Deep-sea bottom currents influencing tracemaker community: An ichnological study from the NW Iberian margin

Abstract

Marine macrobenthic tracemaker communities are controlled by limiting parameters (e.g., oxygen, organic matter availability and hydrodynamic energy, among others) which are determined by ocean/atmosphere dynamics affecting the sea bottom. Over the last few years, detailed ichnological studies have provided information about trace fossils content of contourites and the palaeoenvironmental conditions during deposition. However, there are still some open questions regarding ichnology in contourites, such as how the variation in the intensity of bottom currents could affect the macrobenthic community. Here, we present a trace fossils analysis, combining high-resolution images and CT data processing, of five gravity cores retrieved in the Galicia Interior Basin (GIB) from the NW Iberian margin. The ichnological record from contourites and other deep-sea deposits (i.e., pelagic, hemipelagic, turbiditic and ice rafted detritus layers) in the GIB over the last 60 ky is assessed. A trace fossil assemblage composed of 14 ichnotaxa occurs, mainly belonging to Zoophycos ichnofacies. Seven ichnofabrics were defined based on ichnological features. The distribution of these ichnofabrics is linked to depositional facies. In the contouritic intervals, ichnofabric alternations between Thalassinoides ichnofabric and Palaeophycus ichnofabric reveal changes in sedimentation rate, nutrient availability and substrate consistency. These variations in the ichnological content suggests intermittent deposition during contourite sedimentation in contrast with the continuous process traditionally considered in contourite facies models.