the atmosphere of titan an analysis of the voyager 1 radio occultation measurements abstract two coherently related radio signals transmitted from voyager 1 at wavelengths of 13 cm s band and 3 6 cm x band were used to probe the equatorial atmosphere of titan the measurements were conducted during the occultation of the spacecraft by the satellite on november 12 1980 an analysis of the differential dispersive frequency measurements did not reveal any ionization layers in the upper atmosphere of titan the resolution was approximately 3 10 3 and 5 10 3 electrons cm 3 near the evening and morning terminators respectively abrupt signal changes observed at ingress and egress indicated a surface radius of 2575 0 0 5 km leading to a mean density of 1 881 0 002 g cm 3 for the satellite the nondispersive data were used to derive profiles in height of the gas refractivity and microwave absorption in titan s troposphere and stratosphere no absorption was detected the resolution was about 0 01 db km at the 13 cm wavelength the gas refractivity data which extend from the surface to about 200 km altitude were interpreted in two different ways in the first it is assumed that n 2 makes up essentially all of the atmosphere but with very small amounts of ch 4 and other hydrocarbons also present this approach yielded a temperature and pressure at the surface of 94 0 0 7 k and 1496 20 mbar respectively the tropopause which was detected near 42 km altitude had a temperature of 71 4 0 5 k and a pressure of about 130 mbar above the tropopause the temperature increased with height reaching 170 15 k near the 200 km level the maximum temperature lapse rate observed near the surface 1 38 0 10 k km corresponds to the adiabatic value expected for a dry n 2 atmosphere indicating that methane saturation did not occur in tbis region above the 3 5 km altitude level the lapse rate dropped abruptly to 0 9 0 1 k km and then decreased slowly with increasing altitude crossing zero at the tropopause for the n 2 atmospheric model the lapse rate transition at the 3 5 km level appears to mark the boundary between a convective region near the surface having the dry adiabatic lapse rate and a higher stable region in radiative equilibrium in the second interpretation of the refractivity data it is assumed instead that the 3 5 km altitude level corresponds to the bottom of a ch 4 cloud layer and that n 2 and ch 4 are perfectly mixed below this level these assumptions lead to an atmospheric model which below the clouds contains about 10 ch 4 by number density the temperature near the surface is about 95 k arguments concerning the temperature lapse rates computed from the radio measurements appear to favor models in which methane forms at most a limited haze layer high in the troposphere

geophysical studies of the structure of the appalachian orogen in the atlantic borderlands of canada results of 6000 km of crustal seismic profiling are presented with gravity and aeromagnetic maps for the appalachian orogen in eastern canada wide angle seismic surveys show that the central mobile belt of the orogen has a thinner crust than its margins high velocity lower crust attributed to underplating is found below the former laurentian continental margin in newfoundland and below the magdalen basin potential field data are used to trace the surface zones of the orogen from the northeast newfoundland shelf to cape breton but extrapolation to new brunswick and quebec is unclear because of late paleozoic basin development the central mobile belt of the orogen is only a few tens of kilometres wide in southwest newfoundland and cape breton but broadens substantially to around 200 km elsewhere reflection images show a strong deep crustal fabric that runs along the orogen with a margin that crosses into the avalon zone in southern newfoundland but coincides with the avalon gander zone boundary el

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

the structure evolution and symmetry of the magma poor rifted margins of the north and central atlantic a synthesis abstract magma poor rifted margins consistently show extreme crustal thinning accompanied by normal faulting the serpentinization of the mantle beneath crust thinned to less than 8 2 km and the unroofing of a broad zone of mantle within the continent ocean transition accompanied by the development of detachment and other large offset faults these observations are the logical result of the progressive extension of cool lithosphere away from thermal anomalies such as plumes although the paucity of magmatism may be explained by depth dependent extension of the lithosphere and by pre depleted sub crustal lithosphere rifting above initially cool sub lithospheric mantle also may explain the subsidence deficit observed at some margins synrift subsidence is buffered by the simultaneous influx of warmer oceanic asthenosphere as it extends thins and cools ductile creeping layers in the mid and deep crust become progressively more brittle resulting in increased coupling between the upper and lower crust and eventually the embrittlement of the entire crust faults cutting from the surface across the moho bringing water into the mantle and causing its serpentinization increased coupling and the development of serpentine detachments predict the development of late stage asymmetry once the entire crust is brittle such detachments are imaged on some margins and inferred on others analysis of the crustal structure across conjugate margins shows that these are approximately symmetric until this late stage when they become markedly asymmetric similar analyses show that depth dependent stretching of the crust is insufficient to explain the discrepancy between the amount of the visible extension along faults and the amount of crustal thinning instead this extension discrepancy may be related to the complex evolution of brittle deformation through multiple phases and styles of faulting related to the changes in the rheological character and strength of the lithosphere as it is thinned complex polyphase faulting continues after complete crustal separation resulting in the exhumation of broad expanses of peridotitic basement the top of which is everywhere marked by an exhumed slip surface similar to the corrugated surface observed at mid ocean ridges the similarity in processes between mantle unroofing and seafloor spreading makes the distinction between the cot and true oceanic crust difficult and possibly moot

hyperextension serpentinization and weakening a new paradigm for rifted margin compressional deformation the early eocene magma rich northeast atlantic rifted margins contain a large number of pre breakup and post breakup compressional structures located in abandoned early cretaceous hyperextended basins with crustal stretching factors of 3 4 or more the deformation both predates and postdates the magma rich breakup the hyperextended basins are often underlain by high velocity lower crustal bodies which we argue represent partially serpentinized upper mantle long lived lithospheric weakening and proneness to deformation is proposed to relate to crustal hyperextension probably enhanced by mantle hydration

organic matter size fraction relationships for recent sediments from the orinoco delta venezuela abstract fifteen recent sediment samples from the offshore orinoco delta venezuela were separated by sieving and pipette analysis into seven size fractions ranging from 4o to 10o in 1 o units total organic carbon was determined for each size fraction and the organic matter characterized by pyrolysis and pyrolysis gas chromatography the sediments average 0 98 organic matter with somewhat higher values nearshore nearshore sediments also had higher organic contents in the coarsest fractions and a decrease in organic matter from coarse to fine sediment fractions sediments from further offshore generally show the highest organic contents in the finer fractions pyrolysis showed a low bitumen content and confirmed that the kerogen was dominantly terrestrial and gas prone the observed trends were attributed to sorting of organic matter by its physical characteristics with the denser coarse grained material settling out nearshore and the finer grained material being carried further from shore and settling out with finer grained sediments

extension discrepancy at north atlantic nonvolcanic rifted margins depth dependent stretching or unrecognized faulting rifted margins show an apparent discrepancy between the amount of extension measurable from faults and the amount of crustal or lithospheric thinning determined from wide angle data or subsidence this extension discrepancy has been interpreted in terms of depth dependent stretching in which the upper crust is extended and thinned far less than the rest of the lithosphere here i show that at those nonvolcanic margins where the velocity structure is well known the upper and lower crust appear to thin equally toward the margin implying that the discrepancy is not due to depth dependent stretching but more likely due to unrecognized polyphase and top basement faulting

