modeling equilibrium dynamics of the benguela current system the regional ocean modeling system roms is used to systematically investigate equilibrium conditions and seasonal variations of the benguela system at a resolution of 9 km including both the large scale offshore flow regime and the economically and ecologically important coastal upwelling regime a shelf edge poleward flow exists in the northern benguela region i e north of 28 s and is driven primarily by the wind stress curl via the sverdrup relation as such it is strongly seasonal and is most intense during spring and summer when the wind stress curl is most negative the poleward flow deepens as it moves southward between 25 and 27 s much of it veers offshore because of the nature of the wind stress curl and its interaction with the northwestward path of the benguela current which is influenced by alongshore topographical variations the benguela current is driven by nonlinear interactions of passing agulhas rings and eddies and does not have a striking seasonal signal in the mean state it is characterized by two streams the more inshore stream is topographically controlled and follows the run of the shelf edge the meandering nature of the offshore stream is a result of the preferential path of agulhas rings the model simulates all seven of the major upwelling cells within its domain the three southernmost cells have the strongest seasonal signal and experience their greatest upwelling during spring and summer months whereas the two northernmost cells have less seasonal variability but nevertheless have increased upwelling from autumn to spring and least upwelling in summer and the central benguela upwelling cells experience year round upwelling the effect of topography on coastal upwelling was investigated by smoothing alongshore coastline and topography variations which showed that in all of the seven major upwelling cells upwelling is enhanced on the downstream side of capes

dissolution of biogenic carbonates effects of skeletal structure abstract dissolution of biogenic shallow water carbonates exposed on deep sea moorings indicates that skeletal structure is important for the rate of disintegration of biogenic carbonates besides mineralogy and grain size of particles the aragonites and high mg calcites used represent a wide spectrum of mineralogies and types of skeletal framework the particles were deployed at different water depths on a mooring in the drake passage for 52 days weight loss curves for the various types of particles show the relative importance of the different structural factors for the disintegration of these biogenic carbonates organic coatings intraskeletal pore spaces and sizes and shapes of individual crystallites in the skeletons may be more important than carbonate mineralogy and particle size in cases the presence of internal sediments cement aggregates and natural contaminations and of diatoms incorporated during growth into carbonate skeletons strongly influence the disintegration of the skeletal materials the first step of particle disintegration is the selective removal of impurities this step is analogous to a cleaning of specimens it is succeeded by initial dissolution by strong dissolution and finally by disintegration

diagenesis of a se asian cenozoic carbonate platform margin and its adjacent basinal deposits abstract this study provides insights into the diagenesis of a se asian tertiary carbonate platform and the variations in alteration that occur across platform top margin slope and adjacent basinal deposits a petrographic cathodoluminescent and stable isotopic study allowed evaluation of the diagenesis of the kedango limestone of borneo the kedango carbonate platform developed as a predominantly low to moderate energy system in the semi enclosed marine embayment of the kutai basin during the eocene to miocene early alteration through pervasive micritisation and minor isopachous fringing syntaxial overgrowth and bladed to radiaxial cements was due to marine diagenesis on the basis of limited relatively enriched stable isotope compositions and non luminescent cathodoluminescent cl characters minor early marine cementation formed just in the shallowest platform top and margin deposits and was likely promoted in high energy portions of the platform due to wave and or current activity dissolution cavities banded calcite cements with variable cl characteristics and depleted stable isotope compositions micritic sediment infiltration and alveolar textures are minor features but together are indicative of localised subaerial emergence and meteoric diagenesis the most prevalent and pervasive diagenetic feature of the deposits is the neomorphic alteration and replacement of metastable bioclasts and micritic matrix together with contiguous calcitisation of pore spaces burial fluids with a marine character are inferred as the parent diagenetic fluid since stable isotope compositions for the neomorphic spar is largely consistent with precipitation from se asian oligocene miocene seawater in a burial environment tectonic subsidence the protected semi enclosed marine embayment setting and probably terrestrial runoff together with component variability reflecting local environmental variations are inferred to have been major controlling influences on the diagenesis of the kedango platform variations in diagenesis across bathyal slope and shallow platform deposits of the kedango limestone are not as marked as in other platforms from the region

a cool anomaly off northern california an investigation using ir imagery and in situ data satellite ir imagery and in situ hydrographie data are used to understand better the mesoscale variability of the california current system and to explore the relation of its surface and subsurface thermal structures in august 1982 one of the cool filaments commonly seen in satellite ir images during summer off northern california was sampled hydrographically during an optoma ocean prediction through observation modeling and analysis cruise based on the cool anomaly seen in a series of ir images and the in situ hydrographie data and based on geostrophic calculations a jet entrained upwelled coastal water and advected it rapidly through the warmer waters offshore providing an important cross shore transfer process the anomaly was about 50 km wide and extended vertically to about 40 m the temperature patterns at the surface were well correlated with those to about 30 m below 50 m the surface temperature was better correlated with horizontal temperature gradients i e the thermal wind consistent with strong horizontal advection by the geostrophic jet the cool anomaly was also relatively dense based on investigation of the t s properties the coastal water had been diluted through mixing with columbia river plume water on the northern edge of the anomaly near the temperature front in the shoreward sampled portion of the anomaly and just south of the anomaly interleaving occurred there was also a surface saline anomaly embedded in the cool anomaly near the temperature front the location of the temperature front in the in situ data and in the ir imagery corresponded well the temperature front was tracked in a series of ir images over 2 weeks the reorientation of the seaward extremity of the anomaly from westward to northwestward and the southwestward displacement of its southern boundary at speeds of 2 to 5 km d were consistent with the propagation of mesoscale features evident in successive quasi synoptic surface dynamic topography maps the southwestward displacement was probably also related to surface ekman transport

taphonomic field experiments and the role of the shelf and slope experimental taphonomy initiative abstract fossilization of organism remains is the result of biological physical and chemical processes at work in the environment of deposition the pathways taken by the remains of organisms through death decay burial and diagenesis known as taphonomic pathways affect the fossil record of life in important ways from complete removal and recycling of remains to preservation of hard parts and sometimes to exceptional preservation of soft tissues our understanding of taphonomic processes informs our interpretations of the fossil record and helps in the reconstruction of ancient environments research into taphonomic pathways in modern environments provides important insight into the fossilization process in 1993 a group of paleontologists formed the shelf and slope experimental taphonomy initiative sseti and began a long term comparative study of taphofacies and differential decay of taxonomic groups by placing experimental arrays containing bivalves gastropods decapod crustaceans sea urchins and wood species at multiple marine shelf and slope sites in the bahamas and gulf of mexico the goal of sseti is to observe taphonomic processes over a period of decades to better understand taphonomic pathways for these various groups of taxa in a wide variety of depositional environments beyond the shallow near shore region this special volume brings together eight studies that are the result of the sseti program the focus of this contribution is to first review the body of published work concerned with the fossilization process through the experimental manipulation of the remains of organisms in modern marine environments we also present the methods of the sseti project and its contributions to our understanding of taphonomic processes in relation to carbonate and wood recycling and preservation

unravelling the depositional origins and diagenetic alteration of carbonate breccias carbonate breccias dissociated from their platform top counterparts are little studied despite their potential to reveal the nature of past shallow water carbonate systems and the sequential alteration of such systems a petrographic and stable isotopic study allowed evaluation of the sedimentological and diagenetic variability of the cenozoic batu gading limestone breccia of borneo sixteen lithofacies representing six facies groups have been identified mainly from the breccia clast on the basis of shared textural and compositional features clasts of the breccia are representative of shallow carbonate platform top and associated flank to basinal deposits dominant inputs are from rocky karstic shorelines or localised seagrass environments coral patch reef and larger foraminiferal rich deposits early pre brecciation alteration including micritisation rare dissolution of bioclasts minor syntaxial overgrowth cementation pervasive neomorphism and calcitisation of bioclasts and matrix was mainly associated with marine fluids in a near surface to shallow burial environment the final stages of pre brecciation diagenesis include mechanical compaction and cementation of open porosity in a shallow to moderate depth burial environment post brecciation diagenesis took place at increasingly moderate to deep burial depths under the influence of dominantly marine burial fluids extensive compaction circum clast dissolution seams and stylolites have resulted in a tightly fitted breccia fabric with some development of fractures and calcite cements a degree of facies specific controls are evident for the pre brecciation diagenesis pervasive mineralogical stabilisation and cementation have however led to a broad similarity of diagenetic features in the breccia clasts thereby effectively preserving depositional features of near original platform top and margin environments there is little intra clast alteration overprint associated with subsequent clast reworking and post brecciation diagenesis the diagenetic and to an extent depositional and clast characteristics of the batu gading deposits are diagnostic of breccia origins the predominance of early and pervasive stabilisation of calcitic components pervasive compaction resulting in a fitted texture and paucity of meteoric dissolution or cementation effects are collectively all indicators of slope deposition and lithification these features are comparable with other regional and global examples of submarine slope breccias and consistent with the prior interpretation that the carbonate platform at batu gading developed in a rotating wedge top basin wannier 2009 the results of this study along with regional analogues suggest the potential for reworked carbonates debris in slope settings to be a viable way of investigating carbonate platform variability and their subsequent alteration in the absence of preserved platform top or margin deposits

