Shamalama Posted March 29, 2009 Share Posted March 29, 2009 I've been photographing specimens from my collection for documentation purposes and thought I'd post some from Swatara Gap, PA. A little background first; Swatara Gap is a water gap through Blue Mountain 11 miles NW of Lebanon, PA and 2 miles NW of Lickdale, PA. It's named for an Chief who used the passage frequently when raiding English settlements in the Lebanon valley during the French and Indian War. Today it's used by Interstate 81 to turn north and cross the long linear WSW to ENE trending Blue Mountain. During the construction of the highway a roadcut was made into Ordovician age Martinsburg shales and exposed the rich deposit of fossils contained within. It should be noted that the Martinsburg formation is a mix of thin beds of Sandstone, Siltstone, Shales, Arkosic Limestones and various mixes of the aforementioned that is overlain by the Silurian age Tuscarora Sandstone. In most of the formation there are little to no fossils present because it is thought the formation was a deep basin. The reasoning for the presence of the fossils at Swatara is that they were deposited toward the end of the deposition phase of the Martinsburg as the basin shallowed. In this region it's found as a thin strip along the south face of Blue Mountain with other rocks to the south being part of the Hamburg Klippe. For many years the cut was a popular local collecting site and became world famous for the many well preserved species found including Starfish, Brittlestars, Crinoids and numerous species of Trilobites. The fossils were preserved in a gray-brown organic siltstone often with coatings of orange Limonite. Most well known for the many specimens of the Asteroid Protasterina and blind Trilobite Cryptolithus, the site was doomed to eventually disappear. The main collecting site was a (approx.) 50' high wall of an old road-fill quarry underneath the elevated northbound lanes of I-81. The exposed rocks underlay the southbound lanes of I-81 and it was only a matter of time before collectors removed enough material to threaten the roadbed. To complicate matters the rock often breaks unevenly and is very fragile so one has to often go through quite a bit to get a few good fossils. The site was "closed" in 1990 but collectors continued to visit the site. In 2004 PennDOT removed 20 dump truck loads (approx. 200 cubic yards) of material from the site, as part of an improvement project for I-81, and placed them in an old borrow pit in Swatara State Park near Suedburg, PA (which is in Devonian age Mahantango shales). Once that operation was completed, the site was buried under concrete and large limestone fill. Today nothing is left available for collectors as the entire highwall was buried up to road level. It's possible that another spot could be located nearby but it will be difficult as the surrounding area is heavily forested parkland or private property. For more information visit: http://www.dcnr.state.pa.us/topogeo/collec...swataragap.aspx Now, onto the fossils! Plectorthis? Rafinesquina Sowerbyella Strophomena or Rafinesquina Cryptolithus Enrolled Cryptolithus Isotelus 1 -Dave __________________________________________________ Geologists on the whole are inconsistent drivers. When a roadcut presents itself, they tend to lurch and weave. To them, the roadcut is a portal, a fragment of a regional story, a proscenium arch that leads their imaginations into the earth and through the surrounding terrain. - John McPheeIf I'm going to drive safely, I can't do geology. - John McPheeCheck out my Blog for more fossils I've found: http://viewsofthemahantango.blogspot.com/ Link to comment Share on other sites More sharing options...
Shamalama Posted March 29, 2009 Author Share Posted March 29, 2009 Unknown Trilobite Partial Flexicalymene (or Gravicalymene, I never can tell) Liospira Unknown Crinoid? Brittlestar arms (likely Hallaster) I found this when I was much younger and had no idea that fish were not around in the Ordovician. Wonder what it is? 1 -Dave __________________________________________________ Geologists on the whole are inconsistent drivers. When a roadcut presents itself, they tend to lurch and weave. To them, the roadcut is a portal, a fragment of a regional story, a proscenium arch that leads their imaginations into the earth and through the surrounding terrain. - John McPheeIf I'm going to drive safely, I can't do geology. - John McPheeCheck out my Blog for more fossils I've found: http://viewsofthemahantango.blogspot.com/ Link to comment Share on other sites More sharing options...
Guest solius symbiosus Posted March 29, 2009 Share Posted March 29, 2009 Nice stuff! Looks very similar to the Edenian stuff that I find around here(Central Kentucky). One would think that with the greater clastic load of the water, and proximity to the coast, that the fauna would be different. If you have any papers describing the stratigraphy and environment of the area, I would love to read them. Link to comment Share on other sites More sharing options...
Auspex Posted March 29, 2009 Share Posted March 29, 2009 Thanks for the (unfortunately post-mortem) site guide. Your sampler makes me want to find a likely site, buy it, and open a pay-to-dig quarry. "There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant “Try to learn something about everything and everything about something.” - Thomas Henry Huxley >Paleontology is an evolving science. >May your wonders never cease! Link to comment Share on other sites More sharing options...
RJB Posted March 29, 2009 Share Posted March 29, 2009 Hey Shamalama dude. Your Strophomena or Rafinesquina,, I dont know what size that is, but I found fossils very much the same in New Zealand. They measured between 1/2 and up to 2 inches across. I gave them to my new freind, but I wish I would have kept a couple. Dang it. I was just being nice. RB Link to comment Share on other sites More sharing options...
Frank Menser Posted March 29, 2009 Share Posted March 29, 2009 Sorry to hear of the passing of a great local... Here is a Cryp I bought back in 94 marked only Penn. for local. Looks like it might have come from there. 1 Be true to the reality you create. Link to comment Share on other sites More sharing options...
Dicranurus Posted March 30, 2009 Share Posted March 30, 2009 Unknown Trilobite What a lovely trilobite! It looks odontopleurid. "It seems to me that the natural world is the greatest source of excitement; the greatest source of visual beauty; the greatest source of intellectual interest. It is the greatest source of so much in life that makes life worth living." -Sir David Attenborough Link to comment Share on other sites More sharing options...
Finnfos Posted March 30, 2009 Share Posted March 30, 2009 Nice stuff you have thanks for showing . That Flexicalymene looks similar like those in Morocco. Link to comment Share on other sites More sharing options...
Shamalama Posted March 30, 2009 Author Share Posted March 30, 2009 Sorry to hear of the passing of a great local...Here is a Cryp I bought back in 94 marked only Penn. for local. Looks like it might have come from there. Definitely from the Matrinsburg shales, the Limonite staining gives it away. Probably from Swatara although there are a few other small areas where similar material can be found like near Roxbury, PA. -Dave __________________________________________________ Geologists on the whole are inconsistent drivers. When a roadcut presents itself, they tend to lurch and weave. To them, the roadcut is a portal, a fragment of a regional story, a proscenium arch that leads their imaginations into the earth and through the surrounding terrain. - John McPheeIf I'm going to drive safely, I can't do geology. - John McPheeCheck out my Blog for more fossils I've found: http://viewsofthemahantango.blogspot.com/ Link to comment Share on other sites More sharing options...
Shamalama Posted March 30, 2009 Author Share Posted March 30, 2009 What a lovely trilobite! It looks odontopleurid. Thank you for the compliment, I think it's Acidaspis but there is not enough to positively identify. -Dave __________________________________________________ Geologists on the whole are inconsistent drivers. When a roadcut presents itself, they tend to lurch and weave. To them, the roadcut is a portal, a fragment of a regional story, a proscenium arch that leads their imaginations into the earth and through the surrounding terrain. - John McPheeIf I'm going to drive safely, I can't do geology. - John McPheeCheck out my Blog for more fossils I've found: http://viewsofthemahantango.blogspot.com/ Link to comment Share on other sites More sharing options...
Guest solius symbiosus Posted March 30, 2009 Share Posted March 30, 2009 Thank you for the compliment, I think it's Acidaspis but there is not enough to positively identify. Looks like a Primaspis. Acidaspis has an occiptal spine. Regarding Flexicalymene and Gravicalymene- The Gravicalymene have a more "bell" shaped glabellar furrow; the Flexiclaymene have a more triangular shape. On the pygidium in Gravicalymene, there are 5 interpleural furrows; 6 or 7 on Flexicalymene. Link to comment Share on other sites More sharing options...
Shamalama Posted April 7, 2009 Author Share Posted April 7, 2009 I just found this article in an old copy of Pennsylvania Geology about the Trilobites of Swatara Gap. Dave -Dave __________________________________________________ Geologists on the whole are inconsistent drivers. When a roadcut presents itself, they tend to lurch and weave. To them, the roadcut is a portal, a fragment of a regional story, a proscenium arch that leads their imaginations into the earth and through the surrounding terrain. - John McPheeIf I'm going to drive safely, I can't do geology. - John McPheeCheck out my Blog for more fossils I've found: http://viewsofthemahantango.blogspot.com/ Link to comment Share on other sites More sharing options...
mommabetts Posted April 8, 2009 Share Posted April 8, 2009 Thanks for sharing. Link to comment Share on other sites More sharing options...
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