Browsing Geography and Environment by Author "Barendregt, René W."
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- ItemBiostratigraphic evidence relating to the age-old question of Hannibal's invasion of Italy, I: history and geological reconstruction(Wiley, 2016) Mahaney, William C.; Allen, Christopher C. R.; Pentlavalli, Prasanna; Kulakova, Anna; Young, Jonathan M.; Dirszowsky, Randy W.; West, Allen; Kelleher, Brian; Jordan, Sean; Pulleyblank, C; O'Reilly, Shane; Murphy, B. T.; Lasberg, Katrin; Somelar, Peeter; Garneau, Michelle; Finkelstein, S. A.; Sobol, M. K.; Kalm, Volli; Costa, Pedro J. M.; Hancock, Ronald G. V.; Hart, Kris M.; Tricart, Pierre; Barendregt, René W.; Bunch, Ted E.; Milner, Michael W.Controversy over the alpine route that Hannibal of Carthage followed from the Rhône Basin into Italia has raged amongst classicists and ancient historians for over two millennia. The motivation for identifying the route taken by the Punic Army through the Alps lies in its potential for identifying sites of historical archaeological significance and for the resolution of one of history's most enduring quandaries. Here, we present stratigraphic, geochemical and microbiological evidence recovered from an alluvial floodplain mire located below the Col de la Traversette (~3000 m asl—above sea level) on the French/Italian border that potentially identifies the invasion route as the one originally proposed by Sir Gavin de Beer (de Beer 1974). The dated layer is termed the MAD bed (mass animal deposition) based on disrupted bedding, greatly increased organic carbon and key/specialized biological components/compounds, the latter reported in Part II of this paper. We propose that the highly abnormal churned up (bioturbated) bed was contaminated by the passage of Hannibal's animals, possibly thousands, feeding and watering at the site, during the early stage of Hannibal's invasion of Italia (218 bc).
- ItemBiostratigraphic evidence relating to the age-old question of Hannibal's invasion of Italy, II: chemical biomarkers and microbial signatures(Wiley, 2017) Mahaney, William C.; Allen, Christopher C. R.; Pentlavalli, Prasanna; Kulakova, Anna; Young, Jonathan M.; Dirszowsky, Randy W.; West, Allen; Kelleher, Brian; Jordan, Sean; Pulleyblank, C.; O'Reilly, Shane; Murphy, B. T.; Lasberg, Katrin; Somelar, Peeter; Garneau, Michelle; Finkelstein, S. A.; Sobol, M. K.; Kalm, Volli; Costa, Pedro J. M.; Hancock, Ronald G. V.; Hart, Kris M.; Tricart, Pierre; Barendregt, René W.; Bunch, Ted E.; Milner, Michael W.As discussed in Part I, a large accumulation of mammalian faeces at the mire site in the upper Guil Valley near Mt. Viso, dated to 2168 cal 14C yr., provides the first evidence of the passage of substantial but indeterminate numbers of mammals within the time frame of the Punic invasion of Italia. Specialized organic biomarkers bound up in a highly convoluted and bioturbated bed constitute an unusual anomaly in a histosol comprised of fibric and hemist horizons that are usually expected to display horizontal bedding. The presence of deoxycholic acid and ethylcoprostanol derived from faecal matter, coupled with high relative numbers of Clostridia 16S rRNA genes, suggests a substantial accumulation of mammalian faeces at the site over 2000 years ago. The results reported here constitute the first chemical and biological evidence of the passage of large numbers of mammals, possibly indicating the route of the Hannibalic army at this time. Combined with the geological analysis reported in Part I, these data provide a background supporting the need for further historical archaeological exploration in this area.
- ItemCharacterization of Lower and Middle Pleistocene tephra beds in the southern plains of western Canada(Canadian Science Publishing, 2022) Westgate, John A.; Naeser, Nancy D.; Barendregt, René W.; Pearce, Nicholas J. G.Wellsch Valley tephra, near Swift Current, southwestern Saskatchewan, and Galt Island tephra, near Medicine Hat, southeastern Alberta, have been referenced in the literature since the 1970s, but little is available on their physical and chemical attributes — necessary information if they are to be recognized elsewhere. This study seeks to remedy this situation. Both have a calc-alkaline rhyolitic composition with hornblende, biotite, plagioclase, pyroxene, and Fe–Ti oxides being dominant. They have a similar composition but are not the same. Wellsch Valley tephra has a glass fission-track age of 0.75 ± 0.05 Ma, a reversed magnetic polarity, and was deposited at the close of the Matuyama Chron. Galt Island tephra has an age of 0.49 ± 0.05 Ma, a normal magnetic polarity, and was deposited during the early Brunhes Chron. Rich fossil vertebrate faunas occur in sediments close to them. Major- and trace-element concentrations in their glass shards indicate a source in the Cascade Range of the Pacific Northwest, USA, but differences in trace-element ratios suggest they are not consanguineous.
