The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
Franco Russo - One of the best experts on this subject based on the ideXlab platform.
-
Role of autochthonous versus detrital Micrite in depositional geometries of Middle Triassic carbonate platform systems
Geological Society of America Bulletin, 2016Co-Authors: Adriano Guido, Adelaide Mastandrea, Marco Stefani, Franco RussoAbstract:Middle Triassic platforms (Formazione di Contrin, Upper Anisian) in the Italian Dolomites, southern Alps, record large changes in carbonate production and depositional geometry. The changes include variation in the abundance of detrital Micrite, i.e., allochthonous calcareous mud, relative to the autochthonous Micrite, which formed in situ and was syndepositionally lithified. Carbonate factory dynamics controlled the geometry of the clinostratified slope units and were probably associated with changes in oxygenation. Early Anisian low-relief platforms were followed by late Anisian, high-relief buildups, associated with basinal dysoxic-anoxic environments. The geometric evolution of the platform slopes records a progressive increase in the dip angle of clinostratifications, matched by a deepening evolution of the basinal environments. At the same time, the slope sediments record a gradual change from loose detrital Micrite, characterizing the lower portion, to autochthonous Micrite, dominating the upper part and recording massive syndepositional lithification. The development of the autochthonous Micrite was associated with the preservation of significant amounts of organic matter. This sharp increase in autoMicrite formation was probably induced by a rapid change from oxic to suboxic conditions in the carbonate slope and margin environments, while anoxic conditions developed in the adjacent organic-rich basin (Moena Formation). The low oxygen level promoted the preservation of organic matter and the activity of sulfate-reducing bacteria, which in turn induced in situ deposition of autochthonous Micrite through biomediated processes. This pervasive early cementation and lithification induced the development of steep platform slopes. The conceptual model distilled from this Middle Triassic case can support the interpretation of analogous buildups where the skeletal framework is subordinate to the Micrite component.
-
Microbialites vs detrital Micrites: Degree of biogenicity, parameter suitable for Mars analogues
Planetary and Space Science, 2014Co-Authors: Armando Blanco, Adriano Guido, Adelaide Mastandrea, F. Tosti, Marcella D׳elia, Vincenzo Orofino, F. Mancarella, Sergio Fonti, Franco RussoAbstract:Abstract In upcoming years several space missions will investigate the habitability of Mars and the possibility of extinct or extant life on the planet. In previous laboratory works we have investigated the infrared spectral modifications induced by thermal processing on different carbonate samples, in the form of recent shells and fossils of different ages, whose biogenic origin is indisputable. The goal was to develop a method able to discriminate biogenic carbonate samples from their abiogenic counterparts. The method has been successfully applied to microbialites, i.e. bio-induced microcrystalline carbonate deposits, and particularly to stromatolites, the laminated fabric of microbialites, some of which can be ascribed among the oldest traces of biological activity known on Earth. In this work we show that, by applying our method to different parts of the same carbonate rock, we are able to discriminate the presence, nature and biogenicity of various Micrite types (i.e. detrital vs autochthonous) and to distinguish them from the skeletal grains. To test our methodology we preliminarily used the epifluorescence technique to select on polished samples, skeletal grains, autochthonous and allochthonous Micrites, each one characterized by different organic matter content. The results on the various components show that, applying the infrared spectral modifications induced by thermal processing, it is possible to determine the degree of biogenicity of the different carbonate samples. The results are of valuable importance since such carbonates are linked to primitive living organisms that can be considered as good analogues for putative Martian life forms.
-
The Microbialite-Vermetid Community of the Salento Peninsula in Southern Italy: A Late Miocene Example of AutoMicrite Deposition
Advances in Stromatolite Geobiology, 2010Co-Authors: Alessandro Vescogni, Adriano Guido, Adelaide Mastandrea, Franco RussoAbstract:A carbonate facies made up mainly of Micrite and vermetid shells has been identified in the early Messinian coral reef complex of the Novaglie Formation on the Salento Peninsula of southern Italy. Vermetids (Mollusca, Prosobranchia, and Caenogastropoda) can form large colonies that are usually attached to hard substrates (Vescogni et al. 2008). The Micrite-dominated facies with a large number of vermetid shells (most of them horizontal) is unusual. Moreover, this facies shows completely different sediment textures and organism compositions than the associated reefal carbonates. To explain the origin of this facies and identify the source of the Micrites, field, microfacies and epifluorescence observations were carried out along with scanning electron microscopy (SEM), EDS and FT-IR analyses.
-
AutoMicrite in a 'nummulite bank' from the Monte Saraceno (Southern Italy): evidence for synsedimentary cementation
Sedimentology, 2010Co-Authors: Adriano Guido, Adelaide Mastandrea, Cesare Andrea Papazzoni, Michele Morsilli, Mauro Francesco La Russa, F. Tosti, Franco RussoAbstract:Following introduction of the term ‘nummulite bank’, there has been debate regarding interpretation of these types of deposits as autochthonous (autoMicrite) or allochthonous (detrital Micrite). These banks are made up of large foraminifera and ill-defined fine-grained components. The fine-grained components consist mainly of Micrites. The recognition of autoMicrite has deep implications for the synsedimentary cementation and stabilization of the bank. In order to distinguish between autoMicrite and detrital Micrite, the nanomorphology, geochemistry and organic matter remains in the microfacies of a nummulite bank in the Middle Eocene of Monte Saraceno (Gargano, Southern Italy) were analysed. Optical and scanning electron microscope investigations showed that the Micrites have been recrystallized to aggrading microsparite. Epifluorescence observations on selected Micrite/microsparite areas with peloidal texture revealed the presence of organic matter. Scanning electron microscope analyses on epifluorescent Micrites showed that the microbial peloids have smaller crystal sizes than those in organic matter-depleted areas. The geochemical characterization of extracted organic matter, performed through the functional group analyses by Fourier transform-infrared spectroscopy, shows strong prevalence of the aromatic fraction over the aliphatic and carboxylic ones. These characteristics of organic compounds indicate both their thermal maturation and their likely derivation from degradation of bacterial communities. The local presence of peloidal anti-gravity textures, bright epifluorescence and organic molecules in clotted peloidal areas suggest that the metabolic activity of microbial communities could have induced precipitation of these Micrites and, consequently, the syndepositional cementation of the nummulite bank. This type of cementation can rapidly stabilize sediments and promote the depositional bank geometry.
-
The mud mound nature of the Cassian Platform Margins of the Dolomites A case history: the Cipit boulders from Punta Grohmann (Sasso Piatto Massif, northern Italy)
Facies, 1997Co-Authors: Franco Russo, Adelaide Mastandrea, Claudio Neri, Alberto BaraccaAbstract:The sedimentological features and the microbiofacies of the Cassian platforms (Late Ladinian-Carnian) of the Dolomites can be studied only on the basis of the socalled “Cipit boulders”, that are platform-derived olistoliths and clasts fed to the basin and escaped to the extensive dolomitization affecting the buildups. Our paper deals with the Cipit boulders occurring in the Punta Grohmann section (Wengen and S. Cassiano formations, Late Ladinian, Archelaus and Regoledanus Zones). The dominant microfacies are represented by boundstone, consisting of nearly 60% of micritic limestone occurring both as peloidal or aphanitic Micrite, mostly organized into stromatolitic laminites of thrombolites. The skeletal organism ( Tubiphytes , skeletal cyanobacteria, sphinctozoan sponges, etc.) represent only a minor component of the rock (usually less than 10%). Early cements are widespread and consist both of fan-shaped calcite (replacing former aragonite), bladed isopachous magnesian calcite and radial-fibrous calcite (neomorphic after Mg-calcite). The carbonate platforms from which the olistoliths derive were made up mainly of carbonate mud that underwent early lithification, as witnessed by the considerable amount of early cements: therefore they may be regarded to as mudmounds, and more precisely as microbial mud-mounds, due to the clearly accretionary, organic-controlled nature of most Micrites. The Micrites, subdivided into auto- and alloMicrite on the basis of micromorphological and fabric characteristics, have been tested for epifluorescence. The results confirm the organic control on the deposition of autoMicrite, also in the cases in which a microbial influence is not obvious (i.e. aphanitic Micrite without internal organization).
Adelaide Mastandrea - One of the best experts on this subject based on the ideXlab platform.
-
Role of autochthonous versus detrital Micrite in depositional geometries of Middle Triassic carbonate platform systems
Geological Society of America Bulletin, 2016Co-Authors: Adriano Guido, Adelaide Mastandrea, Marco Stefani, Franco RussoAbstract:Middle Triassic platforms (Formazione di Contrin, Upper Anisian) in the Italian Dolomites, southern Alps, record large changes in carbonate production and depositional geometry. The changes include variation in the abundance of detrital Micrite, i.e., allochthonous calcareous mud, relative to the autochthonous Micrite, which formed in situ and was syndepositionally lithified. Carbonate factory dynamics controlled the geometry of the clinostratified slope units and were probably associated with changes in oxygenation. Early Anisian low-relief platforms were followed by late Anisian, high-relief buildups, associated with basinal dysoxic-anoxic environments. The geometric evolution of the platform slopes records a progressive increase in the dip angle of clinostratifications, matched by a deepening evolution of the basinal environments. At the same time, the slope sediments record a gradual change from loose detrital Micrite, characterizing the lower portion, to autochthonous Micrite, dominating the upper part and recording massive syndepositional lithification. The development of the autochthonous Micrite was associated with the preservation of significant amounts of organic matter. This sharp increase in autoMicrite formation was probably induced by a rapid change from oxic to suboxic conditions in the carbonate slope and margin environments, while anoxic conditions developed in the adjacent organic-rich basin (Moena Formation). The low oxygen level promoted the preservation of organic matter and the activity of sulfate-reducing bacteria, which in turn induced in situ deposition of autochthonous Micrite through biomediated processes. This pervasive early cementation and lithification induced the development of steep platform slopes. The conceptual model distilled from this Middle Triassic case can support the interpretation of analogous buildups where the skeletal framework is subordinate to the Micrite component.
-
Microbialites vs detrital Micrites: Degree of biogenicity, parameter suitable for Mars analogues
Planetary and Space Science, 2014Co-Authors: Armando Blanco, Adriano Guido, Adelaide Mastandrea, F. Tosti, Marcella D׳elia, Vincenzo Orofino, F. Mancarella, Sergio Fonti, Franco RussoAbstract:Abstract In upcoming years several space missions will investigate the habitability of Mars and the possibility of extinct or extant life on the planet. In previous laboratory works we have investigated the infrared spectral modifications induced by thermal processing on different carbonate samples, in the form of recent shells and fossils of different ages, whose biogenic origin is indisputable. The goal was to develop a method able to discriminate biogenic carbonate samples from their abiogenic counterparts. The method has been successfully applied to microbialites, i.e. bio-induced microcrystalline carbonate deposits, and particularly to stromatolites, the laminated fabric of microbialites, some of which can be ascribed among the oldest traces of biological activity known on Earth. In this work we show that, by applying our method to different parts of the same carbonate rock, we are able to discriminate the presence, nature and biogenicity of various Micrite types (i.e. detrital vs autochthonous) and to distinguish them from the skeletal grains. To test our methodology we preliminarily used the epifluorescence technique to select on polished samples, skeletal grains, autochthonous and allochthonous Micrites, each one characterized by different organic matter content. The results on the various components show that, applying the infrared spectral modifications induced by thermal processing, it is possible to determine the degree of biogenicity of the different carbonate samples. The results are of valuable importance since such carbonates are linked to primitive living organisms that can be considered as good analogues for putative Martian life forms.
