bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleomagnetic evidence for multiple Late Pliocene - Early Pleistocene glaciations in the Klondike area, Yukon Territory
Authors: Froese D G , Barendregt R W , Enkin R J , Baker J
Published: April 2011

The Late Pliocene - Early Pleistocene terraces of the Klondike area provide a conformal record of sedimentation which marks the transition from preglacial to glacial conditions, and is one of the most complete records of glaciation and interglaciation in the northern Cordillera. Preglacial sedimentation is recorded in the Lower White Channel gravel that contains a reverse-normal polarity sequence. A re-aggradation of the nonglaciated valleys of the goldfields in response to Late Pliocene cooling is recorded by the Upper White Channel gravel, which is characterized by a dominant normal polarity with a lower reversal likely associated with the first ice-wedge casts. Klondike gravel interfingers with Upper White Channel and is normally magnetized, indicating an equivalent magnetostratigraphic unit. This glaciofluvial gravel provides evidence of extra-basinal clasts, marking a major reorganization of drainage associated with the first advance of the Cordilleran Ice Sheet in western Yukon Territory correlated with the Gauss chron (>2.58 Ma). An intermediate terrace in Klondike valley is overlain by 8 m of fluvial and glaciofluvial gravel named the Midnight Dome gravel. This gravel is mantled by 15 m of loess and hillslope deposits, named the Midnight Dome loess, which preserve at least three interglacial pollen assemblages, and a reverse-normal-reverse-normal polarity sequence assigned to the late Matuyama chron, including Jaramillo subchron (1.07-0.99 Ma), and early Brunhes chron (<0.78 Ma). The oldest glaciations here, based on the preferred interpretation, extend well into the Pliocene (>2.58 Ma) making these among the oldest glacial sediments in North America.
The thermal regime of a retrogressive thaw slump near Mayo, Yukon Territory
Authors: Burn C R
Published: April 2011

The development of a retrogressive thaw slump near Mayo, Yukon Territory, has been traced from initiation by bank erosion (~1949) of the Stewart River to stabilization in 1993-1994. The stabilized headwall of the slump is 450 m from the river, and the slope of the slump floor is 3°. A transect of the slump from the river to the stabilized headwall was drilled in July 1995, to determine the extent and rate of permafrost degradation in the slump floor. Thermistors were placed in access tubes to 12 m depth at five sites, four near the transect and one in undisturbed terrain, to determine the magnitude of thermal disturbance due to slump development. Data loggers at the sites recorded the ground temperature at 1 m depth for two years from August 1995. The annual mean ground temperatures measured by the data loggers varied between 1.2° and 1.8°C in the slump, compared with -2.4°C in undisturbed ground, indicating a disturbance of about 4°C due to slumping. The depth of thaw in the slump floor is consistent with the Stefan solution for thawing of permafrost. Conduction is the dominant mode of heat transfer in the slump, where the soil is fine grained and there is almost no organic horizon. Winter ground temperatures at 1 m depth were nearly 6°C warmer in the slump than in the surrounding forest, even though snow depths were similar, due to the release of latent heat during prolonged frost penetration. These data demonstrate the importance of subsurface conditions on near-surface ground temperatures in winter.
Tectonic setting of the Taltson magmatic zone at 1.92.0 Ga: a granitoid-based perspective
Authors: Chacko Thomas , De Suman K , Creaser Robert A , Muehlenbachs Karlis
Published: April 2011

The Paleoproterozoic Taltson magmatic zone is one of the key tectonic features of western Laurentia. The existing tectonic model for the belt envisions its formation by subduction of oceanic crust beneath a continental margin, followed by direct collision between formerly separate crustal blocks. We tested this model by comparing the large geochemical and isotopic database available for Taltson magmatic zone granitoids with similar databases for Phanerozoic granitoid suites from different tectonic environments. The comparison reveals that the early granitoid suite of the Taltson magmatic zone, which had been ascribed to the subduction phase of orogenesis, lacks the mantle signature apparent in granitoids of Phanerozoic continental-margin arc settings. Instead, both early and late suites appear to have an intracrustal origin, similar to Mesozoic and Cenozoic granitoids of the Cordilleran interior of western North America, which formed in the distant hinterland of a convergent plate margin. In light of these findings, we propose an alternative tectonic model, which envisions formation of the Taltson magmatic zone in a plate-interior rather than a plate-margin setting. Modern-day examples of this setting are found in the mountain belts of central Asia, such as the Tian Shan, which are located many hundreds of kilometres away from the plate margin. The critical feature of these belts that make them an appealing analogue for the Taltson magmatic zone is that there is no subduction zone closely associated with their formation. Rather, magmatism occurs in response to thickening of crust in the continental interior.
Temporal evolution of a deeply eroded orogen: the Nagssugtoqidian Orogen, West Greenland
Authors: Connelly James N , van Gool Jeroen AM , Mengel Flemming C
Published: April 2011

