persistent basement wrenching as controlling mechanism of variscan thin skinned thrusting and sedimentation cantabrian mountains spain abstract in this classical area of thin skinned tectonics current models of the complex fold and thrust belt seem to be approaching a successful synthesis without the necessity for extreme regional bending to account for the characteristic horse shoe form of the orogen fundamental wrench fault zones e g the leon and sabero gordon lineaments whose influence is recorded throughout the palaeozoic stratigraphic history have also played an important role in the sedimentary and structural events of the variscan cycle strike slip motion not only interfered with thrusting far into stephanian times but also effectively controlled molasse fanglomerate sedimentation rendered traceable by multiple clast sources depocentre migration fan skewing and progressive unconformities from the surficial pattern of sedimentation and structure a left stepping pull apart basement structure is deduced it is held responsible for block tilting opposite to the thrusting modifying the backfolding of the thrust sheets and generating the concurrent surficial collapse of its fanglomerate cover it is considered that the persistence of strike slip motion throughout the palaeozoic justifies the conclusion that deeper crustal events of this type may form the source of the thrusting and induce the variable stress orientations in the upper crust to implement the complex near surface deformation the proposed basement configuration fits well into the plate tectonic concept of a palaeo africo iberian promontory to account for the initiation of the ibero armorican arc

offshore granulites from the bay of biscay margins fission tracks constrain a proterozoic to tertiary thermal history over short distances partly as pebbles from albian conglomerates we chose the granulite samples for our fission track study anticipating that they have recorded most of the history of the continental crust in the area and because the origin and emplacement of these rocks is still not clear the results have important implications and show that fission track studies on offshore basement have great potential for furthering our under standing of continental margin pro cesses abstract zircon and apatite fission track ages were determined on granulites dredged along the bay of biscay margins a sample from ortegal spur iberia margin yielded 725 67 ma zircon a sample from le danois bank iberia margin yielded 284 58 ma zircon indicating post variscan cooling apatite from this sample gave 52 2 ma interpreted as final cooling after pyrenean thrust imbrication two other samples from le danois bank have early cretaceous apatite ages 138 7 and 120 8 ma interpreted to result from exhumation during rifting finally a granulite from goban spur armorican margin gave 212 10 ma apatite coinciding with a precursory rifting phase together with published radiometric results these data indicate a precambrian high grade terrane at the site of the current margins the distribution of the granulites on the seafloor reflects tectonic and erosional processes related to a mesozoic rifting and b early tertiary incipient subduction of the bay of biscay beneath iberia

lower cretaceous lacustrine source rocks in northern gabon effect of organic facies and thermal maturity on crude oil quality abstract organic facies variation which is a key factor affecting the quality of hydrocarbon accumulations is characterized for the pre salt freshwater lacustrine source rocks in the interior basin and n komi rift areas in northern gabon by integrating geochemical and geological data the kissenda shales have 0 59 2 23 total organic carbon toc and hydrogen indices hi from 458 93 mghc goc pyrolysis of isolated kerogen and gas chromatography on rock extracts indicate that these samples are overall more waxy than those from the overlying melania shales which have 0 77 4 79 toc and hi from 896 212 in addition hopane sterane ratios and c30 4 methyl sterane indices increase systematically with depth it is proposed that the early cretaceous lacustrine system in northern gabon was initially oligotrophic and contained primarily bacteria and cyanobacteria with a small population of dinoflagellates and botryococcus as trophic level increased through time the food chain length increased eukaryotic organisms became more abundant and diversified steroids increased relative to hopanoids in the sediment and the preserved organic matter became less waxy burial history modeling shows that the onal 1 structure is charged primarily by waxy oils generated from the lower kissenda shales lower wax better quality oils are expected to the southwest where the kissenda shales are more mature and the less waxy melania shales also become effective source rocks thus variation in organic facies and thermal maturity in the cretaceous pre salt source rocks result in commercial production from the rabi field vs the subcommercial discovery in the onal 1 structure

early cretaceous syn rotational extension in the organya basin new constraints on the palinspastic position of iberia during its rotation article i nfo in this study we interpret the paleo stress pattern in the organya basin southern pyrenees northern spain as inferred from the anisotropy of magnetic susceptibility ams of 39 sites distributed over the entire basin combined with information from other cretaceous iberian basins such analysis adds to constrain kinematic reconstructions of the cretaceous rotation of iberia allied with the opening of the bay of biscay and the northward propagation of the north atlantic the organya basin is an inverted cretaceous basin in the hanging wall of the boixols thrust the lithologies are mainly weakly deformed pelagic and hemi pelagic limestones and marls which recorded the aptian 35 counterclockwise rotation of iberia three types of ams fabrics could be distinguished all representing typical intermediate and tectonic fabrics ew magnetic lineations dominate in the eastern part of the basin and are related to crustal shortening during the pyrenean orogeny this interpretation is consistent with structural cross sections across the basin showing more intense shortening in the east in the central part of the basin approximately ns oriented magnetic lineations are observed interpreted as the original extensional direction during basin foundering so in line with results from previous studies ams can still unveil the original extensional direction in an inverted sedimentary basin something which may be difficult to reconstruct from geological data alone the original extension direction in the organya basin is perpendicular to the boixols thrust bounding the basin to the south correction for the aptian rotation of iberia leads us to infer a ne sw oriented extension direction at the onset of the rotation of iberia this extension direction is inconsistent with current plate kinematic reconstructions of the cretaceous rotation and motion of iberia we therefore suggest that during the opening of the bay of biscay and related iberian rotation iberia was in a much more westerly position than assumed in current models and that the rotation of iberia was followed by dominantly eastward translation with respect to southern france prior to n s convergence and shortening in the pyrenees since the latest cretaceous

high thermal maturity in the lower saxony basin intrusion or deep burial abstract the lower saxony basin lsb is situated at the southern rim of the northern permian basin the most important hydrocarbon bearing province in europe in its southern part areas of high thermal maturation up to 6 rr occur which were previously explained as being caused by magmatic intrusions of turonian to santonian age that affected carboniferous to lower cretaceous rocks in this area 2d numerical basin modelling was carried out in order to reconstruct the temperature histories along two parallel n s trending seismic sections along these sections new data about maturity distribution and temperature history were obtained by vitrinite reflectance measurements and apatite fission track analysis for the areas with highest maturity values low coalification gradients were established which agree well with earlier published data on wells further towards the west this new information does not support previous hypotheses on high heat flows from magmatic intrusions even if lateral heat transport is taken into account instead comparisons with a recently published map of the subsurface structure of the lsb indicate that maturity distribution may be closely related to major tectonic structures deep burial of individual structures of the lsb which are bordered by deep e w to ese wnw trending faults is further suggested by a rapidly increasing thicknesses of preserved cretaceous strata towards the south and b structural restoration of one of the seismic sections to achieve a fit between measured and calculated palaeo temperature and vitrinite reflectance data deep burial of carboniferous source rocks during cretaceous time has to be assumed due to an inversion phase in the early and middle upper cretaceous major amounts of sediment were removed and further uplift occurred in tertiary times in contrast the northern part of the lsb experienced maximum burial and temperatures during tertiary times

paleomagnetic evidence for dextral strike slip motion in the pyrenees during alpine convergence mauleon basin france abstract the paleomagnetic study of the aptian albian black marls from the inverted early cretaceous mauleon basin in the northern pyrenees reveals two components of magnetization that both yield negative fold tests the carriers of each component show different unblocking temperatures indicating that ferrimagnetic iron sulphides are the main carriers of the intermediate temperature component itc unblocks around 360 400 c and magnetite is the main carrier of the high temperature component htc unblocks around 460 500 c both components show a clockwise deviation in declination with respect to the reference field directions itc di and htc di both in in situ coordinates the reference direction for stable europe for the cenozoic is d i 001 50 d 5 i 3 however the reversal test for both of the magnetization components in situ is positive the structural evolution of the basin involves transtensional deformation during the main stage of basin formation and inversion during compression with migration of hydrocarbons and development of thrusts and folds with axial planar cleavage secondary magnetizations were acquired at the latest stages of the evolution of the inverted basin post folding as the result of a chemical mechanism and they were blocked during two different and likely close spaced in time polarity chrons the blocking of the two different magnetizations with different carriers implies chemical changes in the environment from anoxic sulphate reduction to oxic inferred clockwise rotation of the paleomagnetic vectors can be interpreted in terms of dextral shear across the north pyrenean zone during the tertiary probably eocene according to the plate tectonic scenario this distributed dextral shear was probably favored by discrete shear along cleavage planes as shown by geologic markers of consistent dextral strike slip motion in non competent units with strong cleavage development there is no evidence of such dextral movement in the south pyrenean zone thus indicating a strong partitioning of deformation during the pyrenean orogeny

the western desert versus nile delta a comparative molecular biomarker study abstract the western desert and the nile delta are prolific petroleum producing basins the correlation and matching between their petroleum systems have been briefly studied overall geochemical and biological marker analyses of twelve crude oil and condensate samples taken from seven oil gasfields located in the nile delta and the western desert basins of egypt were effective in identifying and geographically defining two major oil families related by age and source rock depositional environment these samples were classified respectively as late cretaceous tertiary and jurassic early cretaceous the source rocks giving rise to the late cretaceous tertiary oils are associated with abundant terrestrial organic matter the source rocks giving rise to jurassic early cretaceous oil are presumably generated from a mixed terrestrial marine source meanwhile the western desert oil samples show prominent c 30 steranes elevated c 27 monoaromatic steroids and a distinct homohopane distribution suggesting this oil type is derived from a more marine influenced source rock than terrigenous sourced oil in the nile delta the most crucial geochemical fingerprinting biomarkers that have been used to differentiate between nile delta and the western desert oil are oleananes highly branched isoprenoids hbi sterane isomerization 24 norcholestanes aromatic steroid hydrocarbons and c 30 24 n propylcholestanes

pangaean divergent margins historical perspective abstract pangaean divergent margins caused by the breakup by rifting of that supercontinent display three distinct evolutionary stages in their youth or rift stage divergent margins display a synsediment fault style that has considerable tectonic instability during the mature or drift stage seafloor spreading continental margins are relatively stable and are dominated by thermal subsidence these two stages rifting and drifting are separated in many areas by an unconformity coeval with the oldest associated oceanic crust the breakup unconformity in some areas the onset of seafloor spreading is marked by intense magmatic activity sediment facies the rifting stage range from continental clastics landward of the continental basement hinge and along the flanks of the basin to saline deposits and more open water carbonates in the axial zone of the rift lithologies emplaced during the rift or mature stage of margin development range from shallow clastics carbonates to deep water carbonate siliceous oozes turbidites and contourites some of which were deposited in an anoxic environment deposition then is controlled by changes in configuration of basins changes in sea level and plate migration through several climatic belts during the final or old age of margin development divergence gives way to convergence this stage which generally terminates with continental collision is characterized by tectonism magmatic activity and crustal shortening mesozoic divergent margins along the east west trending former tethys ocean have reached this stage in their evolution

