Microbial-derived pirite as evidence of early diagenetic processes on a Late Holocene shoreface deposits (Sulcis Iglesiente, West Sardinia, Italy) (original) (raw)
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Sedimentary Geology
This article presents a petrographic comparison of the Rosso Ammonitico facies of Western Sicily and the original Rosso Ammonitico Veronese of Northern Italy based on a total of 27 sections. The Rosso Ammonitico has been the subject of numerous controversies that range from bathyal to shallow-water platform sedimentation. Therefore it seemed interesting to verify if the term Rosso Ammonitico has the same geologic connotation from region to region. The Middle-Upper Jurassic Rosso Ammonitico of Western Sicily is a condensed succession formed during a period of extensional synsedimentary tectonics related to the spreading of the Ionian Ocean. Slope-to-basin or pelagic carbonate deposits characterize the sedimentation which consists of reddish mudstones and wackestones. The abundant fauna is composed of radiolarians, protoglobigerinids, Saccocoma, Bositra associated with ammonites. A few ferruginous hardgrounds, Fe–Mn oxide crusts and Mn-coated condensation horizons are also present. Th...
The Palaeocene–Middle Eocene deposits of Sardinia (Italy) and their palaeoclimatic significance
Comptes Rendus Geoscience, 2003
The Palaeocene of southern Sardinia includes a continental ferruginous sedimentation, with a high content of Al and Fe, indicative of a subhumid tropical climate. The subsequent microcodium carbonated detrital microcodium levels, containing an abundant quartzose fraction, rather suggest semiarid conditions. In SW Sardinia, the marine deposits, referred to Late Thanetian-Lower Ypresian (= Ilerdian) times, are limestones including larger foraminifers and contain significant amounts of quartz. A lower content of detrital kaolinite points a sediment source from the surrounding areas with a semiarid climate. The occurrence, at the top of this unit, of small trochospiral rotaliids and larger amount of detrital kaolinite suggests a transition to a rainy tropical climate in the adjacent areas. These limestones pass gradually to carbonate sediments characterized by large amounts of detrital kaolinite and intercalated coal layers, with pollen of tropical palms, attributed to the Late Ypresian (= Cuisian)-Early Lutetian and referred to a humid-subhumid tropical climate. 2003 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Résumé En Sardaigne se sont formées au Paléocène des paléoaltérites ferrugineuses caractérisées par des pourcentages élevés d'aluminium et de fer, indiquant une altération sous climat tropical subhumide. Leur font suite des sédiments carbonatés à microcodium, dont les fragments sont caractérisés par une abondante fraction quartzeuse, qui pourrait indiquer une sédimentation des aires proches ayant une faible couverture végétale dans un climat semi-aride. Dans le Sud-Ouest de la Sardaigne est présente une succession marine carbonatée à grands foraminifères, appartenant au Thanétien supérieur-Yprésien inférieur (= Ilerdien), caractérisée par des pourcentages significatifs de quartz et une faible quantité de kaolinite détritique. Leur présence indiquerait une provenance de zones continentales caractérisées par un climat semi-aride. Dans la portion sommitale de cette succession carbonatée, on trouve de petits rotaliidés et une importante quantité de kaolinite détritique, qui indiqueraient une évolution vers un climat tropical plus pluvieux dans l'arrière-pays. Enfin, le passage à une sédimentation marneuse à argileuse dulçaquicole, caractérisée par la présence d'une grande quantité de kaolinite détritique, avec intercalation de bancs
2000
The Vena del Gesso (Northern Apennines) is a 230 m-thick succession consisting of up to 16 gypsum-shale cycles belonging to the "Lower Evaporites" formed during the Messinian salinity crisis in the Mediterranean. The study of the microbial communities preserved in the gypsum crystals of one complete cycle (6 th cycle at Monte Tondo quarry) showed abundant, regularly arranged filamentous forms that resemble morphologically modern obligate phototrophes, cyanobacteria colonizing modern photic, shallow-water gypsum basins. At least four different bacterial populations have been recognized: a) filamentous type cyanobacteria with characteristic inserted funnel shaped structure resembling the modern Scytonematacean; b) Type 1 organisms consisting of filamentous structures impregnated by clay minerals containing pyrite grains in the outer sheath; c) Type 2 filaments filled by clay minerals with dolomite in the outer sheath; d) Type 3 filamentous organisms with a central hollow tube and an encrusted outer sheath mainly composed of calcium carbonate. These organisms were probably associated with other heterotrophic bacteria as suggested by the presence of dolomite and pyrite structures. The size and preservation suggest that most of these cyanobacteria were likely conducting oxygenic photosynthesis as presently observed in modern solar salt works. It follows that they were living in shallow water settings or settled down from the water column to the bottom of a relatively deep evaporite basin.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2012
Authigenic methane-derived carbonates hosted in upper Miocene slope sediments of the Tertiary Piedmont Basin (NW Italy) are studied by a multidisciplinary approach including petrography, stable oxygen and carbon isotopes of carbonates, as well as lipid biomarkers in order to explore the relationship between microbial activity and carbonate precipitation in the shallow subsurface. The studied rocks show a bed parallel geometry and are characterized by dolomitic intergranular cement, which is typified by positive δ 13 C values as high as + 6.2‰ VPDB. A striking feature of some dolomite beds is an intricate network of septarian-like cracks filled with both injected sediments and polyphasic carbonate cements. Prokaryotic molecular fossils in the dolomite beds comprise archaeol (δ 13 C: − 40‰ VPDB) and various bacterial dialkyl glycerol diethers (DAGEs; δ 13 C: − 30‰ VPDB), strongly suggesting that dolomite precipitation took place at the interface of the zones of archaeal methanogenesis and bacterial sulphate reduction. In contrast, extremely negative δ 13 C values of carbonate cements (as low as − 56.3‰ VPDB) and various archaeal and bacterial molecular fossils (e.g. pentamethylicosane (PMI): − 106‰ VPDB) are recorded in the crack-filling carbonate cements. These cements precipitated due to anaerobic oxidation of methane coupled to sulphate reduction. We propose a scenario for the formation of the diagenetic beds, suggesting that carbonate precipitation was the result of three microbially-driven processes (sulphate reduction, methanogenesis, and, finally, anaerobic oxidation of methane). This unusual sequence was a consequence of a dynamic change of environmental geochemical conditions and fluid circulation patterns that prevailed in the ancient subseafloor during early diagenesis of the unconsolidated sediments. Anaerobic oxidation of methane, which usually predates methanogenesis during increasing burial, postdates methanogenesis in case of the septarian-like beds after the beds were affected by crack formation induced by overcritical pore pressure, allowing the ingress of sulphate-rich water from above and methane-rich water from below.
