Postglacial Environments

Sediment cores taken from several bogs between Long Island and the Champlain Valley recorded the northward migration of eastern forests following the shrub-tundra and park tundra zones over deglacial terrain (Sirkin, 1977). In the vicinity of the terminal moraine, spruce forests replaced tundra around 18,000 years ago, as climate changed from very cold to cold and moist. Spruce forests reached the mid-Hudson Valley only 2,000 years after the ice left, the northern Hudson Valley less than 1,000 years after the ice, and the Champlain Valley only a few hundred years later. Between 11,000 and 9,000 years ago, warm and dry conditions favored the succession of pine forests. Spruce species migrated northward and into higher and wetter habitats, while pine colonized the well-drained out-wash and lake plains of the valley. From 9,000 to 7,000 years ago, oak forests associated variously with pine, hemlock, and hickory overtook the pine-dominated forests as climate cooled.

Sea level rose to establish estuarine conditions in the Hudson. Around 12,000 years ago, the sea flooded into the Hudson Valley through a gap eroded into the terminal moraine across Long Island and Staten Island. The post-Lake Albany lakes in the Champlain Valley must have drained between 12,000 and 11,000 years ago. The river was tidal to Peekskill by 12,000 years before present and estuarine conditions reachedManhattan by 10,280. Salt marsh deposits in the Hudson estuary date from around 11,000 years ago (Newman, 1977), about the same time the sea flooded the Champlain and St. Lawrence valleys.

The estuary retreated slightly around 9,000 years ago but by 7,000 years before present estuarine conditions had reached as far north as Nyack. The estuary reached its maximum northern extent at Peekskill about 6,000years ago. It hasbeenreceding since, perhaps due to sedimentation or continued climate change.

0 0

Post a comment