Rare and Large Calcitic Patagonica pecten bivalve shell discovered on the southeastern coast of Patagonia. The pecten shell has a remarkable iridescent quality, as calcites have penetrated each tissue of the once living clam, in a process of a cell by cell absorption of mineral-rich water the metamorphosis took place. Now completely transformed into a beautiful fossilised curiosity.
Sowerby (1846) listed Santa Cruz as the locality from which Darwin collected some of the specimens described by him. This locality surely refers to the cliffs along the southern coast of the Santa Cruz river estuary, a few kilometres upstream from its opening into the Atlantic Ocean. The rocks exposed throughout these cliffs are included in the Monte Leo ́n Formation, a unit formally described by Bertels (1970). That author subdivided the Mote Leo ́n Formation into two members, a lower member which she called Monte Entrada and an upper member that she named Monte Observacio ́n (Bertels 1978). Of the two, the only one exposed along the cliffs at Santa Cruz is the Monte Entrada Member. The age of this unit is now considered late Oligocene–early Miocene, or even early Miocene (Barreda & Palamarczuck 2000).
Caleta Olivia is a city located at the northeast of the Argentine province of Santa Cruz, on the San Jorge Gulf by the Atlantic Ocean.
Described by D'Orbigny (1842), Sowerby (1846) in a revision of the type specimens of the Tertiary molluscs of Chile and Argentina.