Deltaic Infill of a Deglaciated Arctic Fjord, East Greenland: Sedimentary Facies and Sequence Stratigraphy

Abstract

ABSTRACT The deltaic fill of a deglaciated side-entry fjord in western Jameson Land, East Greenland, shows the record of an interplay between regional and local controls, including climate and relative sea-level change, onshore and offshore topography, and sediment yield. A four-phase model is suggested for the delta development and fjord filling. At the deglaciation stage (phase 1), the newly flooded fjord floor primarily accumulated sediment from reworked glacial material. These deposits were relatively thin, and draped the uneven sea-floor topography. The subsequent onset of paraglacial delta sedimentation (phase 2) was characterized by a high meltwater runoff and extreme sediment yield, and corresponded to the highstand and gradual fall of relative sea level. A Gilbert-type delta with a short distributary plain formed at the head of the tributary fjord, which received a very high amount of fine-grained sediment. The stage of enhanced delta progradation (phase 3) was characterized by decreased sediment yield and runoff, and a rapid fall of relative sea level. Delta progradation was fast because of rapidly decreasing accommodation space, and a solitary river channel deeply incised the delta. The equilibrium stage (phase 4) spanned most of Holocene time and involved a lowered rate of relative sea-level fall. Seasonal runoff supplied limited amounts of sediment to the river mouth, and the delta front became increasingly reworked by wave action and longshore drift. The side-entry fjord, a small deglaciated valley invaded by the sea, was filled chiefly by highstand and regressive systems tracts, whereas relatively little sea-floor aggradation was associated with the transgressive systems tract. The stratigraphic pattern documented in this paper contrasts with the pattern usually reported from nonglaciated incised-valley systems, which are filled mainly by the transgressive systems tract, typically involving a retreating estuarine system. The pattern also differs from some large, gradually deglaciated fjord valleys containing thick, transgressive, glaciomarine deposits accumulated during glacier retreat. The study demonstrates the large variability of valley fills and illustrates the importance of topography, sediment supply, and climate as well as the style of deglaciation on the sediment filling of a fjord valley.