Abstract
ABSTRACT Nineteen ichnotaxa, together with algal and invertebrate remains, and various pseudo-traces and sedimentary structures are described from the Torneträsk Formation exposed near Lake Torneträsk, Lapland, Sweden, representing a marked increase in the diversity of biotic traces recorded from this unit. The “lower siltstone” interval of the Torneträsk Formation contains mostly simple pascichnia, fodinichnia and domichnia burrows and trails of low-energy shoreface to intertidal settings. The assemblage has very few forms characteristic of high-energy, soft-sediment, foreshore or upper shoreface environments (representative of the Skolithos ichnofacies). Uranium-lead (U-Pb) LA-ICPMS analysis of zircon from a thin claystone layer within the “lower siltstone” interval yielded a maximum depositional age of 584 ± 13 Ma, mid-Ediacaran. Most of the zircon is represented by rounded detrital grains that yield dates between 3.3 and 1.0 Ga. Although the age of the basal sandstone-dominated interval of the Torneträsk Formation remains elusive owing to the absence of fossils, the ichnofossil suite from the overlying “lower siltstone” interval lacks deep arthropod trackways, such as Rusophycus and Cruziana, and is suggestive of a very early (Terreneuvian, possibly Fortunian) Cambrian age. The ichnofauna is otherwise similar to early Cambrian trace fossil assemblages from other parts of Baltica, regions further south in modern Europe, and from Greenland.
Highlights
Lower Cambrian sedimentary successions crop out in a thin belt along the eastern front of the Scandinavian Caledonides
The Dividal Group has been considered to be impoverished in body fossils, resulting in some uncertainty regarding the precise age of the formations within the succession
The upper part of the Torneträsk Formation (“upper sandstone” inter val) has yielded no age-diagnostic fossils, the age discre pancy between the possible Terreneuvian age of the “lower siltstone” interval and the much younger Grammajukku Formation, suggests that the phosphorite-bearing conglomerate at the base of the latter defines a significant depositional hiatus. This reconnaissance survey of the fossil biota of the Torneträsk Formation reveals a greater diversity of both body and trace fossils than recorded previously from this unit
Summary
In northernmost Sweden and Norway, these strata are assigned to the Dividal Group. The Dividal Group has been considered to be impoverished in body fossils (see Skovsted et al in press [this volume] for details), resulting in some uncertainty regarding the precise age of the formations within the succession. Studies assigned the Torneträsk Formation to the Ediacaran following the discovery of a putative Ediacara-type organism (Föyn & Glaessner 1979). This taxon, Kullingia concentrica Glaessner, in Föyn & Glaessner (1979), was later interpreted as a scratch circle (Jensen et al 2002) placing significant doubts on the suggested Ediacaran age for the unit
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