shear strength estimation for aknes sliding area in western norway abstract this paper deals with the unstable rock slope at aknes sliding area located in the county of more and romsdal in western part of norway the sliding body has a complex geometry with several sliding planes at different levels involving unfilled joints gouge material brecciated material as well as bridges of intact rock stability of the rock slope strongly depends on the shear strength of the sliding plane s and this paper discusses the shear strength of the materials present ranging between the strength of intact rock and crushed clay containing gouge material estimation of the in situ shear strength at the aknes sliding area is discussed on the basis of triaxial test results and the barton bandis empirical method triaxial tests have been carried out on samples of gouge material from a potential sliding plane and intact rock specimens while the empirical method has been applied for rock joints in the area comparison and correlation with experimental results found in literature have also been made the resultant shear strength range for the zone of sliding has been found to be in the range of 0 5 1 3 mpa depending on the normal stress and the composition of the sliding zone

the tectonic evolution of the south atlantic from late jurassic to present an improved tectonic database for the south atlantic has been compiled by combining magnetic anomaly geosat altimetry and onshore geologic data we used this database to obtain a revised plate kinematic model starting with a new fit reconstruction for the continents around the south atlantic we present a high resolution isochron map from chron m4 to present fit reconstructions of south america and africa that require rigid continental plates result in substantial misfits either in the southern south atlantic or in the equatorial atlantic to achieve a fit without gaps we assume a combination of complex rift and strike slip movements 1 along the south american parana chacos basin deformation zone 2 within marginal basins in south america salado colorado basin and 3 along the benue trough niger rift system in africa these faults are presumed to have been active before or during the breakup of the continents our model describes a successive unzipping of rift zones starting in the southern south atlantic between 150 ma tithonian and approximately 130 ma hauterivian rifting propagated to 38 s causing tectonic movements within the colorado and salado basins subsequently between 130 ma and chron m4 126 5 ma the tip of the south atlantic rift moved to 28 s resulting in intracontinental deformation along the parana chacos basin deformation zone between chron m4 and chron mo 118 7 ma rifting propagated into the benue trough and niger rift inducing rift and strike slip motion after chron mo the equatorial atlantic began to open while rifting and strike slip motion still occurred in the benue trough and niger rift since chron 34 84 ma the opening of the south atlantic is characterized by simple divergence of two rigid continental plates

carbon isotopic changes in benthic foraminifera from the western south atlantic reconstruction of glacial abyssal circulation patterns oxygen and carbon isotopic analyses have been performed on the benthic foraminifer planulina wuellerstorfi in seven late quaternary cores from the vema channel rio grande rise region the cores are distributed over the water depth interval of 2340 to 3939 m which includes the present transition from north atlantic deep water nadw to antarctic bottom water aabw the carbon isotopic records in the cores vary as a function of water depth the shallowest and deepest cores show no significant glacial interglacial difference in 13c four of the five cores presently located in the nadw have benthic foraminiferal 13c that is lower during glacial isotopic stages based on bathymetric gradients in 13c we conclude that like today there were two water masses present in the vema channel during glacial intervals a water mass enriched in 13c overlying another water mass depleted in 13c the largest gradient of change of 13c with depth however occurred at 2 7 km 1 km shallower than the present position of this gradient on the basis of paleontologic and sedimentologic evidence we consider it unlikely that the nadw aabw transition shallowed to this level reduced carbon isotopic gradients between the deep basins of the north atlantic and pacific oceans during the last glaciation suggest that production of nadw was reduced lower production of nadw may have modified the local abyssal circulation pattern in the vema channel region

late cenozoic turbidite and contourite deposition in the southern brazil basin abstract piston and giant gravity cores together with 3 5 khz and seismic profiles reveal a complex pattern of dispersal of bioclastic calcareous turbidites in the southern brazil basin extensive canyons up to 500 m deep dissect the steep north flank of the rio grande rise and serve as conduits for turbidity currents which have eroded modern sediments as well as outcrops of tertiary and late cretaceous strata the resulting turbidites are up to several meters thick in channel axes and commonly several cm thick at distances up to hundreds of km from the canyon source region individual turbidity currents were apparently sufficiently strong to transport fine grained components several hundred meters upslope and several hundred km laterally across the brazil basin the lithology of both proximal and distal turbidites their presence well below the modern ccd and the lack of correspondence between their presence and that of displaced antarctic diatoms verifies that these calcareous deposits are not products of episodic antarctic bottom water flow but originated from a shallow water source area the late pleistocene and holocene witnessed major turbidity current episodes at intervals on the order of 50 000 yrs with at least two episodes coinciding approximately with interglacials following terminations i and ii sediments older than isotopic stage 8 275 000 yrs b p include thinly laminated contourites we interpret these units as intervals of normal pelagic sedimentation which were subsequently reworked under the influence of aabw pulses episodes of intensified aabw flow may have immediately preceded the onset of major glacial episodes extending corrosive eastward flowing aabw to relatively shallow depths 4200 4300 m along the north flank of the rio grande rise the undercutting of outcropping strata by chemical dissolution at the base of the faulted north flank has probably played a critical role in the initiation of canyon cutting episodic slumping due to oversteepening and the generation of debris flows progressively enlarged the canyons upslope in a dendritic pattern and gradually extended the canyons to shallower elevations on the rise vertical crustal displacements associated with the rio grande fracture zone have controlled the pathway of aabw in the southern brazil basin and accentuated the steep relief on the north flank of the rise these two processes have been essential conditions for the extensive canyon cutting and subsequent dispersal of carbonate turbidites over the brazil basin

characterization of alpine rockslides using statistical analysis of seismic signals 1 seismic data analysis is a powerful tool for remote characterization of rock slope failures here we develop quantitative estimates of fundamental rockslide properties e g volume based solely on data from an existing regional seismic network we assembled a data set of twenty known rockslides in the central alps with volumes between 1 000 and 2 000 000 m3 and analyzed their corresponding seismograms common signal characteristics include emergent onsets slowly decaying tails and a triangular spectrogram shape the main component of seismic energy is contained in frequencies below 3 4 hz while higher frequency signals may be caused by block impacts location estimates were generated using automatic arrival time picks and resulted in a mean location error of 10 9 km a linear relationship for the detection limit of a rockslide as a function of volume was identified for our seismic station network to estimate rockslide volume runout distance drop height potential energy and fahrboschung angle of reach we extracted five simple metrics from each seismogram signal duration peak value of the ground velocity envelope velocity envelope area risetime and average ground velocity using multivariate linear regression the combination of duration peak envelope velocity and envelope area best estimated event parameters with r2 values ranging between 0 8 and 0 88 three new rockslides were then used to validate our method and volume runout drop height and potential energy were estimated within the correct order of magnitude when provided with a suitable data set of rockslide events our method can be easily adapted to other regions and seismic networks

combining digital elevation model analysis and run out modeling to characterize hazard posed by a potentially unstable rock slope at turtle mountain alberta canada abstract turtle mountain in alberta canada has become an important field laboratory for testing different techniques related to the characterization and monitoring of large slope mass movements as the stability of large portions of the eastern face of the mountain is still questionable in order to better quantify the volumes potentially unstable and the most probable failure mechanisms and potential consequences structural analysis and runout modeling were preformed the structural features of the eastern face were investigated using a high resolution digital elevation model hrdem according to displacement datasets and structural observations potential failure mechanisms affecting different portions of the mountain have been assessed the volumes of the different potentially unstable blocks have been calculated using the sloping local base level slbl method based on the volume estimation two and three dimensional dynamic runout analyses have been performed calibration of this analysis is based on the experience from the adjacent frank slide and other similar rock avalanches the results will be used to improve the contingency plans within the hazard area

the rio grande fracture zone in the western south atlantic and its tectonic implications abstract a broad zone of linear mappable basement structures is observed north and northeast of the rio grande rise in the south atlantic ocean these structures lie along the same flow line as the sa o paulo ridge the florianopolis high and onshore lineaments suggesting that they all comprise the same tectonic trend the rio grande fracture zone the morphology developed along this fracture zone during the early opening of the south atlantic ocean formed a barrier to open ocean circulation during the aptian and allowed the formation of extensive evaporite deposits to the north of it

analyzing complex rock slope deformation at stampa western norway by integrating geomorphology kinematics and numerical modeling abstract the unstable rock slope stampa above the village of flam norway shows signs of both active and postglacial gravitational deformation over an area of 11 km 2 detailed structural field mapping annual differential global navigation satellite system gnss surveys as well as geomorphic analysis of high resolution digital elevation models based on airborne and terrestrial laser scanning indicate that slope deformation is complex and spatially variable numerical modeling was used to investigate the influence of former rockslide activity and to better understand the failure mechanism field observations kinematic analysis and numerical modeling indicate a strong structural control of the unstable area based on the integration of the above analyses we propose that the failure mechanism is dominated by 1 a toppling component 2 subsiding bilinear wedge failure and 3 planar sliding along the foliation at the toe of the unstable slope using differential gnss 18 points were measured annually over a period of up to 6 years two of these points have an average yearly movement of around 10 mm year they are located at the frontal cliff on almost completely detached blocks with volumes smaller than 300 000 m 3 large fractures indicate deep seated gravitational deformation of volumes reaching several 100 million m 3 but the movement rates in these areas are below 2 mm year two different lobes of prehistoric rock slope failures were dated with terrestrial cosmogenic nuclides while the northern lobe gave an average age of 4 300 years bp the southern one resulted in two different ages 2 400 and 12 000 years bp which represent most likely multiple rockfall events this reflects the currently observable deformation style with unstable blocks in the northern part in between joasete and furekamben and no distinct blocks but a high rockfall activity around ramnanosi in the south with a relative susceptibility analysis it is concluded that small collapses of blocks along the frontal cliff will be more frequent larger collapses of free standing blocks along the cliff with volumes 100 000 m 3 thus large enough to reach the fjord cannot be ruled out a larger collapse involving several million m 3 is presently considered of very low likelihood

