Texas Eagle Ford Exogyra Fossil

[LSCHNELLE]

In early July 2016, I encountered a virtual self-guide field trip posted online by Pete R. Rose, PhD in February 2012. He describes an Eagle Ford (Kef) outcrop exposed in the parking lot of Barton Creek Mall in Austin, Texas. I went there to check it out. The USGS webviewer only designates the area as Georgetown-Del Rio. But, the U.T. Bureau of Economic Geology has an accurate Geologic Quadrangle Map #38 that shows this feature. But, it predates Barton Creek Mall which is not on the map.

Interestingly, the Austin Chalk Atco Member caps the nearby hilltops, but it is heavily weathered to caliche and rusty ferrous minerals. Difficult to find fossils in the transition zone. The South Bosque member is clearly visible and underlain by the Bouldin Flags (BF) Member. The BF has much thicker flaggy beds than I usually see (up to one foot thick). In the lower part of the BF, I extracted this beautiful slab of what I think are Exogyra columbella levis (Meek). The largest ones are ~1" wide. Most of the Kef outcrops I have visited have just fragmented oyster hash. This is the first time, I have seen the complete fossils rather than just rounded fragments.

Also, I think a nearby rock had traces of a fish fin on it. I took a picture just after dark, but left the fossil there. It was a very large rock and a paper-thin fossil remnant. I believe it was about 6 to 8" long.

Anyone have better IDs? I was surprised to see Exogyra in the Kef.

Lee Schnelle

[ynot]

Your "fin" is a mineral vein remnant, not a fossil.

Can not help with the oysters-- nice fossils though!!

Tony

[erose]

Wouldn't write off the "fin" as mineral just yet. Scrappy fish bone is not uncommon in the Eagle Ford.

There are three possible Exogyras from my quick look at Akers and Akers, 2002. E. aquillana Stephenson , E. columbella Meek and E. levis Stephenson. E. levis looks closest to me but your photo is out of focus. The genus Exogyra shows up all the way down in the Glen Rose (Albian) if not lower.

I have tried collecting there several times over the years, as I live rather close by. Each time the mall security came out and chased me off. Each time I was just starting to see good stuff and they showed up before I could really snag anything decent.

[Guguita2104]

Hello!

The oysters are Exogyra, indeed.However I can't help you with the specie.

Regards,

[CraigHyatt]

Exogyra costata are found by the boatload down here in Eagle Pass (Escondido). Some discussion of Eagle Ford Exogyra here, FWIW.

http://www.lib.utexas.edu/books/landscapes/publications/txu-oclc-4530273/txu-oclc-4530273.pdf

http://www.lib.utexas.edu/books/landscapes/publications/txu-oclc-564334/txu-oclc-564334.pdf

Edited July 12, 2016 by CraigHyatt

[LSCHNELLE]

Thanks for all the comments. I will post a better focus picture for you. BTW, mall security finally chased me off after dark. I showed them my PG license to validate my claims. My bright flashlight gave me away. Thankfully, they didn't draw their guns since I had a geologic hammer in my holster.

[LSCHNELLE]

Here is a better picture hopefully. The buff color has a little more pink in reality.

[erose]

From the better focused photos my best guess would be Exogyra levis Stephenson based on the rounder shape and smooth form. E. aquillana seems more elongate and , E. columbella has distinctive radial lines. All are possible Woodbine Group Exogyras.

Note that most Exogyras are limited to distinct time periods with only limited overlap in species/subspecies. For example E. ponderosa and E. costata are always high up in the section.

Security was on me within 5 minutes. I think the trick would be to dress for the mall and carry everything in a big Nordstrom's bag.

[LSCHNELLE]

erose: When is the last time you have been to the Mall outcrops? Landscape elm and oak trees and juniper have grown up significantly and cover all but the highest slopes now. I tried calling Mall security for access permission, but just got the runaround. Thanks for the ID. Over the last 15 months, I have reactivated my 1980s passion for invertebrate and shark tooth fossil hunting. I am into crusher shark teeth now more than anything else. Maybe, we could hunt together some day.

[erose]

It has been a few years. For me lately I have been concentrating on echinoids and other odd bits from the Glen Rose and Walnut Formations. A number of years ago there were some great Eagle Ford exposures up near Round Rock and I made a decent collection of Ptychodus teeth then. That is now almost completely built over.

If you want to meet I will be at the next meeting, Tuesday the 19th, of the Paleontological Society of Austin. All are welcome and you can visit our web site for info. Never any pressure to join but you might meet some nice fellow collectors.

[lcordova]

Erose, wednesday 19th at what time?

Theres a slim chance i can make time....

[LSCHNELLE]

lcordoba: Their website states:

When: Tue, July 19, 7pm – 9pm

Where: Austin Gem and Mineral Society Facility, 6719 Burnet Lane, Austin, TX 78757
(512) 458-9546

Eric: I see that you are President. I will try to make the meeting.

I started back to hunting for trilobites spring 2015 (not too many good ones in Texas, but found a few nice parts in NW Illinois and Texas Hill Country), then moved to echinoids and ammonites before latching more heavily on ptychodus. They are "new" to me.

I could introduce you to a "good" Kgru/Kgrl Salenia Texana contact in Travis County that you may not have seen before.

[lcordova]

A bit late, but better late than never.. I ended up needing to go out of the city but will be on the lookout for your next meetings.

Thanks!