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Genesis and evolution of the Punta del Este Basin, offshore Uruguay: the relationship between crustal structure and normal-to-oblique rifting during the formation of the South Atlantic

Author(s): Phil Thompson BG Group, 100 Thames Valley Park, RG6 1PT, United Kingdom
N. Hurst BG Group, 100 Thames Valley Park, RG6 1PT, United Kingdom
J. Turner BG Group, 100 Thames Valley Park, RG6 1PT, United Kingdom
M. Soto 2 ANCAP, Exploración y Producción, Paysandú s/n esq. Av. del Libertador, 11100 Montevideo, Uruguay
R. Walker BG Group, 100 Thames Valley Park, RG6 1PT, United Kingdom
J. Argent BG Group, 100 Thames Valley Park, RG6 1PT, United Kingdom
G. BAdalini BG Group, 100 Thames Valley Park, RG6 1PT, United Kingdom
S. Wrigley BG Group, 100 Thames Valley Park, RG6 1PT, United Kingdom

The crustal structure along the Uruguayan margin is highly complex and does not fit into conventional rifting models. This complexity has major implications for hydrocarbon exploration in that the relict rift architecture influenced basin evolution and sedimentation until the Late Cretaceous – well into the post-rift (drift) phase – controlling sedimentation along the margin.

Regional 3D and long-offset 2D seismic data from offshore Uruguay show how initial South Atlantic rifting developed normal to the margin but became more margin-oblique over time resulting in the creation of a major oceanic depression that runs up to the Florianopolis High in Brazil. At the southern end, directly offshore Uruguay, a sigmoidal pull-apart basin was created (the Punta del Este Basin) covering over 20,000km2. Limited age data along the margin suggest the depression and the Punta del Este Basin formed over a period of approximately 15my (Hauterivian to mid-Aptian).

The Punta del Este Basin is fault-bounded to the north and south against packages of seaward dipping reflectors (SDRs) and oceanic crust; to the east the basin margin is marked by a faulted contact with oceanic crust. The western margin is marked by the Polonio High, a granitic body interpreted to be part of the Neoproterozoic Dom Feliciano Belt. To the south of this high the basin connects into the La Plata rift, which extended from offshore Uruguay south-west into Northern Argentina.

Underneath the Punta del Este Basin the crust comprises a mix of proto-oceanic crust (i.e. highly stretched/fragmented continental crust), intrusive volcanics and a spectacularly imaged failed spreading centre flanked by SDRs. Regional data shows a significantly elevated Moho under the basin with the highest point directly beneath the spreading centre, with a crustal thickness of 3km locally. Seabed heat flow measurements show a correlation with the underlying crustal structure, with local maxima immediately above the failed spreading centre.

The syn-tectonic fill of the Punta del Este Basin records the transition, both spatially and stratigraphically, from continental to marine conditions. Internally, the fill is dominated by alluvial fans, lacustrine and deltaic deposits along with fault-controlled channel systems. In addition to subaerial and subaqueous sedimentation the basin shows evidence of subaerial and subaqueous (hyaloclastites) volcanism; the latter is particularly prevalent along the south/ eastern basin-bounding faults. The final basin fill is marked by an Aptian-age flooding event which marks the progressive development of fully marine conditions along the margin and the start of sedimentation within the Pelotas Basin.

Following the creation of the Punta del Este Basin South Atlantic rifting continued, resulting in the creation of various oceanic fracture zones. Whilst the Punta del Este Basin and the Meteor fracture zone share a common structural orientation they are not directly linked: the area between the basin and the tip of the fracture zone shows an area of apparent strike-slip faulting, imaged by opposingly dipping fractures within the oceanic crust.


Title:
Genesis and evolution of the Punta del Este Basin, offshore Uruguay: the relationship between crustal structure and normal-to-oblique rifting during the formation of the South Atlantic
Type:
Oral
Origin:
Industry
Day:
2
Session:
2
Daily sequence no.:
19
Lead author last name:
Thompson
Lead author first name:
Phil
Affiliation(s):
BG Group, 100 Thames Valley Park, RG6 1PT
Country:
United Kingdom
Abstract status:
ok
UID:
94