The westernmost sector of the lower-Cambrian Los Navalucillos Formation: microbialites in tidal deposits, Central Iberian Zone, Toledo Mountains, Spain
El sector más occidental de la Formación de Los Navalucillos, Cámbrico inferior: microbialitas en yacimientos mareales de la Zona Centroibérica, Monte de Toledo, España

S. Menéndez¹, M. Rodríguez-Martínez², E. Moreno-Eiris², A. Perejón²

¹Museo Geominero, Instituto Geológico y Minero de España (IGME), Ríos Rosas, 23, 28003 Madrid, Spain. Email: s.menendez@igme.es; ORCID ID: http://orcid.org/0000-0001-6074-9601

²Departamento de Geodinámica, Estratigrafía y Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, C/José Antonio Nováis, 12, 28040 Madrid, Spain. Email: martarm@geo.ucm.es, eiris@ucm.es, aparqueo@ucm.es; ORCID ID: http://orcid.org/0000-0002-4363-5562, http://orcid.org/0000-0003-2250-4093, http://orcid.org/0000-0002-6552-0416

Introduction and geological settingTOP

Lower Cambrian strata are well exposed in the Central Iberian Zone (Iberian Massif). The lithostratigraphic record is formed, from bottom to top, by the Pusa, Azorejo, Los Navalucillos, Soleras and Los Cortijos formations. The lowermost Pusa Formation consists of 2000 m of siltstones, mudstones and finely laminated thin sandstones. This unit is well exposed in La Nava de Ricomalillo and contains acritarchs, some groups of small shelly fossils (SSF) and trace fossils, diverse organic filamentous fossils and trilobites. The presence of archaeocyathan moulds have been reported at the upper part of this unit (Jensen et al., 2010). The Azorejo Formation is formed by 550-600 m of coarse-grained sandstones with significant lateral facies changes and siltstone/sandstone alternations towards the top. Trace fossils as Astropolichnus hispanicus, Diplocraterion isp. are recorded as well as arthropod-type traces (Moreno et al., 1976; Liñán et al., 2004). The Los Navalucillos Formation consists of 150 m of limestones and dolostones interbedded with claystones and siltstones. In this formation the development of calcimicrobial-archaeocyathan boundstones is very common. Archaeocyaths recorded in many of the Los Navalucillos Formation outcrops throughout the Toledo Mountains are characteristic of Zones VI-VII (late Ovetian=Botoman 1-2=Series 2, Stage 3) (Menéndez, 2012, 2014). Trilobites were also mentioned and identified as Granolenus midi (Gil Cid et al., 1976; Liñán & Gámez-Vintaned, 1993). The Soleras Formation is about 200 m thick, and mostly consists of siltstones bearing trilobites such as Andalusiana and Serrodiscus speciosus (Gil Cid, 1981; Liñán et al., 1993). This fauna points to a mid-late Marianian age. The Los Cortijos Formation is made up of 50-60 m of mainly arkosic sandstones with some siltstone interbeds. It contains an an assorted trilobite fauna that suggests Bilbilian age (Liñán et al., 2004 and references within).

The westernmost outcrops of the Los Navalucillos FormationTOP

In the study area, the Los Navalucillos Formation seems conformably overlying the Azorejo Formation. However, the presence of large E-W faults suggests a faulted contact between both formations (Fig. 1). The Los Navalucillos Formation has been interpreted as tidal and shallow-marine carbonate deposits (Gil Cid et al., 1976; Zamarreño et al., 1976; Perejón & Moreno, 1978; Monteserín, 1978; Moreno Serrano & Gómez Pérez, 1986). Lately a comprehensive study has been carried out on the carbonate materials of the whole area, especially focused on microfacies, archaeocyathan systematics and biostratigraphy (Menéndez, 2012, 2014). The westernmost outcrops of the Los Navalucillos Formation occur at La Nava de Ricomalillo area (Fig. 1). There, two localities are known: (i) La Estrella has already been studied by Martín-Caro (1980) and Martín-Caro et al. (1979), where the rocks are strongly affected by contact metamorphism due to the nearby plutonic complex; the presence of archaeocyaths was cited in these same levels, but its poor preservation did not allow their identification; and (ii) the Finca Higueruela succession (FH), best exposed. The latter represents a tidal-related succession, 21 m thick (Fig. 2A), without calcimicrobial-archaeocyathan boundstones, although different microbialites as stromatolites and oncolites are conspicuous (Fig. 2B-D).

Concluding remarksTOP

The two new exposures described here from the westernmost outcrops of the formation, close to La Nava de Ricomalillo area, include: (i) La Estrella, strongly affected by contact metamorphism caused by the nearby plutonic complex; and (ii) the Finca Higueruela succession, where different microbialites as stromatolites and oncolites are present.

ReferencesTOP