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Deep-sea carbonates: Reading the carbon-isotope signal

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Abstract

Zusammenfassung Das Kohlenstoff-Isotopensignal in den Tiefseesedimenten spiegelt ein Zusammenspiel wider, das (1) von den globalen Austauschraten des ozeanischen Kohlenstoffreservoirs mit der Biosphäre, den Böden und den Sedimenten gesteuert wird, (2) in dem ein globaler und regionaler Wechsel in der Produktivität des Oberflächenwassers und (3) interne Veränderungen in der Wassermassen-Struktur und -Zirkulation (Becken-zu-Becken-Fraktionierung, Sauerstoffminimumentwicklung) zum Ausdruck kommen, und (4) in dem eine spezifische Fraktionierung hervorgerufen durch die Milieuänderung im Lebensraum der Organismen und/oder ontogenetische Fraktionierung (»Vitaleffekte«) erscheint. Zusätzliche Komplikationen entstehen aus unterschiedlichen Erhaltungsmöglichkeiten. Es ist unmöglich, alle diese verschiedenen Faktoren vollständig zu isolieren. Als Faustregel kann man annehmen, daß langpenodische Signale, die parallel mit Plankton- und Benthosentwicklungen verlaufen, externe globale Fraktionierungstrends widerspiegeln, während kurzzeitige Signale eher an interne Muster gebunden sind (Fraktionierung innerhalb der Wassermassen). Die verschiedenen Möglichkeiten der Interpretation werden an speziellen Fällen diskutiert: am Übergang Pleistozän zu Holozän, an der Veränderung des Kohlenstoffverhältnisses im Messinium und an dem Monerey-Maximum im Miozän.

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... This inference has also been made from the highly diverse Plio-Pleistocene reefs in south-west Florida (Meeder, 1979). In contrast, in the upwelling scenario (scenario 2) increasingly positive δ 18 O reflects surface water cooling in response to upwelling of cool nutrient-rich subsurface waters, while concomitant increasingly positive skeletal δ 13 C documents enhanced organic productivity (Berger and Vincent, 1986). Below, we will discuss the significance of the δ 18 O cycles for a plausible identification of the mechanisms behind the stable isotope record. ...
... Stable isotope evidence found in molluscan shells, however, remains inconclusive with regard to the origin of high productivity Tao and Grossman, 2010). In contrast to earlier work, we use a positive correlation of bulk δ 18 O and bulk δ 13 C as a signature of upwelling (Figs. 3, 10), which documents the combined effects of SST cooling and enhanced organic productivity on skeletal carbonate production (Berger and Vincent, 1986). The δ 13 C in corals is controlled by a number of factors, and the identification of single factors driving z coral δ 13 C is not currently possible (Swart, 1983). ...
... Most important are the activity of the photosymbionts relative to heterotrophic feeding (P / H ratio) and δ 13 C of the DIC in ambient seawater (Klaus et al., 2013;Swart, 1983;Swart et al., 2010). Organic production by zooxanthellae and plankton preferentially consumes 12 C, driving coral skeletal δ 13 C towards more positive values (Berger and Vincent, 1986;Swart, 1983). A positive bulk skeletal δ 13 C will, therefore, reflect either a high longer-term P / H ratio, organic production, or a combination of both, and specimens displaying positive bulk skeletal δ 13 C in conjunction with positive bulk δ 18 O values will correspondingly reflect increased photosymbiont activity during cool years or prolonged upwelling. ...
Article
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The fast growing calcareous skeletons of zooxanthellate reef corals (z corals) represent unique environmental proxy archives through their oxygen and carbon stable isotope composition (δ18O, δ13C). In addition, the accretion of the skeleton itself is ultimately linked to the environment and responds with variable growth rates (extension rate) and density to environmental changes. Here we present classical proxy data (δ18O, δ13C) in combination with calcification records from 15 massive z corals. The z corals were sampled from four interglacial units of the Florida carbonate platform (USA) dated approximately 3.2, 2.9, 1.8 and 1.2 Ma (middle Pliocene to early Pleistocene). The z corals (Solenastrea, Orbicella, Porites) derive from unlithified shallow marine carbonates and were carefully screened for primary preservation suited for proxy analysis. We show that skeletal accretion responded with decreasing overall calcification rates (decreasing extension rate but increasing density) to warmer water temperatures. Under high annual water temperatures, inferred from sub-annually resolved δ18O data, skeletal bulk density was high, but extension rates and overall calcification rates were at a minimum (endmember scenario 1). Maximum skeletal density was reached during the summer season giving rise to a growth band of high density within the annually banded skeletons ("high density band", HDB). With low mean annual water temperatures (endmember scenario 2), bulk skeletal density was low but extension rates and calcification rates reached a maximum, and under these conditions the HDB formed during winter. Although surface water temperatures in the Western Atlantic warm pool during the interglacials of the late Neogene were ∼2°C higher than they are in the present day, intermittent upwelling of cool, nutrient-rich water mitigated water temperatures off south-western Florida and created temporary refuges for z coral growth. Based on the sub-annually resolved δ18O and δ13C records, the duration of the upwelling episodes causing the endmember 2 conditions was variable and lasted from a few years to a number of decades. The episodes of upwelling were interrupted by phases without upwelling (endmember 1) which lasted for at least a few years and led to high surface water temperatures. This variable environment is likely one of the reasons why the coral fauna is dominated by the eurytopic genus Solenastrea, also a genus resistant to high turbidity. Over a period of ∼50 years, the oldest sub annually resolved proxy record available (3.2 Ma) documents a persistent occurrence of the HDB during winter. In contrast, the HDB forms in summer in modern z corals from the Florida reef tract. We suggest this difference should be tested as being the expression of a tendency towards decreasing interglacial upwelling since the middle Pliocene. The number of z coral sclerochronological records for the Plio-Pleistocene is still rather low, however, and requires more data and an improved resolution, through records from additional time slices. Nonetheless, our calcification data from the warm periods of past interglacials may contribute to predicting the effects of future ocean warming on z coral health along the Florida reef tract. The inconsistent timing of the HDB within single coral records or among specimens and time slices is unexpected and contrasts the common practice of establishing chronologies on the basis of the density banding.
... For example, 5^^C of infaunal taxa such as Uvigerina peregrina and Globobulimina ajfinis is much lighter than that of epifaunal taxa such as Cibicides wuellerstorfi. This is because sediment pore-water is enriched in ^^C by decomposition of isotopically light organic matter (Berger and Vincent, 1986;Gooday, 1988;McCorkle et al., 1990). ...
... Infaunal species such as Uvigerina peregrina and Globobulimina ajfinis show much lighter 5'^C than epifaunal species such as Cibicidoides wuellerstorfi, because pore-water is enriched in as a result of decomposition of isotopically light organic matter (Berger and Vincent, 1986;Gooday, 1988;McGorkle et al., 1990). For that reason, it is recommended to use the epifaunal species for characterisation of the bottom-water 5^^G history. ...
... mediterranensis of core SL-31 are separated from each other, suggesting different levels in the sediments (or different offsets for disequilibrium?), since the deeper habitats are known to yield more depleted 6'^C values than the shallower ones (Berger and Vincent, 1986;Gooday, 1988;McCorkle et al., 1990). ...
Thesis
p>Unprecendently high-resolution study, based on oxygen and carbon isotopes and abundances of both benthic and planktonic foraminifera, has been carried out on cores SLA-9, SL-31, LC-21 and LC-31 from the central Aegean and NE Levantine Seas. We discover several distinct variations both in the isotopic and abundances of the faunae throughout the interval from the Last Glacial Maximum to the Present, which have been interpreted in relation with the bottom water environmental changes. During the deposition of the ~30-15.5 ka BP-interval, the occurrence of high faunal density and diversity dominated by the epifaunal taxa (e.g. C. pachydermus and miliolids) and shallow infaunal taxa (e.g. U. peregrina and B. spathulata ) suggests that bottom water of the eastern Mediterranean was very well ventilated with normal, stable conditions and stable, high flux of organic matter to the sea floor. This organic matter flux was higher at the shallower sites than at the deeper sites, as might be expected with a normal depth-dependent decrease of the organic matter flux to the sea floor. During the 15.5-10 ka BP-interval, dominance of the opportunistic taxa (e.g. G. orbicularis and G. altiformis ) at the expense of both epifaunal and shallow infaunal taxa would suggest an intensive seasonal pulse of organic matter to the sea floor accompanied by reduced deep-water ventilation leading to decrease in the amount of the dissolved oxygen at the deep-sea environment and hence disappearance of epifaunal taxa and shallow infaunal taxa. The S1 internal (10-6 ka BP) was deposited under dysoxic/anoxic conditions in the bottom waters as indicated by the dominance of deep infaunal taxa ( G. affinis and C. mediterranensis ).</p
... Commonly, the interpretation of δ 13 C records is complicated due to a large number of processes potentially influencing the δ 13 C composition of ocean water and fossil hardparts (including taxonomic differences, fluctuations along ontogenic trends, changes in metabolism, regional and temporal changes in primary productivity, upwelling, sea level, ocean currents, or even temperature; Berger and Vincent, 1986;Grossman and Ku, 1986;Wierzbowski, 2002;Auclair et al., 2003;Brand et al., 2003;Lorrain et al., 2004;Korte et al., 2005;McConnaughey and Gillikin, 2008). Furthermore, the spread in δ 13 C values of specimens from the same horizon can be large, which necessitates a higher number of samples in order to reconstruct reliable temporal or spatial trends (Veizer et al., 1999;McArthur et al., 2007). ...
... Although many factors can influence δ 13 C values, it is striking that the pattern within the Kachchh Basin follows the major sea-level changes with a general deepening from the Bajocian to the Oxfordian and again a shallowing until the end of the Jurassic (second-order supercycle; see above). A correlation of δ 13 C values and sea-level changes has been recorded before and positive δ 13 C excursions were connected to transgressive events and storage of organic carbon in marginal sediments or flooded land areas (e.g., Berger and Vincent, 1986;Wierzbowski et al., 2009). In fact, the described long-term δ 13 C trend might be a global signal, because it has also been recorded from the northwestern Tethys by Martinez and Dera (2015) and from Saudi Arabia by Al-Mojel et al. (2018). ...
Article
The stable isotope (δ¹³C, δ¹⁸O) and element (Mg/Ca, Sr/Ca) composition of 374 well-preserved belemnites, bivalves, and brachiopods of the Kachchh and Jaisalmer basins in western India were used to reconstruct climatic changes in the Middle and Late Jurassic time interval. Absolute water temperatures reconstructed from δ¹⁸Oshell values depend on the used δ¹⁸Osea value and equation, but indicate a long-term temperature decrease of around 8–9 °C in the study area from the Bajocian to the Tithonian. Measured Mg/Ca ratios also point to decreasing temperatures, but additionally reflect species-specific factors and a lower Mg/Ca ratio of Jurassic seawater compared to today. The recorded cooling in western India agrees with previous results from neighbouring Madagascar and the Indian Himalayas and can be connected to a drift of Eastern Gondwana into higher latitudes. This palaeogeographic shift is accompanied by changes in sedimentation indicating an increasingly humid climate and in the composition of ecosystems reflecting increasingly cooler water temperatures. High-resolution stable oxygen isotope analyses of three oyster shells point to seasonal temperature changes of 4–5 °C in the Kimmeridgian. The recorded δ¹³C values reflect sea-level changes with a positive excursion in the Oxfordian connected to a major transgressive event. Sr/Ca ratios are observed to follow changes in global ocean chemistry.
... Carbon isotopes (6 13 C) in planktonic foraminifera such as G. bulloides are primarily a reflection of the organic carbon concentrations found in the foraminifera's environment. and vital effects (Berger and Vincent, 1986a). Decreases in b 'C in seawater (reflected by decreases in foraminiferal 613C) indicate increased 12 C addition by organic carbon degradation associated with nutrient influx from upwelling events (Hemleben and Bijma, 1993). ...
... In contrast to the findings of Hill et al. (2004), and in agreement with the results of Torres et al. (2003), we posit that concentric layers of carbonate precipitation occurred as post-depositional diagenesis on the foraminiferal remains within the sediments of ODP Site 888. We believe that the extremely negative 8 13 C values at 110 mbsf (-6.5%o), 115 mbsf (-3.0%o) and 225 mbsf (-3.5%o) are attributable to this secondary calcification process, because the 81 3 C values are too extreme to be the result of primary calcification by vital effects (Berger and Vincent, 1986a). Furthermore, these extremely negative 81"C values occur at depths within the core where both methane and porewater sulfate are relatively high (Fig. 3), providing the primary reactants for anaerobic oxidation of methane. ...
... The present study focuses on reconstructing seawater temperatures based on δ 18 O shell values, but analytical results also include δ 13 C values. The interpretation of stable carbon isotope ratios of fossils is less straightforward, because they are influenced by many factors including taxonomic differences, ontogenetic and metabolic changes, regional and temporal fluctuations in primary productivity, upwelling, sea level, ocean currents, or even temperature (Berger and Vincent, 1986;Grossman and Ku, 1986;Wierzbowski, 2002;Auclair et al., 2003;Brand et al., 2003;Lorrain et al., 2004;Korte et al., 2005). In addition, inter-and intraspecific differences in δ 13 C values can be large even for specimens from the same horizon (e.g., Veizer et al., 1999;McArthur et al., 2007). ...
Article
Stable oxygen isotope values of calcitic marine fossils (δ¹⁸Oshell) were used to calculate the first absolute seawater temperature estimates for the Jurassic of Central Iran. Results indicate a significant long-term warming in the study area through the Middle to Late Jurassic of around 6 °C or more (0.3 to 0.4 °C per million years). Following recent methodological advances in temperature reconstructions, the δ¹⁸Oshell values of bivalves translate into water temperatures slightly warmer than in today’s oceans at comparable latitudes with averages of 26.6 °C in the Middle Jurassic and 32.1 °C in the Late Jurassic. Belemnites would indicate still warmer temperatures, but these values might be less reliable and partly overestimated due to potentially altered specimens. The recorded long-term warming can be explained by a concurrent major plate tectonic shift of Central Iran from temperate to tropical latitudes. The gradual influence of this southward drift is also seen by changes in sedimentation and ecosystem composition. This way, the stable oxygen isotope record of Central Iran is further evidence for the strong impact of plate tectonics on regional long-term climate patterns in the Middle and Late Jurassic.
