Pub Date : 2023-08-07DOI: 10.1080/08120099.2023.2237117
R. Blong
{"title":"Late Quaternary history of the Gumants catchment, Papua New Guinea","authors":"R. Blong","doi":"10.1080/08120099.2023.2237117","DOIUrl":"https://doi.org/10.1080/08120099.2023.2237117","url":null,"abstract":"","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45526748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-03DOI: 10.1080/08120099.2023.2237105
G. Phillips, J. Vearncombe, J. Clemens, A. Day, A. Kisters, B. Heyden, B. Waele
Abstract Copper–gold porphyry deposits are the world’s main source of copper and a significant source of gold. They consist of vein networks and their surrounding alteration zones. Commonly the deposits are centred on narrow intrusions (stocks), but calling these deposits ‘porphyries’ is unjustified because the name carries little descriptive or genetic value. Extensional veins were formed by hydraulic fracturing of the stocks, at depths where open spaces could not be maintained and where fluid pressure approaches lithostatic pressure. The post-crystallisation timing of the veins is important because it indicates that the host stocks could not have been the direct sources of either metals or ore-forming fluids. In the traditional magmatic model, precursor batholiths, lying at depth, are inferred to be the sources of the Cu and Au in the overlying host stocks. In this model, the batholiths are assumed to have crystallised and produced the mineralising aqueous fluids, Cu and Au. However, in many porphyry deposits, the concept of metal and fluid supply from deeper batholiths is problematic. Neither Cu nor Au is strongly enriched during the crystallisation of silicate magmas, and although hypersaline fluids are a characteristic of Cu–Au porphyry deposits globally, the source of the Cl remains unconstrained. There is little evidence that silicate magmas can release such Cl-rich fluids, and it remains unexplained how elevated levels of Cl may be achieved in a silicate magma. Therefore, the starting assumption that these deposits formed predominantly from magmatic sources and processes is questioned. This study has selectively focused on the roles of rheology, rock mechanics, vein control, metal-enrichment processes and the sources of Cl. Non-magmatic processes may be enough to facilitate strong partitioning of Cu and Au into high-temperature, oxidising, high-salinity, hydrothermal fluids to form Cu–Au porphyry deposits. KEY POINTS Mineralised quartz veins were introduced in fluids during hydraulic fracturing of their host intrusions when these stocks were brittle and had cooled significantly below their solidus temperatures. The porphyry intrusions hosting Cu–Au (copper–gold) mineralisation were not the direct sources of either the fluids or the metals. The sources of Cu and Au included large volumes of surrounding and underlying rocks up to kilometres from the sites of deposition. Cu and Au do not become strongly concentrated during crystal fractionation in evolving silicate magmas. Unaltered igneous rocks have relatively low Cl contents, and experiments suggest low Cl solubilities in granitic to granodioritic magmas. It is highly unlikely that all the Cl required for metal complexing and transport was available from within silicate magmas.
{"title":"Formation of Cu–Au porphyry deposits: hydraulic quartz veins, magmatic processes and constraints from chlorine","authors":"G. Phillips, J. Vearncombe, J. Clemens, A. Day, A. Kisters, B. Heyden, B. Waele","doi":"10.1080/08120099.2023.2237105","DOIUrl":"https://doi.org/10.1080/08120099.2023.2237105","url":null,"abstract":"Abstract Copper–gold porphyry deposits are the world’s main source of copper and a significant source of gold. They consist of vein networks and their surrounding alteration zones. Commonly the deposits are centred on narrow intrusions (stocks), but calling these deposits ‘porphyries’ is unjustified because the name carries little descriptive or genetic value. Extensional veins were formed by hydraulic fracturing of the stocks, at depths where open spaces could not be maintained and where fluid pressure approaches lithostatic pressure. The post-crystallisation timing of the veins is important because it indicates that the host stocks could not have been the direct sources of either metals or ore-forming fluids. In the traditional magmatic model, precursor batholiths, lying at depth, are inferred to be the sources of the Cu and Au in the overlying host stocks. In this model, the batholiths are assumed to have crystallised and produced the mineralising aqueous fluids, Cu and Au. However, in many porphyry deposits, the concept of metal and fluid supply from deeper batholiths is problematic. Neither Cu nor Au is strongly enriched during the crystallisation of silicate magmas, and although hypersaline fluids are a characteristic of Cu–Au porphyry deposits globally, the source of the Cl remains unconstrained. There is little evidence that silicate magmas can release such Cl-rich fluids, and it remains unexplained how elevated levels of Cl may be achieved in a silicate magma. Therefore, the starting assumption that these deposits formed predominantly from magmatic sources and processes is questioned. This study has selectively focused on the roles of rheology, rock mechanics, vein control, metal-enrichment processes and the sources of Cl. Non-magmatic processes may be enough to facilitate strong partitioning of Cu and Au into high-temperature, oxidising, high-salinity, hydrothermal fluids to form Cu–Au porphyry deposits. KEY POINTS Mineralised quartz veins were introduced in fluids during hydraulic fracturing of their host intrusions when these stocks were brittle and had cooled significantly below their solidus temperatures. The porphyry intrusions hosting Cu–Au (copper–gold) mineralisation were not the direct sources of either the fluids or the metals. The sources of Cu and Au included large volumes of surrounding and underlying rocks up to kilometres from the sites of deposition. Cu and Au do not become strongly concentrated during crystal fractionation in evolving silicate magmas. Unaltered igneous rocks have relatively low Cl contents, and experiments suggest low Cl solubilities in granitic to granodioritic magmas. It is highly unlikely that all the Cl required for metal complexing and transport was available from within silicate magmas.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"1010 - 1033"},"PeriodicalIF":1.2,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44808498","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-27DOI: 10.1080/08120099.2023.2234964
