dating in key west - Relative age dating inclusions

If a fault cuts across and displaces layers of sedimentary rock, then the fault must be younger than the layers.

But if a layer of sediment buries a fault, the sediment must be younger than the fault.

Principle of baked contacts: The principle of baked contacts states that an igneous intrusion “bakes” (metamorphoses) surrounding rocks, so the rock that has been baked must be older than the intrusion.

- In an undisturbed sequence of strata or lava flows, the oldest is at the bottom of the sequence and the youngest is at the top.

Practice: Which is the oldest rock unit in the sequence below?

The succession of events in order of relative age that have produced the rock, structure, and landscape of a region is called the geologic history of the region.

We can use these principles to determine relative ages of the features.

FIGURE 1 - Any piece of rock (clast) that has become included in another rock or body of sediment must be older than the rock or sediment into which is has been incorporated. Law of Cross-Cutting relations - Any feature that cuts across a rock or body of sediment must be younger than the rock or sediment that it cuts across.

Such cross-cutting features include fractures, faults, or masses of magma that cut across preexisting rocks before they cooled. You should be able to determine the age relationship between the three rock units shown.

- Sedimentary layers (strata) and lava flows were originally deposited as relatively horizontal sheets, like layers in a layer-cake.

It they are no longer horizontal or flat, it is because they have been moved since they were originally deposited.

All extremely ancient species were sea-dwelling single-celled organisms.

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