Fluvial Architecture of Dinosaur Bonebeds in the Cretaceous Judith River Formation, South-Central Montana

WILSON, KEVIN M., Bryn Mawr College, Bryn Mawr, PA, P. DODSON, University of Pennsylvania, Philadelphia, PA, and A. R. FIORILLO, Carnegie Museum, Pittsburgh, PA

Fluvial architecture of dinosaur bonebeds in the Cretaceous Judith River Formation, south-central Montana, has been the subject of intensive paleontological study for many years. However, little has been published on the sedimentology of the formation in this area.

We have completed a preliminary field study of fluvial facies, with a view towards correcting this omission. Initial results include detailed facies descriptions and maps for five quarries along a line of transect stretching some 40 km parallel to depositional dip. Facies identified are predominantly overbank splays and levees, with common point bar/alluvial channel units and occasional small, possibly estuarine sand bodies in parts of the section. Shell beds (mainly oysters) and bedded, 1 m thick coals are also significant in some sections. Preliminary attempts at paleohydrology suggest river channels in some parts of the section were about 100 m wide and 2 m deep; however, other parts of the section exhibit much larger channel widths. Channel stacking is common. Preliminary results uggest a strong correlation between the occurrence of reddish brown carbonaceous silty shales, and dinosaur bone deposits.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)