Stylolites: characteristics and origin

Stylolites are alternating interpenetrating columns of stone that form irregular interlocking partings or sutures in rock strata. They are most common along bedding planes of limestone but some are oblique or even perpendicular to bedding . Although the vast majority of stylolites occur in calcareous rocks, stylolites have been found in sandstone, quartzite and gypsum. The word "stylolite" refers to each individual column of stone. Across section of a group of stylolites parallel to their length presents a rough, jagged line called a "stylolite seam" that resembles the sutures of a human skull. Stylolites always have a dark colored "clay" cap at the ends of the columns. The sides of the columns are typically discolored with a thin film of clay and show parallel flutings or striations that parallel their length. The shapes of individual stylolites vary greatly from broad flat-topped columns to pointed, jagged and tapering forms. After much controversy concerning the origin of stylolites, it is generally believed that they form by a process of chemical solution under pressure in lithified rock along some crack or seam. The interteething is produced because of differential solubilities and pressures within the rock unit. The clay cap on the stylolites is the non-soluble residue of the dissolved rock. Stylolites are only one of the possible end products in the spectrum of limestone responses to stress. They form in limestone units that have structural resistance to stress and contain relatively little clay or silt. Stylolites may play a major role in initiating or preserving oil accumulations in limestone. Where they are formed due to tectonic compression, stylolites may be useful in providing information on paleo-stress patterns.No embarg

Comparable rest-related promotion of spatial memory consolidation in younger and older adults

Flexible spatial navigation depends on cognitive mapping, a function that declines with increasing age. In young adults, a brief period of postnavigation rest promotes the consolidation and integration of spatial memories into accurate cognitive maps. We examined (1) whether rest promotes spatial memory consolidation and integration in older adults; and (2) whether the magnitude of the rest benefit changes with increasing age. Young and older adults learned a route through a virtual environment, followed by a 10-minute delay comprising either wakeful rest or a perceptual task, and a subsequent cognitive mapping task, requiring the pointing to landmarks from different locations. Pointing accuracy was lower in the older than younger adults. However, there was a comparable rest-related enhancement in pointing accuracy in the 2 age groups. Together our findings suggest that (1) the age-related decline in cognitive mapping cannot be explained by increased consolidation interference in older adults; and (2) as we grow older, rest continues to support the consolidation and integration of spatial memories

Formulation and test of a model of positional distortion fields. Third International Symposium on Spatial Accuracy Assessment in Natural Resources and Environmental Sciences, Quebec City [document available at www.ncgia.ucsb.edu/vital

BSTRACT A simple model of positional distortion in vector databases is presented in which positions are distorted by the addition of a vector field. Given two data sets it is possible to observe values of the field at sample points, and to build a complete model by interpolation. We argue that discontinuities in the distortion field are common, though not observed in the absence of features that cross them. A piecewise-constant model is proposed. A variogram is constructed based on distortion directions, using a novel measure, and calibrated using a novel clustering technique based on the properties of the angular variogram.