Glauconitic laminated crusts from hydrothermal alteration of Jurassic pillow-lavas (Betic Cordillera, S Spain): a microbial influence case

Abstract

The green crusts infilling the spaces among pillow-lavas from the Lower Jurassic Median Subbetic (Betic Cordillera, S Spain) are the subject of this textural, mineralogical and geochemical study. Their exceptional laminated morphology and mineral composition made it possible to establish the genetic conditions and different phases of the infilling, while also interpreting the possible influence of microbial activity in the origin and growth of the laminated crusts. Two types of crust were discerned: green laminated crusts and black crusts. The green crusts are mostly composed by glauconite and celadonite, and a minority by smectites, whereas black crusts and lens-shaped nappes are saponitic. The record of filaments and coccoid-shaped forms at different scales from the glauconitic crusts indicates the potential implication of chemoorganotrophic microbes in the precipitation of the glauconite, and the development of laminated textures under lowtemperature hydrothermal conditions. During an early stage, alteration of pillow-lava margins caused by hydrothermal reducing fluids resulted in black films of saponite and calcite filling the void spaces. During a cooling phase, green laminated crusts composed by glauconite and celadonite grew under oxic conditions due to both circulation and diffusion of oxygenated sea-water along inter-pillow spaces, and the chemoorganotrophic microbial activity. A new stage of saponite formation with calcite occurred under higher T and confined/reducing conditions resulting from deposition of marine sediments; finally, calcite and quartz crystallised as the latest product closing the remaining space (or producing geodes) among the pillow-lava bodies.Keywords: Celadonite, Glauconite, Saponite, Hydrothermal, Microbes, Lower Jurassic Resumen Las costras verdes localizadas entre las lavas almohadilladas del Subbético Medio (Cordillera Bética, S España) presentan una morfología laminada excepcional. La caracterización textural, geoquímica y mineralógica de estas costras ha permitido establecer las condiciones bajo las que se formaron e interpretar la posible influencia de la actividad microbiana en el origen, crecimiento y morfología de las mismas. Se han diferenciado dos tipos de costras: costras laminadas verdes y costras negras. Las costras verdes están formadas mayoritariamente por glauconita y celadonita y, en menor proporción, por esmectitas. Las costras negras, sin embargo, son de naturaleza saponítica. La presencia de filamentos y formas cocoidales a diferentes escalas de observación en las costras verdes, sugiere la mediación de microbios quimiorganotróficos en la precipitación de la glauconita así como en el desarrollo de texturas laminadas en un ambiente hidrotermal de baja temperatura. En un primer momento, la alteración de las superficies de las lavas almohadilladas, bajo la influencia de fluidos hidrotermales de carácter reductor que siguieron al depósito de las lavas almohadilladas, produjo láminas negras de saponita y calcita. En una fase de enfriamiento posterior, baj...

Oxfordian neptunian dykes with brachiopods from the southern part of the Kraków-Częstochowa Upland (southern Poland) and their links to hydrothermal vents

“…The zones of shallow-water hydrothermal seepage are well known for particularly intensive growth of bacteria and microbial mats (cf. Stanier and Cohen-Bazire 1977;Tunncliffe 1988Tunncliffe , 1991Tunncliffe , 1992aTaviani 1994;Mounji et al 1998;Dando et al 2000;Tarasov et al 2005;Reolid and Abad 2014), which may have provided nourishment for brachiopods feeding on phytoplankton, bacteria, colloidal and dissolved nutrients (Steele-Petrovič 1976, 1979. According to Little et al (2004), some Mesozoic brachiopod taxa may have had chemosymbionts as well (cf.…”

Jurassic Non-Carbonate Microbialites from the Betic-Rifian Cordillera (Tethys Western End): Textures, Mineralogy, and Environmental Reconstruction

“…In addition, whole-rock analyses of major elements of the crusts were carried out using X-ray fluorescence (XRF), and for trace elements, inductively coupled plasma-mass spectrometry (ICP-MS). Details about methodology (facilities, measurement conditions, standards, and so on) can be found in Reolid and Nieto [51], Reolid and Molina [104], Reolid et al [47], and Reolid and Abad [111]. Trace elements and rare earth elements (REE) are compared in some examples with the Post-Archaean Australian Shales (PAAS) [112] as average bulk composition of the upper continental crust, and with the carbonaceous chondrite [113].…”

“…The transition between inner and outer parts is characterized by a progressive orientation of the crystals through palm-tree branches and progressively larger crystals. Secondary electron and TEM images of Reolid and Abad [111] show that the needle-like coating of the filaments actually consists of idiomorphic lath-like crystals <10.5 µm long and <0.8 µm wide. Some lath-like crystals present clay-flake morphology and small filamentous to coccoid-shaped forms, with < 0.5 µm length and 0.1 µm width.…”

“…%. Moreover, the black crust shows substantial enrichments in some trace elements: Sr (1140 ppm), Ba (2125 ppm), Co (87 ppm), Ni (131 ppm), and Cu (201 ppm), with respect to the bulk composition of the PAAS [111]. The sum of REE in the Mn crust (11 ppm) is very low with respect to the PAAS (183 ppm), the light REE being more abundant than heavy REE.…”

“…The XRD patterns of oriented aggregates corresponding to the green masses show glauconitic mica (glauconite and celadonite), calcite, and a small amount of smectite (saponite according to Reolid and Abad [111]).…”