Bay Group Research Articles

Metastable persistence of pelitic metamorphic assemblages at the root of a Cretaceous magmatic arc – Fiordland, New Zealand

AbstractFour aluminosilicate‐bearing, amphibolite facies pelitic schists sampled from the root of the long‐lived eastern Gondwana continental magmatic arc now exposed in southwest Fiordland, New Zealand, record remarkably different P–T–t histories. The four samples were collected from within 20 km of each other within the Fanny Bay Group and Deep Cove Gneiss near Dusky Sound. Integrated petrography, mineral chemistry, mineral equilibria modelling and in situ electron microprobe chemical dating of monazite shows that the sample of the Fanny Bay Group south of the Dusky Fault records a Carboniferous history with peak conditions of 4–4.5 kbar at 570–590 °C, while one sample of the Deep Cove Gneiss from Long Island records a Cretaceous history with apparent peak conditions of 7.5 kbar at 650 °C. Two other samples of the Deep Cove Gneiss from Resolution Island record mixed Carboniferous and Cretaceous histories with apparent peak conditions of 7 kbar at 650 °C and 3–7 kbar at 640–720 °C. The metapelitic schists on Resolution Island were intruded by arc magmas including the voluminous high‐P Western Fiordland Orthogneiss, yet they lack mineralogical evidence of the Cretaceous high‐P (>12 kbar) event. Analysis of water isopleths in a model system shows that the amount of water accommodated in the rock mineral assemblage increases with pressure. With the exhaustion of all free water, and without the addition of external water, these rocks persisted metastably within the deep arc during the high‐P event. The emplacement of large volumes of diorite (i.e. the Western Fiordland Orthogneiss) into the root of the Early Cretaceous continental magmatic arc did not lead to regional granulite facies metamorphism of the country rock schists, as large volumes of amphibolite facies rock metamorphosed under medium‐P conditions persisted metastably in the deep arc crust.

Genetic relationships among populations of the Argentine ant Linepithema humile introduced into Japan

AbstractSince some colonies of Argentine ant Linepithema humile were discovered in Japan in 1993, populations of this invasive alien ant species have been expanding their distribution. To resolve the number of invasions and the genetic structure in the early stages of introduction, we inferred the genetic structure and relationships among colonies from eight localities, from analyses of eight nuclear microsatellite DNA markers. FST analysis, principal component analysis and assignment test showed that at least three highly genetically differentiated groups of Argentine ants are present in Japan. Populations from Hiroshima Bay were grouped together (Hiroshima, Hatsukaichi, Otake, Iwakuni Central and Iwakuni Kuroiso), while those from Kobe and Yanai were both genetically distant from each other and from the Hiroshima Bay group. Hatsukaichi and Kobe are international seaports, suggesting that the by‐ship invasion occurred at least twice. The invasion route of the Yanai population is unknown at this moment. The Aichi population was genetically distant from that of the Hiroshima Bay group by the difference in allele frequencies, and it was plausible that the Aichi population was introduced from the Hiroshima Bay group by human‐mediated jump dispersal.

Inhibition of NF-κB by (E)3-[(4-methylphenyl)-sulfonyl]-2-propenenitrile (BAY11-7082; BAY) is associated with enhanced 12-O-tetradecanoylphorbol-13-acetate-induced growth suppression and apoptosis in human prostate cancer PC-3 cells

The effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) alone or in combination with an NF-kappaB inhibitor, (E)3-[(4-methylphenyl)-sulfonyl]-2-propenenitrile (BAY 11-7082; BAY), on the growth and apoptosis of human prostate cancer PC-3 cells cultured in vitro or grown in immunodeficient mice were studied. Treatment of cultured PC-3 cells with TPA (0.2-10 ng/ml) for 96 h resulted in growth inhibition and apoptosis in a concentration-dependent manner. BAY inhibited NF-kappaB activity in PC-3 cells as determined by a luciferase reporter assay and enhanced TPA-induced growth inhibition and apoptosis in cultured PC-3 cells. In animal studies, NCr immunodeficient mice were injected subcutaneously with PC-3 cells in Matrigel. Mice with well-established tumors received daily i.p. injections with TPA (100 ng/g body weight/day), BAY (4 microg/g/day), or a combination of TPA (100 ng/g/day) and BAY (4 microg/g/day) for 36 days. Tumor growth occurred in all of the vehicle-treated control mice. The percent of animals with some tumor regression after 36 days of treatment was 0% for the control group, 40% for the TPA group, 50% for the BAY group and 100% for the TPA + BAY group. Mechanistic studies indicated that treatment of the mice with TPA or TPA + BAY decreased proliferation and increased apoptosis in the tumors. Results from our studies indicate that inhibition of NF-kappaB activity is associated with enhanced TPA-induced growth inhibition and apoptosis in PC-3 cells. Inhibition of NF-kappaB activity by suitable pharmacological inhibitors may be an effective strategy for improving the therapeutic efficacy of TPA in prostate cancer.

Plutonic rocks of the Median Batholith in southwest Fiordland, New Zealand: Field relations, geochemistry, and correlation

This paper provides a first description of all major plutonic rock units between Resolution Island and Lake Poteriteri in southwest Fiordland. Plutonic rocks, of which c. 95% are granitoids, comprise c. 60% of the basement in southwest Fiordland. Approximately 50% of the plutonic rocks were emplaced between c. 355 and 348 Ma, 5% at c. 164 Ma, 25%between c. 140 and 125 Ma, and 20% between c. 125 and 110 Ma. These episodes of plutonism occurred in response to terrane amalgamation, continental thickening, and subduction along the convergent margin of Gondwana. Correlatives of Devonian plutonic rocks which occur in Nelson are absent from the area described here. A wide variety of plutonic rocks were emplaced at c. 355–348 Ma. These include relatively small plutons of K‐ and Rb‐rich gabbro‐diorite and members of at least three distinct suites of granitoids. Plutons of two‐mica ± garnet granodiorite, granite, and minor tonalite share affinities with the S‐type Ridge Suite and are the most widespread c. 355–348 Ma old granitoids in southern Fiordland. Plutons rich in Ca, Fe and Zr, depleted in K and Na, and containing quartz diorite, tonalite, and minor granodiorite with the unusual assemblage red‐brown biotite, garnet ± hornblende ± clinopyroxene also occur widely in southern Fiordland. These plutons are similar to peraluminous A‐type granitoids, indicating A as well as I and S‐type plutonism occurred in the Western Province at this time. The Newton River and Mt Evans Plutons have no correlatives amongst c. 355–348 Ma granitoids in southern Fiordland, but their chemistry is similar to that of the older Karamea Suite. Three regional‐scale metasedimentary units—locally fos‐siliferous Fanny Bay Group Buller Terrane rocks in southern Fiordland, Edgecumbe and Cameron Group Takaka Terrane rocks in south‐central Fiordland, and undifferentiated Deep Cove Gneiss high‐grade metasedimentary rocks of western Fiordland—are all stitched by c. 355–348 Ma old plutons, indicating they have been in close proximity since at least c. 355–348 Ma. In south‐central Fiordland, c. 355–348 Ma old plutons cut across fabrics defined by upper amphibolite facies mineral assemblages, indicating low pressure/high temperature metamorphism in this area before this time. The c. 164 Ma old leucocratic Lake Mike Granite is a unique pluton in southwest Fiordland with no obvious correlatives. Plutons emplaced between c. 140 and 125 Ma are similar to the Rahu Suite, although isotopic data are required to confirm this correlation. Rahu Suite plutonism may therefore have begun by c. 140 Ma, rather than c. 120 Ma as previously suggested. Plutons emplaced between c. 125 and 110 Ma have high Sr/Y ratios comparable with the Separation Point Suite. They occur in both an outboard location around Lake Poteriteri and an inboard location around the western end of Dusky Sound. The c. 115 Ma two‐mica garnet granites of the Anchor Island Intrusives #2 probably formed by partial melting of adjacent ortho‐ and paragneisses, indicating that upper amphibolite facies metamorphism in western Dusky Sound occurred during the Early Cretaceous. The Dusky Fault does not pass directly out to the coast through outer Dusky Sound as previously mapped. Instead it merges with the major northeast‐striking Lake Fraser Fault at Cascade Cove, which crosses the outer coast near West Cape. The Last Cove Fault is a minor structure which cannot be traced beyond Last Cove rather than a major fault of regional extent as has been previously suggested.

