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1.
Adriano Guido Antonietta Rosso Rossana Sanfilippo Franco Russo Adelaide Mastandrea 《Geomicrobiology journal》2017,34(10):864-872
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 a shadowed setting, or possibly below the fair weather swell zone. Autochthonous and, subordinately, detrital fractions were observed within the skeletal framework of biotic crusts. The syndepositional lithified fraction occurs mainly as very fine-grained laminations. Clotted peloidal and aphanitic (structureless) textures occur in the micrites as well. Autochthonous micrite is always associated with a 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 compounds derived from sulfate-reducing bacteria. It is likely that a similar microbial mediation was involved in the formation of the autochthonous micrite present in the biotic crusts of the Rumena Cave. 相似文献
2.
Prof. Dr. Franco Russo Dr. Adelaide Mastandrea Dr. Marco Stefani Prof. Dr. Claudio Neri 《Facies》2000,42(1):211-226
Summary This article deals with the discussion of the role of the syndepositional cementation for the growth of the Middle Triassic
pre-volcanic carbonate platforms of the Dolomites (Southern Alps, Northern Italy). The study is concentrated on the Marmolada
Buildup, which escaped the facies destroying dolomitization which affected many surrounding platforms. The investigations
took place within an almost isochronous uppermost Anisian palcogeographic transect, ranging from the platform-top to the margin
and the upper slope. Methods used include geological mapping, sedimentological and paleontological studies, evaluation of
the microfacies, as well as SEM and EDS epifluorescence analyses.
The well bedded platform-top succession consists of intra-bioclast calcarenites and calcirudites, interbedded with subordinate
boundstones, and organized in shallowing upward, meter scale depositional cycles, sometimes capped by subaerial surfaces.
The platform margin belt is rich in boundstones and lacks a primary framework formed by organisms; metazoan skeletons form
less then 5% of the rock volume. The outer margin and the uppermost slope are characterized by decimeter-scale boundstone
blocks, coated and linked to each other by huge amounts of radiaxial fibrous calcite cements, arranged in concentric crusts.
These cements (“evinospongiac”) represent the main component of the margin and upper slope facies.
Epifluorescence analyses suggest the existence of abundant organic residual matter associated not only with the bioclasts
and peloids, but also with the syndepositional cements. Organic matter likely played a significant role in carbonate cementation
and was a key factor for the early lithification of the platform as well as for the sediment production. Minor element microanalyses
reveal an uniform Mg content in different calcite types (2–4 Mole % MgCO3), independently from the primary nature of the components. Late diagenetic sparry calcites exhibit similar Mg values but
no iron. These data point to a homogenization of minor element distribution, probably associated with a slow but long-lasting
semi-closed fluid circulation, possibly related with the Neogene uplifting of the Dolomite Mountains. 相似文献
3.
Prof. Dr. Gerd Flajs Dipl.-Geol. Manfred Vigener Prof. Dr. Helmut Keupp Prof. Dr. Dieter Meischner Dipl.-Geol. Fritz Neuweiler PD Dr. Josef Paul Prof. Dr. Joachim Reitner Dr. Klaus Warnke PD Dr. Helmut Weller Dipl.-Geol. Patrick Dingle Dipl.-Geol. Christian Hensen Prof. Dr. Priska Schäfer Dr. Pascale Gautret Prof. Dr. Reinhold R. Leinfelder PD Dr. Hansmartin Hüssner Dipl.-Geol. Bernd Kaufmann 《Facies》1995,32(1):1-69
Summary This research report contains nine case studies (part II to X) dealing with Palaeozoic and Mesozoic mud mounds, microbial
reefs, and modern zones of active micrite production, and two parts (I and XI) summarizing the major questions and results.
The formation of different types ofin situ formed micrites (automicrites) in close association with siliceous sponges is documented in Devonian, Carboniferous, Triassic,
Jurassic and Cretaceous mounds and suggests a common origin with a modern facies found within reef caves. Processes involved
in the formation of autochthonous micrites comprise: (i) calcifying mucus enriched in Asp and Glu, this type presumably is
linked to the formation of stromatolites, thrombolites and massive fabrics; (ii) protein-rich substances within confined spaces
(e.g. microcavities) result in peloidal pockets, peloidal coatings and peloidal stromatolites, and (iii) decay of sponge soft
tissues, presumably enriched with symbiotic bacteria, lead to the micropeloidal preservation of parts of former sponge bodies.
As a consequence, there is strong evidence that the primary production of micrite in place represents the initial cause for
buildup development. The mode of precipitation corresponds to biologically-induced, matrix-mediated mineralization which results
in high-Mg-calcites, isotopically balanced with inorganic cements or equilibrium skeletal carbonates, respectively. If distinct
automicritic fabrics are absent, the source or origin of micrite remains questionable. However, the co-occurring identifiable
components are inadequate, by quantity and physiology, to explain the enhanced accumulation of fine-grained calcium carbonate.
The stromatolite reefs from the Permian Zechstein Basin are regarded as reminiscent of ancestral (Precambrian) reef facies,
considered the precursor of automicrite/sponge buildups. Automicrite/sponge buildups represent the basic Phanerozoic reef
type. Analogous facies are still present within modern cryptic reef habitats, where the biocalcifying carbonate factory is
restricted in space. 相似文献
4.
Jörn Peckmann James L. Goedert Till Heinrichs Jochen Hoefs Joachim Reitner 《Facies》2003,48(1):241-253
The Late Eocene ‘Whiskey Creek’ deposit (Pysht Formation, Olympic Penisula, Washington State) formed at a methane-seep. Early
diagenetic micrites and aragonite cement have δ13C values as low as −36‰ indicating that the seepage fluids contained methane. With respect to micrite samples, low δ13C values correlate with relatively high δ13O values andvice versa. Ongoing micrite formation after the cessation of the seepage during increased burial might have altered the isotopic composition
of the microcrystalline carbonates toward lower δ13O values and higher δ13C values. Alternatively, the trend in isotope values may reflect a change in the composition of seepage fluids. The principal
difference between these scenarios is the duration of seepage with respect to micrite formation. Two petrographically similar
varieties of blocky calcite spar are related to different carbonate sources. The δ13C values range from −32 to −29‰ for one type of blocky spar and are either the result of methane oxidation or indicate thermal
decarboxylation of organic matter. Low δ18O values are in favour of the latter. For the other type of spar, δ13C values as high as +6‰ indicate carbonate formation within the zone of methanogensis.
The ‘Whiskey Creek’ limestone exhibits a chaotic fabric produced by a variety of processes, including bioturbation, concretionary
carbonate formation, earlyin situ brecciation, carbonate corrosion, and late fracturing of the rock. Two varieties of micrite aggregates are responsible for
the nodular fabric of the limestone. Smoothly-shaped pyritiferous micrite nodules are of diagenetic origin and formed in a
manner similar to that which produces carbonate concretions. Apart from being induced by anaerobic oxidation of methane, their
formation is proposed to be linked to iron reduction and sulphide formation. The second, dominant variety is represented by
irregularly-shaped, nodular to angular micrite aggregates surrounded by massive rims of pyrite, resulting from carbonate corrosion.
A pure, fluorescent seam-micrite, constructive in origin, lines cavities or surrounds micritic aggregates. 相似文献
5.
Adriano Guido Carlos Jimenez Katerina Achilleos Antonietta Rosso Rossana Sanfilippo Louis Hadjioannou Antonis Petrou Franco Russo Adelaide Mastandrea 《Facies》2017,63(3):21
The biostalactites from the Kakoskali cave in Cyprus represent a new example of the complex biotic relationships between skeletal organisms and microbial communities in building bioconstructions of cryptic marine environments. Biostalactites are mainly constituted of polychaetes of the family Serpulidae and, to a lesser degree, foraminifers and bryozoans. Within the skeletal framework of these organisms, two types of microcrystalline calcite (micrite) have been recognized: autochthonous and detrital micrite. The autochthonous fraction is syndepositionally lithified and occurs as clotted peloidal and, subordinately, aphanitic (structureless) textures, suggesting the presence of heterotrophic microbial activities thriving on decaying metazoan organic matter. This fraction is limited to the protected portions of the bioconstructions, especially in the inner and lower parts. The presence of iron and manganesiferous oxidizing bacteria is suggested by the deposition of ferromanganesiferous crusts and Frutexites-like structures. These microbial-induced biomineralizations are the main evidence of carbonatogenetic and Fe–Mn, autotrophic and chemoheterotrophic, bacterial activities. The Kakoskali cave is frequently visited by divers who, during their immersions, resuspend the fine bottom sediment, which later covers the surface of the bioconstructions, disturbing the delicate equilibrium of the biotic association. This perturbation, which is also caused by strong waves and currents, during winter months, reflects on the bioconstruction morphologies, community composition, and colonization pattern. Bioconstructions exhibit an upper smooth surface, produced by few taxa (e.g., polychaetes, foraminifers), hosting a low number of living individuals, and a lower comparably rough surface, colonized by a more abundant community showing a higher species richness. The ratio surface roughness/smoothness is related to micrite sediment type: the upper part is mainly characterized by loose detrital micrite while the internal and lower parts by syndepositional cemented autochthonous micrite. 相似文献
6.
