Ole J. Martinsen1,
Jan S. Ronning3
(1) Norsk Hydro Research Center ASA, Bergen, Norway
(2) Norwegian Technical University, Trondheim, Norway
(3) Norwegian Geological Survey, Trondheim, Norway
Abstract: Ultra-high resolution seismic stratigraphic analysis of a late Pleistocene-Holocene forced regressive shoreline complex, Finnmark, Norway, using ground-penetrating radar
Accretionary forced regressions form depositional units where the shoreline trajectory dips seaward. Although this process is reasonably well understood, the detailed geometries and cyclic construction of such units need to be worked out.
A late Pleistocene-Holocene (0-15 ky) forced regressive shoreline complex in Sandfjorden, Finnmark (Northern Norway) was analysed using ground-penetrating radar which gave resolution down to less than 1m. The reason for this study was to constrain seismic as well as theoretical sequence stratigraphic models.
The data are of very high quality with penetration down 35 m. The lines show descending clinothems with clinoforms which dip seaward at decreasing angles, ranging from 2-10 degrees. The shoreline trajectory, defined by the top of the clinothems, also dips seaward at a decreasing angle, ranging from 5 degrees to less than 1 degree. the decreasing angle of reflector dips is interpreted to record an overall decreasing rate of sea level fall and increased sediment supply over time.
Within the descending clinothems, a cyclic pattern of erosion and deposition can be observed. At least twenty such cycles are observed. The cycles either record very high frequency cycles of sea level change of around 500-750 years duration, or high and low storm intensity cycles. Such high resolution cyclicity has not yet been described form forced regressive complexes.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana