boron isotopes and b ca in benthic foraminifera proxies for the deep ocean carbonate system abstract accurate records of the state of the ocean carbonate system are critical for understanding past changes in pco 2 ocean acidification and climate the chemical principles underlying the proxy of oceanic ph provided by the boron isotope ratio of foraminiferal carbonate are relatively well understood but the proxy s reliability has been questioned we present 76 new multi collector inductively coupled plasma mass spectrometry mc icpms 11 b measurements on a range of benthic foraminifera from 23 late holocene samples from the atlantic that reaffirm the utility of the 11 b ph proxy our boron isotope measurements on 10 benthic foraminifera tests typically yield a precision of 0 25 at 2 s d equivalent to 0 03 ph units 11 b values of epifaunal species are within analytical uncertainty of those predicted from a simple model assuming sole incorporation of b oh 4 from seawater and no vital effects using the independently determined fractionation factor of 1 0272 between 11 b 10 b of aqueous boron species infaunal foraminifera are consistent with this model but record the combined effects of lower pore water 11 b and ph no influence of partial dissolution or shell size on 11 b is observed we have also measured the b ca ratios of the same samples for individual cibicidoides species b ca shows a good correlation with co 3 2 but the b ca of different co occurring species morphotypes varies considerably these effects are not seen in 11 b which may therefore provide a more robust proxy of the ocean carbonate system whilst in theory 11 b and b ca can be combined to provide a quantitative reconstruction of alkalinity and dissolved inorganic carbonate dic in practice this is precluded by propagated uncertainties 11 b data give significant constraints on foraminifera calcification mechanisms and seem most simply explained by incorporation of b oh 4 into a hco 3 pool which is then completely incorporated in foraminiferal caco 3 our demonstration of the predictable variation of 11 b with ph across a wide range of species and locations provides confidence in the application of mc icpms measurements of foraminiferal 11 b to reconstruct past changes in the ocean carbonate system

seawater ph pco2 and co2 3 variations in the caribbean sea over the last 130 kyr a boron isotope and b ca study of planktic foraminifera abstract here a new analytical methodology is described for measuring the isotopic composition of boron in foraminifera using multicollector inductively coupled plasma mass spectrometry mc icpms this new approach is fast 10 samples analysed in duplicate per analytical session and accurate to better than 0 25 at 95 confidence with acceptable sample size requirements 1 3 mg of carbonate a core top calibration of several common planktic and two benthic species from geographically widespread localities shows a very close agreement between the isotopic composition measured by mc icpms and the isotopic composition of b oh 4 in seawater as predicted using the recently measured isotopic equilibrium factor of 1 0272 at the depth of habitat a down core and core top investigation of boron concentration b ca ratio shows that the partition coefficient is influenced by co2 3 complicating the application of this proxy nevertheless it is demonstrated that these two proxies can be used to fully constrain the carbonate system of surface water in the caribbean sea odp site 999a over the last 130 kyr this reconstruction shows that during much of the holocene and the last interglacial period surface water at site 999a was in equilibrium with the atmosphere with respect to co2 during the intervening colder periods although the surface water pco2 was lower than the holocene it was a minor to significant source of co2 to the atmosphere possibly due to either an expansion of the eastern equatorial atlantic upwelling zone or a more local expansion of coastal upwelling in the southern caribbean such reorganisation of the oceanic carbonate system in favour of a larger source of co2 to the atmosphere from the equatorial ocean may require mechanisms responsible for lowering atmospheric co2 during glacial periods to be more efficient than previously supposed

a tectonostratigraphic framework for the mid norway region abstract the tectonostratigraphic analysis presented here aims to establish a broad stratigraphic framework within which the likely distribution of both reservoir and source rock intervals within the deep water voering and more basins can be evaluated in terms of hydrocarbon potential the devonian to triassic interval can be effectively discounted by its extreme depth of burial across most of the study area the middle jurassic is interpreted to provide a potential reservoir target in the gjallar ridge area the cretaceous is seismically mappable across the region and has been divided into five tectonostratigraphic sequences late cretaceous reservoirs are considered to offer targets in the nyk high area six tectonostratigraphic sequences are described within the cenozoic succession paleocene reservoirs are interpreted to offer targets over both the ytterskallen and ormen lange areas of the more basin source rock maturity is critical for exploration success mapping shows the late jurassic earliest cretaceous spekk formation to be overmature over most of the area though the presence of possible dhis indicates the probable presence of major gas accumulations in the region only on the western flank of the vigrid syncline does the spekk shallow sufficiently to lie within the potential oil window it is concluded that the region has the potential to become a significant new hydrocarbon province for the 21st century

co2 over the past 5 million years continuous simulation and new δ11b based proxy data during the past five million yrs benthic 18o records indicate a large range of climates from warmer than today during the pliocene warm period to considerably colder during glacials antarctic ice cores have revealed pleistocene glacial interglacial co2 variability of 60 100 ppm while sea level fluctuations of typically 125 m are documented by proxy data however in the pre ice core period co2 and sea level proxy data are scarce and there is disagreement between different proxies and different records of the same proxy this hampers comprehensive understanding of the long term relations between co2 sea level and climate here we drive a coupled climate ice sheet model over the past five million years inversely forced by a stacked benthic 18o record we obtain continuous simulations of benthic 18o sea level and co2 that are mutually consistent our model shows co2 concentrations of 300 to 470 ppm during the early pliocene furthermore we simulate strong co2 variability during the pliocene and early pleistocene these features are broadly supported by existing and new 11b based proxy co2 data but less by alkenone based records the simulated concentrations and variations therein are larger than expected from global mean temperature changes our findings thus suggest a smaller earth system sensitivity than previously thought this is explained by a more restricted role of land ice variability in the pliocene the largest uncertainty in our simulation arises from the mass balance formulation of east antarctica which governs the variability in sea level but only modestly affects the modeled co2 concentrations

tectonic history along the south gabon basin anomalous early post rift subsidence an integrated study of the south gabon margin south atlantic based on reflection seismic and well data has been performed to quantify tectonic activity a regional profile crossing the entire basin together with subsidence analysis highlights important aspects of the post rift history the most striking event in the margin evolution appears to be the anomalous extra subsidence during the early post rift period characterized by high sedimentation rates equivalent to one third of the syn rift subsidence although the presence of evaporite layers restricts knowledge of the underlying structures essentially composed of pre rift and syn rift sequences the outcome of this post rift tectonic study has strong implications for the rifting history the early post rift subsidence patterns can be related to a high thermal anomaly during the early rifting thermal state of the lithosphere these findings are highly relevant for petroleum system studies and have implications for hydrocarbon generation

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

relating petroleum system and play development to basin evolution west african south atlantic basins abstract sedimentary basins can be classified according to their structural genesis and evolutionary history and the latter can be linked to petroleum system and play development we propose an approach in which we use the established concepts in a new way breaking basins down into their natural basin cycle division then defining the characteristics of each basin cycle including the type of petroleum systems and plays they may contain and comparing them with similar basin cycles in other basins thereby providing a means to learn through a greater population of perhaps not immediately obvious analogues furthermore we introduce the use of the trajectory plot as a new tool in such an analysis this methodology has been applied to the west african south atlantic marginal basins between cameroon and angola and we demonstrate that the similar tectonostratigraphic evolution of the individual basins along this margin has led to the development of similar types of petroleum systems and play level s consequently we can make analogue comparisons among these basins in order to evaluate and predict the presence of potential yet undiscovered hydrocarbon accumulations in less well explored parts of the margin

biomarker distributions in australian oils predominantly derived from terrigenous source material oils found in many australian sedimentary basins contain a relatively high input of terrigenous organic source material a study of a large number of these oils has permitted a number of biomarker distributions to be determined that appear to be characteristic for oils derived from terrigenous source material these features include the presence of sesquiterpanes absence of tricyclic terpanes relatively high concentrations of a c24 tetracyclic terpane predominance of c29 steranes presence of two unidentified c27 and c30 terpanes and virtual absence of 18 h oleanane the latter observation is significant since it appears that 18 h oleanane appears only in oils of tertiary age derived from terrigenous source material an attempt has also been made to compare the results for the australian oils with published results for oils derived from terrigenous source material in other parts of the world the number of reports in the literature for these oils is fairly limited but it appears that some of the observations for the australian oils can be extended to them this study is an initial attempt to devise a classification scheme that can be used to determine the origin of an oil unambiguously from biomarker parameters in order for this approach to be successful a relatively large number of biomarker parameters need to be assigned as characteristic of a particular type of source material

triterpanes and ring a degraded triterpanes as biomarkers characteristic of tertiary oils derived from predominantly higher plant sources abstract a number of oils previously proposed to be derived from terrigenous source materials have been obtained from the taranaki basin new zealand niger delta beaufort mackenzie region taiwan and indonesia and their c24 tetracyclic and c30 pentacyclic terpenoid distributions examined by gc ms and gc ms ms the c24 tetracyclic terpanes are thought to be derived from their corresponding c30 hopane oleanane ursane and lupane counterparts as previously reported a mixture of at least nine c30 pentacyclic terpanes are found to be present with remarkably uniform distributions in oils from these widely separated provinces whilst definitive structures have not been proposed for these compounds information has been obtained as to whether these pentacyclic terpanes are all six membered rings or contain one or two five membered rings the presence of this mixture of tetracyclic and pentacyclic terpanes provides a good indicator for oils derived from terrigenous source materials and in the case of these basins of tertiary age

empirical relationship between ph and the boron isotopic composition of globigerinoides sacculifer implications for the boron isotope paleo ph proxy culture experiments were carried out with the planktonic foraminifera globigerinoides sacculifer at three different ph values 7 6 0 05 8 20 0 05 8 60 0 05 in order to establish the ph dependence of the boron isotopic fractionation between the calcitic tests of g sacculifer and seawater additional objectives were to compare the ph dependences of boron isotopic composition of g sacculifer with that of orbulina universa and inorganic calcite in order to evaluate the robustness of the boron isotope paleo ph proxy the relationship between the boron isotopic composition of g sacculifer and the culture water ph shows heavier boron isotopic values at higher ph this empirical relationship is similar but slightly offset by 3 per mil from that of o universa indicating the presence of biogenic influence vital effect on the boron isotopic composition of foraminifera however comparison of the boron isotopic composition of o universa and g sacculifer with that of inorganic calcite grown over a common ph range shows that inorganic processes are the dominant control on the boron isotopic composition of foraminifera and the vital effects play a small but not insignificant role the results imply that in spite of a small biogenic influence the variation in boron isotopic composition of foraminiferal shells with ph at least for o universa and g sacculifer is consistent with that for inorganic calcite demonstrating the potential of this isotopic signature in foraminifera as a reliable paleo ph proxy

interlaboratory study for coral sr ca and other element ca ratio measurements the sr ca ratio of coral aragonite is used to reconstruct past sea surface temperature sst twenty one laboratories took part in an interlaboratory study of coral sr ca measurements results show interlaboratory bias can be significant and in the extreme case could result in a range in sst estimates of 7 c however most of the data fall within a narrower range and the porites coral reference material jcp 1 is now characterized well enough to have a certified sr ca value of 8 838 mmol mol with an expanded uncertainty of 0 089 mmol mol following international association of geoanalysts iag guidelines this uncertainty at the 95 confidence level equates to 1 5 c for sst estimates using porites so is approaching fitness for purpose the comparable median within laboratory error is 0 5 c this difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the jcp 1 there are many potential sources contributing to biases in comparative methods but traces of sr in ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty consensus values that fulfil the requirements to be certified values were also obtained for mg ca in jcp 1 and for sr ca and mg ca ratios in the jct 1 giant clam reference material reference values with variable fitness for purpose have also been obtained for li ca b ca ba ca and u ca in both reference materials in future studies reporting coral element ca data should also report the average value obtained for a reference material such as the jcp 1

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

rapid and sustained surface ocean acidification during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been associated with the release of several thousands of petagrams of carbon pg c as methane and or carbon dioxide into the ocean atmosphere system within 10 kyr on the basis of the co occurrence of a carbon isotope excursion cie widespread dissolution of deep sea carbonates and global warming in theory this rapid carbon release should have severely acidified the surface ocean though no geochemical evidence has yet been presented using boron based proxies for surface ocean carbonate chemistry we present the first observational evidence for a drop in the ph of surface and thermocline seawater during the petm planktic foraminifers from a drill site in the north pacific ocean drilling program site 1209 show a 0 8 decrease in boron isotopic composition 11b at the onset of the event along with a 30 40 reduction in shell b ca similar trends in 11b are present in two lower resolution records from the south atlantic and equatorial pacific these observations are consistent with significant global acidification of the surface ocean lasting at least 70 kyr and requiring sustained carbon release the anomalies in the b records are consistent with an initial surface ph drop of 0 3 units at the upper range of model based estimates of acidification

oceanic ph control on the boron isotopic composition of foraminifera evidence from culture experiments culture experiments were carried out with the species orbulina universa at four different ph values 7 70 0 05 8 15 0 05 8 60 0 05 and 9 00 0 10 in order to establish the ph dependence of boron isotope fractionation between seawater and foraminifera a clear relationship between the boron isotopic composition of the foraminifera and the ph of the seawater culture solutions was found showing heavier boron isotopic composition at higher ph this finding supports the viability of boron isotopes as a paleo ph tool it is important to note that orbulina universa cultured in natural seawater as well as those obtained from coretop samples have a significantly lighter boron isotopic ratio than globigerinoides sacculifer from coretop samples suggesting that at least for this species a vital effect is active

carbonate dissolution in recent sediments of the eastern equatorial indian ocean preservation patterns and carbonate loss above the lysocline abstract multiple dissolution indices from 45 sediment samples show that the foraminiferal lysocline is near 3800 m in the eastern equatorial indian ocean close to the saturation horizon with respect to calcite in the water column below the lysocline the increase in foraminiferal fragmentation decrease in absolute abundance and progressive modification of planktic foraminiferal assemblages with depth is accompanied by an increasing rate of loss of carbonate from the sediments above the lysocline some dissolution must occur in order to produce the dramatic reduction in foraminiferal numbers up to 60 and the pattern of increased fragmentation with depth however the amount of carbonate actually lost from supralysoclinal sediments reaches at most 20 30 of the total at the depth of the lysocline the principal driving force behind supralysoclinal dissolution is most likely the oxidation of organic matter incorporated into the sediments dissolution above the lysocline has a greater apparent impact on relative preservation in the coarse 150 m fraction than it does on total carbonate loss because of redistribution of carbonate to the finer size fractions as fragments though the effects of dissolution on foraminiferal preservation are clearly visible at all depths the lysocline itself does appear to mark the local onset of large scale loss of dissolved carbonate from the sediments such an interpretation is broadly consistent with models regarding the saturation state of the overlying waters as the principal driving force behind the preservation or dissolution of recent carbonate sediments on the sea floor

boron isotope based seasonal paleo ph reconstruction for the southeast atlantic a multispecies approach using habitat preference of planktonic foraminifera abstract the boron isotopic composition of planktonic foraminiferal shell calcite 11 b cc provides valuable information on the ph of ambient water at the time of calcification hence 11 b cc of fossil surface dwelling planktonic foraminifera can be used to reconstruct ancient aqueous p co 2 if information on a second carbonate system parameter temperature and salinity is available however ph and p co 2 of surface waters may vary seasonally largely due to changes in temperature dic and alkalinity as also the shell fluxes of planktonic foraminifera show species specific seasonal patterns that are linked to intra annual changes in temperature it is obvious that 11 b cc of a certain species reflects the ph and thus p co 2 biased towards a specific time period within a year this is important to consider for the interpretation of fossil 11 b cc records that may mirror seasonal ph signals here we present new multi collector inductively coupled mass spectrometry mc icpms 11 b cc coretop data for the planktonic foraminifera species globigerina bulloides globigerinoides ruber trilobatus sacculifer and orbulina universa and compare them with 11 b borate derived from seasonally resolved carbonate system parameters we show that the inferred season adjusted 11 b cc 11 b borate relationships are similar to existing calibrations and can be combined with published 11 b cc field and culture data to augment paleo ph calibrations to test the applicability of these calibrations we used a core drilled on the walvis ridge in the southeast atlantic spanning the last 330 000 years to reconstruct changes in surface water p co 2 the reconstruction based on g bulloides which reflects the austral spring season was shown to yield values that closely resemble the vostok ice core data indicating that surface water p co 2 was close to equilibrium with the atmosphere during the cooler spring season in contrast p co 2 estimated from 11 b cc of o universa t sacculifer and g ruber that predominantly lived during the warmer seasons exhibits up to 50 ppmv higher values than the vostok ice core data this is probably due to the higher austral summer and fall temperatures as shown by mg ca to be on average 4 c higher than during the cooler spring season accounting for an increase in p co 2 of 4 per 1 c our results demonstrate that paleo ph estimates based on 11 b cc contain a significant seasonal signal reflecting the habitat preference of the recording foraminifera species

boron and magnesium isotopic composition of seawater the isotopic systems of boron and magnesium are increasingly being used as proxies for a number of environmental variables and processes the isotopic composition of seawater for both systems plays a central role in these studies and is an important interlaboratory standard given the long residence times of both elements 10 7 years it is commonly assumed that seawater is isotopically homogenous for these systems yet no systematic studies currently exist here we present the b and mg isotopic composition of 26 28 seawater samples from a number of ocean basins that encompass a significant range in salinity 32 to 38 psu temperature 0 3 to 25 9c and water depth 0 to 1240 m we find no significant or systematic variation for either system in accordance with their long residence times we recommend that the mean values we report 11 b 39 61 0 04 2 s e n 28 25 mg 0 43 0 01 2 s e n 26 26 mg 0 82 0 01 2 s e n 26 be used in future studies involving mg and b isotopes copyright 2010 by the american geophysical union

alkenone and boron based pliocene pco2 records abstract the pliocene period is the most recent time when the earth was globally significantly 3 c warmer than today however the existing pco2 data for the pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo pco2 this disagreement coupled with the general low temporal resolution of the published records does not allow a robust assessment of the role of declining pco2 in the intensification of the northern hemisphere glaciation inhg and a direct comparison to other proxy records are lacking for the first time we use a combination of foraminiferal 11b and organic biomarker alkenone derived carbon isotopes proxies to determine the concentration of atmospheric co2 over the past 5 ma both proxy records show that during the warm pliocene pco2 was between 330 and 400 ppm i e similar to today the decrease to values similar to pre industrial times 275 285 ppm occurred between 3 2 ma and 2 8 ma coincident with the inhg and affirming the link between global climate the cryosphere and pco2

