstone turbidites 2 climatic cycles with cooler conditions linked to high frequency small scale eustatic sea level fluctuations with lowstand shelf edge delta progradation resulting in greater volumes of coarse detrital sediment to the seafloor by hyperpycnal flows this study provides an insight into the likely depositional effects of orbitally induced climate change on the nature and delivery of terrigenous sediment into deep marine environments

middle triassic orbital signature recorded in the shallow marine latemar carbonate buildup dolomites italy a new time frequency analysis of sea level controlled carbonate platform cycles in the middle triassic latemar massif dolomites italy reveals a strong depositional signature with characteristics of dominant forcing by climatic precession modes corresponding to long and short precession components at 1 21 7 k y and 1 17 6 k y underwent amplitude modulations matching earth9s orbital eccentricity with major frequency components at 1 400 k y 1 125 k y and 1 98 k y obliquity appears as a minor component at 1 35 4 k y the latemar signature thus constitutes the oldest pristine milankovitch signature yet observed in the geologic record its fidelity rivals that of the pliocene pleistocene record originally used to confirm the theory of orbitally forced climates this evidence deepens a widely noted disagreement between radiometric and cyclostratigraphic time scales for the latemar buildup the latemar cycles indicate that orbitally forced sea level oscillations were operative in the ice free middle triassic hothouse world

astronomical pacing of late cretaceous third and second order sea level sequences in the foz do amazonas basin abstract because of their relatively reduced tectonic influence post rift sedimentary successions have a propensity to preserve climatically driven cyclicity over long durations here we present an integrated cyclostratigraphic and sequence stratigraphic study of the post rift limoeiro sedimentary formation fm of the foz do amazonas basin offshore brazil which spans the entire late cretaceous epoch almost 35 myr long the principal goal of the present study is to decipher very long multi myr sedimentary cyclicities and their potential origin s in order to delineate the main controlling factors of post rift sediment sequences and packages we used gamma ray gr well log data for cyclostratigarphy and seismic data for sequence stratigraphy time series analysis of gr data shows a rich series of milankovitch frequency bands in particular long period cyclicities 405 kyr 2 4 myr 4 7 myr and 9 5 myr are detected with high fidelity seismic and sequence stratigraphic interpretation shows a striking sea level sl depositional sequence order matching the 4 7 myr orbital cyclicity inferred from cyclostratigraphy longer sl sequences interpreted in previous studies from the limoeiro fm closely match the 9 5 myr gr related orbital cycles thus we infer that the post rift limoeiro fm was deposited continuously under astronomical forcing over the late cretaceous epoch resulting in an extraordinary record of direct base and sea level responses to milankovitch climatic forcing including longer multi myr periodicities the 4 7 myr orbital component is recorded for the first time in sl sedimentary proxies thus allowing here to update sl hierarchical orders we suggest that third order and second order and suborders sl sequences were most likely paced by long period astronomical cycles 2 4 myr eccentricity and 4 7 and 9 5 myr orbital cycles respectively

orbitally forced climate and sea level changes in the paleoceanic tethyan domain marl limestone alternations lower kimmeridgian se france abstract high resolution analysis of multiple climatic proxies was carried out on a 8 5 m lower kimmeridgian interval of a pelagic marl limestone succession at ch teauneuf d oze vocontian basin southeastern france the aim of the study was to characterize the orbitally controlled sedimentary cyclicity and to decipher paleoclimatic and paleoceanographic changes all analysed proxies magnetic susceptibility carbonate content manganese content and bulk carbon and oxygen stable isotopes 13c and 18o respond in synchrony to orbitally forced climate change precession index cycles modulated by short 100 kyr eccentricity cycles are strongly expressed in magnetic susceptibility carbonate and mn contents but less so in 18o obliquity cycles are expressed in manganese and particularly in 13c the orbital forcing was conferred to these rhythmic pelagic sediments via paleoclimatic and paleoceanographic changes as follows detrital input and marine carbonate production are recorded by the magnetic susceptibility and carbonate signals with strong precession cyclicity calcareous nannofossil analysis shows the omnipresence of coccoliths and debris of coccoliths in the marls and limestones suggesting that the carbonate production was in largest part in situ precession index may exert oscillations in the antagonist marine surface productivity and detrital flux processes via solar radiation change oxygenation of the seafloor leading to redox cycles is detected in the manganese signal and supported by the 13c record with a strong expression of the obliquity finally paleotemperature variations were deduced from the 18o record although this latter has been in part perturbed by diagenesis in sum the variations in the studied proxies suggest a depositional model of combined climate and sea level cycles forced in concert by earth s orbital parameters in particular the limestones represent warmer climates and higher sea levels and the marls colder climates and lower sea levels this depositional model concurs with a previous depositional model of deep water carbonates of the german kimmeridgian while is in opposition to a previous one of the same section in the vocontian basin

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

seasonal variations in the siliciclastic fluxes to the western philippine sea and their impacts on seawater end values inferred from 1 year of in situ observations above benham rise

devonian orogen parallel opposed extension in the central norwegian caledonides late orogenic early to middle devonian extension in the scandinavian caledonides was unidirectional in western norway new data from two detachment zones hoybakken and kollstraumen north of the more trondelag fault complex show that bidirectional opposed orogen parallel extension dominated in this region at this time the fault complex acted as a transfer zone for the hoybakken detachment extension and uplift in central norway triggered significant magmatic activity in contrast to the lack of granite intrusions during exhumation of western norway

new insights into the basement structure of the west siberian basin from forward and inverse modeling of grace satellite gravity data 1 the oil and gas rich west siberian basin is underlain by a layer of flood basalts of late permian triassic age that are coeval with the siberian traps the extent and thickness of the basalts are unknown but knowing their thickness is important for discussions on the end permian mass extinction because basalt volume constrains estimates of emitted volatiles we have used grace satellite and terrestrial gravity data to study the structure of the crust and basalt distribution published seismic sections are used to constrain the sediment isopachs and to estimate a depth density function we use published models of crustal thickness and basement depth to reduce the observed gravity field to the basement level the resulting three dimensional density model gives information on density anomalies in the lower crust and upper mantle and on the basalt thickness we identify several rift graben structures that are presumably filled with basalt the lower crust below the west siberian basin shows considerable density variations and these variations allow the region to be divided into four major blocks the eastern part of the basin toward the siberian platform shows an arch shaped density increase in the lower crust that is accompanied by a linear high density anomaly at shallower depths our work demonstrates the way in which the grace gravity field can be applied to map geological structures like buried rifts and large basins the same techniques can be used for other large remote basins such as those in cratonic south america

crustal structure of the outer voring plateau offshore norway from ocean bottom seismic and gravity data four ocean bottom seismograph obs profiles acquired across the continent ocean transition zone of the outer voring plateau have been modeled by inversion and forward modeling of the obs vertical component traces p waves the thickness of the sedimentary layers deposited since the early eocene continental breakup varies from up to 2 2 km above the basaltic inner flows if to a minimum of 0 2 km about 20 km seaward of the voring escarpment ve with a velocity of 1 6 2 55 km s the thickness of the uppermost layer of basalt varies from 0 5 to 4 5 km and its velocity ranges from 3 4 to 5 km s the modeling of the two dip profiles suggests that strongly intruded preopening sedimentary rocks extend 40 km seaward of the ve farther seaward another layer of extrusives intrusives is found beneath the uppermost layer of basalt the lateral variations in velocity in the main crustal layer along the dip profiles indicate that the continent ocean transition extends over a 30 50 km wide zone in between strike profile 3 oceanic 6 6 7 35 km s and strike profile 4 continental 6 1 7 0 km s an up to 7 km thick lower crustal high velocity body 7 1 7 4 km s is interpreted in terms of intrusions in the lower crust beneath and landward of the continent ocean transition the total thickness of the normal oceanic crust is estimated to be 7 9 km the anomalously thick oceanic crust reaches a maximum thickness of about 25 km and the crustal thickness is estimated to be 17 22 km beneath the if gravity modeling of the profiles confirmed all main aspects of the velocity models and provided constraints on the crustal structures toward the ends of the profiles where the ray coverage was low

