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The Teichichnus Ichnofacies: a Temporally and Spatially Recurring Ethological Grouping Characteristic of Brackish-Water Conditions

Pemberton, S. George 1; Gingras, Murray K.1; Dashtgard, Shahin E.2; Bann, Kerrie L.3; MacEachern, James A.2
1 Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada.
2 Earth Sciences, Simon Fraser University, Burnaby, BC, Canada.
3 Ichnofacies Analysis Inc., Calgary, AB, Canada.

Brackish-water trace fossil suites historically have been characterized by their departure from the archetypal Seilacherian ichnofacies. Indeed, brackish-water suites are widely described as “impoverished marine assemblages” or as “depauperate suites”. Commonly found in heterolithic units, brackish-water trace-fossil suites comprise ichnogenera typically occurring in both the Skolithos Ichnofacies and the Cruziana Ichnofacies. Identifying recurring characteristics of brackish-water ichnological suites have been compounded further by the progressive but markedly variable biological invasion of reduced-salinity settings through time.

Despite these challenges, careful analysis of modern settings and of ancient brackish-water deposits through the Phanerozoic has highlighted a recurring ethological grouping, which constitutes the fundamental basis for the erection of a new ichnofacies. In brackish-water settings, endobenthos overwhelmingly construct permanent dwelling structures designed for the purposes of detritus feeding, protection from desiccation and predation, and as a means of buffering salinity changes prevalent at the sediment-water interface. Persistent ichnogenera, whether vertically or horizontally oriented, record the activity of either head-up deposit-feeding organisms, or mobile tracemakers which leave their dwellings in search of food. Secondary behaviors include passive predation, and minor filter-feeding, ostensibly via the pumping of water through the burrow. Such behavioral groupings are largely ascribed to strongly facies-crossing elements, and probably reflect an abundance of omnivores. Ancillary characteristics include diversity impoverishment (including monogeneric suites), morphologically simple structures, general size reduction compared to fully marine counterparts, and juxtaposed vertical and horizontal elements. For the various ichnological suites adhering to this ethological grouping and showing the aforementioned characteristics, we propose a new ichnofacies archetype: the Teichichnus Ichnofacies.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009