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Christopher W. Smart - One of the best experts on this subject based on the ideXlab platform.
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Global bioevents and the Cretaceous/Paleogene Boundary in Texas and Alabama: Stratigraphy, correlation and ocean acidification
Global and Planetary Change, 2019Co-Authors: Malcolm B. Hart, Andrew D. Leighton, Matthew Hampton, Christopher W. SmartAbstract:Abstract With increasing levels of atmospheric pCO2 the oceans are becoming progressively more acidic, with the impact of a lowered pH beginning to affect the calcification of numerous invertebrate groups, including foraminifers, pteropods, heteropods and calcareous nannoplankton. Research on the ecology of foraminifera in the Mediterranean Sea, Gulf of California, Caribbean Sea and elsewhere has shown how modern assemblages are responding to acidification. Experimental work in mesocosms and laboratory cultures are also adding to our knowledge of the response to pH changes. Near Ischia (Italy), natural CO2 vents amongst sea grass meadows are creating low pH environments in which it is possible to observe the response of benthic foraminifera. At a pH of 7.8 the foraminiferal assemblages are already becoming less diverse and below pH 7.6 there are often no calcite-secreting benthic foraminifera. In the Gulf of California, in a deeper-water setting, natural CO2 (and methane) vents are also lowering sea floor pH. The foraminifera show the impact of this change, although the relatively high carbonate saturation ensures that calcite-secreting foraminifers are able to live and reproduce in these relatively low pH environments, only becoming impacted by dissolution effects once dead. Using data from the Cretaceous–Paleogene Boundary in Texas, Alabama and north-west Europe it is clear that the plankton was severely impacted by surface water acidification while the relatively shallow water benthic foraminifera show little change and no visible signs of post-mortem dissolution due to ocean acidification.
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TIMING RECOVERY AFTER THE CRETACEOUS/PALEOGENE Boundary: EVIDENCE FROM THE BRAZOS RIVER, TEXAS, USA
The Journal of Foraminiferal Research, 2017Co-Authors: Andrew D. Leighton, Malcolm B. Hart, Christopher W. Smart, Melanie J. Leng, Matthew HamptonAbstract:As part of an on-going re-assessment of the Cretaceous/ Paleogene Boundary in the Brazos River area, Falls County, Texas, a number of new exposures have been described. One of these, at River Bank South, provides a near continuous record of the lowermost Paleocene. It is from this succession that stable isotope analysis of bulk organic matter (δ13C and C/N) and mono-specific samples of the benthic foraminifera Lenticulina rotulata Lamarck (δ18O and δ13C) yields an orbitally-tuned stable isotope record, which allows the timing of events adjacent to the Cretaceous/Paleogene Boundary to be determined. Using this cyclicity, it is suggested that the on-set of biotic recovery began ∼40,000 years after the impact (near the base of Zone Pα) and that more significant recovery of planktic foraminifera and calcareous nannofossils began close to the base of Zone P1a, some 85,000–100,000 years post-impact. The data also appear to record the presence of the earliest Paleocene DAN-C2 and Lower C29n hyperthermal events and that these events appear to be an accentuated segment of this orbital cyclicity.
