Sediments of the Boss Point, Port Hood, and Parrsboro Formations (Carboniferous) of Nova Scotia were deposited on alluvial plains in tectonically active basins bounded by strike-slip faults. Some basins contain over 1 km of strata of this age. Fining-upward fluvial channel sandstones are about 20 m thick and are composed of a vertical sequence of basal conglomerate, trough cross-beds, ripple lamination, and siltstone. Large-scale lateral accretion surfaces are present and the sandstones are interpreted as meandering river deposits. Flood-plain sediments include crevasse splay sandstones, rooted mudrocks, thin coals, and lacustrine deposits.

The channel sandstones are stacked vertically and many form thick sandstone packages. One 1-km thick sequence, for example, consists of over 75% channel sandstone. There are similarly thick, laterally equivalent, sequences of flood-plain sediment with few or no channel sandstones. It appears, therefore, that meander belts were restricted in their positions for long periods, allowing the unusually thick sequences of channel and coeval overbank sediment to accumulate. The variation from the classic meander-belt model, in which avulsion randomly distributes the meander belts across the alluvial plain through time, was presumably due to differential subsidence rates which caused the meander belts to be restricted to the areas of higher subsidence, thus retarding avulsion frequency.

End_of_Article - Last_Page 955------------