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| Format: | Artículo científico |
| Language: | en |
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Universitat de Barcelona
2004
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| Online Access: | https://www.redalyc.org/articulo.oa?id=50520402 |
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Table of Contents:
- Diagenesis and Geochemistry of Upper Muschelkalk (Triassic) Buildups and Associated Facies in Catalonia (NE Spain): a paper dedicated to Francesc Calvet Jim Marshall Maurice Tucker Ciencias de la Tierra Catalonia Muschelkalk Triassic reefs C and O isotopes Trace element geochemistry Carbonate buildups are well developed in the Triassic Upper Muschelkalk of eastern Spain in the La Riba Unit,but they are completely dolomitised. These mud-mounds with reefal caps have well-developed fibrous and botryoidalmarine cements which were probably high-Mg calcite and aragonite originally. The dolomite is fabricretentive indicating an early origin, but the 18O values are quite negative (average -3.), interpreted as indicatingrecrystallisation during shallow burial, but without fabric destruction. Low Sr and Na contents support this.The 13C signature is quite uniform (~ +1) and this is probably the inherited, original marine CaCO3 value.The Alcover Unit, deposited between and above the La Riba buildups after a sea-level fall terminated moundgrowth, is an organic-rich laminated dolomicrite with exquisitely-preserved fossils. The 18O signature (average3.4) is similar to the La Riba dolomites, also interpreted as suggesting recrystallisation. The 13C values,however, show a stratigraphic trend of increasingly negative (to 5.5) and then more positive to marine values(~0), over a thickness of 10 metres. This is interpreted as a reflection of increasing stratification and developinganoxia, which would have led to the preservation of the special fossils, and then a return to conditions ofmore open-marine circulation. The dolomicrites of the Alcover unit may well have been formed on or close to thesea-floor. Recrystallisation of the dolomites took place during shallow to moderate burial, with the resetting ofthe 18O signatures and loss of Sr. The dolomitisation of the La Riba Unit is attributed to circulating seawater,probably driven by sea-level change, during deposition of the Alcover Unit or shortly thereafter. 2004 artículo científico 1695-6133 https://www.redalyc.org/articulo.oa?id=50520402 en http://www.redalyc.org/revista.oa?id=505 Geologica Acta: an international earth science journal application/pdf Universitat de Barcelona Geologica Acta: an international earth science journal (España) Num.4 Vol.2