Till stratigraphy in New Hampshire: Correlations with adjacent New England and Quebec

Abstract

Although two physically distinct tills of different ages have long been recognized in southern New England, only in the past decade or so has the existence of a similar two-till stratigraphy been recognized in New Hampshire. In southern New England, distinction between the two tills, a lower one and an upper one, initially was based on differences in texture and weathering: the lower compact till has a siltier matrix and an oxidation zone of 10 or more meters; the upper till has a much sandier matrix and an oxidation zone only in the uppermost 1 m. Later, identification of structural features at the contact between the two tills helped to distinguish them. The same stratigraphic relationships are now recognized in all parts of New Hampshire. Excellent exposures at Nash Stream in northern New Hampshire have provided the most complete inland till stratigraphy to date in New England. The tills exposed here are called the Nash Stream (lower) Till and Stratford Mountain (upper) Till; associated deglacial outwash has also been recognized for each of them. The Nash Stream Till is nonoxidized where it is covered by its associated outwash and is oxidized to a depth of 6 to 7 m where it is exposed at the surface. This suggests that a significantly long weathering interval took place before the last ice sheet deposited the Stratford Mountain Till and its associated outwash. The Nash Stream Till, here correlated with the lower till of southern and central New England, may be an early Wisconsinan correlative of the New Sharon Till in Maine and perhaps of the Johnville Till in southeastern Quebec and the Becancour Till in the St. Lawrence Lowland, or it may be even older. The Stratford Mountain Till, of late Wisconsinan Age, is correlated with the surface till throughout New England, and with the Lennoxville Till in Quebec and with at least the upper part of the Gentilly Till in the St. Lawrence Lowland. No middle Wisconsinan units have so far been recognized in New Hampshire and southern New England.