Development of flute-mark assemblages, 2. Evolution of trios of defects

Abstract

Experiments using a bed of hardened Plaster of Paris dissolved beneath a turbulent water stream (practical analogue of natural mud-bed erosion) show that trios of defects evolve into compound flute marks which, at a critical age, become indistinguishable from structures evolved from single defects. The critical age is comparable with 0.6, defined in terms of the erosion velocity of the bed surrounding the mark, duration of erosion, and the overall size of the assemblage of defects. Marks formed from single defects (Allen, 1971) and from paired defects (Allen, 1973) also lose evidence of their parents broadly at this value of the age. Marks grown from trios increase in maximum depth on a similar law to the marks formed from single and paired defects. A natural assemblage of flute marks may be expected during an early stage of evolution to show a progressive reduction in the number-density of structures, as a consequence of the merging of marks produced at sufficiently closely spaced unstable defects.