Cretaceous and Tertiary

Cretaceous and Tertiary strata, which are widely exposed throughout the Operation Porcupine map area, consist of alternating shale- and sandstone-dominant formations. Sandstone-rich Lower Cretaceous strata tend to form a northeast-trending belt, extending from the Tuktoyaktuk Peninsula, through the northern Richardson Mountains, and across the northern edge of Eagle Plain, turning southward along the northern Ogilvie Mountains. Northwestward of the sandstone belt, the succession tends to become shalier. The bulk of these Lower Cretaceous rocks are easterly- to southeasterly-derived, shoreline to shelf sediments, dominated by storm deposits. However, in parts of northern Yukon, some Albian strata contain thick successions of westerly-derived sediment gravity-flow deposits formed during a major tectonic event associated with orogeny in the ancestral Brooks Range. Berriasian to Aptian sedimentation was associated with rift tectonics, and during the late Aptian and Albian, the northern Yukon and adjacent Northwest Territories were subjected to both rifting and compression. A major unconformity separates Lower and Upper Cretaceous strata. Upper Cretaceous and Tertiary strata reflect a different tectono-stratigraphic regime, wherein sediments were derived from the the rising Cordilleran orogen to the south and southwest. Cenomanian to early Maastrichtian sediments were deposited in a cratonic foreland basin, whereas since Late Maastrichtian time, deposition has been on the subsiding continental margin of Canada Basin. Upper Cretaceous and Tertiary strata are dominated by deltaic and delta-front sediments in their onshore and nearshore occurrences, grading into prodelta/shelf, slope and basinal deposits in the offshore areas.