Scientific Colloquium
April 6,  2022
Recorded Presentation

"A Blast from the Past: Geochemical Identity of the Chicxulub Bolide and Immediate Effects of the Impact, recorded at Tanis, North Dakota" 

Robert A. DePalma1, 2; Florentin Maurrasse3; Anton Oleinik2; David A. Burnham4; Loren Gurche4; Jeremy Klingler5; Peter L. Larson6; Thomas Beasley7; Tina Geraki8; Konstantin Ignatyev8; David M. Unwin9; Uwe Bergmann10, 11; Nicholas Edwards11; Roy A. Wogelius1; Victoria Egerton1; Phillip L. Manning1

1. Department of Earth and Environmental Sciences, University of Manchester, UK; 2. Florida Atlantic University Department of Geosciences, Boca Raton, FL; 3. Department of Geology, Florida International University, Miami, Fl; 4. University of Kansas Biodiversity Institute, Lawrence, KS; 5. Department of Biological Sciences, Southwestern Oklahoma University, Weatherford, OK; 6. Black Hills Institute of Geological Research, Hill City, SD; 7. Florida Center for Analytical Electron Microscopy, Florida International University, Miami, Fl; 8. Diamond Lightsource, Oxfordshire, UK; 9. University of Leicester, Leicester, UK; 10. Department of Physics, University of Wisconsin, Madison, WI; 11. Stanford Synchrotron Radiation Lightsource (SSRL), Menlo Park, CA;

The Chicxulub impact, demarking the end of the Mesozoic, is widely regarded as the main driver of the Cretaceous-Paleogene (KPg) mass extinction event. Some long- and short-term detrimental effects attributed to the impact have also been clearly identified, however our understanding of immediate effects on an hour-to-day scale is incredibly limited due to a lack of well-preserved coeval sediment packages with high temporal fidelity. In addition, the identity of the Chicxulub impactor, which was obliterated on contact during the cratering process, has never been conclusively identified.

Here we provide new data from a terminal-Cretaceous locality in the Hell Creek Formation, North Dakota, containing a uniquely preserved sediment package with unusually high temporal fidelity. At the locality, known at Tanis, a massive onshore surge of water, triggered by the impact, deposited an ejecta-bearing drape of sediment that provides one of the most highly constrained (hour-scale) temporal records of the KPg impact in terrestrial strata. The deposit, which contains a unique concentrated death-assemblage of organisms directly attributed to the Chicxulub impact, reveals new aspects of the impact' first damaging effects in unprecedented detail. Biota entombed in the strata also offer new insight into the latest Cretaceous faunas in the Western Interior, resolving a more accurate ecological baseline immediately preceding the KPg mass-extinction. While the extinction itself is well-documented worldwide, much less is known about the immediate fate of specific animal groups from the thriving biomes that immediately preceded the Chicxulub impact. For example, dinosaurs and pterosaurs, both ubiquitous in Mesozoic terrestrial biomes, have thus far never been reported in-situ from deposits immediately below the KPg boundary.

Here we report the first known in-situ pterosaur and dinosaur fossils coincident with the Chicxulub impact event, providing a unique window to examine the only known terminal-Cretaceous examples of these clades in the fossil record, and providing the first direct evidence that these groups existed up to the terminal-Cretaceous extinction event. The pterosaur, consisting of a well-developed semi-articulated prenatal skeleton in ovum, and the dinosaur, a subadult ornithischian (Thescelosauridae), were examined via synchrotron rapid scanning X-ray fluorescence (SRS-XRF), scanning electron microscopy (SEM), and traditional light microscopy, which revealed extensive preservation of soft tissue consisting of distinct signatures of organic residues as well as three-dimensional microstructure. Because the pterosaur embryo comprises the first known specimen from the Late Cretaceous and the only example thus far from North America, it contributes vital information about the prenatal development and early ontogeny of these animals from a time interval for which no such data exists. The ornithischian dinosaur, on the other hand (c.f. Thescelosaurus), is characterized by extensive skeletal articulation within preserved portions of the three-dimensional lithified tubercular skin envelope, providing hitherto unknown details about the integument, appearance, and osseous anatomy of the Thescelosauridae.

We also describe two well-preserved meteoric fragments from the same deposit, directly associated with Chicxulub impact ejecta adjacent to the Tanis biota. The fragments are preserved as inclusions within unaltered glassy ejecta spherules, encapsulated immediately after impact while the glass was still malleable. The ejecta spherules, themselves, were preserved in amber coeval with the impact event, which likely increased their preservation potential and inhibited their usual breakdown to smectitic clay. Geochemical examination using energy dispersive X-ray analysis, laser-ablation inductively-coupled-plasma-mass-spectroscopy, and synchrotron X-ray techniques, provided multiple lines of evidence that support a cosmic origin and chemistry indicative of a CM subtype carbonaceous chondrite. Constraining the identity of the Chicxulub impactor using data from this work, which supports prior hypotheses, helps to fill a critical gap hitherto missing from the Chicxulub story. The findings of this study also help to greatly augment our understanding of the Chicxulub impact event, its effect on ancient biota, and more broadly, provides valuable insight into the dynamic interplay between cosmic bodies and life on Earth.

About Robert DePalma:

Robert DePalma is a vertebrate paleontologist, based out of Florida Atlantic University (FAU), whose focus on terrestrial life of the late Cretaceous, the Chicxulub asteroid impact, and the evolution of theropod dinosaurs, was sparked by a passionate fascination with the past. Robert completed his Bachelor's degree in geology at FAU, earned his Master's degree from the University of Kansas (summa cum laude), and is completing his PhD at the University of Manchester UK. Robert's interest in fossils, osteology, and exploration began at a very young age, and formally kicked off when he started working in the Florida Museum of Natural History prep lab at the age of 14. Robert's fascination with the natural world and artistic media led him to build his skills in drawing, painting, sculpting, fossil preparation, scientific investigation, fleshed reconstructions, museum exhibit design, and visual effects, guided by paleo artist John Gurche, Hollywood visual effects guru Stan Winston, and various professional scientists including Robert Bakker, Larry Martin, Mark Norell, and Walter Alvarez. As a professional scientist, Robert has collaborated with museums and institutions across the globe, including the Florida Museum of Natural History, the University of Kansas Natural History Museum, University of Manchester, American Museum of Natural History, and others. Since 1996 Robert has led over 25 expeditions in the US and abroad in an effort to expand our knowledge of natural history and provide educational opportunity to students from diverse backgrounds. Robert's research work has included the discovery of the first known dinosaur-aged amber insects from the Hell Creek Formation, discovery and description of the giant dromaeosaurid dinosaur Dakotaraptor steini, documentation of the first known fossil of healed dinosaur skin, and research/excavation of dozens of dinosaur skeletons. Robert has appeared in a number of different dinosaur related episodes for the National Geographic Channel, Discovery, PBS, and others, and his scientific work has been published in high-impact journals such as the Proceedings of the National Academy of Sciences, Nature: Scientific Reports, and others. Most recently, Robert has focused on a unique research site, known as Tanis, that preserves evidence of a devastating inundation wave and mass-death assemblage triggered by the Chicxulub impact, a geologic snapshot of the first hours after the impact. Joined by Walter Alvarez, Jan Smit, Florentin Maurrasse, Phillip Manning, and other top scientists, Robert's team is painstakingly documenting the biota that experienced the last moments of the Cretaceous, in an effort to more-precisely decode Earth's last mass extinction. This research adds valuable dimension to our knowledge of the Chicxulub event that killed 75% of species on Earth including non-avian dinosaurs, but is also critical to understanding how life as a whole responds to global-scale hazards. It can therefore play a critical role in helping us to navigate the current global ecological crisis. Robert has been an Adjunct Professor in the Geosciences Department of Florida Atlantic University for over 5 years, where the research continues to this day.

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