Maryland's Mesozoic Park

[EMP]

The Mesozoic is an area that is sorely lacking in my collection. I don't know why, but I just never got around to collecting in it. I never fell in love with dinosaurs or mososaurs like a lot of other people. 

 

That was until fairly recently, when I finally took it upon myself to diversify my collection and get to know better my area's (and in some ways own backyard!) geology and paleontology. I set out to discover more about Maryland's Mesozoic Park. I guess it would be best to start off from the beginning. 

 

I started the journey not knowing what I'd find, but knowing what it was I hoped to find. I wanted a piece of the hallmark of the Mesozoic, the age of reptiles - my very own Old Line State dinosaur! There was only one problem - I didn't know where to find one. I knew generally what formations to look in, but not where, nor even what to look for. So I took up the ole' Google machine and my own literature at home and started uncovering more about where to start looking. That's what lead me to the first site. 

 

A TREK INTO THE TRIASSIC

 

It would be disingenuous to say that I did this all by myself, and I would like to thank @WhodamanHD for helping me out tremendously. Without him I likely never would have gotten this together. 

 

For those who don't know, I'll take the liberty to describe the geology of the Free State. In Maryland, the only Triassic aged rocks exposed are those of the Newark Group, here divided by the Maryland Geological Survey into two formations - the New Oxford and the Gettysburg Shale. Both units are exposed in the Culpeper Basin (centered around the town of Poolesville, Montgomery County, Maryland) and the Gettysburg Basin (centered around, in Maryland, the town of Emmitsburg, Frederick County, Maryland). After several months of searching I was never able to find a good exposure near the famous former quarries around the Seneca region in Montgomery County, which is what lead me to the area near Frederick. Here the Triassic rocks are more readily exposed, with reports of numerous fossil discoveries of dinosaur footprints, plants, fish, and others in the area near Mt. St. Mary's University and Rocky Ridge. The Gettysburg Shale in this region is the most fossiliferous, and that is the one I ended up collecting in. Thanks again to @WhodamanHD for giving me info about the site! 

 

I spent a good hour or so at the Gettysburg Shale site, my mind full of images of that amazing Grallator sp. print I'd know I'd find. Unfortunately, as the shadows started growing and the day grew colder, I was forced to give up my quest without any dinosaur specimens from this unit. Still, it was nice to finally be able to collect in it and get to experience these amazing rocks up close and personal. 

 

The vast majority of the finds from this site were simple trace fossils of I assume to be annelid worms, these being most common in the glossy looking shale. 

[EMP]

I also found some plant elements, mostly just extremely fragmented ones such as these root silts (first image, preserved in the orange-ish iron oxide), but after some searching I was able to come away with a woody plant fragment (the bottom image). 

[EMP]

Of course the best find of the day is the possible footprint I found hidden underneath some shale chips. If it does turn out to be a footprint, it's most likely amphibian I'd say. 

 

All in all the Triassic rocks weren't very yielding, but I sort of half expected that to be the case after reading some forum member's posts about the difficulty of extracting Newark Group fossils. But this didn't deter me at all. Rather, it invigorated me to struggle on to the other Mesozoic bounties Maryland has to offer, and I am glad it did!

[EMP]

THE CRETACEOUS ODYSSEY 

 

The Cretaceous rocks of Maryland are well known for their fossil flora and fauna. The rocks of the lower Cretaceous Potomac Group in Maryland are particularly famous for their being the only source of lower Cretaceous dinosaur fossils east of the Mississippi River. Naturally this made me curious to check out, but once again I had some tough luck. After digging through some old geological reports, I came to find that most (probably like 99%) of the localities for the dinosaur bones and teeth were destroyed. As it turned out, the finds from Maryland's "Dinosaur Alley" (a band stretching roughly from the DC border near Bladensburg through Laurel and Muirkirk north to Baltimore) had occurred mostly in the area's numerous iron and clay mining pits, which at the time were dug by slaves. Here the Arundel Clay in particular bares, what were for the time, fairly significant beds of iron ore in the form of siderite and limonite nodules and concretions. These were exploited alongside abundant lignite deposits, formed from the trees that made up the vast Cretaceous forests some 120-110 million years ago. Over time the iron was exhausted and mining began to cease as richer deposits turned up elsewhere, however many of the pits survived for use in the brick making industry, where they were mined for their rich clay deposits. As far as I know, some of these operations still exist, but are off limits to collecting. 

