spectrally based remote sensing of river bathymetry this paper evaluates the potential for remote mapping of river bathymetry by 1 examining the theoretical basis of a simple ratio based technique for retrieving depth information from passive optical image data 2 performing radiative transfer simulations to quantify the effects of suspended sediment concentration bottom reflectance and water surface state 3 assessing the accuracy of spectrally based depth retrieval under field conditions via ground based reflectance measurements and 4 producing bathymetric maps for a pair of gravel bed rivers from hyperspectral image data consideration of the relative magnitudes of various radiance components allowed us to define the range of conditions under which spectrally based depth retrieval is appropriate the remotely sensed signal must be dominated by bottom reflected radiance we developed a simple algorithm called optimal band ratio analysis obra for identifying pairs of wavelengths for which this critical assumption is valid and which yield strong linear relationships between an image derived quantity x and flow depth d obra of simulated spectra indicated that water column optical properties were accounted for by a shorter wavelength numerator band sensitive to scattering by suspended sediment while depth information was provided by a longer wavelength denominator band subject to strong absorption by pure water field spectra suggested that bottom reflectance was fairly homogeneous isolating the effect of depth and that radiance measured above the water surface was primarily reflected from the bottom not the water column obra of these data 28 of which were collected during a period of high turbidity yielded strong x versus d relations r2 from 0 792 to 0 976 demonstrating that accurate depth retrieval is feasible under field conditions moreover application of obra to hyperspectral image data resulted in spatially coherent hydraulically reasonable bathymetric maps though negative depth estimates occurred along channel margins where pixels were mixed this study indicates that passive optical remote sensing could become a viable tool for measuring river bathymetry copyright 2009 john wiley sons ltd

geochemistry of proterozoic volcanic and granitic rocks from the gold hill wheeler peak area northern new mexico abstract early proterozoic supracrustal and plutonic rocks from the gold hill wheeler peak area in northern new mexico define three populations amphibolite diorite tonalite hornblendite cumulus amphibolite and felsic volcanics and porphyries also present are mid proterozoic granites amphibolites are similar in ti zr cr ni and ree contents to young calc alkaline and arc basalts and diorites and tonalites are similar in composition to young andesites and to high al2o3 tonalites respectively felsic volcanics resemble young felsic volcanics from mature arc systems in their immobile element contents geochemical model studies suggest that the amphibolites hornblendites diorites and tonalites are related by progressive fractional crystallization of a hydrous parent tholeiite magma produced from partial melting of undepleted lherzolite amphibolites represent parent tholeiites modified by olivine removal hornblendite is an early solid residue comprised chiefly of hornblende clinopyroxene and olivine diorite and cumulus amphibolite represent respectively residual solid clinopyroxene plagioclase hornblende and liquid after 50 crystallization tonalite represents a residual liquid after 80 crystallization felsic volcanic rocks are produced by partial melting of a tonalite or diorite source with granulite facies mineralogy in the lower crust granites have a similar origin to felsic volcanics although requiring an inhomogeneous source with the presence of residual hornblende or garnet the calc alkaline igneous rocks in the gold hill wheeler peak area suggest the presence of an arc system in northern new mexico during the early proterozoic the fact that these rocks interfinger with and are overlain by mature clastic sediments favors a model in which a continental arc system is uplited eroded and buried by cratonic sediments from the north

the fluid regime during fracturing of the embla field central trough north sea abstract the deep embla field located in the central trough north sea represents the first oil reservoir in paleozoic rocks to be developed on the norwegian shelf the reservoir consists of braided fluvial and alluvial fan sandstones interlayered with floodplain lacustrine mudstones and volcanics and intrusives extensive fracturing of the reservoir has led to the formation of numerous mineralised veins three main types of mineralised fractures can be identified 1 early diagenetic veins and veins which occur in and around mafic igneous rocks 2 carbonate dominated veins 3 barite clay minerals and bitumen veins this article presents fluid inclusion evidence from fracture filling minerals suggesting that the fractures were important fluid conduits of both petroleum and brine migration the petroleum inclusion data are consistent with an undersaturated oil composition a range in salinity between 23 and 12 wt nacl eq is found for the aqueous inclusions the variation in salinity indicates mixing between a high saline fluid related to evaporites and a fluid with lower salinity microthermometry data suggest that the fracturing events occurred at deep basinal levels at temperatures in excess of 100 c

structure of the musandam culmination sultanate of oman and united arab emirates and the straits of hormuz syntaxis the musandam mountains form a link both in time and space between the late cretaceous ophiolite obduction tectonics of the oman mountains and the late tertiary continental collision tectonics of the zagros fold belt of iran culmination of the musandam shelf carbonates occurred after the turonian maastrichtian thin skinned thrusting of the oman mountains was completed the basal hagab thrust cuts up section to the west from at least mid permian level up to the late cretaceous aruma group and breached up into the overlying previously allochthonous cretaceous hawasina cherts in the hagil window ras al khaimah the shelf carbonates show from 4 to 15 km of westward translation extrapolation of foreland sequences suggests that upper cretaceous aruma group and hawasina complex sediments could occur in the subsurface along the footwall east of the mountain front the hagab thrust and musandam structures plunge south southwest at increasingly greater depth and with decreasing amount of translation and carry all overlying late cretaceous thrust sheets of the oman mountains in a piggy back fashion the eocene lr oligocene pabdeh foredeep developed as a result of loading in front of the musandam thrust sheets wedging out to the south the trailing south eastern edge of the musandam culmination is a hinged listric normal fault downthrowing to the south east up to 2 5 km at bayah and less than 500 m at the western end of batha mahani and is interpreted as a dorsal culmination collapse feature

thermo chronological approach to reservoir diagenesis in the offshore angola basin a fluid inclusion 40 ar 39 ar and k ar investigation 1 microthermometric analyses of fluid inclusions and geochronological surveys of authigenic silicates in neocomian sandstones and albian dolomitic reservoirs from the offshore angola basin have allowed determination of the age and the physical chemical conditions for fluid migration in a late diagenetic stage the 40 ar 39 ar laser probe dating of adularia overgrowths from the albian reservoirs shows that the trapping of primary aqueous and oil inclusions occurred during the early miocene 25 6 or 3 2 ma the k ar age of authigenic illites from the neocomian sandstones is slightly younger 19 or 1 ma and the crystallization of regular illite smectite mixed layers is related to a previous eocene to paleocene diagenetic stage 51 58 ma there appears to have bee both a regional and vertical variation in the salinity of aqueous fluids during the miocene the fluid inclusion trapping temperatures were estimated by correcting the homogenization temperatures of aqueous fluids assuming that pressures during the miocene were close to the present reservoir pressures and by intersecting the isochores of aqueous and oil inclusions assuming they were trapped at strictly similar pressure and temperature conditions the fluid inclusion temperatures are consistent with those derived from the tetrahedral aluminum content aliv of authigenic chlorites 168 206 degrees c in the albian reservoirs at depths between 2350 and 3580 m and 175 237 degrees c in the neocomian sandstones at depths between 2770 and 4470 m in both reservoir formations miocene tempe atures were higher than the present ones and related either to deeper burial or higher geothermal gradient

petroleum migration and mixing in the northwestern junggar basin nw china constraints from oil bearing fluid inclusion analyses abstract abundant oil bearing fluid inclusions are present in four reservoir sandstone samples from the slope and fault zone areas in the northwestern margin of the junggar basin nw china free oil in intergranular pores adsorbed oil on grain surfaces and petroleum in inclusions hosted by mineral grains of these samples were analyzed by gas chromatography and gas chromatography mass spectrometry analytical results indicate similar biomarker distributions in the three bitumen fractions of the samples collected from the slope area which correlate well with characteristic of the source rocks in the lower permian fengcheng formation this is in contrast to the fault zone where the three bitumen fractions vary significantly in their geochemical signatures suggesting that all of the three permian source sequences rocks including the lower permian jiamuhe and fengcheng formations and the middle permian lower wuerhe formation have been mature and contributed to the oils in the fault zone the presence of an unresolved hydrocarbon hump and a full range of unaltered n alkanes in the gas chromatograms of samples collected from the fault zone indicate an earlier hydrocarbon biodegradation and subsequent injection of fresh oils distinctly different from that in the slope area petrographic and microthermometric investigations of oil bearing fluid inclusions suggest a single oil charge in the slope area to the lower triassic reservoir occurring during the late triassic to early jurassic time in the fault zone oil migration and mixing took place mainly during the late triassic to early jurassic and cretaceous followed by gas migration in the tertiary period the different petroleum migration and mixing histories in the slope and fault zones are attributed to the effect of fault controlled oil and gas migration

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation comment and reply reply we were delighted to learn that karlstrom et al 2007 1 had written a comment on our recent article in geology one of our major purposes was to stir debate on the origin of the extensive paleoproterozoic crust of the southwestern united states this reply is intended not so much as a point by

the petroleum characteristics and filling history of the froy field and the rind discovery norwegian north sea abstract the brent group reservoirs of the froy field and the rind discovery norwegian north sea show complex distributions of petroleum and aqueous fluids multiple fluid contacts are present in the rind discovery and the fields show various extent of compartmentalisation due to faulting geochemistry data of core extracts indicate that the two fields have different petroleum sources bhullar karlsen holm backer owe tran 1998 late diagenetic modifications of the reservoir quality consist of quartz cementation followed by carbonate and kaolinite cementation and dissolution of k feldspar fluid inclusion results indicate that filling of the reservoirs occurred after the main phase of quartz cementation at pressure temperature conditions close to the present differences in fluid properties between fault compartments in both fields have been identified fluid inclusion data have proved especially valuable for evaluation of the sealing capacity of faults through time and given evidence for the fault lineament north of both fields to be a time integrated pressure seal except for a lower gas condensate zone in the 25 2 13 compartment of rind the present reservoir fluids are volatile oils close to gas saturation the previous presence of an oil in the lower reservoir zone of 25 2 13 has also been demonstrated the fluid inclusion data indicate that the condensate in 25 2 13 represents a second episode of migration filling rather than phase separation

uv raman spectroscopy of hydrocarbon bearing inclusions in rock salt from the dongying sag eastern china abstract compositions of hydrocarbon bearing inclusions in rock salt halite from the shahejie formation in the dongying sag bohai bay basin eastern china have been analysed by raman spectroscopy coupled with a 244 nm uv laser source the fluorescence effect caused by the conventional visible laser excitation of the aromatic fractions of hc bearing inclusions can be effectively avoided six types of hc bearing inclusions belonging to two generations have been identified in halite according to their hydrocarbon types and petrographic characteristics the presence of hc bearing inclusions in halite provides evidence of crystal fracturing and healing plastic deformation and dynamic recrystallization of rock salt in the dongying sag this proves that rock salt may have repeatedly lost and then recovered its sealing capacity during two stages of oil emplacement water and hydrocarbons were detected by uv raman spectroscopy in the studied samples in both hc bearing inclusions and aqueous inclusions these results are important for understanding the formation conditions of these fluid inclusions and the interactions between the formation water and petroleum in reservoirs our results show that uv raman spectroscopy has a potential to become a powerful tool for analyzing hydrocarbon bearing fluid inclusions trapped in various elements of a petroleum system

hydrocarbon water interactions during brine migration evidence from hydrocarbon inclusions in calcite cements from danish north sea oil fields abstract crude oils in primary and secondary fluid inclusions in calcite from fractures in seven offshore oil fields associated with diapiric salt structures in the danish sector of the north sea were analyzed by capillary column gas chromatography and compared with crude oils produced from the same reservoirs oils from fluid inclusions in all fields show evidence of biodegradation decreased n c17 pristane and n c18 phytane ratios and loss of n c7 2 methyl hexane and 3 methyl hexane relative to methyl cyclohexane and water washing absence of benzene and depletion of toluene some oils in inclusions are extremely enriched in c6 and c7 cyclic alkanes suggesting that these samples contain hydrocarbons exsolved from ascending hotter formation waters compared to inclusion oils the produced oils are less biodegraded but are water washed indicating that both types of oil interacted with large volumes of formation water the carbon isotopic composition of the calcite host of the fluid inclusions in the dagmar and skjold fields is as light as 16 5 pdb and the sulfur isotopic composition of pyrite in and adjacent to the calcite veins in the skjold field is as light as 39 6 cdt indicating that biodegradation of the oils was a source of some of the carbon in the calcite and sulfate reduction was the source of sulfur for the pyrite the evidence for microbial degradation of petroleum is consistent with present day reservoir temperatures 65 96 c but is not consistent with previous estimates of the temperatures of calcite vein filling 95 130 c which are much higher than the temperatures of known occurrences of biodegraded oil

estimation of discharge from three braided rivers using synthetic aperture radar satellite imagery potential application to ungaged basins analysis of 41 ers 1 synthetic aperture radar images and simultaneous ground measurements of discharge for three large braided rivers indicates that the area of active flow on braided river floodplains is primarily a function of discharge a power law correlation is found between satellite derived effective width we and discharge q where we is the water surface area within a braided reach divided by the reach length synthetic values of we and q generated from a cellular automata model of stream braiding display a similar power law correlation power functions that are fit through plots of we and q represent satellite derived rating curves that can subsequently be used to estimate instantaneous river discharge from space with errors ranging from tens to hundreds of cubic meters per second for ungaged rivers changes in relative discharge can be determined from satellite data alone to determine the shape and timing of annual flows in glacierized basins absolute discharge can probably be estimated within a factor of 2 more accurate estimates will require either 1 one or more ground measurements of discharge acquired simultaneously with a satellite image acquisition or 2 successful parameterization of known morphologic controls such as total sinuosity 5 p valley slope bank material and stability and braid channel hydraulic geometry values of total sinuosity 5 p derived from satellite imagery and field measurements from two rivers of braid channel width depth velocity water surface slope and bed material grain size indicate that while the shape of satellite derived we q rating curves may be influenced by all of these variables the sensitivity of flow area to changing discharge is most dependent upon the degree of braiding efforts to monitor river discharge from space will be most successful for intensely braided rivers with high values of total sinuosity subsampling of existing daily discharge records from the iskut river suggests that satellite return times of about 1 week are sufficient for approximating the shape and timing of the seasonal hydrograph in large glacierized basins although errors are large the presented technique represents the only currently available way to estimate discharge in ungauged braided rivers

non recognition of continental tholeiites using the ti y zr diagram continental tholeiites cannot be identified using the ti y zr diagram two hundred and thirteen analyses from 16 localities representing 7 continental tholeiitic provinces all plot outside the within plate basalt field of this diagram

different sources involved in generation of continental arc volcanism the carboniferous permian volcanic rocks in the northern margin of the north china block abstract new zircon u pb dating results on the carboniferous permian volcanic rocks in the northern margin of the north china block ncb indicate their eruption during the early carboniferous to late permian from 347 3 ma to 258 1 ma and a slight decrease of the upper limits of the volcanic sequences from west to east they have a main rock association of basalt basaltic andesite andesite dacite rhyolite tuff and tufaceous sandstone most of them have calc alkaline compositions and exhibit variable sio2 contents from 48 2 wt to 77 1 wt there is no significant gap between the mafic and felsic volcanic rocks in major and trace element classification diagrams indicating that they are not bimodal in composition the carboniferous permian volcanic rocks exhibit subduction related geochemical features such as negative nb and ta anomalies of mafic to intermediate rocks on primitive mantle normalized diagrams indicating they were formed in an andean type continental arc during southward subduction of the paleo asian oceanic plate beneath the northern ncb however their wide range of whole rock sr nd and zircon hf isotopic compositions indicate that their source areas are very complex and different sources were involved in generation of these volcanic rocks geochemical and sr nd hf isotopic results show that the basalt and some andesite were produced by fractional crystallization of mafic magma derived from partial melting of mantle wedge and subducted oceanic crust however most of the intermediate to felsic volcanic rocks were derived from partial melting of lower continental crust there is an increasing input of crustal materials from the carboniferous to permian as indicated by increasing volumes of felsic volcanic rocks in the volcanic sequences the results show that origin of the continental arc volcanism is very complex and both materials from the subducted oceanic crust and sediments mantle wedge and arc continental crust could be involved in their generation for the permian andesite dacite and rhyolitic volcanic rocks there is a striking correlation between their sr nd hf isotopic compositions and those of the underlying basement sr nd hf isotopic differences between the permian intermediate to felsic volcanic rocks from either side of the northern boundary fault of the north china craton suggest that mixture and homogenization of the magmas in the melting assimilation storage hybridization mash zone within this continental arc was incomplete and incomplete homogenization of magmas is likely a common feature of many mash zones within continental arcs our results on the volcanic rocks also show that the final closure of the paleo asian ocean along the solonker suture zone has not been finished prior to the middle permian and the decease of the paleo asian oceanic subduction beneath the northern ncb in its middle western parts is a little earlier than that in its eastern part