origin and evolution of two contrasting thermal groundwaters co2 rich and alkaline in the jungwon area south korea hydrochemical and isotopic evidence in the jungwon area south korea two contrasting types of deep thermal groundwater around 20 33 c occur together in granite compared to shallow groundwater and surface water thermal groundwaters have significantly lower 18o and d values 1 lower in 18o and negligible tritium content mostly 2 tu suggesting a relatively high age of these waters at least pre thermonuclear period and relatively long subsurface circulation however the hydrochemical evolution yielded two distinct water types co2 rich water pco2 0 1 to 2 atm is characterized by lower ph 5 7 6 4 and higher tds content up to 3300 mg l whereas alkaline water pco2 10 4 1 10 4 6 atm has higher ph 9 1 9 5 and lower tds 254 mg l carbon isotope data indicate that the co2 rich water is influenced by a local supply of deep co2 potentially magmatic which enhanced dissolution of silicate minerals in surrounding rocks and resulted in elevated concentrations of ca2 na mg2 k hco3 and silica under lower ph conditions in contrast the evolution of the alkaline water was characterized by a lesser degree of water rock granite interaction under the negligible inflow of co2 the application of chemical thermometers indicates that the alkaline water represents partially equilibrated waters coming from a geothermal reservoir with a temperature of about 40 c while the immature characteristics of the co2 rich water resulted from the input of co2 in na hco3 waters and subsequent rock leaching

displaced antarctic diatoms in vema channel sediments late pleistocene holocene fluctuations in aabw flow abstract displaced antarctic diatoms were identified and counted in a suite of 23 giant gravity cores from the east flank of the vema channel providing a semi quantitative index of late pleistocene holocene fluctuations in antarctic bottom water aabw flow twelve species of antarctic diatoms were counted and three of these nitzschia kerguelensis eucampia antarctica and coscinodiscus lentiginosus occur in sufficient quantity for statistically meaningful interpretations the number of diatom specimens per gram of carbonate free sediment was determined for core top last glacial maximum last interglacial and penultimate glacial maximum intervals antarctic diatoms are abundant in cores from depths in excess of 4100 m and disappear abruptly in core tops between approximately 4125 and 3975 m water depth no specimens of antarctic diatoms are present in cores shallower than 3744 m the top of this transition zone corresponds with the isotherms 1 9 c and the isopycnal 4 45 93 that hogg et al 1982 selected as a suitable reference level between northward and southward flow in the vema channel axis the sediments from the vema channel indicate no significant shallowing or deepening of this level during the glacial or interglacial intervals examined displaced antarctic diatoms are generally less abundant during glacial maxima than during interglacials downcore counts of displaced antarctic diatoms reveal two peaks of dramatically increased abundances at the isotopic stage 6 7 and 3 2 boundaries in other cores within the vema channel from below 3965 m late pleistocene hiatuses are common

contribution of global potential field data to the tectonic reconstruction of the rio grande rise in the south atlantic abstract the application of advanced enhancement techniques for geophysical anomalies to global gravity wgm2012 and magnetic emag2 models sheds light on the complex tectonic evolution of the rio grande rise rgr in the southern south atlantic long wavelength bouguer gravity lows indicate a thicker crust beneath of the ridge whose nature can be related to a microcontinent or an excess of volcanism within the oceanic realm recently dredged continental rocks reinforce the hypothesis of a microcontinent or at least slivers of continental crust however the reserval magnetic pattern of the processed magnetic anomalies provide no evidence of aborted spreading center similar to the well studied jan mayen microcontinent and the surrounding inactive aegir and active kolbeinsey ridges in the north atlantic ocean the reversal magnetic anomalies show a series n s trending parallel stripes roughly follow the current south american coastline and segmented by e w oriented oceanic fracture zones fzs the magnetic stripes are bended eastwards at the rgr showing a more complex magnetic pattern similar to that in the iceland the aborted cruzeiro do sul rift csr and the jean charcot chain jcc are structures that cross the rgr and contribute to the understanding of the tectonic evolution of the south atlantic ocean nw se oriented extensive gravity lows and bathymetric valleys which mark the csr are segmented by e w trending magnetic lineaments related to fzs this structural configuration suggests that the extensional event which formed the rift and the seamounts chain was replaced by strike slip movements along the fzs in addition we constructed a plate kinematic model for the evolution of the rgr based on bathymetric free air and bouguer gravity and magnetic data our model comprises five main stages of the rgr formation and evolution between late cretaceous and paleocene ca 95 60 ma separated by published seafloor isochrones the proposed model suggests that the rgr was built at the mid atlantic ridge by increased magmatism probably related to the tristan da cunha hotspot

numerical analysis of initiation and progressive failure in natural rock slopes the 1991 randa rockslide the 1991 randa rockslide in the swiss alps involved several complex mechanisms relating to geological mechanical and hydrological processes for which no clear trigger can be asserted this paper investigates the concept of progressive failure and the numerical modelling of rock mass strength degradation in natural rock slopes using the randa rockslide as a working example results from continuum i e finite element modelling are presented to illustrate a hypothesis suggesting that initiation of a progressive rock mass degradation process ultimately leading to failure began following deglaciation of the valley below discontinuum distinct element modelling is then applied to investigate the underlying mechanisms contributing to the episodic nature of the rockslide finally the use of a hybrid method that combines both continuum and discontinuum techniques to model fracture propagation are discussed in the context of modelling progressive slide surface development linking initiation and degradation to eventual catastrophic failure

the vema channel physiography structure and sediment current interactions abstract the east flank of the vema channel in the southwestern atlantic is an opportune location for interpreting the pleistocene holocene record of deep thermohaline circulation the channel and the adjacent sediment covered rio grande rise intersect each of the principal sub thermocline water masses of the western atlantic we analyzed a suite of 25 giant gravity cores in transects extending between 1400 and 4150 m depth this interval includes the upper and lower branches of circumpolar water north atlantic deep water and antarctic bottom water the late pleistocene holocene sediments along these transects are pelagic carbonates with excellent stratigraphic continuity shallower and deeper regions are relatively unsuitable due to poor core recovery or widespread erosional unconformities extensive hydrographic and direct current observations near the location of our prime coring transect at 30 s indicate a notable cross channel asymmetry in the abyssal hydrography and velocity structure which is reflected in the underlying lithofacies distribution the near bottom flow field shows marked temporal and spatial variability on a local scale even in the channel axis where one would anticipate relatively steady uniform flow much of this variability appears to reflect the effects of transient mesoscale eddies rather than regional variations in the integrated north ward transport of aabw in spite of temporal variations in the flow field the nadw aabw transition zone appears to have remained remarkably stable over time scales of 10 5 10 6 yrs on geological evidence discussed elsewhere in this volume jones 1984 jones and johnson 1984 this observation is somewhat surprising because in the modern oceans the density contrast between nadw and aabw is relatively small if the transition zone between the two water masses has indeed remained relatively stationary then the density determining water properties t and s may also have remained relatively constant with only the rates of production changing if this interpretation proves correct upon further studies it implies that pale oceanographic interpretations of deep thermohaline flow should in some instances utilize geological indices of non conservative water properties e g co 2 13 c for monitoring paleocirculation changes

before the frank slide the frank slide occurred on the east limb of the turtle mountain anticline which was thrust up along the folded and splayed turtle mountain fault easterly dipping paleozoic limestones and dolomi

from incipient slope instability through slope deformation to catastrophic failure different stages of failure development on the ivasnasen and vollan rock slopes western norway abstract the long term evolution of rock slope failures involves different stages from incipience of slope instability to catastrophic failure through a more or less long lasting slope deformation phase that also involves creeping or sliding topography lithology and structural inheritance are the main intrinsic factors that influence this evolution here we investigate the role of these intrinsic factors on the rock slope failure development of the ivasnasen and vollan rock slopes sunndal valley western norway using a multitechnique approach that includes geomorphologic and structural field mapping kinematic analysis terrestrial cosmogenic nuclide exposure dating topographic reconstruction and deformation quantification ivasnasen is a rock slope failure complex with several past rock slope failures and a present unstable rock slope located on a cataclinal nw facing slope and developed in augen gneiss vollan on the opposite valley side is a deep seated gravitational slope deformation dsgsd affecting the whole mountainside developed in quartzite in the upper part and micaschist in the lower part these different lithologies belong to different nappe complexes that were emplaced and folded into a series of syn and anticlines during the caledonian orogeny these folds lead to different lithologies being exposed in different structural orientations on the opposite valley flanks which in turn leads to different types and evolution of rock slope failures at ivasnasen the 45 55 nw dipping ductile foliation allowed for a fairly simple planar sliding mechanism for the 1 2 million m 3 post glacial rock slope failure failure occurred ca 3 3 ka ago after a short period of prefailure deformation for the present 2 2 million m 3 unstable rock slope at ivasnasen a steepening of the foliation at the toe impedes such a mechanism and up to 10 m of displacement has not lead to a catastrophic failure yet the vollan dsgsd is characterized by a steep major back scarp with its up to 130 m wide graben which opened along the subvertical foliation in the quartzite and a conspicuous array of counter scarps in the micaschist the morphologic features are explained by a flexural toppling mechanism in the micaschist which likely initiated in the lower slope section and propagated retrogressively until reaching the massive quartzite at the back scarp flexural toppling cannot solely explain the total along slope displacement of up to 200 m i e an elongation of 28 creep along a basal shear zone which may have developed in the hinge zone of the flexural toppling combined with shallow valley dipping joints likely accounts for the large elongation implications of this study for the hazard assessment of unstable rock slopes in norway include the relatively rapid development of instabilities in cataclinal slopes and the important insights on long term displacement rates gained from cosmogenic nuclide dating for a better understanding of the evolution of unstable rock slopes

severity and speed of northern hemisphere glaciation pulses the limiting case a brief pulse of ice sheet growth of enormous amplitude predicted by the theory of milankovitch is confirmed by oxygen isotopic and other evidence in pacific and north atlantic cores this glaciation bisected interglacial isotopic stage 7 lasted no more than 23 000 yr from inception to end and resulted in a very large ice volume buildup and a full glacial climatic response of the north atlantic ocean this pulse along with other episodes of rapid and large scale ice growth does not conform to the conventional sawtooth model of slow ice accumulation and rapid ice decay ice growth rates on such pulses can approach the mean ice decay rates on isotopic glacial terminations

