## 2 Geological Setting  
The Bounty Trough is situated on the eastern continental margin of New Zealand's South Island. It is a late Cretaceous failed rift bounded by the Chatham Rise to the north, the Southwest Pacific Ocean to the east, and the Campbell Plateau to the south (Figure 1A) [7; 8; 9]. Developed along the axis of the Bounty Trough, the Bounty Channel is a primary conduit for terpenous sediments transported from South Island into the Southwest Pacific Ocean, ultimately contributing to the development of a terminal submarine fan, i.e., the Bounty Fan (Figure 1A) [9; 11; 14]. The formation of the Bounty Trough is linked to the separation of the New Zealand plateau from Gondwana during the late Cretaceous (~112 Ma) [10; 11; 15]. The geodynamic evolution of the Bounty Trough can be categorized into the syn-rift, post-rift, and syn-rogenic stages (Figure 2) [16; 17; 18; 19], which were related to the changes in the regional stress field and relative motion between the Pacific, Australian, and Antarctic plates. During the syn-rift stage (112-82 Ma), the Bounty Trough experienced horizontal extension, leading to the formation of NE-SW-oriented hornst and graben structures in the trough. Throughout the post-rift stage (82-30 Ma), the trough underwent processes such as differential subsidence, compaction, tilting, and gravitational instabilities. During the final stage of trough formation, syn-orogenic tectonics processes (30 Ma to Recent) led to selective compressional inversion of inherited pre-existing normal faults, and the mild deformation of sediments up to the early Late Miocene age throughout the Bounty Trough, as well as the uplift of the Southern Alps, as a result of the convergence across the Alpine Fault, the plate bound  
Figure 1: **(A)** Location map of the study area (red rectangle) in the offshore of eastern South Island, New Zealand. Dotted arrowed lines represent active ocean currents along the margin. SC: Southland Current; AAIW: Antarctic Intermediate Water; DWBC: Deep Western Boundary Current. **(B)** Enlarged bathymetric map showing the characteristics of the tributary channels (C1 to C3) of the Bounty Channel. Also shown are the locations of available two-dimensional multichannel seismic data (dark gray solid lines). Red solid lines indicate the locations of seismic profiles shown in this paper. Red dots denote petroleum exploration wells. The bathymetric map is derived from the General Bathymetric Chart of the Oceans 2023 Grid [13] (accessed on 10 March 2023 from [[https://www.gebco.net/](https://www.gebco.net/)]([https://www.gebco.net/](https://www.gebco.net/))). ary between the Pacific and Australian plates [20; 21; 22; 23]. Correspondingly, the sedimentary sequence within the Bounty Trough contains a Cretaceous syn-rift sequence of lacustrine, alluvial, and fluvial deposits, overlain by the latest Cretaceous to Eocene post-rift sequence of shallow marine sediments, topped by Oligocene to Recent syn-orogenic sequence of deepwater clastic sediments [18; 24; 25]. The study area is located in water depths of \(\sim\)1200-1300 m at the head of the Bounty Trough, covering tributary channels C1 and C2 of the Bounty Channel (Figure 1B). This study focuses on the Upper Miocene to Recent interval in the syn-orogenic phase (Figure 2), which witnessed the formation and evolution of the tributaries. The modern oceanic currents are present off southeast New Zealand, which from shelf to slope are, respectively: (i) the northward-flowing Southland Current, influences the modern margin to a depth of \(\sim\)800 m [26; 27; 28]; (ii) the Antarctic Intermediate Water (AAIW) is between \(\sim\)800 and 1300 m [14; 29]; and (iii) the Deep Western Boundary Current (DWBC) to flow northward at depths between \(\sim\)2000 and \(\sim\)5000 m [14; 30]. Among the currents, the AAIW flows through the tributary channels C1 and C2 from south to north (Figure 1A).