Diagenetic fluorapatite and aluminum phosphate–sulphate in the Paleoproterozoic Thelon Formation and Hornby Bay Group, northwestern Canadian Shield

In the northwestern part of the Canadian Shield, fluorapatite and a rare-earth element-bearing hydrated aluminum phosphate–sulphate mineral (APS) occur as cements in continental successions near the base of the Paleoproterozoic Thelon Formation (Thelon Basin) and Hornby Bay Group (Hornby Bay Basin). These minerals occupy interstitial sites, form euhedral crystals, display micro-scale zonation, make up part of an unmetamorphosed paragenetic assemblage, and are distributed in correlative units across thousands of square kilometres, suggesting a diagenetic origin. Stratigraphy, geochronology, and other lines of evidence suggest that the Thelon Formation and Hornby Bay Group containing these phosphatic cements, as well as the Ellice Formation and Athabasca Group, are correlative and may have been originally interconnected. The evidence suggests that the basal Thelon Formation and the Hornby Bay Group underwent similar, and approximately coeval, diagenetic mineral paragenesis. Furthermore, the diagenetic fluids in these different locations must have been remarkably similar, especially those that produced the delicate APS mineral. Compared to phosphatic cements in the Hornby Bay and Thelon basins, unmineralized sandstone in the Athabasca Basin contains "crandallite group" and fluorapatite cements higher in the basin fill sequence (Wolverine Point Formation) in tuffaceous sandstone and as relatively early cement in the paragenetic sequence.

Protective Effects of BAY 41-2272 (sGC Stimulator) on Hypertension, Heart, and Cardiomyocyte Hypertrophy Induced by Chronic L-NAME Treatment in Rats

This study evaluated the effects of BAY 41-2272 (BAY), a specific activator of sGC NO-independent action on changes of mean arterial blood pressure, heart and left ventricle weight indexes, cardiomyocyte hypertrophy (Vv) and fibrosis area induced by chronic N-nitro-L-arginine methyl ester (L-NAME) treatment in rats. The animals were divided into (a) control group, (b) L-NAME group, (c) L-NAME+BAY group, and (d) BAY group. Eight weeks of L-NAME treatment caused a significant increase in mean arterial blood pressure when compared with untreated rats (173 +/- 11.1 and 109 +/- 5.0 mm Hg, respectively; P < 0.01). L-NAME + BAY cotreatment abolished the L-NAME-induced hypertension (112 +/- 5.1 mm Hg; P < 0.01). Significant increases in heart and left ventricle weight indexes and in Vv were observed in the L-NAME-treated animals compared with control group, and concomitant treatment with BAY significantly attenuated this hypertrophic effect. Treatment with L-NAME presented several areas of repairing fibrosis in left ventricles, and this effect was also abolished by BAY cotreatment. Our results demonstrate that BAY 41-2272 inhibits hypertension and prevents heart abnormalities (cardiac hypertrophy and increased fibrosis areas) induced by NO synthase inhibition.

Protective effects of BAY 41-2272 (sGC stimulator) on hypertension, heart, and cardiomyocyte hypertrophy induced by chronic L-NAME treatment in rats.

This study evaluated the effects of BAY 41-2272 (BAY), a specific activator of sGC NO-independent action on changes of mean arterial blood pressure, heart and left ventricle weight indexes, cardiomyocyte hypertrophy (Vv) and fibrosis area induced by chronic N-nitro-L-arginine methyl ester (L-NAME) treatment in rats. The animals were divided into (a) control group, (b) L-NAME group, (c) L-NAME+BAY group, and (d) BAY group. Eight weeks of L-NAME treatment caused a significant increase in mean arterial blood pressure when compared with untreated rats (173 +/- 11.1 and 109 +/- 5.0 mm Hg, respectively; P < 0.01). L-NAME + BAY cotreatment abolished the L-NAME-induced hypertension (112 +/- 5.1 mm Hg; P < 0.01). Significant increases in heart and left ventricle weight indexes and in Vv were observed in the L-NAME-treated animals compared with control group, and concomitant treatment with BAY significantly attenuated this hypertrophic effect. Treatment with L-NAME presented several areas of repairing fibrosis in left ventricles, and this effect was also abolished by BAY cotreatment. Our results demonstrate that BAY 41-2272 inhibits hypertension and prevents heart abnormalities (cardiac hypertrophy and increased fibrosis areas) induced by NO synthase inhibition.

Mid-Jurassic age for the Botany Bay Group: implications for Weddell Sea Basin creation and southern hemisphere biostratigraphy

New U–Pb zircon ion-microprobe ages from the alluvial conglomerates and flood plain sediments of the Botany Bay Group demonstrate that sedimentation occurred at c. 167 Ma, coeval with rift-related silicic volcanism in the northern Antarctic Peninsula. In contrast, rift-related volcanism and sedimentation in the southern Antarctic Peninsula (Latady Basin) occurred at c. 183 Ma. The new data indicate that syn-rift sedimentation and volcanism was diachronous from south to north, consistent with early opening of the Weddell Sea embayment by anti-clockwise rotation of the Antarctic Peninsula in the Mid-Jurassic. A definitive date for the Botany Bay Group floras has important implications for Southern Hemisphere biostratigraphic correlations.

Macrofossil floras of the Latady Basin, Antarctic Peninsula

New collections of plant material from the Merrick and Sweeney Mountains provide further evidence of Jurassic floral diversity in the Antarctic Peninsula. Eighteen taxa are recognised, including sphenophytes (Equisetum), ferns (Cladophlebis, Sphenopteris, Coniopteris), Bennettitales (Otozamites, Zamites, Ptilophyllum, Dicytozamites, Williamsonia), conifers (Pagiophyllum, Brachyphyllum, Elatocladus), and other seed plants (Taeniopteris, Archangelskya, Pachypteris). Many of these species occur in floras from the Botany Bay Group (Early‐Middle Jurassic), and other Late Jurassic to Early Cretaceous sites across the Antarctic Peninsula. The plant material from the Latady Basin occurs in two main associations with distinct floristic compositions that reflect local environmental and taphonomic conditions. The richest localities occur in the deltaic settings, where paleosoil and leaf litter layers are preserved. In contrast, relatively little plant material is found in the wholly marine units such as those from the Hauberg Mountains.

The Archean Murmac Bay Group: evidence for a giant Archean rift in the Rae Province, Canada

The lower amphibolite to-granulite facies Archean Murmac Bay Group of the southwestern Rae Province, Canada, formed during continental extension (rifting) of an underlying granitoid basement complex that includes the 3060±40Ma Lodge Bay Granite and the 2999±7Ma Cornwall Bay Granite. The contact between the Murmac Bay Group and the basement complex is an unconformity that is locally marked by polymictic conglomerate. Overlying the conglomerate is basal quartzite of the Murmac Bay Group that contains a laterally extensive (>10km) intraformational oligomictic quartzite-pebble conglomerate that may have formed by uplift during rifting. Distinctive medium- to coarse-grained gabbro dykes and sills that cut both the basement complex and the basal quartzite are interpreted as feeders to stratigraphically overlying tholeiitic basalt flows that have geochemical signatures consistent with formation in a continental rift setting. The quartzite-basalt contact exhibits rare stratigraphic interlayering, and is a horizon along which oxide-and silicate-facies iron formation, dolostone, and pelite locally occur. Ultramafic rocks with komatiitic compositions also intrude these lower stratigraphic units. The upper Murmac Bay Group is dominated by pelitic to psammitic rocks that may represent deepening of the sedimentary basin during continued extension. Ancient approximately 3.62 and >3.7Ga grains dominate the detrital zircon population of the Murmac Bay Group sediments, but deposition occurred after approximately 2.77Ga, the youngest detrital zircon in our study. The age of the Murmac Bay Group is thus constrained as younger than approximately 2.77Ga and older than the crosscutting 2631±12Ma Dead Man and Donaldson Lake Granites.The gross lithological and stratigraphic make-up of the Murmac Bay Group closely resembles that of the Prince Albert, Woodburn Lake and Mary River groups of the northern Rae Province, all three of which have been interpreted as approximately 2.7Ga continental rift successions. We propose that the Murmac Bay Group is correlative with these successions. If correct, the total length of this Neoarchean rift is at least 2000km, extending from Baffin Island to northwestern Saskatchewan, Canada. The supracrustal rocks of the rift record the break-up of a large Paleo- to early Neoarchean continent (Nunavutia), which experienced magmatic events at approximately 3.0, 3.62, and >3.7Ga.

Tectonic setting and regional correlation of Ordovician metavolcanic rocks of the Casco Bay Group, Maine: evidence from trace element and isotope geochemistry

Ordovician metamorphic rocks of the Casco Bay Group are exposed in an approximately 170 km long NE-trending belt (Liberty-Orrington belt) in southern and south-central Maine. Geochemical analysis of rocks within the Spring Point Formation (469±3 Ma) of the Casco Bay Group indicate that it is an assemblage of metamorphosed bimodal volcanic rocks. The mafic rocks (originally basalts) have trace element and Nd isotopic characteristics consistent with derivation from a mantle source enriched by a crustal and/or subduction component. The felsic rocks (originally rhyolites and dacites) were likely generated through partial melting of continental crust in response to intrusion of the mafic magma. Relatively low initial εNd values for both the mafic (−1.3 to +0.6) and felsic (−4.1 to −3.8) rocks suggest interactions with Gander zone continental crust and support a correlation between the Casco Bay Group and the Bathurst Supergroup in the Miramichi belt of New Brunswick. This correlation suggests that elements of the Early to Middle Ordovician Tetagouche-Exploits back-arc basin can be traced well into southern Maine. A possible tectonic model for the evolution of the Casco Bay Group involves the initiation of arc volcanism in Early Ordovician time along the Gander continental margin on the eastern side of the Iapetus Ocean basin. Slab rollback and trenchward migration of arc magmatism initiated crustal thinning and rifting of the volcanic arc around 470 Ma and resulted in the eruption of the Spring Point volcanic rocks in a back-arc tectonic setting.

Revisions to the Paleoproterozoic Sequence A, based on reflection seismic data across the western plains of the Northwest Territories, Canada

Abstract New insights into Proterozoic Sequence A were gained from analysis of reflection seismic data acquired across the western plains of the Northwest Territories, Canada, a re-examination of geological maps of the Coppermine Homocline, and recently published studies in the Cordillera. Results show that the sequence contains four unconformity-bounded sub-sequences and should be, therefore, subdivided. They are informally named here, from oldest to youngest, as A1, A2, A3 and A4. Sequence A1 is laterally restricted and consists of the Bigbear and Fault River formations of the Hornby Bay Group on Coppermine Homocline, seismic Sequence A1 in the subsurface, and is potentially equivalent to the very thick Wernecke Supergroup of the Cordillera. Sequence A2 on Coppermine Homocline consists of the clastic Lady Nye Formation, carbonates of the East River Formation, and the syntectonic clastics of the Kaertok and LeRoux formations of the Hornby Bay Group. Sequence A2 in the subsurface consists of the Basinal, Platformal, and Syntectonic seismic units and does not correlate with strata of the Cordillera. A2 strata in the subsurface and on the homocline were deformed by the intracratonic style Forward Orogeny (ca. 1.66 Ga), which is likely an expression of the Racklan Orogeny, described from the Cordillera. Sequence A3 consists of the Dismal Lakes Group on Coppermine Homocline, seismic Sequence A3 in the subsurface and the Pinguicula Group in the Cordillera. It overlies a regional unconformity that bevelled the underlying Forward Orogeny and Racklan Orogeny structures and completely removed Sequence A2 strata from the region of the present Cordillera. Sequence A4 is made up of the Coppermine River Group on the homocline and the Tweed Lake basalts in the subsurface. No correlative strata have been reported in the Cordillera.

Silurian deformation and metamorphism of Ordovician arc rocks of the Casco Bay Group, south-central Maine

The Casco Bay Group in south-central Maine consists of a sequence of Late Cambrian to Early Ordovician interlayered quartzofeldspathic granofels and pelite (Cape Elizabeth Formation) overlain by Early to Late Ordovician back-arc volcanic (Spring Point Formation) and volcanogenic sedimentary rocks (Diamond Island and Scarboro formations). These rocks were tightly folded and subjected to low-pressure amphibolite-facies metamorphism in the Late Silurian. This phase of deformation and metamorphism was followed by the development of a variety of structures consistent with a period of dextral transpression in Middle Devonian – Early Carboniferous time. Previously dated plutons within the sequence range in age from 422–389 Ma and record a period of prolonged intrusive activity in the region. Similarities in age, volcanic rock geochemistry, and lithologic characteristics argue strongly for a correlation between rocks of the Casco Bay Group and those in the Miramichi belt of eastern Maine and northern New Brunswick. The Cape Elizabeth Formation correlates with Late Cambrian to Early Ordovician sediments of the Miramichi Group (Gander Zone) and the Spring Point through Scarboro formations correlate with Early to Late Ordovician back-arc basin volcanics and volcanogenic sediments of the Bathurst Supergroup. The folding and low-pressure metamorphism of the Casco Bay Group is attributed to Late Silurian to Early Devonian terrane convergence and possible lithospheric delamination that would have resulted in a prolonged period of intrusive activity and elevated temperatures at low pressures. Continued convergence and likely plate reconfigurations in the Middle Devonian to Carboniferous led to widespread dextral transpression in the region.