geochemical characteristics of oils and source rocks in the yamal peninsula west siberia russia abstract eight oil and condensate samples and four samples of possible source rocks from the yamal peninsula northernmost west siberia have been characterized geochemically in order to determine source rocks and their maturity level the high content of c29 steranes m z 217 in extracts combined with geological data indicate nearshore marine and continental depositional environments for cretaceous argillites jurassic source rocks with a predominance of c27 steranes and pr ph ratios of 2 4 2 6 have been deposited in the deeper marine basin and contain oil prone type ii kerogen a number of parameters 20s 20s 20r steranes m z 217 22s 22s 22r hopane hopane moretane m z 191 ratios of tri and monoaromatic steroids m z 231 m z 253 and methylphenanthrene ratios show an increase in maturity with depth from immature cretaceous source rocks to moderately mature jurassic sources bazhenov and tyumen formations oil oil and oil source rock correlations based on genetic parameters and maturity indicators have demonstrated that fluids found in jurassic and cretaceous reservoirs including heavy biodegraded oil from the cenomanian belong to a single family and could be derived jointly from the bazhenov j3 and tyumen j1 2 formations the origin of naphthenic condensate found at shallow depth is still controversial although earlier work has suggested that biodegradation has been a dominant factor in the formation of naphthenic condensates their formation from cretaceous source rocks with type iii kerogen could also be possible

structure and origin of the j anomaly ridge western north atlantic ocean the j anomaly ridge is a structural ridge or step in oceanic basement that extends southwest from the eastern end of the grand banks it lies beneath the j magnetic anomaly at the young end m 4 to m 0 of the m series magnetic anomalies its structural counterpart beneath the j anomaly in the eastern atlantic is the madeira tore rise but this feature has been overprinted by post middle cretaceous deformation and volcanism in order to study the origin and evolution of the j anomaly ridge madeira tore rise system we obtained seismic refraction and multichannel reflection profiles across the j anomaly ridge near 39 n latitude the western ridge flank consists of a series of crustal blocks downdropped along west dipping normal faults but the eastern slope to younger crust is gentle and relatively unfaulted the western flank also is subparallel to seafloor isochrons becoming younger to the south anomalously smooth basement caps the ridge crest and it locally exhibits internal eastward dipping reflectors similar in configuration to those within subaerially emplaced basalt flows on iceland when isostatically corrected for sediment load the northern part of the j anomaly ridge has basement depths about 1400 m shallower than in our study area and deep sea drilling has shown that the northern ridge was subaerially exposed during the middle cretaceous we suggest that most of the system originated under subaerial conditions at the time of late stage rifting between the adjacent grand banks and iberia the excess magma required to form the ridge may have been vented from a mantle plume beneath the grand banks iberia rift zone and channelled southward beneath the rift axis of the abutting mid atlantic ridge resulting edifice building volcanism constructed the ridge system between anomalies m 4 and m 0 moving southward along the ridge axis at about 50 mm yr about m 0 time when true drift began between iberia and the grand banks this southward venting rapidly declined the results were rapid return of the spreading axis to normal elevations division of the ridge system into the separate j anomaly ridge and madeira tore rise and unusually fast subsidence of at least parts of these ridges to depths that presently are near normal this proposed origin and evolutionary sequence for the j anomaly ridge madeira tore rise system closely matches events of uplift and unconformity development on the adjacent grand banks

back arc extension in the okinawa trough the okinawa trough lying to the east of china is a back arc basin formed by extension within continental lithosphere behind the ryukyu trench arc system middle to late miocene uplift associated with normal faulting of the initially adjacent ryukyu nonvolcanic arc and the taiwan sinzi folded belt corresponds to the first rifting phase the timing of rifting is supported by the presence of marine sediments of corresponding age drilled in the northern okinawa trough the rifting occurred after a major early miocene change in the motion of the philippine plate with respect to eurasia and ceased during the pliocene a second rifting phase started about 2 m y ago at the plio pleistocene boundary and has continued until the present time it has proceeded to a more advanced stage in the middle and southern okinawa trough than it has farther north detailed bathymetric sea beam seismic reflection and magnetics data collected during the pop 1 cruise of the r v jean charcot reveal the principal features of the extensional processes the back arc spreading phase started very recently in the southern and middle okinawa trough as exemplified by several en echelon and in some cases overlapping active central graben oriented n70 e n80 e some of these depressions are intruded by volcanic ridges of fresh back arc basalt with associated large magnetic anomalies transform faults between these en echelon active rifts are not obvious we suggest that the major part of the southern okinawa trough is underlain by a thinned continental crust and that except for the system of en echelon rifts of the southern okinawa trough the back arc basin oceanic domain is limited to a width of a few tens of kilometers or less in the axial portion of the trough the system of axial back arc volcanic ridges that occur in the rifts ends at the latitude of okinawa island whereas active volcanoes in the ryukyu arc occur only north of okinawa island we refer to this transition between active arc and back arc volcanism as the volcanic arc rift migration phenomenon vamp globally back arc volcanism propagated from the southern okinawa trough to the okinawa vamp area rifting continues to occur in the northern okinawa trough but is not yet accompanied by associated volcanism the okinawa vamp area is characterized by a series of parallel basaltic ridges oriented n75 e with associated linear magnetic anomalies characteristic of dyke intrusions we suggest that the formation of the back arc oceanic domain took place along the axial back arc extensional zone trending n75 e and that this zone presently ends at the southern extremity of the active volcanic chain the initial phase of formation of back arc basin oceanic crust is non steady state and is characterized by the lack of a developed fracture zone pattern the termination of the vamp area in the direction of the volcanic zone of the arc is consistent with the suggestion of molnar and atwater that the volcanic arc is a fundamental line of weakness which determines where initial back arc spreading occurs apparently back arc extension initially occurred within the continental lithosphere located westward of the ryukyu arc along its whole length but the subsequent back arc volcanism was initiated in the southernmost portion of the region and then moved northward this migration was accompanied by the shutting down of volcanic activity along the abandoned portions of the arc it is this transfer of volcanism that we call the vamp process thus arc and back arc basin volcanism seem to be associated in such a manner that spreading tends to migrate simultaneously with a cessation in volcanic activity along the arc this interplay of arc and back arc activity is probably linked to changes in the parameters of plate convergence since the plate motion in the phillippine sea is oblique to the trench at least in the southern part of the okinawa trough we suggest that the oblique resisting force applied to the edge of the overriding plate engenders the development of en echelon extensional features within and behind the arc the motion of the ryukyu platelet with respect to eurasia is consequently an extensional strike slip motion trending roughly parallel to the okinawa trough

an experimental study of crude oil alteration in reservoir rocks by water washing abstract the objective of this research was to establish the effect of water washing on the physical and chemical properties of crude oils to simulate water washing under reservoir conditions crude oil was washed in sandstone and limestone cores by as much as 240 liters of a degassed bacteria free water over a period of up to 149 days at 90 c 194 f under a confining pressure of 138 bars 2000 psi in a flow through core holder unit the water washed oils were recovered by soxhlet extraction compared to the original oils water washed oils show lower api gravities lower concentrations of light aromatic compounds such as phenanthrene and dibenzothiophene lower metal and sulfur content lower light paraffins with respect to heavy paraffins and isoprenoids more negative stable carbon isotopic ratios for the nso fraction lower diterpane content relative to triterpane content lower c 27 steranes relative to c 30 hopane and 4 methyl sterane and altered bicyclic alkane and aromatic steroid biomarkers oils washed in limestone cores show a more severe reduction in api gravity and loss of aromatics than those in sandstone cores these changes can be used to discern the effects of water washing from those caused by biodegradation deasphalting and maturation of related crude oils diterpane triterpane and sterane biomarkers are little affected by water washing and therefore can be used to correlate water washed oils with related unaltered oils and source rocks and to assess the depositional environments of the source rocks for the water washed oils although these experiments did not produce tarmat tarmat formation by water washing over geological time cannot be ruled out the api gravity sulfur and metal content of oils may be reduced by water injection

geochemical evaluation of upper cretaceous fruitland formation coals san juan basin new mexico and colorado geochemical analyses of coal samples from the upper cretaceous fruitland formation in the san juan basin of new mexico and colorado were used to determine thermal maturity type of kerogen and hydrocarbon generation potential mean random vitrinite reflectance rm of the fruitland coal ranges from 0 42 to 1 54 rock eval pyrolysis data and saturated to aromatic hydrocarbon ratio indicate that the onset of thermal hydrocarbon generation begins at about 0 60 rm and peak generation occurs at about 0 85 rm several samples have hydrogen index values between 200 and 400 indicating some potential for liquid hydrocarbon generation and a mixed type iii and ii kerogen pentacyclic and tricyclic terpanes steranes aromatic steroids and methylphenanthrene maturity parameters were observed through the complete range of thermal maturity in the fruitland coals aromatic pentacyclic terpanes similar to those found in brown coals of australia were observed in low maturity samples but not found above 0 80 rm n alkane depleted coal samples which occur at a thermal maturity of approx 0 90 rm paralleling peak hydrocarbon generation are fairly widespread throughout the basin depletion of n alkanes in these samples may be due to gas solution stripping and migration fromthe coal seams coincident with the development of pressure induced fracturing due to hydrocarbon generation however biodegradation may also effect these samples

rift tectonics on the passive continental margin off galicia spain abstract new migrated multichannel seismic profiles on the starved passive continental margin off galicia spain illustrate the tectonic style of the early cretaceous rifting event which preceded the separation of iberia and north america the main episode of rifting was preceded by other tensional episodes probably of earliest cretaceous and late jurassic age listric faulting associated with rifting was accompanied by large scale mass movements from the crests of the tilted blocks two subaerial erosional surfaces are visible one of late jurassic or earliest cretaceous age was affected by the final faulting episode the other was synchronous with the main phase of rifting and is present only on the upper part of the margin because the central trough was under deep water the significance of a ridge near the ocean continent boundary where altered lherzolite has been dredged and cored is discussed below the tilted blocks which include the basement rocks the seismic horizon s is visible as on the armorican margin its significance is also discussed

