East Arm Research Articles

Time cells in the retrosplenial cortex.

The retrosplenial cortex (RSC) is a key component of the brain's memory systems, with anatomical connections to the hippocampus, anterior thalamus, and entorhinal cortex. This circuit has been implicated in episodic memory and many of these structures have been shown to encode temporal information, which is critical for episodic memory. For example, hippocampal time cells reliably fire during specific segments of time during a delay period. Although RSC lesions are known to disrupt temporal memory, time cells have not been observed there. In this study, we reanalyzed archival RSC neuronal firing data during the intertrial delay period from two previous experiments involving different behavioral tasks, a blocked alternation task and a cued T-maze task. For the blocked alternation task, rats were required to approach the east or west arm of a plus maze for reward during different blocks of trials. Because the reward locations were not cued, the rat had to remember the goal location for each trial. In the cued T-maze task, the reward location was explicitly cued with a light and the rats simply had to approach the light for reward, so there was no requirement to hold a memory during the intertrial delay. Time cells were prevalent in the blocked alternation task, and most time cells clearly differentiated the east and west trials. We also found that RSC neurons could exhibit off-response time fields, periods of reliably inhibited firing. Time cells were also observed in the cued T-maze, but they were less prevalent and they did not differentiate left and right trials as well as in the blocked alternation task, suggesting that RSC time cells are sensitive to the memory demands of the task. These results suggest that temporal coding is a prominent feature of RSC firing patterns, consistent with an RSC role in episodic memory.

Facies Analysis and Sequence Stratigraphy of Plio-Pleistocene Fan Delta Deposits in the East Arm Sulawesi, a case study of Biak Formation, Luwuk, Banggai

Abstract Fan delta deposits were found widespread in the east arm of Sulawesi as the area experienced tectonic uplift during Plio-Pleistocene continental collision, known as Bongka Formation in the western part and Biak Formation in the eastern part. One of key outcrops for Biak Formation was observed in Biak Village, North Luwuk District, Banggai Regency, thus served as the lithotype location for the Biak Formation. The outcrop was a roadcut and had a 50 m long and 25 m high. In general it shows a coarse-grained heterolithic inclined strata dipping southward and overlain by horizontal strata of similar facies. Its sequence stratigraphy was analyzed by examine its facies, facies association, petrography, and paleontology, along a 1:100 scaled measured section. Six lithofacies were identified, namely conglomeratic coralline limestone, conglomeratic coralline limestone, parallel bedding – gradation conglomerate-sandstone, gravely sandstone, conglomerate-sandstone – conglomeratic corraline limestone and gradation conglomerate-sandstone with horizontal bedding. Their lithofacies deposited during Late Pliocene in a transition – inner neritic environment. Their facies association made several depositional system tracts, showing a complete cycle of Highstand System Tract (HST), Sequence Boundary/Correlative Conformity (SB/CC), Lowstand System Tract (LST), Transgressive System Tract (TST), Transgressive Surface (TS) later capped by younger HST and LST. Result of this study suggesting repetitive cyclic depositiona tracts dictated by sea-level eustacy and tectonic uplift. This location served as an ideal outcrop as a textbook example to study sequence stratigraphy in an outcrop scale.

Stratigraphy of Salodik Formation in Batutambung section, Toili, Luwuk, Central Sulawesi

Abstract Salodik Formation is one of the formations representing a continental drift sequence prior to the collision of Banggai Basin, and it was widely cropped out in the East Arm of Sulawesi. The published geological maps of Luwuk dan Batui describe the Salodik Formation as massive and bedded limestone with marl intercalated and sandstone in the lower part, ranging from Eocene to Late Miocene. In Batutambung, Toili, the geological maps showing the Salodik Formation distributed in a NW-SE trend between two ophiolitic land masses, and suggesting intensive tectonic deformation along the trend. Preliminary geological investigations in this area show that Salodik rock sequences varied from other Salodik outcrops in different areas. Detailed stratigraphic measurements and rock sampling have been carried out along the road connecting Toili and Ampanan Tete., yielding a measured stratigraphy of 70 m vertically thick. Nine lithofacies were identified, i.e., coarse-grained sandstone (cS), micritic sandstone (mcS), fine-medium-grained sandstone (fmS), sandstone with coal spar (SMms), Mudrock (mM), micritic mudrock (mcM), Mudstone (MS), Wackestone (WS) and Packstone (PS). Facies association shows the rock sequence has shallowing upward or prograding pattern with depositional environment varies from an open marine, tidal channel, shoal, and restricted marine/ lagoon Based on foraminifera and nannofossil analysis, Salodik Formation in Batutambung section was deposited in Early Miocene (N6 or NN4-NN6), with paleobathymetry from middle to outer neritic. Based on its age and lithology character, the Salodik Formation in Batutambung is equivalent with Matindok Formation in Tomori PSC.

