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16. Carbon Isotope Data from Leg 74 Sediments
Supplementary resource (1)
Data
January 1984
... Главным маркером вулканокластических образований является вулканическое стекло, содержание Мощности и состав вулканокластических отложений с учетом данных smeer-слайдов [16,17,[27][28][29][30][37][38][39][40][41][42] Статистические характеристики Пирокластика (группа 1) Вулканокласто-осадочные прослои (группа 2) составе пеплов фигурируют кальцит, доломит, микрит, опока. Они содержатся в незначительных количествах проб и могут отражать процесс изменения осадков. ...
... Имеется ряд профилей непрерывного сейсмического зондирования центральной части хребта [11,37] с указанием основных границ, которые позволяют сделать стратиграфическую привязку пирокластических горизонтов. Это дает представление об истории и условиях формирования вулканокластических толщ и возможных источниках вулканического материала. ...
... Это дает представление об истории и условиях формирования вулканокластических толщ и возможных источниках вулканического материала. Изучение нескольких ключевых профилей показывает ряд расположенных над фундаментом рефлекторных горизонтов, датируемых границами основных стратиграфических отделов: мел-палеоцен, палеоцен-эоцен, эоцен-олигоцен; отдельно выделяется толща осадков возраста среднего миоцена [10,37]. Эти горизонты отражают основные смены условий осадконакопления в регионе, связанные с повышением уровня моря, изменением гидродинамической обстановки. ...
На основе данных глубоководного бурения (проекты DSDP, ODP) проведено обобщение по распреде-
лению вулканокластического материала в кайнозойском чехле Китового хребта, выделены циклы его
накопления. Доказано, что распределение данного материала в палеогене отражает, в первую очередь,
динамику вулканизма самого хребта. Определены источники вулканокластики, показана возможность
наличия в центральной его части подводных вулканов раннего эоцена. Приведенное сравнение ди-
намики вулканизма хребта с изменениями основных климатических маркеров в осадках указывает на
единство вулканических процессов в регионе с процессами, которые привели к увеличению показа-
телей содержания 13С в осадках и содержания CO2 в атмосфере.
... The pronounced upper Paleocene peak in δ 13 C values around 60 Ma (time scale of Berggren et al., 1985) is clearly present, as is the rapid decline in values at around the Paleocene/Eocene boundary. The peak values of δ 13 C at around 60 Ma are very similar to those at mid-latitude Deep Sea Drilling Project (DSDP) Sites 525,527, and 528 (Walvis Ridge; Shackleton and Hall, 1984), but lower than those at high-latitude Sites 689 and 690 (Shackleton and Hall, 1990). It has been demonstrated for data from the Maud Rise on planktonic and benthic foraminifers (Stott et al., 1990; Kennett and Stott, 1990, 1991), as well as in bulk values (Shackleton and Hall, 1990), that there is a short "overshoot" to very light δ 13 C values at the end of this long-term decline in δ 13 C values. ...
... It is useful, however, to analyze bulk sediment to obtain appropriate data to contribute to our understanding of the history of the oceanic carbon budget (e.g., Shackleton, 1987). In this report we present a data set from Site 762, at low latitudes in the eastern Indian Ocean, to add to and compare with data sets from low latitudes in the Pacific (Shackleton et al., 1985), the mid-latitudes in the southern Atlantic (Renard et al., 1983; Shackleton and Hall, 1984; Shackleton, 1986 ), and high latitudes (Shackleton and Hall, 1990). There are significant spatial variations in δ 13 C in ocean surface waters today (Kroopnick et al., 1977), but the spatial variability in the δ 13 C content of surface sediments is small compared with the range of values observed for the Cenozoic (Shackleton, 1987), which suggests that the bulk sediment record of δ 13 C may be useful in stratigraphic correlations. ...
... The age tie-points are listed inTable 2.Figure 1 shows the δ 13 C record for Hole 762C plotted vs. depth, and on the time scale obtained fromTable 2. The pronounced upper Paleocene peak in δ 13 C values around 60 Ma (time scale of Berggren et al., 1985) is clearly present, as is the rapid decline in values at around the Paleocene/Eocene boundary. The peak values of δ 13 C at around 60 Ma are very similar to those at mid-latitude Deep Sea Drilling Project (DSDP) Sites 525,527, and 528 (Walvis Ridge; Shackleton and Hall, 1984), but lower than those at high-latitude Sites 689 and 690 (Shackleton and Hall, 1990). It has been demonstrated for data from the Maud Rise on planktonic and benthic foraminifers (Stott et al., 1990; Stott, 1990, 1991), as well as in bulk values (Shackleton and Hall, 1990), that there is a short "overshoot" to very light δ 13 C values at the end of this long-term decline in δ 13 C values. ...
Carbon isotope measurements were made on bulk sediments from the Paleogene calcareous sequence recovered at Ocean Drilling Program Site 762 (Hole 762C) on the central Exmouth Plateau, eastern Indian Ocean. The very positive δ 13 C values that characterize the early/late Paleocene boundary and the very rapid trend toward lighter values in the latest Paleocene, as observed at other sites worldwide, are clearly present in the record from Hole 762C, as is the short excursion to extremely light values close to the Paleocene/Eocene boundary. The highest values in the upper Paleocene maximum at Site 762 are close to those at mid-latitude South Atlantic sites on Walvis Ridge, but slightly lower than those from the high latitude Sites 689 and 690 (65°S; Maud Rise, Weddell Sea). These 5 13 C events will be of value in long-distance stratigraphic correlations; especially the short, but extreme excursion at the end of the Paleocene may be useful in clearing up the stratigraphic correlation problems for that interval. Site 762 values for the upper Eocene resemble the pattern at Walvis Ridge more closely than do the values for Sites 689 and 690 (Maud Rise); the latter showed a positive excursion in that interval. The bulk carbon isotopic record seems to be more similar between low-and mid-latitude sites, even in different ocean basins, than between low and high latitudes.
... Oldest article was published in the year 1986 (Renard, 1986). However, there are other previous and contemporaneous publications that used stratigraphic geochemical variation to infer paleoclimate and paleoenvironments and to define specific geochronological or lithostratigraphic boundaries (for example, Keith and Weber, 1964;Scholle and Arthur, 1980;Berger and Vincent, 1981;Romein and Smit, 1981;Odin et al., 1982;Williams et al., 1983;Renard et al., 1984;Shackleton and Hall, 1984;Jorgensen, 1986; and many others and references cited therein). Already 266 articles were published in the year 2014, 254 articles were published in the year 2013, and the year 2012 ranks third with publication of 218 articles. ...
... Cyclic sedimentation has been documented in numerous sedimentary basins that led to the development of cyclostratigraphy (Weedon, 2005) and there are many lines of evidence that relate those cycles to short-term (Milankovitch band) glacio-eustatic pulses (Grammer et al., 1996). Documentation of cyclic nature of stable isotope compositions of sediment records of DSDP and ODP and other sites (for example, Renard et al., 1984;Shackleton and Hall, 1984;Srinivasan, 1989;Pearce and Jarvis, 1991;Bruckschen et al., 1999;Pearce et al., 1999;Korte et al., 2004;Bergström et al., 2006Bergström et al., , 2009Bergström et al., , 2010Ramkumar et al., 2010Ramkumar et al., , 2011 have helped establish the utilities of chemostratigraphy in various fields. ...
... The utility of chemostratigraphy for age determination was demonstrated through documentation of chronological variations of isotopic trends (for example, Sr isotopic curve- Whitford et al., 1996;Denison et al., 1997;Veizer et al., 1997Veizer et al., , 1999Ebneth et al., 2001;Mearon et al., 2003;C and O isotopic curve-Williams et al., 1983;Renard et al., 1984;Shackleton and Hall, 1984;Mount et al., 1986;Koch et al., 1992;Friedman and Chakraborty, 1997;Saltzman and Thomas, 2012; sulfur isotopic curve- Strauss, 1997;Kampschulte et al., 2001; and references cited therein). ...
Sediments are reliable records of changes in physical, chemical, and biological conditions that take place before, during, and after their deposition and express the changes through constituent mineralogical and thus geochemical compositions. Individual sedimentary events create more or less homogeneous bulk chemistry of sediments at varying temporal and spatial scales. Distinguishing these homogeneities and for classification of stratigraphic records and correlation of the strata at varying spatiotemporal scales is emerging to be a reliable method of stratigraphy and is termed as chemostratigraphy a la chemical stratigraphy. This method helps stratigraphic correlation with ease where other formal stratigraphic methods have limitations or fail to achieve required spatiotemporal resolution.The study of geochemical variations in stratigraphic context has gained importance since the 1980s. Chemostratigraphy is, thus relatively a younger branch of geosciences. Attempts on distinguishing depositional units at varying spatiotemporal scales (from local to global and from tidal cycles to few tens of millions of years) have been influenced to a larger extent by the sequence stratigraphic concepts. Contemporaneous developments in sophisticated instrumentation for fast, accurate, and less expensive geochemical analyses have also contributed to the popularity and applications of chemostratigraphy. From a humble beginning of identification of similar geochemical values and similar pattern of geochemical profile, chemostratigraphy has traveled a long way. Currently, a wide variety of techniques and data from other subdisciplines of geosciences are used for distinction/recognition and correlation chemozones/geochemically distinguishable depositional units.Yet, chemostratigraphy consists of vaguely defined and often misleading and/or overlapping terminologies. Through an extensive review of published literature, this chapter attempts to enlist these terminologies namely, chemostratigraphy, chemical stratigraphy, geochemical fingerprinting, geochemical signature, geochemical fingerprint, geochemical marker, geochemical proxy, excursion, shift, fluctuation, perturbation, anomaly, trend, chemostratigraphic index, chemozone, chemochron, resolution, and scale of correlation and provides definitions/explanations. This attempt is made for initiating discussion among the practitioners that may lead to consensus on definitions and standardized usage.Despite, fulfilling the criteria required for any standard stratigraphic method and finding its applications in many different fields, this method/tool remains to be formally given its due. Elucidation of the traits and enlisting the terminologies of chemostratigraphy with the criteria for formal recognition prescribed by International Stratigraphic Commission suggests that chemostratigraphy deserves to be formalized as an independent stratigraphic method.
... [11] Furthermore, long-term carbon isotope records spanning the early Paleogene may deviate from one another. Planktonic and benthic foraminifer d 13 C records from several locations exhibit a $2‰ decrease from the late Paleocene through the early Eocene ($58-53 Ma; Figure 1) [Shackleton and Hall, 1984;Zachos et al., 2001;Hilting et al., 2008]. Within this interval, $1‰ of the drop occurred between the PETM and ETM2. ...
... [28] To quantify the relation between organic matter origin and d 13 C TOC , exogenic trends must be excluded (equation (3)). Bulk carbonate, as well as surface, thermocline and deep ocean foraminifer d 13 C records show a gradual decrease by $2‰ in several ocean basins during the late Paleocene to early Eocene (59-51 Ma) [Shackleton and Hall, 1984;Zachos et al., 2001;Hilting et al., 2008]. Within this trend, the interval from just before the PETM to just after ETM2 ($56-54 M), yields a $1‰ negative shift (Figure 1). ...
... This implies that the long-term (>3 Myr) decrease in the contribution of terrestrial organic matter to the depositional location, has affected the d 13 C TOC signal. As discussed above, another $1‰ of the bulk d 13 C TOC signal can be explained by a change in the exogenic carbon cycle; such a drop has been observed in multiple marine calcite d 13 C records (Figure 1) [Shackleton and Hall, 1984;Zachos et al., 2001;Hilting et al., 2008]. The residual $1‰ shift in the long-term d 13 C MOM curve, from approximately À27‰ to À28‰, suggests a decrease in d 13 C MOM at this location, independent of changes in basic composition or the d 13 C of the global exogenic carbon cycle. ...
Negative stable carbon isotope excursions (CIEs) across the
Paleocene-Eocene thermal maximum (PETM; ˜56 Ma) range between
2‰ and 7‰, even after discounting sections with truncated
records. Individual carbon isotope records differ in shape and magnitude
from variations in the global exogenic carbon cycle through changes in
(1) the relative abundance of mixed components with different
δ13C within a measured substrate, (2) isotope
fractionation through physiological change, and (3) the isotope
composition of the carbon source. All three factors likely influence
many early Paleogene δ13C records, especially across
the PETM and other hyperthermal events. We apply these concepts to late
Paleocene-early Eocene (˜58-52 Ma) records from Lomonosov Ridge,
Arctic Ocean. Linear regression analyses show correlations between the
δ13C of total organic carbon (TOC) and two proxies for
the relative contribution of terrestrial organic components to sediment
TOC: the branched and isoprenoid tetraether index and palynomorphs. We
use these correlations to subtract the terrestrial component from
δ13CTOC and calculate marine organic matter
δ13C. The results show that the magnitude of the CIE in
δ13CTOC across the PETM is exaggerated
relative to the magnitude of the CIE in
δ13CMOM by ˜3‰ due to increased
contributions of terrestrial organic carbon during the event.
Collectively, all carbon isotope records across the PETM and other major
climate-carbon cycle perturbations in Earth's history are potentially
biased through one or more of the above factors. Indeed, it is highly
unlikely that any δ13C record shows the true shape and
magnitude of the CIE for the global exogenic carbon cycle. For the PETM,
we conclude that CIE in the exogenic carbon cycle is likely
<4‰, but it will take additional analyses and modeling to
obtain an accurate value for this CIE.
... 1. Composite bulk sediment d 13 C record for the Jurassic through the Cenozoic (see Methods for site selection criteria). Mesozoic d 13 C data (this study) and Cenozoic d 13 C data (Shackleton and Hall, 1984) are primarily from open ocean Atlantic Deep Sea Drilling Project (DSDP) boreholes (see Methods). Data (Appendix A) are web-archived (http://www.mychronos.chronos.org/~miriamkatz/20040728/). ...
... We constructed a composite bulk sediment d 13 C carb record using new Mesozoic data (this study) and published Cenozoic data (Shackleton and Hall, 1984) (Fig. 1). Comparisons of the new Mesozoic data with shorter-duration published bulk sediment d 13 C records establish that the composite curve records global d 13 C changes in the Cretaceous (Fig. 2). ...
... These results indicate that f org increased during this interval to the highest level of the past 205 Ma (Fig. 4), culminating in the bMonterey Carbon ExcursionQ in which large amounts of organic-rich, diatomaceous sediments were deposited in marginal basins (Vincent and Berger, 1985). The d 13 C carb trend reversed in the Neogene, with values that have decreased by ~2.5x since ~15 Ma (Fig. 1) (Shackleton and Hall, 1984), while d 13 C org values continued to increase (Hayes et al., 1999) (Figs. 1 and 3). This requires a 12 C increase in the mobile carbon reservoir through more 12 C supply and/ or less 12 C burial. ...
The isotopic composition of the global carbon reservoir integrates large kinetic fractionations from photosynthesis with small thermodynamic fractionations from carbonate precipitation. We present concordant delta 13C records of carbonates (delta 13Ccarb) and organic matter (delta 13Corg), along with new carbonate (Ccarb) and organic carbonate (Corg) fluxes for the past ˜205 myrs (Jurassic-Cenozoic) generated from bulk sediment samples from the Atlantic. The new delta 13Corg record greatly refines previous compilations (Hayes et al., 1999) by providing a sample resolution of ˜100-300 kyrs. Model simulations using these delta 13Ccarb and delta 13Corg data provide constraints on carbon sources (mantle and weathering) and sinks (carbonate and organic carbon sedimentation); comparisons with the flux records provide insight on the components of the geological carbon cycle. Stable isotope records indicate that long-term net depletion of 12C from mobile carbon reservoirs was a consequence of an organic carbon burial fraction increase of ˜0.05-0.1 that began in the Jurassic ( ˜200 Ma). Superimposed on the long-term trend are higher-order variations (5-10s of myrs) in delta 13Ccarb and delta 13Corg that show episodic intervals of elevated values. In contrast to paleoceanographic convention, organic carbon burial is often decoupled from global delta 13C variations on the 5-10s of myrs scale. Brief episodes of elevated Corg flux tend to occur near the onset and cessation of these intervals of elevated delta 13Ccarb and delta 13Corg values; prolonged episodes of elevated Ccarb flux tend to correspond to the cessation of extended intervals of elevated delta 13C values. In the latter part of the Cenozoic, the development of beta carboxylation and C4 photosynthetic pathways in phytoplankton and terrestrial plants increasingly influenced delta 13Corg, ultimately contributing to the reversal of the long-term trend in delta 13Ccarb. Thus, the geologic record of the global carbon cycle over the past 205 myr has been influenced by a combination of changes in carbonate burial, organic carbon burial, and biological fixation.
... Large changes in the δ 13 C budget occurred during the late Paleocene to early Eocene (Shackleton and Hall, 1984; Shackleton et al., 1985a, 1985b; Oberhansli et al., 1984; Oberhansli and Toumarkine, 1985; Hsü et al., 1985). The cause of high δ 13 C values and strong surface-water δ 13 C gradients in the late Paleocene Pacific and Atlantic oceans (Boersma and Premoli Silva, 1983; Shackleton et al., 1985a, 1985b) remains controversial ; the high late Paleocene δ 13 C values have been suggested as indicating high global productivity (Shackleton and Hall, 1984), high accumulation rates of sedimentary organic carbon (Shackleton, 1987), and an enhanced oxygen-minimum zone (Shackleton et al., 1985a). The large decrease in δ 13 C values across the Paleocene/Eocene boundary was inferred to represent a global drop in surface ocean productivity (Shackleton et al., 1985b). ...
... Studies have shown that Cibicidoides accurately records deep-water δ 13 C variations (e.g., Graham et al., 1981), and we have successfully used this taxon to reconstruct Oligocene-Miocene carbon isotope fluctuations (Miller and Fairbanks, 1985). Shackleton et al. (1984) found that N. truempyi yielded the same δ 13 C values as Cibicidoides, while the δ 18 θ values were constantly offset from Cibicidoides by about 0.15°/oo; we analyzed paired samples of N. truempyi and Cibicidoides spp. to confirm this (see "Results" section). Isotope measurements were made using a Carousel-48 automatic carbonate preparation device attached to a Finnigan MAT 251 (Table 2). ...
Previous studies document that a major benthic foraminiferal crisis occurred in the latest Paleocene in the Atlantic, Caribbean, and Pacific; a similar faunal turnover occurred in the latest Paleocene throughout the Atlantic sector of the Southern Ocean. At the Leg 114 sites, Stensioina beccariiformis-dominated assemblages were replaced by Nuttallides truempyi-dominated assemblages just prior to the Paleocene/Eocene boundary. The benthic foraminiferal crisis may have been caused by deep-water warming, a drop in food supply, or changing deep-water source regions. Oxygen isotope data show that there is no clear correlation between δ18O changes and extinctions. Similarly, most of the extinctions occurred well after the start of the drop in global 8d13C values, which may, in part, reflect a decrease in productivity. -from Authors
... For example, a modest increase in organic carbon burial over 5 million years (to 11.4 mol C yr −1 ), coupled with increases in 13 Cenriched HCO − 3 (to 1.15 mol C yr −1 ) and decreases in AOM and CH 4 venting (to 0.7 mol C yr −1 and 0.07 mol C yr −1 ), stores ∼12 000 Gt C as CH 4 . It also causes a +0.9 ‰ excursion in δ 13 C and a −1.5 ‰ excursion in δ 34 S, as observed in records (Shackleton and Hall, 1984; Paytan et al., 1998). If CH 4 outputs halve following 200 000 years of cooling after a major CH 4 discharge (to 0.5 mol C yr −1 ), seafloor methane systems partly recharge, accumulating ∼1200 Gt C. ...
... The present work raises a far more vexing problem: why would a large, dynamic gas hydrate capacitor form in the first place? Long-term δ 13 C and δ 18 O records strongly suggest cooling, including in the deep-ocean, and massive storage of organic carbon somewhere during the late Paleocene (Shackleton and Hall, 1984; Zachos et al., 2001 Zachos et al., , 2008). The answer, therefore, might be found at the start of these changes, nominally about 62 Ma (Westerhold et al., 2011). ...
Enormous amounts of 13 C-depleted carbon rapidly entered the exogenic carbon cycle during the onset of the Paleocene-Eocene thermal maximum (PETM), as attested to by a prominent negative carbon isotope (δ 13 C) excursion and deep-sea carbonate dissolution. A widely cited explanation for this carbon input has been thermal dissocia-tion of gas hydrate on continental slopes, followed by release of CH 4 from the seafloor and its subsequent oxidation to CO 2 in the ocean or atmosphere. Increasingly, papers have argued against this mechanism, but without fully considering existing ideas and available data. Moreover, other explanations have been presented as plausible alternatives, even though they conflict with geological observations, they raise major conceptual problems, or both. Methane release from gas hy-drates remains a congruous explanation for the δ 13 C excursion across the PETM, although it requires an unconventional framework for global carbon and sulfur cycling, and it lacks proof. These issues are addressed here in the hope that they will prompt appropriate discussions regarding the extraordinary carbon injection at the start of the PETM and during other events in Earth's history.
