The Influence of Carbonate Platforms on the Global δ13C Values in Carbonate Sediments During the Miocene

It has been shown that Plio-Pleistocene sediments deposited adjacent to Modern carbonate platforms and ramps, such as the Bahamas, Maldives, and Great Barrier Reef, produce records of δ¹³C values unrelated to the global oceanic values as a result of the input of aragonite sediments with relatively positive δ¹³C values. This is particular evident during the past 3 myrs during which the amplitude and frequency of sea level has increased significantly. The question arises as to whether this phenomenon only occurred during Plio-Pleistocene, perhaps only extant during periods of high amplitude sea-level change, or whether such influences also affected earlier times. In order to investigate this we cored a series of sites through Miocene aged sediments in the Maldives archipelago during IODP expedition 359. While all these cores exhibited the phenomenon of increased δ¹³C values during the past 3 myrs, they also appear to show changes remarkably similar patterns of δ¹³C values to these seen in the Monterey event suggesting that older sediments associated with carbonate platforms might track global carbon variations. However, a close comparison of the δ¹³C values with the sedimentary architecture indicates that the apparent correlation with the Monterey Event is probably an artifact. In the Maldives, pulses of isotopically positive sediment are produced during times of relatively high sea level as a result of increase productivity from the shallow water carbonate platforms. While these higher sea levels may also be responsible for an increase burial of organic carbon and therefore linked to the carbon isotopes variations seen in the Monterey (CM1 to CM6), these mechanisms for producing the elevated signals in the oceanic records are different than those in the Maldives. These findings document the influence of platform-derived sediments upon the δ¹³C values of marginal sediments during older time periods than were documented in the Bahamas and further support concern regarding using apparent changes in the records of δ¹³C values of shallow-water sediments to infer information regarding the global carbon cycle.