forecasting cyclic coastal erosion on a multi annual to multi decadal scale southeast african coast abstract coastal erosion on the southeast african coastline shows an apparent 18 year cycle which last peaked in 2006 it is in phase with the longshore sediment transport cycle both these cycles appear to be in phase with the lunar nodal cycle lnc however the dominant tidal erosion driver on this coast appears to be the 4 4 year lunar perigean subharmonic lps we suggest that the apparent 18 year coastal erosion and longshore sediment budget cycle is a response to the 18 year mean annual precipitation cycle this cycle is 180 out of phase with the apparent coastal erosion and longshore sediment transport cycles the summer rainfall areas of southeastern africa show an 18 year map cyclicity which drives river runoff and hence controls sediment input to the coast and nearshore environment the map cycle dominates the coastal sediment budget during the lnc trough and suppresses the lps coastal erosion cycle during this time this explains why lps coastal erosion occurs close to the lnc peak thus although the lps cycle dominates the coastline it is masked during the wet portion of the 18 year map cycle it seems very likely that the lnc drives the map cycle in some way but this process is not known nevertheless these relationships can be used to predict in a general way both cyclic coastal erosion and the longshore sediment volume fluctuation this can be translated into a vital coastal planning tool which has the potential to forecast cyclic coastal erosion and hence significantly reduce the sea defense expenditure bill based on this severe cyclic coastal erosion is anticipated in 2023 and 2024

transitional tensile fracture propagation a status report abstract one model for the development of hybrid shear fractures is transitional tensile fracture propagation a process described as the in plane propagation of a crack subject to a shear traction while held open by a tensile normal stress presumably such propagation leads to a brittle structure that is the hybrid of a joint and a shear fracture crack seal veins with oblique fibers are possible candidates while these veins clearly show shear offset this is not conclusive evidence that a shear traction was present at the time of initial crack propagation many recent structural geology textbooks use a parabolic coulomb mohr failure envelope to explain the mechanics of transitional tensile fracturing however the laboratory experiments cited as demonstrating transitional tensile behavior fail to produce the fracture orientation predicted by a parabolic failure envelope additional attempts at verification include field examples of conjugate joint sets with small acute angles but these conjugate joints form neither simultaneously nor in the stress field required by the transitional tensile model finally linear elastic fracture mechanics provides strong theoretical grounds for rejecting the notion that individual cracks propagate in their own plane when subject to a shear traction these observations suggest that transitional tensile fracture propagation is unlikely to occur in homogeneous isotropic rock and that it is not explained by a parabolic coulomb mohr failure envelope as several recent structural geology textbooks have suggested

construction and evolution of submerged deltaic bodies on the high energy se african coastline the interplay between relative sea level and antecedent controls abstract this paper investigates the interplay between allocyclic controls and antecedent topography in the evolution of submerged coastal landforms including a back stepped delta using high resolution tools we examine the wave dominated thukela shelf and define the major seismic units key features identified comprise incised valleys scoured into bedrock that have overspilled to form lagoons at depths of 50 m these are in turn overlain by two prograding and backstepped sandy delta systems at 40 m and 32 m depth respectively the deltas interfinger with muddy prodelta deposits and are truncated by the holocene ravinement overlain by the contemporary prodelta of the thukela river system a bedrock high separates two physically separate strato morphological zones landward a sediment stripped steep and shallow nearshore zone and seaward a gentle zone downdip where the deltaic accumulations are sited delta development was favoured during sea level stillstands at 40 m and 32 m respectively the step back of the deltas corresponds to sharp increases in the rate of sea level rise associated with meltwater pulses the overall gentle palaeo bathymetric gradient has moderated erosion associated with rising sea level preserving a sandy back stepping delta and a draping mud clinoform submerged delta positioning relates to underlying incised valleys suggesting a synchronous transgressive evolution of the drainage and the delta incised valley network positioning is further governed by late pliocene aged growth faults in the basement rocks the geological framework has acted as a recurring primary control to the geomorphic evolution of the area partitioning accommodation for sediment accumulation and moderating the efficiency of ravinement

localisation of normal faults in multilayer sequences abstract existing conceptual growth models for faults in layered sequences suggest that faults first localise in strong and brittle layers and are later linked in weak and ductile layers we use the discrete element method for modelling the growth of a normal fault in a brittle ductile multilayer sequence the modelling reveals that faults in brittle ductile sequences at low confining pressure and high strength contrast localise first as mode i fractures in the brittle layers low amplitude monoclinal folding prior to failure is accommodated by ductile flow in the weak layers the initially vertically segmented fault arrays are later linked via shallow dipping faults in the weak layers faults localise therefore as geometrically and kinematically coherent arrays of fault segments in which abandoned fault tips or splays are a product of the strain localisation process and do not necessarily indicate linkage of initially isolated faults the modelling suggests that fault tip lines in layered sequences are more advanced in the strong layers compared with weak layers where the difference in propagation distance is most likely related to strength and or ductility contrast layer dependent variations in fault localisation rates generate fringed rather than smooth fault tip lines in multilayers

geomechanics of hydraulic fracturing microseismicity part 1 shear hybrid and tensile events we investigate the geomechanical behavior of hydraulic fracturing induced microseismicity microseismic events are commonly used to discern stimulation patterns and hydraulic fracture evolution however techniques beyond fracture mapping are required to explain the mechanisms of microseismicity in this series we present an approach to combine seismological and geomechanical techniques to investigate how microseismicity relates to propagating hydrofractures as well as existing natural fractures and faults part 1 describes the first analysis step which is to characterize the microseismic events by their source parameters focal mechanisms and fault plane orientations these parameters are used to determine the mechanical conditions responsible for activation of discrete populations or subpopulations of microseismic events that then can be interpreted in their geological and operational context first we compare microseismic fault plane populations from a mississippian barnett shale texas data set that are determined using a traditional double couple model shear only with a tensile source model hybrid events which may be more suitable for hydraulic fracturing conditions second we employ a new method to distinguish fault planes from auxiliary planes using iterative stress inversion and critical stress instability selection criteria the result is an enhanced microseismic characterization that includes geomechanical parameters such as slip tendency and local activation stress state during the operation using this approach on the barnett shale data two microseismic fault sets are resolved an inclined northeast southwest set with dominant shear and a vertical north south set with more hybrid behavior the results are used in part 2 to further investigate the heterogeneity of the stimulations and to compare models for microseismic activation

two episodes of structural fractures numerical simulation of yanchang oilfield in the ordos basin northern china abstract the tight oil sand reservoirs of the yanchang oilfield in the upper triassic yanchang 6 7 and 8 formations t3yc6 7 8 fms in the ordos basin are in the exploration stage two episodes of fractures during the yanshanian and himalayan periods observed in outcrops and cores of the t3yc6 7 8 fms are thought to be the controlling factors for the tight oil sweet spot finite element numerical simulation fes technology is used to perform a three dimensional 3d fracture simulation for a large region during the exploration stage to serve in tight oil reconnaissance for the yanchang oilfield the innovations of our work are mainly shown in the following simulation process 1 three controlling factors including the paleotopography layer thickness and rock mechanical faces are used to construct the 3d geologic model in the simulation 2 the rock mechanical environment characterized by the an gou qiliha zhangjiatan and dongjiahe outcrops the y1011 well cores and the corresponding mechanical experimental parameters is divided into three types as follows the delta front tractive current sand faces df tr s the lacustrine turbidity current sand faces l tu s and the mud faces m 3 the spatial boundary stress conditions are calculated based on the newberry formula for tensional and compressional stress fields considering the synthetical effects of the overburden pressure the pore fluid pressure and the tectonic stress 4 the modified griffith s criterion is used to fit the fracture index by simultaneously taking into consideration the tension and shear fracture mechanisms for the simulation results the predicted fracture index distribution map agrees well with the measured fracture density the yanshanian fractures mainly propagated in the dingbian and an bian areas adjacent to the western thrust belt while the himalayan fractures mainly propagated in the zhidan fuxian and huangling areas adjacent to the weihe graben the simulated fracture index has a positive correlation with the stratigraphic dip and a negative correlation with the layer thickness additionally structural fractures are prone to propagate near the mechanical interface in either the upward or downward penetration direction and are assumed to produce a fracture type sweet spot section in the vertical direction the reservoir oiliness also increases with the simulation fracture index indicating the fracture type tight oil sweet spot of the yanchang oilfield moreover the critical components used in the 3d fracture fes including the 3d geologic model the spatial boundary stress conditions and the fracture index fitted by the modified griffith criterion can be of great significance to produce more accurate numerical simulations during the oil and gas exploration stage in large regions

on the dimensionality of multiparameter microwave image data from thin sea ice in the labrador sea thin ice is typically defined as comprising the world meteorological organization s young and new ice categories referring to sea ice that is less than 0 3 m thick this ice type is an extremely important factor in both the thermodynamic and dynamic properties of both polar and marginal ice covers in the limex 89 experiment spatially and temporally registered multipolarization data from 5 3 and 9 25 ghz sars and from 37 and 90 ghz imaging radiometers were acquired over a region containing a wide range of new ice growth stages in the labrador ice pack the temperatures at the data acquisition time were 10 and correspond to ice growth conditions in this paper the dimensionality of the multifrequency multipolarization active and passive data set is examined to determine the complementarity of the sensor parameters and sensor types for thin ice measurements principal component analysis is used to provide estimates of the information content of individual measurement channels and their combinations various measurement subspaces are examined criteria for channel redundance are proposed and tested and the classification potential of the multidimensional measurement set is tested for thin ice growth stages that are known to present classification difficulties for microwave sensors given six nominally independent sar measurement channels the information space dimension of this subspace is shown to be greater than five the four radiometer channels are shown to have information space dimension two and are redundant in frequency the combined ten element sar radiometer measurement space was shown to have information space dimension eight under the criteria used when the scattering polarization ratios are included

