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Oncolite
Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are very similar to stromatolites, but, instead of forming columns, they form approximately spherical structures. The oncoids often form around a central nucleus, such as a shell fragment, and a calcium carbonate structure is deposited by encrusting microbes. Oncolites are indicators of warm waters in the photic zone, but are also known in contemporary freshwater environments. These structures rarely exceed 10 cm in diameter. Oncolites may have either a porostromate or spongiostromate texture. Most oncolites are spongiostromate, having no recognisable cellular texture or microstructure. Porostromate oncolites are mostly unknown during the Precambrian; since the Eocene they have mostly been confined to freshwater environments. Distribution The appearance of recent or near-recent freshwater oncoids has been documented in two rivers in Bavaria: th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue-green algae, although they are not usually scientifically classified as algae. They appear to have originated in a freshwater or terrestrial environment. Sericytochromatia, the proposed name of the paraphyletic and most basal group, is the ancestor of both the non-photosynthetic group Melainabacteria and the photosynthetic cyanobacteria, also called Oxyphotobacteria. Cyanobacteria use photosynthetic pigments, such as carotenoids, phycobilins, and various forms of chlorophyll, which absorb energy from light. Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes. These are flattened sacs called thylakoids where photosynthesis is performed. Phototrophic eukaryotes such as green plants perform photosynthesis in plast ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Porostromate
"Porostromata" is an antiquated form taxon that refers to fossil cyanobacteria. The term porostromate is also used as a descriptor of textures and microstructure of stromatolites and oncolites which contain tubules or other cellular structures. The group was defined by Pia (1927) as containing calcareous algae bearing calcified tubules; these may run parallel to the growth surface as in ''Girvanella'', ''Sphaerocodium'' or perpendicular, as in ''Hedstroemia'', '' Ortonella'', and '' Mitcheldaenia''; however, in 1937 Pia restricted the group to only ''Girvanella'' and ''Sphaerocodium'', placing the other genera in the Codiaceae. In reality it seems that most or all of the species included in "Porostromata" represent fossils of cyanobacteria. Monty (1981) advocated continued use of porostramata in an informal sense to describe a habit and structure of bacterial colonies, rather than in a taxonomic sense. He defined a "porostromate" microstructure as follows:"Porostromate microst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spongiostromate
"Spongiostromata" is an antiquated form taxon that refers primarily to fossil cyanobacteria. "Spongiostromate" is also used to describe stromatolites and oncolite Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are very similar to stromatolites, but, instead of forming columns, they form approximately spherical structures. T ...s that do not preserve clear tubules or other cellular microstructure. Pia (1927) erected the group to contain calcareous algal fossils that contain no visible cellular structure but which he presumed represented cyanobacteria based on comparisons to modern examples. He divided the taxon into two groups: the '' stromatolithi'' and the ''Oncolite, oncolithi''. Monty (1981) abolished the group as taxonomically uninformative but advocated for the use of "spongiostromata" to describe a form and texture of bacterial fossils. He defined a "spongiostromate" texture as follows:"S ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stromatolites
Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). These microorganisms produce adhesive compounds that cement sand and other rocky materials to form mineral "microbial mats". In turn, these mats build up layer by layer, growing gradually over time. A stromatolite may grow to a meter or more. Although they are rare today, fossilized stromatolites provide records of ancient life on Earth. Morphology Stromatolites are layered, biochemical, accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains in biofilms (specifically microbial mats), through the action of certain microbial lifeforms, especially cyanobacteria. They exhibit a variety of forms and structures, or morphologies, including conical, stratiform, domal, columnar, and branching ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Andean Geology
''Andean Geology'' (formerly ''Revista Geológica de Chile'') is a peer-reviewed scientific journal published three times per year by the National Geology and Mining Service, Chile's geology and mining agency. The journal covers the field of geology and related earth sciences, primarily on issues that are relevant to South America, Central America, and Antarctica with a particular focus on the Andes. The journal was established in 1974 and articles are published in English and Spanish. The editor-in-chief An editor-in-chief (EIC), also known as lead editor or chief editor, is a publication's editorial leader who has final responsibility for its operations and policies. The highest-ranking editor of a publication may also be titled editor, managing ... is Waldo Vivallo (National Geology and Mining Service). References External links * Geology journals Geology of South America Geology of Antarctica Publications established in 1974 Andes Multilingual journals Open ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Salar De Antofalla
Salar de Antofalla is a salt flat in the Andes of Catamarca Province in the Argentine Northwest. The salt flat contains systems of oncoids that grow in the interface between proper salt flat and an adjacent wetlands. The geology surrounding the southern part of Salar de Antofalla is made up of continental (e.i. non-marine) sedimentary rock that deposited from Late Eocene to Early Pleistocene times. References Antofalla Antofalla Antofalla is a Miocene-Pliocene volcano in Argentina's Catamarca Province. It is part of the volcanic segment of the Andes in Argentina, and it is considered to be part of the Central Volcanic Zone, one of the volcanic zones of the Andes. Anto ... Landforms of Catamarca Province Puna de Atacama {{Catamarca-geo-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atacama Desert
The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in the world, and the second driest overall, just behind some very specific spots within the McMurdo Dry Valleys as well as the only hot true desert to receive less precipitation than the polar deserts, and the largest fog desert in the world. Both regions have been used as experimentation sites on Earth for Mars expedition simulations. The Atacama Desert occupies , or if the barren lower slopes of the Andes are included. Most of the desert is composed of stony terrain, salt lakes (''salares''), sand, and felsic lava that flows towards the Andes. The desert owes its extreme aridity to a constant temperature inversion due to the cool north-flowing Humboldt ocean current and to the presence of the strong Pacific anticyclone. The most arid re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Freising
Freising () is a university town in Bavaria, Germany, and the capital of the Freising ''Landkreis'' (district), with a population of about 50,000. Location Freising is the oldest town between Regensburg and Bolzano, and is located on the Isar river in Upper Bavaria, north of Munich and near the Munich International Airport. The city is built on and around two prominent hills: the Cathedral Hill with the former Bishop's Residence and Freising Cathedral, and Weihenstephan Hill with the former Weihenstephan Abbey, containing the oldest working brewery in the world. It was also the location of the first recorded tornado in Europe. The city is 448 meters above sea level. Cultural significance Freising is one of the oldest settlements in Bavaria, becoming a major religious centre in the early Middle Ages. It is the centre of an important diocese. Some important historical documents were created between 900 and 1200 in its monastery: * Freising manuscripts written in Slovenian, b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chiemsee
Chiemsee () is a freshwater lake in Bavaria, Germany, near Rosenheim. It is often called "the Bavarian Sea". The rivers Tiroler Achen and Prien flow into the lake from the south, and the river Alz flows out towards the north. The Alz flows into the Inn which then merges with the Danube. The Chiemsee is divided into the bigger, north section, in the northeast, called , and the , in the southwest. The Chiemgau, the region surrounding the Chiemsee, is a popular recreation area. Origin The Chiemsee was formed, like many other pre-alpine lakes, at the end of the last ice age about 10,000 years ago from a hollow carved out by a glacier (a ). Originally the lake covered an area of almost , which is about three times its present area. Within 10,000 years its area had shrunk to around . Before 1904 the water level was lowered by about a metre. As a result, large areas of dry land were reclaimed. Islands There are three main islands on the lake: Herreninsel ("gentlemen's island" ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
