Home | Session 4 | Shallow Marine Pg 1, 2, 3, 4, 5, 6, 7, 8
Shallow Marine Environments and Paleoenvironments: Reefs, Beaches and Basins
Presented
by Carol Tang
California Academy of Sciences
Complex biology and geology
Your text (Exploring Earth Science, Second Edition, Prentice-Hall, 1999) uses the coral reef as an example of the interplay between biology and geology. While organisms build up the reefs, they also heavily erode the reefs. One of the largest destroyers of carbonate reefs is the parrot fish, which has specially-adapted teeth to take bites of the reef. They swallow the material and digest the organic material and excrete out the gravel and sand.
Siliciclastic systems
- Input of sediment from land
- Active margins (e.g., California) are dominated by siliciclastics because there is a lot of erosion and mountain-building
- Contains carbonates but they are diluted by sands, muds, etc.
- Although lots of organisms live here, they don't build the environment
Beaches are a classic siliciclastic system. In these photographs from UC Santa Barbara, we see the processes and modern beach; and in the cliffs, we can see beaches in the geological record (millions of years old).
Because waves are affected by the sea floor, irregular topography will serve to focus waves and differential erosion can work to shape the coastline. See this example: http://geoserv.geology.wmich.edu/kominz/C12refractheadland.gif
A beach has a vertical profile due to the erosion by waves and tides. See: http://www.onr.navy.mil/focus/ocean/habitats/beaches1.htm
Because waves and tides have different strengths during different times of the year, there are seasonal profiles--in other words, the beach is a dynamic feature. See: http://geoserv.geology.wmich.edu/kominz/C12beach.gif
updated April 1, 2002
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