Lower Paleozoic sediments of central, Cordilleran, and arctic Canada are dominated by two megafacies: supratidal to shallow subtidal carbonates and minor evaporites of the platformal (cratonic) areas, and deeper water dark shales and dark limestones of the slope and basinal areas. Large areas of the platform may be covered or exposed in response to relatively small changes in sea level, whereas sea-level changes in the slope and basinal areas are generally recognized only in changes in the sediments and organism content.Employing multiple lines of evidence from stratigraphic, sedimentologic, and paleontologic data, it is generally possible to recognize bathymetrie changes in local stratigraphic sequences, although present inadequate knowledge of fossil "communities" prevents incorporation of that form of paleobathymetric analysis.Composite sections of platformal areas of the central Mackenzie Valley and Williston Basin and of deformed areas of Cornwallis–Bathurst Islands, northern Yukon, central Mackenzie Mountains, and northeastern British Columbia, as well as central and southern Nevada were examined for indications of sea-level changes. Assuming reasonable correlations between sections of the seven areas, fairly good evidence exists for widespread sea-level changes. Sea-level rises (transgressions) are suggested for the Tremadoc and Arenig, early Caradoc and Ashgill, late early and later Llandovery and earliest Wenlock, latest Wenlock and Ludlow, to some extent the Zlichov and Daleje (Emsian), late Eifel and early Givet, and especially Frasne. Sea-level lowering (regression) is indicated possibly for about the middle Arenig, the Llandeilo, approximately the middle Llandovery, the middle Wenlock, the Pridoli, and the lower Lochkov, and approximately the middle Eifel. Anomalies, probably the result of local orogenic activities, are evident in lower Lochkov, Prag, and upper Givet strata of Nevada and the central Arctic Islands.

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