Thelodont Scales from the Lower Devonian Red Bay Group, Spitsbergen

Scales of nine thelodont taxa are described from the Red Bay Group of Spitsbergen, also characterized by its assemblage of other typical Early Devonian vertebrates. The four thelodont–bearing horizons of the lower Fraenkelryggen Formation yield typical Lochkovian thelodont assemblages, containing Boreania minima, Canonia grossi, Nikolivia depressa sp. nov., Nikolivia elongata, Nikolivia gutta and Turinia pagei. One horizon from the younger Ben Nevis Formation has a similar thelodont assemblage, except for two new taxa; Apalolepis angelica sp. nov. and Turinia barentsia sp. nov. The appearance of Turinia polita and the disappearance of Boreania minima is also characteristic for this assemblage. Comparison with similar faunas from the Northern Hemisphere supports this faunal change and allows further elaboration of Early Devonian thelodont biostratigraphy.

Phylogeography of the tidewater goby, Eucyclogobius newberryi (Teleostei, Gobiidae), in coastal California.

The tidewater goby, Eucyclogobius newberryi, inhabits discrete, seasonally closed estuaries and lagoons along approximately 1500 km of California coastline. This species is euryhaline but has no explicit marine stage, yet population extirpation and recolonization data suggest tidewater gobies disperse intermittently via the sea. Analyses of mitochondrial control region and cytochrome b sequences demonstrate a deep evolutionary bifurcation in the vicinity of Los Angeles that separates southern California populations from all more northerly populations. Shallower phylogeographic breaks, in the vicinities of Seacliff, Point Buchon, Big Sur, and Point Arena segregate the northerly populations into five groups in three geographic clusters: the Point Conception and Ventura groups between Los Angeles and Point Buchon, a lone Estero Bay group from central California, and San Francisco and Cape Mendocino groups from northern California. The phylogenetic relationships between and patterns of molecular diversity within the six groups are consistent with repeated, and sometimes rapid, northward and southward range expansions out of central California caused by Quaternary climate change. Plio-Pleistocene tectonism, Quaternary coastal geography and hydrography, and historical human activities probably also influenced the modern geographic and genetic structure of E. newberryi. The phylogeography of E. newberryi is concordant with phylogeographic patterns in several other coastal California taxa, suggesting common extrinsic factors have had similar effects on different species. However, there is no evidence of a phylogeographic break coincident with a biogeographic boundary at Point Conception.

A new macroflora from the South Orkney Islands, Antarctica: evidence of an Early to Middle Jurassic age for the Powell Island Conglomerate

A macroflora from John Peaks, Powell Island, contains Sagenopteris nilssoniana, Cladophlebis oblonga, Brachyphyllum sp., Elatocladus confertus, and Sphenopteris sp. The macroflora is best correlated with the Botany Bay Group flora, suggesting an Early to Middle Jurassic age for the Powell Island Conglomerate. This age supports new interpretations for the geological evolution of the Antarctic Peninsula that suggest the initial phase of Gondwana break-up was manifested as small rift grabens with continental deposits.

Deformation of the Old Red Sandstone of NW Spitsbergen; links to the Ellesmerian and Caledonian orogenies

Abstract The Late Silurian?-Devonian fluvial deposits of northern Spitsbergen were deposited on basement with Caledonian and earlier metamorphic ages in which two distinct terranes are recognized (Biskayerhalvøya and Krossfjorden). These form part of the central of three major terranes in Svalbard, assembled during the Caledonian Orogeny. The subsequent geological history of the Svalbard area has been strongly influenced by the north-trending structures which were active as transcurrent fault zones at this time. The unconformable base of the Siktefjellet Group, a Late Silurian?-earliest Devonian sequence of coarse conglomerates and breccias, overlain by fluvial sandstones, is preserved only on the Biskayerhalvøya terrane, and the final juxtaposition of the two terranes (during the Haakonian sinistral strike-slip phase) is interpreted to post-date the deposition of these sediments. The Lochkovian Red Bay Group, a sequence of conglomerates, fluvial sandstones and siltstones, was deposited on both terranes. This has been mapped and correlated throughout the basin exposure, allowing the reconstruction of the tectonic history. Sedimentation was influenced by active faulting during deposition of the oldest Wulffberget Formation, but subsequent deposits show little evidence of this. Deposition was interrupted in latest Lochkovian time by renewed sinistral strike-slip faulting, which broke up an area of the basin into rotating fault blocks, across which about 30 km of extension occurred. This was followed by east-west shortening, which uplifted the Red Bay basin and underlying basement, developing large folds, locally with related thrusting. The Monacobreen phase is defined to involve this deformation. The Andr0.000000e+00e Land Group reflects a subsequent renewal of subsidence, and re-establishment of an extensive fluvial basin, occupying an area east of the inverted Red Bay basin. Conglomeratic units that overlie the Red Bay Group are interpreted as the products of the reworking of the uplifted Red Bay basin and its basement. The Latest Devonian-Earliest Carboniferous Svalbardian phase again involved east-west shortening, with limited strike-slip faulting, but it is difficult to discriminate these effects from the Monacobreen phase in the Siktefjellet and Red Bay groups. A review of North Atlantic and Arctic Devonian basins shows that during deposition of the Red Bay and Andrée Land groups, the tectonics of Svalbard was more similar to that of the developing Ellesmerian orogen, than to that of the collapsing Caledonian orogen. A model is proposed that links the repeated extension and shortening seen from Early Devonian time in north Spitsbergen to anticlockwise rotation of the Chukotka-Alaska plate, about an axis near the position of Svalbard during Ellesmerian collision, coupled with minor Caledonian-related strike-slip movement along reactivated fault zones.

