geologic and seismic setting pertinent to dam safety review of duncan dam le barrage duncan est un ouvrage de b c hydro construit sur la riviere duncan dans le sud est de la colombiebritannique au canada entre 1965 et 1967 le barrage repose sur une succession complexe de plus de 380 m de sediments detritiques et fluvio glaciaires dont certains sont permeables et compressibles quelques unites sableuses peuvent presenter un danger de liquefaction en particulier une couche de sable unite 3c ayant jusqu a 23 m d epaisseur les regles sismiques en vigueur actuellement a b c hydro pour les barrages exigent que le barrage duncan soit capable de resister au seisme maximum envisageable mce sans deversement catastrophique du reservoir cet article decrit les conditions geologiques et sismiques dans la region entourant le barrage et le choix des parametres pour les mouvements sismiques du sol des methodes probabilistes ont ete appliquees pour reconstituer les mouvements du terrain correspondant au mce on a estime que l on pourrait avoir un pic d acceleration horizontale du terrain de 0 12 g provenant d un tremblement de terre d amplitude m 6 5 a une distance d environ 50 km pour les analyses dynamiques des sols on a choisi plusieurs cas historiques tires du passe et presentant des caracteristiques semblables a celles du seisme previsionnel

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

carbon isotope stratigraphy in shallow water carbonates implications for cretaceous black shale deposition a barremian to albian succession on mount kanala part of a tethyan isolated carbonate platform was investigated for its 13c variations the limestone sequence is composed of a series of peritidal shallowing upward cycles with clear petrographic evidence for strong early diagenetic overprinting related to repeated subaerial exposure despite significant impact of diagenesis the observed changes in 13c can be very well correlated with deep water sections from different ocean basins and shallow water carbonate platforms in the middle east this lends further support to the applicability of 13c variations for stratigraphic purposes in shallow water limestones using the 13c signal time resolution in lower cretaceous platform carbonates can be significantly increased independent of bio zonations often hampered by ecological variability cyclostratigraphic analysis of the aptian part of the section shows that strong positive excursions of the cumulative departure from mean cycle thickness of the peritidal shallowing upward cycles coincide with global positive 13c excursions this and the fact that positive shifts in the 13c record are preserved within shallow water limestones provide evidence that black shale accumulation in the ocean basins occurred during sea level rise and flooding of platform tops integration of carbon isotope cyclo and sequence stratigraphic results from different carbonate platforms indicate that strong positive global 13c shifts and concurrent organic carbon burial during black shale deposition are ultimately caused by rapid rises of eustatic sea level hence the rate of change of eustatic sea level is considered to play a crucial role in black shale accumulation in the global ocean basins during the cretaceous

burial dominated cementation in non tropical carbonates of the oligocene te kuiti group new zealand abstract cementation of bryozoan echinoid benthic foraminiferal temperate shelf carbonates of the oligocene te kuiti group north island new zealand occurred mainly during subsurface burial the calcite cements in the limestones are dominated by equant and syntaxial rim spar which typically becomes ferroan given an iron supply and compared to the skeletal material with normal marine 18o values from 2 to 1 more depleted in 18o with depth of burial the 18o composition of bulk cement samples ranging from 1 to 7 these trends reflect the establishment in pore waters during sediment burial of reducing conditions and gradually increasing temperatures 20 50 c respectively the 13c values 0 to 3 of the cements remain the same as the host marine shells suggesting the source of carbon in the cements was simply redistributed marine carbonate derived from shell dissolution two gradational burial diagenetic environments influenced by marine derived porewaters are arbitrarily distinguished shallow burial phase and moderate burial phase during the shallow burial phase down to 500 600 m sub bottom depth the carbonates lost at least 25 of their original porosity by mechanical compaction and were selectively cemented by non ferroan or usually ferroan variably luminescent slightly 18o depleted sparry calcite cement 18o 2 to 4 mainly as syntaxial rims about echinoid grains these shallow burial cements form less than about 10 of total cement in the majority of the limestones and their source was probably mainly mild intergranular dissolution of calcitic skeletal fragments accompanying the onset of chemical compaction during the moderate burial phase between about 600 and 1100 m sub bottom depth porosity loss continued typically to about 70 of its original value as a result of pressure solution of calcitic bioclasts associated with more advanced stages of chemical compaction this involved development of a wide variety of non sutured and microstylolitic solution seams including both single and composite wispy or continuous bedding parallel types and non parallel reticulate forms the released carbonate was precipitated as ferroan or non ferroan where iron supply was negligible dull luminescent strongly 18o depleted 18o 4 to 7 mainly equant calcite spar cement occluding available pore space in the limestones

