seabed pockmarks associated with deepwater corals off se brazilian continental slope santos basin several factors bear evidence of chemosynthetic ecosystem occurrence in the brazilian coast these motivated our investigation to sample three pockmarks located on the continental slope off se brazil 26js and 46jw at f700 m depth the crater like features were f1 km in diameter and 100 m in depth and were identified with an echo sounder ek 500 they were sampled along two transects using a rectangular dredge our main objective was to identify possible evidence of a seep related community the surrounding sediments of the pockmarks seem to be filled with coral rubble harboring a rich fauna of metazoans including epilithic and chasmolithic organisms a total of 9565 organisms were sampled the most abundant group was the ophiuroidea followed by cirripedia and polychaeta a number of new occurrences and new species were registered the polychaete worm amelinna was the first record for the atlantic ocean which has been found in reducing habitats such as wood islands the echo sounder records also showed the presence of big deepwater coral mounds associated with the edge of the pockmarks these features are f 20 m in height and from 180 to 360 m wide records of demersal fishes were also registered right above coral mounds the presence of deepwater coral mounds at the edge of pockmarks may be related to the flow of the cold oxygen rich antarctic intermediate water over the bottom or else may benefit from the fertilization of the water by the microseepage of hydrocarbons from the sediment we suggest a more thorough survey in order to map and recognize these environments furthermore our findings may shed some light on new research perspectives concerning the ecology biogeography and evolution of reducing habitats off the brazilian coast d 2004 elsevier b v all rights reserved

elongated depressions associated with pockmarks in the western slope of the norwegian trench abstract terraces or elongated depressions have been surveyed in the western slope of the norwegian trench in origin the depressions seem to be closely related to the formation of pockmarks in the norwegian trench a study area d has been selected in the western slope for the description of the elongated depressions and their associated features an area of similar size e has also been selected in the norwegian trench in order to compare the recent geology of the two areas it is found that the elongated depressions probably are caused by a combination of shallow gas seepage the geometry of subsurface bedding and the action of bottom currents furthermore examples of faulting within soft silty unconsolidated clay is documented by use of deep towed boomer data the existence of such faults could explain how gas migrates through the upper layers

origin and morphology of limestone caves limestone caves form along ground water paths of greatest discharge and solutional aggressiveness flow routes that acquire increasing discharge accelerate in growth while others languish with negligible growth as discharge increases a maximum rate of wall retreat is approached typically about 0 01 0 1 cm yr determined by chemical kinetics but nearly unaffected by further increase in discharge the time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width discharge gradient and pco2 most caves require 104 105 yr to reach traversable size their patterns depend on the mode of ground water recharge sinkhole recharge forms branching caves with tributaries that join downstream as higher order passages maze caves form where 1 steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or 2 discharge or renewal of undersaturation is uniform along many alternate routes flood water can form angular networks in fractured rock anastomotic mazes along low angle partings or sponge work where intergranular pores are dominant diffuse recharge also forms networks and spongework often aided by mixing of chemically different waters ramiform caves with sequential outward branches are formed mainly by rising thermal or h2s rich water dissolution rates in cooling water increase with discharge co2 content temperature and thermal gradient but only at thermal gradients of more than 0 01 c m can normal ground water co2 form caves without the aid of hypogenic acids or mixing artesian flow has no inherent tendency to form maze caves geologic structure and stratigraphy influence cave orientation and extent but alone they do not determine branch work versus maze character

sediment distribution around salt domes and ridges on the louisiana slope abstract salt ridges and domes underlie much of the present louisiana slope the bathymetric expression of underlying salt could be either a mound or a flattening of the normal rate of descent down the slope the mounded salt features form barriers to the gravity driven sediments from the shelf break much industrial research has been done in the search for reservoir sands related to such an obstruction clues to depositional patterns related to salt features may be obtained from studies done in the deep ocean around seamounts located in pathways of ocean bottom currents parallel bedded sediments form fore drifts on the upcurrent side of a seamount these fore drift sediments were deposited where the prevailing ocean bottom currents were locally decelerated by the obstructing seamount in waters overlying the obstruction a taylor column of dead water or a slow cyclonic eddy provides tranquil oceanographic conditions permitting a greater fallout of sediments moats are found on the sides of the obstruction and are the result of erosion or non deposition due to acceleration of deflected waters lee drifts are found on the downcurrent side of the obstruction current gyres result from deceleration of accelerated currents along the obstruction s flanks and a complex sedimentation pattern results flow over the obstruction s top is determined by size and shape of the obstruction relative to size and velocity on the bottom following current a turbulent wave may be set up with sufficient amplitude to influence sedimentation on the downcurrent side there are appreciable differences in the sedimentation patterns influenced by a dome versus a ridge if ocean bottom currents equal gravity driven terrigenous sediment movement and seamounts equal salt domes and ridges then the result of deep ocean surveys are directly applicable to sedimentation on slopes with underlying salt basement the salt related sedimentation pattern of the present slope should be applicable to similar paleo environments

a procedure for landslide susceptibility zonation by the conditional analysis method numerous methods have been proposed for landslide probability zonation of the landscape by means of a geographic information system gis among the multivariate methods i e those methods which simultaneously take into account all the factors contributing to instability the conditional analysis method applied to a subdivision of the territory into unique condition units is particularly straightforward from a conceptual point of view and particularly suited to the use of a gis in fact working on the principle that future landslides are more likely to occur under those conditions which led to past instability landslide susceptibility is defined by computing the landslide density in correspondence with different combinations of instability factors the conceptual simplicity of this method however does not necessarily imply that it is simple to implement especially as it requires rather complex operations and a high number of gis commands moreover there is the possibility that in order to achieve satisfactory results the procedure has to be repeated a few times changing the factors or modifying the class subdivision to solve this problem we created a shell program which by combining the shell commands the gis geographical research analysis support system grass commands and the gawk language commands carries out the whole procedure automatically this makes the construction of a landslide susceptibility map easy and fast for large areas too and even when a high spatial resolution is adopted as shown by application of the procedure to the parma river basin in the italian northern apennines

evidence for sediment eruption on deep sea floor gulf of mexico a large crater has been discovered on the sea floor gulf of mexico in a water depth of 2176 meters deep tow high resolution imagery shows that the crater is cut into a low hill surrounded by near surface concentric faults approximately 2 million cubic meters of ejected sediment forms a peripheral debris field the low hill and faults may be related to mud diapirism or intrusion of gas hydrates into near surface sediments a recent eruption evacuated sediments from the crater apparently because of release of overpressured petrogenic gas

gis techniques and statistical models in evaluating landslide hazard geographical information systems gis and numerical cartography may greatly facilitate the development and use of statistical models for the assessment of regional landslide hazard from a small drainage basin located in central italy relevant geological and geomorphological factors were collected and processed by applying gis technology in particular modules were used which both generate high fidelity digital terrain models and automatically partition the terrain into main slope units the resulting information was then analysed by discriminant analysis which enabled landslide hazard and risk to be evaluated in each slope unit although not lacking drawbacks the method proved to be a feasible and cost effective approach to landslide susceptibility assessment and mapping

equilibrium halite h2o dihedral angles high rock salt permeability in the shallow crust shallow deposits of halite are well known to be impermeable to brines and hydrocarbons yet recent studies of deeply buried salt point toward considerable water halite interaction we have resolved this apparent paradox via experimental determinations of the dihedral angle for the static halite h 2 o system at temperatures of 20 to 300 c and pressures from atmospheric to 2 kbar the halite brine dihedral angle which controls pore fluid connectivity and hence permeability is found to be a sensitive function of both temperature and pressure in sedimentary basins with normal geothermal gradients halite bodies at depths exceeding 3 km will contain a stable interconnected brine filled porosity resulting in permeabilities comparable to those of sandstones our results explain recent observations of major salt fluid interactions at depth and suggest that deep rooted salt diapirs may act as conduits for basinal formation water they also have important implications for the flow of brines around heat producing canisters of high level nuclear waste buried in natural rock salt

gis based landslide susceptibility mapping using analytical hierarchy process and bivariate statistics in ardesen turkey comparisons of results and confirmations abstract the ardesen area is prone to landslides because of the climate conditions geologic and geomorphologic characteristics of the region as in previous years in 2001 due to heavy rainfall there were many landslides resulting in damage and human casualties there is still a great danger of further landslides in the region therefore it is vitally important to prepare a landslide susceptibility map of the region in this study the analytical hierarchy process ahp the statistical index wi and weighting factor wf methods were used to produce and later compare three susceptibility maps for this purpose thematic layers including landslide inventory lithology weathering slope aspect land cover distance to stream drainage density and distance to road were used in this study area 98 of landslides occurred in highly or completely weathered units lithology weathering land cover and slope data layers were found to be important factors in the study area to confirm the practicality of the three susceptibility maps were compared with a landslide activity map containing 16 active landslide zones the outcome was that the active landslide zones do not completely fit into the high and very high susceptibility classes but 81 3 of these landslide zones fall into the high and very high susceptibility zones of the ahp method while this is 62 5 in the case of wi method and 68 8 with the wf method in spite of the results obtained in this study the development of a susceptibility map is usually determined by the needs and available resources the results showed that the ahp method gave a more realistic picture of the actual distribution of landslide susceptibility than the wi and wf methods

a gis based landslide susceptibility evaluation using bivariate and multivariate statistical analyses bivariate and multivariate statistical analyses were used to predict the spatial distribution of landslides in the cuyahoga river watershed northeastern ohio u s a the relationship between landslides and various instability factors contributing to their occurrence was evaluated using a geographic information system gis based investigation a landslide inventory map was prepared using landslide locations identified from aerial photographs field checks and existing literature instability factors such as slope angle soil type soil erodibility soil liquidity index landcover pattern precipitation and proximity to stream responsible for the occurrence of landslides were imported as raster data layers in arcgis and ranked using a numerical scale corresponding to the physical conditions of the region in order to investigate the role of each instability factor in controlling the spatial distribution of landslides both bivariate and multivariate models were used to analyze the digital dataset the logistic regression approach was used in the multivariate model analysis both models helped produce landslide susceptibility maps and the suitability of each model was evaluated by the area under the curve method and by comparing the maps with the known landslide locations the multivariate logistic regression model was found to be the better model in predicting landslide susceptibility of this area the logistic regression model produced a landslide susceptibility map at a scale of 1 24 000 that classified susceptibility into four categories low moderate high and very high the results also indicated that slope angle proximity to stream soil erodibility and soil type were statistically significant in controlling the slope movement

the valhall field a geological overview abstract the valhall field is located within the central graben in the southern part of the norwegian north sea the discovery well 2 8 6 was drilled in 1975 and the field went on production in 1982 production is currently 55 000 barrels of oil per day the valhall field structure trends nw se and has an areal closure in excess of 60 000 acres the hydrocarbon column measures 200 m the structure is located on an elongate anticlinal feature called the lindesnes ridge which developed during late cenomanian to oligocene tectonic movements the geophysical evaluation of the field is complicated by the existence of a gas charged tertiary section which obscures the deeper seismic reflections vertical seismic profiles vsps have been utilized in an attempt to resolve the reservoir configuration reservoirs occur both in the tor formation maastrichtian and in the underlying hod formation turonian coniacian the tor formation is represented by a largely allochthonous chalk facies which thins regionally to the southwest a crestal graben is developed in which the tor formation is locally thick autochthonous chalks are characteristic of the hod formation primary porosity of the chalk varies between 36 to 50 on the crest of structure preservation of such high porosity is primarily due to formation overpressure inhibiting mechanical compaction of the chalk the field contains paraffinic oil of 36 api gravity it originated from the upper jurassic kimmeridge clay formation which is at peak oil generating capacity under the field at present day

a comparison of the gis based landslide susceptibility assessment methods multivariate versus bivariate the purpose of this study is to evaluate and to compare the results of multivariate logical regression and bivariate landslide susceptibility methods in geographical information system gis based landslide susceptibility assessment procedures in order to achieve this goal the asarsuyu catchment in nw turkey was selected as a test zone because of its well known landslide occurrences interfering with the e 5 highway mountain pass

giant pockmarks in a carbonate platform maldives indian ocean abstract circular structures and depressions in carbonate platforms are known to represent karst chimneys or sinkholes which form as a response to rock solution this formation mechanism is plausible for shallow water carbonates which lie in the reach of meteoric diagenesis or fresh water lenses circular structures which occur in deeper waters however need an alternative interpretation such an example of sea floor depressions in more than 300 m deep waters occurs in the inner sea of the maldives carbonate platform in the indian ocean the structures were mapped with multibeam and parasound multi channel seismics were used to link the depressions with structures at depth the circular depressions have diameters of up to 3000 m and depths of up to 180 m the craters are interpreted as pockmarks formed through the venting of gas and fluids gas and fluid lenses below the pockmarks are reflected by bright spots in the seismic sections as well as a reduction of the instantaneous frequency these areas at depth are linked to chimneys connected to faults and drowned oligocene carbonate banks a model is presented that relates the different forms and sizes of the structures to distinct development stages of sea floor deformation to one process early stages of gas and fluid migration into the shallow part of the sedimentary succession induce formation of dome shaped bodies initial gas and fluid escape to the sea floor is reflected by the formation of sand volcanoes and aligned small pockmarks active pockmarks are the deepest and have the shape of truncated cones in cross section mature pockmarks are characterized by erosion of the flanks of the structure by bottom currents late stage pockmarks are bowl shaped in cross section and are to different degrees filled by drift sediments packages of strata revealing high reflection amplitudes and high interval velocities interpreted as microbially mediated carbonate precipitates underlie some of the pockmarks the pockmarks in the maldives show that circular structures other than solution related features can be abundant in carbonate platform deposits and that such structures may be more abundant in the geological record of carbonate platforms as previously thought pockmarks in the maldives indicate that the archipelago is an example of a hydrocarbon system which consists of an isolated oceanic carbonate platform overlying a volcanic basement and lacustrine source rocks

complex pockmarks with carbonate ridges off mid norway products of sediment degassing abstract a new type of pockmark has been discovered off mid norway they contain up to 10 m high ridges of methane derived authigenic carbonate mdac rock the pockmarks were investigated using rovs remotely operated vehicles in 2003 and 2004 the complex pockmarks are located well within the gas hydrate pressure temperature stability field and are associated with a regional bsr bottom simulating reflector our high resolution seismic data demonstrate that the near surface sedimentary bedding dips into vertical pipe structures underlying the pockmarks and that the pipes are deeply rooted the pockmarks are circular in plan view and contain up to 190 m long and 40 m wide ridges formed by up to 4 m wide carbonate rocks piled on top of each other in irregular piles other key features of the complex pockmarks include 1 a distinct fauna with local bacterial mats small tubeworms stalked crinoids and pycnogonids sea spiders and 2 the presence of light hydrocarbon gases c 1 c 5 in clay rich sediments the methane 13 c values range from 54 to 69 pdb suggesting the presence of both bacterial and thermogenic gases during our two day observation periods only micro seepage occurred without ebullition or other visual fluid flow petrography and geochemistry of carbonate blocks from the pockmarks suggest precipitation of methane derived aragonite within the sediments 13 c 52 to 58 pdb we suggest that the complex pockmarks formed by sudden catastrophic fluid flow and that the large carbonate ridges represent dislodged mdacs originally formed subsurface prior to the event subsequent micro seepage is still active and may indicate that the pipes represent fluid flow conduits which transport both bacterial and thermogenic hydrocarbons to the water column our data do not suggest pressure buildup and do not predict future eruptions from the complex pockmarks thus our data rather suggest that the catastrophic formation of the complex pockmarks may be a one time event

interaction between bottom currents and slope failure in the late cretaceous of the southern danish central graben north sea the nw european chalk group was deposited in a deep epicontinental sea traditionally conceived as a quiet depositional setting that was only affected by redeposition along structural highs the chalk sea was however locally affected by powerful bottom currents during some periods three dimensional seismic reflection data from the southern central graben show abundant intra chalk morphological elements concentrated at two stratigraphic levels within the turonian campanian sequence both levels are topped by extensive unconformities the geometry of the elements produced by alongslope processes is interpreted as caused by se directed bottom currents flowing between the bo jens and adda ridges the highest current intensities led to the formation of the two unconformities judged by the occurrence of the largest current formed channels and drifts at these two stratigraphic levels this sea floor topography was locally modified by large scale downslope mass transport stratigraphical coincidence of the largest slumps and bottom current erosion suggests a coupling between downslope and alongslope processes current erosion impinged upon the slopes during periods of highest current speeds destabilizing the slope sediments and triggering slumping the smoothing of the bathymetry following local relaxation of the tectonic inversion accounted for the coeval deactivation of alongslope and downslope processes during the succeeding maastrichtian deposition

the physics of gas chimney and pockmark formation with implications for assessment of seafloor hazards and gas sequestration pockmarks form where fluids discharge through seafloor sediments rapidly enough to make them quick and are common where gas is present in near seafloor sediments this paper investigates how gas might lead to pockmark formation the process is envisioned as follows a capillary seal traps gas beneath a fine grained sediment layer or layers perhaps layers whose pores have been reduced in size by hydrate crystallization gas accumulates until its pressure is sufficient for gas to invade the seal the seal then fails completely a unique aspect of capillary seals releasing a large fraction of the accumulated gas into an upward propagating gas chimney which displaces water like a piston as it rises near the seafloor the water flow causes the sediments to become quick i e liquefied in the sense that grain to grain contact is lost and the grains are suspended dynamically by the upward flow the quickened sediment is removed by ocean bottom currents and a pockmark is formed equations that approximately describe this gas piston water drive show that deformation of the sediments above the chimney and water flow fast enough to quicken the sediments begins when the gas chimney reaches half way from the base of its source gas pocket to the seafloor for uniform near surface sediment permeability this is a buoyancy control not a permeability control the rate the gas chimney grows depends on sediment permeability and the ratio of the depth below seafloor of the top of the gas pocket to the thickness of the gas pocket at the time of seal failure plausible estimates of these parameters suggest gas chimneys at blake ridge could reach the seafloor in less than a decade or more than a century depending mainly on the permeability of the deforming near surface sediments since these become quick before gas is expelled gas venting will not provide a useful warning of the seafloor instabilities that are related to pockmark formation however detecting gas chimney growth might be a useful risk predictor any area underlain by a gas chimney that extends half way or more to the surface should be avoided c 2009 elsevier ltd all rights reserved

landslide hazard evaluation a review of current techniques and their application in a multi scale study central italy in recent years growing population and expansion of settlements and life lines over hazardous areas have largely increased the impact of natural disasters both in industrialized and developing countries third world countries have difficulty meeting the high costs of controlling natural hazards through major engineering works and rational land use planning industrialized societies are increasingly reluctant to invest money in structural measures that can reduce natural risks hence the new issue is to implement warning systems and land utilization regulations aimed at minimizing the loss of lives and property without investing in long term costly projects of ground stabilization government and research institutions worldwide have long attempted to assess landslide hazard and risks and to portray its spatial distribution in maps several different methods for assessing landslide hazard were proposed or implemented the reliability of these maps and the criteria behind these hazard evaluations are ill formalized or poorly documented geomorphological information remains largely descriptive and subjective it is hence somewhat unsuitable to engineers policy makers or developers when planning land resources and mitigating the effects of geological hazards in the umbria and marche regions of central italy attempts at testing the proficiency and limitations of multivariate statistical techniques and of different methodologies for dividing the territory into suitable areas for landslide hazard assessment have been completed or are in progress at various scales these experiments showed that despite the operational and conceptual limitations landslide hazard assessment may indeed constitute a suitable cost effective aid to land use planning within this framework engineering geomorphology may play a renewed role in assessing areas at high landslide hazard and helping mitigate the associated risk

gis based landslide susceptibility mapping for a problematic segment of the natural gas pipeline hendek turkey a segment of natural gas pipeline was damaged due to landsliding near hendek re routing of the pipeline is planned but it requires the preparation of a landslide susceptibility map in this study the statistical index wi and weighting factor wf methods have been used with gis to prepare a landslide susceptibility map of the problematic segment of the pipeline for this purpose thematic layers including landslide inventory lithology slope aspect elevation land use land cover distance to stream and drainage density were used in the study area landslides occur in the unconsolidated to semi consolidated clayey unit and regolith the wf method gives better results than the wi method lithology is found to be the most important aspect in the study area based on the findings obtained in this study the unconsolidated to semi consolidated clayey unit and alluvium should be avoided during re routing agricultural activities should not be allowed in the close vicinity of the pipeline

geometry of allochthonous chalk group members central trough north sea abstract the temporal and spatial distribution of the hydrocarbon bearing late cretaceous and early tertiary allochthonous chalk is of economic importance examination of cores from the uk sector of the central trough has confirmed the correlation of major allochthonous chalk units to wireline log responses dependent on high porosity allochthonous units were recognized from wireline log coverage of over 100 exploration wells in the central trough area correlation indicated extensive apparent lateral continuity of allochthonous sediment packages enabling the establishment of an event stratigraphy a minimum of nineteen major redeposition events were recognized within the late cretaceous maastrichtian and early palaeocene danian chalks essentially synchronous sourcing and redeposition occurred on both margins of the central trough but with a marked dominance of activity along the eastern margin in terms of incorporated sediment volume the described core material was placed in a regional context by means of the event stratigraphy and confirmed a previously proposed relationship of depositional rock type and transport distance this study recognizes five principal mass flow complexes named after their dominant sediment source areas jaeren north hidra south hidra lindesnes and auk the jaeren north hidra and auk flow complexes are here documented for the first time as are other less extensive deposits

cretaceous early tertiary inversion tectonism in the danish central trough abstract the inversion of the danish central trough was heralded by a mild precursor during the late hauterivian before rifting had ended the main inversion took place during the late cretaceous it can be subdivided into several sub phases of which those occurring during the turonian santonian mid maastrichtian and post danian early tertiary are the most pronounced minor inversion tectonism occurred more or less continuously between these major events the turonian santonian event had the greatest impact in the northern part of the danish central trough whereas the effects of later events are most pronounced in the south throughout the late cretaceous danian a gradual change from more brittle deformation with faulting to more plastic deformation characterised by folding and flexuring can be seen

seismic stratigraphy of the chalk group in the norwegian central graben north sea abstract the late cretaceous to early palaeogene chalk group in the norwegian central graben contains prolific hydrocarbon reservoirs that have been producing at high rate for more than forty years based on integration of regionally extensive 3d seismic data and numerous wells this paper describes the seismic development of the chalk group with particular focus to the syndepositional geomorphological features produced by the activity of bottom currents and large scale gravity flows using standard seismic stratigraphic interpretation techniques eight seismic sequence boundaries are identified which in turn define seven seismic stratigraphic sequences characterized by different seismic facies and well log signatures the seismic sequences can be grouped into three sequence groups that reflect the general tectono stratigraphic evolution of the chalk depositional system in the norwegian central graben during the late cretaceous uplift of the lindesnes ridge and the albuskjell anticline due to inversion tectonic and halokinesis modified the physiography of the norwegian central graben basin and affected the style of chalk sedimentation by influencing the location and importance of gravity flows in addition bottom currents sea level fluctuations and environment changes significantly influenced the chalk depositional system creating regional unconformities and influencing the input of terrigenous material in the chalk epeiric sea

surface and subsurface expressions of gas seepage to the seabed examples from the southern north sea expressions of gas seepage observable within north sea seismic and acoustic data include seabed pockmarks seepage plumes in the water column acoustic blanking shallow enhanced reflectors and shallow seismic chimneys three areas were selected for a marine survey in

