dissolution of biogenic carbonates effects of skeletal structure abstract dissolution of biogenic shallow water carbonates exposed on deep sea moorings indicates that skeletal structure is important for the rate of disintegration of biogenic carbonates besides mineralogy and grain size of particles the aragonites and high mg calcites used represent a wide spectrum of mineralogies and types of skeletal framework the particles were deployed at different water depths on a mooring in the drake passage for 52 days weight loss curves for the various types of particles show the relative importance of the different structural factors for the disintegration of these biogenic carbonates organic coatings intraskeletal pore spaces and sizes and shapes of individual crystallites in the skeletons may be more important than carbonate mineralogy and particle size in cases the presence of internal sediments cement aggregates and natural contaminations and of diatoms incorporated during growth into carbonate skeletons strongly influence the disintegration of the skeletal materials the first step of particle disintegration is the selective removal of impurities this step is analogous to a cleaning of specimens it is succeeded by initial dissolution by strong dissolution and finally by disintegration

reprint of comparison of climate signals obtained from encrusting and free living rhodolith coralline algae abstract coralline algae have been used for sclerochronological studies throughout the last decade these studies have focused on two different growth morphologies of the photosynthetic coralline algae massive crusts forming small buildups on hard substrate and free living branching algal nodules known as rhodoliths the latter are generally found on soft substrate where they are frequently overturned by water movement and bottom feeding organisms leaving one side of the rhodolith partially buried in the sediment at any given time here we test whether either of these growth morphologies is more suitable for proxy reconstructions by comparing mg ca ratios a temperature proxy in multiple replicates of rhodoliths of lithothamnion glaciale and in rhodoliths as well as encrusting specimens of clathromorphum compactum with both species being widespread throughout the temperate and arctic regions we have chosen two north atlantic localities at nuuk fjord greenland subarctic and off the southeastern coast of newfoundland canada temperate for this study two to three mg ca ratio transects spanning 18 years of growth were analysed on multiple specimens with encrusting morphologies and along different sides of rhodoliths using laser ablation inductively coupled mass spectrometry and compared to remotely sensed sea surface temperature sst data the length of the common time span used for comparison was limited by growth interruptions in rhodoliths furthermore our comparison is based on the assumption that rhodolith growth increments are annual an assumption that has recently been challenged by mesocosm studies monthly mg ca values from multiple transects within each individual were compared and in samples from nuuk fjord significant correlations were found in 4 of 4 encrusting c compactum 4 of 4 c compactum rhodoliths and 2 of 3 l glaciale rhodoliths in newfoundland significant correlations were found in 6 of 6 encrusting c compactum comparisons average r 0 61 p

micro computed tomography applications for high resolution skeletal density determinations an example using annually banded crustose coralline algae warming and acidification of the world s oceans are expected to have widespread consequences for marine biodiversity and ecosystem functioning however due to the relatively short record of instrumental observations one has to rely upon geochemical and physical proxy information stored in biomineralized shells and skeletons of calcareous marine organisms as in situ recorders of past environments of particular interest is the response of marine calcifiers to ocean acidification through the examination of structural growth characteristics here we demonstrate the application of micro computed tomography micro ct for three dimensional visualization and analysis of growth skeletal density and calcification in a slow growing annually banded crustose coralline alga clathromorphum nereostratum increment width 380 m x ray images and time series of skeletal density were generated at 20 m resolution and rebinned to 40 60 80 and 100 m for comparison in a sensitivity analysis calcification rates were subsequently calculated as the product of density and growth linear extension while both skeletal density and calcification rates do not significantly differ at varying spatial resolutions the latter being strongly influenced by growth rates clear visualization of micron scale growth features and the quantification of structural changes on subannual timescales requires higher scanning resolutions in the present study imaging at 20 m resolution reveals seasonal cycles in density that correspond to summer winter variations in skeletal structure observed using scanning electron microscopy sem micro ct is a fast non destructive and high resolution technique for structural and morphometric analyses of temporally banded paleoclimate archives particularly those that exhibit slow or compressed growth or micron scale structures

carbonates within a pleistocene glaciomarine succession yakataga formation middleton island alaska uplifted during the 1964 alaskan earthquake extensive intertidal flats around middleton island expose 1300 m of late cenozoic early pleistocene yakataga formation glaciomarine sediments these outcrops provide a unique window intooutershelfandupperslopestratathatareotherwiseburiedwithinthesoutheast alaska continental shelf prism the rocks consist of five principal facies in descending order of thickness i extensive pebbly mudstone diamictite containing sparse marine fossils ii proglacial submarine channel conglomerates iii burrowedmudstoneswithdiscretedropstonelayers iv boulderpavements whose upper surfaces are truncated faceted and striated by ice and v carbonates rich in molluscs bryozoans and brachiopods the carbonates are decimetre scale in thickness typically channellized conglomeratic event beds interpreted as resedimented deposits on the palaeoshelf edge and upper slope biogenic components originated in a moderately shallow ca 80 m relatively sediment free mesotrophic sub photicsetting thesecomponentsareamixture of parautochthonous large pectenids or smaller brachiopods with locally important serpulid worm tubes and robust gastropods augmented by sand size bryozoan and echinoderm fragments ice rafted debris is present throughout these cold water carbonates that are thought to have formed during glacial periods of lowered sea level that allowed coastal ice margins to advance near to the shelf edge such carbonates were then stranded during subsequent sea level rise productivity was enabled by attenuation of terrigenous mud deposition during these cold periods via reduced sedimentation together with active wave and tidal current winnowing near the ice front redeposition was the result of intense storms and possibly tsunamis these sub arctic mixed siliciclasticcarbonate sediments are an end member of the phanerozoic global carbonate depositional realm whose skeletal attributes first appeared during late palaeozoic southern hemisphere deglaciation

coralline algal reef frameworks published and unpublished accounts of coralline algal reef frameworks are reviewed the descriptions are divided into frameworks constructed from crustose coralline algae and those constructed from branching corallines crustose frameworks are briefly described and illustrated from the miocene of malta recent coralligene from the mediterranean eocene reefs from spain recent algal reefs of st croix u s virgin is and algal reefs from bermuda branching frameworks are briefly described and illustrated from the recent maerl of the ne atlantic recent mud mounds from florida recent algal reefs from st croix and recent algal ridges on pacific reefs crustose and branching frameworks show an increase in strength of construction early submarine cements and macro borers and a decrease in erodibility from low to high energy environments the occurrence of genera in coralline frameworks is primarily controlled by their geographic and water depth ranges the construction of coralline frameworks is seen as the result of competition for living space on shallow marine hard substrates

geology and evolution of lakes in north central florida fluid exchange between surficial waters and groundwater in karst environments and the processes that control exchange are of critical concern to water management districts and planners high resolution seismic data were collected from 30 lakes of north central florida in each case study lake structure and geomorphology were controlled by solution and or mechanical processes processes that control lake development are twofold 1 karstification or dissolution of the underlying limestone and 2 the collapse subsidence or slumping of overburden to form sinkholes initial lake formation is directly related to the karst topography of the underlying host limestone case studies have shown that lakes can be divided by geomorphic types into progressive developmental phases 1 active subsidence or collapse phase young 2 transitional phase middle age 3 baselevel phase mature and 4 polje drowned prairie broad flat bottom that have one or all phases of sinkhole using these criteria florida lakes can be classified by size fill subsurface features and geomorphology

reconstructing mid to high latitude marine climate and ocean variability using bivalves coralline algae and marine sediment cores from the northern hemisphere quantifying the role and contribution of the world s oceans in past present and future global change is an essential goal in climate paleoclimate and environmental studies although the global oceans interact and influence climate greatly the marine environment is substantially under represented in key climate assessment reports especially during the last millennium ipcc 2007 see palaeoclimate chapter 6 6 the last 2000 years the under representation of marine records in key climate documents likely results from the often imprecise chronologies associated with many marine based archives which greatly hinders singular climate comparisons lag lead phasing relationships with well dated and or annually resolved archives however several marine archive records have excellent chronological constraint in particular many marine bivalve taxa and coralline algae have annual increments that form within their carbonate framework that can be used to establish an absolutely dated chronology via cross dating techniques from the marine environment additionally in some cases where sedimentation rates are high and alternative chronological dating methods exist e g tephrochronology other than radiocarbon measurements often greater than 40 years uncertainty sediment archives can provide continuous sub decadal records of environmental change for centuries to millennia this brief introductory article and accompanying special issue will focus on the utilization of bivalves coralline algae and high resolution marine sediment cores in paleoclimate and environmental studies within the most recent millennium with a focus on the northern hemisphere

