November 17, 2012

Notes from the field bath house quarry

Filed under: Egypt, Field photos — acagle @ 6:41 am

A very little bit of Fayum geology. We have a quarry across the street from our dig house and I’ve been meaning to go check it out for a while now and finally got the opportunity to do so yesterday. I believe in this area what we have is the “Ravine Beds” a middle Eocene series of soft sandstones, claystones, marls, and limestones. These all derive from a marine source, the former Tethys Sea, the much larger precursor to the Mediterranean. At that time the coastline was much further south than it is now and also moved around north and south depending on sea levels, so the deposits generally tend to reflect the location of the shoreline.

Here is a shot of one of the walls:
Desert Fox

The lowest stratum and what makes up the floor of the quarry here is a compact yellow very fine sandy silt; I believe they’ve been using this in our brick making operation. I believe this is a deep-water environment since there are no fossils at all in it and it’s very homogeneous. Above that is a series of different strata, none very thick suggesting a series of different depositional environments over a relatively short period of time. Above that is a layer of finely stratified sand, almost like a dune. Note how it has scoured down to pinch off two sections of the stuff above it. That sand layer is pretty neat actually:

Desert Fox

It’s made up of very thin layers and can be scraped easily with a trowel — I had one of those sort of “wow” moments while scraping it off, knowing that I was the first person to see this grains of sand in almost 40 million years since they were initially laid down. They have slightly different characteristics so some are more cemented together and thus weather at slightly different rates resulting in the jagged-looking sidewall.
Another funny thing about this sandy stuff:
Desert Fox
It’s full of holes! Quite a few of them. I could always tell where this particular stratum was because there would be holes in it. What could be in there? Fox? Hmmmm. .. . .

Desert Fox
If you look reeeeealy close, you can see a young dog sitting outside of the second one from the left. Pretty cushy little home they have there; they go pretty far back and so will stay quite cool in the summer and warm in the winter.

Here’s another of the very complicated sections where the topography when deposition was occurring messed with the nice, neat layer cake stratigraphy:
Desert Fox
The hexagonal(ish) stuff on top is a very dense mudstone that appears to dry like that after it’s been exposed.

What I was really looking for were fossils. None of these so far have had a thing in them, just a bunch of sediment. It took me a while to find something and I ended up going all the way to the rear of the quarry. There, I was walking past what looked like a bunch of rocks that had bird poop on them.

Bird poop?

Ah, no: fossils:
Desert Fox
All invertebrates, including clams, mussels, and something called a scaphopod. There are some others, but I have not yet been able to ID them yet (photo of one later).

Now, these were all rocks sitting on the floor or on a talus slope. Hmmm. . .that means they probably came from higher up, right? Yup.
Desert Fox
This is it in situ. As you can see, all of the shells are broken up, mixed up, and jumbled together. I suspect this happened at the tie of deposition rather than later and probably represents a shoreline or near-shoreline assemblage where the dead critters would be tumbled around in the surf. I found very few whole specimens, though I was able to grab a few small clams and one much larger thing which I will post a photos of later.

Hopefully I’ll get out to the north side of the lake at some point where there are areas of heavy vertebrate fossils, including not only cetaceans (whales) but also larger land mammals and primates.

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