The Role of Climate Variation in Sequence Stratigraphy: Lessons from Analogue Modelling
Bijkerk, Jochem F.; ten Veen, Johan; Postma, George; Mikes, Daniel
Sequence-stratigraphic models for 5th to 6th order, glacio-eustatic sequences based only on relative sea-level variations result in simplified and potentially false interpretations. Glacio-eustatic sea-level variations form only one aspect of cyclic climate variation; other aspects of climate variation (e.g. variations in river run-off) can lead to variable sediment yield, thus adding complexity to sequence stratigraphic patterns normally attributed to sea level variation.
Based on analogue flume models, a significant impact of discharge is observed on the timing and character of sequence boundaries, as well as on changes in the relative importance (sediment volume expression) of systems tracts. Four deltas, generated under influence of an identical sea-level curve, but affected by different discharge cycles are generated in the Eurotank Laboratories: (1) constant discharge; (2) high frequency discharge variations; (3) high discharge leading high sea level by a quarter phase; (4) high discharge lagging high sea level by a quarter phase. High frequency discharge variations show little impact on the overall delta architecture and might provide an explanation why 3rd order sequences in seismic generally do not show higher order climatic overprints. When high discharge leads high sea level, sediment delivery is high during sea-level rise, which results in the poor development of maximum flooding surfaces. Delta front erosion during sea-level fall occurs in multiple, small channels and does not result in a single connected, incised valley. In cases that high discharge lags high sea level, sediment delivery is high during falling sea level and results in rapid progradation during forced regression. Erosion from incised valleys is strong on the proximal delta top but dampened distally due to rapid progradation and valley backfill. During sea-level rise, low discharge result in sediment starvation and well-developed maximum flooding surfaces. Because sea level curves are identical in all models, the differences can be fully attributed to discharge variations.
Discharge variations thus provide an alternative explanation to the amplitude of sea-level fall for generating either Type 1 or 2 erosional unconformities. Based on the different responses of sediment yield to the delta apex, an influence of sea-level variations on the fluvial system is also inferred. A case study for scenario high discharge lagging sea level high stand (scenario 4) is presented.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013