Stratigraphic architecture of Solander Basin records Southern Ocean currents and subduction initiation beneath southwest New Zealand

Abstract

Solander Basin is characterized by subduction initiation at the Pacific‐Australia plate boundary, where high biological productivity is found at the northern edge of the Antarctic Circumpolar Current. Sedimentary architecture results from tectonic influences on accommodation space, sediment supply and ocean currents (via physiography); and climate influence on ocean currents and biological productivity. We present the first seismic‐stratigraphic analysis of Solander Basin based on high‐fold seismic‐reflection data (voyage MGL1803, SISIE). Solander Trough physiography formed by Eocene rifting, but basinal strata are mostly younger than ca. 17 Ma, when we infer Puysegur Ridge formed and sheltered Solander Basin from bottom currents, and mountain growth onshore increased sediment supply. Initial inversion on the Tauru Fault started at ca. 15 Ma, but reverse faulting from 12 to ca. 8 Ma on both the Tauru and Parara Faults was likely associated with reorganization and formation of the subduction thrust. The new seabed topography forced sediment pathways to become channelized at low points or antecedent gorges. Since 5 Ma, southern Puysegur Ridge and Fiordland mountains spread out towards the east and Solander Anticline grew in response to ongoing subduction and growth of a slab. Solander Basin had high sedimentation rates because (1) it is sheltered from bottom currents by Puysegur Ridge; and (2) it has a mountainous land area that supplies sediment to its northern end. Sedimentary architecture is asymmetric due to the Subtropical Front, which moves pelagic and hemi‐pelagic sediment, including dilute parts of gravity flows, eastward and accretes contourites to the shelf south of Stewart Island. Levees, scours, drifts and ridges of folded sediment characterize western Solander Basin, whereas hemi‐pelagic drape and secondary gravity flows are found east of the meandering axial Solander Channel. The high‐resolution record of climate and tectonics that Solander Basin contains may yield excellent sites for future scientific ocean drilling.

Strike-slip Enables Subduction Initiation beneath a Failed Rift: New Seismic Constraints from Puysegur Margin, New Zealand

“…This deepest package is thinnest at the axial plane and thickens both into the fore and backlimbs, indicating it was deposited syn-kinematically with extension at the TFZ. Thus, we re-interpret the upper boundary of unit SLN1-1 to represent the top of the syn-extensional stratigraphic package at the TFZ (CMP ~10000 on SISIE-6b to CMP ~3750 on SISIE-6c), consistent with observations at the Parara-1 borehole (Patel et al, 2020).…”

“…Our seismic image for profile SISIE-6bc (Figure 8) is a composite of two separate PSDM lines, originally called MCS17B and MCS17C. The SISIE-6bc profile crosses obliquely over Tauru High, an uplifted structure caused by intense reverse faulting and folding (Melhuish et al, 1999;Sutherland & Melhuish, 2000;Patel et al, 2020), which we refer to as the Tauru Fault Zone (TFZ). The TFZ consists of four deep-seated crustal faults which can be traced to the Moho (Figure 8b).…”

“…The multifaceted tectonic and sedimentary history of the basin has resulted in a complicated stratigraphic architecture. A seismic well tie is relatively straightforward at the Parara-1 borehole, resulting in a 1D age-depth model derived from biostratigraphic analyses of recovered rocks (Hunt International Petroleum Company, 1976) that can be tied to older industry seismic lines (e.g., Sutherland et al, 2006) and to the SISIE dataset (Patel et al, 2020). Extending this stratigraphic framework throughout the entire Solander Basin is challenged due to sparse seismic coverage, and unfortunately crucial line crossings are above basement highs (SISIE-6b/SISIE-2, SISIE-2/SISIE-3, see Figure 6) where most of the deeper stratigraphic record has either been eroded or not deposited.…”

A Bayesian 3-D linear gravity inversion for complex density distributions: application to the Puysegur subduction system

“…However, an analysis of the possible perturbations to the velocity and density estimates of the Brocher (2005) relationship under a hot geotherm calculated using the MinVel toolbox, using the half-space cooling model with a plate age of 25 Ma for rocks in oceanic regimes and a typical continental geotherm with a conservatively high surface heat flux of 120 mW m -2 for continental regimes, demonstrate that elevated temperature has a negligible impact on the Nafe-Drake predictions relative to the range of densities in our model domain (Figs 11b and c). The rock compositions used in this analysis include basalt (Hacker et al 2003), harzburgitic mantle (Hacker et al 2003), Fiordland orthogneiss (Bradshaw 1990) and a combination of pelagic clays and biogenic ooze (Li & Schoonmaker 2003;Patel et al 2020). The absolute densities estimated for each of these rock types differ insubstantially between low (surface) and warm (25 km depth) temperatures, and the velocity and density both change in accord with one another with that change in temperature, such that the predictive relationship between them remains the same (Fig.…”

“…(c) Comparison of Brocher (2005) density predictions (filled symbols) to MinVel density predictions (open symbols) for low (surface) temperature conditions (blue symbols) and hotter (25 km depth) temperature conditions (red symbols) for characteristic rock types present in the model domain. Carbonate and pelagic sediment compositions are estimated from values in Li & Schoonmaker (2003) and Patel et al (2020). Composition of Fiordland Orthogneiss, taken to represent regional continental crustal rock, is from Bradshaw (1990).…”