Paleosea-Level Records from Late Quaternary Coral Reef Terraces on Araki
Island, Vanuatu; Comparison With Previous Results from Huon Peninsula,
Papua New Guinea
Abstract
New 230Th/238U ages for precisely leveled fossil corals from Araki
Island, Vanuatu, generally corroborate MIS 3 and 4 paleosealevel
estimates from the Huon Peninsula (HP), Papua New Guinea. Corals have
been essential for paleosea-level reconstructions and their timing
because they provide such precise U-series dates. However,
paleosea-level estimates from uplifted corals rely on inferring tectonic
uplift rates in order to subtract them from coral elevations. Uplifted
coral reefs at central Varnuatu and Western Solomons exemplify the
extremely abrupt tectonic rate changes that forearcs can undergo. If
uplift rate changes are not detected and taken into account then
paleosea level estimates could be wrong by tens of meters. Araki Island,
located 2500 km and two plates away from the Huon Peninsula is
tectonically independent. Araki should share a similar paleosea level
history with HP, including Global Isostatic Adjustments, and other
water-loading influences, but should be tectonically different.
Assumptions similar to those used to infer HP sea-level estimates are
applied for the Araki mid-Holocene, MIS 5c, and MIS 5e paleosealevels in
order to constrain MIS 3 and 4 paleosea levels. Before and during MIS 5e
(~130-120 ka) until MIS 5c (~106 ka)
Araki subsided at ~3 mm/yr. At or soon after 106 ka
Araki abruptly began uplifting at a mean rate of ~1.65
mm/yr. This ~1.65 mm/yr mean uplift rate appears to have
prevailed until ~25-30 ka after which uplift accelerated
to a mean rate of ~4.6 mm/yr. These uplift rates imply
MIS 3 and 4 paleosea levels very similar to those inferred from the HP
reef terraces of similar ages. The abrupt changes in vertical tectonics
that our coral ages and elevations imply for Araki Island offer
insightsregarding the remarkably rapid tectonic variability and possible
mechanisms that control convergent margin tectonics as well as the
challenges involved in using the data for paleosea level
reconstructions.