horizontal structures and dynamics of titan s thermosphere 1 the cassini ion neutral mass spectrometer inms measures densities of gases including n2 and ch4 in situ in titan s upper atmosphere we have used data from 13 targeted flybys of titan t5 t32 to construct an empirical model that describes the mean state of the thermosphere in the northern hemisphere giving the n2 and ch4 densities between 1000 and 1600 km as a function of latitude and height the principal features in the inms data are well reproduced by this simple model we find a pronounced oblateness in the thermosphere with densities above 1100 km altitude increasing by around 70 from the northern winter pole to the equator resulting in isobaric surfaces being 45 km higher over the equator than at the northern pole thermospheric temperatures derived from the densities tend to decrease with height from 149 10 k to 140 13 k near 1600 km considerable latitude differences are present in the temperatures below 1200 km near 1000 km altitude temperatures reach 164 6 k at 20 n and 131 6 k near 80 n using our thermosphere general circulation model with this thermal structure imposed we derive thermospheric horizontal wind speeds reaching 150 m s 1 with primarily poleward flow at equatorial latitudes which northward of around 60 n is accompanied by a band of prograde zonal winds of up to 50 m s 1 at high latitudes converging horizontal winds generate regions of strong subsistence we find thermospheric dynamics to be sensitive to coupling from below ch4 abundances are enhanced in the northern polar region which may result from transport by thermospheric winds

crustal thinning mantle exhumation and serpentinization in the porcupine basin offshore ireland evidence from wide angle seismic data new wide angle seismic data were gathered along a 230 km long profile that runs east west across a deep structural feature in the porcupine basin offshore ireland known as the porcupine arch ocean bottom seismometers were deployed at 3 4 km intervals and seismic sources fired every 120 m along it prominent primary and secondary arrivals indicate that the continental crust is extremely thin locally less than 2 km across the basin centre the sedimentary succession is up to 12 km thick and comprises three distinctive seismic layers the two uppermost layers are interpreted as mostly a post rift succession of cretaceous and cenozoic strata the lowest layer thins rapidly towards the basin centre and is interpreted as a succession of predominantly jurassic synrift sediments a strong asymmetry in both the geometry of the crust and the sedimentary layers is probably related to a simple shear mode of extension and the subsidence that it induced crustal thinning is far greater than in the adjacent rockall basin and local exhumation of continental mantle lithosphere may have occurred in parts of the porcupine basin low p n velocities beneath the porcupine arch are compatible with larger amounts of mantle serpentinization than in the rockall basin

sunlight refraction in the mesosphere of venus during the transit on june 8th 2004 abstract many observers in the past gave detailed descriptions of the telescopic aspect of venus during its extremely rare transits across the solar disk in particular at the ingress and egress the portion of the planet s disk outside the solar photosphere has been repeatedly perceived as outlined by a thin bright arc aureole those historical visual observations allowed inferring the existence of venus atmosphere the bright arc being correctly ascribed to the refraction of light by the outer layers of a dense atmosphere on june 8th 2004 fast photometry based on electronic imaging devices allowed the first quantitative analysis of the phenomenon several observers used a variety of acquisition systems to image the event ranging from amateur sized to professional telescopes and cameras thus collecting for the first time a large amount of quantitative information on this atmospheric phenomenon in this paper after reviewing some elements brought by the historical records we give a detailed report of the ground based observations of the 2004 transit besides confirming the historical descriptions we perform the first photometric analysis of the aureole using various acquisition systems the spatially resolved data provide measurements of the aureole flux as a function of the planetocentric latitude along the limb a new differential refraction model of solar disk through the upper atmosphere allows us to relate the variable photometry to the latitudinal dependency of scale height with temperature in the south polar region as well as the latitudinal variation of the cloud top layer altitude we compare our measurements to recent analysis of the venus express virtis m vmc and spicav soir thermal field and aerosol distribution our results can be used a starting point for new more optimized experiments during the 2012 transit event

diagnostics of titan s stratospheric dynamics using cassini cirs data and the 2 dimensional ipsl circulation model abstract the dynamics of titan s stratosphere is discussed in this study based on a comparison between observations by the cirs instrument on board the cassini spacecraft and results of the 2 dimensional circulation model developed at the institute pierre simon laplace available at http www lmd jussieu fr titandbase rannou p lebonnois s hourdin f luz d 2005 adv space res 36 2194 2198 the comparison aims at both evaluating the model s capabilities and interpreting the observations concerning 1 dynamical and thermal structure using temperature retrievals from cassini cirs and the vertical profile of zonal wind at the huygens landing site obtained by huygens dwe and 2 vertical and latitudinal profiles of stratospheric gases deduced from cassini cirs data the modeled thermal structure is similar to that inferred from observations cassini cirs and earth based observations however the upper stratosphere above 0 05 mbar is systematically too hot in the 2d cm and therefore the stratopause region is not well represented this bias may be related to the haze structure and to misrepresented radiative effects in this region such as the cooling effect of hydrogen cyanide hcn the 2d cm produces a strong atmospheric superrotation with zonal winds reaching 200 m s 1 at high winter latitudes between 200 and 300 km altitude 0 1 1 mbar the modeled zonal winds are in good agreement with retrieved wind fields from occultation observations cassini cirs and huygens dwe changes to the thermal structure are coupled to changes in the meridional circulation and polar vortex extension and therefore affect chemical distributions especially in winter polar regions when a higher altitude haze production source is used the resulting modeled meridional circulation is weaker and the vertical and horizontal mixing due to the polar vortex is less extended in latitude there is an overall good agreement between modeled chemical distributions and observations in equatorial regions the difference in observed vertical gradients of c 2 h 2 and hcn may be an indicator of the relative strength of circulation and chemical loss of hcn the negative vertical gradient of ethylene in the low stratosphere at 15 s cannot be modeled with simple 1 dimensional models where a strong photochemical sink in the middle stratosphere would be necessary it is explained here by dynamical advection from the winter pole towards the equator in the low stratosphere and by the fact that ethylene does not condense near the winter pole 80 n some compounds c 4 h 2 c 3 h 4 exhibit an interior minimum in the observed abundance vertical profiles whereas 2d cm profiles are well mixed all along the atmospheric column this minimum can be a diagnostic of the strength of the meridional circulation and of the spatial extension of the winter polar vortex where strong descending motions are present in the summer hemisphere observed stratospheric abundances are uniform in latitude whereas the model maintains a residual enrichment over the summer pole from the spring cell due to a secondary meridional overturning between 1 and 50 mbar at latitudes south of 40 50 s the strength as well as spatial and temporal extensions of this structure are a difficulty that may be linked to possible misrepresentation of horizontally mixing processes due to the restricted 2 dimensional nature of the model this restriction should also be kept in mind as a possible source of other discrepancies

