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1
Vidal, Gonzalo. "Proterozoic and Cambrian bioevents". Spanish Journal of Palaeontology 13, n. 3 (27 febbraio 2022): 11. http://dx.doi.org/10.7203/sjp.23973.
Testo completo
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Astafieva, M. M., S. B. Felitsyn e N. A. Alfimova. "Bacterial Remains in the Lower Proterozoic Red-Colored Quartzites". Paleontological Journal 55, n. 4 (luglio 2021): 447–54. http://dx.doi.org/10.1134/s003103012104002x.
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MOORE, KELSEY R., THEODORE M. PRESENT, FRANK PAVIA, JOHN P. GROTZINGER, JOSEPH RAZZELL HOLLIS, SUNANDA SHARMA, DAVID FLANNERY et al. "BIOSIGNATURE PRESERVATION AIDED BY ORGANIC-CATION INTERACTIONS IN PROTEROZOIC TIDAL ENVIRONMENTS". PALAIOS 37, n. 9 (15 settembre 2022): 486–98. http://dx.doi.org/10.2110/palo.2022.017.
Testo completoAbstract (sommario):
Abstract The preservation of organic biosignatures during the Proterozoic Eon required specific taphonomic windows that could entomb organic matter to preserve amorphous kerogen and even microbial body fossils before they could be extensively degraded. Some of the best examples of such preservation are found in early diagenetic chert that formed in peritidal environments. This chert contains discrete domains of amorphous kerogen and sometimes kerogenous microbial mat structures and microbial body fossils. Our understanding of how these exquisite microfossils were preserved and the balance between organic degradation and mineral formation has remained incomplete. Here, we present new insights into organic preservation in Proterozoic peritidal environments facilitated through interactions among organic matter, cations, and silica. Organic matter from Proterozoic peritidal environments is not preserved by micro- or cryptocrystalline quartz alone. Rather, preservation includes cation-rich nanoscopic phases containing magnesium, calcium, silica, and aluminum that pre-date chert emplacement and may provide nucleation sites for silica deposition and enable further chert development. Using scanning electron microscopy and elemental mapping with energy dispersive X-ray spectroscopy, we identify cation enrichment in Proterozoic organic matter and cation-rich nanoscopic phases that pre-date chert. We pair these analyses with precipitation experiments to investigate the role of cations in the precipitation of silica from seawater. Our findings suggest that organic preservation in peritidal environments required rapid formation of nanoscopic mineral phases through the interactions of organic matter with seawater. These organic-cation interactions likely laid the initial foundation for the preservation and entombment of biosignatures, paving the way for the development of the fossiliferous chert that now contains these biosignatures and preserves a record of Proterozoic life.
4
Gaucher, Claudio, Peter Sprechman e Alejandro Schipilov. "Upper and Middle Proterozoic fossiliferous sedimentary sequences of the Nico Pérez Terrane of Uruguay: Lithostratigraphic units, paleontology, depositional environments and correlations". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 199, n. 3 (24 aprile 1996): 339–67. http://dx.doi.org/10.1127/njgpa/199/1996/339.
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Holm-Denoma, Christopher S., William A. Matthews, Linda K. Soar, Mark W. Longman e James W. Hagadorn. "Provenance of Devonian–Carboniferous strata of Colorado: The influence of the Cambrian and the Proterozoic". Rocky Mountain Geology 57, n. 1 (1 giugno 2022): 1–21. http://dx.doi.org/10.24872/rmgjournal.57.1.1.
Testo completoAbstract (sommario):
ABSTRACT We report new LA-ICP-MS U–Pb detrital zircon ages and sedimentary petrology of silty to sandy limestones and dolostones, as well as calcareous to dolomitic sandstones of the Devonian–Carboniferous (Mississippian) Chaffee Group. We also report new detrital zircon ages from the late Cambrian Sawatch Quartzite, and a U–Pb zircon crystallization age on a late Mesoproterozoic (1087.9 ± 13.5 Ma) granitoid of underlying basement from the Eagle Basin of northwest Colorado. Grain populations in the Chaffee Group are mostly bimodal. More than 84% of zircons centered around a Paleoproterozoic (ca. 1.78 Ga) mode typical of the Yavapai province that forms much of the basement of Colorado and an early Mesoproterozoic (ca. 1.42 Ga) mode typical of A-type granites that intrude this region. A notable late Mesoproterozoic (ca. 1.08 Ga) mode exists in some Chaffee samples, giving those samples a trimodal detrital zircon age distribution. These bipartite or tripartite detrital zircon age modes exist in Cambrian, Devonian, and Carboniferous strata from paleogeographically adjacent successions, but the correlation between the Chaffee zircons is highest with the region’s basal Cambrian sandstones of the Sawatch Quartzite, Flathead Sandstone, and Ignacio Quartzite, which have similar (ca. 1.08 Ga, 1.43 Ga, 1.70 Ga, respectively) zircon populations, and a paucity of > 1.8 Ga grains. This similarity suggests that most grains in the Chaffee Group derive from recycling of these basal sandstones, and that little sediment was derived directly from thenexposed Precambrian basement highs, from the Wyoming craton to the north, or from Paleoproterozoic arcs and orogens to the west and northeast. Minor Mesoarchean to early Paleoproterozoic (ca. 3.00 to 2.40 Ga) grains exist in the Chaffee Group, an attribute shared by the Late Ordovician Harding Sandstone of Colorado’s Front Range, but that is absent from the region’s underlying Cambrian sandstones—suggesting some recycled mixture of Cambrian and Ordovician sedimentary rocks. No near-depositional age grains are present in the Chaffee Group. The youngest grain is Early Devonian (~417 Ma), > 45 million years (m.y.) older than these strata. Additionally, Paleozoic grains are extremely uncommon (< 0.1%; n = 2,927 grains).
