Article

A high-resolution marine 187Os/188Os record for the late Maastrichtian: Distinguishing the chemical fingerprints of Deccan volcanism and the KP impact event

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Abstract

A composite late Maastrichtian (65.5 to 68.5 Ma) marine osmium (Os) isotope record, based on samples from the Southern Ocean (ODP Site 690), the Tropical Pacific Ocean (DSDP Site 577), the South Atlantic (DSDP Site 525) and the paleo-Tethys Ocean demonstrates that subaerially exposed pelagic carbonates can record seawater Os isotope variations with a fidelity comparable to sediments recovered from the seafloor. New results provide robust evidence of a 20% decline in seawater 187Os/188Os over a period of about 200 kyr early in magnetochron C29r well below the Cretaceous–Paleogene Boundary (KPB), confirming previously reported low-resolution data from the South Atlantic Ocean. New results also confirm a second more rapid decline in 187Os/188Os associated with the KPB that is accompanied by a significant increase in Os concentrations. Complementary platinum (Pt) and iridium (Ir) concentration data indicate that the length scale of diagenetic remobilization of platinum group elements from the KPB is less than 1 m and does not obscure the pre-KPB decline in 187Os/188Os. Increases in bulk sediment Ir concentrations and decreases in bulk carbonate content that coincide with the Os isotope shift suggest that carbonate burial flux may have been lower during the initial decline in 187Os/188Os. We speculate that diminished carbonate burial rate may have been the result of ocean acidification caused by Deccan volcanism.

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... The osmium isotope ( 187 Os/ 188 Os) composition of marine sediments is considered one of the most reliable markers of the emplacement of the Deccan Traps in stratigraphic archives of the latest Cretaceous and earliest Paleogene (Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009;Ravizza and VonderHaar, 2012;Hull et al., 2020). Seawater 187 Os/ 188 Os ratios reflect the relative input of mantle-like ("nonradiogenic") Os from mid-oceanic-ridge or other submarine volcanic activity, weathering of primitive basalts, and the influx of extraterrestrial material ( 187 Os/ 188 Os ∼0.13; e.g., Allègre et al., 1999) compared to sources of more radiogenic Os derived from weathering of the continental crust (modern-day riverine average, 187 Os/ 188 Os ∼1.4; Peucker-Ehrenbrink and Jahn, 2001). ...
... In this context, a shift in 187 Os/ 188 Os (i) ratios from ∼0.6 to ∼0.4 around the C30n-C29r magnetochron boundary in uppermost Maastrichtian strata is generally interpreted to reflect the emplacement of juvenile, easily weathered Deccan Trap basalts, which increased the runoff of less radiogenic, mantle-like Os to the global ocean relative to older and more radiogenic crustal material (Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009). This interpretation is consistent with the documentation of the C30n-C29r boundary near the base of the "main" phase of Deccan lavas (Chenet et al., 2007;Schoene et al., 2019;Sprain et al., 2019). ...
... In comparison, a much smaller and 1-2 m.y. older phase of Deccan eruptions does not seem to have resulted in a noticeable change in sedimentary geochemical compositions (Chenet et al., 2009;Robinson et al., 2009). The K-Pg horizon itself is marked by a further drop in recorded 187 Os/ 188 Os (i) values to 0.2 or below, which gradually recovers to ∼0.4 above the boundary. ...
Article
The Cretaceous−Paleogene boundary is marked by a large impact and coeval mass extinction event that occurred 66 m.y. ago. Contemporaneous emplacement of the volcanic Deccan Traps also affected global climate before, during, and after the mass extinction. Many questions remain about the timing and eruption rates of Deccan volcanism, its precise forcing of climatic changes, and its signature in the marine geochemical sedimentary proxy record. Here, we compile new and existing mercury (Hg) concentration and osmium isotope (187Os/188Os) records for various stratigraphic sections worldwide. Both geochemical proxies have been suggested to reflect past variations in Deccan volcanic activity. New data from deep marine pelagic carbonate records are compared to contemporaneous records from shallower marine sites correlated through high-resolution cyclostratigraphic age models. The robustness of the proxy records is evaluated on a common timeline and compared to two different Deccan eruption history scenarios. Results show that the global 187Os/188Os signal is clearly reproducible, while the global Hg record does not form a consistent pattern. Moreover, the deep marine sections investigated do not record clear variations in the Hg cycle, particularly in the latest Cretaceous, prior to the extinction event. A detailed reevaluation of the precise depth of the redistribution of impactor-sourced platinum group elements does not exclude the possibility of a minor drop in 187Os/188Os corresponding with a pulse of Deccan volcanism ∼50,000 years before the Cretaceous−Paleogene boundary. Simple Os isotope mass balance modeling indicates that the latest Cretaceous was marked by significant levels of basalt weathering. CO2 sequestration during this weathering likely overwhelmed the emission of Deccan volatiles, thereby contributing to the end of the late Maastrichtian warming.
... The most notable mantle-like values in the Os isotopic record that can be unambiguously attributed to an enhanced extraterrestrial flux are those associated with the impactor at the Cretaceous-Paleogene boundary (Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009). Osmium isotopes and PGE chemistry have contributed significantly to the long-standing debate over the timing of the environmental impacts of Deccan Traps volcanism and the impactor and its role in driving mass extinction. ...
... Osmium isotopes and PGE chemistry have contributed significantly to the long-standing debate over the timing of the environmental impacts of Deccan Traps volcanism and the impactor and its role in driving mass extinction. Robinson et al. (2009) demonstrated that weathering of the basaltic Deccan Traps in the Late Cretaceous led to a 200 k.y. Late Maastrichtian decline in Osi that stabilized at ∼0.4 before seawater reached the chondritic Osi values and high Os and Ir concentrations coincident with the Chicxulub impact crater, which supports the claim that the environmental effects of LIP emplacement wellpreceded the extinction event. ...
... As noted above, Robinson et al. (2009) recorded a decrease in Osi from weathering of the Deccan Traps prior to the Cretaceous-Paleogene boundary. Other clear examples of nonradiogenic Os isotopic signals derived from basaltic weathering or an increased submarine volcanism flux come from both OAE 2, which spans the Cenomanian-Turonian boundary, and OAE 1a during the Aptian (Turgeon and Creaser, 2008;Du Vivier et al., 2014, 2015Sullivan et al., 2020;Martínez-Rodríguez et al., 2021;Percival et al., 2021). ...
Article
The rhenium-osmium (187Re-187Os) system is a highly versatile chronometer that is regularly applied to a wide range of geological and extraterrestrial materials. In addition to providing geo- or cosmo-chronological information, the Re-Os system can also be used as a tracer of processes across a range of temporal (millennial to gigayear) and spatial scales (lower mantle to cryosphere). An increasing number of sulfide minerals are now routinely dated, which further expands the ability of this system to refine mineral exploration models as society moves toward a new, green economy with related technological needs. An expanding range of natural materials amenable to Re-Os geochronology brings additional complexities in data interpretation and the resultant translation of measured isotopic ratios to a properly contextualized age. Herein, we provide an overview of the 187Re-187Os system as applied to sedimentary rocks, sulfides, and other crustal materials and highlight further innovations on the horizon. Additionally, we outline next steps and best practices required to improve the precision of the chronometer and establish community-wide data reduction procedures, such as the decay constant, regression technique, and software packages to use. These best practices will expand the utility and viability of published results and essential metadata to ensure that such data conform to evolving standards of being findable, accessible, interoperable, and reusable (FAIR).
... Therefore, the low 187 Os/ 188 Os value was not attributed to a local increase in mantle-origin or cosmic components. In the latter case, similarly negative Os isotopic shifts have been confirmed at the time of emplacement of large igneous provinces (LIPs), such as the Central Atlantic magmatic province (CAMP; Cohen and Coe, 2007;Kuroda et al., 2010), Ontong Java Plateau (OJP; Tejada et al., 2009;Bottini et al., 2012), and Deccan traps (Robinson et al., 2009). The emplacement of LIPs led to increased mafic basalt weathering, which shifted the seawater Os isotopic ratios to unradiogenic values. ...
... Emplacement of northern Siletzia igneous rocks has been dated to 53.18 ± 0.17 Ma and 48.364 ± 0.036 Ma (Eddy et al., 2017), possibly coincident with the decrease in the Os isotopic ratios observed at Site 752. The relatively small increase of Os burial flux during the decrease in the Os isotopic ratios (Fig. 4) implies that, if anything, the possible unradiogenic Os inputs to the ocean occurred far from this site or were relatively minor, as with emplacement of continental LIPs during the Mesozoic (i.e., CAMP and Deccan traps; Cohen and Coe, 2002;Robinson et al., 2009;Kuroda et al., 2010). ...
... This comparison is not straightforward, because the Deccan volcanism not only supplied unradiogenic Os but also suppressed radiogenic Os input to the ocean, because the emplaced basalts overlay the radiogenic continental crust (Ravizza and Peucker-Ehrenbrink, 2003a). However, the Deccan volcanism resulted in a seawater 187 Os/ 188 Os decrease of 0.20 during the latest Maastrichtian ( 187 Os/ 188 Os = 0.60 to 0.40; Robinson et al., 2009), and the NAIP volcanism caused a fall of 0.05-0.37 just before the PETM (Wieczorek et al., 2013;Dickson et al., 2015). ...
Article
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Multiple short-term (<10⁵ years) global warming events (“hyperthermals”) occurred throughout the early Eocene. Chemical weathering of continental silicate rocks is considered to have played a key role in recovery from these transient global warming events via consumption of excess atmospheric CO2. However, although evidence of this negative feedback has been reported for the Paleocene–Eocene Thermal Maximum (PETM), the effectiveness of chemical weathering during other transient hyperthermals remains poorly constrained. Here, we newly report early Eocene marine Os isotope records including Eocene Thermal Maximum 2 (ETM2), the I1 event, and ETM3 at Ocean Drilling Program Site 752 in the southern Indian Ocean. We demonstrate that marine ¹⁸⁷Os/¹⁸⁸Os increased during the hyperthermal events that were less severe than the PETM. The intensity of continental silicate weathering increased by 18%–22%, 17%–21%, and 13%–16% during ETM2, the I1 event, and ETM3, respectively, compared to the background conditions. Based on a reconsidered formulation of an Os mass-balance model, the intensity of continental silicate weathering during the PETM was reassessed to be a 34%–42% increase relative to the pre-PETM level. Thus, the continental chemical weathering flux during the Eocene hyperthermals may have been up to half as large as that of the PETM. It is noteworthy that the ordering of the changes in continental silicate weathering did not agree with the ordering of the seawater temperature rise among these events. This weathering–warming inconsistency might be attributable to (1) potential underestimation of continental silicate weathering due to the emplacement of Large Igneous Provinces (LIPs) and related basalt weathering, such as the North Atlantic Igneous Province and Siletzia in western North America, (2) changes in the background level of weathering intensity, and/or (3) a secular decrease in continental weatherability through the long-lasting early Eocene warming trend.
... The broader K-Pg interval also saw Deccan Traps volcanism on the Indian Subcontinent (Hull et al., 2020). Ravizza and Peucker-Ehrenbrink (2003) and Robinson et al. (2009) presented critical data sets of marine osmium isotopic records ( 187 Os/ 188 Os) from sediments of Maastrichtian age that show gradually declining values from ∼0.6-0.4 starting around the magnetic chron boundary between C30n and C29r, which is about ∼400 k.y. prior to the K-Pg boundary. ...
... prior to the K-Pg boundary. The K-Pg boundary itself is marked by a sharp drop of 187 Os/ 188 Os values from 0.4 to 0.15 and then a return to ∼0.4 in the earliest Paleocene (Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009;Ravizza and Von-derHaar, 2012). The gradual decrease and transient sharp drop have been attributed to increased weathering of basalts from the Deccan Traps and the Chicxulub impact event, respectively. ...
... (e.g., Sharma et al., 1997;Burton et al., 1999;Levasseur et al., 1999;Peucker-Ehrenbrink and Ravizza, 2000;Oxburgh, 2001). Therefore, its isotopic composition is useful as a chemostratigraphic correlation tool (e.g., Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009;Ravizza and VonderHaar, 2012;Hull et al., 2020). The composite marine Os isotopic record displays unique variation through the time period from Maastrichtian to Danian (the gray lines in Figs. ...
Article
During Deep Sea Drilling Project (DSDP) Leg 21, Cenozoic and latest Cretaceous sediments were recovered at Site 208 on the Lord Howe Rise, Southwest Pacific. We provide new biostratigraphic, magnetostratigraphic and chemostratigraphic data from Site 208 to constrain the stratigraphy around the Cretaceous-Paleogene (K-Pg) boundary and to determine the depth of the K-Pg boundary more precisely. Biostratigraphic data from calcareous nannofossils indicate a near-continuous succession of sediments from the mid-Maastrichtian (Late Cretaceous) to lowermost Thanetian (Paleocene) at depths of 540−590 m below seafloor (mbsf). The biostratigraphic data suggest that the K-Pg boundary corresponds to a siliceous claystone at the base of an interval of silicified sediments (576.0−576.8 mbsf). Carbonate carbon isotopic composition (δ13Ccarb) reveals a negative shift across this interval, which is consistent with global patterns of δ13C across the K-Pg boundary. Osmium concentration and Os isotopic composition (187Os/188Os) can also be used to identify the K-Pg boundary interval, as it is marked by a peak in Os concentration and a drop in 187Os/188Os values to 0.12−0.15, both of which are the result of the Chicxulub impact event. Our 187Os/188Os data show trends similar to those of coeval global seawater with the lowest value of 0.12−0.16 in the siliceous claystone (576.8 mbsf). However, the concentration of Os is low (<80 pg g−1) in this sample, which suggests that this siliceous claystone was deposited around the K-Pg boundary but may not include the boundary itself. Although the sedimentary record across the K-Pg interval at Site 208 may not be completely continuous, it nevertheless captures a time interval that is close to the Chicxulub impact event.
... Where there is no independent age control, "initial" 187 Os/ 188 Os ratios can be estimated using the isochron approach of measuring samples with different 187 Re/ 188 Os ratios collected from a restricted stratigraphic range (e.g., Cohen et al., 1999). Some Os-isotope records have also been produced from Fe-Mn crusts and oxic metalliferous sediments (e.g., Pegram et al., 1992;Peucker-Ehrenbrink et al., 1995;Burton et al., 1999;Ravizza et al., 2001;Klemm et al., 2005Klemm et al., , 2008Burton, 2006;Robinson et al., 2009). These records do not require a significant correction for Re decay, but may be systematically biased due to the partial liberation of detritally hosted Os phases from the bulk sediment (e.g., Pegram & Turekian, 1999). ...
