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RESEARCH PRODUCT

Mineralverwitterung, tonmineralbildung und rubefizierung in Terrae calcis der slowakei Ein beitrag zum paläoklimatischen aussagewert von kalkstein-Rotlehmen in Mitteleuropa

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Mineral weathering, clay mineral formation and rubefication of Terrae calcis in Slovakia — A contribution to paleoclimatic evidence of limestone Rotlehm (terra rossa) in Central Europe Limestone Rotlehm (Terra rossa) is very often interpreted as a product of intensive mineral weathering and clay formation under subtropic (to tropic) climate. Especially the formation of hematite in soils as the main process of rubefication is generally believed to occur only in warm climates with a seasonal alternation of precipitation and drought. Fossil or relict Terrae rossae in Central Europe are therefore very often considered as witnesses of a corresponding paleoclimate. On the other side many authors consider the Terra rossa as a product of the insoluble residue in limestones which contains material from earlier formed rubefied soils. This viewpoint is known as the residual theory (“Losungs-” or “Ruckstands” theorie). In this case the climate factors for the formation of Terra rossa would be less significant. Besides micromorphological studies mineral optical investigations of the fractions > 2 μm and X-ray investigations of the clay particle fractions 2-0.2 μm and 1. The quantitative composition in the single fractions of the primary minerals and clay minerals of the nine Terrae calcis in comparison with the LR show that the Terrae fuscae of Ludrova(see figs. 1, 10) have a lithologic discontinuity: the clay content of the LR is distinctly higher than in the accompanying Terrae fuscae. For the other Terrae calcis an approximate sedimentarily homogeneity can be assumed. 2. In the Terrae rossae especially near Drevenik (fig. 2), Ivanovce (fig 4) and in “Vo Viniciach” near Levice (fig. 9) and approximately also in the two other Terrae rossae near Levice (fig. 7, 8) no or almost no mineral weathering and clay mineral formation is verifiable. These soils therefore are lithomorphic soils in the sense of the residual theory: their formation was independent of the regional climatic characteristics. 3. In the Terra rossa near Ratnove (fig. 5) the clay content is very high (87%), but the residue of the underlying travertine consists already of 75% clay minerals. Weathering of feldspars and above all of phyllosilicates resulted in a formation of illites and kaolinites. However, the rate of clay formation is low in comparison with interglacial loess soils in the neighbouring Carpathian Basin; the largest part of the clay minerals in this Terra rossa must be regarded as inherited, too. 4. On the other hand, the content of primary minerals > 2 μm in the LR near Kolinany Malok is very high (78%). The clay content of the Terra rossa is about twice as high as in the LR (47% to 22%, fig. 6 K in comparison with 6 L). The weathering of the largest parts of the feldspars and phyllosilicates has resulted in a formation of illites and to a greater extent in a formation of kaolinites. 5. In the Terra fusca from early to middle Pleistocene travertine (fig. 3) only a slight mineral weathering and clay mineral formation is detectable, although the LR contains a larger part of coarse and medium silt (probably loess). For the determination of the iron oxides Mossbauer spectra of the 1. In the Terrae fuscae including their LR of strong brown to reddish yellow colours hematite can not be detected. Goethite is the only iron oxide in these sample pairs. 2. The hematite content determines in nearly all Terrae rossae sample pairs the quite different fraction of red (the hue notation) of the (Munsell) colour. Two exceptions are the Terrae rossae with their LR in Drevenik (fig. 2) and “Vo viniciach” in Levice (fig. 9): in both cases the Terra rossa and its LR have the same or nearly the same colour, but the hematite content in the Terra rossa is quite higher than in the accompanying LR (cf. tab. 2). 3. All Terrae rossae show with respect to their LR an increase of the hematite content, but with remarkable differences. In one of the Terrae rossae in Levice (fig. 8, O-P) the increase of hematite is very pronounced (although no or almost no mineral weathering and clay formation was found). On the other side the increase of the hematite content in the Terra rossa of Ratnovce (fig. 5, G-H) is just detectable (although some mineral weathering especially of phyllosilicates and clay formation has taken place). In the Terra rossa of Kolinany Malok (the only soil with a high mineral weathering and clay formation) the increase of hematite is intermediate (cf. fig. 6, K-L). In the Terra rossa of Ivanovce (fig. 4, E-F) no change in the low hematite content can be observed. But in this exposure a doline filling of a soil sediment (in general 7.5 YR 5/8) is present which contains small fractions of soil with distinct red colour (10 R 4/6). These fractions show a Mossbauer spectrum of pure hematite. These results show that a rubefication in the Terrae rossae could be established, the extent of which is mostly but not always determined by the hematite content and obviously independent of the intensity of weathering; in most of the Terrae rossae no mineral weathering and clay formation was verifiable.