Journal of the Virtual Explorer

Torsvik et al. (1995a) determined a palaeomagnetic pole of 24.3˚S, 268.5˚E from the Nyborg Formation (Table 1), an interglacial unit associated with the Varangian glaciation in northern Norway. They used a Rb-Sr whole rock date of 653 ± 7 Ma, recalculated from Pringle (1973), as the age for the pole. This age was criticised by Harland (1997) and Evans (2000) as not reliable by present standards. Gorokhov et al. (2001) carried out a new Rb-Sr study on clay fractions from the Stangenes (pre-glacial), Nyborg (interglacial) and Stappogiedde (post-glacial) formations of northern Norway. They concluded that the time range of the Vagangian glacial horizons is 630-560 Ma and this provides a conservative estimate of the age of the palaeopole. Recently, Bingen et al (2005), has established that the Moelv Tillite, also part of the Varangian glacials, must be younger than 620 ±14 Ma based of the age of the youngest detrital zircons from a clastic sediment underlying the glacial horizons.

Storetvedt (1966) and Poorter (1972a) studied the 616 ± 3 Ma (Bingen et al., 1998) Egersund dykes from southern Norway, obtaining palaeopoles of 28.0˚S, 232.0˚E and 22.4˚S, 230.8˚E, respectively (Table 1). Eneroth and Svenningsen (2004) studied the Sarek dykes, which have yielded a U-Pb zircon age of 608 ± 1 Ma (Svenningsen, 2001). Although the structural setting of these rocks in the Seve Nappes means that the calculated palaeopole may not be representative for cratonic Baltica, their overall estimation of an equatorial palaeolatitude for Baltica at this time is reasonable. Eneroth and Svenningsen (2004) also argue that the shallow remanence A of the 665 Ma dolerites of the Särv Nappe in southern Sweden may be late Neoproterozoic (Vendian), as the data pass a fold test. Although Bylund and Zellman (1980), the original authors of the Särv Nappe study, interpreted their result as reflecting a Silurian overprint, Bylund (pers. comm., 2004) accepts that the data may be primary and reflect a low-latitudinal position of Baltica in the late Neoproterozoic. A steep inclination in palaeomagnetic data from mafic dykes in the northernmost part of Baltica, in the Sredni Peninsula and in the southern part of the Varanger Peninsula, suggest a high latitude position for Baltica in the Neoproterozoic (Shipunov, 1988; Shipunov and Chumakov, 1991; Torsvik et al., 1995b). However, Guise and Roberts (2002) recently established a 378 ± 2 Ma 40Ar-39Ar plateau age for the one of these dykes (Komagnes dyke). In addition, Popov et al. (2002) mentioned the similarity of Komagnes/Sredni poles to Jurassic poles from Baltica suggesting the younger remagnetisation has potentially affected the region. Thus, the age of the steep magnetisation in the palaeomagnetic data from Sredni and Varanger Peninsulas is uncertain and cannot be used to constrain the Neoproterozoic location of Baltica.

Several palaeomagnetic studies have been carried out in the Fen Carbonatite Complex of the South Norway and associated rocks (Poorter, 1972b; Storetvedt, 1973; Piper, 1988; Meert et al., 1998). These results were summarised by Meert et al. (1998) who suggest a mean pole of 56.0˚S, 330.0˚E, and who also provided a 40Ar-39Ar age of 583 ± 15 Ma for the complex (Table 1). All these palaeopoles are quite concordant but Meert et al. (1998) noted the need for caution as the primary, Neoproterozoic age for the magnetic remanence has not been established and also that the data resembled the Permo-Triassic field directions for Baltica with the Fen Complex located close to the Oslo Rift, a site of widespread igneous activity of similar age.