- ItemChronology and extent of late Cenozoic ice sheets in North America: a magnetostratigraphical assessment(Elsevier, 2011) Barendregt, René W.; Duk-Rodkin, AlejandraThis paper summarises the advances which have been made in the magnetostratigraphic assessment of glacial and interglacial events of the past 3.0 million years, to facilitate the assignment of sediments to the Chrons and subchrons of the geomagnetic polarity timescale. In the absence of absolute dating tools, magnetostratigraphy affords a valuable means of assigning terrestrial ice age deposits to the geologic timescale, and most importantly, allows a correlation to be made with the more complete marine sedimentary record, where oxygen isotopic data also provide a robust paleotemperature record.
- ItemEarly and Middle Pleistocene glaciation of the southern Patagonian plain(Elsevier, 2022) Griffing, Corinne Y.; Clague, John J.; Barendregt, René W.; Ercolano, Bettina; Corbella, Hugo; Rabassa, Jorge; Roberts, Nicholas J.Evidence of at least three Early to Middle Pleistocene glaciations is recorded in the stratigraphic exposures near the outer limit of glaciation in southern Patagonia. At Cabo Vírgenes, at the mouth of the Strait of Magellan, up to 70 m of till, gravel, sand, and stony silt were deposited in a grounding-line environment at the front of the Magellan lobe along a front several tens of kilometres wide. Accommodation space for the sediments was produced by glacio-isostatic depression resulting from the advance of the Magellan lobe to the Atlantic coast. At that time, the ‘moat’ in which the sediments accumulated may have been seaward of the modern Atlantic shoreline because the continental shelf is shallow and sea level was much lower than it is today. The sediments at Cabo Vírgenes are normally magnetized, carry no reversed overprints, and thus probably date to the Brunhes Chron (<0.774 Ma). Seacliff exposures south of the Strait of Magellan along the Atlantic coast of northern Tierra de Fuego expose two tills separated by glaciofluvial sediments. Although not dated, the tills record two advances of the Magellan lobe onto the Atlantic continental shelf. The location of the exposures relative to Cabo Vírgenes indicates that the upper of the two tills may correlate with the Cabo Vírgenes drift. The Tres de Enero highway cut, 90 km northwest of Cabo Vírgenes, exposes lodgement tills deposited during the Great Patagonian glaciation (GPG) – two stacked, normally magnetized tills overlie a reversely magnetized till. Truncated sand wedges separate each of the three tills, indicating that the tills record three separate Early to Middle Pleistocene glaciations. The younger of the two normally magnetized tills, and perhaps both, were deposited in the Brunhes Chron; the lowest, reversely magnetized till records extensive glaciation late during the Matuyama Chron (2.608–0.780 Ma). At Bella Vista in the Río Gallegos valley, a 0.89-Ma-old basalt flow caps a thick unit of normally magnetized glaciofluvial gravel, which was probably deposited during the Jaramillo Subchron (1.075–0.991 Ma), but certainly not later. Sediments at Tres de Enero and Bella Vista show that the GPG is not a single event as originally thought, but rather at least three glaciations, perhaps spanning several hundred thousand years.
- ItemEvidence for Early Pleistocene glaciation from borecore stratigraphy in north-central Alberta(Alberta Energy Regulator, 2016-07) Andriashek, L. D.; Barendregt, René W.Borecores collected from Quaternary sediments in north-central Alberta, Canada, were sampled and studied for paleomagnetic remanence characteristics. A magnetostratigraphy has been established for sediments previously assumed to represent multiple continental (Laurentide) glaciations but for which no geochronology was available. Based on the Quaternary record elsewhere in Alberta and Saskatchewan, it was thought that some of these sediments were deposited during pre-late Wisconsinan glaciations. The Quaternary sedimentary succession of north-central Alberta attains thicknesses up to 300 m within buried valleys and is composed of diamict interbedded with glaciolacustrine and outwash sediments. Most of the sampled units are not accessible from outcrop and their sedimentology and stratigraphy is derived from core data only. In 4 of 16 borecores sampled to date, diamict that correlates with the Bronson Lake Formation till is reversely magnetized, indicating an Early Pleistocene age. Depending on location, this formation is underlain by either Empress Formation sediments or Colorado Group shales, and is overlain by one or more normally magnetized glacigenic sedimentary units of the Bonnyville, Marie Creek, and Grand Centre formations, respectively. This new record of Early Pleistocene glaciation in north-central Alberta places the westernmost extent of earliest Laurentide ice at least 300 km farther west than its previously established limit in the Saskatoon and Regina regions of the Canadian Interior Plains, but still to the east of the maximum extent of the late Wisconsinan (Late Pleistocene) Laurentide Ice Sheet, which extended into the foothills of the Alberta and Montana Rocky Mountains.
- ItemExplosive glaciovolcanism at Cracked Mountain Volcano, Garibaldi Volcanic Belt, Canada(Elsevier, 2022) Harris, Martin A.; Russell, James K.; Barendregt, René W.; Porritt, Lucy A.; Wilson, AlexanderCracked Mountain (CM) is a basaltic volcano within the northern extension of the Cascade volcanic arc into southwest, British Columbia, Canada (i.e. Garibaldi Volcanic Belt) and is dated at 401 ± 38 ka (40Ar/39Ar). The edifice covers an area of ~1.5 km2 and has a volume of 0.18 km3. The volcano features steep margins with local relief of ~250 m (1,650 m a.s.l), is dissected by abundant 0.5 to ~20 m wide extensional cracks with depths up to 30 m, and has a highly eroded top. The edifice is dominated by massive to poorly stratified, moderately to pervasively palagonitized lapilli tuffs, comprising vitric fine ash to lapilli. Juvenile pyroclasts have blocky to highly vesiculated shapes consistent with a phreatomagmatic (i.e. explosive) origin. The lapilli tuffs are intruded by and mingled with coherent to disaggregated lobes of peperitic pillowed lavas. Contacts between lapilli tuff and peperitic pillowed lava show soft-sediment deformation and in-situ quench-fragmentation indicating that the tephra was both unconsolidated and water-saturated at the time of intrusion. Local stacks of pillow lava are found on the margins of the edifice. More than fifty, 0.5 to 3 m wide dykes intrude CM stratigraphy and display, either, peperitic pillowed margins or sharp, chilled margins and columnar-jointing. Measurements of paleomagnetic directions (9 sites) were made for all CM lithofacies and record a single-pole direction indicating a single monogenetic eruption. A glaciovolcanic origin is strongly suggested by the abundant subaqueous lithofacies (i.e. palagonitized tephra, pillows, peperites) and the physiographic setting of the edifice which is well above any drainage that could sustain a standing body of water. The elevation of CM and depth of surrounding valleys indicate syn-eruptive confinement by a paleo-ice sheet that was ≥850 m thick. The edifice shape, size, and surround- ing topography suggest a ‘leaky’ paleolake system capable of supporting ~0.36 km3 of water. The glaciovolcanic origin and the absolute (40Ar/39Ar) age of CM represent an important record of the Cordilleran Ice sheet (CIS) in southwestern BC during the mid-Pleistocene.
- ItemAn extensive late Cenozoic terrestrial record of multiple glaciations preserved in the Tintina Trench of west-central Yukon: stratigraphy, paleomagnetism, palesols, and pollen(NRC Research Press, 2010) Duk-Rodkin, Alejandra; Barendregt, René W.; White, James MThe Tintina Trench in west-central Yukon is a late Miocene graben formed along the antecedent early Tertiary Tintina fault. Since its formation the trench has served as a sediment trap for alluvial and glacial deposits. An extensive record of preglacial, glacial, and interglacial sediments spanning the late Pliocene to late Pleistocene has been preserved and is exposed today in modern landslide scars. This sedimentary record comprises multiple sequences of tills, outwash, mudflows, loess, and paleosols. The glacial sediments are the product of both local (montane) and regional (Cordilleran) ice advances that channeled into the trench, while loess and well-developed paleosols (brunisols and luvisols) reflect nonglacial and interglacial conditions, respectively. The Tintina Trench exposures provide the most complete record of glaciations for the region. Paleomagnetism, paleosols, and palynology provide age constraints for the geological events. A formal stratigraphic nomenclature is proposed for this region. The name West Tintina Trench Allogroup is assigned to the glacial–interglacial and nonglacial strata that occurs above a major regional Miocene–Pliocene unconformity. The allogroup spans the late Pliocene (3.6 Ma) to middle Pleistocene (0.126 Ma), based on magnetostratigraphy and pollen data. The sequence includes an alluvial deposit at the base, overlain by an extensive sequence of tills and outwash, and capped by loess. Paleosols and weathering horizons occur throughout the sequence. Tintina Trench; Beringia; glacial chronology; magnetostratigraphy; early and middle Pleistocene; Yukon paleoenvironments; Yukon paleosols; Yukon pollen; North American glaciations; West Tintina Trench Allogroup.