The east-northeast-trending Paleoproterozoic Nagssugtoqidian Orogen of West Greenland records the response of deep crust to collision of the North Atlantic craton and a lesser known cratonic mass to the north. This paper presents conventional UPb ages of documented magmatic and thermotectonic events within this orogen, thus providing a precise time frame for its development and offering a test of previous spatial and temporal correlations with segments of the Trans-Hudson Orogen of northern Labrador and Quebec. Convergence of the two cratons culminated in a collision that commenced after 1873+74Ma, the crystallization age of the youngest known pre-Nagssugtoqidian, subduction-related intrusion. Earliest collisional deformation was thrust dominated (west-northwest vergent) and caused thickening and consequent heating to peak temperatures by ca. 1850 Ma. Subsequent north-south shortening at elevated temperatures was accommodated by a fold-dominated style of deformation dated at 1825 ± 1 Ma. Between 1821 and 1778 Ma, temperatures remained sufficiently high to generate pegmatites, metamorphic zircon, and titanite, but no major, penetrative structures are known to have formed in this interval. Further shortening between 1779 ± 6 and 1774 ± 6 Ma exploited preexisting fabrics in steep F3fold limbs to form discrete, east-northeast  west-southwest-oriented, sinistral steep belts that are not important crustal boundaries. One of these late, steep belts is cut by 17721761 Ma pegmatites, indicating that deformation was waning by this time. Slow cooling followed the late shearing, with rutile closing in the central Nagssugtoqidian Orogen as late as 1676 ± 10 Ma. The timing of tectonic events in the Nagssugtoqidian Orogen is indistinguishable from that of the QuebecBaffin and Torngat segments of the Trans-Hudson Orogen of northeastern Laurentia. Accepting an intercratonic setting for the Nagssugtoqidian Orogen, this new data require that the QuebecBaffin, Torngat, and Nagssugtoqidian orogens meet in a triple junction offshore. This geometry implies a genetic link between the Rinkian and Nagssugtoqidian belts of West Greenland, thereby defining a middle- to deep-crustal collisional belt more than 900 km wide.
Evidence for initial calcite-aragonite composition of Lower Algal Chert Member ooids and stromatolites, Paleoproterozoic Gunflint Formation, Ontario, Canada
Authors: Sommers M G , Awramik S M , Woo K S
Published: April 2011

The chert members of the Paleoproterozoic Gunflint Formation, Ontario, Canada, are commonly regarded as examples of primary silica chemical sediments. This interpretation is founded upon the ubiquitous nature of silica, high fidelity of preservation of microfossils found within, and lack of observed primary carbonate. Previous arguments for silica replacement of carbonate are based on indirect evidence and are largely dismissed. Thus, Gunflint microfossils are regarded as having lived in a silica-rich environment, which makes them unusual compared to most other pre-Phanerozoic microfossils that are known from silicified carbonates. We present evidence that carbonate was a primary mineral species of the Lower Algal Chert Member (where most of the microbiota are found). Most compelling are iron-stained, low-Mg calcite ooids containing (1) well-preserved growth laminae, (2) textures indicating a disrupted tangential fabric of growth laminae, and (3) quartz crosscutting the growth laminae. These indicate the initial mineral was a carbonate, possibly aragonite. Less-compelling evidence is found in stromatolite columns. Specularite crystals in low-Mg calcite display crosscutting relationships with calcite and quartz indicating that calcite was primary, specularite secondary, and quartz tertiary. The crosscutting relations show that silicification took place in at least two stages. One of the silicification events took place very early in diagenesis. Thus the Gunflint microbiota may not have existed in a radically different environment (silica precipitating) than those of most other known Proterozoic microbiota. High fidelity of preservation of microfossils does not always indicate that the mineral entombing them was the primary mineral precipitated from aqueous solution.
A calcareous foraminiferal faunule from the upper Albian Viking Formation of the Giroux Lake and Kaybob North fields, northwestern Alberta: implications for regional biostratigraphic correlation
Authors: Stelck C R , MacEachern J A , Pemberton S G
Published: April 2011

Arenaceous foraminifera from the upper Albian Viking Formation and associated strata are recorded and charted from five wells in the northwestern portion of the West Alberta Basin, viz. Gulf Giroux Lake 04-11-66-21W5, Candel Arco Giroux Lake 00/10-05-65-20W5, Pan Am B-1 Giroux 02/10-05-65-20W5, Calstan B.A. Kaybob W 02-28-63-20W5, and Chevron Fox Creek 10-15-62-19W5. An anomalous calcareous foraminiferal component in three Gulf Giroux Lake samples is illustrated. Ichnological, sedimentological, and stratigraphic studies of the Viking Formation strata, based on 26 cored intervals, indicate largely transgressive, shallow-marine deposition in the area. The microfaunal and ichnological assemblages indicate a general increase in salinity toward normal marine conditions. Facies analysis demonstrates the stacking of two shoreface parasequences, truncated by wave-ravinement surfaces. The calcareous foraminifera in the Viking Formation are associated with abundant and diverse arenaceous foraminifera, with arctic affinities that we have used for determining the microfaunal zone positions. Biostratigraphic correlation has been made with a calcareous faunule in the lower part of the Hasler Formation, within the expanded Fort St. John Group, found in the southern portion of the Keg River subbasin, Hudson Hope region, northeastern British Columbia. This helps to resolve the problem of correlating the stratigraphically equivalent Paddy Member at the type section near the town of Peace River, Alberta.
The Margaree orthogneiss: an Ordovician, peri-Gondwanan, mafic-felsic igneous complex in southwestern Newfoundland
Authors: Valverde-Vaquero Pablo , Dunning Greg R , van Staal Cees R
Published: April 2011

