3d stratigraphic forward modelling for analysis and prediction of carbonate platform stratigraphies in exploration and production abstract stratigraphic forward modelling sfm has been used to answer important questions in stratigraphic analysis this has been demonstrated through generic modelling of synthetic data and numerous two dimensional 2d real data case studies but the method has rarely been used to further our understanding of specific real three dimensional 3d carbonate data sets by quantitative comparison this paper applies carbonate 3d a sfm program to a hydrocarbon reservoir and outcropping carbonate platforms at both exploration and production scales we show the value of sfm in the exploration and production of hydrocarbons through predicting facies distributions and stratigraphic geometries between wells and by analysing and answering fundamental questions about the formation of specific carbonate strata first the model is tested using the 3d outcrops of a miocene attached carbonate platform at nijar se spain where 78 of mapped facies are matched in the simulations second sfm of an 80 000 km 2 jurassic ramp in ne spain exploration scale predicts new facies in areas without data leads to an improved understanding of ramp evolution modification of the interpreted sea level curve and re interpretation of the main sediment transport direction application to the isolated platform reservoir judy creek devonian canada exemplifies the advantages of applying sfm at reservoir scale the simulations yield information on platform geometries and facies distributions an improved understanding of the factors that control platform evolution and propose a revised sea level history wider applications of sfm in exploration include assessment of the possibilities and probabilities of facies distributions and evaluation and ranking of different interpretations of platform evolution at the reservoir scale facies probability distributions and layer geometries derived from sfm can serve as input into static reservoir models to guide geostatistical simulations

enhanced riverine carbon flux from carbonate catchment to the ocean a comparative hydrogeochemical study on ishigaki and iriomote islands southwestern japan 1 riverine carbon transportation is an important carbon flux connecting reservoirs of the atmosphere continents and oceans the flux is strongly related to the important roles of rivers such as regulation of climate change and buffering of ocean acidification here to evaluate the linkage of such functions of rivers and geological characteristics of the watersheds we present the results of a comparative hydrogeochemical study conducted on small subtropical watersheds of aluminosilicate dominated iriomote island and carbonate based ishigaki island southwestern japan rivers on ishigaki island exhibited much higher alkalinity than rivers on iriomote island which was even higher than the mean value of major rivers in the world such as the saint lawrence and the mississippi this high alkalinity was the result of carbonate dissolution enhanced by soil originated co2 as a result of this high inorganic carbon input the ratio of inorganic carbon and nutrients of the river water was higher than that of marine organic matter such as the redfield ratio making the coastal seas a potential source of co2 for the atmosphere

the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

late pleistocene and holocene vegetation history of the bale mountains ethiopia abstract a sediment core recovered from garba guracha a glacial lake at 3950 m altitude in the bale mountains of ethiopia at the boundary of the ericaceous and afroalpine vegetation belts provides a 16 700 year pollen record of vegetation response to climatic change the earliest vegetation recorded was sparse and composed mainly of grasses amaranthaceae chenopodiaceae and artemisia indicating an arid climate at 13 400 cal bp amaranthaceae chenopodiaceae pollen declined sharply and cyperaceae increased suggesting a change to moister conditions the younger dryas interval is represented by a small increase in artemisia and reduced cyperaceae indicating aridity just after the start of the holocene 11 200 cal bp the upper altitudinal limit of the ericaceous belt rose and woody ericaceous vegetation extended across the sanetti plateau in response to increased moisture and temperature the marked change from clastic to organic lake sedimentation at this time reflects the increase in woody vegetation cover in the lake catchment accompanied by soil stabilisation and increased leaf litter and soil humus content from about 6000 cal bp and especially after 4500 cal bp mid altitude dry afromontane juniper podocarpus forests developed on the northern slopes of the mountains in response to reduced rainfall in a shortened wet season erica shrub and forest decreased in area and altitude and the afroalpine ecosystem expanded on the plateau podocarpus declined from about 2000 cal bp as juniperus increased to its present dominance at 2500 3300 m altitude human impact on the high altitude afroalpine and ericaceous vegetation has been relatively minor confirming that the endemic biodiversity of the ethiopian mountains is a legacy of natural holocene vegetation change following repeated expansion and contraction of the upland ecosystems during the quaternary

the foreslope and toe of slope facies of the middle triassic latemar buildup dolomites northern italy abstract the latemar buildup was a circular carbonate buildup 4 km wide with a central platform core flat bedded interior platform and massive reef margin flanked on all sides by slope facies steeply dipping 30 35 foreslope breccias are present adjacent to the margin and flat lying graded grainstones at the toe of slope slope facies relate directly to depositional profile and slope angle the steeply dipping foreslopes consist of lobate breccia beds that are 25 m thick and a few tens of meters across and extend tens to hundreds of meters downslope some beds are conformably overlain by thinner 1 m thick beds of finer grained carbonate sediment the basal surfaces of the breccias are erosional and are anastamosing in both strike and dip views the breccia rains was derived principally from margin boundstones and deposited by rockfalls and avalanches planar clinoforms extend the entire height of the foreslope hundreds of meters and bracket depositional units clinothems tens of meters thick clinoforms appear to be shear surfaces formed during large slope failures avalanches graded grainstone beds less than 1 m thick are present at the nearly flat lying toe of slope these consist of redeposited shallow water platform interior and reef margin carbonate sands some with nodular limestone caps that are interpreted as proximal carbonate turbidites toe of slope breccias are the downdip extensions of foreslope breccias and pinch out abruptly basinward some slope depositional processes are related to high frequency fourth order and fifth order sea level changes toe of slope graded grainstones correspond to times of platform submergence in contrast foreslope breccia was deposited during both platform submergence and exposure the slope deposits do not record the high frequency cyclic rhythms identified in shallow water platform sections this is attributed to the nature of slope deposition downslope talus transport was episodic and localized graded grainstone beds reflect storm redeposition

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

cyclicities in triassic platform carbonates synchronizing radio isotopic and orbital clocks sedimentary cycles recorded in young sediments are often attributed to fluctuations of the earth s climate on a 10 4 10 6 year scale which in turn is governed by periodic variations in solar insolation linked to orbital milankovitch parameters a spectacular example of cyclic stratal patterns in ancient deposits is the middle triassic latemar carbonate platform w dolomites n italy based on spectral analyses from previous studies a superimposition of precession 20 ka and eccentricity 100 ka controlled sea level fluctuations has been suggested to account for the stacking hierarchy at latemar with 20 ka being assigned to each highest order depositional cycle zircon u pb isotopic ages from volcanic ash layers within the cyclic succession corroborated by biostratigraphic constraints suggest that the average time interval for every individual cycle is significantly smaller than the shortest milankovitch period and therefore challenge previously published interpretations relating distinct spectral peaks to the above mentioned hierarchy however our new spectral data indicate that cyclicities resembling milankovitch characteristics might exist but on an entirely different scale our findings show that frequency spectra should only be interpreted in combination with robust age control they also encourage the search for complementary mechanisms controlling carbonate deposition

the latemar a flat topped steep fronted platform dominated by microbialites and synsedimentary cements abstract facies analyses on the latemar isolated carbonate platform suggest a higher proportion of microbial carbonates compared to literature this is evident especially in the margin upper slope zone where microbial boundstone associated with tubiphytes calcareous sponges botryoidal aragonite and radiaxial fibrous cements extended down to 250 m water depth the latemar flat topped high relief platform has been subdivided into five different facies belts inner and outermost platform margin upper and lower slope each facies belt represents subtidal environments except for the inner platform which is characterized by a peritidal facies association point counting analysis was carried out on ca 90 thin sections to quantify the different platform components microbialite and cements are most abundant they represent respectively ca 40 and ca 34 of the whole platform volume these results suggest that carbonate production at latemar occurred in a m factory microbial carbonates as well as early marine cements are most abundant on the upper slope margin and outermost platform although microbialites are found in all facies belts the presence of supratidal sedimentary facies restricted only to the inner platform and of a completely subtidal outermost platform suggests a new depositional profile for the latemar the central portion is occupied by the flat platform interior cyclically subaerially exposed facies of the subtidal outermost platform surround the inner platform and display a progressive increase in depth toward the margin the margin is submerged and essentially constituted by microbial and cement boundstone the slope is characterized by steep clinoforms 35 dominated by in situ microbialites in the upper middle portion 0 250 m depth evidently precipitated by non light dependent microbially influenced processes the lower slope is mostly detrital poor in platform top derived sediments and dominated by margin and upper slope derived rudstone and grainstone all these observations are in agreement with the slope shedding model observed in the pennsylvanian microbial margin in asturias n spain and allow the interpretation of the latemar as a flat topped steep fronted platform dominated by microbialites and cement boundstones

large scale progradation demise and rebirth of a high relief carbonate platform triassic lombardy southern alps italy abstract the upper anisian to early carnian succession of the middle val brembana pegherolo massif central southern alps of italy records a complete depositional cycle from platform inception to growth demise and rebirth the depositional architecture of this system reflects different evolutionary stages an inception stage which postdates a previous drowning of an anisian carbonate platform with progradation of the carbonate platform from the nucleation areas an aggradational stage with increasing water depth in the basins a progradational stage where steep slopes composed of margin derived breccias develop and a final crisis corresponding to the subaerial exposure of the platform top followed by the deposition of shales in the basin before the rebirth of a different type of carbonate factory the record of this evolution reflects the effects of the change in accommodation space interplay of subsidence and eustacy which controls the type and storage sites of the sediments produced by the carbonate factory the effects of the changes in accommodation space are recorded in the shallow water platform as well as in the intraplatform basins where the sediments delivered at different rates from the platform top are stored as a consequence the aggradational stage corresponds to reduced sedimentation in the basins i e sediments are stored on the platform top whereas during progradation resedimented limestones are more common in the basin subaerial exposure rapidly halted the carbonate production on the platform top while a major input of shales probably reflecting a climate change and or lowering of the base level is recorded in the basin where shales onlap the slope of the previous carbonate system the rebirth of the carbonate factory after subaerial exposure of the platform top is characterized by a different composition of the carbonate factory probably reflecting changes of the environmental conditions the step by step recording of the evolution of the carbonate system represents a unique opportunity to record a seismic scale complete evolutionary cycle of a carbonate system in its different sub environments from the platform top to the basin