- ItemHannibal's trek across the Alps: geomorphological analysis of sites of geoarchaeological interest(University of the Aegean, 2008) Mahaney, William C.; Kalm, Volli; Dirszowsky, Randy W.; Milner, Michael W.; Sodhi, Rana; Beukens, Roelf; Dorn, Ron; Tricart, Pierre; Schwartz, Stéphane; Chamorro-Perez, Eva; Boccia, Sal; Barendregt, René W.; Krinsley, D. H.; Seaquist, E. R.; Merrick, David; Kapran, BarbaraA ~2200 year-old question related to Hannibal’s invasion route across the Alps into Italia, has been argued by classicists without recovery of material evidence. A comparison of topographical descriptions in the ancient literature with environmental parameters in the Alps, attempted here for the first time, provides a database against which various pathways can be assessed. Identification of sites using geological, geomorphological, astronomical, chemical and petrological methods leads to the exclusion of certain transit points and targeting of others where geoarchaeological excavation might yield important evidence related to the military culture of ancient Carthage
- ItemHistorical archaeology of the Hannibalic invasion of Italia: technical applications(Society for Historical Archaeology, 2008) Mahaney, William C.; Milner, Michael W.; Kapran, Barbara; Tricart, Pierre; Schwartz, Stéphane; Barendregt, René W.; Krinsley, David H.; Dorn, Ronald I.; Trapido-Lurie, Barbara; Boccia, Sal; Sodhi, Rana N. S.; Kalm, Volli; Beukens, RoelfPrevious attempts to plot the exact invasion route of the Punic army in 218 B.c. have been limited, with one excep- tion (de Beer 1967, 1969), to analysis of topography and previous historical arguments based on the interpretation of classical texts written by Polybius and livy. eliciting environmental information from classical literature led to a focus on environmental landmarks, including the rockfall that blocked the army on the lee side of the alps, a firing event described by livy, and the regrouping area where the army rested after conflict with the gauls and the trek over a major col of passage into italia.The use of various scientific methods to analyze these three major sites/events has led to a conclusive identification of the invasion route, and sites of interest to geoarchaeologists
- ItemLate Cenozoic geology, Ancient Pacific Margin Natmap Project, report 4: paleomagnetic and geomorphic evidence for Brunhes-age volcanism, Fort Selkirk and Rosebud Creek area, Yukon Territory(Geological Survey of Canada, 2001) Huscroft, Crystal A.; Barendregt, René W.; Jackson, Lionel E.Normally magnetized, valley-filling basalt flows extend more than 10 km down the Yukon River valley from the Fort Selkirk area. These flows are locally overlain by gravel and terminate at the level of the contemporary Yukon River flood plain, suggesting a middle to late Pleistocene age for this previously unrecognized eruptive event. Unlike other valley-filling phases of the Selkirk Volcanic Group, this eruption postdates the Pliocene to early Pleistocene pre-Reid glaciations. Normal magnetism was also determined for basalt flows underlying terraces in the area of the Rosebud Creek-Grand Valley Creek confluence, 60 km to the northwest of the Fort Selkirk area. Based on their unique geomorphic and stratigraphic settings, the Rosebud basalt flows may represent yet another period of Pleistocene volcanism which predates one of the pre-Reid glaciations in the central Yukon Territory.
