shelf to basin temperate skeletal carbonate sediments three kings plateau new zealand abstract three kings plateau is 10 000 km2 in area less than 500 m deep and includes the mainland shelf and submarine ridges and banks centered on three kings islands 34 s off northernmost new zealand the plateau receives little input of terrigenous sediment and lies in a zone of active nutrient upwelling and vigorous wind wave and tidal current activity as a consequence surficial sediments on and about the margins of the plateau are dominantly pure skeletal carbonate sands and gravels which lack mud to depths of 1500 to 3000 m plateau top sediments include a bryozoan calcareous red algal barnacle lithofacies on coarse and rocky substrates and a bivalve bryozoan lithofacies associated with particulate bottoms plateau edge sediments include a bryozoan ahermatypic co al serpulid lithofacies in areas of rugged topography and a bivalve gastropod lithofacies on sandy substrates both grading down slope into a planktic foraminiferal lithofacies by 1500 to 3000 m depth depending on locality the carbonates are dominated by a high mg calcite and or low mg calcite mineralogy with only subordinate aragonite active skeletal production is presently restricted to only about 10 percent of the plateau area principally in regions of rough sea floor topography on submarine cliff faces on bank tops and in in shore portions of the mainland shelf about these areas modern carbonates occur down to depths of 50 to 200 m below which the sediments are mainly relict and include rare glauconite redeposition of plateau derived skeletal carbonates into surrounding basins was especially active during the last glacial low sea level s it is inferred that this is the ultimate fate of the bulk of the shallow marine sediment and that the plateau top itself preserves only a thin laterally discontinuous mixed age and highly condensed sequence of quaternary temperate skeletal carbonates

the apparent paradox of abundant foramol facies in low latitudes their environmental significance and effect on platform development recent studies of low latitude carbonates from se asia and australia have revealed deposits and platform types that do not fit easily into the perceived view of warm water tropical carbonates the sediments are classified as a foramol or foralgal facies and are dominated by non framework building light dependent biota such as perforate larger benthic foraminifera coralline algae and sometimes halimeda although ancient foramol deposits are often interpreted as an indication of non tropical conditions foramol facies have long been known from the tropics yet the environmental conditions in which they form are poorly known the aims of this paper are to evaluate how these deposits are best classified and more importantly whether there are any overriding controls that influence their common development in low latitude areas and if resultant platform development is affected the deposits are all best grouped within the photozoan association james n p 1997 the cool water depositional realm in james n p clarke j a d eds cool water carbonates sepm special publication 56 1 20 an assignment synonymous with warm water conditions the facies were also found to develop in conditions of limited light or oligophoty all the platforms described are characterised by having extensive areas of oligophotic facies generally in water depths extending down from 20 m but sometimes in shallower waters platforms types vary from land attached rimmed shelves homoclinal and distally steepened ramps to isolated banks and platforms but all have extensive moderate to deep photic zone development of oligophotic facies some workers might assign these platforms to the incipiently drowned platform type read j f 1985 carbonate platform facies models american association of petroleum geologists bulletin 69 1 21 however a morphological assignment is preferred here to signify that many of the deposits did not or may not form through drowning limited light in moderate to deeper depths of the photic zone often in regions with a reduced depth euphotic high light zone is seen as key to the extensive development of these deposits and the resultant platforms these conditions are often developed in humid low latitude areas of high terrestrial runoff and therefore regions of reduced water salinity or in areas of nutrient upwelling reduced water clarity due to nutrients plankton blooms suspended particulate matter upwelling and strong currents all promote the development of oligophotic conditions and facies on a regional scale time periods of relative rises in sealevel can also promote oligophotic facies development the findings of this study have broader implications for the development of low latitude platforms beyond australasia and during time periods when non framework building oligophotic biota are dominant sediment contributors the reconstruction of past climatic conditions based on study of foramol grain assemblages requires careful study to distinguish warm water deposits from those formed in cool waters

carbonate factories a conundrum in sedimentary geology abstract describing characterizing and interpreting the nearly infinite variety of carbonate rocks are conundrums intricate and difficult problems having only conjectural answers that have occupied geologists for more than two centuries depositional features including components rock textures lithofacies platform types and architecture all vary in space and time as do the results of diagenetic processes on those primary features approaches to the study of carbonate rocks have become progressively more analytical one focus has evolved from efforts to build reference models for specific phanerozoic windows to scrutinize the effect of climate and long term oscillations of the ocean atmosphere system in influencing the mineralogy of carbonate components this paper adds to the ongoing lively debates by attempting to understand changes in the predominant types of carbonate producing organisms during the mesozoic cenozoic while striving to minimize the uniformitarian bias our approach integrates estimates of changes in ca2 concentration in seawater and atmospheric co2 with biological evolution and ecological requirements of characteristic carbonate producing marine communities the underlying rationale for our approach is the fact that co2 is basic to both carbonates and organic matter and that photosynthesis is a fundamental biological process responsible for both primary production of organic matter and providing chemical environments that promote calcification gross photosynthesis and hypercalcification are dependent largely upon sunlight while net primary production and e g subsequent burial of organic matter typically requires sources of new nutrients n p and trace elements our approach plausibly explains the changing character of carbonate production as an evolving response to changing environmental conditions driven by the geotectonic cycle while identifying uncertainties that deserve further research with metazoan consumer diversity reduced by the end permian extinctions excess photosynthesis by phytoplankton and microbial assemblages in surface waters induced by moderately high co2 and temperature during the early mesozoic supported proliferation of non tissular metazoans e g sponges and heterotrophic bacteria at the sea floor metabolic activity by those microbes especially sulfate reduction resulted in abundant biologically induced geochemical carbonate precipitation on and within the sea floor for example with the opening of tethyan seaways during the triassic massive sponge microbe boundstones the benthic automicrite factory formed steep massive and thick progradational slopes and locally mud mounds as tectonic processes created shallow epicontinental seas photosynthesis drove lime mud precipitation in the illuminated zone of the water column the resulting neritic lime mud component of the shallow water carbonate factory became predominant during the jurassic paralleling the increase in atmospheric pco2 while the decreasing importance of the benthic automicrite factory parallels the diversification of calcifying metazoans phytoplankton and zooplankton with atmospheric pco2 declining through the cretaceous the potential habitats for neritic lime mud precipitation declined at the same time peak oceanic ca2 concentrations promoted biotically controlled calcification by the skeletal factory with changes produced by extinctions and turnovers at the cretaceous tertiary boundary adaptations to decreasing ca2 and pco2 coupled with increasing global temperature gradients i e high latitude and deep water cooling and strategies that efficiently linked photosynthesis and calcification promoted successive changes of the dominant skeletal factory through the cenozoic larger benthic foraminifers protist protist symbiosis during the paleogene red algae during the miocene and modern coral reefs metazoan protist symbiosis since late miocene

nutrient and temperature controls on modern carbonate production an example from the gulf of california mexico in addition to salinity and temperature nutrient concentrations in surface waters are known to have a significant impact on distribution of carbonate producing biota but have never been quantitatively evaluated against different temperatures along a latitudinal transect the western coast of the gulf of california mexico presents a natural laboratory for investigating the influence of oceanographic parameters such as salinity temperature and chlorophyll a a proxy for nutrients on the composition of a range of modern heterozoan and photozoan carbonate environments along a north south latitudinal gradient spanning the entire warm temperate realm 29 n 23 n chlorophyll a measured in situ at half hour resolution is highly variable throughout the year due to short term upwelling and increases significantly from the southern to northern gulf of california salinity in contrast fluctuates little and remains at an average of 35 from south to north carbonate production ranges from oligotrophic mesotrophic coral reef dominated shallow water areas minimum temperature 18 6 c through mesotrophic eutrophic red algal dominated inner shelf carbonate production in the central gulf minimum temperature 16 c and to molluscan bryozoan eutrophic inner to outer shelf environments minimum temperature 13 7 c the gulf of california data supplemented with oceanographic and compositional information from a database compiled from a spectrum of modern carbonate systems worldwide demonstrates the significance of nutrient control in the formation of heterozoan photozoan and transitional heterozoan photozoan carbonate systems and serves as a basis for more accurately interpreting fossil carbonates

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

carbonate systems along nutrient and temperature gradients some sedimentological and geochemical constraints research over the past several decades has clearly demonstrated that changes in the ocean environment have had major impacts on carbonate systems changes in climate ocean circulation and seafloor spreading rates have influenced temperature and seawater chemistry including carbonate saturation state and nutrient availability and thereby have determined boundary conditions for the biota that form carbonate platforms in turn the biota determine accumulation rates and facies zonations thus controlling platform geometry and facies dynamics in the first section of this paper we examine how nutrient availability influences carbonate facies associations we first discuss the role of temperature and nutrient gradients in the modern ocean and their influence on biotic associations then we discuss how carbonate sedimentation can be characterized along nutrient gradients in the second section we review proxies currently used to reconstruct paleoproductivity in open ocean environments and discuss their applicability to neritic carbonate systems we highlight the variety of existing proxies and their limitations and suggest that multiple lines of evidence are needed for valid interpretations our short review discusses sedimentological biogenic and geochemical proxies that can be used to reconstruct past nutrient fluxes and to constrain paleoceanographic controls over the distribution of carbonate associations however it also reveals that more data and case studies are needed that integrate shallow and deep water carbonate sequences and elucidate the links between temperature vs nutrient supplies changes and facies in ancient carbonate sequences

a method for isolating secular geomagnetic variation from shipboard total field measurements a test case in the ne atlantic summary in this pilot study we describe a method for extracting the secular variation constituent of the earth s magnetic field from underway shipboard total intensity magnetic measurements from a large amount of shipboard data obtained in the ne atlantic during the period 1956 to 1988 some 29 000 secular variation values were calculated at cross over points these results are then compared with those obtained from the international geomagnetic reference fields igrf in this region statistical analysis reveals that the shipboard values are able to match and marginally improve upon the igrf values across the oceans so long as the determination is made from a sufficiently large data set of observed values this method thus enables the additional utilization of marine observations in the analysis of secular variation patterns across the oceans which could lead to a more detailed view of these patterns than has been available before

modern heterozoan carbonates from a eutrophic tropical shelf mauritania abstract heterozoan or foramol production is typical in extratropical carbonate sedimentary systems however under mesotrophic to eutrophic conditions heterozoan carbonates also form in tropical settings but such heterozoan tropical sedimentary systems are poorly understood nevertheless distinction between tropical and extratropical heterozoan carbonates in ancient successions is crucial for accurate paleoenvironmental and paleoclimate reconstructions here surficial holocene and pleistocene sediments of the northern mauritanian shelf are studied as an example of a tropical eutrophic carbonate depositional system 11 g l 1 chl a chlorophyll a upwelling nutrient rich waters push onto the wide mauritanian shelf where they can warm up to in excess of 25 c this condition favors production of heterozoan carbonates dominated by bivalves and foraminifers even in this tropical setting in addition sediments are provided by eolian input from the desertic hinterland the resulting sediments are carbonate and mixed carbonate siliciclastic facies in which the carbonates are characterized by a mixture of tropical and cosmopolitan taxa benthic photosynthetic biota are absent while suspension feeding organisms are dominant this foramol grain association on a shelf scale is reminiscent of cool water carbonates therefore recognition of warm water heterozoan carbonates relies on key taxa related to tropical waters within the biota assemblages associated with a highly productive environment

where has all the aragonite gone mineralogy of holocene neritic cool water carbonates southern australia abstract surficial carbonate sediments on the southern continental shelf of australia are cool water in aspect and composed of biogenic particles produced largely during the late quaternary current understanding is that such sediments are calcite dominated as were their older cenozoic counterparts the holocene fraction of these sediments in modern open shelf neritic environments between 30 and 350 meters water depth is however 50 to 80 aragonite scant evidence of significant former aragonite in many cool water carbonate sedimentary rocks implies that most aragonite is lost before such sediments exit the marine diagenetic environment although marine dissolution must be taking place in such settings the conundrum is exacerbated because seawater over the shelf in southern australia is saturated with respect to aragonite it is proposed that the aragonite from skeletons of gastropods infaunal bivalves and certain bryozoans is dissolved in the shallow subsurface probably as the byproduct of bacterial degradation of sedimentary organic matter as a consequence the geological and paleontological record of many cool water carbonates is strongly biased and the inferred original calcitic composition of such sediments is the product of early diagenetic taphonomic loss not selective biogenic productivity the net result is not only dissolution of aragonite but also neomorphism of mg calcite to calcite with a marine geochemical signature synsedimentary aragonite loss by removing caco3 that is usually available for calcite cementation during meteoric diagenesis leads to retarded lithification of these cool water carbonates until deeply buried such removal of a significant carbonate fraction during deposition likely contributes to the low rates of cool water sediment accumulation