effects of seawater carbonate ion concentration and temperature on shell u mg and sr in cultured planktonic foraminifera we investigate the sensitivity of u ca mg ca and sr ca to changes in seawater co3 and temperature in calcite produced by the two planktonic foraminifera species orbulina universa and globige rina bulloides in laboratory culture experiments our results demonstrate that at constant temperature u ca in o universa decreases by 25 7 per 100 mol co3 k g 1 as seawater co3 increases from 110 to 470 mol kg 1 results from g bulloides suggest a similar relationship but u ca is consistently offset by 40 at the same environmental co3 in o universa u ca is insensitive to temperature between 15 c and 25 c applying the o universa relationship to three u ca records from a related species globigerinoides sacculifer we estimate that caribbean and tropical atlantic co3 was 110 70 mol kg 1 and 80 40 mol kg 1 higher respectively during the last glacial period relative to the holocene this result is consistent with estimates of the glacial interglacial change in surface water co3 based on both modeling and on boron isotope ph estimates in settings where the addition of u by diagenetic processes is not a factor down core records of foraminiferal u ca have potential to provide information about changes in the ocean s carbonate concentration below ambient ph ph 8 2 mg ca decreased by 7 5 o universa t o 16 6 g bulloides per 0 1 unit increase in ph above ambient ph the change in mg ca was not significant for either species this result suggests that mg ca based paleotemperature estimates for the quaternary during which surface ocean ph has been at or above modern levels have not been biased by variations in surface water ph sr ca increased linearly by 1 6 0 4 per 0 1 unit increase in ph shell mg ca increased exponentially with temperature in o universa where mg ca 0 85 exp 0 096 t whereas the change in sr ca with temperature was within the reproducibility of replicate measurements copyright 2004 elsevier ltd

growth and linkage of the east tanka fault zone suez rift structural style and syn rift stratigraphic response abstract an integrated tectono stratigraphic analysis of the east tanka fault zone suez rift indicates fault growth by linkage of initially isolated fault segments that is consistent with fault growth models based on displacement length d l scaling laws during the initial 2 4 ma of rifting the east tanka fault zone was composed of two en echelon fault segments c 1 1 5 km long separated by a hanging wall intrabasin high that controlled the geometry of depocentres filled with continental deposits alluvial fan conglomerates were fed through the region between the two fault segments and form a discrete coarse grained body preserved in the immediate hanging wall of the fault zone subsequent stratigraphic patterns indicate that the two faults hard linked to form a single fault zone c 3 5 km long hard linkage of the segments resulted in migration of the zone of maximum displacement and subsidence into the zone of linkage uplift due to the migration of activity caused modification of drainage in the footwall of the fault zone that terminated the growth of the alluvial fan this study demonstrates the need to integrate structural and stratigraphic data when attempting to reconstruct the temporal and spatial evolution of normal fault zones additionally the fault dynamics illustrated have implications for tectono stratigraphic models of rift basins and syn rift stratigraphic evolution

seawater ph control on the boron isotopic composition of calcite evidence from inorganic calcite precipitation experiments experiments involving boron co precipitation with calcite have been carried out inorganically under controlled ph conditions 7 9 0 05 8 3 0 05 and 8 6 0 05 to determine the dependence of the boron isotopic composition 11b of calcite on the ph of seawater another purpose of these experiments was to estimate the magnitude of the biogenic influence on the 11b value of foraminifera by comparing their boron isotopic composition with that of the inorganic calcite over a common ph range the results show a clear relationship between 11b of inorganic calcite and the ph of artificial seawater the variation of boron isotopic fractionation between seawater and calcite with ph estimated from these experiments is similar to that estimated for cultured o universa and the theoretically predicted trend the results also support the hypothesis that b oh 4 is the dominant species incorporated into the calcite structure however the boron isotopic fractionation between seawater and inorganic calcite is lower than that estimated for o universa indicating the presence of a biogenic effect on the boron isotopic composition at least of this species of foraminifera most importantly the results imply that in spite of a small biogenic influence on the boron isotopic composition of foraminifera the variation in 11b of foraminiferal shells with ph at least for o universa is comparable to that for inorganic calcite supporting the potential of this isotopic signature in foraminifera as a reliable paleo ph proxy

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

early generation characteristics of a sulfur rich monterey kerogen this paper documents the critical role of organic sulfur in the early formation of bitumen and oil from a sulfur rich kerogen from the miocene monterey formation in california monterey kerogen commonly contains abundant chemically bound sulfur 8 14 wt which appears responsible for early low temperature generation of heavy sulfur rich petroleum due to the lower energy required to break carbon sulfur bonds compared to carbon carbon bonds hydrous pyrolysis was used to simulate the natural generation of petroleum from a sulfur rich type ii kerogen from the phosphatic member of the monterey shale the amount and distribution of sulfur in the kerogen bitumen and expelled oil generated at various temperatures indicate that 1 initial bitumen and oil generation is directly related to cleavage of weak sulfur linkages and 2 most of the expelled oil is formed by decomposition of bitumen and not directly from the kerogen finally comparison of hydrous pyrolysis results with other type ii kerogens suggests that the temperature of peak bitumen generation is inversely related to the heteroatom content primarily sulfur of the kerogen low temperature bitumen generation is an important exploration concept because kerogen rich in sulfur can generate producible oil at thermal maturities significantly below conventionally accepted values furthermore established relationships between thermal maturity sulfur content and other oil properties such as api gravity can be used to rank exploration prospects

short term biomarker variability in the monterey formation santa maria basin abstract forty eight samples of a 370 ft miocene monterey formation core from the union leroy 51 18 well santa maria basin california are examined for source rock potential and molecular distributions total organic carbon content rock eval pyrolytic yield vitrinite reflectance and distribution of regular steranes tricyclic and pentacyclic terpanes and aromatic steroids are measured the present day temperature range through the sampled interval is estimated to be less than 5 c maturity differences among samples are negligible source rock potential and molecular distribution differences are considered to arise entirely from the effects of source input diagenesis including lithologic effects and migration the sampled section is comprised of siliceous and phosphatic carbonate lithofacies and covariances between geochemical parameters source potential and biomarker distribution and lithofacies are recognized several molecular parameters change systematically with depth lithology including ethylcholestane ratios and c 20 and c 22 sterane and hopane epimer ratios the siliceous lithofacies possesses higher moretane hopane tricyclic pentacyclic terpane and sterane terpane ratios and lower mono mono tri aromatic steroid ratios bisnorhopane hopane ratios are up to 40 times higher in the phosphatic carbonate lithofacies than in the siliceous lithofacies increased relative concentrations of aromatic steroids are attributed to sulfur sterol reactions during very early diagenesis whereas increased relative bisnorhopane amounts are considered to result from massive input of specific anaerobic biota although kerogen elemental ratios change abruptly at the lithofacies boundary molecular distributions within the extractable organic matter change gradually beginning about 30 ft 9m above this interface this gradual change is tentatively attributed to upward migration of hydrocarbons originating in the phosphatic carbonate lithofacies probably through fractures within the lower part of the siliceous lithofacies interval

organic geochemistry of dsdp site 467 offshore california middle miocene to lower pliocene strata abstract results of the analyses of twenty three samples from the middle miocene to lower pliocene strata from dsdp site 467 offshore california are presented the analyses were performed with the aim of determining the origin of the organic matter the stratigraphic section s hydrocarbon generation potential and extent of organic diagenesis organic carbon contents are an order of magnitude greater than those typically found in deep sea sediments suggesting an anoxic depositional environment and elevated levels of primary productivity hydrocarbon generation potentials are above average for most samples the results of elemental analyses indicate that the kerogens are primarily composed of type ii organic matter and are thermally immature analysis of the bitumen fractions confirms that the samples are immature in cores from 541 to 614 meters the gas chromatograms of the c 15 non aromatic hydrocarbon fractions are dominated by a single peak which was identified as 17 h 18 h 21 h 28 30 bisnorhopane this interval is the same area in which the highest degrees of anoxia are observed as reflected by the lowest pristane phytane ratios this correlation may have some implications with regard to the origin of the bisnorhopane and its possible use as an indicator of anoxic depositional conditions within thermally immature sediments

the coordination and distribution of b in foraminiferal calcite the isotopic ratio and concentration of b in foraminiferal calcite appear to reflect the ph and bicarbonate concentration of seawater the use of b as a chemical proxy tracer has the potential to transform our understanding of the global carbon cycle and ocean acidification processes however discrepancies between the theory underpinning the b proxies and mineralogical observations of b coordination in biomineral carbonates call the basis of these proxies into question here we use synchrotron x ray spectromicroscopy to show that b is hosted solely as trigonal bo3 in the calcite test of amphistegina lessonii and that b concentration exhibits banding at the micron length scale in contrast to previous results our observation of trigonal b agrees with the predictions of the theoretical mechanism behind b palaeoproxies these data strengthen the use of b for producing palaeo ph records the observation of systematic b heterogeneity however highlights the complexity of foraminiferal biomineralisation implying that b incorporation is modulated by biological or crystal growth processes

core top calibration of b ca in pacific ocean neogloboquadrina incompta and globigerina bulloides as a surface water carbonate system proxy abstract practical methods for reconstructing past ocean carbonate chemistry are needed to study past periods of ocean acidification and improve understanding of the marine carbonate system s role in the global climate cycles planktic foraminiferal b ca may fill this role but requires better understanding and improved proxy calibrations we used pacific ocean core top sediments to generate new calibrations of the b ca proxy for past carbonate system parameters in two upwelling subpolar species of asymbiotic planktic foraminifera globigerina bulloides and neogloboquadrina incompta both species show significant positive correlation of b ca with calcite saturation calcite and carbonate ion concentration co 3 2 across a broad range of environmental conditions this suggests a calcification rate control on b ca incorporation as calcite regulates calcification rate in agreement with recent inorganic calcite studies this is also consistent with a surface entrapment model of trace element incorporation into caco3 in neither species is b ca significantly correlated with ph suggesting that ph does not directly regulate boron incorporation and that calculation of ph directly from foraminiferal b ca is not suitable correlations between b ca and b oh 4 b oh 4 hco3 and b oh 4 dic are weaker than with calcite boron partition coefficients k d b ca solid b oh 4 hco 3 seawater show little or no correlation with co32 or temperature and vary widely providing no support for application of kd to calculate carbonate system parameters from b ca we also discuss potential effects of depth related dissolution temperature and salinity on b ca these empirical calibrations linking foraminiferal calcite b ca with calcite provide a strong tool for reconstructing the past ocean carbonate system and improve our understanding of the proxy s geochemical basis

