topographically controlled fronts in the ocean and their biological influence headlands islands and reefs generate complex three dimensional secondary flows that result in physical and biological fronts mixing and diffusion processes near these reefs and headlands are quite different from these processes in the open sea and classical advection diffusion models that were developed for the open sea are not valid near shore topographically generated fronts affect the distribution of sediments and they aggregate waterborne eggs larvae and plankton this aggregation influences the distribution and density of benthic assemblages and of pelagic secondary and tertiary predators

tidal mixing and trapping in mangrove swamps lateral trapping in mangrove swamps is a dominant process controlling longitudinal mixing in mangrove fringed tidal rivers in the dry season the effective value of the longitudinal diffusivity is increased by the trapping effect by typically two orders of magnitude from its value in the absence of swamps in the wet season freshwater is trapped within the swamp and the adjoining boundary in the tidal river for long periods following the passage of a short lived flood this may have important ecological implications a fluid mud layer appears to be created by strong tidal currents over colloidal mangrove mud

mechanical basis for low angle normal faulting in the basin and range province low angle normal faults seem to violate the criterion that relates fault dip to stress orientation to explain such faults one must postulate a 45 rotation of principal stress directions at mid crustal depths which is difficult to understand on the basis of previous elastic crust models such a stress rotation is shown to be a natural consequence of a low viscosity lower crust

listric normal faulting stress refraction and the state of stress in the gulf coast basin the close association of overpressured shales and the coincident flattening of listric normal faults has been noted and is usually explained in terms of gravity sliding models however incorporation of overpressure into mohr coulomb frictional faulting theory does not predict normal faults dipping at angles less than 45 even for very low coefficients of friction we suggest that low angle normal faults may form because of a rotation of the maximum principal stress away from vertical with depth such a rotation occurs if a significant contrast in viscosity exists between two adjacent strata such as a normally pressured sandstone and an underlying overpressured shale or evaporite the stress refraction model renders the presence of a preexisting fault plane or an extremely low coefficient of friction unnecessary to explain listric fault geometry and offers a failure mechanism in agreement with frictional faulting theory based on rheological arguments

permian triassic sedimentology of jameson land east greenland incised submarine channels in an anoxic basin the presence of deeply erosive conglomeratic sandstone filled channels around the permian triassic p tr boundary in east greenland has been widely cited as evidence for a major late permian eustatic lowstand facies analysis of such channels and their associated strata in fact suggests that they record part of an intrinsic style of basinal deposition that persisted into early triassic time their origin can be explained without the need to invoke eustatic sea level fall active faulting and hinterland elevation is envisaged to have generated powerful sediment gravity flows that were capable of submarine erosion of fine grained unconsolidated strata stacked turbidite sandstone filled lenses also occur beneath fan delta sandbodies and probably record infill of channels or chutes cut into the subaqueous slopes of such deltas shale successions developed between the incised channel locations record complete p tr transitions in which a rapid onset of anoxic deposition is seen in latest permian time this is the local manifestation of a global anoxic event unusual aspects of the lower triassic sequence in greenland include the presence of well oxygenated intervals stromatolite bioherms and red algae

sedimentology of rift climax deep water systems lower rudeis formation hammam faraun fault block suez rift egypt abstract in most marine rift basins subsidence outpaces sedimentation during rift climax times typically this results in sediment starved hangingwall depocentres dominated by deep marine mudstones with subordinate local development of coarser clastics in the immediate hangingwall derived from restricted catchments on the immediate footwall scarp to highlight the spatial variability of rift climax facies and the controls upon them we have investigated the detailed three dimensional geometry and facies relationships of the extremely well exposed miocene rift climax lower rudeis formation in the immediate hangingwall to the thal fault zone suez rift egypt detailed sedimentological analyses allows the lower rudeis formation to be divided into two contemporaneous depositional systems 1 a laterally continuous slope system comprising hangingwall restricted interpretation of individual facies facies relationships and their spatial variability indicate that deposition in the immediate hangingwall to the thal fault occurred via a range of submarine concentrated density flows surge like turbidity flows mass wasting and hemipelagic processes major controls on the spatial variability and stratigraphic architecture of the depositional systems identified reflect the influence of the steep footwall physiography accommodation and drainage evolution associated with the growth of the thal fault the under filled nature of the hangingwall depocentre combined with the steep footwall gradient result in a steep fault controlled basin margin characterised by either slope bypass or erosion with limited coastal plain or shelf area sediment supply to the slope apron deposits is controlled in part by the evolution and size of small footwall drainage catchments in contrast the localized submarine fan is interpreted to have been fed by a larger antecedent drainage network the structural style of the immediate footwall is also believed to exert a control on facies development and stratigraphic evolution in particular fault scarp degradation is enhanced by fault propagation folding which creates basinward dipping bedding planes in the pre rift footwall strata that large pre rift blocks slide on

review of methods to measure short time scale sediment accumulation this review paper aims at providing a list of methods available to measure sediment accumulation in underwater or intertidal environments over short term periods in the order of hours to months at the most both in situ and under laboratory conditions methods are classified based on two criteria a whether they measure sediment accumulation or sediment elevation change and b whether they allow continuous or discontinuous measurements the main characteristics of each method are outlined along with its vertical resolution its accuracy its temporal resolution its spatial coverage capacity and an indication of its relative cost typical examples of applications are also provided the purpose of this review is to be a starting point for readers who need an overview of existing techniques that measure short term sediment accumulation in order to guide and facilitate for instance the selection of an appropriate technique for a given application with set requirements

structural features in a brittle ductile wax model of continental extension structural features produced during the rifting of continents depend on the layered rheological properties of the crust and lithosphere and in particular on the presence of any transitions between brittle and ductile behaviour1 here we use a wax model to explore the gross structural response of continental lithosphere under pure shear extension in the presence of a continuous brittle ductile transition the wax models were deformed under various boundary conditions to reflect a variety of different regions most notably the basin and range province of north america our experiments show the development of listric normal faults structures common to regions of continental extension we also observe the formation of distributed and discrete rifting and intrusion and occlusion of the upper brittle layer by the ductile lower layer the factor controlling deformation style in each case appears to be the relative thickness of the brittle and ductile layers although a relatively high rate of strain generally promotes discrete rifting

fluxes and exchange of suspended sediment in tidal inlets draining a degraded mangrove forest in kenya abstract this study focuses on sediment exchange in the degraded mwache mangrove forest wetland located in southern kenya it involved measurement of total and particulate organic suspended sediment concentrations tssc and posc tidal water elevation and current velocities results showed that in the heavily degraded backwater zone mangrove forest the ebb and flood tide total sediment fluxes were of same order of magnitude however flood tide sediment fluxes were slightly higher than the ebb ones in the moderately degraded frontwater zone mangrove forest the flood tide sediment fluxes were more than 50 higher than the ebb tide fluxes the peak net sedimentation in the highly degraded backwater zone was 4 g m 2 tide 1 but that in the moderately degraded frontwater zone was 63 g m 2 tide 1 in the frontwater zone of the mangrove forest the peak instantaneous ebb tide sediment flux was 3206 kg tide 1 equivalent to 35 6 g m 2 tide 1 and the flood one 8574 kg tide 1 95 g m 2 tide 1 the peak instantaneous flood and ebb tide particulate organic sediment pos fluxes in the frontwater zone mangrove forest were 1316 kg tide 1 15 g m 2 tide 1 and 587 kg tide 1 6 5 g m 2 tide 1 respectively the peak ebb and flood tide sediment fluxes in the backwater mangrove forest were 3206 kg tide 1 36 g m 2 tide 1 and 3305 kg tide 1 36 7 g m 2 tide 1 respectively in case of pos fluxes in the backwater zone mangrove forest the peak flood period pos flux was 969 kg tide 1 10 7 g m 2 tide 1 while the ebb period one was 484 kg tide 1 5 4 g m 2 tide 1 in both highly degraded backwater and moderately degraded frontwater zone of the mangrove forest there is net import of sediments however the net import is relatively lower in the backwater zone forest where the trapping efficiency is 27 in the moderately degraded frontwater zone of the mangrove forest the sediment trapping efficiency is 65 the net sediment import occurs mainly in periods of high river discharge in both neap and spring tides but occurs only in spring tides during dry season the net accretion rates in the backwater and frontwater zone mangrove forests are 0 25 and 3 5 cm year 1 respectively

european stress contributions from borehole breakouts before about 1986 european measurements of rock stresses were sparse the development of the borehole breakout method has facilitated a dramatic increase in the geographical distribution of rock stress orientations these are derived from data collected routinely for other purposes by the oil coal and gas industries over many years borehole breakouts can be interpreted in term s of the orientation of the stress field in boreholes as a function of depth with the findings related to known stratigraphical boundaries tectonic structures fault and fracture occurrences and to other geological and geophysical stress indicators geographical and depth distributions of stress on local and regional scales are beginning to provide the necessary base from which broad interpretive stress field models can be constructed