the evolution of the porcupine and rockall basins offshore ireland the geological template for carbonate mound development the margins of the deep water sedimentary basins west of ireland contain a number of large clusters provinces of spectacular carbonate mounds and build ups these basins have a complex development history involving the interplay of rift tectonics thermal subsidence igneous activity and oceanographic variations the porcupine and rockall basins both rest upon thin continental crust the consequence of major rift episodes in permo triassic late jurassic and early cretaceous times phases of volcanism occurred in the early cretaceous and especially in the early cenozoic fluid flow within the basins is likely to have been controlled by the overall basin geometry and by the distribution and linkage of permeable strata with fault systems stratal surfaces and unconformities a number of regional unconformities controlled by both basin tectonic and regional oceanographic effects can be mapped and correlated throughout the porcupine and rockall basins the youngest of these unconformities c10 early pliocene can be traced throughout much of the nw european atlantic margin it forms the horizon on which virtually all the carbonate mounds in the basins develop suggesting a geologically instantaneous mound nucleation and growth event although the control on their development is uncertain the mound clusters show a spatial association with lithified strata buried contourite and deltaic deposits slope failure features and with the basin margins analysis of these relationships points to a combination of geological and oceanographic processes controlling mound initiation and growth

early cretaceous motion of flemish cap with respect to north america implications on the formation of orphan basin and se flemish cap galicia bank conjugate margins bouguer gravity anomalies together with deep seismic reflection and magnetic data on both sides of the north atlantic are used to locate the hinge zones of the flemish cap and galicia bank within the iberian and north american plates regions across which there were abrupt changes in lithospheric extension the characteristic shape and alignment of these hinge zones suggest that they were conjugate features generated during chrons m25 m0 late jurassic early aptian around a distally located euler pole of rotation rifting between iberia and north america involved these two larger plates and the two smaller microplates the flemish cap and galicia bank microplates the motion of the microplates which were adjacent to eurasia was much more complex than those of the larger plates the motion between the microplates from chron m25 or older to chron m0 was complicated by the fact that they remained attached to each other for most of the time when regions to the south were rifting apart as a result continental regions landward of these segments were subjected to extension that created the orphan and flemish pass basins on the north american side and the galicia interior basin on the iberian side by comparing the hinge zones delineated off galicia bank and flemish cap using the bouguer anomalies we were able to infer that flemish cap rotated approximately 438 relative to galicia bank and iberia and moved 200 300 km se with respect to north america such motions of flemish cap and galicia bank agree remarkably well with extensional episodes deduced from industry multichannel seismic reflection data acquired in the orphan basin normal fault orientations identified in the west orphan basin trend n0208 and are approximately perpendicular to the flow lines of our proposed flemish cap north american motion during the m25 m0 period which provides an independent constraint on our proposed kinematic model therefore extensional events affected not only the galicia bank flemish cap conjugate margins but also the galicia interior and orphan basins and need to be taken into account in any assessment of the geological development of the iberian and north american continental margins during the intermargins workshop meeting modelling the extensional deformation of the lithosphere imedl held in pontresina in 2004 a benchmark exercise was proposed to model the crustal and mantle rifting processes between the western galicia bank and the se flemish cap conjugate margins where high quality seismic reflection and refraction data exist screech line 1 funck et al 2003 hopper et al 2004 and ise line 17 perez gussinye et al 2003 henning et al 2004 during the meeting it became apparent that additional boundary conditions and constraints were needed to correctly characterize the known extension across the iberian newfoundland margin the aim of this paper is to provide some of these conditions and constraints namely a knowledge of the initial positions of plates and microplates before their separation by sea floor spreading processes the positions of flemish cap and galicia bank are well constrained at chron m0 fig 1a because of the identification of correlatable sea floor magnetic anomalies in both the bay of biscay sibuet et al 2004b and in the north atlantic srivastava et al 2000 the resulting euler pole position was constrained by the geometry of the triple junction that had remained at the mouth of the bay of from karner g d manatschal g pinheiro l m eds imaging mapping and modelling continental lithosphere extension and breakup geological society london special publications 282 63 76 doi 10 1144 sp282 4 0305 8719 07 15 00 the geological society of london 2007 fig 1 a reconstruction of the north atlantic between africa af iberia ib and north america na at chron m0 with respect to eurasia eu as given by srivastava et al 2000 ib eu 43 858n 5 838w 244 768 af eu 43 618n 6 938w 240 898 na eu 69 678n 154 268e 23 178 m0 picks west of ib crosses and east of j c sibuet et al 64

palynofacies investigation of callovian middle jurassic sediments from dsdp site 534 blake bahama basin western central atlantic abstract during the extension of deep sea drilling project dsdp leg 76 a new and previously unpenetrated lithological unit composed mainly of claystones was cored above basalt basement at site 534 in the blake bahama basin the callovian part of the new unit contains interbedded black shales which were hitherto unexpected in this part of the section this paper presents a brief palynological examination of lithofacies kerogen relationships in these sediments and shows that their organic content is almost entirely a function of the re deposition of terrestial and marine organic matter versus the ambient redox conditions of the depositional environment allochthonous organic matter inputs are highest in the interbedded turbidites and decline progressively toward the pelagic black shales in which marine organic matter is comparatively well preserved the significance of various kerogen and palynomorph indices are discussed the study emphasizes the absolute necessity for sedimentologically aware sampling in all palynological and geochemical work on lithologically heterogeneous sequences

extensional tectonics in the jeanne d arc basin offshore newfoundland implications for the timing of break up between grand banks and iberia

crustal structure beneath orphan basin and implications for nonvolcanic continental rifting a wide angle seismic profile was acquired across the northeast newfoundland margin seaward to orphan knoll the profile is complemented by existing multichannel reflection data two online deep wells and other deep seismic reflection and refraction lines modeling of data from 15 ocean bottom seismometers provides the seismic velocity structure for a significant portion of the 400 km wide stretched continental crust on this margin prerift metasedimentary rocks have a topographic relief of up to 5 km with a velocity of 5 2 km s increasing to 5 9 km s unaltered crystalline crust below the metasedimentary section has a velocity range of 6 1 6 5 km s most of the lower crust landward of orphan knoll has a typical continental lower crustal velocity 6 8 7 0 km s and the lower crust shallows significantly beneath orphan knoll our model shows no evidence for the 5 km thick 7 35 km s layer modeled from data of an earlier experiment and interpreted as magmatic underplating but instead indicates that thinned continental crust extends seaward for 360 km without underplating implying nonvolcanic rifting for the ne newfoundland margin we suggest that continental stretching persisted from 180 ma to chron 34n time 101 ma when the final breakup between canada and western europe took place leaving a 400 km wide zone of thinned continental crust underneath the shelf and deep water area of the orphan basin on the landward side of the basin gravity modeling indicates a zone of very thin 6 8 km crust possibly a failed rift center formed as a result of the northward progression of nonvolcanic rifting between canada and europe a possible sub moho reflector suggests generally uniform stretching of the crust and upper mantle and the absence of volcanics and underplating is in contrast to the observations on related rift basins of the grand banks

