Billingen Stage

T. Meidla

Original text from: Raukas, A., Teedumäe, A. (eds). 1997. Geology and Mineral Resources of Estonia. Estonian Academy Publishers, Tallinn. 436 pp. ISBN 9985-50-185-3. Available online at: sarv.gi.ee/geology.

The Billingen Stage (Tjernvik 1956, Jaanusson 1982), understood here in the sense of the upper Billingen Substage of the Latorp Stage (Jaanusson 1960a, Männil 1966, 1990, Männil & Meidla 1994), consists of two distinctive parts in northern Estonia. The lower one is represented by the glauconitic calcareous sandstones and limestones of the upper part of the Leetse Formation (Mäeküla Member, equal to B_Iβ by Lamansky (1905), whereas the glauconitic limestones of the lowermost part of the Toila Formation (Päite Member, equal to B_Iγ by Jaanusson (1951), form the upper half of the Billingen Stage (Table 7, Fig. 31). In some publications, including the detailed lithological study of the Volkhov and Kunda stages by Orviku (1960a), the Päite Member is interpreted as the lowermost unit of the Volkhov Stage. This interpretation is also in use in the Leningrad Region of Russia.

The original concept of the Billingen Stage (Tjernvik 1956) was based on the evidence from the trilobite faunas, but its lower boundary can best be recognized by the distribution of conodonts. In Sweden, it is situated fairly close to the boundary of the Prioniodus elegans Zone and this level is recognizable also in several sections of northern Estonia where it nearly coincides with the lower boundary of the Mäeküla Member in the upper part of the Leetse Formation (Fig. 31).

The Mäeküla Member consists of glauconitic sandstones which are replaced upwards by calcareous sandstones and glauconitic limestones. The lower boundary of this member is lithologically fairly distinct in the klint area, and is marked by the change from poorly cemented silts and sands to well cemented sandstones. For the purposes of correlation, the occurrence of the conodonts Prioniodus elegans Pander and Oepikodus evae (Lindström) is most important (Figs. 31, 32). The thickness of the Mäeküla Member varies from 0 to 0.5 m. Sandy material with the grain-size over 0.1 mm forms up to 80% of the rock, whereas glauconite grains make up some 80% of this fraction. The quartz content varies from 10 to 40% (Mägi 1984, 1990). The highest content of glauconite has been recorded in central northern Estonia. The macrofauna of the Mäeküla Member has not been described monographically but, according to the available evidence, its main, upper part is comparable with the Megistaspides dalecarlicus Zone of Sweden (Fig. 32).

The Päite Member is represented by limestones or dolomites which dominate in the easternmost sequences, with a low content of mainly fine-grained glauconite. The greatest thickness of the member is 1.13 m, and it decreases in the northwest direction. In the Leningrad Region, the presence of several distinctive lithological marker horizons within the equivalents of the Päite Member (roughly equal to the informal Red Dikari Member) has been demonstrated by Dronov et al. 1996, part of those can be supposedly distinguished in northeastern Estonia. On the islands of Väike-Pakri (Photo 18) and Osmussaar, the member is sandy and may contain a layer of calcareous, glauconitic sandstone at the base (Orviku 1960a). The Päite Member is roughly equivalent to the Megistaspis (Paramegistaspis) estonica Zone of Sweden (Fig. 32).

In central Estonia, the presence of the Billingen Stage needs further approval. Glauconitic sandstones occuring locally in a restricted thickness in this area, like in the Äiamaa and Võhma cores (Rõõmusoks 1960, 1983), may belong to this stage but their precise age is not yet clear. Further to the south (at Tartu), the reddish-brown, occasionally glauconitic dolomites may be tentatively assigned to the Billingen Stage. The distribution of the Zebre Formation in Latvia (Ulst et al. 1982) suggests that it extends as far as the southernmost Estonia. In Latvia, the red or mottled clays of the topmost Zebre Formation (Zante Member) contain Megistaspis (Paramegistaspis) estonica (Tjernvik) and a zonal conodont Oepikodus evae (Lindström) (Gailite & Ulst 1975, Ulst et al. 1982), characteristic of the Billingen Stage in several sections of northern Estonia (Mägi 1990, Einasto et al. 1996, see Fig. 31).

Fossil evidence from southern Estonia is too fragmentary to enable the limitation of the Hunneberg and Billingen stages over the study area. Figure 30 shows only their sum thickness. The absence of the Billingen Stage in several sections of the West-Estonian Archipelago (Saaremaa, Hiiumaa) should be mentioned.

The Mäeküla Member contains the oldest Ordovician representatives of articulate brachiopods of the genera Plectella, Panderina, Prantlina and Angusticardinia (Rubel 1961) bryozoans, ostracodes (H. Aru, pers. comm) and trilobites. Frequent occurrence of trilobites (“Megistaspis”) has been recorded in some levels (Orviku 1960a). In the Leningrad Region, the Mäeküla Member yielded the material for original definition of Conodonta by Pander (1830). The yet poorly studied fossil record of the Päite Member contains conodonts, brachiopods, trilobites and ostracodes.