El Rito Formation


The El Rito Formation is a geologic formation in New Mexico dating to the Eocene epoch.

Description

The formation is composed of brick-red well-consolidated sandstone, conglomerate, and breccia. The pebbles are predominantly quartzite, with no volcaniclastics. It crops out over a narrow belt from the southern Tusas Mountains to upper Coyote Creek. In the southern Tusas Mountains, it fills narrow paleovalleys eroded in basement quartzite. Further south, the rock grades from heterogeneous breccia to a poorly sorted conglomerate. The breccia is interpreted as regolith and talus, while the conglomerate is interpreted as a high-energy stream deposit. The distinctive red color is found penetrating joints in the underlying quartzite to depths of several meters. Further south and west, the formation transitions to lighter-colored sandstone. Maximum thickness is. A characteristic feature of the sandstone is the presence of muscovite.
The base of the formation is an angular unconformity with much older beds of Jurassic to Cretaceous age, while the upper contact is an erosional disconformity with the Abiquiu Formation.
Age control is poor due to an almost complete lack of fossils. However, the formation was deposited in the waning phase of the Laramide orogeny under arid conditions. Paleocurrents and conglomerate clast provenance show that the source region was the Brazos uplift to the north and northeast. The formation was deposited in an asymmetrical basin formed in response to compression of the Laramide orogeny, truncated to the west along the Canones fault zone. The El Rito basin likely was continuous with the Galisteo Basin before the opening of the Rio Grande rift separated the two basins starting in the Miocene. The El Rito Formation thus likely correlates with the Diamond Tail and Galisteo Formations.

History of investigation

The formation was named in 1938 by Harold T.U. Smith for exposures along El Rito Creek.

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