Sedimentological evaluation of the Boda Claystone Formation (SW Hungary) based on the analysis of dolomite and siltstone intercalations Pozsgai Emília University of Pécs, Dept. of Geology, Geography M.Sc. Student Supervisor: dr. Konrád Gyula Meeting of Young Geoscientists, 25-26th March 2011, Győr

Geological map of the West Mecsek Mts. (edited by Konrád et al. 2010)

Paleoenvironmental reconstruction (Konrád et al. 2010)

Lithological features of the BCF (edited by Konrád et al. 2010)

As the newest views, are these interbeddings siltstones? The main objective is… The BCF includes various intercalations, which were earlier described as dolomite or dolomarl. As the newest views, are these interbeddings siltstones?

My goal was… To clarify… 1) the petrological and mineralogical composition, 2) the texture, 3) the structure, 4) and the bedding structure of the intercalations. To study a many samples (from outcrops and boreholes) to define different sedimentological structures (types). To contribute the validity process of the laser-induced plasma spectrometer ImaGeo-LIPS  Is that suitable to examine the material of the thin intercalations?!

Importance of the issues Evaluating the interbeddings from a petrological and sedimentological aspect (texture, structure) Clarify the sedimentary environment. Homogenity of the formation? Disposal of the high-level radioactive waste!

Applied methods Field work, geological documentation To summarize and to reappraise the earlier analitical results (XRD, DTG, chemical assay, etc.) Polished sections Thin sections Laser-Induced Plasma Spectrometer (ImaGeo LIPS)

Mineralogical composition of different rock types of the BCF [weight %]

Siltstone intercalations (both samples are thin sections) Dolomite intercalations (both samples are thin sections)

Investigation with the Laser-Induced Plasma Spectrometer (ImaGeo LIPS)  Low-priced, rapid Compatible to field work  Compatible to examine drill cores  Compatible to raster measurement

Polished sections

[Legend: IB = interbedding; C = claystone]

To study the sedimentary structure: Superficies of a drill core Overlie by unbedded, silty claystones with disturbed, inhomogeneous structures Often occur in bunches Overlie on erosional surfaces Normal graded bedding Horizontal bedding (planar lamination) To study the sedimentary structure: Superficies of a drill core Shrinkage cracks and polygons

Disturbed and pedogenic (?) structures (thin section) Cross-bedding structure (left: drill core; right: thin sections)

Summary, conclusion I. My investigations are showing that… 1) The most of the intercalations are siltstones, not dolomites! 2) These fine-grained interbeddings were deposited during floodings ( the intercalations are indicating periods with high precipitation!), so aren’t indicating drying-out events! 3) Rarelier were deposited real dolomites from the shallow water through the evaporation. 4) Dolomite is presenting often as a substance of the matrix.

Summary, conclusion I. 5) After the floodings, when the sediment surface dried out, were evolved the desiccation cracks and desiccation poligons (postsedimentary structures) 6) The sedimentary surface were covered by unbedded sediments with pedogenic structures  I do not consider these lacustrine sediments but were deposited by intermittent currents (mudflows) Thus the known succession of the formation represents the marginal facies of a playa lake.

Summary, conclusion II. (LIPS) The ImaGeo LIPS investigations are suitable to examine the material of the thin intercalations too. It is suitable to measure: drill holes and field samples too!

About the continuance of the investigations?! To recheck the accessible archive drill cores. To refine the geometry of the sedimentary basin trough the interbeddings. To study the paleoenvironmental conditions through fossils, sedimentary structures and the different mikrofacies features. Cyclicity of the intercalations (Halász in press)

Acknowledgements dr. Konrád Gyula, Dezső József, dr. Fedor Ferenc, Halász Amadé, dr. Maros Gyula, Máthé Zoltán, dr. Raucsikné dr. Varga Andrea, dr. Sebe Krisztina

Thank you for your attention!