Characterization of the micrites in the Late Miocene vermetid carbonate bioconstructions, Salento Peninsula, Italy: Record of a microbial/metazoan association (original) (raw)
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Microbial origin for pedogenic micrite associated with a carbonate paleosol (Champagne, France)
Sedimentary Geology, 1999
Micro-rods have been observed in indurated carbonate horizons (30 cm thick) that overlie a periglacial chalk formation, in contact with the present-day soil (Champagne, France). They are numerous in the upper part of the hardened layers. Variations in micro-rod morphologies are related to progressive biomineralization of organic matter, transforming purely organic rods into calcite. Mineralized rods undergo diagenesis and their arrangement evolves from a random mesh fabric to recrystallized micritic platelets to microsparite. Two types of organic micro-rods have been observed: bacilliform and thread-like bacteria. Mineralogically, micro-rods are low-magnesian calcite. Crystallographically, their length is parallel to the (104) axis and they grow along the {010} plane. Micro-rods can be associated with needle-fiber calcite. They increase the CaCO 3 content of the primary matrix and infill its microporosity. Their diagenetic evolution into microsparite contributes to soil layer induration.
Autochthonous Micrite to Aphanodolomite: The Microbialites in the Dolomitization Processes
Geosciences
In the present paper, we examine the influence of micrite types, autochthonous or allochthonous, on the dolomitization processes. The recrystallized and dolomitized Carnian samples from Rifugio Vallandro and Alpe di Specie erratic boulders (South Tyrol, Italy) offer a unique example for studying the relationship between microbialites and dolomitization processes. The comparison between the carbonates of the well-preserved erratic boulders of Alpe di Specie and the isochronous, recrystallized, and dolomitized, samples of Rifugio Vallandro, allows for hypothesizing the role of microbialites on dolomitization processes. The Rifugio Vallandro samples represent variously dolomitized boundstone (made of corals, sponges, and peloidal crusts) with a fine texture (aphanodolomite) which contain organic matter relics, suggesting microbial-mediated mineralization. Geomicrobiological characterization of the microbialites from Alpe di Specie indicates that they formed through microbial metabolic ...
Palaeogeography, Palaeoclimatology, Palaeoecology, 2013
Unusual pendant bioconstructions occur within two submerged caves in the Plemmirio Marine Protected Area, south of Syracuse (SE Sicily). These cm-to dm-sized bioconstructions project downward from the cave roofs. The main framework builders are serpulids belonging to the genera Protula, Semivermilia and Josephella. Encrusting bryozoans, corals, hydrozoans and sponges are subordinately present, whereas bivalves and brachiopods are overall rare. These faunal associations are characteristic of the studied caves, but only in some places they form small bioconstructions that are cemented by microbial carbonates made up by autochthonous, peloidal to clotted peloidal and aphanitic micrite. The autochthonous micrite stabilizes the pendant bioconstructions, herein referred to as biostalactites. The microbial carbonate reveals high contents of bacterial lipid biomarkers. Among the most abundant compounds are mono-O-alkyl glycerol ethers (MAGEs) and branched fatty acids (10-Me-C 16:0 ; isoand anteiso-C 15:0 and-C 17:0), interpreted as biomarkers of sulfate-reducing bacteria. Other compounds preserved in the autochthonous carbonates include lipids derived from marine zoo-and phytoplankton (brassicasterol, dinosterol and monounsaturated short-chain fatty acids), unspecified marine bacteria (saturated and monounsaturated short-chain fatty acids) and land plants (long-chain fatty acids, long-chain alcohols, stigmasterol, sitosterol and campesterol). The observed lipid biomarker signatures are remarkably similar to those of post-glacial reefal microbialites, where microbialite formation in cavities of the coral framework was also mediated by sulfate-reducing bacteria. In the submerged caves of Plemmirio Marine Protected Area, serpulid colonies apparently occur preferentially where freshwater is seeping through crevices in the limestone. The consequent nutrification is believed to favor serpulid aggregation and the growth of other skeletal (i.e., bryozoans and corals) and soft-bodied organisms (i.e., sponges and ascidiae). The resultant accumulation of biomass and its taphonomy provide niches for sulfate-reducing bacteria, which induce carbonate precipitation cementing and stabilizing the biostalactites. The finding of pendant, cemented bioconstructions in the Mazzere and Granchi caves of the Plemmirio Marine Protected Area reveals that sulfate-reducing bacteria are involved in microbialite formation in various cryptic environments. The formation of such peloidal to clotted peloidal microcrystalline carbonates in cryptic ecosystems is a significant factor for the stabilization of different kinds of bioconstructions, spanning from small biostalactites to large reefs.
