Uroza, Carlos A.1, Ron Steel2
(1) University of Wyoming, Laramie, WY (2) University of Texas, Austin, TX
ABSTRACT: Sequence Stratigraphy and Depositional Architecture of a Linked Shelf-Edge Delta-Estuary System in the Battfjellet Formation, West Spitsbergen, Norway
The Eocene Battfjellet Formation in West Spitsbergen provides excellent outcrops showing the geometry and architecture of linked shelf-edge delta-estuary systems. Sand-prone deepwater clinoforms, showing shelf to slope transitions, occur along four mountainsides in Van Keulenfjorden. Facies analysis and sequence stratigraphy applied to two of these clinoform allowed recognition of episodes of delta progradation and subsequent estuary-forming transgressions. The two studied clastic tongues, clinoforms 17 and 18, represent 4th order sequences, the latter prograding eastwards above the former, producing a significant amount of shelf-margin accretion. The prograding shelf deltas were built from prodelta shales, wave-influenced, high-energy river-mouth bars and one to four meter-thick distributary channels. The transgressive component of the upper clinoform was generated by estuaries that developed up to ten meters of clean, well-sorted, cross-stratified sands. The latter, oriented mainly landwards, were generated by flood-dominant tidal currents. The shelf-margin accretion involved two episodes of relative sea-level fall, and three intervals of significant marine flooding. The sequence boundaries merge landwards with erosive surfaces of marine transgression, implying that original fluvial valleys were drowned to became estuaries, leaving no remnant of the fluvial distributaries. The upper sequence boundary, in a slopeward direction, is separated from the transgressive surface by a muddy, lowstand slope system. This work suggests that estuarine valleys develop well in a shelf-edge position (significant fall is usually necessary for deltas to reach the shelf edge), maybe better than in an inner-shelf, highstand position, a conclusion that can be of importance for oil & gas exploration in a shelf setting.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.