Application of ostracod-based carbonate clumped-isotope thermometry to paleo-elevation reconstruction in a hydrologically complex setting: A case study from the northern Tibetan Plateau
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Ostracod
Elevation (ballistics)
Geochronology
Westerlies
Stromatolite
Paleoclimatology
Kalkowsky regarded stromatolites as laminated and microbial. Recognition of unlaminated microbial deposits, and also of biogenicity problems, subsequently resulted in broader definitions of the term stromatolite: (i) microbial but not necessarily laminated, and (ii) laminated but not necessarily organic. The first of these definitions does not discriminate between microbial deposits with markedly differing macrofabrics (such as thrombolite, dendrolite, etc.). The second purposely disregards origins and would apply the term stromatolite to both inorganic and organic deposits. Subsequent recognition of cognate terms (thrombolite, dendrolite, leiolite), and the umbrella term microbialite, has not resolved the question of stromatolite definition. Consequently, at least three long-standing definitions of stromatolite are available. These respectively emphasize the following features: (i) laminated and microbial, (ii) just microbial, (iii) just laminated. It is proposed to stabilize usage by adopting Kalkowsky's key points of laminated and microbial, supplemented by the adjective benthic, as expressed in the definition: 'a stromatolite is a laminated benthic microbial deposit'. This definition excludes non-laminated microbial deposits (e.g. thrombolites) that may have had a different accretion history, and also abiogenic laminites. Doubt concerning biogenicity can be expressed by the descriptors 'probable' and 'possible' stromatolite. The alternative to stipulating a microbial origin for stromatolites would defer, but not ultimately avoid, the key question of their origin.
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Microbial mat
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Stromatolites document microbial interactions with sediments and flowing water throughout recorded Earth history and have the potential to illuminate the long-term history of life and environments. Modern stromatolites, however, provide analogs to only a small subset of the structures preserved in Archean and Proterozoic carbonates. Thus, interpretations of secular trends in the shapes and textures of ancient columnar stromatolites require nonuniformitarian, scale-dependent models of microbial responses to nutrient availability, seawater chemistry, influx of sediment grains, shear, and burial. Models that integrate stromatolite scales, macroscopic organization, and shapes could also help test the biogenicity of the oldest stromatolites and other structures whose petrographic fabrics do not preserve direct evidence of microbial activity. An improved understanding of stromatolite morphogenesis in the presence of oxygenic and anoxygenic microbial mats may illuminate the diversity of microbial metabolisms that contributed to stromatolite growth in early oceans.
Stromatolite
Anoxygenic photosynthesis
Microbial mat
Geologic record
Snowball Earth
Early Earth
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Socheong island is a unique island containing Precambrian stromatolites in South Korea. Most of Socheong stromatolites are domes and columns, occurring as 10 cm to 1 m thick stromatolite beds. Lower parts of the stromatolite beds are predominantly composed of domes, but columns increase toward the upper level of stromatolite beds. In many of the stromatolite beds, inclined columns are easily identifiable, which is generally considered as a result of heliotropism. From general lithology, sedimentary structures, inclined angles and distributional pattern, and structural deformation of sedimentary rocks of Socheong island, the inclination of Socheong stromatolites could be better interpreted as a secondary structural deformation probably after formation of stromatolite columns, rather than as a result of heliotropism. However, at this moment, we do not clearly reject heliotropism interpretation for inclined columns of Socheong stromatolites. This is because the original position of stromatolite columns could have been lost if structural deformation had affected the whole sedimentary rocks of Socheong island.
Stromatolite
Lithology
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Ostracod
Assemblage (archaeology)
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Observations in South America based on paleoenvironmental data for the Last Glacial Maximum (LGM) that shows a generally lower temperatures and reduced precipitation of the region are compared to simulation results from the paleoclimate version of the National Center for Atmospheric Research coupled climate system model. Analyses of the LGM wind simulation for the tropical Atlantic show that the convergence zone does not extend all the way into South American continent during the Austral summer. This would have prevented moisture inflow into the adjacent continental area of equatorial northeastern Brazil. Interpretations of paleoclimate proxy records from this region are consistent with this scenario. In the subtropics, LGM westerlies were weaker and data show characteristics of more humid conditions. At higher latitudes model simulations suggest intensification of the westerlies which, in combination with colder sea surface temperatures would imply less moisture influx into the South American continent from the Atlantic sector. Low lake levels in high southern latitudes and general aridity would support the model findings.
Paleoclimatology
Westerlies
Last Glacial Maximum
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Socheong island is a unique island containing Precambrian stromatolites in South Korea. Most of Socheong stromatolites are domes and columns, occurring as 10 cm to 1 meter thick stromatolite beds. Lower parts of stromatolite beds are predominantly composed of domal stromatolites, while columns increase toward the upper level of stromatolite beds. In many of stromatolite beds, inclined columns are easily identifiable, which is generally considered as a result of heliotropism. From general lithology, sedimentary structures, inclined angles and distributional pattern, and structural deformation of sedimentary rocks of Socheong island, the inclination of Socheong stromatolites could be better interpreted as a secondary structural deformation probably after formation of stromatolite columns, rather than as a result of heliotropism. However, at this moment, we do not clearly reject heliotropism interpretation for inclined columns of Socheong stromatolites. This is because the original position of stromatolite columns were also lost if structural deformation would have affected throughout the whole sedimentary rocks of Socheong island.
Stromatolite
Lithology
Slumping
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ABSTRACT A Holocene paleoclimate record was constructed using two lacustrine cores from the high‐elevation Chilean Andes at ∼30°S latitude. Coarser and more poorly sorted grain‐size distributions and higher C/N ratios were interpreted as evidence for increased storm activity. Wet conditions prevailed from ∼10.8 to 9.5k cal a BP, then transitioned to dry conditions from ∼9.5 to 5.7k cal a BP interrupted by stormy conditions from ∼8.3 to 7.6k cal a BP. Wet conditions returned from ∼5.7k cal a BP to the present, interrupted by aridity from ∼4.1 to 2.2k cal a BP. This paleoclimate record is consistent with others from the region. The wet periods were probably caused by the influence of the Southern Westerlies, while dry conditions resulted from the influence of the Southeast Pacific Anticyclone. The increased storminess from ∼8.3 to 7.7k cal a BP may have been sourced from latitudinal shifts in the Intertropical Convergence Zone and subsequent weakening of the Westerlies, allowing the incursion of convective storms from east of the Andes. This sequence of events is consistent with synoptic conditions during modern easterly sourced storm activity. It is also consistent with modeling studies of the effect on the Southern Hemisphere of the rapid cooling of the North Atlantic Ocean during the 8.2‐ka event.
Westerlies
Paleoclimatology
Intertropical Convergence Zone
Anticyclone
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As the only known modern analogues to Precambrian stromatolites that formed in open marine environments, stromatolites in Exuma Cays, Bahamas, have been the subject of intense investigation for the past decade. Integrated studies relating stromatolite microstructure to microbial populations and processes have provided a model for lamination formation. The stromatolites are formed by lithifying microbial mats, with each subsurface layer representing a community that was, at one time, at the stromatolite surface.
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Microbial mat
Sedimentation
Algal mat
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As a main category of microbial carbonates,the thrombolite together with the oncolite is grouped into microphytolites and is used parallel to the stromatolite,whereas,thrombolites is still called catagraphites.As many stromatolites have clot fabrics,some geologists think that thrombolites can be translated as the Banlishi rather than the Ningkuaishi in Chinese.Thus,some confusion for the terminology of the thrombolite is casued,which may reflect the advancement on the study of the origin of the thrombolite and the microbial carbonate sedimentation.Resently,microbial carbonates are divided into four categories: stromatolite,thrombolite,dendrolite and leiolite. However,this classification does not include the oncolite that is grouped into the stromatolite,i.e.spheroidal stromatolite.While the studies of microbial carbonates have made many achievements,such as the 16 key events of geological evolution of overall formation of microbial carbonates summarized by Riding,the three precipitation forms of microbial carbonates in the Precambrian summarized by Grotzinger and James,and the grouping of blue-green algae into the cyanobacteria.However,it is difficult to clarify the actual growing mechanism of the stromatolite.The observation of the older thrombolites in the Precambrian shows that a concept that the thrombolite is the stromatolite deformed by bioturbation should not be true.Furthermore,the actual mechanism of the thrombolite remains uncertain similar to that of the stromatolite.Importantly,as a particular category of the microbial carbonate,some terminological confusions and changes for the cognition of the origin of the thrombolite provide an important clue for the understanding of the advances on the study of the microbial carbonates.
Stromatolite
Confusion
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