The aim of this work was to find the source of K-feldspars in the Bohemian Upper Carboniferous arkoses, which has remained insufficiently solved to date. A previous study of arkoses in the Plzen Basin by Masek [24] found that “predominantly granites, whose composition had largely not been changed during destruction and denudation,” participated in their origin. Pesek [34] and Havlena and Pesek [5] provided a series of geological proofs for the contribution of clasts of Proterozoic metamorphic slates and greywackes from the west. Nevertheless, more recent works by Pešek [35,36] prefer a contribution from S-SE, particularly in the case of coarse grain clastics.

Petranek [37] and Kukal [17] also discussed a source of arkosic feldspars. While Petranek [37] doubted the main source of Variscean granitoids due to their insufficient denudation, according to Kukal [17], the main source of arkosic feldspars should be granitoid massifs. Klominsky et al. [16] posited a contribution from the area of the Central Bohemian Pluton (S and SE) due to the spectrum of heavy minerals with detritic gold. Vlasimsky [44] also regarded granitoid rocks of the Central Bohemian Pluton, together with Cambrian sediments and volcanites in the same direction, as an important source of the clastic material of arkoses of the Central Bohemian Upper Carboniferous.

The continental intermountainous Upper Carboniferous basins of West and Central Bohemian areas (Plzen /Pilsen/, Manetin, Zihle, Radnice, Kladno-Rakovnik and Mseno-Roudnice basins) were filled with molasse sediments between Moscovian and Asselian (substages Duckmantian to Autunian; 314.2–297.1 Ma [33]). Stratigraphically, four formations are involved: the Kladno Formation (Duckmantian–CCantabrian), subdivided into the Radnice (Duckmantian–BBolsovian) and the Nyrany (Asturian–CCantabrian) members; the Tynec Formation (Barruelian–llowermost Saberian); the Slany Formation (Saberian), subdivided into the Jelenice, Malesice, and Otruby members (the Otruby member can be substituted by Ledce and Kounov members in some places); and the Line Formation (uppermost Stephanian B–llower Autunian). Arkoses (sometimes kaolinized) are present in all four formations.

Oplustil et al. [33] and Martinek, Pesek, and Oplustil [23] discovered four significant hiatuses with a duration of 1–3.6 Ma in the West and Central Bohemian Upper Carboniferous, after which striking changes in the stratigraphy occurred, and tried to connect them with tectonic and climatic phenomena. These hiatuses occur within a boundary that encompasses (1) between the Lower and Upper Radnice Member (313.7–312.6 Ma; lower Bolsovian); (2) between the Radnice and Nyrany members (311.9–308.3 Ma; Leonian orogenetical phase in Bolsovian – Asturian); (3) between the Kladno and Týnec formations (305.9–304.1 Ma; Asturian orogenetical phase in Cantabrian – Barruelian); and (4) between the Slany and Line formations (301.6–300.6 Ma; Intra-Stephanian orogenetical phase in Stephanian B). The second, third, and last cases were accompanied by striking changes in deposition centers and are therefore interpreted as tectonic events (tectonic activity was proven in the Central Bohemian, Litomice, and Jachymov faults [23]. According to Marttnek, Pesek, and Oplustil [23], both tectonic movements and aridization took place within the boundaries of the Tynec and Slany formations.

According to Pesek [34], Havlena and Pesek [6], and Oplustil [32], a deposition center in the Plzen Basin was a deeply cut river valley in the NNE-SSW direction, filled with coarse-grained sediments (conglomerates and arkoses), originating in the Radnice Member. After a hiatus on the boundary of the Radnice and Nyrany members, a change of contribution from the NW direction took place. Even after a hiatus between the Kladno and Tynec formations, a contribution from the NW direction continued in the Plzen Basin, while in the Kladno-Rakovnik Basin, drained at the time of the Radnice Member sedimentation toward NW, the similar deposition centers were of NNE-SSW, NW-SE, and E-W directions, active up to the Line Formation [32].

On the basis of U-Pb geochronology of detritic zircon and monazite in the basin sediments, Zak, Svojtka, and Oplustil [45] discovered mixing of material from local and distant sources of various ages (Archeozoic–MMiddle to Upper Carboniferous). During the consequent inversion of the palaeorelief, a quick uplift of the area to S and SW of today´s basins 330–310 Ma ago (Visean–llowermost Moscovian) and a rapid baring of Moldanubian granitoids occurred to become a supplier of sedimentary filling of the basins, which had arisen freshly in N and NE 314–307 Ma ago (Radnice Member). Therefore, due to the study of detritic zircon and monazite, the opinion of the direction of the contribution changed by 180° as against the previous publications [23,32].

The origin of K-feldspars in the arkoses of the Plzen Basin from the neighboring granitoid massifs was investigated by means of triclinicity by Kuzvart et al. [20]. For the investigation of the origin of K-feldspars in arkoses of Upper Carboniferous basins, the results of Neuzilova´s research into triclinicity and geochemistry of K-feldspars from the Bor Massif granites [28] and Kladruby Massif granites [31], both in the SW, as well as analyses of K-feldspars from granitoids of the Central Bohemian Pluton (S-SE) and other neighboring granite massifs, granite porphyries, Teplice rhyolite, orthogneises, and migmatites [12,25-30,38] have not been used so far and are applied in this paper.

To date, the most detailed X-ray study of the structural arrangement (triclinicity), the molecular composition Or (AbAn), and the chemistry of trace elements (Ba, Sr, Pb, Rb, Sn, and Be) has been carried out on 224 samples of phenocrysts of K-feldspars of granites in the Nejdek part of the Karlovy Vary-Eibenstock Granite Massif [9,11]. The rim of this largest granite body of the West Krusne hory (Erzgebirge) Mts. composite pluton [15] occurs only 20 km NW of today´s rim of the Carboniferous basins (Figure 1). The upper part of the granites of the older intrusive complex (OIC) is disturbed by the intrusion of the younger intrusive complex (YIC) [1,3,21,42]. The intrusion of these post-tectonic granites reached a depth of ca. 2–4 km under the original surface [43]. According to the results of geochronological analyses, the age of the OIC granites lies in the range of 330 to 305 Ma, while the YIC granites are 25 million years younger [2]. The OIC group of so-called mountain granites (mesocratic peraluminic monzo-to-syenogranites) is represented mainly by medium-granular (porphyric) biotitic granite to granodiorite (Nejdek granite). YIC granites form a varied group of intensively fractionated granites here, accompanied by tin mineralization.

Figure 1: Position of the Upper Carboniferous Basins and the Karlovy Vary-Eibenstock Granite Massif.

1 – Upper Carboniferous, Kladno Formation (conglomerate, sandstone, arkose, mudstone) and Tynec Formation (arkose with conglomerate intercalations, red sandstone and mudstone); 2 – Upper Carboniferous – Lower Permian, Slany and Line formations (red sandstone, arkose, conglomerate, mudstone); 3 – younger intrusive complex (YIC) of the Karlovy Vary-Eibenstock granite Massif; 4 – older intrusive complex (OIC) of the Karlovy Vary-Eibenstock granite Massif; 5 – kaolin deposits; 6 – direction of transport of fluvial sediments into the Upper Carboniferous basins.

The strong predominance of perthitic orthoclases (Δ < 0.2) in granites of the OIC as well as the YIC is a result of magmatic origin under high temperatures and relatively rapid crystallization [9] in the vicinity of their original roof. In the case of the granites of YIC, their quick solidification had a subvolcanic character [41].

The published data on the structural arrangement (triclinicity) and the content of trace elements of K-feldspars in the granitoid massifs in the surroundings of the West and Central Bohemian Upper Carboniferous basins were correlated with the results of research into clastic relics of K-feldspars from Upper Carboniferous arkoses (Figures 2 a, b, and c). The collection of 41 samples of K-feldspars from Arkoses represents the whole area of the West and Central Bohemian Upper Carboniferous basins between the towns of Stribro and Velvary, both in the horizontal and vertical (stratigraphic) ranges.

