Pub Date : 2021-11-03DOI: 10.1080/00288306.2021.1987280
D. Craw, C. Rufaut, G. Kerr, Dhanashree Pillai
ABSTRACT Evaporative mineral encrustations have formed on bare substrates at three different sites in the Maniototo basin. Two sites, at Patearoa and Belmont have salts derived primarily from marine aerosols. The Patearoa site has developed on clay-rich pans formed on a terrace eroded by the Taieri River into clay-altered schist basement, and dissolution of albite from altered schist has resulted in precipitation of sodium carbonate with halite, at pH∼10. The Belmont site lies on the flat distal part of an active alluvial fan, and halite-dominated salt encrustations develop on thin dry crusts through capillary action from below. At the nearby Hamiltons historic placer gold mine, excavations exposed clay-altered schist basement beneath Eocene auriferous sediments. Highly fractured and hydrothermally altered fault zones dominate basement, with secondary ankeritic carbonate and pyrite. Water-rock interaction of shallow groundwater in the basement leads to enrichment in dissolved Mg and sulphate that overshadows the marine aerosol components, and evaporative encrustations are dominated by Mg-rich minerals including brucite and epsomite. The halite-dominated sites host rare halophyte ecosystems, but progressive colonisation by adventive species will eventually cover the bare saline substrates. Similar colonisation at the Hamiltons site will result in natural rehabilitation of the abandoned mine site.
{"title":"Contrasting geology and mineralogy of evaporative encrustations in salt-tolerant ecosystems, Maniototo basin, Central Otago, New Zealand","authors":"D. Craw, C. Rufaut, G. Kerr, Dhanashree Pillai","doi":"10.1080/00288306.2021.1987280","DOIUrl":"https://doi.org/10.1080/00288306.2021.1987280","url":null,"abstract":"ABSTRACT Evaporative mineral encrustations have formed on bare substrates at three different sites in the Maniototo basin. Two sites, at Patearoa and Belmont have salts derived primarily from marine aerosols. The Patearoa site has developed on clay-rich pans formed on a terrace eroded by the Taieri River into clay-altered schist basement, and dissolution of albite from altered schist has resulted in precipitation of sodium carbonate with halite, at pH∼10. The Belmont site lies on the flat distal part of an active alluvial fan, and halite-dominated salt encrustations develop on thin dry crusts through capillary action from below. At the nearby Hamiltons historic placer gold mine, excavations exposed clay-altered schist basement beneath Eocene auriferous sediments. Highly fractured and hydrothermally altered fault zones dominate basement, with secondary ankeritic carbonate and pyrite. Water-rock interaction of shallow groundwater in the basement leads to enrichment in dissolved Mg and sulphate that overshadows the marine aerosol components, and evaporative encrustations are dominated by Mg-rich minerals including brucite and epsomite. The halite-dominated sites host rare halophyte ecosystems, but progressive colonisation by adventive species will eventually cover the bare saline substrates. Similar colonisation at the Hamiltons site will result in natural rehabilitation of the abandoned mine site.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":"65 1","pages":"595 - 612"},"PeriodicalIF":2.2,"publicationDate":"2021-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43901613","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 : 2021-10-26DOI: 10.1080/00288306.2021.2000438
Alistair Stronach, T. Stern
ABSTRACT A new basin depth map for the Wellington Central Business District shows a maximum depth of 540 m near the Wellington Stadium. Our new basin geometry constraints are from a residual gravity anomaly study, based on ∼600 new gravity observations. Residual gravity anomalies are as large as −6.2 mGal with uncertainties <0.1 mGal. Two-dimensional gravity models constrained by boreholes that intersect basement are used to generate the basin depth map. Our maximum depth is twice that previously estimated from other geological and geophysical criteria. An onshore extension of the recently discovered Aotea Fault on the western side of Mt Victoria, is also interpreted from the gravity data. A maximum basement offset of up to 130 m and gravity anomaly gradients up to 8 mGal/km are observed across the fault. A secondary splay off the main Aotea Fault is identified in the NW corner of Mt Victoria, and a possible extension to the Lambton Fault is identified beneath the Wellington Railway Station. This new basin depth and fault trace data provide valuable constraints to models of seismic hazard assessment for Wellington City.
{"title":"A new basin depth map of the fault-bound Wellington CBD based on residual gravity anomalies","authors":"Alistair Stronach, T. Stern","doi":"10.1080/00288306.2021.2000438","DOIUrl":"https://doi.org/10.1080/00288306.2021.2000438","url":null,"abstract":"ABSTRACT A new basin depth map for the Wellington Central Business District shows a maximum depth of 540 m near the Wellington Stadium. Our new basin geometry constraints are from a residual gravity anomaly study, based on ∼600 new gravity observations. Residual gravity anomalies are as large as −6.2 mGal with uncertainties <0.1 mGal. Two-dimensional gravity models constrained by boreholes that intersect basement are used to generate the basin depth map. Our maximum depth is twice that previously estimated from other geological and geophysical criteria. An onshore extension of the recently discovered Aotea Fault on the western side of Mt Victoria, is also interpreted from the gravity data. A maximum basement offset of up to 130 m and gravity anomaly gradients up to 8 mGal/km are observed across the fault. A secondary splay off the main Aotea Fault is identified in the NW corner of Mt Victoria, and a possible extension to the Lambton Fault is identified beneath the Wellington Railway Station. This new basin depth and fault trace data provide valuable constraints to models of seismic hazard assessment for Wellington City.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":"66 1","pages":"27 - 41"},"PeriodicalIF":2.2,"publicationDate":"2021-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47495758","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 : 2021-10-25DOI: 10.1080/00288306.2021.1990088
J. Dutilleul, S. Bourlange, Y. Géraud, T. Reuschlé
ABSTRACT Several mechanisms involving excess pore pressure related to gas hydrate have been proposed to explain active creeping at landslides such as the north Hikurangi margin Tuaheni Landslide Complex (TLC). Cores and logging data were retrieved by the International Ocean Discovery Program (IODP) Expeditions 372 and 375 from the South TLC at Site U1517. Here, the evolutions of porosity, pore structure and permeability are determined to assess the compaction state in the landslide and compare it with that of the undeformed sequence at Site U1519. Although no evidence of gas hydrate in the landslide at Site U1517 was identified by the cruise, zones suspected to host gas hydrates below the landslide or at Site U1519 are characterised by higher porosity, pore diameter and permeability. We show that most of the sedimentary section is in hydrostatic conditions, except the base of the TLC at Site U1517 and a zone below the base of the gas hydrate stability zone at Site U1519. These zones might be candidates for excess pore pressure build-up. There is no obvious evidence of the involvement of gas hydrate in active creeping at the TLC, which is more likely induced by hydrogeomechanical processes.
{"title":"Porosity and permeability evolution in the Tuaheni Landslide Complex at Hikurangi margin from IODP Sites U1517 and U1519","authors":"J. Dutilleul, S. Bourlange, Y. Géraud, T. Reuschlé","doi":"10.1080/00288306.2021.1990088","DOIUrl":"https://doi.org/10.1080/00288306.2021.1990088","url":null,"abstract":"ABSTRACT Several mechanisms involving excess pore pressure related to gas hydrate have been proposed to explain active creeping at landslides such as the north Hikurangi margin Tuaheni Landslide Complex (TLC). Cores and logging data were retrieved by the International Ocean Discovery Program (IODP) Expeditions 372 and 375 from the South TLC at Site U1517. Here, the evolutions of porosity, pore structure and permeability are determined to assess the compaction state in the landslide and compare it with that of the undeformed sequence at Site U1519. Although no evidence of gas hydrate in the landslide at Site U1517 was identified by the cruise, zones suspected to host gas hydrates below the landslide or at Site U1519 are characterised by higher porosity, pore diameter and permeability. We show that most of the sedimentary section is in hydrostatic conditions, except the base of the TLC at Site U1517 and a zone below the base of the gas hydrate stability zone at Site U1519. These zones might be candidates for excess pore pressure build-up. There is no obvious evidence of the involvement of gas hydrate in active creeping at the TLC, which is more likely induced by hydrogeomechanical processes.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":"65 1","pages":"201 - 219"},"PeriodicalIF":2.2,"publicationDate":"2021-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45233873","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 : 2021-10-11DOI: 10.1080/00288306.2021.1985529
Ruth M. Corkill, G. Turner
ABSTRACT Palaeomagnetic records from three cores of lake sediment have been merged, producing a new Holocene geomagnetic secular variation record for northern New Zealand. The cores are from Lake Pupuke, a maar lake in Auckland Volcanic Field (AVF). They contain tephra from Rangitoto Volcano (530 ± 10 yr BP), Taupō (1718 ± 10 yr BP), Tūhua/Mayor Island (7637 ± 100 yr BP) and Rotomā tephra from Ōkataina Volcanic Centre (9423 ± 120 yr BP). These tephra dates are supplemented by selected radiocarbon age estimates. The cores were correlated using tephra and fine-scale variations in magnetic susceptibility. The natural remanent magnetisation is strong, stable and carried by fine-grained titanomagnetite from AVF’s basaltic volcanoes. The resulting palaeosecular variation (PSV) record spans from 10,000 to 1500 yr BP. It shows well-defined, millennial-scale swings in direction between 10,000 and 8000 yr BP and between 4000 and 1500 yr BP, while between 8000 and 4000 yr BP variations are of higher frequency and lower amplitude and centre on the geocentric axial dipole field direction. This is in excellent agreement with published PSV records from Mavora Lakes, 1000 km further south, indicating the regional nature of PSV – resulting from broad-scale changes in the circulation of conducting iron-rich fluid of Earth’s outer core.
摘要将三个湖泊沉积物核心的古地磁记录合并，为新西兰北部创造了一个新的全新世地磁长期变化记录。岩芯来自奥克兰火山场（AVF）的马尔湖Pupuke湖。它们包含Rangitoto火山的火山灰岩（530 ± 10 年BP），陶（1718年） ± 10 yr BP），图华/马约尔岛（7637 ± 100 yr BP）和来自Ōkataina火山中心的Rotomātephra（9423 ± 120 年BP）。这些tephra日期由选定的放射性碳年龄估计补充。使用tephra和磁化率的精细尺度变化对岩心进行了关联。天然残余磁化强度强、稳定，由AVF玄武岩火山的细粒钛磁铁矿携带。由此产生的古长期变化（PSV）记录跨度从10000到1500 年BP。它显示了明确的千禧一代规模在10000到8000之间的方向波动 年BP介于4000和1500之间 年BP，在8000到4000之间 yr BP变化具有较高的频率和较低的振幅，并且以地心轴向偶极子场方向为中心。这与Mavora Lakes公布的PSV记录非常一致，1000 再往南公里，表明PSV的区域性——这是由地核富含铁的导电流体循环的大范围变化引起的。
{"title":"A Holocene palaeomagnetic secular variation record from Lake Pupuke, New Zealand","authors":"Ruth M. Corkill, G. Turner","doi":"10.1080/00288306.2021.1985529","DOIUrl":"https://doi.org/10.1080/00288306.2021.1985529","url":null,"abstract":"ABSTRACT Palaeomagnetic records from three cores of lake sediment have been merged, producing a new Holocene geomagnetic secular variation record for northern New Zealand. The cores are from Lake Pupuke, a maar lake in Auckland Volcanic Field (AVF). They contain tephra from Rangitoto Volcano (530 ± 10 yr BP), Taupō (1718 ± 10 yr BP), Tūhua/Mayor Island (7637 ± 100 yr BP) and Rotomā tephra from Ōkataina Volcanic Centre (9423 ± 120 yr BP). These tephra dates are supplemented by selected radiocarbon age estimates. The cores were correlated using tephra and fine-scale variations in magnetic susceptibility. The natural remanent magnetisation is strong, stable and carried by fine-grained titanomagnetite from AVF’s basaltic volcanoes. The resulting palaeosecular variation (PSV) record spans from 10,000 to 1500 yr BP. It shows well-defined, millennial-scale swings in direction between 10,000 and 8000 yr BP and between 4000 and 1500 yr BP, while between 8000 and 4000 yr BP variations are of higher frequency and lower amplitude and centre on the geocentric axial dipole field direction. This is in excellent agreement with published PSV records from Mavora Lakes, 1000 km further south, indicating the regional nature of PSV – resulting from broad-scale changes in the circulation of conducting iron-rich fluid of Earth’s outer core.