Walnut Echs & Crabs

[erose]

It was cloudy this morning and the heat held off to well after noon. I drove a few minutes to a road cut here in Austin that has produced a few good specimens in the past. It is Walnut Formation (Lower Cretaceous) and I usually get a few decent Coenolectypus there. Today I found two types of crab/shrimp claws and 4 (maybe 5) different echinoids. Attached is a scan of the crustacean bits and four of the echinoids: Salenia, Coenolectypus and Loriola. This was the first Salenia from this cut for me but I knew they were there when I found the spines first. I have a few larger Coenolectypus as well as some heart urchins (not sure of the genus yet) I also have a scrappy piece of what I believe is a small Phymosoma.

Excuse the poor depth of field. I used my new scanner and it has surprisingly little depth. Also for scale the largest ech is ~2cm dia.

Edited August 27, 2010 by erose

[JohnJ]

Interesting finds, Eric. Hope you get a chance to photograph them....

[MikeD]

The claws are nice. Something pretty rare for me, so far.

Most new scanners have no depth of field. The old ones work much better for scanner photography and art.

[Uncle Siphuncle]

The Walnut is usually good for a thrill or two....do you think E that you were in the Bee Cave Marl? My impression is that the Bee Cave is one of the more productive zones of the Walnut in your area.

[erose]

The Walnut is usually good for a thrill or two....do you think E that you were in the Bee Cave Marl? My impression is that the Bee Cave is one of the more productive zones of the Walnut in your area.

Yep! In fact within the first 2 meters of the Bee Cave Member. I live within a stones throw of the type section here in west Austin. It's actually named for Bee Cave Road not the town of Bee Cave which is another 8 miles west. There are a number of good exposures of the Walnut along Capital of Texas Highway (aka loop 360) that I hit on a regular basis. In that lower section of the Bee Cave there is a zone that produces lots of small but good stuff like these here. I have a number of other crustacean bits, some odd gastropods with shell, and even a few shark teeth. You go a bit higher and you get into a zone with lots of Loriolas and more heart urchins. Keep going up and you hit the larger Phymosomas. There are about a half dozen different exposures along 360 and Bee Cave Road (FM 2244) that each expose a slightly different section. The largest cut is at 360 and 2244 and there you can see the entire Walnut (3 members) sitting on the Glen Rose and capped by Edwards Limestone.

Today I headed south and hit a site along Canyon Lake. It was seriously hot and I only had 90 minutes but I found some interesting crab material. SO a good two days for crustaceans. I'll post photos as soon as I clean 'em up and takes some photos.

[Uncle Siphuncle]

The Kwa around San Antonio is pretty thin and in my experience not as well exposed as up closer to Austin. In fact I think I read that it really begins petering out south of Wimberley. Echie finds are dominated by well preserved Coenholectypus planatus followed by occasional Loriolia and Heterasters and scarce Phymosomas down this way. Occasionally I find fragmental crab appendages. Engonoceras ammonites are present but tend to be smashed and scattered. Although the sites down here are small and scattered as I said, at least I can get a Walnut fix without driving half way to Dallas to grab some echies...

[erose]

Yeah the Walnut does peter-out south of here. And going west it becomes something different as well. Here in Austin the Walnut is rich with some stuff and there are lots of good echinoids, bivalves and gastropods but the ammonites are like you described, mostly eroded. You also don't find too many Salenias or Tetragrammas. For that reason sometimes we head up to the Ft Hood area, Harker Heights, Killeen and Cooperas Cove and then north near Gatesville Rt 107. There you find lots of those echs (but fewer Coenos & Loris) along with good ammnonites and a few other things.

Recently I have been collecting the Loriolia zones from the Upper Glen Rose. There are a handful of locals near by. I find pockets full of dozens of Loriolas and a few other less common echinoids. The zone also contains Ceratostreon sp. and some other "Walnut" types. But what I want to explore more of is the Lower Glen Rose echinoid beds. The Lower Glen Rose is poorly exposed near Austin. I have been down to Canyon Lake twice and a big road cut on 281 near 46. I imagine there must be other locations in that area but I have not had the time to just do the drive, stop, drive, stop, etc. needed to find them.

Edited September 20, 2010 by erose

[BobC]

There are lots of little productive Walnut spots in this area (I live close to Erose's spot). Did you all know that there is actually a street called "Walnut Clay" and "Edwards" off Mesa? There is also one little sliver of Del Rio clay in the area as well.