Figure 2a: Graphs of Ba/Rb (ppm) contents of K-feldspars in Upper Carboniferous arkoses in comparison with fields of their contents in the Kladruby Massif [31], Sedmihori Stock [31], Merklin Massif and the Tis granite of the Louny Massif [12].

The points mark the studied K-feldspars in Upper Carboniferous arkoses, M = sample of K-feldspar in the Merklin Massif by Krchleby, T = sample of K-feldspar in the Tis granite of the Louny Massif from the borehole Mt-1 (1,680.5 m).

Figure 2b: Graphs of Ba/Rb (ppm) contents of K-feldspars in Upper Carboniferous arkoses in comparison with fields of their contents in the granitoids of the Central Bohemian Pluton [12,25,26,29,30]; the Certovo Bremeno type according to [27].

The points mark the studied K-feldspars in Upper Carboniferous arkoses, M = sample of K-feldspar in the Merklín Massif by Krchleby, T = sample of K-feldspar in the Tis granite of the Louny Massif from the borehole Mt-1 (1,680.5 m).

Figure 2c: Graphs of Ba/Rb (ppm) contents of K-feldspars in Upper Carboniferous arkoses in comparison with fields of their contents in granitoids of the older (OIC) and younger (YIC) intrusive complex of the Krusne hory Mts. [11] and in granite porphyries of the Flaje Massif [12].

The points mark the studied K-feldspars in Upper Carboniferous arkoses, M = sample of K-feldspar in the Merklín Massif by Krchleby, T = sample of K-feldspar in the Tis granite of the Louny Massif from the borehole Mt-1 (1,680.5 m).

The handly separated K-feldspars from Upper Carboniferous arkoses were X-rayed (triclinicity Δ, AbAn_solid, Abf_free) and geochemically (Ba, Sr, Pb, Rb) examined. The X-ray study was carried out on the X-ray difractometer Muller Mikro 111 in the Czech Geological Survey in Prague by the method described by Jiranek [8]. Neither the low grade of weathering nor the initial kaolinization of K-feldspars influence the X-ray-measured values. X-ray triclinicity Δ was measured from the differences of diffraction lines 131 and 131 by the classical method of Goldsmith and Laves [4]: Δ = 12.5 (d_131–dd₁₃₁), where 0 corresponds to sanidine or orthoclase, 0.2–0.9 to transitional microcline, and 0.9–1 to maximal microcline. The content of the AbAn component in a solid solution (AbAn_solid) was determined from the position of diffraction line 201 of K-feldspar according to the graph of Jones, Nesbitt, and Slade [14]. The content of the exsoluted Ab component (Ab_free) was determined according to the graph constructed by Jiránek [8] on the basis of ratios of intensities of diffraction lines 201 of K-feldspar and 201 of albite. The contents of trace elements typical for K-feldspars (Ba, Sr, Pb, and Rb) were determined by the AAS method in the laboratories of the Czech Geological Survey in Prague.

Triclinicity. All 41 samples analyzed are orthoclases, sometimes with an admixture of transitional to maximal microcline with Δ = 0.59–0.99. In 59% of samples, there is a pure orthoclase, in 20% and orthoclase with an admixture of 10% of microcline, in 14% and orthoclase with an admixture of 30% of microcline, and only in 7% of the cases does the content of microcline reach up to 50%. In one case (a sample of Prehorov in the Zihle Basin), there are, besides the prevailing orthoclase, two different microclines with Δ = 0.67 and 0.99. (For comparison: Among 123 samples of K-feldspars in the OIC granites of the Karlovy Vary-Eibenstock Massif, according to Jiranek [9], 83% of pure orthoclase, 12% of orthoclase in mixture with 20–80% of transitional microcline with Δ = 0.44–0.73, and 5% of pure transitional microcline with Δ = 0.19–0.71.)

The content of the AbAn component in the solid solution (AbAn_solid) ranges between 16 and 35% (average 24.6%).

