The tectonothermal evolution of an area located in the core of the Ibero-Armorican Arc (Variscan belt) has been determined by using the conodont colour alteration index (CAI), Kübler index of illite (KI), the Árkai index of chlorite (AI) and the analysis of clay minerals and rock cleavage. The area is part of the Cantabrian Zone (CZ), which represents the foreland fold and thrust belt of the orogen. It has been thrust by several large units of the CZ, what resulted in the generation of a large number of synorogenic Carboniferous sediments. CAI, KI and AI values show an irregular distribution of metamorphic grade, independent of stratigraphic position. Two tectonothermal events have been distinguished in the area. The first one, poorly defined, is mainly located in the northern part. It gave rise to very-low-grade metamorphism in some areas and it was associated with a deformation event that resulted in the emplacement of the last large thrust unit and development of upright folds and associated cleavage (S1). The second tectonothermal event gave rise to low-grade metamorphism and cleavage (S2) crosscutting earlier upright folds in the central, western and southern parts of the study area. The event continued with the intrusion of small igneous rock bodies, which gave rise to contact metamorphism and hydrothermal alteration. This event was linked to an extensional episode due to a gravitational instability at the end of the Variscan deformation. This tectonothermal evolution occurred during the Gzhelian–Sakmarian. Subsequently, several hydrothermal episodes took place and local crenulation cleavage developed during the Alpine deformation.

S. Fiore, J. Cuadros, F.J. Huertas (Editors) (2010) Interstratified Clay Minerals: Origin, Characterization and Geochemical Significance. AIPEA Educational Series, Publication Number 1. This book is a compilation of the lectures presented at the first AIPEA School for Young Scientist held at the University of Bari, just before the 14th International Clay Conference held in Castellanata Marina in June 2009, and it is the first of a new initiative – the AIPEA Educational Series. As the AIPEA promotion in the website states ”The book is an overview and update on the main issues related to interstratified (or mixed-layer) clay minerals, with a clear educational scope. It is accessible to students, providing the basics and the latest information on the several topics and including key literature references.” Edited volumes are difficult to review, particularly when, as is the case with this volume, the chapters cover such a broad range of topics. I will try to do it, keeping in mind the intended clear educational scope , because this is a problem of the book. In some of the chapters there is an inconsistent use of the terminology that can be rather confusing for its potential audience: newcomers to interstratified minerals. This is important because it ignores the recommendations of one of the committees sponsored by the AIPEA: The Nomenclature Committee. This committee (Guggenheim et al ., 2006) recommends the use of the term interstratified instead of mixed layer, or 2:1, 1:1 instead TOT or TO, for the kind of minerals the book deals with. I know how difficult it is to change habits, so I can understand that some authors retain the use of mixed-layer clay minerals, ignoring these recommendations (see chapters 3, 4 and 8); however, I find it more difficult to understand the inconsistent use of both terms (see chapters 1, 2, 5 and 6). Chapter 1. Introduction to Mixed-Layer Clay Minerals (J. Cuadros, S. Fiore and F.J. Huertas). This chapter …

New athyridide brachiopods collected from the Early Devonian of the Cantabrian Zone (NW Spain) include Protathyris praecursor Kozlowski, P. strelnikovi sp. nov., and Athyris butleri sp. nov. The species of Protathyis are the first of the genus to be described from northwestern Spain. Two species referred to Athyris from the Middle-Late Devonian are also described and discussed. These are: A. concentrica (von Buch) of Givetian age and A. howardi sp. nov. of Givetian-Frasnian age.

