Taphonomic analysis of bioclastic accumulations generated by physical modeling of a wave-dominated shallow water system

Abstract

This analysis aims to detail the depositional effects of the shell concentration dynamics (mechanical reworking, winnowing and dynamic bypass) controlled by the waves. Taphonomic parameters such as the shell orientation and positioning, the packing and the percentage content of matrix (by weight), were analyzed from rigid and inconsolidated samples of the simulated deposits, as well as by the image survey of the physical modeling surface. The top-base orientations of the shells were most concordant (> 70%) along the entire simulated profile, but with a higher percentage of oblique and vertical bioclasts in samples from more distal sector of the model, associated to the winnowing and dynamic bypass. The fabric orientation showed bimodal and unimodal tendencies at the intermediate deposits of the profile, associated with the dynamics of mechanical reworking (from breaking zone) and winnowing, and polymodal in the more proximal and distal deposits, associated to the mechanical reworking (from swash zone) and dynamic bypass, respectively. The bivalve shells were mostly concave-down in all simulated deposits. The packing and the percentage of matrix were, respectively, dense and lower (30%) in the deposit generated by the winnowing, being the others with moderate or disperse packing. The taphonomic analysis employed on bioclastic concentrations (coquina) physically modelled as a wave-dominated coastal environment can be used to predict specific sedimentological dynamics of shell accumulation.