... This trend is interrupted by the negative excursion (0.54‰) that characterizes the Paleocene/Eocene boundary. In summary, the evolution of the carbon isotope ratio in the Zumaia section corresponds to the classical Paleocene pattern well known since the works of Létolle and Renard [1980], Shackleton and Hall [1984] and Shackleton [1986]: a long positive excursion culminating during the Thanetian that is flanked by two drastic negative accidents highlighting the K/T and Paleocene/Eocene boundaries. The origin of the Zumaia curve is the importance of the negative excursion occurring during the Early Selandian. ...
... Virtually no other published curve shows such an excursion. Only South Atlantic site 527 [DSDP Leg 74;Shackleton and Hall, 1984] and, in a less obvious way, Antarctica site 690 [DSDP Leg 113;Shackleton and Hall, 1990] and the Contessa Highway section [Gubbio, Italy;Corfield et al., 1991;Coccioni et al., 2012] show a weak negative excursion that seems contemporaneous with that of Zumaia. This origin of the carbon isotope ratio trend from Zumaia could be linked to the high rate of sedimentation in this section during the Selandian, which allows a very detailed d 13 C record, while numerous sedimentary hiatus or gravity events that occur during this period in Tethyan or Atlantic sites disturb the d 13 C record and screen the Early Selandian negative accident. ...
– Well exposed and stratigraphically well constrained by numerous studies, the Zumaia section is one of the
best places to conduct studies on the Palaeocene in basin facies. Thus, this section has been chosen [Schmitz et al.,
2011] as a stratoype of Selandian basal and terminal limits (GSSP: Global boundary Stratotype Section and Point). The
sediments consist of carbonate hemipelagites interbedded with fine carbonate (Maastrichtian to Selandian) and
siliciclastic (Thanetian to Eocene) turbidites.
The purpose of this work is to geochemically characterize the Selandian by trace element contents (strontium and
manganese) and to try to assess the chemical composition of seawater during the Paleocene. Analysis of various separated
granulometric fine fractions show that hemipelagic sediments from the Zumaia section present a high preservation
quality of the original records of trace-element contents. Late burial diagenesis plays only a minor role and geochemical
breaks are not reducible to a change in the nature of carbonate producers.
The strontium contents of Paleocene sediments require that the Sr/Ca ratio of seawater was lower than that in the
present ocean. The Selandian is characterized by a positive excursion of the strontium curve. This accident is also recognized
in several worldwide sections and is related to the platform/basin carbonate sedimentation budget and the intensity
of oceanic hydrothermalism.
The Mn content of hemipelagites is very high and can reach 2500-3000 ppm in the Paleocene. A comparison of
analyses by atomic absorption spectrometry (AAS) and electron paramagnetic resonance (EPR) shows that both Mn2+
(in the calcite lattice) and Mn4+ (as oxide micro nodules) coexist. The Mn content fluctuations are related to the opening
phases of the North Atlantic during the Paleocene by submarine volcanism and hydrothermalism in the North Atlantic
Igneous Province (NAIP).
... For example, a modest increase in organic carbon burial over 5 million years (to 11.4 mol C yr −1 ), coupled with increases in 13 Cenriched HCO − 3 (to 1.15 mol C yr −1 ) and decreases in AOM and CH 4 venting (to 0.7 mol C yr −1 and 0.07 mol C yr −1 ), stores ∼12 000 Gt C as CH 4 . It also causes a +0.9 ‰ excursion in δ 13 C and a −1.5 ‰ excursion in δ 34 S, as observed in records (Shackleton and Hall, 1984; Paytan et al., 1998). If CH 4 outputs halve following 200 000 years of cooling after a major CH 4 discharge (to 0.5 mol C yr −1 ), seafloor methane systems partly recharge, accumulating ∼1200 Gt C. ...
... The present work raises a far more vexing problem: why would a large, dynamic gas hydrate capacitor form in the first place? Long-term δ 13 C and δ 18 O records strongly suggest cooling, including in the deep-ocean, and massive storage of organic carbon somewhere during the late Paleocene (Shackleton and Hall, 1984; Zachos et al., 2001 Zachos et al., , 2008). The answer, therefore, might be found at the start of these changes, nominally about 62 Ma (Westerhold et al., 2011). ...
Enormous amounts of 13C-depleted carbon rapidly entered the exogenic carbon cycle during the onset of the Paleocene-Eocene thermal maximum (PETM), as attested to by a prominent negative carbon isotope (delta13C) excursion and deep-sea carbonate dissolution. A widely cited explanation for this carbon input has been thermal dissociation of gas hydrate on continental slopes, followed by release of CH4 from the seafloor and its subsequent oxidation to CO2 in the ocean or atmosphere. Increasingly, papers have argued against this mechanism, but without fully considering existing ideas and available data. Moreover, other explanations have been presented as plausible alternatives, even though they conflict with geological observations, they raise major conceptual problems, or both. Methane release from gas hydrates remains a congruous explanation for the delta13C excursion across the PETM, although it requires an unconventional framework for global carbon and sulfur cycling, and it lacks proof. These issues are addressed here in the hope that they will prompt appropriate discussions regarding the extraordinary carbon injection at the start of the PETM and during other events in Earth's history.
... During the heart of the most positive δ 13 C carb values within the Louisiana Formation (+6.0‰) f org values reach nearly 0.35 in both cores. The calculation of f org from the H-28 and H-32 cores (Figs. 6 and 7) shows values between 0.15 and 0.2 prior to the Hangenberg Crisis interval, which are similar to modern values of 0.2 (Shackleton and Hall, 1984;Shackleton, 1987), an initial increase in f org during the onset of the crisis up to 0.25, that then eventually increases further to values ~0.35 during the peak of the Hangenberg δ 13 C excursion. This represents a greater than 200% increase in f org from the time of deposition of the lower English River Formation until the middle of the Louisiana Formation, and this increase in the relative rate of organic carbon burial could certainly have been the ultimate mechanism responsible for the global positive carbon isotope excursion. ...
New high-resolution organic (δ¹³Corg) and carbonate (δ¹³Ccarb) carbon isotope data from middle shelf deposits in southeastern Iowa demonstrate decoupled signals during the onset of the Hangenberg Event and across the Devonian-Carboniferous Boundary. High-resolution sampling captures a transient negative excursion in δ¹³Corg during the initiation of rising δ¹³Ccarb values at the onset of the Hangenberg Event that ends prior to the onset of the final rise in δ¹³Ccarb to values greater than +6.0‰ in the Louisiana Limestone. This negative excursion in δ¹³Corg is coincident with a significant increase in Total Organic Carbon (TOC) content in the underlying English River Formation, which likely corresponds to the well-known Hangenberg Black Shale of the classical European sections. The complex behavior of the carbon isotope record recovered here, combined with recently published geochemical data from classical European sections, demonstrate that a succession of geochemical events took place during the initiation of this global biogeochemical event that include a negative excursion in both δ¹³Ccarb and δ¹³Corg prior to the major positive carbon isotope excursion, and that the role of organic carbon burial in this Devonian Oceanic Anoxic Event (OAE) extends well beyond the depositional interval of the Hangenberg Black Shale.
... The calculations of f org shown in Fig. 4 are summarized in Table 1. Prior to the onset of the Mulde Event, δ 13 C carb was approximately +0.25‰, Δ 13 C was approximately +29.5‰, and assigning − 5.0‰ to δ 13 C incoming provides a f org value of ~0.178, which is slightly lower than the modern value of ~0.20 (Shackleton and Hall, 1984;Shackleton, 1987). The f org baseline values are remarkably consistent, albeit slowly increasing, prior to the Mulde Event (Fig. 4). ...
High-resolution paired analyses of δ¹³Ccarb and δ¹³Corg from a new drill core from Gotland, Sweden, demonstrate asynchronous positive change in the carbon isotope records during the onset of one of the major Silurian biogeochemical events known as the Mulde Event or “Big Crisis”. The detailed carbon isotope record presented here provides Δ¹³C (the difference between δ¹³Ccarb and δ¹³Corg) and allows the calculation of changes in organic carbon burial (forg) throughout the late Wenlock. The paired data suggest a ~ 38% increase in forg during the peak of the positive δ¹³Ccarb excursion and the high-resolution record reveals several short-lived inflections in Δ¹³C that have not been previously identified. When combined with sedimentological and sequence stratigraphic data from multiple paleocontinents, the new data presented here provide strong evidence for a transient global decrease in CO2, in support of previous interpretations of regression and global cooling coinciding with the Mulde Extinction Event.
... Specifically, the relative rates of addition and/or removal of organic carbon compared to carbonate carbon to and from the lithosphere reservoirs dominate the long-term carbon cycle. In the present ocean, roughly 20% of all carbon removed from the surficial reservoir into the lithosphere is organic carbon (Shackleton and Hall, 1984;Shackleton, 1987). Any increase or decrease in the relative amount of organic carbon removed or added to the surficial reservoir compared to carbonate carbon will drive a change in the δ 13 C value of DIC in the global ocean (Shackleton, 1987;Berner, 1990;Derry et al., 1992;Des Marais et al., 1992;Hayes et al., 1999;Kump and Arthur, 1999;Sundquist and Visser, 2004). ...
The ¹³C/¹²C value of dissolved inorganic carbon (DIC) in the ocean has varied through time and can be determined from the marine carbonate record as changes in δ¹³Ccarb. These variations provide insight into global carbon cycle dynamics, as well as relative age information (chronostratigraphy) that can be used to correlate sedimentary successions globally. The global carbon cycle includes both short- and long-term components, and their interactions dominate the isotopic record presented in this chapter. The partitioning and sequestration of carbon between organic and carbonate rock reservoirs, and their fluxes to and from the ocean–atmosphere–biosphere system, drive secular changes in the δ¹³C of DIC in the oceans that are ultimately recovered from the stratigraphic record. The pre-Cenozoic data presented here utilize bulk carbonate data for compilation, but a wide range of materials has been analyzed in the literature to produce previous composites. Care must be taken to consider what materials have been analyzed in comparing global carbon isotope records from the literature.
... For the interval prior to the onset of the δ 13 C carb excursion (defined here as the point of maximum rate of positive change, Cramer et al., 2010), δ 13 C carb is approximately +1.5‰ and Δ 13 C is approximately +29.5‰. Utilizing a value of − 5.0‰ for δ 13 C incoming (Derry and France-Lanord, 1996;Hayes et al., 1999;Berner, 2006), we calculate an initial f org value of 0.22, which is similar to the modern-day value of 0.20 (Shackleton and Hall, 1984;Shackleton, 1987). During the onset of the IBE (blue bar in Fig. 3), f org only rises to 0.24 which represents a ~9% increase in organic carbon burial from pre-event values. ...
Paired records of δ¹³Ccarb and δ¹³Corg across the Llandovery-Wenlock boundary demonstrate asynchronous behavior during the onset of the Ireviken Biogeochemical Event (IBE). The extremely high-resolution data produced from the Altajme Core, drilled from Gotland, Sweden, capture a negative excursion in δ¹³Corg during the initiation of the Ireviken Extinction Event (IEE) and prior to the onset of the Ireviken positive δ¹³Ccarb Excursion (ICIE). The record of carbon isotopic changes through this interval illustrate that both Δ¹³C (the difference between δ¹³Ccarb and δ¹³Corg) as well as the relative flux of organic carbon burial (forg) vary in unique ways and at different times during the progression of the IBE. Both process-oriented variables within the global carbon cycle (Δ¹³C and forg) track a series of events that help to demonstrate potential causative mechanisms of both the extinction and carbon cycle perturbation. The sequence of events demonstrated here largely mirror the cascade of events that took place during the Cretaceous Oceanic Anoxic Event 2 (OAE2) and a detailed comparison between the two events is provided here for the first time. The unique insight into the IBE presented in this work results primarily from the novel, nearly Neogene-scale resolution of the paired isotope data, which demonstrates the critical importance of high-resolution chemostratigraphic research to evaluating ancient perturbations to the Earth-life system. Additional data sets of equal or greater resolution through this interval will be critical to evaluate the global synchroneity of these short-lived events during the IBE, and similar high-resolution studies of other Paleozoic biogeochemical events may shed light on potentially similar causative mechanisms.
... Carbonate rocks represent valuable archives of Earth's biogeochemical cycles that record significant physical, chemical and biological events produced by evolution of new organisms, tectonic events, palaeoclimatic and extinction events, as well as periods of intense environmental change. The carbon and oxygen isotope composition of carbonates is of particular interest, with the δ 18 O providing information on temperature and salinity (Emiliani, 1955;Shackleton, 1967;Weber, 1964) while the δ 13 C values of marine carbonates are interpreted as a proxy for changes in plant evolution and physiology and the global carbon cycle through geological time (Veizer, Holser, and Wilgus, 1980;Shackleton and Hall, 1985;Hayes, Strauss, and Kaufman, 1999;Veizer et al., 1999;Bekker et al., 2008;Swanson-Hysell et al., 2010). These signals are often influenced by diagenetic changes during periods of sub-aerial exposure (Allan and Matthews, 1982;Christ et al., 2012;Gross, 1964;Gross and Tracy, 1966;Land, 1967) but can also be prevalent in the submarine realm where δ 13 C and δ 18 O values can be altered during marine burial diagenesis (Marshall and Ashton, 1980;Frank, Arthur, and Dean, 1999;Immenhauser, Creusen, Esteban, and Vonhof, 2000;Mutti and Bernoulli, 2003;Sattler, Immenhauser, Hillgärtner, and Mateu, 2005;Dickson, Wood, Al Rougha, and Shebl, 2008). ...
Diagenetic alteration can produce, modify, or erase significant biogeochemical information recorded in carbon and oxygen (δ13C and δ18O) values of marine carbonates throughout geological time. Understanding the type and extent of alteration experienced by a carbonate deposit can improve sedimentological and geochemical interpretations of events in Earth history. In this study, we present a new application of a statistical approach to aid in the identification and interpretation of sedimentological surfaces in a shallow marine carbonate sequence using a rolling window regression (RWR) analysis. RWR analysis evaluates the degree of covariation between two records and how it changes through time. Geological application of this statistical technique permits a new perspective on the fine scale variability in carbon and oxygen isotope records and the processes that generate them and provides a complementary tool for sedimentological interpretations. In this study, we apply RWR to δ13C and δ18O values from the Clino drilled into the western margin of Great Bahama Bank, a core that has been extensively altered by diagenetic processes, within the vadose, phreatic and marine burial zones. This core penetrates ~676 m of shallow marine to deeper slope deposits and contains a variety of both sedimentological and diagenetic events, including facies transitions, subaerial exposure surfaces, marine hardgrounds, firmgrounds and periods of reduced sedimentation rate. Using more than 1200 analyses of paired δ13C and δ18O values, we have applied a rolling window regression analysis to evaluate how the correlation between these two proxies changes at scales of 10, 30 and 100 m. The results of this study highlight the dynamic evolution of correlations between δ13C and δ18O values within diagenetic zones and in association with diagenetic surfaces and provide context for interpreting covariance in δ13C and δ18O values from the geological record.
... The data above yield an average Neogene rate of net growth (burial-weathering > 0) of the sedimentary C org reservoir of 0:58 X 10 12 mol yr 1 in the Himalayan-Bengal system. The net growth in the size of the global sedimentary C org reservoir can be estimated from the marine carbon isotopic mass balance 25 . Our recent results from a d 13 C model 26 yield a global average net flux to the sedimentary C org reservoir of about 1:1 X 10 12 mol yr over the past 15 Myr. ...
... Bulk rock carbonate carbon isotope records are inferred to track variation in the isotope composition of the ancient DIC pool over time (Scholle and Arthur, 1980;Shackleton and Hall, 1984). By imposing an imbalance in the steady state 1-box model, we can simulate the effect of a carbon cycle reorganization on δ M (or δ 13 C DIC ) (see section "Numerical Calculations of Whole Ocean Carbon Isotope Changes" and Figure 3), and thus put constraints on the maximum 13 C bed−to−bed variation per bandwidth. ...
Preference for certain stable isotopes (isotope fractionation) during enzyme-mediated reactions is a universal aspect of life. For instance, carbon isotopes are fractionated during anabolic (e.g., photosynthate production) and catabolic (e.g., methanogenesis) reactions. These biological processes exert a major control on ambient micro-scale chemical conditions as well as the large-scale exogenic carbon reservoir. Combined with the ubiquity of bio-mediated carbonate mineral nucleation and obligate enzymatic skeletonization, these biochemical reactions and their control on the exogenic carbon pool are known to leave distinct imprints on carbonate minerals which accumulate as sediments throughout Earth’s history. Here, we study the evolution of the marine carbonate-carbon isotope record based on database compilations from the Precambrian and the Phanerozoic. By looking at the frequency distribution of the amplitude of stratigraphic variation at various temporal resolutions, we assess trends in the carbonate-carbon isotope variability. Part of this variation can only be explained by authigenic and diagenetic carbonate mineral additions, which carry metabolic carbon isotope signatures created in the vicinity of cells and secluded (sub-)seafloor micro-environments. It can be envisioned that compartmentalization (membrane enclosed regions), the accumulation of extracellular polymeric substances (biofilms), and restricted fluid exchange in the early diagenetic environment can create sharp isotope gradients that lead to a high-order of micro-scale carbon isotope variability being imprinted in carbonate rock. The frequency of the high-amplitude variation diminishes with the development of more complex life (metazoan-dominated biosphere); presumably through the dispersing action of bioturbation (eradicating these micro-environments), increased grazing pressure and the advent of obligate biomineralization. On the other hand, stark chemical gradients in a world dominated by unicellular life (prokaryotes and to a lesser extent eukaryotes) are thought to leave a distinctly more variable C isotope signature in carbonate rock. An enhanced understanding of the biogenicity of carbonate carbon isotope signatures at multiple spatial and temporal scales provides a baseline that is usable in the search for signs of (past) extraterrestrial life.
... The highest δ 13 C values of the Cenozoic occurred at ca. 58 Ma. From this Paleocene Carbon Isotope Maximum (PCIM), benthic foraminiferal δ 13 C values plunge by approximately 2.5 ‰ to reach a near-Cenozoic minimum at or near the start of the EECO and subsequently rise by approximately 1.5 ‰ across this interval (Shackleton and Hall, 1984; Shackleton, 1986; Zachos et al., 2001 Zachos et al., , 2008 Cramer et al., 2009 ). Benthic foraminiferal δ 13 C records also exhibit prominent negative carbon isotope excursions (CIEs) across the three hyperthermals mentioned above (Kennett and Stott, 1991; Littler et al., 2014; Lauretano et al., 2015). ...
A marked switch in the abundance of the planktic foraminiferal genera
Morozovella and Acarinina occurred at low-latitude sites
near the start of the Early Eocene Climatic Optimum (EECO), a
multi-million-year interval when Earth surface temperatures reached their
Cenozoic maximum. Stable carbon and oxygen isotope data of bulk sediment are
presented from across the EECO at two locations: Possagno in northeast Italy
and Deep Sea Drilling Project (DSDP) Site 577 in the northwest Pacific.
Relative abundances of planktic foraminifera are presented from these two
locations, as well as from Ocean Drilling Program (ODP) Site 1051 in the
northwest Atlantic. All three sections have good stratigraphic markers, and
the δ13C records at each section can be correlated amongst each
other and to δ13C records at other locations across the globe.
These records show that a series of negative carbon isotope excursions (CIEs)
occurred before, during and across the EECO, which is defined here as the
interval between the J event and the base of Discoaster
sublodoensis. Significant though ephemeral modifications in planktic
foraminiferal assemblages coincide with some of the short-term CIEs, which
were marked by increases in the relative abundance of Acarinina,
similar to what happened across established hyperthermal events in Tethyan
settings prior to the EECO. Most crucially, a temporal link exists between
the onset of the EECO, carbon cycle changes during this time and the decline
in Morozovella. Possible causes are manifold and may include
temperature effects on photosymbiont-bearing planktic foraminifera and
changes in ocean chemistry.
... Schimmelmann and DeNiro (1984) measured the isotopic contents of carbon, nitrogen, and hydrogen in organic matter across the freshwater K/T boundary located in the York Canyon exposure of the Raton Basin, New Mexico. They found a shift of 1.8%o to lighter organic carbon isotopic values in the early Tertiary, which parallels a similar shift of l%o-2%o found in marine carbonates from the South Atlantic (Shackleton and Hall, 1984), Israel (Magaritz, 1989), the North Pacific (Zachos et al., 1989), and Tunisia (Keller and Lindinger, 1989). The common finding of the isotope shift in organic and inorganic carbon implies a global perturbation of the carbon cycle. ...
Regional consequences of the biotic extinctions and of the changes in biological productivity that occurred at the time of the Cretaceous/Tertiary (K/T) boundary were investigated by comparison of organic matter in sediments from three southern Tethyan margin locations. Organic matter characterization comprised Rock-Eval pyrolysis and organic carbon measurements. Low concentrations of organic matter precluded additional detailed determinations. At all three locations, the organic matter has been microbially reworked and evidently was deposited in oxygenated marine environments. -Author
... 2015PA002825. planktic taxa [McIntyre and McIntyre, 1971; Berger, 1973a; Anderson and Steinmetz, 1981; Shackleton and Hall, 1984; Perch-Nielsen, 1985; Young et al., 2005; Blaj et al., 2009]. The study of stable isotopes in calcareous nannofossils began when Anderson and Cole [1975] demonstrated that the δ 18 O of planktic foraminifera and the δ 18 O of <44 μm fraction of sediment covaried systematically in Pleistocene sediments and Margolis et al. [1975] showed that the δ 13 C and δ 18 O of planktic foraminifera , benthic foraminifera, and the <44 μm fraction of sediment paralleled each other from the middle Eocene through the Pleistocene at three Deep Sea Drilling Project (DSDP) Sites. ...
... 2015PA002825. planktic taxa [McIntyre and McIntyre, 1971; Berger, 1973a; Anderson and Steinmetz, 1981; Shackleton and Hall, 1984; Perch-Nielsen, 1985; Young et al., 2005; Blaj et al., 2009]. The study of stable isotopes in calcareous nannofossils began when Anderson and Cole [1975] demonstrated that the δ 18 O of planktic foraminifera and the δ 18 O of <44 μm fraction of sediment covaried systematically in Pleistocene sediments and Margolis et al. [1975] showed that the δ 13 C and δ 18 O of planktic foraminifera , benthic foraminifera, and the <44 μm fraction of sediment paralleled each other from the middle Eocene through the Pleistocene at three Deep Sea Drilling Project (DSDP) Sites. ...
To improve the understanding and utility of bulk carbonate stable carbon and oxygen isotope measurements, we examine sediment from cores in the Eastern Equatorial Pacific (EEP) that span the last 8 Ma. We measured δ13C and δ18O in 791 samples from IODP Site U1338 and DSDP Site 573, both located close to the Pacific Equator. In 100 samples, we measured δ13C and δ18O on isolated <63 µm and <38 µm fractions, which concentrates calcareous nannofossil carbonate and progressively excludes foraminiferal carbonate. Bulk carbonate δ13C and δ18O records are similar to published records from other sites drilled near the Equator and seem to reflect mixed layer conditions, albeit with some important caveats involving the precipitation of calcite by coccolithophores. The comparatively lower δ13C and δ18O of the <63 µm and <38 µm fractions in sediments younger than 4.4 Ma is attributed to an increase in deep-dwelling planktic foraminifera material in bulk carbonate, shifting the bulk isotopic signals towards higher values. Bulk carbonate δ13C is similar over 2500 km along the Pacific Equator, suggesting co-varying concentrations and δ13C of DIC within surface waters since 8 Ma. Greater bulk sediment δ13C and δ18O, higher sedimentation rates, and low content of coarse material suggest intensified wind-driven upwelling and enhanced primary productivity along the Pacific Equator between 8.0 and 4.4 Ma, although a full understanding of bulk carbonate records will require extensive future work.
... 2015PA002825. planktic taxa [McIntyre and McIntyre, 1971; Berger, 1973a; Anderson and Steinmetz, 1981; Shackleton and Hall, 1984; Perch-Nielsen, 1985; Young et al., 2005; Blaj et al., 2009]. The study of stable isotopes in calcareous nannofossils began when Anderson and Cole [1975] demonstrated that the δ 18 O of planktic foraminifera and the δ 18 O of <44 μm fraction of sediment covaried systematically in Pleistocene sediments and Margolis et al. [1975] showed that the δ 13 C and δ 18 O of planktic foraminifera , benthic foraminifera, and the <44 μm fraction of sediment paralleled each other from the middle Eocene through the Pleistocene at three Deep Sea Drilling Project (DSDP) Sites. ...
Sediment cores collected from the Eastern Equatorial Pacific Ocean display a clear positive second-order relationship between wet bulk density (WBD) and carbonate content. This has long interested the paleoceanography community because detailed Gamma Ray Attenuation Porosity Evaluator (GRAPE) measurements, which approximate WBD, might be used to determine records of carbonate content at very high temporal resolution. Although general causes for the relationship are known, they have not been presented and discussed systematically on the basis of first principles. In this study, we measure the mass and carbonate content of 50 sediment samples with known WBD from Site U1338, before and after rinsing with de-ionized water; we also determine the mass related proportion of coarse (> 63 μm) material. Samples exhibit clear relationships between WBD, carbonate content, mass loss upon rinsing, and grain size. We develop a series of mathematical expressions to describe these relationships, and solve them numerically. As noted by previous workers, the second-order relationship between WBD and carbonate content results from the mixing of biogenic carbonate and biogenic silica, which have different grain densities and different porosities. However, at high carbonate content, a wide range in WBD occurs because samples with greater amounts of coarse carbonate have higher porosity. Moreover compaction impacts carbonate particles more than biogenic silica particles. As such, a single two-component equation cannot be used to determine carbonate content accurately across depth intervals where both the porosity and type of carbonate vary. Instead, the WBD-carbonate relationship is described by an infinite series of curves, each which represents mixing of multiple sediment components with different densities and porosities. Dissolved ions also precipitate from pore space during sample drying, which adds mass to the sediment. Without rinsing samples, simple empirical relationships between WBD and carbonate content are further skewed by salt dilution.
... They have reported the occurrences of geochemical and other anomalies not across the KTB, but far away from the boundary. According to these studies, an increasing body of evidence pointed to the presence of abrupt δ 18 O and δ 13 C changes associated with the KTB (Romein and Smit, 1981; Hsü et al., 1982; Shackleton and Hall, 1984; Mount et al., 1986; Zachos and Arthur, 1986). At a number of localities, however, δ 18 O and δ 13 C changes were found to be preceding the KTB (Keller et al., 1998Keller et al., , 2003 Adatte et al., 2002a, b; Keller et al., 2008a Keller et al., , 2009a Keller et al., , 2009b Tobin et al., 2012) as defined by the worldwide iridium anomaly (Renard et al., 1984; Williams et al., 1983; Mount et al., 1986; Zachos and Arthur, 1986; Zhao et al., 2002). ...
The mass extinction of fauna and flora during end
Cretaceous has been one of the largest geological events
of the Earth. The environmental and climatic conditions
prevalent prior to, during and after the Cretaceous-Tertiary
boundary have been the subject matter of research for
over three decades. Yet, consensus eludes the geoscientific
community. This paper takes stock of the problem, traces
the various schools of thought, and lists the causes that were
purported to have contributed towards the mass extinction.
The review shows that though two major hypotheses were
advocated as to the causes of mass extinction namely,
bolide impact and Deccan volcanism, there are many other
events/ factors/ mechanisms viz., sea level fluctuation,
ocean acidification, riverine influx, changes in carbon and
sulphur budgets of ocean-atmosphere, release of methane
from gas hydrates, and many other causes either related
(directly or indirectly) or independent of the two major
events. It is also made plain that, not a single model could
convincingly explain all the features recorded in the Late
Cretaceous deposits due to the fact that many different
processes acted at varying spatio-temporal scales and had
their imprints accordingly. Three major facts emerged
from the review namely, a) The KTB as defined by the
ICS working group do not necessarily coincide with mass
extinction worldwide; b) Available data points to multiple
causes and multiple disappearances of taxa leading to
higher faunal turnover across the KTB; and c) While mass
extinction is unequivocally established, a combination
of factors that were in operation prior to and during
the KTB contributed towards extinction. With these,
comparative studies on the Indian stratigraphic sections of
the Cretaceous-Tertiary were also elucidated with special
emphasis on the Late Maastrichtian – Danian stratigraphic
section of the Cauvery Basin.
... The late Paleocene positive ␦ 13 C excursion in the Zumaia section (Fig. 4A) matches remarkably well with values derived from various DSDP and ODP data in the Atlantic, Pacific, and Southern oceans (e.g., Shackleton and Hall 1984;Shackleton 1987;Corfield and Cartlidge 1992;Corfield and Norris 1996). There, the observed carbon-isotope gradients between surface-dwelling and deeper-dwelling, and benthic foraminifera (⌬␦ 13 C), suggest that the positive excursion reflects increased ocean surface productivity (Corfield and Cartlidge 1992;Thompson and Schmitz 1997). ...
The Paleocene to lowermost Eocene Zumaia series, situated along the Basque Coast (northern Spain), consists of pelagic limestones and marlstones with interbedded, mixed calcarenite turbidites. We have compared the composition and frequency of turbidite beds in time, as well as the clay-mineral and bulk-rock carbon isotope composition of the pelagic beds, to discern the factors controlling turbidite deposition. The pelagic beds are coccolithic mudstones with mainly planktic foraminifera. The sources of detrital material to turbidites were the carbonate-producing shelves (bearing Foramol associations) around the evolving Bay of Biscay, and to a minor extent the incipient Pyrenean chain for siliciclastic components. We have found close relationships between variations of turbidite faciès and depositional rates with clay-mineral assemblages and carbon isotopes in the pelagic beds. The latter are in line with global trends. It appears that in the early Bay of Biscay, climate and nutrient availability controlled turbidite sedimentation. The bulk-rock late Paleocene (NP 5-NP 9) positive carbon-isotope excursion coincides with a period of relatively cool and dry climate characterized by the highest frequency of turbidity flow. We propose that during this period globally enhanced latitudinal temperature gradients and strong (hermohaline ocean circulation increased bioproductivity in surface waters by upwelling and/or by wind-driven Ekman pumping. In contrast, warm, perennially wet periods such as the early Paleocene (NP 1-NP 4) and the Paleocene/Eocene transition (upper NP 9-NP 10) are characterized by low frequency of turbidity flow in the basin. This may have been caused by sluggish thermohaline circulation and low carbonate productivity during this time period.