giant irregular pockmark craters in the palaeogene of the outer moray firth basin uk north sea a cluster of irregular pockmark craters of palaeogene age in block 15 18 in the outer moray firth uk north sea have been mapped on 3d seismic data with well control the craters range from 0 5 to 4 km in diameter between 50 and 200 m in depth and have been buried by tertiary subsidence and sedimentation to present day depths of between 1000 and 1400 m sub sea they are circular to elliptical in plan view and are located in a delta front and upper pro deltaic slope position on the dornoch delta the structures are confined to the top of the lower eocene balder formation and regional mapping across the moray firth basin shows they are restricted to an area of ca 15 15 km2 well data show that the craters are sand filled and have excavated an argillaceous and tuffaceous unit the crater filling sands are sealed by overlying mudstone units planar wing like features emanate from the margins of the craters well control indicates that these seismically identified wings consist of sandstone suggesting that the craters have been modified by an episode of sand remobilisation and injection the proposed mechanism for the formation of these structures is large scale fluid eruption probably shallow gas at the early eocene seafloor these craters are significantly larger in size than those typically observed on contemporary sea floors we argue that the gas is more likely to have been sourced from deeper jurassic or carboniferous sediments within the witch ground graben than from shallow biogenic origins these structures rank in scale alongside the largest known pockmarks and demonstrate that natural fluid and hydrocarbon seeps have a long ancestry in this basin

gas seepage as an indicator of deeper prospective reservoirs a study based on exploration 3d seismic data three periods of sustained gas seepage in geological time have been revealed in danish block 5604 26 in the north sea by the use of exploration 3d seismic data the most recent period is indicated by a cluster of seismic chimneys which ties in to buried craters near the seabed and possible present gas escape through the seabed along with amplitude anomalies indicating a shallow gas sand charged by gas migrating from a deeper level the cluster of seismic chimneys indicative of vertical gas migration is visible down to 1 5 s twt 1500 ms and therefore the gas is interpreted as migrating from a deeper stratigraphic horizon below this level it becomes difficult to see the chimneys due to complex faulting the faults may work as gas migration pathways the geometry of the cluster of seismic chimneys indicates that the gas has been migrating from one point the nearest possible source of the gas is an underlying prospect where an oil and gas discovery has been made two earlier periods of gas seepage are indicated by mounds possibly carbonate buildups over gas seepages in pliocene time and similarly buried craters formed by gas seepages in an earlier period in pliocene time the results of this study are that gas seepage is a periodical process in geological time and that its presence and associated features can be used as an indicator of deeper prospective reservoirs

prediction of the occurrence of slope instability phenomenal through gis based hazard zonation slope instability hazard assessment is based on the analysis of the terrain conditions at sites where slope failures occurred in the past for the analysis of the causative factors the application of geographic information systems gis is an essential tool in the data analysis and subsequent hazard assessment three scale levels of hazard mapping are defined a direct experience driven mapping at reconnaissance level a statistical approach to determine the causative factors in a quantitative susceptibility mapping and a methodology at large scale making using of deterministic models

oligocene sequence stratigraphy and basin development in the danish north sea sector based on log interpretations abstract five sequences are defined in the oligocene succession of the danish north sea sector two of the sequences 4 1a and 4 3 have been identified onshore denmark two types of prograding lowstand deposits are recognized sand dominated deposits occur proximally comprising sharp based forced regressive deposits covered with prograding low stand deposits clay dominated prograding lowstand deposits occur distally in the sequences the highstand deposits are proximally represented by thick prograding sandy deposits and distally by thin and condensed intervals the main sediment input direction was from the north and the northeast a succession oif lithofacies from shallow marine facies dominated by sand to outer shelf facies dominated by clay is mapped in each of the sequences an overall southward progradation of the shoreline took place during the oligocene interrupted only by minor shoreline retreats

mass transport in european cretaceous chalk fabric criteria for its recognition although it is a pelagic sediment fine grained calcareous ooze may be mobilized prior to general lithification and redeposited as allochthonous units numerous occurrences of allochthonous chalk have been reported in recent years having been recognized by large scale bedding features seen in outcrop smaller scale internal features such as contorted laminae and larger features such as smeared burrows and imbricated flint nodules attest to a significant amount of soft sediment deformation and synsedimentary slumping in european chalk sections of late cretaceous age truly autochthonous chalks contain complex tiered ichnofabrics and in some cases exhibit a diagenetic nodular fabric that is undisturbed by transport in some situations such as stagnant water conditions autochthonous chalks may exhibit primary lamination although this is very uncommon in european chalk sequences different types of redepositional processes produce an array of varied allochthonous fabrics glide and slump units for example contain internal deformational features produced during sliding ooze flow causes plastic deformation of chalk units internally as well as externally resuspension and fluid flow of chalk sediment produces a deposit having a totally new fabric such as a conglomerate composed of detrital chalk clasts in this paper typical macroscopic sedimentary fabric types are illustrated and the means of identifying them are discussed in terms of bioturbation features in situ diagenetic nodules versus detrital clasts physical deformation structures and development of flints

buried pockmarks on the top chalk surface of the danish north sea and their potential significance for interpreting palaeocirculation patterns three dimensional 3d seismic data from the southern danish north sea were used to analyse the morphology and spatial distribution of depressions in the danian chalk deposit previously these depressions were either interpreted as karst structures or pockmarks the observed depressions occur in an interval from 25 ms below to 12 ms above the top chalk surface three types of depressions were differentiated based on their plan view geometry and their degree of symmetry type 1 comprising sub circular and symmetrical depressions is the dominant group ca 70 type 2 elongated and symmetrical depressions represents only a small fraction ca 5 the elongated and asymmetrical depressions of type 3 compose ca 25 in cross section each depression type can be either characterised by a v or a u shape the maximum size of the depressions ranges from 50 to 580 m with an average internal depth of 10 m we interpret the depressions as pockmarks formed by the expulsion of biogenic or thermogenic fluids at the danian seafloor likely the initial form of the pockmarks has been circular type 1 and was subsequently modified for types 2 and 3 to an elongated form by currents the long axis of the pockmarks is interpreted to represent the effective current direction the inferred direction is sub parallel to the palaeobathymetric contours the 3d seismic interpretation of pockmarks presented in this paper contributes to the understanding of fluid migration and palaeocirculation patterns during the sedimentation of the terminal chalk group in the southern danish north sea