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. 相似文献
7.
Microbialites and global environmental change across the Permian-Triassic boundary: a synthesis 总被引:1,自引:0,他引:1
Kershaw S Crasquin S Li Y Collin PY Forel MB Mu X Baud A Wang Y Xie S Maurer F Guo L 《Geobiology》2012,10(1):25-47
Permian-Triassic boundary microbialites (PTBMs) are thin (0.05-15 m) carbonates formed after the end-Permian mass extinction. They comprise Renalcis-group calcimicrobes, microbially mediated micrite, presumed inorganic micrite, calcite cement (some may be microbially influenced) and shelly faunas. PTBMs are abundant in low-latitude shallow-marine carbonate shelves in central Tethyan continents but are rare in higher latitudes, likely inhibited by clastic supply on Pangaea margins. PTBMs occupied broadly similar environments to Late Permian reefs in Tethys, but extended into deeper waters. Late Permian reefs are also rich in microbes (and cements), so post-extinction seawater carbonate saturation was likely similar to the Late Permian. However, PTBMs lack widespread abundant inorganic carbonate cement fans, so a previous interpretation that anoxic bicarbonate-rich water upwelled to rapidly increase carbonate saturation of shallow seawater, post-extinction, is problematic. Preliminary pyrite framboid evidence shows anoxia in PTBM facies, but interbedded shelly faunas indicate oxygenated water, perhaps there was short-term pulsing of normally saturated anoxic water from the oxygen-minimum zone to surface waters. In Tethys, PTBMs show geographic variations: (i) in south China, PTBMs are mostly thrombolites in open shelf settings, largely recrystallised, with remnant structure of Renalcis-group calcimicrobes; (ii) in south Turkey, in shallow waters, stromatolites and thrombolites, lacking calcimicrobes, are interbedded, likely depth-controlled; and (iii) in the Middle East, especially Iran, stromatolites and thrombolites (calcimicrobes uncommon) occur in different sites on open shelves, where controls are unclear. Thus, PTBMs were under more complex control than previously portrayed, with local facies control playing a significant role in their structure and composition. 相似文献
8.
Microbial contributions to reefal limestones are evident in eastern Australian Lower Devonian microbial frame/bindstones, red algal-microbial-stromatoporoid bindstones, and microbial-stromatoporoid bindstones. Varied microbialite textures, such as stromatolites, thrombolites, and leiolites, originated as accumulations and partial aggregations of calcimicrobes, peloids, and micrites, which also derived from microbial activities. In microbial frame/bindstones, calcimicrobes (e.g., Rothpletzella and Wetheredella) and dense micrite layers covered and bound underlying substrates. Stabilized substrates promoted the subsequent construction of layered, domal, and columnar frameworks, which were produced by combined accumulations and intermixed associations of calcimicrobes and micritic microbialites. Microbes flourished in the microbial-stromatoporoid bindstones and red algal-microbial-stromatoporoid bindstones during repeated growth interruptions of the framework-building skeletal organisms. Microbes bored into and eroded the skeletal frameworks to subsequently leave micritic envelopes, on which microbial and skeletal encrustations took place in turn. The importance of microbial colonization on the skeletal frameworks was first as subsidiary encrusters that helped to preserve them from erosion, and second as modifiers of the spaces suitable for succeeding encrusters. Partial aggregations of Renalcis filled in the interstices of the skeletal and microbial frameworks, thereby enhancing their rigidity.The microbial impacts on the genesis of reefal limestones are: (1) origination of components (calcimicrobes, peloids, and micrites); (2) formation of characteristic microbial textures; (3) main and subsidiary reef construction and encrustation; and (4) destruction of these components, textures, and structures, but also the protection of resultant constructions in turn. The Lower Devonian reefal limestones treated herein, surprisingly, preserve excellent records of a variety of microbial impacts. Similar effects may also have been common, although variable in preservation, in other ancient reefal deposits. 相似文献
9.
