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Wyświetlanie 1-10 z 10
Tytuł:
Reflections on subglacial megafloods: their possible cause, occurrence, and consequence for the global climate
Autorzy:
Loon, A. J. (Tom)
Powiązania:
https://bibliotekanauki.pl/articles/94340.pdf
Data publikacji:
2009
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
jökulhlaup
megafloods
Heinrich events
sliding layer
subglacial lakes
climate change
powódź glacjalna
warstwa poślizgowa
jezioro podlodowcowe
zmiany klimatu
Opis:
Huge water reservoirs exist subglacially, for instance in the form of lakes. Failure of a wall around such a lake underneath the central part of a large ice mass may result in huge water outbursts. The resulting megafloods will rarely be traceable along the ice front, because much power is lost by friction and because the flood spreads subglacially over a large area. Truly giant meltwater outbursts might, however, still have an enormous power when reaching the marginal area of an ice cap. Such a megaflood may both affect the integrity of the ice mass, and help create a sliding layer over which huge ice masses can be easily transported towards the ocean, thus triggering a Heinrich-like event. This would have great impact on the global climate. Some of the Heinrich events that occurred during the past hundreds of thousands of years may well have been due to giant subglacial water outbursts, and such a situation may equally well occur in the time to come.
Źródło:
Geologos; 2009, 15, 2; 115-128
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Possible pitfalls in the procedure for paleobiodiversity-dynamics analysis
Pułapki analizy paleo-bioróżnorodności
Autorzy:
Ruban, Dmitry A.
Loon, A. J. (Tom)
Powiązania:
https://bibliotekanauki.pl/articles/94348.pdf
Data publikacji:
2008
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
biodiversity
taxonomy
biostratigraphy
geochronology
Lazarus taxa
bioróżnorodność
taksonomia
biostratygrafia
geochronologia
taksony Łazarza
Opis:
The changes in the diversity of specific taxa during certain parts of the geological past (paleobiodiversity dynamics) can, in principle, be established by counting the number of the fossil taxa present (worldwide or in a specific study area) in rocks dated for the time interval under study. Numerous obstacles are present, however, for instance in the form of lacking field data, disappeared collections, ambiguous identifications, temporary ‘disappearence’ of taxa, and dating problems. One major problem is the fact that, particularly in regional studies in some countries, a local, regional or national chronostratigraphic terminology is used rather than the chronostratigraphy recommended by the International Stratigraphic Commision of the International Union of Geological Sciences. This hampers international correlation and makes precise global paleodiversity-dynamics analyses extremely difficult. A reliable insight into the true paleodiversity dynamics requires not only that the various problems are recognized, but also that their consequences are eliminated or, if this is impossible, minimized. This is particularly important if the effects of mass extinctions on fauna and flora are investigated. Each analysis of paleobiodiversity-dynamics analysis of phenomena related to mass extinctions should therefore try to quantify the impact that missing data or inaccuracies of any kind may have on the final results; such an analysis should, in addition, try to find a solution for the major problems, so as to avoid significant inaccuracies of the calculated values. Large electronic databases can help, since about a decade, to diminish possible errors in diversity estimates. Paleobiodiversity should preferably be expressed in the form of values with a certain band with, indicating the inaccuracy, rather than in the form of exact values.
