widespread prolonged late middle to late ordovician upwelling in north america a proxy record of glaciation late middle to late ordovician subtidal ramp carbonates of new mexico texas and oklahoma contain abundant spiculitic chert to 70 chert by volume and phosphate 1 5 wt indicating that these rocks formed in an extensive upwelling zone upwelling began in the late middle ordovician ca 454 ma and persisted until the end of the ordovician late ordovician cherty carbonates also occur along the u s cordilleran margin in board of organic rich graptolitic shale and chert the widespread occurrence of late ordovician cherty and phosphatic carbonates on southern and western laurentia in addition to phosphate rich cool water carbonates over much of the north american midcontinent suggests vigorous thermohaline circulation related to prolonged 10 14 ma gondwana glaciation

anatomy of extremely thin marine sequences landward of a passive margin hinge zone neogene calvert cliffs succession maryland u s a abstract detailed examination of neogene strata in cliffs 25 35 m high along the western shore of chesapeake bay maryland reveals the complexity of the surviving record of siliciclastic sequences 150 km inland of the structural hinge zone of the atlantic passive margin previous study of the lower to middle miocene calvert plum point member and choptank formations documented a series of third order sequences 7 10 m thick in which lowstand deposits are entirely lacking transgressive tracts comprise a mosaic of condensed bioclastic facies and regressive highstand tracts are present but partially truncated by the next sequence boundary smaller scale fourth order cyclic units could not be resolved together these sequences constitute t e transgressive and early highstand tracts of a larger second order miocene composite sequence the present paper documents stratigraphic relations higher in the calvert cliffs succession including the upper miocene st marys formation which represents late highstand marine deposits of the miocene second order sequence and younger neogene fluvial and tidal inlet deposits representing incised valley deposits of the succeeding second order cycle the st marys formation consists of a series of tabular units 2 5 m thick each with an exclusively transgressive array of facies and bounded by stranding surfaces of abrupt shallowing these units which are opposite to the flooding surface bounded regressive facies arrays of model parasequences are best characterized as shaved sequences in which only the transgressive tract survives and are stacked into larger transgressive highstand and forced regression sets biostratigraphic analyses by others indicate that this onshore record contains the same number of third order 1 my duration units as present offshore and so thinning landward of the hinge zone was accomplished not by omission or erosion of entire cycles of deposition but instead by omission of some subsidiary elements e g lowstand tracts by erosional shaving of sequence tops removing the entire regressive tract in some sequences by a reduced number of component high order cycles surviving per larger set and by qualitative changes in the anatomy or composition of elements e g condensed transgressive tracts shaved sequences rather than parasequences all of these differences can be attributed to limited accommodation ut preservation of an onshore record of each baselevel cycle was probably also favored by the large amplitude and rapidity of eustatic fluctuations during the miocene

palaeozoic stromatoporoid taphonomy ecologic and environmental significance abstract epibenthic sessile marine organisms such as the aspiculate stromatoporoids show a wide range of growth forms in different settings across palaeozoic carbonate banks and reefs making them useful taphonomic tools in palaeoenvironment analysis field observations of ordovician through late devonian stromatoporoid bearing biostromal and biohermal successions on different palaeocontinents have revealed three main post mortem tapho signatures that affect palaeoecologic analysis 1 variability of physical breakage and bioerosion prior to burial 2 loss of morphologic and taxonomic information due to post burial diagenesis and 3 minor localized reorientation during karstification physical fragmentation abrasion and lesser bioerosion and dissolution represent the main processes responsible for post mortem destruction hydrodynamic behaviour of stromatoporoid clasts was similar to other carbonate skeletal clasts in their rounding and sorting characteristics although bioerosion and bioturbation did not play an important role in palaeozoic stromatoporoid taphofacies characterization a marked increase in bioerosion of stromatoporoids is evident beginning in certain silurian wenlock morphotypes and in some devonian morphotypes stromatoporoids offer varying profiles to shelf currents and seasonal storm surges and apparently have different skeletal strength durability depending on skeletal architecture cyst dominated skeleton architecture appears to have been fairly resistant to fragmentation latilaminae a common skeletal feature in different families of calcified sponges represent inherent zones of weakness that appear to have enhanced equidimensional breakage away from latilaminae to oblate breakage along latilaminar surfaces fragmentation construction of lamina pillar architecture amongst the most common skeletal attributes of siluro devonian stromatoporoids gives the visual impression of varying robustness but this is supported by few data stromatoporoid response to increasing hydrodynamic energies varies greatly from no movement or simple overturning of skeletons to severe fragmentation and size sorting although such variation broadly reflects palaeogeographic setting and thus periodic disturbance by tropical storms familial and generic skeletal traits greatly influenced taphofacies characterization these differences in modularity and ontogeny in the stromatoporoid groups has hampered development of generalized taphofacies models as devised for shell rich deposits taphofacies are not comparable between modern coralgal reefs especially the highly specialized acroporid facies and palaeozoic stromatoporoid bearing reefs for the following reasons significant differences exist in diversity of observable growth strategies nature of attachment of skeletons to substrate and variety of morphotypes probable significant differences in life modes between these groups feeding strategies and positions and areal extent of clonal tissue within the skeletons and their subsequent susceptibility to infestation by microborers and palaeozoic macrobioeroders were fewer than modern representatives and apparently less effective in stromatoporoid taphofacies characterization than modern reef macrobioeroders are for coral taphofacies development

benthic marine calcifiers coexist with caco3 undersaturated seawater worldwide ocean acidification and decreasing seawater saturation state with respect to calcium carbonate caco3 minerals have raised concerns about the consequences to marine organisms that build caco3 structures a large proportion of benthic marine calcifiers incorporate mg2 into their skeletons mg calcite which in general reduces mineral stability the relative vulnerability of some marine calcifiers to ocean acidification appears linked to the relative solubility of their shell or skeletal mineralogy although some organisms have sophisticated mechanisms for constructing and maintaining their caco3 structures causing deviation from this dependence nevertheless few studies consider seawater saturation state with respect to the actual mg calcite mineralogy mg x of a species when evaluating the effect of ocean acidification on that species here a global dataset of skeletal mole mgco3 of benthic calcifiers and in situ environmental conditions spanning a depth range of 0 m subtidal neritic to 5600 m abyssal was assembled to calculate in situ mg x this analysis shows that 24 of the studied benthic calcifiers currently experience seawater mineral undersaturation mg x 1 as a result of ongoing anthropogenic ocean acidification over the next 200 to 3000 years the predicted decrease in seawater mineral saturation will expose approximately 57 of all studied benthic calcifying species to seawater undersaturation these observations reveal a surprisingly high proportion of benthic marine calcifiers exposed to seawater that is undersaturated with respect to their skeletal mineralogy underscoring the importance of using species specific seawater mineral saturation states when investigating the impact of co2 induced ocean acidification on benthic marine calcification