the universal ratio of boron to chlorinity for the north pacific and north atlantic oceans abstract we report seawater boron concentration mg kg 1 and chlorinity values measured in seawater samples n 139 collected at various depths in the north pacific and north atlantic oceans and the east japan sea located in the western temperate north pacific our results indicate that variations in seawater boron concentration are strongly coupled to variations in chlorinity and salinity yielding a mean boron to chlorinity ratio of 0 2414 0 0009 mg kg 1 1 boron to salinity ratio 0 1336 0 0005 mg kg 1 1 this ratio was surprisingly universal throughout the water column in the three marine basins and across widely different ocean surface regimes but differs from the generally accepted ratio of 0 232 0 005 mg kg 1 1 determined by uppstrom 1974 which was based on only 20 measurements at four sites in the tropical pacific ocean in converting total alkalinity to carbonate alkalinity and vice versa for thermodynamic calculations the difference between these two ratios leads to a difference of 5 mol kg 1 in estimates for ocean surface waters where the contribution of borate to total alkalinity is typically greatest we suggest the use of the new boron to chlorinity ratio for predicting seawater boron concentrations using chlorinity or salinity data

evaluating the utility of b ca ratios in planktic foraminifera as a proxy for the carbonate system a case study of globigerinoides ruber b ca ratios in foraminifera have attracted considerable scientific attention as a proxy for past ocean carbonate system however the carbonate system controls on b ca ratios are not straightforward with inline image inline image in situ inline image at saturation correlating best with b ca ratios in benthic foraminifera rather than ph inline image or inline image as a simple model of boron speciation in seawater and incorporation into caco3 would predict furthermore culture experiments have shown that in planktic foraminifera properties such as salinity and b sw can have profound effects on b ca ratios beyond those predicted by simple partition coefficients here we investigate the controls on b ca ratios in g ruber via a combination of culture experiments and core top measurements and add to a growing body of evidence that suggests b ca ratios in symbiont bearing foraminiferal carbonate are not a straightforward proxy for past seawater carbonate system conditions we find that while b ca ratios in culture experiments covary with ph in open ocean sediments this relationship is not seen in fact our b ca data correlate best with inline image a previously undocumented association and in most regions salinity these findings might suggest a precipitation rate or crystallographic control on boron incorporation into foraminiferal calcite regardless our results underscore the need for caution when attempting to interpret b ca records in terms of the ocean carbonate system at the very least in the case of mixed layer planktic foraminifera

rapid analysis of high precision sr ca ratios in corals and other marine carbonates a method for rapid determination of high precision sr ca ratios in scleractinian corals is presented using an inductively coupled plasma atomic emission spectrophotometer samples are corrected for instrument drift using a reference solution similar to the approach used for analysis of stable isotopes using gas source mass spectrometry further correction for variation of the sr ca ratio with ca concentration is accomplished using internal standards the precision once all corrections have been made is better than 0 1 relative standard deviation 1 for samples of similar ca concentration and better than 0 2 for samples with variable ca concentrations this method increases the sample throughput by approximately a factor of 20 relative to thermal ionization mass spectrometry and significantly reduces instrument and per sample costs comparison of sr ca data for a coral from the galapagos islands with an instrumental temperature record shows excellent agreement and demonstrates the potential for application of this technique to samples of modern and fossil scleractinian corals and other marine carbonates including foraminifera

the relationship between shell size and mg ca sr ca δ18o and δ13c of species of planktonic foraminifera the relationship between shell size and mg ca sr ca 18o and 13c of planktonic foraminiferal calcite has been investigated using seventeen species in six different size fractions mg ca increases and sr ca decreases with increasing size except for two globorotaliid species which show the opposite trend the changes in mg ca broadly follow 18o calcification temperatures except that surface and near surface dwelling species show larger changes in mg ca than can be accounted for by differences in calcification temperature derived from 18o the increases in mg ca and decreases in sr ca vary linearly with the well established increase in 13c with size this is consistent with smaller individuals calcifying faster than larger individuals and larger individuals forming calcite that more closely reflects seawater temperature and composition it appears that variations in calcification rate affect mg and sr shell chemistry the observations may account for part of the temporal variability in foraminiferal sr ca within a single size fraction that has been attributed to changes in seawater sr ca

a new boron isotope ph calibration for orbulina universa with implications for understanding and accounting for vital effects boron isotope ratios as measured in planktic foraminifera can be a useful tracer of past ocean ph and hence help to discern the concentration of co2 in the ancient atmosphere however different species of planktic foraminifera demonstrate different patterns of boron isotope variation with ambient seawater ph therefore when applying the proxy to questions in the geological past species specific calibrations are preferable beyond the evolutionary history of a calibrated species we must rely on our understanding of the causes of the observed vital effects in the modern ocean and the applicability of that understanding to extinct species here we present a new open ocean calibration of the planktic foraminifera orbulina universa measured via multi collector inductively coupled mass spectrometry mc icpms unlike other symbiont bearing foraminifera o universa record a 11b 11b and hence ph that is lower than its surrounding seawater but with a ph sensitivity roughly equal to that of aqueous borate ion we discuss the significance of this for application of the boron isotope proxy in deep time with recommendations for best practice and future research directions

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

carbon isotope composition of tropical surface water during the past 22 000 years carbon isotope values of many species of planktonic foraminifera are size dependant values of 13c of individual size fractions are therefore an integration of low 13c values of calcite precipitated in the juvenile growth stage and high values precipitated in later stages in general the selection of a particular size fraction for downcore studies has been subjective analysis of different size fractions of planktonic foraminifera however yields different time series in downcore studies by measuring the 13c of many size fractions the 13c precipitated throughout the growth of the foraminifera can be calculated time series of the 13c of calcite precipitated in the late growth stages of planktonic foraminifera from two nearby cores from the caribbean sea result in a better correlation than time series of constant size fractions these 13c records indicate similar 13c values during the last glaciation and the late holocene and a broad deglacial minimum approximately synchronous with a minimum in the 13c records of benthic foraminifera from intermediate depth atlantic cores the deglacial minimum may be a reflection of the isotopic composition of the underlying intermediate water which may be affected by circulation changes or changes in preformed 13c values and or of the flux of water upwelled into the surface layer the small 0 2 to 0 0 glacial interglacial 13c difference in tropical surface water is also believed to be affected by the chemistry of the underlying source water

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

present water mass calcium carbonate corrosiveness in the eastern south atlantic inferred from ultrastructural breakdown of globigerina bulloides in surface sediments abstract the atlantic is regarded as a huge carbonate depocenter due to an on average deep calcite lysocline however calculations and models that attribute the calcite lysocline to the critical undersaturation depth hydrographic or chemical lysocline and not to the depth at which significant calcium carbonate dissolution is observed sedimentary calcite lysocline strongly overestimate the preservation potential of calcareous deep sea sediments significant calcium carbonate dissolution is expected to begin firstly below 5000 m in the deep guinea and angola basin and below 4400 m in the cape basin our study that is based on different calcium carbonate dissolution stages of the planktic foraminifera globigerina bulloides clearly shows that it starts between 400 and 1600 m shallower depending on the different hydrographic settings of the south atlantic ocean in particular coastal areas are severely affected by increased supply of organic matter and the resultant production of metabolic co2 which seems to create microenvironments favorable for dissolution of calcite well above the hydrographic lysocline

frontal part of the northern apennines fold and thrust belt in the romagna marche area italy shallow and deep structural styles in this study surface geological data resulting from a detailed field survey including structural and biostratigraphic analysis have been integrated with subsurface seismic lines and well logs data in order to reconstruct the tectonic evolution of the external zones of the northern italian apennines in the romagna marche foothills and adriatic sea areas this integrated analysis shows 1 a late messinian to lower pleistocene progression of structural development from the hinterland to the foreland of the studied sector of the thrust belt 2 relatively limited 20 southward increasing amounts of shortening obtained by the construction of line length balanced and restored geological cross sections 3 a regional deformation style characterized by the presence of backthrusts associated with most foreland vergent thrust ramps leading to quasi symmetric uplift and a low critical taper for the wedge typical of foreland fold and thrust belts with a weak basal decollement triassic anhydrites in the present case 4 an important influence of basement faulting which despite a general basement cover decoupling appears to control stress localization in the latter producing linkage of basement and cover stuctures in a combination of thin and thick skinned tectonic styles and 5 contrasting structural styles characterizing deep features as imaged by seismic reflection profiles and shallow ones deep stuctures consist of growth anticlines bounded by major thrust ramps and back limb back thrusts separated by broader open synclines both involving a mesozoic paleogene mainly carbonate passive margin succession in the crestal zones of major anticlines shallow structures affecting neogene terrigenous foredeep sediments show a complex pattern of upright to recumbent folds of tens to hundreds of meters wavelength related to minor thrusts and backthrusts deformation of the mesozoic paleogene multilayer appears to be dominated by thrust propagation in the cores of early formed anticlines developed by buckling instabilities the overlying neogene deposits are detached from the carbonate substratum along the base of the foredeep succession bedding parallel slip occurring along this detachment level appears to be accommodated by the complex structures in the crests of major anticlines where the thrusts lramp to the surface cutting up section complex shallow structures interpreted to accommodate at shallow structural levels the deep deformation would therefore represent a geometrical requirement for maintaining strain compatibility across the shallow detachment level located at the base of the foredeep succession

