High-Latitude Versus Low-Latitude: Capturing the Elusive Signal Using Trace Fossil Suites from the Ancient Record

S. George Pemberton¹, James A. MacEachern², Kerrie L. Bann³, Murray K. Gingras¹, and Thomas D.A. Saunders^4
1 University of Alberta, Edmonton, AB
² Simon Fraser University, Burnaby, BC
³ Ichnofacies Pty, Calgary, AB
⁴ University of Alberta, Edmonton

Modern high- and low-latitude settings display predictable trends in climatic conditions, many of which exert controls on the distributions, behaviors, and sizes of trace-making organisms. Resolving this signal in the ancient record, however, remains elusive, owing to the complex interplay of numerous environmental parameters. Nevertheless, empirical relationships may be attainable through the careful evaluation and comparison of analogous ancient successions.

High-latitude settings are characterized by cooler annual temperatures, seasonal severe storms, and harsh conditions in inshore settings. Shallow marine subtidal suites from icehouse and greenhouse periods are largely indistinguishable in shelf, offshore, and lower shoreface positions. Australian post-glacial Permian units do display, however, marked size increases of Diplocraterion and Rhizocorallium, consistent with observations from beneath the modern Antarctic ice shelf. Seasonality of high-latitude storms is indicated by closely spaced or erosionally amalgamated tempestites, and common equilibrichnia. Low-latitude settings favor less regular, though no less intense hurricanes, leading to isolated event beds and uncommon equilibrichnia.

Empirical observations also suggest some predictable biogeographic trace-fossil distributions that may be partly constrained by paleolatitude. Macaronichnus segregatis in “toe-of-the-beach” associations is distinctive of high-latitude Pacific coastal settings from the Cretaceous to the present. Ophiomorpha species appear partially coincident with North American Cretaceous paleolatitudes, though abundances are greater in temperate to semi-tropical successions. In contrast, abundant and diverse Rosselia species are a more common feature of cold-water settings. Psilonichnus, reflecting crab-generated domichnia, is more common during greenhouse periods and in low-latitude positions. Continued integration of neoichnological analyses with observations from the ancient record is essential for elucidating the high-latitude signal.