Mass Transport Deposits in Malvinas Basin Morphology, Depositional Controls and Seismic Facies

Nunuk Fiptiani, Pedro Bonillo, and Daniel Figueroa
Repsol YPF, Exploration Offshore - Deep water, Buenos Aires, Argentina

Malvinas Basin is located offshore Argentina, between Malvinas and Tierra del Fuego Islands. It is bordered at the south by a fold and thrust belt trending E-W which is the offshore continuation of the Andes Fueguinos.

2D and 3D seismic data mapping revealed the presence of a thick Mass Transport Deposits (MTD) of Oligocene age. It covers an area bigger than 3700 sqkm, with a length of 175 km and a width of 20 km. The thickness of MTD reaches about 1700 meters, laterally thinning towards the North-East. The thickness and geometry would indicate a strong tectonic controlled depositional process.

Two tectonic stages were differentiated. A transtensive one, developed during the Eocene, which creates the accommodation space where the MTD will be deposited and a transpressive one during the Oligocene that generates a fold and thrust belt. The collapse of the frontal thrusting slope associated to such fold and thrust belt, located to the south, will be the source of the MTD.

Based on the bounding surface and internal character the MTD can be divided into two seismic facies. Facies 1 show an erosional base and irregular topography at the top, an internal character from chaotic to hummocky and a transparent to locally high amplitude. Facies 2 in dip view shows downlap at the base and a relatively flat top, the internal character indicates steep dipping to horses of semi continous reflectors and medium amplitude; meanwhile in plan view shows strong curved lineations which were interpreted as pressure ridges. Facies 1 constitutes the main MTD body. According to our interpretation it could be composed by rafted blocks and clasts in a debris flow matrix dominated by mud. Facies 2 deposited on the far end of MTD may represent the latest phase of deposition.

The dominant MTD transport has a NE direction as it is indicated by basal scours and pressure rigdes on the seismic data.

AAPG Search and Discovery Article #90079©2008 AAPG Hedberg Conference, Ushuaia-Patagonia, Argentina