intra and extrabasinal controls on fluvial deposition in the miocene indo gangetic foreland basin northern pakistan the miocene siwalik group upsection the chinji nagri and dhok pathan formations in northern pakistan records evolving fluvial systems within the himalayan foreland basin sedimentological variations are evaluated with respect to local regional and global controls on fluvial deposition and basin filling thick 5 m to tens of metres sandstones are composed of channel bar and fill deposits of low sinuosity meandering and braided rivers which formed large low gradient sediment fans or megafans river flow was dominantly toward the south east the proportion of thick sandstones varies in all siwalik sections on three scales and reflects similar variations in palaeochannel size and grain size 1 small scale variations are generally tens of metres thick and reflect the alternation of thick sandstones channel belt deposits and mudstone dominated strata overbank deposits through the section 2 medium scale variations are roughly one hundred to a few hundreds of metres thick and primarily correspond to changes in channel deposit thickness but also to the degree of superposition of channel deposits and or to changes in the number of channel belt deposits per unit of section and 3 large scale variations formation scale are greater than one km thick and primarily correspond to changes in channel deposit thickness time scales of small medium and large scale variations appear to be on the order of 104 105 and 106 years respectively the chinji nagri transition is characterized by increases in channel deposit proportion sandstone thickness palaeochannel size and discharge mean grain size of sandstones and sediment accumulation rates and a decrease in avulsion period the nagri dhok pathan transition is characterized by decreases in channel deposit proportion sandstone thickness palaeochannel size and discharge mean grain size of sandstones and avulsion period and a further increase in sediment accumulation rates formation boundaries across the potwar plateau decrease in age toward the west the chinji nagri transition ranges in age from 10 9 12 7 ma and the nagri dhok pathan transition ranges in age from 9 3 10 1 ma small scale variations are attributable to repeated river avulsions triggered by autocyclic processes and or mountain front tectonism e g faulting earthquakes medium scale variations are attributable to local changes in the position of large sediment fans also triggered by autocyclic processes and or mountain front tectonism the chinji nagri transition records the diversion or establishment possibly due to river piracy of a larger river system in the area river diversion or piracy probably took place within the mountain belt and is attributable to increasing and spatially variable mountain belt uplift rates and possibly the development of associated mountain front deformational structures the nagri dhok pathan transition records the diversion of the larger river system out of the area and the establishment of a smaller river system this diversion is attributable to progressively increasing rates of mountain belt uplift and basin subsidence the regional palaeoclimate throughout the time interval studied was apparently constant and eustatic sea level changes apparently had no effect on deposition in the area

reappraisal of the beekmantown group sedimentology and stratigraphy montreal area southwestern quebec implications for understanding the depositional evolution of the lower middle ordovician laurentian passive margin of eastern canada detailed lithostratigraphic mapping of the beekmantown group of southwestern quebec has refined the field application of the previously proposed tripartite division of the group i e theresa beauharnois and carillon formations the group is a peritidal dominated succession that accumulated on the epicontinental laurentian passive margin biostratigraphic data based on conodonts from this group indicate an early to early middle ordovician age and are partially time correlative with the wallace creek to naylor ledge strata of the philipsburg group southern quebec this conodont biostratigraphy sheds new light on the temporal evolution and depositional framework of the beekmantown platform the platform evolved as a distally steepened ramp during deposition of the theresa formation and the ogdensburg member of the beauharnois formation early to middle ibexian correlative strata of the philipsburg group include the wallace creek and morgan corner formations which represent outer platform sediments the coarse grained sandstone of the theresa formation accumulated in the innermost platform whereas coarse grained carbonates of the ogdensburg member indicate open marine subtidal to intertidal carbonate sand shoals by late ibexian the platform developed a pronounced margin where thrombolites flourished under high energy conditions these are represented by the thrombolite rich hasting creek and naylor ledge formations of the philipsburg group consequently a broad lagoon formed on the lee side of the platform margin where low energy conditions prevailed and accumulation of burrow mottled dolostones of the huntingdon member of the upper beauharnois formation took place the lagoon became more restricted during the latest stages of the basin fill whiterockian and high intertidal to supratidal sediments of the carillon formation were deposited

deposition diagenetic and hydrothermal processes in the aptian pre salt lacustrine carbonate reservoirs of the northern campos basin offshore brazil abstract the discovery of large oil accumulations in the rift and sag pre salt sections of the campos and santos basins has revived interest in the exploration of the lacustrine carbonate reservoirs in the brazilian and african marginal basins more than half of brazilian oil production originates from the pre salt reservoirs of these offshore basins a study integrating systematic petrography cathodoluminescence scanning electron microscopy microprobe and x ray diffraction was performed on seven wells in the northern campos basin this study highlights the major primary diagenetic and hydrothermal features of the pre salt succession with the aim to improve our understanding of the factors that influence the porosity and permeability distribution in these important lacustrine carbonate reservoirs the pre salt deposits correspond to bioclastic grainstones and rudstones syngenetic crusts of fascicular calcite and intraclastic grainstones and rudstones of reworked crust fragments and calcite spherulites magnesian silicates are frequently associated with carbonate deposits in the sag phase stevensitic laminations constitute the substrate for the precipitation of calcite crusts and spherulites which displace and replace the syngenetic magnesian clay deposits in the rift section stevensitic ooids are mixed with bioclasts or form ooidal arenites pre salt carbonate reservoirs have undergone a complex and heterogeneous diagenetic evolution eodiagenetic processes include the dissolution neomorphism and cementation of bivalve bioclasts in the rift as well as the dissolution of magnesian silicates and their replacement by calcite spherulites silica and dolomite in the sag section burial alterations are commonly associated with hydrothermal fluids carried through faults and fracture systems these fluids promote dolomitization silicification and dissolution at varying degrees and intensities eodiagenetic precipitation and dissolution owing to variations in the lake water chemistry and the episodic flow of hydrothermal fluids under burial conditions control the creation redistribution and obliteration of porosity in the pre salt reservoirs

interpreting avulsion process from ancient alluvial sequences guadalope matarranya system northern spain and wasatch formation western colorado alluvial deposits of the guadalope matarranya system oligocene ebro basin spain and the wasatch formation eocene western colorado provide time integrated records of the process of river channel avulsion these sequences consist of isolated channel belt sandstones incised into and abruptly overlain by flood plain siltstones indicating deposition by avulsive river systems the geometry and distribution of channel incisions suggest that avulsion was not controlled by tectonics climate or base level changes but formed by autocyclic processes measurements from 221 channel fills in the guadalope matarranya system and 38 from the wasatch formation allow us to statistically characterize channel geometries we infer to be associated with establishment and abandonment of individual river avulsions paleoflow depths in both systems average 1 4 to 1 6 m aggradation height superelevation of channel margin levees are on average 0 6 and 1 1 times paleoflow depth in the guadalope matarranya and wasatch systems respectively these results are consistent with values from recently avulsed modern rivers and suggest that 1 flow depth is the appropriate parameter against which to scale the critical superelevation necessary for channel avulsion and 2 the increase in potential energy due to channel perching drives the lateral instability that is needed for avulsion to be successful numerous stacked channel fills indicate repeated reoccupation of the same site by avulsing channels these reoccupation channels indicate that inherited flood plain topography here abandoned channel forms was an important control on the arrival site of newly avulsed channels comparison of our results to others suggests two end member types of avulsion can take place incisional avulsion seen here is characterized by an early incision phase followed by infilling by migrating bar forms aggradational avulsion begins with aggradation followed in time by stream integration into a single downcutting channel we suggest that the type of avulsion is strongly influenced by whether or not the adjacent flood plain is well or poorly drained in both cases subsequent aggradation and channel perching increase the chances that some triggering event will lead to avulsion

variscan and post variscan lead zinc mineralization rhenish massif germany evidence for sulfide precipitation via thermochemical sulfate reduction a mechanical decrepitation device coupled with a gas chromatograph has been used to characterize the molecular composition of gaseous and liquid hydrocarbons contained in minerals application of this technique allows the identification of low molecular weight n alkanes and some aromatic hydrocarbons in sulfides and gangue minerals from epigenetic variscan and post variscan lead zinc deposits in the rhenish massif germany based on the analysis of 200 samples variscan and post variscan mineralization can be distinguished by the composition of associated hydrocarbons variscan sulfides and gangue minerals contain high abundancies of methane in contrast n alkanes in the c2 c9 range and aromatic hydrocarbons benzene toluene are dominant in post variscan mineralization the absence of high molecular weight hydrocarbons in ore minerals suggests highly mature gas associated with hydrothermal activity during which hydrothermal fluids caused an increase in thermal maturation of organic matter and the generation of low molecular weight hydrocarbons in the adjacent organic rich rocks the hydrocarbon compositions contained in fluid inclusions of variscan and post variscan minerals are probably governed by the maturation level of the potential source rocks in variscan time tectonic brines t 175 c generated predominantly methane whereas basement brines t 175 c expelled higher molecular weight hydrocarbons wet gases condensates aromatic hydrocarbons from adjacent rocks during the mesozoic event the specific role of hydrocarbons in sulfide precipitation via thermochemical sulfate reduction is indicated by geochemical characteristics of organic matter associated with the plombieres pb zn deposit in eastern belgium intense alteration phenomena were observed in near ore kerogens compared with unaltered kerogens far from the ore body as well as by a very high maturity 5 40 ro a systematic depletion in 12c towards the vein type mineralization high atomic s c ratios 0 49 and by low atomic h c ratios 0 29 the data suggest that hydrothermal solutions caused a drastic increase in the thermal maturation of organic matter within the adjacent wall rock increased thermal maturation resulted in increased 13c values of organic carbon due to the preferential release of 12c the change in the organic matter to a h depleted and s enriched bulk composition in association with sulfide ores strongly suggests that thermochemical sulfate reduction was responsible for organic degradation thus thermochemical sulfate reduction probably triggered base metal sulfide precipitation in variscan and post variscan ore deposits of the rhenish massif finally based on data from this study and previous investigations new genetic models are presented for both variscan and post variscan mineralization in the rhenish massif

geochemistry of oil inclusions in sulfide related calcites fingerprinting the source of the sulfate reducing hydrocarbons of the pb zn carbonate hosted jubilee deposit of nova scotia canada abstract sulfide precipitation in the context of carbonate hosted base metal deposits has been previously explained by numerous processes including so 4 reduction in the presence of hydrocarbons this model has been suggested for numerous deposits although clear criteria to support the model have not been systematically provided numerous oil inclusions are encompassed by fibrous calcite crystals in finely laminated carboniferous limestone at the base of the windsor group a unit that hosts numerous base metal occurrences in nova scotia particularly the hydrocarbon rich jubilee pb zn deposit in cape breton island oil from two inclusion rich samples from this deposit have been characterised by gas chromatography gas chromatography mass spectrometry gas chromatography isotope ratio mass spectrometry and bulk stable c isotopes as established in the authors former publications the jubilee deposit is a clear metallogenic case for which the ground preparation and mineralisation stages involved reduction of so 4 by hydrocarbons here the question of potential sources of these hydrocarbons is addressed it is postulated that the hydrocarbons that were trapped in the sulfide related calcites at the deposit correlate with previously characterised oil seeps and it is demonstrated that their source is not the marine host carbonates but stratigraphically deeper lacustrine formations of the horton group