molecular measurements of maturity for lias δ shales in n w germany abstract the extractable aliphatic and aromatic hydrocarbons of twenty four lias shales from n w germany have been analysed by gas chromatography mass spectrometry particular attention has been paid to seven molecular measurements of thermal maturation which are based on appropriate ratios of the concentrations and products of certain reactions a sequence of increasing maturity towards the area of the bramscher massiv was determined because the reactions involved occur at different rates they reach completion at different levels of maturity and at variable distance from the centre of the bramscher massiv as defined by iso vitrinite reflectance contours reported previously for rhaetic lias and malm shales this has allowed the designation of zones of increasing maturity the molecular measurements appear more reliable assessors of maturity than vitrinite reflectance for samples less mature than the zone of oil generation but are not applicable to samples from within this zone because the reactions concerned have normally reached completion a mathematical model suggests that the maturity of samples less mature than a vitrinite reflectance of 1 can adequately be explained by substantial subsidence during early and middle cretaceous followed by major uplift and inversion in late cretaceous time without recourse to further heating from a deep seated igneous intrusion

age and structure of the southern rockall trough new evidence abstract the rockall trough separates the rockall plateau microcontinent from the shelf and slope west of the british isles the structure and age of the trough has been the source of considerable discussion although widely considered to be of oceanic origin postulated ages for the spreading range from permian to cretaceous new seismic profiles linked to the ipod sites in the bay of biscay and to oceanic anomalies of known age are used to present a new assessment of the age and structure of the southern rockall trough it is concluded that about 120 km of ocean crust is present in the trough and that spreading took place in the albian maastrichtian interval

unusual biomarker maturation ratio changes through the oil window a consequence of varied thermal history abstract saturated and aromatic biomarker ratios continue to change systematically through the oil window and into the gas condensate window to high vitrinite reflectances r o 1 16 in mature marine and lacustrine mesozoic clastic samples from a south african basin two of the ratios reverse above r o 0 9 these unusual maturation effects result from isolated periods of high rates of maturation increase the basin cooled regionally after the break up of gondwana but high heating rates prevailed during the late cretaceous early tertiary as africa moved across a hotspot and again in the late tertiary as a result of a possible hotspot and hydrothermal event

absolute reconstructions of the paleozoic oceans abstract the orientation of three intraplate magmatic belts the mongolian from 130 to 280 m y south siberian from 320 to 400 m y and baltic from 365 to 400 m y belts which can be considered as hot spot tracks are used together with apparent paleomagnetic pole wander paths to reconstruct true motions of continents during paleozoic times the reconstructions obtained show that the old late precambrian pangea continued to exist in the early paleozoic with an inner arrangement of constituent continents strongly different from that of the late paleozoic pangea the continents were constantly located in the eastern hemisphere only the western hemisphere was occupied by the paleo pacific oceans four oceans existed in paleozoic times between the continents in the eastern hemisphere 1 the iapetus which originated in the late precambrian and closed before devonian times 400 m y 2 the asiatic paleo ocean which originated in the late precambrian and closed 450 m y ago 3 the uralian paleo ocean which opened around 500 m y ago and closed in the latest permian 240 230 m y 4 the paleo tethys which opened in the ordovician 480 450 m y and became the mesozoic tethys life duration of the oceans was 200 400 m y the main trend in the earth s evolution during the paleozoic was a break up of the old precambrian supercontinent and construction of the new late paleozoic pangea

tectonic implications of canyon directions over the northeast atlantic continental margin the basis of this study is a new bathymetric map of the northeast atlantic compiled from previously published maps made from conventional echosounder data plus all sea beam data acquired on board the r v jean charcot since 1977 as most of the sea beam data have been obtained on the continental margin from porcupine seabight to the south of the iberian peninsula a precise picture of the continental slope is given a statistical analysis of the canyons based on 750 measurements reveals that many of the canyons present sharp changes in their direction indicating a structural control mainly linked to the late hercynian trends especially around the iberian peninsula nevertheless the paths of canyons may merely reflect recent gravity processes as in the porcupine seabight canyons locally follow the directions of listric and associated transecting faults permian to triassic and upper jurassic to lower cretaceous as on the celtic margin and every type of tectonic lineament for example the north pyrenean paleogene thrust front which fringes the gouf of cap breton a comparison of diagrams for the northern and southern bay of biscay margin especially trends predating the opening is compatible with a 25 rotation of iberia with respect to europe

seismic image of undercrusted serpentinite beneath a rifted margin during the continental rifting the upper mantle was unroofed and the mantle rocks were transformed into serpentinite at the ocean continent transition of the west galicia margin spain the serpentinite layer several km thick extends probably eastwards beneath the highly thinned continental crust of the margin the serpentinite layer was recently imaged by seismic reflection it is discontinuously and deeply layered as serpentinized peridotite can have densities and seismic velocities comparable to those of the lower continental crust we suggest that undercrusting by serpentinite can play a part in building the lower seismic crust in highly stretched continental rifted areas

geoid pangea and convection abstract we show that the present geoid has a simple low order configuration with an axis of symmetry in the equatorial plane we show further that it is a tennis ball pattern with an equatorial high belt and a polar low one which is clearly controlled by the rotation of the earth finally we show that the outline of pangea between at least 200 ma and 125 ma ago lay along a great circle passing through the paleo poles of rotation thus it also had an axis of symmetry in the equatorial plane this hemispheric super continent configuration ended in middle cretaceous time during a major geologic catastrophe which was accompanied by high rates of spreading hotspot outbreaks and high sea level stands we interpret this evidence in terms of separate steady state lower mantle convection responsible for the present geoid weakly coupled to the upper mantle one this weak coupling leads to the hemispheric continent configuration which ends when excessive heating of the upper mantle due to the insulating continental cap leads to continent dispersal the complete cycle from one supercontinent to the next might be of the order of 400 ma

towards a new concept of the tectogenesis of the pyrenees abstract crustal structures of the central and eastern pyrenees are compared with those of the alps and carpathians by analogy northward subduction underthrusting in the central and eastern pyrenees is proposed southward subduction underthrusting is found along the north iberian margin and western pyrenees hence a flip a change in the direction of subduction underthrusting is postulated between the central and western pyrenees

the role of the ocean in a regional sulfur cycle dimethylsulfide dms concentrations were measured in ocean waters along the west coast of the united states on three cruises during 1983 and 1984 concentrations in surface waters ranged from 13 to 380 ng s l with a summer average of 60 and a winter average of 20 ng s l the flux of sulfur from the ocean to the atmosphere was calculated using the stagnant film boundary layer model to be 28 mg s m2 a on the basis of a non sea salt sulfate residence time of 5 days the calculated net flux of biogenic sulfur to the west coast of the united states is 0 045 tg a this is 4 13 of the combined total anthropogenic emissions from the western united states

late cretaceous and cenozoic intra plate compressional deformations in the alpine foreland a geodynamic model abstract the mesozoic grabens and wrench induced troughs of western and central europe developed in response to triassic early cretaceous intra plate tensional stresses which affected the arctic north atlantic and the tethys borderlands during the rifting phase preceding the opening of the respective oceans this resulted in the fragmentation of the continental crust of the alpine foreland during the late cretaceous and tertiary alpine orogeny collision related compressive stresses exerted on the foreland induced the reactivation of these fracture systems causing the inversion of mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present alpine deformation front the structural style of these inverted basins and basement uplifts is indicative of compressional and transpressional deformations the total amount of crustal shortening associated with these deformations is unlikely to exceed a few tens of kilometres these displacements require a coupling between the foreland and the orogen at the alpine a subduction zones and within the foreland a decoupling at intra crustal levels between the crust and mantle and or at deeper lithospheric levels the example of the alpine foreland indicates that compressive stresses inducing major deformations can be transmitted from a collisional plate boundary through continental lithosphere over distances of up to 1300 km circumstantial evidence suggests that collision related compressive stresses not large enough to give rise to significant deformations can be transmitted through continental lithosphere over even greater distances

paleomagnetism of the lower cretaceous redbeds from northern spain evidence for a multistage acquisition of magnetization abstract an extensive study of the wealden series from the cantabric chain and the sierra de los cameros northern spain reveals that the n r m contains four types of components tentatively classified in decreasing ages the older components group 1 are considered as the primary magnetization they yield a paleomagnetic pole located at lat 41 n long 237 e n 6 k 186 95 5 this pole position implies the existence of a large upper jurassic lower cretaceous swing in the iberian polar wander path the comparison with other polar paths north america africa supports the hypothesis of an initial lower cretaceous rotation of iberia prior to the main mid cretaceous shift the remainder of the components represent remagnetizations the major phase groups 2 and 3 extended from the upper cretaceous to the eocene at least a period closely correlated with the period of convergence between the european and iberian plates the directions of group 3 are characterized by low inclination this is a common behaviour for eocene directions in the mediterranean area previous data obtained from the wealden redbeds largely agrees with the directions of one or other of the groups 2 and 3 as there is strong evidence of an acquisition subsequent to the main mid cretaceous movement of iberia the geodynamical inferences of the paleomagnetic data have to be re examined the last type of components group 4 was built up during recent remagnetization and is of little interest

the effect of lower crustal flow on continental extension and passive margin formation the great variety of styles of continental extension may reflect different crustal thickness and thermal states of continental lithosphere during the initiation of rifting to investigate how these and other factors affect rifting and the development of passive continental margins we develop a simplified model of lithospheric extension we consider the evolution of extensional deformation for a three layer model lithosphere bounded laterally by much stronger lithosphere the cold part of the crust and mantle are treated as thin brittle plastic layers the lower crust is approximated as a thin viscous channel each brittle plastic layer can extend in only one location determined by the strength of the layer shear of the lower crust and buoyancy forces related to both crustal thickness variations and thermally induced density differences the lower crust flows in response to crustal thickness variations and is sheared when the loci of extension for the two brittle plastic layers are horizontally offset a situation we term shear decoupling as in previous studies we see three distinct patterns or modes of extensional deformation that occur under different sets of model parameters the core complex mode the wide rift mode and the narrow rift mode shear decoupling occurs only in cases with a crustal rheology at the weak end of the spectrum of laboratory estimated values we are aware of no observations that require that the upper crust and upper mantle strain at laterally displaced positions we show that for large magnitudes of extension there can be transitions between modes as inferred for some highly extended continental areas predicted patterns of crustal thickness and heat flow for some models are similar to observations at several rifted continental margins including very wide and asymmetric margins

