thermal effects of normal faulting during rifted basin formation 1 a finite difference model abstract a finite difference model is presented describing the thermal structure of a region undergoing fault controlled extension the model is two dimensional and time dependent we combine temperature changes resulting from conduction advection due to fault movements sediment blanketing and heat production cooling curves can be derived at chosen points in the area this study mainly investigates the effect of the extension rate on the thermal field which turns out to be very important 20 km of extension with extension rates of 0 2 2 0 and 20 mm yr yield maximum deviations in temperatures from the steady slate situation of 2 26 and 84 the sediment blanketing effect can even be reversed by variations in the sedimentation rates fast sedimentation leads to crustal cooling slow sedimentation to crustal heating the turning point value is lithology dependent and corresponds to 2 0 mm yr for shale 2 2 mm yr for clay and 1 4 mm yr for sand a sandstone will cause an increased cooling at both high and low velocities our modelling shows that footwall cooling during or immediately after a rifting event cannot be explained by the downwards movement of the adjacent relatively cold hanging wall consequently in areas where such a cooling is observed other cooling mechanisms must play an important role these can be phenomena like footwall uplift or the fading out of an older thermal anomaly

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

contrasting dissolved organic matter quality in groundwater in holocene and pleistocene aquifers and implications for influencing arsenic mobility abstract the discontinuous nature of elevated arsenic as in drinking water wells of west bengal and other regions in the bengal basin has led to increased interest in the role that sediment derived organic matter may play in enhancing reductive dissolution and as mobilization higher as concentrations have been observed in groundwater in reduced holocene grey aquifers when compared to oxidized pleistocene orange aquifers in order to evaluate if the differences in the chemical character of dissolved organic matter dom are present in groundwater in the holocene and the pleistocene aquifers that may influence dissolved as concentrations shallow groundwater and surface water samples were collected from four study sites in murshidabad district west bengal india and analyzed for water chemistry parameters and characteristics of dom for wells known to typically contain high as concentrations in holocene sediments in beldanga 10 4622 g l at 35 45 m depth and hariharpara 5 695 g l at 6 37 depth sites as well as wells characterized by low as concentrations pleistocene sediiments in nabagram 0 16 g l at 20 45 m depth and kandi 5 50 g l at 20 55 m depth detailed dom characterization was carried out using fluorescence spectroscopy and parallel factor analysis parafac results from statistical analysis of a variety of optical absorbance and fluorescence dom properties revealed that the dom in groundwater in the holocene aquifer had high humification index hix and low freshness index values whereas groundwater in the pleistocene aquifer comprised more labile and microbial dom sources consistent with the more labile nature of dom in groundwater in the pleistocene aquifer two ratios 1 humic like to protein like components humic protein and 2 terrestrially derived to microbially derived components terr microb obtained from a four component parafac model were 1 9 and 2 9 times greater respectively in groundwater in the holocene aquifer than in that of the pleistocene aquifer which suggests that the absence of humic like dom may be an important limitation to as mobility

initiation of subsidence in a sedimentary basin underlain by a phase change summary a mechanism of subsidence for axisymmetric sedimentary basins is investigated it is assumed that the subsidence is caused by the super position of the motion of a phase boundary and of the flexure of an elastic lithosphere in response to the loading of the earth s surface by sediment an approximate solution describing the motion of the phase boundary when it is subjected to changes in pressure is used to describe the early stages of the subsidence history of the basin several models have been investigated and are presented to demonstrate how the spatial and temporal characteristics of the sediment deposition affect the suggested mechanism if the basin is wide i e several times the depth to the phase boundary and the sediment deposition is slow in comparison to the phase transition relaxation time the subsidence can proceed at the same rate or even faster than the sedimentation resulting in an acceleration of the sediment accumulation the mechanism investigated does not appear adequate for small scale basins or basins where the sediment accumulated rapidly it is a feasible mechanism for the large cratonic basins where the sediment deposition proceeded at a low rate for a long time

cenozoic postrift domal uplift of north atlantic margins an asthenospheric diapirism model postrift domal uplifts are a distinct feature of the northern north atlantic rifted margins uplifted regions southern norway finnmark svalbard northern united kingdom occur with a typical spacing of 900 km the amount of domal uplift is substantial 1 2 km thermochronological geomorphological and seismic stratigraphic data suggest a coincident neogene onset of uplift postdating north atlantic breakup and predating onset of glaciation the norwegian domes are characterized by strongly negative gravity anomalies and reduced mantle p wave and s wave velocities previous models for uplift around the north atlantic e g glacial erosion intraplate stresses secondary convection fail to explain the above characteristics we present an asthenospheric diapir model based on a rayleigh taylor instability wherein a hot icelandic asthenosphere layer meets cold cratonic lithosphere the generated asthenospheric diapirs and associated partial melting offer a viable explanation for updoming application of this model to the south norwegian dome succesfully explains most of the currently available data

polyphase rift evolution of the voring margin mid norway constraints from forward tectonostratigraphic modeling the mid norwegian voring margin bounding the northern atlantic underwent several rift episodes after the caledonian orogeny permo triassic extension concentrated at the eastern inner margin followed by jurassic cretaceous extension at the center of the margin finally more westward the last rift episode led to continental breakup in the earliest eocene although the general architecture of the margin may be clear the timing and distribution of particularly the oldest rift structures are poorly constrained we use two dimensional forward tectonostratigraphic modeling for better quantitative understanding of the tectonic evolution of the margin two regional profiles crossing the margin have been analyzed modeling of the two profiles integrates the basin shape and fill as well as the underlying crustal structure of the margin the modeling allows us 1 to quantify the distribution and timing of extension of subsequent rift episodes 2 to predict the basin and crustal architecture at deep levels and 3 to test different interpretations of the seismic data the level of lithospheric necking during basin formation is constrained by basement topography and moho depth and lies within the middle crust 20 km furthermore we investigate the migration of the rift axes and the elastic lithospheric strength during the different rift episodes locations of previous extension are not reactivated during renewed rifting instead renewed rifting occurs preferentially in regions where the lithosphere has experienced less extension

north central pacific tropical cyclones impacts of el nino southern oscillation and the madden julian oscillation abstractboth el nino southern oscillation enso and the madden julian oscillation mjo have been documented in previous research to impact tropical cyclone tc activity around the globe this study examines the relationship of each mode individually along with a combined index on tropical cyclone activity in the north central pacific approximately twice as many tropical cyclones form in the north central pacific in el nino years compared with la nina years these differences are attributed to a variety of factors including warmer sea surface temperatures lower sea level pressures increased midlevel moisture and anomalous midlevel ascent in el nino years when the convectively enhanced phase of the mjo is located over the eastern and central tropical pacific the north central pacific tends to have more tropical cyclone activity likely because of reduced vertical wind shear lower sea level pressures and increased vertical motion the convectively enhanced phase of the mjo is also responsible for

crustal fault reactivation facilitating lithospheric folding buckling in the central indian ocean high quality normal incidence seismic reflection data confirm that tectonic deformation in the central indian ocean occurs at two spatial scales whole lithosphere folding with wavelengths varying between 100 and 300 km and compressional reactivation of crustal faults with a characteristic spacing of c 5 km faults penetrate through the crust and probably into the upper mantle both types of deformation are driven by regional large intraplate stresses originating from the indo eurasian collision numerical modelling of the spatial and temporal relationships between these two modes of deformations shows that in agreement with geophysical observations crustal faults are reactivated first with stick slip behaviour subsequent lithospheric folding does not start until horizontal loading has significantly reduced the mechanical strength of the lithosphere as predicted by elasto plastic buckling theory modelling suggests that lithospheric folding does not develop in the absence of fault reactivation crustal fault reactivation therefore appears to be a key facilitating mechanism for oceanic lithospheric buckling in the central indian ocean

a new multilayered model for intraplate stress induced differential subsidence of faulted lithosphere applied to rifted basins in plane horizontal stresses acting on predeformed lithosphere induce differential flexural vertical motions a high precision record of these motions can be found in the sedimentary record of rifted basins originally it was proposed that rifted basins experience flank uplift and basin center subsidence in response to a compressive change of in plane stress which agrees well with observed differential motions subsequently published models predicted that the vertical motions may be opposite because of the flexural state of the lithosphere induced by necking during extension however the total flexural and permanent geometry of the lithosphere underlying the rifted basin is the controlling parameter for the in plane stress caused vertical motions the largest part of this preexisting geometry is caused by faulting in the uppermost brittle part of the crust and ductile deformation in the underlying parts of the lithosphere we present a new multilayered model for stress induced differential subsidence taking into account the technically induced preexisting geometry of the lithosphere including faults in the upper crust as continental lithosphere may exhibit flexural decoupling due to a weak lower crustal layer the new multilayer in plane stress model discriminates the geometries of the separate competent layers at a basin wide scale the new model predicts that a compressive change of in plane force results in basin center subsidence and flank uplift confirming the original hypothesis compared to all previous models the new model requires a lower horizontal stress level change to explain observed differential vertical motions

