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TitleMorphology and seismic stratigraphy of the inner continental shelf off Nova Scotia, Canada: evidence for a -65 m lowstand between 11,650 and 11,250 C14 yr B.P.
AuthorStea, R R; Boyd, R; Fader, G B J; Courtney, R C; Scott, D B; Pecore, S S
SourceMarine Geology vol. 117, (1994), 1994 p. 135-154,
Alt SeriesNova Scotia Department of Natural Resources, Mines and Energy Branches, Contribution Series 94-002
Alt SeriesGeological Survey of Canada, Contribution Series 32193
PublisherElsevier BV
MapsPublication contains 4 maps
Map Info.location, seismic lines location, 1:2,000,000
Map Info.geophysical, seismic, marine, 1:167,000
Mediapaper; on-line; digital
File formatpdf
ProvinceEastern offshore region
AreaScotian Shelf
Subjectsgeophysics; marine geology; bathymetry; continental shelf; seismic interpretations; sea level changes; seismic surveys, marine; glacial deposits; moraines; erosion; deltas; drillholes; Scotian Shelf Drift; Emerald Silt; LaHave Clay; Sambro Delta; sonar surveys, marine; multibeam bathymetry; seismic stratigraphy; Quaternary
Illustrationsmultibeam images; seismic profiles; graphs; cross-sections
AbstractNova Scotia's position near the margin of large Pleistocene ice sheets makes the Scotian Shelf region critical for evaluation of glaciation models and sea-level change. The sea floor of the inner Scotian Shelf was mapped using multibeam bathymetry, a combination of conventional seismic and sonar techniques, and sampling. Multibeam bathymetry provides an areal image of the sea floor. Combining this unique image with sub-bottom seismic imaging, the relationships between sea floor topography and the underlying strata were explored. The inner continental shelf of Nova Scotia can be subdivided into five major terrain "zones". These are the: (1) Truncation Zone, (2) Morainal Zone, (3) Outcrop Zone, (4) Basin Zone and (5) Scotian Shelf End-Moraine Complex. The Scotian Shelf End-Moraine Complex and Basin Zone are glacial-depositional zones at the seaward edge of the inner shelf. Landward of these zones is a region of high relief bedrock, with ridges and valleys largely devoid of surficial sediments extending from 80 to 120 m water depth (Outcrop Zone). This zone is interpreted as a relict bedrock surface, preserved under frozen-bed glacier conditions. To the east of the Outcrop Zone, in similar water depths, are unmodified till ridges overlying bedrock (Morainal Zone). The Truncation Zone is a region of the inner shelf from -90 m to the present shoreline characterized by muted acoustic topography and planar erosional surfaces truncating bedrock and surficial sediments. The Truncation Zone is subdivided into the Valley Subzone, the Transition Subzone, the Platform Subzone and the Estuarine Subzone. The Valley Subzone is typified by sediment-infilled valleys occurring in 75 to 90 m water depths. These valleys contain seismic facies with a ponded style of deposition planed off at the sea floor or by erosional unconformities near the sea floor. The Transition Subzone is marked by a relatively steep "ramp" and terraces. The ramp at the type section extends from 75 to 65 m water depth. The surface of the ramp can be either an erosional unconformity or a depositional surface formed by clinoform beds. The -65 m former shoreline is interpreted as the top of the Transition Subzone ramp surface. At one ramp locality, clinoform beds form part of a progradational sequence called the Sambro Delta. A mussel valve fragment (Mytilus edulis) was obtained from a core in the foresets and radiocarbon dated. An age of 11,650 ┬▒ 110 yr B.P. was obtained, adjusted for isotopic fractionation. Above -65 m the sea floor forms a low relief, gently sloping erosional surface (Platform Subzone). Estuarine deposits have been found above -50 m. The new sea-level curve constructed with the dated -65 m shoreline and recently published data is at variance with calculated RSL curves based on geophysical models, primarily in the amplitudes and rates of RSL change. Reasons for the discrepancies may be late-melting ice and regional variations in lithospheric strength and thickness.

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