Comparative Abrasion of Modern and Fossilized Fish Fragments

Michele Asgar-Deen and Claudia Schroder-Adams
Carleton University, Ottawa, ON

Bone beds are a rich source of paleontological material. However, the processes by which these beds are deposited are poorly understood. Competing theories include mass mortality events due to phytoplankton blooms, transgressive surfaces of erosion, condensed sedimentation and winnowing. Less extensive bone beds surrounded by coarse-grained sediment have been interpreted as lags at the base of migrating channels. These processes have implications for the use of bone beds in paleoecological and sequence stratigraphic studies.

Interpretation of the depositional history of bone beds requires the identification of reworked material. This study tests the hypothesis that reworked phosphatic fossils are significantly more resistant to erosion than unfossilized material. Abrasion of modern and fossil fish teeth, scales and bones is simulated with a rock tumbler and experimental variables are minimized by simultaneous runs with a double-barrelled model. The application of these results towards the identification of reworked material and transport distances are discussed. These distances may be useful in identifying fauna originating from geographically distant communities. Increased understanding of bone bed depositional processes also enhances paleogeographic reconstructions. We present a case study of a regionally extensive bone bed at the base of the Second White Specks Formation near the Cenomanian/Turonian boundary in the Western Interior Sea.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005