fluvial facies model of the ganga river sediments india abstract the river ganga flows from the northwest to the southeast following the lineaments developed in response to the himalayan tectonics ganga sediments show a large number of facies developments throughout the study area from hardwar to kachhla the active channel deposits are marked by the development of large scale facies in gravel and coarse sand small scale facies comprising fine sand silt and clay are developed in inactive channel deposits and overbank deposits the depositional model shows a progressive decrease in particle size thickness of units and scale of cross bedded sets from the lower to the upper parts of sequences as well as from upstream to downstream the sedimentation of the ganga basin is seasonally and tectonically controlled

the rachaya serghaya fault system lebanon evidence of coseismic ruptures and the ad 1759 earthquake sequence 1 the rachaya and serghaya faults are the easternmost fault branches of the dead sea transform fault within the lebanese restraining bend they lie east of the yammouneh fault the main strand of the dead sea transform fault within the restraining bend extend along the western and eastern flanks of the anti lebanon range respectively and show left lateral strike slip movement manifested as offset drainage we studied both faults through combined field investigations in geomorphology and paleoseismology young fault scarps mole tracks pressure ridges and offset streams detected along the faults traces attest to recent coseismic ruptures two paleoseismic investigations highlight their seismogenic potential and indicate earthquake recurrence along them the rachaya and serghaya faults are active and the sources of recent historical earthquakes the last of which might be the 30 october 25 november 1759 ms 6 6 and 7 4 earthquake sequence that caused severe damage in the eastern mediterranean region such a possible correlation suggests that the two faults are probably structurally interconnected as movement on one fault may stimulate movement on the other fault in addition both faults may define together an active seismogenic fault system that accommodates some of the regional displacement that takes place within the lebanese restraining bend our results highlight that the seismogenic potential of the rachaya and serghaya faults must be included in any seismic hazard assessment of the region

deltaic coals of ferron sandstone member of mancos shale predictive model for cretaceous coal bearing strata of western interior the upper cretaceous ferron sandstone member of the mancos shale the coal bearing unit of the emery coalfield in central utah shows accumulation of clastic sediments in a lobate river dominated deltaic system that existed along the western shoreline of the interior cretaceous seaway during late turonian time five cycles of deltaic sedimentation each containing one major coal bed or coal zone are represented a clear genetic relationship exists between the geometries of the major coal beds of the emery field and the geometries of the delta front sandstone units with which they are associated the thicker part of each coal bed extends from the vicinity of the landward pinch out of the associated delta front sandstone landward to a distance of about 10 km this genetic relation forms the basis of a predictive model that can be used in designing more cost effective exploration programs in coal bearing strata of cretaceous age in the western interior

comparison of methods to estimate sediment flux in ancient sediment routing systems abstract the need to predict accurately the volume timing and location of sediments that are transported from an erosional source region into a basin depocentre sink is important for many aspects of pure and applied sedimentological research in this study the results of three widely used methods to estimate sediment flux in ancient sediment routing systems are compared using rich input datasets from two systems eocene south pyrenean foreland basin spain and late pleistocene to holocene gulf of corinth rift basin greece for which mapped dated sediment volumes provide an independent reference value of sediment accumulation rates the three methods are 1 the empirical bqart model which uses values of drainage basin area relief temperature lithology and water discharge 2 empirical scaling relationships between characteristic geomorphological parameters of sediment routing system segments and 3 the fulcrum model which uses the palaeohydrological parameters of trunk river channels to estimate downsystem sediment discharge the bqart model and empirical geomorphological scaling relationships were originally developed using modern sediment routing systems and have subsequently been applied to ancient systems in contrast the fulcrum model uses hydrological scaling relationships from modern systems but was developed principally for application in ancient systems our comparative analysis quantifies the sensitivity of the three methods to their input parameters and identifies the data required to make plausible estimates of sediment flux for ancient sediment routing systems all three methods can generate estimates of sediment flux that are comparable with each other and are accurate to at least one order of magnitude relative to independent reference values the bqart model uses palaeoclimatic and palaeocatchment input data which are accurate for sub modern systems but may be highly uncertain in deep time systems corresponding estimates of sediment flux are most sensitive to the accuracy with which the palaeocatchment area is constrained and to palaeoclimatic parameters that reflect temperature and precipitation the fulcrum model uses palaeohydrological input data its sediment flux estimates are sensitive to palaeochannel dimensions and in particular the duration of bankfull discharge which is invariably difficult to constrain accurately in deep time sediment routing systems this uncertainty can give rise to large potential ranges of sediment flux estimates geomorphological scaling relationships offer comparable order of magnitude accuracy for both sub modern and deep time sediment routing systems in which geomorphological segments can be identified but when used on relatively small sediment routing systems the ranges of sediment volumes deposited can vary greatly limiting the utility of the technique we suggest that methods to estimate sediment flux should be chosen for a particular sediment routing system based on the types and uncertainty of available data where input parameter values are highly uncertain such as in deep time systems monte carlo simulation is an effective tool to calculate probability distributions of estimated sediment flux

sandstone body and shale body dimensions in a braided fluvial system salt wash sandstone member morrison formation garfield county utah excellent three dimensional exposures of the upper jurassic salt wash sandstone member of the morrison formation in the henry mountains area of southern utah allow measurement of the thickness and width of fluvial sandstone and shale bodies from extensive photomosaics the salt wash sandstone member is composed of fluvial channel fill abandoned channel fill and overbank flood plain strata that were deposited on a broad alluvial plain of low sinuosity sandy braided streams flowing northeast a hierarchy of sandstone and shale bodies in the salt wash sandstone member includes in ascending order trough cross bedding fining upward units mudstone intraclast conglomerates single story sandstone bodies basal conglomerate abandoned channel fill multistory sandstone bodies and overbank flood plain heterolithic strata trough cross beds have an average width thickness ratio w t of 8 5 1 in the lower interval of the salt wash sandstone member and 10 4 1 in the upper interval fining upward units are 0 5 3 0 m thick and 3 11 m wide single story sandstone bodies in the upper interval are wider and thicker than their counterparts in the lower interval based on average w t linear regression analysis and cumulative relative frequency graphs multistory sandstone bodies are composed of two to eight stories range up to 30 m thick and over 1500 m wide w t 50 1 and are also larger in the upper interval heterolithic units between sandstone bodies include abandoned channel fill w t 33 1 and overbank flood plain deposits w t 70 1 understanding w t ratios from the component parts of an ancient sandy braided stream deposit can be applied in several ways to similar strata in other basins for example to 1 determine the width of a unit when only the thickness is known 2 create correlation guidelines and maximum correlation lengths 3 aid in interpreting the controls on fluvial architecture and 4 place additional constraints on input variables to stratigraphic and fluid flow modeling the usefulness of these types of data demonstrates the need to develop more data sets from other depositional environments

architecture of the tectonically influenced sobrarbe deltaic complex in the ainsa basin northern spain abstract the syn tectonic sobrarbe deltaic complex eocene of the ainsa basin spanish pyrenees is confined by lateral thrust ramps and influenced by intra basinal growth anticlines six facies associations have been distinguished within the deltaic complex i slope marls and turbidite sandstones ii distal delta front silty and bioturbated sandstones iii proximal delta front and delta plain deposits tidal inlet tidal flat mouth bar bay distributary channel and floodplain environments iv biogenic deposits at flooding surfaces v collapse zone sediments and vi nummulite dominated shallow marine carbonates the deltaic complex comprises four composite sequences which each contain a number of minor sequences of the genetic maximum flooding surface bounded type regressive unconformities and their correlative surfaces separate the composite sequences cs and each cs can be divided into lowstand transgressive and highstand components at the base the comaron cs is a wnw prograding deltaic complex containing six minor sequences characterized by basinward stepping sandstone wedges separated by transgressive mudstones double regressive unconformities are often associated with these sandstone wedges proximally in the basin growth of the intra basinal arcusa anticline caused gentle folding of the comaron cs and syn growth strata at the base of the overlying las gorgas cs contain a prominent forced regressive sandstone wedge the las gorgas sandbody and display thinning of bedsets onto the crest of the anticline moreover it can be demonstrated that relative sea level rise took place in the growth synclines at the same time as a fall in relative sea level occurred on the growth anticlines the tectonic deformation caused a shift in the direction of deltaic progradation towards the north northwest as demonstrated by the well developed clinoforms in the highstand sequence set of the las gorgas cs a second phase of tectonic activity this time triggering large scale collapse of the delta front occurred at the transition between the las gorgas and barranco el solano cs tilting of the basin floor led to the development of coeval transgressive and regressive strata separated by a fulcrum line of zero net vertical movement of the shoreline in the post tilt phase reduced sediment supply and accelerated subsidence led to widespread transgression and a change from clastic to carbonate dominated sedimentation this phase was terminated by a gradual increase in sediment supply causing progradation of a mixed clastic carbonate system dominated by large nummulite banks and bioturbated shoreface marls and sandstones finally a pronounced fall in relative sea level associated with the transition to the buil cs triggered slope instabilities and eventually established fluvial conditions all over the study area with the exception of the anticline crests the relatively high rate of tectonic subsidence in the study area suppressed relative sea level falls resulting in development of discontinuous lowstand strata and bounding surfaces the segmented nature of many regressive unconformities may be related to incremental growth of thrust related structures and each segment is separated from neighbouring segments by gaps of limited vertical and lateral displacement precursors of progressive unconformities are seen in the upper proximal part of the comaron cs by downdip fanning and updip convergence of minor sequences these differentially tilted stratal units provide reliable indicators of syn sedimentary tectonism

