Rhaetian, where it probably signals a climatic change, i.e. a shift in the weathering pattern towards kaolinite, correlated with the disappearance of hematite.
Clay Minerals, (2014) 49, 569–594
Weathering, sedimentary and diagenetic controls of mineral and geochemical characteristics of the vertebrate-bearing Silesian Keuper ´ 1 , * , J . S Z U L C 2 , A . A N C Z K I E W I C Z 1 , K . J E W U Ł A 1 , 3 , M . B A N A S´ 1 J . S´ R O D O N 4 AND L . M A R Y N O W S K I 1 Institute of Geological Sciences, Polish Academy of Sciences Research Centre in Krako´w, ul. Senacka 1, 31-002 Krako´w, Poland, 2 Jagiellonian University, Institute of Geological Sciences, Oleandry 2a, 30-063 Krako´w, Poland, 3 Chemostrat Ltd, Unit 1 Ravenscroft Court, Buttingcross Ind. Estate, Welshpool, Powys, SY21 8SL, UK, and 4 Faculty of Earth Sciences, University of Silesia, Be˛dzin´ska 60, 41-200 Sosnowiec, Poland
(Received 24 April 2014; revised 17 August 2014; Editor: George Christidis)
AB ST R ACT : Mudstones and claystones from the southern marginal area of the European Upper Triassic, midcontinental Keuper basin (Silesia, southern Poland) were investigated using XRD, organic and inorganic geochemistry, SEM, K-Ar of illite-smectite, AFT, and stable isotopes of O and C in carbonates in order to unravel the consequent phases of the geological history of these rocks, known for abundant fossils of land vertebrates, and in particular to evaluate the diagenetic overprint on the mineral composition. The detected and quantified mineral assemblage consists of quartz, calcite, dolomite, Ca-dolomite, illite, mixed-layer illite-smectite, and kaolinite as major components, plus feldspars, hematite, pyrite, chlorite, anatase, siderite, goethite as minor components. Palygorskite, gypsum, jarosite and apatite were identified in places. The K-Ar dates document a post-sedimentary thermal event, 164 Ma or younger, which resulted in partial illitization of smectite and kaolinite. The maximum palaeotemperatures were estimated from illite-smectite as ~125ºC. Apatite fission track data support this conclusion, indicating a 200 160 Ma age range of the maximum temperatures close to 120ºC, followed by a prolonged period of elevated temperatures. These conclusions agree well with the available data on the Mesozoic thermal event, which yielded Pb-Zn deposits in the area. Organic maturity indicators suggest the maximum palaeotemperatures