high resolution stratigraphy in late pleistocene holocene sediments of the vema channel abstract twenty five giant gravity cores ggc were obtained from the southwest flank of the rio grande rise in the summer of 1980 and were analyzed for time slice interpretations of the late pleistocene paleoceanography of the southwestern atlantic the cores span a depth interval of 1430 4148 m encompassing each of the principal deep water masses the suite of cores contains a continuous depositional record of the past 150 000 200 000 years from calcium carbonate oxygen isotope carbon 14 and biostratigraphic analyses it is possible to determine the precision in core to core correlation which is obtainable within this region of relatively low accumulation rates 0 5 2 0 cm 10 3 yrs calcium carbonate analyses were performed on each of the 25 cores at 1 cm sampling intervals using a technique that yields an analytical precision of 0 25 the carbonate curves show glacial interglacial amplitudes of typically 10 30 caco3 higher frequency amplitudes of 2 5 are also present both the glacial interglacial and the higher frequency carbonate signals can be correlated from core to core over the entire depth interval of the transect and are essentially synchronous based on independent stratigraphic control provided in selected cores by 18o 14c and biostratigraphic analyses despite the low sedimentation rates within this particular region we obtain a precision in core to core correlation of 1000 2000 yrs over the late pleistocene holocene these high resolution studies from the vema channel have important implications for interpreting the effects of bioturbation on a given stratigraphic sequence modeling the effects of bioturbation on the abundance and isotopic records of the benthonic foraminifera planulina wuellerstorfi suggests that for the region of the vema channel rio grande rise invalid stratigraphic and paleoceanographic interpretations may result if abundance variations in this species are ignored the results of these analyses show that it is possible to generate detailed stratigraphies in regions that have not previously been selected for high resolution studies solely because of relatively low accumulation rates of sediments our results indicate that carbonate analyses in some regions may provide a distinct advantage over 18o analyses because of the ease of analysis and high precision for identifying low amplitude high frequency fluctuations which can be correlated from core to core at the same time independent stratigraphic control via 18o or 14c is essential to verify whether this technique of carbonate curve matching is valid

abyssal teleconnections interactive dynamics of the deep ocean circulation abstract a teleconnective linkage between two abyssal water masses consists of one or more zones of interaction arranged sequentially in space and time the properties spatial extent and advective nature of one of these water masses are directly influenced by the presence of the other via the zones of interaction the sequence of components in the linkage may in some instances be configured linearly and respond in an irreversible fashion in other instances the linkage is not unidirectional but may include one or more feedback loops representing the dependence of each water mass upon the properties and extent of the other three types of water mass interaction are represented in the modern oceans these are designated as 1 re inforcing 2 lateral blocking re direction and 3 wedging the criteria for discriminating between these types are geometrical yet the physical processes and rates of interaction may be distinguishable between and perhaps characteristics of these different configurations regions of water mass interaction are marked by sharp gradients of water column properties each of which is spatially restricted to a narrow interval of the overall mixing zone sediment characteristics exhibit a similar pattern there is a broad transition zone within which each geological gradient is restricted to a relatively narrow interval one must distinguish between sediment indicators which reflect water properties and those which reflect water column advection and avoid inferring one type of waters characteristic from geological indices which are inappropriate for identifying such characteristics it is not possible to specify a priori all of the components of a teleconnection linkage we can identify critical zones of interaction and search for evidence of threshold events which contributed to the initiation or the breaking of a particular linkage in order to establish the spatial and temporal sequence of components in a complex linkage we must identify the frequency response and phase response spectra in high resolution time series of appropriate paleocenographic indices at key locations

plate kinematics of the south atlantic chron c34 to present a high resolution seafloor spreading history of the south atlantic since chron c34 is constrained by a combination of seasat altimeter data and underway marine geophysical data a set of 45 finite rotation poles defines the relative position of africa and south america at roughly 2 m y intervals a set of 12 stage poles constrain the relative motion of these two plates at 5 to 10 m y intervals the position of the stage poles continuously migrates reflecting the continuously changing azimuths of the fracture zones major changes in spreading direction are observed in the late cretaceous and early cenozoic as the fracture zones sweep out broad s shaped curves similar to the pattern seen on the kane fracture zone in the central atlantic small offset fracture zones were found to be the most accurate recorders of changes in plate motion large offset fracture zones such as the agulhas falkland fracture zone were the least reliable recorders at 30 s spreading rates decrease throughout the late cretaceous from a high of 75 mm yr at the end of chron c34 to a low of 30 mm yr around chron c27 a period of slow spreading between chron c30 and chron c20 corresponds to a zone of fracture zone proliferation an increase in the amplitude of geoid anomalies over fracture zones greater relief on topographic profiles and locally evidence of intraplate crustal deformation spreading rates increase at chron c20 to about 50 mm yr and then gradually decrease during the late paleogene and neogene a comparison of synthetic fracture zones based on the south atlantic stage poles to the observed trends of fracture zones in the equatorial atlantic indicates that the vema and marathon fracture zones were generated by south atlantic spreading as opposed to central atlantic spreading at least as far back as 35 m y ago and possibly 50 m y ago

examples of multiple rock slope collapses from kofels otz valley austria and western norway abstract this paper describes the effects of large massive rock slope failures on subsequent slope stability three examples of large rock slope failures from the austrian alps and norway demonstrate that failure increases the probability of further collapses at kofels austria a holocene rock slope failure several km3 in size filled the otz valley the morphology of the deposits indicates that at least one subsequent failure occurred along the head scarp of the first failure most likely a slide of similar size debris of the second landslide slid over the older deposits forming the famous kofels frictionite at least three rock slope failures all of them in excess of 106 m3 occurred from the same mountainside within the last 6000 8000 years at tafjord in western norway the most recent of these failures in 1934 triggered a destructive tsunami five large failures with volumes 50 000m3 occurred at ramnefjell norway within 50 years two of them caused considerable damage and a large number of death due to the formation of destructive tsunamis two dimensional finite element models of rock slope stability before and after the kofels and tafjord landslides show that massive rock slope failures produce a irregular slopes parts of which are as steep or steeper than the slope before failure and which represent new zones of instability and b zones of weakness related to slow slope deformation and related cracking

the chemistry of geothermal waters in iceland iii chemical geothermometry in geothermal investigations abstract new data from geothermal wells in iceland have permitted empirical calibration of the chalcedony and na k geothermometers in the range of 25 180 c and 25 250 c respectively the temperature functions are t c 1112 4 91 log sio 2 273 15 t c 933 0 993 log na k 273 15 concentrations are expressed in ppm these temperature functions correspond well with the chalcedony solubility data of fournier 1973 and the thermodynamic data for low albite microcline solution equilibria of heloeson 1969 a new co2 geothermometer is proposed which is considered to be useful in estimating underground temperatures in fumarolic geothermal fields its application involves analysis of co2 concentrations in the fumarole steam the temperature function which applies in the range 180 300 c is logco2 37 43 73192 t 11829 103 t2 0 18923t 86 187 logt where t is in k and co2 in moles per kg of steam

late tertiary quaternary magnetostratigraphy and biostratigraphy of vema channel sediments abstract twenty one piston cores in a transect of the vema channel near 31 s were analyzed magnetostratigraphically and biostratigraphically in order to ascertain the depositional continuity in the late tertiary and quaternary the cores span a depth interval of 2941 4235 m and represent three distinct physiographic provinces each of which shows a relatively consistent accumulation pattern the deepest cores are from the broad terraces which flank the vema channel axis on both the west 3650 mm and east 4150 4250 m these cores show the highest accumulation rates in the region 20 m m y 2 and no evidence of unconformities twelve cores from the flanks of the rio grande rise 2941 3950 m show depositional continuity in the late quaternary and normal pelagic accumulation rates 5 10 m m y 2 with evidence in two of the cores for minor erosional hiatuses on a local scale perhaps due to slumping a relatively narrow transition zone between the rio grande rise flanks and the eastern terrace 3950 4150 m shows buried manganese pavements and near outcrops of miocene pliocene strata indicating intermittent erosion during the late tertiary and quaternary perhaps due to episodes of intensified aabw flow modern flow within this transition zone and over the eastern terrace is relatively weak gu 2 cm s 2 and southward the presence of well developed sediment waves on the terrace and buried erosional unconformities upslope to the east suggests substantially higher current velocities during the late tertiary than those present today

synthetic seismogram generation from sediment composition data an initial study in the southwest brazil basin abstract a synthetic seismogram was constructed for deep sea drilling site 515 in the brazil basin by convolving a measured 3 5 khz seismic pulse with a reflectivity profile constructed from geologic parameters acoustic impedance was computed from detailed high resolution carbonate measurements at 10 cm intervals over 62 m of hydraulic piston core section hole 515a the synthetic seismogram and two surface ship 3 5 khz profiles which cross near the site show a striking similarity to each other suggesting that carbonate content is controlling the 3 5 khz record at this site although the interference between pulses reflected from adjacent carbonate peaks occasionally changes the character of the reflected profile specific reflecting horizons can be correlated with particular carbonate peaks previous studies suggest that the carbonate peaks in this core correspond to turbidites the technique can be used to generate synthetic seismograms for sediment cores where the primary physical property information does not exist

quantification of co2 generation in sedimentary basins through carbonate clays reactions with uncertain thermodynamic parameters abstract we develop a methodological framework and mathematical formulation which yields estimates of the uncertainty associated with the amounts of co 2 generated by carbonate clays reactions ccr in large scale subsurface systems to assist characterization of the main features of this geochemical process our approach couples a one dimensional compaction model providing the dynamics of the evolution of porosity temperature and pressure along the vertical direction with a chemical model able to quantify the partial pressure of co 2 resulting from minerals and pore water interaction the modeling framework we propose allows i estimating the depth at which the source of gases is located and ii quantifying the amount of co 2 generated based on the mineralogy of the sediments involved in the basin formation process a distinctive objective of the study is the quantification of the way the uncertainty affecting chemical equilibrium constants propagates to model outputs i e the flux of co 2 these parameters are considered as key sources of uncertainty in our modeling approach because temperature and pressure distributions associated with deep burial depths typically fall outside the range of validity of commonly employed geochemical databases and typically used geochemical software we also analyze the impact of the relative abundancy of primary phases in the sediments on the activation of ccr processes as a test bed we consider a computational study where pressure and temperature conditions are representative of those observed in real sedimentary formation our results are conducive to the probabilistic assessment of i the characteristic pressure and temperature at which ccr leads to generation of co 2 in sedimentary systems ii the order of magnitude of the co 2 generation rate that can be associated with ccr processes

carbon dioxide in clastic rocks and silicate hydrolysis the amount of carbon dioxide in clastic rocks in sedimentary basins increases with depth organic matter dissolved organic species and dissolution of carbonate minerals have been suggested as sources of co sub 2 which increases in abundance with depth and temperature isotopic compositions of aqueous hco sub 3 sup minus gaseous co sub 2 and calcite from conventional hydrocarbon wells and steam assisted recovery of heavy oil suggest that calcite or other carbonate minerals are the source of co sub 2 particularly at higher temperatures detailed examination of the stability of diagenetic minerals such as kaolinite smectite and analcime among others relative to the coexisting waters indicates that silicate hydrolysis is the driving force for dissolution of carbonate minerals and the ultimate source of abundant co sub 2 in clastic rocks in diagenetic environments at temperatures over approximately 100 c

thermal contraction and the state of stress in the oceanic lithosphere nonuniform contraction of the oceanic lithosphere as it cools and thickens following its formation at the axis of a spreading center results in a complex three dimensional state of deviatoric stress which can be separated into two parts a thermal bending stress due to changes in the vertical temperature distribution and a thermal contraction stress due to lateral variations in the vertically averaged temperature we examine thermal contraction stresses due to temperature changes in a thin semi infinite rectangular plate bounded by the spreading center axis two stress free boundaries representing transforms or fracture zones define the plate width or ridge segment length l with the bottom of the elastic plate defined by a prescribed temperature the plate thickens as the square root of age as expected for a thermal boundary layer due to vertical conductive cooling above this prescribed temperature elastic stresses are assumed to relax quickly stresses are obtained by properly accounting for the rate of accumulation of the vertically averaged stress as initially stress free material is added to bottom of the cooling thickening plate the state of thermal contraction stress calculated from this model is characterized by large tensile stresses at the boundaries of the plate and relatively low stresses in the plate interior at the ridge axis ridge parallel tensile stresses are about 300 mpa the same as if the plate were not allowed to contract in this direction along the transform boundary the maximum transform parallel tensile stress occurs at a distance l 2 from the ridge transform intersection where its magnitude is comparable to the stress at the ridge axis the tangential stresses at the plate boundary decrease rapidly with distance from the boundary at a distance of l 4 from the ridge axis the ridge axis parallel stresses are one tenth of their ridge axis magnitude the stress magnitudes are independent of both spreading rate and ridge segment length a large transform parallel tensile stress may control the length of transform offsets thermal bending moments are influenced by the large thermal contraction stresses near the ridge axis however a short distance from the ridge these moments attain their free horizontal contraction values which previous studies have shown to cause observable bending of the plate and a geoid anomaly at fracture zones flexure due to thermal bending moments will concentrate bending stresses at a distance from the fracture zone determined by the flexural length of the plate thus providing a natural length scale controlling the spacing of transforms

influence of tectonic structures on the hope slide british columbia canada abstract the hope slide which occurred on january 9 1965 involved an estimated 47 mm3 of meta volcanics and intrusive rocks previous workers reported the presence of tectonic structures faults and shear zones along the failure surface at the hope slide these tectonic features were investigated in detail to assess their effects on rock mass quality and the related implications for slope stability this paper integrates basic field and laboratory concepts from structural and engineering geology subdividing the failure area into structural domains allowed distinct discontinuity sets to be associated with specific tectonic structures the geological strength index gsi was used to estimate the rock mass damage related to the tectonic structures low gsi values were seen to outline tectonic damage zones point load tests were used to characterise the compressive strength of rocks adjacent to the tectonic structures strength anisotropy tentatively attributed to damage caused by a large shear zone was observed in greenstone samples seepage zones along the failure surface were observed preferentially along shallow discontinuities that dipped downslope and in rock masses of good quality gsi 40 an alternative morphology of the slope failure is proposed by distinguishing between the extent of the surficial damage due to the rock slope failure and the zone of failed material depletion zone for the first time a kinematic mechanism for the hope slide is proposed based on a preliminary 3 dimensional block model a pre 1965 dem was produced from estimates of material lost and gained as reported by previous workers the pre 1965 dem revealed that the tectonic structures recognised during fieldwork bounded the material that failed in the 1965 event

entrainment of debris in rock avalanches an analysis of a long run out mechanism many rock avalanches entrain and liquefy saturated soil from their paths evidence for this includes mud displaced from the margins of rock avalanche deposits substrate material smeared along the base of deposits extrusion of liquefied soil upward through the deposits and increases of volume a hypothesis first suggested in 1881 and since reinforced by several authors suggests that entrainment of substrate material increases mobility although the process has been discussed in the literature for more than 100 years few detailed and quantitative descriptions exist the main purpose of this paper is to describe two recent cases from british columbia canada where rockslides entrained substrate on a very large scale influencing the character of the events estimated volume balance curves based on detailed field mapping are provided for both cases dynamic analyses are carried out using a numerical model and using the same set of rheological parameters the mechanism of material entrainment and displacement is discussed the data suggest that rapid rock failures entraining very large quantities of saturated substrate material represent a special type of landslide transitional between rock avalanche and debris avalanche many rock avalanches can thus be seen as end members of a continuum of phenomena involving rock failure followed by interaction with saturated substrate

rockslide tsunamis in complex fjords from an unstable rock slope at akerneset to tsunami risk in western norway abstract an unstable rock volume of more than 50 million m 3 has been detected in the akerneset rock slope in the narrow fjord storfjorden more romsdal county western norway if large portions of the volume are released as a whole the rockslide will generate a tsunami that may be devastating to several settlements and numerous visiting tourists along the fjord the threat is analysed by a multidisciplinary approach spanning from rock slope stability via rockslide and wave mechanics to hazard zoning and risk assessment the rockslide tsunami hazard and the tsunami early warning system related to the two unstable rock slopes at akerneset and hegguraksla in the complex fjord system are managed by aknes tafjord beredskap iks previously the aknes tafjord project the present paper focuses on the tsunami analyses performed for this company to better understand the effects of rockslide generated tsunamis from akerneset and hegguraksla two and three dimensional site specific laboratory experiments are conducted to study the generation propagation and run up of the wave for several potential rockslide scenarios from akerneset furthermore the two models globouss and dpwaves are applied for numerical simulations of the generation propagation phase and a third model most is applied for numerical simulations of the near shore propagation and inundation of the wave in selected locations strong emphasis is put on verification validation and sensitivity of the numerical models the best match between the numerical simulations and the laboratory experiments is found for the larger scenarios with the linear dispersive solution for the propagation phase the corresponding calculated run up values are remarkably similar to the ones observed during the laboratory experiments during the risk assessment it was found that the rockslide tsunami hazard probability of impact is higher than accepted by the norwegian planning and building act this should at that time prevent any further development in all the exposed areas of the entire fjord system the act is today altered to open for specified further development in the various hazard zones the results of the tsunami analyses are applied in risk management in terms of hazard map production and land use planning two failure scenarios for each of the two unstable rock slopes are designed for the hazard zoning the larger and less probable scenarios 1 in 5000 years are applied for evacuation zones and routes while the smaller and more probable scenarios larger than 1 in 1000 years are applied for location and design of less critical facilities accepted in the inundation zone

fractionally modified flow in a deep ocean channel application to the vema channel the modification of the exchange flow in a deep southern hemisphere passage resembling the vema channel by frictionally induced secondary circulation is investigated numerically the hydrostatic primitive equation model is a two dimensional version of the sigma coordinate princeton ocean model the time dependent response of a stratified along channel flow forced by barotropic or baroclinic pressure gradients is examined near the bottom where the along channel flow is retarded there is cross channel ekman flux that is associated with downwelling on the eastern side and upwelling on the western side of the channel in the presence of stratification the cross channel flow rearranges the density structure which in turn acts on the along channel velocity via the thermal wind relation eventually the cross isobath ekman flux is shut down in the case of baroclinically driven flow of antarctic bottom water through the vema channel the model reproduces the observed shape of the deep temperature profiles and their cross channel asymmetry the model offers an explanation that is alternative or supplementary to inviscid multilayer hydraulic theory that was proposed in earlier studies it explains the extremely thick bottom boundary layers in the center and on the western slope of the channel the deep thermocline is spread out in the west and sharpened in the east and the coldest water is found on the eastern side of the deep trough the modified density field reduces the along channel flow near the bottom and focuses it into a narrow jet on the eastern side of the channel

the helmut geophysical anomaly a regional left lateral transtensional shear zone system connecting santos and campos basins southeastern brazil abstract in the ultradeep water of santos and campos basins eastwards from the area of present day pre salt exploration in southeastern brazil there is a nearly 1000 km long curved magnetic anomaly here named helmut on a magnetic map the anomaly orientation switches from ne sw in santos basin to nearly n s in campos mimicking the curved neoproterozoic shear zone pattern of the basement exposed onshore from the comparison between the position of such anomaly and gravity derived modeling and residual maps it is suggested that the magnetic anomaly also corresponds to a major gravimetric boundary separating different crustal domains this boundary is slightly oblique to the rift related normal fault trend in santos basin based on interpreted 3d seismic data the nne trending normal faults are dragged to the ne direction close to the magnetic anomaly in southern santos basin where an en echelon array of oblique magnetic anomalies occurs which resulted mainly from the left lateral component of an overall transtensional displacement field in regional 2d deep reflection seismic profiles the helmut anomaly is correlated to major eastward dipping down to the basin stepped faults sometimes arranged in a fan like fashion in santos basin and as a landward dipping normal fault zone in campos basin north of the e w araruama transfer zone in some areas the fault zone displaces the base salt reflector and cross cuts the entire stretched continental crust the analysis of potential field and seismic data suggests that the helmut anomaly may be interpreted as a crustal scale shear zone system active after salt deposition during the late aptian regionally the helmut anomaly connects two approximately n s trending branches of the south atlantic rift system the northern branch that runs from espirito santo basin northwards up to the camamu south of the reconcavo tucano jatoba aborted trough and the southern branch running southwards from santos basin through pelotas basin in brazil as far as the basins offshore uruguay and argentina basins southwards extensional faulting of the salt reflector along early nne rift related normal faults and dextral transtension on the nw trending fault zones are all consistent with a sinistral transtensive motion on the ne trending helmut anomaly during the late aptian

bottom current speed in the vema channel recorded by particle size of sediment fine fraction abstract the particle size distribution of the carbonate free silt fraction was determined in forty two core top samples from the east flank of the vema channel in order to allow comparison of the mean particle size with near bottom current speed based on nearby ctd and current meter observations the silt mean particle size fluctuates insignificantly between 1450 3950 m but coarsens markedly below 4000 m under antarctic source bottom currents the top of the zone of coarse sizes approximates the top of lower circumpolar water lcpw at 4000 m the steep gradient to coarsest sizes in the axis of the channel marks the transition to antarctic bottom water aabw the vertical profile of mean particle size on the east flank correlates in general respects with the vertical velocity gradient in the channel axis although the core sites on the east flank are as far as 200 miles from the current meter arrays nevertheless this relationship is used to infer that the non carbonate particle sizes deposited on the east flank of the channel may be an indication of bottom current speed and therefore the mean size is used to reconstruct profiles of mean current speed for three time slices 18 120 and 140 ka b p during glacial isotopic stages 2 and 6 the particle sizes deposited on the east flank of the channel are characterized by finer sizes at nearly all depths and the zone of coarse sizes corresponding to lcpw and aabw deepens during interglacial isotopic stage 5e the particlesize profile is very similar to the modern profile however lcpw and aabw appear to be deeper than at present the finer particle sizes deposited at nearly all depths during glacial periods indicates that the velocity of deep circulation in the atlantic was reduced in response to the ice ages deep circulation during isotopic stage 5e closely resembled modern circulation however aabw production rates may have been less that at present

a late pleistocene time series of bottom current speed in the vema channel abstract a coarsening of the mean particle size of the carbonate free silt fraction from sea floor samples below 4000 m in the vema channel has been used to separate high velocity antarctic bottom water aabw from the overlying slower north atlantic deep water nadw a time series of fluctuations in bottom current speed within the modern aabw nadw transition zone was examined by determining the particle size distribution of sediments from eight gravity cores with a high resolution stratigraphy for the past 250 kyrs the bottom current paleospeed was inferred from a correlation of particle size in seafloor samples with mean current speed from nearby current meters the mean bottom current speed at depths comparable to modern aabw was highest 7 10 cm s during interglacial to glacial transitions corresponding to the oxygen isotopic stage 6 7 and 4 5 boundaries and at present the mean bottom current speed at depths comparable to modern nadw was nearly uniform for most of the past 250 kyrs except during glacial oxygen isotopic stage 2 when the speed dropped to 2 cm s or one half of the present speed the application of the calibrated particle size method to examine bottom current paleospeed allows testing of paleoceanographic models which rely on assumptions or inferences of changes in bottom water production rate during the late pleistocene paleoclimatic fluctuations

seismic patterns of a muddy contourite fan vema channel south brazilian basin and a sandy distal turbidite deep sea fan cap ferret system bay of biscay a comparison abstract the aim of this paper is to discriminate the depositional facies geometries and mechanisms of deposition of contouritic fans from those of turbidite distal fans with a view to provide better resolution of reservoir prediction two examples are analysed the vema contouritic drift in the south brazilian basin and the cap ferret turbiditic fan in the bay of biscaye the vema contourite fan is a neogene mud rich accumulation 200 400 m thick fed by antarctic bottom water bottom currents and located downstream of the rio grande rise it forms one single mound fan shaped body in between two major channels and where the main part of the deep circulation is funnelled into as a result of the morphological and hydrological background the comourite drift progrades mostly downstream the accumulation was built as several depositional units channel levee systems bounded by widespread discontinuities showing erosional patterns this resulted from episodes of strong and or unstable current activity producing the discontinuities alternating with periods of relatively weak and stable currents and major deposition the pliocene quaternary cap ferret distal deep sea fan is a thick 500 m sand rich turbiditic accumulation fed directly by an uplifting mountain range the accumulation is developed downstream of a main turbiditic feeder channel and the volume of sediment involved is much higher than for the vema contourite fan it shows a complex network of shallow channels and low relief levees which merge downstream into thin sandy sheet like deposits several depositional units are stacked vertically each unit is built by the lateral migration of a channel levee system the stacking pattern of the successive units is prograding towards the basin the presence of major discontinuities cutting throughout a whole accumulation and the fairly irregular geometry of the channel levee deposits absence of any obvious migrating trend appear to be the most distinctive features of a contourite fan on the other hand the lateral migration of the channel level geometries and the presence of erosional surfaces of limited extent and restricted to the channels are the main diagnostic features of a distal turbidite fan otherwise the seismo facies are fairly similar in both sedimentary bodies

advective transport of clay minerals in the region of the rio grande rise abstract clay mineral analyses talc normalized were performed on a suite of 40 giant gravity core core tops from the east flank of the vema channel that span the depth interval 1430 4565 m in addition three time slice intervals last glacial maximum 18 000 yrs b p last interglacial 120 000 yrs b p and penultimate glacial maximum 140 000 yrs b p were examined in 25 of these cores the clay mineral chlorite can be used to identify southern source waters aabw in the vema channel the mineralogical identification of the upper limit of aabw occurs at approximately 4000 4100 m in agreement with estimates based upon displaced antarctic diatoms and modern oceanographic data time slice reconstructions of chlorite abundance suggest aabw flow intensity was slightly reduced during glacial relative to interglacial intervals the clay mineral kaolinite reaches maximum concentration at mid depth approximately 3500 m on the rio grande rise but does not appear to be advectively transported to the rise by southward flowing nadw rather kaolinite rich sediments appear to be transported eastward from the sao paulo plateau to the rio grande rise along isopycnals this process is estimated to contribute approximately 13 of the fine grained lithogenic sediments reaching the rio grande rise at approximately 3500 m

inorganic origin of carbon dioxide during low temperature thermal recovery of bitumen chemical and isotopic evidence abstract carbon dioxide produced at low temperatures is the dominant gaseous species evolved during steam assisted thermal recovery of bitumen at the tucker lake pilot cold lake alberta two possible sources for the produced co2 are considered pyrolysis of bitumen and dissolution of carbonate minerals data from natural systems and experiments by other authors suggest that clay carbonate reactions are the dominant source of co2 carbon isotope and chemical analyses of produced gas and water reveal that co2 and hco3 become more enriched in 13c and concentrations of ca2 and hco3 rise during production temperatures in the producing zone are estimated to be between 70 and 220 c using the na k and chalcedony chemical geothermometers and show that production of 13c enriched co2 and hco3 occurs as temperature decreases during production this extends the temperature range at which co2 is known to be produced from carbonates to lower levels than previously noted the 13c of calcite in the reservoir is enriched in 13c giving values as high as 17 4 when the calcite isotopic compositions are combined with temperature data and temperature fractionation equations for calcite co2 and hco3 they show calcite to be the only viable source of co2 bitumen pyrolysis may contribute small amounts of co2 probably by decarboxylation early in the production cycle but cannot contribute significant volumes the recognition of production of co2 by reactive calcite destruction at temperatures between 70 and 220 c suggests that this process may be responsible for the production of large quantities of co2 in natural systems particularly in lithofeldspathic sands and shales with high carbonate content and abundant clays organic acids have been suggested to be the source of co2 in diagenetic fluids but the results presented here suggest that this hypothesis requires more complete investigation

detailed dem analysis of a rockslide scar to characterize the basal sliding surface of active rockslides 1 the basal sliding surfaces in large rockslides are often composed of several surfaces and possess a complex geometry the exact morphology and location in three dimensions of the sliding surface remains generally unknown in spite of extensive field and subsurface investigations such as those at the aknes rockslide western norway this knowledge is crucial for volume estimations failure mechanisms and numerical slope stability modeling this paper focuses on the geomorphologic characterization of the basal sliding surface of a postglacial rockslide scar in the vicinity of aknes this scar displays a stepped basal sliding surface formed by dip slopes of the gneiss foliation linked together by steeply dipping fractures a detailed characterization of the rockslide scar by means of high resolution digital elevation models permits statistical parameters of dip angle spacing persistence and roughness of foliation surfaces and step fractures to be obtained the characteristics are used for stochastic simulations of stepped basal sliding surfaces at the aknes rockslide these findings are compared with previous models based on geophysical investigations this study discusses the investigation of rockslide scars and rock outcrops for a better understanding of potential rockslides this work identifies possible basal sliding surface locations which is a valuable input for volume estimates design and location of monitoring instrumentation and numerical slope stability modeling

post miocene fluctuations of antarctic bottom water paleospeed in the southwest atlantic ocean abstract a gap in the falkland escarpment serves as the primary channel through which antarctic bottom water aabw flows into the argentine basin from the georgia basin the particle size distributions of the biogenic free silt fraction in four cores near the falkland gap and the hiatus frequency at water depths greater than 4000 m throughout the southern ocean are used to infer post miocene aabw paleospeed analysis of aabw paleocirculation indicates episodes of increased bottom current speeds at 5 3 4 5 4 0 3 5 3 3 3 1 2 5 2 3 2 0 1 5 and 1 0 ma these fluctuations in inferred paleospeed are compared to both northern and southern hemisphere paleoceanographic and paleoclimatic events in order to examine the response of bottom water circulation to post miocene climates during the early gilbert middle matuyama 5 3 1 5 ma southern hemisphere climatic events provided the primary forcing mechanisms on aabw activity the model invoked involves increased salinity and overturn of weddell shelf water in response to increased sea ice formation during cold episodes from the late matuyama after 1 5 ma to present fluctuations in warm deep water resulting from northern hemisphere climatic evolution may have been the predominant factor influencing aabw paleospeed these episodes of increased bottom current activity may correlate to periods of mudwave migration in the argentine basin during the past 5 ma the mudwave fields consist of silty siliceous clays deposited in response to enhanced sediment supply and fast moving currents in the interior basin we speculate that the periods of enhanced bottom water activity may have been responsible for major episodes of mudwave growth that began since the late oligocene and have persisted into the holocene

evolution of pliocene to recent abyssal sediment waves on bounty channel levees new zealand abstract levees bordering bounty channel 900 km east of new zealand accommodate a 400 m thick sequence maximum of sediment waves that have formed since pliocene times these bedforms with amplitudes of 2 17 m and wavelengths of 0 6 6 km occur in 4100 4900 m of water and were formed by turbidity currents as indicated by their restriction to levee backslopes the frequent occurrence of turbidites in cores and the preferential but not exclusive development of waves on the left bank levee in accord with the southern hemisphere coriolis deflection the wave field was instigated in the late pliocene when glacially lowered sea level allowed rivers draining the southern alps of south island to discharge directly into bounty channel and its attendant canyons the field grew vertically through the coalescence of small waves into larger bedforms that continually migrated across and up levee backslopes at an average rate of 5 6m 100 yrs wave growth decreased into the late pleistocene probably in response to progressive containment of turbidity currents as the relief of bounty channel increased to 200 m or more the glacial periods of wave growth were interrupted by interglacial interludes of quiescence when the field was draped mainly by pelagic calcareous ooze

hydraulie control and flow separation in a multi layered fluid with applications to the vema channel abstract observations from a recent field experiment in the vema channel are briefly described these show a remarkable change in the configuration of isopycnal surfaces within the channel and the development of thick nearly homogeneous regions near the bottom which are capped by sharp vertical gradients contrary to previous speculation that these bottom boundary layer result from enhanced vertical mixing a dynamical mechanism is explored this involves the hydraulic adjustment of an inertial semi geostrophic flow to the channel geometry first an active two layer flow in a rectangular geometry is studied to show that internal flow separation can occur when the flow is accelerated sufficiently by a narrowing channel almost always this separation accompanies hydraulic control the slowest upstream moving kelvin wave is stopped and upstream and downstream states are not symmetric with respect to the channel width an active three layer flow with a variable bottom profile is then presented as a more

mantle derived carbon in hercynian granites stable isotopes signatures and c he associations in the thermomineral waters n portugal article i nfo na hco3 co2 rich thermomineral waters issue in the n of portugal within the galicia tras os montes region linked to a major nne trending fault the so called penacova regua verin megalineament along this tectonic structure different occurrences of co2 rich thermomineral waters are found chaves hot waters 67 c and also several cold 16 1 c co2 rich waters the 2 h and 18 o values of the thermomineral waters are similar to those of the local meteoric waters the chemical composition of both hot and cold mineral waters suggests that water rock reactions are mainly controlled by the amount of dissolved co2 g rather than by the water temperature stable carbon isotope data indicate an external co2 inorganic origin for the gas 13 cco2 values ranging between 7 2 and 5 1 are consistent with a two component

structural analysis of turtle mountain alberta using digital elevation model toward a progressive failure abstract in 1903 the eastern slope of turtle mountain alberta was affected by a 30 m m 3 rockslide named frank slide that resulted in more than 70 casualties assuming that the main discontinuity sets including bedding control part of the slope morphology the structural features of turtle mountain were investigated using a digital elevation model dem using new landscape analysis techniques we have identified three main joint and fault sets these results are in agreement with those sets identified through field observations landscape analysis techniques using a dem confirm and refine the most recent geology model of the frank slide the rockslide was initiated along bedding and a fault at the base of the slope and propagated up slope by a regressive process following a surface composed of pre existing discontinuities the dem analysis also permits the identification of important geological structures along the 1903 slide scar based on the so called sloping local base level slbl an estimation was made of the present unstable volumes in the main scar delimited by the cracks and around the south area of the scar south peak the slbl is a method permitting a geometric interpretation of the failure surface based on a dem finally we propose a failure mechanism permitting the progressive failure of the rock mass that considers gentle dipping wedges 30 the prisms or wedges defined by two discontinuity sets permit the creation of a failure surface by progressive failure such structures are more commonly observed in recent rockslides this method is efficient and is recommended as a preliminary analysis prior to field investigation

early cretaceous fracture zones in the bay of bengal and their tectonic implications constraints from multi channel seismic reflection and potential field data abstract due to the lack of clearly discernible magnetic anomaly identifications and fracture zones in the bay of bengal bob the early cretaceous plate reconstruction history of eastern gondwanaland remains an unresolved issue with regard to the separation of the east coast of india from the conjugate enderby basin of antarctica based on the correlation of oceanic basement information obtained from a vast amount of deep reflection seismic data we identified 16 nw se trending fracture zones fz1 fz16 in the bob region the trends of these fracture zones at the ecmi indicate two distinctly different sets one set in the direction n25 w to n35 w in the southern part fz1 fz7 and the other set in n50 w fz8 fz15 direction along the northern part these two sets of fracture zones further support the earlier inferences about the segmented nature of the ecmi into southern sheared oblique rifted margin and the northern normal rifted margin while the southern part of the ecmi had formed under slow asymmetric spreading and mixed transform setting with its conjugate western enderby basin the northern part of the ecmi formed after the breakup of the elan bank from india at m2 considering this scenario we infer the presence of late mesozoic younger to m4 anomalies along the ecmi and the subdued nature of magnetic anomalies in the western bob can be explained by the obliquity of fracture zones with respect to the coast as observed in many marginal smooth zones of the world oceans the disposition of the 85 e ridge with respect to the pre evolved bob crust and early cretaceous volcanic episodes in the region together indicate an emplacement of the ridge from 105 ma onwards as a result of a hotspot source related to the kerguelen super plume during its intense eruption activity

investigations of relative plate motions in the south atlantic using seasat altimeter data fracture zones in the world s oceans appear clearly in the seasat altimeter geoid data at wavelengths of about 100 km and less in the north and south atlantic these signatures are stable in form and amplitude from the ridge crest to crust tens of millions of years old and can be mapped across nearly the width of the basin the signatures diminish in amplitude markedly on crust older than 70 to 80 m y b p apparently when thickly covered by sediments because fracture zone trajectories closely approximate plate motion flow lines they may be used to infer the plate kinematic history of the ocean basin in this paper i describe a new method for estimating the relative poles of opening describing the history of motion between two plates by using fracture zone trajectories the method is an iterative inversion whereby the trajectories of synthetic flow lines are linearized with respect to the pole parameters when applied to the seasat altimeter track data a waveform inversion based upon this method is possible in which the altimeter data are modeled using a synthetic geoid fracture zone signal this waveform inversion is applied to 17 prominent fracture zones in the central and south atlantic to estimate the poles of opening between the south american and african plates altogether 1022 seasat fracture zone crossings are used for each of these a waveform comparison is made the new method is found to be robust and converges to a stable set of pole solutions even if the initial flow lines are small circles about a single pole that poorly approximates the observed trajectories the solution poles document a cenozoic change in plate motion near anomaly 13 time 36 m y b p similar to that in the north atlantic at anomaly 1 3 21 time 36 50 m y b p

suspended particulate matter transport through the vema channel richardson m j biscaye p e gardner w d and hogg n g 1987 suspended particulate matter transport through the vema channel mar geol 77 171 184 sixteen month time series measurements of water velocity and light scattering were coupled with hydrographic and suspended particulate matter sections to determine the flux and the variability in flux of suspended particulate matter through the vema channel the northward flux of spm through the vema channel ranged from 3 to 10 5 104 g s 1 with a mean of 6 5 104 g s 1 the largest fluxes were measured in the deepest and eastern portions of the channel with maximum fluxes of suspended particulate matter at specific sites being roughly two to four times the mean flux some of the suspended particulate matter in the channel may be eroded from the channel itself by the swift currents or eddy like features however the known manganese encrustation and hard floor of the channel suggest that the deep channel floor is not a likely source of sediment a primary source of the suspended particulate matter in the channel may be the sediment drifts in the argentine basin with their associated high standing crops of resuspended particulate matter this resuspended material would then be transported by the antarctic bottom water into and through the vema channel into the brazil basin the northward flux of suspended particulate matter through the vema channel is presently a significant but not dominant influence on sedimentation in the brazil basin

the tjellefonna fault system of western norway linking late caledonian extension post caledonian normal faulting and tertiary rock column uplift with the landslide generated tsunami event of 1756 abstract on february 22 1756 approximately 15 7 million cubic meters of bedrock were catastrophically released as a giant rockslide into the langfjorden subsequently three 40 meter high tsunami waves overwhelmed the village of tjelle and several other local communities inherited structures had isolated a compartment in the hanging wall damage zone of the fjord dwelling tjellefonna fault because the region is seismically active in oblique normal mode and in accordance with scant historical sources we speculate that an earthquake on a nearby fault may have caused the already weakened tjelle hillside to fail from interpretation of structural geomorphic and thermo chronological data we suggest that today s escarpment topography of more og trondelag is controlled to a first order by post rift reactivation of faults parallel to the mesozoic passive margin in turn a number of these faults reactivated late caledonian or early post caledonian fabrics normal sense reactivation of inherited structures along much of coastal norway suggests that a structural link exists between the processes that destroy today s mountains and those that created them the paleozoic more trondelag fault complex was reactivated as a normal fault during the mesozoic and probably throughout the cenozoic until the present day its ne sw trending strands crop out between the coast and the base of a c 1 7 km high nw facing topographic great escarpment well preserved kinematic indicators and multiple generations of fault products are exposed along the tjellefonna fault a well defined structural and topographic lineament parallel to both the langfjorden and the great escarpment the slope instability that was formerly present at tjelle and additional instabilities currently present throughout the region may be viewed as the direct product of past and ongoing development of tectonic topography in more og trondelag county in the langfjorden region in particular structural geometry suggests additional unreleased rock compartments may be isolated and under normal fault control although post glacial rebound and topographically derived horizontal spreading stresses might in part help drive present day oblique normal seismicity the normal fault controlled escarpments of norway were at least partly erected in pre glacial times cretaceous to early tertiary post rift subsidence was interrupted by normal faulting at the innermost portion of the passive margin imposing a strong tectonic empreinte on the developing landscape