A. Edgar, I. Sanislav, P. Dirks
Abstract The Clarke River Fault in northeast Queensland records an early Paleozoic history of subduction, accretion and continental suturing. Samples of mafic–ultramafic rocks collected proximal to the Clarke River Fault record oceanic geochemical affinities and comprise alteration assemblages consistent with an ophiolitic origin. The ca 456 Ma Falls Creek Tonalite records a continental-arc geochemical signature and was formed in response to long-lived subduction beneath the Thomson Orogen. Ordovician subduction beneath the Thomson Orogen is broadly coeval with arc magmatism documented in the Lachlan Orogen, which has been associated with the formation of several large porphyry ore deposits. The Falls Creek Tonalite yields adakite-like geochemical signatures that reflect a fertile melt source conducive to the formation of porphyry ore deposits. The outcropping plutons record ductile deformation consistent with mid-crustal depths, and they were emplaced during late syntectonic activity. This implies that the Falls Creek Tonalite was emplaced at too great a depth to have formed porphyry ore deposits. The northern Charters Towers Province shares many geological similarities to the Greenvale Province, where the erosional level may be shallower, and the potential for porphyry deposit formation and preservation may be greater. KEY POINTS Mafic–ultramafic rocks situated along the Clarke River Fault are of ophiolitic origin. The Clarke River Fault is an early Paleozoic suture zone. The northern Tasmanides contain adakitic plutons formed from hydrous, fertile melts, conducive to the formation of porphyry ore deposits.
{"title":"The origin of mafic–ultramafic rocks and felsic plutons along the Clarke River suture zone: implications for porphyry exploration in the northern Tasmanides","authors":"A. Edgar, I. Sanislav, P. Dirks","doi":"10.1080/08120099.2023.2234964","DOIUrl":"https://doi.org/10.1080/08120099.2023.2234964","url":null,"abstract":"Abstract The Clarke River Fault in northeast Queensland records an early Paleozoic history of subduction, accretion and continental suturing. Samples of mafic–ultramafic rocks collected proximal to the Clarke River Fault record oceanic geochemical affinities and comprise alteration assemblages consistent with an ophiolitic origin. The ca 456 Ma Falls Creek Tonalite records a continental-arc geochemical signature and was formed in response to long-lived subduction beneath the Thomson Orogen. Ordovician subduction beneath the Thomson Orogen is broadly coeval with arc magmatism documented in the Lachlan Orogen, which has been associated with the formation of several large porphyry ore deposits. The Falls Creek Tonalite yields adakite-like geochemical signatures that reflect a fertile melt source conducive to the formation of porphyry ore deposits. The outcropping plutons record ductile deformation consistent with mid-crustal depths, and they were emplaced during late syntectonic activity. This implies that the Falls Creek Tonalite was emplaced at too great a depth to have formed porphyry ore deposits. The northern Charters Towers Province shares many geological similarities to the Greenvale Province, where the erosional level may be shallower, and the potential for porphyry deposit formation and preservation may be greater. KEY POINTS Mafic–ultramafic rocks situated along the Clarke River Fault are of ophiolitic origin. The Clarke River Fault is an early Paleozoic suture zone. The northern Tasmanides contain adakitic plutons formed from hydrous, fertile melts, conducive to the formation of porphyry ore deposits.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46759491","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-23DOI: 10.1080/08120099.2023.2232436
S. Kharajiany
Abstract The middle Miocene Fatha Formation is a prominent cap rock for hydrocarbon accumulations in Iraq’s oil fields. It is widely distributed in the Low Folded Zone but less common in the High Folded Zone of Iraq. For the first time, a nannostratigraphic study has been conducted on the formation at the Miryas locality in the High Folded Zone of the Qaradagh Mountain Series, southwest of Sulaimaniyah, Kurdistan Region, Iraq. The Fatha Formation consists of claystone, siltstone, marlstone, gypsum and few limestone beds. Ten samples were taken from marl-rich strata in the upper part of the formation between the red claystones of the Miryas. On the basis of the identified calcareous nannofossils, three biozones are recorded from the upper part of the Fatha Formation: the NN1, NN2 and NN3 zones. The combined stratigraphic ranges of the calcareous nannofossils identified here support the early Miocene–Aquitanian age; Discoaster druggii, Sphenolithus belemnos, S. cometa, S. procerus, S. tintinnabulum, S. delphix and S. capricornutus are marker species of the Aquitanian that have been identified inside the Miryas’s smear slides. These genera/species are also accompanied by the occurrences of Sphenolithus moriformis, Cyclicargolithus floridanus, Reticulofenestra minuta, R. bisecta, S. minuta, S. dictyoda, Coccolithus pelagicus, Helicosphaera carteri and Coronocyclus nitescens. The appearance of Discoaster saundersi at the top of the formation indicates the last occurrence of the NN2 zone of the Aquitanian and first occurrence of the NN3 zone of the Burdigalian. Through this study, for the first time, the early Miocene biozones determined within the Fatha Formation indicate that lower Miocene sediments (facies) were not deposited at some locations in the Qaradagh Mountain Series. Instead, the equivalent cap rock sediments of the Fatha Formation were deposited in the High Folded Zone; this clarifies why accumulation of hydrocarbons is rare within the late Oligocene–earliest Miocene succession in the High Folded Zone rather than the reservoir rocks of the same age in the Low Folded Zone (such as Kirkuk Oil Fields). KEY POINTS First study of nannostratigraphy of the Fatha Formation in the High Folded Zone of Iraq. First study of early Miocene nanno-biozones within the Fatha Formation. First record of NN1, NN2 and NN3 zones within the Fatha Formation.
