A lacustrine record of the early stage of the Miocene Climatic Optimum in Central Europe from the Most Basin, Ohře (Eger) Graben, Czech Republic

Abstract

This study reports on a ß 150 m thick macrofossil-barren sequence of siliciclastic sediments from a Burdigalian age (Early Miocene) freshwater lake. The lake was located within an incipient rift system of the Most Basin in the Ohře (Eger) Graben, which was part of the European Cenozoic Rift System, and had an original area of 1000 km 2 . Sediments from the HK591 core that cover the entire thickness of the lake deposits and some of the adjacent stratigraphic units were analysed by X-ray fluorescence spectroscopy (a proxy for element composition) and magnetic polarity measurement. The element proxies were subjected to frequency analysis, which provided estimated sedimentation rates, and allowed for sediment dating by magnetostratigraphy and orbital tuning of the age model. Based on the resulting age model and the known biostratigraphy, the lake was present between 17.4 and 16.6 Ma, which includes the onset of the Miocene Climatic Optimum in the latest Early Miocene. The identification of orbital forcing (precession, obliquity and short eccentricity cycles) confirms the stability of the sedimentary environment of the perennial lake in an underfilled basin. The dating allowed the sediment record to be interpreted in the context of the current knowledge of the European climate during that period. The stability of the sedimentary environment confirms that precipitation was relatively stable over the period recorded by the sediments.

Petrophysical and geochemical signature of the Hangenberg Events: an integrated stratigraphy of the Devonian-Carboniferous boundary interval in the Northern Rhenish Massif (Avalonia, Germany)

“…The fact that individual element ratios reveal cycles of different order is not so surprising. A recent study of orbitally driven cyclicity in lacustrine sediments (Matys Grygar et al 2014) has shown that, e.g., Al/Si and K/Al recorded eccentricity, obliquity and precession with different sensitivity. K/Al is used as a proxy for clay mineral assemblages (see "Interpretative potential of petrophysical and geochemical proxies") and its cyclic fluctuations can be interpreted as changes in the weathering intensity and processes, which could be directly related to the original climate.…”

Testing the impact of stratigraphic uncertainty on spectral analyses of sedimentary series

“…Orbital forcing can also be detected in a monotonous thick marly section, showing no apparent bedding (e.g. Ghirardi et al, 2014;Matys Grygar et al, 2014). In that case, we instead suggest measuring the total thickness of the sequence several times to assess the potential dispersion of the sample steps.…”

Early stages of clastic deposition in the Most Basin (Ohře Rift, Czech Republic, Early Miocene): timing and possible controls

“…Figures 2 and 3 show the major chemostratigraphic markers for the Most Basin and their lithological descriptions, which are based on several drill cores and local geochemical surveys that have been described in detail elsewhere (Matys Grygar & Mach 2013a, b;Matys Grygar et al 2014). This scheme has been used for the clastic sediments in the Bílina Mine area, which are up to 300 m thick, and in the Libouš Mine area, where they are 120 m thick.…”

“…The chemostratigraphic scheme that was previously published for the Libkovice Member (Matys Grygar & Mach 2013a, b;Matys Grygar et al 2014) is based on the assumption that these sediments were deposited in a single lake whose geochemistry was driven by basin-wide environmental changes. Extending that scheme to the basin periphery and to periods prior to the development of the basin-wide lake (the Holešice Member) is thus challenging because it is assumed that the basin-wide lake was preceded by several isolated water bodies .…”

“…clastic sediments below the Holešice/Libkovice boundary), and stratigraphically correlated lacustrine sediments of the Libkovice Member with a variety of laterally stable local chemostratigraphic horizons (Matys Grygar & Mach 2013a, b;Matys Grygar et al 2014;Fig. 2).…”