Mass-Transport Deposits as Tectonostratigraphic Markers to Unravel the Development of Subduction-Related Sedimentary Basins

Along active margins, the prevalence of thrust ridges and tectonic processes (e.g., uplift, slope oversteepening) is commonly recognized as one of the main recurrent reasons for generating slope failures and mass wasting. The resulting mass-transport deposits (MTDs) are often seen to vary strongly along the margin. Therefore, our work aims at characterizing their nature, origin and significance in context of the tectonostratigraphic evolution of subduction-related sedimentary basins (e.g., trench-slope basins [TSBs]). Here, we present high-resolution outcrop-scale insights on both the characteristics and mechanisms of emplacement of the failed sediments by examining thrust-related MTDs from the Miocene series exposed in the emerged southern portion of the Hikurangi subduction margin (New Zealand). Regional offshore seismic data were also used to offer a broader overview and understanding of these systems through the study of the larger scale geometries and architectures. Results repeatedly highlight the role and importance of the thrust ridges in controlling the TSB infilling. Different styles of MTDs are generated from different structural positions (forelimb and backlimb) and at specific times of thrust-ridge and TSB development, thereby implying that MTDs are powerful tectonostratigraphic markers. These findings, in turn, provided significant clues for better comprehending the evolution of the emerged southern portion of Hikurangi subduction wedge at key periods and, more particularly of two of its TSBs since the onset of subduction. Overall, this study offers new insights on the close interplays between deformation and sedimentation, understandings of which may be key for geohazard, exploration and geodynamic predictions along active margins.