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Abstract

This article uses measurements from outcrops of the Point Loma Formation to define the hierarchical organization of a distributive submarine fan and spatial changes in its constituent parts. A four-tier hierarchy for lobes is documented: bed, element, complex, and system. Across each hierarchical tier, there is an increase in size, duration of deposition, number of cross-cutting relationships, number of superposed stratal units, and degree of compensational stacking. Lobe elements contain systematic axis-to-margin and longitudinal decreases in amalgamation ratio, erosion, net sand content, proportions of sand-rich facies, and maximum grain size, with the exception of shale clasts in fringe position. The cross-sectional aspect ratios of lobe elements in the Point Loma are ~1000, a similar value to those measured in other systems, although aspect ratios are slightly higher at the distal reaches of lobe elements than in proximal locations. The key longitudinal patterns in lobe complexes are decreases in proportion of sand-rich facies, maximum grain size, amalgamation ratio of elements, net sand content, and amount of interelement erosion and a longitudinal increase in the degree of the amount of compensational stacking. Lobe complexes stack laterally and progradationally to build a lobe system.

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