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Book Chapter

A Test of the Gardening Hypothesis for the Trace Fossil Zoophycos

By
Ludvig Löwemark
Ludvig Löwemark
Department of Geology and Geochemistry, Stockholm University, 106 91, Stockholm, Sweden e-mail: Lowemark@gmail.com
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In-Tian Lin
In-Tian Lin
Institute of Earth Sciences, Academia Sinica, P.O. Box 1-55, Nankang, Taipei 115, Taiwan e-mail: itlin@earth.sinica.edu.tw; chwang@earth.sinica.edu.tw
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Chung-Ho Wang
Chung-Ho Wang
Institute of Earth Sciences, Academia Sinica, P.O. Box 1-55, Nankang, Taipei 115, Taiwan e-mail: itlin@earth.sinica.edu.tw; chwang@earth.sinica.edu.tw
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Joachim Schönfeld
Joachim Schönfeld
Leibniz-Institute of Marine Science, IFM-GEOMAR, Dienstgebaeude Ostufer, Wischhofstr. 1-3, D-24148 Kiel, Germany e-mail: jschoenfeld@geomar.de
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Published:
January 01, 2007

Abstract:

The trace fossil Zoophycos has long been considered an archetypical example of a deposit-feeding trace. The important discovery that at least some types of Zoophycos actively introduce surface material into the burrow sparked a new interest in alternative ethological explanations. Recently proposed ethological explanations for the trace fossil Zoophycos include gardening of microorganisms. In the gardening model, organic-rich material is collected on the sediment surface and introduced into the burrow as substrate for the cultivation 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 δ13C between spreiten and adjacent host sediment. In order to test this hypothesis, δ13Corg of spreiten material and directly adjacent host material was measured in 12 host-spreite couples from three cores from the eastern North Atlantic. The results show δ13Corg values ranging from -23.6‰ to -21.6‰ for host sediment and between -23.4‰ and -21.8‰ for Zoophycos material. The difference in the couples is usually only a few tenths of a permil. The minimal difference between Zoophycos and host material suggests that gardening plays an insignificant role. However, the trace material generally displays a significant enrichment in organic carbon compared to surrounding host sediment. Therefore, the gardening hypothesis is rejected in favor of a cache model, where food is squirreled away for poorer times.

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Contents

SEPM Special Publication

Sediment–Organism Interactions: A Multifaceted Ichnology

Richard G. Bromley
Richard G. Bromley
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Luis A. Buatois
Luis A. Buatois
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Gabriela Mángano
Gabriela Mángano
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Jorge F. Genise
Jorge F. Genise
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Ricardo N. Melchor
Ricardo N. Melchor
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SEPM Society for Sedimentary Geology
Volume
88
ISBN electronic:
9781565762909
Publication date:
January 01, 2007

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