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

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

interpretation of aeromagnetic data in the jameson land basin central east greenland structures and related mineralized systems this paper provides a detailed interpretation of several aeromagnetic datasets over the jameson land basin in central east greenland the interpretation is based on texture and lineament analysis o

morphology hydrography and sediment dynamics in a mangrove estuary the konkoure estuary guinea the konkoure estuary in the republic of guinea is a poorly understood atypical mangrove system sediment dynamics in tropical estuaries are controlled by a combination of processes including river discharge morphology salinity erosion and deposition processes the settling of mud physico chemical processes and mangrove swamps here we present a consistent set of data aimed at characterising the estuary and thus increasing our understanding of tropical systems as well as studying the impact of human intervention in the region water elevations current measurements salinity suspended sediment concentrations bathymetry and sediment cover are presented following a 3 year survey of the konkoure estuary here we provide conclusive evidence that the lower konkoure is a shallow funnel shaped mesotidal mangrove fringed tide dominated estuary well mixed during low river discharge the estuary becomes stratified during high river flows and spring tides whereas a salt wedge appears during neap tides the konkoure estuary has been described as hypersynchronous and has three terminal outlets two of which are landward directed attesting to a tidal pumping effect while the third one is seaward directed and is controlled by the mangrove the suspended matter is transported by the tidal effect within the middle estuary and is therefore trapped in the turbidity maximum zone tmz the location of the tmz is river controlled and is correlated with residual currents but not with salinity front a dam constructed 130 km upstream impacts on the hydrodynamics and reduces the salinity intrusion by about 25 it causes an increased low river discharge whereas its efficiency over high river flows is unclear

quantifying extension of passive margins implications for sea level change 1 passive margins form by rifting and extension of continental crust extension of continental crust associated with subduction elsewhere decreases ocean basin volume forcing sea level to rise the amount that the continental crust has been extended can be quantified using total tectonic subsidence which is determined using sediment thickness and water depth data coupled with a model of the rifting process we calculate total tectonic subsidence the amount of extension or stretching factor and thickness of extended continental crust at a 5 min grid resolution for passive margins between 77 n and 70 s our modeled crustal thicknesses correlate well with seismic refraction data from north america and australia and can be used to estimate the change in ocean volume and the impact of extension on sea level the duration of extension is constrained by estimating the onset of rifting and the breakup age which is the time when rifting ceased and seafloor spreading began our results indicate that extension of continental crust has increased sea level by 20 8 m since the start of pangea rifting

currents and sediment transport in mangrove forests abstract a field study of the tidal currents cohesive sediment dynamics and transport of organic carbon in a highly vegetated mangrove swamp was carried out at middle creek cairns australia the interaction of tidal currents and the vegetation generated jets eddies and zones of stagnant waters which were numerically modelled a high value of the manning friction coefficient n 0 1 was derived by the dense vegetation about 80 of the suspended sediment brought in from coastal waters at spring flood tide was trapped in the mangroves corresponding to about 10 12 kg of sediment m 1creek length spring tide resulting in a rise of the substrate by about 0 1 cm year 1 the selective trapping of clay was caused by flocculation of the finer particles in the mangroves there was an indication of a slight inwelling of organic carbon creek water was readily differentiated from mangrove water by large differences in the molecular weight distribution of the dissolved organic carbon

palaeoenvironments of the late triassic rhaetian sea implications from oxygen and strontium isotopes of hybodont shark teeth the oxygen and strontium isotopic composition of 125 teeth of the hybodont sharks lissodus and hybodus from various late triassic rhaetian bone bed localities in the central european basin are used as environmental and ecological tracers for the shallow epicontinental rhaetian sea the preservation of tooth enameloid was ascertained by cathodoluminescence microscopy mean 18op values differ regionally across the rhaetian sea with values of 18 6 0 6 near the western gate 16 1 0 8 in the east 15 4 0 6 in the southeast and 17 7 0 9 in the south the 18op values in the eastern rhaetian sea are 4 5 lower relative to tethyan seawater while teeth from the southern and western parts close to the marine gates are less fractionated the strontium isotopic composition of teeth from most localities is more radiogenic in comparison to late triassic seawater the observed spatial 18op trend in the rhaetian sea indicates a shift from marine to brackish conditions in the south and west towards extensively brackish conditions with salinities of less than 16 in the east thus confirming the existence of two marine gates brackish conditions persisted throughout early rhaetian times and were maintained by increased fluvial discharge from the vindelician bohemian and fennoscandian highs as a result of enhanced atmospheric moisture availability in the course of the rhaetian transgression the 18op values of lissodus and hybodus indicate euryhaline behaviour of rhaetian hybodonts by exceeding modern shark intraspecific variability the lack of accordance in 18op values between different isotopically conspicuous localities in the rhaetian sea contradicts a basin wide migration pattern differences between co site taxa might indicate some degree of niche partitioning

anisotropy pore fluid pressure and low angle normal faults low angle normal faults lanfs are commonly associated with high angle normal faults high pore fluid pressures and foliated fault cores explanations for lanf slip based on high pore fluid pressure critically depend on stress rotations in the fault core zone which have been based on an assumption of isotropy anisotropy fundamentally changes the coupling between pore fluid pressure and effective stress the response of saturated fault core rocks in lanfs can be explored by combining the effective medium theory with anisotropic poroelasticity the nucleation and evolution of lanfs are investigated in a framework of local changes in rock properties and the interaction of a pressurised pore fluid with intrinsic lithological and extrinsic damage anisotropies this quantitative approach enables comparison with detailed field and laboratory measurements of fault rock properties

rheological control on the initial geometry of the raft river detachment fault and shear zone western united states the strain exhumation history and field orientation of a well exposed shear zone and detachment fault in the raft river mountains of northwestern utah a cordilleran metamorphic core complex have been studied to determine the kinematics of ductile shearing and initial orientations of the shear zone and detachment fault mapping and strain and kinematic analysis indicate that the top to the east raft river shear zone initially developed parallel to an unconformity separating archean rocks from overlying proterozoic quartzite and schist for at least 24 km in the shear direction experimental rock deformation data from lithologies similar to the archean and proterozoic rocks suggest the unconformity represented a significant rheological boundary at the deformation temperatures the base of the shear zone was localized along the boundary between relatively weak quartzite above and stronger monzogranite below an extensive thermochronological database is used to reconstruct the position of the basement unconformity in temperature lateral distance coordinates the initial average dip of the shear zone and basement unconformity is estimated between 7 and 30 assuming subhorizontal isotherms and geothermal gradients of 20 40 c km the east dip of the unconformity at the onset of miocene extension is interpreted to have resulted from late eocene unroofing and flexure beneath a top to the wnw extensional shear zone in the western raft river grouse creek and albion mountains the observations from the raft river shear zone suggest that the orientation of some midcrustal shear zones may not reflect the predicted orientation for ductile faults according to ductile failure criteria but rather the orientation of rheological boundaries along which deformation is localized furthermore detachment faults that are superimposed on mylonite during progressive displacement and footwall unroofing may use an inherited mechanical anisotropy from the mylonite and their orientations may not reflect the predicted orientation of shear fractures in isotropic rock the common parallelism between detachment faults and mylonitic foliation may indicate a mechanical and kinematic preference for localization of throughgoing brittle faults parallel to preexisting mylonitic foliation because of this preference studies restricted to detachment faults which lack footwall mylonite or restricted to structural levels between the breakaway and mylonitic front have more bearing on the question of the initial dip of normal sense shear fractures faults within the seismogenic crust

north atlantic marine rifting in the early triassic new evidence from east greenland two early triassic marine rifting events have been recognized in new outcrop data from east greenland increasing our understanding of this important tectonic episode in the development of the ne atlantic norwegian greenland sea a detailed ammonoid stratigraphy together with stratigraphic and radiometric evidence show that the first rifting event took place in the early griesbachian this event was largely confined to major basin margin faults the second rifting event which involved splay faulting and intra basinal fault block tilt is dated as late griesbachian deposition in east greenland took place in half grabens dominated by deep water gravity flow sandstones and mudstones as well as shallow marine conglomerates and sandstones similarly recent core data from offshore mid norway show that deposition on the eastern margin of the norwegian greenland sea took place in deep marine settings dominated by gravity flows this suggests that the early triassic marine realm extended from east greenland to the present day norwegian coastline and that the marine rift basin was significantly wider than previously thought

