Field trip guide-book of the 6th Regional Symposium of the International Fossil Algae Association (original) (raw)
Related papers
The microbial nature of laminated limestones: lessons from the Upper Aptian, Araripe Basin, Brazil
Sedimentary Geology, 2016
The Araripe Basin, located in northeastern Brazil, originated during the Gondwana continental break-up responsible for the opening of the South Atlantic during the Early Cretaceous. In the Araripe Basin, the post-rift Aptian sequence corresponds to the Santana Group, which is composed, in upward succession, of mostly clastic continental and rare carbonate layers of the Barbalha, Crato, Ipubi and Romualdo Formations. The laminated limestones of the Crato Formation were deposited in a lacustrine environment preceding the deposition of the Ipubi Formation evaporites. They are age-equivalent to the limestones of the pre-salt interval of the east coast of Brazil, which contains large petroleum reserves. The excellent preservation of its macrofossils has made the Crato Formation known worldwide as a Fossil Lagerstätte. The limestones are macroscopically homogeneous, and their deposition has been previously attributed to chemical precipitation. Although the carbonate laminites are macroscopically undifferentiated, mineralogical variations, microscopic texture and distinctive biotic aspects supported the characterization of four microfacies: planar laminated, crustiform, nodular and rhythmic. The microfacies analysis indicated a strong and pervasive biological activity in the Crato limestone morphogenesis. Organominerals precipitated by the metabolic action of cyanobacteria and/or sulfate-reducing bacteria and methanogenic-oxidizing archea are represented by calcite and pyrite. Calcified coccoid and filaments are common, furthermore, the presence of calcified biofilms composed of exopolymeric substances (EPS) is ubiquitous. The presence of amorphous organic matter (AOM) and gypsum, particularly in the rhythmic microfacies, indicates anoxic/dysoxic conditions and stressful environments during periods of drought and low lake levels which favored the development and preservation of microbial biofilms. Phytoclasts and miospores when present in the succession indicate an extrabasinal contribution during wetter periods, although the environment remained of very low energy. The evidence of microbial influence in the formation of the laminated limestones of the Crato Formation is of great importance for understanding the excellent preservation of the unit's fossils and for modeling the evolution of the Aptian carbonate sequences in Brazil.
Sedimentology, 2003
Recent dolomitic sediment samples from Lagoa Vermelha, Brazil, were examined microscopically to study the process of bacterial fossilization in carbonate sediments. Bacteria-like bodies were intimately associated with carbonate mineral surfaces, and coatings on the former demonstrate the calcification of single bacterial cells. The bacterial fossilization process in Lagoa Vermelha sediments was simulated in the laboratory by cultivation of mixed and pure cultures of sulphate-reducing bacteria, which were isolated from the Lagoa Vermelha sediments. These cultures produced carbonate minerals that were studied to provide insight into the initiation of the fossilization process. In mixed culture experiments, bacterial colonies became calcified, whereas in pure culture experiments, single bacterial cells were associated with dolomite surfaces. Dolomite nucleated exclusively in bacterial colonies, intimately associated with extracellular organic matter and bacterial cells. Electrophoretic mobility measurements of the bacterial cells in electrolyte solutions demonstrated the specific adsorption of Ca 2+ and Mg 2+ onto the cell surfaces, indicating the role of the bacterial surface in carbonate nucleation and bacterial fossilization. The affinity of the cells for Mg 2+ was related to the capability of the strains to mediate dolomite formation. Combined with sulphate uptake, which dissociates the [MgSO 4 ] 0 ion pair and increases the Mg 2+ availability, the concentration of Mg 2+ ions in the microenvironment around the cells, where the conditions are favourable for dolomite precipitation, may be the key to overcome the kinetic barrier to dolomite formation. These results demonstrate that bacterial fossilization is a consequence of the cell surface involvement in carbonate precipitation, implying that fossilized bacterial bodies can be used as a tool to recognize microbially mediated carbonates.
Microbial carbonate crusts-a key to the environmental analysis of fossil spongiolites?
Facies, 1993
Morphological and geochemical comparisons between modern cryptic microbialites from Lizard Island/Great Barrier Reef and fossil counterparts in the Upper Jurassic (Southern Germany, Dobrogea/Romania) and late Lower Cretaceous (Aptian/ Albian from Cantabria/Spain) spongiolitic environments show that there are common factors controlling the crust formations mostly independent of light despite of diverging (paleo-) oceanographic positions as well as relationships of competitors. Factors such as increased alkalinity ,oligotrophy, and reduced allochthonous deposition are of major importance. Thrombolitic microbialites are interpreted as biologically induced and therefore calcified in isotopic equilibrium with the surrounding sea water. Corresponding with shallowing upward cycles, microbial mats which produce stromatolitic peloidal crusts become more important. Different biomarkers are introduced for the first time extracted and analyzed from spongiolitic limes tones ofLower Kimmeridgian age from Southern Germany.
Colonization strategies of lithobiontic microorganisms on carbonate rocks
Environmental Geology, 2004
Biogenic weathering is caused by the action of lithobiontic organisms. Homogeneous carbonates are predominantly colonized by endolithic species that actively penetrate the rock substratum independent of already existing pores or fissures. The organisms construct a system of ducts and cavities by active dissolution of the substratum. A fresh, noncolonized surface is penetrated by algae and ascomycetes in the first and second year after exposure to the environment. The establishment of complex colonization patterns on and in the substratum by lichens takes several years. In spite of the primary deteriorative effect on their substratum by the organisms, long-term endolithic growth also involves mechanisms that stabilize and preserve the rock surface morphology. A tightly woven cellular network may strengthen the colonized stone. This feature is of importance when natural and building stone are affected by biogenic weathering phenomena.
Facies, 2012
Late Jurassic-Early Cretaceous Š 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 microorganisms , 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.
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.
Sedimentary Geology, 1999
Methane-derived carbonate rocks (Lucina limestone and Marmorito limestone) crop out in Monferrato (NW Italy) and represent one of the first described examples of rocks produced at fossil cold seeps. These rocks, of Miocene age, consist of strongly carbonate-cemented siliciclastic sediments ranging in grain size from mud to coarse sand. The methane-related origin of Monferrato carbonates is based on: (a) outcrop-scale evidence: patchiness of cementation, chemosymbiotic fossil communities, presence of a network of polyphase carbonate-filled veins not related to tectonics; (b) isotope geochemistry: very depleted δ 13 C values, as low as 50‰ PDB; (c) peculiar petrographic features. Diverse microbial communities have been observed in present-day cold seeps. These communities include sulphate-reducing, sulphur-oxidizing and methane-oxidizing bacteria. The present work is focused on the identification and description of fossil evidence of such microbial activity in the Monferrato carbonates. Examples of fossilization of microbial structures are probably represented by pyritic rods and dolomite tubes referable to sulphur-oxidizing and to unspecified bacteria, respectively. Less direct but more abundant evidence has been found through petrographic and SEM studies of seep carbonates. Many features point to the presence of organic clumps or mats capable of trapping sediment and promoting carbonate precipitation: microcrystalline calcite peloids; dolomite crystals with irregular hollow cores; dolomite spheroids with dumbbell-shaped cores; laminated internal sediments lining cavities completely. All these features are interpreted to result from bacterially mediated, sedimentary and diagenetic processes and can therefore be considered as an additional evidence of ancient methane seeps. : S 0 0 3 7 -0 7 3 8 ( 9 9 ) 0 0 0 4 4 -5
