|Age top (Ma)||476.4|
|Age base (Ma)||483.4|
|Age reference||Webby et al., 2004 (eds)|
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 Hunneberg Stage was introduced by Tjernvik (1956) as the Hunneberg Group in Sweden, based mainly on trilobite faunas. During several decades, the stage has been recorded as the lower substage of the Latorp Stage in Estonia (after Jaanusson 1960a, Männil 1966, Männil & Meidla 1994 etc.). Following Jaanusson (1982), Mägi (1984) and Hints et al. (1994) considered this unit in the rank of stage.
During the last years, Sweden has served as the key area for biostratigraphical research of the Ontika Subseries comprising the stages from Hunneberg to Kunda. Detailed studies of the earliest post-Tremadoc sequences by Lindström (1954), Tjernvik (1956), Jaanusson (1963) and several other researchers have been supplemented by recent studies of sequences and distribution of graptolites (Lindholm 1991 a.o.) and conodonts (Löfgren 1993a, b, 1994, 1996). In the East Baltic region, the stratigraphy of the Ontika Subseries has been studied by Lamansky (1905), Öpik (1930b) and Männil (1963a, b, 1966). In Estonia modern biostratigraphy of this interval bases mainly on conodonts studied by Viira (1966, Mägi & Viira 1976, Mägi et al. 1989).
In northern Estonia, the Hunneberg Stage is represented by poorly lithified glauconitiferous terrigenous sediments: glauconitic siltstones of the Klooga Member (thickness up to 2.9 m) and glauconite silt and sand of the Joa Member (up to 1.2 m) which together form the lower, main part of the Leetse Formation (Figs. 30, 31). The content of glauconite is increasing upwards. The glauconitic siltstones of the Klooga Member are dominated by quartz with a supplement of glauconite (Mägi 1970), while the silt- and sandstones of the Joa Member consist mainly of glauconite (50–70%) and quartz (about 10–20%; Mägi 1970, 1984, 1990). The lower boundary of the Leetse Formation and the Hunneberg Stage represents a well defined lithological marker level with the glauconitic sandstones and siltstones overlying conformably, sometimes with a discontinuity surface, the dark-brown argillites of the Türisalu Formation or light-grey clays of the Varangu Formation.
The maximum thickness of the stage reaches 4 m in northwestern Estonia, but usually it is less than 2 m. As the Hunneberg and Billingen stages have not been differentiated in most sections, the thickness map (Fig. 30) shows only total thicknesses for both stages. In western Estonia, mainly on the islands of the West-Estonian Archipelago, the absence of the Hunneberg Stage has been documented from several sections.
In Sweden, the Hunneberg Stage corresponds to the Megistaspis armata and M. planilimbata trilobite zones. The base of the stage is close to that of the Paroistodus proteus conodont zone (Fig. 32, Löfgren 1993a). In the East Baltic, the lower M. armata Zone has been established only with confidence in Latvia (Männil 1966, Ulst et al. 1982). In northern Estonia, the lowermost part of the Leetse Formation has generally been assigned to the Paroistodus proteus Zone (Männik & Viira 1990). In the Mäekalda section, the thin Klooga Member at the base of the Leetse Formation is referred to the Paltodus deltifer Zone (Fig. 31, Mägi 1984).
Among macrofossils, a distinctive assemblage of lingulate brachiopods (Goryansky 1969) has been recorded. It is characterized by Thysanotos siluricus (Eichwald) and Leptembolon lingulaeformis (Mickwitz) constituting the Leptembolon-Thysanotos assemblage, widely distributed in eastern and central Europe (Popov & Holmer 1994).
The fossil evidence from most of central and southern Estonia, is too fragmentary yet for the limitation of the Hunneberg and the overlying Billingen stages. The Hunneberg age of glauconitic sandstones (up to 0.5 m) has been established in the Karula core (Männil 1966), but in most cases the detailed stratigraphy of the undivided Hunneberg–Billingen strata is unclear.
In Latvia, and in some sections in southern Estonia, close to the Estonian - Latvian border, the mudstones of the Zebre Formation, reaching a thickness of 46 m in Latvia, have been considered as equivalents of the Varangu, Hunneberg and Billingen stages (Ulst et al. 1982, see also Fig. 30). The middle part of this formation (Zirni Member) is of Hunneberg age, as it yields a zonal trilobite Megistaspis planilimbata (Angelin) (Fig. 32) and several graptolites, including Tetragraptus phyllograptoides Strandmark, together with a zonal conodont Paroistodus proteus (Lindström) (ibid.). The occurrence of the peripheral parts of the Zebre Formation can be assumed in southern Estonia.