BELANTOSTRAT Belgian contribution to the "Antarctic offshore acoustic stratigraphy project (ANTOSTRAT)"
De Batist, M.; Bart, P.-J.; Vanneste, K. (1997). BELANTOSTRAT Belgian contribution to the "Antarctic offshore acoustic stratigraphy project (ANTOSTRAT)", in: Caschetto, S. (Ed.) Belgian research programme on the Antarctic: scientific results of phase III (1992-1996): 2. A: Hydrodynamics; B: Marine Geophysics. pp. A3/02/002/1-69 In: Caschetto, S. (Ed.) (1997). Belgian research programme on the Antarctic: scientific results of phase III (1992-1996): 2. A: Hydrodynamics; B: Marine Geophysics. Belgian scientific research programme on Antarctica. Federal Office for Scientific, Technical and Cultural Affairs: Brussel. 94 pp., more In: Belgian scientific research programme on Antarctica. Belgian Science Policy Office: Brussel. , more |
| Authors | | Top | - De Batist, M., more
- Bart, P.-J.
- Vanneste, K., more
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| Abstract | The scientific objective of ANTOSTRAT -the "Antarctic Offshore Acoustic Stratigraphy" Project -is to extract Antarctica's Cenozoic glacial history from the sediments of its continental margins, principally by using seismic stratigraphy, where possible calibrated by coring or borehole evidence. The present report summarises the Belgian research efforts and scientific contribution to ANTOSTRAT , with seismic-stratigraphic studies of various portions of the Antarctic continental margin: * The Trinity Peninsula and South Shetland Islands margins of central Bransfield Basin, along the Antarctic Peninsula; * The West-Antarctic continental margins of the Amundsen and Bellingshausen Seas; * The East-Antarctic continental margin of the North-eastern Weddell Sea; These areas are situated along portions of the Antarctic continental margin that exhibit different characteristics, such as different glacial regimes and glacial evolution (West-Antarctica as opposed to East-Antarctica), different depositional processes and environments (semi-enclosed basins, quasi-starved distal glacial-marine environments, deep-sea fan and drift environments, etc.), different preservation potential (subsiding shelf edge in Bransfield Basin as opposed to stable shelf edges in Weddell Sea or along the Amundsen-Bellingshausen margin), etc. The Trinity Peninsula and South Shetland Islands margins of central Bransfield Basin Swath bathymetry data acquired in central Bransfield Basin during the GEBRA- 93 survey reveal new morphological features and trends that shed a light on the ongoing processes of back-arc basin formation and evolution. Basin compartmentalisation and progressive deepening towards the north-east via a series of bathymetrical steps suggests a progressive increase in basin maturity in that direction. The different shapes and sizes of large volcanic edifices dominating the basin-floor morphology can be interpreted in terms of successive evolutionary stages of incipient sea-floor spreading. New high-resolution reflection seismic data indicate that the upper-slope deposits along the Trinity Peninsula margin contain resolvable records of at least three periods -since the Pliocene, beginning of the opening of Bransfield Basin -during which ice sheets advanced to the shelf edge for a significant amount of time. The record of glacial periods of lesser extent is probably not preserved in the upper-slope and shelf deposits as suggested by the strong erosional unconformities. Magnitude of slope progradation varies along the Trinity Peninsula margin and appears to be related to local sources of sediment supply associated with separate glacial troughs. Ice-stream activity within these troughs appears to have varied through time. A thick stack of prograding units is preserved at the mouth of Orleans Trough. Off the mouth of the Antarctic Sound, most of the correlative section has been removed by canyon incision at the Gebra Valley. Development of basin-floor strata appears to be temporally distinct from the development of the prograding upper-slope wedges, the toes of which downlap the basin-floor strata. A drill hole -cf. recently submitted ANTOSTRAT-ODP Proposal - through this basin-floor section would provide an excellent opportunity to constrain the age of the glacial cycles associated with the progradational wedges. The West-Antarctic continental margins of the Bellingshausen and Amundsen seas A regionally-spaced reflection seismic data set has been acquired from the hitherto largely unexplored Bellingshausen and Amundsen Seas along the West Antarctic margin during the ANT XI/3 survey in 1994. These data show the largescale stratigraphic architecture of the continental shelf, slope and rise, and contain a record of the long-term glacial history of the area. On all seismic profiles, the same variation of outer-shelf geometries is observed: (1) a lower unit of mainly aggradational sequences, (2) a middle unit of strongly prograding sequences. and (3) an upper unit exhibiting both progradation and aggradation. The lower aggradational sequences are thought to represent conditions before the onset of the major glacial advance of a grounded ice sheet, whereas the overlying sequences probably record several extended periods of ice-sheet grounding on the shelf since the Middle Miocene. A prominent erosional surface defines the base of a prograding wedge occupying the continental slope along the margin. It is tentatively correlated with the transition from aggrading to prograding sequences on the outer shelf, and may thus reflect an intensification of the bottom-current regime in the lower parts of the palaeoslope at response to the onset of glacial conditions on the continental shelf. Sedimentation on the continental rise appears to have resulted in the construction of large sediment drifts that originate from the interaction of channelised |
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