... In the last decades, stable carbon isotope chemo stratigraphy has been successfully used to increase the stratigraphic resolution of Jurassic and Cretaceous neritic and (hemi-)pelagic carbonate successions (e. g. Scholle and Arthur 1980, Weissert et al. 1985, Berger and Vincent 1986, Jenkyns and Clayton 1986, Schlan ger et al. 1987, Weissert 1989, Lini et al. 1992, Föllmi 1994, Voigt and Hilbrecht 1997, Grötsch et al. 1998, Mene-gatti et al. 1998, Föllmi et al. 2006, Jarvis et al. 2006, Rais et al. 2007, Huck et al. 2013, Wendler et al. 2013, Kakizaki et al. 2013, Price et al. 2016). Looking at a composite carbonate-carbon isotope stratigraphy of the Late Jurassic and Early Cretaceous ( Weissert and Erba 2004) it is evident that the Tithonian and Berriasian stages are characterised by a long period of rather low and stable carbon isotope values. ...
Article
Full-text available
Carbon isotope chemostratigraphy and calpionellid biostratigraphy were used in this study to improve the stratigraphic resolution of the Upper Jurassic–Lower Cretaceous Rayda Formation and examine the expression of the Valanginian C-isotope event in the SE-Tethys. This integrated stratigraphic framework allows for a better correlation between south-eastern and western Tethys records and to obtain a better understanding of the oceanographic system on a regional scale. During the Late Jurassic, a major transgression induced a fast flooding of the Arabian Platform and lead to the deposition of the Rayda Formation. Red crinoidal limestones and submarine hardgrounds at the base of the formation are signs of condensed sedimentation influenced by changing current systems along the passive margin shelf. The following deposition of Maiolicatype micritic limestones with chert nodules recorded the establishment of pelagic conditions which presumed during the earliest Cretaceous and ended with the onset of the hemipelagic sediments of the Salil Formation. The upper part of the Rayda Formation, so far considered as Berriasian-earliest Valanginian in age, is here ascribed to the Upper Valanginian. The established δ13C-curve records the distinct Valanginian C-isotope event (CIE) in the uppermost part of the Rayda Formation and the lowermost part of the Salil Formation. The age of the excursion is underpinned by calpionellid biostratigraphy.
... Such carbon isotope shifts are significant in terms of paleoceanography. According to Berger and Vincent (1986), the excess removal of 1% of the oceanic reservoir of organic carbon produces 0.2‰ of positive shift. The positive isotopic excursion observed in the middle part of the Pitaycachi section has amplitude of 1.3‰, which indicates a significant change in the carbon fluxes in the distal part of the basin during this interval. ...
Article
Full-text available
We used petrofacies analysis and stable isotope data to interpret the isotopic variations in the marine carbonate succession of the Early Cretaceous Mural Formation of northeastern Sonora (Pitaycachi section), Mexico. The petrographic study reveals a range of lithofacies from bioclastic mudstones to boundstones. Allochems consist of corals, algae, rudists, echinoids, sponge spicules, radiolarians, foraminifera and calpionellids. Samples analyzedfor stable isotope are significantly depleted with δ18O values of -15.19‰ to -6.32‰ and exhibit positive δ13C values ranging from 2.91‰ to 4.39‰. The lack of correlation between δ13C and δ18O values also supports a primary marine origin for the δ13C values of limestones from the Pitaycachi section. In the δ13C profile, the Cánova Member shows an upward increasing trend from 3.09‰ to 4.36‰ interpreted to indicate an increase in the rate of marine organic production and/or organic burial in the basin during early Albian time. The abrupt increase in carbon isotope values in the lower part of the section correlates with OAE1b. The shape of the C-isotope curve of the present study is similar to other C-isotope curves from Mexico and other continents (e.g., Vacontian basin, France) indicating that OAE1b may have been global in extent.
... In the last decades, stable carbon isotope chemo strati - graphy has been successfully used to increase the strati - graphic resolution of Jurassic and Cretaceous neritic and (hemi-)pelagic carbonate successions (e. g. Scholle and Arthur 1980, Weissert et al. 1985, Berger and Vincent 1986, Jenkyns and Clayton 1986, Schlan ger et al. 1987, Weissert 1989, Lini et al. 1992, Föllmi 1994, Voigt and Hilbrecht 1997, Grötsch et al. 1998, Mene - gatti et al. 1998, Föllmi et al. 2006, Jarvis et al. 2006, Rais et al. 2007, Huck et al. 2013, Wendler et al. 2013, Kakizaki et al. 2013, Price et al. 2016). Looking at a composite carbonate-carbon isotope stratigraphy of the Late Jurassic and Early Cretaceous (Weissert and Erba 2004) it is evident that the Tithonian and Berriasian stages are characterised by a long period of rather low and stable carbon isotope values. ...
Poster
The time period between the Late Jurassic and the Early Cretaceous experienced dramatic changes in terms of plate configuration and paleoceanography. Perturbations of the global carbon cycle have been determined with the help of carbon isotope data available for different locations around the world. Especially the Western Tethys and North Atlantic regions were examined in great detail. Towards the most eastern part of the Tethys and the Pacific, available data is not very dense and additional information is helpful in order to understand how other paleogeographic regions were affected by the above-mentioned changes. The Oman Mountains preserve a Mesozoic succession, which was deposited at this most eastern part of the Tethys realm. It provides new information on impact of climatic and/or environmental changes in a region, which can be described as a window to the Indo-Pacific Ocean. Stable isotope geochemistry of carbon and oxygen was performed on bulk carbonate samples from sedimentary successions from the Upper Jurassic to Lower Cretaceous formed on the Arabian Platform and outcropping today in the Central Oman Mountains. In addition, calpionellid assemblages were defined on selected samples allowing the definition of some biostratigraphic tie points. On the Arabian platform, the Upper Jurassic is marked by an erosional sequence and sub aerial exposure, which induced the formation of a karstified surface on top of the grain-supported limestones of the Sahtan Formation. The overlying Rayda Formation shows a fining upward succession from reddish packstones and grainstones to light grey mudstones containing chert nodules. The top of the Rayda Formation is defined with the onset of centimeter bedded marl-limestone alterations of the prograding Salil Formation. The measured 􏰏13C values show very stable values between 1‰ and 1.5‰ in the lower part of the Rayda Formation before rapidly increasing towards values of 􏰐3‰ at the uppermost part. After this positive excursion, the values decrease and stay at 􏰐2‰ within the lowermost part of the Salil Formation. The obtained geochemical and biostratigraphic data, together with a detailed description of the facies, allows a reconstruction of the environmental conditions at a paleogeographic position towards the Pacific. Contrary to the stratigraphy found in today’s literature, the here-obtained data indicates that the upper part of the Rayda Formation in the Central Oman Mountains is not Berriasian but Valanginian in age. Further the 􏰏13C values reproduce very nicely the numerous datasets from other locations such as the Southern Alps and the positive excursion found in the uppermost part of the Rayda Formation could be related to the Valanginian Weissert oceanic anoxic event.
... Water molecules with light oxygen isotopes evaporate more easily than those with heavy oxygen isotopes. Positive δ 18 O values are often associated with negative δ 13 C shifts in the Cenozoic isotope record, which have been interpreted as the result of an increased ice volume affecting Earth (Berger and Vincent, 1986). The high CO 2 withdrawals from the air may have provoked a decrease in the world temperatures and the start of a new glaciation (Gouldey et al., 2010) at high latitudes of the Gondwana continent. ...
Article
Full-text available
Turbidity currents, tectonism, debris flow, glaciation and other processes have been regarded as responsible for the generation of Silurian-Carboniferous diamictites found in northern Brazil and South America. Processes that best explain the observed features in some Brazilian strata are produced by glaciation/deglaciation. Four main glacial ages were identified in the Parnaíba Basin in the Paleozoic time. Glacial influenced deposits are present in Early Silurian, Late Devonian, Early Mississippian and Middle Mississippian time in this basin. Glacial diamictites of the same ages are partly recognized in the four Brazilian intracratonic Paleozoic basins and in the Marajó and Sergipe-Alagoas rift basins. However, only in the Parnaíba Basin all the glacial formations are found in the subsurface, except one is also found in outcrops. Glacial features are illustrated and beds dated on the basis of very accurate palynological studies. Many of the primary paleontological determinations from Petrobras bore holes were published in many papers, but also information from boreholes drilled by private (Themag), state mineral department (Departamento Nacional de Produção Mineral-DNPM) and state geological survey company (Companhia de Pesquisa de Recursos Minerais-CPRM) were employed as well as field mapping. Ice ages left clear imprints as shown by sedimentary glacial facies with some striated, faceted and polished clasts; rhythmites with dropstones; exotic boulders; striated pavements and deformed sandstone beds which document deposition under glacial conditions. The purpose of this reexamination is to evaluate the primary sedimentological and paleontological data related to these glaciations, with the inclusion of many illustrations. This review adds some new data and was done because some authors highlight a high degree of uncertainty in the presence of the mentioned Paleozoic glaciations in western Gondwana, especially in Brazil.
... Planktic foraminifera isotope values should be separated into groups related to specific depth habits of studied taxa, assuming the presence of thermal gradients in water columns of Campanian-Maastrichtian basins (cf. Shackleton and Opdyke, 1973;Fairbanks et al., 1980Fairbanks et al., , 1982Alsenz et al., 1983;Berger and Vincent, 1986). Shallow-water dwelling foraminifera should theoretically have lower δ 18 O values than deepwater planktic foraminifers because of higher temperatures at sea surface. ...
Article
Oxygen and carbon isotope data of 11 Lower Campanian and 11 Upper Maastrichtian co-existing rotaliid foraminiferal taxa from Eastern Poland are presented. Pristine preservation of the studied material is documented by studies of cathodoluminescence, elemental contents and micro/nano-structures of foraminiferal tests. The variability in δ¹⁸O and δ¹³C values of the foraminifera is taxon-specific and relatively constant within the investigated intervals. It results from the combination of vital and microhabitat effects. A comparison of the measured isotope signatures with the published data of similar Cretaceous or modern taxa have allowed us to find benthic foraminifera which precipitated oxygen and carbon isotopes in near-equilibrium with bottom water. These are Praebulimina sp., Gyroidinoides globosus, Pullenia jarvisi, and Bolivina incrassata for oxygen, and Cibicidoides voltzianus and Cibicides beaumontianus for carbon isotopes. The observed differences between δ¹³C values of infaunal and epifaunal foraminiferal taxa are related to the presence of δ¹³CDIC (DIC - dissolved inorganic carbon) gradient in the sediment column, which was much higher in the Chełm section. Although planktic foraminifera studied are characterized by different lifestyles, this feature is not mirrored in their oxygen and carbon isotope compositions. This is probably due to effects of vital isotope fractionation and minor thermal and carbon isotope gradients in a part of the water column inhabited by these organisms. The thermal gradient between near surface and bottom waters is calculated to be ca. 4.0 °C, and ca. 7.5 °C for the Early Campanian and the Late Maastrichtian seas of East European Platform, respectively, based on the comparison of δ¹⁸O values of selected planktic and benthic foraminifera.
... Carbon isotope stratigraphy has been extensively used during recent years for stratigraphical correlation on a global scale and for palaeoenvironmental and palaeoceanographical reconstructions of coeval stratigraphical sections of Cretaceous deposits (Voigt et al., 2012;Wendler, 2013). Contrary to biostratigraphy, investigations of the bulk carbonate d 13 C record does not require taxonomic knowledge (e.g., Ripperdan et al., 1992;Saltzman et al., 2000;Herrle et al., 2004;Payne et al., 2004) and during the last decades, the integration of biostratigraphy and chemostratigraphy has received much attention because it can improve the precision of correlations (Berger and Vincent, 1986;Weissert, 1989;Jenkyns et al., 1994;Jarvis et al., 2006;Di Lucia et al., 2012;Frijia et al., 2015). ...
Article
Biostratigraphy, using foraminifera and echinoids, plus high-resolution carbon isotope stratigraphy of the upper Maastrichtian–Danian interval in the western part of the Kopet-Dagh Basin in northeast Iran are outlined. Our study of shallow-marine carbonate platform deposits of the Kalat Formation, rich in larger benthic foraminifera (predominantly Clypeorbis mammillatus Schlumberger, Lepidorbitoides sp. and Siderolites calcitrapoides Lamarck), has allowed the definition of a C. mammillatus-S. calcitrapoides Assemblage Zone, of late Maastrichtian age. Clypeorbis mammillatus is here recorded for the first time from the Maastrichtian Kalat Formation and represents the most easterly find of this taxon in the European faunal province. From Danian strata of the Chehel Kaman Formation three genera (Cyclaster, Echinocorys and Pseudogibbaster) and four species of echinoids were identified. In addition, three planktonic foraminiferal biozones are introduced here for the Danian interval of the Chehel Kaman Formation studied, i.e., Guembelitria cretacea Zone, Eoglobigerina eobulloides–Subbotina triloculinoides Interval Zone (Pα-P1a) and Subbotina triloculinoides Subzone (P1b). The isotope profile obtained correlates with the subtropical Bottaccione/Contessa reference curve for the K/Pg boundary interval and, on a regional scale, with the Maraveh Tapeh section, which represents the δ¹³C positive excursion of KPg-2 and the upper negative excursion of the KPg-3. The K/Pg boundary, placed at the δ¹³C maximum above KPg-3, corresponds in the Qareh Galdy section with sample 2239.
... Water molecules with light oxygen isotopes evaporate more easily than those with heavy oxygen isotopes. Positive δ 18 O values are often associated with negative δ 13 C shifts in the Cenozoic isotope record, which have been interpreted as the result of an increased ice volume affecting Earth (Berger and Vincent, 1986). The high CO 2 withdrawals from the air may have provoked a decrease in the world temperatures and the start of a new glaciation (Gouldey et al., 2010) at high latitudes of the Gondwana continent. ...