an estuarine facies model for the middle jurassic sleipner formation beryl embayment north sea the middle jurassic sleipner formation is sub divided into three units in the beryl embayment area of the north sea the lowermost two units the 9interbedded unit9 and 9lower coal marker9 overlie lower jurassic marine silts and were probably deposited in progressively shallowing coastal environments during a eustatic sea level fall an estuarine deposit overlies the 9lower coal marker9 and was deposited following sea level rise or tectonic subsidence of the area the 9estuarine succession9 forms the bulk of the formation and is composed of seven facies grouped into three facies associations representing sub tidal inter tidal and salt marsh sub environments the sub tidal facies association is dominated by sandstones deposited in tidal channels and sand flats the inter tidal association is characterized by alternations of sandstone and siltstone on a scale of millimetres to several metres and consists of tidal channel sandstones lenticular bedded siltstones and other tidally influenced facies the salt marsh association is dominated by coals and rooted siltstones with minor amounts of creek fill sandstones the estuary mouth probably lay towards the northern end of the embayment where a connection existed through the viking graben to the boreal ocean

comparative analysis of methods used to define eustatic variations in outcrop late cambrian interbasinal sequence development interbasinal correlation of late cambrian cyclic carbonates from the appalachian and cordilleran passive margins the texas craton and the southern oklahoma aulacogen defines six major third order depositional sequences graphic correlation of biostratigraphically constrained strata was used to establish equivalency of stratigraphic sequences between the individual sections relatively isochronous biomere boundaries were used as time datums for lithostratigraphic correlation although the individual sections are composed of different types of meter scale cycles and component lithofacies that reflect the various environmental settings of the localities the overall upward shallowing character of individual sequences is evident the sequences are late cedaria mid crepicephalus late crepicephalus aphelaspis to earliest elvinia elvinia to early saukia and saukia to the cambrian ordovician boundary interbasinal correlation of stratigraphic sequences permits an evaluation of quantitative techniques for determining accommodation history correlation of fischer plots of cyclic successions from separate basins supports a eustatic control of late cambrian sequence development r2 r3 curves derived from subsidence analysis of the late cambrian sections provide good resolution of the second and third order scales of accommodation change and interbasinal correlations of r2 r3 curves also support eustatic control on sequence development comparing the accomodation curves and subsidence analysis with paleobathymetric trends of late cambrian cyclic strata suggests that themore curves may approximate the form of the eustatic sealevel signal a composite eustatic sealevel curve for late cambrian time in north america was created by qualitatively combining the accommodation curves defined by the different techniques for each of the four localities 129 refs 16 figs 3 tabs less

initial assessment of the carbon emission rate and climatic consequences during the end permian mass extinction numerous lines of geochemical and stable isotopic evidence indicate that the end permian mass extinction was accompanied by abrupt climate change induced by co2 addition catastrophic end permian siberian volcanism may have released a large amount of co2 into the atmosphere and pushed the earth s system beyond a critical threshold causing the mass extinction however the injection rate total amount and source of co2 are largely unknown we conducted a suite of simulations using the recently published carbon isotope records and u pb ages from meishan section in zhejiang province china an earth system model of intermediate complexity cgenie http www genie ac uk was used to extract the pattern of co2 release needed to replicate the observed carbon isotope excursion across the permian triassic boundary this analysis leads us to suggest that the source of co2 must have been significantly heavier than typical biogenic or thermogenic methane to explain the significant warming that occurred during and after the extinction event nevertheless as with the paleocene eocene thermal maximum end permian rates of co2 addition were likely small compared with modern fossil fuel burning but considerably more protracted such that the likely total co2 emitted significantly exceeded the modern fossil fuel reserves peak emission rates corresponded to the onset of the maximum extinction interval consistent with carbon cycle disruption including volcanogenic co2 induced warming and perhaps ocean acidification as a trigger for the end permian mass extinction

aftermath of the end cretaceous mass extinction possible biogeochemical stabilization of the carbon cycle and climate in the aftermath of the cretaceous tertiary k t boundary event 65 m y ago pelagic carbonate productivity was greatly reduced for several hundred thousand years a decrease in carbonate productivity by a factor greater than 3 in the absence of some mechanism to remove excess carbonate from the ocean should have resulted in the accumulation of carbon and alkalinity in the oceans this would cause the atmospheric partial pressure of co2 to fall dramatically and the deep ocean to become fully saturated with respect to calcite evidence of such a period of highly calcite saturated oceans with low atmospheric pco2 in the earliest tertiary is lacking suggesting that ocean chemistry may have been buffered by some process or processes shallow water carbonate accumulation rates may depend in part on carbonate ion concentrations and thus shallow water carbonate deposition might act to stabilize ocean chemistry in the face of a dramatic reduction in pelagic productivity in our four box ocean model as the oceanic carbonate ion concentration rises in the face of diminished pelagic carbonate accumulation the shallow water carbonate accumulation rate increases compensating for the reduction in pelagic carbonate accumulation these model results indicate that the carbonate ion feedback on shallow water carbonate sedimentation may have acted to balance oceanic carbon and alkalinity budgets at the k t boundary and furthermore may have been a primary mechanism maintaining high shallow water carbonate accumulation rates prior to the jurassic onset of widespread pelagic carbonate accumulation

heterozoan carbonates in oligotrophic tropical waters the attard member of the lower coralline limestone formation upper oligocene malta abstract photozoan and heterozoan skeletal assemblages are controlled by their trophic requirements i e light based photosynthesis versus other sources and temperature photozoan associations tend to dominate tropical and subtropical waters whereas heterozoan carbonate systems tend to occur in cooler waters and in localised areas that are affected by nutrient rich upwelling or terrestrial runoff because of the wide climatic spectrum in which heterozoan carbonates are found their interpretation is often problematic we present a high resolution analysis of the attard member of the lower coralline limestone formation upper oligocene malta the biotic associations and palaeolatitudinal reconstructions suggest that carbonate sedimentation took place in tropical waters under oligotrophic conditions an important factor controlling the spread of heterozoan assemblages in the late oligocene of malta seems to be related to the palaeoecology and evolution of zooxanthellate the limited capacity of corals to thrive in high light conditions and to form a wave resistant reef promoted the diffusion of heterozoan assemblages

quantification of high frequency sea level fluctuations in shallow water carbonates an example from the berriasian valanginian french jura abstract when quantifying sedimentary processes on shallow carbonate platforms it is important to know the high frequency accommodation changes through time accommodation changes in cyclic successions are often analysed by simply converting cycle thickness to fischer plots this approach is not satisfactory because it does not account for differential compaction possible erosion sea level fall below the depositional surface or subtidal cycles an attempt is made here to reconstruct a realistic high frequency accommodation and sea level curve based on a detailed facies and cyclostratigraphical analysis of middle berriasian to lower valanginian sections in the french jura mountains the general depositional environment was a shallow marine carbonate platform on a passive margin our approach includes the following steps 1 facies interpretation 2 cyclostratigraphical analysis and identification of milankovitch parameters in a well constrained chronostratigraphic framework 3 differential decompaction according to facies 4 estimation of depth ranges of erosion and vadose zone 5 estimation of water depth ranges at sequence boundaries and maximum flooding intervals 6 estimation of mean subsidence rate 7 classification of depositional sequences according to types of facies evolution catch up catch down give up or keep up 8 classification of depositional sequences according to long term sea level evolution rising stable falling 9 calculation of eustatic sea level change for each depositional sequence using the parameters inferred from these scenarios assuming that sea level cycles were essentially symmetrical which is probable in early cretaceous greenhouse conditions 10 calculation of a sea level curve for each studied section 11 comparison of these curves among each other to filter out differential subsidence 12 construction of a composite eustatic sea level curve for the entire studied platform 13 spectral analysis of the calculated sea level curves limitations of the method are those common to every stratigraphic analysis however the method has the potential to improve the original cyclostratigraphical interpretations and to better constrain the high frequency sea level changes that control carbonate production and sediment fluxes