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Xiao, Shuhai, e Qing Tang. "After the boring billion and before the freezing millions: evolutionary patterns and innovations in the Tonian Period". Emerging Topics in Life Sciences 2, n. 2 (29 giugno 2018): 161–71. http://dx.doi.org/10.1042/etls20170165.
Testo completoAbstract (sommario):
The Tonian Period (ca. 1000–720 Ma) follows the ‘boring billion' in the Mesoproterozoic Era and precedes ‘snowball Earth' glaciations in the Cryogenian Period. It represents a critical transition in Earth history. Geochemical data indicate that the Tonian Period may have witnessed a significant increase in atmospheric pO2 levels and a major transition from predominantly sulfidic to ferruginous mid-depth seawaters. Molecular clock estimates suggest that early animals may have diverged in the Tonian Period, raising the intriguing possibility of coupled environmental changes and evolutionary innovations. The co-evolution of life and its environment during the Tonian Period can be tested against the fossil record by examining diversity trends in the Proterozoic and evolutionary innovations in the Tonian. Compilations of Proterozoic microfossils and macrofossils apparently support a Tonian increase in global taxonomic diversity and morphological range relative to the Mesoproterozoic Era, although this is not reflected in assemblage-level diversity patterns. The fossil record suggests that major eukaryote groups (including Opisthokonta, Amoebozoa, Plantae, and SAR) may have diverged and important evolutionary innovations (e.g. multicellularity and cell differentiation in several groups, eukaryovory, eukaryote biomineralization, and heterocystous cyanobacteria) may have arisen by the Tonian Period, but thus far no convincing animal fossils have been found in the Tonian. Tonian paleontology is still in its nascent stage, and it offers many opportunities to explore Earth-life evolution in this critical geological period.
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Duda, Jan-Peter, Hannah König, Manuel Reinhardt, Julia Shuvalova e Pavel Parkhaev. "Molecular fossils within bitumens and kerogens from the ~ 1 Ga Lakhanda Lagerstätte (Siberia, Russia) and their significance for understanding early eukaryote evolution". PalZ 95, n. 4 (dicembre 2021): 577–92. http://dx.doi.org/10.1007/s12542-021-00593-4.
Testo completoAbstract (sommario):
AbstractThe emergence and diversification of eukaryotes during the Proterozoic is one of the most fundamental evolutionary developments in Earth’s history. The ca. 1-billion-year-old Lakhanda Lagerstätte (Siberia, Russia) contains a wealth of eukaryotic body fossils and offers an important glimpse into their ecosystem. Seeking to complement the paleontological record of this remarkable lagerstätte, we here explored information encoded within sedimentary organic matter (total organic carbon = 0.01–1.27 wt.%). Major emphasis was placed on sedimentary hydrocarbons preserved within bitumens and kerogens, including molecular fossils (or organic biomarkers) that are specific to bacteria and eukaryotes (i.e. hopanes and regular steranes, respectively). Programmed pyrolysis and molecular organic geochemistry suggest that the organic matter in the analyzed samples is about peak oil window maturity and thus sufficiently well preserved for detailed molecular fossil studies that include hopanes and steranes. Together with petrographic evidence as well as compositional similarities of the bitumens and corresponding kerogens, the consistency of different independent maturity parameters establishes that sedimentary hydrocarbons are indigenous and syngenetic to the host rock. The possible presence of trace amounts of hopanes and absence of steranes in samples that are sufficiently well preserved to retain both types of compounds evidences an environment dominated by anaerobic bacteria with no or very little inputs by eukaryotes. In concert with the paleontological record of the Lakhanda Lagerstätte, our study adds to the view that eukaryotes were present but not significant in Mesoproterozoic ecosystems.
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Horodyski, Robert J. "Paleontology of proterozoic shales and mudstones: examples from the Belt supergroup, Chuar group and Pahrump group, western USA". Precambrian Research 61, n. 3-4 (marzo 1993): 241–78. http://dx.doi.org/10.1016/0301-9268(93)90116-j.
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PRATT, BRIAN R. "KINNEYIA-TYPE WRINKLE STRUCTURES ON SANDSTONE BEDS: NOT MICROBIALLY INDUCED BUT DEFORMATION FEATURES CAUSED BY SYNSEDIMENTARY EARTHQUAKES". PALAIOS 36, n. 10 (27 ottobre 2021): 313–25. http://dx.doi.org/10.2110/palo.2021.015.
