Environmental change across the Cretaceous-Paleogene boundary: An integrated, multi-proxy approach

The Cretaceous-Paleogene (K-Pg) boundary mass extinction event is inextricably linked to the direct consequences of the Chicxulub impact 66 million years ago. Yet, it has been argued that other environmental factors, such as climate change caused by pre-impact Deccan Traps mantle degassing, and sea-level change across the K-Pg boundary, could have contributed to this mass extinction event. This dissertation aims to clarify to what extent temperature shifts did occur during the late Maastrichtian, and if these temperature shifts are coeval and observed globally. Inorganic and organic geochemical proxies Mg/Ca, d18O and TEX86 are used to reconstruct past temperatures during this interval. Subsequently, ecological change during the late Maastrichtian interval is studied using benthic foraminiferal and dinoflagellate cyst (dinocyst) assemblage data, to demonstrate the possible link between late Maastrichtian climate change and ecology. Furthermore, sea-level changes before, during and after the K-Pg boundary are reconstructed using benthic foraminiferal, dinoflagellate cyst (dinocyst) assemblage and sedimentological data to substantiate if sea-level change potentially could have contributed to the mass extinction event. Finally, to gain more understanding in the post-impact paleoecological and paleoceanographic consequences of the early Danian ‘Living Ocean’ condition, benthic foraminiferal and dinoflagellate cyst (dinocyst) assemblage data from several locations are studied and compared. The magnitude of the late Maastrichtian warming that coincided with the second phase of Deccan Traps outgassing, as well as the timing of the warming, are further constrained in this dissertation. Firstly, a robust method for integrating temperature records is proposed. Using this method, data from two proximal sites in New Jersey and Argentina suggests that the late Maastrichtian warming had a magnitude of 3.9±1.1 °C. Furthermore, this dissertation has substantiated that late Maastrichtian warming affected environment and ecology. Dinocyst assemblages of the New Jersey paleoshelf indicate severe algal blooms during the warming interval. These algal blooms have in turn led to a shift in benthic foraminiferal assemblages, indicating changes in food supply towards the seafloor and benthic foraminiferal ecosystem stress. In Argentina, benthic foraminiferal and dinocyst assemblages suggest an increased freshwater flux into a semi-restricted basin, possibly as a result of an expanded South American thermal low during the warming interval. The link between climate change and the K-Pg boundary mass extinction event remains however unresolved. Benthic foraminiferal and dinocyst assemblages have proven to be less suited for reconstructing sea-level changes when the assemblages are severely disrupted, as was the case directly following the K-Pg boundary mass extinction. Yet, a maximum flooding ~100 kyr before the K-Pg boundary, followed by a regression and a sea-level lowstand between the K-Pg boundary and Zone P1c is suggested by benthic foraminiferal, dinocyst and sedimentological data. Directly following the K-Pg boundary, the benthic foraminiferal assemblages experience a ‘Disaster phase’. This phase is initially characterized by a bloom of endobenthic taxa as result of the post-impact flux of organic matter to the seafloor. After this short-lived initial phase, the second part of the ‘Disaster phase’ is characterized by reduced primary productivity as a result of the collapse of the biological pump. After the ‘Disaster phase’, increasing benthic foraminiferal diversity and species richness indicate a long-term recovery phase, although these do not recover to pre-impact values within the studied intervals (> 300 to 700 kyr) after the K-Pg boundary. This suggests a permanent shift in food supply towards the seafloor after the K-Pg boundary. Furthermore, the widespread occurrence of species such as Alabamina midwayensis and Anomalinoides acutus suggests that after the K-Pg boundary a more cosmopolitan benthic foraminiferal fauna arose from the surviving taxa of the more regionally disparate late Maastrichtian faunas. Finally, compared to other marginal sites, the sites studied in this dissertation show similar benthic foraminiferal turnover rates across the K-Pg boundary. Yet, turnover rates between individual marginal records vary considerable. This difference is probably related to latitude, geographic setting and water depth, as sites with comparable settings show comparable turnover rates.nrpages: 162status: publishe

Stable seafloor conditions, sea level and food supply during the latest Maastrichtian at Brazos River, Texas

The Cretaceous/Paleogene (K/Pg) boundary extinction event is inextricably linked to the Chicxulub impact. Envi- ronmental changes like sea level changes and changes in food supply prior to or after the impact could however have contributed to the biotic turnover. In this study, benthic foraminifera from two cores from the Brazos River area in Texas are quantitatively analyzed in order to reconstruct environmental changes across the K/Pg bound- ary. Cluster analysis as well as non-metric multidimensional scaling reveals three distinct benthic foraminiferal assemblages: an upper Maastrichtian assemblage, a post-impact assemblage, and a lower Danian assemblage. The rather uniform upper Maastrichtian assemblage at Brazos River, composed of e.g. Clavulinoides midwayensis, Gavelinella dumblei, Cibicidoides harperi, Gyroidinoides aequilateralis and Bulimina kickapooensis, indicates a stable paleodepth of about 75–100 m up to the K/Pg boundary. Food supply indicators such as percentage Buliminaceae and foraminiferal numbers suggest a relatively low and stable food supply during this interval. Environmental disruption caused by the Chicxulub impact led to the settlement of a typical pioneer assemblage, characterized by endobenthic morphotypes such as Ammobaculites spp. and Pseudouvigerina naheolensis. During the early Danian, the typical Midway-type benthic foraminiferal shelf fauna (e.g. Alabamina midwayensis, Anomalinoides acutus, Gyroidinoides subangulatus, Praebulimina carseyae and Cibicidoides alleni) developed, indicating a paleodepth of 75–100 m. No clear water depth changes can be derived from the benthic foraminiferal record dur- ing this interval, although the sedimentary record suggests a shallowing followed by a transgressive pulse in Zone P1a. Food supply indicators suggest a lower food supply in the early Danian than during the upper Maastrichtian. Because of the stability of the late Maastrichtian environment we conclude that environmental disruption caused by the impact was most likely the principal cause of the benthic foraminiferal turnover across the K/Pg boundary observed at Brazos River.publisher: Elsevier articletitle: Stable seafloor conditions, sea level and food supply during the latest Maastrichtian at Brazos River, Texas journaltitle: Marine Micropaleontology articlelink: http://dx.doi.org/10.1016/j.marmicro.2015.10.002 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved.status: publishe