... La géochimie isotopique est un outil potentiel pour connaître leur origine. En effet, dans le domaine océanique, le Danien basal est caractérisé par un accident négatif du rapport isotopique du carbone des carbonates (Letolle et Renard, 1980 ; Boersma et Shackleton, 1981 ; Shackleton et Hall, 1984 ; Renard, 1985 ; Zachos et al., 1985 ; Stott et Kennett, 1990a, 1990b). Cet accident, d'amplitude de 1 à 3 ‰, est enregistré aussi bien par le carbonate total (bulk carbonate) que par les foraminifères planctoniques et les particules inorganiques (Minoletti, 2002). ...
The sediments at the Cretaceous-Tertiary boundary record a major crisis of pelagic carbonate producers (calcareous nannofossils and planktonic foraminifera). Nevertheless, Maastrichtian-like nannofossils are found in lowermost Danian sediments. Their origin (reworked vs. survivors) is still under debate. A recently developed protocol leading to separation of the various calcareous components included in the lowermost Danian sediments allows evaluation of the nannofossil isotopic signatures across the Cretaceous-Paleocene boundary. Maastrichtian-like nannofossils found in Danian sediments record isotopic ratios (carbon and oxygen) similar to the Cretaceous ones. These results provide evidence that Maastrichtian-like nannofossils are mostly reworked at Bidart.
... In contrast to the isotopic signal of the fine fraction (and also planktic foraminifera ), the carbon isotopic compositions of benthic foraminifera from Equatorial Pacific and Antarctic Sites (577 and 689, respectively ) increase at and across the boundary, then decrease roughly 0.1 Ma after the boundary (Zachos et al., 1989; Stott and Kennett, 1989). This convergence of planktic and benthic foraminiferal 813C values near the boundary indicates a reduction in the 813C difference between the surface and deep ocean, and is interpreted to indicate a decrease in surface productivity (Shackleton and Hall, 1984; Zachos and Arthur, 1986; Zachos et al., 1989; Stott and Kennett, 1989 ). The carbon isotopic compositions of benthic foraminifera from Site 527 follow the pattern observed for the Antarctic and Equatorial Pacific Sites (Shackleton et al., 1984a). ...
The isotopic composition and diversity of nannofossils were studied in cores from the Deep Sea Drilling Project (DSDP) Sites 525A, 527, 528, and 529 from the Walvis Ridge, South Atlantic to better understand the changes which occurred across the Cretaceous/Tertiary boundary (K/T boundary). The stratigraphic range of the samples is from theArkhangelskiella cymbiformis Zone in the Maastrichtian to theHeliolithus kleinpelli Zone in the Danian. Nannofossil diversity was high (Shannon-Weaver diversity index,H=2.5−3) in the late Cretaceous, but decreased sharply (H≈1) across the K/T boundary. The δ13C values also decrease across the K/T boundary at the four sites, suggesting a reduction in surface productivity in the South Atlantic concomitant with the reduction in diversity. During the Danian, nannofossil diversity and δ13C show some recovery approximately 500–700 k.y. after the boundary event. However, not until 2.5 Ma after the boundary event did diversity become constant. Diversity values similar to those for the late Cretaceous were not attained again in the early Paleocene interval studied. Carbon isotopic compositions similar to those from the Cretaceous were not attained until 4.5 Ma after the K/T event.
... The effects of the critical conditions on global biogeochemical cycles and ecosystem, including the marine and terrestrial biota, have been reported in the numerous studies regarding this climate transient. A prominent negative shift (∼ 3‰) in marine δ 13 C, the Carbon Isotope Excursion (CIE) (Shackleton and Hall, 1984; Kennett and Stott, 1991; Zachos et al., 2001), reflects the input of a large amount of isotopically depleted carbon in the oceanatmosphere system. In the few complete deep-sea sections ...
Studies on a climate extreme as the Paleocene-Eocene Thermal Maximum (PETM, ~ 55 myrs ago) have shown the effects of these critical conditions on global biogeochemical cycles and ecosystem, including the marine and terrestrial biota. A prominent negative shift (~ 3 0/00) in marine delta13C, the Carbon Isotope Excursion (CIE) reflects the input of a large amount of isotopically depleted carbon in the ocean- atmosphere system. Studies of the few complete deep-sea sections recovered to date have shown how global climate, atmospheric CO2 levels, marine carbonate chemistry and continental weathering were dynamically related during the PETM. Together, these changes should have strongly influenced the calcifying organisms living in the surface (photic zone) of the oceans. For this reason, recent investigations have focus on the planktonic community response to the shifts in oceanic environments during the PETM, specifically the response of calcifying microplankton to higher CO2 and lower pH, as well as the possible role of plankton in drawing down CO2. Calcareous nannofossils seem to play an important role in these interrelated mechanisms. For this reason we have performed detailed micropaleontologic analysis (using a SEM) of calcareous nannofossil assemblages in selected samples from selected Paleocene/Eocene deep-sea sediment cores with the purpose of documenting possible influence on assemblage composition and preservation. The sediments studied in detail are from ODP Site 1263 (from Southern East Atlantic, Walvis Ridge) that has been chosen as representative of one of the few complete PETM deep-sea cores. Comparative analyses were performed in few selected samples from sections located at different latitudes in the Atlantic and Pacific oceans (ODP Site 929, paleo-equatorial Atlantic, Ceara Rise; ODP Site 689, high-latitude Southern Atlantic, Maud Rise; ODP Sites 1215 and 1221, Eastern equatorial Pacific; ODP Site 1209, central Pacific, Shatsky Rise). This study documents the different 'behavior' of nannofossils through the different phases of the PETM, at the onset of CIE, within the CIE, and during the recovery interval, and reveals the presence of peculiar morphotypes of Fasciculithus and Discoaster as probably related to the anomalous amount of carbon in the ocean- atmosphere system. Although the anomalous geochemical conditions seems to have had some influence on the nannofossil assemblage composition, it results that local productivity and overall post depositional (diagenetic) conditions were the major controlling factors on nannofossils
... The second problem is a challenge. Long-term δ 13 C records strongly suggest that a massive storage of organic carbon occurred somewhere during the 5 late Paleocene (Shackleton and Hall, 1984), so the answer may lie at the start of the positive δ 13 C excursion, at about 62 Ma (Westerhold et al., 2011). It is important to stress, though, that the building of a huge organic carbon reservoir during the late Paleocene that can subsequently discharge carbon rapidly during the early Eocene presents a conceptual problem to any interpretation for the PETM δ 13 C excursion, if it 10 represents the extreme case of multiple events linked to environmental forcing. ...
Enormous amounts of 13C-depleted carbon rapidly entered the exogenic carbon cycle during the onset of the Paleocene-Eocene thermal maximum (PETM), as attested to by a prominent negative delta13C excursion and widespread seafloor carbonate dissolution. A widely cited explanation for this carbon input has been thermal dissociation of gas hydrate, followed by release of massive CH4 from the seafloor and its subsequent oxidation to CO2 in the ocean or atmosphere. Increasingly, papers have argued against this mechanism, but without fully considering existing ideas and available data. Moreover, other explanations have been presented as plausible alternatives, even though they conflict with geological observations, they raise major conceptual problems, or both. Methane release from gas hydrates remains a congruous explanation for the delta
... 4.2.5. Causes and consequences of Early Eocene nutrient excess at the shelves The Early Eocene warm and stagnating ocean is characterized by highly oligotrophic open ocean surface water masses and generally low productivity rates (Moore et al., 1978;Shackleton and Hall, 1984;Corfield and Shackleton, 1988;Hallock et al., 1991;Pak et al., 1997;Arkaah et al., 2006). In contrast to the open ocean, several marginal shelf basins are characterized by increased nutrient availability Stein et al., 2006). ...
The evolution of the isolated Galala carbonate platform has been studied intensively with respect to the Paleocene–Eocene Thermal Maximum (PETM) and the strong climatic variability from the Late Paleocene to the Early Eocene. In this study, we compare the results of different approaches which deal with the Early Palaeogene evolution of the Egyptian shelf, including new data from the Galala platform. Microfacies analyses along a platform to basin transect reveal a sedimentological response to a massive tectonic uplift along the Syrian Arc-Fold Belt in the Early Eocene. This uplift triggered the restriction of the Egyptian shelf by modulating and weakening Tethyan onshore currents from the North. The increasing deposition of quartz and proliferating gastropods, green algae and radiolaria, which indicate elevated nutrient levels, reflect an intensified eutrophication of shallow-marine platforms and deeper-marine shelf environments. Strongly depleted carbon isotope ratios in the sediments of the Galala succession strongly suggest the presence of restricted conditions throughout the Early Eocene. We assume that a strong climatic divergence with arid conditions on the shelf and humid conditions at the African hinterland triggered intensified chemical weathering at the Nubian–Arabian Craton. The enhanced riverine transport of terrestrial organic material to the North African shelf caused the increased availability of trophic resources and a strong negative shift of carbon isotope ratios between NP10 and NP14a. The recovery to open ocean conditions is linked to the termination of tectonic uplift along the Syrian Arc-Fold Belt in the latest Early Eocene and to stronger ocean currents, caused by increasing latitudinal temperature gradients.
Geochemical records generated from the calcite tests of benthic foraminifera, especially those of the genera Cibicidoides and Uvigerina, provide the basis for proxy reconstructions of past climate. However, the extent to which benthic foraminifera are affected by postdepositional alteration is poorly constrained. Furthermore, how diagenesis may alter the geochemical composition of benthic foraminiferal tests, and thereby biasing a variety of proxy‐based climate records, is also poorly constrained. We present the Foraminiferal Preservation Index (FPI) as a new metric to quantify preservation quality based on objective, well‐defined criteria. The FPI is used to identify and quantify trends in diagenesis temporally, from late Pliocene to modern coretop samples (3.3–0 Ma), as well as spatially in the deep ocean. The FPI identifies the chemical composition of deep‐ocean water masses to be the primary driver of diagenesis through time, while also serving as a supplementary method of identifying periods of changing water mass influence at a given site. Additionally, we present stable isotope data (δ¹⁸O, δ¹³C) generated from individual Cibicidoides specimens of various preservation quality that demonstrate the likelihood of significant biasing in a variety of geochemical proxy records, especially those used to reconstruct past changes in ice volume and sea level. These single‐test data further demonstrate that when incorporating carefully selected tests of only the highest preservation quality, robust paleorecords can be generated.