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

climate induced fluctuations in sea level during non glacial times during periods of time when the earth supports ice caps sea level fluctuates periodically at intervals of 104 105 yr with amplitudes of tens to more than 100 metres these fluctuations result from expansions and contractions of continental ice sheets that occur in phase with the milankovitch periodicities of the earth s orbit1 2 smaller amplitude sea level fluctuations associated with milankovitch periodicities are also evident during warm periods such as the late triassic3 5 which lack strong evidence for continental glaciation6 we argue here that in times of limited ice volume periodic climate induced changes in lake and groundwater storage have the potential to produce small fluctuations in sea level this mechanism could contribute a small component of the sea level change observed in the quaternary period and may dominate the milankovitch eustatic sea level signal during earlier periods with limited ice volume6 we present evidence of contemporaneous milankovitch periodicities in late triassic lake sediments7 and sea level fluctuation3 5 which support the causal link between lake water storage and eustasy

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

use of insolation as a proxy for high frequency eustasy in forward modeling of platform carbonate cyclostratigraphy a promising approach abstract eustatic oscillations driven by milankovitchian astronomical forcing have been interpreted as sea level drivers for high frequency carbonate depositional cycles in studies dating from the mid 1960s forward modeling of these oscillations with respect to their recorded effects on cyclical stacking patterns has only been attempted using generalized parameters for milankovitchian forcing the development of increasingly advanced forward modeling software coupled with the availability of formulas quantifying insolation incoming solar radiation as a function of composite orbital variations allows for the testing of milankovitchian insolation against measured stratigraphy in this case a series of milankovitchian insolation curves were calculated and used to generate proxy sea level curves for use in the carb3d forward modeling package in order to synthesize a series of stacked carbonate strata these synthetic successions are compared against that of the latemar platform middletriassic northern italy which has been interpreted to contain a record of orbital forcing within its stratigraphy while the timing and nature of periodic drivers that affected latemar stratigraphy have stirred a vigorous debate results from this study indicate that use of milankovitchian insolation as a proxy for high frequency sea level oscillations was successful in modeling latemar like stratigraphy with both pure milankovitchian and mixed milankovitchian sub milankovitchian temporal frameworks

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

terrestrial and marginal marine record of the mid cretaceous oceanic anoxic event 2 oae 2 high resolution framework carbon isotopes co 2 and sea level change abstract oceanic anoxic event 2 oae2 c 94 5 93 9 ma offers insight into the mechanisms of past climate change linked to organic productivity and carbon sequestration it has been studied extensively but the vast majority of data come from marine records thus providing an incomplete view of past climate dynamics here we integrate new high resolution data and published records on depositional environments the carbon isotope composition of bulk organic carbon 13corg and plant cuticles 13ccut and stomatal index values a proxy for pco2 in well preserved terrestrial through marginal marine archives of the initial phase of oae2 the study area is located on the western margin of the western interior seaway southwestern utah age constraints are based on a new u pb bentonite age and correlation to an orbitally calibrated interval of the bridge creek limestone n alkane abundance suggests predominance of terrestrial contributions to bulk organic carbon for most samples despite similarities between carbon isotope variations and transgressive regressive shoreline movements it is argued that 13corg and 13ccut are not strongly affected by local variables a series of negative 2 carbon isotope excursions is identified and attributed to changes in the size and isotopic value of the atmospheric co2 reservoir the temporal spacing of these anomalies 80 120 kyr is consistent with changes in insolation modulated by orbital eccentricity a systematic phase shifted relationship between the negative carbon isotope excursions and transgressive increments further suggests a link between carbon cycle perturbations and meter scale sea level change on the 100 kyr time scale a conceptual model involving insolation controlled aquifer charge discharge and biomass burial degradation in the monsoonal belt is proposed the framework presented here is available to facilitate further research on the interplay of terrestrial and oceanic carbon reservoirs during oae2

late triassic to late jurassic evolution of the adriatic carbonate platform and budva basin southern montenegro abstract southeastern montenegro is the only part of the adriatic carbonate platform adcp that bears record of its evolution from a ramp through a distally steepened ramp to a platform in this paper we present the sequence stratigraphy of the late triassic to late jurassic rocks from this part of tethys for the first time in the literature we discovered and described three new facies hardground and cerebroid oolites of the livari supersequence and black pebble conglomerate of the tejani supersequence the mid ramp and lower ramp cherty oolite wackestone and mudstone facies of the livari supersequence as well as oolite conglomerate facies of the stari bar supersequence were partially or completely reinterpreted the middle and late triassic rifting separated the adcp from the other south tethyan carbonate platforms and created the intraplatform budva basin the adcp evolved through three morphologic stages a detached ramp livari supersequence rhaetian early toarcian a distally steepened ramp tejani supersequence early toarcian middle callovian and an accretionary rimmed platform stari bar supersequence oxfordian to neogene the rhaetian regression is marked by a regional unconformity surface that represents a type s sequence boundary at the base of the livari supersequence lowstand wedge of the halobia limestone was the oldest sediment in the budva basin tst and hst of the livari supersequence include supratidal and intertidal inner ramp sediments ooid shoals and cyclic shallowing up parasequences of the mid ramp sedimentation rates were high in the inner ramp while budva basin received relatively thin accumulation of siliceous plankton a brief exposure of supratidal flats and ooid bars represents a type p sequence boundary between the livari and the tejani supersequences which was flooded by the early toarcian transgression tst and hst of the tejani supersequence consist of supratidal lagoon and shoal sediments in the inner ramp and deeper water carbonates of the mid and outer ramp highstand shedding of the sediment from the steepened ramp left thick deposits in the budva basin the bathonian regression is marked by a regional unconformity that represents a type s sequence boundary between the tejani and stari bar supersequences stari bar oolite conglomerate is a lowstand wedge of the stari bar supersequence the middle callovian transgression induced aggradation of ooid shoals deep into the platform interior oxfordian coral reefs created a rimmed platform and restricted export of the shallow carbonates into the budva basin

third order depositional sequences reflecting milankovitch cyclicity the origin of third order depositional sequences remains debatable and in many cases it is not clear whether they were controlled by tectonic activity and or by eustatic sea level changes in oxfordian and berriasian valanginian carbonate dominated sections of switzerland france germany and spain high resolution sequence stratigraphic and cyclostratigraphic analyses show that the sedimentary record reflects milankovitch cyclicity orbitally induced insolation changes translated into sea level fluctuations which in turn controlled accommodation changes beds and bedsets formed in rhythm with the precession and 100 kyr eccentricity cycles whereas the 400 kyr eccentricity cycle contributed to the creation of major depositional sequences biostratigraphical data allow the correlation of many of the 400 kyr sequence boundaries with third order sequence boundaries recognized in european basins this implies that climatically controlled sea level changes contributed to the formation of third order sequences furthermore this cyclostratigraphical approach improves the relative dating of stratigraphic intervals

cenomanian sequence stratigraphy and sea level fluctuations in the tarfaya basin sw morocco we investigated the sequence architecture of two expanded cenomanian successions along a depth transect in the tarfaya basin sw morocco and correlated these successions to published records from northwest europe and india changes in terrigenous material carbonate and organic carbon content carbonate microfacies and foraminiferal biofacies as well as nondepositional and erosional surfaces were used to define depositional sequences and systems tracts we identified two main transgressive cycles in the lower and middle upper cenomanian separated by a major regression at the early middle cenomanian transition sequence boundary ce 3 this regressive interval is characterized by lagoonal low stand deposits indicating an overall sealevel fall of more than 30 m superimposed on the two main transgressive cycles there are 11 third order depositional sequences that correlate to globally recognized sealevel fluctuations and appear to be paced by long eccentricity variations 400 ka period positive carbon isotope excursions in the middle cenomanian 96 0 ma and latest cenomanian 94 0 ma following sealevel lowstands together with planktonic foraminiferal and ammonite datums provide a robust framework for stratigraphic correlation we suggest that the onset of these excursions was triggered by eccentricity minima during periods of low variability in obliquity nodes which probably coincided with glacioeustatic lowstands

