Geologic Sequencing: The order of geologic events The Grand Canyon Gorge

Superposition youngest to oldest Click anywhere in picture to skip back to LAWS.

Correlating Outcrops Shale with trilobites is oldest in “A” 9th Oldest 8th Oldest 7th Oldest 6th Oldest 5th Oldest YOUNGEST 4th Oldest 10th Oldest 9th Oldest 8th Oldest 7th Oldest 6th Oldest 3rd Oldest 5th Oldest 2nd Oldest 4th Oldest 3rd Oldest 2nd Oldest 5th Oldest OLDEST Shale with trilobites is oldest in “A” Conglomerate on bottom in “B” but WAY higher in other outcrops Shale with trilobites is ABOVE gray sandstone so sandstone is older

Shale with trilobites is oldest in “A” Youngest 5th 4th 3rd 2nd 10th 9th 8th 7th 6th 5th 4th 3rd 2nd 5th OLDEST Shale with trilobites is oldest in “A” Sandstone on bottom in “B” but WAY higher in other outcrops Shale with trilobites is ABOVE gray limestone so limestone is older

FOLDS and TILTS: ALWAYS older than the rocks they are found in!

Folded/Tilted Layers

Marker Beds

VOLCANIC ASH LAYER AT THE SAME TIME AS THE DINOSAURS BECAME EXTINCT LEAD SCIENTISTS TO LOOK FOR METEORITE CRATER Chicxulub Crater 65 mya 170 km. Wide

Igneous Intrusion - Cross Cutting: Always younger than the layers they are found in

Cross Cutting Intrusions and Faults: Always younger than the layers they are found in Click to skip back to LAWS.

Taconic Unconformity Late Silurian Limestone Early Ordovician Shale and Sandstone We stopped along the side of the road where engineers had cut into the rock formations to make the road. The unconformity was clearly visible showing banded carbonate rock overlying tilted shales and sandstones. unconformity Taconic Unconformity

Practice: what happened here? Click to see arrows shoot in one at a time. #1= included fragments #2=intrusion, cross-cutting #3= angular unconformity #4=erosion. This is the outcome of the previous slide. 1: Tilting 2: Igneous Intrusion 3: Erosion (unconformity) 4: Deposition of New Layers

The sandstone layer is common to all the columns. Glacial deposits Youngest  The sandstone layer is common to all the columns. Glacial deposits are on top. They are youngest....... and gray limestone is on the bottom. It is oldest. Why do you think the layer of black shale is thicker in column C than in column A? Not sure? Ask your teacher................ Oldest 

Youngest  According to the ‘law of supersposition’ the youngest rock layer will be on top and the oldest layer will be on the bottom Oldest

Here’s another example from a different regents exam. There are four columns from neighboring regions. The numbers represent different fossils found in the rock layers. Unconformities (buried erosional surfaces) indicate that material is missing. Try to find a fossil (number) that is common to all four columns and use it to line them up as in the previous example.

Youngest  Oldest  The fossil common The rock with fossil #6 is the to all columns is #7. The rock with fossil #6 is the youngest because it’s on top. Youngest  Oldest  The rock with fossil #8 is the oldest. It’s on the bottom. The layer with fossil #3 is missing from the rightmost column due to erosion.

Now try to reconstruct the geohistory of this region by listing the layers in order from the oldest to the youngest: Youngest  6 4 1 7,9 2 10 3 Each column by itself is incomplete but by using information from all of them we can develop a complete history of a geologic region. 5 Oldest  8

What is the geologic age of layer B? (1) Cambrian (3) Devonian (2) Ordovician (4) Permian

What is the correct order of development from oldest to youngest?

(1) A fault exists between outcrops A and B. Bedrock outcrops A and B are located at two different locations along the Genesee River in western New York State. Rock layers 1, 2, and 4 are the same in both outcrops. Which statement best explains why rock layer 3 is missing from outcrop B? (1) A fault exists between outcrops A and B. (2) Erosion created an unconformity between rock layers 2 and 4 in outcrop B. (3) A volcanic eruption destroyed rock layer 3 in outcrop B. (4) Metamorphism of outcrop A created rock layer 3.

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Sediments deposited, sea-level lowered, layers intruded, layers tilted, erosion and deposition under sea, sea-level lowered again. Click arrow to continue.

The trip route stays very close to the edge of the Catskill Mountains.

Mr. Orgonik pointing out the Taconic Unconformity

Applying Principles of Relative Dating to Determine Geologic History of an Area The process of matching rocks or geologic events occurring at different locations of the same age is called CORRELATION

Correlation of rock layers often relies upon fossils William Smith (late l700’s) noted that rock layers in widely separated areas could be identified and correlated by their distinctive fossil content This led to the "principle of fossil succession“ Fossils succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content

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1. Which layers are the same? 2. Which layer is older E or F? 3. What is correct sequence of rock layers from oldest to youngest? 4. An unconformity is represented by the interface between which 2 layers?

Which fossil might be found in Devonian rock layers?

Eurypterus NY State Fossil Silurian index fossil

Index fossils – Page 8-9 ESRT Index fossils - any animal or plant that is characteristic of a particular span of geologic time or environment. 2 criteria must be met Life form lived over a wide geographic area – horizontal distribution Life form existed for a short period of time – short vertical distribution

Which letter would make a good index fossil? Location A Location B Location C Rock layer 1 W W Z Rock layer 2 W Z Y Z Rock layer 3 W X X X Z Which letter would make a good index fossil?

OTHER METHODS OF CORRELATION Layers of bedrock exposed (outcrops) on either sides of river valleys/excavations “walking the outcrop” Volcanic ash – large eruption – widely distributed – represents a small time interval LIKE AN INDEX FOSSIL