polarimetric signatures of sea ice 1 theoretical model physical structural and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice physical properties of sea ice constituents such as ice brine air and salt are presented in terms of their effects on electromagnetic wave interactions sea ice structure and geometry of scatterers are related to wave propagation attenuation and scattering temperature and salinity which are determining factors for the thermodynamic phase distribution in sea ice are consistently used to derive both effective permittivities and polarimetric scattering coefficients polarimetric signatures of sea ice depend on crystal sizes and brine volumes which are affected by ice growth rates desalination by brine expulsion drainage or other mechanisms modifies wave penetration and scattering sea ice signatures are further complicated by surface conditions such as rough interfaces hummocks snow cover brine skim or slush layer based on the same set of geophysical parameters characterizing sea ice a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies for interpretation of sea ice polarimetric signatures

larger foraminifera distribution on a mesotrophic carbonate shelf in sw sulawesi indonesia larger symbiont bearing foraminifera typically live in shallow tropical seas in this study the fauna composition of patch reefs scattered over the spermonde shelf sw sulawesi indonesia a mesotrophic carbonate shelf is examined the foraminiferal fauna of the spermonde shelf is characterised by three assemblages a seaward slope a leeward slope and a reef base assemblage this is similar to the fauna composition at palau except that palau s reef flat assemblage is absent the samples group in six clusters the reef base deep exposed slope deep leeward slope shallow leeward slope shallow exposed slope and the southern near shore cluster of the four ecological zones that have been recognised on the spermonde shelf in corals and marine vegetation we cannot distinguish between the two outer shelf zones but we do recognise two near shore zones a northern and a southern one this latter part of the shelf within 4 km of the mainland coast has a less diverse foraminiferal fauna in which the reef base fauna is absent compared to areas with a deeper euphotic zone the deepest living species are absent whereas most other species occur in much shallower water neorotalia calcar and calcarina gaudichaudii however have been found in deeper water due to an absence of suitable habitat in the shallow areas other species like peneroplis planatus and calcarina hispida have only been found in the deepest part of their depth range as reported at okinawa these species show a greater flexibility in their habitat preference than has been observed so far we used our results to test hallock s trophic resource continuum model with actual occurrences of larger foraminifera the predictions of the model are met but patterns for example in calcarinids and peneroplids show that not all taxa react in the same way to the described environmental parameters seasonal climatic conditions in the spermonde archipelago mainly affect species with a long life cycle and deep living species a model is presented that explains why deep living species are more affected by seasonal changes in water transparency than shallow living species

polarimetric signatures of sea ice 2 experimental observations experimental observations of polarimetric signatures are presented for sea ice in the beaufort sea under cold winter conditions and interpreted with the composite model developed in part 1 polarimetric data were acquired in march 1988 with the jet propulsion laboratory multifrequency airborne synthetic aperture radar sar during the beaufort sea flight campaign the experimental area was located near 75 n latitude and spanned 140 145 w longitude selected sea ice scenes contain various ice types including multiyear thick first year and thin lead ice additionally the c band sar on the first european remote sensing satellite provides supplementary backscattering data of winter beaufort sea ice for small incident angles 20 26 at vertical polarization sea ice characterization and environmental data used in the model were collected at the applied physics laboratory drifting ice station to the northeast of prudhoe bay additional data from field and laboratory experiments are also utilized in this analysis the model relates sea ice polarimetric backscattering signatures to physical structural and electromagnetic properties of sea ice scattering mechanisms contributing to sea ice signatures are explained and sensitivities of polarimetric signatures to sea ice characterization parameters are studied

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

growth rate and life span of eocene oligocene nummulites tests inferences from sr ca ratio the problem of growth rate and life span of nummulites foraminifers attaining giant sizes during the eocene has been addressed by analysing their sr ca ratio across the eocene oligocene boundary eob of kutch western india the eocene ratio 1 rapidly decreases during the oligocene 0 5 and is coincident with the extinction of most of the eocene nummulites species a rapid enrichment of 18 o and decrease in both test size and species diversity across the boundary the high sr ca ratio in eocene foraminifers can be explained by their rapid growth under a favourable climatic condition the climatic deterioration e g 18 o cooling across the boundary and during the early oligocene possibly forced the nummulites to adopt a slower growth rate and stunted growth the rapid growth of the eocene nummulites indicates that the giant sizes of these protists need not necessarily involve a large life span

similarities between planktonic and larger foraminiferal evolutionary trends through paleogene paleoceanographic changes abstract the paleogene evolutionary records of planktonic foraminifera and larger benthic foraminifera show parallel patterns in development that may in part reflect changes in nutrient flux to surface waters following the terminal cretaceous extinctions faunas were dominated by a few cosmopolitan opportunistic species more specialized k strategists in both groups diversified during the paleocene dominating into the early eocene consistent with he globally mild climatic regime and probable limited rates of nutrient flux to surface waters high latitude cooling intensified in the middle eocene promoting diversification of less specialized taxa characteristic of cooler and deeper waters higher latitudes meridional upwelling zones and boundary currents geographic ranges of warm water taxa diminished and fragmented yet many species survived thus global diversities during the middle eocene were the highest in the cenozoic as cooling and increased rates of nutrient flux further intensified in the late eocene extinction rates of warm water planktonic and larger benthic species exceeded origination rates of cooler water and less specialized forms so diversity dropped to intermediate levels where it remained through the late eocene and oligocene previous observations that planktonic foraminiferal faunas dominated by warm water taxa are often replaced by cool water faunas even though oxygen isotopes only recorded relatively minor cooling can be reconciled by the explanation that the biotic communities responded to changes in trophic resources and euphotic habitats that accompany the temperature reduction as well as to temperature change itself

