Autocyclic Processes and
Resultant Stratigraphy of Deepwater Fan Experiments
Bloch, Roger B.1, David C.J.D
Hoyal1, Benjamin A. Sheets1, Christopher M. Edwards1,
Vitor Abreu2 (1) ExxonMobil
Upstream Research Company, Houston, TX (2) ExxonMobil
Exploration Company, Houston, TX
Tank experiments emulating depositional
processes on deep water fans demonstrate the relationship between autocyclic flow processes and their resultant surfaces and
deposits. The experiments have constant discharge and sediment flux, and use
crushed plastic in a saline solution to enhance turbidity current density. Fan
growth evolves thus: 1) a distributary channel forms,
2) a lobate deposit develops at channel mouth, 3) the
lobe grows in width and/or height 4) deposition propagates up the channel, and
5) the channel avulses, initiating a new cycle. The resultant stratigraphy reflects these cycles of erosion and
deposition superimposed on longer-term fan progradation.
In proximal positions, an individual cycle produces an erosional
basal surface that is a composite feature created by multiple scouring events.
In strike-oriented section, the depth of scour tends to decrease over time
within a cycle. Backfilling processes yield an architecture dominated by
scour-fill in the stratigraphically lower part of a
cycle and a broader, lobate geometry in the upper
part. In distal positions, lateral migration of lobes produces a shingled and
mounded architecture on a surface of little or no erosion. Overall fan progradation affects the large-scale architecture such that
in proximal regions, scour-fill, unfilled channels and small erosional remnants dominate. In the mid-fan region, lobate deposits of older cycles are incised by younger
cycles dominated by scour-fill. At distal positions, laterally-offset and
vertically-stacked lobes develop. This architecture is compared to seismic
geometry of an East Breaks (
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California