evinosponges in the triassic esino limestone southern alps documentation of early lithification and late diagenetic overprint a carbonate buildup of middle triassic age the esino limestone outcrops in the southern calcareous alps of lombardy n italy along its margin and within the open subtidal facies the esino limestone contains calcite cement filled cavities of cm to m size these features known as evinosponges may form pervasive networks within the host rock the filling consists of concentric isopachous layers of fibrous low mg calcite crystals characterized by strong undulose extinction and bent cleavages the cement crusts are non luminescent under cathodoluminescence but both cements and host rock are cross cut by microfractures filled with bright luminescent calcite related to late void filling sparite mixing of different carbonates is reflected in stable isotope data on the hand specimen scale the oxygen and carbon isotope compositions of cements and host rock show little variation when compared on a regional scale the values cover a broad range from 6l80 pdb 5 to 12 and from 613c pdb o to 3 the linear covariant trends defined by the oxygen and carbon isotope data for different sampling regions reflect the admixture of late isotopically depleted calcite with an isotopically enriched non luminescent calcite of early diagenetic origin the esino limestone fibrous cements which were probably precipitated in the marine or marinemeteoric phreatic environment were affected by late diagenetic processes that caused mineral deformation and isotopic depletion through recrystallization and the admixture of a later calcite these later calcites precipitated from penetrative fluids possibly related to late triassic volcanic activity and or to the late cretaceous early palaeogene alpine orogeny

quantitative compositional analysis of a triassic carbonate platform southern alps italy abstract we have estimated abundance and distribution of automicrite marine cements and skeletal grains in the triassic sella massif an isolated platform flanked by steep 25 35 clinoforms 108 samples were taken at constant intervals from measured sections of the major zones of the platform edifice the platform top margin upper slope and lower slope in a first step carried out in the field and on hand specimen purely detrital deposits were separated from automicrite facies i e beds with automicrite cement filled primary vugs and admixtures of skeletal carbonate and lithoclasts in the second step samples with automicrite facies were thin sectioned and point counted the categories used for point counting were a automicrite b vugs and cement c microspar or neomorphic spar d skeletal grains and e internal sediments at the platform top 46 of samples are pure detrital deposits 27 consist of automicrite facies and 27 are too strongly altered by dolomitization to allow classification at the margin upper slope 68 of samples consist of automicrite facies 22 are pure detrital sediments and 10 are strongly altered at the lower slope 63 are detrital deposits 10 automicrite facies and 27 are extensively dolomitized the most important contributors to the automicrite facies are automicrite 41 on the platform top 29 on the margin upper slope 28 on the lower slope and early marine cement 35 on the platform top 48 on the margin upper slope 27 on the lower slope the amount of skeletal grains is less than 10 the automicrite facies stabilized the platform margin and upper slope automicrite abundant early marine cements and micro organisms such as tubiphytes formed a rigid framework thus substituting for the lack of a metazoan reef on the upper slopes the framework of automicrite facies stabilized the slope but intermittently the automicrite layers are frequently dissected by sediment filled fractures or are broken into clasts we assume that they slid on the layers of loose detritus bigger slides turned into rubbly debris flows that formed metre thick breccias at the lower slope and the proximal basin floor the planar shape and steep angle of the clinoforms indicate that the large scale geometry of the slope was not controlled by the automicrite but rather by non cohesive layers of sand and rubble piled up to the angle of repose the production mode of the sella is comparable of that of a mud mound factory this factory was highly productive in 1 ma the platform aggraded over 300 m and prograded over 2000 m in all directions

depositional facies and stratal geometry of an upper carboniferous prograding and aggrading high relief carbonate platform cantabrian mountains n spain seismic scale continuous exposures of an upper carboniferous bashkirian moscovian carbonate platform n spain provide detailed information about the lithofacies and stratal geometries quantified with differential global positioning system measurements of microbial boundstone dominated steep prograding and aggrading platform margins progradational and aggradational platform to slope transects are characterized by distinct lithological features and stratal patterns that can be applied to the understanding of geometrically comparable high relief depositional systems the bashkirian is characterized by rapid progradation at rates of 415 970 m my 1 characteristic outerplatform facies are high energy grainstones with coated intraclasts ooids and pisoids moderate energy algal skeletal grainstones to packstones and lower energy algal packstone and boundstone units the moscovian aggradational phase is characterized by aggradation rates of 108 m my 1 coated grain shoals are less common whereas crinoidal bars nucleated in well circulated settings below wave base boundstones form a belt 30 300 m wide at the platform break and interfinger inwards with massive algal skeletal wackestones mud rich banks the progradational phase has divergent outer platform strata with basinward dips of 12 to 2 steep clinoforms with dips of 20 28 are 650 750 m in relief and possibly sigmoidal to concave in the lower part the basinward dipping outer platform strata might be depositional for less than 6 consistent with lithofacies deepening seaward the basinward dip is attributed to the downward shift of upperslope boundstone forced by late highstand and relative sea level fall and to compaction induced differential subsidence during progradation the aggradational phase is characterized by horizontally layered platform strata clinoforms steepen to 30 45 reaching heights of 850 m and are planar to concave the evolution from progradation to aggradation at the bashkirian moscovian boundary is attributed to increased foreland basin subsidence and decreased boundstone accumulation rates progradation was primarily controlled by boundstone growth rather than by highstand shedding from the platform top within the major phases aggradational progradational increments are produced by third to fourth order relative sea level

enhanced cenozoic chemical weathering and the subduction of pelagic carbonate the observed trend of increasing oceanic 87sr 86sr ratios during the late cenozoic led raymo et al 1 to propose that chemical weathering rates increased at this time as a result of enhanced weatherability of silicate rocks they suggested that this was due in turn to continential uplift primarily in the himalayas and the andes because weathering involves the reaction of silicates with atmospheric carbon dioxide considerations of changes in weathering rates must take into account the need to balance the global carbon cycle to maintain this balance on timescales greater than 106yr enhanced weathering requires an increased flux of co2 into the atmosphere2 without such an increased flux weathering rates could not increase and one is then forced to search for other explanations for the observed 87sr 86sr trend such as a changing riverine strontium isotope composition3 6 here i assume that the strontium isotope record does indeed reflect enhanced weathering in the late cenozoic but propose that its cause may have been an increased co2 flux arising from the recycling of pelagic sedimentary carbon at subduction zones since the jurassic sedimentary carbonate accumulation has shifted from primarily cratonic to primarily pelagic environments7 11 because sea floor spreading transports pelagic carbonate to and recycles it through metamorphic environments in subduction zones this shift to pelagic carbonate accumulation would provide the increased co2 flux needed to increase weathering rates12 13

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

quantifying rates of syndepositional marine cementation in deeper platform environments new insight into a fundamental process abstract syndepositional marine cementation on carbonate platforms is a fundamental process that results in physical stabilization and lithification of sediments as well as reduction in primary porosity and permeability which may affect the migration of later diagenetic fluids rapid submarine cementation is commonly invoked to explain various aspects of carbonate platform geometry especially related to the preservation of steep slopes but the rates typically reported for cementation in deeper parts of the platform are mostly conjectural in an attempt to quantify the rates of syndepositional cementation in marginal platform environments substrates containing samples of carbonate sand ooids suspended above the sea floor were emplaced at various depths across a modern platform in the bahamas to evaluate the rates of cement growth through direct observation initial results indicate that cementation may lead to partial lithification of carbonate sands within a minimum of 8 months in water depths of up to 60 m these results provide some of the first direct evidence for rates at which cementation can occur in deeper marginal environments and confirms earlier hypotheses that very rapid syndepositional marine cementation may not be limited to very shallow subtidal and intertidal environments

steep microbial boundstone dominated plaform margins abstract seaward progradation of several kilometers has been documented mostly for leeward margin low angle carbonate slope systems with a dominant platform top sediment source however steep and high relief margins fronting deep basins can also prograde and as such are somewhat perplexing characteristics of two prograding carboniferous examples provide a model which may apply elsewhere 1 outcrops in asturias northern spain serve as important analogs for 2 hydrocarbon reservoirs in steep sided isolated platforms of the north caspian basin kazakhstan such as tengiz seismic and well data from tengiz corroborate outcrop patterns for slope development showing progradation of up to 5 and more than 10 km respectively despite the high relief up to 600 m and steep 20 35 nature of these margins the two examples share a highly productive microbial boundstone factory extending from the platform break down the slope to nearly 300 m or more depth and a lower slope dominated by mega breccias and grain flow deposits derived from the margin and slope itself the broad depth range of microbial boundstone increases the potential for production during both lowstands and high stands of sea level and thereby facilitates progradation independent from platform top derived sediment rapid in situ lithification of the boundstone provides stability to the steep slopes but also leads to readjustment through shearing and avalanching what controls the microbial cement boundstone formation remains a debate but its presence is a key factor controlling the progradational geometry of these and possibly other margins this new model of slope shedding has implications for slope readjustment processes and resulting architecture sequence stratigraphic interpretation reservoir characterization and reservoir modeling especially the isotropic character of microbial boundstone will reduce the potential for coherent seismic reflections to develop and possibly invoke under certain stress regimes shattering and fracturing thereby generating significant non matrix permeability key considerations are the contrasts with the bahamian high stand shedding depositional model slope progradation rates that range from 450 to 1500 m my and net growth rates of in situ boundstone of 1000 m my comparable to or higher than accretion rates for metazoan skeletal reef growth

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

evidence for stable sr isotope fractionation by silicate weathering in a small sedimentary watershed in southwestern taiwan abstract radiogenic sr isotopes 87 sr 86 sr are robust for provenance identification in hydrology affected mainly by the age of background lithologies and the degree of chemical weathering however there is limited knowledge concerning the fractionation mechanism of stable sr isotopes 88 sr 86 sr in rivers in this study river water was collected on a weekly to monthly basis throughout dry and wet seasons furthermore to study the variations of radiogenic and stable sr isotopes during intense weathering a major flooding event 2000 mm precipitation in three days typhoon morakot water was captured within a small drainage catchment system 161 km 2 along the hou ku river in southwestern taiwan for a better constraint on the end member compositions bedload sediments suspended particles and several host rocks were sampled for a systematic investigation the carbonate and silicate phases of these solids were chemically separated dissolved major elements indicate that the watersheds were predominated by silicate weathering stable sr isotopes show no significant variation 88 sr 0 24 0 31 temporally and spatially with an average of 0 28 additionally all solids showed lower 88 sr values than the river water while the host rocks had higher 88 sr values 88 sr 0 20 0 26 than the residual weathering products 88 sr 0 08 0 22 indicating preferential leaching of heavy sr into the hydrosphere and leaving light sr in the residual solids results of laboratory acid leaching experiments reveal that dissolution of high 88 sr value minerals occurred at an early stage of weathering the variation of weathering intensity does not alter stable sr isotopes in silicate weathering dominated river water which contains higher stable sr isotopes than the associated sediments the silicatic sedimentary rocks preferentially released higher stable sr isotopes into the hydrosphere during chemical weathering thus leaving lower stable sr isotopes in the residual solids

equatorial convergence of india and early cenozoic climate trends india s northward flight and collision with asia was a major driver of global tectonics in the cenozoic and we argue of atmospheric co2 concentration pco2 and thus global climate subduction of tethyan oceanic crust with a carpet of carbonate rich pelagic sediments deposited during transit beneath the high productivity equatorial belt resulted in a component flux of co2 delivery to the atmosphere capable to maintain high pco2 levels and warm climate conditions until the decarbonation factory shut down with the collision of greater india with asia at the early eocene climatic optimum at 50 ma at about this time the india continent and the highly weatherable deccan traps drifted into the equatorial humid belt where uptake of co2 by efficient silicate weathering further perturbed the delicate equilibrium between co2 input to and removal from the atmosphere toward progressively lower pco2 levels thus marking the onset of a cooling trend over the middle and late eocene that some suggest triggered the rapid expansion of antarctic ice sheets at around the eocene oligocene boundary

onset and ending of the late palaeozoic ice age triggered by tectonically paced rock weathering the onset of the late palaeozoic ice age about 340 million years ago has been attributed to a decrease in atmospheric co2 concentrations associated with expansion of land plants as plants both enhance silicate rock weathering which consumes co2 and increase the storage of organic carbon on land however plant expansion and carbon uptake substantially predate glaciation here we use climate and carbon cycle simulations to investigate the potential effects of the uplift of the equatorial hercynian mountains and the assembly of pangaea on the late palaeozoic carbon cycle in our simulations mountain uplift during the late carboniferous caused an increase in physical weathering that removed the thick soil cover that had inhibited silicate weathering the resulting increase in chemical weathering was sufficient to cause atmospheric co2 concentrations to fall below the levels required to initiate glaciation during the permian the lowering of the mountains led to a re establishment of thick soils whilst the assembly of pangaea promoted arid conditions in continental interiors that were unfavourable for silicate weathering these changes allowed co2 concentrations to rise to levels sufficient to terminate the glacial event based on our simulations we suggest that tectonically influenced carbon cycle changes during the late palaeozoic were sufficient to initiate and terminate the late palaeozoic ice age the late palaeozoic was characterized by glacial cycles numerical simulations suggest that increased silicate weathering due to mountain uplift and soil removal caused atmospheric co2 to fall below the threshold for glaciation

growth mode of middle triassic carbonate platforms in the western dolomites southern alps italy abstract the correlation of carbonate platform and slope sediments with biostratigraphically and radiometrically dated basinal successions in the western dolomites allows the reconstruction of the growth of a middle triassic carbonate platform schlern rosengarten over a time interval of approximately five ammonoid zones reitzi secedensis curionii gredleri archelaus zones the whole platform evolution had a total duration of

forward modelling of carbonate platforms sedimentological and diagenetic constraints from an application to a flat topped greenhouse platform triassic southern alps italy abstract quantitative analysis of depositional systems using numerical models can provide insights into the interaction of sedimentological and diagenetic processes difficult to interpret from observation of the geological products alone numerical models can highlight the interactions between controlling parameters and generate best estimate simulations of case studies from the geological record different data sources e g outcrop data uniformitarian constraints paleogeography need to be considered in the process of defining the parameters required to produce models that honour individual case studies we present a best estimate forward model of a high relief triassic carbonate platform southern alps italy generated using carb3d a 3d process based forward modelling package able to simulate sedimentary facies geometries and early diagenesis of isolated carbonate platforms the parameters used for the presented forward model have been deduced by the study of architectural sedimentological and diagenetic features of the platform and by data from modern and ancient analogues sensitivity analysis is used to tune values of the parameters within ranges defined from field laboratory and uniformitarian constraints critical evaluation of the model allowed 1 verification of the validity of the used parameters 2 evaluation of the interaction between controlling parameters 3 development of a numerical model that can be used for quantitative elaborations furthermore the process of generating the numerical model required a detailed interpretation of field and laboratory data crucial to define the required input parameters modelling the studied carbonate platform also enabled evaluation of the effects of the interaction between productivity environmental energy and creation of accommodation space promoting the understanding of their role on the architecture of carbonate systems forward modelling also allows the integration of data from conventional data sets with data from present day observations and seismic geometries promoting a transition from a qualitative to a semi quantitative quantitative sedimentological approach forward models can further be used to parameterise petrophysical properties of complex geobodies with potential application for the management of georesources

glacial interglacial variation in catchment weathering and erosion paces the indian summer monsoon during the pleistocene abstract silicate weathering via co2 consumption is considered to regulate the long term climate change discriminating silicate versus carbonate weathering from sedimentary records is helpful to understand the coupling relationship between weathering and past climate however owing to the paucity of well dated and continuous records of weathering and erosion the relationship between silicate and carbonate weathering and their links with mountain uplift and glacial interglacial climate remain elusive geochemical analysis of a 666 m core from the heqing basin a paleolake situated at the southeastern margin of the tibetan plateau demonstrates silicate versus carbonate weathering and erosion changes under indian summer monsoon ism conditions spanning the entire pleistocene via respective tracing between rb sr and al na ratios the rb sr record is interpreted as reflecting a competition between clayey silicate origin rb versus carbonate origin sr fluxes whereas al na ratio is a balance between weathering and erosion of silicate minerals both pacing the glacial interglacial cycles of the ism during interglacials strong silicate weathering intensity reflected by low al na values is mainly controlled by warmer temperatures with the reduced variability during 1 82 0 92 ma recalling the pacing of the arabian sea surface temperature amplitudes within glacials the weak carbonate leaching and clay erosion within the older and younger intervals are interrupted by strong clay erosion within the middle interval in conclusion the heqing rb sr and al na records reveal the sensitivity of catchment weathering and erosion to ism changes over glacial interglacial timescales with warmer temperature enhancing silicate weathering and clay formation during interglacials and greater physical erosion during glacials

association of tepees and palaeokarst in the ladinian calcare rosso southern alps italy the ladinian calcare rosso of the southern alps provides a rare opportunity to examine the temporal relationships between tepees and palaeokarst this unit comprises peritidal strata pervasively deformed into tepees repeatedly capped by palaeokarst surfaces mantled by terra rossa palaeokarsts characterized by a regional distribution across the southern alps occur at the base and at the top of the unit local palaeokarsts confined to this part of the platform occur within the calcare rosso and strongly affected depositional facies tepee deformation ranges from simple antiformal structures peritidal tepees to composite breccias floating in synsedimentary cements and internal sediments senile tepees peritidal tepees commonly occur at the top of one peritidal cycle in association with subaerial exposure at the cycle top while senile tepees affect several peritidal cycles and are always capped by a palaeokarst surface cements and internal sediments form up to 80 of the total rock volume of senile tepees the paragenesis of senile tepees is extremely complex and records several superimposed episodes of dissolution cement precipitation fibrous cements laminated crusts mega rays and deposition of internal sediments marine sediment and terra rossa petrographical observations and stable isotope geochemistry indicate that cements associated with senile tepees precipitated in a coastal karstic environment under frequently changing conditions ranging from marine to meteoric and were altered soon after precipitation in the presence of either meteoric or mixed marine meteoric waters stable isotope data for the cements and the host rock show the influence of meteoric water average 18o 5 8 while strontium isotopes average 87sr 86sr 0 707891 indicate that cements were precipitated and altered in the presence of marine triassic waters field relationships sedimentological associations and paragenetic sequences document that formation of senile tepees was coeval with karsting senile tepees formed in a karst dominated environment in the presence of extensive meteoric water circulation in contrast to previous interpretations that tepees formed in arid environments under the influence of vadose diagenesis tepees initiated in a peritidal setting when subaerial exposure led to the formation of sheet cracks and up buckling of strata this porosity acted as a later conduit for either meteoric or mixed marine meteoric fluids when a karst system developed in association with prolonged subaerial exposure relative sea level variations inducing changes in the water table played a key role in exposing the peritidal cycles to marine mixed marine meteoric and meteoric diagenetic environments leading to the formation of senile tepees the formation and preservation in the stratigraphic record of vertically stacked senile tepees implies that they formed during an overall period of transgression punctuated by different orders of sea level variations which allowed formation and later freezing of the cave infills