... The δO 18 curve shows a negative displacement during an anoxic event (hot climate and high sea level) and a positive shift during a glacial event because H 2 O vapor molecules rich in lighter O 16 isotope are trapped in the ice. Positive δ 18 O values are often associated with negative δ 13 C shifts in the Cenozoic isotope record, which have been interpreted as the result of an increased ice volume affecting Earth (Berger and Vincent, 1986). ...
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Abstract. Turbidity currents, tectonism, debris flow, glaciation, and other geologic processes are considered to be responsible for the generation of Silurian-Mississippian diamictites in northern Brazil and South America. The processes that best explain the features observed in Brazilian strata are glaciation/deglaciation. Four main glacial ages were identified in the Parnaíba Basin in the Paleozoic time. Glacially influenced deposits are present in the Early Silurian, Late Devonian, Early Mississippian, and Middle Mississippian in this basin. Glacial diamictites with the same age were partly identified in the four Brazilian intracratonic Paleozoic basins (Solimões, Amazon, Parnaíba and Paraná) and in the Marajó, Jatobá, and Sergipe-Alagoas rift basins. However, all mentioned glacial formations were found in the subsurface in the Parnaíba Basin, except for one that was not observed in outcrops. The glacial features were illustrated and the beds were dated based on very accurate palynological studies. Many of the primary paleontological data based on Petrobras bore holes were published in the literature. In addition, palynological information from boreholes drilled by private companies (Themag), the State Mineral Department (Departamento Nacional de Produção Mineral-DNPM), and the State Geological Survey Company (Companhia de Pesquisa de Recursos Minerais-CPRM) were employed, in addition to field mapping. The purpose of this reexamination is to evaluate primary sedimentological and paleontological data related to these glaciations and include many new illustrations. This review that includes new data was done because several authors highlighted a high degree of uncertainty in the presence of Paleozoic glaciations in western Gondwana, especially in Brazil. Observation: For space reasons, to localize the towns or counties mentioned in the text, the reader may use google search.
... Similar to many VHMS (Huston, 1999), there is no correlation between δ 13 C and δ 18 O (r = 0.03). The observed δ 13 C values of calcite samples could have been derived (i) by mixing seawater carbonate with carbon derived from oxidation of methane produced by degradation of organic carbon (δ 13 C values of -20 to -30‰: Berger and Vincent, 1986) in underlying sedimentary rocks as suggested for some VHMS deposits (Huston, 1999), (ii) by mixing of seawater carbonate with carbon of igneous derivation (δ 13 C values of -5 to -10‰: Ohmoto and Goldhaber, 1997) or (iii) through thermal processing of organic matter, with oxygen supplied from water. Input of marine carbon (with δ 13 C values typically ranging from −3 to +3‰) into the mineralising fluid is possibly shown in the two relatively 13 C-enriched calcite samples (−3.7 and −4.5‰). ...
... The Cenozoic record is compiled from pelagic carbonate shells that are ecologically constrained to well-mixed open marine waters that are isotopically homogenous ( Zachos et al., 2001). These sediments accumulate as a relatively continuous succession on ocean crust at great water depths with little chance of exposure, erosion, or alteration during sea level fall (Berger and Vincent, 1986;Maslin & Swann, 2005;Ravizza & Zachos, 2003). Biostratigraphic dating allows δ 13 C ...
Article
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The composite δ13C record of Neoproterozoic carbonates is characterized by large magnitude (< 18‰ VPDB) swings that have been interpreted to record a) changes in dissolved inorganic carbon in seawater driven by a carbon cycle with different boundary conditions, b) pervasive diagenetic alteration or c) local controls similar to those active in Cenozoic platformal successions. A sedimentological study of the Trezona Formation in the Flinders Ranges of South Australia was conducted to determine the palaeoenvironmental context of the Trezona anomaly, one of the most widely recognized examples of a Neoproterozoic mega‐excursion that occurs beneath glaciogenic sediments of the Marinoan ice age (~ 635 Ma). Stratigraphic mapping identified an unconformity at its base separating it from the shelf deposits of the underlying Enorama Shale. The lower Trezona Formation is dominantly calcareous mudstone with mudcracks, channels, and mud chip and algal flake breccias interpreted to record exposure and desiccation on mudflats, shallow pools and lagoons. A marked increase in microbial carbonate and oolites in the upper Trezona Formation records a relative decline of mud input that terminates with karst. The Trezona Formation is thus interpreted to have been deposited in shallow, localized, salt‐withdrawal basins on the exposed shelf creating a mosaic of poorly connected lagoons and (alkaline) lakes that were intermittently restricted or isolated from the sea. Variations in δ13C and δ18O correspond with facies changes and reflect locally evolving depositional conditions influenced by sills and channels that shifted the seawater to freshwater balance. This restricted setting and range of δ13C values is more similar to Cenozoic platformal deposits (~ 12‰) than the muted (~ 3‰) global seawater variation recorded in pelagic sediments. The anomalous δ13C values in the Trezona Formation may instead provide constraints on the changing terrestrial biosphere directly preceding the evolution and rapid expansion of metazoan life. This article is protected by copyright. All rights reserved.
... The  13 C values of sediments from sites U1466 and U1468 show an increase of 1‰ coincident with the Monterey Event, an event marked by a global increase in the  13 C values of carbonate and organic material of 1 to 2‰ between ca 17 Ma and 13 Ma (Berger & Vincent, 1986;Jacobs et al., 1996;Vincent et al., 1981) (Fig. 5A & B). While the Monterey Event has been recognized principally in pelagic settings, changes in the  13 C values have also identified in locations in which the sediments are heavily influenced by shallower water calcareous organisms such as in the Central Apennines carbonate platforms (Brandano et al., 2017). ...
Article
This study investigates the δ¹³C values of Middle Miocene–Modern drift deposits and periplatform sediments in the Maldives and compares these data with the global δ¹³C values derived from bulk oceanic sediments and foraminifera. This comparison reveals that while the δ¹³C values of the early Miocene periplatform sediments in the Maldives appear to track the global record of δ¹³C values, including increases associated with the Oligocene–Miocene boundary as well as the variations within the Monterey Event; the correlation with the Monterey Event may be coincidental. It is suggested that variations in δ¹³C values do not reflect changes in oceanic dissolved inorganic carbon, but instead pulses of sediment arising from platform progradation that contribute carbonates with elevated δ¹³C values derived from the adjacent shallow‐water atolls. This conclusion is supported both by correlations between the seismic sequence architecture and the δ¹³C values which document progradation of ¹³C‐rich platform sediments, and also by the continuation of the interval of ¹³C‐rich sediments past the end of the Monterey Event at 13 Ma within the drift. This article is protected by copyright. All rights reserved.
... The intensification of Antarctic bottom water formation would have been accompanied by accelerated upwelling of nutrient-rich water, which might have boosted productivity and caused a temporary reduction in pCO 2 . Early to middle Miocene δ 13 C records reflect large-scale changes in organic carbon deposition relative to carbonate sedimentation, and together with wide-spread, large sedimentary organic carbon and phosphatic deposits may indicate a consequent drawdown of atmospheric CO 2 (Vincent and Berger, 1985;Berger and Vincent, 1986). This is partly corroborated by proxy estimates of atmospheric CO 2 based on the alkenone isotope approach insofar as lower intervals of pCO 2 correspond to inferred organic carbon burial events, but there is no evidence for a sharp CO 2 decrease associated with EAIS growth (Pagani et al., 1999) or for a large permanent drop in pCO 2 during the middle Miocene (Pearson and Palmer, 2000). ...
Article
Carbon is one of the key elements in organisms and non-living compounds on Earth. Carbon dioxide and methane are important greenhouse gases in the atmosphere, dissolved inorganic (DIC) and organic carbon (DOC) determine water biogeochemistry, and carbonates are major constituents of marine sediments. Stable carbon isotope ratios (¹³C/¹²C), expressed as δ¹³C values, are widely used in modern Earth sciences. δ¹³CCO2 values of atmospheric carbon dioxide reflect global climate evolution and change. Marine δ¹³CDIC is used as water-mass tracer and helps quantifying the anthropogenic CO2 uptake of the ocean. The δ¹³C values of fossil planktic and benthic carbonates indicate changes in circulation pattern and deep-water ventilation of ancient oceans, as well as paleoproductivity at the sea surface and methane release at the sea floor. The δ¹³COM values of sedimentary organic matter (OM) and compound-specific δ¹³C values of molecular organic biomarkers indicate whether the organic carbon is of marine or terrestrial provenience. Secular δ¹³C variations and excursions in carbonates are important stratigraphic marker and tie points. Here we review the application of stable carbon isotope ratios in ocean water and biogenic carbonates as proxies in paleoceanography, including the atmospheric and sedimentary reservoirs oceanic carbon is in exchange with. Due to the wide use of δ¹³C values in Earth sciences, this overview necessarily does not claim to be complete; rather we focus on field-based stable carbon isotope research and its significance in paleoceanography. This may assist in evaluating general circulation model results and foster development of new innovative proxies.
... Grossman (1984) concluded that there are strong interspecific variations in δ 13 C composition of foraminiferal tests. Interspecific variation in δ 13 C values, may be due to microhabitat difference rather than a vital effect as suggested by Grossman (1984) and Berger and Vincent (1986). The interval between~4800-4500 cal yr BP shows a major change in δ 18 O values of G. ruber and SST at Core SK237-GC04 (Fig. 3c) (Saraswat et al., 2013) as evidenced by a pronounced weak monsoon interval in the eastern Arabian Sea. ...
... In paleoceanographic records, the vertical gradients in δ 13 C DIC between the warm surface ocean (planktonic foraminifera) and average deep ocean (benthic foraminifera) are generally assumed to reflect the integrated efficiency of the ocean's biological soft-tissue pump (Shackleton et al., 1992;Broecker, 1982;Berger and Vincent, 1986). Variations in spatial gradients of deep-ocean δ 13 C DIC are frequently attributed to circulation changes (e.g., Curry and Oppo, 2005) although it has long been known that changes in the preformed properties of paleo-deep water masses are possible (Mix and Fairbanks, 1985;Broecker and Maier-Reimer, 1992;Lynch-Stieglitz and Fairbanks, 1994). ...
Article
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Analysis of observations and sensitivity experiments with a new three-dimensional global model of stable carbon isotope cycling elucidate processes that control the distribution of δ13C of dissolved inorganic carbon (DIC) in the contemporary and preindustrial ocean. Biological fractionation and the sinking of isotopically light δ13C organic matter from the surface into the interior ocean leads to low δ13CDIC values at depths and in high latitude surface waters and high values in the upper ocean at low latitudes with maxima in the subtropics. Air–sea gas exchange has two effects. First, it acts to reduce the spatial gradients created by biology. Second, the associated temperature-dependent fractionation tends to increase (decrease) δ13CDIC values of colder (warmer) water, which generates gradients that oppose those arising from biology. Our model results suggest that both effects are similarly important in influencing surface and interior δ13CDIC distributions. However, since air–sea gas exchange is slow in the modern ocean, the biological effect dominates spatial δ13CDIC gradients both in the interior and at the surface, in contrast to conclusions from some previous studies. Calcium carbonate cycling, pH dependency of fractionation during air–sea gas exchange, and kinetic fractionation have minor effects on δ13CDIC. Accumulation of isotopically light carbon from anthropogenic fossil fuel burning has decreased the spatial variability of surface and deep δ13CDIC since the industrial revolution in our model simulations. Analysis of a new synthesis of δ13CDIC measurements from years 1990 to 2005 is used to quantify preformed and remineralized contributions as well as the effects of biology and air–sea gas exchange. The model reproduces major features of the observed large-scale distribution of δ13CDIC as well as the individual contributions and effects. Residual misfits are documented and analyzed. Simulated surface and subsurface δ13CDIC are influenced by details of the ecosystem model formulation. For example, inclusion of a simple parameterization of iron limitation of phytoplankton growth rates and temperature-dependent zooplankton grazing rates improves the agreement with δ13CDIC observations and satellite estimates of phytoplankton growth rates and biomass, suggesting that δ13C can also be a useful test of ecosystem models.
... The Lau event has been related to the highest δ 13 C positive excursion recorded in the Paleozoic (Fig. 11). While δ 13 C positive excursions are often attributed to enhanced productivity (e.g., Berger and Vincent, 1986;Kump and Arthur, 1999;Herrle et al., 2003), Stricanne et al. (2006) recorded a strong decrease in the abundance of acritarchs and prasinophytes during the Lau event, indicating reduced primary production. Moreover, it has been argued that the extreme amplitude of the Ludfordian δ 13 C positive excursion is too high to be explained by enhanced productivity (Bickert et al., 1997). ...
Article
Phytoplankton form the base of most marine trophic chains and studying their past diversity at regional and global scales can provide valuable insights into the evolution of marine ecosystems and climate history. Using a new database of more than 4000 species of acritarchs and prasinophytes, a comprehensive investigation of the taxonomic diversity trajectories of this marine (micro)phytoplankton throughout the Paleozoic is performed for the first time. This dataset compiles data from published literature, including taxonomic, geographic and stratigraphic information at the stage resolution. Our results highlight five major temporal trends in phytoplankton diversity variation: (i) an initial plateau of moderate richness during the early and middle Cambrian, followed by (ii) a sharp increase from the late Cambrian to the Middle Ordovician, which records the highest Paleozoic diversity of organic-walled phytoplankton (OWP); then, (iii) a protracted decrease during the Late Ordovician to Middle Devonian; (iv) a slight peak in diversity during the Late Devonian, before (v) falling to the lowest richness recorded during the Carboniferous and Permian. The role of phytoplankton during major biotic events is discussed: While phytoplankton evolution may have been a factor in enabling the “Cambrian Explosion”, we do not find a strong relationship between the diversity changes of the phytoplankton and this event and we thus refute the notion that it might have been a major driver of radiations during this interval. However, a strong increase in phytoplankton diversity coincides with the Great Ordovician Biodiversification Event (GOBE), indicating that the profound changes of marine phytoplankton, and thus of the base of marine food webs, enabled diversifications throughout marine ecosystems. A decrease in phytoplankton diversity during the Lower and Middle Devonian points against the hypothesis of phytoplankton triggering the proposed “Devonian Nekton Revolution”. By comparing the results with paleoenvironmental parameters, several factors are found to be possibly related to the long-term diversity trends: Our results indicate that paleogeography and sea-level changes were probably the main drivers of phytoplankton diversity patterns throughout the Paleozoic, while increases in sediment influx provided facilitating conditions for phytoplankton diversification. Atmospheric CO2 concentration as well as temperature and related sea ice cover are found to be further important controlling factors for phytoplankton diversity.