Zmiany w zróżnicowaniu gatunków w pewnych przedziałach czasu przeszłości geologicznej (dynamika paleo-bioróżnorodności) są z zasady ustalane poprzez zliczanie liczby taksonów skamieniałości (na świecie lub na wybranym obszarze) w skałach datowanych na badany interwał czasowy. Tym niemniej procedura ta napotyka wiele przeszkód, np. w postaci braku danych z jakiegoś obszaru, zagubionych kolekcji, niejednoznacznych identyfikacji, czasowego „zaniku” taksonów czy problemów datowania. Jednym z głównych problemów, zwłaszcza w badaniach regionalnych w niektórych krajach, jest stosowanie lokalnej, regionalnej lub krajowej terminologii chronostratygraficznej, a nie chronostratygrafii rekomendowanej przez Międzynarodową Komisję Stratygraficzną przy Międzynarodowej Unii Nauk Geologicznych. Utrudnia to międzynarodowe korelacje i czyni niezwykle trudnym przeprowadzenie precyzyjnej globalnej analizy dynamiki paleo-bioróżnorodności. Wiarygodny wgląd w prawdziwą dynamikę paleo-bioróżnorodności wymaga nie tylko rozpoznania różnych problemów, ale również wyeliminowania ich konsekwencji, a gdy to niemożliwe, zminimalizowania ich. Jest to szczególnie ważne w przypadku, gdy badane są następstwa masowego wymierania fauny i flory. Dlatego każda analiza dynamiki paleo-bioróżnorodności zjawisk związanych z masowym wymieraniem powinna zawierać próbę ilościowego oszacowania wpływu, jakie brakujące dane lub niedokładności jakiegokolwiek rodzaju mogą wywierać na końcowe wnioski. Taka analiza powinna próbować znaleźć rozwiązanie dla głównych problemów, ażeby uniknąć znaczących niedokładności w obliczonych wartościach. Duże elektroniczne bazy danych, dostępne od około 10 lat, mogą pomóc w zmniejszeniu możliwych błędów przy szacowaniu różnorodności. Najlepiej, gdyby paleo-bioróżnorodność była wyrażana w formie wartości w pewnym zakresie, wskazującym na niedokładność, a nie w formie precyzyjnej wartości.
Źródło:
Geologos; 2008, 14, 1; 37-50
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Slide origin of breccia lenses in the Cambrian of the North China Platform: new insight into mass transport in an epeiric sea
Autorzy:
Van, Loon A. J. (Tom)
Han, Zuozhen
Han, Yu
Powiązania:
https://bibliotekanauki.pl/articles/94404.pdf
Data publikacji:
2012
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
breccia lenses
sliding
epeiric sea
Chaomidian Formation
Furongian
North China Platform
poślizg
morze epikontynentalne
formacja Chaomidian
Furong
platforma północnokoreańska
Opis:
An oolite in the Furongian (Late Cambrian) Chaomidian Formation in Shandong Province, China, which was deposited on the North China Platform in an epeiric sea, contains several limestone breccia lenses of various dimensions (centimetres to decimetres thick and decimetres to more than 10 metres in length) in an E-trending section. The oolite, which is approximately 40 cm thick, was originally thicker, as indicated by a planar truncation surface that formed by wave abrasion. The breccia lenses in this oolite are generally mound-shaped with a flat base and a convex top. The western margin of the lenses is commonly rounded whereas the eastern margin commonly has a tail (consisting of a rapidly eastwards thinning breccia horizon that gradually ends in a horizon of isolated clasts). Some of the breccia lenses are underlain by a shear zone. The formation of the breccia lenses cannot be easily explained by normal depositional or deformational processes. It is concluded that the lenses represent fragments of a partly consolidated layer, consisting of both rounded and angular platy clasts, which slid down over a very gently inclined sedimentary surface which acted - possibly together with a water film - as a lubricant layer. During transport, the layer broke up into several discrete bodies that formed small ‘highs’ at the sedimentary surface of the shallow epeiric sea. Subsequently, waves partially eroded the lenses, mostly at their margins, producing their mound-shaped form. Sliding of blocks is known from a wide variety of environments in the sedimentary record; however, this is the first description of the sliding of blocks in an epeiric sea. This indicates that such a low-relief submarine carbonate setting is, like its siliciclastic counterparts, susceptible to this process.
