Abstract: Depositional Environments of Maxon Formation (Lower Cretaceous), Marathon Region, West Texas

Gary Thompson

The Maxon Formation (Lower Cretaceous) is a fluvial-deltaic-shelf deposit that covered approximately 5,800 sq km of West Texas during Early Cretaceous time. Lithologies included in the formation are siltstone, mudstone, sandstone, minor conglomerate, and limestone. The formation ranges in thickness from 20 to 70 m and is bounded by two Cretaceous marine carbonate units, the subjacent Glen Rose and the superjacent Telephone Canyon Formations.

Vertical and lateral trends of primary sedimentary structures, grain size, and rock type allow three facies to be delineated:

Fluvial deposits include point-bar, levee, and flood-basin sandstone and siltstone. Point-bar sandstone bodies are 2 to 15 m thick and multilateral as well as multistory. They display upward-fining sequences in terms of grain size and scale of sedimentary structures, and also possess large-scale accretionary bedding. Levee and flood-basin deposits include ripple cross-bedded sandstone and siltstone, paleocaliche, and plant impressions. The fluvial facies was deposited largely by mixed-load meandering streams.

Deltaic deposits are characterized by a 45-m thick progradational sequence of flyschlike interbeds of sandstone and siltstone. Scale of sedimentary structures, grain size, and bed thickness increase upward. This upward-coarsening sequence is interpreted to have been deposited by a fluvial-dominated, lobate delta.

Shelf deposits consist of sandstone "turbidites," siltstone, mudstone, wackestone, packstone, and grainstone. What are interpreted to be "turbidite" beds fill broad, shallow channels and probably are the products of turbid bottom currents generated by flood discharges from updip distributaries.

These fluvial-deltaic-shelf deposits occur along a north-south facies tract in which the paleocurrent transport direction was southeastward. Progradation was into a low-energy, shallow-marine basin. The close of Maxon deposition is represented by Ophiomorpha-burrowed beds and a vertical transition from sandstone and siltstone into Telephone Canyon limestone.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma