the role of kelp in sediment transport observations from southeast new zealand abstract large marine algae such as kelp can when dislodged remove part of the substrate to which they are attached and subsequently transport it quantification of this process and the causes behind it have rarely been investigated this study examines sediment transport by the kelps durvillaea antarctica and durvillaea willana in southeast new zealand five beaches near dunedin were surveyed weekly for 30 weeks and all beach cast kelp was counted and identified the weight and nature of any attached sediment was also recorded additionally 60 sections of the southeast new zealand coastline totaling 130 km were surveyed once and all beach cast kelp examined rocks were found to be attached to 27 of examined holdfasts usually occurring as a thin veneer the weight per holdfast ranged from 0 1 g to 83 kg with an unusual outlier of 365 kg with a mean weight of 77 1 g se 15 3 n 1560 most holdfasts transported less than 100 g carbonate material occurred on 84 of holdfasts with weights per holdfast ranging from 0 02 to 116 56 g with a mean of 7 8 g se 0 3 n 1695 the character of local rock strongly influences the kelp mediated flux south coast beaches with schist rocks nearby received a significantly greater mean flux 7 49 g m2 year 1 than basalt surrounded peninsula beaches mean flux 0 50 g m2 year 1 kelp transported material provides a small but significant source of sediment to beaches in southeast new zealand and therefore should be considered when constructing sediment budgets in coastal areas this study has shown that it is often necessary for geologists to consider biological processes

spectrally based mapping of riverbed composition abstract remote sensing methods provide an efficient means of characterizing fluvial systems this study evaluated the potential to map riverbed composition based on in situ and or remote measurements of reflectance field spectra and substrate photos from the snake river wyoming usa were used to identify different sediment facies and degrees of algal development and to quantify their optical characteristics we hypothesized that accounting for the effects of depth and water column attenuation to isolate the reflectance of the streambed would enhance distinctions among bottom types and facilitate substrate classification a bottom reflectance retrieval algorithm adapted from coastal research yielded realistic spectra for the 450 to 700 nm range but bottom reflectance based substrate classifications generated using a random forest technique were no more accurate than classifications derived from above water field spectra additional hypothesis testing indicated that a combination of reflectance magnitude brightness and indices of spectral shape provided the most accurate riverbed classifications convolving field spectra to the response functions of a multispectral satellite and a hyperspectral imaging system did not reduce classification accuracies implying that high spectral resolution was not essential supervised classifications of algal density produced from hyperspectral data and an inferred bottom reflectance image were not highly accurate but unsupervised classification of the bottom reflectance image revealed distinct spectrally based clusters suggesting that such an image could provide additional river information we attribute the failure of bottom reflectance retrieval to yield more reliable substrate maps to a latent correlation between depth and bottom type accounting for the effects of depth might have eliminated a key distinction among substrates and thus reduced discriminatory power although further more systematic study across a broader range of fluvial environments is needed to substantiate our initial results this case study suggests that bed composition in shallow clear flowing rivers potentially could be mapped remotely

diagenesis associated with cooling during burial an example from lower cretaceous reservoir sandstones sirt basin libya fluid inclusions in quartz and dolomite cements were used to determine temperature timing origin and function of fluids in the diagenetic evolution of the lower cretaceous upper sarir sandstone sirt basin libya transmitted light backscattered electron and scanning electron microscope sem cathodoluminescence analyses were carried out to determine the paragenesis in quartz overgrowths fluid inclusions along the grain overgrowth boundary yield homogenization temperatures from 130 to 141 degreesc and salinities between seawater and freshwater aqueous fluid inclusions in later quartz overgrowths have homogenization temperatures from 114 to 129 degreesc and salinities between 18 and 21 wt nacl equivalent fluid inclusions in dolomite have variable homogenization temperatures 120 141 degreesc and high salinities 20 22 wt nacl equivalent this trend in homogenization temperatures of fluid inclusions is interpreted as the result of quartz cement precipitation in the presence of hot low salinity connate fluids connected with an increased heat flow related to regional rifting later quartz overgrowths precipitated during regional cooling concurrent with the end of the rifting and after invasion of saline fluids possibly brought in from adjacent areas or refluxed downward during or after times of evaporite deposition this diagenetic history linked to a decreasing heat flow could be common in other aborted rift basins which are important targets for oil exploration

the algal lift buoyancy mediated sediment transport the role of benthic algae as biostabilizers of sediments is well known however their potential to lift and transport sediments remains unclear under low flow conditions matured algal mats may detach from the bed and may lift up sediment thereby causing disturbance to the uppermost streambed sediment we tested the potential of algal mats to lift sediments in 12 indoor flumes filled with sand 0 2 0 8 mm gravel 2 8 mm or a sand gravel mixture 25 75 mass after four weeks the algal mats covered about 50 of the flumes area due to the accumulation of oxygen gas bubbles in the mats that developed from high primary production at 4 5 weeks about half of the algal mats detached from the bed carrying entangled sediments both the area covered by algal mats and detached area were similar among sediment types but the amount of sediment transported tended to be higher for sand and sand gravel mixture compared to gravel our results reveal that biologically mediated sediment transport mainly depends on the development of a dense filamentous algal matrix that traps gas bubbles increasing the mats buoyancy this novel mechanism of sediment transport will occur in shallow ecosystems during low flow periods with the highest impact for sandy sediments

thermal evolution of the kuh e asmari and sim anticlines in the zagros fold and thrust belt implications for hydrocarbon generation abstract mixed layer clay minerals vitrinite reflectance and geochemical data from rock eval pyrolysis were used to constrain the burial evolution of the mesozoic cenozoic successions exposed at the kuh e asmari dezful embayment and sim anticlines fars province in the zagros fold and thrust belt in both areas late cretaceous to pliocene rocks show low levels of thermal maturity in the immature stages of hydrocarbon generation and early diagenetic conditions r0 i s and ro values

shear fracture patterns and connectivity at geometric complexities along strike slip faults shear fracture patterns and connectivity at geometric complexities such as echelon fault steps and fault bends along strike slip faults are investigated by simulating shear fracture propagation paths using a displacement discontinuity boundary element method together with a maximum distortional strain energy density criterion it is shown that shear fracture patterns and connectivity depend on the specific geometric configurations the applied stress orientations and the coefficient of friction for a given initial configuration of the major faults the subsequent patterns of the associated shear fractures and their linkage can be predicted if the remote state of stress and the coefficient of friction are known the analyses of fault geometries commonly encountered in nature have important implications for evaluating the effect of faults on fluid flow and earthquake hazards associated with the geometric complexities along strike slip faults in the upper crust

diagenetic and thermal history of the jurassic tertiary succession of the zagros mountains in the dezful embayment sw iran constraints from fluid inclusions to constraint the diagenetic and thermal history in the mesozoic tertiary succession of the zagros fold belt a study was performed on fluid inclusions trapped in intergranular vug and fracture filling cements in jurassic to miocene outcrop samples collected along the anneh and fahliyan valleys of khuzestan province southwest iran petrographic observations showed at least two systems of fractures that postdate intergranular cementation two different types of oil filled fluid inclusions occur in the intergranular cements and in the first fracture network but they are absent in the second fracture network microthermometry of fluid inclusions was used to determine the temperature and salinity of fluids responsible for mineral precipitation within intergranular cements and calcite fillings the oldest fractures precipitation occurred from high saline fluids in a temperature range of 60 120 c depending on the stratigraphic depth the strong correlation between fluid inclusions temperature and stratigraphic depth suggests that the intergranular cementation and the first fracture filling event occurred prior to structural deformation furthermore this correlation indicates a relatively constant paleogeothermal gradient at the time of cement precipitation of about 28 c km on the contrary fluid inclusions trapped in cements within the second fracture network lack oil and contain freshwater trapped at low temperatures that do not correlate to the stratigraphic position this suggests second fracturing event occurred after oil migration and during or after deformation of the zagros fold belt when the samples were in a near surface position

erosion of biofilm bound fluvial sediments sediment grains in rivers are often bound together and stabilized by bacterial films experiments and mathematical models show that sediments bound by biofilms behave like a single elastic membrane that can rip catastrophically if the river flows fast enough

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

three dimensional modeling of pull apart basins implications for the tectonics of the dead sea basin we model the three dimensional 3 d crustal deformation in a deep pull apart basin as a result of relative plate motion along a transform system and compare the results to the tectonics of the dead sea basin the brittle upper crust is modeled by a boundary element technique as an elastic block broken by two en echelon semi infinite vertical faults the deformation is caused by a horizontal displacement that is imposed everywhere at the bottom of the block except in a stress free shear zone in the vicinity of the fault zone the bottom displacement represents the regional relative plate motion results show that the basin deformation depends critically on the width of the shear zone and on the amount of overlap between basin bounding faults as the width of the shear zone increases the depth of the basin decreases the rotation around a vertical axis near the fault tips decreases and the basin shape the distribution of subsidence normalized by the maximum subsidence becomes broader in contrast two dimensional plane stress modeling predicts a basin shape that is independent of the width of the shear zone our models also predict full graben profiles within the overlapped region between bounding faults and half graben shapes elsewhere increasing overlap also decreases uplift near the fault tips and rotation of blocks within the basin we suggest that the observed structure of the dead sea basin can be described by a 3 d model having a large overlap more than 30 km that probably increased as the basin evolved as a result of a stable shear motion that was distributed laterally over 20 to 40 km

the zagros fold and thrust belt in the fars province iran ii thermal evolution abstract temperature dependent clay minerals and vitrinite reflectance data surface and subsurface geological constraints were used to unravel the burial evolution of the ordovician quaternary sedimentary successions from the inner to the outer zones of the zagros fold and thrust belt in the fars province iran these sedimentary successions were buried to their thermal maxima during early to late diagenesis achieving temperatures corresponding to the immature to early mature stages of hydrocarbon generation they experienced low levels of thermal maturity in the interior fars corresponding to vitrinite reflectance values between 0 38 and 0 66 to mixed layers illite smectite i s with an illite content between 30 and 75 and to ki values between 0 97 and 1 18 2 in the central and coastal fars vitrinite reflectance ranges between 0 35 and 0 51 the illite content in i s displays values between 20 and 85 and ki data are between 0 71 and 1 30 2 in individual anticlines mixed layers i s show an increase of the illite content as a function of stratigraphic age depth suggesting that levels of thermal maturity are controlled by sedimentary burial one dimensional thermal history models allowed us i to estimate the maximum burial experienced by the sedimentary successions and the amount of the sedimentary pile currently removed by erosion ii to determine the thickness of the ophiolite units obducted during late cretaceous time in the high zagros and iii to define the onset of oil generation for the albian source rocks throughout the zagros belt paoleothermal data were used to constrain the geometry of eroded structures in a 253 km long cross section extending from the high zagros to the coastal fars along the cross section lithostatic load slightly decreases towards the foreland e g from 3 65 km to 3 2 km for the bangestan group and the amount of the eroded material varies between 6 km above anticlines in the central and interior fars and 200 m above synclines in the external part of the belt

variation of structural style and basin evolution in the central zagros izeh zone and dezful embayment iran abstract structural style and its relationship to sedimentary facies and the evolution of sedimentary depocenters since late cretaceous times have been studied on the basis of one regional balanced transect and several updated isopach maps in the izeh zone and the dezful embayment central zagros this study relies on fieldwork data existing geological maps seismic data and well information a new structural classification for part of the zagros sedimentary cover is presented to highlight the different mechanical behavior of the formations in the stratigraphic column it shows the existence of several local decollement levels activated during folding these decollement levels separate lithotectonic units which accommodate shortening in different ways the lower paleozoic is the basal decollement level throughout the studied area triassic evaporites albian shales eocene marls and miocene evaporites can act as intermediate decollement levels and present variable facies in the central zagros lateral facies and thickness variations the sedimentary overburden and the close relationship with inherited fault patterns influenced the wavelength amplitude and style of folding in the study area furthermore surface structures do not necessarily coincide with deeper objectives where these disharmonic levels are involved in folding the evolution of sedimentary depocenters from the late cretaceous obduction episode until early miocene collision is described based on updated isopach maps and tectonic subsidence curves this analysis shows continuous compression and movements along n s and nw se trending faults in the zagros basement which predate the neogene zagros folding and influence sedimentation history it also indicates a southwestward migration of the depocenters through time in addition to the basement involvement below some folds during the zagros orogeny

fluid inclusions record thermal and fluid evolution in reservoir sandstones khatatba formation western desert egypt a case for fluid injection a fluid inclusion and petrographic study focused on quartz overgrowths was performed in reservoir sandstones from the jurassic khatatba formation salam oil field egypt s western desert the combination of detailed fluid inclusion petrography and scanning electron microscope sem cathodoluminescence imaging has allowed us to relate individual fluid inclusion assemblages that is the most finely discriminated groups of petrographically associated fluid inclusions to specific growth zones of authigenic quartz establishing the relative timing of entrapment of the inclusions after entrapment fluid inclusions in authigenic quartz have been preserved without reequilibration as indicated by the narrow ranges of homogenization temperatures 4 5 degreesc in most fluid inclusion assemblages three main growth zones are distinguished under sem cathodoluminescence in the quartz overgrowths and are termed q1 q2 and q3 from the oldest to the youngest zone q1 is further subdivided into three subzones and contains abundant primary aqueous inclusions their homogenization temperatures range from 162 to 130 degreesc with the earliest assemblages having the highest temperatures and with some large temperature fluctuations indicated between successive assemblages most q1 inclusions have salinities in the freshwater to seawater range with a trend toward increasing salinity through time zone q2 contains primary aqueous inclusions with homogenization temperatures overall range 148 125 degreesc also recording large temperature fluctuations and cooling events the q2 fluid inclusions have high salinities 5 20 wt nacl equivalent with salinity increasing through time zone q3 contains both aqueous and oil inclusions of primary origin the q3 aqueous inclusions have homogenization temperatures overall range 134 112 degreesc recording overall cooling and high salinities 21 24 wt nacl equivalent in early q3 subzones oil inclusions appear to be of medium gravity undersaturated with respect to gas in later q3 subzones oil inclusions are of gas saturated lighter oil our results indicate that fluid flow involving drastic changes in temperature and salinity was responsible for the precipitation of some of the quartz cement the earliest quartz q1 precipitated from freshwater and seawater at temperatures significantly higher than those expected from the burial history and thermal maturity of these rocks this quartz is interpreted to have precipitated during cooling of injected fluids that originated as hot connate fluids from deeper parts of the basin the q2 precipitation is interpreted to have resulted from episodes of injection of hot saline brines from below late quartz cement q3 precipitated during oil charge from progressively cooler and more saline brines interpreted to have refluxed from the surface it preserves a record of increasing oil maturity and gas saturation through time

shishimuta caldera the buried source of the yabakei pyroclastic flow in the hohi volcanic zone japan drill hole geochronologic and gravity data identify the buried shishimuta caldera beneath post caldera lava domes and lacustrine deposits in the center of the hohi volcanic zone the caldera is the source of the yabakei pyroclastic flow which erupted 1 0 ma ago with a bulk volume of 110 km3 the caldera is a breccia filled funnel shaped depression 8 km wide and 3 km deep with a v shaped negative bouguer gravity anomaly up to 36 mgal neither ring vents nor resurgence was recognized instead post caldera monogenetic volcanism in an extensional setting dominated the area the andesitic breccia has a relatively low density and fills the caldera it possibly formed by fragmentation of disrupted roof rock during the violent yabakei eruption and related collapse fewer normal faults and shallow microearthquakes occur inside the caldera than around it possibly because rocks beneath the caldera are structurally incoherent a profile of shishimuta caldera may be more elongated vertically and have a more intensely fractured zone than that of a valles type caldera

