Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 8

Liczba wyników na stronie
first rewind previous Strona / 1 next fast forward last
Wyniki wyszukiwania
Wyszukiwano:
w słowach kluczowych:  sea-level changes
help Sortuj według:

help Ogranicz wyniki do:
first rewind previous Strona / 1 next fast forward last
EN
At a glance, progress in palaeontology and eustatic reconstructions in the past decade permits to prove or to disprove the possible dependence of Palaeozoic brachiopod generic diversity dynamics on global sea-level changes. However, the available diversity curve is of much lower resolution than the eustatic curve. This problem can be resolved by decreasing the resolution of the latter. The other restriction linked to the chronostratigraphical incompatibility of the available data allows to focus on the Middle Palaeozoic only. A series of mass extinctions and other biotic crises in the Silurian-Devonian does not allow to interpret correctly the results of direct comparison of the brachiopod generic diversity dynamics with global sea-level changes. With the available data, it is only possible to hypothesize that the eustatic control was not playing a major part in diversity dynamics of Middle Palaeozoic brachiopods. The resolution of the stratigraphic ranges of Palaeozoic brachiopods should be increased significantly, and these ranges should be plotted against the most up-to-date geologic time scale. Until this task will be achieved, it is impossible to judge about the existence of any dependence (either full or partial) of the Palaeozoic brachiopod diversity dynamics on global sea-level changes.
EN
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.
EN
In Ordovician times the Łysogóry Region (northern Holy Cross Mts.) was located in the marginal part of Baltica, thus, the sea-level history reconstructed for this palaeocontinent appears to be a good background for discussing relationships between sea-level changes and the studied sedimentary record. However, some stratigraphic gaps, e.g. in the Lower and Middle Ordovician parts of the considered succession are probably due to regional tectonic activity. The upper Middle and Upper Ordovician sedimentary facies of the Łysogóry Region show good correlation with the Late Llanvirn-Caradoc Highstand Interval followed by the Ashgill Lowstand Interval in Baltica (Nielsen, 2004). The most conspicuous facies changes in the Ordovician of the considered region seem to be coeval with 3rd order eustatic events recognized on the sea-level curve from Baltoscandia.
EN
According to their origin, geomorphology and hydrology, the fresh/brackish-water bays and coastal lakes of the Southern Baltic coast can be treated as lagoons. They developed at the time of and as a result of the Atlantic (Litorina) transgression of the Southern Baltica. There are many publications about the origin and evolution of the lagoons and lakes along the Polish coast of the Southern Baltic (e.g. Przybyłowska-Lange, 1973a, b, 1974, 1979, 1981; Zaborowska, 1977; Zachowicz, 1977, 1985; Wypych, 1980a, b; Zachowicz et al., 1982; Bogaczewicz-Adamczak, Miotk, 1985a, b; Dąbrowski et al., 1985; Zachowicz, Zaborowska, 1985; Borówka et al., 2001a, b, 2002). Nevertheless, the origin of the lagoons has not been fully explained. In the light of present-day information the results of earliest investigations often need to be reinterpreted. The aim of this work was the correlation of the published and unpublished pollen and diatom diagrams from Late Pleistocene and Holocene sediments of the Southern Baltic lagoons, and their relation with radiocarbon dating. The pollen and diatom diagrams from the area of north-east Germany and the Curonian Lagoon (Kabailiene., 1999; Jahns, 2000; Kaiser et al., 2000; Endtmann, 2002; Bitinas et al., 2002) have been used for comparison. For the palynological sites, the local pollen assemblage zones (L PAZ) have been identified according to Janczyk-Kopikowa (1987). Comparison of the biostratigraphical data allowed us to define the approach time of the formation of the lagoons in their present-day position on the coast as well as to determine the periods of an accelerated sea-level rise and increased frequency of storm surges (so-called marine transgression phases) when the investigated areas had been under the direct influence of the sea. Such influences are visible about 7000, 6000, 5000 and 4000 years BP. This period of marine influences, about 1000-year long, corresponds very well to the same period of climate oscillations mentioned by Stuiver and Braziunas (1993), Stuiver et al. (1995) and Chapman and Shackelton (2000). The influence of the sea in the Post-Litorina period was associated mainly with the inflow of sea water through more or less developed barriers, so they are not synchronous.
5
Content available remote The epicontinental Lower Jurassic of Poland
EN
During the Early Jurassic times terrigenous, continental, marginal-marine and marine sediments up to 1400 m in thickness were deposited in a large epeiric basin extending across Poland. These strata are defined herein as the Kamienna Group, which is subdivided into 13 lithoformations (Fm.). Lithofacies description, recognition of depositional systems and subsystems and determination of their fluctuation in space and time allowed a high-resolution sequence stratigraphic analysis. Sedimentation in the shallow (usually not more than 10-20 m deep), epeiric Early Jurassic basin of Poland was particularly sensitive to reflect changes in sea level. Except for the ammonite-bearing Pliensbachian deposits in Western Poland, biostratigraphical resolution in marginal-marine and continental deposits is usually of a lesser precision. However, an internally consistent sequence stratigraphic scheme of Poland can be compared with fossiliferous marine sediments of the Ligurian cycle of United Kingdom and France. The minor sequences identified within the Ligurian cycle play a very important role in correlation as they can be recognized in the Polish Basin. Concerning the range of sea level changes, the Exxon model was also adopted and ten of the Exxon Early Jurassic depositional sequences (I-X) were identified in the Polish Lower Jurassic. Transgressive systems tracts prevail in sedimentary record and are represented either by retrogradational or aggradational facies architecture, and high-stand systems tracts are represented by progradational facies architecture. A typical marginal - marine parasequence is usually more complex than a simple "quick flooding-gradual prograding" model - transgressive deposits are usually preserved and "parasequence maximum flooding surfaces" can be distinguished. Correlative significance of transgressive surfaces is enhanced when they are coupled with their nonmarine correlative surfaces. Development of transgression with its coeval effects in continental deposits is discussed and non-marine correlative surfaces of the transgressive surfaces are documented - a "step-wise", retrogradational development of transgression with its nonmarine correlative surfaces within alluvial and deltaic systems is particularly well recognized in the Early Jurassic Polish Basin. The regional cross sections and cross sections of the whole Polish Basin showing dominant depositional systems and sequence stratigraphic correlation, as well as "time-tuned" palaeogeographical maps of the Polish Basin in Early Jurassic are presented. Despite existence of some regional dislocation zones occurring along the edges of the Mid-Polish Trough, which shaped the sedimentation and sediment thickness contrast (for example the Nowe Miasto-Iłża Fault), a gradual decrease of sediment thickness outwards the axis of the Mid-Polish Trough prevails. Additionally, occurrence of conspicuous zones of increased subsidence, which are actually perpendicular to the Mid-Polish Trough (for example the "Mazurian Way") indicates that there is no reason to regard the Mid-Polish Trough in any respect as a "rift basin", at least in the Early Jurassic times. Depositional history of the Early Jurassic in Poland provides a good case study concerning sequence correlation between marine and non-marine sedimentary successions.
6
Content available remote Jurassic ammonites of the North Tibet
EN
New collections from the northern Tibet allow the establishment of the Jurassic ammonite assemblages ranging from the Toarcian to Oxfordian times; they are the Early Toarcian: Cleviceras, Dactylioceras; Early and Middle Aalenian: Planammatoceras, Pleydellia, Erycites; Early Bajocian: Sonninia (Euhoploceras), Haplopleuroceras, Stephanoceras; Late Bathonian: Oxycerites, Homoeoplanulites Choffatia, Neuqueniceras; Middle Callovian: Oxycerites, Homoeoplanulites, Indospinctes (Elatmites), Reineckeites, and Late Oxfordian: Euaspidoceras, Peltomorphites assemblages. Taking into consideration the faunal distribution, facies and lithology four ammonite dispersal events are considered for being under eustatic control: the Sinemurian Angulaticeras dispersal marks the earliest Jurassic invasion into the south margin of the domain. The Cleviceras and Dactylioceras assemblage in association with black shales indicates a most striking Jurassic transgression during the Falciferum Zone time. The earliest Bajocian Sonninia (Euhoploceras), Haplopleuroceras, Stephanoceras assemblage would be more fully considered as one of the strongest candidates of the global sea-level rises. The latest Jurassic transgression took place in the Late Oxfordian, represented by the Euaspidoceras and Epipeltoceras assemblage; afterwards the Kimmeridgian regression sequence, indicated by brackish and none-marine bivalves ended the marine Jurassic record in the domain.