microfacies characteristics of a tropical mangrove fringed shoreline cleveland bay queensland australia sedimentary and taphonomic controls on mangrove facies development mangrove ecosystems strongly influence the sedimentology and geomorphology of contemporary intertidal environments and are known to have occupied similar ecological niches at least as far back as the early cenozoic given this it is remarkable how few records of mangrove occurrence have been reported in the geologic record here a microfacies approach is adopted to examine the characteristics of a contemporary mangrove colonized intertidal succession along an active prograding shoreline in north queensland australia and compared with a proximal mid late holocene preserved intertidal succession this enables a comparison of microfacies development and preservation potential in like for like depositional environments over short temporal and spatial scales in the contemporary intertidal system active shoreline progradation has produced a highly gradational shallowing upward succession mid to low intertidal substrates characterized by an abundant and diverse bioclast especially molluscan fauna and a rich calcareous foraminiferal assemblage are overlain by organic rich upper intertidal mangrove facies characterized by abundant organic material especially wood and bark fragments and a distinct fauna of agglutinated foraminifera the major sedimentary effects of mangrove progradation are to introduce substantial amounts of organic matter into the substrate effectively overprinting the mudflat facies to mix and re texture due to root network development and infaunal bioturbation the sediment substrate and to modify the depth ranges over which infaunal molluscs and foraminifera occur variations in the relative abundance of constituents permit however the clear delineation of mangrove and intertidal mudflat facies whilst an essentially similar facies succession is identifiable in the sub recent many of the diagnostic facies constituents are either not preserved or are present in far lower abundances than in the modern in particular the inferred mangrove units contain far less organic material most wood and root material is absent are essentially devoid of bioclastic material and contain a depauperate agglutinated foraminiferal fauna the primary drivers of this are 1 loss of calcareous foraminifera and bioclasts due to carbonate dissolution 2 loss of agglutinated foraminifera due primarily to biological fiddler crab test degradation and mineralization of their organic binding agents and 3 aerobic and anaerobic degradation of organic material consequently actual criteria for identifying the presence of a former mangrove in this succession are limited such poor preservation even within sub recent mangrove deposits suggest that the longer term preservation potential of key diagnostic criteria is likely to be extremely poor within similar terrigenoclastic dominated organically enriched successions thus whilst mangroves significantly modify and re texture intertidal substrates use may often need to be made of sparsely preserved faunal or floral remains or traces interpreted in the context of the broader intertidal depositional succession to infer the presence of mangrove colonized substrates in the rock record

sticky waters in the great barrier reef the great barrier reef is a mosaic of regions of high and low reef density current meter observations upstream from a region of high reef density revealed that the tidal and low frequency currents were steered away from the region during spring tides but not during neap tides a mathematical model suggests that this effect was due to both tidal friction and to the dissipation of energy by eddies behind reefs at spring tides for a high reef density region this results in a longer residence time at spring tides than at neap tides conversely this effect also diminishes connectivity between regions of high and low reef density at spring tides this process may affect the recruitment and dispersion of fish and other larvae in the great barrier reef it may also invalidate the use of satellite altimetry and tidal harmonic analysis for currents in the great barrier reef

seismic slip on a low angle normal fault in the gulf of corinth evidence from high resolution cluster analysis of microearthquakes the gulf of corinth in western greece is one of the most active extensional zones in the aegean region it is still an open question whether extension can be actively accommodated on low angle faulting or if those faults as seen in geological records have been rotated whilst numerous fault plane solutions obtained from a dense temporary network deployed in the western part of the gulf in july august of 1991 showed one of the nodal planes as a subhorizomal plane slip on the high angle conjugate plane is equally probable from the focal mechanism data rigo et al 1996 since part of the activity occurred in spatial clusters with similar focal mechanisms we used a high resolution cluster analysis to determine the most likely active plane exploiting the waveform similarity of these events relative onset times of p and s waves could be determined at subsample accuracy less than 0 01 s the cluster analyzed here contains 12 evems among these 8 have a well con strained normal faulting fault plane solution with a shal low 12 20 o north dipping plane and a steeply south dipping plane a master evem relocation shows that the relocated 12 hypocenter cemroids are aligned along the low angle plane showing clear evidence for active low angle normal faulting

the relative importance of landward directed tidal sediment transport versus freshwater flood events in the normanby river estuary cape york peninsula australia variation in freshwater discharge into the tropical estuaries of northern australia is extreme between wet and dry seasons and the resultant effect upon sedimentary processes in relation to the geomorphological evolution of the coastal plain is largely undocumented observations of tidal height currents and suspended sediment concentrations were taken over a 3 week period in july 1994 dry season in the mesotidal normanby river estuary northeastern australia the estuary and adjacent inner shelf were surveyed using a 3 5 khz seismic system and an echo sounder and sampled with a total of 175 grab samples and 17 vibrocores sediment sampling occurred in july 1994 december 1994 and march 1996 the latter following the 1995 96 wet season flood tidal currents dominate the estuary at spring tides with peak velocities of 0 85 m s 1 recorded at the mouth measured tidally driven sediment transport is landward at the mid estuary site and extrapolation gives estimates of 15 000 30 000 tonnes of bedload and ca 50 000 tonnes of suspended load moved landward per year the surficial sediments in the main estuarine channel are inferred to be holocene and are 1 delta front sediments which extend to at least 6 km seawards of the mouth 2 lower estuarine silts located at 2 11 km landwards of the mouth and 3 channel dune sands 13 to 50 km i e nearly to the tidal limit all dunes surveyed on the river bed during the dry season showed a strong asymmetry with lee faces consistently facing landward whether surveyed at high or low water indicating landward bedload sediment transport in the dry season an underlying hard regional surface is exposed at 11 13 km landward of the estuary mouth in the absence of direct measurements we have estimated sediment transport during wet season freshwater flood events a major freshwater flood event may transport only 6000 32 000 tonnes of bedload seawards and modern wet season events appear incapable of supplying sand in significant quantities to the inner shelf we infer that for the late holocene the frequency magnitude and duration of wet season events has been insufficient to reverse the landward bedload transport driven by tidal currents in the dry season

ammonoid stratigraphy and sedimentary evolution across the permian triassic boundary in east greenland east greenland is a classical area for the study of the permian triassic transition and the succession is one of the most expanded in the world new ammonoid data from the wordie creek formation have allowed us to better reconstruct the history of the east greenland basin from semi isolated basins with an endemic fauna during latest permian earliest triassic h triviale h martini zones time to well connected open marine shelf basins during the early triassic m subdemissum o commune w decipiens and b rosenkrantzi zone times the east greenland zonation can be correlated with boreal zonations in arctic canada svalbard and northeastern asia it allows precise relative dating and correlation of important events across the permian triassic boundary the new ammonoid data indicate that deposition was continuous across the permian triassic boundary and developed as a marine mudstone mudstone contact in basinal areas of hold with hope northern and southern jameson land correlation of the ammonoid stratigraphy with the fad of hindeodus parvus which defines the base of the triassic in global stratotype section and point gssp in meishan china suggests that the hypophiceras triviale zone is to be referred to the uppermost permian whereas the h martini zone is lowermost triassic accordingly the end permian marine and terrestrial extinctions and associated isotope changes as well as the subsequent adaptive radiations in east greenland took place in latest permian time new boreal faunas and floras were well established and diversified in the hypophiceras triviale zone prior to the beginning of the triassic and the permian triassic boundary in its present definition is no longer reflecting major changes in the earth system it would have been fortunate if a gssp were defined in a protracted section at a point of major environmental perturbations marked by isotope excursions chemical anomalies and mass extinction rather than in the strongly condensed section like meishan at a point which post dates all significant events

fault geometries on uranus satellite miranda implications for internal structure and heat flow abstract miranda a 470 km diameter uranian icy satellite has a surface that exhibits evidence of a complex tectonic history tectonic structures are mostly localized in three regions termed coronae but also form a rift system inferred to be global in extent ridges within the boundary of arden corona and those that make up the 340 chasma part of the global rift system have been interpreted as normal fault blocks using voyager data we test the hypothesis that these arden corona faults as well as those at the northern edge of the 340 chasma are listric in geometry for this testing we use four geometric criteria for listric faults 1 progressive down dip decrease in fault scarp dip 2 progressive down dip increase in back tilted face slope 3 concavity of the exposed scarp surface and 4 presence of a rollover structure results of this analysis support the hypothesis that the faults within the arden corona boundary are listric in geometry but do not strongly support the hypothesis for the faults within the 340 chasma by analogy with terrestrial structures the listric character of faults within the arden corona boundary suggests the presence of a subsurface detachment this detachment likely occurred at miranda s brittle ductile transition zone at the time of faulting measurements of the arden corona fault system geometry are used to estimate depths to the proposed brittle ductile transition zone at the time of faulting resulting in values of 6 7 9 0 km those depths in turn are used to estimate a thermal gradient of 6 25 k km 1 and a surface heat flux of 31 112 mw m 2 the weaker evidence of a listric geometry for the faults of the 340 chasma suggests that those faults did not interact with a brittle ductile transition at the time of their formation our estimated thermal gradient of the arden corona region is consistent with a previous heating event on miranda that was as significant as europa s current resonance induced tidal heating this heating event may be associated with a hypothesized previous tidal resonance of miranda with umbriel and or ariel

dependence of active normal fault dips on lower crustal flow regimes two key questions are raised by the presence in the basin and range province of subhorizontal normal faults which were active in and around the miocene first how did they develop when their existence seems to be precluded by elementary rock mechanics arguments second if they did slip in the recent geological past why do normal faults now active in the brittle upper crust have steeper dips both in the western usa and elsewhere one may now answer both questions by considering the stress field in regions where the isostatic response during extension involves horizontal flow in the plastic lower crust this stress tensor will have inclined principal axes making it possible for normal faults to form with either very steep or subhorizontal dips depending on the sense of flow this can be controlled by environmental conditions which influence rates of hanging wall sedimentation and footwall erosion and thus determine lateral variations in lithostatic pressure in the lower crust regional scale lateral variations in the geothermal gradient caused by subduction can also influence lower crustal flow regimes in adjacent zones of continental extension enabling extension to occur on low angle normal faults dipping away from the active continental margin

