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Provenance of heavy minerals to the Middle and Upper Jurassic epicontinental deposits of NW Poland

Bembenek Kinga, Woronko Barbara, Ziółkowski Piotr

Geological Quarterly

2021

Vol. 65, No. 1

art. no. 2

The source of clastic material supplied to the epicontinental sea during the Middle and Late Jurassic in the Pomeranian Segment of the northern part of the Mid-Polish Trough is analysed, using deposits from the Rzeczyn PIG-1 borehole that represent the Łyna, Chociwel, Brda, Pałuki, Kcynia and Rogoźno formations. Heavy mineral analysis, including weathering indices (ZTR, GZI, RZI and Q) and standardised scores for each mineral species, shows that each formation is characterized by a different heavy minerals association. In each association, transparent minerals include both ultrastable minerals (zircon, tourmaline and rutile), occurring in various proportions, and unstable minerals. This indicates that deposits subject to earlier multiple reworking were eroded from the surrounding landmasses. Most probably these deposits represented Triassic rocks, although fresh weathering covers were also eroded. The main direction of clastic material supply was from the N and NW, and to a lesser degree from the NE. The main reasons for changes in the source areas were probably sea level oscillations, while during regressions, exposed parts of the seabed became source areas of clastic material. Conversely, during transgressions, parts of the seabed became cut off from the supply of clastic material from eroded landmasses.

Epizody intensywnego wietrzenia chemicznego zapisane w profilach hetangu z obrzeżenia Gór Świętokrzyskich (wyniki nowych badań)

Brański P.

Geologia / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie

2009

T. 35, z. 3/1

21-30

Results of new mineralogical and geochemical research on clay deposits of the Rhaetian-Hettangian successions from the Holy Cross Mts. margin (south-eastern part of the epicontinental Polish basin) are presented. The clay mineral assemblages were mostly controlled by climatic conditions and weathering regime. Reworking of ancient sediments and the early diagenesis could modify the clay mineral composition. Some levels of the high kaolinite content at the Triassic-Jurassic boundary suggest intense continental weathering in the humid-subtropical to tropical climate related to the global warming episodes that were recorded on isotope curves from a number of sections in the world.