transition from amagmatic to volcanic margin mantle exhumation in the voring basin before the icelandic plume influence abstract the outer voring basin norwegian sea is an abnormally deep and distal part of the norwegian passive margin known as magma rich yet the lastest borehole drilled in its northernmost part led to a drastic change in the interpretation of seismic reflection data this update motivates a new model for the entire mesozoic eocene rifting period here i evaluate the link between tectonics serpentinization and magmatism in the norwegian margin from the ryazanian valanginian to the palaeocene eocene magmatic breakup maps of the regional nise sandstones and main regional unconformities specifically highlight the fundamental role of the nyk vema structure to understand the basin and to question the deformation timing related to deep structures the top of partially serpentinized mantle is supported by high amplitude reflectors clearly visible on certain seismic lines known as t reflector covered with gravity driven pre exhumation sediments and further deposits a new structural scheme based on the interpretation of 2d and 3d seismic data shows the complex organization of fault networks and constrains a major deformation period between the late campanian and the late palaeocene ocean scale complementary arguments are in good agreement with lower cretaceous mantle exhumation before becoming a volcanic margin in the palaeocene this segment of the norwegian margin appears as amagmatic until the late campanian at least i propose an integrated model since the onset of hyperextension in the end of the jurassic until the cessation of activity of the aegir ridge in the miocene this model has implications regarding the context dependent interpretation of lower crustal bodies the ubiquity of serpentinization and mantle exhumation worldwide and on the hydrocarbon system

an improved velocity model for the crust and upper mantle along the central mobile belt of the newfoundland appalachian orogen and its offshore extension new modelling of wide angle reflection refraction data of the canadian lithoprobe east profile 91 1 along the central mobile belt of the newfoundland appalachian orogen reveals new features of the upper mantle and establishes links in the crust and upper mantle between existing land and marine wide angle data sets by combining onshore offshore recordings the revised model provides detailed velocity structure in the 30 34 km thick crust and the top 30 km of upper mantle the lower crust is characterized by a velocity of 6 6 6 8 km s onshore increasing by 0 2 km s to the northeast offshore beneath the sedimentary basins this seaward increase in velocity may be caused by intrusion of about 4 km of basic rocks into the lower crust during the extension that formed the overlying carboniferous basins the moho is found at 34 km depth onshore rising to 30 km offshore to the northeast with a local minimum of 27 km the data confirm the absence of deep crustal roots under the central mobile belt of newfoundlan

variations in kerogen densities of sediments from the orinoco delta venezuela abstract a method employing the coulter counter technique was used in determining kerogen density for recent sediments of the orinoco delta these sediments contain essentially terrestrial humic organic matter and have kerogen densities ranging from 1 32 to 1 72 g ml 1 with an average of 1 48 g ml 1 a strong correlation was found to exist between kerogen density and offshore distance and depth in the orinoco delta kerogen density varies with offshore distance and depth decreasing consistently at the rates of 0 015 and 4 g ml 1 km 1 respectively the heavy kerogens are associated with shallow near shore areas while lighter kerogens are found in the deep offshore hence offshore distance and depth could be said to be a function of kerogen density

the structure and dynamics of titan s middle atmosphere titan s middle atmosphere is characterized by cyclostrophic winds and strong seasonal modulation cassini cirs observations obtained in northern winter indicate that the stratosphere near 1mbar i

continental lithospheric thinning and breakup in response to upwelling divergent mantle flow application to the woodlark newfoundland and iberia margins abstract depth uniform stretching is not the dominant deformation process for thinning continental lithosphere leading to breakup it cannot explain the observed depth dependent lithosphere stretching and mantle exhumation at rifted continental margins depth dependent lithosphere thinning in which stretching of the lower crust and lithosphere mantle greatly exceeds that of the upper crust has been observed at many non volcanic and volcanic rifted continental margins including conjugate margin pairs passive continental margins show a paucity of brittle deformation in the upper crust during continental lithosphere thinning leading to breakup and sea floor spreading initiation a new model of rifted continental margin formation has been developed that assumes that deformation and thinning of continental lithosphere leading to breakup occurs in response to an upwelling divergent flow field within continental lithosphere and asthenosphere and that this deformation evolves into sea floor spreading the new model successfully predicts depth dependent stretching of continental margin lithosphere for both non volcanic and volcanic margins and mantle exhumation at non volcanic margins both of which are observed but are not explained by existing depth uniform continental lithosphere stretching models the new model provides a balance of extensional strain supplies an explanation for the paucity of synrift brittle deformation and offers a simple transition from prebreakup lithosphere thinning to sea floor spreading the observed diversity of rifted continental margin structure and width of the ocean continent transition can be explained by variability in the form of the upwelling divergent flow field the new upwelling divergent flow model of continental lithosphere thinning leading to continental breakup successfully predicts the observed bathymetry and margin geometry for the most recent segment of sea floor spreading initiation in the woodlark basin in the western pacific and the observed bathymetry and free air gravity anomaly for the newfoundland and iberian margins

lower crustal extension across the northern carnarvon basin australia evidence for an eastward dipping detachment asymmetry and strain partitioning along conjugate margins are often explained in terms of detachment faults nevertheless cogent evidence for their existence remains limited furthermore even when inferred detachment faults are imaged seismically it is difficult to demonstrate that differential displacement has occurred across these surfaces we present tectonic and stratigraphic evidence from the northern carnarvon basin northwest australia that documents the existence of an intracrustal eastward dipping detachment by integrating sequence stratigraphy with kinematic and isostatic models of basin development we conclude that the northern carnarvon basin was formed as a consequence of four extension events 1 a broadly distributed late permian event 2 a predominantly localized rhaetian event responsible for the inception of the barrow and dampier subbasins 3 a localized callovian fault reactivation within the barrow dampier subbasins and 4 a tithonian valanginian event that generated large post valanginian regional subsidence across the northern carnarvon basin with only minor accompanying brittle deformation and erosional truncation the regional distribution and amplitude of the post valanginian subsidence are not consistent with the minor amounts of tithonian valanginian brittle upper crustal extension observed on the margin large portions of the platform were emergent or at very shallow water depths prior to the tithonian valanginian extension to match the distribution and magnitude of the post valanginian thermal type subsidence requires significant lower crustal and mantle extension across the northern carnarvon basin such a distribution of extension implies the existence of an eastward dipping intracrustal detachment having a ramp flat ramp geometry that effectively thinned the lower crust and lithospheric mantle the detachment breached the surface close to the position of the continent ocean boundary west of the exmouth plateau the flat component of the detachment occurred at midcrustal depths 15 km across the plateau and ramped beneath the australian continent lower crustal ductile extension provides a viable mechanism to generate large regional subsidence with little attendant brittle deformation which may explain the paradox that both sides of many conjugate margins appear to be the upper plate

the evolution of titan s detached haze layer near equinox in 2009 1 s aturn s moon titan has a massive atmosphere laden with layers of photochemical haze we report a recent dramatic change in the vertical structure of this haze with a persistent detached layer dropping in altitude from over 500 km to only 380 km between 2007 and 2010 the detached haze layer appears to be a well defined tracer for titan s meridional stratospheric circulation models of which suggest that a pole to pole meridional cell weakens during equinox as solar heating becomes more symmetric these measurements connect the cassini observations with those made by voyager almost one seasonal cycle earlier they place detailed constraints on the seasonal circulation on the sources of photochemical aerosols on the microphysical processes and on the complex interplay of these components citation west r a j balloch p dumont p lavvas r lorenz p rannou t ray ande p turtle 2011 the evolution of titan s detached haze layer near equinox in 2009 geophys res lett 38 l06204 doi 10 1029 2011gl046843

the two titan stellar occultations of 14 november 2003 1 we report the observation of two stellar occultations by titan on 14 november 2003 using stations in the indian ocean southern africa spain and northern and southern americas these occultations probed altitudes between 550 and 250 km 1 to 250 bar in titan s upper stratosphere the light curves reveal a sharp inversion layer near 515 6 km altitude 1 5 bar pressure level where the temperature increases by 15 k in only 6 km this layer is close to an inversion layer observed fourteen months later by the huygens hasi instrument during the entry of the probe in titan s atmosphere on 14 january 2005 fulchignoni et al 2005 central flashes observed during the first occultation provide constraints on the zonal wind regime at 250 km with a strong northern jet 200 m s 1 around the latitude 55 n wind velocities of 150 m s 1 near the equator and progressively weaker winds as more southern latitudes are probed the haze distribution around titan s limb at 250 km altitude is close to that predicted by the global circulation model of rannou et al 2004 in the southern hemisphere but a clearing north of 40 n is necessary to explain our data this contrasts with rannou et al s 2004 model which predicts a very thick polar hood over titan s northern polar regions simultaneous observations of the flashes at various wavelengths provide a dependence of q with q 1 8 0 5 between 0 51 and 2 2 m for the tangential optical depth of the hazes at 250 km altitude

structure and evolution of the galicia interior basin atlantic western iberian continental margin abstract an industrial multichannel seismic reflection data set is presented on the galicia interior basin g i b a sedimentary basin that has been poorly studied until now seismic stratigraphic units defined in other areas of the western iberian continental margin as well as some deeper reflections can also be identified within this basin although they show some particular characteristics the g i b is bounded to the east by a major fault identified beneath the continental shelf and to the west by an alignment of highs western banks the structural framework of the area consists of nnw sse trending normal faults cross cut by ne sw transfer faults the inception of the g i b probably ocurred during triassic times within the late jurassic early cretaceous rifting phase it probably experienced several extensional episodes the most intense one being during valanginian times evidence for compressional tectonic activity in this basin during cenozoic times has also been found when comparing the g i b with the adjacent deep galicia margin a gap in the timing of the main extensional events as well as some differences in the structural styles have been found in a wider regional context an integration of data about the timing of the processes of continental rifting and oceanic spreading along the whole western iberian margin is consistent with a northward propagating rift for the late jurassic early cretaceous phase

titan s stratospheric zonal wind temperature and ethane abundance a year prior to huygens insertion 1 saturn s satellite titan may have stratospheric winds up to 210 m s circling titan in 1 terrestrial day compared to its 16 day rotation theoretical models explaining such super rotating winds are not well constrained by observations of titan or a similar slow rotator venus we report measurements taken in december 2003 of zonal wind near titan s equatorial region including the cassini huygens probe entry latitude super rotating prograde zonal winds of 190 90 m s near 220 km altitude are found from doppler shifted c2h6 gas emission near 12 m confirming high wind velocity even near the equator stratospheric temperature constraints and ethane abundance 8 3 ppm also are retrieved results are not inconsistent with earlier measurements and with recent cassini cirs results but indicate possible variations between titan s hemispheres differences in east and west c2h6 spectral line shapes can be accounted for by different vertical distributions of either c2h6 abundance or temperature or by unidentified dynamical effects

the structure of titan s atmosphere from cassini radio occultations abstract we present results from the two radio occultations of the cassini spacecraft by titan in 2006 which probed mid southern latitudes three of the ingress and egress soundings occurred within a narrow latitude range 31 34 s near the surface and the fourth at 52 8 s temperature altitude profiles for all four occultation soundings are presented and compared with the results of the voyager 1 radio occultation lindal g f wood g e hotz h b sweetnam d n eshleman v r tyler g l 1983 icarus 53 348 363 the hasi instrument on the huygens descent probe fulchignoni m et al 2005 nature 438 785 791 and cassini cirs results flasar f m et al 2005 science 308 975 978 achterberg r k conrath b j gierasch p j flasar f m nixon c a 2008b icarus 194 263 277 sources of error in the retrieved temperature altitude profiles are also discussed and a major contribution is from spacecraft velocity errors in the reconstructed ephemeris these can be reduced by using cirs data at 300 km to make along track adjustments of the spacecraft timing the occultation soundings indicate that the temperatures just above the surface at 31 34 s are about 93 k while that at 53 s is about 1 k colder at the tropopause the temperatures at the lower latitudes are all about 70 k while the 53 s profile is again 1 k colder the temperature lapse rate in the lowest 2 km for the two ingress dawn profiles at 31 and 33 s lie along a dry adiabat except within 200 m of the surface where a small stable inversion occurs this could be explained by turbulent mixing with low viscosity near the surface the egress profile near 34 s shows a more complex structure in the lowest 2 km while the egress profile at 53 s is more stable

limitations of use of organic petrographic techniques for identification of petroleum source rocks organic petrographic and organic geochemical studies have been conducted on 58 sediment samples of differing ages and depositional environments in this study interpretations of petroleum source rock potential based on data from transmitted light microscopy show a poor correlation with those derived from chemical data this lack of correlation arises from the failure to distinguish consistently between hydrogen poor and hydrogen rich amorphous organic matter and inability to detect hydrogen rich components exinite and resinite in coal fragments interpretations based on data from reflected light microscopy show a better correlation with those derived from chemical studies but difficulties still remain these difficulties arise from inability except on the basis of luorescence intensity to distinguish hydrogen rich from hydrogen poor organic matter in a finely dispersed state

