Texas, blessed with an enormous national resource in oil, straddles a buried mountain range whose existence explains in large part the occurence of oil. About 300 million years ago (Pennsylvanian period) the northwest half of Texas was part of a continent that slammed into another continental piece, via the process of plate tectonics, to form part of the supercontinent Pangea . In the process a mountain range was heaved upward along the collision line. This range we now call the Ouachita Mountains . Pieces of this range are still exposed at the surface in Oklahoma, in the Llano uplift northwest of Austin, and around Marathon in southwest Texas. In between, the range lies buried in Texas beneath piles of younger sedimentary rocks.
On the continent side of the uplifted Ouachita Range, in west and northwest Texas, the crust was downwarped in several places in compensation for the adjacent uplift. These downwarps, or basins, continued to settle over millions of years, receiving organic rich deposits of calcareous mud from marine organisms living in shallow seas. Reefs and banks of limestone formed around the edges of the basins from the growth of abundant reef building animals. The organic rich mudstones, and even the basin edge limestones, were the source for much of the oil in West Texas, while the cavernous limestone reefs and banks became the reservoirs to store the oil. A magnificent example of these rocks and their story is to be found at Guadalupe National Park in West Texas.
By 200 million years ago (Jurassic period) Pangea began to pull apart in the great continent-wrenching episode that generated the Earth's present configuration of continents and ocean basins. The Gulf of Mexico began to drop away from the old Ouachita Mountain line as North America and South America seperated. At this early stage, the Gulf was only narrowly connected to to the other oceans, and upon this pan of sometimes ocean sometimes dry flat, thick layers of salt were evaporated. Thus formed the Jurassic aged Louann salt.
The Gulf of Mexico continued to deepen and thousands upon thousands of feet of sediment poured into the basin from the emergent North American continent. These were mainly organic-rich muds, similar in kind to delta deposits at the front of today's Mississippi River. River and shoreline sands were also laid down in this process to form the source reservoir combination that contributed to east Texas' gigantic oilfields. But, the thick pile of Mesozoic and Cenozoic aged sedimentary deposits bore down heavily on the Louann salt over time forcing it upward in tall domes and spikes. Around these domes oil was trapped in profusion.
Hence, Texas has a great amount of oil and gas because there has not been one but two great periods of hydrocarbon generation. First, the oil in West Texas was generated and trapped in a number of basins which developed in Paleozoic time in response to Ouachita mountain building. The second great period of oil generation is the product of later, Mesozoic tectonic forces, which opened the Gulf of Mexico and allowed the deposition of thick organic rich sediments.
The first well to produce oil was drilled in 1866 by Lynn T Barret near Melrose in Nacogdoches County in east Texas. In 1867, Armory Starr and Peyton Edwards brought in a well at Oil Springs in the same area giving Nacogdoches County the first commercial oilfield, pipeline and refinery in the state. However, the first major oil discovery came in 1894 when the city of Corsicana tried to drill a water well and discovered the Corsicana oil field instead! In 1901, the first great gusher and giant field was brought in by Captain Anthony Lucas who drilled Spindletop near Beaumont.
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