{"title":"Calcareous-nannofossil biostratigraphy of the Miocene Fatha Formation at the Miryas section, Qaradagh Mountain Series, Sulaimaniyah, Kurdistan Region, Iraq","authors":"S. Kharajiany","doi":"10.1080/08120099.2023.2232436","DOIUrl":"https://doi.org/10.1080/08120099.2023.2232436","url":null,"abstract":"Abstract The middle Miocene Fatha Formation is a prominent cap rock for hydrocarbon accumulations in Iraq’s oil fields. It is widely distributed in the Low Folded Zone but less common in the High Folded Zone of Iraq. For the first time, a nannostratigraphic study has been conducted on the formation at the Miryas locality in the High Folded Zone of the Qaradagh Mountain Series, southwest of Sulaimaniyah, Kurdistan Region, Iraq. The Fatha Formation consists of claystone, siltstone, marlstone, gypsum and few limestone beds. Ten samples were taken from marl-rich strata in the upper part of the formation between the red claystones of the Miryas. On the basis of the identified calcareous nannofossils, three biozones are recorded from the upper part of the Fatha Formation: the NN1, NN2 and NN3 zones. The combined stratigraphic ranges of the calcareous nannofossils identified here support the early Miocene–Aquitanian age; Discoaster druggii, Sphenolithus belemnos, S. cometa, S. procerus, S. tintinnabulum, S. delphix and S. capricornutus are marker species of the Aquitanian that have been identified inside the Miryas’s smear slides. These genera/species are also accompanied by the occurrences of Sphenolithus moriformis, Cyclicargolithus floridanus, Reticulofenestra minuta, R. bisecta, S. minuta, S. dictyoda, Coccolithus pelagicus, Helicosphaera carteri and Coronocyclus nitescens. The appearance of Discoaster saundersi at the top of the formation indicates the last occurrence of the NN2 zone of the Aquitanian and first occurrence of the NN3 zone of the Burdigalian. Through this study, for the first time, the early Miocene biozones determined within the Fatha Formation indicate that lower Miocene sediments (facies) were not deposited at some locations in the Qaradagh Mountain Series. Instead, the equivalent cap rock sediments of the Fatha Formation were deposited in the High Folded Zone; this clarifies why accumulation of hydrocarbons is rare within the late Oligocene–earliest Miocene succession in the High Folded Zone rather than the reservoir rocks of the same age in the Low Folded Zone (such as Kirkuk Oil Fields). KEY POINTS First study of nannostratigraphy of the Fatha Formation in the High Folded Zone of Iraq. First study of early Miocene nanno-biozones within the Fatha Formation. First record of NN1, NN2 and NN3 zones within the Fatha Formation.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49577427","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-20DOI: 10.1080/08120099.2023.2230598
D. Frankel, D. Thomas, R. Kurpiel, C. Spry, J. Tumney, L. Becerra-Valdivia, Bunurong Land Council, Aboriginal Corporation, B. Jones
Abstract Evidence from bay floor channelling, seismic surveys and core dating has been used to suggest that Port Phillip Bay dried out for a period between about 2800 and 1000 cal. yr BP as sandbars blocked it off from the sea. This model is now supported by the examination of radiocarbon ages from archaeological excavations of Aboriginal shell middens on the shoreline of the Mornington Peninsula on Bunurong Country. This shows a near-continuous use of marine resources by Bunurong people over the last 6000 years for areas south of Rosebud, while those to the north are only of more recent date, following the refilling of the bay in the last millennium. This study provides an example of the integration of traditional, archaeological and geoscience evidence and the way in which local environmental changes impact on society. KEY POINTS Radiocarbon dates from Aboriginal places support the argument that a sandbar blocked much of Port Phillip Bay from the sea between about 2800 and 1000 cal. yr BP. Dates from Aboriginal places south of the sand bar show continuity since the bay formed following the post-Pleistocene rise in sea-levels. Dates north of the sandbar indicate that Aboriginal people began exploiting marine resources in this area once the bay refilled about 1000 years ago.