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

temperatures winds and composition in the saturnian system stratospheric temperatures on saturn imply a strong decay of the equatorial winds with altitude if the decrease in winds reported from recent hubble space telescope images is not a temporal change then the features tracked must have been at least 130 kilometers higher than in earlier studies saturn s south polar stratosphere is warmer than predicted from simple radiative models the c h ratio on saturn is seven times solar twice jupiter s saturn s ring temperatures have radial variations down to the smallest scale resolved 100 kilometers diurnal surface temperature variations on phoebe suggest a more porous regolith than on the jovian satellites

a mechanism to thin the continental lithosphere at magma poor margins crustal thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults instead of multiple normal faults through exhumation of mid crustal and mantle material where continental plates break apart slip along multiple normal faults provides the required space for the earth s crust to thin and subside1 after initial rifting however the displacement on normal faults observed at the sea floor seems not to match the inferred extension2 here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust 10 km by exhumation of mid crustal and mantle material this transitional crust is capped by sub horizontal detachment surfaces over distances exceeding 100 km with little visible deformation our rift model is based on numerical experiments constrained by geological and geophysical observations from the alpine tethys and iberia newfoundland margins3 4 5 6 7 8 9 furthermore we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust the presence of such lower crustal gabbros is well constrained for the alpine tethys system4 9 initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution this is achieved in our models by the formation of weak ductile shear zones

titan s middle atmospheric temperatures and dynamics observed by the cassini composite infrared spectrometer the composite infrared radiometer spectrometer cirs instrument on the nasa cassini saturn orbiter has been acquiring thermal emission spectra from the atmosphere of titan since orbit insertion in 2004 observation sequences for measuring stratospheric temperatures have been obtained using both a nadir mapping mode and a limb viewing mode the limb observations give better vertical resolution and give information from higher altitudes while the nadir observations provide more complete longitude coverage because the scale height of titan s atmosphere is large enough so that emission from a grazing ray is influenced by horizontal temperature variations in the atmosphere we have developed a twodimensional temperature retrieval algorithm for reducing the limb spectra which solves simultaneously for meridional and vertical temperature variations the analyzed nadir mapping data have sampled nearly all longitudes at latitudes from about 90 st o 60 n providing temperatures between pressure levels of about 5 to 0 2 mbar the limb data covers latitudes between about 75 s and 85 n and yields temperatures between about 1 and 0 005 mbar at a small number of longitudes the retrieved temperatures are consistent with early results from nadir observations flasar f m and 44 colleagues 2005 science 308 975 978 between 0 5 and 5 mbar where both results are valid with the warmest temperatures at the equator and much stronger meridional temperature gradients in the northern winter hemisphere than in the southern at higher altitudes not probed by nadir viewing the limb data reveal that the stratopause is nearly 20 k warmer in the northern polar regions than at the equator and southern hemisphere and that the altitude of the stratopause shifts from 0 1 mbar 300 km near the equator to 0 01 mbar 400 km poleward of about 40 n when the gradient wind equation is used to construct a zonal mean wind the reversal in sign of the temperature leads to capping of the winter westerly flow the core of the resulting jet is about 190 m s 1 in magnitude spans between 30 n and 60 n and peaks near 0 1 mbar estimates of the radiative heating associated with the radiative disequilibrium lead to a meridional overturning timescale of about three earth years

formation of the steer s head geometry of sedimentary basins by differential stretching of the crust and mantle if the lithospheric mantle is stretched over a wider region than the crust postrift stratigraphic onlap will occur at basin margins giving rise to a steer s head geometry space problems are avoided by making the total amount of extension in the lithospheric mantle equal to that in the crust the predicted pattern of onlap agrees well with that observed if the lithospheric mantle is stretched over a fractionally wider region than is the crust thus extensive stratigraphic onlap can be produced easily without recourse to sea level rise or flexural rigidity

characterization of zonal winds in the stratosphere of titan with uves 2 observations coordinated with the huygens probe entry 1 the huygens probe has successfully entered titan s atmosphere and landed on its surface on 14 january 2005 with the aim of characterizing the zonal wind flow in titan s stratosphere close to the time of entry coordinated observations were carried out at the very large telescope on the nights of 7 12 14 and 15 january as in our previous investigation luz et al 2005 we used the uves instrument mounted on the kueyen ut2 telescope simultaneously achieving high spectral resolving power and high spatial resolution the field has been derotated in order to align the 0 3 arcsec aperture perpendicularly to titan s rotation axis in this configuration spatial information in the east west direction is preserved in a set of spectra in the direction perpendicular to dispersion we present measurements of zonal winds obtained with the technique of absolute accelerometry the observations were made in the wavelength range 4200 6200 a probing between 115 and 280 km with peak contributions at 200 and 170 km for the lower and upper parts of the domain we detect prograde zonal winds with lower limits 46 and 53 ms 1 at these altitudes these values are close to our previous measurements

crustal structure of the flemish cap continental margin eastern canada an analysis of a seismic refraction profile summary the crustal structure of the ne flemish cap margin was determined along a 460 km long refraction wide angle reflection seismic transect flame line to define the thickness structure and composition of the crust and uppermost mantle along the line a p wave velocity model was developed from forward and inverse modelling of dense airgun shots recorded by 19 ocean bottom seismometers a coincident multichannel seismic profile was used to guide the modelling as reflections could be identified down to moho the model displays a sediment cover of up to 3 6 km thick subdivided into three layers with velocities of 1 8 1 9 km s 1 2 8 3 1 km s 1 and 4 7 4 8 km s 1 for the western part of the flame line over flemish cap the p wave velocity model displays an up to 32 km thick three layer continental crust the continental crust has velocities of 5 8 6 1 km s 1 6 3 6 45 km s 1 and 6 65 6 85 km s 1 and thicknesses of about 5 km 7 km and 20 km in the upper middle and lower layers respectively the thick continental crust thins to a two layer 6 km thick crust upper layer is 5 55 6 0 km s 1 and the layer below is 6 65 6 8 km s 1 over a distance of 45 km s wave velocities are determined in the upper layer of the thick continental crust over flemish cap and the transition zone by assigning poisson s ratios in the p wave velocity model comparison of calculated to observed arrival times gives a poisson s ratio of 0 27 in the upper layer and 0 28 in the layer below which suggests that the composition of the crust is primarily continental in both the thick crust and the thin crust of the transition zone the thin continental crust is stretched over a width of 80 km and is underlain by a layer with velocities of 7 5 7 9 km s 1 we interpret this layer as partially serpentinized mantle which is consistent with observationsfromthenewfoundlandmargintothesouth theserpentinizedmantleterminates 30 km seaward of the thick continental crust at the seaward most end of the thin continental crust a prominent ridge feature is observed the seismic refraction and multichannel seismic data results indicate a mixed character between serpentinized mantle with volcanic extrusions or continental crust the reflection seismic data show a high relief basement from the ridge feature and seaward the flame line crosses magnetic anomaly 34 and extends another 50 km seaward well into oceanic crust the ridge is flanked seaward by a two layer oceanic crust the upper layer layer 2 has velocities of 4 8 5 0 km s 1 for the landward most 35 km of oceanic crust and 4 8 6 2 km s 1 for the seaward 60 km the average thickness of layer 2 is 2 km the lower layer layer 3 has velocities of 6 7 7 2 km s 1 and a thickness of 3 5 km the velocity model is consistent with a sharp onset of seafloor spreading seaward of the ridge feature

