Slump folds within mid-Miocene crevasse-splay deposits: a unique example from the Tomisławice lignite opencast mine in central Poland

Abstract

Non-tec tonic, soft-sed i ment de for ma tion struc tures oc cur in mid-Mio cene cre vasse-splay de pos its ex posed in the Tomisławice lig nite opencast mine in cen tral Po land. The cre vasse-splay cross-strat i fied siliciclastic de pos its are un der lain by con tin u ously folded and rel a tively thick lig nite beds, and over lain by a thin un dis turbed layer of lig nite. Only the mid dle part of the cre vasse-splay suc ces sion is de formed plas tic ally in the form of folds, while the lower and up per most beds are undeformed. Most of the intraformational de for ma tion struc tures are re cum bent folds, while only a few can be clas si fied as up right folds in the ini tial stage of their evo lu tion. The or i gin of these folds is as so ci ated here with a penecontemporaneous slump ing pro cess caused by liq ue fac tion of sandy-muddy sed i ments. The slump ing was trig gered by an in crease in the in clina tion of heterolithic lay ers caused by the compactional sub si dence of an or ganic-rich sub strate-peat. This type of sub sidence oc curred fol low ing a sud den siliciclastic load on top of the un der ly ing and poorly-com pacted peat/lig nite seam. The ini ti a tion and de vel op ment of the slump folds can be ex plained by dif fer en ti ated load ing, com pac tion and liq ue fac tion processes, and the in tro duc tion of a tec tonic agent is un nec es sary.

Acta Geologica Polonica

“…The occurrence of the siliciclastics within the coal seam, in the interpreted case within the MPLS-1, was usually associated with floods in the mire areas. In addition, the lens-like geometry of the entire sand bodies and facies associations pointed to crevasse splays that may have been accumulated in various depositional sub-environments (e.g., Horne et al 1978;Guion 1984;McCabe 1984;Flores 1986;Farrell 2001;Zieliński 2014;Widera 2020). Thus, the deposits of the first crevasse splay described above (Text-fig.…”

“…3A, B). In this case, the lowermost sedimentary facies is represented by a massive gravelly sand -SGm (Widera and Kita 2007). In the higher portion of the section, large-scale trough cross-stratification predominates, such as: St, SGt and STCt.…”

“…They occur in the form of marine glauconitic sands (Tomisławice area) or as lacustrine 'blue clays' and beach 'Koźmin Gravels' that were redeposited into the Neogene (Koźmin and Adamów area) (cf. Text-figs 1 and 2; Widera and Kita 2007;Widera 2010). On the contrary, the Paleogene deposits have not been documented in the area of the Jóźwin IIB and Kazimierz N lignite opencasts.…”

Four in one: a new crevasse-splay complex in the middle Miocene of central Poland

“…This is due to the fact that in recent years, more marginal parts of the deposits have been exploited (even selectively), where the lignite seams are thinner and often interbedded with sands (Widera et al, 2022). So far, in the Tomisławice and Pątnów IIB opencasts, managed by the Konin Lignite Mine, sediments of at least six crevasse splays have been described, where in two cases these splays were superposed (Widera, 2016a(Widera, , 2020Widera et al, 2017aWidera et al, , 2023Chomiak et al, 2019;Chomiak, 2020;Wachocki et al, 2020;Dziamara et al, 2022Dziamara et al, , 2023. They represent subaerial and subaqueous types, as well as deformed and undeformed subtypes of crevasse splays (Widera et al, 2023).…”

“…Some of them, such as the local crevasse splays, were unexpected. In the last few years (2018)(2019)(2020)(2021), several crevasse splays became available for direct observation in the opencasts (Jóźwin IIB, Tomisławice) of the Konin Lignite Mine (Chomiak et al, 2019;Wachocki et al, 2020;Widera, 2020;Dziamara et al, 2022Dziamara et al, , 2023Widera et al, 2022Widera et al, , 2023. It seemed that the limiting of lignite mining in the Konin region would prohibit exposure of any additional crevasse splays of scientific interest.…”