Trace fossils from Lower Palaeozoic ocean-floor sediments of the Southern Uplands of Scotland

Abstract

The Ordovician and Silurian rocks of the Southern Uplands of Scotland have been interpreted as sediments deposited on the northern margin of the Iapetus Ocean. Trace fossils are abundant at many localities in ocean-floor turbidites and mudstones that usually lack all other evidence of life. Twelve ichnogenera are present, and they are mainly meandering locomotion and feeding trails and burrow networks: Dictyodora, Caridolites, Helminthoida, Neonereites, Nereites, Protovirgularia, Gordia, Megagrapton, Paleodictyon, Chondrites, Plano-lites and Skolithos. The trace fossils occur in at least five distinct assemblages and the composition of these was probably controlled by the frequency and nature of the turbidity currents, and possibly by the oxygen content of the mudstones. Where turbidity currents were weak, abundant Dictyodora, together with Caridolites, Neonereites, Nereites, Protovirgularia and Gordia occur in various combinations. Where currents were stronger, traces such as Gordia, Paleodictyon and Megagrapton may be exhumed and cast on turbidite soles, and the sand may contain Skolithos. The ‘deep-sea’ Nereites trace fossil facies is divisible into several assemblages, presumably environmentally controlled.

A diverse ichnofauna from silurian flysch of the aberystwyth grits formation, Wales

“…Examples showing the bow-like form developing into a spiral, have also been photographed on the modern deep ocean floor (Ewing and Davis 1967, figure 2 4 3 , 2 4 4 ) where they are tentatively attributed to enteropneusts. Similar examples, but without the bowed form, have been photographed at depths over 5000 m in the Atlantic Ocean (Johnson et al 1971, p. 73 (Benton 1982). He also figures closely meandering forms of N. macleayi (Benton 1982, figure 6a).…”

“…2-17) as Helminthoida taramelli. Gordia marina has been described from shallow water Lower Cambrian sediments of Newfoundland (Crimes and Anderson 1985) and deep water sediments in the Cretaceous of Alaska (McCann and Pickerill 1988) and Ordovician and Silurian of Scotland, U.K. (Benton 1982). Some of Benton's material, however, shows thin (1-2 mm diameter) strings which are somewhat discontinuous (e.g.…”

The trace fossil Neonereites multiserialis Pickerill and Harland, 1988 from the Devonian Wapske Formation, northwest New Brunswick

“…In such cases assignment to Scalarituba or Nereites could be potentially misleading and even erroneous. This was demonstrated by Pickerill (1981), who vertically sec tioned examples of N. uniserialis and N. biserialis and was unable to discern any Nereites-likz or Scalaritubalike features, and by Benton (1982), who described N. uniserialis occurring in positive epirelief on upper sur faces and lacking any associated structures. (iv) As noted by Fillion and Pickerill (1990b), information in palaeontological studies must be unambiguous, accurate and easily retrievable, otherwise the communicative function of taxonomy is greatly hampered, particularly by changes at the ichnogeneric level at which most bibliographic surveys are undertaken.…”

“…This approach, however, has only been adopted on occasion by authors such as Chaplin (1980), who did not observe the complete 3-dimensional variation of his material, and Seilacher (1983), who described material similar to, but not as ideally preserved as Chamberlain's (1971), as Nere ites, though he still retained Scalarituba and Neonereites (see also D'Alessandro and Bromley, 1987). Indeed, mostauthors (e.g., Tanaka, 1971;Fedonkin, 1977Fedonkin, , 1985Crimes et al, 1981;Benton, 1982;Crimes and Germs, 1982;Palij et al, 1983;Paczesna, 1986;McCann and Pickerill, 1988;Powichrowski, 1989;Gibson, 1989;Narbonne and Aitken, 1990;Crimes and Crossley, 1991) have retained Neonereites and its ichnospecies as distinctive ichnotaxa. In all probabil ity this more universal concensus reflects one or more of the following: (i) Preservational variants such as those described by Cham berlain (1971) and Seilacher (1983) are apparently ex tremely rare in the geological record.…”

Cambro‐Ordovician trace fossils from the SW‐Norwegian Caledonides

“…Irregularly winding burrows with constant diameter and self-crossings represent G. marina as described from different environments (Benton 1982;Crimes and Anderson 1985;Fillion and Pickerill 1990;Uchman 1998). Fillion and Pickerill (1990) acknowledged similarity to Cruziana problematica (as is also the case in the present material) and inferred from it a slender, bilaterally symmetrical arthropod-like or vermiform producer.…”