Skamieniałości śladowe w eoceńskim cienko- i średnioławicowym fliszu strefy bystrzyckiej płaszczowiny magurskiej w Polsce

Alfred Uchman

Abstrakt


TRACE FOSSILS OF THE EOCENE THIN- AND MEDIUM-BEDDED FLYSCH OF THE BYSTRICA ZONE OF THE MAGURA NAPPE, IN POLAND

Summary
The Beloveza Formation (Lowe - Middle Eocene) consists of thin-bedded siliciclastic flysch. The overlying Zeleinikowa Formation (Middle Eocene) is composed of medium bedded flysch containing packages of thin-bedded flysch and thick beds of the turbiditic Łącko marls. The Bystrica Formation (Middle Eocene) consists of medium bedded flysch with packages of thin bedded flysch and thick beds of the black Łącko marls, sometimes with intercalations of hornstones. It contains glauconitic sandstones. The sediments of this formation are black. The Bystrica Formation partially replaces the Zeleinikowa Formation in the middle part of the Bystrica zone in the Magura Nappe. Most sections of the Beloveza and Zeleznikowa Formations contain extremely abundant and diverse ichnofauna, including abundant and diverse graphoglyptids (Paleodictyon, Protopaleodictyon, and others) as well as traces produced by irregular echinoids (Scolicia, Taphrhelminthopsis, Subphyllochorda) . N aviculichnium marginatum, Halymenidium and Spirophycus are also comparatively abundant. Chondrites is rare and represented by small forms. Sabularia simplex and Planolites are most abundant forms occurring in all formations considered. Exceptionally, in sections on the northern slopes of the Gorce Range, the Beloveza Formation is dominated by Chondrites, like in the Bystrica Formation. In general trace fossils, especially the predepositional forms, are less frequent in the Zeleinikowa Formation. The Bystrica Formation is dominated by Chondrites, including large forms, whereas graphoglyptids as well as the forms produced by echinoids are less abundant and diverse. An increase of the ratio of postdepostional forms to predepositional ones is observed. The ichnofauna of most sections of the Beloveza Formation and the Zeleznikowa Formation indicates well oxygenated sediments and moderate crisis in food supply that favoured the high specialization of graphoglyptids. A decrease in abundance and diversity of trace fossils in the Zeleznikowa Formation in comparison to the Beloveza Formation may be related to the lower preservation potential in the more thick bedded flysch. This factor influenced additional ichnofauna of the Bystrica Formation. The ichnofauna of the Bystrica Formation may be related to poorly oxygenated sediments. Occurrence of forms belonging to the Cruziana ichnofacies, such as Thalassinoides, Ophiomorpha, and Rhizocorallium in the discussed formations, together with typical forms of the Nereites ichnofacies, is one of the numerous contradictions in the bathymetric model of trace fossils. Thus, apart from general indication of deep-sea environment, it is difficult to estimate closely range of paleodepth.