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Earth and Space Sciences · Glossary

What is Palaeogeography; palaeogeographic map?

Also known as: palaeogeography · palaeogeographic map

Definition 19.1 University Earth and Space Sciences — Year 2 · Chapter 19 — The Phanerozoic Earth

Palaeogeography is the reconstruction of the geography of a past time: the positions of the continents and oceans, and of their shorelines, mountain belts and seas. A palaeogeographic map shows that geography at one time, on the grid of latitude and longitude of that time.

Today’s coastlines carried back to six times in the plate model of Merdith and others (2021), reconstructed by the GPlates Web Service, in an equal-area Mollweide projection; parallels every 30, meridians every 60. The red dots follow four cities: Paris (P), New York (N), Sydney (S) and Cape Town (C); at 500\, Ma the crust of Sydney is not yet in the model. The shapes are today’s shorelines moved, not the shorelines of those times, and in this palaeomagnetic frame the longitudes are arbitrary.
Today’s coastlines carried back to six times in the plate model of Merdith and others (2021), reconstructed by the GPlates Web Service, in an equal-area Mollweide projection; parallels every 30∘30{}^{\circ}, meridians every 60∘60{}^{\circ}. The red dots follow four cities: Paris (P), New York (N), Sydney (S) and Cape Town (C); at 500 Ma500\,\mathrm{Ma} the crust of Sydney is not yet in the model. The shapes are today’s shorelines moved, not the shorelines of those times, and in this palaeomagnetic frame the longitudes are arbitrary.

Examples

Example 19.2 (Paris drifts north)

In the model, Paris lay at 5.1∘5.1{}^{\circ} N 300 Ma300\,\mathrm{Ma} ago; it lies today at 48.9∘48.9{}^{\circ} N. Its latitude has grown by 43.8∘43.8{}^{\circ}, that is 43.8×111.2=4871 km43.8 \times 111.2 = 4871\,\mathrm{km} along a meridian (111.2 km111.2\,\mathrm{km} per degree on a sphere of radius 6371 km6371\,\mathrm{km}), at a mean rate of 4871/300=16 km4871/300 = 16\,\mathrm{km} per million years, or 1.6 cm1.6\,\mathrm{cm} a year. This is only the northward part of the motion: the palaeomagnetic frame leaves the longitude free, so the true distance travelled was at least this.

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