... U-Pb dating of zircons recovered from ashfall and erosive units interbedded with lava flows has recently allowed the chronology of this event to be improved substantially, with an estimate of ~753 kyrs for 80%-90% of the total eruptive history (Schoene et al., 2015). Os-isotope records from a variety of carbonate successions show reproducible trends in seawater 187 Os/ 188 Os prior to the K-Pg, with a ~20%-25% decrease toward unradiogenic values commencing at the C29r/ C30n boundary, followed by a second decrease toward even more unradiogenic values occurring much closer to the K-Pg itself (Fig. 10.5; Ravizza & Peucker-Ehrenbrink, 2003;Robinson et al., 2009). Os data from K-Pg loca tions in Europe and the United States show that seawater 187 Os/ 188 Os decreased nearly to mantle values of ~0.14 at the acme of the unradiogenic shift prior to the K-Pg. ...
... Such feedbacks may have included the delivery of biolimiting nutrients and sulfate to the oceans, stimulat ing organic matter production and the consequent con sumption of dissolved oxygen in many parts of the oceans (Adams et al., 2010;Jenkyns, 2010). The Os-isotope data sets of Turgeon and Creaser (2008) have since been sup plemented by Du Vivier et al. (2014Vivier et al. ( , 2015, who were able to show how abrupt shifts in 187 Os/ 188 Os (i) ratios toward Robinson et al. (2009). The greyshaded region denotes a shift toward more unradiogenic seawater 187 Os/ 188 Os ratios that are taken to record the rapid weathering of basalts associated with LIP emplacement and/or a reduction in the weathering rate of continental rocks. ...
Chapter
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The emplacement of Large Igneous Provinces (LIPs) throughout the Phanerozoic Eon introduced vast quantities of mafic rocks to the Earth's surface, which were subsequently weathered into the oceans. Osmium isotope data can be used to track these LIP‐related weathering fluxes, providing a global fingerprint of the timing and magnitude of LIP emplacement, and guiding assessments of the impact of these events on ocean biogeochemistry and the regulation of the global climate system. Sedimentary Os isotope records spanning late Phanerozoic LIP events are reviewed herein and new observations from Eocene hyperthermal event ETM‐2 are presented. While Os isotope stratigraphy can provide major constraints on LIP activity in the geological record, it cannot always distinguish whether the extrusive activity was subaerial or submarine. The utility of osmium isotopes as a global tracer of past volcanism may be enhanced when used alongside proxies such as mercury concentrations, which may be more diagnostic of the style of individual episodes of LIP emplacement. Hitherto, only a few high‐resolution Os‐isotope records across Phanerozoic LIPs have effectively exploited the short oceanic residence time of Os. Future high‐resolution studies across suitable, well‐preserved stratigraphic records will significantly improve our understanding of the nature, progression, and consequences of LIP emplacement.
... For consistency, we applied the Bayesian approach to that dataset (25) to estimate a date of 66.016 ± 0.050 Ma ago for the KPB [95% credible interval, internal uncertainties only (13)]. Comparison of our data with recently published 40 Ar/ 39 Ar geochronology from the Deccan Traps and the Chicxulub impact (12, 26) is currently not possible at the necessary level of precision given systematic bias between the two dating methods, primarily related to uncertainty in ages of 40 Ar/ 39 Ar fluence monitors and the values of the 40 K decay constant and physical constants (13). Assuming that the Chicxulub impact coincides exactly with the main phase of extinction, the MCMC model outputs from our Deccan data demonstrate a~90% probability that the Poladpur Formation eruption pulse began tens of thousands of years before the K-Pg mass extinction event. ...
... For consistency, we applied the Bayesian approach to that dataset (25) to estimate a date of 66.016 ± 0.050 Ma ago for the KPB [95% credible interval, internal uncertainties only (13)]. Comparison of our data with recently published 40 Ar/ 39 Ar geochronology from the Deccan Traps and the Chicxulub impact (12, 26) is currently not possible at the necessary level of precision given systematic bias between the two dating methods, primarily related to uncertainty in ages of 40 Ar/ 39 Ar fluence monitors and the values of the 40 K decay constant and physical constants (13). Assuming that the Chicxulub impact coincides exactly with the main phase of extinction, the MCMC model outputs from our Deccan data demonstrate a~90% probability that the Poladpur Formation eruption pulse began tens of thousands of years before the K-Pg mass extinction event. ...
... Alternatively, an increase in surface area of exposed basalt associated with the Poladpur eruptions is possible given current Deccan stratigraphic area/volume models (22) (Fig. 2B). A second downturn in 187 Os/ 188 Os, beginning tens of thousands of years before the KPB, has been interpreted as a downward redistribution of extraterrestrial Os derived from the Chicxulub impactor (40,41). However, this decrease is synchronous with the Poladpur eruption pulse and is thus also consistent with increased weathering of a more extensive Deccan basalt pile. ...
Article
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Two timelines for extinction The Cretaceous-Paleogene extinction that wiped out the nonavian dinosaurs 66 million years ago was correlated with two extreme events: The Chicxulub impact occurred at roughly the same time that massive amounts of lava were erupting from the Deccan Traps (see the Perspective by Burgess). Sprain et al. used argon-argon dating of the volcanic ash from the Deccan Traps to argue that a steady eruption of the flood basalts mostly occurred after the Chicxulub impact. Schoene et al. used uranium-lead dating of zircons from ash beds and concluded that four large magmatic pulses occurred during the flood basalt eruption, the first of which preceded the Chicxulub impact. Whatever the correct ordering of events, better constraints on the timing and rates of the eruption will help elucidate how volcanic gas influenced climate. Science , this issue p. 866 , p. 862 ; see also p. 815
... In numerous studies, marine Os isotopic records preserved in pelagic sediments have been used to detect large volcanic inputs into the ocean; for example, the Deccan Traps at the end-Cretaceous (Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009), the Caribbean-Colombian Plateau and Ontong Java Plateau eruptions in the mid-Cretaceous (Turgeon and Creaser, 2008;Tejada et al., 2009), and the Central Atlantic Magmatic Province at the end-Triassic (Kuroda et al., 2010). Marine Os isotope ratios reflect the relative balance between Os inputs from riverine water ( 187 Os/ 188 Os ~ 1.4) and hydrothermal fluids and extraterrestrial material ( 187 Os/ 188 Os ~ 0.12-0.13) ...
... A rapid decline in riverine water flux is unlikely, because sedimentological and palynological studies clearly show that a humid pulse occurred at the base of the Julian 2 and ended in the early Tuvalian Ruffell, 1989, 1990;Roghi et al., 2010;Mueller et al., 2016). It can also not be explained by an extraterrestrial impact, which would have produced an abrupt 187 Os/ 188 Os i ratio decline followed by a rapid recovery, as observed in the pelagic deposits from the middle Norian (Sato et al., 2013), late Eocene (Paquay et al., 2008), and Cretaceous-Paleogene boundary (Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009). Moreover, no large impact event has been identified in the Carnian (Schmieder and Kring, 2020). ...
Article
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The Carnian Pluvial Episode (CPE) was a global environmental change and biotic crisis that occurred during the Carnian (Late Triassic). The climate during the CPE was characterized by a short-lived period of extreme rainfall, and an extinction of marine taxa is known to have occurred during the latest Julian (i.e. early Carnian). Although these events are considered to have been caused by the Wrangellia Flood Basalt (FB) volcanism, existing studies have found little direct evidence to support this. We investigated the temporal relationship between the eruption of Wrangellia FB and CPE using high-resolution microfossil biostratigraphy and paleo-seawater Os isotope data of an Upper Triassic bedded chert succession from an accretionary complex in Japan, which accumulated in a pelagic deep-sea environment in an equatorial region of the Panthalassa Ocean. Our biostratigraphic analysis, based on conodonts and radiolarians, and osmium isotope data show: (i) a continuous decline of initial Os isotope ratios (¹⁸⁷Os/¹⁸⁸Osi) in the early Julian; (ii) low ¹⁸⁷Os/¹⁸⁸Osi ratios during the late Julian; and (iii) an abrupt increase in ¹⁸⁷Os/¹⁸⁸Osi ratios at the end of the Julian. The decrease in ¹⁸⁷Os/¹⁸⁸Osi ratios throughout the Julian suggests an increased input of unradiogenic Os from the eruption of the Wrangellia FB into the ocean. Moreover, redox-sensitive elements, such as V and U, increased abruptly at the end of the Julian, which is the first evidence of reducing conditions during the CPE within the pelagic deep-sea Panthalassa Ocean. Marine anoxic event in the late Julian has been recognized from widespread deposition of black shales and organic-rich marls in intermediate to shallow water Tethyan sections. Thus, oxygen-depleted conditions occurred at the Tethyan shallow continental margin, as well as in the pelagic deep-sea Panthalassa Ocean, at the end of Wrangellia FB volcanism.
... Assuming that the shared history between the Malwa Plateau and Western Ghats reflects the behavior of a central eruptive center, we can assess whether the basalts on the northern margin of the province are consistent with a center that remained stationary or migrated to the south through time. Existing maps from the southern Deccan LIP show southward attenuation of the formations of the Western Ghats and a consistent onlapping of flow (Robinson et al., 2009;Ravizza and VonderHaar, 2012) and the timing and duration of the four eruptive pulses identified for the Deccan LIP by Schoene et al. (2019) and this study defined by the 95% credible intervals of the youngest and oldest U-Pb zircon eruption age in each pulse. The uncertainty of the U-Pb zircon dates for the C29r/C29n reversal (Schoene et al., 2019), Chicxulub impact (Clyde et al., 2016;Schoene et al., 2019), and C30n/C29r reversal (this study) are also shown. ...
... A 200 kyr period of ∼2.5-8 • C warming and subsequent cooling before the end Cretaceous extinction, named the Late Maastrichtian warming event, has been inferred on the basis of δ 18 O in benthic foraminifera (Fig. 3A: e.g., Li and Keller, 1998;Barnet et al., 2018), pedogenic carbonate (Nordt et al., 2002), and bivalve shells (Petersen et al., 2016), as well as changes in leaf morphology (Wilf et al., 2003). The onset of this excursion is temporally correlative with the first pulse of Deccan volcanism identified by Schoene et al. (2019) and the initial downturn in oceanic 187 Os/ 188 Os toward more radiogenic values (Fig. 3A: Robinson et al., 2009;Ravizza and VonderHaar, 2012), suggesting a potential causal relationship between the two events. Direct CO 2 emissions from basalt are unlikely to cause this magnitude of warming, except at extreme eruption rates (e.g., Self et al., 2006), which is difficult to reconcile with the likely longer duration and lower eruption rates inferred from this first eruptive pulse (Schoene et al., 2019). ...
... Osmium is removed from seawater into sediments in any redox condition (Yamashita et al., 2007) with strong authigenic enrichments in reducing conditions, and to a lesser degree in oxygenated waters (Peucker-Ehrenbrink and . When sediments that incorporate Os are deposited in the open ocean (e.g., in organic matter, Fe-Mn oxides, sulfides, carbonates), they record the isotopic ratio of seawater with high fidelity (e.g., Peucker-Ehrenbrink et al., 1995;Burton et al., 1999;Peucker-Ehrenbrink and Ravizza, 2000;Ravizza and Peucker-Ehrenbrink, 2003;Klemm et al., 2005;Yamashita et al., 2007;Robinson et al., 2009). A study on the effect of bioturbation on the Re-Os isotope system by van Acken et al. (2019) provided evidence for preservation of the authigenic 187 Os/ 188 Os ratio in sediments after being exposed to minor degrees of bioturbation. ...
... Due to the difference in 187 Os/ 188 Os ratio between mantle/extraterrestrial (Os i % 0.13; Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009;Sato et al., 2013) and riverine input (modern average Os i % 1.4; Peucker-Ehrenbrink and , it is possible to distinguish relative contributions of these sources of Os to seawater. There are two primary ways to shift the global oceanic Os isotopic composition from radiogenic to unradiogenic values (as seen at the initiation of the CIE that defines OAE-2). ...
Article
Oceanic anoxic Event 2 (OAE-2) occurred at the Cenomanian-Turonian boundary (∼94.1 Ma) and was a time of profound global changes in ocean chemistry and the carbon cycle. This event was characterized by a positive carbon isotope excursion (CIE) caused by massive organic carbon burial, global greenhouse temperatures, ocean deoxygenation, and changes in ocean life driven by large igneous province (LIP) activity. LIPS throughout the Phanerozoic have had dynamic magma flux, with episodes of major eruptions interspersed with periods of relatively less intense eruptions. A possible trigger for LIP activity throughout the Phanerozoic has been attributed to extraterrestrial impacts because there are multiple contemporaneous occurrences of large craters, LIP activity, and mass extinctions in the geologic record. At the Cenomanian-Turonian boundary, there is a 25 km diameter (rim-to-rim) complex crater in NW Alberta, Canada known as the Steen River impact structure dated at 91 ± 7 Ma (Carrigy and Short, 1968). An alternative explanation for those craters found contemporaneous with LIP activity and mass extinctions is that they were created by large explosive events related to LIP activity. Explosive events associated with mantle plume incubation beneath cratonic lithosphere have been suggested to create geologic features commonly attributed to impacts (e.g., shocked quarts, microspherules, etc.). Currently, the trigger for LIP activity during OAE-2, as well as the duration of LIP activity and the temporal variation and magnitude of eruption rates are not well constrained. To address the issue of LIP eruption rates and the trigger for LIP activity, we examined osmium (Os) abundances and isotopes as well as highly siderophile element (HSE; for this study: Re, Ru, Pd, Os, Ir, Pt) abundance data from a continuous sedimentary section spanning OAE-2. The section is from the Eagle Ford Group in the Iona-1 core, deposited in the Cretaceous Western Interior Seaway (KWIS). We found three high Os concentration intervals with mantle-like initial Osi isotope (initial ¹⁸⁷Os/¹⁸⁸Os) values of ∼0.16. These intervals are interpreted to reflect high-flux LIP magmatism pulses. Between the pulses, lower Os abundances with more radiogenic Osi values of ∼0.20 are observed, which we interpret as low-flux LIP activity between the high-flux periods. This trend of high-and-low flux Os concentration pulses with mantle-like Osi values during the high flux periods is found in another KWIS core (USGS Portland #1) deposited to the north of Iona-1, and in core Deep Sea Drilling Project (DSDP) Site 530 Hole A (hereafter DSDP 530A; drilled off-shore Namibia in the Angola Basin) deposited in the Southern Hemisphere. Before and throughout the Iona-1 core OAE-2 interval, HSE abundance patterns indicate a mantle source for the unradiogenic Os, and are not consistent with an extraterrestrial impact trigger or contribution to LIP activity during OAE-2. This evidence for multiple high-flux pulses of LIP activity driving ocean deoxygenation has implications for the modern ocean, which is currently experiencing deoxygenation. These results provide new constraints on subsequent high-flux periods that extended the event. The first high-flux period started ∼60 Kyr after our selection of the onset of the CIE. The second and third high-flux periods started ∼270 and ∼400 Kyr after the onset of the CIE, respectively. After the third high-flux period, δ¹³Corg and Os isotope ratios shifted back to pre-excursion values over ∼585 kyr. In the Iona-1 core, OAE-2 lasted for 1.04 ± 0.12 Myr based on our selection of the CIE.
