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Seismic stratigraphy of glacial marine units, Maine inner shelf

By
Daniel F. Belknap
Daniel F. Belknap
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R. Craig Shipp
R. Craig Shipp
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Published:
January 01, 1991

Glacial marine sedimentation dominated the inner shelf and coastal lowlands of Maine between ca. 14,000 and 11,000 B.P. Three major seismic facies interpreted as glacial marine deposits beneath the inner shelf are identified by recent high-resolution seismic reflection profiling. These are: (1) GM-M, massive glacial marine sediment, a uniform, draping blanket with abundant ice-rafted detritus, either mud or diamicton; (2) GM-D, conformable glacial marine mud, with a distinct draping geometry, usually well stratified; and (3) GM-P, less well-stratified glacial marine mud with a distinctly ponded, variable geometry. These glacial marine facies are associated with underlying seismic facies interpreted as till, stratified drift and bedrock, and overlying seismic facies interpreted as Holocene littoral and marine facies. The glacial marine facies are contained within one of two seismic stratigraphic sequences, which record rapidly changing sea levels and sedimentary environments. Sequence G is composed of till, stratified drift, and glacial marine mud. It records the deglaciation of the northern Gulf of Maine and Maine coast. It is overlain by a distinct unconformity above the −60-m sea-level lowstand, which grades to a conformity in deeper basins, further overlain by seismic sequence H.

A critical issue concerning deglaciation of the area is identification of deglacial environments. A working hypothesis is that the initial deglaciation, ca. 18,000 to 14,000 B.P., was through a series of small, topographically buttressed, warm-based ice shelves, which were abundantly productive of poorly sorted sediment. These shelves may have formed and disintegrated in a sequential stepwise fashion, temporarily grounding on highs north of the major basins in the Gulf of Maine. After about 14,000 B.P., the ice front was a calving embayment, producing ice-rafted detritus, turbid suspensions, and subaqueous outwash. After 12,500 B.P., the ice margin was terrestrial, feeding melt-water streams and producing little ice-rafted detritus. The Maine inner shelf preserves this sequence in shelf valleys. Elsewhere, erosion during local relative sea-level changes has stripped bedrock highs of the majority of sediments, between the −60-m isobath and the inland marine limit (60- to 132-m elevation).

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Contents

GSA Special Papers

Glacial marine sedimentation; Paleoclimatic significance

John B. Anderson
John B. Anderson
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Gail M. Ashley
Gail M. Ashley
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Geological Society of America
Volume
261
ISBN print:
9780813722610
Publication date:
January 01, 1991

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