EVALUATING THE CARIBBEAN CARBONATE CRASHES LEADING UP TO THE MIDDLE MIOCENE CLIMATIC TRANSITION (9.5 -13.8 MA): DISSOLUTION PROXY RECORDS FROM ODP LEG 165 CARIBBEAN BASIN SITE 1000

Dissolution proxy records developed from ODP Site 1000 identified high frequency (i.e., Milankovitch time scales) to a longer-term (e.g., at the million year time scales) paleoceaonographic changes in the Western Caribbean Basin leading into the Middle Miocene Climatic Transition (13.8 and 9.5 Ma). The two dissolution proxy records developed from ODP Site 1000 included: percent sand size fraction, and benthic/ planktonic (B/P) forminifera ratios. A total of 670 samples were used to develop a high ~ 4 kyr resolution in the upper section (9.5 Ma-12.0 Ma) and a lower ~14 kyr resolution in the lower section of the record ranging between 12.0 Ma and 13.8 Ma. Site 1000 is located in the Pedro Channel, Caribbean Basin, at a water depth of 927 m, making it an ideal location to evaluate the Carbonate crashes previously identified in this region during the Late Miocene at a higher resolution. The B/P ratios was determined based on a count of 300 total forminifera specimens per sample. The percent sand size fraction was found by comparing the weights of the sample before washing in a solution and after washing the sample through a 63µm sieve.

A good correlation between the two data sets exists suggesting that they are robust proxies for evaluating oceanographic changes. Due to lower productivity and higher dissolution the percent sand size fraction shows more foraminifers and less nanofossils. The upper section does not show the percent sand size fraction going above 30% until 13.8 Ma where it goes to 40% as it goes to the Middle Miocene Climatic Transition.

The dissolution events seem to be tied to long-term climatic oceanographic signals at the Milankovitch timescales, and not due to tectonic changes. The trends in the data show a good correlation between the longer-term 1.2myr obliquity, the 400 kyr eccentricity and the 100 kyr eccentricity cycles. The trends seen in the data could be the result from a change in bottom water masses. The carbonate crashes could be due to more corrosive Antarctic intermediate waters entering into the Caribbean Basin from the south.