Chemical signature of two Permian volcanic ash deposits within a bentonite bed from Melo, Uruguay

Abstract

A Permian bentonite deposit at Melo, Uruguay is composed of a calcite-cemented sandstone containing clay pseudomorphs of glass shards (0-0.50 m) overlying a pink massive clay deposit (0.50-2.10m). The massive bed is composed of two layers containing quartz and smectite or pure smectite respectively. The smectite is remarkably homogeneous throughout the profile: it is a complex mixed layer composed of three layer types whose expandability with ethylene glycol (2EG 1EG or 0EG sheets in the interlayer zone which correspond to low-, medium-and high-charge layers respectively) varies with the cation saturating the interlayer zone. The smectite homogeneity through the profile is the signature of an early alteration process in a lagoonal water which was over saturated with respect to calcite. Compaction during burial has made the bentonite bed a K-depleted closed system in which diagenetic illitization was inhibited. Variations in major, REE and minor element abundances throughout the massive clay deposit suggest that it originated from two successive ash falls. The incompatible element abundances are consistent with that of a volcanic glass fractionated from a rhyolite magma formed in a subduction/collision geological context.

Major, trace and rare earth element (REE) characteristics of tuffs in the Yenice-Saraycık area (Demirci, Manisa), Western Anatolia, Turkey

“…The LREE-enriched and relatively flat HREE patterns with the strong negative Eu anomalies also indicate the felsic nature of the tuffs. It is also typical for evolved magmas as noted byCalarge et al, 2006. Similar chondrite-normalized REE patterns have been reported for felsic volcanic rocks byMoghazi, 2003 and Ersoy et.…”

Clay mineralogy, chemistry, and diagenesis of Late Devonian K-bentonite occurrences in northwestern Turkey

“…However, The negative Eu anomaly is commonly attributed to the removal of Eu by plagioclase during fractionation of the melt. This anomaly is typical of evolved magmas (Calarge et al, 2006). K in illite compositions could be sourced from K-bearing primary igneous minerals such as feldspars or micas.…”

Bentonitas da Formação Irati no setor sul da Bacia do Paraná

“…A área estudada localiza-se a leste de Aceguá, na propriedade Fazenda Maria Castelhana, aproximadamente a dois quilômetros da divisa entre Brasil e Uruguai, coordenadas geográficas 31°53'602"S e 54°00'125"W (Figura 1). Essa região tem se notabilizado pela identificação de bentonitas preservadas em diferentes formações da Bacia do Paraná e em ambientes diversos (Formoso et al, 1997(Formoso et al, , 2000Simas et al, 2003;Calarge et al, 2006). Este artigo propõe mostrar resultados do estudo de caracterização detalhada de aspectos mineralógicos e geoquímicos que levaram à identificação de novos níveis de bentonita, cuja presença associada com a Formação Irati ainda não havia sido descrita no setor sul da Bacia do Paraná, tendo-se apenas algumas inferências baseadas no comportamento anômalo dos argilominerais (Delaney e Formoso, 1960).…”

“…Seriam depósitos de queda a partir de erupções sincrônicas ao evento de sedimentação na sequência de folhelhos da Formação Irati, de forma similar ao constatado em unidades mais antigas, como os níveis de tonsteins do Permiano Inferior da Formação Rio Bonito (Formoso et al, 2000;Guerra-Sommer et al, 2008;Simas et al, 2013), ou em unidades mais jovens, como os níveis de bentonita do Permiano Superior da Formação Rio do Rasto (Calarge et al, 2003(Calarge et al, , 2006Albarnaz et al, 2009). A proveniência vulcânica estaria ligada a manifestações da província magmática Permo-Triássica Choiyoi localizada entre a Argentina e o Chile (Rocha-Campos et al, 2004, 2006, 2007, 2011Santos et al, 2006).…”