synchronous detachment folds and coeval sedimentation in the prepyrenean external sierras spain a case study for a tectonic origin of sequences and systems tracts this paper reports on the structural and sedimentary evolution of the middle to late eocene of the prepyrenean external sierras southern pyrenees spain the initiation duration and kinematics of a set of growth structures that developed in a shallow marine depositional setting is documented the detailed analysis of the syntectonic marine sediments not only confirms the already known east to west progression of deformation but also reveals the continued growth of the early formed structures as later ones propagate towards the foreland the sedimentary units coevally deposited with these growth structures are arranged in four depositional sequences their boundaries correspond to flooding surfaces which grade basinwards into correlative conformities they are also indicated by the presence of both angular unconformities and onlap geometries each depositional sequence generally consists of two systems tracts the lower one or transgressive systems tract is formed by up to 400 m of azoic marls deposited in outer ramp areas the upper one or highstand systems tract mainly consists of shallow siliciclastic and carbonate facies up to 200 m thick deposited in middle to inner ramp areas these depositional sequences are interpreted to be controlled by regional tectonic pulses an increase of tectonic activity resulted in the flooding of the basin and in the subsequent deposition of a thick succession of nearly azoic blue marls i e transgressive systems tract the overlying highstand systems tract developed following periods of diminished tectonism with the consequent growth and progradation of shallow carbonate platform facies

multikilometer sized reefs built by foraminifera solenomeris from the early eocene of the pyrenean domain s france n spain palaeoecologic relations with coral reefs abstract solenomeris foraminifera reefs of the early ypresian pyrenean gulf were previously mistaken for red algal or incertae sedis algal reefs solenomeris has recently been referred to the acervulinid foraminifera these foraminifera buildups are described in detail and their palaeoecology is discussed the distribution of these reefs within the languedoc basin demonstrates their preference for bathymetric highs of external platforms in common with coral reefs to which they locally succeed during the early ypresian transgression all solenomeris reefs examined are located either at the outer periphery of a lagoon with small operculina or on the external margin of a carbonate platform characterized by various miliolida they extend into deeper waters than the associated coral reefs even in turbid environments unfavourable for encrusting coralline algae the reconstruction of the palaeoecology of solenomeris shows many similarities with corals however corals probably require higher light and oxygen levels especially when present near their northern limit the global distribution of solenomeris reefs can not be established until their correct identifications have been made instead of algal reefs

naticid drilling predation on gastropod assemblages across the k t boundary in rajahmundry india new evidence for escalation hypothesis abstract one of the important and well documented prey predator interactions in the fossil record is drilling predation done by naticid gastropods which diversified during the cretaceous although drilling frequencies showed fluctuating patterns most of the previous studies argued that naticid drilling predation was less intense during the cretaceous and the modern values were achieved since the paleocene we here present a new dataset of naticid drilling predations involving 31 929 gastropod specimens from the latest maastrichtian infratrappean bed in rajahmundry southern india these specimens belonged to 40 species of 20 families thus representing a spectacular gastropod diversity that was not known until recently from this region we examined 5884 complete or near complete specimens to quantify naticid drilling predation on this assemblage it appeared that drilling frequency was significantly higher from all previous cretaceous values this was true for both assemblage level and lower taxon level results along with high successful drilling and low unsuccessful drilling frequencies site and size stereotypy of drillholes suggest that naticid predators were highly efficient even in the cretaceous predators were prey selective and there was poor correlation between relative abundance and drilling frequency of prey taxa the present maastrichtian assemblage underlies the k t mass extinction level drilling frequency was zero in the straddler prey community in the intertrappean bed found immediately above the k t boundary the absence of any drillhole in surviving prey taxa may be due to sudden reduction in abundance of escalated predators although some prey taxa e g cerithiids continued this emphasizes the role of mass extinction in disrupting predator prey interaction we conclude that naticid drilling induced escalation was already established during the cretaceous and the present find extends the paleobiogeography of naticid predation which was previously reported from the western world up to india

