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Book Chapter

Response To Deglaciation

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Published:
January 01, 1987

Abstract:

On the Maine coast, evidence of local relative sea level 12.5 ka is now exposed 60-80 m above present sea level. At that time, eustatic sea level was at least 70 m below present in most parts of the world. The difference is due to isostatic depression of the Maine coast by the weight of glacial ice. During deglaciation, the sea advanced inland in contact with the retreating margin of the marine-based ice sheet. Due to isostatic rebound and the contours of the land, the ice sheet grounded as much as 150 km inland of the present coast, glaciomarine deltas formed, and the transgression reached a stillstand at what is termed the upper marine limit. Due to differential tilting during rebound, this marine limit is now over 132 m in elevation at its farthest inlet extent. As rebound became dominant, sea level reached to 65 m below present at about 9.5 ka. At that time rebound slowed to about the same rate as that of eustatic sea-level rise. Shorelines were cut and deltas were formed at this lower marine stillstand position. Subsequently, eustatic rise became the predominant mode. Radiocarbon dates on fossil marine mollusks provide timing for this onlap and offlap.

From 7.0 ka to the present, radiocarbon dates on wood and salt marsh peats provide a relatively precise sea-level curve. During the period 4.2--1.5 ka, sea level rose at 1.22 m/1,000 yrs. Before that period, it may have risen more than twice as fast. After 1.5 ka, it slowed to half the mid-late Holocene rate. Recent tide-gauge records show an acceleration in rate to 2--3 mm/yr for the past 40 yrs. Releveling, tide gauges, and other evidence (Anderson and others, 1984) suggest that the coast is being warped downward to the east, possibly due to non-glacially induced neotectonics.

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SEPM Special Publication

Sea-Level Fluctuation and Coastal Evolution

Dag Nummedal
Dag Nummedal
Department of Geology and Geophysics Louisiana State University, Baton Rouge, Louisiana
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Orrin H. Pilkey
Orrin H. Pilkey
Department of Geology Duke University, Durham, North Carolina
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James D. Howard
James D. Howard
Skidaway Institute of Oceanography Savannah, Georgia
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SEPM Society for Sedimentary Geology
Volume
41
ISBN electronic:
9781565760950
Publication date:
January 01, 1987

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