Point Mugu Turbidites
A
cache
by TerryDad2 adopted by BWidget
Hidden:
11/27/2006
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Turbidites are underwater landslides of sediment that cover vast
areas of the deep ocean floor. This series of turbidites are now
just off the Pacific Coast Highway south of Ventura.
 
Turbidites form in the deep ocean near the continental
shelf. Classic turbidite sequences are made up of fining
upward beds of sediment. This means that the grains at the
bottom of the sequence are larger than the grains at the top
of the sequence. In a complete sequence the bottom sediments
are pebble sized conglomerates, followed by coarse then
fine-grained cross-bedded sandstone, then shale, and finally
silt. This series is called the Bouma cycle.
A turbidite is formed by a density flow. In this type of flow,
the fine grained sediments suspended in the water increases the
density of the water. The denser water is then able to suspend
larger particles than it normally would be able to. For example a
rock will sink quickly in pure water, but sink much more slowly in
thick mud.
 Typically, the entire sequence is not seen
because each successive flow will erode off some of the top of
the last sequence, or if the deposit is at the end of the
flow, only the finer layers will be seen.
Usually turbidites form off of a convergent plate margin (where
two plates are colliding). A convergent margin provides the
mountains that are good sources of sediment, sufficiently steep
off-shore slopes and periodic earthquakes to trigger the undersea
landslides.
 That is the case in the sequence of rocks at this
location. Only the fine-grained sand, shale and silt layers
are seen in these cliffs, suggesting that they formed at the
far end of the turbidite. Hundreds and possibly thousands of
density flows occurred to create the tall cliffs of repeating
sand, shale, and silt layers you see in these cliffs.
Turbidites continue to form just off the coast. A pair of deep
marine canyons extend out into the Santa Monica Bay from Mugu
Lagoon and Port Hueneme. These canyons transport loads of sediment
down into the Santa Monica Basin.
Logging requirements:
Send me a note with :
- The text "GCZJNF Point Mugu Turbidites" on the first line
- The number of people in your group.
- In a 3-foot section, how many density flows occurred? Include
how you determined the start and end of each flow.
- Based on the thickness of each of the layers was each event the
same size? Include how you came to that conclusion.
The above information was compiled from the
following sources:
- Wikipedia,
http://en.wikipedia.org/wiki/Turbidite
- SUZANNE REYNOLDS (1987) A recent turbidity
current event, Hueneme Fan, California: reconstruction of flow
properties Sedimentology 34 (1), 129–137.
doi:10.1111/j.1365-3091.1987.tb00565.x
- Field trip guide to the Marin Headlands (Golden
Gate National Recreation Area) and the Point Reyes National
Seashore; Geology of the National Parks, San Francisco State
University, April 20, 2002
Additional Hints (
No hints available
)
(Decrypted Hints)
Find...
 turbidite.jpg
turbidityCurrent.bmp
V570_27.jpg
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Logged Visits (
49 total. Visit the Gallery (16 images)
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Warning.
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Cache find counts are based on the last time the page generated.
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 October 22 by JRMan (1208 found)
Very cool formation. I will e-mail with my best guess of the description. Thanks for the fun spot.
[view this log] | October 3 by Don_J (3238 found)
I'll be honest. I've stopped four times at GZ, and simply cannot figure out the answers. The new cache owner will provide me with the answers, thus I will learn, and on my 5th time by, I will have a proper persective.
Thanks Bill,.and Terry.
[view this log] |  August 28 by BWidget (4898 found)
Point Mugu Turbidites was transferred from TerryDad2 to user BWidget
[view this log] | August 23 by McCachers Simi (482 found)
On our way home from camping. Learned something. TFTC
[view this log] | July 31 by campyc (3206 found)
This is actually a common formation all along this lovely coastline. Nice buckwheat in bloom everywhere, and a few dudleyas. Thanks TD!
[view this log] | |
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Current time: 11/21/2009 7:00:35 PM
Last Updated: 10/29/2009 2:45:08 AM
Rendered: From Database
Coordinates are in the WGS84 datum
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