mesozoic seafloor spreading between iberia europe and north america abstract a new earliest cretaceous palaeogeographic reconstruction for the iberian north american and european plates is proposed which attempts to clarify some of the outstanding reconstruction problems in the region from the time of initial opening to the time of magnetic anomaly 34 the instantaneous motion of iberia can be described by a single rotation about a pole off the southwest coast of france in contrast to many previous proposals the new reconstruction places galicia bank east of flemish cap but satisfies all the constraints imposed by palaeomagnetic studies deep sea drilling project results and magnetic anomaly and ocean continent boundary identifications

fast approximate 1d modelling and inversion of transient electromagnetic data a novel fast and approximate forward modelling routine for time domain electromagnetic responses is presented it is based on the separation of the forward problem into a configuration independent part mapping conductivity as a function of depth onto apparent conductivity as a function of time and a configuration dependent part i e the half space step response the response of a layered model is then found as the half space response for a half space conductivity equal to the apparent conductivity the mapping is ten times faster than traditional accurate forward modelling routines and through stochastic modelling it is found that the standard deviation of the modelling error is 0 7 the forward mapping lends itself to integration in a modern state of the art inversion formulation in exactly the same way as traditionally computed responses and a field example is included where inversion results using the approximate forward response are compared with those of an accurate forward response for helicopterborne transient electromagnetic data in addition to being used in its own right in inversion of transient data the speed and accuracy of the approximate inversion mean that it is well suited for quality control and fast turnaround data delivery of survey results to a client it can also be used in hybrid inversion formulations by supplying initial iterations and high quality derivatives in an inversion based on accurate forward modelling

facies architecture and geometry of a prograding carbonate ramp during the early stages of foreland basin evolution lower eocene sequences sierra del cadi se pyrenees spain this paper describes the early eocene sedimentological evolution of the sierra del cadi carbonate platform during the early development of the southeastern pyrenean foreland basin spain the platform developed as a south facing ramp system located either across the southern margin of a growth anticline within the newly formed basin or along the axial margin of the basin sequences i and ii both comprise basal transgressive systems tracts tsts dominated by a thick succession of outer ramp lime mudstones shallowing upwards into a highstand systems tract hst of mid and inner ramp bioclastic shoals sand banks and lagoonal deposits in sequence iii the tst comprises a thick wedge shaped unit of east to west backstepping inner and mid ramp nummulites shoals and lagoonal deposits progressively overlain by a thick succession of outer ramp lime mudstones and marls of the hst no lowstand systems tracts are recognized sequence boundaries correspond to flooding surfaces which grade basinwards into correlative conformities interpreted to represent the onset of high tectonic activity in the orogenic wedge and resulting high flexural subsidence across the foreland and drowning of inner ramp regions tsts represent continued high flexural subsidence creating accommodation space infilled by high rates of outer ramp sediment accumulation in sequences ii and iii tsts show a pronounced west to east thickening interpreted to represent the effect of variable subsidence across the margins of an uplifting growth anticline within the otherwise flexurally subsiding foreland prograda tional successions that characterize hsts developed during periods of reduced tectonic subsidence both within the foreland and in the orogenic belt allowing the growth and expansion of carbonate ramp facies belts

