Dating volcanic materials through biochronostratigraphic methods applied to hosting strata (example from the Iberian Chain, eastern Spain)

Volcaniclastic accumulations in shallow marine environments are prone to be eroded and transported by sedimentary agents and then resedimented either on contemporaneous or younger substrates. Therefore, dating of the volcanic events through the sediments containing interbedded volcanic layers can lead to errors. A case study of volcanism in the southeastern Iberian Range during the Early and Middle Jurassic is presented. Precise dating of hosting carbonate sediments based on ammonite and brachiopod biochronostratigraphic method has allowed distinguishing 13 volcanic levels of different ages ranging from the early Pliensbachian to the early Bajocian. A set of petrological, geomorphological, sedimentological, and paleontological criteria are applied in order to discriminate primary from secondary (epiclastic) volcaniclastic deposits and thus make it possible to match the ages of primary volcaniclastic deposits with volcanic eruptions. Implementation of such criteria has confirmed that the early Pliensbachian–early Bajocian interval (ca. 20 Ma) corresponds with the actual period of volcanic activity.