sedimentary facies and sequence stratigraphy of the asmari formation at chaman bolbol zagros basin iran abstract the oligocene miocene asmari formation of the zagros basin is a thick sequence of shallow water carbonate in the study area it is subdivided into 14 microfacies that are distinguished on the basis of their depositional textures petrographic analysis and fauna based on the paleoecology and lithology four distinct depositional settings can be recognized tidal flat lagoon barrier and open marine the asmari formation represents sedimentation on a carbonate ramp in the inner ramp the most abundant lithofacies are medium grained wackestone packstone with imperforated foraminifera the middle ramp is represented by packstone grainstone to floatstone with a diverse assemblage of larger foraminifera with perforate wall red algae bryozoa and echinoids the outer ramp is dominated by argillaceous wackestone characterized by planktonic foraminifera and large and flat nummulitidae and lepidocyclinidae three third order depositional sequences are recognized from deepening and shallowing trends in the depositional facies changes in cycle stacking patterns and sequence boundary features

carbonate shelf edge off southern australia a prograding open platform margin the southern continental margin of australia is an extensive shelf that has been a site of cool water carbonate deposition since eocene time the platform has no rim and is swept by high energy waves and swells throughout the year the shelf is deep 40 to 100 m and typified by bryozoan rich sediments the shelf margin is a gentle incline that becomes progressively steeper seaward except where it laps down onto offshore terraces the edge of the eucla platform in the great australian bight is used to illustrate that the margin is a series of extensive prograding clinoforms progradation is interpreted to be the result of off shelf sediment transport and in place carbonate production by actively growing deep water bryozoa and sponges this area is a potential model for ancient high energy platform margins during geologic periods when large skeletal reef building metazoans were scarce

temperate carbonate platform drowning linked to miocene oceanographic events maiella platform margin italy carbonate platform drownings are frequent often synchronous global occurrences yet explanations for these world wide events remain unsatisfactory in the central apennines lower and middle miocene carbonate rocks deposited on a temperate ramp in the maiella platform margin record two episodes of platform drowning followed by hemipelagic sedimentation dated as latest oligocene aquitanian 26 23 ma and as burdigalian langhian 20 16 ma a high resolution stratigraphy based on strontium isotopes allows us to correlate key phases of platform evolution with events recorded in deep water ocean sediments this paper suggests that high weathering rates and nutrient input in the mediterranean during the early and middle miocene possibly linked to the uplift of the tibetan region set the preconditions for platform drowning which were ultimately caused by rapid eustatic sea level rises

deep rhodolith distribution in the pontian islands italy a model for the paleoecology of a temperate sea abstract within the bathymetric range 27 98 m of the soft bottoms investigated off the pontian islands rhodoliths have been classified into three morphological groups 1 the unattached monospecific branches mainly composed of the non geniculate coralline red algae phymatolithon calcareum lithothamnion corallioides and lithothamnion valens 2 the pr lines sensu stricto monospecific little nodules with protuberances or short branches and a compact internal structure normally due to the concentric growth of lithothamnion minervae or lithophyllum racemus over a pebble or a skeletal remain 3 the large multispecific rhodoliths with a boxwork internal structure due to long periods of growth under calm conditions interrupted by episodes of overturning and or partial covering by sediments with evident sedimentary fillings and a first nucleus often difficult to identify a predictive model of distribution of species and growth forms of corallines and peyssonnelians in the framework of the mediterranean circalittoral benthic zonation has been developed along two opposite gradients 1 the frequency of overturning of the rhodoliths and 2 environmental stability of the bottom conditioned by sedimentation rate absolute hydrodynamics of the environment shape and density of the single rhodolith depending on its nucleus

facies analysis and palaeoenvironmental interpretation of the late oligocene attard member lower coralline limestone formation malta the oligocene represents a key interval during which coralline algae became dominant on carbonate ramps and luxuriant coral reefs emerged on a global scale so far few studies have considered the impact that these early reefs had on ramp development consequently this study aimed at presenting a high resolution analysis of the attard member of the lower coralline limestone formation late oligocene malta in order to decipher the internal and external factors controlling the architecture of a typical late oligocene platform excellent exposures of the lower coralline limestone formation occurring along continuous outcrops adjacent to the victoria lines fault reveal in detail the three dimensional distribution of the reef associated facies a total of four sedimentary facies have been recognized and are grouped into two depositional environments that correspond to the inner and middle carbonate ramp the inner ramp was characterized by a very high energy shallow water setting influenced by tide and wave processes this setting passed downslope into an inner ramp depositional environment which was colonized by seagrass and interfingered with adjacent areas containing scattered corals the middle ramp lithofacies were deposited in the oligophotic zone the sediments being generated from combined in situ production and sediments swept from the shallower inner ramp by currents compositional characteristics and facies distributions of the attard ramp are more similar to the miocene ramps than to those of the eocene an important factor controlling this similarity may be the expansion of the seagrass colonization within the euphotic zone this expansion may have commenced in the late oligocene and was associated with a concomitant reduction in the aerial extent of the larger benthonic foraminifera facies stacking pattern analysis shows that the depositional units parasequences at the study section are arranged into transgressive regressive facies cycles this cyclicity is superimposed on the overall regressive phase recorded by the attard succession furthermore a minor highstand correlated with the ru4 ch1 sequence and subsequent minor lowstand ch2 sequence have been recognized the biota assemblages of the attard member suggest that carbonate sedimentation took place in subtropical waters and oligotrophic to slightly mesotrophic conditions the apparent low capacity of corals to form wave resistant reef structures is considered to have been a significant factor affecting substrate stability at this time the resulting lack of resistant mid ramp reef frameworks left this zone exposed to wave and storm activity thereby encouraging the widespread development of coralline algal associations dominated by rhodoliths

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

a three dimensional numerical investigation of a carolina coastal front and the gulf stream rainband abstract a three dimensional mesoscale planetary boundary layer pbl numerical model is used to investigate mesoscale circulations over the carolina coastal and gulf stream baroclinic zones idealized ambient onshore and offshore flows are investigated which represent the synoptic conditions during the intensive observation period 2 iop 2 of the 1986 genesis of atlantic lows experiment gale for the easterly onshore flow a confluence zone appears west of the gulf stream in response to the effect of the oceanic baroclinicity the confluence zone is nearly parallel to the coastline and the sst isotherms with northeasterly southwesterly flow to the west east a shallow coastal front forms below 2 km as the cyclonic shear of the ageostrophic flow becomes strong quasi stationary rainbands are produced by cumulus convection along the coastal front the northern part of the front and the rainbands later encroach inland as the cold air intensity over ground weakens due to onshore warm air advection

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

subtropical carbonates in a temperate realm modern sediments on the southwest australian shelf the southwestern continental margin of australia 19 degrees s 22 degrees s in the western indian ocean is transitional between cool water and warm water carbonate realms it comprises the incipiently rimmed flat topped steep fronted rottnest shelf in the south the uniform subtropical starved carnarvon ramp off shark bay and the ningaloo fringing reef in the north the margin is strongly influenced by the poleward flowing warm nutrient poor leeuwin current which promotes overall downwelling and strong summer equatorward blowing winds which generate local seasonal upwelling the structurally quiescent northern part of the rottnest shelf with minimum accommodation is characterized by luxuriant stands of sea grasses and macrophytes growing on coralline encrusted hardgrounds and rooted in sediments rich in coralline algae and larger symbiont bearing foraminifers together with abundant cool water elements such as bryozoans molluscs and small foraminifers halimeda is poorly calcified and does not contribute to the sediment azooxanthellate corals although present are not common such a sediment pattern has many analogs in the geologic record especially the early cenozoic the incipient rim is a morphologically complex linear ridge system interpreted to be a buried mid pleistocene barrier reef or beach dune complex the northern part of the ridge complex is capped by the houtman abrolhos reef platforms subphotic sediments on the deep outer shelf and upper slope affected by seasonal upwelling are typical cool water poorly sorted bryozoan dominated deposits rich in small foraminifers and sponge spicules the inner part of the more structurally active carnarvon ramp ranges from steep eolianite cliffs to hypersaline environments of shark bay to the ningaloo fringing reef mid ramp sediment especially off shark bay is mostly relict or stranded and foraminifer dominated sand with abundant mg calcite cemented intraclasts these sediments accumulating on a relatively barren seafloor likely represent attenuated carbonate production brought about by downwelling and episodic incursions of saline shark bay derived waters onto the ramp the outer ramp is either planktic foraminiferal sand sorted by strong bottom currents or spiculitic mud such sedimentation patterns should typify the western margins of large ocean basins during those periods in geologic history when circumglobal equatorial circulation was active and equatorial gateways narrow in contrast to eras of supercontinents when cool water carbonate sedimentation and upwelling prevailed in similar settings furthermore because low latitude trade winds relax during glacial epochs and the cool water upwelling belt moves equatorward into otherwise tropical realms temperate and subtropical sedimentation patterns in these regions should oscillate at the 100 ky scale in the stratigraphic record

sub wavebase cross bedded grainstones on a distally steepened carbonate ramp upper miocene menorca spain cross bedded grainstones on carbonate ramps and shelves are commonly related to the locus of major wave energy absorption such as shorelines shoals or shelf breaks in contrast on the early tortonian carbonate platform of menorca balearic islands coarse grained cross bedded grainstones are found at a distance from the palaeoshoreline where they were deposited below the wavebase excellent exposures along continuous outcrops on the sea cliffs of menorca reveal the depositional profile and three dimensional distribution of the different facies belts of the tortonian ramp depositional system basinward from the palaeoshoreline fan deltas and beach deposits pass into 5 km wide gently dipping bioturbated dolopackstone inner and middle ramp then into 12 20 dipping dolograinstone rudstone clinobeds ramp slope and finally into subhorizontal fine grained basinal dolowackestone to dolopackstone outer ramp in this miocene example coarse grained grainstones exist in five different settings other than beach deposits 1 on the middle ramp where cross bedded grainstones were deposited by currents roughly parallel to the shoreline at 40 70 m estimated water depth and are interbedded with gently dipping bioturbated dolomitized packstones 2 on the upper slope where clinobeds are composed mostly of in situ rhodoliths and red algae fragments 3 on the lower slope as small scale bedforms small three dimensional subaqueous dunes migrating parallel to the slope 4 at the transition between the lower slope and the outer ramp where mollusc rich and rhodolithic rudstones and grainstones interbedded in dolomitized laminated wackestones containing abundant planktonic foraminifera infill slide slump scars as upslope backstepping bodies backsets 5 at the toe of the slope where coarse skeletal grainstones indicate bedform migration parallel to the platform margin induced by currents at more than 150 m estimated water depth this late miocene example also illustrates how changes in intrabasinal environmental conditions nutrients and or temperature may produce changes in stratal patterns and facies architecture if they affect the biological system two depositional sequences compose the miocene platform on menorca where a reef rimmed platform prograded onto an earlier distally steepened ramp the transition from the ramp to the reef rimmed platform was effected by an increase in accommodation space caused by ecological changes promoting a shift from a grain to a framework producing biota

