Distal Effects of the Manson Impact in the Cretaceous Terrestrial Record of Montana

PI: Dr. David J. Varricchio, Department of Earth Sciences, Montana State University

The proposed study examines the late Cretaceous terrestrial deposits of Montana for evidence of an impact event.  Analysis of the 74 Ma Manson Impact Structure in central Iowa suggests a low-angle, oblique trajectory from the southeast predicting significant devastation in the downrange direction, i.e. towards Montana.  At the time, a broad coastal plain with a diverse dinosaur fauna occupied much of the state.  Today the Two Medicine and Judith River Formations represent these terrestrial environments. 

Initially, the study focuses on a single, anomalous dinosaur bonebed of extraordinary size.  This horizon represents a single depositional event, contains an abundance of soot, and displays a unique chemical signature.  Research will examine this bonebed for a possible association with the Manson Impact.  Analyses necessary to test this hypothesis include:  examination of the locality for impact evidence, e.g. shocked quartz, tektites and Ir-anomaly; tracking changes in the local flora through palynological studies; survey of the bone condition for clues to their post-mortem history; and establishment of age correlations through radiometric dating and stratigraphic work.  Further research extends these analyses to other promising impact-related horizons.  Potential results include a better understanding of the distal effects and biotic consequences of Manson-sized impacts, a more definitive interpretation of this unusual dinosaur bonebed, a fuller description of the Cretaceous flora of the region, and opportunities to increase public awareness of the significance of impacts in the past and future.


Contact Information

Mail: Dr. David J. Varricchio
Earth Sciences Department
Montana State University
Bozeman, MT 59717
E-mail: djv@montana.edu
Phone: (406) 994-6907
FAX: (406) 994-6923


Montana Space Grant Home
Updated June 20, 2006
msgcwebmaster@physics.montana.edu