| Latest Neoproterozoic to sub-trilobite Cambrian, passive-margin strata in the Mackenzie Mountains (northwestern Canada) are ideal for integrated sedimentological, sequence-stratigraphic, and ichnological analysis of a crucial interval in earth history. Three composite sections have been measured along thirty kilometers of depositional strike. The succession consists (in ascending order) of the Ingta, Backbone Ranges, and Vampire formations, which respectively represent transgressive, regressive, and transgressive conditions.; Ten siliciclastic and three carbonate facies associations are identified. Siliciclastic associations include non-marine, fluvio-deltaic, shoreline, and open-shelf deposits. Carbonates (volumetrically minor) represent distal shelf to shoreface settings. The Ingta Formation was deposited on a wave-dominated open shelf whereas the Backbone Ranges and Vampire formations reflect a spectrum of environments ranging from proximal, wave-influenced, braid-delta to distal, open-marine shelf. Deposition was influenced by non-actualistic factors including absence of land plants, paucity of burrowers, and declining microbial binders.; Analysis of facies-association stacking patterns delineates four types of sequence-stratigraphic unit, each related to an order of relative sea-level change. Parasequences (fifth order) stack into eighteen simple sequences (fourth order), each of 0.8 to 1.0 Ma duration. These stack into three composite sequences (third order), two of which make up a supersequence (short-duration second order). Second-order oscillations influenced overall proximality-distality and expression of simple-sequence boundaries. Interacting second- and third-order oscillations influenced systems-tract development within the simple sequences.; Integration of sequence stratigraphic, sedimentological and ichnological data facilitate testing the Neoproterozoic-Cambrian ichnofossil-biozone paradigm. A matrix showing time (simple sequences) against environment (facies associations) with ichnotaxa plotted in the resultant domains indicates that ichnofossils reliably place the Neoproterozoic-Cambrian boundary high in the Ingta Formation. Burrowers were effectively absent from terrestrial and non-marine deposits and from those deposited under highly turbulent conditions, but were abundant and diverse in shelf settings ranging from marginal marine to distal shelf. Evolution was a first-order control on first appearances, and one terminal Neoproterozoic (Simple Burrows) and three subtrilobite Cambrian biozones (Treptichnus pedum, Rusophycus avalonesis, Cruziana tenella) are recognized and may have global significance. |
