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NARROW
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all geography including DSDP/ODP Sites and Legs
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Canada (1)
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Maine
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Changing paradigms of surficial geology in Maine: From the biblical flood to glaciation
Stratigraphy, paleoceanography, chronology, and environment during deglaciation of eastern Maine
The major deglacial-phase deposits of eastern Maine include stratified end moraines, single and amalgamated ice-margin delta complexes, extensive segmented esker systems that link with marine deltas and fans, and a fossiliferous glacial marine mud (the Presumpscot Formation) that is interbedded with, or drapes, the other deposits. Previous work has determined that deposition within the 40-km-wide swath, which is now the modern coastal zone, occurred between 13,500 and 12,500 B.P. Detailed mapping, measurement of stratigraphic sections and paleocurrents, and calculation of drainage basin area and volume of sediment bodies have led to a better understanding of lithofacies assemblages, depositional processes, sediment sources, and regional geometry of these deposits. The “stratified end moraines,” better described as assemblages of marine fans, measure as much as 15 m high, 100 m wide, and 16 km in length, and were deposited along ice lobe fronts. Proximal vertical sequences are dominated by 15- to 30-cm-thick beds of poorly sorted, pebble-to-cobble gravel locally interbedded with gravelly diamict. Well-sorted, matrix-less (“open-work”) pebble/cobble gravel occurs in channel forms that can be traced tens of meters laterally. Distal sequences consist of laminated beds of medium-to-fine sand capped by silt drapes; climbing ripple cross-stratification is uncommon, and some diamict beds are present. Lithofacies of the delta front, prodelta, and esker core (ice-tunnel deposits) are remarkably similar to those of the fans, differing only in greater degree of dip (deltas), and clast size (ice-tunnel deposits). Paleocurrents of fans show a large dispersion, in some instances indicating flow parallel to the inferred ice margin; proximal beds are deformed, indicating an active ice margin. The ice-margin fan and delta complexes have a combined area of 250 km 2 and total volume of nearly 5 billion m 3 , which strongly suggests that the 2,400-km-long ice-tunnel system (including tributaries) was active along its entire length in order to supply needed sediment. Ice-tunnel deposits filled the distal ends of tunnels as the active ice margin retreated. The geometry and volume of deltas, fans, and ice-tunnel deposits, together with the time constraints, indicate deposition into marine waters at the margin of a complex, multi-lobate, grounded, warm-based ice sheet.
Late Quaternary Sea-Level Changes in Maine
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.
The environmental setting for human colonization of northern New England and adjacent Canada in Late Pleistocene time
Human inhabitants encountered a series of changing environments at the end of the most recent ice age in northern New England. We present our current understanding of the context of colonization of this area by a diversity of human groups some time between 13,000 B.P. and 11,000 B.P., based on archeological evidence and on geological and biological evidence synthesized by Davis and Jacobson (1985). As the Champlain Sea separated the main body of Laurentide ice from the ice cover of northern New England and the Canadian Maritimes about 13,000 B.P., plants and animals began to invade land surfaces exposed by the dissipating ice sheet. Over a few thousand years, the vegetation changed from tundra to woodland to closed forest. There is little direct paleontological evidence for the fauna that lived in those late-glacial ecosystems, but human artifacts from several sites indicate that large mammals were probably hunted prior to the late-Pleistocene extinction of megafauna. We suggest that a shift to greater reliance on caribou hunting would have followed the extinctions. We present a speculative model of how humans adapted to the changing environments and food sources during that dynamic period.
Crustal warping in coastal Maine
Quaternary glaciation, west-central Maine
Late Quaternary Marine Invasion in Maine: Its Chronology and Associated Crustal Movement
Late Wisconsin Fluctuations of the Laurentide Ice Sheet in Southern and Eastern New England
The age of the late Wisconsin maximum of the Laurentide ice sheet off the coast of New England and on Long Island, New York, is not closely designated. Radiocarbon and stratigraphic evidence from Martha’s Vineyard suggests that the glacier margin may have been close to its maximum position as late as 15,300 yrs ago; indirect evidence from Long Island infers that the ice sheet had reached a maximum and had begun to recede prior to 17,000 yrs ago. In any case, by at least 14,200 yrs ago the glacier margin had retreated from its maximum late Wisconsin position at the Ronkonkoma Moraine on Long Island, had constructed recessional frontal deposits, and had retreated north of Rogers Lake on the southern Connecticut coast. Subsequent readvances culminated near Middletown, Connecticut, some time after 15,000 yrs ago, and in Cambridge, Massachusetts, after 14,000 yrs ago. Whether these readvances were synchronous is unknown because of the absence of close limiting dates and because of the lack of evidence for readvance in the intervening area. The northwestward recession of the glacier margin from the present coast in eastern Maine was accompanied by a marine transgression and deposition of hundreds of submarine moraines between 13,500 and 12,500 yrs ago. This general recession was interrupted by a readvance which culminated at the Pineo Ridge Moraine approximately 12,700 yrs ago. Although it may have resulted from general climatic change, the Pineo Ridge readvance just as likely may have been caused by a vastly decreased calving rate associated with isostatic uplift and marine recession from coastal Maine. This is well documented as having occurred simultaneously with the Pineo Ridge readvance. Thereafter, the ice sheet thinned and separated over the highlands of northwestern Maine leaving residual ice to the southeast. Active ice, receding into the St. Lawrence Valley of southeastern Quebec deposited the Highland Front Moraine approximately 12,700 to 12,600 yrs ago. In summary, (1) a major amelioration of climate that began prior to 14,200 yrs ago resulted in very rapid dissipation of the ice sheet in New England at least by 12,500 yrs ago, with the exception of small glaciers that possibly persisted in the highlands; (2) no conclusive evidence has been recognized for any climatic reversals during the dissipation of the ice sheet in New England; and (3) although major events in New England compare with those of the Great Lakes region, no minor events have proven correlation with the possible exception of the Pineo Ridge and Port Huron readvances.