scaling of sedimentation rates and drowning of reefs and carbonate platforms the rule that sedimentation rates decrease as the time interval increases has been examined by a procedure that avoids the mathematical problem of plotting a variable time against its inverse the test confirms that the scaling trend has real physical meaning in the time range of 10 1 108 yr sedimentation rates change roughly proportionally to the inverse of the square root of time this report proposes and evaluates the hypothesis that the growth potential of reefs and carbonate platforms follows the same scaling trend the trend implies that a growth of 104 m yr sustained over 103 yr an upper limit of reef growth in the holocene translates into 102 m yr sustained over 107 yr decrease of the growth potential with increasing time solves the paradox of drowned platforms if the decrease results largely from environmental factors and not simply from increase of the time fraction of subaerial exposure

geochemistry of meteoric diagenesis in carbonate islands of the northern bahamas 2 geochemical modelling and budgeting of diagenesis geochemical characterization and numerical modelling of surface water and ground water combined with hydrological observations provide quantitative estimates of meteoric diagenesis in pleistocene carbonates of the northern bahamas meteoric waters equilibrate with aragonite but water rather than mineral controlled reactions dominate dissolutional lowering of the undifferentiated bedrock surface is an order of magnitude slower than that within soil filled topographic hollows generating small scale relief at a rate of 65 140 mm ka 1 and a distinctive pocketed topography oxidation of organic matter within the subsoil and vadose zones generates an average pco2 of 4 0 10 3 atm which drives dissolution during vadose percolation and or at the water table however these dissolution processes together account for 60 of the average rock derived calcium in groundwaters pumped from the freshwater lens the additional calcium may derive from oxidation of organic carbon within the lens accounting for the high pco2 of the lens waters mixing between meteoric waters of differing chemistry is diagenetically insignificant but evapotranspiration from the shallow water table is an important drive for subsurface cementation porosity generation in the shallow vadose zone averages 1 6 3 2 ka 1 phreatic meteoric diagenesis is focused near the water table where dissolution generates porosity at 1 4 2 8 ka 1 maximum dissolution rates however are similar to those of evaporation driven precipitation which occludes porosity of 4 0 s 0 6 ka 1 this drives porosity inversion from primary interparticle to secondary mouldic vug and channel porosity in the deeper freshwater lens oxidation of residual organic carbon and reoxidation of reduced sulphur species from deeper anaerobic oxidation of organic carbon may generate porosity up to 0 06 ka 1 meteoric diagenesis relies critically on hydrological routing and vadose thickness controlled by sea level as well as the geochemical processes active a thin vadose zone permits direct evaporation from the water table and drives precipitation of meteoric phreatic cements even where mineral stabilization is complete copyright 2007 john wiley sons ltd

prolonged carbonate diagenesis under an evolving late cenozoic climate nullarbor plain southern australia abstract the nullarbor plain in southern australia the largest areal karst on the globe is a 240 000 km2 uplifted succession of cenozoic marine carbonates whose surface has been exposed for 14 to 15 m y the middle miocene nullarbor limestone forms the upper surface of the plain and hosts a complex and prolonged record of meteoric diagenesis such a complete record offers unique insights into the effects of climate tectonics sea level topography and hydrology on the style and placement of numerous diagenetic events in flat low lying carbonate plains alteration took place during three broad phases comprising eight stages that are interpreted to have formed against a background of dramatic climate change middle miocene phase one diagenesis took place under a humid climate and resulted in rapid mineral equilibration calcite cementation extensive karst development and finally widespread lacustrine and palustrine sedimentation resultant palustrine sediments especially terrestrial ooids are now preserved at the surface and in underlying karst cavities latest middle miocene to middle pliocene phase two diagenesis occurred during a prolonged period 8 m y of temperate climate and resulted in initial deep cave dissolution during low sea levels and later shallow cave development in the course of a high sea level onset of a somewhat more arid climate in the latest pliocene led to the development of the modern desolate landscape of the plain this final phase of diagenesis involved creation of solution pits filled with black limestone pebbles open and closed dolines with associated colluvium fill and pervasive pedogenic calcrete the nullarbor plain demonstrates that low lying carbonate plains can have low surficial erosion rates precisely record relative sea level positions be able to have extensive caves with extended periods of arrested calcite precipitation and finally host extensive terrestrial ooid deposits the importance of this comprehensive paragenetic record is its applicability to not only recognize unconformities in the rock record but to better appreciate the climate in which they formed

controls on syndepositional fracture patterns devonian reef complexes canning basin western australia abstract syndepositional fractures are an important feature of high relief carbonate systems and exert a profound control on many facets of platform evolution and reservoir development based on data collected from the canning basin s devonian reef complexes this study characterizes syndepositional fracture patterns as a function of variations in lithofacies depositional position stratigraphic architecture and mechanical stratigraphy fracture parameters such as extension and fracture intensity are documented to vary strongly as a function of lithofacies the highest syndepositional extension values occurring in the microbial facies of the famennian platform margin with extension values three times higher than observed in equivalent frasnian strata position along the depositional profile exerts a strong control on fracture patterns with an approximate two fold increase in syndepositional extension and fracture intensity typically observed from the platform interior to the platform margin syndepositional fracture intensity is shown to vary systematically with changes in platform margin trajectory with high fracture intensities observed in strongly progradational platforms and decreased fracture development in aggradational and retrogradational platforms evidence for the temporal evolution of the mechanical stratigraphy of the devonian reef complexes is presented with early lithified strata effectively behaving as a single large scale 50 150 m mechanical unit during syndepositional fracture development while secondary fractures become increasingly affected by bed scale 0 25 5 m mechanical heterogeneity introduced by progressive diagenesis the results presented here potentially provide a tool for predicting fracture characteristics e g intensity orientation location and vertical extent from limited subsurface data and provide a method for characterizing syndepositional deformation in other systems

coupled two dimensional diagenetic and sedimentological modeling of carbonate platform evolution we have used a new coupled two dimensional diagenetic and sedimentological model to investigate the evolution of a simple aggrading carbonate platform subject to glacio eustatic sea level fluctuations the model employs variable hydrological zones internally defined from platform exposure and climate to provide a framework within which diagenetic processes are simulated at specified rates simulations show a clear stacked sequence of diagenetic zones which are readily recognizable because of their lateral continuity and distinct trends in diagenetic evolution from platform interior to margin however spatial associations between unconformity surfaces and underlying diagenetic zones that suggest causality are misleading the interaction between high amplitude sea level fluctuations and subsidence results in substantial overprinting and a complex diagenetic history that could not be unraveled by traditional stratigraphic and sedimentological methods

highstand versus lowstand deposition on carbonate platform margins insight from quaternary foreslopes in the bahamas abstract examples of both highstand and lowstand deposition have been identified on the upper platform slopes of the tongue of the ocean bahamas highstand deposits consist of a thick wedge of fine grained skeletal and non skeletal sands and carbonate muds derived predominantly from the platform and deposited on slopes of 25 28 these sediments were deposited subsequent to platform flooding and may be more than 30 m thick along open leeward margins in contrast lowstand deposits consists of coarse skeletal sands gravels and boulders deposited on primary depositional slopes of 35 45 these sediments were derived from fringing reefs along the marginal escarpment and deposited during the initial rise of sea level following the last lowstand these variations in depositional character result in a distinctive signature of highstand versus lowstand deposition for steep sided platforms and further elucidate the response of carbonate platforms to high magnitude 5th order scale 20 000 yrs fluctuations in sea level

production and cycling of calcium carbonate in a shelf edge reef system st croix u s virgin islands applications to the nature of reef systems in the fossil record abstract geologic reefs are the end products of not only constructive processes that produce calcium carbonate but also of destructive processes e g bioerosion and wave action that reduce solid substrate to sediment and of physical processes that rework the reef fabric and transport sediment a study was conducted at cane bay on the island of st croix u s virgin islands to quantify the suite of processes that have influenced holocene reef development data on carbonate production reef accretion bioerosion and sediment transport were used to construct a detailed carbonate budget and to apply the findings of this study to the character of reefs observed in the fossil record total carbonate production on the reef ranged from 0 to 5 78 kg m2 per year with a reef wide average of 1 21 kg m2 per year 1 13 by corals 0 02 by coralline algae 0 06 by primarily molluscs forams and echinoderms based on 7 cores only 0 91 kg m2 per year of this have been retained within the reef interior the remaining 0 24 kg m2 per year of sediment along with the 0 06 kg m2 per year contributed directly by molluscs etc are deposited within reef channels and are probably flushed from the reef by major storms of the material recovered in the cores 58 was either loose sediment and rubble or open void space much of the recognizable coral material was demonstrably reworked and out of place accretion rates across the shelf generally increased with water depth as a result of active slumping along the steepening reef face over the past 2 000 3 000 years the importance of detrital material in the reef fabric and the major role played by secondary processes that constantly rework the substrate have resulted in a reef whose interior is more of a garbage pile than an in place assemblage of corals cemented together into a rigid framework the physical similarities between the detrital fabric of the reef at cane bay and those found in many ancient deposits imply that the general processes operating along the cane bay shelf have persisted during much of the evolution of ancient reefs it is proposed that our modern models overemphasize the importance of in place framework as a criterion for an ecologic reef

lithofacies character and architecture across a pennsylvanian inner platform transect sierra de cuera asturias spain abstract seismic scale outcrops of lower pennsylvanian steep margined carbonate platforms in northern spain sierra de cuera cantabrian mountains provide the opportunity to link depositional facies to platform interior architecture lithofacies character vertical stacking patterns and spatial distribution of depositional facies and shallowing upward cycles were investigated to provide a semiquantitative depositional model for inner platform strata a 70 m thick succession of eight shallowing upward cycles 2 5 15 m thick was studied across a 2 km wide transect cycles consist of algal bioherms and skeletal packstone lithofacies association b deposited in an open marine and sub wave base environment which are locally lateral to crinoid dominated packstone lithofacies association d lithofacies association b developed on a transgressive one meter thick high energy coated grain grainstone lithofacies association a and is overlain by open marine to restricted lagoonal deposits lithofacies association c indicative of decreased paleo water depth cycle boundaries are marine flooding surfaces occurring at the base of lithofacies a and the top of lithofacies c petrographic and outcrop evidence of subaerial exposure is conspicuously lacking cycle and lithofacies thickness varies laterally and all the lithofacies can be either continuous for the 2 km width of investigation or discontinuous terminating within tens to hundreds of meters in most of the cycles the lithofacies succession changes laterally because of lateral facies transitions between lithofacies b and d and pinching out of lithofacies a and c meter scale variations in depositional topography are related to the stacked lens shaped bioherms assigned to lithofacies b and appear to control the thickness and lateral continuity of the overlying facies sierra de cuera strata do not resemble other pennsylvanian cycles driven by high frequency high amplitude glacio eustasy which are commonly characterized by subaerial exposure surfaces developed on subtidal deposits except for the absence of peritidal facies and the presence of low relief algal bioherms on the platform top the necessary accommodation to enhance the growth of bioherms on the platform top was probably due to high frequency 100 240 ky moderate amplitude nearly 40 m sea level fluctuations combined with subsidence rates of 70 140 m my tectonic subsidence might have been responsible for the lack of evidence of subaerial exposure surfaces in the examined moscovian strata the studied inner platform lithofacies character and architecture were controlled by the interplay of high frequency changes in accommodation and the presence of meter scale depositional topography attributed to lateral variations of carbonate accumulation

