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The terrigenous clastics of the Nacatoch Formation are a record of short-lived progradational phases within the major Late Cretaceous transgression in the East Texas embayment. Progradation was achieved by deltaic out-building from three fluvial feeder systems along the north and northwest margins of the basin. It is probable that additional sediment was derived from a major "sediment dispersal system" east of the Nacatoch deltas.
The deltaic package of the Nacatoch (131 m, 430 ft) is composed of roughly equal proportions of sandstones and mudstones, with the sandstones ranging from very fine-grained, poorly sorted, and mud-rich, to fine-grained and well-sorted. The sandstones have a feldspathic litharenite and subfeldspathic litharenite composition with increasing compositional maturity in the well-sorted examples. Some of the muddy sandstones are highly bioturbated and carbonaceous.
Vertical and lateral lithofacies changes in the Nacatoch deltas were determined by means of electric-log (resistivity) interpretation and well core data, with support from limited outcrop studies. Dip- and strike-oriented cross sections delineated three major coarsening-upward sandstone units which could be correlated in a shore-parallel direction for 42 km (25 mi). Each sandstone shows evidence of reworking by wave-induced processes and redistribution by longshore currents. The lower two sandstones are separated by a thick mudstone interval interpreted as a minor transgressive event. The highly bioturbated, carbonaceous, mud-rich intervals between the other sandstone units are interdistributary bay fills.
The Nacatoch deltas are lobate and developed in response to moderate sediment input, moderate to low wave-energy flux, and significant longshore current action.
Southwest longshore sediment transport from the Nacatoch deltas gave rise to extensive shelf sands in the western margin of the East Texas basin. These well-sorted sandstones are petroleum reservoirs at shallow depths. The similar well-sorted sandstones of the Nacatoch deltas have the same potential as petroleum reservoirs, given the same structural influence.
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