Relative dating worksheet geology sites for blind dating
Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence.The method of reading the order is called stratigraphy (layers of rock are called strata).The simplest and most intuitive way of dating geological features is to look at the relationships between them.There are a few simple rules for doing this, some of which we’ve already looked at in Chapter 6.The boundary between the two represents a time gap of nearly 300 million years.[SE ]Figure 8.9 The four types of unconformities: (a) a nonconformity between non-sedimentary rock and sedimentary rock, (b) an angular unconformity, (c) a disconformity between layers of sedimentary rock, where the older rock has been eroded but not tilted, and (d) a paraconformity where there is a long period (millions of years) of non-deposition between two parallel layers.The lower sandstone layer is disrupted by two faults, so we can infer that the faults are younger than that layer.
Figure 8.8 The great angular unconformity in the Grand Canyon, Arizona.
Geologists have studied the order in which fossils appeared and disappeared through time and rocks. Fossils can help to match rocks of the same age, even when you find those rocks a long way apart.
This matching process is called correlation, which has been an important process in constructing geological timescales.
The lava flow took place some time after the diorite cooled, was uplifted, and then eroded.
(Hammerhead for scale) [SE]Figure 8.6b Rip-up clasts of shale embedded in Gabriola Formation sandstone, Gabriola Island, B. The pieces of shale were eroded as the sandstone was deposited, so the shale is older than the sandstone.