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The Cretaceous/Paleogene Boundary: Foraminifera, sea grasses, sea level change and sequence stratigraphy
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Malcolm B. Hart, Meriel E.j. Fitzpatrick, Christopher W. SmartAbstract:Abstract The tsunami generated by the Chicxulub impact eroded the uppermost Cretaceous surface of the Gulf Coast region (U.S.A.) forming a distinctive topography that was previously interpreted as a sequence Boundary. At more distal sites, such as Stevns Klint (Denmark), there appears to be no sequence Boundary at the Cretaceous/Paleogene Boundary but there is one within the uppermost Maastrichtian, between the Sigerslev and Hojerup members, and another in the lowermost Paleocene (top of Zone P1a). Both of these surfaces are identified by distinctive, phosphatized, and incipient hardgrounds. The changes in sea level involved in the generation of uppermost Cretaceous sequences are thought to have been minimal as, in the Gulpen and Maastricht formations of the Maastricht area (Netherlands), the presence of sea grasses and their associated foraminifera would indicate that the chalk sea floor remained within the range of water depth that would allow photosynthesis (
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Ocean Acidification in Modern Seas and its Recognition in the Geological Record: The Cretaceous/Paleogene Boundary in Texas and Alabama
2014Co-Authors: Malcolm B. Hart, Andrew D. Leighton, Christopher W. Smart, Laura Rachel Pettit, Iba N. Medina-sánchez, Peter J. Harries, Andrés L. Cárdenas, Jason M. Hall-spencer, Rosa María Prol-ledesmaAbstract:Abstract With increasing atmospheric CO2 the oceans are becoming progressively more acidic, with the lowered pH beginning to impact on the calcification of foraminifera, pteropods, calcareous nannoplankton and other invertebrate groups. Our work in the Mediterranean Sea, Gulf of California, Caribbean Sea, and elsewhere has shown how modern assemblages are responding to acidification. Around Ischia (Italy) natural seafloor CO2 vents are creating a low pH environment in which it is possible to observe the response of benthic foraminifera. At a pH of 7.8, the assemblage is already becoming less diverse and below pH 7.6 there are no calcite-secreting benthic foraminifera. In the Gulf of California, in a deeper-water setting, natural CO2 (and methane) vents are, again, lowering seafloor pH. The foraminifera show the impact of this change, although the relatively high carbonate saturation ensures that calcite-secreting foraminifera are able to live and reproduce in relatively low pH environments, only becoming impacted by dissolution effects once dead. Using data from a number of global bioevents (Triassic/Jurassic Boundary, Cretaceous/Paleogene Boundary and the Paleocene/Eocene Boundary) it is now possible to determine the contribution of acidification to global bioevents, both in the near-surface and in deeper-water environments caused by the migration of the carbonate compensation depth (CCD). In Texas and Alabama, the Cretaceous/Paleogene Boundary successions record no direct evidence of ocean acidification despite the proximity to the Chicxulub impact site and the proposed source of some of the CO2 (in addition to that from the Deccan Volcanic Center in India) required to cause the acidification. Interpretation of changes in the biota during global bioevents is complicated by the changing nature of the oceans through time, which have switched from being aragonitic to calcitic a number of times during the Phanerozoic. The other significant change is that from a ‘Neritan Ocean’ to a ‘Cretan Ocean’ in the mid-Jurassic.
Andrew Conley - One of the best experts on this subject based on the ideXlab platform.
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on transient climate change at the cretaceous paleogene Boundary due to atmospheric soot injections
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Charles G. Bardeen, Rolando R Garcia, Owen B. Toon, Andrew ConleyAbstract:Climate simulations that consider injection into the atmosphere of 15,000 Tg of soot, the amount estimated to be present at the Cretaceous-Paleogene Boundary, produce what might have been one of the largest episodes of transient climate change in Earth history. The observed soot is believed to originate from global wildfires ignited after the impact of a 10-km-diameter asteroid on the Yucatan Peninsula 66 million y ago. Following injection into the atmosphere, the soot is heated by sunlight and lofted to great heights, resulting in a worldwide soot aerosol layer that lasts several years. As a result, little or no sunlight reaches the surface for over a year, such that photosynthesis is impossible and continents and oceans cool by as much as 28 °C and 11 °C, respectively. The absorption of light by the soot heats the upper atmosphere by hundreds of degrees. These high temperatures, together with a massive injection of water, which is a source of odd-hydrogen radicals, destroy the stratospheric ozone layer, such that Earth's surface receives high doses of UV radiation for about a year once the soot clears, five years after the impact. Temperatures remain above freezing in the oceans, coastal areas, and parts of the Tropics, but photosynthesis is severely inhibited for the first 1 y to 2 y, and freezing temperatures persist at middle latitudes for 3 y to 4 y. Refugia from these effects would have been very limited. The transient climate perturbation ends abruptly as the stratosphere cools and becomes supersaturated, causing rapid dehydration that removes all remaining soot via wet deposition.