in situ evaluation of air sea gas exchange parameterizations using novel conservative and volatile tracers measurements of air sea gas exchange rates are reported from two deliberate tracer experiments in the southern north sea during february 1992 and 1993 a conservative tracer spores of the bacterium bacillus globigii var niger was used for the first time in an in situ air sea gas exchange experiment this nonvolatile tracer is used to correct for dispersive dilution of the volatile tracers and allows three estimations of the transfer velocity for the same time period the first estimation of the power dependence of gas transfer on molecular diffusivity in the marine environment is reported this allows the impact of bubbles on estimates of the transfer velocity derived from changes in the helium sulphur hexafluoride ratio to be assessed data from earlier dual tracer experiments are reinterpreted and findings suggest that results from all dual tracer experiments are mutually consistent the complete data set is used to test published parameterizations of gas transfer with wind speed a gas ex change relationship that shows a dependence on wind speed intermediate between those ofliss and merlivat 1986 and wanninkhof 1992 is found to be optimal the dual tracer data are shown to be reasonably consistent with global estimates of gas exchange based on the uptake of natural and bomb derived radiocarbon the degree of scatter in the data when plotted against wind speed suggests that parameters not scaling with wind speed are also influencing gas exchange rates

early history of the atlantic ocean and gas hydrates on the blake outer ridge results of the deep sea drilling project leg 76 leg 76 of the deep sea drilling project achieved two major scientific objectives the first objective was met at site 533 where on the blake outer ridge gas hydrates were identified by geophysical geochemical and geological studies gas hydrate decomposition produced a volumetric expansion of 20 1 of gas volume to pore fluid volume this expansion exceeded by about a factor of four the volume of gas that could be released from solution in pore water under similar conditions the gas hydrate includes methane ethane propane and isobutane but apparently excluded normal butane and higher molecular weight hydrocarbons as predicted from gas hydrate crystallography for the first time marine gas hydrates were tested with a pressure core barrel the second objective was achieved when coring at site 534 in the blake bahama basin sampled the oldest oceanic sediments yet recovered the sequence of oceanic basement and overlying sediments documents the geologic history of the early stages of the opening of the north atlantic ocean in detail the oldest oceanic sediments are red claystones and laminated green and brown claystones of middle callovian age this finding supports the interpretation that the beginning of the modern north atlantic occurred in the early callovian 155 m y b p as much as 20 m y later in time than often previously thought

a north sea southern norway seismic crustal profile summary in this paper results are presented from a seismic refraction experi ment canobe carried out in southern norway ten explosions fired at sea were recorded on land by shifting 13 recording instruments along a pro file with an average station spacing of 5 km the main line runs in a north easterly direction from the south coast at lista along the western margin of the oslo graben into the norsar array with a total length of 5 15 km a separate leg runs across the graben just north of oslo for the first time allow ing a direct comparison of seismic records in the graben with those in the adjacent precambrian shield area the laterally varying crustal structure along the profile is examined by modelling of travel times and amplitudes of p wave arrivals the moho which is the major discontinuity in the lowermost crust appears to sink beneath the coast from 27 km on the seaward side to 34 km onshore the two dimensional modelling procedure adopted proves invaluable in explaining the characteristic amplitude pattern observed in this area beyond the coastal area our picture of the crust is that of a relatively homogeneous one as expected for a shield area there are no indications of significant discontinuities in the crust along the first 300 km of the profile although from the large pg amplitudes within this distance range we infer a strong velocity gradient in the lower crust two structural models are pro posed for the oslo graben where the moho appears to be elevated to between 25 and 29 km

fault development and stress evolution of the post hercynian asturian basin asturias and cantabria northwestern spain abstract the asturian basin an emerged part of the north iberian continental margin has been investigated in terms of fault development and stress evolution the mesozoic history of this domain is mainly linked to the extensional faulting processes which preceded the opening of the bay of biscay preserved jurassic faulted blocks and associated half graben structures bounded by wnw ese to nw se faults are related to a late jurassic kimmeridgian rifting stage this fault system seems to have played a major role during the mesozoic structuring of the basin suggesting an extension oriented approximately ne sw the cenozoic evolution is related to the iberia eurasia convergence and collision leading to compressional and subsequent extensional structures the direction of compression documented in various sites was nnw sse during an initial early middle eocene stage reoriented probably in the oligocene to ne sw this succession of stress regimes was applied to the same three major fault systems ne sw nw se and e w which were inherited from the variscan orogeny some of them having already been involved in the latest stephanian early permian rifting episode during the tertiary compressional phase the nw se trend which is believed to have controlled the late jurassic tectonic development was rejuvenated into dextral strike slip faults whereas the ne sw system moved in a sinistral sense the e w system was reactivated as reverse faults giving rise to a partial inversion of the basin

early opening history of the north atlantic i structure and origin of the faeroe shetland escarpment summary marine geophysical surveys show that the escarpment is the buried feather edge of a thick pile of flood basalts of early eocene age overlying a thinner more widespread layer of basalts of late palaeocene age the escarpment does not therefore define the continent ocean boundary in the southern norwegian sea but instead marks the contemporary shoreline separating terrestrially erupted basalt flows in the north from a restricted shallow water shelf to the south the basalts overlie 5 6 km of mesozoic sediments which have completely buried a large conical flat topped seamount of similar dimensions to anton dohrn and rosemary bank we call this newly postulated body the brendan seamount the mesozoic sediments are at least as old as early cretaceous in age therefore precluding the possibility that the mid cretaceous seafloor spreading episode supposed by some to have created the rockall trough could have also created the thin crust inferred to underlie the faeroe shetland trough and mbre basin

paleomagnetism of permo triassic redbeds from the asturias and cantabric chain northern spain evidence for strong lower tertiary remagnetizations the paleomagnetic analysis of the permo triassic redbeds outcropping in the western part of the cantabric chain and the small mesozoic basin from the asturias shows that these formations have a history of complex magnetization only a few sites did not experience the remagnetization processes and retained original directions the most reliable results yield a paleomagnetic pole located at lat 49 n long 217 e n 11 95 3 7 which is suggested as reliable permo triassic data for the iberian plate two remagnetization phases are recognized a moderate phase predating the folding gave rise to a first overprinting it is connected with the distension which occurred in the pyreneo cantabrian region during the upper jurassic lower cretaceous the main remagnetization phase which occurred after the folding is dated from the lower tertiary and can be related to the compression induced on the northern boundary of iberia from upper cretaceous onwards in some cases this phase led to a complete replacement of the primary magnetization previously published data which were at the time interpreted as being european like in direction are attributed to this phase hence our results do not support the hypothesis of a micro plate called le danois block which was suggested in order to explain these results we believe that there is no paleomagnetic evidence supporting the existence of a complicated boundary between europe and iberia during the mid cretaceous opening of the bay of biscay

western extension of the iberian european plate boundary during the early cenozoic pyrenean convergence a new model abstract a dense seismic net work allows of drawing the western prolongation of the northern boundary of the iberian plate this early cenozoic deformed boundary is disrupted by two prominent nw se transform faults a kinematic reconstruction with a nw late cretaceous lower eocene motion of the iberian plate is proposed the azores biscay rise is interpreted as a short lived subduction zone whereas king s trough could be a transform fault

structure and development of porcupine seabight sedimentary basin offshore southwest ireland the porcupine basin is a deep sedimentary basin on the continental margin west of ireland all available geologic and geophysical data have been used to interpret the history of the basin it contains up to 8 km of cretaceous and younger sediments underlain by an unknown thickness of jurassic and triassic rock gravity and magnetic anomaly models have been used to investigate the nature of the crust beneath the porcupine basin these models suggest a thinned continental crust rather than the oceanic crust previously proposed by some authors although the nature of a narrow zone of crust 10 km thick in the central southern basin cannot be determined conclusively a high amplitude elongate gravity high associated with a negative magnetic anomaly in the axis of the n rthern porcupine seabight correlates with a volcanic ridge probably of early cretaceous age seen on seismic reflection profiles regional geologic and geophysical studies show that the porcupine basin was originally structured in the early mesozoic as part of a complex northeast to north northeast trending intracontinental rift system extending from the grand banks of newfoundland to the present northwest europe continental shelf the basin can be divided into a sequence of segments bounded by north northeast trending normal faults and northwest trending strike slip faults the degree of extension within the basin decreases northward across each strike slip fault accounting for the overall northward narrowing of the basin the early mesozoic rift fabric of the porcupine basin was reactivated during the early cretaceous when the basin became caught up in the northwest trending rift that later evolved into the n rth atlantic this second phase of extension led to subsidence and the accumulation of extreme thicknesses of cretaceous and younger sediments

organic matter maturation under the influence of a deep intrusive heat source a natural experiment for quantitation of hydrocarbon generation and expulsion from a petroleum source rock toarcian shale northern germany four shallow boreholes were drilled in the hils syncline northern germany in order to determine quantitatively the amount of hydrocarbons generated and expelled during maturation of a typical kerogen type ii bearing source rock the holes penetrated the carbonceous lias shales posidonia shale lower toarcian and part of the adjacent dogger and lias mudstones the maturity of the organic matter in the cores recovered ranges from immature 0 48 r0 to overmature 1 45 r0 due to location of the hils syncline in the vicinity of the vlotho massif which is deep seated intrusive body facies variations of the lias within the short geographical distances in the study area are negligible organic matter mass balance calculations were based on detailed organic geochemical analyses of residual material in the lias shales kerogen bitumen etc and on the evidence of a uniform initial composition of these sediments in the study area dead carbon determinations supported this latter criterion but were not used as a parameter in the calculations about 50 of the initial kerogen was transformed into oil gas and inorganic compounds during the vitrinite reflectance increase from 0 48 to 0 88 ro and only marginally more during the maturity increase from 0 88 to 1 45 ro only a small portion of the generated material remained in the source rock even at a relatively early stage of generation 0 68 ro expulsion efficiency of oil plus gas reached a value of 86 at the end of the main generation stage 0 88 ro

volcanic belts as markers of the mesozoic cenozoic active margin of eurasia abstract from the triassic to the present linear belts of calc alkaline volcanism developed along the southern margin of eurasia in the triassic the calc alkaline belt can be traced in turan fore caucasus crimea and dobrogea its development is related to the closure of the paleo tethys when fragments of gondwana iran afghanistan etc were approaching eurasia since the early jurassic calc alkaline volcanism has been related to subduction of the oceanic crust of the mesozoic tethys five stages of calc alkaline volcanic activity can be distinguished early jurassic middle jurassic early cretaceous late cretaceous paleogene and late miocene quaternary the configuration of the volcanic belts the intensity of the volcanism and the chemistry of the erupted products change considerably from stage to stage mesozoic belts were most pronounced in the pontian transcaucasian segment of the margin starting from the late cretaceous and especially in the cenozoic the volcanic belts can be continuously traced from the balkans to afghanistan most of the belts were actually island arcs formed on the fragments of the hercynian of baikalian basement and in this respect similar to the island arc of japan only the incipient island arcs of senonian age formed close to the passive margin of gondwana are the exceptions they were built on oceanic crust and are geochemically close to the mariana arc at certain times early jurassic eocene parallel chains of island arcs existed in general the situation resembled the present day convergent boundary in the western pacific as closure of the tethys proceeded island arcs gave way to marginal continental volcanic belts with wide spread development of high potassium particularly shoshonitic series peaks of volcanic activity in the bajocian late cretaceous eocene and late miocene present alternated with quiet periods and corresponded to the times when the convergence rate between africa and eurasia increased the opening of the back arc basins is reflected in outbursts of basaltic rift type volcanism these outbursts occurred in the toarcian aalenian bathonian late jurassic aptian turonian and early middle eocene

