Dampier Ridge Research Articles

Distribution, development, transformation characteristics, and hydrate prospect prediction of the rift basins of northwest Zealandia in the Southwest Pacific

As the last area with unknown oil exploration potential, Zealandia has attracted the attention of petroleum scientists. Under the constraint of the known rift distribution, the gravity and magnetic anomaly data are utilized to predict the distribution of rift basins, and the balanced cross-section technique and basin simulation technique are utilized to analyze the development of the rift basins and hydrocarbon generation history of source rocks for the hydrate prospect prediction of the rift basins of northwest Zealandia. The time of rifting in Zealandia varies greatly from place to place, and it has experienced extensive rifts, migrated to the east of the Lord Howe Ridge, migrated to the west of the Lord Howe Ridge, migrated to the west of the Dampier Ridge, and finally migrated to both sides of the Lord Howe Ridge and then experienced multiple stages of compression transformation and deep burial transformation. The Upper Cretaceous coal source rock in the rift Ⅱ stage has entered the wet gas generation stage in the deep part of the rift or deeper rift on the eastern side of the Lord Howe Ridge, and the coal-generated wet gas may migrate along the fault and form a gas hydrate in the shallow seabed stable zone.

Crustal Structure Across the Lord Howe Rise, Northern Zealandia, and Rifting of the Eastern Gondwana Margin

AbstractDuring the Late Cretaceous, the fragmentation of eastern Gondwana led to the formation of the narrow eastern Australian margin and the wide Lord Howe Rise during the opening of the oceanic Tasman Basin. To provide crustal‐scale constraints on this margin, a 680‐km‐long, east‐west oriented refraction transect with 100 ocean bottom seismometers was acquired from the Tasman Basin to the Lord Howe Rise. After traveltime tomographic inversion of the first refracted arrivals and reflected arrivals from the Moho, the final P wave velocity model reveals strong variations in crustal thickness. The Tasman Basin is floored by a two‐layered and 7‐km‐thick oceanic crust. To the east, the Middleton Basin separates the Dampier Ridge, with 16‐km‐thick continental crust, from the Lord Howe Rise, where the extended continental crust is 20–23 km thick. Below the Middleton Basin, Moho reflections are recorded at the base of 7‐km‐thick crust. The velocity gradient of this two‐layer crust suggests an oceanic origin for the Middleton Basin. Our results show no clear evidence for mantle exhumation or a sizable igneous intrusion within three separate and relatively narrow (<70 km) necking zones. The northwestern Zealandia margin thus appears to be magma poor and, despite the considerable width of this margin (>1,000 km), the lack of evidence for mantle exhumation, the evidence for oceanic crust under the Middleton Basin, and the narrow necking zones combine to suggest that northern Zealandia is not a hyperextended margin.

Provenance comparisons of Permian to Jurassic tectonostratigraphic terranes in New Zealand: perspectives from detrital zircon age patterns

