the deep water fold and thrust belt offshore nw borneo gravity driven versus basement driven shortening the deep water region offshore nw borneo is an active fold and thrust belt that hosts a signifi cant number of proven hydrocarbon accumulations in the past two mechanisms have been discussed as primary control for neogene to holocene folding and thrusting in this deep water province 1 basement driven crustal shortening and 2 gravity related delta tectonics in this study new balanced interpretations of regional crustal scale depth migrated twodimensional 2 d multichannel seismicrefl ection profi les are presented that provide for the fi rst time quantitative data on tectonic shortening throughout the entire deep water fold and thrust belt of nw borneo we use our tectonic restorations to compare the amount of deep water shortening on the nw borneo slope to the amount of extension across the nw borneo shelf a key result of this balancing study is the observation that pliocene to holocene gravity driven shortening decreases from south to north while the total amount of shortening increases slightly to the north consequently the amount of purely basement driven compression along nw borneo is strongly inferred to increase toward the north because most of the shortening is late pliocene and younger we interpret the tectonic shortening to be ongoing

static bay beach concept for scientists and engineers a review abstract headland bay beach hbb is one of the most prominent physiographic features on the oceanic margin of many countries in the world under the influence of a predominant swell its curved periphery in natural environment may reach static equilibrium and remains stable without sediment supply from updrift and or a riverain source within its own embayment coastal scientists and engineers have attempted to develop mathematical expressions to quantify this ideal bay shape since the 1940s as the scenario with depleting sediment supply has become a common reality on many parts of the world coastline in more recent time some coastal engineers have advocated a rational approach to mimicking the static bay shape found in nature in order to mitigate beach erosion as well as for coastal management nowadays many useful applications have emerged since the publication of the parabolic bay shape equation pbse developed for static equilibrium planform sep in late 1980s the advance in modern computer technologies and international collaboration has further facilitated the exchange of knowledge and applications of this static bay beach concept sbbc this paper reviews the progress on the research in hbb made by geographers and geologists since the 1940s together with the involvement of coastal engineers working on shore protection and management from the 1960s aided by software mepbay developed in 2003 for the pbse several practical examples are demonstrated in this paper for the stability verification of natural and man made bay beaches shore protection mitigating downdrift erosion of a harbour design of recreational bay beach as well as for environmental impact assessment limitations on and clarifications for engineering applications based on the sbbc are also discussed in this paper

compressive and tensile failure of inclined well bores and determination of in situ stress and rock strength in this paper we investigate the occurrence of compressive and tensile failures of arbitrarily inclined well bores under a wide variety of stress conditions the principal assumptions in this analysis are that the rock is isotropic and that it deforms elastically to the point of failure as has been shown by previous investigators for a given stress state and well bore orientation it is straightforward to predict the orientation of the failures around the well bore as well as whether failure is likely to occur depending on such parameters as rock strength and borehole fluid pressure however as the stress state is almost never known in situ we demonstrate how observations of compressive and tensile wall failures in inclined holes can be used to constrain in situ stress orientations and magnitudes if there are independent data on the magnitude of the least principal stress from either leak off or microfrac tests and on the formation pore pressure we further demonstrate how once the stress state is determined it is possible to assess both an upper bound on the effective in situ rock strength and the degree to which increasing the borehole fluid pressure or mud weight can reduce the likelihood of borehole failure through application of this methodology to an inclined well bore in an area of complex faulting in the gulf of mexico we illustrate how it is possible to utilize observations of borehole failures to determine the magnitude and orientation of the stress tensor in areas such as offshore sedimentary basins where drilling inclined well bores is quite common

wave energy distribution and morphological development in and around the shadow zone of an embayed beach abstract background the curved shoreline shape of embayed beaches is one of its most notable characteristics and can be described using the parabolic bay shape equation pbse wave diffraction in and around the shadow zone is often regarded as the primary forcing mechanism leading to the prominent curvature of the shoreline however wave climate variables wave direction directional spreading and wave height are shown to be influential in redistributing wave energy throughout the bay and in the shadow zone methods in this study a process based morphological model delft3d is used for hydrodynamic and morphodynamic simulations of a schematic embayed beach wave forcing conditions are systematically varied between a mixture of time invariant and time varying cases results the role of diffraction is shown to be dominant only when the wave conditions are both narrow banded 30 otherwise as little as 6 variation in wave direction within a 90 range can account for the shoreline curvature in and around the shadow zone conclusion the degree to which wave direction and directional spreading vary through time therefore has a large effect on the equilibrium orientation and shoreline planform of the bay

present day stress field rotations associated with evaporites in the offshore nile delta evaporitic horizons are routinely interpreted to act as mechanical detachment sequences and thus signifi cantly infl uence the structural evolution of sedimentary basins and fold thrust belts however over 30 years of global in situ stress analysis have provided only poor evidence to support this widespread assumption this study examines present day stress orientations inferred from borehole breakout and drilling induced fractures in 44 boreholes in the offshore nile delta a total of 446 breakouts and 19 drilling induced fractures from 37 wells reveal sharply contrasting present day maximum horizontal stress shmax orientations in sequences above and below the extensive messinian evaporites of the eastern nile delta a typical deltaic margin parallel shmax e w in the central and ese wnw in the eastern nile delta is observed in parts of the nile delta that are below or do not contain evaporites however a scattered but largely margin normal nne ssw shmax is observed in sequences underlain by evaporites the 90 variation in present day shmax orientation above and below the messinian salts provides the fi rst convincing in situ evidence that evaporite sequences can act as major mechanical detachment horizons in addition the margin normal shmax orientation is subperpendicular to the strike of nearby active extensional faults indicating the existence of non andersonian faulting in the suprasalt region furthermore the evidence that the messinian evaporites act as an effective mechanical detachment suggests that suprasalt faulting in the eastern nile delta is not the result of basement related deformation and thus raises doubts about the often postulated extension of the suez fault zone into the eastern mediterranean

facies distribution and sedimentary processes on the modern baram delta implications for the reservoir sandstones of nw borneo the baram delta has been classified as wave dominated and as a modern analogue for the prolific tertiary sandstone reservoirs in the baram delta province of nw borneo however the delta s facies distribution and sedimentary processes indicate that sedimentation is presently occurring only on the large mouth bar and that the baram is more properly categorised as a mixed wave and tide influenced delta more than half of the surface area of the mouth bar is dominated by tidal currents and covered with tidally deposited sediments because a relatively large tidal prism controls the nearshore hydrodynamics conversely the widespread tertiary shoreface reservoir sandstones are clearly wave dominant and tidal signatures are absent consequently the baram delta is not an appropriate analogue for most shoreface reservoir sandstones in nw borneo

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

morphometric classification of swell dominated embayed beaches abstract globally embayed beaches are common to hilly and mountainous coastlines they are typically characterised by two headlands that are a primary control on incident wave exposure and beach morphodynamics embayed beaches exist under a range of headland morphologies and degree of embaymentisation here we present a generalised embayment morphometric parameter e which classifies the geomorphological setting of embayed beaches based on the embayment indentation and area we apply this to 168 swell dominated embayed beaches from 6 regions using open access imagery the embayment morphometric parameter e was subjected to k means cluster analysis to identify 4 classes of embayed beaches with increasing e indicating greater headland influence and impact on incident wave exposure the classes range from 1 to 4 with increasing degree of embayment the most common is class 2 43 n 73 which represents embayed beaches that have moderate embayment indentation and headland influence there are clear trends in embayment geometry regardless of location wave climate or tidal regimes within the embayments there were 6 possible headland orientations types h1 h6 the most common 58 n 97 is when both headlands are orientated outwards from the beach h6 and may result in greater morphological beach response from less headland shadowing compared with headlands orientated inwards onto the beach h1 in summary we have developed a simple classification scheme for embayed beaches based on degree of indentation and headland orientation that can be applied to any embayed beach globally

late quaternary stratigraphic evolution of the inner continental shelf in response to sea level change santa catarina brazil abstract the inner continental shelf 0 50 m water depth off santa catarina southern brazil was investigated using seismic stratigraphic methods to identify and interpret the major seismic stratigraphic units and to reconstruct the late quaternary evolution of the inner shelf and coast the stratigraphy comprises a bedrock basement overlain by a thick 30 m unit that comprises in the distal portion laminated muds and sands and in the coast proximal zone offlapping deltaic deposits whose upper surface has been reworked to form alongshore prograding barrier spits deposition of this unit is tentatively attributed to sea levels 20 m msl during the late pleistocene mis 5a or 5c a normal fault in the muddy units with a vertical offset of 3 5 m indicates episodic tectonic activity cut into this unit is a profusion of incised valleys associated with sea level fall ultimately to 120 m at the last glacial maximum lgm the associated subaerial unconformity is only preserved close to shore where it has escaped subsequent wave ravinement this coupled with the well preserved incised valleys implies the underlying substrate to be weakly cohesive material mud the incised valleys display a variety of infilling sediments interpreted variously as basal fluvial sediments estuarine basin infill muds and marginal bar or barrier associated sands deposited during the postglacial marine transgression during a sea level stillstand at ca 50 m a 3 5 km wide planar surface was cut into the unconsolidated coastal plain sediments forming a terrace on which a thick sequence of sands accumulated this unit is regionally developed and the acoustic signature implies it to comprise littoral sand including a large aeolianite component the accumulation of sand on this mainland beach dune system is attributed to establishment of a mature littoral system with strong longshore drift the fact that it rests on an erosional surface that truncates incised valleys suggests the unit to be holocene in age it is interpreted to have been deposited during a still stand in the holocene and to have undergone aggradation and cementation until it was overstepped by sea level rise its surface and the coastal plain to landward were then subject to wave ravinement and a thin ca 5 6 m layer of modern marine sands was deposited on the eroded surface sea level rise continued to the regional glacio isostatic highstand of ca 5 5 m after which regressive strandplains developed in response to a renewed mature longshore drift system similar to that prevailing during the 50 m stillstand of sea level in the intervening period rapid shoreline translation over the low gradient surface inhibited the development of the longshore transport system the three shoreline systems identified show marked differences that relate to sea level change and the influence of the underlying topography shoreline 1 pleistocene highstand developed by localised wave reworking of delta deposits and involved a series of alongshore prograding barrier spits on a shoreline of alternating high relief bedrock and littoral sands in coastal re entrants shoreline 2 50 m was a major accumulation of beach and dune sand deposited as a mainland attached beach dune system on a low lying coastal plain environment shoreline 3 the modern coast comprises a series of headland embayment beaches strandplains and transgressive dunes with a strong bedrock control and a well developed longshore drift system delivering sediment northward