... Phytoplankton prefers to absorb 12 C through photosynthesis, leading to heavier δ 13 C in the upper layer. During the decomposition of sinking organic carbon 12 C is released into the deeper depth levels, which in turn leads to a lighter δ 13 C close to the seafloor (Berger and Vincent, 1986). The differences in δ 13 C records between planktonic and benthic foraminifera have been used as a qualitative indicator of productivity in tropical and subtropical oceans, with larger values indicating a period of increased productivity (Sarnthein and Winn, 1990;Jian et al., 2001;Li et al., 2010). ...
Article
The tropical Pacific played an important role in modulating global climate change during the Pliocene. Studies of tropical Pacific sea surface temperatures covering the period from the Pliocene onwards indicate that changes in the thermal mean state over the tropical Pacific can significantly influence global climate feedbacks and connect the high- and low-latitude climates. Tropical productivity fluctuations are a significant mechanism with respect to the operation of the global carbon cycle. Yet, temporal changes in primary productivity are not well constrained in the western Pacific warm pool (WPWP), where the ocean–climate system is not dominated by upwelling systems. Furthermore, the role of nutricline dynamics in forcing productivity over tectonic timescales remains uncertain. Here we use relatively high-resolution foraminiferal carbon isotope records combined with Ba/Ti ratios obtained from International Ocean Discovery Program (IODP) Site U1490 in the WPWP to reconstruct nutricline depth and paleoproductivity over the period 5.1–2.6 Ma. Our records imply that nutricline and productivity variations were closely coupled over tectonic timescales, implying that the dynamics of the nutricline play a significant role in regulating productivity in the WPWP. The deeper nutricline and lower productivity during 4.8–3.5 Ma might have been fostered by the closure of the Central American Seaway through the thickening of the mixed layer in the WPWP. We relate the overall shallower nutricline and increased productivity during 3.5–3.0 Ma to the restriction of the Indonesian Seaway via the enhanced influence and upwelling of high-latitude southern-source waters.
... There is considerable evidence for a relationship between positive shifts in Cretaceous N 13 C records and ¢rst-order (30-Myr scale) rises in eustatic sea-level (e.g. Scholle and Arthur, 1980;Berger and Vincent, 1986;Arthur et al., 1987;Weissert, 1989;Jenkyns et al., 1994;Mitchell et al., 1996;Voigt and Hilbrecht, 1997;. This association is generally attributed to changes in the partitioning of carbon between organic and carbonate carbon sinks caused by sea-level rise. ...
... The organic carbon may also have affected the dissolved inorganic carbon pool producing a slight negative δ 13 C carb shift ( Fig. 11; cf. Berger and Vincent, 1986). ...
Article
Upper Berriasian chemostratigraphic, clay mineral and calcareous nanofossil data are presented from a precisely dated hemipelagic section of Barlya (Western Balkan, Bulgaria). The section covers an interval from the upper part of the lower Berriasian (Calpionella elliptica Subzone, magnetozone M17r) to the lowermost Valanginian (Calpionellites darderi Subzone, magnetozone M14r). The study aims to reconstruct the major palaeoenvironmental changes (variations in lithogenic input, palaeoredox and palaeoproductivity) and their relation to palaeoclimate and regional tectonic regime, as well as their application to stratigraphic correlations with the Vocontian Basin and Jura Mts. A long-term increase in terrigenous input during the late Berriasian was controlled mostly by the orogenic activity in the NeoTethyan Collision Zone and to a lesser degree by climate humidification, as revealed by variations in kaolinite content and in lithogenic proxies (Ti/K, Th/K, Ti/Al and Zr/Rb ratios). A good correlation is observed between geochemical palaeoproductivity proxies (sedimentation rates of non-detrital (excess or authigenic) portions of P, Zn and Cd) and nannofossil fluxes, determined as the total abundance and species richness. Major calcareous nannofossil peaks, represented by high-diversity and high-abundance nannofossil assemblages, fall within the low-productivity intervals. A smaller peak formed by a low-diversity and high-abundance assemblage, dominated by Watznaueria barnesiae/fossacincta, coincides with the variable, but mostly high-productivity interval, which indicates high plasticity of Watznaueria concerning to environmental conditions. Additionally, trophic changes seem to correspond to bulk rock carbon-isotopic composition, with rising δ¹³Ccarb values in more oligotrophic intervals. This offers perspectives for long-distance chemostratigraphic correlations between pelagic and platform sections, supplementing traditional schemes based on bio- and sequence stratigraphy. A holostratigraphic correlation is proposed between the Western Balkan (Barlya section), Vocontian Basin (Berrias and Monclus sections) and Jura Mts (La Chambotte section) based on bio-, magnetic and carbon-isotope stratigraphy, as well as climatic and palaeoproductivity proxies.
... In contrast, in terms of their Mn-Fe-(Ni + Co + Cu)* and Al 2 O 3 compositions, a hydrothermal source with some continental input is indicated for the Mn-carbonate deposits ( Fig. 21; Zeng and Liu, 1999;Duan et al., 2016). In terms of their δ 13 C V-PDB and δ 18 O V-SMOW values( Fig. 21; Zeng and Liu, 1999;Duan et al., 2016), a seawater source (Berger and Vincent, 1986;Hoefs, 2009) is implicated. It thus appears that the carbonates were deposited from deep seawater with Mn, minor Fe and trace Ni, Co and Cu provided from a later hydrothermal source. ...
Article
The Youjiang Basin in the western part of the South China Block (SCB), preserves the records of the tectonic history from Tethyan, through Paleo-Pacific to Tibetan domains, with coeval formation of diverse types of giant metallic deposits. The prolonged tectonic evolution and its control on the genesis and spatio-temporal distribution of giant metallic deposits in the Youjiang Basin provide a window for a holistic understanding of the tectono-metalligenesis of SCB. Six tectono-metallogenic stages can be recognized in the geological evolution of the basin and their relationship to the geodynamic evolution of the surrounding tectonic units. Subsequent to the closure of the Proto-Tethyan Ocean and collision between the SCB and the Gondwana continent, a late Ordovician to early Silurian intracontinental orogeny along the southern margin of the basin resulted in the formation of Silurian Cu and W skarn deposits. During Devonian to Carboniferous, during the Paleo-Tethyan spreading, the basin experienced rifting and development of a passive continental margin, when sedimentary Mn carbonate ores were deposited in basin facies sequences in the southern part of the basin. On the northern margin, bauxite karsts formed in carbonate rocks within continental-margin sequences. In the Late Permian, the Paleo-Pacific oceanic plate was subducted below the SCB, which most likely induced migration of the coeval Emeishan mantle plume towards the plate margin. Arc volcanism resulted in voluminous ash falls on the carbonate platform and these were subsequently transformed into bauxite in the southern part of basin. Following this, Triassic intraplate shortening induced thin-skinned crustal deformation with associated formation of orogenic Au deposits throughout the basin. In the Jurassic, the Youjiang Basin experienced slab delamination, during which MVT PbZn deposits formed along the northern margin, and clusters of WSn skarns were generated at the centre of the delamination zone on the eastern margin of the basin. Subduction retreated southwards in the Cretaceous, resulting in the formation of Carlin-type Au deposits in the northern part of the basin, and Sn and Cu skarns and associated carbonate replacement PbZn deposits in the central and southern parts. Cenozoic regional denudation and climate change in response to the southeastward propagation of Tibet caused brittle deformation of pre-existing bauxite and Mn orebodies and their further enrichment. The overlap among Paleo-Tethyan, Paleo-Pacific and Tibetan tectonic regimes during the evolution of the Youjiang Basin generated a diverse range of mineral deposit types, including orogenic and Carlin-type Au deposits, both carbonate-replacement and MVT-type PbZn deposits, sedimentary Mn‑carbonate deposits and bauxite in both passive and active continental margins.
... It has been proven that the Late Miocene carbon shift occurred at ODP1148 site in the SCS during this period (Zhao et al., 2001a;Wang et al., 2003a,b). This event is marked by carbon isotopes depletion and a positive shift in oxygen isotopes (Zhao et al., 2001a(Zhao et al., , 2001b, which are consistent with the global event known as the "Messina carbon shift" (Berger and Vincent, 1986) (Fig. 2) in the early Messinian or magnetostratigraphic Chron 6. The "Messina carbon shift" has generally been suggested to have occurred between 6.6 and 5.9 Ma . ...
... There is considerable evidence for a relationship between positive shifts in Cretaceous N 13 C records and ¢rst-order (30-Myr scale) rises in eustatic sea-level (e.g. Scholle and Arthur, 1980;Berger and Vincent, 1986;Arthur et al., 1987;Weissert, 1989;Jenkyns et al., 1994;Mitchell et al., 1996;Voigt and Hilbrecht, 1997;. This association is generally attributed to changes in the partitioning of carbon between organic and carbonate carbon sinks caused by sea-level rise. ...
... A fall in carbon-isotope values during the latest Sinemurian could reflect a decrease in organic-carbon output to global sedimentary reservoirs causing a rise in CO 2 in the oceans and atmosphere; equally, an input of isotopically light carbon from volcanogenic or methanogenic sources would raise concentration of this greenhouse gas (e.g. Scholle, Arthur 1980;Berger, Vincent 1986: Dickens et al. 1995Kump, Arthur 1999). Theoretically, increase in the atmospheric content of this greenhouse gas should have raised global temperatures in the oceans and atmospheres although the data at hand rather suggest that any warming and acceleration of the hydrological cycle was delayed until early Pliensbachian time (Dera et al. 2011;Franceschi et al. 2014;Deconinck et al. 2019). ...
Conference Paper
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The extant biostratigraphic data on Tethyan Bahamian-type platform carbonates of Early Jurassic age from Italy and Spain indicate that many of them ceased to accumulate sediment in latest Sinemurian time (Early Jurassic). In one case, namely that of western Sicily, the date can in all probability be fixed as raricostatum Zone, an interval that may be generally applicable throughout the region. Post-platform sediments can locally be dated as Pliensbachian or Toarcian but in most, if not all cases there is an uncalibrated stratigraphic gap between the top of the shallow-water carbonates and the overlying open-marine or pelagic facies. Two mechanisms likely played a role in terminating the shallow-water carbonate factory: tectonic activity involving uplift of the platform surface and exposure to erosional and solutional activity, and a fall in eustatic sea level that could have achieved the same end. The fact that many Tethyan carbonate platforms did not re-establish themselves during subsequent re-submergence, hence allowing definitive drowning, suggests a degree of widespread environmental deterioration during latest Sinemurian, possibly extending into earliest Pliensbachian time. A negative carbon-isotope excursion of this age, recognized in several European localities, is compatible with the presence of a relatively CO2-rich ocean-atmosphere system extending over the stage boundary interval that prevented formation of a new shallow-water sediment factory until regional subsidence had carried the depositional surface into depths too great for the precipitation and secretion of abundant carbonate minerals.
... events are also characterized by positive carbon isotope (δ 13 C) excursions that have been related to globally enhanced rates of organic carbon burial (e.g. Berger and Vincent, 1986;Kump, 1991). The most prominent of these events were OAE1a during the early Aptian and OAE2 at the Cenomanian-Turonian boundary. ...
Article
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Oceanic anoxic events (OAEs) document major perturbations of the global carbon cycle with repercussions for the Earth's climate and ocean circulation that are relevant to understanding future climate trends. Here, we compare the onset and development of Cretaceous OAE1a and OAE2 in two drill cores with unusually high sedimentation rates from the Vocontian Basin (southern France) and Tarfaya Basin (southern Morocco). OAE1a and OAE2 exhibit remarkable similarities in the evolution of their carbon isotope (δ13C) records, with long-lasting negative excursions preceding the onset of the main positive excursions, supporting the view that both OAEs were triggered by massive emissions of volcanic CO2 into the atmosphere. However, there are substantial differences, notably in the durations of individual phases within the δ13C positive excursions of both OAEs. Based on analysis of cyclic sediment variations, we estimate the duration of individual phases within OAE1a and OAE2. We identify (1) a precursor phase (negative excursion) lasting ∼430 kyr for OAE1a and ∼130 kyr for OAE2, (2) an onset phase of ∼390 and ∼70 kyr, (3) a peak phase of ∼600 and ∼90 kyr, (4) a plateau phase of ∼1340 and ∼200 kyr, and (5) a recovery phase of ∼380 and ∼440 kyr. The total duration of the positive δ13C excursion is estimated at 2700 kyr for OAE1a and 790 kyr for OAE2, and that of the main carbon accumulation phase is estimated at 980 and 180 kyr. The long-lasting peak, plateau and recovery phases imply fundamental changes in global nutrient cycles either (1) by submarine basalt–seawater interactions, (2) through excess nutrient inputs to the oceans by increasing continental weathering and river discharge, or (3) through nutrient recycling from the marine sediment reservoir. We investigated the role of phosphorus in the development of carbon accumulation by analysing phosphorus speciation across OAE2 and the mid-Cenomanian Event (MCE) in the Tarfaya Basin. The ratios of organic carbon and total nitrogen to reactive phosphorus (Corg∕Preact and Ntotal∕Preact) prior to OAE2 and the MCE hover close to or below the Redfield ratio characteristic of marine organic matter. Decreases in reactive phosphorus resulting in Corg∕Preact and Ntotal∕Preact above the Redfield ratio during the later phase of OAE2 and the MCE indicate leakage from the sedimentary column into the water column under the influence of intensified and expanded oxygen minimum zones. These results suggest that a positive feedback loop, rooted in the benthic phosphorus cycle, contributed to increased marine productivity and carbon burial over an extended period of time during OAEs.
... For example, short-term local variations in δ 13 C may reflect a direct response to transgression-regression cycles, which affect the area of shelf and marginal seas as major sinks for organic matter, or changes in oceanic 12 C storage in response to changing ocean circulation Voigt, 2000). Changes in local upwelling may also affect the δ 13 C record, with waters coming from oxygen-minimum zones having lower seawater δ 13 C than near-surface dissolved inorganic carbon (Berger and Vincent, 1986). As such, local oceanographic feedbacks may have produced carbon-isotope excursions partially decoupled from the isotopic composition of the global ocean-atmosphere carbon reservoir. ...
Article
Full-text available
The greenhouse world of the mid‐Cretaceous (~94 Ma) was punctuated by an episode of abrupt climatic upheaval: Oceanic Anoxic Event 2. High‐resolution climate records reveal considerable changes in temperature, carbon cycling, and ocean chemistry during this climatic perturbation. In particular, an interval of cooling has been detected in the English Chalk on the basis of an invasive boreal fauna and bulk oxygen‐isotope excursions registered during the early stages of Oceanic Anoxic Event 2—a phenomenon known as the Plenus Cold Event, which has tentatively been correlated with climatic shifts worldwide. Here we present new high‐resolution neodymium‐, carbon‐, and oxygen‐isotope data, as well as elemental chromium concentrations and cerium anomalies, from the English Chalk exposed at Dover, UK, which we evaluate in the context of >400 records from across the globe. A negative carbon‐isotope excursion that correlates with the original “Plenus Cold Event” is consistently expressed worldwide, and CO2 proxy records, where available, indicate a rise and subsequent fall in CO2 over the Plenus interval. However, variability in the timing and expression of cooling at different sites suggests that, although sea‐surface paleotemperatures may reflect a response to global CO2 change, local processes likely played a dominant role at many sites. Variability in the timing and expression of changes in water mass character, and problems in determining the driver of observed proxy changes, suggest that no single simple mechanism can link the carbon cycle to oceanography during the Plenus interval and other factors including upwelling and circulation patterns were locally important. As such, it is proposed that the Plenus carbon‐isotope event is a more reliable stratigraphic marker to identify the Plenus interval, rather than any climatic shifts that may have been overprinted by local effects.
... The massive accumulation of marine organic matter in the uppermost Ordovician and lowermost Silurian of Africa (Semtner and Klitzsch, 1994) and elsewhere during coeval major transgressions caused the lowering of the CO 2 level in the atmosphere and hydrosphere, resulting in cooling and glaciation. Positive δ 18 O values are often associated with negative δ 13 C shifts in the Cenozoic marine isotope record, which has been interpreted as the result of an increased ice volume affecting Earth (Berger and Vincent, 1986). The high CO 2 withdrawals from the air, due to organic matter accumulation in the sea, may have caused a decrease in global temperatures and the onset of a new glaciation (Caputo, 1994;Gouldey et al., 2010) at higher latitudes of Gondwana. ...
Article
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Turbidity currents, tectonism, debris flows, glaciation, and other geologic processes are considered to be responsible for the generation of Silurian–Mississippian diamictites in northern Brazil. Processes that best account for the features observed in these strata are glaciation, deglaciation and sedimentary deformation. Four main glacial ages are identified to have occurred in the Parnaíba Basin during the Paleozoic. Glacially influenced deposits are found in the Lower Silurian, Upper Devonian, Lower Mississippian, and Middle Mississippian strata. The Parnaíba Basin is characterized by outcrops providing robust lithological evidence for three glacial ages, identified by lithological features and dated by palynological studies. A fourth glaciation, as old as Tournaisian, was recently recognized only in the subsurface of the basin. The glacial features were illustrated and the rocks accurately dated with palynomorphs based on very accurate palynological studies. Additional, palynological information, derives from outcrops and shallow boreholes drilled by a private company (Themag), the National State Mineral Production Department (Departamento Nacional de Produção Mineral -DNPM), and the Brazilian Geological Survey Company (Companhia de Pesquisa de Recursos Minerais-CPRM). The purpose of this reexamination, including many new illustrations, interpretations and conclusions, is to evaluate primary sedimentological and paleontological data related to the above mentioned glaciations. Some authors remain skeptical about the record of Early to early Late Paleozoic glaciations in western Gondwana, especially in Brazil, mainly because evidence provided in the literature is relatively scanty. The Parnaíba Basin provides special conditions for the study of these glaciations, although evidence for each of them varies considerably as discussed in the text.
... These events represent prolonged and intense perturbations of the global carbon cycle (e.g., Arthur et al., 1985) associated with widespread anoxia in most ocean basins. Oceanic Anoxic Events are also characterized by positive carbon isotope ( 13 C) excursions that have been related to globally enhanced rates of organic carbon burial (e.g., Berger and Vincent, 1986;Kump, 1991). The most prominent of these events were OAE1a during the early Aptian and OAE2 at the Cenomanian/Turonian boundary. ...
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Oceanic Anoxic Events (OAEs) document major perturbations of the global carbon cycle with repercussions on the Earth’s climate and ocean circulation that are relevant to understand future climate trends. Here, we compare sedimentation patterns, nutrient cycling, organic carbon accumulation and carbon isotope variability across Cretaceous Oceanic Anoxic Events OAE1a and OAE2 in two drill cores with unusually high sedimentation rates from the Vocontian Basin (southern France) and Tarfaya Basin (southern Morocco). OAE1a and OAE2 exhibit remarkable similarities in the evolution of their δ¹³C excursion with long-lasting negative carbon isotope excursions preceding the onset of both anoxic events, supporting the view that OAEs were triggered by massive emissions of volcanic CO2 into the atmosphere. Based on analysis of cyclic sediment variations, we estimated the duration of the individual phases within the carbon isotope excursions. For both events, we identify: (1) a precursor phase lasting ~ 430 kyr and ~ 130 kyr, (2) an onset phase of ~ 390 and ~ 70 kyr, (3) a peak phase of ~ 600 and ~ 90 kyr, (4) a plateau phase of ~ 1400 and ~ 200 kyr and (5) a recovery phase of ~ 630 and ~ 440 kyr, respectively. The total duration of the positive carbon isotope excursion is estimated as 3400 kyr and 790 kyr and that of the main carbon accumulation phase as 980 kyr and 180 kyr, for OAE1a and OAE 2 respectively. The extended duration of the peak, plateau and recovery phases requires fundamental changes in global nutrient cycles either (1) through excess nutrient inputs to the oceans by increasing continental weathering and river discharge or (2) through nutrient-recycling from the marine sediment reservoir. We investigated the role of phosphorus on the development of carbon accumulation by analysing phosphorus speciation across OAE2 and the mid-Cenomanian Event (MCE) in the Tarfaya Basin. The ratios of organic carbon and total nitrogen to reactive phosphorus (Corg/Preact and Ntotal/Preact) prior to OAE2 and the MCE hover close to or below the Redfield ratio characteristic of marine organic matter. Decreases in reactive phosphorus resulting in Corg/Preact and Ntotal/Preact above the Redfield ratio during the later phase of OAE2 and the MCE indicate leakage from the sedimentary column into the water column under the influence of intensified and expanded oxygen minimum zones. These results suggest that a positive feedback loop, rooted in the benthic phosphorus cycle, contributed to increased marine productivity and carbon burial over an extended period of time during OAEs.
... Our d 11 B cc data suggest a transient p CO 2 decline from about 300 p.p.m. to 140 p.p.m. However, there is little support in our data (or the similar p CO 2 record produced recently 47 on the basis of biomarker carbon isotopes) for a large and permanent drop in p CO 2 during the middle Miocene, as has previously been suggested 8,9,15 . Another prominent step in the global cooling trend occurred in the late Pliocene (between about 4 and 2 Myr ago) 36 which culminated in the onset of major glaciation in the Northern Hemisphere. ...
Conference Paper
Drift sediments recovered from the East Antarctic continental rise at Ocean Drilling Program (ODP) Site 1165 are used to infer variations in East Antarctic Ice Sheet (EAIS) stability and sea ice coverage during the late Miocene and early Pliocene. A significant increase in the deposition of biogenic opal from similar to 5.8 to 5.2 Ma points to an early Pliocene reduction in sea ice and a subsequent increase in biological productivity. Time intervals at similar to 7.2 to 6.6 Ma and similar to 5.2 to 4.8 Ma are characterized by pronounced maxima in the long-term trend of terrigenous matter accumulation (MAR(ter)) indicating high continental erosion rates potentially caused by ice sheet growth. A Southern Ocean wide impact of these events is suggested by similar evidence found at ODP Site 1095 (Antarctic Peninsula). Superimposed on the MAR(ter) maxima we observe enhanced orbital variability in iron accumulation at Site 1165 pointing to a dynamic behavior of the EAIS with waxing and waning ice masses. From the concurrence of these high amplitude ice sheet fluctuations with maximum variance in Earth's obliquity, we propose that the insolation gradient between high and low latitudes affected the delivery of moisture to Antarctica and thus controlled ice volume variations. (c) 2004 Elsevier B.V. All rights reserved.
Chapter
More than 60 global “events” have been identified in the isotopic records of ∂ 13C, ∂ 18O, ∂ 34S and 87Sr/86Sr. Over half of these are carbon isotopic events, about equally divided between positive excursions (or a simple rise) and negative excursions (or a fall). The positive excursions generally have been ascribed to “oceanic anoxic events” or similar incidents of gross storage of organic carbon, and negative isotopic events have been related to a catastrophic reduction of primary productivity, but many records suggest a complex origin. Likewise strontium isotopic shifts are generally related to changes in the balance of inputs to the ocean of light strontium from reaction with MOR basalts and of heavy strontium from uplift and erosion of old cratonic terranes. Despite this variety of origins, most of the isotopic events of these elements have potential for worldwide stratigraphic correlation, with resolution that may equal or exceed that of biostratigraphy. Diagenetic distortion of isotopic profiles should be minimized by screening samples with appropriate textural and trace element criteria.
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Stratigraphic collection of 263 belemnite rostra (guards) from Jurassic to Lower Cretaceous sediments in the Moscow area of Russia, northern German England, New Zealand, and Morocco were analyzed to determine in their delta(18)O and delta(13)C as a proxy for isotopic composition of surface seawater, Internal structures of the rostra were studied using cathodoluminescence and SEM techniques, their trace element (Fe, Mn, Mg;, and Sr), and the stable carbon and oxygen isotope compositions. The average stratigraphic resolution is about 1 Ma. These samples represent a broad range of paleolatitudes and paleoceanographic settings, ranging from 42 degrees N to 82 degrees S, covering boreal to subtropical, brackish to open marine shelf paleoenvironments. The rostra originally contained domains enriched in organic matter that were later replaced by luminescent diagenetic calcite, thereby generating an impression of "seasonal growth rings." Diagenetic calcite accounts for up to 6.8 percent of the rostrum. The trace element content of the rostra range from 227 to 3935 ppm for Mg, 379 to 1514 ppm for Sr, and up to 305 and 3662 ppm for Mn and Fe, respectively. However, selective drilling of only primary calcitic domains resulted in 90 percent of all analyzed samples to fall within the range of trace element values typical for modern low Mg-calcite shells. The chemical and textural data suggest that the primary calcite of the rostra is well preserved, as is its isotopic signature. The delta(13)C and delta(18)O measurements define oscillating temporal bands, of about 3 to 4 permil width, around more or less modern marine values of +2 and -1 permil, respectively, Oxygen isotopes in the well preserved rostra most likely reflect temperature variations within a similar to 14 +/- 8 degrees C range. The observed 3 to permil spread of values between contemporaneous specimens, which is comparable to the scatter of data reported for modern low-Mg calcitic brachiopod shells, probably reflects the diversity of local ecosystems, although some of the spread may be due to real short term temporal variations within single biozones. The delta(13)C values of the rostra define a band similar to that of the oxygen isotopes, and the temporal oscillations of both isotope curves are commonly in phase. The above dataset, complemented by the results of Jones, Jenkyns, and Hesselbo (1994) and Jones and others (1994), yields a composite delta(18)O and delta(13)C variations in belemnite guards for the entire Jurassic-Early Cretaceous interval. For delta(18)O, the oscillating band indicates that the most negative values occur at times of independently postulated global and/or regional anoxic events, such as those in the Toarcian and Kimmeridgian as well as the Aptian. These OAEs appear to be characterized by up to 10 degrees C higher seawater temperatures than the intervening background times. The delta(13)C record shows C-13 depletion for the Kimmeridgian event but enrichment for the other two, suggesting that the delta(13)C temporal oscillations and OAEs are not simply a reflection of surficial productivity due to operation of the biological pump, but rather of changing oceanic circulation patterns due to variations in latitudinal surface temperature gradients.
Article
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The Owadów-Brzezinki quarry is one of the most important paleontological sites in Poland, known for its exceptionally well-preserved Upper Jurassic (Middle Volgian = uppermost Lower Tithonian) fossils. Carbonate deposits of the section record a transition from an offshore to coastal and lagoonal settings and have been studied based on microfacies, micropalaeontological, isotope and chemical proxies. The obtained data point to normal marine conditions during the deposition of the older part of the quarry section in an offshore setting and a gradual transition into lagoonal environment characterized by high-amplitude variations in seawater salinity and oxygenation level of bottom waters, both of which resulted in considerable changes in benthic fauna assemblages or in the total lack of the fauna at some intervals. Above-mentioned conditions during the deposition of the middle part of the quarry section have probably allowed the preservation of diversified fauna with soft tissues. The microfacies and chemical data indicate that dysoxic/anoxic episodes may have occurred not only during the deposition of known fauna-rich beds but also during the deposition of poorly studied, so far, younger part of the section. The uppermost part of the carbonates exposed in the Owadów-Brzezinki quarry originated during the re-appearance of normal marine chemistry mostly in the intertidal-subtidal settings. The depositional conditions of the Owadów-Brzezinki site are non- typical, among famous conservation Lagerstätten, owing to the rapid fluctuations in the oxygenation and salinity of bottom waters.
