Trace fossils from the Late Precambrian–Early Cambrian strata of south eastern Newfoundland (Canada): Temporal and environmental implications

The late Precambrian to Early Cambrian sequences of southeastern Newfoundland have yielded abundant and diverse ichnofaunas below the lowest occurrence of trilobites. The lowest strata examined belong to the Chapel Island Formation, which includes five members. Member I has yielded only Buthotrephis sp., Gordia sp., Harlaniella sp. and Planolites beverleyensis. Member 2 contains Arenicolites sp., Bergaueria sp., Buthotrephis sp., Cochlichnus sp., Curvolithus sp., Didymaulichnus sp., Gordia marina, Gyrolithes polonicus, Monomorphichnus lineatus, Monomorphichnus sp., Neonereites uniserialis, Nereites sp., Phycodes coronatum n. ichnosp., Phycodes cf. pedum, Planolites sp., Protopaleodictyon sp., and Skolithos sp. A similar abundance and diversity of traces is found in Member 3: Astropolichnus ?hispanicus n. ichnogen., Buthotrephis sp., Cochlichnus sp., Didymaulichnus sp., Helminthoida crassa, H. miocenica, Helminthopsis abeli, H. tenuis, Hormosiroidea canadensis n. ichnosp., Monomorphichnus bilinearis, M. lineatus, Monomorphichnus sp., Neonereites uniserialis, Planolites annularis, Skolithos sp., and Taphrhelminthopsis circularis. Member 4 is a mudstone sequence, with minor interbeds of limestone, that contains burrows. These burrows, unnamed for lack of diagnostic features, are present at several levels in the sequence which otherwise appears to be devoid of the trace fossils recorded from Members 1 to 3. Member 5 has yielded Buthotrephis sp., Didymaulichnus miettensis, Palaeophycus tubularis, Phycodes palmatum and Planolites sp. The overlying Random Formation contains the following trace fossils: Arenicolites sp., Buthotrephis sp., Cochlichnus sp., Cruziana fasciculata, Curvolithus sp., Didymaulichnus miettensis, Diplocraterion sp., Gordia molassica, Helminthopsis abeli, Monomorphichnus bilinearis, Monomorphichnus sp., Neonereites uniserialis, Nereites sp., Paleodictyon sp., Phycodes cf. pedum, Planolites sp., Protopaleodictyon incompositum, P. submontanum, Rusophycus avalonensis n. ichnosp., R. bonnarensis, Scolicia sp., Skolithos sp., Squamodictyon sp., and Taphrhelminthopsis circularis. The ichnofaunas associated with the lower and middle parts, respectively, of the Chapel Island Formation indicate that whereas Member 1 may be of latest Precambrian (Vendian) age, Members 2 and 3 are probably of Early Cambrian (Tommotian) age. This probability and the evidence provided by trace fossils for an Early Cambrian (Tommotian) age for the Random Formation implies that the intervening part of the succession, i.e., Members 4 and 5 of the Chapel Island Formation, is also Tommotian. The sediments were all deposited in shallow or relatively shallow water, probably within tidal influence. The occurrence of some trace fossils normally only associated with deep water deposits (e.g., Helminthoida crassa, Paleodictyon, Squamodictyon) suggests that these behavior patterns originated in shallow water in earliest Cambrian times and only later migrated into deep water. The diversity of trace fossils below the lowest trilobites in these and other sections suggests that they may have significant value in defining and correlating the Precambrian/Cambrian boundary.