Late Quaternary sediment accumulations and foraminiferal populations on the slopes of Gladden Basin (offshore Belize) and southern Ashmore Trough (Gulf of Papua) mixed siliciclastic-carbonate systems
Carson, Brooke Elizabeth
Droxler, Andre W.; Dickens, Gerald R.
Doctor of Philosophy
The Belize margin, in the western Caribbean Sea, and Ashmore Trough, in the western Gulf of Papua, represent modern tropical mixed siliciclastic-carbonate depositional systems where significant masses of both river born terrigenous siliciclastics and neritic/pelagic carbonates accumulate at variables rates over space and time. This study examines variations in sedimentolgic and micropaleontologic parameters relative to late Quaternary sea level, climate, and paleoenvironment. This is accomplished through the evaluation of carbonate and siliciclastic accumulations, as well as planktic foraminiferal populations, of a 37.7 m giant piston core (MD02-2532) acquired from the slope of Gladden Basin adjacent to the Belize Barrier Reef, as well as benthic foraminiferal populations of two shorter (11.3 m) piston cores (MV-74 and MV-07/06) acquired on the slopes of Ashmore Trough, adjacent to the northern most extent of the Great Barrier Reef. Neritic carbonate fluxes to the slopes of Gladden Basin are largely regulated by sea level and consistent with well-established highstand shedding depositional concepts. Over the last ∼850 ka, neritic carbonate production (and export to the adjacent slopes) switches on when sea level floods the neritic carbonate regions and switches off when sea level falls and neritic carbonate regions are exposed. Siliciclastic accumulations are also controlled primarily by eustatic sea level fluctuations, with additional influences from local and regional variations in physiography, climate, and/or ocean currents. Planktic foraminiferal taxa of Gladden Basin are typical of tropical to subtropical populations and display significant variations in their downcore relative abundances, suggesting notable changes in surface water masses and oceanographic parameters over the last ∼630 ka. Temperature and salinity, often associated with glacial or interglacial intervals, appear to predominately influence the planktic foraminiferal populations. In Ashmore Trough, benthic foraminiferal relative abundances and multivariate analyses indicate three distinct assemblages whose proportions change over the last ∼83 ka. These assemblages signify distinct paleoenvironmental settings driven by organic carbon flux and sediment supply, as well as changes in sea level. Analysis of these late Quaternary mixed systems provides better understanding of their preservation in the rock record, particularly relative to sea level and sequence stratigraphic concepts.