Late Vendian and Cambrian

In the very beginning of the mature platform stage of development of the SCD, in Late Vendian and earliest Cambrian, the unconformity surface became tilted east, towards the Moscow sedimentary basin. East of the Baltic-Bothnian line, sand, silt, and clay sediments formed a huge uniform blanket that thickened eastwards (Puura et al. 1987, Fig. 3). At the second half of the Early Cambrian, the western part of the SCD was tilted south-and westwards (towards the Iapetus and Tornquist palaeo-oceans), and blanket of sand and silt covered the basement (Fig. 3). Probably, the whole SCD was covered by sediments in the Middle Cambrian (Puura et al. 1987).

A group of Late Vendian and Cambrian craters is found in the area of southeastern Gulf of Bothnia and western Gulf of Finland: Neugrund (Suuroja and Suuroja 2000) in the present marginal platform area within the Lower Cambrian submarine exposure; Soderfjarden and Saaksjarvi (Elo et al. 1992) with shield area (Tables 1 and 2; Fig. 3 and 4). All these structures formed in environments of a thin (<100 m) Late Vendian and Cambrian sedimentary blanket. Two possible Cambrian doublet structures, Suvasvesi N & S (Lehtinen et al. 2002; Werner et al. 2002) are located just northwest of the east-Finland Neoproteozoic crater group (Fig. 1). Lower and Upper Vendian deposits were possibly thickest at the eastern Lake Ladoga and spread at least to Lauhavouri in south-western Finland (Puura et al. 1996). Late Vendian and Cambrian sediments probably covered Iso-Naakkima, Paasselka, Lumparn, and Avike-bukten structures. A single Cambrian crater, Mizarai (Motuza and Gailius 1978), formed on-land into the Vendian and Cambrian sediments and buried under subsequent sediments, is found in the southern Baltic area. Most likely, the Neugrund projectile (Suuroja and Suuroja 2000) hit Cambrian sediments at sea, but in the other cases, there is a lack of information to decide on the land-sea distribution.

Sediments Cambrian

Fig. 3. Past distribution of sedimentary deposits in and around the Svecofennian Crustal Domain (SCD) with its frontiers (white area) after Gorbatschev and Bogdanova (1993). Grey areas mark domains surrounding the SCD. Diagonal lining shows probable distribution of Vendian to earliest Cambrian (Nemakitian-Daldynian) deposits, horizontal, that of late Early Cambrian deposits. Black and white dots are meteorite impact structures penetrating or not penetrating into the crystalline basement, respectively.

Fig. 3. Past distribution of sedimentary deposits in and around the Svecofennian Crustal Domain (SCD) with its frontiers (white area) after Gorbatschev and Bogdanova (1993). Grey areas mark domains surrounding the SCD. Diagonal lining shows probable distribution of Vendian to earliest Cambrian (Nemakitian-Daldynian) deposits, horizontal, that of late Early Cambrian deposits. Black and white dots are meteorite impact structures penetrating or not penetrating into the crystalline basement, respectively.

Fig. 4. Cratering record and histories of crater's structural evolution. Fig. 1 indicates the location and Table 1 the properties of structures. See text for details. * = impact origin is not proved.

m ai

Fig. 4. Cratering record and histories of crater's structural evolution. Fig. 1 indicates the location and Table 1 the properties of structures. See text for details. * = impact origin is not proved.

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