Submarine Fan "Lobes"

G. Shanmugam

Submarine fan "lobes" constitute major hydrocarbon reservoirs throughout the world. Therefore, a clear understanding of their geometry and facies relationships is critical for exploring and exploiting these sandstone bodies effectively. However, a multitude of submarine fan lobe terminologies (e.g., depositional lobe, suprafan lobe, fan lobe, erosional lobe, channelized lobe, ponded lobe, leveed-valley lobe, type I lobe, and type II lobe), advocating widely different meanings, has flourished in the sedimentologic literature. A critical evaluation of this problem has resulted in the following suggestions: (1) lobes are considered to be turbidite sand bodies that develop at the mouths of channels in deep-sea fan environments; (2) the term "depositional lobe" should be restr cted to lower-fan deposits of fans that exhibit facies C and thickening-upward cycles; (3) the term "suprafan lobe" refers to middle-fan deposits of certain small, sand-rich, modern fans that exhibit a convex-upward depositional bulge in seismic reflection profiles; (4) the terms "fan lobe," "erosional lobe," "channelized lobe," "ponded lobe," and "leveed-valley lobe" do not represent true channel-mouth deposits and therefore are potentially confusing; (5) lower-fan sheet sands of large modern fans may not be equivalent to depositional lobes of ancient fans; and (6) popular fan models with lobes are not always applicable because they disregard large modern fans without lobes (e.g., Mississippi fan).

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.