behavior of rare earth elements in a paleoweathering profile on granodiorite in the front range colorado usa abstract a paleoweathering profile on the boulder granodiorite in northern colorado provides an opportunity to trace the behavior of rees from parent rock through a weathering profile into unconformably overlying permian sediments with progressive upward weathering of the granodiorite na2o cao sio2 ta hf co th cr sc cr th zr hf la sc zr y and la th decrease al2o3 and fe2o3t increase and tio2 mgo k2o p2o5 rb zr sc cr co hf nb ta y th u ree ti nb and zr nb increase to maximum values and then either level off or decrease lree enrichment is less in the weathering profile than in the parent granodiorite and although the parent does not have an eu anomaly or only a slight positive anomaly all samples from the weathering profile and overlying sediments have significant negative eu anomalies this observation is especially important in that it shows conclusively that a negative eu anomaly can be produced during chemical weathering of granitoids we suggest these eu anomalies are due to relative enrichment of the other rees and partial loss of eu during the breakdown of plagioclase the boulder weathering profile also has a very minor negative ce anomaly that is within error of a ce anomaly in the parent in the unweathered parent 50 of the ree are contained in sphene and in the case of la also in allanite from 10 20 of the ree are contained in apatite and biotite hornblende and from 7 10 of the hrees are in zircon with exception of eu for which feldspars contribute about 8 negligible amounts of rees occur in the feldspars in weathered samples 75 of the rees are contained in clay minerals the crossover between sphene and clay control of rees occurs over a distance of 1 m near the contact with fresh rock except for their small negative eu anomalies the clay minerals have ree patterns very similar to those of the parent rock isocon plots suggest apparent enrichments of many elements in the boulder weathering profile result from losses of na ca and si during plagioclase weathering in addition variable amounts of sr eu ta nb p and ba were lost during weathering although th u zr y th sc zr hf lu hf and ti zr may have been transferred relatively unchanged from granodiorite parent to the bulk weathering profile most other element ratios and ree distributions were significantly changed during weathering this observation implies that caution needs to be exercised when using ree patterns and element ratios to trace sediment provenance the fact that most element ratios and ree distributions also differ between fountain sediments and the bulk weathering profile may be related to one or a combination of four factors listed in order of probable decreasing importance contribution of other sources to the fountain sediments sorting of minerals during sediment deposition remobilization of elements during diagenesis and leaching of elements by water flow through the upper meter of the weathering profile

late pleistocene and holocene vegetation changes in northeastern brazil determined from carbon isotopes and charcoal records in soils abstract northeastern brazil represents a strategic area in terms of quaternary records of environmental changes in south america due to its distinct semi arid climate in near equatorial latitudes in this study carbon isotope and charcoal distribution records in soils are used to characterize vegetation dynamics forest fires and their relation to climate change since the late pleistocene in the states of ceara piaui and paraiba northeastern brazil at the ceara site the carbon isotope record showed an enrichment trend from 24 to 19 during the early mid holocene indicating an opening of vegetation and expansion of savanna vegetation c 4 plants during this period a trend toward more depleted 13 c values 32 in the late holocene indicates an expansion of forest vegetation c 3 plants a similar trend is observed at the piaui and paraiba sites where values of 24 are associated with open forest vegetation during the late pleistocene in the early mid holocene 13 c values of up to 18 0 suggest the expansion of c 4 plants based on the carbon isotope data it is postulated that from 18 000 cal yr b p to 11 800 cal yr b p 10 000 cal yr b p arboreal vegetation was dominant in northeastern brazil and is associated with humid climates the savanna expanded from 10 000 cal yr b p to 4500 3200 cal yr b p due to a less humid drier climatic phase also supported by the significant presence of fires charcoal fragments in the soil from approximately 3200 2000 cal yr b p to the present carbon isotope records suggest forest expansion and a more humid phase these results form part of a regional pattern since they are in agreement with paleovegetation records obtained in regions of maranhao northeastern brazil and in the amazon and rondonia states northern brazil

strain decoupling across the decollement in the region of large slip during the 2011 tohoku oki earthquake from anisotropy of magnetic susceptibility abstract the integrated ocean drilling program iodp expedition 343 japan trench fast drilling project jfast drilled and cored across the plate boundary decollement at site c0019 near the japan trench where large slip occurred during the 2011 tohoku oki earthquake m w 9 0 anisotropy of magnetic susceptibility ams data obtained from core samples show a striking change in magnetic fabric across the decollement in the frontal prism above the decollement the maximum ams axes display a strong preferred orientation in the northeast southwest direction with the intermediate and minimum ams axes distributed in the vertical plane in the underthrust sediments below the decollement the maximum and intermediate ams axes are subhorizontal but variable in direction and the minimum ams axes display an approximately vertical preferred orientation the ams ellipsoids for all samples have an oblate component but the ams ellipsoids of the underthrust sediments are generally less oblate than those of the frontal prism the magnetic fabric of the sediments in the prism are consistent with horizontal tectonic shortening nearly parallel to the plate convergence direction in the japan trench while that in the underthrust sediments represents a vertical uniaxial strain the magnetic fabrics of the frontal prism and underthrust sediments indicate an abrupt change in strain across the decollement at shallow depths and imply that large co seismic slip occurred along a weak plate boundary decollement that is mainly decoupled over the long term

hydrocarbon plumbing systems of salt minibasins offshore angola revealed by three dimensional seismic analysis analysis of three dimensional seismic data from the lower congo basin offshore angola reveals numerous fluid flow features in the miocene to holocene succession and the potential for large shielded traps underneath basinward overhanging salt structures the fluid flow evidence includes present day sea floor pockmarks clustered above salt structures pliocene pleistocene stacked paleopockmarks and miocene pockmark fields other fluid flow features include high amplitude cylindrical pipe structures 60 to 300 m 197 984 ft wide and 25 to 300 m 82 984 ft high within lower and middle miocene strata thick 150 m 492 ft high reflectivity zones within the pliocene succession associated with bottom simulating reflections and subvertical low amplitude chimneys originating from the deeper section 1 km 0 6 mi beneath the sea floor the miocene pockmark fields occur at a specific horizon suggesting a regional fluid expulsion event at ca 12 ma and the miocene fluid flow regime is interpreted to be dominated by thermogenic fluids supplied via carrier beds and leaking vertically above structural highs the pliocene pleistocene fluid flow regime was dominated by short distance vertical fluid migration and expulsion related to early stage diagenetic processes involving biogenic methane and pore water the present day fluid flow regime is inferred to be dominated by thermogenic fluids primarily controlled by kilometer scale salt flank controlled migration the study emphasizes the use of seismically imaged fluid flow features in hydrocarbon systems analysis by documenting the evolution of an overburden plumbing system through time involving several fluid types and flow regimes depending on the spatiotemporal availability of thermogenic and diagenetic fluids and the tectonostratigraphic occurrence of aquifers traps and seals

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

relating petroleum system and play development to basin evolution west african south atlantic basins abstract sedimentary basins can be classified according to their structural genesis and evolutionary history and the latter can be linked to petroleum system and play development we propose an approach in which we use the established concepts in a new way breaking basins down into their natural basin cycle division then defining the characteristics of each basin cycle including the type of petroleum systems and plays they may contain and comparing them with similar basin cycles in other basins thereby providing a means to learn through a greater population of perhaps not immediately obvious analogues furthermore we introduce the use of the trajectory plot as a new tool in such an analysis this methodology has been applied to the west african south atlantic marginal basins between cameroon and angola and we demonstrate that the similar tectonostratigraphic evolution of the individual basins along this margin has led to the development of similar types of petroleum systems and play level s consequently we can make analogue comparisons among these basins in order to evaluate and predict the presence of potential yet undiscovered hydrocarbon accumulations in less well explored parts of the margin

evidence for a weak and overpressured decollement beneath sediment dominated accretionary prisms we present structural data from several underthrust sequences in southwest alaska that suggest that the deformation regime beneath accretionary prisms is characterized by a subvertical 1 and regionally extensive layer parallel shearing these results contrast markedly with the results obtained from the more shallow parts of accretionary prisms and fold and thrust belts where 1 plunges gently seaward or toward the deformation front on the basis of mohr circle diagrams we propose that these different stress directions are consistent only with a model in which the two regimes are separated by a very weak decollement and calculate coefficient of friction values that range from 0 25 to 0 08 these values are significantly lower than coefficient of friction values calculated for the basal decollement in the taiwan fold and thrust belt e g 0 2 barr and dahlen 1989a and they are also lower than laboratory friction measurements for most rocks e g 0 6 0 8 byerlee 1978 consequently these low values suggest the presence of rocks with unusual material properties e g montmorillonite logan and rauenzahn 1987 or anomalous fluid pressures along the decollement on the basis of the occurrence of shale diapirs the distribution of early veins and the absence of montmorillonite in the underthrust sequences we propose that there was an anomalously high fluid pressure along the decollement fault instead of there being such a low coefficient of friction these results emphasize the importance of dewatering and fluid flow in controlling the position of the decollement which in turn determines how the accretionary prism grows in essence it is the development of a weak overpressured decollement within a thick sediment pile that allows plate convergence to be partitioned into offscraping and underthrusting regimes

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

systematic variation of shear induced physical properties and fabrics in the miura boso accretionary prism the earliest processes during off scraping abstract the interrelations between deformation and variations in the physical properties and fabrics of a shallow level accretionary prism have been clarified using measurements of porosity pore size distribution and the anisotropy of magnetic susceptibility ams within the miura boso accretionary prism central japan based on the mode of deformation this onland example of an off scraped body can be divided into three parts from bottom to top imbricate thrusts corresponding to a decollement zone a thrust unit in the lower part of the off scraped body and an upper coherent unit in the top part of the off scraped body physical properties and fabrics are quite variable in each of the three parts even within a particular lithology these observations reflect each structural unit s individual strain history during shallow off scraping and accretion prior to the accretion the sediments underwent vertical compaction when horizontal compressional stresses subsequently began to deform the sediments precursory shear disturbed the previous compaction fabric accompanied by a pervasive porosity decrease over a zone several tens to hundreds of meters in thickness the porosity decrease occurred by large pore collapse which led to the development of an impermeable over consolidated horizon and inevitable high pore fluid pressures below that controlled the position of the subsequent decollement zone displacement along imbricate thrusts within the decollement zone took place just below the over consolidated horizon where high fluid pressure had been generated here a flattening fabric parallel to the imbricate thrust and associated further porosity and pore size reductions occurred in association with the fault movement these findings imply unrecoverable pre fractured strain information of sediments before being included in the decollement zone and suggest that the precursory formation of an over consolidated zone via grain rearrangement and pore size reduction is an essential control on subsequent large deformation i e within a decollement zone in the shallow part of an accretionary prism especially within lithologically homogeneous material