Carbonate organo-mineral micro- and ultrastructures in sub-fossil stromatolites: Marion lake, South Australia 总被引:1,自引:0,他引:1
Sub-fossil stromatolites (5000-3000 years old) occur on the marginal flat surrounding Marion Lake (South Australia). A micrite/microsparite crystal fabric characterises these fine-grained, well-laminated stromatolites, which lack trapped grains. The internal lamination is characterised by a sub-millimetric alternation of porous and dense laminae. The microfabric of the laminae is ubiquitously composed of a fine (10-20 μm) peloidal texture, with many thinner aphanitic layers. Aggregates of very fine, low-Mg calcite and aragonite constitute both peloidal and aphanitic micrite, which is coated, respectively, by spherulitic and fringing acicular microspar. Micrite, with a high organic matter content, is formed of coalescing nanospheres grading into small polyhedrons, probably composed mainly of aragonite, with less calcite enriched in Mg, Sr, Na and S. Bacteria-like microfossils and relics of extracellular polymeric substance (EPS) occur abundantly within this micritic framework. The former consist of empty moulds and mineralised bodies of coccoid forms, whereas EPS relics consist of sheet-like or filamentous structures that appear both mineralised and more often still preserved as a C-enriched dehydrated substance that represents the main organic matter component of the deposit. Acicular crystals, which show a prismatic elongate shape, are composed of Mg-depleted aragonite that lacks fossils or organic relicts. Degrading EPS and micro-organisms appear gradually to be replaced and entombed by the nanospherical precipitates, implying the existence of processes of organo-mineralisation within an original syn-sedimentary microbial community. Succeeding micron-scale crystals merge to form isolated or connected micritic aggregates (the peloids), followed by the gradual formation of the acicular crystals as purely inorganic precipitates. 相似文献
10.
Palaeozoic cold seep carbonates from Europe and North Africa—an integrated isotopic and geochemical approach 总被引:1,自引:0,他引:1
In this paper, we report the highest and lowest carbon isotope values known from Palaeozoic carbonate rocks. These unusual δ13C values (−50 to +23.5‰) are due to microbial methanogenesis and methanotrophy in Silurian to Carboniferous carbonates. Trace elements were used to decipher the primary mineralogy of the carbonate cements. Very high Sr values and low amounts of Mg, Fe and Mn point toward aragonite precursors, whereas high Fe and Mn values are indicative of primary calcites and allow reconstruction of the redox conditions. Four carbonate deposits are described from the Meseta and the Antiatlas of Morocco, the Pyrenees (France) and the Harz mountains (Germany). The highest δ13C values in concretion below the uppermost Silurian Spinatrypa Mound (Moroccan Meseta) give evidence, that CO2 was produced during methanogenesis. δ13C values between −10 and −32‰indicate that the formation of microbial carbonates and cements in the Middle Devonian Hollard Mound (Antiatlas) and in the Lower Carboniferous sediments of the Iberg (Harz) formed at thermogenetic methane or petroleum seeps. The Late Bashkirian carbonate mound of the High Pyrenees (Tantes Mound) is the first Palaeozoic carbonate with seepage fluids being dominated by biogenic methane. Matrix carbonates exhibit δ13C values as low as −34‰. In some parts, voids make up more than 50 vol% of the mound. They are filled with several generations of cement. The earliest void filling is isopachous fibrous cement, which represents former aragonite. Most negative δ13C values of −50‰were measured in these isopachous fibrous cements. The difference of 55‰in δ13C values between normal sediments and early aragonite cements can only be explained by the contribution of CO2 from anaerobic oxidation of biogenic methane in a cold seep setting. 相似文献
11.
Summary During the Middle and early Late Triassic carbonate ramps and rimmed platforms developed at the northwestern margin of the
Tethys ocean. In the Northern Calcareous Alps, Anisian stacked homoclinal ramps evolved through a transitional stage with
distally steepened ramps to huge rimmed platforms of Late Ladinian to Early Carnian age. Middle Triassic to early Late Triassic
facies and biota of basin, slope and platform depositional systems are described. Special emphasis is given to foraminifers,
sponges, microproblematic organisms and algae.
The Ladinian to early Carnian reef associations are characterized by the abundance of segmented sponges, microproblematica,
biogenic crusts and synsedimentary cements. Among the foraminifers, recifal forms likeHydrania dulloi andCucurbita infundibuliformis (Carnian in age) are reported from the Northern Calcareous Alps for the first time. Some sphinctozoid sponges likeParavesicocaulis concentricus were known until now only from the Hungarian and Russian Triassic. 相似文献
12.
