A Trip Into Inversand

[Shamalama]

Today was a great day to go fossil collecting. The weather was warm but not hot, the sun was screened by clouds and there was no rain. I headed over to Sewell, NJ to join the DVPS (Delaware Valley Paleontological Society) for a trip into the Inversand marl pit. This is a shallow pit that mines the Glauconite rich greensands of the Paleocene aged Hornerstown formation. What we collectors are there for are the Cretaceous aged fossils that can be found within the layers at the pit. Here is a view of the pit as you walk down.

The lowest layers, the Cretaceous aged Navisink foramtion, are under water now but just above it are the green to purple sands of the Hornerstown formation. On top of them are the light tan to brown Vincentown formation and then the Kirkwood formation. The Hornerstown and Vincentown formation are considered to be Paleocene in age, although the very lower reaches of the Hornerstown are thought to be Cretaceous. This puts the K/T boundary within the formation but there is no clear trace or mark of it that can be seen with the naked eye. Tests have been done that show a spike of Iridium within the formation very near the base where it meets the Navisink.

When I got to the site we queued up in line and handed in our paperwork and a small fee to get in. The trip was led by the DVPS but there was a representative from the NJ State Museum on hand. He was helpful throughout the day identifying finds and giving a brief lecture on the geology of the pit. He mentioned that one of the best MFL (main fossil layers) within the Hornerstown was about midway up the formation. He pointed to a white drain pipe and said that marked the approximate location of a lag bed which contained fossils. After a quick orientation and safety lecture we were set loose upon the pit. This being my first visit to the site I took the advice of the expert and headed towards the drain pipe he'd pointed out. It was along the left side of the pit and I think you can see it in the above photo of the pit. There wasn't too much room to walk and dig but I found a spot and started to dig into the sandy layers.

A note here for those of you unfamiliar with East Coast geology. The southern and eastern half of New Jersey is all unconsolidated sand and clay from the Cretaceous up to the Pleistocene. It makes for easy digging but the fossils are not always well preserved.

I'd dug a hole about three feet cubed and had managed to find the lag layer, right where it should have been. I had been told by other collectors that the majority of what is found are steinkerns (molds of the inside of the shell) of Pelecypods. The first thing I found though was something that looked like bone. It turned out to be parts of a turtle shell.

I probed and carefully dug around looking for more shell and found some bits but not the whole turtle. After picking up as much of the shell material as I could I was finding mostly steinkerns. The locals call this a "Squirrel Skull" for obvious reasons but I think I shall label mine as Cucullaea sp., or Ark Shell.

Here is another Cucullaea sp. mold, but different from the first.

As I was digging out the sand, water was leaking in which made things very mucky. Lucky for me the sediments were mostly sand and not clay so it was just wet and gritty. I tried my hand at sifting the sand I was pulling up using a wire mesh colander and my bucket which I'd filled with water. I wasn't having too much luck finding anything with the sifter and mostly spent my time running my hands through the water saturated sands. At times I would pull up an double handful of the sediments and plop it on the surface so I could go through them by hand. The fossils wanted to be found and wouldn't let the Glauconite sand stick to them so one only had to look for something without any sand on it. Upon lifting one such handful out of the hole I felt something sharp scrape my hand. When I looked at the side of the pit I saw the end of a shark tooth sticking out. It turned out to be from an extinct Mackerel shark Archaeolamna kopingensis.

This tooth had not been tossed around in the water very much or by a creek (as in Big Brook or the Rammenessin) so it was in pristine shape. After a few more hours of digging, the sides of my hole started to cave in more often and so I gave up and decided to look elsewhere for a bit. The pit is large enough to host a big group and I think there were easily 30 people on the trip. I stopped by JustBob (Bob) and FossilsofNJ's (John) holes to see how they were doing and they had adopted a different strategy. They had brought along their full size screens and were washing shovel fulls of sand in a small moving stream from a drain pipe. They were finding about the same stuff I was though Bob had scored a worn Mosasaur vertebrae. Since the sediments are Paleocene in age, many of the fossils that are found are thought to have been winnowed out of a Cretaceous formation by underwater currents and then redeposited. This explains the worn nature of the vert and the fact that it was found in Paleocene sediments.