influence of variable rates of neritic carbonate deposition on atmospheric carbon dioxide and pelagic sediments short term imbalances in the global cycle of shallow water calcium carbonate deposition and dissolution may be responsible for much of the observed pleistocene change in atmospheric carbon dioxide content however any proposed changes in the alkalinity balance of the ocean must be reconciled with the sedimentary record of deep sea carbonates the possible magnitude of the effect of shallow water carbonate deposition on the dissolution of pelagic carbonate can be tested using numerical simulations of the global carbon cycle boundary conditions can be defined by using extant shallow water carbonate accumulation data and pelagic carbonate deposition dissolution data on timescales of thousands of years carbonate deposition versus dissolution is rarely out of equilibrium by more than 1 5 x 10 13 mole yr 1 results indicate that the carbonate chemistry of the ocean is rarely at equilibrium on timescales less than 10 ka this disequilibrium is probably due to sea level induced changes in shallow water calcium carbonate deposition dissolution an interpretation that does not conflict with pelagic sedimentary data from the central pacific

climatic and eustatic signals in a global compilation of shallow marine carbonate accumulation rates two of the most important factors that control the accumulation rate of material in carbonate platform environments on geological time scales are climate and eustasy accurately assessing the importance of these interrelated factors through the study of both modern and ancient carbonate facies however is problematic these difficulties arise from both the complexities inherent in carbonate depositional systems and the demonstrable incompleteness of the stratigraphic record here a new compilation of more than 19 000 global phanerozoic shallow marine carbonate accumulation rates derived from nearly 300 individual stratigraphic sections is presented these data provide the first global holistic view of changes in shallow marine carbonate production in response to climate and eustasy on geological time scales notably a clear latitudinal dependence on carbonate accumulation rates is recognized in the data moreover it can also be demonstrated that rates calculated across the last glacial maximum and holocene track changes in sea level in detail the data show that globally averaged changes in carbonate accumulation rates lagged changes in sea level by ca 3 kyr reflecting the commonly observed delay in the response of individual carbonate successions to sea level rise differences between the rates of carbonate accumulation and sea level change over the past 25 kyr ostensibly reflect changing accumulation mode with platform drowning give up mode pervasive during peak early holocene sea level rise followed by a switch to catch up mode accumulation from ca 9 ka to the present carbonate accumulation rates older than the quaternary are typically calculated over time spans much greater than 100 kyr and at these time spans rates primarily reflect long term tectonically mediated accommodation space changes rather than shorter term changes in climate eustasy this finding coupled with issues of stratigraphic incompleteness and data abundance tempers the utility of this and other compilations for assessing accurately the role of climate and eustasy in mediating carbonate accumulation rates through geological time

mesotidal estuarine sequences a perspective from the georgia bight abstract although much has been written about estuaries and estuarine sediments very few facies models have been proposed to date and considerable ambiguity remains in coastal classification schemes current stratigraphic concepts fail to elucidate not only the differences between certain deltaic estuarine and lagoon fill sequences but also the pronounced similarities between many riverine and salt marsh estuarine sequences these distinctive latero vertical successions recent and ancient warrant increased scrutiny and conceptual refinement preliminary stratigraphic models and definitions presented here based largely upon modern georgia estuaries should provide a broad framework for further evaluation and clarification of the above facies relationships from that standpoint an estuarine sequence consists of complex intertidal to subtidal mostly channel form facies dominated to some extent by tidal effects typically displaying abrupt variations in sediment texture and composition and in physical and biogenic sedimentary structures subtle to pronounced salinity gradients may be discernible nevertheless the features most diagnostic of the overall sequence are 1 tidally influenced channel form deposits and 2 characteristic bioturbate textures and trace fossils

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

tidal deposition in the basal upper cambrian mt simon formation in wisconsin the upper cambrian mt simon formation 0 65 m thick is a basal quartz arenite exposed in westcentral wisconsin a detailed field investigation of the physical and biogenic sedimentary structures of the mt simon has led to the recognition of three distinct lithofacies the lower one unconformably overlies precambrian basement rocks it consists of medium to very large scale sets of tabular and trough cross bedded medium to very coarse grained sandstone and pebbly sandstone with minor intercalated horizontal beds of very fine to medium grained sandstone siltstone and shale sparse examples of skolithos and arenicolites are present this facies consists of a very thin sequence of possible braided fluvial and marine foreshore deposits overlain by probable marine shoreface and tidal channel deposits much of the facies seems to represent shallow subtidal deposition in a relatively high energy regime the middle lithofacies consists of two distinctly different subfacies which probably were deposited in a low tidal flat setting the higher energy subfacies consists of small to medium scale sets of tabular and trough crossbedded fine to coarse grained sandstones containing distinct zones dominated by skolithos and arenicolites this subfacies probably represents deposition in meandering tidal channels the lower energy subfacies consists of thinbedded horizontally laminated and ripple cross laminated very fine to medium grained sandstone siltstone and shale with common specimens of cruziana rusophycus and planolites this subfacies probably represents deposition on lower energy tidal flats adjacent to the tidal channels the upper lithofacies consists predominantly of structureless densely bioturbated very fine to coarse grained sandstone containing abundant specimens of skolithos the upper few meters of the facies consists of small to medium scale sets of trough cross bedded very fine to coarse grained sandstone with layers of disarticulated valves of the brachiopod obolus the upper facies probably represents deposition on tidal flats perhaps in a midtidal flat setting characterized by slower sedimentation rates a correspondingly higher degree of bioturbation persistent reworking of shelled macrobenthos and periodic subaerial exposure the mt simon formation is interpreted as a largely progradational regressive shoaling and fining upward tidal sequence a marine interpretation is supported by the widespread occurrence of marine trace fossils within this unit evidence for a tidal origin is seen in the presence of unimodal cross strata associated with reactivation surfaces compound cross strata numerous scour and truncation surfaces lined with intraformational conglomerates common clay drape laminae separating sets of cross strata interference and flat topped ripple marks and desiccation cracks sedimentation continued without apparent interruption as the overlying eau claire formation was deposited also under tidal influence recent reinterpretations of other basal cambrian cratonic quartz arenites together with this new interpretation for the mt simon formation suggest that the long held concept of basal transgressive sandstones deposited as blankets across the craton may be too simplistic for deposition in braided fluvial marginal marine tidal flat tidal channel and marine foreshore and shoreface environments seems indicated