longshore variability of beach states and bar types in a microtidal storm influenced low energy environment beach classification models are widely used in the literature to describe beach states in response to environmental conditions these models were essentially developed for sandy barred to barless beaches in micro to mesotidal environments subject to moderate to high wave energy conditions and have been based on field studies over limited stretches of coast here we further interrogate the performance of the australian beach classification scheme by analysing beach states and corresponding bar types on a regional scale in a storm influenced low wave energy microtidal environment using a large and unique spatial and temporal dataset of supra and subtidal beach morphology and sedimentology the 200 km long coast of the gulf of lions in themediterranean consists of quasi continuous sandy beaches with a well developed double sandbar system all the reported classical beach stateswere observed on this coast from reflective to dissipative alongwith two more unusual states the rock platform constrained beach state which is associated with bedrock outcrops and the non barred dissipative beach statewhich ismore commonly found in large tidal range settings lidar bathymetry shows that the transitions between beach state zones are marked mainly headlands but transitions also occur progressively along stretches of continuous sandy beach the longshore distribution of beach states and associated bar types on a regional scale can be related to the variability of hydrodynamic conditions wave incidence and energy and sediment characteristics particle size however the influence of these parameters on beach state seems to be largely controlled by the geological context such as the presence of a river mouth headland or rock platform finally we assessed the ability of the parameter commonly used to characterise beach states which combines wave characteristics and sediment fall velocity to predict the observed beach states and bar types using a very large set of hydrodynamic and sedimentary data our results based on high frequency spatial sampling show that the fall velocity of the subtidal sediment coupled with wave statistics one month prior the observed beach state strongly improved the predictive power of the parameter

origin of overpressure and pore pressure prediction in the baram province brunei accurate pore pressure prediction is critical in hydrocarbon exploration and is especially important in the rapidly deposited tertiary baram delta province where all economic fields exhibit overpressures commonly of high magnitude and with narrow transition zones a pore pressure database was compiled using wireline formation interval tests drillstem tests and mud weights from 157 wells in 61 fields throughout brunei overpressures are observed in 54 fields both in the inner shelf deltaic sequences and in the underlying prodelta shales porosity vs vertical effective stress plots from 31 fields reveal that overpressures are primarily generated by disequilibrium compaction in the prodelta shales but have been generated by fluid expansion in the inner shelf deltaic sequences however the geology of brunei precludes overpressures in the inner shelf deltaics being generated by any conventional fluid expansion mechanism e g kerogen to gas maturation and we propose that these overpressures have been vertically transferred into reservoir units via faults from the prodelta shales sediments overpressured by disequilibrium compaction exhibit different physical properties to those overpressured by vertical transfer and hence different pore pressure prediction strategies need to be applied in the prodelta shales and inner shelf deltaic sequences sonic and density log data detect overpressures generated by disequilibrium compaction and pore pressures are accurately predicted using an eaton exponent of 3 0 sonic log data detect vertically transferred overpressures even in the absence of a porosity anomaly and pore pressures are reasonably predicted using an eaton exponent of 6 5

insights into the dynamics of an orogenic wedge from lubrication theory implications for the himalayan tectonics abstract using lubrication theory we develop a mechanical model to evaluate the dynamic relation between an orogenic wedge and the overriding plate the model suggests that the subducting plate motion produces a dynamic pressure in the wedge which supports the gravity load of the overriding plate lying above it stable condition a drop in the dynamic pressure results in a rotational collapse of the overriding plate unstable condition we present an analytical solution to provide an estimate of the dynamic pressures in orogenic wedges the lubrication model is also implemented in computational fluid dynamics cfd simulations to perform real scale numerical experiments considering mainly three variables 1 plate convergence angle 2 subduction rate us and 3 viscosity ratio r between the overriding plate and wedge the overriding plates attain mechanical stability when us exceeds a threshold value us otherwise they become unstable as us

characteristics of repeated detached miocene pliocene tectonic inversion events in a large delta province on an active margin brunei darussalam borneo abstract the baram delta province evolved during the middle miocene to present day from a foreland basin to a shelf margin episodic folding events affected the region causing uplift of the hinterland delta progradation and inversion of gravity related faults existing models place the n s and ne sw trending folds in a strike slip transpressional setting new geological mapping and re interpretation of existing data suggest the region is better understood as the development of a west verging thrust belt in a middle miocene foreland basin filled by sandstones and shales of the belait and setap formations with key major folds jerudong and belait anticlines belait syncline forming during the middle miocene as fault bend and fault propagation folds the deformation style is complicated by the predominantly shaley middle miocene pliocene setap formation becoming thicker and more overpressured from south to north onshore where the setap formation is thin or absent the belait formation is attached to the underlying lower miocene and older sequences offshore and in a narrow onshore strip the overpressured setap formation causes deformation in the beltait formation to be detached from the underlying cretaceous tertiary accretionary prism basement the detached style exhibits considerable structural complexity including lift off folds growth faults shale diapirs and pipes onshore thrust and inversion features are dominantly n s trending and began activity in the middle miocene deformation is probably associated with an e w maximum horizontal stress direction in the late miocene around 7 5 ma watters et al 1999 ne sw striking inversion folds developed located mostly over early counter regional faults and associated reactive diapirs folds verge towards the nw when underlain by counter regional faults and towards the s or se when underlain by regional faults folds and diapirs along n s trends were also reactivated continuation of this deformation into the pliocene is largely confined to the offshore area onshore the n s structures no detachment were not reactivated during the pliocene

present day stress field of southeast asia article i nfo it is now well established that ridge push forces provide a major control on the plate scale stress field in most of the earth s tectonic plates however the sunda plate that comprises much of southeast asia is one of only two plates not bounded by a major spreading centre and thus provides an opportunity to evaluate other forces that control the intraplate stress field the cenozoic tectonic evolution of the sunda plate is usually considered to be controlled by escape tectonics associated with india eurasia collision however the sunda plate is bounded by a poorly understood and complex range of convergent and strike slip zones and little is known about the effect of these other plate boundaries on the intraplate stress field in the region we compile the first extensive stress dataset for southeast asia containing 275 a d quality 177 a c horizontal stress orientations consisting of 72 stress indicators from earthquakes located mostly on the periphery of the plate 202 stress indicators from breakouts and drilling induced fractures and one hydraulic fracture test within 14 provinces in the plate interior this data reveals that a variable stress pattern exists throughout southeast asia that is largely inconsistent with the sunda plate s approximately ese absolute motion direction the present day maximum horizontal stress in thailand vietnam and the malay basin is predominately north south consistent with the radiating stress patterns arising from the eastern himalayan syntaxis however the present day maximum horizontal stress is primarily oriented nw se in borneo a direction that may reflect plate boundary forces or topographic stresses exerted by the central borneo highlands furthermore the south and central sumatra basins exhibit a ne sw maximum horizontal stress direction that is perpendicular to the indo australian subduction front hence the plate scale stress field in southeast asia appears to be controlled by a combination of himalayan orogeny related deformation forces related to subduction primarily trench suction and collision and intraplate sources of stress such as topography and basin geometry

geologically constrained morphological variability and boundary effects on embayed beaches abstract headlands rock outcrops and engineering structures impact beach and nearshore dynamics of coastal embayments inducing boundary effects that constrain the lateral and vertical beach variability this study analyses morphological change in six embayed beaches with diverse levels of exposure to wave action and various degrees of geological control in the mesotidal coast of southwestern portugal the aim is to identify whether geological boundaries constrain the morphological behaviour of embayed beaches and assess whether their effects can be decoupled from datasets of morphological change topographic data obtained over a two year period on each of the six embayments were analysed using empirical orthogonal functions eof to decompose temporal and spatial variability in the datasets first and second mode eigenfunctions were explored using time variable linear correlation analysis with several nearshore parameters that include hydrodynamic variables sedimentary and geometric characteristics of each embayment in order to derive forcing response relationships our results demonstrate that natural geological boundaries constrain the morphological behaviour of embayed beaches producing conspicuous alongshore variability in all embayments localised responses induced by lateral and vertical boundary interference with beach and nearshore dynamics include beach rotation topographically controlled rip circulation and restrained profile fluctuation spatial decoupling in cross and longshore responses is accompanied by a temporal decoupling in response times both of which are slower in more constrained embayments from 1 day in exposed embayments to 1 week or more in the most sheltered ones normalised wave power was correlated at the 99 confidence level with the primary mode of morphological variability at most embayments which represent 67 to 94 of the variance in the datasets this correlation stresses the importance of combined parameterization of wave and tide forcing in process response relations between hydrodynamics and morphological change for mesotidal coastal environments lateral and vertical geological boundaries exert their effects fundamentally by restraining longshore sediment transport inducing cellular surf zone circulation and by impacting cross shore sediment transport it is postulated that decreasing sediment abundance and substrate depth intensify vertical boundary effects while higher indentation and wave obliquity enhance the effects of lateral boundaries

the impact of waves and tides on residual sand transport on a sediment poor energetic and macrotidal continental shelf 2019 the authors the energetic macrotidal shelf off south west england was used to investigate the influence of different tide and wave conditions and their interactions on regional sand transport patterns using a coupled hydrodynamic wave and sediment transport model residual currents and sediment transport patterns are important for the transport and distribution of littoral and shelf sea sediments morphological evolution of the coastal and inner continental shelf zones and coastal planning waves heavily influence sand transport across this macrotidal environment median 50 exceedance waves enhance transport in the tidal direction extreme 1 exceedance waves can reverse the dominant transport path shift the dominant transport phase from flood to ebb and activate sand transport below 120 m depth wave tide interactions encompassing radiation stresses stoke s drift enhanced bottom friction and bed shear stress refraction current induced doppler shift and wave blocking significantly and nonlinearly enhance sand transport determined by differencing transport between coupled wave only and tide only simulations a new continental shelf classification scheme is presented based on sand transport magnitude due to wave forcing tide forcing and nonlinear wave tide interactions classification changes between different wave tide conditions have implications for sand transport direction and distribution across the shelf nonlinear interactions dominate sand transport during extreme waves at springs across most of this macrotidal shelf at neaps nonlinear interactions drive a significant proportion of sand transport under median and extreme waves despite negligible tide induced transport this emphasizes the critical need to consider wave tide interactions when considering sand transport in energetic environments globally where previously tides alone or uncoupled waves have been considered

uncertainty in the application of the parabolic bay shape equation part 1 abstract this paper aims to quantify the uncertainty in the application of the parabolic bay shape equation pbse for a bay in static equilibrium by means of expert elicitation a database was generated consisting of the position of the control points that determine the static equilibrium planform sep the elicitation consisted of two parts in part 1 22 expert volunteers were asked to place the three control points that determine the sep on a vertical aerial photograph of taquaras taquarinhas bay a morphologically stable bay in the south of brazil approximately 1800 m in width and with an indentation of 750 m the distribution of the location of the sep along four evenly spaced 200 m profiles in the southern part of the bay was determined the overall bias of the location of the sep calculated over the four profiles was in the order of 41 m landward and the average standard deviation was 116 m these parameters increased when moving alongshore toward the curved section of the bay this means that the uncertainty in the application of the pbse is dependent on the particular point of interest along the bay in part 2 of the elicitation 30 volunteers participated this time the consequence of the placement of the control points the corresponding sep was visible comparing the results from parts 1 and 2 it was observed that when volunteers were directly confronted with the result of the placement of the control points a plotted sep a much smaller variation in the position of the sep occurred this implies that when feedback on the result is provided the pbse is a more robust method

