Late Quaternary Upwarpings of Northeastern North America

Abstract

The crustal upwarpings upon decrease and removal of the load of the last Labradoran ice sheet appear to have occurred spasmodically and intermittently during ages of several hundred to a few thousand years' duration, separated by somewhat longer ages of quiescence. The most important uplifts took place prior to, and during, the first stages of the glacial lakes Algonquin and Iroquois, during the Champlain Sea age, and during the early and the late Postglacial. With the exception of that during the Nipissing age, the long quiescences were caused by increase of the ice or by a balance between supply and wastage; and, when established, they prevailed until the accumulating stresses had increased to the yielding point. The most important quiescences were those during the deglaciation of New England (perhaps regionally equal uplift); during the three-outlet stage of Lake Algonquin, Lake Iroquois proper, and Lakes Vermont and Frontenac; during the Ottawa Sea (possibly some land sinking); and during the Nipissing Great Lakes. Even with quiescence during the uncovering of New England, the contemporaneous retreat of the shoreline, indicated by the weak development of all elevated marine shorelines, can have been produced by a lowering of the sea-level, for the Patrician, Keewatin, and Cordilleran ice sheets were still growing. The Algonquin and the Nipissing quiescences are well proved by exceptionally strong beaches connecting respectively three and two outlets. The Ottawa Sea, whose shore stands at 240 feet altitude at Ottawa, is now believed to be the water body in which the upper marine clay of that region was deposited. The stage was established by a transgression of about 50 feet, produced by rise of the sea-level during quiescence and possibly some sinking of the land. The Ottawa Sea climaxed during the transition from the late Glacial to the Postglacial. The upwarpings appear to have proceeded in accord with R. A. Daly's hypothesis of flow at great depth.