assessing the maturity of oil trapped in fluid inclusions using molecular geochemistry data and visually determined fluorescence colours abstract the thermal maturity of oils extracted from inclusions and the fluorescence colours of oil bearing fluid inclusions have been measured in 36 sandstone samples from australasian oil fields the inclusion oils were analysed using an off line crushing technique followed by gc ms a maturity assessment was made for each inclusion oil using 25 molecular maturity ratios including a newly defined dimethyldibenzothiophene ratio dmdr each inclusion oil was placed in one of 4 maturity brackets approximately equivalent to early mid peak and post oil generation windows the fluorescence colours of oil inclusions were visually discriminated into blue white and yellow plus orange and their proportions estimated using point counting techniques sixteen samples have 85 of oil inclusions with blue fluorescence whilst other samples have more variable fluorescence colours one sample has 100 of oil inclusions with yellow plus orange fluorescence the results show that samples containing mainly blue fluorescing oil inclusions have thermal maturities anywhere within the oil window in particular the molecular geochemical data strongly suggests that oil inclusions with blue fluorescence can have relatively low maturities calculated reflectance

hydrocarbon generation in the permian irati organic rich shales under the influence of the early cretaceous parana large igneous province abstract the increasing global demand for natural gas and petroleum byproducts is turning organic rich shales into an important target for hydrocarbon exploration and production current understanding about hydrocarbon generation in unconventional plays such as oil shales and gas shales is still evolving especially in sedimentary basins where hydrocarbon generation is influenced by magmatism this is the case for the permian oil shales of the irati formation in the parana basin southern south america the irati shales are considered an atypical petroleum system due to thermal effects of the parana large igneous province lip emplaced during the early cretaceous in this context the focus of this study was to characterize the thermal conditions of hydrocarbon generation in the irati formation as well as the composition of related aqueous diagenetic fluids the kerogen from the irati organic rich shales has an aromaticity around 30 ar 30 as determined by carbon nuclear magnetic resonance 13c nmr and vitrinite reflectance ro of around 0 6 fluid inclusions in calcite and quartz veins present aqueous fluids with salinity of 0 5 wt of nacl equivalent and homogenization temperatures greater than 250 c hydrocarbon fluid inclusions were classified as black oil through their vapor fraction volumes fv 1 6 9 1 and homogenization temperatures th in the 60 80 c range methane ch4 or carbon dioxide co2 fluid inclusions were absent within the analyzed calcite and quartz veins the pvt model for trapped fluid inclusions suggests a shallow hydrocarbon petroleum system 2 5 km depth active during the early cretaceous synchronous with the parana lip

morphological effects of different channel forming discharges in a gravel bed river the study analyses the morphological response of a gravel bed river to discharges of different magnitude from moderate events that occur several times a year to a 12 year flood and so defines the range of formative discharges for single morphological units channels bars islands and a range of magnitude of morphological activity from the threshold discharges for gravel transport and minor bar modification up to flows causing major morphological changes the study was conducted on the tagliamento river a large gravel bed river in north eastern italy using two different methods analysis of aerial photographs and field observation of painted gravel particles the available photographs five flights from august 1997 to november 2002 and the two commissioned flights june 2006 and april 2007 do not define periods with a single flood event but the intervals are short enough 11 to 22 months to have a limited number of flood events in each case the fieldwork which involved cross section survey grain size analysis and observation of painted sediments complemented the aerial surveys by allowing analysis of channel response to single flood events substantial morphological changes e g bank erosion of several tens of metres up to more than 100 m associated with flood events with a recurrence interval between 1 1 year and 12 years have been documented multiple forming discharges were defined based on the activity of different morphological units discharges equal to 20 50 of the bankfull discharge are formative for the channels whereas the bankfull discharge 1 1 year flood in this case of the tagliamento river is formative for low bars larger floods but still relatively frequent with a recurrence interval less than five years are required for full gravel transport on high bars and significant morphological changes of islands copyright 2009 john wiley sons ltd

numerical study on the effects of floodplain vegetation on river planform style the effects of floodplain vegetation on river planform have been investigated for a medium sized river using a 2d morphodynamic model with submodels for flow resistance and plant colonization the flow resistance was divided into a resistance exerted by the soil and a resistance exerted by the plants in this way it was possible to reproduce both the decrease in bed shear stress reducing the sediment transport capacity of the flow within the plants and the increase in hydraulic resistance reducing the flow velocities colonization by plants was obtained by instantaneously assigning vegetation to the areas that became dry at low water stages this colonization presents a step forward in the modelling of bank accretion bank erosion was related to bed degradation at adjacent wet cells bank advance and retreat were reproduced as drying and wetting of the computational cells at the channel margins the model was applied to a hypothetical case with the same characteristics as the allier river france the river was allowed to develop its own geometry starting from a straight uniform channel different vegetation densities produced different planforms with bare floodplains the river always developed a braided planform even if the discharge was constant and below bankfull with the highest vegetation density grass the flow concentrated in a single channel and formed incipient meanders lower vegetation density pioneer vegetation led to a transitional planform with a low degree of braiding and distinguishable incipient meanders the results comply with flume experiments and field observations reported in the literature

relationship between the fluorescence color of oil inclusions and thermal maturity in the dongying depression bohai bay basin china part 1 fluorescence evolution of oil in the context of hydrous pyrolysis experiments with increasing maturity abstract the fluorescence evolution of oils has been measured by simulation of petroleum generation and expulsion in a half closed system using hydrous pyrolysis based on four oil prone source rocks type i and ii kerogens from the dongying depression bohai bay basin china the results suggest that the fluorescence characteristics of expelled oil are independent of oil prone kerogen types but are strongly related to oil generation and expulsion processes which are controlled by thermal maturity of source rocks the fluorescence spectral parameters max q650 500 and qf 535 of expelled oils show no obvious variation or even show gradual redshifts when the highest max occurs at peak bitumen generation depending on the expulsion process a blueshift of fluorescence color occurs only during the main oil generation and expulsion stage which immediately follows the peak bitumen generation stage however the expelled oil mainly exhibits green to yellow fluorescence colors 500 nm

an early proterozoic volcanic arc succession in southeastern wyoming the green mountain formation of early proterozoic age in the sierra madre range of southeastern wyoming comprises a bimodal mafic and felsic volcanic assemblage the rocks which are chiefly breccias agglomerates flows and volcaniclastic sediments represent both subaerial and submarine eruptions and in part were redeposited in fluvial and nearshore marine environments volcanic rocks are clearly calc alkaline in character and share a large number of geochemical features in common with continental margin arcs or evolved oceanic arc systems the low mg numbers and ni contents of the basalts require 30 40 olivine fractional crystallization and the high contents of the most incompatible elements high la sm n ratios and low zr nb ratios require an undepleted or enriched mantle source geochemical data are consistent with an origin for the felsic volcanics and associated encampment river granodiorite by shallow fractional crystallization of calc alkaline basalt in a tectonic setting similar to modern ar

hydrocarbon bearing fluid inclusions in calcite filled horizontal fractures from mature posidonia shale hils syncline nw germany abstract hydrocarbon bearing fluid inclusions in calcite filled horizontal fractures from mature posidonia shale 0 88 r o were investigated by microscopic microthermometric and chemical methods the fluid inclusions predominantly contain both a liquid hydrocarbon phase which shows bright uv fluorescence colours yellow brownish light blue and a non fluorescent hydrocarbon gas phase the different uv fluorescence colours probably reflect the different gross chemical compositions of the trapped liquid hydrocarbons the saturated hydrocarbon fraction of the fluid inclusions mostly secondary inclusions predominantly consists of low molecular weight n alkanes c 9 c 12 while c 12 c 22 n alkanes are more abundant in the adjacent rock matrix the molecular composition of the fluid inclusions appears to reflect a mobile hydrocarbon phase which was entrapped within the calcitic fill of the horizontal fractures pressure corrected trapping temperatures were estimated for primary fluid inclusions 123 162 c this temperature range is in agreement with the results from numerical simulation studies which indicate a maximum temperature of 148 c coinciding with the period of fracture formation calcite filling and entrapment of primary fluid inclusions