Henk Brinkhuis - One of the best experts on this subject based on the ideXlab platform.
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Iridium profiles and delivery across the Cretaceous/Paleogene Boundary
Earth and Planetary Science Letters, 2017Co-Authors: Selen Esmeray-senlet, Johan Vellekoop, Kenneth G Miller, Robert M Sherrell, Turgay Senlet, Henk BrinkhuisAbstract:We examined iridium (Ir) anomalies at the Cretaceous/Paleogene (K/Pg) Boundary in siliciclastic shallow marine cores of the New Jersey Coastal Plain, USA, that were deposited at an intermediate distance (∼2500 km) from the Chicxulub, Mexico crater. Although closely spaced and generally biostratigraphically complete, the cores show heterogeneity in terms of preservation of the ejecta layers, maximum concentration of Ir measured (∼0.1–2.4 ppb), and total thickness of the Ir-enriched interval (11–119 cm). We analyzed the shape of the Ir profiles with a Lagrangian particle-tracking model of sediment mixing. Fits between the mixing model and measured Ir profiles, as well as visible burrows in the cores, show that the shape of the Ir profiles was determined primarily by sediment mixing via bioturbation. In contrast, Tighe Park 1 and Bass River cores show post-depositional remobilization of Ir by geochemical processes. There is a strong inverse relationship between the maximum concentration of Ir measured and the thickness of the sediments over which Ir is spread. We show that the depth-integrated Ir inventory is similar in the majority of the cores, indicating that the total Ir delivery at time of the K/Pg event was spatially homogeneous over this region. Though delivered through a near-instantaneous source, stratospheric dispersal, and settling, our study shows that non-uniform Ir profiles develop due to changes in the regional delivery and post-depositional modification by bioturbation and geochemical processes.
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rapid short term cooling following the chicxulub impact at the cretaceous paleogene Boundary
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Johan Vellekoop, Jan Smit, Appy Sluijs, Stefan Schouten, Johan W H Weijers, Jaap Sinninghe S Damste, Henk BrinkhuisAbstract:The mass extinction at the Cretaceous–Paleogene Boundary, ∼66 Ma, is thought to be caused by the impact of an asteroid at Chicxulub, present-day Mexico. Although the precise mechanisms that led to this mass extinction remain enigmatic, most postulated scenarios involve a short-lived global cooling, a so-called “impact winter” phase. Here we document a major decline in sea surface temperature during the first months to decades following the impact event, using TEX86 paleothermometry of sediments from the Brazos River section, Texas. We interpret this cold spell to reflect, to our knowledge, the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere, blocking incoming solar radiation. This impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis.
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Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene Boundary
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Johan Vellekoop, Jan Smit, Appy Sluijs, Stefan Schouten, Johan W H Weijers, Jaap Sinninghe S Damste, Henk BrinkhuisAbstract:The mass extinction at the Cretaceous–Paleogene Boundary, ∼66 Ma, is thought to be caused by the impact of an asteroid at Chicxulub, present-day Mexico. Although the precise mechanisms that led to this mass extinction remain enigmatic, most postulated scenarios involve a short-lived global cooling, a so-called “impact winter” phase. Here we document a major decline in sea surface temperature during the first months to decades following the impact event, using TEX86 paleothermometry of sediments from the Brazos River section, Texas. We interpret this cold spell to reflect, to our knowledge, the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere, blocking incoming solar radiation. This impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis.
Charles G. Bardeen - One of the best experts on this subject based on the ideXlab platform.
