Sedimentary dating

Sedimentary dating

Relative dating does not give a precise age of a rock, but determines whether it is older or younger than another rock – placing rocks in their sequence of formation.

There are laws of relative dating which guide geologists to be able to determine the relative age of rocks.

Using all of these aspects, geologists can look at a cross section of rock strata and determine in relative order which rocks were deposited when.

This gives an idea of the geological history of the area, but does not give a definitive timeframe as to when each event occurred.

Rocks that cool within the Earth’s crust, intrusive igneous rocks, cool slowly and thus have coarse crystalline grains, whereas, rocks that cool on the surface of the Earth, extrusive igneous rocks, cool relatively quickly.

As the cooling happens much faster in extrusive rocks than intrusive rocks, the minerals do not have time to congregate with one another and thus form fine-grained rock.

As well as the igneous rocks found on the Auckland Islands, there are also sedimentary rocks – sandstone, conglomerate and limestone.Different radioactive isotopes are useful for dating different rock samples, as those with a shorter half-life are only useful for dating younger rocks.Whilst relative dating using stratigraphy is useful in showing the sequence of events in a particular location, such as Musgrave Peninsula at the Auckland Islands, the true age of the rocks can be determined using absolute dating.Geological events being significant occurrences as a result of the earth system.Whilst these islands have been shaped over many thousands of years by events such as weathering and erosion, particularly due to glaciation, the main events which formed the islands were two volcanic eruptions.

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Limestone is what is known as a chemically precipitated sedimentary rock.

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