Mesozoic sedimentation on an isolated platform at the eastern entrance to the Strait of Magellan, Tierra del Fuego (Chile)

Abstract

The Magellan Block, located on the modern Atlantic continental platform opposite the Strait of Magellan (Chile), consists of two parallel, northwest trending horsts partly separated by a central graben. Petroleum has been recovered from the Springhill Formation, deposited on this isolated platform during the Valanginian-Barremanian, since 1994. This formation represents an overall transgressive succession with three subcycles of transgression and regression (parasequences) separated by marine flooding surfaces. The two basal parasequences are related either to minor sea level fluctuations or to fault activity, whereas the uppermost cycle reflects a major transgression affecting the whole Magellan Basin. Depositional facies associations include supratidal, intertidal, barrier beach and shoreface environments, generally showing a clear correlation with the paleotopography of the horst blocks. While barrier beaches formed along the topographically higher areas, inter- and supratidal flats and shoreface sediments were deposited on their land- and seaward sides, respectively. Tidal flats also bordered the shallow embayment formed by the central graben. Continued transgression subsequently drowned the island to form a wide, open platform on which the Estratos con Fravella Formation was deposited.