sediment dispersal and quantitative stratigraphic architecture across an ancient shelf two large 200 to 300 km near continuous outcrop transects and extensive well log data ca 2800 wells allow analysis of sedimentological characteristics and stratigraphic architecture across a large area ca 60 000 km2 of the latest santonian to middle campanian shelf along the western margin of the western interior seaway in eastern utah and western colorado usa genetically linked depositional systems are mapped at high chronostratigraphic resolution ca 0 1 to 0 5 ma within their sequence stratigraphic context in the lower part of the studied interval sediment was dispersed via wave dominated deltaic systems with a compound clinoform geomorphology in which an inner wave dominated shoreface clinoform was separated by a muddy subaqueous topset from an outer clinoform containing sand poor gravity flow deposits these strata are characterized by relatively steep net regressive shoreline trajectories 0 1 with concave landward geometries narrow nearshore belts of storm reworked sandstones 2 to 22 km wide offshore mudstone belts 250 km and relatively high sediment accumulation rates ca 0 27 mm year 1 the middle and upper parts of the studied interval also contain wave dominated shorefaces but coeval offshore mudstones enclose abundant isolated tide influenced sandstones that were transported sub parallel to the regional palaeoshoreline by basinal hydrodynamic tidal circulation these strata are characterized by relatively shallow net regressive shoreline trajectories 190 km and relatively low sediment accumulation rates ca 0 11 mm year 1 the change in shelfal sediment dispersal and stratigraphic architecture from i compound clinoform deltas characterized by across shelf sediment transport to ii wave dominated shorelines with isolated tide influenced sandbodies characterized by along shelf sediment transport is interpreted as reflecting increased interaction with the hydrodynamic regime in the seaway as successive shelfal depositional systems advanced out of a sheltered embayment utah bight this advance was driven by a decreasing tectonic subsidence rate which also suppressed autogenic controls on stratigraphic architecture

the calcarenite di gravina formation in matera southern italy new insights for coarse grained large scale cross bedded bodies encased in offshore deposits excellent outcrops of the upper pliocene lower pleistocene calcarenite di gravina around matera southern italy provide continuous exposure of coarse grained clastic basin margin shoreline to offshore facies among these facies the most conspicuous and volumetrically important are the transition slope deposits that form large scale high angle cross bedded lithosomes these are laterally extensive parallel with the paleoshoreline and show seaward progradation we interpret them to represent avalanches of sediment swept out onto a depositional slope below wave base from the shoreface zone by storm waves and wind driven currents three types of building blocks are recognized based on bedding patterns and facies architecture embryonic parasequences mature parasequences and simple sequences parasequences formed during stillstands of sea level and simple sequences during high frequency cycles of relative change of sea level these building blocks are stacked in a backstepping configuration and onlap onto cretaceous limestone substrate backstepping is believed to be due to a tectonically forced transgression that is punctuated by high frequency cycles of sea level modern analogs for these building blocks are the holocene prograding prisms detected in high resolution seismic lines of the mediterranean shelves the reflection patterns of these seismic units resemble the bedding architecture of the matera simple sequences and parasequences and show similarities of shape size position and orientation of coastal setting and direction of progradation comparison of the holocene prisms and the pliocene pleistocene accretional units in matera indicates that they may represent the same begin page 662 genetic process progradation of clastic prisms below the wave base level the matera accretional units also show similarities with other examples of laterally extensive large scale cross bedded sand bodies encased in offshore deposits such as some sandbanks differentiating between these laterally extensive and seaward prograding cross bedded sand bodies and some coarse grained gilbert type deltas is difficult however if interpretations are based only on two dimensional 2 d outcrops in dip section without high resolution data it is also difficult to distinguish between transition slope and prograding shoreface lithosomes this difficulty may be acute where only seismic or well log data are available however certain other architectural characteristics such as stacking and preservation of facies belts and position of bounding surfaces as well as differences in associated sedimentary structures and fossil content may be used for interpretation the matera example provides a mechanism for emplacement in offshore settings of elongate and strandline parallel sand and gravel deposits that prograde seaward and that preserve a coarsening upward internal succession this article offers an interpretation for other ancient examples of large scale cross bedded lithosomes encased in offshore deposits

distinguishing depositional environments in shallow water mixed bio siliciclastic deposits on the basis of the degree of heterolithic segregation gelasian southern italy abstract a new sedimentological technique has been tested in gelasian cross stratified bio siliciclastic deposits cropping out in southern italy lucanian apennine to disentangle paleoenvironmental and model reconstructions for shallow water mixed sediments the proposed method suggests the use of the bioclastic siliciclastic ratio bls and the segregation index s i to evaluate the percentage of the dominant elastic component in a mixed deposit and in order to estimate the degree of the heterolithic segregation between bioclastic and siliciclastic particles the principle of this method is based on the experimental evidence that bioclasts and quartz grains reveal a different physical behavior if entrained by a hydraulic flow of a given energy thus a different internal texture of bioclastic and terrigenous particles in the same sedimentary deposit is regarded as the result of the variation in the energy of a number of hydrodynamic processes that characterize shallow marine settings including waves currents and tides the studied mixed sediments subdivided into facies associations exhibit stratigraphic shoaling upward successions recording repeated transitions from offshore to shoreface environments these trends are documented through the vertical variations in the degree of heterolithic segregation between mixed clastic particles quantified by using the s i introduced in the present study the assessment of the degree of heterolithic segregation is thus proposed as a proxy to distinguish depositional environments related to different water depths in shallow water mixed systems

