GRAIN-SCALE PROCESSES, FOLDING, AND STRATIGRAPHIC DISTURBANCE IN THE GISP2 ICE CORE

Flow disturbances have been shown to alter stratigraphic order in the lower part of the ice sheet in central Greenland. Vertical thin sectio ns of the Greenland Ice Sheet Project 2 ice core show that in the lowe r 30%, the expected c axis-vertical fabric is interrupted by planes of grains (''stripes'') with c axes oriented approximately in the dip di rections of the planes. Stripe-parallel shear produces small-scale fol ds. The stripes can be explained qualitatively by a simple nucleation- and-growth model based on the strong anisotropy of ice-crystal deforma tion. Nucleation probably is sensitive to spatially variable rates of polygonization, producing spatially variable stripe densities. Stripes are modeled to affect the ice viscosity, so variations in stripe dens ity may contribute to viscosity contrasts that might produce larger de formational features and loss of stratigraphic order.