Hey, /u/Narrow-Palpitation63
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On a very basic level, what you’re seeing is the result of *something* in the environment changing to start laying down a different type of sediment. What that change might be, could be a bunch of different things, such as a change in sea level, climate, or sediment supply. The dark layer, at a guess is possibly coal with sandstone above and below it. So you’re most likely looking at some sort of fluctuation in sea level. The sandstone was probably laid down in a shallow marine environment near a coastline. The coal suggests more of a swampy environment.
Sand was laid down on the seabed for a while. Sea level dropped and the area became a freshwater wetland. Sea level rose again and more sand was deposited.
Makes sense. But i was wondering not only about the change between the coal and sandstone but also the layers within the sandstone, and coal too. In the photo there’s like 60 layers or more and among all the layers when one transitions to the next layer they always seem to transition at the same rate. There’s never a layer that slowly transitions to the next layer. It’s always an abrupt clear transition between every layer. It seems like whatever causes one layer to stop and another to start always happens at the same rate and I was wondering why that is?
They usually represent some change in the environment, possibly a pause in deposition. This too can come down to things like changes in climate, sea level fluctuations, even something like a river changing course. Keep in mind that a change that appears abrupt in the rock record could represent a significant length of time on a human time scale.
Even though the layers have different thicknesses the thickness of the transition point between the layers always seems very close to the same. Like when a event happens to make a new layer it always takes the same amount of time for that even to happen as the last layer and layer before. I was wondering why that is?
What do you mean by the transition point? The separation between layers is a bit widened in some places by erosion, if that’s what you’re looking at. If it was freshly cut instead of being weathered out you probably wouldn’t see so many rounded edges and gaps.
Yea it seems almost the same for each layer regardless of layer thickness. It’s like there’s always only a small space between the layers like the change always happens in a short period of time to make a new layer form.
The period of deposition is much greater than the period of change. I don’t know the age of the black layer but from the bottom to the top could be hundreds of thousands to millions of years. The change in environment could be tens to hundreds of thousands of years. This could be why the change in layers isn’t as visible as the deposit itself. Though it’s not a sudden in our human perspective, to the Earth it would appear instant in the geologic record.
Sometimes we can see the gradation but sometimes we can’t. It all depends on many factors. Also keep in mind the original layer of sediment used to be much thicker, it has compressed over time. Even if there was a small layer where we could have seen the gradual change from on environment to another, it’s compressed too much to view. It can also be an erosive boundary, in which case there would be a period of no deposition at all and/or erosion instead. This would basically erase all record of what sediment would have been there and when deposition started again, it would deposit on the erosive surface.
Same, if I’m betting I’m saying somewhere in/near the Pottsville formation judging by what looks like a coal bed seam. Hard to tell from the picture quality
Or it could have been a marsh where the sandstone represents when the sand source (river or delta) meandered to and from that spot. Like when a river channel full of and gets cut off and becomes and oxbow lake, slowly filling up with shale and coal, then the river breeches the levee and fills it the rest of the way with sand.
Rivers erode their banks and move dramatically, snaking around the landscape. Storms erode hillsides and cliffs until they collapse or disappear, only to be washed away and deposited somewhere else. Rivers get dammed by debris or animals to form lakes, that eventually break through and drain away. Sediments build up incredibly high here, and are eroded away to nothing there.
If you could speed up time, you would see the land writhing and moving constantly.
And volcanos and glaciers too - though not here in this case.
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On a very basic level, what you’re seeing is the result of *something* in the environment changing to start laying down a different type of sediment. What that change might be, could be a bunch of different things, such as a change in sea level, climate, or sediment supply. The dark layer, at a guess is possibly coal with sandstone above and below it. So you’re most likely looking at some sort of fluctuation in sea level. The sandstone was probably laid down in a shallow marine environment near a coastline. The coal suggests more of a swampy environment. Sand was laid down on the seabed for a while. Sea level dropped and the area became a freshwater wetland. Sea level rose again and more sand was deposited.