the silurian to permian history of a metamorphic core complex in lofoten northern scandinavian caledonides 1 the lofoten archipelago exposes precambrian baltic basement and caledonian allochthonous sequences within a 1000 km long chain of gravity and magnetic highs and structural culminations along the extended british and norwegian continental shelf previous regional geophysical studies indicate that post caledonian extension and development of the northern norwegian shelf occurred during broadly defined carboniferous permian cretaceous jurassic and early tertiary events structures related to these events are known to young westward we report field structural and 40ar 39ar thermochronologic data from rocks exposed in lofoten that further define the history and style of post caledonian extension the islands of southwest lofoten also represent the most outboard exposures of caledonian basement in northern norway that presumably formed the middle to deep crustal core of the orogen metasedimentary rocks and penetratively deformed basement in lofoten record high grade silurian devonian metamorphism and top to the east hereinafter tops east thrusting followed by episodes of late devonian to early carboniferous tops west ductile extension which progressed into oblique left slip movements the structural style and timing of silurian contraction in this area are remarkably similar to that determined for the more forelandward areas on the mainland 120 km to the east supporting the inference that distal parts of the baltic continental margin that were once deeply subducted are presently exposed in lofoten the timings of post devonian structural events that affected rocks in lofoten are partially constrained by the ages of unconformities and strata known to be preserved in graben flanking the lofoten culmination the radiometric age and structural data presented in this study in combination with stratigraphic constraints suggest a westward progression through time of extensional deformation over a protracted interval of silurian to permian time the latest permian extension in lofoten is largely characterized by brittle structures that formed at conditions substantially less than 300 c compared to the exhumation history of the southern western gneiss region the depth of caledonian continental a type subduction and subsequent unroofing of lofoten are of lesser magnitude and the present erosional level remained in the middle crust for a much longer interval of time the permian 40ar 39ar mineral ages documented in this study are the youngest such ages yet identified in scandinavia these ages relate to episodes of deformation and cooling in response to extensional tectonic events that occurred roughly 100 m y after comparable effects identified on the caledonian mainland our preferred explanation for the carboniferous permian radiometric ages structural evolution and stratigraphic data for lofoten is that they all developed in the context of a long lived cordilleran style metamorphic core complex

sea level fall carbonate production rainy days how do they relate insight from triassic carbonate platforms western tethys southern alps italy the interplay of sea level fall climate and sedimentological changes is recorded across two sequence boundaries at the top of two triassic carbonate platform systems in the western tethys earliest carnian and norian rhaetian boundary in age paleolatitude 18 25 n the sea level falls caused subaerial exposure of the platform top and decreased carbonate production leading to starvation in the intraplatform basins followed by deposition of shale evidence of freshwater input indicates that the change in sedimentation was driven by increased rainfall on the previously arid european hinterland and tethys coast a uniformitarian approach holocene sea level changes and global warming are coupled with changes in the distribution of precipitation implicates global cooling as the probable cause of the observed sea level climate and sedimentological changes global cooling likely triggered the sea level fall by increased storage of fresh water in continental settings and change in seawater density probably coupled with ephemeral ice sheet development possible even during greenhouse intervals such as the triassic furthermore global cooling caused a shift toward the equator of the poleward boundary of the arid belt this model is supported by the traceability of the sequence boundaries and climate sensitive facies from the tethys shelf up to the european continent the observed association of global climate changes sea level fall sedimentological changes and shift toward humid climate documents how climate sensitive facies record the control exerted by global changes on local sedimentation