groin impacts on updrift morphology physical and numerical study abstract groins interfere with coastal dynamics and sediment transport leading to sediments accumulation at the updrift side while at downdrift the erosive process is anticipated due to the lack of sediments to improve numerical modeling capacity to simulate the groins impacts it is necessary to totally understand the shoreline evolution along time and its relationship with the cross shore profiles shape the main goal of this work was to analyze and compare the performance of physical and numerical studies on evaluating the evolution of updrift cross shore profiles geometry and shoreline position after the construction of a groin this study analyzed a coastal stretch updrift of the groin at a prototype and model scales considering the analytical formulation of pelnard considere the numerical model ltc long term configuration and the laboratory tests the laboratory tested scenario was designed with the aim to gather results which could be analyzed and compared with numerical simulations from ltc coelho 2005 allowing its improvement and with the pelnard considere 1956 analytical formulation both at model scale the developed study shows an important difference between ltc and pelnard considere 1956 approaches because the analytical solution for the shoreline in equilibrium does not include the wave refraction effects over the updated bathymetry ltc observed trend of the equilibrium shoreline is not parallel to the initial shoreline and this behavior was confirmed in the laboratory tests it was also observed that the sediment transport capacity has very small impact on the ltc shoreline configuration despite the refraction effects over the updated bathymetries along time the profile shape obtained in laboratory includes bed forms difficult to reproduce in long term numerical modeling evaluation of cross shore profiles because ltc transversal behavior is only based on geometrical considerations and does not represent cross shore sediment transport and its impact on profile geometry

stress regimes in the gulf coast offshore louisiana data from well bore breakout analysis maximum horizontal stress shmax orientations were mapped for the northern gulf of mexico offshore louisiana using borehole breakouts which are commonly used by petroleum and drilling engineers to determine the stress regime for well bore stability analyses and reservoir stimulation the breakout signal is subtle but indicates shmax orientations largely parallel to the strike of the progradational clastic sedimentary wedge in a general northeast southwest direction however significant anomalies exist in the breakout orientations the main anomaly being orthogonal to the principal shmax direction these anomalies were attributed to local perturbations around faults and salt structures and to the effect of the underlying salt the correspondence among the orientation of faults salt intrusions and shmax from breakouts with the strike of the clastic wedge confirms the existence of stress anisotropy in the northern gulf of mexico shelf sediments stress anisotropy is caused by the geometry and orientation of the prograding wedge and its associated gravity driven extension

relationship between structural style overpressures and modern stress baram delta province northwest borneo christopher k morley mark tingay and richard hillis australian school of petroleum university of adelaide adelaide australia rosalind king

spatio temporal fluctuations over chorabari glacier garhwal himalaya india between 1976 and 2017 abstract the current research work deals with the health of chorabari glacier between 1976 and 2017 using multi spectral and multi dated satellite data series of landsat mss tm and etm and resourcesat ii liss iv result closely reveals that the studied glacier receding continuously with inconsistent rate for the last 41 years and rate of receding dominates significantly after 2012 it lost 306 43 61 m total length 7 46 1 48 m a 1 0 074 km2 frontal area 0 0018 km2 a 1 0 31 km2 24 glaciated area 0 007 km2 a 1 0 015 km3 32 60 glaciated volume the upward migration of sla snow line altitude from 5265 m to 5290 m also suggests that the melting process were prevailing during the study tenure an existence of supra glacial lakes and its successive growth over the surface of chorabari glacier further justifies that the temperature of the surroundings has increased significantly and influences the melting process as well the melting process between 1976 and 1990 of the studied glacier directly influenced by the frequent episodes of precipitation and temperature anomalies of central himalayan region during 1960 1990 while the melting process after 1990 is directly influenced by the increase in average mean temperature and decrease in average mean precipitation of garhwal himalayan region the tree ring data of garhwal himalaya region also well matches the precipitation data of imd indian meteorological department the overall analysis explains that the chorabari glacier is retreating continuously since 1976

thrust tectonics along the north western continental margin of sabah borneo widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north west continental margin of sabah in contrast interpretation of reflection seismic data acquired by bgr shows an autochthonous continental terrane comprising an oligocene to early miocene carbonate platform being progressively overthrust by an allochthonous rock complex progressive compression resulted in the development of four structural zones imbricated thrust sheets zone iii two thrust sheet systems one on top of the other zone iv a complex zone with multiphase deformation zone v and piercement ridges zone vi

onshore to offshore trends in carbonate sequence development diagenesis and reservoir quality across a land attached shelf in se asia abstract although isolated miocene buildups in se asia commonly form prolific hydrocarbon reservoirs their equivalents on clastic dominated land attached shelves remain poorly known and underexplored here onshore to offshore trends in carbonate development and reservoir quality are assessed across the nw borneo shelf through study of surface outcrops and subsurface wells a multidisciplinary programme of fieldwork petrography and geochemical analyses allowed evaluation of spatio temporal variations in deposition diagenesis and pore system development together with an assessment of controlling influences in addition to field logging and sample collection 200 samples were studied via transmitted light cathodoluminescent and scanning electron microscopy together with stable isotopic characterisation o c and sr carbonates developed as localised low and higher relief buildups as well as more continuous sheet like deposits in near coast to shelf margin positions molluscs corals larger benthic foraminifera and coralline algae are common constituents most samples show evidence for marine micritisation and just in shelf margin positions isopachous cements however burial diagenesis predominates in the form of compaction neomorphism fracturing late leaching and dolomitisation near coastal carbonates commonly contain siliciclastics as do some shelf margin deposits that interdigitate with or are covered in siliciclastics some early probable meteoric leaching affected inner shelf deposits prior to pervasive neomorphic to blocky poikilotopic calcite cement formation on the basis of 18 o v pdb values of 4 5 to 7 9 equivalent to 18 o v smow values of 0 to 4 at 25 40 c and 13 c v pdb values of 0 6 to 1 6 cementation probably reflects alteration from terrestrial groundwaters in meteoric aquifers derived from the humid landmass of borneo despite this cementation moderate energy inner to mid shelf grainstones from the core of mounded carbonates still retain or have enhanced porosity 18 o v pdb values of 3 6 to 5 4 those for the late dolomites are suggestive of fluids of meteoric origin 18 o v pdb values of 5 2 to 7 4 equivalent to values of 0 3 to 6 3 v smow at 40 60 c critical factors for reservoir quality development in carbonates from siliciclastic dominated shelves in the equatorial tropics are 1 development and preservation of primary porosity 2 cementation associated with meteoric aquifers draining large humid equatorial landmasses and 3 burial leaching and fluid pathways

the effects of a bypass dunefield on the stability of a headland bay beach a case study abstract this paper presents a case study on the modelling of a headland bay beach influenced by sediment input from migrating coastal dunes the study area is the region around the town of ingleses on santa catarina island santa catarina state south eastern brazil ingleses has been threatened by nature at two different fronts at the north eastern side of the town lies ingleses beach a headland bay beach which seems to be subject to persistent erosion in recent years on the south western side the town is threatened by a migrating dunefield which is encroaching onto houses and infrastructure but which has not reached the beach in the past 70 years a second dunefield in the area does not pose a direct threat to the town but passes it on the eastern side and forms an important influence on the development of the beach the sediment influx rate from this dunefield to the beach is 10 000 m3 year to investigate the effect of the dunefields on the morphodynamic system a numerical model has been created using the software packages swan and unibest and the static equilibrium bay shape was determined by the software package mepbay the result of the long term scenario as predicted by unibest agrees rather well with the static equilibrium bay shape found with mepbay this provides sounds basis for the credibility of both models consequently the predicted evolutional trend of the shoreline seems plausible

variability of the rebound hardness as a proxy for detecting the levels of continuity and isotropy in archaeological quartz abstract the equotip hardness tester is applied to different types of quartz and other lithic raw materials in order to determine if variations in the rebound hardness measured by this device may serve as a proxy for detecting the levels of continuity and isotropy of toolstones continuity the amount of cracks and other internal defects and isotropy the measure of the directional properties of a raw material are known to have important effects on the level of consistency and predictability of fractures which in turn is traditionally considered a main factor for defining the flaking quality of a given raw material the results demonstrate the existence of differences among the raw materials analysed in both the average value and the variability of the rebound hardness while cryptocrystalline samples show the most homogeneous results quartz and metamorphic rocks display a comparatively higher variance in the specific case of quartz such variability seems to be mainly caused by the presence of internal planes and discontinuities while anisotropy although also active had played a comparatively modest role the results achieved by the equotip hardness tester suggest that this device could be successfully used for a basic or preliminary estimating of some of the physical and mechanical properties of stone raw materials therefore it is a potential index test for complementing other more accurate laboratory methods

the australian stress map knowledge of the in situ stress field of the australian continent has increased greatly since compilation of the world stress map in 1992 principally by analysis of borehole breakouts and drilling induced tensile fractures in petroleum wells stress orientations are variable across the australian continent as a whole however within 15 of 16 individual stress provinces defined in the australian continent of one to a few hundred kilometres scale mean stress orientations are statistically significant the stress provinces and stress trajectory mapping reveal that there are systematic continental scale rotations of stress orientation within australia unlike many other continental areas stress orientations do not parallel the direction of absolute plate motion nonetheless the regional pattern of stress orientation is consistent with control by plate boundary forces if the complex nature of the convergent northeastern boundary of the indo australian plate and stress focusing by collisional segments of the boundary is recognized

shale tectonics and deformation associated with active diapirism the jerudong anticline brunei darussalam the jerudong anticline provides an outcrop example of multiple phases of diapir growth and interaction with the country rock the n s trending anticline overlies a high angled basement fault zone that was episodically active moving predominantly sinistrally in response to transpressive stresses the earliest stage of deformation in the study area was mid miocene e w to ne sw trending growth faulting and shale diapir growth early normal faults exerted an important influence on the large and small scale bedding geometries and facies changes of syn tectonic shallow marine shoreface and tidal strata in particular there are laterally rapid facies changes and differential rotation of strata across growth faults diapir activity is indicated by the presence of shale dykes which commonly intrude normal fault planes and concordant shale intrusions shale intrusions associated minor thrust faults and normal faults were rotated during a late miocene early pliocene phase of folding related to transpression few shale dykes were intruded during this phase probably because the horizontal principal stresses were relatively large compared with the pore fluid pressure at the end of the transpressive phase shale dykes were intruded into steeply dipping beds as a result of stress relaxation continued uplift and erosion elevated overpressured horizons to a point where hydraulic fracturing reached the surface and holocene age mud volcanoes were developed