Reinterpretation of Salodik Group Performance Based on Facies and Diagenesis Approaches to Classify Reservoir Quality

An integrated study of several methods to characterize a carbonate reservoir provides a comprehensive result on carbonate facies and diagenesis. Therefore, a study on the Tertiary carbonate reservoir at the East Arm of Sulawesi area, Banggai – Sula Basin, is intended to determine the Salodik Group carbonate reservoir facies and diagenesis. Moreover, the purpose of this study is to determine the intensity and implication of syn-depositional or post-depositional processes, and to provide the reservoir final properties values, such as porosity and permeability to classify the reservoir quality. The methods of the study are based on carbonate fieldwork mapping to obtain samples on distributed traverses. Further analyses are the laboratory works to determine facies and diagenesis features on a more detailed scale. This study shows several facies, dominantly classified into reefal packstone, planktonic foraminifera packstone-wackestone, large foram packstone-mudstone, skeletal packstone-wackestone, planktonic-large foraminifera packstone-wackestone, and large foraminifera-red algae packstone. The dominant diagenesis processes are cementation and dissolution. Moreover, meteoric vadose and meteoric phreatic are predominantly the main diagenesis environment of Salodik Group formations. Furthermore, the dominant diagenesis stage is Eogenetic. The post-depositional process or the diagenetic processes, provides a more significant impact on carbonate reservoir properties than the syn-depositional process as shown on lithofacies texture. However, in general, from the younger to the oldest formation of Salodik Group, this shows a decreasing trend of reservoir properties due to the dominantcementation process in the oldest formation. Overall, the reservoir quality referring to porosity value is classified as negligible to excellent. While, based on permeability data, it is classified as the tight to good reservoir.

STUDI KINERJA SIMPANG BERSINYAL PERGERAKAN LALU LINTAS KOTA PAREPARE

Jl. General Ahmad Yani and Jl. A. Mappangara are at a signalized intersection in Parepare City. Because the traffic flow is quite dense, especially during rush hours, this intersection has the potential to cause accidents, congestion, and delays. This study aims to determine the existing condition of the intersection and the performance of the signalized intersection on Jl. General Ahmad Yani–Jl. A. Mappangara Kota Parepare. The method used is quantitative, namely data management in the form of numbers with data analysis using the MKJI 1997 method, which was carried out in March 2021. The results of the research show that the results of data analysis on traffic flow patterns are busiest on Mondays, with afternoon peak hours at 17.00–18.00 WITA. The value of the number of vehicles on the north arm is 1149 pcu/hour, the east arm is 319 pcu/hour, and the south arm is 705 pcu/hour. Performance that occurs at the intersection with a degree of saturation of 0.92 and an average delay of 53.00 sec/smp. The level of road service on the 3 approaches shows poor service with a LOS (Level Of Service) value on the North arm of 43.2 is E, the East arm is 84.51 is F, and the South arm is E. Where the flow is unstable, the traffic volume is quite heavy.

IMPROVING MOBILITY IN KEDIRI CITY WITH MKJI ANALYSIS 1997 AND TIME SLICE AT SIMPANG EMPAT DHOHO PLAZA

The city of Kediri, as the third largest city in East Java, has cultural heritage, history and natural beauty that attracts visitors from various regions. However, population growth and motorized vehicles cause traffic jams. Signalized intersections, which are a solution to control intersection conflicts, require knowledge of intersection saturation flows to plan efficient traffic management. Analysis methods such as MKJI 1997 and Time Slice with Vehicle Operating Cost (BOK) calculations help design effective solutions. This research shows that adjusting cycle times, increasing effective width, and optimizing signals can improve transportation system performance and reduce congestion in Kediri City. Cycle time analysis taking into account factors such as vehicle type, traffic volume, and vehicle speed resulted in a cycle time of 90.7 seconds. The impact can be seen in the Degree of Saturation (DS) at various intersection arms, with service variations from E to F. Research also shows a decrease in waiting time/queuing for signal lights from 135 seconds to 118 seconds, which results in a decrease in the degree of saturation (DS) and changes in time cycle. The use of Smart Traffic Lights and traffic engineering, such as immediate left turns on the east arm and additional signs, is required. Evaluation of congestion cost efficiency shows that changing the value of side barriers can save Rp. 22,679,183 in the next five years.

