Cretaceous carbonaceous rocks from the Norfolk Ridge system, Southwest Pacific: Implications for regional petroleum potential

Abstract

Late Cretaceous carbonaceous rocks have been dredged from two sites on the Norfolk Ridge system northwest of New Zealand. On the West Norfolk Ridge, Raukumara Series (late Cenomanian to late Coniacian, 95-86.5 Ma) coal measure sandstones and mudstones contain dispersed, immature (R O 0.37%), terrestrial (type III) organic matter and have poor petroleum generative potential (TOC 2.2-2.8%, S2 1.2-1.6 mg HC/g rock). However, the in situ coal measure sequence may contain abundant coal seams with excellent generative potential, and thus constitutes a potential source rock formation for the adjacent New Caledonia and Reinga Basins that have thick sections of sediments. The coal measures probably formed in a coastal plain environment subjected to episodic marine incursions. At the second dredge site, near the junction of the Norfolk and Reinga Ridges, a late Piripauan to early Haumurian (Santonian-Campanian, 85-75 Ma) marine shale contains sparse, mixed marine and terrestrial (type II/III) organic matter. Hopane and sterane parameters imply a maturity equivalent to at least 0.6% R o , but the analysed shale has poor generative potential (TOC 0.9%, S2 1.4 mg HC/g rock).Biomarkers suggest that the terrestrial contribution to bitumen in the shale is minor compared with the marine, but kinetic parameters are more consistent with a type III G97050

New Zealand’s deepwater frontier

“…Samples of coaly sediments from the nearby West Norfolk Ridge (Herzer et al, 1999) are Late Cretaceous in age (Cenomanian to Santonian e 95 to 75 Ma), broadly equivalent to the Taniwha and Rakopi formations of Taranaki. Modelling (Herzer et al, 1999;Stagpoole et al, 2000 suggests that coaly source rocks could have started expelling oil around 20 Ma. Assuming a similar productivity and trapping efficiency as for the Northland Basin, the Reinga Basin may have trapped up to 10 billion barrels of oil.…”

“…Although no wells have been drilled, useful samples have been dredged from fifteen sites in and around the basin. These provide some age control for seismic interpretation (Herzer et al, 1997(Herzer et al, , 1999. Gravity and magnetics data were acquired along many of the seismic lines and gravity modelling (Herzer et al, 1997) suggests crustal thicknesses of around 20 km below the Reinga Basin and sedimentary fill of at least 5 km.…”

Rifting and subduction initiation history of the New Caledonia Trough, southwest Pacific, constrained by process-oriented gravity models

“…In addition to the observations described above, evidence for considerable post‐Cretaceous vertical movement is a further indication of significant Cenozoic tectonic activity. The interpreted existence of Late Cretaceous coal facies and shallow‐marine Cretaceous to Palaeocene shelf sediments (Herzer et al 1999; Collot et al 2009) at depths of ∼4000 m below seafloor in the southern parts of the New Caledonia Trough suggest its axis has experienced ∼2500 m of permanent tectonic subsidence (subsidence after correction for sediment infill) since the Palaeocene (Sutherland et al 2010). This permanent tectonic subsidence is what formed the trough, but unconformities interpreted as uplifted marine erosion surfaces on both flanks of the New Caledonia Trough indicate broader Eocene to Miocene transient uplift and then subsidence of ∼1200–1800 m. This motion may be a consequence of backarc mantle upwelling behind the detaching slab and later thermal relaxation following slab rollback (Sutherland et al 2010).…”

Zonate lycophyte spores from New Zealand Cretaceous to Paleogene strata

“…3A -C) occurs in late Albian to early Late Cretaceous (miospore zones LB3 to PM1a) terrestrial and marine strata from the West Coast Region (Norris 1968, Norris & Waterhouse 1970, Waterhouse & Norris 1972, Beck & Nathan 1978, Raine 1984, Fiordland, East Coast Region, and Chatham Islands. The species also occurs in carbonaceous mudstone of zone PM1a age, from a dredge haul on the West Norfolk Ridge (Herzer et al 1999). The oldest faunally dated occurrence is from the late Urutawan Stage at Koranga, Raukumara Peninsula, but, while the species is not known from the Mata Series, its upper range limit is not so precisely known.…”