Abstract

The red bed Esplanade Sandstone is the youngest and uppermost of the four formations that compose the Supai Group of Grand Canyon, Arizona. It ranges from about 200 to 700 feet in thickness within the area and forms a large tabular mass, mostly of very fine-grained sandstone, thickening toward the north. Its age, as determined by fusulinids, brachiopods, and corals, is believed to be Wolfcampian.

The Esplanade rests on an unconformable, channeled surface at the top of the Wescogame Formation (Virgilian age). Its basal deposits in most places consist of a conglomerate of rounded limestone and mudstone gravels, and of terrestrial mudstone and siltstone beds. Its dominant lithology throughout is a very fine-grained, calcareous, red-brown sandstone which is highly cross-stratified and forms a massive, resistant cliff throughout Grand Canyon. In extreme western Grand Canyon sandstone of the Esplanade intertongues with marine dolostone and dolomitic limestone of the Pakoon Limestone.

A conspicuous surface of erosion with small rounded stream channels occurs at the top of the Esplanade Sandstone throughout eastern and central Grand Canyon. This unconformity has not been recognized in the far western part of the area. Everywhere it is covered by the Hermit Shale of Leonardian age.

The depositional environment of the Esplanade Sandstone is interpreted as having been largely estuarine, but with marine deposition along the western margins and lagoonal evaporites accumulating in the northwestern area. Clay minerals of terrestrial types among the sandstones and distinctive varieties of cross-stratification support the concept of a continental origin for these units. Sparse and scattered fusulinids and accumulations of marine bioclasts among the sands suggest extensive transport landward, probably by tidal movements. The medium to large scale of the cross-beds, associated with horizontal beds probably of the upper flow regime, indicate that most of the sandstone was developed in a high-energy environment. Sand transport direction was largely from the northwest as shown by foreset dip direction vectors and by size distribution patterns of sand grains.