Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 15

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
Five Kimmeridgian ammonite faunas occurring at well separated horizons have been recognized in the Janusfjellet Fm., at Wimanfjellet in Sassenfjorden. Together with other ammonite faunas described so far from the Kimmeridgian in Spitsbergen they are arranged into the faunistic sequence, and their correlations with the best known Arctic successions viz. in the East Greenland (Milne Land) and the northern Siberia (Kheta Basin) are discussed. The ammonites of Spitsbergen belong mostly to the family Cardioceratidae which indicates the affiliation of the area to the restricted Boreal Province. However, the faunas corresponding to the Rasenia cymodoce Zone (except its lowermost part) and the Aulacostephanoides mutabilis Zone show in Spitsbergen a marked increase in number of the Subboreal representatives of the Aulacostephanidae. The appearance of aulacostephanids of the Subboreal affinities reflects the faunal invasion from the south.
Three ammonite faunas in the lower part of the Janusfjellet Fm., in the southern Sassenfjorden area have been recognized. The first fauna is correlated with the Stephanoides (= Fasciculatus Subzone) of the Cranocephaloides Zone Upper Bathonian, the second one — with the Calyx Zone of the uppermost Bathonian, and probably also with the Apertum Zone of the lowermost Callovian, and the third one — with the upper part of the Middle Callovian and/or the lower part of the Upper Callovian. The co-occurrence of Cardioceratidae and Kosmoceratidae in the Upper Bathonian in Spitsbergen is indicative of the Subboreal province, whereas the presence of Cardioceratidae and the absence of Kosmoceratidae found in the Middle/Upper Callovian characterize the Boreal province. Thus, within the Boreal Realm the boundaries of the Boreal and the Subboreal provinces shifted through the Spitsbergen area during the Early/Middle Callovian time. In the paleontological part are described the representatives of Kepplerites (subgenera: Seymourites, Toricellites), Costacadoceras, Cadoceras (Paracadoceras), Stenocadoceras, Pseudocadoceras and ?Longaeviceras; a new species, Kepplerites (Toricellites) blrkelundae Kopik, has been established.
3
63%
Early ontogenetic stages of some Ammonitina (mostly Perisphinctidae) are described from the Oxfordian Jagua Formation of western Cuba. Fourty six percent of the sample are specimens attaining the nepionic swelling with more than four septa developed. Juvenile jaw apparatus found for the first time in specimens with only 2,25 whorls, displays primitive elements corresponding to conchorhynch and rhyncholit of nautiloids, litoceratids and phylloceratids. The fauna and sediment features evidence a low water energy and low oxigenated conditions at the bottom during the sedimentation. The juvenile ammonites occur together with numerous adults which are represented by corresponding micro- and macroconchs; it indicates for the proximity of a breeding place.
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.