-
Characterization of the Micrites in the Late Miocene vermetid carbonate bioconstructions, Salento Peninsula, Italy: Record of a microbial/metazoan association
Sedimentary Geology, 2012Co-Authors: A. Guido, Alessandro Vescogni, Adelaide Mastandrea, F. Tosti, F. Demasi, A. Naccarato, A. Tagarelli, F. RussoAbstract:Small carbonate bioconstructions, composed of Micrite and vermetids, occur in the Salento Peninsula (southern Italy) at the base of the reefal early Messinian Novaglie Formation. These lens-shaped bioconstructions are tens of meters in length and up to 2.5 m in thickness, and crop out patchily along the South-Eastern Salento coast line.Micrite is the most abundant component. Its origin and role in this association have been investigated by means of microfacies, epifluorescence, and organic matter analyses. Three different types of Micrite were recognized: (I) not/weakly fluorescent detrital Micrite with a few fine bioclasts; (II) fluorescent Micrite rich in fine bioclasts; (III) fluorescent clotted peloidal Micrite (autoMicrite). The first type of Micrite, mainly present in the basal layer of the carbonate bioconstructions surrounds vermetids in life position. The type (II) and type (III) Micrites occur in the overlying deposits, characterized by sub-horizontally isooriented vermetid shells. The high fluorescence of the type (II) and (III) Micrite can be related to organic matter derived respectively from decaying metazoan and microbial organisms. Twofold organic matter origin was supported by FT-IR and GC-MS analyses, carried out on the extracted organic matter. Micrite (I) shows very low intensity of organic matter functional groups, confirming its abiotic origin. The spectra of the autoMicrite (III) are characterized by the presence of stretching C=C vibrations attributable to alkene and/or unsaturated carboxylic acids, that may be synthesized by microbes. GC-MS investigations indicate the presence of extended hopane series, straight chain saturated (C14, Cl6), monounsaturated (C16, C18), and diunsaturated Cl8-acids, diagnostic of microbial activity. Microbial communities appear to have played a prominent role in the deposition and stabilization of Salento Micrite-vermetid carbonate bioconstructions. The type (III) Micrite, classifiable as microbialite or autoMicrite, can be regarded a sort of “primary framework” of these small “bioconstructions”
-
The Microbialite-Vermetid Community of the Salento Peninsula in Southern Italy: A Late Miocene Example of AutoMicrite Deposition
Advances in Stromatolite Geobiology, 2010Co-Authors: Alessandro Vescogni, Adriano Guido, Adelaide Mastandrea, Franco RussoAbstract:A carbonate facies made up mainly of Micrite and vermetid shells has been identified in the early Messinian coral reef complex of the Novaglie Formation on the Salento Peninsula of southern Italy. Vermetids (Mollusca, Prosobranchia, and Caenogastropoda) can form large colonies that are usually attached to hard substrates (Vescogni et al. 2008). The Micrite-dominated facies with a large number of vermetid shells (most of them horizontal) is unusual. Moreover, this facies shows completely different sediment textures and organism compositions than the associated reefal carbonates. To explain the origin of this facies and identify the source of the Micrites, field, microfacies and epifluorescence observations were carried out along with scanning electron microscopy (SEM), EDS and FT-IR analyses.
-
AutoMicrite in a 'nummulite bank' from the Monte Saraceno (Southern Italy): evidence for synsedimentary cementation
Sedimentology, 2010Co-Authors: Adriano Guido, Adelaide Mastandrea, Cesare Andrea Papazzoni, Michele Morsilli, Mauro Francesco La Russa, F. Tosti, Franco RussoAbstract:Following introduction of the term ‘nummulite bank’, there has been debate regarding interpretation of these types of deposits as autochthonous (autoMicrite) or allochthonous (detrital Micrite). These banks are made up of large foraminifera and ill-defined fine-grained components. The fine-grained components consist mainly of Micrites. The recognition of autoMicrite has deep implications for the synsedimentary cementation and stabilization of the bank. In order to distinguish between autoMicrite and detrital Micrite, the nanomorphology, geochemistry and organic matter remains in the microfacies of a nummulite bank in the Middle Eocene of Monte Saraceno (Gargano, Southern Italy) were analysed. Optical and scanning electron microscope investigations showed that the Micrites have been recrystallized to aggrading microsparite. Epifluorescence observations on selected Micrite/microsparite areas with peloidal texture revealed the presence of organic matter. Scanning electron microscope analyses on epifluorescent Micrites showed that the microbial peloids have smaller crystal sizes than those in organic matter-depleted areas. The geochemical characterization of extracted organic matter, performed through the functional group analyses by Fourier transform-infrared spectroscopy, shows strong prevalence of the aromatic fraction over the aliphatic and carboxylic ones. These characteristics of organic compounds indicate both their thermal maturation and their likely derivation from degradation of bacterial communities. The local presence of peloidal anti-gravity textures, bright epifluorescence and organic molecules in clotted peloidal areas suggest that the metabolic activity of microbial communities could have induced precipitation of these Micrites and, consequently, the syndepositional cementation of the nummulite bank. This type of cementation can rapidly stabilize sediments and promote the depositional bank geometry.