a record of mining and industrial activities in new caledonia based on trace elements in rhodolith forming coralline red algae abstract we investigate the ability of coralline red algae to record historical nickel mining activity that occurred between the early 1960s and 1981 in the coulee river watershed southwest new caledonia laser ablation inductively coupled plasma mass spectrometry la icpms was used to determine high resolution sub annual variations of trace metal ratios mn ca fe ca ni ca and co ca in three 45 years old free living forms of the rhodolith coralline red alga sporolithon durum from ricaudy reef in the inner lagoon of new caledonia 15 km from the coulee river mouth we find increased mn ca and fe ca ratio values track the intensity of mining in the coulee river catchment whereas ni ca ratio values appear more sensitive to the ore type saprolite versus laterite that were targeted during two separate stages of mining activity mn ca fe ca and ni ca decrease following the cessation of mining in 1981 but did not reach current values until 10 years after that date surprisingly co ca variations do not correlate with mining activity but rather increase steadily through the record period we argue this relates to nickel refining and smelting activity over the past half century our results further suggest that the local inter annual rainfall variability may influence the metal concentrations recorded in the rhodoliths during the period of intense mining activity but the link between metal uptake and rainfall is not entirely clear for the entire growth period of the rhodoliths

sedimentology and acoustic mapping of modern rhodolith facies on a non tropical carbonate shelf gulf of california mexico abstract rhodolith facies are characterized by an abundance of free living coralline red algae and are a common feature of modern and ancient carbonate shelves worldwide rhodolith communities contribute significantly to the global calcium carbonate budget and fossil rhodoliths are commonly used to obtain paleoecologic and paleoclimatic information few attempts have been made to quantify the spatial extent of modern rhodolith facies despite their importance and common occurrence combining sediment sampling with acoustic facies mapping this study provides the first set of quantitative data on rhodolith facies distribution in the warm temperate southwestern gulf of california mexico though rhodoliths were the main carbonate producers other important calcareous biota were bivalves 19 bryozoans 13 and corals 6 based on cluster analysis biota were grouped into a rhodolith a rhodolith bivalve coral and a bivalve bryozoa biofacies the acoustic seafloor classification distinguished four acoustic facies which were confirmed by ground truthing an outer shelf silt facies a biogenic sand facies a peripheral rhodolith facies and a central rhodolith facies rhodolith facies covered approximately 40 of the surveyed seafloor 45 km2 results from quantitative analysis of sediment samples and acoustic mapping showed a significant correlation between grain size biofacies and acoustic seafloor facies we successfully applied an acoustic device to provide highly resolved continuous coverage of the seafloor and discriminate modern rhodolith facies from surrounding sediment this has important implications for quantifying rhodolith carbonate production in other regions as well as for ecological and conservation studies

coralline algae are global palaeothermometers with bi weekly resolution abstract high resolution palaeoclimate data are required for the holocene to resolve differences recorded by current proxies the pole to pole distribution of rhodoliths coralline algae with their annual and sub annual calcite bands make these attractive candidates for such a role these bands contain climate information in the form of elemental traces in situ temperature ist was recorded at two rhodolith beds for 1 5 years the concentrations of mgco 3 and srco 3 mol deposited in lithothamion glaciale and phymatolithon calcareum over this 18 month period were determined using electron and ion microprobes highly significant linear relationships exist between mg sr and ist as well as sea surface temperature calibration between mg concentration and ist was used to obtain a 2 year temperature profile from a subfossil rhodolith thallus indicating half the seasonal peak to peak temperature amplitude earlier during the holocene than the present day both slow growing species 1 allowed sampling resolutions of 23 year 1 which is equivalent to 1 reading every 2 weeks sub monthly mg and sr records in rhodoliths make them unique globally distributed palaeothermometers which may help refine regional climate histories during the holocene

marine biota response to clastic sediment influx a quantitative approach abstract there have been few quantitative studies of the effects of siliciclastic and volcaniclastic sediment influx on carbonate producing organisms from the geological record this study presents the results of quantitative field petrographic and acid digestion analyses of samples from three cenozoic shallow water mixed carbonate volcani siliciclastic depositional environments the miocene wonosari formation of south java the miocene batu putih limestone of east borneo and the eocene collsuspina limestone of northeast spain carbonate production in these systems is dominated by larger benthic foraminifera coralline algae and corals analyses of the quantity grainsize and type of volcani siliciclastic sediment within these mixed successions have allowed assessment of the influence of these factors on shallow water carbonate producers larger benthic foraminifera and coralline algae exhibit the greatest tolerance to siliciclastic sediment influx abundant up to 55 and 38 wt respectively at a range of grain sizes to coarse sand platy corals are also present within sediments containing a large proportion of insoluble material geologically averaged rates of clastic accumulation and their potential influences on carbonate producers inferred herein may be difficult to compare directly with the daily and seasonal fluctuations experienced by modern clastic influenced systems however this study may aid our understanding of the likely effects of increased clastic influx today commonly anthropogenically related to marine carbonate environments over longer time periods

