Moresby Trough Research Articles

Glaciation of the northern British Columbia continental shelf: the geomorphic evidence derived from multibeam bathymetric data

We describe a revised understanding of the extent and dynamics of the Cordilleran Ice Sheet on the continental shelf of northern British Columbia, Canada. During the Local Last Glacial Maximum ice streams occupied two of the three shelf‐crossing troughs in Queen Charlotte Sound (Goose Island Trough and Mitchell's Trough). A 25‐km‐wide outlet glacier – the Hecate Glacier – flowed south in Hecate Strait, parallel to the modern coast. It reached a grounding line at the head of Moresby Trough, beyond which an ice shelf may have extended to the edge of the continental shelf. The southern part of the independent Haida Gwaii Ice Cap formed piedmont lobes dissected by tunnel valleys. An emergent area east of the ice cap corresponds with the ‘Hecate Refugium’. Subsequently grounded ice retreated from the shelf troughs. The Hecate Glacier retreated incrementally towards the north. Mainland ice then stabilized along a north–south margin near modern coasts, marked by submarine moraines in the Chatham Sound region and elsewhere. This margin was probably contemporaneous with the margin at Mt. Buxton in the south of the study area, dated at c. 17.6 to 16.6 ka (Darvill et al. 2018). Off southern Haida Gwaii, following a retreat, a glacier margin was established east of Juan Perez Sound, proximal to a sandur plain graded to a water level of −150 m. Proglacial lakes to the north of here were the likely source for an outburst flood that created gravel bedforms and an area of sea‐floor scour. In a final phase, diminished mainland ice was confined to fjords, and retreat inland is marked by a succession of submarine moraines, beginning with a moraine at the Douglas Channel sill. The study has implications for the migration pathways for human migration into the Americas following deglaciation.

Anatomy of the Kitimat fiord system, British Columbia

The geomorphic complexity of the Kitimat fiord system, on the active margin of British Columbia, Canada, is analysed from several perspectives. Sub-glacial landforms and sediments show that grounded ice exiting the fiord system at the last glacial maximum streamed down Moresby Trough towards the Queen Charlotte trough mouth fan. After brief halts on the inner shelf, grounded ice margins cleared the fiord threshold perhaps by c. 15.5kacal.yrsBP, and certainly before 13kacal.yrsBP. Just outside the fiords, meltwater plumes deposited stratified glaciomarine sediments interbedded with submarine slides. Inside the fiords, thick glaciomarine sediments were deposited, and large transverse moraines formed during temporary halts in retreat. Several glacial outburst floods eroded the Kitkiata moraine and deposited distinctive mud deposits. Postglacial sedimentation on fiord floors has been spatially variable: drifts of mud>90m-thick corresponding with areas of low current velocity alternate with areas of non-deposition and erosion corresponding with areas of high velocity. The fiord system hosts more than a hundred morphologically diverse fan deltas that can be classified in the Prior and Bornhold (1989, 1990) system. Submarine mass transport was most frequent immediately following ice retreat (15.5–11.5kacal.yrsBP). The largest event (~1.2km3) involved failure of glaciomarine sediment on a submarine moraine at Squally Channel, and consequent movement of material into the adjacent deep basin. This event occurred post-13kacal.yrsBP. In the postglacial phase, mass transport continued on a lesser scale up to the present day, most intensively in Kitimat Arm. From the perspective of glacial landforms, postglacial sedimentation and mass transport, this Pacific active margin fiord system has some parallels with fiord systems on Canada's east coast passive margin, and with Norwegian fiords, but the intensive development of Holocene fan deltas is strongly distinctive.

Late Quaternary geomorphology, seabed evolution, and terrigenous sediment delivery to the Pandora and Moresby Troughs, Gulf of Papua

An integrated geology and geophysics investigation has been carried out to study the late Quaternary deepwater depositional system in the Gulf of Papua (NSF-MARGINS focus area) focusing on two contrasting depocentres, Pandora and Moresby troughs. The studies incorporate multi-beam bathymetry, sub-bottom sonar, and core data in order to define and map acoustic and lithofacies; and relate depositional processes, sediment routing, timing and geomorphic products that have developed since Marine Isotope Stage (MIS) 3, ca. 40calka. 3D seafloor visualisation is used to infer sedimentary processes responsible for observed morphology, which are then placed into a chronostratigraphic framework using recently published age models of sediment cores.The peak depositional period in Pandora Trough occurred during MIS 2. At that time a large deep-sea channel network linked the Pandora and Moresby troughs, allowing long-distance sediment transport by large turbidity currents from the Papuan mainland to the Coral Sea Basin. Near the LGM, shelf-edge failure led to emplacement of mass-transport deposits on the floor of the Pandora Trough, blocking this pathway for large turbidity currents. Intermittent turbidity currents continued to feed minibasins upslope of the MTD complex until early MIS 1 (earliest Holocene).Along the shelf edge of the Papuan Peninsula, substantial sediment delivery by turbidity currents continued until middle Holocene and perhaps later; combined with bottom currents, these flows contributed to the formation of large sediment waves of Moresby Fan. However, this Holocene turbidite sedimentation does not extend much farther into the Moresby Trough, based on negligible Holocene sediment accumulation deeper in the basin.This study has shown that sediment delivery from fluvial sources to deep basins in the GoP is controlled by a complex interplay of changing sea level, evolving basin bathymetry (influenced by depositional and tectonic processes), and oceanic transport of sediment from shelf to slope. These conditions have created highly localised conduits for shelf to slope sediment delivery that respond both to global forcing (eustatic sea level) as well as local conditions (shelf gradient, mass wasting, currents, and source proximity), resulting in a complex network of deep-sea depositional morphologies active from the Last Glacial Maximum to Holocene time.

Conduits, timing and processes of sediment delivery across a high-relief continental margin: Continental shelf to basin in Late Quaternary, Gulf of Papua

The Gulf of Papua (GoP), between Australia and Papua New Guinea, is the receiving basin for multiple substantial rivers draining southern Papua New Guinea with collective sediment discharge >> 220 million metric tons (Mt) per year, comparable to a continental-scale river, but draining a combined catchment area of only ∼160,000 km2. This study of the deepest marginal basins in the Gulf of Papua was undertaken to build a regional late Quaternary lithofacies and stratigraphic framework to better understand processes, timing, and conduits of sediment delivery from terrestrial and shelf settings to deep marginal basins, using the GoP as a natural laboratory. Methods include observations of sediment-core stratigraphy and physical properties, accelerometer mass spectrometry (AMS) C-14 dates, core x-radiographs and thin sections.Six lithofacies across the deep water Gulf of Papua (GoP) are identified based on core visual and textural observation. Chronological constraints permit an assessment of changes in sediment supply and depositional environments across time and space, from marine isotope stage (MIS) -3 to -1, or in the last 40 cal ka. The sediment delivery to the deep water GoP is dominated by two mechanisms, gravity-driven flows down slopes and into deep sea basin primarily during lowstands in the western portions of the study area, and hemipelagic sediment accumulation during transgression and highstand. Although the sediment flux appears to be overall dominated by sediment-gravity flows, hemipelagic sediment delivery is widespread during periods of sea level highstand. In the eastern portions of the study area, off-shelf sediment delivery continued into the Holocene in sufficient local volumes to produce turbidity currents. This late, localized sediment delivery appears to have been facilitated by oceanographic processes that allowed seaward sediment transport after flooding of the shelf.A simple sediment budget comparing basinal sediment accumulation to modern estimated river-sediment discharge indicates that peak sediment accumulation in proximal basins occurred during MIS-2; and declined thereafter, generally shifting to upper slope locations, except for the eastern margin of Moresby Trough. There, turbidite deposition continued until 7.4 cal ka, well after drowning of the shelf edge. This continued Holocene deep-sea sediment delivery is likely explained by the local narrow shelf width, and the presence of oceanographic processes capable of transporting sediments from shore to shelf edge.

Deep water geomorphology of the mixed siliciclastic‐carbonate system, Gulf of Papua

The Gulf of Papua (GoP) has become a focal point for understanding the deposition and accumulation of siliciclastic and carbonate material along and across a low‐latitude continental margin. Although studies have addressed submarine geomorphological features on the inner and middle shelves, as well as processes that may have led to their formation, the seafloor of adjacent slope regions remains poorly documented. This study presents and interprets results from approximately 13,000 line‐km of multibeam bathymetry, 9500 line‐km of 3.5 kHz seismic, and 122 sediment cores that were collected from the GoP shelf edge and slope, primarily on two cruises (PANASH and PECTEN). Bathymetric maps, in conjunction with the seismic profiles and cores, were used to make extensive observations, descriptions, and interpretations of seafloor geomorphology and begin to address several key issues regarding the delivery and accumulation of sediment. This study divided the GoP slope region into physiographic regions including intraslope basins: Ashmore Trough, southern Pandora Trough, northern Pandora Trough, Moresby Trough and intraslope plateaus/platforms: carbonate platforms and atolls and Eastern Plateau. Ashmore Trough contains a very linear northern margin capped by a drowned barrier reef system. This shelf edge is also defined by a broad promontory with channels extending from its apex, interpreted as a relict shelf‐edge delta. Southern Pandora Trough is characterized by pervasive slope channels and slump scars extending down slope to a thick depocenter and an extensive mass‐transport complex. In contrast, northern Pandora Trough has few visible slope channels. Seismic observations reveal a wedge of sediment extending down slope from northern Pandora Trough shelf edge and filling preexisting bathymetry. Large fold‐and‐thrust‐belt ridges are also present on the seafloor in this region and may act to divert and/or catch sediment, depending on sediment transport direction. Moresby Trough contains a large axial submarine channel that extends almost the entire length of the intraslope basin. In addition, an extensive system of canyons lines the NE margin of Moresby Trough. Mass‐transport deposits have been fed from the canyons and in one case deposited a large (∼2000 km2) mass‐transport complex. Fold‐and‐thrust‐belt ridges also extend into Moresby Trough. Here they trend perpendicular to slope and catch gravity flow deposits on their updip side. GoP carbonate platforms/atolls all display very pronounced scalloped‐margin morphology, which may indicate pervasive mass‐wasting processes on carbonate margins. Northwest Eastern Plateau is dominantly carbonate and displays the characteristic scalloped margin morphology; however, most of the plateau is characterized by parallel seismic reflectors. These seismic observations in conjunction with core data indicate that accumulation on Eastern Plateau is primarily mixed pelagic and hemipelagic sediment. Observations and interpretations of the bathymetry have revealed the deep water GoP to contain very diverse geomorphology and suggest it is a dynamic system influenced by a variety of sediment transport processes, particularly mass wasting and other gravity flow processes.

Excess 210Pb inventories and fluxes along the continental slope and basins of the Gulf of Papua

Sediment samples were collected from continental slopes and marginal basins in the Gulf of Papua and analyzed for excess 210Pb to elucidate transport processes of fine‐ grained particles to this region. Estimated excess 210Pb fluxes of 1.0–12.8 dpm cm−2 a−1 were derived from measured seabed inventories. Highest sediment accumulation rates (0.28–0.35 cm a−1) were measured along the northeastern shelf edge, and they decrease in seaward directions and along isobaths to the southwest. The excess 210Pb flux could result from either focused deposition of high‐210Pb activity sediments from the continental shelf and upper slope or scavenging of 210Pb brought landward from deep‐sea waters. This sediment flux is concentrated in the northeastern Gulf of Papua, where the shelf is narrow and calcium carbonate contents are lowest. Analysis of sedimentary fabric and 210Pb distributions in cores suggests sediment delivery to the slope occurs on a 100‐year timescale as both diffuse hemipelagic deposition as well as turbidity flows. The flux of sediment in turbidity flows is not well constrained but may be producing additional deep‐sea accumulation in the Moresby Trough, as well as export from the study area.

