stress magnitude and orientation in the potiguar basin brazil implications on faulting style and reactivation 1 we analyzed borehole breakout data and drilling induced tensile fractures derived from resistivity image logs run at 10 oil wells to derive the orientation of the maximum horizontal stress shmax from the potiguar basin in the continental margin of brazil stress magnitudes are derived from density logs for the vertical stress mini frac tests for the minimum horizontal stress shmin and rock strength laboratory analysis to estimate the shmax magnitudes we compared these results with the stress regime and shmax orientation derived from nine earthquake series located in the crystalline basement where seismicity is concentrated and previous breakout data from the basin in the basin the shmax gradient is 20 0 mpa km and the shmax shmin ratio is 1 154 indicating a normal tectonic stress regime from 0 5 to 2 0 km whereas the shmax gradient of 24 5 mpa km and shmax shmin ratio of 1 396 indicate a transition from a normal to strike slip stress regime at 2 5 to 4 0 km the deeper stress regime in the basin is similar to that in the basement at 1 12 km depth this transition of the tectonic stress regime is consistent with an incipient tectonic inversion in the basin we note that the shmax orientation rotates from nw se in the western part of the potiguar basin to e w in its central and eastern parts roughly following the shoreline geometry indicating that local features such as flexural stresses influence the local scale 100 km stress pattern we also conclude that the basement is critically stressed but not the basin

the present day stress field of australia abstract the unusual present day crustal stress pattern of the australian continent has been the subject of scientific debate for over 25 years the orientation of maximum horizontal present day stress s hmax in continental australia is unlike all other major tectonic plates in that the stress pattern shows regional variability and it is not oriented sub parallel to the direction of absolute plate motion previous studies on the stress pattern of australia revealed that the complex stress pattern of the continent is controlled at a first order by the superposition of plate tectonic forces exerted at the plate boundaries however prior analysis of the contemporary australian crustal stress pattern have been unable to model or explain the stress pattern observed in most of eastern australia and has not extensively addressed the numerous smaller scale variations in stress orientation the recent development of unconventional reservoirs in australia has resulted in a greatly increased amount of new data for stress analysis in previously unstudied or poorly constrained areas in eastern australia in addition stress analysis in conventional hydrocarbon mineral and geothermal exploration in all other parts of the continent provides the opportunity to review and update the australian stress map asm this study presents the new release of the asm with a total of 2150 stress data records in australia increased from 594 data records in 2003 the 2016 asm contains 1359 data records determined from the interpretation of drilling related stress indicators 650 from earthquake focal mechanism solutions 139 from shallow engineering measurements and two from geological indicators the results reveal four distinct regional trends for the s hmax orientation in australia including a nne ssw s hmax trend in northern and northwestern australia which rotates to a prevailing e w orientation in most western and south australia the orientation of s hmax in eastern australia is primarily ene wsw and swings to nw se in southeastern australia a comparison between the new asm database and neotectonic features further confirms the role of contemporary stress in recent deformation of the australian crust the 2016 asm reveals significant discrepancies between newly observed s hmax orientations and predictions by published geomechanical numerical models for the australian continent forces generated at the boundary of indo australian plate remain the major control on the regional crustal stress pattern in continental australia however the increased data density particularly in eastern australia reveals numerous local perturbations of the stress field that were not previously clearly captured hence the key findings of the new release are that local intra plate stress sources are more significant than previously recognized particularly in eastern australian basins and cause substantial local scale rotations of the present day crustal stress pattern that have not been factored into existing australian stress models

contribution of grain size and compositional data from the bengal fan sediment to the understanding of toba volcanic event abstract toba tephra layers in cores from the bengal fan have been studied to characterize their granulometric mineralogic and geochemical features the layers are silt sized sediments with no significant non volcanic contamination the samples are very homogeneous glass shards have moderate hydration about 6 water a calc alkaline character and a rhyolitic composition the major and trace element compositions indicate an orogenic affinity and coincide with literature data for the youngest toba tephra level ytt 75 ka x ray diffraction xrd data indicate that the glass is the dominant phase with minor feldspar biotite and quartz the grain size analyses of the beds show discontinuous vertical variation and no linear trends from south to north over about 1500 km the vertical granulometric gap of the layers probably represents a single pyroclastic emplacement unit subjected to pre depositional particle aggregation

eruptive history of earth s largest quaternary caldera toba indonesia clarified single grain laser fusion sup 40 ar sup 39 ar analyses of individual sanidine phenocrysts from the two youngest toba indonesia tuffs yield mean ages of 73 plus minus 4 and 501 plus minus 5 ka in addition glass shards from toba ash deposited in malaysia were dated at 68 plus minus 7 ka by the isothermal plateau fission track technique these new determinations in conjunction with previous ages for the two oldest tuffs at toba establish the chronology of four eruptive events from the toba caldera complex over the past 1 2 m y ash flow tuffs were erupted from the complex every 0 34 to 0 43 m y culminating with the enormous 2500 3000 km sup 3 youngest toba tuff eruption caldera formation and subsequent resurgence of samosir island timing of this last eruption at toba is coincident with the early wisconsin glacial advance the high precision sup 40 ar sup 39 ar age eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exceptionally large explosive eruptions

geochemical variability in distal and proximal glass from the youngest toba tuff eruption the youngest toba tuff ytt erupted at ca 74 ka is a distinctive and widespread tephra marker across south and southeast asia the climatic human and environmental consequences of the ytt eruption are widely debated although a considerable body of geochemical data is available for this unit there has not been a systematic study of the variability of the ash geochemistry intrinsic magmatic and extrinsic post depositional chemical variations bring fundamental information regarding the petrogenesis of the magma the distribution of the tephra and the interaction between the ash and the receiving environment considering the importance of the geochemistry of the ytt for stratigraphic correlations and eruptive models it is central to the ytt debate to quantify and interpret such variations here we collate all published geochemical data on the ytt glass including analyses from 67 sites described in the literature and three new samples two principal sources of chemical variation are investigated i compositional zonation of the magma reservoir and ii post depositional alteration post depositional leaching is responsible for up to ca 11 differences in na2o k2o and ca 1 differences in sio2 al2o3 ratios in ytt glass from marine sites continental tephras are 2 higher in na2o k2o and 3 higher in sio2 al2o3 with respect to the marine tephra we interpret such post depositional glass alteration as related to seawater induced alkali migration in marine environments crystal fractionation and consequential magmatic differentiation which produced order of magnitude variations in trace element concentrations reported in the literature also produced major element differences in the ytt glass feo al2o3 ratios vary by about 50 which is analytically significant these variations represent magmatic fractionation involving fe bearing phases we also compared major element concentrations in ytt and oldest toba tuff ott ash samples to identify potential compositional differences that could constrain the stratigraphic identity of the morgaon ash western india no differences between the ott and ytt samples were observed

two views of the cold filament abstract two views of the cold filament first described by weatherly and kelley are presented the first is a local view near 40 n 62 w there its upslope edge is found to be a front which by benthic standards is large its downslope edge was not sampled what distinguishes this benthic front from others is that it is a permanent feature in the abyssal ocean above the cold filament relatively murky detached bottom layers were observed and tracked to where they separated from the bottom at the benthic front apparently these detached layers entrain overlying water a density jump at their base apparently restricts entrainment of underlying water primarily during the detachment process with comparably less entrainment thereafter the second view a regional one comes from examining historical hydrographic sections these indicate that the cold filament extends from the newfoundland ridge westward then southward to 24 n and possibly to 20 n along the base of the continental rise the cold filament i

the northeast brazilian rift system the northeast brazilian rift basins provide important data critical to the understanding of continental rifting processes associated with the opening of the south atlantic these basins represent the locus of intersection of the southern and equatorial branches and some basins yield substantial chronostratigraphic data that constrain the temporal and spatial interaction of the rift phases similar data are not found in its counterpart in africa especially for the neocomian these early cretaceous rift basins of northeast brazil illustrate key three dimensional geometries of intracontinental rift systems mainly controlled by the basement structural framework during the main rift phase syn rift ii neocomian early barremian extensional deformation was distributed over three main rift axes 1 the gabon sergipe alagoas gsa trend 2 the reconcavo tucano jatoba rtj trend and 3 the cariri potiguar cp trend during this phase extensional deformation jumped west from the easternmost basins gsa trend to a series of ne trending intracratonic basins rtj and cp trends characterized by a set of asymmetric half grabens separated by basement highs transfer faults and or accommodation zones these basins are typically a few tens of kilometers wide and trend ne sw roughly perpendicular to the main extension direction during the neocomian preexisting upper crustal weakness zones like the dominantly ne sw trending shear zones of the brazilian pan african orogeny controlled the development of intracrustal listric normal faults internal transverse structures such as transfer faults and accommodation zones were also controlled by the local basement structural framework the megashear zones of pernambuco brazil and ngaundere africa seem to have behaved like a huge accommodation zone accommodating extensional deformation along the rtj gsa trends with simultaneous extension along the cp trend during the late barremian syn rift phase iii a significant change in rifting kinematics occurred when the cp trend was aborted and major rifting initiated at the equatorial branch during the aptian while the equatorial branch and benue trough africa experienced the main rift phase the rtj trend was aborted and the gsa trend developed a transitional phase between the rift and drift stage the gsa trend and the offshore potiguar basin represent the site of continued evolution into passive margin basins following the main rift episode

global crustal stress pattern based on the world stress map database release 2008 the world stress map wsm project is a global compilation of information on the contemporary crustal stress field from a wide range of stress indicators the wsm database release 2008 contains 21 750 stress data records that are quality ranked using an updated and refined quality ranking scheme almost 17 000 of these data records have a c quality and are considered to record the orientation of maximum horizontal compressional stress sh to within 25 as this is almost a triplication of data records compared with the first wsm database release in 1992 we reinvestigate the spatial wave length of the stress patterns with a statistical analysis on a global 0 5 grid the resulting smoothed global stress map displays both the mean sh orientation that follows from the maximum smoothing radius for which the standard deviation is b25 and a countour map that displays the wave length of the stress pattern this smoothed global map confirms that long wave length stress patterns n2000 km exist for example in north america and ne asia these have been used in earlier analyses to conclude that the global stress pattern is primarily controlled by plate boundary forces that are transmitted into the intraplate region however our analysis reveals that rather short wave length of the stress pattern b200 km are quite frequent too particularly in western europe alaska and the aleutians the southern rocky mountains basin and range province scandinavia caucasus most of the himalayas and indonesia this implies that local stress sources such as density contrasts and active fault systems in some areas have high impact in comparison to plate boundary forces and control the regional stress pattern

