ⓘ Madera Formation. The Madera Formation is a geologic formation in northern New Mexico. The formation is a marine limestone, with minor arkosic sandstone, promin ..

                                     

ⓘ Madera Formation

The Madera Formation is a geologic formation in northern New Mexico. The formation is a marine limestone, with minor arkosic sandstone, prominently exposed in the western Jemez Mountains, the Sangre de Cristo Mountains, the Lucero Uplift, atop Sandia Crest, and in the Manzano Mountains. The exposures near Jemez Springs include some of the richest brachiopod fossil beds in North America. Crinoid stems and bryozoans are also part of the fossil assemblage. The formation is also exposed in the canyon of Rio Grande del Rancho south of Talpa, New Mexico, where brachiopods, crinoids, rugose coral, and graptolite fossils can be found. The fossil assemblage dates the Madera Formation to the middle to late Pennsylvanian.

The formation is underlain by the Sandia Formation, with its base typically placed at the first massive marine limestone bed above the shales of the Sandia Formation. It is overlain by the Abo Formation, with the transition typically gradational, with the base of the Abo placed at the top of the last massive marine limestone bed below the fluvial redbeds typical of the Abo.

The stratigraphy of the Madera Formation and the underlying Sandia Formation is unusually controversial, and some geologist promote it to group rank. The lower portion tends to be a gray limestone and the upper an arkosic limestone, and these have been divided into the La Pasada Formation and Alamitos Formation in the southern Sangre de Cristo Mountains. In the Manzano Mountains, the Madera has been divided into the Los Moyos, Wild Cow, and Bursum Formations. Another proposed division in the southeastern Sangre de Cristo Mountains is into the Pourvenir and Alamitos Formations. However, the name "Madera Formation" is deeply entrenched in the literature and continues to be used.

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