Provenance and tectonic implications of Palaeoproterozoic (c. 1740 Ma) quartz porphyry clasts in the basal Old Red Sandstone (Lilljeborgfjellet Conglomerate Formation) of northwestern Svalbard's Caledonides

The Lilljeborgfjellet Conglomerate Formation composes the lower part of the alluvial Siktefjellet Group of northwestern Spitsbergen's Old Red Sandstone succession. Siktefjellet strata are of late Silurian or early Devonian age, but lack precise age-diagnostic fossils. They are unconformably overlain by conglomerates and sandstones of the Red Bay Group, which contain a well established fish fauna of Lochkovian age. The Lilljeborgfjellet Conglomerate rests with a major unconformity on high-grade (with eclogites) schists and gneisses, with associated corona gabbros and granitic gneisses. Previous isotope-age studies have shown that these igneous rocks yield U/Pb ages of c. 950 Ma, and that the eclogite facies metamorphism may be of Caledonian or late Neoproterozoic age. The high P/high T rocks are intercalated with and overlain by schists affected only by Caledonian amphibolite facies metamorphism, recorded by 40Ar/39Ar and Rb/Sr cooling ages of 400–430 Ma.In the Lochkovian Red Bay Group of the Raudfjorden Graben, two horizons of tuffites occur, interbedded with sandstones. New studies of eight zircons from these volcanic rocks have provided single-zircon lead-evaporation ages of c. 950 and c. 1350 Ma; one yielded 440 Ma. All these zircons are probably derived from the underlying basement rocks, the ages being significantly older than the Devonian host strata (c. 410 Ma).The clasts in the Lilljeborgfjellet Conglomerate are generally angular to subrounded and derived locally from the underlying high-grade metamorphic complex. A subordinate (usually less than 1%, but up to about 10%) component of the clasts is a quartz porphyry that is not known in the exposed bedrock anywhere in northwestern Spitsbergen. The quartz porphyries are better rounded than the other clasts; however, the maximum diameter reaches 1.5 metres, indicating that transport distances are unlikely to have exceeded a few kilometres. Three quartz porphyry boulders have been dated by the single-zircon lead-evaporation method and shown to be of Palaeoproterozoic age, yielding ages of 1735±4, 1736±5 and 1739±5 Ma that have not previously been detected in the northwestern part of Svalbard's Caledonides.The quartz porphyry clasts show no evidence of the widespread high-grade tectonothermal activity of Mesoproterozoic and early Palaeozoic age that influenced northwestern Spitsbergen. It is therefore concluded that the most probable source of these clasts lies to the east in the unexposed basement beneath the Old Red Sandstones of the Andrèeland–Dicksonland Graben. The Lilljeborgfjellet quartz porphyry clasts are closely similar in age to the granitic rocks of Ny Friesland. Whereas the latter were subject to Caledonian high amphibolite facies metamorphism, the quartz porphyry clasts have only been affected by a low greenschist facies overprint. Nevertheless, the similarity in age suggests an affinity to Ny Friesland and it is proposed here that the Breibogen–Bockfjorden Fault defines the most important boundary between Svalbard's Caledonian terranes.

