Texas Geologic History

Selected Events in Texas Geologic History

Age millions of years. Uncertainties not shown Period Selected Texas events Other relevant events Non-vertebrate activity
1.8 Quaternary Beginning of Padre Island, the result of sea level rises due to melting glaciers. Marine invertebrates in the Gulf area.
65.5 Tertiary Volcanoes form the peaks in Big Bend.  Last movement of the Balcones fault zone during the Miocene. Damon mound corals develop on a salt dome. Reef building corals, many echinoids, snails, & clams.
145.5 Cretaceous Marine conditions leave behind the limestones we see in Central Texas today. Pilot Knob undersea volcano. Ammonites, oysters, & rudists are abundant. Ammonites & rudists die out during the extinction at the Cretaceous-Tertiary boundary.
199.6 Jurassic Opening of the Gulf of Mexico, salt pans develop.  These rocks are exposed at the surface only in a few places in West Texas. Earliest flowering plants.  




251.0 Triassic Pangaea, the supercontinent of the time, begins to split apart. New ferns & cycads appear. Corals begin to expand in the west Texas marine areas.
299.0 Permian Formation of big sponge & bryozoan reefs (the present- day Guadalupe Mountains). Ferns of all types decline. Early conifers appear. Brachiopods, corals, bryozoa, & crinoids decline during the Permo-Triassic extinction.
318.1 Pennsylvanian Shallow marine environment with deltas in north Texas. Large fern forests leave thin coal beds. Snails, clams, crinoids, bryozoa, & trilobites in the marine areas.
359.2 Mississippian Shallow seas, chaetetid mounds in the Llano region. Ferns abundant. Brachiopods, bryozoa, trilobites, & corals in the marine areas.
416.0 Devonian Most marine rocks of this period are not exposed at  the surface today. Ferns of all types develop in non-marine areas.
443.7 Silurian West Texas shallow seas.  Very few of these rocks are  exposed at the surface today. First land plants. Rare occurrences of brachiopods & corals, although corals evolve rapidly during this time.
488.3 Ordovician Limestone formed in shallow seas.  This is an important source of hydrocarbons in West Texas. Algae/stromatolites occur around the Llano uplift. Corals & brachiopods in the Franklin Mountains near El Paso.
542.0 Cambrian Shallow marine conditions spread over Texas. Outcrops of these rocks can be seen around the Llano uplift. Proliferation of life forms with hard ‘skeletons’. Trilobites roamed the seafloor, along with brachiopods, sponges, snails, & bryozoa.
2500 Proterozoic Oldest exposed rocks in Texas, around 1.9 billion years ago. Some rare algae near the Cambrian boundary.
4600 Archean Simple life forms found as early as 3.5 billion years ago. However, no such fossils have been found in Texas.