depositional environment and hydrocarbon source potential of the lower miocene oil shale deposit in the aleksinac basin serbia abstract the most prolific oil shale deposit in serbia is located in the aleksinac basin and is assigned to the lower miocene depositional environments and hydrocarbon potential were assessed for the aleksinac oil shale and coal layers through bulk geochemical organic petrographical biomarker and carbon isotope data from core samples from a single well maturity parameters vitrinite reflectance tmax biomarker isomerisation ratios prove that the organic matter om is immature a lower lacustrine oil shale sequence is comprised of alternating sandstone and clay rich rocks and some thin coal beds indicating strong variations in depositional environment this stratum is covered with thick sandstone 50 m terminated by the main 4 m thick coal seam that was deposited in a low lying mire as evidenced by high total sulfur and mineral matrix contents the plant input was dominated by angiosperms a relative rise in water level led to the drowning of the swamp and to the deposition of a 60 m thick upper oil shale in a lacustrine environment the om of the oil shale is dominated by kerogen type i lamalginite biomarker data suggest a stratified water column that likely formed due to differences in salinity the stratified water column led to a strictly anoxic environment and photic zone euxinia in a mesosalinar hydrologically closed lake which enabled the accumulation of uncommonly high amounts of organic material average toc 18 0 wt with excellent preservation average hi 743 mg hc g toc

coarse grained deep water sedimentation along a border fault margin of lake malawi africa seismic stratigraphic analysis lake malawi africa serves as an important modern analog for understanding depositional processes in an active rift setting this paper explores the depositional processes and stacking patterns of coarse grained facies across a large fan delta and associated sub lacustrine fan system offshore of the south rukuru river using single channel seismic data coupled with deep water vibracores and gravity cores a companion paper wells et al 1999 discusses the details of the depositional processes of the system inferred from core data using 2900 km of single channel seismic data eight genetic facies were defined based on seismic reflection character external geometry accompanying core data and location within the modern geomorphic system five sand dominated facies include 1 mouth of canyon fan facies 2 progradational fan delta facies 3 channel fill facies 4 canyon fill facies and 5 basin plain fill facies these facies occur as surficial deposits in water depths of more than 600 m suggesting that coarse grained sedimentation characterizes certain localities in even the deepest parts of lake malawi climatically driven lake level changes influenced the internal character of these facies their thickness and to some extent their location within the south rukuru study area however climate was generally subordinate to tectonism in controlling the temporal and spatial distribution of the facies tectonic controls can be categorized as 1 orientation of the first order border fault and intrabasinal faults 2 syndepositional footwall uplift and rotation and 3 temporal changes in the rate and location of maximum subsidence these controls affect the location and stacking of the mouth of canyon fans and the presence and orientation of sub lacustrine canyons and the zone of maximum sediment accumulation and depositional gradients

hydrogen index as reflecting intensity of sulphidic diagenesis in non bioturbated shaly sediments abstract based on 13 published porewater h 2 s and sulphate profiles the amount of h 2 s escaping from non bioturbated shales varies between some few to 45 of the amount of bacterially generated h 2 s this finding permits calculation of the original organic carbon toc or content of immature nonbioturbated shales using toc and sulphur content data in two immature non bioturbated sequences from hungary toarcian and oligocene the first order correlation between hi and toc toc or was found to be stronger than that between hi and toc indicating that sulphate reduction was the leading process both in decrease in toc content and degradation of kerogen source potential

the architectural variability of small scale cycles in shelf and ramp clastic systems the controlling factors many sedimentary successions are composed of metre to decametre scale cycles exhibiting various stratal architectures that depend on the complex interplay among several syndepositional controlling factors these controlling factors may produce extremely different stratal and facies architectures along relatively brief distances in the same basin but in contrast they also may form similar architectures in basins that experience a radically different tectonic setting the recognition of factors that controlled the architecture of small scale cycles therefore is very important to reconstruct the depositional history of sedimentary successions these factors include 1 the interplay between the rate of accommodation development and the rate of sediment supply a s 2 the amplitude and shape of the relative sea level curve 3 the position in the shoreface shelf system 4 the basin physiography 5 the shoreline trajectory 6 the climate driven environmental energy 7 the siliciclastic input vs carbonate production shoreface to shelf small scale cycles can be grouped into three main categories r cycles showing a dominant regressive interval t r cycles with transgressive and regressive intervals of similar thickness t cycles showing a dominant transgressive interval although some depositional settings may favour the deposition of a particular type of cycle these cycle motifs appear to be mainly controlled by the interaction of local and wider scale controlling factors for example t cycles may be present in both subsiding and uplifting settings depending on the interplay between the a s and the other factors cited above as a result r t r and t cycles may be recognized within the same depositional system these evidences suggest that care must be taken to apply general models that predict the stratal architecture of cycles mainly in function of the long term a s the correct prediction of the cycle architecture is important also for hydrocarbon researches as the thickness of potential reservoir deposits is the result of the interplay among factors discussed here

constraining sediment transport to deep marine basins through submarine channels the levant margin in the late cenozoic abstract the recent world class gas discoveries in early miocene sand units offshore israel raises the question of their origin apparently the simplest explanation is to relate them to a fluvial system that arrived from arabia at that time this system predated the modern pliocene nile river supply and existed until captured by the dead sea valley interestingly however very little sedimentation occurred along the levant continental margin before the pliocene in spite of its stepped structure that provided much space for accommodation the only way that sediments could have bypassed the continental margin and arrive at the deep basin without being trapped in the middle is through submarine channels that crossed the continental margin here we explore this possibility using 3 d stratigraphic modeling techniques that quantify the sediment load and the water discharge required to fill the basin by pushing enough sediment through submarine channels we show that such a scenario requires a fluvial system in the order of the largest rivers that exist today on earth in terms of drainage area and water discharge alternatively it requires extreme hydraulic conditions in terms of diffusion coefficients and an elevated drainage basin that could not have existed in the study area we therefore challenge the traditional view of arabia as the main source for oligo miocene deposits in the levant basin and suggest that the basin was mainly fed by a proto nile system that transported clastic material to the north african margin and then farther east by ocean currents in a wider view we demonstrate how numerical modeling can constrain sediment transport through submarine channels as a function of basin geometry and hydraulic conditions and how paleogeographic knowledge can be combined with current data on world rivers to evaluate if modeling results are plausible

novel 3d sequence stratigraphic numerical model for syn rift basins analysing architectural responses to eustasy sedimentation and tectonics syn rift clastic sedimentary systems preserve a complicated stratigraphic architecture that records the interplay of tectonics eustatic sea level and storage and routing of sediments previous conceptual models describe and explain changes in depositional stacking patterns along a fault segment however stacking patterns and the nature of key stratigraphic surfaces is challenging to predict accurately with conventional sequence stratigraphic models that do not consider the three dimensional interplay of subsidence sedimentation and eustasy we present a novel geometric 3d sequence stratigraphic model syn strat which applies temporally and spatially variable fault scale tectonic constraints to stratigraphic forward modelling as well as allowing flexibility in the other controls in time and space syn strat generates a 3d graphical surface that represents accommodation although the model has the capacity to model footwall variation here we present model results from the hangingwall of a normal fault with temporal and spatial dip and strike predictions made of stacking patterns and systems tracts for a given set of controls sensitivity tests are tied to the depositional architecture of field based examples from the loreto basin gulf of california and alkyonides basin gulf of corinth here the relative influence of major sedimentary controls different subsidence histories varying sedimentation distribution including along strike variation in stacking patterns are assessed and demonstrate the potential of syn strat for reducing subsurface uncertainties by resolving multiple scenarios in addition the model demonstrates the nature of diachroneity of key stratigraphic surfaces that can arise in syn rift settings which could be represented by a bypass surface sequence boundary or reservoir seal maximum flooding surface in the rock record enabling a quantitative assessment of these surfaces is critical for prospect analysis in hangingwall half graben fills where these surfaces are heavily relied upon for well correlations that are used for hydrocarbon volume and production rate predictions

early diagenetic alteration of organic matter by sulfate reduction in quaternary sediments from the northeastern arabian sea abstract hemipelagic sediments from the northeastern arabian sea off pakistan were analyzed by geochemical and microscopical methods to study the importance of bacterial degradation processes on the quantity and composition of sedimentary organic matter om on the basis of elemental analysis of total organic carbon toc and total sulfur ts the decay of om by sulfate reducing bacteria were calculated concentrations of total iron reactive iron total nitrogen tn total phosphorus tp and hydrogen indices hi were used to assess organic matter reactivity and redox conditions stable sulfur isotopic compositions provided further information about pathway timing and mechanisms of sulfate reduction microscopical observations indicate that throughout the study area om is amorphous 75 95 in almost all samples with only a small contribution of terrigenous om bacterially mediated sulfate reduction leads to continuously decreasing toc ts ratios from 0 4 m to a burial depth of 2 3 m at this depth the anaerobic oxidation of particulate organic matter ceases sulfate reduction in this narrow interval accounts for the decay of up to 70 of the om which has primarily entered the anoxic domain during the bacterially mediated diagenesis preferential consumption of nitrogen and phosphorus containing organic compounds can be observed and quantified the regeneration of up to 60 of tn and more than 50 of tp can lead to a feedback of nutrients to the seawater this recycling process may contribute to the high productivity in the northeastern arabian sea

photic zone euxinia in the central rhaetian sea prior the triassic jurassic boundary abstract shortly after the deposition of black shales in the rhaetian sea central european basin ceb the triassic jurassic tr j boundary witnessed one of the big five mass extinction events in earth s history aiming at a better understanding of paleoenvironmental changes in the geochemically less well known middle to late rhaetian german subdivision we studied samples from a cored borehole from the central rhaetian sea in nw germany hebelermeer 2 biomarkers palynomorphs and bulk geochemistry all support a marine brackish setting with inputs from terrestrial plants dinosteranes were found throughout the core most likely suggesting the spread of dinoflagellates it is widely accepted that volcanic exhalations during the development of the central atlantic magmatic province camp had a major impact on marine and terrestrial environments in the earliest jurassic e g the development of photic zone euxinia and h2s poisoning of benthic life there is evidence from the studied core however that comparable conditions already thrived in the central rhaetian sea during the middle rhaetian a first indication of euxinia anoxia is evident from low to very low total organic carbon versus total sulfur toc ts ratios

high resolution sequence stratigraphy of clastic shelves vii 3d variability of stacking patterns abstract in the geological record high frequency sequences at the scale of fourth order and lower rank stratigraphic frameworks are usually stacked to compose higher rank lower frequency systems tracts i e sequence sets along dip oriented transects higher rank transgressive normal regressive highstand and or lowstand and falling stage systems tracts are defined by retrogradational upstepping progradational and downstepping progradational stacking patterns of component high frequency sequences respectively however these stacking patterns may vary markedly along depositional strike due to lateral changes in the rates of accommodation and sedimentation resulting in the coeval deposition of different types of higher rank systems tracts in this case surfaces bounding such systems tracts are diachronous along depositional strike moreover if the high frequency sequences that compose the lower frequency systems tracts are laterally continuous the higher rank bounding surfaces are discontinuous along depositional strike consisting of a series of stepped surfaces that can be observed in high resolution studies these aspects have important implications for petroleum exploration and need to be considered in high resolution sequence stratigraphic analysis