reconstructing paleoceanographic conditions during the middle ediacaran evidence from giant ooids in south china abstract the ediacaran was a period of intense environmental change in earth history transient pulses of oxygenation and shifts in ocean chemistry have been interpreted from a range of geochemical proxies including rare earth elements and yttrium rey but it is still a challenge to reconstruct paleoceanographic conditions due to the scarcity of reliable recorder in this study we explore the possibility that a newly discovered deposit of giant ooids in the nanshanping outcrop in south china contains a relatively intact record of the ree composition of ediacaran seawater providing an important window into the redox state of the surface ocean at this time these ooids are relatively large in size 1 6 mm and exhibit densely banded laminae a regional chemostratigraphic correlation shows that the giant ooid bearing succession in south china is in the upper part of the second ediacaran positive carbon isotopic shift ep2 and thus its occurrence was not associated with the shuram excursion additionally the occurrences of giant ooid bearing oolites in different blocks were not synchronous during the middle ediacaran in situ laser ablation analysis of giant ooid cortices reveals that the shale normalized rey patterns are similar to those of modern seawater including depleted light rees superchondritic y ho ratios and positive la anomalies yet no ce anomalies 1 0 0 15 in numerous ooid cortices seems to indicate a suboxidized condition of surface ocean in south china at that time the petrographic and geochemical evidence support the weak diagenetic alteration of the pure giant ooids during burial they formed in open ocean settings with energetic hydrodynamic environments and were affected by early dolomitization that might preserve mostly original petrographic fabrics and rey signatures from further diagenetic overprinting the characteristics of ce anomalies and rey compositions acquired from the giant ooids indicate that the surface ocean was suboxidized in south china during the late stage of ep2 implying the very low atmospheric o2 level at that time our results suggest that giant ooids may be a reliable analytical target that provide a snapshot into palaeoceanographic conditions during this crucial period of dynamic changes in early earth history

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

calcium isotope constraints on the end permian mass extinction the end permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope 13c composition of carbonate minerals several extinction scenarios consistent with these observations have been put forward secular variation in the calcium isotope 44 40ca composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction here we report 44 40ca across the permian triassic boundary from marine limestone in south china the 44 40ca exhibits a transient negative excursion of 0 3 over a few hundred thousand years or less which we interpret to reflect a change in the global 44 40ca composition of seawater co2 driven ocean acidification best explains the coincidence of the 44 40ca excursion with negative excursions in the 13c of carbonates and organic matter and the preferential extinction of heavily calcified marine animals calcium isotope constraints on carbon cycle calculations suggest that the average 13c of co2 released was heavier than 28 and more likely near 15 these values indicate a source containing substantial amounts of mantle or carbonate derived carbon collectively the results point toward siberian trap volcanism as the trigger of mass extinction

coupled δ44 40ca δ88 86sr and 87sr 86sr geochemistry across the end permian mass extinction event abstract we report high resolution high precision 44 40ca 88 86sr and 87sr 86sr records spanning the permian triassic boundary ptb from the meishan and dajiang carbonate successions in south china the goal of the study was to understand the behavior of ca and sr isotopes during a time period in earth history characterized by severe biological and environmental perturbations including a major mass extinction flood basalt volcanism ocean acidification and sea level fluctuations dajiang displays negative 44 40ca and 88 86sr excursions and invariant 87sr 86sr ratios in the

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

a new palaeogeographic reconstruction for the middle jurassic of the northern north sea an estuarine sequence equivalent in age to the brent group deltaic deposits further north is recognized in the central viking graben it indicates a persistent marine connection southwards from the boreal ocean during deltaic accumulation and suggests that the brent delta did not prograde from the south along the graben as previously suggested evidence from the uk north viking graben indicates the brent delta was probably derived transversely rather than axially as were the other jurassic clastic systems infilling the graben

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

experimental study of cross strata development on an undulatory surface and implications relative to the origin of flaser and wavy bedding abstract flume experiments were carried out in order to examine the influence of sedimentation surface undulation upon structural and textural development of cross bedded sedimentation units the evidence of this study indicates that in addition to flow conditions the morphology of the sedimentation surface is a significant factor responsible for the mechanics of bedding formation the relation between the bedding type and the sedimentation surface morphology may be quantitatively expressed by a combination of the symmetry index rsi of sedimentation surface undulation and the parameter a m defined as a ratio of mean amplitude a of sedimentation surface undulation to mean thickness m of the sedimentation unit deposited on this surface flaser and wavy bedding are built of couplets of sandy and muddy elements a single pair of sandy and muddy elements of an individual couplet is known to form by alternate tractional current deposition and slack water suspension settlement as a result of the present study another reasonable mode of origin is proposed an individual pair of sandy and muddy elements may also develop simultaneously in a bed form migrating on an undulatory sedimentation surface under unidirectional flow conditions a sequence of sandy muddy couplets may develop in response to alternate processes of deposition and erosion of such deposits

mid miocene paleoproductivity in the atlantic ocean and implications for the global carbon cycle 1 a prominent middle miocene 17 5 13 5 ma carbon isotope excursion ubiquitously recorded in carbonate sediments has been attributed to enhanced marine productivity and sequestration of 13c depleted organic carbon in marine sediments or enhanced carbon burial in peat lignite deposits on land here we test the hypothesis that the marine 13c record reflects a change in productivity with proxy records from three atlantic ocean sites deep sea drilling program site 608 and ocean drilling program sites 925 and 1265 our multiproxy approach is based on benthic foraminiferal accumulation rates elemental ratios ba al and p al the 13c of bulk sedimentary organic matter and dissolution indices we compare these proxies to benthic foraminiferal 13c values measured on the same samples our results indicate that marine paleoproductivity in the atlantic ocean is not related to the benthic foraminiferal 13c excursion a numerical box model confirms that marine productivity cannot account for the 13c maximum the model shows that sequestration of 1 5 1018 mol c in the terrestrial realm over a period of 3 ma leads to a 0 9 13c increase in the deep ocean which is near the observed records therefore an increase in continental organic carbon sequestration is the most plausible way to enrich the ocean s carbon pool with 13c which is consistent with coeval lignite deposits worldwide the 13c values of bulk sedimentary organic matter parallel the 13c of dissolved inorganic carbon as reflected by benthic foraminiferal 13c values suggesting no significant change in atmospheric pco2 levels over the investigated period

sedimentology and sequence stratigraphy of early syn rift tidal sediments the nukhul formation suez rift egypt abstract facies and tectono stratigraphic models for the tidally influenced miocene nukhul formation are presented based on outcrop data from hammam faraun fault block suez rift egypt deposits of the nukhul formation are attributed to two linked depositional settings offshore to shoreface and estuary settings and were deposited during initial stages of rifting in hanging wall depocenters of early formed propagating fault segments the offshore to shoreface deposits consist of variably bioturbated mudstones that pass gradationally upward to bioturbated bioclastic sandstones the more landward estuary deposits can be separated into a tripartite division of estuary mouth estuary funnel with bayhead delta and upper estuary channel deposits estuarine processes generated a complex intercalation of lithologies with both gradational and sharp facies transitions in the estuary deposits tidal ravinement surfaces are typically characterized by mudstones of the estuary funnel association below passing abruptly up to erosionally based estuary mouth sandstones maximum flooding surfaces are expressed by an abrupt erosional contact separating estuary mouth sandstones below and estuary funnel mudstones above stratigraphic development was strongly influenced by the evolving early rift structure depocenters were narrow 2 5 km wide and elongate 10 km long parallel to the strike of normal fault segments the shoreface shoal prevented wave energy in the estuary and increased the relative influence of tidal currents the elongate fault controlled geometry of the depocenters confined the bayhead delta and further enhanced tidal influence stratal geometry reflects deformation associated with low relief growth folds and surface breaking faults that together formed part of an evolving fault array this basin configuration and associated nukhul stratigraphy is markedly different to tectono stratigraphic models for crustal scale tilted fault blocks that are applicable from late stages of rifting