{"title":"Late Holocene drying of Port Phillip Bay: archaeological and cultural perspectives","authors":"D. Frankel, D. Thomas, R. Kurpiel, C. Spry, J. Tumney, L. Becerra-Valdivia, Bunurong Land Council, Aboriginal Corporation, B. Jones","doi":"10.1080/08120099.2023.2230598","DOIUrl":"https://doi.org/10.1080/08120099.2023.2230598","url":null,"abstract":"Abstract Evidence from bay floor channelling, seismic surveys and core dating has been used to suggest that Port Phillip Bay dried out for a period between about 2800 and 1000 cal. yr BP as sandbars blocked it off from the sea. This model is now supported by the examination of radiocarbon ages from archaeological excavations of Aboriginal shell middens on the shoreline of the Mornington Peninsula on Bunurong Country. This shows a near-continuous use of marine resources by Bunurong people over the last 6000 years for areas south of Rosebud, while those to the north are only of more recent date, following the refilling of the bay in the last millennium. This study provides an example of the integration of traditional, archaeological and geoscience evidence and the way in which local environmental changes impact on society. KEY POINTS Radiocarbon dates from Aboriginal places support the argument that a sandbar blocked much of Port Phillip Bay from the sea between about 2800 and 1000 cal. yr BP. Dates from Aboriginal places south of the sand bar show continuity since the bay formed following the post-Pleistocene rise in sea-levels. Dates north of the sandbar indicate that Aboriginal people began exploiting marine resources in this area once the bay refilled about 1000 years ago.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"890 - 897"},"PeriodicalIF":1.2,"publicationDate":"2023-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46469591","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-17DOI: 10.1080/08120099.2023.2218452
B. Hobbs, A. Ord, J. Vearncombe
Abstract This paper proposes a mechanism called the mode-switching model that is presented as an alternative to the fault-valve model. This mechanism is relevant to open-flow, low-porosity, fluid-saturated systems deforming by pressure solution creep. As opposed to most constitutive models discussed in the geological literature, the yield envelope is capped at high normal stresses, as demonstrated by experimental studies. A low-permeability rock has relatively high pore fluid pressure for a given input fluid flux. This increases the dissolution rate for quartz that in turn leads to a higher-permeability rock, low fluid pressure for the same flux and decreased quartz solubility and deposition, returning to a low permeability. This cycle continues indefinitely so long as the rock mass is stressed, a fluid flux is applied, and pressure solution operates. The high fluid pressure drives the Mohr stress circle to the tensile end of the yield envelope resulting in crack-seal and extensional veins. The low fluid pressure drives the Mohr stress circle to the cap end of the yield envelope resulting in laminated veins in rocks undergoing mineral reactions with large net volume losses coupled with solute transfer. Failure at the cap end of the yield envelope results in displacement discontinuities inclined at high angles to σ 1. Previously, these orientations have been taken to represent reactivated normal faults, an integral component of the fault-valve process. In the model presented, the yield surface prohibits the system ever reaching super-lithostatic pressures. The process of effective stress-driven switching between tensile and cap ends of the yield envelope arises from competition between dissolution and deposition, and is independent of any seismic events, fault reactivation or the episodic breaching of an impermeable seal. It provides a unifying, self-consistent concept for the interpretation of joints, faults and veins in hydrothermal systems. KEY POINTS The open-ended Mohr–Coulomb yield surface is replaced by a capped yield surface, closed at high normal stresses. Failure can occur with decreased fluid pressures resulting in non-Andersonian orientations of failure discontinuities such as veins at high angles to σ 1. Pressure solution in open-flow hydrothermal systems leads to alternations of failure modes at the tensile and cap ends of the yield surface with no need for a seal. Stress-driven oscillations in failure modes, resulting in episodic fluid flow and episodic formation of Andersonian and non-Andersonian failure modes, are an aseismic alternative to fault-valve behaviour.
{"title":"An alternative to the fault-valve model","authors":"B. Hobbs, A. Ord, J. Vearncombe","doi":"10.1080/08120099.2023.2218452","DOIUrl":"https://doi.org/10.1080/08120099.2023.2218452","url":null,"abstract":"Abstract This paper proposes a mechanism called the mode-switching model that is presented as an alternative to the fault-valve model. This mechanism is relevant to open-flow, low-porosity, fluid-saturated systems deforming by pressure solution creep. As opposed to most constitutive models discussed in the geological literature, the yield envelope is capped at high normal stresses, as demonstrated by experimental studies. A low-permeability rock has relatively high pore fluid pressure for a given input fluid flux. This increases the dissolution rate for quartz that in turn leads to a higher-permeability rock, low fluid pressure for the same flux and decreased quartz solubility and deposition, returning to a low permeability. This cycle continues indefinitely so long as the rock mass is stressed, a fluid flux is applied, and pressure solution operates. The high fluid pressure drives the Mohr stress circle to the tensile end of the yield envelope resulting in crack-seal and extensional veins. The low fluid pressure drives the Mohr stress circle to the cap end of the yield envelope resulting in laminated veins in rocks undergoing mineral reactions with large net volume losses coupled with solute transfer. Failure at the cap end of the yield envelope results in displacement discontinuities inclined at high angles to σ 1. Previously, these orientations have been taken to represent reactivated normal faults, an integral component of the fault-valve process. In the model presented, the yield surface prohibits the system ever reaching super-lithostatic pressures. The process of effective stress-driven switching between tensile and cap ends of the yield envelope arises from competition between dissolution and deposition, and is independent of any seismic events, fault reactivation or the episodic breaching of an impermeable seal. It provides a unifying, self-consistent concept for the interpretation of joints, faults and veins in hydrothermal systems. KEY POINTS The open-ended Mohr–Coulomb yield surface is replaced by a capped yield surface, closed at high normal stresses. Failure can occur with decreased fluid pressures resulting in non-Andersonian orientations of failure discontinuities such as veins at high angles to σ 1. Pressure solution in open-flow hydrothermal systems leads to alternations of failure modes at the tensile and cap ends of the yield surface with no need for a seal. Stress-driven oscillations in failure modes, resulting in episodic fluid flow and episodic formation of Andersonian and non-Andersonian failure modes, are an aseismic alternative to fault-valve behaviour.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"958 - 971"},"PeriodicalIF":1.2,"publicationDate":"2023-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43350624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-13DOI: 10.1080/08120099.2023.2221326
