Experimental Studies of Allocyclic Controls on Stratal Architecture of Alluvial and Shallow-Marine Systems

Penny E. Patterson¹, Benjamin A. Sheets¹, John Martin², John W. Snedden¹, Chris Paola², and Chris Ellis^2
1 ExxonMobil Upstream Research Company, Houston, TX
² University of Minnesota, Minneapolis, MN

The relative influence of allocyclic climatic fluctuations on clastic sediment transport and stratal architecture of alluvial and shallow-marine depositional systems is examined through a series of tank experiments conducted at the Saint Anthony Falls Laboratory, University of Minnesota. These experiments focus on allocyclic, climate-related attributes of water discharge, sediment flux, and base level. The experiments were conducted in a basin characterized by uniform, “piston-style” subsidence to minimize the effects of variable accommodation.

Results from the experiments indicate that isolated cycles of water discharge or sediment flux have a relatively weak stratigraphic signature when compared with a case where these are varied concurrently. Further, the rate, duration and geometry of base-level cycles have important consequences for the efficiency of sediment transport as well as stratal architecture. Simple, rapid fall and rise base-level cycles have a limited impact on the depositional basin, resulting in development of narrow incised valleys and progradation of a single, lowstand deltaic system. In contrast, base-level cycles characterized by slightly lower rates of fall with superimposed higher-frequency base-level fluctuations, such as those formed during global glacial cycles, result in more spatially variable incision and fill along the distal region of the alluvial profile. Moreover, the superimposed base-level cycles promote the development of more sand-prone deltaic successions along the shelf margin.

Within a sequence stratigraphic context, the experimental results document the diachronous nature of a sequence boundary that results from combined autocyclic and allocyclic erosion within the incised valley and concomitant basin-ward progradation of the shoreline system.