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Rayminazzi

Creek was a little flooded today made it harder to navigate, started the day with 2 dead drill battery's that I had charged the night before so I decided to move father up to look at some different exposures, started by picking up some matrix for micro's from the bottom of the pecan gap, more on that later, and then some Del Rio clay for the same, (if someone has suggestions for how to wash this faster that would be great) spent the next 2 hours picking up heteromorph mariellas.

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Rayminazzi

More Mariella, Graysonites?

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Rayminazzi

Nautiloid? In some very hard limestone, (Edwards? is upstream a ways)

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Rayminazzi

Now the pecan gap micro's, shark teeth? This is my first time trying micro's so any help or criticism is welcome.

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Rayminazzi

If you see anything you recognize I'd appreciate it.

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Uncle Siphuncle

This stuff is what our typical Georgetown/Del Rio looks like.  The Del Rio is a soft clay that preserves lots of oysters, but the molluscan steinkerns don't hold together too well.  The contact of the Georgetown and Del Rio is the zone you hit here.  Our Georgetown is the Mainstreet equivalent of North TX and presents as a tan somewhat hard, hummocky limestone studded with marcasite crystals and rosettes...and these cool Mariella ammonites among other things including occasional nautiloids.  This zone is poorly exposed in Bexar County so you have done well.  BTW, the Edwards farther upstream gets much harder and the fossil content changes and gets a whole lot more sparse and boring.  

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Uncle Siphuncle

The remanie at the Austin/Pecan Gap contact is sort of a condensed zone of phosphatic fossil molds and shark teeth.  It is composed mostly of rolled Baculites sections, bivalves and gastropods, but I've taken a few good, nickel sized ammonites in it as well, and saw some other cool stuff like little coiled nautiloids come out of the Capitol Cement pit by Nacogdoches and Wurzbach Freeway, where this contact zone is more broadly exposed.  

 

The shark teeth in this zone always have the root dissolved away, leaving just "shells" of enamel remaining.  I guess acidic conditions over time preferentially dissolved the root.  

 

BTW, I talked to your boss today at the shooting range.  

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Uncle Siphuncle

If you want to burn a lunch hour in the creek, I may be able to point us toward some other fossils as well.

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Rayminazzi

That sounds like fun, I don't get lunch hours but on my days off I'm usually free

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Rayminazzi

I'll have more pics of the ones I can clean tomorrow before work

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fossilnut

The "shells" of the shark teeth look like immature forming teeth from the back files. Teeth form from the tip to the root. So these teeth have not developed enough to fill in the enamel  and form a root yet. See attached pic of a miocene tooth. These are rarer finds because of there more fragile condition.

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RJB

Whats with the drill batteries?

 

RB

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Uncle Siphuncle
11 minutes ago, fossilnut said:

The "shells" of the shark teeth look like immature forming teeth from the back files. Teeth form from the tip to the root. So these teeth have not developed enough to fill in the enamel  and form a root yet. See attached pic of a miocene tooth. These are rarer finds because of there more fragile condition.

DSCN5230.JPG

Thank you for bringing up that possibility.  I thought of that as well, but that doesn’t explain why I’ve found scores of teeth from this interval from different parts of town, all in this condition, and fish/mos matl is virtually absent (in this contact zone as well as the underlying Austin Chalk section), yet vert matl is more prevalent farther north in a similar interval.  Local chemistry?  “Things that make you go HMMMMM.”

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caldigger
8 minutes ago, RJB said:

Whats with the drill batteries?

 

RB

My question as well. Do you use drills to weaken the matrix for fossil extraction?

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fossilnut
22 minutes ago, Uncle Siphuncle said:

I thought of that as well, but that doesn’t explain why I’ve found scores of teeth from this interval from different parts of town, all in this condition,

Just throwing this thought out there, some sharks are believed to have swallowed their shed teeth to reabsorb the minerals for more tooth   production. From the pic it looks like some teeth have roots but the ones without look like they are from the same type of shark? I'm not clear as to what mineral(s)  form the root? Are these other teeth from one type of shark?

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Rayminazzi
25 minutes ago, caldigger said:

My question as well. Do you use drills to weaken the matrix for fossil extraction?

 

35 minutes ago, RJB said:

Whats with the drill batteries?

 

RB

 

25 minutes ago, caldigger said:

My question as well. Do you use drills to weaken the matrix for fossil extraction?

I was trying to remove another fossilized from the Austin chalk by drilling holes all around and chiseling between

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Rayminazzi

Here's one of the better mariellas from yesterday with associated neithea and exogyra.

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Rayminazzi

First pick is neithea with exogyra, second pic is rastellum? I don't know. Third is nautiloid.

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Uncle Siphuncle

I concur with your IDs, with the minor revision that Exogyra is actually Ilymatogyra.  The nautiloid is a keeper too.  Can’t see surface ornamentation in this preservation, but if the chamber cross section is narrow I’d hedge toward Paracymatoceras (accompanied by fine, sinuous ribs on surface in clean specimens).  If proportionally thicker/more globose, I’d lean toward Cymatoceras.  At this point you have seen 75% of the normal fauna from the local Kgt.

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Uncle Siphuncle

I concur on the Rastellum eroded in section as well.

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Rayminazzi

So I've been confused about this for a while now, exogyra and ilymatogyra seem to be different names for the same thing or maybe there's a difference I can't find?

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Uncle Siphuncle
1 hour ago, fossilnut said:

Just throwing this thought out there, some sharks are believed to have swallowed their shed teeth to reabsorb the minerals for more tooth   production. From the pic it looks like some teeth have roots but the ones without look like they are from the same type of shark? I'm not clear as to what mineral(s)  form the root? Are these other teeth from one type of shark?

Interesting scenario.  But I’ve found multiple genera and various sizes in the same lag deposit, all in this same preservation.  I can’t explain much of what I encounter with any certainty, nor back it up with any formal paleo tutelage, so my best bet is to try to stay open minded.  I just might learn something.

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Rayminazzi

I'm gonna go with Paracymatoceras on this one

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Heteromorph

Nice finds! Never knew about shark teeth being half dissolved at the base of the Pecan Gap formation.

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