Abstract

A comparison of outer fan sections from different parts of the Kongsfjord Formation Submarine Fan has revealed two types of outer fan lobe sequence, designated Type I and Type II. Both types of lobe sequence contain lobes, including lobe fringe deposits, that are between 2 m and 15 m thick, although Type I lobes are generally less than 10 m thick; there are no obvious differences in bed thickness, grain size, or other sedimentary attributes. The distinction between Type I and Type II lobes is based primarily upon their vertical frequency within fan fringe deposits. Type I lobes are separated by lobe fringe plus fan fringe deposits of similar thickness; therefore, in vertical sections the lobes are regularly spaced. Type II lobes occur sporadically within sections where lobe fringe plus fan fringe deposits vary from tens of centimeters to 70 m. In the two representative sections that illustrate the typological differences, Type I lobes, plus lobe fringe deposits, comprise 60 percent of the section, compared to 22 percent for the Type II lobe sequences. Type I lobe sequences are interpreted as the result of regular lobe switching immediately downfan from the middle fan channels, within a relatively proximal outer fan environment. Type II lobe sequences are interpreted as a consequence of sporadic progradation of lobes in a relatively distal fan environment that usually received fan fringe sedimentation. Type I lobes represent regular and stable deposition controlled by intrafan (intrabasinal) processes, whereas Type II lobes developed because of relatively catastrophic intrafan (e.g., major channel relocation) or extrafan (source control) processes. This distinction may serve as a proximality indicator in outer fan successions.

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