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

mixing of siliciclastic and carbonate sediments in shallow shelf environments the inhibiting effect that siliciclastic material has on carbonate secreting organisms has lead to the generalization that sediments composed of mixtures of carbonate and siliciclastic material should rarely form however many modern and ancient shelf deposits contain a spectrum of sediments that are of mixed composition the processes responsible for this mixing can be grouped into four categories 1 punctuated mixing where sporadic storms and other extreme periodic events transfer sediments from one depositional environment to another 2 facies mixing where sediments are mixed along the diffuse boundaries between contrasting facies 3 in situ mixing where the carbonate fraction consists of the autochthonous or parautochthonous death assemblages of calcareous organisms that accumulated on or within siliciclastic substrates and 4 source mixing where admixtures are formed by the uplift and erosion of nearby carbonate source terranes the allochemical constituents of mixed sediments are both coralgal and foram mollusc in composition the foram mollusc assemblage is the most common because of the effects of increased turbidity unstable substrates and the clogging of filter feeding mechanisms associated with a siliciclastic influx

temporal development of prograding beach shoreface deposits the holocene of kujukuri coastal plain eastern japan abstract prograding beach foreshore deposits with a basal ravinement bed are recognized from detailed ams 14c dating and grain size analyses of holocene deposits of the kujukuri coastal plain facing the pacific coast of japan the holocene deposits are about 20 m thick and consist of an upward shoaling beach foreshore succession that has a basal unconformity overlain by a thin layer of relatively coarse sand the unconformity is a downlap surface which originated from a ravinement surface the overall succession was formed by a prograding beach foreshore system during the highstand in sea level of the last 6000 years poorly preserved fossil shells enclosed in the thin layer of coarse sand at the base of the succession date from the transgressive stage in sea level before 6000 cal yr bp grain size distribution patterns are polymodal in the basal sand layer and unimodal in the remainder of the succession modal classes of the basal part are fine 3 3 2 6 medium 2 3 1 8 and coarse 1 2 1 0 the fine mode and the unimodal grain sizes define an overall upward coarsening trend which correlates with the upward shoaling succession in contrast the medium and coarse modes are restricted to the basal sand and are interpreted as related to the ravinement process the thin basal sand layer an admixture of these modal classes is interpreted as a type of ravinement deposit preserved during sea level highstand no transgressive deposit was preserved on the ravinement surface because sediment supply was so small that the sediment on this surface experienced thorough reworking by storm waves

facies partitioning and sequence stratigraphy of cool water mixed carbonate siliciclastic sediments upper miocene guadalquivir domain southern spain during the late miocene the guadalquivir basin and its satellite basin the ronda basin were under atlantic cool water influence the aim of our study is to develop a sequence stratigraphic subdivision of the ronda basin fill and to provide models for the cool water carbonates the upper miocene of the ronda basin can be divided into three depositional sequences sequence 1 is early tortonian sequence 2 late tortonian to earliest messinian and sequence 3 messinian in age the sediments were deposited in a ramp depositional system sequence 1 is dominated by conglomerates and marls in sequence 2 and sequence 3 carbonate deposits dominate in the inner ramp whereas siliciclastics preferentially occur in the middle and outer ramp bryomol carbonate sediments occur in all sequences whereas rhodalgal carbonates are restricted to sequence 3 in bays protected from siliciclastic influx rhodalgal deposits formed under transgressive conditions a bryomol factory occurs in zones of continuous siliciclastic supply this distribution results from facies partitioning during the flooding of the ronda basin which has a rugged and irregular relief embayments were protected from siliciclastic influx and provided regions with less hydraulic energy

siliciclastic foundations of quaternary reefs in the southernmost belize lagoon british honduras analyses of a closely spaced lattice of seismic profiles from the southernmost belize lagoon combined with logs of nearby drill holes reveal that the quaternary late pleistocene plus holocene reefs and carbonate sediments are growing on siliciclastic sediments which have an alluvial and delta like morphology the residual relief of these coastal plain deposits localized initial coral growth or an accumulation of calcareous skeletal material favored sites for these were elevations such as levees and bars of remnant channels and deltaic lobes

classification of large scale subaqueous bedforms a new look at an old problem sepm bedforms and bedding structures abstract a symposium entitled classification of large scale flow transverse bedforms was convened at the 1987 mid year meeting of sepm in austin texas with the purpose of examining the problems involved in classifying large subaqueous flow transverse bedforms developed in fluvial intertidal and marine environments and recommending changes in nomenclature the consensus of the participants is that despite the wide spectrum of morphologies of large scale flow transverse bedforms excluding antidunes they all occupy a similar position in the lower flow regime sequence between ripples and upper plane bed the wide variety of forms is a reflection of secondary effects such as channelization fluctuating water levels and unsteady and reversing flows the bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1 m to over 1 000 m the symposium panel proposes therefore that they should have only one name dune dune is preferred as it has historical precedence over other terms in use such as megaripple and sand wave the term dune should be modified by rimary descriptors of shape i e 2 d or 3 d and size based on spacing small 0 6 5 m medium 5 10 m large 10 100 m or very large 100 m and the adjective subaqueous when it is important to distinguish them from eolian dunes the panel recommends a morphologically based classification that is descriptive with an underlying genetic rationale second order descriptors such a sediment size and bedform superposition may be used to describe more thoroughly the variety of subaqueous dunes in nature

tidal dunes and sand waves in deep outer shelf environments bajocian se jura france abstract in most studies tidal deposits are associated with shallow water coastal areas in contrast this paper illustrates an ancient deep water tidal environment located on the outer part of the jura shelf the bajocian mid jurassic sediments are composed of fine grained marly limestones that include several crinoidal limestone bars these bioclastic bars are formed by stacked dunes and sand waves showing sedimentary structures typical of tidal environments in order to interpret the sedimentology of the crinoidal limestones the hydrodynamic behavior of crinoidal particles was investigated derived from a sedimentological petrographical and paleontological approach of the area the results indicate that dunes and sand waves formed on the outer shelf at a depth of about 100 150 m under the occasional influence of tidal currents interpretation of seismic reflection data indicates a shelf edge position located about 15 km to the se

pliocene quaternary transpressional evolution of the anzi calvello and northern s arcangelo basins basilicata southern apennines italy as a consequence of deep seated fault reactivation abstract in this paper we report the results of a study of the plio pleistocene anzi calvello basin and the northern sector of the s arcangelo basin southern apennines italy our work suggests that the evolution of the anzi calvello basin is related to the activity of a deep seated roughly nne trending dextral transpressional fault zone camastra transcurrent fault zone ctfz structural control of sedimentation by this structure is indicated by the geometry of the unconformity bounded stratigraphic units as well as by the deformation of the basin fill en echelon n s trending thrusts n to ne trending dextral transpressional faults and nw to nnw striking folds affecting the substratum constitute the surface response to lateral displacement along the ctfz the s arcangelo basin is bounded to the north by a deep seated roughly wnw nw trending sinistral transpressional structure valsinni lateral ramp vlr that terminates northwestward against the ctfz at the surface the vlr is dominated by back thrusts and by transpressional fault zones the vlr has been interpreted as the sinistral lateral ramp of the large scale valsinni thrust anticline and it is inferred to have strongly controlled local deposition within the s arcangelo basin the deep seated structures ctfz and vlr probably represent reactivated pre existing normal and transfer faults affecting the rigid apulian platform that were generated during passive margin evolution as well as during the flexural bending of the apulian lithosphere during the pliocene pleistocene these structures were reactivated as lateral ramps accommodating the thrusting within the apulian platform transpression along the lateral ramps in the apulian platform propagated upwards through the nappe pile giving rise to a complex surface structural pattern and the local development of flower like structures

flume experiments on lower flow regime bed forms in coarse sand thirty five runs were made in a recirculating channel 11 5 m long and 0 92 m wide with four sizes of very well sorted coarse sand to study geometry migration and hydraulics of bed configurations in equilibrium with steady uniform open channel flows at flow depths of about 15 cm equilibrium energy slope and sediment transport rate were measured as well bed phases kinds of bed configurations studied were ripples low flow velocity flat beds with sand transport and dunes identical with megaripples current velocities in none of the runs were high enough for development of an upper flow regime flat bed a plot of mean flow velocity versus sand size for all the runs shows that at low flow velocities the ripple field narrows with increasing sand size and pinches out at about 0 7 mm the field for flatbed transport narrows with decreasing sand size and pinches out at about 0 5 mm just above the ripple field at high flow velocities dunes are the stable phase for all sand sizes studied dune configurations are divided into two subphases two dimensional dunes 2d dunes with fairly straight continuous even crests and no strong localized scour in troughs are formed at relatively low flow velocities three dimensional dunes 3d dunes with strongly sinuous discontinuous uneven crests and strong localized scour pits in troughs are formed at relatively high flow velocities 3d dunes tend to be higher than 2d dunes have larger height spacing ratios and show less variability in height spacing and migration rate dunes can be viewed as kinematic shock waves differences between 2d dunes and 3d dunes lie in the differing importance of shock wave coupling and of sand transport in bed form troughs in both geometry and hydraulic ralationships the 2d dunes and 3d dunes in our flume runs correspond to the relatively regular megaripples at low flow velocities and relatively irregular megaripples at high flow velocities described by other authors from intertidal environments

the use of settling velocity in defining the initiation of motion of heavy mineral grains under unidirectional flow the results of critical threshold experiments on four commonly occurring heavy minerals are described the data are presented in conjunction with comparable quartz data using the non dimensional shields curve and the movability number u ws the results indicate that critical shear stress for material of high density is overestimated by use of shields curve under smooth boundary conditions grain settling velocity is found to be a good indicator for the critical shear stress for grains of a wide density range a physical explanation for the results is proposed

mixed siliciclastic and carbonate sediments a proposed first order textural and compositional classification sediments that are composed of mixtures of siliciclastic and carbonate material occur in both the modern and the ancient to date there is no commonly used classification of this type of sediment a descriptive first order classification system is proposed here that is applicable to most mixed sediments and their lithified equivalents the sediments are composed of four components 1 siliciclastic sand sand sized quartz feldspar etc 2 mud mixtures of silt and clay 3 allochems carbonate grains such as peloids ooids bioclasts and intraclasts 20 m in size and carbonate mud or micrite 20 m in size these components define a tetrahedra whose subdivision produces eight general classes of mixed sediment the name of a class reflects both the dominant grain type and the most abundant antithetic component for example a rock that contains greater than 50 siliciclastic material of which most is sand sized and subordinate allochems is termed an allochemic sandstone other rock names include micritic sandstone allochemic and micritic mudstone sandy or muddy allochem limestone and sandy or muddy micrite prefixes and adjectives can be added to these terms to include dolomitic sediments conglomeratic textures and biogenic constituents

