Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 6

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
2
100%
Scanning electron microscope was used to study columnals of crinoids of Pisocrinus (?) costatus (Shevchenko), Schyschcatocrinus sp., Cyclocaudiculus gracilis Głuchowski, Rhysocamax cristata Moore et Jeffords and Platycrinites minor Głuchowski from Silurian, Devonian and Carboniferous deposits of Poland. The presence of microstructures, interpreted as stereom α and stereom β have been confirmed and the occurrence of what is known as “large” microstructures on the lateral surface of the columnals of Schyschcatocrinus sp. have been stated. Three types within the “large” microstructures have been distinguished, the first of them marked by a close spacing of round, oval or elongated pores, the second — with round, less closely spaced pores and the third — having irregular, labyrinthic furrows and depressions.
3
100%
Givetian and Frasnian crinoid faunas of the Holy Cross Mts and Silesia-Cracow Region are arranged in fourteen assemblages. Their diversity decreases generally from northern to southern regions reflecting crinoid habitat differentiation during either platform or reef phases of facies development. Distributional patterns are superimposed on a six-step general succession of the faunas which was mainly controlled by environmental changes related to eustatic cycles. Nine crinoid species have been identified by calyces, thirteen species are based on stems attributed to calyx genera, and forty-eight kinds of columnals, probably representing distinct species, are classified within artificial supraspecific units. Of them thirteen are new: Anthinocrinus brevicostatus sp. n., Asperocrinus brevispinosus sp. n., Calleocrinus bicostatus sp. n., Calleocrinus kielcensis sp. n., Exaesiodiscus compositus sp. n., Kasachstanocrinus tenuis sp. n., Laudonomphalus pinguicostatus sp. n., Noctuicrinus? varius sp. n., Ricebocrinus parvus sp. n., Schyschcatocrinus delicatus sp. n., Schyschcatocrinus multiformis sp. n., Stenocrinus raricostatus sp. n., and Urushicrinus perbellus sp. n.
Most of 378 upper Eifelian crinoid columnals collected from the lower part of Skały Beds in the Holy Cross Mountains display traces of borings produced by endobionts, but only approximately 20% of them show traces of epibionts. These infested crinoids are represented by 5 stem−based species: Tantalocrinus scutellus, Schyschcatocrinus creber, Gilbertsocrinus vetulus, Pentagonostipes petaloides, and Cycloocetocrinussp. They were fouled by 19 species of suspension−feeding epibionts, including saccamminid foraminiferans, rugose and tabulate corals, cyrtinitid and productid brachiopods, “ctenostome bryozoans”, “cyclostome bryozoans”, cystoporate bryozoans, and rhabdomesid? bryozoans, crinoids, and organisms of uncertain affinities. The majority of these epibionts were opportunistic commensals colonizing living crinoids, and only some utilized dead crinoids as hard substrate for attachment. At least some of these epibionts seem to have settled selectively on particular crinoid host species.
Disarticulated crinoid columnals and pluricolumnals from the Famennian of the Holy Cross area were analysed. Sixteen crinoid taxa were distinguished, only one of which is based on stems attributed to a calyx−based genus, and the others are classified within artificial supraspecific units. Two of these are new: Schyschcatocrinus levis sp. nov. and Cosmocrinus polonicussp. nov. The described crinoid fauna shows distinct extinction−recovery temporal pattern: the Frasnian–Famennian crisis affected 50% of stem−based families and 70% of late Frasnian stem−based genera. The succession of crinoid faunas represented by three faunal intervals has been identified and correlated to standard conodont zones: FIa, Palmatolepis triangularis Zone (relic “Frasnian” crinoid assemblage Schyschcatocrinus delicatus–Calleocrinus kielcensis), FIb, Pa. crepida to Pa. marginifera zones (crinoid assemblage Calleocrinus kielcensis–Schyschcatocrinus levis) and FIc, Pa. trachytera to S. praesulcata zones (crinoid assemblage Cosmocrinus polonicus–Acbastaucrinus affectatus). The succession was controlled mostly by eustatic factors.
Early–Middle Frasnian ostracods and crinoids from Wietrznia in the Northern Kielce subregion of the Holy Cross area were analyzed. Twenty three ostracod species assigned to thirteen named genera, as well as eighteen crinoid species including the representatives of fifteen stem−based taxa were distinguished. For most of the species open nomenclature is applied. The composition of ostracod assemblage changes from moderately diverse in the lower part of the Palmatolepis transitans Zone to poorly diverse in its higher part. Lack of ostracods in the uppermost part of the Pa. transitans Zone and in the Palmatolepis punctata Zone is noted. The crinoid distribution pattern comprises the interval of relatively high diversity, interrupted in the uppermost part of the Pa. transitans Zone, and the interval of temporary recovery in the lower Pa. punctata Zone. Such distribution patterns point to deterioration of environmental conditions across the Early–Middle Frasnian transition, coinciding with a large−scale C−isotopic perturbation superimposed on intermittent, two−step eustatic sea level rise. On the other hand, impoverished, surviving crinoid faunas and absence of ostracods in the Pa. punctata Zone indicate the overall long−term deterioration of life conditions through the major C−isotope anomaly time span. However, this may also result from synsedimentary tectonic pulses, causing block movements and large−scale resedimentation phenomena on the northern slope of the Dyminy Reef during the basal Middle Frasnian sea level rise.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.