AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Intrinsic Controls on the Range of Volumes, Morphologies, and Dimensions of Submarine Lobes
(1) University of Liverpool, Liverpool, United Kingdom.
(2) Chevron ETC, San Ramon, CA.
Across many basins and continental margins, terminal lobes, deposited by turbidity currents in deep-water distributive settings, represent the final site of sediment deposition. As such, lobes are a near complete but cryptic record of climatic, eustatic and tectonic conditions. Based on exceptionally large exposures and high-resolution seismic datasets, lobe dimensions and lobe volumes have been assessed and compared between six different systems: 1) the exhumed Permian Fan 3 lobe complex of the Tanqua Karoo, South Africa; 2) the modern Amazon fan channel-mouth lobe complex, offshore Brazil; 3) a portion of the modern distal Zaïre fan, offshore Angola / Congo; 4) a Pleistocene fan of the Kutai basin, subsurface offshore Indonesia; 5) the modern Golo system, offshore east Corsica, France; and 6) a shallow subsurface lobe complex , offshore Nigeria. These six systems have different source-to-sink configurations, sediment supply characteristics, tectonic settings, (palaeo) latitude, and delivery systems. Despite these differences, the lobe deposits share similar geometric and dimensional characteristics. Lobes are grouped into two distinct populations of geometries that can be related to basin-floor topography. The first population corresponds to areally extensive but thin lobes (average width 14 km × length 35 km × thickness 12 m) that were deposited onto low relief basin floor areas, like the Tanqua Karoo, the Amazon and the Zaïre systems. The second population corresponds to areally smaller but thicker lobes (average width 5 km × length 8 km × thickness 30 m) that were deposited into settings with higher amplitude of relief, like in the Corsican trough, the Kutai basin, and offshore Nigeria. The two populations of lobes, however, share similar volumes (a narrow range around 1 or 2 km3), which suggests that there is a limit to the total volume of sediment that composes individual lobes before they shift to a new locus of deposition. Two explanations can account for the similarity in lobe volumes deposited in very different systems: a similar amount of sediment reaching the basin floor or a tendency for flow to preferentially deposit in depositional lows.