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on transient climate change at the cretaceous paleogene Boundary due to atmospheric soot injections
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Charles G. Bardeen, Rolando R Garcia, Owen B. Toon, Andrew ConleyAbstract:Climate simulations that consider injection into the atmosphere of 15,000 Tg of soot, the amount estimated to be present at the Cretaceous-Paleogene Boundary, produce what might have been one of the largest episodes of transient climate change in Earth history. The observed soot is believed to originate from global wildfires ignited after the impact of a 10-km-diameter asteroid on the Yucatan Peninsula 66 million y ago. Following injection into the atmosphere, the soot is heated by sunlight and lofted to great heights, resulting in a worldwide soot aerosol layer that lasts several years. As a result, little or no sunlight reaches the surface for over a year, such that photosynthesis is impossible and continents and oceans cool by as much as 28 °C and 11 °C, respectively. The absorption of light by the soot heats the upper atmosphere by hundreds of degrees. These high temperatures, together with a massive injection of water, which is a source of odd-hydrogen radicals, destroy the stratospheric ozone layer, such that Earth's surface receives high doses of UV radiation for about a year once the soot clears, five years after the impact. Temperatures remain above freezing in the oceans, coastal areas, and parts of the Tropics, but photosynthesis is severely inhibited for the first 1 y to 2 y, and freezing temperatures persist at middle latitudes for 3 y to 4 y. Refugia from these effects would have been very limited. The transient climate perturbation ends abruptly as the stratosphere cools and becomes supersaturated, causing rapid dehydration that removes all remaining soot via wet deposition.
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On transient climate change at the Cretaceous−Paleogene Boundary due to atmospheric soot injections
Proceedings of the National Academy of Sciences, 2017Co-Authors: Charles G. Bardeen, Rolando R Garcia, Owen B. Toon, Andrew J. ConleyAbstract:Climate simulations that consider injection into the atmosphere of 15,000 Tg of soot, the amount estimated to be present at the Cretaceous−Paleogene Boundary, produce what might have been one of the largest episodes of transient climate change in Earth history. The observed soot is believed to originate from global wild-fires ignited after the impact of a 10-km-diameter asteroid on the Yucatán Peninsula 66 million y ago. Following injection into the at-mosphere, the soot is heated by sunlight and lofted to great heights, resulting in a worldwide soot aerosol layer that lasts several years. As a result, little or no sunlight reaches the surface for over a year, such that photosynthesis is impossible and continents and oceans cool by as much as 28 °C and 11 °C, respectively. The absorption of light by the soot heats the upper atmosphere by hundreds of degrees. These high temperatures, together with a massive injec-tion of water, which is a source of odd-hydrogen radicals, destroy the stratospheric ozone layer, such that Earth’s surface receives high doses of UV radiation for about a year once the soot clears, five years after the impact. Temperatures remain above freezing in the oceans, coastal areas, and parts of the Tropics, but photo-synthesis is severely inhibited for the first 1 y to 2 y, and freezing temperatures persist at middle latitudes for 3 y to 4 y. Refugia from these effects would have been very limited. The transient climate perturbation ends abruptly as the stratosphere cools and becomes supersaturated, causing rapid dehydration that removes all remaining soot via wet deposition.
Pavle I. Premović - One of the best experts on this subject based on the ideXlab platform.
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Cretaceous-Paleogene Boundary Clays from Spain and New Zealand: Arsenic Anomaly and the Deccan Traps
International Letters of Natural Sciences, 2016Co-Authors: Pavle I. PremovićAbstract:High arsenic (As) contents have been reported in numerous Cretaceous-Paleogene Boundary (KPB) clays worldwide including that from Spain (at Caravaca and Agost) and N. Zealand (at Woodside Creek). The Deccan Traps (India) enormous volcanism is one of the interpretations which have been offered to explain this anomaly. This report shows that the estimated surface densities of As in the Boundary clays in Spain and New Zealand strongly contradict that anomalous As was sourced by this volcanic event.
