SURVIVING METAMORPHISM: TAPHONOMY OF FOSSIL ASSEMBLAGES IN MARBLE AND CALC-SILICATE SCHIST

摘要

Devonian massive graphitic marble and calc-silicate schist, belonging to the Lower Formation of the Nevado-Filabride Complex of the Internal Zones of the Betic Cordillera, crop out extensively near Aguilas (Murcia, SE Spain). These rocks contain a rich fossil record even though they have undergone Alpine metamorphism and deformation (350-480 degrees C; 2 Kb). In this paper, we focus on the taphonomic characteristics of the fossil assemblages to infer the depositional processes that can be reconstructed even after metamorphism. The most abundant fossils are crinoids, followed by phacelloid colonial rugose corals, brachiopods, cephalopods (ammonoids and orthoceratids), and possible gastropods and benthic foraminifers. Crinoids occur as isolated columnal ossicles, as well as articulated portions of columns (pluricolumnals). One complete calyx was also found. Taphonomically delicate crinoids are preserved in the calc-silicate schist beds. In the massive marble beds, crinoids occur mostly as disarticulated ossicles, but they still bear delicate ornamental features. Some corals preserve external walls. The low degree of abrasion indicates disarticulation of the crinoids due to exposure in the taphonomic active zone (TAZ), but under low-energy conditions. Articulated crinoids are preserved due to catastrophic burial events. The preservation of the fauna allows the differentiation of background versus event biostratinomic processes even after being highly altered by metamorphism.