structural evolution of inverted basins in the dutch offshore abstract the structural evolution of the dutch central north sea graben and the fault bounded broad fourteens basin is discussed graben formation started during the early triassic and culminated in strong differential subsidence during the late jurassic early cretaceous narrow fault bounded grabens and troughs and broad intervening highs were formed as a result of crustal distension and associated transtensional deformations the thickness of the late jurassic to early cretaceous fill of these basins may have exceeded 3000 m concurrent with the filling of these basins the bordering highs became deeply truncated during the late cretaceous and early tertiary compressive stresses resulted in inversion of these basins whereby movements along their bounding normal faults were reversed giving rise locally to overthrusting as for instance in the broad fourteens and west netherlands basins the timing of these compressional deformations has been palaeontologically dated and coincides with major orogenic events in the alps

the cretaceous palaeogene boundary at stevns klint denmark inversion tectonics or sea floor topography the cretaceous palaeogene boundary interval is exposed over 12 km in the coastal cliff stevns klint denmark an important lowermost danian hardground has been interpreted as an originally horizontal marine abrasion surface its present elevation varies from a few metres below to about 35 m above sea level this relief has traditionally been considered as resulting from late or post danian laramide folding new seismic profiles offshore stevns klint show however that the base chalk reflector is not folded is remarkably planar and has a gentle northward dip thus the folding hypothesis cannot be upheld seismic stratigraphic analysis of the chalk group necessitates a fundamental revision of general ideas of chalk deposition a highly irregular sea floor topography was formed at many levels and includes broad valleys ridges channels drifts and mounds a system of major wnw ese oriented valleys and ridges can be traced into the succession exposed in stevns klint and further inland where it corresponds to the relief of the cretaceous palaeogene boundary the marked topographic elements of the chalk sea floor are elongate with a wnw orientation roughly parallel to the axis of the danish basin and to the sorgenfrei tornquist zone forming the ne border of the basin the sea floor relief undoubtedly reflects the influence of strong contour parallel bottom currents the cretaceous palaeogene boundary succession at stevns klint was thus developed on an underlying sea floor topographic relief of about 40 m recognition of the highly irregular current influenced topography of the late cretaceous sea floor stands in marked contrast to the conventional picture of quiet pelagic deposition of the chalk

the development and seismic expression of synsedimentary features within the chalk of southern england seismic reflection data acquired onshore to the north of bournemouth southern england image clearly a series of prominent concave up troughs or depressions and concave down mounded structures within the white chalk subgroup the chalk lithostratigraphy in the area of study is established from borehole geophysical log correlations these correlations then provide calibration of the seismic reflection data indicating that the structures are concentrated at levels between the lewes nodular chalk formation and tarrant chalk member and towards the base of the portsdown chalk formation onlap downlap and truncation of reflectors are observed with the most dramatic features forming a stacked series directly overlying faulting of jurassic strata similar stratal geometries have been described from comparable levels in the chalk of the north sea and in outcrop in britain and france to many they represent channels formed by submarine erosion and redeposition of the chalk during relative sea level falls linked to tectonics we also interpret a number of apparently incisive structures and slumped infill sequences described here as being of primary syndepositional origin the slumping and the close association of these features with underlying faults and proximity to nearby major crustal faults may be indicative of submarine erosion of the chalk caused by sea level changes linked to syndepositional fault movements however evidence of toplap downlap pairs is also suggestive of more aggradational mounding or laterally migrating surfaces or facies belts the presence of any such structures implies rapid lateral variations in the chalk that would have implications not only for aquifer management and future storage schemes but also during the processing of seismic reflection data and general studies and correlations of the chalk across southern britain

diagnosis of landslide risk for individual buildings insights from prahova subcarpathians romania the aim of this study is to quantify the landslide risk for individual buildings using spatial data in a gis environment a landslide prone area from prahova rivers subcarpathian valley was chosen because of its associated landslide hazards and its impact upon human settlements and activities the bivariate landslide susceptibility index lsi was applied to calculate the spatial probability of landslides occurrence the landslide susceptibility index map was produced by numerically adding the weighted thematic maps for slope gradient and aspect water table soil texture lithology built environment and land use validation curves were obtained using the random split strategy for two combinations of variables a all seven variables and b three variables which showed highest individual success rates with respect to landslides occurrences slope gradient water table and land use the principal pre disposing factors were found to be slope steepness and groundwater table vulnerability was established as the degree of loss to individual buildings resulting from a potential damaging landslide with a given return period in an area risk was calculated by multiplying the spatial probability of landslides by the vulnerability for each building and summing up the losses for the selected return period

reactivation characteristics and dynamic hazard prediction of an ancient landslide in the east margin of tibetan plateau the increasing human engineering activities and frequent extreme weather events have caused extensive reactivation of ancient landslides which are widely developed in the east margin of tibetan plateau the shangyaogou landslide as a typical ancient landslide example in this area was investigated to reveal the reactivation characteristics and its stability was calculated under the continuous rainfall condition with the intensity 30 mm day using the finite element software geo studio the whole movement process and hazard prediction under the different triggering conditions were simulated using the numerical software dan3d the study results showed that 1 under the joint influence of mw 7 9 wenchuan earthquake toe erosion and intensive rainfall multi stage deformations occurred to the front part of the shangyaogou landslide in multiple periods and also indicated a significant potential instability 2 under the continuous rainfall condition when the single effective total infiltration reached about 65 mm the reactivation part will become unstable while the single effective total infiltration reached about 120 mm both reactivation part and posterior part became instability 3 the maximum run out distance of the reactivation part was calculated to be 350 m and the forefront of the accumulation deposit would not reach the residential area when both parts failed simultaneously the maximum run out distance was calculated to be 550 m by considering the thickness and dynamic energy of the accumulation deposits and the vulnerable elements inside the fan area with radius of 150 m would be severely threatened 4 abundant earthquake triggered landslides have been developing in history or in recent years in the eastern margin of tibetan plateau some of them have been partly reactivated due to the increasing human engineering activities and extreme rainfall events and they have a potential for further deformation and failure the presented study methods can provide guidance for local disaster prevention and mitigation and can be used as a reference for the hazard prediction of the similar ancient landslides which have been reactivated