Adriano Guido - One of the best experts on this subject based on the ideXlab platform.
-
Role of autochthonous versus detrital Micrite in depositional geometries of Middle Triassic carbonate platform systems
Geological Society of America Bulletin, 2016Co-Authors: Adriano Guido, Adelaide Mastandrea, Marco Stefani, Franco RussoAbstract:Middle Triassic platforms (Formazione di Contrin, Upper Anisian) in the Italian Dolomites, southern Alps, record large changes in carbonate production and depositional geometry. The changes include variation in the abundance of detrital Micrite, i.e., allochthonous calcareous mud, relative to the autochthonous Micrite, which formed in situ and was syndepositionally lithified. Carbonate factory dynamics controlled the geometry of the clinostratified slope units and were probably associated with changes in oxygenation. Early Anisian low-relief platforms were followed by late Anisian, high-relief buildups, associated with basinal dysoxic-anoxic environments. The geometric evolution of the platform slopes records a progressive increase in the dip angle of clinostratifications, matched by a deepening evolution of the basinal environments. At the same time, the slope sediments record a gradual change from loose detrital Micrite, characterizing the lower portion, to autochthonous Micrite, dominating the upper part and recording massive syndepositional lithification. The development of the autochthonous Micrite was associated with the preservation of significant amounts of organic matter. This sharp increase in autoMicrite formation was probably induced by a rapid change from oxic to suboxic conditions in the carbonate slope and margin environments, while anoxic conditions developed in the adjacent organic-rich basin (Moena Formation). The low oxygen level promoted the preservation of organic matter and the activity of sulfate-reducing bacteria, which in turn induced in situ deposition of autochthonous Micrite through biomediated processes. This pervasive early cementation and lithification induced the development of steep platform slopes. The conceptual model distilled from this Middle Triassic case can support the interpretation of analogous buildups where the skeletal framework is subordinate to the Micrite component.
-
Microbialites vs detrital Micrites: Degree of biogenicity, parameter suitable for Mars analogues
Planetary and Space Science, 2014Co-Authors: Armando Blanco, Adriano Guido, Adelaide Mastandrea, F. Tosti, Marcella D׳elia, Vincenzo Orofino, F. Mancarella, Sergio Fonti, Franco RussoAbstract:Abstract In upcoming years several space missions will investigate the habitability of Mars and the possibility of extinct or extant life on the planet. In previous laboratory works we have investigated the infrared spectral modifications induced by thermal processing on different carbonate samples, in the form of recent shells and fossils of different ages, whose biogenic origin is indisputable. The goal was to develop a method able to discriminate biogenic carbonate samples from their abiogenic counterparts. The method has been successfully applied to microbialites, i.e. bio-induced microcrystalline carbonate deposits, and particularly to stromatolites, the laminated fabric of microbialites, some of which can be ascribed among the oldest traces of biological activity known on Earth. In this work we show that, by applying our method to different parts of the same carbonate rock, we are able to discriminate the presence, nature and biogenicity of various Micrite types (i.e. detrital vs autochthonous) and to distinguish them from the skeletal grains. To test our methodology we preliminarily used the epifluorescence technique to select on polished samples, skeletal grains, autochthonous and allochthonous Micrites, each one characterized by different organic matter content. The results on the various components show that, applying the infrared spectral modifications induced by thermal processing, it is possible to determine the degree of biogenicity of the different carbonate samples. The results are of valuable importance since such carbonates are linked to primitive living organisms that can be considered as good analogues for putative Martian life forms.