architecture and facies distribution of organic clastic lake fills in the fluvio deltaic rhine meuse system the netherlands abstract lakes are prominent features in distal zones of delta plains organic clastic lake fills may form in these lakes which include gyttja and lacustrine deltas understanding of the geometrical properties the facies distribution and the origin of organic clastic lake fills is limited knowledge of their development and composition however will improve our fundamental understanding of both sediment distribution in and evolution of distal delta plains furthermore organic clastic lake fills potentially form connectors in hydrocarbon reservoirs this study aims to describe and explain the characteristics of organic clastic lake fills and thereby to contribute to the understanding of delta evolution especially of distal delta plains a field study conducted in the schoonhoven and angstel vecht areas located in the distal part of the rhine meuse delta the netherlands indicates that organic clastic lake fills developed in peat bounded lakes after an avulsion initiated fluvial sedimentation the characteristics of organic clastic lake fills such as geometry sedimentary facies and sedimentation rates were both qualitatively and quantitatively determined by cross sections geomorphogenetic maps and logs the results show that in the angstel vecht area as much as 30 of the fluvial sand volume is stored in organic clastic lake fills this contrasts to the general notion that overbank deposits do not contain significant portions of sand further the lacustrine setting often results in vertically bounded sediment bodies that include gyttja and underlies clastic depositional facies which show a prominent coarsening upward succession it is concluded that the presence of organic clastic lake fills enlarges the reservoir capacity of ancient fluvio deltaic successions as they contribute to the reservoir volume and also can form connectors between isolated channel belt sand bodies

alluvial architecture of the holocene rhine meuse delta the netherlands ancient fluvial successions often act as hydrocarbon reservoirs sub surface data on the alluvial architecture of fluvial successions are often incomplete and modelling is performed to reconstruct the stratigraphy however all alluvial architecture models suffer from the scarcity of field data to test and calibrate them the purposes of this study were to quantify the alluvial architecture of the holocene rhine meuse delta the netherlands and to determine spatio temporal trends in the architecture five north south orientated cross sections perpendicular to the general flow direction were compiled for the fluvial dominated part of the delta these sections were used to calculate the width thickness ratios of fluvial sandbodies sbw sbt and the proportions of channel belt deposits cdp clastic overbank deposits odp and organic material op in the succession furthermore the connectedness ratio cr between channel belts was calculated for each cross section distinct spatial and temporal trends in the alluvial architecture were found sbw sbt ratios decrease by a factor of ca 4 in a downstream direction cdp decreases from ca 0 7 upstream to ca 0 3 downstream op increases from less than 0 05 in the upstream part of the delta to more than 0 25 in the downstream delta odp is approximately constant 0 4 cr is ca 0 25 upstream which is approximately two times larger than in the downstream part of the delta furthermore cdp in the downstream rhine meuse delta increases after 3000 cal yr bp these trends are attributed to variations in available accommodation space floodplain geometry and channel belt size for instance channel belts tend to narrow in a downstream direction which reduces sbw sbt cdp and cr tectonics cause local deviations in the general architectural trends in addition the positive correlation between avulsion frequency and the ratio of local to regional aggradation rate probably influenced alluvial architecture in the rhine meuse delta the rhine meuse data set can be a great resource when developing more sophisticated models for alluvial architecture simulation which eventually could lead to better characterizations of hydrocarbon reservoirs to aid such usage of the rhine meuse data set constraints for relevant parameters are provided at the end of the paper

longitudinal facies architectural changes of a middle holocene anastomosing distributary system rhine meuse delta central netherlands abstract longitudinal changes in channel planform and facies architecture occur over a 22 km long reach of an anastomosing middle holocene distributary system in the rhine meuse delta central netherlands a geological map and a sequence of cross sections show that the channel belt is characterized by sand body width thickness ratios which decrease within the study area from approximately 25 upstream to well below 10 downstream accompanied by a change in channel planform as indicated by a downstream increase of the number of crevasse splays the lithological composition of the sand body is relatively homogeneous but there is always a well developed fining upward sequence from sandy channel deposits to clayey natural levee deposits within channel vertical aggradation appears to have been restricted during most of the period of activity of the distributary system and since lateral accretion was also limited especially in the downstream part rapid accumulation of channel deposits seems to have occurred predominantly during the avulsion stage leaving a narrow and shallow residual channel as the last remnant the longitudinal change in channel pattern is mainly attributed to a downstream increase in the rate of ground water level rise that resulted from holocene sea level rise in the rhine meuse delta a rate of ground water level rise of 1 5 mm yr 1 is required for the creation of fully developed anastomosing fluvial systems ribbons with a width thickness ratio of

fluid rock interaction processes related to hydrothermal vein type mineralization in the siegerland district germany implications from inorganic and organic alteration patterns altered wallrocks of vein type pb zn sb mineralization siegerland district rheinisches schiefergebirge have been investigated by a combination of inorganic and organic geochemical methods including major and trace element analysis vitrinite reflectance measurements c isotope and elemental analysis of kerogen alteration features of the siliciclastic pelitic psammitic lower devonian wallrocks are increased k na ratios significant desilicification and relative immobility of a number of elements notably al ti zr cr v wallrock kerogens display elevated vitrinite reflectance values decrease in h c atomic ratios coupled with increase in s c atomic ratios and heavier c isotope compositions compared to the unaltered precursor sedimentary rocks interaction processes between the hydrothermal fluids and the respective wallrocks related to injection of high temperature silica undersaturated solutions are dominated by quartz dissolution coupled with sericitization reactions heat transfer due to fluid infiltration convection and wallrock reactions caused fluid cooling which promoted the sequential deposition of quartz and stibnite sulphosalts within the vein systems hydrocarbons detected in ore assemblages of pb zn and sb mineralization were most probably derived from the lower devonian very low grade meta sedimentary rocks high maturity levels and pronounced typical organic alteration patterns indicate that thermochemical so2 4 reduction tsr played an important role in precipitation of metal sulphides the present study demonstrates that a combination of inorganic and organic investigations on fluid rock interaction processes is particularly useful for deciphering precipitation mechanisms of base metal sulphides

alluvial architecture of the holocene lower mississippi valley u s a and a comparison with the rhine meuse delta the netherlands abstract the proportion and arrangement of channel belt deposits in alluvial successions alluvial architecture is not known in detail for most modern settings therefore the alluvial architecture of the holocene lower mississippi valley lmv between greenville mississippi and baton rouge louisiana was studied to improve estimation of parameters relevant to alluvial architecture modeling alluvial architecture parameters sand body width thickness ratio sbw sbt channel belt deposit proportion cdp overbank deposit proportion odp and connectedness ratio cr are estimated from three cross valley sections based on lithologic borings sbw sbt and cdp decrease in a downstream direction for example cdp is 0 6 upstream and 0 3 downstream odp shows an opposite trend and is at a maximum 0 7 in the downstream part of the study area cr is low throughout the study area because most channel belts in our cross sections are unconnected the alluvial architecture in the lmv also seems to change over time because late holocene channel belts tend to be wider than the early holocene channel belts the observed trends in the alluvial architecture parameters are related to the ratio between channel belt width and floodplain width variations in aggradation rate location of the cross sections relative to avulsion sites and differential subsidence the alluvial architecture of the lmv is compared to that of the holocene rhine meuse delta to identify common controls on alluvial architecture despite differences in geographic setting the alluvial architecture of the lmv is similar to that of the rhine meuse delta we conclude that alluvial architecture of both fluvial systems is strongly controlled by channel belt geometry floodplain geometry and aggradation rate these in turn are influenced by extrinsic factors i e base level discharge sediment supply tectonics and pre existing topography as well as intrinsic factors i e lateral channel migration rate subsoil erodibility differential floodplain aggradation and avulsion mechanisms therefore the interaction between extrinsic and intrinsic factors should be considered in all alluvial architecture studies

extreme sulphur isotope fractionation in the deep cretaceous biosphere abstract isotopically light sulphur in sedimentary pyrite was generally predominant during the cretaceous as a consequence of volcanic and hydrothermal activity and bacterial sulphate reduction bsr however we report super high sulphur isotopic compositions of sedimentary pyrite 34 s 89 3 from late mid cretaceous sediments from the central apennines italy these exceptionally high 34 s values are not consistent with current models for interpreting the geological record for sulphur isotopes because these cannot explain the extreme isotopic fractionation observed in our study precise details of the mechanism for producing pyrite so highly enriched in 34 s remain elusive but the large variation in 34 s values 70 within the analysed samples and the considerable micro scale variations in 34 s up to 50 even within a single nodule indicate a complex mechanism of sulphate reduction and pyrite precipitation this includes early removal of isotopically light h 2 s by pyrite precipitation in the water column diffusion and advection of h 2 s and so 4 2 and finally bsr similar but less severe conditions occur in the black sea and in deep ocean sediments these new findings provide new insights for the interpretation of the palaeoceanographic conditions that prevailed during the mesozoic

imprints of hydrocarbon bearing basinal fluids on a karst system mineralogical and fluid inclusion studies from the buda hills hungary calcite veins and related sulphate sulphide mineralisation are common in the buda hills also abundant hypogenic caves are found along fractures filled with these minerals pointing to the fact that young cave forming fluids migrated along the same fractures as the older mineralising fluids did the studied vein filling paragenesis consists of calcite barite fluorite and sulphides the strike of fractures is consistent nnw sse concluding a latest early miocene maximum age for the formation of fracture filling minerals calcite crystals contain coeval primary hydrocarbon bearing and aqueous inclusions indicating that also hydrocarbons have migrated together with the mineralising fluids hydrocarbon inclusions are described here for the first time from the buda hills mixed inclusions i e petroleum with water tail were also detected indicating that transcrystalline water migration took place the coexistence of aqueous and petroleum inclusions permitted to establish the entrapment temperature 80 c and pressure 85 bar of the fluid and thus also the thickness of sediments having been eroded since latest early miocene times was calculated 800 m low salinity of the fluids 1 7 nacl eq wt implies that hydrocarbon bearing fluids were diluted by regional karst water ft ir investigations revealed that co2 and ch4 are associated with hydrocarbons groundwater also contains small amounts of hc and related gases on the basin side even today based on the location of the paleo and recent hydrocarbon indications identical migration pathways were reconstructed for both systems hydrocarbon bearing fluids are supposed to have migrated north westward from the basin east to the buda hills from the miocene on

conditioning a process based model of sedimentary architecture to well data abstract prediction of sedimentary architecture for modeling of fluid flow in hydrocarbon reservoirs and aquifers is accomplished mainly using stochastic structure imitating models because these can be conditioned to data from wells seismic profiles and outcrop analogs conditioning implies that modeled architecture fits all available observations however the sedimentary architecture simulated by such models is commonly unrealistic process based forward models potentially provide more realistic prediction and understanding of sedimentary architecture but these models are not widely used because conditioning to well seismic or outcrop data is considered to be very difficult we show here that conditioning of process based models to well data is possible in principle using a 3d alluvial architecture model as an example this model considers the formation of alluvial deposits as a predominantly deterministic process with a single channel belt moving by avulsion over an aggrading floodplain however the initial floodplain topography is simulated by a random field thus yielding different model output for each run monte carlo simulation was used to produce model realizations that fit five hypothetical vertical wells within predetermined tolerance bands such simulation allows calculation of the probability of occurrence of channel belt deposits for each 3d cell in the 3d block of sediments generated by the model as well as the probability distributions of volumes of channel belt deposits and connectedness ratios adding more conditioning wells increases the precision of model predictions application of this approach in practice will require a major effort particularly in overcoming the anticipated large amounts of computing time

natural levee evolution in the rhine meuse delta the netherlands during the first millennium ce this paper presents reconstructions on natural levee development in the rhine meuse delta the netherlands during the first millennium ce covering the full delta plain it is the first study that performs this on a delta scale which allows seeing the delta wide trends on levee forming controls and their feedbacks we mapped the levee morphology and elevation by combining lidar imagery lithological borehole data soil mapping radiocarbon dates archaeological data and gis reconstruction techniques from the detailed levee reconstructions we quantified natural levee dimensions and evaluated the temporal changes therein the dimensions and the changes therein were then linked to external forcings increasing suspended sediment load variable flooding intensity and to natural preconditions e g delta plain width flood basin configuration we show that natural preconditions are an important control on levee shape this is demonstrated for the upper delta where the relatively narrow delta plain combined with strong compartmentation i e the occurrence of many alluvial ridges and enclosed flood basins caused the flood levels to be amplified allowing the natural levees to grow relatively high compartmentation also seems to have stimulated trapping of coarse grained overbank sediments explaining the clear downstream trend in levee width this effect was probably further aided by the clearance of the riparian forests mainly in the upstream and central delta which caused the coarser fraction of the suspended load to be further dispersed into the flood basin leading to wider levees in the first millennium ce several new river courses formed that avoided the areas of natural levee relief of abandoned alluvial ridges on these fossil alluvial ridges the topographical expression gradually reduced because of widespread flood basin trapping of overbank sediment which led to topographic levelling the natural levees that formed during this period along the new courses appear to be relatively high compared to precursor generations in the upper and central delta this is most likely related to the increased suspended sediment supply and intense flooding regime during their formation the hypotheses generated with this new delta wide overview help to better understand the controls in the development of levees which are important elements in river landscapes and in fluvial sedimentary records 2017 elsevier b v

simple shear experiments on magnetized wax hematite samples c a e s s laboratoire de geophysique interne uniuersite de rennes 1 f 35042 rennes francereceived july 1 1991 revision accepted may 28 1992abstractwe present the results of a series of simple shear experiments on hematite bearing paraffin wax samples homogeneousand continuous deformation was obtained up to a shear strain value of y 1 4 by deforming the samples in atemperature controlled bath and at a constant strain rate of 9x10 5 s r during deformation hematite plateletsprogressively rotate which has been checked by measuring the anisotropy of magnetic susceptibility ams principalsusceptibility directions tend to parallel the corresponding principal strain directions and ams intensity increases withincreasing strain this supports the idea that the hematite population develops a preferred orientation by progressive rigidrotation within the paraffin matrix before each deformation step an isothermal remanent magnetization irm was given to the samples within ara finite strain plane the containing the shear direction and normal to the shear plane with various initial angles to theshear direction ranging from 0 to 180 after each deformation step the irm was measured it showed no deflectiontowards the a finite strain direction in contrast it did show a systematic rotation within the ara plane always in the samesense as the rotation of strain axes e g counterclockwise in sinistral shear furthermore irm deviation is of the sameorder of magnitude for each initial direction from 0 to 180 this contradicts the passive behaviour model that haspreviously been shown to hold for irm in coaxially deformed samples finally we show that in the shear strain range of ourexperiments y 0 to 1 4 the deviation of irm depends only on the shear value and not on its initial direction and thatthis deviation is equal to the rigid rotation angle of the shear strain tensor

organic maturation and ore precipitation in southeast missouri the sulfate reduction plus mixing hypotheses for the formation of mississippi valley type deposits have suffered from an inability to show a plausible mass balance between sulfate possible reductants and sulfide ores and a mechanism for mixing the reduced gas h 2 s with the metal bearing fluid both these problems are resolved by focusing on the gases mostly methane generated from the organic matter in the host carbonate rocks during thermal maturation caused by heat from the hydrothermal solutions in southeast missouri it appears that the volume of the bonneterre formation required to produce all the methane needed to reduce enough sulfate to precipitate all the ores is approximately the same as the volume of the brown rock facies which hosts most of the ore therefore it appears that metal and sulfate bearing solutions entered the bonneterre at lamotte sandstone pinchouts then followed permeability trends which coincided mainly with the oolitic grainstones associated with the stromatolite reef most of which are brown evolution of methane and other reducing compounds from the brown rock resulted in sulfate reduction and precipitation of sulfides several other regional and local factors in the geology of the area are found to be compatible with this idea

hydrocarbon and ore bearing basinal fluids a possible link between gold mineralization and hydrocarbon accumulation in the youjiang basin south china the youjiang basin which flanks the southwest edge of the yangtze craton in south china contains many carlin type gold deposits and abundant paleo oil reservoirs the gold deposits and paleo oil reservoirs are restricted to the same tectonic units commonly at the basinal margins and within the intrabasinal isolated platforms and or bioherms the gold deposits are hosted by permian to triassic carbonate and siliciclastic rocks that typically contain high contents of organic carbon paragenetic relationships indicate that most of the deposits exhibit an early stage of barren quartz pyrite stage i a main stage of auriferous quartz arsenian pyrite arsenopyrite marcasite stage ii and a late stage of quartz calcite realgar orpiment native arsenic stibnite cinnabar dolomite stage iii bitumen in the gold deposits is commonly present as a migrated hydrocarbon product in mineralized host rocks particularly close to high grade ores but is absent in barren sedimentary rocks bitumen dispersed in the mineralized rocks is closely associated and or intergrown with the main stage jasperoidal quartz arsenian pyrite and arsenopyrite bitumen occurring in hydrothermal veins and veinlets is paragenetically associated with stages ii and iii mineral assemblages these observations suggest an intimate relationship between bitumen precipitation and gold mineralization in the paleo petroleum reservoirs that typically occur in permian reef limestones bitumen is most commonly observed in open spaces either alone or associated with calcite where bitumen occurs with calcite it is typically concentrated along pore vein centers as well as along the wall of pores and fractures indicating approximately coeval precipitation in the gold deposits aqueous fluid inclusions are dominant in the early stage barren quartz veins stage i with a homogenization temperature range typically of 230 c to 270 c and a salinity range of 2 6 to 7 2 wt nacl eq fluid inclusions in the main and late stage quartz and calcite are dominated by aqueous inclusions as well as hydrocarbon and co2 rich inclusions the presence of abundant hydrocarbon fluid inclusions in the gold deposits provides evidence that at least during main periods of the hydrothermal activity responsible for gold mineralization the ore fluids consisted of an aqueous solution and an immiscible hydrocarbon phase aqueous inclusions in the main stage quartz associated with gold mineralization stage ii typically have a homogenization temperature range of 200 230 c and a modal salinity around 5 3 wt nacl eq homogenization temperatures and salinities of aqueous inclusions in the late stage drusy quartz and calcite stage iii typically range from 120 c to 160 c and from 2 0 to 5 6 wt nacl eq respectively in the paleo oil reservoirs aqueous fluid inclusions with an average homogenization temperature of 80 c are dominant in early diagenetic calcite fluid inclusions in late diagenetic pore and fissure filling calcite associated with bitumen are dominated by liquid c2h6 vapor ch4 ch4 h2o and aqueous inclusions with a typical homogenization temperature range of 90 c to 180 c and a salinity range of 2 8 wt nacl eq it is suggested that the hydrocarbons may have been trapped at relatively low temperatures while the formation of gold deposits could have occurred under a wider and higher range of temperatures the timing of gold mineralization in the youjiang basin is still in dispute and a wide range of ages has been reported for individual deposits among the limited isotopic data the rb sr date of 206 12 ma for au bearing hydrothermal sericite at jinya as well as the re os date of 193 13 ma on auriferous arsenian pyrite and 40ar 39ar date of 194 6 2 ma on vein filling sericite at lannigou may provide the most reliable age constraints on gold mineralization this age range is comparable with the estimated petroleum charging age range of 238 185 ma and the sm nd date of 182 21 ma for the pore and fissure filling calcite associated with bitumen at the shitouzhai paleo oil reservoir corresponding to the late indosinian to early yanshanian orogenies in south china the close association of carlin type gold deposits and paleo oil reservoirs the paragenetic coexistence of bitumens with ore stage minerals the presence of abundant hydrocarbons in the ore fluids and the temporal coincidence of gold mineralization and hydrocarbon accumulation all support a coeval model in which the gold originated migrated and precipitated along with the hydrocarbons in an immiscible gold and hydrocarbon bearing basinal fluid system

organic geochemistry of the san vicente zinc lead district eastern pucara basin peru abstract isotopic and chemical studies of organic matter of the san vicente mississippi valley type zn pb district hosted in the dolomitic units of the eastern pucara basin peru provide insight into the source of organic matter and of the organic matter ore relationship a large scatter exists in the 13c and 15n values of the highly mature kerogens these bulk data were combined with 13c covariations of the saturated and aromatic fractions of the rock extracts to indicate a contribution of continental higher plant lipids to the marine algal source of the organic matter disseminated in the host carbonate rocks an enrichment in 15n of the kerogens of mineralized samples compared to barren samples suggests that isotopically heavy nitrogen compounds were introduced to the ore fluid the fluid likely leached these compounds from the underlying clastic rocks and other detrital units of the pucara the extracts from mineralized samples are enriched in 13c compared to the associated kerogens this suggests that the rocks in the mineralized areas were stained by a mixture of extrinsic and indigenous bitumens by the use of novel instrumentation such as a gas chromatograph gc coupled to a stable isotope ratio mass spectrometer irms through a combustion c interface gc c irms stable carbon isotope analyses of individual hydrocarbons were also obtained both the molecular and isotopic signatures of the individual hydrocarbons are related to mineralization the variability in the organic molecular parameters and the 13c values of the individual n alkanes and isoprenoids indicate mixing of indigenous hydrocarbons with extrinsic 13c depleted microbially derived hydrocarbons the extrinsic source hydrocarbons were introduced to the mineralization site by the ore fluid or later fluids using the same porosity network oxidative alteration of the migrating hydrocarbons was involved in the thermochemical reduction of sulfate to h2s and precipitation of pyrobitumen large differences 12 in the carbon isotope compositions of long chain c20 n alkanes can be utilized in distinguishing sources of organics in the barren and mineralized samples

longitudinal profile evolution of the rhine meuse system during the last deglaciation interplay of climate change and glacio eustasy fluvial longitudinal profiles reconstructed from abandoned floodplains contain significant evidence about the role of relative sea level vs climatic and tectonic controls on depositional systems two weichselian floodplain surfaces that occur as terraces updip of the hinge zone of the rhine meuse system have recently been mapped beneath the holocene rhine meuse delta the netherlands their vertical offset is several metres in the upstream area and decreases to only 0 4 m in the central part of the delta the older and higher of the two floodplain surfaces is generally assumed to have been formed around the last glacial maximum whereas the younger dates to the younger dryas following a phase of climatically induced fluvial incision during the bolling allerod the downstream convergence of these two floodplain surfaces may be related to the relative rise of sea level forcing the rhine meuse system to become graded to a higher base level during the younger dryas the upper weichselian rhine meuse system then provides an example of a basin marginal fluvial system that responds in terms of its longitudinal profile to the combined effects of upstream control primarily climate change affecting water and sediment flux from the hinterland and downstream control glacio eustatically driven relative sea level change this new evidence may therefore revitalize the presently unfashionable concept of relative sea level control penetrating many hundreds of kilometres inland