Lucien F. Montaggioni 《Geobios》1982,15(2):161-179
The Pleistocene elevated marine carbonate complexes on Mauritius island correspond to three types of depositional zones: (1) reef-crest zone, (2) backreef zone, (3) littoral zone.On reef crests, the primary frame-builders are scleractinian corals (Acroporidae, Faviidae, Poritidae) and crustose coralline algae. The secondary builders are encrusting Foraminifers (Homotrematidae) chiefly, Molluscs (Vermetidae), Bryozoans (Cheilostomata) and Serpulids. Associated internal sediments are coarse to fine sand-sized grainstones or packstones and wakestones. In decreasing order of abundance, skeletal elements include fragments of corals, branched and crustose red algae, Pelecypods, Gastropods, benthonic Foraminifera (Amphisteginidae, Peneroplidae, Calcarinidae, Nummulitidae, Alveolinidae and Homotrematidae), Echinoderms and Alcyonarians; the most abundant mud-sized grains are identified as tunicate spicules. Primary marine cements are needle, palisade, micrite and pelletal ones.The backreef zone is characterized by coarse tomedium grainstones, packstones and wakestones. In addition to pellets the most common components are skeletal in nature; they broadly show the same mode of occurrence as the reef-crest unit. Primary cements locally occur in packed fibrous or micrite form.In littoral areas, well-sorted grainstones to poorlysorted mudstones can be described. The distribution of the various categories of biogenic particles is dependent upon the extent of reef tracts; ancient beaches from narrow reefs are characterized by coralgal facies while consolidated muddy banks in large complexes display high amount of molluscan detritus. Primary cementation appears mainly to be the result of the precipitation of fibrous or micrite calcite.The morphology, biological associations andsediments of these Pleistocene limestones are homologous with those of the adjacent modern environments. 相似文献
13.
Calcification processes of siliceous sponges in Viséan Limestones (Counties Sligo and Leitrim,Northwestern Ireland) 总被引:1,自引:0,他引:1
Dr. Klaus Warnke 《Facies》1995,33(1):215-227
Summary In the Lower Carboniferous limestones and shales of the Benbulben Range, Counties Sligo and Leitrim, northwestern Ireland,
a suite of carbonate nodules, about 1 to 4 cm in diameter, has been sampled and investigated by thin sectioning. The nodules
consist of micritic, peloidal and fenestral fabrics. Many of them contain relics of desma bearing demosponges and hexactinellid
sponge skeletons. The nodules are interpreted as calcified siliceous sponges. Micrite and peloids have been formed via microbial
activity during the decay of the soft sponge tissue. The actual processes are deduced from Recent examples investigated at
Lizard Island, Autralia, byReitner (1993). The skeletal opal was dissolved very early. In places where the skeleton was already embedded in micrite the spicules
are preserved as molds cemented by granular ferroan calcite. The nodules were extensively inhabited by agglutinating polychaetes
and bored by sponges. Micrite clasts have been exported to the surrounding seafloor before the sponges were completely covered
by sediments. Fenestral fabrics represent primary sponge cavities, that may be enlarged due to volume reduction of the soft
tissue during calcification. Some originated from non-calcification of decaying tissue. The granular calcite cement, filling
the fenestral fabrics, contains relics of spicules and faintly visible peloids floating unsupportedly in the cement. These
peloids were probably produced in situ by calcification of organic mucilages that filled the cavities almost entirely. It
is evident that most diagenetic processes occurring within the sponges happened on the seafloor, most likely within the still
living individuals. Possibly the nodules represent a precursor stage of mud mound development. 相似文献
14.
Adelaide Mastandrea Francesco Muto Claudio Neri Cesare A. Papazzoni Edoardo Perri Franco Russo 《Facies》2002,47(1):27-42
Summary The “Calcare di Mendicino” is a mixed carbonatesiliciclastic informal unit of Miocene (Late Tortonian-Early Messinian age),
that crops out extensively in the northwestern part of the Calabria. In the Scannelle quarry near Belsito (Cosenza), four
stratigraphic sections were studied to define the sedimentological and paleoecological setting. The carbonate body records
the development of a deep-water coral bank characterized by a low-diverse community of azooxanthellate scleractinian (Oculina andDendrophyllia) and stylasterine hydrozoans colonies. Two main stages of bioconstruction development can be distinguished: a thicket and
a bank stage. Among the biostromal dwellers the more common are bryozoans, echinoids, benthic foraminifers, gastropods, and
bivalves. A higher content of planktonic foraminifers occur in the thicket stage. The coral bank flourished within the aphotic
zone, with deep currents loaded with nutrients and siliciclastic sediments.
