Wyniki wyszukiwania - BazTech

Ograniczanie wyników

Powiadomienia systemowe

Sesja wygasła!

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: Upper Cenomanian

Sortuj według:

Ogranicz wyniki do:

Siliciclastic input into Upper Cenomanian synorogenic sediments of the High-Tatric Unit, Central Western Carpathians (Tatra Mountains); petrography, geochemistry and provenance

Wolska A., Bąk K., Bąk M.

Geological Quarterly

2016

Vol. 60, No. 4

919--934

The Upper Cenomanian mixed siliciclastic-carbonate succession of the High-Tatric Unit was deposited during the initial stage of basinal closing of the Tatric area, part of the Zliechov (Križna) Basin (Inner Carpathian domain). As a result of tectonic activity taking place at the northern Veporic margin, pulses of siliciclastic input interrupted marine carbonate sedimentation. The siliciclastic material, part of the Zabijak Formation, has been studied along two sections (Pisana Gully and Zdziarski Gully) in the Western Tatra Mountains. Microfacies, petrographic and geochemical analyses reveal a variability of siliciclastic material composed of various types of granitoids and medium- or high-grade metamorphic rocks, with schists and gneisses. Such interpretation is confirmed by the results of elemental chemical analyses, in which immobile trace elements, such as REE, Th, Cr, Co, Zr, and Y were used as indices for sediment provenance. The parent rocks sustained moderate to intense chemical weathering, documented by chemical weathering indices (CIA, PIA, CIW, R). The weathering occurred in a humid climate with relatively high precipitation that caused strong leaching of particles. Chemical indices related to sorting processes suggest that the recycling of the source material was a minor significance. The siliciclastic input displays a waning upward tendency in the sections, which can be associated with diminishing of the source area by gradual inland progradation of a carbonate platform, caused by a global sea level rise during the Late Cenomanian.

Foraminifera and Late Cenomanian-Turonian biostratigraphy of the northern palaeobiogeographic district of Western Siberia

Podobina Vera

Geologos

2013

Vol. 19, No. 3

201--227

The study of 114 core samples from seven borehole sections of the Van-Eganskaya area in the central part of Western Siberia yielded sufficient data to investigate the Late Cenomanian-Turonian foraminifers, palaeoenvironments, and the Late Cenomanian-Turonian biostratigraphy of this poorly studied area. Two Late Cenomanian foraminifer zones were established, viz. a (lower) Saccammina micra - Ammomarginulina sibirica Zone and an (upper) Trochammina wetteri tumida - Verneuilinoides kansasensis Zone. They reflect changes in the species composition of the foraminifer assemblages and lithology of the host rocks of the Uvatskian Horizon. In the lower part of the upper zone, beds with Gaudryinopsis nanushukensis elongatus are present. The changes in the species composition and lithology of the upper Cenomanian resulted from water-depth variations during the Boreal transgression. Two distinct assemblages and two homonymous zones, viz. the (lower) Gaudryinopsis angustus and the (upper) Pseudoclavulina hastata zones occur in the Turonian clayey cap-rocks of the superimposed Kuznetsovskian Horizon. Comparison of the Late Cenomanian-Turonian assemblages from the West-Siberian and Canadian provinces of the same Arctic palaeobiogeographical realm shows that the West-Siberian species are the same as, and closely related to, Canadian taxa, along with geographical subspecies. This comparison allows a detailed correlation, which results in a precise dating of the foraminifer zones.