A CONTRARIAN VIEW OF THE VALLEY HEADS READVANCE

The general understanding of the Valley Heads (VH) “event” is that it was a large-scale re-advance that deposited a thick, valley choking deposit of water-lain drift and by some to have caused significant bedrock erosion. Closer examination of this system in the Cayuga basin demonstrated that many of these characteristics are incorrect and others misleading, at least in that area. Deposits attributed to the VH in Cayuga Inlet Valley consist of a thin, clast-poor till that represents the VH advance. This till is overlain by kame clastics, usually also thin, which represent subsequent ice stagnation. The thick Quaternary fill in that valley consists of an Erie Interstade lacustrine sequence and older deposits of unknown age. The great bulk of VH deposits consist of outwash and valley train clastics south of the kettle-kame terranes; upland till is thin to absent. Only in the distal parts of the VH’s do the deposits become thicker, due to oscillations of the ice front. Data from the Cayuga Trough indicate that the preceding Erie Interstade retreat was only to the vicinity of Ithaca and that the VH re-advance was only a few 10’s of km, which was initially to a position several km south of the generally accepted VH front, defined more by outwash heads than by end moraines. The ice front oscillated about this position followed by a period of stagnation with minor halts or re-advances. This stagnation-generated kettle/kame terrane lasted over much of a millennium and should not be included in the definition of the VH. Subsequent retreat produced many moraines north of Ithaca during the Mackinaw Interstade. The terms inner and outer VH are not useful. Lidar over the area east of Lake Cayuga reveals a field of drumlins in the north, transitioning to megaflutes southward almost to the VH front. In the Fall Creek valley megaflutes are overprinted by crevasse squeeze moraines and several eskers. This pattern, together with the other characteristics of the VH’s strongly suggest that it was basically the result of a water-driven surge, followed by a period dominated by stagnation. This conclusion is becoming more widely accepted and is hardly contrarian. The VH re-advance is barely recognizable in Greenland ice cores (Rasmussen et al., 2014) as a climatic event and is more likely a result of internal ice sheet dynamics.