Your example is localized.
The Permian was a extremely expansive yet shallow sea. The vast majority of production in West Texas is from sedimentary sandstone and shale. Limestone production (ancient coral beds) is small in comparison.
Again, we need to ascertain the genesis of the hydrocarbons and...the industry doesn’t agree that it is simply “dead barnacles and coral”.
Still, the ratio of decay cannot support the amount of petro-hydrocarbons being extracted from the Permian Basin.
You can trace individual coal beds for tens of miles. Go to the Book Cliffs near Moab, Utah. World-class exposures.