Friday Field Foto #76: Thin-bedded turbidites (special repost)
If you’ve been following this blog since mid-2007 you may remember this particular Friday Field Foto.
This is one of my very favorites. This is a photograph from Salt Point State Park along the northern California coast (just south of the town of Gualala*).
These are some beautiful Paleocene (65-56 Ma) turbidite deposits exposed along the beach cliffs. That ultra-high-tech piece of field equipment at right is a wooden stick with 10 cm increments marked on it.
The reason I’m reposting this is because I received a copy of a book in the mail the other day called Earth’s Restless Surface that has this photo in it.
I had forgotten about this … several months ago, the folks who put this book together contacted me about using the above photo. Now that the book is published, they went ahead and sent me a copy, which was very nice.
I haven’t had a chance to read it yet, but it looks quite nice. It is on the topic of Earth surface processes and written for the general reader.
Check it out if you get a chance.
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UPDATE: See Ron’s GigaPan image of this exact same outcrop … it is amazing.
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* say that out loud … it’s fun, right?
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Clastic Detritus 
Wow, great photo. I don’t think I have seen it before. Thanks for reposting. If you don’t mind a scientific question, are all beds laminated and what is the argument for these being turbidites? The thickness variations seem similar to trends in tidally influenced systems.
saxifraga … I think one reason people love this photo so much is because of the rhythmic nature of the bedding.
No, not all the beds are laminated in this succession … especially the thicker (>20-30 cm) ones. But, in this photo, almost every sandstone bed is either parallel-lam’d or ripple lam’d (if I remember correctly, don’t have the section right next to me).
The argument for these being turbidity current deposits is (1) that each of these sand beds grades up slightly, (2) each of the thinner beds are little Tc-Td Bouma layers, (3) orientation of ripple-lam’n is all unidirectional, and (4) there are turbidites above and below this particular horizon for hundreds of meters.
If they were tidal, I’d expect some more directions/orientations of the ripples, and I’d expect some more distinct tidal facies and/or other shallow-water facies stratigraphically nearby.
That said … there are occassions (especially in levee deposits) where gravity flow deposits can resemble tidal facies.
Beautiful beds! I just looked up Gualala to see where it is (south of Point Arena), and found the original native American word meant “where the water flows down.”
Now you’ve done it…
Ron … did you ever get a chance to get some GigaPans at Salt Point? Or elsewhere along CA coast?
I got only one other GigaPan at Salt Point (http://www.gigapan.org/viewGigapan.php?id=14121) due to fading light and incoming bad weather. Had to abandon my plans to GigaPan the rest of the Gualala basin until maybe this summer(?). I did however, swing south thru the Gadsden Purchase and shoot about 50 more GigaPans on my way home. I’ll dribble them out on my blog over the next couple of weeks, but here’s another teaser for you: http://www.gigapan.org/viewGigapan.php?id=15528
Ron … that one of the Western Escarpment of the Guads is fantastic. I gotta get me one of these GigaPan set ups.
Thanks for the explanation. It’s always good to learn new things.
A Jacobs Staff.
I have used one to measure limestone bed thicknesses at the cliffs near Albany.
What are they called again? The Hidelbergs or something…*enh*
Cool turbiditie sequence.
Hi, Brian,
Thanks for your wonderful turbidite photo. I am writing a book(Korean), tentatively titled “Catastrophic History of the Earth.” Can I use your photo? and what can I do for the use? Sorry for not being comments!
Paul
hi, I am studying geology now, can I ask you a question about the scale of this photo, although you have a ruler beside, but what is the exact thickness of each bed?