Jump to content

Virginia - Maryland Aquia & Nanjemoy formations dating?


kate_rose

Recommended Posts

Hi, 

 

We are doing a unit on geology/paleontology in our homeschool with the fossils we find.  I was wondering if anyone knows the difference between the Aquia and Nanjemoy formations.  I know wikipedia is not perfect but I am not an expert and it lists them as separate formations albeit both from the Paleogene.  I have read Paleocene/Eocene border for the Aquia formation.  Is that correct?  The Nanjemoy formation I had not read about before today.  Is it just the same thing on the Maryland side of the River instead of the Virginia side?

 

Thanks for the help,

 

Kate

Link to comment
Share on other sites

It’s not easy to find an exposure of the Nanjemoy formation in which to fossil hunt. It exposes on several points along the Potomac. They have different fauna’s. Nanjemoy contains serrated Otodus (which depending on the amount of serration can have different names). The Aquia typically contains your usual Otodus obliquus. You can see and fossil hunt the Aquia at Purse state park and Douglas point.

  • I found this Informative 2

“...whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” ~ Charles Darwin

Happy hunting,

Mason

Link to comment
Share on other sites

Not all depositional strata are present in all locations. Some were widespread phenomena while others may have been substantially smaller or even extremely small and local. Think of the amount of silt moved per second by the Mississippi River is hundreds of thousands of times greater than that moved by the tiny creek that's 1 foot across flowing through someone's back yard. Some may have been local landslides, etc. That's how we can surmise what may have happened in the past and how long ago. Sometimes a depositional event may occur on one side of a then-extant river, but not have enough "steam" to make it across that river to the other side. If that river still exists, that stratum will be present on one side of the river, but not on the other.

 

 

Mark.

 

Fossil hunting is easy -- they don't run away when you shoot at them!

Link to comment
Share on other sites

5 hours ago, WhodamanHD said:

It’s not easy to find an exposure of the Nanjemoy formation in which to fossil hunt. It exposes on several points along the Potomac. They have different fauna’s. Nanjemoy contains serrated Otodus (which depending on the amount of serration can have different names). The Aquia typically contains your usual Otodus obliquus. You can see and fossil hunt the Aquia at Purse state park and Douglas point.

 

Actually there are a good number of Nanjemoy Formation exposures in both Maryland and Virginia, not only along the Potomac River but also at other river and stream/creek sites.  The Nanjemoy Formation only contains serrated Otodus in the Woodstock Member.  The Woodstock Member also contains Otodus obliquus as does the Potapaco Member of the Nanjemoy Formation.  Below is a 2 1/2 inch Otodus obliquus from the Potapaco B Member of the Nanjemoy Formation of Virginia.

 

156.thumb.JPG.897033814a277f3eb384fd783721f4dd.JPG

 

 

 

Marco Sr.

  • I found this Informative 3

"Any day that you can fossil hunt is a great day."

My family fossil website     Some Of My Shark, Ray, Fish And Other Micros     My Extant Shark Jaw Collection

image.png.9a941d70fb26446297dbc9dae7bae7ed.png image.png.41c8380882dac648c6131b5bc1377249.png

Link to comment
Share on other sites

10 minutes ago, MarcoSr said:

Actually there are a good number of Nanjemoy Formation exposures in both Maryland and Virginia, not only along the Potomac River but also at other river and stream/creek sites. 

Perhaps I should say not well known or accessible to the public. At least I know of no accessible Maryland sites, and the only site I knew of in Virginia is the now-defunct muddy creek site. 

“...whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” ~ Charles Darwin

Happy hunting,

Mason

Link to comment
Share on other sites

7 hours ago, kate_rose said:

Hi, 

 

We are doing a unit on geology/paleontology in our homeschool with the fossils we find.  I was wondering if anyone knows the difference between the Aquia and Nanjemoy formations.  I know wikipedia is not perfect but I am not an expert and it lists them as separate formations albeit both from the Paleogene.  I have read Paleocene/Eocene border for the Aquia formation.  Is that correct?  The Nanjemoy formation I had not read about before today.  Is it just the same thing on the Maryland side of the River instead of the Virginia side?