 

This wouldn't be the end, however. Prince George's County has opened up a park near Laurel called Dinosaur Park, where visitors are able to hunt for fossils at one of the old iron pits. You aren't allowed to keep anything but lignite pieces (the staff assumes all other fossils for their collections), but it is still a nice place to visit once in a while. I visited this site a couple of times, thinking that it was as close as I would get to these seemingly long-gone formations. 

 

The unit exposed in the park is the Arundel Clay, which is believed to be an oxbow lake deposit from early Cretaceous times roughly 110 million years ago. There is still some debate on whether or not it should be classified as an independent formation or just mapped as a member of the Patuxent Formation, but since I'm a stickler for the olden days and it's what I've grown to learn, I'll treat the Arundel as a separate formation from the Patuxent. In Maryland, the Arundel is a rather thin unit covering a fairly small area in a small, discontinuous belt stretching along the length of US-1. It is named after Anne Arundel County, though I'd wager it's most famous exposures are (or rather, were) in PG county near Muirkirk. 

 

The most common fossils from the Arundel are carbonized wood pieces and lignite. Whole trees preserved in situ have been found in the formation in the old quarries, however at Dinosaur Park almost all of these specimens are eroded into much smaller pieces (though they have some nice fossil logs on display). Notice how many of these pieces have maintained their surface characteristics - and look almost identical to their modern relatives!

[Miocene_Mason]

Great report, I’m glad I could help! The dinosaur park thing just kills me, They leave a huge logs there to weather away and any chance of an articulated skeleton is worn away by their no-dig policy. The exposure is so small, in a few years they would empty it if they excavated normally. I guess the funds continue this way, but at least they are exciting the youngins on the subject. Sorry a bit off topic, rant a day keeps the doctor away. 

[Tidgy's Dad]

Nice report. 

Glad you had fun and thanks for sharing. 

[EMP]

1 hour ago, WhodamanHD said:

Great report, I’m glad I could help! The dinosaur park thing just kills me, They leave a huge logs there to weather away and any chance of an articulated skeleton is worn away by their no-dig policy. The exposure is so small, in a few years they would empty it if they excavated normally. I guess the funds continue this way, but at least they are exciting the youngins on the subject. Sorry a bit off topic, rant a day keeps the doctor away. 

 

Yeah I was a bit disappointed too. It's nice to visit once or twice, but it's pretty small like you said and the no dig policy was annoying (though I understand why they do it). What really killed me though was their odd public hours. Wouldn't they want the public to explore as much as possible? They have staff their the whole time, so issues like theft, specimen damage, or what have you wouldn't seem likely. 

 

But thankfully Dinosaur Park isn't the only source of Potomac Group fossils in the area. Once I get enough specimens together I'll add a really cool update to this thread. 

[Kane]

Interesting read and report. Regrettably, I don't think your possible amphibian track is more than just a geologic circumstance.  

[Plax]

any chance there is a late Cretaceous segment of this coming up?

[EMP]

42 minutes ago, Plax said:

any chance there is a late Cretaceous segment of this coming up?

 

I have some more lower Cretaceous ones first, but I have found a few late Cretaceous things I could post. 

[EMP]

CRETACEOUS CONTINUED

 

Of course some lignite pieces wouldn't be enough for me . I've been trying for several years to come across an exposure of the Potomac Group sediments outside of the Dinosaur Park belt, and recently I have finally done so. 

 

An indispensable tool in this whole quest was the excellent Maryland Geological Survey report on the lower Cretaceous rocks of Maryland. The report contains an equally good geological map of the Potomac Group's aerial distribution, albeit from 1911, which has helped me considerably. After looking at the map, the sites I've been collecting at seem to be near the Patuxent-Arundel contact, however I believe it's safe to say that all of my finds come from the basal Patuxent Formation owing to the prominence of "vegetable" (plant) remains and the arkosic and sandy nature of the sediment, something that is common for the Patuxent but not for the Arundel. 

 

The Patuxent Formation is the basal member of the Potomac Group, and represents the lowermost bed of the Cretaceous in Maryland. Originally, back in the 1800s, it was believed that the Patuxent and the Arundel were both latest Jurassic in age due to their dinosaurian remains, many of which were found and documented by professor Marsh. However, others who had been studying the floral compositions of the formations argued a lower Cretaceous age, sparking a sort of controversy around the turn of the century. After a short while the lower Cretaceous age for the Patuxent and Arundel is now believed to be correct due to the floral assemblage of the formations, but it's funny because the report I was using still had the Patuxent listed as late Jurassic (?) age. 

 

In terms of geology the Patuxent is also the basal unit of the Coastal Plain, which bends considerable landward in Maryland due to the structure of the Salisbury Embayment. Although it is part of the Coastal Plain, the Patuxent, and indeed the Potomac Group as a whole, has experienced considerable differential weathering over the years and has helped create numerous hills to the north and east of Washington DC that would become important during the Civil War as locations for some of the forts built by the Union Army to defend the capital from Confederate attack. As such, it is rather difficult to tell when you pass the Fall Line (the contact between the Piedmont and the Coastal Plain) just by driving around, however in general the way to tell would be that the hillsides in Coastal Plain territory would expose unconsolidated clays, sand, gravel, etc. whereas the Piedmont would be predominantly saprolite. In this region, abundant mica in the ground also indicates Piedmont bedrock and a more iron colored dirt tends to indicate the Coastal Plain. 

 

Sounds boring to some, I know, but it's important to understand these things when looking for a potential site. 

 

In terms of paleontology the Patuxent is almost exclusively plant based. In some places in Virginia rare fish remains have been found, but none are known in Maryland. They only non-plant fossils from Maryland are dinosaur, reptilian, and mammal footprints which occur abundantly (but scattered) in some parts of the formation, and of which Ray Stanford has found over 300 of over the years. Due to this and the lithology of the formation the Patuxent is believed to have formed in a low-lying, forested area that was crisscrossed by many streams and rivers. This is, of course, further supported by the regionally abundant presence of conifer (cypress) trees, which are common in such environments today. 

 

Now, what did I find? 

 

Almost all of my finds were from woody conifer plants. These first few images show pieces of bark and twig imprints, often preserved in black carbonaceous material against the orange colored, clayey ironstone. For future reference, I have a tendency to say "woody plant" and, to prevent any confusion, almost all such specimens are gymnosperms. 

[EMP]

This piece depicts a hash of what appears to be gymnosperm elements, poorly preserved but noticeable due to their rectangular shape against the rock. 

 

 

The other two are some more woody plant elements. 

[EMP]

Some more plant hash. The first is a nicely preserved woody plant element, likely a gymnosperm.  The others are mostly unidentifiable assorted hash that were some of the first I collected and took with me as a sort of insurance policy. I wasn't originally planning on finding very many fossils, but after just thirty or so minutes of searching had yielded more specimens than possible to carry back I was delightfully surprised! The Cretaceous rocks are much more fossiliferous in Maryland than the Triassic ones, and it's especially interesting that a unit so steeped in history and fossils hasn't been mentioned at all on the forum before (from what I've seen). 

[EMP]

Now time for the big guns . 

 

An impression of a gastropod shell, a freshwater species to be exact. I'm still looking for an ID on this guy, but from my research no gastropods are recorded from the Patuxent. This has lead me to believe that I might be dealing with the Arundel, where a couple of gastropod species are known, but the lithology and flora say Patuxent. 

 

 

Next up is a special find for me - 120 million year old petrified wood! From Maryland nonetheless! You never hear about Old Line State petrified wood, and I was pretty excited to have found this! It must weigh about ten pounds or so.

 

[EMP]

And of course footprints. I found this one pretty recently, possibly theropod? It's preserved in the mudstone that is a sort of trademark for the Potomac in Maryland. 