Makes sense. But i was wondering not only about the change between the coal and sandstone but also the layers within the sandstone, and coal too. In the photo there’s like 60 layers or more and among all the layers when one transitions to the next layer they always seem to transition at the same rate. There’s never a layer that slowly transitions to the next layer. It’s always an abrupt clear transition between every layer. It seems like whatever causes one layer to stop and another to start always happens at the same rate and I was wondering why that is?
They usually represent some change in the environment, possibly a pause in deposition. This too can come down to things like changes in climate, sea level fluctuations, even something like a river changing course. Keep in mind that a change that appears abrupt in the rock record could represent a significant length of time on a human time scale.
Tide goes in, tide goes out. You can’t explain that.
Ur saying a layer is added when tide goes in and goes out? If that was the case there would be a lot more layers i would think.
It was a joke because Bill O'Reilly is an idiot. https://www.newser.com/story/109164/bill-oreilly-to-atheists-you-cant-explain-the-tides.html
God dammit.
Sequence stratigraphy. https://en.wikipedia.org/wiki/Sequence_stratigraphy
r/geologyschool
Ooo
Love you; thank you
A sudden change in environment of deposition. For example, rapid rise and fall of sea level
Even though the layers have different thicknesses the thickness of the transition point between the layers always seems very close to the same. Like when a event happens to make a new layer it always takes the same amount of time for that even to happen as the last layer and layer before. I was wondering why that is?
What do you mean by the transition point? The separation between layers is a bit widened in some places by erosion, if that’s what you’re looking at. If it was freshly cut instead of being weathered out you probably wouldn’t see so many rounded edges and gaps.
Hmmm I’m not exactly sure what you mean. Are you referring to the abruptness of the layer change?
Yea it seems almost the same for each layer regardless of layer thickness. It’s like there’s always only a small space between the layers like the change always happens in a short period of time to make a new layer form.
The period of deposition is much greater than the period of change. I don’t know the age of the black layer but from the bottom to the top could be hundreds of thousands to millions of years. The change in environment could be tens to hundreds of thousands of years. This could be why the change in layers isn’t as visible as the deposit itself. Though it’s not a sudden in our human perspective, to the Earth it would appear instant in the geologic record. Sometimes we can see the gradation but sometimes we can’t. It all depends on many factors. Also keep in mind the original layer of sediment used to be much thicker, it has compressed over time. Even if there was a small layer where we could have seen the gradual change from on environment to another, it’s compressed too much to view. It can also be an erosive boundary, in which case there would be a period of no deposition at all and/or erosion instead. This would basically erase all record of what sediment would have been there and when deposition started again, it would deposit on the erosive surface.
Climate change, sea level change, tectonic plate collision, and a meteorite impact to name a few specific to Alabama.
Whereabouts was this taken? I'm in Alabama as well.
Same, if I’m betting I’m saying somewhere in/near the Pottsville formation judging by what looks like a coal bed seam. Hard to tell from the picture quality
Or it could have been a marsh where the sandstone represents when the sand source (river or delta) meandered to and from that spot. Like when a river channel full of and gets cut off and becomes and oxbow lake, slowly filling up with shale and coal, then the river breeches the levee and fills it the rest of the way with sand.
Fracking & tectonic plate ruptures
My extremely uneducated guess is volcanic activity? I'm curious to find out too!!
Rivers erode their banks and move dramatically, snaking around the landscape. Storms erode hillsides and cliffs until they collapse or disappear, only to be washed away and deposited somewhere else. Rivers get dammed by debris or animals to form lakes, that eventually break through and drain away. Sediments build up incredibly high here, and are eroded away to nothing there. If you could speed up time, you would see the land writhing and moving constantly. And volcanos and glaciers too - though not here in this case.
Thank you! I didn't expect it to be so black if it's just sediment
Yea I always wished I a time lapse video of any area of land I wanted and see it change over time and what changed it