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

unconventional distribution of facies in a continental rift basin the pliocene pleistocene mangas basin south western new mexico usa the pliocene early pleistocene mangas basin in sw new mexico usa was a n nw trending full graben that changed southward to an eastward tilted half graben unlike the facies distribution predicted in existing models the half graben part of the mangas basin was characterized by broad alluvial fans derived from the footwall scarp smaller hangingwall derived alluvial fans and a shallow closed lake lake buckhorn that locally lapped onto the hangingwall hills the distribution of facies within the full graben part of the mangas basin was also unlike that predicted in current models primarily because of a broad belt of alluvial fan sediment derived from the eastern footwall scarp and a narrow belt of axial fluvial sediment adjacent to the western footwall scarp the distribution of facies in the mangas basin does not appear to have been controlled by the eastward tilt of the floor of the half graben or see saw motion of the floor of the full graben as predicted by existing models but rather by the large size of the alluvial fans on the eastern side of the basin these fans were derived from large high relief catchments on the footwall scarp of the mogollon mountains the uplift of which began during early miocene this example illustrates how earlier uplift and drainage development in a mountain range may influence facies distribution in a younger extensional basin

effects of variations in fault slip rate on sequence stratigraphy in fan deltas insights from numerical modeling results from a newly developed numerical model incorporating tectonic subsidence eustasy and sedimentation are presented for rift basin settings in particular we simulate contemporaneous fan delta deposition subsidence and eustatic sea level variations to investigate the three dimensional nature of depositional sequences in the hanging wall of a normal fault a random walk algorithm is used for sediment delivery from source to shoreline together with a nonlinear three dimensional diffusion equation for sediment movement on steep delta foresets three sediment sources are modeled they are located along strike in areas of low medium and high subsidence rates of hanging wall subsidence eustatic sea level variation and sediment supply are derived from studies of active extensional basins the resulting stratigraphy contains three fan deltas with distinct morphologies and internal stacking patterns sequence boundaries and offlap forced regression are restricted to areas of low subsidence toward the fault tip aggradationally stacked deltaic wedges are along strike where subsidence rates are high near the fault center the simulated geometries compare well to natural examples and highlight along strike sequence variability and the importance of local controls in such settings

isotopic biogeochemistry of the oxford clay formation jurassic uk a total of 165 samples was obtained from the oxford clay formation at seven different sites nearly all were from the peterborough member lower oxford clay but seven were from the stewartby and weymouth members middle and upper oxford clay respectively five samples from the underlying kellaways formation were also examined stratigraphic relationships were estimated on the basis of ammonite subzones and results from all locations can be placed along a single stratigraphic scale the following were determined for all samples abundance and isotopic composition of organic carbon abundances of carbonate carbon and total sulphur and the rock eval pyrolysis parameters hydrogen index oxygen index and t max for a subset of eight samples selected to be representative of geochemical and apparent palaeoenvironmental variations soluble organic compounds were extracted and the isotopic composition of pristane phytane and long chain n alkanes determined by isotope ratio monitoring gas chromatograph mass spectrometry concentrations of organic carbon in samples from the peterborough member ranged from 0 5 to 16 6 and values of total organic carbon toc ranged from 27 7 to 23 1 v pdb shales dominated by epifaunal bivalve assemblages have high concentrations of toc and values of h index approaching 800 indicating preservation of hydrogen rich organic material conversely shell beds and calcareous and silty clay beds have lower abundances of toc and values of h index dropping below 100 indicating extensive oxidation of the organic matter isotopic composition of pristane and phytane in the peterborough and stewartby members average 31 7 those in the weymouth member average 29 8 values of for long chain n alkanes average 28 together these results indicate values for primary inputs as follows terrestrial vascular plants 23 5 peterborough member algae 28 2 stewartby member algae 29 1 weymouth member algae 26 6 comparison of primary values to those of toc indicates that in some cases secondary processes enriched toc relative to primary inputs by as much as 4 palaeontological evidence in these same beds indicates development of extensive food webs and supports attribution of this isotopic enrichment to heterotrophic reworking

tectonically enhanced forced regressions examples from growth folds in extensional and compressional settings the miocene of the suez rift and the eocene of the pyrenees

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

the velocity description of deformation paper 1 theory abstract there are several advantages in using velocities to describe the deformation of the crust and lithosphere induced by extension compression isostasy and other processes 1 the method is very general any deformation style can be described in this way simple examples are pure shear inclined or vertical simple shear bulk rotation airy or flexural isostasy and compaction 2 velocity fields can be combined to model more complex deformation 3 the syn tectonic evolution of parameters such as temperature pressure hydrocarbon maturity and porosity are easily modelled once the deformation velocities are specified 4 the syn tectonic evolution of sedimentary architectures can be modelled using a general tectono sedimentary forward modelling equation which incorporates the deformation velocities these advantages are illustrated by a computer model which simulates clastic sediments prograding into an active half graben formed by extension above a listric fault processes included in this model are compaction of the sediments hanging wall deformation by inclined simple shear and simultaneous footwall deformation to avoid space problems the velocity field for the hanging wall block above the non rigid footwall must obey a simple contact condition

geochemistry and organic petrography of cretaceous sediments of the calabar flank southeastern nigeria abstract detailed bulk geochemistry and organo petrography of outcrop cretaceous sediments with no significant effects of weathering from the calabar flank southeast nigeria were performed to understand the organic carbon source accumulation and degradation and paleo climatic paleoceanographic and paleoenvironmental conditions in west africa during early cretaceous aptian to maastrichtian times this study was based on microscopic elemental analyses organic carbon nitrogen iron and sulphur rock eval pyrolysis and carbon isotope analyses in general the calabar flank shales are characterised by highly variable total organic carbon toc contents which range between 0 1 in aptian albian mfamosing limestone and 9 9 in the awi formation sediments the organic matter om is a mixture of immature to early mature marine and terrigenous om of types iii and iv this is indicated by low hydrogen indices hi value 10 190 mg hc g toc tmax 417 460 c vitrinite reflectance ro 0 39 0 62 ro low to high c n ratios 3 4 1158 0 and high amounts of terrigenous macerals vitrinite inertinite based on carbon isotope c n ratios and sulphate reduction index sri om degradation up to 70 sri 2 5 is most pronounced for shales deposited in a marine environment the geochemical and petrographic data indicate that local factors such as low bioproductivity down slope transport and redeposition of sediments from a fluvial deltaic basin to nearshore facies shallower oxic and mildly oxygen deficient environments humid arid paleogeographic conditions specifically controlled the amount and quality of the om during aptian mastrichtian stages where marine sediments have been assumed to be deposited during the global anoxic events therefore the order of the main factors controlling om content in sediments are input of terrigenous material transported from the land low om productivity by marine photoautotrophs low preservation

self potential signals generated by the corrosion of buried metallic objects with application to contaminant plumes abstractlarge amplitude 100 mv negative electric self potential anomalies are often observed in the vicinity of buried metallic objects and ore bodies or over groundwater plumes associated with organic contaminants to explain the physical and chemical mechanisms that generate such electrical signals a controlled laboratory experiment was carried out involving two metallic cylinders buried with vertical and horizontal orientations and centered through and in the capillary fringe within a sandbox the 2d and 3d self potential sp data were collected at several time steps along with collocated ph and redox potential measurements large dipolar sp and redox potential anomalies developed in association with the progressive corrosion of the vertical pipe although no anomalies were observed in the vicinity of the horizontal pipe this discrepancy was due to the orientation of the pipes with the vertical pipe subjected to a significantly larger eh gradient accounting for the electrical conductivity dis

parasequences allostratigraphic misfits in sequence stratigraphy abstract parasequences were introduced as the building blocks of seismic scale systems tracts in the context of low resolution seismic stratigraphy pitfalls of this concept relate to the definition of parasequence boundaries as lithological discontinuities that mark episodes of abrupt water deepening with this general meaning flooding surfaces may be facies contacts within transgressive deposits or may coincide with different types of sequence stratigraphic surfaces maximum regressive transgressive ravinement or maximum flooding in all cases flooding surfaces are allostratigraphic contacts restricted to coastal and shallow water settings where evidence of abrupt water deepening can be demonstrated flooding surfaces may also be absent from the shallow water systems where conformable successions accumulate during gradual water deepening it follows that 1 parasequences have smaller extent than systems tracts and 2 systems tracts do not always consist of stacked parasequences these limitations prevent the dependable use of the parasequence concept in sequence stratigraphy advances in high resolution sequence stratigraphy show that the scales of sequences and parasequences are not mutually exclusive the two types of units define different approaches to the delineation of stratigraphic cycles at high resolution scales sequences that develop at parasequence scales provide a more reliable alternative for correlation both within and outside of the coastal and shallow water settings rendering parasequences obsolete every transgression that affords the formation of a flooding surface starts from a maximum regressive surface and ends with a maximum flooding surface observed at the scale of that transgression these systems tract boundaries are invariably more extensive than any facies contacts that may form during the transgression flooding surfaces remain relevant to the description of facies relationships but their stratigraphic meaning needs to be assessed on a case by case basis the use of sequences and systems tracts in high resolution studies provides consistency in methodology and nomenclature at all stratigraphic scales irrespective of geological setting and the types and resolution of the data available

drainage development and sediment supply within rifts examples from the sperchios basin central greece drainage systems juxtaposed with modern depositional environments within the sperchios rift allow detailed analysis of the relationships between drainage catchments sediment supply and alluvial fan fan delta geometries prominent footwall escarpments within the rift are created by e w trending normal faults and variations in the topography of these escarpments are related to fault segmentation and bedrock lithology drainage catchments within the rift are classified on the basis of morphology area bedrock lithology and relationship to fault geometries five drainage domains can be identified within the sperchios rift i footwall ii hanging wall iii transfer zone iv axial and v karst domains bedrock lithology has a major control on the size of catchments in all drainage domains in addition topographic lows associated with transfer zones along the border fault are sites of major drainage catchments and act as conduits for sediment supply to the rift variations in drainage catchments the resultant sediment supply and accommodation development along the rift produce a range of stratigraphic architectures along fault segments low sediment supply and high subsidence rates lead to aggradational sequence sets whereas progradational sequence sets develop at transfer zones where rates of sedimentation are high and the rate of subsidence is low

