Potential for stratigraphic folding near ice-sheet centers

Abstract

Lack of agreement between the deep portions of the Greenland Icecore Project (GRIP) and Greenland Ice Sheet Project II (GISP2) ice cores from central Greenland suggests that folds may disrupt annual laycring, even near ice divides. We use a simple kinematic flow model to delincate regions where slope disturbances ("wrinkles") introduced into the layering could overturn into recumbent folds, and where they would flatten, leaving the stratigraphic record intact. Wrinkles are likely to originate from flow disturbances caused internally by inhomogencities and anisotropy in the ice rheological properties, rather than from residual surface structures (sastrugi), or from open folds associated with transient flow over bed topography. If wrinkles are preferentially created in anisotropic ice under divides, where the resolved shear stress in the easy-glide direction can be weak and variable, then the deep intact climate record at Dye 3 may result from its greater distance from the divide. Alternatively, the larger simple shear at Dye 3 may rapidly overturn wrinkles, so that they are not recognizable as folds. The ice-core records from Siple Dome may be intact over a greater fraction of its depth compared to the central Greenland records if its flat bedrock precludes fluctuations in the stress orientation near the divide.