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Bann, Kerrie L.1, Murray K. Gingras2, James A. MacEachern3
(1) University of Alberta, Edmonton, AB
(2) Ichnology Research Group, Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB
(3) Simon Fraser University, Burnaby, BC

ABSTRACT: Changes in Latitude, Changes in Attitude: Two Outstanding Modern Occurrences of the Teredolites Ichnofacies

Teredolites ichnocoenoses are examined from the modern temperate bay-margin of Willapa Bay, Washington, USA and subtropical Moreton Bay of Queensland, Australia. In particular, in situ log-grounds from the upper intertidal zones are considered. The woodground suites are imprinted on in situ roots, broken stumps, and strewn logs. Enclosing substrates variably comprise muds through muddy sands, and contain abundant organic detritus deposited in supratidal marshes. Tidal and wave processes have operated to truncate the swamps, exposing in situ tree-root networks and the lowermost supratidal sediments.
At Willapa Bay, the intertidally exposed stumps and logs support a diverse community of animals and plants. Boring organisms, encrusters and refugium seekers are found on and within the xylic substrates, producing traces that are comparable to ichnofossils reported by paleoichnologists. The wood-boring traces at Willapa Bay are morphologically similar to the ichnogenera Caulostrepsis, Entobia, Meandropolydora, Psilonichnus, Rogerella, Teredolites, Thalassinoides and Trypanites. The Australian subtropical occurrences display borers and refugium seekers, but virtually no encrusters, forming structures attributable to Teredolites and Thalassinoides.
The stratigraphic significance of these modern locales is consistent with previous modern and ancient studies that associate the Teredolites ichnofacies with base-level rise in marginal marine environments, particularly if the xylic materials are more or less in situ. Thus, the Teredolites ichnofacies is more synonymous with the Glossifungites ichnofacies than previously considered. In fact, bored xylic media locally form a coeval surface with adjacent, burrowed firmgrounds and softgrounds. Such modern studies permit the stratigraphic utility of substrate-controlled ichnofacies to be broadened and better understood.

 

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.