Oligocene outcrops at Balanusviken, Forlandsundet
Feyling-Hanssen & Ulleberg (1984) described two outcrops of Oligocene deposits at Balanusviken, Sarsbukta, on the east side of Forlandsundet
(western sequence according to Berg et al. 1999, Map 2, Fig. 1). At Balanuspynten, in the southern end of Balanusviken, they described an 8 metre-thick section of micaceous claystone. At Konglomeratodden, in the northern end of Balanusviken, they recorded a 7 m-thick section with beds of varying lithology including different kinds of conglomerates, sandstone and sandy clay. The micaceous clay was not found at Konglomeratodden, but most likely it occurs below sea level there. Both localities are capped with a glacimarine overburden (Fig. 2).
Sketch of outcrop at Sarsbukta
On the basis of benthic calcareous foraminiferal assemblages in nine samples, these authors divided the sections into two zones: the overlying Astigerina guerichi Zone (TB, samples 226, 228, 232 and 244) and the underlying Bolivina cf. antique Zone (TA, samples 19, 20, 247, 248 and 260, Fig. 2). Among a composite assemblage of 22 taxa for the entire section, Zone TA is distinguished by occurrences of the nominate species as well as Gyroidina soldanii mamillata and Rotaliatina bulimoides. Zone TB is distinguished by the occurrence of the nominate species (Astigerina guerichi guerichi) as well as Angulogerina gracilis, Angulogerina tenuistriata, Alabamina tangentialis and Epistominella oveyi. Turrilina alsatica is common in both zones. Feyling-Hanssen & Ulleberg (1984) assigned a transitional Early to Late Oligocene age to this entire section, and indicate an age equivalent to Subzones NSB 7a to NSB 8a according to King (1989). However, Manum & Throndsen (1986) proposed an age not younger than Late Eocene for the Balanusviken sections based on dinoflagellate cysts.
Eidvin et al. (1998b) carried out Sr isotope analyses on foraminiferal tests from four of these samples (19, 228, 244 and 248) and new dinoflagellate cyst analyses in samples 228 and 248 (Fig. A4). In Eidvin et al. (1998b) we used a 87Sr/86Sr global seawater curve compiled by the Institute for Energy Technology (IFE), Norway based on data from DePaolo (1986), DePaolo & Ingram (1985), Hess et al. (1986), Hodell et al. (1989, 1990, 1991), Koepnick et al. (1985) and Palmer & Elderfield (1985) for numerical age assignments. That resulted in ages close to and slightly younger than the Early/Late Oligocene boundary (based on the time scale of Berggren et al. 1995). According to the look-up table by Howard & McArthur (1997); this results in slightly older ages of latest Early Oligocene (Table 1).
Eidvin et al. (1998b) concluded that most of the recorded dinoflagellate cysts recorded in samples 228 and 248 (Fig. 2) and by Manum & Throndsen (1986) are older Paleogene forms reworked into Oligocene strata.
Sarsbukta, Forlandsundet, western Spitsbergen
| Sample ID | Corrected 87/86Sr | 2S error | Age (Ma) | Laboratory | Analysed fossils |
| 228 | 0.708032 | 0.0000013 | 28.78 | IFE | Calcareous benthic index foraminifera |
| 244 | 0.707946 | 0.0000012 | 30.79 | IFE | Calcareous benthic index foraminifera |
| 248 | 0.707944 | 0.0000011 | 31.06 | IFE | Calcareous benthic index foraminifera |
| 19 | 0.707960 | 0.0000010 | 30.62 | IFE | Calcareous benthic index foraminifera |
Table 1: Strontium isotope data from Oligocene outcrops at Sarsbukta. IFE = Analysed at the Institute for energy technology (at Kjeller, Norway). Sr ratio was corrected to NIST 987 = 0.710248. The numerical age was derived from the SIS Look-up Table Version 3:10/99 of Howard & McArthur (1997). NIST = National Institute for Standard and Technology. Modified from Eidvin et al. (1998b).
References
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