Gainesville Fl. Matrix Fun Facts

[ClearLake]

Earlier this year I was fortunate enough to meet up with @digit in Gainesville Florida where he very graciously provided my wife and I the opportunity to do some matrix fossil hunting in a local stream.  We sieved for a good long time collecting many nice shark and ray teeth as well as other items out of the large portion.  At the end we nearly filled a five gallon bucket with gravel that we ran through essentially window screen in the creek to get out the silt and clay.  My original trip report can be found here:

 

http://www.thefossilforum.com/index.php?/topic/114209-north-florida-fun/&tab=comments#comment-1264293

 

Back at Ken's house, he was nice enough to sort the bucket of matrix into sizes for ease of picking. We then ran the matrix through 3 stacked sifters since we had already picked out anything caught by the 1/4" screen in the stream. The coarsest material from the sifters would have been caught by the 1/8" screen so (1/4" - 1/8" range). The next finer size range would have been (1/8" - 1/12") and the finest would have been (1/12" - 1/20").  We bagged it up into 3 gallon ziplock bags of coarse matrix, 1 gallon bag of the medium and about 2/3 gallon of the fine matrix.  Once home, I dried it out and began the picking and identifying process   See some links below for my ID questions and some answers.  Thanks to all those that helped.

 

http://www.thefossilforum.com/index.php?/topic/119245-florida-mysteries/&tab=comments#comment-1309402

http://www.thefossilforum.com/index.php?/topic/119097-gainesville-shark-teeth-question/&tab=comments#comment-1305867

http://www.thefossilforum.com/index.php?/topic/119485-small-florida-sharkrayfish-teeth-help/&tab=comments#comment-1310743

 

So far, all this you have heard or seen before as numerous folks, including Ken, have made many nice posts about sorting and picking matrix for micro-fossils.  Some of them are pinned under this Micro topic.  What I wanted to impart with this post were the results of my picking efforts, or at least the start of it since I have not gone through all of the matrix by a long shot.  But I think I have gone through enough to give a reasonable summary of what can be found in this material.  After I have gone through more of it, I can always update the info.  You can also search on the forum and find many other excellent posts from members that have looked at this material, but I don't think I have seen a complete summary of what can be found (if I missed it somewhere, sorry).

 

I am not going to post a bunch of pictures of what I found in this thread because I have placed many pictures in an album.  Feel free to check it out if interested:

 

My procedure was to pick though the matrix and remove anything that was a fossil, whether I knew what it specifically was or not.  After that, the first thing I did was a volume calculation to see what percentage of the matrix is fossil material.  Out of the coarsest matrix, the fossils made up 3.2% of the volume, they were a bit less in the medium material (1.9%) and even less in the fine material at 1.1%  When you put it all together (remember there is a lot more of the coarse stuff) it comes out to 2.6% of the bucket was fossil material.  To me it seems like a small number when I think that in nearly every small scoop I put under the scope I would find numerous fossils.  It of course is really only all that interesting if one can compare it to other matrixes, but it gives one an idea of what to expect from this material.

 

My next step was to sort and identify everything.  Easy to say, but that was the hardest part since this matrix was new to me.  I should be able to do future batches of this stuff much more quickly.  Once that was done, I counted the number of specimens of each fossil type and just made a simple spreadsheet of each matrix size. So what did I find?  Here is a sample from the coarsest matrix:

 

Keep in mind, most of these fossils are not complete specimens.  So for example, while there are 608 Mylobatidae ray teeth, only a small percentage are whole teeth, but if they are in that category there was enough present to be able to ID it.  You can see there are over 16% that I know are fossils, but not good enough to be part of one of the listed types or even good enough for me to figure out yet what they are.  With more time (and knowledge??) I can probably ID many of those, but that is for another time.  Were there differences between the three sizes of matrix?  Yes, and I lumped the list of types shown above into broader categories so you can see how the four classes of material (I included the hand collected stuff) compare:

 

  

 

   

 

And lastly, if you put everything together, you can see what type of fossils you are likely to find in the 2.6% of matrix from the creek: lots of rays, lots of sharks and a smattering of other marine material.

 

That's all.  Not sure if anyone else will find this interesting, but I'm sort of a data guy, so it was fun for me to look at it this way.  Thanks for looking.

 

 

[digit]

Wonderful analysis--numbers applied to fossils!

 

I can say that the larger categories percentages by size class make sense to me when I can think about the types of fossils in the creek and their sizes. In particular, things like the tiny fish teeth becoming increasingly more common as the size class gets smaller. There are a lot of Rhizoprionodon shark teeth in the creek so the ballooning of the shark percentage in the medium size (about right for a Rhizoprionodon) checks out. I would bet that the species composition of the "Ray" category (which was consistently the largest) likely shifts through the size classes from the larger eagle ray teeth (myliobatid & aetobatid) down to likely a lot more dasyatids in the finer material. Might be an interesting set of pie charts just focusing on the component taxa of the "Ray" category by size class.

 

Still waiting for the Powerpoint slide deck (and the TED talk) on this.

 

 

Cheers.

 

-Ken

[ClearLake]

1 hour ago, digit said:

I would bet that the species composition of the "Ray" category (which was consistently the largest) likely shifts through the size classes from the larger eagle ray teeth (myliobatid & aetobatid) down to likely a lot more dasyatids in the finer material. Might be an interesting set of pie charts just focusing on the component taxa of the "Ray" category by size class.

I have that (they need cleaned up prior to posting) and you are correct.  Aetobatus decrease in percent in each smaller size class and the Dasyatis increase from <1% in the coarse to >9% in the fine.  The mylobatids still overwhelm all the rays, just because there are so many fragments of them.  If I only counted complete specimens it would be a different story, but then I also probably would not have enough samples to be statistically meaningful.  Maybe by the time I pick through all the rest of the matrix I will have enough!!!

 

1 hour ago, digit said:

Still waiting for the Powerpoint slide deck

Oh trust me, I have it!  haha