Haljala Stage

by L. Hints

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.

Jaanusson (1995) proposed the term Haljala Stage for the unit which comprises the Idavere and Jõhvi chronostratigraphical subdivisions, previously regarded as separate stages. These two subdivisions, now classified as the Idavere and Jõhvi substages (Table 7), comprise most of K‑bentonite beds which lie below the thickest bed (“d” by Jürgenson 1958a) established in eastern Baltic. The substages are difficult to differentiate in southern Estonia, in areas where K-bentonite beds are uncertain or absent. Also the faunal distinction between the substages is rather inconsiderable (Põlma et al. 1988, figs. 9-11). In Estonia, the thickness of the Haljala Stage varies mostly from 10 to 20 m (Fig. 43).

The Idavere Substage comprises the regularly bedded hard bioclastic limestones of the lower, Tatruse Formation and argillaceous limestones with intercalations of marls and some thin K-bentonites of the upper, Vasavere Formation (emended by Männil & Meidla 1994). This substage has the most reduced sequence in northern Estonia and in some places in the surroundings of Tallinn it is entirely missing (Jaanusson 1945). The Tatruse Formation (Põlma et al. 1988) corresponds roughly to Schmidt’s (1881) original concept of “Itfersche Schicht” and the fauna recorded by him and his contemporaries from the “Itfer” belongs only to this formation. The Vasavere Formation contains usually two, but in the west sometimes up to 18 K-bentonite beds, which belong to the Grefsen complex of bentonites (Bergström et al. 1995). In the areas where only beds “a” and “b” (Jürgenson 1958a) are recognizable, the upper bed is regarded as the top of both the Idavere Substage (Männil 1963a) and the Vasavere Formation. In areas farther south where bentonite beds of the Grefsen complex disappear or in the west where they are numerous, a distinction between the Idavere and Jõhvi substages is difficult.

The Jõhvi Substage, which is at its thickest (more than 10 m, Fig. 44) in northwestern Estonia, comprises argillaceous bedded to nodular limestones with argillaceous intercalations in the middle part (Männil & Rõõmusoks 1984, Põlma et al. 1988). These limestones form the lower part of the Kahula Formation (Männil & Meidla 1994). A fairly persistent K‑bentonite bed (bed “c” by Jürgenson 1958a, “Sinsen K-bentonites” by Bergström et al. 1995) occurs close to the boundary between the middle and upper parts of the Jõhvi Substage.

In southern Estonia, the Haljala Stage, 8 - 18 m in thickness, is represented by argillaceous limestones with thin K-bentonite beds and in places with phosphatic ooids of the Adze Formation (Ulst et al. 1970).

In the outcrop area, the lower boundary of the Haljala Stage and the Tatruse Formation is formed by a conspicuous discontinuity surface – a hardground which in places is penetrated by cavities, some 5 cm or even more in diameter at the surface and extending sometimes some 40 cm downwards (Põlma et al. 1988). The limestones above the basal discontinuity (Kisuvere Member) comprise up to 16% of quartz sand. The most detailed stratification of the lowermost beds of the Haljala Stage is based on chitinozoans. The oldest part of the stage, the Armoricochitina granulifera and Angochitina curvata zones (Männil 1986, fig. 5.1.1, Nõlvak & Grahn 1993) occurs in the Laeva area in eastern central Estonia (Fig. 45) where the stage has the maximum thickness (ca. 25 m, Fig. 44, core No. 285). These two zones do not occur in the northenmost sequences, where the Lagenochitina dalbyensis Zone forms the basal part of the substage.

The gap on the boundary between the Kukruse and Haljala stages is rather well expressed by differences between faunas, especially of brachiopods and trilobites in northern Estonia. Both these groups are represented in the Idavere Substage with about 40 species, a few of which occur also in the underlying Kukruse Stage (Rõõmusoks 1970, table 12). The occurrence of several Kukruse bryozoans in the upper part of the Idavere Substage (in the Vasavere Formation) is seemingly of facies origin. The lower boundary of the Haljala Stage is also marked by rather sharp changes in the composition of ostracodes (Põlma et al. 1988, figs. 7, 9-11), though some typical Idavere - Jõhvi species, e.g. Braderupia asymmetrica (Neckaja) appear in the top of the Kukruse Stage. The frequent occurrence of Leiosphaeridia above it, is a rather good marker for the lower boundary of the Haljala Stage. The base of the Haljala Stage is close to both the graptolite Diplograptus multidens Zone and the conodont Baltoniodus gerdae Subzone (Männil 1990, Jaanusson 1995).

The changes in the faunal composition on the transition between the Idavere and Jõhvi substages are continuous which is clearly revealed in core sections, especially by ostracodes (Põlma et al. 1988). Several new macrofossil taxa, such as Toxochasmops maximus (Schmidt), Clinambon anomalus (Schlotheim), presumably appear somewhat higher (1.5 - 2 m, Männil 1963a, b) of the boundary K-bentonite bed between the Idavere and Jõhvi substages.

In the core sections located far away from the outcrop area, the alga Mastopora concava (Eichwald), spicules of Pyritonema subulare (Roemer) and also some brachiopods (Bilobia) occur (Fig. 40), but there is no characteristic species among macrofossils for determination of the lower boundary of the Haljala Stage.