Combined-Flow Generation of Sole Structures, Including Recurved Groove Casts, Associated with Lower Carboniferous Lacustrine Storm Deposits in Nova Scotia, Canada

Abstract

ABSTRACT Sole structures are common on bases of sandstone beds in lacustrine shoreline deposits of the Horton Bluff Formation (Lower Carboniferous), Nova Scotia. The structures include recurved groove casts (the first reported occurrence), other curvilinear grooves, and opposed prod casts. Gutter casts and sinusoid-like chevron marks are associated with these sole marks, but flute casts and other undisputed indicators of unidirectional flow were not noted. Sole structures and gutter casts are oriented normal to the strike of wave-ripple crests and to the elongation direction of hummocky-cross-stratified lenses. Inclined strata within the lenses locally show a preferred migration direction parallel to the elongation direction. The erosional structures are inferred to have been generated during torms in a shallow lake by oscillatory and/or combined flow, the latter possibly associated with longshore currents. These storms also produced hummocky cross-stratification. Wave-formed sole structures may be common in the rock record, and can be recognized by curvilinear shapes, including rare recurved shapes, and bimodal orientations. Care should be taken when interpreting sole structures from wave-influenced settings, because they may not indicate directions of net sediment transport or the orientation of unidirectional currents.