middle holocene avulsion belt deposits in the central rhine meuse delta the netherlands abstract the schoonrewoerd fluvial system in the central rhine meuse delta was active as a rhine distributary between 3900 and 3800 14c years bp based on planform patterns cross sectional facies architecture reconstructed paleodischarge and its short period of activity the schoonrewoerd fluvial system is interpreted to represent a failed avulsion the schoonrewoerd system consists of a complex of ribbon channel sand bodies encased in a lens of clayey deposits and it can be traced for more than 35 km in a downstream direction prominent features of the system are longitudinal facies architecture change with channel sand body width thickness ratio decreasing downstream from 40 to 5 and high lateral facies variability multiple anastomosing sand bodies occur in its upper and middle reaches paleodischarge reconstruction indicates that the schoonrewoerd system was only a minor distributary within the rhine meuse deltaic system specific stream power in the lower reach is estimated to have been low 0 5 to 1 8 w m2 the short period of activity of the schoonrewoerd system suggests that very high floodplain sedimentation rates were associated with the avulsion process with the formation of meters thick fine grained sedimentary successions in 100 years the facies architecture of the short lived schoonrewoerd system is interpreted to reflect the first stages of avulsion broadly analogous to the modern saskatchewan river avulsion in canada smith et al 1989 sedimentology v 36 p 1 23 having escaped from later erosion by a more mature channel belt many other systems often partly eroded with similar facies architecture exist in the west central rhine meuse delta suggesting that avulsion belt deposits are a major component of the holocene delta deposits the facies architecture model of the schoonrewoerd avulsion belt deposits presented in this paper may provide clues for the interpretation of fine grained sedimentary successions in ancient fluviodeltaic deposits

the impact of avulsion on groundwater level and peat formation in delta floodbasins during the middle holocene transgression in the rhine meuse delta the netherlands by redistributing water and sediment in delta plains avulsions of river branches have major environmental impacts notably in changing hydrological and peat forming conditions in floodbasins the central part of the rhine meuse delta with its extensive databases including detailed lithological data and high resolution age control offers a unique opportunity to study middle holocene avulsion impacts on floodbasin groundwater level and peat formation avulsion has caused local accelerations of rising groundwater tables to be superimposed on decelerating base level rise this is evident from comparing single site groundwater rise for multiple floodbasins in the river dominated part of the delta with regionally averaged groundwater rise reconstructions floodbasin type lacustrine versus terrestrial wetland size and openness partly through effects on discharge dispersal affect how strongly the floodbasin groundwater tables respond to avulsion diverted discharge cross sectional lithology repeatedly indicates a shift from high organic wood peat to low organic reed peat in the vicinity of the avulsed channel resulting from changes in water table regime and nutrient status avulsive impact on the floodbasin groundwater table was most pronounced during the transition from transgressive to high stand stage between ca 6000 and 4000 years ago owing to developing floodbasin compartmentalization size reduction confinement resulting from repeated avulsion by way of environmental impacts on groundwater tables and vegetation avulsions thus affect the heterogeneity of floodbasin facies 2017 the author s 2017

limist on the metal content of fluid inclusions in gangue minerals from the viburnum trend southeast missouri determined by laser ablation icp ms the hydrothermal fluids that deposited the ores of the viburnum trend of the southeast missouri district have long been recognized to be sedimentary basinal brines the major element composition of these brines has been well characterized however there have been no attempts to measure their metal content which is only loosely constrained by theoretical solubility relations the present study is an effort to assess the metal content of these mineralizing brines by analyzing fluid inclusions from gangue minerals in the viburnum trend using laser ablation inductively coupled plasma mass spectrometry la icp ms and microthermometry by focusing on gangue minerals instead of metal sulfide minerals interferences from the mineral matrix are avoided a high priority was to determine whether brines of anomalously high metal content were circulating through southeast missouri during the time of mississippi valley type mineralization fluid inclusions in dolomite quartz and calcite gangue from throughout the viburnum trend and representative of the entire paragenesis were analyzed none of the inclusions contained measurable quantities of pb zn or cu and only a few contained measurable quantities of ba which ranged from about 100 to 500 ppm where detection limits were not exceeded they indicated maximum possible concentrations of the element in the fluid inclusion maximum possible concentrations varied from inclusion to inclusion and were controlled by the mass of analyte within the fluid volume the larger or more saline the inclusion the lower the detection limit these results showed that the fluid that deposited quartz calcite and most of the dolomite gangue in the viburnum trend is unlikely to have had order of magnitude concentrations of pb and zn higher than 102 ppm or order of magnitude concentrations of cu higher than 101 ppm concentrations of pb and zn during deposition of stage 3 dolomite could not have been higher than 103 ppm and concentrations of cu could not have been higher than 102 ppm these upper limits on possible metal concentrations with the principal exception of those in stage 3 dolomite fluid inclusions are of magnitude similar to the highest measured concentrations of pb zn cu and ba found in typical sedimentary brines thus the brines responsible for depositing gangue minerals in the viburnum trend are unlikely to have had higher ore metal concentrations than typical basinal brines the lack of temporal overlap between gangue and metal sulfide deposition and the higher k na and lower ca mg ratios in fluid inclusions in the gangue minerals compared with fluid inclusions in the metal sulfides leaves open the possibility that the metal content of the fluid that deposited the sulfides was different from that responsible for depositing gangue however the data show that fluid entering the southeast missouri district was not pervasively metal rich throughout time and that if metal enriched fluid ever entered the district it did so at discrete intervals

formation of a giant zn pb deposit from hot brines injecting into a shallow oil gas reservoir in sandstones jinding southwestern china the association between mineralization and hydrocarbons in sedimentary basins is widely recognized but the nature and significance of their relationships are not fully understood this paper provides an example of metalliferous brines injecting into a palaeo oil gas reservoir to form a world class zn pb deposit jinding china petrographic and microthermometric studies of oil inclusions and pvt simulations suggest that oil and gas were charged in a shallow 1300 m environment before mineralization this environment favoured bacterial sulfate reduction bsr which produced large amounts of h2s that accumulated in the gas cap forceful injection of hot brines penetrated the oil zone to reach the h2s rich gas cap and precipitated sulfide ores individual fluid injection events were short lived and the reservoir was only partly and briefly heated to beyond the bacterial survival temperature episodic injection of metalliferous brines and sustained supply of h2s through bsr resulted in the formation of a large zn pb deposit this article is protected by copyright all rights reserved

lower devonian coaly shales of northern new brunswick canada plant accumulations in the early stages of terrestrial colonization abstract we describe two early devonian occurrences of coaly shale composed mainly of the compacted remains of early plants such that they resemble coal among the earliest thick phytodebris accumulations known the occurrences lie within pragian strata of the val d amour formation and emsian strata of the campbellton formation of northern new brunswick and were deposited in low energy wetlands where they were rapidly buried although the coaly shales did not yield recognizable plant taxa numerous taxa are present in adjacent beds petrographic analysis revealed an average of 80 7 vitrinite predominantly telovitrinite and 18 7 liptinite predominantly sporinite on a mineral matter free basis with a higher vitrinite content than most devonian coals low sulfur content and atomic c n ratios that vary from 44 3 to 82 1 in organic rich samples indicate terrestrial derivation vitrinite reflectance in organic rich samples 21 4 35 6 wt total organic carbon ranges from 0 48 to 1 00 indicating a low degree of thermal alteration that is supported by cross polarization spectra from studies of 13c nuclear magnetic resonance two carbon poor samples were thermally altered to anthracitic rank adjacent to an intrusive body although plants at this time were still comparatively primitive the presence at both sites of specimens with recognizable lignified cellular structures in vitrinite and particularly thick and resistant cuticle may represent an important step in peat development in these early devonian formations diverse assemblages of small vascular plants are present in a range of environments and the plants were sufficiently abundant to form coal like accumulations under suitable burial conditions serving as a proxy for plant biomass and vegetation cover in the early stages of terrestrial colonization

quantitative models of sedimentary basin filling summary quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s dozens of themes and variations have been proposed since then and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties post plate tectonic modelling began with rigid lid models which show the stratigraphic signature of subsidence variation this work introduced the connection between stratigraphy and the rheology of the lithosphere rigid lid models are the simplest type of geometric model in which the sediment surface is assigned prescribed geometries usually corresponding to different depositional environments these can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales for which quasi steady surface topography can be assumed so called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short term transport processes most of the dynamic models proposed to date can be seen as special cases of a single general morpho dynamic equation the most important result of the first wave of quantitative basin filling models is that even relatively simple models can produce reasonable stratal patterns we now have a wide array of tools for exploring scenarios searching for general behaviours and effects and making initial quantitative predictions we have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing the main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed physical experiments which are only just beginning are one means of doing this experimental stratigraphy is a bridge to quantitative field tests which will require collaboration among academic researchers from a wide range of areas and between academia and industry on projects of greater scale and degree of integration than we have seen so far the advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught at all levels

on eustatic sea level history last glacial maximum to holocene abstract this paper addresses the question of the magnitude and time dependence of the globally averaged eustatic rise of sea level that occurred subsequent to the time of last glacial maximum lgm at approximately 21 000 calendar years before present through the analysis of relative sea level rsl histories predicted by a realistic mass conserving and gravitationally self consistent theory of postglacial sea level change it is demonstrated that there are preferred oceanic locations at which this eustatic function is well approximated by local sea level history one such location is the island of barbados in the caribbean sea a site from which a coral based record exists that extends from mid holocene to lgm because of the sea level ambiguity that is inherent to coral based records however it is important that the global ice equivalent eustatic sea level curve inferred on the basis of the barbados data be tested against observations at other locations from which similarly extensive records are also available but which are derived on the basis of sea level indicators which are not subject to the ambiguities inherent to corals it is shown that when the eustatic function employed in the global theoretical model is tuned so as to enable the model to fit the barbados observations where the maximum relative sea level rsl depression is assumed to be near 120 m then the theory misfits the record from the sunda shelf in the indonesian archipelago as well as the record from j bonaparte gulf in northern australia both of these recently published records appear to constrain the lgm low stand of rsl to a value above 120 m the implications of these results for interpretation of the long coral derived records from the huon peninsula of papua new guinea and the island of tahiti are also discussed

