Print this pageA Novel Method Linking Processes and Stratigraphy in a Tidal Environment: Barataria Basin, Louisiana
Howes, Nick C.1; Georgiou, Ioannis Y.2;
Kulp, Mark A.2; FitzGerald, Duncan M.3
(1)Clastics
Research, Shell International Exploration and Production, Houston, TX. (2)
Department of Earth and Environmental Sciences, University of New Orleans, New
Orleans, LA. (3) Department of Earth Sciences, Boston University, Boston, MA.
A novel method is presented to characterize the stratigraphy of a
complex shallow marine environment, complementing outcrop based research, but
providing information on a much larger, 3-D spatial scale. The stratigraphy of
a transgressive tidally dominated basin in the Mississippi River Delta is
reconstructed based on a centennial-scale time-series of bathymetric grids. The
grids have a resolution of ~100m, covering an area of 1800 km2 and
are integrated with hydrodynamic and sediment transport rules to confidently
link the deposits with the processes that formed them. Similar datasets, where
available, will provide crucial validation of process based forward models that
simulate 3-D geometries at 10’s of kilometer scales.
The study site, Baratria Basin, is composed of fluvial deposits
reworked into a multiple-inlet barrier system. Relative sea level rise in Barataria
has approached 10 mm/yr over a 102 yr timescale, resulting in rapid
and substantial morphological changes that are captured by the dataset. The
spatial patterns of deposition and erosion are calculated for each time-step by
differencing the grids, and the resulting stratigraphy is recorded. This method
allows the subsurface geometry of the preserved strata to be determined in the
context of morphological evolution on the surface. It also allows the inverse problem
to be assessed, in which depositional environments are inferred from the
preserved deposits. To forecast the effects of a continued transgression, the
model is extended to include several scenarios of wave ravinement.
Tidal prism is the single most important hydrodynamic parameter forcing the transgressive evolution of the system. Prism refers to the volume of water exchanged through the inlets during a flood tidal cycle, approximated as bay area multiplied by tidal range. Tidal prism will be a fundamental control in any tidally influenced/dominated system as it controls channel development, as described by the O’Brien-Jarrett-Marchi Law: A~Pk, where (A) is the channel cross section area, (P) is the tidal prism, and k~1 (the equation is weakly non-linear). The inlets conform to this relationship, and inlet cross-sectional area has increased by an order of magnitude in response to bay enlargement. This trend implies that the separation between the tidal ravinement surface (~ 65 m depth) and the wave ravinement surface will increase, creating significant preservation potential for channel infill.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.