Abstract

The Upper Paleocene Cape Pillsbury Member on west-central Ellesmere Island, consisting of thick (600+ m), cyclical, calcareous mud-flat and laterally associated mixed mud-sand shelf deposits, provides an example of deposition on a mud-dominated coast. Mud-flat cycles are characterized by laminated mudstone. Cross-bedding is conspicuously rare. Normal 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 commonly are intercalated with the laminated mudrocks, and by hummocky cross-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 the exposed northeast coast of South America. The flowslides are the only potential indicators of ebb-flood tidal reversals in the entire mudstone succession. Most of the mudrock cycles are incised by sand-filled channels. The channels were excavated during a drop in relative sea level (that terminated the preceding cycle). Subsequent filling of channels began when sediment flux in the channels exceeded the rate of sea-level fall. Thin coal seams capping some of the sand-filled channels may be the first indications of early transgression. The next cycle of laminated mudstone accumulated during the succeeding transgressive/progradational 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.

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