geochemical consequences of intense pulse like degassing during the onset of the central atlantic magmatic province the triassic jurassic boundary tjb ismarked by one of the five largestmass extinctions of the phanerozoic and the eruption of a large igneous province the central atlanticmagmatic province camp the tjb is characterized by a carbonate production crisis by negative excursions in the carbon isotopic ratio of buried organic matter and by successive peaks in atmospheric co2 herewe use the numerical model geoclimto explore the possible connections between the camp emplacement and the observed carbon cycle perturbations different degassing scenarios linked to the camp eruption are explored we show that the emission of realistic amounts of co2 that follow a geologically constrained degassing scenario as short termpeaks less than 10 ka leads to successive decrease in carbonate production as observed in the geological record we also calculate the evolution of carbon isotopes and show that our model reproduces the amplitude of the isotopic excursion with a volcanic degassing of co2 characterized by a carbon isotopic composition of 20 such low values could be associated to carbon pools of light isotopic composition located at the transition zone cartigny p 2010 earth and planetary science letters v 296 p 329 339 and not necessarily to biogenicmethane release finally themodel predicts a succession of short term co2 rises with an amplitude in close agreement with available proxy based reconstructions

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

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

regressive and transgressive cycles in a rift basin depositional model and sedimentary partitioning of the middle jurassic hugin formation southern viking graben north sea abstract the jurassic hugin formation consists of shallow marine sandstones that belong to a significant hydrocarbon reservoir in the sleipner area in the norwegian north sea the formation encompasses coarsening upward units of mouth bar and shoreface facies interpreted to record delta outbuilding during regression and fining upward units with tidal channel dune and tidal flat facies interpreted as part of an estuary environment during transgression the correlations reveal that the studied part of the hugin formation consists of 8 sequences each with a transgressive and a regressive unit representing the transgressive systems tract and the highstand systems tract respectively the sequences are stacked retrogradationally landward as a result of rapid tectonic subsidence and rifting of the viking graben rifting led to the development of an elongate graben where tidal currents were amplified wave action damped and longshore drift as sediments supply reduced or absent lowstand and forced regressive systems tracts are not identified and their absence is interpreted to reflect suppression of relative sea level falls in a rapidly subsiding basin where the basin subsidence rate outpaced any potential fall in eustatic sea level through facies interpretation and sequence stratigraphic correlations between wells these regressive and transgressive units are shown to exhibit characteristic thickness trends in the form of sigmoidal shaped wedges stacked in an offset manner in a landward to basinward orientation these thickness trends illustrate sediment partitioning within the sequences and are explained by the relationship between accommodation versus sediment supply in terms of mass balance during regression the focus of sedimentation was pushed basinward and during transgression it was pushed landward as sediments were trapped there the mapping of these sequence stratigraphic units serves as input to reservoir models and to help increase recovery and identify new exploration targets

holocene ooids of aitutaki atoll cook islands south pacific although oolitic sands are widespread throughout the phanerozoic carbonate rock record and they are abundant in some modern shallow marine carbonate systems recent ooids have not been recognized from any locality in the pacific basin on aitutaki atoll cook islands south pacific oolitic sands occur in water depths of 2 1 6 3 m within the lagoon and less abundantly on shallower reef aprons most ooids are between 150 and 300 m in diameter have between 1 and 25 concentric to irregular laminae and occur with peloids and skeletal grains cortical laminae include mg calcite crystals with radial tangential and random orientations the occurrence and distribution of oolitic sands on aitutaki are facilitated by a convergence of hydrodynamic and chemical factors wave driven currents combined either with flow separation over a sharp increase in depth at the reef apron lagoon interface or with oceanward flow in the lee of islands serve to transport ooids without flushing them from the system here ph alkalinity and carbonate supersaturation are at some of the highest levels in the tropical pacific the restricted occurrence of holocene oolitic sands in areas of the pacific and atlantic basins with elevated ph and total alkalinity reflects the importance of carbonate saturation thresholds in limiting the spatial distribution of these sands in modern shallow marine settings these recent examples are consistent with interpretations of the importance of these variables in determining the distribution abundance and cortical mineralogy of oolitic sands throughout the phanerozoic stratigraphic record of carbonate accumulation

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

stratigraphic completeness of carbonate dominated records from continental interiors versus continental margins stratigraphic thinning occurs via condensation and omission at multiple scales abstract over phanerozoic time scales stratigraphic records from continental interiors or cratons are dramatically thinner and are generally assumed to be relatively incomplete with more numerous and longer duration hiatuses compared to records from more rapidly subsiding continental margins however this assumption need not be true for the shorter time scales i e several 106 years and shorter over which accumulation of the preserved stratigraphic record on the continental interior actually takes place this study compares carbonate dominated sedimentary records from the devonian continental interior iowa and continental margin nevada to evaluate whether the continental interior record is 1 miniaturized i e thinner but equally complete 2 comparable in thickness and quality where the sedimentary record is preserved but certain portions of the record are notably absent i e omitted or truncated or 3 so invariably preserved that equivalent stratigraphic packages cannot be recognized compared to the continental margin record this study finds that fourth to fifth order cycles in iowa are on average approximately half as thick and half as numerous compared to the continental margin of nevada moreover the stratigraphic record on the continental margin of nevada is dominated by cycles that are composed of tidal flat and shallow subtidal lithofacies capped by simple flooding surfaces and exhibit catch up or keep up depositional styles the continental interior record in iowa is dominated by cycles that are composed of subtidal lithofacies capped by a range of bounding surfaces and exhibit catch down or give up depositional styles these findings suggest that the thin record in iowa is largely a result of low sedimentation rates associated with suppressed carbonate production in this epeiric sea setting rather than minimal subsidence rates and an increased potential for subaerial exposure and associated loss of record

fluctuations in epeiric sea carbonate production during silurian positive carbon isotope excursions a review of proposed paleoceanographic models positive excursions in the carbon isotopic ratio of marine carbonates 13ccarb are commonly attributed to an increase in the burial ratio of organic versus carbonate carbon in the global oceans regardless of whether this increased deposition of organic carbon was oceanographically or biologically induced the fact that high carbon isotope values are most often attributed to the sequestration and burial of organic carbon remains the notion that high 13ccarb values should be the result of organic rich deposition in epeiric sea settings is not surprising considering that the overwhelming majority of organic carbon burial in the modern oceans occurs in continental shelf and margin settings what is surprising is that major positive carbon isotope excursions during the silurian are recorded in clean carbonate successions with little to no appreciable black shale deposition in epeiric seas in fact silurian 13ccarb excursions occurred during intervals of prolific reef development and an overall expansion of carbonate platform environments globally this discrepancy has sparked considerable debate among silurian carbon isotope specialists but has offered a valuable opportunity to re examine the intricate connections among nutrients primary productivity carbonate sedimentology and the global carbon cycle in the lower paleozoic here we consider several sedimentological and geochemical features of one of these silurian positive carbon isotope 13ccarb excursions and discuss the broader implications of current silurian 13ccarb models to the interpretation of lower paleozoic carbonate sequences

