Miocene–Recent tectonic and climatic controls on sediment supply and sequence stratigraphy: Canterbury basin, New Zealand

The well‐constrained seismic stratigraphy of the offshore Canterbury basin provides the opportunity to investigate long‐term changes in sediment supply related to the formation of a transpressive plate boundary (Alpine Fault). Reconstructions of the relative motion of the Australian and Pacific plates reveal divergence in the central Southern Alps prior to ∼20.1 Ma (chron 6o), followed by increasing average rates of convergence, with a marked increase after ∼6 Ma (late Miocene). A strike–slip component existed prior to 33.5 Ma (chron 13o) and perhaps as early as Eocene (45 Ma). However, rapid strike–slip motion (>30 mm yr −1 ) began at ∼20.1 Ma (chron 6o). Since ∼20.1 Ma there has been no significant change in the strike–slip component of relative plate motion. Sedimentation rates are calculated from individual sequence volumes that are then summed to represent sequence groups covering the same time periods as the tectonic reconstructions. Rates are relatively high (>22 mm yr −1 ), from 15 to ∼11.5 Ma (sequence group 1). Rates decrease to a minimum (<15 mm yr −1 ) during the ∼11.5–6 Ma interval (sequence group 2), followed by increased rates during the periods of ∼6–2.6 Ma (21 mm yr −1 ; group 3) and 2.6–0 Ma (∼25 mm yr −1 ; group 4). Good agreement between sedimentation and tectonic convergence rates in sequence groups 2–4 indicates that tectonism has been the dominant control on sediment supply to the Canterbury basin since ∼11.5 Ma. In particular, high sedimentation rates of 21 and ∼25 mm yr −1 in groups 3 and 4, respectively, may reflect increased plate convergence and uplift at the Southern Alps at ∼6 Ma. The early‐middle Miocene (∼15–11.5 Ma) high sedimentation rate (22 mm yr −1 ) correlates with low convergence rates (∼2 mm yr −1 ) and is mainly a response to global climatic and eustatic forcing.