ENVIRONMENTAL MAGNETIC CHARACTERIZATION OF SEDIMENTS ACROSS THE CRETACEOUS-PALEOGENE BOUNDARY

While the causes of the Cretaceous-Paleogene (KPg) mass extinction have been extensively studied, knowledge about the environmental impacts of the extinction remains lacking. However, rock magnetic techniques are powerful methods for studying paleoenvironments and could be enlisted to study environmental changes between before and after the KPg extinction. Here, rock magnetic techniques: hysteresis analysis, direct current demagnetization (DCD) remanence analysis, and bulk susceptibility analysis, were applied to terrestrial fluvial sediments of the Hell Creek region of northeastern Montana to look for changes in environmental magnetism across the KPg boundary. Samples were collected from five sites from the Hell Creek region from ~1 m below to ~1 m above the Cretaceous-Paleogene boundary (two sites: Lerbekmo and Nirvana, extended above 1 m). Preliminary testing was limited to the more strongly magnetic samples: sandstone, siltstone, and mudstone sediments; seventy samples were tested in total. Bulk susceptibilities of less magnetic coal samples were later analyzed. Previously, such magnetic tests had not been applied to terrestrial sediments. Through the use of hysteresis loops and DCD remanence curves, magnetic properties were able to distinguish between sediments above and below the KPg boundary, proving these methods are viable for studying terrestrial sediments and for discerning environmental changes associated with the mass extinction. Further testing and analysis are necessary before any conclusions can be drawn explaining the differences in magnetic properties across the KPg boundary and what they mean for the circum-KPg environment.

Key words: Hell Creek, KPg mass extinction, paleomagnetism, environmental magnetism