temperate skeletal carbonate sediments on scott shelf northwestren vancouver island canada abstract scott shelf 2000 km 2 centred at scott islands northwestern vancouver island is mainly shallower than 150 m topographically diversified and floored by bedrock outcrops and terrigenous lithic gravels and sands left stranded following the post glacial rise in sea level 13 000 yrs b p it lies in a zone of vigorous wind wave currents and strong tidal flows but is largely starved of modern terrigenous sediment as a consequence it is slowly accumulating a thin discontinuous blanket of clean skeletal carbonate sands and gravels admixed to varying degrees with the underlying terrigenous deposits principal skeletal contributors are infaunal bivalves on coarse sandy and gravelly substrates barnacles on low amplitude gravelly ridges bryozoans on bedrock outcrops and boulders and benthic foraminifera on fine sands in deep 100 m waters south of the scott islands living carbonate benthos are scattered and generally sparse occupying specific ecologic niches and the shelf wide rate of carbonate production is low skeletons are fragmented transported and mixed during storms and are concentrated within bedrock hollows and crevices and shallow depressions between gravel ridges where infaunal bivalves are abundant the carbonates are dominated by aragonite but otherwise the skeletal hashes are predominantly calcitic many grains and especially aragonitic ones are corroded and weakened by epilithic and endolithic bioerosion and probably also by marine and dissolution the most corroded shells have ages of only about 1000 yrs so that their preservation potential is low the character of scott shelf skeletal carbonate deposits reflects their temperate latitude cold water heritage

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 upwelling area off northwest africa a description of phenomena related to coastal upwelling abstract this paper presents a brief review of the oceanography along the upwelling coast of northwest africa the description contains information on seasonal variations of large scale winds ocean circulation and some gross of features of the hydrography characteristic meso scale patterns of currents during the upwelling season between 16 n and 26 n air and water temperature differences during upwelling season diurnal and semi diurnal variations of temperature atmospheric pressure wind and current regional peculiarities canyons and the banc d arguin

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

a late quaternary sedimentary shelf system under hyperarid conditions unravelling climatic oceanographic and sea level controls golfe d arguin mauritania nw africa abstract the sedimentation on the mauritanian shelf off the western saharan desert is strongly influenced by dust supply and is investigated in this study by combining surface mapping shallow acoustic profiling and the analysis of sediment cores coarse grained carbonates dominate wide areas of the open shelf at places where the shelf is exposed to the atlantic ocean the sheltered golfe d arguin in contrast is characterized by muddy shoals in its inner area and locally restricted and wedge shaped muddy depocenters which extend contour parallel in mid shelf settings in both cases cross shelf currents control sediment distribution and accumulation not location or amount of primary eolian input a major discontinuity on the outer shelf is located in 85 110 m water plus sediment depth and is refilled by a sedimentary facies succession of shoreface tidal and open shelf deposits this succession has formed during temporary lower sea levels along the last overall regression mis 4 and mis 3 the last glacial maximum and during the past deglacial sea level rise significant sediment deposition and preservation is limited to very restricted areas concerning the overall shelf architecture sea level was the main factor enabling or suppressing deposition in terms of 1 creating local erosional swales which have favored subsequent trapping and preservation of sediments 2 determining the type of sedimentary facies refilling these depressions under a variety of nearshore conditions 3 interacting with the seafloor morphology and by this controlling timing of initiation and growth geometry of mud wedges these mud wedges have formed since ca 9 cal ka under a continuous sedimentation regime these bodies must have formed in hydraulic equilibrium but they are detached from a defined sediment point source which is in contrast to common mudbelt formation on shelves in general sediment storage on shelves under hyperarid conditions seems to be very limited due to comparably low sediment input strong ravinement activity during changing sea levels significant bypassing and winnowing processes and a low preservation potential of the non cohesive materials these conditions lead to the development of almost sediment starved systems with low subsidence rates over longer geological timescales

heterozoan carbonates in subtropical to tropical settings in the present and past water temperature has received considerable attention as steering factor for the genesis of different types of marine carbonate sediments however parameters other than temperature also strongly influence ecosystems and consequently the carbonate grain associations in the resulting carbonate rock among those factors are biological evolution water energy substrate water chemistry light penetration trophic conditions co2 concentrations and mg ca ratios in the seawater increased nutrient levels in warm water settings for example lead to heterotrophic dominated associations that are characteristic of temperate to cool water carbonates failure to recognize the influence of such environmental factors that shift the grain associations towards heterotrophic communities in low latitudes can lead to misinterpretation of climatic conditions in the past modern analogues of low latitude heterozoan carbonates help to recognize and understand past occurrences of heterozoan warm water carbonates careful analysis of such sediments therefore is required in order to achieve robust reconstructions of past climate