 

Thanks for the help,

 

Kate

 

The Aquia Formation is a Paleocene Formation.  The Nanjemoy Formation is an Eocene Formation.  They are separated by the Marlboro Clay which is at the Paleocene/Eocene bondary.  As you go down river on the Potomac River the formations get younger.  You have exposed Cretaceous Formations down river of Washington DC.  As you go further downriver the formations get younger i.e. Paleocene, Eocene, Miocene.  These formations have different members and zones.  The exposed members and zones on the Maryland side of the Potomac River in some places match exactly the Virginia side and in other places don't.  Some sites on the Potomac River are all Paleocene or Eocene or Miocene, whereas others are a combination of two time ages.

 

Marco Sr.

  • I found this Informative 2

"Any day that you can fossil hunt is a great day."

My family fossil website     Some Of My Shark, Ray, Fish And Other Micros     My Extant Shark Jaw Collection

image.png.9a941d70fb26446297dbc9dae7bae7ed.png image.png.41c8380882dac648c6131b5bc1377249.png

Link to comment
Share on other sites

9 minutes ago, WhodamanHD said:

Perhaps I should say not well known or accessible to the public. At least I know of no accessible Maryland sites, and the only site I knew of in Virginia is the now-defunct muddy creek site. 

 

Most of these sites are not accessible to the public and you need landowner permission or government permits to collect them.  Plus most of these sites are also kept secret by the collectors who do have land owner permission to collect them.

 

Marco Sr.

  • I found this Informative 1

"Any day that you can fossil hunt is a great day."

My family fossil website     Some Of My Shark, Ray, Fish And Other Micros     My Extant Shark Jaw Collection

image.png.9a941d70fb26446297dbc9dae7bae7ed.png image.png.41c8380882dac648c6131b5bc1377249.png

Link to comment
Share on other sites

12 minutes ago, MarcoSr said:

 

Most of these sites are not accessible to the public and you need landowner permission or government permits to collect them.  Plus most of these sites are also kept secret by the collectors who do have land owner permission to collect them.

 

Marco Sr.

Along with the Oligocene and Cretaceous formations, it is one of the more restricted formations in Maryland. For good reason, of course. Still a bit unfortunate though, for the dedicated and scrupulous fossil hunters.

“...whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” ~ Charles Darwin

Happy hunting,

Mason

Link to comment
Share on other sites

Thanks for the wealth of information everybody. 

So Purse is Aquia which is good to know.  It has been joined now with the Nanjemoy Wildlife Management Area which is why I was confused about the Nanjemoy formation. 

A special thanks to Troodon.  Having the references makes it so much easier to figure stuff out on my own.

 

So just out of curiousity . . .  I know the Muddy Creek site has been developed which really sucks but on google maps it appears that the tributary it was on is still there.  Has anyone tried to walk up the creek from below that and see if any of the sediments/fossils have continued to wash out or remain farther downstream in the streambed?  I would think so but if not I may go poke around.  It looks like there is several places the stream can be accessed and it wouldn't be hard to ask the owners if they would be OK with a look-see.     

 

MarcoSr  The change along the rivers course makes sense.  I guess the beds must be tilted a bit.  Beautiful tooth.  

 

One other question.  Some of the shells at Purse park when you look at the Matrix itself are almost chalk-like.  The crumble under the slightest pressure as if they have been exposed to acidic conditions while others right beside them are nice and firm.  Any idea why that is?  I guess they could be from different ages - like erosion/exposure and then infill into a new location with intact shells that then fossilized but it doesn't seem that way.

 

Thanks again,

 

Kate

Edited by kate_rose
more thank yous and questions
Link to comment
Share on other sites

16 hours ago, kate_rose said:

So just out of curiousity . . .  I know the Muddy Creek site has been developed which really sucks but on google maps it appears that the tributary it was on is still there.  Has anyone tried to walk up the creek from below that and see if any of the sediments/fossils have continued to wash out or remain farther downstream in the streambed?  I would think so but if not I may go poke around.  It looks like there is several places the stream can be accessed and it wouldn't be hard to ask the owners if they would be OK with a look-see.    

