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Bathymetric Troughs (bathymetric + trough)

Distribution by Scientific Domains

Earth and Environmental Science	100%

Selected Abstracts

Sedimentary and crustal structure from the Ellesmere Island and Greenland continental shelves onto the Lomonosov Ridge, Arctic Ocean

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010
H. Ruth Jackson
SUMMARY On the northern passive margin of Ellesmere Island and Greenland, two long wide-angle seismic reflection/refraction (WAR) profiles and a short vertical incident reflection profile were acquired. The WAR seismic source was explosives and the receivers were vertical geophones placed on the sea ice. A 440 km long North-South profile that crossed the shelf, a bathymetric trough and onto the Lomonosov Ridge was completed. In addition, a 110 km long profile along the trough was completed. P -wave velocity models were created by forward and inverse modelling. On the shelf modelling indicates a 12 km deep sedimentary basin consisting of three layers with velocities of 2.1,2.2, 3.1,3.2 and 4.3,5.2 km s,1. Between the 3.1,3.2 km s,1 and 4.3,5.2 km s,1 layers there is a velocity discontinuity that dips seaward, consistent with a regional unconformity. The 4.3,5.2 km s,1 layer is interpreted to be Palaeozoic to Mesozoic age strata, based on local and regional geological constraints. Beneath these layers, velocities of 5.4,5.9 km s,1 are correlated with metasedimentary rocks that outcrop along the coast. These four layers continue from the shelf onto the Lomonosov Ridge. On the Ridge, the bathymetric contours define a plateau 220 km across. The plateau is a basement high, confirmed by short reflection profiles and the velocities of 5.9,6.5 km s,1. Radial magnetic anomalies emanate from the plateau indicating the volcanic nature of this feature. A lower crustal velocity of 6.2,6.7 km s,1, within the range identified on the Lomonosov Ridge near the Pole and typical of rifted continental crust, is interpreted along the entire line. The Moho, based on the WAR data, has significant relief from 17 to 27 km that is confirmed by gravity modelling and consistent with the regional tectonics. In the trough, Moho shallows eastward from a maximum depth of 19,16 km. No indication of oceanic crust was found in the bathymetric trough. [source]

Geological constraints on Antarctic palaeo-ice-stream retreat

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2008
Colm Ó Cofaigh
Abstract Submarine landforms preserved in bathymetric troughs on the Antarctic continental shelf show that the style of ice stream retreat across the shelf following the last glacial maximum varied between different troughs. Three styles of retreat are inferred from the geological evidence: rapid, episodic and slow. Rapid retreat by ice stream floatation and calving is recorded by the preservation of a landform assemblage of unmodified streamlined subglacial bedforms including mega-scale glacial lineations (MSGLs) that record streaming flow along these troughs. These elongate bedforms are not overprinted by recessional glacial landforms formed transverse to ice flow such as moraines or grounding-zone wedges, and overlying deglacial sediments are thin. A second type of landform assemblage consists of MSGLs overprinted or interrupted by transverse grounding-zone wedges. This assemblage implies episodic retreat between successive grounding-zone positions. The third type of landform assemblage is that of numerous, closely spaced, recessional moraines and intermittent grounding-zone wedges that overlie and interrupt MSGLs. This assemblage records the slow retreat of grounded ice across the shelf. Variation in the style of ice stream retreat between the different bathymetric troughs indicates that Antarctic palaeo-ice-streams did not respond uniformly to external forcing at the end of the last glacial cycle. Rather, their diachronous retreat reflects the dominance of local controls in the form of bathymetry and drainage basin size. More broadly, these data show that retreat of marine-based ice sheets in areas of reverse bed slope is not necessarily catastrophic, and they provide important constraints for numerical models that attempt to predict the dynamics of large polar ice sheets. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Palaeo-ice streams, trough mouth fans and high-latitude continental slope sedimentation

BOREAS, Issue 1 2003
Colm Ó Cofaigh
The classical model of trough mouth fan (TMF) formation was developed in the Polar North Atlantic to explain large submarine fans situated in front of bathymetric troughs that extend across continental shelves to the shelf break. This model emphasizes the delivery of large volumes of subglacial sediment to the termini of ice streams flowing along troughs, and subsequent re-deposition of this glacigenic sediment down the continental slope via debris-flow processes. However, there is considerable variation in terms of the morphology and large-scale sediment architecture of continental slopes in front of palaeo-ice streams. This variability reflects differences in slope gradient, the relative contributions of meltwater sedimentation compared with debris-flow deposition, and sediment supply/geology of the adjacent continental shelf. TMF development is favoured under conditions of a low (<1°) slope gradient; a passive-margin tectonic setting; abundant, readily erodible sediments on the continental shelf - and thus associated high rates of sediment delivery to the shelf edge; and a wide continental shelf. The absence of large sediment fans on continental slopes in front of cross-shelf troughs should not, however, be taken to indicate the former absence of palaeo-ice streams in the geological record. [source]