Late glacial and Holocene history of the Penobscot River in the Penobscot Lowland, Maine
When the Laurentide ice sheet retreated rapidly (~150 m/a) across the Penobscot Lowland between ~16 and ~15 ka, the area was isostatically depressed and became inundated by the sea. Silt and clay were deposited, but no significant moraines or deltas were formed. The Penobscot River was reborn at ~14...
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ftunivnebraskali:oai:digitalcommons.unl.edu:conservationsurvey-1008 2023-11-12T04:18:51+01:00 Late glacial and Holocene history of the Penobscot River in the Penobscot Lowland, Maine Hooke, Roger LeB. Hanson, Paul R. Belknap, Danile F. Kelley, Alice R. 2016-01-01T08:00:00Z application/pdf https://digitalcommons.unl.edu/conservationsurvey/8 https://digitalcommons.unl.edu/context/conservationsurvey/article/1008/viewcontent/Hanson_HOLOCENE_2016_Late_glacial__DC_VERSION.pdf unknown DigitalCommons@University of Nebraska - Lincoln https://digitalcommons.unl.edu/conservationsurvey/8 https://digitalcommons.unl.edu/context/conservationsurvey/article/1008/viewcontent/Hanson_HOLOCENE_2016_Late_glacial__DC_VERSION.pdf Conservation and Survey Division eskers forebulge Holocene climate Maine Penobscot River terraces Earth Sciences Geology Geomorphology Hydrology Paleontology Physical Sciences and Mathematics Sedimentology Soil Science Stratigraphy text 2016 ftunivnebraskali 2023-10-30T11:30:33Z When the Laurentide ice sheet retreated rapidly (~150 m/a) across the Penobscot Lowland between ~16 and ~15 ka, the area was isostatically depressed and became inundated by the sea. Silt and clay were deposited, but no significant moraines or deltas were formed. The Penobscot River was reborn at ~14 ka when ice retreated onto land in the upper reaches of the river’s East Branch. As isostatic rebound exceeded sea level rise from melting ice, the river extended itself southward. Between ~13.4 and 12.8 ka, it established a course across marine clay and underlying glacial till in the Lowland. Its gradient was low as differential rebound had not begun. Discharge, however, was higher and the river transported and deposited outwash gravel. During the cold, dry Younger Dryas, ~11 ka, eolian sand began to accumulate in dunes in the Lowland. Some of this sand, along with fluvial sediment from the headwaters, was redistributed into terraces along gentler stretches of the river and into a paleodelta in Penobscot Bay. Eolian activity continued to ~8 ka and aggradation in terraces until ~6 ka. The climate became wetter and warmer after ~6 ka, the dunes were stabilized by vegetation, the river began to downcut, and braiding became less intense. Pauses in the downcutting are reflected in discontinuous strath terraces. In due course, the river reencountered the old outwash gravels, marine clay, glacial till, and, in a few places, bedrock. Its profile is now stepped, with gentle, gravel-bedded reaches between bedrock ribs that form rapids. Text Ice Sheet University of Nebraska-Lincoln: DigitalCommons@UNL |
institution |
Open Polar |
collection |
University of Nebraska-Lincoln: DigitalCommons@UNL |
op_collection_id |
ftunivnebraskali |
language |
unknown |
topic |
eskers forebulge Holocene climate Maine Penobscot River terraces Earth Sciences Geology Geomorphology Hydrology Paleontology Physical Sciences and Mathematics Sedimentology Soil Science Stratigraphy |
spellingShingle |
eskers forebulge Holocene climate Maine Penobscot River terraces Earth Sciences Geology Geomorphology Hydrology Paleontology Physical Sciences and Mathematics Sedimentology Soil Science Stratigraphy Hooke, Roger LeB. Hanson, Paul R. Belknap, Danile F. Kelley, Alice R. Late glacial and Holocene history of the Penobscot River in the Penobscot Lowland, Maine |
topic_facet |
eskers forebulge Holocene climate Maine Penobscot River terraces Earth Sciences Geology Geomorphology Hydrology Paleontology Physical Sciences and Mathematics Sedimentology Soil Science Stratigraphy |
description |
When the Laurentide ice sheet retreated rapidly (~150 m/a) across the Penobscot Lowland between ~16 and ~15 ka, the area was isostatically depressed and became inundated by the sea. Silt and clay were deposited, but no significant moraines or deltas were formed. The Penobscot River was reborn at ~14 ka when ice retreated onto land in the upper reaches of the river’s East Branch. As isostatic rebound exceeded sea level rise from melting ice, the river extended itself southward. Between ~13.4 and 12.8 ka, it established a course across marine clay and underlying glacial till in the Lowland. Its gradient was low as differential rebound had not begun. Discharge, however, was higher and the river transported and deposited outwash gravel. During the cold, dry Younger Dryas, ~11 ka, eolian sand began to accumulate in dunes in the Lowland. Some of this sand, along with fluvial sediment from the headwaters, was redistributed into terraces along gentler stretches of the river and into a paleodelta in Penobscot Bay. Eolian activity continued to ~8 ka and aggradation in terraces until ~6 ka. The climate became wetter and warmer after ~6 ka, the dunes were stabilized by vegetation, the river began to downcut, and braiding became less intense. Pauses in the downcutting are reflected in discontinuous strath terraces. In due course, the river reencountered the old outwash gravels, marine clay, glacial till, and, in a few places, bedrock. Its profile is now stepped, with gentle, gravel-bedded reaches between bedrock ribs that form rapids. |
format |
Text |
author |
Hooke, Roger LeB. Hanson, Paul R. Belknap, Danile F. Kelley, Alice R. |
author_facet |
Hooke, Roger LeB. Hanson, Paul R. Belknap, Danile F. Kelley, Alice R. |
author_sort |
Hooke, Roger LeB. |
title |
Late glacial and Holocene history of the Penobscot River in the Penobscot Lowland, Maine |
title_short |
Late glacial and Holocene history of the Penobscot River in the Penobscot Lowland, Maine |
title_full |
Late glacial and Holocene history of the Penobscot River in the Penobscot Lowland, Maine |
title_fullStr |
Late glacial and Holocene history of the Penobscot River in the Penobscot Lowland, Maine |
title_full_unstemmed |
Late glacial and Holocene history of the Penobscot River in the Penobscot Lowland, Maine |
title_sort |
late glacial and holocene history of the penobscot river in the penobscot lowland, maine |
publisher |
DigitalCommons@University of Nebraska - Lincoln |
publishDate |
2016 |
url |
https://digitalcommons.unl.edu/conservationsurvey/8 https://digitalcommons.unl.edu/context/conservationsurvey/article/1008/viewcontent/Hanson_HOLOCENE_2016_Late_glacial__DC_VERSION.pdf |
genre |
Ice Sheet |
genre_facet |
Ice Sheet |
op_source |
Conservation and Survey Division |
op_relation |
https://digitalcommons.unl.edu/conservationsurvey/8 https://digitalcommons.unl.edu/context/conservationsurvey/article/1008/viewcontent/Hanson_HOLOCENE_2016_Late_glacial__DC_VERSION.pdf |
_version_ |
1782335392371965952 |