- ItemLithostratigraphic and magnetostratigraphic data from late Cenozoic glacial and proglacial sequences underlying the Altiplano at La Paz, Bolivia(Elsevier, 2018) Roberts, Nicholas J.; Barendregt, René W.; Clague, John J.We provide lithostratigraphic and magnetostratigraphic data derived from a Plio-Pleistocene continental sediment sequence underlying the Altiplano plateau at La Paz, Bolivia. The record comprises six sections along the upper Río La Paz valley, totaling over one kilometre of exposure and forming a ~20-km transect oblique to the adjacent Cordillera Real. Lithostratigraphic characterization includes lithologic and stratigraphic descriptions of units and their contacts. We targeted gravel and diamicton units for paleomagnetic sampling to address gaps in the only previous magnetostratigraphic study from this area. Paleomagnetic data – magnetic susceptibility and primary remanent magnetization revealed by progressive alternating field demagnetization – are derived from 808 individually oriented samples of flat-lying, fine-grained sediments. The datasets enable characterization of paleo-surfaces within the sequence, correlation between stratigraphic sections, and differentiation of asynchronous, but lithologically similar units. Correlation of the composite polarity sequence to the geomagnetic polarity time scale supports a range of late Cenozoic paleoenvironmental topics of regional to global importance: the number and ages of early glaciations in the tropical Andes; interhemispheric comparison of paleoclimate during the Plio-Pleistocene climatic transition; timing of and controls on inter-American faunal exchange; and the variability of Earth's paleomagnetic field.
- ItemMagnetostratigraphy of late neogene glacial, interglacial, and preglacial sediments in the Saskatoon and Regina areas, Saskatchewan, Canada(Institute of Geophysics of the ASCR, 2012) Barendregt, René W.; Enkin, Randolph J.; Tessler, Dez L.Two new records of glacial stratigraphy obtained from borecores collected in southcentral Saskatchewan are compared to previously published records from Wellsch Valley and Swift Current Creek in southern Saskatchewan. The comparisons are based on magnetostratigraphy and tephrochronology, and describe preglacial, glacial, and interglacial deposits. The new stratigraphy is compared to the composite global marine oxygen isotope record. Although the ages and extents of late Pleistocene continental glaciations are relatively well constrained, they are less well defined for the middle and early Pleistocene. Data presented here highlight recent studies carried out from borecores and outcrops of extensive pre-Illinoian (pre-Saalian) glacial deposits. Based on this new data, at least seven Laurentide (continental) glaciations are recognized in Saskatchewan, and these records are the most extensive to date in the Northern Interior Plains of Canada. The magnetostratigraphic records from the Sutherland Overpass and Wascana Creek sites provide the first evidence of reversely magnetized glacial deposits in the Canadian Prairies. These deposits can be assigned to the latest Matuyama (MIS 20) and indicate that Laurentide (continental) glaciations did not impact southern Saskatchewan until the late Early Pleistocene.
- ItemMagnetostratigraphy of quaternary sections in eastern Alberta, Saskatchewan and Manitoba(Elsevier, 2011) Barendregt, René W.This paper summarises the continental (Laurentide) glacial history of the northern Interior Plains of Canada (Alberta, Saskatchewan, and Manitoba) using magnetostratigraphy, tephrochronology, and paleosol data collected at type sections. The use of borecores for retrieval of oriented till samples for paleomagnetic analysis, is discussed.
- ItemMineralogy and chemistry of late pliocene-early pleistocene palesols on Mount Kenya: weathering indices of relative age and paleoenvironmental reconstruction(Elsevier, 2014) Mahaney, W.C.; Hamilton, T.S.; Barendregt, René W.; Hancock, R.G.V.; Costa, P.Iron and Al extracts as weathering indices in paleosols have been used in many localities to determine relative age, transformation of total chemical element concentrations to secondary forms, translocation of organicallycomplexed Al and long-standing inundation of soils with groundwater. On Mt. Kenya, a succession of paleosols straddling the Olduvai subchron are here analyzed to determine the degree to which Fe/Al extracts assist paleoenvironmental reconstruction, especially relative age determination, genesis and translocation of alteration products and the effect of paleoclimatic deterioration with the advent of glaciation ca. 2.0 Ma, and possibly before. Warmer/humid climate from the onset of the Plio-Pleistocene to the Olduvai subchron, thereafter reverting to a long episode of oscillating drier/wetter ice age perturbations is written into the profile morphologies, mineralogies and chemistries supporting earlier stratigraphic interpretations
- ItemMultiple tropical Andean glaciations during a period of late Pliocene warmth(Nature Research, 2017) Roberts, Nicholas J.; Barendregt, René W.; Clague, John J.The extent and behaviour of glaciers during the mid-Piacenzian warm period illustrate the sensitivity of the cryosphere to atmospheric CO2 concentrations above pre-industrial levels. Knowledge of glaciation during this period is restricted to globally or regionally averaged records from marine sediments and to sparse terrestrial glacial deposits in mid-to-high latitudes. Here we expand the Pliocene glacial record to the tropics by reporting recurrent large-scale glaciation in the Bolivian Andes based on stratigraphic and paleomagnetic analysis of a 95-m sequence of glacial sediments underlying the 2.74-Ma Chijini Tuff. Paleosols and polarity reversals separate eight glacial diamictons, which we link to cold periods in the benthic oxygen isotope record. The glaciations appear to coincide with the earliest glacial activity at high northern latitudes and with events in Antarctica, including the strong M2 cold peak and terminal Pliocene climate deterioration. This concordance suggests inter-hemispheric climate linkages during the late Pliocene and requires that the Central Andes were at least as high in the late Pliocene as today. Our record fills a critical gap in knowledge of Earth systems during the globally warm mid-Piacenzian and suggests a possible driver of faunal migration preceding the large-scale biotic interchange in the Americas during the earliest Pleistocene.