The upper part of the “Calcare di Mendicino” carbonate body has been affected by a pervasive dolomitization destroying almost
completely the sedimentary structures and the biofacies. The lower part, the main object of this paper, preserves the microfacies
but it experienced a widespread recrystallization obliterating the primary geochemical characteristics. The diagenetic history,
partly hidden, reveals three main stages: primary marine with isopachous fibrous cements, deep burial with cavities infilled
by sparry calcite, and meteoric-phreatic with dog-tooth cements. 相似文献
15.
Dr. Andrei V. Dronov 《Facies》1993,28(1):169-180
Summary Several Waulsortian-type mud mounds nearly 500 m thick and about 5 km long occur in the Middle Paleozoic carbonate section
of the Aktur nappe in the mountains on the right bank of Isfara river. These buildups form a well developed barrier system
that stretches along the South Ferganian carbonate platform margin and divides the carbonate complex into a fore-reef and
a back-reef part. The time of the mounds' most active growth was from the Late Silurian (Ludlow) to the Middle Devonian (Eifel).
Three main facies types can be recognized in the mud mounds: 1. micritic core facies, 2. sparitic flank facies and 3. loferitic
capping facies. The central massive or crudely bedded part of the mounds consists of white or light grey clotted micrite.
Macrofossils are rare. The sparitic flank facies in contrast consists of coarse and densely packed crinoidal wackestone-floatstones
with some brachiopod shell debris. Solitary rugose corals, tabulate corals, stromato-poroids and fragments of mollusks are
also abundant. The tops of the mounds are usually covered with loferitic pelmicrites or oolitic grainstone caps. Stromatactis-like
structures are very rare and poorly developed in the South Ferganian mud mounds. However, almostin all such mounds horizons
of calcitic breccias can be found.
In order to explain all the features found in the Fergana mounds an ‘atoll-like’ model has been proposed which starts the
evolution of the mud mounds with a small nucleus bioherm. The main stage of the evolution corresponds to an atoll-like structure
developing on the surface of shallow water platforms. White clotted micrite of the mound core facies is interpreted as a accumulation
of fine-grained sediment in an inner lagoon flanked by crinoidal bar deposits. The mound flank facies represents the atoll
rim deposits from where the carbonate mud is derived. The capping loferitic facies is considered as tidal flat deposit that
developed on top of the buildups during the last stage of its evolution. The knoll shape of the mounds is explained by the
retreat of the atoll flanking crinoidal bars back into the inner lagoon during the rise in sea level. Stromatactis-like structures
of small cavities filled with sparry calcite owe their existence to burrowing organisms. Calcitic breccias are interpreted
as paleokarst collapse breccias. They indicate that the tops of the mud mound became subaerially exposed. Other evidence for
a subaerial exposure can be seen in the occurrence of Variscian ‘black and white’ limestone gravel on the tops of some mud
mounds. According toWard et al. (1970) these sediments were produced above the sea level at the edge of hypersaline lakes situated on islands. 相似文献
16.
Microporous limestones composed of micrite crystals constitute sizeable hydrocarbon reservoirs throughout the world and especially
in the Middle East. However, the crystallization history of micrites is poorly understood. Scanning electronic microscopy
(SEM) with X-ray energy dispersive spectroscopy (EDS) studies give morphological and bulk composition information about micrites,
but no information exists on the distribution of minor elements inside micrite grains. This study proposes Mg maps obtained
with X-ray EDS combined with scanning transmission electron microscopy (STEM) of micrite crystals from the Mishrif reservoir
Formation (Middle East, Cenomanian to Early Turonian). Three types of Mg distribution were observed through micrite crystals
from five different samples: (1) homogenous Mg concentration, (2) small Mg-enriched areas close to the center of the crystal,
and (3) geometric Mg impoverishments near crystal edges and parallel to present crystallographic faces. The homogenous Mg
distribution is the most frequent and is found both in microporous and in tight micrites. The second type of distribution
showing small Mg-enriched areas inside micrite crystals relatively close to their center comes from a microporous sample located
below an emersive surface. These enriched areas may correspond to crystal seeds. The third type of distribution was observed
in micrite crystals from another microporous sample situated just below an emersive surface. The Mg-poor zones probably represent
overgrowths that precipitated in contact with less Mg-rich meteoric fluids. 相似文献
17.
