Slope Sediment Accumulation Over the Last 850 Ky on the Belize Tropical Mixed Siliciclastic-Carbonate Margin

The Belize margin represents a modern tropical mixed siliciclastic-carbonate depositional system where significant masses of both neritic carbonate and siliciclastic sediments mix and accumulate at variables rates over space and time. A 37.7 m long piston core (MD02-3532) retrieved from the lower slope at 330 m of water depth, ~3 km offshore the central Belize Barrier Reef, records these changes over the last ~850 ky. A robust chronology was established using a high-resolution record of planktic oxygen isotopes. Bulk carbonate content varies downcore from low values of 40% to high values of 83%. The highest bulk and fine carbonate MAR (> 3.0 g cm-2ky-1) occur in interglacials of sediments MIS 15 and younger. The fine carbonate material consists of aragonite, primarily from the neritic environment, high magnesium calcite (HMC), primarily from marine cements, and low magnesium calcite (LMC), primarily from calcareous nannoplankton.

Aragonite accumulation varies downcore in phase with the oxygen isotope values, with the highest aragonite MARs typically occur during the late deglaciation and peak interglacials and the lowest aragonite MARs occurring during late interglacial and glacials. Consistent with well-established highstand shedding depositional concepts, neritic carbonate fluxes to the slopes are largely regulated by sea level - switch on when sea level floods the neritic carbonate regions and switch off when sea level falls and neritic carbonate regions are exposed. Elevated MARs of HMC, primarily produced from incipient marine cementation, are typically associated with partially lithified intraclasts formed by intensified boundary currents during late glacials.

The highest siliciclastic MARs are typically recorded during late interglacial and early glacials in addition to some of the glacial to interglacial transitions. The observed siliciclastic accumulations are controlled primarily by eustatic sea level, highest during early sea level regression, with additional influences from local and regional variations in physiography, climate, and/or ocean currents.