The igneous protoliths of the Margaree orthogneiss intruded the peri-Gondwanan rocks of the Port-aux-Basques Complex, in the southwestern corner of the Hermitage Flexure, prior to regional deformation and metamorphism. Field relationships and UPb geochronology indicate that the Margaree orthogneiss represents a 20 km long, mafic-felsic intrusive complex formed by amphibolite, dioritic orthogneiss, 474+14-4 Ma hornblende-bearing tonalitic orthogneiss with mafic enclaves, 472 ± 2.5 Ma and 465 ± 3 Ma biotite-bearing granitic orthogneiss, and minor ultramafic rocks. Most amphibolite have the chemistry of volcanic-arc tholeiite and are interpreted to be coeval with the intrusion of tonalitic and granitic magma with volcanic-arc geochemical signatures. Locally, mafic magmatism continued after the intrusion of the 465 Ma granite. The Margaree orthogneiss and its country rock were overprinted by upper amphibolite-facies metamorphism and deformation associated with the final closure of the Iapetus Ocean. A late-synkinematic granite dates the late stages of the high-temperature regional deformation at 417+7-4 Ma, while metamorphic titanite (411 ± 2 Ma) is interpreted to date extensive recrystallization under amphibolite-facies conditions as Early Devonian. The Margaree orthogneiss is broadly coeval with the plutons that postdate the Early Ordovician Penobscottian arc  passive margin imbrication in central and southern Newfoundland. It also coincides with the extensive late Arenig  early Llanvirn back-arc rifting event along the entire peri-Gondwanan margin of the northern Appalachians. The external position of the Port-aux-Basques Complex with respect to the back-arc elements in the Hermitage Flexure, coupled with the rock types and geochemistry of the orthogneiss, suggest formation of the Margaree orthogneiss in an arc and (or) back-arc transitional setting.
Conodonts and corals in kimberlite xenoliths confirm a Devonian seaway in central Ontario and Quebec
Authors: McCracken Alexander D , Armstrong Derek K , Bolton Thomas E
Published: April 2011

Eighteen samples containing sedimentary rock xenoliths were obtained from cores drilled into eight Mesozoic kimberlite pipes in the Kirkland Lake area, Ontario, and in Ontario and Quebec near Lake Timiskaming. Nine samples from five pipes contained fossils that were used for age determinations. These fossils are Middle or Late Ordovician graptolites, inarticulate brachiopods, and conodonts; Silurian and (or) Devonian conodonts; Early Devonian colonial corals; a Devonian stromatoporoid; and Early to Middle Devonian conodonts. Regionally, conodonts are unaltered (conodont colour alteration index, CAI 1). Conodont CAI values from the xenoliths are elevated (CAI 2), and a few conodonts have surface colour changes, suggesting hydrothermal alteration. Age determinations allow stratigraphic correlation between xenoliths and Paleozoic outcrops. For the Ordovician and Silurian samples, correlations are made to exposures in the nearby Lake Timiskaming outlier. For the Devonian samples, the closest possible correlative outcrops are about 300 km away. These fossils provide the first physical evidence of a connection between a Lake Timiskaming "basin" and other Ontario basins during at least part of the Devonian. These strata persisted at least until the Mesozoic before they were removed by erosion.
Late Maastrichtian age of spherule deposits in northeastern Mexico: implication for Chicxulub scenario
Authors: Stinnesbeck W , Schulte P , Lindenmaier F , Adatte T , Affolter M , Schilli L , Keller G , Stüben D , Berner Z , Kramar U , Burns S J , López-Oliva J G
Published: April 2011

In the La Sierrita area of Nuevo Leon, Mexico, three spherule layers are present and separated from the overlying siliciclastic deposits by up to 6 m of pelagic marls. The marls are of latest Maastrichtian age (Plummerita hantkeninoides (CF1) Zone, Micula prinsii Zone) and deposited under normal pelagic conditions with no significant evidence of reworking or slumping. Original deposition of the spherule layers occurred during the last 300 ka of the Maastrichtian and well prior to the Cretaceous-Tertiary (KT) boundary event. Thus, if the spherules in northeastern Mexico provide critical evidence of an impact at Chicxulub, this impact predates the KT boundary.
Reefs during the multiple crises towards the Ordovician-Silurian boundary: Anticosti Island, eastern Canada, and worldwide
Authors: Copper Paul
Published: April 2011

Multiple latest Ordovician (RawtheyanHirnantian) glaciations in central Africa, with concomitant global sea-level lowstands and cooler, restricted, equatorial carbonate shelves and ramps, interrupted by warmer interstadial highstands, had a dramatic global impact on the tropical shallow-water reef ecosystem and carbonate production. With the Ordovician-Silurian boundary strata on Anticosti Island as a global standard for a carbonate shelf-ramp setting, the latest Ordovician and earliest Silurian reveal three reef phases, ended by three extinctions. The first extinction, towards the end of the Rawtheyan, affected the last "Richmondian"-type reefs (Vaureal Formation, Mill Bay Member). The second extinction was less pronounced, ending with reefs at the base of the Prinsta Member (Ellis Bay Formation), interpreted as the top of the Normalograptus extraordinarius graptolite Subzone. The third and most severe extinction phase capped the Laframboise patch reef complex (Ellis Bay Formation), at the top of the Normalograptus persculptus Zone. In the paleotropics, the Hirnantian interglacials showed higher biodiversity than either the preceding Rawtheyan or following Rhuddanian (early Llandovery) warm intervals, a feature perhaps achieved by high innovation rates via introduction of "Silurian" reef biotas during the Hirnantian. The Anticosti reef succession is compared with latest Ordovician reefs from northwestern Europe (Baltic Basin and U.K.), the northwestern margins of Gondwana (Spain and Austria), the Urals, Siberia, Kazakhstan, northeast Russia, and China. Reefs show a global decline from the late Caradoc through late Ashgill, marked by hiatuses towards the OS boundary. A protracted 34 million-year recovery phase for Early Silurian tropical marine biotas, generally without reefs, marked the succeeding Rhuddanian; full reef recovery was delayed until the mid-Aeronian.
The "Great Extinction" that never happened: the demise of the dinosaurs considered
Authors: Sarjeant William AS , Currie Philip J
Published: April 2011

The concept of a sudden extinction of the dinosaurs, consequent upon the impact of some extraterrestrial object, is so dramatic that it has taken hold upon the imaginations of many scientists, as well as of the general public. The evidence for an impact, at approximately the level of the CretaceousTertiary boundary, is impressive. Whether it was the cause for the iridium concentrations, so widely distributed at that level, remains disputable. The wave of extinctions, so often attributed to the impact, is equally disputable. It is now evident that no clear line can be drawn between the smaller theropod dinosaurs and the birds. In that sense, the dinosaurs are not extinct. The dating of the extinction of the larger saurischians and of the ornithischians, based as it is upon evidence from only one small corner of the globe, is equally disputable. Whenever it happened, that extinction appears to have been the product of natural causes  a slow decline, occasioned by environmental changes, and not an extraterrestrially induced catastrophe. Whether the impact had any effect at all upon the dinosaurs is questionable; if so, it appears to have been not worldwide, but confined to a limited region of the Americas.
W.G.E. Caldwell, B.Sc., Ph.D. (Glasgow), D.Sc. (Sask.), F.R.S.C.  A Career Résumé
Authors: Copper Paul , Jin Jisuo
Published: April 2011

This issue of the Canadian Journal of Earth Sciences is dedicated to Professor Glen Caldwell in honour of his extensive contributions to the field of paleontology and scientific publishing. After receiving his Ph.D. degree from the University of Glasgow in 1957, Dr. Caldwell joined the Department of Geological Sciences at the University of Saskatchewan, where he stayed for more than 30 years. During his tenure, he led the way in launching a new integrated curriculum, including paleobiology, geochemistry, and geophysics, and in organizing and equipping a vigorous research program. Dr. Caldwell also organized two international symposia on Cretaceous rocks of the Western Interior Basin of North America. Over the years he served on and made distinctive contributions to a wide variety of national and international professional organizations, including the American Commission on Stratigraphic Nomenclature, GAC, NSERC, and the International Union of Geological Sciences. Dr. Caldwell served as Vice-President (Research) of The University of Western Ontario from 1988 to his retirement in 1996. He continues to teach and serve various scientific organizations, and he remains a strong advocate for basic research grants.
Structure of the Lac Nominingue  Mont-Laurier region, Central Metasedimentary Belt, Quebec Grenville Province
Authors: Harris L B , Rivard B , Corriveau L
Published: April 2011

The Lac Nominingue  Mont-Laurier region of the Central Metasedimentary Belt, Grenville Province of Quebec, comprises the granulite-facies Bondy gneiss complex (core of the Bondy gneiss dome) and overlying Sourd group metasedimentary rocks. A metamorphic foliation  transposed compositional layering (S1; host to peak-pressure parageneses) has been folded by isoclinal folds (F2 and F3) crosscut by leucosomes that host peak-temperature assemblages. The orthopyroxene isograd cuts obliquely across F3 folds, indicating that 1.201.18 Ga granulite-facies metamorphism post-dated D3. D3 structures are cut by ductile shear zones and boudinaged in D4 and are folded by regional-scale, open, upright northsouth folds (F5). Folds with shallowly dipping axial surfaces (F6) are subsequently developed in the Sourd group. F5 (and probably F6) developed prior to intrusion of the ca. 1165 Ma Chevreuil suite. In the NominingueChénéville deformation zone (NCDZ) east of the Bondy gneiss dome, Chevreuil intrusions contain north-striking magmatic and tectonic foliations. These, along with host gneisses and metasedimentary rocks, are displaced by conjugate ductile shear zones (northeast dextral and south-southeast sinistral) and north-northeast-striking thrusts. Late open folds (F8) with east-northeast-striking axial surfaces produce dome and basin interference patterns. F2 to F5 folds may have formed during either subhorizontal, eastwest contraction or eastwest extension resulting from orogenic collapse or convective lithospheric thinning following crustal thickening during terrane assembly in the Elzevirian orogeny. Structures in the NCDZ imply ESEWNW contraction and NNESSW (orogen-parallel) extension in D7 syn- to post-intrusion of the Chevreuil suite. F8 folds imply a late, Grenvillian SSENNW contraction.
Timing and tectonic setting of Stikine Terrane magmatism, Babine-Takla lakes area, central British Columbia
Authors: MacIntyre D G , Villeneuve M E , Schiarizza P
Published: April 2011

