Submarine canyon systems focusing sub-surface fluid in the Canterbury Basin, South Island, New Zealand

This work uses a high-quality 3D seismic volume from offshore Canterbury Basin, New Zealand, to investigate how submarine canyon systems can focus sub-surface fluid. The seismic volume was structurally conditioned to improve the contrast in seismic reflections, preserving their lateral continuity. It reveals multiple pockmarks, eroded gullies and intra-slope lobe complexes occurring in association with the Waitaki Submarine Canyon. Pockmarks are densely clustered on the northern bank of the canyon and occur at a water depth of 500–900 m. In parallel, near-seafloor strata contain channel-fill deposits, channel lobes, meandering channel belts and overbank sediments deposited downslope of the submarine canyon. We propose that subsurface fluid migrates from relatively deep Cretaceous strata through shallow channel-fill deposits and lobes to latter seep out through the canyon and associated gullies. The new, reprocessed Fluid Cube meta-attribute confirms that fluids have seeped out through the eroded walls of the Waitaki Canyon, with such a seepage generating seafloor depressions in its northern bank. Our findings stress the importance of shallow reservoirs (channel-fill deposits and lobes) as potential repositories for fluid, hydrocarbons, or geothermal energy on continental margins across the world.

www.nature.com/scientificreports/ (a) Decipher the depositional architecture and structure of near-seafloor strata around the Waitaki Submarine Canyon using high-quality 3D seismic data; (b) Investigate the role of submarine canyons in controlling continental-margin architecture and sedimentary processes; (c) Discuss the importance of channel-fill deposits and lobes as capable of focusing fluid flow in deep-offshore basins.

Geological setting
Tectonic evolution of the Canterbury Basin. The eastern part of the South Island comprises a divergent continental margin on which the Canterbury Basin is located (Fig. 1a). This basin lies over thinned continental crust of a discrete tectonic plate (Zealandia) that has broken away from Antarctica and Australia around 80 Ma 25 . The depositional history of the Canterbury Basin has, since then, been controlled by the uplift and erosion of the Southern Alps, marine currents and sea-level change 18,20 . As a result, the basin extends, at present, from a relatively wide continental shelf (~ 100 km) with a depth ranging ~ 140-145 m to a maximum water depth of ~ 1500 m 26 . The Canterbury Basin covers a total area of ~ 50,000 km 2 and is bounded by the Chatham Rise and Bounty Trough (Fig. 1). Its basin fill includes sedimentary units ranging from the Cretaceous to the Holocene in age. Basement rocks consist of the Torlesse Supergroup, a unit dominated by alternating metasediments (greywacke www.nature.com/scientificreports/ and argillites) of Permian to Early Cretaceous ages 26,27 . Cretaceous continental rifting generated several E-W extensional basins, which were subsequently filled by fluvial and paralic sediments of the Horse Range and Katiki formations 26,27 (Fig. 2). The Late Cretaceous marks the onset of post-rift subsidence and subsequent marine transgression in the Canterbury Basin 27 . This led to a change in deposition from terrestrial sandstones and coal (Pukeiwihai Formation, Fig. 2) to marine conglomerates, sandstones, mudstones, siltstones and minor coal measures towards the end of the Cretaceous (Katiki, Moreaki and Hampden formations; Fig. 2). Late Eocene to Early Oligocene units include fine-grained carbonates of the Amuri Limestone, which mark the maximum extent of marine transgression in the Canterbury Basin. Above the Amuri Limestone occurs a regressive sequence.
An Oligocene maximum flooding surface comprises a current-induced stratigraphic surface named the Marshall Paraconformity 27,28 . This paraconformity is overlain by hemipelagic, bioclastic limestones and glauconitic greensands that mark a sharp decrease in the influx of terrigenous sediment into the basin. The Late Oligocene and Early Miocene witnessed important changes in regional tectonics, with uplift of the Alpine fault and erosion of the Southern Alps predominating from thereon in, promoting a rapid influx of terrigenous sediment (mostly siltstones) to the east 20 .  www.nature.com/scientificreports/ The Late Miocene to Recent is marked by the deposition of large, elongated clinoform drifts (contourites), forming the so-called Canterbury Drift 18,29 . These sediment drifts became ubiquitous over the SE New Zealand margin at the end of the Miocene and control the present-day architecture of strata in the Canterbury Basin. Sea-level change and a relative increase in the strength of marine currents acted as primary controls on sedimentation during the Late Quaternary 18 .

Evolution of the Otago Submarine Canyon Complex. The Otago Submarine Canyon Complex com-
prises a set of submarine canyons and gullies that incise the continental shelf and slope of SE New Zealand (Fig. 1b). These canyons have channelised terrigenous sediment into the abyssal Bounty Trough and corresponding fan since the Early Miocene 18,20 . The shelf-slope break in this region is incised by this canyon complex, forming regularly-spaced canyon heads 19,20 .
The Waitaki Submarine Canyon is located in the northern part of the Otago Submarine Canyon Complex (Figs. 1d, 3). The head of this canyon is narrow, steep and continues downslope into a transitional area where a sinuous profile is recorded. The Waitaki Submarine Canyon intersects the North Bounty Channel further downslope. In bathymetric data, numerous seafloor depressions have been identified at the seafloor in the vicinity of the Waitaki Submarine Canyon 19 . This same canyon has been interpreted as an active conduit for sediment since the earliest Pleistocene, and possibly existed as far in time as the early Pliocene 19 .

Results
Canyon physiography. Bathymetric data reveal a shelf-break incised by a network of regularly spaced, sub-parallel submarine canyons (Figs. 1c,d, 3a). Based on the classification scheme proposed by Jobe et al. 5 , the Waitaki Submarine Canyon comprises a Type I canyon that resembles a V-shaped profile in its proximal part (shelf edge), transitioning into a U-shaped profile towards its distal part. Bathymetric cross-sections clearly reveal gradual changes in geometry (profiles A-F, Fig. 3a-g). The Waitaki Submarine Canyon is located in water depths ranging from ~ 400 to 1200 m and shows a NW-SE orientation.
Profile A reveals a V-shaped cross-section where the canyon walls are deeply incised to a depth of ~ 400 m (Fig. 3b). Such a type of cross-section continues from the continental shelf to the shelf break ( Fig. 3c-e; profiles B-D), showing a subsequent increase in the depth of incision from ~ 400 to 1000 m. Moving from the shelf break to the continental slope, the cross-section changes to a U-shaped geometry (Fig. 3f,g; profiles E,F), and the canyon's incision depth increases to ~ 1200 m. The continental slope becomes wavy with alternate ridges and troughs. The head and the sidewalls of the Waitaki Submarine Canyon are steep (~ 10°-20°) on the upper continental slope. Downslope, the canyon gradually widens but its sidewalls remain steep (~ 10°-15°) (Fig. 3h).
The Waitaki Submarine Canyon is structured into three distinct courses: upper, middle and lower. The upper course spans the outer continental shelf and includes the canyon head, steep-walled gullies, and scarps (Fig. 3i). The middle course lies over the shelf break and comprises the channel thalweg. The lower course is located on the continental slope and is characterised by its low-relief sidewalls, further changing into a meandering channel belt-thereby giving rise to a canyon-channel belt system (Fig. 3i).
Seabed morphology in seismic data. Several eroded ridges (ER 1-ER 10) of a typical gullied slope succession are observed on the eastern and western flanks of the Waitaki Submarine Canyon (Fig. 4b,c). Ridges on the eastern flank (ER 1-ER 5) are deeply eroded, resembling a "cat claw" morphology downslope. Ridges show a maximum length and width of ~ 3945 and 1242 m for ER 4 and a minimum length and width of ~ 1887 and 585 m for ER 1. Ridge ER 4 covers a maximum area of 4.8 km 2 , whereas ER 1 reveals a minimum area of 1.02 km 2 ( Table 1).
The eroded ridges on the western flank (ER 5-ER 9) resemble a lobate morphology downslope. They show a maximum length and width of ~ 5599 and 1312 m for ER 5 and a minimum length and width of ~ 911 and 492 m for ER 9. ER 6 has a maximum area of 7.33 km 2 , whereas ER 9 is much smaller and reveals a minimum area of 0.42 km 2 ( Table 1). Tectonic forces uplifted the SW flank of the Waitaki Submarine Canyon and subsequently eroded it, thereby generating accommodation space for sediment routed through the middle and lower reaches of the incised canyon ( Fig. 4a-c).
Seafloor pockmarks are observed on the NE bank and are mostly clustered over the ridges and gullies of the Waitaki Submarine Canyon. These depressions occur at a water depth of approximately 500-900 m ( Fig. 4g-i). Pockmarks are closely spaced in cross-section and present a V-shaped morphology with crests and troughs ( Fig. 4g-i). However, these structures are elliptical or circular in map-view (Fig. 4a).
On the seafloor, the depth of elliptical pockmarks varies between ~ 14.7 and 3.57 m (average of ~ 30.14 m) and diameter ranges from 72.78 to 364.08 m, for an average of ~ 161.95 m (  Fig. 5a). The morphometric plot in Fig. 5a demonstrates that there is an overlap at 20-40 m when considering pockmark depth. When they reach these depths, the diameter of both circular and elliptical pockmarks varies between 50 and 100 m. However, the deepest pockmarks are usually elongated, giving rise to the elliptical sets more frequently observed on the seafloor.  www.nature.com/scientificreports/ moderate-amplitude reflections and, locally, mounded structures ( Fig. 6b-d). Reflections within these mounds are folded. Eocene and Oligocene strata are continuous and comprise multiple tiers of polygonal faults ( Fig. 6bd). The latter faults are associated with strata showing moderate amplitude, continuous reflections. Upwards, the sequence is topped by a regional seismic marker called the Marshall Paraconformity 27 , which separates the Onekakara and the Kekenodon groups. The Kekenodon Group contains strong wavy seismic reflections towards its western part, whereas seismic reflections are continuous and horizontal towards the east. The central part of this stratigraphic unit is the locus of several pull-up reflections ( Fig. 6b-d).
Seismic reflections in the Otakou Group are moderate in amplitude ( Fig. 6b-d). The western flank is characterised by the presence of several elongated clinoforms, named Canterbury Drifts 29 , in which reflections are inclined and sub-parallel. In the study area, these clinoforms are more prominent towards the SW and NE on the dip and strike seismic profiles in Fig. 6b-d. Apart from the latter clinoforms, stacked channel belts marked by V-and U-shaped incisions are observed. www.nature.com/scientificreports/ The seafloor is dissected by the Waitaki Submarine Canyon and structured by alternating troughs and ridges. Laterally inclined packages (LIPs) 6 are observed both on the NE and SW flanks of the canyon. These packages are made of stacked sigmoidal-shaped strata forming a thick sediment wedge ( Fig. 6b-d). The canyon system is underlain by basal lags deposited in the canyon thalweg ( Fig. 6b-d). The seafloor is surrounded by sediment waves in the east and western parts of the study area.
Seismic character of near-seafloor and deeper strata. The seafloor and strata up to a depth ~ 1200 m below the seafloor are wavy and reveal a variety of seismic-reflection patterns ( Fig. 7a-n). In the SW sector of the study area, seismic reflections forming elongated clinoforms show moderate to low amplitude ( Fig. 7a-d,i,j). Strata underlying these clinoforms are wavy, accompanied by moderate-amplitude folded reflections and several V-and U-shaped channels. In the centre of the study area, the seafloor is incised by the larger Waitaki Submarine Canyon and is clear, on selected seismic profiles, that the erosional surface below the canyon contains a basal lag in which reflections are sub-horizontal ( Fig. 7a,b,e,f,k,l). This same basal lag is characterised by presenting high-to moderate-amplitude seismic reflections.  www.nature.com/scientificreports/ High-amplitude reflections in the basal-lag deposits point out to the presence of coarse-grained sands and gravels 30 with alternating moderate-to low-amplitude reflections, suggesting the accumulation of muddy sediment. Strata at a depth between 600 and 1500 m below the seafloor consist of a network of turbidite systems indicating different depositional environments. These elements include thalwegs that transition into distinct sediment lobes to the NE (Fig. 8a,e-f). The root-mean-square attribute map in Fig. 8a shows turbidite elements with moderate-to high-amplitudes, a character indicating the presence of sand-prone sediments transported basinwards through the canyon (Fig. 8a,b-d). Sediment lobes interfinger with several smaller channels (Fig. 8a,e,f,g-i). Such an interpretation suggests these sediment-lobe complexes form a series of interfingering sediment bodies that are chiefly composed of sand (Fig. 8a).
Strata at a depth of ~ 3000-3500 m below the seafloor, within the Cretaceous and Paleocene intervals, reveal a series of mounded structures (Fig. 6a-d). Two distinct circular anomalies resembling craters (CA 1 and CA 2; Fig. 9a-t) are observed above these elevated mounds. These anomalies occur in Eocene strata at a depth between 2200 and 2650 m below the seafloor. Crater CA 1 is characterised by an elliptical geometry at depths between  Table 2. Morphometric parameters of the studied pockmarks. www.nature.com/scientificreports/ 2650 and 2400 m. The outer boundary of CA 1 possess an elongated lobate structure, whereas its inner boundary resembles an elliptical shape (Fig. 9a-d). This elliptical structure contains several circular mounds associated with radial faults (Fig. 9a-d). Towards the SW, crater CA 1 is surrounded by networks of polygonal faults (Fig. 9c,d).
At a depth of 2500-2550 m below the seafloor these same polygonal fault networks surround the eastern and western regions of the CA 1 (Fig. 9e-h).
Crater CA 2 has a circular geometry and occurs at a depth of 2550 m below the seafloor (Fig. 9e,f). Such a circular geometry continues upwards to a depth 2200 m (Fig. 9e-t). The irregular elliptical geometry of CA 1 continues to a water depth of 2350 m, which then achieves a circular shape at a water depth of 2200-2300 m (Fig. 9g-t). Throughout these depth intervals, circular anomalies in CA 1 and 2 are surrounded by polygonal (PFs) and radial faults (RFs). The polygonal faults occur in tiers within Eocene-Oligocene strata. Craters CA 1 and CA 2 reveal an average diameter of ~ 3.619 km and ~ 4.0 km, as recorded by the box-whisker plot in Fig. 9u.

Continental margin architecture as a function of submarine canyon evolution. The Canterbury
Basin is characterised by three different stratigraphic units reflecting multiple transgressive-regressive cycles: (a) the transgressive Onekakara Group, (b) the Kekenodon Group reflecting a highstand in sea level, and (c) the regressive Otakou Group (Fig. 6a-d). The basin witnessed major changes in regional tectonics from late Oligocene to the early Miocene when of the initiation of strike-slip movements in the Alpine fault system 31 , uplift of The TWT structure map of the seafloor, obtained from both seismic and bathymetric data, reveal that the shelf edge is sharply incised by steep canyons and gullies (Figs. 3, 4). These features resemble a Type I canyon following the earlier classification scheme 5 . The geological processes that shape these types of canyon include erosion, and the effect of turbidity currents and high-volume mass flows 2,3,5 . Moreover, it is observed that canyon morphology was maintained by these multiple depositional processes-turbidity currents resulted in the deposition of lateral accretion packages on the banks of the Waitaki Submarine Canyon (Figs. 6, 8). Several studies have considered that turbidite currents lack the ability to erode the continental shelf and slope as they are mostly associated with thick, dilute, muddy and sluggish turbidity flows 3,5,32 . Erosional currents are more vigorous in nature and result in the deposition of high amplitude reflections (or HARs sensu 3,30 ), as observed in the study area below the canyon thalweg and its basal lags (Figs. 6, 8b-d). Furthermore, inter-and intra-canyon geometries are controlled by the deposition of laterally inclined packages, which has led to progradation of a thick sediment wedge (Fig. 6). Remarkable continuity and consistent amplitude responses within these zones suggest that inter-and-intra canyon strata are controlled by the pre-existing seafloor topography and may not be the sole result of current activity. towards the SE coast of South Island is characterized by a narrow and shallow continental shelf (Fig. 1b,d), beneath of which lies the thin continental crust of the Campbell Plateau 20 . The Waitaki Submarine Canyon acted as a transfer zone for transporting sediments from the shelf to the Bounty Trough 19 . At its lower reach (i.e., towards base of the slope) the canyon pathways connect to the North Bounty channel (Fig. 1b), ultimately merging with the south and central channel to form the Bounty Channel at a distance approximately 200 km seawards from the shelf edge. Our structurally-conditioned 3D seismic data show that continuous transport of sediment through shelfincised submarine canyons resulted in the deposition of large volumes of turbidites further downslope in the form of channel overbanks, meandering channel belts, channel-fill deposits and sediment lobes in the NE part of the study area (Fig. 8). The SW region preserves the sinuous channel of the Waitaki Submarine Canyon and overbank deposits (Fig. 8). These basin fill deposits form the key elements of turbidite systems associated with The erosional surface below the thalweg of the Waitaki Submarine Canyon preserves high-amplitude reflections, which are here interpreted to reflect the presence of coarse-grained (essentially sandy) sediment. Furthermore, lateral accretionary packages are observed on the sidewalls of the canyon (Fig. 8). This suggests the concavity of the Waitaki Submarine Canyon to be controlled by two sets of turbidity currents namely (a) weakly erosive currents and (b) highly vigorous erosive currents that are mostly associated with high-amplitude reflections. Sediments downslope are mostly sandy, reflecting with high shear rates at their base, and deposited as a result of high density turbidity currents, when compared to their upslope counterparts. Thus, high-low density turbidity currents associated with variations in shear stress (sensu 37 ) led to the erosion of mud-rich cohesive sediments, thereby transporting sandy sediments downslope. These sand-dominated deposits were further preserved within the lobe complexes and sinuous channel belts in the NE and SW parts of the study area. This is clearly shown by the high-amplitude contrasts within the turbidite elements of these two latter areas (Fig. 8a,e,f).