Y. Zhu, J. Liu, H. Wang, G. Hong, H. Dong, Z. Chen, A. Andrew
Abstract The Pliocene shelf-edge delta (SED) in the Papuan Basin was formed by deposition of the Pliocene Orubadi Formation. On the basis of a comprehensive analysis of seismic, wireline and mud logging, and paleontological data, the stratigraphic framework, depositional system and controlling factors on the SED development were established. The Orubadi Formation includes a parallel unconformity. Internally, two third-order sequences (SQ1/SQ2) are identified, and system tracts within the sequence layers are determined by the onlaps. By tracing changes in the shoreline trajectories within the sequence, the SED was divided into six phases in the study area, with seaward advances of ∼1543–5400 m during a single phase. The thickness of the foreset is ∼309–887 m, exhibiting sigmoid or sigmoid-tangential seismic reflections. The stratigraphic patterns and sedimentary system evolution of the Orubadi Formation are determined by the interplay between sea-level changes, sediment supply, tectonic evolution and paleogeomorphology. The Coral Sea spreading provided accommodation for the SED. The Miocene–Pliocene uplift and the middle Miocene arc–continent collision in northern PNG, which caused uplift and erosion of mountains in the late Miocene to Pliocene, is the major source of sediments. The large sediment supply and sea-level changes from SQ1–SQ2 indicate an overall relative sea-level fall resulted in rapid shelf margin advancement into the basin, with the Miocene carbonate platform edge providing the necessary slope conditions for material transport. This abundant sediment supply led to the significant development of the SED. This study provides robust insights for deep-water oil and gas exploration in the Papuan Basin. KEY POINTS The Pliocene shelf-edge delta (SED) in the Papuan Basin was formed in a compression setting with arc–continent collision. In the Orubadi Formation, the overall trend of sea-level change is decreasing, and the delta is divided into six stages. The Pliocene SED is controlled by the interplay between sea-level changes, sediment supply, tectonic evolution and paleogeomorphological.
{"title":"Sedimentary characteristics and controlling factors of a Pliocene shelf-edge delta in the Papuan Basin","authors":"Y. Zhu, J. Liu, H. Wang, G. Hong, H. Dong, Z. Chen, A. Andrew","doi":"10.1080/08120099.2023.2221326","DOIUrl":"https://doi.org/10.1080/08120099.2023.2221326","url":null,"abstract":"Abstract The Pliocene shelf-edge delta (SED) in the Papuan Basin was formed by deposition of the Pliocene Orubadi Formation. On the basis of a comprehensive analysis of seismic, wireline and mud logging, and paleontological data, the stratigraphic framework, depositional system and controlling factors on the SED development were established. The Orubadi Formation includes a parallel unconformity. Internally, two third-order sequences (SQ1/SQ2) are identified, and system tracts within the sequence layers are determined by the onlaps. By tracing changes in the shoreline trajectories within the sequence, the SED was divided into six phases in the study area, with seaward advances of ∼1543–5400 m during a single phase. The thickness of the foreset is ∼309–887 m, exhibiting sigmoid or sigmoid-tangential seismic reflections. The stratigraphic patterns and sedimentary system evolution of the Orubadi Formation are determined by the interplay between sea-level changes, sediment supply, tectonic evolution and paleogeomorphology. The Coral Sea spreading provided accommodation for the SED. The Miocene–Pliocene uplift and the middle Miocene arc–continent collision in northern PNG, which caused uplift and erosion of mountains in the late Miocene to Pliocene, is the major source of sediments. The large sediment supply and sea-level changes from SQ1–SQ2 indicate an overall relative sea-level fall resulted in rapid shelf margin advancement into the basin, with the Miocene carbonate platform edge providing the necessary slope conditions for material transport. This abundant sediment supply led to the significant development of the SED. This study provides robust insights for deep-water oil and gas exploration in the Papuan Basin. KEY POINTS The Pliocene shelf-edge delta (SED) in the Papuan Basin was formed in a compression setting with arc–continent collision. In the Orubadi Formation, the overall trend of sea-level change is decreasing, and the delta is divided into six stages. The Pliocene SED is controlled by the interplay between sea-level changes, sediment supply, tectonic evolution and paleogeomorphological.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"859 - 875"},"PeriodicalIF":1.2,"publicationDate":"2023-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44951373","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-13DOI: 10.1080/08120099.2023.2225570
J-L. Liu, F. Sun, Y-H Zhou
Abstract The Guandi and Banshigou iron deposits of southern Jilin Province, China, are Algoma-type banded iron formations (BIFs) located in the Eastern Block of the North China Craton (NCC). LA–ICP–MS U–Pb dating shows the magmatic zircons in plagioclase amphibolite from the Guandi BIF (PA–GD) and plagioclase hornblende gneiss from the Banshigou BIF (PHG–BSG) were crystallised at 2556 ± 17 Ma and 2545 ± 27 Ma, respectively, representing the formation age of the BIFs. Metamorphic overgrowth zircons from both samples gave two U–Pb ages of 2452 ± 23 Ma and 2446 ± 70 Ma, indicating the age of metamorphism. The zircon εHf(t) values of PA–GD (–1.3 to +2.8) and PHG–BSG (–1.5 to +2.7) indicate that the magma source was derived from depleted mantle with contamination of crustal material. According to our study, the PA–GD and PHG–BSG were formed in an island arc setting and support previously proposed subduction zone tectonic models for the northeastern NCC during the Neoarchean. KEY POINTS The magmatic zircons from the PA–GD and PHG–BSG were crystallised at 2556 ± 17 Ma and 2545 ± 27 Ma, which represents the formation age of the BIFs. The metamorphic overgrowth zircons from the PA–GD and PHG–BSG gave two ages of 2452 ± 23 Ma and 2446 ± 70 Ma, which represent the age of metamorphism. Major-element and REE data indicate that BIFs precipitated in a mixture of seawater and hydrothermal fluids in an anoxic environment. Geochemical and Hf isotope characteristics of BIFs’ wall rock indicate that the source magma was derived from a depleted mantle wedge metasomatised by subduction-slab melts and contaminated by ancient crust, formed in an island arc setting.
{"title":"The isotope geochemistry of host rocks of the late Archean Guandi and Banshigou banded iron formations, southern Jilin Province: temporal and tectonic significance","authors":"J-L. Liu, F. Sun, Y-H Zhou","doi":"10.1080/08120099.2023.2225570","DOIUrl":"https://doi.org/10.1080/08120099.2023.2225570","url":null,"abstract":"Abstract The Guandi and Banshigou iron deposits of southern Jilin Province, China, are Algoma-type banded iron formations (BIFs) located in the Eastern Block of the North China Craton (NCC). LA–ICP–MS U–Pb dating shows the magmatic zircons in plagioclase amphibolite from the Guandi BIF (PA–GD) and plagioclase hornblende gneiss from the Banshigou BIF (PHG–BSG) were crystallised at 2556 ± 17 Ma and 2545 ± 27 Ma, respectively, representing the formation age of the BIFs. Metamorphic overgrowth zircons from both samples gave two U–Pb ages of 2452 ± 23 Ma and 2446 ± 70 Ma, indicating the age of metamorphism. The zircon εHf(t) values of PA–GD (–1.3 to +2.8) and PHG–BSG (–1.5 to +2.7) indicate that the magma source was derived from depleted mantle with contamination of crustal material. According to our study, the PA–GD and PHG–BSG were formed in an island arc setting and support previously proposed subduction zone tectonic models for the northeastern NCC during the Neoarchean. KEY POINTS The magmatic zircons from the PA–GD and PHG–BSG were crystallised at 2556 ± 17 Ma and 2545 ± 27 Ma, which represents the formation age of the BIFs. The metamorphic overgrowth zircons from the PA–GD and PHG–BSG gave two ages of 2452 ± 23 Ma and 2446 ± 70 Ma, which represent the age of metamorphism. Major-element and REE data indicate that BIFs precipitated in a mixture of seawater and hydrothermal fluids in an anoxic environment. Geochemical and Hf isotope characteristics of BIFs’ wall rock indicate that the source magma was derived from a depleted mantle wedge metasomatised by subduction-slab melts and contaminated by ancient crust, formed in an island arc setting.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"876 - 889"},"PeriodicalIF":1.2,"publicationDate":"2023-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47098444","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-28DOI: 10.1080/08120099.2023.2220120
J. Clemens, C. Fergusson
Abstract Age distributions among the detrital zircon populations in western and central Victorian Paleozoic metasedimentary rocks suggest that most were deposited in Andean-type back-arc environments, with variable proportions of arc and continental sediment sources. Notable exceptions are the upper Cambrian Knowsley East Shale and the Silurian(?) sample of ‘Glen Creek Lithic Sandstone’, which both contain unimodal zircon populations. In the case of the Knowsley East Shale, this age is very close to the inferred depositional age, implying a possible forearc environment, with sediment derived directly from the contemporary volcanic arc. On the other hand, the implied trench environment for the ‘Glen Creek Lithic Sandstone’ is most likely inherited from its very local sediment source in the fault-bounded and mainly Cambrian Glen Creek erosional window. The only analysed rock units that may have been deposited in non-arc settings are the middle Silurian Humevale Siltstone and the Lower Devonian Norton Gully Sandstone. The zircon populations in these units carry strong continental signals, and they may have been deposited in an extensional marine basin bounded by continental blocks. The upper Silurian Grampians Group may have been deposited in a similar rift setting, but the zircon age histogram for this unit suggests that it was more proximal to an arc terrane. These assignments of depositional/tectonic environment should be regarded as indicative only, particularly since the method provides only subtle distinctions between some extensional and convergent settings. However, if the assignments are correct, there are some important implications for the geological history of this part of the Lachlan Orogen. For example, contrary to present perceptions, the Stawell Zone rocks may not have been prominently uplifted during the Ordovician, and the basin in the Bendigo Zone may have been receiving sediment input from further west in the Grampians–Stavely Zone. Key points Early Cambrian to Early Devonian sedimentation in western and central Victoria occurred mainly in back-arc marine basins, initially associated with an Andean-type margin. Locally, some Cambrian sediments were formed in trench or forearc environments, with detritus supplied directly from a contemporary volcanic arc. Cambrian to Silurian back-arc sediments were deposited at varying distances from any active or former arc terranes and with varying but always major contributions of continent-derived sediments. Early Devonian sediments in the Melbourne Zone may have been deposited in what was effectively an intracontinental marine rift.