sea cliff erosion as a function of beach changes and extreme wave runup during the 1997 1998 el nino abstract over time scales of hundreds to thousands of years the net longshore sand transport direction along the central california coast has been driven to the south by north pacific winter swell in contrast during the el nino winter of 1997 1998 comparisons of before and after airborne lidar surveys showed sand was transported from south to north and accumulated on the south sides of resistant headlands bordering pocket beaches this resulted in significant beach erosion at the south ends of pocket beaches and deposition in the north ends coincident with the south to north redistribution of sand shoreline morphology became prominently cuspate with longshore wavelengths of 400 700 m the width and elevation of beaches were least where maximum shoreline erosion occurred preferentially exposing cliffs to wave attack the resulting erosional hotspots typically were located in the embayments of giant cusps in the southern end of the pocket beaches the observed magnitude of sea cliff retreat which reached 14 m varied with the number of hours that extreme wave runup exceeded certain thresholds representing the protective capacity of the beach during the el nino winter a threshold representing the width of the beach performed better than a threshold representing the elevation of the beach the magnitude of cliff erosion can be scaled using a simple model based on the cross shore distance that extreme wave runup exceeded the pre winter cliff position cliff erosion appears to be a balance between terrestrial mass wasting processes which tend to decrease the cliff slope and wave attack which removes debris and erodes the cliff base increasing the cliff slope

geomorphology and preservation potential of coastal and submerged aeolianite examples from kwazulu natal south africa abstract the distribution and geomorphology of aeolianite outcrop on the coast of kwazulu natal south africa are described in the context of its preservation potential in the geological record aeolianite on the contemporary coast comprises discontinuous widely spaced outcrops less than 100 m in longshore extent and typically 50 60 m wide that reflects the combined action of subaerial weathering and physical abrasion in the coastal zone since the mid holocene approximately 7000 yrs the dominant morphological component is an intertidal erosional platform that slopes gently landward it is fronted by a notch in the mid intertidal zone 0 m msl and contains active erosional potholes on its seaward margin the platform surface is encrusted by a variety of marine organisms landward of and contiguous with the intertidal surface are small elevated outcrops of aeolianite in the supratidal zone these comprise a 3 m high seaward scarp with a basal notch in the high intertidal zone 1 m msl gullies in the scarp trap coarse clasts of eroded aeolianite as well as bedrock the upper surface of the supratidal aeolianite is planar with large potholes within which accumulations of coarse clasts and oyster shells have been cemented the upper surface is interpreted as a remnant of an intertidal platform formed at a higher mid holocene sea level the supratidal outcrop is subject to weathering and disintegration major joints divide the outcrop into cuboid blocks with axes of 3 4 m eroded blocks on the seaward face that exceed 1 m diameter remain in situ and become locked in place by repeated shaking smaller blocks that collapse from the seaward face accumulate in small gullies or are dispersed the facet most likely to be preserved in the geological record is the planar intertidal platform the morphology of aeolianite on the contemporary coast is markedly different from submerged aeolianite ridges on the adjacent shelf which are of higher relief wider and more laterally extensive preservation potential of aeolianite under subaerial conditions is low and the widespread high relief aeolianite on the shelf is attributed to rapid inundation or burial during transgression

geomechanical modeling of hydraulic fracturing why mechanical stratigraphy stress state and pre existing structure matter the increasing exploration and production in unconventional resource plays in the past decade has been accompanied by a greater need for understanding the effectiveness of multistage hydraulic fracturing programs particularly in long 1500 m or 5000 ft subhorizontal boreholes laterals traditional analytical analysis techniques for estimating the size and orientation of fractures induced by fluid injection typically result in predictions of relatively long and planar extension mode i bi wing fractures which may not be representative of natural systems although these traditional approaches offer the advantage of rapid analysis neglect of key features of the natural system e g realistic mechanical stratigraphy pre existing natural faults and fractures and heterogeneity of in situ stresses may render results unrealistic for planning executing and interpreting multimillion dollar hydraulic stimulation programs numerical geomechanical modeling provides a means of including key aspects of natural complexity in simulations of hydraulic fracturing in this study we present the results of two dimensional finite element modeling of fluid injection induced rock deformation that combines a coupled stress pore pressure analysis with a continuum damage mechanics based constitutive relationship the models include both the natural mechanical stratigraphic variability as well as the in situ stress state anisotropy and permit tracking of the temporal and spatial development of shear and tensile permanent strains that develop in response to fluid injection our results show that simple long planar fractures are unlikely to be induced in most mechanically layered natural systems under typical in situ stress conditions analyses that assume this type of fracture geometry may significantly overestimate the reach of hydraulically induced fractures and or effectively stimulated rock volume

geomorphological variability among microtidal estuaries from the wave dominated south african coast abstract over 300 independent river outlets exist around the microtidal wave dominated south african coast most of these are located in drowned river valley settings and have acquired their present morphology during the holocene marine transgression a variety of geomorphological forms are identified in these estuaries that result from variation in antecedent topography fluvial sediment supply and marine sediment supply five distinctive estuary types are identified on the basis of contemporary morphodynamics these are categorised into three types of normally open estuary that maintain a semi permanent connection with the open sea and two types of normally closed estuary which are separated from the sea for long periods by a continuous supratidal barrier the contemporary morphodynamics and sedimentary environments of each estuary type are discussed open estuaries include barrier inlet systems maintained by fluvial discharge termed river dominated estuaries and tidal discharge termed tide dominated estuaries a third category of open estuary lacks a supratidal barrier due to inadequate marine sediment availability closed estuaries receive marine influence via barrier overwash and occasional breaching but are typically enclosed behind a continuous supratidal barrier two categories of closed estuary are identified perched and non perched perched estuaries develop behind high berms and maintain a water level above high tide level in the open sea they are often dominated by fresh to brackish water and breach and drain periodically non perched estuaries are developed behind low elevation barriers fronted by wide dissipative beach profiles high overwash frequency introduces marine water into such systems breaching of such estuaries does not produce dramatic draining as the water level may only drop according to the stage of the open sea tidal cycle the variety of estuary types suggests several potential pathways may exist in estuarine development and that the progressive infilling model is an over simplification

shear strength anisotropy of natural london clay the paper reports the shear strength anisotropy of the natural highly overconsolidated london clay from heathrow terminal 5 as established by comprehensive hollow cylinder apparatus hca testing

fracture development in paleozoic shale of chongqing area south china part two numerical simulation of tectonic stress field and prediction of fractures distribution abstract a tectonics sedimentation evolution has been researched in southeast chongqing and the reasonable longmaxi shale highstand system tract hst and transgressive system tract tst geological model were built respectively based on the rock mechanical test and acoustic emission experiment which the samples are from field outcrop and the yuye 1 well the longmaxi shale two dimension tectonic stress field during the cenozoic was simulated by the finite element method and the distribution of fractures was predicted the research results show that the tectonic stress field and the distribution of fractures were controlled by lithology and structure as a result of cretaceous movement there are trough like folds wide spaced synclines battlement like folds similar spaces between synclines and anticlines and ejective folds wide spaced anticlines which are regularly distributed from southeast to northwest in the study area since the strain rate and other physical factors such as the viscosity are not taken into account and the stress intensity is the main factor that determines the tectonic strength therefore the stronger tectonic strength leads the higher stress intensity in the eastern and southeastern study area than in the northwest the fracture zones are mainly concentrated in the fold axis transition locations of faults and folds the regions where are adjacent to faults the fragile mineral contents such as siliceous rock carbonate rock and feldspar in the shelf facies shale from south of the study area are higher than in the bathyal facies and abyssal facies shale from center of the study area the shales characterized by low poisson s ratio and high elastic modulus from south of the study area are easily broken during cenozoic orogenic movement

seismic imaging of migration pathways by advanced attribute analysis alaminos canyon 21 gulf of mexico abstract potential accumulations of gas hydrates in alaminos canyon block 21 ac21 in the gulf of mexico are thought to occur in a shallow sand rich interval stratigraphically separated from sources of free gas below the base of the gas hydrate stability zone bghsz by an intervening thick layer of clay and silt rich sediments availability of sufficient gas charge from depth in addition to local biogenic sourcing is considered key to the formation of gas hydrates in the ghsz implicitly a detailed understanding of geometries associated with fault and fracture networks in relation to potential gas migration pathways can provide additional confidence that seismic amplitude anomalies are related to gas hydrate accumulations delineation of fault and fracture systems from high resolution seismic data in and below the gas hydrates stability zone ghsz was performed using an automated algorithm ant tracking the capturing of small scale detail has particular significance at ac21 revealing a pervasive network of typically small extent discontinuities indicative of fracturing throughout this intervening clay and silt rich layer of mass transport deposits mtds ant tracking features appear to correlate to some extent with potential gas hydrate accumulations supporting the concept that fracturing possibly provides migration pathways albeit via a tortuous complex path this study demonstrates that the ant tracking attribute in conjunction with detailed seismic interpretation and analysis can provide valuable evidence of potential gas migration pathways

the 18 6 yr nodal cycle and its impact on tidal sedimentation abstract the 18 6 yr nodal cycle modulates tidal amplitudes and currents and consequently sedimentation in tide influenced sedimentary environments data are presented which show that such effects are obvious along the coast of the dutch barrier islands and in the sedimentary fill of abandoned channels

