Australia: The Land Where Time Began

A biography of the Australian continent 

Siberian flood basalts

Intercalated volcaniclastics are present in the Siberian flood basalts to varying extent throughout the sections of that province that have been most studied e.g., in Noril’sk (e.g. Fedorenko et al., 1996). There is a vast literature on the Siberian province. The thick, primary phreatomagmatic deposits that underlie the lavas are the most significant volcaniclastics in the Siberian province. The majority of the basal volcaniclastics are less than 30 m thick in the northeast and northwest sections, and are sometimes absent. The volcaniclastics are, however voluminously present as largely massive, featureless outcrops in the central, eastern and southern regions.

All the river cliffs along almost 200 km of the Angara River north of Ust Ilim’sk consist of volcaniclastics with visible outcrops as much as 250 m thick with erosional upper and unexposed basal contacts (Naumov & Ankudimova, 1995). Volcaniclastic units are massive, with no bedding and are rich in sediment, but near the Kata River there is local bedding and accretionary lapilli. Lithic blocks of underlying sedimentary strata are present in some outcrops; an active aquifer and driving force for eruption from depth are indicated by peperites and sediment dykes. Pillow basalts and hyaloclastites are notably absent.

Along the Nizhnaya Tunguska River there are similar deposits extending for 200 km east-west past the town of Tura in middle Siberia. Drill cores indicate that in Tura thee are at least 500 m of tuffs that transition to overlying effusive lavas (Drenov, 1985). Voluminous phreatomagmatism immediately prior to the main stage of effusive lava emplacement is demonstrated by these cores.

Sources & Further reading  

1. Ingrid Ukstins Peate & Linda T. Elkins-Tanton in Schmidt, Anja, Fristad, Kirsten A. & Elkins-Tanton, Linde E. (Eds.), 2015, Volcanism and Global Environmental Change, Cambridge University Press.