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Kelly Limestone
The Kelly Limestone is a geologic formation in New Mexico, United States. Its fossil assemblage is characteristic of the Early to Middle Mississippian.[1] DescriptionThe Kelly Limestone consists of approximately 30 meters (98 ft) of marine limestone.[1] It is found in the Lemitar, Ladron, and Magdalena Mountains of west-central New Mexico, US.[2] The formation rests on Precambrian basement rock and is overlain by the Sandia Formation. The Kelly Limestone is divided into a lower Calosa Member and an upper Ladron Member, which are separated by an unconformity.[1] The Kelly Limestone likely correlates with the Arroyo Penasco Group in northern New Mexico and the Leadville Limestone of Colorado.[1] These were deposited in a major marine transgression (advance of the ocean across the continent) in the Mississippian.[2] Fossil contentThe formation contains fossil conodonts indicating that it ranges from Tournaisian to Visean (Early to Middle Mississippian) in age.[1] The lower Caloso Member contains fossils of the brachiopods Beecheria chouteauensis and Spirifer centronatus and the fusulinids Latiendothyra, Medioendothyra, and Tuberendothyra. The upper Ladron Member contains a diverse fossil assemblage, including brachiopods such as Rhipidomella and Linoproductus, blastoid echinoderms such as Pentremites conoideus, cnidarians such as Zaphriphyllum casteri, and numerous species of microscopic algae and foraminiferans.[2] Economic resourcesThe Kelly Limestone was the principal ore-bearing formation of the historic Magdalena, New Mexico mining district. The ore takes the form of replacement deposits in the limestone produced by nearby igneous intrusions.[3] The best ore was found in the so-called "silver pipes" beds, which were dense dolomitic limestone contrasting with the high-calcium limestone making up most of the rest of the formation.[4] History of investigationThe formation was first named as the Graphic-Kelly Formation by C.L. Herrick in 1904 for exposures near the mining town of Kelly, New Mexico.[5] The hyphenated name was found objectionable, and the formation was renamed as the Kelly Limestone by C.H. Gordon in 1907.[6] In 1976, A.K. Armstrong and B.L. Mamet divided the formation into the Caloso and Ladron Members.[2] See alsoReferences
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