early maastrichtian carbon cycle perturbation and cooling event implications from the south atlantic ocean published stable isotope records in marine carbonate are characterized by a positive 18o excursion associated with a negative 13c shift during the early maastrichtian however the cause and even the precise timing of these excursions remain uncertain we have generated high resolution foraminiferal stable isotope and grey scale records for the latest campanian to early maastrichtian 73 68 ma at two ocean drilling program sites 525 walvis ridge and 690 weddell sea we demonstrate that the negative 13c excursion is decoupled from the 18o increase with a lag of about 600 kyr our 13c records both planktic and benthic show an amplitude for the negative excursion of 0 7 that falls between about 72 1 and 70 7 ma our planktic 18o records indicate an overall increase of 1 2 from 73 to 68 ma at site 690 whereas at site 525 they record a slightly smaller increase 1 that peaks around 70 1 ma with decreasing values thereafter our benthic 18o data indicate an increase of 1 5 at site 525 and 0 7 at site 690 between about 71 4 and 69 9 ma benthic 18o values show different baseline values at the two sites before and after the excursion but the larger increase at site 525 means that the values attained at the peak of the excursion are similar at the two sites we interpret this observation in terms of water mass changes the excursion is interpreted to reflect a cooling of bottom waters in response to the strengthening contribution of intermediate to deep water production in the high southern latitudes rather than increased ice volume the associated carbon cycle perturbations that we observe are interpreted to reflect a weakening of surface water stratification and increased productivity as supported by our grey value data

sub milankovitch and milankovitch forcing on a model mesozoic carbonate platform the latemar middle triassic italy basic shallowing upward cycles shu cycles and five bundled megacycles in the latemar platform have been widely regarded as a model example for precessional and eccentricity forcing in the mesozoic based on bio chronostratigraphic data recent studies questioned this particular type of milankovitch forcing on the latemar cyclic series we present an integrated model that incorporates i new cyclostratigraphic data ii new and existing bio chronostratigraphic data and iii new spectral analyses the basic shu cycles in the latemar reflect sub milankovitch control cycle bundles of 1 4 5 megacycles shu cycles indicate precessional forcing they do not reflect eccentricity superimposed on precessional forcing spectral analyses reveal highly significant ratios in the large scale cycle bundlings stacking patterns of 1 9 9 and 1 24 0 shu cycles represent obliquity and short eccentricity forcing both sub milankovitch and milankovitch forcing potentially controlled shallow subtidal carbonate deposition in mesozoic greenhouse times cyclostratigraphic models require an integrated approach including bio and chronostratigraphic data

insights from the jan mayen system in the norwegian greenland sea i mapping of a microcontinent summary in this contribution we present a model of microcontinent architecture within a system that involves a complex rifted margin setting and different phases of deformation and continental breakup our case study is the jan mayen microcontinent jmmc located in the central part of the norwegian greenland sea we have revised its basement and sedimentary geometries using modern and vintage seismic reflection profiles and updated potential field data the northern part of the jmmc consists of a 10 15 km thick continental crust body flanked by two major sedimentary basins we propose that the microcontinent is divided into six distinct segments characterized by different basement and sedimentary architectures the shallow stratigraphy is well imaged and has been detailed three distinct sedimentary units have been defined together with pronounced reflectors ja red jo and f related to erosional magmatic thermal or uplift events the continent ocean boundary has been revised together with the mapping of the distinct volcanic events that characterize the evolution of the microcontinent a companion paper aims to further detail the interpretation of the jmmc structure presented here by constraining the conjugated mid norwegian and mid east greenland structures

