Early Tertiary bentonites from Svalbard

Abstract

Paleontol'ogical and petrological studies of clay beds in the Basilika Formation (Tertiary age) are presented. The petrology of the beds indicates that their main constituents were derived from volcanic activity and represent bentonites. Differing composition between beds suggests several spatially separated eruptions. The volcanic source area probably lay towards the N of the present Tertiary outcrops of Svalbard. Two foraminiferal assemblages are found in the bentonites: the lower is dominated by arenaceous forms while the upper consists of calcareous species.

Origin of Bentonites and Detrital Zircons of the Paleocene Basilika Formation, Svalbard

“…They were first described by Gripp (1927) as thin, laterally consistent beds of plastic clay and have been observed in several locations within the CTB (Nagy, 1966;Vonderbank, 1970;Major and Nagy, 1972;Dypvik and Nagy, 1978;Major et al, 2001). Dypvik and Nagy (1978) described the bentonites as very fine-grained but poorly sorted, with maximum grain sizes between 15 and 40 µm and consisting of ∼80% clay minerals-mostly illite/smectitewith minor fractions of quartz and feldspar, indicative of altered, aeolian-transported volcanic material. Based on the grain size they concluded that the source area was located at a distance of 100−200 km from the area of deposition but more distant sources were not excluded.…”

“…The NALIP is expressed in flood basalts on eastern Greenlandas well as flood basalts and alkaline tuffs in western central Greenland (Storey et al, , 2007Tegner et al, 1998;Larsen and Pedersen, 2009;Larsen et al, 2016). Moreover, Paleocene bentonites were observed on Svalbard as well as Ellesmere Island and are particularly widespread in the North Atlantic region (Figure 1; Major and Nagy, 1972;Dypvik and Nagy, 1978;Larsen et al, 2003a;Grist and Zentilli, 2004;Reinhardt et al, 2013).…”

“…Tessensohn and Piepjohn, 2000), extensional tectonics were accompanied by magmatism with continental rift signature from the Early Cretaceous onwards until ∼61 Ma (e.g., Tarduno, 1998;Estrada et al, 2001;Maher, 2001;Tegner et al, 2011;Thorarinsson et al, 2011b). During the Paleogene, magmatism in the Arctic was predominantly intrusive and basaltic effusive (e.g., Storey et al, 1998;Tegner et al, 1998;Storey et al, 2007;Thorarinsson et al, 2011b), but explosive volcanic activity also occurred, as evidenced by volcanic ash layers on Ellesmere Island and Svalbard (e.g., Dypvik and Nagy, 1978;Reinhardt et al, 2013). These ash layers are preserved in Paleogene sediments, i.e., in the Eureka Sound Group on Ellesmere Island and in the Central Tertiary Basin on Svalbard (Dypvik and Nagy, 1978;Reinhardt et al, 2013).…”

“…During the Paleogene, magmatism in the Arctic was predominantly intrusive and basaltic effusive (e.g., Storey et al, 1998;Tegner et al, 1998;Storey et al, 2007;Thorarinsson et al, 2011b), but explosive volcanic activity also occurred, as evidenced by volcanic ash layers on Ellesmere Island and Svalbard (e.g., Dypvik and Nagy, 1978;Reinhardt et al, 2013). These ash layers are preserved in Paleogene sediments, i.e., in the Eureka Sound Group on Ellesmere Island and in the Central Tertiary Basin on Svalbard (Dypvik and Nagy, 1978;Reinhardt et al, 2013). Both depocenters are dominated by clastic deposition, and their stratigraphy and provenance are still poorly resolved (e.g., Miall, 1991;Dallmann, 1999).…”

“…This formation comprises deltaic to deep-water clastic sediments (e.g., Steel et al, 1981), supposedly sourced from the east (Steel et al, 1981;Helland-Hansen, 1990;Müller and Spielhagen, 1990), and contains several altered volcanic ash layers that were previously characterized as bentonites (e.g., Gripp, 1927;Nagy, 1966;Dypvik and Nagy, 1978). The primary aim of this study is to geochemically characterize the Basilika bentonites in order to derive information on the origin of their volcanic sources and their plate tectonic environment.…”