Źródło:
Geologos; 2012, 18, 4; 223-235
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Interaction between turbidity currents and a contour current – a rare example from the Ordovician of Shaanxi province, China
Autorzy:
Li, Hua
van Loon, A. J. (Tom)
He, Youbin
Powiązania:
https://bibliotekanauki.pl/articles/950462.pdf
Data publikacji:
2019
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
contourites
turbidites
reworking
Ordos basin
Pingliang formation
kontury
turbidyty
przeróbka
zlewnia
Ordos
Pingliang
Opis:
The silty top parts of graded turbidites of the Late Ordovician Pingliang Formation, which accumulated along the southern margin of the Ordos Basin (central China), have been reworked by contour currents. The reworking of the turbidites can be proven on the basis of paleocurrent directions in individual layers: the ripple-cross-bedded sandy divisions of some turbidites show transport directions consistently into the downslope direction (consistent with the direction of other gravity flows), but in the upper, silty fine-grained division they show another direction, viz. alongslope (consistent with the direction that a contour current must have taken at the same time). Both directions are roughly perpendicular to each other. Moreover, the sediment of the reworked turbidites is better sorted and has better rounded grains than the non-reworked turbidites. Although such type of reworking is well known from modern deep-sea environments, this has rarely been found before in ancient deep-sea deposits. The reworking could take place because the upper divisions of the turbidites involved are silty and consequently relatively easily erodible, while the contour current had locally a relatively high velocity – and consequently a relatively large erosional capability – because of confinement within a relatively narrow trough.
Źródło:
Geologos; 2019, 25, 1; 15-30
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Sedimentary environment and palaeogeography of the ?Palaeocene-Middle Eocene Kashkan Formation, Zagros fold-thrust belt, SW Iran
Autorzy:
Yeganeh, Bizhan Yousefi
Feiznia, Sadat
Loon, A. J. (Tom)
Powiązania:
https://bibliotekanauki.pl/articles/94687.pdf
Data publikacji:
2012
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
Kashkan Formation
Zagros fold-thrust belt
trace fossils
facies architecture
braided river
shoreface
Palaeocene
Eocene
Iran
skamieniałości śladowe
rzeka roztokowa
powierzchnia brzegowa
Palaeocen
Eocen
Opis:
The Kashkan Formation (?Palaeocene to Middle Eocene) in the Zagros fold-thrust belt, SW Iran, which is intercalated between to marine limestone formations, consists of conglomerates, sandstones and siltstones. The sedimentology and the palaeogeography of the Kashkan Formation had not received any attention thus far, but have now been studied in seven sections, situated in the province of Lorestan. The sediments form twelve lithofacies, three ichnosubfacies and seven architectural elements, which are described, depicted and analysed. The analysis leads to the conclusion that most sediments accumulated in a low-sinuosity, low-gradient braided-river system (characterised by mainly unidirectional palaeocurrent directions, and by sheetfloods), that occasionally showed meandering characteristics (represented by overbank deposits and large bars). The deposits of this system closely resemble those of the South Saskatchewan River in Canada, which is considered as the classical example of a sand-bed braided river. The river flowed roughly from North to South, as deduced by palaeocurrent indicators such as imbrication and large- to medium-scale trough cross-stratification (direction measured in the trough axes). This current direction is supported by the southward to south-westward thinning of the formation and by the diminishing average grain size in the same direction. The trace fossils in the Kashban Formation fit all in the Skoyenia ichnofacies, which has here three ichnosubfacies which allow a more detailed palaeoenvironmental reconstruction, indicating that the braided stream passed into the low-energy shoreface zone of a tidally-influenced sea.
Źródło:
Geologos; 2012, 18, 1; 13-36
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The challenge of reconstructing the Phanerozoic sea level and the Pacific Basin tectonics
Autorzy:
Ruban, Dmitry A.
Conrad, Clinton P.
