BajaNomad

Does anyone know the geology of these La Bocana sandstones?

vgabndo - 1-31-2011 at 10:36 PM

Just south of La Bocana there are uplifted sandstones in eroded layers with some of them exhibiting this formation on the upper edge. Very curious. I don't suppose it is any use asking that we keep this to geology?

Baja 2011 second download 01500.jpg - 37kB

vgabndo - 1-31-2011 at 10:41 PM

Here's the side view of the nose cone shown before. They appear to be pure sandstone, and there were several similar "nose cones".

Baja 2011 second download 01600.jpg - 26kB

mtgoat666 - 1-31-2011 at 11:31 PM

Quote:
Originally posted by vgabndo
Does anyone know the geology of these La Bocana sandstones?? Very curious. I don't suppose it is any use asking that we keep this to geology?


Concretions in siltstone, sandstone are simply zones of rock that are more competently cemented, and weather more slowly,... so they stand out as spherical. Sometimes concretions formed like this because of dead critter causing localized geochemical conditions -- in some sed rocks I have seen where you crack the concretions with a hammer and find a fossil in the heart of many of the concretions.
Don't really know Bocana area, but based on general Baja geology, I hazard an educated guess that the sedimentary rocks are probably Miocene (5 to 23 million years old).

p.s. republicans don't fund basic science research, so if scientific knowledge is what you seek, ask a democrat!
:lol::lol:

mcfez - 2-1-2011 at 07:23 AM

Quote:
Originally posted by vgabndo
Just south of La Bocana there are uplifted sandstones in eroded layers with some of them exhibiting this formation on the upper edge. Very curious. I don't suppose it is any use asking that we keep this to geology?


I'm just a stupid guy here but....

These rocks look like they have been rolling back and forth in a water wave action (?)

Geo_Skip - 2-1-2011 at 08:26 AM

mtgoat666 has it exactly right!. Good to fins another commenter who has some Geology comprehension.

Expect fossils in many concretions ( shells)...they are a b-tch to break though..I have a nasty scar on my left thumb from my rock hammer thanks to a Plio-Pleistocene concretion from the Border Park area just north of the border at Tijuana. By the way, the border fence was three rusted strands of barbed wire which wands broken down and buried in sand in 1975!

Great fossils though!

BigOly - 2-1-2011 at 09:07 AM

Now this is interesting.

vgabndo - 2-1-2011 at 10:05 PM

I was amazed at the purity of the sandstone. I couldn't find anything that wasn't sand. Just a clue. and multiple nosecones.

Baja 2011 second download 014 (Small).jpg - 42kB

vgabndo - 2-1-2011 at 10:08 PM

Another view

Baja 2011 second download 017.jpg - 28kB

Bob H - 2-1-2011 at 10:14 PM

Quote:
Originally posted by Geo_Skip
mtgoat666 has it exactly right!. Good to fins another commenter who has some Geology comprehension.

Expect fossils in many concretions ( shells)...they are a b-tch to break though..I have a nasty scar on my left thumb from my rock hammer thanks to a Plio-Pleistocene concretion from the Border Park area just north of the border at Tijuana. By the way, the border fence was three rusted strands of barbed wire which wands broken down and buried in sand in 1975!

Great fossils though!


Geo Skip.... you should get in touch with Georock on this board. She is very good at this stuff also!!

Bob H

BajaDanD - 2-1-2011 at 11:14 PM

There are rock formations in the estuary under water that are shaped just like the one in your picture. also as you drive the road along La bocana estuary you will see the same rocks in many places along the road

woody with a view - 2-2-2011 at 06:49 AM

so there are whale vertebrae fossils inside?

DENNIS - 2-2-2011 at 07:09 AM

Here....Have fun.
--------------


Coastal evolution of Late Cretaceous and Pleistocene rocky shores: Pacific rim of northern Baja California, Mexico
Markes E. Johnson1, Jorge Ledesma-Vázquez2, Hovey C. Clark3 and Jennifer A. Zwiebel3
1Department of Geology, Williams College, Williamstown, Massachusetts 012672Area de Geología, Universidad Autónoma de Baja California, Ensenada, Baja California, Mexico 228003Department of Geology, Williams College, Williamstown, Massachusetts 01267
Abstract
Cretaceous on Cretaceous and Pleistocene on Cretaceous unconformities are mapped throughout a 45 km2 field area surrounding the village of Eréndira on the Pacific coast of northern Baja California, Mexico. The unconformities represent a late Pleistocene rocky shore (120000–130000 ka) directly superimposed on a Campanian–early Maastrichtian rocky shore (77–70 Ma). Superb exposure and preservation of coastal features allow for precise paleogeographic restorations. Physical analysis includes a comparison of rocky-shore composition, configuration, and overall length. Paleoecological analysis permits the recognition and comparison of preferred wave directions. High-intensity, windward biotas during the Late Cretaceous included rock-encrusting rudists and coralline red algae, while low-intensity, leeward biotas were characterized by rock-encrusting oysters, scleractinian corals, and bryozoans. During the Pleistocene, the open coast was exploited by the byssate bivalve Mytilus and boring bivalves including Petricola and Penitella, while more protected settings were dominated by the gastropods Olivella and Saxidomus. Amino-acid analysis of Saxidomus nuttalli yielded an age estimate consistent with the last interglacial epoch (oxygen isotope stage 5e). Wave impact was oblique to the paleoshore during the late Pleistocene; onshore winds were generated from the west. In contrast, wave movement was generated from the east to southeast and parallel to shore during the Late Cretaceous. Field data are integrated with paleogeographic reconstructions and predictive models, including computer models for local and global oceanography. Where different paleogeographies and oceanographic models conflict, field mapping of this sort adds a much needed element of ground truth.

mcfez - 2-2-2011 at 07:50 AM

...... wave movement was generated from the east to southeast and parallel to shore


So....do I win the Chicken dinner for having it right? :o

Cypress - 2-2-2011 at 07:58 AM

DENNIS, Thanks. Thought maybe those Saxidomas had something to do with 'em. Believe the rudists played a larger part than suspected.:D

DENNIS - 2-2-2011 at 08:39 AM

Quote:
Originally posted by mcfez

So....do I win the Chicken dinner for having it right? :o



Of course. We'll put it in the mail this afternoon. You should receive it by dinner time............around the 18th of the month. YUMMY :lol::lol: