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1. Terrestrial evidence for volcanogenic sulfate-driven cooling event ~30 kyr before the Cretaceous–Paleogene mass extinction

   https://doi.org/10.1126/sciadv.ado5478  

   O’Connor, Lauren K; Jerrett, Rhodri M; Price, Gregory D; Lyson, Tyler R; Lengger, Sabine K; Peterse, Francien; van_Dongen, Bart E (December 2024, Science Advances)

   Alongside the Chicxulub meteorite impact, Deccan volcanism is considered a primary trigger for the Cretaceous–Paleogene (K–Pg) mass extinction. Models suggest that volcanic outgassing of carbon and sulfur—potent environmental stressors—drove global temperature change, but the relative timing, duration, and magnitude of such change remains uncertain. Here, we use the organic paleothermometer MBT′_5meand the carbon-isotope composition of two K–Pg-spanning lignites from the western Unites States, to test models of volcanogenic air temperature change in the ~100 kyr before the mass extinction. Our records show long-term warming of ~3°C, probably driven by Deccan CO₂emissions, and reveal a transient (<10 kyr) ~5°C cooling event, coinciding with the peak of the Poladpur “pulse” of Deccan eruption ~30 kyr before the K–Pg boundary. This cooling was likely caused by the aerosolization of volcanogenic sulfur. Temperatures returned to pre-event values before the mass extinction, suggesting that, from the terrestrial perspective, volcanogenic climate change was not the primary cause of K–Pg extinction. 

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2. Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact

   https://doi.org/10.1073/pnas.1905989116  

   Henehan, M. J..; Ridgwell, A.; Thomas, E.; Zhang, S.; Alegret, L.; Schmidt, D. N.; Rae, J. W.; Witts, J. D.; Landman, N. H.; Greene, S. E.; et al (November 2019, Proceedings of the National Academy of Sciences of the United States of America)

   Mass extinction at the Cretaceous–Paleogene (K-Pg) boundary coin- cides with the Chicxulub bolide impact and also falls within the broader time frame of Deccan trap emplacement. Critically, though, empirical evidence as to how either of these factors could have driven observed extinction patterns and carbon cycle perturbations is still lacking. Here, using boron isotopes in foraminifera, we docu- ment a geologically rapid surface-ocean pH drop following the Chicxulub impact, supporting impact-induced ocean acidification as a mechanism for ecological collapse in the marine realm. Subsequently, surface water pH rebounded sharply with the extinction of marine calcifiers and the associated imbalance in the global carbon cycle. Our reconstructed water-column pH gradients, combined with Earth sys- tem modeling, indicate that a partial ∼50% reduction in global ma- rine primary productivity is sufficient to explain observed marine carbon isotope patterns at the K-Pg, due to the underlying action of the solubility pump. While primary productivity recovered within a few tens of thousands of years, inefficiency in carbon export to the deep sea lasted much longer. This phased recovery scenario recon- ciles competing hypotheses previously put forward to explain the K-Pg carbon isotope records, and explains both spatially variable patterns of change in marine productivity across the event and a lack of extinction at the deep sea floor. In sum, we provide insights into the drivers of the last mass extinction, the recovery of marine carbon cycling in a postextinction world, and the way in which ma- rine life imprints its isotopic signal onto the geological record. 

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3. The end-Cretaceous plant extinction: Heterogeneity, ecosystem transformation, and insights for the future

   https://doi.org/10.1017/ext.2023.13  

   Wilf, Peter; Carvalho, Mónica R; Stiles, Elena (January 2023, Cambridge Prisms: Extinction)

   Abstract The Cretaceous–Paleogene (K–Pg) mass extinction was geologically instantaneous, causing the most drastic extinction rates in Earth’s History. The rapid species losses and environmental destruction from the Chicxulub impact at 66.02 Ma made the K–Pg the most comparable past event to today’s projected “sixth” mass extinction. The extinction famously eliminated major clades of animals and plankton. However, for land plants, losses primarily occurred among species observed in regional studies but left no global trace at the family or major-clade level, leading to questions about whether there was a significant K–Pg plant extinction. We review emerging paleobotanical data from the Americas and argue that the evidence strongly favors profound (generally >50%), geographically heterogeneous species losses and recovery consistent with mass extinction. The heterogeneity appears to reflect several factors, including distance from the impact site and marine and latitudinal buffering of the impact winter. The ensuing transformations have affected all land life, including true angiosperm dominance in the world’s forests, the birth of the hyperdiverse Neotropical rainforest biome, and evolutionary radiations leading to many crown angiosperm clades. Although the worst outcomes are still preventable, the sixth mass extinction could mirror the K–Pg event by eliminating comparable numbers of plant species in a geologic instant, impoverishing and eventually transforming terrestrial ecosystems while having little effect on global plant-family diversity. 