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

ironstone deposits hosted in eocene carbonates from bahariya egypt new perspective on cherty ironstone occurrences abstract this paper gives new insight into the genesis of cherty ironstone deposits the research was centered on well exposed unique cherty ironstone mineralization associated with eocene carbonates from the northern part of the bahariya depression egypt the economically important ironstones occur in the naqb formation early eocene which is mainly formed of shallow marine carbonate deposits periods of lowstand sea level caused extensive early dissolution karstification of the depositional carbonates and dolomitization associated with mixing zones of fresh and marine pore water in faulted areas the eocene carbonate deposits were transformed into cherty ironstone with preservation of the precursor carbonate sedimentary features i e skeletal and non skeletal grain types thickness bedding lateral and vertical sequential arrangement and karst profiles the ore deposits are composed of iron oxyhydroxides mainly hematite and goethite chert in the form of micro to macro quartz and chalcedony various manganese minerals barite and a number of subordinate sulfate and clay minerals detailed petrographic analysis shows that quartz and iron oxides were coetaneous and selectively replaced carbonates the coarse dolomite crystals having been preferentially transformed into quartz whereas the micro crystalline carbonates were replaced by the iron oxyhydroxides a number of petrographic sedimentological and structural features including the presence of hydrothermal mediated minerals e g jacobsite the geochemistry of the ore minerals as well as the structure controlled location of the mineralization suggest a hydrothermal source for the ore bearing fluids circulating through major faults and reflect their proximity to centers of magmatism the proposed formation model can contribute to better understanding of the genetic mechanisms of formation of banded iron formations bifs that were abundant during the precambrian

petroleum inclusions in sedimentary basins systematics analytical methods and applications abstract fluid dynamics in sedimentary basins is of tremendous interest both from a scientific and an economic point of view integration between fluid inclusion and present day fluid data provides the time aspect necessary for reconstruction of fluid flow paths and can be used for mapping fluid dynamics both on a regional basin scale or on the more local scale of petroleum reservoirs this paper presents a review of analytical and modelling methods for petroleum in fluid inclusions essentially four types of data for petroleum inclusions can be established through analysis and modelling 1 textures which give indirect information of the time aspect 2 fluid composition 3 fluid properties and 4 pressure temperature of trapping during the last decade development of analytical methods for determination of inclusion fluid compositions has taken place traditional correlation studies for characterisation of maturity and source facies may now therefore include fluid inclusion data the development has also been directed towards an improved understanding of the physical properties of petroleum inclusions although these methods are in their early stages concerning precision and accuracy data necessary for fluid flow modelling such as fluid densities viscosities pressure and temperature can be estimated

regional fluid flow as a factor in the thermal history of the illinois basin constraints from fluid inclusions and the maturity of pennsylvanian coals vitrinite reflectance measurements on pennsylvanian coals in the illinois basin indicate significantly higher thermal maturity than can be explained by present day burial depths an interval of additional sedimentary section now removed by erosion has been suggested to account for the discrepancy although burial could indeed account for the observed maturity levels of organic matter fluid inclusion temperatures provide a stringent additional constraint in this article we combine measurements of coal maturity with fluid inclusion temperatures from three sites to constrain the basin s thermal and burial history the fluorspar district at the illinois basin s southern margin the upper mississippi valley zinc district at the basin s northern margin and a north central location two dimensional numerical modeling of a north south cross section through the basin tests scenarios both with and without regional fluid flow vitrinite reflectance values can be matched assuming burial by 1 8 2 8 km of southward thickening additional post pennsylvanian sedimentary section in the central and northern illinois basin however these burial depths and temperatures are not sufficient to account for the fluid inclusion data to account for both parameters with burial alone does not appear feasible in contrast our best hypothesis assumes a wedge of post pennsylvanian sediment thickening southward to about 1 2 km and a brief period of magmatism in the fluorspar district significant advective heat redistribution by northward regional fluid flow accounts for fluid inclusion temperatures and coal maturities throughout the basin the modeling results demonstrate the potential contribution of advective heat transport to the thermal history of the illinois basin begin page 258

