Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Preservation Potential of Coastal Sediments
(1) ConocoPhillips Company, Houston, TX.
(2) ConocoPhillips, Calgary, AB, Canada.
Coastal sediments are characterized by transgressive/regressive stratigraphy, and their accumulation is broadly determined by the ability of sediment flux to fill the available accommodation. However, a range of erosional surface trajectories control the real facies preservation architecture. During regression, the space between sea level and the sea floor is filled with sediments deposited in delta front, shoreface and tidal flat settings. As the shoreline advances, this progradational sediment wedge is reworked by distributary channels, fluvial channels, and tidal channels. A critical control is the relationship between the original space available and the tidal/fluvial channel depths that are a function of fluvial discharge and tidal prism, and range to over 50 m depth. The tidal/fluvial channel depths are independent of the original space available and are particularly effective during falling relative sea level and in low accommodation settings. An equally important control is the lateral migration extent of tidal/fluvial channels. During transgression, sediment supply to the coastline is reduced and previously deposited sediments are subject to erosion and reworking. Again, preservation architecture is controlled by erosional surface trajectories, particularly those associated with the tidal/fluvial ravinement surface, the tidal ravinement surface and the wave ravinement surface. These processes are controlled by tidal prism and wave energy, are mostly independent of regional accommodation, but capable of creating local self-accommodation. Examples show tidal and tidal/fluvial ravinement surfaces can extend locally to 40 m below sea level, especially if tidal prism increases during transgression. High energy wave ravinement surfaces are capable of regional truncation in excess of 30 m. The transgressive ravinement trajectories can rework all of the sediment in the coastal zone in low accommodation settings, but in higher accommodation settings cannot access the majority of underlying sediments and in these cases may even experience punctuated transgression combined with minor progradation and aggradation. These stratigraphic preservation principles can be applied to both modern and ancient environments, and examples include the Quaternary Mississippi Delta and NSW coast of Australia, the McMurray Formation and Falher Member of Alberta, the Morrow Formation and Hosta Sandstone of SW USA.