shear fractures in anisotropic ductile materials an experimental approach abstract analogue models have been used to investigate the influence of planar mechanical anisotropy on the orientation of shear fractures in an elastoviscous brittle material multilayered models consisting of a mixture of plasticine vaseline and preferentially oriented paper flakes have been coaxially deformed for this purpose the evolution of the orientation length and connectivity of fracture sets has been systematically analysed with progressive coaxial deformation the experimental results show that the orientation of fractures with respect to the deformation axes depends on the orientation of transverse anisotropy two symmetrical sets of shear fractures are formed in models with layering parallel to the extension axis x while the fracture network is asymmetrical with respect to the deformation axes for cases with oblique anisotropy the average dihedral angles between fracture sets are higher than 100 with the obtuse bisector between the two sets oriented perpendicular to layers the stress fields calculated from fracture data differ from the boundary conditions applied by the deformation apparatus this misorientation is related to the degree of anisotropy in models with high oblique anisotropy both fracture arrays rotate in a dextral sense together with layers towards the x axis indicating that the presence of a strong anisotropy controls their evolution with progressive deformation

flexural rotation of normal faults a conceptual model is proposed for the generation of low angle normal faults in metamorphic core complexes the model is based on three assumptions 1 the isostatic response to normal fault motion is of regional extent 2 when a fault segment is significantly rotated from the optimum angle of slip relative to the crustal stress field it is replaced by a new planar fault oriented in the optimum direction and 3 the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust the stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations active low angle normal faults are difficult to reconcile with rock mechanics theories earthquake focal mechanism studies and geochronologic results indicating rapid cooling of core complex rocks the model does not require active fault slip on low angle faults the flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation the anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust this can explain the observed short wavelength of topographic response to normal fault loads the model results in 1 a nearly flat lying abandoned normal fault or detachment below slices of upper plate rocks and sedimentary infill 2 a strong contrast in metamorphic grade across the abandoned detachment 3 rapid movement of lower plate rocks from midcrustal depths to shallower depths these results are qualitatively in agreement with geologic observations for core complexes

rollovers in salt tectonics the inadequacy of the listric fault model abstract rollover anticlines are syn sedimentary extensional structures common in salt tectonics that are classically considered to result from layer bending during hangingwall displacement above a listric normal fault however theoretical considerations and seismic images of natural examples put in question the validity of the listric fault model from which rollover growth is steady state by nature and controlled by the relative displacement of two blocks we used laboratory experiments of gravity driven deformation of brittle ductile models simulating salt tectonics processes to study in which circumstances rollovers are obtained both in time and space it is argued that rollover growth is a nonsteady process that results from a mechanical instability whose critical lifetime can be divided in three characteristic stages birth growth and decay in kinematic terms the development of a synthetic or antithetic rollover requires a three block system an upslope block and a downslope block that move downslope and that separate from each other on top of an extending decollement layer lying above a basement block synthetic and antithetic rollovers developed with upward concave shapes whatever the sense of shear in the salt layer and can pass laterally to each other without transform fault this points out that the concave shape of a rollover base is not an argument in favour of listric faulting the concave shape simply results from the connection between a steeply dipping normal fault and a flat lying or gently dipping decollement

a low angle normal fault in the umbria region central italy a mechanical model for the related microseismicity abstract in the northern apennines the upper crust is thinned by a set of east dipping low angle normal faults lanfs the easternmost and more recent of these lanfs is the altotiberina fault atf located in northern umbria the geometry of the atf has been reconstructed matching surface geology with seismic reflection profiles and borehole data the fault whose average dip is 20 borders the upper pliocene quaternary tiber basin and has a displacement of about 8 km the deeper portion of the atf is located below the axial zone of the northern apennines where the strongest instrumental and historical seismicity is recorded the microseismicity of the region m 1 to evaluate the boundary conditions for the brittle activity of the atf the fault can be reactivated for low values of differential stress 1 3 t 10 mpa and tensile fluid overpressure p f 3 e g v 0 93 in the peculiar situation of the northern apennines the deep emissions of large amounts of co 2 documented in the area can be entrapped in their ascent by structural seals e g atf favouring localised fluid overpressures the impossibility of sustaining p f 3 for wide fault portions counteracted by hydraulic fracturing increased permeability under low effective stress and load weakening behaviour for normal faulting would prevent the nucleation of moderate ruptures along the fault the short lived attainment of p f 3 along small fault portions can account for the microseismic activity located along the atf which occurs on rupture surfaces in the range of 10 1 10 3 km 2

a new high resolution stratigraphic and palaeoenvironmental record spanning the end permian mass extinction and its aftermath in central spitsbergen svalbard abstract research on the permian triassic boundary ptb along the northern margins of pangaea exposed today in the arctic region has been heavily reliant on field observations where data resolution was consequently determined by outcrop condition and accessibility core drilling in central spitsbergen allowed for a near complete recovery of two 90 m cores through the ptb analyses of the core and nearby outcrops include stratigraphic logging and sampling xrf scanning petrography biostratigraphy isotope geochemistry and geochronology the first appearance datum fad of h parvus in svalbard places the base of the triassic ca 4 m above the base of the vikinghogda formation and ca 2 50 m above the end permian mass extinction epme and its associated sharp negative 13c the ptb therefore falls within the reduviasporonites chalastus assemblage zone in svalbard precise u pb tims dating of two zircon crystals in a tephra layer just above the first documented hindeodus parvus in svalbard gives an age of 252 13 0 62 ma high resolution palaeoenvironmental proxies including si kcps kilo counts per second zr rb k ti fe k and v cr indicate a transition towards a more arid climate in the earliest triassic contemporaneous with prolonged bottom water dysoxic anoxic conditions following an increase in volcanic activity in the late permian statistical analysis of zr rb k ti and v cr elemental ratios suggests that the system was impacted by long eccentricity 400 kyr cyclicity the 13c excursion in organic carbon 13corg record signals a large negative carbon isotope excursion cie associated with the mass extinction event but also records a second smaller negative cie ca 22 m above this interval this younger 13corg excursion correlates to similar cies in the dienerian late induan records of other sections notably in the tethys ocean which have been interpreted as recording a small biotic crisis during the post extinction recovery evidence of this negative cie in spitsbergen suggests that the dienerian crisis may have been global in extent the negative 13corg values are associated with evidence for dysoxia or anoxia in the core and the occurrence of tephra layers in the same interval suggests a possible connection between the dienerian crisis and a discrete episode of volcanic activity

experimental models of hangingwall deformation in ramp flat listric extensional fault systems abstract the results of three experimental models of ramp flat extensional fault systems are presented the experiments were constructed from sand and mica layers to form an anisotropic sequence that would respond to the imposed deformation by both faulting and folding the geometry of the underlying detachment controls the deformation in the hangingwall sequence ramp flat detachment geometries produce an upper roll over with a crestal collapse graben system a ramp syncline and fold reverse fault zone and a lower roll over with a crestal collapse graben system short ramp geometries produce only minor perturbations in a larger roll over structure as extension progresses the crestal collapse systems migrate and superimpose earlier systems the models of ramp flat extensional structures produce templates for the interpretation of natural ramp flat listric fault systems

differential sediment trapping abilities of mangrove and saltmarsh vegetation in a subtropical estuary abstract saltmarsh and mangrove are common coastal wetland types and their ability to enhance deposition has been investigated extensively but rarely compared directly this study carried out in situ observations to compare the sediment transport processes between a bare mudflat a mangrove stand and a saltmarsh stand within a subtropical estuary turbidity variations over the latter portion of a spring tide were recorded alongside measurements of flow data to estimate sediment trapping by hydraulic forces under similar hydroperiods in addition vegetation was transplanted to compare the direct sediment trapping by high standings and short seedlings the suspended sediment concentration ssc time series showed an overall reduction between the bare mudflat and the vegetated flats suspended sediment flux estimates revealed that a considerable amount of sediment was trapped by the saltmarsh and the mangrove edges the flux estimates find that the saltmarsh edge is more efficient than the mangrove edge in trapping sediments transported normal to the edge the sediment trapping mechanisms were considered based on two approaches the hydrodynamic related sediment settling and direct trapping by vegetation the calculation of deposition tendency showed that the presence of vegetation altered the flow direction and the tidal asymmetry of the deposition process resulting in a higher deposition tendency during the flood phase to enhance sediment settling in addition to sediment settling vegetation surfaces were found to trap sediments directly in combination with rinsing by precipitation these trapped sediments accumulated on the bed and contributed to the deposition against the background of similar inundation periods the saltmarsh grass showed a greater sediment trapping ability than the mangrove trees in terms of both the hydraulic sediment trapping and the direct trapping by vegetation surface