habitats of larger foraminifera on the upper reef slope of sesoko island okinawa japan larger foraminifera living in the upper 50 m in front of the fringing coral reef northwest off sesoko island japan show strong habitat differences this study closely examines the distributions of larger foraminifers and relates these to a number of key environmental factors using rigorous statistical methods since all larger foraminifera house symbiotic algae light attenuation by the water column is the most important limiting factor that must be dealt with wall structures water energy is also countered by test structure the local topography is responsible for different intensities of hydrodynamic forces which are expressed in various substrates mostly coral rubble and coarse grained sand the genus peneroplis very common on the reef flat clearly prefers hardgrounds of the shallowest slope parts down to 30 m while dendritina is restricted to sandy bottoms and avoids the uppermost meters of the slope it can be found down to 50 m at least alveolinella shows a similar depth distribution to dendritina but is common on hard bottom the distribution of parasorites which is restricted to sandy substrates starts at 20 m and extends to 80 m sorites on the other hand was found only on firm substrates between the reef edge and 50 m the same depth distribution was recorded for amphisorus but this genus is not correlated with specific substrates most of the amphistegina species prefer hardgrounds while amphistegina radiata is also common on sand the calcarinids capable of withstanding high water energy are abundant on firm substrates close to the reef edge only baculogypsinoides inhabits deeper parts of the slope on sandy bottom and avoids the shallowest parts sections with hard substrates are settled by heterostegina even down to 80 m although this genus was occasionally found on sandy bottoms nummulites in contrast is restricted to sands between 20 and 70 m operculina starting at 20 m also prefers sandy substrates but rare individuals were detected on coral rubble and macroids

late pleistocene and holocene sedimentation on the george v continental shelf east antarctica abstract climatically controlled glaciological and oceanographic environmental changes off the george v coast during the late pleistocene and holocene have been reconstructed from changes in sedimentation processes the evolution of a sediment drift deposit mertz drift located in the deep trough on the shelf has been assessed using a sedimentological approach up to 5 5 m long cores have been collected four late pleistocene to holocene sediment units have been distinguished on the basis of their physical properties grain size distributions geochemical characteristics and ages the basal unit 1 is a grey sandy clayey diamicton 27 37 wt sand deposited before 14 000 14 c yr before present 14 c yr bp unit 1 represents a late pleistocene sub ice shelf water lain till overlain by a thin current winnowed sandy sub unit unit 2 is a massive siliceous sandy mud 11 30 wt sand rich in ice rafted debris deposited between about 14 000 and 5000 14 c yr bp it likely represents an open marine setting proximal to a retreating ice front where strong bottom currents were frequent the overlying unit 3 is a laminated siliceous mud and diatomaceous ooze with less terrigenous material 4 5 wt average sand deposited between 5000 and 3000 14 c yr bp the low wet bulk density values 3 and mass specific magnetic susceptibility values 8 m 3 kg of sediments of unit 3 are a consequence of the high content of biogenic material c org content 1 wt biogenic opal averaging 55 wt unit 3 is probably related to a phase of increased sediment accumulation on the drift site and low bottom current activity on the shelf with a stratified upper water column that could have lead to an enhanced primary productivity occurrence of crossed lamination indicates episodes of slightly enhanced bottom currents probably with velocities up to 3 5 cm s the top unit 4 is a bioturbated siliceous sandy mud on average 50 cm thick deposited under an energetic bottom current regime after about 3000 14 c yr bp this regime is probably related to the activation of a brine rejection mechanism and is linked to the formation of high salinity shelf water hssw in a coastal polynya which causes winnowing of the shelf deposits in contrast the mid holocene setting was characterised by weaker bottom currents that together with high inputs of organic material from the photic zone allowed for the deposition of thick fine grained sediments of unit 3 resulting in an anoxic environment

conflicting isotopic and biotic evidence for tropical sea surface temperatures during the tertiary abstract the biotic evidence from a varied group of shallow water organisms including mangroves zooxanthellate corals mainly reefal and larger foraminifera suggests that sea surface temperatures at low latitudes during the tertiary from at least the early eocene to the middle miocene were subtropical to tropical in nature and similar to temperatures prevailing at low latitudes at the present day 20 28 c in a recent paper shackleton 1984 the suggestion is made on the basis of oxygen isotope studies of foraminiferal shells that low latitude sea surface temperatures during the palaeogene and much of the neogene were invariably lower than those in similar regions today with a stable temperature of around 18 c this paper discusses the conflicting evidence for sea surface temperatures obtained from palaeontological and isotopic sources and suggests that palaeotemperatures derived from some isotopic studies are too low to account for the distribution and diversity of many tertiary tropical and subtropical biotas

3d seismic interpretation and structural analysis of z field eastern persian gulf abstract structural analysis of the z hydrocarbon field in the eastern persian gulf is accomplished using 3d seismic data which reveal a domed structure elongated in two axial directions it is understood from underground contour maps that the axial trace of the structure changes from northwest in the north to northeast in the southern part of the structure faults affected by the z structure also show change in their geometry and kinematics such structural attitude possibly took place with the early formed salt diapir which has sustained late strike slip deformation some normal faults have reactivated as strike slip faults which means the arrangement of the strike slip faults is likely influenced by preexisting normal faults the geologic setting and particular geometry of the z structure suggest the role of vertical movements of precambrian hormuz salt in the structure s development salt movements likely started in the early paleozoic and as a result of a releasing bend along a left lateral strike

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

recognition of stratigraphic sequences in carbonate platform and slope deposits empirical models based on microfacies analysis of palaeogene deposits in southeastern spain abstract the functional morphology and life style of foraminifers can be used to determine their former position on the platform and to detect upwards shallowing and deepening trends in sedimentary sequences the sequential analysis of the palaeogene platform deposits of alicante proved to be greatly enhanced by the use of the palaeoecology of foraminifers on the basis of this analysis three different empirical models for platform accommodation cycles could be designed a ramp model distinctive for the lower eocene a combined ramp rimmed model characteristic for the middle and upper eocene and a rimmed model representative for oligocene cycles the change in platform type through time is thought to be a response to climate related changes in growth potential of hermatypic corals possible criteria to distinguish systems tracts in slope deposits on their foraminiferal and clast content are put to the test in a slope section with positive results from the correlation of the southern spanish palaeogene cycles with eurasian african plate boundary events along the pyrenees and with antarctic glaciations it can be concluded that the majority of the cycles are tectonically controlled with glacio eustatic contributions since the middle late eocene boundary

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

arabia eurasia continental collision insights from late tertiary foreland basin evolution in the alborz mountains northern iran a poorly understood lag time of 15 20 m y exists between the initial arabia eurasia continental collision in late eocene to early oligocene time and the acceleration of tectonic and sedimentary processes across the collision zone in the early to late miocene the late eocene to miocene pliocene clastic and shallow marine sedimentary rocks of the kond eyvanekey and semnan basins in the alborz mountains northern iran offer the possibility to track the evolution of this orogen in the framework of collision processes a transition from volcaniclastic submarine deposits to shallow marine evaporites and terrestrial sediments occurred shortly after 36 ma in association with reversals in sediment provenance strata tilting and erosional unroofing these events followed the termination of subduction arc magmatism and marked a changeover from an extensional to a contractional regime in response to initiation of continental collision with the subduction of stretched arabian lithosphere this early stage of collision produced topographic relief associated with shallow foreland basins suggesting that shortening and tectonic loading occurred at low rates starting from the early miocene 17 5 ma flexural subsidence in response to foreland basin initiation occurred fast sediment accumulation rates and erosional unroofing trends point to acceleration of shortening by the early miocene we suggest that the lag time between the initiation of continental collision 36 ma and the acceleration of regional deformation 20 17 5 ma reflects a two stage collision process involving the soft collision of stretched lithosphere at first and hard collision following the arrival of unstretched arabian continental lithosphere in the subduction zone

bryozoan beds in northern italy as a shallow water expression of environmental changes during the oligocene isotope event 1 abstract shifts in carbonate producing biotic communities in the geological record provide evidence of past environmental changes in the neritic realm the shallow marine calcare di nago formation exposed in the san valentino section northern italy covers the late eocene and earliest oligocene the succession is characterized by the occurrence of light dependent biota such as coralline algae and larger benthic foraminifera in the uppermost part of the section however the fossil association is dominated by bryozoans which are filter feeder organisms this ca 12 m thick interval locally contains up to 86 bryozoans while coralline algae as well as larger benthic foraminifera are absent coralline algae and nummulitid foraminifera recover in the upper part of the bryozoan beds whereas orthophragminids do not recover the gradual disappearance of larger foraminifera and coralline algae within the bryozoan dominated deposits is coeval with a pronounced positive shift in 13c based on its biostratigraphic position this positive shift is interpreted to be linked to the positive shift in 13c recognized in deep sea records shortly above the eocene oligocene boundary which in turn is associated to the positive shift in 18o leading to the oi 1 oligocene isotope event 1 cooling phase total phosphorus content increases in the bryozoan beds suggesting enhanced nutrient supply to the neritic ecosystem this phosphorous peak is coeval with the globally recognized increment in ocean productivity around the oi 1 and 13c positive shift thus disappearance of light dependent biota and the dominance of bryozoans in the platform carbonates studied are interpreted to result not necessarily from a deepening of the depositional environment but from the combination of lower sea surface temperatures and the deterioration of underwater light conditions on account of elevated turbidity in surface waters resulting from enhanced primary productivity as bryozoan beds occur in several italian localities around the eocene oligocene boundary they are interpreted to represent the regional expression of neritic carbonate depositional systems to global environmental changes occurring at the dawn of an ice house earth

solidification of leads theory experiment and field observations thin sea ice plays a central role in the surface heat and mass balance of the arctic ocean in order to develop understanding of these balances we describe and analyze highly resolved temperature data taken through the air sea ice interface during the transition from an ice free to an ice covered arctic ocean surface the data were taken to observe the thermodynamic evolution of a lead a process that has previously only been accessible to measurement techniques confined to the lead edge our detailed analysis of the field data is guided by recent theoretical and experimental advances in understanding the phase dynamics of directionally solidified alloys because of the dearth of direct observations we also present time series of the relevant heat fluxes inferred from our data and demonstrate the controlling influence that the internal phase evolution has on these quantities we have previously examined the stability of the brine trapped in a growing sea ice matrix both theoretically and experimentally and now find that haline convection driven from within the growing layer is consistent with this previous work and with the nature of direct turbulence measurements the importance of this process is that although ice growth is continuous the local brine flux commences abruptly only after some time in contrast to what had previously been supposed hence the ice growth process itself is a source of intermittency in oceanic boundary layer turbulence furthermore we find that in this particular situation the sea ice growth is not simply a square root function of time in contrast to the model typically used in numerical simulations by far the most practical methods of studying lead convection are numerical simulations and laboratory models and a strong conclusion of this study is the importance of the proper treatment of the boundary conditions describing the buoyancy flux

the formation and morphology of ice stalactites observed under deforming lead ice during the leadex main field experiment held in april 1992 in the alaskan beaufort sea a number of large ice stalactites were observed growing under young lead ice formation of the stalactites was associated with rafting of the thin highly saline ice the rafting caused the brine to drain rapidly from the ice at a temperature well below the freezing point of the surrounding water which in turn caused ice to form in a hollow cylinder around the brine plume within a 15 h period after the rafting event the stalactites which were located approximately 10 m apart in a line along the up wind edge of a 150 m wide lead had grown to a length of 2 m a detailed structural analysis of the upper part of one of these stalactites revealed that the interior channel down which the brine flowed was bounded by a zone of frazil ice that developed into a shell of columnar ice the growth of the columnar ice was directed radially outward and the c axes of these crystals were oriented perpendicular to their growth direction development of the stalactites illustrates the impact ice deformation can have on the process of brine rejection in freezing leads and potentially on the thermohaline structure of the upper ocean in ther immediate vicinity of the lead

oxygen and carbon isotopic composition of recent larger and smaller foraminifera from the madang lagoon papua new guinea abstract tests of recent benthic foraminifera from the madang lagoon papua new guinea were analyzed for their oxygen and carbon isotopic composition analyses were performed on scuba collected species from backreef and low oxygenated harbor environments covering a depth range of 0 to 45 m both rotaliid and miliolid symbiont bearing species were found to exhibit increasing 18o with depth while only the rotaliids reveal a comparable trend in their 13c composition the general trend of depletion in the heavier isotopes 13c and 18o appears to be depth and light dependant neither the symbiont type nor the nature of the microhabitat appear to affect the magnitude of 18 o 16 o fractionation in larger foraminifers from this environment the carbon isotope patterns of symbiont bearing species revealed distinct differences between rotaliids and miliolids consistently lower 13c values in rotaliid foraminifers may be related to a higher rate of photosynthetic activity the photosynthetic effect of carbon isotope fractionation may be overprinted by the presence absence of an internal carbon pool and or specific modes of biomineralization which may act as isotopic filters foraminifera collected from low oxygenated organic rich sediments in harbor inlets at madang were found to exhibit particularly low 13c values depletion 13c is suggested to be due to oxidative processes in the surrounding organic rich sediment coupled with preferential incorporation of isotopically lighter 12c

