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The Kapp Lyell diamictites (Upper Proterozoic) at Bellsund, Spitsbergen: rock-sequence, sedimentological features, palaeoenvironment

Birkenmajer K.

Studia Geologica Polonica

2010

Vol. 133

7-50

The Upper Proterozoic meta-diamictites (Kapp Lyell Formation) exposed south of Bellsund, central Spitsbergen, believed by many authors to represent the Vendian (Varangian) glacial tillites, have been investigated. Character of their relictic sedimentary features does not confirm, however, its glacial origin. The diamictites formed mainly as debris-flow and slope-creep terrestrial covers derived from frost-shattered steep rocky margins of a predominantly fresh-water depositional basin. The deposition took place under seasonally differentiated moderate-cool climatic conditions comparable to the modern Subarctic periglacial zone, however outside the reach of glaciers and ice-sheet. Uncommon finer-grade varved deposits containing haphazardly distributed clasts (drop- stones) probably formed in shallow fresh-water lakes that froze during winter; the clasts were subsequently dispersed during summer in the lakes as ice-rafted dropstones. Shallow erosional channels infilled with sandstone within the diamictite complex, might be evidences for braided river systems that were active during summer. Rare, well-rounded cannonball-size cobble/boulder beds represent a fossil high-energy, probably marine beach.Uncommon thin limestone intercalations, found in a predominantly coarse-clastic suite, might suggest occasional incursions of a shallow sea.