boulder emplacement on a tectonically stable wave dominated coastline mission rocks northern kwazulu natal south africa abstract the presence of large boulders along rocky coastlines is a useful indicator as to the occurrence and nature of past storms and or tsunami field observations from mission rocks northern kwazulu natal south africa allowed for the assessment of historical high magnitude wave events in the area a total of 143 anomalously large boulders were assessed in terms of their dimensions morphologies and distribution along a regionally developed 3 m raised shore platform based on long intermediate and short axes relationships we calculate boulder masses of up to 9 03 t that were found to have been transported horizontally shoreward for up to 65 m based on geomorphological evidence we infer that the majority of boulders encountered were from a joint bound pre transport setting additionally overturning of the boulders was apparent we assess the boulder field numerically via the numerical model of pignatelli et al 2009 which we deemed most applicable for slab like boulders such as those encountered here results yielded a maximum breaking storm wave height of 11 36 m or a maximum tsunami height of 2 84 m an analysis of swell data revealed that the modelled storm wave heights fell within the range defined by the storm wave records for the area within the past 32 years boulder alignments were likewise compatible with the wave regime of the northern kwazulu natal coastline additional review of offshore seismic records and landslide hazards on the tectonically stable passive margin show that the tsunami hazard for landslides within the area is negligible the findings suggest a storm provenance as the causal mechanism for boulder emplacement at mission rocks

extreme erosion on high energy embayed beaches influence of megarips and storm grouping abstract megarips have long been recognised as an important yet poorly documented mechanism of beach erosion on high energy embayed beaches the persistence and cumulative effect of megarips during storm groups are described from three embayed beaches arrifana mt clerigo and amoreira exposed to high energy wave conditions in the mesotidal bedrock dominated southwestern coast of portugal morphological changes determined by topographic monitoring and supplemented by interpretation of digital imagery over two years revealed the development of storm induced megarips which exerted a major influence on beach erosion differences in megarip influence within and between beaches are related to embayment geometry and orientation which significantly influence the nearshore wave field rip location is topographically controlled being determined by alongshore variations in breaking wave height and obliquity along with interaction of wave driven circulation patterns and embayment nearshore topography moderate beach sand loss during individual storms was linked to the development of megarips with associated rip neck and feeder channels extreme erosion however occurred when megarips and feeder channels persisted during successive storms promoting continued erosion and seaward sediment export observations show that once initiated megarip channels persist for several months and continue to act as conduits for offshore sediment transport under non storm conditions the maintenance of such rip circulation systems driven by morphodynamic feedback reduces beach recovery ability until the rip neck and feeder channels are infilled

observations of sand bar evolution on a natural beach waves currents and the location of the seafloor were measured on a barred beach for about 2 months at nine locations along a cross shore transect extending 255 m from 1 to 4 m water depth the seafloor location was measured nearly continuously even in the surf zone during storms with sonar altimeters mounted on fixed frames the crest of a sand bar initially located about 60 m from the shoreline moved 130 m offshore primarily when the offshore significant wave height exceeded about 2 m with 1 5 m of erosion near the initial location and 1 m of accretion at the final location an energetics type sediment transport model driven by locally measured near bottom currents predicts the observed offshore bar migration but not the slow onshore migration observed during low energy wave conditions the predicted offshore bar migration is driven primarily by cross shore gradients in predicted suspended sediment transport associated with quasi steady near bottom offshore flows these strong 50 cm s currents intensified near the bar crest by wave breaking are predicted to cause erosion on the shoreward slope of the bar and deposition on the seaward side the feedback amoung morphology waves circulation and sediment transport thus forces offshore bar migration during storms

the internal structure of fault zones in basaltic sequences abstract normal faults in basalt along mid ocean ridges and continental rifts play a major role in the formation of topography advection of fluids and the dynamics of biosphere however almost nothing is known of the internal structure of volcanic growth faults at depth where many key processes take place in this paper we present the results of scaled model experiments validated against outcrop studies of a volcanic growth fault system on hawai i the analogue model uses cohesive hemihydrate powder with carefully characterized physical properties a cohesion of 62 pa friction angle of 0 71 and tensile strength of 33 pa imply a length scaling ratio of 1 5000 50 000 between the model and the upper part of extending oceanic crust with a basalt column above a normal fault time lapse imagery high resolution particle image velocimetry and field observations show ground flexure in an initial elastic stage before subvertical mode i fissures propagate from the surface downwards some of the mode i fractures become inactive while others develop into massively dilatant normal faults the dominant processes within the faults are brecciation block rotation and gravitational transport of fragments along the fault maintaining meter sized cavities to a depth of several hundred meters even when these volcanic growth faults are resurfaced a pervasive dilatancy persist within the system if circulating seawater provides a sufficient oxygen supply the large cavities in normal faults at mid ocean ridges could harbour large ocean floor life forms to several hundred meters depth

lateral variation of crustal structure in the ordos block and surrounding regions north china and its tectonic implications abstract crustal thicknesses and poisson s ratios in the ordos block and surrounding regions were estimated by the use of the h k stacking method on teleseismic receiver functions the data came from 353 temporary and permanent seismic stations in 2006 2011 results show that the crustal thickness and poisson s ratio gently vary within the ordos block with an average of 41 3 km and 0 265 respectively consistent with a felsic composition of the crust crustal thicknesses predicted on the basis of airy isostasy are consistent with the estimated thicknesses implying that the topography is approximately compensated the reactivated portion of the north china craton that has undergone mesozoic cenzoic lithospheric thinning is also characterized by the thinning crust while the ordos block maintains normal crustal thickness and average crustal velocity inferred higher densities in the lower crust and the anti correlation between poisson s ratio and crustal thickness in the ordos block may be the result from underplating of mafic magmas in the precambrian around the ordos block the paleoproterozoic khondalite zone in the northern edge has higher poisson s ratio and thickened crust which is consistent with the lower crust being of more mafic composition the weihe shanxi graben in the southeastern edge has mid high poisson s ratio high heat flow and thinning crust which is consistent with the known transtensional tectonic setting in the liupanshan thrust belt along the southwestern edge of the ordos plateau significant variations in crustal thicknesses and poisson s ratios occur on two sides besides a thickened crust a concaved moho implies horizontal shortening of this edge of the ordos block due to its collision with the northeastern tibetan plateau the structural differences between the eastern and western edges of the ordos block reflect that the ordos block is in tectonic stress environment of the western compression and the eastern extension

identifying storm impacts on an embayed high energy coastline examples from western ireland abstract large sections of the western irish coast are characterised by a highly compartmentalised series of headland embayment cells in which sand and gravel beaches are backed by large vegetated dune systems exposure to modally high energy swell renders most of these beaches dissipative in character a mesotidal range c 3 5 4 5 m exists along much of the coast analysis of instrumental wind records from three locations permitted the identification of a variety of storm types and the construction of storm catalogues few individual storms were recorded at all three stations indicating a lack of regional consistency in storm record of the total storms recorded only a small percentage are potentially damaging onshore directed and even fewer span a high tide and thus potentially induce a measurable morphological response at the coast through a combination of historical records meteorological records field observations and wave modelling we attempt to assess the impact of storms quantifiable records of coastal morphology maps air photos and beach profiles are few in number and do not generally record responses that may be definitely attributed to specific storms numerical wave simulations and observations at a variety of sites on the west irish coast however provide insights into instantaneous and medium term decadal storm responses in such systems we argue that beaches and dunes that are attuned to modally high energy regimes require extreme storms to cause significant morphological impact the varying orientation of beaches a spatially nonuniform storm catalogue and the need for a storm to occur at high water to produce measurable change impart site specific storm susceptibility to these embayments furthermore we argue that long period wave energy attenuation across dissipative shorefaces and beaches reduces coastal response to distant storms whereas short period locally generated wind waves are more likely to cause major dune and beach erosion as they arrive at the shoreline unrefracted this apparently variable response of beach and dune systems to storm forcing at a decadal scale over a coastline length of 200 km urges caution in generalising regarding regional scale coastal responses to climatic change

sedimentation on the narrow 8km wide oceanic current influenced continental shelf off durban kwazulu natal south africa abstract the narrow transform margin of southeast africa and its associated sedimentological and hydrodynamic setting differs to other documented continental margins the durban bluff continental shelf is extremely narrow and steep 8 km wide with a gradient ranging from 2 to 8 characterised by a wave and oceanic current dominated regime seismic sequence boundary 2 developed during the last interglacial regression spans the entire shelf separating the holocene sediment wedge seismic unit h from underlying pleistocene deposits a wave ravinement surface marks the holocene transgression comprising a pavement lag of well sorted gravels and bioclastics overlain by inshore reef derived carbonate rich sediments and offshore by quartzose mid shelf sands the shelf sands represent the transgressive holocene to modern sediment wedge forming a seaward thinning unit stacked against the pleistocene blood reef aeolianite beachrock substrate the sediment wedge is dynamic and constantly redistributed by currents associated with the durban eddy inshore of the agulhas current and bottom surge associated with high swells and marine storm events these have been instrumental in shaping large scale shoreface attached and detached sand ridges the presence of mud lenses in the vicinity of blood reef represents deposition from turbid flood waters with preservation facilitated by the morphology of the durban bluff and blood reef palynological results reflecting the local subtropical vegetation and recently introduced neophytes together with radiocarbon dates provide a very recent age for this sediment supporting a terrestrial origin and deposition from a single large flood event

