Cretaceous strata are widely exposed in the northern Yukon and adjacent Northwest Territories, whereas Tertiary to Holocene strata tend to be limited to the Yukon coastal plain, northernmost Richardson Mountains and adjacent to the Mackenzie Delta. However, under Mackenzie Delta and the Beaufort Sea continental shelf there are 14 to 16 km of Upper Cretaceous to Holocene strata, the bulk of which is Tertiary. The succession is characterized by a series of transgressive-regressive depositional cycles, which at the basin margins consist of alternating shale- and sandstone-dominant formations. Many of the sandstone-dominant successions can be traced basinward into shale-equivalent facies. Marine strata are prevalent in the sandstone-rich Lower Cretaceous formations, while Upper Cretaceous and Tertiary strata tend to contain more extensive fluviodeltaic sediments. Three phases of tectonic development are reflected in the Cretaceous-Tertiary stratigraphie record, each phase of sedimentation beginning at a major regional unconformity or transgression. Each unconformity-bounded assemblage was deposited during a period dominated by extension or compression, or a combination of the two. The oldest assemblage includes strata up to the early Aptian, during which extensional tectonics associated with rifting in the proto-Canada Basin was dominant. Epicontinental sedimentation prevailed and was characterized by the deposition of mature quartz arenites derived from the east and southeast. A southwest trending basin margin extended from the Tuktoyaktuk Peninsula area through the northern Richardson Mountains and across the northern edge of Eagle Plain, at the western end of which it appears to have swung south, paralleling the Ogilvie Mountain trend. A belt of sand-rich sediment formed along the basin margin, grading northwestward into shelf mud. Limited periods of basin expansion extended the basin margin to the southeast and south; for example, during the late Hauterivian and Barremian. The second tectonic phase includes upper Aptian and Albian strata. During the Albian, extension still prevailed in the northern areas and helped create deep-water troughs on the oceanward side of the Eskimo Lakes Uplift, through the Blow River area and into the northern Keele Range and Kandik Basin. These Albian troughs have been called the Kugmallit, Blow, Keele, and Kandik troughs respectively. Although extensional tectonics was still a major force, Cordilleran compression began to influence sedimentation. The Blow, Keele and Kandik troughs appear to have been filled from a westerly to southwesterly provenance, an area that was part of the Brooks Range compressional foldbelt. In the Canadian part of the Cordillera, a shallow foreland trough was developing in the Peel Plateau area (Peel Trough) and marine shelf sediments, derived from the south, were being deposited. By the end of the Albian, beginning of the Cenomanian, rifting in the proto-Canada Basin area had ceased, or at least subsided, and sea-floor spreading began in earnest. However, Cordilleran orogenesis began to increasingly impinge on the northen Yukon and is reflected in the development of a series of northward migrating foreland depocentres. From Cenomanian to about middle Maastrichtian time the foreland basin was on the North American craton, but, by the late Maastrichtian, sedimentation had become centred on the subsiding continental margin of Canada Basin.