results and implications of seismic performance studies for duncan dam screening level studies indicated large zones of the foundation soil beneath duncan dam could be triggered to liquefy under the design earthquake resulting in flow slides that could lead to breaching of the dam in these studies estimates of the key soil parameters were obtained from an indirect procedure using penetration tests and seed s chart which is based on field experience during past earthquakes together with empirical correction factors for high confining stress and static bias this is state of the practice procedure in north america and is used because of the difficulty in retrieving and testing undisturbed samples of sand with the high confining stresses present at the site the indirect approach gave very low values of the key liquefaction properties of the soil and the use of such low values in analyses indicated that major and costly remedial measures were required thus a more direct approach was undertaken this involved both direct and semidirect determination of the key soil parame

interpretation of in situ test results from the canlex sites one of the primary objectives of the canadian liquefaction experiment canlex project was to evaluate in situ testing techniques and existing interpretation methods as part of the overall goal to

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

δ18o and marion plateau backstripping combining two approaches to constrain late middle miocene eustatic amplitude d 18 obenthic values from leg 194 ocean drilling program sites 1192 and 1195 drilled on the marion plateau were combined with deep sea values to reconstruct the magnitude range of the late middle miocene sea level fall 13 6 11 4 ma in parallel an estimate for the late middle miocene sea level fall was calculated from the stratigraphic relationship identified during leg 194 and the structural relief of carbonate platforms that form the marion plateau corrections for thermal subsidence induced by late cretaceous rifting flexural sediment loading and sediment compaction were taken into account the response of the lithosphere to sediment loading was considered for a range of effective elastic thicknesses 10 te 40 km by overlapping the sea level range of both the deep sea isotopes and the results from the backstripping analysis we demonstrate that the amplitude of the late middle miocene sea level fall was 45 68 m 56 5 6 11 5 m including an estimate for sea level variation using the d 18 obenthic results from the subtropical marion plateau the range of sea level fall is tightly constrained between 45 and 55 m 50 0 6 5 0 m this result is the first precise quantitative estimate for the amplitude of the late middle miocene eustatic fall that sidesteps the errors inherent in using benthic foraminifera assemblages to predict paleo water depth the estimate also includes an error analysis for the flexural response of the lithosphere to both water and sediment loads our result implies that the extent of ice buildup in the miocene was larger than previously estimated and conversely that the amount of cooling associated with this event was less important

controls of facies and sediment composition on the diagenetic pathway of shallow water heterozoan carbonates the oligocene of the maltese islands relatively few studies have so far addressed diagenetic processes in heterozoan carbonates and the role that sediment composition and depositional facies exert over diagenetic pathways this paper presents a study of oligocene shallow water heterozoan carbonates from the maltese islands we investigate stratigraphic distribution abundance and timing of diagenetic features and their relationship to sediment composition and depositional facies the studied carbonate rocks comprise rud to packstones of the heterozoan association predominantly containing coralline red algae bryozoans echinoids and benthic foraminifers xrd analyses show that all high mg calcite has been transformed to low mg calcite and that no aragonite is preserved diagenetic processes include dissolution of aragonitic biota neomorphism of high mg calcitic biota to low mg calcite and cementation by fibrous bladed epitaxial and blocky cements stable isotopes on bulk rock integrated with petrographic data suggest that the study interval was not exposed to significant meteoric diagenesis we interpret early cementation to have taken place in the marine and marine burial environment the distribution and abundance of early diagenetic features determining the diagenetic pathway can be related to the primary sediment composition and depositional texture sorting and micrite content are important controls over the abundance of diagenetic features

integrated planktonic foraminifera bolboforma and carbon isotope stratigraphy in a mid early late miocene carbonate ramp setting from the acreide area sicily taxa of bolboforma a marine calcareous microfossil group of uncertain origin with affinities to protophytic algae are generally used for biostratigraphy of lower eocene to lower pleistocene marine sediments from high latitudes biostratigraphy based on bolboforma has been applied only rarely to european outcrop sections and very rarely to mediterranean sections three bolboforma and two planktonic foraminifera events are identified and used to interpret the sedimentation rate of the 90 m of slope sediments from the palazzolo section palazzolo acreide area sicily and spanning the interval from 11 9 to approximately 10 5 ma carbon isotope stratigraphy supports the age assigment based on bolboforma and planktonic foraminifera in particular the sediments of the palazzolo section seem to record the latest pulse of the monterey event a major perturbation in the global carbon cycle related to global intensification of upwelling expanded use of the bolboforma may thus improve stratigraphy in outcropping miocene sequences in temperate regions particularly in shallower water facies with poorly resolved planktonic foraminifera and nannofossil stratigraphy

in situ ground freezing to obtain undisturbed samples of loose sand in situ ground freezing with liquid nitrogen can be an excellent technique for obtaining high quality undisturbed samples from a wide range of loose sand deposits with their in situ conditions preserved this paper describes the techniques used during the canlex project to carry out in situ ground freezing and undisturbed sampling of the loose sand deposits encountered at six test sites specific details with respect to the effects of difficult subsoil or ground water conditions encountered at the sites are provided modifications made to the ground freezing and sampling system to accommodate difficult ground conditions are described the actual advance of the freezing front and the consumption of liquid nitrogen are compared with theoretical predictions the dry coring technique utilized to recover undisturbed frozen sand samples is described the void ratios measured for the frozen core samples are compared with void ratio measurements obtained using geophysical logging in boreholes located within a 5 m radius of the freeze pipe the costs associated with in situ ground freezing utilizing liquid nitrogen and coring of the frozen sand at six test sites are presented

phosphorites hardgrounds and syndepositional solution subsidence a palaeoenvironmental model from the miocene of the maltese islands abstract two major phosphorite conglomerate horizons occur throughout the central mediterranean maltese islands within the lower middle miocene globigerina limestone formation the lower conglomerate lies directly upon a hardground and both conglomerates include lithoclasts of hardground material variation in clast size and bed thickness indicates a source area to the west and north of the present day islands of malta and gozo particularly thick phosphorite conglomerates occur in solution subsidence structures in western gozo being developed as a result of synsedimentary seafloor collapse these structures indicate that phosphorite clasts were deposited during several discrete pulses of turbulence punctuated by periods of non depositional hardground formation or normal marine pelagic sedimentation geochemical analysis of the contained phosphorite clasts within the conglomerates shows that p 2 o 5 generally is concentrated around the outer margins of the pebbles and contributes up to 17 by weight of some samples some 654 580 m 3 and 837 870 m 3 of phosphorite bearing strata are contained within the xlendi and qawra subsidence structures respectively the maltese islands represent part of a miocene carbonate shelf whose margin lay nearby to the west and which was subject to periodic erosion by strong currents transporting phosphorite pebbles eastwards to their present sites these currents further contributed phosphorus to semi autochthonous phosphorite developments located within the present maltese area the maltese phosphorites are related to other phosphorite areas in sicily a major province of miocene phosphogenesis is proposed to account for these occurrences it extends along the western margins of the malta ragusa rise

sedimentology and palaeoenvironment of the southeast sicilian tertiary platform carbonates abstract a thick succession of shelf and shelf slope carbonates is developed in southeastern sicily sedimentological aspects of the oligocene to tortonian sequence including distribution and palaeoenvironmental factors are considered a new formation and four new members are proposed in the upper part of the succession the region comprises a western half typically exhibiting the principal deeper water planktonic facies including marls and an eastern area displaying typically inner shelf carbonates and an attenuated succession coralline algal limestones and calcarenites are more typical of this latter region but there are also some volcanic intercalations an attempt is made to relate the hyblean succession to that of the maltese islands which lie at the southern end of this tertiary carbonate platform