Testo completoAbstract (sommario):
ABSTRACT A category of wrinkle structures, often termed Kinneyia structure or Runzel marks, comprises bedding plane features consisting typically of anastomosing, low-relief, flat-topped ridges with intervening depressions. Topographic relief is usually less than a millimeter. They are locally common on the upper surfaces of fine- to medium-grained sandstone beds interbedded with mudstone deposited in offshore settings, especially in Precambrian and lower Paleozoic strata but as young as Cretaceous. For more than the last two decades these wrinkle structures have been widely regarded as due to microbial mats, and have been taken as evidence for dominance in the Proterozoic of microbially stabilized sediment and, in the Phanerozoic, a matground marine benthic ecology which gradually gave way to a mixground ecology. The detailed morphology and cross-cutting relationships demonstrated by a range of specimens of Proterozoic, Cambrian, and Silurian age, however, cast this interpretation into doubt. The relationship between the wrinkled surface and bioclasts such as shells and both prior- and later-formed scour surfaces, and horizontal and vertical burrows show that these wrinkles did not develop due to the surface topography of microbial mats or compaction of microbial mats during burial, but instead formed at the top of a sand bed at the interface with an overlying layer of mud. Deformation is ascribed to vibration from low-magnitude earthquakes. The presence in some units of small-scale sedimentary dikelets and crack arrays that formed later after some stiffening, along with locally associated seismites and other evidence for nearby faulting, show that syndepositional tectonic activity was not unexpected and support the interpretation that this category of wrinkle structures is a type of seismite.
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Tang, Qing, Ke Pang, Guangjin Li, Lei Chen, Xunlai Yuan, Mukund Sharma e Shuhai Xiao. "The Proterozoic macrofossil Tawuia as a coenocytic eukaryote and a possible macroalga". Palaeogeography, Palaeoclimatology, Palaeoecology 576 (agosto 2021): 110485. http://dx.doi.org/10.1016/j.palaeo.2021.110485.
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Jaziri, Adam Yassin, Benjamin Charnay, Franck Selsis, Jérémy Leconte e Franck Lefèvre. "Dynamics of the Great Oxidation Event from a 3D photochemical–climate model". Climate of the Past 18, n. 10 (25 ottobre 2022): 2421–47. http://dx.doi.org/10.5194/cp-18-2421-2022.
Testo completoAbstract (sommario):
Abstract. From the Archean toward the Proterozoic, the Earth's atmosphere underwent a major shift from anoxic to oxic conditions at around 2.4 to 2.1 Ga known as the Great Oxidation Event (GOE). This rapid transition may be related to an atmospheric instability caused by the formation of the ozone layer. Previous works were all based on 1D photochemical models. Here, we revisit the GOE with a 3D photochemical–climate model to investigate the possible impact of the atmospheric circulation and the coupling between the climate and the dynamics of the oxidation. We show that the diurnal, seasonal and transport variations do not bring significant changes compared to 1D models. Nevertheless, we highlight a temperature dependence for atmospheric photochemical losses. A cooling during the late Archean could then have favored the triggering of the oxygenation. In addition, we show that the Huronian glaciations, which took place during the GOE, could have introduced a fluctuation in the evolution of the oxygen level. Finally, we show that the oxygen overshoot, which is expected to have occurred just after the GOE, was likely accompanied by a methane overshoot. Such high methane concentrations could have had climatic consequences and could have played a role in the dynamics of the Huronian glaciations.
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García, Marcelo, Germán Aguilar, María Pía Rodríguez e James Metcalf. "(U-Th)/He ages of Proterozoic-Paleozoic basement rocks from northern Chile (18-19° S) and implications on the Neogene uplift history of the Western Cordillera". Andean Geology 49, n. 3 (30 settembre 2022): 313. http://dx.doi.org/10.5027/andgeov49n3-3402.
Testo completoAbstract (sommario):
In the Western Cordillera of northern Chile, the Proterozoic-Paleozoic Belén Metamorphic Complex is covered by late Oligocene-early Miocene (25-18 Ma) rocks, and both units are involved in west-vergent contractional deformation, which results in exhumation. A Miocene age (18 to 6 Ma) for deformation has been previously constrained by stratigraphy and cross-cutting relationships. To understand the youngest exhumation event and reverse faulting, we obtained 21 (U-Th)/He ages from two samples of the metamorphic rocks and the associate inverse thermal modeling. Five zircon (U-Th)/He ages from one sample are 113 to 226 Ma, very scattered, while five zircon ages from the other, are 20 to 49 Ma. The high dispersion of zircon (U-Th)/He data prevents the geological interpretation of results. Apatite grains from both samples yielded 11 (U-Th)/He ages between 10.4 and 18.7 Ma, with 9 values from 12.0 to 15.5 Ma. A slight positive correlation between apatite single-grain dates and effective uranium for 4 crystals of one sample
suggests relatively slow cooling. The T-t model including these 4 apatite ages shows continuous cooling from 15 to 0 Ma with a relatively more marked cooling period at 11-7 Ma. The middle-late Miocene thermal signal agrees with the geologic evolution of the region and would permit to date the last activity of the Chapiquiña-Belén reverse fault, which
uplifted and exhumed the metamorphic rocks. This signal is relatively similar to that the eastern Altiplano, but differs considerably from that the forearc.
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Repetski, J. E., M. E. Taylor, D. S. Collins, A. R. Palmer, G. D. Wood e R. C. Tobin. "Integrating paleontology, geothermometry, and sedimentology in determining the history of the Reelfoot Basin, southern midcontinent, U.S.A." Paleontological Society Special Publications 6 (1992): 243. http://dx.doi.org/10.1017/s2475262200008030.