comparing vertical profiles of natural tracers in the williston basin to estimate the onset of deep aquifer activation comparing high resolution depth profiles of different naturally occurring environmental tracers in aquitards should yield consistent and perhaps complementary information about solute transport mechanisms and the timing of major hydrogeological and climatological events this study evaluated whether deep continuous profiles of aquitard pore water chloride concentration could provide further insight into the paleohydrology of the williston basin canada than possible using high resolution depth profiles of stable h o isotopes of water 18o 2h pore water samples were obtained from extracts of cores taken over 392 m of the thick cretaceous shale aquitard water samples were also collected from wells installed in the underlying regional sandy aquifer mannville group 93 m thick and from seepage inflows into potash mine shafts to 825 m below ground numerical modeling of the 1 d vertical cl profile supported diffusion dominated solute transport in the shales the modeling also showed a similar time frame for development of the cl profile prior to activation of the aquifer as determined from the 18o profile 20 25 ma however it provided a significantly longer and potentially better constrained time frame for evolution of the profile during the activation phase of the aquifer 0 5 1 ma the dominant paleoevent reflected in present day profiles of both tracers is the introduction of glaciogenic meteoric water to the mannville aquifer underlying the shale during the pleistocene the source area of this water remains to be determined

syn depositional alteration of coral reef framework through bioerosion encrustation and cementation taphonomic signatures of reef accretion and reef depositional events the development of coral reef framework and the preservational character of both in situ and rubble coral is strongly influenced by a range of physical chemical and biologically mediated taphonomic processes these operate at or just below the reef framework water interface and can be defined as having either a constructive or destructive effect upon primary reef framework i e coral constituents constructional activities add additional calcium carbonate to the primary framework structure via secondary framework growth and early cementation destructive processes which remove or degrade primary and secondary framework carbonate are associated with the effects of either physical mainly storm disturbance or biological erosion termed bioerosion key bioeroding groups include the grazing fish and echinoid groups as well as the activities of an array of infaunal borers these include specific groups of sponges bivalves and worms termed macroborers as well as cyanobacteria chlorophytes rhodophytes and fungi termed microborers the relative importance of each process and the rates at which they operate vary spatially across individual reef systems in addition many of these processes leave distinctive signatures on or in the coral framework in some cases e g calcareous encrusters these are the skeletons of the organisms themselves whilst in other cases the organism may leave behind a trace of their activity e g macro and microborers these represent useful palaeoenvironmental tools firstly because they often have good preservation potential and secondly because the range and extent of many of the individual species groups and processes involved exhibit reasonably well constrained environment and or depth related distributions as a result these taphonomically important organisms or processes can be used to delineate between reef environments in core or outcrop and to aid the interpretation of reef depositional processes and events this review summarises current understanding regarding the distribution of these species processes within contemporary reef settings and considers the suites of taphonomic signatures that may aid in the recognition and interpretation of depositional environments and events

ecospace variability along a carbonate platform at the northern boundary of the miocene reef belt upper langhian austria the south western edge of the leitha mountains in the southern vienna basin austria exposes parts of an upper langhian middle badenian shallow water 30 m carbonate platform the study of its ecospace comprises sedimentological and palaeontological data of 4 up to 36 m thick carbonate sections of the mullendorf quarries which have been logged and subjected to detailed investigation and sampling the sedimentary record is dominated by coralline algal debris sands which represent 7 distinct lithofacies bioclastic coralline algal mollusc facies hyotissa facies isognomon facies coral facies rhodolith facies bryozoan facies all these facies are described in detail in respect to lithology and biota and are palaeoecologically interpreted striking features of these limestone successions are periodical intercalations of coral and mollusc rich horizons their formation had been triggered by water turbidity and low amplitude changes in relative sea level these relations are especially interesting as the platform carbonates formed at the northern edge of the langhian peri mediterranean reef belt water turbidity as ecological master factor and depth played the fundamental role in ecosystem and community expression within ecospace the lateral distribution and the ecological relations between the various facies types allow proposing an ecospace occupation model

kilometre scale polygonal seabed depressions in the hatton basin ne atlantic ocean constraints on the origin of polygonal faulting polygonal faulting is a widespread phenomenon in sedimentary basins worldwide it changes basin scale fluid flow patterns and alters the physical properties of the sediments making it important for hydrocarbon exploration and geohazard analysis it is generally accepted that polygonal fault patterns derive from dewatering and compaction of the host sediments but there is debate regarding the processes that control polygonal faulting new multibeam bathymetry data from the hatton basin ne atlantic show up to 10 m deep and 200 600 m wide troughs at the seabed they connect to each other forming polygons that are several hundred metres across i e of similar size as buried polygonal fault systems observed in 3d seismic data the troughs are symmetrical and resemble elongated pockmarks previously unpublished high resolution 2d seismic data from the same area show seismic disturbance zones similar to pipes observed under pockmarks elsewhere as well as faults that have all the characteristics of polygonal fault systems the observation of the wide disturbance zones is enigmatic as they appear to follow the polygonal seafloor pattern the observed extent of the polygonal sediment contraction system is substantial covering almost 37 000 km2 we calculate that some 2600 km3 of possibly carbon bearing fluids have been expelled from this system and we expect that this will affect the benthic ecosystems although so far there is only limited evidence for chemosynthetic habitats

factors controlling sediment preservation on a north jamaican fringing reef a process based approach to microfacies analysis abstract compositional characteristics of limestones are fundamental to the interpretation of depositional environments with an assumption that preserved grain assemblages preserve sufficient evidence of initial sediment input to enable delineation of environments it is acknowledged however that a range of early diagenetic processes including encrustation fragmentation abrasion microboring dissolution cementation and recrystallization may influence grain preservation potential and thus bias the composition of resultant grain assemblages this study examines the effects and relative importance of a range of early diagenetic processes across a fringing reef at discovery bay north jamaica physical processes abrasion and fragmentation are most important at shallow fore reef sites whilst back reef sites are dominated by biochemical processes including microboring recrystallization biofilm related calcification and dissolution grain susceptibility to each process is highly variable and influenced by mineralogy and skeletal structure coral fragments for example are most susceptible to the effects of microboring whereas halimeda plates are most susceptible to dissolution extensive alteration of grain assemblages is predicted within the back reef where dissolution of coral and halimeda occurs because of intense microboring and pore water undersaturation fore reef assemblages by contrast remain relatively unaltered results have implications both for improved ecological interpretation of carbonate sedimentary sequences and for understanding of how and why carbonate microfacies develop

displacement geometry in the volume containing a single normal fault fault displacements measured in coal mines and from seismic data are used to develop a model describing the near field displacements associated with an ideal single normal fault displacement on a fault surface ranges from a maximum at the center of the fault to zero at the edge or tip line the tip line is elliptical with the shorter axis of the ellipse parallel to the displacement direction contours of equal displacement form concentric ellipses centered on the point of maximum displacement displacement gradients vary with fault size and with mechanical properties of host rock fault radius to maximum displacement ratios range from 5 to 500 plotting of displacement contour diagrams and knowledge of displacement gradients are useful in interpreting seismic reflectio data both for quality control of interpretations and for quantitative extrapolation of limited data displacements associated with faulting decrease systematically with increasing distance along the normal to the fault surface this decrease is seen as reverse drag in both hanging wall and footwall hanging wall rollover and tilting of the reflectors cannot be used to distinguish listric from planar normal faults even where fault block rotation can be demonstrated neither listric fault geometry nor a flat detachment surface is geometrically necessary because faulting is accommodated by ductile deformation rigid fault bounded blocks cannot exist except in some special circumstances related to a free surface the displacements within the rock volume affected by a single fault are not simply related to regional extension apparent horizontal extension by faulting varies from one layer to another and a significant proportion of the extension in a basin may be due to ductile deformation

the control of stress history and flaw distribution on the evolution of polygonal fracture networks abstract we use boundary element models of fracture propagation and linkage to investigate the factors controlling the development of two dimensional multi directional polygonal fracture networks characterised by a large number of abutting intersections between fractures the position and orientation of a number of fracture seeds are prescribed in the model which propagate when the applied stress reaches a critical value according to linear elastic fracture mechanics theory the applied boundary condition is a remote isotropic horizontal tension where the stress is increased at a steady rate throughout each model to simulate continued fracture growth realistic polygonal systems are developed with the boundary element model simulations which are comparable with those observed in natural systems such as those found within eocene and oligocene mudrocks in the north sea and on the surface of mars if conditions exist where a small number of fracture seeds propagate and develop significant structures before others then these will dominate the resulting fracture network geometry not only do such early structures represent the largest fractures in the system they also significantly modify the stress field around them preventing some other seeds from developing and influencing the propagation paths of nearby fractures fracture seeding distribution and the rate at which the stress is increased are found to be the most significant parameters affecting the development of fracture network geometry these results suggest that the geometry of evolving fracture networks should be considered not only in terms of the mechanical properties of the deforming material but also in terms of the stress rate driving deformation

