Post by Ryan on Nov 22, 2010 2:20:12 GMT -5
Some friends and I took advantage of the unseasonably warm day we had today in Pittsburgh (55F) to hit the fossil hole. We were all watching some football and at around 28-3 we felt we could leave our TVs confident we had ruined everyone in Oakland CA's day.
Today we made some really interesting observations about our collecting spot. Due to threatening rotten shale overburden, we were forced to prospect for fossils in another area of the hole.
We worked up and down, right and left, and found that the fossils were really only located in one particular layer of the shale. Above this layer were very few if any fossils and those that did exist were very small and "choppy" in nature. Below the layer there was a different type of rock. Below was more consistant with limestone than shale/slate.
We deduced that prior to the fern occurance, the area was covered by a deeper lake or shallow sea. Then, as the water receded, the ferns came.
The period that promoted the growth of ferns must have been shallow swamp or river delta which would produce cyclical layers of silt and mud to form the shale. The ferns then, must be similar in strain or perhaps ancestors of Elodea, or common water weed. Elodea, for the non-botany folks, grows in very shallow to medium depth waters and lives immersed in very shallow water with only a small white flower protruding into the air above. They propigate by shedding branches which then float away, sprout roots, and grow elsewhere when they find other shallow water to inhabit. This actually comprises most of the plants' propagation with seed production being secondary in importance. The plant likes nutrient rich silty mud.
It only seems to make sense that the fossils occured the year or years that the water receded and left the ferns dying in the sun. The wilted ferns were probably hardened by frying in the sun and were able to leave imprints in the soft, recently underwater, mud. Then, as the plant decomposed, the sun further baked the impression into the mud. Once covered by more mud, it became trapped for eons waiting for us to dig em up.
The reproduction of this strain would explain why fragments and branches of fern exist; crossed over each other and randomly distributed in the shale.
Above the fossiliferous layer, the barren shale must represent the first few years the ground was dry. the small and few ferns that exist above must have washed up as the receding water lapped on shore during rainy high water periods.
The paleontologists might be saying" Well, DUHHH! -or- "Nope, that isnt what happened" But we all agreed from the geology and VERY specific layer of shale bearing ferns that this is what must have happened. We were witnessing the receding of an ancient lake or sea giving way to swampy delta and then to dry land.
ALSO, there is a layer of black limestone below the shale called the Brush Creek limestone with fossils of small Bivalves and Brachiopods. It is part of whats called the Lower Conemaugh Formation. The Brachiopods are very large in the black hard limestone at the bottom of the exposure possibly suggesting deeper water. Above this, the limestone gets (much) lighter in color and the Brachiopods get smaller and shallow water Bivalvia appear. This graph is from an old geologic text I used to find Wurtzite and Sphalerite polymorphs near this area once. Its old and only sort of correct in scale but gives an idea of what Im talking about.
Above the shale outcropping, the shale gets lighter in color and eventually a layer of sandstone capps it off.
I could be 180 degrees off but from what I observed today, I feel like Im at least on the right track. Ok On to the pictures.
Here's the days take, doesnt look like much. Just a bunch of flat dark slate.
Looking closer, this biggie is the best piece of the day. Here's a picture of it and two detail close-ups:
Then there were some smaller pieces that came out but these few had really great impressions on them. Nice relief and contrast:
Note the PA state quarter ;D Thats gonna be my new thing. Wherever I find my pieces can be identified by whatever state quarter I scale them with. Ryan = Dork.... I know...
And lastly, some little guys with really good fossils:
Thanks for looking. Ill probably give away most of what I got today. People been asking me for a few. Had to restock my supply. Always a pleasure ;D As for my "science report", I may be right, I may be wrong. Feel free to comment either way.
Today we made some really interesting observations about our collecting spot. Due to threatening rotten shale overburden, we were forced to prospect for fossils in another area of the hole.
We worked up and down, right and left, and found that the fossils were really only located in one particular layer of the shale. Above this layer were very few if any fossils and those that did exist were very small and "choppy" in nature. Below the layer there was a different type of rock. Below was more consistant with limestone than shale/slate.
We deduced that prior to the fern occurance, the area was covered by a deeper lake or shallow sea. Then, as the water receded, the ferns came.
The period that promoted the growth of ferns must have been shallow swamp or river delta which would produce cyclical layers of silt and mud to form the shale. The ferns then, must be similar in strain or perhaps ancestors of Elodea, or common water weed. Elodea, for the non-botany folks, grows in very shallow to medium depth waters and lives immersed in very shallow water with only a small white flower protruding into the air above. They propigate by shedding branches which then float away, sprout roots, and grow elsewhere when they find other shallow water to inhabit. This actually comprises most of the plants' propagation with seed production being secondary in importance. The plant likes nutrient rich silty mud.
It only seems to make sense that the fossils occured the year or years that the water receded and left the ferns dying in the sun. The wilted ferns were probably hardened by frying in the sun and were able to leave imprints in the soft, recently underwater, mud. Then, as the plant decomposed, the sun further baked the impression into the mud. Once covered by more mud, it became trapped for eons waiting for us to dig em up.
The reproduction of this strain would explain why fragments and branches of fern exist; crossed over each other and randomly distributed in the shale.
Above the fossiliferous layer, the barren shale must represent the first few years the ground was dry. the small and few ferns that exist above must have washed up as the receding water lapped on shore during rainy high water periods.
The paleontologists might be saying" Well, DUHHH! -or- "Nope, that isnt what happened" But we all agreed from the geology and VERY specific layer of shale bearing ferns that this is what must have happened. We were witnessing the receding of an ancient lake or sea giving way to swampy delta and then to dry land.
ALSO, there is a layer of black limestone below the shale called the Brush Creek limestone with fossils of small Bivalves and Brachiopods. It is part of whats called the Lower Conemaugh Formation. The Brachiopods are very large in the black hard limestone at the bottom of the exposure possibly suggesting deeper water. Above this, the limestone gets (much) lighter in color and the Brachiopods get smaller and shallow water Bivalvia appear. This graph is from an old geologic text I used to find Wurtzite and Sphalerite polymorphs near this area once. Its old and only sort of correct in scale but gives an idea of what Im talking about.
Above the shale outcropping, the shale gets lighter in color and eventually a layer of sandstone capps it off.
I could be 180 degrees off but from what I observed today, I feel like Im at least on the right track. Ok On to the pictures.
Here's the days take, doesnt look like much. Just a bunch of flat dark slate.
Looking closer, this biggie is the best piece of the day. Here's a picture of it and two detail close-ups:
Then there were some smaller pieces that came out but these few had really great impressions on them. Nice relief and contrast:
Note the PA state quarter ;D Thats gonna be my new thing. Wherever I find my pieces can be identified by whatever state quarter I scale them with. Ryan = Dork.... I know...
And lastly, some little guys with really good fossils:
Thanks for looking. Ill probably give away most of what I got today. People been asking me for a few. Had to restock my supply. Always a pleasure ;D As for my "science report", I may be right, I may be wrong. Feel free to comment either way.