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

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

environmental factors influencing skeletal grain sediment associations a critical review of miocene examples from the western mediterranean the presence of foramol rhodalgal and bryomol skeletal grain associations in ancient shallow marine limestones is commonly interpreted as evidence for non tropical palaeoclimate despite temperature being only one of several factors influencing skeletal grain associations such interpretations neglect the multitude of factors other than temperature that influence carbonate producing biota these include nutrients water energy water transparency depth of the sea floor salinity oxygen ca2 and co2 concentrations mg ca ratio alkalinity substrate requirements competitive displacement as well as biological and evolutionary trends this uniformitarian approach also disregards the probability that conditions of present day biological systems may not be representative of past conditions of analogous systems here the importance of considering these other factors is illustrated through two examples of carbonate platforms in the western mediterranean these platforms are dominated by foramol rhodalgal and bryomol associations of miocene age in spite of having formed in tropical conditions the platforms discussed are 1 the lower tortonian ramp on menorca balearic islands and 2 the lower middle miocene ramps of the central apennines italy evidence for tropical conditions in the mediterranean during the period of growth of these platforms is provided by species of red algae and larger foraminifera by data from coeval continental basins and by global oxygen isotope data

rapid expansion of greenland s low permeability ice slabs in recent decades meltwater runoff has accelerated to become the dominant mechanism for mass loss in the greenland ice sheet1 3 in greenland s high elevation interior porous snow and firn accumulate these can absorb surface meltwater and inhibit runoff4 but this buffering effect is limited if enough water refreezes near the surface to restrict percolation5 6 however the influence of refreezing on runoff from greenland remains largely unquantified here we use firn cores radar observations and regional climate models to show that recent increases in meltwater have resulted in the formation of metres thick low permeability ice slabs that have expanded the greenland ice sheet s total runoff area by 26 3 per cent since 2001 although runoff from the top of ice slabs has added less than one millimetre to global sea level rise so far this contribution will grow substantially as ice slabs expand inland in a warming climate runoff over ice slabs is set to contribute 7 to 33 millimetres and 17 to 74 millimetres to global sea level rise by 2100 under moderate and high emissions scenarios respectively approximately double the estimated runoff from greenland s high elevation interior as predicted by surface mass balance models without ice slabs ice slabs will have an important role in enhancing surface meltwater feedback processes fundamentally altering the ice sheet s present and future hydrology observations and regional climate models show that the increasing coverage of ice slabs on the greenland ice sheet could lead to a global sea level rise of up to 74 millimetres by 2100

a skeletal assemblage classification system for non tropical carbonate deposits based on new zealand cenozoic limestones abstract cenozoic limestones in new zealand are mainly skeletal grainstones and packstones formed under non tropical climatic conditions in open marine shelf or ramp environments following petrographic analysis of the nature and abundance of the skeletal components in nearly 500 samples of these limestones a complete linkage cluster analysis identified seven major skeletal assemblages that may be regarded as subdivisions of the single foramol skeletal association defined by lees and buller 1972 for temperate region carbonate deposits the seven assemblages are given contracted names as follows a barnamol barnacle bivalve dominated b bimol bivalve dominated c bryomol bryozoan bivalve dominated d echinofor echinoderm benthic foraminiferal dominated e nannofor nannofossil planktonic foraminiferal dominated f rhodalgal calcareous red algal dominated and g rhodechfor calcareous red algal echinoderm benthic foraminiferal dominated a composite triangular classification diagram has been devised for naming the skeletal assemblage of an unknown sample on the basis of its three main skeletal components the diagram successfully characterises more than 85 of the new zealand cenozoic limestone samples and also appears to be applicable for the skeletal assemblage designation of many overseas examples of non tropical carbonate deposits limitations relate mainly to locally common skeletal types e g serpulids brachiopods that are presently not incorporated into the new zealand based scheme the general ecological preferences of the main skeletal contributors in each of the seven skeletal assemblages form a basis for relating the assemblages to broad shelf habitats consequently as well as the benefits of providing a more consistent skeletal assemblage terminology for comparative studies between different workers the scheme can assist with the paleoenvironmental interpretation of non tropical skeletal carbonate facies

cretaceous marine nutrients greenhouse carbonates and the abundance of turritelline gastropods abstract modern marine carbonate sediments accumulate where carbonate producing organisms are abundant and siliciclastic input is low such accumulations occur today in two main environments and may be characterized as warm low nutrient wln also known as tropical or chlorozoan carbonates or cool high nutrient chn also known as cool water temperate nontropical foramol or heterozoan carbonates few carbonates form today in warm high nutrient whn conditions because such environments are very rare modern wln environments occur mainly in low latitudes where nutrients from upwelling or terrestrial runoff are low modern chn environments occur mainly in middle to high latitudes where nutrients mostly from upwelling are abundant however whn depositional environments may have been widespread during the cretaceous and paleogene during these times upwelled nutrient rich waters would in general have been warmer than they are today nutrients in these waters supported diverse carbonate produc

