This anoxic setting of the deeper waters in the ocean is a result several factors including increased global  levels, higher sea levels, increased organic productivity and decay, Milankovitch cyclicity, and restricted thermohaline currents in the Western Interior Seaway. The lower section of the Eagle Ford consists of organic-rich, pyritic, and fossiliferous marine shale's which marks the maximum flooding surface, or peak of deepest water in its deposition. The different fauna that was present in the Eagle Ford suggests the waters were calm and within the photic zone.
This specific anoxic environment of the deeper ocean waters is a result of several factors including increased global levels, higher sea levels, organic productivity and decay, Milankovitch cycles, and restricted thermohaline currents in the Western Interior Seaway. The lower section of the Eagle Ford formation consists of organic-rich, pyritic, and fossiliferous marine shales that indicate the maximum depth reached by the water during its deposition. The diverse fauna present in the Eagle Ford suggests that the waters were calm and within the photic zone.