rip currents mega cusps and eroding dunes abstract dune erosion is shown to occur at the embayment of beach mega cusps o 200 m alongshore that are associated with rip currents the beach is the narrowest at the embayment of the mega cusps allowing the swash of large storm waves coincident with high tides to reach the toe of the dune to undercut the dune and to cause dune erosion field measurements of dune beach and rip current morphology are acquired along an 18 km shoreline in southern monterey bay california this section of the bay consists of a sandy shoreline backed by extensive dunes rising to heights exceeding 40 m there is a large increase in wave height going from small wave heights in the shadow of a headland to the center of the bay where convergence of waves owing to refraction over the monterey bay submarine canyon results in larger wave heights the large alongshore gradient in wave height results in a concomitant alongshore gradient in morphodynamic scale the strongly refracted waves and narrow bay aperture result in near normal wave incidence resulting in well developed persistent rip currents along the entire shoreline the alongshore variations of the cuspate shoreline are found significantly correlated with the alongshore variations in rip spacing at 95 confidence the alongshore variations of the volume of dune erosion are found significantly correlated with alongshore variations of the cuspate shoreline at 95 confidence therefore it is concluded the mega cusps are associated with rip currents and that the location of dune erosion is associated with the embayment of the mega cusp

apparent dynamic stability of the southeast african coast despite sea level rise the coast of southeast africa is dominated by sandy beaches that tend to be confined within log spiral or headland bound embayments investigations using serendipitous air imagery data set have been previously undertaken and conclusions drawn about the stability of the coast we show that conclusions drawn from this data with respect to the high water mark hwm position are fraught with errors which include tidal state pressure regime beach slope high swell erosion seasonal and multi annual changes we highlight and discuss these sources of error together with their magnitudes the most significant of these are the high swell seasonal and multi annual variations from case studies we show that the seasonal beach rotation and long term beach width variation are responsible for tens of metres of unaccounted hwm variation 30 to 50 m is common with maximums reaching 60 to 100 m overall the southeast african coastline appears to be in a state of long term dynamic equilibrium there is no evidence of any sea level rise forced transgression in the coastal sediment budget despite sea level rise slr if such a signal is in fact present it is lost within the beach width variation some southeast african coastal reaches are suffering chronic erosion but these are related to anthropogenic impacts the extreme difficulty of placing a hwm with any temporal validity on this coast precludes the routine use of the bruun rule although no transgressive signature is found there is evidence of a decreasing coastal sand budget as a result of anthropogenic or natural climate change or both this decrease in the coastal sand volume is likely to result in increased future erosion copyright 2016 john wiley sons ltd

using fault displacement and slip tendency to estimate stress states abstract we suggest that faults in high slip tendency orientations tend to develop larger displacements than other faults consequently faults that accumulate larger displacements are more likely to be reliable indicators of the longer term stress field and should be weighted accordingly in paleostress estimation application of a stress inversion technique that uses slip tendency analyses and fault displacements to interpret populations of coherent normal faults within the balcones fault system of south central texas provides stress estimates that are consistent with established regional stress analyses although the method does not require measurement of slip directions these data where available and sensitivity analyses of the angular mismatch between measured slip directions and those predicted by inverted stress states provide high confidence in the stress estimates generated using slip tendency analyses close inspection of the fault orientation and displacement data further indicates that subpopulations of faults with orientations different from the regional pattern have formed in response to stress perturbations generated by displacement gradients on an adjacent seismic scale fault

significance of brittle deformation in the footwall of the alpine fault new zealand smithy creek fault zone abstract the smithy creek fault represents a rare exposure of a brittle fault zone within australian plate rocks that constitute the footwall of the alpine fault zone in westland new zealand outcrop mapping and paleostress analysis of the smithy creek fault were conducted to characterize deformation and mineralization in the footwall of the nearby alpine fault and the timing of these processes relative to the modern tectonic regime while unfavorably oriented the dextral oblique smithy creek thrust has kinematics compatible with slip in the current stress regime and offsets a basement unconformity beneath holocene glaciofluvial sediments a greater than 100 m wide damage zone and more than 8 m wide extensively fractured fault core are consistent with total displacement on the kilometer scale based on our observations we propose that an asymmetric damage zone containing quartz carbonate chlorite epidote veins is focused in the footwall damage zone asymmetry likely resulted from the fact that the hanging wall was mostly deformed at greater depth than the footwall rather than resulting from material contrasts across the fault plane kinematic inversions on mineralized fractures within the damage zone suggest veins formed in the current stress regime from fluids comparable to those now circulating in the footwall the smithy creek fault zone is therefore a rare exhumed example of the modern footwall hydrothermal system and of a structure actively accommodating footwall deformation near the alpine fault zone two significantly less mature subvertical faults having narrow 20 cm or less damage zones and similar orientations to nearby strike slip segments of the alpine fault crosscut the mineralized zone at smithy creek we envisage that hydrothermal mineralization strengthened the fault core causing it to widen as later slip was partitioned into the now weaker surrounding damage zone with progressive alteration formation of favorably oriented faults became preferable to reactivation of the existing structure

impacts of the tectonic stress field on natural gas migration and accumulation a case study of the kuqa depression in the tarim basin china stress fluid and temperature are three of the major factors that impact natural gas migration and accumulation in order to study the influences of tectonic stress field on natural gas migration and accumulation in low permeability rocks we take the kuqa depression as an example and analyze the evolution of the structure and tectonic stress field at first then we study the influences of tectonic stress field at different tectonic episodes on fractures and fluid potentials through the numerical simulation method on the section across the kl2 gas field we summarize two aspects of the impact of the tectonic stress field on natural gas migration and accumulation firstly under the effects of the tectonic stress field the rock dilation increases with the added stress and strain and when the shear stress of rock exceeds its shear strength the shear fractures are well developed on one hand the faults which communicate with the hydrocarbon source rocks become the main pathways for natural gas migration on the other hand these positions where fractures are well developed near faults can become good reservoirs for natural gas accumulation secondly because fluid potentials decrease in these places near the faults where fractures are well developed natural gas can migrate rapidly along the faults and accumulates the impact of tectonic stress fields on natural gas migration and accumulation allows for hydrocarbon migration and accumulation in the low permeability rocks in an active tectonic compressive setting

quantifying cretaceous cenozoic exhumation in the otway basin southeastern australia using sonic transit time data implications for conventional and unconventional hydrocarbon prospectivity in prospective basins affected by exhumation uncertainty commonly exists regarding the maximum burial depths of source reservoir and seal horizons one such basin is the otway basin an important gas province in southeastern australia which has witnessed several exhumation events here we present estimates of net exhumation magnitudes for 110 onshore and offshore petroleum wells based on the sonic transit time analyses of lower cretaceous fluvial shales our results show significant post albian net exhumation in the eastern onshore otway basin 1500 m 4920 ft and a generally minor net exhumation 200 m 655 ft elsewhere in the otway basin consistent with estimates based on thermal history data the distribution of net exhumation magnitudes in relation to mid cretaceous and neogene compressional structures indicates that exhumation was dominantly controlled by short wavelength basin inversion driven by plate boundary forces deeper burial coupled with high geothermal gradients in the onshore eastern otway basin and along the northern basin margin during the early cretaceous have rendered lower cretaceous source rocks mostly overmature with any remaining hydrocarbons from the initial charge likely to be trapped in tightly compacted reservoirs and or secondary fracture related porosity however the embrittlement of these reservoirs during their deeper burial may present opportunities for the development of low permeability plays through hydraulic fracturing where smectite clay minerals are illitized source rocks at near maximum burial at present day are at temperatures suitable for gas generation with key controls on prospectivity in these areas including the sealing potential of faulted traps and the relationship between charge and trap development

bar trough generation on a natural beach mechanisms for bar trough generation are examined using velocities measured in the field applied to the bowen 1980 bailard 1981 energetics based sediment transport model measurements consist of a cross shore array of nine electromagnetic current meters spanning the surf zone and daily bathymetric surveys during a 10 day period during which two storms occurred when the bathymetry evolved from a three dimensional terrace to a well developed linear bar the model predicts bed and suspended load transport separately based on various velocity moments the velocities are partitioned into mean currents low frequency infragravity and shear instabilities 0 05 hz to determine the relative importance of various mechanisms to the total transport velocity moments are computed over 90 min intervals to resolve tidal fluctuations tidal signatures were apparent in all modes of transport predicted transport rates are integrated and compared with daily cross shore bathymetric profiles averaged over a 400 m length of beach the suspended load terms were an order of magnitude greater than bed load terms owing to the low fall velocity of the fine grain sand within the surf zone model results for this experiment indicate the dominant mechanism for bar development was sediments mobilized by the strong longshore current and incident short waves within the surf zone and transported offshore by the mean undertow and shoreward transport onshore due to short wave velocity skewness using standard coefficients the model correctly predicted the first order movement of the bar during storms but underpredicted trough development and did not always perform well during mild wave conditions

multiple origins of obsidian pyroclasts and implications for changes in the dynamics of the 1300 b p eruption of newberry volcano usa the pyroclastic deposits of the 1300 b p eruption of newberry volcano or usa contain minor amounts of obsidian 1 6 wt the volatile h2o and co2 contents and textures of these clasts vary considerably ftir measurements of h2o in obsidian pyroclasts range from 0 1 to 1 5 wt indicating equilibration pressures 20 mpa co2 contents are low 10 ppm except in clasts that also contain xenolith powder that provided a local co2 source obsidian clasts exhibit a range of color and textural types that changed in relative proportion as the eruption progressed together these data indicate that there were multiple origins of obsidian and that the dominant source changed during the eruption early in the eruption obsidian was almost entirely black or grey microlite bearing and probably derived from dikes or wall rock fractures filled with vanguard magma or tuffisite that together with wall rocks were eroded and incorporated into the eruption column as the vent widened later in the eruption following a brief cessation of activity the proportion of obsidian to wallrock lithic clasts increased and new types of obsidian dominated types that represent remnants of a shallow conduit plug welded fallback material from within the conduit and sheared and degassed magma from near the conduit walls analysis of bubble shapes preserved within obsidian indicates that shear stresses and shear rates varied by over two orders of magnitude with maxima of 88 kpa and 10 2 3 s 1 respectively based on an assumed magma temperature of 850 c furthermore the highest shear rates and stresses and the shortest flow times 10 20 min are preserved in clasts that also contain wall rock the longest deformation times 5 and 8 h correspond to two microlite rich clasts suggesting that the higher microlite content results from slower ascent rates and or longer magma residence times at shallow levels differences between obsidian pyroclasts from the newberry eruption and those of the mono craters may relate to the nature of the conduit feeding the two events from this comparison we conclude that obsidian can provide information on time scales and mechanisms of pre fragmentation magma ascent

poisson s ratio values for rocks abstract compared to other basic mechanical properties of rocks poisson s ratio is an elastic constant of which the significance is generally underrated yet in rock mechanics there is a considerable number of diverse areas which require a prior knowledge or estimation of the value of poisson s ratio this paper examines the values and applications of poisson s ratio in rock mechanics following an historical account of the initial controversy whether it was a material constant or not the effects of poisson s ratio in the elastic deformation of materials intact rocks and rock masses are briefly reviewed also the reported values of poisson s ratio for some elements materials and minerals are compiled while typical ranges of values are presented for some rocks and granular soils finally poisson s ratio classifications are recommended for isotropic intact rocks

impact of interlayer slip on fracture prediction from geomechanical models of fault related folds understanding and interpreting the timing location orientation and intensity of natural fractures within a geologic structure are commonly important to both exploration and production planning activities here we explore the application of finite element based geomechanical models to fracture prediction our approach is based on the idea that natural fractures can be interpreted or inferred from the geomechanical model derived permanent strains for this analysis we model an extensional fault tip monocline developed in a mechanically stratified limestone and shale sequence because field data exist that can be directly compared with model results the approach and our conclusions however are independent of the specific structural geometry the presence or absence of interlayer slip is shown to strongly control the distribution and evolution of strain and this control has important implications for interpreting fractures from geomechanical models

shoreface morphodynamics of a high energy steep and geologically constrained shoreline segment in northern ireland abstract the shoreface a complex and poorly understood part of the coastal zone plays a critical role in sediment transport processes between the beach and the inner shelf this two year study examined the surface and subsurface architecture and the process response mechanisms of a high energy steep and geologically constrained shoreface segment 1 20 m depth in northern ireland fourteen sequential bathymetric surveys covering an area of 2 km2 were compared and analysed in order to investigate seabed changes and their relationship to wave and wind forcing results reveal that the shoreface is highly dynamic and complex an examination of high energy conditions and lower than average energy conditions revealed significant periods of both accretion and erosion these complex morphodynamic responses are attributed mainly to a combination of antecedent pre survey morphology differences in wind forcing and coastal surges a comparison of seabed changes over 2 yr reveals net shoreface accretion which is attributed to inner shelf to shoreface sediment transport over the same period the adjacent west strand beach showed moderate erosion the study provides information on the morphodynamics of a steep high energy embayment shoreface a coastal environment which has received little previous attention

natural fractures in shale a review and new observations natural fractures have long been suspected as a factor in production from shale reservoirs because gas and oil production commonly exceeds the rates expected from low porosity and low permeability shale host rock many shale outcrops cores and image logs contain fractures or fracture traces and microseismic event patterns associated with hydraulic fracture stimulation have been ascribed to natural fracture reactivation here we review previous work and present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization orientation and size patterns a wide range of shales have a common suite of types and configurations of fractures those at high angle to bedding faults bed parallel fractures early compacted fractures and fractures associated with concretions these fractures differ markedly in their prevalence and arrangement within each shale play however constituting different fracture stratigraphies differences that depend on interface and mechanical properties governed by depositional diagenetic and structural setting several mechanisms may act independently or in combination to cause fracture growth including differential compaction local and regional stress changes associated with tectonic events strain accommodation around large structures catagenesis and uplift fracture systems in shales are heterogeneous they can enhance or detract from producibility augment or reduce rock strength and the propensity to interact with hydraulic fracture stimulation burial history and fracture diagenesis influence fracture attributes and may provide more information for fracture prediction than is commonly appreciated the role of microfractures in production from shale is currently poorly understood yet potentially critical we identify a need for further work in this field and on the role of natural fractures generally

longshore sand waves at southampton beach new york observation and numerical simulation of their movement abstract this paper describes measurements and numerical simulations of the movement of longshore sand waves observed at southampton beach long island new york these large morphologic features are created by periodic opening of a small inlet and subsequent welding of its ebb shoal to the beach longshore sand waves are wave like forms that maintain identity while moving along the shore and represent a simple type of collective sediment movement or largescale coastal behavior despite being described as early as 1939 few measurements of longshore sand waves have been made and their dynamic behavior is not well understood eleven longshore sand waves were identified along southampton beach and have an average length of 0 75 km and an amplitude of 40 m migration speed was greatest under winter wave action and reached an average 1 09 km year 1 and yearly average speed including summer calms was a much lower 0 35 km year 1 during a 16 month observation period the longshore sand waves did not disperse during their steady migration westward in the direction of predominant wave incidence and longer waves moved faster than those with smaller wavelengths a numerical model of shoreline change including both standard particulate longshore sand transport and a component describing migration of a longshore sand wave is developed in which the velocity of the wave is related to the calculated longshore discharge of water the model shows wave refraction to be an important mechanism contributing to the longevity of longshore sand waves acting to retard the otherwise expected diffusion model calculations of the migration of a single longshore sand wave agree quantitatively with the observations

hybrid fracture and the transition from extension fracture to shear fracture fracture is a fundamental mechanism of material failure two basic types of brittle fractures are commonly observed in rock deformation experiments extension opening mode fractures and shear fractures for nearly half a century it has been hypothesized that extension and shear fractures represent end members of a continuous spectrum of brittle fracture types however observations of transitional fractures that display both opening and shear modes hybrids in naturally deformed rock have often remained ambiguous and a clear demonstration of hybrid fracture formation has not been provided by experiments here we present the results of triaxial extension experiments on carrara marble that show a continuous transition from extension fracture to shear fracture with an increase in compressive stress hybrid fractures form under mixed tensile and compressive stress states at acute angles to the maximum principal compressive stress fracture angles are greater than those observed for extension fractures and less than those observed for shear fractures fracture surfaces also display a progressive change from an extension to shear fracture morphology

fractures in sandstone reservoirs with ultra low permeability a case study of the upper triassic yanchang formation in the ordos basin china the upper triassic yanchang formation in the ordos basin central china is a typical sandstone reservoir with an ultra low permeability high angle tectonic fractures and diagenetic fractures such as near horizontal bedding fractures intragranular fractures and grain boundary fractures are abundant fractures are major pathways and enhance fluid flow in sandstone reservoirs with ultra low permeability because of their weak lateral continuity and their small apertures under lithostatic pressure bedding fractures make a relatively small contribution to the overall permeability of reservoirs as they are both of small size and low permeability intragranular fractures and grain boundary fractures mainly improve the connectivity of reservoirs by connecting the matrix pores high angle tectonic fractures control the fluid movement in the ultra low permeability reservoirs under the effect of different successive tectonic stress fields four assemblages of high angle tectonic fractures developed in the sandstone reservoirs under the present day stress differently oriented fractures have different connectivities apertures and permeabilities the northeast southwest fractures parallel to the maximum principal stress have a good connectivity large apertures and a high permeability forming the dominant flow paths knowledge of these paths can be used for optimizing well placement because of their sensitivity to pressure fractures in different directions will show varying apertures as the formation pressure decreases therefore the permeability of the fractures of different orientations and its impact on reservoirs vary at different developmental stages

hybrid failure field evidence and influence on fault refraction abstract the occurrence of hybrid failure the transition from tensile to shear failure has been controversial production of hybrid failure in laboratory experiments in recent years has strengthened the case for hybrid failure but field recognition has remained elusive in this paper we present data from a small displacement fault in the hidden valley fault zone at canyon lake gorge texas which is refracted through mechanically layered carbonates and exhibits surface characteristics expected for hybrid failure on steep fault segments we discuss field criteria for identifying hybrid fractures and the deformation conditions under which hybrid failure is to be expected documented field examples of hybrid fractures are rare yet presence of hybrid fractures can be useful indicators of stress conditions at the time of failure specifically hybrid fractures are likely indicators of tensile minimum effective stress and low differential stress at failure