EN
The review article presents a problem of the Quaternary sea-level changes as a result of the global change in the climate, glaciations and deglaciations of a hight and mid-latitude regions and also neotectonic processes. The first is discussed a global, regional and local causes of sea-level changes in the light of distribution and present-day elevation of ancient remnant of coast lines in the world. The second a variations modelling of a scale sea-level rise during Postglacial period are presented. The local tendency of sea level changes in different region of the world is discussed. Next, the present-day tendency and causes of sea-level changes and possibilities of its short and long-term predictions are presented.
EN
The paper deals with sedimentary evolution of the condensed Ordovician sequence outcropping in Mójcza village, near Kielce (Central Poland), basing on microfacies analysis. The occurrence of fossils, their preservation and mineral composition enabled the author to distinguish five microfacies types. The Mójcza section is generally composed of grainstones and packstones which form the Mójcza Limestone Formation, and calcareous claystones intercalated with wackestones assigned to the Zalesie Formation. The deposition of limestones from the Mójcza section took place on the outer part of drowned isolated carbonate platform of temperate water setting in uniform sedimentary conditions with low accumulation rate. This environment, located in the upwelling current activity area, was favourable for phosphatization of sediment. Abundance of ferruginous ooids in the upper Llanvirn, Llandeilo and upper Caradoc sediments suggests highstand sea-level conditions during Middle and Upper Ordovician.
PL
Skondensowany profil z Mójczy koło Kielc tworzą wapienie ordowickie, należące do formacji z Mójczy (późny arenig-karadok) i formacji z Zalesia (aszgil). W składzie ziarnowym wapieni dominują bioklasty i ooidy (żelaziste i kalcytowe). W mniejszej ilości (w dolnej części profilu) występują intraklasty, peloidy i kwarc. Zasadnicze znaczenie wśród bioklastów mają małżoraczki, szkarłupnie, trylobity, mniejsze zaś ramienionogi, mszywioły, mięczaki i igły gąbek. Bioklasty w znacznej mierze są zabradowane i często połamane. Charakterystyczną ich cechą jest obecność powłok fosforanowych. Na powierzchni wielu bioklastów często można obserwować ślady drążącej działalności mikroorganizmów. Na podstawie składników ziarnowych i ich wzajemnych relacji wapienie z profilu mójczańskiego podzielono według klasyfikacji R.J. Dunhama (1962), na: grainstony piaszczysto-bioklastyczne, grainstony bioklastyczne, grainstony-pakstony bioklastyczne, grainstony ooidowo-bioklastyczne i pakstony-wakstony małżoraczkowe. Cztery pierwsze grupy tworzą formacje wapieni z Mójczy, ostatnia zaś występuje w formacji z Zalesia i w najwyższej części formacji wapieni z Mójczy. Zespół faunistyczny tworzący wapienie w profilu mójczńskim jest taksonomicznie zbliżony do zespołu współczesnych platform węglanowych umiarkowanej chłodnej strefy klimatycznej. Sedymentacja wapieni z profilu mójczańskiego odbywała się w dość stabilnym środowisku, w warunkach wolnego tempa akumulacji, co zaznaczyło się znaczną kondensacją osadu. Przypuszczalnie zbyt wolna [produkcja węglanu wapnia nie mogła nadążyć za tempem wzrostu poziomu morza, sprzyjając zatopieniu platformy węglanowej, Brak korali rafotwórczych i glonów wapiennych sugeruje sedymentację poniżej strefy fotycznej, na głębokości od 80 do około 120 m, gdzie prądy spowodowane bardzo silnymi sztormami przerabiały zdeponowany osad. Na obszarze współczesnych platform położonych w klimacie umiarkowanym strefa abrazji wywołana falowaniem sztormowym znajduje się na głębokości 50-75 m. Depozycja osadów formacji z Zalesia odbywała się w dystalnej części szelfu zewnętrznego. Do rejonu tego docierały osłabione prądy sztormowe generowane w płytszym morzu. Rozkład litofacji, charakter sedymentacji węglanowej oraz porównanie ze współczesnymi środowiskami węglanowymi sugerują w środkowym i wyższym ordowiku w regionie kieleckim Gór Świętokrzyskich rozwój zatopionej, izolowanej platformy węglanowej. W profilu z Mójczy zaznaczone są dwa epizody związane z wysokim poziomem morza, poprzedzone dwoma epizodami transgresywnymi - wczesnolanwirnskim i wczwesnokaradockim - korelowane w skali regionalnej i globalnej.
first rewind previous Strona / 1 next fast forward last
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.