Comparison of ESR and TIMS U/Th dating of marine isotope stage (MIS) 5e, 5c, and 5a coral from Barbados- implications for palaeo sea-level changes in the Caribbean

摘要

Electron spin resonance (ESR) dating of coral has become an efficient geochronological tool in supporting morphostratigraphic studies carried out on Barbados during the last 10 years. The newly developed approach for D_E determination (D_E-D_(max) plot procedure) improves the precision of ESR dating of Pleistocene coral, and therefore permits differentiation between the main marine isotope stages (MIS) 5, 7, 9 and 11 and also between sub-stages 5e, c and a. This study compares results of ESR and TIMS Uranium series dating (U/Th) of emergent Last Interglacial coral reef terraces from Barbados, and presents some implications for the timing and extent of sea-level changes during marine isotope stages (MIS) 5e, c and a. Both dating methods indicate a distinct formation of up to three coral reef terraces during MIS 5e, at approximately 132 ka (ESR) to 128 ka (U/Th), at c. 128 ka (ESR) and at c. 120 ka (U/Th) to 118 ka (ESR). It is also highly probable that three reef terraces were developed during MIS 5c between c. 103 ka (U/Th) and 105 ka (ESR). The formation of two separate coral reefs during MIS 5a is recognized for the first time on Barbados, with an age estimate for the older MIS 5a-2 reef of 85 ka (ESR) or 84 ka (U/Th), and an age estimate for the younger MIS 5a-l reef terraces of 74 ka (ESR) or 77 ka (U/Th). Assuming a constant uplift rate of 0.276 m/ka at the south coast of Barbados, sea-level reached its maximum during MIS 5e-3 and MIS 5e-2 between 132 and 128 ka ago. After this, sea-level declined reaching a level of c. -11 m below present sea level approx. 118-120 ka ago (MIS 5e-1). During the substage 5c sea-level was generally lower than in substage 5e. It reached relative maxima at c. -13, -20 and -25m during MIS 5c (approx. 105ka) and formed three distinct coral reef terraces probably in relative short time intervals. For the first time, a double sea-level oscillation is recognized on Barbados during MIS 5a: an early MIS 5a-2(c. 85 ka) with a sea-level places at approx. -21 m, and a late MIS 5a-l sub-stage (c. 74 or 77 ka) with a sea-level at approx. -19 m below present sea level.