fine grained carbonates in nearly closed reef environments mataiva and takapoto atolls central pacific ocean abstract the nature origin and mode of accumulation of fine grained carbonate sediments have been investigated in the nearly enclosed lagoons of two french polynesian atolls mataiva and takapoto the fine sized fraction 20 m is substantially higher in amount 70 of the total fine sediments on average than the mud portion and may increase volumetrically 90 99 in some localities aragonite is the predominant mineral present 90 of the total calcium carbonate the fines appear to be mainly skeletally derived the silt fraction includes coral and molluscan detritus sponge chips juvenile benthic foraminiferans and other biogenic debris the mud is chiefly composed of aggregated nanograins ascidian spicules skeletal nanograins coral generated mainly and coccoliths a minor part of the mud is certainly of non skeletal origin some portion of freely deposited fines fill cavities or are attached upon sand grain surfaces they are associated with scattered inorganic precipitates and contribute to the formation of micrite envelopes and aggradation of host grains such a process is highly significant in the total carbonate budget of the reef the fine carbonate sediments result directly from the biological disintegration of nearby buildups mainly through the boring activity of sponges and lithophagid molluscs we suggest that the authigenic mud sized crystallites are controlled in their precipitation both by carbonate supersaturation and anoxic conditions seasonally affecting the interstitial sediment waters enclosed atoll lagoons are relatively self governing environments of deposition which are influenced by long term quiescent water situations rather than by rare catastrophic events

bathymetric zonation of modern microborers in dead coral substrates from new caledonia implications for paleodepth reconstructions in holocene corals abstract microboring endoliths were studied in dead modern corals collected at various depths and in growth position on la surprise atoll in new caledonia eight taxa of microborers were regularly observed three cyanobacteria hyella caespitosa mastigocoleus testarum and plectonema terebrans two chlorophytes ostreobium quekettii and phaeophila dendroides and three fungal forms dodgella priscus and two unidentified fungi the relative abundance of each taxon was determined in the modern corals throughout the studied sampling interval from 0 down to 40 m water depth this allowed us to propose for the first time a bathymetric model based on microendolith assemblages colonizing in situ hard substrates of corals in this model the occurrence of the cyanobacteria hyella and mastigocoleus indicates a bathymetric range from 0 down to a water depth of 3 and 6 m respectively the chlorophyta o quekettii associated with the cyanobacterium p terebrans and fungi is dominant from 10 to 40 m depth which is the lower limit of our sampling the distribution ranges of individual taxa observed in the dead coral substrates from new caledonia are much narrower than those reported in the literature for other substrates the bathymetric model based on distribution of microborers in modern corals was then applied to interpret the trace assemblages of microborers observed in holocene corals collected by drilling on two reef sites of new caledonia la surprise islet in the vicinity of the sampling sites of the modern corals and the barrier reef of bayes on the ne coast of grande terre the paleodepth interpretations performed at various levels along the cores allow identification of several shallowing upward sequences during the last 7000 years of reef growth in new caledonia differences in the thickness of these sequences between la surprise and bayes sites were interpreted as differences in the space available for accommodation between the two sites in turn related to the differential subsidence that affected new caledonia during holocene times the use of the microendolith trace assemblages in paleodepth reconstructions of holocene reefs from new caledonia allowed detection of relative sea level variations finer than those deduced from changes in coralgal assemblages

deep seated faults and hydrocarbon leakage in the snohvit gas field hammerfest basin southwestern barents sea abstract high quality 3d seismic data are used to analyze the history of fault growth and hydrocarbon leakage in the snohvit field southwestern barents sea the aim of this work is to evaluate tectonic fracturing as a mechanism driving hydrocarbon leakage in the study area an integrated approach was used which include seismic interpretation fault modeling displacement analysis and multiple seismic attribute analysis the six major faults in the study area are dip slip normal faults which are characterized by complex lateral and vertical segmentation these faults are affected by three main episodes of fault reactivation in the late jurassic early cretaceous and paleocene fault reactivation in the study area was mainly through dip linkage the throw distance plots of these representative faults also revealed along strike linkage and multi skewed c type profiles the faults evolved through polycyclic activity involving both blind propagation and syn sedimentary activity with their maximum displacements recorded at the reservoir zone the expansion and growth indices provided evidence for the interaction of the faults with sedimentation throughout their growth history soft reflections or hydrocarbon related high amplitude anomalies in the study area have negative amplitude reverse polarity and are generally unconformable with structural reflectors the interpreted fluid accumulations are spatially located at the upper tips of the major faults and gas chimneys four episodes of fluid migration are inferred and are linked to the three phases of fault reactivation and neogene glaciations hydrocarbon leakage in the snohvit gas field is driven by tectonic fracturing uplift and erosion the interpreted deep seated faults are the main conduits for shallow hydrocarbon accumulations observed on seismic profiles

a method to estimate groundwater depletion from confining layers 1 although depletion of storage in low permeability confining layers is the source of much of the groundwater produced from many confined aquifer systems it is all too frequently overlooked or ignored this makes effective management of groundwater resources difficult by masking how much water has been derived from storage and in some cases the total amount of water that has been extracted from an aquifer system analyzing confining layer storage is viewed as troublesome because of the additional computational burden and because the hydraulic properties of confining layers are poorly known in this paper we propose a simplified method for computing estimates of confining layer depletion as well as procedures for approximating confining layer hydraulic conductivity k and specific storage ss using geologic information the latter makes the technique useful in developing countries and other settings where minimal data are available or when scoping calculations are needed as such our approach may be helpful for estimating the global transfer of groundwater to surface water a test of the method on a synthetic system suggests that the computational errors will generally be small larger errors will probably result from inaccuracy in confining layer property estimates but these may be no greater than errors in more sophisticated analyses the technique is demonstrated by application to two aquifer systems the dakota artesian aquifer system in south dakota and the coastal plain aquifer system in virginia in both cases depletion from confining layers was substantially larger than depletion from the aquifers

selective reverse reactivation of normal faults and deformation around reverse reactivated faults in the mesozoic of the somerset coast abstract normal faults exposed in the triassic jurassic limestones and shales of the somerset coast were formed during the mesozoic development of the bristol channel basin reverse reactivation of some of these normal faults occurred during late cretaceous to early tertiary north south contraction the contraction is also evident from thrusts and conjugate strike slip faults preferential reactivation of the normal faults is attributed to 1 decreased fault plane friction 2 domino block rotation 3 displacement magnitude and 4 fault connectivity the geometries of overlapping and underlapping zones in reactivated fault zones are dependent on the existing structural geometry two distinctive styles of displacement accommodation occur between reverse reactivated normal faults 1 formation of a network of strike slip faults conjugate about nne ssw and 2 oblique steeply dipping reverse faults interaction between strike slip and an existing fault is dependent on whether the normal fault was reactivated the range of structures related to the north south contraction has been incorporated into a single deformation model controlled by the northwards movement of the hanging wall of the quantock s head fault pure dip slip movement occurred in the centre of its curved fault trace with a sinistral component at the western tip and a dextral component of displacement and strike slip block rotations occurred at the eastern tip shortening of these blocks was achieved through development of a strike slip fault network and nw striking thrusts in an underlap zone loading of the footwall by the hanging wall block modified the local stress system to allow formation of oblique steeply dipping reverse faults

a laboratory model of thermocline depth and exchange fluxes across circumpolar fronts a laboratory experiment has been constructed to investigate the possibility that the equilibrium depth of a circumpolar front is set by a balance between the rate at which potential energy is created by mechanical and buoyancy forcing and the rate at which it is released by eddies in a rotating cylindrical tank the combined action of mechanical and buoyancy forcing builds a stratification creating a large scale front at equilibrium the depth of penetration and strength of the current are then determined by the balance between eddy transport and sources and sinks associated with imposed patterns of ekman pumping and buoyancy fluxes it is found that the depth of penetration and transport of the front scale like l and wel2 respectively where fw g9 e we is the ekman pumping g9 is the reduced gravity across the front f is the coriolis parameter and l is the width scale of the front last the implications of this study for understanding those processes that set the stratification and transport of the antarctic circumpolar current acc are discussed if the laboratory results scale up to the acc they suggest a maximum thermocline depth of approximately h 5 2 km a zonal current velocity of 4 6 cm s 21 and a transport t 5 150 sv 1 sv 106 m3 s 21 not dissimilar to what is observed

the alteration of sparry calcite crystals in a vadose setting grand cayman island calcite crystals that cement the dolostone clasts in a karst breccia from grand cayman island have been substantially altered as a result of infestation by algae and or fungi as well as etching that may or may not be related to organic activity the features produced include 1 borings 2 constructive micrite envelopes 3 spiky calcite 4 almond shaped etch pits 5 crystal surfaces with a blocky topography and 6 etched crystal surfaces that suggest some of the crystals may have grown by spiral growth spar calcite crystals in a vadose setting can be subjected to complex chemical and physical processes that are commonly mediated by algae and or fungi these microorganisms are capable of removing caco3 from substrates via dissolution transporting that caco3 elsewhere and then directly or indirectly causing its reprecipitation during the calcification of their filaments and or the formation of the constructive micrite envelopes the extensive alteration of calcite cements in the karst brecci

howe lake a hydrodynamic blowout structure howe lake formerly called goudie lake is an unusual feature of southeast saskatchewan almost perfectly circular diameter 295 m it is much deeper 26 m than almost any other prairie lake i

satellite images of upwellings and cold filament dynamics as transient effects of violent air sea interactions downstream from the island of sardinia western mediterranean sea a systematic analysis of thermal satellite images of upwellings and cold filament dynamics downstream from the island of sardinia western mediterranean sea covering the years 1984 1985 1989 1990 1993 and 1994 is discussed for this sea the main transient atmospheric forcing comes from bursts of the mistral a north western wind which downstream from sardinia affects a rather calm basin the tyrrhenian sea in early summer particularly clear effects of atmospheric forcings such as gyres upwellings and cold filaments can be observed our analysis provides not only a systematic insight into these phenomena but also some experimental evidence of a novel mechanism of cold filament formation and evolution indeed in july 1989 a nice set of satellite images shows a cold filament rooted to the shallowest part of the wide shelf off olbia which meanders offshore for a few days under the effect of the mistral and of the general circulation it is of interest to underline how stably the filament is rooted to the shelf so that in only one image it appears as an elongated straight segment also the filament s potential vorticity is discussed in order to gain some insight into shelf water fluxes detachment depths and velocities relative to such phenomena

