Quaternary Sea Level Fluctuations on a Tectonic coast: New ²³⁰Th/²³⁴U Dates from the Huon Peninsula, New Guinea

Abstract

Emerged coral reef terraces on the Huon Peninsula in New Guinea were reported in a reconnaissance dating study by Veeh and Chappell 1970. Age definition achieved was not good for several important terraces, and we report here a series of new 230Th/234U dates, which further clarify the history of late Quaternary eustatic sea level fluctuations. More than 20 reef complexes are present, ranging well beyond 250,000 yr old: we are concerned with the seven lowest complexes. Major reef-building episodes dated by 30Th/234U are reef complex I at 5–9 ka (kilo anno = 1000 yr), r.c. IIIb at 41 ka (four dates), r.c. IV at 61 ka (four dates), r.c. V at 85 ka (two dates), r.c. VI at 107 ka (two dates), and r.c. VII at 118–142 ka. Complex II was previously dated by 14C at 29 ka: this age has not yet been confirmed, and may be only a lower limit. The reef crests were built during or immediately before intervals of sea level maxima, when rates of rising sea level and tectonic uplift briefly coincided. The culmination of each reef-building episode was only a few thousand years in duration, and multiple dates from the same reef complex generally group within the statistical errors of the individual dates.Several methods can be used to estimate the altitude of each sea level maximum relative to present sea level. The least complicated is to calculate mean tectonic uplift rate for each profile of the terraces, and use the mean rate to calculate the tectonic displacement of each dated reef complex on that profile. The difference between the present altitude of a reef complex and its calculated tectonic uplift gives the paleosea level at the time the reef grew. We estimate uplift rates for six surveyed sections by calibrating against published paleosea level estimates from Barbados and elsewhere, viz 125 ka, paleosea at +6 m; 103 ka, −15 m; 82 ka, −13 m. For each section the individual uplift rates for reefs V, VI, and VIIb are within 5% of their section means. Using the mean rates. paleosea level estimates for reef crests II, IIIB, and IV are made for each section. Consistency of estimates between sections is good, giving −28 m for the 60 ka paleosea level, around −38 m for the 42 ka level and −41 m for the 28 ka level (if the age is older the paleosea level would be lower. Using the mean uplift rates, the 82 ka and 103 ka paleosea levels are also estimated for each section: all individual estimates are plotted graphically, and a sea level curve drawn. The reef stratigraphy indicates sea level lowerings between each dated reef crest: the crests probably represent the interstadials of the Wisconsin (Würm, Weichsel) Glaciation, and intervening lower levels correspond to stadials. Since the last time of eustatic sea level higher than the present (about 125 ka), five sea level maxima occurred at roughly 20-ka intervals, none being as high as the present.

Age Dating and the Orbital Theory of the Ice Ages: Development of a High-Resolution 0 to 300,000-Year Chronostratigraphy

“…Dates for terraces corresponding to our events 5.1 (79,250 yr; stage 5a), 5.33 (103,290 yr; stage 5c), and 5.51-5.53 (122,560-125,190 yr; stage 5e) have been given for New Guinea (Bloom et al, 1974): 82,000, 103,000, and 124,000 yr; Barbados (Fairbanks and Matthews, 1978): 82,000, 105,000, and 125,000 yr; and Haiti (Dodge et al, 1983): 81,000, 108,000, and 130,000 yr. Mix and Ruddiman (1986, Fig . 3) show the last glacial maximum (our event 2.2; 17,850 yr) having a i4C age ranging from 13,000 to 19,000 yr.…”

Mass Spectrometric 14C and U-Th Measurements in Coral

“…They have been dated previously at 125.7 and 123.0 ka BP . Samples KWA-Q-1, FRT-F-1 and SIAL-E-1 are from the Huon Peninsula, Papua, New Guinea (Chappell 1974;Bloom et al 1974). All of the samples were well preserved, with corallites intact.…”

“…Modern carbon could be introduced during recrystallization of the coral, or from the addition of modern calcite as over- (Bloom et al 1974) growths on the coral framework. Matthews (1968) has shown that the diagenesis of coral from Barbados depends on kinetic factors and climate.…”

Quaternary geology of the North Kaipara Barrier, Northland, New Zealand

“…During this regressional period, valleys were enlarged along the barrier. The sea-Ievel curve of Chappell (1974) and Bloom et al (1974) shows a major regression al period between 220 000 and 160000 years B.P., with a small transgression at 180000 years B.P., and a possible transgression at 200000 years. Assuming Chappell's (1975) uplift rate of 0.3 mm/year for the North Kaipara area, local relative sea levels during the minima would have been about -55 m at 205000 years, -69 m at 190000 years, and -118 m at 160000 years B.P.…”