Thermal evolution of the Palaeozoic–Triassic sequences of the Carnic Alps has been characterized by b cell dimension and Kübler Index (illite “crystallinity”) of K-white micas (KI), Árkai Index (AI) of chlorites, clay mineral assemblages and conodont Colour Alteration Index (CAI). Data indicate at least two metamorphic events, Variscan and Alpine. In the older event high anchizonal conditions predominated although epizonal conditions were reached over wide areas. It was characterized by low-intermediate pressure facies. The thermal peak was mainly due to an extensional regime during the Bashkirian. A younger thermal overprint generated by Alpine orogeny was of lower grade, reaching high diagenetic–anchizonal conditions characterized by high-pressure facies. Inverted metamorphic patterns are associated with middle to late Miocene thrusting. Hydrothermal alteration in the northern part of the region can be linked with emplacement of Oligocene plutons and high heat flow along the Periadratic lineament.

Analysis of the conodont colour alteration index and the Kübler index of illite allowed us the characterization of four types of very low‐ or low‐grade metamorphism in the Cantabrian Zone (CZ) and determination of their regional and temporal distribution. These types are: (1) an orogenic Variscan metamorphism present only in restricted areas of the western and north‐western parts of the CZ where epizonal conditions are reached; (2) a burial metamorphism that appears in the basal part of some nappes, where anchizonal conditions are sometimes achieved; the thermal peak preceded emplacement of the nappes; (3) a late‐Variscan metamorphism in the southern and south‐eastern parts of the CZ; a cleavage, cutting most of the Variscan folds, is associated with this metamorphism, which has been related to an extensional episode; (4) a contact metamorphism and hydrothermal activity associated with minor intrusive bodies. The extension continued after the Variscan deformation giving rise to hydrothermal activity during Permian times.

The measurement of the Kubler Index KI [i.e., the full width at half maximum (FWHM) value of the X-ray powder diffractometric first basal reflection of illite - dioctahedral K-white mica, formerly called also illite "crystallinity" (IC)], is rather simple and quick; however, the delimitation of the KI zones still remains controversial at present, mostly because of the numerous factors that affect the standardization and inter-laboratory calibration of the KI scale. The differences reported between the KI values and scales among different laboratories are considered to be due to (I) X-ray diffractometer settings for measurement of FWHM, (2) sample-preparation procedures, and (3) techniques of measuring or obtaining the FWHM values from the line profiles. The effects of (1) are monitored by the use of polished-slate inter-laboratory standards. In order to consider the effects of differences in sample-preparation, Warr and Rice (1993,1994) distributed inter-laboratory "CIS" standards in the form of (meta)pelitic rock chips and a muscovite flake that require both preparation and measurement in the various laboratories. The "CIS" values given by these authors for these standards were purportedly converted to the Kubler scale using a calibration curve based on measurements on a set of polished-slate slabs and a muscovite flake prepared by Kisch as inter-laboratory KI standards. However, these "CIS" values are much broader than those obtained by virtually all other laboratories, and are considered anomalous; the "raw" data as restored from these "CIS" values are implausibly broad. Comparison with the "raw" values of Warr and Rice suggests that the high- and low-grade boundaries of the anchizone in their "CIS" scale are 0.295 and 0.49-0.50 degrees Delta 20, much broader than the Kubler-equivalent 0.25 and 0.42 degrees Delta 20. Similarly, regressions of the "CIS"-equivalent against the slate-slab calibrated Kubler-equivalent values of several laboratories show that the purportedly Kiibler-equivalent anchizone-boundary values of 0.25 and 0.42 degrees Delta 20 in the "CIS" scale in fact correspond to much narrower Kiibler values. Consequently. the use of the CIS scale boundaries results in increasing confusion when CIS-calibrated KI values are used for petrogenetic purposes in regional comparisons. This discrepancy is likely to reflect errors in the conversion of the "raw" FWHM values into Kubler equivalents. Data on inter-laboratory chip standards are difficult to evaluate unless the "raw", uncalibrated data are also given: such data should be included in all papers reporting on KI.