sea level changes shoreline journeys and the seismic stratigraphy of central luconia miocene present offshore sarawak nw borneo abstract central luconia is a geological province of the sarawak basin offshore nw borneo characterised by extensive development of miocene to recent carbonate build ups in the subsurface many of these build ups are reservoirs for hydrocarbons this study focuses on shelf wide stratigraphic architecture from which implications are drawn for the stratigraphic sealing potential of the deltaic clastics a stratigraphic model is proposed whereby clastic sediments surrounding the carbonate build ups are interpreted as stacked low relief deltas deposited in response to high frequency oscillation of the sea level the deltas are shown to have frequently prograded beyond carbonate build ups as a result of interaction between eustacy and deposition deltaic topsets are juxtaposed against carbonate build ups providing migration routes for hydrocarbons most of the carbonate reservoirs are consequently underfilled with hydrocarbon columns limited to the youngest onlapping stratigraphic sequence

analysis of temperature variability and determination of apparent thermal diffusivity in sandy intertidal sediments at the german north sea coast abstract temperature was measured at depths of 1 10 30 75 and 170 cm in fine sandy intertidal sediments by means of specially designed temperature lances the measurements cover a period from february to october 2007 and have a temporal resolution of 5 min stochastic as well as recurrent processes due to the solar cycle and due to tide induces flooding and drying of the sediment surface lead to a complex composition of the time series curves spectral analyses based on fast fourier transformation fft reveal that temperature variability at the sediment water air interface is widely controlled by recurrent processes with period lengths of 4 93 6 1 8 19 12 24 h and 354 h 14 7 days the importance of the higher frequencies decreases with increasing sediment depth at a depth of 30 cm the 24 h and the 14 7 days cycles mainly determine the temperature development over time while at 75 cm sediment depth contour temperature varies only along the 14 7 days cycle as well as within the seasonal cycle using cross correlation analysis the time necessary for a temperature signal at the surface to trigger a response at a sediment depth of 10 30 and 75 cm was calculated as 1 4 7 0 and 73 1 h respectively utilizing an alternate approach fft derived temperature peak to peak amplitude values and phase angles of up to 9 different cycles were used to calculate apparent thermal diffusivity in different sediment depths the thermal diffusivity decreases from approximately 6 9 10 7 m 2 s 1 from the surface down to a sediment depth of 75 cm the specially designed instrumentation has proven to be robust and precise enough to record high resolution time series of sediment temperature in different depths the time series analysis of the data clearly shows that the temperature variability in the intertidal sediments to a high degree can be explained by recurrent solar and or tidal effects so the methods and results presented in this paper can help to answer questions which are related to sediment temperature in tidal flat environments

effect of moderate shock waves on magnetic susceptibility and microstructure of a magnetite bearing ore this study demonstrates a relationship between changes of magnetic susceptibility and microstructure developing in minerals of a magnetite bearing ore experimentally shocked to pressures of 5 10 20 and 30 gpa shock induced effects on magnetic properties were quantified by bulk magnetic susceptibility measurements while shock induced microstructures were studied by high resolution scanning electron microscopy microstructural changes were compared between magnetite quartz amphibole and biotite grains in the 5 gpa sample a sharp drop of magnetic susceptibility correlates with distinct fragmentation as well as with formation of shear bands and twins in magnetite at 10 gpa shear bands and twins in magnetite are accompanied by droplet shaped nanograins in this shock pressure regime quartz and amphibole still show intensive grain fragmentation twins in quartz and foam shaped highly porous amphibole are formed at 20 and 30 gpa the formation of porous minerals suggests that shock heating of these mineral grains resulted in localized temperature spikes the identified shock induced features in magnetite strongly advise that variations in the bulk magnetic susceptibility result from cooperative grain fragmentation plastic deformation and or localized amorphization and probably postshock annealing in particular the increasing shock heating at high pressures is assumed to be responsible for a partial defect annealing which we suggest to be responsible for the almost constant values of magnetic susceptibility above 10 gpa

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

the influence of wave wind and tide forced currents on headland sand bypassing study case santa catarina island north shore brazil abstract investigations of headland sand bypassing are still an under reported subject in the literature this paper aims to understand the contribution of currents forced by different mechanisms such as tides winds i e local wind acting over the ocean surface generating currents without considering wave generation and waves as they approach break on the coast to headland sand bypassing the study was carried out in an area comprising a series of seven headlands with varying wave exposure due to changes in shoreline orientation and increasing tidal influence close to a relatively large bay this paper uses a calibrated and validated process based model delft3d to simulate a series of scenarios including spring and neap tides during flood and ebb conditions and a range of wind and wave scenarios that encompass both average and extreme conditions the results indicate that waves are the main driving force for the headland bypassing as they transport sand at rates two orders of magnitude higher than tide or wind driven sediment transport the tide driven currents can only transport sediment during spring tides in locations where the currents are intensified it is also demonstrated that the wave direction plays an important role in sediment transport in exposed areas with larger headlands a combination of wave directions is required to first transport sediment offshore out of the beach and secondly to transport sediment alongshore and back to the next beach whereas in areas with little variation in wave direction exposure the same oblique wave direction is responsible for the entire headland bypassing process this is the first time the contribution of tide winds and wave generated sediment transport to headland bypassing have been studied

influence of mixtures of grain size populations on the parametric and modal characteristics of coastal sands herault mediterranean sea france abstract grain size distributions in lower beach and nearshore sands of a segment of the coast of the golfe du lion france were analyzed by a parametric method and by modal analysis the results have been considered both in a spatial framework delineating geographically distinct sedimentary compartments and cells and in a morphodynamic framework separating the dynamic components of the shoreline berm collision zone inner bar outer bar lower shoreface modal statistics indicate that a mixture of three dominant components end members contributes to the grain size distribution gsd of the sediments fine sand sedimentary type i modal value 0 195 mm i 0 35 medium and coarse sand st ii modal value 0 680 mm i 0 8 and very coarse sand and gravel st iii i modal value 2 3 mm i 1 5 quasi log normal one component gsds form a minority group and mixtures produce various apparently unimodal sands and bimodal sediments a large variation of grain size indices results from mixing a simulation of mixing of log normal populations close to the end members shows the great sensitivity of parameters sorting skewness and kurtosis to small changes in the compositional formula of the mixture the procedure followed supplies a good preliminary tool enabling rapid identification and localization of the main sand sources on a regional scale these components derive from potential sources available in the region well known from previous studies st i originates from the river rhone and provides the textural base for most of the sediments st ii and iii form a local component originating either from fluvial input aude orb and herault rivers or from the nearshore reworking of ancient quaternary sediments and late holocene beachrocks each st takes on local aspects in relation to the morphological environment but the regional scale of the study was too large to precisely reflect the local morphodynamic regime a significant change in the st i sorting of bar sands is however observed probably due to the net offshore migration reported for the bar system

morphological response to storms in an embayed beach having limited sediment thickness abstract the morphological response of a wave dominated embayed beach to large storms was investigated via field data collection and numerical simulation hydrodynamic and morphological field data collected in haeundae beach facing sse in the south eastern corner of korea were analysed during the southerly storm waves i e almost shore normal direction the upper part sediments of the beach were eroded and redistributed to the surf zone meanwhile easterly storm waves transported sediment from east to west resulting in coastline advancement in the west and retreat in the east in order to investigate the morphological response of the beach with limited sediment availability under storm conditions the numerical model xbeach was used with the assumption of unlimited sediment availability the southerly storms led to overestimation of sediment transports and unrealistic erosion and deposition patterns in the middle part of the beach in contrast the model results with the option of sediment layer thickness showed good agreement with the erosion and deposition patterns analysed from field data this suggests that sediment availability can be one of the key factors in determining the morphological response in a wave dominated embayed beach where sediment supply from neighbouring beaches or rivers is limited

recent surface displacements in the upper rhine graben preliminary results from geodetic networks abstract datasets of the gnss upper rhine graben network gurn and the national levelling networks in germany france and switzerland are investigated with respect to current surface displacements in the upper rhine graben urg area gurn consists of about 80 permanent gnss global navigation satellite systems stations the terrestrial levelling network comprises 1st and 2nd order levelling lines that have been remeasured at intervals of roughly 25 years starting in 1922 compared to earlier studies national institutions and private companies made available raw data allowing for consistent solutions for the urg region we focussed on the southern and eastern parts of the investigation area our preliminary results show that the levelling and gnss datasets are sensitive to resolve small surface displacement rates down to an order of magnitude of 0 2 mm a and 0 4 mm a respectively the observed horizontal velocity components for a test region south of strasbourg obtained from gnss coordinate time series vary around 0 5 mm a the results are in general agreement with interseismic strain built up in a sinistral strike slip regime since the accuracy of the gnss derived vertical component is insufficient data of precise levelling networks is used to determine vertical displacement rates more than 75 of the vertical rates obtained from a kinematic adjustment of 1st order levelling lines in the eastern part of urg vary between 0 2 mm a and 0 2 mm a indicating that this region behaves stable higher rates up to 0 5 mm a in a limited region south of freiburg are in general agreement with active faulting we conclude that both networks deliver stable results that reflect real surface movements in the urg area we note however that geodetically observed surface displacements generally result from a superposition of different effects and that a separation in tectonic and non tectonic processes needs additional information and expertise

present day stress and neotectonic provinces of the baram delta and deep water fold thrust belt abstract we present the first present day stress orientation measurements across a delta and deep water delta toe fold thrust belt stress and neotectonic data for nw borneo reveal three discrete neotectonic provinces an inverted inner shelf province where present day maximum horizontal stress h is oriented margin normal an extensional delta top province h is margin parallel and a compressional delta toe province h is margin normal we interpret the delta top and delta toe data to reflect that compression in the fold thrust belt is coupled to delta top extension and that the inverted inner shelf province reflects the location of this system on an active margin