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":"65 1","pages":"582 - 594"},"PeriodicalIF":2.2,"publicationDate":"2021-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46430336","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 : 2021-10-10DOI: 10.1080/00288306.2021.1984257
M. Maitra, K. Bassett
ABSTRACT Sedimentary facies analysis of conglomerate deposits in the Greymouth Rift Basin has identified the latest Cretaceous to Paleocene alluvial fan and fan delta environments on the northwestern side. The Gravelly Braided River Facies Association is interpreted as high energy, braided river streamflow in a streamflow-dominated alluvial fan environment. The Gravelly Delta Front Facies Association was deposited by high bedload mouth bars and channel avulsion. The Gravelly Prodelta Facies Association is interpreted as high-density turbidity currents, and subaqueous debris flows in a fan delta slope environment. Bedding geometries suggest the fan deltas were Hjulström-types formed on lower angle slopes. The gradual decrease in conglomerate thickness from northwest to southeast indicates that the primary basin bounding fault was located offshore to the northwest, most likely the Cape Foulwind-Canoe Fault Zone. Overall facies distribution and paleoflow directions indicate the Greymouth Basin formed as a half-graben in a purely extensional setting with no strike-slip movement. The presence of contemporaneous sub-basins in the West Coast region suggests they likely experienced similar depositional history to the Greymouth Basin. Our findings agree with previous models from the Taranaki Basin that indicate that rifting was purely extensional, suggesting that the West Coast-Taranaki Rift System recorded primarily orthogonal extension.
{"title":"Alluvial fans and fan deltas in the Paparoa Formation, Greymouth Basin: a new rift model","authors":"M. Maitra, K. Bassett","doi":"10.1080/00288306.2021.1984257","DOIUrl":"https://doi.org/10.1080/00288306.2021.1984257","url":null,"abstract":"ABSTRACT Sedimentary facies analysis of conglomerate deposits in the Greymouth Rift Basin has identified the latest Cretaceous to Paleocene alluvial fan and fan delta environments on the northwestern side. The Gravelly Braided River Facies Association is interpreted as high energy, braided river streamflow in a streamflow-dominated alluvial fan environment. The Gravelly Delta Front Facies Association was deposited by high bedload mouth bars and channel avulsion. The Gravelly Prodelta Facies Association is interpreted as high-density turbidity currents, and subaqueous debris flows in a fan delta slope environment. Bedding geometries suggest the fan deltas were Hjulström-types formed on lower angle slopes. The gradual decrease in conglomerate thickness from northwest to southeast indicates that the primary basin bounding fault was located offshore to the northwest, most likely the Cape Foulwind-Canoe Fault Zone. Overall facies distribution and paleoflow directions indicate the Greymouth Basin formed as a half-graben in a purely extensional setting with no strike-slip movement. The presence of contemporaneous sub-basins in the West Coast region suggests they likely experienced similar depositional history to the Greymouth Basin. Our findings agree with previous models from the Taranaki Basin that indicate that rifting was purely extensional, suggesting that the West Coast-Taranaki Rift System recorded primarily orthogonal extension.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":"65 1","pages":"555 - 581"},"PeriodicalIF":2.2,"publicationDate":"2021-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47126184","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 : 2021-10-06DOI: 10.1080/00288306.2021.1977343
A. McArthur, J. Bailleul, F. Chanier, A. Clare, W. McCaffrey
ABSTRACT The fill of trench-slope basins is complex, varying temporally, laterally, and longitudinally. New data from the Neogene stratigraphy of the Akitio Sub-basin, Wairarapa, are presented to investigate such fill variation. The preserved basin fill spans an area 70 km long by 10 km wide, representing deposits from a trench-slope basin. Integration of sedimentological, micropalaeoentological, and geological mapping data charts basin fill evolution. Over 15 km of strata were logged, defining 17 lithofacies associations, which were mapped across the basin; these are interpreted to represent both shallow and deep-water environments. The deep-water strata show a temporal evolution from ponded turbidite deposition, to a period of basin spill via conduits connecting to downstream basins, development of aggradational channel-levees, and finally unconfined submarine fan deposition. Shallow marine deposits mostly developed on the up-dip basin margin occur contemporaneously with basinal mass-transport deposits, and in association with the growth of basin bounding structural ridges. Comparison with the evolution of the offshore, actively filling Akitio Trough highlights controls on trench-slope basin fill: a first-order influence of external controls, e.g. tectonism to create the basin; a second-order progression from under- to overfilled; and third-order lateral variation reflecting autogenic process and the effects of local structures on seafloor gradients. These factors combine to vary sedimentation in trench-slope-basins spatially and temporally.
{"title":"Lateral, longitudinal, and temporal variation in trench-slope basin fill: examples from the Neogene Akitio sub-basin, Hikurangi Margin, New Zealand","authors":"A. McArthur, J. Bailleul, F. Chanier, A. Clare, W. McCaffrey","doi":"10.1080/00288306.2021.1977343","DOIUrl":"https://doi.org/10.1080/00288306.2021.1977343","url":null,"abstract":"ABSTRACT The fill of trench-slope basins is complex, varying temporally, laterally, and longitudinally. New data from the Neogene stratigraphy of the Akitio Sub-basin, Wairarapa, are presented to investigate such fill variation. The preserved basin fill spans an area 70 km long by 10 km wide, representing deposits from a trench-slope basin. Integration of sedimentological, micropalaeoentological, and geological mapping data charts basin fill evolution. Over 15 km of strata were logged, defining 17 lithofacies associations, which were mapped across the basin; these are interpreted to represent both shallow and deep-water environments. The deep-water strata show a temporal evolution from ponded turbidite deposition, to a period of basin spill via conduits connecting to downstream basins, development of aggradational channel-levees, and finally unconfined submarine fan deposition. Shallow marine deposits mostly developed on the up-dip basin margin occur contemporaneously with basinal mass-transport deposits, and in association with the growth of basin bounding structural ridges. Comparison with the evolution of the offshore, actively filling Akitio Trough highlights controls on trench-slope basin fill: a first-order influence of external controls, e.g. tectonism to create the basin; a second-order progression from under- to overfilled; and third-order lateral variation reflecting autogenic process and the effects of local structures on seafloor gradients. These factors combine to vary sedimentation in trench-slope-basins spatially and temporally.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":"65 1","pages":"105 - 140"},"PeriodicalIF":2.2,"publicationDate":"2021-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43524349","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 : 2021-10-06DOI: 10.1080/00288306.2021.1977341
C. Nelson, A. Lawless, S. Nodder, H. Zwingmann
ABSTRACT A unique 10–140 cm thick veneer of greensand and glauconite-rich deposits (10–80 wt% glauconite) presently sits atop central Chatham Rise (CR) in water depths of 200-500 m. The glauconite is dominated by chemically mature, polished ovoidal and lobate pellets, with a 10–12 Å phyllosilicate structure and K-Ar ages of 7–5 Ma, indicating that the glauconite pellets are predominantly allogenic (i.e. derived/reworked) grains, and not of in situ authigenic origin. Glauconite possibly evolved from seafloor alteration of detrital and/or volcanogenic smectitic clays, likely concentrated within organic-rich faecal pellets under unique paleoceanographic conditions (nutrient cycling, upwelling, carbon isotope gradients) within the latest Miocene Subtropical Front. The distribution of glauconite abundance suggests a ‘glauconite factory’ existed at this time about Reserve Bank on western central CR. The pellets were dispersed eastwards along the crest by intensified bottom currents within the dynamic Subtropical Frontal zone, perhaps during the numerous glacial periods of lowered sea level throughout the Plio-Quaternary. The bioturbated greensand veneer, and its mix of other reworked Neogene and Quaternary skeletal, phosphatic and siliciclastic components, rest unconformably on mainly Early Oligocene chalks, forming a highly condensed, relict/palimpsest deposit that alone embodies the last up to 30 My of sedimentation history atop central CR.