seismic volcanostratigraphy of the norwegian margin constraints on tectonomagmatic break up processes voluminous volcanism characterized early tertiary continental break up on the mid norwegian continental margin the distribution of the associated extrusive rocks derived from seismic volcanostratigraphy and potential field data interpretation allows us to divide the more voring and lofoten vesteralen margins into five segments the central more margin and the northern voring margin show combinations of volcanic seismic facies units that are characteristic for typical rifted volcanic margins the lofoten vesteralen margin the southern voring margin and the area near the jan mayen fracture zone show volcanic seismic facies units that are related to small volume submarine volcanism the distribution of subaerial and submarine deposits indicates variations of subsidence along the margin vertical movements on the mid norwegian margin were primarily controlled by the amount of magmatic crustal thickening because both the amount of dynamic uplift by the icelandic mantle plume and the amount of subsidence due to crustal stretching were fairly constant along the margin thus subaerial deposits indicate a large amount of magmatic crustal thickening and an associated reduction in isostatic subsidence whereas submarine deposits indicate little magmatic thickening and earlier subsidence from the distribution of volcanic seismic facies units we infer two main reasons for the different amounts of crustal thickening 1 a general northward decrease of magmatism due to increasing distance from the hot spot and 2 subdued volcanism near the jan mayen fracture zone as a result of lateral lithospheric heat transport and cooling of the magmatic source region furthermore we interpret small lateral variations in the distribution of volcanic seismic facies units such as two sets of inner seaward dipping reflectors on the central voring margin as indications of crustal fragmentation

high frequency depositional cycles in the muschelkalk middle triassic of southern poland origin and implications for germanic basin astrochronological scales abstract high frequency depositional cycles are often used for long distance correlations within sedimentary basins and constructing high resolution chronostratigraphic scales calibrated to the orbital clock such an approach has been used for the tropical epicontinental muschelkalk sea covering most of europe in the middle triassic this paper aims at establishing the spatial extent and internal architecture of shallow marine muschelkalk cycles within a small 120 by 50 km area of the germanic basin to identify their local vs regional distribution and cycle forming mechanisms three groups of cycles are distinguished 1 peritidal cycles representing a tidal flat lagoon system which experienced longer periods of emersion 2 shallow subtidal cycles formed around the fair weather wave base and 3 deep subtidal cycles developed around the storm wave base the three cycle types differ markedly in the composition facies homogeneity sedimentary trends hierarchical organization continuity and degree of lateral changeability and complexity which collectively translates into the ease of cycle recognition despite the differences the defined cycles do not extend laterally beyond the studied area and have laterally variable facies heterogeneities sedimentary trends and thicknesses this variability resulted from more or less mosaic infilling of accommodation space reflecting local bathymetry physicochemical conditions and carbonate production and accumulation rates on the platform accommodation space evolved by the interplay of eustatic sea level fluctuations regional subsidence and synsedimentary tectonic block movements but the contribution of these factors changed over time and was to varying degrees masked for each of the three cycle types by intrinsic sedimentary processes the study shows that middle triassic cycles of the germanic basin have a local to sub regional distribution and thereby are inappropriate for basin wide correlations and chronostratigraphic inferences it also strengthens the opinion of several workers that correlation of idealized cycles is unrealistic without checking the horizontal continuity of facies and key surfaces directly in the field

structural comparison of archetypal atlantic rifted margins a review of observations and concepts abstract in this study we compare three pairs of conjugate rifted margins that are often referred to as archetypes of rift systems despite numerous differences a remarkable first order structural similarity appears between the magma poor iberia newfoundland the magma rich mid norway east greenland and the sediment rich angola brazil rifted margins typical is the seaward arrangement of distinct domains proximal necking distal and outer that each present specific comparable structural characteristics our study also suggests that magma rich systems may go through a stage of hyper extension indicating that extreme crustal thinning does not preclude a magmatic breakup in this contribution we clarify the definition of a number of terms introduced recently in rifted margin studies we review the major features constitutive of these key referenced systems discuss their similarities and differences and examine how the related deformation modes develop in the life cycle of a rift that goes to seafloor spreading we conclude that the distinct domains observed in the margin architecture represent distinct stages in the evolution of rifted margin independently of their later evolution into magma poor or magma rich environments

large scale facies change in the middle eocene south pyrenean foreland basin the role of tectonics and prelude to cenozoic ice ages abstract the present study reports a sedimentological analysis of the guara limestone formation deposited during the lutetian in the sierras exteriores in the south pyrenean foreland basin we provide a detailed facies analysis of the carbonates to precise the paleoenvironmental context during their deposition we show that those limestones are mainly composed of shallow water foraminifers and were deposited in relative shallow water environments