- ItemPliocene and Early Pleistocene glaciation and landscape evolution on the Patagonian Steppe, Santa Cruz province, Argentina(Elsevier, 2020) Clague, John J.; Barendregt, René W.; Menounos, Brian; Roberts, Nicholas J.; Rabassa, Jorge; Martinez, Oscar; Ercolano, Bettina; Corbella, Hugo; Hemming, Sidney R.At least seven late Pliocene tills cap plateaus (mesetas) south of Lago Viedma, just east of the Andes in Argentine Patagonia. Chronologic constraints on the tills are provided by 40Ar/39Ar ages and magnetic polarities on associated basalt flows and sediments. The tills were deposited by piedmont glaciers that reached at least 80 km east of the crest of the Andes and flowed on a low-relief surface sloping gently downward in that direction. The oldest of the tills is about 3.6 Ma old. Glacial deposits dating to the Pliocene-Pleistocene transition are present at least 40 km beyond the east limit of the Pliocene tills at Lago Viedma, and tills of similar age occur at Condor Cliff in the Río Santa Cruz valley to the southeast. A sequence of at least seven Early Pleistocene (2.1–1.1 Ma) tills is present between basalt flows in the Cerro del Fraile meseta south of Lago Argentino. The glaciers that deposited these Early Pleistocene tills reached far beyond the Marine Isotope Stage 2 limit in the Río Santa Cruz valley. Based on positions, extents, and ages of the un-deformed, basalt-capped mesetas flanking Lago Viedma, we conclude that the topography in this area was profoundly changed during the Pleistocene – the low to moderate relief Pliocene surface was deeply incised by glaciers that became increasingly confined to, and flowed within, troughs. The valley floors today are up to 1350 m below the late Pliocene surface.
- ItemPliocene and pleistocene volcanic interaction with cordilleran ice sheets, damming of the Yukon River and vertebrate palaeontology, Fort Selkirk volcanic group, west-central Yukon, Canada(Elsevier, 2012) Jackson, L.E.; Nelson, F.E.; Huscroft, C.A.; Villeneuve, M.; Barendregt, René W.; Storer, J.E.; Ward, B.C.Neogene volcanism in the Fort Selkirk area began with eruptions in the Wolverine Creek basin ca. 4.3 Ma and persisted to ca. 3.0 Ma filling the ancestral Yukon River valley with at least 40 m of lava flows. Activity at the Ne Ch’e Ddhäwa eruptive center overlapped with the last stages of the Wolverine Creek eruptive centers. Hyaloclastic tuff was erupted between ca. 3.21 and 3.05 Ma. This eruption caused or was coincident with damming of Yukon River. The first demonstrable incursion of a Cordilleran ice sheet into the Fort Selkirk area was coincident with a second eruption of the Ne Ch’e Ddhäwa eruptive center ca. 2.1 Ma. The Ne Ch’e Ddhäwa subglacial mound was erupted beneath at least 300 m of glacial ice (Ne Ch’e Ddhäwa Glaciation). The Eruption of the Fort Selkirk center occurred between the last eruption of Ne Ch’e Ddhäwa and Fort Selkirk Glaciation (ca. 2.1e1.5 Ma). Till and outwash from Fort Selkirk Glaciation are conformably overlain by nonglacial sediments that contain the Fort Selkirk tephra (fission track dated at ca. 1.5 Ma). These nonglacial sediments also preserve a short magnetic reversal (reversed to normal) identified as the Gilsá polarity excursion. Temporal control and sedimentology constrain Fort Selkirk Glaciation and the Fort Selkirk Local Fauna to marine isotope stage 54. Rapid and extensive eruption of the Pelly eruptive center filled the Yukon River valley with 70 m of lava which buried these glacial and nonglacial sediments and dammed Yukon River. Local striations and erratic pebbles occur on the last of these lava flows. They document a subsequent incursion of glacial ice during the last 500 ka of the Matuyama Chron (Forks Glaciation). The last major eruption of mafic lava occurred in the middle Pleistocene west of (early Holocene) Volcano Mountain in basin of Black Creek: lava flowed down the valley presently occupied by Black Creek and dammed Yukon River in the area of the Black Creek confluence. This eruption predated the middle Pleistocene Reid Glaciation. Minor volcanism has continued in this area since the middle Pleistocene at Volcano Mountain.