comparison between the galicia and aquitaine margins abstract there is a great similarity between the galicia margin and the aquitaine margin i e the aquitaine basin and the north pyrenean zone in particular the timing of the rifting as well as the resulting structures exposure of perodotite tilted fault blocks normal and transverse faults half grabens are practically the same this comparison leads to the interpretation that the northern side of the pyrenean fold belt is inherited from the mesozoic deep passive margin of europe the cenozoic thrust sheets and reverse faults of the northern pyrenees zone are tentatively interpreted as former rift structures tilted blocks and listric faults which were removed during the convergence of the iberian and european plates during the paleocene and eocene

geochemistry of selected oils and rocks from the central portion of the west siberian basin russia six analyzed oils produced from middle jurassic to upper cretaceous strata in the middle ob region of the west siberian basin show biomarker and stable carbon isotope compositions indicating an origin from the upper jurassic bazhenov formation the chemical compositions of these oils are representative of more than 85 of the reserves in west siberia kontorovich et al 1975 bazhenov sourced oil in cenomanian strata in the van egan field underwent biodegradation in the reservoir resulting in a low api gravity an altered homohopane distribution and the appearance of 25 norhopanes without alteration of the steranes high api gravity oil from the salym field has surpassed the peak of the oil window consistent with abnormally high temperatures and pressures in the bazhenov source rock from which it is produced the remaining oils are very similar including samples from valanginian and bathonian callovian intervals in a sequence of stacked reservoirs in the fedorov field bazhenov rock samples from the study area contain abundant oil prone marine organic matter preserved under anoxic conditions organic matter in a bazhenov core from the pokachev 58 well was compared with the oils because it is thermally mature and shows total organic carbon toc 13 8 wt and hydrogen index values hi 489 mg hc g toc representative of the average for the formation 10 7 wt for 840 samples 420 mg hc g toc for 75 samples other rocks in the middle ob region are far less likely to have generated these oils than the bazhenov formation no prospective source rocks older than middle jurassic were available geochemical analyses indicate a lack of thermally mature hauterivian or younger source rocks in the study area core samples from the lower cretaceous frolov formation either are thermally immature hauterivian or show little oil generative potential berriasian valanginian the upper jurassic vasyugan formation shows lower oil generative potential than the bazhenov formation the average toc for vasyugan rocks is 3 20 wt 240 samples average atomic h c ratios for vasyugan and bazhenov kerogens are 0 90 10 samples and 1 13 25 samples respectively the vasyugan formation cannot be excluded as a source rock because insufficient sample was available for biomarker analysis core from the lower to middle jurassic tyumen formation in the yemyegov 15 well was compared with the oils because it is thermally mature and shows toc and hi values 2 78 wt and 137 mg hc g toc respectively indicating slightly more favorable oil generative characteristics than the average for the formation 2 75 wt for 720 samples 95 mg hc g toc for 25 samples the core contains terrigenous gas prone organic matter that shows no relationship with the analyzed oils

the newfoundland basin ocean continent boundary and mesozoic seafloor spreading history the ocean continent boundary in the newfoundland basin is defined as the seaward limit of a continental margin magnetic smooth zone east of the grand banks this boundary is marked by a prominent nne trending magnetic anomaly that is correlated with the j anomaly 115 m y south of flemish cap the smooth zone boundary strikes approximately 060 and is approximately 15 m y younger magnetic anomaly trends suggest two directions of motion during separation of iberia and north america the first phase of motion commencing at j anomaly time with a spreading center strike of 015 produced a rifted margin along the grand banks south of the newfoundland seamounts no spreading occurred north of the seamounts during this phase implying a counter clockwise rotation of iberia and no grand banks galicia bank separation the second phase began at about 102 m y with a shift of the pole of rotation to a location near paris producing a ridge orientation of approximately 060 this spreading center extended north and east into the northern newfoundland basin and bay of biscay producing a rifted margin south of flemish cap and opening of biscay this ridge geometry produced a component of extension across the newfoundland fracture zone and the southeastward migration of the resultant leaky transform fault between 102 m y and the next pole shift produced the volcanic edifice of the southeast newfoundland ridge fracture zone trends during this phase also exerted strong control on volcanism within the newfoundland seamount province this activity ceased at about 97 m y the date at which the second phase ended is not well defined by presently available data a rrr triple junction existed in the northeastern newfoundland basin western biscay region for a short time prior to anomaly33 34 80 m y which marks the inception of a continuous mid atlantic ridge spreading center between the newfoundland and charlie gibbs fracture zones

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

structural and sedimentological evolution of part of the west central spanish pyrenees in the late tertiary during the late oligocene and early miocene the frontal thrust complex of one of the south pyrenean thrust sheets the guarga or gavarnie sheet became emergent to form part of the northern margin of the ebro basin the principal structures in the frontal thrust complex show a progressive development from a simple recumbent fold in the west to an emergent thrust in the east southward movement at the thrust front decreased from east to west and in the west the thrust tip line is buried these structures influenced miocene continental sedimentation on two scales the emergent thrust front formed an orographic barrier to rivers draining the higher pyrenees these rivers passed around the barrier rather than across it and the positions of the apices of fluvial distributary systems in the ebro basin were thus controlled by the low points in the structure of the thrust front on a smaller scale sedimentary sequences and syn depositional structures in small alluvial fan bodies at the basin margin were controlled by late thrust movements in the adjacent frontal thrust complex syn depositional faults folds and unconformities in the alluvial fan conglomerate sequences can be related to movements on individual faults within the thrust complex

dmsp removal and dmso production in sedimenting particulate matter in the northern north sea work was conducted to establish if the downward flux of sedimenting material represents a sink for particulate dimethylsulphoniopropionate dmsp and to investigate the fate of this dmsp within the sedimenting material four sediment traps were successfully deployed for a maximum of 24 h in the northern north sea between the 5th june and the 1st july 1999 after recovery samples were taken immediately and analysed for levels of dimethylsulphide dms dimethylsulphoxide dmso and dmsp any remaining trap material was incubated in the dark at in situ seawater temperature for a maximum of 120 h results from the sediment traps showed that only 1 of the dmsp standing stock was lost daily due to sedimentation however results from the incubation experiment demonstrated not only that the downward flux of dmsp is underestimated due to its degradation within the trap material with between 30 and 47 of the dmsp being lost over 48 h but also that up to 21 of the dmsp lost may be converted to dmso these results clearly demonstrate that dmso is generated within sedimenting material

biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of opalinus clay and posidonia shale in northern switzerland abstract samples from two argillaceous formations opalinus clay and posidonia shale of near identical maturity from northern switzerland were subjected to a geochemical characterisation of organic matter and to confined system pyrolysis experiments throughout the study area the characteristics of organic matter are similar indicating a spatially homogeneous sedimentary facies posidonia shale contains marine organic matter deposited in a reducing environment while a predominantly terrigenous source and a more oxidising environment of deposition was identified for opalinus clay in the western and central parts of the study area organic maturity is close to the onset of oil generation in the easternmost part a higher maturity has been reached due to a deeper burial below thick tertiary molasse deposits isothermal pyrolysis experiments were conducted at temperatures between 250 and 390 c over 24 h bitumen yields increase along similar pathways for both opalinus clay and posidonia shale but the maximum values are displaced by 10 20 c data pertaining to maturity were determined from gc ms analyses of saturated hydrocarbons and specific attention was given to c 29 sterane and c 32 hopane isomerisation ratios the evolution of these parameters with rising temperature is slightly different in the two formations which is attributed to the contrasting organic facies the pyrolysis data together with literature data from natural basins were used to calculate kinetic parameters for c 29 sterane and c 32 hopane assuming a single step isomerisation scheme according to the arrhenius law the resulting values based on pyrolysis data alone are very similar to those based on the combination of pyrolysis and natural data activation energies are similar in both formations while the frequency factors are up to one order of magnitude higher for posidonia shale when compared to opalinus clay for the benken site maximum temperature during cretaceous burial was calculated on the basis of the kinetic data using the tti approach the resulting temperatures of 75 80 c are 5 10 c below those derived in the literature from apatite fission track analysis vitrinite reflectance and basin modelling

palaeomagnetism and isotopic age data from upper cretaceous igneous rocks of w portugal geological correlation and plate tectonic aspects summary palaeomagnetic results and k ar age data for the sintra and sines intrusive complexes w portugal and further details on the palaeomagnetic structure of the lisbon volcanics are reported the sintra complex consists of two main intrusive phases having been emplaced in the upper cretaceous at around 90 ma and 75 ma respectively the radiometric results show that the sines complex formed concurrently with the second sintra magmatism the early main sintra pluton has a characteristic magnetization of d 358 i 27 95 3 3 this remanence direction is defined by gabbros and diorites as the granitic rocks constituting the bulk of the complex are shown to possess stable secondary magnetization imposed during quaternary weathering the characteristic magnetization of the younger intrusive event as defined by the sines rocks has a mean direction of d 041 i 41 95 3 3 these two upper cretaceous palaeomagnetic directions are significantly different at the 95 per cent probability level the lisbon volcanics show the presence of the 75 ma magnetization suggesting that also this volcanic complex dates from the upper cretaceous in addition the palaeomagnetic results from the lisbon complex have given further substance to a previously reported magnetization component with shallow inclination and north northwest declination now defined by d 333 i 14 95 7 4 it is inferred that this magnetization which has a dual polarity structure formed through low temperature oxidation in late cretaceous to lower tertiary time the declination difference between the 90 ma and 75 ma magnetizations may be interpreted in terms of a two phase rotation of iberia in the upper cretaceous prior to the assumed late cretaceous early tertiary secondary magnetic imprint implying a counterclockwise rotation of minimum 40 followed by a clockwise rotation of similar magnitude however if the relevant palaeomagnetic reference frame for iberia before and after its independent tectonic movements in the late cretaceous is the african plate then the clockwise rotation is about 20 larger than the counterclockwise one apparently accounting for the compressive tectonism in the bay of biscay