Dynamic analysis of geophysical characteristics of Una-Una Volcanic Island, Sulawesi, Indonesia

The Una-Una Volcanic Island is an active and isolated island, and its deep structure and dynamic causal mechanism have yet to be fully understood. The island is situated in Tomini Bay, between the north and east arms of Sulawesi Island in Indonesia. Around 5 Ma, the Sula Islands collided with the east arm of Sulawesi Island, which caused the subduction and retreat of the North Sulawesi Trench. Additionally, a sinistral strike-slip of roughly 4 cm/a initiated at the Palu-Koro fault on the western side of Sulawesi Island, ultimately leading to the formation of the isolated Una-Una Volcanic Island in Tomini Bay. Here, we utilized gravity, seismic, magnetic, and heat flow data to calculate the geophysical characteristics of three-dimensional temperature, velocity, and viscosity of the northern Sulawesi region. The results of our research showed that the crust in the northern region of Sulawesi Island is primarily characterized by brittle deformation. However, the presence of a southward-inclined weak layer in the crust, which resulted from the subduction of the North Sulawesi Trench, caused the region between the terrain and the Moho surface to exhibit a combination of brittle and ductile deformation. The weak zone in the crust in the northern region of Sulawesi Island is the primary controlling factor for the development of sinistral strike-slip. The uplift of the crustal weak area below the Una-Una Volcanic Island was caused by the southward subduction of the North Sulawesi Trench and the northward push of the Banggai-Sula microblock, ultimately leading to the formation of the Una-Una Volcanic Island in Tomini Bay.

New Insight on the Active Fault System in the Halmahera Volcanic Arc, Indonesia, Derived from the 2022 Tobelo Earthquakes

Abstract On 9 January 2022, two shallow earthquakes occurred in the east arm of Halmahera, Indonesia, with magnitudes of Mw 5.2 and 5.4 felt at III–V modified Mercalli intensity. The existence of the causative fault for the earthquakes was unknown. One possible explanation is that the earthquakes were caused by the activity of an inactive fault striking in the southeast–northwest direction, and possibly linked to the volcanic activities in Halmahera. Thus, further analysis of their characteristics is crucial to identify the previously an inactive fault. In this study, we relocated the associated earthquake hypocenters using the double-difference method with an updated velocity model, and determined the focal mechanisms by employing full waveform inversion using moment tensor analysis. The focal parameters were used to analyze the static stress changes. The relocated hypocenters show specific hypocenter clusters, aligning in the north–south direction, associated with left-lateral faulting mechanisms. This north–south alignment differs from the northeast–southwest trend of some other active faults in Halmahera. We propose that the newly found Tobelo fault dips at an angle of around 80° to the west. The seismic stress change from the mainshock and the foreshock of the Tobelo earthquakes corresponds with the distribution of the aftershocks. A detailed analysis of unidentified faults in the high seismicity area is essential to comprehend the tectonic study of Halmahera Island and its seismic hazard assessments.