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

cooling in rifting sequences during increasing burial depth due to heat flow decrease two case histories are presented to give evidences for sediment cooling during increasing burial depth due to heat flow decrease at the end of crustal stretching in extensional settings the first refers to the lower cretaceous succession accumulated in a strongly subsiding trough within the sirt basin libya the second relates to the mesozoic succession of the lombardian basin nw italy formed during late triassic early jurassic rifting of the northern margin of the adriatic microplate in both cases heat flow decreasing at the end of crustal stretching overbalanced the thermal effect of increasing burial depth causing a net cooling of rocks these examples provide an alternative to exhumation for explaining cooling events recorded by rifting sedimentary sequences

history of basin formation and tectonic evolution at the termination of a large transcurrent fault system deformation mode of central kyushu japana abstract the central part of the kyushu island is a locus of active arc volcanism associated with subduction of the philippine sea plate being located at a bend in the boundary between the philippine sea and eurasian plates a complicated lateral displacement has generated half grabens a zone of strike slip and rhomboidal basins filled with volcanic material in central kyushu initial northward subduction in latest miocene time activated the n s trending kokura tagawa tectonic line ktl as a left lateral slip fault that bounds the western margin of the area of volcano tectonic depression the hohi volcanic zone which was initially formed about 6 ma ago the depocenter which is now called kuju basin in the hohi volcanic zone was at the corner of the ktl and the e w trending median tectonic line mtl relative convergence direction of the philippine sea plate shifted counterclockwise at about 1 5 ma and active motion on the ktl declined at the same time west northwestward subduction enhanced right slip on the mtl geologic gravimetric and seismic data indicate that the mtl has shifted its active trace northward in central kyushu as far as 10 km as a result the depocenter adjacent to the transcurrent fault migrated northeastward in the hohi volcanic zone specifically from kuju basin pliocene via shonai basin early quaternary to beppu bay basin late quaternary the latest depocenter of the beppu bay is surrounded by active faults that clearly delineate a rhomboidal basin on the mtl central kyushu exemplifies the basin forming history and tectonic evolution at the termination of a large transcurrent fault system

the effect of buoyant biofilms on the erodibility of sublittoral sediments of a temperate microtidal estuary an in situ benthic flume sea carousel was deployed at eight stations along a transect upper south cove nova scotia to examine the influence of biofilms on sediment erodibility subsamples of the material eroded within the sea carousel were collected by pumping and were analyzed for suspended particulate matter spm undisturbed syringe cores of the seabed were also collected and analyzed for major physical properties bulk density mineralogy grain size and organic character chlorophyll pheopigment colloidal carbohydrate organic content strong relationships between erosion thresholds and rates and sediment chlorophyll r2 0 948 r 0 875 and colloidal carbohydrate 6 0 854 r 0 774 content were observed suggesting that both pigment and mucilage biotilm variables serve as good indicators of sediment stability erosion rates varied by a factor of 7 along the station transect while erosion thresholds varied only by a factor of 2 thus erosion rate was a more sensitive indicator of trends in sediment stability than was erosion threshold x ray computed tomography revealed the presence of a buoyant chlorophyll containing gel mud in the uppermost millimeters of the sediment column the sectioning of undisturbed syringe cores revealed that the buoyant layer was associated with the surface chlorophyll layer the reduction of sediment weight geostatic load in the surface biogenic layer may have a significant effect on sediment erodibility and explain the low erosion thresholds observed in this estuary

three dimensional models of deformation near strike slip faults we use three dimensional elastic models to help guide the kinematic interpretation of crustal deformation associated with strike slip faults deformation of the brittle upper crust in the vicinity of strike slip fault systems is modeled with the assumption that upper crustal deformation is driven by the relative plate motion in the upper mantle the driving motion is represented by displacement that is spectied on the bottom of a 15km thick elastic upper crust everywhere except in a zone of finite width in the vicinity of the faults which we term the shear zone stress free basal boundary conditions are specified within the shear zone the basal driving displacement is either pure strike slip or strike slip with a small oblique component and the geometry of the fault system includes a single fault several parallel faults and overlapping en echelon faults we examine the variations in deformation due to changes in the width of the shear zone and due to changes in the shear strength of the faults in models with weak faults the width of the shear zone has a considerable effect on the surficial extent and amplitude i c1 j l c i rl l b blhi aill i srizcxi ld 3 rr ij i n flail 3il i dilitiiiat df ti ijtluii clicili c i i zor tz a j t s ii acmes strong fault lnnlds havs lnore luc tlixd dxz a ac tip of tne faults and the deformation is partly distributed outside the fault zone the dimensions of large basins along strike slip faults such as the rukwa and dead sea basins and the absence of uplift around pull apart basins fit models with weak faults better than models with strong faults our models also suggest that the length to width ratio of pull apart basins depends on the width of the shear zone and the shear strength of the faults and is not constant as previously suggested we show that pure strike slip motion can produce tectonic features such as elongate half grabens along a single fault rotated blocks at the ends of parallel faults or extension perpendicular to overlapping en echelon faults which can be misinterprete d to indicate a regional component of extension zones of subsidence or uplift can become wider than expected for transform plate boundaries when a minor component of oblique motion is added to a system of parallel strike slip faults