Popov et al. (2002) recently reported a high-quality palaeopole of 25.3˚N, 312.2˚E from the late Neoproterozoic strata from the Winter Coast, White Sea region, Russia (Table 1). This section is marked by the occurrence of Ediacara fauna (Fedonkin, 1981) and dated at 555 ± 3 Ma by a U-Pb zircon age on volcanic ash layers interstratified with the sediments (Martin et al., 2000). The primary nature of their Z remanence component is supported by reversal, stratigraphic, and consistency tests. Z-type remanence was recently reported from West Ukraine by Nawrocki et al. (2004) and from two other locations in the Winter Coast area by Popov et al. (2005; Table 1). Popov et al. (2002) also noted the palaeopole of Piper (1981) from the Alnø Carbonatite Complex, an inferred correlative of the Fen Complex and dated at 584 ±13 Ma (Anderson, 1996), which is relatively close to the Winter Coast pole and far from the Fen pole (Meert et al., 1998), but the quality of the data is poor. Walderhaug et al. (2003) restudied the Alnø Complex and briefly mentioned a steep primary magnetisation. They also reported a 40Ar-39Ar age for the complex of 589 Ma but as the details of the paleomagnetic and age data are yet to be fully published, the quality of this information cannot be critically evaluated.

Lewandowski and Abrahamsen (2003) published a palaeopole of 40.0˚S, 357.0˚E from the Lower Cambrian Nesko Sandstone of Bornholm Island that has an age of around 545-530 Ma based on biostratigraphy (Table 1). Despite its resemblance of the well-known Permian poles of Europe, they argue for the primary nature of this remanence on the basis of its better grouping than the overprint remanence from other formations of the area. Torsvik and Rehnström (2001) reported a palaeopole of 56.0˚N, 296.0˚E from the Lower Cambrian Torneträsk Formation in northern Sweden suggesting a medium to high palaeolatitude for Baltica at that time (Table 1). Primary remanence of the pole was not demonstrated and it is also close to the Jurassic part of the Eurasian Apparent Polar Wander Path (e.g. Smethurst et al., 1998).

Palaeomagnetic poles have been determined on a diverse range of late Neoproterozoic to Cambrain rock units from Baltica and overall suggest a low latitude position (cf. Eneroth and Svenningsen, 2004). However, only the poles from the Winter Coast (Popov et al., 2002) and the Nyborg Formation (Torsvik et al., 1995a) have a clearly established primary remanence with only the former also having a precise age. In all other cases, late Paleozoic or Jurassic remagnetization cannot be excluded.

Murthy et al. (1992) studied six dykes of the Long Range swarm of Labrador. Three of them yield a coherent direction for the remanence with a palaeopole at 10.8˚N, 334.3˚E, whereas three others gave different and diverged directions, interpreted as anomalous. The coherent remanence is probably primary as it is supported by a baked contact test. Meert et al. (1994) reinterpreted this data, suggesting the anomalous direction from dyke 1, dated at 615 ± 2 Ma by Kamo et al. (1989) to be primary, but did not justify why they rejected the coherent data which included the baked contact test. The coherent direction was suggested by Torsvik et al. (1996) as representative for Laurentia at 550 Ma on the basis of the K-Ar dates available at that time (Murthy et al., 1992). However, Kamo and Gower (1994) have subsequently obtained an age of 615 Ma based on U-Pb baddeleyite and zircon from dyke 4. They argued that the coherent direction is representative for Laurentia at that time. The anomalous direction from the one dyke used by Meert et al (1994) may record a large secular variation or excursion of the geomagnetic field and we do not consider this direction to be valid in constraining the position of Laurentia.

Palaeomagnetic data from the Cloud Mountain basalts (Deutsch and Rao, 1977), part of the Lighthouse Cove Formation of Williams and Stevens (1969), revealed a palaeopole at 5ºS, 352ºE close to that of their inferred intrusive source, the Long Range Dykes (e.g. Bostock, 1983). Murthy et al. (1992) also studied the Double Mer Formation in northern Labrador, which is close to that from the Long Range Dykes, but the age of the formation is uncertain. Double Mer sediments postdate the Grenvillian deformation and some workers (Gower, 1988 and references therein) correlate them with the Cambrian Bradore Formation of Newfoundland, but alternative correlations are also possible (Gower, 1988).

