A Test of the Gardening Hypothesis for the Trace Fossil Zoophycos
Ludvig Löwemark, In-Tian Lin, Chung-Ho Wang, Joachim Schönfeld, 2007. "A Test of the Gardening Hypothesis for the Trace Fossil Zoophycos", Sediment–Organism Interactions: A Multifaceted Ichnology, Richard G. Bromley, Luis A. Buatois, Gabriela Mángano, Jorge F. Genise, Ricardo N. Melchor
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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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Sediment–Organism Interactions: A Multifaceted Ichnology
The field of Ichnology bridges the gap between the areas of paleontology and sedimentology, but has connections to many subdisciplines within these areas. Biogenic structures record the behavior of their tracemakers and provide valuable information in paleoecologic and paleoenvironmental analysis. As in situ ethologic structures, trace fossils or ichnofossils yield valuable insights into the paleoecology of ancient benthic communities and the environmental dynamics of depositional systems. Ichnology is truly a multifaceted field, and a broad selection of its facets is represented in the 28 papers of this volume. The papers are the product of Ichnia 2004, the First International Congress on Ichnology, convened by Jorge F. Genise and held from 19 to 23 April 2004 at the Museo Paleontológico Egidio Feruglio in Trelew, Patagonia, Argentina. Seven papers connected with the congress, containing ichnotaxonomy, were published separately, in Ichnos, volume 13, issue 4. Several symposium volumes, books, and short-course notes have been published in recent years and ichnology can be considered a particularly active research area in steady growth. The 28 papers herein are arranged in five groups that reveal the broad scope of ichnology.