Overview of the Gams Stratigraphic Section

[14]  The geological setting of the stratigraphic sequence near Gams (Knappengraben) was previously characterized by Kollmann (1964) and Lahodynsky (1988), who ascribed it to the Nierntal Formation (chron 29R). The portion of the sequence below the K/T boundary layer consists of alternating calcareous marlstone and marly limestone, and the portion above the boundary layer is dominated by clays with variable contents of Ca carbonate and occasional sand-silt beds. A detailed lithological-geochemical characterization of the clay boundary layer was presented in our earlier publications [Grachev et al., 2005, 2007].

[15]  In order to reproduce the conditions under which the K/T boundary clay layer was formed, we studied the chemistry of allogenic minerals to identify their source rocks. Inasmuch as the thickness of the boundary layer is a few centimeters and with regard for our earlier materials [Grachev et al., 2005, 2007], we thoroughly examined allogenic minerals from the lower, middle, and upper portions of the sequence (A. F. Grachev et al., in press, 2008). Each of these portions was characterized by its inherent paragenetic association of minerals, which was of principal importance for our reconstructions of the conditions under which the boundary layer was produced.

[16]  Because of its resistance to mechanical wearing, spinel plays a key role in reproducing the paleogeographic environment [Lenaz et al., 2000; Zhu et al., 2004, 2005; and others]. For the Eastern Alps, where our study area is located, the first data on the chemistry of detrital spinel in the Mesozoic sedimentary rocks, including the Upper Gosau Cretaceous-Paleogene Group, were published in [Pober and Faupl, 1988].


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