insights into the magmatic architecture of the oslo graben by petrophysically constrained analysis of the gravity and magnetic field 1 a new model of the crustal structure of the oslo graben with a special emphasis on the location of magmatic intrusions is presented based on the interpretation of gravity and magnetic data constrained by petrophysical data seismics and surface geology three dimensional modeling shows that the gravity high above the oslo rift is caused by a combination of crustal thinning and the presence of a high density body in the upper crust related to precambrian gneiss complexes at the western flank of the rift the short wavelength gravity anomalies are correlated with the outcropping low density magmatic rocks of permian age that extend to the depths of 1 5 4 km in addition simultaneous modeling of aeromagnetic data sets collected at two flight altitudes 50 and 3400 m using susceptibility and remanence within a range of reasonable magnetic properties suggests an underlying intrusion with a depth extent up to 15 km magnetization and density of the intrusion are increasing with depth leading to a small density contrast but a large contrast in magnetization with the surrounding rocks therefore only modeling of the magnetic field can resolve the nature of the deep intrusions the three dimensional model provides a new estimate of the volume of magmatic material in the oslo graben system 63 000 km3 this is only two thirds of the values proposed earlier 95 000 km3 as we disregard high volume magmatic underplating correlation with structural data surface geology and deep lithospheric features shows that the distribution of extrusive rocks in the oslo rift can be related to the timing and onset of rifting

deep structure of the voring margin the transition from a continental shield to a young oceanic lithosphere the present day lithospheric structure across the norwegian margin in the voring region is presented the voring margin is characterized by the presence of large volume of magmatic underplating thick mesozoic basins and prominent crustal thinning results from recent deep seismic experiments in the voring basin and voring marginal high and 3 d gravity modelling have been implemented in a regional 2 d lithospheric transect that runs from the norwegian caledonian belt to the oceanic domain crossing the transition between the precambrian fennoscandian baltic shield and the cenozoic northern north atlantic oceanic lithosphere the modelling approach integrates elevation gravity geoid and heat flow data under the assumptions of thermal steady state and local isostasy the results confirm and refine the major trends of the crustal geometry which is characterized by a moho depth varying from about 45 km beneath the caledonian thrusts to 30 km beneath the trondelag platform to 20 14 km beneath the voring basin and to 13 km in the oceanic domain the lithosphere thins from the norwegian caledonian belt 190 km thick to the oceanic domain 60 km in a stepwise manner reflecting the progressive seawards migration of lithospheric deformation since the paleozoic our lithospheric thickness results are different from those predicted by post rift lithospheric cooling models in the oceanic domain observed residual bathymetry 600 m is interpreted as the remaining effect of a deep seated thermal perturbation during the upper cretaceous which would also produce a heat flow anomaly of 15 mw m 2 alternatively residual bathymetry can be interpreted in the absence of thermal anomalies as produced by depletion of the sublithospheric mantle extending down to 130 230 km depth depending on the density contrast 10 30 kg m 3

high velocity breakup related sills in the voring basin off norway multichannel seismic reflection profiles in the hel graben v0ring basin reveal a sill complex at approximately 5 km depth it is associated with exceptionally high 7 4 km s 1 seismic wide angle velocities the existence of observable wide angle arrivals shows that the sills act as efficient waveguides seismic reflection data and amplitude modeling constrain the thickness of individual sills to approximately 100 m sonic logs from sills of similar thickness on the nearby utgard high show an average velocity of 7 0 km s 1 such high velocities require an olivine gabbroic sill composition and emplacement under conditions which allowed growth of relatively large crystal sizes a possible reason for such an emplacement environment is the hei graben s role as an intrusion center during breakup volcanism this would provide the necessary duration of the magmatic activity as well as locally increased melt volumes and cooling times sill complexes of this kind decrease the accuracy of determined velocity fields and crustal geometries below the top of the sill complex affecting depth conversion and gravity modeling furthermore the results question the concept of lower crustal bodies as large scale homogeneous accumulations of mafic melt