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

miocene c isotope signature from the central apennine successions italy monterey vs regional controlling factors the c isotope composition of a miocene carbonate succession from the latium abruzzi sector of the central apennines was studied to evaluate the influence of local vs global factors in changing d 13 c we propose that the oligo miocene igneous activity of the western mediterranean and the closure of the indo pacific connection influenced climate change and mediterranean sea water circulation the huge aquitanian burdigalian volcanic activity during the formation of the

aphotic zone carbonate production on a miocene ramp central apennines italy the lower miocene latium abruzzi platform was a low angle ramp that developed under tropical to subtropical conditions but was dominated by bryomol and rhodalgal sediment associations the aquitanian to serravallian sequence described here paraconformably overlies the cretaceous limestones it consists of a lowstand systems tract a transgressive systems tract and a highstand systems tract based on facies analysis and on the light dependence of biotic associations the ramp is divided into three parts an inner ramp a middle ramp and an outer ramp the inner ramp facies are represented by a few metres of coral framestone rhodolith floatstone rudstone and balanid macroids floatstone without wave related structures the middle ramp consists of structureless bioclastic grainstone to packstone floatstone and rudstone with rhodoliths and larger foraminifera the outer ramp facies proximal sector are composed of crudely stratified bryozoan dominated packstone to floatstone which extend over the whole platform the outer ramp facies intermediate sector are represented by wackestone packstone and rarely grainstone with foraminifera and echinoid fragments the final depositional profile of the ramp was strongly influenced by the main organisms producing sediment during the lowstand the resulting profile is a ramp type during the transgressive phase the rapid spreading of the outer ramp facies belt as a consequence of the enhanced productivity of the light independent biota is believed to be promoted by a change from oligotrophic to eutrophic conditions climate and or tectonics are presumed to have played an important role in continental runoff and then in the nutrients delivery during the highstand phase the system returns to rates of production uniform throughout the platform the high rates of carbonate production occurring in the aphotic zone are quite unusual in tropical settings and represent a provocative trend in apparent contrast with the common idea about the locus of the most significant carbonate production as derived from the tropical model the example described here shows that carbonate production and accumulation below the photic zone might be higher than in the shallow euphotic zone even in tropical conditions d 2003 elsevier science b v all rights reserved

carbonate production and offshore transport on a late jurassic carbonate ramp kimmeridgian iberian basin ne spain evidence from outcrops and computer modelling

computer simulation of reef growth light is one of the major controls on reef growth and carbonate production the growth of present reef builders depends largely upon the amount of light available for photosynthesis as light decreases with water depth so does reef growth the computer model presented extends this principle by combining two functions one for photosynthesis and the other for the extinction of light in water the model is used to simulate the growth of alacran reef mexico two reefs of the great barrier reef and the reefs of the windward platform of st croix us virgin islands the model also gives an accurate simulation of the growth of fore reef walls in belize in agreement with the accretion hypothesis developed for this feature

modern carbonate and terrigenous clastic sediments on a cool water high energy mid latitude shelf lacepede southern australia the wide lacepede shelf and narrow bonney shelf are contiguous parts of the south eastern passive continental margin of australia the shelves are open generally deeper than 40 m covered by waters cooler than 18 c and swept by oceanic swells that move sediments to depths of 140 m the lacepede shelf is proximal to the delta of the river murray and the coorong lagoon shelf and upper slope sediments are a variable mixture of holocene and late pleistocene quartzose terrigenous clastic and bryozoa dominated carbonate particles bryozoa grow in abundance to depths of 250 m and are conspicuous to depths of 350 m they can be grouped into four depth related assemblages coralline algae the only calcareous phototrophs are important sediment producers to depths of 70 m active benthic carbonate sediment production occurs to depths of 350 m but carbonate sediment accumulation is reduced on the open shelf by continuous high energy conditions the shelf is separated into five zones the strandline is typified by accretionary sequences of steep shoreface beach and dune carbonate siliciclastic sediments similar shoreline facies of relict bivalve limestone cobble ridges are stranded on the open shelf the shallow shelf c 40 70 m deep is a wide extremely flat plain with only subtle local relief it is a mosaic of grainy quartzose palimpsest facies which reflect the complex interaction of modern bioclastic sediment production dominated by bryozoa and molluscs numerous highstands of sea level over the last 80 000 years modern mixing of sediments from relatively recent highstands and local introduction of quartz rich sediments during lowstands the middle shelf c 70 140 m deep is a gentle incline with subtle relief where holocene carbonates veneer seaward dipping bedrock clinoforms and local lowstand beach complexes carbonates are mostly modern uniform clean coarse grained sands dominated by a diverse suite of robust to delicate bryozoa particles produced primarily in situ but swept into subaqueous dunes the deep shelf edge c 140 250 m deep is a site of diverse and active bryozoa growth resulting accumulations are characteristically muddy and distinguished by large numbers of delicate branching bryozoa the upper slope between 250 and 350 m depth contains the deepest platform related sediments which are very muddy and contain a low diversity suite of delicate branching cyclostome bryozoa this study provides fundamental environmental information critical for the interpretation of cenozoic cool water carbonates and the region is a good model for older mixed carbonate terrigenous clastic successions which were deposited on unrimmed shelves