Multiphase magnetic fields in the galaxy NGC 3627

ABSTRACT Magnetic fields play an important role in the formation and evolution of a galaxy, but it is challenging to measure them by observation. Here, we study the Seyfert galaxy NGC 3627’s magnetic field orientations measured from the synchrotron polarization observed with the Very Large Array and from the Velocity Gradient Technique (VGT) using spectroscopic data. The latter employs the magnetohydrodynamical turbulence’s anisotropy to probe the magnetic fields. Being applied to the CO (2–1) and H α emission lines obtained from the PHANGS-ALMA and PHANGS-MUSE surveys, it reveals the magnetic field orientation globally consistent with the polarization. The agreement of the VGT-CO and polarization suggests that the magnetic fields associated with synchrotron emission also percolate through star-forming regions. The VGT-H α measurement reveals the magnetic fields in the warm ionized medium that permeates the disc and disc’s vicinity so that it exhibits less agreement with polarization. We find prominent radial fields measured by synchrotron polarization appear in the transition regions from the spiral arms to the galactic bar, while such morphology is less apparent in the VGT-CO and VGT-H α measured magnetic fields. The radial fields suggest that the magnetic torque is important in removing orbiting gas’ angular momentum. We notice that magnetic fields inferred from the dust polarization, VGT-CO, and synchrotron polarization are different in the east arm. We interpret this difference as arising from the fact that the three measurements are tracing the magnetic fields associated with pre-collision, the mixture of pre-collision and post-collision, and post-collision flows, respectively.

Abiogenic gas seepage from serpentinite at Tanjung Api, Tomini Bay, East Sulawesi

Oil and gas seeps are common across the Indonesia region and are usually associated with breached anticlines or faults in Cenozoic or Mesozoic sedimentary basins, where they were generated from biogenic or thermogenic conversion of organic matter in sediments. In contrast, the methane gas at Tanjung Api in East Sulawesi is emerging from an area of ultramafic mantle rocks, which are part of the large East Sulawesi Ophiolite Complex.Tanjung Api is a prominent cape along the South side of Tomini Bay (also called the Gorontalo Basin, along the north shore of the East Arm of Sulawesi). The name means ‘Fire Cape’ and reflects the presence of several burning gas seeps on the beach. This phenomenon must have been active and known for more than 150 years, as the name was already shown on Dutch topographic maps in 1869, and possibly earlier.In this brief review of the enigmatic Tanjung Api gas seeps, we argue that the gas is not a conventional, organic-derived hydrocarbon gas, but an abiogenic (or abiotic), gas, dominated by isotopically anomalous methane and hydrogen, which formed from the serpentinization of ultramafic rocks.

KINEMATIC ANALYSIS OF BALANTAK FAULT USING FAULT-SLIP DATA IN BALANTAK AREA, BANGGAI REGENCY, CENTRAL SULAWESI

Balantak is one of the sub-districts in Banggai Regency, Central Sulawesi Province. The research area is along the Balantak Strike-Slip Fault. This study presents geological mapping with focus on the deformation style that occurred within the area. The study provides an analogue of strike-slip structural trap types in convergent setting to support oil and gas field development. This research method was conducted using field observation and kinematic analysis of fault-slip data. Lithology in the study area that is part of the Banggai-Sula microplate has the characteristics of sedimentary rocks that are grainstone intercalating calcareous sandstone and rudstone consisting of limestone fragments. While part of the Sulawesi East Arm has crystalline rocks in the form of ultramafic-mafic rocks such as Peridotite, Serpentinite, Gabbro and Basalt. Structural analysis along the strike-slip fault indicates the collision of Banggai-Sula with Sulawesi East Arm on the side part of the micro-plate generates thrust fold belt along with well-developed uniform tearing faults present. The orientation and shape of the strain ellipsoid is pure shear transpression with the Balantak Fault as its plane of movement. The characteristic of the structure pattern complying with the model shows that the type of structures is en echelon thrusts and folds while the tearing faults are Riedel synthetics of the Balantak dextral Strike-Slip Fault that developed offset on the fold structures.

BIOSTRATIGRAPHY ANALYSIS OF BARBATOS-1 EXPLORATION WELL IN TOMORI BLOCK, BANGGAI BASIN, EAST ARM OF SULAWESI

A biostratigraphic analysis was carried out on 60 samples taken from the Barbatos-1 Well, located within the Tomori Block, Banggai Tertiary Basin, East Arm of Sulawesi. The Barbatos-1 well was selected for this study because it is composed of rock sequences which are the main reservoir in the Tomori Block. Biostratigraphic analysis was conducted to determine the relative age and depositional environment of the sample. The age of the sample is determined based on the interval zone. The depositional environment is estimated based on the ratio of plankton (P/B ratio) and fossil facies. The results revealed that the rock formations studied were deposited in the Miocene to Holocene age. The lowest layer is the Orbulina bilobata-Zone which was deposited at N10 – N12 (lower Middle Miocene) in the bathyal environment. The layer above is a biozonation of Globorotalia menardii, deposited at N12 – N14 (upper Middle Miocene) in a neritic environment. The next layer is the biozonation of Sphaeroidinella subdehiscens – Globigerina praebulloides which was deposited at N14 – N17 (Middle Miocene – Late Miocene) in the bathyal environment. The topmost layer is the biozonation of Orbulina universa – Globigerinoides immaturus which was deposited at N17 – N23 or Pliocene – Holocene in the bathyal environment. In the top two layers, there are fossil fragments that come from older rock layers (Early Tertiary).