larger foraminifera as depth indicators in carbonate depositional environments abstract studies of living larger foraminifera have provided several breakthroughs pertinent to the use of their ancient analog in paleoenvironmental interpretation the first of these insights is that modern larger foraminifera are nutritionally dependent upon algal symbionts and are morphologically adapted to house those symbionts the second is that algal symbiosis is energetically highly advantageous under nutrient deficient conditions such as those prevalent in well developed modern coral reef environments in addition experimental evidence demonstrates that the availability of light and water turbulence in the environment end page 477 influences shapes and sizes of modern foraminifera by analogy assemblage composition including the presence and abundance or absence of planktonic and smaller benthic species along with shapes and size distributions of the larger foraminifera can be used in paleodepth analysis and to supplement other petrographic evidence in carbonate facies interpretation among the current limitations of the use of larger foraminifera as paleodepth indicators are the complications caused by taxonomic heterogeneity of both the larger foraminifera and their algal symbionts nevertheless the potential for use of larger foraminifera in paleoenvironmental analysis is tremendous as is the potential benefit of further studies of both modern and ancient assemblages of larger foraminifera end of article last page 478

recent foraminifera tracers of oceanic water movements in the southwestern lagoon of new caledonia abstract water movements in the southwestern lagoon of new caledonia are controlled mainly by tidal currents and by a wind driven surface current to the northwest balanced by a subsurface return current to the southeast during each rising tide oceanic water inflows over the barrier reef through the passes and between the scattered reefs of the southeast the distribution of planktonic foraminiferal tests shows that most of the superficial oceanic water is pushed by the southeast trade winds to the inner part of the bay de boulari the distribution of some benthic species especially gypsina globula reuss and pyrgo denticulata brady is also related to an oceanic inflow the distribution of their tests follows the trajectory of subsuperficial oceanic water penetrating into the lagoon through the passes and gives a clear picture of these water movements this image based on thanatocoenoses can be preserved after diagenesis therefore its possible utilization in similar paleoenvironments can be considered

contemporary tectonic stress pattern of the persian gulf basin iran abstract the contemporary crustal stress pattern is important to several aspects of earth sciences such as reservoir geomechanics neotectonic deformation and geodynamic modelling the persian gulf basin is a petroliferous region in southern iran that hosts hundreds of petroleum wells and hence the knowledge of the present day stress is critical for any exploration and production in this region in addition to geo resources this region has a great economic importance and the in situ stresses provide key insights on neotectonic and seismic hazard of the basin however there is limited in situ stress information in the persian gulf region in this study we analyse 8 km of borehole image logs in 20 wellbores in the persian gulf in order to provide a clear picture of the stress pattern in this region our wellbore stress analyses provide 35 quality ranked maximum horizontal stress orientations shmax data records in addition we compile 27 earthquake focal mechanisms in the study region from different seismic catalogues and published literature and present the first comprehensive quality ranked in situ stress map of the persian gulf basin with 62 data records which can be used as a valuable source of information for future exploration and seismic hazard assessment the resulting database suggests that the shmax azimuth in central and western persian gulf is ne sw parallel to the arabia eurasia tectonic plate convergence which demonstrate the key role of relative plate motion in the present day stress pattern of these areas however the shmax azimuth in the eastern part of the study area is nw se which is different from the central and western persian gulf the nw se shmax azimuth is consistent with other geological and geophysical observations that suggest an indentor model for musandam peninsula oman in the zagros makran syntaxis

winners and losers stable isotopes and microhabitats of living archaiadae and eocene nummulites larger foraminifera abstract this paper discusses isotopes in larger foraminiferal calcite from two contrasting settings modern florida bay dominated by archaiadae the winners and the upper eocene barton clay of england locally dominated by nummulites the losers the archaiads plus peneroplids and soritids were mainly collected from thalassia leaves they yield signatures that closely reflect strong isotopic gradients in sea water across florida bay and the outer patch reefs isotopic signatures of eurytopic androsina lucasi record extreme conditions to the north of the bay which includes 13 c evidence for much nutrient regeneration such tolerance of relatively eutrophic conditions may explain the capacity of archaiadae for survival in the caribbean region during the neogene isotopes of nummulites prestwichianus from the basal bartonian compare more closely with data from living nummulite heterostegina 18 o indicates a yearly growth cycle under tropical bottom water temperatures with an annual range of approximately 2 5 c carbon isotopes show a trend towards heavier values with growth here related to decelerating rates of calcification and perhaps the additional effects of test thickening on carbon isotope fractionation by endosymbionts the nummulitic data indicate a much more stable carbon and nutrient cycle in the basal barton clay than seen in the florida bay mudmound assemblage this is consistent with their presumed stenotopic and oligotrophic life habit it could well explain their vulnerability to extinction after the mid eocene and the post aquitanian decline of larger rotaliids and reefs in the caribbean region

the role of nutrient availability in bioerosion consequences to carbonate buildups abstract zooxanthellate organisms which are among the major carbonate producers on coral reefs are highly adapted to nutrient deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant reef dwelling bioeroding organisms on the other hand seem to increase in abundance with increasing availability of nutrient and food resources maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion the dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability nutrient availability may also influence development of carbonate facies in reef systems that develop in oligotrophic waters skeletal sands and framework should dominate carbonate buildups in systems that develop in mesotrophic waters enhanced bioerosion should reduce much of the skeletal material to carbonate muds increasing the prevalence of mud rich facies eutrophic conditions should result in bioeroded hardgrounds and carbonate depositional hiatuses when carbonate accumulation rates fail to equal or exceed rates of local relative sea level rise reefs drown bored and lithified pavements with crusts of ferromanganese oxides phosphates or glauconite often separate shallow reef from overlying deeper water deposits nondeposition bioerosion and evidence for low redox potentials at the sediment water interface all implicate excess nutrient availability as a factor in reef drowning some carbonate depositional hiatuses and bioerosional surfaces are local phenomena evidence of responses to local increases in nutrient availability resulting from submergence of soils runoff or topographic upwelling others appear to reflect regional or worldwide events because many carbonate producing organisms have life history strategies specialized to nutrient deficient conditions they are unable to compete when nutrients become plentiful events that triggered ocean turnover or sharp increases in the rate of deep ocean circulation would have increased sea surface nutrient availability worldwide such eutrophication could have caused widespread extinctions in reef communities because eutrophication promotes bioerosion details of the fossil records of those events are probably lost in bioerosional hiatuses

development of sea ice in the weddell sea we report on the development and physical properties of sea ice in the central and eastern weddell sea the investigations were part of the winter weddell sea project 1986 which extended over the months of july through december major elements of the glaciological part of this study included continuous shipborne observations of sea ice conditions and occasional helicopter reconnaissance flights extensive measurements of snow and ice thicknesses at daily ice stations and detailed analyses of sampled ice cores from each ice station textural investigations of the sampled ice revealed the dominance of frazil ice in the central weddell sea and the occurrence of an additional ice class called platelet ice together with the commonly known frazil and congelation ice in the coastal region of the eastern weddell sea these results in combination with the visual ice observations reveal two major mechanisms for sea ice generation in the antarctic which were not sufficiently well accounted for in previous investigations in the central weddell sea a cycle of pancake ice formation and its growth into consolidated floes seems to be the dominant process of the advancing sea ice edge in the coastal waters the growing sea ice cover consists to a considerable degree of ice platelets which are formed in the underlying water column in front of the ice shelf edges thus congelation ice growth which is mainly controlled by atmospheric thermodynamic forcing seems to be of less importance in the central and south eastern weddell sea than for example in the arctic basin

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

new insights into quaternary glacial dynamic changes on the george v land continental margin east antarctica abstract the continental margin of the george v land represents the seaward termination of one of the largest sub glacial basins the wilkes basin of the east antarctic ice sheet eais and hence is a potentially useful site for the investigation of the cenozoic glacial history of antarctica because the seafloor morphology relates strictly to recent glacial marine sedimentary processes we have compiled all available echo soundings data collected until the year 2001 and integrated the data set with satellite altimetry data as a result we have produced a new bathymetric map of the margin covering an area of more than 80 000 km 2 with a spatial resolution of about 1 km the bathymetric data have been integrated with sub bottom profiler data with the purpose of defining sedimentary processes and their variations during the quaternary the continental shelf of the wilkes land margin is characterised by alternating banks and glacial troughs connected to sub marine canyons that cut into the continental slope our study focussed on the continental rise where asymmetrical ridges alternate with large deep sea channels the ridges have a long gentle eastern side and short steep western side with axis elongated approximately in north south direction perpendicular to the margin the channels represent the main sediment drainage pattern feeding the ridge depositional system found along the continental rise the sediment is supplied to the continental shelf edge by ice sheets and sediment gravity flows are considered the main process for sediment supply to the rise the modern sedimentary environment of the deep margin is affected by turbiditic down slope sediment transfer with a minor contribution from along slope contour currents the wega channel is currently affected by transport and settling of sediment through high salinity shelf water hssw originating on the continental shelf we infer that thermohaline circulation has contributed to sediment transport and deposition since the mid pleistocene

larger foraminifera from the chagos archipelago their significance for indian ocean biogeography abstract the chagos archipelago is a series of atolls situated in the centre of the indian ocean close to the equator and geographically isolated by surface water currents and deep water barriers from other areas of shallow water environments the region is exposed to small tides and periods of strong winds the combined effects of these is to cause relatively high energy conditions to exist in the shallow waters around the reefs the bottom sediments are coarse grained and they form a mobile substrate although the coral faunas are diverse seagrasses are rare the larger foraminifera 1 4 mm are principally amphisorus hemprichii heterostegina depressa and operculina ammonoides many of the tests are damaged due to postmortem transport and consequently depth distributions are distorted however a ammonoides is confined to the deeper waters of the lagoon other taxa 1 4 mm in size are widely distributed in modest abundance overall the diversity of the fauna is lower than that observed in atolls of the mauritius and comoro island groups this is attributed to geographic isolation

continental shelf record of the east antarctic ice sheet evolution seismo stratigraphic evidence from the george v basin abstract the late quaternary ice sheet ice shelf extent in the george v basin east antarctica has been reconstructed through analyses of chirp sub bottom profiles integrated with multi channel seismic data and sediment cores four glacial facies related to the advance and retreat history of the glaciated margin have been distinguished facies 1 represents outcrop of crystalline and sedimentary rocks along the steep inner shelf and comprises canyons once carved by glaciers facies 2 represents moraines and morainal banks and ridges with a depositional origin along the middle inner shelf facies 3 represents glacial flutes along the middle outer shelf facies 4 is related to ice keel turbation at water depths 775 m with drape sheet and mound characters and numerous undisturbed sub bottom sub parallel reflectors facies md1 b a fluted sediment drift deposit at water depth

facies patterns and stratal geometries clues to the nature of the platform margin during the paleocene northeast sirte basin libya abstract the sirte basin of libya is a mesozoic tertiary rift basin comprising a series of horsts and grabens which were formed as a result of collapse of a n s trending arch in late cretaceous time the paleocene section is made up of two shallowing upward cycles where each cycle is under and overlain by deeper pelagic facies a gradual shallowing trend from basin to shallow platform is seen in both bio and lithofacies these are interpreted as representing prograding ramps with no evidence of a significant break in slope between the basin and the adjacent platform the fact that most facies are dominated by micrites suggests that deposition was in a low energy setting possibly on a leeward margin these ramps were initially foram dominated platforms setting the style for later tertiary ramps large forams filling the role of inner mid ramp carbonate producers after the demise of the rudist coral assemblage at the end of the cretaceous based on local and regional information a number of episodes of relative sea level change can be recognized the two shallowing upward ramp cycles are interpreted as representing two highstand system tracts the precipitation of evaporites in the lower cycle appears to be associated with the earlier highstand system tract culminating during a sea level lowstand a drop in sea level during the late paleocene is also invoked to explain the interpreted influx of meteoric waters following the later highstand this event resulted in the creation of good mouldic and vuggy porosities thus making these porous inner mid ramp facies potential targets for hydrocarbon exploration on a basin wide scale this event is also very important because all the paleocene reservoirs at least in the eastern sirte basin seem to be related to this possible subaerial exposure event

