Taphonomic pathways and comparative biofacies and taphofacies in a Recent intertidal/shallow shelf environment

Abstract

The development of taphonomic approaches to facies analysis requires a foundation in facies‐based actualistic studies. Modern intertidal and shallow shelf environments at Provincetown Harbor. northern Cape Cod, Massachusetts (USA) provide an opportunity to compare pattcrns and controlling factors in molluscan biofacies and taphofacies distributions. Variation in faunal composition, ecologic variables, and taphonomic attributes of molluscan death assemblages produce distinct patterns of environmental zonation: (1) Faunal composition (biofacies) primarily tracks variation in substrate type among environments (sand, rock, peat, and Zostera marina beds). (2) Ecologic variables (equitability, infauna: epifauna ratio, gastropod:bivalve ratio, and predation on M. mercenaria) appear to reflect tidal exposure time. (3) Taphononic attributes (fragmentation, abrasionm, corrosion, bioerosion, and encrustation) of the common bivalve M. mercenaria track environmental energy, in particular its effects on the stability and reworking of hardparts at the sediment surface. Shells in different environments proceed along different taphonomic pathways ‐ the order of acquisition of taphonomic features by hardparts. An encrustation/bioerosion‐dominated pathway characterizes low energy environments; the upper intertidal and deeper subtidal. An abrasion‐dominated pathway characterizes the high energy lower intertidal and shallow subtidal. Contrasting pathways produce distinct proportions of taphonomic attributes in time‐averaged samples; proportions that delineate taphofacies. Integrated taxonomic, ecologic and taphonomic data provide a more complete picture of environmental processes than any approach alone. Taphonomic data not only furnish information not readily provided by other approaches, but free paleoecology from the constraints of taxonomic uniformitarianism.