(1) Göteborg University, Gothenburg, Sweden
ABSTRACT: When During the Lowstand Do Basin-Floor Fans Form: Implications from Eocene Central Basin of Spitsbergen
Four basin-floor fans were studied by measuring detailed vertical sections and lateral mapping. The basin-floor fans have a three-fold architecture. (1) The Lower Segment (LS) consists of basinwards younging, prograding clinoforms that downlap into underlying marine shales. Individual clinoforms consist of upwards coarsening and thickening packages of turbidite beds. (2) The Middle Segment (MS) is based by an erosion surface that can be traced across the fans, and that rises landwards through the stratigraphy. The MS reaches farthest out into the basin. (3) The Upper Segment (US) is based by a flooding surface that brings muddy turbidites at the top of the sandstones of the MS. The US consists of upwards-younging clinoforms that step successively landwards. The progradation, together with the regional erosion surface at the top, indicate that the LS was deposited during a relative sea-level fall. The erosion surface, interpreted as the sequence boundary, developed when sea-level was lowest at the shelf edge. The MS represents maximum progradation of the system, and was deposited during early lowstand. The landwards-stepping US indicates a relative sea-level rise, and was deposited during later stages of lowstand, but before the late lowstand wedge time. Sequence boundary is placed at the regional erosion surface, rather than at the base of the fans, because (1) this surface corresponds to the lowest sea level, (2) this surface correlates into main canyon base, feeding the basin-floor systems, (3) MS reaches furthest out into the basin, whereas LS is absent in the distal fans.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.