Abstract
Fjords are globally significant sedimentary archives that record the relationship between glacial, tectonic, and marine processes. Fiordland, on the southwest coast of New Zealand, hosts one of the most extensive temperate fjord provinces in the Southern Hemisphere, yet its postglacial evolution has remained poorly constrained. This study integrates high‐resolution seismic reflection data with existing geomorphic mapping across 15 fjords to reconstruct the regional deglaciation and sedimentary history following the Last Glacial Maximum. The resulting seismostratigraphic framework provides the first region‐wide chronology of marine inundation and sediment accumulation across Fiordland. Two principal depositional phases are identified: a basin‐confined unit representing pre‐marine infill deposited during and immediately following early glacier retreat, and an overlying marine unit that drapes the fjord floors following marine inundation. Uplift‐corrected sill depths combined with global and regional sea‐level curves reveal that marine inundation progressed asynchronously across Fiordland, with first inundation occurring as early as ∼16.9 ka and final fjords becoming marine by >8.7 ka, coincident with rapid sea‐level rise during Meltwater Pulses 1A and 1B. Post‐inundation sedimentation reflects a transition from high‐energy glacial deposition to low‐energy marine accumulation controlled by catchment size, fjord geometry, and tectonic setting. This reconstruction highlights Fiordland's role as efficient sediment and carbon traps, while preserving records of postglacial environmental change in temperate fjord systems. The integrated approach presented here offers a template for evaluating how tectonic, climatic, and eustatic processes collectively shape fjord evolution.