Investigations into the Occurrence and Distribution of Bioturbation in Tidally-Influenced Sedimentary Environments
Creators: Melnyk, Scott A.
Publisher: name: University of Alberta Library
Year: 2024

<p>Tidally-influenced sedimentary environments are regions where sediment deposition is strongly influenced by the regular ebb and flow of tides. These natural processes result in distinctive and often heterogeneous patterns of sediment distribution and sedimentary structures, both physical and biological. This thesis explores the occurrence and distribution of bioturbation in these environments, with the aim of gaining a deeper understanding of the interplay between physico-chemical stressors and their impact on the ichnological record.</p>

<p>Chapter 1 provides a historical overview and a current analysis of the scientific field, offering essential background information for the subsequent sections of this thesis. The chapter covers the fundamental aspects of process ichnology and its relevance in the context of tidal systems. Furthermore, it explores how bioturbation distribution and intensity may be used in ichnological analysis to shed light on sedimentation dynamics and thereby paleoenvironmental conditions.</p>

<p>Chapter 2 demonstrates the usefulness of photogrammetry in constructing robust neoichnological datasets. Low-level drone photography allowed for the collection and analysis of visual and spatial data from photogrammetric reconstructions. This data was used to assess the relationship between shorebird track distributions and various environmental and ecological factors. The results show that the track record at each site represents a shorebird flock that traversed the tidal flats in such a way as to optimize foraging success. These findings provide context for interpretations of shorebird tracks in the rock record and illustrate the breadth of data that can be collected using photogrammetry.</p>

<p>Chapter 3 builds upon the techniques outlined in Chapter 2 to assess the distribution of infauna and their burrows at White Rock, British Columbia. Point counting of burrow openings across intertidal dunes allowed the comparison of burrow distribution to elevation. A strong inverse relationship is observed, with burrows being considerably more abundant in the topographically-low interdune areas. This study shows that changes in burrow abundance can arise from local variations in pore water content and food availability, particularly in intertidal settings that experience minimal sedimentation rate or grain size variability.</p>

<p>Chapter 4 provides detailed documentation of a herring gull producing an unusual biodeformational structure that had not yet been reported along the west coast of North America. The resulting structure comprises a series of nested, concavo-convex sediment mounds and a terminal bowl-shaped impression. The aims of this chapter are to document the trace–tracemaker association, outline the sedimentological and ecological significance of the structure, and provide a means of comparison with similar structures.</p>

<p>Chapter 5 investigates the effectiveness of measuring the bioturbation intensity of a particular sedimentary deposit from bedding planes displaying vertical trace fossil assemblages (i.e., piperock). Computer simulations are used to evaluate the variability associated with estimating bioturbation intensity from limited exposure. Subsequently, the results are compared to field data to evaluate the model&#39;s validity and applicability. These comparisons reveal a notable level of accuracy when attributing bioturbation intensities to piperock ichnofabrics based on bedding plane exposures.</p>

<p>Chapter 6 introduces a conceptual framework for the interpretation of inclined heterolithic stratification using the distribution of bioturbation at the bed scale. Core data from the Lower Cretaceous McMurray Formation was used to relate the presence of bioturbation to periods of increased marine influence. This data was used to demonstrate that in environments increasingly dominated by tides (e.g., estuaries), mud deposition is most associated with periods of elevated river discharge, while sand deposition and redistribution is more prevalent during tidal dominance. These findings critically refine paleoenvironmental interpretations of fluvio-tidal settings that experience seasonal changes in fluvial discharge.</p>