experimental studies of collapse calderas we present experiments to investigate the formation of calderas using inflatable balloons in a medium of fused alumina powder this system provides a model of a magma chamber in an homogeneous elastic media which scales to volcanic systems in terms of geometry and strength of the media three kinds of experiment were performed i the balloon was inflated and then deflated simulating pre emption tumescence and caldera collapse ii the balloon was deflated without prior inflation simulating caldera formation without pre eruption tumescence iii three balloons were inflated and deflated in a line simulating multiple magma chambers the influence of magma chamber shape was investigated using different shaped balloons balloon inflation formed a dome with a surface pattern of shallow polygonal fractures centrally and radial fractures peripherally uplift occurs along deep inward dipping concentric reverse faults deflation generated depressions with an outer set of concentric ring fractures surrounding a central funnel formed by sagging along numerous minor faults some of which formed during doming during collapse the concentric reverse faults were converted to normal faults and the radial normally faulted fractures were converted to reverse faults without prior tumescence an outer set of near vertical ring faults surround a flat central depression due to collapse of a coherent block an inner set of outward dipping reverse ring faults also develop the experimental caldera area increased with balloon size and increased as the balloon depth decreased for a given balloon volume and depth collapse area is significantly smaller if doming had occurred prior to collapse arcuate fractures can provide the pathways for magma ascent during pre emption tumescence smith bailey 1968 but the shallow radial and polygonal fracture systems may also influence vent location changes in fault geometry and sense of movement extension to compression and vice versa occur when subsidence initiates and can account for changes in vent location that occur in many eruptions multiple overlapping collapse calderas are associated with magma chamber migration whereas nested calderas can result from the activity of a single magma chamber

reefal coralline algal build ups within the arctic circle morphology and sedimentary dynamics under extreme environmental seasonality abstract carbonate frameworks secreted by phototrophic organisms within the arctic circle are not well documented underwater surveys of the inner shelf off troms northern norway 70 n reveal extended fixed algal build ups which are fringed by rhodolith belts affected by storms reefd growth by coralline algae under temperature and light regimes of extreme seasonality is made possible because of a decoupling of carbon fixation during summer and utilization of stored carbon during the period of winter darkness although the annual growth of the framework constructing algae is comparatively low the annual carbonate production rate is similar to subtropical tropical counterparts because of a remarkably high standing stock early diagenetic alteration is restricted to intraparticle cementation processes which start in vivo bioerosional destruction is the dominant control on the preservation of high latitude build ups preservation of holocene autochthonous coralline algal biostromes is enhanced by rapid burial during storm events redeposition during storms is the most important process in forming a distinct sedimentary facies zonation

the environments of production and deposition of calcareous sediments on the shelf west of scotland the dominant calcareous organisms and sediment characteristics are described for eight different physical settings on the shelf west of scotland each having a different depth substrate and degree of hydrodynamic exposure the principal sites of carbonate production are on shallow rocky substrates where barnacles molluscs echinoderms and serpulids are the dominant calcareous organisms in sheltered shallow sandy zones molluscs echinoderms and benthic foraminiferans are the active producers though the sediments are commonly barnacle rich where tidal currents are enhanced between islands and the waves are suppressed calcareous red algae phymatolithon calcareum and mussel shells build localised banks in deep open shelf water molluscs are the major skeletal contributor to the sediment though on rocky sea beds bryozoans serpulids and echinoderms are important the major sites of deposition are where persistent hydro and aero dynamic conditions sweep together grains from active production sites e g sand ribbons or beaches and dunes adjacent to shallow rocky platforms or in sinks where the physiographic configuration favours the deposition and retention of locally produced sediment or sediment derived from suspension the well sorted cross bedded beach and dune sands commonly contain 75 caco3 in sheltered depressions bioturbated muds accumulate with up to 30 calcite silt which is probably the breakdown product of barnacles and benthic foraminiferans