coastal response to late stage transgression and sea level highstand coastal morphologic features associated with past shoreline transgressions and sealevel highstands can provide insight into the rates and processes associated with coastal response to the modern global rise in sea level along the eastern and southern brazilian coasts of south america 6000 years of sea level fall have preserved late stage transgressive and sea level highstand features 1 4 m above present mean sea level and several kilome ters landward of modern shorelines gps with real time kinematics data ground penetrating radar stratigraphy and radiocarbon dating within a 2 3 km wide river associated strandplain in central santa catarina southern brazil uncovered a diverse set of late stage transgressive and highstand deposits here the highstand took the forms of 1 an exposed bedrock coast in areas of high wave energy and low sediment supply 2 a 3 8 m high transgressive barrier ridge where landward barrier migration was prohibited by the presence of shallow bedrock and 3 a complete barrier island complex containing a 5 2 m high barrier ridge washover deposits a paleo inlet and a backbarrier lowland formed in a protected cove with ample sediment supply from small local streams and the erosion of upland sediments similar signatures of the mid holocene highstand can be traced across all coastal brazilian states this study presents the fi rst complete compilation of the diversity of these sedimentary sequences they are broadly classifi ed here as exposed bedrock coasts type a back barrier deposits type b transgressive barrier ridges type c and barrier island complexes type d according to localized conditions of upland migration potential wave exposure and sediment supply these brazilian systems present a paradigm for understanding future coastal response to climate change and accelerated sea level rise the recognition of a minimum threshold sea level rise rate of 2 mm yr 1 above which transgression proceeded too rapidly for the formation of these stable accretionary shoreline features demonstrates the nonlinearity of coastal response to sea level change and the site specifi city of conditions associated with the formation of each highstand deposit type even within a single small embayment demonstrates the non uniformity of that response

interaction between critical wedge geometry and sediment supply in a deep water fold belt the late miocene holocene deep water fold and thrust belt of offshore northwestern borneo displays one of the most acute angles recorded for a submarine critical taper wedge the very low surface 1 2 5 and basal detachment 2 5 dips require basal pore fluid pressures near lithostatic pressure for the wedge to propagate at such angles in the deep water environment sedimentary processes act against the wedge attaining critical taper in places of lower sedimentation rates the fold and thrust belt extends to the base of the slope and dips 1 5 2 5 in areas of the highest sedimentation rates baram delta the slope has a lower angle 1 and the slope continues beyond the limit of the fold and thrust belt slope morphology changes along the margin from concave up relatively low sedimentation rate low shortening rate to convex up relatively high sedimentation rate low shortening rate to stepped relatively low sedimentation rate high shortening rate

ridge forces absolute plate motions and the intraplate stress field torque poles are calculated for a variety of possible forces acting on the plates including ridge push slab pull and collisional resistance these torque poles are then compared to the directions of absolute plate motions there is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the north american south american pacific cocos and eurasian plates simple slab pull torques correlate well with absolute motion azimuths for the pacific nazca and cocos plates and moderately well with the absolute motion azimuth of the indoaustralian plate collisional resistance torque poles correlate with the absolute motion azimuth of the eurasian plate only the correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves torque poles for various forces are also compared with several long wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions in general ridge torque directions agree well with the orientations of maximum horizontal stresses for stable north america western europe and south america and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag collisional resistance forces can also explain the alignment of stresses in western europe for the indoaustralian plate the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate other processes in addition to collisional resistance must be important for the indo australian plate ridge push forces may account for a significant portion of the long wavelength features of the intraplate stress field especially away from continental collisions such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism as previously suggested slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates

present day stress orientation in brunei a snapshot of prograding tectonics in a tertiary delta the baram delta province of nw borneo is unusual when compared with most other tertiary deltas as it has built up upon an active margin hence structures observed in the baram delta province are the result of both margin parallel gravity driven deltaic tectonics and approximately margin normal transpressive tectonics associated with the active margin image and dipmeter logs have been examined for breakouts and drilling induced tensile fractures ditfs in 47 wells throughout brunei breakouts and ditfs observed in 19 wells suggest that the maximum horizontal stress is oriented margin normal nw se in the proximal parts of the basin and margin parallel ne sw in the outer shelf region the margin parallel outer shelf stress field is interpreted as a local deltaic stress field caused by the shape of the clastic wedge the margin normal maximum horizontal stress in the inner shelf is interpreted to reflect basement stresses associated with the active margin however the maximum horizontal stress in the inner shelf is approximately perpendicular to the strike of miocene pliocene normal growth faults suggesting that maximum horizontal stress in the inner shelf has rotated from margin parallel deltaic to margin normal basement associated over time hence approximately the same stress rotation has occurred over time in the inner shelf as is currently observed spatially from the outer to inner shelf the spatial and temporal stress rotations in brunei are thus interpreted to be the result of deltaic and basement associated tectonic regimes that are prograding basin wards the proximity of the active margin has resulted in progressive uplift and inversion of the hinterland that has forced the delta system to prograde rapidly the zone of active deltaic growth faulting and margin parallel maximum horizontal stress has shifted basin wards prograded as the delta system has rapidly prograded across the shelf after uplift and delta progradation the old growth faults of the inner shelf ceased being active and have then been successively reactivated by a similarly prograding margin normal inversion front

tidal strait to embayment seismic stratigraphy and evolution of a rock bounded embayment in the context of holocene sea level change abstract elongate rock framed santa catarina island partly encloses a low energy marine embayment that communicates with the ocean via narrow rock bounded inlets with ebb and flood tide deltas the bay shoreline consists of low energy sandy beaches strandplains mangroves and bayhead deltas while the exposed atlantic shoreline comprises a series of headland embayment littoral cells in a linked north directed longshore drift system new and previously published seismic stratigraphic investigations enable assessment of the palaeogeographic geomorphic evolution of the area since the early holocene at a sea level of ca 50 m a sandy mainland attached shoreline complex dune and beach developed on a coastal plain setting some 6 7 km offshore of the present shoreline north of the island a barrier island and tombolo were formed in a coastal re entrant adjacent to the northern entrance to florianopolis bay the open coast beach dune system was overstepped by rapid sea level rise during mwp 1b whereas the barrier island and tombolo continued to accrete until mwp 1c when they too were overstepped the back island embayment contains up to 40 m of sediment overlying an irregular bedrock surface it was initially flooded during mwp 1c and the early muddy sedimentation suggests a distal sheltered marine embayment the subsequent development of many large bioherms on bedrock and mud suggests a change to more fully marine conditions as sea level continued to rise in the north bay these were subsequently enveloped by tidal dunes migrating north from the mid bay the vertical stacking of 3 d and 2 d sandy bedforms suggests that a tidal strait had developed with strong tidal currents radiating from a constriction in the vicinity of modern florianopolis city the strong tidal currents may be linked to the holocene sea level high that is well documented for this region a fall in sea level from this highstand coupled with accumulation of tidal strait sediments reduced the tidal prism and strength of tidal currents in the bay at the same time regressive beachridge plains developed in open coast and bay environments this coincided with development of the contemporary tidal inlet complexes at the north and south outlets of the bay as a consequence the upper surface of the tidal strait sand deposits experienced tidal ravinement and the bay switched to a sheltered back barrier environment dominated by deposition of mud and silt which blanket the contemporary bay floor the tidal inlets sequestered sand from the littoral drift system in ebb and flood tide deltas which created breaks in the longshore drift system causing littoral sediment to accumulate at the north of the island in a series of spits and promoting strandplain development south of the island

behavior of grain size characteristics on reflective and dissipative foreshores broken bay australia abstract beach morphology wave current dynamics or sediment attributes such as grain size changes and sorting processes intrinsically characterize each other the extreme cases of the morphological spectrum include reflective beaches which are steep and devoid of inshore topographic expression or surf zone circulation and dissipative beaches which are flat and have inshore barred topography with attendant longshore currents and rips for a study of four beaches in broken bay australia representing these morphological extremes four facts become obvious first reflective beaches have rapid variaiton in foreshore grain size alongshore mean settling velocity changes greater than 0 3 log10 cm sec km grain size changes greater than 0 2 mm km whereas dissipative beaches have weak r variation mean settling velocity changes approximate 0 1 log10 cm sec km grain size changes less than 0 1 mm km second the pattern on reflective foreshores remains fixed over time whereas the pattern on dissipative foreshores varies to the point that size gradients can reverse direction within one year third this temporal variation reflects the directional width of the incoming wave spectra and not changes in the level of wave power reflective beaches have waves approaching almost shore normal because of the nullification of deep water variation by wave refraction or by the sheltering effects of headlands wave approach on dissipative beaches varies daily and the beach planform and sediment must respond over time to this variation fourth grain size changes fit one of two postulates the energy postulate states that grain size and sorting increase along a foreshore as energy increases the drift postulate states that grain size increases downdrift the energy postulate is more appropriate on reflective beaches whereas the drift postulate accounts for the difference in the magnitude of grain size changes alongshore between reflective and dissipative beaches on reflective foreshores coarse material is naturally concentration at the base of the swash zone because of gravity effects or shear sorting in backwash larger grains here move faster alongshore than finer ones near the top of the foreshore because longshore currents at the base of the swash are stronger than the zigzag motion of swash drift further up the beach face this drift sorti g produces strong longshore size gradings on the foreshore this effect is negated on dissipative beaches by swash bore transport of coarse grains upslope by dilution with inshore sediment that has undergone preferential movement of fines alongshore in suspension and by locally reversed longshore currents near rips

planform and mobility in the meaipe maimba embayed beach on the south east coast of brazil the meaipe maimba embayed beach mmeb on the south east coast of brazil has been subject to anthropogenic pressures since the 70 s in this study we discuss the adequacy and contribution of the parabolic planform model to determine the planform and variability of the mmeb taking into consideration variation in wave conditions the role of different controlling conditions on the planform variability is analyzed as well as the morphological and planform mobility mmeb exhibited a new configuration in response to the construction of a harbor which interrupted the longshore sediment transport after four decades three particular morphodynamic sectors have been recognized along the beach the central sector is more exposed to normal wave incidence and cross shore processes predominate the northern and southern sectors are influenced by wave diffraction processes around the headlands and port respectively in the northern sector the presence of secondary headlands and inner islands imposed a geomorphological control on beach morphology and coastal processes the use of the parabolic planform model provided useful insights for the assessment of potential planform mobility since the decadal shoreline evolution combined with beach profiles and sediment characteristics allowed understanding of the beach mobility processes and supported the interpretation of modeling results

effects of density contrasts on the orientation of stresses in the lithosphere relation to principal stress directions in the transverse ranges california the influence of stresses arising from horizontal density contrasts on the orientation and relative magnitudes of principal stresses in an otherwise uniform lithospheric stress field is investigated a simple model is constructed in which a local deviatoric stress due to a density anomaly embedded within or just below the lithosphere and a regionally constant deviatoric stress field are each approximated by biaxial tensors the net stress field is obtained from the sum of the two both the relative magnitudes of principal stresses and the magnitude of the angular difference in principal stress direction of the summed tensor compared with that obtained in the absence of buoyancy forces depend on two parameters the first is the ratio where is a measure of the magnitude of the regional deviatoric stress and is the magnitude of the stress arising from buoyancy forces associated with the density anomaly the second parameter is the angle between the trend of the density anomaly and the direction of maximum compressional stress that obtains in the absence of any perturbation by the local buoyancy forces the directions of the principal axes of the total stress field are found to differ by up to 90 from those of the reference stress field the model is applied to the transverse ranges california where the observed 23 difference in orientation of principal horizontal compressive stress compared with the principal compressive stress direction in central california constrains the predicted value of to be approximately 0 4 this is consistent with an independently calculated range of in which is inferred from seismological constraints on the magnitude of density variations underneath the transverse ranges and is inferred from observations of heat flow along the san andreas fault in central california the agreement between the two estimates of supports the hypothesis that the observed differences in horizontal principal stress orientation in california can be explained by the combined influence of a local negative buoyancy force under the transverse ranges and a regional stress field associated with transcurrent deformation within the pacific north american plate boundary zone the observed counterclockwise angular difference in principal horizontal stress direction in the transverse ranges compared with central california implies that the plane of maximum right lateral shear stress is also rotated counterclockwise relative to that in central california this supports the possibility that the big bend in the san andreas fault may be a consequence of the negative buoyancy forces acting in the transverse ranges and not the cause of transverse ranges formation as has often been assumed

drilling induced tensile wall fractures implications for determination of in situ stress orientation and magnitude abstract detailed investigation of failure of the borehole wall in two scientific drilling projects the german ktb kontinentales tiefbohrprogramm der bundesrepublik deutschland and the european geothermal research project at soultz sous forets france has lead to new insight in the phenomena of tensile fractures induced in the wellbore wall during drilling comparison of the orientation of the fractures with the orientation of the horizontal principal stress known from breakout and hydraulic fracturing analysis demonstrates that these fractures are reliable indicators of the orientation of the maximum horizontal principal stress s h a model for the initiation of the fractures is presented which points out the important influences of a the tectonic stress state b increased mud pressures during drilling operation and c thermal stresses induced by circulation of relatively cold drilling mud analysis of drilling induced fractures in the gpk1 borehole at soultz sous forets where the magnitude of s h is known from hydraulic fracturing experiments demonstrates the validity of this model for the initiation of the fractures further a new method is proposed to estimate the magnitude of s h from the occurrence of drilling induced fractures and knowledge of thermally induced stress and pumping pressure during drilling the method is successfully applied to both ktb boreholes an independent method to estimate the magnitude of s h based on the analytical calculation of the stress intensity factor for drilling induced fractures taking into consideration both increased mud pressure and thermal stress is also presented application of this method confirms the results derived with the analysis described above additionally the evaluation of the orientation of the fractures with respect to the wellbore axis indicates that over major depth sections of the investigated wells the vertical stress is a principal stress

deepwater north west borneo hydrocarbon accumulation in an active fold and thrust belt in the deepwater acreage of north west borneo an active offshore fold and thrust belt hosts a number of proven hydrocarbon accumulations and promises to deliver considerable additional hydrocarbon volumes as a result of ongoing exploration campaigns typical trapping geometries observed in this neogene large scale linked fold and thrust belt are hanging wall anticlines foreland folds and ridges and sub thrust footwall cut offs commercial drilling targets lie within the deformed miocene and pliocene sediment pile and these have been charged with oil and gas from a petroleum system that is still active at the present day a major challenge here is to avoid drilling traps that have expelled their hydrocarbons during periods of active deformation and uplift in recent geological time studies of tectonic deformation phases are beginning to illuminate some key controls on trap formation and hydrocarbon retention history this paper focuses on providing an overview of the north west borneo deepwater fold and thrust belt and introduces some key issues and challenges for future hydrocarbon exploration in the region

variation in vertical stress in the baram basin brunei tectonic and geomechanical implications the vertical or lithostatic stress is an important factor in tectonic and geomechanical studies and is commonly used in the prediction of pore pressures and fracture gradients however the vertical stress is not always calculated in situ and the approximation of 1 0 psi ft 22 63 mpa km is often used for the vertical stress gradient vertical stress has been determined in 24 fields in the baram basin brunei using density log and checkshot velocity survey data the baram basin shows a variation in vertical stress gradient between 18 3 and 24 3 mpa km at 1500 m depth below the surface this variation has a significant effect on in situ stress related issues in field development such as wellbore stability and fracture stimulation the variation is caused by a bulk rock density change of 2 48 2 07 g cm 3 from the hinterland of the delta to its front differential uplift and erosion of the delta hinterland and undercompaction associated with overpressure are the interpreted causes of the density and hence vertical stress variation q 2004 elsevier ltd all rights reserved

shoreline evolution in an embayed beach adjacent to tidal inlet the impact of anthropogenic activities abstract embayed beaches are widely distributed around the world their shoreline evolution is controlled primarily by the upstream headland and prevailing wave conditions tidal inlets are also ubiquitous in sandy coasts they are quite dynamic and act as a sediment source or sink depending on the sediment transport pattern and budget an embayed beach may develop downstream of a tidal inlet if a protruding headland is formed at the inlet owing to either natural processes or human construction in this study gaolong bay located downstream of a tidal inlet qinglan inlet in wenchang city hainan island china is used as an example to examine the effects of an upstream tidal inlet on the evolution of an embayed beach emphasis is placed on the impact of anthropogenic activities such as landfilling and jetty construction historical remote sensing data were collected and the evolution of the shoreline from 1998 to 2018 was analyzed the shoreline change pattern in gaolong bay was identified with the empirical orthogonal function eof method and the mechanisms behind these changes were explored with a coupled current wave sediment transport modeling system our results indicate that the construction of an artificial peninsula and a jetty beside the inlet channel dramatically changed the evolution of the gaolong bay shoreline defying the classical expectation of shoreline retreat downdrift of a tidal inlet a clockwise shoreline rotation was prevalent in gaolong bay with the shadow zone accreting and the distal zone retreating along with an overall shoreline propagation translation the static equilibrium shoreline planform model model of equilibrium of bay beaches mepbay was further used to predict the future evolution of the shoreline this study demonstrates that an embayed beach downdrift of a tidal inlet can exhibit a complex response to human interventions at the inlet and highlights the necessity of considering adjacent shoreline changes when assessing the impact of inlet stabilization

application of the ads method to predict a hidden basal detachment nw borneo fold and thrust belt abstract the nw borneo margin is characterized by a complex deepwater fold and thrust belt despite previous studies the definition of a univocal detachment level for folding and thrusting is still lacking the area depth strain ads method can be used to determine the location for a detachment in areas lacking data and to balance geological cross sections this study applies the ads method to the central part of the nw borneo fold and thrust belt to predict a structurally conclusive detachment level in an area lacking a seismic detachment reflection seismic interpretations were completed after the ads determination of the basal detachment providing input for a 2d sequential restoration that delivered values on shortening distribution and shortening rate the kinematic and mechanic analyses presented document that the central part of the nw borneo fold and thrust belt is affected by both near and far field stresses and that the far field crustal shortening component becomes more important northward this work demonstrates that the ads method can be effectively applied in fold thrust belt settings with limited information on the detachment supports in a quantitative way the tectonic and stratigraphic interpretation of seismic reflection data and provides a robust structural base for the restoration of balanced cross sections including the reconstruction of syn kinematically eroded stratigraphy

dynamic equilibrium planform of embayed beaches part 2 design procedure and engineering applications abstract the design of equilibrium beach systems employing beach nourishment techniques in conjunction with coastal support structures has received increased interest from coastal engineers in recent years one such solution to remedy coastal erosion problems is to design an equilibrium pocket beach in order to stabilize the shoreline such coastal landforms may exist in nature in static or dynamic equilibrium states the concept of the static equilibrium planform sep has received much more attention from coastal engineers than that paid to the dynamic equilibrium planform dep this paper presents a design procedure for embayed beaches in dynamic equilibrium which have a specific net littoral drift rate the proposed methodology employs the net sediment transport rate passing through the bay together with the time series of the wave climate impinging on the beach in order to compute the angle d this angle represents the difference in degrees between the direction of the mean wave energy flux at the diffraction point ef and the orientation of the dynamic equilibrium beach db to be utilized in a newly derived dep formula to predict the shoreline shape in the long term the procedure was applied and validated using prototype bays in dynamic equilibrium with different net sediment transport rates along the brazilian coast producing good results furthermore it was employed as a tool to investigate the influence of changes in the net annual littoral drift rate on the dep shape in a case study along the spanish coast taken together these confirm its utility as a valuable tool for coastal management and engineering practice

post earthquake coastal evolution and recovery of an embayed beach in central southern chile abstract earthquakes and tsunamis are significant factors for change along active margin shores and influence coastal evolution the chilean coast was affected in 2010 by a subduction earthquake with a magnitude of mw 8 8 and also by a trans pacific tsunami which generated violent geomorphologic changes and damaged homes following these events the magnitude of the changes which affect chile s central southern coast 37 s and the role of subduction earthquakes in coastal evolution on a historical scale were investigated at lebu bay an embayed beach data were generated for variations in time and space along the shoreline topographical and bathymetric changes in the bay and for morphodynamic littoral processes logarithmic and parabolic models were applied to the shoreline along with map overlays in order to determine changes the shoreline processes were analyzed based on statistics for waves tides and sediment transport for pre and post tsunami conditions an average accretion rate of 2 80 m year 1984 2010 was established for the shoreline with a strong trend towards accretion in the last 30 years a parabolic function best represented the general form of the shoreline although the presence of a river in the concave zone affected the fit in this sector two factors controlled historical changes on the beach one of anthropic origin in addition to the earthquake and tsunami on february 27th 2010 the post earthquake recovery was fast and currently the beach is in a stable condition despite the inter seismic subsidence process previous to the event this coastal system showed a high resilience in the face of coastal geomorphological changes induced by high impact natural disturbances however the opposite occurred in relation to changes induced by anthropogenic disturbances

balancing deformation in nw borneo quantifying plate scale vs gravitational tectonics in a delta and deepwater fold thrust belt system abstract recent gps measurements demonstrate that nw borneo undergoes 4 6 mm of plate scale shortening a year which is not accommodated by plate scale structures the only geological structure in nw borneo described to accommodate on going shortening is the baram delta system located on the outer shelf to basin floor delta toe fold thrust belts are commonly thought to be caused by margin normal compressional stresses generated by margin parallel upslope gravitational extension the baram delta system is divided into three neotectonic provinces 1 an inactive onshore and inner shelf region of inversion superimposed on an older extensional deltaic province 2 an outer shelf region of present day deltaic extension and 3 a compressional delta toe however it is uncertain whether compression in the delta toe area is purely driven by gravity i e shortening is less than upslope extension or if there is a component of regional shortening involved which can only be demonstrated if shortening is greater than upslope extension in order to quantify the balance between the shortening related to the upslope gravitational extension and the shortening related to the regional geodynamic framework in the baram delta system we have used a geomechanical code based on the finite element method and conservation of mass and momentum dynel 2d this enabled us to reconstruct the tectonic evolution of the delta and to demonstrate for the first time that the total shortening observed in the delta toe does not balance against the active extension in the delta top with the system exhibiting 1 8 shortening overall or 2 0 km this additional shortening is therefore attributed to plate scale shortening across nw borneo produced by far field compression using a convergence rate of 4 mm y 1 demonstrated by gps measurements the delta toe has accommodated far field compression only in the last 0 5 my