Crystallite thickness distributions (CTDs) of fundamental illite particles have been determined for a set of pelitic samples from Palaeozoic rocks. Observed CTD shapes are of two main types, asymptotic and lognormal, and these shapes evolve systematically with increasing metamorphic grade. The shapes of the CTDs are explained by two growth stages; (1) an early stage of simultaneous nucleation and growth, during which the asymptotic profiles of CTDs were established, and (2) a later stage of surface-controlled growth without further nucleation, giving rise to the lognormal shapes. The transition from the diagenesis zone to the anchizone, as determined from the Kubler index, is marked by a change in CTD shape from asymptotic to lognormal.

Type specimens of 14 Lower Paleozoic athyridid species from the James Hall collection are selected or recognized, photographically illustrated, and briefly described and discussed.

La distribucion y caracteristicas de las zonas metamorficas en la transicion diagenesismetamorfismo, establecidas mediante la cristalinidad de la illita y el indice de alteracion de color de los conodontos, han permitido distinguir dos episodios de metamorfismo varisco en la Zona Cantabrica (ZC). El primero es el metamorfismo regional del NO de la Peninsula, que esta representado en pequenas areas de las partes O, NO y SO de la ZC, donde se llegan a alcanzar condiciones epizonales, y lleva asociado un clivaje generalizado; este episodio tambien se presenta como un metamorfismo de enterramiento que en la parte basal de algunos mantos alcanza condiciones anquizonales, estando cortado por los cabalgamientos basales de las principales unidades, por lo que el pico termico es anterior al emplazamiento de estas. El segundo episodio es un metamorfismo tardivarisco con dos manifestaciones diferentes: una es de caracter diastatermico y se desarrolla principalmente en las partes central y suroriental de la ZC, llevando asociado un clivaje que corta a la mayor parte de las estructuras; la otra es un metamorfismo de contacto alrededor de pequenos cuerpos intrusivos.

The transition from diagenesis to very low-grade metamorphism has been characterized by conodont colour alteration index (CAI), illite crystallinity (IC), clay-mineral assemblages and rock fabric in a transect (Cape Penas-Cape Torres) located in the Cantabrian Zone (northwest Spain). IC values show a northwest to southeast change from epizonal to diagenetic values. CAI values show a general congruence for low- and high-grade areas. This correlation indicates that CAI values for the epizone are > 5.5, the anchizone 5.5 greater than or equal to CAI > 4, and the diagenetic zone less than or equal to 4. Cleavage develops in incompetent rocks with CAI values greater than 3, mainly by pressure solution. Temperature increases towards the inner parts of the orogen (towards the northwest) and is considered to be related to the tectonic superposition caused by thrusting and folding. A gradient of 35 degrees C/km is inferred for the transect. in the southeastern sector of the section there are several thermal anomalies that are attributed to the presence of epithermal fluids.