history of carbonate ion concentration over the last 100 million years abstract instead of having been more or less constant as once assumed it is now apparent that the major ion chemistry of the oceans has varied substantially over time for instance independent lines of evidence suggest that calcium concentration ca2 has approximately halved and magnesium concentration mg2 approximately doubled over the last 100 million years on the other hand the calcite compensation depth and hence the caco3 saturation has varied little over the last 100 my as documented in deep sea sediments we combine these pieces of evidence to develop a proxy for seawater carbonate ion concentration co32 over this period of time from the calcite saturation state which is proportional to the product of ca2 times co32 but also affected by mg2 we can calculate seawater co32 our results show that co32 has nearly quadrupled since the cretaceous furthermore by combining our co32 proxy with other carbonate system proxies we provide calculations of the entire seawater carbonate system and atmospheric co2 based on this reconstructed atmospheric co2 is relatively low in the miocene but high in the eocene finally we make a strong case that seawater ph has increased over the last 100 my

modeled estimates of global reef habitat and carbonate production since the last glacial maximum estimated changes in reef area and caco3 production since the last glacial maximum lgm are presented for the first time based on a model reefhab which uses measured environmental data to predict global distribution of reef habitat suitable reef habitat is defined by temperature salinity nutrients and the depth attenuated level of photosynthetically available radiation par caco3 production is calculated as a function of par when minimum par levels were chosen to restrict reef growth to 30 m depth and less modern reef area totaled 584 746 10 km global carbonate production which takes into account topographic relief as a control on carbonate accumulation was 1 00 gt yr 1 these values are close to the most widely accepted estimates of reef area and carbonate production and demonstrate that basic environmental data can be used to define reef habitat and calcification to simulate reef habitat changes since the lgm the model was run at 1 kyr intervals using appropriate sea level and temperature values these runs show that at the lgm reef area was restricted to 20 of that today and carbonate production to 27 due primarily to a reduction in available space at the lower sea level and secondarily to lower sea surface temperatures nonetheless these values suggest that reef growth prior to shelf flooding was more extensive than previously thought a crude estimate of reef released co2 to the atmosphere since the lgm is of the same order of magnitude as the atmospheric co2 change recorded in the vostok ice core which emphasizes the role of neritic carbonates within the global carbon cycle this model currently addresses only the major physical and chemical controls on reef carbonate production but it provides a template for estimating shallow tropical carbonate production both in the present and in the past as such the model highlights several long standing issues regarding reef carbonates particularly in terms of better defining the roles of light temperature aragonite saturation state and topography on reef calcification

the sedimentology stratigraphy and preservation of intertidal deposits in the minas basin system bay of fundy abstract intertidal sediments of the minas basin a macrotidal estuary at the head of the bay of fundy can be subdivided into six major facies tidal marsh beach mudflat sandflat channel lag and sandbar each is characterized by its grain size distributions sedimentary structures and biological communities these sedimentary facies occur in three types of high to low tide zonation depending on the local sediment source and wave and current energy the holocene stratigraphy presently preserved in the upper intertidal zone of minas basin consists of a relatively thin on the average less than 1 2 m wedge of sediment overlying bedrock only in a few sheltered locations where deposits accumulate to several meters is the marine transgressive stratigraphy well represented the hypothetical progradational or marine regressive stratigraphy of upper intertidal sediments would probably resemble from top to bottom the high to low tide sequence of facies occurring today on sheltered tidal flats lebensspuren would provide the most reliable representation of the ecology of intertidal sediments in minas basin they are useful in delineating communities as well as being sensitive indicators of sediment deposition microfauna are too easily transported or reworked field data from relict intertidal deposits dated 2300 3400 yr b p indicate calcareous organism hard parts would probably provide a biased fossilized record indirect evidence is discussed which suggest in situ dissolution of shells in certain intertidal sediments

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

biological and physical forcing of carbonate chemistry in an upwelling filament off northwest africa results from a lagrangian study the mauritanian upwelling system is one of the most biologically productive regions of the world s oceans coastal upwelling transfers nutrients to the sun lit surface ocean thereby stimulating phytoplankton growth upwelling of deep waters also supplies dissolved inorganic carbon dic high levels of which lead to low calcium carbonate saturation states in surface waters with potentially adverse effects on marine calcifiers in this study an upwelled filament off the coast of northwest africa was followed using drifting buoys and sulphur hexafluoride to determine how the carbonate chemistry changed over time as a result of biological physical and chemical processes the initial phtot in the mixed layer of the upwelled plume was 7 94 and the saturation states of calcite and aragonite were 3 4 and 2 2 respectively as the plume moved offshore over a period of 9 days biological uptake of dic 37 mol kg 1 reduced pco2 concentrations from 540 to 410 atm thereby increasing phtot to 8 05 and calcite and aragonite saturation states to 4 0 and 2 7 respectively the increase 25 mol kg 1 in total alkalinity over the 9 day study period can be accounted for solely by the combined effects of nitrate uptake and processes that alter salinity i e evaporation and mixing with other water masses we found no evidence of significant alkalinity accumulation as a result of exudation of organic bases by primary producers the ongoing expansion of oxygen minimum zones through global warming will likely further reduce the caco3 saturation of upwelled waters amplifying any adverse consequences of ocean acidification on the ecosystem of the mauritanian upwelling system

discontinuities in carbonate successions identification interpretation and classification of some italian examples abstract the growing use of unconformities as bounding surfaces for new types of stratigraphic units seems not to be matched by a corresponding effort on process oriented researches on unconformities themselves this paper aims at giving a contribution to classification and understanding of discontinuities in carbonate successions from the outcrop perspective based on some italian examples a number of integrated criteria geometry sedimentology diagenesis biostratigraphy is proposed to recognise stratigraphic breaks old terms are discussed and sometimes redefined while some new terms are introduced the term discontinuity surface ds is proposed as a general one to indicate any stratigraphic interface where an interruption of sedimentation can be proved a ds can be characterized as a firm ground or a rock ground depending on its coherence at the moment of the renewal of sedimentation polygenic and simple omission surfaces are separated within firm grounds if a recognizable gap is either present or not a third kind of firm ground revealed only by biostratigraphy has been called hidden discontinuity surface two categories of rock grounds are also distinguished hard grounds and inherited rock grounds if respectively generation of the ds and or deposition of the overlying sediments took place in the same environment of the underlying sediments or not a genetic interpretation for each type of discontinuity is proposed the largest variety of ds s occurs in pelagic sediments some discontinuities hard grounds and simple omission surfaces are attributed to increased bottom current activity during sea level falls others polygenic omission surfaces and hidden ds s are interpreted as submarine slide scars either with or without the overprint due to exposure on the seafloor the ds s separating different facies e g platform and pelagic ones are interpreted to be due to tectonics the relevance of the recognized ds s to sequence stratigraphy is briefly discussed