... A further proxy for global climate changes induced by the Deccan Traps is provided by the seawater osmium (Os) isotopic record, which is a function of the mixing of radiogenic fluxes from riverine inputs and the alteration and weathering of juvenile (Wilf et al., 2003); (D) Osmium isotopic record from bulk carbonate from ODP 1262 core (Ravizza and VonderHaar, 2012) and the Bottacione (Gubbio, Italy) outcrop (Robinson et al., 2009); the low magnetic susceptibility interval at (E) Gubbio (Ellwood et al., 2003) and (F) Bidart (France) (Font et al., 2011); mercury content (ppb) of the K-Pg transition at Bidart (Font et al., 2016). basalts. ...
... The ocean residence time of Os is relatively short and the 187 Os/ 188 Os ratio of basalt is low ($0.1) compared to late Mesozoic seawater ($0.6). Os isotopic data from marine carbonates (Ocean Drilling Program-ODP-and Deep Sea Drilling Program-DSDP-sites) show a 20% decline in seawater 187 Os/ 188 Os during the late Maastrichtian event in the early magnetochron C29r, and a second more pronounced decrease some tens of thousands of years prior to the K-Pg boundary attributed to the weathering of Deccan lava flows and/or to diagenetic redistribution or physical mixing of meteoritic Os down-section (Ravizza and VonderHaar, 2012;Robinson et al., 2009). The striking synchronism between the pre-K-Pg Os decline and the enormous eruption of the Poladpur Formation calculated by Schoene et al. (2019) is rather consistent with increased weathering rates of extensive Deccan basalts (Fig. 3). ...
... A number of events have been proposed as potential sources of the non-radiogenic Os during this period. These include emplacement of large igneous provinces such as the Deccan Traps (Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009) and the first eruptive phase of the North Atlantic Igneous Province (Peucker-Ehrenbrink and , as well as weathering of exhumed large ophiolites such as the Papuan Ultramafic Belt (Fig. 9b; Lus et al., 2004;Peucker-Ehrenbrink and Ravizza, 2012). It is unclear, however, how much these events contributed to the 187 Os/ 188 Os decline given the significant time gaps between them and the long duration of the decline. ...
... Os isotope data sources: LL44-GPC3 = Pegram and Turekian (1999); DSDP 549 = Ravizza et al. (2001); CD29-2 = Klemm et al. (2005); ODP 886C = Ravizza (2007); ODP 690C and ODP 1262B = Ravizza and VonderHaar (2012) and ODP 865 = Rolewicz (2013). Not shown are initial 187 Os/ 188 Os ratios for late Maastrichtian (65.5 to 68.5 Ma) sediments from ODP 690, DSDP 577 and DSDP 525 (Robinson et al., 2009) that agree well with the data from Ravizza (2007) and Ravizza and VonderHaar (2012). NAIP = North Atlantic Igneous Province; Papuan UMB = Papuan Ultramafic Belt; PETM = Paleocene-Eocene Thermal Maximum. ...
Article
In the middle–late Paleocene, a marine, organic-rich sedimentary unit (Waipawa Formation [Fm]) in which the organic matter was derived mainly from terrestrial plants was deposited in many of New Zealand's sedimentary basins. The unique organofacies of this formation has not been identified in any other time interval within the geological history of the Southwest Pacific, indicating that unusual climatic and oceanographic conditions likely prevailed during this time. It has, therefore, attracted wide scientific interest due to its significance for regional and global reconstruction of the early Paleogene transitional climate as well as potential for oil and gas production. Scarcity of age-diagnostic fossils, presence of unconformities and lack of volcanic interbeds have, however, hindered precise dating and correlations of all the known occurrences of the formation. Here, rhenium‑osmium (Re-Os) geochronology has yielded the first radiometric age for the formation (57.5 ± 3.5 Ma), which is consistent with available biostratigraphic age determinations (59.4–58.7 Ma). Further, a comparison of Re-Os, bulk pyrolysis, sulfur and palynofacies data for the Waipawa Fm with those of more typical marine sediments such as the underlying Whangai Fm supports the interpretation that the chelating precursors or fundamental binding sites responsible for uptake of Re and Os are present in all types of organic matter, and that these elements have a greater affinity for organic chelating sites than for sulfides. The results also indicate that sedimentation rate may not play a dominant role in enhanced uptake of Re and Os by organic-rich sedimentary rocks. The initial ¹⁸⁷Os/¹⁸⁸Os values for the Waipawa (~0.28) and Whangai (~0.36) formations are broadly similar to those reported for coeval pelagic sediments from the central Pacific Ocean, further constraining the low-resolution marine ¹⁸⁷Os/¹⁸⁸Os record of the Paleocene. We present a compilation of ¹⁸⁷Os/¹⁸⁸Os values from organic-rich sedimentary rocks spanning the period between 70 and 50 Ma which shows that seawater Os gradually became less radiogenic from the latest Cretaceous, reaching a minimum value in the earliest late Paleocene (~59 Ma) during the deposition of Waipawa Fm, and then increased through the later Paleocene and into the early Eocene. The composite Os isotope record broadly correlates with global temperature (δ¹⁸O and TEX86) and carbon isotope (δ¹³C) records from the middle Paleocene to early Eocene, which is inferred to reflect climate-modulated changes in continental weathering patterns.
... Besides the Cretaceous-Paleogene boundary event itself, the continuous and complete sedimentary records in Gubbio provide the opportunity to investigate the signatures of other events preceding and following the Cretaceous-Paleogene boundary event (e.g., Coccioni et al., 2012Coccioni et al., , 2013. A decline in the marine osmium isotopic ( 187 Os/ 188 Os) record a few hundred thousand years before the Cretaceous-Paleogene boundary was interpreted as a chemostratigraphic marker for the beginning of the second and main phase of Deccan volcanism (Ravizza and Peucker-Ehrenbrink, 2003) and was also identifi ed in the Bottaccione Gorge section at Gubbio (Robinson et al., 2009). The mass extinction itself was followed by an ecological recovery (e.g., D'Hondt et al., 1998;Coxall et al., 2006;Coccioni et al., 2010;Schulte et al., 2010). ...
... This drop has also been identifi ed 5-6 m below (~300-400 k.y. before) the Cretaceous-Paleogene boundary in the BOT section (Robinson et al., 2009). Benthic foraminiferal δ 18 O values (Li and Keller, 1998;Barnet et al., 2017), and to some extent bulk carbonate δ 18 O records (Thibault et al., 2016a) and other temperature proxies , also show a clear warming a few hundred thousand years before the Cretaceous-Paleogene boundary. ...
... Besides the Cretaceous-Paleogene boundary event itself, the continuous and complete sedimentary records in Gubbio provide the opportunity to investigate the signatures of other events preceding and following the Cretaceous-Paleogene boundary event (e.g., Coccioni et al., 2012Coccioni et al., , 2013. A decline in the marine osmium isotopic ( 187 Os/ 188 Os) record a few hundred thousand years before the Cretaceous-Paleogene boundary was interpreted as a chemostratigraphic marker for the beginning of the second and main phase of Deccan volcanism (Ravizza and Peucker-Ehrenbrink, 2003) and was also identified in the Bottaccione Gorge section at Gubbio (Robinson et al., 2009). The mass extinction itself was followed by an ecological recovery (e.g., D'Hondt et al., 1998;Coxall et al., 2006;Coccioni et al., 2010;Schulte et al., 2010). ...
... This drop has also been identified 5-6 m below (~300-400 k.y. before) the Cretaceous-Paleogene boundary in the BOT section (Robinson et al., 2009). Benthic foraminiferal d 18 O values (Li and Keller, 1998;Barnet et al., 2017), and to some extent bulk carbonate d 18 O records (Thibault et al., 2016a) and other temperature proxies , also show a clear warming a few hundred thousand years before the Cretaceous-Paleogene boundary. ...
Chapter
Central Italy has been a cradle of geology for centuries. For more than 100 years, studies at the Umbria and Marche Apennines have led to new ideas and a better understanding of the past, such as the Cretaceous-Paleogene (K-Pg) boundary event, or the events across the Eocene-Oligocene transition from a greenhouse to an icehouse world. The Umbria-Marche Apennines are entirely made of marine sedimentary rocks, representing a continuous record of the geotectonic evolution of an epeiric sea from the Early Triassic to the Pleistocene. The book includes reviews and original research works accomplished with the support of the Geological Observatory of Coldigioco, an independent research and educational center, which was founded in an abandoned medieval hamlet near Apiro in 1992.
... The pattern of change we find in δ 11 B sw is broadly similar to temporal trends in a number of other related biogeochemical signals, such as oceanic 87/86 Sr, 187/188 Os, and δ 7 Li. Here we take published 87/86 Sr and δ 7 Li from Misra and Froelich (2012) Ravizza (1993); Ravizza and Turekian (1992); Ravizza andPeucker-Ehrenbrink (2003b, 2003a); Reusch et al. (1998); Robinson et al. (2009). For each signal, we assume that data constraints have Gaussian uncertainty (with magnitude given with original estimates, except in the case of 87/86 Sr where an illustrative uncertainty is used), which allows us to perform a straightforward Gaussian Process reconstruction, with the residence time of each element informing the length scale used ( 87/86 Sr-5.1 Myr (Broecker & Peng, 1982), δ 7 Li-2.8 ...
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The boron isotope ratio of seawater (δ¹¹Bsw) is a parameter which must be known to reconstruct palaeo pH and CO2 from boron isotope measurements of marine carbonates. Beyond a few million years ago, δ¹¹Bsw is likely to have been different to modern. Palaeo δ¹¹Bsw can be estimated by simultaneously constraining the vertical gradients in foraminiferal δ¹¹B (Δδ¹¹B) and pH (ΔpH). A number of subtly different techniques have been used to estimate ΔpH in the past, all broadly based on assumptions about vertical gradients in oxygen, and/or carbon, or other carbonate system constraints. In this work we pull together existing data from previous studies, alongside a constraint on the rate of change of δ¹¹Bsw from modeling. We combine this information in an overarching statistical framework called a Gaussian Process. The Gaussian Process technique allows us to bring together data and constraints on the rate of change in δ¹¹Bsw to generate random plausible evolutions of δ¹¹Bsw. We reconstruct δ¹¹Bsw, and by extension palaeo pH, across the last 65Myr using this novel methodology. Reconstructed δ¹¹Bsw is compared to other seawater isotope ratios, namely Sr87/86 87/86Sr{}^{87/86}\mathrm{S}\mathrm{r}, Os187/188 187/188Os{}^{187/188}\mathrm{O}\mathrm{s}, and δ⁷Li, which we also reconstruct with Gaussian Processes. Our method provides a template for incorporation of future δ¹¹Bsw constraints, and a mechanism for propagation of uncertainty in δ¹¹Bsw into future studies.
... Os isotopic ages of sample 6K#1207R01 obtained by fitting the 187 Os/ 188 Os ratios to the paleo-seawater 187 Os/ 188 Os curve. Data sources: Ravizza (1993), Oxburgh (1998), Reusch et al. (1998), Pegram and Turekian (1999), Ravizza et al. (2001), Ravizza andPeucker-Ehrenbrink (2003a, 2003b), Dalai et al., (2005Dalai et al., ( ,2006, Paquay et al., (2008Paquay et al., ( ,2014, Nielsen et al. (2009), Robinson et al. (2009), Peucker-Ehrenbrink and Ravizza (2012, Ravizza and VonderHaar (2012), van der Ploeg et al. (2018), Kuwahara et al. (2021), and Tanaka et al. (2022). ...
... However, certain studies have found no compelling evidence supporting a significant pulse of atmospheric CO 2 coinciding with the K-Pg event (Milligan et al., 2019). Nevertheless, certain records do support a negative d 13 C excursion, coupled with a warming period and a decline in osmium isotope values around the K-Pg transition (Robinson et al., 2009;Henehan et al., 2016;Barnet et al., 2018;Hull et al., 2020). In addition to carbon, fixed nitrogen incorporation is crucial for photosynthesis in various organisms. ...
... Thermogenic carbon from the Vindhyan basin sediments may thus have contributed to the end-Maastrichtian warming. The initiation of activity within the Malwa Plateau also coincides with the reduction in the 187 Os/ 188 Os values of ocean sediments toward more radiogenic values (Ravizza & VonderHaar, 2012;Robinson et al., 2009), implying an increase in the mantle contribution. While the steepest and most apparent decline occurs within Chron 29R, sampling density at Bottacione, Italy, suggests that multiple minor excursions to more radiogenic Os isotopic values occurred within Chron 30N and could be a result of Malwa basalts eroding into the global marine system. ...
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The eruptive history of the Malwa Plateau Subprovince of the Deccan Traps is addressed by dating 21 lavas spanning the exposed stratigraphic extent, using the ⁴⁰Ar/³⁹Ar method applied to plagioclase separates. Major, minor, and trace element geochemistry was determined for each of the dated lavas and four additional ones. Dating results indicate that the eruptions began prior to 66.8 Ma, at least 400 ka before the oldest known lava in the more extensively studied Western Ghats, representative of the main Deccan province, to the south. Eruption rates peaked from 66.4 to 66.3 Ma and then diminished until 65.6 Ma. The peak in eruption rates coincides with the well‐documented Late Maastrichtian Warming event. Malwa lavas show some major and trace element affinities with geochemically defined lava flow formations of the Western Ghats, but are generally out of the stratigraphic sequence manifest in the Western Ghats. The distinct geochemical evolution of Malwa Plateau lavas compared with those of the Western Ghats is at least in part a consequence of differences in crustal composition between the two subprovinces. Modeling of REE concentration patterns of Malwa lavas suggests that they were derived by slightly lower degrees of partial melting, at lower mantle temperatures and depths, than those in the Western Ghats. The Malwa Plateau thus appears to record an earlier, cooler stage of the Deccan plume's evolution and continued to erupt through a large part of the lifetime of the main Deccan province.
... 21 reported an increase in the extraterrestrial 3 He flux during the Turonian. However, in this study, we did not find apparent declines of the 187 Os/ 188 Os and PGE enrichment that is observed in the massive meteorite impact event 55 (Fig. 5). A possible explanation for this discrepancy between the present findings and those of Farley et al. ...
