[Turtle]

My idea here is to have a place for interesting geology that does not merit its own thread or as a place to expand on interesting geology brought up in other threads that may drift off topic.

I know! Let's start with varves!

BRB...collecting data....

[Turtle]

Here's the varve start from the GW thread:

Originally Posted by Turtle

Note my current location and nomination. I could spit on Amboy from my chair. Speaking of Amboy, roadcuts, Coopers, and global warming, if not shakiness of belief, there is a magnificant 40 to 60 foot high varve just East of Amboy on a roadcut. The individual layers measure no more than 2 or 3 mm if I recall. Not sure what formal analysis on it is around, but I visited it on a geology course field trip. Might hold some info on past climate in the area. I'll get back to y'all on it; maybe even do a field trip.

Originally Posted by Turtle

Roger that; done & done. I think the varve I visited is the boldened reference. Can we say ice age?

http://pubs.usgs.gov/sim/2004/2826/Arl_geol_text.pdf

I checked my map, and the above varve referenced in the USGS report is West of Amboy & I now don't think it's the one I visited. I recall it was at least 12 to 15 miles East of the above feature, either near or within the Gifford Pinchot National Forest boundary.

In any case, the varve I met showed layering of alternating lighter & darker material, which like tree rings corresponds to seasons. The varve is the sedimentary remnant of a mountain lake formed behind a glacial block, and during warm weather the lake was open water and the heavier material sinks quickly. During the cold season when the lake is frozen over, the lighter organic material has time and stillness under the ice that allows it to sink. Also found in the varve I met, ice-floated erratics; cobble size stones that found there way out onto the ice, and then fell to the bottom at the thaw.

Field trip is in the planning.

Post Script: Map coordinates for Bald Mountain:
45º 55' 09.71" N
122º 34' 17.83" W
Google Earth has some photgraphs from GE Community from around the area, and using the change elevation view feature puts the terrain in perspective.

[Turtle]

Originally Posted by Turtle

... I checked my map, and the above varve referenced in the USGS report is West of Amboy & I now don't think it's the one I visited. I recall it was at least 12 to 15 miles East of the above feature, either near or within the Gifford Pinchot National Forest boundary.

In any case, the varve I met showed layering of alternating lighter & darker material, which like tree rings corresponds to seasons. The varve is the sedimentary remnant of a mountain lake formed behind a glacial block, and during warm weather the lake was open water and the heavier material sinks quickly. During the cold season when the lake is frozen over, the lighter organic material has time and stillness under the ice that allows it to sink. Also found in the varve I met, ice-floated erratics; cobble size stones that found there way out onto the ice, and then fell to the bottom at the thaw.

Field trip is in the planning.

Yesterday I went & searched out the varve, and not only found it but several others along the road. I have a lot of photos, video, and notes to work up into a full report, but attached below is one small sample of what we found. The photo features a couple of ice-rafted erractics in the deposit. More to come.

[freeztar]

Awesome Turtle!

More pics! More pics!

[Turtle]

Originally Posted by freeztar

Awesome Turtle!

More pics! More pics!

Patience young Geology Knight. The varves were just part of the trip, and all video is still in post-production. To slake your thirst a bit, here's the coordinates of 3 varve locations we visited. The first is the location for the photo above. It is not clear to me if these are all part of one lake, or separate small lakes?

A quick shout-out to Racoon & Buffalo, whose help was invaluable in the investigation of this interesting geology. You fellas rock! .

45º 56' 41" N
122º 16' 28" W
Elevation: 838 Feet

45º 56' 44" N
122º 16' 06" W
Elevation: 771

45º 55' 34" N
122º 13' 32" W
Elevation: 1122 Feet

[Turtle]

45º 56' 41" N
122º 16' 28" W
Elevation: 838 Feet

The varve at this location, we measured at 33 feet from crest to road level. Video to come of that process, but the still image below has some interesting aspects. Note the crouching figure near the base for scale, but more importanly the bright area higher up on the escarpment. This brighness is due to water leaking out of the formation and reflecting the sunlight and we happened to get on scene at just the right time.

We also collected some samples, which I have in plastic bags, and as soon as practical I plan to make some high-res scans @1200dpi so we can better see the component particles.

[Turtle]

Originally Posted by Turtle

45º 56' 41" N
122º 16' 28" W
Elevation: 838 Feet

The varve at this location, we measured at 33 feet from crest to road level. Video to come of that process.

Buffalo, Racoon, & Turtle measure a varve.

If we estimate an average thickness of 3/8" per annual deposit, then this exposed portion represents ~1,056 years. I don't know if, or how far, the deposit continues below the road-bed level.

YouTube - Measuring a Varve

[Thunderbird]

Have there been any fossils recoverd from this deposit?

[Turtle]

Originally Posted by Thunderbird

Have there been any fossils recoverd from this deposit?

My thoughts exactly. I have not found a formal study of this exact deposit, nor seen mention of fossils in the reports I have read. It seemed logical to me, and we did look purposefully for fossils but found none.

I have a composite video rendering for posting that is a compilation of all the clips I took at this first site. I hasten slowly....

[Turtle]

The round holes in the face appear to contain some kind of bees.

YouTube - Extreme Varving