The Valdorria carbonate platform, in northern Spain, features a well-preserved and continuous outcrop of a Bashkirian platform to basin transect. During the Asatauian (late Bashkirian), the platform growth changed gradually from a progradational to an aggradational mode, recording 10 most likely short-eccentricity-controlled cyclothems. The facies of the platform-top and slope have been mapped, and the architecture of each cyclothem schematically reconstructed. The distribution of microbial carbonates (microbially mediated precipitates), skeletal (grazers/burrowers, corals/filter feeders, algae, foraminifera, Osagia-like oncoids and Thartarella-Terebella worm tubes) and non-skeletal grains (faecal pellets) has been quantified for the transgressiveregressive periods of deposition (transgressive, maximum flooding, early and late regressive intervals) of each cyclothem. This study shows that the distribution of microbial carbonates, skeletal and non-skeletal grains along a carbonate platform transect is variable through time and mainly governed by a set of measurable interconnected factors regulating the local palaeoenvironments: the water depth and the wave energy (facies) along the platform profile (inner, outer, break, slope) during periods of sea-level fluctuations (transgressive to regressive intervals of deposition). Auloporid corals, siliceous sponges, phylloid algae and Osagia-like oncoids are characteristic of a low-energy environment situated from estimated palaeo-water depths of 25 to 80 metres below sea level (mbsl onward) that formed in the outer platform during the maximum-flooding intervals. Anthracoporella-Archaeolithoporella boundstone is characteristic of the moderate-energy environments created in the horizontal inner-platform during the transgressive intervals. Microbially mediated precipitates are reliable indicators of the slope and Masloviporidium(?) indicator of low-energy environments of the upper slope. On the platform-top, Ungdarella and Donezella are more abundant during the early regressive intervals than during any other interval. Stacheoids are mainly present in the water depth range of 10 to 60 mbsl, tournayellids from 15 to 35 mbsl and archaediscids from 15 to 75 mbsl, all in low-to moderate-energy conditions. Rugose corals are common in the water depth range of 5 to 35 mbsl, either during the transition from the early to the late regressive intervals, as solitary forms or forming boundstone, or during periods of higher sea-level stand, as solitary forms in floatstone. Fenestellids, fistuliporids and trilobites occur mainly in the slope, but are also common in the platform top during the maximum flooding and/or the early regressive intervals. Archaeolithoporella is a reliable indicator of the platform top deposits, but its abundance is closely linked to the presence of adequate substrates. A high abundance in the assemblage of gastropods, endothyrids, palaeotextulariids, bradyinids and fusulinids characterizes the platform top shallow-water coated-grain grainstones formed under high-energy currents during the late regressive intervals. Tetrataxids act as encrusters on microbial precipitates of the slope or on phylloid algae and Archaeolithoporella of the platform top, but are also observed as nuclei of coated grains. Brachiopods are more abundant in low-to moderateenergy and 35 to 55 mbsl environments that prevailed during the transgressive intervals. Faecal pellets were commonly observed in low-energy environments, from 50 to 325 mbsl, at the platform break and in the slope, and the same applies for Thartarella-Terebella worm tubes that are virtually absent in high-energy deposits. Finally, crinoids, lasiodiscids and tuberitinids are randomly distributed and are not indicative of any specific environment.
Carbonate Crystals Precipitated by Freshwater Bacteria and Their Use as a Limestone Consolidant
Applied and Environmental Microbiology, 2009
Bacterial carbonate precipitation is known to be a natural phenomenon associated with a wide range of bacterial species. Recently, the ability of bacteria to produce carbonates has been studied for its value in the conservation of limestone monuments and concrete. This paper describes investigations of carbonate crystals precipitated by freshwater bacteria by means of histological (Loeffler's methylene blue and alcian blue-periodic acid-Schiff stain) and fluorescence (CTC [5-cyano-2,3-ditolyl tetrazolium chloride]) stains, determination of cell viability inside carbonate crystals, and pore size reduction in limestone by image analysis. Carbonate crystals were found to be composed of bacteria embedded in a matrix of neutral and acid polysaccharides. Cell viability inside the carbonate crystals decreased with time. On stone, bacteria were found to form carbonate crystals, with only a few bacteria remaining as isolated cells or as cell aggregates. Pore size was reduced by about 50%...