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The Turonian age (~ 90–94 Ma) was the hottest geological interval in the Cretaceous and also marked by the K3 event, a pronounced enrichment of ³He in pelagic sediments (i.e., massive input of extraterrestrial materials). Here, we present Os isotopic (¹⁸⁷Os/¹⁸⁸Os) and platinum group element (PGE) data from Turonian sedimentary records. After a sharp unradiogenic shift during the end-Cenomanian oceanic anoxic event 2, the ¹⁸⁷Os/¹⁸⁸Os ratios declined continuously throughout the Turonian, which could be ascribed to the formations of several large igneous provinces (LIPs). Because the interval with the most unradiogenic ¹⁸⁷Os/¹⁸⁸Os ratios (i.e., enhanced LIP volcanism) does not correspond to the warmest interval during the mid-Cretaceous, additional sources of CO2, such as subduction zone volcanism or the kimberlite formation, may explain the Cretaceous Thermal Maximum. As Os isotope ratios do not show any sharp unradiogenic shifts and PGE concentrations do not exhibit a pronounced enrichment, an influx of fine-grained cosmic dust to the Earth’s surface, possibly from the long-period comet showers, can be inferred at the time of the ³He enrichment during the mid-Turonian K3 event. Our findings highlight the different behaviors of ³He and PGE information in the sedimentary rocks during the input of fined-grained extraterrestrial materials.
... To investigate these relationships, the Os isotopic variations ( 187 Os/ 188 Os) in the sedimentary record can be used to constrain the causal link between enhanced volcanism and the onset of marine environmental perturbations in the marine environment (Leckie et al., 2002;Matsumoto et al., 2022;Peucker-Ehrenbrink and Ravizza, 2000;Du Vivier et al., 2014;Georgiev et al., 2013;Wieczorek et al., 2013). In previous studies, marine Os isotopic records preserved in pelagic sediments have been used to detect large volcanic inputs into the ocean throughout some sites, including the end-Cretaceous Deccan traps at the end of the Cretaceous (Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009), the Caribbean-Colombian Plateau and Ontong Java Plateau eruptions in the mid-Cretaceous (Turgeon and Creaser, 2008;Tejada et al., 2009), and the Central Atlantic Magmatic Province at the end of Triassic (Kuroda et al., 2010). The composition of seawater osmium isotope ( 187 Os/ 188 Os) reflects the mixing of radiogenic Os weathered from the continental crust ( 187 Os/ 188 Os =~1.4; ...
... The REY composition of the Kawame umber supports the hypothesis described above. The less negative Ce anomalies in the Kawame umber and red chert than in younger umbers and present-day hydrothermal ferromanganese sediments (Fig. 12b) indicate that conditions in Panthalassa during the Late Devonian were less oxidative than in the Late Ravizza et al. (1999Ravizza et al. ( , 2001a; deep-sea sediments, Dalai et al. (2005Dalai et al. ( , 2006, Kuwahara et al. (2021), Nozaki et al. (2019b), Ohta et al. (2020), Oxburgh (1998), Paquay et al. (2008Paquay et al. ( , 2014, Ravizza (1993), Ravizza et al. (2001b), Ravizza andPeucker-Ehrenbrink (2003a, 2003b), Reusch et al. (1998), Robinson et al. (2009) Cretaceous to Cenozoic ocean. In contrast, pelagic chert of the Upper Kellwasser Event at Bancheng, southern China, shows almost no to slightly positive Ce anomalies (i.e., Ce/Ce* ≈ 1; Ning et al., 2008;Fig. ...
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The Late Devonian, during which one of the “Big Five” Phanerozoic mass extinction events occurred, was one of the most important time intervals in Earth history. Nevertheless, the paucity of deep-sea records due to subduction has hampered elucidation of the pelagic environment during the Late Devonian in Panthalassa. However, ancient hydrothermal ferromanganese sediments, which were deposited on the abyssal seafloor and then accreted onto continental margins, are preserved as umber deposits and exposed in accretionary prisms. These sediments can provide key information to characterize the paleo-ocean. An Upper Devonian (Famennian) umber deposit is exposed in Kawame Quarry, Nedamo Belt, northeastern Japan. We investigated the bulk chemical composition and osmium isotopic ratio (¹⁸⁷Os/¹⁸⁸Os) of the Kawame umber to discuss the pelagic environment of the Panthalassa Ocean during the Late Devonian. The Kawame umber shows positive correlations between Fe content and the levels of P, V, Os, and rare earth elements, suggesting that hydrothermal Fe-oxyhydroxide particles adsorbed these elements from ambient seawater in the same way as hydrothermal ferromanganese sediments in the present-day ocean. Newly obtained initial ¹⁸⁷Os/¹⁸⁸Os values of Late Devonian seawater are 0.49–0.57, lower than that of present-day seawater (~1.06) and comparable to Paleogene and Late Cretaceous values. One of the most remarkable characteristics of the Kawame umber is its markedly high Fe levels (up to 90 wt%) compared to present-day seafloor hydrothermal ferromanganese sediments and younger umber deposits in Japanese accretionary complexes. Because seawater ¹⁸⁷Os/¹⁸⁸Os values were not notably different from those during the Paleogene and Late Cretaceous, anomalously vigorous hydrothermal activity in the Late Devonian is unlikely to have caused the increased Fe deposition. The rare earth element patterns of the Kawame umber (normalized to post-Archean average Australian shale) show weaker negative Ce anomalies than those of younger umbers and present-day hydrothermal ferromanganese sediments, suggesting that the Kawame umbers were deposited under less oxidizing conditions. Considering that many red beds were deposited at ~370 Ma, during recovery from the oceanic anoxic events (OAEs) of the Late Devonian (early Famennian), the anomalous Fe enrichment in the Kawame umber likely reflects enhanced oxidization and precipitation of abundant dissolved Fe during the post-OAE transition from anoxic to oxic conditions.
... Assessing the timing and style of emplacement of distal onshore and offshore records, constraining the eruptive tempo of pre-K-Pg and post-K-Pg eruptions at the sub-1000 yr timescale, and further constraints on the timing and magnitude of passive degassed volatiles, would greatly improve our understanding of Deccan's role in the K-Pg mass extinction and recovery. There is already a large amount of work on globally distributed stratigraphic sections (e.g., foram assemblages, carbon and oxygen isotopes, mercury) coeval with the Deccan Traps and the K-Pg boundary to help assess how Deccan volcanism affected the ecosystems (Hull et al., 2020;Birch et al., 2016;Witts et al., 2018;Scasso et al., 2020;Robinson et al., 2009;Woelders et al., 2017;Font et al., 2016;Sial et al., 2016;Punekar et al., 2016;Li and Keller 1998;Fendley et al., 2019;Tobin et al., 2012;Alvarez et al., 2019;Sinnesael et al., 2019;Keller et al., 1996). ...
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This volume pays tribute to the great career and extensive and varied scientific accomplishments of Walter Alvarez, on the occasion of his 80th birthday in 2020, with a series of papers related to the many topics he covered in the past 60 years: Tectonics of microplates, structural geology, paleomagnetics, Apennine sedimentary sequences, geoarchaeology and Roman volcanics, Big History, and most famously the discovery of evidence for a large asteroidal impact event at the Cretaceous–Tertiary (now Cretaceous–Paleogene) boundary site in Gubbio, Italy, 40 years ago, which started a debate about the connection between meteorite impact and mass extinction. The manuscripts in this special volume were written by many of Walter’s close collaborators and friends, who have worked with him over the years and participated in many projects he carried out. The papers highlight specific aspects of the research and/or provide a summary of the current advances in the field.
... The decrease in the abundance of infaunal taxa (M4b morphogroup) and the presence of the abundance of two epifaunal species (M2b and M4a morphogroups) suggest a drastic decrease in the food supply to the seafloor associated with nether the catastrophic mass extinction at the K/Pg boundary (Zachos and Arthur, 1986;Thomas 1990a, b;Kuhnt and Kaminski, 1993;D'Hondt et al., 1998;Widmark, 2000;Alegret et al., 2001Alegret et al., , 2003 nor the Deccan volcanic corresponds to the latest Maastrichtian global warming (Li and Keller, 1998a;Keller et al., 2002aKeller et al., , b, 2011aKeller et al., , 2011bRavizza and Puecker-Ehrenbrink, 2003;MacLeod et al., 2005;Quillévéré et al., 2008;Robinson et al., 2009;Coccioni et al., 2010;Punekar et al., 2014b). These changes in agglutinated foraminiferal assemblages were interpreted as resulting from the drop-in food supply to the benthos (e.g., Kuhnt and Kaminski, 1993;Thomas, 1990a, b;Alegret et al., 2001Alegret et al., , 2003Culver, 2003). ...
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The present authors used the scanning electron microscopy and energy dispersive spectroscopy methodology as a standard approach for micropaleontological studies to detect test internal morphological and compositional features of agglutinated foraminifera grains collected from Maastrichtian-Paleogene of the Dakhla Oasis of Egypt. Five main morphogroups dominate Lower Kharga Member,the mixture of infaunal and epifaunal morphogroups indicating mesotrophic conditions during that time.All evolving new species found in the Early Paleocene are small and species richness remains low with small simple test morphologies resembling the under zone CF3 with a new appearance of morphogroup epifaunal flattened planispiral. Zone CF3 of Lower Kharga Member is characterized by the appearances of small-sized Trochammina which are associated with stressful environmental conditions. Zone P1c of the Upper Kharga Member is characterized by high percentages of calcareous agglutinated foraminifera and abundance of granular calcite and hyaline tests, which explained a sufficient quantity of calcium carbonate dissolved in the water and warm water basin. The strong decrease in diversity and heterogeneity of the assemblages, as well as the drastic drop in the number of infaunal elongated morphogroup coincident with the hiatus between CF3 and P1c (Maastrichtian/Danian boundary), indicate a dramatic decrease in the food supply to the sea-bottom floor.
... For example, Os isotope data have been used to infer an abrupt decline in seawater 187 Os/ 188 Os ratios by the impact events that occurred during the late Eocene (Paquay et al., 2008) and at the K/Pg boundary (Ravizza and Peucker-Ehrenbrink, 2003). In addition, marine Os isotopic records have been also used to detect large volcanic inputs into the ocean; for example, the Deccan Traps at the end-Cretaceous (Ravizza and Peucker-Ehrenbrink, 2003;Robinson et al., 2009), the Caribbean-Colombian, Ontong Java, and Southern Kerguelen Plateau eruptions in the mid-Cretaceous (Turgeon and Creaser, 2008;Tejada et al., 2009;Matsumoto et al., 2020), the CAMP at the end-Triassic (Cohen and Coe, 2002;Kuroda et al., 2010), and the Wrangellia flood basalt volcanism in the Carnian (Nozaki et al., 2019;Tomimatsu et al., 2021). ...
Article
The Norian and Rhaetian transition (Late Triassic) is characterized by a faunal turnover in major pelagic groups, such as radiolarians, conodonts, and ammonoids. Although catastrophic events such as emplacements of large igneous provinces and/or extraterrestrial impacts have been suggested to account for this biotic turnover, firm evidence based on geochemistry of sedimentary successions is still lacking. In order to assess environmental changes across the Norian/Rhaetian boundary (NRB), we report high–resolution stratigraphic variations for whole-rock major, trace, and highly siderophile element abundances, together with ReOs isotope ratios for the Sasso di Castalda section in Lagonegro Basin, southern Italy. The section consists of a continuously exposed sequence of upper Norian (Sevatian) through the lower Rhaetian of a deep basinal deposits. Our data demonstrated that the upper Norian section records important events in stratigraphically ascending order: (1) a depositional environment moved below the Carbonate Compensation Depth, leading to the carbonate-biosilica transition associated with a slight depletion of elements favored in heavy minerals such as Zr, Hf, and Ti, (2) an input of Rochechouart impact components detected by platinum-group element anomaly, and (3) a transient change of redox state into low oxygen (dysoxic to suboxic) conditions marked by increases of V, U, and Re. This sequence of events suggests that the Rochechouart impact predates the major environmental changes resulting in faunal turnover at the NRB. Although their direct causal relationships are highly questionable given the small size of impactor and the interval between the impact horizon and the NRB, the possibility of triggering subsequent environmental and biotic collapses cannot be ruled out. This study provides the first identification of Rochechouart impact horizon in marine strata, which could be an important event marker for further studies on contemporaneous sections in the Lagonegro Basin and other localities.
... Notably, an abrupt decline in the seawater 187 Os/ 188 Os ratio was identified at the Cretaceous-Paleogene boundary (in conjunction with greatly enhanced Os concentrations) and was attributed to a large meteorite impact and followed by a rapid recovery to crust-like values (Peucker-Ehrenbrink et al., 1995;Peucker-Ehrenbrink and Ravizza, 2000;Peucker-Ehrenbrink and Jahn, 2001;Paquay et al., 2008). Similar, but less sharp, decreases in the Os isotopic ratio are reported for the late Maastrichtian (attributed to the Deccan volcanism) (Robinson et al., 2009) and for the Eocene-Oligocene transition (attributed either to enhanced ultramafic weathering or an increased influx of extraterrestrial material (Ravizza and Peucker-Ehrenbrink, 2003). The detection of such global seawater 187 Os/ 188 Os excursions reflects the comparably long residence time of Os in seawater (of *28,000 years) (Paquay and Ravizza, 2012;Georg et al., 2013) in comparison with typical ocean mixing times of ca. ...
Article
Banded iron formations (BIFs) were deposited before and concurrent with the Great Oxidation Event at ∼2.33 Ga. They provide useful archives that document the transformation of the Precambrian hydrosphere from anoxic to progressively oxygenated conditions. Their formation involves removal of oceanic Fe by either inorganic or biologically promoted Fe2+ oxidation, or both. To evaluate depositional settings, elemental sources that affect seawater chemistry, and oxidation pathways, we present the first combined highly siderophile element (HSE) and Fe-Os isotope study for the ∼2.7 Ga Temagami BIF, Abitibi Greenstone Belt, Ontario (Canada). HSE abundances and 187Os/188Os ratios show no systematic variation between alternating magnetite and (meta)chert bands of the Temagami BIF. Whereas HSE concentrations mostly resemble modern crustal values, present-day 187Os/188Os ratios range from ∼0.17 to ∼10.8. Magnetite samples define a regression line corresponding to an age of 2661 ± 126 Ma. A chondrite-like 187Os/188Os initial value is in agreement with earlier studies on Neoarchean marine sediments and is thought to reflect seawater composition, which, unlike modern oceans, is dominated by mantle-like 187Os inventory most likely derived from deep-sea hydrothermal vents. Our δ56Fe data vary from about +0.6‰ to +0.9‰ and define a sawtooth-like pattern between alternating magnetite and (meta)chert layers. Partial oxidation of hydrothermally sourced Fe(II) and a lack of microbially mediated dissimilatory iron reduction provide the most plausible explanation for the positive δ56Fe values. Notably, our δ56Fe data for Temagami are in accord with trends defined by literature results for other Algoma-type BIFs that were deposited throughout the Archean.