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

determining continuous basins across conjugate margins the east orphan porcupine and galicia interior basins of the southern north atlantic ocean abstract the east orphan porcupine and galicia interior basins are several of the most promising basins for hydrocarbon exploration along the rifted continental margins of the southern north atlantic ocean despite having formed at similar geological times the basins exhibit fundamental differences in symmetry crustal thickness sedimentary cover thickness and amount of extension interpretation of seismic reflection and well data was integrated with published 3d grids of depth to basement and moho proxy depth to interpret and restore select seismic reflection lines publicly available kinematic evolution models were also integrated to evaluate and compare the restored seismic reflection lines in a more global regional context interpretation of five seismo stratigraphic units and three tectonostratigraphic megasequences along the east orphan porcupine and galicia interior basins reveals similar seismic character for each unit and comparable tectonic history the structural restoration of the selected lines indicates that evolution sedimentary cover thickness faulting style crustal structure and kinematic evolution of the east orphan and porcupine basins differ significantly a variable and asymmetrical crustal structure is found in the east orphan basin contrasting with the elongated and symmetric porcupine and galicia interior basins rift domain maps of the three basins reveal that they are each underlain by hyperextended crust with possible exhumed mantle in the centre of the porcupine basin based on a holistic analysis of the results obtained the linkage between the east orphan and the porcupine basins seems implausible but rather a contemporaneous relationship is interpreted moreover a potential connection between the galicia interior basin and the porcupine basin during the early to late jurassic is proposed such scenarios imply an oblique and synchronous rifting evolution around the bay of biscay triple junction of the southern north atlantic

traveltime tomography of a dense wide angle profile across orphan basin abstractwe used first arrivals and moho reflections from the 500 km long orphan basin wide angle velocity experiment obwave profile with 3 5 km instrument spacing to construct a traveltime tomography section and to delineate the moho discontinuity across the orphan basin the orphan basin is a failed rift located offshore newfoundland canada showing thinned continental crust over an unusually wide region we observed 1 a zone of extreme crustal thinning 7 km thick crust with no evidence for mantle serpentinization 2 basement morphology exhibiting tilted blocks linked to the crustal thinning and 3 a thicker central crustal segment that is probably related to prerift structural inheritance comparison with the adjacent jeanne d arc basin to the southeast suggested the presence of a decoupling zone between the two basins accommodating the difference in extension rates there was a good correlation between the tomographic velocities and the reflection structure derived from a coincident seismic

regional anomalies of sediment thickness basement depth and isostatic crustal thickness in the north atlantic ocean abstract we calculate the anomalous basement topography for the north atlantic ocean from 30 to 70 n latitude and from 0 to 70 w longitude at a resolution of roughly 6 6 km using grids of total sediment thickness and observed and predicted sea floor bathymetry to correct for the effects of isostatic sediment loading and lithospheric age plotting this residual topography for various plate reconstructions during opening of the north atlantic we delineate consistent patterns of basement highs related to variations in hotspot related volcanism in addition to iceland and the azores we recognize three centers of excess volcanism at the mid atlantic ridge the milne seamounts and azores biscay rise 75 40 ma the southeast newfoundland ridge and madeira tore rise 130 110 ma and the east and west thulean rises 60 50 ma the duration of volcanic activity ranges from 8 to 10 m y thulean rises to 60 m y iceland and thus it appears that both long and short lived hotspots coexist even in relatively close proximity in contrast during the period 110 60 ma we observe little excess volcanism during either continental breakup or seafloor spreading we estimate isostatic crustal thickness from the anomalous basement depths after first removing dynamic effects created by mantle flow maximum thicknesses of volcanic features from 30 km beneath the greenland iceland faeroe ridge to 15 km beneath the azores biscay rise are broadly consistent with seismic data and predictions of decompression melting widths of volcanic features indicate that thickening primarily occurs within 100 200 km of hotspots except along continental margins that rifted at the time of the hotspot activity i e east greenland and the hatton rockall bank we observe conjugate structures south of greenland and edoras bank where excess volcanism appears to have extended beyond the margin proper and into oceanic crust similar conjugate features appear in the labrador sea south of davis strait finally we identify anomalous oceanic regions adjacent to some continental margins where unusually low values of predicted crustal thickness suggest either additional variations in plate properties or non isostatic effects within the mantle

comparison of lithosphere structure across the orphan basin flemish cap and irish atlantic conjugate continental margins from constrained 3d gravity inversions regionally constrained 3d gravity inversion results on the orphan basin flemish cap and the irish atlantic conjugate continental margins are compared to investigate crustal structure early rifting history and geological evolution of this part of the north atlantic the full crustal density anomaly distributions provide some of the first depth images of how rifted structures compare along and across these conjugate margins broad similarities in crustal structure are identified with some noticeable differences linked to rifting and crustal stretching processes extreme crustal thinning stretching factors 3 5 is indicated beneath much of the southern porcupine basin the western half of west orphan basin the eastern half of jeanne d arc basin the southeastern half of east orphan basin and in pockets beneath rockall basin this appears to have resulted in the serpentinization and possible exhumation of mantle lithosphere on the irish atlantic and flemish cap margins but not beneath orphan basin a simple evolution model is proposed for the early stages of rifting between the margins it is suggested that ancient orogenic sutures played an important role in controlling the northward migration of rifting and the rotation and displacement of flemish cap out of orphan basin supplementary material enlarged maps from this paper are available at www geolsoc org uk sup18527

