Multiple Orders of Relative Sea-level Change in an Earliest Cambrian Passive-margin Succession, Mackenzie Mountains, Northwestern Canada

Abstract

ABSTRACT Earliest Cambrian siliciclastic strata in the Mackenzie Mountains (Ingta, Backbone Ranges, and Vampire Formations) contain deposits of a variety of shelf, nearshore, and fluvio-deltaic depositional environments. The strata contain a hierarchical succession of sequence-stratigraphic units. Parasequences, simple depositional sequences (at least eighteen), composite sequences (three), and supersequences (one complete and part of another) have all been recognized within the succession. These units appear to record the interactions between at least five orders of relative sea-level cyclicity and formed on time frames that were broadly consistent with possible eustatic origin. Type-two sequence boundaries (generally considered rare in siliciclastic settings) appear to be common in this succ ssion, and it is suggested that location on the paleoshelf, as well as sea-level variation, can influence the character and interpretation of sequence-stratigraphic units, especially in isolated successions. While the units most easily recognized and correlated (simple and composite sequences) are the result of third- and fourth-order sea-level cycles, second-order fluctuations seem to have exerted a significant control on sequence characteristics. The general proximality/distality of the succession is apparently controlled in large part by second-order oscillations, and the nature and expression of the sequence boundaries that demarcate the simple sequences are also influenced by sea-level variations of second order. In a similar fashion, second- and third-order sea-level interactions c n influence systems-tract development within simple sequences and may determine the presence or absence of a TST within the simple sequences.