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Sep. 3rd, 2007 09:26 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
hertinknessAll right... this is a blog entry that I've been wanting to write for a while: The History of the Finger Lakes.
The Finger Lakes started off, as far as we can tell, on Earth, so we'll skip the part about accretion, heavy bombardment, and atmospheric development, and just hit the more relevant bits first because the rest of it is all common to everywhere else on the planet.
The surficial rocks are pretty interesting because of where they're from, not because of what they are: the shales, limestones and sandstones that go all the way to the igneous/metamorphic basement are from the Catskill Delta, which formed as a result the second stage of mountain building of the Appalacian Mountains, known as the Acadian Orogeny. The Acadian is the second largest continental collision in the building of that mountain belt, and the two culprits were early Europe and early North America. However, the laws of nature basically state that as soon as something sticks up, it gets worn down- and the dynamic between tectonics and erosion is actually another really freakin' cool story that I have to blog about some other time. But I digress: the rock at the surface in the Finger Lakes region is actually one big freakin' huge delta deposit that extends for hundreds of miles: if you're driving from State College to Watkins Glen, you never leave it. The rivers that formed it flowed from the now defunct Acadian mountains into the epicontinental Kaskaskia Sea, which made most of Pennsylvania excellent fishing grounds, if anyone was around to fish in the Devonian.
Eventually, the Kaskaskia Sea retreated, putting an end to almost continual sedimentation since the Precambrian in that particular basin. There was more to it, but we'll never know exactly what- years of erosion have wiped out whatever record there was in the rocks after the Devonian. And there was more. Mud just doesn't magically transform into shale- it takes time, heat and pressure, and those can only come together under thousands of feet of other sediments. Unfortunately, that's all gone now, so we can only speculate on what happened.
I imagine that after the sea disappeared, the rivers flowed on, covering the region in massive floodplain deposits of Mississippi River scale. Ancient freshwater fish that are forever lost swam there, changing their bodies to escape the dunkleosteos that waited for them just out beyond the deltas. Swamps, giant forests of conifers, sprung up in old oxbow bends, and the plants eventually adapted to spread beyond as the swamps dried up as the land uplifted and the Appalachians underwent their third and final orogeny. Dinosaurs likely lived and died upon the mountains, but we will never know them. We will never know the fantastic mammals that came afterward, save for those unlucky few that fell into a peat bog or ancient lake at the end of the last ice age; and we can not know them because of what happened next.
NEXT TIME: The Ice Age and the rest of the Cenozoic
The Finger Lakes started off, as far as we can tell, on Earth, so we'll skip the part about accretion, heavy bombardment, and atmospheric development, and just hit the more relevant bits first because the rest of it is all common to everywhere else on the planet.
The surficial rocks are pretty interesting because of where they're from, not because of what they are: the shales, limestones and sandstones that go all the way to the igneous/metamorphic basement are from the Catskill Delta, which formed as a result the second stage of mountain building of the Appalacian Mountains, known as the Acadian Orogeny. The Acadian is the second largest continental collision in the building of that mountain belt, and the two culprits were early Europe and early North America. However, the laws of nature basically state that as soon as something sticks up, it gets worn down- and the dynamic between tectonics and erosion is actually another really freakin' cool story that I have to blog about some other time. But I digress: the rock at the surface in the Finger Lakes region is actually one big freakin' huge delta deposit that extends for hundreds of miles: if you're driving from State College to Watkins Glen, you never leave it. The rivers that formed it flowed from the now defunct Acadian mountains into the epicontinental Kaskaskia Sea, which made most of Pennsylvania excellent fishing grounds, if anyone was around to fish in the Devonian.
Eventually, the Kaskaskia Sea retreated, putting an end to almost continual sedimentation since the Precambrian in that particular basin. There was more to it, but we'll never know exactly what- years of erosion have wiped out whatever record there was in the rocks after the Devonian. And there was more. Mud just doesn't magically transform into shale- it takes time, heat and pressure, and those can only come together under thousands of feet of other sediments. Unfortunately, that's all gone now, so we can only speculate on what happened.
I imagine that after the sea disappeared, the rivers flowed on, covering the region in massive floodplain deposits of Mississippi River scale. Ancient freshwater fish that are forever lost swam there, changing their bodies to escape the dunkleosteos that waited for them just out beyond the deltas. Swamps, giant forests of conifers, sprung up in old oxbow bends, and the plants eventually adapted to spread beyond as the swamps dried up as the land uplifted and the Appalachians underwent their third and final orogeny. Dinosaurs likely lived and died upon the mountains, but we will never know them. We will never know the fantastic mammals that came afterward, save for those unlucky few that fell into a peat bog or ancient lake at the end of the last ice age; and we can not know them because of what happened next.
NEXT TIME: The Ice Age and the rest of the Cenozoic
