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Sequence Stratigraphic Analysis of a Back-Tilted Subsiding Basin Experimental Deposit

Mohd Noor Azudin, Ahmad Nazmi *1; Hajek, Liz 1; Petter, Andrew 2; Paola, Chris 2; Al-Abbad, Abrar 1
(1) Geosciences, Penn State University, State College, PA.
(2) St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN.

Sequence stratigraphy is a useful tool that is widely used for petroleum exploration and correlation in clastic strata. Although broadly applied, many models emphasize the interaction of sediment supply, subsidence, and sea-level changes in passive-margin settings, where subsidence increases with distance from the sediment source. However, in many sedimentary basins, including those in foreland and some rift settings, highest subsidence rates occur in the proximal portion of a basin, with subsidence decreasing with distance from the source. The degree to which basin-subsidence geometry influences the deposition and preservation of key sequence-stratigraphic surfaces and facies patterns remains relatively unconstrained.

To examine the relationship between subsidence geometry and sequence development, an experiment was conducted at the Experimental EarthScape (XES) facility (U of Minnesota St. Anthony Falls Laboratory) in which sediment and water supply, base level, and basin subsidence can be independently controlled. In the XES-10 run, basin subsidence was steady, but spatially varying, with highest subsidence rates near the upstream end of the basin and slower subsidence rates downstream. Base level was varied throughout the run, including a slow and rapid base-level cycle of the same amplitude, and a compound base-level cycle that included six rapid cycles superimposed on one slow cycle. Sediment and water supply were held constant during each phase of the experiment. XES-10 was designed to replicate conditions of a previous experiment (XES-02) with the same series of base-level cycles in a fore-tilted subsidence pattern.

Significant sequence-stratigraphic surfaces (including sequence boundaries, transgressive surfaces, and maximum flooding surfaces) can be identified for each of the eight base-level cycles, though transgressive and maximum-flooding surfaces are not well preserved in first three superimposed cycles (those on the falling limb of the overall compound cycle). Well preserved fluvial onlap surfaces are common and appear to be more distinct in the XES-10 run than in the XES-02 experiment, and sequence boundaries are difficult to trace upstream where channelized deposits dominate the stratigraphy.

These results suggest that basin-subsidence patterns influence preservation potential of key stratigraphic surfaces. Consequently, sequence-stratigraphic interpretations should account for potential preservation differences between tectonic settings.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California