Ethology of the Zoophycos-producer: Arguments against the gardening model from δ13Corg evidences of the Spreiten Material

Abstract

Recently proposed ethological explanations for the trace fossil zoophycos include gardening of microorganisms. Because microorganisms are known to fractionate strongly against 13C, especially under low oxic to anoxic conditions, it is argued that any gardening activity in the trace would result in a noticeable shift in δ 13Corg between spreiten and adjacent host sediment. In order to test this hypothesis, δ13C org of the Spreiten Material and directly adjacent host material was measured. Measured δ13Corg in a glacial section of the core ranges from -22.6 to -22.9 ‰ for host sediment and between -22.8 and -23.2 ‰ for Zoophycos material. In an interglacial section the Zoophycos material measures -21.9 ‰, whereas the host material ranges from -21.2 to -21.4 ‰. The minimal difference between Zoophycos and host material suggests that gardening plays an insignificant role. The gardening hypothesis is therefore rejected in favor of a cache model, where food is squirreled away for poorer times.