three dimensional model of alluvial stratigraphy theory and applications abstract a three dimensional model of alluvial stratigraphy has been developed to simulate the spatial distribution proportion and connectedness of coarse grained channel belt deposits in alluvial strata as a function of channel belt width floodplain width bankfull channel depth channel belt and overbank sedimentation rates avulsion location and period compaction and tectonism tilting and faulting in this model a floodplain surface of variable width and length is occupied by a single channel belt changes in floodplain topography are produced by spatial and temporal variation of channel belt and floodplain deposition rates and by compaction and local or regional tectonism the location and timing of avulsions are determined by local changes in floodplain slope relative to channel b lt slope and by flood magnitude and frequency the diverted channel belt follows the locus of maximum floodplain slope at the end of each simulation architectural parameters are calculated including channel deposit proportion and connectedness and the dimensions of channel belt sandstone bodies three dimensional perspective diagrams mesh surfaces and two dimensional stratigraphic sections can be plotted to illustrate depositional surfaces time planes and the location and geometry of coarse grained channel belt deposits within finer grained overbank deposits the model predicts that channel belt proportion and connectedness and dimensions of sandstone bodies vary as a function of distance from avulsion points and cross section orientation upstream from avulsion points sandstone bodies have low width thickness ratios because of aggradation in a fixed channel belt immediately downstream from avulsion points channel belts tend to be connected resulting in sandstone bodies with high width thickness ratios avulsion sequences develop where points of avulsion shift up valley with a progressive decrease in avulsion period such sequences may produce successions in which channel belt proportion and connectedness vary vertically with a cyclic period of 103 to 105 years down valley increases in aggradation rate or down valley decreases in floodplain slope for example associated with a rise in base level may result in an increase in channel belt proportion and connectedness because of high avulsion frequencies in down valley regions of the floodplain down valley decreases in aggradation rate as in alluvial fans foreland basins and during base level fall may result in high avulsion frequencies in up valley parts of the floodplain tectonic tilting and faulting locally increase avulsion probabilities and channel belts generally shift toward areas of maximum subsidence under certain conditions however depositional topography may cause channels to shift away from areas of maximum subsidence channel deposit proportion and connectedness are gen rally high near downthrown areas of the floodplain but distribution clustering of channel belts may not be a reliable indicator of fault geometry or displacement models of alluvial architecture that consider only sediment accumulation rate as the main controlling factor are oversimplified the three dimensional model presented here predicts many of the features of channel behavior observed in modern rivers but there is a pressing need for better models and adequate natural data to test them

middle and late holocene avulsion history of the river rhine rhine meuse delta netherlands at present little evidence is available on avulsion rates avulsion frequencies and interavulsion periods of aggrading fluvial systems over time scales of millenia the large number of high quality 14c ages from the holocene rhine meuse delta central netherlands enables a detailed assessment of such avulsion parameters and an evaluation of the factors controlling avulsion frequency 14c histogram analysis indicates that instantaneous avulsion coexistence of successive channel belts for less than a few centuries has dominated in this area interavulsion periods were typically 1000 yr although values of 500 or 5000 yr have also been found avulsion frequency was especially large prior to 4300 cal yr b p indicating a strong control by aggradation rate in turn controlled by sea level rise in addition periods with high avulsion frequency appear to correlate with time intervals characterized by large scale transgressive tendencies the time interval with the largest number of coexisting distributaries corresponds to the period with dominance of anastomosing fluvial style

deep burial hydrothermal alteration of the pre salt carbonate reservoirs from northern campos basin offshore brazil evidence from petrography fluid inclusions sr c and o isotopes abstract petrographic mineralogical elemental isotopic and fluid inclusion analyses were integrated to unravel the diagenetic evolution of brazilian pre salt lacustrine carbonate reservoirs of northern campos basin southeast brazilian margin detailed thin section and cathodoluminescence petrography scanning electron microscopy and electron microprobe analyses established a paragenetic evolution of diagenetic processes and products comprising extensive dolomitization silicification and dissolution a paragenesis including saddle dolomite macrocrystalline calcite mega quartz sr barite celestine fluorite dickite sphalerite galena and other metallic sulfides filling fractures and dissolution porosity and aqueous fluid inclusions with homogenization temperatures of 92 152 c and salinities between 13 and 26 wt eq nacl characterized a hydrothermal system with some analogy to carbonate hosted pb zn mississippi valley mvt and irish type deposits petroleum inclusions and solid bitumen testify atypical oil generation and migration associated with the hydrothermal flow the host pre salt spherulitic and fascicular carbonates present highly radiogenic 87sr 86sr ratios indicating strong interaction with continental crust materials hydrothermal phases show 18o values more negative than syngenetic and diagenetic carbonates the 13c values are interpreted as result of interaction between the hydrothermal fluids and the host rocks the combined data set provides clear evidence of intense hydrothermal alteration of northern campos basin pre salt reservoirs at deep burial conditions 2 km possibly related to late cretaceous or more probably paleogene magmatic activity mixed sourced fluids bearing a basinal signature fed the hydrothermal system and promoted dissolution of the host rocks the hydrothermal alterations had strong impact on the porosity permeability and heterogeneity contributing together with the associated fracturing to the excellent production performance of the pre salt reservoirs

avulsion the relative roles of autogenic and allogenic processes abstract avulsion the abandonment of all or part of a channel belt in favor of a new course is controlled by both autogenic intrabasinal and allogenic extrabasinal processes however their relative roles are not known well the rhine meuse delta is without doubt the best studied delta regarding holocene avulsion processes based on studies of this delta an overview is given of 1 allogenic and autogenic processes influencing different aspects of avulsion 2 the relative importance of these processes in time and space and 3 observations that can be used to differentiate autogenic and allogenic causes of avulsion the following avulsion parameters are quantified and their allogenic and or autogenic nature are discussed period of activity of channel belts period between beginning and end of overbank sedimentation by the river channel interavulsion period time period between successive avulsions of a channel belt avulsion frequency number of avulsions per time interval in a given area and avulsion location in the rhine meuse delta the period of activity of the holocene channel belts varies considerably but shows no significant trend over time whereas extrabasinal factors climate base level and tectonics changed this suggests that this parameter is mainly autogenic controlled the average interavulsion period increased from 8000 cal yr bp to 2800 cal yr bp and decreased since then significant fluctuations occurred on a shorter time scale a maximum variability in the interavulsion period occurred between 3200 and 1800 cal yr bp this was a time when large channel belts gradually came into existence during this period the avulsion frequency also reached a maximum the long term increasing trend in interavulsion period is related to the decreasing rate of sea level rise the decreasing interavulsion period since 2800 cal yr bp can be explained by increased discharge and sedimentation resulting in an increase in the number of avulsions seven avulsion sequences as predicted by the mackey and bridge mackey s d bridge j s 1995 three dimensional model of alluvial stratigraphy theory and application journal of sedimentary research b65 1 pp 7 31 model may be recorded in the holocene dataset of the rhine meuse suggesting a periodicity of 500 600 yr each avulsion sequence coincides with a peak in the avulsion frequency the periodicity of 500 yr in the avulsion frequency is proposed to be autogenic however there is also a long term trend in the avulsion frequency that can be related to sea level rise and after 3000 14c yr bp to climate change and human influence avulsion locations are not randomly distributed over the delta and are related to the allogenic factors relative sea level rise local tectonics and changes in discharge and sediment load

reactive flow models of ore formation in the southeast missouri district two dimensional numerical reactive transport modeling was used to investigate the deposition of pb zn cu ores in the southeast missouri district central united states by two potential mechanisms cooling of a fluid carrying metals and reduced sulfur and mixing of two fluids one enriched in metals but poor in sulfur and the other enriched in reduced sulfur but poor in metals the mechanisms were studied within the context of the topography driven ground water flow regime established in the ozark region by the late paleozoic alleghanian orogeny the models integrated geology fluid flow heat and solute transport and chemical reaction generating the most complete depiction yet of potential ore forming processes in southeast missouri both mechanisms were found capable of generating important characteristics of the mineralization patterns observed in the field but fell short in other respects in models of the cooling hypothesis mineralization was indeed found to be concentrated within the southeast missouri portion of the ozark region this was primarily because of the fact that mineralizing fluid underwent very little temperature change as it traversed the ozark region until it arrived in southeast missouri where its temperature decreased significantly the important association of mineralization with local basement highs within the southeast missouri district was also produced caused by local increases of fluid velocity over the crests of the basement highs smaller scale models however revealed much of the mineralization to be concentrated within the basal lamotte sandstone rather than the overlying bonneterre dolomite where it is actually concentrated in the field this model result stemmed directly from the fact that permeability and therefore fluid velocities were higher in the lamotte than in the bonneterre a further discrepancy with field observations was the high predicted concentrations of quartz which exceeded those of galena by over two orders of magnitude models of the mixing hypothesis also led to the regional concentration of mineralization in southeast missouri provided vertical dispersivities in the lamotte sandstone and bonneterre dolomite the formations that transmitted the two different types of fluids were low when dispersivities were high mineralization was produced more uniformly along the flow path in further conformity with field observations ore was concentrated in the bonneterre dolomite and particularly around the basement highs demonstrating the importance of the lamotte pinch outs in causing the fluids to mix the models reproduced well the observed vertical zonation in metals which was controlled by the relative solubility differences among the primary sulfide ore minerals however though mixing was induced by the configuration of the local geology its intensity was relatively low leading to ore grades that were considerably less than would be expected from geochemical grounds alone because the flow regime is predominantly laminar the two fluids tended to miscibly displace one another rather than vigorously mix with one another while still potentially a viable ore forming mechanism under conditions of high local dispersivity high dissolved metal and sulfur concentrations or high fluid velocity the mixing hypothesis as typically formulated in southeast missouri is nonetheless much less efficient than previously supposed greater efficiency could possibly be generated by reaction of aqueous species with solid phases in the matrix or gas e g h 2 s being generated in the matrix

the mixing hypothesis and the origin of mississippi valley type ore deposits anderson 1991 proposed that methane generated from the heating of kerogen in the wall rocks of mississippi valley type mvt deposits diffuses into the ore zone reducing sulfate and precipitating the ore minerals this hypothesis has been tested by calculating the diffusion of methane from wall rock into a flowing solution at 150 c methane pressures in the ore zone quickly reach a steady state which depends on the assumed methane pressure in the wall rock and the flow velocity calculated methane pressures in the ore solution are not sufficient to generate a gas phase but other dissolved gases such as co 2 may contribute sufficiently to make this happen sulfate reduction and sulfide precipitation will occur whether or not a gas phase forms but many mvt ores have a tabular form or are located in the upper part of breccias suggesting that there was a gas phase control recent experimental results chou and burruss 2007 offer an explanation for the fact that very light carbon isotopes are not commonly found in mvt deposits the main obstacles to further development of these ideas is our lack of understanding of the thermochemical sulfate reduction reaction and the fact that little attention has been paid to possible sources of methane in the vicinity of ore deposits