the anatomy of a freezing lead winter leads are regions of intense ice growth with resultant large fluxes of heat to the atmosphere and salt to the ocean they constitute a major source of new ice in the arctic basin during the 1988 drift phase of the coordinated eastern arctic experiment we were afforded a unique opportunity to conduct a detailed long term study of a freezing lead measurements were made from september 17 to november 18 during which time the ice grew from open water to a thickness of 0 56 m cores were removed from the lead ice on a routine basis and analyzed for ice temperature salinity density and structure from these measurements the derived quantities of brine volume porosity heat flux to the atmosphere and salt flux to the ocean were computed in addition to this 2 month time series study of ice cores the spatial variation in lead ice properties was investigated on september 30 thin section studies of ice structure indicated that the upper 0 05 0 15 m of the ice sheet was granular and that the lower portion was columnar typically a portion of the granular layer was snow ice once the transition from granular to columnar ice had occurred granular ice did not reappear as the ice grew thicker the c axes of the ice crystals became aligned within the horizontal plane this alignment direction corresponded closely with the inferred direction of the current at the ice water interface vertical temperature profiles in the ice were approximately linear salinity profiles were usually c shaped with bulk salinities ranging from 9 to 6 before stabilizing at 6 for ice thicker than 0 35 m core data were used to compute the flux of heat to the atmosphere and the flux of salt to the ocean for seven time intervals during the experiment heat fluxes ranged from 89 to 29 w m2 with an average of 50 w m 2 roughly 3 times the corresponding value from multiyear ice the flux of salt from the lead ice to the ocean varied from 0 51 to 0 06 kg m 2 d 1 averaging 0 21 kg m 2 d 1

recognising macrophyte vegetated environments in the rock record a new criterion using hooked forms of crustose coralline red algae abstract the role of macrophytes such as seagrasses in influencing deposition in shallow marine environments has long been understood they affect sediment textures such that they do not reflect ambient hydrodynamic conditions and so the recognition of ancient vegetated environments is important for accurate palaeoenvironmental analysis however there is little direct fossil evidence of such plants in the rock record and so the presence of former macrophyte cover generally has to be inferred from indirect evidence based on the characteristics of modern macrophyte vegetated environments we present a new criterion for the recognition of vegetated environments in the rock record based upon a distinctive hooked form of crustose coralline red algae that is definitively indicative of growth on seagrasses and also on other macrophytes with similarly flattened blades and has been recognised from both modern inhaca island mozambique and fossil the eocene of oman seagrass beds

ripple cross laminated sediments on the east antarctic shelf evidence for episodic bottom water production during the holocene abstract biosiliceous sediments sampled from a submarine valley system on the continental shelf of east antarctica contain intervals of ripple cross lamination interspersed with massively bedded units based on radiocarbon dates from one core collected on the mac robertson shelf the most intensely cross laminated sediments were deposited between 6 and 3 5 kyr bp with isolated cross laminae deposited at other times in the holocene the cross laminated sediments are interpreted here as a signal of episodic density currents flowing across the outer shelf which result from the formation of high salinity shelf water hssw this hssw is formed in winter by brine rejection during sea ice formation and by the exchange and cooling of upwelled saline slope water and it contributes to the bottom water produced along the continental margin of antarctica if this interpretation of the cross laminae is correct then bottom water formation and export from the east antarctic shelf has exhibited temporal and probably also spatial variability throughout the holocene such variability would have implications for oceanographers attempting to quantify antarctic bottom water production rates based only on present day observations

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

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

development of a papua new guinean onshore carbonate reservoir a comparative borehole image fmi and petrographic evaluation abstract the depositional and diagenetic controls on carbonate platform evolution are notoriously heterogeneous and difficult to determine from standard subsurface wireline logging techniques here a combined borehole image fmi fullbore formation microimager and petrographic study allowed evaluation of depositional and diagenetic trends across an australasian subsurface buildup that is a major recent gas discovery the elk and antelope gas fields are hosted in tertiary reefal platformal and associated deep water carbonates in the present day foothills region of the fold and thrust belt in the gulf province of papua new guinea a full suite of fmi logs 2800 m and 292 thin sections mainly from sidewall cores and cuttings from both platform flank and shallow water deposits were evaluated during this study despite the obvious scale differences between the datasets there was some correlation between the independent petrography and fmi studies for a picking major facies boundaries and b interpretation of depositional environments the latter particularly for slope and deep water deposits however thin section petrography proved critical in understanding primary depositional textures and secondary alteration features through the shallow water carbonates where complex diagenetic overprinting had strongly impacted original fabric and or in regions affected by gas smearing the petrographic study allowed more detailed examination of diagenesis and its impact on rock fabric which links to the fmi textures component analysis and depositional textures identified in thin section are good indicators of original depositional environment full fmi coverage allowed textural definition on a dm m scale identification and characterisation of vertical changes and likely large scale variations in depositional environments and sequences it was clear from combining the results of the two studies that diagenesis as well as depositional fabric had a strong impact on resultant fmi facies the diagenetic overprinting would have been difficult to extract from the fmi data without the benefit of the petrographic work this study shows the merits of selective petrographic analysis to calibrate the quality of facies interpretation from fmi images and proved critical for enhancing and in places revising initial fmi interpretations

