The Austin Chalk Formation continues to be an active exploration and production target in the northern onshore Gulf of Mexico (GOM). A regional study (Texas and Louisiana) of over 40 cores from the Austin Chalk has delineated the general lithofacies that compose the section. These lithofacies are the “building blocks” that are organized into repeating stacking patterns observed across the GOM. The recognition of these stacking patterns provides the general facies architecture to incorporate into exploration and drilling strategies. There are four general in-place lithofacies and several auxiliary lithofacies. The general lithofacies are differentiated by mineralogy and degree of bioturbation, which are characteristics that are linked to redox conditions and thus TOC content and source rock richness. Lithofacies 1 is a marly chalk that is highly bioturbated with both vertical and horizontal burrows. The general TOC is less than 0.5% and mean pyrite is 0.3%. Lithofacies 2 is a marly chalk to chalky marl that is highly bioturbated with only horizontal burrows and can be very argillaceous (to over 60%). TOC averages 1% and pyrite is 1.2%. Lithofacies 3 is poorly to a moderately laminated marly chalk and is sparsely horizontally burrowed parallel to laminae. Approximate mean TOC is 1.5% and mean pyrite is 1.4%. Lithofacies 4 is well-laminated marly chalk with rare or no burrows. Average TOC is 2% and mean pyrite is 2.1%. The progression from lithofacies 1 to 4 parallels an increase in anoxia and this is strongly mirrored by increases of TOC and pyrite abundance. Based on the predominance of a coccolith-hash matrix with planktic foraminifers and calcispheres in all lithofacies, a deeper shelf, below storm wave base depositional environment is proposed. Lithofacies 1–4 represent background sedimentation; they may be punctuated by the auxiliary lithofacies which represent discrete events. In the upper Austin Chalk (Maverick and San Marcos Arch areas), volcanism was active and an extensive mass-wasting complex formed (debrites and hyperconcentrated flow deposits). In this interval, and less common in the other Austin Chalk intervals, altered ash beds are present. The lithofacies patterns are in part controlled by the paleogeographic features present during Austin Chalk time. In the deeper Maverick Basin, East Texas Basin, and areas in Louisiana away from the Sabine Arch, organic-rich lithofacies 3 and 4 are common in the lower part of the section with lithofacies 1 and 2 dominating the upper part of the section. On the San Marcos Arch and near the Sabine Arch, lithofacies 3 and 4 are rare and lithofacies 1 and 2 dominate. The distribution of lithofacies 3 and 4 control source rock potential of the Austin Chalk. Porosity is also in part controlled by lithofacies; therefore, the understanding of lithofacies is a basic requirement for approaching exploration of the Austin Chalk Formation.