-
The Microbialite-Vermetid Community of the Salento Peninsula in Southern Italy: A Late Miocene Example of AutoMicrite Deposition
Advances in Stromatolite Geobiology, 2010Co-Authors: Alessandro Vescogni, Adriano Guido, Adelaide Mastandrea, Franco RussoAbstract:A carbonate facies made up mainly of Micrite and vermetid shells has been identified in the early Messinian coral reef complex of the Novaglie Formation on the Salento Peninsula of southern Italy. Vermetids (Mollusca, Prosobranchia, and Caenogastropoda) can form large colonies that are usually attached to hard substrates (Vescogni et al. 2008). The Micrite-dominated facies with a large number of vermetid shells (most of them horizontal) is unusual. Moreover, this facies shows completely different sediment textures and organism compositions than the associated reefal carbonates. To explain the origin of this facies and identify the source of the Micrites, field, microfacies and epifluorescence observations were carried out along with scanning electron microscopy (SEM), EDS and FT-IR analyses.
-
AutoMicrite in a 'nummulite bank' from the Monte Saraceno (Southern Italy): evidence for synsedimentary cementation
Sedimentology, 2010Co-Authors: Adriano Guido, Adelaide Mastandrea, Cesare Andrea Papazzoni, Michele Morsilli, Mauro Francesco La Russa, F. Tosti, Franco RussoAbstract:Following introduction of the term ‘nummulite bank’, there has been debate regarding interpretation of these types of deposits as autochthonous (autoMicrite) or allochthonous (detrital Micrite). These banks are made up of large foraminifera and ill-defined fine-grained components. The fine-grained components consist mainly of Micrites. The recognition of autoMicrite has deep implications for the synsedimentary cementation and stabilization of the bank. In order to distinguish between autoMicrite and detrital Micrite, the nanomorphology, geochemistry and organic matter remains in the microfacies of a nummulite bank in the Middle Eocene of Monte Saraceno (Gargano, Southern Italy) were analysed. Optical and scanning electron microscope investigations showed that the Micrites have been recrystallized to aggrading microsparite. Epifluorescence observations on selected Micrite/microsparite areas with peloidal texture revealed the presence of organic matter. Scanning electron microscope analyses on epifluorescent Micrites showed that the microbial peloids have smaller crystal sizes than those in organic matter-depleted areas. The geochemical characterization of extracted organic matter, performed through the functional group analyses by Fourier transform-infrared spectroscopy, shows strong prevalence of the aromatic fraction over the aliphatic and carboxylic ones. These characteristics of organic compounds indicate both their thermal maturation and their likely derivation from degradation of bacterial communities. The local presence of peloidal anti-gravity textures, bright epifluorescence and organic molecules in clotted peloidal areas suggest that the metabolic activity of microbial communities could have induced precipitation of these Micrites and, consequently, the syndepositional cementation of the nummulite bank. This type of cementation can rapidly stabilize sediments and promote the depositional bank geometry.
Thomas H Nash - One of the best experts on this subject based on the ideXlab platform.
-
Life in extreme environments: survival strategy of the endolithic desert lichen Verrucaria rubrocincta
Naturwissenschaften, 2008Co-Authors: Laurence A. J. Garvie, Frank Bungartz, L. Paul Knauth, Stan Klonowski, Thomas H NashAbstract:Verrucaria rubrocincta Breuss is an endolithic lichen that inhabits caliche plates exposed on the surface of the Sonoran Desert. Caliche surface temperatures are regularly in excess of 60°C during the summer and approach 0°C in the winter. Incident light intensities are high, with photosynthetically active radiation levels typically to 2,600 μmol/m^2 s^−1 during the summer. A cross-section of rock inhabited by V. rubrocincta shows an anatomical zonation comprising an upper Micrite layer, a photobiont layer containing clusters of algal cells, and a pseudomedulla embedded in the caliche. Hyphae of the pseudomedulla become less numerous with depth below the rock surface. Stable carbon and oxygen isotopic data for the caliche and Micrite fall into two sloping, well-separated arrays on a δ^13C–δ^18O plot. The δ^13C_PDB of the Micrite ranges from 2.1 to 8.1 and δ^18O_SMOW from 25.4 to 28.9, whereas δ^13C_PDB of the caliche ranges from −4.7 to 0.7 and δ^18O_SMOW from 23.7 to 29.2. The isotopic data of the Micrite can be explained by preferential fixing of ^12C into the alga, leaving local ^13C enrichment and evaporative enrichment of ^18O in the water. The ^14C dates of the Micrite range from recent to 884 years b.p., indicating that “dead” carbon from the caliche is not a significant source for the lichen-precipitated Micrite. The endolithic growth is an adaptation to the environmental extremes of exposed rock surfaces in the hot desert. The Micrite layer is highly reflective and reduces light intensity to the algae below and acts as an efficient sunscreen that blocks harmful UV radiation. The Micrite also acts as a cap to the lichen and helps trap moisture. The lichen survives by the combined effects of biodeterioration and biomineralization. Biodeterioration of the caliche concomitant with biomineralization of a protective surface coating of Micrite results in the distinctive anatomy of V. rubrocincta .
-
anatomy of the endolithic sonoran desert lichen verrucaria rubrocincta breuss implications for biodeterioration and biomineralization
Lichenologist, 2004Co-Authors: Frank Bungartz, Laurence A. J. Garvie, Thomas H NashAbstract:The anatomy of the endolithic, calcicolous lichen Verrucaria rubrocincta Breuss is described using optical and scanning electron microscopy. This lichen is locally abundant in caliche plates of open desert pavements in the Sonoran Desert of south-western Arizona. The endolithic growth of V. rubrocincta is distinctly layered. The upper layer is a fine-grained calcite (Micrite). This layer is sparsely penetrated by hyphae and therefore cannot be interpreted as a lithocortex sensu stricto. Beneath the Micrite is the photobiont layer. Below this photobiont layer hyphae form a pseudo- medulla penetrating up to 1 cm into the caliche. Calcium oxalates occur in the pseudomedulla but are absent from uninhabited caliche. The analogy of a greenhouse describes the ecophysiological adaptations of this endolithic growth to the environmental extremes of the Sonoran Desert. The Micrite acts as a roof and the photobiont layer and pseudomedulla represent the greenhouse interior. Verrucaria rubrocincta has thus evolved a strategy to successfully establish and survive within an extreme environment. Our study illustrates biodeterioration and biomineralization processes acting simultaneously within a single lichen species. Mineralogical evidence suggests that the Micrite on the thallus surface is biologically induced. The hyphae of the lichen biodeteriorate the caliche thus forming the pseudomedulla. Simultaneously with this process Micrite forms at the surface protecting the thallus from exposure and counter-balancing rock degradation. These combined effects of biodeterioration and biomineralization do not markedly accelerate erosion because inhabited and uninhabited areas of the same plate show similar surface heights.
F. Tosti - One of the best experts on this subject based on the ideXlab platform.
-
Microbialites vs detrital Micrites: Degree of biogenicity, parameter suitable for Mars analogues
Planetary and Space Science, 2014Co-Authors: Armando Blanco, Adriano Guido, Adelaide Mastandrea, F. Tosti, Marcella D׳elia, Vincenzo Orofino, F. Mancarella, Sergio Fonti, Franco RussoAbstract:Abstract In upcoming years several space missions will investigate the habitability of Mars and the possibility of extinct or extant life on the planet. In previous laboratory works we have investigated the infrared spectral modifications induced by thermal processing on different carbonate samples, in the form of recent shells and fossils of different ages, whose biogenic origin is indisputable. The goal was to develop a method able to discriminate biogenic carbonate samples from their abiogenic counterparts. The method has been successfully applied to microbialites, i.e. bio-induced microcrystalline carbonate deposits, and particularly to stromatolites, the laminated fabric of microbialites, some of which can be ascribed among the oldest traces of biological activity known on Earth. In this work we show that, by applying our method to different parts of the same carbonate rock, we are able to discriminate the presence, nature and biogenicity of various Micrite types (i.e. detrital vs autochthonous) and to distinguish them from the skeletal grains. To test our methodology we preliminarily used the epifluorescence technique to select on polished samples, skeletal grains, autochthonous and allochthonous Micrites, each one characterized by different organic matter content. The results on the various components show that, applying the infrared spectral modifications induced by thermal processing, it is possible to determine the degree of biogenicity of the different carbonate samples. The results are of valuable importance since such carbonates are linked to primitive living organisms that can be considered as good analogues for putative Martian life forms.
