Abstract
A correlation of bivalve biostratigraphic units recognized in different regions around the Pacific is attempted. Thesame bivalve groups and frequently the same genera are used in both northern and southern regions, involving monotaceans and pectinaceans for the Lower Jurassic and inoceramids for the Middle Jurassic. Five Lower Jurassic assemblage zones have been recognized in Argentina. A Meleagrinella faunule is found in Toarcian-Aalenian deposits and a Propeamussium andium Assemblage Zone spans the lowest Bajocian. One faunule and four assemblage zones are proposed for the Bajocian-Callovian of Argentina based on the distribution of inoceramid faunas: Retroceramus cf. inconditus faunule; Parainoceramus? westermanni, R. marwicki, R. patagonicus and R. stehni Assemblage Zones. All of them are accurately calibrated against the local ammonite zonation. Relation of these bivalve assemblages with Northeast and Far-East Russia bivalve zonations shows approximately equivalent distributions in time for similar groups, though most South American assemblages consistently seem to be somewhat younger than their Boreal counterparts. The comparison shows that direct correlation between bivalve zones is possible, especially between relatively close regions. Furthermore, knowledge obtained from Andean faunas can be applied to adjust the age of local units based on bivalves, such as the New Zealand stages.
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