Jan Smit on Resolving a Single Hour of the Cataclysm 66 Million Years Ago
Jan Smit is Emeritus Professor of Event Stratigraphy at the Free University of Amsterdam. Initially a paleontologist studying planktonic foraminifera, he became intrigued by what appeared to be extremely sudden events in the fossil record, especially at the boundary between the Cretaceous and the Paleogene, known as the KT boundary. He describes the unprecedented discovery of a thick surge deposit in North Dakota containing an extraordinarily well-preserved assemblage of fossils that document the final moments of the Cretaceous. He is pictured (left) at the Tanis site with Robert DePalma, who first identified the site and is pointing to the gills of a paddlefish lying upside down and containing numerous tektites.
Listen to the podcast here or wherever you listen to podcasts.
Scroll down for illustrations that support the podcast. And add your comments at the bottom of the page.
Note - playing the podcast is not supported on Internet Explorer; please use any other browser, or listen on Spotify, Apple Podcasts, etc.
Podcast Illustrations
The Deccan Traps
The Deccan traps are extensive thick sequences of lava that were erupted at the close of the Cretaceous. Before the asteroid impact hypothesis, the climatic cooling and atmospheric toxicity resulting from the gases emitted during this prolific series of eruptions were thought to be the principal cause of the end-Cretaceous mass extinction.
Courtesy of Courtney Sprain
The sequences of lava within the Deccan Traps near Mahabaleshwar are over 3,300 meters thick.
Courtesy of Gerta Keller, Department of Geosciences, Princeton University
The Tanis Site in North Dakota
Maps of the Tanis site in North Dakota. A: Regional context showing the large sea covering central North America during the Cretaceous. The map shows previously known tsunami locations (black dots) and the Tanis site (star) on an ancient river draining into the inland sea. B: Photo and interpretation showing the 2.5-meter-thick surge event deposit overlying sandstone deposited as a point-bar in the Tanis river. C: Diagram (not to scale) of the event deposit setting. The event deposit (1) covers the slope of a sandy bar of a meander (2). The densest carcass accumulations (3) were found just below Cretaceous-Paleogene boundary deposits (4) that directly overlay the event deposit.
DePalma et al., PNAS, (2019) 116, 8190
Graphic log of the Tanis surge deposit showing the distribution of the tektites (ejecta spherules) and fossils. The Iridium layer is indicated at the top, just below the 1-2-cm-thick clay layer (tonstein) that is a global marker of the Cretaceous-Paleogene boundary.
DePalma et al., PNAS, (2019) 116, 8190
A: Freshwater paddlefish just below a nacreous marine ammonite shell (inset). B: Diagram showing the fish carcasses oriented by the flow direction. C: Mass grave of fish carcasses.
DePalma et al., PNAS, (2019) 116, 8190
Tektites in the Gills of the Fossilized Fish
Jan Smit’s rendering of a paddlefish swallowing tektites suspended in the water.
Closeup of the fish that Robert DePalma is pointing to in the top image on this page. The curved bones are the upper and lower jaw of a paddlefish, which was buried upside down. The small light spherules within the red circle are tektites caught in the gills.
Courtesy of Jan Smit
Detailed images of tektites in the fish gills. A & B: X-ray of a fossil sturgeon head. C & D: Microtomography images of another fish specimen with microtektites embedded between the gill rakers.
DePalma et al., PNAS, (2019) 116, 8190
A: Spherules within amber found at Tanis. B: An exposed unaltered spherule stuck within amber.
DePalma et al., PNAS, (2019) 116, 8190