lowstand carbonates highstand sandstones the sedimentary facies sediment dynamics and sequence architecture of modern high energy shelves in the mid and high latitudes are largely governed by wave abrasion processes cool water carbonates may form there if the influx and or net accretion of siliciclastics is kept at a minimum little dilution of the carbonate produced in situ is generally promoted by a wide epicontinental shelf subdued topography of the adjacent mainland the predominance of limestone outcrops and an arid climate the aforementioned requirements are rarely met and thus will automatically lead to the formation of mixed siliciclastic cool water carbonates such an example is found in the early to mid miocene lagos portimao formation algarve s portugal which formed on a narrow high energy shelf of the atlantic ocean that was bounded by a mountain range the sediments of the formation consist of fossiliferous sandstone fs shell beds and rhodolith blankets along strike the stratification of the formation is monotonous for tens of kilometres and well exposed in coastal cliffs whereas no outcrops of dip sections exist the bulk skeletal composition of the sediments is typical for the warm temperate climatic zone various endo and epibenthic bivalves bryozoans coralline algae echinoderms gastropods and large foraminifers heterostegina in some very rare beds a few isolated not framework forming specimens of zooxanthellate corals porites tarbellastrea indicate temporally elevated surface water temperatures close to the lower threshold of the coral reef ecosystem in sandstones the fauna is well preserved and burrowing bivalves are commonly found in life position in limestone beds the state of preservation of the grains ranges from intact to disintegrated and abraded specimens we infer an accumulation of the shell beds through winnowing of fine materials siliciclastic sand and carbonate mud at wave abrasion depth and concentration of calcareous skeletons associated with the subsequent attraction of new epibiota in a complex shell bed the vertical alternation of fossiliferous sandstone and shell beds and in phase variations of the photo index photic biota vs bryozoans and bryozoan index bivalves vs bryozoans is envisaged to document variations of water depth and sea level sandstone units built up when wave abrasion depth wad rose above the sea floor during tst and early hst whereas the shell beds formed during lst when the wad for sand intersected with the sea floor clastic sediments were probably brought on the outer shelf during early transgression and by longshore currents sea level signatures inferred in the mixed siliciclastic cool water carbonate shelf setting of s portugal therefore significantly deviate from conventional concepts of carbonate sequence stratigraphy which were developed for flat topped platforms successful interpretations of ancient mixed sequences must therefore take into consideration the processes of production concentration and accretion of the carbonate sediments

settling velocities and entrainment thresholds of biogenic sands shell fragments under unidirectional flow settling velocities and entrainment thresholds of biogenic sedimentary particles under unidirectional flow conditions are derived on the basis of settling tower and laboratory flume experiments material consisting predominantly of equant blocks shell fragments of cerastoderma edule density s 2800 kg m 3 or of mica like flakes and elongate rods mytilus edulis fragments s 2720 kg m 3 are used in separate series of experiments differences in the measured settling and threshold properties are related primarily to particle shape the selection of a characteristic length scale for non spherical grains is investigated by comparing two approaches used to define the grain size d of the sediment samples grain settling and sieve analysis that are used to derive data for the threshold criteria in terms of the shields and movability diagrams the empirical curves effectively predict the threshold conditions for any grain shape provided that grain size is defined in terms of grain settling velocity however a functional distinction is made between the characteristic hydraulic grain size defined by grain settling for grain transport applications and the actual physical grain size defined by sieve analysis

growth processes and melange formation in the southern apennines accretionary wedge abstract the southern apennines owe their present geometry to the subduction of an apulian continental lithospheric slab and are thus best interpreted as an accretionary wedge southward the apenninic thrust front branches on to the still active ionian wedge which is related to the present calabro sicilian subduction the interpretation of conventional seismic reflection profiles and exploration wells combined with geologic field studies biostratigraphy and structural geology provide constraints for a geodynamic model for the post messinian growth of the apenninic prism our model for the apennines is a good analogy for submerged oceanic accretionary prisms in both instances features such as out of sequence thrusts underplating and duplexes are viewed as processes to explain the thickening of accretionary wedges syntectonic terrigenous deposits have accumulated in the synclines developed above the flats of pliocene thrust faults these depocenters represent piggy back basins younger accretion at the eastern border of the accretionary wedge has led to a progressive uplifting and tilting of the already emplaced thrust sheets including a continous westward migration of the depocenters in the piggy back basins during pliocene and early quaternary times a contrary west to east migration of the depocenters locally occurred where preexisting flats of pliocene thrust faults have been refolded rather than only being rotated dewatering processes and effects of overpressures on undercompacted sediment deformations can also be studied in the southern apennines melanges and broken formations form an important component of the trench apparently restricted to the base of tectonic nappes listric normal faults are a major structural element which preserves in combination with the erosion of topographic highs and resedimentation in the piggy back basins a uniform geometric shape critical taper for the prism the age and location of these distensive or gravitational effects are also discussed

modelling tidal current induced bed shear stress and palaeocirculation in an epicontinental seaway the bohemian cretaceous basin central europe lower to middle turonian deposits within the bohemian cretaceous basin central europe consist of coarse grained deltaic sandstones passing distally into fine grained offshore sediments dune scale cross beds superimposed on delta front clinoforms indicate a vigorous basinal palaeocirculation capable of transporting coarse grained sand across the entire depth range of the clinoforms ca 35 m bi directional alongshore oriented trough cross set axes silt drapes and reactivation surfaces indicate tidal activity however the bohemian cretaceous basin at this time was over a thousand kilometres from the shelf break and separated from the open ocean by a series of small islands the presence of tidally influenced deposits in a setting where co oscillating tides are likely to have been damped down by seabed friction and blocked by emergent land masses is problematic the imperial college ocean model a fully hydrodynamic unstructured mesh finite element model is used to test the hypothesis that tidal circulation in this isolated region was capable of generating the observed grain size distributions bedform types and palaeocurrent orientations the model is first validated for the prediction of bed shear stress magnitudes and sediment transport pathways against the present day north european shelf seas that surround the british isles the model predicts a microtidal to mesotidal regime for the bohemian cretaceous basin across a range of sensitivity tests with elevated tidal ranges in local embayments funnelling associated with straits increases tidal current velocities generating bed shear stresses that were capable of forming the sedimentary structures observed in the field the model also predicts instantaneous bi directional currents with orientations comparable with those measured in the field overall the imperial college ocean model predicts a vigorous tide driven palaeocirculation within the bohemian cretaceous basin that would indisputably have influenced sediment dispersal and facies distributions palaeocurrent vectors and sediment transport pathways however vary markedly in the different sensitivity tests accurate modelling of these parameters in this instance requires greater palaeogeographic certainty than can be extracted from the available rock record

nearshore and alluvial facies in the sant llorenc del munt depositional system recognition and development abstract the eocene sant llorenc del munt fan delta complex forms a part of the coarse grained foreland basin fill of the southeastern margin of the ebro basin it was sourced from the rising catalan coastal range in the se and shows an overall northwesterly progradation during a time period of approximately six million years coarse clastic deposits coarse sands and gravels dominated this fan delta whereas finer grained sands silts and muds were deposited laterally off active sedimentation sites or in the more marine area depositional processes were clearly influenced by the high sediment input giving a dominance of sediment gravity flow deposits the sediments studied have been grouped into four distinct facies belts including coastal plain proximal fan delta front distal fan delta front and fan delta slope sediments respectively the facies belts combine to form the nearshore and coastal alluvial reaches of the fan delta system developed during a transgressive phase lasting some 50 000 years

selective grain entrainment by a current from a bed of mixed sizes a reanalysis the selective entrainment of grains by a current from a bed of mixed sizes and densities is important to grain sorting processes that lead to the formation of placers in sands and to armored beds in gravels existing field and laboratory measurements of selective entrainment depart systematically from the standard threshold curves such as that of shields which are based on experiments with nearly uniform grain sizes entrainment measurements from beds of mixed sizes form trends which obliquely cross the threshold curves for uniform grains the crossing point being roughly at the median diameter of the size distribution due to this crossover the coarser size fractions of the distribution require lower flow stresses for their entrainment than if they formed uniform beds while the finer size fractions require higher stresses than uniform beds with deposits having medians in the range of medium sand through gravel the larger the individual particle within the mixed sizes the greater the flow stress required for its entrainment in this case the smaller grains are preferentially entrained possibly leading to bed armoring in contrast if the median is in the fine to medium sand range the smallest grains in the bed of mixed sizes are the most difficult to entrain due to sheltering by the larger grains where grain density is also involved this sorting can lead to the formation of placers a variety of empirical relationships is considered to quantify the evaluation of selective entrainment from deposits of mixed sizes but no single formulation is satisfactory for all data sets

current challenges to esr dating abstract electron spin resonance dating is applicable to a wide range of materials found at quaternary sites and which can generally be assured to exhibit zero signals at the time to be dated t 0 local inhomogeneity in external dose rates may contribute to dispersion in apparent dates but average dates may still be good estimates of site ages testing of u uptake models by u series measurements shows that both early and continuous uptake can occur possibly even in the same site problems of signal lifetime determination and diagenesis are reviewed

wave formed structures and paleoenvironmental reconstruction clifton h e and dingier j r 1984 wave formed structures and paleoenvironmental reconstruction in b greenwood and r a davis jr editors hydrodynamics and sedimentation in wave dominated coastal environments mar geol 60 165 198 wave formed sedimentary structures can be powerful interpretive tools because they reflect not only the velocity and direction of the oscillatory currents but also the length of the horizontal component of orbital motion and the presence of velocity asymmetry within the flow several of these aspects can be related through standard wave theories to combinations of wave dimensions and water depth that have definable natural limits for a particular grain size threshold of particle movement and that of conversion from a rippled to fiat bed indicate flow velocity limits the ratio of ripple spacing to grain size provides an estimate of the length of the near bottom orbital motion the degree of velocity asymmetry is related to the asymmetry of the bedforms though it presently cannot be estimated with confidence a plot of water depth versus wave height h h diagram provides a convenient approach for showing the combination of wave parameters and water depths capable of generating any particular structure in sand of a given grain size natural limits on wave height and inferences or assumptions regarding either water depth or wave period based on geologic evidence allow refinement of the paleoenvironmental reconstruction the assumptions and the degree of approximation involved in the different techniques impose significant constraints inferences based on wave formed structures are most reliable when they are drawn in the context of other evidence such as the association of sedimentary features or progradational sequences

