Actuotaphonomic model of the mollusk fauna of Laguna de Mandinga, Veracruz, Mexico

Abstract

Introduction: The taphonomic attributes of a faunal assemblage provide information about which agents affect both, the distribution and preservation of ancient or newly-formed biogenic materials, during their depositional and post-depositional processes.
 Thus, actuotaphonomy is a valuable tool to the reconstruction of fossil communities, as it establishes analogies between observable processes in the present and those that happened in the past.
 Objective:The taphonomic attributes of a marginal marine environment were analyzed, in order to assess the origin of fragmentation, bioerosion and incrustation processes and the role of these characteristics in the deterioration of current sediment accumulations of mollusks (gastropods and bivalves), to generate an actuotaphonomic model that could be applyable to analogous ecosystems to Laguna de Mandinga (Mandinga Lagoon), in Veracruz, Mexico.
 Methods: The material came from a shell-remain accumulation called "El Conchal". A batch of 1,697.9 g was processed, selecting 1,165 complete specimens, of which 5 genera of bivalves and 4 genera of gastropods were identified. Results: The taphonomic analysis showed that fragmentation and bioerosion have a medium attribute, which may be due to energy, constant rework and exhumation of the remains at the lagoon's water-sediment interface; three biogeneous agents were identified: Entobia isp, Oichnus and Caulostrepsi, being Caulostrepsi the less abundant. The incrustation showed of poor degree since the ecosystem intrinsic conditions did not allow many encrusting organisms to grow properly, however, these organisms are represented by calcareous tubes of serpulid polychaetes, bryozoans with calcareous skeleton and barnacles.

Occurrence and Preservation of Gastropod Shells in Recent Riverine and Estuarine Sediments of Chennai, SE-India

“…At the shell surface high abundance of boreholes can cause significant disintegration of shell matter. Such patterns are considered as endolithic microborings that can be produced by fungal hyphae, branched filamentous cyanobacteria, algae, clionid sponges or by annelid worms (17)(18)(19) . The occurrence of biogenic encrustation on gastropod shells is negligibly rare and confined to two specimens from the Muttukadu sediments, which show an undefined organic layer in one case and faint circular overgrowths with diameters of 0.8 to 1.0 mm.…”