low temperature diagenetic metamorphic and magmatic contributions of external co2 gas to a shallow ground water system abstract a small 2 low temperature 2 gas overpressured gently dipping paleozoic carbonate aquifer rests on precambrian granite in a narrow canyon along the eastern edge of the rocky mountain front range colorado the carbonate aquifer is bounded on three sides by granite and in the down dip direction by the front range fault the fault in a major continental intraplate zone of weakness along which magmatic fluids and gases could migrate to the surface and near surface from great depths the fault has also overthrusted slices of carbonate and clastic rocks several kilometres below the granitic basement stable isotopic 2 h and 18 o and discharge temperature data suggests that carbonate aquifer ground waters are of meteoric origin and have not circulated to depths greater than the base of the carbonate aquifer 650 m elevated co 2 and the 13 c of hco 3 in the carbonate aquifer suggest an external crustal source of co 2 gas 3 he 4 he o 2 n 2 and ar n 2 gas ratios indicate gas contributions from both magmatic and atmospheric sources atmosphere contributions account for about 25 of the exsolving gas whereas magmatic co 2 accounts for 7 to 14 possible external co 2 sources which are consistent with the mean hco 3 13 c 2 4 pdb are clay carbonate mineral diagenesis or low temperature metamorphism of siliceous carbonate rocks that have been overthrust by 3 to 6 km of granite diagenetic or metamorphic co 2 mixed with some magmatic gas appears to have migrated from the source rock area upward along the ute pass thrust fault until it encountered the shallow carbonate aquifer ground water system where it was further diluted with atmospheric gas

why did the 1756 tjellefonna rockslide occur a back analysis of the largest historic rockslide in norway abstract on 22 february 1756 the largest historically recorded rockslide in norway took place at tjelle in the langfjord western norway the rockslide created three displacement waves of up to 50 m in height that caused 32 casualties and destroyed most houses and boats along the shores of the langfjord the trigger and contributing factors leading to the tjellefonna rockslide are largely unknown and even seismic triggering has previously been suggested this study provides a thorough back analysis of the tjellefonna rockslide using detailed geomorphological engineering geological and tectonic field mapping in combination with topographic reconstructions bathymetry analysis volume estimations and numerical slope stability analysis the back scarp and eastern flank of the tjellefonna scar form several tens of meter high rock walls while the basal failure surface and other parts of the scar are covered by rock avalanche debris that extend from the back scarp down to the bottom of the langfjord the rockslide occurred in granodioritic gneisses with variably developed metamorphic foliation that is folded and strike parallel to the fjord two prominent fault zones are present in close proximity to the tjellefonna scar one is steeply se dipping tjelle fault while the other one is sub horizontal to shallow se dipping ritlehamran fault both fault zones are linked to the more trondelag fault complex with one of its branches forming the langfjord lineament and probably also the faults at tjellefonna additionally there are four persistent joint sets that together with the metamorphic foliation and the tjelle fault define the back scarp of the rockslide and give a fracturing of the rock mass corresponding to a geological strength index gsi of 45 55 the gsi decreases significantly to 10 20 in the fault zones which form distinct weakness zones in the rock slope volume estimates based on a reconstruction of the ante rockslide topography range from 9 3 to 10 4 million m 3 which is lower than previous volume estimates 12 15 million m 3 large portions of the failed rock mass remained on land and only approximately 3 9 million m 3 entered the fjord the observed discontinuities in the rock mass at tjellefonna do not allow for a simple kinematic failure mechanism due to the lack of moderately se dipping structures the basal failure surface was most likely not composed of a single structure but of a complex interplay of fault zones metamorphic foliation joints and broken rock bridges numerical slope stability modelling highlights that weak fault zones are essential for the development of the failure surface over a long time this progressive failure was likely aided by low to medium magnitude earthquakes that are frequent in the region numerical slope stability modelling and historical accounts suggest however that heavy long lasting rainfall was the triggering factor for the 1756 tjellefonna rockslide rather than an earthquake

the evolution of the rio grande rise in the southwest atlantic ocean abstract the rio grande rise a major aseismic rise in the western south atlantic ocean is composed of two portions with distinct morphologies and geological histories the western portion of the rise wrgr is a large elliptical bulge with its crest at a mean depth of about 2000 m numerous guyots protrude from its main platform the crust underlying this portion of the rise is older than 80 m y b p and was formed at a spreading center probably situated close to the sea level a widespread volcanic event affected this region during the eocene and generated several volcanic islands located at the center of the present wrgr this eocene volcanism is responsible for the unusual high elevation of this region and for the generation of the observed guyots much less is known about the eastern portion of the rio grande rise ergr it has a north south trend parallel to the present south atlantic spreading center is bounded by fracture zones is in a conjugate position to part of the walvis ridge in the eastern south atlantic and may represent an abandoned spreading center

reservoir processes in steam assisted recovery of bitumen leming pilot cold lake alberta canada compositions mixing and sources of co produced waters abstract chemical and isotopic analyses of aqueous species in co produced waters from cyclic steam bitumen recovery wells at the leming pilot cold lake alberta canada show the dominant control of co produced water chemistry to be mixing of waters of natural origin with injected water and condensed steam co produced waters from early cycles are characterized by highly transient compositions and temperature relative to later cycles which show more subdued trends with time production of injected water and condensed steam can be detected by freshening of co produced water and interaction with a vapour phase can be detected by a decrease in 13c of dissolved carbonate with no concomitant decrease in the salinity of co produced waters mixing diagrams with cl as a conservative component have been constructed and are to show progressive mixing of relatively fresh injected water and condensed steam with more saline waters of natural origin mixing considerations imply the existence of at least two water of natural origin one is produced typically in early cycles and is characterized by relatively high hco3 concentrations molar cl hco3 ratios 50 and probably originates in water saturated sandstones which occur adjacent to the bitumen reservoirs

geoid roughness and long wavelength segmentation of the south atlantic spreading ridge the configuration of accreting plate boundaries tends to reflect the geometry of the original continental break up yet there are also many indications that the detailed pattern of spreading ridge and transform fault segments may be an inherent part of the spreading process itself1 2 the mid atlantic ridge for example is segmented with a typical spacing of 40 km between transform faults3 4 here we use the short wavelength 25 110 km part of the seasat altimetry data set to derive a map of the geoid rough ness in the south atlantic between 1 n and 39 s this map reflects changes in the local amplitude envelope of the geoid signal primarily associated with topography zones of high roughness correlate with major fracture zones aseismic ridges and the mid atlantic ridge the most remarkable feature is that the roughness is not uniform along the ridge but displays quasi periodic variations with a wavelength of 400 km a segmentation an order of magnitude larger than described so far which has persisted for at least 60 myr this segmentation may reflect either fabric generated at the ridge by normal plate tectonic processes1 5 or small scale convective instabilities rising from 80 km deep region of the upper mantle3 6 7

new insights of the tectonic and sedimentary evolution of the rio grande rise south atlantic ocean abstract oceanic plateaus such as the rio grande rise rgr comprise crucial pieces of information about the opening of the south atlantic ocean and the evolution of associated lithospheric plate margins a detailed seismostratigraphic assessment of the volcano sedimentary package of the rgr was conducted in its western portion based on correlations between seismic data and dsdp site 516f the approximately 330 km long seismic transect is characterized by a complex array of normal faults related to extensional tectonics from late cretaceous to the miocene and probably into the present day along the cruzeiro do sul rift the bathymetric and seismic data reveal a the presence of deep faults that rise from the basement to the sea floor b the occurrence of several seamounts with tops at a water depth below 1000 m and c prominent graben structures that represent unidentified volcanic intrusions indicative of the reactivation of lower miocene faults by younger extensional events based on integration of older data with the results presented here we propose a five stage tectono sedimentary model for the western portion of the rgr 1 the first basaltic flow began to form the rio grande rise in the coniacian santonian 2 extensional movements caused rifting during the uplift of the large volcanic structures 3 volcanic islands emerged above sea level increasing the deposition of volcanic breccia and ash layers 4 after the volcanism ceased thermal subsidence took place over the entire rise with intense erosion and sedimentation and 5 the uppermost sedimentary layers were deposited in pelagic conditions and offset by sub vertical normal faults

a morphologic characterisation of the 1963 vajont slide italy using long range terrestrial photogrammetry abstract the 1963 vajont slide in northeast italy is an important engineering and geological event although the landslide has been extensively studied new insights can be derived by applying modern techniques such as remote sensing and numerical modelling this paper presents the first digital terrestrial photogrammetric analyses of the failure scar landslide deposits and the area surrounding the failure with a focus on the scar we processed photogrammetric models to produce discontinuity stereonets residual maps and profiles and slope and aspect maps all of which provide information on the failure scar morphology our analyses enabled the creation of a preliminary semi quantitative morphologic classification of the vajont failure scar based on the large scale tectonic folds and step paths that define it the analyses and morphologic classification have implications for the kinematics dynamics and mechanism of the slide metre and decametre scale features affected the initiation direction and displacement rate of sliding the most complexly folded and stepped areas occur close to the intersection of orthogonal synclinal features related to the dinaric and neoalpine deformation events our analyses also highlight for the first time the evolution of the vajont failure scar from 1963 to the present

an oceanwide view of palaeogene plate tectonic events abstract the tectonic events taking place during the palaeogene are discussed ocean by ocean three predominant periods of tectonic changes are determined separating periods of continuous stable seafloor spreading these periods of change occur at the palaeocene eocene boundary 56 53 m y at the eocene oligocene boundary 42 35 m y and during the early middle eocene 35 30 m y during the course of writing this review it became very evident how much marine surveying and data analysis took place during the early 1970s this decade showed great leaps forward in our understanding of seafloor anatomy and tectonics

paleo oceanography global ocean evolution paleoceanography one of the youngest branches of earth sciences is concerned with the development of oceanic circulation through geologic time this is a multifaceted and integrated endeavor since none of the subdisciplines is easily separated from the others the field is holistic in character and includes the history and effects of bottom intermediate and surface circulation patterns planktonic and benthonic biogeographic development and rates of organic evolution the history of biogenic productivity and dissolution and their effect on sediment distribution and the consequences of sea level change paleoceanography was largely born of the deep sea drilling project dsdp and continues to be nourished by it because problems are of global scope the appetite for new sediment core material is large and is being supplied by numerous expeditions of dsdp this article is a brief overview of a number of advances that have occurred in paleoceanography and related fields during the period from 1979 to 1982 because of page limitations all publications cannot be cited which is not meant to indicate any lack of importance

