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Abstract
AbstractA 27 m core collected on the sea floor near Juan de Nova island at 1,909 m depth in the SW Indian Ocean preserves a high‐resolution record of carbonate sediment export to the deep sea over the past 1 Myr. Core chronology was established using calcareous nannofossil biostratigraphy and benthic foraminiferal δ18O. Throughout the core, preserved highstand intervals (MIS 1, 5, 7, 9, 11, 13, 15, 23 and 25) are marked by an increase in the aragonite content within the sediment. Aragonite is likely sourced from the nearby Juan de Nova carbonate platform ca 10 km to the south, and is interpreted as resulting from flooding of the platform top. Platform inundation allows carbonate muds to be winnowed from their original shallow‐water environment of deposition, suspended in the water column, and redeposited onto the proximal slopes and within the basin. Sharp increases in aragonite content at the beginning of each highstand interval can be used to estimate the approximate sea‐level range when platform flooding occurred; results show that the depth of the platform top has likely changed little over the past 1 Myr due to balanced aggradation and subsidence. Previously hypothesized large‐scale aragonite dissolution cycles are evidenced by a disproportionally low aragonite increase during MIS 11. This study provides a new, exceptionally long record of highstand shedding, expanding the known occurrences of the process to the southern Indian Ocean and supporting its importance as a globally significant depositional mechanism that impacts deep‐sea stratigraphic records.
Highlights
Unlike terrigenous sediments, carbonates are usually exported to the deep sea in greater abundance during periods of relatively high sea‐level
The relationship described here between aragonite content, accumulation rate and past sea‐level change is consistent with the depositional mechanism of highstand shedding, where carbonate sediments are exported off of flat‐topped platforms and into the deep sea during times when the platform is inundated by sea water (Schlager et al, 1994)
Deep‐sea sediments from a 27 m piston core near Juan de Nova island are characterized by cyclical variations in aragonite content that correspond to Late Quaternary glacial– interglacial episodes
Summary
Carbonates are usually exported to the deep sea in greater abundance during periods of relatively high sea‐level. Carbonate content in sediments adjacent to flat‐topped platforms has often been seen to increase and decrease proportionally with sea‐level change (Chabaud et al, 2016; Paul, Reijmer, Fürstenau, Kinkel, & Betzler, 2012; Reymer, Schlager, & Droxler, 1988), reflecting the production and export of carbonate. This study provides a new, high‐resolution example of the highstand shedding concept, validating it as a primary control on sedimentary character and sedimentation rate in this undocumented region of the deep‐sea area near carbonate platforms
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