the role of nearshore slope on cross shore surface transport during a coastal upwelling event in gulf of finland baltic sea abstract the wind induced coastal upwelling process often contains a mid phase that involves coherent long living cross shore surface jets of cooler water these jets extend to 40 45 km from the coast and tend to start from particular coastal locations we develop a simple method for evaluating the depth in the water column from where the upwelled water originates we also test the hypothesis that the development of cross shore surface jets may be triggered by some permanent characteristics such as the bathymetry or the slope of the nearshore seabed the analysis is performed for a strong and well documented upwelling in the gulf of finland the baltic sea using high resolution bathymetry data satellite derived sea surface temperature surface currents measured by in situ drifters and properties of water masses in two sampling locations the results indicate that the cross shore jets originate exclusively from the shore sections with much steeper slopes 0 0075 than in the rest of the study area the cooler water most likely origins from intermediate water masses at depths between 15 and 30 m the resulting identification of the source depth of the upwelled water and its spatial location assists in understanding the flux of nutrients during upwelling events and their link to the onset of cyanobacteria blooms

biogeological signatures of microboring cyanobacterial communities in marine carbonates from cabo rojo puerto rico abstract the occurrence of carbonate boring organisms in marine and continental environments is well known and accounts for substantial rates of sediment and sedimentary rock reworking at the geological scale many case studies have documented the importance of cyanobacteria in near surface environments but nearly all have relied upon morphological descriptions in this study we applied a polyphasic approach to evaluate euendolithic cyanobacterial assemblages from a variety of carbonaceous marine substrates using electron microscopy cultivation and molecular genetic techniques the limitations and biases of the different methods became evident none could be deemed optimal and each failed to detect much or some of the extant diversity in the samples in general sem tended to underestimate the diversity of morphologically simple community members and cultivation yielded a very biased view of the community all approaches however congruently detected differences in community structure between soft substrates and hard substrates with the latter displaying communities of higher complexity in spite of these differences the geological and sedimentary imprints of the boring community exemplified in the formation of well structured micritic envelopes of re worked carbonate were uniform throughout the samples implying that the mechanism of action is common and most likely universal our results speak for the merits of a multidisciplinary approach and provide cautionary implications for paleoenvironmental reconstructions

belemnite taphonomy upper jurassic western tethys part i biostratinomy abstract a detailed taphonomic analysis was performed on 188 belemnites and 56 thin sections from the pozo canada section external prebetic as well as 101 belemnites and 31 thin sections from the rio segura internal prebetic both from the upper oxfordian lower kimmeridgian this manuscript is focused on biostratinomic features and a second part is focused on fossildiagenetic aspects the belemnites correspond to hibolithes and less commonly belemnopsis biostratinomic features including size fragmentation corrasion microboring and encrustation were analysed in each specimen using petrographic conventional cathodoluminescence epifluorescence and scanning electron microscopy techniques fragmentation affects the phragmocone and the rostrum cavum and is usually transversal and rarely longitudinal through the apical line isolated fragments of epirostrum are common corrasion produces irregular surfaces microborings are very common represented by a fungal hyphae b fascichnus dactilus like and scolecia filosa like borings cyanobacteria c entobia sponges d large microborings with y shaped branching diameter 100 500 m subparallel to rostrum surface e large cylindrical to ellipsoidal borings related to cirripeds and f palaeconchocelis starmachii rhodophyte microbes and sessile foraminifera vinelloidea bullopora tolypammina thurammina placopsilina and subdelloidina are the main encrusters microbial films are composed of dense micrite or clotted peloidal microfabrics the biostratinomic features analysed in the belemnite rostra are clearly influenced by the lithofacies and shelf setting the intensity of corrasion microborings and encrustation by indicating time exposure help establish which lithofacies shows the highest sedimentation rate the belemnites from internal prebetic lithofacies that is the outer shelf deposits lumpy limestone and lumpy oncolitic limestone present high values of corrasion microboring and encrustation thereby indicating long time exposure in sharp contrast belemnites from the lithofacies of the external prebetic represent deposition in mid shelf environments spongiolithic limestone spongiolithic marl peloidal limestone and marl limestone rhythmite featuring higher clay content

assessing subsidence rates and paleo water depths for tahiti reefs using u th chronology of altered corals we present uranium thorium chronology fora 102 m core through a pleistocene reef at tahiti french polynesia sampled during iodp expedition 310 tahiti sea level we employ total and partial dissolution procedures on the older coral samples to investigate the diagenetic overprint of the uranium thorium system although alteration of the u th system cannot be robustly corrected diagenetic trends in the u th data combined with sea level and subsidence constraints for the growth of the corals enables the age of critical samples to be constrained to marine isotope stage 9 we use the ages of the corals together with o based sea level histories to provide maximum constraints on possible paleo water depths these depth constraints are then compared to independent depth estimates based on algal and foraminiferal assemblages microbioerosion patterns and sedimentary facies confirming the accuracy of these paleo water depth estimates we also use the fact that corals could not have grown above sea level to place a maximum constraint on the subsidence rate of tahiti to be 0 39 m ka with the most likely rate being close to the existing minimum estimate of 0 25 m ka

stratigraphy and structure of pleistocene collapse in the regina low saskatchewan canada the regina low is a collapse structure formed as a result of dissolution of salt from the middle devonian prairie evaporite formation in this study collapse has affected the upper cretaceous pierre shale and the ardkenneth and snakebite members of the bearpaw formation of the montana group the mennon dundurn and warman formations of the sutherland group and the floral and battleford formations of the saskatoon group a structural closure of 125 175 m approximates the thickness of the middle devonian prairie evaporite formation in the early pleistocene about 54 m of collapse took place in eastern regina accounting for the preservation of snakebite member major collapses of about 58 and 86 m took place in northern regina during deposition of middle pleistocene pre illinoian dundurn formation the final major collapse of about 127 m took place in northeastern regina between deposition of the lower and upper tills of the floral formation eighty seven metres of this collapse took place during depos

microendolithic structures from the fort payne formation lower mississippian kentucky and tennessee implications for the paleoenvironment of carbonate mud mounds abstract resin cast embedment and naturally occurring internal molds have revealed an assemblage of microendoliths from the lower mississippian fort payne formation microendoliths produced by the heterotrophs orthogonum lineare orthogonum giganteum and saccomorpha clava dominate this unit as well as the phototroph produced traces ichnoreticulina elegans and fascichnus dactylus a chlorophyte ostreobium quekettii and cyanobacterium hyella caespitosa respectively they were found within a variety of fossil substrates including solitary corals bryozoans brachiopods and gastropods with a notable absence in all trilobites and echinoderms the fort payne from the lake cumberland dale hollow region of southern kentucky northern tennessee contains a suite of fossiliferous green shale deposits with isolated locations of enigmatic carbonate mud mounds the latter commonly referred to as waulsortian mounds in other geographical areas have been the center of much speculation in the past few decades and the paleoenvironmental parameters behind their formation remain controversial using the aforementioned microendoliths a sense of the light availability within the illinois basin can be determined the assemblage of ichnotaxa uncovered is representative of light conditions spanning from dysphotic to aphotic using previously constrained depth parameters that indicate a depth of no more than 100 m a dysphotic environment suggests that the water column was eutrophic presumably due to high productivity within the illinois basin this would seem to corroborate several other inferences about the early mississippian including the growing number of suspension feeding echinoderms the restructuring of phytoplanktonic communities and increased nutrient flux from a developing terrigenous floral weathering regime in the early mississippian

an offshore eddy in the california current system part i interior dynamics abstract from january 9 to 17 1981 detailed observations of the horizontal and vertical structure beneath one of the quasi permanent semi stationary mesoscale offshore eddy signatures in the california current system ccs discussed by bernstein breaker and whritner 1977 burkov and pavlova 1980 and simpson 1982 were made the vertical sections of temperature and density show the presence of three layer system a subsurface warm core eddy whose diameter is about 150 km at the 7 c isotherm is the dominant feature a warm surface layer which extends to a depth of 75 m lies over the eddy between the warm surface layer and the subsurface warm core eddy there is a cold core region which extends to a depth of about 200 m there is a high degree of symmetry about the vertical axis of rotation vertical sections of salinity and dissolved oxygen are entirely different from sections of temperature and density diagrams of water mass characteristics confirm that the core of the eddy found between 250 600 m consists of inshore water from the california undercurrent cu below about 700 m local waters from the deep poleward flow dpf have been incorporated into the eddy the observed distributions of properties t s o 2 are inconsistent with a single local generation process for the eddy system radial distributions of angular velocity normalized gradient velocity and relative vorticity support the use of a gaussian radial height field as an initial condition in eddy models possible reasons why ccs eddies may differ dynamically from gulf stream rings are given in the text at the time the observations were made the system as a whole was in near geostrophic balance local geostrophic balance however cannot explain the observed distribution of properties and structure the observed symmetry in the structure of the eddy system chemical evidence simpson 1984 biological distributions haury 1984 and satellite images of the cc koblinsky simpson and dickey 1984 suggest that lateral entrainment of warm oceanic and cold coastal water into the upper two layers of the three layer system by the subsurface eddy is a likely generation mechanism for the cold core region the coastal origin of the frontal structure along the northeastern quadrant and the oceanic origin of the frontal structure along the southwestern quadrant of the eddy system further support lateral entrainment as a generation mechanism for the cold core this entrainment makes the ccs eddy system different from cold core rings in the gulf stream and rather similar to some warm core eddies found in the east australian current the presence of cu water in the core of this eddy raises the question of how cu water was transported from the continental slope eddy generation mechanisms other than baroclinic instability of the cc may be required to explain the distribution persistence and core composition of offshore mesoscale eddies in the ccs there is evidence that barotropic in addition to baroclinic processes may be important

secondary rock structures and the regional hydrogeology of claystone rich cretaceous strata williston basin saskatchewan canada the geometry and spatial distribution of a polygonal fault system pfs and collapse features within cretaceous strata predominantly mudstones and claystones were investigated using three high resolution three dimensional seismic datasets of the williston basin saskatchewan canada mapping of the planform geometry and fault throw distributions throw depth t z profiling shows that the pfs present in the colorado group and pierre fm has a vertical extent of 200 330 m variation in the lateral planform geometry is attributed to the relative rates of stress accumulation during early development of the planar faults and is constrained using sequence stratigraphic principles the mean fault dip is 60 12 number of measurements n 225 the t z profiles appear as partial c type profiles demonstrating that at least half of the total height of the pfs was removed during post cretaceous erosion the presence of polygonal faults in equivalent strata of the western interior sedimentary basin wisb sug

impacts of light penetration on the bathymetry of reef microboring communities implications for the development of microendolithic trace assemblages abstract sediment samples recovered from three proximate reef environments in north jamaica characterised by different light penetration regimes reveal marked variations in the bathymetric range of sediment microboring communities in contrast to clear water environments assemblages developed in turbid water conditions undergo both bathymetric restriction and compression in their range in clear water sites the upper photic lower photic zone transition occurs between depths of 20 30 m this is marked by a shift from a predominance of cyanobacterial e g eurygonum nodosum scolecia filosa fasciculus frutex and fasciculus dactylus and chlorophyte e g rhopalia catenata fasciculus grandis reticulina elegans and scolecia botulifera traces to assemblages dominated by the traces e nodosum and s filosa cyanobacteria f grandis chlorophyte palaeoconchocelis starmarchii rhodophyte and orthogonum fusiferum and saccomorpha sphaerula fungi at sites characterised by intermediate levels of turbidity this same assemblage transition occurs at around 15 20 m depth and at the most turbid site at depths of only 5 10 m integration of assemblage data and light readings indicates that this transition occurs where percentages of surface light illumination are reduced to around 10 15 compression of the lower photic zone is so extreme at the most turbid site that microboring assemblages at only 30 m depth show evidence of a transition to an assemblage associated with dysphotic

possible sources driving the potential vorticity structure and long wave instability of coastal upwelling and downwelling currents it is well known that upwelling and downwelling currents are unstable to perturbations less is however known about the physical mechanism responsible for the observed and modeled instabilities it is shown that the origin of the long wave barotropic baroclinic instability observed on upwelling currents has to be sought among diabatic or thermobaric mechanisms in particular the role of mixing associated with kelvin helmholtz instability and of wind forcing is investigated low richardson numbers occur when the pycnocline outcrops at the sea surface the criterion for instability ri 1 4 can be reached in a narrow region close to the upwelling front permitting kelvin helmholtz instability and mixing this can precondition the current for long wave instability by transforming the current s potential vorticity a constant wind can likewise modify the potential vorticity the resulting potential vorticity anomaly is always negative for both upwelling and downwelling currents and this anomaly interacts with the outcropped front destabilizing it examples are provided via numerical calculations using an idealized front a wind stress is an effective means of inducing the negative pv necessary for instability with wind kelvin helmholz instability when present merely modifies the instability characteristics in addition upwelling fronts are always less stable than comparable downwelling fronts

regional hydrogeochemistry of the carbonate rock aquifer southern manitoba middle ordovician to middle devonian carbonates in the manitoba lowlands form an extensive aquifer system along the eastern edge of the williston basin the aquifer is divided into fresh and saline portions by a series of topographic lows defined by major river systems and lakes that create a north south trending hydraulic divide east of this divide ca mg hco3 fresh waters are derived by active modern day recharge focused in the sandilands and interlake regions stable isotope and geochemical data indicate that na cl saline waters west of the divide are a mixture of original basin brines and glacial melt water pushed into the basin during pleistocene glaciation high na cl and cl br ratios are consistent with significant salt dissolution by glacial melt water

shallow faults upper cretaceous clinoforms and the colonsay collapse saskatchewan reflection seismic data in the vicinity of the colonsay potash mine near saskatoon saskatchewan reveal numerous shallow normal faults with vertical displacements of as much as 25 m the faults cut the glacial deposits and upper cretaceous rocks to a maximum depth of about 400 m horizontal length ranges from a few hundred to a few thousand metres similar faults are also exposed in several widely separated open pit coal mines of southern saskatchewan and may be common elsewhere in the prairies such faulting is considered to be a result of tertiary to quaternary extensional tectonics and may have been aided in this region by the melting of gas hydrates the study area includes the east flank of the colonsay collapse a subsidence structure caused by dissolution and removal of salt in the 200 m thick devonian prairie evaporite formation salt was removed in two stages prior to or during early glacial time and in late glacial time subsidence was gradual with no observable faulting a complex of clinofor

numerical simulation of coastal upwelling and inerfacial instability of a rotaion and stratified fluid the evolution of the coastal upwelling and interfacial instability of a stratified and rotating fluid is studied numerically by using large eddy simulation upwelling is generated near the sidewall of a rotating annulus by the shear at the top the fluid initially consists of a stably stratified two layer structure with a narrow interface separating the two layers the large scale motion of the flow is simulated by solving the time dependent non hydrostatic incompressible navier stokes and scalar transport equations while the small scale motion is represented by a dynamic subgrid scale model the upwelling process contains both stable and unstable stratification the vertical structure of upwelling consists of a persistent primary front a trailing mixing zone on the shore side of the front and a temporary secondary front which leads a top inversion layer the longshore velocity profile has two maxima which occur at the edge of the sidewall boundary layer and at the density front the upwelled density front is unstable to azimuthal perturbations and baroclinic waves develop and grow to large amplitude pairs of cyclonic and anticyclonic waves appear at the front which form jet streams the secondary front is unstable to azimuthal perturbations its instability and the associated drop of the top inversion layer take the form of radial bands which subsequently break up into isolated patches and eventually sink the computed values of various upwelling time and length scales are compared to and are in good agreement with past experimental data

stratigraphy and structure of a late wisconsinan salt collapse in the saskatoon low south of saskatoon saskatchewan canada an update the saskatoon low is a collapse structure that formed as a result of dissolution of salt from the middle devonian prairie evaporite formation in this study the collapse has affected the upper cretaceous lea park judith river and bearpaw formations of the montana group the early and middle pleistocene mennon dundurn and warman formations of the sutherland group and the late pleistocene floral battleford and haultain formations of the saskatoon group locally the collapse is about 180 m which is about equal to the thickness of the salt the first phase of collapse took place after deposition of the ardkenneth member of the bearpaw formation and before glaciation or during a pre illinoian glaciation the second phase of collapse occurred during the battleford glaciation late wisconsinan prior to deposition of the battleford formation the saskatoon low was glacially eroded removing the sutherland group and the floral formation after the glacial erosion up to 110 m of soft till of the battle

microborings in early cambrian phosphatic and phosphatized fossils abstract a small proportion of phosphatic and phosphatized fossils mostly microfossils extracted from lower cambrian qiongzhusian lime mudstones of deeper water aspect belonging to the yu anshan and shuijingtuo formations of south china is perforated by microborings these microborings are present in bradoriid and phosphatocopine arthropod carapaces lingulid brachiopod valves microdictyon plates and tommotiid sclerites their absence in co occurring phosphatized eodiscid trilobite exoskeletons and palaeoscolecid worm trunk fragments indicates a substrate specificity that suggests the boring microorganism was heterotrophic extracting particular residual organic compounds present in only certain bioclast types microborings occur as meandering tunnels and grooves on bioclast surfaces and most are 10 20 m wide and circular in cross section the euendoliths were thus able to live partly exposed as well as within the substrate tunnel and groove walls bear a distinct longitudinal sculpture of straight striae separated by cuspate ridges 1 2 m apart that parallel the microboring never twisting the microborings accord with the ichnotaxon microptychoites fuquanensis dong in dong et al dong y ji q wang s 1984 the discovery of microscopic trace fossils in the sinian doushantuo formation in southwestern china scientia geologica sinica 346 347 in chinese the fluted sculpture appears to have no modern analogue but may have arisen by localized secretions at the tip of a bundle of filaments this kind of microboring had been previously reported from phosphatic substrates of ediacaran earliest cambrian middle cambrian and probably early devonian age but appears to have no recent counterpart

reversal of the regional scale flow system of the williston basin in response to pleistocene glaciation low 18o values of formation waters collapse structures related to salt dissolution hydrodynamic blowout structures and biodegradation of oils all suggest a significant influx of fresh water into the williston basin along the outcrop belt in southern and central manitoba during pleistocene glaciation the thickness of the continental ice sheet over manitoba would have provided sufficient potentiometric drive to reverse the regional scale flow system of the williston basin the dynamic nature of the flow system suggests that modern day pressure distributions may not be good proxies for ancient petroleum migration pathways as is commonly assumed