channel patterns braided anabranching and single thread a new channel pattern classification is presented based on theoretically derived channel pattern discriminant functions the thresholds are formulated as power laws that relate the critical slope associated with a change in channel pattern to dimensionless discharge and relative bank strength one threshold demarcates the boundary between stable single thread channels both straight and meandering and stable multiple thread channels anabranching another threshold separates anabranching from braided channels where braided channels are considered to be fundamentally unstable the exponents of the thresholds are nearly identical to that in the threshold equation originally proposed by leopold and wolman 1957 and the coefficients are quite similar as well an analysis of their data set using our dimensionless approach reveals that no fundamental difference exists between meandering and straight patterns and thus data from both types are grouped together under the more general heading of single thread channels furthermore we demonstrate that over a limited range of conditions an unstable single thread channel can form stable multiple threads but that for systems far from the threshold bounding the single thread channels the number of divisions required to produce stable anabranches grows geometrically this motivates a separation of multiple thread channels into anabranching and braided types our theoretical thresholds are then compared against several large data sets of field data and the results broadly confirm our proposed thresholds

early proterozoic oceanic crust in the northern colorado front range implications for crustal growth and initiation of basement faults 1 early proterozoic oceanic crust exposed in a shear zone in the northern colorado front range provides insight into the tectonic evolution of the colorado province tectonically intermingled mylonitic amphibolite locally pillowed metagabbro clinopyroxenite metachert and melange are preserved within the buckhorn creek shear zone west of fort collins whole rock geochemical data support formation of the igneous protoliths in an oceanic environment major and trace element data overlap samples from modern oceanic ridges and are distinct from modern arc trends metagabbros and clinopyroxenites preserve a subhorizontal lineation defined by igneous pyroxenes core and mantle microstructures indicate initial deformation at temperatures 900 c secondary amphiboles define both subhorizontal and subvertical lineations kinematic analysis indicates that the rocks experienced e w strike slip deformation prior to and during amphibolite facies metamorphism followed by n s shortening 40ar 39ar data from secondary hornblende yield age steps as old as 1 9 ga based on the chemical data and kinematic evidence for strike slip deformation we propose that the buckhorn creek rocks originated at an oceanic ridge transform intersection the high t pyroxene fabrics formed during ocean floor deformation prior to 1 7 ga regional deformation of the colorado province the buckhorn creek fragment likely represents original oceanic basement for 1 8 1 7 ga arc magmatism and sedimentation that ultimately formed the colorado province continental crust reactivation of original oceanic fracture zones may be responsible for the network of regularly spaced northeast trending shear zones in colorado once formed subvertical transform faults are likely to survive the transition from oceanic to continental crust and persist as long lived crustal discontinuities

a proterozoic volcano plutonic terrane gunnison and salida areas colorado early proterozoic supracrustal rocks near gunnison and salida colorado include tholeiitic basalt dacite to rhyolite and intercalated sedimentary rocks these were intruded by essentially synchronous gabbroic sheets folded and intruded by major plutons ranging from quartz diorite to granite preservation of primary volcanic and sedimentary features is good to excellent sedimentary rocks in the gunnison area are mostly turbidite wackes whereas near salida they are mostly near source volcaniclastic rocks u pb age measurements on zircons indicate that the earliest bimodal volcanic rocks erupted between 1770 and 1760 m y ago and were intruded by granitic plutons between 1760 and 1750 m y ago renewed bimodal volcanism occurred between 1740 and 1730 m y ago and was followed by a period of deformation producing two fold sets before 1725 m y ago when the first of a series of younger plutons was emplaced the compositions and features of the sedimentary rocks and their association with volcanics are con

early proterozoic bimodal volcanic rocks in central colorado u s a part i petrography stratigraphy and depositional history abstract early proterozoic metamorphic rocks of the salida area include two exceptionally well preserved sections of undeformed volcanogenic rocks a northern section nearly 4000 m thick and a southern section 1700 m thick the stratigraphic and lithologic character of the sections are the same indicating that they were formed contemporaneously in the same subaqueous environment the suite is strongly bimodal consisting of felsic volcaniclastic rocks 50 mafic volcanic and volcaniclastic rocks 22 and gabbro diabase sheets 23 the remaining rocks are mostly pelitic metasediments the felsic rocks which dominate the upper portions of both sections comprise four distinct facies crystal lithic tuff breccia crystal lithic lapilli breccia tuff bedded tuff and massive tuff lithic fragments are typically foreign dominated by pelitic material crystal clasts are feldspar mainly plagioclase and quartz sequences of these facies representing cycles of eruptive activity are uniform in thickness and extend along strike for the entire width of precambrian exposure up to 4 km but individual facies units especially the coarser ones are limited in their lateral extent individual sequences average about 100 m thick but continuous exposures of felsic rocks locally exceed 600 m primary sedimentary structures and vertical and lateral variations indicate deposition typically following remobilization as debris flows and turbidites in a shallow marine environment of low relief mafic volcanic and volcaniclastic rocks form accumulations up to 600 m thick and extend uniformly for several kilometers along strike although individual units are more restricted laterally the principal rock types are basalt flows basaltic lithic breccia pillow lava pillow breccia bedded basaltic lapillistone and laminated basaltic tuff all deposited in a submarine setting accumulations typically including several types are interbedded with felsic rocks but mechanical mixing of mafic and felsic volcaniclastics is rare suggesting separate eruptive centers for the mafic and felsic volcanics the northern section may be more proximal than the southern section as indicated by the greater abundance of flows the thicker sheets of gabbro and the greater abundance of mafic rocks relative to felsic rocks gabbro diabase sheets up to 350 m thick and dominantly concordant intrude throughout both sections they are characterized by lack of internal differentiation simple mineralogy consisting of plagioclase and hornblende pseudomorphous after pyroxene and sub ophitic texture the minor pelitic material indicates that the area was accessible to continental sediment sources although their location is not known the salida bimodal volcanic suite is part of a more extensive accumulation of similar 1700 1800 ma supracrustal rocks that extends west to the gunnison area and perhaps south into northern new mexico

the response of braided planform configuration to flow variations bed reworking and vegetation the case of the tagliamento river italy morphological features of braided rivers bars channels and pools experience major changes in area shape and spatial distribution as a response to i the pulsation of discharge during a flood and ii the bed evolution induced by floods in this work at a station relationships between water level and planform configuration were investigated on the tagliamento river a large gravel bed braided river in northeast italy over a 2 year study period comprising three bankfull events and several small to medium floods the analysis was performed on two 1 km long reaches characterized by different riparian vegetation cover ground based images with an hourly temporal resolution were acquired using software controlled digital cameras bars channels pools and vegetated patches were manually digitized on more than 100 rectified images sequences of constant level images spanning the study period were used to quantify the impact of floods on the stability of at a station relationships and on the turnover rate of water bodies the analysis shows that wetted area increased almost linearly with water level in both reaches the average number of branches per cross section peaked at intermediate flow levels increasing from 2 at low flow up to 6 7 the number of branches displayed the largest fluctuations over time with significant changes produced also by moderate floods turnover rates were high in both reaches with more than 30 of wetted areas at low flow converting into bare gravel in less than 2 months vegetation colonization was found to limit the mobility of the low flow channels over time by concentrating the flow in fewer deeper anabranches the number of channels per cross section was 30 40 less in the vegetated reach and the proportion of low flow water bodies in the same position after 12 months increased from 3 to 14 copyright 2012 john wiley sons ltd

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

tectonic cycles in southern africa abstract the recurrence of major geological events within the 3600 ma stratigraphic record of southern africa suggests a periodicity of320 25ma for at least the last 3200 ma this periodicity is reflected in major episodes of continental volcanism granitoid plutonism orogeny reciprocity of terrestrial and marine dominated sequences platform carbonate sedimentation glaciation and first order changes in sea level these serve to define 11 completed megacycles each introduced by a major rifting event accompanied by listric faulting alluvial sedimentation in restricted fault bound troughs volcanism and a type granitoid plutonism prior to 3200 ma continental rift magmatism occurred subaqueously due to very high early archean sea levels resulting in pillow lavas and a lack of interbedded terrigenous siliciclastics the long term reciprocity of terrestrial and marine dominated sequences records eustatic first order changes in sea level with highstands characterized by generally humid warm continental climates low relief and tropical afforestation on the other hand lowstand climates were hot and arid with high relief and widespread desertification thick marine sequences accumulate in areally extensive epeirogenic basins without significant volcanism or faulting and commonly are divided into an early phase of open shelf sedimentation followed by deposition in a brackish marine foreland basin within openshelf environments an early phase of biochemical precipitation and or siliciclastic reworking along linear shorelines is separated from a later phase involving rapid deposition of immature siliciclastics along lobate shorelines evolution of the foreland basin is related to orogenic activity and the isolation of an epeiric sea which sometimes developed the characters of a barred basin marine dominated sequences display a deterministic stacking of lithofacies important glacial epochs commonly occur midway through first order regression sometimes with lesser events closely following peak transgression potentially they display 320 ma periodicity but with an unexplained mid proterozoic gap glaciation is related to the combined effect of climatic cooling associated with first order regression and depletion of atmospheric co2 by biological uptake associated with platform carbonate development terrestrial volcanism is believed to be the main contributor of atmospheric co2 climatic change is accompanied by cyclical patterns of cratonic weathering and pedogenesis