implications of the seismic structure for the orogenic evolution of the pyrenean range abstract the dynamic evolution of the pyrenees is discussed in the light of geophysical data recent deep seismic sounding have revealed the crustal structure of the pyrenees which is used to test the different evolutionary models proposed until now the crustal thickness of the paleozoic axial zone paz and the north pyrenean zone npz differ by more than 10 km ranging from about 30 km in the npz to 40 50 km in the paz the transition from paz to the npz identified at the surface as the north pyrenean fault npf is sharp at depth and marked by a vertical step at least in the eastern half of the range the npz is characterized by additional throws and dips of the moho in the east whereas in the west a heterogeneous middle to lower crust is encountered with high velocity anomalies the seismic results suggest that the paz and the npz belong to different plates the npf being the plate boundary these results are inconsistent with evolutionary models involving lithospheric subduction or crustal doubling and intracratonic rifting with the main tectonic lineations following nne ssw directions they rather suggest that after a period of extension two main orogenic events took place a phase involving shearing and thinning which affected mainly the present day npz and a later compressive phase which explains the building up of the chain the thickening of the crust and the enhancement of a pre existing difference in crustal thickness between the european and iberian plates

the mesozoic tertiary evolution of the aquitaine basin the aquitaine basin situated in southwest france with an area of about 60 000 km 2 has the form of a triangle which opens towards the atlantic bay of biscay and is limited to the north by the hercynian basement of brittany and the massif central and to the south by the pyrenean tertiary orogenic belt beneath the tertiary sequence 2 km thick and which outcrops over much of the basin a mesozoic series up to 10 km thick rests generally on a tectonized hercynian basement but locally it covers narrow nw se trending post orogenic trenches of stephano permian age the mesozoic history can be subdivided into four major structural sedimentary episodes 1 during a triassic taphrogenic phase a continental evaporitic complex developed with associated basic magmatism 2 throughout the jurassic a vast lagoonal platform developed initially lower lias as a thick evaporitic sequence followed by a uniform shale carbonate unit indicating a relative structural stability 3 the end of the jurassic and the lower cretaceous saw a fragmentation of this platform due to an interplay between the iberian and european tectonic plates resulting in an ensemble of strongly subsident sub basins 4 during the upper cretaceous and until the end of the neogene the evolution of the aquitaine basin was influenced by the pyrenean orogenic phase with the development towards the south of a trench infilled by flysch which from the upper eocene is succeeded by a thick post orogenic molasse complex the main hydrocarbon objectives in the basin are situated in the jurassic platform e g the lacq giant gas field and the cretaceous sub basins e g the cazaux and parentis oil fields to date production has been about 4 times 10 7 m 3 of oil and about 15 times 10 10 m 3 of gas since the first gas discovery st marcet in 1939

geophysical constraints on the deep structure of a limited ocean continent subduction zone at the north iberian margin 1 late cretaceous to cenozoic convergence between iberia and europe led to the partial closure of the bay of biscay with limited southward subduction of oceanic crust below the north iberian margin inclined sub moho reflections and diffractions observed in deep seismic reflection profiles shot across the margin are especially well represented in two reflection profiles escin 3 2 and escin 3 3 these two profiles have been chosen to test if the sub moho reflections correspond to true primary deep events and provided that they are reflecting off the subduction zone to investigate its deep structure spectral analysis together with travel time estimation and migration allow us to characterize a number of these sub moho events as deep source low frequency 19 hz reflections and diffractions synthetic seismograms were generated by three dimensional seismic modeling of a sub moho southward dipping surface interpreted to correspond to the top of subducted oceanic crust comparison between the real and synthetic data show that inclined low frequency sub moho reflections in both escin 3 2 and escin 3 3 profiles may correspond to reflections from southward subducted bay of biscay oceanic crust geoid free air gravity and absolute topography modeling provides additional constraints on the lithospheric scale structure of this limited ocean continent subduction zone beneath the north iberian margin

formation of non volcanic passive margins a composite model applies to the conjugate galicia and southeastern flemish cap margins one of the most controversial issues in geology today is the way the lithosphere extends the galicia margin is a particularly good place to adress this problem as it is fairly sediment starved has clear upper crustal structure well imaged by a variety of seismic reflection profiles and has well control to calibrate seismic data observed subsidence is compared with extension of the uppermost crust of the entire margin as computed from the geometry of tilted fault blocks imaged on a series of parallel seismic lines the pure shear or stretching model clearly accounts for the extension of the upper continental margin but not for the lower margin where the s reflector zone a prominent zone of intra crustal reflectors is present i suggest that the s reflector zone is a detachment zone accomodating decreasing displacement towards the continent and that this detachment zone active since the beginning of rifting outcrops on the canadian side and corresponds to the steep southeastern flemish cap continental slope pure shear is the mechanism which affects the whole lithosphere but in the upper part of the crust the rifting mechanism is locally simple shear where the detachment zone is active

occurrence of pockmarks on the ortegal spur continental margin northwestern iberian peninsula a total of 445 pockmarks were observed on the upper continental slope of the northwest corner of the iberian peninsula the ortegal spur area by swath bathymetric and ultrahigh resolution seismic data the pockmarks are u v and w shaped and have terraces or indentations in cross section and are dish shaped circular to oval in plan view they occur on the surface of the seabed and buried within the plio quaternary and neogene sediments four types of pockmarks were identified and mapped on the basis of their plan view and cross section morphology regular irregular asymmetric and composite the concentration of pockmarks is attributed to seepage of fluids migrating up dip from deeper parts of the sedimentary basin a linear high density concentration with a nnw to n ne and ese trend of pockmarks is observed above inferred basement faults that do not affect the quaternary succession these pockmarks are thus caused by seepage of thermogenic gas and or other pore fluids from deeper late cretaceous units and their distribution may help to improve our understanding of the fluid system and migration regime in this part of the galicia continental margin

a new kinematic model for iberia further palaeomagnetic and isotopic age evidence abstract palaeomagnetic results and k ar age data from the algarve igneous province have uncovered three ancient relative field components it is inferred that the principal magnetization of the monchique complex with a mean direction of d 42 i 181 95 4 5 was acquired at around the time of the pluton s emplacement some 72 2 ma ago a second magmatic pulse affected the region at 68 2 ma leaving behind a relative field component of d 42 i 341 95 1 7 furthermore an overprinted magnetization characterized by shallow inclination and somewhat smeared northwesterly southeasterly declination most likely originates from the lower tertiary the new palaeomagnetic data are seen in conjunction with previously published upper cretaceous results from the sintra and sines intrusive complexes the resulting database gives entirely new perspectives for evaluating the plate tectonic history of the peninsula in upper cretaceous lower tertiary time a two phase rotation of the iberian micro plate an anticlockwise one of 40 followed by a clockwise one of 70 is clearly in evidence the net clockwise rotation provided a major impetus for the compressive deformation in the pyrenees and the bay of biscay and led to extensive remagnetization of older rock formations in the northern regions of iberia previous palaeomagnetic conclusions in favour of a single anticlockwise rotation of 35 supposed to be directly connected with the formation of the bay of biscay appear to be artefacts which stem from an incorrectly adopted palaeomagnetic reference frame

paleocene eocene potential source rocks in the avengco basin tibet organic geochemical characteristics and their implication for the paleoenvironment abstract the avengco basin is located in the western part of the tibetan plateau and is similar to the nima basin in the central part of the plateau and the lunpola basin in the eastern part in terms of sedimentary characteristics and tectonic settings which are well known to provide a good source rock potential however the organic geochemical characteristics of the paleocene eocene potential source rocks in the avengco basin have been under debate thirty four marl and mudstone outcrop samples of the niubao formation in the avengco basin were collected and subjected to the following analyses total organic carbon toc rock eval pyrolysis stable carbon isotopes of kerogen gas chromatography gc and gas chromatography mass spectrometry gc ms here we present the results indicating the organic matter of the upper niubao formation is mainly composed of type ii kerogen with a mixed source which is dominated by algae however the lower niubao formation has the less oil prone type ii iii kerogen and the sources of the organic matter are mainly terrestrial plants with less plankton in addition the samples are thermally immature to marginally mature the niubao formation was deposited in an anoxic oxic environment which was brackish with an imperceptible stratified water column the upper niubao formation has a medium to good hydrocarbon generating potential however the lower niubao formation has a zero to poor hydrocarbon generating potential

evolution of porosity and pore types in organic rich calcareous lower toarcian posidonia shale low and high resolution petrographic studies have been combined with mineralogical toc rockeval and porosity data to investigate controls on the evolution of porosity in stratigraphically equivalent immature oil window and gas window samples from the lower toarcian posidonia shale formation a series of 26 samples from three boreholes wickensen harderode and haddessen in the hils syncline was investigated the main primary components of the shales are microfossiferous calcite 30 50 clay minerals 20 30 and type ii organic matter toc 7 15 hi 630 720 mg gc in immature samples characteristic sub centimetric light and dark lamination reflects rapid changes in the relative supply of these components total porosities decrease from 10 to 14 at ro 0 5 to 3 5 at ro 0 9 and then increase to 9 12 at ro 1 45 these maturity related porosity changes can be explained by a the primary composition of the shales b carbonate diagenesis c compaction and d the maturation micro migration local trapping and gasification of heterogeneous organic phases calcite undergoes dissolution and reprecipitation reactions throughout the maturation sequence pores quantifiable in sem ca 50 nm account for 14 25 of total porosity at ro 0 5 sem visible macropores1 are associated mainly with biogenic calcite at this maturity clays and organic matter are not visibly porous but nevertheless hold most of the shale porosity porosity loss into the oil window reflects a compaction b carbonate cementation and c perhaps the swelling of kerogen by retained oil in addition porosity is occluded by a range of bituminous phases especially in microfossil macropores and microfractures in the gas window mineral hosted porosity is still the primary form of macroporosity most commonly observed at the organic inorganic interface increasing porosity into the gas window also coincides with the formation of isolated spongy and complex meso and macropores within organic particles related to thermal cracking and gas generation this intraorganic porosity is highly heterogeneous point counted macroporosity of individual organic particles ranges from 0 to 40 with 65 of organic particles containing no macropores we suggest that this reflects the physicochemical heterogeneity of the organic phases plus the variable mechanical protection afforded by the mineral matrix to allow macroporosity to be retained the development of organic macroporosity cannot alone account for the porosity increase observed from oil to gas window major contributions also come from the increased volume of organic micro and meso porosity and perhaps by kerogen shrinkage

