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BOLETÍN DE LA SOCIEDAD GEOLÓGICA MEXICANA http://dx.doi.org/10.18268/BSGM2008v60n2a2 |
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Beidellite–nontronite clays in Neogene sediments from Cuitzeo–Charo lacustrine basin Michoacán, México. Geological setting and paleoenvironmental implications
Arcillas del tipo beidellita–nontronita en sedimentos neógenos de la cuenca lacustre Cuitzeo–Charo, Michoacán, México. Contexto geológico e implicaciones paleoambientales
Isabel Israde–Alcántara1 ,*, Jasinto Robles–Camacho2, José Manuel Domínguez3
1 Departamento de Geologia y Mineralogía, Instituto de Investigaciones Metalúrgicas. Universidad Michoacana de San Nicolás de Hidalgo, Cd. Universitaria, 58000 Morelia, Michoacán, México.
2 Laboratorio de Arqueomería de Occidente, Instituto Nacional de Antropología e Historia, Centro INAH Michoacán, Madero Oriente 799, Centro, 58000 Morelia, Michoacán, México.
3 Competencia de Catalizadores y Productos Químicos, Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas 152, 07730 México, D. F., México.
* This email address is being protected from spambots. You need JavaScript enabled to view it.
Abstract
Lacustrine and fluviolacustrine deposits of the Charo sequence crop out extensively along tens of kilometres, and they overlie the Miocene volcanic sequences of the Mil Cumbres Complex in an E–W oriented basin. Eastwards of Morelia city (central Mexico), layers of non lithified clayey sediments of about 3 m in thickness are overlaid by massive diatomite deposits developed during the Miocene–Pliocene in the Cuitzeo palaeolake. Major outcrops are located south and east of the village of Charo at the Las Pulgas, Lomas Blancas and Tzitzimeo sites; all having similar mineralogical facies and strati graphic correlation. Field studies, petrography and X–ray fluorescence spectrometry (XRF) indicated that the parent rock was mainly of andesitic composition with minor daciticrhyolitic components. The source of the raw material was located in the upper topographic levels of the present horst–graben system. The diagenetic clays were identified as smectites. The central part of the Las Pulgas column shows a beidellite–nontronite (B–N) association. Likewise, 27A1–NMR and Móssbauer spectroscopies confirm the B–N character. Interlaid and overlying diatomite strata indicate a lacustrine environment, favourable to the development of secondary clays. The stability of lacustrine conditions gave place to an incipient stratification (smectite–illite), better developed in the middle part of the clayey levels.
Key words: Beidellite–nontronite clays, Cuitzeo basin, lacustrine neogene palaeoenvironments, Neogene, stratigraphy, diatomite.