One of the “Big Five” mass extinctions in the Phanerozoic Eon occurred at the Cretaceous–Paleogene (K–Pg) boundary (66.0 million years ago). The K–Pg mass extinction was triggered by a meteorite impact that produced a crater at Chicxulub on the Yucatán Peninsula, Mexico. The following environmental perturbations might have been induced by the Chicxulub impact and acted as the killing mechanisms for the K–Pg mass extinction: (1) sunlight shielding, (2) sulfuric and nitric acid rain, (3) CO2-induced global warming, (4) ultraviolet penetration, and (5) toxic effects of ground-level ozone. The details of these perturbation events are summarized in this chapter. Based on evidence in sedimentary rocks, we could confirm whether such perturbation events occurred or not. However, it was difficult to reconstruct quantitatively the magnitudes and durations for such perturbation events because the necessary time-resolved information (yearly to millennium-scale) is lacking.
Elemental and isotope chemostratigraphies are used as tracers for glacial events, buildup of volcanic gases during glaciations (e.g., CO2), role of volcanism in mass extinction, salinity variation, redox state of the ocean and atmosphere, and provenance, among other applications. The use of isotope systems (C, O, S, N, Sr, Nd, Os), nontraditional stable isotope systems (e.g., Ca, Mg, B, Mo, Fe, Cr, Li), and elemental composition or elemental ratio (e.g., V, Ir, Mo, P, Ni, Cu, Hg, Rb/K, V/Cr, Zr/Ti, Li/Ca, B/Ca, Mg/Ca, I/Ca, Sr/Ca, Mn/Sr, Mo/Al, U/Mo, Th/U) in chemostratigraphy, especially across major chronological boundaries, are reviewed in this chapter. Furthermore, it is discussed what validates chemostratigraphy as a formal stratigraphic method.
Analyses were made of benthic foraminifers > 149 micrometer fractions of sediments from five depth-graded sites, 525, 526, 527, 528 and 529, down the flanks of the Walvis Ridge into the southern Angola Basin. Faunal contamination, in part attributed to the coring process, is prevalent through the Miocene at Sites 525, 526 and 528, where extremely large and some modern specimens are emplaced in the faunas. Oligocene-age taxa from Sites 526 and 529 were studied in the greatest detail, in order to allow comparison of faunas from deep water and intermediate water depths through this time.-from Author
Calcareous nannofossils (mainly coccoliths) have been important constituents of pelagic carbonates since the Early Jurassic, accounting for over 50% of some Tertiary sediments and around 30% of Recent oozes. Coccolith biosynthesis by calcareous nannoplankton forms an important role in marine biogeochemical cycles, contributing to the fluxes of carbon and calcium from the hydrosphere to the lithosphere. Most coccoliths are thought to descend through the water column ‘sealed’ within the faecal pellets of zooplankton grazers. This mode of sedimentation ensures that a constant supply of nannofossil carbonate, largely free from dissolution effects, reaches the ocean floor. Although post-depositional dissolution and diagenesis may modify coccolith biocoenoses, patterns of accumulation of coccoliths in sediments do reflect the oceanographic regimes of the overlying surface waters. Calcareous nannofossils are useful as tools for studying palaeoclimatic change and also form very good biostratigraphic markers.
Carbonate precipitation is a major process in the global carbon cycle. It was recently proposed that authigenic carbonate (carbonate precipitated in situ at the sediment–water interface and/or within the sediment) played a major role in the carbon cycle throughout Earth’s history. The carbon isotopic composition of authigenic
carbonates in ancient oceans have been assumed to be significantly lower than that of dissolved inorganic carbon (DIC) in seawater, as is observed in the modern oceans. However, the δ13Ccarb values of authigenic carbonates in the past has not been analyzed in detail. Here, we report authigenic carbonates in the uppermost Guadalupian (Middle Permian) rocks at Chaotian, Sichuan, South China. Monocrystalline calcite crystals <20 mm long are common in the black mudstone/chert sequence that was deposited on a relatively deep anoxic slope/basin along the continental margin. Textures of the crystals indicate in situ precipitation on the seafloor and/or within the sediments. The calcite precipitation corresponds stratigraphically with denitrification and sulfate reduction in the anoxic deep-water mass, as indicated by previously reported nitrogen and sulfur isotope records, respectively. Relatively high δ13Ccarb values of the authigenic carbonates (largely −1 ‰) compared with those of organic matter in the rocks (ca. −26 ‰) suggest that the main carbon source of the carbonates was DIC in the water column. The calcite crystals precipitated in an open system with respect to carbonate, possibly near the sediment–water interface rather than deep within the sediments. The δ13Ccarb values of the carbonates were close to the δ13CDIC value of seawater due to mixing of 13C-depleted remineralized organic carbon (that was released into the water column by the water-mass anaerobic respiration) with the large DIC pool in the oceans. Our results imply that δ13Ccarb values of authigenic carbonates in the anoxic oceans might have been systematically different from the values in the oxic oceans in Earth’s history, controlled by the depth of the redoxcline in the water column and sediments. If our model is correct, authigenic carbonates with relatively high δ13Ccarb values in the ancient anoxic oceans may have had a less substantial influence on the bulk δ13Ccarb values in geologic records than has been previously suggested.
: Variations in the 13 C/ 12 C value of total dissolved inorganic carbon (DIC) in the world’s oceans through time have been documented through stratigraphic study of marine carbonate rocks (δ 13 C carb ). This variation has been used to date and correlate sediments. The stratigraphic record of carbon isotopes is complex because the main process fractionating 12 C from 13 C is photosynthesis, with organic matter depleted in the heavy isotope ( 13 C). The carbon isotope record (on the geological time scales considered here) is to a large extent defined by changes in the partitioning of carbon between organic carbon and carbonate, and therefore linked directly to the biosphere and the global carbon cycle. This chapter summarizes δ 13 C carb variations through geologic time compiled from multiple literature sources. Materials analyzed for curve-construction differ between authors and between geological time periods, and one should carefully consider whether skeletal carbonate secreted by specific organisms or bulk carbonate has been used in evaluating or comparing carbon isotope stratigraphic records. Mid-Jurassic through Cenozoic curves have been mainly derived from pelagic carbonates, and exhibit low amplitude δ 13 C carb variability (from −1 to +4‰) relative to curves for the earlier part of the record (from −3 to +8 ‰ for the Phanerozoic, from −15 to +15‰ for the Proterozoic and Archean). The Mid-Jurassic and older curves are dominantly based on data from platform carbonates, which show greater variability and more spatial heterogeneity. The different character of carbon isotope curves derived from older platform carbonates as compared to younger pelagic records may reflect primary and/or diagenetic processes, difference in paleoenvironments, difference in calcifying organisms, or inherent changes in the global carbon cycle with geologic time and biotic evolution (e.g., changes in reservoir size).
The Pelotas Basin, located on the SE Brazilian shelf, has evolved since the Aptian. Stratigraphical data from the basin can be used for delineation of the unconformity-bounded units (synthems) on the shelf, which is a first step towards a full understanding of its stratigraphic architecture, evolution, and hydrocarbon potential. Hiatuses in the Cenozoic succession of the Pelotas Basin are established with both biostratigraphic (planktonic foraminifers and calcareous nannofossils) and isotopic (87Sr/86Sr) data. The seven recognised hiatuses are dated respectively as (1) Palaeocene (Danian- Thanetian), (2) Palaeocene/Eocene boundary (Thanetian-Ypresian), (3) Eocene (Ypresian-Lutetian), (4) Eocene-Oligocene (Lutetian-Rupelian), (5) early-late Oligocene (Rupelian-Chattian), (6) early Miocene (Aquitanian-Burdigalian), and (7) middle-late Miocene (Serravallian-Tortonian). These intervals between the hiatuses are correlated with those of the Santos and Campos Basins north from the Pelotas Basin.
The breaks in sedimentation that these basins have in common occurred (1) at the Palaeocene-Eocene and (2) Eocene-Oligocene transitions, (3) in the early Miocene, and (4) in the middle-late Miocene. These main unconformities outline five synthems on the SE Brazilian shelf, viz. the SEBS-1 (Palaeocene), SEBS-2 (Eocene), SEBS-3 (Oligocene), SEBS-4 (early-middle Miocene) and SEBS-5 (late Miocene-Holocene). The above unconformities are correlated with those established in the Cenozoic sedimentary successions of different regions such as Western Siberia, Arabia, NW and NE Africa, peninsular India, S Australia, the Gulf of Mexico, NW Europe, and South Africa.
The only regional unconformity, near the Oligocene/Miocene boundary, coincides with the nearly-global sedimentation break. The latter was resulted from a climatic event, i.e., the ‘Mi-1 glaciation’. Thus, a eustatic origin is supposed for this regional unconformity. The other regional unconformities also correspond to global sea-level falls (probably with an exception for the Palaeocene/Eocene surface), which suggests that global eustatic movements controlled the development of the regional synthem architecture.
The Kallamedu Formation, deposited during Late Maastrichtian is the thickest and largest sprawling non-marine/coastal stratigraphic unit of the Ariyalur Group, Cauvery basin, South India. However, it had attracted scanty attention from geoscientists owing to its poorly fossiliferous and weathered nature besides the paucity of good exposures. Understanding the depositional conditions of the Kallamedu Formation was necessitated due to the recent finding of continuous exposure of Maastrichtiah-Danian stratigraphic records namely, the Kallankurichchi Formation, the Kallamedu Formation and the Niniyur Formation near Niniyur and presumption of sauropod nesting site there. In this chapter, we report the textural properties of Kallamedu Formation sandstones and draw inferences on depositional and climatic conditions prevalent. The results indicate that the Kallamedu Formation was deposited under coastal plain environment that was periodically inundated by freshwater overflown from ephemeral river channels. The facies characteristics indicate deposition in river channel, flood plain, and overbank micro-environments located adjoining coastal region. Sediment availability was scarce and thus older sedimentary rocks were recycled through erosion-deposition during flood seasons. Predominance of riverine origin and transport of sediments by rolling and suspension mode are indicated by textural properties. Climatic conditions prevalent were inferred to be dry-humid alternations, principally influenced under seasonal/monsoonal conditions. Massive, monotonous, thick to very thick beds and other contact relationships together with mineralogical and textural properties of the Kallamedu Formation suggest the prevalence of flash floods under the influence of anomalous climatic conditions, that might have destabilized the environmental conditions and destructed the ecological niches, contributing towards dwindling and extinction of taxa during end-Cretaceous.