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

elevated levels of dimethylated sulfur compounds in lake bonney a poorly ventilated antarctic lake lake bonney is a permanently ice covered lake in the mcmurdo dry valleys antarctica the lake has two chemically stratified lobes referred to as the east and west lobes each with distinct biogenic sulfur profiles dimethylsulfoniopropionate dmspp and dimethylsulfoxide dmsop exceeded 32 and 2 nmol l 21 respectively in the photic surface waters of the lake maximum dmspp levels occurred in the deep chlorophyll layer of both lobes a zone dominated by chrysophytes and chlorophytes which are thought to be the source of dimethylated sulfur in the deep waters of the lake following sedimentation and biogeochemical processing waters beneath the chemoclines of both lobes are cold 08c saline 3 times seawater suboxic and devoid of phytoplankton biomass and activity dimethylsulfide dms levels 330 nmol l 21 in the deep west lobe are among the highest recorded in a natural aquatic ecosystem in contrast saline waters of the deep east lobe contain relatively little dms 70 nmol l 21 but high dmsod 270 nmol l 21 with the latter being the highest observed in any natural aquatic ecosystem we argue that the differences in the biogenic sulfur profiles between the deep waters of the two lobes arise principally from subtle differences in the redox conditions found in each lobe

thinned and subsided continental crust on the rifted margin of eastern canada crustal structure thermal evolution and subsidence history summary seismic refraction measurements were carried out using ocean bottom seismometers over foundered continental crust in orphan basin and flemish pass on the continental margin north east of newfoundland tau p travel time inversion synthetic seismogram analysis and conventional layered model calculations were applied to the data the results show that these outer regions of the margin are underlain by thinned continental crust with a total depth to the m discontinuity of about 22 km there are two main crustal layers with p velocities of about 6 1 and 7 0 km s 1 which appear to be homogenous and separated by sharp interfaces these are overlain by a layer in which p velocities are about 5 5 km s 1 this is interpreted to be precambrian or palaeozoic basement mesozoic and cenozoic sediments cover the basement rocks and are over 4 km thick the results imply that crustal thinning to about 50 per cent of the original crustal thickness occurred the gravity anomaly data show that the thin crust has a maximum horizontal extent of about 450 km from the ocean continent boundary near orphan knoll landward to the outer continental shelf the subsidence history and thermal evolution of the region was computed assuming that the observed thinning is produced by horizontal extension of the lithosphere it is suggested that extension can only satisfy the observed crustal structure and elevation of the margin during the rift phase if more extension took place in the lower lithosphere than in the upper lithosphere the computed subsidence is compared to the observed subsidence and the total amounts of subsidence are similar however the shape of the observed subsidence curves measured in deep exploratory wells differs significantly from the predicted subsidence assuming cooling began when final continental breakup occurred in the late cretaceous the temperature distribution within the lithosphere due to extension may be related to the flexural rigidity of the plate as a function of both time and position across the margin therefore it is suggested that the response of the lithosphere to sediment loading and the large amplitude of the gravity shelf edge anomalies are directly related to the thermal history of the region

longitudinal evolution of the suez rift structure egypt abstract a three dimensional study of the structure of the suez rift has been carried out using field and subsurface data in an attempt to determine the role of transverse faults and the longitudinal evolution of the rift as in most intracontinental rifts the structure of the gulf of suez area is governed by normal faults and tilted blocks whose crests constitute the main target of exploratory wells the fault pattern consists of two major sets of trends 1 1 longitudinal faults parallel to the rift axis and created in an extensional regime where 3 was trending ene wsw and 2 2 transverse faults with a n s to nne ssw dominant trend the transverse faults are inherited passive discontinuities while most of the longitudinal faults were created during neogene times in a purely extensional regime both sets were simultaneously active producing a zigzag pattern and rhombic shaped blocks the transverse faults can show horizontal strike slip components and act as relays between major normal faults although the suez rift appears as a simple narrow elongated trough dominated by two almost symmetrical shoulders its internal structure is asymmetrical cross profiles show that all the major blocks are tilted in the same direction however the tilt direction changes twice along the rift to the north and to the south of the rift the blocks are tilted eastward while in the central part they are tilted westward to the north the change of dip is accompan ed by a graben type twist zone without transverse faulting at least in the neogene series to the south the change of dip is accompanied by a more complex structure involving both a major transverse fault and a horst type twist zone in this latter case the transverse fault does not cut through the entire rift balanced cross sections established from subsurface data show that the tilt angle and the amount of extension increase from north to south while the width of the blocks decreases indicating a pole of opening close to the northern end of the gulf minimum values for the amount of opening range from 5 km in the north to about 20 km in the south

palaeotectonic reconstruction of the central alpine mediterranean belt for the neogene abstract the structural patterns of the central alpine mediterranean belt ranging from the eastern balearic sea to the western aegean sea have been reconstructed for 10 and 20 ma b p they have been obtained in the frame of the africa europe convergence through a step by step rigid plastic reconstruction using available geological and palaeomagnetic data all domains outlined in the present situation are shown in the palaeotectonic reconstructions while the structural pattern at 10 ma b p is similar to that of the present except for the tyrrhenian region that at 20 ma b p differs from it in most areas the well known adriatic promontory of the african plate is recognizable in both pictures and at 20 ma its original boundaries are revealed as strongly deformed flysch belts the adriatic promontory was broken up in the early or middle miocene into two microplates of comparable sizes the norther one is the adriatic microplate s s which suffered counter clockwise rotation by 20 relative to africa around the alpine apenninic whirl centre the southern one is the apulian microplate first outlined in the present work including the south apenninic and the apulian s s south of the gargano peninsula platforms which suffered no rotations relative to africa but which moved towards the northeast of it the primary reason for the break up of the adriatic promontory was most probably the opening of the balearic ligurian sea since 10 ma the adriatic and apulian microplates were again integral with africa or perhaps they moved towards the west relative to africa pushed by the turkish microplate the orogeny in the area discussed is mostly linked with collisional processes on the boundaries of the adriatic apulian unit

sequence stratigraphy in the upper cretaceous of the basco cantabrian basin northern spain the sedimentary cycles of the cenomanian to maastrichtian were investigated in the basco cantabrian basin bcb in northern spain provinces of alava vizcaya and burgos the depositional area was a distally steepened carbonate ramp which extended from catalonia northwestwards to the basque country the investigated sediments range from calciturbidites and pelagic marls to marl limestone alternations deposited on a distal carbonate ramp shallow marine limestones marls and intertidal clastics and carbonates were deposited on the proximal part of the carbonate ramp the establishment of a regional sequence analysis is based on the investigation of seismic profiles well logs and outcrop sections examples of outcrop sections are interpreted in terms of sequence stratigraphy unconformities of third and second order cycles depositional geometries systems tracts the sequence stratigraphic interpretation of outcrop sections is based on facies analysis interpretation of observed depositional geometries and correlation of unconformities and marine flooding surfaces through the basin a biostratigraphic framework is established based on ammonites inoceramids planktonic and benthic foraminifera as a result a regional sequence stratigraphic cycle chart is presented and compared with published global cycle charts the correlation of the regional cycle chart with published cycle charts is good in the cenomanian and turonian several sequence boundaries in the bcb are shifted by up to one biozone compared with the global chart some type 1 boundaries of the standard chart are only type 2 in the bcb important type 1 boundaries in the bcb are top geslinianum zone with a 100 m lowstand wedge at the basis of the sequence sequence boundary 92 2 base petrocoriense zone with a 250 m shallowing upwards lowstand wedge at the basis sequence boundary 89 2 and within the syrtale zone sequence boundary 85 0

kinematic evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we present an updated series of kinematic reconstructions of the major plates around the tethys from the atlantic ocean to the pamirs between the early jurassic and the present this set is used elsewhere as a basis for paleogeographic maps of the entire region the problems related to the positions of the continents in the lower triassic are also discussed no direct analyses of magnetic anomalies and fracture zones in the atlantic have been made rather all available poles and rotations have been tested in order to eliminate or minimize possible kinematic errors the reconstructions are shown for nine key geological periods which correspond to well recognized magnetic anomalies except for the jurassic cretaceous boundary and the cretaceous tertiary boundary which correspond to interpolated positions paleolatitudes have been drawn using the study of westphal et al 1986 an attempt has been made to take into account the displacements caused by formation of the continental margins and basins by stretching the resulting relative vector of motions along the northern boundary of the tethys shows a significant change 80 m y ago left lateral motion with compression dominates before whereas right lateral motion with compression dominates after to the east rates of motion vary by a factor of three with time and four maxima can be clearly related to tectonic events in the late jurassic late cretaceous eocene and post middle miocene to the west north of apulia on the contrary the motion rate has not changed significantly since the early cretaceous and is close to 1 cm yr as an average these rather complex adjustments in rates and directions of relative motion are produced in great part through a complex migration of the africa eurasia pole of rotation and seem to be mostly governed by the tectonics of the tethys plate boundary

paleoconstraints during rifting of the northeast atlantic passive margins the northeast atlantic passive margins formed during the early cretaceous phase of rifting from goban spur to galicia bank these margins are characterized by a tilted fault block geometry well defined by numerous single channel and multichannel seismic data stress directions cannot be deduced from these structural data but recently withjack and jamison 1986 have described the strain states and fault patterns produced by oblique rifting using experimental and analytical techniques we have applied these techniques to the northeast atlantic continental margins all types of extensional margins are represented there with pure extensional rifting goban spur and west galicia margins oblique rifting north spanish and celtic margins and close to pure wrenching armorican margin the rifting directions are parallel to the adjacent oceanic fracture zones or flow lines defined in the northeast atlantic and in the bay of biscay except for the west galicia margin where a 20 difference exists this difference could be within the error range of the method or could be due to a slight relative motion between galicia bank and iberia during rifting globally the coherence between rifting and spreading directions is an argument in favor of the validity of the method on the basis of kinematic arguments the motion of iberia with respect to eurasia has an eastward component related to the west to east motion of africa with respect to eurasia while iberia was a small plate whose motion was roughly coupled to africa this is confirmed by our analysis we conclude that during both the rifting and spreading episodes in the bay of biscay the motion of iberia with respect to eurasia was in the southeastward direction recently boillot 1984 suggested that iberia moved about 150 km southwestward with respect to eurasia during the rifting phase and then moved in the southeastward direction during the spreading phase we suggest that the boillot hypothesis could be wrong

crustal transition between continental and oceanic domains along the north iberian margin from wide angle seismic and gravity data deep crustal features of the transition between the north iberian mainland and the bay of biscay are constrained from new wide angle seismic and gravity data velocity depth models are derived from far offset recordings onshore of two n s marine profiles complemented with new refraction data inland and tested against models that fit the gravity anomalies important lateral variations are inferred along the north iberian margin in the western transect a variscan crust is documented from the mainland across the continental shelf and a rapid crustal thinning beneath the slope marks the transition to the oceanic domain the eastern transect shows an outstanding crustal thickening beneath the coastline moho depths around 50 km and a gradual thinning across the shelf differences are related to the v shape of the bay of biscay that causes a w e transition along the margin from a short lived oceanic subduction to continental collision during the tertiary oblique convergence between europe and iberia

