Report on the occurrence of chemosynthetic bivalve fossils in Sison, Pangasinan

Geologic mapping conducted in the Northern Cement Corporation (NCC) Quarry in Brgy. Labayug, Sison, Pangasinan yielded a Late Miocene assemblage of chemosynthetic bivalves. The bivalves were mostly observed in blocks scattered in the quarry area, although a block was observed as a clast in a conglomerate layer. The bivalves are set in a calcareous sandy matrix, and are interpreted to have been transported due to their mostly fragmented nature and different orientations/positions. They were preliminary identified as belonging to the chemosynthetic genera Anodontia, Lucinoma and Meganodontia . Carbon isotope analysis of the matrix confirms their chemosynthetic nature, which are possibly derived from a methane-influenced environment. The study is one of the very few published report of fossil chemosythetic bivalves in the Philippines, adding to the two earlier studies by Majima et al. (2007; 2010) in Leyte Island (Central Philippines). This study, hopefully, would contribute to the study of the taxonomy and distribution of chemosynthetic bivalves in the Philippines.