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Cretaceous-Paleogene Boundary Clays from Spain and New Zealand: Arsenic Anomalies
Open Geosciences, 2015Co-Authors: Pavle I. PremovićAbstract:Abstract Remarkably high arsenic (As) contents have been reported in numerous Cretaceous-Paleogene Boundary (KPB) clays worldwide including those from Spain (at Caravaca and Agost) and New (N.) Zealand (at Woodside Creek). Two interpretations have been offered to explain this anomaly. The first one suggests that this As was generated by the combustion of fossil fuels (such as crude oil, coal or oil shales) near the Chicxulub impact site and the second interpretation proposes the post-impact combustion of the global biomass at the KPB. Both types of combustion were presumably triggered by the Chicxulub impactor. This report shows that the estimated surface densities of As in Spain and N. Zealand strongly contradict the fossil fuel hydrocarbons/biomass hypotheses. In addition, we also show that previously reported global abundances of As at KPB are greatly overestimated. The high abundances of iron (Fe) in the ejecta layers from Spain and N. Zealand lead us to a working hypothesis that a major fraction of their anomalous As was adsorbed from seawater by the Fe-oxides. These oxides were mainly derived of Fe from the vaporized carbonaceous chondrite impactor. These were originally deposited on the local (topographically high) oxic soils in Spain and N. Zealand and then laterally transported to the KPB sites by the impactinduced surface waters.
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Soot in Cretaceous-Paleogene Boundary clays worldwide: is it really derived from fossil fuel beds close to Chicxulub?
Central European Journal of Geosciences, 2012Co-Authors: Pavle I. PremovićAbstract:High soot contents have been reported in Cretaceous-Paleogene Boundary (KPB) clays worldwide. One of the interpretations suggests this material comes from combustion of fossil fuels such as crude oil, coal or oil shales near the Chicxulub impact site. Combustion was triggered by the KPB impactor. In this Note, I show that the estimated mass of crude oil (or fossil hydrocarbons in general) burned (ca. 10^17–10^19 g), based on the average amount of soot (0.0022–0.012 g cm^−2) or elemental carbon (0.011 g cm^−2) found at the marine KPB sites, contradicts the fossil hydrocarbons hypothesis.
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The conspicuous red "impact" layer of the Fish Clay at Højerup (Stevns Klint, Denmark)
Geochemistry International, 2009Co-Authors: Pavle I. PremovićAbstract:The marine Cretaceous-Paleogene Boundary (KPB) section at Hojerup-Fish Clay consists of a very thin red smectite-rich carbonate-poor (“impact”) layer overlain by a thick black marl. Similar red layers are found in the KPB sections at Agost in Spain and El Kef in Tunisia.
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Cretaceous-Paleogene Boundary (KPB) Fish Clay at Højerup (Stevns Klint, Denmark): Ni, Co, and Zn of the black marl
Geologica Acta, 2008Co-Authors: Pavle I. Premović, Bratislav Ž. Todorović, Maja N. StankovićAbstract:The black marl of the Fish Clay at Hojerup is mainly made up of biogenic calcite and cheto-Mg-smectite. We suggest that the formation of the smectite occurred during the latest Maastrichtian (or earlier) and that it represents a short period of rapid redeposition through coastal erosion occurring at the Cretaceous-Paleogene Boundary (KPB) sea level lowstand. The smectite of the black marl shows enhanced concentrations of Ni, Co, and Zn. The predominant source of these metals was probably the impact-ejecta fallout deposited on the top of nearby soil which was leached by the impact-induced-acidic surface waters. Most of the content of Ni and Co in the smectite is derived from the chondritic component of the fallout, but the ultimate origin of Zn may have been the impact-target rocks. Incorporation of the metals into the smectite took place during the KPB but before its redeposition at the Fish Clay site. The biogenic calcite-rich fraction of the black marl also shows high concentrations of Ni, Co, and Zn. The ultimate source of the metals was also probably the impact-ejecta fallout on the nearby soil at Stevns Klint. Enrichments of Ni in the biogenic calcite-rich/smectite fractions of the black marl represent the sudden input of the metal into the seawater at the KPB.