New bedrock mapping completed as part of the Nechako NATMAP Project indicates that the area between Babine and Takla lakes in central British Columbia is underlain by rocks of the Early Permian Asitka, Late Triassic Takla, and Early to Middle Jurassic Hazelton volcanic-arc assemblages of the Stikine Terrane. These are cut by large composite stocks of quartz diorite, granodiorite, and quartz monzonite previously mapped as the Late Triassic to Early Jurassic Topley intrusions. New U/Pb (n = 6) and laser 40Ar/39Ar (n = 10) isotopic age dates reported in this paper suggest there are two distinct ages of plutons: the Topley intrusive suite with isotopic ages between 218 and 193 Ma; and, east of Babine Lake, the new Spike Peak intrusive suite with isotopic ages ranging from 179 to 166 Ma. West of the main plutonic belt is a thick volcanic succession of subaerial, porphyritic andesite flows, volcanic breccias, and rhyolitic ash-flow tuffs that have isotopic ages between 185 and 174 Ma. These rocks are assigned to the Saddle Hill Formation of the Hazelton Group. The plutonic roots of this proximal arc assemblage are most likely the coeval and compositionally similar plutons of the Spike Peak intrusive suite that have been unroofed in the area east of the Takla Fault. Major oxide and trace element data support the interpretation that the Topley and Spike Peak granitic rocks formed in a juvenile volcanic-arc environment and that magmatism is related to melts generated above a long-lived subduction zone of unknown orientation.
A paleoecological analysis of a southern permafrost peatland, Charlevoix, Quebec
Authors: Zimmermann Claudia , Lavoie Claude
Published: April 2011

The southernmost site where permafrost has been located in the QuebecLabrador peninsula is in a peatland on the subalpine summit of Lac des Cygnes Mountain (47°41'N, 70°36'W). Because of the thickness of its peat deposit, this site contains rich ecological information about the history of the peatland and its surrounding subalpine environment. We conducted a detailed macrofossil analysis to reconstruct the 6000-year history of the peatland. In general, the development of the Lac des Cygnes Mountain peatland has followed the classic succession of rich fen  poor fen  bog found in other peatlands in subarctic, boreal, and temperate environments. An abrupt decline in all tree macrofossils ca. 4000 BP suggests that a major deforestation event occurred on the summit of Lac des Cygnes Mountain. The exact cause of this deforestation event is unknown, but fire is a possible factor. The lack of absolute chronological resolution near the top of the macrofossil record precludes proper dating of permafrost inception, but the balance of evidence appears to indicate that the permafrost is modern.
Late Quaternary glacial and interglacial environments of the Nechako River - Cheslatta Lake area, central British Columbia
Authors: Plouffe A , Levson V M
Published: April 2011

The Quaternary stratigraphy of the Nechako River  Cheslatta Lake area of central British Columbia is described and interpreted to reconstruct the late Quaternary history of the region. Exposures of glacial and nonglacial sediments deposited prior to the last glaciation (Fraser) are limited to three sites. Pollen assemblages from pre-Fraser nonglacial sediments at two of these sites reveal forested conditions around 39 000 BP. During the advance phase of the Fraser Glaciation, glacial lakes were ponded when trunk glaciers blocked some tributary valleys. Early in the glaciation, the drainage was free in easterly draining valleys. Subsequently, the easterly drainage was blocked either locally by sediments and ice or as a result of impoundment of the Fraser River and its tributaries east of the study area. Ice generally moved east and northeast from accumulation zones in the Coast Mountains. Ice flow was influenced by topography. Major late-glacial lakes developed in the Nechako River valley and the Knewstubb Lake region because potential drainage routes were blocked by ice.
Imbricate architecture of the upper Paleozoic to Jurassic oceanic Cache Creek Terrane, central British Columbia
Authors: Struik L C , Schiarizza P , Orchard M J , Cordey F , Sano H , MacIntyre D G , Lapierre H , Tardy M
Published: April 2011

Upper Paleozoic to Lower Jurassic oceanic rocks of the Cache Creek Terrane near Fort St. James, in central British Columbia, form a stack of thrust sheets cut by steeply dipping strike-slip faults. Paleontologically dated upper Paleozoic strata include bioclastic shallow-water limestone and ribbon chert. Isotopically dated Permian rocks consist of tonalite sills and stocks and rhyolite flows intercalated with basalt flows. Paleontologically dated lower Mesozoic rocks include greywacke, sandstone, siltstone, argillite, ribbon chert, conglomerate, limestone, and basalt tuff. Trembleur Ultramafite unit of the Cache Creek Complex, in places part of an ophiolite suite, forms thrust sheets and klippen that overlie lower Mesozoic sedimentary rocks. Sedimentological, lithochemical, paleontological, petrological, and textural comparisons with other areas and established models demonstrate that Cache Creek Terrane is an accretionary complex, a structurally stacked assemblage of rocks that originated in diverse and disparate oceanic paleoenvironments. These environments include spreading ridge, oceanic plateau, atoll, trench fill, and possibly arc. Internal imbrication of the terrane is as young as Early Jurassic, as determined from fossil evidence, and the minimum age of obduction of the thrust stack westward onto Stikine Terrane is Middle Jurassic, as determined from dating of a crosscutting pluton. Triassic blueschist and eclogite of Cache Creek Terrane are interpreted to have been primarily uplifted to upper crustal levels during Triassic subduction. Cache Creek Terrane, as a remnant of that subduction process, and caught in the collision between Stikine and Quesnel terranes, marks the position of a lithosphere-scale suture zone, the Pinchi Suture.
Redefinition of the Wild Bight Group, Newfoundland: implications for models of island-arc evolution in the Exploits Subzone
Authors: MacLachlan Kate , O'Brien Brian H , Dunning Greg R
Published: April 2011

