Maija E. Schellpeper1, Ronald J. Steel1
(1) University of Wyoming, Laramie, WY
ABSTRACT: A Shelf-Edge Delta-to-Estuary Couplet in the Eocene of Spitsbergen
Sand-prone, shelf-slope clinoforms of the Eocene Battfjellet Formation provide an excellent outcrop analog for understanding sedimentology and stratigraphy of shelf-edge delta to estuarine couplets and their linkage landwards and basinwards. The study clinoform records coupled delta progradation to the shelf-edge and slope channel incision during relative sea level fall and estuarine filling on the rise. The shelf-edge delta regressive succession occurs as 3-m to 6-m scale coarsening upward mouth bars commonly topped by conglomeratic distributary channels. The mouth bars are very sandy with little to no mud occurring at the tops of plane parallel laminated to rippled and bioturbated units. Transgression produces coarse-grained, tidally-influenced channels and bars in cosets up to 13 m thick that fill an erosional low created by fluvial/deltaic incision into the earlier forced-regressive deltas.
Large-scale architecture is characterized by a lens-shaped shoreline sandstone body (delta/estuary couplet) 20 m to 26 m thick and over 5 km long, bounded by wedge-shaped shales. In proximal areas shales occur above and below the main sandstone body, expanding landward to 12 m thick and pinching out seaward. Prodelta and marine shales/siltstones pinchout landward and expand seaward, thereby bounding the main sandstone body.
Recent seismic-based studies on forced-regressive shelf-edge deltas do not identify estuaries associated with these deltas, even though increased incision associated with forced regression would create a topographic low ideal for estuary filling. We suspect that many of these shelf-edge deltas have associated transgressive estuaries, thereby increasing reservoir quality on the outer shelf.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado