COMPARATIVE TAPHONOMY AND FAUNAL COMPOSITION OF SHELLY CHENIERS FROM NORTHEASTERN BAJA-CALIFORNIA, MEXICO

This report presents the results of comparative taphonomic and faunal analyses of shelly cheniers (mollusk-dominated lag concentrations) fro m the tidal flats of northeastern Baja California, Mexico. Three gener ations of cheniers that differ in age and in the duration and complexi ty of their taphonomic history were sampled for taphonomic and faunal analyses. The three generations, although all dominated by the bivalve mollusk Mulinia coloradoensis, differ significantly in their taxonomi c composition due to taphonomic and/or biological differences. Taphofa cies analysis of 4,334 shells of M. coloradoensis described by nine va riables indicated that the shells accumulated in the cheniers are rare ly affected by biological processes and moderately affected by physica l processes. The shells collected from the chenier surface have poorer preservation than the subsurface ones, indicating that taphonomic deg radation is mostly a surface phenomenon. Multivariate analyses discrim inate the chenier generations even when the poorly preservable luster variables are excluded from the analysis. Chenier shelly assemblages a re taphonomically distinct from assemblages formed in other marine env ironments. They are characterized by a very low intensity of bioerosio n and encrustation.