Ichnological Criteria for Discerning High-Latitude Conditions

Murray K. Gingras¹, George Pemberton¹, Kerrie L. Bann², Shahin E. Dashtgard³, and James A. MacEachern^3
1Earth & Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada
²Ichnofacies Analysis Inc., Calgary, AB, Canada
³Department of Earth Sciences, Simon Fraser, Burnaby, BC, Canada

High-latitude settings show predictable trends in climatic conditions that influence the distributions, behaviors, and sizes in some groups of tracemaking organisms. Resolving this signal in the ancient record is challenging, owing to the interplay of numerous environmental parameters.

Cold water results in lowered metabolism and extended life spans in animals. Additionally, due to increasing gas solubility in cold waters, dissolved oxygen contents are much higher therein. The higher availability of oxygen in cold water has been positively correlated to animal size. These factors favor larger body size and are expressed in Timofeev’s proposition: body sizes increase along a declining temperature gradient.

The distribution of trace-making animals is greatly influenced by the severe conditions of high-latitude intertidal and shallow-water environments. Intertidal settings tend to preclude crustacean-colonization, resulting in reduced occurrences of Thalassinoides and Psilonichnus in high-latitude tidal flats. Therein, Polychaete-generated structures are more common. The highest biomass in high-latitude settings resides on the mid / outer shelf, a marked contrast to low and mid-latitude settings where biomass is highest in bays, estuaries, and the inner shelf. This results in the dislocation of the Cruziana Ichnofacies basinwards and suppresses the Zoophycos Ichnofacies. Regarding specific ichnogenera, Rosselia abundances and morphologic complexities are heightened in cold-water settings. Macaronichnus segregatis occupying “toe-of-the-beach” positions occur in high-latitude locales. Basinward displacement of echinoids in cold water favors robust and abundant Scolicia. Finally, because high-latitude settings are prone to high-frequency storms, trace fossils such as Rosselia, Lingulichnus, Diplocraterion, and Rhizocorallium commonly show signs of re-adjustment.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery