THE EVOLUTION OF BUCTOUCHE-SPIT, NEW-BRUNSWICK, CANADA

Buctouche Spit is an 11-km long sandy spit on the northeast shore of N ew Brunswick, Canada. It is a typical flying spit, having a narrow pro ximal section which is characterized by a single foredune that is pron e to overwash and transgression, and a much wider prograding distal se ction which is characterized by a well-developed foredune backed by a series of relict foredunes. An optical-luminescence dating method in w hich infrared stimulation is used on potassium feldspars was developed for this study. It is a very promising method for dating Holocene dep osits, yielding good resolution and having simplicity of measurement. The luminescence ages obtained indicate that Buctouche Spit extended a t a rate of similar to 4 m yr(-1) between 715+/-45 years ago and 240+/ -25 years ago. This extension rate equates to a distal end accumulatio n rate of similar to 56,000 m3 yr(-1) for this period. At this rate of accretion, the present Buctouche Spit would have formed during the pa st 2000 years. The core data indicate that the spit is greater than or equal to 2200 years old, which is consistent with the preceding estim ate. Since 240+/-25 years ago, the rate of sediment accumulation at Bu ctouche Spit has apparently been falling. The accumulation rate betwee n 1839 and 1945 was similar to 23,000 m(3) yr(-1), less than half of t he historic rate of similar to 56,000 m(3) yr(-1). Since 1945, the dis tal end of Buctouche Spit has not prograded/extended measurably. This is because Buctouche Spit's present vertical growth rate is, at most, equal to the rate of relative sea-level rise at the spit and may be as little as half of the rate of relative sea-level rise. Present sedime nt supply to Buctouche Spit is probably <16,000 m(3) yr(-1). It is lik ely that the much larger sediment supply required to sustain an histor ic accretion rate of similar to 56,000 m(3) yr(-1) was derived from th e reworking of a former sandy barrier located seaward, and possibly up drift of, the present spit. Buctouche Spit is now in a limited sedimen t supply situation and it has become a constrained spit. Sediment is b eing eroded from the centre section of the spit, transported to the di stal end, and then carried away by ebb-tidal currents. The centre sect ion of the spit will likely breach within the next hundred years. If a breach (or breaches) becomes permanently established in the centre se ction of the spit, the distal end will suffer significant erasion and may be destroyed. After this, the cycle of rebuilding and landward mig ration would Likely start again at a new location landward of the pres ent spit as relative sea level continues to rise. It is concluded that the key to understanding Buctouche Spit's long-term evolution is reco gnizing that it is migrating landward both by continuous processes lik e overwash, and by the more discrete and catastrophic process of overs tepping.