Shallow marine Paleodictyon from the Upper Ordovician Georgian Bay Formation of southern Ontario

Abstract

Two specimens, and a possible third, of the ichnotaxon Paleodictyon are documented from shallow-water marine strata of the Upper Ordovician Georgian Bay Formation of southern Ontario. Its occurrence indicates that previous suggestions of a post-Early Cambrian palaeoenvironmental retreat of Paleodictyon into deeper water require some modification. Instead, the operative migratory process, at least to the Late Ordovician and possibly even longer, was one of expansion and not of retreat.
 
 RÉSUMÉ
 Deux spécimens, et possiblement un troisieme, de la trace fossile Paliodictyon sont reconnus dans des strates marines peu profondes de la Formation de Georgian Bay de l'Ordovicien supérieur du sud de l’Ontario. Sa présence indique que les suggestions précédentes d'une retraite paléo-environnementale post-Cambrien précoce de Paliodictyon en eaux plus profondes nécessitent quelques modifications. À la place, le processus migratoire operatif, au moins jusqu'à l'Ordovicien tardif et possiblement encore plus longtemps, en était un d'expansion et non de retraite.
 
 [Traduit par la rédaction]

Colonization of the deep‐marine environment during the early Phanerozoic: the ichnofaunal record

“…These are important ethological categories in shallow-marine settings of latest Proterozoic and early Phanerozoic age (Hofmann and Patel 1989, Figures 6a±c and 7;Crimes and Fedonkin 1994 , Figures 1 and 2; and references therein); they are, with rare exceptions (e.g. Paleodictyon in Upper Ordovician shallow-marine sediments; Stanley and Pickerill 1993), absent in such environments after the Cambrian. The timing of this is coincident with the ®rst widespread appearance of examples of agrichnia and pascichnia in deep-marine environments during the Ordovician (Figure 2).…”

“…There is, however, no reason to suspect that preservation of agrichnia would have been less likely in the Cambrian than subsequently. Paleodictyon, for example, occurs throughout the Phanerozoic in a variety of different environments and is consistently preserved in a similar manner (Crimes and Anderson 1985;Stanley and Pickerill 1993;Seilacher 1977b); only rare fossil examples (e.g. Seilacher 1977b, Plate 1a) and Recent material within box-cores (Ekdale 1980) have a different toponomy.…”

SEDIMENTOLOGY: The ichnoassemblages of the Abad Member (Tortonian–Messinian), Vera Basin, SE Spain: implications for the regional tectonic and palaeogeographical evolution

“…Häntzschel, 1975; Ernst & Zander, 1993; Fürsich, Taheri & Wilmsen, 2007). Paleodictyon , for example, has been reported from shallow-marine locations in the Lower Palaeozoic (Stanley & Pickerill, 1993), while Gierlowski-Kordesch & Ernst (1987) and Ernst & Zander (1993) have reported it in Upper Cretaceous-age midshelf deposits where it was associated with other ichnofossils considered typical of the Nereites ichnofacies (e.g. Cosmorhaphe , Spirorhaphe , Urohelminthoida ).…”

Trace fossils and biofabrics at the Precambrian–Cambrian boundary interval in western Mongolia

“…There has recently been discussion as to whether the network burrow Paleodictyon shows a post-Early Cambrian retreat from shallow water (e.g. Crimes & Fedonkin, 1994), or whether rare post-Cambrian shallow-water occurrences rather indicate an expansion, with shallow-water forms lingering at least until the Carboniferous (Stanley & Pickerill, 1993).…”