geomorphology and sequence stratigraphy due to slow and rapid base level changes in an experimental subsiding basin xes 96 1 subsidence is a major factor in the accumulation and architecture of natural basin fills a recently built experimental facility experimental earthscape facility xes at st anthony falls laboratory of the university of minnesota incorporates for the first time a flexible subsiding floor in its design thus the experimental basin can model erosion and deposition associated with independent variations in sediment supply absolute base level change and rates and geometries of subsidence the results of the first experiment in a prototype basin 1 1 6 0 8 m are described here wherein the stratigraphic development associated with first slow and then rapid base level cycles in a basin that has a sag geometry has been analyzed a videotape of the experiment and subsequent serial slicing of the dried strata in the basin allow interpretation of the sequence development under conditions of precisely known changes of absolute base level subsidence and sedimentation relative base level changes which strongly varied in the basin owing to the sag geometry of subsidence seem to exert primary control on sedimentary patterns although autocyclic changes were also important style of sequence boundaries differed between slow and fast base level falls during the slow base level fall an incised valley developed once the shoreline prograded out of the zone of maximum subsidence suggesting that incision at the shoreline may be very sensitive to changes in relative base level once started however the valley quickly widened by knickpoint retreat into a broad low relief erosion surface that stretched across the entire basin as erosion took place at the knickpoint deposition occurred immediately downflow so both the knickpoint and the upstream limit of deposition migrated landward together producing a strong time transgressive erosion and onlap sequence the stratigraphic begin page 818 record of this sequence boundary is a single yet very subtle widespread unconformity that becomes conformable downstream which is difficult to trace in stratigraphic cross section in contrast the incised valley that formed during the rapid base level fall was relatively narrow deep and lengthened over time as deposits at the mouth of the valley were gradually exposed and incised through wholesale backfilling of the incised valley did not begin until the rapid base level rise started as a result the rapid base level change produced a more easily recognized incised valley in the stratigraphic record than did the slow base level change potential reservoir development within the strata is evaluated by means of a gray scale proxy for porosity four distinctive zones of enhanced reservoir quality occurred in the basin the most proximal part of the basin the upper part of growth fault bounded sedimentary wedges deep water forced regressive systems tract composed of grainflow deposits and transgressive systems tract formed during the rapid base level rise this distribution of relatively porous units suggests that for a variety of reasons rapid sea level cycles may produce the best reservoir units

tidal influence on self potential measurements long term surface and borehole self potential sp monitoring was conducted in the uk chalk aquifer at two sites the coastal site is c 1 7 km from the coast and the inland site is c 80 km from the coast at both sites power spectral density analysis revealed that sp data contain the main ocean tidal periodic components however the principal lunar component m2 the dominant ocean tidal component was most significant at the coastal site the m2 signal in surface referenced sp data at the inland site was partly due to telluric currents caused by the geomagnetic ocean dynamo earth and or atmospheric tides also contributed as the sp power spectrum was not typical of a telluric electric field the m2 component in borehole referenced data at the inland site was below the significance level of the analysis method and was two orders of magnitude smaller than the m2 signal in borehole referenced sp data at the coastal site the tidal response of the sp data in the coastal borehole is therefore primarily driven by ocean tides these cause changes in fluid pressure and chemical concentration gradients within the coastal aquifer leading to time varying electrokinetic and exclusion diffusion potentials borehole referenced sp measurements could be used to characterize and monitor tidal processes in coastal aquifers such as the intrusion of seawater

localization and quantification of leakages in dams using time lapse self potential measurements associated with salt tracer injection the self potential method is the only non intrusive method that is directly sensitive to the flow of the pore water in a porous material we propose the use of a new protocol of self potential measurements associated with a brine injection to locate leakages in earth dams and to quantify their permeability indeed a brine solution injection upstream of an earth dam in the assumed leakage zone is able to change the electrical conductivity of the medium in turn this decreases the magnitude of the electrokinetic contribution of the self potential signals that are related to the flow of the seepage water the evolution of this anomalous self potential signal expected to be positive with respect to a reference state prior the salt injection can be measured at the ground surface with a network of non polarizing electrodes the seepage flow inside the dam is localized from the evolution in space and time of the resulting transient self potential signals associated with the transport of the brine the mean permeability of the preferential flowpath can be determined this method is first applied to a laboratory test to show how the passage of a salt tracer affects the self potential response then we apply this new methodology to a field test site a dam with a proven leakage located in the south of france at this test site self potential mapping was first performed to locate the preferential flow path then a network of non polarizing electrodes was used to perform time lapse self potential measurements at the dam crest during a brine injection occurring upstream of the seepage zone we used two lines of 16 non polarizing electrodes each from the time lapse data the permeability of the leaking area was estimated inside one order of magnitude

the origin of hydrocarbon source rocks in the austrian molasse basin eocene oligocene transition organic rich rocks schoneck formation from five wells representing a section across the northern paleo slope of the austrian molasse basin were studied using a multi method approach including petrography x ray diffraction organic and inorganic geochemistry and c and n isotopes of the organic material organic matter accumulation commenced during the latest eocene and was dependent on variations of currents salinity organic productivity and nutrient supply initial marl deposition and phosphorite formation under dysoxic conditions was followed by organic rich mud deposition associated with benthic and photic zone anoxia this paleoceanographic situation resembles the first isolation of the western central paratethys deposition of organic rich rocks terminated during lower oligocene time when changing current patterns and decreasing salinity caused a breakdown of water column stratification even though the schoneck formation is an excellent source rock major differences exist in the petroleum potential of the schoneck formation deposited in upper and lower basin slope settings the schoneck formation from the upper slope is characterised by toc contents up to 12 and hi values between 500 and 600 mghc gtoc in the lower slope settings toc values are generally below 2

geochemical characteristics of chilean upwelling sediments at 36 s abstract we examined the cycling of c s fe and the trace elements te ag cd mo mn re and se in chilean upwelling sediments from water depths of 127 2744 m at 36 s the sediments are clay rich with moderate total organic carbon toc and low biogenic caco3 contents for the shallow site within oxygen minimum zone omz which shows some thioploca biomass highest observed toc contents correspond to highest productivity induced toc flux and or enhanced preservation under o2 deficient conditions pyrite formation may be restricted by the concurrent presence of elemental s in thioploca and or the availability of reactive iron in the other sediments 370 m water depth pyrite formation is strongly restricted due to the low availability of metabolizable toc for sulfate reduction calculations of the degree of bacterially mediated remineralization suggest that more nitrogen than toc was remineralized by sulfate reduction than expected from redfield c n relationship manganese is significantly depleted due to reductive dissolution of mn hydr oxides within all sediments mo is only significantly enriched vs the lithogenic background in the shallow core implying anoxic conditions contents of re and mo as well as re mo ratios indicate suboxic conditions for the other cores cd and re contents decrease with increasing water depth reflecting decreasing reducing conditions in contrast authigenic ag contents increase with water depth suggesting enrichment controlled by seawater availability and or opaline input and not redox conditions elevated se contents in all cores may be either due to bio detrital input or diffusion from seawater accumulation rates of toc ts and te off chile are in the same order as those from the gulf of california and lower than those off peru distinct seasonality in upwelling and dilution of chilean sediments with terrigenous material lead to rather low metabolizable toc contents and lower te trapping capacity

organic matter preservation and sulfur uptake in sediments from the continental margin off pakistan abstract the bulk and molecular geochemical characteristics of a suite of kerogens isolated from organic matter rich sediments from the pakistan margin has been characterised by elemental analysis rock eval pyrolysis and pyrolysis gas chromatography py gc special attention was given to the geochemistry of alkylthiophenes which are thought to reflect the incorporation of sulfur into organic matter om in the context of early diagenetic sulfate reduction organically bound sulfur comprises up to 60 of total sedimentary sulfur the weight ratios for organic sulfur s org over organic carbon c org varies from 0 01 in some of the recently deposited sediments to 0 11 in older samples the results show that sulfur incorporation into organic matter occurs primarily within the upper few meters of the sediments the amount of sulfur which can be incorporated into the organic matter clearly depends on the quality of om the hydrogen index values hi which characterise the total amount of generated hydrocarbon equivalents of the pyrolysate in mg hc equiv g c org are related to the extent of reworking of organic matter either in the water column or at the sediment water interface or to remineralization processes by sulfate reduction itself which is strongly controlled by the availability of reactive iron high quality organic matter characterised by elevated hi values is capable of sequestering higher amounts of sulfur as expressed by the thiophene content which represent the organically bound sulfur of the pyrolysate in mg g c org as indicated by the ratio of thiophenes versus hi which characterises the proportion of thiophenes in the total pyrolysate sulfurisation of organic matter seems to be terminated at a ratio of 0 01

origin and transformation of organic matter in pliocene pleistocene mediterranean sapropels organic geochemical evidence reviewed abstract drilling of deep water post messinian sedimentary sequences by odp legs 160 and 161 in the mediterranean sea has shown that occurrence of organic carbon rich sapropels and sapropel like sediments extends from the levantine basin westward into the alboran basin in the eastern mediterranean sapropel deposition started in the early pliocene whereas in the western basin the onset of sapropel formation occurred later in the early pleistocene precessional cycles are apparently the primary external forcing for sapropel formation nevertheless the pattern of sapropel occurrence suggests that the precessional influence is modulated by the glaciation cycles large differences were observed in the organic carbon contents of sapropels recovered in the eastern and western mediterranean correspondence between organic carbon contents rock eval hydrogen index values and elemental c n ratios indicate that both variations in the production and preservation of marine organic matter have led to the accumulation of high amounts of organic matter in sapropels molecular organic geochemical compositions of sapropels from the eastern mediterranean further confirm that the major fraction of organic matter in sapropels is derived from marine algal sources and has undergone variable oxidation enhanced marine productivity and improved preservation of organic matter is central to sapropel formation accumulation of increased amounts of land derived material at times of sapropel formation is also evidenced supporting the hypothesis of significant periodic freshwater discharges