Channel-fill deposits and lobes: are they capable of focusing fluid in deep-offshore basins? Deposits within the sediment lobes are high permeable zones that host significant amount of fluids migrating from deeper strata 23 . Tectonic movements during the Late Miocene to Recent, followed by incision of the Waitaki Submarine Canyon, generated the necessary conditions to breach the seal intervals covering these reservoirs, thereby allowing the fluids to migrate through overlying sediments and feed the mapped seafloor pockmarks (Fig. 10a,b).
Early research has demonstrated that pockmarks indicate past or ongoing fluid expulsion processes in which the dissociated fluid is predominantly related to hydrocarbon migration 38 . In this regard, elongated or elliptical pockmarks over seafloor are more active in streaming fluids (gas and liquids) through sediments, and the evolution of such depressions is commonly related to escape of hydrocarbon fluids from underlying fluid sources 9,38 .
Previous research has also shown that seafloor depressions in the Otago shelf and the surrounding zones are the result of modifications by submarine currents of the Southland Front, which significantly altered the size and alignment of these structures 21 . These results were more recently rebuked by proof that recent and past fluid flow in the Canterbury Basin originates from Cretaceous strata 39 . In this work, it is observed that the mapped pockmarks are clustered at a water depth of 500-900 m, with depressions varying in depth from 12 to 55 m (Fig. 4a-c). These pockmarks distinctly show two different morphologies, i.e., circular and elliptical or elongated, in which the most abundant are the elongated depressions occurring over the northern banks of the Waitaki Submarine Canyon (Fig. 8). We infer that fluid seepage at the seafloor, including active structures feeding hydrocarbon-rich fluids, formed the elliptical or elongated pockmarks mapped in this work (Fig. 4a-c).
To understand the story of fluid migration in the study area, an attempt has been made to employ machine tools to our dataset. The machine learning technique uses an artificial neural network to design a hybrid attribute called as the Fluid Cube meta-attribute that captures subsurface fluid flow events from the 3D seismic data (Fig. 10b). This has been successfully applied in other prospects by 40,41 . The meta-attribute distinctly confirms the presence of fluids sourced from the Cretaceous sediments and migrating through the Eocene and Oligocene strata. It also reveals fluid seepage above the Marshall Paraconformity; migrated fluids are trapped within the channel lobes and fans, which acts as shallow reservoirs. In addition, the fluids use the eroded gullies of the canyon as pathways to migrate onto the seafloor. Our 3D Fluid Cube efficiently strengthens these interpretations, www.nature.com/scientificreports/ stressing the importance of fluid migration through Paleogene and Neogene sediments in the Canterbury Basin (Fig. 10c). It also demarcates the presence of shallow hydrocarbon and potential geothermal reservoirs in the NE part of the study area.

Conclusions
A high-resolution 3D depth-converted seismic volume allowed us to investigate the structural morphology of a submarine canyon, the Waitaki Submarine Canyon, and the role of this canyon system in focusing fluid flow along the Otago shelf, SE New Zealand. The main conclusions of this study are as follows: 1. The Waitaki Submarine Canyon is a Type I canyon, incised at the shelf-break and reveals a V-shaped crosssection near the continental shelf. It changes into a U-shaped cross-section on the continental slope. The canyon is located in water depths ranging from ~ 400to 1200 m and shows a common NW-SE orientation. 2. The head of the canyon is sharp, concave, and incises both the upper continental shelf and the shelf break. It dips at ~ 10°-20° on the upper continental slope, gradually widening downslope. The gullied slope succession of the canyon is associated with several eroded ridges. 3. The morphology and development of the canyon is significantly influenced by sediment supplied from hinterland sources, the Southland Current and regional tectonic activity. 4. The presence of channel-fill deposits and lobes near the seafloor hints at the occurrence of shallow hydrocarbon reservoirs in the study area. 5. Focused fluid flow is observed throughout the study area, whereby fluid migrates from deep Cretaceous sediments through mounded structures observed in Palaeocene-Oligocene strata. It is funnelled in the shallow channel-fill deposits and lobes, being lost (seeped out) through the Waitaki Submarine Canyon. 6. The new reprocessed Fluid Cube meta-attribute captures this geological scenario with great accuracy and resolution from the depth-migrated seismic volume.
