More Crestmont serpentinite

25 May 2015

I’ve done some more poking around in the fat part of the serpentinite patch. Today I’ll show photos from three localities, as marked below on the geologic map (where “sp” means serpentinite).

crestmont-geomap

The first locality is a truly spectacular exposure at the intersection of Crestmont and Kimberlin Heights Drives.

crestmont-kimberlin

The neighbors have made an effort to love this inhospitable stone, as you can see in this closeup.

kimheights-closeup

But serpentinite is not only very low in calcium and extremely rich in magnesium; it also tends to have high levels of toxic metals such as nickel, cadmium and chromium. Serpentine soils tend to be thin and poor (see this helpful Forest Service page). You can see that the little palms are almost dead, and on the upper slope even the pampas grass, one of California’s toughest invasives, is looking peaked.

I didn’t climb on this exposure—there wasn’t time and the rock has treacherous footing. It’s full of texture, though, and this exposure higher up on Kimberlin Heights suggests that it’s pretty chunky.

kimheights-exposure

Locality 2 is on the next street down, Colgett Drive, which is too new to be shown on the base map above. It exposes serpentinite all the way to the end, where I collected this fragment to take home.

crestmont-blue-specimen

I wanted to inspect it as closely as I know how. I have several hand lenses as well as a teeny pocket microscope that gets me up to 45X. With those tools, I perceive that the rock consists of blue bits the color of glaucophane in a matrix of light-colored serpentine. I continue to think of it as blueschist, but I’ll save that discussion for a later post. The point is, just because this area is mapped as serpentinite doesn’t mean it’s 100 percent one thing or another. But for all practical purposes this area is serpentine rock.

Locality 3 is the spot on Crestmont Drive I showed in my very first post, back in 2007. It looks a lot better now. You could creep around the fence and give it a good examination.

crestmont-ur-exposure

There are a couple of interesting things going on here. First is that just around the corner on the left side, where Butters Drive intersects Crestmont, the rock abruptly changes to the Knoxville Formation (KJk), a nice brown mudstone. The geologic map puts a thrust fault there separating the two rocks.

Second is that on the righthand side you can see signs of the pavement being disrupted by some sort of ground movement. Cracking related to it extends across the road. That has taken place in the 7-1/2 years since I last came here. I went to inspect it more closely, but my attention was drawn instead to an unusual sight: a swarm of bees gathered on open ground.

crestmont-bees

I lingered long enough to take two shots, but after the first one I sensed dozens of bees zipping past both my ears, so I let the poor critters be. It was a raw day, and I hope they found a new space to set up housekeeping.

The fossil treasury of UCMP

18 May 2015

Last month, as part of Cal Day, they were giving backstage tours at the UC Museum of Paleontology. The day is a mob scene, but on the last tour of the afternoon I had a fine time being shown around by two of the museum’s scientists.

The collection is vast, the world’s largest university collection. Only part of it is in the Valley Life Science building. There’s also a building in Richmond, and there are great accumulations of tar-seep fossils (from La Brea and McKittrick) housed in Sather Tower—the Campanile—because they smelled too much to keep with the others.

The collection at Valley Life Sciences is housed in huge cabinets that slide along tracks to open enough space to pull out the drawers. Many of those drawers are full of microfossils.

UCMPmicros

These are a huge part of California’s heritage. It was a thorough knowledge of microfossils in the rocks of the Central Valley and Southern California that informed and guided our petroleum industry. California remains America’s fourth-largest oil and gas producing state thanks to this scientific-industrial heritage.

But naturally, the museum had some of their photogenic specimens out. This Triceratops horn, with slices sawn off to expose its interior, was a privilege to hold. Unfortunately, the Bay area has no dinosaur fossils at all, although a few marine vertebrates from Mesozoic times have been found.

triceratop-horn

This ammonoid shell was interesting because it has a beautiful set of tooth marks on it, courtesy of a mosasaur. In the corner of the photo is a drawing of the specimen, as published in a scholarly paper.

mosa-chomp

Mosasaur fossils, to my knowledge, are not known from California either. Not yet, anyway.

And this thing sitting on the floor gave me joy. It’s a stump from the world’s first forest, dug up in rocks of Middle Devonian age in upstate New York.

psaronius-erianus

The inscription reads, “Psaronius Erianus Dawson / [Hamilton Group] Tree Fern / GILBOA, Schoharie Co. NY.” The Gilboa forest was first excavated in the 1870s. When I was on About.com, I featured Gilboa in my list of geo-attractions of New York state, and I hope you’ll seek it out if you’re ever there.

This specimen was undoubtedly part of an exchange of fossils between UC Berkeley and the State Museum of New York, a traditional way for paleontologists to enrich each other’s collections. It was surely a source of pride for Joseph Le Conte, the geologist who was the University of California’s first president. His fossil collection was the nucleus of today’s museum.


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