7 CENTURIES OF TAPHONOMIC VARIATION IN EOCENE FRESH-WATER FISHES PRESERVED IN VARVES - PALEOENVIRONMENTS AND TEMPORAL AVERAGING

Eocene lake beds of Horsefly, British Columbia, are preserved in varve s, or discrete yearly layers representing seasonal changes in the lake . These varves allow study of temporal variation and rates of change i n morphological and ecological characters on a very short time scale. One of the most sensitive indicators of the paleoenvironmental conditi ons on the floor of the lake may be the taphonomic condition of the fi shes, which vary between perfectly articulated and completely disartic ulated skeletons. Patterns of disarticulation correspond to those prod uced by scavengers. The taphonomy supports the hypothesis that the lak e was warm monomictic, circulating in the winter, at which time scaven gers could gain access to the bottom of the lake. Larger-scale environ mental events (on the order of hundreds of years) are suggested by the fact that the proportion of well-preserved specimens reached two peak s within the seven centuries of deposition, one peak during the second century and another during the fifth and sixth centuries. These resul ts clearly demonstrate two principles: that taphonomy can be a sensiti ve indicator of paleoenvironmental conditions, and that temporal avera ging can affect the taphonomic properties of this fossil site, and pre sumably of others with equal or lower time resolution.