Complexity of glacial dispersal and hydromorphic processes in till geochemistry Edited by Marja Liisa Räisänen and Maria Nikkarinen Geological Survey of Finland, Special Paper 34, 5– 2 0 , 2003.

SULPHUR IN SOIL VERTICAL PROFILES IN PIRKANMAA REGION, SOUTHERN FINLAND by Maria Nikkarinen and Pekka Lestinen Nikkarinen, M. & Lestinen, P. 2003. Sulphur in soil vertical profiles in Pirkanmaa region, southern Finland. Geological Survey of Finland, Special Paper 34, 5–20, 5 figures and 5 tables. The study area is located in the Paleoproterozoic Svecofennian domain in the Pirkanmaa region, Finland. The bedrock consists of mica gneisses which have graphite and sulphide minerals as common accessories. The overburden is dominantly composed of c. 5 m thick glacial till. Vertical variation and different forms of sulphur in seven profiles in the Pirkanmaa region were studied by using different extraction methods. The mobile sulphur fractions were studied with four selective leaches: water-soluble, sodiumdihydrogenphosphate, ammonium acetate and ammoniumoxalate. Influence of sulphur bearing bedrock can be observed in the sulphur content of vertical soil profiles. The influence of the groundwater table is distinct in the S cycling. The amount of the total S content does not predict the amount of easily soluble forms of S. There is no correlation between the total S and partial extracts. In average, the amount of S in all partial extractions was less than 10% of the total. Secondary precipitations of Fe-oxides were estimated to be the major host of mobile S. Weathering of primary sulphides has advanced at different rates in the different profiles. The depth does not seem to be the most dominant factor in these profiles controlling weathering and oxidation conditions as it was expected based on the previous studies. Key words (GeoRef Thesaurus, AGI): geochemistry, soils, till, sulfur, chemical analysis, leaching, Hattula, Aitolahti, Pirkkala, Vedentaka, Finland Maria Nikkarinen and Pekka Lestinen Geological Survey of Finland, P.O. 1237, FIN-70211 KUOPIO, FINLAND E-mail: [email protected]

INTRODUCTION

In nature, sulphur (S) occurs widely distributed as inorganic and organic compounds. In the bedrock, it is very unevenly distributed as metal-sulphides and to a lesser extent as various sulphates such as gypsum and anhydrite (CaSO4). Most common sulphide species are pyrite (FeS2 ), marcasite (FeS2 ), pyrrho-

tite (FeS), chalcopyrite (CuFeS2 ), galena (PbS), sphalerite (ZnS), pentlandite ((Fe,Ni)9S8) and arsenopyrite (FeAsS). The irregular distribution of sulphur in rocks and the insufficient amount of analyses are the main reasons for the large discrepancies between estimates of the concentration of S in rocks 5

Geological Survey of Finland, Special Paper 34 Maria Nikkarinen and Pekka Lestinen

of different regions. Approximate average abundances are 100 mg/kg for ultramafic magmatic rocks, 300 mg/kg for mafic magmatic rocks, 400 mg/kg for felsic magmatic rocks and 3000 mg/kg for shales (Govett 1983; and references therein). Black shales and schists containing graphitic carbon can be exceptional rich in sulfur, and e.g. in Finland contents up to 20% S has been observed (LoukolaRuskeeniemi 1992). In Finnish glacial tills, sulphur has been observed to occur both as primary sulphides as well as secondary precipitates (Peuraniemi 1982). Its abundance in the till fines (