FLUTE-LIKE MARKS AND ASSOCIATED STRUCTURES FROM THE CARBONIFEROUS PORT HOOD FORMATION OF EASTERN CANADA - EVIDENCE OF SECONDARY ORIGIN IN ASSOCIATION WITH SEDIMENT INTRUSION

Flutes have been described and interpreted for many years as sole mark s, preserved in positive relief on the bases of sandstone beds, and fo rmed on underlying firm mud substrates mainly by corrasion at the sedi ment/water interface by fluvial, tidal, or turbidity currents. Structu res resembling flutes (herein termed flute-like marks, or FLMs) from f luvial sandstone of the Port Hood Formation (mid-Carboniferous) of wes tern Cape Breton Island are present not only on the undersides, but al so on the vertical, inclined, stepped, and top surfaces of sandstone b eds in contact with mudstone bodies. These occurrences are difficult t o reconcile with primary sedimentary processes, even allowing for comp lex and fortuitous preservation, e.g., by erosion of slumped mudstone bodies or as scoured and overturned mudstone boulders. The presence of associated soft-sediment deformation structures, such as convolute be dding, mudstone diapirs, and mud-injection structures, some of which a lso have flute-like marks on their surfaces, suggests that these struc tures are explained more readily by sediment intrusion (rheoplasis) th an by current scour and infill. Since flute-like marks have been recog nized as positive-relief structures on both upper and inclined mudston e-sandstone interfaces in modern tidal-flat environments and on experi mental injection structures, we reemphasize that they should not be re garded as excellent criteria for indicating ''way-up'' and paleocrrren t direction.