Palaoenvironmental conditions during Pliocene and Pleistocene in the Southwest Iberian Margin: Ichnological analysis of sedimentary record from IODP Expedition 339

Abstract

International Ocean Discovery Program Expedition 339 took place in the Gulf of Cadiz and the Western Iberian Margin during the end of 2011 and the beginning of 2012, aimed to arrive at a better understanding of Mediterranean Outflow Water evolution, to study the contourite deposits generated by this water mass, and to derive a marine reference climate section from the Pleistocene. Several disciplines are involved in the study of the drilled cores, ichnology being one of them due to its usefulness in palaeoenvironmental studies, providing information about parameters such as oxygen level, food supply or substrate consistency, and hence about the environmental changes involved (i.e., palaeoclimate, atmosphere/ocean dynamics, etc.). This PhD Thesis, based on ichnological analysis of the retrieved marine cores from the expedition, focuses on its use for palaeoenvironmental interpretations during the Pliocene and Pleistocene. Results regarding the ichnological content throughout the studied cores reveal that, in general, sediments were deposited under good oxygen levels and nutrient availability, although some intervals related with dysaerobic conditions can be also identified. More detailed and integrative studies allow for characterization of the palaeoenvironmental evolution during particular intervals, as those corresponding to Marine Isotope Stages 12 and 11, showing that changes in trace fossil features can be linked to surface productivity and food supply variations, and correlated to foraminifera information. This relation between ichnological attributes and productivity is also demonstrated by Zoophycos distribution during glacial-interglacial variations, which may even be used as a proxy, its presence associated with intermediate sedimentation rate and seasonal high productivity in Neogene hemipelagic deposits. All these advances prove the usefulness of ichnology in the study of modern marine cores, supporting the ichnological approach as a tool in drilling expeditions.