Consolidated Maritime Boundaries between Australia and Papua New Guinea Diagram AU/PNG-08 Refer previous GeoCat 65642 Treaty text and coordinates can be found at: http://www.austlii.edu.au/au/other/dfat/treaties/1985/4.html

Eleven ammonite species from five localities in the Ieru Formation, western Papua New Guinea, are described. Four are identified with the well known and widely distributed Cenomanian species of the Acanthoceratidae, Calycoceras (Newboldiceras) newboldi (Kossmat), C. (N.) cf orientale Matsumoto and others, C. (N.) annulatum Collignon and Acanthoceras rhotomagense (Brongniart). Other Cenomanian taxa are three indeterminable acanthoceratid species, C. (Calycoceras) sp. nov .(?), Calycoceras subgenus et sp. indet., and Acanthoceras sp. indet., as well as Pachydesmoceras sp. nov. and Chimbuites aff. mirindowensis Wright. The Turonian species Romaniceras deverioides (de Grossouvre) was found with Placenticeras aff. tamulicum (Blanford); several fragments, probably from the Star Mountains, are also referred to P. aff. tamulicum.

The new genus Quasicyclammina is described from the Lagaip Beds of upper Paleocene age in the Wabag area, Papua New Guinea; it is placed in the subfamily Cyclammininae of the family Lituolidae. This new genus has an agglutinated test wall, slightly asymmetrical test, short internal longitudinal partitions, and an asymmetrical interiomarginal aperture. Three species are described, Q. breviseptum sp. nov., Q. compressa sp. nov. and Q. inflata sp. nov., separated on the number of the chambers In the outer whorl and on the maximum diameter/thickness ratio. A new species of the genus Thalmannammina, T. anfracta, is also described.

The Karumba Basin in its present form coincides areally with the Gulf of Carpentaria and the river systems draining into it. The Basin is mainly of Cainozoic age, epi-cratonic, and superimposed on the Mesozoic Carpentaria Basin of the Trans-Australian Platform Cover. The development of the Karumba Basin related to the separation of Australia from Antarctica, and to subsequent plate margin events in New Guinea, in contrast to the evolution of the Carpentaria Basin which probably correlated with plate convergence to the east. The structural basin contains four main sets of deposits, each primarily resulting from an uplift episode. The oldest set, the Bulimba Formation, is probably of late Cretaceous-Paleocene age; the next, the Wyaaba Beds and equivalents, is Miocene to early Pliocene; the third, the Yam Creek Beds and equivalents, is of Pliocene age; the youngest began accumulating in the late Pliocene and is still being deposited. The total thickness of the four sets is about 400 m; they occupy a relatively small part of the present Karumba structural Basin.

Recordings of P seismic waves from a Novaya Zemlya nuclear explosion at 26 sites on the east Papuan peninsula show that there are significant apparent departures (residuals) from travel-times calculated using average earth models. The residual at Port Moresby (PMG) differs by between +0.3 and +0.5 seconds from previous attempts to assign a station effect there. Without precise times and locations of the Novaya Zemlya events it is not possible to determine the proportions of the residual due to source effects and velocity anomalies in the mantle. It is shown that complex crustal structure in the east Papuan region accounts for a significant proportion of the station residuals, which differ from the PMG residual by between -0.72 seconds and +1.41 seconds. There is a tendency towards more negative residuals on the northeast side of the Papuan peninsula.

Recent geological mapping in the north coast ranges of Papua New Guinea has recognised a Paleogene island arc. This arc is believed to have faced southward, and formed at the northeastern boundary of the Indo-Australian plate. The arc collided with continental crust of the Indo-Australian plate to the south; collision is thought to have occurred first in the west in the Early Miocene and to have progressed eastwards. Crustal shortening on collision resulted in foreland-type folding and thrusting at the continental margin, emplacement of ophiolite allochthons from the arc-trench gap at the collision zone, and uplift and fracturing of the accreted arc. Post-collision plate adjustments are thought to include extensive trans- current faulting about the former plate boundary, southward thrusting of part of the arc (Finisterre-Huon block), and extensive faulting in a complex linear zone extending from south of Manus Island through New Ireland and the Solomon Islands. Present-day interaction between the Indo-Australian and Pacific plates is spread over a wide zone in which at least two minor plates are involved. Despite previous claims, plots of the most accurately located earthquake foci define a northward-dipping seismic zone beneath the Late Cainozoic volcanoes at the southern margin of the Bismarck Sea. We find no evidence to substantiate a reversal of arc polarity at any time after the Mid-Tertiary collision. Mid to Late Cainozoic magmatism in central Papua New Guinea appears to have been triggered by uplift inducing partial melting of mantle modified by Cretaceous subduction. The present-day northward-dipping seismic zone is believed to be a vestige of the Early Tertiary subduction zone; the hanging slab is now slowly sinking and equilibrating with the mantle. If northern New Guinea can be considered to be the type example of a continent/island-arc collision then reversal of arc polarity may not be a necessary consequence of such collisions.

On 20 July 1975 a major earthquake (MS7.9) shook the northern islands of the Solomon Islands chain. Damage amounting to at least $300,000 (Australian) occurred in the southern Bougainville/Shortland Islands region, where earthquake intensities were estimated to be MMVII-VIII. A tsunami with maximum amplitude of about two metres followed the earthquake and caused further damage. The earthquake caused landsliding, liquefaction, subsidence, slumping of roads and wharfs, and damage to villages, small government and mission buildings, and to the mining installations at Panguna. Aftershock epicentres were in a roughly elliptical area of 12 500 square kilometres off the southwestern coast of Bougainville. Focal depths were in the range 30-70 km. A fault-plane solution and the pattern of aftershocks indicate that the principal earthquake was associated with underthrusting of the Solomon Sea crust beneath Bougainville, in a northeasterly direction and with a dip of about 37°. The faulting associated with the 20 July 1975 earthquake appears to be the extension of faulting associated with a 1974 earthquake series. An aseismic zone, centred at 6°S, 154°E, exists immediately northwest of the 1975 earthquake fault zone, between zones where major earthquakes have occurred since 1970. It is considered to be a likely place for a major earthquake in future.

Four distinct volcanic rock types are found above a conjectured mantle hot spot in St Andrew Strait, northern Papua New Guinea. Hypersthene-normative basalts on Baluan Island are geochemically similar in most respects to those on oceanic islands and, together with voluminous alkali-rich rhyolites on Tuluman, Lou, and Pam Islands, constitute a strongly bimodal rock suite. The rhyolites are regarded as partial melts of basaltic crust isotopically similar to the basalts of Baluan, though with lower Sr, Rb, and Ba contents. In contrast, quartz-tholeiite basalts in the Fedarb Islands are isotopically distinct from the Baluan basalts. Dacite is also present in the Fedarb Islands, but not all of its geochemical features are consistent with a derivation by crystal fractionation from Fedarb quartz tholeiite. Like Iceland, St Andrew Strait may be underlain by a hot mantle diapir that has produced basaltic magmas as well as partial melting of basaltic crust.

At this scale 1cm on the map represents 1km on the ground. Each map covers a minimum area of 0.5 degrees longitude by 0.5 degrees latitude or about 54 kilometres by 54 kilometres. The contour interval is 20 metres. Many maps are supplemented by hill shading.

This series of maps covers the whole of Australia at a scale of 1:250 000 (1cm on a map represents 2.5km on the ground) and comprises 513 maps. This is the largest scale at which published topographic maps cover the entire continent.