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| Titel |
The stratigraphy and crustal structure of the rift shear transition off Argentina |
| VerfasserIn |
Katharina Becker, Dieter Franke, Michael Schnabel, Bernd Schreckenberger, Charlotte M. Krawczyk |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053379
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| Zusammenfassung |
| The southern Argentinean margin has been surveyed during a cruise in 2004 collecting
multichannel seismic profiles with a length of ~ 1340Â km acquired together with gravimetric
and magnetic data. Here, we focus on six selected profiles imaging the area at the
transition from the rifted to the sheared margin at the Falkland Agulhas Fracture Zone
(FAFZ).
We propose a regional stratigraphic concept composed of six seismic marker horizons.
We use the stratigraphy of the North Falkland Graben (NFG) based on observations in the
industry well Jacinta to distinguish the sediments on the continental shelf. In the deep sea we
interpret the stratigraphy based on a modified concept of earlier studies. A new
formation with Barremian age is introduced. This is the oldest postrift formation
identified in this part of the Argentine Basin. A widespread unconformity at the
Cretaceous/Tertiary boundary is reported in the North Falkland Graben and adjacent DSDP
wells. In contrast to earlier studies, we interpret this unconformity as a marker
horizon.
Based on structural features the margin can be divided in two segments defined
by the N-S trending rifted margin segment and the SW trending sheared margin
segment. The sheared margin segment formed by the FAFZ is characterized by a steep
escarpment. The FAFZ is a narrow, 15-17Â km wide zone, defined by nearly vertical faults
with vertical offsets of ~ 2000Â m at the main fault. A continuation of the FAFZ in
northward direction could not be confirmed. Probably due to the presence of the
FAFZ the oceanic crust is highly dissected by steep faults. Tectonic activity of
the shear zone is mainly observed until Aptian time. Minor activity of the FAFZ
occurred until the Cretaceous/Tertiary boundary. The rifted margin segment in contrast
exhibits a slowly inclining continental shelf. The rifted margin segment is not of the
volcanic type, as there are no seaward dipping reflectors. The margin has been rather
affected by limited/no breakup related magmatism. The transition from continental to
oceanic crust (COT) on the rifted margin segment occurs within a 40Â km wide
zone, while the COT at the sheared margin segment is outlined as a more abrupt
transition.
The study area is less affected by synrift grabens than previously suggested. As there are
almost no synrift grabens observed along the rifted margin, we suggest that the North
Falkland Graben is confined south of 47.5°S, i.e. it does not reach the Argentine margin.
However, on the continental shelf north of the Falkland Islands there are several synrift
grabens. The early extension resulting in the formation of the NFG thus had a wider E-W
extent, but was limited to the North. |
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