spatial and temporal distribution of sand containing basin fills in the holocene rhine meuse delta the netherlands the quantitative significance of coarse grained deposits in the overbank realm such as crevasse splay deposits has not been studied at the delta scale or at the holocene timescale such knowledge would be beneficial for understanding and explaining sediment distribution in delta plains this study addresses delta scale distribution of sand containing basin fills and their sand body proportion variability based on eight valleywide cross sections in the holocene rhine meuse delta in the netherlands we found that sand containing basin fills form 7 1 of the fluviodeltaic wedge of which splay deposits are most frequently observed midway between the delta apex and the coast organic clastic lake fills and bay head delta deposits in contrast are limited to the distal delta plain over four successive periods between 9000 and 800 cal yr bp the largest proportions of splay deposits remain at 50 150 km downstream of the upstream shifting delta apex we show that intermediate floodbasin widths between 3 1 and 3 6 km in the holocene rhine meuse delta yield the highest proportions of splay deposits high rates of base level rise and wide floodplains both facilitate the creation of accommodation which in turn provides conditions for peat forming wetlands in which organic clastic lake fills can develop the results show that sand bodies form 26 30 of sand containing basin fills this proportion is shown to be controlled by among other variables channel planform and superelevation of the trunk channel and substrate composition we conclude that potentially large volumes of nonchannel sand bodies exist in distal delta plains they constitute up to 39 of the reservoir volume in the distal rhine meuse delta and yield relatively high connectedness ratios 2011 by the university of chicago all rights reserved

modelling holocene relative sea level observations from the caribbean and south america abstract holocene data from the caribbean and the atlantic coast of south america have been critically assessed and a subset of the best quality data are presented these data cover a large north south geographic extent and display a distinct spatial variation we make the first comparisons of this data set to predictions based on a realistic model of glaciation induced sea level change with the main aims of understanding the cause of the observed spatial trend and estimating a eustatic signal for the holocene the spatial variation is dominated by the influence of the ice and ocean mass redistribution on sea level change with the ice induced effect dominating the observed north south trend a best fitting model is applied to estimate a holocene eustatic signal from the observations we find that the model corrected data are consistent with a relatively rapid rise of 7 8 mm yr in the early holocene with a marked reduction in this rate around 7 cal kyr bp from this time until present the model corrected data suggest that the volume of mass transfer between ice sheets and oceans was no more than 1 m eustatic sea level equivalent

sedimentary products of avulsions in the holocene rhine meuse delta the netherlands abstract the main objective of this study was to describe the characteristics of deposits related to avulsion to determine if avulsion locations can be recognized by characteristic sediment architecture in the rhine meuse delta the majority of avulsion sites is accompanied by crevasse splay deposits with a relatively large areal extent these crevasse splay complexes occur near the base of the overbank deposits of the newly formed channel belt and are similar to avulsion belt deposits described by smith et al sedimentology 36 1989 1 can j earth sci 35 1998 453 the lithology of all investigated crevasse splay deposits ranges from coarse sand to silty clay sand is concentrated in crevasse splay channels and silty and sandy clay occurs as distal deposits and as levee deposits between the channels the total volume of sand is small relative to clay and silt of a total of 91 avulsion sites three sites were studied in detail one each representing the sedimentary architecture of a full nodal avulsion a failed avulsion and a crevasse splay complex that did not lead to avulsion it is concluded that dating evidence of the abandoned and newly formed paleo channel is always required to verify if avulsion really occurred although the presence of large scale sandy crevasse splay deposits in combination with two main meandering channels often indicates avulsion based on a 2 d outcrop or just one cross section it is impossible to determine whether a splay complex was associated with an avulsion or not because the architecture and lithology in both cases can be identical not all avulsion locations are characterized by crevasse splay deposits there are two possible explanations for this 1 splay deposits were eroded by the newly formed channel or 2 splay deposits were never formed this may be a result of reoccupation of an old channel in this case avulsive flow is immediately appropriated by the pre existing channel and no large scale splay formation occurs alternatively splay deposits were not formed because avulsion resulted from headward erosion

organic matter and clay anomalies associated with base metal sulfide deposits abstract organic matter and clay mineral anomalies surround the polaris gays river and gaspe mines base metal sulfide deposits the polaris mine in the canadian arctic is an mvt deposit formed by low temperature solutions homogenization temperatures t h 105 120 c and is characterized by a zone of pure illite above a kaolinite envelope surrounding the deposit these clay mineral assemblages are laterally replaced by kaolinite illite and chlorite corrensite zones while the background assemblage in the host rocks is illite interstratified illite smectite chlorite the organic matter reflectance r o shows two trends depending on the permeability and chemical reactivity of the host rock 1 an increase with depth above the ore zones in the overlying impermeable shaly cap rock r o reaches a maximum value of 1 3 above the ore compared to 0 8 in equivalent country rocks 2 an anomalous decrease with depth in the mineralized carbonate horizon that hosts the deposit the gays river mine nova scotia is a medium temperature t h 250 c carbonate hosted deposit associated with the replacement of well crystallized detrital illite and chlorite by smectite forming a halo around the main ore zone and by kaolinite and chlorite corrensite within the ore zone reflectance and its absolute variability increase in the host rocks toward the ore zone adjacent to the deposit 0 8 to 1 88 and shows a relatively low r o in the ore the economic mineralization at gaspe mines quebec is a typical high temperature skarn and porphyry copper deposit with the concomitant clay mineral alteration assemblages chlorite corrensite illite smectite chlorite illite and almost pure illite with traces of chlorite the first assemblage is observed within the ore zone and extends slightly outside the procellanite halo smectite is also found near the mineralization but its limit of occurrence is wider than the chlorite assemblage the illite assemblage is found outside the chlorite zone and is present as irregular tongues r o increases 1 2 to 15 approaching ore over a lateral distance of 60 km in the bleached zone the organic matter exhibits mosaic and degasification textures and isotropic alteration rims with very low r o these three deposits as well as others studied by the authors are centrally located within thermal aureoles whose size and intensity correlate directly with increasing temperature of formation the decreasing values of r o in the ore zones of these deposits and the associated authigenic clay minerals reflect changes in chemical conditions due to precipitation of sulfides and to reaction of the ore and post ore fluids with host rocks

sulfur isotope evidence for thermochemical reduction of dissolved sulfate in mississippi valley type zinc lead mineralization bongara area northern peru the bongara area northern peru contains mississippi valley type mvt zn pb mineralization hosted in late triassic jurassic carbonate rocks of the pucara group mineralization is interpreted to have formed during the late cretaceous peruvian orogenic event florida canyon and florcita located within 30 km of each other in the bongara area were studied to determine the origin and possible sources of sulfur in the mineralization one hundred and two in situ sulfur isotope analyses were determined on sphalerite galena and pyrite the narrow and symmetric distributions of the sphalerite 1 34s values are consistent with sulfate reduction in an open system with regard to sulfate the 34s values of sphalerite 1 from florida canyon 13 7 to 14 2 v cdt median 1 9 v cdt are lower and more variable than those for florcita 6 2 to 19 3 v cdt median 15 9 v cdt sphalerite 2 34s 0 3 to 17 6 v cdt median 2 4 v cdt postdating sphalerite 1 probably formed in a closed system with regard to sulfate the geologic setting fluid inclusion microthermometry and 34s values indicate that thermochemical reduction of dissolved sulfate tsr was the principal h2s production mechanism for metal precipitation possible sources of sulfate include late cretaceous seawater 34s 18 to 21 and evaporitic sulfate minerals in the middle late triassic chambara condorsinga formations 34s 12 to 15 and or in the late jurassic sarayaquillo formation 13 to 18 reduced sulfur from thermal cracking of organosulfur compounds and probably also remnants of h2s formed by bacterial sulfate reduction bsr might have been present during metal precipitation in florida canyon sample scale 34s variations observed in some samples from both areas reflect variable proportions of sulfate from different sources temperature effects on isotopic fractionation from sulfate to sulfide and the addition of reduced sulfur from organic compounds sample scale 34s variations can be interpreted as evidence for in situ sulfate reduction during mineralization this study places constraints on the mineralization mechanism the nature of sulfate reduction and the source of sulfur in mvt mineralization in northern peru the observed sample scale 34s variations lend support to the conclusion that in situ thermochemical sulfate reduction can occur during mineralization in these environments

assessing the role of bitumen in the formation of stratabound cu ag deposits insights from the lorena deposit las luces district northern chile abstract stratabound cu ag deposits located in north central chile have been grouped into two ns parallel belts according to the age of their volcanic and volcanoclastic host rocks deposits from the cretaceous belt are characterized by an unusual assemblage of cu sulfides with migrated hydrocarbons whereas the presence of organic matter has not yet been recognized in deposits from the jurassic belt here we report the first evidence of pyrobitumen in a jurassic stratabound cu ag deposit and evaluate its role in ore formation we present a micro analytical study of pyrobitumen associated with cu fe sulfides in the lorena deposit located in northern chile our approach involved a combination of surface and drill core sample characterization fe sem observations empa and xrf mapping of pyrobitumen in addition we determined the speciation of sulfur in pyrobitumen by using synchrotron xanes two main events of hypogene mineralization were identified at lorena deposit i e a pre ore and a main cu ore stage the pre ore stage is characterized by globularly shaped pyrobitumen and minor pyrite and a widespread albite alteration of the andesite host rock pre ore pyrite was replaced by chalcopyrite bornite and chalcocite providing evidence for a late cu inception in the main cu ore stage chalcocite is often associated with sharp edged angular pyrobitumen most likely indicating remobilization or a later pulse of hydrocarbons empa data show that pyrobitumen at lorena is enriched in fe 0 02 1 74 wt cu 0 02 0 87 wt s 0 01 0 43 wt and cl 0 01 0 4 wt other elements detected include v co ni cr sb as ag and au both ag and au were only detected in a few spots with au reaching up to 600 ppm desktop and synchrotron xrf mapping shows that s is homogeneously distributed within pyrobitumen with lower s concentrations observed at grain rims on the other hand empa wds x ray maps show that cu precipitated on pyrobitumen grain surfaces filling fractures and forming veinlets in addition textures showing the presence of micro to nano sized pyrobitumen inclusions within both pre ore pyrite and main ore chalcocite grains point unequivocally to the interaction of hydrothermal fluids with hydrocarbons during the formation of this deposit the high s concentrations measured in pyrobitumen and the presence of organosulfur compounds detected by xanes can be attributed to an organic source the pre ore assemblage is interpreted as formed from a petroleum aqueous fluid connate waters mixture that migrated from the sedimentary source rock into the jurassic host rocks where pyrite and pyrobitumen precipitated in the andesite late cu bearing hydrothermal fluids interacted with this pyrobitumen pyrite assemblage to form cu sulfides either by replacement of pyrite or precipitation we conclude that some of the s contained in pyrobitumen could have been released during interaction with the cu bearing hydrothermal fluid contributing at least partially to the s budget required for sulfide mineralization in the main ore stage our results provide evidence supporting pyrobitumen fluid interaction as a key process in the formation of the lorena deposit and possibly other stratabound cu ag deposits in chile