Characteristic of the Mount Colo Volcano, Una-Una Island, Central Sulawesi Province: Tectonic Evolution and Disaster Mitigation

The Una-Una Island is in the Gulf of Tomini, Central Sulawesi Province. This island is a soliter active volcano island with Mount Colo as volcano name. The island is located between the North Arm and East Arm of Sulawesi, which are having complex tectonic regime, situated between two subduction zones. Volcanic rocks from Una-Una Island are basaltic-trachyandesite until trachydasite composition with magma affinity is calk-alkaline, high-K calk-alkaline and shoshonite. Tectonic reconstruction in this area started at Miocene (15 Ma) where the Celebes Sea Plate subducted below the North Arm of Sulawesi with a gentle slope produced adakite-type volcanic rocks. Along with the continuous subduction process and increasingly steep angle of subduction, the magma source then underwent. Intensive movement of the Banggai-Sula microcontinent, resulted in obduction of the ophiolite during collision, whereas volcanic activity in Una-Una Island and surrounding islands are still ongoing. Recent eruption of the Mount Colo in 1983 produced abundant of pyroclastic material with acid silica and still adakite type composition with mineralogical assemblages consist of hornblende-phlogophite-biotite, gives the impression that it originated from the same magma sources. According to composition of magma and eruption history which were produced magmatic explosion followed by pyroclastic surge, flow and fall, the disaster mitigation focus to eruption forecasting through visual and instrumental monitoring provide by Centre for Volcanology and Geological Hazard Mitigation, Geological Agency, Ministry of Energy and Mineral Resources Republic of Indonesia.

Tectonic implications of the gravity signatures of the Midcontinent Rift and Grenville Front

North America's Midcontinent Rift (MCR) and Grenville Front (GF) jointly record aspects of the complex history of the assembly of Rodinia. The ~1100 Ma MCR, remaining from a failed major rifting event, is exposed along Lake Superior and well defined by gravity, magnetic, and seismic data. The GF, which results from collisions with Laurentia, is exposed in and identified by seismic and potential field data in Canada. In the eastern U.S., lineated gravity highs extending southward from Michigan to Alabama, along the trend of the front in Canada, have been interpreted either as a buried Grenville Front or as part of the MCR's east arm. We explore this issue by examining the gravity signatures of the MCR and GF. Both the MCR's arms have pronounced gravity highs, with the west arm's greater than the east arm's. Combining the gravity observations with seismic data suggests that the west arm contains 20–25 km thickness of volcanics, whereas the east arm contains 10–15 km of volcanics. Along the Grenville Front in Canada, thickened crust along the northern portion causes a broad gravity low, whereas the stacked thrusts along the southern portion cause essentially no gravity signature. Hence the lineated gravity highs in the eastern U.S. appear similar to those along the remainder of the MCR, and unlike those on either portion of the GF. These data favor the gravity anomalies traditionally interpreted as the Grenville Front in the eastern U.S. as instead being part of the MCR's east arm. A thrust sheet structure like that of the southern Canadian Grenville Front - which would have essentially no gravity effect - could also be present along the MCR's east arm, as implied by recent EarthScope seismic data.

Paleoproterozoic Iron Oxide Apatite (IOA) and Iron Oxide-Copper-Gold (IOCG) mineralization in the East Arm Basin, Northwest Territories, Canada

