The Ordovician in Northwest region, Mexico

Paleontology and geology

The northern part of this region was near the edge of the continent during the Ordovician, and shallow to deep waters of the continental shelf, slope, and ocean basin extended over the rest of the region. Some areas that would become part of this region existed as a series of volcanic islands out in the ocean, while other areas had not formed yet. These waters were home to graptolites, conodonts, trilobites, and brachiopods. Fossils of these animals are preserved in the some of the limestones, sandstones, and shales deposited in the seas. Although many rocks from this period have been eroded away or are buried below the surface, some deposits can be found in the north and west. These exposures are too small to appear on this map, but a few may be included in the undifferentiated Paleozoic rocks. Other more detailed maps may also show them. Some rocks in the north may have been deposited elsewhere and later moved to their present location. Geologists continue to study how and when they formed.