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.

Wind‐driven depth‐averaged circulation in Queen Charlotte Sound and Hecate Strait

Abstract We develop a wind‐driven depth‐averaged model of the circulation on the continental shelf around the Queen Charlotte Islands. The model captures a major feature of the winter current‐meter observations: a flow in Moresby Trough against the direction of the prevailing winds. Moresby Trough is a steep submarine canyon cutting across the shelf from the Pacific Ocean to the mainland. The flow patterns revealed by simulated drifters lead to four generalizations about the depth‐averaged, wind‐driven flow: (1) the flow is subject to strong topographic steering, (2) the exchange between Queen Charlotte Sound and the Pacific Ocean is limited to small regions near Cape St James and Cape Scott, (3) the exchange between Queen Charlotte Sound and Hecate Strait is controlled by Moresby Trough, and (4) the observed outflows past Cape St James are not explained by the dynamics of this model.

Origin and late quaternary tectonism of a western Canadian continental shelf trough

Analyses of high resolution and multi-channel seismic profiles from the central continental shelf of western Canada ascribe a late Quaternary glacial origin to large-scale troughs. Along the margins of Moresby Trough, one of three large-scale cross-shelf bathymetric depressions in Queen Charlotte Sound, seismic profiles within Quaternary sediments show a divergence of reflectors, thickening and folding of seismic units, and concavity of reflectors suggestive of drag. Compactional subsidence, growth faulting, and compaction faulting are also observed. Fault traces commonly terminate below the seabed. Deformation of Quaternary sediments due to faulting is plastic in nature and maximum offset of reflectors is 2.5 m. The observed Quaternary deformation appears to be a product of rapid deposition, loading and subsidence of late Quaternary sediment, which is unrelated to seismic activity. In addition, Quaternary faulting was probably activated by post-glacial loading and isostatic rebound of consolidated Tertiary strata along the margins of continental shelf troughs. The presence of mass movement (slump or debris flow) deposits overlying lithified Tertiary strata along the flanks of Moresby Trough provides the only evidence of seismic activity in the study area. The lack of a mud drape over these deposits implies a late Holocene age for the timing of their emplacement. The Quaternary troughs are incised into Tertiary-aged sedimentary fill of the Queen Charlotte basin. Previous workers had interpreted seafloor escarpments paralleling the trough margins to indicate that the location of Moresby Trough was controlled by renewed or continued activity on Tertiary-aged faults. A multi-channel seismic line across Moresby Trough shows that such an escarpment on the seafloor does not correlate to faults either in the Tertiary basin fill or the underlying basement. Tertiary reflectors are continuous underneath Moresby Trough; the seafloor escarpment is an erosional feature and was not created by reactivation of Tertiary structures. Trough erosion and subsequent fill (up to 175 m thick) are entirely of Quaternary age.

Neotectonics and Sedimentation on the Central Continental Shelf of Western Canada

Analysis of high resolution seismic profiles from the central Canadian continental shelf provides substantial evidence for Quaternary faulting. Along the northwestern margin of Moresby Trough, one of three largescale Quaternary canyons cutting across the shelf, a divergence of reflectors, thickening of seismic units, and concavity of reflectors suggestive of drag are seen along the downthrown side of listric normal faults. Faulting appears to be syndepositional. Some of the faults are interpreted as growth or compaction faults. Fault traces commonly terminate below the seabed. Deformation of Quaternary sediments due to faulting is non-brittle in nature, and maximum offset of the reflectors thus far seen is 2.5 m. It is suggested that the Quaternary faulting observed is a product of rapid deposition and loading of late Quaternary sediment rather than being related to seismicity. A multichannel survey in the Queen Charlotte basin gives an excellent image of structure of the sediment-basement interface and Tertiary sedimentary fill. In the Queen Charlotte Sound the basin is divided into several subbasins that are bounded by normal faults. Three crossings of Quaternary canyons show that they cut into sedimentary fill in the subbasins as well as basement highs; from this observation it is inferred that theremore » is little control on their location from Tertiary structure. Several features in the data indicate that Tertiary structures are not being reactivated. Basement has less than 0.2 s relief under Moresby through and steep gradients in the seafloor cannot be correlated with basement topography. Canyon erosion and subsequent fill (up to 175 m thick) are probably of Quaternary age and seem to act independently of Tertiary structure.« less

