ENVIRONMENTAL CONTROL ON SHELL-SCULPTURE OF THE MIOCENE PECTINID ?CHLAMYS? ACTINODES (SOWERBY, 1846) (PATAGONIA, ARGENTINA)

DEL RÍO, CLAUDIA JULIA; SANTELLI, MARÍA BELÉN; MÁRQUEZ, FEDERICO

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2016 vol. 53 p. 645 - 654

0002-7014

The byssated pectinid "Chlamys" actinodes (Sowerby, 1846) is anabundant and widely distributed species in the sedimentites of the Puerto MadrynFormation (Late Miocene), exposed in the northeastern sector of the Patagonian region(Valdes Peninsule, Chubut Province). The exterior sculpture of this species is highlyvariable, and the 2D geometric morphometric method herein performed, allowed therecognition of two morphotypes that reflect differential development of shell-sculpturein response to variation of the hydraulic energy conditions in littoral settings. On onehand, it is defined a high-plicae morphotype, represented by specimens with prominentcoarse-sculptured shells, inhabited firm-sandy or shell-gravel substrates developed inhigh energy environments of the lower shoreface, recorded in the Transgressive Phaseof the sequence. On the other hand, a low-plicae morphotype is recognized and consistsof fine-sculptured specimens that are associated to sandy substrates of the upper andmiddle offshore marine settings, recorded in the Maximum Highstand Phase, and placedimmediately above the maximum flooding surface. In these facies, hydraulic energyconditions are restricted to soft tidal currents, being much lower than those developed inthe environments inhabited by specimens with coarse sculptured shells.