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

history of seawater carbonate chemistry atmospheric co 2 and ocean acidification humans are continuing to add vast amounts of carbon dioxide co2 to the atmosphere through fossil fuel burning and other activities a large fraction of the co2 is taken up by the oceans in a process that lowers ocean ph and carbonate mineral saturation state this effect has potentially serious consequences for marine life which are however difficult to predict one approach to address the issue is to study the geologic record which may provide clues about what the future holds for ocean chemistry and marine organisms this article reviews basic controls on ocean carbonate chemistry on different timescales and examines past ocean chemistry changes and ocean acidification events during various geologic eras the results allow evaluation of the current anthropogenic perturbation in the context of earth s history it appears that the ocean acidification event that humans are expected to cause is unprecedented in the geologic past for which sufficiently well preserved records are available

heterozoan carbonates when where and why a synthesis on parameters controlling carbonate production and occurrences abstract in modern and phanerozoic times heterozoan carbonates group a large array of depositional environments from the poles to the tropics this global assessment reviews the critical parameters and controlling factors of heterozoan carbonates i stratigraphic and global distributional trends ii oceanographic and trophic relationships and iii biological and sedimentary processes well documented case studies n 129 have been investigated when facies and stratigraphic attributes were available and when environmental settings such as oceanography climate and paleogeography were clearly identified these case studies occur during specific periods of time in the sedimentary record e g late ordovician early carboniferous early permian and neogene while they are absent during others e g triassic and jurassic periods during greenhouse to icehouse transitions and those with active thermohaline circulation are particularly conducive for heterozoan carbonates based on global oceanographic patterns and existing ecological and hydrodynamic regime classifications hallock 2001 pedley and carannante 2006 james and jones 2015 a process based classification scheme is proposed that distinguishes two main heterozoan carbonate systems i a highly productive system characterized by suspension feeding biota and ii an oligo mesotrophic warm temperate system characterized by red algal and seagrass derived biota eight depositional models are proposed that combine i the source of energy for metabolic activities that allow the carbonate producing biota to thrive and ii hydrodynamics and physiography of the depositional system that control the sediment accumulation the local and platform scale based profiles can be used to complement the facies approach of james and jones 2015

a simple model for the caco3 saturation state of the ocean the strangelove the neritan and the cretan ocean 1 a simple model of the caco3 saturation state of the ocean is presented it can be solved analytically and is intended to identify the fundamental controls on ocean carbonate ion concentration it should also attract researchers unfamiliar with complex biogeochemical models despite its limitations the model calculated caco3 saturation state of today s ocean agrees well with observations in general the model reveals three distinctly different modes of operation the strangelove ocean of high supersaturation which is dominated by inorganic caco3 precipitation 2 the neritan ocean of indefinite saturation dominated by biogenic shallow water caco3 precipitation and 3 the cretan ocean of low saturation dominated by biogenic pelagic caco3 precipitation in the latter mode the deep ocean co32 is remarkably stable provided that the biogenic production of caco3 exceeds the riverine flux of ca2 and co32 this explains the overall constancy of the saturation state of the ocean documented over the last 100 ma the model is then used to address diverse questions one important result is that the recovery of the oceanic carbonate chemistry from fossil fuel neutralization in the future will be accelerated due to expected reduced biogenic calcification

a middle eocene carbon cycle conundrum a 500 000 year long period of warmth in the middle eocene was marked by high atmospheric carbon dioxide concentrations and prolonged dissolution of carbonate in the deep oceans numerical simulations attempting to capture these features identify gaps in our understanding of the causes of this and similar perturbations

coals associated with tidal sediments in the wilcox group paleogene south texas abstract the several coal seams in 50 m of wilcox strata on the chacon creek east lignite property in south texas are closely associated with tidal sediments the coal bearing sequence is underlain by greenish bioturbated sandstone deposited in open marine water the sediments between the coals and cutting the coals consist of coarsening and fining upward sequences of interbedded sandstone and mudstone with lenticular wavy and flaser bedding and ripple laminated and cross bedded sandstone the sediments contain marine dinoflagellates and palynomorphs of an inland flora most of the sediment accumulated in tidal channels each coal is underlain by rooted strata usually an underclay palynomorphs in the lignite suggest the peat accumulated in low lying swamps dominated by tupelo trees these swamps lay along the landward margin of a tidal channel complex the channel complex probably extended 10 to 30 km inland from the main coastline repeated regressive and transgressive episodes with corresponding expansion and contraction of the peat swamps within the estuarine complex would explain the coal bearing sequence at chacon creek east

calcium and calcium isotope changes during carbon cycle perturbations at the end permian negative carbon and calcium isotope excursions as well as climate shifts took place during the most severe mass extinction event in earth s history the end permian 252 ma investigating the connection between carbon and calcium cycles during transient carbon cycle perturbation events such as the end permian may help resolve the intricacies between the coupled calcium carbon cycles as well as provide a tool for constraining the causes of mass extinction here we identify the deficiencies of a simplified calcium model employed in several previous studies and we demonstrate the importance of a fully coupled carbon cycle model when investigating the dynamics of carbon and calcium cycling simulations with a modified version of the long term ocean atmosphere sediment carbon cycle reservoir model which includes a fully coupled carbon calcium cycle indicate that increased weathering rates and ocean acidification potentially caused by siberian trap volcanism are not capable of producing trends observed in the record as previously claimed our model results suggest that combined effects of carbon input via siberian trap volcanism 12 000 pg c the cessation of biological carbon export and variable calcium isotope fractionation due to a change in the seawater carbonate ion concentration represents a more plausible scenario this scenario successfully reconciles 13c and 44ca trends observed in the sediment record as well as the proposed warming of 6 c

holocene sediments of wistari reef towards a global quantification of coral reef related neritic sedimentation in the holocene wistari reef within the southern great barrier reef is a shallow coral reef platform featuring a very clearly defined leeward accretionary wedge of carbonate sediments the total global area of shallowly submerged coral reef has been quantified as 255 000 km 2 the question then becomes what additional area of sediment of significant thickness is associated with the measured shallow reef areas t at wistari reef the leeward sedimentary wedge has an area and a thickness that are roughly equal to the holocene sediments that have accumulated on the platform several important observations can be made from these data firstly the area of significant neritic carbonate sedimentation 1 m ka associated with coral reefs is near 500000 km 2 secondly the production rate of neritic carbonates at wistari reef is almost 50 less than the accumulation rate needed to obtain the volume of holocene reef sediments observed this implies that both production and accumulation neritic carbonate must have been more than a factor of two higher in the early to mid holocene c 2001 elsevier science b v all rights reserved

implications for neoarchaean ocean chemistry from primary carbonate mineralogy of the campbellrand malmani platform south africa the precipitation of calcite and aragonite as encrustations directly on the seafloor was an important platform building process during deposition of the 2560 2520 ma campbellrand malmani carbonate platform south africa aragonite fans and fibrous coatings are common in unrestricted shallow subtidal to intertidal facies they are also present in restricted facies but are absent from deep subtidal facies decimetre thick fibrous calcite encrustations are present to abundant in all depositional environments except the deepest slope and basinal facies the proportion of the rock composed of carbonate that precipitated as encrustations or in primary voids ranges from 0 to 65 depending on the facies subtidal facies commonly contain 20 35 in situ precipitated carbonate demonstrating that neoarchaean sea water was supersaturated with respect to aragonite carbonate crystal growth rates were rapid compared with sediment influx rates and the dynamics of carbonate precipitation were different from those in younger carbonate platforms the abundance of aragonite pseudomorphs suggests that sea water ph was neutral to alkaline whereas the paucity of micrite suggests the presence of inhibitors to calcite and aragonite nucleation in the mixed zone of the oceans