This study reveals the presence of shallow hydrocarbon reservoirs underneath the Waitaki Submarine Canyon that may be potential exploration targets along the continental margin of New Zealand. Moreover, it is an important case study documenting the geological processes associated with shelf-slope depositional systems and associated geohazards.

Data and methods
The data used in this study include a depth migrated 3D seismic volume comprising 810 inlines and 2967 crosslines, and latest gridded bathymetric data 42 (Figs. 1, 3). The seismic volume was acquired by the R/V Polarcus Alima 43 in December 2013 and covers an area of 650 km 2 . Water depth in the surveyed region ranges from 100 to 1600 m. The primary goal of the seismic survey was to provide accurate images of submarine canyons and underlying structures, identify shallow submarine channels and resolve velocity variations due to local geology such as shallow gas seeps, limestone intervals, and deeper volcanic sills 44 . The recognition of the Waitaki Submarine Canyon is based on the criteria proposed by 2 in which submarine canyons are 'defined as steep walled, sinuous valleys with V-shaped cross-sections, axes slopping outwards' .
The interpreted seismic data were processed to a bin size of 25.0 m by 12.5 m, a record length of 8.2 s, and to a 2 ms sampling rate 43 . Data processing also included noise attenuation, multiple elimination, broadband processing, regularisation, velocity modelling, pre-stack depth migration, gather flattening, demultiple followed by stacking and post-stack processing. The length of the depth migrated seismic cube is 8 km.
This work uses a newly prepared depth-migrated seismic cube of the Endurance seismic survey procured for academic research by the New Zealand Petroleum and Minerals (NZP&M). This depth-migrated seismic volume was considered the best dataset for this study as one can directly and accurately compute morphometric parameters (thickness, length, width, area etc.) rather than having to use velocity data for time-depth conversion. The volume is displayed using SEG's American polarity convention, whereby an increase in acoustic impedance is represented by a positive-amplitude black reflection.
The bathymetric data used in this study comprise the most recent bathymetric grid developed by the Nippon Foundation-GEBCO. The grid is a continuous, global terrain model for ocean and land with a spatial resolution of 15 arc seconds 45 . The gridded data set is an amalgamation of land topography with measured and estimated seafloor bathymetry 42 . The bathymetry data were initially examined to map the geometry of the Waitaki Submarine Canyon (Fig. 3a-i). The depth-migrated seismic cube was then used for a detailed interpretation of the seafloor, associated seafloor depressions and underlying structures.
Prior to seismic interpretation, the depth-migrated seismic cube was structurally conditioned using a structure-oriented filter (SOF), named herein as dip-steered median filter (DSMF) so as to improve the resolution of geologic structures. This filter has been successfully applied to different offshore prospects 42,43,46,47 . The DSMF applies median statistics over seismic amplitudes following the stored seismic reflection dips and azimuth at every sample location from a pre-processed steering cube, which is prepared through a dip-steering process based on the phase-based dip algorithm 48 . In this work, the filtering of the seismic cube was performed using a 3 × 3 median filtering step-out. The key objective behind this filtering technique is to differentiate between the dip-azimuth of the seismic reflectors and overlying noise, therefore removing random noise from the data while preserving the amplitudes and enhancing the lateral continuity of the seismic events. Seismic interpretation involved mapping of the seafloor top from seismic data and morphometric analysis of the features observed over the seafloor. Furthermore, a machine learning approach was used to visualize fluid migration through the seafloor. This approach has successfully been previously applied by authors 42,43 in the Taranaki and Canterbury Basins, offshore New Zealand.
Seventy-five (75) seafloor depressions, herein referred to as pockmarks, were identified in this work. Their morphometric properties such as depth, diameter and flank gradients were interpreted from detailed seafloor maps and seismic profiles. The parameters above were used to ascertain the morphometry of the mapped www.nature.com/scientificreports/ pockmarks. Seismic attribute slices at different depths below the seafloor were used to interpret sub-seafloor structures.

Data availability
The data, used in applying this approach, was procured from the New Zealand