Integrated palynostratigraphy and magnetostratigraphy of the Middle and Upper Buntsandstein in NE Poland - an approach to correlating Lower Triassic regional isochronous horizons

摘要

Despite years of research, Lower Triassic deposits of the epicontinental Central European Basin still lack a detailed stratigraphy that would allow regional correlation of isochronous horizons. The best chronostratigraphic results have up to now been achieved by microspore-based biostratigraphy and magnetostratigraphy. Integrated palynostratigraphic and magnetostratigraphic investigations, carried out on Buntsandstein cores from northeastern Poland representing the eastern margin of the basin, have made precise correlations with the better-explored basin centre. The Lidzbark and Malbork formations of the Bartoszyce IG 1 borehole were examined by means of palynology and palaeomagnetic studies. Further palaeomagnetic studies were applied to the Lidzbark, Malbork and Elblag formations of the Nidzica IG 1 borehole and the Elblag Fm. of the Pastek IG 1. Two spore-pollen assemblages were distinguished representing the Densoisporites nejburgii Subzone of the D. nejburgii Zone within the lower part of the Lidzbark Fm. and the lowermost part of the Malbork Fm. Mostly reversed polarity was detected within the lower part of the succession investigated, whereas normal polarity prevailed within its upper part. A normal polarity local zone was correlated with the undivided Tbn6-Tbn7 standard magnetozones of western Poland. The reversely polarized part of the succession corresponds most probably to the Tbr5 standard magnetozone. The base of the Tbn6-Tbn7 magnetozone can serve as a good correlation horizon for regional reconstructions.