particle transport in the bari canyon southern adriatic sea to define the sediment transport pathways along the southern adriatic shelf and slope two oceanographic cruises were carried out in the southern adriatic in july 2004 and in march april 2005 to study the role of the bari canyon system on sediment dispersal three moorings including sediment traps and current meters have been deployed near the bottom at depths of 600 m for one year march 2004 march 2005 two moorings were deployed within the canyon station b in the northern branch and station c in the southern branch and one on the adjacent open slope north of the canyon system station a total mass fluxes tmfs measured by sediment traps were always higher in the canyon than on the adjacent slope the highest values were measured at station c average 8 07 g m 2 d 1 roughly double those of station b 3 07 g m 2 d 1 and the lowest outside the canyon at station a 1 69 g m 2 d 1 the highest tmf were recorded in spring 2004 a period characterized by the lowest water temperatures and the highest current speeds up to 72 cm 1 which were associated with the highest across slope current component along the canyon axes the simultaneous variations of fluxes occurring at the three stations imply that similar processes are active along the entire southern adriatic margin and that they are amplified inside the canyon in spring a vein of southward flowing north adriatic dense water naddw was observed along the adriatic shelf this was related to an enhanced across slope current component which was responsible for the higher particle fluxes both on the open slope and at the canyon stations these data suggest that the bari canyon is an efficient conduit for sediment from the adriatic continental shelf to the deep basin downcore profiles of 210 pb in sediments collected below the traps have been used to estimate sediment mass accumulation rates mars on a century scale on the open slope the annual trap flux recorded in 2004 2005 was lower than mar on the contrary in the bari canyon the annual trap flux was higher than mar indicating that the lateral advection of particles becomes predominant and that a fraction of the particles intercepted by sediment traps was only in transit through the canyon 2007 elsevier b v all rights reserved

the sao vicente earthquake of 2008 april and seismicity in the continental shelf off se brazil further evidence for flexural stresses summary the continental margin and shelf of most stable intraplate regions tend to be relatively more seismically active than the continental interior in the southeast continental margin of brazil a seismiczoneextendsfromriograndedosultoespeismicactivityoccurring mainly along the continental slope and suggesting a close relationship with flexural stresses caused by the weight of the sediments in this region earthquakes with magnitudes larger than 5m b occurevery20 25yr onaverage thefocalmechanismsolutionsofpreviousearthquakes in this zone indicated reverse faulting on planes dipping approximately 45 with horizontal p axes the recent 5 2m b earthquake of 2008 april 23 occurred 125 km south of s ao vicente and was well recorded by many stations in se brazil as well as at teleseismic distances in north america and africa its focal depth was 17 km locating the hypocentre in the lower crust a well determined focal mechanism solution shows one vertical nodal plane and one subhorizontal nodal plane thep a ndt axes exhibit large dips which were confirmed by ar egional moment tensor inversion this unusual orientation of the fault mechanism can be attributed to a rotation of the principal stress directions in the lower crust caused by flexural effects due to the load of recent sedimentation

subsidence rings and fracture pattern around dolines in carbonate platforms implications for evolution and petrophysical properties of collapse structures abstract this work focuses on the study of collapse dolines which are the most expressive collapse structures in carbonate rocks and their relations with preexisting and syn collapse fractures the study area has two fracture sets that were formed before folding early n s e w and late ne sw nw se striking sets which concentrate most of the dissolution in the region and allow the formation of the dolines we define subsidence rings as the circular and ellipsoidal concentric zones around collapse structures which are subjected to subsidence due to major collapses and represent locations where new fractures are formed in these subsidence rings the downfaulted topography plunges towards the doline center and reaches more than 10 m in relation to unaffected areas away from dolines the topographic data indicate that the mean radius of the combined rings is twice the radius of the collapse which corresponds to the closed depression due to failure and downfall of blocks the subsidence process enlarges links preexisting fractures and forms a new set of semicircular concentric opening mode fractures here named collapse fractures increases in the apertures and densities of these fractures occur towards the dolines which increases fracture porosity around collapse structures fractures are reactivated as normal faults close to the main collapse at the doline edge this increase in fracture intensity could represent an indicator of permo porous quality improvement in these areas further this fracturing increases structural instability raising the risk of accidents in areas built on soluble carbonate rocks since the affected area may be much larger than previously predicted subsidence rings around collapse dolines could merge with other rings from neighboring collapse structures and potentially increase porosity and permeability as well as linking areas in carbonate reservoirs

local and regional scale impacts of the 74 ka toba supervolcanic eruption on hominin populations and habitats in india abstract the toba supervolcanic eruption of 74 000 years ago is argued to have devastated homo sapiens populations causing a human population bottleneck through a combination of rapid global climatic deterioration and ecological disruption following the widespread ash fall this dramatic eruption the largest in at least the last 2 million years is hypothesized to have shaped the genetic structure and diversity of human populations today past assessments of toba s human impacts however have been predominantly theoretical using archaeological and geological evidence from sites in india this study addresses toba s local scale impacts on hominin technology behavior demography and habitats in two valleys in india the jurreru and middle son valleys using paleoclimatological and volcanological data regional scale impacts throughout india are inferred a refugia hypothesis is presented that argues for variation in the scale of toba s impact throughout india driven by regional differences in monsoonal dynamics geography and topography areas of north west india the indo gangetic plain and parts of the deccan to the east of the western ghats are argued to have been the most affected whereas areas of southern and eastern india may have preserved the largest refugia for hominin populations

understanding tectonic stress in the oil patch the world stress map project knowledge of the present day tectonic stress is essential for numerous applications in petroleum exploration and production and in civil and mining engineering such as improving the stability of boreholes and tunnels and enhancing petroleum production through natural or induced fractures the world stress map wsm project is a collaborative project between academia industry and government that is building a comprehensive global database of present day stress information to better understand the state and sources of contemporary tectonic stress in the lithosphere figure 1

inter well scale natural fracture geometry and permeability variations in low deformation carbonate rocks regional natural fracture networks often show variations on a scale below that captured by seismic reflection data this variability is not considered in most reservoir models but likely impacts uncertainties in permeability we quantify this uncertainty using a database of 13 000 fractures in nine outcrops digitised in the carbonate jandaira formation potiguar basin brazil distance between outcrops is on average 11 km with a minimum of 300 m which is comparable to the distance between wells in naturally fractured reservoirs in between outcrops significant variations exist in orientation intensity length and topology using discrete fracture matrix flow models we model the permeability of each deterministic pattern and find that small changes in geometry and topology result in permeability variations that are not captured by connectivity based analyses such as percolation probabilities particularly when the matrix is permeable the permeability variations associated with subseismic scale fracture variability are not captured in conventional stochastic models but can be captured using deterministic outcrop models with flow through discrete fractures the deterministic models provide a permeability range associated with subseismic fracture variability that can be assigned to grid cells of fractured reservoir flow models as an alternative to assuming constant permeability in the absence of subseismic scale deformation

a centennial scale organic walled dinoflagellate cyst record of the last deglaciation in the south adriatic sea central mediterranean abstract a high resolution study of sea surface temperature sst and primary productivity changes during the last deglaciation in the south adriatic sea is presented on the basis of organic walled dinoflagellate cysts dinocysts compared with stable oxygen and carbon isotope records derived from globigerina bulloides two more defined warming phases between 14 75 and 14 10 cal kyr bp gi 1e and between 13 85 and 13 25 cal kyr bp gi 1c and perhaps a mild one between 12 95 and 12 60 cal kyr bp gi 1a interrupted by two cold events between 14 10 and 13 85 cal kyr bp gi 1d and between 13 25 and 12 95 cal kyr bp gi 1b are highlighted weaker sst oscillations occurred within the relatively stable periods gs 2a 17 00 14 75 cal kyr bp gs 1 or younger dryas 12 60 11 60 cal kyr bp and early holocene several dinocyst proxies used to evaluate surface primary productivity suggest that the cold events gi 1d and gi 1b are associated with episodes of both enhanced primary productivity and perhaps improved organic matter preservation due to reduced deep water formation phases of more pronounced increased surface primary productivity without stagnation in bottom waters are recorded during gi 1c and early gs 1 freshwater po river discharge seems to be the cause of enhanced productivity during event gi 1c at 13 4 cal kyr bp and probably during gi 1d

stress field of italy mean stress orientation at different depths and wave length of the stress pattern we have studied the stress pattern of italy using a dataset with 590 data records from the world stress map database release 2008 and 106 new data records to test the hypothesis the mean orientation of maximum horizontal stress sh is different at different depth sections for this we split the dataset into a shallow 0 6 km and a deep 6 40 km depth section for the data analysis we used a new statistical tool that calculates the mean sh orientation on a 0 2 grid the tool takes into account the distance to each grid point number and quality of the data records within the search radius and the radial distribution the result is a smoothed italian stress map that displays both the mean sh orientation and the wave length of the stress pattern the stress pattern does not vary in depth except for two areas sardinia and southern apulia therefore stress data from different depths can be used to estimate the mean sh orientation and the wave length of the stress pattern in italy furthermore the smoothed italian stress map reveals that most of italy has short wave length stress patterns 150 km this indicates that the stress field is not controlled by first order stress sources of plate tectonics i e the convergence of africa with respect to eurasia but that second order stress sources such as topography density strength contrasts and major faults systems are of great importance in four regions western part of the alps northern tuscany northern adriatic sea calabria and eastern part of sicily the wave length is 100 km high values of the circular variance of the mean sh orientation observed here are driven by third order local stress sources such as basins or local neotectonic structures

basement fabric controls rift nucleation and postrift basin inversion in the continental margin of ne brazil abstract in passive continental margins the brittle reactivation of shear zones and their role in the deformation and deposition of sedimentary basins are still a matter of debate in this research we investigated the role of the brittle reactivation of precambrian shear zones in the nucleation of rift and postrift faults in the onshore portion of the sergipe alagoas and pernambuco basins in northeastern brazil we combine and interpret a dataset of aeromagnetic and topographic data associated with reflection seismic and borehole data to analyze the evolution of a portion of the atlantic continental margin of brazil our results indicate that in the crystalline basement the magnetic lineaments are correlated with ductile structures as shear zones and the continuity of these lineaments in the sergipe alagoas and pernambuco basins is interpreted as the shear zones below the sedimentary cover of these basins we document the following phases of the brittle reactivation of basement shear zones 1 the opening of the south atlantic ocean in the early cretaceous under an extensional stress regime and 2 tectonic inversion induced by the mid atlantic ridge push and the andean cordillera rise in the neogene quaternary under a predominantly strike slip stress regime during the rift phase the brittle reactivation of the shear zones controlled the locations and architectures of the rifts these structures acted as zones of weakness and were reactivated as normal faults the brittle reactivation of shear zones was still active during the postrift phase and was responsible for the development of compressional structures the reverse faulting and related folding pattern indicate tectonic inversion in the late cretaceous cenozoic the structures formed during the postrift phase under a strike slip regime are consistent with the present day stress field indicating that tectonic inversion is an active phase of the brazilian margin

major element geochemistry of glass shards and minerals of the youngest toba tephra in the southwestern south china sea an ash layer newly discovered in core md01 2393 from the southwestern south china sea has been studied in order to characterize its major element features the layer 4 0 cm thick light grayish and silt size occurs right at the marine isotope stage 4 5 transition ca 74 kyr ago the morphology and geochemistry of glass shards combined with oxygen isotope and carbonate stratigraphy confirm the youngest toba eruption in northern sumatra as the origin of the ash layer major element data on mineral crystals i e biotite plagioclase and hornblende from the ash layer suggest that biotite is phenocrystic while hornblende and some plagioclase are xenocrystic implying that these xenocrysts were incorporated into the youngest toba magma before the eruption q 2005 elsevier ltd all rights reserved

short distance variability in slope bed forms along the southwestern adriatic margin central mediterranean abstract the slope of sw adriatic margin sam is impinged today by two bottom water masses of thermohaline origin that interact constructively along a preferred path the levantine intermediate water liw generated in the eastern mediterranean through intense evaporation and flowing along the contour and the north adriatic dense water naddw formed on the shallow north adriatic and cascading episodically off the shelf these two southward flowing bottom water masses impact the upper slope which is characterized by an irregular physiographic setting and together create the bottom current deposits e g fine grained contourite drifts and sediment waves and related erosional features e g furrows scours comet marks this study is focussed on a small open slope area of the sam ca 35 25 km where high resolution seismic data allow observe elongated contour parallel scours widespread erosion surfaces accompanied by wide crescent shape scours and furrow fields and giant comet marks spatially associated and genetically linked along a common current path further downslope and away from this highly energetic current path a field of sediment waves migrates upcurrent and shows bifurcated crests in some cases the downcurrent limbs of the sediment waves display a well defined erosional character on seismic profiles and furrows on side scan sonar mosaics all bottom current features observed are in equilibrium with the present day oceanographic regime as documented by the available current metre data moreover sediment cores suggest that the sediment waves are actively migrating during the present interglacial possibly implying that bottom waters formation was enhanced after the shallow adriatic shelf was drowned during the late quaternary eustatic rise the sam slope represents therefore an ideal site to improve our understanding of the depositional impact of bottom currents along the mediterranean margins and may provide useful hints on the activity of bottom currents elsewhere on the mediterranean margins

the unsteady post rift stage of the south american passive margin based on the tectono sedimentary evolution of the onshore paraiba basin ne brazil abstract the post rift tectono sedimentary history of passive margins has been an issue of increased interest after the perception of their unsteady nature during the neogene and quaternary the evolution of the eastern south america margin might be benefited from investigations of the sedimentary record in a number of marginal basins the paraiba basin is of particular interest to discuss the post rift evolution of the south american passive margin because it represents the last bridge with the african plate this work aims to analyze the post rift sedimentary record of the onshore paraiba basin as a contribution to discuss the neotectonic history of the south american passive margin surface and subsurface data were integrated from outcrops deep stratigraphic profiles airborne geophysical maps and remote sensing products the depositional and denudational processes in this basin were a result of tectonic subsidence and uplifting tectonics after the main rifting phase are indicated by abundant structures including normal reverse and strike slip faults as well as folds that affected the neogene and late pleistocene sedimentary deposits the ductile and brittle deformation resulted mainly from multiple reactivations of e w ne sw and nw se trending basement shear zones the deformation mechanism included distension and compression under a strike slip regime tectonic reactivations even during the late pleistocene support an unsteady south atlantic passive continental margin throughout the post rifting stage

quaternary fault control on the coastal sedimentation and morphology of the sao francisco coastal plain brazil abstract the role of neotectonic faulting in shaping topography and controlling sediment deposition has been increasingly documented along the stable continental margin of south america but the level of the present day tectonic stability of this margin is still a matter of debate this paper presents an investigation of the effects of quaternary fault reactivation on the sao francisco coastal plain sfcp this feature is a 56 km long progradational coastal plain located in the sergipe alagoas basin along the continental margin of brazil the sfcp is bounded on the west by a system of normal faults striking n s to ne sw the horst that bounds this plain is capped by the miocene barreiras formation and quaternary debris flow and fluvial deposits whereas the graben is filled with braided stream deposits and sandy beach ridge sediments the faulting contributed to the generation of accommodation space for the deposition of coastal sediments on the plain these processes started with the reactivation of cretaceous faults during the miocene during the quaternary fault reactivation and associated soft sediment deformation occurred between 82 and 8 3 ka with minor pulses between 1700 and 60 cal yr bp several faults along this margin are tectonically active and may represent the onshore continuation of gravitational collapses that have been documented offshore along the continental shelf and slope

dense low salinity outflow from the adriatic sea under mild 2001 and strong 1999 winter conditions 1 quasi synoptic temperature salinity and oxygen measurements in the adriatic and northern ionian seas mediterranean sea during two different winter conditions are presented in addition to the confirmation of previous knowledge about deepwater formation in the eastern mediterranean measurements give more insight into processes in the adriatic sea in winter and especially into the fate of the dense low salinity water masses transported by the west adriatic current wac and its spreading into the ionian sea a mild winter season without dense water production in the shallow areas of the adriatic sea was encountered during a cruise in february 2001 dense water outflow restricted to the deeper parts of the strait of otranto was nevertheless present during that mild winter and also in previous records of a cruise in autumn 1999 thus even in times of no deepwater production in the southern adriatic sea observations reveal a continuous flow of adriatic deep water adw through the strait of otranto and downslope in the northern ionian sea strong winter conditions are represented by a cruise carried out in february 1999 at that time cold and fresh water with density higher than that of south adw was observed on the italian shelf the dense coastal current is continued around cape santa maria di leuca at the heel of the italian boot in the gulf of taranto where the width of the shelf rapidly decreases dense coastal water is released to depth and transformed by intrusion and mixing with ambient water plumes and patches with horizontal extensions smaller than distances of a station grid are resolved by towed measurements in the 200 m upper layer with a multisensor chain products of coastal water transformation may be found at any depth on the western slopes of the ionian sea the new observations of dense water carried by the wac and plunging down to the level of neutral buoyancy in the gulf of taranto seem to confirm the hypothesis that the wac could be the origin of cold lenses found below the thermocline in the central ionian sea sellschopp and onken 2000

seafloor evidence for the interaction between cascading and along slope bottom water masses 1 the steep slope of the sw adriatic margin central mediterranean is impacted today by two water masses having markedly different origin but a similar southward flow component the levantine intermediate water liw and the north adriatic deep water naddw the liw forms through evaporation in the eastern mediterranean and enters the adriatic along a counterclockwise path the naddw forms through winter cooling on the north adriatic shelf and cascades across the western slope of the south adriatic basin bathymetric and side scan sonar tobi images of the sw adriatic margin accompanied by chirp sonar profiles define an area of extreme seafloor complexity characterized by a variety of sediment waves erosional scours longitudinal furrows and giant comet marks these distinctive bottom current features are not randomly distributed but appear genetically linked and have a consistent down current arrangement we ascribe this seafloor pattern to the constructive interference of the highly saline liw flowing along the slope between 200 and 600 m water depth and the cold naddw plunging off shelf obliquely to the slope stratigraphic data indicate that this oceanographic regime has been active since the last glacial interglacial transition the cascading naddw is density driven but is not short lived as a turbidity current would be consequently the interaction between downslope and along slope currents is here more dynamical as two water masses act simultaneously over a prolonged interval somewhat diverting their paths and leading to locally enhanced energetic conditions at the seafloor

fallout of volcanic ash to the deep south china sea induced by the 1991 eruption of mount pinatubo philippines an ongoing sediment trap experiment in the central south china sea provided the opportunity to investigate directly the mode and rates of a medial fallout of volcanic ash following the june 15 1991 eruption of mount pinatubo philippines within less than three days after the release of the major eruption plume ash accumulation 9 kg m 2 was simultaneously recorded by traps positioned in 1190 and 3730 m water depth at a distance of 586 km to the west of the volcano a numerical simulation of the fallout reveals that the vertical trajectories of the pyroclasts in both the atmosphere and ocean were controlled by particle aggregation the aggregation process caused a premature subaerial fallout of fine grained ash after crossing the air sea interface vertical settling of the ash clusters was enhanced by absorption of water leading to settling rates of more than 1670 m d aggregates were observed at all depths and their rapid settling is reflected in identical pyroclast spectra in intermediate and deep water this implies that particle sorting must have been complete in the upper water column and that the fallout was not perturbed by oceanic currents the tephra blankets an area of 37 10 4 km 2 in a fan shaped westward distribution which reflects the prevailing direction of the upper level winds our data show that atmospheric tephra dispersal patterns are recorded almost instantaneously on the deep sea floor and corroborate the key role of deep sea ash layers as highly reliable chronostratigraphic markers and as a geological tool to infer ancient wind fields

stress observations and driving force models for the south american plate stress observations are compared to predictions of driving force models for the south american plate stress observations have the potential to give detailed information about the forces driving the plates in that sets of forces with the same net torque can produce quite different stress patterns for a two dimensional vertical section model of a plate there are three conditions for dynamical equilibrium the net forces and the net torque about any point must all be zero these conditions are used to estimate the magnitudes of forces as a function of age with ridge push and slab pull as active forces and plate drag and slab resistance as passive forces the results are consistent with earlier published models and indicate that the primary balance for an oceanic plate is between slab pull and the resisting drag forces we generalize the model for the possible forces driving the south american plate and compare with observed stress measurements and kinematics the south american plate has a small slab pull component amounting to about one fifth the ridge push force with the other components reasonably isolated geographically thus the plate balance is largely between ridge push and plate drag this gives an opportunity of resolving the effects of trench suction or collision at the subduction zones most remarkable is the nearly uniform e w orientation of the regional stress field shmax directions which is extensional in the high andes a second feature is the n s orientations in the amazon basin the two dimensional horizontal stress patterns are compared for successive models of combinations of driving forces models with ridge push slab pull at the scotia and caribbean arcs and trench suction near the west coast balanced by plate drag produce similar stress patterns to those observed the magnitude of a possible trench suction force is estimated using a model with an eddy between the nazca slab and the overlying south american plate

laboratory models of bay type continental shelves in the winter abstract a laboratory experiment consisting of a shallow sea of constant depth bounded by a deep ocean through a uniformly sloping continental rise was conducted the experiment is cooled from above and there is a region that exhibits sinking convection cells which form the coldest water this water then spills off the rhs of the shallow sea as a density current looking downstream for counterclockwise rotation and forms bottom water in the deep experimental ocean there are three regimes for very slow scaled rotations there is one big gyre in the shallow sea and the sinking convection region is near the coast for faster rotations there are two or three gyres and for even faster rotations there are many gyres in this latter case the sinking regions are very patchy and sporadic comparison with theoretical estimates of temperature difference between the coldest shelf water and the offshore water based upon the assumption that the density current removes all the cold water was good but yield

glass chemistry in volcaniclastic sediments of odp leg 107 site 650 sedimentary sequence provenance and chronological implications abstract a detailed chemical investigation of volcanic glass fragments from volcaniclastic strata 6 tephras 1 volcanic debris flow 12 volcanic turbidites of odp leg 107 site 650 sedimentary sequence leads to a varied pattern in terms of both provenance and age constraints the six analyzed tephra strata indicate a provenance from at least three different volcanic provinces aeolian campanian and sicilian channel pantelleria island the older tephra strata 021 018 012 have a large amount of orogenic rhyodacite rhyolite deposits that may be attributed to the aeolian province although no subaerial coeval volcanic activity of similar composition has so far been documented in the aeolian arc tephra 007 is related to the pantelleria island activity and particularly to an ignimbrite episode dated circa 130 ka tephra strata 005 and 003 have a clear campanian provenance and are correlated with analogous tephra layers observed in the tyrrhenian and ionian seas dated circa 107 and 60 ka respectively in the oldest portion of the sequence from 1 3 to 0 13 ma the volcaniclastic sediments were only derived from the aeolian domain whereas in the latest 130 ka the campanian influx becomes much more predominant therefore a general k enrichment trend is observed in the temporal sequence of all the analyzed samples almost 700 point analyses which may be related both to a variation in the source area and to the specific pleistocene magmatic evolution of the peri tyrrhenian volcanic provinces

plate boundary forces are not enough second and third order stress patterns highlighted in the world stress map database 1 the world stress map project compiles a global database of contemporary tectonic stress information of the earth s crust early releases of the world stress map project demonstrated the existence of first order plate scale stress fields controlled by plate boundary forces and second order regional stress fields controlled by major intraplate stress sources such as mountain belts and zones of widespread glacial rebound the 2005 release of the world stress map project database provides for some areas high data density that enables us to investigate third order local stress field variations and the forces controlling them such as active faults local inclusions detachment horizons and density contrasts these forces act as major controls on the stress field orientations when the magnitudes of the horizontal stresses are close to isotropic we present and discuss examples for venezuela australia romania brunei western europe and southern italy where a substantial increase of data records demonstrates some of the additional factors controlling regional and local stress patterns

all toba tephra occurrences across peninsular india belong to the 75 000 yr b p eruption abstract a controversy currently exists regarding the number of toba eruptive events represented in the tephra occurrences across peninsular india some claim the presence of a single bed the 75 000 yr old toba tephra others argue that dating and archaeological evidence suggest the presence of earlier toba tephra resolution of this issue was sought through detailed geochemical analyses of a comprehensive suite of samples allowing comparison of the indian samples to those from the toba caldera in northern sumatra malaysia and importantly the sedimentary core at odp site 758 in the indian ocean a core that contains several of the earlier toba tephra beds in addition two samples of toba tephra from western india were dated by the fission track method the results unequivocally demonstrate that all the presently known toba tephra occurrences in peninsular india belong to the 75 000 yr b p toba eruption hence this tephra bed can be used as an effective tool in the correlation and dating of late quaternary sedimentary sequences across india and it can no longer be used in support of a middle pleistocene age for associated acheulian artifacts

continental scale rheological heterogeneities and complex intraplate tectono metamorphic patterns insights from a case study and numerical models abstract continental plates are built over long periods of time through successive extensional and compressional cycles they are therefore rheologically heterogeneous this heterogeneity should significantly influence the mechanical response of the continental lithosphere during collision processes the study of the neoproterozoic borborema shear zone system of northeast brazil highlights a systematic link between marked changes in its tectono metamorphic pattern and the pre existing structure of the plate that is characterized by juxtaposition of continental domains either comprising an old basement palaeo to eoproterozoic or accreted during an extensional event between 1 0 and 0 7 ga in neoproterozoic time when the shear zone system was developed these domains displayed different geotherms and lithospheric thicknesses and therefore contrasted rheological behaviours we use numerical models simulating the mechanical evolution of a continental plate comprising multiple thermally induced rheological heterogeneities submitted to compression to investigate how these heterogeneities may affect strain localization and the distribution of deformation regimes and vertical strain within the plate from the very beginning of the deformation weak and stiff heterogeneities induce strain localization due to a lower initial effective viscosity or to stress concentrations at their tips respectively shear zones propagate from the heterogeneities and finally coalesce forming a network of high strain zones bounding almost underformed blocks within this network shear zones transfer strain between the different heterogeneities and model boundaries the evolution of the system depends essentially on the geometrical distribution of heterogeneities and on their strength contrast relative to the surrounding lithosphere the resulting finite strain field is heterogeneous and displays rapid lateral variations in vertical and or rotational deformation such a heterogeneous strain distribution may induce contrasted magmatic metamorphic and uplift evolutions within an orogenic belt as observed in the borborema shear zone system and other collisional belts

analysis of the south american intraplate stress field the first order south american intraplate stress field was modeled through a finite element analysis to evaluate the relative contribution of plate boundary forces and intraplate stress sources the finite element mesh consisted of 3100 nodes in a network of 5993 equal area triangular elements which provided a spatial resolution of about 1 at the equator an important aspect of our modeling is the inclusion of topographic forces due to the cooling oceanic lithosphere along the mid atlantic ridge e g ridge push the continental margins along the east coast of brazil and argentina and the elevated continental crust e g the andean cordillera predicted intraplate stresses for two representations of the western collisional boundary forces are evaluated pinned collisional boundaries and applied collisional boundary forces constraint for the modeling was provided by information about the orientation of the maximum horizontal compressive stress shmax provided by 217 stress indicators from the world stress map project as well as by shmax magnitude estimates and torque information from previous investigations our modeling results demonstrate that the first order features of the observed stress field can be explained with simple tectonic models which balance the torque acting on the plate either with a fixed western margin or drag forces applied along the base of the plate the predicted intraplate stress field is characterized by a nearly uniform e w shmax orientation throughout most regions of the plate with stress magnitudes generally less than 20 mpa averaged over a 100 km thick lithosphere significant perturbation of this regional stress field occurs in the western part of the plate in response to forces associated with the high topography of the andes although the magnitude of the collisional boundary forces acting along the western margin remains poorly constrained we estimate a plausible upper bound on the force per unit length acting along the peru chile trench to be about 2 5 1012 n m 1 while some of our models are consistent with a driving basal drag to balance the torques acting on the plate the magnitude of the drag torque is small compared to the contribution from other sources of stress such as the ridge push force

dense water bottom currents in the southern adriatic sea in spring 2012 abstract in february 2012 a severe cold spell in the european region triggered a massive production of very dense water on the northern mediterranean sea shelves the spreading phase of the newly formed dense water was extensively studied in the adriatic sea by means of 2 ship surveys and 5 moorings fully equipped to monitor the flow of the bottom layer for the adriatic sea opposite to the gulf of lions the area of cascading is far from the source area and this implies substantial modifications adjustments and dilution of the source water mass along its path with a spreading phase lasting several months indeed all the moorings detected events although weaker than in the preceding months until june 2012 the surveys detected 2 branches of naddw on the shelf the first branch not denser than 29 7 kg m3 and the second branch not denser than 29 5 kg m3 despite the extremely dense water generated in the northern adriatic during events of dense water flow moorings recorded temperatures generally between 12 5 and 13 c seldom less temperatures along the shelf break also did not fall below 13 c at depths greater than 400 m turbulent mixing therefore heavily modified the cascading plumes which left the shelf with thicknesses between 10 and 30 m mooring data in the lowermost 100 mab suggest that the thickness of the cascading layer increased by several tens of meters downslope as a consequence of entrainment detraining frictional layers as well as locations of active cascading were identified mostly by isolated casts highlighting the submesoscale domain of the downsloping plumes the use of ladcp data allowed identification of very energetic bottom flow 40 50 cm s in many locations with otherwise little signature in tracers not previously observed the bari canyon system bcs was so far recognized as a hot spot for cascading in the southern adriatic however during the 2012 event this is not the only preferred site for cascading significant dense flow was detected in other locations the northernmost mooring site closer to the inception of the cascading process in particular showed active cascading and several dynamical differences from the bcs denser water with thinner boundary layer events organized in multiple pulses with sub inertial periodicity and with very short duration 12 h to 1 day that is generally not seen in other locations

3 d geometry and luminescence chronology of quaternary soft sediment deformation structures in gravels northeastern brazil abstract this paper reports and describes soft sediment deformation in gravels and gravelly sediments in quaternary alluvial deposits of the potiguar basin northeastern brazil deformation structures were measured in terms of geometry size and relationship with sedimentary bedding using geological mapping and ground penetrating radar tl and osl irsl methods following mar and sar protocols were used to date sediments and soft sediment deformation events our results indicate that soft sediment deformation structures are widely distributed in several stratigraphic intervals of alluvial channel deposits in a low lying topographic valley depending on their geometry and composition two types of soft sediment deformation structures occur pockets and dome like load structures these structures resulted from the shaking of sediments with a reverse density gradient system which caused collapse and realignment of pebbles these features are similar in morphology and size to modern examples of seismically induced soft sediment deformation in coarse sediments tl and osl ages indicate that sediment deposition and associated soft sediment deformation occurred at least six times from 352 ka to 9 ka

a geometrically based method for predicting stress induced fracture aperture and flow in discrete fracture networks modeling of fluid flow in naturally fractured reservoirs is often done through modeling and upscaling of discrete fracture networks dfns the two dimensional fracture geometry required for dfns is obtained from subsurface and outcropping analog data however these data provide little information on subsurface fracture aperture which is essential for quantifying porosity and permeability apertures are difficult to obtain from either outcropping or subsurface data and are therefore often based on fracture size or scaling relationships but these do not consider the orientation and spatial distribution of fractures with respect to the in situ stress field using finite element simulations mechanical aperture can be modeled explicitly but because changes in fracture geometry require renewed meshing and simulating this approach is not easily integrated into subsurface dfn modeling workflows we present a geometrically based method for calculating the shear induced hydraulic aperture that is an aperture of up to 0 5 mm 0 02 in that can result from shear displacement along irregular fracture walls the geometrically based method does not require numerical simulations but it can instead be directly applied to dfns using the fracture orientation and spacing distributions in combination with an estimate of the regional stress tensor and orientation the frequency distribution of hydraulic aperture from the geometrically based method is compared with finite element models constructed from five real fracture networks digitized from outcropping pavements these networks cover a wide range of possible geometries and spatial distributions the geometrically based method predicts the average hydraulic aperture and equivalent permeability of fractured porous media with error margins of less than 5

ultra distal tephra deposits from super eruptions examples from toba indonesia and taupo volcanic zone new zealand abstract voluminous rhyolitic eruptions from toba indonesia and taupo volcanic zone tvz new zealand have dispersed volcanic ash over vast areas in the late quaternary the 74 ka youngest toba tuff ytt eruption deposited ash over the bay of bengal and the indian subcontinent to the west the 340 ka whakamaru eruption tvz deposited the widespread rangitawa tephra dominantly to the southeast in addition to occurrences northwest of vent extending across the landmass of new zealand and the south pacific ocean and tasman sea with distal terrestrial exposures on the chatham islands these super eruptions involved 2500 km 3 and 1500 km 3 of magma dense rock equivalent dre respectively ultra distal terrestrial exposures of ytt at two localities in india middle son valley madhya pradesh and jurreru river valley andhra pradesh at distances of 2000 km from the source caldera show a basal primary ashfall unit 4 cm thick although deposits containing reworked ash are up to 3 m in total thickness exposures of rangitawa tephra on the chatham islands 900 km from the source caldera are 15 30 cm thick at more proximal localities 200 km from source rangitawa tephra is 55 70 cm thick and characterized by a crystal rich basal layer and normal grading both distal tephra deposits are characterized by very fine ash with high pm 10 fractions and are crystal poor glass chemistry stratigraphy and grain size data for these distal tephra deposits are presented with comparisons of their correlation dispersal and preservation using field observations ash transport and deposition were modeled for both eruptions using a semi analytical model hazmap with assumptions concerning average wind direction and strength during eruption column shape and vent size model outputs provide new insights into eruption dynamics and better estimates of eruption volumes associated with tephra fallout modeling based on observed ytt distal tephra thicknesses indicate a relatively low

