New zealand marine terraces: uplift rates.

WL iLLiAM B. BULL AND ALAN F. Cooper (1) identify as marine terrace remnants 18 "notches" or steps at altitudes up to 1700 m on the ridge crests southeast of the Alpine fault, New Zealand. They infer late Quatemary uplift rates on this upthrown side of the fault at three study areas. Their conclusions are based on (i) morphology ofthe steps, which are said to resemble eroded marine cliffs and shore platforms; (ii) the presence of quartz beach pebbles on 16 of the 18 steps; and (iii) linear correlation of step altitudes with the sea-level peaks derived from the Huon Peninsula, New Guinea terraces (2). These lines of evidence should be critically examined. With respect to point (i), three-dimensional terrace morphology is not preserved. For the most part the steps occur on narrow, essentially knife-edge ridge crests perpendicular to the Alpine fault and inferred former coastline. The shore-parallel continuity of up to 3 km is not apparent. Step altitudes of the Fox-Franz Josef area listed in table 3 (1) appear to have been derived from the peaks on a histogram of all altitudes of steps discernible on a topographic map (3). The lack of correspondence between the table 3 altitudes and those of the "type" sections at Stony Creek listed in table 2 (1) demonstrates either that this procedure is unreliable or that there is no consistent set of step altitudes in the Fox-Franz Josef area, or both. The widely scattered rounded quartz pebbles with frosted surfaces and high-energy impact marks (1, 4) can equally or preferably be interpreted as (probable Holocene) gizzard stones of one of the eight or nine species ofmoa (5), ostrich-like birds (Order Dinorithiformes) 1 to 3 m tall, formerly widespread in New Zealand, but becoming extinct in the last few hundred years. The analysis ofBull and Cooper assumes a one-to-one correspondence of erosional marine terraces with the sea-level peaks inferred from the essentially constructional deltaic and coral terraces ofNew Guinea described by Chappell (2), a doubtful proposition as emphasized by Chappell (6). High apparent uplift rates of 5 to 8 mm per year, with permissible errors of30 m or more, lead one to suspect that almost any semiregular sequence of altitudes could be matched "successfillly" to the New Guinea sea-level curve. In the present case, the suspicion is compounded by the coincidence of an apparent increase in uplift rate about 135,000 years