mixed carbonate siliciclastic sedimentation on a tectonically active margin example from the pliocene of baja california sur mexico bioclast rich coarse grained deposits in the pliocene loreto basin provide a record of mixed carbonate and siliciclastic sedimentation at the steep hanging wall margin of this small fault controlled basin sedimentary facies consist of sand to gravel sized carbonate debris mixed with volcaniclastic sand and gravel in a proximal to distal facies tract that includes matrix rich and matrix poor shelly conglomerate impure calcirudite and calcarenite mixed composition turbidites and bioturbated calcarenitic sandstone carbonate material was produced by mollusks and other benthic organisms on a narrow high energy shelf and mixed with volcaniclastic sand and gravel in cross shelf channels these mixtures were transported down a steep subaqueous slope by debris flows grain flows and turbidity currents forming foresets and bottomsets of marine gilbert type deltas this style of mixed carbonate siliciclastic sedimentation has not been documented in detail elsewhere but should be locally abundant in the stratigraphic record of fault bounded basins particularly those with cool or nutrient rich waters that support relatively few binding and framework building faunas recognition of similar facies in other settings can provide useful insights into ancient conditions of carbonate production oceanography climate and tectonics

pleistocene strike slip tectonics in the lucanian apennine southern italy structural studies carried out in the lucanian apennines southern italy show that strike slip faulting was the principal mode of deformation of this area during middle upper pleistocene time w nw to e se trending left strike slip fault systems dissect the entire apennine mountain belt and affect the preexisting thrust geometry strike slip faults activated by a roughly e w shortening are characterized by different geometries representing the surface response to lateral motion occurring along deep seated structures the occurrence of different structural patterns which characterize different segments of strike slip system is related to 1 the depth of a major decoupling surface which separates the upper tectonic multilayered horizon apennines thrust belt system from the lower rigid horizon apulian belt in which strike slip structures have originated and 2 the geometric relationships between the strike slip faults and the thrust belt pattern which characterize the upper horizon the different segments of the strike slip system are interpreted as internal deformation developed within a crustal shear zone this zone which corresponds to the boundary between the apulian block and the apennine chain is characterized by sinistral movement as a response to the northwesterly convergent motion of the african plate with respect to europe

biocalcarenite and mixed cool water prograding bodies of the mediterranean pliocene and pleistocene architecture depositional setting and forcing factors

experiments on the entrainment threshold of well sorted and poorly sorted carbonate sands few studies have examined the hydrodynamic behaviour of carbonate sediments the data presented here are the result of preliminary research on entrainment in well and poorly sorted carbonate sands experiments were performed using naturally occurring sediments in a tilting recirculating freshwater flume results indicate that when of similar size shape and density the transport threshold of carbonate sands is similar to that of quartz however owing to their lower density and often platy or irregular shape skeletal sands require a lower shear stress to initiate transport because the density of carbonate particles may increasingly vary with grain size the threshold of motion in coarse carbonate grains may differ more markedly from that of quartz in poorly sorted samples results show that the coarse grained constituents move before the finer grained components grain properties and boundary layer dynamics are believed to explain this phenomenon rollability of the larger grains combined with physical trapping and immersion within a low velocity sublayer are believed to prevent finer particles from moving given the appropriate sediments and flow conditions it may therefore be possible to deposit and preserve fine grained sediments in a flow regime typically thought to transport such materials

transgressive surfaces of erosion as sequence boundary markers in cool water shelf carbonates abstract although sequence stratigraphy was first conceptualized in and applied to siliciclastic successions its methodology and concepts are applicable to the carbonate regimen provided that potential modifications to the existing models are appreciated that take into account the specificities of carbonate systems we demonstrate that some properties inherent to isolated i e continent detached shallow water temperate carbonate systems including their typical low diagenetic potential due to the prevalance of calcitic mineralogies the critical role exerted by storm waves and tidal currents on sediment dynamics e g shedding of sediments at wave abrasion depth during highstand and lowstand conditions and uneven sea bed topographies cause both the genesis and preservation of subaerial unconformities to be uncommon thereby rendering their use as sequence boundaries inappropriate instead transgressive surfaces of erosion tses that formed as wave base shifts upwards during early rise of relative sea level are readily identifiable in the field extensive and by their very nature are preserved in the rock record typically at the base of upward deepening stacked facies in pliocene cool water carbonate successions from new zealand the tses are characterized by starved sedimentation and burrowed network development and are overlain by coarse bioclastic shoreface sediments and shell beds in most cases the surfaces top truncate shoaling upward deposits but also deepening upward stacking facies in places emersive events rarely correspond to actual physical surfaces but diagenetic evidence preserved beneath tses indicates that occasionally subaerial surfaces had previously developed and were later modified into tses therefore we propose that tses are the most adequate unconformities to define high order depositional sequences 20 250 ka in the studied successions because by contrast with emersion surfaces their formation and preservation are not dependent upon cool water sedimentary facies and mineralogy and are favoured by the dynamics of the setting i e wave base shift and accommodation creation during relative sea level rise

