Fairway Basin and Ridge New Caledonia Basin and Norfolk Ridge

Basin Details and Geological Overview

The Fairway Basin, New Caledonia Basin and Norfolk Ridge are NW–SE to NNW–SSE-trending structural and bathymetric elements located to the east of the Lord Howe Rise (LHR). They extend for approximately 1000km through the Australian, French (New Caledonian) and New Zealand marine jurisdictions. Water depths are typically < 500–2000m over the crest of the Norfolk Ridge and 1500–3500m over the Fairway and New Caledonia basins. The Fairway and New Caledonia basins are separated by the NW–SE-trending Fairway Ridge in the north and the NNW–SSE-trending northern West Norfolk Ridge in the central and southern segments. The southern part of the Fairway Basin merges with the northwesterly extension of the offshore Taranaki Basin that has recently been named the Aotea Basin. The boundary between the Fairway and Aotea basins is marked by a ridge extending SSE from the Lord Howe Rise (the East Lord Howe Spur). Like the LHR, the basins and ridges of the area formed through rifting during the Late Cretaceous to Paleocene break-up of the former eastern Gondwana margin. During the Cenozoic, convergent tectonism along the eastern margin of the Australian Plate extensively affected the area.

The New Caledonia Basin should not be confused with the elongate bathymetric low that has recently been re-defined as the New Caledonia Trough. This regional physiographic feature, lying at 2000–3500m water depth and extending from southwest of New Caledonia to the offshore Taranaki Basin, is underlain by the deepwater portions of New Caledonia, Fairway and Aotea basins, and the northern West Norfolk Ridge. The New Caledonia Trough cuts across the structural boundaries of these basins, suggesting that the formation of the trough post-dates crustal extension that formed the basins.

The area has remained a scientific and petroleum exploration frontier. The existing data coverage consists of widely spaced regional seismic lines, gravity, magnetic, multibeam bathymetry and rock/sediment sample data. There are no petroleum exploration wells and the DSDP 206 drill hole provides the sole well constraint. A few recent marine surveys, some within the Australian territory, have contributed to improving the geological knowledge of the area. The Geoscience Australia survey GA-232 (2001) filled a gap in regional seismic data coverage in the central segment and recovered rock and core samples that provide information on the magmatic and depositional history. The French–New Caledonian ZoNéCo 11 survey (2004) acquired deep reflection and refraction seismic data to image the crustal structure of the northern segment. The Australian–French AUSFAIR–ZoNéCo 12 survey (2006) acquired core samples in the northern and cental segments to test for the occurrence of gas hydrates in the sub-bottom sediments and to measure heatflow. The survey also recovered rock samples that have constrained the timing of Late Cretaceous magmatism and marine deposition in the region.

ProvExplorer

• Fairway Basin Details and Geological Overview
• Fairway Ridge Details and Geological Overview
• New Caledonia Basin Details and Geological Overview
• Norfolk Ridge Details and Geological Overview

Structural Elements

The structural elements of the region are aligned parallel to the general trend of the LHR. An extension of the Barcoo–Elizabeth–Fairway Lineament originating in the Tasman Sea separates the Fairway and New Caledonia Basins into northern and central–southern segments. The northern segment is entirely within French (New Caledonian) jurisdiction and is characterised by a NW–SE structural trend. The central–southern segment is mostly within Australian jurisdiction and exhibits a NNW–SSE trend. In addition, an extension of the Vening–Meinesz Fracture Zone dextrally offsets the Norfolk and the West Norfolk ridges and the eastern flanks of the Lord Howe Rise, marking the southern end of the New Caledonia and Fairway basins.

The Fairway Basin is 120–200km wide, bounded to the west by the eastern flank of the LHR, and to the east by the Fairway and northern West Norfolk ridges. It occupies the transition between the structural high of the LHR and the low of the New Caledonia Basin. The seafloor above the Fairway Basin slopes gently eastward to the Fairway and northern West Norfolk ridges. The steeply sloping western boundary with the LHR is marked by sediment slumps. Refraction and deep reflection seismic, gravity and magnetic data indicate that the Fairway Basin is underlain by highly extended continental crust approximately 15km thick. The northern segment is characterised by shallower water depths (1500–2500m) and comparatively thick (4–5km) syn- and post-rift sediments containing mud diapirs. The central–southern segment generally lies at water depths of over 2500m and sediment thicknesses are 2km or less.

