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| Format: | Artículo científico |
| Language: | en |
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Academia Brasileira de Ciências
2005
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| Online Access: | https://www.redalyc.org/articulo.oa?id=32777211 |
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Table of Contents:
- Carbonate cements in contemporaneous beachrocks, Jaguaribe beach, Itamaracá island, northeastern Brazil: petrographic, geochemical and isotopic aspects Núbia C. Guerra Chang H. Kiang Alcides N. Sial Multidisciplinaria (Ciencias Naturales y Exactas) Holocene beachrocks earlydiagenesis O and Cisotopes HolocenebeachrocksoftheJaguaribebeach,StateofPernambuco,northeasternBrazil,consistofhorizontal,cementedlayersapproximately40cmthick.Thecementshowsthreetexturalvarieties:(a)calciferous,surroundingsiliciclasticgrains,(b)micritic,withanacicularfringe;and(c)cryptocrystallinecalciteinpores.Earlycementationtookplaceatthewatertablebelowbeachridges,wheregeochemical,hydrodynamicand,perhaps,alsomicrobiologicalconditionsfavoredrapidprecipitationofaragoniteand/orhigh-Mgcalcite.δ13Cvaluesrangefrom1.8to+1.5◦/◦◦fordissolvedcarbonateininterstitialwaterandfrom+0.2to+2.1◦/◦◦forbioclasticcomponents.δ18Ovaluesrangefrom2.8to+0.5◦/◦◦forseawater,freshwaterandinterstitialwater.δ13Cvaluesanddiageneticfeaturessuggestthatcementationoccurredinmeteoric-vadoseand/ormarine-phreaticwaterbylossofCO2duringevaporationoftheinterstitialwater.Locally,superimposedlow-Mgcalcitecementspointtosubsequentfreshwaterinfluence.Total-rockcementcompositionofverticallystackedbeachrockbedsattheJaguaribebeachshowsthatthehighestbeachrockbedisolderthantheone(ofsamepetrographiccomposition)situatedatthecurrentgroundwaterlevel.Thisimpliesadownwardprogressionofcementation,whichprobablyfollowedthesea-levelfallafteralocalhighstand. 2005 artículo científico 0001-3765 https://www.redalyc.org/articulo.oa?id=32777211 en http://www.redalyc.org/revista.oa?id=327 Anais da Academia Brasileira de Ciências application/pdf Academia Brasileira de Ciências Anais da Academia Brasileira de Ciências (Brasil) Num.2 Vol.77