Recognition of allochthonous Mississippian foraminiferal assemblages using taphonomical alterations

摘要

Microfacies analysis of upper Visean and Pendleian platform limestones from southwestern Spain shows that assemblages of smaller foraminifera contain many allochthonous specimens. A tool to identify allochthonous specimens is taphonomic analysis of destructive processes and post-mortem displacement during the biostratinomic stage. Abrasion, bioerosion and encrustations occur during the biostratinomic stage, and usually lead to the destruction of tests. In contrast to these processes, some hydraulic processes do not lead to the destruction of tests, only to their redistribution. Hydraulic displacements of tests are also produced in the biostratinomic stage through grading, sorting and reorientation. These processes have been usually recognized in macrofossils, and more rarely in microfossils. In the latter group, observations are mostly restricted to the external morphology and thus, taphonomic processes have been rarely documented in thin-sections.