Modeling of stratigraphic architectural patterns in extensional settings—towards a conceptual model

Abstract

Our earlier studies on active continental extensional basins revealed that high-frequency changes in sea/lake-level, spatially heterogeneous subsidence/uplift and multiple sources of sediment supply with varying rates and directions are the main factors that influence the formation of stratigraphic architectural patterns. Thus, the evolving stratal geometry results from the sea/lake-level—[time], subsidence—[time, space] and sediment supply—[time, space, direction, composition] functions. The stratigraphic simulation results presented here demonstrate that Type 1 and 2 unconformities and conformities may develop in segments of an extensional basin during a sea/lake-level fall depending on the local subsidence rates. These different surfaces can be time-equivalent along the basin margin. A sea/lake level rise can either form a highstand systems tract (HST) or a transgressive and an overlying highstand systems tract (HST), depending on the sediment supply. A decrease and a subsequent increase in sediment supply during a stable base level stand can produce the same architectural patterns (backstepping of transgressive systems tract (TST) and aggradational or progradational patterns of HST) as a rise in the base level at constant sediment supply. Stratigraphic architectures built from multiple sediment sources show a variety of patterns as responses to spatial and temporal changes in intensities of individual sediment supply sources. Some of the possible end members of these interfingering architectural patterns have been simulated and classified. Changes in direction of sediment supply may lead to the formation of onlap-surfaces similar to unconformities.