Global sea-level has changed in a cyclic manner through geologic history,but the regularities of these changes are yet to be fully understood.Despite certain(and sometimes significant)differences,the available Mesozoi...Global sea-level has changed in a cyclic manner through geologic history,but the regularities of these changes are yet to be fully understood.Despite certain(and sometimes significant)differences,the available Mesozoic eustatic curves permit the outlining of long-term eustatic cycles,which are provi-sionally defined as cycles recognizable at the stage level and higher.Interpretation of the Triassic eustatic curves indicates two orders of long-term cycles and a lst-order sea-level rise throughout the entire period.The Jurassic eustatic curves imply cyclicity of one or two orders,and a 1st-order eustatic rise during the entire period is also evident.Most challenges are interpretations for the Cretaceous;two to four orders of long-term eustatic cycles can be established for this period.Generally,the hierarchy of the long-term eustatic cycles might have changed through the Mesozoic.If so,and if one considers differences of cycles of the same order between the periods of this era,it is difficult to apply"standard"hierarchical classifications to the documented cycles.The hypothetical uncertainty of the hierarchy of the Mesozoic long-term eustatic cycles is an imoortant challenge for modern researchers.展开更多
Long-term geological processes are usually described with curves reflecting continuous changes in the characteristic parameters through the geological history, and such curves can be employed directly for recognition ...Long-term geological processes are usually described with curves reflecting continuous changes in the characteristic parameters through the geological history, and such curves can be employed directly for recognition of episodic(relatively long-term) events linked to these changes. The episodic events can be classified into several categories according to their scale(ordinary and anomalous events), "shape"(positive, negative, and neutral events), and relation to long-term trend change(successive, interruptive,facilitative, stabilizing, transformative, increasing, and decreasing). Many types of these events can be defined depending on the combination of the above-mentioned patterns. Of course, spatial rank,duration, and origin can be also considered in description of these events. The proposed classification can be applied to events in some real long-term geological processes, which include global sea-level changes,biodiversity dynamics, lithospheric plate number changes, and palaeoclimate changes. Several case examples prove the usefulness of the classification. It is established that the Early Valanginian(Early Cretaceous) eustatic lowstand(the lowest position of the sea level in the entire Cretaceous) was negative,but ordinary and only interruptive event. In the other case, it becomes clear that the only end-Ordovician and the Permian/Triassic mass extinctions transformed the trends of the biodiversity dynamics(from increase to decrease and from decrease to increase respectively), and the only Cretaceous/Paleogene mass extinction was really anomalous event on the Phanerozoic biodiversity curve. The new palaeontological data are employed to reconstruct the diversity dynamics of brachiopods in Germany(without the Alps) and the Swiss Jura Mountains. The further interpretation of the both diversity curves implies that the Early Toarcian mass extinction affected the regional brachiopod faunas strongly, but this event was only decreasing(biotic radiation continued after it, although "restarted" from the lower point)similarly to the end-Triassic and Cretaceous/Paleogene mass extinctions. The number of lithospheric plates decreased in the Early Cretaceous; however, the previous trend to increase in this number reestablished after the noted event. The Oi-1 glaciation in the very beginning of the Oligocene was anomalous event, but it only stabilized the earlier trend of temperature decline and did not transform it.Further development of the comprehensive classification of geological events is necessary. For instance,it has become clear that the Silurian environmental perturbations and the Cretaceous oceanic anoxic events should be classified as discrete events that differ essentially from episodic events, the latter of which are relevant to continuous changes in geological processes.展开更多