- ItemProvenance and deposition of glacial Lake Missoula lacustrine and flood sediments determined from rock magnetic properties(Elsevier, 2015) Hanson, Michelle A.; Enkin, Randolph J.; Barendregt, René W.; Clague, John J.Repeated outburst flooding from glacial LakeMissoula,Montana, affected large areas of Washington duringMarine Oxygen Isotope Stage 2 (29–14 ka).We present the first high-resolution rock magnetic results from two sites that are critical to interpreting these outburst floods and that provide evidence of sediment provenance: glacial Lake Missoula, the source of the floods; and glacial Lake Columbia, where floodwaters interrupted sedimentation. Magnetic carriers in glacial LakeMissoula varves are dominated by hematite,whereas those in outburst flood sediments and glacial Lake Columbia sediments aremainly magnetite and titano-magnetite. Stratigraphic variation of magnetic parameters is consistent with changes in lithology. Importantly, magnetic properties highlight depositional processes in the flood sediments that are not evident in the field. In glacial Lake Columbia, hematite is present in fine silt and clay deposited near the end of each flood as fine sediment settled out of the water column. This signal is only present at the end of the floods because the hematite is concentrated in the finer-grained sediment transported from the floor of glacial LakeMissoula, the only possible source of hematite, ~240 km away.
- ItemRecent investigations of the 0-5 geomagnetic field recorded by lava flows(2015-06-12) Johnson, Catherine L.; Constable, Catherine G.; Tauxe, Lisa; Barendregt, René W.; Brown, Laurie L.; Coe, Rob; Gans, Phil; Layer, Paul; Mejia, Vicky; Opdyke, Neil D.; Singer, Brad; Staudigel, Hubert; Stone, DavidWe present a synthesis of paleomagnetic directional data collected from 873 lava flows at 17 different locations under the collaborative Time Averaged geomagnetic Field Initiative (TAFI). The data range from 05 Ma in age, and provide new high quality data with improved spatial coverage. Data quality at each site is measured using k, the best estimate of the Fisherian precision parameter, and its influence on inclination anomaly and VGP dispersion is evaluated by systematically excluding data with successively higher values of k. When combined with regional compilations from NW USA, SW USA, Japan, New Zealand, Hawaii, Mexico, S. Pacific and the Indian Ocean, a data set of 2283 pairs of declination and inclination data, with k>100, and VGP latitudes greater than 45 is obtained. This is a more than 7fold increase over similar quality data in the existing Global Paleomagnetic Database (GPMDB). The new data set spans 78 S to 53 N, and has sufficient temporal and spatial sampling to allow characterization of latitudinal variations in the timeaveraged field (TAF) and paleosecular variation (PSV) for the Brunhes and Matuyama epochs, and for the 0–5 Myr interval combined. PSV, as measured by dispersion of virtual geomagnetic poles, shows less latitudinal variation than predicted by current statistical PSV models. Variation of inclination anomaly with latitude is assessed using 2parameter zonal TAF models – these have axial quadrupole contributions of 2% – 4% of the axial dipole term, and axial octupole contributions of 3% – 5%. Approximately 2% of the octupole signature is likely the result of bias incurred by averaging unit vectors. The new data set provides significant improvement over previous compilations, and can contribute to a new generation of global paleomagnetic field models.