Abstract

SIERRA-ROJAS, María Isabel  and  MOLINA-GARZA, Roberto Stanley. The Zicapa Formation of southern Mexico: stratigraphic revision, sedimentology and sedimentary environments. Rev. mex. cienc. geol [online]. 2014, vol.31, n.2, pp.174-189. ISSN 2007-2902.

The Lower Cretaceous of western Mexico has been interpreted as the record of magmatism and sedimentation in an island arc system, separated of the continental margin by a marginal basin, east of which a system of carbonate platforms was developed on the pre-Mesozoic basement. The sedimentological characteristics and facies relations of the Zicapa Formation in northern Guerrero and southern Puebla allow us to infer the presence of calc-alkaline magmatism in western margin of mainland Mexico during the Early Cretaceous, prior to the development of the Albian Guerrero-Morelos platform. The Zicapa Formation deposited in a continental environment near the coast with the presence of ~130 Ma intermediate volcanism and evidences of, at least, one transgression. To improve the knowledge of the Early Cretaceous stratigraphy of southern Mexico, we suggest to divide the Zicapa Formation into five members: the Cerro La Cruz Member which consists of a basal conglomerate, San Juan de las Joyas Member, made of limestone, the Ajuatetla Member of siliciclastic and transitional marine environment, the San Andrés Member with volcanosedimentary character and the río Poblano Member, dominated by red siltstone and shale interbedded with some limestone. The maximum depositional age for the medium part (San Andrés Member) of the Zicapa Formation is 133±1.3 Ma, from detrital zircon U-Pb laser-ablation geochronology. Strata of the Chapolapa, Atzompa, and Xonamanca formations, together with the Zicapa Formation support interpretation of a convergent margin in western Oaxaquia during Barremian-Aptian time.

Keywords : sedimentary facies; calcalkaline volcanism; Early Cretaceous; Zicapa Formation; Mexico.