on the morphological development of embayed beaches abstract the typically curved and stable planform shape of embayed beaches is often observed in the presence of rigid headlands the long term alongshore equilibrium shape is variable and is controlled by headland geometry cellular circulation patterns and wave obliquity at the shoreline we use a process based morphological model to simulate the development of embayed beaches depending on different environmental conditions and geological settings i e topography and geometry the embayment is allowed to develop from an initially straight beach to one which is curved under idealized wave forcing conditions and without external sediment input bay development can be approximated with an exponential function with coefficients representing rate of growth and bay size long term shoreline cutback is both uniform shoreline translation and non uniform shoreline rotation and is parameterized alongshore gradients in flow and transport patterns are related to long term non uniform shoreline cutback rotation of the beach ceases as the bay matures leading to a curved shoreline planform which is a remnant of decaying erosion processes

contraction and extension in northern borneo driven by subduction rollback abstract during the paleogene the proto south china sea was subducted beneath northern borneo subduction ended with early miocene collision of the dangerous grounds reed bank north palawan block and the sabah cagayan arc much of northern borneo then became emergent forming the top crocker unconformity later in the early miocene subsidence resumed it is proposed that northward subduction of the celebes sea initiated formation of the sulu sea backarc basin followed by subduction rollback to the se this formed a volcanic arc which emerged briefly above sea level and collapsed in the middle miocene as rollback continued the sulu arc was active during middle and late miocene between sabah and the philippines rollback drove extension in northern borneo and palawan accompanied by elevation of mountains crustal melting and deformation offshore there were two important extensional episodes the first at about 16 ma is marked by the deep regional unconformity and the second at about 10 ma produced the shallow regional unconformity both episodes caused exhumation of deep crust probably on low angle detachments and were followed by granite magmatism the nw borneo palawan trough and offshore sabah fold and thrust belt are often interpreted as features resulting from collision regional compression or subduction however there is no seismicity dipping slab or volcanicity indicating subduction nor obvious causes of compression the trough developed after the middle miocene and is not the position of the paleogene trench nor the site of neogene subduction inboard of the trough is a thick sediment wedge composed of an external fold and thrust belt and internal extensional zone with structures broadly parallel to the trough the trough is interpreted as a flexural response to gravity driven deformation of the sediment wedge caused by uplift on land that resulted from extension with a contribution of deep crustal flow

nearshore hydrodynamics at pocket beaches with contrasting wave exposure in southern portugal abstract pocket beaches on rocky coasts with headlands that control hydro sedimentary processes are considered to be constrained sedimentary systems generally with limited sediment inputs pocket beaches face severe changes over time under worst case scenarios these changes can result in the loss of the beach causing waves to directly attack adjacent cliffs studies of nearshore hydrodynamics can help to understand such changes and optimise sediment nourishment procedures the present work contributes to the knowledge of hydrodynamic forcing mechanisms at pocket beaches by providing a comprehensive description of the nearshore circulation at two beaches with contrasting wave exposures two pocket beaches in southern portugal were studied by combining field measurements of waves and currents with numerical models stwave and bouss 2d the aim of this analysis was to evaluate nearshore hydrodynamics under different wave exposure forcing conditions e g variable wave heights directions and different tidal levels the results show that the beach circulation can rapidly shift from longshore to rip dominated depending on changes in both the offshore wave direction and tidal levels waves with higher obliquity for both low and moderate wave energy conditions tend to generate longshore circulation in all considered tidal stages while waves with lower obliquity tend to produce rip flow with higher velocity rip currents during low to intermediate tidal stages the results indicate that the location and intensity of rip currents strongly depend on geomorphological constraints that is the control exerted by shore platforms a larger morphological control is observed at mean sea level because most platforms are submerged exposed during high low tide and therefore exert less control on nearshore circulation

effect of borehole deviation on breakout orientations well bore breakouts are zones of spalling and fracture that form on opposite sides of a well bore and tend to change the cross sectional shape of the borehole from circular to roughly elliptical in vertical holes drilled in areas where one principal stress sv is vertical breakouts tend to form at opposite ends of the borehole diameter parallel to the least compressive horizontal principal stress direction sh this paper uses an analytical elastic solution for stress at the wall of a borehole to analyze the rotation of breakout orientations away from the direction of sh as the borehole deviates from the direction of the vertical principal stress the calculated orientations of breakouts in deviated boreholes depend on the type of faulting regime in which the well was drilled i e normal strike slip or thrust on the deviation angle o of the borehole axis from vertical on the angle between the horizontal projection of the borehole axis and the direction of sh and on the relative magnitudes of the three principal stresses sh sh the greatest compressive horizontal stress and sv in the strike slip faulting regime regardless of the values of sv sh and sh a borehole must deviate at least 35 from vertical before the horizontal projection of the breakout orientation differs by more than 10 from sh in the normal and thrust faulting regimes however the borehole deviation angle ocrit required to rotate projected breakout orientations by 10 from sh approaches zero as the value of sh approaches that of sh in the thrust faulting regime only about 3 of all combinations of sv sh and sh will produce ocrit values less than 10 while about 12 of all such combinations will yield ocrit 10 in the normal faulting regime about 12 and 33 of such combinations will yield ocrit 20 in the thrust and normal faulting regimes respectively careful study of changes in breakout orientation as a function of borehole deviation may improve the resolution of inferred stress directions when studying breakouts in deviated boreholes in these two faulting regimes

incompatible stress regimes from geological and geomechanical datasets can they be reconciled an example from the carnarvon basin western australia abstract knowledge of the in situ stress field is essential in petroleum basins as it exerts a prime control over seal integrity fracture stimulation wellbore stability and fluid flow previous geomechanical analysis of australia s carnarvon basin the continent s premier hydrocarbon region highlights a normal to strike slip fault stress regime however neotectonic evidence and contemporary seismicity suggest the possibility of a strike slip to reverse fault stress regime we attempt to reconcile these conflicting datasets through new analysis of the in situ stresses principal stress magnitudes and orientations were defined with data from 76 previously unanalysed petroleum wells wellbore image logs yield a maximum horizontal stress orientation of 113 n consistent with modelling of the stress field throughout the indo australian plate vertical stress magnitudes are estimated to range from 20 mpa km 1 to 22 4 mpa km 1 leak off tests lot from 42 wells are analysed using two methodologies one assuming tensile failure as traditionally accepted the other assuming shear failure as outlined by couzens schultz and chan 2010 and result in two different sets of horizontal stress magnitude estimates traditional interpretation of lots results in a minimum horizontal stress gradient of 16 8 mpa km 1 and a maximum horizontal stress gradient of 21 8 mpa km 1 the new method for lot interpretation results in a minimum horizontal stress gradient of 18 1 mpa km 1 and a maximum horizontal stress gradient of 25 4 mpa km 1 inclined natural fractures observed at lot depths supports application of the new method of lot interpretation traditional interpretation of stress magnitudes implies a normal to strike slip fault stress regime while the new method implies a strike slip fault stress regime this latter interpretation is favoured by the authors as it allows for a reconciliation of the geological and geomechanical datasets the assessment undertaken herein allows for reinterpretation of stress magnitudes in seismically active basins hosting differing geomechanical and neotectonic regimes potentially altering existing understanding of seal integrity fracture stimulation wellbore stability and fluid flow

quantitative impact of structural inheritance on present day deformation and seismicity concentration in intraplate deformation zones abstract structural inheritance i e paleo tectonic areas acting as weakened domains appear to be a key element localizing the seismicity in intraplate deformation zones however the impact of structural inheritance on the observed present day seismicity and strain rate concentration remains to be quantified in this study we quantify through 2d numerical modeling the localization and amplification factor of upper crustal strain rates induced by structural inheritance our 2d models are constrained by intraplate velocity boundary conditions and include rheology laws that accounts for inherited strain weakening in both the brittle and ductile layers of the lithosphere the role of structural inheritance is investigated for different localization of the weakened domain in the lithosphere for an average intraplate geotherm moho temperature ca 500 c brittle weakening i e inherited faults alone induces a limited amplification factor of upper crustal strain rates of ca 4 ductile weakening can increase the amplification factor to ca 7 when localized in the lower crust but has no effect when localized in the lithospheric mantle overall the amplification factors of upper crustal strain rates vary between 1 and 27 depending on the location of the weakened area in the lithosphere and on the different possible net driving forces crustal strengths amounts of weakening and geotherms these model amplification factors are in reasonable agreement with those derived from gps and seismicity data over large spatial scale several hundreds of kilometers in north america

deepwater fold and thrust belt classification tectonics structure and hydrocarbon prospectivity a review abstract deepwater fold and thrust belts dwftbs are classified into near field stress driven type 1 systems confined to the sedimentary section and type 2 systems deformed by either far field stresses alone or mixed near and far field stresses dwftbs can occur at all stages of the wilson cycle up to early stage continent continent collision type 1 systems have either weak shale or salt detachments they occur predominantly on passive margins but can also be found in convergent related areas such as the mediterranean and n borneo examples include the niger and nile deltas the west coast of africa and the gulf of mexico type 2 systems are subdivided on a tectonic setting basis into continent convergence zones and active margin dwftbs continent convergence zones cover dwftbs developed during continent arc or continent continent collision and those in a deepwater intracontinental setting e g w sulawesi makassar straits active margins include accretionary prisms and transform margins the greatest variability in dwftb structural style occurs between salt and shale detachments and not between tectonic settings changes in fold amplitude and wavelength appear to be more related to thickness of the sedimentary section than to dwftb type in comparison with shale salt detachment dwftbs display a lower critical wedge taper more detachment folds long and episodic duration of deformation and more variation in vergence structures unique to salt include canopies and nappes accretionary prisms also standout from other dwftbs due to their relatively long continuous duration rapid offshore propagation of the thrust front and large amount of shortening in terms of petroleum systems many similar issues affect all dwftbs these include the oceanward decrease in heat flow offshore increase in age of mature source rock and causes of trap failure e g leaky oblique and frontal thrust faults breach of top seal by fluid pipes one major difference between type 1 and type 2 systems is reservoir rock high quality continent derived quartz rich sandstones are generally prevalent in type 1 systems more diagenetically reactive minerals derived from igneous and ophiolitic sources are commonly present in type 2 systems or many are simply poor in well developed turbidite sandstone units however some type 2 systems particularly those adjacent to active orogenic belts are partially sourced by high quality continent derived sandstones e g nw borneo s caspian sea columbus basin in some cases very high rates of deposition in accretionary prisms adjacent to orogenic belts coupled with uplift due to collision results in accretionary prism related fold belts that pass laterally from sub aerial to deepwater conditions e g s caspian sea indo burma ranges the six major hydrocarbon producing regions of dwftbs worldwide gulf of mexico niger delta nw borneo brazil west africa s caspian sea stand out as differing from most other dwftbs in certain fundamental ways particularly the very large volume of sediment deposited in the basins and or the great thickness and extent of salt or overpressured shale sdetachments

morphodynamics of structurally controlled headland bay beaches in southeastern brazil a review abstract this paper presents a comprehensive review on the interaction between hydrodynamic processes beach morphology and sedimentology at large scale coastal behaviour along the coastline of santa catarina between laguna and sao francisco island a microtidal east coast swell environment with headland and bay geomorphologies the parabolic bay shape equation has proven to be a convenient and practical tool for studying the stability of the headland bay beaches tombolos and salients in santa catarina the beaches exhibit different patterns of sediment removal as a function of the degree of beach curvature in highly curved beaches there is a well developed shadow zone and a range of morphodynamic conditions from a sheltered low energy beach adjacent to the downdrift headland to a high energy exposed beach on the straight end of the headland bay beach the less curved beaches instead tend to show more uniform behaviour since they are directly exposed to incident waves there is no obvious relationship between average wave height and mean grain size showing the importance of sediment source to characterize the sedimentary distribution patterns in the study area the analysis of beaches showed that beach morphodynamics and sequence profiles for a bay headland coast in a microtidal east coast environment is a function of geological inheritance e g distance between headlands and orientation nearshore and inner shelf morphology coastal plain morphology and sediment source and hydrodynamic factors wave conditions oceanic wave exposure and relative tidal range

dynamic equilibrium planform of embayed beaches part 1 a new model and its verification abstract equilibrium beach formulations are useful tools for diagnosing and managing coastal engineering problems providing solutions for beach erosion problems headland bay beaches hbbs can be used as equilibrium coastal systems for stabilizing coastlines and mitigating erosion problems these embayed beaches may exist in a state of static or dynamic equilibrium throughout the literature several equations can be found for obtaining the static equilibrium planform sep of headland bay beaches hbbs with almost negligible net littoral drift rates however the formulations used to define the dynamic equilibrium planform dep of embayed beaches with specific net sediment transport rates are scarce and based on a limited number of studies this paper proposes a new derived formula for obtaining the planform shape of hbbs in dynamic equilibrium conditions the formula represents a general form of the parabolic bay shape equation pbse with modified coefficients as a function of both the wave obliquity and the net littoral drift rate passing through the bay q the angular difference d between the direction of the mean wave energy flux at the diffraction point of the headland and the beach orientation down coast is also incorporated in the proposed formula the model was verified against natural hbbs in dynamic equilibrium with different net littoral drift rates along the brazilian coast producing good results

seismic images of a collision zone offshore nw sabah borneo multichannel reflection seismic data from the southern south china sea refraction and gravity modelling were used to investigate the compressional sedimentary structures of the collision prone continental margin off nw borneo an elongated imbricate deepwater fan the toe thrust zone bounds the northwest borneo trough to the southeast the faults separating the individual imbricates cut through post early miocene sediments and curve down to a carbonate platform at the top of the subsiding continental dangerous grounds platform that forms the major detachment surface the age of deformation migrates outward toward the front of the wedge we propose crustal shortening mechanisms as the main reason for the formation of the imbricate fan at the location of the in the past defined lower tertiary thrust sheet tectonostratigraphic province a high velocity body was found but with a much smaller extend than the previously defined structure the high velocity structure may be interpreted either as carbonates that limit the transfer of seismic energy into the sedimentary layers beneath or as paleogene crocker sediments dissected by remnants of a proto south china sea oceanic crust that were overthrust onto a southward migrating attenuated continental block of the dangerous grounds during plate convergence

present day stress orientations and tectonic provinces of the nw borneo collisional margin received 23 september 2009 revised 17 may 2010 accepted 9 june 2010 published 16 october 2010 1 borehole failure observed on image and dipmeter logs from 55 petroleum wells across the nw borneo collisional margin were used to determine maximum horizontal stress sh orientations combined with seismic and outcrop data they define seven tectonic provinces the baram delta deepwater fold thrust belt exhibits three tectonic provinces its inner shelf inverted province sh is nw se margin normal its outer shelf extension province sh is ne sw margin parallel and its slope to basin floor compression province sh is nw se margin normal in the inverted province sh reflects inversion of deltaic normal faults the sh orientations in the extension and compression provinces reflect deltaic gravitational tectonics the shale and minibasin provinces have been recognized in offshore sabah in the shale province sh is n010 e which aligns around the boundary of a massif of mobile shale currently no data are available to determine sh in the minibasin province in the balingian province sh is ese wnw reflecting ese absolute sunda plate motions due to the absence of a thick detachment seen elsewhere in nw borneo the central luconia province demonstrates poorly constrained and variable sh orientations these seven provinces result from the heterogeneous structural and stratigraphic development of the nw borneo margin and formed due to complex collisional tectonics and the varied distribution and thicknesses of stratigraphic packages

headland sand bypassing quantification of net sediment transport in embayed beaches santa catarina island north shore southern brazil abstract this paper presents a comprehensive study of headland bypassing around seven headlands with different orientations and degrees of wave and tide induced current exposure located on the northern shore of santa catarina island southern brazil it encompasses an extensive dataset including detailed in situ measurements of bathymetry beach profiles sediment transport traps waves currents and tides the entrained sediment decreased in magnitude towards the more sheltered coast while maintaining comparable sediment grain distributions supporting the hypothesis of a connection between beaches based on in situ measurements a numerical model was calibrated waves currents and tides and validated with errors representing 11 of the magnitude of the measurements furthermore three sediment transport formulae were tested to identify the one that best reproduced the processes at the study site a model using tides winds and full wave spectra as input was run to identify the general net trend of annual sediment transport in the study area aiming to identify if where headland bypassing occurs the results show that headland sand bypassing does occur in the study area confirming the anticlockwise sediment transport pathway the present work highlights the role of sediment bypassing on embayed headland bound beaches which are usually considered to be closed cells

vertically transferred overpressures in brunei evidence for a new mechanism for the formation of high magnitude overpressure overpressures in sedimentary basins are commonly assumed to be the result of two distinct and separate mechanisms disequilibrium compaction and fluid expansion however the potential for overpressures to be redistributed or transferred to other pressure compartments over time has been seldom considered and rarely demonstrated pore pressure data and velocity effective stress plots from 61 fields across the baram delta province of brunei northwest borneo reveal that two different types of overpressure occur in stratigraphically defined sections the basal pro delta shales contain overpressures generated by disequilibrium compaction whereas the overlying sand shale deltaic sequence contains overpressures that appear to be generated by fluid expansion however the geology of the deltaic sequences and high magnitude of the pore pressures precludes the overpressures in the deltaic sequences being generated by any conventional fluid expansion mechanism such as kerogen to gas maturation or clay diagenesis the fluid expansion overpressures are located in fields that were inverted during the pliocene an event that resulted in large scale fluid migration from the pro delta shales into the deltaic sequences including charging of the numerous oil fields in the inner shelf hence we propose that the overpressures in brunei provide the first evidence for a new overpressuring mechanism whereby overpressured fluids have been vertically transferred from the pro delta shales into the deltaic sequences during basin inversion furthermore vertical transfer may be a mechanism for explaining overpressures observed in basins that have been recently uplifted or inverted

effects of rock anisotropy and heterogeneity on stress distributions at selected sites in north america abstract provinces of regionally consistent horizontal stress orientations persist throughout the upper crust and these may contain local areas where horizontal stress h orientations seem to rotate relative to the regional stress orientations in a consistent manner we suggest that the concept of an inclusion with anisotropy and heterogeneity of mechanical properties may be useful to explain some cases of h rotations h rotations up to 50 and magnitude changes of 40 could reasonably be expected based on simulations patterns correlate well with crustal observations rotation of h orientation reaches 25 to 58 in the different cases studied we also model a strike slip fault zone as a soft inclusion showing reorientations of hmax which agree with observed rotations near the murre fault in the jeanne d arc basin canada results imply that understanding the behaviour of soft and stiff inclusions or expanding and contracting thermal inclusions for that matter can help explain a number of geophysical and geological phenomena related to stress patterns

thunder bay ontario was not a pathway for catastrophic floods from glacial lake agassiz a series of airgun single channel seismic reflection profiles from thunder bay and the adjacent isle royal trough of lake superior suggest that water from glacial lake agassiz did not catastrophically drain into lake superior at this locality as has been previously suggested thunder bay is underlain by a relatively smooth bedrock surface the double bedrock sill at its mouth is not significantly incised and no subaqueous fans occur at the base of the escarpment into the superior basin the thunder bay area contains none of the features observed further north in lake superior which have been interpreted as flood related from earlier seismic surveys these previously reported northern features are interpreted as resulting from a younger post marquette catastrophic release of lake agassiz water the absence of such features in the thunder bay area suggests that lake agassiz did not drain catastrophically through the bay at the beginning of the younger dryas cold interval

exhumation of west sundaland a record of the path of india abstract the indian plate commenced its northward migration towards eurasia in the early cretaceous the lateral effect of this migration on the western edge of the sunda plate in southeast asia still remains equivocal in order to assess this effect we evaluate several key sectors characterized by deep crustal exhumation along a n s transect from the southern malay peninsula to the east himalayan syntaxis the evaluation is aided by a structural analysis of vertical movements and basin development five major metamorphic domes with similar geodynamic evolution maximum p t burial conditions and exhumation are studied exhumation of these domes migrated with time between late cretaceous in the stong complex north malaysia in the south and late miocene in the gaoligong shear zone south china in the north as documented by published work and our new fission track data presented herein deformation is characterized by a n s oriented extension that followed the more regional e w oriented plate tectonic shortening creating local core complexes and syn kinematic magmatism in the footwall of crustal scale detachments which displays a consistent temporal northward migration the n s extension was associated with the onset of hanging wall deposition in the sedimentary basins of western sundaland e g malay sumatra and thai basins during continuous exhumation of the footwall to upper brittle levels our multifaceted analysis of structural and thermochronological data shows a similar succession of tectonic thermal and sedimentary events in west sundaland that was driven by the gradual northward migration of india starting from cretaceous times we infer that the principal mechanism was driven by the subduction of an excess topography of greater india rifted continental margin during its underplating resulting in uplift thermal anomalies extensional exhumation and associated subsidence