sedimentology and alluvial architecture of the bajo barreal formation upper cretaceous in the golfo san jorge basin outcrop analogues of the richest oil bearing fluvial succession in argentina abstract this study addresses the sedimentology architecture and dimensions of fluvial deposits in the bajo barreal formation upper cretaceous in the codo del senguerr anticline golfo san jorge basin argentina the stratigraphic framework of the 450 650 m thick alluvial succession was carried out through description and interpretation using 18 detailed sedimentary logs along a 4 5 km wide exposure where 314 fluvial channels were analysed the bajo barreal formation is a high accommodation fluvial succession dominated by fine grained floodplain deposits with isolated to vertically stacked sheet like low sinuosity or braided fluvial channels of limited lateral mobility clustered in several coeval channel belts in which fluvial channels were relocated by avulsion the lower member consists of reworked ash fall materials preserved in floodplain areas 78 floodplain sandstones 4 and fluvial channels 18 the mean thickness of sandbodies is 2 96 m n 118 and mean true width is 112 m mean w t 43 with thicker and wider sandbodies in upper levels of the member the upper member consists of grey siltstones and mudstones preserved in extensive lowland areas 78 and fluvial channels 19 with scarce preservation of sandstones in the proximal floodplain 3 fluvial channels are narrow low sinuosity sheets with comparable thickness mean 3 21 m n 196 but greater width than those of the lower member mean width 147 m mean w t 50 paleoflow data from 298 fluvial sandbodies indicates a paleoflow direction toward the se az 112 rivers flowed parallel to inherited early cretaceous normal faults and are oriented to high angle 70 to the current axis of the codo del senguerr anticline suggesting that the uplift of the anticline occurred after the deposition of the formation the variation in geometry of fluvial channels in both members of the bajo barreal formation could help in planning and developing primary and or enhanced oil recovery projects in nearby oilfields and provide data necessary for modelling the subsurface connectivity of hydrocarbon reservoirs

evolving alluvial stratigraphy and thrust front development in the west jaca piggyback basin spanish pyrenees in the southwestern pyrenees distinctive alluvial mega sequences correlate with the development of a shallow mountain front thrust structure the pena flexure the flexure evolved during the oligocene to early miocene and is interpreted as a duplex marking the limit of thrust front advance three main depositional facies preserved completely across the pena flexure are described a pre thrust emergence high sinuosity fluvial sequence the c 2300 m thick sheet sandstone facies of the campodarbe formation a syn thrust emergence conglomeratic alluvial fan sequence the c 1100 m thick conglomeratic facies of the bernues formation and a post thrust emergence low sinuosity fluvial sequence the 700 m thick ribbon sandstone facies of the uncastillo formation collectively their continuous exposure across the pena flexure provides a more or less complete record of the sedimentary evolution of a mountain front syn deformational features in the alluvial fan sequence of the bernues formation and marked contrasts in palaeochannel morphology sandstone body geometry and palaeocurrent patterns between the two fluvial sequences are best understood by invoking a strong tectonic control over their deposition an increased rate of vertical sediment accretion was a key process in determining fluvial style the onset of major thrusting led to more rapid basin floor subsidence thereby promoting a change from lateral to vertical accretion as channels responded to the rising base level