Chapter
The "Latest Paleocene Thermal Maximum" (or LPTM) ca. 55 Ma was characterized by a 4 to 6 °C rise in deep ocean water temperature and an extraordinary injection of ¹²C-rich carbon into the exogenic carbon cycle. The best explanation for the carbon cycle perturbation is that the bottom water warming converted massive amounts of marine gas hydrate to free CH4 gas, and this CH4 was added to the ocean. If correct, basic models for the global carbon cycle must be reconstructed with a gas hydrate "capacitor" so that large quantities of ¹²C-rich carbon can be stored and released over time. Although recent work has discussed CH4 release from gas hydrate, the first operational model of the global carbon cycle including CH4 storage is presented here both conceptually and mathematically. Using the Blake Ridge gas hydrate deposit as an example, the capacitor contains three internal reservoirs: dissolved gas, gas hydrate and free gas. Carbon enters dissolved gas through methanogenesis of organic matter. Upon saturation of pore waters, carbon is transferred to gas hydrate and then free gas at appropriate temperature and pressure conditions. Carbon leaves free gas to the exogenic carbon cycle through anaerobic CH4 oxidation or, if there is no overlying gas hydrate, direct injection to the water column. Because the amount and location of free gas depends on temperature, the capacitor can suddenly release massive amounts of ¹²C-rich carbon with abrupt bottom water warming. When the "gas hydrate" capacitor is connected to a Paleogene exogenic carbon cycle and subjected to a SOC warming, the response is similar to that observed for the LPTM.
Book
Paleoceanographic proxies provide infonnation for reconstructions of the past, including climate changes, global and regional oceanography, and the cycles of biochemical components in the ocean. These prox­ ies are measurable descriptors for desired but unobservable environmental variables such as tempera­ ture, salinity, primary productivity, nutrient content, or surface-water carbon dioxide concentrations. The proxies are employed in a manner analogous to oceanographic methods. The water masses are first characterized according to their specific physical and chemical properties, and then related to particular assemblages of certain organisms or to particular element or isotope distributions. We have a long-standing series of proven proxies available. Marine microfossil assemblages, for instance, are employed to reconstruct surface-water temperatures. The calcareous shells of planktonic and benthic microorgan­ isms contain a wealth of paleoceanographic information in their isotopic and elemental compositions. Stable oxygen isotope measurements are used to detennine ice volume, and MglCa ratios are related to water temperatures, to cite a few examples. Organic material may also provide valuable infonnation, e. g. , about past productivity conditions. Studying the stable carbon isotope composition of bulk organic matter or individual marine organic components may provide a measure of past surface-water CO 2 conditions within the bounds of certain assumptions. Within the scope of paleoceanographic investigations, the existing proxies are continuously evolving and improving, while new proxies are being studied and developed. The methodology is improved by analysis of samples from the water column and surface sediments, and through laboratory experiments.
Chapter
Inorganic geochemistry is used indirectly for reservoir rock analysis. Carbon and oxygen stable isotopes, strontium isotopes, and elemental concentrations are used for this purpose. In isotope analysis, the ratio of the heavier to the lighter isotope type is measured. This ratio is compared to a standard. The difference is positive if the sample contains heavier isotopes and is negative if it is reached in light isotopes. The fractionation has a major role in isotope values of different samples. Vital effects, for example, cause negative excursion in organisms. Both carbon and oxygen isotope ratios are used for sequence stratigraphy and reservoir zonation, recognition of nonconformities, and hiatuses and mass extinctions. Paleotemperature can be calculated by oxygen isotope ratios. The balance between continental and mantle Sr input to the oceans determines the variations of this isotope. The result is used for absolute age dating and understanding sea-level fluctuations. Elemental analysis of the rocks also provides some important proxies for interpreting paleoenvironmental conditions, stratigraphic correlations, facies classifying, provenance studies, and the rate of weathering. Uranium geochemistry has attracted more attention in recent years because it is available from many reservoirs through spectral gamma logging. Rate of erosion and redox conditions, as well as original mineralogy are inferred from uranium distribution in a studied formation. Sample selection is very important in geochemical analysis because the final results and interpretations strongly depend on sample type, distance from each other, and final quality control. Studies of some of these aspects and their applications are just at their beginning stages.
Article
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This work presents the analysis of C and O isotope values behavior in the carapace of ostracodes and foraminifera from the Romualdo Formation, Araripe Basin – PE. The analized samples were collected in three outcrops (Arrojado, Canastra and Cedro) located in the cities of Exu and Araripina. The de δ18O values ranged from -10.1‰ to -10.2‰ VPDB and the δ13C values ranged between -12,6‰ to +2.7‰ VPDB. The results for oxygen data indicate high temperature of waters and the deposition of marine limestones in all outcrops. For the carbon isotopic data in the Arrojado and Canastra outcrops, the values indicate an anoxic environment with high content of organic matter. In Cedro outcrop, a positive variation occurs indicating an increase in primary production, also associated to an anoxic event, and the positive values are interpreted as a transgressive pulse. These results indicate that Cedro outcrop, located in the middlesouth portion of the basin, has environmental characteristics with greater marine influence than in the Arrojado and Canastra outcrops, located in the southwest portion.
Article
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Palynology of the Neogene marine stratigraphic sequences in tropical latitudes is poorly studied Most studies focus on lower to middle Miocene deposits in the Caribbean, emphasizing the biostratigraphic value of dinoflagellate cysts. The palynological and calcareous nannofossil analysis of 50 samples from DSDP Hole 502A and their integration with the paleomagnetic and planktonic foraminifera data reveal a detailed and reliable chronostratigraphic framework, and the interpretation of the paleobathymetric and paleoenvironmental evolution of the sequence. Fossil content in a continuous late Tortonian to late Gelasian (~7.56-1.80 Ma) sequence of deep-marine sediments serves to calibrate ages of dinoflagellate cysts, and comparison with high latitude records reveals synchronous (Operculodinium janduchenei, Selenopemphix dionaeacysta, Barssidinium taxandrianum, and Lejeunecysta interrupta) and asynchronous events (Quadrina? condita) with biostratigraphic potential for the southwestern Caribbean Sea. Our results highlight the importance of analyzing continental palynomorphs in deep-marine deposits to increase the temporal resolution of future palynostratigraphic schemes. Micropaleontogical data indicate a lower bathyal–abyssal environment and four paleoceanographic settings defined by changes in surface water productivity. These intervals fluctuate from mesotrophic-oligotrophic (~7.56–6.31 Ma) to eutrophic (~6.18–4.98 Ma), oligotrophic (~4.74–3.41 Ma), and mesotrophic surface water conditions (~3.26–1.80 Ma). Changes in trophic conditions are strongly related to the paleoceanographic reorganization associated with the constriction and complete closure of the Central American Seaway, seasonal upwelling episodes, and the input of terrigenous organic matter probably transported from southern Central America and northern South America by turbidity currents.
Conference Paper
The palynology of marine stratigraphic sequences in the Neogene at tropical latitudes is still scarcely studied. The palynological content of 112 samples from ODP Hole 999A and DSDP Hole 502A from the Colombian Caribbean basin was analyzed to improve the knowledge about the spatio-temporal distribution of marine palynomorphs. The age model based on calcareous nannofossils, planktonic foraminifera, and magnetostratigraphic data indicated a continuous record from the Aquitanian to the Gelasian and the Tortonian to the Gelasian in Holes 999A and 502A, respectively. A low palynological recovery from the Early Miocene to the Middle Miocene, and intervals of moderate to good palynological recovery from the Middle Miocene to the Late Pliocene were recorded. The palynological association contains a higher proportion of coastal and neritic dinoflagellate cysts (dinocysts), compared with the oceanic species, together with abundant terrigenous material, in which pteridophyte spores are predominant. The comparison of our fossil records with those found in mid and high latitudes, allow to detect dinocysts with a biostratigraphic potential such as Quadrina? condita, Selenopemphix armagedonnensis, Operculodinium janduchenei, Minisphaeridium latirictum, Trinovantedinium ferugnomatum, and Selenopemphix dionaeacysta. Moreover, Lejeunecysta interrupta, Barssidinium taxandrianum, Selenopemphix conspicua, and Lejeunecysta hatterasensis were recorded for the first time in the Neotropical region. The continental palynological assemblages reveal synchronous events with a biostratigraphic potential for regional correlations, and several diachronic events compared to the records from Panama and the zonations of northern South America. These events include Palaeosantalaceaepites cingulatus, Psilastephanoporites herngreenii, Ladakhipollenites? caribbiensis and Echitricolporites mcneillyi, among others. Our preliminary results highlight the potential of the continental palynomorphs, deposited in deep marine environments, to establish more accurate time correlations with coetaneous continental deposits. Calibration of dinocyst events in future works and their integration with information of continental palynomorphs will increase the temporal resolution of palynostratigraphic schemes in the region and will contribute to reduce the gap for a better understanding of the latitudinal control of dinocyst species.
Chapter
The climatic history of the Arctic has been a matter of debate ever since the systematic sampling and study of seafloor sediments commenced several decades ago. The early Soviet investigators (Sacks, Belov, and Lapina, 1955), using radium distribution in sedimentary cores, estimated that rates of sediment accumulation in the entire basin were 1.2–2 cm/103 yr. These values are an order of magnitude higher than rates based on uranium series isotope dates (Ku and Broecker, 1967; Herman and Osmond, 1984; Chapter 22 of this volume). Linkova (1965) was the first to determine the magnetic polarity of Arctic basin sedimentary cores. Her studies demonstrated conclusively that sediment accumulation rates on topographic highs, such as the Lomonosov Ridge, are extremely slow, ~1–3 mm/103 yr. Similar results were obtained for the Alpha-Mendeleev Rise (Hunkins et al., 1971; Aksu, 1985a; Aksu and Mudie, 1985).
Article
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High-resolution biostratigraphic analyses of Miocene deep-sea cores reveal eight intervals of widespread hiatuses in the world ocean at 23.0 22.5, 20.0 18.0, 16.0 15.0, 13.5 12.5, 12.0 11.0, 10.0 9.0, 7.5 6.2, and 5.2 4.7 m.y. ago. In complete sections these hiatuses correspond to intervals of cool faunal and floral assemblages, rapid enrichment of delta18O, and sea-level regressions. These factors suggest that Miocene deep-sea hiatuses result from an increased intensity of circulation and corrosiveness of bottom currents during periods of increased polar refrigeration.
Conference Paper
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Oxygen and carbon isotopic data from mixed species of the benthic foraminifer Cibicidoides at Site 574 in the equa- torial Pacific are compared with benthic foraminiferal isotopic data from equatorial Pacific Site 77 (Keigwin and Keller, 1984) and western North Atlantic Site 563 (Miller and Fairbanks, 1983, in press). Cibicidoides within the age range of ~ 33 to 35 Ma (within the early Oligocene) at the Pacific sites were lower in δ 13C than those of the same age from the North Atlantic site. For those from ~26 to 33 Ma (late early to late Oligocene), the equatorial Pacific and western North Atlantic δ13C values were similar, whereas for those from ~26 to 12 Ma (latest Oligocene to Miocene) (see Miller and Fairbanks, 1983), Pacific values were lower. We suggest that this reflects bottom-water production analogous to modern North Atlantic Deep Water (NADW) in the early Oligocene and latest Oligocene to Miocene and reduced pro- duction of "NADW" in the late early to late Oligocene. High δ 18 θ values (approximately 2.0‰) were recorded at Site 574 for Cibicidoides at 36 Ma (earliest Oligocene); high, oscillating δ 18 θ values occurred from 30 to 29 Ma (near the early/late Oligocene boundary). These intervals of high δ 18 θ values apparently represent either bottom waters colder than at present or the presence of significant continental ice sheets. We suggest that major periods of continental glacia- tion occurred at approximately 36 and from 29 to 30 Ma.
Article
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Recent measurements1,2 on ice samples from Camp Century (Greenland, 77°10'N, 61°08'W), Byrd Station (Antarctica, 80°01'S, 110°31'W) and Dome C (74°40'S, 125°10'E) suggest that during the late part of the last glaciation the atmospheric CO2 concentration was significantly lower than during the Holocene. Further investigation of this natural increase of the atmospheric CO2 concentration in the past should aid our understanding of the climatic implications of the man-made CO2 increase since the beginning of industrialization3. Here we report new and precise measurements of the CO2 concentration of the air occluded in bubbles of ice samples from Camp Century and Byrd Station, using a new dry extraction technique. The extracted gases were analysed with an IR-laser spectrometer (IRLS). Samples from 22 different depths were analysed from each core. The samples are distributed over a depth interval corresponding approximately to the past 40,000 yr. In addition results for ice samples from selected depth horizons from a colder region (North Central, Greenland 74°37'N, 39°36'W) and from a warmer region (Dye-3, Greenland 65°11'N, 43°50'W) are given. Based on these results we estimate the trend of the atmospheric CO2 concentration during the past 40,000 yr.
Article
Up to now a few critical points and C and O shifts can be recognised in different Cenozoic sedimentary sections and may serve as datum levels for worldwide, stratigraphic correlations. The critical points are: the beginning of the M Eocene (c50myr) and in the M Miocene (c15myr) for del18O curves, in the M Miocene (c18myr) for del13C curves. 3 major oxygen shifts, corresponding to a rapid increase of about 1%o in the del18O are at the end of the Eocene, in the U Oligocene and in the M Pliocene. 2 major oxygen shifts corresponding to a rapid decrease in the del13C are at the Maastrichtian-Danian limit and at - 6.2myr. These critical points and C and O shifts almost certainly reflect abrupt changes in the geochemical and thermal structure of the oceans. -from English summary
Chapter
Data in the tropical Indian Ocean show an excursion of d13C signals toward heavier values, lasting for about 4 million years. The excursion terminates at approximately 13.5 Ma. The Chron 16 Carbon shift coincides with the cessation of an early Miocene warming trend. Hypothesizes that a feedback loop was established. An initial increase in the planetary temperature gradient started thermocline development which led to organic carbon extraction at the ocean margins which resulted in a drop in atmospheric carbon dioxide concentration. Concomitant cooling (reverse greenhouse effect) strengthened thermocline development, leading to further cooling. The loop was broken when available nutrients were used up. -from Authors
Article
Oxygen-18 records of benthic foraminifera from northeastern Atlantic and Southern Ocean cores are significantly different. This difference indicates that the deep water in the northeastern Atlantic Ocean during the last Ice Age was at least 1.3 °C cooler than in modern times. We show here that the occurrence of such a cold deep water mass implies that the North Atlantic was a sink for dense surface waters, replacing the Norwegian Sea where ice cover and stratification prevented the formation of deep water.