Latest Maastrichtian dinocyst and benthic foraminiferal records of Bass River, Meirs Farm and Search Farm sediment cores, New Jersey, USA

Phytoplankton responses to a ~ 350 kiloyear long phase of gradual late Maastrichtian (latest-Cretaceous) global warming starting at ~ 66.4 Ma can provide valuable insights into the long-term influences of global change on marine ecosystems. Here we perform micropaleontological analyses on three cores from the New Jersey paleoshelf, to assess the response of phytoplankton using cyst-forming dinoflagellates and benthic ecosystems using benthic foraminifera. Our records show that this Latest Maastrichtian Warming Event (LMWE), characterized by a 4.0 ± 1.3 ⁰C warming of sea-surface waters on the New Jersey paleoshelf, resulted in a succession of nearly monospecific dinoflagellate cyst assemblages, dominated by the species Palynodinium grallator. This response, likely triggered by the combination of warmer and seasonally thermally-stratified seas, appears to have been more intense at offshore sites than at nearshore sites. The LMWE, and related dinoflagellate response, is associated with an impoverished benthic ecosystem. A wider geographic survey of literature data reveals that the dominance of P. grallator is a marker for the LMWE throughout the northern mid-latitudes. While the dinocyst assemblage returned to a stable, normal marine community in the last tens of thousands of years of the Maastrichtian, benthic foraminiferal diversity remained slightly suppressed. Increased ecosystem stress during the latest Maastrichtian potentially primed global ecosystems for the subsequent mass extinction following the K-Pg boundary Chicxulub impact

Phytoplankton community disruption caused by latest Cretaceous global warming

Phytoplankton responses to a ~ 350 kyr (kiloyear) long phase of gradual late Maastrichtian (latest Cretaceous) global warming starting at ~ 66:4 Ma can provide valuable insights into the long-term influences of global change on marine ecosystems. Here we perform micropaleontological analyses on three cores from the New Jersey paleoshelf to assess the response of phytoplankton using cyst-forming dinoflagellates and benthic ecosystems using benthic foraminifera. Our records show that this latest Maastrichtian warming event (LMWE), characterized by a 4.0±1.3 °C warming of sea surface waters on the New Jersey paleoshelf, resulted in a succession of nearly monospecific dinoflagellate-cyst assemblages, dominated by the species Palynodinium grallator. This response, likely triggered by the combination of warmer and seasonally thermally stratified seas, appears to have been more intense at offshore sites than at nearshore sites. The LMWE, and related dinoflagellate response, is associated with an impoverished benthic ecosystem. A wider geographic survey of literature data reveals that the dominance of P. grallator is a marker for the LMWE throughout the northern midlatitudes. While the dinocyst assemblage returned to a stable, normal marine community in the last tens of thousands of years of the Maastrichtian, benthic foraminiferal diversity appears to have remained slightly suppressed. Increased ecosystem stress during the latest Maastrichtian potentially primed global ecosystems for the subsequent mass extinction following the Cretaceous Paleogene (K-Pg) boundary Chicxulub impact

Organic geochemistry and biomarker data from Baffin Bay surface sediments

Samples were collected from Baffin Bay in 2008, 2015, and 2017 aboard the CSS Hudson and Amundsen research vessels. The box core and triggers cores were collected at water depths ranging from 267 to 2373 m below sea level. This dataset includes bulk geochemical and lipid biomarker proxy data from these samples. Bulk geochemical datasets include % carbon, % nitrogen and their stable isotopes as measured by EA-IRMS (Elemental Analyzer linked to an Isotope Ratio Mass Spectrometer). Lipid biomarker proxy data include highly-branched isoprenoids and sterols as measured by GC-MS (Gas Chromatograph linked to a Mass Spectrometer) and isoprenoid/hydroxylated glycerol dialkyl glycerol tetraethers as measured by HPLC-MS (High Performance Liquid Chromatography linked to a Mass Spectrometer). Highly-branched isoprenoid and sterol data are presented as concentrations whereas isoprenoid/hydroxylated glycerol dialkyl glycerol tetraethers data are presented as relative abundance. All analytical measurements were performed at the University of Colorado Boulder. Further information on the data and interpretations can be found in Harning et al. (2023)