The New Caledonia Basin is on average 150km wide and is bounded by the Fairway and northern West Norfolk ridges to the west, and the Norfolk Ridge and the island of New Caledonia to the east. The seafloor is generally flat. The northern segment is characterised by syn- and post-rift sediments up to 8km thick that are underlain by rift fault blocks. This part of the New Caledonia Basin is believed to be underlain by highly extended continental crust 10–15km thick. The central–southern segment has thinner sediments (up to 4km), underlain by flat basement topography and crust that is less than 10km thick. The associated positive gravity anomaly and magnetic lineations indicate that this segment is underlain by oceanic or transitional crust.

The Norfolk, West Norfolk and Fairway ridges are structural highs composed of continental crust. Triassic and Jurassic continental igneous rocks and Upper Cretaceous syn-rift sedimentary and volcaniclastic rocks have previously been collected from these areas. Cenozoic intraplate volcanism has subsequently overprinted these structural elements, e.g. Norfolk Island. The boundary of the Norfolk and West Norfolk ridges with the New Caledonia and Fairway/Aotea basins is defined by a faulted scarp with active sediment slumps.

Stratigraphy

The syn- and post-rift sedimentary successions in the Fairway and New Caledonia basins overlie a highly faulted basement. Major faulting occurred during the Late Cretaceous continental rifting, which restricted initial deposition to fault-bounded depocentres. This event is part of a regional extension event which also resulted in the formation of the Middleton and Tasman Sea basin to the west. Post-rift deposition took place predominantly under thermal subsidence and was less affected by faulting. Subsidence in the central New Caledonia Basin was enhanced by the emplacement of oceanic crust during the Paleocene. Eocene–Oligocene regional tectonism, probably related to the obduction events in New Caledonia and Northland, widely affected deposition in the region through fault reversal, uplift and erosion of the Fairway, Norfolk and West Norfolk ridges, eastward tilting of the northern New Caledonia Basin, and remobilisation of Cretaceous mudstones as diapirs in the northern Fairway Basin. The entire region has been affected to varying degrees by intraplate volcanism during the Cenozoic.

The sedimentary succession may be broadly subdivided into:

The Oligocene–Recent succession is typically 400–800m thick. The Cretaceous–Eocene succession in the Fairway and New Caledonia basin is generally thicker and attains thicknesses of over 2500–3000m in some areas. The Cretaceous–Eocene succession may be thin or absent over areas of the Fairway, Norfolk and West Norfolk ridges.

Petroleum Systems and Hydrocarbon Potential

Much of the previous petroleum exploration interest in the Fairway and New Caledonia basins and the adjacent LHR related to the possibility of vast gas hydrate occurrences within the post-rift sediments. This interpretation was based on the bottom simulating reflectors (BSRs) seen on regional seismic data. These reflectors have a positive polarity and are located typically at 500–700m below the seafloor. However, a recent re-appraisal based on newly acquired data has indicated that the BSRs are most likely to be an Opal-A/Opal-CT diagenetic boundary.

The Fairway and New Caledonia basins may have potential for conventional petroleum resources. The basins are contiguous structurally (via Aotea Basin) and share a similar stratigraphy with the deepwater part of the offshore Taranaki Basin. The shallow-water part of the Taranaki Basin is a proven oil- and gas-producing basin. Although the massive Neogene sediment loading experienced in the shallow-water Taranaki Basin is absent, basin modelling indicates that the New Caledonia and Fairway basins have sufficient sediment thickness in parts for hydrocarbon generation, if source rocks are present. In the deepwater Taranaki, Reinga and Aotea basins and over the West Norfolk Ridge, seismic data indicate widespread presence of coaly rocks that correlate with the Rakopi Formation, the principal source of oil in the shallow-water Taranaki Basin. Upper Cretaceous coal is also known from onshore New Caledonia, immediately east of the northern New Caledonia Basin. Coaly potential source rocks may also occur within the pre-rift succession forming the basement to the basins and the ridges, e.g. the inferred continuation of the Mesozoic Murihiku Supergroup from New Zealand thorugh the area. Deposition within fault-bounded depocentres may also have produced organic-rich marine potential source rocks in the Cretaceous syn-rift successions of the Fairway and New Caledonia basins. Potential reservoir rocks may include Cretaceous–Paleogene fluvial and marine sandstones and Cenozoic turbidite sands. Trapping styles may include horsts, tilted fault blocks and various stratigraphic plays. Structural traps may also be associated with the Eocene–Oligocene tectonic deformation.

Key References