high sediment yields and cool wet winters test of last glacial paleoclimates in the northern mediterranean opposing models have been proposed for last glacial paleoclimates in the mediterranean area to discriminate between the alternative models we calculate variations in sediment yield within a high resolution stratigraphic framework developed for the alkyonides basin central greece latest quaternary highstand deposits are distinguised from lowstand lake corinth deposits on the basis of seismic reflection data and micropaleontological and palynological analyses of drop cores after depth conversion and calculation of solid sediment masses in successive time slices sediment discharge rates during the last glacial lowstand interval ca 70 12 ka are shown to have exceeded discharge rates during the preceeding interglacial highstand interval ca 128 70 ka by 60 implying enhanced seasonality during the glacial period with cool dry summer and wet winter conditions in the region sediment yield calculations can thus provide an empirical test of paleoclimate models and offer input to sequence stratigraphic models

sedimentation and tectonic geomorphology adjacent to major active and inactive normal faults southern greece the active psatha skinos normal fault is uplifting a contrasting variety of lithologies in its footwall including mesozoic limestones ophiolitic peridotites and poorly consolidated plio pleistocene sediments of the inactive megara basin in the latter basin linear marginal uplands border the sedimentary fill and are interpreted as degraded and segmented scarp lines which exhibit features such as facetted spurs drainage domains are defined as groups of drainage basins sharing a common tectono geological substrate contrasting domains in the footwall of the active fault have given rise to spectacular differences in drainage basin growth and form in the uplifting footwall raised coastal terrace levels are present at about 10 and 40 m the latter have yielded corals dated at between 90 126 ka and have enabled us to calculate uplift and erosional rates extrapolation of these rates indicate that some 350 m of footwall relief has been produced over approximately 1 ma most of the sediment eroded from the uplifting footwall is presumed to have been re sedimented into the alkyonides gulf basin plain during this time the prominent footwall unconformity so produced forms a fine modern analogue to features seen in ancient syn rift tilt blocks such as the viking graben footwall uplift has also backtilted the former depositional surface of the megara basin and caused reversal of flow in its axial drainage domain a variety of depositional environments are documented in the subsiding hangingwall to the coastal fault including syn quake talus cones alluvial fans intra fan marshes and swamps truncated fans transgressive barriers and spits

electrical burst signature of pore scale displacements 1 electric field bursts were passively observed when a nonwetting fluid displaced a wetting fluid in a porous material drainage as well as during imbibition experiments a sandbox experiment was conducted to study these electrical disturbances using a network of very sensitive nonpolarizing electrodes located at the top surface of the tank drainage exhibited many more electrical bursts with a higher magnitude than imbibition these events were only observed during drainage or imbibition not prior to or after the water flowed inside the porous sandbox we point out the possible relationship between the formation of haines jumps and the occurrence of these electrical bursts these bursts show a power law distribution during drainage with a power law exponent of about 1 7 in agreement with a previous published study using acoustic and hydroacoustic events imbibition does not display such a power law relationship

late syn rift sequence architecture and sedimentary evolution of a continental rift basin a case study from fulongquan depression of the songliao basin northeast china abstract as an important stage in continental rift basin evolution late syn rift stage is characterized by the combination of broad crustal subsidence and episodic pulses of extension sequence architecture and sedimentary filling process during this period present a certain particularity due to distinctive tectonic subsidence and variable influencing factors this paper analyzes sequence stratigraphy and sedimentary facies development and their evolution in the fulongquan depression a continental rift basin of the songliao basin and discusses the determinants influencing the sequence architecture and depositional systems evolution during late syn rift stage a major transition in the depositional systems from predominantly lacustrine and correlated depositional systems to fluvial floodplain settings was recorded in the evolution of basin fill this gradual and slow peneplanation is the final response to the decrease of differential subsidence the spatial and temporal variability of sedimentary evolution are mainly associated with specific growth history of the major boundary faults sequence stratigraphic units recognized in the fulongquan depression are likely corresponded to different episodic pulses of extension respectively each sequence can be further divided into a lowstand systems tract lst transgressive systems tract tst and highstand systems tract hst maximum differential subsidence and water deepening mainly occur in the lst the expanded tst and hst of each sequence tend to be developed in a broader thermal subsidence regime the depositional systems transition and detrital provenance changes usually occur in the hst throughout the late syn rift stage in addition to major changes of provenance systems tectonic movement is likely to be the main factor in controlling the variations of sediment supply with the decrease of tectonic activity the impact of climate changes and lake level fluctuations on basin filling tends to be increased

sedimentology and microfacies of a mud rich slope succession in the carboniferous bowland basin nw england uk a paucity of studies on mud rich basin slope successions has resulted in a significant gap in our sedimentological understanding in these settings here macro and micro scale analysis of mudstone composition texture and organic matter was undertaken on a continuous core through a mud dominated slope succession from the marl hill area in the carboniferous bowland basin six lithofacies all dominated by turbidites and debrites combine into three basin slope facies associations sediment starved slope slope dominated by low density turbidites and slope dominated by debrites variation in slope sedimentation was a function of relative sea level change with the sediment starved slope occurring during maximum flooding of the contemporaneous shelf and the transition towards a slope dominated by turbidites and then debrites occurring during normal or forced shoreline progradation towards the shelf margin the sediment starved slope succession is dominated by type ii kerogen whereas the slope dominated by low density turbidites is dominated by type iii kerogen this study suggests that mud dominated lower slope settings are largely active depositional sites with consistent evidence for sediment traction additionally the composition and texture of basin slope mudstones as well as organic content vary predictably as a function of shelf processes linked to relative sea level change

changing lake dynamics and sequence stratigraphy of synrift lacustrine strata in a half graben an example from the triassic ischigualasto villa union basin argentina well exposed triassic rift strata from the ischigualasto villa union basin nw argentina include a 80 to ca 515 m thick lacustrine dominated package that can be correlated across a half graben using key stratigraphic surfaces sequence boundaries lacustrine flooding surfaces and forced regressive surfaces the characteristics of the synrift lacustrine fill in different parts of the half graben have been examined and the mechanisms controlling sedimentation inferred a variety of sedimentary environments are recognized including volcaniclastic floodplain mildly saline lake and playa lake offshore lacustrine delta front to fluvial dominated and wave dominated deltas distributary and fluvial channel and interdistributary bay the succession can be divided into four stratigraphic sequences ss1 to ss4 the oldest of which ss1 contains volcaniclastic fluvial and saline lake deposits it is thickest close to the western border fault zone reflecting more rapid subsidence here accommodation exceeded sediment and water input during ss1 the second and third sequences ss2 and ss3 mark the onset of widespread lacustrine sedimentation reflecting a balance between accommodation creation and water and sediment fluxes sequences ss2 and ss3 are represented by offshore meromictic lacustrine and deltaic deposits the latter mostly sourced from the flexural and southern axial margins of the half graben the presence of stacked parasequences bound by lacustrine flooding surfaces is related to climatically induced lake level fluctuations superimposed on variable rates of subsidence on the controlling rift border fault zone the youngest sequence ss4 is represented by the deposits of littoral lacustrine and shallow shelf deltas distinguished by a change in lithofacies palaeocurrents and sandstone composition suggesting a switch in sediment supply to the footwall margin to the nw the change in the sediment source is related to reduced footwall uplift the possible presence of a relay ramp and or supply from a captured antecedent drainage network during ss4 the rate of creation of accommodation was exceeded by the sediment and water discharge the stratigraphic evolution of lacustrine strata in the half graben was mainly controlled by tectonic processes including subsidence rate and the growth and evolution of the border fault zone but changing climate inducing changes in water balance and lake level and autocyclic processes delta lobe switching were also important

denudation vertical crustal movements and sedimentary basin infill denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass recent empirical results from a wide range of sources are presented on the rates of these processes denudation alone can cause non tectonic isostatic surface uplift of the right magnitude predicted by theory a case is made following ahnert for a single linear relationship although with much scatter between denudation rate and mean drainage basin relief for large basins some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one dimensionality and neglect of suspended and washload contributions basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland but problems arise in the apportionment of the various hinterland fluxes that occur in real world three dimensional basins sediment yields in smaller half graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields examples are given from extensional basins in the western usa and greece the length of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed through the fractal form of hack s law and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands

hydrocarbon distribution in coals and in dispersed organic matter of different maceral compositions and maturities more than 60 samples from 5 coal seams and adjacent siltstones and sandstones were selected from a well through westphalian b sediments from northern germany in order to study bitumen generation and migration the cores were drilled between 1200 und 1530 metres depth in this interval vitrinite reflectance rr is increasing from 0 70 to 0 92 results reveal high hydrocarbon generation potentials for all coal samples but not for adjacent clastic rocks although maceral compositions of both are quite similar yields and compositions of thermal extracts from the coals depend on maceral compositions and rank however the bulk of the already generated bitumen has not been removed during natural coalification and is not easily releasable by thermovaporisation a mass balance based on elemental composition of dull coals indicates that in the rather narrow rank interval 0 70 0 92 rr a total mass loss of 20 may have occurred by migration this is evidenced by a loss of about 20 of the original hydrogen the rest being stored in the coals

sequence stratigraphy and architectural variability in growth fault bounded basin fills a review of plio pleistocene stratal units of the crotone basin southern italy field examples from the pliocene to pleistocene succession of the crotone basin document the variability of stratal architecture in syntectonic units deposited in normal fault bounded basins relatively thick trangressive intervals are common within these successions as shown in the zinga 2 zinga 3 and strongoli stratal units transgressive packages are formed by lagoonal mudstones that are abruptly overlain by shoreface sandstones aggradational highstand shallow marine packages are typical of the lower pliocene succession in half graben basins these deposits resulted from balanced conditions between the rate of sediment supply and the rate of creation of accommodation relatively thick forced regressive deposits are common within basins during phases where the accommodation supply ratio is low e g the middle pleistocene san mauro sandstone these deposits influenced by growth faulting and folding recorded base level lowering linked to glacio eustasy a complex stratal architecture may be the consequence of the alternation between tectonic subsidence and uplift e g the serra piani stratal unit such variations are thought to be related to the onset of an earliest mid pliocene transpressional tectonic phase the studied deposits therefore show a marked tectonic control that strongly influenced their stratal architecture these examples represent interesting cases of sequence stratigraphic analysis in growth faulted contexts