factors controlling shelf sediment dispersal along the southeast african continental margin abstract four major factors control sediment dispersal along the southeast african continental margin 1 morphology of the upper continental margin 2 wave regime and wind driven circulation 3 influence of the agulhas current and 4 sediment supply these factors interact on various scales to produce a unique regional sediment dispersal pattern the continental shelf is very narrow and the adjacent slope extremely steep the shelf platform is interrupted by a number of structural offsets and locally the shelf break is dissected by numerous submarine canyons the nearshore zone down to about 60 m waterdepth is dominated by a high energy swell regime and in most places is underlain by a thin wedge of sandy sediment this wedge appears to have achieved dynamic equilibrium with the prevailing energy regime and additional sediment is rapidly dispersed and fed into a sandstream situated on the central shelf where the agulhas current dominates sediment transport along some parts of the coast the sediment wedge is dammed behind a drowned coastal dune ridge within the sandstream sediment is transported alongshelf until a structural offset is reached where sediment spills over the shelf break four major localities for off shelf transport are recognized between maputo and port elizabeth most of the suspended load appears to be expelled from the system without being deposited on the shelf in the lee of each offset a clockwise gyre is developed which produces return flow currents capable of moving sediment northward thereby creating bedload partings in the vicinity of these partings depositional features are observed that are similar to those normally associated with tidal regimes e g bedforms migrating in opposite directions most of the bedload sediment entering the system is eventually deposited in well defined sinks situated in the lee of structural offsets this model applies only to inter glacial high sea level situations accompanied by strong western boundary flow of the agulhas current

geologic control in the nearshore shore oblique sandbars and shoreline erosional hotspots mid atlantic bight usa abstract beach and nearshore morphology defined primarily by slope and sandbar development is very dynamic and is largely controlled by waves currents and regional sediment characteristics results presented here challenge this long established concept and suggest that underlying framework geology may also exert a first order control on nearshore morphology by influencing the stability and or persistent re establishment of large scale sandbar morphology and position as well as surface sediment characteristics repeated sub bottom chirp and swath bathymetry surveys of the nearshore 2 10 m depths covering over 56 km of the north carolina outer banks and southeastern virginia indicate the following 1 development of shore oblique sandbars adjacent to large gravel outcrops that are surface exposures of the underlying geologic strata 2 identical re development or sustained maintenance of large scale sandbar morphology and position before and after very energetic conditions 3 vertical and horizontal heterogeneity of lithology and grain size and a minimum volume of sand ranging from 0 to 1 5 m thick and 4 close spatial alignment between the location of outcrops shore oblique bars and shoreline erosional hotspots a hypothesis is proposed from these findings that links framework geology to bar morphodynamics and sorted bedforms and ultimately erosional hotspots sediment transport and shoreline evolution models based solely on waves and currents and an assumption of unlimited and uniform sediment may be inadequate in similar heterogeneous sand limited regions

storm swash terraces a previously overlooked element of the cliff shore platform system storm swash terraces are a distinctive and previously unreported component of the cliff shore platform sedimentary system they consist of laminated marine sands and gravels with occasional large rounded clasts and fine muddy laminae the planar deposits dip gently seaward are up to 1 m thick at the seaward margin and thin landwards forming a wedge they are laterally continuous over tens of meters in a coast parallel dimension they occur in coastal re entrants at the rear of boulder beaches and shore platforms at elevations between 1 and 9 m above contemporary high tide level the terrace sediments represent deposition at the limit of wave run up during extreme storms during such events wave energy is largely dissipated by a shore platform and or boulder beach but sufficient energy remains to carry water and fine sediment to higher levels where it then accumulates the deposition and preservation of storm swash terraces depend on a coastal topography that combines partial wave energy dissipation on a shore platform or boulder beach with available depositional space to landwards these deposits contain a sedimentary record of past storminess on high energy coasts that has yet to be exploited

longshore size grading on a boulder beach abstract longshore size sorting on boulder beaches has not previously been reported in a boulder beach comprising beachrock slabs we report systematic longshore clast size grading the boulder beach at mission rocks south africa is deposited on an elevated 3 m msl shore platform and comprises imbricated clasts up to 5 m in the a axis dimension 9 tonnes the clasts are derived from adjacent intertidal beachrock and eolianite outcrops and are emplaced during high magnitude wave events four distinct downdrift fining cells are present each is 40 50 m long the sorting is attributed to post emplacement clast redistribution in which the smallest clasts are transported most frequently by lower magnitude storms and therefore travel farthest downdrift the updrift cell boundary is marked by boulders 5 m in length that exceed the transport threshold for all but the most energetic of storms while the downdrift limit contains clasts 0 3 m in length this mechanism of longshore size sorting does not rely on variations in longshore wave power as does cell development on sand and gravel beaches the alongshore sorting via multiple high and variable magnitude events over a period of time distinguishes these coarse clast deposits from those of single extreme events whether storms or tsunamis

submerged barrier shoreline sequences on a high energy steep and narrow shelf abstract late pleistocene holocene shoreline sequences and associated shelf stratigraphy are described from a high gradient high wave energy shelf although shoreline preservation by overstepping is considered unlikely in such an environment as a result of intense ravinement during shoreline translation the development and preservation of two distinct shorelines at 100 m and 60 m are evident and attributed to century to millennial scale periods of stillstand during these periods shoreline equilibrium forms developed characterised by early diagenesis of beachrock and aeolianite between these features the shelf is dominated by erosional surfaces reflecting ravinement during periods of slowly rising sea level where shorelines are not preserved areas of scarping in the ravinement surface at similar depths to the adjoining shorelines represent rocky headlands separating the sandy coastal compartments where the depositional shorelines formed shoreline preservation by overstepping was facilitated by rapid relative sea level rise associated with meltwater pulses 1a and 1b although the features preserved are likely to represent only the cemented cores of the coastal dunes and linear beachrock outcrops formed the steep antecedent shelf gradient fostered the erosion of significant portions of the shorelines by ravinement with loose sediment re organised into a thick post ravinement drape the removal of shorelines during ravinement was countered by the rapid rate of sea level rise and early sub tropical diagenesis it is clear that due to the combined effects of subtropical diagenesis long periods of stillstand and drowning by meltwater pulses the governing controls on shoreline preservation can be over ridden by combinations of local climatic and global eustatic factors

control of mechanical stratigraphy on bed restricted jointing and normal faulting eagle ford formation south central texas outcrops of the middle eagle ford formation in south central texas reveal well developed joint networks in subhorizontal competent carbonate chalk beds and less well developed networks in interlayered incompetent calcareous mudrock beds northeast striking bed perpendicular joints in competent beds have the longest trace lengths and are abutted by northwest striking joints all observed joints terminate vertically in incompetent beds normal faults are common but less abundant than joints dominantly dip north northwest or southeast and are abutted by the joint sets and thus predated jointing the faults cut multiple competent and incompetent beds providing vertical connectivity across mechanical layering products of hybrid and shear failure the dip of these faults is steep through competent beds and moderate through incompetent beds resulting in refracted fault profiles with dilation and calcite precipitation along steep segments fluid inclusions in fault zone calcite commonly contain liquid hydrocarbons rare two phase fluid inclusions homogenized between about 1 40 and 58 c and 2 90 and 100 c suggesting trapping of aqueous fluids at elevated temperatures and depths on the order of 2 km 6562 ft fluid inclusion and stable isotope geochemistry analyses suggest that faults transmitted externally derived fluids these faults likely formed at depths equivalent to portions of the present day oil and gas production from the eagle ford play in south texas faults connect across layering and provide pathways for vertical fluid movement within the eagle ford formation in contrast to vertically restricted joints that produce bed parallel fracture permeability these observations elucidate natural fractures and induced hydraulic fracturing within the eagle ford formation

contrasting geomorphological storm response from two adjacent shorefaces shorefaces play a critical role in cross shore sediment transport between the beach and inner shelf particularly during storm conditions a comparison and examination of storm driven sedimentary changes on two adjacent shorefaces in northern ireland located only 5 km apart revealed significantly different geomorphological responses the steeper shoreface at west strand responded with extensive sediment deposition across almost the entire shoreface in contrast with the more dissipative and quasi linear shoreface at portstewart which mostly showed nearshore bar changes results from the two sites which have similar wave wind characteristics and seabed sediments suggest that i cross shore morphology ii immediately previous antecedent shoreface morphodynamic behaviour and iii the presence or lack of offshore sand appear to be the primary controls on storm driven sedimentary changes attributed to the high energy event copyright 2015 john wiley sons ltd

the use of boulders for characterising past tsunamis lessons from the 2004 indian ocean and 2009 south pacific tsunamis tsunamis are high energy events capable of transporting extremely heavy loads including boulders we compare boulder deposits created by two modern tsunami events the 2004 indian ocean and the 2009 south pacific tsunamis where the boulder sources were in similar topographic settings and for which we have accurate data on the wave characteristics boulder distribution preferential orientation and numerical simulation of boulder transport are discussed a comparison between the impacts of the south pacific and indian ocean tsunamis shows similar characteristics such as limited landward extent and the absence of landward fining differences between the results from modelling and field data are most probably caused by variables such as coastal plain roughness buildings trees microtopography particle shape and boulder collision during transport that are summarised as coefficients in the mathematical models characterising modern events through coarse sediment deposits provides valuable information to help identify and interpret palaeo tsunami imprints on coastal landscapes

storms and shoreline configuration abstract spectral analysis of the 1962 great atlantic coast storm penetration overwash along the outer banks of north carolina and fenwick island maryland reveals along the coast periodicities ranging in wavelength from 14 km to 15 km periodicities with similar wavelengths exist in long term mean rates of change of the shoreline and storm surge penetration line this suggests the location and magnitude of storm deposits and storm hazards along the atlantic coast are systematically distributed