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

close mass balance of long term carbon fluxes from ice core co 2 and ocean chemistry records on geological timescales carbon dioxide enters the atmosphere through volcanism and organic matter oxidation and is removed through mineral weathering and carbonate burial an analysis of ice core co2 records and marine carbonate chemistry indicates a tight coupling between these processes during the past 610 000 years which suggests that a weathering feedback driven by atmospheric co2 leads to a mass balance between co2 sources and sinks on long timescales feedbacks controlling long term fluxes in the carbon cycle and in particular atmospheric carbon dioxide are critical in stabilizing the earth s long term climate it has been hypothesized that atmospheric co2 concentrations over millions of years are controlled by a co2 driven weathering feedback that maintains a mass balance between the co2 input to the atmosphere from volcanism metamorphism and net organic matter oxidation and its removal by silicate rock weathering and subsequent carbonate mineral burial1 2 3 4 however this hypothesis is frequently challenged by alternative suggestions many involving continental uplift and either avoiding the need for a mass balance or invoking fortuitously balanced fluxes in the organic carbon cycle5 6 7 8 9 here we present observational evidence for a close mass balance of carbon cycle fluxes during the late pleistocene epoch using atmospheric co2 concentrations from ice cores10 11 12 we show that the mean long term trend of atmospheric co2 levels is no more than 22 p p m v over the past 610 000 years when these data are used in combination with indicators of ocean carbonate mineral saturation to force carbon cycle models the maximum imbalance between the supply and uptake of co2 is 1 2 during the late pleistocene this long term balance holds despite glacial interglacial variations on shorter timescales our results provide support for a weathering feedback driven by atmospheric co2 concentrations that maintains the observed fine mass balance

lithium isotopes in speleothems temperature controlled variation in silicate weathering during glacial cycles terrestrial chemical weathering of silicate minerals is a fundamental component of the global cycle of carbon and other elements past changes in temperature rainfall ice cover sea level and physical erosion are thought to affect weathering but the relative impact of these controls through time remains poorly constrained this problem could be addressed if the nature of past weathering could be constrained at individual sites in this study we investigate the use of speleothems as local recorders of the silicate weathering proxy li isotopes we analysed 7li and li in speleothems that formed during the past 200 ka in two well studied israeli caves soreq and tzavoa as well as in the overlying soils and rocks leaching and mass balance of these soils and rocks show that li is dominantly sourced from weathering of the overlying aeolian silicate soils speleothem 7li values are ubiquitously higher during glacials 23 than during interglacials 10 implying more congruent silicate weathering during interglacials where congruent means a high ratio of primary mineral dissolution to secondary mineral formation these records provide information on the processes controlling weathering in israel consideration of possible processes causing this change of weathering congruency indicates a primary role for temperature with higher temperatures causing more congruent weathering lower 7lispeleo the strong relationship observed between speleothem 7li and climate at these locations suggests that li isotopes may be a powerful tool with which to understand the local controls on weathering at other sites and could be used to assess the distribution of weathering changes accompanying climate change such as that of pleistocene glacial cycles

translating milankovitch climate forcing into eustatic fluctuations via thermal deep water expansion a conceptual link sedimentological evidence indicates metre scale cyclic changes in global sea level during mesozoic greenhouse climates the cyclicity is thought to be due to milankovitch forcing the absence of continental ice caps requires other mechanisms than glacier build up to explain these variations we propose that thermal expansion of the entire oceanic water column may partly explain the observed sea level variations on milankovitch timescales using existing climate model results we show that an increase in deep water temperature of 2 c and a corresponding sea level rise of 1 7 m by thermal expansion can be induced by milankovitch forcing via increased formation of warm deep waters in low latitudes

groundwater circulation and geochemistry of a karstified bank marginal fracture system south andros island bahamas abstract on the east coast of south andros island bahamas a major bank marginal fracture system characterised by vertically extensive cavern systems blue holes is developed sub parallel to the steep sided deep water re entrant of the tongue of the ocean in addition to providing a discharge route for meteoric mixed and geochemically evolved saline groundwaters a strong local circulation occurs along the fracture system this generates enhanced vertical mixing within voids of the fracture system evidenced by the increasing mixing zone thickness and the thinning and increasing salinity of brackish lens waters from north to south along the fracture system furthermore tidally driven pumping of groundwaters occurs between the fracture and adjacent carbonate aquifer affecting a zone up to 200 m either side of the fracture the resultant mixing of groundwaters of contrasting salinity and pco2 within and along the fracture system and with the surrounding aquifer waters together with bacterial oxidation of organic matter generates significant potential for locally enhanced diagenesis undersaturation with respect to calcite within the fresh or brackish salt water mixing zone is observed in the fracture system and predicted in the adjacent aquifer while mixing between the brackish fracture lens and surrounding high pco2 fresh waters causes dissolution of aragonite but not calcite the latter gives rise to considerable secondary porosity development because active tidal pumping ensures continued renewal of dissolutional potential this is evidenced by calcium and strontium enrichment in the brackish lens which indicates porosity generation by aragonite dissolution at a maximum rate of 0 35 ka 1 up to twice the average estimated for the fresh water lens in contrast saline groundwaters are depleted in calcium relative to open ocean waters suggesting the formation of calcite cements the development of a major laterally continuous cavernous fracture zone along the margin of the carbonate platform permits enhanced groundwater flow and mixing which may result in generation of a diagenetic halo at a scale larger than that generally recognised around syn sedimentary fractures in fossil carbonates this may be characterised by increased secondary porosity where a relative fall in sea level results in exposure and formation of a meteoric groundwater system or cementation by marine calcite both below this meteoric system and where the bank surface is flooded by seawater

accommodation and sedimentary architecture of isolated icehouse carbonate platforms insights from forward modeling with carb3d abstract a fundamental control on the evolution of carbonate platforms is accommodation the space available for sediment deposition here we adopt a sensitivity analysis approach using the process based forward model carb3d to quantitatively investigate the sedimentary response of isolated carbonate platforms to individual accommodation drivers of eustasy subsidence and surface dissolution sediment production the mechanism invoked to fill accommodation is also investigated fourth order milankovich driven sea level cycles dominate icehouse carbonate sedimentology with 400 ky cycles modulating the effect of 100 ky cycles of comparable magnitude when both cycles are present both overwhelm higher frequency lower amplitude fifth order cycles which are rarely preserved on the platform top subsidence is a fundamental control on sedimentary stacking patterns sequence boundary frequency sbf and platform geometry with rapid subsidence increasing the preservation of platform top sequences most icehouse platforms are subject to extended periods of platform top exposure missed beats when the platform top remains emergent at a sea level maximum are common and create non milankovich sbfs furthermore during platform emergence surface lowering via surface dissolution also creates accommodation for the subsequent platform flooding event with surface dissolution rates in humid climates comparable to moderate rates of subsidence however accommodation generation by surface dissolution is self limiting in as much as accommodation generated by dissolution is rapidly refilled on flooding sediment production is a key control on unfilled accommodation which our simulations suggest is considerable on icehouse platforms increased shallow water 3 m depth sediment production enhances intra platform bathymetric relief between the margin and interior this is driven in large part by a higher sedimentation rate at the margin than in the interior platforms can be flooded to depths up to 45 m during marine transgressions and accommodation often remains unfilled there are two distinct phases of platform top sedimentation during the transgression and early highstand platform margins accumulate at a greater rate than interior sediments generating differential intra platform bathymetry subsequently accommodation in the interior fills by forced regression and progradation from the margins into the platform interior numerical forward models can augment our understanding of icehouse carbonate platform evolution by identifying the nature of the sedimentary response to individual controls they can thus contribute to improving characterization of carbonate reservoirs in icehouse platforms such as the large hydrocarbon fields in the north caspian and s e asia

metamorphic decarbonation silicate weathering and the long term carbon cycle the seawater 87sr 86sr curve implies a 50 100 myr episodicity in weathering rate which requires a corresponding variation in co2 degassing from the solid earth to the atmosphere it is proposed that this is caused by orogenesis which both produces co2 as a result of metamorphic decarbonation reactions and consumes extra co2 as a consequence of erosion enhanced weathering global climate on the geological time scale is therefore conttolled by the difference between the relatively large and variable orogenic moderated degassing and weathering co2 fluxes

