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Lines of Evidence
for Past Change

Lines of Evidence for Past Change:

Energy transfer, transportation,
and deposition

Where Does All the Sediment Go?

  • Sedimentary basins

  • Erosion vs. depositional energy

  • Marine and non-marine sedimentary environments

Image courtesy UCMP

SF Bay: A Modern Sedimentary Basin

  • Circulation within the bay

  • Where does the sediment come from?

  • Note the large watershed draining to SF Bay

Image courtesy
http://virga.sfsu.edu/courses/geol103/labs/estuaries/partIIIA.html

SF Bay: Where Else Does the Sediment Come From?

Hydraulic gold mining, 1890

Streams of water wash material through bedrock cuts.

Placer gold mining, 1930

Woman using a rocker at a placer mine.

Images courtesy
http://www.consrv.ca.gov/cgs/information/publications/
library/cd_98_001/selected_photos.htm

SF Bay: Human Alteration

Green = Wetlands

Red = Population Centers

Yellow Dots = Major Earthquakes

images from 1850, 1900, 1940, 1990

Image from Andersen et al., 2001, USGS Bulletin 2188

SF Bay: Alcatraz Dredge Disposal Site

Bay floor, 1890s style

Alteration of the bay floor

Modern-day bathymetry

Note growth of the mound
Images courtesy http://sfbay.wr.usgs.gov/access/mapping/multibeam/alcatraz1894.html

Interpreting the Sedimentary Record


Image courtesy
http://tornado.sfsu.edu/geosciences/classes/lwhite/time.htm

Laws of Stratigraphy:

  • Original horizontality
  • Superposition
  • Lateral continuity
  • Fossil succession

Related Concepts:

  • Cross-cutting relationships
  • Unconformities

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