geochemical modeling of the madison aquifer in parts of montana wyoming and south dakota stable isotope data for dissolved carbonate sulfate and sulfide are combined with water compo sition data to construct geochemical reaction models along eight flow paths in the madison aquifer in parts of wyoming montana and south dakota the sulfur isotope data are treated as an isotope dilution problem whereas the carbon isotope data are treated as rayleigh distillations all reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the madison limestone the geochemical reaction models indicate that the dominant groundwater reaction in the madison aquifer is dedolomitization calcite precipita tion and dolomite dissolution driven by anhydrite dissolution sulfate reduction ca mg2 ina cation exchange and halite dissolution are locally important particularly in central montana the groundwater system is treated as closed to c02 gas from external sources such as the soil zone or cross formational leakage but open to c02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer the computed mineral mass transfers and modeled sulfur isotopic composition of madison anhydrites are mapped throughout the study area carbon 14 groundwater ages adjusted for the modeled carbon mass transfer range from modem to about 23 000 years b p and indicate flow velocities of 7 7 ftlyr 2 1 26 5 rnlyr most horizontal hydraulic conductivities calculated from darcy s law using the average 14 c flow velocities are within a factor of 5 of those based on digital simulation the calculated mineral mass transfer and adjusted 14 c groundwater ages permit determination of apparent rates of reaction in the aquifer the apparent rate of organic matter oxidation is typically 0 12 jlidol uyr sulfate and to a lesser extent ferric iron are the predominant electron acceptors the kinetic biochemical fractionation of 34 s between sulfate and hydrogen sulfide is approximately 44 o at 25 c with a temperature variation of

two layer model of shear driven coastal upwelling in the presence of bottom topography a stratified two layer fluid is brought to solid body counterclockwise rotation inside a cylindrical tank having a conical bottom with a radial topographic ridge a stress is then applied to the top surface by means of a clockwise differentially rotating disk the resulting ekman layer flux causes the top layer to spin down and the interface to rise near the wall and to descend a t the centre of the tank as this process continues the interface front between the two layers intersects the disk surface and after that migrates away from the wall and allows the bottom fluid to contact the disk directly the migration of the front continues until a steady state is reached the front becomes stationary and the system is in geostrophic balance the first sign of upwelled flow at the surface always occurs as a high speed jet like plume at the bottom topography and only at a later time does a uniform upwelled flow appear a t the surface upstream of the topography this plume which always forms near the downstream edge of the topography migrates in advance of the upstream front to produce an upwelling maximum at the bottom topography the final width of the upstream flow in steady state conditions is estimated by a simple theoretical model which is in good agreement with the experimental results we have an experimental criterion to predict the occurrence of travelling baroclinic waves on the upstream front on the downstream side of the ridge large standing waves are observed with significant upwelling within them under some circumstances cyclones pinch off from the upstream front the plume on the ridge and the crests of the large downstream standing waves we present criteria to predict the occurrence of these pinch off processes

basin scale wind forced dynamics of the seasonal southern south china sea gyre 1 using observed wind forcing the seasonal development and disappearance of the near surface anticyclonic gyre in the southern south china sea is modeled along with associated dynamic features forced by monsoon winds the ocean circulation in the south china sea alternates between a single cyclonic gyre during the winter northeast monsoon and a double gyre cyclonic anticyclonic in the northern southern south china sea during the summer southwest monsoon reversing the western boundary current along vietnam with each shift of the monsoon regime during the summer southwest monsoon the poleward western boundary current converges with the equatorward western boundary current of the northern gyre turning offshore to create an eastward jet and flanking dipole recirculation near 13 n the development and timing of the eastward jet and recirculations are consistent with large scale basin dynamics the subsequent transition to the winter northeast monsoon regime destroys the recirculation cells and eastward jet employing high resolution 1 5 layer and 2 0 layer numerical models we demonstrate the applicability of large scale dynamics to the deeper central basin of the south china sea specifically showing that the gyre scale circulation governs the development of the eastward jet and dipole recirculations the destruction of the recirculations by the monsoon winds each autumn is also modeled this effort highlights the dominance of monsoon wind forcing in the south china sea s basin scale dynamics

the growth and propagation of synsedimentary faults abstract offset of each syn fault horizon across a synsedimentary i e growth fault records the throw subsequent to its deposition allowing successive growth stages of a fault to be determined this technique has been applied to synsedimentary faults mapped on 3d seismic datasets to distinguish between faults which propagated laterally during growth faults which did not propagate laterally for significant growth periods and faults in which the lateral dimensions of the active surface decreased during their growth these different fault tip line behaviours result in characteristic lateral and dip parallel fault displacement variations fault propagation rates have been measured for 10 fault tips the maximum propagation rate is 15 km my for gravity driven faults and 3 km my for tectonically driven faults rates of fault propagation decrease with elapsed time from the initiation of faulting with tip line stasis and retreat becoming dominant in the later stages of fault growth static and retreating lateral tip lines are associated with overlap of the fault strain field with that of a neighbouring fault most often with the formation of a fault relay zone

microborer ichnocoenoses in quaternary corals from new caledonia reconstructions of paleo water depths and reef growth strategies in relation to environmental changes abstract coral reef growth and development depend on several environmental factors including tectonic and climatic parameters and local ecological drivers reef growth is especially sensitive to sea level variations paleo water depth reconstructions are essential tools used to determine reef growth patterns during different periods of reef growth assemblages of corals and or coralline algae have been commonly used in such paleodepth reconstructions this study shows that using microendolith ichnocoenoses can sometimes provide better accuracy than traditional coralgal analyses particularly in the depth range 0 10 m where coralgal assemblages usually show broad distribution ranges holocene and pleistocene cores from two barrier reef sites on the west coast of grande terre in new caledonia are examined here holocene reef development at these sites feature examples of microendolith ichnocoenoses that document rapid environmental changes and small sea level variations of about 2 5 m in amplitude and record these changes with more accuracy than coral and coralline algae assemblages which are highly dependant on the hydrodynamic energy of the setting during the pleistocene which was less chronologically constrained the microendolith ichnocoenoses also reflect paleo water depths and reef growth patterns at different periods of reef history

natural tracer profiles across argillaceous formations argillaceous formations generally act as aquitards because of their low hydraulic conductivities this property together with the large retention capacity of clays for cationic contaminants has brought argillaceous formations into focus as potential host rocks for the geological disposal of radioactive and other waste in several countries programmes are under way to characterise the detailed transport properties of such formations at depth in this context the interpretation of profiles of natural tracers in pore waters across the formations can give valuable information about the large scale and long term transport behaviour of these formations here tracer profile data obtained by various methods of pore water extraction for nine sites in central europe are compiled data at each site comprise some or all of the conservative tracers anions cl br water isotopes delta 18 o delta 2 h and noble gases mainly he based on a careful evaluation of the palaeo hydrogeological evolution at each site model scenarios are derived for initial and boundary pore water compositions and an attempt is made to numerically reproduce the observed tracer distributions in a consistent way for all tracers and sites using transport parameters derived from laboratory or in situ tests the comprehensive results from this project have been reported in mazurek et al 2009 here the results for three sites are presented in detail but the conclusions are based on model interpretations of the entire data set in essentially all cases the shapes of the profiles can be explained by diffusion acting as the dominant transport process over periods of several thousands to several millions of years and at the length scales of the profiles transport by advection has a negligible influence on the observed profiles at most sites as can be shown by estimating the maximum advection velocities that still give acceptable fits of the model with the data the advantages and disadvantages of different conservative tracers are also assessed the anion cl is well suited as a natural tracer in aquitards because its concentration varies considerably in environmental waters it can easily be measured although the uncertainty regarding the fraction of the pore space that is accessible to anions in clays remains an issue the stable water isotopes are also well suited but they are more difficult to measure and their values generally exhibit a smaller relative range of variation chlorine isotopes delta 37 cl and he are more difficult to interpret because initial and boundary conditions cannot easily be constrained by independent evidence it is also shown that the existence of perturbing events such as the activation of aquifers due to uplift and erosion leading to relatively sharp changes of boundary conditions can be considered as a pre requisite to obtain well interpretable tracer signatures on the other hand gradual changes of boundary conditions are more difficult to parameterise and so may preclude a clear interpretation

oceanic variability off the central california coast abstract mesoscale variability off the central california coast is strongly influenced by coastal upwelling and related processes off point sur there is significant space time variability in oceanic properties over periods of days and distances of several tens of km however the internal density field averaged over space ca 120km alongshore and time ca 18 days reveals the expected characteristics of a coastal upwelling regime including an equatorward surface jet 25km to 40km offshore and weaker poleward flow below 150m and within 20km of the coast upper ocean circulation is strongly influenced by the bathymetry offshore to water depths of at least 1000m based on repeated horizontal grids of oceanographic stations horizontal correlation scales for temperature are of the order of 30km in the upper 100m hence a horizontal sampling rate of ca 10km is desirable vertical correlation scales for temperature are of the order of 100m hence a vertical sampling rate of ca 10m is desirable similarly there are indications of a temporal correlation scale of a few weeks hence a temporal sampling rate of ca a few days is desirable empirical orthogonal functions eofs in the cross shore vertical plane suggest the influence of coastally trapped motions within 40km of the coast with an intense alongshore near surface transient coastal jet located ca 20km offshore sudden spring transitions to coastal upwelling conditions are often pronounced in coastal temperature records and they may precede the offshore migration of the major upwelling front by at least a month or more the spring transitions occur over a period of about a week in 1980 the spring transition propagated poleward along the california coast at a speed of ca 64km d 1 during spring and summer movement of a coastal upwelling front often located between 15km and 50km offshore is a major contributor to cross shore variability the upwelling front meanders with an alongshore scale of about 80km a time scale of 30 to 40 days and an amplitude scale of 10km rms based on satellite infrared ir imagery the along shore mean position of the major upwelling front migrates offshore during spring and summer offshore displacement of the front may be caused by ekman transport over periods of days to weeks and by rossby wave dispersion over longer periods during summer a time dependent offshore scale based on rossby wave dynamics was more appropriate than the baroclinic rossby radius every three to four years during 1971 through 1984 el nino episodes produced interannual variability in coastal sea surface temperature sst off central california most of the warming occured during fall and winter el nino episodes were often followed by major spring transitions the recent 1982 1983 episode was 2 to 3 c warmer than the three previous episodes over the past 14 years and its influence lasted almost twice as long

