Fracturing and Cementation in the Miocene Vilobí Gypsum Unit (Penedès Half-Graben, Ne Spain)
| Autor: | Martínez Rodríguez, Cristina, Baqués, Vinyet, Playà, E., Moragas, Mar, Travé, A. |
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| Přispěvatelé: | Generalitat de Catalunya, Ministerio de Economía y Competitividad (España) |
| Rok vydání: | 2011 |
| Předmět: | |
| Zdroj: | Digital.CSIC. Repositorio Institucional del CSIC instname |
| Popis: | 28th IAS meeting of Sedimentology, 5-8/7 2011 ,Zaragoza, Spain The Vilobí Gypsum Unit (upper Burdigalian) is located in the Penedès half-graben (northeast of the Iberian Peninsula). This unit consists of a succession up to 60 m of primary (limited to the top interval) and secondary (the predominant form) gypsum with both laminated and banded facies. This succession was formed in a gypsiferous coastal salina that periodically underwent emersion episodes. During these episodes, early diagenetic anhydrite (both nodular-banded facies and enterolithic levels interbedded within the gypsum) formed in a sabkha setting. This succession has been affected by both ductile (folds and microfolds) and brittle (faults and joints) deformations. Structures of ductile deformation are interpreted to have been caused by syn-sedimentary deformation, whereas those of brittle deformation are related to Neogene extensional stages recorded in the region. Brittle structures are partly or totally cemented by fibrous and/or crystalline (tabular, megacrystalline) gypsum. A number of families of fragile structures have been distinguished: -Family 1 are NE-SW trending extensional faults infilled with fibrous gypsum growing perpendiculary or sigmoidally to fracture plane (growing syn-tectonically), tabular crystalline cement and megacrystalline gypsum (totally infilling the dissolution-enlarged fault planes). -Family 2 are ENE-WSW trending normal faults with the same infillings as Family 1. -Family 3 are NE-SW to ENE-WSW trending thrust faults with fibrous gypsum cement. -Family 4 are sub-parallel joints located on the upper block (hanging wall) of the local faults. These joints are totally cemented by crystalline cement; exfoliation planes of the crystals are perpendicular to joint aperture. -Family 5 and Family 6 correspond to joints forming an orthogonal system; typically the planes are dissolved and enlarged and the cements of these structures are different from those associated with Family 4, with bigger crystals (megacrystals up to 25 cm). The gypsum rocks of the Vilobí Unit display isotope compositions between +17.8 and +22.3¿ for sulphur, and from +12.4 to +18.6¿ for oxygen, while the cements are heavier, from +21.8 to +25.1¿ and from +14.3 to +19.2 for sulphur and oxygen, respectively. Additionally, isotope signals of the infillings show an increasing trend from the youngest cements (fibrous gypsum) to the latest ones (megacrystals). These data suggest chemical recycling processes of the previous sulphates, both the host-gypsum rocks and the youngest cements. The conjugate extensional faults (Family 1 and 2) were formed during the latest stages of the major rifting episode (lower to middle Langhian). Family 4 is attributed to an early post-rift event (middle to upper Langhian), while Family 3 is related to the upper Langhian-lower Serravallian minor compressive stage (with reactivation of the pre-existing extensive faults and deformation and reorientation of the initial fibrous cement). Family 5 and 6 were formed during a late post-rift event (probably upper Serravallian-Messinian). Financial support by I+D+I research projects CGL2010-18260, CGL2009-11096 and Grup Consolidat deRecerca “Geologia Sedimentària” (2009 SGR-1458). |
| Databáze: | OpenAIRE |
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