volcanic and structural history of the hohi volcanic zone central kyushu japan more than 5000 km3 of magmatic material was erupted in pliocene pleistocene times in a volcano tectonic depression i e the hohi volcanic zone hvz in central kyushu japan the eruptive deposits consist mainly of andesite lava flows and large scale pyroclastic flow deposits their eruptions were accompanied by the formation of an ew oriented graben 70 km 45 km under regional ns extensional stress pre tertiary basement rocks are absent on the surface of the graben but occur at depth having subsided up to 3 km radiometric ages of volcanic rocks on the surface show zoned isochrons from 5 ma at the margin to 0 3 ma in the center of the hvz the youngest center of age zonation coincides with a 30 mgal negative bouguer gravity anomaly radiometric ages of rocks from drill cores are older toward the bottom of the graben reaching a maximum of at least 4 ma volcanic activity concentrated over time toward the center of the graben and buried successively erupted material areas of active volcanism in the hvz became smaller and changed in style during the 5 ma history of activity volcanism of the early stage 5 2 ma was characterized by voluminous eruptions of andesitic lava flows that formed lava plateaus and were intruded by ew oriented feeder dikes perhaps related to fissure eruptions in contrast late stage volcanism 2 0 ma resulted primarily in andesitic to dacitic lava domes with features of monogenetic volcanoes produced at low eruption rates the hvz shows unimodal volcanism dominated by andesitic and dacitic lavas with a small amount of rhyolite and only traces of basalt these characteristics differ from those that typify volcanism in most other extensional areas erupted material in the hvz is of the calc alkali and high alkali tholeiite series and shows no significant chemical changes over 5 ma except for an increase in k2o after 1 6 ma the net horizontal displacement along normal faults indicates that the hvz widened by about 10 20 across the graben at an average rate of 0 1 cm yr i interpret the hvz to be neither a pull apart structure of the pre tertiary basement nor the result of propagation of the okinawa trough but rather the earliest stage of rifting when vertical subsidence caused by normal faulting is compensated by filling with volcanic material

negligible microbial matground influence on pre vegetation river functioning evidence from the ediacaran lower cambrian series rouge france supported by shell international exploration and production b v under research framework agreement pt38181

fluid rock interactions associated with regional tectonics and basin evolution an integrated approach consisting of fracture analysis petrography carbon oxygen and strontium isotope analyses as well as fluid inclusion micro thermometry led to a better understanding of the evolution of fluid rock interactions and diagenesis of the upper permian to upper triassic carbonates of the united arab emirates the deposited carbonates were first marked by extensive early dolomitization during progressive burial the carbonates were affected by dolomite recrystallization as well as precipitation of vug and fracture filling dolomite quartz and calcite cements after considerable burial during the middle cretaceous sub vertical north south oriented fractures f1 were cemented by dolomite derived from mesosaline to hypersaline fluids upon the late cretaceous maximum burial and ophiolite obduction sub vertical east west fractures f2 were cemented by dolomite dc2 and saddle dolomite ds derived from hot highly saline fluids then minor quartz cement has precipitated in fractures from hydrothermal brines fluid inclusion analyses of the various diagenetic phases imply the involvement of increasingly hot 200 degrees c saline brines 20 to 23 nacl eq through one dimensional burial history numerical modelling the maximum temperatures reached by the studied rocks are estimated to be in the range of 160 to 200 degrees c tectonically driven flux of hot fluids and associated diagenetic products are interpreted to have initiated during the late cretaceous maximum burial and lasted until the oligocene miocene compressional tectonics and related uplift the circulation of such hydrothermal brines led to partial dissolution of dolomites dc2 and ds and to precipitation of hydrothermal calcite c1 in new mainly oriented north south f3 and pre existing reactivated fractures the integration of the obtained data confirms that the diagenetic evolution was controlled primarily by the interplay of the burial thermal evolution of the basin and the regional tectonic history hence this contribution highlights the impacts of regional tectonics and basin history on diagenetic processes which may subsequently affect reservoir properties

paleotemperatures from fluid inclusions advances in theory and technique fluid inclusions in diagenetic minerals can be used to determine paleotemperatures three sets of observations are necessary to make accurate interpretations 1 detailed petrography to establish the relative time of formation of the inclusions 2 careful analysis of the burial and tectonic history of the host rocks to tie diagenesis to the geologic history of the basin and finally 3 analysis of the phase behavior and chemical composition of individual inclusions to define the pressure volume temperature pvt properties of the trapped fluids

offset on the main recent fault of nw iran and implications for the late cenozoic tectonics of the arabia eurasia collision zone summary we use drainage patterns geological markers and geomorphological features to determine a right lateral offset of 50 km and possibly as much as 70 km on the main recent fault in nw iran this fault trends nw se and forms the ne border of the zagros mountains it accommodates the strike slip component of the n s convergence between arabia and eurasia with the ne sw shortening component being accommodated in the zagros fold belt its 50 km strike slip offset implies a shortening of 50 km in the fold belt and 70 km total n s convergence accommodated in the nw zagros this is a substantial fraction of the 85 140 km overall arabia eurasia convergence expected over the last 3 5 ma if the main recent fault initiated at that time as seems likely from geological arguments it has a horizontal slip rate of at least 10 17 mm yr 1 and should be the source of frequent earthquakes of ms 6 7 as has been seen in the 20th century and the earlier historical record the similarity of the offsets and probable ages of the north anatolian and main recent faults suggests that they have been active as an almost continuous zone of right lateral shear on the north edge of the arabian and anatolian plates since the early pliocene