off shelf fluxes across the southern adriatic margin factors controlling dense water driven transport phenomena abstract the northern adriatic sea is a basin where dense shelf waters form during winters if the following favorable conditions are attained high salinities mainly related to low river water discharge po river in primis during fall season and strong heat fluxes induced by cold and dry bora wind events blowing from north east extremely favorable conditions to northern adriatic dense waters naddw formation characterized winter 2012 when following several months of low po river runoff a strong event of cold air outbreak cao occurred from the end of january until mid february consequently the mean temperature of northern adriatic waters dropped to about 6 c and exceptional densities potential density anomaly locally exceeding 30 0 kg m 3 were reached the production and spreading mechanisms of dense water in the adriatic sea have been modeled by means of the coawst coupled ocean atmosphere wave sediment transport modeling system the model builds upon a high resolution 1 km spaced horizontal grid fully 3 d primitive equations hydrodynamic model coupled with a phase averaged wave model and sediment routines and is driven by simulated atmospheric forcings the dataset used to assess model outputs relies on the measurements acquired during the dedicated field campaigns operation dense water a set of two rapid response cruises carried out in southern adriatic during winter 2012 and by five mooring arrays deployed in the southern adriatic margin sam that allowed the continuous acquisition of temperature salinity currents and suspended matter samples results from the integrated data model approach suggest that the naddw propagates along the shelf to the southern basin following both a shallower vein and a deeper stream with a process characterized by a strong variability mean value of 0 31 sv with peaks rapidly growing in the first weeks after the cao up to 2 19 sv additionally coawst capability to couple different numerical models allowed to disentangle the relative importance of aspects on dense water generation mixing and spreading demonstrating how coupled runs can lead to volumes up to 50 larger with respect to uncoupled simulations additional light is shed on the transport pathways off the shelf and on possible sediment transport phenomena in the area in this benefiting from an unprecedented spatial resolution and a new bathymetry reflecting very high resolution data acquired via multi beam techniques although dense water propagation appears as a relatively large scale process involving the whole western side of the sam topographic local discontinuities and seabed slopes appear crucial in triggering descent and governing flow patterns the presence of suspended sediment along the water column despite not significantly influencing the overall fluxes across sections is responsible of pulling part of the veins towards deeper zones

new geochemical evidence for the youngest toba tuff in india abstract new geochemical data on tephra samples from a layer present at several archeological sites in india support correlation of this layer to the youngest toba tuff erupted from northern sumatra about 74 000 yr ago the data show that the indian tephra layer is not a correlative of older tephra erupted from toba as has been suggested on the basis of artifact assemblages previously published geochemical data on the indian tephra beds was based on bulk ash samples containing mineral and clay contaminants and the resulting variability in analyses did not allow identification or discrimination of individual eruptive events our new data were collected on individual glass shards and small purified glass separates which have greater resolving power in fingerprinting acheulian and paleolithic artifacts found at some of the indian tephra sites do not reflect the antiquity of the tephra bed as they occur in fluvial sediments and may be reworked

in situ stress state in the nankai accretionary wedge estimated from borehole wall failures we constrain the orientations and magnitudes of in situ stress tensors using borehole wall failures borehole breakouts and drilling induced tensile fractures detected in four vertical boreholes c0002 c0001 c0004 and c0006 from nw to se drilled in the nankai accretionary wedge the directions of the maximum horizontal principal stress shmax indicated by the azimuths of borehole wall failures are consistent in individual holes but those in c0002 margin parallel shmax are nearly perpendicular to those in all other holes margin normal shmax constrained stress magnitudes in c0001 and c0002 using logged breakout widths combined with empirical rock strength derived from sonic velocity as well as the presence of the drilling induced tensile fractures suggest that the stress state in the shallow portion of the wedge fore arc basin and slope sediment formations is predominantly in favor of normal faulting and that the stress state in the deeper accretionary prism is in favor of probable strike slip faulting or possible reverse faulting thus the stress regime appears to be divided with depth by the major geological boundaries such as unconformities or thrust faults the margin perpendicular tectonic stress components in the two adjacent sites c0001 and c0002 are different suggesting that tectonic force driven by the plate pushing of the philippine sea plate does not uniformly propagate rather the stress field is inferred to be influenced by additional factors such as local deformation caused by gravitation driven extension in the fore arc and thrusting and bending within individual geologic domains

the role of tectonics in the late quaternary evolution of brazil s amazonian landscape tectonic reactivation has long been suggested to have occurred over several areas of the amazonian lowland in the neogene holocene numerous landscape changes documented in this region particularly variations in fluvial dynamics and morphologies have nevertheless been exclusively attributed to climatic fluctuations minimizing the effect of tectonics over the neogene holocene evolution of the amazon basin can result in a distorted interpretation of the sedimentary record and as a consequence equivocal paleoclimatic reconstructions climate has often prevailed as a hypothesis to explain changes in fluvial dynamics possibly due to the still scarce synthesizing publications focusing exclusively on the neotectonic influence over this region the present work provides a review of existing data focusing on quaternary tectonics over a large area of the amazonian lowland the existing information is complemented by original morphostructural data on quaternary terrains from this region which were acquired through remote sensing the goals were to analyze the geographic extent of late quaternary deposits and to determine the impact of tectonics on their development and on the latest evolution of the amazon drainage basin the analysis shows that 1 the amazonian lowland experienced geographically widespread sedimentation in the late pleistocene holocene 2 sedimentation was promoted by the creation of new depositional sites mostly likely resulting from tectonic activity and 3 tectonic reactivation impacted the latest evolution of this entire region with particular influence on drainage basins as revealed by river courses with an abundance of morphostructural lineaments evidencing fault control hence the nw ne nearly n s and to a lesser extent w e morphostructural trends recorded in all areas investigated here are generally associated with strike slip deformation in addition they are conformable with the main orientation of tectonic structures from adjacent crystalline rocks of the precambrian basement they also match tectonic trends documented in neogene and younger sedimentary deposits from this and several other areas of northeastern brazil furthermore some are detected locally in the subsurface by geophysical data furthermore a profusion of morphostructural anomalies is imprinted on the surface of neogene holocene deposits of the amazonian lowland the main ones consisting of 1 highly asymmetric modern drainage basin still undergoing organization with anomalous patterns i e trellis sub dendritic sub parallel and rectangular that often vary from one another frequent river captures and rivers flowing in contrary directions along the time and straight channels that form triangular shapes or triple junctions or with local meandering and subtle enlargements 2 an abundance of channels floodplains lakes and entire valleys with straight and orthogonal margins that locally form rhombic shapes or which may be laterally displaced 3 fluvial rias i e rivers that became enlarged as their mouth were barred bounded by sharp and orthogonal lineaments which result in rectangular shapes 4 termination of megafans into rhombic shaped depressions bounded by straight lineaments or their lateral displacement several kilometers apart and 5 rivers with asymmetric terraces laterally displaced by faults these observations together are consistent with a landscape controlled by neotectonic activity the modern seismogenic record which reveals even high magnitude earthquakes indicates active deformation over the amazonian lowland at the present time the neotectonic history of the amazonian lowland is explained within the context of an overarching mechanism most likely related to intraplate stresses this was probably caused by reactivation of pre existing structures since the neogene that was most likely promoted by activity along oceanic fracture zones and transform faults of the brazilian equatorial margin as well as tectonism in the andean region

ytt ash from quaternary sediments of kapileshwar area purna alluvial basin central india abstract a thick pocket of volcanic ash 2 5 m represented by various shades of gray powdery massive to laminated in nature hosted in yellowish brown thinly bedded laminated silty clay lithocolumn has been studied for its preservational and geochemical aspects the ash column shows preservations of both primary and reworked ashes which are distinguishable on the basis of their field criteria including colors bedding geometries and thicknesses petrological study of the same reveals high representation of glass shards with bubble wall blocky and pumice morphologies minor occurrences of light and heavy minerals and unidentifiable admixture of fine grained sediments geochemistry of both bulk ash and glass shards through icp aes and epma respectively suggest high percentages of sio2 al2o3 na2o and k2o ree data generated through icp ms show strong negative eu anomaly the effects of weathering or aqueous solution on the geochemistry are also noticeable as evident by the variations in the values of both mobile and immobile elements however the data obtained from both bulk ash and glass shards are within the limits of ytt composition calm to very low energy environment of deposition is suggested for their deposition paleoclimatic proxies represented by rhizoliths rhizospheres rhizolith balls ant traces and vertebrate remains preserved in the pre tephra succession have also been commented

a synthesis of the ionian sea hydrography circulation and water mass pathways during poem phase i abstract in this paper we revisit with a thorough in depth analysis the dataset collected in the hydrographic surveys of the international collaborative programme poem physical oceanography of the eastern mediterranean in the period 1986 1987 the work has two major objectives the first is to refine the dynamic picture of the ionian upper thermocline sub basin scale circulation rather less definitive than the dynamic picture of the levantine sea circulation the second is to identify the pathways of the major water masses of the basin not only in the near surface but also in the intermediate and deep layers to our knowledge this is the first work defining the pathways of the levantine intermediate water liw and of the adriatic deep water adw eastern mediterranean deep water emdw that characterize the intermediate and deep circulations the major novel results can be summarized as follows in the upper thermocline 1 the atlantic ionian stream ais jet entering the sicily straits bifurcates into two main branches at 37 n 17 e it advects the modified atlantic water maw into the ionian sea interior the first branch turning directly southward encloses an overall anticyclonic area comprising multiple centers around which the maw is advected 2 the second ais branch extends further into the northeastern ionian where it too turns southward before crossing the entire ionian sea meridionally advecting maw on its left side and ionian surface water isw on its right this branch of the jet is confined to the ionian margin and does not pass around the pelops gyre 3 a new water mass the lsw is formed in the levantine basin and enters the cretan passage then is first veered cyclonically south of crete by the cretan gyre and successively is entrained anticyclonically around the pelops gyre and then enters the aegean sea 4 a permanent cyclone located in the northeastern ionian determines the pathway of mixed adriatic surface water ionian surface water asw isw 5 a permanent cyclone is found in all the surveys near the tip of the italian boot this novel analysis of the liw pathways shows that 1 the major source of intermediate liw during the period 1986 1987 was actually in the levantine sea liw formed there entered the cretan passage was veered cyclonically by the cretan gyre south of crete and then entered the southern ionian sea the major liw pathway was westward directly to the sicilian straits 2 secondary important liw pathways were determined by the interior structures the strong pelops anticyclone was entraining liw around its periphery and was determining the liw northward pathway that closely followed the eastern greek coastline it was along this pathway that liw entered the otranto strait a further branch of liw was entrained and recirculated around the multiple ionian anticyclones ia of the western ionian sea 3 the cretan cyclone is a feature confined to the upper thermocline intermediate layer it disappears at 400 dbar while the pelops anticyclone is strongly barotropic below the upper 100 dbar and penetrates quite intense down to 800 dbar 4 a further completely novel result concerns the new water mass found in the deep layer that spreads on the 29 15 kg m3 isopycnal surface this water mass characterized by high salinity and high oxygen content is formed inside the aegean sea and is observed to spread out all around the cretan arc straits the final fully novel result is the demonstration of a second pathway for the adw exiting from the otranto strait that is transformed into emdw and occupies the abyssal layers of the ionian sea interior the traditional pathway for emdw is along the isobaths along the western side of italy but adw was observed to be exiting from the otranto strait in the eastern hellenic trench at 39 5 n both during poem on86 and poem as87 this second pathway for emdw follows isobath contours along the western side of greece the two emdw routes converge and merge between 36 n and 35 n so producing a deep layer of emdw that occupies uniformly the abyssal plain of the interior of the ionian sea

first toba supereruption revival little has been known about the earliest toba eruptive episodes that created the largest known caldera complex of quaternary age here we report evidence for the eastward dispersal of the oldest toba tuff in south china sea sediments to 2500 km away from the source the tephra deposits occur below the brunhes matuyama geomagnetic boundary 778 ka and slightly above the australasian microtektite layer 793 ka calibrated by astronomically tuned oxygen isotope stratigraphy the middle pleistocene toba eruption occurred during the deglaciation at 788 2 2 ka according to the tephra occurrence between marine isotope stages 20 and 19 this refined age is in good agreement with the 4 0 ar 3 9 ar date of 800 20 ka for the toba tephra layer d from ocean drilling program odp site 758 but significantly younger than the commonly cited ar ar age of 840 30 ka the eruption expelled at least 800 1000 km 3 dense rock equivalent of rhyolitic magma on the basis of the widespread tephra fall deposit in the basins of the indian ocean and the south china sea in spite of its exceptional magnitude the timing of this major eruption does not indicate a causal linkage between this event and a long term global climatic deterioration

the impact of cascading currents on the bari canyon system sw adriatic margin central mediterranean abstract the bari canyon system bcs is a peculiar erosional depositional feature characterised by two main almost parallel conduits emanating from a broad crescent shaped upper slope region when viewed in cross sections parallel to the margin bcs appears markedly asymmetric with a right hand southern side that is higher and steeper about 800 m in relief and more than 30 steep the left hand side of the canyon is instead much smoother as a consequence bottom currents flowing along the slope from the north enter the canyon and interact with its complex topography leading to preferential deposition on the up current side of pre existing morphological relief where mass failure deposits generate morphologic relief outside the canyon sediment is preferentially deposited up current n ward bcs includes three main ew oriented sediment conduits canyon c to the south channel b in the central area and moat a in the north channel b shows a well developed levee deposit on its right hand side and appears markedly straight and erosional on the upper slope the deepest portion of channel b is substantially abandoned and draped but still shows a subdued thickening of the draped unit north and up current of pre existing morphologic relief confirming the impact of along slope flowing currents canyon c is flanked by erosional walls all the way to the basin floor where deep sea furrows develop with a nw se orientation today dense water formation in the adriatic is seasonally modulated and displays a significant variability on inter decadal scales dense water formation during glacial intervals was likely different from the modern because most of the north adriatic shelf was subaerially exposed and the deep water mixing in the south was likely reduced as suggested by paleoceanographic reconstructions the growth patterns of bcs since the lgm are characterised by concurrent erosion of the upper portion of channel b and of the lower portion of canyon c it is possible that flows through the straight narrow and steep upper segment of channel b spill over its right hand levee in ca 600 m water depth where the relief of levee b on the channel floor is minimal and enter canyon c where substantial erosion takes place in this view the upper portion of canyon c where hard grounds and corals are encountered is flushed by currents characterised by reduced turbidity while the lower part of canyon c collects additional flows from upper channel b

the adriatic sea hydrography and circulation in spring and autumn 1985 1987 abstract the adriatic basin wide circulation and its temporal variability are reviewed on the basis of results from the analysis of hydrographic data collected during four poem cruises major well known features in the circulation are revealed in the data set which covers the period from october 1985 to april 1987 a prominent signal associated with the seasonal variability is identified in the water outflowing along the italian coast differences between autumn and spring in the vein of cold and fresh water flowing along the italian shelf manifest mainly in the temperature field during the stratified season the fresh water spreads over the entire surface layer of the southern adriatic on the other hand during spring when the sea is vertically homogeneous the fresh water remains confined to the surface longshore boundary layer over the entire length of the italian coast layers below the seasonal thermocline at the eastern portion of the sea display very weak seasonal signals a strong signal associated with the inter annual variations also has been documented from the analysed data set it mainly appears in the salinity field it is shown that in spring 1986 the salinity averaged over the entire water column north of the palagruza sill is lower by 0 3 psu than in spring 1987 a similar but less prominent difference is noted in the southern adriatic an attempt is made to associate these differences with variations in climatic conditions over the area the river runoff and the mediterranean water inflow

numerical modeling of flexural stresses in the upper crust of ne brazil implications for stress regimes in intraplate settings abstract we model the contribution of the stresses generated by the topography and density heterogeneities in the stress field of ne brazil and the interplay between these and regional stresses our model consists of a horizontally layered elastic slab the lithosphere that floats above an inviscid fluid the asthenosphere where the surface load is generated by the topography and bathymetry and the internal loads are calculated from the bouguer anomalies the deviatoric flexural stresses are calculated in the fourier domain our results showed local flexural stresses with magnitudes comparable to those of the plate wide stresses and mainly controlled by the long wavelength bouguer anomalies scenarios for the total stress field were calculated by superposing different values for an e w oriented regional compression we predict the stress axes orientations and stress regimes for the equatorial margin and the pernambuco shear zone pesz region however we highlight the importance of spreading stresses not considered here in rotating the maximum horizontal compression shmax predictions the prediction of stress regime and stress axes orientation in pesz using low to zero regional compression suggest that a decoupling of the shallow stresses from the plate wide stresses might occur in this region another possible explanation found was that the spreading stresses might counterbalance the regional stresses we conclude that the superposition of principally flexural and plate wide stresses explains reasonably the observed stress regimes and shmax orientations in a great part of ne brazil furthermore flexural stresses are playing an important role in the reactivation of the pesz possibly controlling the stress field

new occurrence of youngest toba tuff in abyssal sediments of the central indian basin abstract volcanic glass and pumice found in siliceous abyssal sediments of the central indian basin south of the equator have previously been assigned various origins including intra basin volcanism indonesian arc and krakatau rhyolitic glass shards dispersed in sediments from 8 cores that we have examined are compositionally identical to those of fallout deposits of the youngest toba tuff erupted at 74 ka from northern sumatra the correlation extends the distribution of coarse 63 m glass shards some 1500 km south of the previously known fallout zone and into the southern hemisphere reaching latitudes of ca 14 s this provides evidence for bi hemispheric dispersal of the ash cloud and supports global dispersal of gas and aerosols from the eruption such dispersal could have facilitated the global impact of the eruption

impacts of data sampling on the interpretation of normal fault propagation and segment linkage abstract throw distance t d and throw depth t z plots are widely used by researchers and industry to examine the growth of normal faults this study uses high quality three dimensional 3d seismic and outcrop information to review the effect of data sampling on the interpretation of normal fault growth the results show that the accuracy of t d and t z data and of resulting fault slip tendency and leakage factor analyses are dependent on the sampling strategy followed by interpreters and field geologists i e on a sampling interval fault length ratio for discrete structures in particular this work demonstrates that significant geometric changes in t d plots occur when a module error ei for the ratio is larger than 6 9 for faults of all scales and growth histories this implies that a minimum number of measurements should be gathered on discrete faults to produce accurate t d and t z plots and that the number of measurements is dependent on fault length with no prior knowledge of fault segmentation a value of 0 05 should be applied when interpreting faults to fulfil the pre requisite of a i

youngest toba tuff in the son valley india a weak and discontinuous stratigraphic marker abstract investigation of the climatic and environmental impacts of the youngest toba tuff ytt 74 ka bp eruption of toba volcano sumatra is crucial for understanding the consequences of the eruption for contemporaneous human populations the middle son valley in india was the first locality on the indian subcontinent where the ytt was reported the ash bed forms a discontinuous layer stretching for over 30 km along the river here we report on the stratigraphic contexts of ytt ash layers in alluvial deposits of the middle son valley in order to reconstruct the taphonomy of the ash deposits and the dynamic of their deposition although the distal ash has been studied since the 1980s its stratigraphic integrity and the mechanisms and pathways involved in its transport and deposition have bit previously been assessed we find that the ytt occurrences in the middle son valley may not be reliable chronostratigraphical markers for millennial scale palaeoenvironmental reconstruction

the 73 ka toba super eruption and its impact history of a debate abstract toba volcano in northern sumatra is located at the intersection of two major tectonic lineaments in one of the most seismically active regions in the world and its caldera is considered the largest quaternary caldera on earth the most recent toba explosive eruption at 73 ka was an order of magnitude larger than that of tambora in 1815 and has a volcanic explosivity index of 8 the exceptional magnitude of this super eruption and the widespread distribution of the younger toba tuff ytt in marine cores in the indian ocean the arabian sea and the south china sea have prompted sustained debate as to its global and regional impact on climate ecosystems and prehistoric human populations however despite climate modelling and appeals to a variety of proxy climatic data including geochemistry pollen analysis archaeology and stable isotopes the extent of the impact remains unclear in order to achieve better progress in the future greater care is needed to obtain higher resolution and more precise chronologies from the marine and terrestrial proxy records used to test whether or not the 73 ka toba super eruption had a significant environmental impact records from speleothems and ice cores have much to offer in this regard

postrift stress field inversion in the potiguar basin brazil implications for petroleum systems and evolution of the equatorial margin of south america rifting and related normal stress regime in the equatorial continental margin of brazil ceased during the late cretaceous when the stress regimes in eastern south america and west africa changed to induce strike slip or reverse motion in this study we explore the postrift tectonic geomorphic magmatic and sedimentary responses to stress changes using the potiguar basin the easternmost basin in the equatorial margin of brazil as a case study we use field and topographic data 2d seismic reflection lines vertical electric soundings and geochronological and borehole data to constrain the stress evolution of the potiguar basin from the late cretaceous to the quaternary discussing the role of basin inversion on sedimentation and landforms our results indicate the presence of two strike slip stress regimes after rifting the first stress field sf1 occurred from late cretaceous to the middle miocene and consisted of a n s oriented maximum subhorizontal compression and an e w oriented extension the second stress field sf2 took place from the middle miocene to the present day and included subhorizontal e w to nw se compression combined with n s and ne sw subhorizontal extension emplacement of volcanic rocks occurred along transtensional faults with a principal peak during sf1 at 20 30 ma and a subordinate peak during sf2 at 5 10 ma in response to shortening during sf2 a 70 km long and 50 km wide dome formed where marine miocene strata were uplifted to 250 m asl this uplift induced the displacement of alluvial channels away from the dome anticlines formed by transpression along the main ne sw striking faults during both sf1 and st2 acted as traps in the petroleum system similar shifts and stress field inversions documented in other areas of the brazilian continental margin are consistent with the neogene rise of the andes and may have implications for reconstructing the tectonic history of the equatorial atlantic margin of south america

fracturing and calcite cementation controlling fluid flow in the shallow water carbonates of the jandaira formation brazil the shallow marine carbonate rocks of the jandaira formation have been subject to significant permeability variations through time due to various events of fracturing and calcite cementation as a consequence the jandaira formation accommodated fluid flow only during specific moments in time we reconstructed these episodes of fluid flow based on isotope characterizations and microscope characteristics of calcite veins and host rock cements the jandaira formation which belongs to the post rift sequence of the potiguar basin in northeast brazil was deposited from the turonian onward until a marine regression exposed it in the campanian due to the subaerial exposure meteoric waters flushed out marine connate waters leading to an event of early diagenesis and full cementation of the jandaira formation fluid flow through the resulting impermeable carbonate formation appears to be closely related to fracturing fracturing in the late cretaceous induced a drastic increase in permeability giving rise to extensive fluid circulation host rock dissolution associated to the circulating fluids led to calcite vein cementation within the fracture network causing it to regain an impermeable and sealing character in the research area fluid flow occurred during early burial of the jandaira formation at estimated depths of 400 900 m this study documents the first application of fluid inclusion isotope analysis on vein precipitates which allowed full isotopic characterization of the paleo fluids responsible for calcite vein cementation the fluid inclusion isotope data indicate that upwelling of groundwater from the underlying acu sandstones provided the fluids to the fracture network in miocene times renewed tectonic compression of a lower intensity created a secondary fracture network in the jandaira formation the density of this fracture network however was too low to induce a new episode of fluid circulation as a result this tectonic event is associated with the development of barren extensional fractures