kerogen facies and maturity of the kimmeridge clay formation in southern and eastern england abstract the upper jurassic kimmeridge clay formation of southern and eastern england was deposited under anoxic or dysaerobic conditions in a stratified shelf sea anoxic conditions developed in the intra shelf weald and central channel basins of southern england and the cleveland basin of eastern england with generally dysaerobic conditions in the flanking shelf areas only in the basin margins such as in northern scotland were oxic bottom water conditions prevalent the maturity and distribution of the kerogen facies which can be explained in terms of the palaeogeography and burial history of the upper jurassic of southern and eastern england are discussed along with the effects of their variation on commonly used geochemical parameters relationships to clay mineralogy are also examined kerogens are largely type ii amorphous sapropels of marine origin with variable amounts of terrestrially derived type iii material type iii kerogens predominate in the basin margin areas whereas type ii kerogens are restricted to the basin centres over the intermediate shelf areas mixed type ii type iii kerogens are prevalent both the sedimentation rate and differential organic matter preservation can be demonstrated to be the major controls on the kerogen facies of the kimmeridge clay formation variations in the kerogen facies appear to be responsible for the often spurious and scattered maturity measurements from the kimmeridge clay formation using vitrinite reflectance spore coloration and rock eval pyrolysis parameters the results often conflicting with geological models for the post jurassic burial history this appears to be due to the highly variable content of terrestrial and recycled type iii kerogens from older sediments in the mudstones causing the conventional maturity indices to often not reflect the true maturity of the autochthonous marine type ii kerogens

the influence of the evolution of the pyrenees on adjacent basins abstract important thicknesses of syn and post orogenic sediments are observed in the southern part of the aquitaine basin and in the north of the ebro basin their deposition cannot be explained only as a result of the extensional history of the early cretaceous thus the influence of the compression associated with the pyrenees formation upon the subsidence of these basins is studied europe and iberia are considered to behave as two semi infinite elastic plates the evolution through time of the sedimentary thicknesses is explained by the deflections of these two plates induced not only by the topographic load of the pyrenees but also by additional forces 10 12 n m that may have their origin in the formation of a cold lithospheric root during the shortening a series of calculations is presented for an approximately north south profile across the aquitaine basin the pyrenees and the ebro basin a good fit for the shape of the basins and the gravity anomalies was obtained with flexural rigidities of 1 5 10 23 nm for the northern plate and the outer part of the southern plate and 1 4 10 21 nm for the inner part of the southern plate

structure and evolution of the passive margin of the eastern tethys abstract an extensive passive margin was formed in the triassic along the periphery of arabia including the tauric carbonate platform this event is related to the opening of the mesozoic tethys when a number of microcontinents split off from gondwana triassic extension and continental rifting resulted in the formation of a structural pattern which is uniform from the dinarides to oman it includes the following elements 1 1 shelf 2 2 continental slope 3 3 deep basin probably with a floor of attenuated sialic crust 4 4 inner carbonate platform in the jurassic cretaceous stable conditions prevailed influenced only by eustatic oscillations of the sea level turbidites accumulated on the continental rise while cherts and radiolarites were deposited in the deep basins hawasina pichakun antalya pindus below the ccd level sedimentation on the shelf was controlled by north northeast transverse tectonic elements which also continued across the passive margin dividing it into a number of segments collision with an island arc led to obduction of the oceanic crust deformation of the passive margin and overthrusting of its sedimentary cover onto the arabian shelf obduction and deformation lasted for about 10 m y and created a new tectonic pattern with concentric structural zones surrounding the arabian promontory these zones include 1 1 the flysch basin a remnant of the closing tethys 2 2 an uplift a site of periodical emergence and erosion corresponding to the frontal part of the ophiolitic nappes 3 3 the border furrow a depocenter of low energy calcareous marls 4 4 the arabian shield constantly emerged during the tertiary tectonic deformation of these zones caused by the collision of arabia with eurasia began prior to the early miocene and it is still going on data on afghanistan demonstrate that its central part the gelmend argandab and kabul blocks belonged during the paleozoic and early mesozoic to the continental shelf of india

dimethylsulphide and dimethylsulphoniopropionate in the south west indian ocean sector of east antarctica from 30 to 80 e during broke west abstract we investigated the spatial and vertical variations of dimethylsulphide dms dissolved particulate and total dimethylsulphoniopropionate dmspd dmspp and dmspt in the south west indian ocean sector of east antarctica between 30 80 e and south of 62 s from january to march 2006 twenty seven sites were examined and mean concentrations in the upper 150 m of the water column were for dms 8 nm range nd 63 nm dmspd 5 nm nd 36 nm dmspp 11 nm nd 38 nm and dmspt 16 nm nd 54 nm the highest concentrations of the sulphur compounds occurred in the western sector of the study area on the antarctic shelf and across the antarctic slope front region asf of the eastern weddell gyre ewg in the cosmonaut sea concentrations were lower north of the asf region of the ewg and in the eastern sector of the antarctic circumpolar current acc and the greater prydz bay gyre pbg circulation in the cooperation sea the influence of melting pack ice on dms and dmspd concentrations was apparent in this study but was predominantly restricted to a few stations in the cosmonaut sea early in the voyage dms concentrations were extremely high at stations in the western sector of the marginal ice zone miz in the early part of the study mean 25 nm reaching concentrations as high as 63 nm at station 42 decreasing to a mean concentration of 5 5 nm in the reduced miz to the east in the seasonal mixed layer sml water 4 50 m from the acc and ewg mean dms concentrations were 5 nm whilst very low concentrations of dms occurred under forming sea ice 0 5 nm mean dmspp concentrations in the top 50 m of the miz stations across the survey were closely similar 18 20 nm and slightly higher than sml waters 13 14 nm whilst mean dmspd concentrations were 275 and 100 higher in samples from the miz stations 8 15 nm compared with sml waters 4 nm in the eastern sector the coastal region across the shelf break and asf region was largely free of ice and there was generally no elevation of dmspd mean 4 nm this suggests that biological processes associated with the pack or fast ice in the asf region of the western sector of the survey in conjunction with the oceanography of the region may have caused the high concentrations of dms and dmspd observed at latitudes 67 s whilst filtration affects did influence dmspd concentrations at a few sites it was clear that elevated dms and dmspd concentrations occurred in the top 50 m and winter water ww layers of miz stations and in high salinity shelf water hssw at specific locations on the antarctic shelf and likely reflected melting sea ice dms and dmspp were also detected below the euphotic zone in modified circumpolar deep water mcdw on the antarctic slope with dmspp possibly transported there in sedimenting detritus and faecal material the significant concentrations of dms detected in lower mcdw 0 42 1 1 nm and antarctic bottom water aabw 2 7 nm were likely to have been transported to these depths in wintertime as dense shelf water overflows from the cape darnley and prydz bay source regions the high concentrations of dms and dmspd observed in the surface waters of the miz further support the importance of the antarctic region and the sea ice zone to the global sulphur cycle

novel type of crust produced during continental rifting a normal oceanic crust cannot be generated after continental crust splitting of rifts filled by a thick pile of young sediments the magma released by the rising mantle is trapped mainly in these sediments as basalts sills and plugs the sediments are themselves metamorphosed by the heat flux from the underlying mantle a metasedimentary crust is formed in direct contact with an abnormal mantle vp 7 5 km s l produced by partial serpentinization

new constraints on the formation of the non volcanic continental galicia flemish cap conjugate margins numerous multichannel seismic data acquired on the starved continental margin off galicia show that the prominent intra crustal s reflector is observed only below the oceanward portion of the continental margin close to the ocean continent boundary superficial extension has been computed from the geometry of the well imaged tilted fault blocks of the entire margin by using a series of parallel seismic lines specifically designed for this purpose the pure shear model clearly accounts for the lithospheric extension of the continentward portion of the continental margin but not for the oceanward portion of the continental margin where the s reflector is present the s reflector is a detachment zone which presents a decreasing offset in the direction of the continent and this detachment zone has been active since the beginning of rifting recent kinematic reconstructions show that the conjugate margin to galicia is the southeastern flemish cap margin from the few seismic profiles available on this canadian margin a major master fault is observed beneath the continental slope and is interpreted as the outcropping portion of a main detachment zone identified on the galicia margin as the s reflector the proposed mechanism of extension for these two conjugate margins is pure shear which affects the whole lithosphere but in the upper part of the crust the rifting mechanism is either pure shear for the continentward portion of the galicia margin or simple shear for the oceanward portion of the galicia and the whole southeastern flemish cap margins where the detachment zone is active i consider that pure shear is the basic lithospheric mechanism and that simple shear is a mechanism which affects only the upper crust

seismic structure of the northern continental margin of spain from escin deep seismic profiles abstract by the end of the carboniferous the crust of the continental shelf in northwestern spain was made up of deeply rooted structures related to the variscan collision from permian to triassic times the tectonic setting had changed to mainly extensional and the northern iberian continental margin underwent rifting during late jurassic early cretaceous times along with sea floor spreading and the opening of the bay of biscay until the late cretaceous subsequently the northern iberian margin was active during the north south convergence of eurasia and iberia in the tertiary a multichannel seismic experiment consisting of two profiles one north south escin 4 crossing the platform margin offshore asturias and another escin 3 crossing the platform margin to the northwest of galicia was designed to study the structure of the northern iberian margin the escin 4 stacked section reveals inverted structures in the upper crust within the le danois basin north of the steep continental slope escin 4 shows a thick sedimentary package from 6 to 9 5 s two way travel time twt within this latter package a 40 km long north tapering wedge of inclined mainly south dipping reflections is thought to represent a buried alpine age accretionary prism in the north western part of the escin 3 escin 3 1 stacked section horizontal reflections from 6 5 to 8 5 s correspond to an undisturbed package of sediments lying above oceanic type basement in this part of the line a few kilometres long strong horizontal reflection at 11 2 s within the basement may represent an oceanic moho reflection also a band of reflections dips gently towards the southeast from the base of the gently dipping continental slope the part of escin 3 line that runs parallel to the nw galicia coast escin 3 2 is characterized by bright continuous lower crustal reflections from 8 to 10 s beneath the lower crustal reflectivity a band of strong reflections dips gently toward the southwest from 10 to 13 5 s the part of escin 3 that parallels the northern margin escin 3 3 shows good reflectivity in all levels upper crustal reflections image the sedimentary fill of probable mesozoic to recent basins mid crustal reflectivity is characterized by dipping reflections until 8 s that are probably related to compressional variscan features the lower crustal level shows layered reflections between 8 and 12 s dipping reflections are found below the continental moho