Gams stratigraphic sections, Gams bei Hieflau, Landl, Liezen District, Styria, Austriai

Regional Level Types
Gams stratigraphic sections	Exposure
Gams bei Hieflau	Village
Landl	Municipality
Liezen District	District
Styria	State
Austria	Country

In the upper course of the Gams river (Gamsbach), the Cretaceous/Tertiary (K/T) boundary follows more or less the base of the valley. Because of wide-spread Pleistocene deposits, a thick soil cover and the vegetation, rocks are generally outcropping along streams and in roadcuts. They are therefore temporary in most cases.


The material thoroughly studied by Grachev and coauthors (see references below) has been recovered from three outcrops:

- Outcrop Gams 1 or Knappengraben section (coordinates: 47°39.783' N, 14°52.982' E - see place marker on the map), located 700 m south of the abandoned farmhouse Kronsteiner at the crossing between the forest road and the Knappengraben stream. The outcrop is presently protected by a fenced shelter and is only accessible by permission. It exposes a section of the Nierental Formation across the K/T boundary. Beds are dipping at 40° towards SSE. The base is formed by pale grey, late Maastrichtian shaly limestones with a well-defined ichnofauna. The transitional boundary layer consists of dark grey plastic clay containing small mica particles. It is overlain by grey clays and thin, yellowish to brown fine-grained, sandstone layers;

- Outcrop Gams 2 (coordinates: 47°39.47' N, 14°52.05' E) located E of the old Haid sawmill. It is a river cut on the right (north) side of the Gamsbach, just above the alluvial flat. Nierental Formation with the K/T boundary is exposed at a length of approximately 10 m. The rocks dip at 15–30° towards SW. A neptunian dike extends into the Maastrichtian limestone from the top towards a depth of 1 m. Its infilling consists of clay with high mica content. Although it has been formed before the deposition of the transitional layer the composition of clays in virtually the same;

- Outcrop Gams 3 (coordinates: 47°39.79' N, 14°52.54' E) located on the left bank of the Gamsbach, 350 m W of the abandoned farm house Kronsteiner. The sequence is the same as in the previous outcrops. The rocks dip at 45° towards S.


The 2-cm-thick transitional layer at the K/T boundary shows a significant vertical geochemical zonation the from the bottom to the top. According to Grachev et al. (2008) and Grachev (2009), at the first stage (duration approximately 1500 years at conservative estimates of the sedimentation rate), the transitional layer formed under the influence of volcanic ash; it is marked by the presence of titaniferous magnetite, gold, copper, and sulfides (pyrite, arsenopyrite, galena, pentlandite, pyrrhotite, and sphalerite), as well as high concentrations of Ir, As, Zn, Cu, Cr, and other elements. At the second stage, the sedimentation pattern was influenced by the fall of an asteroid (meteorite), traces of which are recorded as pure nickel globules, awaruite, moissanite, and diamond crystals.


All minerals listed here have been found in the transitional clay layer at the K/T boundary. From a mineralogical point of view the following phases, found in in the ultraheavy fraction (ore minerals) of the lower part of the transitional layer, are particularly interesting:
-rhenium (Grachev et al., 2008 a; Grachev, 2009), as grains less than 30 μm in size from the Gams 2 section. Their composition is quite similar to that of pure rhenium with traces of Fe (0.07 wt.%);
-platinum not alloyed with other metals (Grachev, 2009). Native platinum has been discovered under the study of residue fraction of clay. After dissolution of 200 g of clay with HF and HCl, ten grains of platinum by total volume of8×10⁴μm³ in a residue of 16 mg by weight were found. The simple recalculation gives the content of Pt in clays about 10 ppb. Microprobe analyses of these Pt grains showed the existence of pure platinum not alloyed with other metals (seven grains). Such result is unusual because pure platinum is unknown in nature. Attention was paid to the specific morphology of such Pt grains: they have the irregular shape outlines with well-developed branching, tree-like and transverse-hummocky structures. Furthermore, extremely surprising is the occurrence of a thin film of Pt on the surface of a rounded zircon grain. In Grachev's opinion, it means that film of Pt has been formed in situ due to authigenic flux from sea water during the transitional layer deposition. Platinum was initially dispersed in sea water as a result of volcanic aerosol settling;
- silver andpalladium-silver series (Grachev, 2009). Two different Ag-bearing phases were recognized in the lower part of transitional layer of Gams 2 section. The first one is native silver, whose composition corresponds to 98.7% of Ag. It occurs as twin crystals and its outline resembles the silver crystals formed in primary hydrothermal veins. The second one is represented by nugget plates, less than 20 μm in size, of a palladium-silver alloy of compositionAg₄₇Pd₅₃, i.e.Ag_0.93Pd_1.07. This phase is similar toUM1992-06-E:AgPd. However, palladium and silver are completely miscible and there is a complete solid solution between palladium and silver. According to the IMA–CNMNC rule of the dominant constituent, this alloy in which palladium predominates, although very rich in silver, is termedpalladium;
-α-brass with compositionCu₆₇Zn₃₃, i.e.Cu_2.71Zn_1.29 (Grachev, 2009);
-unnamed (Ni-Cu-Zn-Sn alloys) with Ni in the range 52.33-82.44 wt.%, Cu 10.33-33.23 wt.%, Zn 0.00-19.77 wt.%, and Sn 0.00-30.61 wt.% (Grachev, 2009).

Other Regions, Features and Areas containing this locality

References