Analysis of lithofacies cyclicity in the Miocene Coal Complex of the Bełchatów lignite deposit, southcentral Poland
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Date
2015-12
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Instytut Geologii UAM
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Abstract
Markov chain analysis was applied to studies of cyclic sedimentation in the Coal Complex of the Bełchatów mining
field (part of the Bełchatów lignite deposit). The majority of ambiguous results of statistical testing that were caused
by weak, statistically undetectable advantage of either cyclicity over environmental barriers or vice versa, could be explained
if only the above-mentioned advantages appeared in the neighbourhood. Therefore, in order to enhance the
credibility of statistical tests, a new approach is proposed here in that matrices of observed transition numbers from
different boreholes should be added to increase statistical reliability if they originated in a homogeneous area. A second
new approach, which consists of revealing statistically undetectable cyclicity of lithofacies alternations, is proposed
as well. All data were derived from the mining data base in which differentiation between lithology and sedimentary
environments was rather weak. For this reason, the methodological proposals are much more important than details of
the sedimentation model in the present paper. Nevertheless, they did reveal some interesting phenomena which may
prove important in the reconstruction of peat/lignite environmental conditions. First of all, the presence of cyclicity in
the sedimentation model, i.e., cyclic alternation of channel and overbank deposits, represents a fluvial environment. It
was also confirmed that the lacustrine subenvironment was cut off from a supply of clastic material by various types
of mire barriers. Additionally, our analysis revealed new facts: (i) these barriers also existed between lakes in which
either carbonate or clay sedimentation predominated; (ii) there was no barrier between rivers and lakes in which clay
sedimentation predominated; (iii) barriers were less efficient in alluvial fan areas but were perfectly tight in regions of
phytogenic or carbonate sedimentation; (iv) groundwater, rather than surface flow, was the main source of CaCO3 in
lakes in which carbonate sedimentation predominated; (v) a lack of cyclic alternation between abandoned channels and
pools with clayey sedimentation; (vi) strong evidence for autocyclic alternation of phytogenic subenvironments and
lakes in which carbonate sedimentation predominated was found in almost all areas studied.
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Keywords
Markov chain method, cyclic sedimentation, vertical succession of lithofacies
Citation
Geologos, 2015, 21, 4, pp. 285-302
ISBN
978-83-232187-4-6