The Wild Bight Group and correlative plutonic rocks of the South Lake Igneous Complex comprise one of the accreted, Ordovician, peri-Gondwanan, oceanic terranes of the Newfoundland Appalachians. Recent field work and isotopic ages from the eastern Wild Bight Group require that the stratigraphic sequence be redefined. A package of bimodal volcanic rocks, which forms the oldest part of the group and contains all of its volcanogenic massive sulphide deposits, is redefined as the Glovers Harbour Formation. This formation is correlative with intra-oceanic ophiolitic sequences elsewhere in the Exploits Subzone. Previous stratigraphic nomenclature for the upper Wild Bight Group is largely retained, although the lithological variation within and spatial distribution of the Omega Point, Seal Bay Brook, and Pennys Brook formations are revised, and the Side Harbour Formation is included as part of the Seal Bay Brook Formation. The upper Wild Bight Group is interpreted to represent a second and distinct arc sequence that formed on the Gondwanan continental margin. There is a ca. 10 million-year hiatus in volcanic activity between the Glovers Harbour Formation and upper Wild Bight Group, although marine sedimentation was likely continuous during this time. This hiatus corresponds with Penobscot deformation and obduction of Exploits Subzone ophiolites onto the Gander Zone farther to the east and south. The Glovers Harbour Formation is correlated with the Tea Arm and Saunders Cove formations of the Exploits Group, whereas the upper Wild Bight Group can be correlated in some detail with the New Bay and Lawrence Head formations. The upper Wild Bight Group and correlative rocks of the Exploits Group are interpreted to represent the arc and back arc, respectively, of the same Middle Ordovician arc system.
Facies interpretation of Middle Carboniferous to Lower Permian Pope succession limestone of Cache Creek Group, Fort St. James, central British Columbia
Authors: Sano H , Rui L
Published: April 2011

Lithostratigraphy and microfacies of the Bashkirian to Asselian Pope succession limestone of the Cache Creek Group near Fort St. James, central British Columbia, were lithologically grouped into five facies associations A to E. On the basis of fusulines and conodonts, facies associations A to D and the lower part of facies association E are time-equivalent, ranging from the lower Bashkirian to lower Kasimovian, and the upper part of facies association E is dated as upper Gzhelian to Asselian. The Pope succession limestone is interpreted to have been built on a basaltic basement of an oceanic plateau or seamount in an open-ocean realm. The limestone is devoid of terrigenous grains, is associated with basaltic rocks, and laterally grades into deeper-water spicular cherts. Microfacies analysis of facies associations A to E showed that they exhibit characteristic facies of (A) deep-water basinal setting, (B) marginal basin to lower slope, (C) shallow-subtidal bank margin, (D) peritidal algal mound on the bank margin, and (E) shallow-subtidal bank margin to intertidal lagoonal flat,. Moscovian to Asselian rocks of facies associations C, D, and E record an upward increase of low-relief encrusting calci-microbes as rock-builders. This tendency is closely correlated with that in limestone buildups mapped from the Panthalassan Ocean. The abundance of phylloid algal plates and the reefal facies of the Moscovian rocks of facies association D are the same as the reef-building phylloid algae of the Bashkirian to Sakmarian limestone of both the Tethyan and Panthalassan oceans. The Pope succession limestone has many similarities in tectonic, stratigraphic, sedimentologic, and paleontologic aspects to the Akiyoshi buildup, a representative Panthalassan buildup in a Permian subduction-related accretionary complex in Japan. The timing of the increasing importance of the calci-microbes and phylloid algae in the Pope and Akiyoshi buildups is also correlatable.
Ubiquity of anomalous fading in K-feldspars and the measurement and correction for it in optical dating
Authors: Huntley D J , Lamothe M
Published: April 2011

Anomalous-fading rates were measured in K-feldspars separated from 49 sediment samples, mainly from North America. The intensity of the optically stimulated luminescence was found to decrease linearly with the logarithm of time since irradiation between 2 days and ~1 year of storage at room temperature. Anomalous-fading rates ranged from 2% to 10% per decade, a decade being a factor of 10 in time since irradiation. The sample provenances were sufficiently varied that anomalous fading appears to be ubiquitous. We have experimented with correction of optical ages for anomalous fading on the assumption that the observed fading can be extrapolated a further four decades in time. The corrected ages are in satisfactory agreement with independent ages. These results are restricted to the low-dose region of the dose response and are not expected to be applicable to samples older than ~2050 ka.
Depositional environments of Quaternary lacustrine travertines and stromatolites from high-altitude Andean lakes, northwestern Argentina
Authors: Valero-Garcés Blas L , Arenas Concha , Delgado-Huertas Antonio
Published: April 2011

Four distinctive depositional subenvironments of fossil travertines and stromatolites are identified in three high-altitude (35004000 m above sea level) lacustrine basins: El Peinado, San Francisco (Las Coladas Salar subbasin), and Las Peladas (southern Andean Altiplano, northwestern Argentina). These late Quaternary occurrences are characterized using geomorphological, sedimentological, petrographic, and stable isotopic data. Stromatolites of cyanobacterial origin only develop in shallow lacustrine margins of El Peinado basin. In the same basin, macrophytic travertines occur both near thermal spring seepage areas along the lake margin as in situ facies and in littoral lacustrine environments up to water depths of several metres as phytoclastic travertine facies. The stromatolites and macrophytic travertines have relatively heavy δ18O compositions, suggesting initial16O-depleted waters and (or) evaporation effects through time. Their high δ13C compositions are interpreted as a reflection of intense CO2evasion from the thermal groundwaters feeding the lakes. Similar laminated travertine facies, with no petrographic evidence for biotic origin, occur in both Las Coladas and Las Peladas basins. Neither petrographic nor isotopic data alone can differentiate between these two cases. Besides, diagenetic overprint in Las Peladas facies precludes the use of isotopic values as original isotopic signatures. However, the depositional environmental conditions defined by the geomorphological and sedimentological features are different. Laminated aragonitic crusts in Las Coladas basin formed in a shallow, saline lake and are associated with shoreline and terrace deposits cemented by aragonite. These travertine crusts represent periods of spring,16O-rich discharge to the lake, as suggested by the lighter oxygen isotopic compositions. In contrast, travertines from Las Peladas occur as laminated calcitic and aragonitic units intercalated at the top of fining-upward sequences composed of conglomerates, sandstones, and intraclastic limestones. Sedimentological data suggest that these travertines originated in fluvial-influenced lake margins during low lake-level episodes.
Lithospheric structure across the craton-Cordilleran transition of northeastern British Columbia
Authors: Welford J Kim , Clowes Ron M , Ellis Robert M , Spence George D , Asudeh Isa , Hajnal Zoltan
Published: April 2011

The lithospheric structure of the transition from the craton to the Cordillera in northeastern British Columbia is interpreted from inversion of seismic refraction  wide-angle reflection data along a 460-km profile, and from 3-d (3-dimensional) inversion and 2.5-d forward modelling of Bouguer gravity data. The seismic profile extends westward from the sediment-covered edge of cratonic North America across the Foreland and Omineca morphogeological belts to the eastern boundary of accreted terranes, beyond the Tintina Fault. Across the ancient cratonic margin, the resultant models reveal a westward-thickening package of low upper crustal velocities (6.2 km/s and less) and low densities to almost 20 km depth below the Western Canada Sedimentary Basin, overlying a west-facing ramp of higher velocities and densities in the middle and lower crust. These features are inferred to represent passive-margin sediments deposited on the ancient rifted margin during the mid-to-late Proterozoic and early Paleozoic. A wedge-shaped high-velocity (7.3 km/s) crustal layer at the base of the crust beneath the edge of cratonic North America is interpreted to be the result of magmatic underplating during rifting. In the Cordilleran Foreland Belt, high velocities (6.4 km/s) in the upper 5 km of the crust indicate rocks upthrust from the middle crust. A narrow trench of low velocities in the near-surface, which is imaged ~20 km to the west of the inferred location of the Tintina Fault, is interpreted to represent the actual location of the fault or a major splay. From east to west, the Moho decreases in depth from ~40 km to ~34 km below the rifted margin of ancestral North America, then defines a small root at ~38 km depth below the high topography and upper crustal velocities of the eastern Foreland Belt, and gradually shallows to ~34 km beneath the Omineca belt. An enigmatic laterally heterogeneous upper mantle has anomalously high velocities (up to 8.3 km/s) beneath the Foreland Belt, flanked by regions of low velocities (7.77.8 km/s). Results indicate that the location of the Cordilleran deformation front west of the ramped cratonic margin directly affected the tectonic evolution of the region.
Paleoproterozoic carbonatitic ultrabasic volcanic rocks (meimechites?) of Cape Smith Belt, Quebec
Authors: Baragar W RA , Mader U , LeCheminant G M
Published: April 2011

A 500 m-thick lens of carbonatitic ultrabasic lapilli tuffs and lavas interbedded with platformal Povungnituk sediments in the foreland of the Cape Smith Belt is its earliest known magmatism and may relate to its initial rifting. The sequence comprises tuffs capped in part by effusives. Accretionary and cored lapilli in the tuffs and pillows in the lavas suggest emplacement in a shallow marine environment. Its current assemblage of antigorite, chlorite, talc, and (in part primary?) carbonate, magnetite, ilmenite, minor chromite, and phlogopite results from probable concurrent hydrothermal alteration and subsequent greenschist regional metamorphism. Surviving accessory minerals: apatite, monazite, zircon, rutile, and aeschenite(?) are widespread but scarce. Carbonate (mostly dolomite) is a major and integral component of the rock and interpreted as an original, albeit recrystallized, magmatic constituent. Magnetite is conspicuous in the tuffs: as lapilli and lapilli cores, locally as giant crystals, and as stringers. Except in subhedral groundmass crystals, its negligible TiO2 is evidence of its hydrothermal reconstitution. Compositions of chromite cores and rare relicts of phlogopite crystals are consistent with mantle derivation. Rock compositions are low in SiO2 (<35%) and Al2O3 (<3%), high in MgO (>25 wt.%) and alkaline. The immobile incompatible elements (e.g., Zr, average 260 ppm; Nb, average 130 ppm) and the light rare-earth elements are enriched. The rocks are compositionally similar to type Siberian meimechites and closely resemble the "meimechite"carbonatite eruptives of Castignon Lake, Labrador Trough. Based on experimental evidence, Lac Leclair magmas are interpreted as originating by minor partial melting of carbonated mantle at ~100 km depths and reaching the surface via conduits opened by deep rifting that initiated the Cape Smith segment of the Trans-Hudson Orogen.
Early Proterozoic magmatism in Yukon, Canada: constraints on the evolution of northwestern Laurentia
Authors: Thorkelson Derek J , Mortensen James K , Creaser Robert A , Davidson Garry J , Abbott J Grant
Published: April 2011