Late Silurian and Early Devonian stratigraphy and probable strike-slip tectonics in northwestern Spitsbergen

The stratigraphy of the Siktefjellet and Red Bay groups of northwestern Spitsbergen is revised in the light of new fieldwork. An early Early Devonian (Lochkovian) age is indicated by the rich fossil vertebrate faunas of the Red Bay Group. The underlying Siktefjellet Group is likely to be Late Silurian in age, although there is no direct fossil evidence of this. The most abundant sediment type in the two groups is fine-grained fluvial sandstone, although conglomerates and lacustrine siltstones also occur. The conglomerates that predominate in the lowest parts of both groups imply the presence of fault scarps at the surface. There has been much debate about the importance of strike-slip faulting in the area, particularly in relation to the major north–south trending Raudfjorden and Breibogen faults. Between these faults, the Biskayerhuken–Holtedahlfonna terrane contains a zone for which the deliberately genetic name ‘Siktefjellet Strike-slip Zone’ is proposed. This zone is characterized by evidence for a succession of events that, taken together, suggest a history of continuing, repeated strike-slip. These events were: (1) the tectonism and metamorphism of the basement (Krossfjorden Group) and the emplacement of the high-grade Richarddalen Complex, (2) development of crush zones in the basement, (3) deposition of the Siktefjellet Group in two distinct basins (perhaps of pull-apart origin), (4) deposition of the Red Bay Group (first as discrete scarp-related conglomerates, and then as part of a more stable fluvial basin), (5) localized compressional deformation of the Siktefjellet and Red Bay groups.

The Proterozoic Thule Supergroup, Greenland and Canada: history, lithostratigraphy and development

A new lithostratigraphic scheme for the Proterozoic (Neohelikian-Hadrynian) intracratonic Thule Basin of northern Baffin Bay is presented. This basin, preserved between 76° and 79° N in Greenland and Ellesmere Island, Canada, contains little deformed and unmetamorphosed strata at least 6 km thick that are referred to the Thule Supergroup. The succession is composed of continental to shallow marine sediments with prominent red bed units, and one main interval of basaltic volcanic rocks. Diabase sills representing both the Mackenzie (Neohelikian) and Franklin (Hadrynian) magmatic episodes occur at certain levels.&#x0D; The bulletin has three main parts. The forerunner of the new supergroup, the Thule Group, is infamous for the nomenclatorial chaos that has surrounded its use. Consequently the first part is a historical summary as background to the definitive nomenclatorial revision. The second and main part on lithostratigraphy splits the Thule Supergroup into 36 formal divisions: 5 groups, 15 formations and 16 members. Twenty geological maps show the regional distribution of the defined units that are represented by 78 stratigraphic logs and sections. The third part summarises basin development as a restricted or semi-restricted depocentre on the northern margin of the Canadian-Greenlandic shield. Evolution was controlled by block faulting and basin sagging in a divergent plate regime.&#x0D; The Smith Sound Group, up to 700 m thick, represents the northern platform and basin margin equivalent of the Nares Strait and Baffin Bay Groups of the central basin. Composed of sandstones and shales with subordinate stromatolitic carbonates, the Smith Sound Group represents an overall shelf environment with long-lasting conditions for shallow water to subaerial deposition. Supratidal to marginally marine and intermittently lacustrine sedimentation prevailed.&#x0D; The Nares Strait Group, up to 1200 m thick and representing the basal strata of the central basin, is composed of sandstones and basaltic volcanics including flows, sills and volcaniclastic deposits, as well as shale- and carbonate-dominated intervals. The Group represents deposition in alluvial plain, littoral and offshore environments, with accompanying terrestrial tholeiitic volcanicity.The Baffin Bay Group, overlying conformably the previous group, represents the most widespread strata of the Thule Basin reaching a maximum thickness of up to 1300 m. Sandstones and quartz-pebble conglomerates, with important intervals of shales and siltstones, represent mixed continental to marine shoreline environments with an interval of deeper water deposition, possibly in a prodelta or offshore basin.&#x0D; The Dundas Group, 2 to 3 km thick and following the previous group along a gradational contact, comprises sandstones, siltstones and shales with lesser amounts of carbonate and evaporit. Deposition was in an overall deltaic to offshore environment.&#x0D; The youngest strata, the Narssarssuk Group, 1.5 to 2.5 km thick, are preserved in a graben on the south-eastern margin of the basin. The cyclic carbonate - red bed siliciclastic sequence with evaporites represents deposition in a low-energy, hypersaline, peritidal environment in conditions perhaps analogous to modern coastal sabkhas.