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

3d seismic characterisation of an array of blind normal faults in the levant basin eastern mediterranean the geometry throw distribution and kinematics of an array of blind normal faults were investigated using a high resolution 3d seismic dataset located in the levant basin offshore israel to establish criteria allowing true blind faults to be distinguished from minor synsedimentary faults a detailed analysis of throw distribution on the fault planes shows that the displacement exhibits a crudely concentric pattern about a maximum region located centrally on a fault plane as expected for ideal blind faults however vertical displacement profiles do not exhibit classical linear or triangular profiles but are mostly flat topped or hybrid in type comparison of unrestricted blind faults to those that interacted with a mechanical boundary or another structure suggests that such interactions significantly modify the throw spatial distribution on a fault plane to distinguish small synsedimentary faults from blind faults we use a combination of three criteria to assess whether a fault grew by blind propagation 1 plunging upper tip region and complementary pattern in the throw contours 2 presence of upper tip propagation fold and 3 absence of stratigraphic evidence that the fault interacted with the free surface

grain susceptibility to the effects of microboring implications for the preservation of skeletal carbonates the boring activity of microendolithic organisms such as cyanobacteria chlorophytes rhodophytes and fungi represents a major destructive process affecting sediment preservation within reef environments this study demonstrates the presence of two distinct assemblages of microborers within sediments collected from the fringing reefs of north jamaica correlating to the upper 18 m depth photic zones the upper photic zone assemblage is dominated by cyanobacteria and chlorophytes whilst rhodophytes and fungi become more abundant with increasing water depth most significant from a grain preservation perspective is the variable nature of grain infestation observed between different reef sites and different carbonate grain types the highest degree of grain infestation occurs within shallow low energy back reef environments and the most susceptible grains at all sites are corals molluscs and foraminifera coralline algae halimeda and echinoid fragments are rarely heavily infested high rates of infestation at back reef sites result in rapid diminution of the most susceptible grains especially coral which are either underrepresented or contribute only to the finer sediment fractions in the subsurface fore reef grain assemblages undergo relatively little alteration microboring therefore has potential to bias the fossil record by removing the most susceptible skeletal grains the impact of microboring upon back reef grain assemblages must be considered when attempting to model depositional processes within both modern and ancient reef environments

temporal shifts in reef lagoon sediment composition discovery bay jamaica discovery bay north jamaica forms a large 1 5 km wide deep up to 56 m embayment that acts as a sink for reef derived and lagoonal carbonate sediments since the mid 1960s the bay has also provided a sink for inputs of bauxite sediment that are spilled during loading at a boat terminal constructed within discovery bay bauxite has accumulated across much of the southern section of the bay with surficial sediments presently composed of up to 35 weight non carbonate cores recovered from sites on the western side of the bay provide a stratigraphic record of this history of bauxite contamination across water depths from 5 to 25 m the bauxite influenced upper sediment horizons are clearly visible in each core from the distinctive redebrown colouration of the sediment these sediments are composed of approximately 10 noncarbonate bauxite and have fe contents of around 2e3000 mg g up to 7000 mg g the thickness of this upper bauxite contaminated sequence increases down transect approximately 18 cm in the shallowest core to around 47 cm in the deepest core and in each core overlies a sequence of clean lagoon carbonates these typically are poorly sorted carbonate sands with variable amounts of coral rubble down core data on caco3 and fe content provide a chemical record of decreasing sediment contamination with depth with the lower clean carbonates composed of only around 2 non carbonate and 700 mg g fe down core sediment constituent data also indicate significant changes in sediment production at the shallowest sites at depths of 5 and 10 m sediment assemblages have shifted from diverse assemblages of coral mollusc amphiroa and halimeda in the clean lagoon sands to assemblages dominated by halimeda and amphiroa within the surficial sediments at the deeper sites no major down core shifts in sediment constituents occur these sites thus record a rather complex history of changes in sediment composition and chemistry clear shifts in chemistry and stratigraphy occur in all the cores and reflect progressive bauxite contamination in the near surface horizons these inputs however do not appear to have directly affected carbonate production since the major constituent changes appear to be a response to more regional declines in coral community and reef status 2005 elsevier ltd all rights reserved

rate of dissolution of carbonate sediments by microboring organisms davies reef australia abstract skeletal carbonate sediments on the lagoon floor of davies reef great barrier reef australia are subject to intense attack by microboring organisms principally algae the rate at which this microboring process dissolves carbonate was measured experimentally fresh unbored molluscan sand samples placed in the shallow lagoon 5 m water depth experienced a weight loss of about 0 9 g 30 g sample or 3 in one year due to dissolution of carbonate by microborers revealed by direct measurement of weight change and point count analysis this figure may be converted to about 350 g caco3 dissolved m2 lagoon floor year which is equivalent to between 18 and 30 of the sediment influx rate to this lagoon averaged over the past 9 000 years consideration of the exp rimental design suggests that the experiment underestimated the true rate of microboring in lagoon floor sediments we conclude that the extent of microboring in carbonate sands may provide information on the rate of sediment deposition and that dissolution of carbonate sediments by microborers is a significant factor in whole reef caco3 budgets

paleohydrogeology of the cretaceous sediments of the williston basin using stable isotopes of water 1 hydraulic and isotopic data collected from aquifers are routinely used to characterize hydrogeological conditions within sedimentary basins but similar data from confining units are generally not collected despite their ability to provide insights on important water solute transport controls we characterized paleogroundwater flow and solute transport mechanisms across 384 m of cretaceous shale aquitard in the williston basin canada using high resolution depth profiles of water isotopes 18o 2h water samples were also collected from wells installed in the underlying regional sandy aquifer mannville fm 93 m thick and from seepage inflows into potash mine shafts to 825 m below ground the 1 d numerical transport modeling of 18o profiles provided insight into large scale long term solute transport in both cretaceous sediments and the basin despite the potential for significant advective migration during glaciations molecular diffusion appears to be the dominant solute transport mechanism through the aquitard simulations suggest average vertical groundwater velocities of 0 05 m 10 ka and an average excess hydraulic head of 10 m these values are much less than anticipated by successive glaciations the dominant paleoevent reflected in present day profiles is introduction during the pleistocene of glaciogenic meteoric water to the aquifer underlying the shale likely along an aquifer outcrop area east of the site or through local vertical conduits simulations suggest these recharge events occurred during one or more glacial periods the isotopic profile over the upper 25 m of pleistocene till and shale is consistent with glacial deposition and transport processes within these units over the holocene past 10 ka

scleractinian assemblages under sediment input their characteristics and relation to the nutrient input concept abstract in the geological record scleractinian dominated turbid water bioconstructions that accumulated under substantial terrigenous input along with shallow neritic marls rich in well preserved corals are common these occurrences indicate that beyond some threshold the ecologic and taphonomic effects of sedimentation prevail over the effects of nutrification field data and experiments on recent corals show that some taxa cope well with terrigenous turbidity and sedimentation and acclimate to increased heterotrophy colonial corals resilient to sediment input commonly are massive to platy forms of high skeletal plasticity and with large polypars to effectively reject sediment or are branched species providing a very small sedimentation area cleaned by feeble currents or small polyped massive taxa that tolerate intermittent veneering by sediment these corals may comprise siltation assemblages of recent turbid water reefs and level bottoms in siliciclastic environments conversely excess input of even low amounts of dissolved inorganic nutrients into clear waters adversely affects many coral species fossil turbid water bioconstructions twb were situated in inner shelf to shore zone settings or near storm wave base on shelves or ramps did not stack into reef complexes mostly show a cluster to segment fabric are scarce in or devoid of frame pores with marine cement and lacked a high carbonate slope relative to fossil clear water buildups preserved in pure limestone successions fossil twb contain moderately diverse coral assemblages with an increased proportion of sediment resistant forms aside from coral behaviour that is elusive in fossils the sediment resistance of corals was mainly determined by colony shape and polypar size but small polyped sediment tolerant corals became common since the early cretaceous late jurassic to cretaceous turbid water coral assemblages are dominated by plocoid or thamnasterioid forms corresponding cainozoic assemblages consist mainly of cerioid and plocoid taxa in fossil twb bioerosion and encrustation are similar or higher than in contemporaneous clear water buildups under higher sediment input accumulation of discrete twb was quenched and level bottoms of both corals and soft substrate biota formed in the resulting coral marls depending on turbidity sedimentation and substrate stability the coral fauna consists largely of both solitary corals and mainly sediment resistant pseudocolonial colonial forms or is dominated by solitary corals many corals show growth anomalies resulting from partial mortality due to episodic rapid sedimentation and unstable substrate in coral marl environments because of terrigenous input nutrient levels probably were elevated yet macroboring and encrustation are very scarce beyond some threshold of terrigenous sediment input and accumulation the ecologic and taphonomic effects of sedimentation and unstable substrate prevail over the effects of nutrient enrichment during the meso cainozoic evolution of scleractinians increasing photoautotrophy and progressive invasion of oligotrophic environments is in contrast to a late cretaceous to cainozoic increase in the relative number of reefs in marginal marine siliciclastic settings this trend may be explained by second order sea level fall and shrinking of epicontinental carbonate seas and isolated platforms driving corals to more narrow attached shelves and by a wider total trophic range in which distinct coral assemblages can thrive as a result of coral evolution and diversification

subglacial recharge into the western canada sedimentary basin impact of pleistocene glaciation on basin hydrodynamics brine springs discharging from devonian carbonates of the western canada sedimentary basin have distinct water chemistry from brines in laterally equivalent units deeper in the basin stable isotope data suggest that the brine springs originated as pleistocene meltwater these waters are interpreted to originate as an influx of subglacial meltwater related to a reversal of the basin scale flow system caused by the overriding ice sheet esker distribution shows a notable relationship between shield and sedimentary rocks an integrated sedimentary basin ice sheet model supports the interpretation that high permeability carbonate units acted as preferential subglacial drains that in turn affected esker development the fluid flow history of the western canada sedimentary basin is characterized by back and forth movement through geological time in response to changing boundary conditions modern day flow systems may not then be indicative of historic movement of economic fluids through the basin

growth of normal faults in multilayer sequences a 3d seismic case study from the egersund basin norwegian north sea abstract we investigate the structural style and evolution of a salt influenced extensional fault array in the egersund basin norwegian north sea through analysis of 3d reflection seismic and well data analysis of fault geometry morphology throw distribution and syn kinematic strata reveal an intricate but systematic style of displacement and growth suggesting an evolution of 1 initial syn sedimentary fault growth contemporaneous with salt mobilization initiated during the late triassic 2 cessation of fault activity and burial of the stagnant fault tips and 3 subsequent nucleation of new faults in the cover above contemporaneous salt re mobilization initiated during the late cretaceous with downward propagation and linkage with faults stage 3 was apparently largely controlled by salt mobilization in response to basin inversion as reactivated faults are located where the underlying salt is thick while the non reactivated faults are found where salt is depleted based on the 3d throw analyses we conclude that a combination of basement faulting and salt re mobilization is the driving mechanisms behind fault activation and reactivation even though the sub and supra salt faults are mainly geometrically decoupled through the salt a kinematic coupling must have existed as sub salt faults still affected nucleation and localization of the cover faults

late cretaceous cenomanian to campanian paleoenvironmental history of the eastern canadian margin of the western interior seaway bonebeds and anoxic events abstract upper cretaceous strata in the pasquia hills of the northern manitoba escarpment eastern saskatchewan canada provide a detailed paleoenvironmental and sea level record of the eastern margin of the western interior seaway sediments deposited during the cenomanian turonian greenhorn marine cycle are dominantly black mudstones deposited in a stratified water column with bottom water anoxia recurrently reaching into the photic zone a middle cenomanian sea level lowstand event followed by transgression left a series of bonebeds within the belle fourche member of the ashville formation indicating a sedimentary environment starved of coarse siliciclastics maximum sea level resulted in the formation of limestone beds within the favel formation further favoured by reduced terrigenous sediment input compared to the western margin limestone sedimentation was followed by a phase of increased freshwater input under lower sea level conditions and reducing zoo and phytoplankton diversities during final greenhorn regression eastern saskatchewan probably turned into a restricted basin severely limiting marine circulation poor or absent benthic foraminiferal assemblages and biomarker analysis suggest prevailing watermass stratification throughout the cenomanian turonian transgressive regressive cycle this was caused either by a freshwater lid stratification of boreal and tethyan derived watermasses or both to various intensities affected by changing sea level basin oxygenation during niobrara time varies between localities along the eastern margin as documented by presence absence of benthic and planktic foraminifera

diagenesis and fracturing of a large scale syntectonic carbonate platform abstract the influence of coeval tectonics on carbonate platform development is widely documented yet the diagenesis of such syntectonic platforms is barely evaluated an outcrop petrographic and geochemical study details here for the first time the diagenesis of the tonasa limestone formation developed in an extensional regime in central indonesia this equatorial carbonate system was affected by block faulting tilt block rotation differential uplift and subsidence throughout its eocene to early miocene history wilson 1999 wilson et al 2000 the tonasa carbonate platform is dominated by alteration in shallow to deeper burial depths by fluids with predominantly marine precursor origins mechanical and chemical compaction features are common as are a range of mainly burial related granular mosaic blocky and equant calcite cements earlier marine cements and meteoric influences are rare being highly localised to block faulted highs and or bathymetrically upstanding platform margin areas early marine micritisation of allochems was common on the platform top tectonic uplift together with a major oceanic throughflow current are thought to be key influences on localised karstification meteoric diagenesis and marine cementation the distribution and orientation of faults fractures and calcite veins together with evidence for their relative timing are the strongest manifestation of tectonism coeval with diagenesis there is concordance in the orientation and timing of structures affecting the tonasa platform with those basin wide with the potential for reactivation of pre existing basement fabrics tectonic subsidence including fault associated differential subsidence controlled the degree of burial diagenesis impacting different areas of the platform a predominance of burial diagenetic features and dearth of earlier marine or meteoric cementation is seen in other tertiary equatorial platforms and is partly attributed to 1 predominance of non framework building larger benthic foraminifera and or algae that are prone to remobilisation have low production rates and limited potential to build to sea level and 2 high runoff due to the equatorial humid climate contributing to lowered marine salinities in se asia underlying tectonic reasons for the preponderance of a regional diagenetic signature over a syntectonic one fracturing excepted are 1 development on the flanks of a backarc basin not on typical continental crust 2 key platform influencing structures are oblique to the main extensional direction in the basin and 3 development in an overall subsiding tectonic regime post dating basin initiation the aim here is that this study will contribute to understanding diagenetic alteration of syntectonic carbonate platforms and those from equatorial regions

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

wind and topography influence on an upwelling system at the eastern hainan coast 1 during the summer monsoon an upwelling dominates east of hainan island which can be observed by means of field studies and satellite sea surface temperature images the centers of cold water at the surface always show a strong patchiness a 3 d high resolution model is applied to study the impact of the topography on the wind driven upwelling system the experiments show that the upwelling favoring wind is the main driving force and we concluded that the formation of the centers of cold water at the surface significantly depends on the strength of southwesterly and southerly winds moreover the internal waves are generated at the shelf break representing the most prominent interaction between inner shelf and open ocean the alongshore topographic variations play an important role in the distribution of the upwelling centers this combined effect of wind and topography leads to the following processes 1 when the southwesterly or southerly wind is strong enough topographic variations cause upwelling centers at the downstream side of topographic high and a downwelling center at the upstream side which in turn lead to density variations 2 these density variations cause additional pressure gradients which advect the upwelling centers toward the northeast 3 a longer period of upwelling favorable winds support the advection processes which cause an enlargement of the cold water centers all these processes together can explain the observed uneven distribution of upwelling centers

microboring and taphonomy in middle oxfordian to lowermost kimmeridgian upper jurassic from the prebetic zone southern iberia abstract microboring was investigated through thin section analysis of oxfordian rocks from the prebetic zone betic cordillera southern spain microboring description and distribution were analysed as was their correlation with traits such as the type and size of bioclasts and microtaphonomic features encrustation and fragmentation single and branching microboring are the two major morphological groups differentiated microborers were not identified but by their patterns of distribution in the bioclasts and in the environmental setting are assumed to be phototrophic microboring only affected bioclasts with higher values of microboring index mbi registered in thicker ammonoid shells and serpulids and lower ones in ostracods foraminifera and small bivalves gastropods and echinoderms a very close direct relationship exists between bioclast size and microboring abundance as well as between the microboring mbi and encrustation indexes ei used in contrast a clear relationship between mbi and the fragmentation index fi has not been proved microboring activity has been interpreted to be related to both bioclast size and time exposure of bioclasts on the seafloor the latter resulting directly proportional to the rate of sedimentation in low energy environments the studied features mbi fi ei and bioclast mean size were analysed taking into account the stratigraphic intervals investigated i transversarium zone to lower bifurcatus zone ii upper bifurcatus zone iii bimammatum zone and iv planula zone p p and the trends registered were interpreted as a final consequence of relative sea level fluctuations stratigraphic intervals i and iv characterised by higher values in mbi and ei were related to lower sedimentary rates during increasing distality in a context of relative sea level rise which is consistent with the development of transgressive system tract tst conditions stratigraphic intervals ii and iii showing lower values in mbi and ei are related to higher sedimentation rates and decreasing distance from shore during relative sea level falls which are in accordance with developing highstand system tract hst and shelf margin wedge smw conditions data obtained and interpretations agree with the general ecostratigraphic context in the studied area previously proposed by the authors