GY 111 Lecture Notes
D. Haywick (2008-09)
GY 111 Lecture Note Series
Sedimentary Environments 4: Carbonates
A) Shelf Terminology
B) Reefs, atolls and oolites
C) Evaporites and evaporate basins
Reference: Press et al., 2004, Chapter 7; Grotzinger et al., 2007, Chapter 5 pages 108, 120-127;
GY 111 Lab manual Chapter 3
A) Shelf Terminology
So far in the sedimentology component of GY 111, we have focused on siliciclastic sedimentary
environments that were restricted to
or shoreline areas (e.g., alluvial fans, rivers,
deltas, beaches). Today, we start to get our feet wet.
Continents are surrounded by relatively shallow water. These are the
they are remarkably inconsistent in width. In the Gulf of Mexico near were we live, the shelf is
very wide, almost 80 miles in fact. It is also wide along the eastern seaboard of the United States.
In contrast, the shelf along the western seaboard of the country (e.g., California, Oregon) is
narrow (in some places, only a few miles wide). The reason is that the west coast is a tectonically
active region and the Gulf of Mexico/eastern shoreline is not. We call it a
which more or less means “boring”, at least as far as volcanoes and earthquakes are
concerned. Wide shelves occur along coastlines that are tectonically inactive which are areas
where sediment has been being deposited for a long, long, long time. The shelf is officially
defined as the region surrounding continents where the water ranges from 10 m
to 150 or 200 m
The end of the shelf is marked by a relatively sudden increase in slope at the
near 0º on the shelf to 3º along the
). The deepest part of the ocean (the
) like the shelf is relatively flat, but here is water is incredibly deep (5000 m or more!).
Sedimentation on most shelves is restricted to the zone nearest the shoreline. The rest of the shelf
may be devoid of any recent sediment. These areas are considered
because the last time
they received sediment was during the height of the last ice age approximately 18,000 years ago.
You will recall that the nearshore zone which includes beaches extends outward from the shoreline to the
place where the water depth reaches 10 m.