co2 production in tar sand reservoirs under in situ steam temperatures reactive calcite dissolution abstract recovery of highly viscous oil from some of the deeper oil sand deposits of northern alberta canada is made possible through injection of heat by steam or hot water flooding of the reservoirs the rise in temperature lowers the viscosity of the bitumen allowing it to be produced the increase in temperature accelerates the reactions between the matrix and pore minerals of the formation and can produce reaction products which can significantly alter the permeability of the reservoir if carbonate minerals are present in the reservoir inorganic co 2 may also be a reaction product the grand rapids reservoir consists of relatively clean quartz sand containing 7 wt kaolinite 1 wt calcite and a trace of smectite core floods of this sand by a neutral nacl brine at 265 c 8 2 mpa overburden pressure 6 0 mpa fluid pressure and a flow velocity of 0 4 pore volumes per hour were used to determine the potential for hydrothermal reactions between clays and carbonate minerals in a natural reservoir sand reaction progress was followed by continuous sampling of the production fluids the produced water was analyzed and the phase chemistry was calculated back to the run conditions using the computer code solmneqf mass balance considerations on produced total inorganic carbon tic show that calcite broke down very quickly the maximum in co 2 production occurring after only one pore volume of fluid had passed through the core the ca released from the breakdown of calcite was incorporated in the formation of smectite as was shown by post run clay mineral analysis by the following unbalanced chemical reaction calcite kaolinite h 4 si0 4 ca smectite h 2 0 co 2 silica was supplied by the dissolution of quartz silica concentrations analyzed in the production fluid were depressed from those predicted by previously published quartz rate equations because of the rapid rate of smectite synthesis these observations were used to formulate the following model for the passage of the first pore volume of nacl brine through the core initially calcite is present throughout the core as the brine enters the inlet of the core it equilibrates with calcite the brine remains in equilibrium with calcite throughout the core as quartz and kaolinite react to form smectite this model was tested with the computer code path ubc using co 2 production as a measure of the progress variable a best fit was achieved to the produced fluid chemistry by varying relative dissolution rates of kaolinite and quatz and varying the suppression of precipitation of certain minerals

thermal generation of carbon dioxide and organic acids from different source rocks carbon dioxide and organic acids are claimed to play an important role in sandstone diagenesis in the present work hydrous pyrolysis was used for a qualitative comparison of the relative potential of different source rocks to generate organic acids and carbon dioxide in addition the carbon isotopic composition of the generated carbon dioxide was determined experiments with three immature source rocks are described a miocene brown coal from germany a coal from the middle jurassic ness formation in the northern north sea and a rich marine type ii source from the late jurassic kimmeridge clay formation onshore u k both coal samples are typically humic a stepwise heating program from 150 to 365 c was used closed pyrex tubes containing immature coal rmm 0 37 were heated in order to measure vitrinite reflectance evolution the experimental results were related to vitrinite reflectance as a maturity reference parameter and to a kinetic model using kinetic parameters for carbon dioxide generation burnham a k and sweeney j j 1989 geochim cosmochim acta53 2649 2657 differences in the yiels and carbon isotopic composition were obtained between the marine type ii source rock and the coals organic acid generation converted between 1 and 3 of the organic carbon carbon dioxide was the major oxygen containing component with molar yields 5 10 times that of organic acids the experimental yields of organic acids and carbon dioxide were compared to a first order kinetic model for carbon dioxide generation and a reasonable correspondence in the transformation ratio curves was observed

the wide angle seismic image of a complex rifted margin offshore north namibia implications for the tectonics of continental breakup highlights up to 33 km thick dominantly gabbroic crust beneath walvis ridge massive gabbro addition with subjacent cumulates to the cob south of walvis ridge slow upper mantle at 35 km depth beneath etendeka plateau 4 6 km thick oceanic crust in the angola basin north of florianopolis transform velocity models suggest a dominant tectonic control on the location of magmatism abstract voluminous magmatism during the south atlantic opening has been considered as a classical example for plume related continental breakup we present a study of the crustal structure around walvis ridge near the intersection with the african margin two wide angle seismic profiles were acquired one is oriented nnw sse following the continent ocean transition and crossing walvis ridge a second amphibious profile runs nw se from the angola basin into continental namibia at the continent ocean boundary cob the mafic crust beneath walvis ridge is up to 33 km thick with a pronounced high velocity lower crustal body towards the south there is a smooth transition to 20 25 km thick crust underlying the cob in the walvis basin with a similar velocity structure indicating a gabbroic lower crust with associated cumulates at the base the northern boundary of walvis ridge towards the angola basin shows a sudden change to oceanic crust only 4 6 km thick coincident with the projection of the florianopolis fracture zone one of the most prominent tectonic features of the south atlantic ocean basin in the amphibious profile the cob is defined by a sharp transition from oceanic to rifted continental crust with a magmatic overprint landward of the intersection of walvis ridge with the namibian margin the continental crust beneath the congo craton is 40 km thick shoaling to 35 km further se the velocity models show that massive high velocity gabbroic intrusives are restricted to a narrow zone directly underneath walvis ridge and the cob in the south this distribution of rift related magmatism is not easily reconciled with models of continental breakup following the establishment of a large axially symmetric plume in the earth s mantle rift related lithospheric stretching and associated transform faulting play an overriding role in locating magmatism dividing the margin in a magma dominated southern and an essentially amagmatic northern segment

53mn 53cr ages of kaidun carbonates 53mn 53cr ages of kaidun carbonates abstract we report the 53mn 53cr systematics of three dolomite grains from two different ci1 clasts contained within the kaidun meteorite breccia three internal isochrones result in initial 53mn 55mn ratios of 4 2 0 4 10 6 4 6 1 3 10 6 and 5 2 1 1 10 6 these initial values are consistent with those measured for dolomite in the orgueil ci1 chondrite hoppe et al 2007 petitat et al 2009 but significantly lower than the initial ratio determined by hutcheon et al 1999 from a combination of different carbonate types within various lithologies of the kaidun meteorite we construct an accretion scenario for the kaidun breccia by comparing the mineralogy and formation time scales of carbonates in the kaidun ci1 lithologies to the analogous ones of the ci1 chondrite orgueil in orgueil dolomite precipitation precedes the formation of the first bruennerite grains by a few million years hoppe et al 2007 petitat et al 2009 as the ci1 clasts in kaidun lack breunnerite grains and considering that aqueous alteration occurred prior to reaccretion of the various clasts onto the kaidun parent body e g macpherson et al 2009 we hypothesize that after rapid accretion and early aqueous alteration occurring within the first approximately 4 myr after solar system formation impact disruption of several asteroids and their reassembly into the kaidun parent asteroid was complete within an additional approximately 2 myr this confirms that aqueous alteration impact and reaccretion of material in the asteroid belt were early processes that began contemporaneously with chondrule formation

the origin and formation of co2 gas pools in the coal seam of the yaojie coalfield in china abstract high concentrations of co 2 have been observed in the no 2 coal seam in the yaojie coalfield a number of instantaneous co 2 outbursts occurred during coal mining the co 2 concentration range in the eastern coalfield is 18 79 to 96 6 the 13 c co 2 values are mainly in the range of 5 0 to 1 0 pdb suggesting an inorganic origin of co 2 the 3 he 4 he ratios are 0 6 25 9 10 8 and the r ra is 0 0042 0 185 which is a characteristic of crust derived co 2 gas the dynamic thermal metamorphism of the f19 ductile brittle shear zone is believed to result in the release of co 2 from basement marble formations which show an inorganic source of co 2 in the yaojie coalfield the regional geological evolution and multi periodical f19 fault movement control the formation migration and accumulation of the co 2 in addition to the development of co 2 gas pools in the yaojie coalfield the f19 fault played multiple roles in the generation transport and sequestration of gas during the co 2 formation the displacement of ch 4 carbonate generation and pore structure transformation of coal due to a series of physical and chemical effects occurred after co 2 flux into the coal seams

sampling statistic limitations on benthic foraminifera chemical and isotopic data abstract analyses of benthic foraminiferal isotopic and chemical properties are typically done on a small number of individuals often 5 10 because benthic sediment mixing produces a mix of individuals whose properties were determined at times encompassing several thousand years a sampling of several individuals does not adequately represent the average mixture a quantitative statistical analysis shows that this effect places a fundamental limit on measurement precision in cores especially where rapid environmental changes occur over short vertical distances the fundamental parameters defining this limit are the rate of change of the property per unit distance and the effective mixing depth in cores found in the vema channel rio grande rise region where sedimentation rates are about 1 cm ka 1 and mixing depths are about 3 cm a single sampling of six individuals can produce a result that has an expected one sigma standard deviation of 6 25 of the observed range precision can be improved by using more individuals or running more replicate analyses but the result only improves as the square root of the number of individuals or replicates this effect is illustrated by cd ca and isotopic data from low 0 7 cm ka 1 and moderate 1 5 cm ka 1 sedimentation rate cores although precision is compromised the most in low sedimentation rate cores this effect contributes to imprecision in high sedimentation rate cores as well

bottom current controlled sedimentation a synthesis of the contourite problem abstract an overview of the main items concerning deep bottom current controlled deposits is presented these include the definition of contourites their processes of deposition and facies characteristics contourite drift types and seismic patterns the interplay of turbidity and bottom current processes and the correlation between bottom current processes and global changes in climate sea level from this discussion several of the more significant problems are highlighted which we believe should be priority targets for future research 1 identification of contourites especially in ancient series where they are interbedded with turbidites and other facies 2 refinement of the numerous parameters used as tracers of palaeocirculation patterns 3 understanding the interaction between the different types of bottom currents and also between bottom current and other deep water processes 4 distinction in the sedimentary record between the effects of short time scale bottom current variations due to regional causes like benthic storms and geological scale current fluctuations related to climatic or astronomic control 5 understanding the control of glacial interglacial climatic cycles on the nature and rate of contourite deposition