Resumen de Caracterización morfológica de los nodulos silíceos de la Fm Hoya (Tabuenca, Zaragoza): implicaciones genéticas

Francisco Javier Torrijo Echarri, Juan Miguel A. Mandado Collado, M. E. Bona Artazos

• Siliceous nodules of the Devonian deposits in the "Hoya Formation" (Tabuenca, Zaragoza) were studied. The nodules are included in lutites, and contain quartz, opaque minerals and clays. Our morphologic study reveals that they are spheres and spheroids, with a grey colour and 0.3 to 9.6 cm of diameter, and grade into the direction of stratification. This spherical morphology is the result of isotropic structure of host sediment, and it indicates a growth mechanism by diffusion and a short transport mechanism. The existence of distorted lamination indicate that its central section was cemented before that its outer section, and that its growth was passive, by a mechanism of porosity filler into clays.

  These nodules growth during the precompactacional stage during early diagenesis.