coralline algal growth increment widths archive north atlantic climate variability over the past decade coralline algae have increasingly been used as archives of paleoclimate information encrusting coralline algae which deposit annual growth increments in a high mg calcite skeleton are amongst the longest lived shallow marine organisms in fact a live collected plant has recently been shown to have lived for at least 850 years based on radiometric dating while a number of investigations have successfully used geochemical information of coralline algal skeletons to reconstruct sea surface temperatures less attention has been paid to employ growth increment widths as a temperature proxy here we explore the relationship between growth and environmental parameters in clathromorphum compactum collected in the subarctic northwestern atlantic results indicate that growth increment widths of individual plants are poorly correlated with instrumental sea surface temperatures sst however an averaged record of multiple growth increment width time series from a regional network of c compactum specimens up to 800 km apart reveals strong correlations with annual instrumental sst since 1950 hence similar to methods applied in dendrochronology averaging of multiple sclerochronological records of coralline algae provides accurate climate information a 115 year growth increment width master chronology created from modern collected and museum specimens is highly correlated to multidecadal variability seen in north atlantic sea surface temperatures positive changes in algal growth anomalies record the well documented regime shift and warming in the northwestern atlantic during the 1990s large positive changes in algal growth anomalies were also present in the 1920s and 1930s indicating that the impact of a concurrent large scale regime shift throughout the north atlantic was more strongly felt in the subarctic northwestern atlantic than previously thought and may have even exceeded the 1990s event with respect to the magnitude of the warming

mobility of maerl siliciclastic mixtures impact of waves currents and storm events abstract maerl beds are free living non geniculate coralline algae habitats which form biogenic reefs with high micro scale complexity supporting a diversity and abundance of rare epifauna and epiflora these habitats are highly mobile in shallow marine environments where substantial maerl beds co exist with siliciclastic sediment exemplified by our study site of galway bay coupled hydrodynamic wave sediment transport models have been used to explore the transport patterns of maerl siliciclastic sediment during calm summer conditions and severe winter storms the sediment distribution is strongly influenced by storm waves even in water depths greater than 100 m maerl is present at the periphery of wave induced residual current gyres during storm conditions a combined wave current sediment mobility index during storm conditions shows correlation with multibeam backscatter and surficial sediment distribution a combined wave current mobilization frequency index during storm conditions acts as a physical surrogate for the presence of maerl siliciclastic mixtures in galway bay both indices can provide useful integrated oceanographic and sediment information to complement coupled numerical hydrodynamic sediment transport and erosion deposition models

petrogenesis of cenozoic temperate water calcarenites south australia a model for meteoric shallow burial diagenesis of shallow water calcite sediments abstract the gambler limestone is one of several extensive shallow water shelf carbonates of eocene to miocene age exposed along the southern margin of australia it is a muddy to grainy bryozoan calcarenite with accessory benthonic foraminifers and echinoids the sediments originally composed almost entirely of calcite or mg calcite have been in vadose and phreatic environments for over 10 ma yet are virtually unlithified the only cements of any consequence are epitaxial on echinoids numerous karst features dolines caves speleothems and surface karren attest to prolonged residence in the meteoric zone the gambler limestone is presently one of the best fresh water aquuifers in australia most flow occurs through intergranular pores in sediments with over 30 porosity cementation is by minor intergranular pressure solution which has developed under overburden of less than 100 m the overlying naracoorte limestone miocene a calcarenite of warmer water aspect contains numerous aragonite molds and is well cemented we propose that such cool water limestones are a better model for the meteoric diagenesis of calcite sediments of all ages than are aragonite rich tropical sediments it is probable that many similar early and middle paleozoic calcite limestones may have been in the meteoric zone for prolonged periods yet contain little or no petrographic or geochemical record of such exposure