 

I collected Muddy Creek for years before the main collecting area was sold to a developer.  The vast majority of the fossils were collected through digging and sieving directly in a fossil dense bone bed layer in the Potapaco B Member of the Nanjemoy Formation that was present only in a very small stretch of the creek.  Most of the creek is exposed Potapaco A Member of the Nanjemoy Formation which has an extremely low fossil density.  Because of the rolling nature of the ground along the creek it is in only very small isolated areas that the Potapaco B Member of the Nanjemoy is exposed.   You won't find much at all walking the creek.  The area was inundated with trespassers when news of the site leaked out.  Illegal collectors left all kinds of trash, rutted roads, and even cut down landowner trees to make access to the creek easy.  Most of that area along the creek is now posted and most of the landowners in the area do not want to see collecting again.

 

Marco Sr.

"Any day that you can fossil hunt is a great day."

My family fossil website     Some Of My Shark, Ray, Fish And Other Micros     My Extant Shark Jaw Collection

image.png.9a941d70fb26446297dbc9dae7bae7ed.png image.png.41c8380882dac648c6131b5bc1377249.png

Link to comment
Share on other sites

That is sad to hear Marco.  It is always a bummer when a inconsiderate folks ruin in for others.  I don't want to make anyone more upset than they already are.  Well, I will have to hit the internet and read a bunch to see if my boys and I can find another place to access that layer - it sounds really amazing.  Thanks for answering my question. 

 

Kate 

Link to comment
Share on other sites

1 hour ago, kate_rose said:

That is sad to hear Marco.  It is always a bummer when a inconsiderate folks ruin in for others.  I don't want to make anyone more upset than they already are.  Well, I will have to hit the internet and read a bunch to see if my boys and I can find another place to access that layer - it sounds really amazing.  Thanks for answering my question. 

 

Kate 

 

After over 20 years of searching the Muddy Creek area, we only found a couple of spots with the good bone bed layer exposed.

 

Marco Sr.

"Any day that you can fossil hunt is a great day."

My family fossil website     Some Of My Shark, Ray, Fish And Other Micros     My Extant Shark Jaw Collection

image.png.9a941d70fb26446297dbc9dae7bae7ed.png image.png.41c8380882dac648c6131b5bc1377249.png

Link to comment
Share on other sites

Marco,

 

Well I won't ask you for your secret spots.  I wouldn't want an internet generated mob to descend.

But it can't hurt for me to look on my own right.  I am not a trespasser and I hunt with one or both of my 10 year old boys.  I figure there has to be a geological map somewhere with enough detail to show where likely spots are.  From today's reading I found that it looks like there used to be an exposure on the beltway over in Maryland.  It has of course been developed but looking in the creek might be worth the time.  I love exploring and I often find something cool to see even if its not fossils.  

 

It is sad that the amazing spot on muddy creek was destroyed.  I hope scientists got out what they needed before it happened.  The good news is that erosion continues right?

 

Kate

Link to comment
Share on other sites

9 hours ago, kate_rose said:

Marco,

 

Well I won't ask you for your secret spots.  I wouldn't want an internet generated mob to descend.

But it can't hurt for me to look on my own right.  I am not a trespasser and I hunt with one or both of my 10 year old boys.  I figure there has to be a geological map somewhere with enough detail to show where likely spots are.  From today's reading I found that it looks like there used to be an exposure on the beltway over in Maryland.  It has of course been developed but looking in the creek might be worth the time.  I love exploring and I often find something cool to see even if its not fossils.  

 

It is sad that the amazing spot on muddy creek was destroyed.  I hope scientists got out what they needed before it happened.  The good news is that erosion continues right?

 

Kate

 

Kate

 

I wouldn't discourage anyone from doing whatever legal collecting that they want to do.  It is the illegal collecting that I do have a major problem with.

 

You really don't get much erosion at all yearly in creeks.  Unless you get some major weather event like a hurricane that drops 20 inches of rain you won't even notice creek erosion, not like the high cliff erosion along the rivers that happens every year.

 

I pretty much donate everything that I find in Virginia and work with a number of museums and researchers (currently 13) so I get access to a number of sites that the general public doesn't.  The Potapaco B sites that I have access to which I helped find are scientific digs and we still continue to find specimens of scientific interest.

 

Good luck with your Beltway investigation.  All the sites we collected years ago are pretty much gone, covered by malls, stadiums etc.  There is one site where a creek is still accessible but most of the creek old collecting area is fenced in with the entire area posted.

 

Marco Sr.

"Any day that you can fossil hunt is a great day."

My family fossil website     Some Of My Shark, Ray, Fish And Other Micros     My Extant Shark Jaw Collection

image.png.9a941d70fb26446297dbc9dae7bae7ed.png image.png.41c8380882dac648c6131b5bc1377249.png

Link to comment
Share on other sites

Quote
4 hours ago, MarcoSr said:

Kate

 

I wouldn't discourage anyone from doing whatever legal collecting that they want to do.  It is the illegal collecting that I do have a major problem with.

 

You really don't get much erosion at all yearly in creeks.  Unless you get some major weather event like a hurricane that drops 20 inches of rain you won't even notice creek erosion, not like the high cliff erosion along the rivers that happens every year.

 

I pretty much donate everything that I find in Virginia and work with a number of museums and researchers (currently 13) so I get access to a number of sites that the general public doesn't.  The Potapaco B sites that I have access to which I helped find are scientific digs and we still continue to find specimens of scientific interest.

 

Good luck with your Beltway investigation.  All the sites we collected years ago are pretty much gone, covered by malls, stadiums etc.  There is one site where a creek is still accessible but most of the creek old collecting area is fenced in with the entire area posted.

 

Marco Sr.

 

Marco,

 

Well if I encounter anything of interest I will PM you but it sounds like you have your hands full with your sites already.  I have worked in science and I know the value of data and that messing that up means information lost forever in many cases.  I would not want to screw that up for someone else trying to complete their work.  You are lucky that you can contribute to the field in such a meaningful way.  So I am a zoologist not a geologist or paleontologist but I do know that usually folks want the fossils right from the strata where they are preserved and not after erosion has removed them from that context.  Are you getting to do excavation?  If so that is really cool.

 

I assume that the folks you work with don't want anything collected from beaches or anything as that is out of context.  I also assume that stuff in stream beds is the same for the most part.  We have really only been to Purse State Park so far here plus sites in Texas where we recently moved from and a couple of random states as we did cross country trips. 

 

I know erosion is most often a slow process (though along creeks in Costa Rica that I worked on it can be quite significant).  I just was trying to put a positive hopeful spin on a sad event and I had noticed when we were kayaking to Purse the other day that erosion along the Potomac can be pretty significant. 

 

Respectfully,

 

Kate

 

 

Link to comment
Share on other sites

15 hours ago, kate_rose said:

I love exploring and I often find something cool to see even if its not fossils.  

@kate_rose, Good!! Self-discovered fossil sites are the best, giving the most complete satisfaction (even if the fossils are not the best of the best, but hey, everything was done yourself!). Enjoy your adventures and good luck!

 

On 28.5.2019 at 6:47 AM, kate_rose said:

One other question.  Some of the shells at Purse park when you look at the Matrix itself are almost chalk-like.  The crumble under the slightest pressure as if they have been exposed to acidic conditions while others right beside them are nice and firm.  Any idea why that is? 

Same species? Same matrix block?

There can be cracks/fissures in the matrix, resulting in complete dissolution of fossils along the crack, "chalking" a few cm away and completely fresh ones a few more cm away from the crack. More diffuse infiltration of meteoric water in some zones is also a possibility.

 

On 28.5.2019 at 6:47 AM, kate_rose said:

I guess they could be from different ages - like erosion/exposure and then infill into a new location with intact shells that then fossilized but it doesn't seem that way.

Correct! The chalky ones would not have survived transport / redeposition.

Franz Bernhard

Link to comment
Share on other sites

I believe the more consolidated patches are simply so because dissolved minerals such as iron and calcium carbonate have dropped out of solution and solidified the sand together in those spots. 

“...whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” ~ Charles Darwin

Happy hunting,

Mason

Link to comment
Share on other sites

1 hour ago, kate_rose said:

Are you getting to do excavation? 

 

Kate

 

I rarely surface collect anymore.  Almost everything I do is excavation.  I'll help excavate and remove a Miocene Cetacean this weekend that my older son just found.  Museum people want us to get it out before it gets ruined by poachers.

 

Fossils found in-situ definitely have more scientific value because of the provenance.  In a lot of areas of the country they salt beaches for kids fossil hunts.  Once that happens, there is little scientific value to anything that comes from that beach.  Also lots of fossil contaminants get dropped on heavily collected beaches totally unintentionally by collectors.

 

Marco Sr.

"Any day that you can fossil hunt is a great day."

My family fossil website     Some Of My Shark, Ray, Fish And Other Micros     My Extant Shark Jaw Collection

image.png.9a941d70fb26446297dbc9dae7bae7ed.png image.png.41c8380882dac648c6131b5bc1377249.png

Link to comment
Share on other sites

 

On 5/29/2019 at 1:52 PM, FranzBernhard said:
On 5/28/2019 at 12:47 AM, kate_rose said:

One other question.  Some of the shells at Purse park when you look at the Matrix itself are almost chalk-like.  The crumble under the slightest pressure as if they have been exposed to acidic conditions while others right beside them are nice and firm.  Any idea why that is? 

 

  Franz - The block actually was a chunk of oyster shells all glued together (you know how they grow on top of each other).  I got one nice oyster shell specimen off of it.  It was a weird combo of soft pockets of sand and harder pieces of slightly fused sandstone all around the shells.  When think about it, as I worked the soft sand out of the pockets pieces of chalky shell would come off but the harder shells mostly stayed glued together.  I think I was looking at redeposition of the chalky shells.  I thought it was from the Aquia formation but on reflection it probably came from farther up on the cliffs to the side of the small beach we were searching.  I didn't find any teeth or anything in it.  Nothing but oysters and a couple very soft/crumbly spiral shells.  

 

On 5/29/2019 at 3:19 PM, WhodamanHD said:

I believe the more consolidated patches are simply so because dissolved minerals such as iron and calcium carbonate have dropped out of solution and solidified the sand together in those spots.

DaMan - you are probably right about why it sticks together although I would guess how deep it was buried and whether or not it was under much pressure matters as well.  Not all the matrix there is sandy though.  On one end of the beach I was scooping into the sand and I hit a clay layer which seemed to have shells etc. in it too.  I didn't focus there since clay is much harder to sift through than sand.  I don't know if I am at the "Purse Park" everyone talks about since I couldn't find a site description anywhere and it has been joined with the Nanjemoy Wildlife Management Area so I think the signage has been taken down. We just went out on one of the beaches with access and started looking but then we met a local and she kindly pointed us toward a beach along the shore where she found good material. 

 

On 5/29/2019 at 3:21 PM, MarcoSr said:

I rarely surface collect anymore.  Almost everything I do is excavation.  I'll help excavate and remove a Miocene Cetacean this weekend that my older son just found.  Museum people want us to get it out before it gets ruined by poachers.

Marco - Amazing!  You are lucky and so is the Museum.

Link to comment
Share on other sites

3 hours ago, kate_rose said:

Nothing but oysters and a couple very soft/crumbly spiral shells.

Oyster shells are composed of calcite and the spiral gastro shells are composed of aragonite. Aragonite is an unstable modification of calcium carbonate and is much more prone to dissolution than calcite. Shell structure itself is also different.

There are extensive miocene oyster beds in my area and I have not seen any chalky oyster shell. But they can crumble to splintery, but still sturdy, fragments upon weathering. Other, aragonitic, shells and gastro shells weather to chalky material.

Franz Bernhard

Link to comment
Share on other sites

×
×
  • Create New...