Stratygrafia mikrofaunistyczna górnej kredy rowu Nysy (Sudety środkowe)

Abstract

Stratigraphy based upon Foraminifera of Upper Cretaceous deposits, Nysa Graben Central Sudetes The Nysa Graben was formed after the deposition of Upper Cretaceous sediments, probably during the Laramide Revolution, at the turn of the Cretaceous and the Tertiary. The sediments that fill up the Nysa Graben belong to the Cretaceous of Central Sudetes (Fig. 1 A, B). In the southern part of the Nysa Graben they lie almost horizontally over cristalline schists and Precambrian amphibolites, and in the northern part over the Rotliegendes sandstone. The Cretaceous sea entered the area of the Central Sudetes from the Lausitz Basin in the Middle Cenomanian and the transgression reached its maximum in the Early and Middle Turonian. The marine sedimentation was going on until the late Coniacian. This, however, has been proved only in the Nysa Graben. The surface onto which the sea transgressed was relatively flat with a few broad folds. The thickness of the Cretaceous deposits in the Nysa Graben varies (like in the remaining part of the Middle Sudetes) and ranges from 400 to 900 m. The variation in thickness of the Cretaceous in the Nysa Graben are due to the asymmetry of the basement, noticeable from the upper part of the Middle Turonian. The asymmetry caused considerable local depressions in the eastern and the southern part of the Graben, where Cretaceous deposits are uncommonly thick (Fig. 1A). Ten lithostraitigraphic units can be differentiated in the profile of Cretaceous deposits in the Nysa Graben. These units have been variously named by various authors. This inconsistency made the author of the present paper accept conventional signatures to denote the units (see Fig. 18). The sedimentation of Cretaceous deposits in the Nysa Graben begins and ends with sandstones. At the bottom there are Cenomanian yellow sandstones with glauconite (Kpg), which are locally underlain by basal conglomerates. At the top, there are Coniacian sandstones (Kpz), which are pale in colour, medium grained, intercalated with gravel and carbonized plant detritus. Marls, greatly varied, are the dominant rocks of the profile in question. There are clayey marls (Kmils Kmi2, Kmp), clayey siliceous marls, and siliceous marls, the latter with different degree of resistance (Kmg, Km, Kmk, Km in). They all make up a rather monotonous formation, which is divided by Quadersandstein (Kpc) in the northern and middle part of the Graben. Material for research Up to now, stratigraphie divisions of Cretacous deposits in the Nysa Graben have been based mainly on macrofauna (scarce and unevenly distributed along the profile) and on lithological analogies to the Saxonian and Bohemian Cretaceous (Fig. 19). The rich microfauna of the Nysa Graben Cretaceous deposits has never been dealt with in details. For micropalaeontological investigation samples were taken along 7 basal profiles between Krosnowi ce Kłodzkie in 'the North and the state border in the South (Fig. 1A, 2, 4—8). The profiles contain 80 large outcrops, which, after an appropriate correlation, represent the full profile of Cretaceous deposits in this area (Fig. 17). The richest microfauna has been obtained from clayey marls (Kmij, Kmi2) and from siliceous marls (Km in), situated in the middle part of the profile. Sandy marls with glauconite (Kmg) and the upper part of clayey marls with sandstone intercalations and siderite concretions (Kmp) (Fig. 18, Table 1) — both contain scarce and badly preserved microfauna. No microfauna has been traced in sandstone intercalations (Fig. 18). 250 samples were taken for microfauna investigation. 180 samples contained Foraminifera. 