The Paleoproterozoic East Arm Basin of Canada hosts polymetallic vein, iron oxide–apatite (IOA), and potential iron oxide–copper–gold (IOCG) mineral occurrences, mainly associated with a belt of ca. 1.87 Ga intermediate-composition sills termed the Compton intrusions. Advances in our knowledge of the East Arm Basin and of IOA and IOCG deposits within the broader context of iron oxide and alkali-calcic alteration systems enables a new regional analysis of this mineralization and facilitates comparison of these mineral occurrences and host rocks to the nearby Great Bear magmatic zone IOCG districts. The Compton intrusions and co-magmatic Pearson Formation volcanic rocks are comparable in age and composition to intrusive plus volcanic rocks of the Great Bear magmatic zone that host IOA–IOCG mineralization. Taking into account fault displacements, emplacement of Compton intrusions and Pearson Formation volcanic rocks are also consistent with the architecture of modern arcs, supporting a direct relationship with the Great Bear subduction zone. Trace element patterns of uraninite contained in IOA occurrences of the East Arm Basin are also similar to the patterns of uraninite from the Great Bear magmatic zone occurrences, consistent with both regions having experienced similar iron oxide and alkali-calcic alteration and mineralization. Our new results indicate that exploration for IOA, IOCG, and affiliated deposits in the East Arm Basin should focus on delineating increased potassic-iron alteration types and fault/breccia zones associated with these systems through field mapping and application of geochemical, radiometric, magnetic, and gravity surveys.

English

Usipa Engraulicypris sardella is the most abundant small pelagic species in Lake Malawi. It plays an important part in the lake communities’ economy and food security. However, much remains unknown on their stock status and bioeconomic importance. This study is carried out to estimate the maximum economic yield and maximum sustainable yield for Usipa fishery in the South-east arm of Lake Malawi. Structured quantitative questionnaire was used to collect information from 139 informants on the price of usipa landings and cost of fishing effort. Catch and effort data for Usipa were used in a biomass dynamic model (ASPIC) to estimate key parameters (r, q and k). A bioeconomic model was further developed based on the Gordon- Schaefer model using cost and revenues of the Usipa fisheries to derive the Maximun Sustainable Yield (MSY) and the Maximum Economic Yield (MEY). Model estimates of MSY and MEY were 9,228.8 and 8,227.1 tonnes, respectively. The corresponding fishing effort was estimated to be 40,000 net-hauls and 30,000 net-hauls at MSY and MEY, respectively. Revenues at MSY were estimated at MWK42.280 billion, while at MEY the revenues were MWK39.309 billion. The analysis shows that the current effort of 65,232 net-hauls has a yield of 6,000 tonnes, indicating that the Usipa fishery is currently overexploited over the optimum bio-economic level and even beyond the open access yield. We recommend reducing the fishing effort by 54% to realize the best economic benefits (Production at MEY) and end overfishing to protect the fishery from biological and economic collapses. Key words: Usipa, bioeconomic, chilimira, catch per unit effort, maximum economic yield, South east arm.

Age and Paleobathymetry of Salodik Group in PohPagimana section, East Arm of Sulawesi Based on Foraminiferal Assemblages

Planktonic and benthic foraminiferal assemblages were used for age and paleobathymetry analysis of outcropping carbonate succession of the Salodik Group in Poh–Pagimana section, East Arm of Sulawesi. Twenty spot samples of carbonate rocks were collected from cut slope along the road between Poh and Pagimana. Age analysis conducted for each sample by its planktonic foraminifera assemblages and group into their age interval. The age range from Early Eocene to Pliocene. Benthic foraminiferal assemblages indicate paleobathymetry ranging from middle shelf to upper bathyal settings. Age analysis of the studied section show an older sediments (Early–Middle Eocene) overlie younger sediment (Early Miocene). This is interpreted as the evidence of thrust fault in the Poh–Pagimana section as part of thrust sheets of Batui thrust complex which imbricated on deformation zone. The youngest sediment which have suffered deformations shown by disordered age sequence is Pliocene in age (N20-21). The Eocene to Pliocene carbonate succession in the studied section was deposited relatively in the more basinward position compared to the carbonate-dominated sediments in the Tomori area which was deposited in the more landward position.

