Weird nodules in Severn Formation?

[NickG]

In parts of the Severn Formation in eastern Maryland, I will periodically find layers that are very dense with nodules. Has anyone else noticed something like this?

[patelinho7]

I’m about to visit some Severn localities and I will keep an eye out. 
 

In the meantime@Andúril Flame of the West

[Andúril Flame of the West]

Always good to see others exploring the Severn! What type of nodules are you referring to?

 

I have no experience with the eastern Severn, but siderite concretions do occur in the western exposures of the formation. These concretions are often found in the upper layers of the Severn and contain mollusk shells. Perhaps I will have to consider scouting farther east. 

 

I believe that some sections of the Severn near Bowie also contained unfossiliferous ironstone concretions. There was an old thread by @MDPaleoceneGeo that had some good pictures of these concretions in situ and once removed from the matrix. However, I cannot locate this post. Perhaps it was somehow deleted/lost during the server migration .

Edited December 23, 2023 by Andúril Flame of the West

[NickG]

I need to dig some photos up but these are very small and black-gray. They are not ferrous. 

[historianmichael]

@NickG you can find small black phosphatic pebbles at the boundary of the Severn-Aquia. The boundary is a lag and represents the loss of several millions of years in time. My understanding is that these pebbles are from that lag. You can also find tiny broken shark teeth in the layer.

Edited December 24, 2023 by historianmichael

[NickG]

55 minutes ago, historianmichael said:

@NickG you can find small black phosphatic pebbles at the boundary of the Severn-Aquia. The boundary is a lag and represents the loss of several millions of years in time. My understanding is that these pebbles are from that lag. You can also find tiny broken shark teeth in the layer.

That would make sense to me based on where I see these pebbles the most. I assume you’re saying in these spots the Brightseat either didn’t deposit or was washed out before the deposition of the Aquia?

 

At one site, I continue to find reasonable sized shark teeth including whole teeth intermixed with those pebbles. 🤔 Not as big or as nice as what is produced at Bowie but still pretty decent. 

[NickG]

1 hour ago, historianmichael said:

@NickG you can find small black phosphatic pebbles at the boundary of the Severn-Aquia. The boundary is a lag and represents the loss of several millions of years in time. My understanding is that these pebbles are from that lag. You can also find tiny broken shark teeth in the layer.

Is there a paper that has documented this phenomenon? I have heard a rumor one person associated with CMM thought this represented a coprolite layer but that has never made sense to me as they don’t have any coprolite like features. 

[historianmichael]

8 hours ago, NickG said:

That would make sense to me based on where I see these pebbles the most. I assume you’re saying in these spots the Brightseat either didn’t deposit or was washed out before the deposition of the Aquia?

 

At one site, I continue to find reasonable sized shark teeth including whole teeth intermixed with those pebbles. 🤔 Not as big or as nice as what is produced at Bowie but still pretty decent. 

My understanding is that in these places the Brightseat eroded away.

 

8 hours ago, NickG said:

Is there a paper that has documented this phenomenon? I have heard a rumor one person associated with CMM thought this represented a coprolite layer but that has never made sense to me as they don’t have any coprolite like features. 

I am not aware of a paper describing the phenomenon. The interpretation is anecdotal based on other lag sites along the ACP that also have these tiny pebbles.

Edited December 24, 2023 by historianmichael

[NickG]

1 hour ago, historianmichael said:

My understanding is that in these places the Brightseat eroded away.

 

I am not aware of a paper describing the phenomenon. The interpretation is anecdotal based on other lag sites along the ACP that also have these tiny pebbles.

Thanks! I got your email too and replied. Have a good holiday break!