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

provenance analysis of muddy sandstones abstract a new approach to determine the precursor grains of detrital and diagenetic clay in sandstones requires a reiterative use of optical microscopy and electron beam microanalysis excluding muddy sandstone successions from analysis of the siliciclastic fill of a basin may lead to incomplete if not erroneous provenance interpretation because of biased samping of the sediments to minimize problems inherent in muddy sandstones we have combined a two tier optical modal analysis with energy dispersive x ray analysis edxa to identify precursors of clay this is a new method of point counting and estimating the mineral compositions of muddy sandstones because we apply the principle of identifying the mineral under the cross hair albeit on a micron scale we call this the new or modified g zzi dickinson method calculations of mass balance type using the results of this new method may be performed to reconstruct the original composition of the parental detrital material we have used muddy siliciclastic rocks outcrop and core samples of siltstones and sandstones from the oligocene intra arc medicine lodge beds of southwestern montana usa for this study eocene volcanic rocks of the challis region and thrusts that have transported pre cenozoic sedimentary and metasedimentary rocks in this region were the sources of the siliciclastic sediments results of modal analysis by the standard gazzi dickinson method and by the new modified gazzi dickinson method using both optical and edxa on a micron scale plot in different clusters in a qfl diagram our results show that the standard gazzi dickinson method is not truly independent of grain size even in the context of provenance analysis on the other hand the modified version has the promise of achievi g truly mineralogical modal petrologic analysis of detrital rocks of any grain size

optimized fast hankel transform filters in the linear digital filter theory for calculation of hankel transforms it is possible to find explicit series expansions for the filter coefficients a method is presented for optimizing the hankel filters calculated in this way for a certain desired accuracy of computation the sampling density and filter length are minimized by choosing the parameters determining the filter characteristics according to the analytical properties of the input function a new approach to the calculation of the filter coefficients has been developed for these optimized filters the length of the filters may be further reduced by introducing a shift in the sampling scheme

scalloped bank margins beginning of the end for carbonate platforms bathymetric seismic reflection and satellite data have revealed the common existence of a new type of carbonate bank margin scalloped margin throughout the gulf of mexico and the caribbean region these large up to tens of kilometres across irregular convexbankward embayments are interpreted as predominantly erosional features produced by large scale failure of platform margins in tectonically active areas they may be triggered by earthquake shocks whereas in stable regions they may more likely be the result of undercutting by dissolution and or deep water currents scalloped margins are common in the south eastern bahamas this suggests that these relatively small isolated bahama banks may be erosional remnants of once larger platforms the processes that create scalloped margins may result in erosional deep water carbonate basins and potentially the demise and disintegration of carbonate platforms

middle miocene oceanographic event in the eastern gulf of mexico implications for seismic stratigraphic succession and loop current gulf stream circulation analysis of 1 500 km of high resolution single channel air gun seismic reflection profiles correlated with two drill cores demonstrates that the central west florida carbonate ramp slope experienced an oceanographic event in the middle miocene that resulted in a major stratigraphic break or succession of depositional sequences during the long term eustatic sea level rise in the early to middle miocene carbonate shelf margin deposition was characterized by seaward prograding sigmoidal clinoforms that built both laterally and vertically shelf margin sediments were relatively fine grained and rich in dolomite total organics and clay minerals approximately 12 15 m y ago tectonically controlled oceanographic closure of the isthmus of panama and or increased climatic gradients resulted in an intensification of oceanic circulation increased flow velocity of the loop current truncated antecedant clinoforms along the mid miocene shelf margin as the loop current for the first time became a dynamic oceanographic barrier to off shelf sediment transport carbonate deposition along the west florida slope changed dramatically from a series of prograding clinoforms to a pelagic slope front fill system bounded on its landward margin by contour current flow of an invigorated loop current shelf margin sediments presently represented as a condensed sequence became more carbonate rich coarser grained lower in organic content and depleted in dolomite our results suggest that oceanographic events can generate major seismic stratigraphic breaks that result in the succession of depositional sequences and systems along continental margins and that they may be as important as eustatic oscillations our data also suggest that modern loop current gulf stream circulation was initiated in the middle miocene controlled by tectono oceanographic and or climatic processes the challenge now is to identify seismic stratigraphic scale oceanographic events in the rock record differentiate them from eustatic responses and evaluate their paleoenvironmental significance