... Although geochemical signatures ascribed to Deccan volcanism, such as 187 Os/ 188 Os excursions and Hg enrichments, have been recognized prior to the K-PgB (Robinson et al., 2009;Font et al., 2016Font et al., , 2018Keller et al., 2020), several paleo-ecological and paleoclimate studies (e. g. Thibault and Gardin, 2010;Thibault et al., 2016;Hull et al., 2020;Gilabert et al., 2021) have shown that the influence of the Deccan volcanism during the latest Maastrichtian did not contribute to the K-PgB mass extinction (although this is disputed by some; e.g. ...
Article
After the Chicxulub impact and mass extinction at the Cretaceous-Paleogene boundary (K-PgB), ecosystems haltingly recovered under unstable conditions. An early Danian (65.9 Ma) perturbation of the carbon cycle known as DanC2, which includes two carbon isotopic excursions (CIEs), has been ascribed to inputs of greenhouse gases through large-scale volcanism of the Deccan Traps. However, the relationship between DanC2, volcanism and environmental and climatic changes during the early Danian remains ambiguous. Based on stable isotopes, calcium carbonate content, magnetic susceptibility and planktic foraminifera, we present a paleoenvironmental, paleoclimatic and paleoceanographic reconstruction of the early Danian from the Caravaca section, Spain, one of the most complete and continuous K-PgB sections worldwide. The paleobiological response of planktic foraminifera suggests very volatile environmental conditions during the first 230 kyr of the Danian, as reflected in the rapid succession of opportunistic/generalist blooms and episodic high occurrences of aberrant specimens. According to our age model, the Dan-C2 has been identified at the Caravaca section from 65.92 to 65.74 Ma. No evidence of strong carbonate dissolution through ocean acidification was observed in the Dan-C2 interval or the rest of the studied section, excluding the K-PgB clay bed. We find that blooms of highly eutrophic Chiloguembelitria and increases in aberrant planktic foraminifera coincided with a major early Danian eruptive episode of Deccan Traps (Ambelani Formation), occurring before the DanC2. Conversely, during both Dan-C2 CIEs, less opportunistic taxa thrived, indicating changes in the upper part of the water column. This study demonstrates that the relationship between marine biota and climate change was very complex and rapidly changing during the early Danian. In addition, we propose that the Deccan volcanism had adverse effects on marine plankton, mostly through strong eutrophication, while an increased water column stratification during the Dan-C2 event resulted in a transient boost in the recovery of ecosystems. You can download the final version of the manuscript using this link: https://authors.elsevier.com/a/1dFjG73N%7E2s3e
... A decline in the marine 187 Os/ 188 Os ratio (Robinson et al., 2009) provides the most unequivocal geochemical evidence for the timing in the marine sedimentary record of this latest Maastrichtian high-flux magma pulse. Although some authors have suggested an increased input of volcanogenic Hg during the latest Maastrichtian (e.g., Sial et al., 2016;Font et al., 2016, Font et al., 2017) the patterns are not consistent between sites or through time (Percival et al., 2018), suggesting this proxy cannot be used as a reliable and consistent stratigraphic marker of Deccan volcanism. ...
Article
A global warming episode in the Late Cretaceous, the Latest Maastrichtian Warming Event (LMWE), has been commonly linked to both the onset of massive Deccan Trap volcanism and the start of a planktic foraminiferal mass extinction prior to the Cretaceous/Paleogene boundary (KPB). The mechanisms that drove the LMWE are still under discussion, but radiometric dating of the onset of the main phase of the Deccan volcanism supports a temporal coincidence and permits a potential mechanistic link. Here we evaluate the planktic foraminiferal record, carbonate content and stable carbon and oxygen isotopes in the Caravaca section, in order to characterize paleoenvironmental change related to the LMWE. We identified negative d 13 C and d 18 O excursions in bulk carbonate from 66.35 to 66.14 Ma, i.e.~310 to~100 kyr before the KPB, which can be stratigraphically correlated to the LMWE and a major pulse of Deccan Traps volcanism. Within this warm interval, we identified high values in the fragmentation index of planktic foraminiferal tests, episodes of very high abundance of the low oxygen tolerant genus Hetero-helix, a decrease of thermocline dwellers, dwarfing in Contusotruncana contusa tests, and an increase in the biserial morphotype of Pseudoguembelina hariaensis with elongated terminal chambers. However, the environmental disturbance during the LMWE did not cause changes in the planktic foraminiferal extinction rate. At Caravaca, the warming associated with LMWE was followed by a gradual cooling up to the KPB suggesting no extended interval of perturbed environments before the KPB extinction due to Deccan volcanism.
... Correlations and Synthesis). A clue that CAMP volcanic aerosols or ash events could be the source of the PGE anomalies is provided by the PGE elemental ratios (Norris et al., 2000;Robinson et al., 2009) that allow discrimination of the Ir sources. NiS Fire Assay data for this are available from the sections at Exeter (Fig. 12.2), Partridge Island ( Fig. 12.4), and Sidi Rahal (Fig. 12.6). ...
Chapter
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Multiple lines of evidence suggest that volcanic and thermogenic gas emanations from the voluminous eruptions of the Central Atlantic Magmatic Province (CAMP) triggered the end‐Triassic mass extinction. However, a comparison of the timing and duration of the biotic and environmental crises with the timing and duration of the magmatic activity is difficult with existing data, especially when comparing the sedimentary archives below radioisotopically dated CAMP lavas. Here, we report multiple iridium anomalies interpreted to be the remnants of weathered basaltic ashes or aerosols of CAMP eruptions from three basins across a 15° swath of paleolatitude. Milankovitch‐controlled climate cycles pace the lacustrine strata of these basins, and in conjunction with paleomagnetic reversal stratigraphy and abundant palynological data, allow us to constrain the timing of magmatic events to be coincident with the extinctions. Thus, platinum group element concentrations provide geochemical traces of CAMP eruptions and can serve as potential proxies for CAMP eruptive pulses in both marine and nonmarine Triassic‐Jurassic boundary successions, permitting evaluation of correlations worldwide.
... The unclear evidence for sedimentary Hg enrichments suggests that this volcanism did not greatly influence the Hg cycle, possibly because a large part of the LIP volcanism at that time was likely submarine and any Hg emissions may have been less efficiently dispersed, generating the major spatial variability in mercury records associated with that event (see Percival et al., 2018). Similarly, while peaks in Hg and Hg/TOC have been reported from numerous end-Cretaceous sequences, the LIP volcanism associated with Cretaceous-Paleogene times (the Deccan Traps in India) commenced ~300 kyr earlier (e.g., Renne et al., 2015;Schoene et al., 2015), and is well documented in the sedimentary record by osmiumisotope evidence for major weathering of mantle-derived basalts (Ravizza & Peucker-Ehrenbrink, 2003;Robinson et al., 2009). Currently, there is little evidence for a perturbed Hg cycle during those 300 kyr (see Percival et al., 2018), suggesting that perhaps the initial Deccan volcanism had less of an impact on the global Hg inventory up until just prior to the extinction. ...
Chapter
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Volcanic activity associated with the emplacement of Large Igneous Provinces (LIPs) has been linked to most Phanerozoic extinctions/episodes of major environmental change. In recent years, mercury (Hg) enrichments and elevated mercury/total organic carbon (Hg/TOC) ratios have been increasingly utilized as a marker of volcanism in sedimentary records deposited distally from LIPs. The proxy is based on the premise that volcanism is a major natural source of the element to the atmosphere, and was especially important prior to anthropogenic emissions. To date, end‐Permian and end‐Triassic records illustrate the strongest use of Hg as a volcanic proxy; aided by supporting evidence (including Hg isotopes) for LIP eruptions and/or volatile emissions. Sedimentary records of several other events also document Hg enrichments in at least one region, suggesting regional or global Hg‐cycle perturbations potentially linked to volcanism at those times. The Cenomanian‐Turonian Oceanic Anoxic Event appears to be an exception, with Hg/TOC peaks documented in a small minority of studied records, suggesting minimal Hg‐cycle disturbance at that time. Even for events that apparently featured a global‐scale Hg‐cycle perturbation, variable Hg enrichments across individual archives of that same crisis indicate that the complex biogeochemical cycling of the element can strongly influence local/regional aquatic, biological, or sedimentary processes to alter the precise signature of any worldwide disturbance. Recent studies are beginning to investigate these complexities, but further work is needed to fully explore the nuances of Hg in the geological record, and how it can be best employed as a proxy for LIP volcanism.
... The final Maastrichtian appearance of photozoan reefal biota at the top of the Khirmanjo section could signal the partial recovery of the carbonate factory, which in turn maybe connected to the late Maastrichtian warming (e.g. Li & Keller, 1998;Linnert et al., 2014;Robinson et al. 2009) ( Figure S 3.7). Collectively, shifts in the association types in our studied sections closely follow the global climate trends during the Maastrichtian. ...
Thesis
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Unlike today’s prevailing terrestrial features, the geologic past of Central Asia witnessed marine environments and conditions as well. A vast, shallow sea, known as proto-Paratethys, extended across Eurasia from the Mediterranean Tethys to the Tarim Basin in western China during Cretaceous to Paleogene times. This sea formed about 160 million years ago (during Jurassic times) when the waters of the Tethys Ocean flooded into Eurasia. It drastically retreated to the west and became isolated as the Paratethys during the Late Eocene-Oligocene (ca. 34 Ma). Having well-constrained timing and paleogeography for the Cretaceous-Paleogene proto-Paratethys sea incursions in Central Asia is essential to properly understand and distinguish the controlling mechanisms and their link to Asian paleoenvironmental and paleoclimatic change. The Cretaceous-Paleogene tectonic evolution of the Pamir and Tibet and their far-field effects play a significant role on the sedimentological and structural evolution of the Central Asian basins and on the evolution of the proto-Paratethys sea fluctuations as well. Comparing the records of the sea incursions to the tectonic and eustatic events has paramount importance to reveal the controlling mechanisms behind the sea incursions. However, due to inaccuracies in the dating of rocks (mostly continental rocks and marine rocks with benthic microfossils providing low-resolution biostratigraphic constraints) and conflicting results, there has been no consensus on the timing of the sea incursions and interpretation of their records has been in question. Here, we present a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy as well as a detailed paleoenvironmental analysis for the Cretaceous and Paleogene proto-Paratethys Sea incursions in the Tajik and Tarim basins, in Central Asia. This enables us to identify the major drivers of marine fluctuations and their potential consequences on regional and global climate, particularly Asian aridification and the global carbon cycle perturbations such as the Paleocene-Eocene Thermal Maximum (PETM). To estimate the paleogeographic evolution of the proto-Paratethys Sea, the refined age constraints and detailed paleoenvironmental interpretations are combined with successive paleogeographic maps. Regional coastlines and depositional environments during the Cretaceous-Paleogene sea advances and retreats were drawn based on the results of this thesis and integrated with existing literature to generate new paleogeographic maps. Before its final westward retreat in the Eocene, a total of six Cretaceous and Paleogene major sea incursions have been distinguished from the sedimentary records of the Tajik and Tarim basins in Central Asia. All have been studied and documented here. We identify the presence of marine conditions already in the Early Cretaceous in the western Tajik Basin, followed by the Cenomanian (ca. 100 Ma) and Santonian (ca. 86 Ma) major marine incursions far into the eastern Tajik and Tarim basins separated by a Turonian-Coniacian (ca. 92-86 Ma) regression. Basin-wide tectonic subsidence analyses imply that the Early Cretaceous invasion of the sea into the Tajik Basin is related to increased Pamir tectonism (at ca. 130 – 90 Ma) in a retro-arc basin setting inferred to be linked to collision and subduction. This tectonic event mainly governed the Cenomanian (ca. 100 Ma) sea incursion in conjunction with a coeval global eustatic high resulting in the maximum geographic extent of the sea. The following Turonian-Coniacian (ca. 92-86 Ma) major regression, driven by eustasy, coincides with a sharp slowdown in tectonic subsidence related to a regime change in Pamir tectonism from compression to extension. The Santonian (ca. 86 Ma) major sea incursion was more likely controlled dominantly by eustasy as also evidenced by the coeval fluctuations in the west Siberian Basin. During the early Maastrichtian, the global Late Cretaceous cooling is inferred from the disappearance of mollusk-rich limestones and the dominance of bryozoan-rich and echinoderm-rich limestones in the Tajik Basin documenting the first evidence for the Late Cretaceous cooling event in Central Asia. Following the last Cretaceous sea incursion, a major regional restriction event, marked by the exceptionally thick (≤ 400 m) shelf evaporites is assigned a Danian-Selandian age (ca. 63-59 Ma). This is followed by the largest recorded proto-Paratethys sea incursion with a transgression estimated as early Thanetian (ca. 59-57 Ma) and a regression within the Ypresian (ca. 53-52 Ma). The transgression of the next incursion is now constrained as early Lutetian (ca. 47-46 Ma), whereas its regression is constrained as late Lutetian (ca. 41 Ma) and is associated with a drastic increase in both tectonic subsidence and basin infilling. The age of the final and least pronounced sea incursion restricted to the westernmost margin of the Tarim Basin is assigned as Bartonian–Priabonian (ca. 39.7-36.7 Ma). We interpret the long-term westward retreat of the proto-Paratethys Sea starting at ca. 41 Ma to be associated with far-field tectonic effects of the Indo-Asia collision and Pamir/Tibetan plateau uplift. Short-term eustatic sea level transgressions are superimposed on this long-term regression and seem coeval with the transgression events in the other northern Peri-Tethyan sedimentary provinces for the 1st and 2nd Paleogene sea incursions. However, the last Paleogene sea incursion is interpreted as related to tectonism. The transgressive and regressive intervals of the proto-Paratethys Sea correlate well with the reported humid and arid phases, respectively in the Qaidam and Xining basins, thus demonstrating the role of the proto-Paratethys Sea as an important moisture source for the Asian interior and its regression as a contributor to Asian aridification. We lastly study the mechanics, relative contribution and preservation efficiency of ancient epicontinental seas as carbon sinks with new and existing data, using organic rich (sapropel) deposits dated to the PETM from the extensive epicontinental proto-Paratethys and West Siberian seas. We estimate ca. 550-1000 Gt organic C burial, a substantial amount compared to previously estimated global total excess organic C burial (ca. 1700-2900 Gt) is focused in the proto-Paratethys and West Siberian seas alone. We also speculate that enhanced organic carbon burial later over much of the proto-Paratethys (and later Paratethys) basin (during the deposition of the Kuma Formation and Maikop series, repectively) may have majorly contributed to drawdown of atmospheric carbon dioxide before and during the EOT cooling and glaciation of Antarctica. For past periods with smaller epicontinental seas, the effectiveness of this negative carbon cycle feedback was arguably diminished, and the same likely applies to the present-day.