Many gastropod taxa went extinct during the Late Cretaceous.The stratigraphic ranges of 268 genera permit to establish the longevity of extinction victims for each stage of this epoch."Young"taxa(originated ...Many gastropod taxa went extinct during the Late Cretaceous.The stratigraphic ranges of 268 genera permit to establish the longevity of extinction victims for each stage of this epoch."Young"taxa(originated within B epochs before the extinction)prevailed among victims of the extinctions in all stages.The proportion of"old"taxa(originated before the Cretaceous)that went extinct was the highest in the Cenomanian,and it was the lowest in the Coniacian and the Maastrichtian.It appears that the end-Cretaceous mass extinction affected chiefly"young"taxa.However,the comparison with the earlier time intervals suggests that this pattern of selectivity by generic longevity was not specific for the noted catastrophe,but,in contrast,it was typical for the entire Late Cretaceous.The latest Cenomanian environmental perturbation(OAE2)caused a stronger extinction of"old"taxa,and thus,this biotic crisis was less selective by generic longevity.This hypothesis,however,is not proven by the statistical test.展开更多
Sedimentary successions in the northwestern Gulf of Suez provide important clues to the understanding of the geological evolution of NE Africa during the middle and late Eocene.This study focuses on detailed facies an...Sedimentary successions in the northwestern Gulf of Suez provide important clues to the understanding of the geological evolution of NE Africa during the middle and late Eocene.This study focuses on detailed facies analyses in order to characterize the depositional environments and system tracts of the Bartonian-Priabonian succession cropping out in this area.Bartonian-Priabonian carbonate deposits in five stratigraphic sections constitute,from base to top,the Gebel Hof,Observatory,Sannur,Qurn,and Wadi Hof Formations.These formations contain four local assemblage zones of larger benthic foraminifers.Analyses of litho-,bio-,and microfacies in the succession resulted in the recognition of 12 lithofacies types.These lithofacies are represented by packages of lime-mudstones,wackestones,packstones,pack-to grainstones,grainstones,rudstones,boundstones and dolomites.These lithofacies have been grouped into four geneticallyrelated facies associations that represent,respectively,tidal flats/shallow subtidal,restricted-shelf/lagoonal,shoal bar,and outer-shelf lagoon/reefal depositional environments in a downslope shallow-marine inner-ramp setting.The vertical transitions of these facies associations,representing facies changes through time,imply fluctuations of the regional sea level.The two peaks in the Bartonian correspond to well-known global eustatic sea-level rises;the pronounced Priabonian regression must be ascribed to the known global eustatic sea-level fall in combination with regional tectonic activity.The facies distribution suggests that the study area was located in the direct vicinity of some islands during the Bartonian-Priabonian.展开更多
文摘Global sea-level has changed in a cyclic manner through geologic history,but the regularities of these changes are yet to be fully understood.Despite certain(and sometimes significant)differences,the available Mesozoic eustatic curves permit the outlining of long-term eustatic cycles,which are provi-sionally defined as cycles recognizable at the stage level and higher.Interpretation of the Triassic eustatic curves indicates two orders of long-term cycles and a lst-order sea-level rise throughout the entire period.The Jurassic eustatic curves imply cyclicity of one or two orders,and a 1st-order eustatic rise during the entire period is also evident.Most challenges are interpretations for the Cretaceous;two to four orders of long-term eustatic cycles can be established for this period.Generally,the hierarchy of the long-term eustatic cycles might have changed through the Mesozoic.If so,and if one considers differences of cycles of the same order between the periods of this era,it is difficult to apply"standard"hierarchical classifications to the documented cycles.The hypothetical uncertainty of the hierarchy of the Mesozoic long-term eustatic cycles is an imoortant challenge for modern researchers.