Symons and Chiasson (1991) reported a palaeopole of 46.3˚N, 301.4˚E from the Callander alkaline complex of northern Ontario (Table 1), Canada, supported by a baked contact test. This result suggests a high-latitude position of Laurentia. There are several dates of the Callander Complex, which were summarized by Symons and Chiasson (1991) who estimated the age at 575 ± 5 Ma. This is supported by a U-Pb age of 577 ± 1 Ma (S. Kamo, pers. comm., 2004).

The palaeomagnetic study of the 564 ± 9 Ma Catoctin Volcanic Province (Meert et al., 1994) revealed two stable components of magnetization (Table 1). These are Catoctin A, with a steep inclination at 43.0˚N, 308.0˚E and Catoctin B, with a shallow inclination at 4.0˚N, 13.0˚E. Both components are bipolar. There is evidence for the primary nature of both components (see also discussion of Pisarevsky et al., 2000, Meert and Van der Voo, 2001, and Pisarevsky et al., 2001 for details).

Tanczyk et al. (1987) also found a two-component magnetisation in the Sept Iles Intrusion (Table 1). The rigorous baked contact test proved the primary nature of the shallow remanence (A, 20.0ºS, 321.0ºE) of the main intrusion dated at 565 ± 4 Ma (Higgins and van Breemen, 1998). Cross-cutting dykes of unknown age carry a steep remanence component B (Tanczyk et al., 1987, 59.0˚N, 296.0˚E). Kirschvink et al. (2003) confirmed the presence and primary nature of the Sept Iles A component in the main intrusion as well as the presence of the B component in the cutting dykes. They also dismissed the possibility of introducing of a regional tilt corrections that has been applied in some re-interpretations for the Sept Iles remanence components (e.g. Symons and Chiasson, 1991; Meert et al., 1994; Torsvik et al., 1996).

The 573 ± 32 Ma Buckingham lavas in Quebec yielded a palaeopole of 9.5˚N, 340.8˚E (Dankers and Lapointe, 1981), close to that determined for the Long Range dykes (Table 1). Palaeomagnetic data from the sediments of the Rainstorm Member of the Johnnie Formation in Nevada (Van Alstine and Gillett, 1979) revealed a similar remanence direction at 10.0˚N, 342.0˚E (Table 1). The age constraints for this formation are imprecise. However, recent correlation of the Rainstorm Member with late Neoproterozoic strata in different parts of the world suggest a Varangian/Marinoan (~ 620 Ma) age (Corsetti and Kaufman, 2003; Wernicke and Hagadorn, 2000; Abolins et al., 1999; Hodych et al., 2004). If so, the palaeomagnetic data from the Johnnie Formation are broadly coeval to those from the Nyborg Formation (Torsvik et al., 1995a).

The 550 Ma Skinner Cove Formation in western Newfoundland (Cawood et al. (2001) contains a low latitude remanence of 15˚S, 337˚N, which is primary as evidenced by an intraformational conglomerate test (McCausland and Hodych, 1998). The unit occurs within the Humber Arm allochthon (Williams and Cawood, 1989), but is inferred not to have been transported far and to have lain at, or near, the Laurentian margin (Cawood et al., 2001; Hodych et al., 2004). A similar pole was obtained from the Lower Cambrian Bradore Formation (~530-520 Ma, Cawood et al., 2001) in St. John Bay, western Newfoundland (Rao and Deutsch, 1976) which is not included in Table 1 due to low reliability index. Several other Early to Middle Cambrian palaeomagnetic results from Laurentia also have lower reliability index, but all show low palaeolatitudes (Black, 1964; Spall, 1968; Rao and Deutsch, 1976; Watts et al., 1980).