NEW EVIDENCE FOR 2 HIGHSTANDS OF THE SEA DURING THE LAST INTERGLACIAL, OXYGEN-ISOTOPE SUBSTAGE-5E

Sedimentologic, stratigraphic, and geochronologic analyses of a previo usly undescribed carbonate section on Oahu, Hawaii, provide new eviden ce for two distinct sea-level highstands on Oahu during the last inter glacial period (oxygen isotope substage 5e). Whereas electron-spin-res onance and uranium-series ages (122 +/- 8 ka to 152 +/- 25 ka, and 115 +/- 10 ka to 160 +/- 15 ka, respectively) of in situ corals place the age of the deposits within substage 5e, it is the unique sequence of strata found in these exposures that reveals the two transgressions. A highstand lagoonal deposit of coral-algal bafflestone is overlain by large seaward-dipping slabs of beachrock. The beachrock, deposited dur ing a mid-5e regression, is in turn overlain by a second highstand lag oonal deposit. This sequence was deposited in a broad, shallow, back-r eef embayment that was very sensitive to fluctuations in sea level. El sewhere, along much of the shoreline of Oahu, an in situ coral-algal f ramestone (Waimanalo Formation), representing the initial 5e highstand , is erosionally truncated on its upper surface. This erosional unconf ormity represents the mid-5e lowstand and separates the framestone fro m overlying, seaward-dipping, planar-bedded grainstone and rudstone (L eahi Formation) that accumulated during the second 5e highstand.