Effect of benthic mixing on the information content of deep-sea stratigraphical signals

Abstract

Benthic mixing or bioturbation affects sediments in various ways, including: (1) the production of trace fossils, (2) mechanical and/or chemical alteration of the sediment, and (3) filtering or smearing stratigraphical signals¹. Because mixing alters both the slopes and amplitudes of any recorded events, some knowledge of the process is essential for the correct interpretation of the signals. In view of recent trends towards high-resolution stratigraphy^2,3 and signal unmixing^4–6, the frequency characteristics of the benthic mixing filter must be understood to determine which types of signals can be detected after mixing. Analyses of ash and tektite profiles in deep-sea cores from various geographical regions indicate that even signals from cores having sedimentation rates as high as 7 cm kyr⁻¹ will show severe attenuation of frequencies higher than 0.35 cycles kyr⁻¹ (periods shorter than 2.9 kyr) resulting in loss of ability to resolve closely-spaced events. Most signals will experience much more serious high-frequency attenuation, however. The severity of high frequency loss is directly related to sedimentation rate (R = 0.97 for the cores examined), suggesting that this is the most important variable to take into account when considering a core for palaeoceanographic or palaeoclimatic study.