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

structural styles in the frontal zones of the southern apennines italy an example from the molise district structural interpretation of available geological and geophysical data from the molise area southern italy demonstrates that the frontal zones of this sector of the apennines are characterized by a threefold zoneography defined by distinct structural styles resolved geometry of both pellicular and deep seated structures and their relationships constrain possible reconstructions for the undeformed pre miocene southeastern margin of the afro adriatic continent and its neogene deformation history identification of peculiar structural associations in the foreland foredeep complex and reinterpretation of relevant stratigraphic data suggest that deformation in this sector of the apennines has already reached the most external apulian domains and is possibly migrating at present toward the currently active adriatic foredeep of the molisan thrust system

piggyback basin development and thrust belt evolution structural and palaeostress analyses of plio quaternary basins in the southern apennines abstract in southern italy structural analysis of the intramontane pliocene quaternary terrigenous basins of sant arcangelo and ofanto shows that they are piggyback basins the recent uplift of the southern apennines provides good conditions for carrying out detailed studies of palaeostresses in relation to structure and sediment accumulation in such piggyback basins we demonstrate that in the pleistocene sant arcangelo marine basin a single n70 compression induced a complex pattern of folds and strike slip faults in contrast the older pliocene ofanto basin reveals a polyphase history characterized by successive tilts and palaeostresses according to different compressions in both basins compressional stresses are syn depositional the geometry of the sedimentary infill of these basins provides information on the thrusting activity in terms of location geometry and age we point out that in addition to sedimentary and structural studies including interpretation of seismic reflection data palaeostress analyses provide a valuable tool for deciphering development and evolution of compressional basins in a fold and thrust belt

investigation of organo carbonate associations in carbonaceous chondrites by raman spectroscopy abstract carbonates record information regarding the timing nature and conditions of the fluids circulating through asteroid parent bodies during aqueous alteration events determining carbonate abundances and their relationships with organic matter improves our understanding of the genesis of major carbonaceous components in chondritic materials in this study five cm2 carbonaceous chondrites cm2 2 nogoya cm2 3 jbilet winselwan cm2 5 murchison cm2 santa cruz and cm2tii wisconsin range 91600 were studied with raman spectroscopy carbonates were identified in these meteorite samples by the distinctive raman band in the 1100 cm 1 region representing the symmetric stretching vibration mode 1 of the co 3 2 anion carbonates identified in the meteorite samples are all calcite with the exception of a single dolomite grain in nogoya the v 1 positions of the cm calcites are 2 3 cm 1 higher than in pure calcite which suggests that they contain significant impurity cations typical graphitic first order d and g bands were identified in the meteorite matrix as well as in 25 of the analyzed carbonate grains from the raman results we postulate that the carbonates might not have formed under equilibrium conditions from a single fluid the first generation of carbonate is interpreted to have formed from highly oxidized fluids that led to the oxidation of organic matter om and produced carbonates that are om barren the second generation of carbonate was formed from a more evolved aqueous fluid with the presence of om the raman parameters of the organics in carbonates clearly deviate from the matrix om which suggests that the carbonate organics contain very different carbonaceous components that are distinct from the typical amorphous om of the cm matrix the occurrence of different generations of carbonate in close proximity may be partly responsible for the wide range in estimated ages of carbonates in carbonaceous chondrites reported in previous studies

the record of tidal cycles in mixed silici bioclastic deposits examples from small plio pleistocene peripheral basins of the microtidal central mediterranean sea the pliocene pleistocene peripheral marine basins of the mediterranean sea in southern italy from basilicata and western calabria to northern and eastern sicily represent tectonically formed coastal embayments and narrow straits here units of cross stratified mixed silici bioclastic sand 25 to 80 m thick record strong tidal currents the central mediterranean sea has had a microtidal range of ca 35 cm and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out of phase reversal of the tidal prism in narrow straits linking the tyrrhenian and ionian basins the siliciclastic sediment was generated by local bedrock erosion whereas the bioclastic sediment was derived from the contemporaneous foramol type cool water carbonate factories the cross strata sets represent small to medium sized 10 to 60 cm thick two dimensional dunes with mainly unidirectional foreset dip directions these tidalites differ from the classical tidal rhythmites deposited in mud bearing siliciclastic environments firstly the foreset strata lack mud drapes and instead show segregation of siliciclastic and bioclastic sand into alternating strata secondly the thickness variation of the successive silici bioclastic strata couplets measured over accretion intervals of 2 to 3 m and analysed statistically reveal only the shortest term diurnal and semi diurnal tidal cycles thirdly the record of diurnal and semi diurnal tidal cycles is included within the pattern of neap spring cycles differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea with the tidal currents locally enhanced in peripheral basins it is suggested that this particular facies of mud free silici bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub tidal environment of straits and embayments and the shortest term tidal cycles

biofilm related calcification sediment trapping and constructive micrite envelopes a criterion for the recognition of ancient grass bed environments micrite envelopes are a common feature in carbonate sediments and are typically associated with the micrite filling of borings produced by microendolithic organisms these are referred to as destructive micrite envelopes and have long been recognized as reflecting an important early diagenetic process recent analysis of sediments collected from back reef environments at discovery bay north jamaica however has demonstrated envelope formation on the surfaces of carbonate grains clearly distinct from the micrite filling of microborings such constructive envelopes occur almost exclusively in sediments from grass bed environments and are always intimately associated with biofilms comprising abundant mucilage cyanobacteria bacteria and diatoms it is suggested that these envelopes represent a product of both biologically mediated micrite precipitation occurring within the biofilm mucilage and around the biofilm components i e cyanobacteria and diatoms and associated trapping of carbonate mud and fine grained sediment their recognition only within grass bed sediments may enable their use as a diagnostic feature of grass bed environments or vegetation stabilized substrates in the rock record

