Quantitative characterisation of contourite deposits using medical CT

Abstract

Five sediment cores, retrieved from four different depositional contouritic morphological settings (a sheeted drift, a confined mounded drift, a mounded elongated drift and a plastered drift) from the Northern Gulf of Cadiz and the Alboran Sea have been analysed using medical X-ray computed tomography (medical CT). A quantitative approach has been used, resulting in a workflow that delineates several radio-density ranges based on the Hounsfield Unit (HU) histogram of each core and tracks these ranges throughout the cores. In order to derive the geological significance, the radio-density ranges of all cores have been compared to non-destructive, continuous chemical and physical proxies as well as grain size measurements. The highest correlations occurred between high HU and proxies indicating elevated bottom currents, such as Zr/Al and sortable silt. Additionally, a continuous increase in average HU and inferred bottom current velocities, needed for the creation of the specific contourite setting, could be observed throughout the five cores. Despite imperfections and the requirement of additional research, promising results have been obtained which could improve the detection of diagnostic criteria for contourites. Moreover, the CT data can give more conclusive evidence on the nature of the (contourite) sedimentary sequence boundaries.