-
Characterization of the Micrites in the Late Miocene vermetid carbonate bioconstructions, Salento Peninsula, Italy: Record of a microbial/metazoan association
Sedimentary Geology, 2012Co-Authors: A. Guido, Alessandro Vescogni, Adelaide Mastandrea, F. Tosti, F. Demasi, A. Naccarato, A. Tagarelli, F. RussoAbstract:Small carbonate bioconstructions, composed of Micrite and vermetids, occur in the Salento Peninsula (southern Italy) at the base of the reefal early Messinian Novaglie Formation. These lens-shaped bioconstructions are tens of meters in length and up to 2.5 m in thickness, and crop out patchily along the South-Eastern Salento coast line.Micrite is the most abundant component. Its origin and role in this association have been investigated by means of microfacies, epifluorescence, and organic matter analyses. Three different types of Micrite were recognized: (I) not/weakly fluorescent detrital Micrite with a few fine bioclasts; (II) fluorescent Micrite rich in fine bioclasts; (III) fluorescent clotted peloidal Micrite (autoMicrite). The first type of Micrite, mainly present in the basal layer of the carbonate bioconstructions surrounds vermetids in life position. The type (II) and type (III) Micrites occur in the overlying deposits, characterized by sub-horizontally isooriented vermetid shells. The high fluorescence of the type (II) and (III) Micrite can be related to organic matter derived respectively from decaying metazoan and microbial organisms. Twofold organic matter origin was supported by FT-IR and GC-MS analyses, carried out on the extracted organic matter. Micrite (I) shows very low intensity of organic matter functional groups, confirming its abiotic origin. The spectra of the autoMicrite (III) are characterized by the presence of stretching C=C vibrations attributable to alkene and/or unsaturated carboxylic acids, that may be synthesized by microbes. GC-MS investigations indicate the presence of extended hopane series, straight chain saturated (C14, Cl6), monounsaturated (C16, C18), and diunsaturated Cl8-acids, diagnostic of microbial activity. Microbial communities appear to have played a prominent role in the deposition and stabilization of Salento Micrite-vermetid carbonate bioconstructions. The type (III) Micrite, classifiable as microbialite or autoMicrite, can be regarded a sort of “primary framework” of these small “bioconstructions”
-
AutoMicrite in a 'nummulite bank' from the Monte Saraceno (Southern Italy): evidence for synsedimentary cementation
Sedimentology, 2010Co-Authors: Adriano Guido, Adelaide Mastandrea, Cesare Andrea Papazzoni, Michele Morsilli, Mauro Francesco La Russa, F. Tosti, Franco RussoAbstract:Following introduction of the term ‘nummulite bank’, there has been debate regarding interpretation of these types of deposits as autochthonous (autoMicrite) or allochthonous (detrital Micrite). These banks are made up of large foraminifera and ill-defined fine-grained components. The fine-grained components consist mainly of Micrites. The recognition of autoMicrite has deep implications for the synsedimentary cementation and stabilization of the bank. In order to distinguish between autoMicrite and detrital Micrite, the nanomorphology, geochemistry and organic matter remains in the microfacies of a nummulite bank in the Middle Eocene of Monte Saraceno (Gargano, Southern Italy) were analysed. Optical and scanning electron microscope investigations showed that the Micrites have been recrystallized to aggrading microsparite. Epifluorescence observations on selected Micrite/microsparite areas with peloidal texture revealed the presence of organic matter. Scanning electron microscope analyses on epifluorescent Micrites showed that the microbial peloids have smaller crystal sizes than those in organic matter-depleted areas. The geochemical characterization of extracted organic matter, performed through the functional group analyses by Fourier transform-infrared spectroscopy, shows strong prevalence of the aromatic fraction over the aliphatic and carboxylic ones. These characteristics of organic compounds indicate both their thermal maturation and their likely derivation from degradation of bacterial communities. The local presence of peloidal anti-gravity textures, bright epifluorescence and organic molecules in clotted peloidal areas suggest that the metabolic activity of microbial communities could have induced precipitation of these Micrites and, consequently, the syndepositional cementation of the nummulite bank. This type of cementation can rapidly stabilize sediments and promote the depositional bank geometry.