gravity slide and resedimentation processes in a miocene carbonate ramp hyblean platcau southeastern sicily abstract more than twenty sharp based channel form structures occur in the miocene palazzolo formation carbonates within a distally steepened se sicilian miocene carbonate ramp contemporaneous biota indicate deposition in water depths of 70 150 m fully exposed structures commonly exceed one kilometre along palacostrike their bases are concordant with the host strata but these steepen to 15 in proximity of their margins internal bedding planes generally are concordant with the basal truncation surface the lithologies of the channel fills are similar to the host sediment there is little evidence that these structures are erosional since they contain neither breccias nor turbidites rather they are interpreted as the product of gravitational sliding involving thin detached sheets of consolidated ramp carbonates the resulting irregular topography was draped by redeposited fine grained carbonate sediments once healed and further oversteepened renewed gravity sliding occurred this resulted in a 250 m thick slide dominated succession in a zone 4 km wide located between the outer ramp apron comprised of coralline algal and foraminifera rich sediments and basin margin pelagic marls this phenomenon although unusual in shallow water settings is well known from modern continental slope environments sliding was probably triggered by seismicity in the region associated with two known mesozoic basement faults an alternative hypothesis involving pressure gradient build up along distally steepened ramp zones during storm surges is dismissed as a cause although this mechanism may have facilitated resedimentation of seafloor sediments over the slide zone

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

a survey of current trends in near surface electrical and electromagnetic methods electricalandelectromagnetice emmethodsfornearsurface investigations have undergone rapid improvements over the past few decades besides the traditional applications in groundwater investigations natural resource exploration and geological mapping a number of new applications have appeared these include hazardous waste characterizationstudies precision agricultureapplications archeological surveys and geotechnical investigations the inclusion of microprocessors in survey instruments development ofnewinterpretationalgorithms andeasyaccesstopowerful computers have supported innovation throughout the geophysical community and the e em community is no exception most notable are development of continuous measurement systems that generate large dense data sets efficiently these have contributed significantly to the usefulness of e em methods by allowing measurements over wide areas without sacrificing lateral resolution the availability of theseluxuriantdatasetsinturnspurreddevelopmentofinterpretation algorithms including laterally constrained 1d inversionaswellasinnovative2d and3d inversionmethods taken together these developments can be expected to improve the resolution and usefulness of e em methods and permit them to be applied economically the trend is clearly towarddensesurveyingoverlargerareas followedbyhighly automated post acquisition processing and interpretation to provide improved resolution of the shallow subsurface in a cost effectivemanner

fossil predaceous gastropod borings from nigeria abstract predation of naticids and muricids has been studied in the ameki formation eocene the investigation shows that six types of holes are found in the ameki gastropod and bivalve prey in identifying the borers of a particular hole type the mode of life of the most preferred prey species is used as a diagnostic parameter infaunal prey species are bored by naticids epifaunal prey is bored by muricids the presence of a boss at the base of an incomplete hole and countersunk holes are the additional criteria for identifying naticid borings if the living habits of the preferred eocene ameki prey are used as a criterion to distinguish between naticid and muricid borings then the steepness of holes the presence or absence of correlation between hole size and shell size the bevelled or ragged nature of the outer rim of a hole and the preferred site for boring become less valuable as distinguishing features

middle cambrian carbonate platform collapse southeastern canadian rocky mountains regional erosion features termed megatruncation surfaces at the seaward margin of a middle cambrian carbonate platform in southeastern british columbia are inferred to be the proximal parts of gravity slide scars comparable in scale and morphology to modern examples in the caribbean region the surfaces truncate up to 200 m of outer platform strata and have low angle to near vertical headwalls they can be traced a minimum of 56 km along depositional strike and appear to extend at least 8 km basinward of the platform edge they therefore profoundly affect regional stratigraphy