a comparative study of the northwest africa and eastern equatorial pacific upwelling zones as sources of co2 during glacial periods based on boron isotope paleo ph estimation paleo ph reconstructions based on boron isotopic composition of foraminifera have been used to estimate glacial interglacial changes in surface ocean pco2 of the northwest african upwelling zone on comparison with a similar study for the eastern equatorial pacific upwelling zone it can be concluded that the two major upwelling zones acted quite differently during the glacial periods as compared to today while the ph of the surface ocean off northwest africa was 0 2 0 07 units higher during the glacial period compared to that during holocene there was no significant glacial interglacial change in the surface ocean ph in the eastern equatorial pacific carbonate chemistry reconstructions based on the estimated ph changes suggest that the ocean atmosphere pco2 gradient off northwest africa was lower by at least 70 40 atm during glacial periods compared to during the holocene in contrast the ocean atmosphere pco2 gradient in the eastern equatorial pacific was higher by at least 80 40 atm during glacial periods as compared to during the holocene hence the eastern equatorial pacific upwelling system was a significantly larger source of co2 to the atmosphere while the one off northwest africa was a significantly smaller source of co2 during the last glacial period the pco2 reconstructions further indicate that in spite of higher glacial productivity compared to during the holocene neither of the two areas became a sink of co2

carbon isotopic compositions of 28 30 bisnorhopanes and other biological markers in a monterey crude oil abstract an immature tar like oil api 3 13 c 23 6 vs pdb from the miocene monterey formation offshore california was selected for a study of carbon isotopic signatures of individual biomarkers the three principal stereoisomers of 28 30 bisnorhopane c 28 have within analytical precision identical carbon isotopic compositions average 13 c 32 3 0 4 and are considerably depleted in 13 c compared to the whole oil these 28 30 bisnorhopanes bnh differ isotopically from c 29 and c 30 17 h hopanes 25 8 and 26 1 and c 31 c 35 extended hopanes 13 c 27 7 and suggest different precursors for the c 28 hopanes than for c 29 c 35 hopanes the relative depletion of bnh of almost 9 compared to the isotopic composition of the whole oil suggests that these hopanes derive from chemoautotrophic bacteria possibly not yet identified h 2 s oxidizers which utilize 13 c depleted substrates the c 29 and c 30 hopanes are within analytical precision isotopically identical 26 and similar to algal derived compounds e g c 27 steranes 25 9 which is consistent with a cyanobacterial source for these hopanes an archaebacterial biomarker 1 1 biphytane 13 c 25 5 likely derived from methanogens is also isotopically similar to c 27 sterane norpristane pristane and phytane liberated by desulfurization of the aromatic and polar maltene fractions show isotopic compositions similar to the same isoprenoids in the free lipids of the bitumen total range from 24 5 to 27 5 this isotopic similarity supports a common origin for the free and sulfur bound forms of these isoprenoids this origin could be algal and or archaebacterial lipids which both show isotopic compositions within the range of the c 18 c 20 isoprenoids like other marine derived organic matter this monterey oil does not show the strong 13 c depletion typical for methylotroph derived compounds characteristically found in organic matter of lacustrine origin this may indicate fundamental differences of methane recycling processes in marine sulfate dominated as compared to lacustrine environments

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

geochemical characteristics of tertiary oils derived from siliceous sources in japan russia and u s a abstract siliceous sourced tertiary oils from the circum pacific area of japan russia and the u s a have a heavy carbon isotope composition monomodal n alkane distributions and nearly identical regular sterane compositions with a predominance of c 27 homologues these are consistent with open marine depositional environments dominated by diatomaceous organic matter however a number of alkane and biomarker parameters such as pr ph cpi relative concentration of 28 30 bisnorhopane and the c 35 c 34 homohopane ratio indicate more oxic depositional environments for the source rocks of japan and russia in contrast to the california monterey formation sourced oils petroleums with low maturity levels from the north sakhalin basin russia and the akita basin japan have lower concentrations of asphaltenes and sulphur and are characterized by higher api gravities a correlation of extractable organic matter from source rocks vs the least matured petroleums demonstrates that oil expulsion in siliceous shales of the akita basin occurs at a maturity level corresponding to r o 0 65 which is in the range of the conventional oil window r o 0 6 1 1

a novel microbial hydrocarbon degradation pathway revealed by hopane demethylation in a petroleum reservoir abstract the origin of 25 norhopanes is controversial despite their abundance in many biodegraded oils in a biodegraded oil reservoir we found concomitant and directionally opposite changes with depth in the concentrations of certain 17 hopanes and their 17 25 norhopane counterparts demonstrating microbially induced demethylation of hopanes these observations suggest a hitherto unknown biodegradation mechanism and provide insight into the poorly understood process of natural petroleum biodegradation

calibration of the boron isotope proxy in the planktonic foraminifera globigerinoides ruber for use in palaeo co2 reconstruction abstract the boron isotope ph proxy applied to mixed layer planktic foraminifera has great potential for estimating past co2 levels which in turn is crucial to advance our understanding of how this greenhouse gas influences earth s climate previous culture experiments have shown that although the boron isotopic compositions of various planktic foraminifera are ph dependent they do not agree with the aqueous geochemical basis of the proxy here we outline the results of culture experiments on globigerinoides ruber white across a range of ph 7 5 8 2 and analysed via multicollector inductively coupled plasma mass spectrometry mc icpms and compare these data to core top and sediment trap samples to derive a robust new species specific boron isotope ph calibration consistent with earlier culture studies we show a reduced ph dependency of the boron isotopic composition of symbiont bearing planktonic foraminifera compared to borate ion in seawater we also present evidence for a size fraction effect in the 11b of g ruber finally we reconstruct atmospheric co2 concentrations over the last deglacial using our new calibration at two equatorial sites odp site 999a and site geob1523 1 these data provide further grounding for the application of the boron isotope ph proxy in reconstructions of past atmospheric co2 levels

experimental measurement of boron isotope fractionation in seawater abstract the boron isotopic composition of marine carbonates is considered to be a tracer of seawater ph use of this proxy benefits from an intimate understanding of chemical kinetics and thermodynamic isotope exchange reactions between the two dominant boron bearing species in seawater boric acid b oh 3 and borate ion b oh 4 however because of our inability to quantitatively separate these species in solution the degree of boron isotope exchange has only been known through theoretical estimates in this study we present results of a spectrophotometric procedure wherein the boron isotope equilibrium constant 11 10 k b is determined empirically from the difference in the dissociation constants of 11 b oh 3 and 10 b oh 3 in pure water 0 6 mol kg 1 h 2 o kcl and artificial seawater within experimental uncertainty our results show no dependence of 11 10 k b on temperature but 11 10 k b at 25 c in pure water was statistically different than results obtained in solutions at high ionic strength 11 10 k b of the seawater s 35 b t 0 01 mol kg 1 h 2 o at 25 c is 1 0272 0 0006 this result is significantly larger than the theoretical value used in numerous paleo ph studies 11 10 k b 1 0194

biomarkers in tertiary melange western olympic peninsula washington u s a abstract middle eocene to middle miocene melange and broken formations are exposed in the coastal outcrops along the west side of the olympic peninsula washington a petroleum geochemical assessment of these geologic units has included the investigation of biomarker compounds a comparison was made of biomarkers in an oil sample from a middle miocene reservoir penetrated in the medina no 1 well with biomarkers in extracts from two samples of middle eocene ozette melange one sample having a strong petroliferous odor and the other sample lacking this characteristic odor distribution patterns of n alkanes tricyclic terpanes pentacyclic triterpanes steranes and diasteranes are remarkably similar in the oil and rock extracts biomarker maturity parameters indicate higher maturity in the oil relative to the extracts the presence of 17 h 23 28 bisnorlupane 18 h and 18 h oleanane and de a lupane and an odd carbon number dominance of the n alkanes in the oil and extracts seems to tie the hydrocarbons to a common source that has a significant terrigenous component

the petroleum geochemistry of the termit basin eastern niger abstract sixty crude oils from the termit basin eastern niger were analysed using biomarker distributions and bulk stable carbon isotopic compositions comprehensive oil to oil correlation indicates that there are two distinct families in the termit basin the majority of the oils are geochemically similar and characterized by low pr ph pristane to phytane ratios and high gammacerane c 30 hopane ratios small amounts of c 24 tetracyclic terpanes but abundant c 23 tricyclic terpane and lower 13 c values for saturated and aromatic hydrocarbon fractions all of these geochemical characteristics indicate possible marine sources with saline and reducing depositional environments in contrast oils from well dd 1 have different geochemical features they are characterized by relatively higher pr ph and lower gammacerane c 30 hopane ratios higher amounts of c 24 tetracyclic terpane but a low content of c 23 tricyclic terpane and relatively higher 13 c values for saturated and aromatic hydrocarbon fractions these geochemical signatures indicate possible lacustrine sources deposited under freshwater suboxic oxic conditions this oil family also has a unique biomarker signature in that there are large amounts of c 30 4 methylsteranes indicating a freshwater lacustrine depositional environment the maturity of the termit oils is assessed using a number of maturity indicators based on biomarkers alkyl naphthalenes alkyl phenanthrenes and alkyl dibenzothiophenes all parameters indicate that all of the oils are generated by source rocks within the main phase of the oil generation stage with equivalent vitrinite reflectance of 0 58 0 87