Oceanic ridge crest processes constitute a vigorous frontier of
multidisciplinary research with global ramifications in the earth,
atmospheric and biologic sciences. This deep ocean frontier is gradually
opening in response to investigations which are elucidating the role of
these processes in the lithosphere, hydrosphere, atmosphere and
biosphere, and the application of advanced instrumental and interpretive
techniques which are increasing the quality and quantity of data. These
techniques include crustal drilling with borehole logging (Deep Sea
Drilling Project reports), high-resolution bathymetry (Sea Beam, etc.),
side-scan sonar (SeaMARC I and II, GLORIA, etc.), imagery with video and
photography, multichannel seismics, determination of water column
properties (CTD with rosette sampler, etc.), and submersible
applications.
The late Paleocene to early Eocene was marked by major changes in Earth surface temperature and carbon cycling. This included at least two, and probably more, geologically brief (<200-k.yr.) intervals of extreme warming, the Paleocene-Eocene thermal maximum (PETM) and the Eocene thermal maximum-2 (ETM-2). The long-term rise in warmth and short-term “hyperthermal” events have been linked to massive injections of 13C-depleted carbon into the ocean-atmosphere system and intense global climate change. However, the causes, environmental impact, and relationships remain uncertain because detailed and coupled proxy records do not extend across the entire interval of interest; we are still recognizing the exact character of the hyperthermals and developing models to explain their occurrence. Here we present lithologic and carbon isotope records for a 200-m-thick sequence of latest Paleocene–earliest Eocene upper slope limestone exposed along Mead Stream, New Zealand. New carbon isotope and lithologic analyses combined with previous work on this expanded section shows that the PETM and ETM-2, the suspected H-2, I-1, I-2, and K/X hyperthermals, and several other horizons are marked by pronounced negative carbon isotope excursions and clay-rich horizons. Generally, the late Paleocene–early Eocene lithologic and δ13C records at Mead Stream are similar to records recovered from deep-sea sites, with an important exception: lows in δ13C and carbonate content consistently span intervals of relatively high sedimentation (terrigenous dilution) rather than intervals of relatively low sedimentation (carbonate dissolution). These findings indicate that, over ∼6 m.yr., there was a series of short-term climate perturbations, each characterized by massive input of carbon and greater continental weathering. The suspected link involves global warming, elevated greenhouse-gas concentrations, and enhanced seasonal precipitation.
Carbon and oxygen isotope records from carbonate fractions in marls overlying the K/T boundary in southern Israel are used to interpret paleoenvironmental changes and the history of early diagenetic events in the earliest Tertiary. The δ13C record of the whole rock does not significantly depart from the original values and reflects the global productivity drop shortly after the K/T boundary and the subsequent recovery. Fine fraction oxygen isotope values reflect the addition of carbonate cement highly depleted in 18O throughout the profile. The δ18O record demonstrates two main episodes in which contact with fresh water affected the sediments. One is below a short hiatus at planktic foraminiferal subzone transition PO/P1a (Guembelitria cretacea/Parvularugoglobigerina eugubina) and the other at an pyrite- rich clay layer near the top to planktic foraminiferal subzone P1b (‘Globigerina’ taurica). The latter event suggests introduction of sapropelic bottom conditions in the oceanic paleoenvironment.
Large imbalances in the relative net CO2 flux over the last 100 m.y. are obtained from independently derived estimates of CO2 uptake by weathering and organic carbon burial and of CO2 outgassing assumed proportional to the mean mid-ocean ridge (MOR) spreading and mantle plume production (MPP) rates. Increasing the river flux of Ca, Mg, P, and C by 50% since 30 Ma to parallel the proposed increase in the Sr river flux needed to explain the Sr isotopic evolution of seawater [Richter et al., 1992] has a large impact on the global carbon cycle by reducing the excess net CO2 imbalance in the late Cenozoic. CO2 uptake is calculated by assuming that 19% of the Ca river flux and 60% of the Mg river flux are derived from weathering silicates and that Mg is removed in the oceans by 1:1 molar exchange reactions with calcsilicates. An increase in the Mg river flux combined with an overall decrease in the MOR spreading rate predicts as much as a factor of 2 increase in the seawater Mg concentration since 100 Ma. The net organic carbon burial flux (burial minus weathering) largely reflects changes in the bulk carbonate delta13C record and, to a lesser extent, variations in the net carbonate burial flux and mean delta13C value of the carbonate weathering flux. Organic carbon burial efficiency is markedly less than that of P from the middle middle Miocene to the present because of early diagenetic transfer of organic P to francolite and oxidation of organic carbon during reworking of margin sediments by sea level fluctuations. The large CO2 imbalance of the Late Cretaceous requires significantly less carbonate subduction or greater weathering rates. A CO2 balance can be achieved in the Miocene by decreasing the proposed increase in river fluxes by up to half or by variably increasing the amount of carbonate subducted. Variations in shallow water carbonate burial, and hence the global carbonate record, are currently too poorly known to differentiate between the above possibilities. The decrease in the excess CO2 flux generally parallels the trend to cooler climate inferred from the delta18O record, but periods of large CO2 imbalance generally precede delta18O shifts by several million years.
At the Palaeocene/Eocene (P/E) boundary, some 55 Ma, a major transient global warming ("Palaeocene/Eocene Thermal Maximum"; PETM) affected the Earth system with significant biotic and abiotic changes. In particular, the hallmark of the PETM is a strong and complex negative carbon isotope excursion (CIE), that has been related to a huge and catastrophic release of methane from marine gas hydrates. Because the PETM might represent an analogue in the past of the present anthropogenic accelerated emission of greenhouse gases, it has attracted a good deal of interest with both data collecting and modelling efforts. However, as stated by Röhl and coworkers, "understanding the complete sequence of events that caused the PETM and elucidating the detailed nature of the environmental changes that took place will ultimately require high-quality records from a range of different latitudes and depths and from all of the major ocean basins". In this paper we document the occurrence of an expanded record of the PETM in the Vallone Bellunese area (Southern Alps, NE Italy), representative of bathyal depths of the central western Tethys, where the available records are scarce and condensed. We have carried out fieldwork along with paleontological (calcareous nannofossils, planktic and benthic foraminifera), mineralogical and geochemical (major elements, trace elements, stable carbon isotopes) analyses, that show that in the eastern flank of the Vallone Bellunese the PETM is well recorded. It is easily recognized in the field because it corresponds to a 2--3 meters thick package of reddish clays and marls (Clay Marly Unit, CMU) inserted in the calcareous-marly sediments of the "Scaglia Rossa" Formation. The CMU is widely traceable in the region and nicely matches the lithologic anomaly observed worldwide at the P/E boundary. We have reconstructed a composite section (the Forada section), extended from the latest Maastrichtian to the lowermost Eocene (NP10), that contains an apparently expanded documentation of the PETM. The carbon stable isotope data show the well known late Paleocene (NP7-NP8) delta13C maximum (2,5 ppm), followed in the latest NP9 by a stepped decrease by 1--1,5 ppm. The minimum values (-1,96 ppm) are observed at the base of the CMU, in correspondance with the extinction of at least 22 cosmopolitan species of benthic foraminifera. Above the CMU, in concomitance with the increase of the carbonate contents, there is a gradual exponential return of delta13C to the latest Paleocene values (≈1 ppm). The CIE covers an interval that is ca. 4.3 meters thick, i.e. more expanded than in all other sections we are aware of. The calcareous plankton eco- and biostratigraphy suggest a complete record. The interval containing the CIE is characterized by lithologic (marl-limestone couplets), minero-geochemical (Ca and hematite) and paleontological (radiolaria abundance) cycles. We have preliminary evaluated that the CIE encompasses 10/11 precessional cycles. This finding is in agreement with the recent evaluation of the duration of CIE obtained in the expanded ODP Site 690 at Maud Rise (Antartica). Apparently, the Forada section does represent a useful reference for facing the PETM problems from a central western Tethys perspective.
Zusammenfassung Quantitative Akkumulationsanalyse an tertiären kalkigen Nannofossilien ermöglicht eine genaue Auswertung ihrer Extinktionsmuster und, daraus folgend, ihres biostratigraphischen Wertes. Bei der Akkumulation von Species tritt öfters eine Variabilität hervor, die darauf hinweist, daß dichte Probenintervalle zur Einschätzung wahrer Ausbreitung nötig sind. Die erreichbare stratigraphische Auflösung wird von der Akkumulationsrate des Sediments und von der Tiefe der durch Bioturbation bewirkten Sedimenthomogenisierung festgelegt. Am Extinktionszeitpunkt zeigt die Akkumulation ein scharfes Abklingen, welches von einem Schweif stark reduzierter Akkumulation gefolgt wird, dessen Dauer im Bereich 2–3×103 bis 4–5×105 Jahren liegt. Es wird gezeigt, daß dieser Scheif entweder Akkumulation echter Produktion oder auch postdepositionelle Umlagerung vertritt. Wegen der Schwierigkeit, diese beiden bewirkenden Mechanismen zu unterscheiden, überragen biostratigraphische Indikatoren, definiert durch das rasche Abklingen, im Hinblick auf Synchronität und Erkennbarkeit diejenigen, die durch das absolut letzte Auftreten einer Spezies definiert sind.
The geochemical events (negative shifts in delta C-13 and delta O-18, and Mn peak) associated with the "Schistes carton" of Quercy (SW France) do not appear to be due only to lithological variations and a differential diagenesis. They correspond to the Lower Toarcian global event and seem to be connected to a destabilization phase of gas hydrates. During its oxidation by seawater, the release of methane gas with a very low carbon isotopic ratio (-60%) led to the production of CO2 and carbonates with a negative delta C-13. The consumption of oxygen in the seawater resulted in conditions that were first dysoxic and then anoxic. The reduction of burrowing and bioturbation associated with this oxidation resulted in the laminated appearance of the "Schistes carton". The decrease in the oxygen content led to a decrease in MnO2 microparticles present in the water column and sediments. This created a complementary source of Mn2+ that was incorporated into the carbonates produced during this event. Furthermore, an increase in the average seawater temperature (delta O-18) appears associated with this event. Finally, the apparent diachronism of geochemical events in the Boreal and the Tethyan realms is discussed.
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.
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