cenozoic carbon cycle imbalances and a variable weathering feedback abstract the long term stability of earth s climate and the recovery of the ocean atmosphere system after carbon cycle perturbations are often attributed to a stabilizing negative feedback between silicate weathering and climate however evidence for the operation of this feedback over million year timescales and in response to tectonic and long term climatic change remains scarce for example the past 50 million years of the cenozoic era are characterized by long term cooling and declining atmospheric co2 p co 2 during this interval constant or decreasing carbon fluxes from the solid earth to the atmosphere suggest that stable or decreasing weathering fluxes are needed to balance the carbon cycle in contrast marine isotopic proxies of weathering i e 87sr 86sr 7 li and 187os 188os are interpreted to reflect increasing weathering fluxes here we evaluate the existence of a negative feedback by reconstructing the imbalance in the carbon cycle during the cenozoic using the surface inventories of carbon and alkalinity only a sustained 0 25 0 5 increase in silicate weathering is necessary to explain the long term decline in p co 2 over the cenozoic we propose that the long term decrease in p co 2 is due to an increase in the strength of the silicate weathering feedback i e the constant of proportionality between the silicate weathering flux and climate rather than an increase in the weathering flux this increase in the feedback strength which mirrors the marine isotope proxies occurs as transient 1 million year timescales remains invariant to match the long term inputs of carbon over the cenozoic this results in stable long term weathering fluxes even as p co 2 decreases we attribute increasing feedback strength to a change in the type and reactivity of rock in the weathering zone which collectively has increased the reactivity of the surface of the earth increasing feedback strength through the cenozoic reconciles mass balance in the carbon cycle with the marine isotopic proxies of weathering and may explain why there are periods when the earth system is more sensitive to carbon cycle perturbations

growth of syndepositional faults in carbonate strata upper permian capitan platform new mexico usa abstract the upper permian capitan platform new mexico is cut by syndepositional faults and fractures these are parallel to platform margin and cluster within strata that steepen and thicken abruptly into the basin faults are steep dip slip have measurable displacements of up to 24 m are typically associated with growth strata and mostly tip out blindly within the platform basinward throwing faults are typically reverse and are steeper than shelfward throwing faults which have normal geometry the sense of displacement across some initially basinward throwing faults changed as they developed these patterns indicate that faults were rotated as they grew synkinematic rotation of faults is interpreted to have occurred due to syndepositional compaction driven down to basin tilting of the capitan platform faults grew through interaction with inherited fractures and by segment linkage vertically separated fault segments had a tendency to grow downward to link with underlying segments thus promoting accumulation of displacement across faults without vertical propagation of fault tips four fault types are distinguished on the basis of structures associated with their upper terminations i faults breaking free surface ii faults tipping out within non folded growth strata iii faults tipping out below growth monoclines and iv buried faults with no expression on free surface fault tips evolved from one type into another in response to variations in the rates of fault growth and deposition fault tip structures also vary laterally over distance of 750 1400 m inferably as a result of variable distances from fault centres

atmospheric co2 consumption by chemical weathering in north america abstract co 2 consumption by chemical weathering is an integral part of the boundless carbon cycle whose spatial patterns and controlling factors on continental scale are still not fully understood a dataset of 338 river catchments throughout north america was used to empirically identify predictors of bicarbonate fluxes by chemical weathering and interpret the underlying controlling factors detailed analysis of major ion ratios enables distinction of the contributions of silicate and carbonate weathering and thus quantifying co 2 consumption extrapolation of the identified empirical model equations to north america allows the analysis of the spatial patterns of the co 2 consumption by chemical weathering runoff lithology and land cover were identified as the major predictors of the riverine bicarbonate fluxes and the associated co 2 consumption other influence factors e g temperature could not be established in the models of the distinguished land cover classes artificial surfaces dominated by urban areas increase bicarbonate fluxes most followed by shrubs grasslands managed lands and forests the extrapolation results in an average specific bicarbonate flux of 0 3 mmol km 2 a 1 by chemical weathering in north america of which 64 originates from atmospheric co 2 and 36 from carbonate mineral dissolution chemical weathering in north america thus consumes 50 mt atmospheric co 2 c per year about half of that originates from 10 of the area of north america the estimated strength of individual predictors differs from previous studies this highlights the need for a globally representative set of regionally calibrated models of co 2 consumption by chemical weathering which apply very detailed spatial data to resolve the heterogeneity of earth surface processes

stable carbon cycle climate relationship during the late pleistocene a record of atmospheric carbon dioxide co2 concentrations measured on the epica european project for ice coring in antarctica dome concordia ice core extends the vostok co2 record back to 650 000 years before the present yr b p before 430 000 yr b p partial pressure of atmospheric co2 lies within the range of 260 and 180 parts per million by volume this range is almost 30 smaller than that of the last four glacial cycles however the apparent sensitivity between deuterium and co2 remains stable throughout the six glacial cycles suggesting that the relationship between co2 and antarctic climate remained rather constant over this interval

a genetic classification of carbonate platforms based on their basinal and tectonic settings in the cenozoic abstract this paper reassesses the usefulness of the morphological classification of carbonate platforms into rimmed shelves and ramps whilst the existing classifications have value in describing platform margin morphology at any one time the terms rimmed shelf and ramp are less successful at categorising the entire morphology and stratigraphy of carbonate platforms research on cenozoic carbonate platforms from a range of different tectono stratigraphic settings indicates that the basinal and tectonic setting of a platform can be used to erect a first order genetic classification of carbonate platforms the basinal and tectonic setting of carbonate platforms is shown to control their occurrence the overall 3 d platform morphology the large scale stratigraphic features and depositional sequences climate ocean chemistry and biological evolution control grain types facies and some elements of platform margins but not the larger scale features considered in this new classification from a review of well exposed outcropping and seismically imaged cenozoic platforms it is proposed that eight types of carbonate platform can currently be recognised and characterised based on their basinal and tectonic setting fault block salt diapir subsiding margin offshore bank volcanic pedestal thrust top delta top and foreland margin carbonate platforms these eight types are described using information from cenozoic platforms worldwide and the controls on their development are discussed many platform types e g subsiding margin offshore bank salt diapir thrust top and foreland margin are typical of particular classes of sedimentary basins others e g fault block volcanic pedestal and delta top are more widespread in their occurrence and occur in a range of basin types the value of this classification is that it is genetic rather than morphological the classification reflects the entire morphology and large scale stratigraphy of the platform and the controls on its development in addition the platform models can be used to understand the details of less well exposed or seismically imaged platforms so that they can be characterised and understood in terms of tectono sedimentary processes conversely the classification also provides valuable information on basin evolution as carbonate platforms house information on palaeoenvironments sea level change and are sensitive recorders of the tectonic environment

carbon export and hco3 fate in carbonate catchments a case study in the karst plateau of southwestern china abstract the consumption of co 2 due to carbonate weathering is thought to be an important terrestrial sink for atmospheric co 2 however the reaction and fate of weathering products may significantly affect the magnitude of the sink carbon mass balances were determined in hongfeng lake a small artificial lake located in the carbonate plateau of sw china this was accomplished by measuring the concentrations of dic dissolved inorganic c doc dissolved organic c poc particulate organic c and co 2 partial pressure in lake waters inflows and outflows and in surrounding spring waters results show that maximum dic mainly hco 3 derived from carbonate weathering by co 2 to doc ratios in the catchment export load reach 21 implying that as much as 80 of the exported primary production is in the form of hco 3 and therefore the co 2 consumed by carbonate weathering and subsequent dic export is a critical component of the c balance in this ecosystem this exported hco 3 subsidizes c cycling of aquatic ecosystems in the catchment and 32 excluding carbonate derived c returns to the atmosphere as co 2 evasion through the fluvial and lacustrine water air interface and 10 is stored in lake sediment this lake has a small co 2 emission rate 13 2 3 9 mmol m 2 d 1 or 0 097 mol m 2 a 1 relative to catchment area compared to mean values for many reservoirs found in temperate and tropical climatic zones this is likely due in part to low organic c loads supplied by the karst dominated catchment and low lake water doc concentrations the estimate indicates that more c 39 returns to the atmosphere and much less 13 is stored in sediments implying that the c sink of carbonate weathering may not be as significant as once thought

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

steady and non steady state carbonate silicate controls on atmospheric co2 two contrasting hypotheses have recently been proposed for the past long term relation between atmospheric co2 and the carbonate silicate geochemical cycle one approach berner 1990 suggests that co2 levels have varied in a manner that has maintained chemical weathering and carbonate sedimentation at a steady state with respect to tectonically controlled decarbonation reactions a second approach raymo et al 1988 applied specificlly to the late cenozoic suggests a decrease in co2 caused by an uplift induced increase in chemical weathering without regard to the rate of decarbonation according to the steady state first hypothesis increased weathering and carbonate sedimentation are generally associated with increasing atmospheric co2 whereas the uplift second hypothesis implies decreasing co2 under the same conditions an ocean atmosphere sediment model has been used to assess the response of atmospheric co2 and carbonate sedimentation to global perturbations in chemical weathering and decarbonation reactions although this assessment is theoretical and cannot yet be related to the geologic record the model simulations compare steady state and non steady state carbonate silicate cycle response the e fold response time of the co2 weathering feedback mechanism is between 300 and 400 ka the response of carbonate sedimentation is much more rapid these response times provide a measure of the strength of steady state assumptions and imply that certain systematic relations are sustained throughout steady state and non steady state scenarios for the carbonate silicate cycle the simulations suggest that feedbacks can maintain the system near a steady state but that non steady state effects may contribute to long term trends the steady state and uplift hypotheses are not necessarily incompatible over time scales of a few million years

