Paadla Stage

by H. Nestor

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 present unit was treated by Schmidt (1892) as the Ilionia Schichten (Beds) of the “Obere Oeselsche Gruppe”. Bekker (1925) introduced the geographical name Paadla and considered these beds as a substage of the Saaremaa Stage. Aaloe (1963b) included equivalents of the present-day Himmiste beds earlier correlated with the Kaarma Stage. Aaloe et al. (1976) redefined the upper boundary of the stage excluding the Tahula beds and gave the current stratification of the stage (Table 8).

The historical stratotype of the stage - Paadla quarry, has been destroyed. The Kuressaare-GI (Kingissepa) drill core in the interval of 19.8 to 43.4 m has been chosen as the neostratotype of the stage (Nestor 1993). The rocks of the Paadla Stage occur in middle and southern Saaremaa, on Kihnu and Ruhnu islands and in the western part of the Tõstamaa Peninsula in mainland Estonia. The outcrop forms a 12–20-km-wide belt passing through midsouthern Saaremaa from the vicinity of Karala to Kõiguste and extending eastwards as far as the Tõstamaa Settlement on mainland (Fig. 73B). The main localities are cliffs at Roopa and Katri, quarries at Lümanda, Himmiste-Kuigu, Kogula, Kaarma and Uduvere and the walls of the Kaali meteorite crater. The full thickness of the stage varies from 2.8 m in the Kihnu borehole to 28.4 m in the Kaugatuma borehole, increasing westwards (Table 9).

The Paadla Stage consists of various bioclastic, pelletal and argillaceous limestones containing coral-stromatoporoid bioherms and biostromes in the west and different primary and secondary dolomites in the east. The base of the stage coincides with the top of the Soeginina pattern dolomites of the Rootsiküla Stage, overlain by argillaceous limestones and dolomites with Didymothyris didyma and Ilionia prisca.

In Estonia, the Paadla Stage contains a rather specific shallow-water fauna of corals, stromatoporoids, agnathans, brachiopods and molluscs in the north-west, more diverse shelly fauna in the south-west, and almost barren dolomites in the east. The most typical species are as follows (abbreviations: pd - Paadla Formation, tr - Torgu Formation, kh - Kihnu Formation, S - Sauvere beds, H - Himmiste beds, U - Uduvere beds, m.pt. - middle part, u.pt. - upper part): Conochitina latifrons Eisenack (tr), Angochitina elongata Eisenack (tr), Parallelostroma typicum (Rosen) (pd), Lophiostroma schmidtii (Nicholson) (pd), Thecia swindereniana (Goldfuss) (pd), Laceripora cribrosa Eichwald (pdU), Phaulactis cyathophylloides Ryder (pd), Didymothyris didyma (Dalman) (pd, tr), Howellella elegans Muir-Wood (pd, tr), Ilionia prisca Hisinger (pd, tr), Cardiola interrupta Sowerby (pd, tr), Megalomphala taenia (Lindström) (pdU), Hemsiella hemsiensis Martinsson (pdU, tr u.pt.), Neobeirichia nutans (Kiesow) (tr), Hammariella pulchrivelata Martinsson (pdU, tr), Amygdalella paadlaensis Sarv (pd, tr), Balizoma obtusus (Angelin) (pdU), Ozarkodina crispa (Walliser) (pdU, tr u.pt.), O. cf. snajdri (Walliser) (tr m.pt.), Tremataspis mammillata Pander (pdH, kh), Phlebolepis elegans Pander (pd, tr, kh), Andreolepis hedei Gross (pdU, tr u.pt.). The presence of chitinozoan species Conochitina latifrons and C. lauensis enables to correlate the strata of the Paadla Stage in Estonia with scanicus to tauragensis (leintwardinensis) graptolite zones of middle Ludlow in Latvia which suggests that the basal Ludlow beds are probably absent (Nestor & Nestor 1991).

In Estonia, the Paadla Stage is represented by the Paadla, Torgu and Kihnu formations (Aaloe et al. 1976) laterally replacing one another (Fig. 73). The Paadla Formation occurs in the southern part of Saaremaa, except the Sõrve Peninsula. It is dominated by argillaceous biomicritic to sparitic limestones and dolomites with bands of marlstones, coral-stromatoporoid biostromes, pelletal and coquinoid (Didymothyris) limestones. The formation is subdivided into the Sauvere, Himmiste and Uduvere beds (Klaamann 1970a). The Sauvere beds are represented by nodular argillaceous bioturbated biomicritic limestones (pack- and wackestones), containing small bioherms in the west and being gradually replaced by argillaceous dolomites towards the east. The Himmiste beds are mainly represented by micro- to cryptolaminated argillaceous dolomites with the remains of eurypterids and agnathans. They also contain bands of pelletal-skeletal grainstones at the base and (less often) at the top. The well-known Kaarma building dolomite is tentatively attributed to these beds now (Einasto in Kaljo & Nestor 1990, p. 173). The Uduvere beds are represented by variable rocks of shallow-water genesis: skeletal-, pelletal- lithoclastic-, oncolitic grainstones, packstones and rudstones, interbedded with bands of marlstones, coral-stromatoporoid biostromes, etc. Rocks are partly or totally dolomitized, particularly east of the Kuressaare Town.

The Torgu Formation spreads on the Sõrve Peninsula and Ruhnu Island. It mainly consists of nodular argillaceous biomicritic limestones with rather rich shelly fauna, but corals and stromatoporoids are rare.

The Kihnu Formation is distributed on the Tõstamaa Peninsula and Kihnu Island. It is represented by monotonous platy dolomites (below) and argillaceous dolomites (above) of reduced thicknesses containing agnathans of Paadla and Kuressaare ages, respectively (Einasto et al. 1977), and consequently spanning from the Paadla to Kuressaare Stage.