MARINE HIGH MG CALCITE CEMENTS IN TEREDOLITES-BORED FOSSIL WOOD - EVIDENCE FOR COOL PALEOCLIMATES IN THE EOCENE LA-MESETA FORMATION, SEYMOUR-ISLAND, ANTARCTICA

The Eocene La Meseta Formation on Seymour Island, Antarctica, contains a diverse and abundant invertebrate and vertebrate fauna and as such, is of key paleontological importance. Associated with this marine fau na is abundant angiosperm and conifer fossil wood, which commonly cont ains Teredolites borings. These borings are either infilled by elastic sediment, forming geopetal structures, or by calcite cements. The cem ents usually comprise two generations of radial-fibrous high-Mg calcit e, post-dated by equant sparry calcite. The radial-fibrous cement is l argely non-luminescent, non-ferroan calcite. However, within individua l generations of radial-fibrous calcite there is a transition from non -ferroan non-luminescent to ferroan, orange-luminescent calcite at the margins of the fringing cement. These radial-fibrous cements have del ta(18)O values of between -0.28 and 1.9 parts per thousand VPDB, delta (13)C values of 1.72 to -42.59 parts per thousand, and Mg (ppm) values of between 18360 and 26735. On the basis of cement-fabric, stable iso tope, and trace element data, these cements are interpreted as having precipitated from marine pore waters with total dissolved carbon deriv ed from both methane oxidation and an inorganic marine carbon source. As HMC cements are diagenetically unstable, the preservation of these cements is remarkable, and (m)ust reflect very limited post sea-floor diagenesis. In addition, the cement oxygen isotope data are consistent with previous results for molluscs from the La Meseta Formation. Thes e wood cements retain a primary environmental geochemical signature wi th precipitation from cold marine pore waters at or near the sediment- water interface A cool-to cool-temperate climate is indicated for the lower late early to Early middle Eocene part of the La Meseta Formatio n. These data support the view that Antarctic climates deteriorated si gnificantly by tate early to early middle Eocene times.