aspects of depositional processes of organic matter in sedimentary basins abstract quantitative evaluation of source rocks is a prerequisite for assessing realistic petroleum potential in target basins such an evaluation includes information about the actual occurrence of organic rich beds their stratigraphic placement specific locations in sedimentary sequences lateral extension geometry at the scale of the basin and their organic facies variations richness and quality to achieve this evaluation current methods rely on analytical data alone for several years an attempt has been made to elaborate a predictive approach based on the integration of the various factors controlling the accumulation and distribution of organic matter in sedimentary basins in order to try to model the process the main effort has been devoted to the control of the production of biomass according to paleogeography and paleoclimatology and to the control of the degradation of organic matter according to the development of oxygen starved water bodies depositional processes which are certainly a key factor to understand the internal variations and the distribution of organic bearing sediments have been largely overlooked examples of modern environments e g black sea caspian sea lake bogoria show that the distribution of the organic matter in anoxic basins is generally organized in a concentric pattern with a centripetal increase of organic content towards the depocenters where the sediment thickness is the greatest such a feature which can be related to the hydrodynamic properties of the organic particles is of paramount importance as far as the distribution of petroleum potential is concerned this centripetal concept with its implications for source rocks evaluation is well exemplified in the lower jurassic of the north sea and in the lias of the paris basin however this pattern can be strongly affected in anoxic basins when extensive gravity transport mechanisms cause redeposition of sediments in such a situation sediments including their specific organic contents are redistributed along transit pathways in lake tanganyika these modes of transport drive a significant amount of altered organic matter towards the deepest parts of the basin resulting in a marked lateral heterogeneity of the organic facies in the bottom sediments similar processes might contribute to the complex pattern of the distribution of organic facies seen in the upper jurassic of the north sea on the other hand gravity flows can introduce organic rich sediments into basins where environmental conditions would otherwise have been unfavorable for organic accumulation a dramatic example of such a situation is provided by the several hundred metres thick sequence of organic rich turbidites and debris flows deposited since the late miocene at the base of the continental slope off south west africa

calculating the long term displacement rates of a normal fault from the high resolution stratigraphic record early tethyan rifting french alps displacement rates of normal faults deduced from stratigraphic data are often unreliable here we calculate the velocity of motion on a normal fault from the variations in accommodation potential on both sides of the fault within a highresolution time frame established by biostratigraphy and physical stratigraphy our example is the ornon normal fault bounding the early jurassic bourg d oisans basin formed during tethyan rifting we show that motion on the fault was discontinuous when examined at high resolution and over a long time interval during a first interval hettangian to sinemurian arietites bucklandi zone a low rate of displacement 202 423 m myr 1 coeval with diffused extensional deformation throughout the sedimentary basin is observed a second interval of localized deformation early sinemurian caenisites turneri zone is characterized by higher rates of displacement on the fault 1846 m myr 1 our results concur with recent numerical models identifying the main stages of extensional deformation

tectonosedimentary evolution of the deep iberia newfoundland margins evidence for a complex breakup history most of the conceptual ideas concerning sedimentary architecture and tectonic evolution of deep rifted margins are based on either intracontinental rift basins or proximal margins both of which underwent only small amounts of crustal thinning in this paper we investigate the tectonosedimentary and morphotectonic evolution related to continental breakup of the highly extended deep iberia newfoundland margins our results show that continental breakup is a complex process distributed in time and space on the basis of mapping of dated seismic units and borehole data we are able to identify two major phases of extension during a first phase dated as tithonian to barremian 145 128 ma deformation is related to exhumation of mantle rocks basins become younger oceanward and fault geometry changes from upward to downward concave resulting in complex sedimentary structures and basin geometries a second phase dated as latest aptian 112 ma overprints previously exhumed mantle and accreted juvenile oceanic crust over more than 200 km leading to the formation of basement highs the observed complex breakup history challenges classical concepts of rifting and leads to new interpretations for the tectonosedimentary evolution of deep rifted margins

probing titan s atmosphere with the 1995 august stellar occultation abstract on 1995 august 21 saturn s moon titan occulted the 13th magnitude star gsc5254 00997 the predawn event was observed at 2 3 m with the nasa 3 0 m infrared telescope facility we measured the average atmospheric scale height between latitudes 50 s and 67 s by fitting isothermal models to the immersion portion of the occultation lightcurve within the altitude range of 300 to 500 km we find an isothermal scale height of titan s sunset atmosphere of 55 9 km our derived temperature of 180 30 k is consistent with modeled temperature profiles derived from voyager 1 iris observations a coustenis and b bezard 1995 icarus 115 126 140 and the 28 sagittarii occultation event w b hubbard et al 1993 astron astrophys 269 541 563 the atmospheric albedo asymmetry due to low level haze caldwell et al 1992 icarus 96 1 9 is inferred from the difference in titan s center of light determined from precise astrometric measurements of images of titan and the star before and after the occultation and the actual center of titan determined from the occultation analysis we find the southern hemisphere to be brighter than the northern hemisphere a result consistent with combes et al 1997 icarus 129 482 497 gibbard et al 1999 icarus 139 189 201 and smith et al 1996 icarus 119 336 349

early diagenesis of marine organic matter alteration of the carbon isotopic composition in two distal carbonate turbidites labelled a and e from the madeira abyssal plain oxidation of organic matter om has been accompanied by a reduction in hydrogen index hi and change in the isotopic composition of carbon since the emplacement of turbidite 0 5 ka ago 35 of the om in the upper part has been oxidised by oxygen and nitrate diffusing from sea water into the sediment there is an accompanying decrease of 0 3 in 13c om and a decrease of 25 in hi turbidite e was emplaced about 73 ka and was exposed to bottom water for 12 3 ka before being buried beneath later turbidites during exposure oxygen and nitrate diffused into its upper part and oxidised 50 of the toc without an accompanying change in isotopic composition further oxidation of the more refactory organic components decreased toc by a further 25 and decreased 13c by 2 5 oxidation also reduced hi by 50 from originally low values unless corrected for the isotopic changes accompanying extended oxic and suboxic degradation of organic matter in sediments will give rise to erroneous estimates of marine terrestrial om ratios

tectonic implications of exposure of lower continental crust beneath the iberia abyssal plain northeast atlantic ocean geophysical evidence we present new seismic data from a basement high beneath the southern iberia abyssal plain that appears from the latest ocean drilling program odp results and indirectly from various seismic observations to consist of lower continental crustal material this is a unique opportunity to use seismic profiles and other geophysical evidence to investigate the tectonic process which led to the exhumation of these rocks we infer that the lower crust was exhumed at the seafloor and then uplifted toward the end of rifting our results lead to the following new observations low angle detachment faults previously reported along the east west lusigal 12 profile across the southern iberia abyssal plain penetrate both the 3 10 km thick continental crust and unusually the uppermost mantle processing of new multichannel seismic reflection profiles across the basement high on which odp sites 900 1067 and 1068 are located reveals that the high is bounded by a previously unsuspected steep landward dipping normal fault on its east flank basement cores from the above odp sites also reveal that the high is not capped by the previously predicted early syn rift sediment but by rocks from the lower continental crust these unexpected observations are incorporated into a new tectonic model of the development of this part of the west iberia margin which is also consistent with other geophysical observations a novel feature of this model is the proposal that the seaward edge of the continental crust is thinned to 3 6 km by a currently poorly understood process the model implies three stages of deformation 1 lithospheric extension principally by symmetric pure shear which leads to a 10 km thick crust in which the lower crust is largely absent over the axial zone and the crust mantle boundary forms a shear zone 2 further thinning and then dissection of the most distal continental crust by seaward dipping low angle normal faults 3 inception of a high angle landward dipping normal fault that offsets the tectonized crust mantle boundary and uplifts the lower crust to the crest of the basement high on which odp sites 900 1067 and 1068 were drilled