Abstract

It is hypothesized that if depositional velocities for Bouma A beds are greater than those for B beds, and B beds greater than C beds, then the morphologies of flute casts associated with A, B and C beds might be different. Four width parameters, two length parameters, maximum depth of erosion, and grain size were therefore measured on 1511 flutes representing 264 beds, mainly in the Ordovician Cloridorme Formation of Gaspe, Quebec. Plan view flute morphology can be characterized by nose shape; a spectrum of shapes from pointed to bulbous was demonstrated. In vertical cross-section, the maximum depth, and distance of this point from the nose can he combined into the parameter B ( = L md /D max ). Study of 77, 56 and 58 flutes on one B bed and two C beds, respectively, showed wide ranges in flute morphology, and no systematic differences between the B and C beds Q-mode factor analysis of one flute from each of 200 beds showed a spectrum of shapes from deep bulbous flutes (associated with A beds) to shallower pointed flutes (associated with B and C beds). Grain size on A beds (-3 to +4 phi) was greater than on B (-2 to +4 phi) and C (0 to +5 phi) beds, and flutes on A beds have a greater absolute width than those on B and C beds. Study of associated sole marks showed that 1, flute tend to occur with other flutes on A beds, but occur with tool and organic marks on B and C beds; 2, organic marks are not associated with flutes on A beds; and 3, longitudinal ridges occur with flutes on A beds but not on B and C beds. In the absence of organic marks on A beds, formation of wide, rounded-nosed flutes appear to be accompanied by bulk erosion of the substrate. Because the flutes were filled by deposition from suspension without bed traction of grains, tool marks tend to be absent. There is a strong contrast between A, and B and C beds, because on B and C beds, flutes were cut without bulk substrate removal, and were filled by traction load with simultaneous formation of tool marks.

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