flow depth scaling in alluvial architecture and nonmarine sequence stratigraphy example from the castlegate sandstone central utah u s a changes in the proximity and arrangement of channel belt sandstone bodies in the rock record and associated unconformities in alluvial successions i e alluvial architecture and nonmarine sequence stratigraphy are often interpreted to reflect changes in basin boundary conditions including subsidence and sea level such interpretations do not often consider how the size of a depositional system influences alluvial architecture and sequence stratigraphy we investigate how paleoflow depth scaling affects fluvial stratigraphic interpretations using the castlegate sandstone campanian at its type section in central utah as an example using lidar imaging channel preservation and paleoflow depths are estimated from bar clinoforms throughout the unit and these data are compared to scour spacing scour continuity and mudstone content within the study interval within the castlegate sandstone bar clinoforms are routinely close to fully preserved i e rollover of the upper part of the bar is present and an overall increase in paleoflow depth up section is coincident with changes in other alluvial architecture characteristics including increases in scour surface spacing and mudstone abundance up section this suggests that alluvial architecture commonly ascribed to changes in accommodation may result primarily from changes in the scale and style of fluvial deposition rather than accommodation limited reworking and amalgamation additionally although sequence boundaries have previously been identified in the section no scour surfaces deeper or more extensive than what could be produced autogenically by large rivers typical of the castlegate system were found in the study interval this study demonstrates that estimates of paleoriver depth can enhance studies of alluvial architecture and provide a more robust basis for correlating and interpreting fluvial deposits

fault zone reactivation kinematics and mechanisms the kinematics and mechanisms of fault zone reactivation are reviewed reactivation is dependent upon fault zone orientation and the existence of weak mylonites along these zones the recognition of reactivation within mylonite zones and the softening processes that first concentrate deformation into these and secondly provide a weak medium for reactivation are discussed attention is given to the darling mobile zone western australia and the redbank zone see obee white this symposium as examples of reactivated zones

the fluvial architecture of the upper buntsandstein in the iberian basin central spain the cercadillo sandstone and siltstone css formation forms the upper part of the buntsandstein fluvial facies in the western margin of the iberian basin sedimentation was controlled by two major pre triassic tectonic systems the iberian ranges system nw se and the central system ne sw fluvial sedimentation during this period took place in coexisting braided and meandering channels together with associated ephemeral episodes this unusual association was due to a combination of structural control by the main normal faults coupled with large discharge fluctuations the css formation consists of two major fluvial sequences with very similar vertical patterns comprising low sinuosity stream deposits that pass upwards into high sinuosity deposits associated with extensive floodplain sediments a widespread calcrete horizon is developed at the top of the lower sequence and a surface with pedogenic features is present at the top of the upper sequence these horizons are interpreted to be the result of subaerial exposure during a period of no subsidence and equilibrium in the erosion sedimentation processes in the area probably due to quiescent periods on the master faults that delineate the basin minor changes within the sequences are probably due to discharge fluctuations of a climatic origin whereas the general vertical trend of the sequences is suggested to be tectonically controlled palaeocurrent data show a general flux of sediments to the south east parallel to the axis of the iberian basin but the final part of the upper sequence palaeocurrents to the north east are interpreted to indicate a local reactivation of secondary transverse faults in the south east part of the study area

the functioning of sediment routing systems using a mass balance approach example from the eocene of the southern pyrenees abstractsediment routing systems link source regions undergoing erosion with depositional sinks and involve a volumetric or mass budget understanding how these source to sink systems function is key to stratigraphic prediction but estimation of their surface sediment discharges and depositional fluxes on geological time scales is a challenging problem we recognize a paleosediment routing system from the geological record in the mid late eocene escanilla formation and time equivalents of the tectonically active wedge top region of the southern pyrenees by mapping the 200 km long fairway of the escanilla sediment routing system we obtain the sediment budget and grain size fractionation of three time intervals each of 2 5 2 6 m yr duration over the time period 41 6 33 9 ma four thousand cubic kilometers of sediment sourced principally from two feeder systems in the high pyrenees was deposited in a period of 7 7 m yr the positions of moving boundaries characterized by rapid reduction in the perc