seismic geomorphology and growth architecture of a miocene barrier reef browse basin nw australia abstract the cenozoic succession of browse basin is characterized by a carbonate system that developed from a non tropical ramp in eocene lower miocene times to a tropical rimmed platform in the middle miocene the evolution of the platform was unraveled through the interpretation of the seismic geomorphology and borehole data of the middle miocene tropical reef system the first reef structures developed during the early middle miocene as narrow linear reef belts with an oblique orientation with respect to shelf strike direction subsequently they prograded toward the platform margin to form a barrier reef with a minimum length of 40 km the barrier reef itself comprises three distinct ridges separated by progradational steps the second and third step are separated by a karstified horizon which is interpreted to represent the global sea level fall shortly before the serravallian tortonian boundary the following third ridge formed in a slightly downstepped position during the sea level lowstand and initial transgressive phase further sea level rise during the early tortonian first drowned the barrier reef system and subsequently also the patch reefs and relic atolls that had established in a backstepped position in the platform interior the similar evolution of the browse basin reef system and other contemporaneous carbonate systems indicates a strong impact of eustatic sea level changes relatively large subsidence rates in the study area possibly augmented the eustatic sea level rise in the tortonian and hence contributed to the drowning of the reef system however the initiation and final demise of the reef system was also governed by global and regional climate variations the first seismically defined reefs developed simultaneous to a maximum in the transport capacity of the indonesian throughflow which brings warm low salinity waters to the north west shelf reef drowning followed the restriction of this seaway close to the middle to early miocene boundary this near closure of the indonesian seaway possibly led to a regional amplification of the global middle to late miocene cooling trend and hampered the potential of the reef system to keep up with the rising sea level

landslide susceptibility delineation in the ar rayth area jizan kingdom of saudi arabia using analytical hierarchy process frequency ratio and logistic regression models mountain areas in the southern western corner of the kingdom of saudi arabia ksa frequently suffer from various types of landsides induced by rainstorms and anthropogenic activities to mitigate these problems landslide susceptibility mapping and classification is important to develop quick and safe mitigation or remediation measures and to help the decision making in future planning by identifying the most vulnerable areas this paper summarizes the findings of a landslide susceptibility analysis in the ar rayth area jizan ksa using an analytical hierarchy process ahp frequency ratio fr and logistic regression lr models with the aid of gis tools and remote sensing data the landslide inventory map was prepared according to historical data interpretation of high resolution satellite images geo eye 0 5 m resolution and quickbird 0 6 m resolution topographic maps 1 10 000 and verified by field investigations an inventory map with 253 landslides locations was extracted from many sources the landslide inventory was randomly divided into two datasets 75 for training the models and 25 for validation an enhanced thematic mapper plus 15 m satellite image acquired in 2006 was used for determining the normalized difference vegetation index a contour map 1 10 000 with a 10 m contour interval was converted to digital elevation model 10 m resolution and subsequently converted to slope slope aspect curvature elevation and drainage networks geological data obtained with the help of satellite images were used to prepare lithological units and lineaments roads were digitized from the high resolution image and a rainfall map was prepared from the rainfall gauges distributed throughout the study area all these data were used to construct a spatial database using gis and image processing three landslide susceptibility maps were constructed one on the basis of a heuristic method using an ahp the other two on the basis of landslide inventories and causative factors using fr and lr furthermore each causative factor s weight was determined according to these three models and landslide susceptibility indices were calculated for verification receiver operating characteristic curves were calculated and the areas under the curve auc for success rate are 0 755 0 828 and 0 749 and for prediction rate are 0 708 0 781 and 0 727 for the ahp fr and lr respectively in addition the percentage of existing training landslides data in high and very high zones of the susceptibility maps is of 73 2 85 31 and 88 59 and for the validation landslides data is 73 2 85 31 and 88 59 for the ahp fr and lr respectively the findings indicated that the values of auc are above 0 7 for both success and prediction rate which indicate these three models are suitable for susceptibility analysis also percent of training and validation landslides data of high and very high zones indicate that lr model is more accurate followed by fr model and ahp model

gas induced erosion features in the north sea pockmarks are prominent features on the seafloor at two main regions of the north sea the south fladen area and the norwegian trench the pockmarks vary in size from 5 m across to about 150 m and in depth from 1 m to about 20 m some of the features consist of several very small unit pockmarks these are probably gas induced erosion features and found only in soft finegrained marine and glaciomarine sediments they are probably caused by shallow or deep seated gas or fluid release through the seabed whereby the finest particles are thrown into suspension and redistributed by nearbottom currents on the north sea plateau a small pockmarked area has recently been found a close relationship exists here between mobile gas in the upper sediments faulting in the soft sediments and the morphology of the seabed other morphological features in the north sea such as coast parallel depressions and elongated depressions or terraces are also interpreted here as gas induced erosion products this applies yet again to the mottled seabed features which appear as patches of high reflectivity on side scan sonar records from the north sea plateau they correspond to shallow seabed depressions on the deep towed boomer records judging from reported observations from several shallow seas world wide volatile transport through the seabed is probably quite common and several morphological features are undoubtably induced by this process several erosion features of similar origin are probably common also in deep ocean basins

chalk fields along the lindesnes ridge eldfisk abstract eldfisk field lies on the lindesnes ridge northwest of the valhall and hod fields and to the southeast of edda in block 2 7 of the norwegian north sea the field has a complex geological history and reservoir geometry seismic reflection data is strongly gas affected and degraded over the majority of the field the geological model of the field was based exclusively on well data and the model was inadequate to explain some of the production characteristics or to identify additional prospective well locations in 1982 a programme of vertical seismic profiling vsp was started in the northern part of the field the seismic data provided by vsp have improved and confirmed the geological model provided some explanations for production variances and identified further areas of interest

elongate depressions on the southern slope of the norwegian trench skagerrak morphology and evolution abstract multibeam echosounder surveys conducted on the southern slope of the norwegian trench between norway and denmark show that elongate depressions interpreted as current modified pockmarks are widespread in water depths of 100 500 m in the holocene recent succession the long axes of the depressions are oriented at an angle of about 15 downslope relative to the depth contours the long axes appear to almost exactly parallel the effective bottom currents in this part of the skagerrak the present current directions were probably established about 4000 years ago following a major shift in the oceanographic circulation pattern the most characteristic feature of the depressions is their large size with maximum depths of 45 m widths of 400 m and lengths of 2 km strong bottom currents continuously transport particles thrown into suspension by the seepage process away from the pockmarks and prevent further deposition continuous seepage of shallow gas at fixed pockmark sites over long time periods combined with generally high sedimentation rates are thought to be responsible for the exceptional size of many depressions the shallow gas probably has a mixed biogenic thermogenic origin however the thermogenic component is considered to be most important for the formation of pockmarks seepage from permeable layers in the jurassic cretaceous bedrock is evidenced by linear rows of depressions above these horizons while pockmarks above sub surface faults indicate gas seeps also from there in shallow water areas the shape and size of pockmarks are locally dependent on their location with respect to giant sand waves which trend sub parallel to the depth contours and are interpreted to be of late weichselian to early holocene age in deeper water areas the pockmarks have been further modified by gravity slides caused by collapse of steep pockmark walls

pockmarks and the recent geology of the central section of the norwegian trench a small area of 3 1 km2 in the norwegian trench has been selected for a detailed analysis of possible relationships between the recent geology and the formation of pockmarks two sets of side scan sonar and deep towed boomer dts data were used for the analysis the most recent deposit is unit 1 consisting of finely layered soft silty clays unit 1 has been divided into three seismic subunits 1a 1b and 1c based upon the boomer records the underlying unit 2 is seismically homogeneous consisting of stiff silty sandy clay with fragments of chalk most of the irregularities in the surface of unit 2 are found to be furrows traversing the study area in a n s general direction the seabed is heavily pockmarked mean density 30 km2 and some of the pockmarks are asymmetric with steep ese walls the maximum pockmark depth within the study area is 5 8 m and the maximum wall angle is about 12 in addition to describing the recent geology and surface pockmarks the following features are described and their relationship with pockmark formation discussed 1 sloping reflectors found below some of the pockmarks 2 columnar disturbances seen under many of the buried pockmarks and 3 masked reflectors intermittent strong reflectors found within subunit 1a which are probably caused by a raised gas concentration in porous layers pockmarks and associated features are assumed to be caused by gas escaping through the seabed a possible gas migration mechanism through the interface between units 1 and 2 and through unit 1 is also discussed

a scale dependent model to represent changing aerodynamic roughness of ablating glacier ice based on repeat topographic surveys turbulent fluxes make a substantial and growing contribution to the energy balance of ice surfaces globally but are poorly constrained owing to challenges in estimating the aerodynamic roughness length z0 here we used structure from motion sfm photogrammetry and terrestrial laser scanning tls surveys to make plot scale 2 d and 3 d microtopographic estimations of z0 and upscale these to map z0 across an ablating mountain glacier at plot scales we found spatial variability in z0 estimates of over two orders of magnitude with unpredictable z0 trajectories even when classified into ice surface types tls derived surface roughness exhibited strong relationships with plot scale sfm z0 estimates at the glacier scale a consistent increase in z0 of 0 1 mm d 1 was observed space for time substitution based on time since surface ice was exposed by snow melt confirmed this gradual increase in z0 over 60 d these measurements permit us to propose a scale dependent temporal z0 evolution model where unpredictable variability at the plot scale gives way to more predictable changes of z0 at the glacier scale this model provides a critical step towards deriving spatially and temporally distributed representations of z0 that are currently lacking in the parameterisation of distributed glacier surface energy balance models less

topography of the top chalk surface on and offshore denmark abstract a time structure map of the top of the upper cretaceous danian chalk group the top chalk surface in the entire danish sector is presented the present topography of the top chalk surface is a result of various erosional and tectonic events taking place during the cenozoic the analysis shows that the cenozoic is characterised by significant reactivation of the mesozoic structural elements of which the central graben the ringkobing fyn high and the sorgenfrei tornquist zone are the most important a tectonically controlled relief caused the generation of widespread sheet like erosion on the ringkobing fyn high and incisions along the margins of ringkobing fyn high during the mid paleocene incisions in the northern part of the danish sector formed valleys which probably transported sediment towards the west the present topography of top chalk in the eastern part of the danish sector is highly influenced by the late cenozoic erosion of the uplifted eastern margin of the north sea basin the topography of top chalk also reflects the distribution of mobile zechstein salt as collapse structures follow the pitch out line of mobile salt onto the ringkobing fyn high and numerous salt structures deformed the top chalk surface

cenozoic evolution of the eastern danish north sea this paper provides a review of recent high resolution and conventional seismic investigations in the eastern danish north sea and describes their implications for the development of the eastern north sea basin the results comprise detailed time structure maps of four major unconformities in the eastern danish north sea the top chalk surface mid paleocene near top oligocene the mid miocene unconformity and base quaternary the maps show that the eastern danish north sea has been affected by faulting and salt diapirism throughout the cenozoic carbonate mounds erosional valleys and pockmark or karst like structures were identified at the top of the upper cretaceous danian chalk group strike parallel erosional features and depositional geometries observed at near top oligocene and at the mid miocene unconformity indicate that these major sequence boundaries can be attributed to large scale lateral changes in sediment supply directions increases in sediment flux to the southeastern north sea at the eocene oligocene transition and in the post middle miocene appear to correlate with similar events world wide and with long term 18o increases indicating forcing by global factors i e eustasy and climate stratal geometries observed on the seismic data indicate that the so called neogene uplift of the eastern danish north sea may have been hundreds of metres less than previously suggested it is argued that late cenozoic uplift of the basin margin and of mountain peaks in southern norway may have been caused entirely by isostatic uplift of the crust in response to accelerated late cenozoic denudation and dissection of topography created in the paleogene the late cenozoic periods of accelerated denudation and incision rates were most likely driven by climatic deterioration and long term eustatic lowering rather than active late cenozoic tectonics the cause of which is conjectural a series of shallow thrust structures and an associated system of deep buried valleys were mapped thrust faulting most likely occurred in response to gravitational loading at the margin of an advancing ice sheet and it was followed by deep incision due to subglacial melt water erosion probably during the elsterian glaciation