EOCENE FALLING-STAGE DELTAS AND ASSOCIATED UPPER SLOPE CHANNELS: AN OUTCROP STUDY OF A DEEPWATER FEEDER SYSTEM (CENTRAL SPITSBERGEN BASIN)

Outcrops along Van Keulenfjorden on Spitsbergen record the progradation of an early Tertiary shelf margin in the Central Spitsbergen Basin, in particular, a series of falling-stage deltas that generated coeval slope and basin floor turbidites. These deposits are visible in seismic scale, sub-parallel to the depositional profile. Source area for the sediments was located 30 km to the west in a contemporaneous fold and thrust belt.

Field work on a single falling-stage delta system on Storvola and Brogniartfjellet concentrated on the shelf, shelf-edge, and upper slope portions of the early depositional profile. These deposits are linked downslope with a basin floor fan. A dominant facies on the shelf edge and upper slope, in addition to upwards-coarsening rippled, delta-front sandstones, was upper-stage, plane-parallel lamination in fine-medium sandstones. This facies, particularly in channels at the base of the outcrop, suggests that a high sediment volume fluvial system reached the shelf edge during falling-stage or early lowstand of a relative sea-level cycle, dumping sandy hyperpycnal flows into upper slope channels on an otherwise shale-prone setting. Earlier work has concluded that the basin floor fan was fed by turbidites of hyperpycnal origin. Rippled sets between plane-parallel sets indicate waning flow, or alternatively, pulsating flow within a turbidity current. Chaotic slump deposits, prominent at the shelf break are in agreement with rapid deposition of sediments on a delta front.

Current-ripple and low-angle cross strata are dominant on the shelf whereas flat-laminated sand beds dominate on the slope. Base level fall may have been punctuated as shown by three or four parasequences. Intervals of landward-migrating dunes at the top of parasequences record minor transgressions imprinting the overall regressional character of the clinoform. Channelization at the base of at least one of the parasequences suggests a strong fluvial system and/or rapid base level fall. Overlying heterolithic sediments represent a late lowstand prograding wedge. The late lowstand wedge is separated from the early lowstand by an interval of marine shale extending across the mid to outer shelf. The entire clinoform is overlain by shale from a major marine transgression.