{"title":"Latest Miocene (Kapitean/Messinian) glauconite and the central Chatham Rise greensand: an enigmatic, highly condensed, relict/palimpsest deposit on the modern seafloor","authors":"C. Nelson, A. Lawless, S. Nodder, H. Zwingmann","doi":"10.1080/00288306.2021.1977341","DOIUrl":"https://doi.org/10.1080/00288306.2021.1977341","url":null,"abstract":"ABSTRACT A unique 10–140 cm thick veneer of greensand and glauconite-rich deposits (10–80 wt% glauconite) presently sits atop central Chatham Rise (CR) in water depths of 200-500 m. The glauconite is dominated by chemically mature, polished ovoidal and lobate pellets, with a 10–12 Å phyllosilicate structure and K-Ar ages of 7–5 Ma, indicating that the glauconite pellets are predominantly allogenic (i.e. derived/reworked) grains, and not of in situ authigenic origin. Glauconite possibly evolved from seafloor alteration of detrital and/or volcanogenic smectitic clays, likely concentrated within organic-rich faecal pellets under unique paleoceanographic conditions (nutrient cycling, upwelling, carbon isotope gradients) within the latest Miocene Subtropical Front. The distribution of glauconite abundance suggests a ‘glauconite factory’ existed at this time about Reserve Bank on western central CR. The pellets were dispersed eastwards along the crest by intensified bottom currents within the dynamic Subtropical Frontal zone, perhaps during the numerous glacial periods of lowered sea level throughout the Plio-Quaternary. The bioturbated greensand veneer, and its mix of other reworked Neogene and Quaternary skeletal, phosphatic and siliciclastic components, rest unconformably on mainly Early Oligocene chalks, forming a highly condensed, relict/palimpsest deposit that alone embodies the last up to 30 My of sedimentation history atop central CR.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":"65 1","pages":"529 - 554"},"PeriodicalIF":2.2,"publicationDate":"2021-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46249818","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 : 2021-10-04DOI: 10.1080/00288306.2021.1978509
Daniel E. Tek, A. McArthur, M. Poyatos‐Moré, L. Colombera, C. Allen, Marco Patacci, W. McCaffrey
ABSTRACT Deep-water channels can be bound by overbank deposits, resulting from overspilling flows, which are often ornamented with sediment waves. Here, high-resolution bathymetry, backscatter, and 2D and 3D seismic data are integrated to discern the controls on flow processes on the overbank areas of the Hikurangi Channel. Qualitative seismic interpretation and quantitative analyses of sediment wave morphologies and distributions are conducted through the shallowest 600 m of stratigraphy up to the seafloor. Four outer-bend wave fields are present throughout the studied stratigraphy on the landward margin (left margin looking down-channel) only. Originally closely spaced or combined, these fields evolved to become spatially separated; two of the separate wave fields became further subdivided into distinct outer- and inner-bend fields, whose constituent waves developed distinct differences in morphology and distribution. Sediment wave character is used to interpret the direction and strength of overbank flow. Nine controls on such flow and associated deposition are identified: flow versus conduit size, overbank gradient, flow tuning, Coriolis forcing, contour current activity, flow reflection, centrifugal forcing, interaction with externally derived flows, and interaction of overspill from different locations. Their relative importance may vary across parts of overbank areas, both spatially and temporally, controlling wave field development such that: (1) outer-bend wave fields only develop on the landward margin; (2) the influence of centrifugal force on outer-bend overbanks has increased through time, accompanying a general increase in channel sinuosity; (3) inner-bend wave fields on the landward margin form by the interaction of Coriolis-enhanced inner-bend overbank flow, and outer-bank flow from up-channel bends; (4) inner-bend fields on the oceanward margin form by the interaction of axial flow through wave troughs, and a transverse, toward-channel flow component. This work has implications for interpreting overbank flow from seafloor and seismic data, and for palaeogeographic reconstructions from outcrop data.
{"title":"Controls on the architectural evolution of deep-water channel overbank sediment wave fields: insights from the Hikurangi Channel, offshore New Zealand","authors":"Daniel E. Tek, A. McArthur, M. Poyatos‐Moré, L. Colombera, C. Allen, Marco Patacci, W. McCaffrey","doi":"10.1080/00288306.2021.1978509","DOIUrl":"https://doi.org/10.1080/00288306.2021.1978509","url":null,"abstract":"ABSTRACT Deep-water channels can be bound by overbank deposits, resulting from overspilling flows, which are often ornamented with sediment waves. Here, high-resolution bathymetry, backscatter, and 2D and 3D seismic data are integrated to discern the controls on flow processes on the overbank areas of the Hikurangi Channel. Qualitative seismic interpretation and quantitative analyses of sediment wave morphologies and distributions are conducted through the shallowest 600 m of stratigraphy up to the seafloor. Four outer-bend wave fields are present throughout the studied stratigraphy on the landward margin (left margin looking down-channel) only. Originally closely spaced or combined, these fields evolved to become spatially separated; two of the separate wave fields became further subdivided into distinct outer- and inner-bend fields, whose constituent waves developed distinct differences in morphology and distribution. Sediment wave character is used to interpret the direction and strength of overbank flow. Nine controls on such flow and associated deposition are identified: flow versus conduit size, overbank gradient, flow tuning, Coriolis forcing, contour current activity, flow reflection, centrifugal forcing, interaction with externally derived flows, and interaction of overspill from different locations. Their relative importance may vary across parts of overbank areas, both spatially and temporally, controlling wave field development such that: (1) outer-bend wave fields only develop on the landward margin; (2) the influence of centrifugal force on outer-bend overbanks has increased through time, accompanying a general increase in channel sinuosity; (3) inner-bend wave fields on the landward margin form by the interaction of Coriolis-enhanced inner-bend overbank flow, and outer-bank flow from up-channel bends; (4) inner-bend fields on the oceanward margin form by the interaction of axial flow through wave troughs, and a transverse, toward-channel flow component. This work has implications for interpreting overbank flow from seafloor and seismic data, and for palaeogeographic reconstructions from outcrop data.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":"65 1","pages":"141 - 178"},"PeriodicalIF":2.2,"publicationDate":"2021-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47040052","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 : 2021-09-19DOI: 10.1080/00288306.2021.1975777
C. Bloom, T. Stahl, A. Howell
ABSTRACT The distribution of ground motion, displacement, and secondary hazards around active faults is defined by the interaction of tectonic and site characteristics including fault kinematics. As a result of this complexity, recommendations for fault setback distances or avoidance zones are necessarily simplified. We observed distributed vertical coseismic displacement from the 2016 Mw 7.8 Kaikōura earthquake up to c. 500 m on either side of the sinistral-reverse Papatea fault. On average, c. 32% (2.13 m) of vertical displacement was measured at distances >50 m from the Papatea fault. Additionally, in places, there is strong asymmetry where displacement was accommodated over a wider area in the hanging wall of the fault, a common observation around many dip-slip fault ruptures globally. We compare the distribution of displacement around the Papatea fault to the current fault avoidance zone and find that increasing the size of the fault avoidance zone by 10 m captures 11% more area with a high gradient of vertical displacement. Given these results and similar findings for other faults globally, we recommend that existing standards for fault avoidance zones be evaluated to ensure their ongoing efficacy.
{"title":"Distributed displacement on the Papatea fault from the 2016 Mw 7.8 Kaikōura earthquake and implications for hazard planning","authors":"C. Bloom, T. Stahl, A. Howell","doi":"10.1080/00288306.2021.1975777","DOIUrl":"https://doi.org/10.1080/00288306.2021.1975777","url":null,"abstract":"ABSTRACT The distribution of ground motion, displacement, and secondary hazards around active faults is defined by the interaction of tectonic and site characteristics including fault kinematics. As a result of this complexity, recommendations for fault setback distances or avoidance zones are necessarily simplified. We observed distributed vertical coseismic displacement from the 2016 Mw 7.8 Kaikōura earthquake up to c. 500 m on either side of the sinistral-reverse Papatea fault. On average, c. 32% (2.13 m) of vertical displacement was measured at distances >50 m from the Papatea fault. Additionally, in places, there is strong asymmetry where displacement was accommodated over a wider area in the hanging wall of the fault, a common observation around many dip-slip fault ruptures globally. We compare the distribution of displacement around the Papatea fault to the current fault avoidance zone and find that increasing the size of the fault avoidance zone by 10 m captures 11% more area with a high gradient of vertical displacement. Given these results and similar findings for other faults globally, we recommend that existing standards for fault avoidance zones be evaluated to ensure their ongoing efficacy.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":"66 1","pages":"217 - 227"},"PeriodicalIF":2.2,"publicationDate":"2021-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49525253","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 : 2021-09-15DOI: 10.1080/00288306.2021.1969956
K. Clark, R. Morgenstern
ABSTRACT The Auckland region does not have a historic record of significant tsunamis but modelling suggests the eastern coastline could be exposed to tsunamis from the Kermadec Trench with wave amplitudes of up to 10 m on Great Barrier Island/Aotea and 1–5 m on the mainland. Paleotsunami research could contribute to filling the disconnect between historic records and tsunami modelling by providing a tsunami record over a time span of thousands of years that is more likely to capture the long recurrence intervals of great subduction earthquakes at the Kermadec Trench. Here we review existing paleotsunami information and results of new field studies in the Auckland region (primarily on Great Barrier Island/Aotea). Three sites (Tāwharanui, Whangapoua Beach and Harataonga Bay) have strong evidence of Holocene paleotsunami but the dating of the inferred paleotsunamis at all sites is relatively poor. The coastline of Auckland and its neighbouring regions offer our most promising sites to better understand the size and frequency of large to great Kermadec Trench earthquakes and this information could be of critical importance for understanding tsunami risk in New Zealand.
{"title":"The paleotsunami record of the Auckland region and implications for understanding tsunami hazards","authors":"K. Clark, R. Morgenstern","doi":"10.1080/00288306.2021.1969956","DOIUrl":"https://doi.org/10.1080/00288306.2021.1969956","url":null,"abstract":"ABSTRACT The Auckland region does not have a historic record of significant tsunamis but modelling suggests the eastern coastline could be exposed to tsunamis from the Kermadec Trench with wave amplitudes of up to 10 m on Great Barrier Island/Aotea and 1–5 m on the mainland. Paleotsunami research could contribute to filling the disconnect between historic records and tsunami modelling by providing a tsunami record over a time span of thousands of years that is more likely to capture the long recurrence intervals of great subduction earthquakes at the Kermadec Trench. Here we review existing paleotsunami information and results of new field studies in the Auckland region (primarily on Great Barrier Island/Aotea). Three sites (Tāwharanui, Whangapoua Beach and Harataonga Bay) have strong evidence of Holocene paleotsunami but the dating of the inferred paleotsunamis at all sites is relatively poor. The coastline of Auckland and its neighbouring regions offer our most promising sites to better understand the size and frequency of large to great Kermadec Trench earthquakes and this information could be of critical importance for understanding tsunami risk in New Zealand.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":"65 1","pages":"507 - 528"},"PeriodicalIF":2.2,"publicationDate":"2021-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45598845","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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