observations on sediment mobility in a large gravel bed river article this study investigates sediment mobility in a large gravel bed river tagliamento river northeastern italy field data were used to identify the morphological effectiveness of a range of flows floods with recurrence interval b1 to 3 5 year and for a detailed analysis of the partial transport condition the analyses were carried out on three cross sections where a number of areas representative of different morphological units main and secondary channels low and high bars islands were painted grain size of the painted area was measured using a photographic method monitoring of bed mobility during the study period supplied new photographs of the painted areas measurements of size and travel distance of the mobilized particles and estimate of flow depth after each flood event our analyses have shown that with dimensionless shear stress around 0 073 17 n m 2 the morphological effect over the painted areas was primarily partial transport while with stresses n0 1 25 n m 2 the bed experienced full mobility i e all the painted particles were transported or totally buried full sediment mobility was observed on lower morphological units i e main and secondary channels under floods with very high frequency rib1 y whereas on the low bars full mobility occurred under floods with a recurrence interval slightly n1 year instead fine deposition and partial transport conditions were observed on the higher bars even after the largest of the monitored floods ri 3 5 y the analysis of the partial transport condition relies on more than 3500 measurements of particle travel distance travel distances range from a few centimetres up to 22 m the transported particles were generally finer than the painted sediments and the analysis of the sediment transport ratio revealed that partial transport occurred under equal mobility conditions for particles finer than 32 mm and under size selective mobility for coarser fractions this appears to be corroborated for db32 mm by the insensitiveness of particle transport distance to particle sizes even if the exponent 1 of the relationship between the dimensionless shear stress and the maximum transported diameter would suggest that all fractions are transported under equal mobility conditions

channel adjustment and a test of rational regime theory in a proglacial braided stream the upstream reach of the sunwapta river alberta provides a useful quasi experimental field case of channel adjustment in a proglacial stream historically the formation of a proglacial lake deprived the river of its coarse sediment supply for several decades and lead to a dramatic decrease in braiding intensity close to the lake while braiding intensity increased further downstream this response to the reduction of gravel input is consistent with previous experimental results subsequent construction activity and channelization close to the lake have contributed to the continuation of these temporal and spatial trends in channel pattern the current state of adjustment of the river morphology can be explained in the context of these historical changes using rational regime equations the study reach has no tributaries and bed material size decreases twofold along the reach while width and braiding intensity increase yet channel slope decreases by only 10 the absence of any significant change in discharge downstream along the reach allows testing of regime equations under conditions in which discharge is held constant the current downstream trends in slope and fluctuations in width are predicted reliably from rational regime equations but not by the existing empirical hydraulic geometry relations the rational equations incorporate the effect of grain size and slope on channel width and the effect of width and grain size on channel slope the regime equations are successful even though they were devised for single channel gravel streams the small 10 decrease in slope along the reach despite a halving of median grain size is attributed to the counteracting positive effect on slope of the downstream increase in braiding intensity and width the downstream increase in braiding intensity must be largely the result of decreasing grain size this confirms the influence of grain size on channel pattern thresholds and demonstrates using spatial transitions in channel pattern that channel pattern predictions based on stream power alone are inadequate

channel morphology and bedload pulses in braided rivers a laboratory study bedload pulses in gravel bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology bedload transport and channel morphology were measured in a small scale generic model of braided gravel bed streams two experiments are described in which braided channels developed in a 14 m 3 m sand tray total bedload output from the tray was weighed every 15 minutes stream bed geometry was surveyed every four hours pulses were observed in the bedload output time series and were qualitatively related to the channel morphology immediately upstream of the measuring section the bagnold 1980 bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading underprediction occurred when applied to degrading channels aggradation was associated with channel multiplication and bar deposition channel pattern simplification occurred when degradation took place and bars emerged from the water flow development of phases of aggradation and degradation is dependent upon the three dimensional geometry of the stream beds spatial and temporal feedback loops can be identified enabling links between channel morphology and bedload transport rate to be directly identified

synthetic saline aqueous and hydrocarbon fluid inclusions trapped in calcite at temperatures and pressures relevant to hydrocarbon basins a reconnaissance study abstract we conducted reconnaissance experiments to synthesize aqueous and hydrocarbon inclusions trapped in calcite at conditions relevant to petroleum basins and characterize the microthermometric properties of such inclusions fluid inclusions fis were synthesized in a system of saline aqueous solution 5 or 20 wt nacl coexisting with either heavy crude oil or gasoline under gas undersaturated conditions from 90 to 210 c and 200 550 bar the synthetic inclusions are not representative of gas bearing systems and methane ch 4 was not detected in any aqueous inclusions the fis are mainly distributed along planar healed cracks indicating that the inclusions formed by fracture healing in the calcite crystal microthermometric measurements were conducted on coeval aqueous and hydrocarbon inclusions and raman spectroscopic analyses were done on aqueous inclusions to determine the properties of fis trapped at these conditions homogenization temperatures of synthetic fis are mostly lower than the experimental trapping temperature although the fis show high variability in measured homogenization temperature results allow comparison of t h values for each sample with the expected t h isochores and pressure corrections calculated for the system h 2 o nacl the latter parameters are broadly consistent with the known pvtx properties of h 2 o nacl fluids suggesting little effect of hydrocarbons on the homogenization behavior although the low precision of the t h data limits this assessment nevertheless this result is not unexpected considering that light hydrocarbons gas is not present in the experiments as corroborated by raman spectroscopy a consequence of using dead oil in the experiments simulation of gas bearing petroleum basins will require additional protocols for producing gas either by in situ cracking of the starting hydrocarbon material or by other means the reconnaissance experiments documented here provide a basis for such future experiments

early proterozoic bimodal volcanic rocks in central colorado u s a part ii geochemistry petrogenesis and tectonic setting abstract the early proterozoic supracrustal rocks of the salida area of central colorado consist of strongly bimodal sequences of volcanogenic rocks the mafic rocks basalts basaltic volcaniclastics and related gabbro sheets are distinctly tholeiitic display a strong iron enrichment trend and typically contain less than 50 sio 2 the felsites are rhyolites to dacites and contain more than 70 sio 2 major and trace element modeling show that the mafic rocks underwent two stages of crystal fractionation the first involving olivine and plagioclase the second involving plagioclase and clinopyroxene fractionation occurred within individual injections as they rose toward the surface rather than in a single magma chamber at depth field relations and major element data support the derivation of the felsic rocks from a magma generated by anatexis of sialic crust however the low sr and high heavy ree concentrations in these rocks are not compatible with a partial melting model and suggest that the felsic volcanic rocks could have been derived by extensive fractional crystallization of the mafic magma normalized trace element abundances and trace element ratios of the mafic rocks are most like continental flood basalts such as the columbia river basalts they also display some similarity to immature back arc basin tholeiites developed on continental crust such as those of the sarmiento complex the felsic rocks have strong chemical affinities to within plate rhyolites rather than calc alkaline rhyolites from orogenic areas the chemical data as well as the petrographic stratigraphic and regional field data all indicate that the early proterozoic supracrustal rocks of the salida area developed along a continental margin probably within an immature back arc basin underlain by sialic crust remnants of the arc system of similar age may lie to the south in northern new mexico and southwestern colorado

