Paleontology and geology
Ordovician rocks in the Southeastern Region of Mexico were deposited on the continental shelf, slope, and ocean basin off the coast of Gondwana. They include limestones, sandstones, and shales, as well as igneous rocks that formed on the ocean floor when small land masses broke away from that continent. Some of these deposits contain fossils of animals that lived in the seas, including trilobites, brachiopods, cephalopods, echinoderms, gastropods, conodonts, sponges, and ostracods. Subsequent collisions have altered, folded, faulted, and pushed these rocks up. Over time, many Ordovician rocks were eroded or buried and the few remaining exposures are too small to appear on this map. Some may be shown on the map of undifferentiated Paleozoic rocks or on other more detailed maps.