restoration of the depression structure at the eastern part of central kyushu japan by means of dislocation modeling abstract we have attempted to restore a subsurface structure in the eastern part of central kyushu japan by combining fault motions which were modeled as dislocation planes embedded in an elastic isotropic half space the simulated crustal deformation pattern was compared with the subsurface structures estimated from gravity anomalies and or seismic prospecting the modeling procedure successfully restored all tectonic basins in the area without any need for motive forces for uplift or subsidence the results also suggest that two major tectonic events have occurred in this region those are 1 the formation of half graben caused by north south extension and 2 the formation of the pull apart basin caused by east west compression

the application of fluid inclusions to migration of oil and diagenesis in petroleum reservoirs abstract fluid inclusions can be used to interpret thermal history and petroleum maturation and migration relative to burial history temperature pressure and composition data collected from fluid inclusions are used to determine the environment of diagenesis and the timing of cementation and migration cements in petroleum reservoirs contain both oil and aqueous fluid inclusions fluorescence spectroscopy is used to identify oil inclusions and to determine the maturity of entrapped oil the lifetime of fluorescence induced by a pulsed laser is related to the api gravity of entrapped oil interpretation of fluid inclusion data depends on knowing the origin of fluid inclusions and the probability that they survive in the burial environment those aspects of fluid inclusion study are investigated by synthesizing oil and aqueous inclusions in calcite crystals in laboratory experiments examples of how fluid inclusions are used to determine the physico chemical environments of diagenesis in petroleum reservoirs and the timing of cementation and migration are given for the wealden basin england the mishrif formation dubai the smackover formation gulf coast u s a and jurassic sandstones offshore norway in the wealden basin temperature data from fluid inclusions are used to determine that oil migration occurred in the cretaceous and that the reservoir rocks have been uplifted to varying degrees at a time after migration distribution of oil inclusions indicates that generation and migration of oil was principally in the western part of the basin the geochemistry of oil inclusions in calcite cements from the mishrif formation dubai are used to determine the type and maturity of entrapped oil temperature data from oil and water inclusions are used to relate reservoir diagenesis to burial history and the migration of oil in deep smackover reservoirs oil contains h 2 s the origin of the h 2 s is examined by study of fluid inclusions containing h 2 s in jurassic sandstones offshore norway fluid inclusion studies show that silica cementation is related to burial depth whereas a later calcite cementation originated from invasion of a hot fluid

progressive unconformities within an evolving foreland fold thrust belt zagros mountains a major angular unconformity between the bakhtyari conglomerates and the underlying agha jari formation has long been interpreted as indicating that orogeny in the zagros simply folded zone took place in plio pleistocene times this study uses field evidence of unconformities between older units in conjunction with geological maps and cross sections to argue that the front of the zagros simply folded zone has propagated in time and space these unconformities indicate that deformation started as early as end eocene in the northeast of the simply folded zone and propagated progressively to the southwest where unconformable contacts are only seen between younger units as shortening continued the southwest migration of the deformation front drove the foreland basin in front of it to its present position along the persian gulf and mesopotamia the climax of orogeny took place at end pliocene time when the most extensive unconformity in the zagros simply folded zone developed between the upper bakhtyari formation and older units active seismicity and documented present uplift imply that the simply folded zone is still propagating southwestward

the geology of the kuh e dalneshin area of southern iran and its bearing on the evolution of southern tethys the kuh e dalneshin area lay close to the northern margin of the arabian continent during mesozoic and palaeogene times recent mapping has shown that except perhaps in the late cretaceous it was inactive until it collided with central iran in the miocene the collision represented by a neogene melange zone in the ne resulted in the zagros orogeny and is expressed in the shelf sediments by folding parallel faulting and a possible arcuate sinistral shear in the late cretaceous a localized deepening of the shelf dates from the cenomanian a narrow trough in the w subsided to abyssal depths in the turonian following a period of faulting a more wide spread subsidence affected the shelf in the coniacian and santonian autochthonous cherts and associated sediments accumulated basaltic volcanics were erupted in the ne part of this basin and permian to cenomanian neritic exotic blocks were derived presumably from an uplift at the shelf edge the rocks from the outer edge of this basin slid westwards over their autochthonous counterparts probably in the campanian accompanied by further gliding of masses of earlier mesozoic cherts which had previously been emplaced on the continental margin a sheet of mantle peridotite partly serpentinized and enclosing neritic and metamorphic exotics in turn slid into the basin shelf sedimentation was renewed in the late campanian or maestrichtian but the transgression did not reach the area until the eocene the derivation and emplacement of the allochthonous rocks in the late cretaceous are still imperfectly understood alternative models are discussed one involving gliding from an aborted spreading ridge along the continental margin the other more conventionally based on subduction processes a preference is expressed for the former

control of cambrian evaporites on fracturing in fault related anticlines in the zagros fold and thrust belt orientation and distribution of fractures in the oligocene early miocene asmari formation a major reservoir rock of the zagros petroleum system were investigated in two anticlines of the zagros fold and thrust belt the sim and kuh e asmari anticlines developed in the areas of the zagros characterized by the occurrence and absence of cambrian evaporites at the bottom of the stratigraphic pile respectively the aim was to outline major differences in terms of fracture spacing and saturation organic matter maturity and clay minerals based geothermometers suggest that the depth of deformation for the top of the asmari formation in the kuh e asmari anticline was in the range of 1 5 2 7 km assuming a geothermal gradient of 22 5 c km the asmari formation in the sim anticline probably experienced a slightly deeper sedimentary burial maximum 3 km with a geothermal gradient of 20 c km the spacing of fractures is generally 2 3 times larger i e strain accommodated by fracturing is smaller in the sim anticline than in the kuh e asmari anticline this is consistent with regional geological studies analogue and numerical models that suggest that thrust faults geometry and related folds are markedly different in the absence or presence of a weak decollement evaporites the larger spacing in the sim anticline is also consistent with higher temperature predicted for the asmari formation in this area by contrast the orientation of fractures with respect to the fold axes is the same in both anticlines the fracture systems are rather immature in both anticlines the amount and density of fractures in the twofolds are controlled by regional occurrence absence of salt and probably different burial rather than local features fold geometry

paleotemperatures from fluid inclusions in halite method verification and a 100 000 year paleotemperature record death valley ca abstract maximum homogenization temperatures of fluid inclusions thmax in halite laboratory grown crystals and modern samples death valley ca match maximum brine temperatures during halite precipitation maximum brine temperatures during halite precipitation in death valley late april 1993 34 4 c agree with thmax 34 c and correlate well with average maximum air temperatures in april 31 3 c and may 37 6 c thmax may be used for paleoclimate interpretations based on the close relationship between saline lake temperatures and average air temperatures from modern settings lower homogenization temperatures demonstrably below the temperatures at which halite grew are interpreted to reflect collapse of some fluid inclusion walls due to the pressure difference between the inside and outside of inclusions by only using thmax the problems of anomalously low homogenization temperatures due to possible collapse of fluid inclusions are avoided halite samples from 30 stratigraphic intervals 90 to 0 m 100 to 0 ka core dv93 1 death valley ca were used to measure homogenization temperatures of fluid inclusions virtually all homogenization temperatures from core dv93 1 are below the modern thmax of 34 c halite precipitation late april 1993 lacustrine halites deposited in a perennial saline lake 35 to 10 ka have thmax between 19 c and 30 c which suggests brine temperatures approximately 4 c to 15 c below modern late april values ephemeral saline lake halites precipitated 60 to 35 ka have thmax between 23 c and 28 c 6 to 11 c below modern values the highest thmax value in the 100 ka record up to 35 c is from a halite sample formed approximately 100 ka in a climate regime somewhat colder than the modern

a quantitative approach to sedimentary surface structures contoured by the interplay of microbial colonization and physical dynamics in the tidal flats of mellum island southern north sea biofilms and microbial mats generated largely by cyanobacteria colonize the sedimentary surfaces biostabilization effects and biomass enrichment influence erosional and depositional dynamics resulting from tidal flushing and storm surges the overlapping of both biological and physical forces causes the development of characteristic sedimentary structures to obtain a quantitative expression of the degree of effectiveness of microbial colonization in the formation of structures in an extended tidal area a modification index mod i was developed based on the following values i the proportion of mat covered area related to a defined investigation area ia ii the degree of steepness of slope angles of raised erosional remnants is and iii the degree of microbial levelling of a rippled sedimentary surface in the mod i was calculated for several defined regions within the study area and both winter and summer situations were considered the mod i values show first that the lower intertidal zone is characterized by index values approaching zero this implies that microbially induced effects in this zone are negligible even in summer second the upper intertidal zone is characterized by lower index values in winter and relatively high values in summer this implies a predominantly seasonal control on the biofilm development in this zone third in the lower supratidal zone the index values are almost identical during both winter and summer this implies non seasonal biological effects in this zone concomitant empirical studies on the composition of microbial mats and films suggest that the dominant microbial type influences the mod i value

diagenetic and oil migration history of the kimmeridgian ascla formation maestrat basin spain abstract the marine limestones of the kimmeridgian ascla formation in the maestrat basin reached more than 3500 m in burial depth during the cretaceous era despite containing organic rich intervals mature in parts of the basin its potential as oil source rock has been either overlooked or questioned a petrographic geochemical and fluid inclusion fi study of the cements of the ascla was performed in order to unravel its diagenetic and thermal evolution we particularly sought evidence of oil migration and its timing three sequences of cement were distinguished sequence 1 fills the primary porosity and began with fe poor calcites with geochemistry and fis consistent with precipitation from marine derived waters during shallow burial these calcites were followed by burial cements including ferroan calcite dolomite and minor celestite and barite sequence 2 consists of mg rich fracture filling calcite cement zones the earlier ones are ferroan and contain primary aqueous and oil fis with homogenization temperatures suggesting precipitation at temperatures as high as 117 c sequence 3 is dominated by fracture filling calcites with geochemistry and fis indicating precipitation at low temperatures less than 50 c from meteoric waters cross cutting relationships with compressional microstructures indicate that sequence 3 formed after the eocene oligocene tectonic inversion of the basin oil fis in sequence 2 provide evidence that light oils migrated through the ascla formation via fractures and microfractures these oils were likely generated in the organic rich marls of the basal part of the ascla the paragenetic sequence and burial history are consistent with oil generation when the ascla was at or close to maximum burial depth but before the eocene alpine tectonism which likely formed the structural traps in the basin oil generation and migration occurred long before this event therefore it is probable that early traps were breached by the alpine structures and that potential in this basin sector is low