quantitative reconstruction of early holocene and last glacial climate on the balkan peninsula using coupled hydrological and isotope mass balance modelling abstract we investigate the modern hydrology of lake ohrid macedonia albania using a combined hydrological and isotope based modelling approach and present a new evaluation of contemporary water balance and palaeoclimate estimates the combined model is able to estimate hydrological components that cannot be directly measured and indicates that sublacustrine spring inflow is in the order of 50 higher than previous estimates and groundwater outflow comprises approximately a third of overall water outflow in combination with sediment core oxygen isotope data we used the combined model to quantitatively reconstruct past climate in particular precipitation during the early holocene and last glacial period calculated precipitation in the early holocene was higher than the value for present day and was approximately 44 lower than present during the last glacial assuming the majority of precipitation fell as snow the estimated amount of precipitation in the last glacial would have been high enough to provide refugial conditions at lake ohrid and to support the continuous existence of arboreal vegetation in the catchment the improved understanding of the modern isotope hydrology of lake ohrid is fundamental for explaining the systematics of past isotope variation and providing context for extended sediment records from the lake which will provide longer term palaeoclimate reconstructions covering multiple glacial interglacial cycles

carbonate deposition in restricted basins a pliocene case study from the central mediterranean northwestern apennines italy abstract carbonate depositional models are often informed by the study of platforms of good lateral continuity and sizable thickness because of their significance in petroleum geology however spatially restricted and more ephemeral carbonate accumulations can be an important but frequently overlooked component of otherwise siliciclastic dominated or mixed carbonate siliciclastic systems pliocene successions of tuscany and the tyrrhenian shelf northern apennines italy record a regional pulse of nontropical carbonate deposition across several restricted basins that has not yet been precisely constrained in its genesis and correlation this study investigates the stratigraphic expression of these carbonates to extract general aspects applicable to carbonate sedimentation across tectonically structured and physiographically complex shelves analyses of the extension composition facies and sequence stratigraphic architecture of the studied piacenzian carbonate units are complemented by new biostratigraphic and magnetostratigraphic data which document the slightly diachronous development of the carbonates within mediterranean planktonic foraminifera subzones mpl4b and mpl5a and magnetic polarity chron c2an the carbonate units are part of a regionally defined tectonically controlled sequence and represent the first transgressive unit overlying the basal sequence boundary but are also found in the regressive portion of the sequence collectively the units document the establishment of a shallow marine carbonate factory dominated by calcareous red algae the larger benthic foraminifer amphistegina and heterozoan skeletal components along the margins of a complex archipelago like coastal domain a review of the studied successions and other examples from the literature indicates that carbonate accumulations in settings with varied coastal physiography and active partitioning of depocenters are generally characterized by a spatial discontinuity b an overall skeletal association consistent across separate basins but with local variability in dominant skeletal components c preferential accumulation along basin margins or over isolated structural highs not in direct proximity to a hinterland with major drainage systems d predominance of low to moderate energy facies e preferential onset of deposition during transgression with possible development of mixed carbonate siliciclastic facies and f differing internal stratigraphic architecture tied to the specific subsidence and uplift history of coeval individual basins these observations built upon the study of mid piacenzian carbonate units from the central mediterranean contribute to the refinement of carbonate facies models and their application in the fields of sequence stratigraphy and basin analysis

facies analysis and sequence stratigraphy of a miocene warm temperate carbonate ramp montagna della maiella italy abstract the uppermost oligocene lower miocene to upper miocene ramp carbonates from montagna della maiella italy form a supersequence bounded by deeply incised truncation surfaces this supersequence is subdivided into four sequences each sequence is composed of skeletal limestones in its lower part and marly limestones in its upper part the lower parts of the sequences are foramol limestones which suggest deposition in the warm temperate climate zone changes in climate oceanography and relative sea level combined to control sedimentation in the four sequences in the lower parts of the two older sequences the skeletal sands built dunes suggesting high energy conditions the dominant skeletal grains in the oldest sequence are larger foraminifers and in the next sequence they are bryozoans this change reflects cooling around the time of the aquitanian burdigalian boundary in the lower parts of the two younger sequences of middle and late miocene age sediment sheets with red algal bryozoan oncoids suggest deposition under calmer conditions transgressive and highstand systems tracts are recognized in all sequences a shelf margin systems tract may be exposed in the second oldest sequence in contrast to the situation that exists when warm water carbonates are deposited sedimentation of the foramol limestones on this isolated ramp was unable to balance accommodation during sea level rise this led to hemipelagic sedimentation during sea level highstands conglomerates resulted from reworking along flooding surfaces

a numerical study of a shallow sea front generated by buoyancy flux generation mechanism abstract we studied numerically the frontogenesis of shallow sea fronts such as are observed in the kii channel japan during winter under conditions of sea surface cooling and buoyancy influx from coast and open ocean numerical experiments were carried out in a vertically two dimensional basin with a new model nh model without using the hydrostatic approximation and the convective adjustment considering the vertical acceleration term in the momentum equation intermittent gravitational convections with a large aspect ratio were produced in the frontal region to intensify the horizontal convergence and to strengthen the horizontal density gradient consequently a front in the tracer distribution had a sharpness comparable to the observed front in the kii channel and 3 6 times the sharpness in an h model using the hydrostatic approximation and the convective adjustment in the present model situation this effect of gravitational convections on sharpening a front in the nh model is equivalent to t

gulf stream meanders in the south atlantic bight 1 scaling and energetics as the gulf stream flows along the outer edge of the southeastern united states continental shelf it meanders on and offshore creating frontal eddies which influence the exchange of water between the shelf and the adjacent atlantic ocean on weekly timescales the dynamics controlling the development of such features in this region the open quotes south atlantic bight close quotes or sab is the subject of this pair of papers in the present paper the authors provide the background on the subject summarize the length time and velocity scales associated with these features and discuss meander energetics as simulated by a numerical model the scaling indicates that significant ageostgrophic dynamics may be crucial to the development of these flows and that the semigeostrophic equations may provide the simplest description of the system these nonlinear dynamics may permit complex interactions among meander modes and with topography resulting in the observed behavior of the gulf stream in the sab the princeton ocean model was tuned for conditions which prevail in the southern south atlantic bight and idealized numerical simulations of gulf stream meanders and associated frontal eddies were performed the system was found to be sensitive to both the amplitude and period of a small perturbationmore applied at the southern boundary the energetics indicate that the development of these features is controlled by a mixture of both baroclinic and barotropic instabilities of the mean gulf stream flow tantalizing hints of a period doubling phenomenon are present in the energy conversion time series 47 refs 12 figs 4 tabs less

ecological control of sedimentary accommodation evolution from a carbonate ramp to rimmed shelf upper miocene balearic islands abstract stratal patterns and facies architecture develop in response to sediment flux and the available space for sediment accumulation accommodation in siliciclastic systems these two parameters are independent in carbonates however they are highly interdependent 1 sediment input production highly depends on biological systems and consequently on intrabasinal conditions nutrients temperature salinity etc 2 sediment dispersal depends on the production loci and on the interaction between the amount and type of sediment being produced and the hydraulic energy additionally biological processes binding baffling framework construction and even cementation frequently modify it 3 accommodation is not an independent factor with respect to sediment input type efficiency and area of the carbonate factory depend on sea level changes and sea floor morphology the base level for sediment to accumulate accommodation depends on the type and locus of sediment being produced the upper miocene carbonate platforms of the balearic islands illustrate how changes in intrabasinal environmental conditions nutrients and or temperature produce changes in stratal patterns and facies architecture if they affect the biological system during early tortonian carbonate production occurred both in the shallow euphotic zone foramol and in the deeper oligophotic zone rhodalgal originating a distally steepened ramp during late tortonian and early messinian carbonate production mainly occurred in the euphotic zone where framework producing biota coral reefs formed a rimmed platform although deposited under similar conditions of high frequency sea level fluctuations these two types of platforms exhibit different internal facies architecture and distribution of heterogeneities because of differences in base level in carbonates base level for sediment accumulation depends on the type and amount of sediment being produced on the production loci and on the processes controlling sediment dispersal base level for the loose foramol rhodalgal sediment associations of the ramp was controlled by wave and storm base and the associated currents whereas base level for the framework dominated reef complex was sea level furthermore the increase on effective accommodation space to allow the reef rimmed shelf to prograde onto the distally steepened ramp both platforms being depositional sequences resulted from an ecological change rather than significant relative sea level change namely by the shift from grain to framework producing biota the euphotic framework producing biota was able to fill the accommodation space existing between wave and storm base level and sea level that was not previously filled by the loose bioclasts

glacial eustasy during the cenozoic sequence stratigraphic implications a newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the cretaceous tertiary boundary and provides an independent test of sequence stratigraphic based eustatic curves the isotope record shows several eustatic episodes that are consistent with the geological record of ice sheet evolution the first evidence for the existence of an ice sheet in east antarctica occurs near the lower middle eocene boundary base of the lutetian stage there is no evidence for a large ice sheet on antarctica prior to this time however strata of this age are lacking over most of the continent the isotope curve also indicates that the ice sheet experienced phases of growth during the late eocene and middle oligocene followed by a decrease in volume in the early miocene the ross sea stratigraphic record indicates initial evolution of the west antarctica ice sheet during the early miocene by the middle miocene the ice sheet spread across the ross sea weddell sea and antarctic peninsula continental shelves the pliocene pleistocene record of glaciation in antarctica includes numerous glacial erosion surfaces on the continental shelf indicating repeated advance and retreat of both east and west antarctica ice sheets these volume changes in the antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting northern hemisphere ice sheets there is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle eocene this correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle eocene

nutrients sea level and tectonics constrains for the facies architecture of a miocene carbonate ramp in central italy in the western part of the central apennines lower middle miocene carbonates were deposited on a tropical subtropical carbonate ramp they record two long term cycles the first of which is illustrated in this paper between 21 and 17 5 ma miocene carbonates paraconformably overlying the cretaceous limestones record a transgressive event during a time of global 2nd order sea level lowstand it is postulated that this deviation is related to an increase in tectonic subsidence between 17 5 ma and 16 15 ma with a progressive relative sea level rise the inner middle ramp facies belt stepped back whereas the bryozoan dominated outer ramp facies belt stepped back but simultaneously prograded this bloom of suspension feeding organisms is interpreted to reflect an increased nutrient availability hence a change from oligotrophic to eutrophic conditions strontium isotope dates constrain correlation of the second phase with a eutrophic event possibly linked to the influence of the neighbouring apenninic accretionary wedge and foredeep system

temperate carbonates on a modern low energy isolated ramp the balearic platform spain abstract this paper presents a depositional model for a temperate low energy carbonate ramp based on descriptive studies of five areas around the balearic islands of mallorca and menorca this low energy ramp differs significantly from other present day temperate carbonate platforms that are primarily high energy open shelves it is characterized by the following lithofacies from shore to basin 1 lagoon 2 barrier island 3 shallow subtidal 4 inner ramp 5 middle ramp and 6 distal ramp subaqueous carbonate dunes are present near slope breaks off menorca and cabrera but they are not representative of the entire ramp balearic ramp sediments differ in composition texture biology and degree of cementation from those on modern low energy tropical ramps balearic ramp carbon tes lack ooids and peloids hermatypic coral buildups and calcareous green algae except in one restricted bay where halimeda is relatively common red algal sands and gravels extend to depths of up to 90 m and are coarser than their strandplain equivalent lime sands skeletal allochems consist of the bryomol rhodalgal association marine cementation is rare and the carbonate fraction of deep water muds is mainly mg calcitic and calcitic in composition aragonite is rare except for the red alga peyssonnelia which is composed of aragonite it is neither a dominant skeletal constituent nor common as a cement the mediterranean sea off mallorca and menorca is a low energy temperate oligotrophic clear water environment the depositional model for the region is an isolated platform configured as a homoclinal ramp ancient counterparts of the balearic ramp are present in the neogene of the mediterranean tethys and the paratethys and though the constituents of fossil assemblages vary with time the biota of the balearic ramp such as bryozoans red algae echinoderms and mollusks ranges from the paleozoic era to the present echinodermal bryomols passing to basinal muds on carbonate ramps are particularly characteristic of the early carboniferous in north america and europe this suggests that the balearic islands temperate ramp may be more representative of some ancient carbonate sequenc s than either temperate high energy open shelves or tropical ramps in the present oceans

response of surface water masses and circulation to late quaternary climate change east of new zealand a series of cores from east of new zealand have been examined to determine the paleoceanographic history of the late quaternary in the sw pacific using planktonic foraminiferal data distinct shifts of species can be seen between glacial and interglacial times especially south of chatham rise east of south island foraminiferal fragmentation ratios and benthic planktonic foraminiferal ratios both show increased dissolution during glacials especially isotope stage 2 to the south of chatham rise the present day subtropical convergence appears to be tied to the chatham rise at 44 s but during glacial times this rise separated cold water to the south from much warmer water to the north with an associated strong thermal gradient across the rise we estimate that this gradient could have presented as much as an 8 c temperature change across 4 of latitude during the maximum of the last ice age there is only weak evidence of the younger dryas cool event but there is a clear climatic optimum between 8 and 6 4 ka with temperatures 1 2 c higher than the present day the marine changes compare well with vegetational changes on both south and north island

oligo miocene carbonate platform evolution in the northern margin of the asmari intra shelf basin sw iran abstract this study is based on seven outcrops along a regional transect in the central subdivision of the zagros foreland basin this ne sw trending transect extends for 140 km and covers the northern margin of the asmari intra shelf basin in dip direction from proximal to distal results of facies analysis led to the recognition of eight facies associations planktonic wkt nummulitic eu f r alg lr pkt coralgal f r bdt lr lpbf p g epy r pbf p g dol m and trgs along the depositional dip direction they are dominated by large and flat rotalids e g nummulites lepidocyclina and spiroclypeus coral and coralline red algae e g build up features porcellaneous benthic foraminifera e g archaias peneroplis and borelis and fossiliferous lime mud spatial and temporal distribution of these facies associations conform five platform types with different depositional profiles a a nummulites bearing mixed terrigenous carbonate distally steepened ramp lower rupelian b a nummulitidae lepidocyclina bearing carbonate distally steepened ramp upper rupelian lower chattian c a coral bearing flat topped open shelf middle upper chattian d an aquitanian homoclinal ramp and e a very shallow water burdigalian carbonate shelf amongst these platform types the late rupelian early chattian carbonate ramp additionally consists of three successive phases and the middle late chattian flatted top open shelf was developed in two phases the changes in platform type resulted from changes in the carbonate producing biotas sediment redistribution processes and significant impact of relative sea level changes

orbital forcing recorded in subtidal cycles from a lower miocene siliciclastic carbonate ramp system central italy metre scale siliciclastic carbonate cycles are the basic depositional motif of the lower miocene guadagnolo formation outcropping in the central apennines the mechanisms which formed the mixed lithology cycles are still a matter of debate the mixed siliciclastic carbonate system discussed in this paper provides a new case study to illustrate the role of orbital forcing in controlling the facies evolution and cyclic stacking of small scale sequences deposited on the outer sector of a ramp two sections are discussed that display mixed siliciclastics and carbonates arranged in upward shallowing cycles each cycle shows an upward decrease in the terrigenous input and a parallel increase in benthic fauna time series analyses indicate the cyclic carbonate terrigenous pattern to be largely controlled by orbital forcing in the milankovitch frequency band coupling of climate change and sea level fluctuations in tune with orbital cycles are proposed as driving mechanisms

