Sediment Record of Falling Sea
Level
Wolfgang Schlager1 and Georg Warrlich2
1 Vrije Universiteit/Earth & Life Sciences, Amsterdam, Netherlands
2 PDO, Muscat, Oman
In the standard model of sequence stratigraphy, sea
-
level
fall is recorded as an extensive erosional hiatus that constitutes the sequence boundary. Significant sedimentation is resumed near the
sea
-
level
minimum. However, subsequent observations revealed that commonly a sediment body is formed during relative fall – the FST (falling-stage
systems
tract or forced-regressive wedge
systems
tract). We employed the modelling programs STRATA and CARBONATE 3D to explore for carbonates and siliciclastics under what conditions an FST is produced and when the record resembles the standard model. It turns out that the parameter space for the formation of an FST is large compared with the parameter space for the standard model. The characteristic continuous unconformity of the standard model requires either a highly asymmetric
sea
-
level
curve with a very rapid fall or rapid erosion of the subaerially exposed highstand tract. We were unable to produce the anatomy of the standard model, i.e. a continuous unconformity and only minor erosion of the preceding highstand tract, with a sinusoidal
sea
-
level
curve. Observations in the Quaternary, where
sea
-
level
fluctuations are well constrained, are compatible with the modelling results: geometries resembling the standard model are common during extremely rapid
sea
-
level
falls (e.g. 22-18 ka B.P.), while falling-stage
systems
tracts
were formed during slower
sea
-
level
falls (e.g. 60-22 ka B.P.). Discrimination between FST and HST is very difficult if the
systems
tracts
are severely eroded. Interpretation of FST's as HST's may lead to wrong geobody geometries in reservoir models and, in carbonates, to underestimation of exposure-related porosity.