Questioning the microbial origin of automicrite in Ordovician calathid-demosponge carbonate mounds
Sedimentology, 2017
Calathid-demosponge carbonate mounds are a feature of Early to Middle Ordovician shallow marine carbonate depositional environments of tropical to subtropical paleolatitudes. These mounds contain an important amount of autochthonous non-skeletal microcrystalline Cacarbonate (automicrite) conventionally considered microbial in origin. Here, the automicrite of calathid-demosponge carbonate mounds (Tarim Basin, northwest China) is broken down to five distinct fabrics: an in situ peloidal-spiculiferous fabric (AM-1), an in situ peloidal fabric (AM-2), an aphanitic-microtubular fabric (AM-3), a minipeloidal fabric (AM-4) and a laminoid-cerebroid fabric (AM-5). Type AM-1 occurs with AM-2 being succeeded by an This article is protected by copyright. All rights reserved. assemblage of AM-3 and AM-4. Types AM-4 and AM-5 are separated by an erosional disconformity. A good correlation of fluorescence and cathodoluminescence of automicrites indicates that induced and supported organomineralization produced automicrite, probably via the permineralization of non-living organic substrates adsorbing dissolved metal-humate complexes. Using a spreadsheet with six parameters and 17 characters, AM-1 to AM-4 turn out to be non-microbial in origin. Instead, these automicrites represent relics of calcified metazoan tissues such as siliceous sponges, non-spiculate sponges or the basal attachment structures of stalked invertebrates. Fabric AM-5 is a microbial carbonate but is post-mound in origin forming a drape within a reefal framework established by AM-4. The five automicritic fabrics, individually or as an assemblage, are a common element of Ordovician calathiddemosponge carbonate mounds in general. The reassessment of the origins of these automicritic fabrics holds consequences for the understanding of the Great Ordovician Biodiversification Event in terms of community structure, reef ecology and reef evolution. Episodically, these fabrics are also present in other carbonate buildups stretching from the Neoproterozoic over the entire Phanerozoic Eon. The massive calcification of metazoan soft tissue (AM-1 to AM-4) characterizes episodes and conditions of enhanced marine calcification and might be of value to refine secular trends of pCO 2 , Ca-concentration and Mg/Ca ratio at the scale of individual sedimentary basins.
…, 2011
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 matterdepleted 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 antigravity 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.
Matrix micrite δ13C and δ18O reveals synsedimentary marine lithification in
but one that is submitted to known limitations. Main reasons for the often ambiguous value of many micritebased isotope data sets are the unknown origin of the micrite components and their poorly resolved diagenetic history. Here we present carbon and oxygen-isotope data retrieved from Oxfordian to Tithonian Ammonitico Rosso nodular micrites sampled from three sections in the Betic Cordillera (Southern Spain). All three sections were correlated and sampled using a rigorous biostratigraphic framework. A noteworthy feature is that analyzed matrix micrites are more conservative in terms of their isotopic composition than other carbonate materials commonly considered to resist diagenetic alteration under favourable circumstances. Remarkably, this refers not only to δ13C ratios, which reflect the typical Late Jurassic global trend, but also to δ18O ratios that range around 0.3‰. The 18O-enriched oxygen-isotope ratios are considered to represent diagenetic stabilization of carbonate ooze under the influence of marine porewaters within the sediment–water interphase (i.e., the immature sedimentary section, usually submitted to biogenic activity). This interpretation agrees with the very early lithification of micrite noduleswith cements precipitated frommarine porewaters, enriched by the dissolution of aragonite skeletals (i.e., ammonite shells). According to the model proposed, low sedimentation rates as well as rapid early marine differential cementation, under the influence of currents and seawater pumping, affected the sediment–water interphase of epioceanic swells where deposition resulted in early lithified Ammonitico Rosso facies. The data obtained show that special care must be taken to prevent oversimplified interpretations of carbonate archives, particularly in the context of epioceanic settings.