... The final Maastrichtian appearance of photozoan reefal biota at the top of the Khirmanjo section could signal the partial recovery of the carbonate factory, which in turn maybe connected to the late Maastrichtian warming (e.g., Li & Keller, 1998;Linnert et al., 2014;Robinson et al., 2009) ( Figure S7). Collectively, shifts in the association types in our studied sections closely follow the global climate trends during the Maastrichtian. ...
Article
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The timing and mechanisms of the Cretaceous sea incursions into Central Asia are still poorly constrained. We provide a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy together with detailed paleoenvironmental analyses of Cretaceous records of the proto‐Paratethys Sea fluctuations in the Tajik and Tarim basins. The Early Cretaceous marine incursion in the western Tajik Basin was followed by major marine incursions during the Cenomanian (ca. 100 Ma) and Santonian (ca. 86 Ma) that reached far into the eastern Tajik and Tarim basins. These marine incursions were separated by a Turonian‐Coniacian (ca. 92–86 Ma) regression. Basin‐wide tectonic subsidence analyses imply that the Early Cretaceous sea incursion into the Tajik Basin was related to increased Pamir tectonism. We find that thrusting along the northern edge of the Pamir at ca. 130–90 Ma resulted in increased subsidence in a retro‐arc basin setting. This tectonic event and coeval eustatic highstand resulted in the maximum observed geographic extent of the sea during the Cenomanian (ca. 100 Ma). The following Turonian‐Coniacian (ca. 92–86 Ma) major regression, driven by eustasy, coincides with a sharp slowdown in tectonic subsidence during the late orogenic unloading period with limited thrusting. The Santonian (ca. 86 Ma) major sea incursion was likely controlled by eustasy as evidenced by the coeval fluctuations in the west Siberian Basin. An early Maastrichtian cooling (ca. 71–70 Ma), potentially connected to global Late Cretaceous trends, is inferred from the replacement of mollusk‐rich limestones by bryozoan‐ and echinoderm‐rich limestones.
... Therefore, the incorporation of mantle sulfide components into the carbonatitic melt accounts well for the high PGE and Ni, Cu contents of the carbonatitic xenoliths. This conclusion is also supported by the Os isotopic compositions: sedimentary carbonate has much higher 187 Os/ 188 Os (∼0.6) (Robinson et al., 2009) than that of mantle peridotite (0.115-0.122), but contains very low Os contents (Fig. 3b). 187 Os/ 188 Os ratios of the Dalihu carbonatitic xenoliths negatively correlate with Os content, and fall along a sedimentary carbonate-mantle peridotite mixing trend (Fig. 3b). ...
... Similar patterns are noted in records from the South Atlantic Walvis Ridge and the North Pacific Shatsky Rise ( Fig. 2 and figs. S18 and S19) (42,46). The similarity of these records across three such widespread localities and four sites (Fig. 2) suggests that they provide a largely complete record of magnetochron C29r. ...
Article
An impact with a dash of volcanism Around the time of the end-Cretaceous mass extinction that wiped out dinosaurs, there was both a bolide impact and a large amount of volcanism. Hull et al. ran several temperature simulations based on different volcanic outgassing scenarios and compared them with temperature records across the extinction event. The best model fits to the data required most outgassing to occur before the impact. When combined with other lines of evidence, these models support an impact-driven extinction. However, volcanic gases may have played a role in shaping the rise of different species after the extinction event. Science , this issue p. 266
... Since the first application of the Os isotope system to impact events 15 , many studies have used Re-Os isotope systematics for better understanding of impactites and the effects of impact events on the Earth as well as for estimates of the impactor size [16][17][18][19][20] . Arguments based on Os geochemistry suggest that Os concentrations exceeding 1,000 ppt and conspicuous negative 187 Os/ 188 Os excursions as low as ~0.23 can only be produced by large influxes of unradiogenic Os from ultramafic rocks or meteoritic materials 17,20,21 . ...
Article
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Meteorite impacts have caused catastrophic perturbations to the global environment and mass extinctions throughout the Earth’s history. Here, we present petrographic and geochemical evidence of a possible impact ejecta layer, dating from about 11 Ma, in deep-sea clayey sediment in the Northwest Pacific. This clay layer has high platinum group element (PGE) concentrations and features a conspicuous negative Os isotope anomaly (¹⁸⁷Os/¹⁸⁸Os as low as ~0.2), indicating an influx of extraterrestrial material. It also contains abundant spherules that include pseudomorphs suggestive of porphyritic olivine as well as spinel grains with euhedral, dendritic and spherical forms and NiO contents as great as 23.3 wt%, consistent with impact ejecta. Osmium isotope stratigraphy suggests a most plausible depositional age of ~11 Ma (Miocene) for this layer, as determined by fitting with the seawater evolution curve. No large impact crater of this age is known on land, even within the relatively large uncertainty range of the relative Os age. Thus, we suggest that an unrecognised impact event in the middle or late Miocene produced the impact ejecta layer of the Northwest Pacific.
... Chondritic meteors have an Os isotopic ratio similar to that of Earth's mantle, and extraterrestrial impacts result in a strong, rapid excursion to unradiogenic (i.e., closer to 0) marine 187 Os/ 188 Os ratios (Luck and Turekian, 1983;Koeberl, 1998;Reimold et al., 2014; Figure 1). The only two such excursions in the Cenozoic are Chicxulub ( Figure 1b) and the late Eocene (~35 million years ago; Poag et al., 1994;Bottomley et al., 1997) dual impacts at Chesapeake Bay on the North American Atlantic coastal plain and Popigai in Siberia (Figure 1c; Robinson et al., 2009;Peucker-Ehrenbrink and Ravizza, 2012). Such Os isotope excursions would only be expected from chondritic impactors, but it is important to note that the scale of the impact is not necessarily reflected in the size of the Os excursion (Morgan, 2008). ...
Article
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Oceanic impact structures and their exploration via scientific drilling.
... Chondritic meteors have an Os isotopic ratio similar to that of Earth's mantle, and extraterrestrial impacts result in a strong, rapid excursion to unradiogenic (i.e., closer to 0) marine 187 Os/ 188 Os ratios (Luck and Turekian, 1983;Koeberl, 1998;Reimold et al., 2014; Figure 1). The only two such excursions in the Cenozoic are Chicxulub ( Figure 1b) and the late Eocene (~35 million years ago; Poag et al., 1994;Bottomley et al., 1997) dual impacts at Chesapeake Bay on the North American Atlantic coastal plain and Popigai in Siberia (Figure 1c; Robinson et al., 2009;Peucker-Ehrenbrink and Ravizza, 2012). Such Os isotope excursions would only be expected from chondritic impactors, but it is important to note that the scale of the impact is not necessarily reflected in the size of the Os excursion (Morgan, 2008). ...
... Dashed curves represent exponential fitting with half-heights of 4.6 cm and 0.43 cm, respectively cited as a trigger of the extinctions. However, the main eruptive phase of the Deccan Traps preceded the K-Pg boundary (Robinson et al. 2009;Schoene et al. 2015). In this chapter, the environmental perturbations induced by the meteorite impact are briefly reviewed. ...
Chapter
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.
... A decline in seawater 187 Os/ 188 Os ratio was also recorded throughout the global ocean just below the KPg boundary (Robinson et al., 2009) ( Figure 5.6). The authors indicated the second (main) phase of Decan volcanism as the cause of such isotopic decline but the process by which volcanism could generate such isotopic anomaly was not described. ...
Thesis
The KPg mass extinction (~66 Ma) and the PETM (~56 Ma) are both abrupt and global climate events in Earth’s history. The KPg mass extinction is commonly attributed to the Chicxulub impact, but in the last decades it has been linked to the Deccan volcanism. The abrupt warming during the PETM is attributed to methane release from seafloor sediments as consequence of the ocean warming due to the North Atlantic Igneous Province (NAIP) volcanic activity. The mechanisms by which these magmatic events led to global climate changes are still poor constrained. A recent approach combining rock magnetic techniques and mineralogical data provided interesting benchmarks to identify period of iron oxides dissolution linked to environmental acidification. Here, magnetic techniques such as magnetic susceptibility and isothermal remanent magnetization are applied to two marine sections encompassing the KPg (Zumaia, Spain) and PETM (Egypt, GSSP) transitions, in order to provide new insights to identify period of severe environmental changes in the geological record and their link to magmatic activity. The magnetic results obtained for both sections, Zumaia and Dababiya, correlate with biostratigraphic, mineralogical and geochemical data from previous studies at different sections worldwide, demonstrating not only the reliability of the data as well as the global dimension of both events. The data obtained for Zumaia supports an important climate event preceding the KPg boundary. Volcanic markers like magnetite dissolution previously identified in Bidart and Gubbio are confirmed here in the case of the Zumaia section. Magnetite depletion also corroborates the presence of akaganéite and Mercury at Zumaia to support the volcanic theory. On a global scale, these markers correlate with global warming, an increase in atmospheric CO2, environmental acidification via acid rains and presence of high stress opportunistic planctik foraminifera blooms. This climate perturbation also corresponds to the age of the main Deccan eruptions, recently dated by U-P method on zircon, reinforcing the link with the Deccan traps. In contrary to the KPg transition, the PETM at Dababiya is characterized by an increase in magnetite content, which is interpreted as the dissolution of carbonate and relative enrichment in detrital materials (clays). In addition, high concentration of goethite is observed along the section, specially above the PETM, where an increase in biological productivity is observed (Khozyem et al., 2015). In the PETM interval goetite decreases considerably. Goethite content at Dababiya is interpreted as the diagenetic oxidation of pirite and thus an indicator of anoxia during PETM. The increase in magnetite and decrease in goethite at the PETM also correlates with higher ratios of V/Cr, indicative of anoxic conditions (Khozyem et al., 2015). The high magnetite/low goetite interval at Dababiya also correlates with the Carbon Isotope Excursion (CIE) minimum that characterizes the PETM and with a calcite and foraminifera disappearance, supporting an ocean acidification starting below the PE boundary. Mercury enrichments in the same interval, together with negative excursions of 187Os/188Os, supports the role of volcanism (NAIP) to initiate the concomitant warming and sea level rise that mark the PETM. Comparasion of the magnetic properties of the KPg and PETM highlight different climate processes: dissolution of detrital magnetite onland in the case of KPg point environmental acidification by acid rains, whereas ocean acidification due to methane release and subsequent carbonate dissolution characterized the PETM. These findings provide new clues to identify climate and environmental acidification in the geological record and improve our understanding of future anthropogenic climate changes.
Article
Reconstructions of past oceanic redox conditions, based on the measurement of metal distributions and their stable-isotope ratios in marine sediments, have now become more commonplace, providing new constraints on past environmental change. Almost all of these records, however, are based on organic-rich black-shale and carbonate sedimentary archives, which have formed primarily in low-latitude regions. This limitation leads to incomplete geographic coverage that complicates the global-scale interpretation of the results. In this study, the potential of oceanic ‘red beds’ and grey shales as new archives of past environmental conditions are explored to complement the datasets derived from other lithologies and extend reconstruction efforts to mid- to high-latitude regions. Our records originate from open-marine red and grey shales from two sedimentary sections spanning the Late Cretaceous Oceanic Anoxic Event 2 (OAE 2) in New Zealand, formerly deposited at high southern latitudes in the palaeo-Pacific Ocean at c. 94 Ma and where contemporaneous black-shale and/or carbonate successions do not exist. Access to the seawater-derived, authigenic fraction of the bulk sediment is essential for reconstructing past marine redox state at these mid- to high-latitude locations. Therefore, a series of leaching experiments using reagents of progressively increasing concentration were conducted to determine the best method for isolating the authigenic Fe- and Mn-(oxyhydr)oxide fraction from the red and grey shale lithologies. Chemostratigraphic re- cords for the concentrations of a suite of redox-sensitive metals (Fe, Mn, Co, Ni, Mo, Cr, V and U), as well as the U-isotope palaeo-redox tracer (238U/235U; reformulated as δ238U), were obtained. These records imply that leaching with 6 M HCl at room temperature is the best of the tested methods for the selective extraction of the Fe- and Mn-(oxyhydr)oxide phase, whilst minimising the contribution from older inherited detrital material that potentially could confound the interpretation of the chemostratigraphic records. This method offers potential for reliably constraining the authigenic distributions of redox-sensitive elements in red and grey shales, provided Fe- and Mn-(oxyhydr)oxides are predominantly of authigenic origin and constitute at least 5 % of the mineralogy. By contrast, for the investigation of the U-isotope system, a larger Fe- and Mn-(oxyhydr)oxide proportion in the sediment for an ocean–atmosphere perturbation event recording more severe changes in ocean redox conditions and bigger U-isotope shifts than observed for OAE 2 are both necessary to obtain reliable results.
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Strata-bound ferromanganese (Fe–Mn) deposits (umbers) are thought to have formed by precipitation of Fe–Mn oxyhydroxides derived from seafloor hydrothermal activity at a mid-oceanic ridge. Fe–Mn oxyhydroxides effectively adsorb various elements (e.g., P, V, As, rare earth elements, and Os) dissolved in seawater. Of these elements, osmium (Os) is particularly important for reconstructing the Earth’s surface environment during formation of the deposits. Here we report the Os and rhenium (Re) contents and marine Os isotopic ratio (¹⁸⁷Os/¹⁸⁸Os)i of the early Permian reconstructed from the Kunimiyama umber deposit in the Northern Chichibu Belt, central Shikoku, southwest Japan. The Kunimiyama umbers exhibit comparable to slightly lower Os (42–183 ppt) and much lower Re (1.3–49 ppt) contents than other umbers in Japanese accretionary complexes and modern seafloor metalliferous sediments, the latter of which are regarded as umber precursors. The (¹⁸⁷Os/¹⁸⁸Os)i ratio of the Kunimiyama umbers is 0.523–0.676, which is comparable to or slightly higher than the values of the middle to Late Cretaceous and early Paleogene. This work is the first report of seawater Os isotope ratios in the Panthalassa Ocean of the early Permian, representing an important achievement in understanding the marine Os isotopic record of the Paleozoic Era.