glacial weathering sulfide oxidation and global carbon cycle feedbacks connections between glaciation chemical weathering and the global carbon cycle could steer the evolution of global climate over geologic time but even the directionality of feedbacks in this system remain to be resolved here we assemble a compilation of hydrochemical data from glacierized catchments use this data to evaluate the dominant chemical reactions associated with glacial weathering and explore the implications for long term geochemical cycles weathering yields from catchments in our compilation are higher than the global average which results in part from higher runoff in glaciated catchments our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals to evaluate the effects of glacial weathering on atmospheric pco 2 we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon dic generated by weathering reactions compared with nonglacial weathering glacial weathering is more likely to yield alkalinity dic ratios less than 1 suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of co 2 to the atmosphere back of the envelope calculations indicate that oxidative fluxes could change ocean atmosphere co 2 equilibrium by 25 ppm or more over 10 ky over longer timescales co 2 release could act as a negative feedback limiting progress of glaciation dependent on lithology and the concentration of atmospheric o 2 future work on glaciation weathering carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals

geochemistry of meteoric diagenesis in carbonate islands of the northern bahamas 1 evidence from field studies processes driving carbonate diagenesis in islands of the northern bahamas are investigated using major ion dissolved oxygen and dissolved organic carbon analyses of water samples from surface and ground waters and measurements of soil gas pco2 meteoric waters equilibrate with aragonite but reactions are water controlled rather than mineral controlled and drive dissolution rather than concurrent precipitation of calcite surface runoff waters equilibrate with atmospheric pco2 and rapidly recharge the vadose zone limiting subaerial bedrock dissolution to only 6 6 15 mg l 1 ca pco2 of soil gas measured in the summer wet season 7 4 s 3 7 10 3 atm is elevated compared with that of the atmosphere despite the thin skeletal organic nature of the soil and the discontinuous soil cover soil waters retained in surface pockets are equilibrated with respect to aragonite and have dissolved 51 s 19 mg l 1 ca this is substantially less than the 93 s 18 mg l 1 ca in samples from pumping boreholes that sample meteoric waters from the freshwater lens the high pco2 of the freshwater lens 16 s 8 3 10 3 atm for pumping boreholes suggests that significant additional co2 may be derived by oxidation of soil and surface derived organic carbon within the lens the suboxic nature of the majority of the freshwater lens and the observed depletion in sulphate support this suggestion and indicate that both aerobic and anaerobic oxidation may take place shallow lens samples from observation boreholes are calcite supersaturated and have a lower pco2 than deeper lens waters indicating that co2 degasses from the water table driving precipitation of calcite cements we suggest that the geochemical evolution of waters in the vadose zone and upper part of the freshwater lens may be determined by the presence of a body of ground air with pco2 controlled by production in the freshwater lens and soil and by degassing to the atmosphere copyright 2007 john wiley sons ltd

calciturbidite composition related to exposure and flooding of a carbonate platform triassic eastern alps the compositional variation of calciturbidites pedata potschen formation deposited adjacent to the dachstein formation carbonate platform in the triassic hallstatt basin was analysed using detailed field measurements and point counting of thin sections the 35 m long section is located in the northern calcareous alps of austria six point count groups were distinguished separating basinal from platform derived input summary statistics cluster and correspondence analysis of the point count data reveals a close relationship between the biota present on the dachstein carbonate platform and the calciturbidite composition the variations in turbidite composition are attributed to fluctuations in sea level and resulting flooding and exposure of the platform which alternately created and destroyed shallow water habitats on the platform top

triassic carbonate buildup flanks in the dolomites northern italy breccias boulder fabric and the importance of early diagenesis the flanks of middle triassic carbonate buildups in the dolomites show well developed clinostratification with typical angles of 30 40 this paper focuses on the metre scale fabric of these clinoforms and sets these within the context of their large scale and microscopic features clinoform stratification is caused by fibrous cement crusts by stylolites paralleling a vague stratification and by pelagic limestone interbedded with the lower portions of the clinoforms these parts of the clinoforms locally exhibit a boulder fabric a fracture system subvertical to clinostratification is filled by fibrous cements and marine internal sediment the analysis of clinoform fabric indicates that parts consist of in situ automicrite other parts of the clinoforms are made up of breccia the breccias occur as isolated pockets and lenses with random orientation and dimensions ranging from a few square decimetres to hundreds of square metres the breccias have gradual contacts with the unbrecciated host rock breccia components are mostly angular show a microfacies similar to that of the unbrecciated host rock and are composed of millimetre to decimetre sized particles that generally float in radiaxial fibrous cement matching grain boundaries are common calcite cement typically makes up 20 and 40 vol of the brecciated areas clinostratification the fracture system brecciation and boulder fabric point to gravity induced deformation of in situ flank deposits rather than gravity induced depositional processes brecciation appears to result from translational sliding millimetres to metres on the steep buildup flanks which caused fracturing of the vaguely stratified automicrite followed by displacive growth of fibrous cement cementation occurred in a shallow burial marine phreatic environment because cement clasts are virtually absent from the flank derived gravity flows in the adjoining basinal sediments displacive cement growth indicates a volume increase of the clinoforms during diagenesis of up to 20 40 vol and can account for the local drag of buildup interior limestones similarly the boulder fabric appears to be a diagenetic feature which resulted from differential settling of incompletely lithified boundstone and grainstone and the interbedded pelagic limestone

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

stable runoff and weathering fluxes into the oceans over quaternary climate cycles the effect of glacial interglacial cycles on surface weathering rates has been unclear a beryllium based proxy for weathering shows minimal variations in the input of silicate weathering products to the oceans for the past two million years

potential origins of 400 500 kyr periodicities in the ocean carbon cycle a box model approach 1 cenozoic proxy records of both the isotopic composition of dissolved inorganic carbon in the oceans 13cdic and deep ocean carbonate preservation show significant periodicities in the range 400 500 kyr sensitivity analysis of the ocean carbon cycle to potential variability on this timescale in patterns of global oceanic primary productivity and or continental weathering fluxes is performed using a 7 box ocean atmosphere model the data constraints imposed by plio pleistocene proxy records of 13cdic carbonate preservation and atmospheric pco2 variability allow different scenarios to be evaluated forcing with the global oceanic primary production ratio of inorganic and organic carbon leads to the relative phases of response most consistent with the proxy data however only when changes also occur in total marine primary production can the observed relative amplitudes of 13cdic and pco2 variability also be reproduced this scenario is consistent with oscillations between a highly productive coccolithophore rich global ocean and a less productive diatom rich one such oscillations have been proposed to originate from the orbital eccentricity cycle leading to changes in seasonality and thus silica utilization in the southern ocean however the period of response in model 13cdic is always close to that of the forcing function used and thus a significant discrepancy remains between the orbital eccentricity cycle period of 413 kyr and the observed 500 kyr 13cdic periodicity seen in the pleistocene

chemical weathering and associated co2 consumption in the mahanadi river basin india abstract chemical weathering of continents is one of the major geochemical processes which consumes atmospheric co2 and exerts a strong impact on the global climate the major ion chemistry of the mahanadi river basin one of the largest river basins in india is determined to investigate the sources of major ions and their spatio temporal variability chemical weathering rates and associated co2 consumption in the basin the results reveal that the ions in the basin are dominated by ca and hco3 the total dissolved solids 215 mg l 1 in monsoon and 270 mg l 1 in pre monsoon and total cation concentration 2367 eq in monsoon and 3214 eq in pre monsoon in the basin are relatively higher than the global average the dissolved loads in the basin are dominantly controlled by rock weathering particularly chemical weathering of silicates and carbonates the estimated chemical weathering rates based on the forward model are 44 94 t km 2 yr 1 in monsoon and 2 45 t km 2 yr 1 in pre monsoon with annual average chemical weathering rate of 23 7 t km 2 yr 1 the contribution of silicate weathering rates in the basin is 32 and 1 55 t km 2 y 1 during monsoon and pre monsoon period respectively the estimated co2 consumption rate associated with chemical weathering in the basin is 13 3 105 mol km 2 yr 1 during monsoon and 0 66 105 mol km 2 yr 1 during pre monsoon period with an average annual rate of 6 9 105 mol km 2 yr 1 which is higher than the global average the net rate of co2 consumption by silicate weathering is estimated to be approximately 4 78 105 mol km 2 yr 1 it is observed that the runoff and lithology are the major factors influencing chemical weathering in the basin however the basin elevation has a good negative correlation with chemical weathering rate

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

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

sub milankovitch and milankovitch forcing on a model mesozoic carbonate platform the latemar middle triassic italy basic shallowing upward cycles shu cycles and five bundled megacycles in the latemar platform have been widely regarded as a model example for precessional and eccentricity forcing in the mesozoic based on bio chronostratigraphic data recent studies questioned this particular type of milankovitch forcing on the latemar cyclic series we present an integrated model that incorporates i new cyclostratigraphic data ii new and existing bio chronostratigraphic data and iii new spectral analyses the basic shu cycles in the latemar reflect sub milankovitch control cycle bundles of 1 4 5 megacycles shu cycles indicate precessional forcing they do not reflect eccentricity superimposed on precessional forcing spectral analyses reveal highly significant ratios in the large scale cycle bundlings stacking patterns of 1 9 9 and 1 24 0 shu cycles represent obliquity and short eccentricity forcing both sub milankovitch and milankovitch forcing potentially controlled shallow subtidal carbonate deposition in mesozoic greenhouse times cyclostratigraphic models require an integrated approach including bio and chronostratigraphic data