Article
Information on the history of the atmospheric CO2 content and the 13C/12 and 14C/C ratios is recorded in natural ice. Measurements on samples from very cold accumulation regions show that CO2 is occluded not only in air bubbles, but also in the ice lattice. The two CO2 components are of similar size. It is very difficult to measure CO2 in the bubbles and CO2 in the ice lattice separately. By melting the samples and extracting the evolving gases in two fractions, it is possible to estimate CO2 concentration in the bubbles and the ice lattice. Enrichment or depletion of CO2 in the bubbles by exchange with the ice is difficult to estimate. Information about this effect is expected from 13C/12C analysis on the extracted CO2 fractions.To investigate whether atmospheric CO2 content was different during the last glaciation than during the present one, sets of 16 and 20 samples distributed over the last 40,000 years from the two deep ice cores from Camp Century (North Greenland) and Byrd Station (West Antarctica) were measured. The time scales for the two cores are based on a rheological model. Results and conclusions are: — The data series from both cores show similar trends correlated to a certain degree to the δ18O profiles.— For both cores, the values for the CO2 concentration of the first fraction, considered to best represent the atmospheric composition, show lower values during glaciation than in the Holocene, with a minimum before the end of glaciation.— Low CO2 concentrations in the first fractions (200ppm) of certain samples are a strong indication that the atmospheric CO2 concentration during last glaciation was lower than during the postglacial. These low concentrations indicate that, at that time, CO2 concentration in the atmosphere could have been lower than today by a factor of 1.5. Possible explanations for such a change in atmospheric CO2 content as well as its influence on atmospheric 14C/C ratio and on the radiation balance is discussed.
Article
An increase in atmospheric pCO2 during deglaciation, of about 100 ppm, has been ascribed to a change in the chemistry of the ocean (Broecker, 1982, Progr. Ocn. 11, 151). It appears that Broecker's phosphate-extraction model has to be modified by decoupling a fertility decrease of the ocean from organic carbon buildup on the shelves, because of constraints from the amplitude and timing of the foraminiferal δ13C signal. Denitrification and carbon/carbonate rain ratios are possible mechanisms. Buildup of shelf carbonates, during deglacial transgression, may deliver a considerable amount of CO2, to the atmosphere, through decreasing the alkalinity of upper ocean waters. This mechanism relies heavily on a decrease in oceanic mixing rate, to retard equilibration with the deep sea. The Holocene increase in the dissolution of deep sea carbonates may yield constraints on shelf carbonate buildup (basin-shelf transfer). Very few cores from the deep-sea floor have been studied in sufficient detail to produce tests for these various hypotheses.
Article
When ranked according to deviation from isotopic equilibrium, deep-sea benthic foraminifera exhibit no correlation between the rankings for oxygen and for carbon. Both rank sequences are stable from east to west in the equatorial Pacific (fertility-independent) and from Glacial to post-Glacial (time-independent). Records for the past 15,000 yr suggest marked changes in deep-sea circulation during this time interval.
Article
Carbon isotopic analyses of benthonic foraminifera from palaeomagnetically dated piston core RC12-66 (east equatorial Pacific Ocean) show a permanent decrease in delta13C of ~ 0.50/00 in the upper reversed interval of palaeomagnetic Epoch 6 (about 6.3 Myr BP). Magnetostratigraphic and biostratigraphic correlations reported here suggest that this decrease is isochronous with a similar carbon shift observed at localities elsewhere in the Indo-Pacific region.
Article
Laminated, diatomaceous sediments of the Gulf of California consist of regularly alternating light-colored (diatom-rich) and dark-colored (clay-rich) laminae, approximately 2 mm. thick. The mean contents of opal (as diatom frustules) and quartz in the laminae, determined by X-ray diffraction methods, are: light-colored laminae, 52.4 per cent opal and 7.0 per cent quartz; dark-colored laminae, 26.5 per cent opal and 10.0 per cent quartz. The laminae cannot be distinguished on the basis of the contained diatom assemblages, only on the total contents of biogenous and terrigenous materials. Rates of deposition, determined by radiocarbon dating of organic and carbonate carbon in selected core sections, demonstrate that one light-colored lamina and one dark-colored lamina are deposited in a year, and a couplet of laminae constitute a varve. Phytoplankton production in the central Gulf of California is reasonably constant throughout the year, but river discharge fluctuates greatly during a year as a result of to...
Article
We present a revised Neogene geochronology based upon a best fit to selected high temperature radiometric dates on a number of identified magnetic polarity chrons (within the late Cretaceous, Paleogene, and Neogene) which minimizes apparent accelerations in sea-floor spreading. An assessment of first order correlations of calcareous plankton biostratigraphic datum events to magnetic polarity stratigraphy yields the following estimated magnetobiochronology of major chron- ostratigraphic boundaries: Oligocene/Miocene (Chron C6CN): 23.7 Ma; Miocene/Pliocene (slightly younger than Gilbert/Chron 5 boundary): 5.3 Ma; Pliocene/Pleistocene (slightly younger than Olduvai Subchron): 1.6 Ma. Changes to the marine time-scale are relatively minor in terms of recent and current usage except in the interval of the middle Miocene where new DSDP data reveal that previous correlations of magnetic anomalies 5 and 5A to magnetic polarity Chrons 9 and 11, respectively, are incorrect. Our revized magnetobiostratigraphic correlations result in a 1.5-2 m.y. shift towards younger magneto- biochronologic age estimate in the middle Miocene. Radiometric dates correlated to bio- and magnet- ostratigraphy in continental section generally support the revized marine magnetobiochronology presented here. Major changes, however, are made in marine-non-marine correlations in the Miocene in Eurasia which indicate African-Eurasian migrations through the Persian Gulf as early as 20 Ma. The 12.5 Ma estimate of the Hipparion datum is supported by recent taxonomic revisions of the hipparions and magnetobiostratigraphic correlations which show that primitive hipparions first arrived in Eurasia and North Africa at c.12.5 Ma and a second wave in the tropics (i.e. Indian and central Africa) at c. 10 Ma.
Article
O18/O16, C13/C12, and magnesium analyses were performed on a large number of Recent planktonic Foraminifera from South Pacific Ocean sediments. Results show that oxygen isotopic temperatures of Foraminifera tests may be used to locate ocean currents and to define the orientation of large crustal plates relative to the earth's rotational poles. Selective solution effects may cause isotopic temperatures of some species to become progressively colder with increasing water depth of the sediments from which they are taken. Where this is not taken into account, erroneous conclusions may result from the comparison of isotopic temperatures of samples from different locations. Depths at which Foraminifera secrete their tests appear to be determined by density and ultimately by osmotic equilibration with surrounding sea water. Susceptibility of Foraminifera tests to selective solution after death increases with magnesium content. Carbon isotope ratios correlate crudely with both temperature and salinity. The C13/C12 ratio of dissolved or particulate carbon in the oceans is probably the most important factor in determining the C13/C12 ratio of the test.
Article
Ice cores contain information on climatic variations and their causes. Recent results obtained on the new deep ice core drilled in 1981 at Dye 3, South Greenland, in the frame of the US-Danish-Swiss Greenland Ice Sheet Program are: Comparison of the δ 180 variations in the Greenland ice cores with those in European lake carbonate exhibits strong similarities and provides time marks (13,000, 11,000, 10,000 B.P.) for the Late-Glacial section of the ice cores; CO2 concentration measurements in the occluded air indicate low (180–200 ppm) CO2 concentrations 30,000 to 15,000 B.P. and an increase to ca. 300 ppm around 13,000 B.P.,. The CO2 increase might reflect a change in the ocean circulation at the end of the last glaciation and could have contributed to the establishment of the Holocene environmental conditions; 10Be concentration measurements on samples covering the last 50,000 yaers show a correlation with δ 180, low δ 180 values corresponding to high 10Be concentrations (atoms per g of ice). Probably this mainly reflects changes in the rate of precipitation in the northern hemisphere. Based on the ice core information climatic events during the Glacial-Postglacial transition are discussed.
Article
Analysis of the air enclosed in polar ice (~0.1 ml per g of ice1) provides one of the most promising ways of discovering atmospheric composition over the past 100,000 yr. Until now, because of an apparent but not well understood enrichment of CO2 in the trapped air, all attempts to reconstitute the ancient atmospheric CO2 content from polar ice have failed2-6. We have obtained CO2 contents that can reasonably be considered representative of present or past atmospheric contents using a new method of air extraction. The results reported here, based on the CO2 analysis of two deep Antarctic cores including the last climatic interchange, strongly suggest that during the coldest part of the last Ice Age (20,000-15,000 yr ago) the atmospheric CO2 content was half (0.016%) that of today's level (0.033%).
Article
The Mediterranean Sea became isolated from the world ocean in the late Miocene and underwent a `crisis of salinity' during which vast deposits of evaporites were laid down in pre-existing depressions. The final connection with the Atlantic is believed now to have been the Betic Strait entering into the Mediterranean from Andalusia, Spain. Although the closing of this connection, known as the Iberian Portal, is related to largescale plate movements which brought Africa into direct contact with southern Europe, its final severing may have resulted from glacial-eustatic lowering of the global ocean. Further stratigraphic resolution of late Miocene sea-level and ice-volume changes is sought to verify the eustatic-fall hypothesis.
Article
New data from three Tasman Sea cores support Keigwin's [1] observation that the delta13C of Pacific benthic foraminifera (and by inference bottom-water TCO2) decreased by 0.70/00 at about 6.5 Myr B.P. Simple box models are developed and used to test several hypotheses about the cause of the delta13C decrease. We favor the idea that the delta13C shift was due to a rapid change in TCO2 cycling within the oceans (such as would result from either a decrease in upwelling rate, or an increase in the fraction of PO43- reaching the deep oceans in particulate organic matter and a corresponding drop in the preformed PO43- concentration). The delta13C decrease across the shift might reflect either a global decrease in upwelling rate, or a different abyssal circulation pattern before the shift.
Article
13C/12C ratios of Miocene benthic foraminifera from 22 Pacific Ocean sites vary with time but are similar at almost all sites in any restricted interval. delta13C values are correlated with sea levels inferred from onlap/offlap curves, reflecting the deposition of greater amounts of organic matter on the continental shelves during transgressions. Differences in delta13C between sites are correlated with local differences in biological productivity in the overlying surface waters. 13C/12C values of benthic foraminifera show promise as indicators of marine paleoproductivity.
Article
The oxygen isotopic record in deep-sea sediments is a chief source of information on ocean and climate history of the Tertiary period. Traditionally interpretations have focused on the relative importance of temperature change and of polar ice buildup as dominant generating factors1–6. Effects of diagenesis have been largely ignored. Here I show that recrystallization must not be neglected: with reasonable assumptions it can account for much of the familiar Cenozoic trend in the oxygen isotopic composition of foraminifera. Recent studies7,8 indicate that there may be considerable recrystallization of Tertiary carbonates with very significant effects on isotopic compositions. Specifically, the work of Baker et al. 7 suggests that there could be total recrystallization in sediments deposited as recently as the early Tertiary.
Article
Benthic foraminifera are protozoans found throughout the deep-sea environment, secreting a test of calcium carbonate or constructing a test of cemented sediment particles (agglutinated or arenaceous foraminifera). In typical deep-sea sediments, the organic cement of agglutinated taxa degrades upon burial in the sediment and, consequently, few specimens survive in the fossil record. In contrast, calcareous species are well preserved in most oceanic sediments, except at abyssal depths where most carbonate sediment is dissolved because of high levels of carbonate under-saturation of the bottom waters. Although benthic foraminifera have been widely used in studies of Cenozoic palaeoceanography, little is known about the ecology of deep-sea species. I present here an analysis of living (stained) benthic foraminifera within the upper 15 cm of deep-sea sediments, which reveals species-specific microhabitat preferences, with distinct morphological features found with epifaunal and infaunal species. The existence of infaunal habitats suggests that the distribution of certain foraminifera is not directly controlled by overlying bottom-water conditions, but by physicochemical conditions within the sediments. The microhabitat preferences may also explain interspecific carbon isotope differences, as existing data show that infaunal foraminifera generally have lower δ 13C isotope values than epifaunal species.
Chapter
Sea-surface temperature (SST), salinity gradients, and enhanced productivity of coastal upwelling regions leave a marked imprint on the oxygen and carbon stable isotopic composition of foraminiferal shells. For a better understanding of these isotopic signals, we systematically analyzed planktonic and benthic species from surface sediment samples and plankton tows from the eastern Atlantic continental margin (12–35°N). Due to seasonal variations of the Trade Wind regime, centers of coastal upwelling where SST is much below normal migrate markedly in latitude, from ti~12°N during late winter to ~30°N during late summer, and continue to be active throughout the year at 20–23°N. As a result, nearshore seasonal temperature variations are low north of 20°N, but unusually high near 15°N. The δ¹⁸O values of shells of Globigerinoides sacculifer and Globigerinoides ruber (pink and white) delineate the pattern of SST during summer and δ¹⁸o values for Globorotalia inflata reflect the SST during winter. Oxygen isotopes of Globigerina bulloides document the temperature ranges of the upwelling seasons. The combined isotopic record of G. ruber white and G. inflata clearly reveals the latitudinal variations of seasonality and the annual mean SST, thus documenting the longterm position of upwelling cells during the different seasons in the sediments.
Article
This contribution is a summary of our studies on late Miocene isotope stratigraphy. We interpret the results using simple models and present additional evidence that the δ 13C shift at 6.2 Ma was a time-stratigraphic event. The average deep-water metabolic CO2 and nutrient content remained unchanged across the δ 13C shift, but the net flow of deep waters towards the North Pacific was intensified. The late Miocene deep-ocean density structure was similar to that of today's oceans, and bottom water temperatures were 1°C warmer if constant ice volume is assumed.