thermomechanical structure of european continental lithosphere constraints from rheological profiles and eet estimates summary the eet equivalent elastic thickness of the lithosphere is a measure of the integrated lithospheric strength it is directly related to the mechanical thickness and rheology of the crustal and mantle lithosphere we present a comparison of eet estimates and strength profiles based on the extrapolation of rock mechanics data for different parts of the european and eurasian continental lithosphere we discuss the temporal and spatial variations in the mechanical thickness and strength inferred from data for precambrian segments of europe s lithosphere variscan europe and the alpine collision belt this analysis demonstrates important spatial and temporal variations in lithospheric rigidity for orogenic belts and sedimentary basins in eastern and western europe and asian parts of eurasia the eet estimates based on synthetic rheological profiles constrained by newly available geophysical data are consistent with the estimates of eet derived from flexural studies of sedimentary basins forelands and orogenic belts these rheological profiles suggest weakening of the major parts of the european and eurasian continental lithosphere by decoupling of the crustal and upper mantle parts a comparison with the seismicity depth distribution for some selected sites suggests that the intra plate seismicity is essentially restricted to the upper crustal parts of europe s lithosphere providing additional support to the notion of the decoupled lithosphere the presence of intra plate stress fields can explain a significant part of the observed variations in eet estimates within individual thermotectonic age groups a comparison of wavelengths of crustal and lithospheric folding with observations shows these wavelengths to be consistent with estimates of eet inferred from the rheological response of basins and orogens at more moderate levels of intra plate stress

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

bayesian change point analysis of tropical cyclone activity the central north pacific case bayesian analysis is applied to detect change points in the time series of annual tropical cyclone counts over the central north pacific specifically a hierarchical bayesian approach involving three layers data parameter and hypothesis is formulated to demonstrate the posterior probability of the shifts throughout the time from 1966 to 2002 for the data layer a poisson process with gamma distributed intensity is presumed for the hypothesis layer a no change in the intensity hypothesis and a single change in the intensity hypothesis are considered results indicate that there is a great likelihood of a change point on tropical cyclone rates around 1982 which is consistent with earlier work based on a simple log linear regression model a bayesian approach also provides a means for predicting decadal tropical cyclone variations a higher number of tropical cyclones is predicted in the next decade when the possibility of the change point in the early 1980s is taken into account

development of the north viking graben inferences from laboratory modelling abstract the north viking graben is a classic sedimentary basin in the north sea that has been thoroughly studied over the last decade despite the amount and quality of seismic and well data now available the processes of extension remain unclear and the relationship between sedimentation and deformation is still a matter of debate we present the results of small scale laboratory modelling the models are made with sand and silicone putty to simulate brittle and ductile behaviour on a crustal scale the experiments were designed to study the effects of a the degree of coupling between brittle and ductile layers b the obliquity of extension and c the reactivation of inherited crustal scale structures the results are used to discuss the symmetry of extensional processes on crustal and lithospheric scales as well as the relationship between sedimentation and deformation it is proposed that the asymmetry of faulting in the upper crust and the nearly symmetric thinning of the whole crust are not mutually exclusive a model involving nearly pure shear on the lithospheric scale is used to explain the development of an asymmetrical basin at shallow level in addition this model accounts for the nearly horizontal stratification of lower cretaceous sediments the basal cretaceous unconformity which caps many of the normal faults and the localization of deformation to the west of the graben during the lower cretaceous

the abrupt shift of typhoon activity in the vicinity of taiwan and its association with western north pacific east asian climate change bayesian analysis is applied to detect changepoints in the time series of seasonal typhoon counts in the vicinity of taiwan an abrupt shift in the typhoon count series occurs in 2000 on average 3 3 typhoons per year have been noted before 2000 1970 99 with the rate increasing to 5 7 typhoons per year since 2000 2000 06 this abrupt change is consistent with a northward shift of the typhoon track over the western north pacific east asian region and an increase of typhoon frequency over the taiwan east china sea region the northward shift of the typhoon track tends to be associated with typhoon enhancing environmental conditions over the western north pacific namely the weakening of the western north pacific subtropical high the strengthening of the asian summer monsoon trough and the enhanced positive vorticity anomalies in the lower troposphere based on observational analysis and model simulations warm sea surface temperature anomalies over the equatorial western and central pacific appear to be a major factor contributing to a northward shifted typhoon track

numerical simulation of rifting in the northern viking graben the mutual effect of modelling parameters numerous basin modelling studies have been performed on the viking graben in the northern north sea during the past decades in order to understand the driving mechanisms for basin evolution and palaeo temperature estimations in such modelling it is important to include lithospheric flexure the values derived for the lithospheric strength by these studies vary considerably i e up to a factor of 30 in this study which is based on new interpretation of a regional transect we show that both the estimated value of the effective elastic thickness and the derived b profile are dependent on the assumed value of the depth of necking the use of models that implicitly set the level of necking at a depth of 0 km generally leads to an underestimation of the lithospheric strength and an overestimation of the thinning factors in the northern viking graben a necking depth at intermediate crustal levels gives results comparable to the observations extension by faulting is modelled to be a significant factor in conclusion rifting in the northern viking graben can be explained with various models of effective elastic thicknesses eet varying from 1 km for a zero necking depth to the depth of the 450 jc isotherm for an intermediate level of necking it is also shown that the development of the basin during the post rift phase cannot be explained by pure shear simple shear extension two mechanisms are proposed here to explain the post rift subsidence pattern namely intra plate stress and phase boundary migration the two extreme models for eet mentioned above 1 km for a zero necking depth to the depth of the 450 jc isotherm for an intermediate level of necking give very different responses to compressional stress the latter gives basically no response for realistic intra plate stress d 2004 elsevier b v all rights reserved