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

late quaternary climatic change in france estimated from multivariate pollen time series abstract in regions like southern france where usual analytical techniques are unsatisfactory due to the heavy influence of human activity and the existence of a complex climate the quantitative reconstruction of climate from pollen is particularly difficult that is why an original method has been performed the first step of the method based on best analogs estimation and multiple regression is to calculate a relationship between climate monthly temperature and precipitation and modern pollen spectra for data from 182 sites the result is called the analog climate the second step of the method an original combination of canonical correlation and principal components analyses extracts the common information from several fossil pollen sequences to produce a so called paleobioclimate this step removes the effects of local differences in the vegetation among nearby sites and also reduces the effects of human disturbance in the third step the signals obtained from the first two steps are merged by kalman filter into a final reconstruction where the noise is reduced by around 37 the results presented with a 95 confidence level suggest that the pleni wurm was 7 to 13 c colder than present and had 20 to 60 less precipitation than today this large confidence takes into account the climatic diversity of the region at 13 000 yr b p the climate reached the modern level of precipitation but the temperature was just less than present the subsequent decrease of precipitation is less important than that of temperature this fact may explain the advance of alpine glaciers during the younger dryas preboreal warming was abrupt 3 to 4 c per 500 yr and precipitation increased more slowly

depositional development of the muskeg lake crevasse splay in the cumberland marshes canada crevasse splays are common geomorphological features in alluvial and deltaic floodplains although crevasse splays can develop into full avulsions thereby transforming large areas of floodbasins little is known about their sedimentary and geomorphological development at the decadal scale and their avulsion potential we used aerial photography and lithological cross sections to reconstruct crevasse splay formation in the largely unmanaged floodplain of the saskatchewan river in the cumberland marshes saskatchewan canada based on surface geomorphology and subsurface deposits various stages of crevasse splay development were described which were linked to both external forcing and internal morphodynamics initial splay deposition following a levee breach during a large flood occurred as a broad but relatively thin sandy sheet in a down basin direction in the receiving backswamp area in a next phase these primary crevasse splay deposits blocked local down basin flow thereby forcing the crevasse splay channel in a direction perpendicular to the parent channel and original floodbasin gradient this created an asymmetrical splay sequence composition which differs in appearance from more commonly observed dendritic crevasse splays it is concluded that sedimentation patterns in the splay have been influenced by inherited effects of previously formed deposits feedbacks of the original floodbasin gradient and earlier stages of splay formation are suggested as prominent mechanisms in creating the current morphology orientation and architecture of its deposits

carbon and oxygen isotope study of hydrothermal carbonates in the zinc lead deposits of the san vicente district central peru a quantitative modeling on mixing processes and co2 degassing abstract carbon and oxygen isotope studies of the host and gangue carbonates of mississippi valley type zinc lead deposits in the san vicente district hosted in the upper triassic to lower jurassic dolostones of the pucara basin central peru were used to constrain maiels of the ore formation a mixing model between an incoming hot saline slightly acidic radiogenic pb sr fluid and the native formation water explains the overall isotopic variation 13 c 11 5 to 2 5 relative to pdb and 18 o 18 0 to 24 3 relative to smow of the carbonate generations the dolomites formed during the main ore stage show a narrower range 13 c 0 1 to 1 7 and 18 o 18 7 to 23 4 which is explained by exchange between the mineralizing fluids and the host carbonates combined with changes in temperature and pressure this model of fluid rock interaction explains the pervasive alteration of the host dolomite i and precipitation of sphalerite i the open space filling hydrothermal white sparry dolomite and the coexisting sphalerite ii formed by prolonged fluid host dolomite interaction and limited co 2 degassing late void filling dolomite iii or calcite and the associated sphalerite iii formed as the consequence of co 2 degassing and concomitant ph increase of a slightly acidic ore fluid widespread brecciation is associated to co 2 outgassing consequently pressure variability plays a major role in the ore precipitation during the late hydrothermal events in san vicente the presence of native sulfur associated with extremely carbon light calcites replacing evaporitic sulfates e g 13 c 11 5 altered native organic matter and heavier hydrothermal bitumen from 27 0 to 23 0 13 c points to thermochemical reduction of sulfate and or thiosulfate the 13 c and 18 o values of the altered host dolostone and hydrothermal carbonates and the carbon isotope composition of the associated organic matter show a strong regional homogeneity these results coupled with the strong mineralogical and petrographic similarities of the different mvt occurrences perhaps reflects the fact that the mineralizing processes were similar in the whole san vicente belt suggesting the existence of a common regional mineralizing hydrothermal system with interconnected plumbing

late weichselian and holocene palaeogeography of the rhine meuse delta the netherlands abstract a large number of lithological borehole descriptions 14c dates archaeological artefacts and gradients of palaeochannels were used to reconstruct the holocene development of the rhine meuse delta data were stored in a geographical information system database that enables generation of palaeogeographical maps for any time during the holocene the time resolution of the palaeogeographic reconstruction is about 200 years during the holocene avulsion was an important process resulting in frequent shifts of areas of clastic sedimentation palaeogeographic evolution of the rhine meuse delta is mainly governed by complex interactions among several factors these are 1 location and shape of the late weichselian palaeovalley 2 sea level rise which resulted in back filling of the palaeovalley 3 peat formation which was most extensive in the western part of the back barrier area especially between 4000 and 3000 14c yr bp this more or less fixed the river pattern at that time and resulted in few avulsions 4 neotectonics differential tectonic movements of the peel horst and roer valley graben seem to have influenced river behaviour formation of an asymmetrical meander belt location of avulsion nodes especially from 4500 to 2800 14c yr bp when the rate of sea level rise had decreased after 2800 14c yr bp the sea level rise further decreased and the tectonic influence still may have influenced avulsions but from then on other factors became dominant 5 increased discharge sediment load and or within channel sedimentation after 2800 14c yr bp river meanders of rhine distributaries as well as the single channel of the meuse show remarkable increases in wavelength interpreted as a result of increased bankfull discharge and sediment load increased discharge may initially have been caused by a higher precipitation after 2000 14c yr bp both discharge and sediment load seem to have increased as a result of human influence alternatively decreasing gradients as a result of sea level rise may have caused an increased within channel sedimentation and channel widening which would also lead to increased meander wavelengths 6 composition of the river banks meandering river channels tend to adhere to the sandy margins of the late weichselian palaeovalley and a high channel sinuosity is found in areas where river banks consist of sand 7 marine ingressions e g the ad 1421 st elizabeth s flood caused large scale erosion in the southwestern part of the fluvial deltaic plain 8 human influence since about ad 1100 human influence dominated the palaeogeographic evolution rivers were embanked and dredged meanders were cut off and for the meuse a new distributary canal the bergsche maas was dug in ad 1904 discharge distribution over the various channels is strictly controlled nowadays an unusual feature of the delta is the prolonged existence of the oude rijn channel belt

geology and stratigraphy of fluvio deltaic deposits in the ivishak formation applications for development of prudhoe bay field alaska significant remaining reserves in prudhoe bay field are confined within deltaic rocks at the base of the triassic ivishak sandstone the initial stratigraphic characterization of the prudhoe bay reservoir was lithostratigraphically based and it depicted this basal reservoir interval as tabular zones between marine shale and overlying coarse grained fluvial sandstones a reassessment of this interval based on cores and genetic stratigraphic correlations depicts en echelon offlapping fluvially dominated deltaic wedges reservoir quality rocks occur in distributary mouth bar distributary channel and fluvial facies associations a paleogeographic reconstruction of one delta lobe includes an alluvial plain crossed by channels of possibly braided or low sinuosity rivers this alluvial plain graded into a delta plain cut by distributary channels that fed distributary mouth bars on a broad delta front river dominance is inferred from the abundance of unidirectional current structures normally graded beds soft sediment deformation and general absence of wave formed tidal and biogenic structures slumping and growth faulting locally replaced coarsening upward deltaic successions with sharp based overthickened mouth bar and distributary channel deposits mudstones deposited following delta lobe abandonment form laterally extensive flow barriers between lobes compartmentalization is most pronounced distally where deltaic sandstones are overlain by and pass laterally into marine shale proximally fluvial and deltaic sandstones are juxtaposed across erosional contacts improving reservoir continuity this stratigraphic interpretation is corroborated by production and surveillance data plus an interference test locally stratigraphy and poor waterflood performance reflect completions in diachronous sandstones that originated in separate deltaic lobes previously poor well performances were attributed to sandstone pinch outs in some cases production can be enhanced with recompletions rather than infill drilling nonconventional wells planned and completed with the benefit of detailed facies association correlations currently are recovering millions of barrels of previously bypassed oil

spatial variation of overbank aggradation rate and its influence on avulsion frequency river avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges and the associated increase in cross valley slope relative to either the down channel slope or the down valley slope the latter is termed the slope ratio in the present paper therefore spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion dominated models of alluvial architecture detailed evidence on centennial to millennial scale floodplain deposition has to date been largely unavailable new data on such long term overbank aggradation rates from the rhine meuse and mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto and can be similar to observations for single overbank floods this leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios potentially resulting in increased avulsion frequencies a revised input parameter for overbank aggradation rate was used in a three dimensional model of alluvial architecture to study its effect on avulsion frequency realistic patterns of avulsion and interavulsion periods 1000 years were simulated with input data from the holocene rhine river with avulsions occurring when the slope ratio is in the range 3 5 however caution should be practised with respect to uncritical use of these numbers in different settings evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value irrespective of whether critical slope ratios are used as in the present study or superelevation as has been proposed by other investigators

experimental study of avulsion frequency and rate of deposition in existing models of alluvial architecture it is typically assumed that mean avulsion frequency is independent of sedimentation rate however if avulsion is driven by superelevation of a river bed above its surrounding flood plain one might expect avulsion rate to increase with sedimentation rate we have carried out a series of experiments with laboratory scale fluvial fans in which we measured the frequency of apical avulsions as a function of mean sedimentation rate on the fan avulsion frequency increased strongly with increasing sedimentation rate and then stabilized as mass flows began to influence deposition in the regime of increasing avulsion frequency the added volume of sediment needed to trigger an avulsion decreased with increasing sedimentation rate although our experimental results cannot simply be scaled up to natural rivers they suggest the possibility of coupling between avulsion frequency and sedimentation rate that would be strong enough to change qualitatively the results of existing models of alluvial architecture these models should be applied with caution until avulsion mechanics are better understood

factors controlling the holocene avulsion history of the rhine meuse delta the netherlands abstract the avulsion history of the holocene rhine meuse delta the netherlands was reconstructed on a timescale of millenia using detailed paleogeographic maps based on approximately 200 000 lithological borehole descriptions over 1150 14c ages and 36 000 archaeological artifacts gradient lines were constructed for all channel belts these allowed determination of gradients paleo flow direction relative age of channel belts and time correlation of undated channel belt fragments avulsion sites were inferred from the paleogeographic reconstruction at least 91 avulsions occurred over the past 10 000 years of which 82 could be dated with an accuracy of 200 14c years the location and shifting of holocene avulsion sites in the rhine meuse delta in space and time are related to 1 relative sealevel rise in the early holocene avulsions could not take place because rivers were still incised around 7500 yr bp avulsions occurred in the western part of the present delta as a result of backfilling of the late weichselian valley between 7500 and 3700 yr bp the zone where avulsions occurred shifted inland as a result of relative sealevel rise 2 neotectonics between 4900 and 1700 yr bp the location of avulsion sites seems to have been influenced by neotectonic movements of the upthrown peel horst four out of six avulsion nodes in the rhine meuse delta were located in the peel horst fault zones 3 increased discharge and or within channel sedimentation from 2800 until about 1500 yr bp avulsion sites were located all over the delta during this time the number of channels was high and avulsion frequency reached a maximum at a time when aggradation rate decreased with a reduction in the rate of sealevel rise after 2000 yr bp meander wavelength of alluvial channels increased considerably the increased meander wavelength and the high avulsion frequency are attributed to increased bankfull discharge or within channel sedimentation leading to channel widening or both 4 human influence between 1000 and 650 yr bp all the rivers were embanked and avulsions could no longer take place the few that occurred were induced by humans

