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alliecat1881

Iron Sandstone Concretions At Calvert Cliffs

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alliecat1881

Hi everyone! I'm new here, but I plan on being an active poster. Geology and paleontology are my passions. I was out at Calvert Cliffs yesterday and the erosion is in full-swing, yielding many a Chesapecten. I also came across plenty of iron sandstone concretions. Everything I have read on the web is about the Navajo concretions in Colorado which are spherical. Obviously these are not spherical and their abundance at the cliffs in all manner of shapes and sizes is intriguing. I was wondering if any of you know how these formed? My geology professor was stumped (he has a doctorate in invertebrate paleontology, not geology, so I can understand). Here are a couple in situ inasmuch as this is where they landed after eroding out of the cliff face. I realize I am guilty of a major faux pas by not including something to scale these formations. One of the photos you can see my shoe so it gives some inkling as to their size. However, I figure you have plenty of experience among you all to know exactly what it is I'm talking about so hopefully this isn't an issue.

https://www.flickr.com/photos/alliecat1881/15642517576/in/photostream/

https://www.flickr.com/photos/alliecat1881/15046115813/in/photostream/

I am really looking forward to some insight! Anyone who somehow has yet to acquire a Miocene bivalve, now's your time!

https://www.flickr.com/photos/alliecat1881/15479680839/in/photostream/

-Allison

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EasternShore88

Welcome to the site Allison! Wish I could be of some help but I am new to this and still learning with each passing day. There are some very knowledgeable people on this site that I'm sure will be by shortly with some insight!

Andrew

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jpc

welcome form WY, Allison, and nice explantion, painshill.

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alliecat1881

Thanks for the welcome everyone, and thanks painshill for the great explanation. Most of the formations remind me of cypress knees or cypress tree roots, but I didn't want to make any assumptions. Seeing as the cypress was very prevalent during the Eocene in our area (and still are) maybe what they appear to be is what they are remnants of... and maybe I can somehow attribute this phenomenon to the bolide impact 35mya. Maybe maybe. I'm only halfway through my first college geology course, but I know enough to actually understand the words you used! I'm learning.

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Plax

this is "bog iron" and should show up on a google search. it should be in the base of loose sands higher up in the section. Bog Iron was mined as iron ore in earlier times in the US. iron fixing bacteria are also in evidence as coatings in you section photo, they are rusty colored slimes of a sort.

All of what Painshill says above is accurate also (of course). I think the rock in your pictures is the laminar form of bog iron though. You might google "indian paint pots" for more information on some of the ironstone concretions also found in your area. The exposure pics you provided all look Miocene to me. Your ironstone doesn't look like fossil.

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alliecat1881

Thanks for the input, Plax. Given the area (Calvert Cliffs is mostly Miocene) you're probably right. At least I knew it was iron ;)

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