Distribution of recent benthic foraminifera in a subarctic fjord-delta: Tana, Norway

Abstract

Analysis of benthic foraminifera (living + dead fauna) in surface sediments from a deltaic and fjord environment at Tana, northern Norway, shows a marked contrast in foraminiferal assemblages between delta platform and delta slope-fjord basin provinces, and a correspondence between test abundance, percentage living of total foraminifera and inferred rate of sedimentation. The relatively shallow (<25 m), high-energy, sandy delta platform province is characterized by an absence or low abundance of foraminifera and a dominance of calcareous forms. Delta plain and tidal strait environments of this province contain a sparse Elphidium albiumbilicatum assemblage and a resedimented Cibicides lobatulus assemblage, respectively. The deeper (25–125 m), lower energy, silty-sandy to sandy-muddy delta slope-fjord basin province is characterized by a relatively high abundance of foraminifera and a dominance of agglutinated forms comprising an Adercotryma glomerata-Spiroplectammina biformis assemblage. Foraminiferal abundance in the delta slope-fjord basin province tends to increase with increasing depth and distance from the river mouth, suggesting a correlation with sedimentation rate. A generally high percentage of living foraminifera is thought to mainly reflect high sedimentation rates in the deltaic environment. Local variations in foraminiferal abundance, percentage living foraminifera, and faunal composition are ascribed mainly to local variations in sedimentation rates and processes, and postmortem changes.