b ca in planktonic foraminifera as a proxy for surface seawater ph boron isotope systematics indicate that boron incorporation into foraminiferal caco3 is determined by the partition coefficient k d frac left rm b rm ca right rm caco3 left rm b left rm oh right 4 rm hco 3 right rm seawater and b oh 4 hco3 seawater providing in principle a method to estimate seawater ph and pco2 we have measured b ca ratios in globigerina bulloides and globorotalia inflata for a series of core tops from the north atlantic and the southern ocean and in globigerinoides ruber white from ocean drilling program odp site 668b on the sierra leone rise in the eastern equatorial atlantic b ca ratios in these species of planktonic foraminifera seem unaffected by dissolution on the seafloor k d shows a strong species specific dependence on calcification temperature which can be corrected for using the mg ca temperature proxy a preliminary study of g inflata from southern ocean sediment core chat 16k suggests that temperature corrected b ca was 30 higher during the last glacial correspondingly ph was 0 15 units higher and aqueous pco2 was 95 atm lower at this site at the last glacial maximum the covariation between reconstructed pco2 and the atmospheric pco2 from the vostok ice core demonstrates the feasibility of using b ca in planktonic foraminifera for reconstructing past variations in ph and pco2

seismic stratigraphy of camamu basin northeastern brazil the camamu basin is located at the northeastern brazilian coastline and has significant hydrocarbon potential in both shallow and deep water settings however despite an already operating productive gas field the basin is not well known herein a regional stratigraphic interpretation of the rift the transitional and the drift megasequences is reported based on a data set of 152 post stacked 2d seismic lines 1 3d seismic cube and 34 wells with eletro logs the study revealed that the rift megasequence is much more complex than previously thought in the southern region of the camamu basin five rift sequences were mapped while in the northern region in the area of the regional tectonic lineament known as the salvador transcurrent zone stz seven rift sequences were recognized this difference suggests a tectonic control during the rifting process because the northern region is intensely affected by shear stress induced by transcurrent tectonics of the stz during the crustal breakup for the post rift or transitional phase associated with thermal subsidence installed after the rift as well as for the drift succession the tectonic control exerted by salvador s transcurrent zone is not detectable and the tectono sedimentary evolution of the basin follows the general pattern of the brazilian marginal basins

biomarker distributions in oils from the akita and niigata basins japan abstract oils from the akita and niigata basins japan are characterized by the predominance of c 15 c 17 alkanes pristane phytane ratio 27 regular steranes and the presence of c 26 steranes these are consistent with the marine depositional environment of the source rocks however geochemical parameters for the niigata basin petroleums show higher terrestrial input and are characterized by enhanced concentrations of oleanane tetracyclic terpane and c 29 steranes abundances of diasteranes in oils are controlled both by maturation and lithology of source rocks comparatively low concentrations of diasteranes in the akita oils can be attributed to the low abundance of clay minerals in their siliceous source rocks oils from the akita and niigata basins can be well discriminated on the basis of geochemical indicators using factor analysis evaluation of maturity levels of oils from the akita basin shows that oil expulsion occurred at lower maturity levels in siliceous shales than in argillites in the niigata basin

reconstructing past ocean ph depth profiles measurement of boron isotope compositions in species of planktonic foraminifera that calcified their tests at different depths in the water column are used to reconstruct the ph profile of the upper water column of the tropical ocean results for five time windows from the middle miocene to the late pleistocene indicate ph depth profiles similar to that of the modern ocean in this area which suggests that this method may greatly aid in our understanding of the global carbon cycle

biomarker geochemistry of the miocene monterey formation west san joaquin basin california implications for petroleum generation abstract much of the miocene monterey formation of california is rich in biogenic sediment especially organic matter and silica because of the geologic structure the monterey in the subsurface near lost hills in the san joaquin basin forms a natural laboratory for the study of the diagenetic responses of these materials rocks of similar age and lithology are buried to depths ranging between 500 and 3500 m and are thus exposed to a temperature range of 45 130 c the diagenetic progression of silica from opal a to opal ct to microquartz is well documented in monterey burial history studies however diagenetic indicators need to be established below the depth of complete conversion of opal ct to quartz which may be very shallow 1500 m or less at lost hills conventional maturity indicators are problematic the scarcity of vitrinite in many monterey samples hampers reflectance measurements in addition values that are measured may be anomalously low maximum pyrolysis temperatures are depressed due in part to high heavy bitumen content biomarker geochemistry provides effective alternative maturity indicators of particular interest are the stereochemical variations observed in the assemblages of steranes and triterpanes extracted from oil well core samples for example the 20s 20r ratio of 5 h 14 h 17 h 24 ethylcholestane increases from 0 09 to 0 56 over the depth range cited samples from petroleum accumulation zones are distinguished by anomalously mature biomarker assemblages considering their depth of burial this indicates that these bitumens are as mature as the deepest non production zone sample 3430 m even though they are from much shallower depths 580 1572 m other maturity and or migration indicators confirm this such as the relative increases in amounts of 14 h 17 h steranes rearranged steranes and tricyclic terpanes thus it appears that any immature indigenous bitumen in production zone samples is overwhelmed by a mature component which presumably migrated updip from deeper warmer strata since much oil is produced from shallow organic rich fractured monterey shales early in situ generation has previously been hypothesized however while both source and reservoir rock are lithologically similar and lie within the same formation biomarker geochemistry indicates that substantial generation occurs only in deeply buried monterey shales

norcholestane in miocene onnagawa siliceous sediments japan abstract a significant amount of 24 norcholestane with 20r 5 h 14 h 17 h stereochemistry is often found in marine siliceous sediments of the middle miocene onnagawa formation japan some onnagawa siliceous sediments are abnormally abundant in 24 norcholestane the primary production in the northeastern japan sea during the middle miocene was markedly increased due to the invasion of nutrient rich cold seawater from the north accompanied by the tectonic opening of the japan sea 24 norcholestane in high relative abundance is derived mainly from the marine diatoms which were enhanced during this event the drastic ecological change caused by rapid tectonic opening of the japan sea and global climatic deterioration during middle miocene time is suggested to be influential in the formation of 24 norcholestane rich onnagawa siliceous sediments

vital effects and beyond a modelling perspective on developing palaeoceanographical proxy relationships in foraminifera this paper primarily reviews our recent work on the biology and geochemistry of foraminifera with respect to their use as paleoceanographic proxies our approach to proxy validation and development is described primarily from a modeler s point of view the approach is based on complementary steps in understanding the inorganic chemistry inorganic isotope fractionation and biological controls that determine paleo tracer signals in organisms used in climate reconstructions integration of laboratory experiments field and culture studies theoretical considerations and numerical modeling holds the key to the method s success we describe effects of life processes in foraminifera on stable carbon oxygen and boron isotopes as well as mg incorporation into foraminiferal calcite shells stable boron isotopes will be used to illustrate our approach we show that a mechanism based understanding is often required before primary climate signals can be extracted from the geologic record because the signals can be heavily overprinted by secondary non climate related phenomena moreover for some of the proxies fundamental knowledge on the thermodynamic inorganic basis is still lacking one example is stable boron isotopes a paleo ph proxy for which the boron isotope fractionation between the dissolved boron compounds in seawater was not precisely known until recently attempts to overcome such hurdles are described and implications of our work for paleoceanographic reconstructions are discussed

la mc icp ms study of boron isotopes in individual planktonic foraminifera a novel approach to obtain seasonal variability patterns abstract boron isotope 11b analysis using bulk foraminifera samples is a widely used method to reconstruct paleo sea water ph conditions although these analyses exhibit high analytical precision short term information is lost due to the pooling of tests with distinct and diverse boron isotope signatures resulting in average values for the time interval encompassed in the sample here we present and assess the analysis of 11b of individual foraminifera by means of laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms to obtain seasonal variability patterns and to test the limits of precision of la mc icp ms on the planktonic foraminifera orbulina universa the results show that relative seasonal differences of 11 can be captured from either uncleaned or cleaned individual o universa tests with an average precision of 2 9 2 se the 11b variability among foraminifera representing the same season is on average 7 4 2 sd irrespective of cleaning state with our approach analyses on oxidatively cleaned o universa do not require the use of a matrix matched standard to obtain b isotope values in the range of those expected for solution multi specimen analyses our results are useful for considering the potential spread caused by foraminifera vital effects and for obtaining information of seasonal ranges of ph and possible bias related to seasonality hidden within conventional solution based 11b analyses

