Delta-influenced foraminiferal facies and sequence stratigraphy of Paleocene deposits in Spitsbergen

Abstract

The Paleocene Firkanten Formation of the Central Basin of Spitsbergen is a succession of terrigenous clastic sediments, interpreted as a major depositional sequence, formed in deltaic coastal plain, delta front and prodelta environments. The present study combines diagnostic features of foraminiferal facies with sedimentary data to elucidate this sequence stratigraphic development. Deposition was initiated by an early Paleocene transgression which led to the deposition of a delta plain to coastal marine sediment package forming the low stand and transgressive systems tracts; these includes coal swamp, lacustrine, lagoonal and barrier deposits. The lagoonal shales are characterised by an agglutinated foraminiferal assemblage of extremely low diversity indicative of hyposaline conditions. Shoreface sandstones overlying the lagoonal strata are interpreted as sand barriers reworked by the advancing transgression. These sandstones are succeeded by a package of prodelta silty shales, which in the lower part includes the maximum transgressive interval. The foraminiferal assemblage of the prodelta shales is also agglutinated but reveals increased diversities suggesting open marine conditions. The prodelta shales and overlying delta front sandtones form a succession of coarsening upwards parasequences of deltaic progradation, representing the regressive systems tract. The entirely agglutinated low diversity nature of the foraminiferal assemblages is in part attributable to the deltaic impact. The restricted character of the faunas is additionally accentuated by the effects of the Paleogene Boreal province.