The content of the exsoluted Ab component (Ab_free) is equal to zero in 95% of samples, which indicates that the original perthitic albite was secondarily leached off because albites and plagioclases undergo kaolinization earlier than K-feldspars. Only four samples from two boreholes in the Kladno-Rakovník Basin, three from the borehole Kralovice Ke-4 (depth 432.1–762.1 m; Otruby Member of the Slany Formation and Nyrany Member of the Kladno Formation) and one from the borehole Martineves Mt-1 (depth 455.5 m; Line Formation), contain 6.3–7.0% of Ab_free and indicate the freshness of feldspars at greater depths.

Contents of Ba range between 1,155–3,341 ppm (average 2,303 ppm), contents of Sr 136–590 ppm (average 257 ppm), contents of Pb 60–121 ppm (average 87 ppm), and contents of Rb 231–458 ppm (average 350 ppm).

The values of triclinicity and the trace element contents in K-feldspars of Upper Carboniferous arkoses for individual basins are stated in Table 1, together with the values for K-feldspars in the OIC of the Karlovy Vary Massif. The same results for the Kladno, Tynec, Slany and Line formations are stated in Table 2. No significant differences between K-feldspars of individual basins and formations were found, and therefore, in seeking the primary source of K-feldspars, it was possible to use the statistical sets for the West and Central Bohemian Upper Carboniferous as a whole.

Table 1: Summary of results of measurement of K-feldspars in Upper Carboniferous arkoses for individual basins in comparison with K-feldspars of the older intrusive complex (OIC, mountain granites) of the Nejdek part of the Karlovy Vary Massif.

n = number of samples; Φ = average; Δ = triclinicity, Or = orthoclase, Mi = microclase, Ab = albite, An = anorthite.

Table 2: Summary of results of measurement of K-feldspars in Upper Carboniferous arkoses for individual members and formations of the West and Central Bohemian basins.

n = number of samples; Φ = average; Δ = triclinicity, Or = orthoclase, Mi = microcline, Ab = albite, An = anorthite.

The structural properties and trace element content of K-feldspars in Upper Carboniferous arkoses were compared with the structural properties and trace element content of 63 separated K-feldspars phenocrysts from mountain granites (OIC) of the Nejdek part of the Karlovy Vary Massif [9, 11]. For their comparison, the binary Ba and Rb diagram (Figure 2c), the elements entering into the K-feldspars lattice preferentially in the extreme phases of their crystallization (Ba in the oldest and Rb in the youngest types of granites), was used.

The appearance of K-feldspars in Upper Carboniferous arkoses (white to pink, originally big phenocrysts with rare inclusions of quartz and biotite, sporadically muscovite) and their structural arrangement and trace element contents point to their intrusive origin. The dimensions of K-feldspar grains, even at a considerable distance of 90 km from the possible sources, show that their origin must have been in porphyric types of granitoids. The uniformity of all the examined K-feldspars of the West and Central Bohemian Upper Carboniferous arkoses indicates that they originated from one single source. The supply of K-feldspars to the whole investigated area from this source occurred during the period 17.1 Ma (314.2–297.1 Ma; Moscovian–Asselian), during which 7.5 Ma represented the sedimentation hiatuses, indicating the long-term exposure of a large, relatively homogeneous granite massif.

The values of K-feldspars triclinicity, without the parallel geochemical data, are not an unambiguous source indicator because they do not differ among the various granitoid rocks in such a range as the contents of trace elements. A good many candidates (granite massifs) for the source of K-feldspars in Upper Carboniferous arkoses, chosen on the basis of triclinicity values and of chronologically corresponding age towards Upper Carboniferous sediments, can be excluded by the determination of trace elements typical for the various phases of K-feldspars genesis, particularly geochemically opposite Ba and Rb (Figures 2 a, b, and c).

The Merklín Massif (in the S) and Tis granite of the Louny Massif (in the N), on which the Carboniferous sediments of the Plzen basin directly transgrade, were the only local and chronologically closely limited sources of Arkoses feldspars on the basis of the Carboniferous in the respective areas. A sample drawn from the basis of the transgrading Nyrany Member in the Merklin Carboniferous relics 2 km NE of Krchleby points to the dissimilar character of K-feldspars of the Merklin Massif (Or100Mi0; AbAn_solid  31 %; Ab_free 0.5 %; Ba 439 ppm; Sr 18 ppm; Pb 34 ppm; Rb 114 ppm; Figures 2 a,b,c), and similarly the sample of K-feldspars from the borehole Martineves Mt-1 from the basis of Radnice Member of the Kladno Group, transgrading over Tis granite (Louny Massif) at a depth of 1,680.5 m (Ba 296 ppm; Sr 46 ppm; Pb 41 ppm; Rb 173 ppm; Figures 2 a,b,c). Moreover, K-feldspars of the Cista-Jesenice Massif (a component of the Louny Massif) are, according to Kuzvart et al. [20], microclines with Δ = 0.78–0.93. K-feldspars of the Stod Massif (SW), according to the same authors [20], also have increased triclinicity (Δ = 0.25–0.36). Likewise, K-feldspars of the Kladruby Massif in SW (360–330 Ma) have 57.5% microclines with Δ = 0.63–1.00 [31], and besides, they have different trace chemistry (higher Ba and lower Rb [12]. Therefore, the granitoids of the Merklin, Stod, and Kladruby Massifs, or an extensive body of Tis granites of the Louny Massif, could not have been a significant source of K-feldspars in Upper Carboniferous arkoses (Figure 2a). 

Owing to the different values of the measured parameters, the majority of the Central Bohemian Pluton, including the Certovo Bremeno type or the Cervena type with microclines (Figure 2b), the YIC granites of the Krusne hory Mts. pluton (Figure 2c), granite porphyries (Flaje Massif), Teplice rhyolite, Luzice granites and orthogneises, and granites, orthogneises, and migmatites of the Moldanubicum, can also be excluded as a possible source.

Trace element contents similar to those of K-feldspars in Upper Carboniferous arkoses, as well as being found in the granites of the OIC of the Karlovy Vary Massif, are present only in K-feldspars of the marginal type of the Central Bohemian Pluton and Moldanubian granites of the Weinsberg and Eisgarn types. Nevertheless, these could hardly serve as a source material for arkoses owing to the limited dimensions of bodies in the case of the marginal type and, in the case of Moldanubian granites, owing to the fact that they might have only become a possible source during the sedimentation of the Radnice Member (as shown by results from the works of Zak, Svojtka, and Oplustil [45], despite the greater distance of transport towards the Kladno-Rakovnik Basin. The marginal type of the Central Bohemian Pluton could provide a source of K-feldspars only in the case that it would form an extensive mantle of the pluton during the long period of 17.1 Ma that we do not consider probable. The only possible source of K-feldspars of Carboniferous arkoses remains therefore mountain (normal) granites of the older intrusive complex (OIC) of the Krusne hory Mts., exposed today in the Slavkov and Nejdek-Eibenstock parts of the Karlovy Vary Massif.

The results of measurement of K-feldspars from the OIC and Upper Carboniferous arkoses are not always identical in all aspects (see, for example, a comparison of recorded values in Table 1 and a correlation of Ba/Rb in K-feldspars of Upper Carboniferous arkoses with the OIC of the Nejdek part of the Karlovy Vary Massif in Fig. 2c). The more striking differences occurred, however, only in the case of the contents of the albite-plagioclase component in the solid solution (AbAn_solid). This parameter is higher in K-feldspars from arkoses and points to their lesser degree of exsolution. Such a disproportion can be explained by exposure of the uppermost part of the massif with a lesser grade of exsolution of the albite-plagioclase feldspars in the period of Upper Carboniferous sedimentation. Some K-feldspars from arkoses have relatively increased Rb contents compared to K-feldspars in today´s granites of the OIC (Figure 2c), which presupposes earlier magmatic phases. The character of K-feldspars shows a source from the OIC rocks, which must have already been denudated at the beginning of the Kladno Formation sedimentation, even though it might have concerned rocks slightly different from the currently exposed rocks of the same granite massif.

The most eastern samples we have been studying (boreholes Berovice Br-5 and Martineves Mt-1) occur at a considerable distance of up to 90 km from today´s rim of the Karlovy Vary Massif. Therefore, the horizontal and vertical range of the Carboniferous basins required huge volumes of the source porphyric granitoids, and it is questionable whether today´s dimensions of the Karlovy Vary Granite Massif indicate that it was sufficiently large to supply them. However, it is necessary to realize that besides the granite feldspars, other regional rocks also took a considerable share in the sedimentary filling of the Carboniferous basins [5,35,36], and arkoses represent only a part of the basin filling material that arises from fierce runoffs of mechanically weathered granite material (bolson type of sedimentation).

Directions of Transport of Arkoses Source Material and Position of Arkoses in the Sedimentary Area of Upper Carboniferous Basins

While according to the current results of investigation of the West and Central Bohemian Upper Carboniferous basins, the material should have been transported predominantly from S-SW [45] or from N [23], the results of our study of K-feldspars give evidence at least for the source of big arkosic feldspars to be NW in the area of today´s Karlovy Vary Massif, both for the whole time of sedimentation (314.2–297.1 Ma; Moscovian–Asselian) and in the whole basin range up to a minimal distance of 90 km from the source. The same direction of input (NW) was unambiguously confirmed by a sedimentological study of the Nyrany Member sediments in the Kaznejov quarry with the application of paleofluvial analyses [22].

Primarily after the boundary between the Radnice and Nyrany members (Bolsovian–AAsturian) in which the Leonian orogenetical phase occurred, fierce runoffs from the source area started, as it is proved by the whole fragments of mechanically disintegrated granite material in boreholes Kozolupy Kp-19 (69.10 m, Nyrany Member) and Vochov Vo-6 (67.30 m, Tynec Formation) in the Plzen Basin and even in the borehole Lotous Lo-6 (491.00 m, Tynec Formation) in the Kladno-Rakovnik Basin. This sedimentation hiatus of tectonic origin is an important geological event, starting with the large-scale baring of the Karlovy Vary-Eibenstock Massif granites. It represents the strengthening of the invasion of detritic material from the Krusne hory Mts. mountain granites into the Nyrany Member and Tynec Formation of the Plzen and Manetin basins. However, the question of origin from the only NW source complicates the presence of detritic gold in both the Manetin and Plzen basins [16]. Particularly the mineralogical composition of heavy minerals (garnet, ilmenite, rutile, staurolite, tourmaline, monazite, native gold, but also cassiterite and topaz) points to the polygenetic origin from various rocks of the Krusne hory Mts. crystalline complex and the Barrandian Neoproterozoic and Paleozoic.

In view of the fact that arkoses do not fill up the whole sedimentary profile of the basins, an explanation of the K-feldspar origin might be repeated runoffs of mechanically weathered granite material from the predecessor of today´s Karlovy Vary Massif, while material of different compositions also came from other directions. It was enabled by the NW direction of contribution, functioning in the larger part of both basins for the whole period of sedimentation. Runnoffs of Upper Carboniferous arkosic material must have been very fierce (bolson type of sedimentation), because sometimes whole blocks of unweathered granite material, whose disintegrated remains were found not only in the borehole cores in the Plzen Basin but also in the varied runoff layers in the far-out Kladno-Rakovnik Basin (ca 82 km from the rim of the Karlovy Vary Massif), were delivered.

Notes on the Genesis of Kaolin Deposits in Arkoses of Upper Carboniferous Basins

As opposed to Pouba and Spinar [40], Pouba [39], Kuzvart  [18], Kuzvart et al. [20] and Kuzvart, Krelina and Matl [19], who considered kaolin deposits in all four Upper Carboniferous formations as uniform in genesis (kaolinization of arkoses immediately after sedimentation with possible continuation of the kaolinization processes in the Cretaceous up to the Miocene in some cases), Jiranek [7], Jiranek, Muller, and Schwaighofer [13] and Wilson and Jiranek [45] posited different ways for the genesis of the deposits of kaolins.

No kaolin deposits are still known from the Radnice Member of the Kladno Formation (Duckmantian–BBolsovian). The kaolinitization in the Nyrany Member (Asturian–Cantabrian; e. g., the deposits of Chlumcany, Orlík, Ledce, Obora, and Tymakov) did not occur in the Carboniferous but in near-surface conditions of the younger favorable climatic periods (Cretaceous–Miocene).

On the other hand, the biggest European continental kaolin deposits of Kaznjov and Horni Briza did not originate by kaolinization of sedimentary arkoses, but by sedimentation in the fluviolacustrine facies (a system of open lakes in the deeply cut, probably tectonically predisposed valley of NNE-SSW direction, presupposed by Pesek [34] and Oplustil [32]) under oxidation conditions as conglomerates and sandstones with clay (kaolinite) cement. In this process, kaolinite originated from pre-sedimentary kaolinization of feldspars ex situ, predominantly during transport. Kaolinitization of the bigger clasts of feldspars might have been finished after sedimentation, while in the Cretaceous–Miocene, deferrization of kaolins took place. 

These conclusions were first evidenced by field observations [7]: (1) alternation of kaolin beds and non-kaolinized arkoses (0.X–X m) in the lower portions of the deposits of Horni Briza and Kaznejov; (2) abundant intercalations of kaolinitic clays and siltstones (often of dark red colour), representing redeposited earlier kaolinized material, which would moreover have been a barrier to penetrating kaolinization solutions in the case of post-sedimentary kaolinization (Lojka et al. [22] found also interlayers of paleosoils); (3) findings of fresh feldspar clasts inside intensively kaolinized rocks (which Kuzvart [18] incorrectly considered as a proof of  incomplete post-sedimentary kaolinization); and (4) geochemical characteristics, non-corresponding to the primary kaolinic profiles (irregular distribution of the major and trace elements in the vertical profile, common growth of trace elements, alkalis, and REE with the declining content of kaolinite [10]). While the content of kaolinite in this type of sediment (i.e., differently granular sandstones and conglomerates) does not change with the depth due to the fluent contribution of already kaolinized material, in the case of post-sedimentary kaolinization of arkoses, the kaolinite content should distinctly decline with the depth.

These conclusions were later supported by electronic microscopy (SEM) [13]. The sedimentary origin of kaolinite in the deposits of Horni Briza and Kaznejov is shown by all-direction-oriented isolated hexagonal plates of kaolinite, which in the case of kaolinitization in situ from feldspars would be arranged parallel and would have filled up the original space of feldspar in the shape of more or less hexagonally limited columns. In addition, the SEM images also show that non-abundant, bigger clasts of fresh feldspar transported in the clay suspension were kaolinitized after sedimentation.

The genesis of the kaolins in the Tynec Formation (Barruelian-Saberian) and rare kaolin deposits in the Slany Formation can hardly be recognized due to the fact that no such deposit is exploited at present. Kaolins in arkose sandstones of the Line Formation (Stephanian C–AAutunian) in the surroundings of Podborany were partly kaolinized immediately after sedimentation, and their kaolinization was completed in the Cretaceous up to the Miocene.

K-feldspars in Upper Carboniferous arkoses of the West and Central Bohemian basins were analyzed by X-ray and AAS, and the results were compared with known data for K-feldspars in granitoides of the Bohemian Massif. All K-feldspars samples studied both in the areal and stratigraphic extent (Moscovian-Asselian) present a uniform type that corresponds to the K-feldspars of the older intrusive complex (OIC) of the Karlovy Vary Massif situated NW of the basins. Occasional strong runoffs of the granitoid material from that granite massif supported the K-feldspars of arkoses into the basins. Kaolinization of their feldspars took place differently in the particular formations: pre-sedimentary in the case of the deposits of Kaznejov and Horni Briza in the Nyrany Member, synsedimetary and post-sedimentary in the Line Formation, and post-sedimentary in the rest of the deposits in the Nyrany Member of the Kladno Formation.

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