marine carbonate factories a global model of carbonate platform distribution platform carbonates are a major component of the earth system but their spatial distribution through geological times is difficult to reconstruct due to the incompleteness of geological records sampling heterogeneity and their intrinsic complexity beyond this complexity carbonates are not randomly distributed in the world oceans neither in the modern nor in the past and thus global trends exist in the present review we focus on the understanding of the spatial distribution of carbonate production at a global scale we use a deterministic approach which focuses on discriminating components stratigraphic architectures and environmental features to relate shallow water carbonate production to oceanographic parameters the work is based on extensive literature reviews on carbonate platforms ecological niche modelling coupled with deep time general circulation models is used to calibrate a predictive tool of carbonate factory distribution a carbonate factory function is set up that is based on sea surface oceanographic parameters temperature salinity and primary productivity the model was tested using remote sensing and in situ oceanographic data of modern times while outputs of paleoceanographic models are utilized for lower aptian cretaceous modelling the approach allows determining four neritic carbonate factories that are called the marine biochemical photozoan photo c and heterozoan factories the model finely simulates the global distribution of lower aptian and modern carbonate platforms carbonate factories appear to thrive for specific ranges along the environmental gradient of carbonate saturation this conceptual scheme appears to be able to provide a simple universal model of paleoclimatic zones of shallow water marine carbonates

major perturbation of ocean chemistry and a strangelove ocean after the end permian mass extinction the severe mass extinction of marine and terrestrial organisms at the end of the permian period c 251 ma was accompanied by a rapid 1 ma decrease in sedimentary burial of organic carbon in the early triassic

regional sedimentology and petroleum geology of marine late bathonian valanginian sandstone in the north sea abstract a large number of marine late bathonian valanginian sandstone units have been identified in the north sea north of the mid north sea high this paper discusses their complex areal distribution and outlines sedimentological models the sandstone formations are interpreted as shallow marine transgressive and regressive units interbedded with beach lagoonal and coastal plain deposits coarse grained scarp fed fans occur along fault controlled rift margins the total proven recoverable reserves in these sandstone reservoirs are 2 3 x 10 9 ton oil equivalent of which approximately one third is oil the play types are intimately linked with the mesozoic rift system of the viking witch ground and central grabens along this rift system the sand units provide good trapping potential and they are generally interbedded with or lie immediately below the kimmeridgian ryazanian source rocks so that migration paths are relatively simple and migration efficiency is high

sequence stratigraphic hierarchy of the upper devonian foreknobs formation central appalachian basin usa evidence for transitional greenhouse to icehouse conditions abstract the foreknobs formation upper devonian upper frasnian to basal famennian comprises the uppermost marine strata of the progradational catskill clastic wedge of the south central appalachian mountains virginia west virginia usa the foreknobs formation consists of 14 lithofacies arranged in four facies associations which record the following depositional settings 1 storm dominated distal to proximal offshore to shoreface facies association a 2 sharp based conglomeratic shoreface facies association b 3 fluvial redbed facies association c and 4 incised valley fill ivf facies association d vertical juxtaposition and stacking patterns of lithofacies and facies associations permit recognition of a hierarchy of three scales of cyclicity up to 70 short term 5th order cycles each averaging 65 kyr consist of coarsening upward parasequences of storm dominated offshore marine facies in the distal setting which correspond to high frequency unconformity bound sequences hfs of fluvial redbed strata overlain by offshore marine strata in the proximal setting these facies relationships are a consequence of 10 15 m of sea level fluctuations up to 12 intermediate term 4th order cycles each averaging 375 kyr consist of stacked 5th order cycles the 4th order cycles are bounded by regressive surfaces of marine erosion rsme at the base of sharp based conglomeratic shoreface sandstones in the distal setting that correspond with paleosols in the proximal setting in some cases the 5th order cycles within each 4th order cycle exhibit stacking patterns indicative of increasing or decreasing accommodation space these facies relationships are a consequence of 25 35 m of sea level fluctuations three complete and portions of two additional 3rd order cycles each averaging 1 12 myr consist of stacked 4th order cycles the 3rd order sea level trends reflected in the foreknobs formation are nearly identical to published eustatic sea level curves incised valley fills are present at one of the 3rd order cycle boundaries and are a consequence of a 35 45 m sea level fluctuation the amplitudes of the inferred sea level fluctuations are comparable to the expansion and contraction of ice volumes within the current greenland and antarctic ice sheets which suggests glacioeustasy was the primary control on sea level fluctuations and cyclicity within the foreknobs formation such an interpretation is consistent with knowledge of devonian climate transitioning from middle devonian greenhouse to late devonian icehouse as indicated by evidence of glaciation during parts of the late devonian in south america and the appalachians

generic types of stratigraphic cycles controlled by eustasy thought experiments imply that stratigraphic cycles controlled directly by eustasy include keep up catch up catch down foreshortened or truncated and give up variants different patterns of thick ness and facies being governed by the interplay of sedimentation rate and accommodation space most examples of these types are in addition base cutout cycles wherever lowstands of sea level dropped below the top of the underlying cycle overall thicknesses of multiple cycles at any locale are controlled ultimately by net subsidence rate accordingly even keep up and catch up cycles can faithfully record full accommodation only where tectonic subsidence during cycle formation paced eustatic fluctuation paradoxically however only condensed cycles that fortuitously compensate for syncycle tectonic subsidence can accurately record the eustatic amplitude as adjusted for water loading

a geoclim simulation of climatic and biogeochemical consequences of pangea breakup large fluctuations in continental configuration occur throughout the mesozoic while it has long been recognized that paleogeography may potentially influence atmospheric co2 via the continental silicate weathering feedback no numerical simulations have been done because of the lack of a spatially resolved climate carbon model geoclim a coupled numerical model of the climate and global biogeochemical cycles is used to investigate the consequences of the pangea breakup the climate module of the geoclim model is the foam atmospheric general circulation model allowing the calculation of the consumption of atmospheric co2 through continental silicate weathering with a spatial resolution of 7 5 long 4 5 lat seven time slices have been simulated we show that the breakup of the pangea supercontinent triggers an increase in continental runoff resulting in enhanced atmospheric co2 consumption through silicate weathering as a result atmospheric co2 falls from values above 3000 ppmv during the triassic down to rather low levels during the cretaceous around 400 ppmv resulting in a decrease in global mean annual continental temperatures from about 20 c to 10 c silicate weathering feedback and paleogeography both act to force the earth system toward a dry and hot world reaching its optimum over the last 260 myr during the middle late triassic in the super continent case given the persistent aridity the model generates high co2 values to produce very warm continental temperatures conversely in the fragmented case the runoff becomes the most important contributor to the silicate weathering rate hence producing a co2 drawdown and a fall in continental temperatures finally another unexpected outcome is the pronounced fluctuation in carbonate accumulation simulated by the model in response to the pangea breakup these fluctuations are driven by changes in continental carbonate weathering flux accounting for the fluctuations in area available for carbonate platforms the simulated ratio of carbonate deposition between neritic and deep sea environments is in better agreement with available data