orbitally paced climate oscillations across the oligocene miocene boundary the late oligocene and early miocene periods some 21 to 27 million years ago have generally been viewed as times of moderate global warmth and ice free conditions yet several lines of evidence suggest that this interval was punctuated by at least one and possibly several episodes of high latitude cooling and continental glaciation1 2 3 here we present stable isotope and per cent coarse fraction data from an equatorial western atlantic deep sea sediment core that provide high resolution records of the climate variability across the oligocene miocene transition 22 5 25 7 million years ago a strong 40 kyr periodicity in the oxygen isotope record is consistent with a high latitude orbital obliquity control on ice volume and temperature orbital influences are also apparent at precession and eccentricity frequencies including a series of 400 kyr oscillations that culminate in distinct maxima at the oligocene miocene boundary about 23 7 million years ago covariance between the carbon and oxygen isotope records suggests that the oceanic carbon cycle may have contributed to global cooling during the 400 kyr cycles particularly at the oligocene miocene boundary

cenozoic global sea level sequences and the new jersey transect results from coastal plain and continental slope drilling the new jersey sea level transect was designed to evaluate the relationships among global sea level eustatic change unconformity bounded sequences and variations in subsidence sediment supply and climate on a passive continental margin by sampling and dating cenozoic strata from coastal plain and continental slope locations we show that sequence boundaries correlate within 0 5 myr regionally onshore offshore and interregionally new jersey alabama bahamas implicating a global cause sequence boundaries correlate with 18o increases for at least the past 42 myr consistent with an ice volume glacioeustatic control although a causal relationship is not required because of uncertainties in ages and correlations evidence for a causal connection is provided by preliminary miocene data from slope site 904 that directly link 18o increases with sequence boundaries we conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since 42 ma we speculate that prior to this the growth and decay of small ice sheets caused small amplitude sea level changes 20 m in this supposedly ice free world because eocene sequence boundaries also appear to correlate with minor 18o increases subsidence estimates backstripping indicate amplitudes of short term million year scale lowerings that are consistent with estimates derived from 18o studies 25 50 m in the oligocene middle miocene and 10 20 m in the eocene and a long term lowering of 150 200 m over the past 65 myr consistent with estimates derived from volume changes on mid ocean ridges although our results are consistent with the general number and timing of paleocene to middle miocene sequences published by workers at exxon production research company our estimates of sea level amplitudes are substantially lower than theirs lithofacies patterns within sequences follow repetitive predictable patterns 1 coastal plain sequences consist of basal transgressive sands overlain by regressive highstand silts and quartz sands and 2 although slope lithofacies variations are subdued reworked sediments constitute lowstand deposits causing the strongest most extensive seismic reflections despite a primary eustatic control on sequence boundaries new jersey sequences were also influenced by changes in tectonics sediment supply and climate during the early to middle eocene low siliciclastic and high pelagic input associated with warm climates resulted in widespread carbonate deposition and thin sequences late middle eocene and earliest oligocene cooling events curtailed carbonate deposition in the coastal plain and slope respectively resulting in a switch to siliciclastic sedimentation in onshore areas oligocene sequences are thin owing to low siliciclastic and pelagic input and their distribution is patchy reflecting migration or progradation of depocenters in contrast miocene onshore sequences are thicker reflecting increased sediment supply and they are more complete downdip owing to simple tectonics we conclude that the new jersey margin provides a natural laboratory for unraveling complex interactions of eustasy tectonics changes in sediment supply and climate change