shoreward intrusion of upper layer warm water by prescribed shelf break temperature perturbation and surface wind stress a new mechanism for mid shelf frontogenesis in shelf waters off the carolina capes is proposed based on results from three numerical experiments using a three dimensional coastal ocean model we find that quasi geostrophic currents induced by a density temperature anomaly at the shelf break may advect upper layer waters from the shelf break to the mid shelf this process can cause mid shelf frontogenesis even in the absence of favorable wind forcing however persistent northerly winds can substantially enhance mid shelf frontogenesis and increase the along shore scale of the mid shelf fronts off the carolina capes

short paper a standardized model for tethyan tertiary carbonate ramps low latitude carbonates in massive and clinoform bedded sheets termed ramps occur throughout the tertiary tethyan realm and are characterized by recurring biofacies usually including large foraminifera rhodolithic algae coralgal patch reef and gastropod dominated sequences all can be interpreted broadly within a standardized tertiary carbonate ramp model biota can be used to define precise palaeobathymetric zones which have a predictive utility in palaeoenvironmental modelling especially where data are limited the carbonate ramp model of earlier authors has been elaborated by read 1982 and ramp formation occurs mostly in passive margin and extensional tectonic settings ramps are characterized by slope gradients of less than 1 degree and once established are conservative to change much use has been made of the ramp model for palaeozoic and mesozoic lithofacies modelling in contrast published work on cenozoic ramps is limited however tethyan ramps are particularly widespread and extend tens to hundreds of kilometres along strike and occupy tens of kilometres of slope many studies have dealt with cenozoic ramp associations and sequences e g pedley 1983 reiss hottinger 1984 purser 1973 and have demonstrated the diversity of biotal and sediment detail but without ascribing them to a ramp model biota were quick to adapt to the tertiary environments left vacant after the k t boundary extinction events new genera of foraminifera mollusca bryozoa and echinoder mata rapidly replaced the extinct forms in bursts of innovative opportunism codiacean algae rhodophyta and marine angiosperms were equally adaptive colonizers of the carbonate platforms novel biofacies associations were derived from

nonvolcanic tectonic islands in ancient and modern oceans 1 most oceanic islands are due to excess volcanism caused by thermal and or compositional mantle melting anomalies we call attention here to another class of oceanic islands due not to volcanism but to vertical motions of blocks of oceanic lithosphere related to transform tectonics sunken tectonic islands capped by carbonate platforms have been previously identified along the vema and romanche transforms in the equatorial atlantic we reprocessed seismic reflection lines did new facies analyses and 87sr 86sr dating of carbonate samples from the carbonate platforms a 50 km long narrow paleoisland flanking the vema transform underwent subsidence erosion and truncation at sea level it was then capped by a 500 m thick carbonate platform dated by 87sr 86sr at 11 10 ma three former islands on the crest of the romanche transverse ridge are now at 900 m bsl they show horizontal truncated surfaces of oceanic crust capped by 300 m thick carbonate platforms with 10 6 ma sr isotopic ages these sunken islands formed due to vertical tectonics related to transtension transpression along long offset slow slip transforms another tectonic sunken island is atlantis bank an uplifted gabbroic block along the atlantis ii transform sw indian ridge 700 m bsl a modern tectonic island is st peter and st paul rocks a rising slab of upper mantle located at the st paul transform equatorial atlantic cold tectonic islands contrast with hot volcanic islands related to mantle thermal and or compositional anomalies along accretionary boundaries and within oceanic plates or to supra subduction mantle melting that gives rise to islands arcs

mesozoic syn and postrifting evolution of the central apennines italy the role of triassic evaporites abstractjurassic cretaceous syn and postrift successions from the central apennines were backstripped to gain information on the mesozoic evolution of the passive margin of the adriatic plate early jurassic rifting led to the development of a horst and graben paleogeography the latium abruzzi carbonate platform and the sabina umbria marche pelagic basin subsidence curves were built for both carbonate platform and pelagic basin domains from original and literature stratigraphic data the paleodepositional depths of the deepwater sediments were reconstructed from field geology data including new paleontological data it is proposed that after the deposition of lower hettangian shallow water carbonates an abrupt increase in paleowater depth to 600 1000 m occurred during the late hettangian sinemurian synrift stage the postrift stage was characterized by basin filling with decreasing paleowater depths during the jurassic and by a new deepening during the cretaceous our backstripping curves show

miocene unconformities in the central apennines geodynamic significance and sedimentary basin evolution abstract this paper shows the results obtained from an integrated study geology biostratigraphy and geochemistry carried out on the miocene edimentary deposits in central italy in order to define the timing of the sedimentary basin evolution this paper deals also with the causes of the unconformities recorded in these basins in the miocene deposits of the latina valley and the ernici simbruini mts several unconformities which distinguish different stratigraphic sequences have been recognized d 0 d 1 d 2 d 3 and d 4 for each unconformity a general description together with a geodynamical significance is provided in particular d 0 unconformity appears to be related to a regional tectonic event adria europe collision as a consequence the adria lithosphere folded and the area underwent a regional erosive event d 1 d 2 and d 3 unconformities have had a more local tectonic control since they represent the stratigraphic record of the migration of the apennines thrust belt foredeep system d 1 and d 2 unconformities are related to the late tortonian foredeep stage whereas d 3 is linked to the early messinian piggy back stage moreover the d 4 unconformity which took place during the messinian piggy back stage is strictly linked to the sea level drop of the messinian salinity crisis in this paper the genesis and evolution of a late tortonian foreland basin is also stressed latina valley foredeep basin finally taking into account sequence boundaries nannofossil biostratigraphy and geochemistry isotopic data a comparison with the curve of the 3rd order of the relative coastal onlap haq et al 1988 has been attempted in order to distinguish the unconformities controlled either by tectonic or eustatic processes

tide influenced high energy environments and rhodolith associated carbonate deposition on the outer shelf and slope off the miyako islands southern ryukyu island arc japan sediments distributed off the miyako islands southern ryukyus japan include rhodoliths larger foraminifera cycloclypeus and or bryozoan dominated carbonates of low mud content on the outer insular shelf and planktonic foraminiferal mud free carbonate sand on the slopes sidescan sonograms show large scale 2 d subaqueous dunes in the deeper shelf sediments which suggest a nw se flow direction sea bottom photographs of the slope sediments to depths of 1000 m show small scale 2 d or 3 d ripples those sedimentologic features suggest the existence of relatively high speed currents on both the shelf and slope in the area current direction and velocity have been directly measured to clarify the origin and character of the current governing the area where the rhodoliths large foraminifera are distributed the results of measurements carried out at 14 stations at depth ranges of 14 to 799 m show that the direction and velocity of the currents on the shelf and slope change semi diurnally at most shelf stations the currents at high tide are to the north northwest i e from the pacific ocean to the east china sea conversely the currents at low tide are to the south southeast from the east china sea to the pacific ocean on the slope current movements are to the west at high tide and to the east at low tide it is concluded therefore that the currents on the shelf and slopes are tidally related current speed is small in protected areas and is high on the open shelf and shelf slopes the ryukyu island arc interrupts the tidal northwestern and southeastern flow this interaction probably develops substantial turbulence and topography induced upwelling and therefore forms a natural site for the formation of mud free and or coarse sediments with rhodoliths and large formainifera

tectonic control on the architecture of a miocene carbonate ramp in the central apennines italy insights from facies and backstripping analyses abstract analyses of facies associations and biotic assemblages integrated with backstripping analysis are presented to improve understanding of the development of a shallow water miocene carbonate ramp in the central apennines italy with special reference to the relationships between tectonic subsidence and the internal architecture of the ramp subsidence curves were calculated for six measured sections located in different sectors of the platform dating is derived from sr isotope analyses from previous studies and regional correlations corrections for eustasy and paleobathymetry were deduced from biota and facies analyses the subsidence curves show rates that vary both in space and time by analysing the vertical motions in different sectors of the ramp over a fixed time span burdigalian to tortonian it was possible to evaluate the control on platform architecture exerted by tectonically induced changes in sea floor bathymetry and highlight the effects of tectonic migration most analysed sites experienced a short period of tectonic uplift or stability followed by a period of slow subsidence this preceded increased subsidence which resulted in drowning of the shallow water carbonate platform the stability uplift is progressively younger towards the north eastern sectors that correspond to progressively more external zones of the foreland relative to the apenninic orogenic belt the subsequent drowning is related to the diachronous down flexure of the adriatic lithosphere due to its eastward retreating subduction under the apennines the small magnitude of the uplift suggests that the formation of a foreland bulge due to subduction related flexure of the adriatic plate was probably not the responsible mechanism hence this uplift is related to the development of proto thrusts or to the propagation of compressive stresses in the foreland these vertical motions influenced the geometry of the platform during the 17 5 16 ma stage during this period the platform was characterised by exceptional progradation of the bryomol dominated proximal outer ramp facies belt this rapid spreading may be induced by the combined effect of increased eutrophic conditions and a contemporaneous decrease in the sea floor bathymetry resulting from the tectonic uplift from the tortonian onwards when the platform became involved in the eastward migrating foredeep system the tectonic subsidence curve records a short period of fast tectonic subsidence rates followed by a period of slow subsidence or slight uplift during basin drowning and infilling respectively

carbonate ramp depositional systems from a late jurassic epeiric platform iberian basin spain a combined computer modelling and outcrop analysis no counterparts to epeiric sea carbonate ramps are known in present day environments this hinders the interpretation of the factors controlling the growth and evolution of these depositional settings in this study we analyse the facies and geometries of two jurassic examples both from outcrop study and through computer modelling this analysis is constrained by two important features of these oxfordian and kimmeridgian ramps firstly they are very well exposed allowing accurate reconstruction of a 200 km section from proximal to distal ramp environments and secondly a time framework for correlation section reconstruction and modelling is provided by a well defined ammonite biostratigraphy the modelling results in a synthetic stratigraphy which closely matches the reconstructed cross sections and when integrated with the field study constrains and provides additional quantitative data on the following aspects of carbonate ramp systems resedimentation by storms is an important process in maintaining the ramp profile through time down ramp transport distances of between 25 and 40 km are indicated from the distribution of storm beds and shallow water allochems and from model matching known stratigraphic thicknesses and geometries modelling sediment production within the time constraints from the ammonite biozones indicates that shallow water carbonate production was 1 2 orders of magnitude less than that predicted for present day open marine carbonate platforms deeper water production rates were reduced by lesser amounts these proportionally higher outer ramp production rates also help to maintain ramp geometries through time the enigmatic slope crest of ramps is shown to result from a combination of higher shallow water production and erosion rates together with loss of accommodation during highstands and high stillstands in the modelled sea level curves the most parsimonious modelling of the two ramp sequences comes from a relative sea level curve composed of a linear subsidence component superposed by 20 and 100 kyr cycles on a third order cycle the third order cycles and their timing do not correspond to those of the exxon curve