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

cretaceous flexural history of northern oman mountain foredeep united arab emirates an important feature of the middle cretaceous arabian continental margin was the regional upwarping in the foreland of the northern oman mountains we interpret this upwarp as an early expression of a cratonward migrating peripheral swell associated with the emplacement of the semail ophiolite onto the margin subsurface stratigraphic data indicate that the swell was expressed during the cenomanian and attained its maximum relief during the turonian by the santonian further downflexure of the margin took place around an axis west of the study area burying the then inactive turonian swell beneath the deposits of the westward expanding foreland basin we suggest that establishment of the later more cratonward flexural regime took place abruptly rather than as a continuo sly migrating wave the middle cretaceous swell axis paralleled the present day axis of the oman mountains the upwarp was slightly asymmetric to the east and loosely constrained estimates of its width and height are 150 km and 244 93 mi and 800 ft respectively the dimensions suggest an anomalously low flexural rigidity 1022 n m for the middle cretaceous continental lithosphere we attribute this low apparent rigidity to the combined effects of remnant thermal and mechanical processes of an earlier rifting event and compression of the margin during the cretaceous emplacement of the semail ophiolite the small dimensions of the middle cretaceous swell suggest that other continental margins with similar geologic histories may also have narrow extinct swells buried beneath foreland deposits such swells may have significant impact on the entrapment of hydrocarbons as we propose for the sajaa margham trend

braided channel pattern and palaeohydrology using an index of total sinuosity abstract channel patterns are commonly represented as discrete types e g straight meandering braided separated by threshold values of slope and discharge however for gravel bed river patterns an index of total sinuosity p can be defined which varies continuously with both stream power per unit channel belt length represented as the product of mean annual flood and valley gradient and median bed material diameter an empirical relationship between p and these controlling variables can be used to provide palaeo hydrological reconstructions for braided stream traces on terrace fragments as an alternative to methods based on bed material sizes and criteria for the threshold of grain motion

fluid inclusion petrography and tectonic burial history of the al ali no 2 well evidence for the timing of diagenesis and oil migration northern oman foredeep cores cut in shallow marine lower and middle cretaceous carbonates in the al ali no 2 well umm al qaiwain united arab emirates display a five stage sequence of calcite cementation fracturing and stylolitization these stages are correlated with the tectonic history of the northern oman orogeny occurrence of fluorescent hydrocarbon fluid inclusions is restricted to stage 2 and stage 3 fracture filling calcites that are crosscut by stylolites stylolite formation during rapid burial beneath abyssal campanian foredeep sediments restricts hydrocarbon migration to post mid cenomanian and pre mid campanian time

stratigraphy and petrogenesis of the grande ronde basalt from the deep canyon country of washington oregon and idaho deep canyons cut by the snake salmon grande ronde and imnaha rivers near the point where washington oregon and idaho join expose 800 m of grande ronde basalt flows the grande ronde basalt erupted 16 5 to 14 5 m y b p makes up 85 vol of the columbia river basalt group an area enclosing 1 000 km 2 of the deep canyon country dominated by this basalt was mapped and samples from 16 measured sections in the grande ronde basalt were analyzed for major minor and trace elements three magnetostratigraphic units r 1 n 1 and r 2 were helpful in mapping the area using physically distinct flows the magnetostratigraphic units and certain chemical variations a detailed flow by flow stratigraphy was developed and the lateral extent of many individual flows was traced the number of flows and thickness of each stratigraphic unit decrease from west to east these tholeiitic flows are fine grained and aphyric clinopyroxene and plagioclase are the predominant minerals but olivine orthopyroxene pigeonite and accessory minerals are minor but important phases the flows are primarily of the low mg chemical type with lesser amounts of the high mg chemical type a cyclical trend in the over all major and trace element chemistry through the stratigraphic section is dominated by a ca rich clinopyroxene chemistry rare earth elements show significant light over heavy enrichment but overall patterns remain similar from flow to flow a small negative eu anomaly is present in many flows three models employing fractional crystallization schemes and one combining fractional crystallization and partial melting were tested using least squares modeling a petrogenetic model is proposed wherein partial melting of a heterogeneous clinopyroxene dominated mantle supplied magma that ascended to the crust was temporarily stored and recurrently erupted during storage new basaltic melt with slightly different isotopic and trace element abundances was added and mixed into the liquid that remained after previous eruptions orthopyroxene plagioclase and to a lesser extent olivine fractionated from these temporarily stored liquids upon eruption clinopyroxene and plagioclase with accessory minerals crystallized at the surface

reply to comment by oxtoby on assessing the maturity of oil trapped in fluid inclusions using molecular geochemistry data and visually determined fluorescence colours the authors welcome the opportunity to respond to some of the comments of oxtoby 2002 regarding their recent paper george et al 2001 we will respond to the two main topics that have been raised by oxtoby 2002 firstly the petrological procedures used and secondly the possible causes for the wide maturity range of blue fluorescing oil inclusions the issue of the relationship of fluorescence colour and api gravity raised by oxtoby 2002 was not discussed in the paper

diagenesis of the palaeo oil water transition zone in a lower pennsylvanian carbonate reservoir constraints from cathodoluminescence microscopy microthermometry and isotope geochemistry abstract oil water transition zones in carbonate reservoirs represent important but rarely studied diagenetic environments that are now increasingly re evaluated because of their potentially large effects on reservoir economics here data from cathodoluminescence and fluorescence microscopy isotope geochemistry microthermometry and x ray tomography are combined to decipher the diagenetic history of a 5 m long core interval comprising the oil water transition zone in a lower pennsylvanian carbonate reservoir the aim is to document the cementation dynamics prior during and after oil emplacement in its context of changing fluid parameters intergrain porosity mean values of 7 are present in the upper two sub zones of the oil water transitions zone but values sharply increase to a mean of 14 in the lower sub zone grading into the water saturated portions of the reservoir and a very similar pattern is observed for permeability values in the top of the water filled zone cavernous porosity with mean values of about 24 is found carbonate cements formed from the earliest marine to the late burial stage five calcite ca 1 through 5 and one dolomite dol phase are recognized with phase ca 4b recording the onset of hydrocarbon migration carbon and oxygen cross plots clearly delineate different paragenetic phases with ca 4 representing the most depleted 13c ratios with mean values of about 21 during the main phase of oil emplacement arguably triggered by far field alpine tectonics carbonate cementation was slowed down and eventually ceased in the presence of hydrocarbons and corrosive fluids with temperatures of 110 140 c and a micro hiatal surface formed in the paragenetic sequence these observations support the oil inhibits diagenesis model the presence an earlier corrosion surface between phase ca 3 and 4 is best assigned to initial pulses of ascending corrosive fluids in advance of hydrocarbons the short lived nature of the oil migration event found here is rather uncommon when compared to other carbonate reservoirs the study is relevant as it clearly documents the strengths of a combined petrographic and geochemical study in order to document the timing of oil migration in carbonate reservoirs and its related cementation dynamics

hydrocarbon migration and accumulation of the suqiao buried hill zone in wen an slope jizhong subbasin bohai bay basin china abstract the hydrocarbon migration and accumulation of the suqiao deep buried hill zone in the jizhong subbasin the bohai bay basin eastern china was investigated from the perspective of paleo fluid evidence by using fluid inclusions quantitative fluorescence techniques qgf total scanning fluorescence method tsf and organic geochemical analysis results show that the current condensate oil gas reservoirs in the study area once were paleo oil reservoirs in addition the reservoirs have experienced at least two stages of hydrocarbon charge from different sources and or maturities during the deposition of the oligocene dongying formation ed the deep ordovician reservoirs were first charged by mature oils sourced from the lacustrine shale source rocks in the fourth member of shahejie and kongdian formations es4 ek and then adjusted at the end of ed period subsequently by virtue of the tectonic movement since the deposition of the neogene minghuazhen formation nm the reservoirs were mainly charged by the gas that consisted of moderate to high maturity condensate and wet gas sourced from the es4 ek lacustrine shale source rocks and mature coal derived gas sourced from the carboniferous permian c p coal bearing source rocks meanwhile the early charged oil was subjected to gas flushing and deasphalting by the late intrusion of gas the widely distributed hydrocarbon inclusions the higher qgf index and foi the frequency of oil inclusions values in both gas oil and water zone are indicative of early oil charge in addition combined with the homogenization temperatures of the fluid inclusions