balancing aggradation and progradation on a vegetated delta the importance of fluctuating discharge in depositional systems vegetation is an important component of constructional landscapes as plants enhance deposition and provide organic sediment that can increase aggradation rates to combat land loss we conducted two sets of laboratory experiments using alfalfa medicago sativa to determine the effects of plants on channel organization and large scale delta dynamics in the first set we found that rapid vegetation colonization enhanced deposition but inhibited channelization via increased form drag that reduced the shear stress available for sediment entrainment and transport a second set of experiments used discharge fluctuations between flood and base flow or interflood interfloods were critical for reworking the topset via channel incision and lateral migration to create channel relief and prevent rapid plant colonization these low flow periods also greatly reduced the topset slope in the absence of vegetation by removing topset sediment and delivering it to the shoreline floods decreased relief by filling channels with sediment resulting in periods of rapid progradation and enhanced aggradation over the topset surface which was amplified by vegetation the combination of discharge fluctuations and vegetation thus provided a balance of vertical aggradation and lateral progradation we conclude that plants can inhibit channelization in depositional systems and that discharge fluctuations encourage channel network organization to naturally balance against aggradation thus variations in discharge are an important aspect of understanding the ecomorphodynamics of aggrading surfaces and modeling vegetated deltaic systems and the combined influences of plants and discharge variations can act to balance vertical and lateral delta growth

studies of a mangrove basin tuff crater new zealand iii the flux of organic and inorganic particulate matter abstract water samples were collected at 15 min intervals over 11 tidal cycles from a tidal creek draining the mangrove covered basin of tuff crater auckland new zealand the samples were filtered and total suspended sediment tss inorganic suspended sediment iss and organic suspended sediment oss were determined variation in tss was high the concentration varied over a tidal cycle and during over bank flows concentrations were lowest at or near slack high water covariance between tss concentrations and velocity and discharge meant that the calculation of particulate matter flux over tidal hemicycles was particularly dependent on the method of estimating tidal flux the hypsometrically based volumetric method was found to be inappropriate predicting a positive budget import more often than observed instead particulate matter budgets were calculated by means of the velocity area method and indicate a net export of tss iss and oss floating macrodetritus was observed on both the flood and ebb tides but a net export was found on the two tides monitored it is considered that on an annual basis floating macrodetritus export accounts for less than 2 of the detrital production in the basin and organic suspended sediment export from the basin is less than 3 kg c ha 1 day 1 and is below the rate of detrital production it is implied that a proportion of the organic detritus produced in this basin is degraded and recycled in situ

rapid and synchronous collapse of marine and terrestrial ecosystems during the end permian biotic crisis a newly studied permian triassic p tr boundary section in jameson land east greenland contains an abundant and well preserved marine fauna as well as terrestrial palynomorphs for the first time it is possible to compare the biotic crises of the marine and terrestrial realms using the same samples from the same section the sediments record a negative excursion in 13 c carb values of 8 9 and in 13 c org values of 10 11 the presence of the conodont hindeodus parvus combined with the 13 c carb record enables correlation with the proposed global stratotype section at meishan this shows that the greenland section is the most expanded p tr section known collapse of the marine and terrestrial ecosystems took between 10 and 60 k y it took a further few hundred thousand years for the final disappearance of permian floral elements collapse of the terrestrial and marine ecosystems began at the same stratigraphic level and preceded the sharp negative excursion in the 13 c record

coastal tidally driven circulation and the role of water exchange in the linkage between tropical coastal ecosystems water circulation and exchange processes in a shallow semi enclosed tropical bay were studied in southern kenya gazi bay through measurements of tidal elevations salinity temperature dissolved oxygen and current velocities at stations established in mangrove creeks seagrass beds and coral reef zones occurrence of wide shallow entrance lack of topographic controls sills and the orientation of the bay entrance with respect to dominant tidal water circulation patterns accounts for the high rates of exchange 60 90 of the volume per tidal cycle between the inshore and offshore waters high flushing rates are coupled with short residence times in the order of 3 4 h the dominant water circulation driving force is the semi diurnal tide causing a strong reversing current in the mangrove creeks 0 6 ms 1 and low magnitude current in the seagrass and coral reef zones 0 30 ms 1 tidal asymmetry characterized by stronger ebb flows than flood flows in the mangrove creeks partly promotes the net export of organic matter to the seagrass beds the brackish and turbid water plume in the mangrove creeks and south western region of the bay is trapped along the coast and in the mangrove swamp and does not reach the coral reef the freshwater influx via rivers and direct rainfall in the bay accounts for a volume of 305 000 m3 of which 20 is lost as a result of enhanced evapotranspiration which is also responsible for a salinity maximum zone 38 in the upper region of the bay covered by mangroves

comment on the permian triassic transition and the onset of mesozoic sedimentation at the northwestern peri tethyan domain scale palaeogeographic maps and geodynamic implications by s bourquin a bercovici j lopez gomez j b diez j broutin a ronchi m durand a arche b linol and f amour palaeogeography palaeoclimatology palaeoecology 299 2011 265 280 abstract the recent paper by bourquin et al 2011 describes the regional palaeogeographic evolution of the late permian to middle triassic on a pan european scale whilst useful data and interpretations are provided for their southern and intra variscan belt domains additional well and seismic data from the central and northern north sea and the atlantic margin region together with results from recent publications allow us to refine and improve their interpretation of their northern domain the presence of a regional unconformity at the permian triassic boundary with only localised induan sedimentation is less clear in the northern region where multiple extensional events through late permian and triassic time led to the development of localised footwall and rift flank unconformities as arctic rifting propagated southwards and entered the north sea and the atlantic margin regions the hardegsen unconformity may be locally identifiable in the southern portion of the northern domain but again forms one of a number of unconformities marking the onset of rifting data from the northern domain suggest that early triassic aeolian activity was ubiquitous on the distal fringes of terminal fluvial systems but with no evidence of the discrete episode of increased aridity in the smithian identified in the south the onset of vegetation cover in the northern domain was also more diachronous in this region appearing in the central north sea at approximately the same time as muschelkalk flooding of the adjacent southern permian basin and later in basins further to the north in most cases the middle triassic fluvial systems in the north were terminal in nature failed to discharge into marine basins and were not exorheic in character their advance and retreat was independent of sea level fluctuations or the presence of a marine water body and fluvial expansion and retreat aeolian reworking and vegetation cover appear to have been linked to catchment runoff the disconnect with the observations to the south may be in part a product of the more northern latitudinal position of these systems or at least that of the headwaters of the fluvial drainage

flow of mantle fluids through the ductile lower crust helium isotope trends heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust minimum 3he 4he ratios in surface fluids from the northern basin and range province western north america increase systematically from low crustal values in the east to high mantle values in the west a regional trend that correlates with the rates of active crustal deformation the highest ratios occur where the extension and shear strain rates are greatest the correspondence of helium isotope ratios and active transtensional deformation indicates a deformation enhanced permeability and that mantle fluids can penetrate the ductile lithosphere even in regions where there is no substantial magmatism superimposed on the regional trend are local high 3he 4he anomalies indicating hidden magmatic activity and or deep fluid production with locally enhanced permeability identifying zones with high resource potential particularly for geothermal energy development

hydrocarbon generation induced microcracking of source rocks laboratory measurements of ultrasonic velocity and anisotropy in kerogen rich black shales of varying maturity suggest that extensive bedding parallel microcracks exist in situ in most mature source rocks undergoing the major stage of hydrocarbon generation and migration given the normal faulting regime with the vertical stress being the maximum principal stress typical of most sedimentary basins this microcrack alignment cannot be accounted for using simplified fracture mechanics concepts this subhorizontal microcrack alignment is consistent with 1 a model of local principal stress rotation and deviatoric stress reduction within an overpressured formation undergoing hydrocarbon generation and with 2 a strong mechanical strength anisotropy of kerogen rich shales caused by bedding parallel alignment of kerogen microlayers microcracks originate within kerogen or at kerogen illite interfaces when pore pressure exceeds the bedding normal total stress by only a few mpa due to the extremely low fractu

the northwestern margin of the basin and range province part 2 structural setting of a developing basin from seismic and potential field data abstract surprise valley in northeastern california offers an ideal opportunity to examine the structural setting of a developing extensional basin due to its late miocene to recent activity in isolation from other major normal fault bound basins seismic velocity and potential field modeling help determine the nature of basin fill and identify intra basin faults based on a detailed gravity and magnetic profile we identify shallow subsurface basalt flows and several faults within the valley that may accommodate hundreds of meters of vertical offset possibly cutting and offsetting the 30 east dipping surprise valley fault that rotated during footwall tilting of the adjacent warner mountains some of these intra basin faults correspond with mapped quaternary fault scarps but others have no surface expression these faults may represent the currently active fault system within the basin if so they would indicate that basin development is transitioning away from the main range front normal fault to a new set of steep intra basin faults that are more favorable for accommodating regional transtensional strain

triassic sediments of the inner moray firth scotland early rift deposits patterns of triassic sedimentation in the inner moray firth are examined in the light of a new model of continental rift sedimentation that has been developed in the tertiary to recent rifts of east africa the major tectonic control during the trias was the great glen fault to the northwest which can be shown to have been moving in dip slip fashion at this time the structure of the firth appears to have resembled the simple half graben that makes up the great east african rift system deposits both thicken and get finer towards the fault sediments found in off shore wells are dominated by laminated fine sand and silty clay with sporadic evaporites similar sequences are characteristic of or associated with ephemeral lakes in modern semi arid continental rift settings no alluvial fans have been detected close to the faulted margin again this is consistent with general patterns of sedimentation against boundary faults in the kenyan rift the coarsest sedimentary sequences in the moray firth are on the unfaulted margin to the south around burghead they consist of fluviatile lake shore and aeolian deposits the fluvial sediments show evidence of tectonically induced cycles of sedimentation which are interpreted in terms of waves of detritus working down the drainage system beds dominated by pebbly horizontal laminae and reminiscent of steep straight and shallow ephemeral streams alternate with troughed sands of deeper more sinuous but equally ephemeral rivers these are the coarsest sediments of the unfaulted margin of the basin however the lack of thick conglomerate sheets which are a feature of east african sequences at equivalent positions within the rift basin suggests only small scale fault activity and a relatively subdued topography during triassic times this is supported by evidence of extensive calichification during the rhaetic which produced a top trias marker horizon found throughout the inner moray firth

remarks on the derivation of the paleostress system from inferred faults on deep seismic reflection records abstract geological dip slip faults have become a common feature of interpreted deep crustal seismic reflection records the applicability of anderson s theory of faulting to these cases as argued by previous workers would allow the derivation of the paleostress system from the dip angle of the fault knowledge of paleostress would obviously be important in constraining tectonic reconstructions two well constrained examples of crustal dip slip faults inferred from deep seismic reflection data from the wind river mountains wyoming and the riddleville buried triassic jurassic basin georgia u s a suggest that in certain cases the approach can yield reasonable estimates of the coefficient of static friction and the paleostress system from deep reflection defined faults this study however also notes that the sensitivity of the calculation of the coefficient of static friction and thus stress to the fault dip angle together with ambiguities often involved in measuring angles of deep seismic reflectors may make such estimates meaningless in cases where true dip angles cannot be precisely determined

holocene pollen records from caution bay southern mainland papua new guinea this study presents new palynological data from caution bay south central papua new guinea png it explores holocene mangrove transitional events along a tide dominated shoreline and expands reconstructive detail for the wider southern png lowlands coinciding with recent regional archaeological research this study also holds implications for interpretations of the holocene settlement of caution bay and long term people landscape interactions data demonstrate a late holocene mangrove to mudflat transition with vegetation patterns largely a function of low sediment loading sedimentary redistributions and salinisation upon sea level decline c 2000 cal yr bp these trends appear unique to caution bay highlighting a variety of holocene shoreline vegetation changes along the png south coast each dependent on geomorphologic setting and hydrological fluxes further work is required to elucidate vegetation change inland of the coastal zone greater understanding of burning patterns and an archaeological collaboration are required to determine more concisely dryland plant spatial and temporal variability

upper permian as a new play model on the mid norwegian continental shelf investigated by shallow stratigraphic drilling a 750 m thick fully marine succession of sandstones coarse grained turbidites shales and reworked sabkha sediments has been cored on the eastern margin of the mid norwegian shelf the succession has been dated as upper permian lower triassic and is comparable to rocks of the same age exposed onshore east greenland these data demonstrate that the marine depositional basin between greenland and norway extended much farther east than previously thought reddish shallow marine sandstones in the lower 170 m of the cored succession probably represent reworking of older sedimentary rocks present to the east of the drill sites this suggests that upper devonian lower permian sediments were deposited on caledonian basement east of the present day limits of the basin the cored succession also contains source rocks that can be stratigraphically correlated with the oil prone source rocks of the upper permian ravnefjeld formation onshore east greenland some of the cored sandstone intervals were stained with light nonbiodegraded oil that most likely was sourced from upper permian or alternatively lower triassic mudstones reworked fragments of reef building organisms in upper permian turbidites and upper permian carbonates encountered in an exploration well on the nordland ridge indicate that carbonate deposition and reef building occurred on structural highs on the trondelag platform the observations from the cored successions are key elements in a new paleozoic play model on the mid norwegian continental shelf and include the first evidence for the existence of an upper permian source rock in the area with upper permian carbonates or sandstones or triassic jurassic sandstones as reservoir begin page 108

geometry and kinematics of the triassic rift basin in jameson land east greenland the triassic rift basin along the east greenland margin described in this paper is represented by ne sw trending basins and highs segmented by nw se trending transfer zones coarse grained sediments along the eastern side of jameson land are shown to be hosted in half graben structures belonging to the carlsberg fjord basin that is bounded by nw dipping normal faults mapped and described after fieldwork in the klitdal area in liverpool land new aeromagnetic and electromagnetic data together with new drill cores allow the re interpretation of available seismic lines showing the continuation of the triassic rift basin toward the sw where it is buried under the upper triassic post rift sediments and the jurassic successions of the jameson land basin the n s trending liverpool land interpreted as the boundary block of the triassic basin is shown to represent a structural high inherited from the late carboniferous tectonics and faulted during the triassic rifting the carlsberg fjord basin and the klitdal fault system described in this paper should be seen as analogues to the helgeland basin in the norwegian offshore that is bounded by the ylvingen fault zone and to the papa and west of shetlands basins that are bounded by the spine fault the triassic rift zone and transfer faults on both conjugate margins shows a straightforward correlation with the trends of the initial spreading line and fracture zones of the north east atlantic indicating a possible inheritance of the triassic rifting

sediment transport and trapping in marsh systems implications of tidal flux studies although the concept that marshes act as major sediment sinks may be accurate when viewing them over the last few millennia tidal transport studies suggest considerable variability with most marshes presently exporting material on an annual basis high salinity marshes along the mid atlantic coast of the united states appear to be losing 1 2 kg m 2 yr 1 while submerged upland marshes on the delmarva peninsula are eroding at rates of up to 14 kg m 2 yr 1 by comparison at least one deltaic marsh on the dutch coast along with several estuarine marshes appear to be accumulating sediment in order to assess the trapping ability of marshes in large estuaries we constructed a sediment budget for chesapeake bay which included a variety of wetland types calculations indicate that estuarine marshes trap 5 11 of the annual chesapeake bay sediment input or about one half that previously estimated it appears that most sedimentation in estuaries and perhaps other coastal systems occurs in subtidal flats below the limit of emergent marsh vegetation as mud flats become vegetated and estuarine infilling proceeds there may be a tendency for tidal currents to become ebb dominated which promotes a net export of particulates the extent to which major storm events are capable of returning enough material to balance the long term accretionary budget of tidal marshes and keep them abreast of rising sea level is open to question differences in tidal dynamics seasonal changes in sea levels and higher temperatures may help explain why in the u s southern marshes are more susceptible to export and eventual erosion than northern marshes we hypothesize that another factor the recent reductions of terrigenous sediment inputs from the southern river systems of the u s may also be critical sediment starvation may have led to undernourishment of wetland systems of the coastal zone over the last half century which may be reflected in the net export measured in the tidal marshes in this region furthermore we postulate that changes in sediment inputs are more important than eustatic sea level rise in causing the past losses of marshes which are now undergoing mass erosion thus future wetland survival will depend as much as particulate inputs to the coastal zone as on the prospects of a global rise in sea level and more efforts should be made to quantify the sediment budgets of tidal marshes

40ar 39ar thermochronology of late and postorogenic extension in the caledonides of north central norway abstract we report 40ar 39ar mineral cooling data that elucidate the timing and style of devonian late orogenic extensional collapse and permian triassic postorogenic continental rifting in the north central norwegian caledonides 40ar 39ar mineral cooling ages from ductile extensional shear zones that have either excised or reactivated caledonian thrust faults along the western flanks of two major basement domes indicate that late orogenic extensional deformation in this region occurred during the early ca 409 388 ma and late devonian ca 371 355 ma these extensional pulses are consistent with events recently identified by workers investigating areas to the south of our study area the timing and style of the early devonian event supports the northern continuation of the devonian orogen parallel scoop shaped extensional deformation documented in the central norwegian caledonides late devonian extension on the other hand was orogen orthogonal this late devonian event is similar in timing and ki

