Aure Trough Research Articles

Siliciclastic influx and burial of the Cenozoic carbonate system in the Gulf of Papua

An extensive carbonate system in the Gulf of Papua (GoP), developed in the late Oligocene–middle Miocene, was buried by huge influx of siliciclastics originated from Papua New Guinea. Major episodes of siliciclastic influx in the carbonate system are related to tectonic activity in the fold and thrust belt during the Oligocene Peninsular Orogeny, late Miocene Central Range Orogeny, and late Pliocene renewed uplift and exhumation of peninsular region. Siliciclastics did not influence the carbonate deposition during the late Oligocene–middle Miocene, since they were accumulated in the Aure Trough, proximal foreland basin protecting the carbonate system. The most significant burial of the carbonate system started during the late Miocene–early Pliocene in the result of the Central Range Orogeny. However, the largest influx was related to the renewed uplift of the Papuan Peninsula during the early late Pliocene. The shelf edge prograded ∼150 km and formed more than 80% of the modern shelf. This high siliciclastic influx was also enhanced by the “mid” Pliocene global warmth period and intensified East Asian monsoons at 3.6–2.9 Ma. Although many publications exist on carbonate–siliciclastic mixing in different depositional environments, this study helps understand the carbonate–siliciclastic interactions in space and time, especially at basinal scale, and during different intervals of the carbonate system burial by siliciclastic sediments.

PROSPECTIVITY OF THE DEEPWATER GULF OF PAPUA AND SURROUNDS IN PAPUA NEW GUINEA (PNG)—A NEW LOOK AT A FRONTIER REGION

Despite limited well control and paucity of seismic data, a regional study of the deepwater portion of the Gulf of Papua, Papua New Guinea (PNG), indicates a number of large structures at a variety of stratigraphic levels that are capable of holding significant volumes of hydrocarbons. The main structural elements east of the Fly River Platform the Pandora Ridge, Pandora Trough, Aure Trough, Port Moresby Trough and the northern portion of the Eastern Plateau were established during the Paleozoic and further enhanced by Late Cretaceous to Early Paleocene Coral Sea rifting in the southeast. Structuring in the region is mostly basement involved and extensional, and is overprinted by a later compressional pulse. Extensional and compressional regimes produce many potential traps. To date, exploration in the Gulf of Papua has been sporadic and mainly focussed in shallow water depths. The new reprocessed seismic data indicate the following Paleozoic to Recent plays, some of which contain multiple reservoir-seal pairs, sourced by non-marine and marine source rocks:extensional Paleozoic rift fault blocks;Upper Jurassic to Lower Cretaceous turbidites (Iagifu- Hedina-Toro sandstone equivalents);Campanian to Middle Paleocene Coral Sea synrift sandstone and basin floor fan equivalents (Pale/Barune Formations and equivalents);Middle Paleocene break-up unconformity fault blocks and intra-basinal highs;Upper Paleocene to Lower Eocene Pima Sandstone equivalent associated with the Middle Paleocene uplift and erosion;Oligocene to Lower Miocene lowstand deltas and turbidites;Miocene to Recent biohermal build-ups (possibly including a new limestone high, the Box Ridge, in front of the Pandora Ridge); Karstified Darai Limestone equivalent sealed by Aure Beds claystones;Miocene to Recent lowstand deltas and turbidites;Eocene to Pliocene stratigraphic onlaps flanking main structural highs; and,compressional plays associated with the Pliocene to Recent collision of the PNG and Pacific plates.

Cenozoic tectonics of New Guinea

Major hydrocarbon discoveries have been made in eastern and westernmost New Guinea, and there is great potential for additional discoveries. Although the island is a type locality for arc-continent collision during the Cenozoic, the age, number, and plate kinematics of the events that formed the island are vigorously argued. The northern part of the island is underlain by rocks with oceanic island arc affinities, and the southern part is underlain by the Australian continental crust. Based on regional sedimentation patterns, it is argued herein that the Cenozoic tectonic history of the island involves two distinct collisional orogenic events.The first Cenozoic event, the Peninsular orogeny of Oligocene age (35–30 Ma), was restricted to easternmost New Guinea. Emergent uplifts that shed abundant detritus resulted from the subduction of the northeastern corner of the Australian continent beneath part of the Inner Melanesian arc. This collision uplifted the Papuan ophiolite and formed the associated mountainous uplift that was the primary source of siliciclastic sediments that largely filled the Aure trough. Between the Oligocene and Miocene, the paleogeography of the region was similar to present-day New Caledonia. The continental crust under central and western New Guinea remained a passive margin.The second event, the Central Range orogeny, began in the latest middle Miocene, when the bulldozing of Australian passive-margin strata first created emergent uplifts above a north-dipping subduction zone beneath the western part of the Outer Melanesian arc. The cessation of carbonate shelf sedimentation and widespread initiation of siliciclastic sedimentation on top of the Australian continental basement is dated at about 12 Ma. This collision emplaced the Irian ophiolite and created the present mountainous topography forming the spine of the island.

ABSTRACT: The tectonic implications of rapid vertical facies changes in the Yule Island Section, Aure Trough, Papua New Guniea

ABSTRACT: The tectonic implications of rapid vertical facies changes in the Yule Island Section, Aure Trough, Papua New Guniea

A review of the petroleum potential of Papua New Guinea with a focus on the eastern Papuan Basin and the Pale Sandstone as a potential reservoir fairway

Abstract Substantial oil seeps were first reported from the eastern Papuan Basin in 1911, and oil has since been produced from the sub-surface, but not in commercial quantities. A significant discovery of gas in 1986 sparked an upsurge of activity within the adjacent western Papuan Basin. From 1986 to 1992, 13 new hydrocarbon discoveries were made, which included four major oil fields, and an oil pipeline for export purposes was then opened in 1992. This activity did not spread to the eastern Papuan Basin due to a perceived lack of good reservoir and the last well drilled there was over 30 years ago. In 1986, a potentially excellent reservoir, the Pale (Pah leh) Sandstone was discovered in outcrop in the eastern Papuan Basin. Thus the Papuan Basin as a whole remains an extremely prospective basin. However, due to high infrastructure costs most activity has recently been focussed on the already proven reservoir potential of the Late Jurassic Imburu and Toro Formations in the western section. The extent of the Imburu-Toro Formation reservoir in the western section of the Papuan Basin is well documented. It was deposited as several regressive episodes within an overall transgressive, passive-margin, clastic sequence. In the eastern section, the Late Cretaceous Pale Sandstone was deposited in a barrier island or strand-plain environment. Lateral equivalents of the Pale Sandstone and the potential for a new reservoir fairway have been documented for a strike length of approximately 400 km. This fairway is coincident with the northeast edge of the western Papuan Basin and on the northern edge of the Aure and Port Moresby Troughs of the eastern Papuan Basin. All the commercial oil accumulations and seeps found in the Papuan Basin before 1992 have been attributed to the Jurassic, with peak generation occurring in the Late Cretaceous prior to the formation of existing structures. In 1992 an oil seep was discovered which is geochemically very different to all the other oils found in the Papuan Basin. This was found to the north and east of the present discoveries that occur within the western Papuan Basin. The oil seep is indicative of undiscovered Tertiary source rock, which is currently at or near peak generation. However, most of this source rock in the north may be covered by overthrusted allochthonous terrain. The Aure Trough was a Late Cretaceous to Tertiary rift basin that later developed into an Oligocene to Mid-Miocene foreland basin depocentre occurring on the northern and eastern margin of the Papuan Basin. It is proposed in this paper that mature Tertiary source rocks which occur within this foreland basin and the Pale Sandstone reservoir may form a significant petroleum system on the northeastern rim of the western Papuan Basin and within the eastern Papuan Basin.

Subsidence of the Gulf of Papua in the Cenozoic

The Gulf of Papua, between Papua New Guinea and the northeastern Australian margin, contains thick Cenozoic strata. We have examined the subsidence history using data from eight wells in the Gulf of Papua. Four are in the western Gulf region overlying Paleozoic basement and four are in the eastern Gulf near the Aure trough. Backstripping results show two subsidence episodes for the western wells. The first episode, from early Cenozoic to Oligocene, may be due to a small amount of lithospheric stretching associated with the opening of the Coral Sea. The second, from Early Miocene to the present, has a substantially higher subsidence rate which cannot be explained by a Paleocene rifting event. The Late Oligocene-Late Miocene episode of rapid subsidence in the Aure trough, to the east, appears to be a significant factor affecting the subsidence of the western Gulf of Papua during this period. To test this, we computed the expected deflection from flexure due to the load of the Aure trough strata and find a profile similar to that observed. The model used had an effective elastic thickness similar to those for rifted continental margins, thus implying a relatively weak lithosphere. In addition, the predicted position of the forebulge in the western Gulf occurs where Oligocene strata are absent, suggesting post-depositional uplift and hence facilitating the growth of Early Miocene reefs.

Papua new Guinea analogue for the late Permian environment of northeastern New South Wales, Australia

The late Cenozoic Moresby Arc System of Papua New Guinea is explored as an analogue of the late Permian Tamworth Arc System in northeastern New South Wales. Matched elements are the northeastern Sydney Basin with the Aure Trough; the Glen Innes Basin (new name) with the Cape Vogel Basin; and the median basement zone of the Tamworth Arc System with the Owen Stanley Mountain Arc of the Moresby Arc System, involving the recognition of a Permian Tamworth Mountain Arc. The Tamworth Mountain Arc, the crest of which is inferred to have lain just southwest of the trace of the Peel Fault, shed voluminous dominantly epiclastic detritus southwest into the Sydney Basin and lesser amounts to the northeast where the remnants of the Glen Innes Basin suggest a fill dominated by pyroclastic ashflow tuffs in and around cauldron complexes close to sea-level. The two arc systems share a gross pattern of development involving inception of a major arcuate fault with accompanying tectonic emplacement of ultramafics and outflow of basalt in the fore-arc trough, followed by progressive uplift of a mountain arc feeding concomitantly subsiding flanking basins, with concurrent volcanism most active in the back-arc basin.

REGIONAL GEOLOGY AND HYDROCARBON POTENTIAL OF THE MESOZOIC OF THE WESTERN PAPUAN BASIN, PAPUA NEW GUINEA

Jurassic and Cretaceous clastics of the Western Papuan Basin provide reservoir and source potential for hydrocarbon accumulation. Early Jurassic coarse clastics from sources in the south and west cover a wide stable platform area, while finer grained equivalents were deposited in a deepening trough along the east and northeast margins. A Middle Jurassic transgression deposited a thick shale unit over most of the basin, followed by a return to sand and silt deposition in the Late Jurassic-Early Cretaceous. Eocene/Miocene structuring in the north formed the Omati Trough which filled with deep water Miocene carbonates. This was followed by shallow water carbonates which cover the Western Papuan Basin. Mountain ranges to the north and northeast were the source for thousands of feet of poorly sorted Plio- Pleistocene sediments which were dumped in the rapidly subsiding Aure Trough and spread as a veneer over the remainder of the Papuan Basin.Geochemical studies indicate that adequate source rocks exist within the Mesozoic shales and these reach maturity at a depth of about 2700m. The Mesozoic shales correlate more closely with the various oil and condensate seeps than do the Miocene carbonates which are generally too immature over much of the basin to be considered as a significant oil source.The stable platform, except for the Omati Trough, has undergone very little tectonic movement since the Triassic and this has severely restricted the formation of structural traps suitable for hydrocarbon entrapment. Better structuring exists to the east of a Mesozoic hinge-line running approximately north- south just offshore from the present-day coastline, but lack of good Mesozoic reservoir sands in this area limits the hydrocarbon prospects. The most prospective area is the structured margin of the Omati Trough, where tilted fault blocks provide traps for hydrocarbons generated from the underlying shales of the Cretaceous and Jurassic, but difficult terrain and high exploration costs make for high risk exploration.

STRATIGRAPHIC AND STRUCTURAL DEVELOPMENT OF THE AURE TROUGH AND ADJACENT SHELF AND SLOPE AREAS

The Aure Trough is a partially submerged south-southeasterly trending eugeosyncline which comprises the main axial zone of sedimentation in the Cainozoic Papuan Geosyncline. It is bounded to the west by a broad stable miogeosynclinal shelf and slope, and to the east by a narrow unstable shelf.Onshore the trough consists of 10 000 m of deep-water sediments. These extend offshore where the axis of sedimentation coincides with the axis of a present day bathymetric feature, the Moresby Trough. Sediments are folded into north-trending linear anticlines and broad synclines; anticlines are ruptured by thrust faults and offshore by diapiric intrusion of mudstone. The western slope (5000 m of fine marine sediments) and shelf (2500 m of deltaic and shallow marine sediments) are relatively undeformed. Over the eastern shelf, 5000 m of folded fluviatile, deltaic and shallow marine sediments are transitional eastwards to 2000 m of relatively undeformed sub-aerial volcanics. Variations in sedimentary lithologies can be correlated with periods of volcanic activity associated with periods of uplift.The sediments of the Cainozoic Papuan Geosyncline unconformably overlie Mesozoic and Eocene sediments. West of the Aure Trough the Mesozoic and Eocene rocks are weakly deformed shelf sediments derived from the Australian continent; east of the trough they are strongly deformed, metamorphosed and partly volcanogenic. The nature, thickness and extent of these sediments beneath the Aure Trough is not known.The Mesozoic to Eocene sequence accumulated around the margins of the Australian continent in an arcuate geosynclinal basin. Early Cainozoic interaction of the Australian and Pacific plates resulted in deformation of the outer margins of this geosyncline and in the partial emergence of mainland Papua New Guinea. Erosion of this landmass and volcanic activity provided the main source of sediment for the Cainozoic Papuan Geosyncline. Development of the Aure Trough may be related to opening of the Coral Sea Basin in the Eocene; geophysical evidence suggests crustal thinning.Numerous oil and gas seepages have encouraged petroleum exploration throughout the area since 1911. No economic reserves have been located in the Tertiary section, but wells west of the Aure Trough have encountered gas and some oil of probable Mesozoic origin.

Geology of Eastern Papua

Eastern Papua is a southeasterly trending mountainous peninsula with islands to the east and southeast, between 7° to 12° S. and 146° to 155° E. The peninsula and islands consist of a linear core of Mesozoic sialic metamorphic rocks flanked by Mesozoic and younger mafic rocks, and partly concealed by still younger sedimentary and volcanic rocks. The Mesozoic sialic rocks are exposed in a belt 900 km long and up to 60 km wide. They consist of Cretaceous (and possibly older) sediments which were metamorphosed during the Paleocene or Eocene. Metamorphic grade is generally greenschist facies, but is higher in the D9Entrecasteaux Islands and on part of Misima Island; lawsonite occurs mainly within a few kilometers of the Owen Stanley fault which bounds the mainland metamorphics on the north and northeast. Mesozoic mafic rocks include peridotite, gabbro and basalt of the Papuan ultramafic belt, metabasalt exposed in the Suckling-Dayman mountain block and on Normanby and the Deboyne Islands, and unmetamorphosed basalt elsewhere on the mainland. These rocks are, at least in part, Cretaceous. Younger mafic rocks include Eocene basalt on the southeastern mainland, and upper Oligocene and lower and middle Miocene tuff and lava at scattered localities. Eocene sediments consist of chert and deep-water limestone along the south coast of the mainland at Port Moresby and Magarida, and Eocene clastic sediments inland from Port Moresby and near Tapini. No lower or middle Oligocene rocks are known. Upper Oligocene, Miocene and Pliocene sediments in the Aure Trough (145° to 146° E.) have a maximum thickness of about 12,000 m; the sediments are mainly alternating mudstone and graywacke, and are probably turbidites. Middle Miocene reef limestone on the eastern hinge line of the trough at 146° E. is 1,000 m thick. Middle Miocene and younger clastic sediments in the Cape Vogel Basin (150° E.) are at least 4,000 m thick. Pliocene and Quaternary volcanic rocks range in composition from basalt to rhyolite and include some potash-rich rocks. Intrusive rocks include Eocene tonalite in the ultramafic belt, Oligocene? gabbro near Port Moresby, middle Miocene granodiorite west of Salamaua, middle Miocene potash-rich intrusives on the southeastern mainland, Pliocene andesitic porphyries near Wau, and Pliocene granodiorite in the D9Entrecasteaux Islands. The Cretaceous (and possibly older) sialic sediments are thought to have been metamorphosed during the early Eocene at the time of emplacement of the Papuan ultramafic belt. The ultramafic belt is thought to be part of a thrust slice of oceanic mantle and crust which rode over or was underridden by the Cretaceous sediments on a low-angle fault (the Owen Stanley fault). The metamorphic rocks were partly exposed during the middle or late Eocene but there was no major land mass in the area until the upper Oligocene. During the upper Oligocene, Miocene and Pliocene the sialic metamorphic rocks emerged, perhaps isostatically. Erosion of the resulting mountain block and contemporary volcanism and limestone development contributed great volumes of sediment to the Aure Trough and lesser volumes to the Cape Vogel basin. The history of the area can be interpreted in terms of interaction between Australian and Pacific lithospheric plates and opening of the Coral Sea by rifting.

THE GRAVITY FIELD AND STRUCTURE OF PAPUA AND NEW GUINEA

Interpreted in the light of existing geological knowledge a regional gravity survey of eastern New Guinea defines the major tectonic units of the area and clarifies its tectonic history. At least 7000 metres of Mesozoic sediments are present in a basin extending from the Aure Trough to West Irian, but reaching its maximum development in the Southern Highlands area. To the south and west of tlfis basin the Fly River platform exhibits an undulating basement resulting from northwest-towest-trending faults or flexures of Lower Cretaceous age. The Kubor Range, forming part of the northern margin of the Southern Highlands basin, appears to have been an intermittently-positive area since the early Mesozoic. Anomalies over the Papuan Ultrabasic Belt are consistent with the origin of this body as a thrust of subcrustal material from the northeast. Originating during the Cretaceous the thrust uplifted metamorphics overlying the ultrabasics, and this rising land northeast of the present Owen Stanley Range provided a source for thick Tertiary sedimentation in the Aure Trough. Transcurrent faulting in the Cape Vogel area separates the small and rising Cape Vogel Basin from the Northern Papuan Basin over the subsiding northeastern edge of the ultra-basic belt. More than 8000 metres of Miocene and younger sediments are present in a basin extending from the Markham valley through to the lower Sepik, the sediments being uplifted by thrusting in the Adelbert, Finisierre and Saruwuged Ranges. The sedimentary section through the Sepik valley is generally less than 3000 metres, with local increases to about 5000 metres in the Nuku Basin and to a possibily greater depth in the Upper Sepik August Rfver Basin.(somatic and free-air anomalies indicate that a zone of isostatic and tectonic instability extends the length of the northern coast of eastern New Guinea. To the south and east of this zone, which is generally less than 150 kilometres wide, the Owen Stanley block, the central highlands and the southern platform are in a state of much greater stability. This present distribution of stable and unstable regions lends support to the concept of the evolution of New Guinea as a series of orogenic zones developing on, and becoming incorporated in, the northeastern margin of the Australian continent.

THE GEOLOGY OF WESTERN PAPUA

Two principal phases of sedimentary deposition are known in Western Papua, the Mesozoic and Tertiary. Knowledge of older sediments is limited to a small outcrop of Permian on the western end of the Kubor Range beneath which are granites and metamorphic rocks forming basement.The Mesozoic rocks outcrop in the central ranges of New Guinea and have been penetrated in 20 wells in the southern coastal area. Elucidation of the detailed Mesozoic structure and stratigraphy is incomplete but the outline of the history of sedimentation is emerging and appears to be similar in broad structural pattern to that of the overlying Tertiary sequence.Folding emergence and erosion occurred at the end of the Mesozoic in response to epeirogenic uplift of the northeastern margin of the Australian continent; with the subsequent Tertiary transgression being represented for the most part by Eocene and Oligocene limestones of limited thickness. On the basis of facies characteristics and sediment thickness it appears that during the Miocene western Papua was the site of an arcuate orthogeosynclinal complex. In the sector north of tilte Papuan Gulf the subdivision into a eugeosynclinal and miogeosynclinal trough is clearly represented by the development, in Kereruan times, of the Aure Trough and the Omati Basin. During the Lower and Middle Miocene huge thicknesses of greywackes and shales were deposited in the Aure Trough and westwards and southwestwards of the trough a limestone succession consisting mainly of basinal, fore -reef limestones and shoal reefs was developed over an area some 200 miles wide with its maximum thickness at Ornati. Definition of limestone facies within this huge limestone area is still incomplete. The Upper Miocene was marked by widespread development of argillaceous and arenaceous facies with only minor development of limestone. Movements during the Upper Miocene led to restriction of the Pliocene basin of sedimentation and the formation of shallow water arenaceous rocks with lesser mudstones and coals. The final major phase of folding and uplift probably began in late Pliocene times and has continued to the present day, accompanied by vulcanism and vigorous erosion.