formation and preservation of an overstepped segmented lagoon complex on a high energy continental shelf the duration of shoreline occupation at a given sea level coastal response to sea level change and the controls on preservation of various shoreline elements can be recognized by detailed examination of submerged shorelines on the continental shelf using bathymetric and seismic observations this article documents the evolution and preservation of an incised valley and lithified barrier complex between 65 m and 50 m mean sea level on a wave dominated continental shelf the barrier complex is preserved as a series of aeolianite or beachrock ridges backed by laterally extensive back barrier sediments the ridges include prograded cuspate lagoonal shoreline features similar to those found in contemporary lagoons the incised valley trends shore parallel behind the barrier complex and records an early phase of valley filling followed by a phase of extensive lagoonal sedimentation beyond the margins of the incised bedrock valley sea level stability at the outer barrier position ca 65 m enabled accumulation of a substantial coastal barrier that remained intact during a phase of subsequent slow sea level rise to 58 m when the lagoon formed these lagoonal sediments are stripped seawards by bay ravinement processes which caused the formation of several prograded marginal cuspate features an abrupt rise in sea level to 40 m correlated with melt water pulse 1b enabled the preservation of thick lagoonal sediments at the top of the incised valley fill and preservation on the sea bed of the cemented core of the barriers this situation is unique to subtropical coastlines where early diagenesis is possible the overlying sandy sediment from the uncemented upper portion of the barriers is dispersed by ravinement partly burying the ridges and protecting the underlying sediments the high degree of barrier or shoreline preservation is attributed to rapid overstepping of the shoreline early cementation in favourable climatic conditions and the protection of the barrier cores by sand sheet draping

fault and fracture systems in a fold and thrust belt an example from bolivia this paper presents an outcrop analog study of fractures in low porosity sandstones in the subandean thrust belt we analyze the evolution of fault and joint systems in these sandstones quantify their density along the structural trend and identify the main factors controlling their variability we show that faults and joints occur at different scales in a hierarchical fashion as a consequence of progressive shearing the first generation is an orthogonal set of joints one parallel and the other perpendicular to the bedding azimuth shearing along these joints transformed them into small faults and created new sets of fractures oblique to the bedding attitude linkage of these small faults facilitated the formation of larger faults with significant strike slip offset shearing along bedding planes created subvertical splay joints that induced the formation of conjugate normal faults in this thrust belt subordinate strike slip and normal faults are concomitant products of compressive deformation this study documents a hierarchical correspondence between spacing of structural heterogeneities and stratigraphic architecture we measured spacings of joints and outcrop scale faults along the backlimb of the abra del condor anticline we subdivided the structural discontinuities into four main groups joints small faults intermediate faults and fault zones spacing of joints small faults and intermediate faults has a lognormal distribution whereas spacing of fault zones shows a normal distribution the mean of these distributions is about the same as the thickness of the confining stratigraphic intervals therefore spacing and dimensions of joints and faults have a first order relationship to the thickness of the confining stratigraphic sequences

spatial and temporal variations in incised valley systems from the durban continental shelf kwazulu natal south africa abstract the evolution of several incised valley systems from the kwazulu natal shelf is compared over time these represent the shelf extension of the collective durban harbour drainage system and the mgeni mhlanga and mdloti rivers two main ages of incision are apparent early santonian cretaceous and late pleistocene holocene the early valleys formed by tectonic controls namely phases of higher frequency base level fall superimposed on lower frequency higher order transgression the results are complex networks of stacked compound valleys that have been exploited by some of the younger networks formed by glacio eustatic fall prior to the last glacial maximum lgm of 18 ka bp the valley fills have evolved from high energy basal fluvial deposits low energy central basin fines mixed energy estuarine mouth plug deposits clay rich flood deposits through capping sandy shoreface deposits the earliest fills are dominated by central basin deposits and were underfilled as a result of low gradient and limited sediment supply the more recent late pleistocene holocene fills have significantly thicker fluvial deposits as a result of increased gradient and stream competence during the later stages of valley and shelf evolution the youngest valleys show a situation of differential evolution along the valley length due to varying rates of sea level rise in the holocene initial rapid sea level rise caused drowning and overstepping of the outer segment of the incised valley whereas slower rates of sea level rise in the late holocene caused shoreface ravinement of the inner mid segments of the valley this differential exposure to accommodation has resulted in a sedimentological partitioning between tide dominated facies in the outer valley segment and river dominated facies in the inner segment cf cooper 2001

contrasting styles of swell driven coastal erosion examples from kwazulu natal south africa during 2006 2007 the kwazulu natal coast of south africa was exposed to several large swell events ho 3 m near the peak of the lunar nodal cycle causing shoreline recession the largest swell hs 8 5 m struck the coast on the march equinox 18th 20th and generated a strong storm return flow observations made before during and after record dramatic coastal erosion shoreline recession of up to 40 m and substantial property damage this swell event removed the semi continuous nearshore bar system and conditioned the coast such that lesser subsequent swell events accomplished much greater amounts of coastal erosion than expected up to 100 m at certain erosion hotspots because waves reached the coast without significant energy dissipation subsequent bar generation rebuilt the inshore bars within six months the styles of erosion during the march 07 event and other 2007 swells were markedly different lesser swells are focused by headlands and result in megarip development and activation of erosion hotspots the march 07 event still water level was raised equinoctial spring high tide and a storm surge of 0 33 0 45 m to a level that rendered most headlands and erosion hotspots ineffective and resulted in laterally extensive erosion of soft shorelines results record cumulative effects of successive swell events on coastal behaviour that proved to be critical in enabling erosion to proceed at rapid rates after the coast had been initially destabilized unlike hurricanes and tsunamis surges associated with swell events are relatively minor and therefore extensive erosion is linked with high lunar tides there is circumstantial evidence that swell induced erosion follows the broad 18 6 yr lunar nodal tidal cycle when the chances of large swells coinciding with high water levels are increased

microfracturing in the upper triassic sichuan basin tight gas sandstones tectonic overpressure and diagenetic origins the western sichuan basin located at the front of the longmen mountain in the western sichuan province of china is a foreland basin formed in the late triassic the upper triassic xujiahe formation in the basin is an ultralow permeability and low porosity tight gas sandstone reservoir microfractures such as intragranular microfractures grain edge microfractures and transgranular microfractures are abundant in the tight sandstones microfractures improve storage and permeability and impact distribution of natural gas microfractures reflect tectonic overpressure and diagenetic origins using quartz and calcite fluid inclusions and burial history tectonic microfractures were determined to be formed at the end of the triassic the end of the cretaceous and the end of the neogene early pleistocene microfractures related to overpressure being tension microfractures are commonly filled with bitumen and were formed at the middle to late cretaceous when the maximum pressure coefficients were 1 6 to 2 1 in the middle to late neogene the pressure coefficient was reduced to less than 1 3 because of fault activity and tectonic uplift in the southwestern sichuan basin and these tension microfractures closed and were filled with calcite the transition of stress state from compression to tension by overpressure is the reason that tension microfractures were formed in the compression setting diagenetic fractures were formed at the end of the late triassic to jurassic under intense compaction grain crushing crackle fractures in quartz and cleavage fractures in feldspar formed intragranular microfractures some transgranular microfractures caused by diagenesis are along the bedding plane and parallel to the directional mineral grains

geophysical and geological tests of tectonic models of the north china craton abstract the geometry and timing of amalgamation of the north china craton have been controversial with three main models offering significantly different interpretations of regional structure geochronology and geological relationships one model suggests that the eastern and western blocks of the ncc formed separately in the archean and an active margin was developed on the eastern block between 2 5 and 1 85 ga when the two blocks collided above an east dipping subduction zone a second presumes the eastern block rifted from an unknown larger continent at circa 2 7 ga and experienced a collision with an arc perhaps attached to the western block above a west dipping subduction zone at 2 5 ga and the 1 85 ga metamorphism is related to a collision along the northern margin of the craton when the ncc joined the columbia supercontinent a third model suggests two collisions in the central orogenic belt at 2 1 and 1 88 ga but recognizes an early undated deformation event recent seismic results reveal details of the deep crustal and lithospheric structure that support both the second and third models showing that subduction beneath the central orogenic belt was west directed and that there is a second west dipping paleosubduction zone located to the east of the cob dipping beneath the western block ordos craton the boundaries identified through geophysics do not correlate with the boundaries of the trans north china orogen suggested in the first model and the subduction polarity is opposite that predicted by that model high pressure granulite facies metamorphism at 1 85 ga is not restricted to the tnco as suggested by the first model but is documented across the ncc as predicted by the second model suggesting a major continent continent collision along the north margin of the craton at 1 85 ga further it has recently been shown that in the southern tnco there is no record of metamorphism at circa 1 85 ga but only at 2 7 2 5 ga showing that the tnco as defined as a circa 1 85 ga orogen does not exist this is further confirmed by recent re os isotopic studies which show that the subcontinental lithospheric mantle beneath the southern cob is late archean in age and that a province in the northern ncc is circa 1 8 ga correlating with the proposed collision belt of the ncc with the columbia supercontinent across the entire ncc the cob is an archean convergent belt re worked in the paleoproterozoic and the paleoproterozoic tectonism is widespread across the ncc as predicted by the model whereby the previously amalgamated eastern and western blocks experienced a continental collision with columbia at circa 1 85 ga but uplift exhumation rates are slow necessitating a re evaluation of the tectonic models of the ncc

