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

MARQUEZ F; DEL RIO CJ; SANTELLI MB

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

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

0002-7014

The byssated pectinid ?Chlamys? actinodes (Sowerby, 1846) is an abundant and widely distributed species in the sedimentites of the Puerto Madryn Formation (Late Miocene), exposed in the northeastern sector of the Patagonian region (Valdes Peninsule, Chubut Province). The exterior sculpture of this species is highly variable, and the 2D geometric morphometric method herein performed, allowed the recognition of two morphotypes that reflect differential development of shell-sculpture in response to variation of the hydraulic energy conditions in littoral settings. On one hand, it is defined a high-plicae morphotype, represented by specimens with prominent coarse-sculptured shells, inhabited firm-sandy or shell-gravel substrates developed in high energy environments of the lower shoreface, recorded in the Transgressive Phase of the sequence. On the other hand, a low-plicae morphotype is recognized and consists of fine-sculptured specimens that are associated to sandy substrates of the upper and middle offshore marine settings, recorded in the Maximum Highstand Phase, and placed immediately above the maximum flooding surface. In these facies, hydraulic energy conditions are restricted to soft tidal currents, being much lower than those developed in the environments inhabited by specimens with coarse sculptured shells.