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Extraterrestrial impacts are one of the most ubiquitous processes in the solar system, reshaping the surface of rocky bodies of all sizes. On early Earth, impact structures may have been a nursery for the evolution of life. More recently, a large meteorite impact caused the end Cretaceous mass extinction, killing 75% of species on the planet, including non-avian dinosaurs, and clearing the way for the dominance of mammals and eventual evolution of humans. Understanding the fundamental processes associated with impact events is critical to understanding the history of life on Earth and the potential for life across the solar system and beyond. Scientific ocean drilling has generated irreplaceable data on impact processes. The Chicxulub impact is the single largest and most significant impact event that can be studied by sampling modern ocean basins, and marine sediment cores have been instrumental in quantifying the climatological and biological effects of the impact. Recent drilling in the Chicxulub Crater has already significantly advanced our understanding of fundamental impact processes, notably the formation of peak rings in large impact craters. These results raise a number of new questions waiting to be addressed with further drilling. Extraterrestrial impacts have been controversially suggested as drivers for many important paleoclimatic events in the Cenozoic, up to and including the Younger Dryas stadial at the end of the last glacial maximum. However, marine sediment archives (e.g., Osmium isotopes) provide a long term archive of major impact events in recent Earth history and show that, other than the end Cretaceous, major paleoclimatic events are not driven by impacts.
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A high-resolution (10–20 kyr) record of variations in CaCO3 content and dissolution was established for latest Cretaceous (last 0.7 Myr) deep-sea sediments from the South Atlantic Ocean (DSDP Site 516 from the Rio Grande Rise, and sites 525 and 527 from the Walvis Ridge). The degree of fragmentation of planktonic foraminifera (DFP) was used as a measure of calcite dissolution. High negative correlations between DFP and other independent measures of carbonate dissolution (percentage of sand fraction, absolute abundance of planktonic foraminifera, and planktonic/benthic foraminiferal ratio) validate its use as a sensitive index of calcite dissolution in upper Maastrichtian deep-sea sediments.
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[1] Abstract: We investigate the use of loess as a proxy for the concentration and isotopic composition of highly siderophile elements, specifically Os, in the upper continental crust. The 187 Os/ 188 Os, platinum group element, and Re concentrations of 16 loess samples from China, Europe, and South America, previously analyzed for major, trace element, and Sr and Nd isotope composition, reveal subtle differences between loess provinces. Despite those differences, the 187 Os/ 188 Os of 1.05 ± 0.23is surprisingly homogenous. Average 187 Os/ 188 Os as well as average Os (31 pg/g) and Ir (22 pg/g) concentrations are similar to the lower limit of previous estimates for average upper continental crust, whereas Ru, Pt, and Pd concentrations are intermediate between previous estimates. We argue that hydrogenous enrichment of Os in riverine sediments led Esser and Turekian [1993] to overestimate the Os concentration of upper continental crust (50 pg/g). On the basis of this argument and correlations with major and trace elements we propose that average platinum group element concentrations of loess (i.e., 31 pg Os/g, 22 pg Ir/g, 210 pg Ru/g, 510 pg Pt/g, 520 pg Pd/g) are a proxy for the upper continental crust. We further suggest that the nonchondritic average Os/Ir of 1.4 reflects the combined effects of radiogenic ingrowth of Os from Re decay over the mean lifetime of the upper continental crust and preferential return of Os to the crust during subduction. Rhenium concentrations scatter significantly, with highest values in loess derived from organic-rich sedimentary rocks. Low median Re concentrations most likely reflect depletion of loess in organic matter, an important sink for Re in the upper continental crust. An average 187 Re/ 188 Os of 34.5 was calculated on the basis of the measured 187 Os/ 188 Os and Nd model ages. This value corresponds to a Re concentration of 198 pg/g. Correcting measured 187 Os/ 188 Os = 1.05 and inferred 186 Os/ 188 Os = 0.119871 (from 190 Pt/ 188 Os = 0.0176) for the older mean age (2.2 Gyr) of upper continental crust compared to loess (1.6 Gyr) yields average upper crustal 187 Os/ 188 Os of 1.40 and 186 Os/ 188 Os of 0.119885.
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Detailed analyses of well-preserve d carbonate samples from across the Cretaceous/Tertiary boundary in Hole 577 have revealed a significant decline in the δ13C values of calcareous nannoplankton from the Maestrichtian to the Danian Age accompanied by a substantial reduction in carbonate accumulation rates. Benthic foraminifers, however, do not ex- hibit a shift in carbon composition similar to that recorded by the calcareous nannoplankton, but actually increase slightly over the same time interval. These results are similar to the earlier findings at two North Pacific Deep Sea Drill- ing Project locations, Sites 47.2 and 465, and are considered to represent a dramatic decrease in oceanic phytoplankton production associated with the catastrophic Cretaceous/Tertiary boundary extinctions. In addition, the change in car- bon composition of calcareous nannoplankton across the Cretaceous/Tertiary boundary at Hole 577 is accompanied by only minor changes in the oxygen isotope trends of both calcareous nannoplankton and benthic foraminifers, suggest- ing that temperature variations in the North Pacific from the late Maestrichtian to the early Danian Age were insignificant.
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A paleomagnetic investigation of the Late Cretaceous sediments of the Maud Rise, Antarctica, recovered in Holes 689B and 690C provides a fairly complete magnetostratigraphic record ranging from Chron C33N through Chron C29R. The Cretaceous/Tertiary boundary is shown to occur in Chron C29R at Site 690. -Author
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Decreases in the seawater 187Os/188Os ratio caused by the impact of a chondritic meteorite are indicative of projectile size, if the soluble fraction of osmium carried by the impacting body is known. Resulting diameter estimates of the Late Eocene and Cretaceous/Paleogene projectiles are within 50% of independent estimates derived from iridium data, assuming total vaporization and dissolution of osmium in seawater. The variations of 187Os/188Os and Os/Ir across the Late Eocene impact-event horizon support the main assumptions required to estimate the projectile diameter. Chondritic impacts as small as 2 kilometers in diameter should produce observable excursions in the marine osmium isotope record, suggesting that previously unrecognized impact events can be identified by this method.
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In a study of ODP Hole 689B no iridium (Ir) anomaly was found in Sections 1 through 6 of Core 25X or in Core 26X from the top down to section 2, 3-12 cm. The background Ir abundance averaged 11 parts per trillion (ppt) and a clay-enriched region had nearly the same average, 26 ± 12 ppt. If the Cretaceous-Tertiary (K-T) contact is in the region studied, then sedimentation was not continuous, and the K-T boundary was probably either not deposited or it was eroded away. In a study of Cores 15X and 16X of ODP Hole 690C, an iridium peak with a maximum abundance of 1566 ± 222 ppt was found in Section 4 of Core 15X at 39-40 cm with a half-width of 6.6 cm. Background abundances were ~ 15 ppt and distinctly higher Ir abundances were observed from 119 cm below to 72 cm above the main peak. The Ir distri-bution below the main peak is attributed to bioturbation by organisms with burrows extending at least 0.4 m. The Ir distribution above the main peak may be due to the same cause but other explanations may be significant. There are variable enrichments of clay in the mainly CaC0 3 sediment of Core 15X, and the stratigraphically lowest part of the most abundant clay deposits is found (within 2 cm) in the same position as the main Ir peak. The clay de-posit, which is estimated to be about 50% of the sediment, extends upward ~ 19 cm and then slowly decreases to a background level of 10% over 1 m. The degree of homogeneity of the clay-rich interval suggests it was not due to epi-sodic volcanism but may have been due to a decrease of the CaC0 3 deposition rate which was possibly triggered by the impact of a large asteroid or comet on the Earth.
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The discovery of the platinum-group element (PGE) enrichment in the Cretaceous–Tertiary (K–T) boundary impact layer popularized the use of PGEs as geochemical event markers and prompted an explosion of interest in these elements whose geochemical behavior is poorly understood. Instead of concentrating on the more easily analyzed PGEs (e.g., iridium), many studies now include the entire group. Analytical methods have been improved to the point where small samples (≤5 g) can be analyzed confidently at the sub-ppb level, allowing the determination of the distribution of PGEs in the oceans, atmosphere and biosphere.The presence or absence of a PGE anomaly is often used as a criterion for determining whether an event horizon is impact-related, however, to date, only the K–T boundary yields a distinct PGE anomaly with positive interelement correlations and solar interelement ratios. Terrestrial sources such as volcanic emissions are also being investigated as potential contributors to PGE anomalies at other Phanerozoic event horizons.Primary signatures (e.g., interelement ratios), characteristic of the PGE source, may be altered during various high and/or low temperature processes. For example, fractionation during impact melting, vaporization/condensation, remobilization, redistribution and diagenesis can obscure original signatures and make determination of the PGE source difficult. Future research might be directed towards establishing the behavior of the PGEs during such processes.
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Iridium, Pd, Pt, and Au were determined in sections from the Bottaccione Gorge and Contessa Valley, Gubbio, Italy, by radiochemical neutron activation. Shales and limestones were sampled from 2.85 m above to 219 m below the Cretaceous/Tertiary (K/T) boundary. Metal enrichment was evaluated by comparing the boundary shale region with the lower part of the section (background). Iridium is concentrated by 63 times in the boundary shales in comparison with the background, whereas other metals are enriched by no more than 2.2 times. The enrichment of Ir is not confined to the boundary shales but extends approximately 2 m above and below this horizon. Within this Ir-rich region there are four distinct Ir maxima in addition to the major Ir enrichment in the K/T boundary shales. Iridium maxima are stratigraphically coincident with maxima in abundances of shocked minerals characteristic of explosive volcanism. Limestones are much lower in noble metals than shales, and their Ir contents in the K/T boundary region are largely accounted for by their minor clay mineral contents. The time represented by the 4 m of Ir-rich section is at least 3 x 105 yr, if published sedimentation rates are used. To sustain an increased Ir flux over this period and to account for the Ir distribution near the K/T boundary, intense volcanic activity is a preferred alternative to impact of extraterrestrial material.
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Seawater 187 Os/ 188 Os ratios for the Middle Miocene were reconstructed by measuring the 187 Os/ 188 Os ratios of metalliferous carbonates from the Pacific (DSDP 598) and Atlantic (DSDP 521) oceans. Atlantic and Pacific 187 Os/ 188 Os measurements are nearly indistinguishable and are consistent with previously published Os isotope records from Pacific cores. The Atlantic data reported here provide the first direct evidence that the long-term sedimentary 187 Os/ 188 Os record reflects whole-ocean changes in the Os isotopic composition of seawater. The Pacific and the Atlantic Os measurements confirm a long-term 0.01/Myr increase in marine 187 Os/ 188 Os ratios that began no later than 16 Ma. The beginning of the Os isotopic increase coincided with a decrease in the rate of increase of marine 87 Sr/ 86 Sr ratios at 16 Ma. A large increase of 1 in benthic foraminiferal 18 O values, interpreted to reflect global cooling and ice sheet growth, began approximately 1 million years later at 14.8 Ma, and the long-term shift toward lower bulk carbonate 13 C values began more than 2 Myr later around 13.6 Ma. The post-16 Ma increase in marine 187 Os/ 188 Os ratios was most likely forced by weathering of radiogenic materials, either old sediments or sialic crust with a sedimentary protolith. We consider two possible Miocene-specific geologic events that can account for both this increase in marine 187 Os/ 188 Os ratios and also nearly constant 87 Sr/ 86 Sr ratios: (1) the first glacial erosion of sediment-covered cratons in the Northern Hemisphere; (2) the exhumation of the Australian passive margin-New Guinea arc system. The latter event offers a mechanism, via enhanced availability of soluble Ca and Mg silicates in the arc terrane, for the maintenance of assumed low CO 2 levels after 15 Ma. The temporal resolution (three samples/Myr) of the 187 Os/ 188 Os record from Site 598, for which a stable isotope stratigraphy was also constructed, is significantly higher than that of previously published records. These high resolution data suggest oscillations with amplitudes of 0.01 to 0.02 and periods of around 1 Myr. Although variations in the 187 Os/ 188 Os record of this magnitude can be easily resolved analytically, this higher frequency signal must be verified at other sites before it can be safely interpreted as global in extent. However, the short-term 187 Os/ 188 Os variations may correlate inversely with short-term benthic foraminiferal 18 O and bulk carbonate 13 C variations that reflect glacioeustatic events.
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We estimate the fall time of the K/T sulfuric acid aerosols considering the interaction with silicate condensates. We found that more than 70% of sulfuric acid aerosols would have fallen within two days and that oceanic pH decreases dramatically.
Article
Flow-by-flow reanalysis of paleomagnetic directions in two sections of the Mahabaleshwar escarpment, coupled with analysis of intertrappean alteration levels shows that volcanism spanned a much shorter time than previously realized. The sections comprise the upper part of magnetic chron C29r, transitional directions and the lowermost part of C29n. Lack of paleosecular variation allows identification of four directional groups, implying very large (40 to 180 m thick) single eruptive events (SEEs) having occurred in a few decades. Paleomagnetism allows temporal constraints upon the formation of 9 out of 23 thin red bole levels found in the sections to no more than a few decades; the two thickest altered layers could have formed in 1 to 50 ka. The typical volumes of SEEs (corresponding to magnetic directional groups) are estimated at 3000 to 20,000 km3, with flux rates ∼100 km3 a−1, having lasted for decades. Flood basalt emission can be translated into SO2 injection rates of several Gt a−1, which could have been the main agent of environmental change. The total volume of SO2 emitted by the larger SEEs could be on the order of that released by the Chicxulub impact. Moreover, each SEE may have injected 10 to 100 times more SO2 in the atmosphere than the deleterious 1783 Laki eruption. The detailed time sequence of SEEs appears to be the key feature having controlled the extent of climate change. If several SEEs erupted in a short sequence (compared to the equilibration time of the ocean), they could have generated a runaway effect leading to mass extinction.
Article
New osmium (Os) isotope and platinum group element (PGE) concentration data are used in conjunction with published 3He and Th isotope data to determine the relative proportions of lithogenic, extraterrestrial and hydrogenous iridium (Ir) in a Pacific pelagic carbonate sequence from the Ocean Drilling Program (ODP) Site 806 on the Ontong Java Plateau (OJP). These calculations demonstrate that lithogenic and extraterrestrial contributions to sedimentary Ir budget are minor, while hydrogenous Ir accounts for roughly 85% of the total Ir. Application of analogous partitioning calculations to previously reported data from a North Pacific red clay sequence (LL44-GPC3) yields very similar results. Total Ir burial fluxes at Site 806 and LL44-GPC3 are also similar, 45 and 30pgcm−2kyr−1, respectively. Average Ir/3He and Ir/xs230Thinitial ratios calculated from the entire Site 806 data set are similar to those reported earlier for Pacific sites. In general, down-core profiles of Ir, 3He and xs230Thinitial, are not well correlated with one another. However, all three data sets show similar variance and yield sediment mass accumulation rate estimates that agree within a factor of two. While these results indicate that Ir concentration has potential as a point-paleoflux tracer in pelagic carbonates, Ir-based paleoflux estimates are likely subject to uncertainties that are similar to those associated with Co-based paleoflux estimates. Consequently, local calibration of Ir flux in space and time will be required to fully assess the potential of Ir as a point paleoflux tracer. Measured 187Os/188Os of the OJP sediments are systematically lower than the inferred 187Os/188Os of contemporaneous seawater and a clear glacial–interglacial 187Os/188Os variation is lacking. Mixing calculations suggest Os contributions from lithogenic sources are insufficient to explain the observed 187Os/188Os variations. The difference between the 187Os/188Os of bulk sediment and that of seawater is interpreted in terms of subtle contributions of unradiogenic Os carried by particulate extraterrestrial material. Down-core variations of 187Os/188Os with Pt/Ir and Os/Ir also point to contributions from extraterrestrial particles. Mixing calculations for each set of several triplicate analyses suggest that the unradiogenic Os end member cannot be characterized by primary extraterrestrial particles of chondritic composition. It is noteworthy that in efforts aimed at determining the effect of extraterrestrial contributions, 187Os/188Os of pelagic carbonates has greater potential compared to abundances of PGE. An attempt has been made for the first time to estimate sediment mass accumulation rates based on amount of extraterrestrial Os in the OJP samples and previously reported extraterrestrial Os flux. Throughout most of the OJP record, Os isotope-based paleoflux estimates are within a factor of two of those derived using other constant flux tracers. Meaningful flux estimates cannot be made during glacial maxima because the OJP sediments do not record the low 187Os/188Os reported previously. We speculate that this discrepancy may be related to focusing of extraterrestrial particles at the OJP, as has been suggested to explain down-core 3He variations.