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4. Rapid macrobenthic diversification and stabilization after the end-Cretaceous mass extinction event

   https://doi.org/10.1130/G47589.1  

   Rodríguez-Tovar, Francisco J.; Lowery, Christopher M.; Bralower, Timothy J.; Gulick, Sean P.S.; Jones, Heather L. (July 2020, Geology)

   Previous ichnological analysis at the Chicxulub impact crater, Yucatán Peninsula, México (International Ocean Discovery Program [IODP]/International Continental Scientific Drilling Program [ICDP] Site M0077), showed a surprisingly rapid initial tracemaker community recovery after the end-Cretaceous (Cretaceous-Paleogene [K-Pg]) mass extinction event. Here, we found that full recovery was also rapid, with the establishment of a well-developed tiered community within ~700 k.y. Several stages of recovery were observed, with distinct phases of stabilization and diversification, ending in the development of a trace fossil assemblage mainly consisting of abundant Zoophycos, Chondrites, and Planolites, assigned to the Zoophycos ichnofacies. The increase in diversity is associated with higher abundance, larger forms, and a deeper and more complex tiering structure. Such rapid recovery suggests that favorable paleoenvironmental conditions were quickly reestablished within the impact basin, enabling colonization of the substrate. Comparison with the end-Permian extinction reveals similarities during recovery, yet postextinction recovery was significantly faster after the K-Pg event. The rapid recovery has significant implications for the evolution of macrobenthic biota after the K-Pg event. Our results have relevance in understanding how communities recovered after the K-Pg impact and how this event differed from other mass extinction events. 

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5. A stable isotope-based investigation of mammalian paleoecology across the Cretaceous/Paleogene boundary in the Denver Basin, Colorado, U.S.A.

   Breyak, Annie; Fricke, Henry; Wainwright, Jensen; Blumenthal, Scott; Chritz, Kendra; Lyson, Tyler; Krause, David; Chester, Stephen (November 2024, Society of Vertebrate Paleontology)

   Understanding and mitigating the e ects of our ongoing biodiversity crisis requires a deep-time perspective on how ecosystems recover in the aftermath of environmental catastrophes. The mass extinction event at the Cretaceous/Paleogene (K/Pg) boundary (ca. 66 Ma) represents a natural laboratory wherein the tempo and mode of biotic recovery can be studied with high chronostratigraphic resolution. Although the morphological evolution of mammals across this event has been reconstructed from skeletal remains, the exact nature of any changes in dietary preference remains unknown. A primary goal here is to fill this gap by investigating how ecological preferences of mammals, reflected by diet, changed from the Late Cretaceous, when they shared landscapes with dinosaurs, to the earliest Paleogene, when they did not. To accomplish this, carbon and oxygen isotope ratios of fossil tooth enamel (bioapatite) were measured using laserablation mass spectrometry in order to infer animal diet and drinking water sources, which vary depending on the niche occupied by an animal. Fossil teeth were collected from two sites located within 400 meters of one another within the West Bijou Creek field area of the Denver Basin, one 9 meters (~128 ky pre-K/Pg) below the boundary (teeth from ceratopsian and hadrosaurid dinosaurs and the multituberculate mammal Mesodma, as well as gar fish scales), and the other 4 meters (~57 ky post-K/Pg) above (Mesodma teeth and gar fish scales). Carbon isotope ratios (δ13C) of Mesodma tooth enamel vary significantly across the K/Pg boundary, with Late Cretaceous teeth having lower and more variable δ13C (-10.1 to -16.4‰, n=4) and early Paleocene teeth having higher and less variable δ13C (-5.3 to 9.0 ‰, n=5), the latter being similar to values for Late Cretaceous dinosaurs. These results suggest Mesodma had very di erent dietary behaviors following the extinction event, presumably a result of the disappearance of non-avian dinosaurs as well as 57% of North American plants, both of which made new food sources and niches available to them. These results also hint at a decoupling of behavioral change from morphological change, at least in the case of Mesodma, over 10 ky timescales. Isotopic analysis of teeth from other Late Cretaceous and earliest Paleogene mammalian taxa is ongoing and will hopefully allow for more detailed interpretations of ecological change across the K/Pg extinction event in the Denver Basin. 

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