origin of a cool water oligo miocene deep shelf limestone eucla platform southern australia the abrakurrie limestone is an areally extensive bryozoan rich unit within the eucla platform a tertiary carbonate shelf which caps the central part of the southern australian continental margin the onshore portion the topic of this study has been exposed since middle miocene time and lies beneath the nullarbor plain the rocks are fine sand to granule sized calcarenites composed of bryozoans bivalves benthic foraminifera and echinoids with lesser numbers of brachiopods solitary corals and serpulids they conspicuously lack significant numbers of planktonic foraminifera and coralline algae most bryozoan remains are from delicate branching cyclostomes although delicate branching robust branching foliose fenestrate multilaminar encrusting and free living cheilostomes are variably abundant in specific units the poorly lithified sequence is punctuated by well cemented layers with erosional tops which are interpreted as hardgrounds the limestone is interpreted as a cool water deep shelf deposit which accumulated in water depths generally greater than 50 m on the inner part of the eucla platform a model which involves deposition and cementation on a carbonate shelf swept by open ocean swells is proposed to explain the style of sedimentation the shelf is envisaged as partitioned by the depth of the zone of wave abrasion sediments were produced throughout but accumulated only below this depth when the seafloor was above this depth it was an environment of cementation and erosion the vertical sequence correlates in a general way with the global sea level model for the mid cenozoic while accumulation rates for southern australian carbonates are similar to rates of cool water carbonate deposition elsewhere c 2 5 cm kyr 1 the rate of abrakurrie accumulation is much less suggesting that significant time periods are represented by the hardgrounds

non seagrass meadow sedimentary facies of the pontinian islands tyrrhenian sea a modern example of mixed carbonate siliciclastic sedimentation abstract the soft bottom of the mediterranean continental shelf is characterized by a heterozoan skeletal assemblage sensu james n p 1997 the cool water carbonate depositional realm in james n p clarke j eds cool water carbonates spec publ soc sediment geol vol 56 pp 1 20 although the contemporary presence of terrigenous and skeletal carbonate sediments has been well established tortora p 1996 depositional and erosional coastal processes during the last postglacial sea level rise an example from the central tyrrhenian continental shelf italy j sed res 66 391 405 fornos j j ahr w m 1997 temperate carbonates on a modern low energy isolated ramp the balearic platform spain journal of sedimentary research 67 364 373 fornos j j ahr w m 2006 present day temperate carbonate sedimentation on the balearic platform western mediterranean compositional and textural variation along a low energy isolated ramp in pedley h m carannante g eds 2006 cool water carbonates depositional systems and palaeoenvironmental controls geological society london special publications 255 pp 121 135 the interactions between carbonate and terrigenous siliciclastic sedimentation has not been documented well enough a total of 33 surface sediment samples from the pontinian shelf tyrrhenian sea central mediterranean have been analysed sampling stations range from 15 to 250 mwd meter water depth and are located along five transects ponzaw ponzanw ponza ne ponza e zannone plus four samples collected around palmarola island sectors colonized by seagrass meadows have not been sampled a total of 6 sedimentary facies f and 10 microfacies mf have been recognized by using component analyses grain size percentage sorting carbonate content and authigenic mineralization rate these facies and microfacies represent the pontian islands shelf sedimentation in the interval between the upper infralittoral and the epibathyal zones that represent shelf break and upper slope sedimentation the maerl facies f4a b mf4a b and the skeletal sands f2a b mf2a1 mf2a2 mf2b fall within the circalittoral zone the circalittoral zone in the water depth interval between 82 m and 112 m display relict facies f6 mf6 finally facies f5 siliciclastic sands includes subfacies f5b mf5b located in the circalittoral zone at depths of 49 to 101 mwd and restricted to the western and eastern sectors of ponza and subfacies f5a in the upper infralittoral zone 15 mwd 25 mwd where erosional processes prevail carbonate content analyses indicate that maximum carbonate production on the pontinian shelf took place in the 60 80 mwd interval facies f4 maerl represents the environment characterized by the highest carbonate production rates in the pontian area siliciclastic carbonate mixing took place in the infralittoral zone and in the lower circalittoral zone in the infralittoral zone erosional processes on the rocky shoreline produced lithoclasts and vulcanoclastic deposits that were reworked by wave induced near shore currents in the lower circalittoral zone the prolific production by photic biota red algae ends while skeletal remains of the aphotic environment mixes with planktonic sediments characterized by low carbonate values sand 63 m 2 mm is the dominant grain size class however gravel dominated facies f4 maerl are present in water depths 50 to 112 mwd which are significantly below the storm wave base glauconite mineralization appears on the pontinian shelf from 50 mwd and increases in abundance along the deeper bathymetries the compositional characteristics of relict facies f6 shows the concurrence of biota assemblages of the infralittoral and circalittoral zones likely representing the record of the last holocene transgressive event 18 ky and expressed by the overlapping of components of different environments