Testo completoAbstract (sommario):
The northeast-trending Reelfoot basin, extending from northeast Arkansas and westernmost Tennessee into southeastern Missouri, southernmost Illinois, and westernmost Kentucky, is geologically, and socioeconomically, significant because it is co-extensive with the New Madrid Seismic Zone, one of the most seismically active areas of the central and eastern United States. The basin has been periodically active from its inception as a rift basin in the Proterozoic to the present and has accumulated up to at least 5,000 m of sediment, including up to at least 1 km of Cretaceous and Tertiary sedimentary strata near the head of the Mississippi Embayment. Structural and stratigraphic interpretations within the subsurface pre-Mesozoic part of the basin have been based almost entirely on geophysical and physical stratigraphic criteria; these interpretations have been loosely constrained due to an extreme sparsity of drillhole data through the Paleozoic sequence. Recent analysis of Cambrian and Ordovician fossils (conodonts, palynomorphs, brachiopods, and trilobites) from cuttings and core from a very few drillholes allows establishment of the beginnings of a verifiable stratigraphy for this part of the sequence. The paleontological data also provide (1) biofacies evidence for interpretations of the depositional setting during part of the Late Cambrian and Early Ordovician interval and (2) thermal maturation data pertaining to the post-depositional geothermal history of these strata.Upper Cambrian phosphatic brachiopods and trilobites provide improved correlations between strata in the basin, the Ozark shelf to the northwest, and the Upper Mississippi River Valley. Cold-water-realm palynomorphs and trilobites from siliciclastic rocks of turbiditic origin in the central part of the Reelfoot basin support an interpretation, based on sedimentary structures in a short interval of core, of a deep-water basinal origin for these strata.Lower Ordovician conodonts provide a biostratigraphy for the carbonate rocks of this part of the sequence; correlations can be made with the shallow-water sequences of the Knox, Prairie du Chien, and Arbuckle Groups, and the Ozark sequence of the adjacent shelf areas to the east, north, and west. The uppermost Lower Ordovician strata in the basin record a short-term incursion of cooler water environments, reflected by the character of both the conodont fauna and the lithofacies. The youngest Paleozoic dates known from the basin south of the Pascola arch are latest Ibexian (Early Ordovician).Thermal alteration indices of both the Cambrian palynomorphs (organic-walled microphytoplankton) and Ordovician conodonts in the deeper parts of the basin, corroborated by fluid inclusion thermometry, vitrinite reflectance, and other geochemical techniques, are of higher values than predicted using any published estimates of overburden burial. These maturation values most likely reflect burial enhanced by the passage of hydrothermal fluids on a regional scale; they place constraints on interpretations of the tectonothermal evolution of the basin.
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Baldermann, Andre, Oliver Wasser, Elshan Abdullayev, Stefano Bernasconi, Stefan Löhr, Klaus Wemmer, Werner E. Piller, Maxim Rudmin e Sylvain Richoz. "Palaeo-environmental evolution of Central Asia during the Cenozoic: new insights from the continental sedimentary archive of the Valley of Lakes (Mongolia)". Climate of the Past 17, n. 5 (29 settembre 2021): 1955–72. http://dx.doi.org/10.5194/cp-17-1955-2021.
Testo completoAbstract (sommario):
Abstract. The Valley of Lakes basin (Mongolia) contains a unique continental sedimentary archive, suitable for constraining the influence of tectonics and climate change on the aridification of Central Asia in the Cenozoic. We identify the sedimentary provenance, the (post)depositional environment and the palaeo-climate based on sedimentological, petrographical, mineralogical, and (isotope) geochemical signatures recorded in authigenic and detrital silicates as well as soil carbonates in a sedimentary succession spanning from ∼34 to 21 Ma. The depositional setting was characterized by an ephemeral braided river system draining prograding alluvial fans, with episodes of lake, playa or open-steppe sedimentation. Metamorphics from the northern adjacent Neoarchean to late Proterozoic hinterlands provided a continuous influx of silicate detritus to the basin, as indicated by K–Ar ages of detrital muscovite (∼798–728 Ma) and discrimination function analysis. The authigenic clay fraction is dominated by illite–smectite and “hairy” illite (K–Ar ages of ∼34–25 Ma), which formed during coupled petrogenesis and precipitation from hydrothermal fluids originating from major basalt flow events (∼32–29 and ∼29–25 Ma). Changes in hydroclimate are recorded in δ18O and δ13C profiles of soil carbonates and in silicate mineral weathering patterns, indicating that comparatively humid to semi-arid conditions prevailed in the late(st) Eocene, changing into arid conditions in the Oligocene and back to humid to semi-arid conditions in the early Miocene. Aridification steps are indicated at ∼34–33, ∼31, ∼28 and ∼23 Ma and coincide with some episodes of high-latitude ice-sheet expansion inferred from marine deep-sea sedimentary records. This suggests that long-term variations in the ocean–atmosphere circulation patterns due to pCO2 fall, reconfiguration of ocean gateways and ice-sheet expansion in Antarctica could have impacted the hydroclimate and weathering regime in the basin. We conclude that the aridification in Central Asia was triggered by reduced moisture influx by westerly winds driven by Cenozoic climate forcing and the exhumation of the Tian Shan and Altai Mountains and modulated by global climate events.