thin skinned extensional tectonics on a salt detachment northern kwanza basin angola abstract thin skinned extension on a salt detachment of a style known as raft tectonics characterizes deformation of the late aptian to recent section in the northern kwanza basin angola large rafts and intervening grabens are interpreted to have developed as a result of gravity gliding increased dip and gravity spreading asymmetrical loading of a sedimentary wedge major raft movement occurred primarily from the middle tertiary but some deformation appears to have started as early as late cenomanian or early turonian times individual grabens measure up to 70 km in length 15 km in width and nearly 3 km in depth and show switching polarities in the sense of thickening of the tertiary sedimentary infill graben geometries were controlled by syndepositional extension and the local availability of salt from the data examined which includes both seismic and well data the grabens appear to become younger from east to west reflecting basinward progression of the deformation as the age relationships could be related to insufficient sampling of strata deposited in complex sedimentation patterns they may have no relevance to the timing of the deformation the diachronous deformation is therefore speculative extension in the northern kwanza basin is estimated at 60 the outermost raft is translated 55 km westwards in addition to the extensional structures compressional folds thrust faults and salt structures mark the toe of the gravity gliding and spreading system all of the rafts lie within the african portion of the aptian salt basin on rifted continental crust and they are generally unrelated to structures below the salt biostratigraphy and lithostratigraphy indicate that the grabens formed on the shelf and upper slope from the middle eocene associated compressional features developed near the slope rise the unusual expression of raft tectonics is attributed to a combination of 1 the presence of a salt layer 2 a stable basement configuration that allowed quiescent accumulation of the raft sequence and 3 an increase in basin dip and sediment supply

modern sangamon and yarmouth soil development in loess of unglaciated southwestern illinois abstract the thebes section in unglaciated southwestern illinois contains a well preserved 500 kyr loess paleosol sequence with four loesses and three interglacial soils various magnetic mineralogical and elemental properties were analyzed and compared over the thickness of soil sola these proxies for soil development intensity have the following trend yarmouth geosol sangamon geosol modern soil quartz plagioclase zr sr and tio 2 na 2 o ratios were most sensitive to weathering frequency dependent magnetic susceptibility and anhysteretic remanent magnetization greatest in a horizons also correspond well with soil development intensity neoformed mixed layered kaolinite expandables suggestive of a warm humid climate were detected in the sangamon and yarmouth soil sola clay illuviation in soils was among the least sensitive indicators of soil development differences in properties among interglacial soils are interpreted to primarily reflect soil development duration with climatic effects being secondary assuming logarithmic decreases in weathering rates the observed weathering in the sangamon geosol is consistent with 50 kyr of interglacial weathering oxygen isotope stage 5 compared to 10 kyr for the modern soil oxygen isotope stage 1 we propose that the yarmouth geosol in the central midwest formed over 180 kyr of interglacial weathering including oxygen isotope stages 7 9 and 11

late mesozoic gravity sliding and oxfordian hydrocarbon reservoir potential of the northern yucatan margin abstract the stratigraphy and structural evolution of the western florida margin is much better understood than its northern yucatan conjugate because previous hydrocarbon exploration has been more extensive on the florida margin in the deep water northeastern gom the post salt section records late jurassic cretaceous gravity sliding of rafted blocks along a basinward dipping layer of callovian salt this study uses approximately 31 000 line km of 2d seismic data to describe a coeval area of widespread gravity sliding along the less studied northern yucatan margin we define three structural domains based on their distinctive salt structures and associated deformation 1 a region in the northeastern study area consists of relatively undeformed late jurassic cretaceous section underlain by 0 300 m thick salt 2 areas in the central and southwestern study area contain late mesozoic gravity slides defined by 300 600 m thick salt rollers and normal faults rooted onto a 1 4 basinward dipping salt detachment and 3 the distal margin of the western and central study area exhibits large salt diapirs up to 6 km tall that deform quaternary stratigraphic units in the central yucatan study area containing late mesozoic gravity slides a stratigraphic unit equivalent to the productive oxfordian norphlet sandstone of the deep water northeastern gom is identified based on its similar seismic character reconstructing the extent of this norphlet equivalent unit along the yucatan margin to its location during oxfordian deposition places it adjacent to an extensive area of norphlet sandstone mapped in the deep water northeastern gom by previous authors our reconstruction suggests a 48 000 km2 fairway of potential aeolian late jurassic reservoirs on the yucatan and campeche margins that includes productive reservoirs in the southeastern bay of campeche which previous authors correlated with the norphlet formation

late quaternary paleosols stratigraphy and landscape evolution in the northern pampa argentina the field properties micromorphology grain size geochemistry and optically stimulated luminescence osl ages of two late quaternary sections have been used to reconstruct the sequence of pedosedimentary processes and to provide insights into landscape evolution in part of the northern pampa of argentina paleosols developed in paludal sediments adjacent to the parana river at baradero and in loess at lozada can both be correlated and linked to other sites thus enabling for the first time the tentative recognition and tracing of a diachronous soil stratigraphic unit that probably spans the equivalent of at least part of marine oxygen isotope stage ois 5 the paleosol at lozada was truncated and buried beneath fluvial sediments during the time span of ois 4 and 3 eolian gradually replaced paludal inputs at baradero over this period and there were also two clearly defined breaks in sedimentation and development of paleosols the period corresponding to ois 2 was marked by significant loess accumulation at both sites with accretion continuing into the mid holocene only at lozada the more developed nature of the surface soil at baradero probably reflects a combination of a moister climate and a longer soil forming interval

stratigraphic record of translation down ramps in a passive margin salt detachment abstract ramp syncline basins filled with synkinematic sediments record the incremental translation history and translation rates of strata transported over basement ramps on passive margins movement of strata over a stratabound salt detachment is stratigraphically recorded as an isopach thick on the seaward side of a monoclinal ramp this growth syncline gradually moves seaward down and then off the monocline as if on a conveyor belt this shift creates accommodation space for a new isopach thick to form just landward of the older one repetition of this cycle creates a shingled series of isopach thicks within the ramp syncline basin kinematic forward models and restored cross sections from the kwanza basin angola show that the stratigraphic pattern of ramp syncline basins is most influenced by three factors 1 the relative rates of translation and aggradation control the curvature of the axial trace of the growth synclines 2 bathymetric scarps above basement ramps can create spectacular seaward dipping onlap surfaces 30 km long downdip adjoining ramps generate stacked interfering onlap surfaces 3 salt diapirs or anticlines are commonly shortened at the top of the ramp especially where this coincides with the base of the continental slope diapir shortening provides a buffer to absorb sliding from its landward side and impede sliding on its seaward side this buffering can have a major control on the entire gravity spreading system containing the diapirs

tropical rain forest and climate dynamics of the atlantic lowland southern brazil during the late quaternary palynological analysis of a core from the atlantic rain forest region in brazil provides unprecedented insight into late quaternary vegetational and climate dynamics within this southern tropical lowland the 576 cm long sediment core is from a former beach ridge valley located 3 km inland from the atlantic ocean radio carbon dates suggest that sediment deposition began prior to 35 000 14c yr b p between ca 37 500 and ca 27 500 14c yr b p and during the last glacial maximum lgm ca 27 500 to ca 14 500 14c yr b p the coastal rain forest was replaced by grassland and patches of cold adapted forest tropical trees such as alchornea moraceae urticaceae and arecaceae were almost completely absent during the lgm furthermore their distributions were shifted at least 750 km further north suggesting a cooling between 3 c and 7 c and a strengthening of antarctic cold fronts during full glacial times a depauperate tropical rain forest developed as part of a successional sequence after ca 12 300 14c yr b p there is no evidence that araucaria trees occurred in the atlantic lowland during glacial times the rain forest was disturbed by marine incursions during the early holocene period until ca 6100 14c yr b p as indicated by the presence of microforaminifera a closed atlantic rain forest then developed at the study site

epeirogenic motions of africa as inferred from cretaceous shoreline deposits epeirogenic motions can be quantified if paleodatum planes can be recognized these motions have been determined for the time interval mid cretaceous cenomanian to recent in continental africa using the vertical displacement of ancient shoreline sediments and other nearshore or low elevation deposits that are inferred to represent a cenomanian sea level datum plane the cretaceous trans saharan seaway brought shoreline sediments deep into the african continental interior and additional data suggest that most of the remaining terrestrial regions were also low lying during the cenomanian the present elevations of the sea level sediments indicate that large portions of africa have undergone epeirogenic uplift since the cenomanian the character of the motions in north africa can be described as small scale high amplitude 3 km doming separated by relatively flat lying areas of deposition the largest single epeirogenic feature is the uplift associated with red sea and east african rift development the timing of post cenomanian epeirogenic motions can be further constrained using paleontologic k ar faulting paleodrainage and sedimentary data the most likely causal mechanism for african epeirogeny may be hot spot activity reflective of the mantle convection regime underlying the african lithosphere

evidence for mechanical decoupling of the upper plate at the nankai subduction zone constraints from core scale faults at nantroseize sites c0001 and c0002 1 detailed analyses of cores from two drill sites landward of the nankai trough provide constraints on the evolution of stress across the sw japan subduction zone core scale faults at sites c0001 and c0002 suggest changing stress geometries that shed light on mechanical coupling across this plate boundary normal faults dominate the record of brittle strain in both the sedimentary cover and the upper accretionary prism and these cut older shear zones and vein structures based on cross cutting relations normal faults postdate thrust faults with the latter interpreted to be inactive the normal faults in contrast are consistent with contemporary stress proxies such as borehole breakout and anelastic strain recovery data stress inversion for faults that are restored to original orientations using paleomagnetic data reveal that thrusting has accommodated trench subperpendicular shortening associated with interplate coupling this phase of deformation is overprinted by normal faulting attributed to mechanical decoupling of the upper plate from the lower plate in response to the underplating of anomalously weak sediments between an out of sequence thrust and the decollement these observations suggest that core scale faults record a stress history that is to date not apparent from in situ stress proxies such as borehole breakout data or anelastic strain recovery data we conclude that the brittle faults provide a unique record of changing stress conditions that can be recognized only through coring

identification and numerical modelling of hydrocarbon leakage in the lower congo basin implications on the genesis of km wide seafloor mounded structures abstract we present a combined approach of interpretation of 2d seismic reflection data and numerical modelling of hydrocarbon generation and migration across the southern slope of the lower congo basin in order to investigate the factors controlling timing and distribution of hydrocarbon leakage in this area we identified three main families of past and present day leakage features 1 mid upper miocene seismic chimneys concentrated basinwards and ending up on buried pockmarks 2 plio pleistocene chimneys rather clustered to the east of the study area and ending up in seafloor pockmarks and 3 fewer scattered chimneys identified within the miocene sequences ending up in shallow enhanced reflectors flat spots stratigraphic and structural elements seem to control the distribution of these features at least two major events of leakage occurred during the middle late miocene and intermittently during the pliocene present external factors as sediment supply are associated to the miocene leakage event whilst internal structural elements probably triggered the pliocene to present day leakage a major seabed morphological feature represented by a margin paralleled belt of more than 1 km wide mounds was identified above growth faults to the east of the study area data constrained 2d hc generation and migration modelling suggests a genetic link between these structures and vertical migration leakage of thermogenic methane sourced from either currently mature oligo miocene source rocks or secondary cracking and further expulsion from over mature upper cretaceous source rocks hence the mounds are likely to represent a lineation of methane derived carbonate build ups despite the natural limitations of a 2d migration model when combined and calibrated with observations from seismic data it can be used as a valid tool to assess petroleum migration routes in sedimentary basins to the best of our knowledge this is the first integrated approach combining both seismic observations and numerical modelling carried out in the angola basin

age and climate of the late saalian and early eemian in the type area amsterdam basin the netherlands abstract lake deposits of late saalian mis 6 and early eemian mis 5e age in glacially excavated basins in the central part of the netherlands provide a high resolution stable isotope and pollen record of the glacial interglacial transition late saalian warm conditions were interrupted by a cold dry interval at the saalian eemian boundary which we correlate to the kattegat stadial and heinrich event 11 this cold interval ties our continental climate record to that of the marine oxygen isotope based time scale oxygen isotope data from this sequence indicate that the subsequent early eemian saw a quick recovery to warm interglacial climatic conditions which was reached already during the pioneer phase of the vegetation the sea transgressed the lake 1 kyr after the start of the eemian and highstand was reached 2 kyr later precipitation increased just prior to transgression of the sea into the lake causing important changes in the vegetation transgression of the isostatically rebounding area once covered by the baltic ice sheet is of early eemian age and becomes younger from the former centre of the ice sheet along the baltic sea to its margin in the netherlands the highstand cannot precede the start of the eemian as the area was emerging assuming that the effect of the isostatic rebound is small along the margin of the former ice sheet and by using the australian u th ages of the eemian highstand coral reefs combined with the duration of the eemian pollen zones derived from the annually layered lake deposits of bispingen it is concluded that the eemian in the netherlands starts at 131 ka

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

magnetic and structural fabrics of the melange in the shimanto accretionary complex okinawa island implication for strain history during decollement related deformation the magnetic fabrics of the melange in the shimanto accretionary complex of okinawa island were obtained from the anisotropy of magnetic susceptibility ams data the magnetic fabrics show a marked contrast between the structurally lower and upper parts of the melange the lower part records deformation in the footwall of the decollement d1 whereas the upper part documents that in the hanging wall of the decollement d2 in the lower part of the melange the magnetic fabrics show good correlations with s1 layer parallel foliation reflecting strain geometries under layer perpendicular flattening as s c fabrics were locally developed by heterogeneous shear during d1 some of the previous magnetic fabrics were rotated with s1 in this case the resultant magnetic fabrics reflect s surfaces and maximum ams axes are reoriented parallel to shear directions without clear change in shape and anisotropy degree of the ams ellipsoids thus s surfaces did not act as flattening planes but may represent the deformation through independent particulate flow and mechanical rotation the lower part of the melange was pervasively sheared during d2 reflecting that it laid immediately above the decollement however d1 magnetic fabrics were not modified because shear strain was accomplished by brittle microfaults without development of penetrative strain in contrast penetrative strain was significant in the upper part of the melange resulting in the magnetic fabrics recording incremental strain associated with d2 therefore deformation mechanism and proximity to a decollement play an important role on development of magnetic fabrics in a melange

palaeohydrology vegetation and climate since the late illinois episode 130 ka in south central illinois abstract our interpretation of pollen and ostracode successions from four basins in south central illinois provides a new synthesis of palaeovegetation palaeohydrology and palaeoclimate for the period from the late illinois episode about 130 000 years ago to near the end of the wisconsin episode about 25 000 years ago correlations of pollen biozones between raymond pittsburg and bald knob basins are the basis for identifying the late illinois glacial sangamon interglacial wisconsin glacial and hudson interglacial episodes glacial episodes were identified primarily by the presence of picea pollen and the ostracode limnocythere friabilis whereas interglacial episodes were identified by quercus pollen and by the ostracodes candona caudata and heterocypris punctata within interglacial and glacial episodes pollen and ostracode assemblages varied with changes in moisture balance local palaeohydrology was assessed primarily on the basis of environmental tolerance indices of ostracodes and the stable isotope c o stratigraphy of ostracodal calcite regional moisture balance was assessed from multivariate analyses of the pollen successions three climatic regimes occurred during the sangamon episode 1 one regime was characterised by precipitation exceeding evaporation that promoted basin overflow this climate was inferred from the high percentages generally 80 of deciduous forest pollen peaks in the abundance of liquidambar and fagus pollen indicate that winters may have been slightly warmer and effective moisture slightly greater than at present 2 the second climatic regime was continental similar to the present climate of illinois in which precipitation is equal to or just less than evaporation this climate is inferred from abundant ambrosia pollen 40 to 60 and abundant nektic swimming ostracode valves which suggest a shallow lake these conditions probably developed in association with a heat low over the interior of north america during marine oxygen isotope stages 5e and 5c associated with the transition between the first two climates are fossils of the subtropical ostracode heterocypris punctata and the giant tortoise geochelone crassiscutata that suggest short periods in winter when polar low pressure systems did not extend into illinois as they do today 3 the third climatic regime occurred during the transition from the sangamon interglacial episode to the wisconsin glacial episode a severely continental climate is indicated by the heat tolerant ostracode pelocypris tuberculatum variable 18o values of ostracode valves and high environmental tolerance index values for the ostracode assemblages the weedy chenopodiaceae and amaranthaceae families grew on exposed mudflats the tree pollen associated with this type of climate included low percentages of picea and liquidambar an assemblage that has no modern analogue we suggest that this transitional climatic regime was associated with the large scale changes in the climate system during marine oxygen isotope stage 4

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

net local removal of floodplain sediment by river meander migration abstract erosion from the banks of meandering rivers causes a local influx of sediment to the river channel most of the eroded volume is usually replaced in nearby point bars however the typical geometry of river bends precludes the local replacement of all eroded material because i point bars tend to be built to a lower elevation than cutbanks and ii point bars tend to be shorter than the eroding portion of cutbanks because of channel curvature in a floodplain that is in equilibrium i e neither increasing nor decreasing in volume sediment eroded from cut banks must be replaced elsewhere on the floodplain the local imbalance caused by differences in bank height should be balanced primarily by overbank deposition while the local imbalance caused by curvature should be balanced primarily by deposition in abandoned stream courses or oxbow lakes estimates of these local imbalances based on remotely sensed measurements of bank geometry and channel migration have been made on four systems in the united states a 91 km reach of the pearl river in louisiana and mississippi a 62 km reach of the bogue chitto river in louisiana a 35 km reach of the neuse river in north carolina and a 2 7 km reach of the vermillion river in minnesota for these systems the total local imbalance integrated over many bends ranged from 0 36 to 2 27 m 3 yr m of valley length 0 15 to 1 32 m 3 yr m of channel length or 7 to 45 of gross cutbank erosion with a typical value of about 17 when compared with gauged suspended sediment data the measurements provide estimates of the relative importance of floodplains for storing material transported by a river system the data suggest that even if the studied systems are near long term mass balance equilibrium as opposed to undergoing net deposition or erosion almost all of the sand and in some cases much of the silt and clay in transit through these systems is likely to have spent some time stored in an upstream floodplain

pedogenesis of a catena of the farmdale sangamon geosol complex in the north central united states abstract the farmdale sangamon geosol pedocomplex consists of the sangamon geosol and the overlying farmdale geosol which form the most extensive terrestrial record of the last interglacial to glacial transition in the midwest united states the geosol complex formed for upwards of 100 ka extending from the end of mis 6 through 4 for the sangamon geosol then the farmdale geosol for during a brief episode at the end of mis 3 following slow accumulation and pedogenic modification of eolian silt deposited on top of the sangamon geosol our study site consists of a buried paleo hillslope transect that forms a catena enabling evaluation of slope effects on interglacial scale soil formation the sangamon geosol is formed in calcareous and illitic glaciogenic sediment along the catena the sangamon geosol profiles display some morphological changes namely in terms of colors that we interpret as indicators of differences in drainage most thickness and horizonation characteristics are similar all along the transect with intact upper sola horizons ae and e horizons that overlie clay enriched bt horizons the bt horizons contain abundant clay that exists as illuvial clay coatings matrix infills and as mosaic speckled domains the clay originated both by in situ weathering and through illuviation from the clay depleted upper sola slope does not appear to affect bt characteristics beyond redder hues of the matrix and clay coatings in the upper slope position with depth effects of carbonate leaching and infilling of clay in the matrix decrease and clay coatings are restricted to walls of voids adjacent to aggregates clay mineralogy shows illite depletion but no interstratified kaolinite expandable minerals indicating the degree of weathering is not as great as is typical of sangamon geosol profiles formed in loess or in glaciogenic sediment of the central illinois type area clay mineralogy is also stratified with depth coincident with particle size which probably indicates sorting of layers of illitic dolomite and shale variation of horizon and profile characteristics appears to largely be a function of particle size variability and stratification than topographic position in the catena the influence of hillslope position on soil redistribution during formation of the sangamon geosol appears negligible given the uniformity of upper solum horizon thickness and sandy particle size characteristics so we conclude that a bioturbation and rainwash origin of the upper solum and the texture contrast in these profiles is not the best process model explanation we suggest that the base rich nature of these soils led to ecosystem characteristics that discouraged erosion and encouraged infiltration and a lessivage type origin of the texture contrast no convincing evidence of mis 6 through mis 4 loess occurs at this site the farmdale geosol formed in the robein silt which is roxana silt mis 3 loess that was redistributed downslope the robein silt is thicker and finer in the topographic low and indicates the cooler and forested environmental conditions during mis 3 were conducive to downslope movement of soil and also produced greater differences in drainage induced soil morphological changes in the farmdale geosol

on the mechanical role of smectite in subduction zones smectites a group of hydrated phyllosilicate minerals are often a main component of sediments entering a subduction zone they are common in hemipelagic sediments and consist of an authigenetic component that arises from the alteration of volcanic ash intercalated in the sediment and a detrital component smectite rich strata are structurally weak retain water and are highly porous a review of sediment lithology in subduction zones around the world suggests that decollement zones may preferentially form in smectite rich horizons one consequence of this observation is that the assignment of high frictional resistance to materials in a decollement may be unwarranted at deeper structural levels smectite is transformed to illite a mechanically stronger mineral estimates of the depth of this transition coincide with the depth at which earthquakes are first detected along plate interfaces i speculate that the smectite illite transition in subduction zones may be an important component of sediment consolidation processes that trigger interplate seismicity

raft tectonics the effects of basal slope angle and sedimentation rate on progressive extension abstract in the gulf of guinea the upper cretaceous tertiary sedimentary cover has undergone gravity gliding above an aptian salt layer for various basal slope angles from 0 to 4 gliding started during albian time and evolved up to the present with variable sedimentation rates faulting patterns are seen to vary in particular as a function of the basal slope angle and the syn kinematic sedimentation rates a series of laboratory experiments on small scale models is used to study the effects of the two parameters mentioned above models are composed of two layer slabs with newtonian silicone putty at the base to represent a basal salt decollement and dry sand on top to represent the sedimentary overburden models are allowed to deform under their own weight for various basal slope angles ranging from 0 to 5 with two different syn kinematic sedimentation rates it is shown that the basal slope angle controls the location of faulting in the overburden within a single downslope deformation domain for values smaller than 2 and within two domains lying downslope and upslope for higher values of the width of the deformation domains also varies as a function of overburden faulting always starts with syn kinematic grabens which evolve into symmetric or asymmetric grabens or into tilted blocks bounded by listric normal faults while synthetic listric normal faults characterize the downslope deformation domains both synthetic and antithetic listric normal faults can occur in the upslope deformation domain ductile deformation within the basal decollement layers results from variable combinations of pure shear and simple shear interaction of ductile deformation in the ductile decollement layer with faulting in the overburden locally produces complex and heterogeneous strain patterns notably within salt rollers finally increasing rates of syn kinematic sedimentation are seen to increase the rate of downslope displacement and to enhance and favour the development of listric normal faults