sediment transport processes on an active submarine fault escarpment gulf of corinth greece abstract sediment transport processes on the escarpment of a listric fault in the tectonically active and terrigenous sediment dominated corinth graben in greece are studied using 3 5 khz and airgun profiles and sidescan sonar images the whole of the slope area is affected by gravitational mass movements slumps debris mud flows and liquified and turbidity flows in canyon fan systems large volumes of sediment are transported through slumping debris mud and turbidity flows into the basin here they build coalescing fans which consist of intercalations of debris flow deposits and turbidites in delta front slope fan apron systems sediments are transported radially downslope through slumping debris mud flows liquified flows and high density turbidity flows into the basin where they build coalescing fan aprons these consist of massive homogenized deposits fluxoturbidites in shelf slope systems retrogressive rotational slumping is the dominant instability feature however due to the sharp increase in the slope gradient caused by the slumping debris and turbidity flows are triggered the major factors responsible for triggering gravitational mass movements in the region are earthquakes high sedimentation rates off the river mouths and heavy rainfalls and high seas these mass movements appear to occur at least once every 2 yrs as indicated by the failure of submarine cables

sulphur incorporation in jurassic marine mudrocks and their bitumens at low thermal maturity cleveland basin england abstract the distribution of sulphur between pyrite kerogen elemental sulphur and the aromatic fraction of mudrock bitumens has been quantitated in two cored sections of immature marine kimmeridgian strata which have experienced different levels of thermal stress strata in the two boreholes ebberston and reighton were deposited in different basinal settings basinal marine and platform respectively and occasional euxinic laminated horizons are present at ebberston otherwise dysoxic deposition was the norm at both localities pyrite the dominant sulphur carrier in all the mudrocks has a sulphur isotopic composition consistent with mineralisation in a system mainly open to sulphate diffusion kerogens are mostly low sulphur atomic s c and account for between 5 and 10 of rock sulphur although occasionally up to 30 kerogen sulphur is closely correlated with toc and highest in laminated mudrocks consistent with most effective sulphurization of kerogen under anoxic conditions although kerogen compositions in both cores vary with organic richness no systematic differences in organic input between the borehole localities are recognised geochemically some thermal effects on sulphur geochemistry are therefore interpreted from a comparison of stratigraphically equivalent sections from the two cores bitumen yields and abundances of aromatic sulphur in the more thermally stressed ebberston section although variable are generally much higher than in the reighton section and are partly related to kerogen sulphur content this is tentatively attributed to thermal release of additional extractable bitumen from macromolecules elemental sulphur s0 in bitumen is unrelated in abundance to other sulphur species and isotopically heavier than coexisting pyrite overprinting of minor preserved diagenetic s0 by secondary oxidation of pyrite appears likely the distributions of individual sulphur aromatic compound classes have features related both to maturity and stratigraphy

numerical modelling of syntectonic subaqueous sedimentation the effect of normal faulting and a relay ramp on sediment dispersal abstract relay ramps are common in extensional settings and play a significant role in sediment dispersal as they control sedimentary pathways unlike for subaerial settings the impact of subaqueous relay ramps on sediment dispersal and clastic sedimentation is less studied in these subaqueous cases numerical approximations could be a good approach to understand syntectonic sedimentation considering this a numerical model is used to study the sedimentary infill in an extensional basin specifically related to a relay ramp system the study is carried out using a novel program that merges a discrete element code for tectonic deformation and a stratigraphic modelling code for sedimentation to perform a test study two configurations are designed with one normal fault and with two overlapping normal faults linked by a relay ramp to these initial configurations three different deformation velocities 10 5 and 2 cm y are applied in dip slip direction these scenarios are considered as initially submerged the same incoming amount of three different terrigenous sediments is considered in all the experiments these sediments are transported basinward in suspension by processes of advection dispersion and diffusion finally these examples also include four different boundary conditions for the sedimentary model which define the source area location for the incoming water and sediment results show that the source area location in relation to the available accommodation space plays the major role in the distribution of different sediment types into the basin nonetheless when the source area for water and sediment is defined as regional and parallel to the fault the grain size distribution obtained by the two overlapping faults configuration has clear asymmetries when compared with the ones obtained by one fault configurations therefore the different extensional experiments allow concluding that the relay ramp configuration can play an important role in the distribution of the sediments into the basin

evolution of stratigraphic sequences in multisegmented continental rift basins comparison of computer models with the basins of the east african rift system this article presents a series of numerical simulations of the stratigraphic evolution of continental rift basins we model the geomorphic and tectonic processes acting in this depositional environment which contrasts with the traditional approach of modeling the settling of sediments especially in marine clastic basins what is new in our model is that it can simulate the formation of basins with linked half grabens which is a fundamental feature of rift systems the attributes of the numerical simulations such as the overall morphology basin architecture drainage systems and stratigraphy are in good agreement with digital elevation models and reflection seismic lines of the basins of the east african rift system specifically the tanganyika and malawi rifts

relationships between fault controlled subsidence and preservation of shallow marine small scale cycles example from the lower pliocene of the crotone basin southern italy abstract the northern part of the crotone basin southern italy was characterized by the activity of pliocene growth faults bounding half graben sub basins the thickest unit deposited during growth fault activity is the lower pliocene belvedere formation up to 450 m thick which shows a small scale highly regular rhythmic cyclicity this sandstone unit was deposited in a shallow marine environment and its accumulation was mostly influenced by storm processes and locally by flows in tectonically confined areas the meter scale cycles are represented by rhythmic alternations between shell rich intervals characterized by storm structures or large scale cross sets and shell poor sandy intervals that are commonly burrowed and poorly stratified the better preserved cycles commonly show a fining upward trend with minor progradation in their upper part and may be bounded at the base by a shell lag the deposition of large scale cross sets is thought to be the consequence of the creation of fault scarps which led to tectonic confinement in the half graben basins in the tectonically confined areas tidal currents were enhanced and large subaqueous dunes migrated the evidence suggests that the observed cyclicity was generated by sea level and climatic variations that controlled the sediment input into the basin the relationship between large scale cross sets and tectonic confinement demonstrates that local extensional tectonics significantly influenced the sedimentation the excellent preservation of the observed small scale cycles is thought to be the consequence of deposition in the highly subsiding half graben sub basins on the structural highs this cyclicity is amalgamate and less appreciable the data presented may be significant for a better understanding of the role of subsidence in preserving sedimentary successions in these growth faulted settings

organic geochemistry of an anoxic cycle a case history from the oligocene section hungary total organic carbon extractable organic matter sulfur content kerogen type and saturated hydrocarbons have been determined in 25 core samples from an approximately 100 m thick section of the oligocene tard clay near budapest the tard clay records a five million year long anoxic cycle initiated by isolation of the sea development of a positive water balance and resulting density stratification and terminated by the re opening of access to the sea the lower non and moderately laminated shales record the build up of anoxia they contain 0 5 5 0 of organic carbon and type iii kerogen their saturated hydrocarbon fractions show high abundance of phyllocladanes biomarkers characterising coniferae derived organic matter the overlying moderately and strongly laminated sediments containing 1 5 5 0 organic carbon a predominance of hopanes over the n alkanes and type ii kerogen show the imprint of increased planktonic productivity the nutrients needed for this high productivity were liberated by alteration processes of contemporaneous volcanic glass the upper part of the strongly laminated shales containing a maximum of 2 organic carbon and type iii kerogen deposited after the termination of volcanic ash falls records a drop of planktonic productivity at the top of the tard clay the weak lamination and the low content 1 of organic carbon signifies the end of the bottom water oxygen depletion due to the destruction of density stratification of the water column

extension of carbon flux estimation to oxic sediments based on sulphur geochemistry and analysis of benthic foraminiferal assemblages a case history from the eocene of hungary abstract the amount and type of organic matter om chemical and mineralogical compositions and the amount and isotopic ratio of sulphur were measured and benthic foraminiferal assemblages were analysed in a 70 m thick core section comprising marine marls from the eocene of hungary on the basis of benthic foraminiferal oxygen index bfoi the studied sediments were deposited under a range of anoxic to oxic bottom water conditions the amount of corg mineralised during early burial was calculated in two steps first carbon mineralised by sulphate reduction was calculated from the amount of sedimentary sulphur corrected for escaped oxidised h2s by taking into account the isotopic composition of sulphur then on analogy of recent sediments which are deposited with a similar rate of sedimentation and beneath bottom waters of similar o2 content carbon loss by aerobic respiration was estimated a good stratigraphic control and knowledge of variation of mineralogical composition along the section permitted to estimate past variation of local organic carbon flux cflux from calculated original corg contents during deposition of the studied strata cflux first decreased from 1 16 to 0 41 g corg m2 y then it progressively increased to 1 81 g corg m2 y changes in local cflux are explained by changes in water depth flux of terrestrial organic components and availability of nutrients liberated by alteration of products of the coeval pyroclastic activity

late quaternary evolution of the gulf of patras greece tectonism deltaic sedimentation and sea level change abstract the gulf of patras is an actively subsiding late cenozoic graben in western greece that receives deltaic sediment from the large acheloos and evinos rivers the late quaternary sedimentation history of the gulf is interpreted from 3 5 khz profiles numerous short cores and airgun seismic profiles a widespread unconformity represents the isotopic stage 2 marine lowstand when the gulf was subaerially exposed subsequent deltaic progradation and associated coastal transgression was greatest during the 13 10 5 ka slowdown in sea level rise and the period of stable sea level since the mid holocene switching of delta distributaries can be related to the known evolution of the subaerial parts of the deltas the stage 2 unconformity provides a datum for quantitative determination of rates of subsidence the central graben is subsiding at rates of 3 5 mm yr rates in the northern part of the gulf average 1 2 mm yr this is consistent with a listric faulting model for the origin of the modern patras graben

statistical analysis of forward stratigraphic models in complex salt provinces the central scotian basin case study predicting vertical and lateral facies variations in various depositional environments remains a major challenge in the oil and gas industry because it impacts petroleum system assessments and the associated exploration risking phase the use of multidisciplinary constraints geomorphology geology geophysics in forward stratigraphic models sheds light on the complex interaction of local regional and global driving mechanisms that influence sediment transport and deposition along continuously evolving landscapes in this paper we develop an integrated statistical approach to examine the sensitivity of forward stratigraphic models in complex salt provinces to several parameters including water discharge sedimentary load grain size and associated diffusion coefficients and slope this statistical analysis was applied to the barremian albian sequence of the central scotian basin canada and highlights the influence of complex salt kinematics on sediment pathway diversion and accumulation around salt domes and canopies forward stratigraphic modeling results point to regions of higher probability of lower cretaceous sandy reservoirs automating simulation runs significantly reduced the time required to achieve a statistically valid number of simulations and allowed the sensitivity of the model to be evaluated