neotectonic reactivation of shear zones and implications for faulting style and geometry in the continental margin of ne brazil abstract the eastern continental margin of south america comprises a series of rift basins developed during the breakup of pangea in the jurassic cretaceous we integrated high resolution aeromagnetic structural and stratigraphic data in order to evaluate the role of reactivation of ductile neoproterozoic shear zones in the deposition and deformation of post rift sedimentary deposits in one of these basins the paraiba basin in northeastern brazil this basin corresponds to the last part of the south american continent to be separated from africa during the pangea breakup sediment deposition in this basin occurred in the albian maastrichtian eocene miocene and in the late quaternary however our investigation concentrates on the miocene quaternary which we consider the neotectonic period because it encompasses the last stress field this consisted of an e w oriented compression and a n s oriented extension the basement of the basin forms a slightly seaward tilted ramp capped by a late cretaceous to quaternary sedimentary cover 100 400 m thick aeromagnetic lineaments mark the major steeply dipping ductile e w to ne striking shear zones in this basement the ductile shear zones mainly reactivated as strike slip normal and oblique slip faults resulting in a series of miocene quaternary depocenters controlled by ne e w and a few nw striking faults faulting produced subsidence and uplift that are largely responsible for the present day morphology of the valleys and tablelands in this margin we conclude that precambrian shear zone reactivation controlled geometry and orientation as well as deformation of sedimentary deposits until the neogene quaternary

observations on a bottom vein of dense water in the southern adriatic and ionian seas we discuss the motion and spreading of a bottom vein of very dense marine water which originates 29 4 in winter through cooling and evaporation processes resulting from the violet bora wind blowing over the shallow north adriatic sea into the deepest layers of the southern adriatic and ionian seas eastern mediterranean basin our analysis is focused on the peculiar physical processes that control this bottom flow we first describe the vein motion in the southern adriatic sea in which this current follows approximately the isobaths in partial accordance with the conservation of potential vorticity and the main mixing process of dense water with levantine intermediate water occurring in an offshore oriented canyon near bari this canyon causes a deepening and flattening of the original vein of dense water such that downstream the water can be observed only on the otranto sill at depths of 800 m with 29 25 the subsequent flow in the ionian sea follows approximately the 900 m isobath in the gulf of taranto and along the calabrian and east sicilian coasts in agreement with the results of smith s and killworth s theoretical models of steady motion of density driven currents over a regular slope in a rotating system for stratified fluids

cascading dense shelf water during the extremely cold winter of 2012 in the adriatic mediterranean sea formation flow and seafloor impact

a continuing intraplate earthquake sequence near joao câmara northeastern brazil preliminary results shallow seismicity along a well defined section of reactivated precambrian basement near joao c mara brazil 5 5 s 33 7 w has continued since august 1986 a magnitude 4 3 event on 21st august with a decaying aftershock sequence and another main shock aftershock sequence which started in september were followed by a magnitude 5 1 event on 30th november and 11 events of magnitude 4 or above up to february 1987 a network of up to four vertical component short period seismometers with smoked paper recorders has been deployed since late august 1986 several thousand events have been recorded above magnitude 0 and activity was still being recorded about 10 events per day in may 1987 simple velocity structure good transmission and impulsive s arrivals on almost all seismograms combine to facilitate reliable hypocentral locations even for this sparse network and epicenters define a 25 km linear pattern of seismicity with northeasterly strike approximately coincident with a precambrian structural trend a composite fault plane solution shows dextral shear along this strike with a small normal component fault plane solutions and epicenter distribution in northeastern brazil suggest an overall picture of e w regional compression

seismicity and stresses in the brazilian passive margin abstract seismicity and stresses along the brazilian continental margin show different patterns between the northeastern and southeastern regions in the northeastern margin earthquakes tend to occur onshore under a strike slip regime with horizontal compression parallel to the northern coast line in the southeastern margin higher seismicity is observed offshore in areas where the continental crust was highly extended during the south atlantic rifting in the mesozoic three new events in the southeast continental shelf are shown to have reverse faulting mechanisms from waveform modeling of short period teleseismic p waves multiple depth phases reflections from the top and bottom of the water layer and double reflections in the water layer could be identified and better constrained the hypocenters to middle and upper crustal depths in south america models of intraplate stresses caused by plate boundary forces and spreading effects due to the continental oceanic crustal transition indicate higher compressional stresses in the se offshore area as compared with the continental area in agreement with the observed higher seismicity and reverse faulting mechanisms the combination of regional stresses local flexural effects from thick sedimentary loads and a presumably weaker crust from mesozoic thinning explains the main patterns of seismicity in the northeastern and southeastern brazilian margins

stress orientations in brazilian sedimentary basins from breakout analysis implications for force models in the south american plate summary regional patterns of crustal stresses in brazil were studied with a detailed breakout analysis performed in 541 wells distributed throughout the country 481 from basins along the continental margin and 60 from intracratonic basins a total of about 591 km of cumulative well length digitally sampled at 0 15 m intervals was analysed most intervals 80 per cent are confined between 400 and 4000 m only wells that deviate less than 10d from the vertical were considered for a given well 1 the mean orientation and the standard deviation of each interval with breakouts were calculated 2 all intervals with mean breakout orientations less than 10d from the orientation of the hole deviation were discarded 3 all intervals with standard deviations less than 12d were selected 4 the selected breakouts were weighted by their interval length to calculate the mean orientation and standard deviation of the whole well and 5 the final results were classified according to the world stress map criteria thus 16 wells were classified as a a total of 7 2 km of breakouts 42 as b 7 1 km 78 as c 7 4 km 205 as d 3 3 km 184 as e 0 7 km and 16 were discarded in most basins the breakout orientations from different wells were usually consistent for qualities a b and c allowing a good estimate of the regional maximum horizontal stress shmax wells classified as quality d showed a large scatter the regional shmax determined from breakouts is generally in good agreement with the available nearby focal mechanisms the main trends of shmax are 1 nw se parallel to the coast along the equatorial marginal basins 2 e w in the alagoas basin 3 nne ssw parallel to the coast in the sergipe and reconcavo basins and 4 nw se in the middle amazon basin in the equatorial and eastern continental margins north of 15ds breakouts and focal mechanism measurements indicate that the shmax orientation is remarkably parallel to the coastline following a 90d bend of the coast in northeastern brazil because the theoretically predicted intraplate stresses in northern brazil trend about wnw to ene e g meijer 1995 coblentz richardson 1996 we interpret our observations as indicating that local sources of stress at the continental margins e g flexural stresses and lateral density contrasts dominate the plate wide stresses and may have been underestimated in theoretical stress models of the south american plate the new stress data 136 a c quality out of a population of 541 wells cover a region of mid plate south america where only 23 data points had been compiled previously in the world stress map database the more detailed observed patterns of the intraplate stress field should be helpful in better constraining future models of the forces driving the south american plate

the valle di manche section calabria southern italy a high resolution record of the early middle pleistocene transition mis 21 mis 19 in the central mediterranean abstract the on land marine valle di manche section crotone basin calabria southern italy one of the candidates to host the gssp of the middle pleistocene ionian stage preserves a manifold record of independent chronological paleoclimatic and stratigraphic proxies that permit a straightforward correlation with marine and terrestrial reference records at the global scale in particular the section holds an excellent record of the matuyama brunhes magnetic reversal which occurs in the midst of marine isotope stage mis 19 we report on a complete revision of the section that improves dramatically the available dataset especially in the stratigraphic interval straddling the lower middle pleistocene boundary our benthic 18o record provides evidence that the matuyama brunhes transition the stratigraphic position of which is marked by a prominent tephra the pitagora ash occurred during full mis 19 in agreement with many records worldwide we obtained an age of 786 9 5 ka for the matuyama brunhes magnetic reversal and pinpointed the paleomagnetic transition of to a 3 cm thick interval indicating that the event was very fast since the section fulfills all the requirements to host the gssp of the ionian stage we propose that the boundary should be placed at the base of the pitagora ash ca 12 5 cm below the midpoint of the matuyama brunhes reversal

environmental impact of the 73 ka toba super eruption in south asia abstract the cooling effects of historic volcanic eruptions on world climate are well known but the impacts of even bigger prehistoric eruptions are still shrouded in mystery the eruption of toba volcano in northern sumatra some 73 000 years ago was the largest explosive eruption of the past two million years with a volcanic explosivity index of magnitude 8 but its impact on climate has been controversial in order to resolve this issue we have analysed pollen from a marine core in the bay of bengal with stratified toba ash and the carbon isotopic composition of soil carbonates directly above and below the ash in three sites on a 400 km transect across central india pollen evidence shows that the eruption was followed by initial cooling and prolonged desiccation reflected in a decline in tree cover in india and the adjacent region carbon isotopes show that c 3 forest was replaced by wooded to open c 4 grassland in central india our results demonstrate that the toba eruption caused climatic cooling and prolonged deforestation in south asia and challenge claims of minimal impact on tropical ecosystems and human populations

utilization of observations of well bore failure to constrain the orientation and magnitude of crustal stresses application to continental deep sea drilling project and ocean drilling program boreholes

limited global change due to the largest known quaternary eruption toba 74 kyr bp abstract the 74 kyr bp super eruption of toba volcano in sumatra is the largest known quaternary eruption on the basis of preserved deposits the eruption magnitude has been estimated at 7 10 15 kg 2800 km 3 of dense magma the largest sulphate anomaly in the greenland ice sheet project 2 core has been identified as fallout from toba s stratospheric aerosol veil correlation of the sulphate and oxygen isotope stratigraphy of the ice core suggests that the toba eruption might have played a role in triggering a millennium of cool climate prior to dansgaard oeschger event 19 although a comparable stadial preceded event 20 a possible 6 yr duration volcanic winter immediately following the eruption has also been proposed as the cause of a putative bottleneck in human population supporting in a general way the garden of eden model for the origin of modern humans however along with counter arguments regarding the timing of any demographic crash there remain major gaps in our understanding of the 74 kyr bp toba eruption that hinder attempts to model its global atmospheric and climatic and hence human consequences the tephra record reveals basic aspects of the eruption style but calculations of the duration and hence intensity and plume height of the event are poorly constrained furthermore estimates of the sulphur yield of the erupting magma central to predictions of its atmospheric and climatic impacts vary by two orders of magnitude 3 5 330 10 10 kg previous estimates of globally averaged surface cooling of 3 5 c after the eruption are probably too high a figure closer to 1 c appears more realistic the volcanological uncertainties need to be appreciated before accepting arguments for catastrophic consequences of the toba super eruption