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

changing atmospheric co2 concentration was the primary driver of early cenozoic climate the early eocene climate optimum eeco which occurred about 51 to 53 million years ago was the warmest interval of the past 65 million years with mean annual surface air temperature over ten degrees celsius warmer than during the pre industrial period subsequent global cooling in the middle and late eocene epoch especially at high latitudes eventually led to continental ice sheet development in antarctica in the early oligocene epoch about 33 6 million years ago however existing estimates place atmospheric carbon dioxide co2 levels during the eocene at 500 3 000 parts per million and in the absence of tighter constraints carbon climate interactions over this interval remain uncertain here we use recent analytical and methodological developments to generate a new high fidelity record of co2 concentrations using the boron isotope 11 b composition of well preserved planktonic foraminifera from the tanzania drilling project revising previous estimates although species level uncertainties make absolute values difficult to constrain co2 concentrations during the eeco were around 1 400 parts per million the relative decline in co2 concentration through the eocene is more robustly constrained at about fifty per cent with a further decline into the oligocene provided the latitudinal dependency of sea surface temperature change for a given climate forcing in the eocene was similar to that of the late quaternary period this co2 decline was sufficient to drive the well documented high and low latitude cooling that occurred through the eocene once the change in global temperature between the pre industrial period and the eocene caused by the action of all known slow feedbacks apart from those associated with the carbon cycle is removed both the eeco and the late eocene exhibit an equilibrium climate sensitivity relative to the pre industrial period of 2 1 to 4 6 degrees celsius per co2 doubling 66 per cent confidence which is similar to the canonical range 1 5 to 4 5 degrees celsius indicating that a large fraction of the warmth of the early eocene greenhouse was driven by increased co2 concentrations and that climate sensitivity was relatively constant throughout this period

tectonic systems tract and depositional architecture of the western border of the triassic iberian trough central spain abstract during the permian and triassic a sedimentary wedge developed overlying a listric normal fault on the western border of the iberian trough central spain an area was selected for study that provides optimal conditions for a detailed analysis to be made of relationships between geometric strata arrangements tectonic control and sedimentary responses the excellent quality of the outcrops allows the observed patterns of strata to be related to fault growth and developmental of the basin the recognition and mapping of local discontinuities throughout the study area were possible packages of similar strata with different angularity can be discerned between the two main discontinuities geometrical relationships can be established for depositional unit boundaries the architectural style and sediment dispersal patterns interpreted as the results of interactions between sedimentation and tectonics are integrated into a three dimensional tectono sedimentary facies model to explain the basin s infilling is interpreted to be tectonic the rift related three dimensionally linked depositional systems recognized might be defined as tectonic systems tract prosser s 1993 rift related linked depositional systems and their seismic expression in williams g d dobb a eds tectonics and seismic sequence stratigraphy geol soc london spec publ 71 35 66 five such tracts are recognized and related to specific phases of tectonic development

facies distribution as a response to early rift tectonic activity in the sergipe alagoas basin northeastern brazil abstract accommodation rates in rift basins are mainly controlled by tectonics however during early rift stages normal fault activity is dispersed and incipient which makes it difficult to recognize the effects of early crustal extension the sedimentary stacking pattern of rift related depositional environments can be decisive to address this question this paper aimed to evaluate the stratigraphic record of the tithonian berriasian serraria formation sergipe alagoas basin brazil which was deposited in the afro brazilian depression as a result of the early extension of west gondwana in total 14 lithofacies were described interpreted and arranged into 7 facies associations at the base of the formation bars and sand sheets were deposited by low discharge braided channels which were deposited on top of lacustrine mudstones of the bananeiras formation there is a change in stratigraphic architecture in the middle of the section where fluvial channels become deeper due to increasing discharge promoting an increase in grain size of the transported bedload and greater rates of coarse sand and gravel bar stacking rare crevasse channels and restricted aeolian dune fields occur adjacent to braided channel belts upwards the serraria formation becomes dominated by delta front and delta plain deposits the fluvial and aeolian facies associations represent a progressive decrease in accommodation while the upper fluvio deltaic interval means an increase in accommodation pointing to the early rift stage climax the fluvial caioba sandstone on top of the serraria formation indicates reestablishment of fluvial drainage either due to decreasing tectonism or due to low accommodation at the time of deposition thus the sedimentary stacking pattern of serraria formation represents higher frequency cycles within an early rift tectonic system tract

mg ca thermometry in planktic foraminifera improving paleotemperature estimations for g bulloides and n pachyderma left planktic foraminiferal mg ca ratios have become a fundamental seawater temperature proxy in past climate reconstructions due to the temperature dependence of mg uptake into foraminiferal calcite however empirical calibrations for single species from methodologically consistent data are still lacking here we present species specific calibrations of mg ca versus calcification temperature for two commonly used species of planktic foraminifera globigerina bulloides and neogloboquadrina pachyderma left based on a series of southern ocean and north atlantic core tops combining these new data with previously published data we derive an integrated g bulloides mg ca temperature calibration for mid and high latitudes of both hemispheres between 2 and 18 c where mg ca 1 006 0 032 e0 065 0 003 tiso r2 0 82 g bulloides is found to calcify deeper in the southern ocean 200 m than in the north atlantic top 50 m we also propose a mg ca temperature calibration to describe the temperature response in n pachyderma left that calcified away from the influence of sea ice in the southern ocean valid between 1 and 9 c of the form mg ca 0 580 0 016 e0 084 0 006 tiso r2 0 70 these calibrations account for uncertainties on mg ca measurements and calcification temperature that were carefully estimated and propagated using monte carlo iterations the 1 propagated error in mg ca derived temperatures is 1 1 c for g bulloides and 0 9 c for n pachyderma left for the presented data sets geographical extension of genotypes must be assessed when choosing to develop regional or global calibrations

saturate biomarkers and aromatic sulfur compounds in oils and condensates from different source rock lithologies of kazakhstan japan and russia abstract representative petroleums from the seven basins of kazakhstan russia and japan were analyzed using gas chromatography with dual fid fpd and gc ms the present study has shown that the deviation in relative concentrations of aromatic sulfur compounds in petroleums could be related to the type of source rock all oil samples were classified into three groups on the basis of the relative abundance of aromatic sulfur compounds biomarker distribution and lithology of source rock the first group of oils derived from carbonate source rocks is rich in aromatic sulfur compounds such as methylbenzothiophenes mbt and methyldibenzothiophenes mdbt and poor in dibenzothiophene dbt compared to methylated homologs the second group derived from siliceous and siliceous carbonate source rocks contains various types of benzothiophenes and dibenzothiophenes including dbt the third group originating from argillaceous rocks has lower concentrations of aromatic sulfur compounds and especially of methylated benzothiophenes

dynamic processes controlling evolution of rifted basins abstract the extension of the lithosphere controlling the development of rifted basins is driven by a combination of plate boundary forces frictional forces exerted on the base of the lithosphere by the convecting asthenosphere and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system although mantle plumes are not a primary driving force of rifting they play an important secondary role by weakening the lithosphere and by controlling the level of rift related volcanic activity a distinction between active and passive rifting is only conditionally justified the extension of the lithosphere depending on its rate and magnitude and the potential temperature of the asthenosphere can cause by adiabatic decompression partial melting of the lower lithosphere and upper asthenosphere in rift systems the level and timing of volcanic activity is highly variable the lack of volcanic activity implies passive rifting an initial passive rifting stage can be followed by a more active one during which magmatism plays an increasingly important role magmatic destabilization of the moho may account for the frequently observed discrepancy between upper and lower crustal extension factors combined with evidence for thermal thinning of the mantle lithosphere this suggest that the volume of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models the structural style of rifts is controlled by the rheological structure of the lithosphere the availability of crustal discontinuities that can be tensionally reactivated the mode orthogonal or oblique and amount of extension and the lithological composition of pre and syn rift sediments simple shear extension prevails in rifts that subparallel the structural grain of the basement pure shear extension is typical for rifts cross cutting the basement grain pre existing crustal and mantle lithospheric discontinuities contribute to the localization of rift systems the duration of the rifting stage of extensional basins is highly variable stress field changes can cause abrupt termination of rifting in major rift systems progressive strain concentration on the zone of future crustal separation entails abandonment of lateral rifts depending on constraints on lateral block movements crustal separation can be achieved after as little as 9 my and as much as 280 my of rifting activity syn rift basin subsidence is controlled by isostatic adjustment of the crust to mechanical stretching of the lithosphere its magmatic inflation and thermal attenuation of the mantle lithosphere post rift basin subsidence is governed by thermal reequilibration of the lithosphere asthenosphere system deep seated thermal anomalies related to syn rift pull up of the asthenosphere lithosphere boundary have decayed after 60 my by about 65 and after 180 my by about 95 the magnitude of post rift subsidence is a function of the rift induced thermal anomaly and crustal density changes the potential temperature of the asthenosphere and initial water depths intraplate stresses can have an overprinting effect on post rift subsidence stretching factors derived from post rift subsidence analyses must be corrected for such effects

changes in ph in the eastern equatorial pacific across stage 5 6 boundary based on boron isotopes in foraminifera estimates of paleo ph for the eastern equatorial pacific ocean across the oxygen isotopic stage 5 6 boundary have been made based on the boron isotopic composition of planktonic orbulina universa and benthic mixed species foraminifera from core v19 28 the estimated deep ocean ph during the penultimate glacial period was about 0 3 0 1 ph units higher compared to the modern deep ocean this is consistent with previously estimated deep ocean ph changes across the stage l 2 boundary in the western equatorial pacific and tropical atlantic thus arguing against the possibility that the benthic foraminifera analyzed to estimate deep ocean ph changes have been significantly affected by anomalous local environment and or diagenesis the estimated changes in the deep ocean carbonate chemistry require a decoupling of several kilometers between the saturation horizon and the lysocline during the glacial periods though such a decoupling could be achieved by enhanced respiration co2 driven calcite dissolution in sediments during glacial periods it lacks support from the calcite sedimentary records the boron isotopic compositions of planktonic foraminifera on the other hand indicate no significant ph change in the eastern equatorial pacific surface ocean during the glacial interglacial transition this is inconsistent with an expected higher surface ocean ph during the glacial period due to lower atmospheric pco2 and is also in contrast with the previously estimated boron isotope based glacial interglacial ph change of 0 2 0 1 ph units in the western equatorial pacific and tropical atlantic the lack of change in eastern equatorial pacific surface ocean ph between glacial interglacial periods could be attributed to less nutrient utilization efficiency and or enhanced calcite production during glacial periods such a decrease in nutrient utilization efficiency and or increase in calcite production would lead to a greater disequilibrium between the pco2 of eastern equatorial pacific surface ocean and that of the atmosphere making this part of the ocean a greater source of co2 to the atmosphere during glacial periods compared to today