Prof. Dr. Gabriele Carannante Dr. Roberto Graziano Dr. Gerardo Pappone Dr. Daniela Ruberti Prof. Dr. Lucia Simone 《Facies》1999,40(1):1-24
Summary In the Late Cretaceous the carbonate platforms modified the organization of their depositional systems owing to vast and complex
geologic events. In this view, detailed analyses have been made on Senonian shelf-to-slope rudist-bearing limestones resting
on pre-Coniacian erosive surfaces or slope facies in the Nurra region (northwestern Sardinia, Italy), in the central-southern
Apennines and in the Gargano area (central-southern Italy). The main characteristic of the analyzed deposits is the spreading
of rudists in a context of foramol-type calcite-dominated benthonic sediment-producer communities.
The reconstructed Senonian depositional environments match a large complex of unprotected shelves that produced loose, diagenetically
stable mollusc-dominated bioclastic debris which were not involved in significantin situ cementation processes. High energy episodes led to repeated and more or less total remobilization of the sedimentary sheet.
On the shelves, both storm- and wind-induced currents and waves exercised a strong driving control on the sedimentary arrangement
of the shifting biogenic sediments. The latter constituted large coalescing sheets of winnowed, loose, fine-to-coarse skeletal
sands. Sandy sediments were easily involved in remobilization processes across the shelves toward the redepositional sites.
Transport modality largely depended on the granular composition of the sediments. The early and almost continuous sweeping
of the finer fraction (bioeroded-derived silt) resulted in an effective pre-sorting of the skeletal debris stored in the Senonian
open shelf settings.In situ preservation potentiality of the produced skeletal material was low and huge amounts of sands may have concurred in forming
slope aprons.
In the studied successions a two-stage evolution is documented during the Senonian.
Owing to the peculiar characteristics of the foramol-type open shelves (e.g., physiography, sediment production and composition),
the sediment distribution patterns of the Senonian rudist-bearing carbonate factories and their response to sea level fluctuations
were strongly modified with respect to the commonly accepted carbonate platform chlorozoan standard model. Major progradational
episodes of marginal sands occurred during both relative lowstands and terminal highstands of sea level. During transgressive
phases only where the sediment production was sustained (southern Tethyan carbonate platforms), the rudist-bearing depositional
systems might have dampened the typical drowning tendency of the foramol open shelves. 相似文献
– | - All over the latest Turonian-early Campanian interval the rudist-bearing shallow neritic platforms retreated, with seabed opening and deepening, and an underfeeding of the slope occurred. Probably, only where rudists strongly dominated the shelf assemblages (as in the case of the southern Tethyan carbonate platforms), their relatively high rate of bioclastic sediment production and supply might partially compensate for the increased accommodation space reducing the effects of the early Senonian transgressive phase. |
– | - In the late Senonian a huge amount of foramol skeletal sands prograded over the upper slope by means of impressive gravitative flows suggesting that main depocenters moved down-slope. The persistence of healthy, producing foramol open-shelves may be inferred by the occurrence of compositionally coherent displaced skeletal sands even if reduced findings of late Campanian-Maastrichtian shallow water limestones are known characterized by a clear upward shallowing trend. A reduced accommodation space in shallow water settings may have enhanced the high off-bank sand dispersion via an increased winnowing action exerted on loose foramol-bioclastic sediments in periods in which the shelf tops were exposed to intense current winnowing. The generalized down-slope migration of the main depocenters occurred during the late Senonian regressive phase. |
18.