the regional intraplate stress field in south america a compilation of lithospheric stress directions for continental south america and the inferred major patterns of the regional intraplate stress field are presented stress orientations are based primarily on earthquake focal mechanisms and quaternary fault slip inversion published in the literature four new focal mechanisms based on short period p wave modeling and selected centroid moment tensor solutions published by u s geological survey consistent with p wave first motions at south american and other world wide standard seismograph network stations are also included in the data base the observed patterns of intraplate stresses may be useful in constraining numerical models of the plate driving forces in the south american plate in the andean plateau altitudes greater than 3000 m n s extensional stresses predominate e w compressional stresses are observed in the sub andean and platform regions extending up to about 1000 km east of the andes the maximum horizontal stress shmax is uniformly oriented in the e w direction throughout western south america averages of the shmax direction at grid points spaced 2 5 o were taken as representing the regional field the e w direction of this regional field is not affected by the change of strike of the andean chain nor by the contact of a flat subducted slab underneath the regional shmax direction is oriented 15 o more clockwise than the direction of the nazca plate convergence the difference between the regional shmax orientations and the absolute plate motion may be only about 6 o this may indicate that contact forces with the nazca plate may not be the only major contributor to the intraplate stresses in western south america the eastern limit of this andean stress province seems to coincide with aseismic regions in the upper amazon basin and in the paraml basin in the central amazonian region seismicity and stress data suggest a seismic province with n s compressional stresses the origin of these stresses is not yet clearly understood but could possibly be related to lower crustal loading along the middle amazon basin in northeastern brazil seismicity is characterized by upper crustal strike slip earthquakes bordering the potiguar marginal basin a model is proposed for this region in which the stress field is the result of a superposition of regional e w compressional stresses and local extensional stresses oriented perpendicular to the continental margin possibly related to density contrasts and sediment loading in the continental shelf

stress evolution and seismic hazard of the dead sea fault system abstract we calculated the stress evolution for the central part of the dead sea fault system 30 5 n 34 5 n from 551 to 2005 through modelling the static stress changes due to 14 historical earthquakes with m s 6 0 superimposed by tectonic loading from relative plate motion from the results of our numerical models we identified two segments with high positive changes in coulomb failure stress cfs exceeding 4 mpa a 90 km long segment of the jordan fault south of the sea of galilee and a 30 km long segment east of the dead sea these segments could result in m s 7 4 and m s 6 8 earthquakes respectively in contrast to similar stress evolution models of other continental transform faults our results support only partly the hypothesis that coseismically induced static stress changes control the spatial succession of earthquakes we calculated on each rupture plane the mean of cfs and the maximum cfs due to the stress changes of all preceding earthquakes the results of the calculated mean cfs values reveal that only 6 out of 13 earthquakes could have been triggered the subsequent earthquake from the analysis of the maximum cfs values we find that 8 out of 13 earthquakes could have triggered the subsequent earthquake since our model results are sensitive to location and magnitude of historical earthquakes and the tectonic loading rates of the fault segments we emphasize the need for further paleoseismological studies and current slip rate estimation from continuously observing gps arrays and geological investigations taking into account that six large cities beirut damascus haifa tel aviv amman and jerusalem are in close proximity with distances between 30 and 150 km to the jordan segment the seismic risk is probably higher than accounted before

investigation of present day in situ stresses and pore pressure in the south cambay basin western india implications for drilling reservoir development and fault reactivation abstract this work presents the assessment of present day stresses and pore pressures in a prolific onshore hydrocarbon bearing field located in the southern cambay basin western india through the development of a comprehensive geomechanical model a c quality wellbore breakouts inferred from the available four arm caliper logs and anisotropy analyses of dipole shear sonic logs indicate a ne n40 e to n50 e azimuth for maximum horizontal stress shmax pore pressure characterisation reveals mild overpressure in the lower eocene shale caused by disequilibrium compaction resulting from high sedimentation rates vertical stress sv was derived from density logs and a poroelastic strain model was employed to quantify the minimum shmin and maximum horizontal stress components shmax being later validated with leak off tests based on the relative magnitudes of three principal in situ stress components post rift strata upper eocene and younger reveal a normal faulting regime sv shmax shmin whereas a normal fault to strike slip faulting shmax sv shmin transition is observed in the syn rift unit lower eocene and older the mohr coulomb rock failure criterion was utilised to depict the shear failure gradient to prevent wellbore instability and results were validated with caliper logs we have also analysed the fault reactivation potential at reservoir level using frictional fault theory and stress polygons the results indicate that a minimum of 31 increase in pore pressure by fluid injection and hydraulic fracturing treatment can cause shear slippage of critically oriented faults resulting in induced seismicity our study has helped to understand the interplay between stress states and pore fluid pressure and their impact on reservoir development drilling and completion design and fault stability analysis in any given oil and gas field

fault plane solutions of intraplate earthquakes in brazil some constraints on the regional stress field abstract determination of intraplate stress fields is fundamental for a better understanding of the forces driving the plates in the south american plate few earthquakes away from the plate boundaries have been recorded by enough stations to have the nodal planes well determined the fault plane solutions of four recent events in central and northern brazil were determined these solutions were compared with previously determined solutions of other events in central and southeast brazil a statistically reliable estimation of the stress field for all of brazil is not yet possible on the basis of these data near the atlantic coast however the data are compatible with a regional stress field with the maximum compressive stress oriented parallel to the expected direction of ridge push or of south america s absolute plate motion mendiguren and richter 1978 farther to the west the stress field changes the direction of the maximum compressive stress seems to be aligned n s rather than e w almost all earthquakes analysed show reverse or strike slip focal mechanisms one event in central brazil however shows normal faulting thus the stress field in brazil is certainly not uniform and in some areas local sources of stress may predominate over regional fields

toba ash on the indian subcontinent and its implications for correlation of late pleistocene alluvium the toba ash occurs extensively in the indian subcontinent and marks a ca 74 000 yr old event in the bay of bengal and indian ocean it is about 10 cm thick whereas in several alluvial basins it is usually 1 3 m thick the latter occurs in a partly reworked state but as nearly chemically pure first cycle sediments the ash has a broad northwesterly dispersal pattern samples of ash from the indian subcontinent compare closely with the youngest 74 000 yr b p toba tuff and the deep sea toba ash in bulk chemical composition ree signature and bubble wall shard morphology however a more proximally located and thicker 2 5 m ash bed from the alluvial basins in the gneissic area and close to east coast has a lower magnitude negative eu anomaly possibly because of minor contamination by feldspathic silt quaternary sediments in the central narmada and middle son basins contain rich late and middle pleistocene mammalian and cultural records based on the presence of the ash layer marker and stratigraphic relations late pleistocene sediments within the subcontinent can be correlated with those from central india and the deep sea

dynamics of particles along the western margin of the southern adriatic processes involved in transferring particulate matter to the deep basin abstract the southern adriatic is an area of dense shelf water dsw cascading and open ocean convection the impact of dsw cascading events in transferring organic matter to the deep benthic community and in producing a wide range of bedforms along the continental margin has been highlighted in recent years in order to improve our knowledge on the interannual variability of the dsw cascading with the ultimate goal to understand timing of dsw formation and transport as well as the cascading process its variability in intensity and duration and the ultimate impact of the dense water on the deep sea in march 2009 we deployed an instrumented mooring in a field of sediment waves 860 m depth located down current to the bari canyon in march 2010 a second mooring was installed in the northern channel of the canyon winters 2009 2010 and 2011 were mild and particularly wet and the po river discharge remained relatively high throughout the whole winter hence we expected weak dense shelf water formation associated with a shallow shelf water overflowing off the adriatic shelf by contrast in winter 2012 the north adriatic experienced a severe cold wave with ne bora winds and reduced fresh water input these weather conditions allowed the formation of extremely dense shelf water three additional moorings were quickly deployed during this cold event in the southern adriatic sea to investigate the spatial variability of particle and organic matter fluxes exiting from the adriatic continental shelf under the influence of a strong dsw cascading event slow near bottom currents never exceeding 40 cm s 1 were recorded between march 2009 and february 2012 water temperatures depicted minor negative shifts total mass fluxes tmfs were low annual avg 1 7 2 8 g m 2 d 1 and 0 3 0 6 g m 2 d 1 in the canyon and in the sediment wave field respectively and peak values 6 8 g m 2 d 1 but showed significant seasonal and interannual variability fluxes in the canyon were higher than those measured in the sediment wave field at deeper water depth mass flux peaks during the 2112 dsw cascading were up to 5 times higher than the peaks of previous years up to 18 70 g m 2 d 1 with a spatial variability mainly driven by the localized pathways of dsw cascading in the canyon near bottom currents exceeded 70 cm s 1 and temperature dropped to 12 2 c while current speeds were high also at 1200 m depth 60 cm s 1 in the moat surrounding the dauno seamount surprisingly mass flux peaks occurred from the 16th february to the 1st of march 3 4 weeks ahead of the usual dsw occurrence suggesting an early arrival of the dsw the deep dsw cascading was the main process driving the particle transfer across the southern adriatic margin during late winter spring 2012 mooring data showed a nw se gradient of temperature and kinetic energy from upslope to basin floor indicating slope transverse flow modulated by local obstruction caused by the rugged seafloor topography bari canyon is one of the sites of dsw flow and in this area we have the possibility to extend observations back in time using continuous mooring data since 2009 and previous published materials this approach allowed evaluation of additional mechanisms of particle transport e g open ocean convection storm driven downward transport shallow dense water cascading that are particularly relevant in years when the dsw formation is less vigorous and cascading processes are sluggish the small amplitude of total mass flux peaks the weak currents and the relatively high and constant temperatures recorded during 2009 2010 and 2011 springs are consistent with an enhanced vertical particle rain from a mid water nepheloid layer triggered in turn by a shallow cascading of not particularly dense shelf water detaching from the seafloor when reaches its neutral buoyancy thus the intensity of dsw cascading shallow vs deep plays a first order control on the particulate fluxes through the western margin of the southern adriatic while storm induced sediment transport can occasionally be relevant too

the 1986 1988 intraplate earthquake sequence near joao câmara northeast brazil evolution of seismicity abstract the 1986 1988 intraplate earthquake sequence near joao c mara 5 5 s 35 7 w has been among the most significant in northeast brazil this century some 14 000 events were recorded in the 18 months from august 1986 including fifteen above magnitude 4 0 and one of 5 1 4000 buildings were damaged a local network of four portable seismographs was operated during most of the period augmented by a nine station telemetric network between may 1987 and april 1988 the temporal and spatial distribution of this seismicity is examined and determination of unusually good hypocentres is made possible by the simple velocity structure good signal transmission and impulsive p and s arrivals on most seismograms activity has been closely confined to a 28 km linear zone with a strike of 040 except for some small events along a parallel zone displaced laterally by 12 km neither zone has been related to any surface feature some unusual characteristics have raised concern about possible future seismicity the largest event occurred four months after the onset of activity and after several weeks of relative quiescence a 5 km intermediate section of the inferred fault has so far experienced only a few very small events

passive margin evolution initiation of subduction and the wilson cycle we have constructed finite element models at various stages of passive margin evolution in which we have incorporated the system of forces acting on the margin depth dependent rheological properties and lateral variations across the margin we have studied the interrelations between age dependent forces geometry and rheology to decipher their net effect on the state of stress at passive margins lithospheric flexure induced by sediment loading dominates the state of stress at passive margins this study has shown that if after a short evolution of the margin time span a few tens of million years subduction has not yet started continued aging of the passive margin alone does not result in conditions more favourable for transformation into an active margin although much geological evidence is available in support of the key role small ocean basins play in orogeny and ophiolite emplacement evolutionary frameworks of the wilson cycle usually are cast in terms of opening and closing of wide ocean basins we propose a more limited role for large oceans in the wilson cycle concept