Monday, 27 August 2007
1.PS-25
Authigenic clay minerals in rock matrices and fractures from CRP-2 and CRP-3 cores (Antarctica)
Giovanna Giorgetti, Department of Earth Sciences, Università di Siena, via Laterina 8, Siena, Italy, Terry J. Wilson, School of Earth Sciences, Ohio State University, 125 S. Oval Mall, Columbus, OH 43210-1522, Cristina Millan, Ohio State Univeristy, Columbus, OH 43081, and Fulvia Aghib, Istituto per le Dinamiche dei Processi Ambientali, CNR, via mangiagalli 34, Milano, Italy.
Authigenic clay minerals have been identified through a scanning and transmission electron microscopy study in Oligocene sediments from CRP-2 and CRP-3 cores and in Devonian sandstones and in Jurassic dolerites in CRP-3 core (Ross Sea, Antarctica). Authigenic clay minerals in rock matrices and faults/veins in the Oligocene sediments in both cores consist mostly of dioctahedral smectites, rarely of berthierine/chlorite intergrowths, and illite. Al, K-rich smectites and kaolinite occur in the Devonian sandstones; trioctahedral smectites, berthierine/chlorite intergrowths, and Fe-hydroxides develop in the altered dolerites. These data indicate that the composition of the secondary phases depends on the geochemistry of the rock they grow in. Within each sample, the same authigenic minerals form in the matrix and in the vein/fault. Textures indicate that clays precipitated from fluids which circulated in the system during contemporaneous diagenetic and faulting events that affected the sedimentary sequences recovered in CRP-2 and -3 cores.