quantitative controls on the regional geometries and heterogeneities of the rayda to shu aiba formations northern oman using forward stratigraphic modelling abstract the complex geometry of carbonate systems is influenced by a multitude of physical as well as biological processes the lower cretaceous carbonates of northern oman are characterised by a variability of regional scale geometries with expected vertical and lateral facies variations the main environmental and tectonic controls acting on the depositional processes of the lower cretaceous ramps and platforms through space and geological time in 4 dimensions are only partially understood in this study we use a 4d dionisosflow forward stratigraphic modelling fsm approach to explore the role of i eustasy ii subsidence iii initial paleobathymetry and iv wave energy to generate carbonate stacking patterns and heterogeneities carbonate production was maintained constant through deposition multi disciplinary and multi scale datasets were used i e seismic well and field data to constrain the fsm input parameters and sensitivity analysis was carried out to validate or refute some depositional model hypotheses results show that basement topography and eustasy have the greatest influence on the progradational geometries and the lateral continuity of clinoform architectures during the tithonian to valanginian second order super sequence in the valanginian to aptian super sequence subsidence was the primary control for the observed aggradational stacking pattern lateral and vertical stacking of carbonate lithologies textures as well as facies are thus apprehended through this fsm approach leading to a better assessment of petroleum systems elements as reservoir seal and trap

stable carbon isotopes of amorphous kerogens from phanerozoic sedimentary rocks amorphous kerogens from phanerozoic sedimentary rocks may be divided into two groups on the basis of their 13c values h amorphous kerogens have isotopic values in the range of 24 to 20 per mil and l amorphous kerogens have isotopic values in the range of 35 to 26 per mil the occurrence of amorphous kerogens in the intermediate isotopic range from one rock unit in the data set suggests a weak continuum may exist between these two groups phytoplankton and to a lesser extent zooplankton and bacteria are considered to be the precursors for both kerogen types a plausible explanation for this dichotomy may be found in the source of co2 utilized by phytoplankton which is considered to be controlled by environmental factors h amorphous kerogens are expected to occur in silled basins that are overlain by expansive well circulated deep 500 m water where the prevailing source of carbon in the photic zone is atmospheric derived co2 conversely l amorphous kerogens are expected to occur in restricted basins that are overlain by stratified shallow 200 m water where the prevailing source of carbon in the photic zone may be organic derived co2

earthquake clustering inferred from pliocene gilbert type fan deltas in the loreto basin baja california sur mexico a stacked sequence of pliocene gilbert type fan deltas in the loreto basin was shed from the footwall of the dextral normal loreto fault and deposited at the margin of a marine basin during rapid fault controlled subsidence fan delta parasequences coarsen upward from marine siltstone and sandstone at the base through sandy bottomsets and gravelly foresets to gravelly nonmarine topsets each topset unit is capped by a thin shell bed that records marine flooding of the delta plain several mechanisms may have produced repetitive vertical stacking of gilbert deltas 1 autocyclic delta lobe switching 2 eustatic sea level fluctuations 3 climatically controlled fluctuations in sediment input and 4 episodic subsidence produced by temporal clustering of earthquakes we favor hypothesis 4 for several reasons but hypotheses 2 and 3 cannot be rejected at this time earthquake clustering can readily produce episodic subsidence at spatial and temporal scales consistent with stratigraphic trends observed in the loreto basin this model is supported by comparison with paleoseismological studies that document clustering on active faults over a wide range of time scales earthquake clustering is a new concept in basin analysis that may be helpful for understanding repetitive stratigraphy in tectonically active basins

the marine photosynthetic carbon isotopic fractionation remained constant during the early oligocene abstract the oligocene has recently been suggested as a time of drastic decrease of marine photosynthetic carbon isotopic fractionation mphcif leading to a separation of 13 c depleted 13 c pre neogene and 13 c rich 13 c 24 neogene quaternary marine kerogen a more exact timing of this change in fractionation is hindered by the scarcity of well preserved marine kerogen in oligocene sedimentary records we have analyzed 13 c values of about 40 kerogen samples from the often anoxic early oligocene sediments of the hungarian paleogene basin and the carpathian flysch belt the bulk of the well preserved marine kerogen covering a time span between 35 0 and 31 5 m y has 13 c values more negative than 26 5 while marine kerogens from the boundary of early and late oligecene 30 5 m y representing a local ephemerous anoxic event have 13 c values between 23 1 and 23 3 the unambiguously low 13 c values of the early oligocene marine kerogens prove that the recently suggested global decrease of the mphcif could not have begun before the end of the early oligocene the high 13 c values of marine kerogens from the early late oligocene boundary may have been caused by a decrease in mphcif at the end of the early oligocene alternatively they may indicate a local depletion of hco 3 in the photic zone

fate of organic carbon and reduced sulphur in dysoxic anoxic oligocene facies of the central paratethys carpathian mountains and hungary

differentiating the effect of episodic tectonism and eustatic sea level fluctuations in foreland basins filled by alluvial fans and axial deltaic systems insights from a three dimensional stratigraphic forward model many studies of foreland basins have recognized a hierarchical organization in the stacking of sequences deposited by axial deltaic and alluvial fan systems the hierarchy is often explained in terms of the competing control of eustasy and pulsed tectonic subsidence and the different frequencies at which these processes operate unravelling the relative contributions of tectonic and eustatic controls on the sequence stacking pattern is a fundamental question in foreland basin analysis yet this is difficult because of the lack of independent stratigraphic evidence in this study a three dimensional numerical model is presented which aids in the interpretation of alluvial successions in foreland basins filled by transverse and axial depositional systems under conditions of variable tectonism and eustatic sea level change the tectono sedimentary model is capable of simulating the hierarchical stratigraphic response to both eustatic and tectonic forcing and is of higher resolution than previous models of foreland basin filling numerical results indicate that the onset of tectonic activity is reflected by rapid retrogradation of both depositional systems and by widespread flooding and onlap of carbonate sediments syntectonic fluvial patterns on the axial deltaic plain are dominated by bifurcating channels swiftly relocating in response to the general rise in relative sea level induced by flexural subsidence the resulting surface morphology of the axial delta is convex upwards syntectonic eustatic sea level fluctuations result in parasequence scale packages of retrograding and prograding fan and delta sediments bounded by minor flooding surfaces and type 2 sequence boundaries incised channels are rare within the syntectonic parasequences and are formed only during phases of tectonic quiescence when eustatic falls are no longer compensated by the subsidence component in the rise in relative sea level suites of amalgamating axial channels corresponding to multiple eustatic falls delineate the resulting type 1 unconformities coarse grained incised channel fills are found in the zone between the alluvial fan fringes and the convex upward body of the axial delta as the axial streams tend to migrate towards this zone of maximum accommodation

a combined sedimentological and organic geochemical study of the jurassic cretaceous janusfjellet formation svalbard norway abstract sedimentological facies and organic geochemical analyses of surface samples from black shales of the janusfjellet formation jurassic cretaceous svalbard have been undertaken in order to obtain a better insight into the problems concerning depositional processes and burial history pyrolysis nmr and microscopic data suggest a type iii kerogen in the janusfjellet formation however there are significant variations of the kerogen composition throughout this formation saturated aliphatic fractions of the rock extracts have been analyzed by gc and gc ms differentiation of the gc traces was achieved by using a q mode factor analysis by this analysis two factors were revealed to explain the depositional development of the formation the gc and gc ms analysis of the saturated aliphatic fraction suggest a more marine character of the organic source material than the kerogen analyses the sedimentological and organic geochemical data indicate generally oxic conditions during deposition of the janusfjellet formation under these conditions the labile lipid rich marine parts of the source material have been more degraded than the relatively stable terrestrially derived organic matter resulting in a type iii kerogen composition

sulphur and carbon isotopic composition of power supply coals in the pannonian basin hungary abstract the present work is an attempt to establish the stable isotope database for mesozoic to tertiary coals from the pannonian basin hungary maceral composition proximate analysis sulphur form sulphur isotopes organic and pyritic and carbon isotopes were determined this database supports the assessment of the environmental risks associated with energy generation the characterization of the formation and the distribution of sulphur in the coals used the maceral composition the sulphur composition the c s isotopic signatures and some of the geological evidences published earlier show that the majority of these coals were deposited in freshwater and brackish water environments despite the relatively high average sulphur content however the upper cretaceous eocene and lower miocene formations also contain coal seams of marine origin as indicated by their maceral composition and sulphur and carbon chemistry the majority of the sulphur in these coals occurs in the organic form all studied sulphur phases are relatively rich in 34s isotopes 34sorganic 12 74 34spyrite 10 06 on average this indicates that marine bacterial sulphate reduction played a minor role in their formation in the sense that isotopic fractionation was limited it seems that the interstitial spaces of the peat closed rapidly during early diagenesis due to a regime of high depositional rate leading to a relative enrichment of the heavy sulphur isotopes

recurring patterns of total organic carbon and source rock quality within a sequence stratigraphic framework sequence stratigraphy has been combined with total organic carbon toc analysis from well logs core and cuttings to develop a model of toc accumulation in marine source rocks routine well profiling of toc in marine source rocks has revealed that recurrent patterns in the vertical distribution of toc occur that can be explained with sequence stratigraphic concepts the model assumes that the principle controls on organic carbon accumulation are 1 the presence of low oxygen conditions at the sediment water interface and 2 sedimentation rate under these circumstances toc will vary inversely with terrigenous clastic influx if accommodation is high clastic influx is low in distal locations and the resulting weight percent toc in basinal sediments is increased th maximum toc in a vertical profile through a single marine sequence probably correlates to the maximum flooding surface toc decreases above this surface due to increasing sediment dilution during highstand progradation and decreases below it with the higher sedimentation rate of the older transgressive systems tract commensurate with toc increase towards the maximum flooding surface the organic matter type becomes more marine and therefore increasingly oil prone several marine source rock examples are presented as well as a lacustrine example which also conforms to the marine model