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Culver, Stephen J., John E. Repetski, John Pojeta e David Hunt. "Early and Middle(?) Cambrian metazoan and protistan fossils from West Africa". Journal of Paleontology 70, n. 1 (gennaio 1996): 1–6. http://dx.doi.org/10.1017/s0022336000023052.
Testo completoAbstract (sommario):
Supposed Upper Proterozoic strata in the southwest Taoudeni Basin, Guinea and Senegal, and from the Mauritanide fold belt, Mauritania, have yielded mostly poorly preserved small skeletal fossils of metazoan and protistan origin. Problematic, but possible echinoderm material and spicules of the heteractinid sponge Eiffelia dominate the Taoudeni Basin assemblage. The age of the material is not certain but the paleontologic data suggest an Early Cambrian age for the stratigraphically lowest faunas, and a Middle Cambrian age is possible for the stratigraphically highest collections.
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Botor, Dariusz, Stanisław Mazur, Aneta A. Anczkiewicz, István Dunkl e Jan Golonka. "Thermal history of the East European Platform margin in Poland based on apatite and zircon low-temperature thermochronology". Solid Earth 12, n. 8 (20 agosto 2021): 1899–930. http://dx.doi.org/10.5194/se-12-1899-2021.
Testo completoAbstract (sommario):
Abstract. The Phanerozoic tectonothermal evolution of the SW slope of the East European Platform (EEP) in Poland is reconstructed by means of thermal maturity, low-temperature thermochronometry, and thermal modelling. We provide a set of new thermochronometric data and integrate stratigraphic and thermal maturity information to constrain the burial and thermal history of sediments. Apatite fission track (AFT) analysis and zircon (U-Th)/He (ZHe) thermochronology have been carried out on samples of sandstones, bentonites, diabase, and crystalline basement rocks collected from 17 boreholes located in central and NE Poland. They penetrated sedimentary cover of the EEP subdivided from the north to south into the Baltic, Podlasie, and Lublin basins. The average ZHe ages from Proterozoic basement rocks as well as Ordovician to Silurian bentonites and Cambrian to lower Carboniferous sandstones range from 848 ± 81 to 255 ± 22 Ma with a single early Permian age of 288 Ma, corresponding to cooling after a thermal event. The remaining ZHe ages represent partial reset or source ages. The AFT ages of samples are dispersed in the range of 235.8 ± 17.3 Ma (Middle Triassic) to 42.1 ± 11.1 Ma (Paleogene) providing a record of Mesozoic and Cenozoic cooling. The highest frequency of the AFT ages is in the Jurassic and Early Cretaceous prior to Alpine basin inversion. Thermal maturity results are consistent with the SW-ward increase of the Paleozoic and Mesozoic sediments thickness. An important break in a thermal maturity profile exists across the base Permian–Mesozoic unconformity. Thermal modelling showed that significant heating of Ediacaran to Carboniferous sedimentary successions occurred before the Permian with maximum paleotemperatures in the earliest and latest Carboniferous for Baltic–Podlasie and Lublin basins, respectively. The results obtained suggest an important role of early Carboniferous uplift and exhumation at the SW margin of the EEP. The SW slope of the latter was afterward overridden in the Lublin Basin by the Variscan orogenic wedge. Its tectonic loading interrupted Carboniferous uplift and caused resumption of sedimentation in the late Viséan. Consequently, a thermal history of the Lublin Basin is different from that in the Podlasie and Baltic basins but similar to other sections of the Variscan foreland, characterized by maximum burial at the end of Carboniferous. The Mesozoic thermal history was characterized by gradual cooling from peak temperatures at the transition from Triassic to Jurassic due to decreasing heat flow. Burial caused maximum paleotemperatures in the SW part of the study area, where the EEP was covered by an extensive sedimentary pile. However, further NE, due to low temperatures caused by shallow burial, the impact of fluids can be detected by vitrinite reflectance, illite/smectite, and thermochronological data. Our new results emphasize the importance of using multiple low-temperature thermochronometers and thermal modelling in connection with thermal maturity analysis to elucidate the near-surface evolution of platform margins.
17
Palacios, Teodoro. "Gonzalo Vidal (1943-1997): una vida dedicada a la investigación en micropaleontología del Precámbrico". Spanish Journal of Palaeontology 13, n. 3 (27 febbraio 2022): 5. http://dx.doi.org/10.7203/sjp.23972.
Testo completoAbstract (sommario):
El comienzo del año 1997 nos trajo una triste noticia, el profesor Gonzalo Vidal había fallecido el 10 de enero en Uppsala (Suecia) a causa de un infarto. Para los que le conocíamos y habíamos tenido el honor de compartir su trabajo, suponía una ausencia irreparable tanto en el sentido personal como en el científico; para la comunidad científica, la perdida de uno de los mejores investigadores que ha dado la ciencia española en el campo de la Paleontología. Sus investigaciones estaban centradas en el estudio de microbiotas de edad Proterozoico-Cámbrico (1.700- 500 Ma.) y su área de investigaci6n abarcaba todo el mundo; como el mismo solía decir, la ciencia aborda problemas cuya solución no depende de las fronteras
18
Schopf, J. William. "Precambrian Prokaryotes and Stromatolites". Notes for a Short Course: Studies in Geology 18 (1987): 20–33. http://dx.doi.org/10.1017/s0271164800001482.
Testo completoAbstract (sommario):
In terms of biochemical and intracellular organization, living systems can be divided into two major “Superkingdoms,” eukaryotes and prokaryotes.Eukaryotes, comprising the more advanced and later evolving Superkingdom, include unicellular or multicellular organisms (viz., members of the Kingdoms Protista, Fungi, Plantae and Animalia) characterized by nucleus-, mitochondrion-, and (in plants and some protists) chloroplast-containing cells that are capable typically of mitotic cell division. Paleontologic evidence indicates that the eukaryotic cell originated during the Middle Proterozoic, probably about 1.4 to 1.5 Ga ago (Schopf and Oehler, 1976).Prokaryotes, comprising the more primitive and earlier evolving Superkingdom, include microbial microorganisms (viz., members of the Kingdom Monera: bacteria, cyanobacteria, archaebacteria, and prochlorophytes) characterized by cells that lack membrane-bound nuclei, mitochondria, chloroplasts, and similar organelles and that reproduce by non-mitotic and non-meiotic division. Some authors (e.g., Woese and Fox, 1977) subdivide prokaryotes (monerans) into two kingdoms, the Kingdom Archaebacteriae (including methanogenic, extremely halophilic and some thermoacidophilic bacteria) and the Kingdom Eubacteriae (including all non-archaebacterial prokaryotes), based on the chemistry of their cell walls, membranes, transfer RNA's and RNA polymerase subunits. Paleontologic evidence indicates that prokaryotes originated early in Earth history - the group was extant, morphologically varied and evidently physiologically advanced at least as early as 3.3 to 3.5 Ga ago (Schopf and Packer, 1987).
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Zabini, Carolina, e Maria Antônia Michels Souza. "Três conceitos biológicos/paleontológicos que seguem as diretrizes dos PCN do ensino médio para aplicação em aulas de Biologia". Terrae Didatica 12, n. 2 (2 agosto 2016): 104. http://dx.doi.org/10.20396/td.v12i2.8646319.
Testo completoAbstract (sommario):
Este artigo visa apresentar três exemplos de aplicação de temas paleobiológicos aplicáveis a salas de aulas do Ensino Médio (EM), conforme as sugestões de interdisciplinaridade de conteúdo em Biologia encontradas nos parâmetros curriculares nacionais (PCNEM). O principal objetivo é fornecer, a professores do EM, exemplos de conceitos que não estão facilmente acessíveis a eles na bibliografia destes anos iniciais. O uso destes conceitos em aula visa não somente formar alunos com conhecimentos práticos e contextualizados (para a vida profissional), mas também conhecimentos mais amplos e abstratos, com o intuito de que adquiram uma visão cultural ampla e construam sua visão de mundo (formação do cidadão). Os conteúdos abordados são as mudanças ecológicas ocorridas no Éon Proterozoico, resultantes da atividade biótica, a evolução das ciências e o tempo profundo. Cada conceito é dividido em três partes: contextualização e aplicação, detalhamento da abordagem e atividade. Na contextualização o embasamento teórico e o referencial bibliográfico do assunto são fornecidos. No detalhamento sugerem-se as formas de abordagem do conteúdo em sala de aula, a união a conceitos de áreas externas à Biologia e os materiais necessários à aplicação da atividade. Por fim, há a explanação da atividade em si. Os três conceitos (mudanças ambientais passadas, desenvolvimento da ciência e tempo profundo) não se referem somente à Paleontologia, mas ao próprio desenvolvimento das Ciências em geral. Envolvem também contextos paleoambientais e questões centrais na evolução dos organismos e de nosso planeta, fornecendo uma visão ampla de assuntos que normalmente são vistos em sala de aula de maneira compartimentalizada. Tais exemplos em aula devem ser abordados de maneira interdisciplinar, devendo, sempre que possível, contar com a participação de mais de um professor
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Sawin, Robert S., Evan K. Franseen, Greg A. Ludvigson, W. Lynn Watney e Ronald R. West. "Precambrian Nomenclature in Kansas". Current Research in Earth Sciences, 11 aprile 2013, 1–5. http://dx.doi.org/10.17161/cres.v0i259.11840.
Testo completoAbstract (sommario):
The informal stratigraphic term "Precambrian" is replaced by formal nomenclature--Proterozoic and Archean Eonothems/Eons--and the informal term Hadean. The Phanerozoic Eonothem/Eon, representing all rocks younger than the Proterozoic, is added. The Proterozoic is further divided into Paleoproterozoic, Mesoproterozoic, and Neoproterozoic Erathems/Eras. The name Rice Formation (Scott, 1966) is abandoned, and the use of the informal term "Rice unit" is recommended. The proposed name Rice Series (Berendsen, 1994) is not accepted. These changes are adopted by the Kansas Geological Survey (KGS) and the stratigraphic nomenclature of Zeller (1968) has been revised accordingly.
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Sawin, Robert S., Evan K. Franseen, Greg A. Ludvigson, W. Lynn Watney e Ronald R. West. "Precambrian Nomenclature in Kansas". Current Research in Earth Sciences, 11 aprile 2013, 1–5. http://dx.doi.org/10.17161/cres.v0i259.11840.