sedimentation in shallow to deep water carbonate environments across a sequence boundary effects of a fall in sea level on the evolution of a carbonate system ladinian carnian eastern lombardy italy in the concarena pizzo camino massif lombardy basin southern alps italy the lateral transition from ladinian carnian carbonate platforms to coeval intraplatform basins is preserved the succession records the sedimentological evidence of a sea level fall on a flat topped platform with a narrow marginal reef rim and its effects in the adjacent deeper water basin repeated high frequency exposures of the platform top are recorded by a peritidal supratidal succession that overlies subtidal inner platform facies of the former highstand system tract hst on the slope and in the basin the sea level fall is recorded by a few metre thick succession of bioclastic packstones these facies directly lie on coarse clinostratified breccia bodies slope facies of the former hst or on resedimented well bedded dark laminated limestones basinal facies of the hst this facies distribution indicates that during the sea level fall carbonate production on the platform top decreased rapidly and that sedimentation in the basin was mainly represented by condensed facies microfacies record an enrichment during low stand in pelagic biota packstones with radiolarians and spiculae whereas the occurrence of platform derived shallow water materials is limited to thin lenses of reworked and micritized fe rich oolites and bioclasts mainly pelecypods and echinoderms the facies association in the concarena pizzo camino massif demonstrates that a highly productive carbonate factory was almost completely turned off during the emergence of the platform top at a sequence boundary leading to low stand starvation in the basin the reconstruction of the stratigraphic evolution of the concarena pizzo camino carbonate platform therefore represents a significant case history for the study of the behaviour of ancient carbonate systems during a fall in sea level independent of its origin eustatic or tectonic

limestone weathering in eastern australia part 2 surface micromorphology study results from long term microerosion meter mem studies indicate that microenvironments are characterized by different erosion rates a complementary study carried out on the same sites examines the microscale morphology in each environment optical and scanning electron microscopy were used to identify a range of features thought to reflect different processes under subaerial conditions micromorphology is dominated by biological weathering features owing to the presence of microflora sites permanently covered by soil or stream water have only dissolution etch features though stream sites may exhibit microfractures sites with periodic exposure exhibit both dissolution and biological etch features the natural environment is more accurately reflected by allowing some microflora colonization of mem sites rather than preventing colonization by artificial means

evidence for mass dependent isotopic fractionation of strontium in a glaciated granitic watershed abstract the stable isotope composition of strontium expressed as 88 86sr may provide important constraints on the global exogenic strontium cycle here we present 88 86sr values and 87sr 86sr ratios for granitoid rocks a 150 yr soil chronosequence formed from these rocks surface waters and plants in a small glaciated watershed in the central swiss alps incipient chemical weathering in this young system whether of inorganic or biological origin has no resolvable effect on the 87sr 86sr ratios and 88 86sr values of bulk soils which remain indistinguishable from bedrock in terms of sr isotopic composition although due in part to the chemical heterogeneity of the forefield the lack of a resolvable difference between soil and bedrock isotopic composition indicates that these soils have thus far witnessed minimal net loss of sr a low degree of chemical weathering is also implied by bulk soil chemistry the isotopic composition of sr in streamwater is more radiogenic than median soil reflecting the preferential weathering of biotite in the catchment streamwater 88 86sr values however are indistinguishable from bulk soil 88 86sr values implying that no resolvable fractionation of sr isotopes takes place during release to the weathering flux in the damma forefield analyses of plant tissue reveal that plants rhododendron and vaccinium preferentially assimilate the lighter isotopes of sr such that their 88 86sr values are significantly lower than those of the soils in which they grow additionally 88 86sr values of foliar and floral tissues are lower than those of roots contrary to observations for ca for which sr is often used as an analogue in weathering studies we suggest that processes that discriminate against sr in favour of ca due to the different nutritional requirement of plants for these two elements are responsible for the observed contrast

compaction and decompaction algorithms for sedimentary carbonates abstract the mechanical compaction behavior of shallow marine carbonate sediments has been investigated to develop carbonate compaction algorithms and decompaction curves that can be used in stratigraphic restoration backstripping analyses and quantitative models for simulation of carbonate stratigraphy deep water chalks and calcareous oozes are not treated here empirical porosity depth data for carbonate sediments have been compiled and compared with experimentally derived compaction curves to derive appropriate porosity depth curves for shallow water carbonate muds and sands the curves are exponential in form this review indicates that mud rich shallow marine carbonates behave differently than sand rich grain supported sediments with regard to reduction in porosity and thickness quantitative analysis of compaction behavior in carbonate sediments reveals that barring early cementation carbonate muds suffer significant thickness reduction early in their burial history and at shallow depths e g 50 thickness reduction with about 150 200 m overburden however primary porosities of carbonate muds approximately 70 80 are reduced only to about 42 under that overburden thus the potential exists for significant retention of primary porosity in carbonate muds in the form of microporosity this indicates that interparticle cementation with or without chemical compaction is required to transform muddy carbonate sediments into lithified rock in the absence of early lithification carbonate sands compact more slowly than muds primary interparticle porosities of about 40 45 can be maintained in the first 200 300 m of burial with little thickness reduction

controls on early diagenetic overprinting in icehouse carbonates insights from modeling hydrological zone residence times using carb3d abstract icehouse carbonate diagenesis is complex with carbonate sequences being exposed to multiple meteoric hydrozones vadose zone freshwater lens mixing zone on multiple occasions a forward modeling approach using carb3d has enabled quantitative exploration of the nature of this diagenetic overprinting by explicit simulation of meteoric hydrozone residence times during evolution of an isolated carbonate platform a sensitivity analysis was performed encompassing the fundamental controls on hydrozone residence time frequency and magnitude of sea level variation subsidence rate and climate the latter via its effect on freshwater lens thickness and rate of dissolutional lowering of the land surface residence time within all meteoric hydrozones is characterized by a high degree of lateral continuity vertical continuity is much more limited with significant variations on a fourth order sequence scale across the platform below sequence boundaries prolonged exposure to the vadose zone results from multiple missed beats when the platform remains exposed at relative sea level maxima overprinting gives total meteoric residence times significantly in excess of the duration of exposure of the overlying sequence boundary there is a hierarchy of eustatically driven overprint cycles with higher frequency cyclicity modifying the primary signal generated by lower frequency cycles fifth order cycles thus have only a minor impact on hydrozone residence times whilst third order seismic scale cycles are a critical control and could be used as a first order approximation of the amount of diagenetic overprinting subsidence has a strong control on residence time with greater overprinting at lower subsidence rates but in high subsidence regimes sediment packages move below the zone of meteoric water influence sufficiently rapidly that residence time can be minimal high land surface dissolution rates which result from a wetter climate remove a large proportion of the subaerially exposed sediment and reduce vadose zone residence time higher effective recharge can increase the thickness of freshwater lens and mixing zones which increases residence times significantly residence times in the vadose zone can be directly linked to a sequence stratigraphic framework but for the freshwater lens and the mixing zone this is possible only with a well constrained relative sea level history

mechanistic links between the sedimentary redox cycle and marine acid base chemistry the redox state of earth s surface is controlled on geological timescales by the flow of electrons through the sedimentary rock cycle mediated largely by the weathering and burial of c s fe phases these processes buffer atmospheric po at the same time co influxes and carbonate burial control seawater acid base chemistry and climate over long timescales via the carbonate silicate cycle however these two systems are mechanistically linked and impact each other via charge balance in the hydrosphere here we use a low order earth system model to interrogate a subset of these connections with a focus on changes that occur during perturbations to electron flow through the sedimentary rock cycle we show that the net oxidation or reduction of the earth s surface can play an important role in controlling acid base processes in the oceans and thus climate and suggest that these links should be more fully integrated into interpretive frameworks aimed at understanding earth system evolution throughout precambrian and phanerozoic time

enhanced weathering and co2 drawdown caused by latest eocene strengthening of the atlantic meridional overturning circulation on timescales significantly greater than 105 years atmospheric pco2 is controlled by the rate of mantle outgassing relative to the set point of the silicate weathering feedback the weathering set point has been shown to depend on the distribution and characteristics of rocks exposed at the earth s surface vegetation types and topography here we argue that large scale climate impacts caused by changes in ocean circulation can also modify the weathering set point and show evidence suggesting that this played a role in the establishment of the antarctic ice sheet at the eocene oligocene boundary in our simulations tectonic deepening of the drake passage causes freshening and stratification of the southern ocean strengthening the atlantic meridional overturning circulation and consequently raising temperatures and intensifying rainfall over land these simulated changes are consistent with late eocene tectonic reconstructions that show drake passage deepening and with sediment records that reveal southern ocean stratification the emergence of north atlantic deep water and a hemispherically asymmetric temperature change these factors would have driven intensified silicate weathering and can thereby explain the drawdown of carbon dioxide that has been linked with antarctic ice sheet growth we suggest that this mechanism illustrates another way in which ocean atmosphere climate dynamics can introduce nonlinear threshold behaviour through interaction with the geologic carbon cycle during the latest eocene declining atmospheric co2 levels led to the inception of the antarctic ice sheet simulations suggest that the deepening of the drake passage caused climate changes that enhanced continental weathering and co2 drawdown

modelling the phanerozoic carbon cycle and climate constraints from the 87sr 86sr isotopic ratio of seawater a numerical model describing the coupled evolution of the biogeochemical cycles of carbon sulfur calcium magnesium phosphorus and strontium has been developed to describe the long term changes of atmospheric carbon dioxide and climate during the phanerozoic the emphasis is on the effects of coupling the cycles of carbon and strontium various interpretations of the observed phanerozoic history of the seawater 87sr 86sr ratio are investigated with the model more specifically the abilities of continental weathering volcanism and surface lithology in generating that signal are tested and compared it is suggested that the observed fluctuations are mostly due to a changing weatherability over time it is shown that such a conclusion is very important for the modelling of the carbon cycle indeed it implies that the conventional belief that the evolution of atmospheric carbon dioxide and climate on a long time scale is governed by the balance between the volcanic input of co2 and the rate of silicate weathering is not true rather carbon exchanges between the mantle and the exogenic system are likely to have played a key role too further the increase of the global weathering rates with increasing surface temperature and or atmospheric co2 pressure usually postulated in long term carbon cycle and climate modelling is also inconsistent with the new model other factors appear to have modulated the weatherability of the continents through time such as mountain building and the existence of glaciers and ice sheets based on these observations a history of atmospheric carbon dioxide and climate during phanerozoic time consistent with the strontium isotopic data is reconstructed with the model and is shown to be compatible with paleoclimatic indicators such as the timing of glaciation and the estimates of cretaceous paleotemperatures