文摘Long-term geological processes are usually described with curves reflecting continuous changes in the characteristic parameters through the geological history, and such curves can be employed directly for recognition of episodic(relatively long-term) events linked to these changes. The episodic events can be classified into several categories according to their scale(ordinary and anomalous events), "shape"(positive, negative, and neutral events), and relation to long-term trend change(successive, interruptive,facilitative, stabilizing, transformative, increasing, and decreasing). Many types of these events can be defined depending on the combination of the above-mentioned patterns. Of course, spatial rank,duration, and origin can be also considered in description of these events. The proposed classification can be applied to events in some real long-term geological processes, which include global sea-level changes,biodiversity dynamics, lithospheric plate number changes, and palaeoclimate changes. Several case examples prove the usefulness of the classification. It is established that the Early Valanginian(Early Cretaceous) eustatic lowstand(the lowest position of the sea level in the entire Cretaceous) was negative,but ordinary and only interruptive event. In the other case, it becomes clear that the only end-Ordovician and the Permian/Triassic mass extinctions transformed the trends of the biodiversity dynamics(from increase to decrease and from decrease to increase respectively), and the only Cretaceous/Paleogene mass extinction was really anomalous event on the Phanerozoic biodiversity curve. The new palaeontological data are employed to reconstruct the diversity dynamics of brachiopods in Germany(without the Alps) and the Swiss Jura Mountains. The further interpretation of the both diversity curves implies that the Early Toarcian mass extinction affected the regional brachiopod faunas strongly, but this event was only decreasing(biotic radiation continued after it, although "restarted" from the lower point)similarly to the end-Triassic and Cretaceous/Paleogene mass extinctions. The number of lithospheric plates decreased in the Early Cretaceous; however, the previous trend to increase in this number reestablished after the noted event. The Oi-1 glaciation in the very beginning of the Oligocene was anomalous event, but it only stabilized the earlier trend of temperature decline and did not transform it.Further development of the comprehensive classification of geological events is necessary. For instance,it has become clear that the Silurian environmental perturbations and the Cretaceous oceanic anoxic events should be classified as discrete events that differ essentially from episodic events, the latter of which are relevant to continuous changes in geological processes.
文摘Many gastropod taxa went extinct during the Late Cretaceous.The stratigraphic ranges of 268 genera permit to establish the longevity of extinction victims for each stage of this epoch."Young"taxa(originated within B epochs before the extinction)prevailed among victims of the extinctions in all stages.The proportion of"old"taxa(originated before the Cretaceous)that went extinct was the highest in the Cenomanian,and it was the lowest in the Coniacian and the Maastrichtian.It appears that the end-Cretaceous mass extinction affected chiefly"young"taxa.However,the comparison with the earlier time intervals suggests that this pattern of selectivity by generic longevity was not specific for the noted catastrophe,but,in contrast,it was typical for the entire Late Cretaceous.The latest Cenomanian environmental perturbation(OAE2)caused a stronger extinction of"old"taxa,and thus,this biotic crisis was less selective by generic longevity.This hypothesis,however,is not proven by the statistical test.
文摘Sedimentary successions in the northwestern Gulf of Suez provide important clues to the understanding of the geological evolution of NE Africa during the middle and late Eocene.This study focuses on detailed facies analyses in order to characterize the depositional environments and system tracts of the Bartonian-Priabonian succession cropping out in this area.Bartonian-Priabonian carbonate deposits in five stratigraphic sections constitute,from base to top,the Gebel Hof,Observatory,Sannur,Qurn,and Wadi Hof Formations.These formations contain four local assemblage zones of larger benthic foraminifers.Analyses of litho-,bio-,and microfacies in the succession resulted in the recognition of 12 lithofacies types.These lithofacies are represented by packages of lime-mudstones,wackestones,packstones,pack-to grainstones,grainstones,rudstones,boundstones and dolomites.These lithofacies have been grouped into four geneticallyrelated facies associations that represent,respectively,tidal flats/shallow subtidal,restricted-shelf/lagoonal,shoal bar,and outer-shelf lagoon/reefal depositional environments in a downslope shallow-marine inner-ramp setting.The vertical transitions of these facies associations,representing facies changes through time,imply fluctuations of the regional sea level.The two peaks in the Bartonian correspond to well-known global eustatic sea-level rises;the pronounced Priabonian regression must be ascribed to the known global eustatic sea-level fall in combination with regional tectonic activity.The facies distribution suggests that the study area was located in the direct vicinity of some islands during the Bartonian-Priabonian.
