Ocean basins near the Scotia–Antarctic plate boundary: Influence of tectonics and paleoceanography on the Cenozoic deposits |
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| Authors: | A Maldonado F Bohoyo J Galindo-Zaldívar J Hernández-Molina A Jabaloy F J Lobo J Rodríguez-Fernández E Suriñach J T Vázquez |
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| Institution: | (1) Instituto Andaluz Ciencias de la Tierra, CSIC/Universidad Granada, 18002 Granada, Spain;(2) Departamento de Geodinámica, Universidad de Granada, 18071 Granada, Spain;(3) Facultad de Ciencias del Mar, Departamento de Geociencias Marinas, Universidad de Vigo, 36200 Vigo, Spain;(4) Departament de Geodinàmica i Geofísica, Universitat de Barcelona, 08028 Barcelona, Spain;(5) Facultad de Ciencias del Mar, Universidad de Cádiz, 11510 Puerto Real, Cádiz, Spain |
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| Abstract: | The distribution of seismic units in deposits of the basins near the Antarctic–Scotia plate boundary is described based on
the analysis of multichannel seismic reflection profiles. Five main seismic units are identified. The units are bounded by
high-amplitude continuous reflectors, named a to d from top to bottom. The two older units are of different age and seismic
facies in each basin and were generally deposited during active rifting and seafloor spreading. The three youngest units (3
to 1) exhibit, in contrast, rather similar seismic facies and can be correlated at a regional scale. The deposits are types
of contourite drift that resulted from the interplay between the northeastward flow of Weddell Sea Bottom Water (WSBW) and
the complex bathymetry in the northern Weddell Sea, and from the influence of the Antarctic Circumpolar Current and the WSBW
in the Scotia Sea. A major paleoceanographic event was recorded by Reflector c, during the Middle Miocene, which represents
the connection between the Scotia Sea and the Weddell Sea after the opening of Jane Basin. Unit 3 (tentatively dated ∼Middle
to Late Miocene) shows the initial incursions of the WSBW into the Scotia Sea, which influenced a northward progradational
pattern, in contrast to the underlying deposits. The age attributed to Reflector b is coincident with the end of spreading
at the West Scotia Ridge (∼6.4 Ma). Unit 2 (dated ∼Late Miocene to Early Pliocene) includes abundant high-energy, sheeted
deposits in the northern Weddell Sea, which may reflect a higher production of WSBW as a result of the advance of the West
Antarctic ice-sheet onto the continental shelf. Reflector a represents the last major regional paleoceanographic change. The
timing of this event (∼3.5–3.8 Ma) coincides with the end of spreading at the Phoenix–Antarctic Ridge, but may be also correlated
with global events such as initiation of the permanent Northern Hemisphere ice-sheet and a major sea level drop. Unit 1 (dated
∼Late Pliocene to Recent) is characterized by abundant chaotic, high-energy sheeted deposits, in addition to a variety of
contourites, which suggest intensified deep-water production. Units 1 and 2 show, in addition, a cyclic pattern, more abundant
wavy deposits and the development of internal unconformities, all of which attest to alternating periods of increased bottom
current energy. |
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| Keywords: | Ocean basin development Seismic stratigraphy Contourite drifts Antarctic palaeoceanography Antarctic Circumpolar Current Weddell Gyre |
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