Sedimentary structures and paleocurrents in a Tertiary deltaic succession, northern Banks Basin, Arctic Canada

Abstract

The Eureka Sound Formation of northern Banks Basin is a deltaic unit of Paleocene to Eocene age. A basal member of shale, approximately 100 m thick, passes vertically and, in part, laterally into a succession of sand, silt, shale, and lignitic coal approximately 1000 m thick, which is referred to as the cyclic member because of the abundance of coarsening-upward cycles, averaging 7.4 m in thickness.Sand beds in the cyclic member can be divided into four lithofacies: (1) A facires dominated by medium- to large-scale planar crossbedding, formed by channel processes, including lateral point bar accretion, in the delta plain environment. (2) A predominance of medium-scale trough and (minor) planar crossbeds, formed by migrating dunes in distributary mouth bar sands. (3) A predominance of small-scale ripple-marks, formed by low energy, unimodal currents in distal distributary mouth sands. (4) A lack of current structures, indicating quiet-water, interdeltaic and prodeltaic deposition. The distribution of these four facies outlines a series of small lobate deltas.Paleocurrent data suggest a pattern of radiating distributaries within each delta lobe. Directional variance, when analyzed at various levels of the sedimentary structure hierarchy, provides information regarding channel sinuosity and enables comparisons to be made with other deltaic deposits. High variance for the directions of the distributaries is consistent with a fluvially dominated delta.