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Pochodzenie sfosfatyzowanych gąbek z warstwy dańskiego piaskowca glaukonitowego z Nasiłowa (dolina środkowej Wisły)

Świerczewska-Gładysz E., Olszewska-Nejbert D.

Przegląd Geologiczny

2006

Vol. 54, nr 8

710-719

The sponge fauna from the Danian glauconitic sandstone as exposed at Nasiłów, contains all species known from the underlying Upper Maastrichtian siliceous chalk and, additionally, some species not documented hitherto from the latter unit. The stratigraphic ranges of the all studied sponges indicate their Late Maastrichtian age; there are no Danian sponges in the glauconitic sandstone. Two assemblages of sponges may be distinguished in the glauconitic sandstone, based on the analysis of the infilling of their interspicular space: 1) sponges infilled with phosphatized siliceous chalk and 2) sponges infilled with phosphatized glauconitic siliceous chalk. Petrographic study indicates that the host deposit of the first assemblage was a siliceous chalk. The second type originated from a glauconitic siliceous chalk unit, probably equivalent to the so-called Żyrzyn Beds of Late Maastrichtian age. The glauconitic chalk orginally overlain the siliceous chalk at Nasiłów, but has been subsequently eroded. Detailed analysis of the relations between two types of infillings allows to distinguish a latest Maastrichtian stage of erosion after deposition of the siliceous chalk, not recognised by previous authors. In this erosional stage, phosphatized sponges originally embedded in siliceous chalk were re-exposed and subsequently buried during the deposition of the glauconitic siliceous chalk unit.