bioclastic carbonate sedimentation on a high latitude tide dominated shelf northeast orkney islands scotland abstract shell sands and gravels cover much of the shallow orkneys shelf at 59 n accumulating locally into 30 m high banks at rates up to 540 g m2 yr 67 cm l 000 yr overall the orkney shelf sedimentation rate is approximately 10 cm l 000 yr compared with 3 cm 1 000 yr for the entire scottish continental shelf major sandbanks are located off headlands that produce circulation loops in the tidal flow regional sandwave orientations reveal a clockwise transport of sediment around the islands probably resulting from storm wave reinforcement of the tidal asymmetry combined with the net inflow of atlantic water into the north sea carbonate production is high from the modiolus epifauna modiolus shell gravels commonly containing glycymeris pass laterally into comminuted shell sands within the euphotic zone down to 40 m dead shells are weakened by echinoid biting algal boring and limpet grazing boring by fungi and clionid sponges and grazing by chitons are common but not depth restricted sediments contain 89 95 carbonate on the level bottom offshore but 94 99 in sandwaves mean values for the main skeletal components are bivalves 46 barnacles 18 bryozoans 11 and serpulids 7 calcareous algal gravels occur in sheltered areas less than 20 m deep bryozoa typify lower energy offshore environments while more durable barnacle and serpulid debris is concentrated in sandwave fields the sediments are dominantly calcitic and have a high preservation potential

modern non tropical mixed carbonate siliciclastic sediments and environments of the southwestern gulf of california mexico abstract modern mixed carbonate siliciclastic warm temperate environments were studied in the southern gulf of california goc mexico the combined heterozoan and photozoan character is defined by the absence of true coral reef structures calcareous green algae and non skeletal grains and the dominance of rhodoliths unattached coralline red algae mollusks and small coral patch reefs the major carbonate producing environments are pocket bays a shallow carbonate bioherm high energy rocky and sandy shorelines and mid shelf settings sediments characterizing the pocket bays display heavily bioturbated bioclastic wackestone and grainstone textures the rhodolith dominated bioherm is composed of coarse sediments exhibiting grainstone and rudstone textures with fine material being winnowed away by tidal currents rocky and sandy shorelines are characterized by erosion and mixing of up to boulder size granitic and volcaniclastic material with coralline red algal and molluskan carbonates the mid shelf settings are defined by a silt and fine sand sized non carbonate matrix mixed with abundant molluskan fragments and foraminifera peak carbonate production takes place between 10 and 15 m water depth below 40 m production significantly decreases combined with a steep increase in the amount of siliciclastics this is in contrast to many temperate and cool water mixed carbonate siliciclastic systems where most carbonate production occurs in mid to outer shelf settings a full spectrum of sediments from pure carbonates 90 100 carbonate allochem carbonates 50 90 carbonate and allochemic mud or sand

glacigenic sediments on a passive continental margin as exemplified by the barents sea abstract reflection seismics data borehole data and gravity cores have been used to map the sedimentary facies of the epicontinental southwestern barents sea its continental margin and adjacent coastal areas an upper unconformity with a glacially eroded morphology extends over most of the continental shelf up to 300 m of stratiform glacigenic sediments overlie this unconformity these sediments can be grouped into seismic units which are separated by smooth or irregular erosional surfaces each sequence may be up to 150 m thick normally with a lateral extent of 100 300 km three dominant seismic signatures may be discerned semi transparent stratified and chaotic reflection patterns these sediments are partly glacifluvial in origin but on the whole they represent more or less tectonized glacimarine deposits the deeper troughs on the continental shelf contain an undeformed postglacial glacimarine marine trough fill the greatest thickness up to 1000 m of glacigenic sediments occurs at the shelf break and below the upper slope the depocentres are situated at trough mouth fans the sediments comprise several prograding sequences with a complex sigmoid oblique character indicating alternating upbuilding and depositional bypass erosion in the topset segment small and large scale slide scars are observed on the upper slope and debris lobes on the lower slope a marked progradation seems to have occurred during the plio pleistocene glacial periods this progradation also resulted in an unstable slope with various types of sediment gravity flows currents flowing along the slope were established during interglacials and gullying by cold dense shelf water and downslope transport occurred maximum net sedimentation rates are 0 2 m ka continental slope 0 4 m ka shelf break 0 1 m ka shelf stratiform diamictons 1 m ka shelf trough fills and 60 m ka fjord trough fills

carbonates calibrated against oceanographic parameters along a latitudinal transect in the gulf of california mexico trophic resources are an important control governing carbonate production though this importance has long been recognized no calibration exists to quantitatively compare biogenic assemblages within trophic resource fields this study presents a field calibration of carbonate producers in a range of settings against high resolution in situ measurements of nutrients temperature and salinity with its latitudinal extent from 30 to 23 n the gulf of california mexico spans the warm temperate realm and encompasses nutrient regimes from oligo mesotrophic in the south to eutrophic in the north accordingly from south to north carbonates are characterized by i coral dominated shallow carbonate factories 5 20 m water depth with average sea surface temperatures of 25 c min 18 c max 31 c average salinities of 35ae06 and average chlorophyll a levels which are a proxy for nutrients of 0ae25 mg chl a m 3 max 0ae48 min 0ae1 ii red algal dominated subtidal to inner shelf carbonate formation 10 25 m in the central gulf of california exhibiting average temperatures of 23 c min 18 c max 30 c average salinities of 35ae25 and average chl a levels of 0ae71 chl a m 3 max 5ae62 min 0 iii molluskan bryozoan rich inner to outer shelf factories in the northern gulf of california 20 50 m with average sea surface temperatures of only 20 c min 13 c max 29 c average salinities of 35ae01 and average contents of 2ae2 mg chl a m 3 max 8ae38 min 0 by calibrating sedimentological data with in situ measured oceanographic information in different environments the response of carbonate producers to environmental parameters was established and extrapolated to carbonates on a global scale the results demonstrate the importance of recognizing and quantifying trophic resources as a dominant control determining the biogenic composition and facies character of both modern and fossil carbonates

development patterns of an isolated oligo mesophotic carbonate buildup early miocene yadana field offshore myanmar abstract the development history of an oligo mesophotic early miocene isolated carbonate system 160 m in thickness forming the uppermost part of the oligo miocene yadana buildup northern andaman sea has been evidenced from the integration of sedimentological core studies from 4 wells cumulated core length 343 m well correlations seismic interpretation and analysis of the ecological requirements of the main skeletal components three types of carbonate factory operated on the top of the platform depending on water depth turbidity and nutrient level 1 a scleractinian factory developing under mesophotic conditions during periods of high particulate organic matter supplies 2 an echinodermal factory occupying dysphotic to aphotic area of the platform coevally with the scleractinian factory 3 a large benthic foraminiferal coralline algal factories prevailing under oligo mesophotic and oligo mesotrophic conditions the limited lateral changes in facies between wells together with the seismic expression of the yadana buildup suggest deposition on a flat topped shelf carbonate production and accumulation on the yadana platform was mainly controlled by light penetration nutrient content and hydrodynamic conditions scleractinian rich facies resulted from transport of coral pieces derived from mesophotic environments mounds and deposited in deeper low light mud rich environments in which lived abundant communities of suspension feeders such as ophiuroids changes in monsoonal intensity terrestrial runoff from the irrawaddy river upwelling currents and internal waves activity during the early miocene are likely responsible for significant variations in water turbidity and nutrient concentration in the andaman sea thus promoting the development of an oligo mesophotic incipiently drowned platform

effects of early sea floor processes on the taphonomy of temperate shelf skeletal carbonate deposits abstract cool water shelf carbonates differ from tropical carbonates in their sources modes and rates of deposition geochemistry and diagenesis inorganic precipitation marine cementation and sediment accumulation rates are absent or slow in cool waters so that temperate carbonates remain longer at or near the sea bed early sea floor processes occurring between biogenic calcification and ultimate deposition thus take on an important role and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool water carbonate deposits the physical breakdown processes of dissociation breakage and abrasion are mediated mainly by hydraulic regime and are always destructive impact damage reduces the size of grains removes structure and therefore information and ultimately may transform skeletal material into anonymous particles abrasion is highly selective amongst and within taxa their skeletal form and structure strongly influencing resistance to mechanical breakdown dissolution and precipitation are the end members of a two way chemical equilibrium operating in sea water in cool waters inorganic precipitation is rare there is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor but test maceration and early loss of aragonite in particular are reported dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter strong bioturbation and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits laboratory experiments demonstrate that surface to volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution biological processes on the sea floor include encrustation and bioerosion encrustation a constructive process may be periodic or seasonal and can be reversed it produces both information and material bioerosion in contrast is destructive and permanent in temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor on the order of hundreds to thousands of years overall processes on the temperate sea floor may combine to destroy more carbonate than they produce and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected where preservation does occur in such a destructive regime the effects of early sea floor processes will be key determinants of the deposit resulting in a taphofacies characteristic of temperate shelf carbonate sediments