The Vena del Gesso (Northern Apennines) is a 230 m-thick succession consisting of up to 16 gypsum-shale cycles belonging to the "Lower Evaporites" formed during the Messinian salinity crisis in the Mediterranean. The study of the microbial communities preserved in the gypsum crystals of one complete cycle (6 th cycle at Monte Tondo quarry) showed abundant, regularly arranged filamentous forms that resemble morphologically modern obligate phototrophes, cyanobacteria colonizing modern photic, shallow-water gypsum basins. At least four different bacterial populations have been recognized: a) filamentous type cyanobacteria with characteristic inserted funnel shaped structure resembling the modern Scytonematacean; b) Type 1 organisms consisting of filamentous structures impregnated by clay minerals containing pyrite grains in the outer sheath; c) Type 2 filaments filled by clay minerals with dolomite in the outer sheath; d) Type 3 filamentous organisms with a central hollow tube and an encrusted outer sheath mainly composed of calcium carbonate. These organisms were probably associated with other heterotrophic bacteria as suggested by the presence of dolomite and pyrite structures. The size and preservation suggest that most of these cyanobacteria were likely conducting oxygenic photosynthesis as presently observed in modern solar salt works. It follows that they were living in shallow water settings or settled down from the water column to the bottom of a relatively deep evaporite basin.
Sedimentary Geology
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”.
Microbial Biomineralization in Biotic Crusts from a Pleistocene Marine Cave (NW Sicily, Italy)
Geomicrobiology Journal, 2017
Biotic crusts occurring in the Early Pleistocene Rumena Cave, in NW Sicily, have been analyzed from a geomicrobiological point of view. The crusts consist largely of scleractinians and of subordinate bryozoans and serpuloideans, all typical of submarine cave biota. Encrustations document a blind cave in shadowed setting, or possibly below the fair whether swell zone. Autochthonous and, subordinately, detrital fractions were observed within the skeletal framework of biotic crusts. The syndepositional lithified fraction occurs mainly as very finegrained laminations. Clotted peloidal and aphanitic (structureless) textures occur in the micrites, as well. Autochthonous micrite is always associated with significant amount of organic matter remains. In caves from the Plemmirio area in SE Sicily the autochthonous microbial micrite, occurring in the bioconstructions, contains bacterial lipid biomarkers, including abundant
Sedimentology, 2000
Lower Messinian stromatolites of the Calcare di Base Formation at Sutera in Sicily record periods of low sea-level, strong evaporation and elevated salinity, thought to be associated with the onset of the Messinian Salinity Crisis. Overlying aragonitic limestones were precipitated in normal to slightly evaporative conditions, occasionally influenced by an influx of meteoric water. Evidence of bacterial involvement in carbonate formation is recorded in three dolomite-rich stromatolite beds in the lower portion of the section that contain low domes with irregular crinkly millimetre-scale lamination and small fenestrae. The dominant microfabrics are: (i) peloidal and clotted dolomicrite with calcite-filled fenestrae; (ii) dolomicrite with bacterium-like filaments and pores partially filled by calcite or black amorphous matter; and (iii) micrite in which fenestrae alternate with dark thin wispy micrite. The filaments resemble Beggiatoa-like sulphur bacteria. Under scanning electron microscopy, the filaments consist of spherical aggregates of dolomite, interpreted to result from calcification of bacterial microcolonies. The dolomite crystals are commonly arranged as rounded grains that appear to be incorporated or absorbed into developing crystal faces. Biofilm-like remains occur in voids between the filaments. The dolomite consistently shows negative d 13 C values (down to )11AE3&) and very positive d 18 O (mean value 7AE9&) that suggest formation as primary precipitate with a substantial contribution of organic CO 2 . Very negative d 13 C values (down to )31AE6&) of early diagenetic calcite associated with the dolomite suggest contribution of CO 2 originating by anaerobic methane oxidation. The shale-normalized rare earth element patterns of Sutera stromatolites show features similar to those in present-day microbial mats with enrichment in light rare earth elements, and M-type tetrad effects (enrichment around Pr coupled to a decline around Nd and a peak around Sm and Eu). Taken together, the petrography and geochemistry of the Sutera stromatolites provide diverse and compelling evidence for microbial influence on carbonate precipitation.