a geologic deconstruction of one of the world s largest natural accumulations of co2 moxa arch southwestern wyoming geologic sequestration of anthropogenic carbon dioxide co2 is one of the most promising approaches to safely and effectively reduce emissions of co2 created through the oxidation of fossil fuels methods used by the petroleum industry in the characterization of hydrocarbon accumulations can be used to assess potential subsurface traps for sequestration purposes in this article we use these approaches to evaluate the characteristics of a naturally occurring accumulation of co2 in western wyoming the moxa arch is a 200 km 124 mi long basement involved anticline the mississippian madison formation and the ordovician bighorn dolomite contain the most co2 within the structure relict anhydrite in these and other paleozoic units was an important factor in evolving hydrocarbons into co2 through inorganic thermal sulfate reduction and more importantly in creating a seal to hold large columns of buoyant gas fluid inclusion data sets have been particularly useful in understanding the sealing characteristics of the units within the moxa arch and affirming that the devonian jefferson mississippian amsden and triassic dinwoody and woodside formations have been very effective seals existing pressure data reveal that the two gas columns in the madison and bighorn formations lie on a similar gradient and share a common gas water contact yet are likely not in hydraulic communication currently all available data suggest that both reservoirs share a fault dependent spill point by reconciling the spill points of the gas in the madison and bighorn reservoirs their compositions their initial and current pressures their seal and the uncertainties associated with injection of co2 can be identified and potentially derisked with additional information if the madison and bighorn are filled to their fault dependent spill point it implies that additional storage capacity in the reservoir can only be obtained by production of the original gas column this uncertainty may be abated if data from future drilling demonstrates that neither the madison formation nor the bighorn dolomite have a fault dependent spill point suggesting that these structures are underfilled with respect to their closure and possess additional storage capacity

assessment of morphological changes induced by flow and flood pulses in a gravel bed braided river the tagliamento river italy large gravel bed braided rivers show a highly dynamic evolution where even moderate flow pulses can produce significant morphological adjustment an estimation of network variations is needed by river authorities as well as by ecologists for better managing river ecosystems however few field investigations have been performed to measure the effect of unsteady discharges in braided rivers in this paper we report on the morphological changes induced by six different floods in a 1 km long reach of the tagliamento river italy topographic surveys were performed after each significant flood and an automatic digital camera continuously monitored the planimetric configuration repeated measurements of cross section profiles allowed the quantification of the transported sediments volume and in particular provided a basis to estimate the percentage of the floodplain subject to morphological evolution data analysis showed a good relationship between peak flow level active width and mean bed level changes similarly lateral channel shifting is likely to increase for larger floods monitoring of a range of discharges up to bankfull conditions revealed a fundamental difference between flow pulses events on the average occurring one or more times per year and flood pulses with a return period larger than two years the morphological evolution in the former case is mainly limited to a few active branches and is locally driven by bank erosion at the bend apex on the other hand larger floods induce a complete reworking of the network configuration where bifurcations and confluences play a crucial role single morphological units like branches nodes bars are no longer recognizable after this type of event braided rivers are therefore characterized by the occurrence of two different spatial and temporal scales that force the ecosystem dynamics

dynamics of fluid inclusion alteration in sedimentary rocks a review and discussion abstract fluid inclusions represent small volumes of interstitial fluids in crystal imperfections flaws during crystal growth and or deformation the entrapped fluids are commonly believed to preserve information on the composition pressure and temperature of fluid inclusion formation and later diagenetic alterations it is now known that fluid inclusions can be dynamic structures responsive to thermal and tectonic stresses by plastic and brittle deformation of the entrapping mineral wall these dynamic responses may include both morphologic and volumetric changes a comparison of measured fluid inclusion homogenization temperatures with sample burial depths for diagenetic studies from around the world show a strong positive correlation this correlation suggests that fluid inclusion stretching which results in increased homogenization temperatures is a common phenomenon associated with burial diagenesis burial diagenesis shifts and spreads the measured homogenization temperatures towards maximum burial conditions confining mineralogy shape size and composition of the fluid inclusions are important factors in determining the mode and degree of fluid inclusion deformation stretching classical fracture mechanics theory of predicts that plastic and brittle deformation of the surrounding mineral crystall will occur with burial and that annealing retrograde stretching of the strain in the inclusion walls will not occur in low temperature regimes experimental theoretical and field studies all indicate that fluid inclusions will react dynamically to burial diagenesis by increases in measured homogenization temperatures with increased burial it is suggested that this relationship can be selectively used to help determine the approximate maximum thermal exposures experienced by a sedimentary rock

crustal evolution of southern laurentia during the paleoproterozoic insights from zircon hf isotopic studies of ca 1 75 ga rocks in central colorado lu hf depleted mantle model tdm ages obtained by analysis of zircons previously dated by u pb methods demonstrate that ca 1 75 ga bimodal paleoproterozoic rocks in the gunnison salida region of central colorado and by extension in much of the southwestern u s were formed by partial melting of preexisting crustal rocks the ages of which mostly ages greater than 2 0 ga indicate that range from 1 83 to 1 87 ga some calculated lu hf tdm even older crust was probably involved consistent with the limited presence of ca 2 5 ga xenocrystic zircons in some rocks these results suggest that rocks related to the trans hudson and penokean orogens are cryptically present much farther to the south than previously believed coupled with the bimodality of the volcanic suite in central colorado and indeed in much of the southwestern u s these results indicate that in contrast to current juvenile arc accretion models melting of older crust related to extensional tectonics played an important role in the genesis of many magmatic rocks between 1 6 and 1 8 ga

the topographic signature of vegetation development along a braided river results of a combined analysis of airborne lidar color air photographs and ground measurements 1 this paper combines archived remotely sensed data airborne lidar and digital color air photographs with nonsynchronous ground observations including observations of topographic form and vegetation cover and growth to test the hypothesis that colonization of exposed river sediments by riparian trees has an impact on channel form and to quantify any impact that is identified this is achieved along a 21 km reach of the braided gravel bed tagliamento river in northeast italy where the width of the braided corridor typically exceeds 800 m lidar data are analyzed to extract a 2 m resolution digital evolution model dem and determine riparian vegetation extent height and structure within the active corridor aerial photographs are used to map the topography of the submerged parts of the corridor these data are divided into 1 km length subreaches which possess strong contrasts in vegetation height and extent joint analysis of vegetation and morphological properties of these subreaches reveals significant associations between vegetation properties and reach morphology residuals from a gamma function fitted to the topographic data for each subreach show a good fit with poorly vegetated reaches but a weakening fit with increasing vegetation cover largely as a result of the appearance of secondary peaks in the elevation frequency distribution associated with the heavily vegetated areas furthermore the overall skewness and kurtosis of the elevation frequency distribution within each of the subreaches are both significantly correlated with vegetation extent height median elevation and growth rate indicating a clear topographic signature of vegetation development along this braided river that reflects sediment accumulation within and around the vegetated patches

ecosystem expansion and contraction dynamics along a large alpine alluvial corridor tagliamento river northeast italy riverine floodplains are pulsing ecosystems that expand and contract with changing flow in this study we quantified large scale expansion and contraction dynamics of surface waters along a 41 5 km braided section of the last remaining semi natural large alpine gravel bed river tagliamento river ne italy to assess surface subsurface exchange patterns we measured discharge and vertical hydraulic gradients at multiple locations along the corridor we identified two river sections delineated by distinct geomorphic knickpoints in the upper 29 km section i losing zone surface flow decreased on average by 2 5 0 8 m3 s 1 per river km in the downstream 12 5 km section ii gaining zone surface flow increased on average by 0 3 0 1 m3 s 1 per river km the losing zone experienced frequent and extensive drying and rewetting cycles the length of the dry river section was measured over a 1 5 year period using differential gps up to 23 km of section i fell dry at the surface frequent and irregular flow pulses led to rapid expansions of the wetted channel at velocities of up to 3 km h 1 while the subsequent contraction velocities were less than 0 5 km h 1 water level was linearly regressed against the total length of the dry river section r2 0 74 p 0 0001 this relationship in combination with a continuous stage record was used to evaluate expansion and contraction dynamics over a 4 year period timing frequency magnitude spatial extent and duration of expansion and contraction dynamics reflected the flashy flow regime of the tagliamento river including a high intra and inter annual variability of surface drying and rewetting our study emphasizes that even small changes in flow can cause major increases or decreases of ecosystem size thereby creating a highly dynamic and harsh environment for both terrestrial and aquatic organisms copyright 2007 john wiley sons ltd