seismic heating signatures in the japan trench subduction plate boundary fault zone evidence from a preliminary rock magnetic geothermometer frictional heating during earthquake rupture reveals important information on earthquake mechanisms and energy dissipation the amount of annealing varies widely and is as yet poorly constrained here we use magnetic susceptibility versus temperature measurements during cycling to increasingly elevated temperatures to constrain the maximum temperature a slip zone has experienced the case study comprises sheared clay cored from the japan trench subduction plate boundary fault zone decollement which accommodated the large slip of the 2011 mw 9 0 tohoku oki earthquake the decollement was cored during the integrated ocean drilling program iodp expedition 343 the japan trench fast drilling project jfast heating signatures with estimated maximum temperatures ranging from 300 to over 500 c are determined close to the multiple slip surfaces within the decollement since it is impossible to tie a specific slip surface to a certain earthquake thermal evidence for the cumulative effect of several earthquakes is unveiled this as yet preliminary rock magnetic geothermometer would be a useful tool to detect seismic heating along faults that experienced medium temperature rise a range which is difficult to assess with other approaches

tectonostratigraphic development in the eastern lower congo basin offshore angola west africa abstract as in all aptian salt basins off western africa the post rift evolution of the lower congo basin offshore angola was greatly influenced by raft tectonics we suggest that rafting in the lower congo basin took place during relatively short periods 7 10 ma characterized by high strain rates separated by longer periods 15 35 ma characterized by low strain rates the high strain rate periods are dated as aptian late cretaceous late eocene late oligocene and late miocene recent with respect to the tertiary development we have obtained a positive correlation between sedimentary thickness and cumulative stretching suggesting sedimentary loading as an important driving mechanism for raft tectonics during the tertiary two different types of depocentres developed these are i broad first order depocentres governed by regional subsidence and ii narrower elongated second order depocentres governed by growth on active faults within the study area the depocentres seem to have migrated from the west towards the east

from soft sediment deformation to fluid assisted faulting in the shallow part of a subduction megathrust analogue the sestola vidiciatico tectonic unit northern apennines italy

elevated fluid pressure and extreme mechanical weakness of a plate boundary thrust nankai trough subduction zone pore fluid pressure is a key parameter governing both the shear strength of faults and the conditions for seismic and tsunamigenic slip on subduction zone megathrusts however quantitative constraints on this parameter based on in situ data in these or any faults have proven elusive using seismic interval velocities derived from a three dimensional seismic reflection survey we compute porosity fluid pressure and effective stress at the plate interface in the nankai trough subduction zone offshore southwestern japan to 20 km down the fault dip using well constrained locally calibrated empirical relationships between velocity porosity and effective stress we show that the fault and immediately subjacent footwall are nearly undrained implying that the subduction megathrust slips under a shear stress of

complexity in a cellular model of river avulsion abstract we propose a new model of river avulsion that emphasizes simplicity self organization and unprogrammed behavior rather than detailed simulation the model runs on a fixed cellular grid and tracks two elevations in each cell a high elevation representing the channel levee top and a low one representing the channel bottom the channel aggrades in place until a superelevation threshold for avulsion is met after an avulsion is triggered a new flow path is selected by steepest descent based on the low values of elevation flow path depends sensitively on floodplain topography particularly the presence of former abandoned channels several behavioral characteristics emerge consistently from this simple model 1 a tendency of the active flow to switch among a small number of channel paths which we term the active channel set over extended periods leading to clustering and formation of multistory sand bodies in the resulting deposits 2 a tendency for avulsed channels to return to their previous paths so that new channel length tends to be generated in relatively short segments and 3 avulsion related sediment storage and release leading to pulsed sediment output even for constant input each of these behaviors is consistent with observations from depositional river systems a single valued threshold produces a wide variety of avulsion sizes and styles larger nodal avulsions are rarer because pre existing floodplain topography acts to steer flow back to the active channel channel stacking pattern is very sensitive to floodplain deposition this work highlights the need to develop models of floodplain evolution at large time and space scales to complement the improving models of river channel evolution

conditions for branching in depositional rivers it is often taken for granted that rivers organize transport into a single active channel in some net depositional environments however flow of water and sediment is distributed in several stable channels such branching rivers may be confined in valleys anabranching or anastomosed or unconfined on deltas distributaries and their existence confronts us with the very basic question of what governs the spatial organization of channel patterns in sedimentary landscapes current models for equilibrium channel morphology cannot predict the occurrence of branching rivers because they do not consider dynamical processes such as avulsion i e the rapid abandonment of a channel in favor of a new path at lower elevation the requisite conditions for avulsion have been the subject of ongoing debate here we resolve the conditions leading to channel avulsion and show that branching rivers occur when avulsion is the dominant mechanism of lateral channel motion a compilation of field and laboratory data demonstrates that avulsion frequency scales with the time required for sedimentation on channel beds to produce a deposit equal to one channel depth from the relative rates of bank erosion and channel sedimentation we derive a dimensionless mobility number that accurately predicts the conditions under which anabranching and distributary channels occur results may be directly applied to modeling landscape evolution over human and geologic time scales and for inverting formative environmental conditions from channel deposits on earth and other planetary surfaces

seafloor facies related to upward methane flux within a giant pockmark of the lower congo basin the origin of the cold fluid venting from a giant pockmark within the lower congo basin has been elucidated based upon results of precise mapping submersible dives gravity coring and isotopic analyses realized under a total ifremer cooperative project zaiango and biozaire projects during four dives of the ifremer rov victor 6000 the bottom was filmed hard and soft samples were lifted from the sediment and water samples were collected with a ctd rosette system the detailed dip map shows that the 800 m wide giant pockmark is a composite feature due to the coalescence of multiple 100 m wide depressions that displays a broad range of biological mineralogical and chemical features on the seafloor leading to a seafloor anomaly recorded on the multibeam imagery methane rich fluids migrating through the sedimentary column from a buried palaeochannel clearly react with the sulphate rich circulating sea water to produce hydrogen sulphide and bicarbonate ions this situation leads to a concentrical arrangement of the sedimentary facies with methane related features in the centre and sulphide related features at the periphery this organization is correlated with high levels of methane up to 20 mol l measured in the centre of the giant pockmark responsible for the crystallization of gas hydrates at the bottom in this model the concentrical organization of mineralogical and biological features reflects a geochemical partitioning related to the peripheral progressive mixing of the methane flux

paleohydrology and paleoclimate of the past 33 000 years at the tamandua river central brazil abstract deposits of the tamandua river contain evidence for four major paleohydrologic stages in the last 33 000 years a wet period between 33 000 and 20 000 14 c yr b p produced a high water table that allowed organic rich deposition in the tamandua valley a dry interval 17 000 10 000 14 c yr b p produced sandy deposits of braided channels and alluvial fans river aggradation during this period probably resulted from a high sediment load promoted by intense slope erosion and from flash floods a wet period after 10 000 and before 6000 14 c yr b p was marked by reduced slope erosion and by high discharge that led to erosion of the valley fill during that time forests developed widely in brazil a drier climate after 6000 14 c yr b p caused a reduction of discharge but allowed a high water table to be maintained

rates of flood plain sedimentation on the central amazon river field measurements of water and sediment discharge and floodplain topography numerical simulations of hydrology and landsat data on sediment concentrations were combined to estimate rates of transport and the fate of water and sediment in a 200 km reach of the central amazon river results from field data collected during the annual flood in july 1986 indicate that sediment was transported to the flood plain at rates ranging from 3 to 5 t d 1 m 1 with percentage deposition 80 yielding vertical rates of 0 8 to 1 6 cm day comparable rates were calculated from geographic information system overlays of numerically simulated specific water discharge and land sat derived sediment concentrations rates for july 31 1977 include 4 to 18 t d 1 m 1 of transport onto the flood plain and an average of 64 deposition at vertical rates from 0 4 to 3 3 cm d a 1 m higher flow on august 2 1989 yielded on average higher rates of transport onto the flood plain 8 to 15 t d 1 m 1 but lower percentage 46 deposition implying vertical rates between 0 3 and 2 9 cm d

inferences on sediment strength and fault friction from structures at the aleutian trench the structural relations of conjugate thrust faults and the master decollement imaged in a research level processed multichannel seismic reflection record across the eastern aleutian trench allow quantitative estimates of the sediment strength and friction across thrust boundaries of the subduction zone these estimates are derived from geometric relations between faults and from the overall geometry of accreted prisms they suggest the presence of high pore fluid pressures that result in low levels of friction along a master decollement and on the main bounding thrust faults in the accreted sediment therefore coupling in the immediate trench area apparently does not contribute significantly to the generation of horizontal compression upslope

climatic events during the late pleistocene and holocene in the upper parana river correlation with ne argentina and south central brazil most quaternary studies in brazil are restricted to the atlantic coast and are mainly based on coastal morphology and sea level changes whereas research on inland areas is largely unexplored the study area lies along the parana river state of parana brazil at 22 43 s latitude and 53 10 w longitude where the river is as yet undammed paleoclimatological data were obtained from 10 vibro cores and 15 motor auger holes sedimentological and pollen analyses plus tl and 14c dating were used to establish the following evolutionary history of late pleistocene and holocene climates first drier episode 40 000 8000 bp first wetter episode 8000 3500 bp second drier episode 3500 1500 bp second present wet episode 1500 bp present full size table table options view in workspace download as csv climatic intervals are in agreement with prior studies made in southern brazil and in northeastern argentina

late quaternary vegetation dynamics in the southern amazon basin inferred from carbon isotopes in soil organic matter abstract carbon isotopes of soil organic matter som were used to evaluate and establish the chronology of the vegetation dynamics of an ecosystem presently composed of savannas surrounded by forests the study was carried out on a 200 km transect along highway br 319 on the border of amazonas and rondonia states in southern amazon brazil large ranges in 13 c values were observed in som collected from profiles in the savanna 27 to 14 and forest regions 26 to 19 reflecting changing distribution of 13 c depleted c 3 forest and 13 c enriched c 4 savanna vegetation in response to climate change these results indicate that from about 17 000 to 9000 14 c yr b p the study area was covered by forest vegetation between approximately 9000 and 3000 14 c yr b p savanna vegetation expanded at the expense of the forest although the expansion of savanna did not occur with the same intensity along the study transect this process was very clearly registered by 13 c enrichment in the som since 3000 14 c yr b p the carbon isotope data suggest that forested regions have expanded this study adds to the mounting evidence that extensive forested areas existed in the amazon during the last glaciation and that savanna vegetation expanded in response to warm and dry conditions during the early to middle holocene

absence of last glacial maximum records in lowland tropical forests abstract environmental conditions of the lowland tropical forests during the last glacial maximum lgm between ca 20 000 and 18 00014c yr b p are reevaluated in terms of dating control and lithology analyzed in seven pollen records from south america the reevaluation shows that probably in none of the published records are lgm sediments present or abundant this conclusion is based on the occurrence of abrupt lithologic changes coupled with changes in sedimentation rate interpolated from radiocarbon dates these findings suggest that the lgm was represented probably by a hiatus of several thousand years indicative of drier climates than before or after

the long term evolution of the congo deep sea fan a basin wide view of the interaction between a giant submarine fan and a mature passive margin zaiango project abstract we have integrated the relatively unknown distal domains of the lower congo basin where the main depocenters of the congo submarine fan are located with the better constrained successions on the shelf and upper slope through the analysis of thousands of km of 2d seismic reflection profiles off shore the congo angola passive margin the basin architecture is depicted by two ca 800 km long regional cross sections through the northern congo and southern angola margin a large unit deposited basinward of the aptian salt limit is likely to be the abyssal plain equivalent of the upper cretaceous carbonate shelf that characterized the first post rift deposits in west equatorial african margins a latest turonian shelf deepening event is recorded in the abyssal plain as a long period coniacian eocene of condensed sedimentation and basin starvation the onset of the giant tertiary congo deep sea fan in early oligocene following this event reactivates the abyssal plain as the main depocenter of the basin the time space partitioning of sedimentation within the deep sea fan results from the interplay among increasing sediment supply margin uplift rise of the angola salt ridge and canyon incision throughout the neogene oligocene early miocene turbidite sedimentation occurs mainly in nw se grabens and ponded inter diapir basins on the southern margin angola seaward tilting of the margin and downslope salt withdrawal activates the up building of the angola escarpment which leads to a northward congo shift of the transfer zones during late miocene around the miocene pliocene boundary the incision of the congo submarine canyon confines the turbidite flows and drives a general basinward progradation of the submarine fan into the abyssal plain the slope deposition is dominated by fine grained hemipelagic deposits ever since results from this work contribute to better understand the signature in the ultra deep deposits of processes acting on the continental margin as well as the basin wide sediment redistribution in areas of high river input

tectonic features of the japan trench convergent margin off sanriku northeastern japan revealed by multichannel seismic reflection data near the japan trench convergent plate margin the seaward edge of the continental plate is deformed by subduction of the oceanic plate we report the results of a multichannel seismic survey in the northern japan trench in which this deformed zone is demarcated from the rigid continental framework by a pronounced landward dipping reflector the oceanic plate also undergoes deformation as the two plates interact in the subduction processes resulting in a progressive deformation or destruction of a horst structure along the top of the subducting oceanic crust this may eventually lead to the formation of a smooth plate boundary at the greater depth more than 45 km landward from the trench axis a smooth reflector suggesting a stable slip plane is visible along and above the oceanic crust our data indicate that the deformed zone pinches out landward 60 km from the axis at 13 km depth and the slip plane becomes less obvious there seismicity of interplate earthquakes rapidly increases landward from this location leading us to speculate that this is where coupling at the plate boundary becomes strong enough for earthquakes to occur we conclude that the updip limit of the seismogenic zone of interplate earthquakes in the study area is characterized by the tectonic feature of a pinchout of the deformed sediments which overlie the subducting oceanic crust

bulls eye pockmarks and polygonal faulting in the lower congo basin relative timing and implications for fluid expulsion during shallow burial abstract this study describes a new type of pockmark association from the lower congo basin offshore west africa consisting of up to 8 stacked paleopockmarks separated by intervals of drape and onlap fill the stacked paleopockmarks occur within the depocentres of polygonally faulted plio pleistocene sediments and are distributed evenly in the downslope parts of two salt mini basins the majority of the stacked pockmarks initiated synchronously in the late pliocene 3 ma with a subordinate initiation phase in the mid pliocene 4 ma the primary agents in pockmark formation are interpreted to be pore water expelled during early stage compaction together with biogenic methane bottom simulating reflections bsrs associated with free gas overlain by gas hydrates are currently found in the area it is speculated that biogenic methane accumulated within and below a clathrate cap which was repeatedly breached forming pockmarks at discrete horizons separated by intervals of draping sedimentation the mid and late pliocene pockmark initiations appear to coincide with sea level falls following periods of relatively stable highstand conditions several subsequent pockmark horizons may similarly correlate with subsequent sea level falls during the late pliocene and early pleistocene the stacked paleopockmarks are completely surrounded by polygonal faults and consistently occur within polygonal fault cells that crosscut the succession containing the stacked pockmarks early stage compaction and dewatering of the pliocene sediments thus preceded polygonal faulting providing a constraint on the conditions leading to polygonal faulting of the fine grained host sediments the relationship documented here is interpreted as due to the presence of a hydrate cap in the plio pleistocene mini basins which may have retarded the normal compaction processes and facilitated pockmark formation by allowing the build up of gas hydrate and free gas in the basin centres the relative timing and spatial relationships implies that fluids expelled due to polygonal faulting were not implicated in pockmark formation in this area

paleoenvironmental reconstruction of the lower mogi guacu river basin sao paulo state brazil morphopedosedimentary records and fluvial processes abstract the mogi guacu river rises in bom repouso minas gerais state brazil in the mantiqueira ridge and flows into the rio pardo river at an elevation of 483 m in pontal sao paulo state brazil after running a 530 km long course especially along the lower mogi guacu basin the river morphology is extremely sinuous characterized by intense processes of channel migration avulsion abandonment and reactivation of the channel producing an extensive alluvial plain composed of a series of associated relief forms and sedimentary facies among these forms point bar deposits by lateral accretion abandoned meanders paleo channels and fluvial terraces are notable features in this sense the objective of this work was to investigate whether these features could be linked to environmental changes to reach this goal soil properties of a catena of the jatai ecological station luiz antonio sao paulo state were analyzed in four sectors slope terrace i terrace ii and alluvial plain the results from grain size determination geochemical and isotopic studies dating paleopalynology coal fragments and micromorphology are presented in this paper from these analyses a paleo environmental evolution divided in three stages is proposed for the area 130 000 ybp upper pleistocene when the mogi guacu river base level was approximately 6 m above the present one a drier second phase 10 250 years bp lower holocene when an organic horizon was formed inside of an abandoned meander oxbow lake and a third phase 2096 ybp upper holocene of reactivation of a warm and humid climate that promoted the development of a two meters thick typic udifluvent in a sector where the mogi guacu river no more floods due to the incision of its thalweg reaching more than six meters depth in the last 130 000 years bp thus this paper used a fluvial geomorphologic approach and its interplay with climate to understand how the landscape was shaped from upper pleistocene to holocene however neotectonics might have played a relevant role as well not only in the mogi guacu river basin but also in the parana sedimentary basin

vegetation dynamics during the late pleistocene in the barreirinhas region maranhao state northeastern brazil based on carbon isotopes in soil organic matter abstract the study place is in the barreirinhas region maranhao state northeastern brazil a vegetation transect of 78 km was studied among four vegetation types restinga coastal vegetation cerrado woody savanna cerradao dense woody savanna and forest as well as three forested sites around lagoa do caco located approximately 10 km of the transect soil profiles in this transect were sampled for 13c analysis as well as buried charcoal fragments were used for 14c dating the data interpretation indicated that approximately between 15 000 and 9000 14c yr b p arboreal vegetation prevailed in the whole transect probably due to the presence of a humid climate approximately between 9000 and 4000 3000 14c yr b p there was the expansion of the savanna probably related to the presence of drier climate from 4000 3000 14c yr b p to the present the results indicated an increase in the arboreal density in the area due to the return to a more humid and probably similar climate to the present the presence of buried charcoal fragments in several soil depths suggested the occurrence of palaeofires during the holocene the vegetation dynamic inferred in this study for northeastern brazil is in agreement with the results obtained in areas of amazon region based on pollen analysis of lake sediments and carbon isotope analysis of soil organic matter som implying than similar climatic conditions have affected these areas during the late pleistocene until the present

use of micromorphology for palaeoenvironmental interpretation of complex alluvial palaeosols an example from the mill creek formation albian southwestern alberta canada abstract field observations are often not sufficient for process based interpretations of palaeosols particularly where they form parts of thick aggradational pedocomplexes within alluvial successions under such conditions micromorphology provides genetic temporal and spatial information on soil forming processes that is critical to an understanding of past environmental conditions thick alluvial successions of the albian mill creek formation contain abundant evidence of pedogenesis but few well developed palaeosol profiles and therefore provide an ideal case study in which to demonstrate the usefulness of micromorphological data for palaeoenvironmental interpretation the micromorphological features of greatest interpretive value are types of clay coatings and ferruginous segregations structure and fabric papules evidence of bioactivity and ferruginous concretions provide information on geomorphic surface stability and assist in reconstructing temporal changes in drainage conditions while individual features can provide some palaeoenvironmental information the relationships of features to one another and assemblages of features provides additional information when analysed hierarchically to establish a sequence of sedimentologic and pedogenic events a common recurring sequence of palaeoenvironmental events subject to local variations can be recognized throughout the mill creek formation the presence of illuvial clay requires that water percolated through the soil and that the soil periodically dried out so that the translocated clay was retained dark reddish clay coatings indicate clay illuviation under freely drained conditions while pale yellow and silty clay coatings suggest that phases of free drainage alternated with phases of poorly drained or saturated soil conditions the presence of iron depletion coatings iron nodules and quasiferrans indicates that these units were at least periodically saturated and the occurrence of multiple overlapping phases within single thin sections demonstrates that redox conditions fluctuated strongly suggesting development in the vadose zone recent soils containing similar assemblages of features develop under warm temperate seasonal climates alternating phases of well drained and saturated conditions on the mill creek floodplains are attributed to changing sediment supply and local palaeogeomorphology rather than to any major regional climate change this type of process based micromorphological analysis should have broad application in other complex pedogenically modified alluvial successions and similar studies would lead to a more detailed understanding of ancient palaeoenvironments

independent active microplate tectonics of northeast asia from gps velocities and block modeling 1 independent okhotsk and amurian microplate motions are tested using velocities from 123 gps sites 80 from within the proposed okh and amu plate boundaries used to constrain the plate kinematics of northeast asia a block modeling approach is used to incorporate both rigid block rotation and near boundary elastic strain accumulation effects in a formal inversion of the gps velocities models include scenarios with and without independent okh and amu plate motion our modeling favors scenarios with independent okh and amu motion based on the application of f test statistics the independent okh plate rotates 0 231 deg myr clockwise with respect to north america about a pole located north of sakhalin the modeled amu plate rotates 0 298 deg myr counterclockwise with respect to nam about a pole located west of the magadan region the plate motion parameters of the independent plates are consistent with the kinematics inferred from earthquake focal mechanism solutions along their boundaries

strain partitioning across a subduction thrust fault near the deformation front of the hikurangi subduction margin new zealand a magnetic fabric study on iodp expedition 375 site u1518 abstract understanding the distribution of strain along thrust and splay faults in active accretionary systems is crucial to understand the mechanical properties of the sediments and the strength of the fault zone and its slip behavior this paper investigates the distribution of strain through sediment compaction and texture development across the p paku fault a major splay fault near the deformation front of the hikurangi subduction margin new zealand using the anisotropy of magnetic susceptibility technique ams international ocean discovery program site u1518 penetrated hanging wall fault zone and footwall sequences to a maximum depth of 484 9 meters below seafloor a total of 330 discrete samples was subjected to ams measurements and magnetic remanence data used to reconstruct the axial orientation of each sample in a geographic reference frame the ams display distinct fabric differences between hanging wall through the fault zone and footwall domains demonstrating that strain is partitioned across the fault zone hanging wall sequences show a strike parallel northeasterly lineation of kmax and weakly prolate shapes typical for a component of northeast southwest lateral shortening in contrast footwall sequences are more oblate and show a clustering of kmax in northerly direction this demonstrates that strain in the footwall is dominated by gravitational loading however a component of sub horizontal east westerly strain parallel to the convergence direction of the pacific plate exists strain decoupling between hanging and footwall sequences occurs near the top of the p paku fault zone differences in the degree of magnetic susceptibility between footwall sediments incorporated into the fault zone and the underlying undeformed footwall sequences are indicative for the progressive dewatering of the underconsolidated footwall sequences

how fast are soil forming processes in quaternary sediments of a tropical floodplain a case study in southeast brazil abstract floodplains are depositional features of a channel valley associated with a specific climatic and hydrologic regime of a drainage basin in tropical conditions sediments can be quickly weathered by soil forming processes and tend to obliterate pre existing sedimentary structures therefore the objective of many studies on floodplains is to identify and discuss such sedimentary features mostly those related to the morphology of channel deposits additionally a qualitative approach to identify aspects of pedological evolution in these environments has been attempted in few studies the purpose of this study was to interpret the intensity and the time of alluvial sediment weathering by pedogenetic processes in tropical humid conditions soil profiles were analyzed in different environments of deposition in the pardo river floodplain southeast brazil by accounting for sedimentary facies and pedological features supported by multi proxy data provided from geochemistry macro and micromorphology grain size total carbon total nitrogen 13 c isotopic analysis and 14 c osl optically stimulated luminescence dating based on the results we identified that pedogenetic features and soil horizon distributions were closely related to sediment architecture grain size and position in the floodplain in the pardo floodplain fluvic gleysols loamic and clayic with moderately to strongly developed structures were identified in overbank fine sediments fluvic cambisols clayic were found in abandoned paleomeanders fluvic cambisols loamic in sandy scrollbars gleyic acrisols clayic cutanic differentic in channel deposits which presented a 130 cm thick bt horizon with illuvial clay coatings and histosols fluvic with high contents of total carbon 11 9 and 26 8 in histic horizons in small scale avulsive systems deposits were dated to between 35 000 and 700 years bp 13 c isotopic data revealed a trend toward enriched values in older samples 14 21 in which c 4 plants dominated and a relative impoverishment of the values in more recent samples 26 9 to 27 9 this result was consistent with the tendency of the distribution of c 3 plants to increase over that of c 4 plants favored by the warmer and wetter climate since the upper holocene in this study a fluvic gleysol profile of

growth fault rollover systems birth growth and decay growth fault rollover systems are extremely common structures of thin skinned extensional systems resulting from gravity gliding above salt their development is studied using laboratory experiments based on brittle ductile models where the sedimentary cover and synkinematic sediments are simulated using brittle sand and the underlying decollement layer by viscous silicone putty the experiments are compared to natural examples from seismic lines the experimental results are used to present the evolution of growth fault rollover systems these being the result of a finite amplitude instability with three distinct stages birth growth and decay each of these stages is identified with typical structures which can be recognized on seismic sections a discussion is presented on the interactions in time and space between synthetic and antithetic listric faults parallel and transverse to the direction of displacement

evolution of an ancient coastal plain palaeosols interfluves and alluvial architecture in a sequence stratigraphic framework cenomanian dunvegan formation ne british columbia canada to date discussion of changes in alluvial style and in the character of palaeosols in relation to changes in accommodation and sediment supply on floodplains has primarily been from a conceptual standpoint few case studies are available against which to test ideas one hundred and thirty metres of non marine strata of the dunvegan formation were examined in 14 closely spaced sections in the canyon of the kiskatinaw river ne british columbia canada this site was located about 120 km inland from the transgressive limit of the contemporary marine shoreline and represents almost exclusively freshwater environments fluvial channels in the kiskatinaw river section are of two types small single storey very fine to fine grained sandstone ribbons with w t ratios 30 are interpreted as the deposits of meandering rivers filling incised valleys interchannel facies include the deposits of crevasse channels and splays lakes floodplains and palaeosols floodplain palaeosols consist of laterally heterogeneous simple palaeosol profiles and pedocomplexes similar to modern entisols inceptisols and hydromorphic soils interfluve sequence bounding palaeosols adjacent to incised valleys are laterally continuous up to 3 m thick and can be reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure colour degree of rooting and 3 micromorphological features such as evidence of bioturbation clay coatings ferruginous features and sphaerosiderite interfluve palaeosols are similar to modern alfisols and ultisols correlation of the local stratigraphic succession with the regional sequence stratigraphic framework based on 2340 well logs and 60 outcrop sections shows that the vertical changes in coastal plain character more coals and lakes vs more pedogenesis can be related to relatively high frequency base level cycles eustatic that are expressed as transgressive regressive marine cycles in downdip areas regional isopach maps show that these cycles were progressively overprinted and modified by an increasing rate of tectonic subsidence in the north and west the character of palaeosols developed on aggrading floodplains primarily reflects local sediment supply and drainage in contrast well developed interfluve palaeosols record pedogenesis during periods of reduced or negative accommodation base level fall vertical changes in floodplain palaeoenvironments and palaeosol types reflect changes in accommodation rate the detailed micromorphological analysis of interfluve palaeosols represents a powerful application of an under used technique for the recognition of key surfaces in the geological record this has broad implications for non marine sequence stratigraphy

magnetic fabric and weak deformation in sandstones of accretionary prisms of the flysch and klippen belts of the western carpathians mostly offscraping indicated abstract the magnetic fabric of sandstones in thrust sheets of the flysch belt of the western carpathians is basically sedimentary in origin in minority of specimens slightly affected by deformation which is generally very weak corresponding to the earliest deformation stage and to types i ii in terms of the magnetic fabric classification of the accretionary prisms by pares et al 1999 and aubourg et al 2004 respectively this indicates an absence of the return flow during the subduction process the deformation is weaker in the thrust sheets located at the margins of the flysch belt the danice and silesian thrust sheets in the west and the bile karpaty and oravska magura thrust sheets in the east than in the fore magura raca and bystrica thrust sheets located in the centre of the flysch belt in the danice and silesian thrust sheets the weak deformation reflects their sedimentation on the northern european slope of the flysch belt basin and relatively short transport during their thrusting over the foredeep in the bile karpaty and oravska magura thrust sheets that are located near the subduction zone the weak deformation is explained by assuming early offscraping and frontal accreting of these thrust sheets in the pieniny klippen belt the deformation of the palaeogene sandstones peri klippen palaeogene is stronger than that in the marginal thrust sheets danice silesian bile karpaty and oravska magura thrust sheets of the flysch belt but weaker than that in the central thrust sheets fore magura raca and bystrica thrust sheets of the flysch belt this is in an apparent contradiction with strong macroscopic deformation of mesozoic rocks of the pieniny klippen belt but understandable realizing that the sediments of the peri klippen palaeogene were deformed only during the neoalpine orogenies in palaeogene and neogene after the main deformation late cretaceous in the pieniny klippen belt

deformation and fluid pressure variation during initiation and evolution of the plate boundary decollement zone in the nankai accretionary prism 1 the plate boundary decollement zone in the muroto region of the nankai accretionary prism records deformation and consolidation histories that have been affected by temporal changes in fluid pressure microstructural observations and chemical analysis demonstrate that the decollement zone initiated in an interval of porous clayey sediments characterized by cementation due to intergranular bonding of authigenic clays crosscutting relations of microstructures indicate that the decollement zone records two compactive deformations the early compactive deformation involved destruction of porous cemented structure probably caused by fluid pressure fluctuation the late compactive deformation was characterized by clay particle rotation and porosity collapse along the sets of slip surfaces resulting in zones of preferred orientation of clay particles these compactive deformations led to significantly higher bulk densities within the decollement zone compared to the compaction trend of the overlying prism sediments elevated fluid pressure following compactive deformations induced an overconsolidated state within the decollement zone with fluid filled dilatant fractures bulk density abruptly decreases at the top of the underthrust sediments but there is no microstructural evidence for cementation fluids in the dilated fractures and underconsolidated underthrust sediments are potential sources for the elevated fluid pressure in and below the decollement zone resulting in mechanical decoupling of the accretionary prism from underthrust sediments the fault fluid interactions in the muroto region may be applicable to other convergent plate margins where high temperature associated with the subduction of a spreading ridge or hot young oceanic crust enhances diagenesis and cementation

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

dynamic interactions between the gulf of guinea passive margin and the congo river drainage basin 1 morphology and mass balance 1 a sediment budget between the congo river drainage basin and the western african margin in the gulf of guinea is proposed on the basis of published and unpublished offshore tertiary isopach maps and onshore digital elevation analysis the overall denudation of that area may be as high as 3 5 106 km3 with a maximum of 10 coming from mesozoic and cenozoic covers the southern part of the congo river basin related to uplift of the south african and kalahari shields appears as the most immature from the morphologic standpoint but provides one third of the present day sediment production it represents a maximum denudation of 150 000 km3 on the easternmost part east african rift drainage basins show a more mature relief and a maximum denudation of 270 000 km3 which can increase to 570 000 km3 if the congo drainage basin had extended up to the east branch of the rift these values are confidently established from the existence of remnant geological surfaces and can explain the volume of tertiary sediment in the gulf of guinea during upper cretaceous the most important accumulations of sediments correspond to the ogooe and kwanza fans which shows that the organization of continental drainage was different as was potential source of sediments in the northern part of the present day congo river drainage basin there was a compressional episode during santonian that may have caused significant relief and erosion along a benue chad axis

melange and its seismogenic roof decollement a plate boundary fault rock in the subduction zone an example from the shimanto belt japan 1 the mugi melange located in western shikoku of the shimanto belt shows systematic y p deformation fabrics formed by microshear and pressure solution that penetrate throughout the melange pile magnetic susceptibility ellipsoids obtained from the anisotropy of magnetic susceptibility ams are highly oblate maximum and minimum axes of the ellipsoids are consistent with the shear orientation of the melange and the mean pole of p surfaces respectively this agreement suggests that the mugi melange was formed as a result of underthrusting of trench filling sediment vitrinite reflectance ranges from 2 52 to 3 08 which corresponds to a maximum paleotemperature of 180 200 c pseudotachylyte evidence of a seismogenic slip was found in the upper boundary roof fault of the mugi melange however there is not a thermal gap between the melange and the overlying coherent piles and the temperature from vitrinite reflectance gradually rises downward from the coherent piles to the melange beyond the boundary fault which suggests that paleoisotherms parallel the boundary fault orientation the isotherms in the seismogenic zone are estimated as subparallel to the plate boundary decollement therefore the setting of the cataclastic boundary fault which includes pseudotachylyte appears to be a major plate boundary thrust or a subhorizontal splay fault a probable geologic setting that accounts for the mugi melange and the seismogenic roof fault is partitioning of the slip along the plate boundary fault in space and time interseismic slip in the melange and seismic slip along the roof fault