54 samples were selected for a detailed analysis. The selection was made on the basis of the composition of a particular Foraminifera assemblage, its abundance, its stratigraphical position and the preservation of fossils. There were differeneiated 64 species of Foraminifera (Table 1). Apart from Foraminifera, one can also observe in the samples: frequent Ostracoda, oval coprolits, rare Radiolaria, sponge spicules, and minute fish teeth. Circle diagrams (Fig. 10—16) represent the Foraminifera assemblages from particular lithostratigraphic units, the characteristics of which has been completed by the method of quantitative analysis. Each diagram corresponds to the composition of the assemblage typical for each unit, in which about 200 Specimens were counted and labelled according to their genus. Arenaceous benthonic Foraminifera are to be found in all the investigated samples. They form the richest and varied assemblages in clayey marls intercalated with sandstones (Kmp) in the upper part of the profile in question (Fig. 15, 16, Table 1). An increase in the amount of arenaceous Foraminifera takes place at the expense of the amount of the planktonie Foraminifera. In the upper part of the profile (Kmp), there appear primitive arenaceous Foraminifera of the Families Astrórhizidae, Saccaminidae, Ammodiscidae known also from Flysch deposits. Calcareous benthonic Foraminifera prevail in all the assemblages. In clayey marls intercalated with sandstones and containing siderite concretions (Kpm), the more arenaceous Foraminifera, the less there are of calcareous Foraminifera. The quantitative change does not, however, entail a qualitative one (Fig. 10—16, Table 1). The richest and most varied assemblage of calcareous Foraminifera is to be found in the clayey marls of the middle part of the profile in question (Kmi(1) Kmi(2), Fig. 13 and 15). Planktonic Foraminifera occur in all the investigated samples; their quantity, however, varies considerably. They form assemblages poor in species but occasionally rich in specimens. They are most frequent in the siliceous marls of the middle part of the profile (Kmin), where they constitute as much as 50% of the total quantity of the Foraminifera (Fig. 14). In the upper part of the profile (Kmp) the quantity of planktonic Foraminifera is small and it goes down to 2,4% of total quantity of the Foraminifera (Fig. 16). Microfaunal zones and the characteristic assemblages of Foraminifera in the Upper Cretaceous of the Nysa Graben For a stratigraphie analysis of the deposits under consideration 29 species were selected from the list of the determined Foraminifera (Table 1). All of them had a short vertical range, and have often been referred to as index fossils, or the characteristic Turonian and Coniacian forms (Fig. 3, 18). As the basis of the stratigraphie interpretation of the selected species, the data established by the following authors were taken into consideration: K. Pożaryska (1954, 1957), J. Hofker (1956, 1957), V. P. Vassilenko (1954, 1961), V. S. Akime z (1961), E. Gawor-Biedowa and E. Witwicka (1960), H. Hiltermann and W. Koch (1962), E. Trümper (1963, 1968) and E. Gawor-Biedowa (1972). There are the following index and characteristic Foraminifera of the Turonian and Coniacian of the Nysa Graben: (Pl. I—III): Spiroplectammina praelonga (Reuss) , Verneuïlina muensteri Reuss, Dorothia trochus (d’Orbigny), D. turris (d‘Orbigny), Neoflabellina rugosa (d’Orbigny), Palmula baudouiniana (d’Orbigny), P. cf. suturalis (Cushman), P. jarvisi (Cushman) , Pyramidina turonica (Akimez) , Hedbergella infracretacea (Glaessner), H. caspia (Vassilenko), Rotalipora cushmani turonica (Brotzen) , Globotruncana marginata (Reuss), G. ventricosa White, G. paraventricosa (Hofker), G. concavata (Brotzen), G. lapparenti coronata (Bolli), G. lapparenti tricarinata (Quereau), G. lapparenti lapparenti (Brotzen) , G. lapparenti bulloides (Vögler), G. lapparenti angusticarinata (Gandolfi), Globorotalites subconicus (Morrow) , Stensioina granulata (Olbertz), S. exsculpta exsculpta (Reuss), S. exsculpta gracilis (Brotzen), Gavelinella berthelini (Keller), G. kelleri (Mjatliuk), G. moniliformis moniliformis (Reuss), G. ammonoides (Reuss). Almost all the selected species occur in more than one lithostratigraphic unit (cf. Tabela 1). On the basis of the distribution of the above mentioned species and the composition of the assemblages of Foraminifera in particular lithostratigraphic units one can differenciate 4 microfaunistic zones in the Cretaceous of the Nysa Graben: 3 of them in the Turonian, and one in the Coniacian (Fig. 18). These zones do not strictly correspond to that of the macrofaunistic ones (Fig. 19) differenciated by S. Radwański (1966 b). The Gavelinella berthelini zone — Lower Turonian The zone is comprised of marls between the Upper Cenomanian glauconite sandstone (Kpg) and the Middle Turonian Quadersandstein (Kpc) (Fig. 18). Both sandstone units have no microfauna. This zone is characterized by common specimens of G. berthelini (Pl. 1, Fig. 5a-c), rare specimens of Rotalipora cushmani turonica (Pl. 2, Fig. 6a-c), Hedbergella injracretacea (Pl. 2, Fig. 4a-c), H. caspia (Pl. 2, Fig. 5a-c), Globotruncana marginata (Pl. 2, Fig. 7a-c, 8a-c), and iby numerous species of Lenticulina and Globorotalites. The Hedbergella caspia zone — Middle Turonian The zone is constituted by dark grey siliceous marls (Kmk) and by Quadersandstein at the bottom (Kpc) (Fig. 18). The bottom border line of the zone is marked by the lack of G. berthelini and by the appearance of Globotruncana ex gr. lapparenti. The top border line is marked by the appearence of species familiar for the Upper Turonian e.g. Stensioina granulata (cf. Fig. 3, 18). In the said zone one can find numerous specimens of H. caspia (Pl. 2, Fig. 5a-c). In the Cretaceous of the Russian platform H. caspia does not go far beyond the border-line of the Upper Turonian. The assemblage of Foraminifera in this zone is also constituted by numerous species of Lenticulina and Nodosaria, and by rare specimens of Globotruncana, Gavelinella and Globorotalites (cf. Table 1). The Stensioina granulata zone — Upper Turonian The zone is comprised of three lithostratigraphic units, two of them are clayey marls (Kmij and Kmi2), and siliceous marls (Km in) (Fig. 19) which separate them. The zone is characterized by numerous specimens of S. granulata (Pl. I, Fig. 6a-c), Gavelinella kelleri (Pl. 1, Fig. 4a-c), Spiroplectammina praelonga (Pl. 3, Fig. lla-b) and Verneuilina muensteri (Pl. 3, Fig. 12a, b). These species appear in the uipper part of the Middle Turonian; they are, however, characteristic for the Upper Turonian, where they are still more numerous. (Fig. 3). The upper border line of the zone is indicated by the appearence of some species, characteristic for the Coniacian e.g. of Stensioina exsculpta group. The assemblage of Foraminifera in this zone is very rich and varied (cf. Table 1). Specimens of G. lapparenti lapparenti and G. ventricosa are most frequent. The above three microfaunistic zones which can be differentiated in the Upper Cretaceous of the Nysa Graben prove the validity of the usually assumed tripartite division of the Turonian in the Sudetes. The Stensioina exsculpta exsculpta zone — Lower Coniacian The zone is represented in grey clayey marls intercalated with sandstones and containing siderite concretions (Kmp) (Fig. 18). The bottom border line of the zone is indicated by the presence of Stensioina exsculpta exsculpta, S. exsculpta gracilis and Neoflabellina rugosa. The upper border line cannot be indicated, as the Idzików sandstones, situated above, have no microfauna. Primitive arenaceous Foraminifera are also included into the assemblage of Foraminifera of this zone. Comments on sedimentary environments An analysis of the Foraminifera assemblages from particular lithostratigraphic units made possible an attempt to establish the changes of ecological conditions during the sedimentation of the Upper Cretaceous deposits in the Nysa Graben. Sedimentological observations and the results of the investigation of the co-existing macrofauna have also been taken into consideration according to S. and Z. Radwański (1966, 1966 b). It is probable that the Upper Cretaceous deposits in the Nysa Graben were formed in a fairly warm epicontinental sea. The asymmetry of the Graben existing throughout the sedimentary period, was the cause of local depressions. In those depressions, in the late Turonian, there could have existed deeper sea conditions. The Upper Cretaceous sea in the Nysa Graben was temporarily linked with the open sea, although in a limited way. The composition of the microfauna assemblages implies a connection with the North German sea, which must have existed particularly in the early part of the Late Turonian. Ecological changes in the Nysa Graben reflect the course of the transgressive — regressive cycle in all the Central Sudetes. The transgression started in the Cenomanian, and the process of widening and deepening of the sea went on until the late part of the Middle Turonian. The regressive stage lasted until the Late Coniacian. Large quantities of sandstones during the cycle imply a closeness to a continent, and they might have resulted from some sudden filling-up of the basin.