Geometría de las silicificaciones en las areniscas miocenas de la montaña de Montjuíc (Barcelona)

D. Parcerisa ^[1] ; D. Gómez-Gras ^[1] ; M. Thiry ^[3] ; F. Calvet ^[2]
1. [1] Universitat Autònoma de Barcelona
  
  Universitat Autònoma de Barcelona
  
  Barcelona, España
2. [2] Universitat de Barcelona
  
  Universitat de Barcelona
  
  Barcelona, España
3. [3] Ecole des Mines de Paris, Centre d’informatique Géologique
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Localización: Geotemas (Madrid), ISSN 1576-5172, Nº. 2, 2000 (Ejemplar dedicado a: IV Congreso del Grupo Español del Terciario (Tremp, 19-21 septiembre, 2000)), págs. 171-174
Idioma: español
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Resumen
- The Monjuïc hill is located in the S of Barcelona city. This hill is constituted by an alternance of lutitic units and conglomerate / sandstone units. These materials are interpreted as deltaic deposits formed during the Lower - Middle Miocene. The source area is the Collserola massif, that is located at the NW of Montjuïc, where Palaeozoic materials crop out. In a diagenetical point of view, authigenic silica formation was essential in the sandstone cementation. This process conferred to the original sediment its present characteristical hardness. Anyway, burial diagenesis did not occur. Two main diagenetic micro-facies with characteristic associations of authigenic minerals can be identified by microscopical analysis: 1. Non-silicified micro-facies: They are present in the less permeable materials where cementation is scarce. Cementation generally forms layers or nodules ofcalcite spar cement that fills interparticle porosity. 2. Silicified micro-facies: They are characterised by the presence of different silica varieties and other minor secondary authigenic minerals. The study of geometrical relationships between silicified and non-silicified micro-facies shows the main silicification paths. In the most permeable facies, silicification occurs across the bedding, whereas in less permeable facies it occurs across fractures.