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The use of the terms trace, mark and structure

Vallon L. H., Rindsberg A. K., Martin A. J.

Annales Societatis Geologorum Poloniae

2015

Vol. 85, No. 3

527--528

Mark, trace and structure have been in consistently used in ichnology for many years; we wish to clarify the origins and to prescribe correct usage of these terms. The origins of the words are ancient and complex; in the twentieth century they were given clear definitions as ichnologic terms. Seilacher (1953) defined a mark (German Marke) as a physical (abiogenic) sedimentary structure, as in the common terms sole mark, flute mark, but not bite mark or scratch mark. Trace has been defined many times; we recommend the consensus definition of Bertling et al. (2006) as “a morphologically recurrent structure resulting from the life activity of an individual organism (or homotypic or ganisms) modifying the substrate”; this in cludes dwelling trace, feeding trace, bite trace. Structure, as implied in another consensus paper (Frey, 1973), is a neutral term for geologic patterns resulting from either biogenic or abiogenic processes. Use of the three terms in a clear consistent manner will aid communication both among ichnologists and between ichnologists and their colleagues in other fields.

Neoichnology of an Arctic fluvial point bar, North Slope, Alaska (USA)

Martin A. J.

Geological Quarterly

2009

Vol. 53, No 4

383-396

This study is the first to describe the neoichnology of an Arctic fluvial point bar (Colville River, Alaska, USA) and examine the sedimentological effects of tracemakers in this sedimentary setting. Seasonal extremes in discharge and sediment deposition in this system result in sandwaves, current ripples, gravel bars and mud veneers, with the latter forming extensive mudcracks. Organismal traces are abundantly represented in sandy mudflats on the downstream portion of the point bar and are characterized by: (1) abundant shallow horizontal invertebrate burrows and surface trails, directly comparable to Treptichnus, Cochlichnus and Aulichnites; (2) avian tracks and (3) large mammal tracks. Treptichnus-like burrows are attributed to dipteran larvae tracemakers, whereas Cochlichnus- and Helminthoidichnites-like trails were likely from nematodes or oligochaetes. Avian tracks are primarily from seagulls, geese, swans and plovers; mudcracks were connected directly to tracks, which developed as a result of in creased amounts of sunlight available during the polar summer. Mam mal tracks were dom i nated by those of caribou (Rangifer tarandus), but include grizzly bear (Ursos arctos) and other mammals. Caribou herds significantly impacted emergent and submergent mudflat surfaces through advection of saturated thixotropic muds and dry sand, while also fracturing mudcracked zones, and hence actively produced mud clasts. Vertebrates thus can cause considerable mixing, redistribution and erosion of sediments in Arctic point bars with only a few months of activity. Ichnodiversity was low but accompanied by high trace abundance, reflecting fa vorable hydrodynamic, solar and atmospheric conditions throughout a polar summer. In contrast, sedimentation and bioturbation are absent during winter months, when ice cover prevents organismal interactions with fluvial sediments. As a reult, the ichnocoenose does not fit easily into paradigms of previously defined continental ichnofacies (e.g., Mermia and Scoyenia) and is more like a composite ichnofacies. These findings can thus serve as a starting point for more detailed studies of circum polar point bars, while also adding new perspectives to the interpretation of trace fossils in circum polar fluvial environments.