Article
Carbon and oxygen isotopic analyses have been performed on live-stained aragonitic and calcitic benthic foraminifera and dissolved inorganic carbon (DIC) from the Southern California Borderland to examine carbon isotopic fractionation in foraminifera. Temperature, salinity and pH data have also been collected to permit accurate determination of the δ13C of bicarbonate ion and thus aragonite-HCO3 and calcite-HCO−3 isotopic enrichment factors (ϵar-b and ϵcl-b, respectively). Only species which precipitate in 18O equilibrium have been considered.ϵar-b values based on Hoeglundina elegans range from 1.9%. at 2.7°C to 1.1%. at 9.5°C. Only the lower temperature values agree with a tentative carbon isotope equilibrium equation for aragonite based on the data of Rubinson and Clayton (1969) and Emrich et al. (1970). The temperature dependence of ϵar-b is considerably greater than the equilibrium equation would predict and may be due to a vital effect.The calcitic foraminifera Cassidulina tortuosa, Cassidulina braziliensis, and Cassidulina limbata, Bank and Terrace dwellers, have similar δ13C values and yield an average ϵcl-b value of −0.2 ± .1%. between 8° and 10°C. Calcitic Uvigerina curticosta, Uvigerina peregrina, and megalospheric B. argentea, Slope and Basin dwellers, are −0.7 ± .1%. enriched relative to ambient bicarbonate for 3 to 9°C. No temperature dependence for ϵcl-b was observed for the species in either habitat. The ϵcl-b values for Cassidulina species are close (± 0.3%.) to the values given by the tentative equilibrium curve for calcite, while Uvigerina and Bolivina species give values 0.2–0.8%. less. The ϵcl-b difference between the Cassidulina species and the Uvigerina and Bolivina species is attributed to the incorporation of 13C-depleted pore water DIC by the latter group rather than to taxonomic or temperature differences.
Article
A search for stable-isotopic signals and biostratigraphic events in Deep Sea Drilling Project (DSDP) cores to improve chronologic resolution with an aim to reconstruct the paleoenvironment of the preglacial and postglacial Miocene oceans has led to the recognition of an apparently global decrease in the benthic foraminiferal delta 13C in the latest Miocene. This carbon-isotopic shift is consistently bracketed by the first evolutionary appearances of several taxa of phytoplankton the ages of which have been accurately estimated from paleomagnetically dated piston cores. The first appearance of nannofossils Amaurolithus primus and A. delicatus at 6.25 m.y. B.P. and the diatoms Thalassiosira praeconvexa and Nitzschia miocenica elongata at 6.10 and 6.00 m.y. B.P., respectively, and the carbon-isotopic shift itself (dated between 6.10 and 5.90 m.y. B.P.) provide convenient synchronous events to aid in the reconstruction of the late Miocene world ocean. Magnetostratigraphically estimated ages of other useful late Miocene nannofossil events include first appearances of Discoaster quinqueramus at 8.00 m.y. B.P., D. surculus at 6.40 m.y. B.P., Amaurolithus tricorniculatus s.s. at 5.70 m.y. B.P., A. amplificus at 5.65 m.y. B.P., and Ceratolithus acutus at 5.20 m.y. B.P., and the last appearances of D. quinqueramus at 5.45 m.y. B.P. and A. amplificus at 5.30 m.y. B.P.
Article
Causes of change in deep water delta13C can be either global or local in extent. Global causes include (1) climatically-induced changes in the amount of terrestrial biomass which alter the average carbon isotopic composition of the oceanic reservoir1, and (2) erosion and deposition of organic-rich, continental shelf sediments during sea level fluctuations which change the mean oceanic carbon: phosphorus ratio2. Regional gradients of delta13C are created by remineralization of organic detritus within the deep ocean itself thus reflecting the distribution of water masses and modern thermohaline flow. Changes in a single geological record of benthic foraminiferal delta13C can result from any combination of these global and abyssal circulation effects. By sampling a large number of cores collected over a wide bathymetric range yet confined to a small geographical region we have minimized the ambiguity. We can assume that each delta13C record was equally affected by global causes of delta13C variation. The differences seen between the delta13C records must, therefore, reflect changes in the distribution of delta13C in the deep ocean. We interpret these differences in distribution in terms of changes in the ocean's abyssal circulation. Benthic foraminiferal carbon isotopic evidence from a suite of Sierra Leone Rise cores indicates that the deeper parts of the eastern Atlantic basins underwent a reduction in [O2] during the maximum of the last glaciation. Reduced advection of O2-rich deep water through low-latitude fracture zones, associated with increased delivery of organic matter to the deep ocean, lowered the delta13C of deep water SigmaCO2 at all depths below the sill separating the eastern and western Atlantic basins.3 This decreased advection into the eastern Atlantic Ocean coincides with the overall decrease in deep water production in the North Atlantic during the last glacial maximum4-7.
Oxygen isotopic compositions of the tests of planktonic foraminifera from several Deep Sea Drilling Project sites provide a general picture of low-latitude marine temperatures from Maastrichtian time to the present. Bottom temperatures determined from the isotopic compositions of benthonic foraminifera are interpreted as being indicative of high-latitude surface temperatures. Prior to the beginning of middle Miocene time, high- and low-latitude temperatures changed in parallel fashion. Following an apparently small and short-lived drop in temperature near the Tertiary-Cretaceous boundary, temperatures remained warm and relatively constant through Paleocene and early and middle Eocene time; bottom temperatures then were on the order of 12°C. A sharp temperature drop in late Eocene time was followed by a more gradual lowering of temperature, culminating in a late Oligocene high-latitude temperature minimum of about 4°C. A temperature rise through early Miocene time was followed in middle Miocene time by a sudden divergence of high- and low-latitude temperatures: high-latitude temperatures dropped dramatically, perhaps corresponding to the onset of major glaciation in Antarctica, but low-latitude temperatures remained constant or perhaps increased. This uncoupling of high-and low-latitude temperatures is postulated to be related to the establishment of a circum-Antarctic circulation similar to that of today. A further drop in high-latitude temperatures in late Pliocene time probably signaled the onset of a major increase in polar glaciation, including extensive sea-ice formation. Early Miocene, small-amplitude (1 per mil) sympathetic fluctuations in isotopic compositions of planktonic and benthonic foraminifera have been identified. These have a period of several hundred thousand years. Superimposed upon these are much more rapid and smaller fluctuations (0.2 to 0.5 per mil) with a period of about 80,000 to 90,000 yr. This is similar to the period observed for Pleistocene isotopic temperature fluctuations. In low latitudes, much smaller vertical temperature gradients seem to have existed during Maastrichtian and Paleogene time than exist at present. The absence of a sharply defined thermocline during early Tertiary time is also suggested.
Article
Oxygen and carbon isotope stratigraphies are given for the planktonic foraminifer Globoquadrina venezuelana (a deep-dwelling species) at 3 DSDP sites located along a N-S transect at approx 133oW across the Pacific equatorial high-productivity zone. The records obtained at Sites 573 and 574 encompass the lower Miocene. At Site 575 the record includes the middle Miocene and extends into the lowermost lower Miocene. The time resolution of the planktonic foraminifer isotope record varies from 50 000-500 000yr. The benthic foraminifer Oridorsalis umbonatus was analyzed for isotope composition at a few levels of Site 575. Isotope stratigraphies for all 3 sites are compared with carbonate, foraminifer preservation, and grain size records. We identified a number of chemostratigraphic signals that appear to be synchronous with previously recognized signals in the W equatorial Pacific and the tropical Indian Ocean, and thus provide useful tools for chronostratigraphic correlations. The sedimentary sequence at Site 573 is incomplete and condensed, whereas the sequences from Sites 574 and 575 together provide a complete lower Miocene record. The expanded nature of this record, which was recovered with minimum disturbance and provides excellent calcareous and siliceous biostratigraphic control, offers a unique opportunity to determine the precise timing of early Miocene events. Paleomagnetic data from the hydraulic piston cores at Site 575 for the first time allow late early Miocene paleoceanographic events to be tied directly to the paleomagnetic time scale. For instance major carbonate dissolution event in the late early Miocene, starting at approximately 18.7 Ma, is associated with the enrichment in 13C. The maximum dissolution is coeval with the Chron 16 Carbon Shift. It corresponds to a prominent acoustic horizon that can be traced throughout the equatorial Pacific.-from Authors
Article
Significant short-term carbon isotope fluctuations are present in Cretaceous pelagic limestones from widely distributed onshore sections in the Circum-Atlantic-western Tethyan region. More than 1000 closely spaced samples were analyzed during this study. At least seven major delta/sup 13/C excursions can be correlated from section to section. The most important heavy events occur near the Aptian-Albian and Cemonanian-Turonian boundaries, whereas light events are near the Jurassic-Cretaceous, Albian-Cemonanian, Turonian-Coniacian, and Cretaceous-Tertiary boundaries. The association of events with stage boundaries and the consistent correlation of events between stratigraphic sections provides a significant new tool for time-rock correlation independent of standard biostratigraphic techniques. The temporal association of these carbon isotope events with stage boundaries (faunal and floral events), global eustatic sea-level variations, and oceanic anoxic events demonstrates the potential usefulness of carbon isotope studies in interpreting variations in paleo-oceanic circulation. Furthermore, the association of carbon isotope variations with anoxic events is potentially useful for evaluation of the precise timing and the magnitude of preservation of organic matter in deep-sea and continental-margin sediments. Thus, isotopic studies may aid in estimating potential hydrocarbon resources in largely unexplored oceanic basins or along continental margins. 12 figures, 1 table.
Chapter
Increase in CO2 levels two to tenfold (10x being upper limit) seems required to approximate Cretaceous temps. This is in addition to geographic forcings.
Article
Previous studies of benthic foraminiferal isotopic composition have demonstrated that a latest Eocene-earliest Oligocene benthic foraminiferal δ18O increase occurred in the Pacific, Southern and Atlantic Oceans1-9. A Middle Miocene δ18O increase has been noted in the Pacific, Southern and South Atlantic Oceans1-3,7,10,11 and tentatively identified in the North Atlantic12,13. Due to the incomplete nature of the North Atlantic stratigraphical record14,15, however, the Oligocene to Middle Miocene isotopic record of this ocean is poorly understood. In the modern ocean, the North Atlantic and its marginal seas has a critical role in abyssal circulation, influencing deep- and bottom-water hydrography as far away as the North Pacific16-18. We now report oxygen isotope measurements on Oligocene to Middle Miocene (12-36 Myr BP) benthic foraminifera in the western North Atlantic which show two periods of enriched 18O values: early Oligocene and early Middle Miocene. These enriched intervals are interpreted as resulting, in part, from the build-up of continental ice sheets. The Oligocene to Middle Miocene δ13C record shows three cycles of enrichment and depletion of large enough magnitude to be useful for time-Stratigraphical correlations. Within the biostratigraphical age resolution, δ18O and δ13C records correlate with records from other oceans, helping to establish a useful Tertiary isotopic stratigraphy. An Atlantic-Pacific δ13C contrast of 0.3-0.9‰ during the latest Oligocene to Middle Miocene (12-26 Myr BP) indicates North Atlantic deep and bottom-water production analogous to modern North Atlantic deep water (NADW).
Article
Stable isotope results from seven Miocene Deep Sea Drilling Projects in the equatorial and southwest Pacific Ocean, previously correlated using carbon isotope stratigraphy, have been examined, discussed, and interpreted in terms of the development of the Miocene Pacific Ocean. The most obvious features of the benthonic foraminiferal stable isotopic records are a major increase inδ18O(∼1.0‰) during the Middle Miocene, a series of long-term oscillations (2–3 My) of amplitude 0.5–0.75‰ and a decrease inδ13C values (0.5–;1.0‰) during the latest Miocene. Planktonic foraminiferalδ18O records show different trends for high and low latitude regions. In the equatorial Pacific, planktonicδ18O values actually decrease during the Miocene whereas in the higher southern latitudes planktonicδ18O values become more positive in response to cooling surface waters.
Article
Changes in the surface salinity distribution in the World Ocean, by changing the extent of sea ice in the North Atlantic and Antarctic, can lead to climatic change. By reducing the water vapor flux across Central America, the salinity of the North Atlantic is reduced. If this change persists over a sufficient length of time, a glacial climate could be initiated. An examination of the “Little Ice Age” tends to confirm this hypothesis. A return to an interglacial climate may be the result of overextension of glaciers followed by stagnation of the bottom water. Stagnation is terminated by geothermal heating at the ocean floor, followed by vertical mixing of the warmed, saltier water into the subarctic gyre of the North Atlantic. This, in turn, results in a reduction of sea ice and in climatic warming.
Article
Detailed oxygen and carbon isotope stratigraphies for two species of benthic foraminifera (Planulina wuellerstorfi; Oridorsalis umbonatus) are compared between two box cores, spanning the period of deglaciation and Holocene. Within-core stratigraphies are quite well correlated, between-core signals less so. Vertical mixing and (possibly) horizontal redeposition processes disturb the signals. Nevertheless, there is a strong suggestion of fluctuations in the ambient bottom-water conditions, fo the entire time span considered.
Chapter
The clearest records of changes in chemistry of the exogenic cycle are found in mineral inventories (NaCl, CaSO4, Ccarb, Corg, P), isotope ratios (δ34Ssft, δ13Ccarb, 87Sr/86Srcarb,87Sr/86Srapt), 87Sr/86Srapt), and trace elements (Ce/Laaptand heavy metals in black shales) vs. age. While these variations can be simplistically modelled in the long-term to confine all variations to the larger sedimentary reservoirs, there are several reasons to assert that some of the variability is internal to the smaller oceanic (and atmospheric) reservoirs, especially for short-term events. These are controlled by complex feedback loops, perhaps ultimately forced by plate-tectonic activity cycles. Many links are only speculative.
Article
Precise and detailed measurements have been made of the 13C content of both planktonic and benthic foraminifera in core V 19-30. Using the approach developed by Broecker, a record of atmospheric CO2 concentration during the past 120,000 years has been derived which provides independent confirmation that the CO2 concentration in the glacial-age atmosphere was much lower than it is today.