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

basin evaluation using burial history calculations an overview burial history calculations available to the petroleum geologist include plots of burial history and geohistory porosity and conductivity as a function of depth and lithology as well as the results obtained from algorithms to handle unconformities and backstripped crustal subsidence calculations that predict the breakdown of kerogen to hydrocarbons in terms of time and temperature and methods for determining heat flow from geologic models and vitrinite reflectance data inputs required for these calculations include depths of formation tops ages of formation tops lithologies of formations depths of water at deposition of the different formations porosities of the formations as a function of depth bottom hole temperatures and or formation temperatures and any ke ogen content and vitrinite reflectance values as functions of depth sources of many of these data may be well logs well reports geologic papers and or seismic sections the paper considers how parameters can be extracted from burial history calculations to construct maps that can be compared to the current locations of oil and gas fields and so used to locate and rank prospective acreage these parameters include the potential source rock maturity of a formation plotted as a function of time and depth the thermal history of any hydrocarbons associated with the potential source rock the rate of sediment accumulation of a formation as a function of time and subsidence rate of a formation as a function of time subsidence rate includes total subsidence compaction induced subsidence isostatic response to sediment load and backstripped crustal subsidence total subsidence minus the effects of compaction and isostatic response

geochemistry of the dubois greenstone succession an early proterozoic bimodal volcanic association in west central colorado abstract the dubois greenstone succession an early proterozoic supracrustal succession in west central colorado is composed of fine grained felsic volcaniclastic sediments ash flow tuffs and tholeiitic flows sills and dikes the volcanic rocks comprise a bimodal suite of tholeiite and rhyolite the tholeiites are divided into two groups group i exhibiting nearly flat ree patterns 20 30 chondrites and group ii with light ree enriched patterns 40 70 chondrites these groups can be produced by two stage melting of an undepleted or enriched garnet lherzolite source in which garnet remains in the residue of only the first melting stage which produces group ii magmas the felsic magmas can be produced by partial melting of a high grade gneiss in the lower crust in which zircon is entrained in the magma the dubois greenstone succession appears to have formed by felsic and mafic subaqueous eruptions in which some ash flows upon entering water underwent phreatomagmatic explosions giving rise to detritus which formed the volcaniclastic sediments although tectonic setting cannot be assigned to the succession with a high degree of confidence an immature back arc basin developed on sialic crust in consistent with most data

the permian hybrid petroleum system in the northwest margin of the junggar basin northwest china in this paper we define the concept of a hybrid petroleum system for the permian petroleum system in the northwest margin of the junggar basin by documenting the complexity in its formation and evolution it is termed hybrid because there are three source rock sequences seven reservoir caprock combinations and three petroleum events and multiple source rocks source the same reservoir and the same source rocks also feed multiple reservoirs the mahu sag centre is the petroleum source area with three sets of source rocks dark shale of the lower permian jiamuhe formation black shale of the lower permian fengcheng formation and black shale of the middle permian lower wuerhe formation the reservoir rocks include volcanic and clastic rocks of upper carboniferous to lower cretaceous age mainly characterized by alluvial conglomerate and sandstone there are three sets of ultimate caprocks among which the mudstone of the upper triassic baijiantan formation is the most important due to its wide distribution throughout almost the whole northwest margin and greatest thickness up to 300 m whereas the lower jurassic and lower cretaceous mudstone acts as an effective seal oil and gas were generated mainly during the middle late permian late triassic and middle jurassic early cretaceous the reconstruction of the oil filling history shows that the three source rocks charged reservoirs mainly in three geologic intervals with common mixing of oils from different sources and or with different maturities these three hydrocarbon charges coincide with the three main stages of petroleum generation related to the hercynian indosinian and yanshannian orogenies during these three petroleum events oil and gas migrated along the migration framework controlled by faults unconformities and good permeability reservoir rocks the faults are mainly well developed and episodically active thrust faults and secondary faults as a result the permian petroleum system in the northwest margin of the junggar basin is hybrid

prediction of discharge from water surface width in a braided river with implications for at a station hydraulic geometry 1 the total discharge of small braided rivers can be monitored nearly continuously using ground based orthorectified oblique images and a locally derived relationship between mean water surface width in a reach and total discharge with accuracy of the order of 10 the width discharge relationship is nearly linear over the normal range of summer flows measured in this proglacial stream the width discharge relation for a given location and channel configuration is transferable to adjacent reaches with different morphology with little loss in accuracy however the prospect of a more universal relation for braided rivers is remote because of differences in channel geometry and hydraulics between rivers the classical at a station hydraulic geometry exponent for width in this case is approximately 1 05 which is unique well above that observed in the few other braided rivers for which this has been derived and implies almost no change in mean velocity and depth with changing stage

quantitative fluorescence techniques for detecting residual oils and reconstructing hydrocarbon charge history abstract two new fluorescence techniques quantitative grain fluorescence qgf and quantitative grain fluorescence on extract qgf e can detect palaeo oil zones and current residual oil zones in petroleum wells respectively qgf and qgf e measure the fluorescence emission spectra of trace fluorescence from reservoir grains and their extracts qgf is measured on dry disaggregated reservoir grains after a cleaning procedure involving solvent hydrogen peroxide and acid whereas qgf e is measured on the solvent extract from the qgf cleaned grains palaeo oil zones have distinct qgf spectra with spectral peaks between 375 and 475 nm and elevated fluorescence intensities compared with spectra for rocks that have always been water saturated current and residual oil zones have distinct qgf e spectra with spectral peaks at around 370 nm and elevated qgf e intensities compared with that for current water zones both qgf and qgf e responses increase upwards from the palaeo oil water and residual oil water contacts respectively an oil producing well from timor sea nw australia was investigated in detail using the qgf and qgf e techniques to illustrate how they can be used to reconstruct hydrocarbon migration history

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

floodplain stages in the braided ngaruroro river new zealand this study investigates floodplain deposits in the braided ngaruroro river new zealand to characterize and quantify the spatial extent of deposits at different stages of development using a sequence of aerial photography depositional surfaces were mapped and then assigned a floodplain development stage based on age the discharge causing inundation and field observations of sediment and vegetation characteristics the ensemble of floodplain deposits makes up 40 of the river valley the remainder being the active river bed stabilizing bars and mature floodplains dominate the floodplain ensemble while the existence of stabilizing bars points to a recent shift or fluctuation in controlling conditions the extent and location of mature units suggest an earlier change in hydrologic and sediment supply conditions that limited braidtrain mobility mosaics of different aged deposits range from simple two stage mosaics to more complex arrangements of three and four stages in the rapid evolution from stabilized bars to mature floodplains a large amount of fine grained sediment is stored in the ngaruroro river valley highlighting the possibility of finding extensive fine grained facies in the ancient sedimentary record of braided systems understanding floodplain ensembles and their controls will contribute to effective restoration of braided rivers

high temperature diagenesis in shallow chalk reservoir skjold oil field danish north sea evidence from fluid inclusions and oxygen isotopes samples of calcite filled fractures from the chalk reservoir of the skjold oil field were studied by fluorescence microscopy cathodoluminescence microscopy fluid inclusion microthermometry and oxygen and carbon stable isotope and trace element analyses two generations of calcite infilling are tentatively related to two major phases of faulting caused by salt movements owing to recrystallization of the first generation of infillings the chemical isotopic and fluid inclusion data only apply to the later generation results of the fluid inclusion studies suggest a precipitation temperature of the infilling calcite significantly above what it should be applying today s geothermal gradient 52 c km or 2 85 f 100 ft to the past this higher temperature indic tes that hot water ascending from deeper strata may have flushed the reservoir apparently during a late miocene to pliocene faulting phase when ring faults guided the water to the reservoir this feature may be typical of most chalk reservoirs in the danish central graben where diapirs have penetrated the chalk

dynamic single thread channels maintained by the interaction of flow and vegetation most rivers on earth today flow as a single channel in some cases with occasional islands and follow a more or less sinuous course however single thread channels have proven difficult to reproduce and study experimentally experimental self formed channels tend to widen and subdivide leading to a braided pattern cohesive sediment has been the main mechanism studied for stabilizing banks and producing a single thread channel we show how laboratory experiments using vegetation to stabilize banks can organize the flow and convert the planform morphology from braided to single thread our experimental strategy a repeated cycle of short periods of high water discharge alternating with longer periods of low discharge accompanied by plant seeding and growth leads to the evolution of a dynamic self maintaining single thread channel with well defined banks and floodplain by eliminating weak flow paths the vegetation corrals the water into a single dominant channel until the reduction in total wetted width leads to a new self organized state in which the flow removes vegetated area as fast as it is produced the new channel is deeper and has a broader distribution of depths than the braided one with channel size adjusted to carry almost all the flood flow the resulting system maintains a dynamic steady state via similar mechanisms to those that operate in meandering channels in the field specifically erosion at the outside of bends bend growth and bar development our methodology provides a basis for experimental development of self sustaining high amplitude meanders and has applications for river management and basic research purposes

geochemistry of the archean low to high grade transition zone southern india the transition zone between archean low and high grade rocks in southern india represents eroded crustal levels representative of 15 20 km it is comprised chiefly of tonalitic gneisses with some varieties showing incipient charnockitization and of minor amounts of granitic gneiss and charnockite both of which appear to have developed from the tonalitic gneisses