Sismoestratigrafía y edificación sedimentaria del margen SE y fondo de cuenca de la Cuenca Central de Bransfield (Antártida Occidental)

• Autores: Eulàlia Gràcia i Mont, Gemma Ercilla Zárraga, Miquel Canals Artigas, María José Prieto
• Localización: Boletín de la Real Sociedad Española de Historia Natural. Sección geológica, ISSN 0583-7510, Tomo 93, Nº 1-4, 1997 (Ejemplar dedicado a: Ciencia antártica: el papel del SCAR), págs. 63-71
• Idioma: español
• Texto completo no disponible (Saber más ...)
• Resumen
  • español

    El recubrimiento sedimentario del margen SE y fondo de cuenca de la Cuenca Central de Bransfield (CCB) está constituido por dos secuencias sísmicas dispuestas sobre el basamento acústico fracturado: la Secuencia Inferior, también fracturada y restringida al margen; y la Secuencia Superior constituida por sedimentos de origen glacio-marino. Dentro de la Secuencia Superior se han diferenciado dos grupos de unidades sísmicas en base a su distribución en la cuenca: las unidades de talud y las de fondo de cuenca. Las primeras constituyen cuñas sedimentarias en el borde de la terraza superior del talud, y ocasionalmente, a las salidas de los surcos de la plataforma, alcanzan ampliamente el centro de la cuenca. Las unidades de fondo de cuenca tienen morfología tabular, y contienen cuerpos lobulares y canaliformes en las zonas proximales. Ambos tipos de unidades sísmicas se interdigitan en la base del talud.

    La distribución y características sísmicas que presentan los dos tipos de unidades indican que los procesos sedimentarios que las originaron son diferentes y separados en el tiempo, sugiriendo una acentuada ciclicidad en la edificación sedimentaria de la CCB.

  • English

    The Bransfield Basin is located on the northern tip of the Antarctic Peninsula, West Antarctica. It is a young back-arc basin placed in a geodinamically complex zone of microplates. The recent and active basin opening allows the recognition of processes of incipient rifting. The highs of Deception and Bridgeman islands divide the Bransfield Basin into three subbasins, Western, Central and Eastern, of which only the Central one is studied in the present work. Geographic, geodynamic and sedimentary frameworks make the Central Bransfield Basin an excellent example of a young basin influenced by glaciomarine sedimentary processes.

    The SE margin of the Central Bransfield Basin, offshore of the northern tip of the Antarctic Peninsula, shows a complex morphology, with a narrow, 200 m deep shelf and a step-like slope. A wide wavy platform, developed down to 700 m depth, is dominated by sedimentary progradation. It is cut by several glacial troughs. Beneath the platform, a steep slope let down to an irregular sedimentary rise. The basin floor is mostly flat and descends from 1000 to 1950 m deep towards the NE. Six large volcanoes form a discontinuous NNE-SSW-trending lineation which separates the basin floor into two parts, northwards and southwards of the volcanic lineament.

    Overlying a complex acoustic basement, the sedimentary cover of the SE margin and basin floor of the Central Bransfield Basin reveals the presence of a Lower Sequence whose distribution, internal configuration and fracturation indicate its syntectonic origin during the initial episodes of basin opening. A regional unconformity separates the Lower Sequence from an Upper Sequence composed of four seismic units located at the slope (1, 3, 5, and 7) and four seismic units located on the basin floor (2, 4, 6, and 8). Both types of units interfinger at the base of the slope, indicating alternating sedimentary conditions and processes in the sedimentary basin fill. This alternation has been interpreted in terms of glacial and interglacial episodes.

    Slope units are deposited during glacial periods, when the ice-sheet grows and advances seaward. The ice sheet moves over the shelf and the platform forming abrasion surfaces. Coarsed unsorted sediments, transported subglacially are deposited on the grounding line and form the slope units. In the Antarctic Peninsula margin they are specially developed in front of the mouths of the glacial troughs.

    Basinal units are deposited at the end of glacial periods and during the later interglacial periods. They are mainly formed by mass wasting processes, firstly triggered by the isostatic rebound of the margin after the ice-sheet retreat. Later, during the interglacial, high density currents through the troughs of the shelf and slope play a main role acting as source of sediment supply which form the basinal units. Pelagic and/or hemipelagic sediments are also deposited during this period.