Nuevas microbialitas de arqueociatos y trombolitos del Bilbiliense (Cámbrico inferior) de la Formación Láncara (Cordillera Cantábrica, norte de España)

Recent palaeontological and microfacies studies carried out on the Láncara Formation (early Cambrian) provide evidence for an interesting, previously undescribed association of archaeocyaths (Salce locality) and microbialites (Salce and Barrios de Luna localities). The archaeocyathan assemblage consists of Archaeocyathus laqueus (Vologdin, 1932) and Pycnoidocyathus erbiensis (Zhurav leva , 1955), indicating an early Bilbilian age (Stage 4, Series 2, Cambrian) for these materials. The analysis of the upper part of the lower member has allowed differentiation of eleven carbonate facies that have been grouped into: i) non-skeletal grain packstone-grainstone, ii) fenestral mudstone-packstone, iii) heterolithic stylonodular facies, iv) microbialites, v) bioclast-intraclast packstone-grainstone. Archaeocyaths occur reworked in stylonodular facies as well as forming small archaeocyaths-thrombolitic patches (centimetre-scale). The archaeocyath-rich thrombolitic microbialites from Salce were developed in very shallow subtidal conditions surrounded by other microbialites and small lenticular intertidal bars in the inner ramp. Toyonian biostratigraphic and paleobiogeographic analyses have also been carried out. After the comparison with Toyonian archaeocyathan rich facies from Gondwana, it has become evident that the early Cambrian record from the Cantabrian Mountains provides the richest generic assemblage from Gondwana for Toyonian time.Los recientes estudios paleontológicos y de análisis de microfacies de los materiales carbonatados de la Formación Láncara (Cámbrico inferior) han deparado el hallazgo de una inédita asociación de arqueociatos (localidad de Salce) y microbialitas (localidades de Salce y Barrios de Luna). La asociación de arqueociatos está constituida por Archaeocyathus laqueus (Vologdin, 1932) y Pycnoidocyathus erbiensis (Zhurav leva , 1955), lo que indica una edad Bilbiliense (Piso 4, Serie 2, Cámbrico) para estos materiales. En el análisis de los niveles carbonatados, a techo del miembro inferior, se han distinguido once tipos de facies que han sido agrupadas en: i) packstone-grainstone de granos no esqueléticos, ii) mudstone-packstone con fábrica fenestral, iii) facies estilonodulares heterolíticas, iv) microbialitas, v) packstone-grainstone bioclásticos e intraclásticos. Los arqueociatos aparecen resedimentados en las facies estilonodulares y formando pequeños parches trombolíticos (escala centimétrica). Las microbialitas de arqueociatos y trombolitos de Salce se desarrollaron en condiciones submareales muy someras rodeadas de otras microbialitas y pequeñas barras lenticulares en zonas intermareales de la rampa interna. Se han realizado análisis bioestratigráficos y paleobiogeográficos para el Toyoniense. Tras comparar las facies del Toyoniense ricas en arqueociatos de Gondwana, se manifiesta de manera evidente que el registro del Cámbrico inferior de la Cordillera Cantábrica aporta la asociación genérica más rica de Gondwana durante el Toyoniense

Structural control of fluid flow on a carbonate platform margin: an example from the Otavi Mountainland, Namibia

The present study focuses on the northwestern OML, southwest of the mining town of Tsumeb. The dominating structure in this area is the NW-SE striking Guinas Fault. The Guinas Fault is a shear zone that divides an area, which is different in sense of stratigraphic features, the grade of pre-, syn- and post- Damaran deformation and the type and grade of mineralisation. The northern area is enriched by Cu-rich base metal sulphides, whereas the southern area is almost barren.conferenc

Late- to post-Variscan, large scale “hydrothermal” dolomitization in the Iglesiente area, southwestern Sardinia: geologic/geodynamic setting, fluid flow and porosity evolution.

Fieldtrip Guidebook for the 27th IAS Meeting, September 2009, Alghero Ital