After a while, I was not having luck finding that same lag bed elsewhere so I headed back to where I had started to maybe dig the collapsed hole out again. About six feet away from my original hole another collector had dug and abandoned a 4'x4' hole and it was filled with water. The sides were in good shape and didn't seem like they would be prone to cave-in so I decided to prospect a little. I dug the pit about two feet deeper and found the lag bed again. I was pulling out lots of steinkerns, some in better shape than others but nothing spectacular. I dug into the wall of the pit again and suddenly I spotted something.... different. It was an Ammonite!

This is my first NJ Ammonite and it is a Sphenodiscus lobatus. It may only be a partial but that is not uncommon for New Jersey since most of the shells of invertebrates have long since been dissolved away leaving only a clay steinkern. There were some other pieces of the Ammonite but most of them had decided to fall apart and not even retain the chamber shape. I'm happy enough with this quarter section as the suture lines are just stupendous.

I dug for another hour or so and found a few more steinkerns and a broken shark vertebrae but that was it for my finds. I packed up my stuff and wandered over to where Bob and John were to tell them I was leaving. When I got there, John was pulling out parts of another turtle and it looked like he had more than I did. I couldn't tell if he had enough for a whole shell or just part but it was better than the pieces I found. After chatting for a bit we each made our way out of the pit and back to the cars. It was another successful trip for me and I hope to get back into the pit in the future (as long as it doesn't close, which is might).

Here is my haul, the turtle shell is in the bag on the lower left.

[Auspex]

No bird material this time, eh? It is known from there!

Thanks for the great report, and welcome to vert-land

[non-remanié]

Very nice informative report as always and nice finds. I should have gone on this trip, but I have had absolutely no luck digging there in the past despite moving quite large amounts of greensand. But that's how it goes...

[MikeDOTB]

Great report!

[cowsharks]

Interesting report. Great pic of the place. Considering you found so little, do you think you will return for future digs? You did find a couple neat specimens, but boy, it sounds like you had to put in a lot of work for little return on your investment. Are there any micro's there? I might have considering screening that material and brought home a 5gal bucket full to sort through. I think it's cool that they actually let folks dig huge holes there.

Daryl S.

[barefootgirl]

Great report and I love that tooth. Awesome day and finds.

[MikeD]

Looks like an interesting place. Nice tooth.

[nala]

Great report and nice haul,congrats Dave !

[Terry Dactyll]

Dave... Looks a great place to collect... The 'squirrel skull' shell cast is awsome... and great tooth, beautiful colour...

[Scylla]

Inversand has been on my "collect there someday" list for a few years now, your report brought me there, thanks

[Shamalama]

Thanks for the comments and kudos guys!

Auspex: I was hoping for something birdy as our guide told me that 14 of the 100 or so cretaceous aged bird bones found in the US have come from that pit. Alas, all we got were annoyed looks from the local Goose population.

Cowshaks: All the collecting there involves moving large amounts of greensand. I must have dug a couple of cubic meters worth of sediment during my day there. Some people dug even more than that and found less than I did. It's all hit or miss but once you find the lag layer you have a better chance of finding something.

Scylla: hopefully you get a chance to go into Inversand. The rumor is that they are going to close the pit and let it flood soon since they aren't getting much business right now in this economy. India was a big buyer for use in water purifiers/softners but that has been down lately.

[Just Bob]

As always great report Dave.

Here are a couple pictures of John(fossilsofnj) digging out his turtle with me and Dave Parris from the NJ state museum looking on.

[xonenine]

great report and pictures, thanks!

[Diplotomodon]

Cool! Sounds like you had a lot of fun. Great job on finding the ammonite---they're pretty rare 'round here.

Again, nice trip! I wanna go there!

[fossilsofnj]

How can one get that dirty and not be having fun?

I can now follow up with a picture of some of the turtle scutes I was pulling out when Dave left. I was too tired from the day to do any more than wash them off and fit together the obvious. This represents less than half the bone recovered including a significant portion of the plastron (bottom of the turtle) pictured in the upper right hand corner. Everything needs to dry out before I start the task of gluing this critter back together.

We have a tentative identification of Agomphus tardus from Dave Parris of the New Jersey State Museum. While I need to do more research, I did find one source that reports Agomphus tardus to be terrestrial, interesting for a marine environment.

While fragmentary turtle scutes are probably the most common bone found in NJ, it is considered uncommon in our area to find any significant amount that can easily be identified as coming from a single individual. Being an active marl mining operation, Inversand is one of the few remaining locations in NJ where one can dig in-situ without violating one or more of the ordnances that abound in this state. Let’s hope that we may continue to enjoy the privilege for many more years.

John

[non-remanié]

Very nice! To say the least, you sure deserve it. Hopefully it can be nicely pieced back to together

How can one get that dirty and not be having fun?

I can now follow up with a picture of some of the turtle scutes I was pulling out when Dave left. I was too tired from the day to do any more than wash them off and fit together the obvious. This represents less than half the bone recovered including a significant portion of the plastron (bottom of the turtle) pictured in the upper right hand corner. Everything needs to dry out before I start the task of gluing this critter back together.

We have a tentative identification of Agomphus tardus from Dave Parris of the New Jersey State Museum. While I need to do more research, I did find one source that reports Agomphus tardus to be terrestrial, interesting for a marine environment.

While fragmentary turtle scutes are probably the most common bone found in NJ, it is considered uncommon in our area to find any significant amount that can easily be identified as coming from a single individual. Being an active marl mining operation, Inversand is one of the few remaining locations in NJ where one can dig in-situ without violating one or more of the ordnances that abound in this state. Let's hope that we may continue to enjoy the privilege for many more years.

John

[DeloiVarden]

My back hurts just from reading your report. I especially like the tooth!

[fossilnoggin]

john, that is a very nice find! i was wondering why you were so quiet in that new hole you were digging i would have liked to have found at least a shark tooth. still, would like to go back if we are fortunate to get another chance to go. thanks for letting me borrow your screen. it was very helpful.

[cowsharks]

As always great report Dave.

Here are a couple pictures of John(fossilsofnj) digging out his turtle with me and Dave Parris from the NJ state museum looking on.

Oh man, that stuff looks soft! With a water source just a few feet away, I think I would have been filling 5-gallon buckets of material and sifting it in the water. Does anyone do that? I think I would use 1/4" screens with window screen underneath to catch the micro stuff - if there is any?

Thanks for posting the pics. I always wondered what that place looked like up close.

Daryl S.

[fossilnoggin]

Oh man, that stuff looks soft! With a water source just a few feet away, I think I would have been filling 5-gallon buckets of material and sifting it in the water. Does anyone do that? I think I would use 1/4" screens with window screen underneath to catch the micro stuff - if there is any?

Thanks for posting the pics. I always wondered what that place looked like up close.

Daryl S.

it is very soft stuff. the main fossiliferous layer is just above the navesink, which is chocolate brown and much harder. so it is relatively easy to find the mfl. water constantly fills the holes you dig, so it makes for a lot of work, cave-ins and all. and you have to be lucky as well. i screened a lot of the mfl, worked very hard, and had very little luck. many people had screens. i do think there are forams to be found if your screen diameter is small enough. you can also dig up the mfl and go through it by hand, that is how soft it is.

[squali]

Great report Dave. You seemed to make out well with the pristine tooth, and the ammonite is Awesome.

I was there with my 2 kids who seemed to have as much fun collecting the green marl as the fossils.

It is an unpredictable place to collect but removing fossils insitu is kinda rare in the n.j. cretaceous. I got wrapped up on the other side of the kt boundary, digging mostly in the mid hornerstown fossil layer for the survivors. Really hope to get back there now that I have a feel for the place.

[Nandomas]

I am sorry I missed this fantastic report. Thanks Dave

[BlazeXploder]

Did you dig out the rest of the chambers of that ammonite? I noticed there were a couple loose around it.

[Shamalama]

BlazeX,

I did dig a clay mass out from the area where the ammo was found and once it dried I saw more chambers but nothing that was intact or salvageable. Sometimes the Steinkerns turn to soft clay very quickly.

[JimB88]

You mean you can just pick up fossils without having to chip them out of diamond hard limestone...whoaaaaa

kidding..Ive always wanted to go to a place where the fossils are already prepped so to speak.

Good report and great finds!

Edited June 8, 2011 by JimB88