chlorozoan versus foramol lithofacies in upper cretaceous rudist limestones abstract the study of upper cretaceous limestones of the nurra region northwestern sardinia italy that crop out with open shelf rudist rich deposits has shown that during the early senonian coniacian santonian interval sediments characterized by assemblages dominated by molluscs with variable amounts of red algae bryozoa and echinoids replaced sediments including hermatypic corals green algae and variable amounts of non skeletal grains these latter components were largely dominant in the previous carbonate shelf contexts of the nurra during jurassic early cretaceous times becoming less numerous until they disappeared in the transgressive deposits that followed the tectonically induced middle cretaceous emersion phase a rhodalgal association typical of anomalous tropical areas or transitional ones has been recognized in the replacing limestones that may be more generically considered foramol type deposits this seems to document conditions of stress in the waters impinging on the nurra carbonate platform during the coniacian santonian transition the observation that in the late cretaceous a similar evolutionary trend seems to have characterized many shallow neritic successions from many different areas leads us to hypothesize more general causes of stress e g induced upwellings on the marginal sectors of the shelves increased oceanic overturns and hyperproductivity due to terrestrial runoff on post emersive transgressed substrata peculiar oceanic conditions were able to create depositional contexts that were considerably changed with respect to the previous ones such that the more opportunistic forms of the foramol assemblages flourished the change in dominant assemblages resulted in a different organization of the sediment as a response to the different producing communities the resulting temperate type carbonate shelves were characterized by a low growth potentiality essentially due to a higher dispersion rate and this could have facilitated their drowning

cool water carbonates in a paleoequatorial shallow water environment the paradox of the auernig cyclic sediments upper pennsylvanian carnic alps austria italy and its implications distinct parts of limestones within the upper paleozoic auernig group of the carnic alps austria and italy are characteristic of cool water carbonates the carnic alps were between 5 n and 10 s paleolatitude during the late carboniferous a position confirmed by dasyclad algae and fossil plants the floral association occurrence of coal seams and absence of evaporites indicate a humid tropical environment the entire section lacks abiotic components of typical warm water limestones no ooids and no aggregates occur within the auernig group parts of the limestones show surprisingly a cool water association of high diversity bryozoans brachiopods crinoids red algae sponge spicules and entomozoan ostracodes the genesis of these limestones atypical for a paleoequatorial setting cannot be explained by changes in salinity bathymetry or terrigenous input the water temperature possibly linked with upwelling nutrient supply and paleoceanographic currents is the most convincing cause of this unusual association paleoceanographic changes are interpreted as linked to contemporaneous glaciation deglaciation cycles in gondwana this paper shows that cool water carbonates in shallow water environments are not necessarily nontropical as generally interpreted future studies should consider water temperature oceanic circulation and availability of nutrients supplementary to bathymetry salinity and latitude related climate in interpretation of carbonate components

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

provenance of present day eolian dust collected off nw africa 1 atmospheric dust samples collected along a transect off the west african coast have been investigated for their physical grain size distribution mineralogical and chemical major elements composition on the basis of these data the samples were grouped into sets of samples that most likely originated from the same source area in addition shipboard collected atmospheric meteorological data modeled 4 day back trajectories for each sampling day and location and total ozone mapping spectrometer aerosol index data for the time period of dust collection february march 1998 were combined and used to reconstruct the sources of the groups of dust samples on the basis of these data we were able to determine the provenance of the various dust samples it appears that the bulk of the wind blown sediments that are deposited in the proximal equatorial atlantic ocean are transported in the lower level 900 hpa ne trade wind layer which is a very dominant feature north of the intertropical convergence zone itcz however south of the surface expression of the itcz down to 5 s where surface winds are southwesterly we still collected sediments that originated from the north and east carried there by the ne trade wind layer as well as by easterly winds from higher altitudes the fact that the size of the wind blown dust depends not only on the wind strength of the transporting agent but also on the distance to the source hampers a direct comparison of the dust s size distributions and measured wind strengths however a comparison between eolian dust and terrigenous sediments collected in three submarine sediment traps off the west coast of nw africa shows that knowledge of the composition of eolian dust is a prerequisite for the interpretation of paleorecords obtained from sediment cores in the equatorial atlantic