non hydrostatic modeling of drag inertia and porous effects in wave propagation over dense vegetation fields a new wave vegetation model is implemented in an open source code swash simulating waves till shore the governing equations are the nonlinear shallow water equations including non hydrostatic pressure besides the commonly considered drag force induced by vertical vegetation cylinders drag force induced by horizontal vegetation cylinders in complex mangrove root systems as well as porosity and inertia effects are included in the vegetation model providing a logical supplement to the existing models the vegetation model is tested against lab measurements and existing models good model performance is found in simulating wave height distribution and maximum water level in vegetation fields the relevance of including the additional effects is demonstrated by illustrative model runs we show that the difference between vertical and horizontal vegetation cylinders in wave dissipation is larger when exposed to shorter waves because in these wave conditions the vertical component of orbital velocity is more prominent both porosity and inertia effects are more pronounced with higher vegetation density porosity effects can cause wave reflection and lead to reduced wave height in and behind vegetation fields while inertia force leads to negative energy dissipation that reduces the wave damping capacity of vegetation overall the inclusion of both effects leads to greater wave reduction compared to common modeling practice that ignores these effects but the maximum water level is increased due to porosity with good model performance and extended functions the new vegetation model in swash code is a solid advancement toward refined simulation of wave propagation over vegetation fields

episodic burial and exhumation of the southern baltic shield epeirogenic uplifts during and after break up of pangaea cratons are conventionally assumed to be areas of long term stability however whereas precambrian basement crops out across most of the baltic shield palaeozoic and mesozoic sediments rest on basement in southern sweden and thus testify to a complex history of exhumation and burial our synthesis of published stratigraphic landscape analysis and new apatite fission track analysis data reveals a history involving five steps after formation of the extremely flat sub cambrian peneplain 1 cambrian to lower triassic rocks accumulated on the peneplain interrupted by late carboniferous uplift and exhumation 2 middle triassic uplift removed the palaeozoic cover along the south western margin of the shield leading to formation of a triassic peneplain with a predominantly flat relief followed by deposition of upper triassic to lower jurassic rocks 3 uplift that began during the middle jurassic to earliest cretaceous caused denudation leading to deep weathering that shaped an undulating hilly relief that was buried below upper cretaceous to oligocene sediments 4 early miocene uplift and erosion produced the south smaland peneplain with scattered hills 5 early pliocene uplift raised the miocene peneplain to its present elevation leading to reexposure of the sub cretaceous hilly relief near the coast our results thus provide constraints on the magnitude and timing of episodes of deposition and removal of significant volumes of phanerozoic rocks across the southern portion of the baltic shield late carboniferous middle triassic and mid jurassic events of uplift and exhumation affected wide areas beyond the baltic shield and we interpret them as epeirogenic uplifts accompanying fragmentation of pangaea caused by accumulation of mantle heat beneath the supercontinent early miocene uplift affected north west europe but not east greenland and thus likely resulted from compressive stresses from an orogeny on the eurasian plate early pliocene uplift related to changes in mantle convection and plate motion affected wide areas beyond north east atlantic margins

effects of layering and anisotropy on fault geometry the geometry and orientation of faults are examined using several field examples of small scale 1 with dihedral angles usually of about 50 as predicted by the coulomb theory of failure in layered rocks the geometry of faults varies with the orientation of layering with respect to the stress field where 1 is approximately normal to layering or anisotropy conjugate faults also develop symmetrically about 1 where rocks have interbedded layers with different mechanical behaviours however faults tend to initiate orthogonal to the more brittle layers i e originate as extension fractures sub parallel to 1 but oblique to the less brittle layers as the fault steps through the layering pull aparts are developed which may reduce the dihedral angle where 1 is oblique c 25 75 to anisotropy one set of faults is developed at a high angle to layering with another at a low angle usually showing a ramp flat geometry large dihedral angles up to 90 may result and 1 does not bisect this angle where 1 is approximately parallel to layering two cases can be recognized where 3 is approximately normal to layering faults with layer parallel flats and contractional ramps develop where 2 is approximately normal to layering conjugate faults develop which are symmetrical about 1 the geometry resembling that in isotropic rocks these observations are in agreement with rock deformation experiments which show the strong effect of anisotropy on fault orientation but the observations incorporate the effects of layering of materials with different deformation characteristics

efficient three dimensional reconstruction of aquatic vegetation geometry estimating morphological parameters influencing hydrodynamic drag abstract aquatic vegetation can shelter coastlines from energetic waves and tidal currents sometimes enabling accretion of fine sediments simulation of flow and sediment transport within submerged canopies requires quantification of vegetation geometry however field surveys used to determine vegetation geometry can be limited by the time required to obtain conventional caliper and ruler measurements building on recent progress in photogrammetry and computer vision we present a method for reconstructing three dimensional canopy geometry the method was used to survey a dense canopy of aerial mangrove roots called pneumatophores in vietnam s mekong river delta photogrammetric estimation of geometry required 1 taking numerous photographs at low tide from multiple viewpoints around 1 m2 quadrats 2 computing relative camera locations and orientations by triangulation of key features present in multiple images and reconstructing a dense 3d point cloud and 3 extracting pneumatophore locations and diameters from the point cloud data step 3 was accomplished by a new sector slice algorithm yielding geometric parameters every 5 mm along a vertical profile photogrammetric analysis was compared with manual caliper measurements in all 5 quadrats considered agreement was found between manual and photogrammetric estimates of stem number and of number mean diameter which is a key parameter appearing in hydrodynamic models in two quadrats pneumatophores were encrusted with numerous barnacles generating a complex geometry not resolved by hand measurements in remaining cases moderate agreement between manual and photogrammetric estimates of stem diameter and solid volume fraction was found by substantially reducing measurement time in the field while capturing in greater detail the 3d structure photogrammetry has potential to improve input to hydrodynamic models particularly for simulations of flow through large scale heterogenous canopies

dynamics flushing and trapping in hinchinbrook channel a giant mangrove swamp australia hinchinbrook channel is a 44 km long tidal channel connected at its northern and southern ends to the continental shelf of the great barrier reef the channel drains 164 km 2 of mangrove swamps it also drains the herbert river the dynamics within the channel and the flushing of the fringing mangrove swamps were studied both in the field and using numerical models the dominant currents are tidal semi diurnal and are due to two nearly identical tidal waves entering the channel at its norhtern and southern openings and meeting in the middle the mangrove swamps contribute significantly to the tidal dynamics when the herbert river discharge is small net residual currents are negligible even in the presence of wind and the residence time of water is about 2 months flushing of the fringing mangrove swamps is largely controlled by the trapping effect in the mangrove swamps and is slow with an e fold residence time of about 54 days on the northern end the mangrove fringed channel is wide and shallow and a barotropic coastal boundary layer is formed due to shallow water effects and trapping in mangrove swamps this results in a long term 2 weeks trapping of water along the mangrove fringed coast in calm weather thus coastal waters are continuously exchanged and mixed with mangrove swamp waters but mixing between coastal and offshore waters is much slower

geochemical variations of core sediments of pichavaram lagoon southeast coast of tamil nadu india a provenance and paleoenvironmental study the present study aims to identify the natural and anthropogenic imprints left by the accumulation of elements and to determine identify the current level of enrichment of major oxides in the pichavaram mangrove sediments pichavaram mangrove is a dynamic intertidal environment lying in between the vellar and coleroon estuaries in the cauvery delta along the east coast of india in the present study results of texture studies reveal highly variable depositional environment in upper and lower portion of core 1 and middle portion of core 2 in both the cores decrease in grain size is observed in the upper portion which may suggest that the sediments in the upper portion were deposited at low energy condition mn al mg al ca al ti al p al and k al ratios are found to be low in the both the core samples ti elemental ratio is lower in both core samples indicating that ti concentrations in marine sediments are the best indicators of lithogenous material flux to the marine environment the concentration of various elements in the core can be summarized as si al fe mn mg ca ti p k the pia values of core 1 indicate that the sediments were derived from predominant weathering up to 40 cm and the remaining sediments derived from unweathered matrices plagioclase index of alteration pia values of most of the downcore samples of core 2 are found to be more than 40 suggesting the predominance of weathering activity low pia values are observed at the depth of 54 70 cm indicating the moderately weathered nature of the sediments in the study area positive correlation between fe and mg and their negative relationship with silica indicates the presence of ferromagnesian debris in top of the sediments major oxide geochemistry indicates a heterogeneous and moderately weathered to unweathered source for the sediments of the present study area