the chronology of the eocene tectonic and stratigraphic development of the eastern pyrenean foreland basin northeast spain abundant and clearly exposed relationships between structures and syntectonic sedimentary rocks in the southern pyrenees make this area particularly suitable for detailed studies of the sequential development of a collisional orogenic belt during the pyrenean orogeny major shortening occurred in the eastern pyrenees in eocene and early oligocene times until now individual tectonic and depositional events have been only loosely defined temporally by biostratigraphic data in order to provide a more precise chronological framework four new magnetostratigraphic sections spanning 8 km of eocene strata and encompassing 18 m y have been developed in the eastern pyrenees of northern spain the ages of nine major depositional sequences in the eastern pyrenean foreland have been specified within the context of these chronologic data beginning with the early eocene transgression that commenced at 58 ma the timing of numerous tectonic events that occurred during the subsequent 16 m y can also be delineated including the initial emplacement of the pedraforca thrust sheet 58 54 ma the development of the pedraforca breakback thrusts 47 5 40 ma at a mean shortening rate of 2 4 mm yr rotation of the pedraforca footwall three intervals of motion along the vallfogona thrust 42 5 44 0 40 5 41 5 and

sediment production and dispersal on foraminifera dominated early tertiary ramps the eocene el garia formation tunisia larger benthic foraminifera nummulites are common within eocene circumtethyan limestones despite their importance as sediment producers contradictions in the literature constrain current understanding about the location of the nummulites factory the el garia fm was deposited on a ramp with localized palaeohighs and whilst some authors suggested that the locus of nummulites production was in shallow water across the palaeohighs others concluded that production was significantly reduced over these palaeohighs and concentrated in the surrounding deeper 30 60 m water there are also marked dissimilarities between recent models in terms of the continuity correlation and resolution of depositional sequences to assess these models we integrate studies of the architecture and geometry of the el garia fm with detailed taphonomic biometric biofabric and palaeoecological characterization of nummulites tests we conclude that the highest rates of sediment production occurred in euphotic water over the palaeohighs and in nearshore environments nummulites on the palaeohighs were transported into the surrounding deeper water by oceanic and storm currents that swept the platform top producing a nummulitic sediment package that thickened and became increasingly fine grained and fragmented into outer ramp environments this transport exerted a major control on development of the ramp like geometries often seen at outcrop our findings question the validity of a recent sequence stratigraphic model that identifies decimetre scale milankovitch cycles even in largely allochthonous bio retextured mid outer ramp sediments our findings also suggest that the thin packages of el garia fm on the palaeohighs which have previously been interpreted as condensed sections that can be correlated with thicker more distal accumulations actually represent remnants of the sediment that was produced on the highs and exported into the basin

three dimensional sedimentary framework of the carbonate ramp slope of central west florida a sequential seismic stratigraphic perspective the sequential post early cretaceous stratigraphic evolution of the carbonate ramp slope of central west florida has been determined via the integration of 1 500 km of seismic reflection profiles with drillcores piston cores and rock dredge hauls our goal has been to gain insight into and increase our knowledge and understanding of carbonate ramps in general as well as to develop a model for potential application to the rock record our results which focus on the neogene indicate that the three dimensional sedimentary framework of the west florida ramp slope has developed in response to the interplay of a number of processes including 1 regional tectonic subsidence 2 long term sea level change 3 short term sea level oscillations 4 large scale gravity collapse 5 a major paleoceanographic event 6 fluctuating intensity of oceanic circulation 7 lateral migration of ocean currents and 8 open ocean upwellang and pelagic carbonate production during the early cretaceous seismic sequence vi the continental margin of west florida was a large shallow water carbonate evaporate platform that had persisted since late stages of continental rifting in the jurassic during the mid cretaceous seismic sequence v terrigenous sediment nutrient influx terminated platform growth and deposited a layer of neritic marl for the next 60 m y during a long term eustatic highstand in the late cretaceous paleogene seismic sequence iv the present west florida slope was an open ocean deep water marginal plateau that accumulated pelagic carbonates following a eustatic lowstand in the late oligocene 30 m y ago the carbonate ramp slope of central west florida began to take shape as a low relief ramp margin built seaward into the early and middle miocene seismic sequences iii and ii in the latest early miocene large scale gravity collapse generated a slope basin that was rapidly filled by prograding clinoforms in the middle miocene 12 15 m y ago intensification of oceanic circulation truncated antecedent clinoforms blocked off shelf sediment transport and stimulated pelagic carbonate production this oceanographic event resulted in the succession of seaward prograding clinoforms by a slope front fill pelagic depositional system that has survived numerous sea level oscillations into the present seismic sequence i