Darwin Harbour – a partnership approach to understanding and evaluating environmental challenges

Darwin Port plays a critical role in the Northern Territory’s export-oriented economy and in supporting the economy of northern Australia more generally. Darwin Port is the only true multi-modal port in northern Australia, with direct connectivity to southern Australia and beyond via the southern rail link. The port has developed rapidly over the past decades, with redevelopment of the Waterfront Precinct, development of numerous residential marinas, construction of the East Arm Wharf and marine supply base, and construction and operation of liquefied gas processing and export facilities. Future development plans include Middle Arm Industrial Precinct and Marine Industry Park. These developments have resulted in an order of magnitude increase in dredging requirements, an increase in vessel traffic and an increase in public focus on environmental quality within the harbour. A coordinated, multi-agency approach to understand the complex marine environment of Darwin Harbour has underpinned much of the development activity and provided a sound scientific basis to evaluate potential environmental impacts associate with past and future developments. Through a hierarchical process of environmental assessment and identification and mitigation potential risks, the Australian Institute of Marine Science has partnered with industry, government and other research providers to deliver projects to map and assess habitats, monitor environmental attributes and evaluate potential impacts, and provide environmental information in novel and accessible ways to support harbour operations and inform strategic planning. The partnership approach adopted for Darwin Harbour serves as a model for leveraging resources to understand and manage environmental and operational risks in northern ports.

Imaging the Velocity Structure of Rayleigh Wave in Sulawesi Island Using Ambient Noise Tomography

Ambient Noise Tomography (ANT) had been applied to describe the Rayleigh wave group velocity model in the crust part ofSulawesi Island. The research data were vertical component waveform data from July 2016 to December 2017 of 25 INA TEWSBMKG network seismograph in Sulawesi Island. In general, the steps of conducting research are divided into several parts,namely single data preparation, crosscorrelation and stacking, cross-correlogram analysis, measurement of dispersion curves,velocity tomography and the last is the interpretation of research results. The estimated travel time of the Rayleigh wave group for both 5 s and 12 s periods was obtained from the time delay of the cross-correlation result. The tomography process was conducted by using FMST v1.1 where forward and inverse modeling was performed iteratively. The modeling result for the period5 s showed that the distribution of negative anomalies corresponded to volcanoes and Inter-Volcano plains which were Quarterold. For the period 12 s, the east arm of Sulawesi Island had a lower velocity anomaly than around other regions on the Sulawesi Island. This indicated that the tectonic activity and geological condition of Sulawesi Island was complex.

Athapuscow aulacogen revisited: Geochronology and geochemistry of the 2046 Ma Union Island Group mafic magmatism, East Arm of Great Slave Lake, Northwest Territories, Canada

The Slave craton underwent widespread extension during the Paleoproterozoic. The East Arm basin of Great Slave Lake formed during this period and preserves a protracted record of sedimentation and volcanism in the southeastern Slave craton. Within the East Arm basin package, the Union Island Group represents voluminous mafic volcanism with subordinate sedimentary strata. We report the first high precision U–Pb zircon and baddeleyite dates for the Union Island Group; 2045.8 ± 1.0 Ma for a volcaniclastic unit from the lower basalt formation and 2042.7 ± 3.0 Ma for a diabase intrusion within volcaniclastic horizons in the lower basalt formation. We fundamentally revise the lower basin stratigraphy and demonstrate that the Union Island Group is the oldest identified supracrustal package in the East Arm basin, ∼120 Myr older than previously thought. This revised stratigraphy is supported by detrital zircon provenance age distribution in two Union Island Group sedimentary samples, which is dominated by 2.76–2.56 Ga ages, reflecting prominent input from the local Archean Slave basement.The Union Island Group contains two geochemically distinct mafic volcanic packages. The lower basalt package is predominantly alkaline, characterized by an OIB-like chemical signature with high and variable incompatible element contents (108–438 ppm Zr, 13–62 ppm Nb). In contrast, the upper basalt package is tholeiitic, contains much lower and uniform incompatible element contents (83–101 ppm Zr, 2–4 ppm Nb), and has an E-MORB-like chemical signature. Both packages display overlapping, depleted time-integrated εNd(i) values (+1.1 to +3.2). Petrological modeling suggests the lower package originated as OIB-like melts from the asthenosphere that interacted with a depleted reservoir; the upper package was produced by larger degree of partial melting of a similar mantle source, in addition to possible lithospheric input. The petrogenesis established in this study is consistent with a passive continental rift origin for the Union Island Group magmatism and is further supported by geochemical similarities with Proterozoic and Phanerozoic rift successions. We therefore propose that the 2046 Ma Union Island Group represents an incipient rift basin sequence formed during Paleoproterozoic extension that marked the initial breakup of the southern margin of the Slave craton from a pre-Laurentia supercontinent.