Paper No. 42-8
Presentation Time: 11:25 AM
LATE PLEISTOCENE PALEOSEALEVELS INFERRED FROM FOSSIL FORAMINIFERA, GULF ST VINCENT, SOUTHERN AUSTRALIA
In Gulf St Vincent, South Australia, two species of Elphidium provide a numerical relationship with respect to water depth: E. crispum, hosting photosynthetic symbionts, prefers shallow water where sunlight illuminates the sea floor; E. macelliforme ranges into the deeper, cooler, darker waters. Bioclastic carbonate sediments were deposited in the Gulf during interglacial times of higher sea level. In glacial episodes the sea did not extend into the gulf. During the Last Glacial Maximum ca. 23 ka, sea level was 120-130 m lower than that of today; with the onset of global warming ca. 18 ka, glacial meltwater raised sea level to that of today. From the deepest part of the Gulf, ca. -40 m, core SV#23 extracted sediments comprising a Holocene interval of 1.5 m and a late Pleistocene succession of 2.5 m. Finite 14C ages derived from shell indicate a timeframe of ca. 35 to 45 ka for deposition of the Pleistocene sediments. Amino acid racemization (AAR) analyses of tests of E. macelliforme provide supporting data. The extent of racemization for glutamic and aspartic acids signify deposition within the cold interstadial Marine Isotope Stage 3. The extent of AAR conforms to a discrete range of D/L values down-core that transform to numeric ages of 30 to 57 ka. Of the fossil foraminifera preserved in SV#23, the two species of Elphidium are particularly abundant. Using their known relationship to modern water depth in Gulf St Vincent, a sea level curve was derived for the late Pleistocene interval. Water depth at the core site had been ca. 20 m. Although a generalized picture of relative sea level for this time is lower than -50 m, and as much as -75 m, numerous high amplitude Greenland interstadial events, as identified in the North Greenland Ice Core Project (NGRIP) within the last glacial cycle may explain short-term marine flooding of Gulf St Vincent (NGRIP Interstadials 5 to 16). These short-term events over periods ranging between 500 and 2500 years involved warming of up to 50-75% of that registered in the transition from fully glacial to interglacial conditions with concomitant sea-level changes. The deuterium record from the Antarctic Vostok ice core, 500-1,000 m, representing ca. 35 to 60 ka, reveals four discrete episodes of warming. The oldest of these might correlate with sea level higher than -50 m at 45 to 50 ka and a shallow sea at the SV#23 site.