摘要维多利亚时代西部和中部古生代变质沉积岩碎屑锆石种群的年龄分布表明，大多数沉积在安第斯型弧后环境中，弧源和大陆沉积源的比例各不相同。值得注意的例外是上寒武纪诺斯利东部页岩和志留纪（？）的“Glen Creek Lithic Sandstone”样品，它们都含有单峰锆石种群。就诺斯利东页岩而言，该年龄与推断的沉积年龄非常接近，这意味着可能存在弧前环境，沉积物直接来自当代火山弧。另一方面，“Glen Creek Lithic Sandstone”的隐含沟槽环境很可能是从断层边界的、主要是寒武纪Glen Creck侵蚀窗中的非常局部的沉积物来源继承而来的。唯一被分析的可能在非弧形环境中沉积的岩石单元是志留纪中期的Humvale粉砂岩和下泥盆纪的Norton Gully砂岩。这些单元中的锆石种群带有强烈的大陆信号，它们可能沉积在以大陆块为界的伸展海洋盆地中。上志留系Grampians群可能沉积在类似的裂谷环境中，但该单元的锆石年龄直方图表明，它更接近弧形地体。沉积/构造环境的这些分配应被视为只是指示性的，特别是因为该方法只提供了一些伸展和会聚环境之间的细微区别。然而，如果任务是正确的，则对拉克伦造山带这一部分的地质历史有一些重要意义。例如，与目前的看法相反，Stawell带的岩石在奥陶纪期间可能没有显著隆起，本迪戈带的盆地可能一直在接受来自Grampians–Stavely带更西部的沉积物输入。维多利亚州西部和中部的早寒武纪至早泥盆纪沉积主要发生在弧后海洋盆地，最初与安第斯型边缘有关。在当地，一些寒武纪沉积物是在海沟或弧前环境中形成的，碎屑直接来自当代火山弧。寒武纪至志留纪弧后沉积物沉积在距离任何活动或弧前地体不同的距离处，并且大陆沉积物的贡献各不相同，但始终是主要的。墨尔本带的早泥盆纪沉积物可能沉积在实际上是陆内海洋裂谷的地方。
{"title":"Zircon age distributions and implied tectonic settings of early Cambrian to Early Devonian sedimentation in western and central Victoria","authors":"J. Clemens, C. Fergusson","doi":"10.1080/08120099.2023.2220120","DOIUrl":"https://doi.org/10.1080/08120099.2023.2220120","url":null,"abstract":"Abstract Age distributions among the detrital zircon populations in western and central Victorian Paleozoic metasedimentary rocks suggest that most were deposited in Andean-type back-arc environments, with variable proportions of arc and continental sediment sources. Notable exceptions are the upper Cambrian Knowsley East Shale and the Silurian(?) sample of ‘Glen Creek Lithic Sandstone’, which both contain unimodal zircon populations. In the case of the Knowsley East Shale, this age is very close to the inferred depositional age, implying a possible forearc environment, with sediment derived directly from the contemporary volcanic arc. On the other hand, the implied trench environment for the ‘Glen Creek Lithic Sandstone’ is most likely inherited from its very local sediment source in the fault-bounded and mainly Cambrian Glen Creek erosional window. The only analysed rock units that may have been deposited in non-arc settings are the middle Silurian Humevale Siltstone and the Lower Devonian Norton Gully Sandstone. The zircon populations in these units carry strong continental signals, and they may have been deposited in an extensional marine basin bounded by continental blocks. The upper Silurian Grampians Group may have been deposited in a similar rift setting, but the zircon age histogram for this unit suggests that it was more proximal to an arc terrane. These assignments of depositional/tectonic environment should be regarded as indicative only, particularly since the method provides only subtle distinctions between some extensional and convergent settings. However, if the assignments are correct, there are some important implications for the geological history of this part of the Lachlan Orogen. For example, contrary to present perceptions, the Stawell Zone rocks may not have been prominently uplifted during the Ordovician, and the basin in the Bendigo Zone may have been receiving sediment input from further west in the Grampians–Stavely Zone. Key points Early Cambrian to Early Devonian sedimentation in western and central Victoria occurred mainly in back-arc marine basins, initially associated with an Andean-type margin. Locally, some Cambrian sediments were formed in trench or forearc environments, with detritus supplied directly from a contemporary volcanic arc. Cambrian to Silurian back-arc sediments were deposited at varying distances from any active or former arc terranes and with varying but always major contributions of continent-derived sediments. Early Devonian sediments in the Melbourne Zone may have been deposited in what was effectively an intracontinental marine rift.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"801 - 814"},"PeriodicalIF":1.2,"publicationDate":"2023-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44696851","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-28DOI: 10.1080/08120099.2023.2222795
G. Williams, A. Andrew
Abstract Vertically accreted, cyclic tidal rhythmites—laminated, fine-grained sandstones, siltstones and mudstones—occur in the late Cryogenian glaciogenic Elatina Formation (ca 635 Ma) and early Cryogenian Sturt Formation (ca 660 Ma) in the South Flinders Ranges region of the Adelaide Rift Complex within the Adelaide Superbasin, and in Cryogenian strata from Nicholson 2 drill hole in the eastern Officer Basin, South Australia. The rhythmites provide insights into Cryogenian littoral environments. The Elatina rhythmite was deposited during an interstadial and the Sturt rhythmite during early glacial advance, whereas the Nicholson 2 rhythmite is assigned to interglacial beds. The resultant raised sea levels and drowned valleys provided the tidal inlets, ebb-tidal deltas, estuaries and fjords favouring rhythmite deposition. The rhythmites display semidiurnal and diurnal (lunar day) tidal laminae grouped in fortnightly neap–spring cycles and record the semiannual tide. Periods of 26.2 ± 0.9 