Testo completoAbstract (sommario):
The informal stratigraphic term "Precambrian" is replaced by formal nomenclature--Proterozoic and Archean Eonothems/Eons--and the informal term Hadean. The Phanerozoic Eonothem/Eon, representing all rocks younger than the Proterozoic, is added. The Proterozoic is further divided into Paleoproterozoic, Mesoproterozoic, and Neoproterozoic Erathems/Eras. The name Rice Formation (Scott, 1966) is abandoned, and the use of the informal term "Rice unit" is recommended. The proposed name Rice Series (Berendsen, 1994) is not accepted. These changes are adopted by the Kansas Geological Survey (KGS) and the stratigraphic nomenclature of Zeller (1968) has been revised accordingly.
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Bittencourt, Jonathas S., Matheus Kuchenbecker, André Gomide Vasconcelos e Karin E. B. Meyer. "O REGISTRO FÓSSIL DAS COBERTURAS SEDIMENTARES DO CRÁTON DO SÃO FRANCISCO EM MINAS GERAIS". Geonomos, 31 dicembre 2015. http://dx.doi.org/10.18285/geonomos.v23i2.710.
Testo completoAbstract (sommario):
O registro fóssil dos depósitos sedimentares proterozoicos, paleozoicos e mesozoicos do Cráton do São Francisco inclui estruturas de origem microbiana (microbialitos, oncólitos), palinomorfos terrestres e marinhos, microfósseis silicosos e carbonáticos de origem marinha, metazoários neoproterozoicos, artrópodes, uma variedade de bioturbações, vertebrados actinopterígios, sarcopterígios e dinossauros. Com exceção dos microbialitos, que são amplamente distribuídos, os fósseis são relativamente escassos se comparados com a extensão geográfica dos depósitos e concentrados em alguns horizontes estratigráficos excepcionais. A raridade dos achados pode ser explicada pela falta de prospecção nas áreas mais distantes das localidades tradicionalmente conhecidas, e também ao baixo potencial de preservação dos fósseis em ambientes deposicionais do Meso e Neoproterozoico, ou de regimes climáticos extremos, i.e. glacial para o Paleozoico e desértico para as porções mesozoicas da Bacia Sanfranciscana. Trabalhos recentes de prospecção, no entanto, têm revelado um potencial significativo para novas descobertas, especialmente na região norte de Minas Gerais. Parte dos registros cenozoicos está distribuída em bacias restritas incluindo as de Gandarela e Fonseca (Eoceno-Mioceno), onde basicamente se preservou folhas de angiospermas e gimnospermas, palinomorfos e insetos, e a Bacia de Juatuba, com registro predominante de folhas de angiospermas O Quaternário constitui uma exceção do ponto de vista da diversidade e abundância de fósseis, especialmente devido à ampla ocorrência de mamíferos em sistemas cársticos. A descontinuidade dos depósitos sedimentares no Cráton do São Francisco mostram hiatos de cerca de 250 milhões de anos entre as seções fossilíferas paleozoicas e de cerca de 125 milhões de anos (Eocretáceo ao Pleistoceno) para a fauna de vertebrados. Palavras-chave: paleontologia, bacias sedimentares, registro fóssil, Proterozoico, Mesozoico, Cenozoico Abstract: THE FOSSIL RECORD OF THE SEDIMENTARY COVERS OF THE SÃO FRANCISCO CRATON IN MINAS GERAIS. The fossil record of the Proterozoic, Paleozoic and Mesozoic sedimentary deposits of the São Francisco Craton includes microbial structures (microbialites and oncoliths), terrestrial and marine palynomorphs, siliceous and calcareous marine microfossils, Neoproterozoic metazoans, arthropods, a variety of bioturbations, actinopterygians, sarcopterygians and dinosaurs. Except for the microbialites, which are widely distributed, the fossils are relatively scarce if compared with the geographic extension of the deposits and concentrated in some exceptional sedimentary horizons. The rarity of the findings can be explained by the lack of fieldwork far from the localities traditionally explored, and the low potential of fossil preservation in paleoenvironments of Paleo and Mesoproterozoic or those under extreme climatic regimes, i.e. glacial for the Paleozoic rocks and desertic for most of the Mesozoic rocks within the Sanfranciscana Basin. On the other hand, recent works have revealed a significant potential for new discoveries, especially in northern Minas Gerais. Part of the Cenozoic record is distributed across restrict basins, including Gandarela and Fonseca (Eocene-Miocene), where basically leaves of angiosperms and gymnosperms, palynomorphs and insects are preserved, and the Juatuba Basin, with predominant record of angiosperm leaves. The Quaternary is an exception of fossil diversity and abundance, due to the widespread occurrence of mammals in karstic deposits. The discontinuity of the sedimentary deposits in the São Francisco Craton shows gaps in the fossil record, which encompass c. 250 my between the Neoproterozoic and Paleozoic, and c. 125 my (Early Cretaceous to Pleistocene) for the vertebrate fauna. Keywords: paleontology, sedimentary basins, fossil record, Proterozoic, Mesozoic, Cenozoic
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García, Marcelo, Germán Aguilar, María Pía Rodríguez e James Metcalf. "(U-Th)/He ages of Proterozoic-Paleozoic basement rocks from northern Chile (18-19°S) and implications on the Neogene uplift history of the Western Cordillera". Andean Geology 49, n. 3 (7 giugno 2022). http://dx.doi.org/10.5027/andgeov49n3-3477.
Testo completoAbstract (sommario):
In the Western Cordillera of northern Chile, the Proterozoic-Paleozoic Belén Metamorphic Complex is covered by late Oligocene-early Miocene (25-18 Ma) rocks, and both units are involved in west-vergent contractional deformation, which results in exhumation. A Miocene age (18 to 6 Ma) for deformation has been previously constrained by stratigraphy and cross-cutting relationships. To understand the youngest exhumation event and reverse faulting, we obtained 21 (U-Th)/He ages from two samples of the metamorphic rocks and the associate inverse thermal modeling. Five zircon (U-Th)/He ages from one sample are 113 to 226 Ma, very scattered, while five zircon ages from the other, are 20 to 49 Ma. The high dispersion of zircon (U-Th)/He data prevents the geological interpretation of results. Apatite grains from both samples yielded 11 (U-Th)/He ages between 10.4 and 18.7 Ma, with 9 values from 12.0 to 15.5 Ma. A slight positive correlation between apatite single-grain dates and effective uranium for 4 crystals of one sample suggests relatively slow cooling. The T-t model including these 4 apatite ages shows continuous cooling from 15 to 0 Ma with a relatively more marked cooling period at 11-7 Ma. The middle-late Miocene thermal signal agrees with the geologic evolution of the region and would permit to date the last activity of the Chapiquiña-Belén reverse fault, which uplifted and exhumed the metamorphic rocks. This signal is relatively similar to that the eastern Altiplano, but differs considerably from that the forearc.
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Fraga, Lucio Mauro Soares, Soraya de Carvalho Neves, Gabriela Luiza Pereira Pires, Adriano Luiz Tibães e Alexandre Uhlein. "ESTROMATÓLITOS COLUNARES NA BASE DO GRUPO MACAÚBAS, NORDESTE DA SERRA DO ESPINHAÇO (MG): PALEONTOLOGIA E AMBIENTE DE SEDIMENTAÇÃO". Geonomos, 31 luglio 2013. http://dx.doi.org/10.18285/geonomos.v21i1.254.
Testo completoAbstract (sommario):
Na região nordeste da Serra do Espinhaço Meridional são encontrados metassedimentos da base do Grupo Macaúbas,constituídos por quartzitos, camadas de metapelitos e rochas metacarbonáticas, depositadas em diferentes ambientes de sedimentação:continental, transicional e marinho. Na Formação Domingas ocorrem camadas de metapelitos contendo lentes isoladas de dolomitos comum rico conteúdo paleontológico formado por estruturas estromatolíticas colunares. Em trabalhos de campo recentes foram encontradas edescritas duas lentes de dolomitos na região de Inhaí (região da Fazenda Boqueirão) e uma lente já conhecida, localizada na calha do RioJequitinhonha. Nestas regiões foram descritas a morfologia e a geometria das estruturas biogênicas, além da petrografia das rochascarbonáticas e das rochas metapelíticas associadas. Este estudo concentra-se na descrição dos morfotipos de estromatólitos, classificadosde acordo com sua macro e mesoestrutura, conforme o grau de herança laminar e o tipo de ramificações encontradas. Desta forma, foramidentificados dois morfotipos distintos de estromatólitos onde, as formas cônicas sem ramificações, apresentaram alto grau de herançalaminar, sendo então classificados como Conophyton garganicum. As formas ramificadas, geralmente com dicotomas paralelos e decrescimento muito convexo, foram classificadas como Jacutophyton. A geometria dos corpos dolomíticos, o conteúdo paleontológico e suaposição estratigráfica associada a sedimentação pelítica, sugerem que estas rochas foram formadas a partir de precipitações bioquímicasem águas pouco profundas (submaré rasa) dentro de um ambiente costeiro.Palavras Chaves: Estromatólito; Grupo Macaúbas; Proterozóico; Conophyton; Jacutophyton. ABSTRACTCOLUMNAR STROMATOLITES AT THE BASE OF MACAÚBAS GROUP, NORTHEST OF ESPINHAÇO RIDGE (MG): PALEONTOLOGYAND SEDIMENTARY ENVIRONMENT- The rocks at the base of the Macaúbas Group that outcrop in the northeastern of Espinhaço Ridge areconstituted mainly by quartzites followed by layers of metapelites and metacarbonates rocks, deposited in fluvial, marine and coastalenvironments, of Neoproterozoic age. At the top of metapelites layers of the Domingas Formation, occur isolated lens of dolomitescontaining a rich paleontological content composed of columnar estromatolitics structures. After recently field trips where they wereidentified news lenses of dolomites in the Boqueirão Farm (Inhaí/Diamantina region) and the lens already know, in the Jequitinhonha river,trough was described the morphology and geometry of biogenic structures found, besides the petrography of carbonates and metapeliticrocks associated. In this study the stromatolites were classified by the macro and mesostructures, depending on the degree of laminar andheritage branch type found. In this way, were described two distinct morphotypes of stromatolites where conical shapes without branches,showed a high degree of laminar heritage, being so classed as Conophyton garganicum. The branched shapes, usually with paralleldicotomas and convex growth were classified as Jacutophyton. The geometry of the dolomitic bodies, the paleontological content andstratigraphic position association of pelitic sedimentation, suggest that these rocks were formed from biochemical precipitation in waterssufficiently deep (subtidal shallow) within a coastal environment.Keywords: Stromatolites; Macaúbas Group; Proterozoic; Conophyton; Jacutophyton.