RECONSTRUCTING THE HISTORY OF CARIBBEAN CARBONATE CRASHES DURING THE LATE MIOCENE (9.5- 12 MA): ODP LEG 165 SITE 1000A CARIBBEAN BASIN

Two dissolution proxy records [foraminiferal benthic/ planktonic (B/P) ratios and sand percent] developed from ODP Site 1000 identified long-term increase and decrease in dissolution in the Caribbean Basin between 11.8 and 10.8 Ma as well as a strong short (100 kyr) eccentricity signal superimposed over these trends. Site 1000 is located in the Pedro Channel, Caribbean Basin, at a water depth of 927 m. Approximately 90% of the sand percent and ~50% completed for the B/P ratios have been completed for the high-resolution (4 kyr) records being constructed between 12.0 and 9.5 Ma. The Sand % was obtained by comparing the weights of before and after washing the sample through a 63μm sieve. The B/P ratio was determined based on the count of 300 representative foraminifera per sample.

A comparison of the data shows a good correlation between the two proxies - low sand percent values align well with the high B/P ratios and are interpreted to represent higher dissolution rates. Previous lower resolution studies indicate five Caribbean carbonate crashes that occurred between 12.0 and 10.0 Ma. In contrast, our higher-resolution data reveal that major carbonate crashes occur at the short (100 kyr) eccentricity time scales. A long-term increase in dissolution occurs between 11.8 and 11.3 Ma, culminating in a ~200 kyr long dissolution event between 11.3-11.1 Ma, with a gradual decrease afterwards to ~10.8 Ma.

With our higher resolution records, we conclude that the carbonate crashes were controlled by oceanographic changes at the 100-kyr frequency. Dissolution increases may have been caused by influx of North Pacific Intermediate Waters through the Central American Seaway (CAS). The long-term dissolution event at circa 11.2 Ma does not correlate to any global climatic/ oceanic events and therefore we speculate that it may be due to an ephemeral deepening of the CAS.