Invertebrate ichnology of the Triassic of the Point Lepreau and St. Martins regions, southern New Brunswick
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Date
1990
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University of New Brunswick
Abstract
Triassic non-marine strata of Point Lepreau, southern New Brunswick, are included in the Lepreau Formation, which represents a succession from alluvial fan to braided fluvial to prograding alluvial fan subenvironments. The controversial Lepreau River red beds are found, on the basis of accumulated evidence and new petrographic study, to be petrographically and probably chronostratigraphically distinct from the red beds of the Lepreau Formation. The Triassic non-marine strata of the St. Martins area, southern New Brunswick, belong to three formations . The basal Honeycomb Point Formation includes alluvial fan, fluvial, and aeolian subenvironments. The medial Quaco Formation represents a very large fluvial system and the overlying Echo Cove Formation represents alluvial fan to fluvial conditions. Semi-arid conditions probably prevailed during the deposition of the Triassic red beds of both Point Lepreau and St. Martins.
Ichnological study of the entire Lepreau Formation and of selected strata in the Triassic of St. Martins reveals an ichnofauna showing relatively high diversity for a nonmarine setting. The Lepreau Formation contains Ancorichnus coronus Frey, Pemberton, and Fagerstrom, 1984, Ancorichnus cf. ancorichnus Heinberg, 1974, cf. Aulichnites isp. Fenton and Fenton, 1937, Cruziana problematica (Schindewolf, 1921), cf. Fuersichnus isp. Bromley and Asgaard, 1979, Gordia marina Emmons, 1844, Palaeophycus striatus Hall, 1852, Palaeophycus isp. Hall, 1847, Planolites isp. Nicholson, 1873, Rusophycus isp. Hall, 1852, Skolithos linearis Haldeman, 1840, cf. Skolithos isp. Haldeman, 1840, cf. Steinichnus isp. Bromley and Asgaard, 1979, Taenidium isp. Heer, 1877, "inclined meniscate burrows" and "surface pit structures". The St. Martins exposures containAncorichnus cf. ancorichnus Heinberg, 1974, Gordiamarina Emmons, 1844, Palaeophycus isp. Hall, 1847, Planolites isp. Nicholson, 1873, cf. Skolithos isp. Haldeman, 1840, and Taenidium isp. Heer, 1877.
Preservation is a major contributing factor to the morphologies observed, and is especially important in the taxonomic interpretation of simple horizontal and vertical burrows and horizontal burrows possessing a meniscate backfill. Effects of weathering and the common occurrence of the trace fossils in medium-grained, unimodal sandstones (which do not favour preservation of fine-scale morphological features) are the dominant factors influencing preservation. The poor preservation may have resulted in erroneous conclusions regarding diversity. Diversity is highest in braided fluvial settings, particularly in medium-grained sandstone facies. The assemblages as a whole are assignable to the Scoyenia ichnofacies, though assemblages associated with certain sub-environments may not be. Facies-crossing ichnotaxa dominate, both in the Triassic of Point Lepreau and of St. Martins, reinforcing the necessity of considering whole ichnofaunal assemblages when drawing palaeoenvironmental conclusions.