the monterey event in the mediterranean a record from shelf sediments of malta oligo miocene carbonate platform and shelf sediments outcropping on the maltese islands provide an excellent archive of the paleoceanography of the central mediterranean a sequence of shallow water limestones than shelf limestones and marls followed again by shallow water limestones reflects drowning of a carbonate platform the establishment of a shelf environment and in the late miocene renewed progradation and aggradation of shallow water carbonates the sequence recording the deepening of the maltese platform contains several phosphorite hardgrounds and phosphorite pebble beds these phosphorites were dated with strontium isotopes major episodes of phosphogenesis occurred between 25 and 16 ma and they are coeval with those phosphorite events reported from florida and north carolina a miocene carbon isotope and oxygen isotope stratigraphy was established on planktic and benthic foraminifera and on bulk samples a major carbon isotope excursion with an amplitude of up to l between 18 and 12 5 ma can be correlated with the globally recognized monterey carbon isotope excursion this is the first record of this event both in shallow water sediments and in the mediterranean the carbon isotope excursion precedes an oxygen isotope excursion which also was recognized in deep sea records major episodes of phosphogenesis and platform drowning preceded the carbon isotope excursion by up to millions of years

the canadian liquefaction experiment an overview the canadian geotechnical engineering community has completed a major collaborative 5 year research project entitled the canadian liquefaction experiment canlex the main objective of the project was to study the phenomenon of soil liquefaction which can occur in saturated sandy soils and is characterized by a large loss of strength or stiffness resulting in substantial deformations in many areas of canada large structures are constructed on or comprise sandy soils e g some major hydroelectricity earth dams and many tailings impoundments in the mining industry the behaviour of loose sandy soils can be difficult to predict but can have a significant financial impact on these types of engineering structures consequently the intent of the canlex project was to improve the overall understanding of soil liquefaction this paper provides an overview of the canlex project outlining the project objectives major achievements and conclusions four companion papers describe different aspects of the pr

post liquefaction stability and deformation analysis of duncan dam duncan dam is a 39 m high zoned embankment and is founded on a deep deposit of unconsolidated sediments consisting of sands silts and gravels that are susceptible to liquefaction during earthquake loading a comprehensive program of field laboratory and analytical investigations was conducted to evaluate the liquefaction potential of the foundation soils and performance of the dam during an earthquake this paper describes the evaluation procedures and analyses and presents results of the post liquefaction stability and deformation analysis of the dam analyses were carried out based on the total stress approach using two methods namely the lab method and seed s method the lab method is a site specific direct laboratory based approach utilizing soil parameters from laboratory tests on undisturbed soil samples obtained in situ after freezing the ground seed s method is indirect and is based on field penetration data and past experience from earthquakes the lab method indicates that the residual

liquefaction analysis of duncan dam using strength ratios b c hydro performed extensive seismic safety studies for duncan dam in the late 1980s and early 1990s the results of these studies indicated that duncan dam was reasonably safe from liquefaction induced failure a recently proposed liquefaction analysis procedure that uses strength ratios to assess liquefaction triggering and post triggering stability was used to revisit the liquefaction analysis of duncan dam when compared to the detailed field and analytical studies performed by b c hydro the proposed liquefaction analysis procedure predicts i similar zones of liquefaction within a contractive unit of foundation sand ii similar shear strengths at the triggering of liquefaction yield shear strength and at large strain liquefied shear strength and iii similar post triggering factors of safety for slope stability the good agreement suggests that the strength ratio based liquefaction analysis approach is relatively robust and is suitable for screening level studies for large projects or m

evaluation of liquefaction potential of foundation soils at duncan dam a comprehensive program of field laboratory and analytical investigations was carried out to evaluate the potential of liquefaction for the foundation soils at duncan dam duncan dam was completed in 1967 under the columbia river treaty in southeastern british columbia the 39 m high zoned embankment dam is founded on a sequence of sands silts and gravels some of the foundation soils may liquefy during earthquake loading and this would affect the stability and performance of the dam the liquefaction studies were carried out in two phases to characterize the engineering properties of the foundation soils and to assess its potential for triggering liquefaction using the total stress approach this paper describes methods of assessment of liquefaction potential using soil parameters based on field penetration data seed s method and laboratory testing of undisturbed soil samples obtained in situ after freezing the ground lab method and presents the results of triggering analysis influence of confin