morphology and weathering trends of the sangamon soil complex in south central indiana in relation to paleodrainage abstract three paleodrainage groups are proposed for profiles of the farmdale sangamon soil complex in south central indiana the groups good intermediate and poor are differentiated on the basis of matrix colors and color patterns genetic support for the groupings is provided by morphological trends still evident following 100 000 yr of pedogenesis and burial by late wisconsinan loess depth of carbonate leaching solum thickness and argillic horizon thickness all decrease with poorer drainage clay mineralogy also reflects paleodrainage illite degradation is intense in all profiles but profiles with good drainage have poorly crystalline interstratified expandable minerals while well crystalline smectites dominate in profiles with poor drainage remanent aggregation in former a horizons is stronger in more poorly drained profiles while the effects of structural overprinting from the modern soil increase with better modern drainage soil morphology mineralogy and parent material paleolandscape position of sangamon profiles are all internally consistent with color development under soil hydrological conditions during the last interglacial to glacial transition the occurrence frequency of each drainage group indicates that the sangamon soilscape was better drained than now and morphology and clay mineral evidence suggests that areas with poor drainage did not experience the extreme seasonal groundwater shifts that the modern landscape experiences

african oil past present and future eighty three sedimentary basins cover 50 of africa s 11 7 million square miles hydrocarbons are produced from 20 of these basins and a further 13 have non produced hydrocarbons yet of all the basins only 18 have been explored through a semi mature stage this paper presents a simplified classification of basins in africa africa s recoverable hydrocarbon reserves of 100 billion barrels of oil equivalent account for 7 of the world s total proven reserves this paper documents that reserve base s development through time together with the significant discoveries oil and gas occurrences and the play potential of each basin type are systematically described with examples demonstrating exploration problems regarding particular basins africa contains an abundance of unexplored sedimentary basins that should demonstrate relatively high success ratios but which must be evaluated with some caution because of political fiscal and logistical concerns end page 339

geological controls on focused fluid flow associated with seafloor seeps in the lower congo basin a synthesis of backscatter imagery coupled with a large 3d seismic dataset in the lower congo basin lcb reveals a patchy distribution of features interpreted to be associated with fluid seepage from 300 m to 2500 m water depth with the exception of one region of anomalous backscatter positive relief mounds all inferred seep sites occur in negative relief pockmarks the extensive 3d seismic dataset in the lcb offers a unique opportunity to study the plumbing system that is feeding surface cold seep systems and in general to reconstruct the relationship between tectonics and fluid flow in continental margins the fluid seeps in the lcb are associated with morphologically stratigraphically or tectonically controlled focused fluid flow the integration of the geophysical datasets backscatter imagery coupled to 3d seismic clearly indicates that fluid seeps are not randomly distributed but their seabed organization reflects 1 the location of the underlying structure reservoir or trap where the fluids are coming from 2 the geometry and morphology of the reservoir trap and 3 the discontinuities in the sedimentary column along which fluids have migrated in the lcb seafloor pockmarks are always associated with underlying tectonic structures fault zones salt diapirs polygonal faults or buried sedimentary bodies turbiditic channels erosional surfaces whereas they never occur above sub horizontal parallel stratified fine grained sediments even if triggering processes can not be clearly defined here we propose a model of seafloor fluid seep organization which represents a new tool for identifying the geometry of flow pathways and the underlying buried bodies where the fluids are originating from this qualitative 3d model provides insight into the geohydrologic processes of continental margins

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part i meso and macro scopic scale there is considerable variability in the thickness structure and macroscopic deformation style within shale prone major thrust zones which also impacts the structural style in the overlying and sometimes the underlying section the properties and percentages of clay minerals and percentages of organic material quartz and calcite affect fault zone weakness and behaviour the distribution of competent units within a shale prone zone can also significantly affect fault zone architecture even over short strike distance of 10s to 100s of metres other influences include high pore fluid pressures and associated veins deformation of the fault zone may disrupt the original principal displacement zones and force them to relocate including switching lithologies calcite veins can become concentrated locally in the fault zone and become a focus of fault zone weakness we still need many more descriptions of shale prone fault zones to understand the potential variations in thrust sheet structural style caused by differences in shale detachment characteristics the variations in structural style in the hanging walls of shale detachments are broad and range between the sledge runner style in many appalachian examples and the extensive closely spaced imbricate style of the osen roa detachment southern norway such contrasts are related to several factors including thrust sheet mechanical stratigraphy thickness of the overburden lateral continuity of the detachment detachment mechanical properties composition pore fluid pressures presence absence of higher level detachments and strain rate in many structural locations and at many scales shale prone sequences will pile up to produce over thickened masses cleavage duplexes s c fabrics duplexes imbricates pseudo duplexes and vein formation can all contribute to the thickening at nested scales a mixture of brittle and solution diffusion processes overall cause the affected unit to exhibit flow like characteristics while the broad principles are now well established considerable work remains to be done understanding the full range of structural geometries associated with shale detachments what factors regarding the nature of the detachments affect overlying structural styles rates of deformation and the controls on deformation mechanisms within the thrust zones

pedogenesis of plinthite during early pliocene in the mediterranean environment case study of a buried paleosol at podere renieri central italy abstract a complex buried paleosol at podere renieri at montalcino central italy formed during a series of continental episodes within an interval of pliocene marine sediments from about 4 1 to 4 8 my bp the aim of this work was to document the kind of pedogenesis which occurred throughout this time and in particular the plinthite formation plinthite soft and hard is poor in organic carbon neutral or subalkaline dominated by illite and enriched in iron and chromium the main differences between soft and hard plinthite are attributed to soil structure which is absent in hard plinthite and to the abundance of iron depleted zones which are much larger in soft plinthite variations in mineralogy chemistry and genesis of soft and hard plinthite can be ascribed to the specific environment of plinthite formation close to the pliocene sea pedogenetic evidence indicates that plinthite evolved in a hot and humid paleoclimate showing a progressive increase in seasonality and that low grade plinthite formation occurred in a time span of a few hundred thousand years soils with low grade plinthite have agronomic value in their suitability for the production of high quality brunello di montalcino wine

reconnaissance study of the ancient zaire congo deep sea fan zaiango project analysis of more than 19 000 km of multichannel seismic reflection data from the zaiango project covering the zaire deep sea fan allowed us to identify the oceanic crust and five seismostratigraphic units on the basin floor and abyssal plain in the absence of a direct stratigraphic tie the time frame is provided by long distance correlations a stratigraphic model for the evolution of the zaire deep sea fan is proposed a widespread major regional unconformity representing probably the eocene oligocene transition marks a drastic change of sedimentation pattern in the basin floor a pelagic aggradational sequence albian eocene overlying the oceanic crust gives way to an onlapping prograding sequence of turbidite deposits oligocene recent this change marks the onset of the ancient zaire deep sea fan triggered by the climatic change related to the greenhouse icehouse shift at the eocene oligocene transition which was responsible for a drastic increase in continental erosion and terrigenous sedimentary supply to the margin the volume of the fan is at least 0 7 mkm 3 much broader and thicker than formerly assumed a short lived episode of rapid facies progradation

concept of equilibrium profile in deep water turbidite system effects of local physiographic changes on the nature of sedimentary process and the geometries of deposits

along arc structural variation of the plate boundary at the japan trench margin implication of interplate coupling 1 at the japan trench convergent margin many large interplate earthquakes of greater than m7 5 frequently occur their epicenters have uneven distribution mostly located in the northern area to investigate the relationship between this distribution and tectonic structures we have conducted multichannel seismic surveys since 1996 our data show two kinds of interplate sedimentary units a wedge shaped unit and a channel like unit both units have a lower p wave velocity than the basal part of the overriding island arc crust the wedge shaped unit having a velocity of 2 3 km s is widely distributed over the forearc region in the northern area its thickness decreases with depth becoming several hundred meters at a depth of 12 km the channel like unit having a velocity of 3 4 km s is observed in the southern area extending in the downdip direction its thickness reaches 2 km at a depth of 12 km if the low velocity of these units results from the existence of fluid as many authors assume the units being thick implies higher fluid content assuming constant porosity considering that fluid reduces basal friction and with an assumption that fluid available at a specific interface is proportional to the total fluid content in the sediment the thickness variation of the units would cause different degrees of coupling at the plate boundary along the arc this may provide one explanation for the regional disparity in the interplate earthquake occurrence in the margin furthermore we attempt to call attention to the possibility that the channel like sediment works as a shear stress releaser

pliocene shortening direction in nankai trough off kumano southwest japan sites iodp c0001 and c0002 expedition 315 anisotropy of magnetic susceptibility analysis for paleostress 1 integrated ocean drilling program expedition 315 recovered cores from accretionary units which are overlain by cover sequences at a site on the hanging wall of the mega splay fault c0001 and at a seaward margin of a forearc basin c0002 in nankai trough off kumano japan in order to investigate the amount and the style of deformation and shortening direction of the accretionary prism units anisotropy of magnetic susceptibility ams of cored samples were measured ams of the late pliocene to late miocene accretionary prism at c0001 reveals a deformed magnetic ellipsoid prolate type and a restored direction of the ams orientation indicates northwest southeast shortening which is the same as the present day stress field measured by borehole breakout the older miocene accretionary prism cored beneath the forearc basin at c0002 does not show a typical prolate type but more oblate feature in parallel to plunged bedding planes this type can be interpreted as an intermediate type between prolate and oblate types by indicatives of ams parameters which was formed under a bedding vertical loading and a relatively weakly lateral compaction the restored ams orientation of the accretionary prism beneath the forearc basin also indicates the northwest southeast shortening which is different from the present day principal horizontal stress orientations at c0002 it is supposed that the shortening direction had been recorded in pliocene time probably when the sequence was sited in the outer wedge the northwest southeast directions of ams in the pliocene time agree with the past subducting direction of the philippine sea plate since the pliocene

stress state in the largest displacement area of the 2011 tohoku oki earthquake the 2011 moment magnitude 9 0 tohoku oki earthquake produced a maximum coseismic slip of more than 50 meters near the japan trench which could result in a completely reduced stress state in the region we tested this hypothesis by determining the in situ stress state of the frontal prism from boreholes drilled by the integrated ocean drilling program approximately 1 year after the earthquake and by inferring the pre earthquake stress state on the basis of the horizontal stress orientations and magnitudes estimated from borehole breakouts and the increase in coseismic displacement during propagation of the rupture to the trench axis in situ horizontal stress decreased during the earthquake the stress change suggests an active slip of the frontal plate interface which is consistent with coseismic fault weakening and a nearly total stress drop

holocene paleosols of the upo wetland korea their implications for wetland formation abstract a 4 490 m long core up 1 was recovered from the marginal part of the upo wetland the wetland is a typical riverine wetland in korea and has been designated as a protected wetland in accordance with the international ramsar treaty we studied the holocene environmental changes of the upo wetland and the depositional conditions under which the upo wetland formed the core is divided into four units on the basis of grain size distribution abundance of mottles and vertical color variation unit 1 has undergone pedogenic processes resulting in variably weak to moderate soil profile development unit 1 paleosols are regarded as synsedimentary soils of floodplain origin and the radiocarbon data suggest that the whole paleosol profile spans the last 5790 years the boundaries between the soil horizons are not clear cut probably due to a repeated cycle of accumulation denudation and soil forming processes the recurrence of these processes initiated the development of the upo wetland the lower boundary of unit 2 lies at about 2300 14c yr bp the beginning of the subatlantic age in korea the lack of intense soil formation and abundant clay content in unit 2 indicate that the geomorphologically stable wetland was developed around the coring site at that time this means that the depositional environment changed from a floodplain to a stable continuously submerging wetland setting an abrupt change in sediment textures was detected in unit 3 which commenced formation around 1000 900 14c yr bp indicative of geological events such as inundations or inflows of slope wash sediments anthropogenic deforestation and plowing around the upo wetland area might have started at that time

broad weak regions of the nankai megathrust and implications for shallow coseismic slip abstract deep within the nankai trough subduction zone the plate boundary thrust slips along a well imaged megasplay fault system during the megathrust earthquakes that regularly strike southwest japan the routing of the active plate boundary thrust along an upward branching splay fault causes deep underthrusting of an unusually thick section of material attached to the subducting ocean crust here we present three dimensional seismic reflection data that shows this unusually thick section is fluid rich sediment that results in broad weakly coupled regions of the megathrust down into the updip end of the seismogenic zone the weakly coupled regions lie above an underthrust low seismic impedance presumed to be low velocity and low density sediment section that is between one and two kilometers thick and covers 3300 km2 at least one eighth of the total rupture area of the 1944 mw 8 1 tonankai earthquake this underthrust sediment section is broader and much deeper than inferred at other margins sediment underthrusting into the normally well coupled seismogenic zone likely releases fluids and elevates fluid pressure which reduces inter plate coupling along portions of the megasplay fault and allows coseismic rupture to propagate to unusually shallow depths and generate large tsunami as inferred for the 1944 tonankai event splay faults may be a common yet transient mechanism for developing weak subduction zone thrusts

strain decoupling across the decollement of the barbados accretionary prism the interrelation between deformation styles and behavior of fluids in accretionary prisms is under debate particularly the possibility that overpressuring within the basal decollement may enable mechanical decoupling of the prism from the subducting material anisotropy of magnetic susceptibility ams data from sediments spanning the basal decollement of the barbados accretionary prism show a striking progression across this structure that strongly supports the hypothesis that it is markedly overpressured in the accretionary prism above the decollement the minimum ams axes are subhorizontal and oriented nearly east west whereas the maximum ams axes are oriented nearly north south and shallowly inclined at the top of the decollement the minimum ams axes orientations abruptly change to nearly vertical this orientation is maintained throughout the decollement and in the underthrust sediments below the ams orientations in the prism sediments above the decollement are consistent with lateral shortening due to regional tectonic stress as the minimum axes generally parallel the convergence vector of the subducting south american plate and the maximum axes are trench parallel because the orientations of the ams axes in deformed sediments usually parallel the orientations of the principal strains the ams results indicate that the incremental strain state in the barbados prism is one dominated by subhorizontal shortening in contrast the ams axes within and below the decollement are consistent with a strain state dominated by vertical shortening compaction this abrupt change in ams orientations at the top of the decollement at site 948 is a direct manifestation of mechanical decoupling of the off scraped prism sediments from the underthrust sediments the decoupling horizon occurs at the top of the decollement zone coinciding with the location of flowing high pressure fluids

compositional and fluid pressure controls on the state of stress on the nankai subduction thrust a weak plate boundary abstract we show that both fault mineralogy and regional excess fluid pressure contribute to low resolved shear stresses on the nankai subduction plate boundary off southwest japan ring and direct shear tests indicate that saturated clay minerals in the fault possess intrinsically low residual friction coefficients r at stress levels between 1 0 and 40 mpa the direct shear r values for purified smectite are 0 14 0 02 for illite 0 25 0 01 and for chlorite 0 26 0 02 for point load velocities of 0 0001 mm s these clay minerals dominate the nankai subduction decollement zone illite plus quartz is mechanically important in the altered incoming muroto section and the predicted decollement r should lie between 0 2 and 0 32 this low residual strength together with elevated fluid pressure limits shear stresses to below 4 mpa within the frontal 50 km of the subduction system consistent with the low wedge taper in this region a higher wedge taper off the ashizuri peninsula indicates basal shear stresses rise slightly along strike towards this region our analysis indicates lower fluid pressures must predominantly be responsible because only small second order along strike variations in r are predicted to occur as a result of variations in smectite and total clay content these variations should be further reduced at depth under the wedge as smectite is diagenetically altered to illite however our data suggest the low r values of the clay rich decollement still limit shear stresses to between 17 and 29 mpa within the frontal 50 km of the wedge consistent with other estimates of plate boundary weakness indeed we propose that it should be expected that subduction plate boundaries like nankai will be weak because of the intrinsic presence of clay rich faults and moderate fluid overpressures our data do not support the hypothesis that the smectite to illite reaction directly controls the onset of seismogenic behavior deep in the nankai system because there is already a mechanical dominance of illite rather than smectite in the shallow decollement zone and we find all the clay phases tend to velocity strengthen however temperature activated clay diagenesis and dehydration may cause secondary changes in the fault properties and state of stress across the up dip limit of the seismogenic zone

excursus on gravity gliding and gravity spreading abstract the terms gravity gliding and gravity spreading have long been used to describe deformation driven by gravity alone however the traditional definitions of these terms cannot be applied unambiguously in many situations the primary difficulties arise because rocks are not ideally rigid detachment surfaces may not be planar substrates may be deformable and rock bodies do not deform in isolation the term gravity spreading is still useful if it is simply defined as gravity driven lateral extension and vertical contraction regardless of basal slope and coherence of the body i suggest that the term gravity gliding should be used rarely and only if the defining characteristics are clearly stated and understood in most cases more detailed descriptions should be used instead of or in addition to either of these terms to capture the behavior of rock masses deforming under gravity

magnetic fabric development in the tertiary accretionary complex in the boso and miura peninsulas of central japan it has been demonstrated that the anisotropy of magnetic susceptibility ams is a sensitive indicator for distinguishing various processes that had acted during and after the deposition of sediments recently much attention has been focused on proving its usefulness in distinguishing early deformation signatures in sediments which show no visible grain scale deformation here we present the ams results of the neogene miura group of central japan which was formed by arc arc collision tectonics with subdivisions of two contrasting tectonic provinces the southern province a highly deformed accretionary prism and slope basin and the northern province a gently deformed forearc basin samples were collected from 21 sites in both tectonic settings we obtained from axes orientations three typical fabric domains considered to represent sedimentary tectonically deformed and their intermediate types the shape parameters of ams also revealed distinctions clearly sedimentary fabrics are more foliated and anisotropic deformed fabrics show a more prolate shape and are closer to being isotropic the sedimentary fabrics predominate in the northern forearc basin sequence whereas the intermediate and deformed fabrics occur predominantly in the southern province the general trend of the shape of the magnetic fabric in studied sediments reveals a clear evolution in the pattern of the isotropic tectonic fabric constructed from foliated sedimentary fabric

constraining uplift and denudation of west african continental margin by inversion of stacking velocity data an inverse model has been developed to determine the magnitude of denudation at seabed and subsurface unconformities by using root mean square rms stacking velocity data derived from processing a set of seismic reflection profiles this approach provides superior spatial coverage in comparison to other methods such as vitrinite reflectance apatite fission track and sonic velocity modeling which are restricted to borehole locations the model assumes exponential porosity decay with depth and a standard velocity porosity relationship in order to compute a synthetic rms velocity profile denudation values at two levels in the stratigraphy are then adjusted until the fit between the model and the data is optimized successful modeling is dependent upon independent estimates of the initial porosity of sediment since significant trade off occurs between initial porosity and denudation application to the west african shelf shows that 0 5 1 km of denudation occurred along the entire margin probably during late neogene times the amount of denudation decreases oceanward and was probably triggered by regional tilting associated with initiation and or regeneration of continent wide mantle convective upwelling which is thought to have affected much of subequatorial africa a subsurface oligocene unconformity represents as much as 2 5 km of denudation and was probably produced by initiation of an oceanic current

overcoming pitfalls of vitrinite reflectance measurements in the assessment of thermal maturity the case history of the lower congo basin abstract vitrinite reflectance has been always considered the most reliable thermal maturity indicator in sedimentary basins nevertheless the reliability of vitrinite reflectance measurements can be affected by many external factors that change from basin to basin e g organic facies temperature and pressure conditions leading to wide uncertainties in thermal modelling calibration and thus in the evaluation of timing and amount of hydrocarbons generation we demonstrate that in case of vitrinite suppression and or retardation in siliciclastic successions the classical sweeney and burnham kinetics do not match the actual thermal evolution of the basin in these cases thermal evolution can be successfully modelled using a complementary approach based on smectite illitization kinetics or more appropriate kinetics e g presro tm and t p ro to evaluate the effect of pressure on organic matter maturation where pressure data are available this approach was applied in the lower congo basin where 32 cuttings from a 5 km deep well drilled in the upper oligocene miocene malembo formation have been analysed to derive organic and inorganic constraints to model the basin thermal evolution vitrinite and bitumen reflectance measurements show values between 0 3 and 1 0 along the well whilst the illite content of mixed layer i s ranges between 35 and 88 passing from r0 to r1 to r3 stacking order with increasing depth present day temperature distribution through the well indicates a geothermal gradient of about 40 c km and measured pressures show an overpressured interval between 3 and 4 km depth retardation and suppression phenomena affected vitrinite reflectance in this interval but did not influence smectite illitization the comparison between thermal maturity scenarios constrained by organic and inorganic thermal indicators shows differences in the calculation of the depth of the onset of hydrocarbon generation that is overestimated of about 500 m in the lower miocene interval when only suppressed retarded vitrinite reflectance values are used to calibrate models

flow processes and sedimentation in unidirectionally migrating deep water channels from a three dimensional seismic perspective three dimensional seismic data were used to infer how bottom currents control unidirectional channel migration bottom currents flowing towards the steep bank would deflect the upper part of sediment gravity flows at an orientation of 1 degrees to 11 degrees to the steep bank yielding a helical flow circulation consisting of a faster near surface flow towards the steep bank and a slower basal return flow towards the gentle bank this helical flow model is evidenced by the occurrence of bigger muddier suggested by low amplitude seismic reflections lateral accretion deposits and gentle channel wall with downlap terminations on the gentle bank and by smaller sandier indicated by high amplitude seismic reflectors channel fills and steep channel walls with truncation terminations on the steep bank this helical flow circulation promotes asymmetrical depositional patterns with dipping accretion sets restricted to the gentle bank which restricts the development of sinuosity and yields unidirectional channel migration these results aid in obtaining a complete picture of flow processes and sedimentation in submarine channels