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The Ediacaran-Cambrian Chapel Island Formation of Newfoundland revisited: Evaluating changes in ecospace utilization by early animals

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Abstract

The Cambrian GSSP (ca. 540 Ma) is marked by the appearance of complex trace fossil from the Treptichnus pedum Ichnofossil Assemblage Zone in the Chapel Island Formation (CIF) at Fortune Head, Newfoundland in Canada (Brasier et al., 1994). The CIF is a 1000+ m-thick, mostly continuous siliciclastic succession that ranges from the late Ediacaran to Cambrian Stage 2. Our present study has relogged this section in detail using the most up to date ichnotaxonomy and facies interpretation. Ichnologic work also focussed on reporting bioturbation index (BI; sensu Taylor & Goldring, 1993) and bedding plane bioturbation index (BPBI; sensu Miller & Smail, 1997) and measuring trace fossil width and depth. Tiering and ecospace utilization were evaluated based on this data. Similar depositional environments reoccur through the Fortunian and Cambrian Stage 2 intervals of the CIF, allowing comparisons of ichnofaunas formed in similar environmental settings at different times. The Fortunian is then characterised by surficial to shallow-tier, diverse assemblages, whereas the Cambrian Stage 2 displays shallow- to deep-tier, moderately to poorly diverse assemblages. Ichnologic analysis through the CIF indicates a temporal increase in burrow size, BI, BPBI and depth of penetration (Gougeon et al., 2018, 2019). Change in ecospace utilization results from the ecologic engineering effects related to the appearance of large sediment bulldozers and deep-tier suspension feeders during the Fortunian-Cambrian Stage 2 transition (Mángano and Buatois, 2014; Gougeon et al., 2018, 2019). The bioturbation by deposit feeders and the bioadvective effects of suspension feeders significantly altered the benthic habitat, causing modifications of the sediment structure, sediment stability and increased pore water and solute movements deeper within the sediment.
The Ediacaran-Cambrian Chapel Island Formation of Newfoundland revisited:
Evaluating changes in ecospace utilization by early animals
Gougeon, R.C.1,*, Mángano, M.G.1, Buatois, L.A.1, Narbonne, G.M.1,2 & Laing, B.A.1
1Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, S7N 5E2,
Canada
2Department of Geological Sciences and Geological Engineering, Queen’s University,
Kingston, ON, K7L 3N6, Canada
*gougeon.romain@gmail.com
The Cambrian GSSP (ca. 540 Ma) is marked by the appearance of complex trace fossil
from the Treptichnus pedum Ichnofossil Assemblage Zone in the Chapel Island Formation
(CIF) at Fortune Head, Newfoundland in Canada (Brasier et al., 1994). The CIF is a 1000+ m-
thick, mostly continuous siliciclastic succession that ranges from the late Ediacaran to
Cambrian Stage 2. Our present study has relogged this section in detail using the most up to
date ichnotaxonomy and facies interpretation. Ichnologic work also focussed on reporting
bioturbation index (BI; sensu Taylor & Goldring, 1993) and bedding plane bioturbation index
(BPBI; sensu Miller & Smail, 1997) and measuring trace fossil width and depth. Tiering and
ecospace utilization were evaluated based on this data. Similar depositional environments
reoccur through the Fortunian and Cambrian Stage 2 intervals of the CIF, allowing comparisons
of ichnofaunas formed in similar environmental settings at different times.
The Fortunian is then characterised by surficial to shallow-tier, diverse assemblages,
whereas the Cambrian Stage 2 displays shallow- to deep-tier, moderately to poorly diverse
assemblages. Ichnologic analysis through the CIF indicates a temporal increase in burrow size,
BI, BPBI and depth of penetration (Gougeon et al., 2018, 2019). Change in ecospace utilization
results from the ecologic engineering effects related to the appearance of large sediment
bulldozers and deep-tier suspension feeders during the Fortunian-Cambrian Stage 2 transition
(Mángano and Buatois, 2014; Gougeon et al., 2018, 2019). The bioturbation by deposit feeders
and the bioadvective effects of suspension feeders significantly altered the benthic habitat,
causing modifications of the sediment structure, sediment stability and increased pore water
and solute movements deeper within the sediment.
References:
Brasier, M.; Cowie, J. & Taylor, M. (1994). Decision on the Precambrian-Cambrian boundary
stratotype. Episodes, 17: 3-8.
Gougeon, R.C.; Mángano, M.G.; Buatois, L.A.; Narbonne, G.M. & Laing, B.A. (2018). Early
Cambrian origin of the shelf sediment mixed layer. Nature communications, 9: 1909.
Gougeon R.C.; Mángano G.M.; Buatois L.A.; Narbonne G.M. & Laing B.A. (2019). The role
of Psammichnites in the origin of an Early Cambrian shelf sediment mixed layer. XV
International Ichnofabric Workshop, Abstracts, 17-18.
Mángano, M.G. & Buatois, L.A. (2014). Decoupling of body-plan diversification and
ecological structuring during the Ediacaran-Cambrian transition: evolutionary and
geobiological feedbacks. Proceedings of the Royal Society B, 281: 20140038.
Miller, M.F. & Smail, S.E. (1997). A semiquantitative field method for evaluating bioturbation
on bedding planes. Palaios, 12: 391-396.
Taylor, A.M. & Goldring, R. (1993). Description and analysis of bioturbation and ichnofabric.
Journal of the Geological Society, 150: 141-148.
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