anatomy of a transgressive lag panther tongue sandstone star point formation central utah the panther tongue of the star point formation in central utah contains a variety of transgressive lag deposits that when mapped regionally show a sensitive dependence upon pre existing topography of the palaeoshoreline the panther tongue consists of a coarsening upward sandstone wedge that prograded into the western interior seaway during late cretaceous santonian time high resolution sequence stratigraphic analysis revealed that this member was deposited during the long distance 50 km regression and transgression of a delta into shallow marine environments containing basal highstand forced regression lowstand and transgressive systems tracts based on grain size clast composition lateral extent and stratigraphic position the coarse sandstones on top of the panther tongue were classified into four types 1 simple 2 dispersed 3 oxidized and 4 local lags the simple lag is composed of dark grey coarse sandstone with oyster fragments and shark teeth this lag is typically extensively bioturbated and massive laminated and cross bedded units are also common this type of coarse sandstone is interpreted as a typical transgressive lag the dispersed lag differs in that it contains abundant mud and commonly occurs as multiple beds in thick intervals of muddy sandstone mixing of bay estuarine and shallow marine mud with simple lag sand may be responsible for deposition of this type of coarse sandstone the oxidized lag is distinctive in its reddish colour with extensive bioturbation and is commonly overlain by a simple lag the local lag is composed of thin bedded dark grey coarse sandstone occurring locally between the mouth bar and distributary channel the variation in types grain size and bed thickness of the coarse grained lags was mainly controlled by antecedent topography as suggested by immediately underlying lithofacies relatively thick 30 cm simple lags are present on top of mouth bar sandstones whereas dispersed lags are common on top of the distributary channel sandstone and in bay estuarine and shallow marine mudstones erosion of topographic highs mouth bar resulted in relatively thick accumulation of simple lags in topographic low areas such as distributary channel estuary bay and shallow marine environments fine grained muddy sands that were eroded from the nearby topographic highs were redeposited intermittent storm waves transported coarse sands both landward and seaward forming a dispersed lag the net effect was reworking of local topographic relief during overall transgression forming an apparently planar transgressive surface of erosion

pliocene pleistocene sequences bounded by subaerial unconformities within foramol ramp calcarenites and mixed deposits salento se italy nine discrete metre scale sequences of early pliocene to middle pleistocene age were deposited in the small novoli graben salento peninsula puglia s italy they consist of carbonate and mixed carbonate siliciclastic sediments deposited on a slowly subsiding foreland ramp skeletal concentrations and intervening less fossiliferous intervals have been examined to provide information on major environmental parameters and infer the dynamics of their changes taphonomic and palaeoecological analyses indicate that storm induced waves and currents reduced sediment input and settling behaviour of components were the main factors controlling the features of the various shellbed types the concentrations were formed below fair weather wave base in low stress inner to outer shelf environments and are often associated with surfaces or intervals that are characterized by sedimentary condensation vertical change in the fossil content within individual cycles indicates water depth changes that were parallel to climatic fluctuations hence may result from glacio eustatic sea level changes most sequences are bounded by subaerial karstic unconformities because of the regional setting of low subsidence rate the record of the relative sea level fluctuations is incomplete episodes of subaerial exposure and concomitant effects of vadose diagenesis are documented by i diagenetic changes leading to hardening of unconformity horizons ii local subvertical solution pits developed in the vadose zone below unconformity surfaces iii networks of polygonal cracks below unconformities and iv infilling of solution pits and polygonal cracks with vadose silt and marine sediment inwashed during transgressions following the subaerial stages lower sequences are characterized by tighter cementation and significant increase in moldic and vuggy porosity due to superimposition of the diagenetic effects of repeated high amplitude sea level fluctuations

palinspastic restoration and paleogeographic reconstruction of the peri tyrrhenian area during the neogene abstract this paper presents the results of research carried out on the paleogeographic and geodynamic post collisional evolution of the peri tyrrhenian area from the southern alps to sicily during this post collisional evolution a back arc area thrust belt foredeep system developed in which the following tectono sedimentary zones can be distinguished from the external to the internal ones the foreland zone connected to the foredeep through a slope generally controlled by normal faults the foredeep an assymmetric depression with strong subsidence related to the compressional activity of the thrust zone the chain whose outward migration from the late oligocene onward was discontinuus with important stages of crisis partially connected to the mechanical response of different crustal thicknesses existing in the foreland the discontinuous satellite basins developed within the thrust belt the back arc basins developed in the inner part of the chain where the superposition of the extensional tectonics over previous compressional domains causes the fragmentation of the thrust belt leading to its destruction according to this model seven palinspatic maps are discussed regarding the following time intervals late oligocene 25 24 m y burdigalian 22 20 m y langhian 17 16 m y serravallin 15 13 m y tortonian 10 9 m y late messinian 5 5 5 3 m y and early pliocene 5 3 4 6 m y during five of these time intervals significant geodynamic modifications occurred in the whole peri tyrrhenian area leading to paleogeographic changes in any case the geodynamic evolution of the whole area seems clearly controlled by the activity of important bundles of tectonic lines transversal to the chain which in the same time interval in the outermost part of the thrust belt separated areas with different values of shortening and in tthe most internal zones separated segments having different amount of extension these tectonic lines certainly have a crustal significance and have probably acted along previous formed discontinuities