formation and structure of refrozen cracks in land fast first year sea ice 1 this study characterizes the healing process and structure of undeformed linear parallel sided flooded cracks in land fast sea ice field investigations and refreezing experiments were performed in mcmurdo sound ross sea antarctica between 1998 and 2002 data from a two dimensional thermistor array are used to show that the ice water interface of freezing cracks is arch shaped due to bidirectional heat flow to the surrounding ice cover and to the atmosphere ice growing laterally into the crack is found to desalinate over a prolonged period of time until the isotherms are approximately horizontal superposition of heat flow to the atmosphere and to the host sea ice sheet allows the refreezing progress to be modeled analytically close to the ice air interface the salinity is higher at the sides of wide refrozen cracks than it is at the center however deeper down and in narrower cracks in general the salinity is higher at the center than at the sides a finite volume computational fluid dynamics cfd model reproduces the generally arch shaped alignment of brine pockets this pattern is attributed to convection in the mushy layer crystals are found to grow upstream into the crack due to a salinity gradient in the buoyant convective flow

revised age of proximal deposits in the zagros foreland basin and implications for cenozoic evolution of the high zagros the regionally extensive coarse grained bakhtiyari formation represents the youngest synorogenic fill in the zagros foreland basin of iran the bakhtiyari is present throughout the zagros fold thrust belt and consists of conglomerate with subordinate sandstone and marl the formation is up to 3000 m thick and was deposited in foredeep and wedge top depocenters flanked by fold thrust structures although the bakhtiyari concordantly overlies miocene deposits in foreland regions an angular unconformity above tilted paleozoic to miocene rocks is expressed in the hinterland high zagros the bakhtiyari formation has been widely considered to be a regional sheet of pliocene pleistocene conglomerate deposited during and after major late miocene pliocene shortening it is further believed that rapid fold growth and bakhtiyari deposition commenced simultaneously across the fold thrust belt with limited migration from hinterland ne to foreland sw thus the bakhtiyari is generally interpreted as an unmistakable time indicator for shortening and surface uplift across the zagros however new structural and stratigraphic data show that the most proximal bakhtiyari exposures in the high zagros south of shahr kord were deposited during the early miocene and probably oligocene in this locality a coarse grained bakhtiyari succession several hundred meters thick contains gray marl limestone and sandstone with diagnostic marine pelecypod gastropod coral and coralline algae fossils foraminiferal and palynological species indicate deposition during early miocene time however the lower miocene marine interval lies in angular unconformity above 150 m of bakhtiyari conglomerate that in turn unconformably caps an oligocene marine sequence these relationships attest to syndepositional deformation and suggest that the oldest bakhtiyari conglomerate could be oligocene in age the new age information constrains the timing of initial foreland basin development and proximal bakhtiyari deposition in the zagros hinterland these findings reveal that structural evolution of the high zagros was underway by early miocene and probably oligocene time earlier than commonly envisioned the age of the bakhtiyari formation in the high zagros contrasts significantly with the pliocene quaternary bakhtiyari deposits near the modern deformation front suggesting a long term 20 myr advance of deformation toward the foreland

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

physical properties of summer sea ice in the fram strait the physical properties of sea ice in the fram strait region of the greenland sea were examined during june and july 1984 in conjunction with the marginal ice zone experiment field program most of the ice sampled within fram strait during this period was multiyear thicknesses and other properties indicated that none of the multiyear ice was older than 4 to 5 years snow cover on the multiyear ice averaged 29 cm while that on first year ice averaged only 8 cm deep this difference may be related to enhanced sublimation of the snow on the thinner first year ice the salinity profiles of first year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment are substantially less saline than earlier cores thin section examinations of crystal structure indicate that about 75 of the ice consisted of congelation ice with typically columnar type crystal structure the remaining 25 consisted of granular ice with only a few occurrences of snow ice the granular ice consisted primarily of frazil found in small amounts at the top of floes but mainly observed in multiyear ridges the horizontally oriented crystal c axes showed various degrees of alignment ranging from no alignment to strong alignments in which the alignment direction changed with depth implying a change in floe orientation with respect to the ocean current at the ice water interface during ice growth evidence of crystal retexturing was observed in the upper meter of nearly every multiyear core this retexturing consisting of grain boundary smoothing and nearly complete obliteration of the ice platelet brine layer substructure is attributed to summer warming

using sea ice to measure vertical heat flux in the ocean results of an experiment performed at drifting ice station fram i in the arctic ocean northwest of spitzbergen during march may 1979 indicate that sensible heat flux from the ocean to the ice cover was less than 2 w m 2 the estimate is based on measurements of temperature gradient growth rate and salinity of young sea ice uncertainty in the magnitude of the heat flux results more from evidence of horizontal inhomogeneity in the growing ice sheet than from measurement errors

syndepositional dissolution of calcareous foraminifera in modern shallow water sediments abstract dissolution of calcareous tests in waters undersaturated with respect to calcium carbonate causes postmortem changes to assemblages of modern benthic foraminifera comparison of the percentage of agglutinated tests in the living and dead assemblages from the same sample enables the amount of dissolution to be quantified re examination of data from the continental shelf off new york and the estuarine chezzetcook inlet canada reveals major dissolution losses which lead to dead assemblages rich in agglutinated tests it is probable that partial dissolution of the calcareous component of modern assemblages is more widespread than has been recognised

grain susceptibility to the effects of microboring implications for the preservation of skeletal carbonates the boring activity of microendolithic organisms such as cyanobacteria chlorophytes rhodophytes and fungi represents a major destructive process affecting sediment preservation within reef environments this study demonstrates the presence of two distinct assemblages of microborers within sediments collected from the fringing reefs of north jamaica correlating to the upper 18 m depth photic zones the upper photic zone assemblage is dominated by cyanobacteria and chlorophytes whilst rhodophytes and fungi become more abundant with increasing water depth most significant from a grain preservation perspective is the variable nature of grain infestation observed between different reef sites and different carbonate grain types the highest degree of grain infestation occurs within shallow low energy back reef environments and the most susceptible grains at all sites are corals molluscs and foraminifera coralline algae halimeda and echinoid fragments are rarely heavily infested high rates of infestation at back reef sites result in rapid diminution of the most susceptible grains especially coral which are either underrepresented or contribute only to the finer sediment fractions in the subsurface fore reef grain assemblages undergo relatively little alteration microboring therefore has potential to bias the fossil record by removing the most susceptible skeletal grains the impact of microboring upon back reef grain assemblages must be considered when attempting to model depositional processes within both modern and ancient reef environments

