Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Accommodation Succession Method and Mass Balance Analysis: Predicting Sediment Distribution and Stratigraphic Architecture
(1) ExxonMobil Upstream Research Company, Houston, TX.
(2) University of Minnesota, Minneapolis, MN.
The accommodation succession method was proposed to facilitate the construction of sequence stratigraphic frameworks honoring the five basic geologic observations: lithofacies, lithofacies associations, vertical stacking, stratal terminations and geometries. The key geometric element to be observed is the paleo-shelf break trajectory, which is used to interpret changes in accommodation on the shelf. Shelf-break trajectory translates in 4 stacking patterns: retrogradational, aggradational, progradational and degradational. However, rather than being discrete entities, these stacking patterns often transition from one to another due to sedimentary fill of predictable changes in the rate of shelfal accommodation creation and destruction through time. A resulting motif in a depositional succession starting with negative accommodation on the shelf (subaerial unconformity and its correlative conformity when coastal onlap begins), to maximum accommodation rate and back to negative again is: progradational to aggradation (PA systems tract), followed by retrogradation (R systems tract), and by aggradation to progradation to degradation (APD systems tract).
Sequence stratigraphic surfaces bounding systems tracts are defined by stratal terminations, changes in vertical stacking, and at the changes in direction of a shelf-break trajectory during a depositional succession. Changes in shelf-break trajectory mark landward-basinward shifts in depocenter (location of thickest deposition), driven by changes in accommodation creation rate relative to sedimentation rate. We therefore view sequence-stratigraphic surfaces as both the result,and primary indicators of, shifts in sedimentation distribution sediment mass balance).
Depositional mass balance of a sedimentary package can be analyzed through the mass-balance transformation (c(x), Strong et al., 2005) or by defining the depositional center as the mean depositional position of the package (centroid, sensu Martin at el., 2008). c(x) measures the fraction of all supplied sediment deposited upstream of a specific position in a sedimentary package. Due to the downstream loss of sediment and the associated grain size decrease induced by deposition, changes in the distribution of deposition will cause changes in depositional architecture and a downstream migration of facies belts (Strong et al., 2005).