Paleodepositional setting of the Late Cretaceous Pautût Flora from West Greenland as determined by sedimentological and plant taphonomical data

Abstract

Preservation of the Santonian/Campanian Pautût Flora in West Greenland is mainly the result of a high energy river system that flowed across a well vegetated delta plain to carry and deposit plant parts and terrestrial clastic sediments into a low energy marine setting. A diverse flora is represented mainly in three depositional settings: (1) a dominant angiosperm vegetation preserved with fern and a few conifer species is found within backswamp lakes possibly near rivers; (2) conifer organs and a sparse angiosperm leaf association occur in nearshore marine deltaic deposits dominated by fluvial sedimentation; and (3) a unique Pautût angiosperm vegetational assemblage with a few conifer and cycad species preserved in a brackish to fully marine bay setting. Fossil plant material preserved in the backswamp lakes and fluvial settings probably were deribed mostly from local sources indicating that angiosperms were able, to a degree, to invade into the backswamp Arctic habitats considered to have been dominated by conifers. However, these backswamp habitats probably were short-lived oxbow lakes with a successional angiosperm vegetation. Plant material in the fully marine setting is allochthonous, very diverse, and probably derived mostly from the upper delta palin. The observed differences within the fossil plant assemblages deposited in the marine setting, those containing mostly conifer parts occur in nearshore marine environments as compared to assemblages with mostly angiosperm leaves in more distal marine environments, are used to interpret sorting of different plant parts due to individual taphonomical characters. This means that the heavier conifer cones in the nearshore marine setting sank sooner than the lighter leaves, which were dispersed further out to sea. Strengthening the argument for sorting is that both types of plant parts had a final resting position due to subaqueous transport. The unique angiosperm leaf assemblage found in the fully marine setting is used to support the interpretation that the upper delta plain levees, or extrabasinal sites, were inhabited by a vegetational community distinct from that near the backswamp areas of the lower delta plain. There are a few angiosperm species in common between the distal and nearshore marine and the backswamp lake settings. These species are found througout the Pautût area and exemplify a riparian element which was more prone to enter a depositional regime. Nearshore habitats were inhabited by non-woody plants.