Forearc basin stratigraphy resulting from syntectonic sedimentation
during accretionary wedge growth: Insights from sandbox analogue
experiments
Abstract
Forearc basin stratigraphy is expected to record a detailed history of
the deformation and growth pattern of an accretionary wedge. However,
the relationship between syntectonic basin sedimentation and growth of a
wedge remains poorly understood, including (1) how deformation of the
wedge modifies the basin stratigraphy and (2) how syntectonic
sedimentation influences deformation of the wedge. In this study, we
conducted scaled analogue sandbox experiments to reproduce accretionary
wedges with and without syntectonic sedimentation. The results show that
basin stratigraphy varied with the growth pattern of the accretionary
wedge. In the case that wedge growth was dominated by trenchward
accretion, the depositional area migrated landward. In contrast,
prolonged underthrusting caused the sediment layers to be tilted
landward and the depocenter to migrate landward. The occurrence of two
types of basin stratigraphy (i.e., trenchward and landward migration of
the depocenter) reflects a contrast in strength of the basal shear
resistance between the inner and outer parts of the wedge due to
sedimentation on the wedge. A change in the magnitude of normal stress
acting on the wedge base likely influenced the mode of deformation of
the wedge. A phase dominated by underthrusting can result in the
combining a retro-wedge basin with a wedge-top basin, and yield a wide
area of accommodation space in the forearc basin. These results suggest
that forearc basin stratigraphy is influenced by the growth pattern of
an accretionary wedge that is affected by syntectonic sedimentation.