ABSTRACT

The most incongruous stratigraphic unit in the Earp Formation (Pennsylvanian-Permian) is the“Jelly Bean” conglomerate (JBC), a unit rarely more than 5 m thick, but occurring over 15,000 km2. The JBC consists mostly of clast-supported chert-pebble and limestone-clast conglomerate, litharenite, and pebbly sandstone, whereas most of the Earp Formation is marine limestone, siltstone, and shale. The JBC lies on eroded siltstone or limestone, and is capped conformably by siltstone. The JBC is probably a braided-stream deposit as indicated by presence of fluvial dunes and ripples, amalgamated bar and channel conglomerates, imbricated clasts, channeled underbeds, and lack of point bars. Paleocurrents were generally southward. The thinness and widespread occurrence of the JBC suggest a uniform, gentle paleoslope down which the streams flowed.

Deposition of the JBC occurred at about the climax of the Marathon phase of the Ouachita orogeny in west Texas and northern Mexico. The age and location of the JBC, which fringes cratonic North America, indicate that it was related to the late Paleozoic convergence of North and South America, and may have resulted from flexural forebulging caused by thrusting in the Marathon orogene and associated sedimentation in a foredeep.

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