the effects of callianassa bioturbation on the preservation of carbonate grains in davies reef lagoon great barrier reef australia abstract coring air life excavation and tracer sediment experiments in the lagoon floor sediments of davies reef revealed that callianassid shrimp had produced during their feeding a 5 60 cm thick surface layer of moderately to poorly sorted gravel free sediment above very poorly sorted gravelrich sediment the subsurface gravel is epilithic in origin close to reef framework but consists predominantly of infaunal molluscs through most of the lagoon these infaunal skeletons tend to be buried rapidly in a well preserved state escaping the microboring that attacks all grains on the surface two geologically significant points emerge first the surface layer will not get preserved in its present form and any analyses of surface samples can give a false impression of the accumulating sedimen pile and the prevailing hydraulic regime and second the combination of continuous fine sediment recycling and surface microboring can lead to a bias in the fossil reefal limestone record with epilithic organisms seemingly subordinate to infaunal molluscs

arabia eurasia collision and the forcing of mid cenozoic global cooling the end of the eocene greenhouse world was the most dramatic phase in the long term cooling trend of the cenozoic era here we show that the arabia eurasia collision and the closure of the tethys ocean gateway began in the late eocene at 35 ma up to 25 million years earlier than in many reconstructions we suggest that global cooling was forced by processes associated with the initial collision that reduced atmospheric co2 these are 1 waning volcanism across southwest asia 2 increased organic carbon storage in paratethyan basins e g black sea and south caspian 3 increased silicate weathering in the collision zone and 4 a shift towards modern patterns of ocean currents associated with increased vigour in circulation and organic productivity

a latest carboniferous warming spike recorded by a fusulinid rich bioherm in timor leste implications for east gondwana deglaciation abstract during the late paleozoic and early mesozoic timor lay in the northern part of the north south east gondwana rift system along which the western margin of australia later developed discovery of a latest gzhelian bioherm in the central highlands of timor leste has implications for latest carboniferous earliest permian climate history and deglaciation in basins further south in the rift system limestone outcrop of the maubisse formation near the village of kulau is recognized as a bioherm with a massive lower unit including reef framework at the base and a bedded grainstone upper unit the bioherm developed on a basalt substrate in warm shallow water as indicated by photozoan assemblages in the massive lower unit foraminifera belonging to 17 genera are recorded from the bioherm these include representatives of the families biseriamminidae biwaellidae bradyinidae cornuspiridae lasiodiscidae palaeotextulariidae pseudotaxidae ozawainellidae schubertellidae schwagerinidae staffellidae and textrataxidae twenty one species have been referred to known types and 12 species are left in open nomenclature the assemblage probably belongs within the uppermost gzhelian schwagerina robusta ultradaixina bosbytauensis zone although a possible lowest asselian correlation cannot be excluded the bioherm is the oldest carbonate unit so far recorded from the maubisse formation and the oldest sedimentary unit biostratigraphically dated in timor the dominantly heterozoan composition of the skeletal component of the limestone except for the basal photozoan assemblage and the taxonomic diversity of the larger foraminifera suggest a subtropical environment consistent with a paleolatitude of about 40 s the late pennsylvanian was a time of glaciation that in australia is represented by a significant stratigraphic hiatus in basins to the south of timor in the east gondwana rift system the development of the kulau bioherm during the latest gzhelian may have coincided with a global warming spike that led to rapid melting of continental ice sheets and a substantial influx of glacigene sediment alternating diamictite and mudstone in the southern basins

meco and alpine orogenesis constraints for facies evolution of the bartonian nummulitic and solenomeris limestone in the argentina valley ligurian alps

organic carbon as a palaeoenvironmental indicator in the marine realm recent developments in biogeochemistry have made accessible all information currently known to be present in sedimentary organic compounds i e the carbon skeleton structure the positions of functional groups and stable carbon isotope ratios this combined information has strengthened the applications of sedimentary organic compounds as biomarkers and palaeoenvironmental indicators this review summarizes the most important biomarkers and their applications in reconstructing marine palaeoenvironments and processes the marine environment is characterized by the combined presence of specific compounds such as organic sulphur compounds dinosteroids 24 n propylsteroids even in trace amounts high amounts of c hbi hydrocarbons and the absence of long chain n alkanes with odd over even predominance bicadinanes and specific higher plant triterpenoids e g oleanane furthermore palaeoenvironmental conditions such as photic zone anoxia hypersalinity microbial sulphate reducing activity algal blooming palaeo upwelling and palaeo surface seawater temperature are indicated by molecular and or isotopic characteristics biomarkers from terrestrial sources are included because land derived organic matter is an important contributor to coastal and shallow marine environments a short case study within a holocene terrestrial marine setting florida bay usa is also presented to illustrate the reconstruction of transgressive regressive trends using selected organic compounds

growth rate and salinity profile of first year sea ice in the high arctic this paper describes the growth of sea ice and the salinity profiles observed in eclipse sound near pond inlet baffin island canada during the winter of 1977 78 a numerical method of calculation has been developed to incorporate the variations in snow conditions and physical properties of ice and snow during the growth season it is shown that the growth rate can be predicted reasonably well it is also shown that the vertical salinity profile in the ice towards the end of the season provides a record of previous climatological conditions a dependence has been shown between the predicted growth rate and the measured salinity

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

growth of and brine drainage from nacl h2o freezing a simulation of young sea ice 1 a numerical simulation is used to predict the early time evolution of the solidification and brine drainage of a binary nacl h2o mixture the mathematical formulation is based on continuum mixture theory as outlined by bennon and incropera 1987 and medjani 1993 results yield a simple relationship between surface temperature and cumulative salt mass draining from the ice additionally a scaling analysis of the energy equation leads to a simple parameterization for ice thickness results compare well with existing laboratory measurements however the delay in onset of brine drainage reported in the literature is not supported by these results images generated using continuum salinity and liquid fraction data overlaid with streamlines generated from velocity data provide a reasonable qualitative resemblance to laboratory observations of nacl h2o ice growth