Devil's Lake

Geology of Devil’s Lake

• Bedrock quartzite

  • Cliff

  • Purplish

  • Very hard!

• Hypothesis on how the quartzite formed: Quartzite forms as running water deposits loose grains of sand and then something happened to make it into the hard rock

  • this man is sick of us…but what is happening…

  • Identifying grains within the rock

  • Intertidal Zone: where the water levels rise and fall during the course of a day

    • No trees and stuff grow there

• The fast-flowing floodwater ERODES (erosion) the loose mud, rocks, sound, and sediment, and move it along the current

• When the flood starts to die, the water slows/looses energy and sets down participles (deposition)

• How do we know a flood occurred?

  • Odd depositions, dead/less vegetation or buried land

  • Plants and animals mixed with seashell and seaweed

  • Seaweed and shells in normal growth positions

  • Principle of Horizontality: when a current deposits stuff, it tends to deposit them in horizontal/flat line layers

• New hypothesis of quartzite: loose grains of sand were deposited in horizontal layers/beds and then something happened to turn it into the hard rock we see today

  • We observed vertical layers

• New hypothesis on how quartzite formed: loose grains of sand were deposited in flatline layers and then something happened to tip them vertically, then something happened to turn into the hard rock we see

  • Mountains!!

    • Twisted, contorted, and vertical layers

    • But no mountains in wi

  • Initially running water deposited loose grains of sand in flatline beds, then something happened to tip and upend these beds into mountains, then something happened to turn into the hard rock we see today

• Ripple marks are sedimentary deposits from water running over the sand or something

  • Can connected into y/tuning fork shapes

  • Ripple features on a cliff with positive relief associated with them

    • Ripple marks must form when the beds are flatline, then something happens to tip them up vertically

    • Cliff is depositional layer from mountain building due to ripple marks

    • Faster water moves, the more it can erode

• Curve Collapse Beds:

  • cross beds form as the ripple migrates

• Firehose Logic: we have the adaptor to hook a fire hose to a garden hose (the water comes out at 10 gals/sec), so the garden hose will shoot out FASTER

• The faster that water moves, the more it will erode

• A→B = water speeding up; B→C = water slowing down

• Cross beds form as the ripple migrates due to deposition

  • Crossbedding in quartzite would give evidence to the running water formation hypothesis

    • There IS crossbedding in quartzite → it once was vertical

• How to make sand grains into very hard rock?

  • Add heat/increase temp & increase pressure

• Quartzite is a metamorphic rock

  • Meta: change

  • Morph: shape

  • Metamorphic rocks change when increase temp, increase pressure

  • Recrystallize → this changing process

• As we get deeper into the Earth, pressure & heat increase

  • Burial & ramming the material are 2 ways to change

    • Happens through a cooking process

• Fossil: any evidence for a previous lifeform

  • Ex: dino footprints, shells, bones, poop, etc.

  • Quartzite hasn’t contained fossils

  • Quartzite Outcrop:

• Deposit Sand (horizontal) → Bury Sand (increase temp, increase pressure, metamorphosize quartzite) → Mountain Building (vertical) → Erode Mountains → Deposit Conglomerate to Ocean-Beach with Increased Sea Level → Deposit Sand with Increased Sea Level → Seas Went Away (Decreased Relative Sea Level)

• Sandstone is a sedimentary rock, where tiny pieces form together

  • Striations - associated with glaciers!

    • drawing!!!!!!

• Vertical rocks typically mean MOUNTAINS, but there are no mountains at Devil’s Lake state park…

  • Where did the WI mountains go?

    • Glaciers caused the mountains to erode (removed them) the sand at the bottom of the glacier caused striations

    • These many different eroded rocks would get scattered around in the path of the glacier. The glacier blends everything, moves anything, & disperses rocks

    • An asteroid/meteor could have pulverized the mountain

      • Look for crater or extraterrestrial minerals like iridium

        • Scattered rocks in a circle of debris → Angular shape

    • An earthquake could have done it

      • But no, because no SHARP angles on rocks

• Relative Geological Time Scale

  • Born some time before today

• vs. Absolute Geological Time

  • Born on this day, on this week, in this month, in this year

• Angular Unconformity — Siccar Point, Scotland

  • Establishment of modern Geology

Relative Geologic Time Scale

• Precambrian Era (4.6 billion-541 million years ago)

  • Oldest era

  • Like missing pages from a book — missing things to read

  • Quartzite from Devil’s Lake State Park is from this era

• Paleozoic Era (541 million-252 million years ago)

  • Paleo means old btw

  • Oldest life

  • First “normal” shelled organisms

  • Sandstone from Devil’s Lake State Park is from this era

• Mesozoic Era (252 million-66 million years ago)

  • Medium life

  • Age of the Dinosaurs

• Cenozoic Era (66 million years ago-now)

  • Most recent

  • Age of Mammals

• How to make this an absolute geologic time scale?

  • Carbon dating of fossils

  • Radioactivity - one element changing to a different element

    • Spontaneously changes giving off matter and/or energy

    • Use “radioactive clocks”

    • The number of protons that are present within the nucleus of an atom is what controls the name of an element

      • Atomic Number

        • “fingerprint” for an element

      • Atomic mass

        • number of protons plus number of neutrons

• Half-Life (of a radioactive substance): the amount of time it takes for one half of the parents to break down into daughter products

  • Uranium 238 is more stable than Carbon 14 since it has a longer half life

    • The older the rock, the more lead we should see, and the less uranium we should see

  • After one half-life, only 50% of the original isotope should remain