THE GENERA GLYCYMERIS, AEQUIPECTEN AND ARCTICA , AND ASSOCIATED MOLLUSK FAUNA OF THE LOWER PLEISTOCENE ARDA RIVER SECTION (NORTHERN ITALY)

The Lower Pleistocene marine succession of the Arda River, cropping out at Castell'Arquato (Northern Italy), is well exposed, continue and richly fossiliferous. Itconsists of sandstones, siltstones and claystones and it is topped by continental conglomerates which indicate a major sea level drop. In the present paper  Glycymeris glycymeris, Glycymeris inflata, Glycymeris insubrica, Aequipecten scabrella, Aequipecten opercularis  and  Arctica islandica  are described and revised. In addition, the associated fauna is illustrated, and its biostratigraphic and palaeoclimatic significance is analyzed. This study points out that: 1) the fauna has a high biodiversity, comprising 159 taxa; bivalves are dominant, followed by gastropods, corals, serpulids, brachiopods, echinoids, arthropods (e.g. barnacles), bryozoans and scaphopods; 2) The last occurrences of the bivalves  Aequipecten scabrella  ,  Glycymeris inflata  and  Chama placentina  , the first occurrence of  Arctica islandica  and the last occurrences of the gastropods  Turritella tricarinata pliorecens  and  Nassarius prysmaticus  suggest a late Gelasian-Calabrian age (Early Pleistocene) for the investigated marine succession; 3) the occurrence of boreal guests, such as  Arctica islandica, Pseudamussium peslutrae  and possibly  Mytilus edulis,  testify to a climatic change with a shift from warm to cold seawater temperatures.