Northern Labrador Shelf glacial chronology and depositional environments
Huntec deep-tow records, 3.5 and 12 kHz echo-sounder profiles backed by airgun reflection, cores, and 14 C dates delineate 10 mappable acoustic/morphologic units between 57°N and 61°N on the northern Labrador Shelf. These include: I—section composed of numerous horizontal reflectors with minimal sca...
| Published in: | Canadian Journal of Earth Sciences |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Canadian Science Publishing
1982
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1139/e82-013 http://www.nrcresearchpress.com/doi/pdf/10.1139/e82-013 |
| Summary: | Huntec deep-tow records, 3.5 and 12 kHz echo-sounder profiles backed by airgun reflection, cores, and 14 C dates delineate 10 mappable acoustic/morphologic units between 57°N and 61°N on the northern Labrador Shelf. These include: I—section composed of numerous horizontal reflectors with minimal scattering and smooth microrelief; II—acoustically transparent section with numerous subparallel, draped reflectors at its base—it underlies unit I in basin centers; III—section marked by intense scattering, point reflectors, and a rough microrelief; IV—section exhibiting strong scattering as in III, but with smooth microrelief and obvious terraces; V(a,b)—outcropping portions of II-type sediments variably dissected; VI—outcrops of II exhibiting warping, acutely intersecting reflectors and undulating mesorelief; VII(a,b)—areas of strong macrorelief with ridges and wedge- or lens-shaped reflectors and strong scattering; VII—section exhibiting strong macrorelief as in VII(a,b) but with somewhat rougher microrelief.A thin (<1 m) ubiquitous surface-sediment veneer that is not clearly identifiable on acoustic profiles is 14 C dated at [Formula: see text]. Unit II dates between 9770 and 8380 BP and unit III at 10 260 BP. These dates are based on shells. Unit I is inferred to span the interval <8380 to >6050 BP. Total organic carbon dates from units I and II are deemed too old by as much as 17 000 years because of the introduction of reworked older carbon.The data suggest the following sequence of glaciation and deposition: (1) ice grounds on the shelf and upper slope during the glacial maximum; (2) shelf-basinal and bank portions of the ice sheet begin basal melting before 9770 and ca. 10 260 BP, respectively; (3) degrounding of the ice in shelf basins and admission of sea water by 9770 BP, perhaps at first beneath ice shelves; (4) deposition of fine-grained glacial muds in basins as runoff from actively ablating valley glaciers on Labrador finds its way into fjord-like embayments in the ice sheet (ca. 9770–8380 BP); ... |
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