experimental investigation of sediment dominated vs tectonics dominated sediment transport systems in subsiding basins abstract models of stratigraphic architecture make testable predictions regarding the subsurface spatial density and connectivity of channel sandstone bodies in subsiding basins here we test one of these predictions that lateral gradients of subsidence rate in alluvial basins tend to draw channels to local subsidence maxima and thus increase the subsurface stacking density of channel sand bodies in the vicinity of subsidence maxima here we define channel steering as any change in channel course due to lateral gradients in subsidence focusing on the attraction of channels to regions of high subsidence we examine the hypothesis that steering is controlled by the tilting ratio the ratio of the rate of lateral tilting to that of lateral channel mobility with steering effects expected to increase as the tilting ratio increases we present measurements of channel steering from experiments in which we varied the tilting ratio over four stages the experiments used a relay ramp geometry with laterally variable uplift and subsidence initially with a small value of the tilting ratio we did not detect noticeable channel steering through reductions in input sediment discharge qs and water discharge qw we decreased channel mobility in later stages while keeping the subsidence regime the same this resulted in systematic increases in the tilting ratio and in observable steering towards regions of high subsidence interestingly the increase in tilting rate relative to channel mobility also resulted in a preference for channel occupation over uplift regions as channels were trapped by incision into the rising surface we also develop theory to predict when the strength and duration of pulsed tilting events are sufficient to steer channels as with the theory for steady subsidence the new theory suggests that pulsed events must be strong enough and long lived enough to produce comparable cross basin to down basin transport slopes an experimental stage with pulsed tectonics supports this theory finally we document autogenic shoreline transgressions in the relay zone during deformation these transgressions produce downstream to upstream facies translation of the sand coal boundary in the preserved stratigraphy and illustrate a mechanism by which transgressions can develop without external cause

geochemistry of mississippi valley type mineralizing fluids of the ozark plateau a regional synthesis the compositions of fluid inclusions hosted in ore and gangue minerals from mississippi valley type mvt pb zn ba deposits of the ozark plateau region were measured to develop a regional hydro geochemical conceptual model for ore emplacement this model may explain the diverse compositions of fluids involved in mineral precipitation the ore precipitation mechanism and the temporal change in composition of fluids invading the ore districts the conceptual model additionally provides evidence for what factors may have controlled deposit size stratigraphic location and zn pb ratio high pb concentrations up to 1 0009s of ppm were identified in sphalerite hosted fluid inclusions from all of the region9s districts if these high pb concentrations were transported in the same fluid with sulfide then total sulfur concentration in the fluid must have been low mass balance calculations demonstrate that the arkoma basin a presumed source basin for the mineralizing fluids is too small to have contained enough fluid to precipitate the observed masses of sulfur in the larger mvt districts given the low sulfide concentrations that could coexist in the fluid with such high concentrations of pb high methane concentrations in sphalerite hosted fluid inclusions from all of the region9s districts in dolomite hosted fluid inclusions from the tri state and northern arkansas districts and quartz hosted fluid inclusions from the northern arkansas district suggest that the prevailing redox conditions during mvt mineralization were reducing making it unlikely that sulfate was transported in large concentrations in the fluids during sphalerite precipitation assuming saturation with respect to carbon dioxide measured methane concentrations in sphalerite hosted fluid inclusions would have required oxygen fugacity to have been at least two log units below the sulfate predominance field boundary fluid inclusion methane concentrations can also be used to estimate minimum burial depths of mineralization of about 0 08 to 1 2 km available evidence indicates that sulfide mineral precipitation in the ozark plateau mvt districts most likely occurred primarily as a result of the introduction of sulfide into a pb and zn rich ore fluid in the two larger mvt districts sulfide may have been supplied by local organic and sulfur rich carbonate facies an apparent mixing line between high ca na ratio and low ca na ratio fluids hosted predominantly in main stage sulfide minerals and paragenetically late minerals respectively indicates the ore fluid was relatively ca enriched the lack of continuity in high pb concentrations in fluid inclusions in sulfide and nonsulfide minerals from across the mineral parageneses suggests that the ore fluids entered the districts intermittently and or had variable metal contents over time

avulsion frequency avulsion duration and interavulsion period of holocene channel belts in the rhine meuse delta the netherlands abstract avulsion parameters greatly influence alluvial architecture because they determine channel density and interconnectedness reliable data on avulsion parameters is still scarce from a detailed reconstruction of the holocene avulsion history of the whole rhine meuse delta we determined quantitative values for the avulsion parameters avulsion frequency avulsion duration and interavulsion period in the rhine meuse delta the number of coeval channels is related to the avulsion frequency calibrated 14c intensity histograms are used to analyze 14c dates of beginning and ending river activity the histograms show that instantaneous and gradual avulsions were almost equally important in the rhine meuse delta a high avulsion frequency occurred from 8000 to 7300 cal yr bp a total of 17 avulsions i e 2 43 avulsions 100 years during this period the avulsion frequency was related to the high rate of sea level rise which induced fluvial sedimentation in the present near coastal area after 7300 cal yr bp avulsion frequency decreased as a result of a continuously decreasing rate of sea level rise from 7300 to 3200 cal yr bp avulsion frequency was low 35 avulsions took place within 4100 years 0 85 avulsions 100 years approximately 5000 cal yr bp the coastal barriers became closed and large scale peat formation occurred this resulted in fixation of the river channels and low cross valley gradients reducing the chances for avulsion between 3200 and 1400 cal yr bp avulsion frequency was high again a total of 34 avulsions i e 1 89 avulsions 100 years as a result of increased discharge and or within channel sedimentation which enhanced chances for avulsion the period of activity of channel belts shows no significant trend on the time scale of the holocene it is highly variable and averages 1280 820 cal yr the avulsion duration fluctuates between less than 200 and 1250 cal years and averages 335 cal years the avulsion duration shows no significant trend through time and remained constant until at least 1900 cal yr bp avulsion duration seems not to be influenced by aggradation rate average interavulsion period is shorter than the period of activity of channel belts and is approximately 945 cal years in the rhine meuse delta on the time scale of the holocene interavulsion period and avulsion duration are on average constant therefore the number of coeval channels is directly related to avulsion frequency available evidence from other rivers and deltas around the world however suggests that the relationship between these avulsion parameters is not everywhere the same

variability of channel belt dimensions and the consequences for alluvial architecture observations from the holocene rhine meuse delta the netherlands and lower mississippi valley u s a abstract over the past decades many studies have focused on the dimensions of channel belt sand bodies referred to as channel belts in fluvial deposits because of their relevance for hydrocarbon exploration and production some field studies have revealed a significant downstream decrease of channel belt width and width thickness ratio along the length of the channel belt to verify whether this is a common feature in fluviodeltaic settings eight holocene channel belts in the rhine meuse delta the netherlands were selected and one in the lower mississippi valley u s a we determined channel belt geometry width or width thickness ratio using geological geomorphological maps and detailed cross sections based on borings it was found that the width of channel belts encased in cohesive deposits decreases by a factor of 4 to 6 5 in a downstream direction along the length of the channel belts the width thickness ratio decreases by a factor of 2 5 to 5 on the other hand the width of a channel belt incised in a noncohesive substrate remains constant along its entire course these observations are related to longitudinal changes in bank erodibility and stream power it is suggested that bank erodibility is the dominating factor determining the geometric properties of channel belts and the variability therein at least in the rhine meuse delta the currently available alluvial architecture models most likely overestimate sand quantities and connectedness in alluvial successions because channel belt dimensions are held constant in all models we therefore propose that the factors bank erodibility and stream power which influence width and width thickness ratio of channel belts should be incorporated in future alluvial architecture models in order to make more realistic estimates of sand quantities in river deltas

processus d alteration thermique physico chimique et biologique de constituants organiques et genese d une mineralisation sulfuree le gite zn pb de la florida cantabria espagne the la florida lead zinc deposit cantabria spain which is hosted by urgonian carbonates is located on the border of the basco cantabric lower cretaceous basin the stratiform orebody which is composed of sphalerite galena and barite in iron dolostones occurs in an envelope of dolostone organic matter studies have been carried out on samples from this deposit to understand its genesis and later evolution the results of this work reveal the immatury of the autochthonous organic matter despite a slight paleothermal anomaly centred on the deposit various alteration processes have affected the hydrocarbons associated with autochthonous organic matter and or allochthonous bitumens namely geochromatographic fractionation water washing and biodegradation together with previous geological work the results of this study are consistent with epigenetic and or diagenetic emplacement of the mineralization the proposed genetic scheme involves hydrothermal fluids that would have acquired at least so

late quaternary sea level change and isostatic and tectonic land movements along the belgian dutch north sea coast geological data and model results early and middle holocene sea level data from belgium plot ca 2 m above data from the western netherlands reflecting differential tectonic and isostatic movements the total uplift rate of belgium relative to the western netherlands decays gradually from 0 66 m kyr 1 at 7500 cal yr bp to less than 0 25 m kyr 1 since 5000 cal yr bp the tectonic component of this relative movement inferred from eemian sea level data is in the order of 0 06 to 0 16 m kyr 1 the isostatic component of the uplift is related to the last phase of the collapse of a peripheral bulge under the netherlands and the dutch and german sectors of the north sea and to hydroisostatic subsidence of the north sea basin caused by water loading as sea level rose comparisons with isostatic rebound models show that they predict well the holocene isostatic movement between belgium and the western netherlands and that the predictions are improved when the tectonic component is removed from the observations preliminary evaluation of sea level data from the dutch sector of the north sea shows that glacio hydroisostatic subsidence relative to belgium was significantly greater than for the western netherlands coastal area and spatially highly variable copyright 2002 john wiley sons ltd

insights into ore genesis of the jinding zn pb deposit yunnan province china evidence from zn and in situ s isotopes abstract the jinding zn pb deposit located in the mesozoic cenozoic lanping basin of southwest china has ore reserves of 220 mt with an average grade of 6 1 zn and 1 3 pb the mineralization is hosted by sandstone in the early cretaceous jingxing formation and limestone breccia in the paleocene yunlong formation mineralization in both types of host rocks is characterized by a paragenetic sequence beginning with marcasite sphalerite stage 1 followed by pyrite marcasite sphalerite galena stage 2 and then galena sphalerite pyrite sulfate carbonate stage 3 pyrite from these stages have different 33 s compositions with pyrite from stage 1 averaging 9 6 stage 2 averaging 8 9 and stage 3 averaging 0 3 sphalerite hosted by the sandstone has similar 66 zn values ranging from 0 10 to 0 30 in all stages of the mineralization but sphalerite samples from the limestone breccia hosted ore show variable 66 zn values between 0 03 and 0 20 our data on sphalerite precipitated during the earlier stages of mineralization has a constant 66 zn value and cogenetic pyrite displays a very light sulfur isotope signature which we believe to reflect a sulfur source that formed during bacterial sulfate reduction bsr the stage 3 sphalerite and pyrite precipitated from a late influx of metal rich basinal brine which had a relatively constant variable 66 zn isotopic composition due to open system isotope fractionation and a near zero 33 s composition due to the influence of abiotic thermochemical sulfate reduction from observed sulfates in the host rock