ecology of extant nummulitids and other larger benthic foraminifera applications in palaeoenvironmental analysis abstract larger benthic foraminifera lbf are important contributors to modern and ancient tropical shallow marine sediments over the past 30 years a substantial body of literature has built up on the ecology of modern lbf especially in terms of their environmentally sensitive depth distribution reproductive strategy and morphology and the symbiotic relationship between many larger foraminifera and photosynthetic algae over the same period the extinct genus nummulites which is abundant in eocene sediments of southern europe north africa and the arabian peninsula has increasingly been studied principally because significant volumes of hydrocarbons have been discovered reservoired within nummulitic limestones offshore tunisia and libya the modern ecological studies of lbf provide a powerful tool with which to develop palaeoecological models for fossil nummulites and other symbiont bearing larger foraminifera in the rock record

the middle eocene seeb formation of oman an investigation of acyclicity stratigraphic completeness and accumulation rates in shallow marine carbonate settings abstract the middle eocene seeb formation represents deposition on one of the earliest modern style carbonate platforms i e influenced by seagrasses and mangroves and presents an opportunity to explore controls on the preservation of cenozoic carbonate lithofacies in the study area the seeb fm is dominated by an anomalously thick approximately 250 m and uniform package of shallow marine platform interior sediments these nodular indistinctly bedded shallow subtidal sediments display no evidence for relative sea level change such as subaerial exposure features and lack the shallowing upwards cyclothems that have characterized carbonate sediments deposited in platform interior settings throughout much of the rock record particularly during greenhouse periods we conclude that this is a consequence of thorough bio retexturing of the sediment by burrowing organisms and the roots of marine vegetation which destroyed primary fabrics facies diversity evidence for cyclicity and missing time horizons such as cycle bounding exposure surfaces it seems possible that the remarkable thickness of apparently acyclic seeb fm sediment that built up may reflect increased bio disturbance of the shallow marine environment following the late cretaceous expansion of seagrasses and mangroves a similar lack of peritidal cyclothems may be common to many cenozoic shallow marine carbonate deposits missing time horizons in limestones reflecting erosion or nondeposition have been identified by some authors to explain discrepancies between low calculated accumulation rates of ancient sediments and higher rates measured in comparable modern environments however our studies of the seeb fm suggest that the significance of such missing time horizons in ancient sediments may have been overstated and that apparent differences between modern and ancient accumulation rates are a consequence of the extrapolation of unrepresentative localized high rates of modern sediment production to large platform scale areas our study reinforces the idea that modern sediment production and accumulation rates may be much lower than previously thought because they are typically measured in highly productive areas such as seagrass beds and do not take into account the highly variable nature of carbonate production storage erosion and destruction across platforms therefore far less missing time needs to be inferred for ancient sediments to account for any imbalance between modern and ancient sediment accumulation rates

platform margin collapses and sequence stratigraphic organization of carbonate slopes cretaceous eocene gargano promontory southern italy we describe the sequence stratigraphic organization and the associated sedimentological characteristics of cretaceous to eocene slope and base of slope carbonate successions the study area is located in the gargano promontory which belongs to the stable foreland of southern italy the succession consists of three superimposed depositional sequences separated by major unconformities the upper two sequences are clear examples of sequence stratigraphic organization in fact they both start with huge megabreccia wedges lst followed upward by thin pelagic units tst and a thick package of calciturbidites and debrites that alternate with pelagic mudstone hst the cretaceous highstand systems tract is clearly arranged in a number of coarsening upward cycles while the eocene one which also comprises a toplap shallow water unit is not the gargano stratigraphic palimpsest and the entire margin of the apulia platform show remarkable similarities with present day carbonate platform margins and slopes where irregular convex bankward embayments suggest large scale failures it is clear that classic sequence stratigraphic organization can result from simple platform dismantling having no or little time relation with global sea level fluctuations in fact as the margin failure lst interrupts the carbonate production a period of starvation tst along the entire slope and base of slope follows necessarily finally when the margin once again becomes active and productive sediment exportation starts again and the system begins to prograde hst

quasi 3d modeling of airborne tem data by spatially constrained inversion we present a new methodology spatially constrained inversion sci that produces quasi 3d conductivity modeling of electromagnetic em data using a 1d forward solution spatial constraints are set between the model parameters of nearest neighboring soundings data sets models and spatial constraints are inverted as one system the constraints are built using delaunay triangulation which ensures automatic adaptation to data density variations model parameter information migrates horizontally through spatial constraints increasing the resolution of layers that would be poorly resolved locally sci produces laterally smooth results with sharp layer boundaries that respect the 3d geological variations of sedimentary settings sci also suppresses the elongated artifacts commonly seen in interpretation results of profile oriented data sets in this study sci is applied to airborne time domain em data but it can also be implemented with other ground based or airborne data types

thrust sequences in the eastern spanish pyrenees detailed mapping of the south pyrenean zone in the eastern spanish pyrenees shows that a great number of alpine thrusts affect the basement and the cover the geometry of the thrust structures and their propagation sequence can be interpreted from balanced sections the folding dies out downwards from the higher thrust sheets to the lower ones and demonstrates a piggy back thrusting sequence these thrusts form a duplex the sole thrust of this duplex is the vallfogona thrust the roof thrust is rooted somewhere within the axial zone the thrusts climb southwards from the axial zone basement up into tertiary cover sediments these thrusts have been folded so that they now dip to the south and form the southern side of the axial zone antiformal stack locally smaller antiformal stacks developed and produced strong folds in the higher thrust sheets the south pyrenean zone studied is equivalent to the gavarnie nappe and the connection between them below the detached south pyrenean central unit may be the nogueres zone

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

transient electromagnetic sounding for groundwater the feasibility of using the transient electromagnetic sounding ts or tdem method for groundwater exploration can be studied by means of numerical models as examples of its applicability to groundwater exploration we study four groundwater exploration problems 1 mapping of alluvial fill and gravel zones over bedrock 2 mapping of sand and gravel lenses in till 3 detection of salt or brackish water interfaces in freshwater aquifers and 4 determination of hydrostratigraphy these groundwater problems require determination of the depth to bedrock location of resistive high porosity zones associated with fresh water determination of formation resistivity to assess water quality and determination of lithology and geometry respectively the ts method is best suited for locating conductive targets and has very good vertical resolution unlike other sounding techniques where the receiver transmitter array must be expanded to sound more deeply the depth of investigation for the ts method is a

catastrophic collapse of the west florida carbonate platform margin a large truncation surface has been discovered on seismic reflection profiles along the distally steepened ramp of the west florida carbonate platform margin this structure interpreted as a submarine slide scar is at least 120 km across and up to 30 km wide the slide has removed as much as 300 350 m of late paleogene and early neogene strata collapse occurred in the middle miocene within an episode of seaward progradation during a relative sea level highstand postcollapse depositional sequences thicken abruptly across the structure this suggests catastrophic slope failure gravitational instability created by high rates of sediment accumulation is believed to have been the triggering mechanism such large scale platform margin collapse is likely to generate megabreccia debris flows as well as aid in the landward retreat of precipitous high relief carbonate escarpments