Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Heavy minerals in sediments of the southern part of the Krkonoše Piedmont Basin in the context of changes of individual Permo-Carboniferous formations


Tamara Sidorinová, Marcela Stárková

Geoscience Research Reports 50, 2017, pages 215–220
Map sheets: Jičín (03-43)

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Published online: 18 December 2017

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Heavy mineral suites from the southern part of the Krkonoše Piedmont Basin at the Nová Paka area were studied. There were sampled Carboniferous lithostratigraphic units - Kumburk, Syřenov and Semily Formations, and Permian unit the Vrchlabí Formation. This study is focused on determination of heavy mineral associations within the individual formations.
Fourteen samples were taken from fluvial and delta coarse-grained sandstones and conglomerates for heavy mineral and pebble analysis. Modal composition of heavy fraction was studied using optical microscopy and there were done semiquantitative estimates of all minerals. All samples show high contents of Fe secondary minerals (30-80 vol. %). Only the most persistant minerals in significant amount are preserved (tourmalines, rutiles and zircones), while others are preserved in small or accessory amounts (apatites, garnets, staurolites, micas). Heavy mineral assemblages are very similar in all samples. The most variable association of HM was found in sediments of the Semily Formation. Prevailing tourmalines are supposed to be from granitoids. The apatit-tourmaline index AT (100 × apatite/apatite + tourmaline), and rutile-zircon index RuZi (100 × rutile/rutile + zircon) are different in Carboniferous (the Kumburk, Syřenov and Semily formations) and Permian (Vrchlabí Formation) beds.
Grain roundness is not perfect, the preservation of crystal shapes have only zircon and rutile. Grain fragments are angular or subangular, consequently not too long transport is thought to have occurred.
All macroscopically observed pebbles are subangular or suboval, and there are oval pebbles in the Vrchlabí Formation. Quartz and metamorphic rocks predominate, while granitoids are represented only up to 5 vol. %. Carboniferous sandstones and conglomerates in the Vrchlabí Formation were also observed.