U–Pb detrital zircon ages (LAM-ICPMS) are reported for 20 greywackes and sandstones from seven major tectono-stratigraphic terranes of the Eastern Province of New Zealand (Cretaceous to Carboniferous) to constrain sediment provenances. Samples are mainly from three time horizons: Late Permian, Late Triassic and Late Jurassic. Age datasets are analysed as percentages in geological intervals, and in histogram and cumulative probability diagrams. The latter discriminate significant zircon age components in terms of terrane, sample stratigraphic age, component age, precision and percentage (of total set). Zircon age distributions from all samples have persistent, large Triassic–Permian, and very few Devonian–Silurian, populations, features which exclude a sediment provenance from the early Palaeozoic, Lachlan Fold Belt of southeast Australia or continuations in New Zealand and Antarctica. In the accretionary terranes, significant Palaeozoic (and Precambrian) zircon age populations are present in Torlesse and Waipapa terranes, and variably in Caples terrane. In the fore-arc and back-arc terranes, a unimodal character persists in Murihiku and Brook Street terranes, while Dun Mountain–Maitai terrane is more variable, and with Caples terrane, displays a hybrid character. Required extensive Triassic–Permian zircon sources can only be found within the New England Fold Belt and Hodgkinson Province of northeast Australia, and southward continuations to Dampier Ridge, Lord Howe Rise and West Norfolk Ridge (Tasman Sea). Small but significant Palaeozoic (and Precambrian) age components in the accretionary terranes (plus Dun Mountain–Maitai terrane), have sources in hinterlands of the New England Fold Belt, in particular to mid-Palaeozoic granite complexes in NE Queensland, and Carboniferous granite complexes in NE New South Wales. Major and minor components place sources (1) for the older Torlesse (Rakaia) terrane, in NE Queensland, and (2) for Waipapa terrane, in NE New South Wales, with Dun Mountain–Maitai and Caples terrane sources more inshore and offshore, respectively. In Early Jurassic–Late Cretaceous, Torlesse (Pahau) and Waipapa terranes, there is less continental influence, and more isolated, offshore volcanic arc sources are suggested. There is local input of plutonic rock detritus into Pahau depocentres from the Median Batholith in New Zealand, or its northward continuation on Lord Howe Rise. Excepting Murihiku and Brook Street terranes, all others are suspect terranes, with depocentres close to the contemporary Gondwanaland margin in NE Australia, and subsequent margin-parallel, tectonic transport to their present New Zealand position. This is highlighted by a slight southeastward migration of terrane depocentres with time. Murihiku and Brook Street terrane sources are more remote from continental influences and represent isolated offshore volcanic depocentres, perhaps in their present New Zealand position.

PROSPECTIVITY OF THE OFFSHORE SYDNEY BASIN: A NEW PERSPECTIVE

Approximately 40 per cent of the 52,000 km2 Sydney Basin lies in shallow waters (less than 200 m) off the central New South Wales coast. Containing more than 5,000 m of Permo-Triassic marine and non-marine sediments, and having been the subject of several previous exploration campaigns, no wells have been drilled in the offshore despite widespread numerous occurrences of oil and gas onshore.The Sydney Basin, together with the Bowen and Gunnedah basins, form a major longitudinal Permo-Triassic basinal complex stretching 2,500 km down the eastern margin of Australia. Whereas the onset of this basinal development may have been extensional, reinterpretation of seismic and other geophysical data highlight the potential role played in the early development of the Sydney Basin by easterly directed compression. A compressional style is to be contrasted with the dominantly extensional style interpreted by others for the adjacent onshore areas. The most conspicuous structural element in the offshore, the Offshore Uplift, is interpreted to represent the western overthrust edge of the Currarong Orogen. Accepting the Panthalassan margin geometry of Veevers and Powell (1994) it follows that the Offshore Uplift and restored Dampier Ridge would have constituted a 'greater Currarong Orogen'. A series of progressive westerly directed thrust fronts may have been established across the Panthalassan margin, including the uplifted western margin of the Currarong Orogen, which over-rode and created a thrust load onto the eastern margin of the Lachlan Fold Belt. Much of the Early Permian development of the Sydney Basin therefore could have resulted as a consequence of foreland loading. This is consistent with depositional trends including the overall westerly directed marine transgression which dominated the sedimentary record of the Early Permian. Alternatively, this marine transgression may represent the sag phase induced along a segment of the Bowen-Sydney rift system that had been offset by the Hunter River Transverse Zone from the Gunnedah Basin to a site coincident with the Offshore Syncline.Previous interpretations identified structural development of the Currarong Orogen as either a Cretaceous (Tasman Sea rift related) or Middle to Late Permian phenomena. Early Permian structural growth of the offshore Uplift has important implications for petroleum exploration. The major impediment to exploration appears to be the perception that the Sydney Basin lacks suitable reservoir targets and is gas-prone. Potential source and seal sequences occur extensively within both Early Permian marine shales and siltstones and Early and Late Permian coal measure sequences. The emerging uplift provided a major sediment provenance area and represented a barrier behind which restricted anoxic conditions flourished, conditions favouring the preservation of organic matter. Late Permian and Triassic sequences are absent across the crestal portions of the uplift. However, the emerging, sea-ward facing flank of the uplift would have been subject to marginal and shallow marine, wave-base, barrier and strand bar deposition during the Lower Permian, conditions known in the onshore to favour better reservoir development.Gas demand to the greater Sydney region is anticipated to exceed supply by the year 2000, and new gas markets are being eagerly sought in time for the expiration, in 2006, of the current contract under which gas is supplied to Sydney via the Moomba pipeline.Cretaceous, Tasman Sea rift related, structuring is subordinate to that of the earlier compressional and wrench related structuring. Several new structural targets have been added to the existing inventory of prospects and leads, including some now considered optiminally located with respect to source rock and reservoir development.