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

lower and middle jurassic alkaline magmatism in the egersund sub basin north sea abstract core samples from the egersund sub basin of the north sea reveal two distinct phases of strongly alkaline potassic magmatic activity the oldest rocks are phlogopite leucitebearing trachyte dyke s dated at 178 ma k ar method on phlogopites this lower jurassic pliensbachian magmatic activity is related to the early stages of rifting in the north sea the other magmatic phase of middle jurassic age is represented by strongly alkaline potassic basalt lavas of apparently subaerial origin and correlates with extensive volcanism in the piper forties fields in the central part of the north sea

role of scale interactions in the abrupt change of tropical cyclone in autumn over the western north pacific tropical cyclone tc activity in autumn september november over the western north pacific experienced an abrupt change in 1998 which can be detected by the bayesian change point analysis during the decade before the regime shift 1988 1997 the occurrence frequency of tc genesis increased significantly over the tropical western pacific where the seasonal cyclonic flow intraseasonal oscillation iso and synoptic scale eddy sse were all strengthened compared to those observed in the decade after 1998 1998 2007 the tc trajectories also exhibited spatial differences during the active decade the tcs had a higher probability to move westward into the philippine sea and the south china sea and recurved northeastward toward the east of japan meanwhile the northwestward propagating tcs approaching taiwan and southeastern coast of china were reduced to understand the role of mean flow iso sse interaction in the decadal changes of sse and associated tc activity we diagnosed a newly proposed sse kinetic energy ke equation that separates the contributions of seasonal mean circulation and iso to the sse the results show that during the active tc decade the sse obtained higher ke from both mean flow and iso through eddy barotropic energy conversion when the enhanced sse momentum flux interacted with the strengthened monsoon trough and vigorous iso cyclonic anomaly over the western tropical pacific the increased sse ke contributed positively to the increased tc genesis over the main genesis region 7 5 20 n 130 170 e it also benefited the growth of tcs over the philippine sea and the south china sea during the active decade the decadal change in tc frequency over the extratropics was related to the eddy baroclinic energy conversion instead of the barotropic conversion associated with scale interaction during the active tc decade sse gained more less ke from the sse available potential energy over the east of japan the east china sea favoring disfavoring the succeeding development of tcs in this region

bayesian rainfall variability analysis in west africa along cross sections in space time grid boxes abstract this paper proposes an approach for analyzing rainfall variability over west africa during the 1950 90 period three grid boxes corresponding to three selected areas over west africa have been constructed for each candidate area the set of annual grid maps are stored in 3d matrices reflecting time and geographical position called here space time grid boxes each space time grid box contains grid points corresponding to a given gauging year the bayesian procedure based on a single shifting model is applied to grid points extracted from mean meridional and latitudinal cross sections of each space time grid box two different problems are considered the first is the detection of a change while the second is the estimation of the changepoint and its amplitude under the assumption that a change has occurred the bayesian single shift model is applied on grid points extracted from each cross section a latitude latitude and longitude longitude analysis of the rainfall climatology changes is

cenozoic sequence stratigraphy of the central and northern north sea basin tectonic development sediment distribution and provenance areas the cenozoic succession in the central and northern north sea has been investigated to establish a regional sequence stratigraphic framework changes in sediment distribution indicate a complex pattern of regional vertical movements along older palaeozoic and mesozoic structures in cenozoic times these vertical movements mainly related to tectonic processes along the continental margin to the north and north west were responsible for the generation and removal of provenance areas for sediments delivered to the north sea basin through cenozoic time during the early through middle palaeogene sediments were mainly sourced from areas in the west and from the atlantic margin in the north uplift in the northern north sea in the late eocene was in the earliest oligocene followed by marked basin subsidence and tectonic uplift of southern norway a similar pattern of tectonic movements resulted in subaerial exposure of the northern north sea in the early miocene followed by significant tectonic subsidence in the basin and along the atlantic margin in late miocene pliocene times at the same time southern norway was uplifted and became a major sediment source after the miocene pliocene subsidence uplift events glacial processes in southern norway and fluvial processes in a large drainage area east and south east of the north sea were responsible for the main sediment influx to the north sea the cenozoic depositional sequences in the north sea developed in close interaction with regional tectonic movements and changes in provenance areas tectonic movements in north west europe overprinted global sea level changes so that the generation of depositional sequences and sequence boundaries apparently occurred independently of the rate of eustatic sea level change