incised submarine canyons governing new evidence of early triassic rifting in east greenland abstract regional studies of the uppermost permian and lowermost triassic successions in central east greenland have shown that sedimentation took place in half grabens during two phases of active rifting the permian triassic boundary locally contains submarine canyons up to several kilometres wide and several tens of metres deep formed in latest permian or earliest triassic times sandy and conglomeratic turbidites filling the canyons are highly variable in architecture depending on the structural setting and the geometry of the submarine canyons bounding surfaces also change character because of an asymmetric subsidence pattern of tilted fault blocks the submarine canyons have been studied on wegener halvo where exposures allow tracing of several canyons from the slope to the basin floor setting the canyons are interpreted to have developed from fluvial incised valleys furthest updip on the fault block and from turbidity current erosion further downdip the canyons have a se nw elongation while palaeocurrents were unimodal towards the nw reflecting the dip of the rotated fault block the canyon fill turbidites were deposited by consequent drainage on a nw dipping ramp like hangingwall slope within a half graben in areas between the canyons the permian triassic boundary is onlapped by triassic mudstones of offshore marine origin the studied succession is grouped into two facies associations 1 submarine gravity flow sandstones and conglomerates and 2 suspension deposited shales and mudstones traced down dip the submarine canyon fills display a change from chaotic conglomeratic and coarse sandy high density turbidites proximally to organised sandy turbidites basinwards farthest basinward a remarkable basin floor fan with well developed giant scale foresets is observed this trend reflects canyon widening and a decrease in gradient at the basin floor progradation of the turbidites was probably controlled by westward tilting of the fault block causing a steeper slope and subaerial exposure of a larger part of the proximal hangingwall above the fulcrum this resulted in erosion of the crestal area of the block that is upper permian and older successions and led to an increase in sediment supply to the downdip area accommodation space was created below fulcrum and downdip transgression governed back filling of the submarine canyons the observed eastward onlap of ammonite zones in shales and mudstones between the canyons was contemporaneous with the filling of the canyons a later drowning of the updip catchment caused decrease or shut off of sediment supply leading to deposition of shales and mudstones blanketing the sandy turbidites in the canyons the tilt of the studied fault block is interpreted to have caused simultaneous transgression below the fulcrum and regression with bypass or erosion above the fulcrum it is concluded that the tilted fault block setting has important consequences for sequence stratigraphic interpretations due to the asymmetric subsidence causing drastic changes in bounding surface character tectonism and sediment supply were the main controls on the stratigraphic architecture of the studied lower triassic succession on wegener halvo

moist and the continuity of crustal reflector geometry along the caledonian appalachian orogen new aspects of the deep structure of the scottish caledonides are revealed by the moine and outer isles deep seismic reflection traverse moist the caledonian foreland is underlain by an easterly dipping strongly reflecting surface cutting through the moho and traceable to more than 45 km depth thrusts within the foreland basement and caledonian orogen have been reactivated as normal faults bounding half grabens filled with sediments of late palaeozoic to mesozoic age the moine thrust which carries rocks of the orogen over lewisian foreland dips at 20 25 to the e on moist and is either a the westernmost of a series of easterly dipping reflections thrusts which flatten or terminate at 17 20 km depth or b a thrust lying further e which structurally overlies these easterly dipping reflectors by comparison with easterly dipping reflections on cocorp lines in the northern and southern appalachians the latter interpretation is preferred implying that many of the easterly dipping reflections on moist correspond to off shelf metasedimentary rocks with slivers of basement stacked and imbricated against the lewisian basement edge regional seismic refraction and conductivity data from northern scotland suggest that regions of the caledonian orogen have lower mid crustal velocity gradients and higher conductivities than the foreland which might be explained by this interpretation of the easterly dipping reflections despite similarities in crustal reflector geometries there are important differences between the moist and cocorp lines including 1 a remarkably continuous relatively horizontal moho seen on moist data at about 25 km depth and 2 the sedimentary basins offshore from northern scotland which have formed by reactivation under crustal extension of the easterly dipping thrusts furthermore it is probable that the easterly dipping reflectors in these areas of the moist and cocorp lines were formed at different times in the early palaeozoic

patterns of tidal flooding within a mangrove forest coombabah lake southeast queensland australia tidal flooding and surface drainage patterns have often been used to describe mangrove species zonation however in mangrove forests exhibiting little topography ambiguous species distributions and or few species such approaches are ineffective we identified four physiognomic mangrove forest types riverine fringing overwash and basin at coombabah lake a tidal lake in southeast queensland australia and investigated tidal flooding patterns using synoptic surveys of tidal observations at the local standard port combined with local water depth observation subsequently three sub types of the basin forest type were identified 1 deep basin forest with mature trees 50 cm standing water and 3 tides per year 2 medium depth basin forest with intermediate tree development 15 30 cm standing water and 20 40 tides per year and 3 shallow basin forest with relatively recent mangrove establishment 5 15 cm standing water and 80 tides per year these three basin sub types were found to flood at different tide heights with the shallow basin flooding for tides above mean high water springs and the deep basin flooding only for tide heights approaching the highest astronomical tide we propose that these basin types represent a succession in mangrove forest development that corresponds with increasing water depth and tree maturation over time the succession not only represents increasing age but also change in basin substrate composition this is manifest as increasing pneumatophore density and an increasing area of basin surface occupied by contiguous pneumatophore cover as a result it seems that mangrove development is able to modify tidal flooding into the basin by increasingly impeding water movement

high frequency fluctuations in redox conditions during the latest permian mass extinction abstract new high resolution geochemical and sedimentological data from fiskegrav east greenland reveal fluctuations in marine redox conditions associated with the final disappearance of bioturbating organisms during the latest permian mass extinction lpme sedimentological observations imply a transgressive episode and associated geochemical evidence for decreasing oxygen availability and the establishment of persistently ferruginous fe 2 rich conditions implies the shoreward migration of oxygen deficient waters the long term decline in dissolved oxygen do availability could have been exacerbated by increasing water temperatures reducing the solubility of oxygen and promoting thermal stratification mixing of the water column could have been further inhibited by freshwater influxes that could have generated salinity contrasts that reinforced thermal stratification enhanced runoff could also have increased the delivery of nutrients to the marine shelf stimulating biological oxygen demand bod during the transition to persistently ferruginous conditions we identify intervals of intermittent benthic meiofaunal recolonization events that we attribute to small transient increases in do availability the mechanism controlling these fluctuations remains speculative but given the possible centennial to millennial scale frequency of these changes we hypothesise that the mid latitude setting of fiskegrav during the late permian was sensitive to changes in atmospheric circulation patterns which may have influenced local precipitation and intermittently modulated some of the processes promoting anoxia

origin of regional rooted low angle normal faults a mechanical model and its tectonic implications rooted listric low angle normal faults 20 of regional extent have been recognized widely in the past few years in the north american cordillera and elsewhere the low angle geometry of these crustal scale normal faults conflicts with anderson s 1942 classic theory of faulting in that theory the orientations of principal stresses are assumed to be vertical and horizontal the predicted dip angle of normal faults is about 60 rather than 20 or less recent geological and geophysical studies in the mid tertiary extensional terrane of southeastern california and western arizona suggest that thick mylonitic gneisses in the lower plates of low angle detachment faults may represent unidirectionally sheared laminar flow in and below the midcrust directed ductile flow possibly related to the gravitational spreading of thickened lower crust may induce a shearing traction on the horizontal or subhorizontal base of the brittle upper crust thus the orientations of the principal stresses can no longer be vertical and horizontal at this interface a simple elastic model incorporates the effect of basal shearing due to gravitational spreading on stress distributions in an elastic upper crust this model shows that parallel belts of compression and extension can be produced if a shearing traction acting on the base of the elastic upper crust is considered in particular appropriate stress conditions for the formation of regional low angle normal faults 20 can be produced by the superposition of two stress fields a basal shear stress field induced by the basal shear traction and a contractional stress field in which the horizontal deviatoric stress is compressional and the vertical gradient of the horizontal normal stress component is constant this superposed stress field may represent a tectonic setting where a stress field with compressional deviatoric stress induced by plate subduction or convergence is superposed on a basal shear stress field induced by gravitational spreading of thickened lower crust these results may explain both puzzling parallel belts of extension and compression and the occurrence of major low angle normal faults in some orogenic systems

variation of the regional stress tensor at the western great basin boundary from the inversion of earthquake focal mechanisms the orientation of the principal axes of the regional stress tensor in and near the western great basin boundary is calculated from the inversion of earthquake focal mechanism data data were taken from three regions along the western great basin sierra nevada boundary mammoth lakes round valley and chalfant valley and at two regions within the great basin interior mono walker lake and west central nevada the depth range is similar for all data earthquakes are essentially restricted to the uppermost 16 km of the crust the stress tensor changes from the great basin boundary to the basin interior for example the extension direction changes by about 50 from roughly e w at the boundary in the west to roughly nw se inside of the basin in the boundary region the mean t axis inferred from focal mechanisms rotates clockwise by 27 from n64 e in the mammoth lakes area to n91 e in the chalfant valley about 50 km southeast of mammoth lakes however the components of the best fitting stress tensors in the two regions vary only by 12 so that a common stress tensor with a greatest principal stress azimuth of n10 w and a least principal stress azimuth of n80 e both components nearly horizontal favoring strike slip describes the seismic deformation of the boundary region quite well the stress tensors for the mono region and west central nevada have similar greatest and least principal stress azimuths northeasterly and northwesterly respectively however the plunges of the greatest principal stress are different nearly horizontal for the mono area and about 45 for central nevada reflecting the strong contribution of normal faulting in the central nevada earthquake data the resulting values which describe the relative sizes of the three stress components vary from 0 5 to 0 65 which indicates that the magnitudes of the three principal stresses are of similar size

estuarine flocs their size settling velocity and density the size and settling velocity of flocs of suspended sediments from the chesapeake bay were measured in laboratory experiments and in the field the curves between floc diameter and settling velocity showed a non stoke s relationship that was best described by the following settling velocity cm s 1 73 floc diameter cm 0 78 furthermore the relationship between floc diameter and settling velocity indicated that the floe density decreased as the floes increased in size in addition to changing density a cylinder shape was found to be the best shape factor