kinetic analysis of california petroleum source rocks by programmed temperature micropyrolysis three california shales were examined by micropyrolysis to determine laboratory pyrolysis kinetics samples from the modelo formation with 6 16 wt s in kerogen monterey formation with 13 58 wt s in kerogen and with 8 88 wt s and 13 16 wt o in kerogen exhibited shift in tmax and principal discrete distribution energies of 54 and 57 51 and 52 and 65 and 59 kcal mol respectively these results are evidence that laboratory decomposition kinetics of high sulfur kerogens and in particular monterey kerogens appear not to be governed by organic sulfur content alone particularly because the kinetic parameters for the 13 16 wt o monterey sample were well outside the range generally seen for type i ii and ii s kerogens and closer to type iii kerogens

core top 14c ages as a function of latitude and water depth on the ontong java plateau radiocarbon measurements on core tops from the ontong java plateau confirm a previous finding by berger and killingley 1982 that at any given water depth cores taken on the equator have higher accumulation rates and younger core top ages than their off equator counterparts further these new results fortify the conclusion by broecker et al 1991 that the increase in core top radiocarbon age with water depth rules out homogeneous dissolution within the pore waters as the dominant mechanism either most of the dissolution must occur prior to burial or it must occur during the first pass through the respiration co2 rich upper pore waters after which the calcite grains become armored against further dissolution a puzzling aspect of this new data set is that despite the sizable difference in accumulation rate the extent of dissolution as measured by either the caco3 content or the ratio of caco3 in the 150 m size fraction to that in the 63 m fraction is no different off than on the equator in order to reconcile the results of this study with those obtained by hales and emerson 1996 using in situ electrodes it is necessary to call upon calcite armoring

biological marker distribution and significance in oils and rocks of the monterey formation california abstract the biological marker distributions of several oils core extracts and solid bitumens of the monterey formation of california have been studied sterane terpane and monoaromatic steroid hydrocarbons were analyzed in samples from the san joaquin los angeles ventura and santa maria basins the sterane patterns of both oils and extracts are characterized by 1 a low relative concentrations of diasteranes 2 b low 20s 20r 5 14 17 ethylcholestane ratios 3 c relatively high concentrations of cholestane vs methyl and ethylcholestane isomers san joaquin basin samples contain significant amounts of the 5 isomer which is generally absent in samples from other basins the carbon number distribution of 5 14 17 20r steranes is similar for all oils regardless of api gravity depth or basin location and is suggestive of open marine depositional conditions for the source material involved 17 h l8 h 21 h 28 30 bisnorhopane is present in almost all samples certain san joaquin basin oils and extracts contain 1 a a series of 25 nor hopanes including 25 28 30 trisnorhopane 2 b a distinctive monoaromatic steroid hydrocarbon distribution 3 c an aliphatic hydrocarbon fraction devoid of n paraffins biological marker characteristics suggest that the monterey oils examined originated early in the maturational sequence from elastics poor source material api gravities of the monterey formation oils examined vary monotonically with 1 a bisnorhopane hopane ratios 2 b aromatized regular sterane ratios and 3 c the concentration of monoaromatized steranes relative to terpanes and regular steranes these oil gravity correlations exist regardless of sample depth or basin location

atmospheric carbon dioxide concentration across the mid pleistocene transition the dominant period of pleistocene glacial cycles changed during the mid pleistocene from 40 000 years to 100 000 years for as yet unknown reasons here we present a 2 1 million year record of sea surface partial pressure of co2 pco2 based on boron isotopes in planktic foraminifer shells which suggests that the atmospheric partial pressure of co2 pco2 was relatively stable before the mid pleistocene climate transition glacial pco2 was approximately 31 microatmospheres higher before the transition more than 1 million years ago but interglacial pco2 was similar to that of late pleistocene interglacial cycles 450 000 years ago these estimates are consistent with a close linkage between atmospheric co2 concentration and global climate but the lack of a gradual decrease in interglacial pco2 does not support the suggestion that a long term drawdown of atmospheric co2 was the main cause of the climate transition

3d seismic analysis of the structure and evolution of a salt influenced normal fault zone a test of competing fault growth models abstract in this paper we determine the structure and evolution of a normal fault system by applying qualitative and quantitative fault analysis techniques to a 3d seismic reflection dataset from the suez rift egypt our analysis indicates that the october fault zone is composed of two fault systems that are locally decoupled across a salt bearing interval of late miocene messinian age the sub salt system offsets pre rift crystalline basement and was active during the late oligocene early middle miocene it is composed of four planar nw se striking segments that are hard linked by n s striking segments and up to 2 km of displacement occurs at top basement suggesting that this fault system nucleated at or more likely below this structural level the supra salt system was active during the pliocene holocene and is composed of four nw se striking listric fault segments which are soft linked by unbreached relay zones segments in the supra salt fault system nucleated within pliocene strata and have maximum throws of up to 482 m locally the segments of the supra salt fault system breach the messinian salt to hard link downwards with the underlying sub salt fault system thus forming the upper part of a fault zone composed of i a single amalgamated fault system below the salt and ii a fault system composed of multiple soft linked segments above the salt analysis of throw distance t x and throw depth t z plots for the supra salt fault system isopach maps of the associated growth strata and backstripping of intervening relay zones indicates that these faults rapidly established their lengths during the early stages of their slip history the fault tips were then effectively pinned and the faults accumulated displacement via predominantly downward propagation we interpret that the october fault zone had the following evolutionary trend i growth of the sub salt fault system during the oligocene to early middle miocene ii cessation of activity on the sub salt fault system during the middle miocene to early pliocene iii stretching of the sub and supra salt intervals during pliocene regional extension which resulted in mild reactivation of the sub salt fault system and nucleation of the segmented supra salt fault system which at this time was geometrically decoupled from the sub salt fault system and iv pliocene to holocene growth of the supra salt fault system by downwards vertical tip line propagation which resulted in downward breaching of the salt and dip linkage with the sub salt fault system the structure of the october fault zone and the rapid establishment of supra salt fault lengths are compatible with the predictions of the coherent fault model although we note that individual segments in the supra salt array grew in accordance with the isolated fault model our study thereby indicates that both coherent and isolated fault models may be applicable to the growth of kilometre scale basin bounding faults furthermore we highlight the role that fault reactivation and dip linkage in mechanically layered sequences can play in controlling the three dimensional geometry of normal faults

surface ocean ph response to variations in pco2 through two full glacial cycles abstract knowledge of past atmospheric pco 2 is important for evaluating the role of greenhouse gases in climate forcing ice core records show the tight correlation between climate change and pco 2 but records are limited to the past 900 kyr we present surface ocean ph and pco 2 data reconstructed from boron isotopes in planktonic foraminifera over two full glacial cycles 0 140 and 300 420 kyr the data co vary strongly with the vostok pco 2 record and demonstrate that the coupling between surface ocean chemistry and the atmosphere is recorded in marine archives allowing for quantitative estimation of atmospheric pco 2 beyond the reach of ice cores

past changes in biologically mediated dissolution of calcite above the chemical lysocline recorded in indian ocean sediments abstract in a deep sea sediment core recovered from a site lying well above the local lysocline several organic geochemical proxies and two different calcite dissolution indicators are compared in order to evaluate the relationship between calcite dissolution and paleoproductivity over the past three glacial interglacial cycles the degree of foraminiferal break up and the caco3 particle size distribution both point to significant periods of dissolution every 22 kyr during glacial stages and substages these dissolution events are concomitant with periods of enhanced primary productivity as indicated by the abundance of several biomarkers alkenones cholesterol brassicasterol keto ol used here to indicate changes in paleoproductivity dissolution fluctuations are highly coherent and in phase with the estimated paleoproductivity variations providing strong evidence that the observed dissolution is due to organic matter remineralization within the sediments rather than to changes in co32 concentration in the overlying water column

ground truthing the boron isotope paleo ph proxy in planktonic foraminifera shells partial dissolution and shell size effects 1 sediment samples from the ontong java plateau in the pacific and the 90 east ridge in the indian ocean were used to investigate whether shell size and early diagenesis affect 11b of the symbiont bearing planktonic foraminifer globigerinoides sacculifer in pristine shells from both study locations we found a systematic increase of 11b and mg ca with shell size shells in the sieve size class 515 865 m revealed 11b values 2 1 to 2 3 higher than shells in the 250 380 m class this pattern is most likely due to differences in symbiont photosynthetic activity and its integrated effect on the ph of the foraminiferal microenvironment we therefore suggest smaller individuals must live at approximately 50 100 m water depth where ambient light levels are lower using the empirical calibration curve for 11b in g sacculifer only shells larger than 425 m reflect surface seawater ph partial dissolution of shells derived from deeper sediment cores was determined by shell weight analyses and investigation of the shell surface microstructure by scanning electron microscopy the 11b in partially dissolved shells is up to 2 lower relative to pristine shells of the same size class in agreement with a relatively higher weight loss in smaller shells samples from the ontong java plateau show a more pronounced dissolution effect than larger shells on the basis of the primary size effect and potential postdepositional dissolution effects we recommend the use of shells that are visually pristine and in the case of g sacculifer larger than 500 m for paleoreconstructions