characterization and development of subsurface fractures observed in the marcellus formation appalachian plateau north central pennsylvania we report on subsurface deformation features measured from recently acquired core and image logs from the marcellus formation in north central pennsylvania supplemented with data collected from valley and ridge outcrop the subsurface data are from an area that bridges a gap in existing published data between outcrop in the valley and ridge province of pennsylvania and the relatively undeformed outcrop exposed on the appalachian plateau of new york we find one distinct set of vertical veins that strike orthogonal to appalachian plateau fold axes and an associated set of low angle reverse faults and stylolites that strike parallel to fold axes as the trend of the fold axes changes around the pennsylvania salient the trend of associated mesostructures changes to maintain kinematic compatibility with the shortening direction change along the salient these structures are interpreted to support a single although possibly protracted strain event during alleghanian deformation as opposed to multiple events previously interpreted to occur in different regions and stratigraphic levels within the fold belt the veins are associated with clusters of bedding plane slip surfaces which are found at distinct mechanical stratigraphic positions where the competence contrast between shale and stiff limestone units is greatest we interpret this association to indicate that bed parallel shear within detachment zones provides the sufficient driving force required to nucleate vertical veins and the decoupling of beds accommodates extension orthogonal to the shortening direction although these veins are oriented orthogonal to the present day maximum principal horizontal stress they remain propped open by crystalline cements homogenization temperatures of fluid inclusions trapped in the veins combined with one dimensional burial and thermal history models suggest that the pervasive vein set formed during the late pennsylvanian permian during the alleghanian orogeny

orbitally forced sedimentary rhythms in the stratigraphic record is there room for tidal forcing the imprint of orbital cycles which result from the varying eccentricity of the earth s orbit and changes in the orientation of its axis have been recognised throughout the phanerozoic rock record variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions common oceanographic principles however show that the ocean tide also responds to variations in the orbital parameters the ocean tide has not yet been considered to be a valid additional transfer mechanism for the orbital variations in geological studies of milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations and the role of long term variations of the ocean tide has not yet been appreciated variations in the ocean tide related to changing eccentricity at present 0 0165 theoretical maximum 0 0728 affect a variety of oceanographic and sedimentary processes in addition to the widely accepted paradigm of orbitally forced insolation changes the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing organic productivity and tidal processes in shallow seas and deep water variations of the ocean tide in relation to the 18 6 year lunar nodal cycle which has no insolation counterpart by which they may be obscured indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide in analogy with the 18 6 year lunar nodal cycle orbital variations of the tide on milankovitch time scales are likely to have affected sedimentary systems in the past

outcrop architecture of a fluvio lacustrine succession upper triassic yanchang formation ordos basin china abstract although several studies have considered the sedimentary facies of the upper triassic yanchang formation in terms of their hydrocarbon potential in the petroliferous ordos basin such studies have mostly interpreted subsurface data and few have systematically examined the detailed outcrop based anatomy of this succession this study characterizes a series of well exposed outcrop sections along an 80 km long e w oriented series of road cuttings in the southeast ordos basin to reconstruct the sedimentary architecture of a fluvio lacustrine succession and determine the principal controls that governed the style of accumulation and preservation the yanchang formation is divided into 10 depositional units chang 10 base to chang 1 top that record the sedimentary evolution of a series of large scale fluvial systems that constructed delta front and pro delta bodies as they entered a large interior draining lake detailed analysis of the internal architectures of the delta front bodies records the mechanism of growth of a large scale shallow water delta succession lacustrine subaqueous distributary channels are composed of 3 15 m thick sandstone fills such channelized bodies are highly elongate and many can be traced several kilometres such bodies can be shown to be commonly associated with thin bedded mouth bar and subaqueous interdistributary bay deposition the progradational architecture of the delta front elements is difficult to recognize on outcrop scale deposits of the chang 10 to 1 units record 4 major lacustrine transgressive regressive cycles during the late triassic transgressive events are signified by the widespread occurrence of 10 20 m thick oil shale prone intervals regressive events are signified by the progradational stacking towards the basin centre of sandstone prone facies associations mainly accumulated in fluvial channel delta plain and upper delta front environments the uppermost chang 1 interval records late stage filling of the lacustrine basin the transgressive regressive cycles equate to sequences that can be correlated across the region development of which was controlled by a combination of changes in the rate of tectonic subsidence the rate of sediment delivery from the basin margin hinterland and climate factors that were themselves influenced by intracontinental growth of the neighbouring qinling orogen

pitfalls of using entrenched fracture relationships fractures in bedded carbonates of the hidden valley fault zone canyon lake gorge comal county texas characterizing natural fracture systems involves understanding fracture types faults joints and veins patterns orientations sets and spacing within sets size distributions penetration across layering aperture and trace length and timing relationships traditionally observation based relationships to lithology mechanical stratigraphy bed thickness structural position failure mode and stress history have been proposed for predicting fracture spacing along with the relative abundance of opening mode fracture versus faults in fractured rocks developing a conceptual fracture model from these relationships can be a useful process to help predict deformation in a fractured reservoir or other fractured rock systems a major pitfall when developing these models is using assumptions based on general relationships that are often site specific rather than universal in this paper we examine a mixed carbonate shale sequence that is cut by a seismic scale normal fault where fracture attributes do not follow commonly reported fracture relationships specifically we find 1 no clear relationship between frequency or spacing of opening mode fractures joints and veins and proximity to the main fault trace and 2 no detectable relationship between fracture spacing and bed thickness however we did find that 1 the frequency of small displacement faults is strongly and positively correlated with proximity to the main fault trace 2 fracture networks change pattern and failure mode extension versus shear fracture from pavement to pavement through the mechanically layered stratigraphic section and 3 faults are more abundant than opening mode fractures in many areas within the fracture network we interpret that the major fracturing initiated near maximum burial under relatively high differential stress conditions where shear failure dominated and that mode 1 extension fracturing occurred later under lower differential stress conditions filling in between earlier formed shear fractures we conclude that whenever possible site specific observations need to be carefully analyzed prior to developing fracture models and perhaps a different set of fracture network rules apply in rocks where shear failure dominates and mechanical stratigraphy influences deformation

fault zone deformation controlled by carbonate mechanical stratigraphy balcones fault system texas normal faults in cretaceous carbonates in the balcones fault system provide important analogs for fault zone architecture and deformation in carbonate reservoirs worldwide mechanical layering is a fundamental control on carbonate fault zones relatively planar faults with low displacement gradients develop in massive strong clay poor limestones and dolomites in less competent clay rich strata shale beds impede fault propagation resulting in fault related folding and locally steep bedding dips faults in clay poor massive limestones and dolomites tend to be steep 70 or more whereas weaker clay rich limestones develop faults with shallower dips 60 or less fault zone rocks show evidence of cataclasis cementation deformation of cement by mechanical twinning and pressure solution and multiple generations of cement with differing degrees of deformation indicating contemporaneous cementation and fault slip in stratigraphic sequences consisting of both competent and incompetent strata the ratio of incompetent to competent strata by thickness is a useful guide for inferring the relative rates of fault displacement and propagation low displacement to propagation ratios associated with competent strata generate low displacement gradients inhibiting fault related folding conversely high displacement to propagation ratios associated with incompetent strata promote high displacement gradients and fault related folding

rapid beachrock cementation on a south african beach linking morphodynamics and cement style rapid cementation 5 years of beachrock is reported from the wave dominated microtidal coastline of durban south africa the beachrock is developing at mean sea level on a steep 10 30 reflective beach prone to periodic erosion by high energy wave action the most recent erosional event resulted in retrogradation of the beach by up to 10 m landward of the beachrock outcrop discussed in this study transmitted light microscopy and scanning electron micrographs show the precipitation of two dominant cement types which are linked to the beachface morphodynamics during the accreted beach phase when the locus of beachrock formation lay well landward of the beachface in the undersaturated upper intertidal to supra tidal backbeach meniscus cements were precipitated following a period of erosion associated with a landward shift of the beachface the incipient beachrock was then exposed to saturated conditions which promoted growth of acicular cements contemporary beachrock cementation occurred very rapidly 5 years between significant erosional events the observed cement textures record short term beach progradation and retrogradation but are similar to those typically associated with longer term regression and transgression

wave influences in contemporary and mesoarchaean stromatolites abstract contemporary shore platform stromatolites sps are becoming well known we describe the physical environment and macrostructures from contemporary shore platform stromatolites sps on the wave dominated southeast african coast this was then compared with mesoarchaean 2 97 ga stromatolites from white umfolozi 100 km inland we use the tinley manor sps occurrence as the basis for physical environmental comparison but where necessary draw on evidence from other sps environments sps and mesoarchean umfolozi stromatolites contain similar stromatolitic structures and wave deposits the sps environment is wave dominated and the occurrence of similar sedimentary structures associated with the mesoarchean umfolozi stromatolites indicates a paleoenvironment associated with waves the contemporary tinley manor sps wave climate is robust and from this locality we have identified broad limits in which sps can develop and be preserved applying this knowledge to the mesoarchaean white umfolozi stromatolites suggests that they formed in a protected wave climate where wave incursions were less frequent both these wave influenced settings are were subject to very low siliciclastic input the frequency of marine sediment input appears to be a limiting factor on microbialite growth in both the contemporary sps and archaean examples

behaviour of beach profiles during accretion and erosion dominated periods beach profiles have been surveyed at monthly intervals between 1972 and 1988 at moruya on the south coast of new south wales australia four profile sites have been used as a data set to provide an understanding of changes to beach volume width and shape moruya beach represents a moderately high energy microtidal environment which responds in a dramatic way to major storm events such as those experienced in the mid 1970s this study distinguishes between profile characteristics associated with such a period erosion dominated or edp compared with periods when accretion dominated adp accompanied by foredune expansion in both height and width