QUEENSLAND PLATEAU AND CORAL SEA BASIN STRATIGRAPHY, STRUCTURE AND TECTONICS

Seafloor spreading in the Coral Sea Basin is dated by Deep Sea Drilling Project Site 287 as Early Eocene (51 my bp). This requires normal rifting and breakup of an extended Australian continent including the Queensland. Papuan and Louisiade Plateaus as well as the Cretaceous portions of East Papua. A reconstruction based on continental and plateau margin physiography and Papua-New Guinea geology points to a pole of relative opening at lat. 11.3° S., long. 141.3° E. This results in left-lateral transform motion along the Moresby Trough and Bismarck-Lagaip Fault Zones through breakup, plus the deformation of the Owen Stanley sediment pile, and emplacement of the Papuan Ultramafic Belt.Following initiation of sea-floor spreading, subsidence commenced at what are now the marginal plateaus bordering the Coral Sea Basin. A widespread unconformity spanning the late Eocene-mid Ollgocene can be recognised on all plateaus as well as in the basin proper. This is attributed to the commencement of a significant equatorial circulation pattern in the deepening basin and over the subsided plateaus. Stabilisation of this equatorial circulation pattern permitted coral reef development on residual basement highs on the marginal plateaus and eventually) on the subsiding Queensland continental shelf and Papuan stable platform areas in the late Oligocene-early Miocene.On the basis of seismic refraction and gravity evidence, rift valley sequences up to 3 km thick are inferred beneath the Queensland and Townsville Troughs and bordering the Queensland and Papuan Plateaus. Though seismic refraction data are lacking, similar sequences are also inferred beneath parts of the Eastern and Marion Plateaus. Bligh Trough and Louisiade Rise. The age of this pre-breakup rifting is suggested to be mid Cretaceous-Palaeocene although direct evidence is absent.Gravity modelling over the Queensland Trough, Plateau and Coral Sea Basin supports the interpretation from seismic reflection and refraction data. Continental crustal structure with a deep metamorphic layer is indicated for the Queensland Trough and Plateau with a depth to the Moho of 22-28 km. The continental/ocean crust transition occurs towards the base of the continental slope at a water depth of up to 4.5 km along the Queensland Plateau. Crust beneath the Coral Sea abyssal plain is oceanic with a depth to mantle of 11-13 km.

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.

Submarine valley systems around the Coral Sea Basin (Australia)

Several major and a host of minor submarine valleys and canyons lead into the deep (4,650 m) Coral Sea Basin from the surrounding land, reef, and submarine plateau areas. Moresby Valley, 500 km long, and comprising Pandora Trough, Moresby Trough, and Moresby Canyon, plus all their tributary canyons, is an integrated submarine drainage system that collects sediment from nearly the entire Papuan coast and channels it onto the floor of the basin. The Bligh System, including Queensland Trough, Bligh Trough, and Bligh Canyon, drains a 900 km sweep of the Great Barrier Reef coast of Queensland, and parts of the Queensland Submarine Plateau. Reflection profiles of the valleys show that they are mainly located in structural depressions, but that the submarine relief has been further accentuated by erosional entrenchment of the valleys into older, probably pelagic, sediments to a depth of as much as 750 m. Since the time of the entrenchment, the valleys and many canyons have been backfilled by as much as 500 m of sediment (assuming a sound velocity of 2 km/sec in the fill). The valleys may be thought of as graded, and their filling is assigned to adjustments in the long profiles of the valleys as the Coral Sea Basin fills with sediment.