Research paper
Crassostrea patagonica (d’Orbigny, 1842) shell concentrations from the late Miocene of Río Negro province, NE Patagonia, Argentina
ROSA DOMÈNECH
IRBio y Departament d’Estratigrafi a, Paleontologia i Geociències Marines, Facultat de Geologia, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain. rosa.domenech@ub.edu
Corresponding author
ESTER A. FARINAT
Departamento de Geología, Universidad Nacional del Sur, San Juan 670, 8000 Bahía Blanca, Argentina. farinati@uns.edu.ar
JORDI MARTINELL
IRBio y Departament d’Estratigrafi a, Paleontologia i Geociències Marines, Facultat de Geologia, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain. jmartinell@ub.edu
ABSTRACT
The Río Negro Formation (late Miocene-early Pliocene) mainly consists of continental deposits, but it contains a middle member of marine origin. It represents a transgressive-regressive sequence that can be seen at several outcrops along the N Patagonian coast. The taphonomical approach to the El Espigón marine deposits permits the identification of four main layers containing different kinds of skeletal accumulation, which mainly consists of oyster shells [Crassostrea patagonica (d’Orbigny, 1842)]. These concentrations display three different morphologies (pouches, pavements and bouquets) with a different taphonomic signature. These deposits were formed in shallow marine environments influenced by wave activity that produced valve concentrations of different entities. They contain several shell beds that represent event, composite, hiatal to lag skeletal concentrations. Trace of bioturbation in the sediment (Thalassinoides, Teichichnus) and bioerosion on the shells (Entobia, Gastrochaenolites, Caulostrepsis), and encrusters (cirripeds, bryozoans), are also abundant in the outcroup and constitute common components of these Miocene materials. Layers 1 and 2 of the sequence were deposited in shoreface(foreshore environments at the beginning of a highstand systems tract, while layers 3 and 4 were deposited at the end, or at the beginning of a forced regression, in foreshore environments, A final erosional episode cut the top of layer 4, which truncated the abundant bioturbation developed there.
Keywords: Taphonomy, shellbeds, ichnology, bioerosion, bioturbatio, Neogene.
How to cite: Domènech, R., Farinati, E.A. & Martinell, J. 2014. Crassostrea patagonica (d’Orbigny, 1842) shell concentrations from the late Miocene of Río Negro province, NE Patagonia, Argentina. Spanish Journal of Palaeontology, 29 (2), 165-182.
Received 31 May 2013, Accepted 08 January 2014, Published 31 December 2014
https://doi.org/10.7203/sjp.29.2.17799