Discussion and reply: Dampier Ridge, Tasman Sea, as a stranded continental fragment

Discussion and reply: Dampier Ridge, Tasman Sea, as a stranded continental fragment

Dampier Ridge, Tasman Sea, as a stranded continental fragment∗

Dredging of the Dampier Ridge recovered small fragments of granite, gabbro and sandstone. Dating of the igneous samples by the U‐Pb, K‐Ar and Rb‐Sr methods yielded precise ages mainly in the range 250 to 270 Ma, mid‐Permian. An imprecise Sm‐Nd mineral age of ∼ 310 Ma might reflect slightly earlier emplacement of the gabbro. A granitic fragment has a composition approximating that of a minimum melt. Taken together with the Late Palaeozoic emplacement ages and other geochemical and geophysical data, the evidence strongly supports the conclusion that the Dampier Ridge is a continental fragment, formerly part of eastern Australia, with its present location a consequence of continental rifting and opening of the Tasman Basin by sea‐floor spreading.

Marine magnetic anomalies over the Lord Howe Rise and the Tasman Sea: Implications for the magnetization of the lower continental crust

Marine geophysical and geological data provide evidence for a continental origin of the Lord Howe Rise, a submarine plateau east of Australia. Our marine geomagnetic data reveal a long-wavelength anomaly associated with the western margin of the rise. Forward and inverse modeling shows that the anomalies can be best explained by strong magnetization of the lower crust of the Lord Howe Rise. A geomagnetic map of the northern Tasman Sea that includes Dampier Ridge, another elongated piece of presumably continental crust, shows positive anomalies over areas of continental origin and negative ones over the deep sea basin. This indicates higher values of the product of magnetization times thickness for the continental crust than for the oceanic crust. Three-dimensional model calculations show that the high magnetization in the lower crust of eastern Australia is limited to a maximum depth of 15–20 km. This is in accordance with geothermal results that indicate the Curie isotherm is at a shallow depth there. The anomalies of the Tasman Sea are negative due to the negative part of the edge anomaly on the seaward side of the continental margin. It is not necessary to hypothesize strong reversed magnetization in the lower oceanic crust and upper mantle.

Design and operation of a deep seismic survey in the Tasman Sea Basin

Deep crustal reflections, appearing at two-way times of 6–20 s, are characterised by a low signal-to-noise ratio and a low-frequency content (~ 5–30 Hz). Optimising the visibility of these reflections requires that: 1.(1) the source energy be concentrated in this band;2.(2) the receiver be as long as practically possible;3.(3) the shot spacing be as snail as possible.An airgun array simulation program was used to investigate the effect of operating a 10-gun array at different depths. It predicted that the source energy could be enhanced at low frequencies by running the gun array at depths of up to 25 m, which would improve the signal-to-noise ratio for deep reflectors by a factor of 2 relative to the same array at 7.5 m depth at the expense of some loss of temporal resolution.The receiver length was limited to 4.4 km by the number of cable sections available and the maximum tension allowable in the cable. It was configured as 88 channels of 50 m length. To reduce the shot spacing, minimise the tow noise and reduce tension in the cable, the ship speed was reduced to 4 knots. A cable depth of 20 m was chosen to reduce sea state noise and keep the receiver ghost notch frequency outside the frequency band of interest.A variety of operational problems was encountered. Fish bites holed 50% of the total cable inventory and cable sections were damaged when they sank below their maximum rated depth after being holed. Shot-generated noise was the limiting factor in deep water. Despite these problems, useful data were obtained over the Lord Howe Rise, Dampier Ridge, Gippsland Basin margin and the deep abyssal plain and the survey demonstrated the use of an airgun array tuned for maximum energy.

Evolution of the Tasman Sea reappraised

We reexamined available marine magnetics data from the Tasman Sea and reidentified sea-floor spreading anomalies in the southern portion of the basin. From the revised magnetic lineations and fracture zones we calculated new finite rotations which descrobe the evolution of the basin in terms of a simple two-plate spreading system active between about 82 and 60 m.y. ago. Allowing for the probable continental origin of the Dampier ridge, the predicted displacement of the western margin of the Lord Howe rise relative to the eastern Australian margin in the northern Tasman basin is consistent with their observed separation. Thus, the controversial episode of subduction of Tasman basin crust at the east Australian margin proposed in earlier studies is no longer necessary.

Crustal structure across the Tasman Sea

Abstract A crustal section across the Tasman Sea between latitudes 31° S and 35° S has been obtained by interpreting continuous gravity measurements with the aid of previous seismic measurements. A quasi-continental type of crust exists under the Dampier Ridge (crustal thickness 20 km), Lord Howe Rise (26 km), West Norfolk Ridge (21 km), and Norfolk Ridge (21 km). The crust beneath the New Caledonia Basin is of oceanic type (9 km). Short wavelength gravity and magnetic anomalies over Lord Howe Rise, West Norfolk Ridge, and Norfolk Ridge suggest that dense, magnetic, intrusive rocks occur within or beneath a thin (< 1 km) sediment cover. The thickness of the sediments in the centre of the New Caledonia Basin is about 1 km and increases to about 2 km at the foot of the Lord Howe Rise and about 3 km at the foot of the West Norfolk Ridge.

On supposed extinct mid-ocean ridges in the Tasman sea: (Comments on a paper by W.J.M. van der Linden)

Recent data show that the crust beneath Dampier Ridge has a ‘quasi-continental’ thickness, and therefore can not be an extinct mid-ocean ridge. By analogy, Three Kings Rise is also regarded as sialic in origin.

“Two-way Stretch” of Sialic Crust and Plate Tectonics in the South-west Pacific

ANALYSES of seismic and continuous gravity measurements over the northern Tasman Sea1 have confirmed the existence of “quasi-continental” crust (20–26 km thick) beneath the parallel ridges—Norfolk Ridge, Lord Howe Rise and Dampier Ridge—that extend north-westward from New Zealand (Fig. 1). The intervening major trough, New Caledonia Basin, is shown to have a floor of true oceanic thickness (9 km).

Sediments and stratigraphy of deep-sea cores from the Tasman Basin

Abstract Twelve deep-sea cores from the northern Tasman Sea are described and grouped according to sediment characteristics and foraminiferal faunas. Six of the cores from the area between Australia and the Dampier Ridge consist dominantiy of clastics which have been derived from the Australian continental shelf and slope mainly by turbidity currents. Intervening periods when pelagic sedimentation was dominant have occurred. These cores were all taken from depths near the carbonate solution boundary and consequently calcareous foraminiferal tests in the pelagic intervals have been affected by solution. East of Dampier Ridge six cores were taken from the Lord Howe Rise, New Caledonia Basin, and Norfolk Ridge. These consist almost entirely of the calcareous remains of planktonic organisms, mainly foraminifera. Most of the cores are uppermost Pleistocene and Holocene in age, but in one core from the western slope of the Lord Howe Rise Middle to Upper Miocene sediment is unconformably overlain by uppermost Pl...

Morphology of the Tasman sea floor

Abstract As a result of the r.v. Oceanographer's 1967 and m.v. Taranui's 1968 cruises, new bathymetric information has been obtained in the Tasman Sea. The new data, together with Conolly's (1969) interpretation of Tasman Sea floor morphology, support hypotheses on Tasman Basin evolution in which the Dampier Ridge is considered an extinct mid-ocean ridge in the central Tasman Basin. Emphasis is placed on the morphology of the ridge, of the Tasmantid and Lord Howe Island chains of seamounts, and of Lord Howe Rise.

Extinct mid-ocean ridges in the Tasman sea and in the Western Pacific

Recent magnetic surveys in the Tasman Sea suggest the Dampier Ridge to be an extinct or dormant mid-ocean ridge. The concept of ancient sea-floor spreading activity provides an attractive explanation of the structural evolution of the South West Pacific. The concept may also explain the anomalous position of island arcs and trenches in the Western Pacific.