SHORELINE TRANSGRESSION & REGRESSION (XES 96-1)

Provided by: Chris Paola, St. Anthony Falls Laboratory & Dept. of Geology and Geophysics, University of Minnesota

This shows part of experiment XES 96-1 at the Experimental Earthscape Facility, St. Anthony Falls Hydraulic Laboratory, University of Minnesota. This basin is c. 1.6 m long x 1 m wide, the floor subsides in a sag-like geometry. See a description of the experiment and results at:

http://www.geo.umn.edu/people/profs/PAOLA.html

and then link to the Jurassic Tank site

and also

http://faculty.gg.uwyo.edu/heller/index.htm

then link to Experimental Basin Study

Also descriptions of the experiment and some of the results can be seen in:

Paola, C. and 11 others, 2001, Experimental Stratigraphy: GSA Today, in submission.

and

Heller, P.L., Paola, C., Hwang, I-G., John, B., Steel, R., 2001, Geomorphology and Sequence Stratigraphy Due To Slow And Rapid Base-level Changes In An Experimental Subsiding Basin (XES 96-1): AAPG Bulletin, in press.

The sediment used in the experiment consists of fine grained quartz and coal sand. Since the coal sand is less dense it tends to be transported farther out into the basin, acting as a proxy for finer grained sediment in real systems.

xessl.mov: Rapid base level fall and then slow base level falls

Total length = 84 seconds (4.9 MB)

Fast Fall - Incised valley development during a rapid fall in base level. Key features are labled in the movie. The incised valley that forms in relatively narrow, steep walled, and lengths basinward as delta at channel mouth is exposed by continued base level fall. Growth faults develop during base level fall.

Slow Fall - In this experiment absolute base level fall takes place at rates similar to basin subsidence. The geometry and rates of subsidence of the basin floor is balanced such that the shoreline progrades from a zone of relative base-level rise (i.e. absolute base level fall is slower than basin subsidence producing a slow relative rise) into a zone of relative base-level fall (i.e. rate of all of absolute base level is faster than basin subsidence). At this point (see Figure), which is where the video starts, a nickpoint rapidly cuts headward back to the source. As the nickpoint retreats, the slight increase in sediment supplied just downstream forces deposition. Thus as the knick point steps to the right so to does the attendant zone of aggradation. Over time the valley widens into a broad basin-scale unconformity. See discussion in Heller et al., (2000) for details.

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