--> Abstract: Rapid Emplacement, Dewatering and Colonization of Muddy Substrates in Estuarine Systems: Implications for the Recognition of Stratigraphically Significant Surfaces, by Curtis D. Lettley, Murray K. Gingras, and S. George Pemberton; #90039 (2005)

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Rapid Emplacement, Dewatering and Colonization of Muddy Substrates in Estuarine Systems: Implications for the Recognition of Stratigraphically Significant Surfaces

Curtis D. Lettley, Murray K. Gingras, and S. George Pemberton
University of Alberta, Edmonton, AB

The application of substrate-controlled ichnofacies has contributed greatly to the recognition of stratigraphically important discontinuities within the rock record. In order for such a surface to be of use in genetic stratigraphy, it must be allocyclic and of regional scope. Firm ground ichnofossil assemblages (i.e. the Glossifungites ichnofacies) can be ubiquitous in estuarine deposits, occurring along areally restricted, autocyclically generated surfaces. Due care must therefore be exercised when interpreting the stratigraphic significance of these assemblages and the surfaces they demarcate.

Within estuarine depositional settings, many processes contribute to rapid development of firm mud substrates. Swift accumulation of mud is promoted through salinity flocculation of large quantities of introduced suspended load and convergent transport under the influence of estuarine circulation. Subsequent firming of mud substrates can be influenced by salinity induced syneresis, desiccation and/or compaction.

The colonization of autocyclically generated firm mud substrates is illustrated with examples from modern and ancient datasets (primarily the Shepody River, New Brunswick and the McMurray Formation, Alberta). Several features allow for the differentiation of these firm ground occurrences from those developed along bounding discontinuities. Stratigraphically significant firm grounds are regionally mappable, exhibit a cross-cutting relationship with underlying softground burrowing, and are typically associated with a clear juxtaposition of facies and the development of a lag. In contrast, firm grounds of low stratal importance are areally restricted, developed in substrates lacking clear softground bioturbation, are not associated with a shift of depositional environment and lack the development of a distinct lag.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005