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 fauna is abundant angiosperm and conifer fossil wood, which commonly contains Teredolites borings. These borings are either infilled by elastic sediment, forming geopetal structures, or by calcite cements. The cements usually comprise two generations of radial-fibrous high-Mg calcite, post-dated by equant sparry calcite. The radial-fibrous cement is largely non-luminescent, non-ferroan calcite. However, within individual 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 delta(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 isotope, and trace element data, these cements are interpreted as having precipitated from marine pore waters with total dissolved carbon derived 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. These wood cements retain a primary environmental geochemical signature with 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 Formation. These data support the view that Antarctic climates deteriorated significantly by tate early to early middle Eocene times.