Loon, A. J. (Tom)
Powiązania:
https://bibliotekanauki.pl/articles/94614.pdf
Data publikacji:
2010
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
sea-floor bathymetry
dynamic topography
sea-level changes
plate tectonics
Pacific
Panthalassa
Phanerozoic
batymetria dna morskiego
dynamiczna topografia
zmiany poziomu morza
płyty tektoniczne
Pacyfik
Opis:
The relationships between the interior dynamics of our planet and global sea level can be unravelled when plate-tectonic reconstructions are available for the entire Earth. A review of global tectonics reveals significant deficiencies in our understanding of the geodynamic evolution of the Pacific (Panthalassa or Proto-Pacific) during the Cambrian-Jurassic time-span. This particular, but major, shortcoming presents a true challenge for modern geoscientists, who are encouraged to produce a detailed plate-tectonic reconstruction of the Pacific for the pre-Cretaceous in order to advance our understanding of Phanerozoic sea-level change. A set of approaches, including geological/geophysical modelling, investigation of accretionary prisms, palaeobiogeographical studies, and careful examination of eustatic sea-level changes, are proposed that will help geoscientists tackle the challenge of understanding how Pacific geodynamics affected global sea level during the Phanerozoic.
Źródło:
Geologos; 2010, 16, 4; 235-243
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A new type of slumping-induced soft-sediment deformation structure: the envelope structure
Autorzy:
Byun, Uk Hwan
van Loon, A. J. (Tom)
Kwon, Yi Kyun
Ko, Kyoungtae
Powiązania:
https://bibliotekanauki.pl/articles/950457.pdf
Data publikacji:
2019
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
Gyeokpori Formation
Cretaceous
lacustrine environment
slumping
conglomerate
kreda
środowisko jeziorne
opadanie
konglomerat
Opis:
The sediments of the Cretaceous Gyeokpori Formation in south-western South Korea accumulated in a lake in which mainly siliciclastic rocks were deposited, with some interbedded volcaniclastics. The nearby volcanic activity resulted in unstable lake margins inducing a dominance of gravity-flow deposits. The high sedimentation rate facilitated soft-sediment deformation on the sloping margin. The deposition of numerous gravity-flow deposits resulted in a vertically heterolithic stratification. The slumps are composed of different lithologies, which is expressed in different types of deformation due to the difference in cohesion between sandy and mussy layers within the slumps. Coarser-grained (cohesionless) slumps tend to show more chaotic deformation of their lamination or layering. The difference in slumping behaviour of the cohesive and non-cohesive examples is explained and modelled. A unique soft-sediment deformation structure is recognized. This structure has not been described before, and we call it ‘envelope structure’. It consists of a conglomerate mass that has become entirely embedded in fine-grained sediment because slope failure took place and the fine-grained material slumped down with the conglomerate ‘at its back’. The cohesive laminated mudstone formed locally slump folds that embedded the non-cohesive overlying conglomerate unit, possibly partly due to the bulldozing effect of the latter. This structure presumably can develop when the density contrast with the underlying and overlying deposits is exceptionally high. The envelope structure should be regarded as a special – and rare – type of a slumping-induced deformation structure.
Źródło:
Geologos; 2019, 25, 2; 111-124
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Glacial Terminations II and I as recorded in NE Iceland
Autorzy:
Vliet-Lanoë, Brigitte
Guðmundsson, Agust
Guillou, Hervé
Guégan, Soléne
Loon, A. J. (Tom)
Vleeschouwer, François
Powiązania:
https://bibliotekanauki.pl/articles/94567.pdf
Data publikacji:
2010
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
ice-stream patterns
palaeolake
deglaciation
Last Glacial Maximum
mid-Eemian cooling
Iceland
paleojezioro
deglacjacja
ostatnie zlodowacenie
Islandia
Opis:
Volcanism in eastern Iceland has controlled the changes in glacier- and river-drainage patterns and the sedimentary budget, particularly during the Middle and Late Pleistocene. The glacial extent in NE Iceland appears to be related to the impact of volcanic activity, not only on the ice-stream dynamics, but also on the sedimentary successions. Analysis of the Jökuldalur and Jökulsa á Brù records results in a new interpretation of the changes in ice extent and flow direction for at least the last two glaciations. From MIS 8 onward, the development of the Snæfell volcano apparently forced the ice stream that derived from the Vatnajökull ice cap to take another course; it also affected the offshore sedimentary budgets at the new outlet at Vopnafjördur. The MIS 6 ice sheet was thick and extensive, and associated with an ice-stream diversion to the North. The thick sedimentary complex of palaeolake Halslón was formed close to an outlet of the Vatnajökull, the Brùarjökull, during Termination II and a part of the MIS 5e interglacial. The deposits formed during MIS 5e record two climate optima interrupted by two successive glacial advances correlated with the mid-Eemian cooling. The deposits of the Weichselian deglaciation (Termination I) are much more limited in thickness. During the Last Glacial Maximum and the Late Glacial, glaciers also seem to have been restricted in the Jökulsa á Brù area. Valley glaciers issued from the Brùarjökull re-advanced several times in the Jökuldalur only during at least the Older Dryas, the Younger Dryas and the Preboreal. NE Iceland has undergone considerable deglaciation since the Bølling. In contrast to the conclusions of previous studies, the results presented here are consistent with data on the glaciations in other Nordic regions and can increase the understanding of the mid-Eemian cooling.
