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Observations on Ichnology, Taphonomy and Epibiota in the Freshwater Realm Open Access

Descriptions

Other title
Subject/Keyword
Ichnology
Epibiotic
Gastropod
Bivalve
River
Microboring
Fluvial
Biomat
Caddisfly
Freshwater
Epibiont
Boring
Scoyenia
Lotic
Microbial Mat
Mollusc
Extracellular Polymeric Substances
Oichnus
Trichoptera
Mermia
Channel
Nacreous
EPS
Biofilm
Epibiota
Unionid
Periostracum
Taphonomy
Ichnofacies
Aragonite
Lockeia
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Lawfield, Andrew, M. W.
Supervisor and department
Gingras, Murray (Earth and Atmospheric Sciences)
Pemberton, George (Earth and Atmospheric Sciences)
Examining committee member and department
Catuneanu, Octavian (Earth and Atmospheric Sciences)
Zonneveld, John-Paul (Earth and Atmospheric Sciences)
Craig, Douglas (Biological Sciences)
Buatois, Luis (Department of Geological Sciences, University of Saskatchewan)
Department
Department of Earth and Atmospheric Sciences
Specialization

Date accepted
2013-12-19T10:52:58Z
Graduation date
2014-06
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Ichnology concerns the study of interactions between organisms and both soft and hard substrates. Actualistic observation of a modern day river channel molluscan assemblage including unionid and sphaeriid bivalves and gastropods within the Saint John River, Fredericton, New Brunswick, Canada reveals their production of almond shaped Lockeia like resting traces, together with varied, horizontally aligned furrowed, meandering, looping and spiral plan view locomotion/grazing traces. These traces occur within a shifting sand softground substrate. An emersion event associated with a low water level allowed collection of unionid samples, amongst which Elliptio complanata predominates, alongside Lampsilis radiata and Anodonta implicata. Detailed analysis of shell material, with methodologies including scanning electron microscopy (SEM) reveals microboring, various taphonomic signatures and the development of biofilm and extracellular polymeric substances (EPS). These are often associated with one another and their location closely influenced by the shell structure. Taphonomic decay of the shells was noted, with the external periostracum and prismatic aragonite layers decaying, particularly in the umbonal region. Physical puncturing and tearing penetrate the periostracum. Exposed regions of nacreous aragonite are smoothed by a combination of chemical interaction with the water column and physical abrasion from agitated silt and sand sediments. Surface pitting and circular to ovoid penetrations with morphologies comparable to Oichnus borings are noted and their formation is tentatively attributed to bacterial decay processes. In marine settings, the outer protective periostracum of molluscs often possesses physical and chemical defence mechanisms intended to inhibit the attachment of epibiota. Our observations suggest their absence from unionids, with final instar larval or pupal stage Trichoptera, including Goera, Neophylax and Helicopsyche selectively attached to regions of intact periostracum in preference to exposed aragonite on dead shells. In addition, live unionids can display thick growths of cyanobacterial or cyanophyte dominated microbial mat. Biofilm and extracellular polymeric substances, with bacterial, diatomaceous and filamentous components are also observed, often displaying a close association with both microboring and the shells conchiolin layers. Several styles of microboring are noted, with predominantly surficial and both simple tubular and complex network penetrative styles observed. Microborings may be attributed to cyanobacterial, cyanophyte and fungal activity.
Language
English
DOI
doi:10.7939/R3QM3Q
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Lawfield, A.M.W. and Pickerill, R.K. 2006. A Novel Contemporary Fluvial Ichnocoenose: Unionid Bivalves and the Scoyenia-Mermia Ichnofacies Transition. Palaios. Volume 21. Pages 391-396.

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