neap–spring cycles displayed by the Elatina rhythmite and ∼27 neap–spring cycles by the Nicholson 2 rhythmite mark the non-tidal annual variation of sea level, which results from seasonal surface winds and changes in atmospheric pressure and temperature acting on the waters of marine shelves and marginal seas. The strong annual signals and absence of dropstones in the Elatina and Nicholson 2 rhythmites indicate that respective marine shelves and marginal seas were ice-free during rhythmite deposition. The Sturt rhythmite, by contrast, shows a weak annual period of ∼27 neap–spring cycles and contains dropstones and till pellets, indicating that the adjacent marine shelf and sea were largely ice-covered. Paleotidal data for the Elatina rhythmite have illuminated Earth’s late Cryogenian paleorotation and the Moon’s orbit, and paleomagnetic studies of the Elatina rhythmite indicated a low paleolatitude for late Cryogenian glaciation. Contrary to recent modelling by others, strong tides existed at shallow-water continental margins during Cryogenian glaciations. Key Points Cyclic tidal rhythmites are associated with early and late Cryogenian (ca 660 and ca 635 Ma) glaciogenic successions and interglacial beds in South Australia. Rhythmite deposition occurred when raised sea levels provided the coastal environments favouring rhythmite deposition. The rhythmites display semidiurnal and diurnal tidal laminae grouped in fortnightly cycles, and record the semiannual tide and the non-tidal annual variation of sea level. Strong tides existed at shallow-water continental margins during early and late Cryogenian low-latitude glaciations and the interglacial interval.
{"title":"Strong tides during Cryogenian glaciations: tidal rhythmites from early and late Cryogenian glacial successions and interglacial beds, South Australia","authors":"G. Williams, A. Andrew","doi":"10.1080/08120099.2023.2222795","DOIUrl":"https://doi.org/10.1080/08120099.2023.2222795","url":null,"abstract":"Abstract Vertically accreted, cyclic tidal rhythmites—laminated, fine-grained sandstones, siltstones and mudstones—occur in the late Cryogenian glaciogenic Elatina Formation (ca 635 Ma) and early Cryogenian Sturt Formation (ca 660 Ma) in the South Flinders Ranges region of the Adelaide Rift Complex within the Adelaide Superbasin, and in Cryogenian strata from Nicholson 2 drill hole in the eastern Officer Basin, South Australia. The rhythmites provide insights into Cryogenian littoral environments. The Elatina rhythmite was deposited during an interstadial and the Sturt rhythmite during early glacial advance, whereas the Nicholson 2 rhythmite is assigned to interglacial beds. The resultant raised sea levels and drowned valleys provided the tidal inlets, ebb-tidal deltas, estuaries and fjords favouring rhythmite deposition. The rhythmites display semidiurnal and diurnal (lunar day) tidal laminae grouped in fortnightly neap–spring cycles and record the semiannual tide. Periods of 26.2 ± 0.9 neap–spring cycles displayed by the Elatina rhythmite and ∼27 neap–spring cycles by the Nicholson 2 rhythmite mark the non-tidal annual variation of sea level, which results from seasonal surface winds and changes in atmospheric pressure and temperature acting on the waters of marine shelves and marginal seas. The strong annual signals and absence of dropstones in the Elatina and Nicholson 2 rhythmites indicate that respective marine shelves and marginal seas were ice-free during rhythmite deposition. The Sturt rhythmite, by contrast, shows a weak annual period of ∼27 neap–spring cycles and contains dropstones and till pellets, indicating that the adjacent marine shelf and sea were largely ice-covered. Paleotidal data for the Elatina rhythmite have illuminated Earth’s late Cryogenian paleorotation and the Moon’s orbit, and paleomagnetic studies of the Elatina rhythmite indicated a low paleolatitude for late Cryogenian glaciation. Contrary to recent modelling by others, strong tides existed at shallow-water continental margins during Cryogenian glaciations. Key Points Cyclic tidal rhythmites are associated with early and late Cryogenian (ca 660 and ca 635 Ma) glaciogenic successions and interglacial beds in South Australia. Rhythmite deposition occurred when raised sea levels provided the coastal environments favouring rhythmite deposition. The rhythmites display semidiurnal and diurnal tidal laminae grouped in fortnightly cycles, and record the semiannual tide and the non-tidal annual variation of sea level. Strong tides existed at shallow-water continental margins during early and late Cryogenian low-latitude glaciations and the interglacial interval.","PeriodicalId":8601,"journal":{"name":"Australian Journal of Earth Sciences","volume":"70 1","pages":"751 - 762"},"PeriodicalIF":1.2,"publicationDate":"2023-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43631464","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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