STRONTIUM-BASED NERITIC CARBONATE SHEDDING RECORD AT IODP 325 HOLE 58A ON THE CENTRAL GREAT BARRIER REEF UPPER SLOPE: EVIDENCE FOR A DROWNED GBR DURING THE PEAK PENULTIMATE SEA-LEVEL HIGHSTAND (MIS-5E)
Because of Hole 58A’s close proximity to the modern GBR and its shallow water depth, glacial-interglacial 100-120 m sea level fluctuations trigger dramatic sedimentation and energy changes. Globigerinoides ruber (white) were picked and analyzed to produce a high resolution oxygen isotope record that clearly exhibits cyclic δ18O variations corresponding to MIS 1-7 or the last 220Ky. The disappearance of G. ruber (pink) at 28.5 m confirms that the interval between 30-28 m, characterized by a sharp δ18O decrease, corresponds to TII. During the early TII, Sr counts slightly peak in response to an early intermediate highstand and then reach the lowest levels between 130-123 Ka, MIS 5e maximum sea level. On the other hand, highest Sr count levels are observed as sea level fell from MIS 5e to 5d at intermediate levels (20-40 mbsl). This is uncharacteristic compared with dozens of shallow cores along the GBR upper slope that record the Last Deglaciation and Holocene, suggesting that the central GBR was drowned during MIS-5e following the TII rapid sea level rise and recovered during relatively stable but lower sea levels of MIS 5d-5a. Carbonate sediment trends at Hole 58A compare well with records at Holes 820A and 819, also from the Central GBR upper slopes and, therefore, strengthen our interpretation and conclusions.