Microbial deposits in upper Miocene carbonates, Mallorca, Spain
The Santanyí Limestone, a 30–35-m thick upper Miocene limestone succession cropping out in Mallorca, contains abundant microbialite deposits, the shape, microstructure and texture of which was controlled by environmental factors: depth, energy and salinity. Three main types of microbialites are distinguished: (1) domed (DNOS) and stratiform, mostly undulate (UNOS) non-oolitic stromatolites, (2) undulate oolitic laminites (UOL) and (3) domed-oolitic thrombolites (DOTs). Based on lithofacies associations and occurrence of microbialite types, the Santanyí Limestone succession is subdivided into five stratigraphic units (I to V) separated by sharp surfaces. Within units II, III and V, the vertical evolution of microbialites was induced by changes in accommodation space/depth: (1) intertidal/very-shallow subtidal conditions at the base were induced by flooding over a wide area, (2) continued sea-level rise caused submergence to subtidal conditions, and (3) a significant bathymetric decrease created the sharp surface bounding these units. In units II and III, NOS accumulated in variable energy and depth conditions, as buildups with thick, somewhat discontinuous and mostly non-isopachous lamination, surrounded by oolitic grainstones with wave and current structures and oolitic intraclasts. In contrast, thin and generally regular and smooth lamination of NOS in unit V suggests, along with the absence of oolite grainstones and macrobiota, calm and restricted, maybe more saline, conditions. UOL, consisting of oolitic layers separated by thin micritic laminae, developed adjacent to NOS in units II and III and to DOT at the lower part of unit III, in shallow-water and low-energy conditions. Both ooids andmicrite laminae have evidence for biogenesis. Micritized ooids containing microbial remains are common. Micritic laminae in UOL and the dark micritic laminae in NOS are thought to represent bacterially enhanced calcite precipitation and lithification during periods of low sedimentation. Oolitic thrombolites containing macrobiota are only present in unit III. They represent deeper and openmarine conditions affected by high-energy events, in which microbially mediated precipitation favoured microbialite accretion and lithification.
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.
Facies, 2010
Shallow-marine microporous limestones account for many carbonate reservoirs. Their formation, however, remains poorly understood. Due to the lack of recent appropriate marine analogues, this study uses a lacustrine counterpart to examine the diagenetic processes controlling the development of intercrystalline microporosity. Late Miocene lacustrine microporous micrites of the Madrid Basin (Spain) have a similar matrix microfabric as Cenomanian to Early Turonian shallow-marine carbonates of the Mishrif reservoir Formation (Middle East). The primary mineralogy of the precursor mud partly explains this resemblance: low-Mg calcites were the main carbonate precipitates in the Cretaceous seawater and in Late Miocene freshwater lakes of the Madrid Basin. Based on hardness and petrophysical properties, two main facies were identified in the lacustrine limestones: a tight facies and a microporous facies. The tight facies evidences strong compaction, whereas the microporous facies does not. The petrotexture, the sedimentological content, and the mineralogical and chemical compositions are identical in both facies. The only difference lies in the presence of calcite overgrowths: they are pervasive in microporous limestones, but almost absent in tight carbonates. Early diagenetic transformations of the sediment inside a fluctuating meteoric phreatic lens are the best explanation for calcite overgrowths precipitation. Inside the lens, the dissolution of the smallest crystals in favor of overgrowths on the largest ones rigidifies the sediment and prevents compaction, while partly preserving the primary microporous network. Two factors appear essential in the genesis of microporous micrites: a precursor mud mostly composed of low-Mg calcite crystals and an early diagenesis rigidifying the microcrystalline framework prior to burial.
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