Assessing controls on the distribution of ichnotaxa in submarine fan environments, the Basque Basin, Northern Spain

Abstract

The Cretaceous to Eocene aged Basque Basin in northern Spain preserves a variety of submarine fan related environments of deposition in well exposed outcrops. Here, quantitative trace fossil data is calibrated to sedimentologically defined environments of deposition. Nine environments of deposition are assigned according to sedimentary facies associations, depositional architecture and stratigraphic context. The preserved trace fossil assemblages are interpreted in terms of extrinsic palaeoecological, and intrinsic taphonomical and depositional environment controls. In channel related environments, diverse pre-depositional dominated assemblages are prevalent in marginal settings. These are replaced by low diversity post-depositional dominated assemblages in more axial positions within the system. Lobe related environments display a higher level of diversity and bioturbation intensity in more distal/off axis (lobe fringe) environments compared to the most axial lobe environments that preserve low diversity, and exclusively post-depositional assemblages (dominated by Ophiomorpha). Diverse pre- and post-depositional assemblages are common in fan fringe deposits, with less diverse assemblages dominated by post-depositional ichnotaxa (particularly Zoophycos) in basin floor fan deposits. The use of ‘sub-ichnofacies’ is found to only aid characterisation of trace fossil assemblages based on a general (proximal–distal) position within a submarine fan system. Tier preservation of trace fossil assemblages is almost exclusively determined by the depth of erosion that a substrate is subjected to. As such, colonisation style (pre- versus post depositional) and ethological groupings are proposed as being the most powerful tool in assisting sedimentological observations in assigning environments of deposition.