Publication details
Quantitative compositional analysis of the Lochkovian-Pragian boundary event at „Na Chlumu Quarry“ (Prague Synform, Czech Republic)
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| Year of publication | 2015 |
| Type | Conference abstract |
| Citation | |
| Description | The Barrandian area (Prague Synform, Bohemian Massif) is a stratotype area for the Lochkovian-Pragian boundary event, which is connected with faunal and facies overturns associated with a global sea level fall. Carbonate compositional variations were studied on 49 samples from ~100 m thick section “Na Chlumu Quarry” to provide an insight into the nature of this event. Principal component and cluster analysis were applied on grain size and compositional point count data. Biased patterns resulting from covariance structure of closed data were reduced by using the log-ratio methodology. The allochem composition corresponds to heterotrophic carbonate producer assemblage while the geometry of carbonate bodies suggest a ramp setting for the Lower Devonian carbonates of the Prague Synform. The compositional data analysis indicates that the Praha Formation succession represents a distinct lowstand- to transgressive succession, with a prominent sequence boundary situated close to the Lochkovian/Pragian stage boundary. This is consistent with petrophysical patterns at numerous sections across the Prague Synform as well as with data from elsewhere. The principal component analysis and hierarchical clustering show a clear separation of different microfacies types according to dominance of the corresponding patterns. These effects are highlighted due to relative scale property and scale invariance of the original samples, taken into account by the log-ratio methodology. |
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