shallow burial diagenesis of skeletal carbonates selective loss of aragonite shell material miocene to recent queensland plateau and queensland trough ne australia implications for shallow cool water carbonates in burial environments carbonate sediments undergo mineralogical stabilization and increasing lithification with depth as yet however little knowledge exists with respect to the corresponding effects on fossil preservation and taphonomic modification of the original sediment composition countings of particles 63 m in miocene to recent periplatform sediments odp leg 133 ne australia exhibit a clear trend of reduction of skeletal aragonite downcore low and high mg calcite grains occur in a continuous order of magnitude over the studied interval 600 m sub bottom depth original microtextures are retained in high mg calcite biota although converted to low mg calcite thus the conversion to low mg calcite appears to occur without introducing a significant quantitative bias aragonite skeletons pelagic gastropods however exhibit a successive exposure of deeper crystal layers and a chalky preservation with burial depth which we interpret to result from dissolution hints for the originally more numerous existence of aragonite biota exist in soft sediments and chalks by the presence of internal moulds shells replaced by microspar and mouldic porosity in early cemented hardgrounds in deep sections barren of aragonite the number of casts and replaced shells remains unchanged and is insignificant as compared to aragonitic biota probably originally present within the sediment 2 in ooze chalk vs 30 50 of grains in modern periplatform sediments therefore palaeontological information must be significantly biased through selective removal of aragonite rates of preservation and destruction depend on external factors during sediment accretion sedimentation rates clay content total organic carbon content and rates of fluid flow within the sediment these observations are relevant with respect to the diagenetic potential and patterns of fossil preservation in little cemented calcitic cool water carbonates because they may originally have contained more aragonite biota as important constituents of an ecosystem than is commonly suspected and calcite aragonite ratios in ancient carbonate sediments may not necessarily reflect original input signals climate or sea level

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

black shales and carbon isotopes in pelagic sediments from the tethyan lower jurassic detailed sampling and analysis of jurassic pelagic limestones and marls from italy hungary and switzerland have enabled construction of an isotope stratigraphy across the pliensbachian toarcian boundary with resolution to the zonal level the oxygen isotope record is unremarkable the carbon isotopes however show two positive excursions one relatively minor during the pliensbachian margaritatus zone subnodosus subzone the other more major during the toarcian early falciferum zone where a maximum 13c value of 4 52 pdb is attained these intervals are known to be favoured periods of organic rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record a comparable phenomenon has been documented from the cenomanian turonian boundary in the cretaceous where it has been referred to the influence of an oceanic anoxic event some italian sections spanning this lower jurassic interval contain organic rich shales in the falciferum zone the isotopic signatures from their included locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve carbon isotopes from the organic carbon itself are extremely negative falling to 33 pdb and in one section examined in detail correlate with the calcium carbonate content of the shales they may reflect a partial change to a non calcified planktonic biota during deposition of this lime poor interval possibly responding to upwelling and increased fertility of near surface waters the onset of upwelling may have been as early as spinatum tenuicostatum zone time that is at the pliensbachian toarcian boundary

secular variations in the carbonate chemistry of the oceans over the cenozoic abstract oceanic carbonate chemistry during the cenozoic has affected the climatology ecology and marine geology of our planet yet we have limited means to know the evolution of that chemistry due to a lack of preserved and unaltered seawater samples and a continuing paucity of proxies modeling is often used to address this problem here we offer a simple data driven secular timescale inverse model for the mean cenozoic carbonate chemistry of the oceans inputs for the model include carbonate compensation depth ccd caco3 burial seawater temperature atmospheric co2 and carbonate ion records as well as a simple set of original but justified assumptions the model retrodicts the total dissolved inorganic carbon dic carbonate alkalinity calk and ph of the surface and deep waters of the ocean the retrodicted dic and calk records do not indicate any unusually elevated values in the early cenozoic as found in some past studies if the ccd record from lyle et al 2008 is employed the changes in dic and calk appear entirely related to changes in the alkalinity input to the pelagic oceans and atmospheric co2 however with the ccd from palike et al 2012 the increases in dic and calk during the last 15 ma reflect the effects of ocean cooling using either ccd record our model provides consistent retrodictions of the available ph record our results are not consistent with many past modeling assumptions such as constancy of alkalinity in surface waters or the ratio of shallow and deep carbonate ion concentrations finally we use our results to provide new estimates of atmospheric co2 based on boron isotopes and find significantly lower co2 values in the early cenozoic than previous values