Origin of marls from the Polish Outer Carpathians: lithological and sedimentological aspects
Authors: Górniak Katarzyna 
Published: May 2018

Outcrops of marls, occurring within the sandstone-shaly flysch deposits of the Polish part of Outer Carpathians, considered to be locus typicus of these rocks, were described, measured and sampled. Lithologic features of marls, representing 15 complexes of different age and occurring in 15 complexes of various tectonic units, are presented (Fig. 1, 2). The present studies were concerning Jurassic marls from the Silesian Unit (Goleszów Marls), Upper Cretaceous marls from the Skole and Sub-Silesian Units (Siliceous-Fucoid and Węgierka Marls and Węglowka, Frydek, Jasienica and Zegocina Marls respectively), and Eocene-Oligocene marls from the Magura, Fore-Magura and Skole Units (Łącko, Zembrzyce, Budzów, Leluchów and Niwa, as well as Grybów and Sub-Cergowa and Dynów Marls respectively). The former opinions on lithology, age, formal subdivision, sedimentation conditions and genesis of these rocks are discussed (Table 1, 2; Fig. 1). Detailed description of the above mentioned marl-bearing complexes are presented and for each of them the typical lithological features are determined (Tables 3 - 20). The results of profiling are presented against the background of geological studies of the Carpathian marls. The results of lithologic studies are compared to form a classification scheme and are used as the basis of distinguishing genetic types of marls. Moreover, the interpretation of the conditions of sedimentation of these rocks is presented.

According to the present author’s studies, in the outcrops of marls considered to be locus typicus of the above mentioned rocks, there are both monolithic and polylithic complexes exposed. The polylithic complexes contain apart from marls intercalations of arenaceous-shaly flysch (Table 19). Event sedimentation of marly facies, appearing at different times and in various parts of the Carpathian basin is the result of periodically repeating conditions favouring the sedimentation of marls. Carpathian marls seem to be lithologically diversified. This is a natural for these rocks, uniting in variable proportions the features of limestones, clays, siliceous and clastic rocks. Depending on the proportions of these components, they display the features of the dominant one. The lithologies of Carpathian marls do not depend on their age and position in the sedimentation basin. Nevertheless, apart from visible differentiation of marls they show many common lithologic features: fine grain size, in general corresponding to silty-clayey fraction, variable but usually considerable thickness of beds of nonarenaceous variety of marls (0.5 - 1000 cm) and small thickness of arenaceous one (2 - 62 cm). In the majority of marly complexes, the arenaceous variety, starved ripplemarks, thin sandstone beds and sandy lamines occur in bottom parts of marly beds. The majority of marls display variably developed lamination and the occurrence of burrows (Table 19). Taking into account the Ghibaudo’s (1992) classification it was estimated that the marls in question can be assigned to three finest grained lithofacies: M (mud beds), MT (mud-silty couplets) and MS (mud-sand couplets) as well as to the MyG facies (muddy gravel). These lithofacies appear in marly complexes in various proportions (Table 20). Internal structures of beds are evidence of settling grains from suspension (depositional interval e2), interrupted with different intensity by deposition from traction (depositional intervals b, d and e1), and reworking of sediments by weak bottom currents (depositional intervals c and c0). The occurrence of similar lithologic features in marls of different age that come from different tectonic units is evidence of the repeating of similar sedimentation conditions, favouring the development of marly facies, at different times and in different parts of sedimentation basin of the Outer Carpathians.

According to the present author’s analysis, there is a distinct relationship between the appearance of marls and tectonic evolution of the Outer Carpathian basin. Marls initiate sedimentation, indicate reconstruction stages and are closing the deposition in the Outer Carpathian basin (Fig. 1). Marls appear in the Polish part of Outer Carpathians in Upper Jurassic, initiating sedimentation in the northern Tethyan domain. Subsequently, they occur within Upper Cretaceous sandy-shaly flysch, indicating the reconstitution stage of Outer Carpathian basin and from Eocene to Oligocene are completing the deposition in successively closing basins (Fig. 1). The appearance of marls indicates the stages of tectonic evolution of the Outer Carpathians. The opening and reconstitution of a basin is accompanied by appearance of marls distinguished as preorogenic (Goleszów, Siliceous-Fucoid, Węgierka. Frydek and Żegocina Marls), their closing - synorogenic marls (Lącko, Budzów, Zembrzyce, Leluchów, Niwa, Grybów, Sub-Cergowa and Dynów Marls). Marls represent sediments redeposited from shelves to deeper parts of basins in the form of muds (M, MT and MS facies) and as olistostromes and olistoliths (MyG facies) (Tables 19, 20). Marls redeposited in the form of olistoliths appear in the stage of opening of the Outer Carpathian basin on the boundary of the Jurassic/Cretaceous period (Goleszow Marls) and in the stage of its Upper Cretaceous reconstitution (Baculite and Zegocina? Marls). In the complexes containing redeposited marls in the form of muds, submarine slumps occur (Table 19). These features indicate tectonic disquiet accompanying deposition of marls. Among the marls studied, dark coloured rocks appear (black, bluish-gray, greenish-gray) and olive and light- coloured (creamy, beige), as well as variegated and red (Table 19). The differentiation of colours indicates sedimentation of Carpathian marls both in oxygenated environments and those that are oxygen-depleted. The analysis of evolution of the Carpathian basins indicates that they were starved basins during sedimentation of marls. Limited supply of clastic material in such basins suggests the discussion on the source of the clay minerals - one of essential components of marls. The occurrence of pyroclastic strata in sediments of the same age (Fig. 1) suggests their origin to be related to volcanic material.

The data of other authors, and the detailed profiling by the present author of outcrops that are considered to be locus typicus of marls and the appearance of which indicates a distinct correlation to tectonics of the Outer Carpathians, allowed to the present author to systematize and broaden the geological knowledge concerning the evolution of the marly facies in the northern part of the Tethyan Ocean. The conditions of sedimentation of marls deduced from the analysis of evolution of sedimentation basin of the Outer Carpathians and from lithologic data can be summarized as follows:

- marls appear episodically in the Outer-Carpathian basin (mono- and polylithic complexes) and determine the stages of its tectonic evolution; they initiate the stages of opening and indicate the reconstitution of basins (preorogenic marls) and closing sedimentation cycle (synorogenic marls);

- marls were deposited under conditions of tectonic disquiet (the presence of MyG facies), accompanied by volcanic activity (occurrence if pyroclastic rocks within chronostratigraphic equivalents of the marls studied);

- marly deposits were formed both under oxidizing and oxygen-depleted conditions, i.e. when the availability of oxygen in the bottom sediments was limited (variable colouration);

- marls represent the deposits of debris flows (MyG facies) redeposited from shelves in lithified form into zones that are situated close to the basin margins (olistoliths) and as resuspensed shelf muds accumulating within basinal sediments in the seafloor depressions (trap sediments) by suspension settling mechanism and periodically reworked by currents (M, MT, and MS facies).