numerical modelling of depositional sequences in half graben rift basins a three dimensional numerical model of sediment transport and deposition in coarse grained deltas is used to investigate the controls on depositional sequence variability in marine half graben extensional basins subject to eustatic sea level change using rates of sea level change sediment supply and fault slip reported from active rift basins the evolution of deltas located in three contrasting structural settings is documented 1 footwall sourced deltas in high subsidence locations near the centre of a lault segment 2 deltas fed by large drainage catchments at fault tips and 3 deltas sourced from drainage catchments on the hangingwall dip slope different es in the three dimensional form and internal stratigraphy of the deltas result from variations in tilting of the hangingwall and the impact of border fault slip rates on accommodation development because subsidence rates near the centre of fault segments are greater than all but the fastest eustatic falls footwall sourced deltas lack sequence boundaries and are characterized by stacked highstand systems tracts high subsidence and steep bathymetry adjacent to the fault result in limited progradation in contrast the lower subsidence rate settings of the fault tip and hangingwall dip slope deltas mean that they are subject to relative sea level fall and associated fluvial incision and forced regression low gradients and tectonic tilting of the hangingwall influence the geometry of these deltas with fault tip deltas preferentially prograding axially along the fault creating elongate delta lobes in contrast broad sheet like delta lobes characterize the hangingwall dip slope deltas the model results suggest that different systems tracts may be coeval over length scales of several kilometres and that key stratal surfaces defining and subdividing depositional sequences may only be of local extent i urthermore the results highlight pitfalls in sequence stratigraphic interpretation and problems in interpreting controlling processes from the preserved stiatigraphic product

primary alteration oxidation of marine algal organic matter from oil source rocks of the north sea and norwegian arctic new findings abstract the presence of partially oxidized algal organic matter in oil prone marine source rocks is the rule rather than the exception partially oxidized algal kerogen can still act as a significant source of liquid hydrocarbons however the corresponding peak of c12 hydrocarbon generation is shifted to a considerably lower maturity level compared with that of the classical type ii kerogen the extent of primary alteration oxidation of marine algal kerogen is monitored by means of solid state microfluorescence spectroscopy a new parameter the primary alteration factor paf is established and the relationships between paf and h c o c hi toc and between paf and 0 13c are determined the present data show large variations in the bulk chemistry of immature marine algal kerogens and reveal evidence for gradational dehydrogenation oxidation of the source organic matter this contrasts with the recently proposed mechanism for kerogen formation sem analysis reveals a relationship between the physical breakdown of algal organic matter and the formation of liptodetrinite ftir analysis shows that the incorporation of primary oxygen in the kerogen macromolecules is not in the form of carbonyl or carboxyl functionalities the presence of highly unreactive stable oxygen associated with aromatic structures in partially oxidized algal kerogen is suggested by resistance of the kerogen to graphitization the ftir data also suggest the presence of aryl ether oxygen the present findings raise fundamental questions regarding the mechanisms of kerogen cracking and kerogen formation and have important implications for petroleum exploration

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

stochastic inversion of permeability and dispersivities from time lapse self potential measurements a controlled sandbox study 1 we test the ability of the self potential method to provide information that can be used to invert the permeability and the dispersivities of a porous material we first formulate the semi coupled system of equations describing the occurrence of self potential signals associated with the transport of salt in a porous material like sand two contributions in the source current density arise from the electrokinetic coupling associated with the flow of the pore water and the diffusion potential due to the gradient in the activity of the salt a controlled laboratory sandbox experiment is performed to show that time lapse self potential measurements can be used to invert in a bayesian framework the permeability and dispersivities

upward increase of kerogen δ13c in the peru margin upper oligocene possible implications for the cenozoic evolution of atmospheric co2 abstract carbon isotopic composition of predominantly marine kerogen in latest oligocene mudstones of the peru margin odp 682a hole shows an about 3 5 increase with decreasing age py gc and elemental c n ratio analysis of the kerogen plus sulphur isotopic study together with earlier knowledge on geological setting and organic geochemistry results in a better understanding of depositionary environment and allows to separation of the influence of concentration of water dissolved carbon dioxide ce on kerogen 13c from that of other factors bacterial degradation sea surface temperature dic 13c productivity and admixture of land plant om based on this analysis the major part of the kerogen shift is considered as a result of the latest oligocene decrease of marine photosynthetic carbon isotopic fractionation in the peru margin photic zone which in turn possibly reflects a simultaneous drop in atmospheric co2 level uncertainties in the evaluation of the factors affecting the marine photosynthetic carbon isotopic fractionation and the extent of ocean atmosphere disequilibrium do not permit calculation of the decrease of the atmospheric co2

rift related sedimentary evolution and its response to tectonics and climate changes a case study of the guaizihu sag yingen ejinaqi basin china abstract distinguished from most existing rift basin evolutionary models the succession of deep water deposits in the guaizihu sag were mainly developed during rift initiation instead of the greatest tectonic subsidence phase this paper focuses on the detailed analysis of rift related sequence stratigraphy and sedimentary evolution in this continental rift sag and discusses tectonic and climatic controls on filling patterns the deposits of the guaizihu sag can be ascribed to four major depositional systems alluvial fan and fan delta braided delta sublacustrine fan and shallow to deep lacustrine deposits they are in part contemporaneous and some succeeding each other forming five sequence units and corresponding substages of basin evolution i rift initiation ii early rift climax iii middle rift climax iv late rift climax and v late syn rift substages with the onset of fault movement and hot humid climate conditions the first substage is characterized by a number of poorly linked depocenters which consist of alluvial fan fan delta and deep lacustrine deposits with organic rich mudstones the second substage is associated with an enhanced activity of border faults and block rotation this unit is dominated by lacustrine deposits but fan or braided delta and sublacustrine fans also can be observed the third substage is marked by the maximum subsidence rate and shallow lakes fringed by fan and braided deltas the arid environment is likely to be the main factor controlling the lithofacies and filling characteristics of this unit during the fourth substage two early sub sags gradually converged to form a uniform one the relative tectonic quiescence and climate fluctuations sub humid to sub arid favored carbonate deposition the late syn rift unit which is dominated by fine grained deposits is a consequence of degradation of source area mostly tectonic this study shows that the effects of tectonics and climate on lacustrine sedimentation are intimately interwoven tectonism determines the sag structure stratigraphic architecture and spatial distribution pattern of depositional systems climatic conditions superimposed on tectonics tends to be the major control on sediment supply lithofacies types and sedimentary features

overlapping faults intrabasin highs and the growth of normal faults normal fault systems bounding extensional basins are typically adjoined by a series of subbasins separated by intrabasin highs the strata within these basins form syndepositional anticlines and synclines whose axes are transverse to the strike of the main bounding fault one possible explanation for these intrabasin highs is that they result from persistent along strike deficits in fault displacement such deficits are incompatible with scaling relationships observed between fault displacement and length based on large populations of faults we present data from active normal faults within the basin and range province and from inactive normal faults of the newark basin of eastern north america demonstrating a clear correlation between the along strike position of overlapping splay faults and the location of intrabasin highs as well as syndepositional transverse folds summed displacements for all faults within an intrabasin high are comparable to the displacements on faults bounding flanking subbasins o

a model of rift basin evolution constrained by first order stratigraphic observations the stratigraphy of many nonmarine rift basins records a common sedimentological history consisting of a relatively abrupt increase of water depth followed by a slower shoaling upward trend we explore in this paper the origin of these sequences through a three dimensional physical model that incorporates the affects of fault growth flexure erosion sedimentation and isostasy fault growth is assumed to occur in a self similar manner and is treated as dislocations inducing flexure in a thin elastic plate topography generated by faulting and flexure is allowed to undergo diffusion to simulate erosive and sedimentary processes isostatic response to the redistribution of mass results in additional flexure of the thin plate the model is tested using two models of fault growth and we compare the numerical results with the stratigraphy observed in nonmarine rifts basins generated using a constant lengthening rate mode of fault growth fail to reproduce the stratigraphy of continental rift basins we find that the commonly observed stratigraphic succession of lacustrine to fluvial conditions requires the displacement rate of the bounding fault to decrease with time consistent with opening at a relatively constant areal extension rate

a study of sulphur enrichment in the humic fraction of marine sediments during early diagenesis abstract the evolution of the sulphur content of humic acids extracted from a near shore sediment core was investigated special attention was taken to avoid s contamination of the humic materials during extraction the s c ratios increased continuously with depth to values which strongly suggest s addition to the humic matrix during early diagenesis by reactions between organic matter and h2s or its oxidation products their light isotopic composition supports this view however subsequent isotopic exchange has obscured the mechanism initially involved since a large fraction of the enrichment occurred above the sulphidic zone redox boundaries such as the interface of anoxic microniches within more oxidized zones or the sulphidic suboxic boundary of the sediment column must have been important sites for s addition bioturbation by increasing the contact between sedimentary zones of a different redox regime will likely enhance such processes

influence of normal fault growth and linkage on the evolution of a rift basin a case from the gaoyou depression of the subei basin eastern china abstract it is widely acknowledged that the growth and linkage of a boundary fault affects the evolution of the accompanying sedimentary basin and exerts a strong influence on its sedimentary characteristics in this study we attempt to discuss the evolution of a boundary fault and rift basin by using seismic interpretation incremental fault throw and growth rate distance g d profile which are more suitable parameters than the expansion index in rift basins where footwall strata are missing because of erosion or a depositional hiatus therefore the gaoyou depression is taken as an example the gaoyou depression is the largest hydrocarbon bearing depression in the subei basin which is a representative rift basin in eastern china the depression is bounded to the south by the jiangdu wubao fault zone which includes the zhen 1 wu 1 zhen 2 and wu 2 faults using high resolution three dimensional seismic data the zhen 1 wu 1 fault can be subdivided into four segments based on its g d profile the shaobo fanchuan liuwushe and liulu segments growth rates indicate that the zhen 1 wu 1 fault and the zhen 2 and wu 2 faults developed successively from the late cretaceous to the miocene during rifting of the gaoyou depression and that development of the zhen 2 and wu 2 faults was controlled by the zhen 1 wu 1 fault the four segments of the zhen 1 wu 1 fault were linked with each other by the time the zhen 2 and wu 2 faults formed in the late paleocene an evolution model of the gaoyou depression is set up in this study integrating the fault activity with previous sedimentological studies we suggest that the evolution of the gaoyou depression was controlled by the jiangdu wubao fault zone rather than by a single fault successive slip of the zhen 1 wu 1 fault and the zhen 2 and wu 2 faults caused subsidence and migration of the depocenters this study presents a case investigation of the effects of boundary faults on rift basins in eastern china

an oligocene sink for organic carbon upwelling in the paratethys a synoptic review of the organic carbon content kerogen type biogenic siliceous sediments and planktonic remains is attempted for the often anoxic oligocene early miocene sediments of the paratethys covering a large area between the rhine valley and the aral sea on this basis stratification of the sea and intensity of planktonic productivity are discussed for different parts of the paratethys the eastern parathethys and some parts of the central and western paratethys show a black sea like stable stratificatin while the bulk of the anoxic sediments in the carpathian flysch basin are interpreted to have an upwelling origin the supposed flysch ocean upwelling regime has no good recent analogue although it shows similarities with the bay of california high rate of corg burial laminated diatomaceous sediments and turbiditic intercalations and offshore nw africa abundant fresh water discharge sediments of a brackish water incursion are widespread on the bottom of the np 23 zone from earliest oligocene to early miocene a continuous narrowing of the anoxic sedimentary belt towards the east european platform is observed

sedimentology and sequence stratigraphy of a transfer zone coarse grained delta miocene suez rift egypt this study focuses on miocene sedimentation and stratigraphic evolution in a major transfer zone at the northern tip of the thal fault segment gulf of suez the succession generally shoals upwards from offshore mudstone containing pro delta turbidites into conglomeratic delta foresets and topsets with sandstone dominated shoreface facies coexisting laterally despite this upward shoaling key stratal surfaces marking abrupt changes in relative sea level allow the succession to be divided into four stratal units the stacking pattern of the stratal units suggests an initial relative sea level rise that generated a major marine flooding surface a relative sea level fall followed resulting in widespread exposure and incision during the ensuing relative sea level rise a lowstand coarse grained delta and coeval shoreface succession prograded several kilometres basinward the stratigraphic development of the transfer zone delta is in marked contrast to that of aggradationally stacked deltas that occur near the centre of the baba sidri fault segment further south at the transfer zone low rates of subsidence and accommodation development coupled with a high sediment supply derived from a large fault tip drainage catchment have produced a strongly progradational delta subject to marked changes in relative sea level in the fault centre location however higher rates of accommodation development coupled with lower rates of sediment supply from footwall catchments have produced aggradationally stacked deltas the results from this study have implications for sequence stratigraphic models and hydrocarbon exploration within extensional basins

the subsurface structure and stratigraphic architecture of rift related units in the lishu depression of the songliao basin china abstract this contribution reports the basin configuration feature stratigraphy and sedimentary architecture of the lishu depression in the songliao basin china the activity rate distribution and style of local faulting demonstrate the timing and extent of regional rifting distinct episodes of compressional tectonic activity caused uplift and exposure of strata evident as the traditional syn and post rift stages of basin evolution these episodes led to the sequential denudation of the upper jurassic huoshiling formation lower cretaceous yingcheng and denglouku formations and corresponding regional unconformities acting in tandem with regional compression activity along the major boundary faults influenced the evolving basin configuration as well as seismic sequences and sedimentary patterns seismic well log and drill core data described here show subdivision sections of the lishu depression strata according to discrete phases of the traditional syn rift stage of deposition we refer to these sub stages as the initial rifting the intensive rifting and the recession phases the basin configuration shifted from a graben half graben configuration during the initial rifting phase to a dustpan shaped half graben pattern during the subsequent phase of intensive rifting and finally into a gentle sedimentary basin during the final recession phase the early seismic sequence divides into a lowstand systems tract lst transgressive systems tract tst and highstand systems tract hst evidence of the lst within the seismic sequence becomes less apparent with the intensive rifting phase while the hst occupied an increasing proportion of the section the shallow water depositional fill formed during the final recession phase consists only of tst and hst components depositional environment then shifts from alluvial fan and shallow lacustrine systems to fan delta braided delta lake and finally to a braided fluvial setting the vertical stacking pattern shifts from retrogradational to progradational to aggradational identification of sub structural units and interpretation of their genetic relationships helps clarify basin evolution and thus serves larger scale continental basin analysis

the vertical compartmentalization of reservoirs an example from an outcrop analog crotone basin southern italy the lower pliocene shallow marine successions deposited within half graben subbasins exposed in the northern crotone basin southern italy are good examples illustrating the variable development of small scale cycles 2 15 m 6 6 49 ft thick within the hanging wall blocks of normal growth faults shallow marine small scale cycles forming the successions deposited near the immediate hanging wall of half graben subbasins show a clear alternation between well cemented shell rich intervals and weakly cemented siliciclastic sandstones in contrast the shallow marine successions deposited in hanging wall dip slope locations and in the footwalls show a poorly preserved cyclicity related to lower subsidence rates and a higher degree of cycle amalgamation the vertical alternation between well cemented carbonate rich intervals and less cemented sandstones creates a marked heterogeneity in the permeability of these shallow marine half graben fills which are sealed by impermeable offshore and lagoonal mudstones and may be considered as an outcrop analog of potential reservoirs as a consequence of the well developed cyclicity therefore the potential reservoir is vertically compartmentalized this feature tends to vanish toward the hanging wall dip slopes where the cyclicity is remarkably less appreciable the correct prediction of geometry and effective volume of reservoirs and in particular the recognition of their vertical compartmentalization have an important impact on hydrocarbon exploration and production the developed conceptual model of compartmentalized half graben fill may be useful in several contexts to study fault bounded basins from a reservoir point of view

selective aerobic and anaerobic degradation of lipids and palynomorphs in the eastern mediterranean since the onset of sapropel s1 deposition abstract selective degradation of organic matter in sediments is important for reconstructing past environments and understanding the carbon cycle here we report on compositional changes between and within lipid classes and kerogen types represented by palynomorph groups in relation to the organic matter flux to the sea floor and oxidation state of the sediments since the early holocene for central eastern mediterranean site abc26 this includes the initially oxic but nowadays anoxic presapropelic interval the still unoxidised lower part of the organic rich s1 sapropel its postdepositionally oxidised and nowadays organic poor upper part as well as the overlying postsapropelic sediments which have always been oxic a general 2 3 times increase in terrestrial and marine input during sapropel formation is estimated on the basis of the total organic carbon toc pollen spore dinoflagellate cyst n alkane n alkanol and n alkanoic acid concentration changes in the unoxidised part of the sapropel the long chain alkenones 1 15 diols and keto ols loliolides and sterols indicate that some plankton groups notably dinoflagellates may have increased much more apart from the terrestrial and surface water contributions to the sedimentary organic matter anomalous distributions and preservation of some c 23 c 27 alkanes alkanols and alkanoic acids have been observed which are interpreted as a contribution by organisms living in situ comparison of the unoxidised s1 sapropel with the overlying oxidised sapropel and the organic matter concentration profiles in the oxidised postsapropelic sediments demonstrates strong and highly selective aerobic degradation of lipids and palynomorphs there seems to be a fundamental difference in degradation kinetics between lipids and pollen which may be possibly related with the absence of sorptive preservation as a protective mechanism for palynomorph degradation the n alkanes impagidinium and nematosphaeropsis are clearly more resistant than toc the n alkanols and n carboxylic acids are about equally resistant whereas the pollen all other dinoflagellate cysts and other lipids appear to degrade considerably faster which questions the practice of normalising to toc without taking diagenesis into account selective degradation also modifies the relative distributions within lipid classes whereby the longer chain alkanes alcohols and fatty acids disappear faster than their shorter chain equivalents accordingly interpretation of lipid and palynomorph assemblages in terms of pre or syndepositional environmental change should be done carefully when proper knowledge of the postdepositional preservation history is absent two lipid based preservation proxies are tested the diol keto ol oxidation index based on the 1 15c 30 diol and keto ols doxi and the alcohol preservation index api whereby the former seems to be the most promising

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing

control of the preservation of organic matter by productivity and sulphate reduction in kimmeridgian shales from dorset uk abstract the kimmeridgian shales of dorset uk have a very wide range of total organic carbon toc content and hydrogen index hi these cyclic changes of organic carbon accumulation are usually interpreted in terms of biomass changes induced by variations in productivity the influence of such variations on the intensity of sulphate reduction and consequently on the preservation of organic carbon were studied the pyrite content does not reflect the full extent of sulphate reduction for sediments with a toc content greater than 10 when easily reducible iron is no longer available h 2 s is preferentially fixed as organic compounds in algal bodies a sulphate reduction index sri initial c org residual c org was calculated for each sediment on the basis of the sulphate reduction reaction stoichiometry and a drastic change in sulphate reduction intensity was seen for toc contents of about 10 above this value the sri is low and decreases with increasing toc content the sediments are rich in organic carbon composed of well laminated stacked algal bodies and were probably deposited at an oxygen depleted water sediment interface in this instance the quality and the amount of organic matter buried depends directly on the organic fluxes towards the redox interface it is assumed that the high relative input of organic matter which can be metabolized exceeds the availability of sulphate in the pore waters so that part of it escapes sulphate reduction and is probably degraded by other processes methanogenesis for toc contents less than 10 the sri is higher and variable the sediments show traces of burrowing and the depositional conditions are thought to be dysaerobic it is proposed that under such conditions bioturbation brings both sulphate and reducible iron into the sediment and that sulphate reduction mainly expressed by the presence of pyrite consumes all the available organic matter which can be metabolized the strong variability in the intensity of sulphate reduction depends on various parameters such as the genetic type of planktonic organic matter the method of transportation to the sediment and possibly the earlier oxic degradation during transportation

three dimensional numerical modeling of coarse grained clastic deposition in sedimentary basins a three dimensional numerical model of clastic deposition in sedimentary basins is used to investigate the development of coarse grained deltas in response to relative sea level changes the model incorporates fully three dimensional sediment delivery and deposition together with incised channel formation and slope failure a combined random walk steepest descent algorithm is used to simulate sediment delivery from a drainage basin outlet to the depositional shoreline together with a nonlinear three dimensional diffusion equation for modeling slope dependent sediment erosion transport and deposition when sediment channels transport pathways are out of a specified grade advective erosion occurs thereby increasing the total sediment supply delivered to the basin multiple sediment sources into a basin can be simulated together with tectonic subsidence and eustatic sea level changes the model results presented display many of the key features observed in both modern and ancient coarse grained deltas during periods of slowly changing and high relative sea level highstands a broad delta front progrades approximately radially away from the sediment source conversely incised channels are developed during rapid falls of relative sea level leading to localized deposition of deltaic lobes at the mouths of these channels the incised channels initiate at the exposed delta front and propagate backward toward the sediment source the rate of growth of incised channels is shown to be an important control on delta morphology sediment distribution and lowstand lobe size and location lobes are particularly well developed during periods of slowly changing low relative sea level lowstands periods of rapid rise of relative sea level lead to flooding and infilling of incised channel systems and a rapid landward shift in deposition transgressions incised channels and delta lobes are best developed in a model where tectonic subsidence is similar to that expected for hanging wall sourced deltas in extensional half graben settings in contrast both channels and lobes are less well developed in a model where tectonic subsidence is similar to that expected for footwall sourced deltas in such settings many of the features developed in the models are by their nature three dimensional and two dimensional analysis of the model results can lead to erroneous interpretations of the causes of along strike variability these aspects of sequence variability have important implications for the application of the sequence stratigraphic methodology to many sedimentary basins