Ichnological analysis of ancient contouritesscientific and economic implications

Laburpena

Contourites, as deposits from thermohialine-induced geostrophic bottom currents, provide essential paleoenvironmental (i.e., ecological, depositional) information, especially on ocean circulation and climate change. Furthermore, the economic interest in contourite deposits has increased significantly during the last decades, being considered an important unconventional reservoir in hydrocarbon exploration. All of this determines the important advance in the knowledge of this facies, and in its application in paleoclimatology and paleoceanography research as well as in petroleum exploration. However, the recognition and characterization of ancient contourite deposits are not always an easy matter, being in most of the cases difficult to discriminate from other deep-sea facies (i.e., pelagites/hemipelagites, turbidites). Recently, ichnological approach has been revealed as a very useful tool in contourite research. On this base, this PhD Thesis focus on the ichnological analysis of ancient contourite outcrops, to advance in the characterization and differentiation of this facies, its use for palaeoenvironmental reconstructions, and its interest in reservoir characterization. With this purpose two main ancient contourite drift successions were selected: a) Late Miocene channelized clastic contourite deposits at Morocco and, b) Eocene-Miocene calcareous contourite drift deposits at Cyprus. Obtained ichnological information, including ichnofabrics and ichnofacies, allows characterization of different types of contourites, as well as its differentiation respect to hemipelagites and turbidites. In general contourites are usually characterized by high trace fossil abundance and low ichnodiversity, but significant differences occurs respect to the particular type. Specific palaeoenvironmental conditions during contourite deposition have been interpreted, showing that bottom currents played an important role on deep-sea macrobenthic community, specially providing a high nutrient supply to the seafloor. The bioturbation´s influence on petrophysical properties (i.e., porosity) of contourite deposits is also demonstrated, as exemplified with Macaronichnus trace fossil. Characterization of ichnological attributes may be a key factor for evaluating the real potential of these unconventional reservoirs. All these advances prove the usefulness of ichnology in the study of ancient contourites, supporting the ichnological approach as a tool in palaeoenvironmental, sedimentological and reservoir characterization of contourite facies.