ABSTRACT. Investigation of the crystallinity of K-white micas in early Permian rocks from the Nambucca Block, NSW, reveals a metamorphic pattern with the highest grade (epizonal) rocks in an east-west trending zone which changes transitionally to lower grade (anchizonal) rocks to the south and north. Chlorite crystallinity values show a similar pattern, but in some cases do not agree with the Kubler index values from the same location owing to peak broadening caused by the overlap of the (002) chlorite-vermiculite peak and the (001) peak of chlorite. The usefulness of this parameter as a grade indicator is thus limited, unless deconvolution programs are applied. b0 cell parameters of K-white micas in slates indicate intermediate P facies series metamorphism (b0=9.023; sd=0.020), which accords with an interpretation based on mineral assemblages in metabasites. The much wider range in b0 values noted in these rocks, compared to those formed under similar metamorphic conditions in other terrains, is attributed to a wide range in bulk chemical composition. Temperatures of formation based on AI'V contents of chlorites and chlorites in mixed-Iayer clays, range from 216°-231°C in the anchizonal rocks to 244-349°C in epizonal rocks. RESUMEN. Caracterizacion del metamorfismo de muy bajo grado en el bloque Nambucca (NSW, Australia). El estudio de la cristalinidad de las micas blancas potasicas en rocas del Permico Inferior del Bloque Nambucca, Nueva Gales del Sur, ha puesto en evidencia un modelo metamorfico con las rocas de grado mas alto (epizona) con una distribucion este-oeste, cambiando gradualmente a rocas de grado menor (anquizona) hacia el sur y el norte. Los valores de la cristalinidad de la clorita muestran una distribucion similar, pero son mas variables y con frecuencia no coinciden con los valores de la cristalinidad de las micas blancas potasicas de la misma zona, debido al ensanchamiento producido por el solapamiento del pico (002) de la clorita-vermiculita y el (001) de la clorita. La utilidad de este parametro como indicador de grado es, por tanto, limitada, a no ser que se utilicen metodos de descomposicion de los diagramas de difraccion de rayos X. El parametro b0 de las micas blancas potasicas de las pizarras indica series de metamorfismo de presion intermedia (b0=9.023; sd=0.020), que esta de acuerdo con la interpretacion basada en las asociaciones minerales en las metabasitas. Los valores maximos de b0 observados en esta zona, en comparacion con los que se obtienen en otros terrenos afectados por condiciones metamorficas similares, se atribuyen a un intervalo mayor de la composicion quimica global. Las temperaturas de formacion, obtenidas a partir de los contenidos en Aliv de las cloritas y de las cloritas en los interestratificados, oscilan entre 216° y 231°C en las rocas 3nquizonales y 244-349°C en las rocas epizonales.

Samples of underclays corresponding to nine different coal beds of the María Luisa coal seam in the Aller valley (Asturias, Spain) were collected to determine whether their mineralogy and geochemistry could be used for correlation. The underclays are dominated by illite, with an average abundance of 46%, and contain smaller amounts of chlorite, kaolinite (chlorite always more abundant), paragonite, pyrophyllite, mixed-layer illite/smectite (I/S), and mixed-layer muscovite/paragonite. This mineralogical association along with the illite “crystallinity” values (mean values of “crystallinity” in air-dried and ethylene glycol-solvated illite are 0.48° and 0.35°2 θ , respectively) suggest that the samples have undergone very low-grade metamorphism. No consistent variation in the mineral components with increasing depth below the coal was noted. The presence of chlorite and K-feldspar precludes the development of the underclays by extensive leaching by acid swamp waters and thereby suggests that their mineral composition was determined largely by provenance. Thirty-seven mineralogical and geochemical variables were treated by stepwise discriminant analysis. The variables that best served as discriminators between the underclays were: illite + I/S contents of both the whole rock and clay fraction, illite “crystallinity” of the clay fraction in both air-dried and glycolated patterns, pH of the samples, and the elements (in order of atomic number) Na, Al, K, Ca, Ti, V, Sr, Zr, Nb, Ba. The Molino underclay is clearly distinct from the other eight underclays, suggesting its potential use in regional correlation.

ABSTRACTMinute, lamellose concentric micro-frills are described on the external surfaces of the Devonian brachiopod Athyris campomanesi (Verneuil & Archiac). The micro-frills are very regularly spaced with a separation of approximately 0.5 mm, are inclined anteriorly and antero-laterally, and become more or less recurved peripherally down towards the valve surface. These micro-frills must have been secreted by outward extensions of epithelium, presumably resulting from an increase in the rate of cell proliferation or extension in the marginal zone. Extrapolating from the known growth rates of living brachiopods, it seems probable that the micro-frills formed very rapidly, within a matter of days or hours. In life the micro-frills would have formed minute channels around the peripheries of both valves, similar in form and function to rain gutters. As such they probably functioned as baffle chambers, within which excess paniculate material from the inhalant feeding currents would have accumulated. Such particulate material is likely to have been moved laterally from the median axis of the shell down to the sediment surface under the effects of gravity and in vitro shell movements. Each micro-frill may only have functioned in this fashion for a matter of weeks before being rendered ineffective by the forward growth of the valve margin, at which stage it would have been abandoned and replaced by a subsequently formed micro-frill.