Article
A detailed study was made of the oceanic 187Os/186Os variation through the Cenozoic by using a hydrogen peroxide leaching procedure on a pelagic clay core from the North Pacific (Long Lines-44 GPC3). A 6% H2O2 solution was used. The range of 187Os/186Os obtained by this procedure was between 2 and 8.2. A milder leach (0.15% H2O2) in three out of four samples yielded a slightly higher 187Os/186Os value than the stronger leach implying that the stronger leach released some meteoritic Os with 187Os/186Os of 1. Using published 3He concentrations in GPC3 and cosmic dust 3He and Os fluxes to deep-sea sediments, the extraterrestrial Os concentration was estimated for each core segment and subtracted to yield “corrected” values of 187Os/186Os. The results based on the milder leaching protocol and the 3He correction protocol yield similar values. The “corrected” ocean water 187Os/186Os pattern for the past 25 million years is similar to that obtained by other workers and is compatible with other results for the entire Cenozoic. The variation with time in GPC3, uniquely, provides a statigraphic signature for the Paleogene.
Article
Most mass extinctions coincide in time with outpourings of continental flood basalts (CFB). Some 20 years ago, it was shown [Courtillot, V., Besse, J., Vandamme, D., Montigny, R., Jaeger, J.-J., Cappetta, H., 1986. Deccan flood basalts at the Cretaceous/Tertiary boundary? Earth Planet. Sci. Lett. 80, 361–374; Courtillot, V., Feraud, G., Maluski, H., Vandamme, D., Moreau, M.G., Besse, J., 1988. Deccan flood basalts and the Cretaceous/Tertiary boundary. Nature 333, 843–846; Duncan, R.A., Pyle, D.G., 1988. Rapid eruption of the Deccan flood basalts at the Cretaceous/Tertiary boundary. Nature 333 841–843] that the age of the Deccan traps was close to the Cretaceous–Tertiary (KT) boundary and its duration under 1 Myr. We have undertaken a new geochronological study, using the (unconventional) 40K–40Ar Cassignol–Gillot technique which is particularly well suited to the potassium-poor Deccan lavas. The mean of 4 determinations from the topmost (Ambenali and Mahabaleshwar) Formations is 64.5±0.6 Ma. They straddle the C29r/C29n reversal boundary for which they provide a new constraint. The mean age of 3 determinations from the oldest (Jawhar) Formation is 64.8±0.6 Ma. The difference in age between top and bottom of a 3500 m composite section, probably comprising 80% of the total Deccan volume, is statistically insignificant, with the overall mean age being 64.7±0.6 Ma (N=7). Our results are consistent with the most recent 40Ar/39Ar determinations [Knight, K.B., Renne, P.R., Halkett, A., White, N., 2003. 40Ar/ 39Ar dating of the Rajahmundry Traps, eastern India and their relationship to the Deccan traps. Earth Planet. Sci. Lett. 208, 85–99; Knight, K.B., Renne, P.R., Baker, J., Waight, T., White, N., 2005. Reply to ‘40Ar/39Ar dating of the Rajahmundry Traps, Eastern India and their relationship to the Deccan Traps: Discussion’ by A.K. Baksi. Earth Planet. Sci. Lett. 239, 374–382], confirming that there should be no systematic difference between the two methods when they are used in an optimal way. An earlier, smaller but significant, pulse of volcanism between 68 and 67 Ma, extending over at least 500 km in latitude in the northern part of the Deccan CFB has also been identified. After 2 to 3 Ma of quiescence, the second, major phase of volcanism occurred near 65 Ma, expanding over most of the area covered by the first pulse and another 500 km to the South, consistent with drift of India by 300 to 450 km at ∼150 mm/yr during the quiescence period. New paleontological data from the remote Rajahmundry section [Keller, G., Adatte, T., Gardin, S., Bartolini, A., Bajpai, S., Humler, E., in prep. The Cretaceous–Tertiary boundary in Deccan Traps of the Krishna–Godavari Basin of southeastern India. EPSL to be submitted] suggest that this second pulse can itself be divided into two major pulses, one starting in C29r and ending at the KT boundary, the second starting in the upper part of C29r and ending within C29n.
Article
A suite of basaltic rocks sampled over a vast exposure and stratigraphic thickness in the Deccan traps has been investigated for Os isotopic systematics. The results plot on a very well defined Re–Os isochron corresponding to an age of 65.6±0.3 Ma (2σ uncertainty). This age is in excellent agreement with previous K–Ar and Ar–Ar data. Os data also imply a short duration of volcanism, which should have important implications on mantle geodynamics. The 187Os/188Os initial ratio is typically chondritic: 0.12843±0.00047 (2σ) and indicates that metasomatism and crustal contamination played only a very minor role in the Re–Os budget during formation of the Deccan traps.
Article
A suite of 18 Deccan mafic rocks including 14 basalts and four dolerite dykes from seven different localities in the Maharashtra region of the western Deccan volcanic province were analyzed for Ir, Pt, Pd and Au by radiochemical neutron activation analysis (Ir, Pd and Au) and lead fire assay (Pt, Pd and Au) with ICP–MS finish. To provide additional petrogenetic insight, major elements, a suite of trace elements including rare earth elements (REEs), and Sr and Nd isotopic compositions were also determined. Based on the distribution of Ir values, two subsets of samples were distinguished. One includes 14 samples with average Ir concentration of 0.024 ppb, and the other, a much smaller group of four samples, averages 0.21 ppb Ir or some 10 times the average concentration of the larger group. These two subsets are differentiated by other compositional properties in addition to noble metal contents. These include lower REE, higher transition element (Ni, Cr) and S contents, large negative Nb–Ta anomalies in mantle normalized profiles, more radiogenic Sr and very negative εNd isotopic compositions in the Ir-rich group. In addition, Pd, Pt and Au averages are lower in the Ir-rich group.
Article
We present a terrestrial record of stable carbon and oxygen isotopes from paleosol carbonate for climate interpretations between ca. 71.0 and 63.6 Ma. Isotopic ratios point to covarying and elevated atmospheric CO2 pressures and temperatures between ca. 70.0 and 69.0 Ma and ca. 65.5 and 65.0 Ma. These two greenhouse episodes were characterized by atmospheric CO2 levels between 1000 and 1400 ppm V (V = volume) and by mean annual temperatures in west Texas between 21 and 23 °C (∼35°N paleo-latitude). Atmospheric CO2 and temperature relations indicate that a doubling of pCO2 was accompanied by an ∼0.6 °C increase in temperature. A temperature gradient of ∼0.4 °C per degree of latitude is proposed for North America across the Cretaceous-Tertiary boundary when comparing temperature proxies from west Texas with paleobotanical work in North Dakota. Our data demonstrate strong coupling between terrestrial climates and ocean temperatures that were possibly forced by Deccan trap volcanic degassing, leading to dramatic global climate changes.
Article
We present a global synthesis of the evolution of the climate/ocean system from the late Campanian at approximately 75 Ma to the end of the Maastrichtian at 65 Ma. This study is based on published and new oxygen and carbon isotope data of benthic and planktic foraminifera from a number of deep-sea sites, spanning the high to the low latitudes. Most of the sites were at depths that in the modern oceans are bathed by intermediate- water masses. The δ18O records of planktic and benthic foraminifera from most locations indicate that surface and intermediate waters cooled during the period 75 to 65.5 Ma, particularly at high latitudes. Model surface-water temperatures, based on δ18O values averaged for 1-m.y. intervals at each of the sites and corrected for the latitudinal variation of seawater δ18O using the present seawater latitudinal δ18O variation, indicate that the latitudinal thermal gradient increased from 10 to 13 °C. Superimposed on the long-term trend there were two episodes during which, on a global scale, benthic foraminiferal δ18O values increased substantially, and then decreased. The first episode occurred between 71 and 69.5 Ma; the second began between 68 and 67.5 Ma, and terminated at about 65.5 Ma. During the first episode, the thermohaline circulation changed, and cool intermediate depth waters derived from high-latitude regions penetrated temporarily to the tropics, resulting in tropical Pacific intermediate waters becoming cooler than those in the high southern latitudes. Benthic foraminiferal δ13C values suggest that these cool waters may have been derived from high northern latitudes. The level of the carbonate compensation depth (CCD) shallowed substantially in the Pacific, Indian, and South Atlantic basins, although surface-water productivity may have increased during the time of altered thermohaline circulation. At the same time, the CCD deepened in the North Atlantic, where deep waters were warm and salty, and formed locally. From 67.5 to 65.5 Ma, intermediate waters in the southern high latitudes were cooler than those in other basins, indicating that the thermohaline circulation operated on a mode more similar to the present circulation. Both episodes of cooler intermediate water can be correlated with eustatic sea-level curves, suggesting that sea level was the most likely mechanism to change the circulation and/or source(s) of intermediate- deep waters. At 65.5 Ma, surface and intermediate waters warmed globally by about 3-4 °C, and then cooled slightly at about 65.1 Ma. We suggest this increase in marine temperatures correlates with the timing of the main episode of Deccan Trap flood basalt eruptions and may have been caused by greenhouse global warming.
Article
In the latest Paleocene an abrupt shift to more negative delta13C values has been documented at numerous marine and terrestrial sites [Bralower et al., 1997; Cramer et al., 1999; Kaiho et al., 1996; Kennett and Stott, 1991; Koch et al., 1992; Stott et al., 1996; Thomas and Shackleton, 1996; Zachos et al., 1993]. This carbon isotope event (CIE) is coincident with oxygen isotope data that indicate warming of surface waters at high latitudes of nearly 4°-6°C [Kennett and Stott, 1991] and more moderate warming in the subtropics [Thomas et al., 1999]. Here we report 187Os/188Os isotope records from the North Atlantic and Indian Oceans which demonstrate a >10% increase in the 187Os/188Os ratio of seawater coincident with the late Paleocene CIE. This excursion to higher 187Os/188Os ratios is consistent with a global increase in weathering rates. The inference of increased chemical weathering during this interval of unusual warmth is significant because it provides empirical evidence supporting the operation of a feedback between chemical weathering rates and warm global climate, which acts to stabilize Earth's climate [Walker et al., 1981]. Estimates of the duration of late Paleocene CIE [Bains et al., 1999; Bralower et al., 1997; Norris and Röhl, 1999; Röhl et al., 2000] in conjunction with the Os isotope data imply that intensified chemical weathering in response to warm, humid climates can occur on timescales of 104-105years. This interpretation requires that the late Palcocene thermal maximum Os isotope excursion be produced mainly by increased Os flux to the ocean rather than a transient excursion to higher 187Os/188Os ratios in river runoff. Although we argue that the former is more likely than the latter, we cannot rule out significant changes in the 187Os/188Os ratio of rivers.
Article
A latest Maastrichtian global warming event, which began approximately 450 k.y. and ended about 22 k.y. prior to the K/T boundary, is associated with the pole-ward migration of the warm-water planktonic foraminifer Pseudotextularia elegans. The warming event was apparently inititated by greenhouse warming due to the main outpouring of the Deccan Traps in India and is now well documented in the North and South Atlantic Oceans and in North America by the poleward migration of warm-water planktonic foraminifera and subtropical vegetation. A cooling trend ca 22 kyr prior to the K/T boundary caused marine δ18O values to return to climatic conditions recorded prior to the onset of warming and thus does not represent a significant change in long-term climate. Planktonic foraminifera responded by migration to the latest Maastrichtian global warming and cooling before their mass extinction at the K/T.
Article
The known temporal relationship between the benthic foraminiferal delta 18O record and the marine Os isotope record is used to reinterpret the absolute chronology and paleoceanographic context of an episode of organic carbon burial on the West African margin Ocean Drilling Program (ODP) Site 959. Although organic-rich sediments require significant corrections for in situ decay of 187Re to 187Os, these results demonstrate the utility of the marine Os isotope record for chemostratigraphic correlation of organic-rich sediments that are devoid of age diagnostic microfossils with pelagic carbonate sequences. Revision of the ODP Site 959 chronology shifts the age assignment of an interval of biosiliceous, organic-rich sediment deposition from the Oligocene to the late Eocene and earliest Oligocene, likely culminating with the first major glaciation of the Oligocene (Oi1). We speculate that enhanced organic carbon burial over much of the West African margin may have contributed to drawdown of atmospheric carbon dioxide before and during the Oi1 event and suggest that Os isotope chemostratigraphy provides a valuable tool for further exploring this possibility.
Article
We report new187Os/186Os data and Re and Os concentrations in metalliferous sediments from the Pacific to construct a composite Os isotope seawater evolution curve over the past 80 m.y. Analyses of four samples of upper Cretaceous age yield187Os/186Os values of between 3 and 6.5 and187Re/186Os values below 55. Mass balance calculations indicate that the pronounced minimum of about 2 in the Os isotope ratio of seawater at the K-T boundary probably reflects the enormous input of cosmogenic material into the oceans by the K-T impactor(s). Following a rapid recovery to187Os/186Os of 3.5 at 63 Ma, data for the early and middle part of the Cenozoic show an increase in187Os/186Os to about 6 at 15 Ma. Variations in the isotopic composition of leachable Os from slowly accumulating metalliferous sediments show large fluctuations over short time spans. In contrast, analyses of rapidly accumulating metalliferous carbonates do not exhibit the large oscillations observed in the pelagic clay leach data. These results together with sediment leaching experiments indicate that dissolution of non-hydrogenous Os can occur during the hydrogen peroxide leach and demonstrate that Os data from pelagic clay leachates do not always reflect the Os isotopic composition of seawater.