Źródło:
Geologos; 2010, 16, 4; 201-222
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Depositional environment of the Bagh-e-Vang Formation – the only occurrence of upper Lower Permian in Iran
Autorzy:
Yegane, Bizhan Yousefi
Van Loon, A.J. (Tom)
Fard, Sakine Arefi
Farahpour, Mohammad Mehdi
Sharahi, Safoora Yasbolaghi
Powiązania:
https://bibliotekanauki.pl/articles/1841615.pdf
Data publikacji:
2021
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
limestones
microfacies analysis
transgression conglomerate
barrier deposits
lagoonal environment
Tabas Block
wapienie
analiza mikrofacjalna
konglomerat
transgresja
osady
laguna
Opis:
A transgression of the Tethys Ocean occurred in east central Iran, like in other areas of the Tethys Ocean, around the Yakhtashian/Bolorian (regional chronostratigraphical units corresponding with the Artinskian/Kungurian of the Early Permian) transition. This led to the development of a carbonate platform that is represented in the Shirgesht area on the northern part of the Tabas Block by the Bagh-e-Vang Formation, which constitutes the only known sedimentary unit from the late Early Permian in Iran. Field data and thin-section analysis indicate deposition on a carbonate ramp with barriers separating a lagoonal area with intertidal mud flats from the open-marine environment. The overall transgres-sive development is indicated by the presence of open-marine sediments on top of the barrier and lagoonal sediments.
Źródło:
Geologos; 2021, 27, 1; 1-14
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Engineering-geological and geotechnical investigations for risk assessment of the University Olympic Village in Izmir (Turkey)
Autorzy:
Kıncal, Cem
Koca, Mehmet Yalçın
Yılmaz, H. Recep
Akgün, Mustafa
Özyalın, Şenol
Eskişar, Tuğba
Akçığ, Zafer
Loon, A. J. (Tom)
Powiązania:
https://bibliotekanauki.pl/articles/94556.pdf
Data publikacji:
2010
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
engineering geology
hazard maps
bearing capacity
Izmir
Turkey
geologia inżynierska
mapy zagrożenia
nośność statyczna
Turcja
Opis:
The Metropolitan Municipality of Izmir (Turkey) designated a steeply inclined area for the construction of buildings to house the participants of the Izmir University Olympic Games. Before the construction activities could start, engineering geological and geotechnical investigations had to be carried out in order to establish which zones in the area were suitable for safe constructions. Seismic studies, borings and laboratory tests yielded the data, which were used for preparing five hazard maps in a GIS environment. The construction activities based on the results of this complex investigation appeared successful. The engineering geological investigations included geotechnical measurements on core samples obtained from the boreholes (core drilling) and laboratory testing. The rock-quality designation (RQD%) values of the rock units were determined and used in the rock-mass classification (rock-mass rating method) as an in-put parameter and in the calculation of the bearing capacity of the various rock units. Geophysical surveys were carried out to determine the seismic velocity of the rocks at the site. A short overview is provided of the main problems that had to be dealt with, and of the successive steps taken to solve the engineering-geological problems. Determination of these problems is necessary for adequate land-use planning and construction activities.
Źródło:
Geologos; 2010, 16, 1; 43-57
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
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