Northwestern Laurentia, after cratonization at about 1.85 Ga, underwent a series of tectonic and magmatic events during the Proterozoic that were followed by separation of Laurentia from another landmass, probably Australia. The oldest magmatic event produced the Bonnet Plume River Intrusions (BPRI), which intruded the Wernecke Supergroup as short dikes and small stocks. The BPRI are hydrothermally altered tholeiitic diorites, gabbros, and subordinate anorthositic and syenitic rocks, with trace element signatures consistent with a rift origin. Depleted mantle model ages range from 2.29 to 2.57 Ga and εNdvalues range from +0.7 to 1.7. An increasing crustal component is apparent in rocks with more evolved compositions. Four UPb zircon ages (1705.9 ± 0.7, 1709.4 ± 1.4, 1711.1 ± 5.1, and 1713.6 ± 12.7 Ma) indicate a Paleoproterozoic age for the BPRI. These dates constrain the age of the Wernecke Supergroup to [Formula: see text] ca. 1710 Ma, making it the oldest supracrustal succession in western Laurentia, e.g., >240 Ma older than the Belt Supergroup of southeastern British Columbia and the northwestern United States. The Wernecke Supergroup was deposited in the first rift basin to open along the western margin of Laurentia, but was later inverted by the pre-1.6 Ga Racklan Orogeny, an event possibly influenced by transmission of compression from the Yavapai and Mazatzal orogenies in southern Laurentia. The Neoproterozoic southwestern United States  east Antarctica (SWEAT) reconstruction, which places Australia next to northwestern Laurentia, is supported by linkages between Paleoproterozoic and Mesoproterozoic geological features in northwestern Canada and Australia.
Conodonts from the Kechika Formation and Road River Group (Lower to Upper Ordovician) of the Cassiar Terrane, northern British Columbia
Authors: Pyle Leanne J , Barnes Christopher R
Published: April 2011

This study examines the lower Paleozoic stratigraphy of the Cassiar Terrane from three key sections comprising an east-west transect across the terrane. The Cassiar Terrane, west of the Northern Rocky Mountain Trench, consists of a Neoproterozoic to Triassic succession and is a fragment of the Cordilleran Miogeocline that has been displaced northward. The amount of displacement from its original position remains controversial. Conodonts from the Cassiar Terrane have been previously reported from only a few reconnaissance studies. More than 3000 m of strata have been measured and examined in detail and 85 conodont samples collected. A total of 926 identifiable conodont elements are assigned to 31 species representing 21 genera. The conodonts are mainly representative of the Midcontinent Faunal Realm, but some also represent the Atlantic Realm. Conodonts from the upper Kechika Formation and base of the Road River Group are Early Ordovician (Tremadocian) in age, and those from the upper Road River Group range into the Upper Ordovician (Caradocian). The detailed Ordovician stratigraphy and temporal constraints established by conodont biostratigraphy provide for correlation to coeval facies of ancestral North America. The onset of Road River sedimentation in the mid-Tremadocian is, however, older than that in the Macdonald Platform to the east (early Arenigian). This onset timing may help link the Cassiar Terrane to a specific part of the miogeocline from which it was transported.
Cranial morphology of Sinornithosaurus millenii Xu et al. 1999 (Dinosauria: Theropoda: Dromaeosauridae) from the Yixian Formation of Liaoning, China
Authors: Xu Xing , Wu Xiao-Chun
Published: April 2011

The recent discovery of the early dromaeosaurid Sinornithosaurus millenii Xu et al. 1999 is especially important for our understanding of maniraptoran evolution, particularly of avian origins. This paper presents a thorough description of the skull of this species, revises the diagnosis based on cranial features, and discusses similarities to those of other dromaeosaurids and Archaeopteryx. Distinctive cranial characteristics of S. millenii include the presence of a deep excavation on the posteroventral margin of the premaxilla, a diastema between the premaxillary and maxillary teeth, a number of pits and ridges on the anterolateral surface of the antorbital fossa, long posterolateral process of the parietal that are sharply posteriorly directed, the column-like margin of the pterygoid process of the quadrate, the bifurcated posterior end of the dentary, and a distinctive groove posterior to the anterior carina on the lingual surface of the premaxillary tooth crowns. The present study on the skull of S. millenii provides new information on the poorly known cranial anatomy of dromaeosaurid dinosaurs, revealing that dromaeosaurids share more similarities with Archaeopteryx than previously thought. It also provides evidence suggesting that early dromaeosaurids are more bird-like than the later, more derived ones, thus contradicting claims that more bird-like dinosaurs appeared later in fossil record than the earliest birds.
MECHANISM AND KINETICS OF EXPANSION IN THE ALKALI-CARBONATE ROCK REACTION
Authors: Gillott J. E.
Published: April 2011

Certain fine-grained argillaceous dolomitic limestones show an increase in solid volume when placed in strong alkali. Mineralogical analysis shows that the dolomite is replaced by magnesium hydroxide (brucite), calcium carbonate, and alkali carbonate. This reaction does not account directly for the expansion, as the volume of the solid products is less than the volume of the dolomite.Expansion is shown to be the result of an increase in solid volume that results from water uptake. The behavior is accounted for by a hypothesis that may be summarized as follows.(1) Alkaline attack on the dolomite crystals releases included clay in an "active" state with an unwetted surface.(2) Some of the Ca++ and Mg++ ions probably present on exchange sites are replaced by Na+ ions.(3) Development of a hydrated double layer made up of oriented water molecules, cations near the newly exposed clay surface, and anions further from the surface.(4) Development of the double layer and accompanying hydration processes cause the water uptake, which leads to expansion.