MUD-FLAT CYCLES, INCISED CHANNELS, AND RELATIVE SEA-LEVEL CHANGES ON A PALEOCENE MUD-DOMINATED COAST, ELLESMERE ISLAND, ARCTIC CANADA

The Upper Paleocene Cape Pillsbury Member on west-central Ellesmere Is land, consisting of thick (600+ m), cyclical, calcareous mudflat and l aterally associated mixed mud-sand shelf deposits, provides an example of deposition on a mud-dominated coast. Mud-flat cycles are character ized by laminated mudstone. Cross-bedding is conspicuously rare. Norma l grading of mudstone laminae suggests that deposition from suspension was significant. Storms also were common on this mud-dominated coast, as evidenced by beds of locally derived mud-chip conglomerate that co mmonly are intercalated with the laminated mudrocks, and by hummocky c ross-stratification in the deeper shelf facies. Soft-sediment folding and microfaulting is ubiquitous in the mudrock facies. The deformation is analogous to flowslides in muddy tidal flats now accumulating on t he exposed northeast coast of South America. The flowslides are the on ly potential indicators of ebb-flood tidal reversals in the entire mud stone succession. Most of the mudrock cycles are incised by sand-fille d channels. The channels were excavated during a drop in relative sea level (that terminated the preceding cycle). Subsequent filling of cha nnels began when sediment flux in the channels exceeded the rate of se a-level fall. Thin coal seams capping some of the sand-filled channels may be the first indications of early transgression. The next cycle o f laminated mudstone accumulated during the succeeding transgressive/p rogradational phase, but the distinction between these two components is not clear. The mud-flat and shelf facies were mostly progradational , accumulating during successive rises and high stands of relative sea level.