the influence of bulk shape factors on settling velocities of natural sand sized sedimentary suites settling rates of natural sand size particles are influenced to some extent by their shapes and this may be an important factor in using settling rates to estimate grain size in order to gauge the sensitivity of this influence two natural sand populations from the mesozoic nubian sandstones of southern israel with a high probability of being similar in their bulk shape characteristics were examined in sieved fractions for their shape characteristics and settling rates fine surface features roundness and surface roughness were evaluated using fourier shape analytical methods significant differences in bulk shape were detected and their influence on settling rates was measured empirically in a settling tube the most marked differences were in the coarse grain sizes and to a lesser extent in the intermediate sizes sampling of raw settling data at closely spaced time intervals yielded high resolution grain size frequency plots which were usually polymodal in nature subtle shape contrasts which are an important influence on settling rates are thus an important consideration when working at this level of sensitivity natural sand populations which have followed a more varied provenance or process pathway could be expected to have even greater contrasts in settling rates than the samples analysed here thus it is recommended that the bulk shape factor should be taken into account in order to minimize errors in the conversion of settling times to grain size an easy method outlined in this paper is through the establishment of an empirically derived calibration curve for each individual suite of sand undergoing analysis sieved samples derived from a split of the total composite sample undergoing analysis forms the basis of the calibration and hence a correction factor converting sieve diameters to true diameters must be applied in this research nominal section diameters were obtained optically through an image analyser

tectonic control on fluvial styles the balfour formation of the karoo basin south africa abstract the balfour formation represents a fully fluvial succession of late late permian earliest triassic age which accumulated in the foredeep of the karoo basin during the overfilled phase of the foreland system the lack of a coeval marine environment within the limits of the preserved karoo basin provides an opportunity to study the stratigraphic cyclicity developed during a time when accommodation was solely controlled by tectonics the balfour stratigraphy is composed of a succession of six third order fluvial depositional sequences separated by subaerial unconformities they formed in isolation from eustatic influences with a timing controlled by orogenic cycles of loading and unloading sediment accumulation took place during stages of flexural subsidence whereas the bounding surfaces are related to stages of isostatic uplift the vertical profile of all sequences displays an overall fining upward trend related to the gradual decrease in topographic slope during orogenic loading at the same time an upward change in fluvial styles can be observed within each sequence from initial higher to final lower energy systems the actual fluvial styles in each location depend on paleoslope gradients and the position of the stratigraphic section relative to the orogenic front proximal sequences show transitions from braided to meandering systems whereas more distal sequences show changes from sand bed to fine grained meandering systems the average duration of the balfour stratigraphic cycles was 0 66 my i e six cycles during 4 my no climatic fluctuations are recorded during this time with the long term climatic background represented by temperate to humid conditions

integration of channel and floodplain suites ii vertical relations of alluvial paleosols abstract extrachannel sediments of the lower eocene willwood formation which were subdivided into different pedofacies or developmental stages exhibit two well developed orders of pedofacies sequences over which a grosser scale cyclicity is superposed simple sequences with thicknesses measured in meters are comprised of one or more soil profiles that are bounded above and below by pedogenically unmodified crevasse splay deposits on a larger scale compound pedofacies sequences are tens of meters thick and consist of several simple sequences sandwiched between channel sandstones between these sandbodies pedogenic maturity of the multistorey paleosols progressively increases and then decreases upwards in response to episodic avulsion formation of both compound and simple pedofacies seq ences was largely controlled by local patterns of deposition and erosion that produced vertical variability in both rate of sediment accumulation and parent material because paleosol maturity also reflects the effects of extrabasinal factors a pedofacies megasequence which is hundreds of meters thick developed in response to changes in tectonic activity through willwood time comparison between willwood deposits in the northern and central parts of the bighorn basin also reveals that areally differing sediment accumulation rates and thereby basin subsidence rates can be interpreted from large scale pedofacies sequences consequently paleosols are useful in determining changes in relative rates of sediment accumulation that are controlled by both intrabasinal and extrabasinal factors

kinematics around a large scale oblique ramp southern pyrenees spain the gavarnie thrust sheet of the southern pyrenees is bound to the east and west by 40 km long transverse zones producing a rectilinear thrust sheet within the boltana region the northwest corner of the gavarnie thrust sheet is well exposed the locale is used to characterize the strain and kinematic patterns and detailed geometry of an oblique ramp over a variety of scales the hanging wall of the gavarnie thrust fault in the area was transported toward 200 and contains two regional scale north south trending anticlines in the vicinity of the oblique ramp the strike of the gavarnie thrust fault and the trend of hanging wall fold axes are 0 180 the magnitude of shortening accommodated by regional scale fold and fault development is constant at 25 along the length of the ramp the orientation of instantaneous and finite shortening axes on meso and grain scales was inferred from the attitudes of cleavage mesoscale folds and faults carbonate mechanical twins and the geometry of finite strain finite and instantaneous shortening axes are subhorizontal and remain perpendicular to the gavarnie thrust ramp within a 10 km wide zone in the footwall and a 20 km wide zone in the hanging wall outside of the halo of footwall and hanging wall ramp deformation the principal shortening directions consistently trend 200 parallel to thrust transport directions throughout the south pyrenean thrust belt the parallelism of instantaneous and finite principal strain axes suggests that grain scale deformation was rionrotational total shortening measured within the footwall of the gavarnie thrust fault decreases from 60 adjacent to the thrust ramp to 10 approximately 10 km away from the ramp while principal shortening directions determined over scales ranging from millimeters to kilometers show a consistent pattern in the boltana region they differ by as much as 90 from tectonic convergence directions between iberia and eurasia during the alpine orogeny 80 18 ma determined from magnetic anomaly patterns in the central atlantic and bay of biscay divergence between plate convergence directions and alpine south pyrenean shortening directions suggests that 200 km of nw se convergence was apparently partitioned into the north and south pyrenean thrust zones which were shortened 167 km the iberian range which accomodated 30 km of shortening 10 km of shortening accomodated in the catalan coastal range and 100 km of right lateral strike slip accomodated within the internides

transverse fold evolution in the external sierra southern pyrenees spain fault slip data are used to reconstruct varying tectonic regimes associated with transverse fold development along the eastern and southern margins of the jaca basin southern pyrenees spain the spanish pyrenean foreland consists of thrust sheets and leading edge decollement folds which developed within piggyback basins guara formation limestones on the margins of the jaca basin were deposited synchronously with deformation and are exposed in the external sierra within the transverse folds principal shortening axes determined from p and t dihedra plots of fault slip data show a shift from steep shortening in stratigraphically older beds to nne ssw horizontal shortening in younger beds older strata are characterized by extensional faults interpreted to result from halotectonic salt tectonics deformation whereas younger strata are characterized by contraction and strike slip faults interpreted to result from thrust sheet emplacement the interpretation of the timing for the shortening axes in the younger strata is supported by the observation that these axes are parallel to shortening axes determined from finite strain analysis calcite twins and regional thrusting directions determined from fault related folds and slickenlines this study shows that fault population analysis in syntectonic strata provides an opportunity to constrain kinematic evolution during orogeny

microcodium revisited root calcification products of terrestrial plants on carbonate rich substrates abstract microcodium is a problematic calcitic microfeature of many calcretes and calcareous paleosols in the cretaceous and tertiary continental and marine successions of the peri tethyan realm the main controversy about the microcodium structures is their origin and possible relation with calcified plant roots microcodium and rhizogenic root formed microfabrics were studied in calcrete profiles within the paleocene shallow marine carbonate succession in southwestern slovenia the prominent laminar calcrete horizons contain abundant calcite aggregates 150 m to 1 cm in size with perfectly preserved structural details of plant root tissues morphology and structure of these aggregates indicate that they formed through biologically controlled precipitation of calcium carbonate within the root cortical cells the morphologies intermediate between the typical microcodium aggregates composed of a single layer of individual elongate pyramidal or prismatic crystals of calcite measuring 100 500 m in length and 20 70 m in width and calcified roots with multilayer arrangement of isodiametric cells were observed and this supports previous rhizogenic interpretations of microcodium structures intermediate forms show that the typical microcodium aggregates formed through morphological transformation of the root tissue by growth of the calcite within the cortical cells which distorted the cell shape calcification of roots and the creation of microcodium structures can be explained as an effective nutrient acquiring mechanism used by certain types of terrestrial plants inhabiting nutrient poor calcareous substrates the widespread occurrence of microcodium in almost unaltered shallow marine limestones indicates that its formation took place during early stages of paleosol development probably reflecting specific types of vascular plants of a pioneer community that were able to colonize carbonate substrates during the early phases of subaerial exposure

quantifying the kinematics of detachment folds using three dimensional geometry application to the mediano anticline pyrenees spain the kinematics of detachment folds have been described by three different models 1 hinge migration is responsible for fold amplification 2 fold amplification is due to limb rotation and 3 both hinge migration and limb rotation cause fold amplification a numerical method is proposed to determine which of these mechanisms is responsible for the formation of natural detachment folds this procedure consists of measuring and plotting geometric data collected from cross sections constructed across the termination of a fold where shortening dies out laterally or in an area with a lateral shortening gradient assuming that observed spatial variations in fold geometry reflect temporal geometric evolution the procedure allows determination of equations that govern the kinematics of the particular detachment fold analyzed to validate the results obtained from the application of this technique to natural examples they must be contrasted with other indicators of fold amplification mechanisms such as microstructures mesostructures and syntectonic sediment patterns this analysis is applied to an asymmetric growth fold the mediano anticline in the southern pyrenees of spain and shows that it grew due to limb rotation and minor hinge migration these data coupled with analysis of the growth stratal patterns using reverse and forward modeling techniques are used to derive deformation rates and to display the kinematics of this fold

stratigraphy and static connectivity of braided fluvial deposits of the lower escanilla formation south central pyrenees spain this study addressed the architecture and dimension distributions of fluvial deposits of the olson member of the escanilla formation through analysis of outcrops in the southern buil syncline ainsa basin south central pyrenees spain the olson member consists of wide multistory channels alternating with mud rich intervals composed of flood plain deposits and isolated individual channels field descriptions and a combination of terrestrial light detection and ranging data and digital orthophotographs were used to map and document the abundance distribution and dimensions of sandstone bodies these data show that channels are distributed according to the local stratigraphic framework and differential subsiding areas morphology width depth and sinuosity of the channels throughout the sequence evolve according to their stratigraphic position during low accommodation periods channels stacked laterally forming wide multistory channel belts under these conditions single channels have a mean width to thickness w t ratio of 49 during high accommodation periods single channels have a mean w t ratio of 29 moreover the tendency of narrower and thicker channels having developed during high accommodation periods is also clearly observable vertically from the base to the top of high accommodation intervals throughout the sequence this pattern of deposition results in increasing vertical connectivity even in mud rich high accommodation periods a geocellular three dimensional model has been performed using object based simulations a succession of stochastic simulations was performed from the simplest one random simulations to more elaborated simulations integrating successively outcrop observations these simulations serve to image sandstone bodies connectivity evolution according to outcrop observations and sedimentologic knowledge subsurface application of such vertical channel morphology evolutions and distribution could lead to more predictive flow unit definitions and extensions

a new approach for outcrop characterization and geostatistical analysis of a low sinuosity fluvial dominated succession using digital outcrop models upper triassic oukaimeden sandstone formation central high atlas morocco the use of digital outcrop models in combination with traditional sedimentological field data improves the accuracy and efficiency of qualitative and quantitative characterization of outcrop analogs for reservoir modeling purposes in this article we apply an innovative methodology of outcrop characterization to an upper triassic fluvial dominated system exposed in extensive outcrops with limited three dimensional 3 d exposure qualitative analysis of the study outcrop allows the subdivision of the formation into three architectural intervals each interval can be further subdivided into subintervals on the basis of architectural style this subdivision provides information on reservoir compartmentalization which is used for zonation of the geocellular model qualitative analysis also provides valuable information on reservoir facies distribution a new technique termed perpendicular projection plane is presented as a tool for quantitative analysis of outcrops with reduced 3 d exposure this technique improves the accuracy of apparent width measurements of geobodies exposed in outcrops which are subparallel to paleoflow the quantitative analysis provides a detailed data set of geobody dimensions to use as conditioning data for analog reservoir models statistical analysis of the dimensions provides empirical relationships to apply in subsurface analog systems to reduce uncertainty related to stochastic modeling approaches

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

facies analysis depositional environment interpretation and lithostratigraphic architecture to predict reservoir potential of the devonian ravendale interval in the bancannia trough western darling basin se australia this paper discusses the facies sequence character for sandstone rocks of the subsurface upper middle devonian and upper devonian ravendale interval in the bancannia trough western darling basin the integration of multiple correlation techniques recognition of changes in core and cutting facies electrofacies and lithostratigraphic facies associations has helped define an internal stratigraphic correlation framework for the ravendale interval this provides a powerful tool for understanding the distribution of the lithostratigraphic architectural controls on reservoir potential this study has re evaluated the stratigraphic boundaries of the ravendale interval bottom and top using marked changes in gamma ray and sonic log characteristics and depth estimates of the boundaries were derived from the wireline log data in the bancannia south 1 bancannia north 1 and jupiter 1 wells the internal stratigraphy of the ravendale interval consists of 20 facies and 19 subfacies that define 4 facies associations fa these facies associations are characterised as facies association a faa a braided channel fill system facies association b fab a meandering channel fill system facies association c fac a multistory fluvial channel fill complex system and facies association d fad a meandering channel delta system the ravendale interval has been subdivided into five wireline log lithostratigraphic units ri1 ri2 ri3 ri4 and ri5 in ascending order in the three available wells use of the suggested wireline log lithostratigraphic unit correlations versus facies association of the ravendale interval has the potential to refine existing stratigraphic sequence schemes and given the higher resolution and more detailed correlation may significantly improve subsurface sedimentological framework relationships in lithostratigraphic unit reconstructions wireline log correlations indicate that potentially productive sand rich units of the major ravendale interval in the bancannia trough can be correlated over large distances suggesting significant continuity into lightly drilled and undrilled areas and aid in the prediction of potential hydrocarbon bearing reservoirs within the darling basin region

the geometry of fluvial channel bodies empirical characterization and implications for object based models of the subsurface the distribution of channel deposits in fluvial reservoirs is commonly modeled with object based techniques constrained on quantities describing the geometries of channel bodies to ensure plausible simulations it is common to define inputs to these models by referring to geologic analogs given their ability to reproduce complex geometries and to draw upon the analog experience object based models are considered inherently realistic yet this perceived realism has not hitherto been tested by assessing the outputs of these techniques against sedimentary architectures in the stratigraphic record this work presents a synthesis of data on the geometry of channel bodies derived from a sedimentologic database with the following aims 1 to provide tools for constraining stochastic models of fluvial reservoirs in data poor situations and 2 to test the intrinsic realism of object based modeling algorithms by comparing characteristics of the modeled architectures against analogs an empirical characterization of the geometry of fluvial channel bodies is undertaken that describes distributions in and relationships among channel body thickness cross stream width and planform wavelength and amplitude object based models are then built running simulations conditioned on six alternative analog informed parameter sets using four algorithms according to nine different approaches closeness of match between analogs and models is then determined on a statistical basis results indicate which modeling approaches return architectures that more closely resemble the organization of fluvial depositional systems known from nature and in what respect none of the tested algorithms fully reproduce characteristics seen in natural systems demonstrating the need for subsurface modeling methods to better incorporate geologic knowledge

sedimentological response of an alluvial system to neogene thrust tectonics atacama desert northern chile the llano de la paciencia is a thrust sheet top basin in which the sedimentological and topographic evolution can be linked to thrust tip propagation it is an elongate gravel plain which borders the salar de atacama a major intermontane basin in the andean forearc of northern chile the llano is bounded to the west by the cerros de purilactis a cretaceous paleocene sequence uplifted by the frontal domeyko thrust the eastern margin of the llano is formed by the cordillera de la sal which was uplifted by a linked back thrust frontal thrust system the salar de atacama is thus divided into a number of discrete sub basins the llano de la paciencia the pampa visachita and the western sub llano which from east west are bounded by the cordillera de la sal the northern imbricates and the ignimbrite back thrust two phases of sedimentological evolution can be distinguished within the llano on the basis of quaternary to recent sediment dispersal patterns initially phase 1 alluvial fan lobes prograded eastwards into the main salar de atacama basin subsequently uplift of the cordillera de la sal deflected drainage systems southwards parallel to the structural strike these phase 2 alluvial deposits drain into the salar de atacama at the lateral termination of the cordillera de la sal frontal thrust in places where thrust tip ramps are emergent within the llano gullies have been incised into the drainage pathways this has resulted in the reworking of the early phase 1 gravels and progradation of the phase 2 fan lobes the evolution of the llano de la paciencia illustrates the close link between topography and syntectonic alluvial drainage patterns in an arid intermontane basin