Late Jurassic–Early Cretaceous ?tramberk-type reef limestones are known from some parts of the Southern Carpathians in Romania. The Upper Jurassic deposits mainly consist of massif reef limestones including a variety of microbialites associated with micro-encrusters. They played an important role in the formation and evolution of the reef frameworks and thus are of significant importance for deciphering the depositional environments. For our study, the most important encrusting organisms are Crescentiella morronensis, Koskinobullina socialis, Lithocodium aggregatum, Bacinella-type structures, Radiomura cautica, Perturbatacrusta leini, Coscinophragma sp., and crust-forming coralline sponges such as Calcistella. Based on microscopic observations, microbial contribution to reef construction is documented by the abundance of dense micrite, laminate structures, clotted, thrombolithic or peloidal microfabrics, constructive micritic cortices, biogenic encrustations and cement crusts, as well as by other types of microbial structures and crusts. Most of the investigated carbonate deposits can be classified as “coral-microbial-microencruster boundstones” which are characteristic for the Intra-Tethyan domain. Their paleogeographical significance is indicated by the presence of many features comparable with carbonate deposits of rimmed platform systems from the Northern Calcareous Alps or Central Apennines. Based on the distribution of the facies and facies associations within the carbonate sequences under study we can distinguish slope and external shelf margin environments. The microbial crusts, the encrusting micro-organisms, and in some cases the syndepositional cements have stabilized and bound the carbonates of the slope facies types. Subsequently, the stable substrate favored the installation of coral-microbial bioconstruction levels. 相似文献
19.
The ability to recognize the former existence of microbes as well as the biological origin of marine precipitates, such as putative microbialites, is crucial for understanding the development and history of early life on Earth. Increasingly, such rocks hold keys to understanding the geochemical evolution of the oceans and linked Earth systems. Vital trace elements previously have received relatively little attention as clues to the origin of carbonate rocks, and low abundance transition elements in particular, have been difficult to analyse in carbonate matrices for technical reasons. We have used laser ablation–inductively coupled plasma–mass spectroscopy for the in situ measurement of a broad suite of vital transition metals in Late Devonian reefal limestones that contain coeval microbialite (the calcimicrobe Renalcis), stromatoporoid sponge skeleton, early marine cement, and later diagenetic cement. Comparative experiments conducted in two different ion extraction modes determined theoretical detection limits for transition elements on NIST reference material SRM 612. Analyses of NIST glasses SRM 614 and 616 demonstrate accuracy relative to previously published data. On that basis we have identified significant enrichment of the vital elements V, Sn, Cu and Zn within the Renalcis. The stromatoporoid skeleton by contrast is enriched only in V. Earliest cements, which also may have been mediated to some degree by microbial biofilms on the basis of their morphology, show a much smaller degree of enrichment, and later cements show no enrichment, with the exception of Zn, which is concentrated in the latest cement. Fine particulate carbonate sediments (micrite) show variable metal enrichments that are attributable to varying contributions from detrital siliciclastic contamination. Renalcis was also enriched above the sponge and cements in regards to Mn, Cd, Co, and possibly Cr, but at less robust levels. Molybdenum and Sb were found not to be enriched in the Renalcis, and Ni, although clearly very low in concentration, could not be evaluated owing to its high detection limit. We additionally were able to identify specific zones of contamination in Renalcis encountered as the laser drilled deeper into the carbonate. Time resolved analysis allows exclusion of such contaminants from integration into the results. Successful application of the new technique will now allow us to assess metal uptake in ancient carbonates with implications for interpreting the biogenicity of putative microbialites. 相似文献
20.
Elisa Garuglieri Ramona Marasco Charlene Odobel Viswasanthi Chandra Thomas Teillet Camila Areias Mónica Sánchez-Román Volker Vahrenkamp Daniele Daffonchio 《Environmental microbiology》2024,26(2):e16573
Micritization is an early diagenetic process that gradually alters primary carbonate sediment grains through cycles of dissolution and reprecipitation of microcrystalline calcite (micrite). Typically observed in modern shallow marine environments, micritic textures have been recognized as a vital component of storage and flow in hydrocarbon reservoirs, attracting scientific and economic interests. Due to their endolithic activity and the ability to promote nucleation and reprecipitation of carbonate crystals, microorganisms have progressively been shown to be key players in micritization, placing this process at the boundary between the geological and biological realms. However, published research is mainly based on geological and geochemical perspectives, overlooking the biological and ecological complexity of microbial communities of micritized sediments. In this paper, we summarize the state-of-the-art and research gaps in micritization from a microbial ecology perspective. Since a growing body of literature successfully applies in vitro and in situ ‘fishing’ strategies to unveil elusive microorganisms and expand our knowledge of microbial diversity, we encourage their application to the study of micritization. By employing these strategies in micritization research, we advocate promoting an interdisciplinary approach/perspective to identify and understand the overlooked/neglected microbial players and key pathways governing this phenomenon and their ecology/dynamics, reshaping our comprehension of this process. 相似文献