 

 

 

[Fossildude19]

Hmm. Not sure that last one is a track.  

You might contact either of these folks to have a look at it. 

 

Emma C. Rainforth

Patrick Getty

[Miocene_Mason]

@EMP that’s pretty good looking, sometimes they will have undulations in them. Another resource is This, you can contact Peter Kranz this way.

[King of Snarge]

I remember seeing an article in the Calvert Marine Museum newsletter about 20 years ago. The article described a field trip to a pit mine for Arundel Clay. One of the members was milling around the parking lot and found a dino tooth on the ground there.

[EMP]

10 hours ago, King of Snarge said:

I remember seeing an article in the Calvert Marine Museum newsletter about 20 years ago. The article described a field trip to a pit mine for Arundel Clay. One of the members was milling around the parking lot and found a dino tooth on the ground there.

 

Some people are just born lucky I suppose . I never did find any dinosaur stuff at Dinosaur Park, some croc material, but that's fairly common. 

[EMP]

A short update. Another woody plant I found recently. This one is in a chunk of conglomerate it looks like, which is pretty interesting. I've never seen this before in all of my years collecting. 

 

[Miocene_Mason]

That’s cool! Looks like he inclusion is quartz? Wonder what the underlying formation is, the one that filled those Cretaceous rivers with rocks.

[Miocene_Mason]

On 4/2/2018 at 11:51 AM, EMP said:

I'm still looking for an ID on this guy, but from my research no gastropods are recorded from the Patuxent

Somehow missed that. Sounds like something to ask Mr. Kranz about. Assuming you haven’t already, shall I send him an email? I’d send him a pic and ask’em what he thinks. 

[EMP]

1 hour ago, WhodamanHD said:

Somehow missed that. Sounds like something to ask Mr. Kranz about. Assuming you haven’t already, shall I send him an email? I’d send him a pic and ask’em what he thinks. 

 

I'm busy right now with a bunch of other projects, and still working on the tetrapod footprints from earlier. If you want to email him I'm okay with that (I don't mean to impose anything on you). Just note that I'm not 100% positive that particular piece is indeed the Patuxent Formation, probably more like 85-90%. I'll probably need better pictures though. 

 

As for the plant specimen, that is the Patuxent Formation. In the Mid-Atlantic region the Patuxent is the lowermost formation of the Coastal Plain and sits right on top of the Piedmont rocks along the Fall Line. Those quartz pieces are thus from Piedmont rocks further west, which were eroded into the then narrower coastal area that the Patuxent Formation was being accumulated in. What's even better is that I actually found a piece of quartz sandstone with a Cambrian worm burrow in it at the Cretaceous site, as well as a piece of Devonian shale with a spiriferid imprint! That was pretty interesting. 

 

But as a side note if that exists then the Dunkard rocks you were looking into could have some stuff, as I know conglomerate is somewhat common in the Dunkard. 

[Miocene_Mason]

10 hours ago, EMP said:

What's even better is that I actually found a piece of quartz sandstone with a Cambrian worm burrow in it at the Cretaceous site, as well as a piece of Devonian shale with a spiriferid imprint!

That’s amazing! Though it would make sense, it’s before the glaciers shaved off the top of the piedmont plateau. 

[EMP]

We had some torrential rain here a little while ago, and then got some rain earlier this week. But as the saying goes, April's showers bring....April's fossils? I'm sure that's it....  

 

Anyways I had a little bit of time to collect at the Patuxent Formation site again, and suffice to say the rains brought down some new stuff. I've been meaning to become more selective in what I bring home, but every time I go I try to bring back anything I can - I don't want to leave anything out in the elements and risk getting weathered. I guess that's a good problem to have though, right? All the recent finds have been plants, but there's no problem in that!

 

Just some of the typical stuff, woody plant fragments. On the plus side I've finally gotten a pretty solid ID for my previous petrified wood find. I believe it's a Sequoia sp., in part because that's the only genus I see listed as occurring in the Patuxent Formation of Maryland.